RU2639893C2 - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

FIELD: engine devices and pumps.SUBSTANCE: exhaust gas purification system comprises an exhaust gas purifying catalyst 20, an air-fuel ratio sensor 41 from an outlet side, and a control device performing control of air-fuel ratio to control air-fuel ratio of exhaust gas and control fault diagnostics for diagnostics of air-fuel ratio sensor from outlet side. When controlling air-fuel ratio, the control device alternately and periodically switches air-fuel ratio of exhaust gas flowing in exhaust gas purification catalyst, between rich air-fuel ratio and lean air-fuel ratio. When performing control of the fault diagnostics, the control device evaluates that the sensor of the air-fuel ratio from the outlet side has become defective, when by means of air-fuel ratio control, the air-fuel ratio of exhaust gas is made rich in air-fuel ratio, and outlet air-fuel ratio of air-fuel ratio sensor from outlet side changes from air-fuel ratio which is richer than the predetermined lean air-fuel ratio to lean air-fuel ratio.EFFECT: generating the exhaust gas purification system for internal combustion engine which is capable to provide fault diagnostics when the air-fuel ratio sensor from the outlet side has a fault in the form of cracked element.8 cl, 18 dwg

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an exhaust gas purification system for an internal combustion engine.

State of the art

[0002] An exhaust gas purification system is known comprising air-fuel ratio sensors located on the inlet side in the exhaust gas flow direction and on the exhaust side in the exhaust gas flow direction with respect to the exhaust gas purification catalyst located in the exhaust channel of the internal combustion engine. In such an internal combustion engine, the output of the intake air-fuel ratio sensor is used as a basis for feedback control so that the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst becomes the target air-fuel ratio. In addition, the target air-fuel ratio is alternately set to the air-fuel ratio, which is richer than the stoichiometric air-fuel ratio (hereinafter referred to simply as “rich air-fuel ratio”), and to the air-fuel ratio, which is poorer than the stoichiometric air-fuel ratio (hereinafter referred to simply as “poor air-fuel ratio”) (for example, PLT 1).

[0003] In particular, in the internal combustion engine, which is described in PLT 1, when the air-fuel ratio corresponding to the output signal of the exhaust-side air-fuel ratio sensor (hereinafter also referred to as the "output air-fuel ratio") becomes rich preset the air-fuel ratio, which is richer than the stoichiometric air-fuel ratio, or becomes even smaller, the target air-fuel ratio switches to a lean air-fuel ratio, while yes, the amount of oxygen accumulation in the exhaust gas purification catalyst becomes a predetermined switching reference accumulation amount that is less than the maximum amount of oxygen accumulation, or becomes even larger, the target air-fuel ratio is switched to a rich air-fuel ratio. According to PLT 1, due to this, it is considered possible to suppress the outflow of NO _X from the exhaust gas purification catalyst.

Link Index

Patent Literature

[0004] PLT 1. International Patent Publication No. 2014 / 118892A

PLT 2. Japanese Patent Publication No. 2006-343281A

SUMMARY OF THE INVENTION

Technical challenge

[0005] In this regard, if the element forming part of the air-fuel ratio sensor is cracked, and the air-fuel ratio of the exhaust gas around the air-fuel ratio sensor is essentially a stoichiometric air-fuel ratio or a lean air-fuel ratio , the output air-fuel ratio of the air-fuel ratio sensor becomes substantially equal to the actual air-fuel ratio of the exhaust gas. However, when the air-fuel ratio of the exhaust gas around the air-fuel ratio sensor is rich in the air-fuel ratio, the output air-fuel ratio of the air-fuel ratio sensor sometimes becomes an air-fuel ratio different from the actual air-fuel ratio of the exhaust gas, in particular , poor air-fuel ratio.

[0006] Thus, when the air-fuel ratio sensor has a cracked element, sometimes it is not possible to accurately determine the air-fuel ratio of the exhaust gas near the air-fuel ratio sensor. Thus, when using the air-fuel ratio sensor that produces an erroneous output signal caused by the cracked element to perform the above-mentioned control of the target air-fuel ratio, sometimes it is no longer possible to eliminate the release of NO _X , etc. from an exhaust gas purification catalyst.

[0007] Therefore, in view of the aforementioned problem, it is an object of the present invention to provide an exhaust gas purification system for an internal combustion engine that is capable of diagnosing a malfunction when the exhaust air-fuel ratio sensor has a malfunctioning cracked element.

The solution of the problem

[0008] In order to solve the above problem, according to a first aspect of the invention, there is an exhaust gas purification system for an internal combustion engine comprising an exhaust gas purification catalyst located in an exhaust channel of an internal combustion engine, an air-fuel ratio sensor on an exhaust side located in an exhaust channel from the exhaust side of the exhaust gas purification catalyst in the direction of the exhaust gas flow, and a control device that controls the air-fuel ratio d To control the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst, and to control a fault diagnosis for diagnosing the air-fuel ratio sensor from the exhaust side to a malfunction based on the output air-fuel ratio of the air-fuel ratio sensor from the exhaust side, in which ,

when controlling the air-fuel ratio, the control device alternately and periodically switches the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst between a rich air-fuel ratio that is richer than a stoichiometric air-fuel ratio and a poor air-fuel ratio which is poorer than the stoichiometric air-fuel ratio, and,

when managing the fault diagnosis, the control device estimates that the exhaust air-fuel ratio sensor has become faulty when the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst is made rich in the air-fuel ratio by controlling the air-fuel ratio and the output air-fuel ratio of the exhaust air-fuel ratio sensor on the exhaust side changes from the air-fuel ratio, which is richer than predetermined the lean poor set air-fuel ratio, which is poorer than the stoichiometric air-fuel ratio, by the air-fuel ratio, which is poorer than the poor set air-fuel ratio.

[0009] According to a second aspect of the invention, there is a first aspect of the invention, in which when controlling the air-fuel ratio, the control device further performs feedback control of the amount of fuel supplied to the combustion chamber of the internal combustion engine, such that the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst becomes the target air-fuel ratio, and performs training control adjusting the parameter related to air-fuel based on the output air-fuel ratio of the exhaust air-fuel ratio sensor, when controlling the air-fuel ratio, the control device alternately switches the target air-fuel ratio between the rich air-fuel ratio and the poor air-fuel ratio, and when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor becomes a predetermined rich predetermined air-fuel ratio, which is god even if the stoichiometric air-fuel ratio or becomes even smaller, switches the target air-fuel ratio from a rich air-fuel ratio to a poor air-fuel ratio, with learning control, the control device adjusts the parameter related to the air-fuel ratio based on total excess oxygen, which is the total amount of oxygen that becomes excessive when you try to make the air-fuel ratio you cotton gas flowing into the exhaust gas purification catalyst with a stoichiometric air-fuel ratio over a period of oxygen increase from the moment the target air-fuel ratio is switched to a lean air-fuel ratio until it is again switched to a rich air-fuel ratio, and the total insufficient amount oxygen, which is the total amount of oxygen that becomes insufficient when trying to make an air-fuel exhaust ratio about the gas flowing to the exhaust gas purification catalyst with a stoichiometric air-fuel ratio over a period of time when oxygen decreases from the moment the target air-fuel ratio is switched to a rich air-fuel ratio until it is again switched to a lean air-fuel ratio, so that the difference between the total excess oxygen and the total insufficient oxygen becomes less, and if it is estimated that the air-fuel ratio sensor with the exhaust side it became faulty when the target air-fuel ratio is set to a rich air-fuel ratio, the control device stops correcting the parameter related to the air-fuel ratio based on the total insufficient oxygen at this time, even if after that the output air-fuel ratio the exhaust air-fuel ratio sensor becomes rich with a predetermined air-fuel ratio, or less, and the target air-fuel ratio is switched on a poor air-fuel ratio.

[0010] According to a third aspect of the invention, there is a second aspect of the invention in which, when the target air-fuel ratio is set to a rich air-fuel ratio, the output air-fuel ratio of the exhaust air-fuel ratio sensor from the exhaust side changes from the air-fuel ratio, which is richer than the poor predetermined air-fuel ratio, by the air-fuel ratio, which is poorer than the poor predetermined air-fuel ratio, and based on this, it is estimated that the sensor the air-fuel ratio from the exhaust side has become faulty, and the control device calculates the total insufficient amount of oxygen in the time period from the moment the target air-fuel ratio switches to the rich air-fuel ratio for the last time until the output air-fuel ratio of the air-fuel sensor the fuel ratio on the exhaust side changes from an air-fuel ratio, which is richer than a poor predetermined air-fuel ratio, by an air-fuel ratio which is poorer than the poor predetermined air-fuel ratio, and adjusts the parameter related to the air-fuel ratio so that the difference between the total insufficient oxygen and the total excess oxygen becomes smaller.

[0011] According to a fourth aspect of the invention, there is a second or third aspect of the invention, wherein the control device alternately switches the target air-fuel ratio between a constant rich set air-fuel ratio that is richer than a stoichiometric air-fuel ratio and a constant poor set air-fuel ratio -fuel ratio, which is poorer than the stoichiometric air-fuel ratio, and the control device makes a rich degree of rich established air shno-fuel ratio less if using fault diagnosis control is estimated that the sensor air-fuel ratio with the exhaust side has become faulty.

[0012] According to a fifth aspect of the invention, there is a fourth aspect of the invention, in which when controlling the air-fuel ratio, if, as one cycle, the time period of setting the target air-fuel ratio to the rich air-fuel ratio and to the poor air-fuel ratio is determined according to once for each, the control device makes the rich degree of the rich established air-fuel ratio less if the ratio of the number of times it is estimated that the sensor is air-fuel of the relationship with the graduation party has become faulty, with respect to the number of cycles, is the predetermined ratio or more.

[0013] According to a sixth aspect of the invention, there is any of the first to fifth aspect of the invention, in which when controlling the air-fuel ratio, the control device switches the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst from the rich air-fuel ratio to a lean air-fuel ratio when the output air-fuel ratio of the exhaust air-fuel ratio sensor from the exhaust side becomes a predetermined rich predetermined air-fuel ratio by a ratio that is richer than the stoichiometric air-fuel ratio, or becomes even smaller, and switches the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst from a poor air-fuel ratio to a rich air-fuel ratio when the amount of accumulation oxygen in the exhaust gas purification catalyst becomes a predetermined switching reference amount of oxygen that is less than the maximum amount of oxygen accumulation, or becomes e more more.

[0014] According to the present invention, there is an exhaust gas purification system for an internal combustion engine capable of diagnosing a malfunction when the exhaust air-fuel ratio sensor has such a malfunction in the form of a cracked element.

Brief Description of the Drawings

[0015] FIG. 1 is a view schematically showing an internal combustion engine in which a malfunction diagnostic apparatus according to the present invention is used.

FIG. 2 is a schematic sectional view of an air-fuel ratio sensor.

FIG. 3 is a view showing the relationship of the applied voltage V and the output current I at various air-fuel ratio A / F of the exhaust gas.

FIG. 4 is a view showing the relationship of the air-fuel ratio and the output current I when the applied voltage V is constant.

FIG. 5 is a timing chart showing a change in the amount of oxygen storage and the like. in the inlet exhaust gas purification catalyst during normal operation of the internal combustion engine.

FIG. 6 is a schematic sectional view of an air-fuel ratio sensor having a cracked element.

FIG. 7 is a timing chart of an air-fuel ratio correction amount, etc.

FIG. 8 is a functional block diagram of a control device.

FIG. 9 is a flowchart showing a control program for controlling the setting of the correction value of the air-fuel ratio.

FIG. 10 is a block diagram showing a control program for controlling a fault diagnosis, which diagnoses an exhaust air-fuel ratio sensor for a fault.

FIG. 11 is a flowchart showing a control program for controlling setting of a rich set air-fuel ratio and a lean set air-fuel ratio.

FIG. 12 is a timing diagram similar to FIG. 5, showing changes in the amount of oxygen accumulation in the exhaust gas purification catalyst from the exhaust side, etc.

FIG. 13 is a timing chart of a central control air-fuel ratio, etc.

FIG. 14 is a view showing a relationship between an exhaust gas flow rate flowing near the exhaust side air-fuel ratio sensor and an exhaust air-fuel ratio sensor on the exhaust side.

FIG. 15 is a timing chart showing changes in the correction amount of the air-fuel ratio, etc. when the exhaust air-fuel ratio sensor has a cracked element.

FIG. 16 is a timing diagram similar to FIG. 15 showing changes in the correction amount of the air-fuel ratio, etc.

FIG. 17 is a functional block diagram of a control device.

FIG. 18 is a block diagram showing a control program for learning control.

Description of Embodiments

[0016] An embodiment of the present invention will be explained in detail below with reference to the drawings. It should be noted that in the following explanation, the same reference elements are assigned to the same constituent elements.

[0017] General Description of an Internal Combustion Engine

FIG. 1 is a view schematically showing an internal combustion engine using an exhaust gas purification system according to a first embodiment of the present invention. As seen in FIG. 1, the position 1 indicates the engine block, 2 - the cylinder block, 3 - the piston reciprocating inside the cylinder block 2, 4 - the cylinder head mounted on the cylinder block 2, 5 - the combustion chamber formed between the piston 3 and the head 4 cylinder blocks, 6 - intake valve, 7 - intake passage, 8 - exhaust valve, and 9 - exhaust passage. The intake valve 6 opens and closes the intake passage 7, while the exhaust valve 8 opens and closes the exhaust passage 9.

[0018] As shown in FIG. 1, the spark plug 10 is located in the central part of the surface of the inner wall of the cylinder head 4, while the fuel injector 11 is located on the side of the surface of the inner wall of the cylinder head 4. The spark plug 10 is configured to generate a spark in accordance with the ignition signal. Further, the fuel injector 11 injects a predetermined amount of fuel into the combustion chamber 5 in accordance with the injection signal. It should be noted that the fuel injector 11 can also be positioned to inject fuel into the inlet 7. In addition, in the present embodiment, gasoline with a stoichiometric air-fuel ratio of 14.6 is used as fuel. However, an internal combustion engine that employs the exhaust gas purification system of the present invention may also use a different fuel other than gasoline, or a fuel mixed with gasoline.

[0019] The inlet passage 7 of each cylinder is connected to the equalization receiver 14 through the corresponding inlet branch pipe 13, while the equalization receiver 14, in turn, is connected to the air purifier 16 through the inlet pipe 15. Inlet passage 7, inlet branch pipe 13, equalization the receiver 14, and the inlet pipe 15 form an inlet channel. Further, a throttle valve 18 is located inside the intake manifold 15, which is actuated by a throttle valve actuator 17. The throttle valve 18 may be controlled by a throttle valve actuator 17 so as to vary the inlet section of the inlet.

[0020] On the other hand, the exhaust passage 9 of each cylinder is connected to the exhaust manifold 19. The exhaust manifold 19 has a plurality of branch pipes that are connected to the exhaust passages 9, and a pipe on which all branch pipes are assembled. The pipe of the exhaust manifold 19 is connected to the housing 21 on the inlet side, which houses the exhaust gas purification catalyst 20 on the inlet side. The inlet side housing 21 is connected through the exhaust pipe 22 to the exhaust side housing 23, which houses the exhaust gas purification catalyst 24 on the exhaust side. The exhaust passage 9, the exhaust manifold 19, the housing 21 on the inlet side, the exhaust pipe 22 and the housing 23 on the exhaust side form an exhaust channel.

[0021] The electronic control unit (ECU) 31 is a digital computer that is equipped with components connected together via a bi-directional bus 32, such as RAM (random access memory) 33, ROM (read-only memory) 34, MPC (microprocessor) 35, input port 36 and output port 37. A flow meter 39 is installed in the intake pipe 15 to determine the flow rate of air flowing through the intake pipe 15. The output signal of the flow meter 39 is supplied through a corresponding analog-to-digital conversion a body (ADC) 38 at the inlet port 36. In addition, an inlet-side air-fuel ratio sensor 40 is installed on the exhaust manifold 19 pipe, which senses the air-fuel ratio in the exhaust gas flowing inside the exhaust manifold 19 (i.e., the exhaust gas heading to the intake side exhaust purification catalyst 20). Additionally, an exhaust-side air-fuel ratio sensor 41 is disposed in the exhaust pipe 22, which senses the air-fuel ratio in the exhaust gas flowing inside the exhaust pipe 22 (i.e., the exhaust gas flowing from the intake side exhaust gas purification catalyst 20 and the guide to the exhaust gas purification catalyst 24 from the exhaust side). The output signals of these sensors 40 and 41 of the air-fuel ratio also come through the corresponding ADC 38 to the input port 36. It should be noted that the configuration of the sensors 40 and 41 of the air-fuel ratio will be explained below.

[0022] Further, the accelerator pedal 42 has a load sensor 43 connected thereto, which generates an output voltage proportional to the pressure applied to the accelerator pedal 42. The output voltage of the load sensor 43 is supplied to the input port 36 through the corresponding ADC 38. The crankshaft angle sensor 44 generates an output pulse every time, for example, the crankshaft rotates 15 degrees. This output pulse is supplied to the input port 36. The MPC 35 calculates the engine speed based on the output pulse of the crankshaft angle sensor 44. On the other hand, the output port 37 is connected via respective drive circuits 45 to spark plugs 10, fuel injectors 11, and a throttle valve actuator 17. It should be noted that the ECU 31 acts as a control device that controls the air-fuel ratio to control the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20, and control the fault diagnosis for diagnosing the air-fuel ratio sensor 41 with the exhaust side to a fault based on the output air-fuel ratio of the air-fuel ratio sensor 41 on the exhaust side.

[0023] The intake side exhaust gas purification catalyst 20 and the exhaust side exhaust gas purification catalyst 24 are three-way catalysts that have oxygen storage capacity. More specifically, the exhaust gas purification catalysts 20 and 24 are three-way catalysts that include a support member made of ceramic, supported by a precious metal that has a catalytic effect (e.g., platinum (Pt)), and a substance that has the ability to oxygen accumulation (e.g. cerium oxide (CeO ₂ )). The three-component catalyst has the ability to simultaneously clean unburned HC, CO, and NO _X when the air-fuel ratio of exhaust gas flowing into the three-component catalyst is maintained at a stoichiometric air-fuel ratio. In addition, when the exhaust gas purification catalysts 20 and 24 accumulate a certain amount of oxygen, unburned HC and CO and NO _X are purified at the same time, even if the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalysts 20 and slightly deviates from the stoichiometric air -fuel relations, in the rich side or the poor side.

[0024] Accordingly, if the exhaust gas purification catalysts 20 and 24 have an oxygen storage capacity, that is, if the oxygen storage amount of the exhaust gas purification catalysts 20 and 24 is less than the maximum oxygen storage amount, then when the air-fuel exhaust gas ratio flowing into the exhaust gas purification catalysts 20, 24 becomes somewhat poorer than the stoichiometric air-fuel ratio, the excess oxygen contained in the exhaust gas accumulates in the catalysts 20, 24 exhaust gas. Therefore, the surfaces of the exhaust gas purification catalysts 20 and 24 are maintained at a stoichiometric air-fuel ratio. As a result, on the surfaces of the exhaust gas purification catalysts 20 and 24, unburned HC, CO, and NO _X are removed simultaneously. At this time, the air-fuel ratio of exhaust gas flowing from the exhaust gas purification catalysts 20 and 24 becomes a stoichiometric air-fuel ratio.

[0025] On the other hand, if the exhaust gas purification catalysts 20 and 24 can release oxygen, that is, if the oxygen storage amount of the exhaust gas purification catalysts 20 and 24 is greater than zero, then when the air-fuel ratio of the exhaust gas flowing to the catalysts 20, 24 of exhaust gas purification, it becomes somewhat richer than the stoichiometric air-fuel ratio, oxygen, which is insufficient to reduce unburned HC and CO contained in the exhaust gas, is discharged from the exhaust purification catalysts 20 and 24 gas. Therefore, the surfaces of the exhaust gas purification catalysts 20 and 24 are maintained at a stoichiometric air-fuel ratio. As a result, on the surfaces of the exhaust gas purification catalysts 20 and 24, unburned HC, CO, and NO _X are cleaned simultaneously. At this time, the air-fuel ratio of the exhaust gas flowing from the exhaust gas purification catalysts 20 and 24 becomes the stoichiometric air-fuel ratio.

[0026] Thus, when the exhaust gas purification catalysts 20 and 24 accumulate a certain amount of oxygen, even if the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalysts 20 and 24 deviates somewhat from the rich stoichiometric air-fuel ratio, or the poor side, unburned HC, CO and ΝΟ _X are cleaned simultaneously, and the air-fuel ratio of exhaust gas flowing from the exhaust gas purification catalysts 20 and 24 becomes stoichiometric air-fuel attitude.

[0027] Explanation of the air-fuel ratio sensor

In the present embodiment, as the sensors 40 and 41 of the air-fuel ratio, the glass-limit current-air ratio sensors are used. FIG. 2 will be used to illustrate the design of the air-fuel ratio sensors 40, 41. Each of the air-fuel ratio sensors 40 and 41 is equipped with a solid electrolyte layer 51, an exhaust side electrode 52 located on the surface of one side thereof, an atmosphere side electrode 53 located on the other side surface thereof, a diffusion stabilization layer 54 that stabilizes the diffusion of the exhaust passage gas, a reference gas chamber 55, and a heating portion 56 that heats the air-fuel ratio sensors 40 or 41, in particular, a solid electrolyte layer 51.

[0028] In particular, in each of the glass-type air-fuel ratio sensors 40 and 41 in the present embodiment, the solid electrolyte layer 51 has a cylindrical shape with one closed end. Atmospheric gas (air) is introduced inside the reference gas chamber 55, which is formed inside the solid electrolyte layer 51, and a heating portion 56 is located there. An atmosphere side electrode 53 is located on the inner surface of the solid electrolyte layer 51. An exhaust side electrode 52 is located on the outer surface of the solid electrolyte layer 51. On the outer surface of the solid electrolyte layer 51 and the exhaust side electrode 52, a diffusion stabilization layer 54 covering them is located. It should be noted that a protective layer (not shown) may be arranged outside the diffusion stabilization layer 54 to prevent liquid precipitation and the like. on the surface of the diffusion stabilization layer 54.

[0029] The solid electrolyte layer 51 is formed from a sintered body of ZrO ₂ (zirconia), HfO ₂ , ThO ₂ , Bi ₂ O ₃ or other oxides that conduct oxygen ions in which CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ , etc., are mixed as a stabilizer. Further, the diffusion stabilization layer 54 is formed of a porous sintered body obtained from alumina, magnesium oxide, silicon oxide, spinel, mullite, or other heat-resistant inorganic substances. In addition, the exhaust side electrode 52 and the atmosphere side electrode 53 are made of platinum or other precious metal with high catalytic activity.

[0030] In addition, between the exhaust side electrode 52 and the atmosphere side electrode 53, the voltage of the sensor V is supplied by the voltage control device 60, which is installed in the ECU 31. In addition, the ECU 31 is equipped with a current detection section 61 that determines the current I flowing between by these electrodes 52 and 53 through the solid electrolyte layer 51 when the sensor voltage is applied. The current which is determined by this current detecting portion 61 is the output current I of the air-fuel ratio sensors 40 and 41.

[0031] The air-fuel ratio sensors 40 and 41 thus configured have a voltage-current (VI) characteristic, as shown in FIG. 3. As is clear from FIG. 3, the output current I of the air-fuel ratio sensors 40 and 41 becomes the larger, the larger (poorer) the air-fuel ratio of the exhaust gas, i.e. exhaust air-fuel ratio A / F. In addition, on line VI of each exhaust air-fuel ratio A / F, there is a region parallel to the voltage axis of the sensor V, that is, a region where the output current I does not change at all, even if the voltage of the sensor V changes. This voltage region is called “ area of limiting current. " The current at this time is called the "current limit." In FIG. 3, the limiting current region and the limiting current when the exhaust air-fuel ratio is 18 are designated as W ₁₈ and Ι ₁₈ .

[0032] FIG. 4 is a view showing the relationship between the exhaust air-fuel ratio and the output current I when the applied voltage V is made constant and is about 0.45 V (FIG. 3). As will be understood from FIG. 4, in the sensors 40 and 41 of the air-fuel ratio, the output current varies linearly (proportionally) with respect to the exhaust air-fuel ratio, while the higher (i.e., poorer) the exhaust air-fuel ratio, the greater the output current I of the sensors 40 and 41 of the air-fuel ratio. In addition, the air-fuel ratio sensors 40 and 41 are configured such that the output current I becomes zero when the exhaust air-fuel ratio is a stoichiometric air-fuel ratio.

[0033] It should be noted that, as the air-fuel ratio sensors 40 and 41, instead of the air-fuel ratio limit current sensor having the structure shown in FIG. 2, it is also possible to use a multilayer type current limit air-fuel ratio sensor.

[0034] Basic air-fuel ratio control

Next, the basic air-fuel ratio control in the internal combustion engine of the present embodiment will be summarized. When controlling the air-fuel ratio in the present embodiment, feedback control is performed based on the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 to control the amount of injected fuel from the fuel injector 11 so that the output air-fuel ratio the intake air-fuel ratio sensor 40 became the target air-fuel ratio. That is, in the air-fuel ratio control in the present embodiment, feedback control is performed based on the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 so that the air-fuel ratio of the exhaust gas flowing to the catalyst 20 purification of exhaust gas from the intake side, became the target air-fuel ratio. It should be noted that “output air-fuel ratio” means the air-fuel ratio, which corresponds to the output value of the air-fuel ratio sensor.

[0035] Further, in controlling the air-fuel ratio of the present embodiment, the target air-fuel ratio is set based on the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41, and the like. More specifically, when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 becomes rich in the air-fuel ratio, the target air-fuel ratio is set to the lean set air-fuel ratio. As a result, the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 also becomes a poor established air-fuel ratio. In this case, the “poor established air-fuel ratio” is a predetermined constant air-fuel ratio, which is poorer than the stoichiometric air-fuel ratio (air-fuel ratio serving as a control center) by a certain amount, and, for example, is from 14.65 to 20, preferably from 14.65 to 18, more preferably from 14.65 to 16 or so. In addition, the lean set air-fuel ratio can be expressed as the air-fuel ratio obtained by adding a positive correction value of the air-fuel ratio to the air-fuel ratio serving as a control center (in the present embodiment, the stoichiometric air-fuel ratio). In addition, in the present embodiment, when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 becomes rich with a predetermined air-fuel ratio (e.g., 14.55), which is slightly richer than the stoichiometric air-fuel ratio, or even less, an estimate is made that the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 has become rich in the air-fuel ratio.

[0036] If the target air-fuel ratio is changed to a lean set air-fuel ratio, the excess / lack of oxygen in the exhaust gas that flows to the intake side exhaust gas purification catalyst 20 is added together. “Excess / lack of oxygen” means the amount of oxygen that becomes excess, or the amount of oxygen that becomes insufficient (excess HC, CO, etc., hereinafter referred to as unburned gas), when trying to make an air-fuel ratio of exhaust gas, which flows to the inlet side exhaust gas purification catalyst 20 by a stoichiometric air-fuel ratio. In particular, when the target air-fuel ratio is a poor established air-fuel ratio, the exhaust gas that flows to the intake side exhaust gas purification catalyst 20 becomes oxygen excess. This excess oxygen accumulates in the intake side exhaust purification catalyst 20. Therefore, the total amount of excess / lack of oxygen (hereinafter also referred to as the “total excess / lack of oxygen”) can be said to express the estimated amount of oxygen accumulation OSA by the inlet exhaust gas purification catalyst 20.

[0037] It should be noted that the excess / deficiency of oxygen is calculated based on the output air-fuel ratio of the air-fuel ratio sensor 40 from the intake side and the calculated amount of intake air into the combustion chamber 5, which is calculated based on the output signal of the flow meter 39, and etc., or the amount of fuel supplied from the fuel injector 11, and the like. More specifically, the excess / deficiency of OED oxygen is calculated, for example, using the following formula (1):

where 0.23 is the oxygen concentration in the air, Qi is the amount of fuel injected, AFup is the output air-fuel ratio of the intake-side air-fuel ratio sensor 40, and AFR is the air-fuel ratio serving as a control center (in the present embodiment implementation, mainly stoichiometric air-fuel ratio).

[0038] If the total excess / lack of oxygen obtained by cumulatively adding the thus calculated excess / lack of oxygen becomes a predetermined switching reference value (which corresponds to a predetermined switching reference quantity of Cref accumulation) or more, i.e. in an embodiment of the present invention, it becomes a predetermined switching reference amount Cref or more, then the target air-fuel ratio, which was previously a poor set air-fuel ratio, is set to a rich set air-fuel ratio. The rich set air-fuel ratio is a predetermined constant air-fuel ratio, which is somewhat richer than the stoichiometric air-fuel ratio (air-fuel ratio serving as a control center), and is, for example, from 12 to 14.58, preferably from 13 to 14.57, more preferably from 14 to 14.55, or so. Furthermore, the rich set air-fuel ratio can be expressed as the air-fuel ratio obtained by adding the negative correction value of the air-fuel ratio and the air-fuel ratio serving as a control center (in the present embodiment, the stoichiometric air-fuel ratio ) It should be noted that, in the present embodiment, the difference between the rich set air-fuel ratio and the stoichiometric air-fuel ratio (rich degree) is set to the difference between the poor set air-fuel ratio and the stoichiometric air-fuel ratio (poor degree) or smaller.

[0039] After that, when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 again becomes rich with the predetermined air-fuel ratio or less, the target air-fuel ratio is again made poor by the set air-fuel ratio. Next, a similar operation is repeated. Thus, in the present embodiment, the target air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 is alternately and periodically set to the lean set air-fuel ratio and the rich set air-fuel ratio. In other words, in the present embodiment, the air-fuel ratio of exhaust gas flowing to the intake side exhaust gas purification catalyst 20 alternately switches between the rich air-fuel ratio and the lean air-fuel ratio.

[0040] An explanation of air-fuel ratio control using a timing chart

With reference to FIG. 5, the operation explained above will be explained in detail. FIG. 5 is a timing chart of the AFC value of the air-fuel ratio correction, the output air-fuel ratio AFup of the intake side air-fuel ratio sensor 40, the amount of oxygen accumulation OSA by the intake side exhaust gas purification catalyst 20, the total excess / deficiency of oxygen ΣΟΕD of the output air-fuel ratio sensor 41 AFdwn air-fuel ratio from the exhaust side, and the concentration of NO _X in the exhaust gas flowing out of the catalyst 20 with the exhaust gas purifying vpus hydrochloric hand, when the control air-fuel ratio control of the present embodiment.

[0041] It should be noted that the AFC correction amount of the air-fuel ratio is a correction amount related to the target air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20. When the AFC value of the air-fuel ratio correction is 0, the target air-fuel ratio is set to the air-fuel ratio, which is equal to the air-fuel ratio serving as the control center (hereinafter referred to as the “central control air-fuel ratio”) (hereinafter embodiment, stoichiometric air-fuel ratio). When the AFC value of the air-fuel ratio correction is a positive value, the target air-fuel ratio becomes an air-fuel ratio that is poorer than the central control air-fuel ratio (in the present embodiment, a poor air-fuel ratio), wherein when the air-fuel ratio correction value AFC is a negative value, the target air-fuel ratio becomes an air-fuel ratio that is richer, h m central control air-fuel ratio (in the present embodiment, the rich air-fuel ratio). In addition, “central control air-fuel ratio” means the air-fuel ratio, to which is added the AFC value of the correction of the air-fuel ratio in accordance with the operating state of the engine, that is, the air-fuel ratio, which is the reference when changing the target air-fuel ratio fuel ratio in accordance with the AFC value of the air-fuel ratio correction.

[0042] In the example shown in FIG. 5, in a state until time t ₁ , the AFC correction amount of the air-fuel ratio is set to the rich set correction amount AFCrich (corresponding to the rich set air-fuel ratio). That is, the target air-fuel ratio is set to a rich air-fuel ratio. At the same time, the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40 becomes rich in the air-fuel ratio. Unburned gas and the like contained in the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 is cleaned in the intake side exhaust gas purification catalyst 20. At the same time, the amount of OSA oxygen storage in the intake side exhaust purification catalyst 20 is gradually reduced. Since, due to cleaning in the intake side exhaust gas purification catalyst 20, unburned gas, and the like, is not contained in the exhaust gas flowing from the intake side exhaust gas purification catalyst 20, the output air-fuel ratio AFdwn of the sensor 41 is air The fuel ratio on the downstream side is essentially a stoichiometric air-fuel ratio. Since the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 is a rich air-fuel ratio, the amount of NO _X discharged from the intake side exhaust gas purification catalyst 20 is substantially zero.

[0043] If the amount of OSA of oxygen storage in the intake side exhaust gas purification catalyst 20 is gradually reduced, the amount of OSA of oxygen storage is approaching zero. At the same time, a portion of the unburned gas flowing to the intake side exhaust gas purification catalyst 20 starts to flow, without being cleaned, from the intake side exhaust gas purification catalyst 20. As a result, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 gradually decreases, and at time t ₁ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches a rich predetermined air-fuel ratio AFrich.

[0044] In the present embodiment, if the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes rich with a predetermined air-fuel ratio AFrich or less to increase the oxygen storage amount OSA, the air-fuel ratio correction amount AFC is switched by poor set AFClean correction value (corresponding to poor set air-fuel ratio). In addition, at this time, the cumulative excess / deficiency of ΣOED oxygen is reset to zero.

[0045] It should be noted that in the present embodiment, the air-fuel ratio correction amount AFC is switched when the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches the rich predetermined air-fuel ratio AFrich. This is because if the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 is sufficient, then the air-fuel ratio of exhaust gas flowing from the intake side exhaust gas purification catalyst 20 sometimes deviates quite a bit from the stoichiometric air-fuel ratio . In other words, a rich predetermined air-fuel ratio is set to an air-fuel ratio, which the air-fuel ratio of exhaust gas flowing from the intake side exhaust gas purification catalyst 20 never reaches if the amount of oxygen accumulation in the exhaust gas purification catalyst 20 the inlet side is sufficient.

[0046] When the target air-fuel ratio is switched to a lean air-fuel ratio at time t ₁ , the air-fuel ratio of exhaust gas flowing to the intake side exhaust gas purification catalyst 20 changes from the rich air-fuel ratio to lean air fuel ratio. If the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 changes to a lean air-fuel ratio at time t ₁ , the amount of oxygen accumulation OSA in the intake side exhaust gas purification catalyst 20 increases. In addition, with this, the total excess / deficiency of ΣOED oxygen is also gradually increasing.

[0047] Therefore, the air-fuel ratio of the exhaust gas flowing out from the intake side exhaust gas purification catalyst 20 is changed to a stoichiometric air-fuel ratio, and the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 returns to the stoichiometric air-fuel ratio. At this time, the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 is a poor air-fuel ratio, however, there is sufficient reserve for oxygen storage ability in the intake side exhaust gas purification catalyst 20, and therefore oxygen contained in the incoming exhaust gas is accumulated in the intake side exhaust purification catalyst 20, and NO _{X is} removed by reduction. Therefore, the release of NO _X from the inlet side exhaust gas purification catalyst 20 becomes substantially zero.

[0048] Further, if the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 increases, at time t ₂ , the oxygen storage OSA amount in the intake side exhaust gas catalyst 20 reaches the switching reference accumulation amount Cref. Therefore, the cumulative excess / deficiency ΣOED of oxygen reaches the switching reference value OEDref, which corresponds to the switching reference amount of Cref accumulation. In the present embodiment, if the total oxygen excess / deficiency ΣOED becomes the OEDref switching reference value or more, oxygen storage in the intake side exhaust gas purification catalyst 20 is stopped by switching the air-fuel ratio correction value AFC to the rich set correction value AFCrich. Therefore, the target air-fuel ratio is made a rich air-fuel ratio. In addition, at this time, the cumulative excess / deficiency of ΣOED oxygen is reset to 0.

[0049] It should be noted that the switching accumulation reference amount Cref is set to a sufficiently small amount so that the oxygen storage amount OSA does not reach the maximum oxygen storage amount Cmax, even if an unintentional deviation of the air-fuel ratio occurs due to sudden acceleration of the vehicle, etc. For example, the switching reference amount of Cref accumulation is set to 3/4 or less of the maximum amount of oxygen accumulation Cmax before using the intake gas purification catalyst 20, preferably 1/2 or less of this value, more preferably 1/5 or less than this value. As a result, the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich before the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches a poor predetermined air-fuel ratio, which is slightly poorer than the stoichiometric air-fuel ratio (e.g. 14.65, poor air-fuel ratio, in which the difference from the stoichiometric air-fuel ratio is almost the same as the difference between rich specified air-fuel ratio and stoichiometric air-fuel ratio).

[0050] At time t ₂ , if the target air-fuel ratio is switched to a rich set air-fuel ratio, the air-fuel ratio of exhaust gas flowing to the intake side exhaust gas purification catalyst 20 changes from a lean air-fuel ratio to rich air-fuel ratio. Since the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 contains unburned gas, and the like, the oxygen storage amount OSA in the intake side exhaust gas purification catalyst 20 is gradually reduced. At this time, the volume ΝΟ _X discharged from the intake side exhaust gas purification catalyst 20 is substantially zero.

[0051] The amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 is gradually reduced, and at time t ₃ , similar to time t ₁ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches a rich predetermined air-fuel ratio AFrich. Because of this, the air-fuel ratio correction amount AFC is switched to the lean set correction amount AFClean. Further, the cycle of the above time moments t ₁ -t ₃ is repeated.

[0052] As is clear from the above explanation, according to the present embodiment, it is possible to continuously suppress the amount ΝΟ _X discharged from the intake side exhaust gas purification catalyst 20. That is, provided that the above control is performed, it is essentially possible to make the quantity ΝΟ _X discharged from the intake side exhaust gas purification catalyst 20 substantially zero. In addition, the cumulative time period for calculating the cumulative excess / deficiency of ΣOED oxygen is short, therefore, in comparison with the case of cumulative addition of values over a long period of time, the calculation error can be prevented. For this reason, the release of ΝΟ _X due to an error in calculating the total excess / deficiency of ΣΟΕD oxygen is practically excluded.

[0053] Further, in general, if the amount of oxygen accumulation in the exhaust gas purification catalyst is kept constant, the ability of the exhaust gas purification catalyst to accumulate oxygen decreases. That is, in order to maintain the high ability of the exhaust gas purification catalyst to accumulate oxygen, the amount of oxygen accumulation in the exhaust gas purification catalyst must fluctuate. In reflection of this, according to the present embodiment, as shown in FIG. 5, the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 constantly fluctuates up and down, therefore, the oxygen storage capacity does not drop.

[0054] It should be noted that in the above embodiment, during the time t ₁ -t ₂ times, the air-fuel ratio correction amount AFC is maintained on the lean set correction amount AFClean. However, during this time period, the AFC value of the air-fuel ratio correction need not be kept constant. It can be set to change, for example, to a gradual decrease. Alternatively, during the time period t ₁ -t ₂ , it is also possible to temporarily set the AFC value of the air-fuel ratio correction to a value less than 0 (for example, a rich set correction amount, etc.).

[0055] Similarly, in the above embodiment, during the time t ₂ -t ₃ times, the air-fuel ratio correction amount AFC is maintained at the rich set correction amount AFCrich. However, during this time period, the AFC value of the air-fuel ratio correction need not be kept constant. It can be set to change, for example, a gradual increase. Alternatively, during the period t ₂ -t ₃ times, it is also possible to temporarily set the AFC value of the air-fuel ratio correction to a value that is greater than 0 (for example, a poor set correction amount, etc.).

[0056] It should be noted that, in the present embodiment, the AFC value of the air-fuel ratio correction, that is, the target air-fuel ratio is set using the ECU 31. Therefore, it can be said that the ECU 31 continuously or periodically makes the target air-fuel ratio the fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 by the lean air-fuel ratio until the amount of oxygen accumulation OSA in the intake side exhaust gas purification catalyst 20 is estimated be equal to or equal to the switching accumulation reference Cref when the air-fuel exhaust gas ratio detected by the exhaust-side air-fuel ratio sensor 41 becomes rich in the predetermined air-fuel ratio or less, and continuously or periodically makes the target air-fuel ratio rich air-fuel ratio until the air-fuel ratio of the exhaust gas detected by the exhaust-side air-fuel ratio sensor 41 becomes rich nnym air-fuel ratio or less, not allowing that amount OSA oxygen storage has reached the maximum amount of oxygen storage Cmax, when the amount OSA oxygen storage in the catalyst 20 purifying an exhaust gas inlet side is judged to be equal to the switching reference number Cref accumulation or more.

[0057] Simply put, in the present embodiment, it can be said that the ECU 31 switches the target air-fuel ratio (that is, the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20) to the lean air-fuel ratio ratio, when the air-fuel ratio detected by the exhaust-side air-fuel ratio sensor 41 becomes rich in the predetermined air-fuel ratio or less, and switches the target air-fuel ratio (i.e., air the o-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20) to the rich air-fuel ratio when the OSA amount of oxygen storage in the intake side exhaust gas purification catalyst 20 becomes a switching reference accumulation amount Cref or more.

[0058] Cracked air-fuel ratio sensor element

In this regard, as a malfunction occurring in the aforementioned air-fuel ratio sensors 40, 41, mention may be made of cracking of an element forming the air-fuel ratio sensor 40 or 41, that is, a phenomenon referred to as a “cracked element”. More specifically, sometimes a crack occurs that passes through the solid electrolyte layer 51 and diffusion stabilization layer 54 (C1 in FIG. 6), or a crack that passes through the solid electrolyte layer 51 and diffusion stabilization layer 54 plus two electrodes 52, 53 ( C2 in Fig. 6). If such a cracked element occurs, as shown in FIG. 6, the exhaust gas enters the reference gas chamber 55 through the cracked portion.

[0059] As a result, when the air-fuel ratio of the exhaust gas around the air-fuel ratio sensors 40, 41 is a rich air-fuel ratio, the exhaust gas with the rich air-fuel ratio enters the reference gas chamber 55. Because of this, the exhaust gas with a rich air-fuel ratio is distributed in the reference gas chamber 55, and the oxygen concentration around the atmosphere side electrode 53 decreases. On the other hand, also in this case, the exhaust side electrode 52 is exposed to the exhaust gas through the diffusion stabilization layer 54. For this reason, the difference in oxygen concentration between the region near the atmosphere side electrode 53 and the region near the exhaust side electrode 52 drops, and as a result, the output air-fuel ratio of the air-fuel ratio sensors 40, 41 becomes a poor air-fuel ratio. That is, if the air-fuel ratio sensor 40 or 41 has a cracked element, even if the air-fuel ratio of exhaust gas around the air-fuel ratio sensor 40 or 41 is a rich air-fuel ratio, the output air-fuel ratio of the sensor 40 or 41 The air-fuel ratio eventually becomes a poor air-fuel ratio.

[0060] On the other hand, if the air-fuel ratio of the exhaust gas around the air-fuel ratio sensors 40, 41 is a poor air-fuel ratio, such a reverse phenomenon does not occur for the output air-fuel ratio. This is because if the air-fuel ratio of the exhaust gas is a lean air-fuel ratio, the output current of each sensor 40 or 41 of the air-fuel ratio depends on the amount of oxygen that reaches the surface of the exhaust side electrode 52 through the diffusion stabilization layer 54, more than the difference in the air-fuel ratio of the two sides of the solid electrolyte layer 51.

[0061] If, thus, the air-fuel ratio sensor 40 or 41 has a cracked element when the air-fuel ratio of the exhaust gas near the air-fuel ratio sensor 40 or 41 is a rich air-fuel ratio, an output is ultimately erroneous signal. For this reason, for example, if the exhaust-side air-fuel ratio sensor 41 has a cracked element when performing the above-mentioned air-fuel ratio control, then the air-fuel ratio control cannot be further performed as necessary. For this reason, it becomes necessary to quickly diagnose that the exhaust air-fuel ratio sensor 41 has a cracked element malfunction.

[0062] Fault Diagnostics

Therefore, in the present embodiment, the aforementioned malfunction property is used in the form of a cracked element of the exhaust side air-fuel ratio sensor 41 for diagnosing a malfunction in the form of a cracked element of the exhaust air-fuel ratio sensor 41. More specifically, when managing the diagnosis of a malfunction, if, due to the aforementioned control of the air-fuel ratio, the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 is made rich in the air-fuel ratio, it is estimated that the sensor 41, the air-fuel ratio from the exhaust side becomes defective when the output air-fuel ratio of the sensor 41 of the air-fuel ratio from the exhaust side changes from the air-fuel ratio I, which is richer than the poor given the air-fuel ratio in the air-fuel ratio that is poorer than poor predetermined air-fuel ratio.

[0063] Furthermore, in the present embodiment, if, due to the control of the fault diagnosis, it is estimated that the exhaust air-fuel ratio sensor 41 has become faulty, the absolute value of the rich set correction amount is made smaller, that is, the rich degree less established rich air-fuel ratio. In addition, in the present embodiment, if it is estimated that the exhaust air-fuel ratio sensor 41 has become faulty, the absolute value of the lean set correction amount is made smaller, that is, the lean degree of the lean set air-fuel ratio is made smaller. This situation will be explained with reference to FIG. 7.

[0064] FIG. 7 is a timing chart of the AFC value of the air-fuel ratio correction, the output air-fuel ratio AFup of the intake side air-fuel ratio sensor 40, the oxygen storage amount OSA in the intake side exhaust gas purification catalyst 20, the total excess / deficiency of oxygen ΣΟΕD, and an output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41. The dashed line in the figure shows the tendency when the exhaust side air-fuel ratio sensor 41 does not have a cracked element malfunction, while the solid line in the figure shows the trend when the exhaust side air-fuel ratio sensor 41 has a cracked element .

[0065] In the example shown in FIG. 7, until time t ₁ , the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich, thus, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 becomes rich in the air-fuel ratio. In particular, the rich correction setpoint AFCrich at this time is made the first rich correction setpoint AFCrich1. At the same time, the amount of OSA oxygen storage in the intake side exhaust purification catalyst 20 gradually decreases and approaches zero. Because of this, part of the unburned gas and the like flowing into the intake side exhaust gas purification catalyst 20 starts to flow without removal of the exhaust gas by the catalyst 20 from the intake side.

[0066] If unburned gas or the like. starts to flow out of the intake side exhaust gas purification catalyst 20, when the exhaust air-fuel ratio sensor 41 does not have a cracked element malfunction, then, as shown by the broken line in the figure, at the time t ₁ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes a rich air-fuel ratio. However, when the exhaust-side air-fuel ratio sensor 41 has a cracked element malfunction, then, as shown by the solid line in the figure, at time t ₁ , the output air-fuel ratio AFdwn of the exhaust-side air-fuel ratio sensor 41 changes, essentially from a stoichiometric air-fuel ratio to a poor air-fuel ratio.

[0067] That is, if the exhaust side air-fuel ratio sensor 41 has a cracked element malfunction when the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich, that is, when the air-fuel ratio correction amount AFC set to a negative value, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 changes from a ratio that is less than the lean set air-fuel ratio e AFlean, poor in a predetermined air-fuel ratio AFlean or more. In the present embodiment, at a time t1 when such a change in the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is made, it is estimated that the exhaust-side air-fuel ratio sensor 41 has a cracked element malfunction. Because of this, in the present embodiment, it is possible to accurately diagnose a malfunction in the form of a cracked element of the exhaust air-fuel ratio sensor 41.

[0068] In the example shown in FIG. 7, at time t1, a malfunction diagnostic indicator that is set to ON when the exhaust side air-fuel ratio sensor 41 becomes malfunctioning is set to ON. In addition, in the present embodiment, when the assessment is thus made, the exhaust air-fuel ratio sensor 41 has a cracked element malfunction, for example, the signal lamp of the vehicle on which the internal combustion engine is mounted is turned on.

[0069] Further, when, at time t1, it is estimated that the exhaust air-fuel ratio sensor 41 has a cracked element malfunction, the absolute value of the rich set correction amount AFCrich and the absolute value of the poor set correction amount AFClean go to decline. In the example shown in FIG. 7, the rich correction setpoint AFCrich changes from the first rich correction setpoint AFCrich1 to the second rich correction setpoint AFCrich2 with a lower absolute value than the first rich correction setpoint AFCrich1 (| AFCrich ₁ |> | AFCrich ₂ |). In addition, the lean set correction amount AFClean changes from the first lean set correction amount AFClean1 to the second lean set correction amount AFClean2 with a lower absolute value than the first lean set correction amount AFClean1 (| AFClean ₁ ]> | AFClean ₂ |). Therefore, a rich degree of a rich established air-fuel ratio and a poor degree of a poor established air-fuel ratio are decreasing.

[0070] Because of this, at time t1, the rich degree of exhaust gas flowing out from the intake side exhaust gas purification catalyst 20 falls, and the rich degree of the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 drops. For this reason, the concentration of unburned gas, etc. in the exhaust gas flowing from the intake side exhaust gas purification catalyst 20 falls, and therefore, deterioration of the situation with exhaust gas emission can be avoided. It should be noted that, in the present embodiment, both the absolute value of the rich set correction value AFCrich and the absolute value of the poor set correction amount AFClean are reduced. However, there is no need to reduce both values. It is also possible to make only the absolute value of the rich setpoint AFCrich correction decrease.

[0071] In the example shown by the solid line in FIG. 7, even after it has been estimated that the exhaust-side air-fuel ratio sensor 41 has a cracked element malfunction, the aforementioned air-fuel ratio control continues in the usual manner. For this reason, as explained above, the air-fuel ratio correction value AFC is switched from the rich correction set value AFCrich to the lean correction set value AFClean when the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes rich set air-fuel ratio fuel ratio AFrich or less. For this reason, at time t1, the AFC correction amount of the air-fuel ratio does not switch to the lean set correction amount AFClean, but is maintained at the rich set correction amount AFCrich in the usual manner. For this reason, the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 is maintained substantially at zero in the usual manner.

[0072] It should be noted that in the aforementioned embodiment, if it is estimated that the exhaust air-fuel ratio sensor 41 has a cracked element malfunction, the vehicle warning light is turned on. However, in order to increase the accuracy of the estimate, it is also possible to turn on the vehicle warning light if the number of times it is estimated that the exhaust air-fuel ratio sensor 41 has a cracked element malfunction for a predetermined period of time is a predetermined number of times or more. Alternatively, if you determine the time period for setting the AFC correction value of the air-fuel ratio in the rich set correction value AFCrich and in the poor set correction value AFClean once as “1 cycle”, you can turn on the vehicle warning light when the ratio of the number time, when it is estimated that the sensor 41 of the air-fuel ratio from the exhaust side has a malfunction in the form of a cracked element, with respect to the number of such cycles is the ratio Ra (0 <Ra <l) or more.

[0073] Similarly, in the above embodiment, if it is estimated that the exhaust-side air-fuel ratio sensor 41 has a cracked element malfunction, made once, the absolute value of the rich set correction value AFCrich and the absolute value of the poor set correction value AFClean go down. However, in order to avoid inadvertently changing the set correction values, it is also possible to make the absolute values of the set correction values decrease if the number of times that it is estimated that the exhaust air-fuel ratio sensor 41 has a malfunction in the form of a cracked element is a predetermined number of times or more over a period of time. As an alternative, it is also possible to make the absolute values of the set correction values decrease if the ratio of the number of times when it is estimated that the air-fuel ratio sensor from the exhaust side becomes faulty amounts to the specified ratio Ra (0 <Ra < 1) or more.

[0074] It should be noted that in the above embodiment, when controlling the air-fuel ratio, when the air-fuel ratio detected by the exhaust-side air-fuel ratio sensor 41 has become rich in the predetermined air-fuel ratio or less, the target air-fuel ratio switches to poor air-fuel ratio. In addition, when the cumulative excess / deficiency ΣΟΕD of oxygen becomes a predetermined switching reference value OEDref or more, the target air-fuel ratio is switched to a rich air-fuel ratio. However, as a control of the air-fuel ratio, another control may also be used. As such a control, for example, a control can be considered in which, when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 becomes poor or predetermined air-fuel ratio, the target air-fuel ratio switches to a rich air-fuel ratio ratio, while when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 becomes rich with a predetermined air-fuel ratio or earlier, the target air-fuel ratio switches to a lean air-fuel ratio. Even if such control is performed, the air-fuel ratio sensor 41 from the exhaust side can similarly be diagnosed for a malfunction in the form of a cracked element.

[0075] Explanation of Specific Management

Next, with reference to FIG. 8-11, the control device in the present embodiment will be more specifically explained. The control device in the present embodiment is configured to include functional blocks A1-A8, as shown in the block diagram of FIG. 8. Below, with reference to FIG. 8, various function blocks will be explained. The operations of these function blocks A1-A8 are mainly performed by the ECU 31.

[0076] Calculation of the amount of fuel injected

First, the calculation of the amount of fuel injected will be explained. When calculating the amount of fuel injected, the means A1 for calculating the intake air into the cylinder, the means A2 for calculating the basic fuel injection, and the means A3 for calculating the fuel injection are used.

[0077] The intake air calculating means A1 in the cylinder calculates the amount of intake air Ms each cylinder based on the intake air flow Ga, the engine speed NE, and the map or calculation formula stored in the ROM 34 of the ECU 31. The intake air flow Ga is measured by the flow meter 39 and engine revs NE are calculated based on the output of the crankshaft angle sensor 44.

[0078] The basic fuel injection calculation means A2 divides the amount of Ms intake air into the cylinder calculated by the intake air calculator A1 by the target air-fuel ratio AFT to calculate the base quantity Qbase of injected fuel (Qbase = Mc / AFT). The target air-fuel ratio AFT is calculated by the target air-fuel ratio setting means A6 explained below.

[0079] The fuel injection calculating means A3 adds the later explained F / B correction value DFi to the base quantity of injected fuel Qbase, which was calculated by the basic fuel injection calculating means A2 to calculate the quantity of injected fuel Qi (Qi = Qbase + DFi). The command is transmitted to the fuel injector 11, while the fuel in the thus calculated quantity Qi of injected fuel is injected from the fuel injector 11.

[0080] the calculation of the target air-fuel ratio

Next, calculation of the target air-fuel ratio will be explained. When calculating the target air-fuel ratio, the oxygen excess / deficiency calculation means A4, the air-fuel ratio correction amount calculating means A5, and the learning amount calculating means A6 are used.

[0081] The oxygen excess / deficiency calculation means A4 calculates the total oxygen excess / deficiency ΣOED based on the amount of fuel injected Qi calculated by the fuel injection calculating means A3 and the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40. For example, the oxygen excess / deficiency calculation tool A4 calculates the total oxygen excess / deficiency ΣOED by multiplying the difference between the output air-fuel ratio AFup of the intake air-fuel ratio and the central control air-fuel ratio AFR by the quantity of fuel injected Qi, and by cumulative addition of works.

[0082] The air-fuel ratio correction amount calculating means A5 calculates the air-fuel ratio correction amount AFC based on the total oxygen excess / deficiency ΣOED calculated by the oxygen excess / deficiency calculation means A4 and the output air-fuel ratio AFdwn of the air-fuel sensor 41 relationship with graduation. More specifically, the air-fuel ratio correction amount AFC of the target air-fuel ratio is calculated based on the flowchart shown in FIG. 9.

[0083] The target air-fuel ratio setting means A6 adds up the air-fuel ratio correction amount AFC, which was calculated by the target air-fuel ratio correction calculating means A5, with the central control air-fuel ratio AFR (in the present embodiment, the stoichiometric air-fuel ratio fuel ratio) to calculate the target air-fuel ratio AFT. The target air-fuel ratio AFT calculated in this way is supplied to the basic fuel injection calculation means A2 and the later explained air-fuel ratio deviation calculating means A7.

[0084] Calculation of the correction amount F / B

Next, the calculation of the correction amount F / B based on the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 will be explained. When calculating the correction amount F / B, the air-fuel ratio deviation calculating means A7 and the F / B correction calculating means A8 are used.

[0085] The air-fuel ratio deviation calculating means A7 subtracts the target air-fuel ratio AFT, which was calculated by the target air-fuel ratio setting means A6, from the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 to calculate deviations of the DAF air-fuel ratio (DAF = AFup-AFT). This deviation of the DAF air-fuel ratio is a value that expresses the excess / shortage of the amount of fuel supplied to provide the target air-fuel ratio AFT.

[0086] The F / B correction calculation means A8 processes the deviation of the air-fuel ratio DAF, which was calculated by the air-fuel ratio deviation calculation means A7 using proportional integral differential processing (PID processing) to calculate the DFi value of the F / B correction with the purpose of compensating for the excess / lack of fuel supplied based on the following formula (2). The F / B correction value DFi thus calculated is supplied to the fuel injection calculating means A3.

[0087] It should be noted that in the above formula (2), Kp represents a predetermined proportional gain (proportional constant), Ki represents a predetermined integral gain (integral constant), and Kd represents a predetermined derivative gain (derivative constant). In addition, the DDAF is a temporary derivative of the DAF deviation of the air-fuel ratio and is calculated by dividing the difference between the current updated deviation of the DAF of the air-fuel ratio and the previously updated deviation of the DAF of the air-fuel ratio by the time corresponding to the update interval. In addition, the SDAF is the time integral of the deviation of the DAF air-fuel ratio. This SDAF time integral is calculated by adding the current updated DAF deviation of the air-fuel ratio and the previously updated SDAF time integral (SDAF = SDAF + DAF).

[0088] A control flowchart for setting a correction value of the air-fuel ratio

FIG. 9 is a flowchart showing a control program for setting the AFC value of the air-fuel ratio correction. The control program shown in the figure is executed by interruption at each defined time interval. As shown in FIG. 9, first, in step S11, an assessment is made whether the condition for calculating the AFC value of the air-fuel ratio correction is met. A case where the condition for calculating the AFC value of the air-fuel ratio correction is met is, for example, a case where normal operation is performed in which feedback control is performed, for example, a case where fuel cut-off control is not performed. When an assessment is made in step S11 that the condition for calculating the AFC value of the air-fuel ratio correction is met, the program proceeds to step S12.

[0089] Next, in step S12, an assessment is made whether the poor set indicator Fl is set to “OFF”. The poor indicator set Fl is an indicator that is set to “ON” when the AFC value of the air-fuel ratio correction is set to the poor set value of the AFClean correction, and is set to “OFF” in other cases. When it is judged in step S12 that the poor set indicator Fl is set to “OFF”, the program proceeds to step S13. In step S13, an assessment is made whether the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is rich with a predetermined air-fuel ratio AFrich or less. If it is estimated that the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is larger than the rich predetermined air-fuel ratio AFrich, the program proceeds to step S14. In step S14, the air-fuel ratio correction amount AFC is maintained at the rich set correction amount AFCrich, and the control program ends.

[0090] On the other hand, if the amount of OSA of oxygen storage in the intake side exhaust gas purification catalyst 20 decreases, and thus, the air-fuel ratio of exhaust gas flowing from the intake side exhaust gas purification catalyst 20 decreases, then in step S13, estimating that the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is a rich predetermined air-fuel ratio AFrich or less. In this case, the program proceeds to step S15, and the air-fuel ratio correction amount AFC is switched to the lean set correction amount AFClean. Next, in step S16, the poor set indicator Fl is set to “ON”, after which the control program ends.

[0091] If the lean set indicator Fl is set to “ON”, at the next repetition of the control program, in step S12, it is estimated that the lean set indicator Fl is not set to “OFF”, and thus, the program proceeds to step S17. In step S17, an assessment is made whether the cumulative excess / deficiency ΣΟΕD of oxygen from the point in time when the air-fuel ratio correction amount AFC was switched to the lean set correction amount AFClean is smaller than the switching reference value OEDref. If it is estimated that the total oxygen excess / deficiency ΣΟΕD is less than the switching reference value OEDref, the program proceeds to step S18, and the air-fuel ratio correction amount AFC is constantly set to the lean set correction amount AFClean and maintained. Next, the control program ends. On the other hand, if the amount of oxygen accumulation in the intake side exhaust gas purification catalyst 20 increases, ultimately, in step S17, an estimate is made that the total oxygen excess / deficiency ΣΟΕD is equal to or greater than the switching reference value OEDref, and thus , the program proceeds to step S19. In step S19, the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich. Next, in step S20, the poor set indicator Fl is reset to “OFF”, and then the control program ends.

[0092] Flowchart for Malfunction Diagnostics Management

FIG. 10 is a block diagram showing a control program for controlling a fault diagnosis in relation to the diagnosis of the exhaust-air ratio 41 from the exhaust side to the fault. The illustrated control program is executed by interruption at regular intervals

[0093] As shown in FIG. 10, first, in step S31, an assessment is made whether the condition for diagnosing the malfunction is met. A case where the condition for diagnosing a malfunction is fulfilled, for example, is a case where the aforementioned air-fuel ratio control, etc., is performed. When, in step S31, it is judged that the condition for diagnosing the malfunction is fulfilled, the program proceeds to step S32.

[0094] In step S32, an assessment is made whether the AFC value of the air-fuel ratio correction is set to a value less than 0 with the above control to set the correction value of the air-fuel ratio, that is, whether the target air-fuel ratio is a rich air-fuel ratio . If, in step S32, it is estimated that the AFC correction amount of the air-fuel ratio is set to less than 0, that is, if it is estimated that the target air-fuel ratio is a rich air-fuel ratio, the program proceeds to step S33.

[0095] In step S33, an assessment is made whether the stoichiometric indicator Fs is set to OFF. The stoichiometric indicator Fs is an indicator that is set to ON when the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich, and the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes the air-fuel ratio, which is smaller than the lean set AFlean air-fuel ratio, and is close to the stoichiometric air-fuel ratio, otherwise a stoichiometric indicator p Fs is set to OFF. When, in step S33, the stoichiometric indicator Fs is set to OFF, the program proceeds to step S34.

[0096] In step S34, an assessment is made whether the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is smaller than the lean predetermined air-fuel ratio AFlean. Immediately after the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich, the air-fuel ratio of exhaust gas flowing from the intake side exhaust gas purification catalyst 20 becomes essentially a stoichiometric air-fuel ratio, thus in step S34, it is estimated that the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is less than the poor predetermined air-fuel ratio AFlea n, and the program proceeds to step S35. In step S35, the stoichiometric indicator Fs is set to ON, and the control program comes to an end.

[0097] If the stoichiometric indicator Fs is set to ON, in the next step, the control program, the program proceeds from step S33 to step S36. In step S36, an assessment is made whether the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is poor or predetermined AFlean air-fuel ratio or more, that is, whether the output air-fuel ratio AFdwn from the air-fuel ratio has changed which is less than the lean predetermined air-fuel ratio AFlean, into the lean predetermined air-fuel ratio AFlean or greater. If it is estimated that the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 has not become poor set AFlean air-fuel ratio or more, the control program is coming to an end. On the other hand, if, in step S36, it is judged that the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 has become poor set AFlean air-fuel ratio or more, the program proceeds to step S37. At step S37, it is estimated that the exhaust-side air-fuel ratio sensor 41 is faulty, and the program proceeds to step S38. In step S38, the stoichiometric indicator Fs is set to OFF, and the control program comes to an end.

[0098] On the other hand, if, in step S32, it is estimated that the AFC value of the air-fuel ratio correction is set to 0 or more, that is, if it is estimated that the target air-fuel ratio is a poor air-fuel ratio , the program proceeds to step S39. At step S39, an assessment is made whether the stoichiometric indicator Fs is ON. If the target air-fuel ratio was set to the rich air-fuel ratio before setting to the lean air-fuel ratio, and, in step S35, the stoichiometric indicator Fs was set to ON, the program proceeds to step S40. In this case, when the target air-fuel ratio was set to the rich air-fuel ratio last time, this means that the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 did not then become a poor estimated air-fuel ratio AFlean or more. For this reason, in step S40, it is judged that the exhaust side air-fuel ratio sensor 41 is operational. Next, in step S41, the stoichiometric indicator Fs is again set to OFF, and the control program comes to an end. If the stoichiometric indicator Fs is again set to OFF, in the next step of the control program, in step S39, it is estimated that the stoichiometric indicator Fs has not switched to ON, and the control program is coming to an end.

[0099] A control block diagram for changing an established air-fuel ratio

FIG. 11 is a flowchart showing a control program for controlling setting of a rich set air-fuel ratio and a lean set air-fuel ratio. The illustrated control program is executed by interruption at constant time intervals.

[0100] First, in step S51, it is judged whether the judgment in step S37 of FIG. 10 that the exhaust side air-fuel ratio sensor 41 is defective. When it is estimated that, in step S37, the exhaust side air-fuel ratio sensor 41 has not been judged to be defective, the program proceeds to step S52. In step S52, the rich correction setpoint AFCrich is set to the first rich correction setpoint AFCrich1. Therefore, in steps S14 and S19 of the flowchart shown in FIG. 9, the air-fuel ratio correction amount AFC is set to the first rich set correction amount AFCrich1.

[0101] Next, in step S53, the lean set correction amount AFClean is set to the first lean set correction amount AFClean1. Therefore, in steps S15 and S18 of the flowchart shown in FIG. 9, the air-fuel ratio correction amount AFC is set to the first lean set correction amount AFClean1.

[0102] On the other hand, if, in step S51, it is estimated that the exhaust-side air-fuel ratio sensor 41 has been judged to be faulty, the program proceeds to step S54. In step S54, the rich correction setpoint AFCrich is set to the second rich correction setpoint AFCrich2 (| AFCrich ₂ | <| AFCrich ₁ ). Therefore, in steps S14 and S19 of the flowchart shown in FIG. 9, the air-fuel ratio correction amount AFC is set to the second rich set correction amount AFCrich2.

[0103] Next, in step S55, the lean set correction amount AFClean is set to the second lean set correction amount AFClean2 (| AFClean ₂ | <| AFClean ₁ |). Therefore, in steps S15 and S18 of the flowchart shown in FIG. 9, the air-fuel ratio correction amount AFC is set to the second lean set correction amount AFClean2.

[0104] Second Embodiment

Next, with reference to FIG. 12-18, an exhaust gas purification system according to a second embodiment of the present invention will be explained. The configuration and control in the exhaust gas purification system according to the second embodiment are substantially similar to the configuration and control in the exhaust gas purification system according to the first embodiment, with the exception of the points that are explained below.

[0105] Deviation on the intake air-fuel ratio sensor

When the engine housing 1 has a plurality of cylinders, sometimes there is a deviation between the cylinders in the air-fuel ratio in the exhaust gas discharged from the cylinders. On the other hand, the intake-side air-fuel ratio sensor 40 is located on the exhaust manifold 19, however, depending on the location, the degree to which the sensor 40 senses the air-fuel ratio on the inlet side of the exhaust gas discharged from each cylinder is different between the cylinders. As a result, the air-fuel ratio of the exhaust gas that is discharged from the particular cylinder is strongly affected by the exhaust air-fuel ratio of the exhaust air-fuel ratio sensor 40 from the exhaust side. Therefore, when the air-fuel ratio of exhaust gas discharged from a specific cylinder becomes an air-fuel ratio that is different from the average air-fuel ratio of exhaust gas discharged from all cylinders, a deviation occurs between the average air-fuel ratio and the exhaust air the fuel ratio of the intake-side air-fuel ratio sensor 40. That is, the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 deviates to the rich side or the poor side from the average air-fuel ratio of the actual exhaust gas.

[0106] In addition, hydrogen in the unburned gas, and the like, passes through the diffusion stabilization layer of the air-fuel ratio sensor at high speed. Therefore, if the hydrogen concentration in the exhaust gas is high, the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40 deviates to the lower side (i.e., the richer side) relative to the actual air-fuel ratio of the exhaust gas.

[0107] If a deviation occurs in the exhaust air-fuel ratio of the intake side air-fuel ratio sensor 40 in this manner, even if the above control is performed, sometimes ΝΟ _X and oxygen flow from the intake side exhaust gas purification catalyst 20, or the concentration of unburned gas , etc., arising from it, becomes higher. This phenomenon will be explained below with reference to FIG. 12.

[0108] FIG. 12 is a timing chart of the OSA amount of oxygen storage in the intake side exhaust gas purification catalyst 20, and the like, similar to FIG. 5. In FIG. 12 shows a case where the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 deviates to the rich side. In the figure, the solid line at the output air-fuel ratio AFup of the intake side air-fuel ratio sensor 40 shows the output air-fuel ratio of the intake-side air-fuel ratio sensor 40. On the other hand, the dashed line shows the actual air-fuel ratio of the exhaust gas flowing around the air-fuel ratio sensor from the intake side 40.

[0109] In the example also shown in FIG. 12, in a state until time t ₁ , the AFC correction amount of the air-fuel ratio is set to the rich set correction amount AFCrich, and therefore, the target air-fuel ratio is set to the rich set air-fuel ratio. At the same time, the output air-fuel ratio AFup of the inlet-side air-fuel ratio sensor 40 becomes the air-fuel ratio equal to the rich set air-fuel ratio. However, since, as explained above, the output air-fuel ratio of the exhaust side air-fuel ratio sensor 40 deviates to the rich side, the actual air-fuel ratio of the exhaust gas becomes the air-fuel ratio, which is poorer than the rich set air-fuel ratio . That is, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 becomes less (richer) than the actual air-fuel ratio (broken line in the figure). For this reason, that is, since the actual air-fuel ratio of the exhaust gas deviates to the poor side, the rate of decrease in the amount of OSA of oxygen storage in the intake side exhaust gas purification catalyst 20 is slowed down.

[0110] Further, in the example shown in FIG. 12, at time t ₁ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches the rich predetermined air-fuel ratio AFrich. Therefore, as explained above, at time t ₁ , the AFC correction amount of the air-fuel ratio is switched to the lean set correction amount AFClean. Accordingly, the target air-fuel ratio is switched to the lean set air-fuel ratio.

[0111] At the same time, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 becomes an air-fuel ratio equal to the lean set air-fuel ratio. However, as explained above, the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 deviates to the rich side, and therefore, the actual air-fuel ratio of the exhaust gas becomes the air-fuel ratio, which is poorer than the poor set air-fuel ratio . That is, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 becomes smaller (richer) than the actual air-fuel ratio (broken line in the drawing). Therefore, the rate of increase in the OSA amount of oxygen accumulation in the intake side exhaust gas purification catalyst 20 becomes faster, and the actual amount of oxygen entering the intake side exhaust gas purification catalyst 20 while the target air-fuel ratio is set to poor is set the air-fuel ratio becomes larger than the switching reference amount of Cref accumulation.

[0112] Thus, if the intake air-fuel ratio output AFup of the intake air-fuel ratio sensor 40 deviates when the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean, the poor degree of exhaust air-fuel ratio of the current in the inlet side exhaust gas purification catalyst 20 becomes larger. For this reason, even if the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 does not reach the maximum oxygen storage amount Cmax, not all oxygen flowing to the intake side exhaust gas purification catalyst 20 may accumulate. Sometimes, NO _X or oxygen ultimately flows from the intake side exhaust purification catalyst 20. Furthermore, at time t ₂ , the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 becomes a switching reference accumulation amount Cref or more. If, at approximately time t ₂ , such aforementioned unintentional deviation of the air-fuel ratio and the like occurs, NO _X or oxygen may flow from the intake side exhaust gas purification catalyst 20.

[0113] From the above it follows that it becomes necessary to determine a deviation in the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40, and it becomes necessary to correct the output air-fuel ratio and the like. based on the calculated deviation.

[0114] Learning Management

Therefore, in this embodiment of the present invention, in order to compensate for deviation of the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 during normal operation (i.e., when feedback control is performed based on the above-mentioned target air-fuel ratio) , learning management is performed. This learning management will be explained below.

[0115] In this case, the period of time from the moment the target air-fuel ratio is switched to the lean air-fuel ratio until the moment when the total excess / deficiency ΣΟΕD of oxygen becomes the switching reference value OEDref or more, that is, until the moment the target air-fuel is switched The relationship again into a rich air-fuel ratio will be defined as the “oxygen increase time period”. Similarly, the period of time from the moment the target air-fuel ratio is switched to the rich air-fuel ratio to the moment when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 becomes rich with the predetermined air-fuel ratio or less, i.e., the moment the target air-fuel ratio is switched back to the lean air-fuel ratio, it will be defined as the “oxygen reduction time period”. In the learning control of the present embodiment, the total excess oxygen is calculated as the absolute value of the total excess / deficiency ΣOED of oxygen during the oxygen increase time period. It should be noted that the total excess amount of oxygen expresses the total amount of oxygen becoming excess when trying to make the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 into a stoichiometric air-fuel ratio over a period of time for increasing oxygen. In addition, the total insufficient amount of oxygen is calculated as the absolute value of the total excess / deficiency ΣOED of oxygen during the time period of oxygen reduction. It should be noted that the total insufficient amount of oxygen expresses the total amount of oxygen becoming insufficient when trying to make the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 to the stoichiometric air-fuel ratio during the oxygen reduction time period. In addition, the central control air-fuel ratio AFR is corrected so that the difference between the indicated total excess oxygen and the total insufficient oxygen becomes smaller. In FIG. 13 shows this state.

[0116] FIG. 13 is a timing chart of the central control air-fuel ratio AFR, the air-fuel ratio correction amount AFC, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40, the oxygen storage amount OSA in the intake-side exhaust gas purification catalyst 20 , the total excess / deficiency ΣOED of oxygen, the output air-fuel ratio AFdwn of the exhaust-side air-fuel ratio sensor 41, and the training amount sfbg. In FIG. 13 shows a case similar to FIG. 12, where the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 deviates to the lower side (rich side). It should be noted that the training amount sfbg is a value that varies in accordance with a deviation of the output air-fuel ratio of the intake-air ratio sensor 40 and is used to correct the central control air-fuel ratio AFR in the present embodiment. In addition, in the figure, the solid line at the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 indicates an air-fuel ratio corresponding to the output air-fuel ratio of the intake-side air-fuel ratio sensor 40, and the dashed line indicates the actual the air-fuel ratio of the exhaust gas flowing around the air-fuel ratio sensor on the inlet side 40. In addition, the single-dot line indicates the target air-fuel ratio set, i.e. the air-fuel ratio of the stoichiometric air-fuel ratio plus the AFC value of the air-fuel ratio correction and the training sfbg value.

[0117] In the example shown in FIG. 13, similarly to FIG. 5 and 12, in a state until time t ₁ , the central control air-fuel ratio is set to a stoichiometric air-fuel ratio, and the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich. At this time, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40, as shown by the solid line, becomes the air-fuel ratio corresponding to the rich set air-fuel ratio. However, since the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 is rejected, the actual air-fuel exhaust ratio is an air-fuel ratio that is poorer than the rich set air-fuel ratio (broken line in FIG. 13). However, in the example shown in FIG. 13, as is clear from the broken line of FIG. 13, the actual air-fuel ratio of the exhaust gas until time t ₁ becomes a rich air-fuel ratio, which is poorer than the rich set air-fuel ratio. Therefore, the amount of oxygen accumulation in the intake gas purification catalyst 20 is gradually reduced.

[0118] At time t ₁ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches the rich predetermined air-fuel ratio AFrich. Because of this, as explained above, the AFC correction amount of the air-fuel ratio is switched to the lean set correction amount AFClean. After time t ₁ , the output air-fuel ratio of the intake-side air-fuel ratio sensor 40 becomes the air-fuel ratio corresponding to the lean set air-fuel ratio. However, due to the deviation of the output air-fuel ratio of the intake-air ratio 40, the actual air-fuel ratio of the exhaust gas becomes the air-fuel ratio, which is poorer than the poor set air-fuel ratio, i.e., the air-fuel ratio fuel ratio with a greater degree of depletion (see dashed line in Fig. 13). Therefore, the amount of OSA oxygen storage in the intake side exhaust purification catalyst 20 increases rapidly.

[0119] On the other hand, the excess / deficiency of OED oxygen is calculated based on the inlet side of the air-fuel ratio AFup of the inlet-side air-fuel ratio sensor 40. However, as explained above, a deviation occurs in the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40. Therefore, the calculated excess / deficiency of OED oxygen becomes a value that is less than the actual excess / deficiency of OED oxygen (i.e., less oxygen). As a result, the total excess / deficiency ΣΟΕD of oxygen becomes less than the actual amount.

[0120] At time t ₂ , the total oxygen excess / deficiency ΣΟΕD reaches the switching reference value OEDref. Therefore, the AFC correction value of the air-fuel ratio is switched to the rich set correction amount AFCrich. Therefore, the target air-fuel ratio is set to a rich air-fuel ratio. At this time, the actual amount of OSA oxygen storage, as shown in FIG. 13 becomes larger than the switching reference accumulation amount Cref.

[0121] After time t ₂ , similar to the state until time t ₁ , the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich, and accordingly, the target air-fuel ratio is set to the rich air-fuel ratio. Also at this time, the actual air-fuel ratio of the exhaust gas is an air-fuel ratio, which is poorer than the rich established air-fuel ratio. As a result, the inlet side exhaust gas purification catalyst 20 becomes slower in the rate of decrease in the amount of OSA oxygen storage. In addition, as explained above, at time t ₂ , the actual oxygen storage amount in the intake side exhaust gas purification catalyst 20 becomes larger than the switching reference accumulation amount Cref. Therefore, time passes until the actual amount of OSA oxygen storage in the intake side exhaust purification catalyst 20 reaches zero.

[0122] At time t ₃ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches the rich predetermined air-fuel ratio AFrich. Because of this, as explained above, the AFC correction amount of the air-fuel ratio is switched to the lean set correction amount AFClean. Therefore, the target air-fuel ratio is switched from the rich established air-fuel ratio to the poor established air-fuel ratio.

[0123] In the present embodiment, as explained above, the total oxygen excess / deficiency ΣOED is calculated from time t ₁ to time t ₂ . In this regard, if you rely on the time period from the moment when the target air-fuel ratio switches to the lean air-fuel ratio (time t ₁ ), until the calculated amount of oxygen accumulation OSA in the exhaust gas purification catalyst 20 becomes the reference side switching Cref accumulation amount or more (the time point t _2), as the "period of time larger Tinc oxygen", in the present embodiment, the cumulative excess / deficiency oxygen calc ΣΟΕD slyaetsya during Tinc time increasing oxygen. In FIG. 13, the absolute value of the total oxygen excess / deficiency ΣΟΕD during the Tinc period of oxygen increase time from time t ₁ to time t ₂ (total excess oxygen) is shown as R ₁ .

[0124] This cumulative excess amount _of oxygen R ₁ corresponds to the amount of OSA oxygen storage at time t ₂ . However, as explained above, in calculating the excess / deficiency of OED oxygen, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 is used, and a deviation occurs in this output air-fuel ratio AFup. Therefore, in the example shown in FIG. 13, the total excess amount _of oxygen R ₁ from time t ₁ to time t ₂ becomes less than a value that corresponds to the actual amount of oxygen storage OSA at time t ₂ .

[0125] Furthermore, in the present embodiment, the cumulative excess / deficiency ΣOED of oxygen is also calculated from time t ₂ to time t ₃ . In this regard, if we rely on a period of time from the moment when the target air-fuel ratio switches to the rich air-fuel ratio (time moment t ₂ ) to the moment when the output air-fuel ratio AFdwn of the air-fuel ratio sensor 41 is side reaches a predetermined rich air-fuel ratio AFrich (time point t _3), as the "period of time Tdec oxygen reduction", in the present embodiment, the total excess / deficiency oxygen ΣOED calculated ne iodine Tdec time reduction of oxygen. In FIG. 13, the absolute value of the total excess / deficiency ΣOED of oxygen during the time period Tdec of oxygen reduction from time t ₂ to time t ₃ is shown as F ₁ .

[0126] This cumulative insufficient amount _of oxygen F ₁ corresponds to the total amount of oxygen produced by the exhaust gas purification catalyst 20 from the inlet side from time t ₂ to time t ₃ . However, as explained above, a deviation occurs in the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40. Therefore, in the example shown in FIG. 13, the total insufficient amount _of oxygen F ₁ from time t ₂ to time t ₃ is greater than a value that corresponds to the total amount of oxygen released by the exhaust gas purification catalyst 20 from the inlet side from time t ₂ to time t ₃ .

[0127] In this regard, during the Tinc period of the oxygen increase time, oxygen accumulates in the intake side exhaust gas purification catalyst 20, while during the oxygen decrease time period Tdec, the accumulated oxygen is completely discharged. Therefore, the cumulative excess oxygen amount R ₁ and the cumulative oxygen deficiency F ₁ should essentially be the same. However, as explained above, when a deviation occurs in the output air-fuel ratio of the intake-side air-fuel ratio sensor 40, the cumulative value changes in accordance with the deviation. As explained above, when the output air-fuel ratio of the air-fuel ratio sensor 40 from the intake side deviates to the lower side (rich side), the total insufficient amount _of oxygen F ₁ becomes larger than the total excess oxygen amount R ₁ . Conversely, when the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40 deviates to the larger side (the poor side), the total insufficient amount _of oxygen F ₁ becomes less than the total excess oxygen amount R ₁ . In addition, the difference ΔΣΟΕD between the total excess oxygen quantity R ₁ and the total insufficient oxygen quantity F ₁ (= R ₁ -F ₁ , hereinafter referred to as “excess / deficiency error”) expresses the degree of deviation of the output air-fuel ratio of the air-fuel ratio sensor 40 on the inlet side. We can assume that the larger this error ΔΣΟΕD of excess / deficiency, the greater the deviation in the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40.

[0128] Therefore, in the present embodiment, based on the excess / deficiency error ΔΣΟΕD, the central air-fuel ratio AFR is corrected. In particular, in the present embodiment, the central control air-fuel ratio AFR is adjusted so that the difference ΔΣΟΕD between the total excess oxygen amount R ₁ and the total insufficient oxygen quantity F ₁ becomes smaller.

[0129] More specifically, in the present embodiment, the training amount sfbg is calculated using the following formula (3), and the central air-fuel ratio AFR is corrected using the following formula (4).

It should be noted that in the above formula (3), “n” denotes the number of calculations or time. Therefore, sfbg (n) is the current calculated value or the current training value. In addition, “k ₁ ” in the above formula (3) is a gain that indicates the degree to which the excess / deficiency AΣOED error is reflected in the central air-fuel ratio AFR. The larger the gain value “k ₁ ”, the greater the correction amount of the central control air-fuel ratio AFR. In addition, in the above formula (4), the base central control air-fuel ratio AFRbase is the central control air-fuel ratio, which is used as the base, and is the stoichiometric air-fuel ratio in the present embodiment.

[0130] At time t _{3 of} FIG. 13, as explained above, the learning amount sfbg is calculated based on the total excess oxygen amount R1 and the total insufficient oxygen quantity F1. In particular, in the example shown in FIG. 13, since the absolute value F _{1 of the} total oxygen excess / deficiency during the oxygen reduction time period Tdec is greater than the absolute value R _{1 of the} total oxygen excess / deficiency during the oxygen increase time period Tinc, at the time t ₃ , the learning value sfbg decreases.

[0131] At this time, as can be understood from the above formula (4), the central control air-fuel ratio AFR is adjusted based on the training amount sfbg. In the example shown in FIG. 13, the training amount sfbg is a negative value, and therefore, the central control air-fuel ratio AFR becomes a value that is smaller than the basic central control air-fuel ratio AFRbase, i.e., the rich side value. Accordingly, the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst 20 from the inlet side is adjusted to the rich side.

[0132] As a result, the deviation of the actual air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 with respect to the target air-fuel ratio after time t ₃ becomes smaller than before time t ₃ . Therefore, the difference between the dashed line indicating the actual air-fuel ratio and the single-dot line indicating the target air-fuel ratio after time t ₃ becomes smaller than the difference until time t ₃ .

[0133] Furthermore, also after the time t ₃ , an operation similar to the operation during the interval from the time t ₁ to the time t ₂ is performed. Therefore, at time t ₄ , if the cumulative excess / deficiency ΣOED of oxygen reaches the switching reference value OEDref, the target air-fuel ratio is switched from the lean set air-fuel ratio to the rich set air-fuel ratio. Further, at time t ₅ , when the output current Irdwn of the exhaust side air-fuel ratio sensor 41 reaches the rich predetermined air-fuel ratio AFrich, the target air-fuel ratio again switches to the lean set air-fuel ratio.

[0134] The period from time t ₃ to time t ₄ , as explained above, corresponds to the oxygen increase time period Tinc. Therefore, the absolute value of the total excess / lack of oxygen EOED during this period is expressed by the total excess oxygen amount R _{2 of} FIG. 13. In addition, the period from time t ₄ to time t ₅ , as explained above, corresponds to the oxygen reduction time period Tdec, and therefore the absolute value of the total oxygen excess / deficiency ΣOED during this period is expressed by the total insufficient amount _of oxygen F ₂ with FIG. 13. In addition, the training sfbg is updated based on the difference ΣOED (= R ₂ -F ₂ ) between the total excess oxygen R ₂ and the total insufficient oxygen F ₂ by using the above formula (3). In the present embodiment, a similar control is repeated after time t ₅ and, because of this, the training amount sfbg is periodically updated.

[0135] By updating the learning control sfbg value in the learning control as shown above, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 is gradually separated from the target air-fuel ratio, however, the actual air-fuel ratio of the exhaust gas current into the exhaust gas purification catalyst 20 from the inlet side, gradually approaching the target air-fuel ratio. Due to this, it is possible to gradually compensate for the deviation in the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40.

[0136] It should be noted that, as explained above, the training sfbg is updated based on the cumulative excess / deficiency ΣΟΕD of oxygen during the Tinc period of oxygen increase and the cumulative excess / deficiency ΣOED of oxygen in the period Tdec of oxygen reduction time immediately following this Tinc period oxygen increase time. This is so that, as explained above, the total amount of oxygen accumulated on the intake side exhaust gas purification catalyst 20 during the oxygen increase time period Tinc, and the total amount of oxygen discharged from the intake side exhaust gas purification catalyst 20 to the immediately following the Tdec period of oxygen reduction time has become equal.

[0137] Furthermore, in the present embodiment, the learning sfbg value is updated based on the cumulative oxygen excess / deficiency Σ заD for one oxygen increase time period Tinc and the cumulative oxygen excess / deficiency ΣΟΕD for one oxygen decrease time period Tdec. However, the training amount sfbg can be updated based on the total value or average value of the cumulative oxygen excess / deficiency Σ заD for a plurality of oxygen increase time periods Tinc, and the total value or average value of the cumulative oxygen excess / deficiency ΣΟΕD for a plurality of oxygen reduction time periods Tdec.

[0138] Furthermore, in the present embodiment, based on the training amount sfbg, the central control air-fuel ratio is adjusted. However, another parameter related to the air-fuel ratio can also be adjusted based on the training sfbg. As another parameter, for example, the amount of fuel supplied to the combustion chamber 5, the output air-fuel ratio of the inlet-side air-fuel ratio sensor 40, the correction amount of the air-fuel ratio, and the like can be mentioned.

[0139] It should be noted that in the present embodiment, as the control of the air-fuel ratio, the other aforementioned control may also be performed. More specifically, another control, for example, can be considered a control where the target air-fuel ratio switches to a rich air-fuel ratio when the output air-fuel ratio of the exhaust-side air-fuel ratio sensor 41 becomes poor preset air-fuel ratio or more , and the target air-fuel ratio switches to a lean air-fuel ratio when the output air-fuel ratio of the air-fuel ratio sensor 41 to the exhaust side it becomes rich with a given air-fuel ratio or less.

[0140] In this case, the total insufficient oxygen is calculated as the absolute value of the total excess / lack of oxygen during the period of oxygen reduction from the moment when the target air-fuel ratio switches to the rich air-fuel ratio until the moment when the output air-fuel ratio the exhaust side air-fuel ratio sensor 41 becomes rich with a predetermined air-fuel ratio or less. In addition, the total excess oxygen is calculated as the absolute value of the total excess / lack of oxygen during the period of oxygen increase from the moment when the target air-fuel ratio switches to a lean air-fuel ratio until the output air-fuel ratio of the sensor 41 is air - the fuel ratio on the exhaust side becomes poor given air-fuel ratio or more. In addition, the central control air-fuel ratio, etc. adjusted so that the difference between these combined excess oxygen and total insufficient oxygen becomes smaller.

[0141] Therefore, summarizing the above, in the present embodiment, it can be said that when learning control based on the total excess oxygen in a period of time, oxygen increases from the moment the target air-fuel ratio is switched to the lean air-fuel ratio until it is switched again in a rich air-fuel ratio, and the cumulative insufficient amount of oxygen in the period of time of oxygen reduction from the moment of switching the target air-fuel ratio If the air-fuel ratio is reached before it is again switched to a poor air-fuel ratio, the parameter relating to the air-fuel ratio is adjusted so that the difference between these combined excess oxygen and total insufficient oxygen becomes smaller.

[0142] Processes in the presence of a cracked element

As explained above, if the exhaust side air-fuel ratio sensor 41 has a cracked element, mainly when the exhaust gas air-fuel ratio near the exhaust side air-fuel ratio sensor 41 is a rich air-fuel ratio, the air-fuel output the ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes a poor air-fuel ratio. However, sometimes this phenomenon does not occur, depending on the flow rate of the exhaust gas flowing near the exhaust air-fuel ratio sensor 41.

[0143] FIG. 14 is a view showing the relationship between the exhaust gas flow rate near the exhaust side air-fuel ratio sensor 41 and the exhaust air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41. In FIG. 14 shows a case where the air-fuel ratio of exhaust gas flowing near the exhaust-side air-fuel ratio sensor 41 has become a rich air-fuel ratio, which is slightly richer than the stoichiometric air-fuel ratio. In addition, the circular marks in the figure show a case of using a conventional sensor without a cracked element, while the triangular marks in the figure show a case of using a sensor having a cracked element.

[0144] As is clear from FIG. 14, when the exhaust gas flow rate near the exhaust side air-fuel ratio sensor 41 is large, if the exhaust-side air-fuel ratio sensor 41 does not have a cracked element, the output air-fuel ratio AFdwn will correspond to the actual air-fuel exhaust gas ratio. Therefore, in the example shown in FIG. 14, the output air-fuel ratio AFdwn becomes the air-fuel ratio, which is slightly richer than the stoichiometric air-fuel ratio. On the other hand, if, at this time, the exhaust side air-fuel ratio sensor 41 has a cracked element, as explained above, the output air-fuel ratio AFdwn will become a poor air-fuel ratio. In contrast, when the exhaust gas flow rate near the exhaust side air-fuel ratio sensor 41 is small, regardless of whether or not the exhaust-side air-fuel ratio sensor 41 has a cracked element, the output air-fuel ratio AFdwn will correspond to the actual air-fuel ratio of the exhaust gas and will become the air-fuel ratio, which is slightly richer than the stoichiometric air-fuel ratio.

[0145] Thus, the reason why, further, if the exhaust air-fuel ratio sensor 41 has a cracked element, and the exhaust gas flow rate is small, the above phenomenon does not appear to be as follows. That is, if the flow rate of the exhaust gas flowing near the exhaust side air-fuel ratio sensor 41 is small, then the flow rate of the exhaust gas that enters the reference gas chamber 55 through the cracked portion becomes smaller. For this reason, even if the exhaust gas enters the reference gas chamber 55 through this crack, the oxygen concentration near the atmosphere side electrode 53 does not change much. As a result of this, the output air-fuel ratio AFdwn of the exhaust-side air-fuel ratio sensor 41 also does not change, and a correct air-fuel ratio is output.

[0146] erroneous training due to a cracked element

When the exhaust side air-fuel ratio sensor 41 has a cracked element, the output air-fuel ratio shows the above-mentioned processes, thus, when performing the above-mentioned learning control, sometimes the learning amount is ultimately erroneously updated. This erroneous update of the learning amount will be explained with reference to FIG. fifteen.

[0147] FIG. 15 is a timing chart of parameters when the exhaust side air-fuel ratio sensor 41 has a cracked element, such as: intake air amount Ms, central control air-fuel ratio AFR, air-fuel ratio correction amount AFC, oxygen storage amount OSA in upstream exhaust gas purification catalyst 20, cumulative excess / deficiency of oxygen ΣOED, output air-fuel ratio AFdwn of the air-fuel ratio sensor 41 with the exhaust sfbg ones and the value of education. In the example shown in FIG. 15, the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 does not have an error.

[0148] In the example shown in FIG. 15, in a state until time t ₁ , the AFC correction amount of the air-fuel ratio is set to the rich set correction amount AFCrich. For this reason, the amount of OSA oxygen storage in the intake side exhaust purification catalyst 20 is gradually reduced, and unburned gas, etc. begins to flow from the exhaust gas purification catalyst 20 from the intake side at approximately time t ₁ . At this time, the amount of Ms of intake air to the combustion chamber 5 of the internal combustion engine is relatively small, and accordingly, the exhaust gas flow rate near the exhaust-side air-fuel ratio sensor 41 is relatively small. For this reason, if the air-fuel ratio of the exhaust gas flowing near the exhaust side air-fuel ratio sensor 41 becomes a rich air-fuel ratio, at the same time, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 also becomes a rich air-fuel ratio. As a result of this, in the illustrated example, at time t1, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes rich with a predetermined air-fuel ratio AFrich or less. For this reason, the AFC correction value of the air-fuel ratio is switched from the rich set correction amount AFCrich to the lean set correction amount AFClean.

[0149] If, at time t1, the air-fuel ratio correction amount AFC switches to the lean set correction amount AFClean, the amount of oxygen accumulation OSA in the intake side exhaust gas purification catalyst 20 is gradually increased. In addition, together with this, the total excess / deficiency ΣΟΕD of oxygen also gradually increases and at time t2 reaches the switching reference value OEDref. For this reason, at time t2, the AFC correction amount of the air-fuel ratio is switched from the lean set correction amount AFClean to the rich set correction amount AFCrich.

[0150] If the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich, the amount of oxygen accumulation OSA in the intake side exhaust gas purification catalyst 20 is gradually reduced. At about time t3, the amount of OSA oxygen storage in the intake side exhaust gas purification catalyst 20 reaches substantially zero. For this reason, at about time t3, unburned gas, etc. starts to flow from the exhaust gas purification catalyst 20 from the intake side.

[0151] At this time, in the example shown in FIG. 15, the amount of Ms of intake air into the combustion chamber 5 of the internal combustion engine becomes relatively large. Accordingly, the exhaust gas flow rate near the exhaust side air-fuel ratio sensor 41 is also relatively large. For this reason, if the air-fuel ratio of the exhaust gas flowing near the exhaust side air-fuel ratio sensor 41 becomes rich in the air-fuel ratio, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes poor in the air-fuel ratio. fuel ratio. Therefore, at the time t3, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 becomes poor set AFlean or higher, and it is estimated that the exhaust-side air-fuel ratio sensor 41 has a malfunction in the form cracked item.

[0152] However, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 does not become rich with the predetermined air-fuel ratio AFrich or less, so that the air-fuel ratio correction amount AFC continues to be maintained at the rich set correction amount. For this reason, unburned gas, etc. flows from the intake side exhaust gas purification catalyst 20 and, in addition, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 is maintained at an air-fuel ratio that is greater than the lean predetermined AFlean air-fuel ratio.

[0153] After that, in the example shown in FIG. 15, at time t4, the amount of intake air Ms decreases, and the exhaust gas flow rate near the exhaust side air-fuel ratio sensor 41 becomes relatively lower. For this reason, the output air-fuel ratio AFdwn of the exhaust-side air-fuel ratio sensor 41 changes to a correct air-fuel ratio corresponding to the actual air-fuel ratio of the exhaust gas. As a result of this, at time t5, the output air-fuel ratio AFdwn of the exhaust-side air-fuel ratio sensor 41 becomes rich with the predetermined air-fuel ratio AFrich or less. For this reason, the air-fuel ratio correction amount AFC is switched from the rich set air-fuel ratio AFCrich to the poor set air-fuel ratio AFClean.

[0154] In this case, as explained above, the oxygen reduction time period used when the training amount sfbg is calculated becomes the time period from the moment the target air-fuel ratio is switched to the rich air-fuel ratio to the moment when the output air-fuel ratio the exhaust side air-fuel ratio sensor AFdwn ratio 41 reaches the rich predetermined AFrich air-fuel ratio (or until the target air-fuel ratio switches to lean air shno-fuel ratio). For this reason, if we calculate the time period for the reduction of oxygen in this way, the period of time for the reduction of oxygen ultimately becomes extremely long. As a result of this, the total oxygen deficiency F ₁ from time t ₂ to time t ₅ becomes larger than the total oxygen excess R ₁ from time t ₁ to time t ₂ . As shown in FIG. 15, the sfbg training value is significantly reduced. As a result of this, despite the fact that the output air-fuel ratio of the intake-air-air ratio sensor 40 does not have an error on the intake side, the learning amount sfbg changes, and the learning amount is ultimately updated erroneously. As a result of this, as shown in FIG. 15, the central control air-fuel ratio AFR ultimately erroneously changes.

[0155] Updating the amount of training during a malfunction in the form of a cracked element

Therefore, in the present embodiment, when the target air-fuel ratio is set to the rich air-fuel ratio, if it is estimated that the exhaust-side air-fuel ratio sensor 41 has become faulty, even if after that the output air-fuel ratio AFdwn of the sensor 41 is air -fuel ratio on the exhaust side becomes rich with a predetermined air-fuel ratio AFrich or less, and the target air-fuel ratio is switched to a poor air-fuel ratio, cor The fraction of sfbg training based on the cumulative insufficient amount of oxygen stops at this time.

[0156] Further, in the present embodiment, if, when the target air-fuel ratio is set to the rich air-fuel ratio, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 changes from the air-fuel ratio, which richer than the poor predetermined AFlean air-fuel ratio by the air-fuel ratio, which is poorer than the poor predetermined AFlean air-fuel ratio, and therefore it is estimated that the air-fuel ratio sensor 41 On the exhaust side, I became faulty, the absolute value of the total excess / deficiency ΣΟΕD of oxygen during this period of time from the moment the target air-fuel ratio was switched to the rich air-fuel ratio for the last time until the output air-fuel ratio AFdwn of the sensor 41 the exhaust fuel ratio changes from an air-fuel ratio that is richer than a poor predetermined AFlean air-fuel ratio, to an air-fuel ratio that is poorer than a poor adannoe air-fuel ratio AFlean, calculated as cumulative oxygen insufficient number F, and the difference between the thus calculated total insufficient oxygen amount of F and R cumulative excess amount of oxygen becomes smaller by adjusting the sfbg learning. Below, with reference to FIG. 16, a method for updating a learning amount according to the present embodiment will be explained.

[0157] FIG. 16 is a timing diagram similar to FIG. 15 showing an AFC value of an air-fuel ratio correction, etc. In FIG. 16 shows a case where the air-fuel output ratio AFup of the intake side air-fuel ratio sensor 40 has a small error. Also in the example shown in FIG. 16, until time t ₃ , the trend of the parameters is the same as in the example shown in FIG. fifteen.

[0158] Furthermore, in the example also shown in FIG. 16, at time t ₃ , the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 reaches a poor predetermined air-fuel ratio AFlean, and it is estimated that the exhaust-side air-fuel ratio sensor 41 has a failure in the form cracked item. At this time, as is clear from FIG. 16, the amount of OSA oxygen storage becomes substantially zero, and accordingly, in fact, the exhaust gas with a rich air-fuel ratio flows from the intake side exhaust gas purification catalyst 20. Therefore, the total excess / deficiency ΣΟΕD of oxygen from time t ₂ to time t ₃ indicates the amount of oxygen discharged from the exhaust gas purification catalyst 20 from the inlet side from time t ₂ to time t ₃ and corresponds to the amount of oxygen accumulation in the catalyst 20 purification of exhaust gas from the inlet side at time t ₂ . That is, the period from time t ₂ to time t ₃ corresponds to the oxygen reduction time period Tdec in FIG. 13, while the cumulative excess / deficiency ΣOED of oxygen from time t ₂ to time t ₃ corresponds to the total insufficient oxygen amount F shown in FIG. 13.

[0159] For this reason, if the output air-fuel ratio AFup of the intake-side air-fuel ratio sensor 40 is not deviated, the total excess oxygen amount R ₁ during the time Tinc of the increase in oxygen from time t ₁ to time t ₂ , and the cumulative insufficient amount F _{1 of} oxygen during the time period Tdec of the decrease in oxygen from time t ₂ to time t ₃ become the same values. However, when the intake air-fuel ratio sensor 40 has a deviation, these combined excess oxygen amount R ₁ and the cumulative insufficient oxygen quantity F ₁ become different values.

[0160] Therefore, in the present embodiment, the training amount sfbg is calculated according to the above formula (3) based on the difference between the total excess oxygen amount R ₁ during the oxygen increase time period Tinc from time t ₁ to time t ₂ and the total insufficient amount F ₁ oxygen during the oxygen reduction Tdec time from the time t ₂ until time t _3, the time when the output air-fuel ratio sensor 41 AFdwn air-fuel ratio at the outlet side becomes poor specify in stuffy AFlean-fuel ratio or larger, that is, the difference of the excess / ΔΣΟΕD fault (= R ₁ -F _1). In addition, the central control air-fuel ratio AFR is calculated according to the above formula (4) based on the calculated learning amount sfbg.

[0161] As a result of this, in the example shown in FIG. 16, the total insufficient amount _of oxygen F ₁ is greater than the total excess oxygen amount R ₁ , so that at time t _{3 the} learning value sfbg decreases. In addition, as a result of this, the central control air-fuel ratio AFR is decreasing. Due to this, according to the present embodiment, even if the exhaust air-fuel ratio sensor 41 has a cracked element malfunction, the learning value sfbg can be updated accordingly, and accordingly, the deviation in the output air-fuel ratio of the sensor 40 can be appropriately compensated. air-fuel ratio on the intake side.

[0162] Furthermore, in the example shown in FIG. 16 in the same manner as in the example shown in FIG. 15, at time t ₄ , the amount of intake air Ms decreases, and the flow rate of exhaust gas flowing near the exhaust side air-fuel ratio sensor 41 becomes relatively lower. For this reason, the output air-fuel ratio AFdwn of the exhaust side air-fuel ratio sensor 41 changes to a rich air-fuel ratio at time t ₄ , and, at time t ₅ , becomes rich in a predetermined air-fuel ratio AFrich or less . For this reason, the AFC value of the air-fuel ratio correction is switched from the rich set air-fuel ratio AFCrich to the poor set air-fuel ratio AFClean.

[0163] At this time, in the present embodiment, at time t ₅ , the update of the learning value sfbg is stopped and, accordingly, the correction of the central control air-fuel ratio AFR is stopped. As explained with reference to FIG. 15, if the training amount sfbg is updated based on the cumulative oxygen deficiency from time t ₂ to time t ₅ , the training amount sfbg is ultimately erroneously updated. In the present embodiment, at time t ₅ , the training value sfbg is not updated based on the cumulative lack of oxygen from time t ₂ to time t ₅ , thereby erroneously updating the training value sfbg is prevented.

[0164] It should be noted that in the above embodiment, at time t ₃ , the training value sfbg is updated, however, the training value sfbg need not be updated at this time. That is, for a different reason than that the exhaust side air-fuel ratio sensor 41 has a cracked element when the air-fuel ratio correction value AFC must be set to the rich set correction value AFCrich, the output air-fuel ratio AFdwn of the sensor 41, the exhaust-side air-fuel ratio sometimes becomes poor set AFlean air-fuel ratio or more. Such a case, for example, can be considered the case when the engine load suddenly changes, and the air-fuel ratio of the exhaust gas flowing to the intake side exhaust gas purification catalyst 20 suddenly changes, etc. In this case, erroneous updating of the learning amount is prevented by not updating the learning amount sfbg at time t ₃ .

[0165] An explanation of the control in the second embodiment

Next, with reference to FIG. 17 and FIG. 18, the control device in the present embodiment will be explained in more detail. The control device in the present embodiment, as shown in FIG. 17 is configured to include function blocks A1-A10. Among them, the functional blocks A1-A8 are similar to the functional blocks A1-A8 in the first embodiment, thus basically their explanation is omitted.

[0166] In the learning amount calculating means A9, the learning amount sfbg is calculated based on the output air-fuel ratio AFdwn of the exhaust-side air-fuel ratio sensor 41, the total oxygen excess / deficiency ΣOED calculated by the oxygen excess / deficiency calculation means A4, and t .d. More specifically, the learning amount sfbg is calculated based on the learning control block diagram shown in FIG. 18. The training value sfbg thus calculated is stored in RAM 33 of the ECU 31 and is not erased even if the ignition key of the vehicle on which the internal combustion engine is installed is turned OFF.

[0167] In the means for calculating the central control air-fuel ratio A10, the central control air-fuel ratio AFR is calculated based on the base central control air-fuel ratio AFRbase (for example, the stoichiometric air-fuel ratio) and the training amount sfbg calculated by the calculation means A9 learning values. More specifically, as shown in the above formula (4), the central control air-fuel ratio AFR is calculated by adding the learning amount sfbg to the base central control air-fuel ratio AFRbase.

[0168] The target air-fuel ratio setting means A6 calculates the target air-fuel ratio AFT by adding the air-fuel ratio correction amount AFC calculated by the air-fuel ratio correction amount calculating means A5 to the central control air-fuel ratio AFR calculated by the means A10 calculates the central control air-fuel ratio.

[0169] Learning Management Flowchart

FIG. 18 is a block diagram showing a control program for learning control. The illustrated control program is executed by interruption at regular intervals.

[0170] As shown in FIG. 18, first, in step S61, an assessment is made whether the condition for updating the training amount sfbg is fulfilled. The case where the update condition is satisfied is, for example, the case when normal control is performed, etc. In step S61, if an assessment is made that the condition for updating the training amount sfbg is fulfilled, the program proceeds to step S62. In step S62, an assessment is made whether the poor set indicator Fl is set to ON. The poor installed indicator Fl is an indicator that is set in the control program to control the setting of the air-fuel ratio correction amount shown in FIG. 9. When, in step S62, it is judged that the poor set indicator Fl has been set to ON, that is, when the air-fuel ratio correction amount AFC is set to the poor correction correction amount AFC, the program proceeds to step S63.

[0171] In step S63, an assessment is made whether the present time interval is the switching interval of the air-fuel ratio correction amount AFC. More specifically, an assessment is made whether, in the interval from the moment the control program ended the last time to the moment when it started this time, the AFC value of the air-fuel ratio correction is switched from the rich set value AFCrich to the poor set value AFClean correction. When it is judged at step S63 that the present time interval is not a switching interval of the air-fuel ratio correction amount AFC, the program proceeds to step S64. In step S64, the cumulative excess / deficiency of ΣΟΕD oxygen is increased by the current excess / deficiency of OED oxygen.

[0172] If, after this, the target air-fuel ratio switches to the rich air-fuel ratio, in the next repetition of the control program, in step S62, it is estimated that the poor set indicator Fl has been set to OFF, and the program proceeds to step S65 . At step S65, an assessment is made whether the present time interval is a switching interval of the air-fuel ratio correction amount AFC. More specifically, an assessment is made whether, in the interval from the moment when the control program ended the last time to the moment when it started this time, the AFC value of the air-fuel ratio correction was switched from the poor set value AFCrich of the correction to the rich set value AFClean correction. When, in step S65, it is judged that the present time interval is a switching interval of the air-fuel ratio correction amount AFC, the program proceeds to step S66. In step S66, the cumulative excess oxygen amount Rn is made the absolute value of the current cumulative oxygen excess / deficiency ΣOED. Next, in step S67, the cumulative excess / deficiency ΣOED of oxygen is reset to 0, and the control program comes to an end.

[0173] In the next repetition of the control program, usually in step S62, it is estimated that the poor set indicator Fl is set to OFF, and in step S65, it is estimated that the present time interval is not a switching interval of the air-fuel ratio correction amount AFC. In this case, the present control program proceeds to step S68. In step S68, the cumulative excess / deficiency of ΣOED oxygen is increased by the current excess / deficiency of OED oxygen.

[0174] After that, if the target air-fuel ratio switches to the lean air-fuel ratio, in the next repetition of the control program, in step S62, it is estimated that the poor set indicator Fl is set to ON, and, in step S63, the assessment is made that the present time interval is the switching interval of the AFC value of the air-fuel ratio correction. In this case, the present control program proceeds to step S69. At step S69, an assessment is made whether the exhaust-side air-fuel ratio sensor 41 has been judged to be faulty, while the target air-fuel ratio has been set to the rich air-fuel ratio. If, in step S69, it is judged that the exhaust air-fuel ratio sensor 41 has not been judged to be faulty, the program proceeds to step S70.

[0175] In step S70, the total insufficient oxygen Fn is made the absolute value of the current total oxygen excess / deficiency ΣOED. Next, in step S71, the total excess / deficiency ΣΟΕD of oxygen is reset to “0”. Next, in step S72, the training amount sfbg is updated based on the total excess oxygen Rn calculated in step S66 and the total insufficient oxygen Fn calculated in step S70, and the control program is coming to an end. The training value sfbg updated in this way is used to adjust the central control air-fuel ratio AFR according to the above formula (4).

[0176] On the other hand, when it is judged in step S69 that the exhaust side air-fuel ratio sensor 41 has been judged to be faulty, the program proceeds to step S73. In step S73, the cumulative excess / deficiency ΣOED of oxygen obtained in the period of time from the moment when the AFC correction amount of the air-fuel ratio is switched to the rich set correction amount AFCrich until the output air-fuel ratio AFdwn of the air-fuel ratio sensor 41 on the downstream side, becomes a poor predetermined air-fuel ratio AFlean or greater, calculated as the cumulative insufficient amount of oxygen Fn. Next, in step S71, the total excess / deficiency ΣΟΕD of oxygen is reset to “0”. Next, in step S72, the training amount sfbg is updated based on the total excess oxygen Rn calculated in step S66 and the total insufficient oxygen Fn calculated in step S73, and the control program is coming to an end. The training value sfbg updated in this way is used to adjust the central control air-fuel ratio AFR according to the above formula (4). It should be noted that in order to prevent erroneous updating of the learning amount, if it is judged in step S69 that the exhaust air-fuel ratio sensor 41 has been judged to be faulty, the learning quantity sfbg may not be updated in step S72.

[0177] It should be noted that in the aforementioned first embodiment and the second embodiment, when it is judged that the exhaust air-fuel ratio sensor 41 has a cracked element malfunction, the absolute value of the rich set correction amount AFCrich and the absolute value of the poor set AFClean correction values decrease. As a result of this, the rich degree of the rich set air-fuel ratio formed from the central control air-fuel ratio plus the rich set value AFCrich of the correction goes down. In addition, the poor degree of the poor established air-fuel ratio formed from the central control air-fuel ratio plus the poor set AFClean correction value is decreasing.

[0178] However, when it is estimated that the exhaust air-fuel ratio sensor 41 has a cracked element malfunction, it is rather not the absolute value of the rich set correction amount AFCrich and the absolute value of the poor set correction amount AFClean, but the rich set air-fuel fuel ratio and poor installed air-fuel ratio can be adjusted directly. In this case, when an assessment is made that a malfunction in the form of a cracked element has occurred, a rich degree of a rich established air-fuel ratio and a poor degree of a poor established air-fuel ratio may decrease.

List of Reference Items

[0179] 1. engine housing

5. combustion chamber

7. inlet passage

9. exhaust passage

19. exhaust manifold

20. intake side exhaust gas purification catalyst

24. exhaust gas purification catalyst

31. ECU

40. intake air-fuel ratio sensor

41. exhaust air-fuel ratio sensor

Claims (23)

1. An exhaust gas purification system for an internal combustion engine, comprising an exhaust gas purification catalyst located in an exhaust channel of an internal combustion engine, an exhaust air-fuel ratio sensor disposed in an exhaust channel from an exhaust side of an exhaust gas purification catalyst in an exhaust flow direction gas, and a control device that controls the air-fuel ratio to control the air-fuel ratio of the exhaust gas flowing in the catalytic converter purifying an exhaust gas, the fault diagnosis and control for diagnosing the sensor air-fuel ratio at the outlet side fault based on the output of air-fuel ratio sensor air-fuel ratio at the outlet side, wherein when controlling the air-fuel ratio, the control device alternately and periodically switches the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst between a rich air-fuel ratio that is richer than a stoichiometric air-fuel ratio and a poor air-fuel ratio which is poorer than the stoichiometric air-fuel ratio, and, when managing the fault diagnosis, the control device estimates that the exhaust air-fuel ratio sensor has become faulty when the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst is made rich in the air-fuel ratio by controlling the air-fuel ratio and the output air-fuel ratio of the exhaust air-fuel ratio sensor on the exhaust side changes from the air-fuel ratio, which is richer than predetermined the lean poor set air-fuel ratio, which is poorer than the stoichiometric air-fuel ratio, by the air-fuel ratio, which is poorer than the poor set air-fuel ratio. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein when controlling the air-fuel ratio, the control device further performs feedback control of the amount of fuel supplied to the combustion chamber of the internal combustion engine, so that the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst becomes the target air-fuel ratio, and performs learning control adjusting a parameter related to the air-fuel ratio based on the output air-fuel ratio of the air-fuel sensor vnogo relationship with the outlet side, when controlling the air-fuel ratio, the control device alternately switches the target air-fuel ratio between the rich air-fuel ratio and the poor air-fuel ratio, and when the output air-fuel ratio of the exhaust air-fuel ratio sensor becomes a predetermined rich predetermined air -fuel ratio, which is richer than the stoichiometric air-fuel ratio, or becomes even smaller, switches the target air-fuel ratio elations from the rich air-fuel ratio to a poor air-fuel ratio, when learning control, the control device corrects the parameter related to the air-fuel ratio based on the total excess oxygen, which is the total amount of oxygen that becomes redundant when trying to make the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst, the stoichiometric air-fuel ratio in the period of time when the oxygen increase from the moment of switching the target air-fuel ratio n and the poor air-fuel ratio until it is again switched to a rich air-fuel ratio, and the total insufficient oxygen amount, which is the total amount of oxygen that becomes insufficient when trying to make the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst , stoichiometric air-fuel ratio in the period of time of oxygen reduction from the moment the target air-fuel ratio is switched to rich air-fuel ratio until its new switch in a poor air-fuel ratio, so that the difference between the total amount of excess oxygen and total insufficient oxygen becomes smaller, and if it is estimated that the exhaust air-fuel ratio sensor has become faulty when the target air-fuel ratio is set to a rich air-fuel ratio, the control device stops adjusting the parameter related to the air-fuel ratio based on the total insufficient amount of oxygen in this time, even if after that the output air-fuel ratio of the exhaust air-fuel ratio sensor on the exhaust side becomes rich in the predetermined air-fuel ratio ratio, or less, and the target air-fuel ratio switches to a lean air-fuel ratio. 3. The exhaust gas purification system for an internal combustion engine according to claim 2, wherein, when the target air-fuel ratio is set to a rich air-fuel ratio, the output air-fuel ratio of the exhaust air-fuel ratio sensor from the exhaust side changes from air-fuel a relationship that is richer than a poor predetermined air-fuel ratio, by an air-fuel ratio that is poorer than a poor predetermined air-fuel ratio, and based on this, it is estimated that the sensor the exhaust gas ratio on the exhaust side has become faulty, and the control device calculates the total insufficient amount of oxygen during the time period from the moment the target air-fuel ratio switches to the rich air-fuel ratio for the last time until the output air-fuel ratio of the air-sensor the fuel ratio on the exhaust side changes from the air-fuel ratio, which is richer than the poor predetermined air-fuel ratio, by the air-fuel ratio which is poorer than the poor predetermined air-fuel ratio, and adjusts the parameter relating to the air-fuel ratio so that the difference between the total insufficient oxygen and the total excess oxygen becomes smaller. 4. The exhaust gas purification system for an internal combustion engine according to claim 2, wherein when controlling the air-fuel ratio, the control device alternately switches the target air-fuel ratio between the constant rich established air-fuel ratio, which is richer than the stoichiometric air-fuel ratio, and the constant poor established air-fuel ratio, which is poorer than the stoichiometric air fuel ratio, and the control device makes the rich rich air-fuel ratio less established if, by using the fault diagnosis control, it is estimated that the exhaust air-fuel ratio sensor has become malfunctioning. 5. The exhaust gas purification system for an internal combustion engine according to claim 3, wherein when controlling the air-fuel ratio, the control device alternately switches the target air-fuel ratio between the constant rich established air-fuel ratio, which is richer than the stoichiometric air-fuel ratio, and the constant poor established air-fuel ratio, which is poorer than the stoichiometric air fuel ratio, and the control device makes the rich rich air-fuel ratio less established if, by using the fault diagnosis control, it is estimated that the exhaust air-fuel ratio sensor has become malfunctioning. 6. The exhaust gas purification system for an internal combustion engine according to claim 4, wherein when controlling the air-fuel ratio, if as a single cycle we determine the time period of setting the target air-fuel ratio to the rich air-fuel ratio and to the poor air-fuel ratio, once for each, then the control device makes the rich degree of the rich established air-fuel ratio less if the ratio of the number of times it is estimated that the exhaust air-fuel ratio sensor has become faulty with respect to the number of cycles is a predetermined ratio or more. 7. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein when controlling the air-fuel ratio, if as a single cycle we determine the time period of setting the target air-fuel ratio to the rich air-fuel ratio and to the poor air-fuel ratio, once for each, then the control device makes the rich degree of the rich established air-fuel ratio less if the ratio of the number of times it is estimated that the exhaust air-fuel ratio sensor has become faulty with respect to the number of cycles is a predetermined ratio or more. 8. The exhaust gas purification system for an internal combustion engine according to any one of paragraphs. 1-7, in which, when controlling the air-fuel ratio, the control device switches the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst from the rich air-fuel ratio to the lean air-fuel ratio when the output air-fuel ratio of the air-fuel ratio sensor to the exhaust side becomes a predetermined rich predetermined air-fuel ratio, which is richer than the stoichiometric air-fuel ratio, or becomes even smaller, and switches the air-fuel ratio of the exhaust gas flowing to the exhaust gas purification catalyst from the lean air-fuel ratio to the rich air-fuel ratio when the amount of oxygen accumulation in the exhaust gas purification catalyst becomes a predetermined switching reference amount of oxygen that is less than the maximum amount of oxygen accumulation, or even greater.

Images