JP2007198325A - Control device of cylinder direct-injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a reduction in HC by quick activation of a catalyst and post-combustion by largely retarding an ignition timing. <P>SOLUTION: When an internal combustion engine for which the early increase in the temperature of a catalytic converter is requested is started in a cool state, the ignition timing ADV is retarded to approximately 10 to 50° ATDC, a first fuel injection I1 is performed during the compression stroke, and a second fuel injection I2 is performed at the time 10 to 20° CA before the ignition timing ADV during the expansion stroke. A compact air-fuel mixture lump is formed near an ignition plug by the first spray, and a richer air-fuel mixture lump is locally formed on the inside thereof near the ignition plug by the second spray and ignited. Robustness against variations for each cycle is increased and the occurrence of HC in a quench area and a clevis is reduced. A fuel pressure is variably controlled so that a variation in penetration due to a variation in the pressure inside a cylinder by a load can be compensated for. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an in-cylinder direct injection type spark ignition internal combustion engine that directly injects fuel into a cylinder, and in particular, at a cold start in which early temperature rise (early activation) of an exhaust system catalytic converter is required. It relates to control of injection timing and ignition timing.

  In Patent Document 1, as a catalyst warm-up method for a direct injection spark-ignition internal combustion engine, a period from the intake stroke to the ignition timing when the exhaust gas catalytic converter is in an unwarmed state lower than the activation temperature. In this case, it is possible to spread the fuel by the late injection in which the air-fuel mixture having a partial air-fuel ratio concentration is formed in the combustion chamber, the fuel is injected before this late injection, and the fuel of the late injection and the combustion of the late injection And at least two split injections of early injection for generating an air-fuel mixture leaner than the stoichiometric air-fuel ratio in the combustion chamber, and retarding the ignition timing by a predetermined amount from the MBT point, and no engine load A technique is described in which the ignition timing is set before the compression top dead center in the region, and the ignition timing is retarded until the compression top dead center in the low speed and low load region excluding the no-load region. The latter-stage injection is performed, for example, at 120 ° BTDC to 45 ° BTDC after the middle of the compression stroke.

Further, Patent Document 2 was previously proposed by the present applicant. By utilizing the in-cylinder turbulence caused by the spray energy of high-pressure fuel injection, the combustion in which the ignition timing is retarded until after compression top dead center is performed. As an example, it is disclosed that the first fuel injection is performed in the latter half of the compression stroke, and the second fuel injection is performed immediately before the ignition of the expansion stroke. ing.
Japanese Patent No. 3325230 Japanese Patent Laid-Open No. 2005-214039

  However, in Patent Document 1, the first fuel injection (early injection) is performed during the intake stroke, and the second fuel injection (late injection) is performed from 120 ° BTDC to 45 ° BTDC during the compression stroke. Therefore, the combustion stability is low. In particular, in the no-load region, the ignition timing is set to before compression top dead center (BTDC ignition). Therefore, the exhaust temperature rise and the HC reduction due to the ignition timing retard cannot be sufficiently achieved.

  In addition, if the first injection is performed during the intake stroke, the fuel enters the quench region and the clevis in the combustion chamber and becomes a source of HC generation.

  On the other hand, in Patent Document 2, the first fuel injection is performed in the latter half of the compression stroke, and the second fuel injection is performed immediately before the ignition of the expansion stroke. However, depending on the in-cylinder turbulence due to the second fuel injection, Since combustion is established, a high fuel pressure is required. As a result, combustion is relatively fast (compared to the case where the fuel pressure is low), and there is still room for improvement in terms of an increase in exhaust temperature and a reduction in HC associated therewith.

The present invention includes a fuel injection valve that directly injects fuel into a cylinder and an ignition plug, and also includes fuel pressure variable means that variably controls the fuel pressure supplied to the fuel injection valve, and ignites the fuel in a predetermined operating state. In a cylinder direct injection spark ignition internal combustion engine that performs super retard combustion with the timing set after compression top dead center,
During super retard combustion, the first fuel injection is performed during the compression stroke to form a rich air-fuel mixture in a part of the combustion chamber near the spark plug,
A second fuel injection is performed during the expansion stroke at a timing preceding the ignition timing by a predetermined period so that a locally richer air-fuel mixture reaches the ignition plug at the ignition timing,
While igniting in a state where a two-stage stratified mixture is formed in a part of the combustion chamber near the spark plug,
The fuel pressure is controlled so as to compensate for a change in penetration due to a change in in-cylinder pressure.

  That is, in the present invention, a compact stratified mixture is formed in the combustion chamber by two fuel injections at a relatively low fuel pressure without depending on the spray energy of the fuel injection. In particular, at the ignition timing, a locally rich air-fuel mixture is present in the vicinity of the spark plug due to the spray of the second fuel injection, and surrounds the periphery of the spark plug rather than the stoichiometric air-fuel ratio by the first fuel injection. A rich and lean air-fuel mixture exists near the spark plug. That is, a compact stratified mixture having two different concentrations is formed, and ignition is performed in this state. It is desirable that the air-fuel mixture produced by the first fuel injection does not diffuse throughout the combustion chamber.

  According to such a combustion method, stable combustion is possible with respect to a minute change in rotational speed or a minute load change for each cycle. Since both fuel injections are performed at a relatively low fuel pressure in a place where the in-cylinder pressure is high, the spray becomes compact and hardly enters the quench region or the clevis, thus suppressing the generation of HC. In addition, since a relatively low fuel pressure can be used, the combustion speed can be suppressed, which is advantageous in increasing the exhaust temperature and reducing HC.

  On the other hand, when the in-cylinder pressure near the top dead center changes due to the load of the internal combustion engine, the external air pressure, etc., the penetration (penetration force) of the injected fuel spray, that is, the spray reach distance changes. For example, when the load increases, the cylinder pressure increases as the amount of air increases, so that the penetration decreases. Therefore, in particular, the spray of the second fuel injection does not reach the vicinity of the spark plug correctly at the expected timing. Conversely, if the load and thus the in-cylinder pressure is low and the penetration is higher than the intended one, the spray diffuses excessively and enters the quench region or clevis, for example, without forming a compact stratified mixture. Therefore, in the present invention, the fuel pressure is controlled so as to compensate for such a change in penetration due to a change in the in-cylinder pressure.

  For example, during super retard combustion, the fuel pressure is controlled to be higher as the load is larger, and similarly, the fuel pressure is controlled to be higher as the external pressure is higher. Alternatively, when a variable valve mechanism or variable compression ratio mechanism that changes the actual compression ratio is provided, the cylinder pressure near the top dead center changes with the change of the actual compression ratio. The higher the ratio, the higher the fuel pressure is controlled. As a result, an appropriate stratified mixture is formed without being affected by the change in the in-cylinder pressure, and stable combustion is ensured.

  According to the present invention, the combustion stability of the super retard combustion in which the ignition timing is set after the compression top dead center is improved. For example, at the time of cold start, early activation of the catalyst and reduction of HC are achieved by increasing the exhaust temperature. can do. In addition, stable combustion is possible without being affected by changes in in-cylinder pressure accompanying changes in load, actual compression ratio, and the like.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration explanatory view showing a system configuration of a direct injection type spark ignition internal combustion engine to which the present invention is applied.

  An intake passage 4 is connected to the combustion chamber 3 formed by the piston 2 of the internal combustion engine 1 via an intake valve (not shown), and an exhaust passage 5 is connected via an exhaust valve (not shown). Has been. The intake passage 4 is provided with an air flow meter 6 for detecting the amount of intake air, and an electronically controlled throttle valve 7 whose opening degree is controlled via an actuator 8 by a control signal. The exhaust passage 5 is provided with a catalytic converter 10 for purifying exhaust gas, and air-fuel ratio sensors 11 and 12 are provided on the upstream side and the downstream side, respectively. Further, the upstream air-fuel ratio sensor 11 is provided. Is provided with an exhaust gas temperature sensor 13 for detecting the exhaust gas temperature at the inlet side of the catalytic converter 10.

  A spark plug 14 is disposed at the central top of the combustion chamber 3. A fuel injection valve 15 that directly injects fuel into the combustion chamber 3 is disposed on the side of the combustion chamber 3 on the intake passage 4 side. The fuel that has been regulated to a predetermined pressure by the high-pressure fuel pump 16 and the pressure regulator 17 is supplied to the fuel injection valve 15 via the high-pressure fuel passage 18. Therefore, when the fuel injection valve 15 of each cylinder is opened by the control pulse, an amount of fuel corresponding to the valve opening period is injected. Reference numeral 19 denotes a fuel pressure sensor that detects the fuel pressure, and 20 denotes a low-pressure fuel pump that sends fuel to the high-pressure fuel pump 16. Here, the pressure regulator 17 is configured to change the fuel pressure of the fuel supplied to the fuel injection valve 15 within a relatively wide range as the fuel pressure varying means.

  In addition, the internal combustion engine 1 is provided with a water temperature sensor 21 for detecting the engine cooling water temperature and a crank angle sensor 22 for detecting a crank angle. Further, an accelerator opening sensor 23 is provided for detecting the amount of depression of the accelerator pedal by the driver.

  The fuel injection amount, injection timing, fuel pressure, ignition timing, etc. of the internal combustion engine 1 are controlled by the control unit 25. The control unit 25 receives detection signals from the various sensors described above. The control unit 25 determines whether to use a combustion method, that is, homogeneous combustion or stratified combustion, according to the engine operating conditions detected by these input signals, and in response to this, opens the electronic control throttle valve 7. The fuel injection timing and fuel injection amount of the fuel injection valve 15, the ignition timing of the spark plug 14, the fuel pressure by the pressure regulator 17, and the like are controlled.

  After completion of warm-up, normal stratified combustion operation or homogeneous combustion operation is performed. For example, in a predetermined region on the low speed and low load side, as normal stratified combustion operation, fuel injection is performed at an appropriate time in the compression stroke, and ignition is performed at a time before the compression top dead center. The fuel spray is collected in a layered manner in the vicinity of the spark plug 14, thereby realizing, for example, stratified combustion with a lean air-fuel ratio. Further, in a predetermined region on the high speed and high load side, as normal homogeneous combustion operation, fuel injection is performed during the intake stroke, and ignition is performed in the vicinity of the MBT point before the compression top dead center. In this case, the fuel becomes a homogeneous mixture in the cylinder.

  The present invention performs super retard combustion so that the exhaust gas temperature becomes high at the time of cold start of the internal combustion engine 1 where early temperature rise of the catalytic converter 10 is required. The fuel injection timing and ignition timing will be described with reference to FIG.

  FIG. 2 shows an example of the fuel injection timing and ignition timing during super retard combustion, and the ignition timing ADV is set to 10 ° to 50 ° ATDC in order to obtain a sufficiently high exhaust temperature. . That is, the period B is 10 ° to 50 ° CA. Further, the first fuel injection I1 is performed during the compression stroke, and the second fuel injection I2 is performed during the expansion stroke. The first fuel injection I1 is for forming a rich air-fuel mixture that spreads in a part of the combustion chamber 3 in the vicinity of the spark plug 14, and from the fuel injection timing (specifically, the fuel injection start timing) to the ignition timing. The period C until ADV is set to 50 ° to 140 ° CA, for example. In other words, the fuel injection timing is set so that the fuel spray by the first fuel injection I1 diffuses in the combustion chamber 3 to some extent but does not diffuse excessively. When the period C is excessively long, the fuel spray is excessively diffused, and the fuel component enters the quench region or the clevis.

  Then, the second fuel injection I2 during the expansion stroke is performed at a timing preceding the ignition timing ADV by a predetermined period A so that a locally richer air-fuel mixture reaches the ignition plug 14 at the ignition timing ADV. Done. The period A from the fuel injection timing (specifically, the fuel injection start timing) to the ignition timing ADV basically correlates with the distance from the fuel injection valve 15 to the spark plug 14, for example, 10 ° to 20 ° CA. is there.

  At this time, the air-fuel ratio (the average air-fuel ratio of the entire combustion chamber by two injections) is set to the stoichiometric air-fuel ratio or slightly lean (about 16 to 17). Thereby, a necessary and sufficient amount of oxygen necessary for the afterburning of HC is ensured.

  Further, since combustion is performed without depending on the disturbance due to the energy of the fuel spray, a relatively low fuel pressure is used as the fuel pressure within a range where combustion is established as will be described later. The fuel pressure is controlled according to the load so as to compensate for the penetration change due to the in-cylinder pressure change.

  By performing the fuel injection as described above, at the ignition timing ADV, as shown in FIG. 3, a compact stratified air-fuel mixture having a two-stage concentration surrounding the spark plug 14 is formed. That is, by the first fuel injection I1, a first air-fuel mixture richer than the stoichiometric air-fuel ratio is formed in a part of the combustion chamber 3 in the vicinity of the spark plug 14 as indicated by reference numeral 31, and 2 A richer second air-fuel mixture resulting from the second fuel injection I2 is locally formed in the vicinity of the spark plug 14 as indicated by reference numeral 32. Both fuel injections are performed toward a field where the in-cylinder pressure in the vicinity of the top dead center is high and the fuel pressure is relatively low. The outside is basically a fresh air layer where fuel is not diffused. Then, in this state of stratification, the second air-fuel mixture 32 is ignited by the spark plug 14 and combustion is performed relatively slowly.

  In the retarded combustion according to the method of the present invention, the injection timing of the first fuel injection I1 hardly affects the combustion stability, that is, the misfire rate and torque fluctuation, and the fluctuation of the injection timing of the second fuel injection I2 is misfired. The effect on the rate and torque fluctuation is small.

  FIG. 4 shows the change in misfire rate and torque fluctuation when the expansion stroke injection, that is, the injection timing of the second fuel injection I2 is changed from the optimal injection timing. In the characteristics of the embodiment, the injection timing slightly changes. However, the misfire rate and torque fluctuation do not deteriorate rapidly. On the other hand, in the characteristics of the reference example in which the entire amount is injected at a time during the expansion stroke, if the injection timing changes even slightly from the optimal injection timing, the misfire rate and torque fluctuation are rapidly deteriorated.

  Therefore, in the present invention, even if the optimum value of the injection timing of the second fuel injection I2 changes due to a minute change in the rotational speed or a minute load for each cycle, the misfire rate and torque fluctuation increase. Stable combustion can be obtained. In other words, the robustness against cycle changes is high.

  Further, in the present invention, the air-fuel mixture becomes compact and the fuel component does not enter the quench region or the clevis, so that HC generated from these portions is reduced.

  Further, as shown in FIG. 5 (a), in the combustion method of the present invention, even if the fuel pressure is lowered, the deterioration of combustion (for example, torque fluctuation) is small, and on the other hand, by reducing the fuel pressure, As shown in the figure, the exhaust gas temperature is higher, and accordingly, as shown in (c), the HC emission amount is reduced. This is because by lowering the fuel pressure, the combustion becomes slower and the combustion is performed later. Therefore, in the present invention, it is desirable to reduce the fuel pressure within a range where combustion is established. As a result, the exhaust temperature can be increased and HC can be further reduced.

  On the other hand, as shown in FIG. 6, the reach of the spray injected from the fuel injection valve 15, that is, the penetration, tends to decrease as the in-cylinder pressure at the time of injection increases. As described above, when the load increases, the in-cylinder pressure relatively increases as the air amount increases. Further, the penetration correlates with the fuel pressure, and the penetration increases as the fuel pressure increases as shown in FIG. Therefore, in this embodiment, as shown in FIG. 8, the fuel pressure is variably controlled in accordance with the load so that the fuel pressure increases as the in-cylinder pressure, that is, the load increases. As a result, the change in penetration due to the load and the change in penetration due to the fuel pressure cancel each other, and the influence of the change in in-cylinder pressure can be eliminated. That is, the desired stratified mixture can be secured more stably, and stable ignition / combustion becomes possible.

  The in-cylinder pressure is affected not only by the load but also by the external air pressure and the actual compression ratio. Therefore, for example, the external air pressure may be detected or estimated, and the fuel pressure may be variably controlled correspondingly. Alternatively, in an internal combustion engine equipped with a variable compression ratio mechanism, it is desirable to variably control the fuel pressure according to the compression ratio that is variably controlled. For example, in an internal combustion engine having a variable valve mechanism on the intake valve side, if the intake valve closing timing is variably controlled, the actual compression ratio and thus the in-cylinder pressure changes. Variable control is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The characteristic view which shows the fuel injection timing and ignition timing of the super retard combustion of this invention. Explanatory drawing which shows the state of the stratified mixture formed in a combustion chamber. The characteristic view which shows the relationship between the injection timing of expansion stroke injection, (a) torque fluctuation, and (b) misfire rate. The characteristic view which shows the relationship between a fuel pressure, (a) torque fluctuation, (b) exhaust temperature, (c) HC discharge | emission amount. The characteristic view which shows the relationship between a cylinder pressure and penetration. The characteristic view which shows the relationship between a fuel pressure and penetration. The characteristic view which shows the characteristic of the fuel pressure with respect to in-cylinder pressure (load).

Explanation of symbols

3 ... Combustion chamber 10 ... Catalytic converter 14 ... Spark plug 15 ... Fuel injection valve 17 ... Pressure regulator 25 ... Control unit

Claims (10)

A fuel injection valve for directly injecting fuel into the cylinder and an ignition plug are provided, and fuel pressure variable means for variably controlling the fuel pressure supplied to the fuel injection valve is provided, and the ignition timing is compressed in a predetermined operating state. In a direct injection spark ignition internal combustion engine that performs super retard combustion set after dead center,
During super retard combustion, the first fuel injection is performed during the compression stroke to form a rich air-fuel mixture in a part of the combustion chamber near the spark plug,
A second fuel injection is performed during the expansion stroke at a timing preceding the ignition timing by a predetermined period so that a locally richer air-fuel mixture reaches the ignition plug at the ignition timing,
While igniting in a state where a two-stage stratified mixture is formed in a part of the combustion chamber near the spark plug,
A control apparatus for a direct injection spark ignition internal combustion engine, wherein the fuel pressure is controlled to compensate for a change in penetration due to a change in in-cylinder pressure.   2. The control device for a direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition timing in the super retard combustion is 10 ° to 50 ° CA after compression top dead center.   3. The control device for a direct injection type spark ignition internal combustion engine according to claim 1, wherein a period from an injection start timing of the second fuel injection to an ignition timing is 10 ° to 20 ° CA. 4.   The in-cylinder direct injection spark ignition internal combustion engine according to any one of claims 1 to 3, wherein a period from an injection start timing to an ignition timing of the first fuel injection is 50 ° to 140 ° CA. Control device.   The control device for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 4, wherein the air-fuel ratio in the super retard combustion is a stoichiometric air-fuel ratio or slightly lean.   The in-cylinder direct injection spark ignition internal combustion engine according to any one of claims 1 to 5, wherein the super retard combustion is executed when a temperature increase of the exhaust gas is required as a predetermined operation state. Engine control device.   The control device for a direct injection type spark ignition internal combustion engine according to any one of claims 1 to 6, wherein a low fuel pressure is used within a range where combustion is established.   8. The control device for a direct injection spark ignition internal combustion engine according to claim 1, wherein the fuel pressure is controlled to be higher as the load is larger during super retard combustion.   The variable valve mechanism or the variable compression ratio mechanism for changing the actual compression ratio is further provided, and the fuel pressure is controlled to be higher as the actual compression ratio is higher during super retard combustion. A control apparatus for an in-cylinder direct injection type spark ignition internal combustion engine. The control apparatus for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 7, wherein the fuel pressure is controlled to be higher as the external pressure is higher during super retard combustion.

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