JP4274055B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to a control device and a control method for an internal combustion engine that generates power by burning a mixture of fuel and air in a cylinder.

  2. Description of the Related Art Conventionally, as a control device for an internal combustion engine, the amount of heat generated during a combustion stroke is calculated for each cylinder angle for each cylinder based on an in-cylinder pressure sensor provided in each cylinder and a pressure signal from each in-cylinder pressure sensor. What is provided with the calculating means is known (for example, refer patent document 1). In this control device for an internal combustion engine, the fuel supply amount (air-fuel ratio in each cylinder) to each cylinder is corrected so that the heat generation amount in each cylinder becomes the same level based on the calculation result of the calculation means.

  Conventionally, there has been known an internal combustion engine that includes an assist air device that ejects a part of intake air as assist air in the vicinity of a nozzle hole of a fuel injection valve, and a self-diagnosis device that performs failure diagnosis of the assist air device. (For example, refer to Patent Document 2). In this internal combustion engine, the amount of heat generated in one cycle is calculated based on the combustion pressure of the engine, and the calculated amount of generated heat is divided by the amount of heat generated per unit fuel and converted into the amount of fuel actually used for combustion. Is done. Then, failure diagnosis of the assist air device is executed based on the ratio between the converted fuel amount and the fuel amount injected by the fuel injection valve.

JP-A-63-268951 Japanese Patent Laid-Open No. 06-346824

  However, in the conventional apparatus as described above, basically, the in-cylinder pressure (combustion pressure) detected by the in-cylinder pressure detecting means is integrated for each minute unit crank angle, thereby generating a heat generation amount (generated heat amount). Is calculated. For this reason, the calculation load in the conventional apparatus is enormous, and from this point, it is practically difficult to apply the conventional technique to, for example, a vehicle internal combustion engine.

  Therefore, an object of the present invention is to provide a practical control device and control method for an internal combustion engine that can easily execute highly accurate engine control and determination of an engine operation state with a low load.

  An internal combustion engine control apparatus according to the present invention includes an in-cylinder pressure detecting means for detecting in-cylinder pressure and an in-cylinder pressure detecting means in an internal combustion engine control apparatus for generating power by burning a mixture of fuel and air in a cylinder. The ratio of the actual heat generation amount to the heat generation amount during complete combustion based on the product of the in-cylinder pressure detected by the value obtained by multiplying the in-cylinder volume at the time of detection of the in-cylinder pressure by a predetermined index And a control means for executing at least one of setting a predetermined control amount and determining the engine operating state based on the control parameter calculated by the calculation means. And

  In this case, it is preferable that the calculation means calculates the product value at two predetermined points and calculates the control parameter based on the difference between the product values between the two predetermined points and the fuel supply amount or the intake air amount.

  One of the two predetermined points is preferably set after the intake valve is opened and before the start of combustion, and the other is set after the start of combustion and before the exhaust valve is opened.

  Further, when the control means sets the air-fuel ratio of the air-fuel mixture within a region smaller than the stoichiometric air-fuel ratio, the control means sets a control amount for correcting the air-fuel ratio of the air-fuel mixture so that the control parameter matches the target value. preferable.

  Further, the control means may execute a misfire determination in the cylinder based on the control parameter.

  In this case, the control means preferably determines that the cylinder is in a misfire state when the value of the control parameter is below a predetermined threshold.

  Further, the control means may perform abnormality determination of the injector that injects fuel based on the control parameter.

  Further, the apparatus further comprises combustion state determination means for determining the combustion state in the cylinder, and the control means determines that the combustion state in the cylinder is stable by the combustion state determination means, and the control parameter has a predetermined threshold value. If it falls below, it is preferable to determine that an abnormality has occurred in the injector.

  The control apparatus for an internal combustion engine according to the present invention may further include air-fuel ratio setting means for setting a control amount for making the air-fuel ratio of the air-fuel mixture coincide with a target value, and the amount of fluctuation of the control parameter has a predetermined value. If it exceeds, it is preferable that the control amount of the air-fuel ratio setting means is held at the previous value.

  In this case, the air-fuel ratio setting means preferably calculates the actual air-fuel ratio of the air-fuel mixture based on the actual heat generation amount and sets the control amount based on the calculated actual air-fuel ratio.

An internal combustion engine control method according to the present invention is a control method for an internal combustion engine that generates power by burning a mixture of fuel and air in a cylinder.
(A) detecting the in-cylinder pressure;
(B) Based on the product value of the in-cylinder pressure detected in step (a) and a value obtained by raising the in-cylinder volume at the time of detection of the in-cylinder pressure by a predetermined index, the amount of heat generated during complete combustion is Calculating a control parameter indicating a heat amount ratio of the actual heat generation amount;
(C) including a step of executing at least one of setting a predetermined control amount and determining the engine operating state based on the control parameter calculated in step (b).

  According to the present invention, it is possible to realize a practical internal combustion engine control device and control method that can easily execute highly accurate engine control and engine operation state determination with low load.

The inventors of the present invention have made extensive studies to enable highly accurate control of the internal combustion engine and determination of the engine operating state while reducing the calculation load, and as a result, first, when the crank angle is θ. The in-cylinder pressure detected by the in-cylinder pressure detecting means is P (θ), the in-cylinder volume when the crank angle is θ (when detecting the in-cylinder pressure P (θ)) is V (θ), When the specific heat ratio is κ, the product value P (θ) of the in-cylinder pressure P (θ) and a value V ^κ (θ) obtained by raising the in-cylinder volume V (θ) to a specific heat ratio (predetermined index) κ. ) · V ^κ (θ) (hereinafter referred to as “PV ^κ ” as appropriate). The inventors of the present invention have a correlation as shown in FIG. 1 between the change pattern of the heat generation amount Q in the cylinder of the internal combustion engine with respect to the crank angle and the change pattern of the product value PV ^κ with respect to the crank angle. I found. In FIG. 1, −360 °, 0 °, and 360 ° correspond to the top dead center, and −180 ° and 180 ° correspond to the bottom dead center.

In FIG. 1, the solid line shows the in-cylinder pressure detected at predetermined minute crank angles in a predetermined model cylinder and the value obtained by raising the in-cylinder volume at the time of detection of the in-cylinder pressure by a predetermined specific heat ratio κ. The product value PV ^κ which is a product is plotted. In FIG. 1, the broken line is calculated and plotted with the heat generation amount Q in the model cylinder as Q = ∫dQ based on the following equation (1). In either case, for simplicity, κ = 1.32.

As can be seen from the results shown in FIG. 1, the change pattern of the heat generation amount Q with respect to the crank angle and the change pattern of the product value PV ^κ with respect to the crank angle are almost the same (similar), and in particular, Before and after the start of combustion of the air-fuel mixture (at the time of spark ignition for a gasoline engine and at the time of compression ignition for a diesel engine) (for example, in the range from about −180 ° to about 135 ° in FIG. 1) It can be seen that the change pattern of the product value PV ^κ agrees very well. And if the correlation between the heat generation amount Q in the cylinder and the product value PV ^κ found by the present inventors is used, a value corresponding to the actual heat generation amount (actual heat generation amount) of the internal combustion engine is obtained. Based on the product value PV ^κ taken and the fuel supply amount set by the fuel supply amount setting means or the intake air amount detected by the intake air amount detection means, the heat generation amount (theoretical value) at the time of complete combustion The control parameter γ indicating the heat amount ratio of the actual heat generation amount can be calculated with high accuracy at an extremely low load.

  Here, according to the study by the present inventors, when the internal combustion engine is operated under a predetermined condition, the value of the control parameter γ indicating the heat quantity ratio and other parameters such as the air-fuel ratio of the air-fuel mixture have a predetermined correlation. It has also been shown to show. Further, if the fuel supplied to the internal combustion engine is almost completely burned in the cylinder, it depends on the actual heat generation amount (actual heat generation amount) in the internal combustion engine, the fuel supply amount, and the like. The ratio of the heat generation amount to the theoretical value (heat ratio: control parameter γ) is basically a constant value considering heat transfer to the combustion chamber wall, heat of vaporization, etc. When an abnormality or the like of the fuel supply means occurs and the engine operating state changes, a remarkable change is recognized in the value of the control parameter γ indicating the heat quantity ratio.

Therefore, after obtaining the control parameter γ indicating the heat amount ratio of the actual heat generation amount to the heat generation amount (theoretical value) at the time of complete combustion based on the product value PV ^κ and the supply amount of fuel, the control parameter γ With this, you can easily execute highly accurate and responsive engine control and engine operation determination without requiring high-load calculation processing by setting a predetermined control amount and determining the engine operating state. It becomes possible to do. In the present invention, “control amount setting” includes the calculation of the control amount itself such as the air-fuel ratio of the air-fuel mixture and the setting (calculation) of the control amount for correcting the air-fuel ratio of the air-fuel mixture. included.

  In this case, it is preferable that the calculation means calculates the product value at two predetermined points and calculates the control parameter γ based on the difference between the product values between the two predetermined points and the fuel supply amount or the intake air amount.

As described above, the product value PV ^κ focused by the present inventors reflects the heat generation amount Q in the cylinder of the internal combustion engine, and is between two predetermined points (for example, the start of combustion in the cylinder (spark ignition) Alternatively, the difference in product value PV ^κ at two points before and after compression ignition) is the amount of heat generated in the cylinder between the two points ∫dQ (dQ is changed from, for example, crank angle θ ₁ to crank angle θ ₂ (where θ ₁ <Θ ₂ ] integrated value, the same applies hereinafter), and can be calculated with extremely low load. Therefore, if the difference between the product values PV ^κ between two predetermined points and the fuel supply amount or intake air amount are used, the calculation load is greatly reduced and the actual heat generation amount (theoretical value) during complete combustion is reduced. A control parameter γ (γ ′) indicating the heat quantity ratio of the heat generation amount can be obtained. In this case, it is preferable that one of the two predetermined points is set after the intake valve is opened and before the start of combustion, and the other is set after the start of combustion and before the exhaust valve is opened.

  In addition, when the air-fuel ratio of the air-fuel mixture is set within a region that is smaller (rich) than the stoichiometric air-fuel ratio, the control means corrects the air-fuel ratio of the air-fuel mixture so that the control parameter γ matches the target value. It is preferable to set a control amount.

  The inventors have also paid attention to the relationship between the control parameter γ indicating the heat ratio and the air-fuel ratio of the air-fuel mixture in the cylinder. That is, as shown in FIG. 2, in the region where the air-fuel ratio of the air-fuel mixture in the cylinder is smaller (rich) than the stoichiometric air-fuel ratio (14.7), the air-fuel ratio of the air-fuel mixture decreases (is enriched). ), The heat is absorbed by the unburned fuel, so that the control parameter γ indicating the heat quantity ratio decreases substantially in proportion to the air-fuel ratio of the air-fuel mixture. Therefore, in the rich region, if the control amount for correcting the air-fuel ratio of the air-fuel mixture, such as the fuel supply amount correction value, is set so that the control parameter γ indicating the heat ratio becomes the target value, the mixture in the cylinder It is possible to keep the air-fuel ratio of the gas close to a desired target value smaller than the theoretical air-fuel ratio with high accuracy.

  The control means preferably performs in-cylinder misfire determination based on the control parameter γ, and preferably determines that the in-cylinder is in a misfire state when the value of the control parameter γ is below a predetermined threshold. .

  That is, the value of the control parameter γ indicating the heat ratio when the cylinder is in a misfire state is a value at normal time (when the fuel supplied to the internal combustion engine is almost completely burned in the cylinder). Therefore, if such a configuration is adopted, the misfire state in the cylinder can be accurately determined with a low load.

  Furthermore, it is preferable that the control means performs abnormality determination of the injector that injects fuel based on the control parameter γ.

  That is, the value of the control parameter γ indicating the heat ratio in the case where an abnormality occurs in the injector that injects the fuel is also significantly different from the normal value. Therefore, if such a configuration is adopted, the abnormality of the injector is reduced. It becomes possible to determine with high accuracy.

  In this case, if it is determined that the combustion state in the cylinder is stable by the means for determining the combustion state in the cylinder, and the control parameter γ falls below a predetermined threshold value, an abnormality has occurred in the injector. Judgment can be made.

  That is, for example, it is originally required that the control parameter γ falls below a predetermined threshold even though it is determined that the rotational fluctuation (rotational angular velocity) of the internal combustion engine is small and the combustion state in the cylinder is stable. This indicates that the amount of fuel being supplied is not being supplied into the cylinder. Therefore, by adopting such a method, it becomes possible to easily and accurately determine the deterioration or clogging of the injector that is the cause of the fuel supply failure (fuel injection failure).

  Further, if the value of the control parameter γ exceeds a predetermined threshold when the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio, it can be determined that an abnormality has occurred in the injector.

  In other words, the fact that the control parameter γ exceeds the predetermined threshold value even though the air supply amount is set so that the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio means that fuel leaks from the injector. This indicates that there is residual fuel in the cylinder. Therefore, if such a method is employed, it is possible to easily and accurately determine the presence or absence of fuel leakage in the injector.

  The control device for an internal combustion engine according to the present invention may further include air-fuel ratio setting means for setting a control amount for making the air-fuel ratio of the air-fuel mixture coincide with a target value, and the amount of change in the control parameter γ is a predetermined value. When the value exceeds the value, it is preferable that the control amount of the air-fuel ratio setting means is held at the previous value.

  That is, if the in-cylinder combustion state is good (complete combustion), the control parameter γ indicating the heat quantity ratio changes as shown in FIG. In some cases or when the in-cylinder combustion state deteriorates, the actual heat generation amount decreases, so the value of the control parameter γ also varies according to the actual heat generation amount. For this reason, for example, when the air-fuel ratio of the air-fuel mixture is controlled based on the actual heat generation amount or the control parameter γ, if the air-fuel ratio control is executed without considering the fluctuation of the control parameter γ, the air-fuel ratio becomes the target value. May deviate from In view of these points, if the amount of fluctuation of the control parameter γ exceeds a predetermined value, the control amount for setting the air-fuel ratio of the air-fuel mixture to the target value is held at the previous value. Good. As a result, the air-fuel ratio of the air-fuel mixture can be always kept within a preferable range.

  The air-fuel ratio setting means preferably calculates the actual air-fuel ratio of the air-fuel mixture based on the actual heat generation amount, and sets the control amount based on the calculated actual air-fuel ratio. As a result, for example, the actual air-fuel ratio of the air-fuel mixture can be acquired with extremely high responsiveness compared to the case of using an air-fuel ratio sensor (oxygen sensor).

  Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.

  FIG. 3 is a schematic configuration diagram showing an internal combustion engine according to the present invention. The internal combustion engine 1 shown in FIG. 1 generates power by burning a fuel / air mixture in a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. Is. Although only one cylinder is shown in FIG. 3, the internal combustion engine 1 is preferably configured as a multi-cylinder engine, and the internal combustion engine 1 of the present embodiment is configured as a four-cylinder engine, for example.

  The intake port of each combustion chamber 3 is connected to an intake pipe (intake manifold) 5, and the exhaust port of each combustion chamber 3 is connected to an exhaust pipe (exhaust manifold) 6. In addition, an intake valve Vi that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port are provided for each combustion chamber 3 in the cylinder head of the internal combustion engine 1. Each intake valve Vi and each exhaust valve Ve are opened and closed by, for example, a valve operating mechanism (not shown) having a variable valve timing function. Further, the internal combustion engine 1 has a number of spark plugs 7 corresponding to the number of cylinders, and the spark plugs 7 are disposed in the cylinder heads so as to face the corresponding combustion chambers 3.

  The intake pipe 5 is connected to a surge tank 8 as shown in FIG. An air supply line L1 is connected to the surge tank 8, and the air supply line L1 is connected to an air intake port (not shown) via an air cleaner 9. A throttle valve (in this embodiment, an electronically controlled throttle valve) 10 is incorporated in the middle of the air supply line L1 (between the surge tank 8 and the air cleaner 9). On the other hand, as shown in FIG. 3, a front-stage catalyst device 11 a including a three-way catalyst and a rear-stage catalyst device 11 b including a NOx storage reduction catalyst are connected to the exhaust pipe 6.

  Furthermore, the internal combustion engine 1 has a plurality of injectors 12, and each injector 12 is arranged in the cylinder head so as to face the corresponding combustion chamber 3 as shown in FIG. 3. Each piston 4 of the internal combustion engine 1 is configured as a so-called deep dish top surface type, and a recess 4a is formed on the upper surface thereof. In the internal combustion engine 1, fuel such as gasoline is directly injected from each injector 12 toward the recess 4 a of the piston 4 in each combustion chamber 3 in a state where air is sucked into each combustion chamber 3. As a result, in the internal combustion engine 1, the fuel / air mixture layer is formed (stratified) in the vicinity of the spark plug 7 so as to be separated from the surrounding air layer. And stable stratified combustion can be performed. The internal combustion engine 1 of the present embodiment is described as a so-called direct injection engine, but is not limited to this, and the present invention can be applied to an intake pipe (intake port) injection type internal combustion engine. Not too long.

  Each of the spark plugs 7, the throttle valve 10, the injectors 12, the valve operating mechanism and the like described above are electrically connected to an ECU 20 that functions as a control device for the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, etc., all not shown. As shown in FIG. 3, various sensors including the crank angle sensor 14 of the internal combustion engine 1 are electrically connected to the ECU 20. The ECU 20 uses the various maps stored in the storage device and the spark plug 7, the throttle valve 10, the injector 12, the valve operating mechanism, etc. so as to obtain a desired output based on the detection values of various sensors. To control.

  Further, the internal combustion engine 1 has in-cylinder pressure sensors (in-cylinder pressure detecting means) 15 including a semiconductor element, a piezoelectric element, an optical fiber detection element, or the like, corresponding to the number of cylinders. Each in-cylinder pressure sensor 15 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 3, and is electrically connected to the ECU 20. Each in-cylinder pressure sensor 15 detects the in-cylinder pressure in the corresponding combustion chamber 3 and gives a signal indicating the detected value to the ECU 20. Further, an exhaust air / fuel ratio sensor (oxygen sensor) 16 is installed in the exhaust pipe 6. The exhaust air / fuel ratio sensor 16 is also electrically connected to the ECU 20, detects the air / fuel ratio of the exhaust gas flowing through the exhaust pipe 6, and gives a signal indicating the detected value to the ECU 20. The detection values of the in-cylinder pressure sensors 15 and the exhaust air / fuel ratio sensor 16 are sequentially given to the ECU 20 every predetermined time, and are stored and held in a predetermined storage area (buffer) of the ECU 20 by a predetermined amount.

  Next, the operation of the internal combustion engine 1 will be described with reference to FIG. When the internal combustion engine 1 is started and then transitions from the idle state to the idle off state, as shown in FIG. 4, the ECU 20 determines a target torque of the internal combustion engine 1 based on a signal from an accelerator position sensor (not shown). At the same time, an intake air amount (opening of the throttle valve 10) and a fuel injection amount (fuel injection time) qF from each injector 12 are set according to the target torque using a map prepared in advance (S10). Further, the ECU 20 sets the opening of the throttle valve 10 to the opening obtained in S10 in S12, and injects the fuel of the amount qF determined in S10 during each intake stroke from each injector 12, for example.

Further, the ECU 20 monitors the crank angle of the internal combustion engine 1 based on a signal from the crank angle sensor 14. Then, the ECU 20 sets the first timing (timing at which the crank angle becomes θ ₁ ) set for each combustion chamber 3 after the opening of each intake valve Vi and before ignition by each spark plug 7. Then, based on the signal from the in-cylinder pressure sensor 15, the in-cylinder pressure P (θ ₁ ) when the crank angle becomes θ ₁ is obtained. Further, the ECU 20 calculates the in-cylinder pressure P (θ ₁ ) and the in-cylinder pressure V (θ ₁ ) when detecting the in-cylinder pressure P (θ ₁ ), that is, when the crank angle is θ _1. A product value P (θ ₁ ) · V ^κ (θ ₁ ), which is a product of a value κ (in this embodiment, κ = 1.32) raised to a power, is calculated for each combustion chamber 3, The data is stored in the storage area (S14).

The first timing is preferably set to a timing sufficiently before the time point at which combustion starts in each combustion chamber 3 (at the time of ignition). In this embodiment, the first timing is, for example, a crank The timing at which the crank angle indicated by the signal from the angle sensor 14 becomes −60 ° (θ ₁ = −60 °, that is, 60 ° before top dead center) is set. Further, the value of V ^κ (θ ₁ ) (in this embodiment, the value of V ^κ (−60 °)) is calculated in advance and stored in the storage device.

After the processing of S14, ECU 20, for each combustion chamber 3, even after ignition by the spark plug 7, the second timing (crank angle which is set before the opening of the exhaust valve Ve is theta ₂ (Timing), the in-cylinder pressure P (θ ₂ ) when the crank angle becomes θ ₂ is obtained based on the signal from the in-cylinder pressure sensor 15. Further, the ECU ₂₀ calculates the in-cylinder pressure P (θ ₂ ) and the in-cylinder pressure P (θ ₂ ), that is, the specific volume of the in-cylinder volume V (θ ₂ ) when the crank angle becomes θ _2. A product value P (θ ₂ ) · V ^κ (θ ₂ ), which is a product of a value κ (in this embodiment, κ = 1.32) and a value raised to a power, is calculated for each combustion chamber 3, Store in the storage area (S16). The second timing is preferably set to a timing at which the combustion of the air-fuel mixture in the combustion chamber 3 is substantially completed. In the present embodiment, the second timing is indicated by a signal from the crank angle sensor 14, for example. The crank angle θ is set to 90 ° (θ ₂ = 90 °, ie, 90 ° after top dead center). The value of V ^κ (θ ₂ ) (in this embodiment, the value of V ^κ (90 °)) is calculated in advance and stored in the storage device.

When the product values P (θ ₁ ) · V ^κ (θ ₁ ) and P (θ ₂ ) · V ^κ (θ ₂ ) are obtained as described above, the ECU 20 determines the first and second values for each combustion chamber 3. The difference in product value PV ^κ between the two timings,
ΔPV ^κ = P (θ ₂ ) · V ^κ (θ ₂ ) −P (θ ₁ ) · V ^κ (θ ₁ )
And is stored in a predetermined storage area of the RAM (S18). As described above, the difference ΔPV ^κ is the heat generation amount ∫dQ in each combustion chamber 3 between the second timing and the first timing (between two predetermined points), that is, from the first timing. It shows the amount of heat generated in the combustion chamber 3 until the second timing. When obtaining the difference Pv ^kappa of product value PV ^kappa every combustion chamber 3, ECU 20 calculates all the combustion chambers 3 average Q _est of the difference Pv ^kappa of product value PV ^kappa and ₍₌ Q estnew), the RAM The data is stored in a predetermined storage area (S20). Thus, by taking the average of the difference ΔPV ^κ for all the combustion chambers 3, it is possible to reduce the influence of the combustion variation between the combustion chambers 3 on the subsequent processing. In such an averaging process, a correction coefficient that takes into account the difference in the filling rate between the combustion chambers 3 may be introduced, and the data of each combustion chamber 3 may be multiplied by the correction coefficient.

By the processes from S14 to S20 described above, the average value Q _est of the difference ΔPV ^κ of the product value PV ^κ that favorably reflects the heat generation amount between the first timing and the second timing is calculated easily and quickly. Will be. Thereby, compared with the case where the in-cylinder pressure is integrated for each minute unit crank angle and the heat generation amount in each combustion chamber 3 is calculated, the calculation load in the ECU 20 can be greatly reduced.

  When the processing in S20 is completed, the ECU 20 determines in accordance with which operation mode the internal combustion engine 1 should be operated at this stage (S22). The internal combustion engine 1 of the present embodiment has a stoichiometric operation mode in which the air-fuel ratio of the mixture of fuel and air in each combustion chamber 3 is set to the stoichiometric air-fuel ratio (fuel: air = 1: 14.7). A lean operation mode in which the air-fuel ratio of the air-fuel mixture is set to a desired target air-fuel ratio larger than the stoichiometric air-fuel ratio, and the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is set to a desired target air-fuel ratio smaller than the stoichiometric air-fuel ratio. Can be operated under any of the rich operation modes. Then, in S22, the ECU 20 determines whether or not the stoichiometric operation mode should be executed based on parameters such as the rotation speed, load, throttle opening, accelerator pedal depression acceleration, and the like.

When it is determined in S22 that the stoichiometric operation mode should be executed, the ECU 20 determines the average value Q _estnew of the difference ΔPV ^κ of the product value PV ^κ calculated in S20 with the current ignition in each combustion chamber 3. The deviation ΔQ from the average value Q _estold of the difference ΔPV ^κ of the product value PV ^κ calculated in S20 with the previous ignition in each combustion chamber 3 is
ΔQ = Q _estnew −Q _estold
(S24).

Here, as shown in FIG. 5, when the air-fuel ratio of the air-fuel mixture is smaller than the stoichiometric air-fuel ratio (rich), the change (rate) of the heat generation amount ∫dQ between two predetermined points is the lean region When the air-fuel ratio of the air-fuel mixture in the combustion chamber 3 exceeds the stoichiometric air-fuel ratio and enters the lean region, it suddenly decreases. Therefore, the deviation ΔQ between the current calculated value Q _Estnew and the previous calculated value Q _Estold of the difference between the product value PV ^kappa between two predetermined points showing a heat generation amount ∫DQ (heat generation amount of inclination in FIG. 5) If maintained in the vicinity of a predetermined value (within a predetermined range), in each combustion chamber 3, the heat generation amount ∫dQ between two predetermined points is kept substantially constant before and after one ignition, and the air-fuel mixture The air-fuel ratio is also kept substantially constant.

  Therefore, when the ECU 20 obtains the deviation ΔQ in S24, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is compared with the stoichiometric air-fuel ratio by comparing the deviation ΔQ with a predetermined threshold value δ (negative predetermined value). Is greater (lean) or not (S26). If the ECU 20 determines that the air-fuel mixture in each combustion chamber 3 is lean (the deviation ΔQ is equal to or less than the threshold δ) in S26, the ECU 20 slightly increases the fuel injection amount from each injector 12. A fuel injection amount correction value is set to (S28). Thus, even if the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is larger than the stoichiometric air-fuel ratio during execution of the stoichiometric operation mode, the air-fuel mixture in each combustion chamber 3 is enriched, and each combustion chamber 3 It is possible to bring the air-fuel ratio of the air-fuel mixture in 3 close to the stoichiometric air-fuel ratio.

  When the ECU 20 determines in S26 that the air-fuel mixture in each combustion chamber 3 is not lean, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is smaller (richer) than the stoichiometric air-fuel ratio. The correction value of the fuel injection amount is set so as to slightly decrease the fuel injection amount from each injector 12 as needed (S30). As a result, even if the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is smaller than the stoichiometric air-fuel ratio during execution of the stoichiometric operation mode, the air-fuel mixture in each combustion chamber 3 is made lean so that each combustion chamber 3 can be made close to the stoichiometric air-fuel ratio. In the present embodiment, the correction value of the fuel injection amount set in S28 and S30 is a predetermined constant amount, but the correction value depends on the difference between the deviation ΔQ and the threshold value δ. It may be calculated.

On the other hand, when it is determined in S22 that the stoichiometric operation mode should not be executed, that is, the lean operation mode or the rich operation mode should be executed, the ECU 20 sets the lean operation mode as shown in FIG. It is determined whether or not to drive (S32). If it is determined that it should perform the lean operation mode in S32, ECU 20 reads the target values Q _t of the heat generation amount corresponding to the target air-fuel ratio in the lean operation mode from the storage unit, the product value obtained in S20 The difference e between the average value Q _est and the target value Q _t of the difference ΔPV ^κ of PV ^κ
e = Q _est −Q _t
(S34). Then, the ECU 20 calculates (sets) a correction value of the fuel injection amount so that the deviation e obtained in S34 is zero using a map prepared in advance or a predetermined function formula (S36).

Here, as shown in FIG. 5, when the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 becomes larger than the stoichiometric air-fuel ratio (lean), the heat generation amount ∫dQ between two predetermined points becomes empty. As the fuel ratio increases, the air fuel ratio decreases approximately in proportion to the sudden change point (lean limit) before the misfire. Therefore, in the region where the air-fuel ratio of the air-fuel mixture is larger than the stoichiometric air-fuel ratio (lean region), the average value Q _est and the target value Q _t of the difference ΔPV ^κ of the product value PV ^κ between the two predetermined points obtained in S20 By making the deviation e of the air-fuel ratio zero, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 can be maintained at a desired target air-fuel ratio that is larger (lean) than the stoichiometric air-fuel ratio. That is, in the internal combustion engine 1, during the lean operation mode, feedback control is performed so that the average value Q _est of the difference ΔPV ^κ of the product value PV ^κ approaches the target value Q _t . As a result, the internal combustion engine 1 performs a so-called lean limit operation in which the air-fuel mixture in each combustion chamber 3 is made as lean as possible to the vicinity of the lean limit in FIG. 5 by appropriately setting the target value Q _t of the heat generation amount. It is also possible to execute.

If it is determined in S32 that the lean operation mode should not be executed but the rich operation mode should be executed, the ECU 20 determines the product value PV ^κ obtained in S20 as shown in FIG. By dividing the average value Q _est of the difference ΔPV ^κ by the fuel injection amount qF set in S10 and multiplying this by a predetermined conversion factor α, the actual heat with respect to the heat generation amount (theoretical value) at the time of complete combustion A control parameter γ indicating the calorific ratio of the generated amount,
γ = Q _est / qF × α
(S38). In the calculation processing of S38, the use of the conversion coefficient α may be omitted, and the average value Q _est may be divided by the fuel injection time and may be multiplied by another conversion coefficient.

In this way, when the control parameter γ indicating the heat quantity ratio and irrelevant to the load condition is obtained, the ECU 20 obtains the target value γ _t of the control parameter γ corresponding to the target air-fuel ratio in the rich operation mode from the storage device. At the same time as reading, the deviation between the control parameter γ determined in S38 and the target value γ _t is calculated. Then, the ECU 20 calculates (sets) a correction value of the fuel injection amount so that the deviation becomes zero using a map prepared in advance or a predetermined function formula (S40). That is, in the internal combustion engine 1, feedback control is performed to bring the control parameter γ closer to the target value γ _t in the rich operation mode.

Here, as described with reference to FIG. 2, in the region where the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is smaller (rich) than the stoichiometric air-fuel ratio, the air-fuel ratio of the air-fuel mixture decreases (rich). As the heat is absorbed by the unburned fuel, the control parameter γ indicating the heat quantity ratio decreases approximately in proportion to the air-fuel ratio of the air-fuel mixture. Therefore, if a control amount for correcting the air-fuel ratio of the air-fuel mixture such as a fuel injection correction value is set so that the control parameter γ indicating the heat ratio becomes the target value γ _t , the air-fuel mixture in each combustion chamber 3 is set. It is possible to accurately maintain the desired air-fuel ratio smaller (rich) than the stoichiometric air-fuel ratio.

  As described above, in the stoichiometric operation mode, the ECU 20 sets a correction value for the fuel injection amount in S28 or S30. In the lean operation mode, the ECU 20 sets a correction value for the fuel injection amount in S36. In the mode, a correction value for the fuel injection amount is set in S40. When the ECU 20 returns to S10, the fuel injection amount (fuel injection time) from each injector 12 is set based on the correction value of the fuel injection amount set in S28, S30, S36 or S40 (while adding or subtracting). At the same time, the opening degree of the throttle valve 10 is set, and the processes after S12 are executed again. Such a series of processes is repeated by the ECU 20 while the idle-off state is continued.

As a result, in the internal combustion engine 1, in the stoichiometric operation mode, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is determined using the difference ΔPV ^κ of the product value PV ^κ that well reflects the heat generation amount between two predetermined points. Since it is set close to the theoretical air-fuel ratio with high accuracy, the region where the ratio λ between the supply air amount and the theoretical air amount is λ = 1 can be expanded. In the internal combustion engine 1, even in the lean operation mode, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is determined by using the difference ΔPV ^κ of the product value PV ^κ that well reflects the heat generation amount between two predetermined points. The predetermined target air-fuel ratio that is larger than the theoretical air-fuel ratio is accurately set. Furthermore, when the rich operation mode, the control parameter indicating the amount of heat ratio of the actual heat production to the heat generation amount at the time of complete combustion on the basis of the difference Pv ^kappa and the fuel injection amount qF of product value PV ^kappa (theoretical value) gamma is Using this control parameter γ, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is accurately set to a predetermined target air-fuel ratio that is smaller than the stoichiometric air-fuel ratio.

As described above, the air-fuel ratio control of the internal combustion engine 1 is executed by using the difference ΔPV ^κ of the product value PV ^κ reflecting the heat generation amount between two predetermined points, and thus obtained in the exhaust system of the internal combustion engine 1. It is possible to eliminate the problems of so-called detection delay and transport delay that are recognized when controlling the in-cylinder air-fuel ratio based on the exhaust air-fuel ratio, etc. (feedback control), greatly improving the responsiveness and accuracy of air-fuel ratio control. Can be improved. Moreover, since the burden of purification of the catalyst can be reduced by realizing highly accurate air-fuel ratio control, the catalyst device can be made compact.

  Note that the control amount for correcting the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is not limited to the correction value of the fuel injection amount, but in the correction value of the throttle opening or the internal combustion engine equipped with the exhaust gas recirculation system. A correction value for the exhaust gas recirculation amount may be used, or these may be combined as appropriate. That is, in the processes of S28, S30, S36, and S40, in order to correct the air-fuel ratio of the air-fuel mixture in each combustion chamber 3, at least one correction value such as the fuel injection amount, the throttle opening, the exhaust gas recirculation amount, etc. It only has to be set. Furthermore, it goes without saying that the present invention can be applied not only to gasoline engines but also to diesel engines.

Further, based on the fact that the air-fuel ratio of the air-fuel mixture in the combustion chamber 3 is substantially proportional to the heat generation amount Q in the lean region (see FIG. 5), the value Q _est indicating the actual heat generation amount and the mixing in each combustion chamber 3 If a map or the like that defines the relationship with the air air-fuel ratio (actual air-fuel ratio) is prepared in advance, the actual air-fuel ratio corresponding to the value Q _est can be calculated from the map or the like. Therefore, in S34 and S36 of FIG. 6, the actual air-fuel ratio is calculated according to the value Q _est indicating the actual heat generation amount, and the target air-fuel ratio determined according to the determined actual air-fuel ratio, the engine speed and the engine load. And a control amount (for example, a correction value of the fuel injection amount) for correcting the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 may be set according to the deviation.

  Further, in the rich region, the control parameter γ indicating the heat quantity ratio decreases substantially in proportion to the air-fuel ratio of the air-fuel mixture (see FIG. 2), so that the control parameter γ showing the heat quantity ratio and the combustion chamber 3 If a map or the like that defines the relationship with the air-fuel ratio (actual air-fuel ratio) of the air-fuel mixture is prepared in advance, the actual air-fuel ratio corresponding to the control parameter γ can be calculated from the map or the like. Therefore, in S38 and S40 of FIG. 6, the actual air-fuel ratio is calculated according to the control parameter γ, and the deviation between the determined actual air-fuel ratio and the target air-fuel ratio determined according to the engine speed and engine load is determined. A control amount (for example, a correction value of the fuel injection amount) for correcting the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 may be set according to the deviation.

Thus, if the product value PV ^κ described above is used, the air-fuel ratio of the internal combustion engine 1 can be accurately detected. This makes it possible to obtain the actual air-fuel ratio of the air-fuel mixture with extremely high responsiveness compared to the case where an air-fuel ratio sensor (oxygen sensor) is used, for example. Become.

  By the way, the value of the control parameter γ indicating the heat quantity ratio used in the control of the internal combustion engine 1 is normal (when the fuel supplied to the internal combustion engine 1 is in a state where any combustion chamber 3 is in a misfire state). This value is significantly lower than the value when the combustion chamber 3 is almost completely combusted. Using this point, in the internal combustion engine 1 of the present invention, the misfire determination process for each combustion chamber 3 using the control parameter γ is executed according to the procedure shown in FIG.

The misfire determination process in FIG. 7 is executed by the ECU 20 of the internal combustion engine 1 at predetermined time intervals, for example, and the ECU 20 performs substantially the same procedure as described with reference to FIG. 4 when it is time to execute the misfire determination process. For each combustion chamber 3, the control parameter γ is set based on the difference ΔPV ^κ of the product value PV ^κ between the first and second timings, the fuel injection amount qF, and the conversion coefficient α.
γ = ΔPV ^κ / qF × α
(S50).

  When the control parameter γ is obtained in S50, the ECU 20 determines, for each combustion chamber 3, whether or not the control parameter γ is lower than a predetermined first threshold value g1 (for example, g1 = 0.3). (S52). If the ECU 20 determines in S52 that the control parameter γ for at least one of the combustion chambers 3 is below the first threshold value g1, the ECU 20 considers the inside of the combustion chamber 3 to be in a misfire state, A predetermined warning is displayed (S54).

  On the other hand, when it is determined in S52 that the control parameter γ of all the combustion chambers 3 is equal to or greater than the first threshold value g1, the ECU 20 further sets the control parameter γ for each combustion chamber 3 in advance. It is determined whether or not a threshold value g2 (g2> g1, for example, g2 = 0.8) is less than 2 (S56). In S56, when it is determined that the control parameter γ is lower than the second threshold value g2 for at least one of the combustion chambers 3, the ECU 20 considers that the interior of the combustion chamber 3 is in a semi-misfire state, and the combustion is performed. A counter (not shown) corresponding to the chamber 3 is incremented by 1 (S58).

  After the process of S58, the ECU 20 determines whether or not the count value of the counter (incremented counter) exceeds a predetermined threshold value (S60). When the ECU 20 determines that the count value of the counter exceeds a predetermined threshold value in S60, that is, when the ECU 20 determines that the number of occurrences of misfire in the combustion chamber 3 exceeds the threshold value, the counter Is reset (S62), the combustion chamber 3 is regarded as being completely misfired, and a predetermined warning is displayed (S54).

  As described above, in the internal combustion engine 1, the misfire state in each combustion chamber 3 is accurately performed at a low load based on the control parameter γ indicating the heat amount ratio of the actual heat generation amount to the heat generation amount (theoretical value) during complete combustion. Will be judged. Such misfire determination processing is executed using a control parameter γ that is irrelevant to a load condition or the like, so that it is not necessary to prepare a threshold value for each of various conditions. Therefore, it is possible to greatly reduce the burden caused by the map and threshold matching required for such misfire determination processing.

  If it is determined in S56 that the control parameter γ is not less than the second threshold value g2 for all the combustion chambers 3, and if the count value of the counter does not exceed a predetermined threshold value in S60. If it is determined, the ECU 20 considers that no misfire state has occurred so as to issue a warning in any combustion chamber 3, stops the misfire determination process, and waits until the next determination timing.

  In the internal combustion engine 1, as described above, the misfire state determination process in the combustion chamber 3 is executed using the value of the control parameter γ indicating the heat ratio, but an abnormality has occurred in the injector 12 that injects fuel. In this case, the value of the control parameter γ is also significantly different from the normal value. In the internal combustion engine 1 of the present invention, using this point, the abnormality determination process of each injector 12 using the control parameter γ is executed according to the procedure shown in FIGS.

  FIG. 8 is a flowchart showing a procedure for determining whether there is deterioration or clogging of the injector 12 that causes fuel supply failure (fuel injection failure) among the abnormality of the injector 12. In this case, the ECU 20 of the internal combustion engine 1 first obtains the rotational angular velocity (rotational fluctuation) of the crankshaft based on the signal from the crank angle sensor 14 when the predetermined abnormality of the injector is determined. It is determined whether or not the calculated rotational angular velocity is below a predetermined threshold (S70). When the ECU 20 determines in S70 that the rotational angular velocity (rotational fluctuation) of the crankshaft is below a predetermined threshold and the combustion state in each combustion chamber 3 is stable, the injector 12 in FIG. The abnormality determination process is executed.

That is, when the ECU 20 determines that the combustion state in each combustion chamber 3 is stable, the first and second timings are set for each combustion chamber 3 in substantially the same manner as described with reference to FIG. The control parameter γ based on the difference ΔPV ^κ of the product value PV ^κ , the fuel injection amount qF, and the conversion coefficient α,
γ = ΔPV ^κ / qF × α
(S72).

  When the control parameter γ is obtained in S72, the ECU 20 determines for each combustion chamber 3 whether or not the control parameter γ is below a predetermined threshold value g3 (for example, g3 = 0.5) (S74). . Here, although the rotational fluctuation (rotational angular velocity) of the internal combustion engine 1 (crankshaft) is small and the combustion state in each combustion chamber 3 is determined to be stable, the actual amount of heat generated during complete combustion is not affected. The fact that the control parameter γ indicating the heat amount ratio of the heat generation amount is lower than the predetermined threshold value g3 indicates that the amount of fuel originally required is not supplied into the combustion chamber 3. Accordingly, the ECU 20 displays a warning indicating that a fuel injection failure has occurred due to deterioration or clogging of the injector 12 for the combustion chamber 3 in which the control parameter γ is below the predetermined threshold value g3 (S76). Thus, in the internal combustion engine 1, it is possible to easily and accurately determine deterioration or clogging of the injector 12 that causes fuel injection failure.

  FIG. 9 is a flowchart showing a procedure for determining the presence or absence of fuel leakage in the injector 12 among the abnormalities of the injector 12. In this case, the ECU 20 of the internal combustion engine 1 first determines whether or not the stoichiometric operation mode is executed (S80) when the predetermined abnormality determination of the injector is executed (S80). When it is determined that the engine is operating under the control, the abnormality determination process of the injector in FIG. 8 is executed.

  When it is determined in S80 that the internal combustion engine 1 is operating under the stoichiometric operation mode, the ECU 20 determines each combustion chamber 3 based on a signal from the exhaust air / fuel ratio sensor 16 installed in the exhaust pipe 6. The air-fuel ratio of the air-fuel mixture at is acquired (estimated) (S82). Then, the ECU 20 determines whether or not the acquired air-fuel ratio in each combustion chamber 3 is lower than the stoichiometric air-fuel ratio (whether it is rich) (S84).

  If it is determined in S84 that the air-fuel ratio of the air-fuel mixture in all the combustion chambers 3 is not lower than the stoichiometric air-fuel ratio (not rich), at least the fuel is supplied to each combustion chamber 3 excessively. In other words, it is not considered that fuel leakage occurs in each injector 12. Therefore, in this case, the ECU 20 ends the injector abnormality determination process at this stage and waits until the next determination timing is reached.

On the other hand, when it is determined in S84 that the air-fuel ratio of the air-fuel mixture in any one of the combustion chambers 3 is lower than the stoichiometric air-fuel ratio (becomes rich), the ECU 20 uses a predetermined map or the like. The opening of the throttle valve 10 is increased in accordance with the deviation between the air-fuel ratio in the combustion chamber 3 and the stoichiometric air-fuel ratio (14.7), and air is supplied so that the air-fuel ratio in the combustion chamber 3 becomes the stoichiometric air-fuel ratio. The amount is increased (S86). Thereafter, the ECU 20 performs, in substantially the same manner as the procedure described with reference to FIG. 4, for each combustion chamber 3, the difference ΔPV ^κ of the product value PV ^κ between the first and second timings, the fuel injection amount qF, and Based on the conversion coefficient α, the control parameter γ is
γ = ΔPV ^κ / qF × α
(S88).

  When the control parameter γ is obtained in S88, the ECU 20 determines for each combustion chamber 3 whether or not the control parameter γ exceeds a predetermined threshold value g4 (for example, g4 = 1) (S90). Here, when it is determined that the air-fuel ratio of the air-fuel mixture in a certain combustion chamber 3 is rich (S84), the air supply amount is reset so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 3 becomes the stoichiometric air-fuel ratio. Regardless of the set value (S86), the value of the control parameter γ for the combustion chamber 3 still exceeds the predetermined threshold value g4 (S90), from the injector 12 provided in the combustion chamber 3 This indicates that fuel is leaking and residual fuel is present in the combustion chamber 3.

  Therefore, if the ECU 20 determines in S90 that the control parameter γ for any one of the combustion chambers 3 exceeds the threshold value g4, a problem of fuel leakage occurs in the injector 12 provided in the combustion chamber 3. A warning to the effect is displayed (S92). Thus, in the internal combustion engine 1, it is possible to easily and accurately determine the presence or absence of fuel leakage in the injector 12. If it is determined in S90 that the values of the control parameters γ of all the combustion chambers 3 do not exceed the predetermined threshold value g4, the ECU 20 ends the injector abnormality determination process at this stage, and the next determination timing Wait until

FIG. 10 is a flowchart showing another procedure for controlling the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 in the internal combustion engine 1. The routine shown in FIG. 10 can be executed when it is determined in S22 of FIG. 5 that the lean operation mode or the rich operation mode should be executed. In this case, the ECU 20 first determines whether or not the lean operation mode should be executed (S300). When the ECU 20 determines that the lean operation mode should be executed in S300, the fuel injection amount set in S10 is the average value Q _est of the difference ΔPV ^κ of the product value PV ^κ obtained in S20 of FIG. By dividing by qF and multiplying this by a predetermined conversion coefficient α, a control parameter γ indicating the heat amount ratio of the actual heat generation amount to the heat generation amount (theoretical value) at the time of complete combustion,
γ = Q _est / qF × α
(S302). In this case, the conversion coefficient α may be omitted, and the average value Q _est may be divided by the fuel injection time and multiplied by another conversion coefficient.

In this way, when the control parameter γ indicating the heat ratio and irrelevant to the load condition or the like is obtained, the ECU 20 determines whether or not the value of the control parameter γ is equal to or greater than a predetermined threshold (S304). When it is determined that the value of γ is equal to or greater than the threshold value, the air-fuel ratio (actual air-fuel ratio) of the air-fuel mixture in each combustion chamber 3 is calculated based on the value Q _est indicating the actual heat generation amount (S306). Then, the ECU 20 obtains a deviation between the target air-fuel ratio determined according to the engine speed and the engine load and the actual air-fuel ratio obtained in S306, and corrects the air-fuel ratio of the air-fuel mixture in each combustion chamber 3. An amount (for example, a correction value of the fuel injection amount) is set according to the deviation (S308).

In the present embodiment, based on the fact that the air-fuel ratio of the air-fuel mixture in the combustion chamber 3 is substantially proportional to the heat generation amount Q in the lean region (see FIG. 5), the value Q _est indicating the actual heat generation amount and each combustion chamber 3 is prepared in advance, and the ECU 20 reads out the actual air-fuel ratio corresponding to the value Q _est from the map in S306. As described above, if the actual air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is calculated based on the value Q _est indicating the actual heat generation amount in the lean region, for example, compared to the case where an air-fuel ratio sensor (oxygen sensor) is used. It becomes possible to obtain the actual air-fuel ratio of the air-fuel mixture with extremely high responsiveness, and the exhaust air-fuel ratio sensor 16 in the exhaust pipe 6 can be omitted.

On the other hand, if it is determined in S304 that the value of the control parameter γ is below the threshold value, the ECU 20 does not calculate the actual air-fuel ratio based on the value Q _est indicating the actual heat generation amount, and each combustion chamber 3 The actual air-fuel ratio of the air-fuel mixture at is maintained at the previous (previous cycle) calculated value (S310). Here, if the combustion state in each combustion chamber 3 is good under the lean operation mode (if it is complete combustion), the control parameter γ indicating the heat quantity ratio is as shown in FIG. The value is almost constant. On the other hand, for example, when any one of the combustion chambers 3 is in a misfire state or when the combustion state in any one of the combustion chambers 3 is deteriorated, the actual heat generation amount is reduced. The value of γ also decreases according to the actual heat generation amount.

Therefore, when the value of the control parameter γ falls below the threshold value, that is, when the fluctuation amount of the control parameter γ from the fixed value exceeds a predetermined value, the value Q _est indicating the actual heat generation amount is used. Thus, even if the air-fuel ratio of the air-fuel mixture is calculated, an accurate actual air-fuel ratio cannot be obtained, and a control amount for correcting the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 using such an actual air-fuel ratio is not obtained. If set, the air-fuel ratio may deviate from the target value. In consideration of such points, in this embodiment, when it is determined that the value of the control parameter γ is below the threshold value and the fluctuation amount of the control parameter γ exceeds the predetermined value, the combustion chamber 3 in each combustion chamber 3 is determined in S310. The actual air-fuel ratio of the air-fuel mixture is held at the previous (previous cycle) calculated value.

  Thus, under the routine of FIG. 10, when the combustion state in at least one of the combustion chambers 3 is deteriorated, the actual sky obtained when the combustion state is good immediately before in S308. Since the control amount for correcting the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 is set based on the fuel ratio, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 can always be kept within the preferred range. In S304, instead of determining whether or not the value of the control parameter γ is greater than or equal to a predetermined threshold value, a variation amount (deviation from the previous value) of the control parameter γ is obtained, and the variation amount is equal to or less than the predetermined threshold value. It may be determined whether or not.

  After the processing of S308, the ECU 20 sets the fuel injection amount (fuel injection time) from each injector 12 based on the set control amount (while adding or subtracting), and sets the opening of the throttle valve 10, for example, The processes after S12 in FIG. 5 are executed again. If it is determined in S300 that the rich operation mode should be executed, the ECU 20 executes, for example, the processes after S38 in FIG.

If it is determined in S300 that the rich operation mode should be executed, the average value Q _est is divided by the intake air amount (set in S10) and multiplied by a predetermined conversion factor. Thus, the control parameter γ ′ indicating the ratio of the actual heat generation amount to the heat generation amount (theoretical value) at the time of complete combustion is obtained, and it is determined that the fluctuation amount of the control parameter γ ′ exceeds a predetermined threshold value. In this case, the actual air-fuel ratio of the air-fuel mixture in each combustion chamber 3 may be held at the previous (previous cycle) calculated value. Thereby, even if the combustion state in at least one of the combustion chambers 3 deteriorates during the rich operation mode, the air-fuel ratio of the air-fuel mixture in each combustion chamber 3 can be always kept within a preferable range.

It is a graph which shows the correlation with the product value PV ( ^kappa) used in this invention, and the amount of heat generation in a combustion chamber. 3 is a graph showing a correlation between an air-fuel ratio of an air-fuel mixture in a combustion chamber and a control parameter γ indicating a heat quantity ratio. 1 is a schematic configuration diagram showing an internal combustion engine according to the present invention. 4 is a flowchart for explaining the operation of the internal combustion engine of FIG. 3. It is a graph which shows the correlation with the air fuel ratio of the air-fuel | gaseous mixture in a combustion chamber, and the amount of heat generation between two predetermined points. 4 is a flowchart for explaining the operation of the internal combustion engine of FIG. 3. FIG. 4 is a flowchart for explaining misfire determination processing in the internal combustion engine of FIG. 3. FIG. FIG. 4 is a flowchart for illustrating injector abnormality determination processing in the internal combustion engine of FIG. 3. FIG. 6 is a flowchart for explaining another example of the abnormality determination process for the injector in the internal combustion engine of FIG. 3. 6 is a flowchart showing another procedure for controlling the air-fuel ratio of the air-fuel mixture in the internal combustion engine of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder block 3 Combustion chamber 4 Piston 5 Intake pipe 6 Exhaust pipe 7 Spark plug 8 Surge tank 9 Air cleaner 10 Throttle valve 11a, 11b Catalyst device 12 Injector 14 Crank angle sensor 15 In-cylinder pressure sensor 16 Exhaust air-fuel ratio sensor L1 Supply Air line Ve Exhaust valve Vi Intake valve

Claims (12)

In a control device for an internal combustion engine that generates power by burning a mixture of fuel and air in a cylinder,
In-cylinder pressure detecting means for detecting in-cylinder pressure;
Based on the product value of the in-cylinder pressure detected by the in-cylinder pressure detecting means and the cylinder volume at the time of detection of the in-cylinder pressure by a predetermined exponent, the actual heat with respect to the heat generation amount at the time of complete combustion A calculation means for calculating a control parameter indicating a heat quantity ratio of the generated amount;
Based on the control parameter calculated by the calculation means , setting of a control amount for correcting the air-fuel ratio of the air-fuel mixture, determination of in-cylinder misfire, determination of in-cylinder combustion state, and injector for injecting fuel And a control unit that executes at least one of the abnormality determinations .   The arithmetic means calculates the product value at two predetermined points and calculates the control parameter based on a difference between the product values between the two predetermined points and a fuel supply amount or an intake air amount. The control device for an internal combustion engine according to claim 1.   The one of the two predetermined points is set after the intake valve is opened and before the start of combustion, and the other is set after the start of the combustion and before the exhaust valve is opened. Control device for internal combustion engine.   The control means sets a control amount for correcting the air-fuel ratio of the air-fuel mixture so that the control parameter matches a target value when the air-fuel ratio of the air-fuel mixture is set within a region smaller than the stoichiometric air-fuel ratio. The control apparatus for an internal combustion engine according to any one of claims 1 to 3.   5. The control device for an internal combustion engine according to claim 1, wherein the control unit executes misfire determination in the cylinder based on the control parameter.   6. The control device for an internal combustion engine according to claim 5, wherein the control means determines that the cylinder is in a misfire state when the value of the control parameter is below a predetermined threshold value.   The control device for an internal combustion engine according to any one of claims 1 to 6, wherein the control means performs abnormality determination of an injector that injects fuel based on the control parameter. A combustion state determining means for determining a combustion state in the cylinder;
The control means determines that an abnormality has occurred in the injector when the combustion state in the cylinder is determined to be stable by the combustion state determination means and the control parameter falls below a predetermined threshold value. The control device for an internal combustion engine according to claim 7, wherein the determination is made.   The control means determines that an abnormality has occurred in the injector when the value of the control parameter exceeds a predetermined threshold when the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio. The control device for an internal combustion engine according to claim 7.   Air-fuel ratio setting means for setting a control amount for causing the air-fuel ratio of the air-fuel mixture to coincide with a target value is further provided, and when the amount of fluctuation of the control parameter exceeds a predetermined value, the control amount of the air-fuel ratio setting means is 2. The control apparatus for an internal combustion engine according to claim 1, wherein the control value is held at a previous value.   The air-fuel ratio setting unit calculates an actual air-fuel ratio of the air-fuel mixture based on the actual heat generation amount, and sets the control amount based on the calculated actual air-fuel ratio. Control device for internal combustion engine. In a control method of an internal combustion engine for generating power by burning a fuel / air mixture in a cylinder,
(A) detecting the in-cylinder pressure;
(B) Based on the product value of the in-cylinder pressure detected in step (a) and a value obtained by raising the in-cylinder volume at the time of detection of the in-cylinder pressure by a predetermined index, the amount of heat generated during complete combustion is Calculating a control parameter indicating a heat amount ratio of the actual heat generation amount;
(C) Based on the control parameter calculated in step (b), setting of a control amount for correcting the air-fuel ratio of the air-fuel mixture, determination of in-cylinder misfire, determination of in-cylinder combustion state, and fuel A control method for an internal combustion engine, comprising: performing at least one of abnormality determinations of an injector that injects fuel .

Images