JP2006144642A - Controller and control method for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller and a control method for an internal combustion engine for optimizing combustion start time in a combustion chamber satisfactorily. <P>SOLUTION: This internal combustion engine 1 for generating power by burning air-fuel mixture of fuel and air in the combustion chamber 3 is provided with a cylinder internal pressure sensor 15 for detecting cylinder internal pressure and an ECU 20. Usually, the ECU 20 calculates a combustion ratio MFB at predetermined timing based on the cylinder internal pressure detected by the cylinder internal pressure sensor 15 and sets ignition time SA so that the combustion ratio MFB agrees with a target value. When it is determined that the internal combustion engine 1 is in a transition condition, the ECU 20 estimates the optimum ignition time in the combustion chamber 3 based on load KL and the number of revolutions NE of the internal combustion engine 1, cylinder internal pressure Pe in an exhaust process, and cylinder temperature Tc at intake bottom dead center. <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.

  Conventionally, in order to set the ignition timing of the air-fuel mixture in the combustion chamber of the internal combustion engine to an optimal timing (MBT: Minimum advance for Best Torque) that can produce a large torque and does not cause knocking, A method of predicting basic ignition timing by adding a predetermined ignition delay time to the value obtained by dividing the gas weight by the basic value of unburned gas density and the basic value of laminar flame velocity, and converting the added value into a crank angle. Is known (for example, see Patent Document 1). In this method, the total gas weight, the unburned gas density basic value, and the laminar flame speed basic value are obtained based on the load (filling efficiency) and rotation speed of the internal combustion engine, the amount and density of gas, and the like. There is also known a method of advancing or retarding the ignition timing based on the combustion ratio in the combustion chamber in order to set the ignition timing of the air-fuel mixture in the combustion chamber of the internal combustion engine to an optimal timing (MBT) ( For example, see Patent Documents 2 and 3.)

Japanese Patent Laid-Open No. 10-30535 Japanese Examined Patent Publication No. 62-53710 Japanese Patent Laid-Open No. 9-189281

  However, the above-described conventional method for predicting the ignition timing requires a large number of man-hours for estimating the amount of unburned gas and the total gas amount. In this respect, this predicting method is applied to, for example, a vehicle internal combustion engine. It has been difficult in practice. If the ignition timing is set based on the combustion ratio in the combustion chamber as described above, so-called response delay may be a problem depending on the operating conditions of the internal combustion engine.

  Therefore, an object of the present invention is to provide a control device and a control method for an internal combustion engine that can favorably optimize the combustion start timing 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 relates to the load and rotation speed of the internal combustion engine and the state in the combustion chamber. Combustion start timing prediction means for predicting an optimal combustion start timing in the combustion chamber based on a predetermined parameter is provided.

  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 is a predetermined method related to the load of the internal combustion engine, the rotational speed, and the state in the combustion chamber. And a step of predicting an optimal combustion start time in the combustion chamber based on the parameters.

  According to the present invention, it is possible to realize a control device and a control method for an internal combustion engine that can favorably optimize the combustion start timing in the combustion chamber.

  In the internal combustion engine to which the control device according to the present invention is applied, the combustion start timing predicting means is operated in the combustion chamber under predetermined conditions based on predetermined parameters related to the load and rotation speed of the internal combustion engine and the state in the combustion chamber. The optimal combustion start time is predicted. Thus, by using the information in the combustion chamber in addition to the load and the rotational speed of the internal combustion engine for the prediction of the combustion start timing (spark ignition timing or compression ignition timing), the residual gas in the combustion chamber, for example, during the transition Even under unique conditions such as when the number of fuel cells increases, the combustion start time can be obtained with high accuracy.

In this case, it is preferable that the parameters include at least one of the in-cylinder pressure during the exhaust stroke and the temperature in the combustion chamber at a predetermined timing. That is, the combustion start timing prediction means preferably predicts the optimum combustion start timing (predicted value SA ′) in the combustion chamber using the following prediction formula (1). In the prediction formula (1), w _{1 to} w ₅ are coefficients determined experimentally and empirically, KL is the load (filling efficiency) of the internal combustion engine, and NE is the rotational speed of the internal combustion engine. Pe is the in-cylinder pressure during the exhaust stroke, and Tc is the temperature in the combustion chamber (in-cylinder temperature).

Specifically, the load KL and the rotational speed NE of the internal combustion engine are values at the time of prediction of the combustion start timing using the prediction formula (1), and the in-cylinder pressure Pe during the exhaust stroke is detected during the previous cycle. Is the value to be The in-cylinder temperature Tc is the temperature in the combustion chamber at the intake top dead center in the target cycle, and the value can be determined using the following equation (2). In Equation (2), P _TDC is the in-cylinder pressure at the intake top dead center, V is the V _TDC, that is, the in-cylinder volume at the intake top dead center, and M _TDC is the charged gas at the intake top dead center. It is a quantity and R is a gas constant.

  By using the prediction formula (1), it is possible to predict the combustion start timing with high accuracy. However, the terms of the predicted in-cylinder pressure Pe and in-cylinder temperature Tc in (1) above may be omitted as appropriate in accordance with the operating conditions of the internal combustion engine, the calculation load, and the like. That is, the number of terms in the prediction formula (1) for predicting the combustion start timing may be changed according to the operating conditions of the internal combustion engine.

  The control device for an internal combustion engine according to the present invention calculates an in-cylinder pressure detecting means for detecting an in-cylinder pressure in the combustion chamber, and a combustion ratio at a predetermined timing based on the in-cylinder pressure detected by the in-cylinder pressure detecting means. It is preferable to further comprise a combustion rate calculation means and a combustion start timing calculation means for calculating the combustion start timing in the combustion chamber so that the combustion ratio calculated by the combustion rate calculation means matches the target value.

  Under such a configuration, the combustion start timing is switched between the prediction of the combustion start timing described above and the calculation of the combustion start timing based on the combustion ratio in the combustion chamber (feedback control of the combustion start timing) according to the operating conditions. It is possible to always perform the optimization of the above.

  Further, when the combustion of the air-fuel mixture in the combustion chamber is started based on the combustion start timing predicted by the combustion start timing prediction means, the combustion start timing prediction means is predicted together with the combustion ratio calculated by the combustion ratio calculation means. The deviation between the combustion start timing and the combustion start timing calculated by the combustion start timing calculation means is preferably fed back to the combustion start timing calculation means.

  Under such a configuration, while the predicted value of the combustion start timing prediction means is used as the combustion start timing, the combustion start timing calculation means includes the combustion ratio calculated by the fuel ratio calculation means and the combustion start timing prediction means. The combustion start timing is continuously calculated on the basis of the deviation between the predicted value and the calculated value of the combustion start timing calculation means. As a result, so-called antiwindup can be achieved, and overshoot at the time of transition from the prediction of the combustion start time to the calculation of the combustion start time based on the combustion ratio can be reliably suppressed.

  Further, when the internal combustion engine is in a transient state, it is preferable to start the combustion of the air-fuel mixture in the combustion chamber based on the combustion start timing predicted by the combustion start timing prediction means.

  Generally, in a transient state, even if the combustion start timing is calculated based on the combustion ratio in the combustion chamber, it may be difficult to determine the optimum combustion start timing with good responsiveness. Therefore, when the internal combustion engine is in a transient state, the value predicted by the combustion start timing prediction means is determined as the combustion start timing, and the air-fuel mixture in the combustion chamber is preferably ignited or ignited. Thereby, even in a transient state, it is possible to satisfactorily optimize the combustion start timing in the combustion chamber.

  Further, the control apparatus for an internal combustion engine according to the present invention is based on the determination means for determining whether or not the deviation between the combustion ratio and the target value is within a predetermined range, and the combustion start timing calculated by the combustion start timing calculation means. Used to predict the combustion start timing by the combustion start timing predicting means when the determination means determines that the deviation between the combustion ratio and the target value is within a predetermined range after the combustion of the air-fuel mixture in the combustion chamber is started. It is preferable to further comprise means for optimizing the coefficient of the prediction formula to be obtained.

  Under such a configuration, when the calculated value of the combustion start timing calculation means is used as the combustion start timing, the combustion ratio and the target value are approximately the same, and the combustion start timing in the combustion chamber is generally optimal. If so, the coefficients of the prediction formula are optimized. Thus, when the calculation of the combustion start time using the prediction formula is executed from the state in which the calculation of the combustion start time based on the combustion ratio is executed, the combustion start time by the combustion start time prediction means It is possible to improve the prediction accuracy.

  The combustion start timing calculation means includes an integration circuit for calculating the combustion start timing based on a deviation between the combustion ratio and the target value, and a fluctuation of the combustion ratio calculated by the combustion ratio calculation means between a predetermined cycle has a predetermined value. In the case of exceeding, it is preferable to include a proportional circuit that adds a value obtained by multiplying the deviation between the combustion ratio and the target value by a predetermined gain to the output of the integrating circuit.

  By adopting such a configuration, it is possible to accurately calculate the optimal combustion start timing (spark ignition timing or compression ignition timing) while quickly converging the fluctuation of the combustion ratio between cycles.

  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. Further, in FIG. 1, the broken line is calculated and plotted as Q = ∫dQ / dθ · Δθ based on the following equation (3) for the heat generation amount 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 (4), 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 in-cylinder pressure P (θ) in accordance with the above equation (3) and the following equation (5) and the combustion ratio at the timing when the crank angle = θ in the above model cylinder. Calculated based on the above and plotted. Also in this case, for simplicity, κ = 1.32.

  Further, 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 closed and before the start of combustion, and after the start of combustion and before the exhaust valve is opened. It is preferable that the combustion ratio calculation means sets the difference between the product values between the first timing and the second timing, and between the first timing and the predetermined timing. It is preferable to calculate the combustion ratio based on the difference between the product values at.

In this case, if the crank angle at a 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. The difference {P (θ ₀ ) · V ^κ (θ ₀ ) −P (θ ₁ ) · V ^κ (θ ₁ )} is expressed as the difference between the product timing PV ^κ between the first timing and the second timing { Dividing by P (θ ₂ ) · V ^κ (θ ₂ ) −P (θ ₁ ) · V ^κ (θ ₁ )} and multiplying by 100 can be obtained. 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, 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, and the like, all not shown. As shown in FIG. 3, various sensors including the crank angle sensor 14 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. .

  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.

  As shown in FIG. 4, the ECU 20 has an integrator (integration circuit) I for setting the ignition timing of the internal combustion engine 1. The integrator I has a combustion ratio MFB and a target value (target MFB, 50% in the present embodiment) at a predetermined timing (8 ° after top dead center in the present embodiment) calculated for each cycle according to the procedure described later. The ignition timing is calculated (set) for each combustion chamber 3 on the basis of the deviation (so that the deviation is zero). In other words, the integrator I ignites the target combustion chamber 3 by adding a value obtained by multiplying the deviation between the combustion ratio MFB and the target value by a predetermined gain Ki to the previously calculated ignition timing value. Calculate the time. Thus, in the internal combustion engine 1, basically, the ignition timing is feedback controlled so that the combustion ratio MFB matches the target value, and the ignition timing in each combustion chamber 3 is set almost optimally, so that knocking does not occur. In this way, a large torque can be obtained from the internal combustion engine 1.

  In the internal combustion engine 1, the ECU 20 repeatedly executes the ignition timing setting routine shown in FIG. 5 for each combustion chamber 3. In this case, the ECU 20 first determines whether the operation state of the internal combustion engine 1 is steady (is not a transient state) based on a signal from an accelerator position sensor (not shown) that detects the depression amount (operation amount) of the accelerator pedal. It is determined whether or not (S10). When the ECU 20 determines that the operation state of the internal combustion engine 1 is steady in S10, the ECU 20 further determines whether or not the ignition timing should be feedback-controlled so that the combustion ratio MFB matches the target value (S12).

In S12, for example, a negative determination is made when the internal combustion engine 1 is started. In this case, the ECU 20 sets a predetermined ignition setting flag to “1” in S13, and then measures in S15 with an air flow meter (not shown). The load (filling efficiency) KL of the internal combustion engine 1 at that time is acquired based on the amount of intake air or the opening degree of the throttle valve 10 and the engine at that time based on the signal from the crank angle sensor 14. The rotational speed NE is acquired. Further, in S15, the ECU 20 reads out the in-cylinder pressure Pe at a predetermined timing during the exhaust stroke of the previous cycle from the predetermined storage area for the target combustion chamber 3, and increases the intake air pressure of the current cycle from the predetermined storage area. The in-cylinder pressure _PTDC at the dead point is read out, and the temperature (in-cylinder temperature) Tc in the combustion chamber 3 at the intake top dead center is obtained from the above equation (2).

Then, the ECU 20 substitutes these parameters into the prediction formula (1) to calculate a predicted value SA ′ of the ignition timing of the target combustion chamber 3 (S17). In the present embodiment, the above-described coefficients w _{1 to} w ₅ are stored in the storage device, and the ECU 20 includes a computing unit C (see FIG. 7) that calculates the predicted value SA ′ of the ignition timing. The calculator C calculates the predicted value SA ′ of the ignition timing using the load KL, the rotational speed NE, the in-cylinder pressure Pe, the in-cylinder temperature Tc, and the coefficients w _{1 to} w ₅ acquired in S15. Note that, in S13 and S15, in a case that can not get the pressure Pe and cylinder pressure P _TDC in the cylinder if it does not already exist, these values are set to "zero", the cylinder pressure in the prediction equation (1) Terms for Pe and in-cylinder temperature Tc are omitted. When the ignition timing SA ′ thus set arrives, as will be described in detail later, ignition by the spark plug 7 is executed in the target combustion chamber 3 (see S22), and further ignition is executed. A combustion ratio MFB at a predetermined timing is calculated for the combustion chamber 3 (see S24).

  On the other hand, if it is determined in S12 that the ignition timing should be feedback controlled based on the combustion ratio MFB, the ECU 20 sets (maintains) the ignition setting flag to “0” in S14. Further, the integrator I of the ECU 20 calculates the ignition timing of the target combustion chamber 3 based on the deviation between the combustion ratio MFB calculated during the previous cycle and the target value (target MFB = 50%) in S24. (S16). Further, the ECU 20 determines whether or not the predetermined proportional term flag is “1” (S18). When it is determined in S18 that the proportional term flag is “1”, the proportional term is added (added) to the output of the integrator I, and the value obtained by adding the proportional term to the output of the integrator I is the ignition timing. It is set as SA (S20).

  That is, as shown in FIG. 4, the ECU 20 has a proportional circuit P that multiplies the deviation between the combustion ratio MFB and the target value by a predetermined gain Kp, and when the proportional term flag is “1”, The switch S in FIG. 4 is turned on, whereby the proportional term Kp × (target MFB−combustion ratio MFB) is added to the output of the integrator I (S20). When it is determined that the proportional term flag is “0”, the process of S18 is skipped and the output of the integrator I is set as the ignition timing SA as it is. When the ignition timing SA set in this way arrives, ignition by the spark plug 7 is executed in the target combustion chamber 3 (S22).

When ignition by the spark plug 7 is executed in S22, the ECU 20 calculates a combustion ratio MFB at a predetermined timing for the combustion chamber 3 in which ignition has been executed, and stores it in a predetermined storage area (S24). When calculating the combustion ratio MFB at S24, ECU 20, first, from a predetermined storage area for the combustion chamber 3 to be, first timing (crank angle before closing after and ignition of the intake valve Vi is theta 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. Further, the first timing θ ₁ , the second timing θ _2, and the threshold value γ may be set according to the engine speed and the load. In this case, the first timing θ ₁ , the second timing A map that defines θ ₂ and the threshold value γ according to the rotational speed and load of the internal combustion engine 1 may be prepared.

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 (6) (S24). 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.

The ECU 20 determines whether or not the above-described ignition setting flag is “0” after the processing of S24 (S26). When it is determined in S26 that the ignition setting flag is “0” and the ignition timing SA is set based on the combustion ratio MFB, the ECU 20 is at least one cycle before (preferably, stored in a predetermined storage area). Read out the combustion rate MFB _old of several cycles before), and calculates the absolute value ΔMFB of the deviation between the combustion rate MFB calculated in S24 and the combustion rate MFB _old (S28). Further, the ECU 20 determines whether or not ΔMFB calculated in S28 is below a predetermined threshold (positive predetermined value) ε (S30). When it is determined in S30 that ΔMFB is below the threshold ε, the ECU 20 sets the proportional term flag to “0” (S32). If the ECU 20 determines that ΔMFB is greater than or equal to the threshold value ε in S30 and the change in the combustion ratio between cycles is large, the ECU 20 sets the proportional term flag to “1” (S34).

After the processing of S32 or S34, the ECU 20 determines that the absolute value | MFB-50 | obtained by subtracting the target value “50%” from the combustion ratio MFB obtained in S24 is a predetermined threshold (positive predetermined value). It is determined whether or not γ or less (S36). That is, in S36, a combustion ratio MFB at the time when the crank angle calculated in S24 becomes θ _{0 =} 8 °, the theoretical value of the combustion rate when the crank angle becomes θ _{0 =} 8 ° (target value) 50 A deviation from (%) is obtained, and it is determined whether or not the deviation is equal to or smaller than a threshold γ and whether or not the deviation is equal to or larger than −γ.

When the ECU 20 determines in S36 that | MFB-50 | is equal to or less than the threshold value γ and the ignition timing SA calculated based on the combustion ratio MFB is substantially optimal, the successive least squares method ( RLS) is used to optimize the coefficients w _{1 to} w ₅ of the prediction formula (1) for predicting the ignition timing (S38). In S38, the ECU 20 determines the load (filling efficiency) KL and engine speed NE of the internal combustion engine 1 when calculating the ignition timing in S16, the in-cylinder pressure Pe at a predetermined timing during the exhaust stroke of the previous cycle, and the current cycle. The in-cylinder temperature Tc at the intake top dead center is acquired (note that these parameters are substantially the same as those acquired in S15). Then, the ECU 20 performs coefficients w _{1 to} w satisfying the ignition timing SA used in S20 under the load KL, the rotational speed NE, the in-cylinder pressure Pe, and the in-cylinder temperature Tc by a sequential least square method. ₅ is updated, and the coefficients w _{1 to} w ₅ stored in the storage device are updated with the new values calculated in S38.

As described above, in the internal combustion engine 1, when the ignition timing SA calculated by the ECU 20 (integrator I or the like) is used, the combustion ratio MFB and the target value (50%) substantially coincide, and the target combustion chamber When it is determined that the ignition timing SA at 3 is almost optimal, the coefficients w _{1 to} w ₅ of the prediction formula (1) are optimized and updated (S38). As a result, when the ignition timing SA ′ using the prediction formula (1) is predicted from the state where the ignition timing SA is calculated based on the combustion ratio MFB, the ignition timing SA ′ is calculated. The prediction accuracy can be improved. If it is determined in S26 that the ignition setting flag is “1”, the processing from S28 to S38 described above is skipped.

  After the execution of the process of S38 or when a negative determination is made in S26, the ECU 20 executes the processes after S10 described above again. Here, in S30, ΔMFB is equal to or greater than the threshold value ε, and it is determined that the variation in the combustion ratio between cycles is large. If the proportional term flag is set to “1” in S34, S10 and S12 are performed. In S18 after each affirmative determination is made at, it is determined that the proportional term flag is “1”. Accordingly, in this case, the next processing of S20 is executed, and a value obtained by adding a proportional term to the output of the integrator I is set as the ignition timing SA. Thereby, in the internal combustion engine 1, when the fluctuation of the combustion rate MFB between cycles is large, it is possible to quickly converge it and calculate the optimal ignition timing with high accuracy.

  FIG. 6 is a flowchart for explaining the procedure for setting the ignition timing when it is determined in S10 that the internal combustion engine 1 is in a transient state. As shown in FIG. 6, even when it is determined in S10 that the internal combustion engine 1 is in a transient state, the integrator I of the ECU 20 calculates the combustion ratio MFB and the target value (target MFB = target MFB = calculated during the previous cycle). 50%), the ignition timing SA is calculated for the target combustion chamber 3 and stored in a predetermined storage area (S40). However, when the internal combustion engine 1 is in a transient state, the ignition timing SA calculated in S40 is invalid and is not used as the actual ignition timing. After the process of S40, the above-described prediction formula (1) is obtained. Using this, the ignition timing SA ′ is obtained (S42, S44).

  In other words, in a transient state, even when the ignition timing SA is calculated based on the combustion ratio MFB in the combustion chamber 3, it may be difficult to determine the optimum ignition timing with good responsiveness. On the other hand, in addition to the load KL and the rotational speed NE of the internal combustion engine 1, by using the prediction formula (1) using information in the combustion chamber 3 such as the in-cylinder pressure Pe and the in-cylinder temperature Tc as parameters, Appropriate ignition timing can be obtained with high accuracy even under special conditions such as when the residual gas in the combustion chamber 3 increases during the transition. Therefore, when it is determined in S10 that the internal combustion engine 1 is in a transient state, the value SA ′ calculated using the prediction formula (1) is determined as the ignition timing, and thereby the ignition in the combustion chamber 3 is determined. It becomes possible to optimize the time well.

In S42, the ECU 20 acquires the load (filling efficiency) KL of the internal combustion engine 1 at that time based on the intake air amount measured by an air flow meter (not shown) or the opening degree of the throttle valve 10, and the crank angle. Based on the signal from the sensor 14, the engine speed NE at that time is acquired. Further, in S42, the ECU 20 reads out the in-cylinder pressure Pe at a predetermined timing during the exhaust stroke of the previous cycle from the predetermined storage area for the target combustion chamber 3, and increases the intake air pressure of the current cycle from the predetermined storage area. The in-cylinder pressure _PTDC at the dead point is read out, and the temperature (in-cylinder temperature) Tc in the combustion chamber 3 at the intake top dead center is obtained from the above equation (2).

Then, the ECU 20 (calculator C) substitutes these parameters into the prediction formula (1) to calculate the predicted value SA ′ of the ignition timing of the target combustion chamber 3 (S44). Also step S42 and S44, in a case that can not get the pressure Pe and cylinder pressure P _TDC in the cylinder if it does not already exist, these values are set to "zero", the cylinder in the prediction equation (1) The terms of pressure Pe and in-cylinder temperature Tc are omitted. When the ignition timing SA ′ thus set arrives, ignition by the spark plug 7 is executed in the target combustion chamber 3 (S46).

  When ignition is executed in the target combustion chamber 3 in S46, the combustion ratio MFB at a predetermined timing is calculated for the combustion chamber 3 in S48, and the calculated combustion ratio MFB is shown in FIG. Thus, the feedback is made to the integrator I. Then, after S48, when the ignition timing SA ′ calculated using the prediction formula (1) in S44 and the ignition timing SA calculated by the integrator I in S40 do not coincide with each other within a predetermined range. The switch S2 in FIG. 7 is turned on to the right side in the figure, the deviation (SA′−SA) between them is obtained, and a value obtained by multiplying the calculated deviation (SA′−SA) by a predetermined gain Ke is shown in FIG. As shown in FIG. 5, the feedback is fed back to the integrator I (S50). When the ignition timing SA ′ and SA are substantially equal (SA′≈SA), the switch S2 in FIG. 7 is turned on on the left side in the figure, and the deviation here is (SA−SA), that is, “zero”. Is calculated. Therefore, in this case, the feedback amount to the integrator I becomes zero, and only integration control is performed.

  Thereby, it is determined in S10 that the internal combustion engine 1 is in a transient state, and while the value SA ′ calculated using the prediction formula (1) is used as the ignition timing, the integrator I determines in S48 of the previous cycle. Thus, the ignition timing SA is continuously calculated based on the combustion ratio MFB calculated in this way and the deviation between the ignition timing SA ′ calculated in S50 of the previous cycle and the ignition timing SA. As a result, so-called antiwindup can be achieved, and the processing of the ECU 20 determines the ignition timing based on the combustion ratio MFB from the prediction (S40 to S50) of the ignition timing SA ′ using the prediction formula (1). It is possible to reliably suppress overshoot when shifting to calculation (S14 to S38).

  After the process of S50, the ECU 20 executes the processes after S10 described above again. Thereby, in the internal combustion engine 1, the calculation of the ignition timing based on the combustion ratio MFB (S14 to S38) and the prediction of the ignition timing SA ′ using the prediction formula (1) (S40 to S50) according to the operating conditions. As a result, the ignition timing can be optimized at all times.

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. It is a control block diagram for demonstrating the setting of the ignition timing by the control apparatus by this invention. It is a flowchart for demonstrating the control procedure of the ignition timing by the control apparatus by this invention. It is a flowchart for demonstrating the control procedure of the ignition timing by the control apparatus by this invention. It is a control block diagram for demonstrating the setting of the ignition timing by the control apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 3 Combustion chamber 7 Spark plug 10 Throttle valve 12 Injector 14 Crank angle sensor 15 In-cylinder pressure sensor 20 ECU
Ve exhaust valve Vi intake valve C computing unit I integrator

Claims (10)

In a control device for an internal combustion engine that generates power by burning a mixture of fuel and air in a combustion chamber,
An internal combustion engine comprising combustion start timing prediction means for predicting an optimal combustion start timing in the combustion chamber based on a predetermined parameter related to a load and a rotation speed of the internal combustion engine and a state in the combustion chamber. Control device.   2. The control device for an internal combustion engine according to claim 1, wherein the parameter includes at least one of an in-cylinder pressure during an exhaust stroke and a temperature in the combustion chamber at a predetermined timing. 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;
The combustion start timing calculation means for calculating the combustion start timing in the combustion chamber so that the combustion ratio calculated by the combustion ratio calculation means coincides with a target value. Control device for internal combustion engine.   When the combustion of the air-fuel mixture in the combustion chamber is started based on the combustion start timing predicted by the combustion start timing prediction means, the combustion start timing prediction means predicts together with the combustion ratio calculated by the combustion ratio calculation means. 4. The control apparatus for an internal combustion engine according to claim 3, wherein a deviation between the combustion start timing calculated and the combustion start timing calculated by the combustion start timing calculation means is fed back to the combustion start timing calculation means.   5. The internal combustion engine according to claim 3, wherein when the internal combustion engine is in a transient state, combustion of the air-fuel mixture in the combustion chamber is started based on the combustion start timing predicted by the combustion start timing prediction unit. Engine control device. Determination means for determining whether a deviation between the combustion ratio and the target value is within a predetermined range;
After the start of combustion of the air-fuel mixture in the combustion chamber based on the combustion start timing calculated by the combustion start timing calculation means, the deviation between the combustion ratio and the target value is within a predetermined range by the determination means. 6. The apparatus according to claim 3, further comprising: means for optimizing a coefficient of a prediction formula used for prediction of the combustion start timing by the combustion start timing prediction means when it is determined that Control device for internal combustion engine.   The combustion start timing calculation means includes an integration circuit that calculates a combustion start timing based on a deviation between the combustion ratio and the target value, and a fluctuation of the combustion ratio calculated by the combustion ratio calculation means between predetermined cycles is predetermined. 7. A proportional circuit that adds a value obtained by multiplying a deviation between the combustion ratio and the target value by a predetermined gain to the output of the integration circuit when the value exceeds the value. A control device for an internal combustion engine according to claim 1.   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 3, 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 a first timing set after the intake valve is closed 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. 9. The control apparatus for an internal combustion engine according to claim 8, 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 method for controlling an internal combustion engine, comprising: predicting an optimal combustion start timing in the combustion chamber based on predetermined parameters related to a load, a rotational speed of the internal combustion engine, and a state in the combustion chamber.

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