JP5598427B2 - Cylinder air-fuel ratio variation abnormality detecting device for multi-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to an apparatus for detecting a variation abnormality in an air-fuel ratio between cylinders of a multi-cylinder internal combustion engine.

  In general, in an internal combustion engine equipped with an exhaust gas purification system using a catalyst, a mixture ratio of air and fuel in an air-fuel mixture burned in the internal combustion engine, that is, an air-fuel ratio, is used to efficiently remove harmful components in exhaust gas with a catalyst. Control is essential. In order to perform such air-fuel ratio control, an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine, and feedback control is performed so that the air-fuel ratio detected thereby follows a predetermined target air-fuel ratio.

  On the other hand, in a multi-cylinder internal combustion engine, since air-fuel ratio control is normally performed using the same control amount for all cylinders, even if air-fuel ratio control is executed, the actual air-fuel ratio may vary between cylinders. If the degree of variation is small at this time, it can be absorbed by air-fuel ratio feedback control, and harmful components in the exhaust gas can be purified by the catalyst, so that exhaust emissions are not affected and there is no particular problem.

  However, for example, if the air-fuel ratio between the cylinders varies greatly due to failure of the fuel injection system of some cylinders or the valve mechanism of the intake valve, exhaust emissions become worse, which becomes a problem. It is desirable to detect such a large air-fuel ratio variation that deteriorates the exhaust emission as an abnormality.

For example, in the internal combustion engine disclosed in Patent Document 1, it is first determined that the air-fuel ratio between the cylinders of the internal combustion engine is in an imbalance state based on the calculated value of the air-fuel ratio feedback control. In the internal combustion engine, main air-fuel ratio feedback control is executed based on the detection result of the A / F sensor provided on the upstream side of the purification catalyst in the exhaust passage, and the O ₂ sensor provided on the downstream side of the purification catalyst. Sub air-fuel ratio feedback control is executed based on the detection result. When the average value of the calculated values of the sub air / fuel ratio feedback control exceeds the normal value, it is determined that the air / fuel ratio between the cylinders is in an imbalance state. Further, in the internal combustion engine of Patent Document 1, when it is determined that there is an air-fuel ratio abnormality between the cylinders, a process of reducing the fuel injection time of the injectors of each cylinder by a predetermined time is executed, thereby causing misfire. It is identified that the cylinder in which the air-fuel ratio has occurred is the cylinder in which the air-fuel ratio imbalance has occurred.

JP 2010-112244 A

  In a multi-cylinder internal combustion engine, fuel injection amount change control for forcibly changing the fuel injection amount to each cylinder is executed. It is possible to detect that the state is imbalanced. However, if the amount of change in the fuel injection amount is excessive, output fluctuation due to this will be excessive, and drivability may be deteriorated. On the contrary, if the change amount of the fuel injection amount is too small, the output fluctuation due to this becomes too small, and there is a possibility that the abnormality in variation in the air-fuel ratio between cylinders cannot be sufficiently detected.

  Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to execute such fuel injection amount change control so as to appropriately detect a variation in air-fuel ratio between cylinders.

  According to one aspect of the present invention, the fuel injection amount forcibly increasing or decreasing the fuel injection amount of the predetermined target cylinder so that the change amount of the fuel injection amount of the predetermined target cylinder gradually increases. Fuel injection amount change control means for executing change control, and whether or not the output fluctuation amount related to the predetermined target cylinder obtained along with the execution of the fuel injection amount change control has reached a predetermined output fluctuation amount When the determination means and the determination means determine that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the fuel of the predetermined target cylinder by the fuel injection amount change control at that time There is provided an inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine, comprising detection means for detecting an abnormality in variation in air-fuel ratio between cylinders based on a change amount in an injection amount.

  In the multi-cylinder internal combustion engine inter-cylinder air-fuel ratio variation abnormality detection device, the fuel injection amount is determined before the determination unit determines that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount. A first abnormality determination unit that determines that there is an abnormality in the air-fuel ratio variation between cylinders when the amount of change in the fuel injection amount of the predetermined target cylinder by the change control exceeds a predetermined amount can be further provided.

  The inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine has a first engine rotation speed before the determination means determines that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount. The second abnormality determining means for determining that there is an abnormality in the air-fuel ratio variation between cylinders when the predetermined rotational speed is exceeded.

  The inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine has a first engine rotation speed before the determination means determines that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount. (2) A first stopping means for stopping the fuel injection amount change control when the engine speed falls below a predetermined rotational speed or when the engine rotational speed has decreased by a predetermined rotational speed or more can be further provided.

  In the multi-cylinder internal combustion engine inter-cylinder air-fuel ratio variation abnormality detecting device, an engine stall prevention control execution means for performing engine stall prevention control for increasing an intake air amount in order to prevent engine stall due to a decrease in engine rotation speed, and the fuel injection amount When the engine stall prevention control is executed when the change control is executed, the fuel injection amount change control may be further stopped by a second stop unit.

1 is a schematic view of an internal combustion engine according to a first embodiment of the present invention. It is a graph which shows the output characteristic of a pre-catalyst sensor and a post-catalyst sensor. It is a time chart for demonstrating the value showing rotation fluctuation. It is a time chart for demonstrating another value showing rotation fluctuation. It is a graph which shows the change of rotation fluctuation when fuel injection quantity is increased or decreased. It is a figure which shows the mode of the increase in fuel injection quantity, and the change of the rotation fluctuation | variation before and behind the increase. It is a flowchart in a 1st embodiment. It is a flowchart in 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the first embodiment will be described.

  FIG. 1 schematically shows an internal combustion engine according to the first embodiment. An illustrated internal combustion engine (engine) 1 is a V-type 8-cylinder spark ignition internal combustion engine (gasoline engine) mounted on an automobile. The engine 1 has a first bank B1 and a second bank B2, and the first bank B1 is provided with odd-numbered cylinders, that is, # 1, # 3, # 5, and # 7 cylinders. B2 is provided with even-numbered cylinders, that is, # 2, # 4, # 6, and # 8 cylinders. The # 1, # 3, # 5, and # 7 cylinders form the first cylinder group, and the # 2, # 4, # 6, and # 8 cylinders form the second cylinder group.

  Each cylinder is provided with an injector (fuel injection valve) 2. The injector 2 injects fuel into the intake passage of the corresponding cylinder, particularly into an intake port (not shown). Each cylinder is provided with a spark plug 13 for igniting the air-fuel mixture in the cylinder. The ignition order in the engine 1 is the order of # 1, # 8, # 7, # 3, # 6, # 5, # 4, and # 2 cylinder.

  The intake passage 7 for introducing the intake air includes a surge tank 8 as a collective portion, a plurality of intake manifolds 9 connecting the intake ports of each cylinder and the surge tank 8, and the upstream side of the surge tank 8. Are formed by the intake pipe 10 and the like. The intake pipe 10 is provided with an air flow meter 11 and an electronically controlled throttle valve 12 in order from the upstream side. The air flow meter 11 outputs a signal having a magnitude corresponding to the intake flow rate.

  A first exhaust passage 14A is provided for the first bank B1, and a second exhaust passage 14B is provided for the second bank B2. The first and second exhaust passages 14 </ b> A and 14 </ b> B are joined upstream of the downstream catalytic converter 19. Since the structure of the exhaust system upstream of the merge position is the same in both banks, only the first bank B1 side will be described here, and the second bank B2 side will be given the same reference numeral in the drawing and description thereof will be omitted. To do.

  The first exhaust passage 14A includes exhaust ports (not shown) of the cylinders # 1, # 3, # 5, and # 7, an exhaust manifold 16 that collects exhaust gases of these exhaust ports, and an exhaust manifold 16 A compartment is formed by an exhaust pipe 17 or the like installed on the downstream side. The exhaust pipe 17 is provided with an upstream catalytic converter 18. A pre-catalyst sensor 20 and a post-catalyst sensor 21 that are air-fuel ratio sensors for detecting the air-fuel ratio of the exhaust gas are installed on the upstream side and the downstream side (immediately and immediately after) of the upstream catalytic converter 18, respectively. Thus, one upstream catalytic converter 18, one before catalyst 20, and one after catalyst 21 are provided for a plurality of cylinders (or cylinder groups) belonging to one bank. It is also possible to separately provide the downstream catalytic converter 19 without joining the first and second exhaust passages 14A and 14B.

  The engine 1 is provided with an electronic control unit (hereinafter referred to as an ECU) 100 that performs various functions as various control means (control device) and various detection means (detection unit). The ECU 100 includes a CPU (not shown), a storage device including a ROM and a RAM, an input / output port, and the like. In addition to the air flow meter 11, the pre-catalyst sensor 20 and the post-catalyst sensor 21, the ECU 100 includes a crank angle sensor 22 for detecting the crank angle of the engine 1 and an accelerator opening sensor 23 for detecting the accelerator opening. The water temperature sensor 24 for detecting the temperature of the engine cooling water and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 100 controls the injector 2, spark plug 13, throttle valve 12, etc. so as to obtain a desired output based on detection values of various sensors and the like, and controls the fuel injection amount, fuel injection timing, ignition timing, throttle opening degree. Control etc.

  Such an ECU 100 functions as a fuel injection control unit, an ignition control unit, an intake air amount control unit, an air-fuel ratio control unit, and the like. As will be described in detail later, the engine 1 is equipped with an inter-cylinder air-fuel ratio variation abnormality detection device, and the ECU 100 detects fuel injection amount change control means, determination means, and inter-cylinder air ratio variation abnormality. Each function of the detection means is substantially assumed.

  The throttle valve 12 is provided with a throttle opening sensor (not shown), and a signal from the throttle opening sensor is sent to the ECU 100. The ECU 100 normally feedback-controls the opening of the throttle valve 12 (throttle opening) to an opening determined according to the accelerator opening.

  Further, the ECU 100 detects the amount of intake air per unit time, that is, the amount of intake air based on the signal from the air flow meter 11. The ECU 100 detects the load of the engine 1 based on at least one of the detected accelerator opening, throttle opening, and intake air amount.

  The ECU 100 detects the crank angle itself and the rotational speed of the engine 1 based on the crank pulse signal from the crank angle sensor 22. Here, “the number of rotations” means the number of rotations per unit time and is synonymous with the rotation speed. In the present embodiment, it means rpm per minute. The ECU 100 calculates the output fluctuation amount, and in this embodiment, the rotation fluctuation amount, as will be described later, based on the output of the crank angle sensor 22 as the output detection means.

  Then, ECU 100 normally sets the fuel injection amount (or fuel injection time) using data or the like previously stored in the storage device based on the intake air amount and the engine rotation speed, that is, the engine operating state. Based on the fuel injection amount, fuel injection from the injector 2 is controlled. In addition, the fuel injection amount by such normal fuel injection control is referred to herein as a normal fuel injection amount.

  The ECU 100 also functions as an engine stall prevention control execution unit that executes engine stall prevention control to prevent engine stall due to a decrease in engine rotation speed. The ECU 100 increases the possibility that an engine stall occurs when the engine rotational speed becomes excessively low after the engine starts. Therefore, when the engine rotational speed is lower than the predetermined rotational speed, the ECU 100 increases the intake air amount and the fuel injection amount. Secure low-speed torque. This is executed here by substantially increasing the intake air amount, specifically by forcibly increasing the throttle opening. This is because the air-fuel ratio feedback control, which will be described later, is included in the control of the engine 1, so that the fuel injection amount increases as the intake air amount increases. Note that the fuel injection amount may be forcibly increased simultaneously with the increase of the intake air amount. Further, as a control of the intake air amount for preventing engine stall, when a supercharger is provided, a control for positively operating the supercharger may be executed. For example, in this case, the supercharger can be operated with an electric motor.

  By the way, the pre-catalyst sensor 20 is a so-called wide-range air-fuel ratio sensor, and can continuously detect an air-fuel ratio over a relatively wide range. FIG. 2 shows the output characteristics of the pre-catalyst sensor 20. As shown in the figure, the pre-catalyst sensor 20 outputs a voltage signal Vf having a magnitude proportional to the detected exhaust air-fuel ratio (pre-catalyst air-fuel ratio A / Ff). The output voltage when the exhaust air-fuel ratio is stoichiometric (theoretical air-fuel ratio, for example, A / F = 14.5) is Vreff (for example, about 3.3 V).

On the other hand, the post-catalyst sensor 21 is a so-called O ₂ sensor and has a characteristic that the output value changes suddenly at the stoichiometric boundary. FIG. 2 shows the output characteristics of the post-catalyst sensor 21. As shown in the figure, the output voltage when the exhaust air-fuel ratio (post-catalyst air-fuel ratio A / Fr) is stoichiometric, that is, the stoichiometric equivalent value is Vrefr (for example, 0.45 V). The output voltage of the post-catalyst sensor 21 changes within a predetermined range (for example, 0 to 1 V). Generally, when the exhaust air-fuel ratio is leaner than stoichiometric, the output voltage Vr of the post-catalyst sensor is lower than the stoichiometric equivalent value Vrefr, and when the exhaust air-fuel ratio is richer than the stoichiometric, the output voltage Vr of the post-catalyst sensor is higher than the stoichiometric equivalent value Vrefr. Get higher.

  The upstream catalytic converter 18 and the downstream catalytic converter 19 are each composed of a three-way catalyst and simultaneously purify NOx, HC and CO, which are harmful components in the exhaust gas, when the air-fuel ratio A / F of the exhaust gas flowing into each of them is close to the stoichiometric ratio. To do. The air-fuel ratio width (window) that can simultaneously purify these three with high efficiency is relatively narrow.

  Therefore, during normal operation of the engine 1, the ECU 100 executes air-fuel ratio control (stoichiometric control) for controlling the air-fuel ratio of the exhaust gas flowing into the upstream catalytic converter 18 in the vicinity of the stoichiometric. In this air-fuel ratio control, the air-fuel ratio of the air-fuel mixture (specifically, the fuel injection amount) is feedback-controlled so that the exhaust air-fuel ratio detected by the pre-catalyst sensor 20 becomes a stoichiometric value that is a predetermined target air-fuel ratio. Fuel ratio control (main air-fuel ratio feedback control) and auxiliary air-fuel ratio control that feedback-controls the air-fuel ratio (specifically, fuel injection amount) of the air-fuel mixture so that the exhaust air-fuel ratio detected by the post-catalyst sensor 21 becomes stoichiometric. (Auxiliary air-fuel ratio feedback control). Specifically, in the main air-fuel ratio feedback control, in order to make the current exhaust air-fuel ratio detected based on the output of the pre-catalyst sensor 20 follow a predetermined target air-fuel ratio, a first correction coefficient is calculated, Control is performed to adjust the fuel injection amount from the injector 2 based on the first correction coefficient. Further, in the auxiliary air-fuel ratio feedback control, control is performed such that the second correction coefficient is calculated based on the output of the post-catalyst sensor 21 and the first correction coefficient obtained in the main air-fuel ratio feedback control is corrected. Is done. However, in the present embodiment, the predetermined target air-fuel ratio, that is, the reference value (target value) of the air-fuel ratio is stoichiometric, and the fuel injection amount corresponding to this stoichiometric (referred to as stoichiometric equivalent amount) is the fuel injection amount reference value ( Target value). However, the reference values for the air-fuel ratio and the fuel injection amount may be other values.

  The air-fuel ratio control is performed on a bank basis or on a bank basis. For example, the detection values of the pre-catalyst sensor 20 and the post-catalyst sensor 21 on the first bank B1 side are used only for air-fuel ratio feedback control of the # 1, # 3, # 5, and # 7 cylinders belonging to the first bank B1. This is not used for the air-fuel ratio feedback control of the # 2, # 4, # 6, and # 8 cylinders belonging to the second bank B2. The reverse is also true. Air-fuel ratio control is executed as if there were two independent in-line four-cylinder engines. In the air-fuel ratio control, the same control amount is uniformly used for each cylinder belonging to the same bank.

  For example, in some cylinders (particularly one cylinder) of all the cylinders, a failure of the injector 2 or the like may occur, and variations in air-fuel ratio (imbalance) may occur between the cylinders. For example, for the first bank B1, the fuel injection amount of the # 1 cylinder becomes larger than the fuel injection amounts of the other # 3, # 5, and # 7 cylinders due to poor closing of the injector 2, and the air-fuel ratio of the # 1 cylinder is This is a case where the air-fuel ratio of the other # 3, # 5, and # 7 cylinders is greatly shifted to the rich side.

  Even at this time, if a relatively large correction amount is given by the above-described air-fuel ratio feedback control, the air-fuel ratio of the total gas (exhaust gas after joining) supplied to the pre-catalyst sensor 20 may sometimes be stoichiometrically controlled. However, looking at each cylinder, # 1 cylinder is larger and richer than stoichiometric, and # 3, # 5, and # 7 cylinders are leaner than stoichiometric. Is clear. In view of this, the present embodiment is equipped with a device that detects such a variation in air-fuel ratio between cylinders.

  Here, a value that is an imbalance rate is used as an index value that represents the degree of variation in the air-fuel ratio between cylinders. The imbalance rate is the ratio of the fuel injection amount of the cylinder (imbalance cylinder) causing the fuel injection amount deviation when only one cylinder among the plurality of cylinders causes the fuel injection amount deviation. Thus, it is a value indicating whether or not there is a deviation from the fuel injection amount of the cylinder (balance cylinder) that does not cause the fuel injection amount deviation, that is, the reference injection amount (corresponding to the normal fuel injection amount). When the imbalance rate is IB (%), the fuel injection amount of the imbalance cylinder is Qib, and the fuel injection amount of the balance cylinder, that is, the reference injection amount is Qs, IB = (Qib−Qs) / Qs × 100. The greater the imbalance rate IB, whether positive or negative, the greater the fuel injection amount deviation between the imbalance cylinder and the balance cylinder, and the greater the air-fuel ratio variation.

  On the other hand, when the fuel injection amount of a predetermined target cylinder is actively or forcibly increased or decreased, and thus changed, that is, based on the rotational fluctuation of the target cylinder at least after the increase or decrease, a variation abnormality is detected. can do.

  First, rotational fluctuation will be described. The rotational fluctuation is included in the output fluctuation of the engine 1 and means a change in the engine rotational speed or the crankshaft rotational speed. In this specification, a value representing rotational fluctuation, that is, a value representing the degree of rotational fluctuation is referred to as a rotational fluctuation amount. For example, a value (amount) obtained by measuring a time required for the crankshaft to rotate by a predetermined angle and calculating the measured value can be used as the rotation fluctuation amount. It will be understood that various values can be used as the rotational fluctuation amount in the following description using FIG. 3 and FIG. 4.

  FIG. 3 shows a time chart for explaining the rotation fluctuation. The illustrated example is an example of an in-line four-cylinder engine, but it will be understood that the present invention can also be applied to a V-type eight-cylinder engine as in this embodiment. The ignition order in the in-line four-cylinder engine of FIG. 3 is the order of # 1, # 3, # 4, and # 2 cylinders.

  In FIG. 3, (A) shows the crank angle (° CA) of the engine. One engine cycle is 720 (° CA), and the crank angle for a plurality of cycles detected sequentially is shown in a sawtooth shape in the figure.

  FIG. 3B shows the time required for the crankshaft to rotate by a predetermined angle, that is, the rotation time T (s). Here, the predetermined angle is 30 (° CA), but may be another value (for example, 10 (° CA)). The longer the rotation time T, the slower the engine rotation speed. Conversely, the shorter the rotation time T, the faster the engine rotation speed. The rotation time T is detected by the ECU 100 based on the output of the crank angle sensor 22.

  FIG. 3C shows a rotation time difference ΔT described later. In the drawing, “normal” indicates a normal case in which no air-fuel ratio shift occurs in any cylinder, and “lean shift abnormality” indicates an imbalance rate IB = −30 (%) for only the # 1 cylinder. This shows an abnormal case where the lean deviation of is occurring. The lean deviation abnormality can be caused by, for example, clogging of an injector nozzle hole or a poor valve opening.

  First, the rotation time T at the same timing of each cylinder is detected by the ECU. Here, the rotation time T at the timing of compression top dead center (TDC) of each cylinder is detected. The timing at which the rotation time T is detected is referred to as detection timing.

  Next, at each detection timing, the ECU calculates a difference (T2−T1) between the rotation time T2 at the detection timing and the rotation time T1 at the immediately preceding detection timing. This difference is a rotation time difference ΔT shown in (C), and ΔT = T2−T1.

  Normally, the rotational speed increases in the combustion stroke of a cylinder after the crank angle exceeds TDC, and therefore the rotational time T decreases. In the subsequent compression stroke of the next ignition cylinder, the rotational speed decreases and the rotational time T increases. To do.

  However, as shown in (B), when the # 1 cylinder has an abnormal lean shift, even if the # 1 cylinder is ignited, a sufficient torque cannot be obtained and the rotational speed is difficult to increase. The rotation time T is increased. Therefore, the rotation time difference ΔT in the # 3 cylinder TDC is a large positive value as shown in (C). The rotational time and rotational time difference in the # 3 cylinder TDC are defined as the rotational time and rotational time difference of the # 1 cylinder, respectively, and are represented by T1 and ΔT1, respectively. The same applies to the other cylinders.

  Next, since the # 3 cylinder is normal, when the # 3 cylinder is ignited, the rotational speed increases sharply. As a result, at the timing of the next # 4 cylinder TDC, the rotation time T is only slightly reduced compared to that of the # 3 cylinder TDC. Therefore, the rotation time difference ΔT3 of the # 3 cylinder detected in the # 4 cylinder TDC is a small negative value as shown in (C). Thus, the rotation time difference ΔT of a certain cylinder is detected for each ignition cylinder TDC.

  In the subsequent # 2 cylinder TDC and # 1 cylinder TDC, the same tendency as in the case of the # 4 cylinder TDC is observed, and both the rotation time difference ΔT4 of the # 4 cylinder and the rotation time difference ΔT2 of the # 2 cylinder detected at both timings are both. It is a small negative value. The above characteristics are repeated every engine cycle.

  Thus, it can be seen that the rotation time difference ΔT of each cylinder is a value representing the rotation fluctuation of each cylinder, and is a value correlated with the air-fuel ratio deviation amount of each cylinder. Therefore, the rotation time difference ΔT of each cylinder can be used as an index value of the rotation fluctuation of each cylinder, that is, the rotation fluctuation value or the rotation fluctuation amount. As the air-fuel ratio deviation amount of each cylinder increases, the rotational fluctuation of each cylinder increases and the rotation time difference ΔT of each cylinder increases.

  On the other hand, as shown in FIG. 3C, in the normal case, the rotation time difference ΔT is always near zero.

  In the example of FIG. 3, the case of the lean deviation abnormality is shown. However, the reverse tendency of the rich deviation, that is, the case where a large rich deviation occurs in only one cylinder has the same tendency. This is because when a large rich shift occurs, combustion is insufficient due to excessive fuel even when ignited, and sufficient torque cannot be obtained, resulting in large rotational fluctuations.

  Next, with reference to FIG. 4, an example of another value representing the rotation fluctuation, that is, another rotation fluctuation amount will be described. FIG. 4 (A) shows the crank angle (° CA) of the engine as in FIG. 3 (A).

  FIG. 4B shows an angular velocity ω (rad / s) which is the reciprocal of the rotation time T. ω = 1 / T. As a matter of course, the larger the angular velocity ω, the faster the engine rotational speed, and the smaller the angular velocity ω, the slower the engine rotational speed. The waveform of the angular velocity ω has a shape obtained by vertically inverting the waveform of the rotation time T.

  FIG. 4C shows an angular velocity difference Δω, which is a difference in angular velocity ω, similarly to the rotation time difference ΔT. The waveform of the angular velocity difference Δω also has a shape obtained by vertically inverting the waveform of the rotation time difference ΔT. “Normal” and “lean deviation abnormality” in the figure are the same as those in FIG.

  First, the angular velocity ω at the same timing of each cylinder is detected by the ECU. Again, the angular velocity ω at the timing of compression top dead center (TDC) of each cylinder is detected. The angular velocity ω is calculated by dividing 1 by the rotation time T.

  Next, at each detection timing, the ECU calculates a difference (ω2−ω1) between the angular velocity ω2 at the detection timing and the angular velocity ω1 at the immediately preceding detection timing. This difference is the angular velocity difference Δω shown in (C), and Δω = ω2−ω1.

  Normally, the rotational speed increases in the combustion stroke of a cylinder after the crank angle exceeds TDC, so the angular speed ω increases. In the subsequent compression stroke of the next ignition cylinder, the rotational speed decreases, and the angular speed ω decreases.

  However, as shown in (B), when the # 1 cylinder has an abnormal lean shift, even if the # 1 cylinder is ignited, a sufficient torque cannot be obtained and the rotational speed is difficult to increase. The angular velocity ω at is small. Therefore, the angular velocity difference Δω in the # 3 cylinder TDC is a large negative value as shown in (C). The angular velocity and the angular velocity difference in the # 3 cylinder TDC are the angular velocity and the angular velocity difference of the # 1 cylinder, respectively, and are represented by ω1 and Δω1, respectively. The same applies to the other cylinders.

  Next, since the # 3 cylinder is normal, when the # 3 cylinder is ignited, the rotational speed increases sharply. As a result, at the timing of the next # 4 cylinder TDC, the angular velocity ω is only slightly increased compared to that of the # 3 cylinder TDC. Therefore, the angular velocity difference Δω3 of the # 3 cylinder detected in the # 4 cylinder TDC is a small positive value as shown in (C). Thus, the angular velocity difference Δω of a certain cylinder is detected for each ignition cylinder TDC.

  In the subsequent # 2 cylinder TDC and # 1 cylinder TDC, the same tendency as in the case of the # 4 cylinder TDC is observed, and both the angular velocity difference Δω4 of the # 4 cylinder and the angular velocity difference Δω2 of the # 2 cylinder detected at both timings are both. It is a small positive value. The above characteristics are repeated every engine cycle.

  Thus, it can be seen that the angular velocity difference Δω of each cylinder is a value representing the rotational fluctuation of each cylinder and is a value correlated with the air-fuel ratio deviation amount of each cylinder. Therefore, the angular velocity difference Δω of each cylinder can be used as an index value of the rotation fluctuation of each cylinder. As the air-fuel ratio deviation amount of each cylinder increases, the rotational fluctuation of each cylinder increases, and the angular velocity difference Δω of each cylinder decreases (increases in the minus direction).

  On the other hand, as shown in FIG. 4C, in the normal case, the angular velocity difference Δω is always near zero.

  As described above, there is a similar tendency in the case of reverse rich shift abnormality.

  Next, changes in rotational fluctuation when the fuel injection amount of a certain cylinder is actively increased, that is, forcibly increased or decreased to change the air-fuel ratio in the cylinder will be described with reference to FIG. However, in this case, when the fuel injection amount is actively increased or decreased, the operation of the throttle valve 12 and the like is controlled so that the intake air amount does not change.

  In FIG. 5, the horizontal axis represents the imbalance rate IB, and the vertical axis represents the angular velocity difference Δω as an index value of rotation fluctuation, that is, the amount of rotation fluctuation. Here, the imbalance rate IB of only one cylinder among all eight cylinders is changed, and the relationship between the imbalance rate IB of the one cylinder and the angular velocity difference Δω of the one cylinder at this time is indicated by a line a. Here, the one cylinder is referred to as an active target cylinder. All the other cylinders are balance cylinders, and the stoichiometric equivalent amount is injected as the reference injection amount Qs.

  In the horizontal axis of FIG. 5, IB = 0 (%) means a normal case where the imbalance ratio IB of the active target cylinder is 0 (%) and the active target cylinder is injecting a stoichiometric amount. The data at this time is indicated by plot b on line a. When moving from the state of IB = 0 (%) to the left side in the figure, the imbalance rate IB increases in the positive direction, and the fuel injection amount becomes excessive, that is, a rich state. On the contrary, when moving from IB = 0 (%) to the right side in the figure, the imbalance rate IB increases in the minus direction, and the fuel injection amount becomes too small, that is, a lean state.

  As can be seen from the characteristic line a, even if the imbalance ratio IB of the active target cylinder increases in the positive direction from 0 (%) or increases in the negative direction, the rotation fluctuation of the active target cylinder increases, and the active target cylinder increases. The angular velocity difference Δω tends to increase in the minus direction from near zero. As the imbalance rate IB increases from 0 (%), the slope of the characteristic line a becomes steeper, and the change in the angular velocity difference Δω with respect to the change in the imbalance rate IB tends to increase.

  Here, as indicated by an arrow c, it is assumed that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder from the stoichiometric equivalent amount (IB = 0 (%)) by a predetermined amount Δf1 is executed. . In the illustrated example, the imbalance rate is increased by approximately 40 (%). At this time, since the slope of the characteristic line “a” is gentle in the vicinity of IB = 0 (%), the angular velocity difference Δω does not change significantly after the increase, and the difference between the angular velocity differences Δω before and after the increase is extremely small. .

  On the other hand, as shown by plot d, consider a case where a rich shift has already occurred in the active target cylinder and the imbalance rate IB has a relatively large positive value. In the illustrated example, a rich shift of about 50 (%) occurs in the imbalance rate. As indicated by an arrow e from this state, assuming that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder by the same amount Δf1, the slope of the characteristic line a is steep in this region. Therefore, the angular velocity difference Δω after the increase is greatly changed to the minus side before the increase, and the difference between the angular velocity differences Δω before and after the increase is increased. In other words, the rotational fluctuation of the active target cylinder increases as the fuel injection amount increases.

  Therefore, it is possible to detect a variation abnormality based on at least the angular velocity difference Δω of the active target cylinder after the increase when the fuel injection amount of the active target cylinder is forcibly increased by a predetermined amount.

  That is, when the angular velocity difference Δω after the increase is smaller than a predetermined negative abnormality determination value α as shown in the figure (Δω <α), it is determined that there is a variation abnormality and the active target cylinder is identified as an abnormal cylinder. Can do. Conversely, if the angular velocity difference Δω after the increase is not smaller than the abnormality determination value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  Alternatively, as shown in the drawing, it is possible to detect a variation abnormality based on the difference dΔω of the angular velocity difference Δω before and after the increase. In this case, if the angular velocity difference before the increase is Δω1 and the angular velocity difference after the increase is Δω2, the difference dΔω can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive abnormality determination value β1 (dΔω> β1), it can be determined that there is a variation abnormality, and the active target cylinder can be identified as an abnormal cylinder. Conversely, when the difference dΔω does not exceed the abnormality determination value β1 (dΔω ≦ β1), at least the active target cylinder can be determined to be normal.

  The same can be said when forced reduction is performed in a region where the imbalance rate is negative, that is, when fuel injection amount reduction control is executed. As indicated by an arrow f, it is assumed that fuel injection amount reduction control is executed to forcibly reduce the fuel injection amount of the active target cylinder from the stoichiometric equivalent amount (IB = 0 (%)) by a predetermined amount Δf2. In the illustrated example, the imbalance rate is reduced by about 10%. At this time, since the slope of the characteristic line a is relatively gradual, the angular velocity difference Δω after the decrease is only slightly smaller than before the decrease, and the difference between the angular velocity differences Δω before and after the increase is small.

  On the other hand, as shown by the plot g, let us consider a case where a lean shift has already occurred in the active target cylinder and the imbalance rate IB has a relatively large negative value. In the illustrated example, a lean shift of about −20 (%) occurs in the imbalance rate. As indicated by an arrow h from this state, assuming that the fuel injection amount reduction control for forcibly reducing the fuel injection amount of the active target cylinder is performed by the same amount Δf2, the slope of the characteristic line a is relatively steep in this region. Therefore, the angular velocity difference Δω after the weight reduction is greatly changed to the minus side before the weight reduction, and the difference between the angular velocity differences Δω before and after the weight reduction becomes large. That is, the rotational fluctuation of the active target cylinder increases due to the decrease in the fuel injection amount.

  Therefore, it is possible to detect an abnormal variation in the air-fuel ratio between cylinders based on at least the angular velocity difference Δω of the active target cylinder after the reduction when the fuel injection amount of the active target cylinder is forcibly reduced by a predetermined amount.

  That is, if the angular velocity difference Δω after the reduction is smaller than a predetermined negative abnormality determination value α as shown in the figure (Δω <α), it is determined that there is a variation abnormality and the active target cylinder is identified as an abnormal cylinder. Can do. Conversely, if the angular velocity difference Δω after the reduction is not smaller than the abnormality determination value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  Alternatively, as shown in the drawing, it is possible to detect a variation abnormality based on the difference dΔω of the angular velocity difference Δω before and after the weight reduction. Also in this case, the difference dΔω between them can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive abnormality determination value β2 (dΔω> β2), it can be determined that there is a variation abnormality and the active target cylinder can be identified as an abnormal cylinder. Conversely, when the difference dΔω does not exceed the abnormality determination value β2 (dΔω ≦ β2), at least the active target cylinder can be determined to be normal. Note that the abnormality determination value β1 at the time of increase and the abnormality determination value β2 at the time of decrease may be different or the same.

  It will be understood that the abnormality detection and the abnormal cylinder identification can be performed by the same method even when the rotation time difference ΔT is used as the index value of the rotation fluctuation of each cylinder, that is, the rotation fluctuation amount. Further, other values than those described above can be used as the index value of the rotational fluctuation of each cylinder.

  FIG. 6 shows, as an example, an increase in the fuel injection amount for all eight cylinders and a change in rotational fluctuation before and after the increase. The upper row is before the increase, and the lower row is after the increase. As shown in the left end column in the left-right direction, as an increasing method, here, all cylinders are increased uniformly and simultaneously by the same amount. That is, in the example of FIG. 6, the predetermined target cylinder is all cylinders. Before the increase, a valve opening command is issued to inject the stoichiometric amount of fuel to the injectors 2 of all the cylinders, and after the increase, a predetermined amount of fuel is injected into the injectors 2 of all the cylinders by a predetermined amount more than the stoichiometric amount. A valve opening command is issued.

  In addition to the method of increasing all the cylinders at the same time, there is a method of increasing the number of cylinders in order and alternately in an arbitrary number of cylinders. For example, there is a method of increasing the amount by one cylinder, increasing the amount by two cylinders, or increasing the amount by four cylinders. The number of cylinders to be increased and the cylinder number can be arbitrarily set.

  As the number of target cylinders increases, there is a merit that the total increase time can be shortened, and there is a demerit that exhaust emission deteriorates. Conversely, the smaller the number of target cylinders, there is a merit that deterioration of exhaust emission can be suppressed, but there is a demerit that the total increase time becomes longer.

  Similar to FIG. 5, the angular velocity difference Δω is used as an index value of the rotation fluctuation of each cylinder.

  For example, in the normal state shown in the center column in the left-right direction, that is, when there is no air-fuel ratio deviation abnormality in any cylinder, the angular velocity difference Δω of all the cylinders is almost equal to 0 before the increase, There is little rotation fluctuation of the cylinder. Further, even after the increase, the angular velocity difference Δω of all the cylinders is almost equal and slightly increases in the minus direction, and the rotational fluctuations of all the cylinders do not increase that much. Therefore, the difference dΔω in the angular velocity difference before and after the increase is small.

  However, when the abnormality is shown in the right end column in the left-right direction, the behavior is different from that in the normal state. At the time of this abnormality, a rich shift abnormality corresponding to an imbalance rate of 50% occurs only in the # 8 cylinder, and only the # 8 cylinder is an abnormal cylinder. In this case, the angular velocity difference Δω of the remaining cylinders other than the # 8 cylinder is approximately equal to 0 before the increase, but the angular velocity difference Δω of the # 8 cylinder is slightly larger in the minus direction than the angular velocity difference Δω of the remaining cylinder.

  Nevertheless, there is not much difference between the angular velocity difference Δω of the # 8 cylinder and the angular velocity difference Δω of the remaining cylinders. Therefore, depending on the angular velocity difference Δω before the increase, abnormality detection and abnormal cylinder identification cannot be performed with sufficient accuracy.

  On the other hand, after the increase, the angular velocity difference Δω of the remaining cylinders is almost equal and slightly changes in the minus direction compared to before the increase, but the angular velocity difference Δω of the # 8 cylinder greatly changes in the minus direction. Therefore, the difference dΔω in angular velocity difference before and after the increase in the # 8 cylinder is significantly larger than that in the remaining cylinders. Therefore, using this difference, abnormality detection and abnormal cylinder identification can be performed with sufficient accuracy.

  In this case, only the difference dΔω between the # 8 cylinders becomes larger than the abnormality determination value β1, so that it is possible to detect that there is a rich shift abnormality in the # 8 cylinder.

  It will be understood that the same method can be adopted when the fuel injection amount is forcibly reduced to detect a lean deviation abnormality of any cylinder.

  As described above, in order to detect an abnormality in the air-fuel ratio variation between cylinders, as described above, the control for forcibly changing the fuel injection amount or changing the fuel injection amount, that is, the fuel injection amount change control is performed, and the rotational fluctuation amount It is effective to increase. However, in the fuel injection amount change control described above, the fuel injection amount is changed to a certain amount at a stretch. Therefore, if the predetermined target cylinder that is the target of the fuel injection amount increase control has already undergone a considerable rich shift with respect to other normal cylinders, the fuel injection amount of the predetermined target cylinder If the amount is increased greatly, a large output fluctuation may occur with respect to the predetermined target cylinder. This leads to a deterioration in drivability and may make the driver feel uncomfortable.

  Therefore, in the fuel injection amount change control of the present embodiment, the fuel injection amount of the predetermined target cylinder is not greatly shifted from the reference injection amount at once, but the change amount of the fuel injection amount of the predetermined target cylinder is gradually increased. The fuel injection amount of a predetermined target cylinder is changed step by step so as to be. When the rotational fluctuation amount related to the predetermined target cylinder reaches a predetermined rotational fluctuation amount, an abnormality in the air-fuel ratio variation between the cylinders is detected based on the change amount in the fuel injection amount of the predetermined target cylinder at that time. The Here, the predetermined rotation fluctuation amount is determined in consideration of the possibility of making the driver feel uncomfortable, and may be determined so as not to cause such an uncomfortable feeling or to hardly feel it. Specifically, even when a predetermined rotational fluctuation amount occurs, the predetermined rotational fluctuation amount may be determined so that a drivability change that can be perceived by the driver does not occur. it can.

  Hereinafter, based on the flowchart of FIG. 7, the control for detecting an abnormality in the air-fuel ratio variation between cylinders in the first embodiment, that is, the air-fuel ratio diagnosis control in the present embodiment will be described.

  First, when the engine 1 is started, the change counter C1 is set to zero in step S701, and the fuel change amount Δf is set to zero in next step S703.

  In the next step S705, it is determined whether or not the vehicle is in a predetermined operating state. This determination is executed by the ECU 100, and here is executed based on the engine speed and the engine load detected as described above. For example, when the engine is in a predetermined operation state after the engine is started, an affirmative determination is made in step S705. As an example, when the engine cooling water temperature is a predetermined temperature (for example, 70 ° C.) or more, the load is within a predetermined range, and the engine rotation speed is in a predetermined engine rotation speed range, the operation state that satisfies all of In step S705, an affirmative determination is made.

  When an affirmative determination is made in step S705, it includes the time when the air-fuel ratio feedback control is being executed so that the exhaust air-fuel ratio follows the stoichiometry in order to more suitably perform exhaust purification by the catalytic converter 18 as described above. obtain. Therefore, the determination in step S705 can correspond to a determination as to whether or not the air-fuel ratio feedback control is executed so that the exhaust air-fuel ratio follows the predetermined target air-fuel ratio. In particular, the predetermined target air-fuel ratio is the stoichiometric value here. It is. However, the predetermined target air-fuel ratio can be other than stoichiometric. In the present invention, the fact that such air-fuel ratio control is performed can be included in the condition for executing the abnormality detection of the inter-cylinder air-fuel ratio variation, but it may not be included.

  If an affirmative determination is made in step S705 because it is a predetermined operation state, it is determined in step S707 whether or not the change counter C1 is zero. Here, since the change counter C1 is zero, an affirmative determination is made, and the predetermined amount f1 is added to the fuel change amount Δf in step S709. Until now, the fuel change amount Δf has been zero, so that the fuel change amount Δf becomes the predetermined amount f1. The predetermined amount f1 is not a very large amount, and is an amount equivalent to about 5 (%) as an imbalance rate, for example.

  Then, in step S711, fuel injection amount increase control of the fuel injection amount change control is executed for a predetermined period, and data accompanying this is recorded, particularly data based on the output of the crank angle sensor 22 as output detection means. In the fuel injection amount increase control, the fuel injection amount of the predetermined target cylinder is increased and changed by the fuel change amount Δf set in step S709. The fuel injection amount increase control can be executed in accordance with various settings as described above. In the present embodiment, the fuel injection amount increase control is executed simultaneously for all eight cylinders as shown in FIG. The predetermined period is a period corresponding to at least one cycle.

  In the next step S713, the rotation fluctuation amount is calculated as the output fluctuation amount. Here, the angular velocity difference Δω is calculated as described above as the rotational fluctuation amount of each cylinder.

  In step S715, it is determined whether or not the angular velocity difference Δω calculated in step S713 is equal to or smaller than a first predetermined value. This determination is performed for each of the angular velocity differences Δω calculated in step S713. If at least one of them is equal to or less than the first predetermined value, an affirmative determination is made in step S715. The first predetermined value is previously determined based on an experiment as a predetermined output fluctuation amount, here a predetermined rotation fluctuation amount, that does not cause a change in drivability that can be perceived by the driver. Further, the first predetermined value is previously determined based on experiments as an output fluctuation amount that can be sufficiently and appropriately identified when there is an abnormality in variation in air-fuel ratio between cylinders.

  If a negative determination is made in step S715, the process returns to step S709, and a predetermined amount f1 is added to the fuel change amount Δf. Until now, the fuel change amount Δf has been f1, so that the fuel change amount Δf becomes “2 × f1”.

  In the next step S711, fuel injection amount increase control for increasing the fuel injection amount of all the cylinders that are the predetermined target cylinders is executed for a predetermined period by the fuel change amount Δf set in the most recent step S709. Data is recorded.

  Then, in the next step S713, the angular velocity difference Δω is similarly calculated as the rotation fluctuation amount of each cylinder. In step S715, whether each of the angular velocity differences Δω calculated in step S713 is equal to or less than a first predetermined value. Is determined.

  As described above, by executing the fuel injection amount increase control, until the angular velocity difference Δω of any cylinder becomes equal to or smaller than the first predetermined value, that is, the output fluctuation amount of any cylinder becomes equal to or greater than the predetermined output fluctuation amount. Until the predetermined output fluctuation amount is reached, the change amount of the fuel injection amount of the predetermined target cylinder is gradually increased. In the present embodiment, the fuel change amount Δf in the fuel injection amount increase control is increased by a predetermined amount f1, but the change amount of the fuel injection amount may be gradually reduced. In addition, this invention does not exclude that the change width of fuel injection quantity is enlarged in steps. Further, the fuel change amount Δf in the first fuel injection amount increase control, that is, the initial value of the fuel change amount is the same as the change amount of the fuel injection amount in the present embodiment, but may be different.

  In step S715, since the angular velocity difference Δω is equal to or smaller than the first predetermined value, an affirmative determination is made. In step S717, it is determined whether the fuel change amount Δf is equal to or smaller than the first fuel amount. When the fuel change amount Δf is equal to or less than the first fuel amount, the difference in angular velocity Δω of at least one cylinder of the predetermined target cylinder becomes equal to or less than the first predetermined value by changing the fuel injection amount by a small amount. The at least one cylinder must have had a considerable rich shift from the beginning. Therefore, if the determination in step S717 is affirmative because the fuel change amount Δf is equal to or less than the first fuel amount, an abnormality flag is set so as to correspond to the determination in step S719 that there is an abnormality in the air-fuel ratio variation between cylinders. Is turned ON, and the flow ends. As a result, a warning lamp (not shown) that can be provided on the front panel of the driver's seat is turned on, and the driver or the mechanic is informed that there is a variation in the air-fuel ratio between cylinders. Note that the abnormality flag is OFF in the initial state.

  On the other hand, if a negative determination is made in step S717, 1 is added to the change counter C1 in step S721, and the process returns to step S703. In step S703, the fuel change amount Δf is set to zero, and in the next step S705, it is determined whether or not the engine is in a predetermined operating state as described above. If an affirmative determination is made in step S705 because it is a predetermined operation state, it is determined in step S707 whether or not the change counter C1 is zero. Here, since the change counter C1 is 1, a negative determination is made, and a predetermined amount f2 is added to the fuel change amount Δf in step S723. Since the fuel change amount Δf is set to zero in step S703, the fuel change amount Δf becomes the predetermined amount f2. The predetermined amount f2 is not a very large amount, and is, for example, an amount corresponding to about 2 (%) in terms of an imbalance rate.

  In the next step S725, the fuel injection amount reduction control is executed as the fuel injection amount change control for a predetermined period, and the data accompanying this is recorded, in particular, the data based on the output of the crank angle sensor 22 as the output detection means. In the fuel injection amount reduction control, the fuel injection amount of a predetermined target cylinder is reduced and changed by the fuel change amount Δf set in the most recent step S723. The fuel injection amount reduction control can be executed according to various settings as described above. In this embodiment, the fuel injection amount reduction control is executed for all eight cylinders at the same time as shown in FIG. The predetermined period is a period corresponding to at least one cycle.

  In the next step S727, the angular velocity difference Δω is calculated in the same manner as in step S713. In step S729, it is determined whether or not the angular velocity difference Δω calculated in step S727 is equal to or smaller than a second predetermined value. This determination is performed for each of the angular velocity differences Δω calculated in step S727. If at least one of them is equal to or less than the second predetermined value, an affirmative determination is made in step S729. The second predetermined value is determined based on an experiment in advance as a predetermined output fluctuation amount that does not cause a change in drivability that can be perceived by the driver. In particular, here, the second predetermined value is the first predetermined value in step S715. Although it is different from the predetermined value, it may be the same. The second predetermined value is determined based on experiments in advance as an output fluctuation amount that can be sufficiently and appropriately identified when there is an abnormality in variation in air-fuel ratio between cylinders.

  If a negative determination is made in step S729, the process returns to step S723, and the predetermined amount f2 is added to the fuel change amount Δf. Until now, since the fuel change amount Δf was f2, the fuel change amount Δf becomes “2 × f2”.

  Then, in step S725, fuel injection amount reduction control for reducing the fuel injection amount of all the cylinders that are the predetermined target cylinders by the fuel change amount Δf set in the most recent step S723 is executed for a predetermined period, and the data associated therewith Is recorded. Then, in the next step S727, the angular velocity difference Δω of each cylinder is similarly calculated, and in step S729, it is determined whether or not the angular velocity difference Δω calculated in step S727 is equal to or smaller than a second predetermined value.

  Thus, until the angular velocity difference Δω of any cylinder becomes equal to or smaller than the second predetermined value by execution of the fuel injection amount reduction control, that is, the output fluctuation amount of any cylinder becomes equal to or greater than the predetermined output fluctuation amount. Until the predetermined output fluctuation amount is reached, the change amount of the fuel injection amount of the predetermined target cylinder is gradually increased. In the present embodiment, the fuel change amount Δf in the fuel injection amount reduction control is increased by a predetermined amount f2, but the change amount of the fuel injection amount may be gradually reduced. In addition, this invention does not exclude that the change width of fuel injection quantity is enlarged in steps. Further, the fuel change amount Δf in the first fuel injection amount reduction control, that is, the initial value of the fuel injection amount is the same as the change amount of the fuel injection amount in the present embodiment, but may be different.

  In step S729, since the angular velocity difference Δω is equal to or smaller than the second predetermined value, an affirmative determination is made. In step S731, it is determined whether the fuel change amount Δf is equal to or smaller than the second fuel amount. When the fuel change amount Δf is less than or equal to the second fuel amount, the difference in angular velocity Δω of at least one of the predetermined target cylinders is less than or equal to the second predetermined value due to a small change in fuel injection amount. The at least one cylinder must have had a considerable lean shift from the beginning. Therefore, since the fuel change amount Δf is equal to or less than the second fuel amount, when an affirmative determination is made in step S731, the above-described step S719 is reached to correspond to the determination that there is an abnormality in the air-fuel ratio variation between the cylinders. The abnormality flag is turned ON, and the flow ends.

  Note that if a negative determination is made in step S731, the flow ends. This means that a normal determination is made that there is no abnormality in variation in the air-fuel ratio between cylinders.

  Here, after the engine 1 is started and before it stops, the detection control of the air-to-cylinder air ratio variation abnormality described according to FIG. 7 is executed only once. However, this control may be executed at an appropriate time. For example, the control can be executed when the operating time of the engine 1 or the travel distance of the vehicle on which the engine 1 is mounted becomes a predetermined value.

  In this way, the fuel injection amount change control for changing the fuel injection amount of the predetermined target cylinder in a stepwise manner so that the change amount of the fuel injection amount of the predetermined target cylinder gradually increases is obtained. When the output fluctuation amount related to the predetermined target cylinder reaches the predetermined output fluctuation amount, an abnormality in the air-fuel ratio variation between cylinders is detected based on the change amount in the fuel injection amount of the predetermined target cylinder at that time.

  However, since the air-fuel ratio diagnostic control with such fuel injection amount change control is executed for a certain period of time, some measure is executed in the event that some trouble occurs or some kind of control occurs. It is hoped that

  When the fuel injection amount change control is executed and before the predetermined rotational fluctuation amount is obtained (before an affirmative determination is made in step S715 or S729), the engine rotational speed exceeds the first predetermined rotational speed. That is, when the engine speed increases so as to change by more than the predetermined rotational speed, it does not match that the fuel injection amount is changed so as to deteriorate the combustion state of the predetermined target cylinder. Therefore, in such a case, the part responsible for the function of the second abnormality determination means of the ECU 100 stops the control (including the fuel injection amount change control) even during the air-fuel ratio diagnosis control, The abnormality flag is set to ON so as to determine that there is an abnormality in the air-fuel ratio variation between cylinders. The first predetermined rotation speed may be a rotation speed obtained by adding 1000 rpm to the predetermined rotation speed corresponding to the predetermined operation state in step S705, for example.

  Further, when the fuel injection amount change control is executed, in particular, when the fuel injection amount reduction control is executed, and before the predetermined rotational fluctuation amount is obtained (affirmative determination is made in step S715 or S729). The engine stall may occur when the engine speed falls below the second predetermined speed or when the engine speed drops by a predetermined speed or more. Therefore, in such a case, the part responsible for the function of the first cancellation unit of the ECU 100 stops the control (including the fuel injection amount change control) even during the air-fuel ratio diagnosis control. In such a case, the abnormality flag may be turned ON. Note that the second predetermined rotation speed is, for example, 500 rpm.

  Further, when the engine stall prevention control is executed when the fuel injection amount change control is executed, even in such a case, the part responsible for the function of the second stop means of the ECU 100 is the air-fuel ratio diagnosis control. Even in the middle (including fuel injection amount change control), the control is stopped. This is to prevent engine stall more reliably. In such a case, the abnormality flag may be turned ON.

  As described above, the fuel injection amount change control is executed when in a predetermined operation state. For example, if the accelerator pedal is depressed at this time and the accelerator opening suddenly increases, the fuel injection amount change control is executed. There is a possibility that the output fluctuation due to the injection amount change control cannot be detected properly. Therefore, in such a case, even during the air-fuel ratio diagnosis control (including fuel injection amount change control), the control is stopped. However, in this case, once stopped, the diagnostic control can be started again from the middle or from the beginning.

  Next, a second embodiment according to the present invention will be described. Since the configuration of the engine to which the second embodiment is applied is substantially the same as the configuration of the engine 1 to which the first embodiment is applied, description of the components of the engine of the second embodiment is omitted below. . The control in the second embodiment is characterized by the control in the first embodiment in the points described below, and generally includes the control in the first embodiment. In addition, the said deformation | transformation in 1st Embodiment, etc. can be applied similarly to 2nd Embodiment.

  The air-fuel ratio diagnosis control according to the second embodiment of the present invention will be described below with reference to the flowchart of FIG. However, Steps S801 to S809, S813 to S825, and S829 to S835 in FIG. 8 generally correspond to Steps S801 to S731 in FIG. 7, respectively, and thus description thereof will be substantially omitted below.

  Consider the case where the change counter C1 is zero. Since the change counter C1 is zero, if an affirmative determination is made in step S807, a predetermined amount f1 is added to the fuel change amount Δf in step S809. Since the fuel change amount Δf is zero when the process first reaches step S809 after the engine is started, the fuel change amount Δf becomes the predetermined amount f1.

  In step S811, it is determined whether or not the fuel change amount Δf set in step S809 is equal to or less than a third fuel amount that is a predetermined amount. The third fuel amount in step S811 is determined in advance based on experiments.

  When an affirmative determination is made in step S811 because the fuel change amount Δf is equal to or less than the third fuel amount, in step S813, fuel injection amount increase control for increasing the fuel injection amount of a predetermined target cylinder by the fuel change amount Δf is predetermined. It is executed for a period of time and the accompanying data is recorded. Then, in the next step S815, the angular velocity difference Δω of each cylinder is calculated, and in step S817, it is determined whether or not the angular velocity difference Δω calculated in step S815 is equal to or less than a first predetermined value.

  If the negative determination is made in step S817 because the angular velocity difference Δω is not less than or equal to the first predetermined value, the process returns to step S809, and the predetermined amount f1 is added to the fuel change amount Δf.

  As described above, by executing the fuel injection amount increase control, the fuel change amount Δf of the fuel injection amount increase control is gradually increased until the angular velocity difference Δω of any cylinder becomes equal to or less than the first predetermined value.

  In step S809, a predetermined amount f1 is further added to the fuel change amount Δf, so that the fuel change amount Δf becomes “n × f1”. However, here, n is an integer equal to or greater than 2, and is related to the third fuel amount in step S811. Therefore, at this time, since the fuel change amount Δf exceeds the third fuel amount in step S811, a negative determination is made. As a result, in step S821, the abnormality flag is turned on to correspond to the determination that there is an abnormality in the air-fuel ratio variation between cylinders, and the flow ends.

  As described above, when the fuel change amount Δf in the fuel injection amount increase control exceeds the third fuel amount before the angular velocity difference Δω becomes equal to or less than the first predetermined value, the portion that functions as the first abnormality determination unit of the ECU 100. Determines that there is an abnormality in the air-fuel ratio variation between cylinders (detects an abnormality). This is because, even though the fuel injection amount of the predetermined target cylinder is forcibly changed by a considerable amount, the corresponding output fluctuation is not detected, and in this case, there is a possibility that there is an abnormal variation in the air-fuel ratio between cylinders. Because there is. Further, in such a case, continuing the fuel injection amount change control may adversely affect the operation of the engine 1.

  Next, consider a case where the change counter C1 is 1. Since the change counter C1 is 1, if a negative determination is made in step S807, a predetermined amount f2 is added to the fuel change amount Δf in step S825. Since the fuel change amount Δf is zero when the process first reaches step S825 after the engine is started, the fuel change amount Δf becomes the predetermined amount f2.

  In step S827, it is determined whether or not the fuel change amount Δf set in step S825 is equal to or less than a fourth fuel amount that is a predetermined amount. The fourth fuel amount in step S827 is determined in advance based on experiments.

  When an affirmative determination is made in step S827 because the fuel change amount Δf is equal to or less than the fourth fuel amount, in step S829, fuel injection amount reduction control for reducing the fuel injection amount of a predetermined target cylinder by the fuel change amount Δf is predetermined. It is executed for a period of time and the accompanying data is recorded. Then, in the next step S831, the angular velocity difference Δω of each cylinder is calculated, and in step S833, it is determined whether or not the angular velocity difference Δω calculated in step S831 is equal to or smaller than a second predetermined value.

  If the negative determination is made in step S833 because the angular velocity difference Δω is not less than or equal to the second predetermined value, the process returns to step S825, and the predetermined amount f2 is added to the fuel change amount Δf.

  As described above, by executing the fuel injection amount reduction control, the fuel change amount of the fuel injection amount reduction control is gradually increased until the angular velocity difference Δω of any cylinder becomes equal to or smaller than the second predetermined value.

  In step S825, a case where a predetermined amount f2 is further added to the fuel change amount Δf and the fuel change amount Δf becomes “m × f2” is considered. However, here, m is an integer of 2 or more, and is related to the fourth fuel amount in step S827. Therefore, at this time, a negative determination is made in step S827 because the fuel change amount Δf exceeds the fourth fuel amount. As a result, in step S821, the abnormality flag is turned ON, and the flow ends.

  As described above, when the fuel change amount Δf in the fuel injection amount reduction control exceeds the fourth fuel amount before the angular velocity difference Δω becomes equal to or smaller than the second predetermined value, the first ECU 100 of the ECU 100 has the same reason as above. The part responsible for the function of the abnormality determination means determines that there is an abnormality in the air-fuel ratio variation between cylinders (detects an abnormality).

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable.

  For example, in the above embodiment, the angular velocity difference Δω is adopted as the rotation fluctuation amount, but various values including the above-described values such as the rotation time difference ΔT may be used as the rotation fluctuation amount. The output fluctuation amount is not limited to the rotation fluctuation amount. For example, a value based on the in-cylinder pressure detected based on the output from the in-cylinder pressure sensor serving as the in-cylinder pressure detecting means may be used as the output fluctuation amount.

  Further, the present invention can be applied to a multi-cylinder engine having two or more cylinders of various types, and not only a port injection type engine but also an in-cylinder injection type engine, an engine using gas as fuel, and the like. Can be applied.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine
2 Injector 11 Air flow meter 12 Throttle valve 13 Spark plug 18 Upstream catalytic converter 20 Pre-catalyst sensor 22 Crank angle sensor 23 Accelerator opening sensor 100 Electronic control unit (ECU)

Claims (4)

Fuel injection amount change control for executing fuel injection amount change control for forcibly increasing or decreasing the fuel injection amount of the predetermined target cylinder so that the change amount of the fuel injection amount of the predetermined target cylinder gradually increases Means,
Determination means for determining whether or not an output fluctuation amount related to the predetermined target cylinder obtained in accordance with execution of the fuel injection amount change control has reached a predetermined output fluctuation amount;
When it is determined by the determination means that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the change in the fuel injection amount of the predetermined target cylinder by the fuel injection amount change control at that time Detecting means for detecting an abnormality in air-fuel ratio variation between cylinders based on the amount ;
Before the determination means determines that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the change amount in the fuel injection amount of the predetermined target cylinder by the fuel injection amount change control is determined. An inter-cylinder air-fuel ratio variation abnormality detection device for a multi-cylinder internal combustion engine, comprising: a first abnormality determination unit that determines that there is an abnormality in variation in air-fuel ratio between cylinders when a predetermined amount is exceeded. Fuel injection amount change control for executing fuel injection amount change control for forcibly increasing or decreasing the fuel injection amount of the predetermined target cylinder so that the change amount of the fuel injection amount of the predetermined target cylinder gradually increases Means,
Determination means for determining whether or not an output fluctuation amount related to the predetermined target cylinder obtained in accordance with execution of the fuel injection amount change control has reached a predetermined output fluctuation amount;
When it is determined by the determination means that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the change in the fuel injection amount of the predetermined target cylinder by the fuel injection amount change control at that time Detecting means for detecting an abnormality in air-fuel ratio variation between cylinders based on the amount;
When the engine rotation speed exceeds the first predetermined rotation speed before the determination means determines that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the cylinder-to-cylinder air ratio variation abnormality Second abnormality determining means for determining that there is
An inter-cylinder air-fuel ratio variation abnormality detection device for a multi- cylinder internal combustion engine. Fuel injection amount change control for executing fuel injection amount change control for forcibly increasing or decreasing the fuel injection amount of the predetermined target cylinder so that the change amount of the fuel injection amount of the predetermined target cylinder gradually increases Means,
Determination means for determining whether or not an output fluctuation amount related to the predetermined target cylinder obtained in accordance with execution of the fuel injection amount change control has reached a predetermined output fluctuation amount;
When it is determined by the determination means that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the change in the fuel injection amount of the predetermined target cylinder by the fuel injection amount change control at that time Detecting means for detecting an abnormality in air-fuel ratio variation between cylinders based on the amount;
Before the determination means determines that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, or when the engine rotation speed falls below the second predetermined rotation speed, or the engine rotation speed is predetermined. First stopping means for stopping the fuel injection amount change control when the rotational speed is reduced by more than a rotation speed ;
An inter-cylinder air-fuel ratio variation abnormality detection device for a multi- cylinder internal combustion engine. Fuel injection amount change control for executing fuel injection amount change control for forcibly increasing or decreasing the fuel injection amount of the predetermined target cylinder so that the change amount of the fuel injection amount of the predetermined target cylinder gradually increases Means,
Determination means for determining whether or not an output fluctuation amount related to the predetermined target cylinder obtained in accordance with execution of the fuel injection amount change control has reached a predetermined output fluctuation amount;
When it is determined by the determination means that the output fluctuation amount related to the predetermined target cylinder has reached the predetermined output fluctuation amount, the change in the fuel injection amount of the predetermined target cylinder by the fuel injection amount change control at that time Detecting means for detecting an abnormality in air-fuel ratio variation between cylinders based on the amount;
An engine stall prevention control execution means for performing engine stall prevention control for increasing the intake air amount in order to prevent engine stall due to a decrease in engine rotation speed;
Second stop means for stopping the fuel injection amount change control when the engine stall prevention control is executed when the fuel injection amount change control is executed;
The painting Bei, inter-cylinder air-fuel ratio variation abnormality detection apparatus for a multi-cylinder internal combustion engine.

Images