Control device for engine

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] The present invention relates to an engine control device. [Background technology]

[0002] Generally, there is a method for improving exhaust purification performance by controlling the fuel injection amount to a predetermined amount that makes the air-fuel ratio lean after engine start, thereby suppressing the emission of HC and quickly increasing the catalyst temperature of the exhaust purification device to promote activation. At this time, the air-fuel ratio is made lean to a predetermined value that is close to the stability limit, but to the extent that misfire does not occur.

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

[0004] [Patent Document 1] JP-A-9-53492 (see paragraphs 0002,0003, etc.) [Patent Document 2] JP 2012-202333 A (see paragraphs 0027-0029, FIG. 3, etc.) Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Documents 1 and 2, after the engine is started, the fuel injection amount is controlled to a predetermined value. If the engine speed fluctuation exceeds a predetermined threshold value, the engine determines that there is a possibility of misfire and starts combustion feedback control to increase the fuel injection amount.

[0006] However, in an engine having multiple cylinders, a phenomenon in which the air-fuel ratio differs between cylinders, that is, a so-called cylinder-to-cylinder air-fuel ratio deviation, may occur. The cylinder-to-cylinder air-fuel ratio deviation may be caused by various reasons, such as clogging of the injector due to aging, foreign matter getting caught in the needle, or poor electrical conduction. When the cylinder-to-cylinder air-fuel ratio deviation occurs, the engine rotation fluctuation increases, so that a control is performed to increase the fuel injection amount and stabilize the combustion by a combustion feedback control. This may cause the exhaust gas from a cylinder with a normal air-fuel ratio to deteriorate. If the threshold value is set to a large value so that the increase in the fuel injection amount is difficult to operate in order to suppress such deterioration of the exhaust gas, a problem may occur in which the necessary increase in the fuel injection amount is not performed in an operating state in which an increase in the fuel injection amount is originally required, such as when heavy fuel is mixed in and fuel atomization is insufficient, or when an exhaust gas recirculation device fails.

[0007] Therefore, an object of the present invention is to suppress deterioration of exhaust gas even when an air-fuel ratio deviation occurs between cylinders in combustion feedback control that controls the air-fuel ratio in response to engine rotation fluctuations during the period from engine start to the transition to air-fuel ratio feedback control. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides an engine control device comprising an injection device which supplies fuel to an engine having a plurality of cylinders, an air-fuel ratio detection means which detects the air-fuel ratio of the engine, an air-fuel ratio feedback control means which performs air-fuel ratio feedback control which controls the air-fuel ratio in accordance with the detection result of the air-fuel ratio detection means, a combustion feedback control means which performs combustion feedback control which is performed from the time the engine is started until the air-fuel ratio feedback control is started and which increases the amount of fuel injection by the injection device when a rotational fluctuation of the engine is detected, and an inter-cylinder air-fuel ratio deviation detection means which detects an inter-cylinder air-fuel ratio deviation fault among the plurality of cylinders, and wherein when the inter-cylinder air-fuel ratio deviation detection means detects the occurrence of an inter-cylinder air-fuel ratio deviation fault, the combustion feedback control means limits the increase in the amount of fuel injection by the injection device when a rotational fluctuation of the engine is detected.

[0009] Here, the inter-cylinder air-fuel ratio deviation detection means can detect the magnitude of the degree of the inter-cylinder air-fuel ratio deviation fault, and the combustion feedback control means can adopt a configuration in which the greater the degree of the fault, the greater the restriction on the increase in the fuel injection amount when a rotational fluctuation of the engine is detected.

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

[0011] In each of these aspects, the combustion feedback control means can be configured to increase the fuel injection amount by a predetermined amount each time a rotation fluctuation of the engine is detected, and when the inter-cylinder air-fuel ratio deviation detection means detects the occurrence of an inter-cylinder air-fuel ratio deviation fault, the combustion feedback control means can be configured to set the predetermined amount lower than when the occurrence of an inter-cylinder air-fuel ratio deviation fault is not detected.

[0012] The engine further includes an exhaust purification device provided in an exhaust passage, and the air-fuel ratio detection means includes a first air-fuel ratio detection means including a linear air-fuel ratio sensor provided in the exhaust passage upstream of the exhaust purification device, and an O 2 and second air-fuel ratio detection means consisting of a sensor, wherein the inter-cylinder air-fuel ratio deviation detection means detects an inter-cylinder air-fuel ratio deviation fault based on a peak count, which is the number of times that 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 an integrated value of a lean residence time, which is the time during which 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 on either one of them. Effect of the Invention

[0013] In combustion feedback control, which controls the air-fuel ratio in response to engine rotation fluctuations during the period from engine start-up until transition to air-fuel ratio feedback control, deterioration of exhaust gas can be suppressed even when an air-fuel ratio deviation occurs between cylinders. [Brief description of the drawings]

[0014] [Figure 1] 1 is an overall view showing a schematic diagram of an engine control device according to an embodiment of the present invention; [Diagram 2] 4 is a time chart illustrating an example of control. [Diagram 3] 11 is a flowchart illustrating an example of control. [Figure 4] 10 is a time chart showing a specific relationship between pieces of control information. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is an overall view showing the configuration of a control device for an engine 1 according to the present invention.

[0016] The engine 1 is a four-cylinder engine for automobiles. As shown in FIG. 1, the engine has four cylinders 2 arranged in parallel, an intake passage 4 leading to an intake port that feeds air into each cylinder 2, an exhaust passage 5 leading from an exhaust port, an injection device 10 that supplies fuel to each cylinder 2, and the like. Note that FIG. 1 shows only members and means directly related to the present invention, and other members and the like are omitted. Also, the drawing shows an example having four cylinders 2, but the engine may have two or more cylinders, and the cylinders do not have to be arranged in series. Also, although the injection device 10 is configured to inject fuel directly into each cylinder 2, it may be configured to inject fuel into the intake port.

[0017] A throttle valve 3 for adjusting the flow area is provided in the upstream portion of the intake passage 4, making it possible to adjust the amount of intake air. In addition, an air-fuel ratio detection means for detecting the air-fuel ratio in the exhaust passage 5 is provided in the exhaust passage 5. As the air-fuel ratio detection means, a first air-fuel ratio sensor (first air-fuel ratio detection means) 12 is attached to a post-junction exhaust passage 11 downstream of the junction of the passages of the exhaust manifold. At the end of the post-junction exhaust passage 11 toward the downstream side, an exhaust purification device 13 equipped with a catalyst or the like for removing nitrogen oxides and the like in the exhaust is attached further downstream of that, and a second air-fuel ratio sensor (second air-fuel ratio detection means) 14 is attached as an air-fuel ratio detection means further downstream of that, and a muffler 15 or the like is provided further downstream of that.

[0018] The devices necessary for the operation of the engine, including the throttle valve 3 and the direct injection device 10, are each controlled by an electronic control unit 30 provided in a vehicle equipped with this engine 1. In addition, 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 is equipped with an air-fuel ratio feedback control means 31 that controls the air-fuel ratio in the cylinder 2. The air-fuel ratio feedback control means 31 controls the throttle valve 3 to adjust the amount of intake air in the intake passage 4. The air-fuel ratio feedback control means 31 also adjusts the amount of fuel injected from the direct injection device 10 into the cylinder 2. The exhaust gas from each cylinder 2 is discharged into the exhaust passage 5, purified by the exhaust purification device 13, and then discharged through the muffler 15.

[0020] The air-fuel ratio feedback control means 31 controls the air-fuel ratio to a target air-fuel ratio set according to the operating state of the engine. In detail, it performs main feedback control to control the amount of fuel supplied to the engine so that the value of a first air-fuel ratio sensor 12 (Linear Air Fuel Ratio Sensor) arranged upstream of the exhaust purification device in the exhaust passage of the engine coincides with the target air-fuel ratio.

[0021] However, the first air-fuel ratio sensor 12 (linear air-fuel ratio sensor) located upstream of the exhaust purification device 13 has a problem in that the values ​​it obtains fluctuate greatly. In addition, since the first air-fuel ratio sensor 12 receives and detects gas exhausted from the parallel exhaust passage 5, the impact on detection accuracy varies from cylinder to cylinder. Furthermore, the air-fuel ratio has its own quirks in the cylinder 2, and not all cylinders 2 behave in the same way. For this reason, there are cases where the main feedback control using the first air-fuel ratio sensor 12 alone is not able to respond to driving conditions. To correct this, a second air-fuel ratio sensor 14 (rear O 2 In addition, sub-feedback control is performed to complement the control value performed by the main feedback control based on the value of the air-fuel ratio sensor. These main feedback control, sub-feedback control, etc. are collectively called air-fuel ratio feedback control.

[0022] As described above, the air-fuel ratio feedback control is performed based on the output values ​​of the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 14. However, the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 14 are not sufficiently activated immediately after the engine is started, and the air-fuel ratio feedback control cannot be performed accurately. Therefore, the electronic control unit 30 is provided with a combustion feedback control means 32 that performs combustion feedback control by setting the fuel injection amount to a predetermined initial value and correcting and controlling the fuel injection amount according to engine rotation fluctuations during a predetermined time period from the engine start. The combustion feedback control is a control that increases the amount of fuel supplied to the engine by the injector 10 to stabilize the engine rotation when a misfire of the engine is detected due to engine rotation fluctuations during engine operation with fuel injection at the initial value after the engine is started. The initial value may be, for example, a value that causes the exhaust gas emission amount to fall below a predetermined target value, and is preferably a value that causes the air-fuel ratio to be lean. The initial value may be determined in advance by an experiment or the like. Furthermore, a misfire of the engine is detected when the engine rotation fluctuation exceeds a predetermined value. After the combustion feedback control ends, the air-fuel ratio feedback control is started. The period of the combustion feedback control is usually a short period of time, about 20 to 30 seconds, from the start of the engine.

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

[0024] A method for detecting an inter-cylinder air-fuel ratio deviation failure by the inter-cylinder air-fuel ratio deviation detection means will be described below with reference to Fig. 4. Note that detection of an inter-cylinder air-fuel ratio deviation failure by the following method uses 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, that is, during operation of air-fuel ratio feedback control.

[0025] Generally, when an inter-cylinder air-fuel ratio deviation fault occurs, unburned gas is generated. However, because the diffusion speed 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, which 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 tries to correct this by correcting the air-fuel ratio to the lean side, which is an insufficient amount of fuel. Therefore, the catalyst of the exhaust 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, sub-feedback control is performed to correct the air-fuel ratio targeted by the main feedback control to the rich side according to the time spent in the lean state, i.e., the lean stay time, in order to suppress the deterioration of exhaust gas. This correction using the lean stay time is called long-time correction, and the correction amount is called the long-time correction amount.

[0026] 4(a) to (f) are time charts showing a state in which an inter-cylinder air-fuel ratio deviation fault has occurred in the information of the first air-fuel ratio sensor 12. In the high frequency output component of the value of the first air-fuel ratio sensor 12 in FIG. 4(a), data that exceeds a predetermined range of rich / lean judgment values ​​appears. The number of times this range is exceeded (the number of judgments) is counted for each sampling counter period that indicates the passage of each predetermined period in FIG. 4(b). As shown in FIG. 4(c), the number of judgment counts acquired for each sampling counter period is relatively high during the sampling counter period F0 to F1, but is relatively low during the sampling counter period F1 to F2. The number of judgments in each sampling counter period is temporarily stored.

[0027] The fault determination counter in FIG. 4(d) increments the count each time the fault determination value is exceeded in each sampling counter period, and decrements the count if the fault determination value is not exceeded in each sampling counter period. The averaging counter in FIG. 4(e) indicates how many sampling counter periods the fault determination counter count is accumulated for. In the figure, the peak average value is calculated using four times up to F4, but this is not particularly limited, and in order to increase the number of data and improve the accuracy of the determination, it is preferable that the total sampling counter period is 100 seconds or more. In any case, the total number of determinations for the sampling counter period up to that point is divided by the total period to obtain the peak average value in FIG. 4(f) (see symbols P1 and Q1 in the figure). If the peak average value exceeds the deterioration determination value, it can be determined that there is a possibility that a fault due to an air-fuel ratio deviation between cylinders has occurred. Also, when the fault determination counter becomes zero, as in F6, it is determined that the occurrence of a fault due to an air-fuel ratio deviation between cylinders has been confirmed, and an alarm is issued to the driver, etc.

[0028] 4(g)-(j) are time charts showing a state in which an inter-cylinder air-fuel ratio deviation fault has occurred in the information of the second air-fuel ratio sensor 14. FIG. 4(g) shows the information of the air-fuel ratio by the second air-fuel ratio sensor 14, and FIG. 4(h) shows the real-time correction amount based on the information of the second air-fuel ratio sensor 14. If the information obtained by the second air-fuel ratio sensor 14 is leaner than the lean predetermined value (lean judgment voltage) set on the lean side (see the sections R1-R2 and R5-R6 in the figure), the air-fuel ratio feedback control means 31 performs control to rich correct the target air-fuel ratio. If the information obtained by the second air-fuel ratio sensor 14 is richer than the lean predetermined value (lean judgment voltage) set on the rich side (see the sections R3-R4 and R7 onward in the figure), the air-fuel ratio feedback control means 31 performs control to lean correct the target air-fuel ratio.

[0029] FIG. 4(i) shows the retention judgment value obtained by filtering the real-time correction amount based on the information obtained by the second air-fuel ratio sensor 14. FIG. 4(j) shows the lean residence time (integrated value of lean residence time) calculated by the time when the retention judgment value exceeds the rich judgment value and the time when it is equal to or less than the lean judgment value. When the retention judgment value exceeds the rich judgment value, the lean residence time is added according to the elapsed time, and when it is equal to or less than the lean judgment value, the lean residence time is subtracted according to the elapsed time. When the retention judgment value exceeds the lean judgment value and is equal to or less than the rich judgment value, the lean residence time maintains its value. The symbols S1 to S7 in the figure correspond to the symbols T1 to T7, respectively. According to this lean residence time, a long-time correction amount for correcting the air-fuel ratio targeted by the main feedback control to the rich side is set, and sub-feedback control for suppressing deterioration of exhaust gas is performed. 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 that an inter-cylinder air-fuel ratio deviation fault has occurred. If the lean residence time exceeds a fault judgment value that is greater than the deterioration judgment value, it is determined that an inter-cylinder air-fuel ratio deviation fault has occurred, and an alarm is issued to the driver, etc.

[0030] In this way, the inter-cylinder air-fuel ratio deviation detection means 33 detects 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 number of peaks of the high-frequency output of the rear O air-fuel ratio sensor used as the second air-fuel ratio sensor 14. 2 An inter-cylinder air-fuel ratio deviation fault can be detected based on the integrated value of the lean residence time obtained from the sensor information, or on either one of them.

[0031] In the combustion feedback control, as shown in FIG. 2(a) or FIG. 2(b), it is assumed that there is information that there is a possibility of an inter-cylinder air-fuel ratio mismatch fault occurring during the previous operation. In FIG. 2(a), the symbol a2 indicates a deteriorated state in which the deterioration judgment value a0 is exceeded and there is a possibility of an inter-cylinder air-fuel ratio mismatch fault occurring. The symbol a1 indicates a normal state in which the deterioration judgment value a0 is not exceeded and there is no inter-cylinder air-fuel ratio mismatch fault occurring. In FIG. 2(b), the symbol b2 indicates a deteriorated state in which the deterioration judgment value b0 is exceeded and there is a possibility of an inter-cylinder air-fuel ratio mismatch fault occurring. The symbol b1 indicates a normal state in which the deterioration judgment value b0 is not exceeded and there is no inter-cylinder air-fuel ratio mismatch fault occurring.

[0032] FIG. 2(c) shows the fluctuation of the engine speed. Based on the fluctuation of the speed in FIG. 2(c), the speed deviation in FIG. 2(d) is calculated. At each point of d1, d2, d3, d4, etc. where the speed deviation is equal to or less than the half misfire judgment value, in the case of normal combustion feedback control, a correction control is performed to correct the fuel injection amount from the initial value by a predetermined amount as shown by the line of e1 in FIG. 2(e). In this embodiment, the fuel injection amount is increased by the correction control. After the fuel injection amount is increased, the fuel injection amount is gradually decreased until the rotation fluctuation is detected again. That is, if the rotation fluctuation occurs many times in a short period of time, the fuel injection amount is gradually increased, and if the rotation fluctuation does not occur for a long period of time, the fuel injection amount is decreased toward the initial value. In this way, the engine is operated with the fuel injection amount at the initial value as much as possible while stabilizing the engine rotation. At this time, the fuel injection amount has an upper limit value and a lower limit value, and is set so that the fuel injection amount does not exceed the predetermined upper limit value and does not fall below the predetermined lower limit value. However, if the engine is in a deteriorated state where there is a possibility that an inter-cylinder air-fuel ratio mismatch fault has occurred, as shown by the reference symbol f1, control is performed to limit the amount of fuel injection correction by the correction control to a low value. In this embodiment, the upper limit of the fuel injection amount is reduced compared to the normal state (a state where no inter-cylinder air-fuel ratio mismatch fault has occurred). The reference symbol e0 in the figure indicates the upper limit of fuel injection in the normal state, and the reference symbol f0 indicates the lower upper limit of fuel injection limited in the deteriorated state.

[0033] Here, in the combustion feedback control, in relation to the fuel increase correction amount in the normal state, not only is it possible to control to reduce the upper limit of the fuel increase correction amount in the deteriorated state, but it is also possible to control to set the fuel increase correction amount to zero (no fuel increase correction) in the deteriorated state. Also, instead of reducing the upper limit of the fuel increase correction amount in the deteriorated state, it is also possible to control to reduce the fuel injection amount that is increased when engine rotation fluctuation occurs, so that the fuel increase correction amount is less likely to reach the upper limit.

[0034] It is also possible to control the degree to which the correction amount is reduced based on the details of the inter-cylinder air-fuel ratio deviation failure or the possibility of the failure. For example, it is possible to control the degree to which the fuel increase correction amount is restricted (the upper limit of the correction amount is lowered) based on the deviation amount of the air-fuel ratio of the failed cylinder 2 in the inter-cylinder air-fuel ratio deviation failure (deviation amount from the normal air-fuel ratio, or deviation amount from the air-fuel ratio of the other cylinders 2) as the deviation amount increases. As factors for determining the deviation amount of the air-fuel ratio of the failed cylinder 2, 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 number of peaks of the high-frequency output of the rear O air-fuel ratio sensor used as the second air-fuel ratio sensor 14, and the number of peaks of the high-frequency output of the linear air-fuel ratio sensor used as the second air-fuel ratio sensor 15 are used. 2 These include the various elements of the integrated value of the lean residence time based on sensor information.

[0035] For example, a threshold value can be set for the number of peaks, and the grades can be divided into two or three or more grades with the threshold in between, and a different degree of restriction on the correction amount can be set for each grade. Also, a threshold value can be set for the lean residence time, and the grades can be divided into two or three or more grades with the threshold in between, and a different degree of restriction on the correction amount can be set for each grade. The adjustment of the degree of restriction on the correction amount based on the number of peaks and the adjustment of the degree of restriction on the correction amount based on the grade of the lean residence time may be used alone or in combination.

[0036] In the flow chart of FIG. 3, the adjustment of the degree of limiting the correction amount according to the number of peaks and the adjustment of the degree of limiting the correction amount according to the grade of the lean residence time are used in combination. In step S1 of FIG. 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 equal to or greater than the deterioration determination value. If it is equal to or greater than the deterioration determination value, the engine is in a deteriorated state, and the process proceeds to step S4. In step S4, the correction amount upper limit value in the combustion feedback control performed at the next engine start, that is, at the engine start after the determination of the inter-cylinder air-fuel ratio deviation fault, is changed, and as a result, the improvement of the exhaust gas is realized in step S5. In step S2, if it is not equal to or greater than the deterioration determination value, the process proceeds to step S3. In step S3, it is determined whether the lean residence time of the second air-fuel ratio sensor 14 is equal to or greater than a predetermined value. If the lean residence time is equal to or greater than the predetermined value, the engine is in an inter-cylinder air-fuel ratio deviation fault state, and the process proceeds to step S4, and the correction amount upper limit value in the combustion feedback control performed at the next engine start is changed. If the lean residence time is not equal to or longer than the predetermined value, the system is in a normal state in which no inter-cylinder air-fuel ratio deviation fault has occurred, so the system proceeds to step S5, and the combustion feedback control performed at the next engine start is set to normal combustion feedback control, without changing the upper correction amount value. [Explanation of symbols]

[0037] 1 Engine 2 Cylinder 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 purification 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 Means for detecting air-fuel ratio deviation between cylinders

Claims

1. an injector for supplying fuel to an engine having a plurality of cylinders; an air-fuel ratio detection means for detecting an air-fuel ratio of the engine; an air-fuel ratio feedback control means for performing an air-fuel ratio feedback control for controlling the air-fuel ratio in accordance with a detection result of the air-fuel ratio detection means; a combustion feedback control means for performing a combustion feedback control during a period from when the engine is started until the air-fuel ratio feedback control is started, the combustion feedback control being for increasing the amount of fuel injected by the injector when a rotational fluctuation of the engine is detected; an inter-cylinder air-fuel ratio deviation detection means for detecting an inter-cylinder air-fuel ratio deviation fault among the plurality of cylinders; Equipped with An engine control device in which, when the inter-cylinder air-fuel ratio deviation detection means detects the occurrence of an inter-cylinder air-fuel ratio deviation fault, the combustion feedback control means reduces the amount of increase in the fuel injection amount by the injection device, which increases when a rotation 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 value, and when the inter-cylinder air-fuel ratio deviation detection means detects the occurrence of an inter-cylinder air-fuel ratio deviation fault, the combustion feedback control means sets the upper limit value lower than when the occurrence of an inter-cylinder air-fuel ratio deviation fault is not detected.

2. the inter-cylinder air-fuel ratio deviation detection means is capable of detecting a degree of a malfunction of the inter-cylinder air-fuel ratio deviation malfunction, the combustion feedback control means increases the limitation on the increase in the fuel injection amount when a rotation fluctuation of the engine is detected as the degree of the failure 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 a rotational fluctuation of the engine is detected, When the occurrence of an inter-cylinder air-fuel ratio deviation fault is detected by the inter-cylinder air-fuel ratio deviation detection means, the combustion feedback control means sets the predetermined amount lower than when the occurrence of an inter-cylinder air-fuel ratio deviation fault is not detected. The engine control device according to claim 1 or 2.

4. The engine further includes an exhaust gas purification device provided in an exhaust passage of the engine. The air-fuel ratio detection means includes a first air-fuel ratio detection means including 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 comprising a sensor; Equipped with The cylinder air-fuel ratio deviation detection means 4. The engine control device according to claim 1, wherein an inter-cylinder air-fuel ratio deviation fault is detected based on a peak count, which is the number of times that 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 an integrated value of a lean residence time, which is the time during which 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 on either one of them.

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