JP2004019542A - Abnormality detector of oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine abnormality of an oxygen sensor on the downstream side of a catalyst constantly in a shortest time irrespective of an operational condition of an internal combustion engine. <P>SOLUTION: An air-fuel ratio sensor and an oxygen sensor are disposed on the upstream side and the downstream side of a catalyst, respectively. While the oxygen sensor generates a rich output (Step 108) and the air-fuel ratio sensor generates a lean output (Step 110), the amount of oxygen flowing into the catalyst is integrated to obtain the oxygen occlusion capacity Cmax of the catalyst (Step 114). When the calculated with reference to occlusion capacity Cmax exceeds the maximum oxygen occlusion α of the catalyst (Step 116), abnormality of the oxygen sensor is determined (Step 118). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an abnormality detection device for an oxygen sensor, and particularly to an abnormality detection device for detecting an abnormality in an oxygen sensor disposed downstream of a catalyst for purifying exhaust gas.
[0002]
[Prior art]
BACKGROUND ART Conventionally, as disclosed in, for example, JP-A-6-273371, a system including an oxygen sensor downstream of a catalyst for purifying exhaust gas of an internal combustion engine is known. This system enriches the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine when the oxygen sensor is generating a lean output, and thereafter, when the output of the oxygen sensor does not reverse to a rich output until a predetermined time has elapsed. Has a function of determining abnormality of the sensor.
[0003]
When the air-fuel ratio of the air-fuel mixture is made rich, exhaust gas containing unburned components such as HC and CO, that is, exhaust gas lacking oxygen, flows into the catalyst. When oxygen is stored in the catalyst, HC and CO are oxidized inside the catalyst by releasing the oxygen. As a result, a clean exhaust gas containing no HC or CO flows out downstream of the catalyst.
[0004]
If the air-fuel ratio of the mixture is maintained at a rich level, all of the oxygen in the catalyst is eventually consumed, and exhaust gas containing HC and CO, that is, exhaust gas lacking oxygen, flows downstream of the catalyst. When a normal oxygen sensor touches such exhaust gas, the output is inverted to a rich output. When the output of the oxygen sensor does not reverse after the time required for all the oxygen in the catalyst to elapse after the air-fuel ratio of the air-fuel mixture is made rich, Is determined. According to such a method, it is possible to accurately detect the abnormality of the oxygen sensor.
[0005]
[Problems to be solved by the invention]
Incidentally, the time required for all the oxygen in the catalyst to be consumed varies depending on the flow rate of the exhaust gas flowing into the catalyst. Then, the flow rate of the exhaust gas flowing into the catalyst changes according to the operating state of the internal combustion engine. For this reason, in the above-mentioned conventional system, the time required for all the oxygen in the catalyst to be consumed after the air-fuel ratio is enriched changes according to the operating state of the internal combustion engine and the like.
[0006]
Under such circumstances, in order to always accurately judge the abnormality of the oxygen sensor, the above-mentioned predetermined time, that is, the time to wait for the reversal of the sensor output after enriching the air-fuel ratio is determined by the exhaust gas flow rate. Must be set as the minimum value. For this reason, in the above-described conventional system, in a situation where a large amount of exhaust gas is generated, after the mixture is made rich, an unnecessarily long time is required until an abnormality of the oxygen sensor is determined. I needed to.
[0007]
The present invention has been made in order to solve the above-described problem, and is intended to always determine the abnormality of the oxygen sensor disposed downstream of the catalyst in a shortest time regardless of the operation state of the internal combustion engine. It is an object of the present invention to provide an abnormality detection device that can perform the abnormality detection.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an abnormality detection device that detects an abnormality of an oxygen sensor disposed downstream of a catalyst that purifies exhaust gas, in order to achieve the above object,
An upstream sensor that is arranged upstream of the catalyst and emits an output according to the exhaust air-fuel ratio;
The oxygen calculated by the catalyst is calculated by integrating the amount of oxygen in the exhaust gas flowing into the catalyst during a period in which the oxygen sensor generates a rich output and the upstream sensor generates a lean output. A storage capacity calculation means for obtaining a storage capacity, and a shortage of oxygen in exhaust gas flowing into the catalyst during a period when the oxygen sensor is generating a lean output and the upstream sensor is generating a rich output. At least one of discharge capacity calculating means for calculating the calculated oxygen storage capacity of the catalyst by integrating the amount,
When the calculated oxygen storable amount exceeds the maximum oxygen storage amount of the catalyst, abnormality determination means for determining an abnormality of the oxygen sensor;
It is characterized by having.
[0009]
Further, the second invention is based on the first invention,
The upstream sensor is an air-fuel ratio sensor that detects an exhaust air-fuel ratio,
Air-fuel ratio difference calculating means for obtaining a difference ΔA / F between the air-fuel ratio detected by the upstream sensor and the stoichiometric air-fuel ratio;
Fuel supply amount detection means for detecting a fuel supply amount to the internal combustion engine,
The storage capacity calculation means includes an oxygen amount calculation means for calculating an oxygen amount in exhaust gas based on the ΔA / F and the fuel supply amount,
The discharge-time capacity calculation means includes oxygen deficiency calculation means for calculating an oxygen deficiency in exhaust gas based on the ΔA / F and the fuel supply amount.
[0010]
Further, a third invention is the first or the second invention, wherein
Comprising at least one of forced lean means used in combination with the storage capacity calculation means, and forced rich means used in combination with the release capacity calculation means,
The forced lean means is a means for leaning the target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine while the oxygen sensor emits a rich output,
The forcible rich means is means for making the target air-fuel ratio of the air-fuel mixture rich while the oxygen sensor is generating a lean output.
[0011]
In a fourth aspect, in the third aspect,
With both the forced lean means and the forced rich means,
By continuously operating the forced rich means and the forced lean means, a reversal control means for reversing the target air-fuel ratio between rich and lean whenever the output of the oxygen sensor is reversed is provided. I do.
[0012]
In a fifth aspect, in the third or fourth aspect,
When the abnormality of the oxygen sensor is determined, the target air-fuel ratio is set by the forced lean unit, and the target air-fuel ratio is set by the forced rich unit. .
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals, and redundant description will be omitted.
[0014]
Embodiment 1 FIG.
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10.
[0015]
An air flow meter 18 is arranged in the intake passage 12 downstream of the air filter 16. The air flow meter 18 is a sensor that detects an intake air amount Ga flowing through the intake passage 12. A throttle valve 20 is provided downstream of the air flow meter 18. Further, a fuel injection valve 22 for injecting fuel to an intake port of the internal combustion engine 10 is disposed in the intake passage 12.
[0016]
A catalyst 24 communicates with the exhaust passage 14. The catalyst 24 can occlude a certain amount of oxygen. When NOx is contained in the exhaust gas, the catalyst 24 purifies the exhaust gas by reducing it, and also removes the oxygen released in the process of the reduction. Can be occluded. Further, when unburned components such as HC and CO are contained in the exhaust gas, the catalyst 24 can purify the exhaust gas by oxidizing them while releasing the stored oxygen. .
[0017]
In the exhaust passage 14, an air-fuel ratio sensor 26 is disposed upstream of the catalyst 24, and an oxygen sensor 28 is disposed downstream of the catalyst 24. The air-fuel ratio sensor 26 is a sensor that outputs an output according to the exhaust air-fuel ratio. The air-fuel ratio sensor 26 can detect the air-fuel ratio of the exhaust gas immediately after being discharged from the internal combustion engine 10, that is, the air-fuel ratio of the exhaust gas before being purified by the catalyst 26.
[0018]
The oxygen sensor 28 is a sensor that greatly changes the output according to the presence or absence of oxygen in the exhaust gas. Therefore, according to the oxygen sensor 28, it is possible to accurately detect whether or not oxygen is present in the exhaust gas flowing downstream of the catalyst 24.
[0019]
FIG. 2 is a diagram for explaining the configuration of the oxygen sensor 28. As shown in FIG. 2, the oxygen sensor 28 includes a heater 30 and an element layer 32. The element layer 32 is configured to surround the heater 30. An electrode 34 formed so as to surround the vicinity of the tip of the heater 30 is incorporated in the element layer 32. Further, inside the element layer 32, an air space 36 which receives supply of the air is formed. Further, outside the element layer 32, a measurement gas chamber 40 surrounded by a cover 38 is formed.
[0020]
The electrode 34 generates an electromotive force according to the presence or absence of oxygen on the surface exposed to the atmosphere chamber 36 and the surface exposed to the measurement gas chamber 40, respectively. The oxygen sensor 28 outputs the difference between the electromotive forces as a sensor output. When the exhaust gas containing oxygen is led to the measurement gas chamber 40, the electrode 34 is raised on both the surface exposed to the atmosphere chamber 36 and the surface exposed to the measurement gas chamber 40 in response to the presence of oxygen. Emit power. In this case, the oxygen sensor 28 emits an output of almost 0V.
[0021]
On the other hand, when the exhaust gas containing no oxygen is introduced into the measurement gas chamber 40, the electrode 34 generates an electromotive force corresponding to the presence of oxygen on the surface exposed to the atmosphere chamber 36, and is exposed to the measurement gas chamber 40. The surface generates an electromotive force corresponding to the absence of oxygen. In this case, the oxygen sensor 28 outputs about 1V.
[0022]
As described above, the output of the oxygen sensor 28 largely changes depending on whether or not the exhaust gas flowing downstream of the catalyst 24 contains oxygen. Therefore, according to the output of the oxygen sensor 28, it is accurately detected whether the exhaust gas containing oxygen or the exhaust gas containing no oxygen is flowing downstream of the catalyst 24. be able to.
[0023]
As shown in FIG. 1, the system according to the present embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 is a unit for controlling the operation of the system according to the present embodiment. The outputs of the various sensors described above are supplied to the ECU 50, and the above-described fuel injection valves 22 are connected to the ECU 50. The ECU 50 can control the fuel injection amount based on those sensor outputs.
[0024]
Next, the operation of the system of the present embodiment will be described.
In the present embodiment, during normal operation, the ECU 50 executes stoichiometric control. In the stoichiometric control, the fuel injection amount is controlled such that the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 is maintained near the stoichiometric air-fuel ratio (stoichiometric). More specifically, the fuel injection amount is controlled such that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 26 repeats rich and lean with a small width across the stoichiometric air-fuel ratio.
[0025]
While the exhaust air-fuel ratio is lean, exhaust gas containing NOx flows into the catalyst 24. At this time, the catalyst 24 purifies the exhaust gas by reducing NOx, and stores the oxygen generated as a result. Therefore, while the exhaust air-fuel ratio is lean, the oxygen storage amount in the catalyst 24 shows an increasing tendency. When the exhaust air-fuel ratio is inverted to rich, exhaust gas containing HC and CO flows into the catalyst 24. At this time, the catalyst 24 oxidizes HC and CO while releasing the stored oxygen. As a result, clean exhaust gas flows downstream of the catalyst 24.
[0026]
While the ECU 50 is executing the stoichiometric control, the above-described storage and release of oxygen by the catalyst 24 are repeated. As a result, clean exhaust gas continuously flows downstream of the catalyst 24. For this reason, according to the system of the present embodiment, good exhaust emission characteristics can be realized during normal operation.
[0027]
The ECU 50 executes the active control when a predetermined execution condition is satisfied. In the active control, each time the output of the oxygen sensor 28 is inverted, the target air-fuel ratio of the air-fuel mixture is changed between a predetermined rich target value (for example, 14.1) and a predetermined lean target value (for example, 15.1). Inverted.
[0028]
FIG. 3 is a timing chart for explaining the operation of the system when the active control is executed under the condition that the oxygen sensor 28 is functioning normally. More specifically, FIG. 3A shows a change in the target air-fuel ratio during execution of the active control (waveform {circle around (1)}) and a change in the exhaust air-fuel ratio A / F detected by the air-fuel ratio sensor 26 (waveform {circle around (1)}). 2 ▼). FIG. 3B shows a change in the output of the oxygen sensor 28 (waveform {circle around (3)}).
[0029]
The timing chart shown in FIG. 3 shows an example in which the stoichiometric control is executed until time t1, and then the active control is started. In this example, at time t1, the output of the oxygen sensor 28 is inverted from the rich output to the lean output, and the target air-fuel ratio is changed from the stoichiometric air-fuel ratio to the rich target value with the start of the active control. .
[0030]
When the target air-fuel ratio is set to the rich target value, the ECU 50 thereafter gradually increases the fuel injection amount until the exhaust air-fuel ratio A / F detected by the air-fuel ratio sensor 26 reaches the rich target value. As a result, the exhaust air-fuel ratio A / F becomes a value near the rich target value after a certain delay after the time t1.
[0031]
While the exhaust air-fuel ratio A / F is maintained at a rich value, rich exhaust gas, that is, oxygen-deficient exhaust gas containing HC and CO flows into the catalyst 24. When such an oxygen-deficient exhaust gas flows into the catalyst 24 holding the stored oxygen, the oxygen in the catalyst 24 is released, and the oxidation (purification) of HC and CO is performed. Then, in this case, a clean exhaust gas containing oxygen flows downstream of the catalyst 24. For this reason, while the catalyst 24 holds the stored oxygen, the output of the oxygen sensor 28 located downstream thereof is maintained as a lean output.
[0032]
In FIG. 3, time t2 indicates the time when all the stored oxygen in the catalyst 24 has been released. When all the stored oxygen in the catalyst 24 has been released, the catalyst 24 cannot release oxygen into the exhaust gas. Therefore, when such a situation is reached, oxygen-deficient exhaust gas including HC and CO begins to flow downstream of the catalyst 24. As a result, at time t2, the output of the oxygen sensor 28 is inverted from the lean output to the rich output.
[0033]
The ECU 50 can recognize that the catalyst 24 has released all the stored oxygen when the output of the oxygen sensor 28 is inverted in this way. In the active control, when the output of the oxygen sensor 28 is inverted in this way, at that time (t2), the target air-fuel ratio is inverted to the lean target value.
[0034]
At time t2, when the target air-fuel ratio is changed to the lean air-fuel ratio, the ECU 50 thereafter gradually reduces the fuel injection amount until the exhaust air-fuel ratio A / F detected by the air-fuel ratio sensor 26 reaches the lean target value. Decrease. As a result, the exhaust air-fuel ratio A / F becomes a value near the lean target value after a certain delay after the time t2.
[0035]
While the exhaust air-fuel ratio A / F is maintained at a lean value, lean exhaust gas, that is, exhaust gas with an excessive amount of oxygen containing NOx, flows into the catalyst 24. When exhaust gas containing NOx flows into the catalyst 24 having a sufficient oxygen storage capacity, the catalyst 24 stores the resulting oxygen while reducing NOx. In this case, a clean exhaust gas containing no oxygen flows downstream of the catalyst 24. For this reason, while the catalyst 24 has sufficient oxygen storage capacity, the output of the oxygen sensor 28 located downstream thereof is maintained as a rich output.
[0036]
In FIG. 3, a time t3 indicates a time point when oxygen having the full oxygen storage capacity is stored in the catalyst 24. When the catalyst 24 stores oxygen to its full capacity, the oxygen in the exhaust gas starts to flow downstream of the catalyst 24 thereafter. As a result, at time t3, the output of the oxygen sensor 28 is inverted from the rich output to the lean output.
[0037]
When the output of the oxygen sensor 28 is inverted in this way, the ECU 50 can recognize that the catalyst 24 is in a state of storing oxygen to its full capacity. In the active control, when the output of the oxygen sensor 28 is inverted in this way, the target air-fuel ratio is inverted to the rich target value at that time (t3). Then, during execution of the active control, the process of inverting the target air-fuel ratio between the rich target value and the lean target value is continued each time the output of the oxygen sensor 28 is inverted (time t4, t5).
[0038]
As described above, during the execution of the active control, the state in which the catalyst 24 fully stores oxygen and the state in which the stored oxygen is completely released are repeatedly realized with the reversal of the target air-fuel ratio. The area indicated by hatching in FIG. 3 (A) indicates a period during which the empty catalyst 24 stores oxygen up to the full capacity, or a catalyst storing oxygen up to the full capacity, in the process of switching between these two states. 24 corresponds to the period during which oxygen is released until empty. Therefore, during these periods, if the amount of oxygen flowing into the catalyst 24 is integrated (at the time of occlusion) or if the amount of oxygen deficiency in the exhaust gas flowing into the catalyst 24 is integrated (at the time of release), the catalyst 24 Can be obtained by calculation. A specific method for calculating Cmax will be described later.
[0039]
As described above, according to the system of the present embodiment, when the oxygen sensor 28 is functioning normally, the active control is executed, so that the oxygen storage capacity Cmax of the catalyst 24 can be obtained by calculation. The oxygen storage capacity Cmax tends to decrease as the catalyst 24 deteriorates. In the present embodiment, the ECU 50 can detect the state of the deterioration based on Cmax calculated by the above method.
[0040]
FIG. 4 is a timing chart for explaining the operation of the system when the active control is executed under the situation where the oxygen sensor 28 is abnormal. Waveforms (1) to (3) shown in FIGS. 4 (A) and 4 (B) show changes in the target air-fuel ratio (waveforms), respectively, as in the cases shown in FIGS. 3 (A) and 3 (B). (1)), changes in the exhaust air-fuel ratio A / F detected by the air-fuel ratio sensor 26 (waveform (2)), and changes in the output of the oxygen sensor 28 (waveform (3)).
[0041]
The timing chart shown in FIG. 4 shows an example in which the stoichiometric control is executed until time t1, and then the active control is started. In this example, at time t1, the target air-fuel ratio is changed from the stoichiometric air-fuel ratio to the rich target value with the start of the active control.
[0042]
When the target air-fuel ratio is set to the rich target value, the ECU 50 thereafter gradually increases the fuel injection amount until the exhaust air-fuel ratio A / F reaches the rich target value. As a result, the exhaust air-fuel ratio A / F becomes a value near the rich target value after a certain delay after the time t1. While the exhaust air-fuel ratio A / F is maintained at a rich value, oxygen-deficient exhaust gas including HC and CO flows into the catalyst 24. While the occlusion remains in the catalyst 24, HC and CO are oxidized (purified), and a clean exhaust gas containing oxygen flows downstream of the catalyst 24. Then, when all the oxygen in the catalyst 24 is consumed, the oxygen-deficient exhaust gas including HC and CO starts to flow downstream of the catalyst 24 (time t2).
[0043]
When the oxygen sensor 28 is functioning normally, the output of the oxygen sensor 28 is inverted at that time (t2) as described with reference to FIG. However, when an abnormality occurs in the oxygen sensor 28, the output of the oxygen sensor 28 does not reverse even after the oxygen-deficient exhaust gas starts to flow downstream of the catalyst 24, as shown in FIG. The situation where the lean output is maintained may occur.
[0044]
During execution of the active control, an inversion command of the target air-fuel ratio is issued in response to the inversion of the output of the oxygen sensor 28. Therefore, when the output of the oxygen sensor 28 does not reverse, the target air-fuel ratio is also maintained at the rich target value, as shown in FIG. In a region indicated by hatching in FIG. 4A, the ECU 50 attempts to calculate the oxygen storage capacity Cmax of the catalyst 24 by integrating the oxygen deficiency in the exhaust gas flowing into the catalyst 24. Indicates the period. In this case, the above-described integration is executed for an unreasonably long time, so that the calculated oxygen storage capacity Cmax becomes an unreasonably large value. Therefore, in the present embodiment, if the calculated value of the oxygen storage capacity Cmax becomes unduly large due to the execution of the active control, the ECU 50 determines the abnormality of the oxygen sensor 28 at that time, The execution of the active control is stopped.
[0045]
FIG. 5 shows a flowchart of a control routine executed by the ECU 50 in the present embodiment to realize the above functions.
In the routine shown in FIG. 5, first, it is determined whether or not the abnormality determination of the oxygen sensor 28 has been completed (step 100).
[0046]
If it is determined that the abnormality determination has already been completed, the current processing cycle ends immediately. On the other hand, when it is determined that the abnormality determination has not been completed, it is next determined whether or not the active control execution condition is satisfied (step 102).
[0047]
As a result, if it is determined that the execution condition of the active control is not satisfied, the current processing cycle is immediately ended. On the other hand, when it is determined that the execution condition is satisfied, it is next determined whether or not the output of the oxygen sensor 28 is inverted from the previous processing cycle to the current processing cycle (step 104). ).
[0048]
When it is determined that the output of the oxygen sensor 28 is inverted, it can be determined that the oxygen sensor 28 is functioning normally. Therefore, when such a determination is made, it is determined that the oxygen sensor 28 is normal thereafter, and the current processing cycle is ended (step 106).
When it is determined that the oxygen sensor 28 is normal by the process of step 106, it is recognized that the abnormality determination has been completed at that time. Therefore, if this routine is started again after the execution of step 106, the completion of the abnormality determination is determined in step 100.
[0049]
If it is determined in step 104 that the output of the oxygen sensor 28 is not inverted, then it is determined whether or not the output of the oxygen sensor 28 is a rich output (step 108). .
That is, taking the timing chart shown in FIG. 3 as an example, it is determined whether the state shown at time t2-t3 or the state shown at time t4-t5 is formed.
[0050]
When it is determined that the output of the oxygen sensor 28 is a rich output, it is further determined whether or not the output of the air-fuel ratio sensor 26 is lean (step 110).
That is, in the case of the period from time t2 to t3 in FIG. 3 or the period from time t4 to t5 as an example, it is determined whether or not a state of a period indicated by hatching is formed during those periods. .
[0051]
As a result, if it is determined that the condition of step 110 is not satisfied, the target air-fuel ratio has been inverted to the lean target value, but the air-fuel ratio of the exhaust gas flowing into the catalyst 24 is still lean at this time. You can determine that there is no. In this case, the value of the storage time Cmax is reset to the initial value (step 112).
The “storage time Cmax” is the oxygen storage capacity of the catalyst 24 calculated by integrating the amount of oxygen flowing into the catalyst 24 in the process of storing oxygen in the catalyst 24.
[0052]
On the other hand, if it is determined in step 110 that the exhaust air-fuel ratio A / F is lean, the target air-fuel ratio is inverted to the lean target value, and the air-fuel ratio of the exhaust gas flowing into the catalyst 24 is made lean. Can be determined to be. In this case, the storage time Cmax is calculated according to the following equation (step 114).
Cmax = CmaxO + 0.23 × ΔA / F × Fuel amount
Here, CmaxO is the initial value (0) of Cmax or the latest value of Cmax calculated in the past, and 0.23 is the oxygen ratio in the air. ΔA / F is a value obtained by subtracting the stoichiometric air-fuel ratio from the exhaust air-fuel ratio A / F detected by the air-fuel ratio sensor 26. Further, the Fuel amount is the amount of fuel supplied to the internal combustion engine 10 during the startup cycle (for example, 65 msec) of this routine. Here, the ECU 50 detects the Fuel amount based on the fuel injection amount calculated by another routine.
[0053]
In the above equation, “ΔA / F × Fuel amount” on the right side corresponds to the unburned air amount flowing into the catalyst 24 during the startup cycle of this routine. Then, a value obtained by multiplying the value by 0.23 corresponds to the unburned oxygen amount. Therefore, according to the above equation, every time step 114 is executed, the integrated value of the amount of oxygen (adsorbed) flowing into the catalyst 24 during the startup cycle of this routine can be obtained.
[0054]
In the routine shown in FIG. 5, it is next determined whether or not the occlusion time Cmax calculated by the process of step 114 is larger than the determination value α (step 116).
The determination value α is an initial value of the oxygen storage capacity of the catalyst 24, that is, a value corresponding to the oxygen storage capacity of the catalyst 24 at the factory shipment stage. The oxygen storage capacity of the catalyst 24 may decrease with time, but does not increase. For this reason, when Cmax exceeding α is calculated, it can be determined that the output of the oxygen sensor 28 has not been inverted for an improperly long period, that is, that the oxygen sensor 28 has an abnormality.
[0055]
If it is determined in step 116 that Cmax> α does not hold, it is still not possible to determine whether or not the oxygen sensor 28 is abnormal. In this case, thereafter, the current processing cycle is ended while the determination of the abnormality determination is suspended.
[0056]
On the other hand, if it is determined in step 116 that Cmax> α is satisfied, it is determined that the oxygen sensor 28 has a rich abnormality (step 118).
When the rich abnormality of the oxygen sensor 28 is determined by the process of step 118, it is recognized that the abnormality determination is completed at that time. Therefore, if the present routine is started again after the execution of step 118, the completion of the abnormality determination is determined in step 100. The “rich abnormality” of the oxygen sensor 28 is an abnormality in which the output of the oxygen sensor 28 sticks to the rich side and no lean output is generated.
[0057]
When the rich abnormality of the oxygen sensor 28 is determined, a command to stop the active control is issued (step 120), and then the current processing cycle ends.
[0058]
In the routine shown in FIG. 5, when it is determined in step 108 that the output of the oxygen sensor 28 is not a rich output, it can be determined that the output is a lean output. Taking the timing chart shown in FIG. 3 as an example, in this case, it can be determined that the state shown at time t1-t2 or the state shown at time t3-t4 is formed.
[0059]
When the above determination is made, it is next determined whether or not the output of the air-fuel ratio sensor 26 is rich (step 122).
That is, for example, during the period from time t3 to t4 in FIG. 3, it is determined whether or not the state of the period indicated by hatching is formed during that period.
[0060]
As a result, if it is determined that the condition of step 122 is not satisfied, the target air-fuel ratio has been inverted to the rich target value, but the air-fuel ratio of the exhaust gas flowing into the catalyst 24 has not been enriched at this time. You can determine that there is no. In this case, the value of the discharge Cmax is reset to the initial value (step 124).
In addition, “Cmax at the time of release” is the oxygen storage capacity of the catalyst 24 calculated by integrating the shortage of oxygen in the exhaust gas flowing into the catalyst 24 in the process of releasing oxygen from the catalyst 24.
[0061]
On the other hand, if it is determined in step 122 that the exhaust air-fuel ratio A / F is rich, the target air-fuel ratio is inverted to the rich target value, and the air-fuel ratio of the exhaust gas flowing into the catalyst 24 is further enriched. Can be determined to be. The discharge Cmax is calculated in accordance with the same arithmetic expression (Cmax = CmaxO + 0.23 × ΔA / F × Fuel amount) as in step 114 (step 126).
However, the “ΔA / F × fuel amount” calculated in step 126 is the amount of oxygen necessary to burn unburned components (HC, CO) in the exhaust gas, that is, the oxygen deficiency in the exhaust gas. It is. According to the process of step 126, the integrated value of the amount of oxygen released from the catalyst 24 during the startup cycle of this routine can be obtained.
[0062]
In the routine shown in FIG. 5, it is next determined whether or not the release time Cmax calculated by the process of step 126 is larger than the determination value α (step 128).
The determination value α is an initial value of the oxygen storage capacity of the catalyst 24, as described above.
[0063]
If it is determined in step 128 that Cmax> α is not established, it is still not possible to determine whether or not the oxygen sensor 28 is abnormal. In this case, thereafter, the current processing cycle is ended while the determination of the abnormality determination is suspended.
[0064]
On the other hand, if it is determined in step 128 that Cmax> α is satisfied, it is determined that the oxygen sensor 28 is lean (step 130).
When the lean abnormality of the oxygen sensor 28 is determined by the process of step 130, it is recognized that the abnormality determination is completed at that time. Therefore, if the present routine is started again after the execution of step 130, it is determined in step 100 that the abnormality determination is completed. The “lean abnormality” of the oxygen sensor 28 is an abnormality in which the output of the oxygen sensor 28 sticks to the lean side and a rich output is not generated.
[0065]
When the lean abnormality of the oxygen sensor 28 is determined, the execution of the active control is stopped, and then the processing of step 120 is executed, and then the current processing cycle is ended.
[0066]
As described above, according to the routine shown in FIG. 5, during execution of the active control, under the condition that the catalyst 24 should store oxygen (the output of the oxygen sensor 28 is rich and the output of the air-fuel ratio sensor 26 is Is lean), the Cmax at the time of occlusion can be obtained by calculation. Then, when the calculated Cmax exceeds the initial value of the oxygen storage capacity, it is possible to immediately determine the abnormality of the oxygen sensor 28 at that time, and to further stop the active control.
[0067]
In addition, according to the routine shown in FIG. 5, during the execution of the active control, under the condition that the catalyst 24 should release oxygen (the output of the oxygen sensor 28 is lean, and the output of the air-fuel ratio sensor 26 is rich. Under certain circumstances), the Cmax at the time of release can be determined by calculation. Then, when the calculated Cmax exceeds the initial value of the oxygen storage capacity, it is possible to immediately determine the abnormality of the oxygen sensor 28 at that time, and to further stop the active control.
[0068]
According to the above method, it is possible to always determine the abnormality of the oxygen sensor 28 in the shortest time according to the operating state of the internal combustion engine 10, that is, according to the flow rate of the exhaust gas. Then, the active control is immediately stopped after the abnormality of the oxygen sensor 28 is detected, so that the amount of unpurified exhaust gas discharged into the atmosphere can be minimized. Therefore, according to the system of the present embodiment, when an abnormality occurs in the oxygen sensor 28, the abnormality can be accurately determined in a short time, and deterioration of the emission characteristics can be suppressed to a sufficiently small level. it can.
[0069]
Incidentally, in the oxygen sensor 28 used in the present embodiment, in addition to the abnormality due to the short circuit or the disconnection, the abnormality due to the element crack may occur. In the case of an abnormality such as a short circuit or a disconnection, the sensor output sticks to one of the outputs, so that it is possible to determine whether there is an abnormality by checking whether or not a change occurs in the sensor output. On the other hand, whether or not there is an abnormality due to element cracking cannot be determined by such a method.
[0070]
That is, the element crack abnormality of the oxygen sensor 28 is an abnormality in which a crack occurs in the element layer 32 shown in FIG. When this abnormality occurs, the atmosphere guided to the atmosphere layer 36 can enter the measurement gas chamber 40 from the crack.
FIG. 6 is a graph showing a comparison between a normal output characteristic (solid line) of the oxygen sensor 28 and an output characteristic (dashed-dotted line) when the element crack occurs. As shown in this figure, the oxygen sensor 28 in which the element crack has occurred emits similarly low output when the air-fuel ratio of the exhaust gas is rich and lean, and is relatively high near the stoichiometric air-fuel ratio. Emits output.
[0071]
When the oxygen sensor 28 has an output characteristic as shown by a dashed line in FIG. 6, it cannot be determined whether or not there is an abnormality depending on whether or not the sensor output changes. Further, since the oxygen sensor 28 is disposed downstream of the catalyst 24, it cannot be determined from the output of the air-fuel ratio sensor 26 whether the exhaust gas flowing around the oxygen sensor 28 is actually rich or lean. . For this reason, even if the output of the air-fuel ratio sensor 26 and the output of the oxygen sensor 28 are simply compared, the presence or absence of an element crack abnormality cannot be determined.
[0072]
On the other hand, according to the method used in the present embodiment, the state in which the oxygen sensor 28 emits an output near 0 V continues under a situation in which rich exhaust gas flows around the oxygen sensor 28. In this case, an abnormality in the sensor is detected immediately thereafter. For this reason, the system according to the present embodiment can accurately determine the presence / absence of an element crack abnormality of the oxygen sensor 28 in a short time.
[0073]
By the way, in the above-described first embodiment, active control for repeatedly inverting the target air-fuel ratio is performed in order to determine whether or not the oxygen sensor 28 is abnormal. However, the present invention is not limited to this. is not. That is, in order to determine the abnormality of the oxygen sensor 28, it is not always necessary to invert the target air-fuel ratio between the rich target value and the lean target value. The air-fuel ratio may be merely fixed at one of the rich target value and the lean target value.
[0074]
In the first embodiment described above, in order to determine whether the oxygen sensor 28 is abnormal, the target air-fuel ratio is set to the rich target value or the lean target value, and the air-fuel ratio is forcibly set to rich or lean. However, the present invention is not limited to this. In other words, the presence or absence of an abnormality in the oxygen sensor 28 may be determined using a time when the air-fuel ratio is necessarily rich or lean, such as during execution of fuel cut.
[0075]
In the first embodiment, the difference ΔA / F between the exhaust air-fuel ratio A / F detected by the air-fuel ratio sensor 26 and the stoichiometric air-fuel ratio and the fuel supply amount (fuel amount) to the internal combustion engine 10 are determined. The amount of oxygen flowing into the catalyst 24 and the amount of oxygen deficiency in the exhaust gas flowing into the catalyst 24 are calculated based on this, but the present invention is not limited to this. That is, the oxygen amount and the oxygen deficiency may be calculated based on the intake air amount detected by the air flow meter 18 and the fuel supply amount (fuel amount) without using ΔA / F as a basis. Good.
[0076]
When such a calculation method is used, unlike the case of the first embodiment, it is not necessary to measure the air-fuel ratio A / F upstream of the catalyst 24. Therefore, when such a calculation method is used, the sensor disposed upstream of the catalyst 24 may be an oxygen sensor instead of the air-fuel ratio sensor.
[0077]
Further, in the above-described first embodiment, in the execution process of the routine shown in FIG. 5, the inversion of the output of the oxygen sensor 28 is recognized once, so that the normality is determined (see steps 104 and 106). ), The present invention is not limited to this. That is, the normality determination of the oxygen sensor 28 may not be performed until both the inversion from the rich output to the lean output and the inversion from the lean output to the rich output are recognized.
[0078]
In the first embodiment, the air-fuel ratio sensor 26 corresponds to the “upstream sensor” in the first aspect of the present invention, and the ECU 50 executes the processing in step 114 to perform the first The “storage capacity calculation means” of the first invention executes the processing of step 126, and the “discharge capacity calculation means” of the first invention executes the processing of steps 116, 118, 128 and 130. By doing so, the “abnormality determining means” in the first invention is realized.
[0079]
In the first embodiment described above, the ECU 50 calculates “A / F by subtracting the stoichiometric air-fuel ratio from the exhaust air-fuel ratio in step 114 or 126” to calculate “air-fuel ratio difference calculation” in the second invention. The "means" detects the Fuel amount, thereby realizing the "fuel supply amount detecting means" in the second invention. The ECU 50 calculates the amount of oxygen in the exhaust gas based on ΔA / F and the amount of Fuel in the above step 114, whereby the “oxygen amount calculating means” in the second aspect of the present invention performs By calculating the oxygen deficiency in the exhaust gas based on ΔA / F and the Fuel amount, the “oxygen deficiency calculation means” in the second aspect of the present invention is realized.
[0080]
In the first embodiment described above, the ECU 50 sets the target air-fuel ratio to the lean target value during execution of the active control, whereby the “forced lean means” in the third aspect of the present invention sets the target air-fuel ratio to By setting the target value to the rich target value, the “forced rich means” in the third aspect of the present invention is realized.
[0081]
In the first embodiment, the ECU 50 inverts the target air-fuel ratio between the rich target value and the lean target value every time the output of the oxygen sensor 28 is inverted during execution of the active control. The "inversion control means" in the fourth invention is realized.
[0082]
In the first embodiment described above, the “forced setting prohibition unit” in the fifth aspect of the present invention is realized by the ECU 50 executing the process of step 120.
[0083]
【The invention's effect】
Since the present invention is configured as described above, it has the following effects.
According to the first aspect, the calculated oxygen storage capacity of the catalyst can be obtained by any of the methods described below.
{Circle around (1)} The oxygen amount in the exhaust gas is integrated during a period in which the oxygen sensor generates a rich output and the upstream sensor generates a lean output. That is, the amount of oxygen flowing into the catalyst (the amount of oxygen adsorbed on the catalyst) is integrated during a period in which the exhaust gas containing oxygen flows into the catalyst and the clean exhaust gas flows out of the catalyst.
(2) The oxygen deficiency in the exhaust gas is integrated during a period when the oxygen sensor is generating a lean output and the upstream sensor is generating a rich output. That is, during the period when the oxygen-deficient exhaust gas flows into the catalyst and the clean exhaust gas flows out of the catalyst, the oxygen deficiency in the exhaust gas flowing into the catalyst (the oxygen amount released from the catalyst) Is integrated.
Further, according to the first invention, when the calculated oxygen storage amount obtained by the above method exceeds the maximum oxygen storage amount of the catalyst, it is possible to determine the abnormality of the oxygen sensor. According to such a method, it is possible to always accurately determine the abnormality of the oxygen sensor in the shortest time regardless of the operation state of the internal combustion engine.
[0084]
According to the second aspect, the difference ΔA / F between the air-fuel ratio (the air-fuel ratio of the exhaust gas flowing into the catalyst) detected by the upstream sensor and the stoichiometric air-fuel ratio and the amount of fuel supplied to the internal combustion engine are provided. In addition, the amount of oxygen in the exhaust gas or the amount of oxygen deficiency can be accurately calculated.
[0085]
According to the third aspect, in order to obtain the calculated oxygen storage capacity in the process of storing oxygen by the catalyst, the target air-fuel ratio of the air-fuel mixture can be made lean while the oxygen sensor is outputting a rich output. it can. In this case, the exhaust gas flowing into the catalyst can be forcibly made an exhaust gas containing oxygen.
Further, according to the present invention, the target air-fuel ratio of the air-fuel mixture can be made rich while the oxygen sensor emits a lean output in order to obtain the calculated oxygen storage capacity in the process of releasing oxygen from the catalyst. it can. In this case, the exhaust gas flowing into the catalyst can be forcibly made an oxygen-deficient exhaust gas.
[0086]
According to the fourth aspect, each time the output of the oxygen sensor is inverted, the target air-fuel ratio can be inverted between rich and lean. Therefore, according to the present invention, a state in which oxygen is fully stored in the catalyst and a state in which all oxygen in the catalyst has been completely released can be alternately created, and a process in which those states are created Thus, the calculated oxygen storage capacity can be accurately calculated.
[0087]
According to the fifth aspect, when it is determined that the oxygen sensor is abnormal, it is possible to prohibit execution of the process of forcibly setting the air-fuel ratio of the air-fuel mixture to rich or lean. Therefore, according to the present invention, it is possible to prevent unpurified exhaust gas from continuing to flow downstream of the catalyst while the oxygen sensor is abnormal.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration of a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of an oxygen sensor included in the system according to the first embodiment.
FIG. 3 is a timing chart for explaining an operation of the system according to the first embodiment when active control is performed under a condition where the oxygen sensor is functioning normally.
FIG. 4 is a timing chart for explaining an operation of the system according to the first embodiment when active control is performed in a situation where an abnormality has occurred in the oxygen sensor.
FIG. 5 is a flowchart of a control routine executed in the system according to the first embodiment.
FIG. 6 is a diagram for explaining output characteristics of an oxygen sensor included in the system of the first embodiment.
[Explanation of symbols]
10 Internal combustion engine
24 catalyst
26 Air-fuel ratio sensor
28 Oxygen sensor
50 ECU (Electronic Control Unit)

Claims (5)

An abnormality detection device that detects an abnormality of an oxygen sensor disposed downstream of a catalyst that purifies exhaust gas,
An upstream sensor that is arranged upstream of the catalyst and emits an output according to the exhaust air-fuel ratio;
The oxygen calculated by the catalyst is calculated by integrating the amount of oxygen in the exhaust gas flowing into the catalyst during a period in which the oxygen sensor generates a rich output and the upstream sensor generates a lean output. A storage capacity calculation means for obtaining a storage capacity, and a shortage of oxygen in exhaust gas flowing into the catalyst during a period when the oxygen sensor is generating a lean output and the upstream sensor is generating a rich output. At least one of discharge capacity calculating means for calculating the calculated oxygen storage capacity of the catalyst by integrating the amount,
When the calculated oxygen storable amount exceeds the maximum oxygen storage amount of the catalyst, abnormality determination means for determining an abnormality of the oxygen sensor;
An oxygen sensor abnormality detection device, comprising: The upstream sensor is an air-fuel ratio sensor that detects an exhaust air-fuel ratio,
Air-fuel ratio difference calculating means for obtaining a difference ΔA / F between the air-fuel ratio detected by the upstream sensor and the stoichiometric air-fuel ratio;
Fuel supply amount detection means for detecting a fuel supply amount to the internal combustion engine,
The storage capacity calculation means includes an oxygen amount calculation means for calculating an oxygen amount in exhaust gas based on the ΔA / F and the fuel supply amount,
2. The oxygen sensor according to claim 1, wherein the discharge capacity calculating unit includes an oxygen deficiency calculating unit that calculates an oxygen deficiency in the exhaust gas based on the ΔA / F and the fuel supply amount. 3. Abnormality detection device. Comprising at least one of forced lean means used in combination with the storage capacity calculation means, and forced rich means used in combination with the release capacity calculation means,
The forced lean means is a means for leaning the target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine while the oxygen sensor emits a rich output,
3. The oxygen sensor abnormality detecting device according to claim 1, wherein said forced rich means is means for making a target air-fuel ratio of said air-fuel mixture rich while said oxygen sensor is generating a lean output. . With both the forced lean means and the forced rich means,
By continuously operating the forced rich means and the forced lean means, a reversal control means for reversing the target air-fuel ratio between rich and lean whenever the output of the oxygen sensor is reversed is provided. The abnormality detection device for an oxygen sensor according to claim 3. When the abnormality of the oxygen sensor is determined, the target air-fuel ratio is set by the forced lean unit, and the target air-fuel ratio is set by the forced rich unit. The oxygen sensor abnormality detection device according to claim 3 or 4.

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