JP2000265873A - Combustion control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothen a transfer from spark ignition combustion to self ignition combustion and to perform stable combustion till an engine warming state after the engine is started by exactly predicting warming state of the engine forming self ignition combustion. SOLUTION: An ECU 1 controlling an engine 10 is provided with a combustion switching part 2 switching a spark ignition control and a compression self ignition control. The combustion switching part 2 is provided with a cylinder pressure acquiring part 3 predicting cylinder pressure in the vicinity of a compression top dead center, a cylinder temperature acquiring part 4 predicting a cylinder temperature in the vicinity of the compression top dead center and a combustion form judging part 5 judging the formation or non-formation of a compression self ignition combustion condition based on cylinder pressure and the cylinder temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a combustion control device for an internal combustion engine, and more particularly to a combustion control device for an internal combustion engine that can switch between spark ignition combustion and compression self-ignition combustion.

[0002]

2. Description of the Related Art In order to improve the thermal efficiency of a gasoline engine, the theoretical thermal efficiency is improved by reducing the intake throttle by a throttle valve and making the air-fuel mixture lean, thereby reducing the pump loss and increasing the specific heat ratio of the working gas. There are known techniques for improving the quality. However, in the conventional spark ignition engine, when the air-fuel ratio is made lean, the combustion period becomes longer, and the combustion stability deteriorates. For this reason, there is a limit to lean air-fuel ratio.

As means for solving the above problem, Japanese Patent Laid-Open No.
As disclosed in JP-A-71279, means for causing homogeneous charge compression auto-ignition combustion is proposed. This is because in a two-cycle engine, an exhaust control valve capable of controlling the opening degree of the exhaust port is provided near the exhaust port, and by controlling the exhaust control valve, the in-cylinder pressure is controlled to cause self-ignition combustion. I have.

In a gasoline engine, when the in-cylinder pressure and the in-cylinder temperature increase to some extent near the compression top dead center,
The air-fuel mixture in the combustion chamber is activated and becomes very easily ignited, and even without spark ignition, self-ignition occurs at a plurality of points in the combustion chamber and combustion spreads rapidly. Accordingly, even when the air-fuel ratio is lean, the combustion period is not prolonged as compared with spark ignition, and stable combustion at a leaner air-fuel ratio is possible. Further, since the air-fuel ratio is lean, the combustion temperature decreases, and NOx can be significantly reduced.

[0005]

The self-ignition combustion is strongly influenced by the cylinder pressure and the cylinder temperature in addition to the air-fuel ratio. When the cylinder pressure and the cylinder temperature decrease, the combustion becomes unstable. , Driving performance deteriorates. Therefore, it is necessary to shift to self-ignition combustion after engine warm-up as spark ignition combustion during warm-up after engine start.

However, in the prior art, since the engine warm-up state is not determined according to the in-cylinder pressure and the in-cylinder temperature, it is difficult to optimally switch between self-ignition combustion and spark ignition combustion. However, there has been a problem that the driving performance becomes unstable and the driving performance deteriorates.

In the case of self-ignition combustion, a high compression ratio is set because the required in-cylinder pressure and in-cylinder temperature are high. The air-fuel ratio is lean to suppress knocking and the like. For these reasons, there has been a problem that the temperature of the exhaust gas decreases during self-ignition combustion, activation of the catalyst is delayed, and emission deteriorates.

As a countermeasure, the ignition timing is retarded,
A method of raising the exhaust gas temperature by slowing down the combustion is used. However, in self-ignition combustion in which the combustion period is short and the combustion position is near top dead center, it is difficult to increase the retard amount at the combustion position, and the effect of increasing the exhaust gas temperature is small.

In a conventional example, Japanese Patent Application Laid-Open No. 62-51727, the exhaust gas temperature is raised by reducing the amount of air and enriching the air-fuel ratio. However, in this method, when the amount of air is reduced, the in-cylinder pressure decreases. In self-ignition combustion that is strongly affected by in-cylinder pressure, the self-ignition combustion becomes unstable when the in-cylinder pressure decreases, so that there is a problem that operability deteriorates.

Japanese Patent Application Laid-Open No. Hei 8-296463 proposes a technique in which the compression ratio is made variable by a variable valve timing mechanism. However, in this conventional example, the compression ratio is reduced on the high load side to suppress knocking, and the compression ratio is high on the low load side. For this reason, there has been a problem that the exhaust gas temperature generally drops immediately after the start, in which low-load operation such as idling is common, and the activation of the catalyst is delayed.

The present invention has been made in view of the above problems, and accurately predicts a warm-up state of an engine in which self-ignition combustion is established from in-cylinder pressure and in-cylinder temperature. The object of the present invention is to provide an internal combustion engine in which the transition to the internal combustion engine becomes smooth and stable combustion can be realized from the start of the engine until the engine is warmed up.

It is another object of the present invention to provide a clean internal combustion engine that controls self-ignition combustion during warming-up of a catalyst, raises the temperature of exhaust gas, activates the catalyst early, and reduces emissions. .

[0013]

According to the first aspect of the present invention,
In order to solve the above problems, in a combustion control apparatus for an internal combustion engine capable of switching between spark ignition combustion and compression self-ignition combustion,
In-cylinder pressure acquisition means for measuring or predicting in-cylinder pressure near compression top dead center, in-cylinder temperature acquisition means for measuring or predicting in-cylinder temperature near compression top dead center, the in-cylinder pressure and the in-cylinder And a combustion mode determining unit configured to determine whether the compression self-ignition combustion condition is satisfied or not based on the temperature.

According to a second aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to the first aspect, wherein the in-cylinder pressure obtaining means is based on an intake pressure, a compression ratio, and an engine temperature. The gist is that the in-cylinder pressure is predicted and the in-cylinder temperature obtaining means predicts the in-cylinder temperature based on the intake air temperature, the compression ratio, and the engine temperature.

According to a third aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to the first or second aspect, wherein the catalyst for purifying exhaust gas and the catalyst for estimating the activity of the catalyst are provided. An activity estimating unit and a compression ratio changing unit for changing a compression ratio of the internal combustion engine, further comprising: when the catalyst activity estimating unit does not estimate that the catalyst has been activated, the compression ratio changing unit changes the compression ratio of the internal combustion engine. The gist of the present invention is to change the compression ratio to a lower compression ratio than the basic compression ratio and perform compression self-ignition combustion.

According to a fourth aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to the first or second aspect, wherein the catalyst for purifying exhaust gas and the catalyst for estimating the activity of the catalyst are provided. An activity estimating means, and an expansion ratio changing means for changing an expansion ratio of the internal combustion engine, further comprising: when the catalyst activity estimating means does not estimate that the catalyst has been activated, the expansion ratio changing means changes the internal combustion engine. The gist of the present invention is to perform compression auto-ignition combustion by changing the expansion ratio to a lower expansion ratio than the basic expansion ratio.

According to a fifth aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to the first or second aspect, wherein the catalyst for purifying exhaust gas and the catalyst for estimating the activity of the catalyst are provided. And an activity estimating means, wherein when the catalyst activity estimating means does not estimate that the catalyst has been activated, the compression self-ignition combustion is prohibited and the spark ignition combustion is performed.

According to a sixth aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to the third aspect of the present invention, further comprising a catalyst conversion rate estimating means for estimating a catalyst conversion rate of the catalyst. When the catalyst conversion rate estimated by the catalyst conversion rate estimation means falls below a predetermined level,
The gist of the present invention is to perform compression auto-ignition combustion at a compression ratio lower than the basic compression ratio.

According to a seventh aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to the fourth aspect, further comprising a catalyst conversion rate estimating means for estimating a catalyst conversion rate of the catalyst. When the catalyst conversion rate estimated by the catalyst conversion rate estimation means falls below a predetermined level,
The gist is to perform compression self-ignition combustion at a lower expansion ratio than the basic expansion ratio.

According to an eighth aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine according to any one of the first to fifth aspects, wherein a catalyst conversion rate of the catalyst is estimated. When the catalyst conversion rate estimated by the catalyst conversion rate estimation means falls below a predetermined level, compression self-ignition combustion is prohibited and spark ignition combustion is performed. .

[0021]

According to the first aspect of the present invention, there is provided a combustion control apparatus for an internal combustion engine capable of switching between spark ignition combustion and compression self-ignition combustion. Measuring or predicting the internal pressure, measuring or predicting the in-cylinder temperature near the compression top dead center by the in-cylinder temperature acquisition means, based on the in-cylinder pressure and the front in-cylinder temperature, establishment of the compression self-ignition combustion condition or Since the failure is determined, the condition under which the self-ignition combustion stably occurs can be accurately predicted, and the combustion state can be smoothly shifted from the spark ignition combustion to the self-ignition combustion. Therefore, stable combustion can be performed from after the engine is started until after the engine is warmed up, and it is possible to significantly reduce fuel consumption and purify exhaust gas without impairing drivability.

According to the second aspect of the present invention, in addition to the effect of the first aspect, the in-cylinder pressure obtaining means is configured to control the cylinder pressure based on an intake pressure, a compression ratio, and an engine temperature. The cylinder pressure is predicted based on the intake air temperature, the compression ratio, and the engine temperature. Therefore, the cylinder pressure is directly detected based on the intake temperature, the compression ratio, and the engine temperature. Without using an expensive in-cylinder pressure sensor or an in-cylinder temperature sensor that directly detects the in-cylinder temperature, it is possible to accurately predict the conditions under which auto-ignition combustion occurs stably and to achieve high durability. An accurate and inexpensive combustion control device for an internal combustion engine can be provided.

According to the third aspect of the present invention, in addition to the effect of the first or second aspect of the present invention, when it is not estimated that the catalyst for purifying exhaust gas has been activated,
Since the compression ratio changing means changes the compression ratio of the internal combustion engine to a lower compression ratio than the basic compression ratio to perform compression self-ignition combustion, the change in the compression ratio raises the temperature of the exhaust gas and promptly activates the catalyst. And the time required for exhaust gas to be sufficiently purified can be shortened.

According to the present invention, in addition to the effects of the first and second aspects of the present invention, when the catalyst for purifying exhaust gas is not estimated to be activated,
The expansion ratio changing means changes the expansion ratio of the internal combustion engine to a lower expansion ratio than the basic expansion ratio to perform the compression self-ignition combustion. And the time required for exhaust gas to be sufficiently purified can be shortened.

According to the fifth aspect of the present invention, in addition to the effects of the first and second aspects of the present invention, when the catalyst for purifying exhaust gas is not estimated to be activated,
Since the compression self-ignition combustion is prohibited and the spark ignition combustion is performed, the temperature of the exhaust gas can be increased, the catalyst can be quickly activated, and the time until the exhaust gas is sufficiently purified can be shortened.

According to the sixth aspect of the present invention, in addition to the effect of the third aspect, when the catalyst conversion rate estimated by the catalyst conversion rate estimation means falls below a predetermined level. However, since compression auto-ignition combustion is performed at a compression ratio lower than the basic compression ratio, when the catalyst temperature decreases due to low load operation after the catalyst has been activated, the catalyst conversion rate decreases. Also, by changing the compression ratio, the temperature of the exhaust gas can be raised, the conversion of the catalyst can be raised quickly, and the time until the exhaust gas is sufficiently purified can be shortened.

According to the present invention, in addition to the effect of the fourth aspect, when the catalyst conversion rate estimated by the catalyst conversion rate estimation means falls below a predetermined level, Since the compression auto-ignition combustion is performed at a lower expansion ratio than the basic expansion ratio, even when the catalyst temperature is lowered due to low load operation after the catalyst is once activated, the catalyst conversion rate is also reduced. By changing the expansion ratio, the temperature of the exhaust gas can be raised, the conversion of the catalyst can be quickly raised, and the time until the exhaust gas is sufficiently purified can be shortened.

According to the present invention, in addition to the effects of claims 1 to 5, the catalyst conversion rate estimated by the catalyst conversion rate estimating means is reduced below a predetermined level. In this case, compression self-ignition combustion is prohibited and spark ignition combustion is performed, so if the catalyst temperature decreases due to low load operation after the catalyst has been activated once, and the catalyst conversion rate decreases, Also raises the temperature of the exhaust,
The conversion rate of the catalyst can be quickly increased, and the time until exhaust gas is sufficiently purified can be shortened.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings. [First Embodiment] FIG. 1 is a system configuration diagram showing a first embodiment of a combustion control apparatus for an internal combustion engine according to the present invention and a configuration of an engine to be controlled. 1, an engine 10 includes an intake valve 11, an exhaust valve 12, a piston 13, an intake pressure sensor 14 for detecting a pressure in an intake pipe, and an intake temperature sensor 1 for detecting a temperature in the intake pipe.
5, a water temperature sensor 16 for detecting a cooling water temperature, a fuel injection device 17 for injecting fuel into an intake pipe, and a spark plug 18
And The fuel injection device 17 may be installed at a position where the fuel is directly injected into the cylinder.

An electronic control unit (hereinafter abbreviated as ECU) 1 for controlling the engine 10 is composed of, for example, a microcomputer having an external or built-in memory for storing programs and various control maps, and an intake pressure sensor. 14, a combustion injection amount and an ignition timing are calculated based on signals from the intake air temperature sensor 15 and the water temperature sensor 16, and signals are sent to the combustion injection device 17 and the spark plug 18 based on the calculation results.

The ECU 1 further includes a combustion switching unit 2 for switching between spark ignition control and compression self-ignition control, which is a feature of the present invention. The combustion switching unit 2 controls the in-cylinder pressure near the compression top dead center. An in-cylinder pressure acquiring unit 3 as an in-cylinder pressure acquiring unit for predicting; an in-cylinder temperature acquiring unit 4 as an in-cylinder temperature acquiring unit for predicting an in-cylinder temperature near the compression top dead center; A combustion mode determination unit 5 is provided as a combustion mode determination unit that determines whether the compression self-ignition combustion condition is satisfied or not based on the in-cylinder temperature.

FIG. 2 is a flowchart showing a schematic flow of the combustion control of the present embodiment, which is realized, for example, as a program of a microcomputer constituting the ECU 1.

First, step 10 (hereinafter, step is referred to as S
, The intake pressure sensor 14 and the intake temperature sensor 15
The intake air pressure, intake air temperature, and cooling water temperature are measured by the water temperature sensor 16. Then, using the measured pressure and temperature, the in-cylinder pressure near the compression top dead center is predicted (S
11) Similarly, the in-cylinder temperature near the compression top dead center is predicted (S12).

Next, based on the in-cylinder pressure and the in-cylinder temperature, a combustion mode determination for determining whether or not the compression self-ignition combustion condition is satisfied is performed (S13). And
If the compression self-ignition combustion condition is not satisfied according to the determination result of S13, the spark ignition combustion control is started (S1).
4) If the compression self-ignition combustion condition is satisfied, the self-ignition combustion control is started (S15). S10 to S1 above
The routine of No. 5 is started before the engine is started and at regular intervals after the engine is started, and the combustion mode can be switched according to the determination result of S13.

Here, the range in which the self-ignition combustion is established will be described. FIG. 3 is a diagram showing the air-fuel ratio at which self-ignition is established with respect to the in-cylinder pressure and the in-cylinder temperature at the compression top dead center. Auto-ignition combustion is strongly affected by in-cylinder pressure and in-cylinder temperature. When the top dead center cylinder pressure and the top dead center cylinder temperature are taken as the cylinder pressure, self-ignition combustion is not established unless the pressure and the temperature exceed a certain value. Also, the higher the pressure and temperature,
The air-fuel ratio becomes lean.

FIG. 6 shows the target air-fuel ratio with respect to the engine speed and the torque. The air-fuel ratio becomes richer as the torque and the rotation speed increase. After the engine is started, low-speed operation and low-load operation such as idling are often performed, and the target air-fuel ratio is lean. Therefore, in order to shift to self-ignition combustion, the engine warms up,
It is necessary that the pressure and temperature in the cylinder are above a certain level.

Here, the engine cooling water temperature is taken as the engine temperature. FIG. 4 shows the compression start cylinder temperature with respect to the intake air temperature and the cooling water temperature. When the temperature of the engine is low, the fresh air cannot be warmed, so that the compression start temperature decreases. Therefore, the higher the intake air temperature and the cooling water temperature, the higher the temperature in the compression start cylinder, and the lower the intake air temperature and the cooling water temperature, the lower the compression start cylinder temperature.

FIG. 5 shows the compression start cylinder pressure with respect to the intake pressure and the cooling water temperature. For the same reason as the compression start temperature, the higher the intake pressure and cooling water temperature, the higher the compression start cylinder pressure, and the lower the intake pressure and cooling water temperature, the lower the compression start cylinder pressure. The means for calculating the temperature of the engine may be the oil temperature or the time after starting, in addition to the cooling water temperature.

If the compression start cylinder pressure P1 and the compression start cylinder temperature T1 are known, and if the compression process is a polytrope change, the cylinder pressure P2 at the compression top dead center and the cylinder temperature T2 at the compression top dead center are as follows. It can be calculated from equations (1) and (2).

[0040]

P1 = Pin × ε ＾ n (1) T2 = Tin × ε ＾ (n−1) (2) where ε is a compression ratio, n is a polytope index, and X ＾
Y represents X to the power of Y.

As described above, when the cooling water temperature is taken as the engine temperature, the cylinder pressure and the cylinder temperature at the compression top dead center can be predicted from the intake pressure, the intake temperature, and the cooling water temperature. It is possible to predict a warm-up state of the engine as a condition. As a result, the conditions for establishing the self-ignition combustion can be accurately predicted, and the switching between the self-ignition combustion and the spark ignition combustion can be smoothly performed after the start of the engine.

The operation of the first embodiment described above will be described with reference to the flowchart of FIG. First,
In S20, the required engine speed N and the required torque T are detected. Next, in S21, a target air-fuel ratio is calculated from a map of the engine speed N and the torque T as shown in FIG.

Next, at S22, the intake pressure Pin and the intake air temperature Tin
Is detected, and the cooling water temperature Tw is detected in S23. Next, in S24, the compression start in-cylinder pressure P1 and the compression start in-cylinder temperature T1 are calculated from the cooling water temperature Tw, the intake pressure Pin, and the intake temperature Tin using a map as shown in FIGS.

Next, in step S25, the compression top dead center pressure P2 and the compression top dead center temperature T2 are calculated from the compression start in-cylinder pressure P1 and the compression start in-cylinder temperature T1 using equations (1) and (2). . Here, the polytropic index is, for example, n = 1.33.
Further, the polytropic index may be given from the engine speed, torque or target air-fuel ratio.

Next, the combustion mode is determined by comparing the target air-fuel ratio calculated in S21 with the air-fuel ratio of self-ignition combustion determined by the compression top dead center pressure P2 and the compression top dead center temperature T2 (S2).
6). If the target air-fuel ratio is leaner than the self-ignition stability limit air-fuel ratio, the combustion becomes unstable during self-ignition, and the process proceeds to S27 to perform spark ignition combustion. If the target air-fuel ratio is richer than the self-ignition stability limit air-fuel ratio, self-ignition becomes possible.
Proceed to 8 to perform self-ignition combustion.

As described above, by controlling, the combustion mode can be optimally controlled in accordance with the warm-up state of the engine, and the fuel efficiency and exhaust gas can be improved without impairing drivability.

As a modification of the present embodiment, a cylinder pressure sensor and a cylinder temperature sensor are provided to measure the pressure and temperature in the cylinder directly in synchronization with the crank angle detected by the crank angle sensor, for example. From the measurement result, the in-cylinder pressure and the in-cylinder temperature near the top dead center may be obtained. When the pressure and temperature in the cylinder are directly measured in this way, near the top dead center, the change in the volume of the combustion chamber with respect to the crankshaft rotation angle is small. Even if there is an error of several degrees in the rotation angle, it hardly affects the measurement accuracy.

[Second Embodiment] Next, a second embodiment of the present invention will be described. FIG. 8 shows the configuration of the second embodiment. The configuration of the second embodiment is different from the configuration of the first embodiment shown in FIG. 1 in that a catalyst 20 for purifying emissions in an exhaust system and a catalyst temperature sensor 21 for measuring a catalyst temperature.
And a catalyst activity estimating unit 6 are added.

In this embodiment, when the self-ignition combustion after engine warm-up is established, the catalyst activity is predicted and
When the catalytic activity is delayed, spark ignition combustion is performed by prohibiting self-ignition combustion.

FIG. 9 is a graph showing a comparison of exhaust gas temperatures of spark ignition combustion and self-ignition combustion. The self-ignition combustion has a shorter combustion period than the spark ignition combustion, and the combustion ends near the top dead center. Therefore, the thermal efficiency is high and the exhaust gas temperature is extremely low. Therefore, if the low-load operation continues even after the engine warm-up, the activity of the catalyst is delayed, and the emission deteriorates.

After the activation of the catalyst, the rate of increase in the catalyst temperature increases due to heat generated by the chemical reaction in the catalyst section (FIG. 10). Therefore, before the catalyst is activated, the exhaust gas temperature is raised as spark ignition combustion to promote the catalytic activity, and after the catalyst is activated, autoignition combustion is performed.

When the catalyst temperature is used as an index indicating the catalyst activity, as shown in FIG. 10, before the catalyst temperature after the engine warm-up reaches the activation temperature (T50), under the condition that the self-ignition combustion is established. Also prohibits self-ignition combustion and performs spark ignition combustion.

The operation of the second embodiment described above is described with reference to FIG.
This will be described with reference to the flowchart of FIG. In S30, the warm-up state of the engine is determined. When the engine is warming up, spark ignition combustion is performed in S31. If the engine has been warmed up, the process proceeds to S32, where the catalyst temperature sensor 21 detects the catalyst temperature (Tcat). Next, in S33, the catalyst activity is determined by the catalyst activity estimation unit 6. If the catalyst temperature Tcat is lower than the catalyst activation temperature (T50), it is determined that the catalyst is not active, and spark ignition combustion is performed in S31. Where T
50 is, for example, T50 = 200 ° C. Catalyst temperature Tcat
Is higher than the catalyst activation temperature (T50), it is determined that the catalyst has been activated, and self-ignition combustion is performed in S34.

As described above, by estimating the catalyst activity and optimally controlling the combustion mode depending on the catalyst activation state, the catalyst can be activated early and emission can be reduced.

[Third Embodiment] Next, a third embodiment of the present invention will be described. The configuration of the third embodiment is shown in FIG.
Is the same as that of the second embodiment shown in FIG. In the present embodiment, the catalyst activity is determined by the target catalyst temperature and the catalyst temperature sensor 21.
Is determined from the difference from the measured catalyst temperature.

FIG. 12 is a graph showing the change in the catalyst temperature with respect to the elapsed time after the start. Before the catalyst activity where the catalyst temperature Tcat is lower than the catalyst activation temperature T50, the difference ΔTcat between the target catalyst temperature T0 and the catalyst temperature Tcat is calculated to predict the catalyst activity. If ΔTcat is larger than the determination value, it is determined that the activity of the catalyst is delayed, so that self-ignition combustion is prohibited, spark ignition combustion is performed, and the exhaust gas temperature is raised.
On the other hand, if ΔTcat is smaller than the judgment value, the catalyst is judged to be activated as intended, and self-ignition combustion is performed to improve fuel efficiency.

The operation of the third embodiment described above will be described with reference to the flowchart of FIG. S4
Steps from 0 to S43 are the same as the flowchart of the second embodiment shown in FIG. In the present embodiment, S
Even if it is determined in 43 that the catalyst is not active, the process proceeds to S45 without immediately shifting to spark ignition combustion. In S45, the target catalyst temperature T0 is calculated. This is calculated from FIG. 12 based on the elapsed time after starting. In S46, a difference ΔTcat between the target catalyst temperature and the actual catalyst temperature Tcat is calculated. Here, ΔTcat is the judgment value α (α is, for example, 20 ° C.)
If it is larger than the threshold value, it is determined that the catalyst activity is delayed, and S4
Proceed to 1 to perform spark ignition combustion. If ΔTcat is smaller than α, it is determined that the delay of the catalyst activity is small, and S44
To perform self-ignition combustion.

As described above, by predicting the catalyst activity from the difference between the target catalyst temperature and the actual catalyst temperature, and optimally controlling the combustion mode depending on the catalyst activation state,
Fuel efficiency can be improved by self-ignition combustion while minimizing deterioration of emissions.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. The configuration of the fourth embodiment is shown in FIG.
Is the same as that of the second embodiment shown in FIG. This embodiment is characterized in that the catalyst activity is determined from the difference between the target catalyst heating rate and the actual catalyst heating rate.

FIG. 14 is a graph showing a change in the catalyst temperature with respect to the elapsed time after the start. Before the catalyst activity when the catalyst temperature Tcat measured by the catalyst temperature sensor 21 is lower than the catalyst activation temperature T50, the target catalyst heating rate dT0 / dt.
And the actual catalyst heating rate dTcat / dt to predict the catalyst activity. When dTcat / dt is smaller than the judgment value, it is judged that the activity of the catalyst is delayed, so that self-ignition combustion is prohibited, spark ignition combustion is performed, and the exhaust gas temperature is raised. If dTcat / dt is larger than the determination value, the catalyst is determined to be activated as intended, and self-ignition combustion is performed to improve fuel efficiency.

The operation of the fourth embodiment described above will be described with reference to the flowchart of FIG. The control flow is almost the same as that of the flowchart of the third embodiment shown in FIG. 13, but S55 and S56 are different. The different parts will be described below. At S55, the target catalyst heating rate d
Calculate T0 / dt. This is calculated from FIG. 14 based on the elapsed time after starting. In step S56, the target catalyst heating rate dT0 /
dt and the actual catalyst heating rate dTcat / dt are compared.
Here, when dTcat / dt is smaller than the target value dT0 / dt (for example, 5 ° C./s), it is determined that the catalyst activity is delayed, and the routine proceeds to S51, where spark ignition combustion is performed. dTcat /
When dt is larger than dT0 / dt, it is determined that the delay of the catalyst activity is small, and the process proceeds to S54, in which self-ignition combustion is performed.

As described above, the catalyst activity is predicted from the difference between the target catalyst heating rate and the actual catalyst heating rate, and the combustion mode is optimally controlled according to the catalyst activation state, thereby reducing the emission deterioration. While minimizing fuel consumption, self-ignition combustion can improve fuel efficiency.

[Fifth Embodiment] Next, a fifth embodiment of the present invention will be described. FIG. 16 shows the configuration of the fifth embodiment.
Shown in The configuration of the fifth embodiment is different from the configuration of the second embodiment shown in FIG. 8 in that a valve timing control unit 7 is provided inside the ECU 1, and a drive unit of the intake valve 11 is provided with a variable intake timing mechanism 22. The exhaust valve 12 includes a variable exhaust timing mechanism 23 in the drive section thereof.

This embodiment is characterized in that when self-ignition combustion after engine warm-up is established, the catalyst activity is predicted, and the compression ratio is reduced before the catalyst is activated.

FIG. 17 is a graph showing the exhaust gas temperature with respect to the compression ratio in the self-ignition combustion. As the compression ratio becomes lower, the exhaust gas temperature rises as much as the thermal efficiency decreases.

FIG. 18 is a graph showing a change in the exhaust gas temperature when the compression ratio is changed. The self-ignition combustion is performed after the engine is warmed up. However, the self-ignition combustion with the reduced compression ratio has a higher exhaust gas temperature than the high compression ratio, so that the catalyst can be activated earlier.

Therefore, before the catalyst is activated, although the fuel efficiency slightly decreases, the compression ratio is reduced from the basic compression ratio to increase the exhaust gas temperature, and the operation is performed at a low compression ratio.
As a result, early activation of the catalyst is achieved, and emission can be reduced.

The compression ratio is changed by using the variable intake timing mechanism 22 and the variable exhaust timing mechanism 23 under the control of the valve timing control unit 7 to delay the closing timing of the intake valve and to adjust the opening timing of the exhaust valve. This is done by advancing. The variable intake timing mechanism 22 and the variable exhaust timing mechanism 23 may use a helical spline mechanism that changes the phase between the cam pulley and the camshaft, or may use a plurality of cam profiles by switching. Furthermore, if an electromagnetically driven intake / exhaust valve is used,
Flexible variable timing control can be performed. Also,
The compression ratio may be changed by using a variable mechanism such as a piston or a connecting rod.

The operation of the fifth embodiment described above will be described with reference to the flowchart of FIG. The flow of the control is almost the same as the flow chart of the second embodiment shown in FIG. 11, but differs from S63 onward. less than,
The different parts will be described. The catalyst activity is determined in S63,
If the catalyst is active, the process proceeds to S64, where the basic compression ratio is set. If the catalyst is not active, a low compression ratio is set in S65. In S66, self-ignition combustion control is started.

As described above, by estimating the catalyst activity and performing auto-ignition combustion with the compression ratio optimally set according to the catalyst activation state, the fuel consumption is improved, and the emission is reduced depending on the early activation of the catalyst. it can.

[Sixth Embodiment] Next, a sixth embodiment of the present invention will be described. The configuration of the sixth embodiment is shown in FIG.
Is the same as the configuration of the fifth embodiment shown in FIG. In contrast to the fifth embodiment in which the compression ratio is changed by changing the timing of the intake valve 11, in the present embodiment, the exhaust valve 12 is changed.
The difference is that the expansion ratio is changed by changing the timing.

The present embodiment is characterized in that when the self-ignition combustion after engine warm-up is established, the catalyst activity is predicted, and the expansion ratio is reduced before the catalyst is activated.

FIG. 20 is a graph showing the exhaust gas temperature with respect to the expansion ratio in the self-ignition combustion. As the expansion ratio becomes lower, the exhaust gas temperature rises as much as the thermal efficiency decreases. Further, in order to achieve self-ignition combustion, it is necessary to set the compression ratio to some extent high. Therefore, there is a limit in reducing the compression ratio. On the other hand, in the case of the expansion ratio, a low expansion ratio can be achieved while keeping the compression ratio high, so that the exhaust gas temperature can be further raised as compared with a change in the compression ratio.

Therefore, before the catalyst is activated, although the fuel efficiency slightly decreases, the expansion ratio is set to a low expansion ratio lower than the basic expansion ratio in order to raise the exhaust gas temperature. As a result, early activation of the catalyst is achieved, and emission can be reduced. The expansion ratio is changed by using the variable exhaust timing mechanism 23 controlled by the valve timing control unit 7 to advance the opening timing of the exhaust valve.

FIG. 21 shows the operation of the sixth embodiment described above.
This will be described with reference to the flowchart of FIG. The flow of the control is almost the same as the flow chart of the fifth embodiment shown in FIG. 19, but differs from S73. Next, different points will be described. The catalyst activity is determined in S73, and if the catalyst is active, the process proceeds to S74 and the basic compression ratio is set. If the catalyst is not active, a low compression ratio is set in S75.
In S76, the self-ignition combustion control is started.

As described above, the catalyst activity is predicted, and the self-ignition combustion in which the expansion ratio is optimally set according to the catalyst activity state is performed, so that the fuel consumption is improved and the emission is reduced by the early activation of the catalyst. it can.

[Seventh Embodiment] Next, a seventh embodiment of the present invention will be described. The configuration of the seventh embodiment is shown in FIG.
The configuration is the same as that of the fifth embodiment shown in FIG.

In this embodiment, when the auto-ignition combustion after the activation of the catalyst is established, the catalyst conversion rate is predicted and
When the catalyst conversion rate decreases, the compression ratio is reduced or the expansion ratio is reduced. The conversion rate of the catalyst is also referred to as conversion efficiency.
If o, the conversion rate η is represented by η = (Ci−Co) / Ci.

If the low-load self-ignition combustion continues for a long time after the activation of the catalyst after the completion of the warming-up, the catalyst temperature decreases and the conversion rate of the emission deteriorates. Therefore, when the conversion of the catalyst is reduced, the temperature of the exhaust gas is raised by setting the compression ratio to a low compression ratio or setting the expansion ratio to a low expansion ratio. As a result, the catalyst temperature rises and the conversion rate rises, so that emissions can be reduced.

FIG. 22 shows the conversion with respect to the catalyst temperature.
The lower the catalyst temperature, the worse the conversion. Therefore, the catalyst conversion can be predicted from the catalyst temperature.

FIG. 23 shows the operation of the seventh embodiment described above.
This will be described with reference to the flowchart of FIG. The catalyst activity is determined in S80. If the catalyst activity is determined, the catalyst temperature Tcat is detected in S82. In S83, the catalyst conversion rate η is calculated. This calculates the catalyst conversion rate η from the catalyst temperature Tcat with reference to a graph as shown in FIG. Next, in S84, the catalyst conversion rate η is determined. When the catalyst conversion rate η is larger than the determination value β, it is determined that the catalyst conversion rate is sufficiently high, and the routine proceeds to S86, where the basic compression ratio (or the basic expansion ratio) is set. When the catalyst conversion rate η is smaller than the determination value β, it is determined that the catalyst conversion rate is lower than the request, and the process proceeds to S85, where a low compression ratio (or a low expansion ratio) is set. In S87, the self-ignition combustion control is started.

As described above, the catalyst conversion rate is predicted, and the self-ignition combustion in which the compression ratio or the expansion ratio is optimally set according to the catalyst conversion rate is performed. Emissions can be reduced. In the present invention, when the conversion is extremely low, self-ignition may be prohibited and spark ignition may be performed.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing a first embodiment of a combustion control device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing a schematic operation of the first embodiment.

FIG. 3 is an explanatory diagram of a self-ignition combustion establishment range.

FIG. 4 is a diagram illustrating a compression start cylinder temperature with respect to an intake air temperature and a cooling water temperature.

FIG. 5 is a diagram illustrating a compression start cylinder pressure with respect to an intake pressure and a cooling water temperature.

FIG. 6 is a diagram illustrating a target air-fuel ratio with respect to an engine speed and a torque.

FIG. 7 is a control flowchart illustrating the operation of the first embodiment.

FIG. 8 is a system configuration diagram showing a configuration of a second embodiment.

FIG. 9 is a diagram illustrating the exhaust gas temperature with respect to the combustion mode.

FIG. 10 is a diagram illustrating a combustion mode with respect to a catalyst temperature.

FIG. 11 is a control flowchart illustrating the operation of the second embodiment.

FIG. 12 is a diagram illustrating a catalyst temperature with respect to a post-start time.

FIG. 13 is a control flowchart illustrating the operation of the third embodiment.

FIG. 14 is a diagram for explaining a catalyst temperature rise rate with respect to a time after starting.

FIG. 15 is a control flowchart illustrating the operation of the fourth embodiment. .

FIG. 16 is a system configuration diagram showing a configuration of a fifth embodiment.

FIG. 17 is a diagram illustrating the exhaust gas temperature with respect to the compression ratio.

FIG. 18 is a diagram illustrating a catalyst temperature with respect to a post-start time.

FIG. 19 is a control flowchart illustrating the operation of the fifth embodiment.

FIG. 20 is a diagram illustrating the exhaust gas temperature with respect to the compression ratio and the expansion ratio.

FIG. 21 is a control flowchart illustrating the operation of the sixth embodiment.

FIG. 22 is a diagram illustrating a conversion rate with respect to a catalyst temperature.

FIG. 23 is a control flowchart illustrating the operation of the seventh embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ECU 2 combustion switching unit 3 in-cylinder pressure acquisition unit 4 in-cylinder temperature acquisition unit 5 combustion type determination unit 10 engine 11 intake valve 12 exhaust valve 13 piston 14 intake pressure sensor 15 intake temperature sensor 16 water temperature sensor 17 fuel injection device 18 ignition plug

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 45/00368 F02D 45/00 368S F02P 9/00 305 F02P 9/00 305Z (72) Inventor Takayuki Arai 2F, Takara-cho, Kanagawa-ku, Kanagawa-ku, Nissan Motor Co., Ltd.F-term (reference) BA00 BA16 BA22 BA23 CA01 CA02 DA02 DA10 DA25 DA27 EA04 EA07 EA11 EB08 EC01 FA02 FA11 FA20 FA21 FA22 FA27 FA32 FA36 FA38 3G092 AA01 AA02 AA06 AA11 AA12 BA10 DA03 DD03 DD10 DE03S DG01 DG09 EA08 FA14 EA11 FA04 HA14Z HC01Z HC03Z HD02X HD02Y HD02Z HE03Z HE04Z HE06Z HE08Z HF19Z 3G301 HA01 HA0 2 HA04 HA19 JA02 JA20 JA21 JB09 KA01 KA05 LA07 LB04 MA00 NA08 NB02 NB11 NB15 NC02 NE23 PA07Z PA10Z PC00Z PC01Z PC05Z PD12A PD12B PD12Z PE03Z PE04Z PE06Z PE08Z PF16Z

Claims (8)

[Claims] An in-cylinder pressure acquisition means for measuring or predicting an in-cylinder pressure near a compression top dead center in a combustion control apparatus for an internal combustion engine capable of switching between spark ignition combustion and compression self-ignition combustion. An in-cylinder temperature acquisition unit that measures or predicts an in-cylinder temperature near a point, and a combustion mode determination unit that determines whether a compression auto-ignition combustion condition is satisfied or not based on the in-cylinder pressure and the in-cylinder temperature. A combustion control device for an internal combustion engine, comprising: 2. The in-cylinder pressure obtaining means predicts the in-cylinder pressure based on an intake pressure, a compression ratio, and an engine temperature, and the in-cylinder temperature obtaining means includes an intake temperature, a compression ratio, and an engine temperature. The combustion control device for an internal combustion engine according to claim 1, wherein the in-cylinder temperature is predicted based on the following. 3. A catalyst for purifying exhaust gas, a catalyst activity estimating means for estimating the activity of the catalyst, and a compression ratio changing means for changing a compression ratio of the internal combustion engine. 2. A compression auto-ignition combustion by changing a compression ratio of the internal combustion engine to a compression ratio lower than a basic compression ratio by the compression ratio changing means when it is not estimated that the catalyst is activated. The combustion control device for an internal combustion engine according to claim 2. 4. A catalyst for purifying exhaust gas, a catalyst activity estimating means for estimating the activity of the catalyst, and an expansion ratio changing means for changing an expansion ratio of the internal combustion engine. 2. A compression auto-ignition combustion by changing an expansion ratio of the internal combustion engine to a lower expansion ratio than a basic expansion ratio by the expansion ratio changing means when it is not estimated that the catalyst is activated. The combustion control device for an internal combustion engine according to claim 2. 5. A catalyst for purifying exhaust gas, and a catalyst activity estimating means for estimating the activity of the catalyst, wherein when the catalyst activity estimating means does not estimate that the catalyst has been activated, compression ignition 3. The combustion control apparatus for an internal combustion engine according to claim 1, wherein combustion is prohibited and spark ignition combustion is performed. 6. A catalyst conversion rate estimating means for estimating a catalyst conversion rate of the catalyst, wherein when the catalyst conversion rate estimated by the catalyst conversion rate estimating means falls below a predetermined level, a basic compression ratio 4. The combustion control device for an internal combustion engine according to claim 3, wherein compression self-ignition combustion is performed at a lower compression ratio. 7. A catalyst conversion rate estimating means for estimating a catalyst conversion rate of the catalyst, wherein when the catalyst conversion rate estimated by the catalyst conversion rate estimating means falls below a predetermined level, a basic expansion ratio The combustion control device for an internal combustion engine according to claim 4, wherein the compression self-ignition combustion is performed at a lower expansion ratio. 8. A catalyst auto-ignition means for estimating a catalyst conversion rate of the catalyst, wherein when the catalyst conversion rate estimated by the catalyst conversion rate estimation means falls below a predetermined level, compression auto-ignition is performed. The combustion control device for an internal combustion engine according to any one of claims 1 to 5, wherein combustion is prohibited and spark ignition combustion is performed.