Engine control device

Abstract

To suppress deterioration of exhaust gas even when an inter-cylinder air-fuel ratio deviation occurs in combustion feedback control.SOLUTION: In combustion feedback control, which is performed between engine start-up and the start of air-fuel ratio feedback control and which increases the fuel injection amount when engine rotation fluctuations are detected: when the occurrence of an inter-cylinder air-fuel ratio deviation fault between a plurality of cylinders is detected, the increase in a fuel injection amount, which is increased when engine rotation fluctuations are detected in the combustion feedback control, is reduced, or the fuel injection amount is controlled so that the fuel injection amount in the combustion feedback control does not exceed an upper limit value; and when the occurrence of an inter-cylinder air-fuel ratio deviation fault is detected, the upper limit value of the fuel injection amount in the combustion feedback control is set to be lower than that when the occurrence of an inter-cylinder air-fuel ratio deviation fault is not detected.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to an engine control device.

Background Art

[0002] Generally, after engine startup, by controlling the fuel injection amount to a predetermined value where the air-fuel ratio becomes lean, HC emissions are suppressed, the catalyst temperature of the exhaust purification device is raised early to promote activation, and there is a method of improving exhaust purification performance. At this time, the air-fuel ratio is made lean up to a predetermined value just within the stability limit so as not to cause misfire.

[0003] After that, when the warm-up of the exhaust purification device is completed, the control shifts to air-fuel ratio feedback control used in a normal operating state other than startup (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As in Patent Documents 1 and 2 above, after engine startup, control is performed to set the fuel injection amount to a predetermined value. At this time, when the engine speed fluctuation becomes larger than a predetermined threshold value, combustion feedback control that determines that there is a possibility of misfire and increases the fuel injection amount is activated.

[0006] However, in engines with multiple cylinders, a phenomenon called inter-cylinder air-fuel ratio mismatch can occur, where the air-fuel ratio differs between cylinders. Inter-cylinder air-fuel ratio mismatch can be caused by various factors, such as injector clogging due to aging, foreign matter getting stuck in the needle, or poor electrical contact. When inter-cylinder air-fuel ratio mismatch occurs, the engine's rotational speed fluctuates significantly, so combustion feedback control works to increase the fuel injection amount to stabilize combustion. This can potentially worsen the exhaust gas from cylinders with a normal air-fuel ratio. If the threshold for increasing the fuel injection amount is set to a large value to suppress such deterioration of exhaust gas, a problem may arise where the necessary increase in fuel injection amount is not performed in operating conditions where it is actually needed, such as when heavy fuel is mixed in and fuel atomization is insufficient, or when the exhaust gas recirculation system malfunctions.

[0007] Therefore, the objective of this invention is to suppress the deterioration of exhaust gas even when a mismatch in the air-fuel ratio occurs between cylinders in combustion feedback control, which controls the air-fuel ratio in accordance with engine rotation fluctuations from engine startup to the transition to air-fuel ratio feedback control. [Means for solving the problem]

[0008] To solve the above problems, this invention provides an engine control device comprising: an injection device that supplies fuel to an engine having multiple cylinders; an air-fuel ratio detection means for detecting the air-fuel ratio of the engine; an air-fuel ratio feedback control means for performing air-fuel ratio feedback control to control the air-fuel ratio according to the detection result of the air-fuel ratio detection means; a combustion feedback control means performed from engine startup until the start of the air-fuel ratio feedback control, which increases the amount of fuel injected by the injection device when it detects a rotational fluctuation of the engine; and an inter-cylinder air-fuel ratio misalignment detection means for detecting an inter-cylinder air-fuel ratio misalignment fault between the multiple cylinders. When the inter-cylinder air-fuel ratio misalignment detection means detects the occurrence of an inter-cylinder air-fuel ratio misalignment fault, the combustion feedback control means employs an engine control device that limits the increase in the amount of fuel injected by the injection device when it detects a rotational fluctuation of the engine.

[0009] Here, the inter-cylinder air-fuel ratio deviation detection means is capable of detecting the magnitude of the inter-cylinder air-fuel ratio deviation failure, and the combustion feedback control means can adopt a configuration that increases the limit on the increase in the fuel injection amount when detecting engine rotation fluctuations as the degree of failure increases.

[0010] Furthermore, the combustion feedback control means controls the fuel injection amount so that the fuel injection amount in the combustion feedback control does not exceed the upper limit, and when the inter-cylinder air-fuel ratio deviation detection means detects the occurrence of an inter-cylinder air-fuel ratio deviation failure, the combustion feedback control means can adopt a configuration in which the upper limit is set lower than when the occurrence of an inter-cylinder air-fuel ratio deviation failure is not detected.

[0011] In each of these embodiments, the combustion feedback control means increases the fuel injection amount by a predetermined amount each time it detects a rotational fluctuation of the engine, and when the inter-cylinder air-fuel ratio deviation detection means detects the occurrence of an inter-cylinder air-fuel ratio deviation failure, the combustion feedback control means can adopt a configuration that sets the predetermined amount lower than when the occurrence of an inter-cylinder air-fuel ratio deviation failure is not detected.

[0012] Furthermore, the engine may have an exhaust purification device provided in the exhaust passage, and the air-fuel ratio detection means may include a first air-fuel ratio detection means consisting of a linear air-fuel ratio sensor provided in the exhaust passage upstream of the exhaust purification device, and a second air-fuel ratio detection means consisting of an O2 sensor provided in the exhaust passage downstream of the exhaust purification device, and the inter-cylinder air-fuel ratio deviation detection means may employ a configuration that detects an inter-cylinder air-fuel ratio deviation failure based on the number of peaks, which is the number of times the output of the first air-fuel ratio detection means in the air-fuel ratio feedback control deviates from a predetermined range including stoichiometry, and the cumulative value of the lean residence time, which is the time the output of the second air-fuel ratio detection means in the air-fuel ratio feedback control falls below a predetermined value on the lean side, or either of these. [Effects of the Invention]

[0013] In combustion feedback control, which controls the air-fuel ratio in accordance with engine speed fluctuations from engine startup to the transition to air-fuel ratio feedback control, deterioration of exhaust gas can be suppressed even when a mismatch in the air-fuel ratio between cylinders occurs. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic overall diagram showing an engine control device that illustrates one embodiment of the present invention. [Figure 2] This is a timing chart illustrating a control example. [Figure 3] This is a flowchart illustrating an example of control. [Figure 4] This is a time chart showing the relationships between specific control information. [Modes for carrying out the invention]

[0015] Embodiments of this invention will be described based on the drawings. Figure 1 is an overall diagram showing the configuration of the control device for the engine 1 of this invention.

[0016] Engine 1 is a four-cylinder engine for automobiles. As shown in Figure 1, it has four cylinders 2 arranged in parallel, and is equipped with an intake passage 4 leading to an intake port that supplies air into each cylinder 2, an exhaust passage 5 drawn out from an exhaust port, and an injection device 10 that supplies fuel to each cylinder 2. Note that Figure 1 shows only the components and means directly related to this invention, and other components are omitted from the illustration. Also, although the drawing shows an example with four cylinders 2, the engine can have two or more cylinders, and the cylinder arrangement does not have to be in series. Furthermore, although the injection device 10 is shown to inject fuel directly into each cylinder 2, it may also inject fuel into the intake port.

[0017] A throttle valve 3 is provided in the upstream portion of the intake passage 4 to adjust the flow area, allowing for adjustment of the intake air volume. The exhaust passage 5 is provided with an air-fuel ratio detection means for detecting the air-fuel ratio within the exhaust passage 5. As an air-fuel ratio detection means, a first air-fuel ratio sensor (first air-fuel ratio detection means) 12 is attached to the post-merging exhaust passage 11, which is downstream of the confluence of each passage in the exhaust manifold. Further downstream of the post-merging exhaust passage 11, an exhaust purification device 13 equipped with a catalyst to remove nitrogen oxides and other substances from the exhaust is installed, and further downstream, a second air-fuel ratio sensor (second air-fuel ratio detection means) 14 is installed as an air-fuel ratio detection means, and further downstream, a muffler 15 and the like are provided.

[0018] The components necessary for the operation of the engine, including the throttle valve 3 and the in-cylinder injection device 10, are controlled by an electronic control unit 30 installed in the vehicle equipped with this engine 1. Furthermore, various information from the first air-fuel ratio detection means 12, the second air-fuel ratio detection means 14, etc., is transmitted to the electronic control unit 30.

[0019] The electronic control unit 30 includes an air-fuel ratio feedback control means 31 for controlling the air-fuel ratio in the cylinder 2. The air-fuel ratio feedback control means 31 controls the throttle valve 3 to adjust the intake air amount in the intake passage 4. Also, the air-fuel ratio feedback control means 31 adjusts the amount of fuel injected from the in-cylinder injection device 10 into the cylinder 2. The exhaust of each cylinder 2 is discharged into the exhaust passage 5, and after being purified by the exhaust purification device 13, it is discharged through the muffler 15.

[0020] The air-fuel ratio feedback control means 31 controls the air-fuel ratio so as to achieve the target air-fuel ratio set according to the operating state of the engine. Specifically, main feedback control is performed to control the fuel supply amount to the engine so that the value of the first air-fuel ratio sensor 12 (linear air fuel ratio sensor) disposed upstream of the exhaust purification device in the exhaust passage of the engine matches the target air-fuel ratio.

[0021] However, the first air-fuel ratio sensor 12 (linear air fuel ratio sensor) upstream of the exhaust purification device 13 has a problem that the variation of the obtained value is intense. Also, since the first air-fuel ratio sensor 12 detects the gas exhausted from the parallel exhaust passages 5, the influence on the detection accuracy differs for each cylinder. Furthermore, the air-fuel ratio has a tendency for each cylinder 2, and not all cylinders 2 exhibit the same behavior. Therefore, there are cases where the main feedback control by the first air-fuel ratio sensor 12 alone cannot cope with the operating conditions. To correct this, sub-feedback control is also performed to complement the control value of the main feedback control based on the value of the second air-fuel ratio sensor 14 (rear O2 sensor) provided downstream of the exhaust purification device 13. These main feedback control, sub-feedback control, etc. are collectively referred to as air-fuel ratio feedback control.

[0022] As described above, air-fuel ratio feedback control is performed using the output values ​​of the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 14. However, immediately after engine startup, the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 14 are not sufficiently activated, making it impossible to perform accurate air-fuel ratio feedback control. Therefore, the electronic control unit 30 is equipped with a combustion feedback control means 32 that sets the fuel injection amount to a predetermined initial value from engine startup until a predetermined time has elapsed, and performs combustion feedback control that corrects and controls the fuel injection amount according to engine rotation fluctuations. Combustion feedback control is a control that stabilizes engine rotation by increasing the amount of fuel supplied to the engine by the injection device 10 when a misfire in the engine is detected due to engine rotation fluctuations during engine operation with fuel injection at the initial value after engine startup. The initial value can be, for example, a value such that the exhaust gas emission amount falls below a predetermined target value, and a value such that the air-fuel ratio becomes lean is desirable. The initial value can be determined in advance through experiments or other means. Engine misfires are detected when the engine rotation fluctuation exceeds a predetermined value. After the combustion feedback control is complete, the air-fuel ratio feedback control is initiated. The combustion feedback control period is usually short, about 20 to 30 seconds from the time the engine is started.

[0023] Furthermore, the electronic control unit 30 is equipped with inter-cylinder air-fuel ratio misalignment detection means 33 for detecting inter-cylinder air-fuel ratio misalignment failures between multiple cylinders 2. There are various methods for detecting inter-cylinder air-fuel ratio misalignment failures, but in this embodiment, information from the air-fuel ratio detection means is utilized. When an inter-cylinder air-fuel ratio misalignment failure is detected during operation, the presence or absence of the failure and the details of the failure are stored in the electronic control unit 30, and this storage is used for combustion feedback control after engine startup at the next start of operation. Note that the phrase "detecting an inter-cylinder air-fuel ratio misalignment failure" in this embodiment and the claims includes not only detection of a confirmed inter-cylinder air-fuel ratio misalignment failure, but also detection of a possibility that an inter-cylinder air-fuel ratio misalignment failure has occurred.

[0024] The method for detecting inter-cylinder air-fuel ratio misalignment faults using inter-cylinder air-fuel ratio misalignment detection means will be explained below with reference to Figure 4. Note that the detection of inter-cylinder air-fuel ratio misalignment faults using the following method utilizes information from the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 14, and is therefore performed after the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 14 are activated, i.e., during the operation of air-fuel ratio feedback control.

[0025] Generally, when an inter-cylinder air-fuel ratio misalignment occurs, unburned gas is generated. However, because the diffusion rate of hydrogen in the unburned gas is faster than that of oxygen, the output of the first air-fuel ratio sensor 12 tends to shift to the rich side, where there is an excess of fuel. When the output of the first air-fuel ratio sensor 12 shifts to the rich side, the main feedback control attempts to correct this by adjusting the air-fuel ratio to the lean side, where there is an excess of fuel. As a result, the catalytic converter of the exhaust gas purification device operates in a lean atmosphere. At this time, the output of the second air-fuel ratio sensor 14 also becomes lean. If this state continues, the sub-feedback control attempts to suppress the deterioration of exhaust gas by adjusting the target air-fuel ratio to the rich side according to the time spent in the lean state, i.e., the lean stay time. This adjustment using the lean stay time is called long-time adjustment, and the amount of adjustment is called the long-time adjustment amount.

[0026] Figures 4(a) to 4(f) are time charts showing the state in which a cylinder-to-cylinder air-fuel ratio misalignment failure has occurred in the information from the first air-fuel ratio sensor 12. In Figure 4(a), the high-frequency output component of the value from the first air-fuel ratio sensor 12 shows data that exceeds the range of a predetermined rich / lean judgment value. The number of times this range is exceeded (judgment count) is counted for each sampling counter period shown in Figure 4(b), which represents the progression of predetermined periods. As shown in Figure 4(c), the number of judgment counts obtained for each sampling counter period is relatively high between sampling counter periods F0 and F1, but relatively low between sampling counter periods F1 and F2. The number of judgment counts for each sampling counter period is temporarily stored.

[0027] The fault detection counter in Figure 4(d) increments the count each time the fault detection value is exceeded during each sampling counter period, and decrements the count if the fault detection value is not exceeded during each sampling counter period. The averaging counter in Figure 4(e) shows how many sampling counter periods are used to accumulate the fault detection counter count. In the figure, the peak average value is calculated using four samples up to F4, but this is not the only option. To increase the amount of data and improve the accuracy of the judgment, it is preferable that the total sampling counter period be 100 seconds or more. In any case, the total number of judgments for the sampling counter periods up to that point is divided by the total period to obtain the peak average value in Figure 4(f) (see symbols P1 and Q1 in the figure). If the peak average value exceeds the degradation detection value, it can be determined that there is a possibility of an inter-cylinder air-fuel ratio misalignment fault occurring. Also, as in F6, when the fault detection counter becomes zero, it is determined that an inter-cylinder air-fuel ratio misalignment fault has occurred, and an alarm is issued to the driver.

[0028] Furthermore, Figures 4(g) to 4(j) are time charts showing the state in which a cylinder-to-cylinder air-fuel ratio misalignment failure occurs, based on the information from the second air-fuel ratio sensor 14. Figure 4(g) shows the air-fuel ratio information from the second air-fuel ratio sensor 14, and Figure 4(h) shows the real-time correction amount based on the information from the second air-fuel ratio sensor 14. The air-fuel ratio feedback control means 31 performs control to richen the target air-fuel ratio if the information obtained from the second air-fuel ratio sensor 14 is leaner than the predetermined lean value (lean judgment voltage) set on the lean side (see the sections R1 to R2 and R5 to R6 in the figure). Also, the air-fuel ratio feedback control means 31 performs control to leanen the target air-fuel ratio if the information is richer than the predetermined rich value (lean judgment voltage) set on the rich side (see the sections R3 to R4 and R7 onwards in the figure).

[0029] Figure 4(i) shows the retention judgment value obtained by filtering the real-time correction amount based on the information obtained from the second air-fuel ratio sensor 14. Figure 4(j) shows the lean retention time (integral value of lean retention time) calculated from the time the retention judgment value exceeds the rich judgment value and the time it is less than or equal to the lean judgment value. If the retention judgment value exceeds the rich judgment value, the lean retention time is increased according to the elapsed time, and if it is less than or equal to the lean judgment value, the lean retention time is decreased according to the elapsed time. If the retention judgment value exceeds the lean judgment value and is less than or equal to the rich judgment value, the lean retention time remains at that value. The symbols S1 to S7 in the figure correspond to the symbols T1 to T7, respectively. Subfeedback control is performed to suppress the deterioration of exhaust gas by setting a long-time correction amount that corrects the target air-fuel ratio to the rich side according to this lean retention time, which is controlled by the main feedback control. Furthermore, if the lean residence time exceeds the deterioration judgment value, the inter-cylinder air-fuel ratio deviation detection means 33 determines that there is a possibility of an inter-cylinder air-fuel ratio deviation failure occurring. Also, if the lean residence time exceeds a failure judgment value which is greater than the deterioration judgment value, the occurrence of an inter-cylinder air-fuel ratio deviation failure is confirmed, and an alarm is issued to the driver.

[0030] Thus, the inter-cylinder air-fuel ratio deviation detection means 33 can detect an inter-cylinder air-fuel ratio deviation failure based on the number of peaks of the high-frequency output of the linear air-fuel ratio sensor used as the first air-fuel ratio sensor 12, the cumulative value of the lean residence time based on information from the rear O2 sensor used as the second air-fuel ratio sensor 14, or either of the above.

[0031] In combustion feedback control, consider a scenario where, as shown in Figure 2(a) or Figure 2(b), there is information indicating a possible inter-cylinder air-fuel ratio misalignment failure during the previous operation. In Figure 2(a), symbol a2 indicates a degraded state where the degradation judgment value a0 is exceeded, and there is a possibility of an inter-cylinder air-fuel ratio misalignment failure occurring. Symbol a1 indicates a normal state where the degradation judgment value a0 is not exceeded, and no inter-cylinder air-fuel ratio misalignment failure has occurred. In Figure 2(b), symbol b2 indicates a degraded state where the degradation judgment value b0 is exceeded, and there is a possibility of an inter-cylinder air-fuel ratio misalignment failure occurring. Symbol b1 indicates a normal state where the degradation judgment value b0 is not exceeded, and no inter-cylinder air-fuel ratio misalignment failure has occurred.

[0032] Figure 2(c) shows the fluctuations in engine speed. Based on the fluctuations in engine speed in Figure 2(c), the engine speed deviation in Figure 2(d) is calculated. At points d1, d2, d3, d4, etc., where the engine speed deviation is below the half-misfire detection value, a normal combustion feedback control would perform a correction control to adjust the fuel injection amount from the initial value by a predetermined amount, as shown by the line e1 in Figure 2(e). In this embodiment, the fuel injection amount is increased by the correction control. After increasing the fuel injection amount, the fuel injection amount is gradually decreased until rotational fluctuations are detected again. That is, if rotational fluctuations occur many times in a short period, the fuel injection amount is gradually increased, and if no rotational fluctuations occur for a long period, the fuel injection amount decreases toward the initial value. In this way, the engine is operated with the fuel injection amount as close to the initial value as possible while stabilizing the engine speed. At this time, the fuel injection amount has an upper limit and a lower limit, and is set so that the fuel injection amount does not exceed a predetermined upper limit and does not fall below a predetermined lower limit. However, if the system is in a degraded state where a cylinder-to-cylinder air-fuel ratio misalignment failure may be occurring, control is performed to limit the amount of fuel injection correction by the correction control to a low value, as shown by symbol f1. In this embodiment, the upper limit of the fuel injection amount is reduced compared to the normal state (a state in which no cylinder-to-cylinder air-fuel ratio misalignment failure has occurred). Symbol e0 in the figure indicates the upper limit of fuel injection in the normal state, and symbol f0 indicates the lower value of the fuel injection upper limit that is limited in the degraded state.

[0033] In combustion feedback control, under normal conditions, the fuel enrichment correction amount is adjusted. Under degraded conditions, control is not only possible to reduce the upper limit of the fuel enrichment correction amount, but also to set the fuel enrichment correction amount to zero (no fuel enrichment correction is performed) under degraded conditions. Furthermore, instead of reducing the upper limit of the fuel enrichment correction amount under degraded conditions, control is also possible to reduce the amount of fuel injected to increase the fuel when engine rotation fluctuations occur, making it difficult for the fuel enrichment correction amount to reach the upper limit.

[0034] Furthermore, it is possible to control the degree to which the correction amount is reduced based on the nature of the inter-cylinder air-fuel ratio misalignment failure or the possibility thereof. For example, based on the amount of air-fuel ratio misalignment of the faulty cylinder 2 in an inter-cylinder air-fuel ratio misalignment failure (the amount of misalignment from the normal air-fuel ratio, or the amount of misalignment from the air-fuel ratio of other cylinders 2), it is possible to control the degree to which the fuel enrichment correction amount is restricted (lowering the upper limit of the correction amount) as the amount of misalignment increases. Factors for determining the amount of air-fuel ratio misalignment of the faulty cylinder 2 include the number of peaks of the high-frequency output of the linear air-fuel ratio sensor used as the first air-fuel ratio sensor 12, and the cumulative value of the lean residence time based on information from the rear O2 sensor used as the second air-fuel ratio sensor 14.

[0035] For example, a threshold can be set for the number of peaks, and the data can be divided into two or more grades around that threshold, with different limits on the correction amount set for each grade. Similarly, a threshold can be set for the lean dwell time, and the data can be divided into two or more grades around that threshold, with different limits on the correction amount set for each grade. The adjustment of the correction amount limit based on the number of peaks and the adjustment of the correction amount limit based on the lean dwell time grade can be used individually or in combination.

[0036] In the flowchart of Figure 3, the degree of limitation of the correction amount is adjusted by both the number of peaks and the grade of the lean residence time. In step S1 of Figure 3, the high-frequency output component of the first air-fuel ratio sensor 12 is detected. In step S2, it is determined whether the high-frequency output component is above the degradation judgment value. If it is above the degradation judgment value, it is a degraded state and the process moves to step S4. In step S4, the upper limit of the correction amount in the combustion feedback control performed at the next engine start, i.e., after the determination of an inter-cylinder air-fuel ratio misalignment failure, is changed, and as a result, the exhaust gas is improved in step S5. In step S2, if it is not above the degradation judgment value, the process moves to step S3. In step S3, it is determined whether the lean residence time of the second air-fuel ratio sensor 14 is above a predetermined value. If the lean residence time is above the predetermined value, it is an inter-cylinder air-fuel ratio misalignment failure state and the process moves to step S4, where the upper limit of the correction amount in the combustion feedback control performed at the next engine start is changed. If the lean residence time is not greater than or equal to a predetermined value, it is considered a normal state with no inter-cylinder air-fuel ratio misalignment failure, so the process proceeds to step S5, and the combustion feedback control performed at the next engine start is the normal combustion feedback control, without changing the upper limit of the correction amount. [Explanation of Symbols]

[0037] 1 Engine 2 liters 3. Throttle valve 4 Intake passage 5. Exhaust passage 10 Injection device (in-cylinder injection device) 12. First air-fuel ratio detection means (first air-fuel ratio sensor) 13 Exhaust purifying device 14. Second air-fuel ratio detection means (second air-fuel ratio sensor) 30 Electronic control unit 31 Air-fuel ratio feedback control means 32 Combustion Feedback Control Means 33. Cylinder-to-cylinder air-fuel ratio deviation detection means

Claims

1. An injection system that supplies fuel to an engine having multiple cylinders, An air-fuel ratio detection means for detecting the air-fuel ratio of the engine, An air-fuel ratio feedback control means that performs air-fuel ratio feedback control to control the air-fuel ratio according to the detection result of the air-fuel ratio detection means, A combustion feedback control means is performed from the time the engine starts until the air-fuel ratio feedback control is started, and when it detects a rotational fluctuation of the engine, it increases the amount of fuel injected by the injection device. Inter-cylinder air-fuel ratio deviation detection means for detecting inter-cylinder air-fuel ratio deviation failures between the aforementioned multiple cylinders, Equipped with, The inter-cylinder air-fuel ratio deviation detection means detects an inter-cylinder air-fuel ratio deviation failure during the air-fuel ratio feedback control during the previous engine operation. An engine control device in which, when the inter-cylinder air-fuel ratio misalignment failure is detected by the inter-cylinder air-fuel ratio misalignment detection means, the combustion feedback control means reduces the amount of fuel injection by the injector that is increased when a rotational speed fluctuation of the engine is detected in the combustion feedback control, or controls the fuel injection amount so that the fuel injection amount in the combustion feedback control does not exceed an upper limit, and when the inter-cylinder air-fuel ratio misalignment failure is detected by the inter-cylinder air-fuel ratio misalignment detection means, the combustion feedback control means sets the upper limit lower than when the inter-cylinder air-fuel ratio misalignment failure is not detected.

2. The inter-cylinder air-fuel ratio deviation detection means is capable of detecting the amount of deviation in the air-fuel ratio in the inter-cylinder air-fuel ratio deviation failure. The combustion feedback control means increases the limit on the increase in the fuel injection amount when detecting engine rotation fluctuations as the amount of deviation in the air-fuel ratio increases. The engine control device according to claim 1.

3. The combustion feedback control means increases the fuel injection amount by a predetermined amount each time it detects a rotational fluctuation of the engine. When the inter-cylinder air-fuel ratio misalignment detection means detects the occurrence of an inter-cylinder air-fuel ratio misalignment fault, the combustion feedback control means sets the predetermined amount lower than when the occurrence of an inter-cylinder air-fuel ratio misalignment fault is not detected. The engine control device according to claim 1 or 2.

4. The engine further includes an exhaust purification device provided in the exhaust passage of the aforementioned engine. The air-fuel ratio detection means comprises a first air-fuel ratio detection means consisting of a linear air-fuel ratio sensor provided in the exhaust passage upstream of the exhaust purification device, and an O ２ A second air-fuel ratio detection means consisting of a sensor, Equipped with, The inter-cylinder air-fuel ratio deviation detection means is An engine control device according to any one of claims 1 to 3, which detects an inter-cylinder air-fuel ratio deviation failure based on the number of peaks, which is the number of times the output of the first air-fuel ratio detection means in the air-fuel ratio feedback control deviates from a predetermined range including stoichiometry, and the cumulative value of the lean residence time, which is the time the output of the second air-fuel ratio detection means in the air-fuel ratio feedback control is below a predetermined value on the lean side, or either of these.

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