JP6866040B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to a control device for an internal combustion engine accompanied by an exhaust gas recirculation device.

Internal combustion engines mounted on vehicles are often accompanied by an EGR device that reduces the combustion temperature of the air-fuel mixture in the cylinder _{to reduce NO x emissions while reducing pumping loss.} In the EGR device, the exhaust passage and the intake passage of the internal combustion engine are connected via the EGR passage, and a part of the combustion gas generated in the cylinder is returned to the intake passage via the EGR passage and mixed with the intake air. An EGR valve that opens and closes the EGR passage is provided on the EGR passage, and the amount of recirculation of the EGR gas can be adjusted by operating the opening of the EGR valve.

If the EGR valve fails, it interferes with proper EGR control, leading to instability of combustion, deterioration of emissions, or knocking. Therefore, the vehicle is equipped with a diagnostic (self-diagnosis) mechanism that diagnoses the presence or absence of EGR valve failure online, and when a failure is detected, notifies the driver of the failure and keeps a record in the storage device. To.

EGR valve diagnosis is performed during a fuel cut that suspends fuel supply to the cylinder. In diagnostics, the EGR valve is intentionally opened and closed during fuel cut, the pressure in the intake passage when the valve is closed and when the valve is opened are measured, and based on this, the presence or absence of EGR valve failure is determined (for example). , See patent document below).

Japanese Unexamined Patent Publication No. 2011-252399

The electronic control unit that controls the operation of the internal combustion engine measures the amount of fresh air (air or oxygen) that flows into the cylinder during fuel cut and even when performing EGR valve diagnosis. The operation is continuously and iteratively executed. This is because the fuel cut is finished in response to the driver stepping on the accelerator pedal or the shift lever or select lever is operated to the neutral range, and the cylinder is filled when the fuel supply to the cylinder is restarted. This is because it is necessary to promptly determine the fuel injection amount commensurate with the amount of fresh air to be produced.

On that basis, conventionally, the total amount of gas flowing into the intake passage via the EGR passage during diagnosis is regarded as fresh, and the amount of fresh air flowing into the cylinder is calculated.

On the other hand, in recent internal combustion engines, the inlet of the EGR passage constituting the EGR device is connected not upstream but downstream of the three-way catalyst for exhaust gas purification in the exhaust passage. This is because the exhaust gas flowing downstream of the catalyst contains a smaller amount of impurities such as soot as compared with that upstream of the catalyst.

When the fuel cut is started, fresh air will flow into the cylinder and the exhaust passage. However, the gas flowing downstream of the catalyst contains combustion gas and / or unburned fuel components for some time from the start of the fuel cut. Therefore, if the EGR valve is opened immediately after the start of the fuel cut, the gas containing the combustion gas and the unburned fuel component in addition to the fresh air will return from the exhaust passage to the intake passage.

Nevertheless, if the total amount of recirculated gas is regarded as fresh air, the amount of fresh air flowing into the cylinder is calculated, and the fuel injection amount is determined in proportion to the amount of fresh air, it is larger than the amount actually required. Will inject the amount of fuel. As a result, immediately after the end of the fuel cut, the air-fuel ratio of the air-fuel mixture filled in the cylinder becomes excessively rich, or the oxygen in the air-fuel mixture becomes insufficient and combustion becomes unstable, resulting in an unreasonable engine speed. There was concern that a decline would occur.

In order to avoid such a decrease in engine speed, it is conceivable to wait for a certain delay time to elapse after starting the fuel cut, and then to start diagnostics accompanied by opening the EGR valve. However, the length of the execution period of one fuel cut is often relatively short, and in that case, the diagnosis of the EGR valve cannot be completed, that is, the chance of diagnosis tends to be scarce.

The present invention has been made by paying attention to the above problems for the first time, and an object of the present invention is to prevent instability of engine rotation due to diagnostics of an EGR valve performed during fuel cutting. ..

In the present invention, a control device for controlling an internal combustion engine having an exhaust gas recirculation device provided with an EGR valve in an EGR passage that communicates a downstream portion of an exhaust purification catalyst in an exhaust passage with a predetermined portion of an intake passage. Therefore, during the fuel cut in which the fuel supply to the cylinder of the internal combustion engine is temporarily interrupted, the EGR valve is opened and closed to perform the diagnosis of determining the presence or absence of the EGR valve failure, and the diagnosis is performed during the fuel cut. When the diagnosis is performed, the output of the air fuel ratio sensor that detects the air fuel ratio of the gas flowing downstream of the catalyst in the exhaust passage is calculated when calculating the amount of fresh air filled in the cylinder immediately after the end of the fuel cut. A control device for an internal combustion engine was constructed to reduce and correct the amount of fresh air according to the air-fuel ratio indicated by the signal.

Further, in the present invention, an internal combustion engine having an exhaust gas recirculation device provided with an EGR valve in the EGR passage communicating the downstream portion of the exhaust gas purification catalyst in the exhaust passage and the predetermined portion of the intake passage is controlled. It is a control device that performs diagnosis to determine whether or not there is a failure of the EGR valve by opening and closing the EGR valve during the fuel cut that temporarily suspends the fuel supply to the cylinder of the internal combustion engine. When the diagnosis is performed inside, when calculating the amount of fuel to be injected immediately after the end of the fuel cut, the output signal of the air fuel ratio sensor that detects the air fuel ratio of the gas flowing downstream of the catalyst in the exhaust passage is used. If the air-fuel ratio shown is richer than the air-fuel ratio indicated by the output signal of the air-fuel ratio sensor under the condition that only fresh air flows almost or completely downstream of the catalyst, it is compared with the case where it is not. A control device for an internal combustion engine was constructed to reduce and correct the fuel injection amount.

During the diagnosis, the air-fuel ratio indicated by the output signal of the air-fuel ratio sensor is the output signal of the air-fuel ratio sensor under the condition that only fresh air flows almost or completely downstream of the catalyst. When it becomes equivalent to the air-fuel ratio indicated by, it is preferable to gradually reduce the reduction correction amount of the fresh air amount or the fuel injection amount after a lapse of a predetermined time from that point.

The internal combustion engine controlled by the control device according to the present invention is particularly such that the EGR passage is connected to a location near the installation location of the air-fuel ratio sensor in the exhaust passage or a location upstream of the air-fuel ratio sensor. is there.

According to the present invention, it is possible to prevent instability of engine rotation due to diagnostics of the EGR valve performed during fuel cutting.

The figure which shows the structure of the internal combustion engine for a vehicle and the control device in one Embodiment of this invention. The timing diagram which shows the content of the process executed by the control device of the same embodiment.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle according to the present embodiment. The internal combustion engine of the present embodiment is a spark-ignition 4-stroke gasoline engine, and includes a plurality of cylinders 1 (one of which is illustrated in FIG. 1). An injector 11 for injecting fuel is provided in the vicinity of the intake port of each cylinder 1. Further, a spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives the application of the induced voltage generated by the ignition coil and induces a spark discharge between the center electrode and the ground electrode. The ignition coil is integrally built in the coil case together with the igniter which is a semiconductor switching element.

The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. An air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream on the intake passage 3.

The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 to the outside from the exhaust port of each cylinder 1. An exhaust manifold 42 and a three-way catalyst 41 for purifying exhaust gas are arranged on the exhaust passage 4. Air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the gas flowing through the exhaust passage 4 are installed upstream and downstream of the catalyst 41 in the exhaust passage 4. _{Each of the air-fuel ratio sensors 43 and 44 may be an O 2} sensor having a non-linear output characteristic with respect to the air-fuel ratio of the exhaust gas, and is a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas. There may be.

The external EGR device 2 includes an external EGR passage 21 that connects the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3, an EGR cooler 22 provided on the EGR passage 21, and an EGR passage. The element is an EGR valve 23 that opens and closes 21 and controls the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a predetermined position downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined position downstream of the throttle valve 32 in the intake passage 3, specifically, the surge tank 33.

The ECU 0, which is a control device for the internal combustion engine of the present embodiment, is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

The input interface of ECU0 has a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle output from a crank angle sensor (engine rotation sensor) that detects the rotation angle of the crank shaft and the engine rotation speed. Signal b, accelerator opening signal c output from a sensor that detects the accelerator pedal depression amount or throttle valve 32 opening as accelerator opening (so to speak, output required for internal combustion engine, required load factor), intake passage Intake temperature / intake pressure signal d output from the intake air temperature / intake pressure sensor that detects the intake air temperature and intake pressure downstream of the throttle valve 32 (particularly in the surge tank 33) in No. 3, and cooling that suggests the temperature of the internal combustion engine. The cooling water temperature signal e output from the water temperature sensor that detects the water temperature, the air fuel ratio signal f output from the air fuel ratio sensor 43 that detects the air fuel ratio of the gas on the upstream side of the catalyst 41, and the gas empty on the downstream side of the catalyst 41. An air-fuel ratio signal g output from the air-fuel ratio sensor 44 that detects the fuel ratio, and a brake signal output from a sensor (brake switch, master cylinder pressure sensor, etc.) that detects that the brake pedal has been depressed or the amount of depression of the brake pedal. h etc. are input.

From the output interface of ECU 0, the ignition signal i for the igniter of the spark plug 12, the fuel injection signal j for the injector 11, the opening control signal k for the throttle valve 32, and the opening control for the EGR valve 23. Outputs signal l and the like.

The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates an operation parameter, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, h necessary for the operation control of the internal combustion engine via the input interface, and obtains the required fuel injection amount and fuel injection timing (once). Various operating parameters such as fuel injection pressure (including the number of fuel injections for combustion), fuel injection pressure, ignition timing, required EGR rate (or EGR gas amount), and the like are determined. The ECU 0 applies various control signals i, j, k, l corresponding to the operation parameters via the output interface.

First, the ECU 0 calculates the amount of fresh air (air or oxygen) filled in the cylinder 1 from the intake pressure and intake temperature in the surge tank 33, the engine speed, the opening degree of the EGR valve 23, and the like. The basic injection amount TP corresponding to is determined. Map data that defines in advance the relationship between the intake pressure and intake temperature in the surge tank 33, the engine speed, the opening degree of the EGR valve 23, and the estimated value of the amount of fresh air filled in the cylinder 1 in the memory of the ECU 0. Is stored. The ECU 0 searches the map using the current intake pressure and intake air temperature in the surge tank 33, the engine speed, the opening degree of the EGR valve 23, etc. as keys, and obtains an estimated value of the amount of fresh air filled in the cylinder 1. .. Needless to say, the basic injection amount TP is proportional to the fresh air amount filled in the cylinder 1.

Next, in normal times, this basic injection amount TP is corrected by a feedback correction coefficient FAF determined according to the air-fuel ratio of the gas on the upstream side and / or the downstream side of the catalyst 41. Generally, the feedback correction coefficient FAF is adjusted according to the deviation between the air-fuel ratio actually measured via the air-fuel ratio sensors 43 and 44 and the target air-fuel ratio (usually in the vicinity of the theoretical air-fuel ratio 14.6). That is, the feedback correction coefficient FAF increases when the measured air-fuel ratio is lean with respect to the target air-fuel ratio, and decreases when the measured air-fuel ratio is rich with respect to the target air-fuel ratio. In this air-fuel ratio feedback control, for example, the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined temperature, the fuel is not being cut, the power is not being increased, and a predetermined time has elapsed from the start of the internal combustion engine, and the air-fuel ratio sensors 43, 43. This is performed when all the conditions such as the fact that the intake pressure is normal while the vehicle is active are satisfied.

Then, the final fuel injection time (energization time for the injector 11) T is calculated by taking into account various correction coefficients K determined according to the condition of the internal combustion engine and environmental conditions and the invalid injection time TAUV of the injector 11. The fuel injection time T is
T = TP x FAF x K + TAUV
Will be. The ECU 0 inputs a signal j to the injector 11 for the fuel injection time T, opens the injector 11 to inject fuel.

On the other hand, when the predetermined fuel cut condition is satisfied, the ECU 0 executes a fuel cut that interrupts the fuel supply to the cylinder 1, that is, stops the fuel injection from the injector 11. The ECU 0 determines that the fuel cut condition is satisfied when at least the amount of depression of the accelerator pedal is 0 or less than a threshold value close to 0 and the engine speed is higher than the fuel cut permitted speed. During the fuel cut, the throttle valve 32 is opened to a predetermined opening degree that does not depend on the amount of depression of the accelerator pedal (0 or close to 0), or the throttle valve 32 is fully closed.

After the start of the fuel cut, the ECU 0 ends the fuel cut, that is, restarts the fuel injection from the injector 11 when a predetermined fuel cut end condition is satisfied. The ECU 0 determines that the fuel cut end condition is satisfied by either that the amount of depression of the accelerator pedal exceeds the threshold value, the engine speed has decreased to the fuel cut return speed, and the like. Needless to say, after the fuel cut end condition is satisfied, the opening degree of the throttle valve 32 is made to follow the opening degree according to the depression amount of the accelerator pedal.

ECU 0 of this embodiment carries out diagnosis of EGR valve 23 during fuel cut. In this diagnosis, the EGR valve 23 is intentionally opened and closed during fuel cutting, and the intake pressure in the surge tank 33 when the EGR valve 23 is fully closed and the EGR valve 23 when the EGR valve 23 is opened to a predetermined opening degree. The intake pressure in the surge tank 33 is measured. Then, based on the measured intake air pressure, it is determined whether or not the EGR valve 23 is out of order. For example, if the difference between the intake pressures of both is equal to or greater than the determination threshold value, it is determined that the EGR valve 23 is operating normally, and if it is below the determination threshold value, the EGR valve 23 is stuck and is not operating normally. To do.

The ECU 0 continuously and repeatedly executes the calculation of the amount of fresh air flowing into the cylinder 1 during the fuel cut and also when the diagnosis of the EGR valve 23 is performed. In the diagnosis of the EGR valve 23, since the EGR valve 23 is opened, a part of the gas flowing downstream of the catalyst 41 in the exhaust passage 4 returns to the surge tank 33 of the intake passage 3 via the EGR passage 21. This gas, which flows into the intake passage 3 via the EGR passage 21 when the EGR valve 23 is opened, is almost or completely fresh after a certain amount of time has passed from the start of the fuel cut, but the fuel cut It contains a considerable amount of combustion gas and / or unburned fuel components for a while from the start.

Therefore, the ECU 0 of the present embodiment calculates the amount of fresh air filled in the cylinder 1 during the fuel cut for performing the diagnosis of the EGR valve 23 and immediately after the end of the fuel cut, for the time being, the EGR passage. The current surge tank, assuming that the total amount of gas flowing into the intake passage 3 via 21 is fresh (in other words, assuming that the current opening degree of the EGR valve 23 is 0). An estimated value of the amount of fresh air filled in the cylinder 1 is obtained based on the intake pressure and intake temperature in 33, the engine speed, and the like.

Then, the ECU 0 estimates the amount of fresh air filled in the cylinder 1 according to the current air-fuel ratio of the gas flowing downstream of the catalyst 41 in the exhaust passage 4, which is actually measured via the air-fuel ratio sensor 44. Weight loss correction. The correction amount for reducing the fresh air amount, so to speak, the amount for discounting the above estimated value of the fresh air amount is increased as the air-fuel ratio of the gas flowing downstream of the catalyst 41 is richer and decreased as the air-fuel ratio is leaner. In FIG. 2, the thin solid line represents the estimated value of the fresh air amount obtained from the above-mentioned map data, and the thick broken line represents the fresh air amount as a result of adding the weight loss correction to the estimated value.

More specifically, from the air-fuel ratio (corresponding to fresh air) indicated by the output signal g of the air-fuel ratio sensor 44 when only fresh air flows almost or completely downstream of the catalyst 41, the current air-fuel ratio sensor 44 The larger the deviation value obtained by subtracting the air-fuel ratio of the actually measured gas indicated by the output signal g of, that is, the richer the air-fuel ratio of the gas flowing downstream of the catalyst 41, the more the estimated value of fresh air quantity. Reduce the discount rate for riding on. The discount rate referred to here is a positive number of 1 or less, and becomes 1 when the air-fuel ratio of the actually measured gas indicated by the output signal g of the air-fuel ratio sensor 44 is lean, which is almost equal to that of the fresh air, and the actually measured gas. The richer the air-fuel ratio of, the smaller it becomes from 1 (closer to 0). The ECU 0 fills the cylinder 1 during the fuel cut for performing the diagnosis of the EGR valve 23 and immediately after the fuel cut is completed by multiplying the estimated value of the fresh air amount obtained from the above map data by the discount rate. Calculate the amount of fresh air to be produced, and then calculate the basic amount TP of the fuel injection amount at the same time. As a result of discounting the amount of fresh air charged in the cylinder 1, the basic injection amount TP proportional to this is also discounted, and the fuel injection amount T is reduced.

However, if the air-fuel ratio sensor 44 that detects the air-fuel ratio of the gas downstream of the catalyst 41 is an O ₂ sensor instead of a linear A / F sensor, the air-fuel ratio of the gas flowing downstream of the catalyst 41 must be accurately grasped. It may not be possible to only read whether the air-fuel ratio of the gas is rich or lean compared to the target air-fuel ratio (or theoretical air-fuel ratio). In this case, if the air-fuel ratio indicated by the output signal g of the air-fuel ratio sensor 44 is richer than the target air-fuel ratio, the discount rate for multiplying the estimated fresh air quantity is made smaller, and the air-fuel ratio is the target air-fuel ratio. If it is leaner than the fuel ratio, it is conceivable to increase the discount rate or set it to 1.

Further, as shown in FIG. 2, during the diagnosis of the EGR valve 23, the air-fuel ratio of the gas indicated by the output signal g of the air-fuel ratio sensor 44 is almost equal to that of the fresh air. If this happens, the amount of fresh air filled in the cylinder 1 or the correction amount for reducing the fuel injection amount TP is gradually reduced after _{the time t 2} when a predetermined time elapses from _{that point t 1, that is, the estimated value of the fresh air amount.} Gradually bring the discount rate to 1 to 1. Gas flowing into the time t ₂ after the downstream of the catalyst 41 in the exhaust passage 4 to the surge tank 33 of the intake passage 3 through the EGR passage 23 is changed to the full fresh air without the combustion gas and unburned fuel components Because it goes.

Similarly, even after the diagnosis of the EGR valve 23 is completed during the fuel cut and the EGR valve 23 is fully closed, the amount of fresh air filled in the cylinder 1 or the correction amount for reducing the fuel injection amount TP is gradually reduced. Is preferable.

In the present embodiment, the exhaust gas recirculation device 2 provided with the EGR valve 23 is attached to the EGR passage 21 that communicates the downstream portion of the exhaust gas purification catalyst 41 in the exhaust passage 4 with the predetermined portion of the intake passage 3. Diagnosis that is a control device 0 that controls the internal combustion engine and determines whether or not the EGR valve 23 has failed by opening and closing the EGR valve 23 during a fuel cut that temporarily interrupts the fuel supply to the cylinder 1 of the internal combustion engine. When the diagnosis is performed during the fuel cut, the amount of fresh air filled in the cylinder 1 is calculated immediately after the end of the fuel cut, and is downstream of the catalyst 41 in the exhaust passage 4. The control device 0 of the internal combustion engine that reduces and corrects the amount of fresh air according to the air fuel ratio indicated by the output signal g of the air fuel ratio sensor 44 that detects the air fuel ratio of the gas flowing through the exhaust gas is configured.

Further, in the present embodiment, the exhaust gas recirculation device 2 provided with the EGR valve 23 in the EGR passage 21 communicating the downstream portion of the exhaust gas purification catalyst 41 in the exhaust passage 4 and the predetermined portion of the intake passage 3 is provided. The control device 0 that controls the incidental internal combustion engine operates the EGR valve 23 to open and close the EGR valve 23 to determine whether or not the EGR valve 23 has failed during the fuel cut during the fuel cut that temporarily suspends the fuel supply to the cylinder 1 of the internal combustion engine. Diagnosis is carried out, and when the diagnosis is carried out during the fuel cut, the gas flowing downstream of the catalyst 41 in the exhaust passage 4 is calculated when calculating the amount of fuel to be injected immediately after the end of the fuel cut. The air fuel ratio indicated by the output signal g of the air fuel ratio sensor 44 that detects the air fuel ratio of the air fuel ratio is indicated by the output signal g of the air fuel ratio sensor 44 under the condition that only fresh air flows almost or completely downstream of the catalyst 41. When it is richer than the air fuel ratio, the control device 0 of the internal combustion engine is configured to reduce and correct the fuel injection amount as compared with the case where it is not.

According to the present embodiment, even if the diagnosis of the EGR valve 23 is started immediately after the start of the fuel cut and the combustion gas and / or the gas containing the unburned fuel component returns from the exhaust passage 4 to the intake passage 3. The amount of fresh air filled in the cylinder 1 can be accurately estimated, and the fuel injection amount can be set to an appropriate amount commensurate with the amount of fresh air. Therefore, it is possible to prevent the instability of the engine rotation due to the diagnosis of the EGR valve 23 performed during the fuel cut.

In addition, since it is permissible to carry out diagnostics of the EGR valve 23 immediately after the start of fuel cut without waiting for the elapse of the delay time, it becomes possible to properly complete the diagnostics, and the opportunity for diagnostics is necessary and sufficient. Is secured in.

Since the EGR passage 21 is connected to the vicinity of the installation location of the air-fuel ratio sensor 44 in the exhaust passage 4 or a location upstream of the air-fuel ratio sensor 44, the gas detected by the air-fuel ratio sensor 44. The time lag between the fluctuation of the air-fuel ratio of EGR valve 23 and the fluctuation of the air-fuel ratio of the gas recirculated from the exhaust passage 4 to the intake passage 3 via the EGR passage 21 due to the diagnosis of the EGR valve 23 becomes small. This is effective for further improving the calculation accuracy of the fresh air amount charged in the cylinder 1.

The present invention is not limited to the embodiments described in detail above. The specific configuration of each part and the specific processing procedure can be variously modified without departing from the spirit of the present invention.

The present invention can be applied to the control of an internal combustion engine mounted on a vehicle or the like.

0 ... Control device (ECU)
1 ... Cylinder 2 ... Exhaust gas recirculation (EGR) device 21 ... EGR passage 23 ... EGR valve 3 ... Intake passage 32 ... Throttle valve 4 ... Exhaust passage 41 ... Catalyst 44 ... Air-fuel ratio sensor b ... Crank angle signal d ... Intake temperature -Intake pressure signal g ... Air-fuel ratio sensor output signal j ... Fuel injection signal l ... EGR valve opening control signal

Claims (4)

A control device that controls an internal combustion engine with an exhaust gas recirculation device provided with an EGR valve in the EGR passage that communicates a location downstream of the catalyst for exhaust purification in the exhaust passage with a predetermined location in the intake passage.
During fuel cut, which temporarily interrupts the fuel supply to the cylinder of the internal combustion engine, the EGR valve is opened and closed to perform diagnostics to determine whether or not the EGR valve has failed.
When the diagnosis is performed during the fuel cut, the air-fuel ratio of the gas flowing downstream of the catalyst in the exhaust passage is detected when calculating the amount of fresh air filled in the cylinder immediately after the end of the fuel cut. An internal combustion engine control device that reduces and corrects the amount of fresh air according to the air-fuel ratio indicated by the output signal of the fuel ratio sensor. A control device that controls an internal combustion engine with an exhaust gas recirculation device provided with an EGR valve in the EGR passage that communicates a location downstream of the catalyst for exhaust purification in the exhaust passage with a predetermined location in the intake passage.
During fuel cut, which temporarily interrupts the fuel supply to the cylinder of the internal combustion engine, the EGR valve is opened and closed to perform diagnostics to determine whether or not the EGR valve has failed.
When the diagnosis is performed during the fuel cut, the output of the air-fuel ratio sensor that detects the air-fuel ratio of the gas flowing downstream of the catalyst in the exhaust passage when calculating the amount of fuel to be injected immediately after the end of the fuel cut. If the air-fuel ratio indicated by the signal is richer than the air-fuel ratio indicated by the output signal of the air-fuel ratio sensor under the condition that only fresh air flows almost or completely downstream of the catalyst, then and otherwise. An internal combustion engine control device that reduces and corrects the fuel injection amount in comparison. During the diagnosis, the air-fuel ratio indicated by the output signal of the air-fuel ratio sensor is the output signal of the air-fuel ratio sensor under the condition that only fresh air flows almost or completely downstream of the catalyst. The control device for an internal combustion engine according to claim 1 or 2, wherein when the air-fuel ratio becomes equivalent to the air-fuel ratio indicated by, the reduction correction amount of the fresh air amount or the fuel injection amount is gradually reduced after a lapse of a predetermined time from that time. .. The control device for an internal combustion engine according to claim 1, 2 or 3, wherein the EGR passage is connected to a location near the installation location of the air-fuel ratio sensor in the exhaust passage or a location upstream of the air-fuel ratio sensor.

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