JP2006144672A - Controller and control method for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress torque fluctuation caused in accordance with control of an air-fuel ratio in a combustion chamber satisfactorily. <P>SOLUTION: This internal combustion engine 1 is provided with a cylinder internal pressure sensor 15, an air-fuel ratio sensor 16, and an ECU 20. The ECU 20 determines a rich/lean condition of an air-fuel ratio in the combustion chamber 3 based on a value detected by the air-fuel ratio sensor 16, sets fuel injection amount so that the air-fuel ratio in the combustion chamber 3 agrees with a theoretical air-fuel ratio in accordance with the result of rich/lean determination, and calculates ignition time based on deviation of a combustion ratio at predetermined timing obtained based on cylinder internal pressure detected by the cylinder internal pressure sensor 15 and a target combustion ratio. When the ECU 20 determines that the air-fuel ratio in the combustion chamber 3 is in a rich condition based on the rich/lean determination of the air-fuel ratio, it compensates ignition time calculated based on the combustion ratio to suppress torque fluctuation of the internal combustion engine 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

In general, in an internal combustion engine in which the air-fuel ratio of fuel and air in the combustion chamber is set to the stoichiometric air-fuel ratio, rich / lean determination of the air-fuel ratio in the combustion chamber using an air-fuel ratio sensor (O ₂ sensor) is performed. According to the result, the fuel injection amount is set so that the air-fuel ratio in the combustion chamber matches the stoichiometric air-fuel ratio. An internal combustion engine that is feedback-controlled so that the air-fuel ratio matches the stoichiometric air-fuel ratio in this way is the same as the air-fuel ratio in the combustion chamber in order to suppress torque fluctuations that occur with the air-fuel ratio feedback control. One that further corrects the ignition timing in accordance with the deviation from the air-fuel ratio is known (for example, see Patent Document 1).

JP-A-7-83150

  However, when air-fuel ratio feedback control is executed, torque fluctuations are satisfactorily suppressed even if the ignition timing is further corrected according to the deviation between the air-fuel ratio and the stoichiometric air-fuel ratio in the combustion chamber, as in the conventional example. There were many things that could not be done.

  Accordingly, an object of the present invention is to provide a control device and a control method for an internal combustion engine that can satisfactorily suppress torque fluctuations that occur with the control of the air-fuel ratio in the combustion chamber.

  An internal combustion engine control apparatus according to the present invention is an internal combustion engine control apparatus that generates power by burning a mixture of fuel and air in a combustion chamber, and an air-fuel ratio determination means that performs rich / lean determination of the air-fuel ratio in the combustion chamber And a fuel supply amount setting means for setting a fuel supply amount to the combustion chamber so that the air-fuel ratio in the combustion chamber matches the target air-fuel ratio according to the determination result of the air-fuel ratio determination means, and the in-cylinder pressure in the combustion chamber. In-cylinder pressure detecting means for detecting, combustion ratio calculating means for calculating a combustion ratio at a predetermined timing based on the in-cylinder pressure detected by the in-cylinder pressure detecting means, combustion ratio calculated by the combustion ratio calculating means, and target combustion The combustion start timing calculation means for calculating the combustion start timing in the combustion chamber based on the deviation from the ratio and the air fuel ratio in the combustion chamber are reduced by the air fuel ratio determination means. When it is determined to be, characterized by comprising a correction means for correcting to the combustion start timing is calculated by the combustion start timing calculation means torque fluctuation of the internal combustion engine is suppressed.

  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 combustion chamber, and performs a rich / lean determination of an air-fuel ratio in the combustion chamber, and the determination result Accordingly, the fuel supply amount to the combustion chamber is set so that the air-fuel ratio in the combustion chamber matches the target air-fuel ratio, the combustion ratio at a predetermined timing is calculated based on the in-cylinder pressure in the combustion chamber, and the combustion The combustion start timing in the combustion chamber is calculated based on the deviation between the ratio and the target combustion ratio, and when it is determined that the air-fuel ratio in the combustion chamber is rich, the calculated combustion start timing is used as the torque fluctuation of the internal combustion engine. It corrects so that it may be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus and control method of an internal combustion engine which can suppress suitably the torque fluctuation which generate | occur | produces with control of the air fuel ratio in a combustion chamber are attained.

  In the internal combustion engine to which the control apparatus according to the present invention is applied, the fuel supply amount setting means causes the fuel supply amount to the combustion chamber so that the air-fuel ratio in the combustion chamber matches the target air-fuel ratio according to the determination result of the air-fuel ratio determination means. Thus, feedback control is performed so that the air-fuel ratio in the combustion chamber matches the target air-fuel ratio. Further, in the internal combustion engine, the combustion start timing calculating means generally determines the optimum combustion start timing (spark ignition timing or spark ignition timing based on the deviation between the combustion ratio and the target combustion ratio at a predetermined timing calculated based on the in-cylinder pressure. Compression ignition timing) is calculated.

  The combustion start timing calculated by the combustion start timing calculation means is such that the correction means eliminates torque fluctuations of the internal combustion engine only when the air-fuel ratio determination means determines that the air-fuel ratio in the combustion chamber is rich. Corrected (retarded or advanced). As a result, the convergence of torque fluctuations generated with the control of the air-fuel ratio in the combustion chamber (feedback control) can be improved as compared with the case where the combustion start timing is corrected regardless of the determination result of the air-fuel ratio determination means. Therefore, it is possible to favorably suppress the torque fluctuation.

  The correction means preferably sets a correction amount to be added to the calculated value of the combustion start timing calculation means based on the fuel supply amount set by the fuel supply amount setting means.

  According to such a configuration, when the air-fuel ratio in the combustion chamber is determined to be rich by the air-fuel ratio determining means, the correction amount of the combustion start timing for suppressing the torque fluctuation generated along with the control of the air-fuel ratio is set. It becomes possible to determine appropriately.

  Further, when the air-fuel ratio determining means determines that the air-fuel ratio in the combustion chamber is rich, the output of the combustion start timing calculating means is fixed to a predetermined value, or the deviation between the combustion ratio and the target value is Preferably it is set to zero.

  The calculation of the combustion start timing (feedback control of the combustion start timing) based on the deviation between the combustion ratio and the target value by the combustion ratio calculation means described above, and the correction of the combustion start timing (retard or advance) by the correction means If both are executed, the combustion start timing may gradually shift to the retard side or the advance side. Therefore, when the air-fuel ratio determination means determines that the air-fuel ratio in the combustion chamber is rich and correction of the combustion start timing by the correction means is executed, whether the output of the combustion start timing calculation means is fixed to a predetermined value. Alternatively, the feedback control of the combustion start timing may be stopped by setting the deviation between the combustion ratio and the target value to zero. As a result, it is possible to reliably suppress the combustion start timing from gradually shifting to the retard side or the advance side.

  The correction means preferably reduces the value of the target combustion ratio so that the combustion start timing calculated by the combustion start timing calculation means is retarded.

  Under such a configuration, the combustion start timing is calculated based on the deviation between the combustion ratio and the target combustion ratio at a predetermined timing regardless of the determination result of the air-fuel ratio determination means. It becomes possible to stabilize the control of the start time.

  Further, the combustion ratio calculation means calculates the combustion ratio based on the product value of the in-cylinder pressure detected by the in-cylinder pressure detection means and a value obtained by raising the in-cylinder volume at the time of detection of the in-cylinder pressure by a predetermined index. It is preferable.

The present inventor has intensively studied to reduce a calculation load when calculating a combustion ratio at a predetermined timing for a certain combustion chamber. As a result, when the crank angle is θ, the present inventor sets the in-cylinder pressure detected by the in-cylinder pressure detection means to P (θ), and when the crank angle is θ (the in-cylinder pressure P (θ) ) And the specific heat ratio is κ, the in-cylinder pressure P (θ) and the in-cylinder volume V (θ) are expressed as a specific heat ratio (predetermined index) κ. Attention was paid to the product value P (θ) · V ^κ (θ) (hereinafter referred to as “PV ^κ ” as appropriate) with the raised value V ^κ (θ).

The inventor has found that the change pattern of the heat generation amount Q in the combustion chamber 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 have a correlation as shown in FIG. It was. 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 is plotted. In FIG. 1, the broken line is calculated and plotted as Q = ∫dQ / dθ · Δθ based on the following equation (1) based on the amount of heat generation Q in the model cylinder. In either case, for simplicity, κ = 1.32. In FIG. 1, −360 °, 0 °, and 360 ° correspond to the top dead center, and −180 ° and 180 ° correspond to the bottom dead center.

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.

In a preferred embodiment of the present invention, the correlation between the heat generation amount Q in the combustion chamber and the product value PV ^κ is used to detect the in-cylinder pressure detected by the in-cylinder pressure detecting means and the in-cylinder pressure. Based on the product value PV ^κ with the in-cylinder volume, a combustion ratio MFB that is a ratio of a heat generation amount up to a predetermined timing between the two points with respect to a total heat generation amount between the two points is obtained. Here, if the combustion ratio in the combustion chamber is calculated based on the product value PV ^κ , the combustion ratio in the combustion chamber can be obtained with high accuracy without requiring high-load calculation processing. That is, as shown in FIG. 2, the combustion rate obtained based on the product value PV ^κ (see the solid line in the figure) is substantially the same as the combustion rate obtained based on the heat generation rate (see the broken line in the figure). To do.

  In FIG. 2, the solid line represents the combustion ratio at the timing when the crank angle = θ in the model cylinder described above, calculated according to the following equation (2), and plotted based on the detected in-cylinder pressure P (θ). Is. However, for simplicity, κ = 1.32. In FIG. 2, the broken line indicates the combustion ratio at the timing when the crank angle = θ in the above model cylinder, according to the above equation (1) and the following equation (3), and the detected in-cylinder pressure P (θ). Calculated based on the above and plotted. Also in this case, for simplicity, κ = 1.32.

  Further, the predetermined timing is set between a first timing set after the intake valve is opened and before the start of combustion, and a second timing set after the start of combustion and before the exhaust valve is opened. Preferably, the combustion ratio calculation means is based on the difference between the product values between the first timing and the second timing and the difference between the product values between the first timing and the predetermined timing. It is preferable to calculate the combustion rate.

In this case, if the crank angle at the predetermined timing is θ ₀ , the combustion ratio MFB at the predetermined timing at which the crank angle = θ ₀ is the product value PV ^κ between the first timing and the predetermined timing. Difference {P (θ ₀ ) · V ^κ (θ ₀ ) −P (θ ₁ ) · V ^κ (θ ₁ )} as a difference between product values PV ^κ between the first timing and the second timing. It can be obtained by dividing by {P (θ ₂ ) · V ^κ (θ ₂ ) −P (θ ₁ ) · V ^κ (θ ₁ )} and multiplying by 100. Thereby, it becomes possible to obtain | require a combustion ratio accurately based on the in-cylinder pressure detected in three points, and a calculation load can be reduced significantly.

  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 to which the control device according to the present invention is applied. 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. 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 and an exhaust valve Ve are provided for each combustion chamber 3 in the cylinder head of the internal combustion engine 1. Each intake valve Vi opens and closes a corresponding intake port, and each exhaust valve Ve opens and closes a corresponding exhaust port. Each intake valve Vi and each exhaust valve Ve are operated 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 is connected to the surge tank 8, and the air supply line is connected to an air intake port (not shown) via an air cleaner 9. A throttle valve (electronically controlled throttle valve in this embodiment) 10 is incorporated in the middle of the air supply line (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 disposed so as to face the inside of the corresponding intake pipe 5 (inside the intake port) as shown in FIG. Each injector 12 injects fuel such as gasoline into each intake pipe 5. Although the internal combustion engine 1 of the present embodiment is described as a so-called port injection type gasoline engine, the present invention is not limited to this, and it goes without saying that the present invention can be applied to a so-called direct injection type internal combustion engine. . Needless to say, the present invention can be applied not only to a gasoline engine but also to a diesel engine.

Each of the spark plugs 7, the throttle valve 10, the injectors 12, and the valve mechanism are electrically connected to the 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, and the like, all not shown. As shown in FIG. 3, various sensors such as a crank angle sensor 14 and an air-fuel ratio sensor (O ₂ sensor) 16 provided in the exhaust pipe 6 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 (relative pressure) in the corresponding combustion chamber 3 and gives a signal indicating the detected value to the ECU 20. The detection value of each in-cylinder pressure sensor 15 is sequentially given to the ECU 20 every predetermined time (predetermined crank angle), corrected to an absolute pressure, and stored and held in a predetermined storage area (buffer) of the ECU 20 by a predetermined amount. .

  In the internal combustion engine 1 configured as described above, basically, the air-fuel ratio of the fuel and air in each combustion chamber 3 during operation is set to the theoretical air-fuel ratio (about 14.7). That is, the air-fuel ratio sensor 16 in the exhaust pipe 6 outputs a voltage corresponding to the oxygen concentration in the exhaust gas flowing through the exhaust pipe 6, and the ECU 20 takes into account the response delay of the air-fuel ratio sensor 16 and the like. Thus, the rich / lean determination of the air-fuel ratio in each combustion chamber 3 is performed based on the detection value of the air-fuel ratio sensor 16. When the ECU 20 determines that the air-fuel ratio in the combustion chamber 3 is larger (lean) than the stoichiometric air-fuel ratio based on the detection value of the air-fuel ratio sensor 16, the predetermined air-fuel ratio flag is set to “0”. (Maintenance) and increase correction of the fuel injection amount τ from the injector 12 according to a predetermined procedure.

  When the ECU 20 determines that the air-fuel ratio in the combustion chamber 3 is smaller (richer) than the stoichiometric air-fuel ratio based on the detection value of the air-fuel ratio sensor 16, the air-fuel ratio flag is set to "1". At the same time, the fuel injection amount τ from the injector 12 is corrected to decrease in accordance with a predetermined procedure. Note that both the fuel injection amount increase correction and the decrease correction can be performed by a step change, a continuous change, or a combination of both. Thus, in the internal combustion engine 1, the fuel injection amount τ is set according to the result of the air / fuel ratio rich / lean determination using the air / fuel ratio sensor 16 except when a predetermined condition such as at the start is satisfied. As a result, feedback control is performed so that the air-fuel ratio in the combustion chamber 3 matches the stoichiometric air-fuel ratio. This feedback control is performed so that the detected value (median value) of the air-fuel ratio matches the target value (theoretical air-fuel ratio).

  Further, the ECU 20 has a proportional integration circuit for setting the ignition timing of the internal combustion engine 1 as shown in FIG. This proportional integration circuit includes a combustion rate MFB and a target combustion rate (target MFB, 50 in this embodiment) at a predetermined timing (8 ° after top dead center in this embodiment) calculated for each cycle according to the procedure described later. %) Is calculated (set) for each combustion chamber 3 so that the deviation becomes zero. Thereby, in the internal combustion engine 1, basically, the ignition timing is feedback-controlled so that the combustion ratio MFB matches the target combustion ratio, and the ignition timing in each combustion chamber 3 is set almost optimally, so that knocking occurs. Thus, a large torque can be obtained from the internal combustion engine 1.

  Next, the control procedure of the combustion start timing, that is, the ignition timing in the internal combustion engine 1 will be described with reference to FIGS.

  In the internal combustion engine 1, the air-fuel ratio feedback control as described above is executed, and the ignition timing setting routine of FIG. 6 is repeatedly executed for each combustion chamber 3. In this case, the ECU 20 first reads the value of the above-mentioned air-fuel ratio flag (S10), and whether or not the air-fuel ratio in the combustion chamber 3 that is the target of setting the ignition timing is rich (smaller than the theoretical air-fuel ratio). Determine (S12).

If it is determined in S12 that the air-fuel ratio in the target combustion chamber 3 is rich, the ECU 20 determines the fuel injection amount of the current cycle from the predetermined storage area (the fuel injection that has been corrected for reduction through other routines). Amount) τ is read out. Then, the ECU 20 sets the ignition timing correction amount (here, the retard amount) dSA based on the fuel injection amount τ, and stores it in a predetermined storage area (S14). In the present embodiment, the ignition timing correction amount dSA is:
dSA = w ₁ · τ + w ₂
It is determined as However, _{w 1} and _{w 2,} experimental, is a coefficient determined empirically. In S14, the ECU 20 sets the value of the combustion ratio MFB fed back to the proportional integration circuit to 50% in order to set the control deviation of the proportional integration circuit to “zero”.

  On the other hand, if it is determined in S12 that the air-fuel ratio in the target combustion chamber 3 is lean (greater than the theoretical air-fuel ratio), the ECU 20 sets the ignition timing correction amount dSA to “0”, and is predetermined. (S16). In S16, the ECU 20 executes a process for allowing the value of the combustion ratio MFB calculated in S24 described later to be fed back directly to the proportional integration circuit.

When the processing of S14 or S16 is completed, the ECU 20 (proportional integration circuit) performs target combustion based on the deviation between the combustion ratio MFB calculated during the previous cycle and the target combustion ratio (50%) in S24 described later. The ignition timing SA _MFB of the chamber 3 is calculated (S18). Further, the ECU 20 adds the ignition timing correction amount dSA stored in the predetermined storage area to the ignition timing SA _MFB calculated by the proportional integration circuit, and the ignition timing SA is calculated as SA = SA _MFB + dSA.
(S20). When the ignition timing set in S20 arrives, ignition by the spark plug 7 is executed in the target combustion chamber 3 (S22).

  Here, when it is determined in S12 that the air-fuel ratio in the target combustion chamber 3 is rich, a process of setting the control deviation in the proportional integration circuit to “zero” is executed in S14. In S18, the feedback control of the ignition timing by the proportional integration circuit is substantially prohibited, and the ignition timing for the target combustion chamber 3 output from the proportional integration circuit has the same value as the previous time. In S20, the ignition timing correction amount dSA calculated in S14 is added to the output of the proportional integration circuit. Therefore, the ignition timing SA set in S20 is set to the ignition timing of the previous ignition timing. The value is retarded by the correction amount dSA.

  Thus, when it is determined in S12 that the air-fuel ratio in the target combustion chamber 3 is rich, the ignition timing correction amount dSA is appropriately determined in S14, and the ignition timing is substantially fed. It will be forward controlled. On the other hand, if it is determined in S12 that the air-fuel ratio in the target combustion chamber 3 is lean, the ignition timing correction amount dSA is set to “zero” in S14, and the proportional integration is performed. Since the feedback of the combustion ratio MFB to the circuit is allowed, the ignition timing SA set in S20 is a value calculated by the proportional integration circuit so that the combustion ratio MFB coincides with the target combustion ratio (almost optimal ignition Time).

When ignition is executed in S22, the ECU 20 calculates a combustion ratio MFB at a predetermined timing for the combustion chamber 3 in which ignition is executed (S24). When calculating the combustion ratio MFB in S24, the ECU 20 first starts from a predetermined storage area for the target combustion chamber 3 at the first timing after the intake valve Vi is opened and before ignition (the crank angle is θ _1). In-cylinder pressure P (θ ₁ ) at the timing), in-cylinder pressure P (θ ₂ ) at the second timing (timing at which the crank angle becomes θ ₂ ) after ignition and before the exhaust valve is opened, The in-cylinder pressure P (θ ₀ ) at a predetermined timing that is predetermined between the timing and the second timing and has a crank angle = θ ₀ (where θ ₁ <θ ₀ <θ ₂ ) is read out. .

The crank angle θ ₁ is preferably set to a timing sufficiently before the time point at which combustion starts in the combustion chamber 3 (at the time of ignition), and is set to −60 °, for example. The crank angle θ ₂ is preferably set to a timing at which combustion of the air-fuel mixture in the combustion chamber 3 is almost completed, for example, 90 °. Furthermore, the predetermined timing between the first timing and the second timing has a crank angle θ ₀ = 8 ° (empirically and empirically known that the combustion ratio MFB is approximately 50% ( The timing is set to 8 ° after top dead center. Note that the crank angle at which the combustion ratio MFB is approximately 50% varies depending on the cooling loss of the internal combustion engine, and slightly varies from 8 ° after top dead center depending on the model. In addition, when the stratified charge combustion operation is executed or in the case of a diesel engine, an optimum combustion start time (MBT) corresponding to each of the two may be obtained, and the combustion ratio at the MBT can be easily calculated.

When the ECU ₂₀ reads out the in-cylinder pressure P (θ ₁ ), the in-cylinder pressure P (θ ₀ ), and the in-cylinder pressure P (θ ₂ ), the product value when the crank angle becomes θ ₁ , θ _0, and θ _2. P (θ ₁ ) · V ^κ (θ ₁ ), P (θ ₀ ) · V ^κ (θ ₀ ) and P (θ ₂ ) · V ^κ (θ ₂ ) are calculated. That is, the ECU 20 determines the in-cylinder pressure P (θ ₁ ) and the in-cylinder pressure P (θ ₁ ), that is, the in-cylinder volume V (θ ₁ ) when the crank angle is θ ₁ , the specific heat ratio κ. In this embodiment, a product value P (θ ₁ ) · V ^κ (θ ₁ ), which is a product of the value raised to the power of κ = 1.32, is calculated. Similarly, the ECU 20 obtains a product value P (product which is a product of the in-cylinder pressure P (θ ₀ ) and the value obtained by raising the in-cylinder volume V (θ ₀ ) when the crank angle becomes θ ₀ by the specific heat ratio κ. θ ₀ ) · V ^κ (θ ₀ ), in-cylinder pressure P (θ ₂ ), and the value obtained by raising the in-cylinder volume V (θ ₂ ) when the crank angle is θ ₂ by the specific heat ratio κ A product value P (θ ₂ ) · V ^κ (θ ₂ ), which is a product, is calculated. The values of V ^κ (θ ₁ ), V ^κ (θ ₀ ), and V ^κ (θ ₂ ) are calculated in advance and stored in the storage device.

The ECU 20 then determines the product values P (θ ₁ ) · V ^κ (θ ₁ ), P (θ ₀ ) · V ^κ (θ ₀ ) and P (when the crank angles are θ ₁ , θ ₀ and θ _2. Using θ ₂ ) · V ^κ (θ ₂ ), the combustion ratio MFB at the timing when the crank angle becomes θ ₀ is calculated from the following equation (4) (S20). As a result, the combustion ratio can be obtained with high accuracy based on the in-cylinder pressures P (θ ₁ ), P (θ ₀ ), and P (θ ₂ ) detected at the three points, thereby greatly reducing the calculation load. be able to. In this way, when the combustion ratio MFB is calculated in S24, the ECU 20 executes the processes after S10 again.

As described above, by repeatedly executing the ignition timing setting routine of FIG. 6, the ignition timing SA _MFB calculated by the proportional integration circuit is obtained only when the air-fuel ratio in the combustion chamber 3 is determined to be rich. As shown in FIG. 7, the angle is retarded so as to eliminate the torque fluctuation of the internal combustion engine 1. As a result, as shown in FIG. 4, torque fluctuations that occur with the feedback control of the air-fuel ratio are compared with the case where the ignition timing is corrected regardless of the result of the rich / lean determination (see the broken line in FIG. 4). Since the convergence can be improved, the torque fluctuation can be satisfactorily suppressed.

  In S14, the air-fuel ratio feedback control is performed by calculating the ignition timing correction amount (retard amount) dSA based on the fuel injection amount τ corrected in accordance with the rich / lean determination result of the air-fuel ratio. Accordingly, it is possible to appropriately determine the ignition timing correction amount dSA for suppressing the torque fluctuation generated along with the above. As can be seen from FIG. 7, when the air-fuel ratio in the combustion chamber 3 is rich, torque fluctuation can be suppressed even if the ignition timing is advanced. Accordingly, in S14, the advance amount may be set based on the fuel injection amount τ corrected in accordance with the result of the air / fuel ratio rich / lean determination. However, since the response (sensitivity) of the torque change with respect to the ignition timing correction amount is better when the ignition timing is retarded, the retard amount is set in S14 as in this embodiment. It is more advantageous to do so.

  Further, under the routine of FIG. 6, when it is determined in S12 that the air-fuel ratio in the target combustion chamber 3 is lean, the feedback control of the ignition timing by the proportional integration circuit is stopped. By executing both the feedback control and the correction of the ignition timing (addition of the ignition timing correction amount dSA) in S20, the ignition timing SA is retarded (if the advance amount is set in S14, the advancement is performed). It is possible to reliably suppress the gradual shift to the (corner side). In order to stop the feedback control of the ignition timing by the proportional integration circuit, instead of setting the control deviation (deviation between the combustion ratio MFB and the target value) in the proportional integration circuit to zero in S14, the output of the proportional integration circuit May be executed to fix to a predetermined value (previous value or value corresponding to MBT).

  FIG. 8 is a flowchart for explaining another ignition timing setting routine that can be executed in the internal combustion engine 1 described above.

  The ignition timing routine of FIG. 8 is also repeatedly executed for each combustion chamber 3 by the ECU 20. In this case, the ECU 20 first reads the value of the air-fuel ratio flag (S30), and determines whether or not the air-fuel ratio in the combustion chamber 3 to be set for the ignition timing is rich (smaller than the theoretical air-fuel ratio). (S32). If it is determined in S32 that the air-fuel ratio in the target combustion chamber 3 is rich, the ECU 20 sets the target combustion ratio given to the above-described proportional integration circuit to “40%” (S34). . If the ECU 20 determines in S12 that the air-fuel ratio in the target combustion chamber 3 is lean, the ECU 20 sets the target combustion ratio to be given to the above-described proportional integration circuit to “50%” (S36). .

When the process of S34 or S36 is completed, the ECU 20 (proportional integration circuit) performs target combustion based on the deviation between the combustion ratio MFB calculated during the previous cycle and the target combustion ratio (50%) in S42 described later. The ignition timing SA _MFB of the chamber 3 is calculated (S38). When the ignition timing SA _MFB calculated in S38 arrives, ignition by the spark plug 7 is executed in the target combustion chamber 3 (S40). Further, when ignition is executed in S40, the ECU 20 calculates the combustion ratio MFB at a predetermined timing (8 ° after top dead center) for the combustion chamber 3 in which ignition is executed according to the same procedure as S24 in FIG. (S42), and the processes after S30 are executed again.

Here, if it is determined in S32 that the air-fuel ratio in the target combustion chamber 3 is rich, in S34, the value of the target combustion ratio is a value (50%) for obtaining the optimal ignition timing. As shown in FIG. 9, the ignition timing SA _MFB calculated in S38 is reduced when the target combustion ratio value is set to 50%, that is, the combustion is performed in S12. Compared to the case where it is determined that the air-fuel ratio in the chamber 3 is lean, the angle is retarded.

Therefore, even under the ignition timing setting routine of FIG. 8, the ignition timing SA _MFB calculated by the proportional integration circuit is shown in FIG. 9 only when it is determined that the air-fuel ratio in the combustion chamber 3 is rich. In this way, the angle is retarded so as to eliminate the torque fluctuation of the internal combustion engine 1. This makes it possible to improve the convergence of torque fluctuations generated with air-fuel ratio feedback control, compared to the case where the ignition timing is corrected regardless of the result of rich / lean determination. It becomes possible to suppress.

  Further, under the routine of FIG. 8, regardless of the result of rich / lean determination of the air-fuel ratio, the ignition timing is calculated based on the deviation between the combustion ratio MFB at the predetermined timing and the target combustion ratio, and the combustion ratio MFB Therefore, the ignition timing control can be stabilized. Note that the value of the target combustion ratio set in S34 is not limited to “40%”, and can be arbitrarily determined within a range in which torque fluctuations that occur with air-fuel ratio feedback control can be suppressed. .

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. It is a graph which shows the correlation of the combustion rate calculated | required based on product value PV ( ^kappa) , and the combustion rate calculated ^| required based on a heat release rate. It is a schematic block diagram which shows the internal combustion engine to which the control apparatus by this invention was applied. FIG. 4 is a timing chart for explaining the operation of the internal combustion engine of FIG. 3. FIG. FIG. 4 is a control block diagram for explaining setting of ignition timing in the internal combustion engine of FIG. 3. 4 is a flowchart for illustrating an ignition timing setting routine executed in the internal combustion engine of FIG. 3. It is a graph which shows the correlation with the ignition timing when the air fuel ratio in a combustion chamber changes, and the torque of an internal combustion engine. 6 is a flowchart for explaining another ignition timing setting routine that can be executed in the internal combustion engine of FIG. 3. It is a graph which shows the correlation with ignition timing and the target combustion ratio at the time of setting ignition timing based on the combustion ratio in a combustion chamber.

Explanation of symbols

1 Internal combustion engine 3 Combustion chamber 7 Spark plug 12 Injector 14 Crank angle sensor 15 In-cylinder pressure sensor 16 Air-fuel ratio sensor 20 ECU
Ve Exhaust valve Vi Intake valve

Claims (7)

In a control device for an internal combustion engine that generates power by burning a mixture of fuel and air in a combustion chamber,
Air-fuel ratio determination means for performing rich / lean determination of the air-fuel ratio in the combustion chamber;
Fuel supply amount setting means for setting a fuel supply amount to the combustion chamber so that an air-fuel ratio in the combustion chamber matches a target air-fuel ratio in accordance with a determination result of the air-fuel ratio determination means;
In-cylinder pressure detecting means for detecting the in-cylinder pressure in the combustion chamber;
A combustion ratio calculating means for calculating a combustion ratio at a predetermined timing based on the in-cylinder pressure detected by the in-cylinder pressure detecting means;
Combustion start timing calculating means for calculating a combustion start timing in the combustion chamber based on a deviation between a combustion ratio calculated by the combustion ratio calculating means and a target combustion ratio;
When the air-fuel ratio determination means determines that the air-fuel ratio in the combustion chamber is rich, the combustion start timing calculated by the combustion start timing calculation means is corrected so that torque fluctuations of the internal combustion engine are suppressed. A control device for an internal combustion engine, comprising: correction means for performing the operation.   The correction means sets the correction amount to be added to the calculated value of the combustion start timing calculation means based on the fuel supply amount set by the fuel supply amount setting means. Control device for internal combustion engine.   When the air-fuel ratio determining means determines that the air-fuel ratio in the combustion chamber is rich, the output of the combustion start timing calculating means is fixed to a predetermined value, or the combustion ratio and the target value The internal combustion engine control device according to claim 1, wherein the deviation of the internal combustion engine is set to zero.   2. The control device for an internal combustion engine according to claim 1, wherein the correction unit decreases the value of the target combustion ratio so that the combustion start timing calculated by the combustion start timing calculation unit is retarded. .   The combustion ratio calculation means calculates the combustion ratio based on a product value of an in-cylinder pressure detected by the in-cylinder pressure detection means and a value obtained by raising the cylinder volume at the time of detection of the cylinder pressure by a predetermined index. The control device for an internal combustion engine according to claim 1, wherein the control device calculates the internal combustion engine.   The predetermined timing at which the combustion rate is calculated by the combustion rate calculating means is set to the first timing set after the intake valve is opened and before the start of combustion, and after the start of combustion and before the exhaust valve is opened. The combustion ratio calculation means is set between the second timing, the difference between the product values between the first timing and the second timing, the first timing, and the predetermined timing. 6. The control apparatus for an internal combustion engine according to claim 5, wherein the combustion ratio is calculated based on a difference between the product values with respect to the timing of the engine. In a control method of an internal combustion engine for generating power by burning a mixture of fuel and air in the combustion chamber,
A rich / lean determination of the air-fuel ratio in the combustion chamber is performed, and in accordance with the determination result, a fuel supply amount to the combustion chamber is set so that the air-fuel ratio in the combustion chamber matches a target air-fuel ratio, and the combustion The combustion ratio at a predetermined timing is calculated based on the in-cylinder pressure in the chamber, the combustion start timing in the combustion chamber is calculated based on the deviation between the combustion ratio and the target combustion ratio, and the air-fuel ratio in the combustion chamber is rich. And determining that the calculated combustion start timing is corrected so as to suppress torque fluctuations of the internal combustion engine.

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