JP2006348843A - Cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To actualize a reduction of HC due to early activation of a catalyst and after-burn by greatly delaying an ignition timing while avoiding the instability of combustion in a high speed region. <P>SOLUTION: At cold start of an internal combustion engine which requires the early temperature rise of a catalyst converter, the ignition timing is set to be after a compression top dead center and super retard combustion is performed to inject fuel before the ignition timing but after the compression top dead center. Disturbance in a cylinder is improved by high pressure fuel injection right before the ignition timing and flame propagation is accelerated, therefore actualizing stable combustion. A pressure regulator controls fuel pressure to be higher as an engine speed is higher. Although an actual cycle time is shorter as the engine speed is higher, the fuel pressure is made higher to activate disturbance due to spraying energy and quicken the combustion, thus avoiding the instability of the combustion. <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 an intake stroke to an ignition timing when the exhaust gas catalytic converter is in an unwarmed state lower than an 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.
Japanese Patent No. 3325230

  For early activation of the catalyst when the internal combustion engine is cold and HC reduction due to afterburning, retarding the ignition timing is effective. To obtain a greater effect, ignition after compression top dead center (ATDC) Ignition) is desirable. In order to perform stable combustion by ATDC ignition, it is necessary to shorten the combustion period. For this reason, it is necessary to increase the combustion speed (flame propagation speed) by strengthening the turbulence in the cylinder.

  In order to strengthen such disturbance, it is conceivable that the disturbance is generated in the cylinder by the energy of the fuel spray injected at a high pressure in the cylinder.

  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. Yes. As described above, before the last fuel injection is before the compression top dead center, even if the spray generates turbulence in the cylinder, the turbulence is attenuated after the compression top dead center, and the flame propagation in ATDC ignition Does not contribute to speed increase.

  For example, FIG. 5 shows the magnitude of turbulence in a cylinder when a gas flow control valve (for example, a tumble control valve) provided in an intake port is operated and when such a gas flow control valve is not provided. As shown, the turbulence (part A) generated during the intake stroke by operating the gas flow control valve attenuates with the progress of the compression stroke, and is temporarily accompanied by the collapse of the tumble flow in the latter half of the compression stroke. Although the turbulence increases (the portion indicated by reference symbol B), after the compression top dead center, as shown by the reference symbol C, it rapidly attenuates, and combustion improvement (improving flame propagation) using the turbulence cannot be expected so much. The same applies to turbulence caused by fuel spray, and even if turbulence is generated by fuel injection before compression top dead center, it does not contribute to ignition combustion after compression top dead center.

  For this reason, ATDC ignition is more advantageous for increasing exhaust temperature and reducing HC, but combustion stability is not established. Therefore, in Patent Document 1, the ignition timing is set to before compression top dead center (BTDC ignition) in the no-load region. Yes.

  The present invention aims to improve the combustion stability in ATDC ignition for early activation of the catalyst, reduction of HC, and the like based on such a situation.

  The present invention provides a control device for an in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and includes an ignition plug. When the exhaust gas temperature needs to be raised, such as when the engine is cold, the ignition timing is set after the compression top dead center, and super retard combustion is performed to inject fuel before the ignition timing and after the compression top dead center. It is characterized by that. In the NOx trap catalyst that adsorbs NOx, the sulfur component (SOx) adheres to the catalyst, so that the NOx adsorption performance deteriorates. However, it is also possible to raise the temperature of the exhaust gas during the SOx release process using the above-mentioned super retard combustion. In the present invention, in particular, the fuel pressure in the super retard combustion is controlled such that the higher the engine speed, the higher the fuel pressure.

  It is desirable that the fuel pressure in the super retard combustion is increased in proportion to the square of the engine speed.

  It is desirable that the fuel pressure is corrected to be higher as the fuel injection timing before the ignition timing and after the compression top dead center is retarded.

  In other words, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but the in-cylinder turbulence is generated and strengthened by the fuel injection performed during the expansion stroke after the compression top dead center. Flame propagation with ATDC ignition is facilitated. Therefore, super retard combustion with the ignition timing after the compression top dead center is established stably.

  Here, the higher the engine speed, the shorter the actual time for the cycle. In order to perform stable combustion, it is necessary to accelerate the combustion. In the present invention, the higher the engine speed, the higher the fuel pressure, the stronger the gas flow in the cylinder generated by the fuel spray, the more active the combustion, and the higher the combustion speed. Therefore, stable combustion can be ensured even in the engine high speed region.

  The fuel spray flow rate is proportional to the square root of the fuel pressure. Therefore, if the fuel pressure is proportional to the square of the engine speed, a flow field proportional to the engine speed can be generated by fuel spray, and the combustion period can be made substantially equal regardless of the engine speed.

  Further, in the above-mentioned super retard combustion, the exhaust gas temperature rises as the fuel injection timing before the ignition timing and after the compression top dead center is delayed, and it is advantageous for reduction by HC afterburning, As the fuel injection timing is delayed, the combustion tends to become unstable. On the other hand, if the fuel pressure is corrected to be higher according to the delay of the fuel injection timing, the gas flow is strengthened and the combustion speed is increased, so that instability of combustion can be avoided.

  According to the present invention, it is possible to sufficiently ensure the combustion stability of the super retard combustion in which the ignition timing is set after the compression top dead center. For example, at the time of cold start, the catalyst is activated early and the HC due to the afterburning. Reduction can be achieved. In particular, even if the engine speed increases, the fuel pressure is given high, so that the combustion does not deteriorate.

  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 the combustion method, that is, the homogeneous combustion or the stratified combustion, in accordance with the engine operating conditions detected by these input signals, and according to this, the electronic control throttle valve 7 is opened. The fuel injection timing and fuel injection amount of the fuel injection valve 15, the fuel pressure of the pressure regulator 17, the ignition timing of the spark plug 14, and the like are controlled. After the warm-up is completed, 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 before the compression top dead center. Done. The fuel spray is collected in the vicinity of the spark plug 14, thereby achieving extremely lean stratified combustion with an air-fuel ratio of about 30 to 40. 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. As the homogeneous combustion operation, there are homogeneous stoichiometric combustion in which the air-fuel ratio is the stoichiometric air-fuel ratio and homogeneous lean combustion in which the air-fuel ratio is lean about 20 to 30 depending on the operating conditions.

  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 three examples of super retard combustion. In Example 1, the ignition timing is set to 15 ° to 30 ° ATDC (for example, 20 ° ATDC), and the fuel injection timing (specifically, the fuel injection start timing) is shown. Is set after the compression top dead center and before the ignition timing. At this time, the air-fuel ratio is set to the stoichiometric air-fuel ratio or slightly lean (about 16 to 17).

  That is, in order to promote catalyst warm-up and reduce HC, ignition timing retardation is effective, and ignition after top dead center (ATDC ignition) is desirable, but in order to perform stable combustion with ATDC ignition, It is necessary to shorten the combustion period, and for this purpose, flame propagation due to turbulence must be promoted. As described above, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but in the present invention, by the high pressure fuel injection performed during the expansion stroke after the compression top dead center. The gas flow is generated, and thereby the turbulence in the cylinder can be generated and strengthened. Therefore, flame propagation by ATDC ignition is promoted and stable combustion is possible.

  The second embodiment in FIG. 2 is an example in which the fuel injection is divided into two, and the first fuel injection is performed during the intake stroke, and the second fuel injection is performed after the compression top dead center. The ignition timing and the air-fuel ratio (the air-fuel ratio obtained by combining the two injections) are the same as those in the first embodiment.

  As described above, when fuel injection (intake stroke injection) is performed during the intake stroke prior to fuel injection after the compression top dead center (expansion stroke injection), disturbance due to fuel spray in the intake stroke injection is attenuated in the latter half of the compression stroke. However, since the injected fuel is diffused throughout the combustion chamber and contributes to the promotion of HC afterburning by ATDC ignition, the HC reduction and It is effective for raising the exhaust temperature.

  In the third embodiment of FIG. 2, the fuel injection is divided into two, the first fuel injection is performed in the compression stroke, and the second fuel injection is performed after the compression top dead center. As described above, when the fuel injection (compression stroke injection) is performed during the compression stroke prior to the fuel injection after the compression top dead center (expansion stroke injection), the compression stroke injection is compared with the intake stroke injection of the second embodiment. However, since the disturbance of the turbulence due to the fuel spray is delayed, the turbulence due to the first fuel injection remains, and the second fuel injection is performed after the compression top dead center, which is generated by the first fuel injection. The turbulence can be strengthened to promote the turbulence, and the gas flow can be further strengthened near the compression top dead center.

  In the case of Example 3, the first compression stroke injection may be in the first half of the compression stroke, but if it is set in the second half of the compression stroke (after 90 ° BTDC), the disturbance near the top dead center can be further increased. In particular, if the first compression stroke injection is 45 ° BTDC or later, more desirably 20 ° BTDC or later, the gas flow after compression top dead center can be further enhanced.

  As described above, according to the super retarded combustion of the first to third embodiments, the turbulence in the cylinder can be generated and strengthened by the fuel spray immediately before the ignition, and the flame propagation is promoted to perform stable combustion. be able to. In particular, by retarding the ignition timing from 15 ° to 30 ° ATDC, a sufficient afterburning effect for early activation of the catalyst and reduction of HC can be obtained. In other words, even if the ignition timing is greatly delayed in this way, the fuel injection is delayed until just before that, and the generation time of the turbulence is also delayed, so that the combustion improvement by improving the flame propagation can be achieved.

  On the other hand, the fuel pressure at the time of the above-mentioned super retard combustion is controlled so that the higher the high speed side, the higher the fuel pressure with respect to the change in engine speed. More specifically, the fuel pressure increases in proportion to the square of the engine speed. As described above, in order to perform stable combustion in the high speed region, it is necessary to accelerate the combustion faster than the low speed region, but by increasing the fuel pressure from the low speed region, the in-cylinder generated by the energy of the fuel spray Minute turbulence, that is, minute gas flow becomes more active, and the combustion speed increases. Therefore, the influence of the engine speed is offset and stable combustion can be ensured even in the high speed range.

  FIG. 3 shows an example of a change in combustion stability with respect to a change in engine speed when the fuel pressure is low (dashed line) and when the fuel pressure is high (solid line). As shown in FIG. However, the combustion stability is good, and on the low speed side, the combustion stability is better at low fuel pressure. Therefore, the instability of combustion in the high speed region can be avoided by increasing the fuel pressure as the engine speed increases as indicated by the arrows in the figure.

  Further, as described above, the exhaust gas temperature rises as the injection timing of the fuel injection (expansion stroke injection) after the compression top dead center in the super retard combustion is delayed, and can be reduced by HC afterburning. As shown in FIG. 2, the combustion tends to become unstable as the injection timing of the expansion stroke injection is delayed. However, when comparing the case where the fuel pressure is low (broken line) and the case where the fuel pressure is high (solid line), the gas flow is strengthened at the high fuel pressure, so that the instability of combustion due to the retard of the injection timing is small. Therefore, as indicated by an arrow in the figure, if the fuel pressure is corrected to be higher with the delay of the fuel injection timing, instability of combustion can be avoided even when the injection timing is set to the more retarded side.

  The super retarded combustion of the present invention can also be used for releasing sulfur poisoning when a NOx trap catalyst is used as the exhaust system catalytic converter 10. The NOx trap catalyst adsorbs NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and releases the adsorbed NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is rich, and purifies by catalytic action. However, when the sulfur component (SOx) in the fuel is bound to the catalyst, the NOx adsorption performance is lowered. For this reason, it is necessary to perform a process (so-called sulfur poisoning release) for forcibly raising the temperature of the catalyst and releasing SOx at an appropriate time. The super retarded combustion according to the present invention can obtain a very high exhaust temperature, and therefore is suitable for the sulfur poisoning release processing of this NOx trap catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the system structure of the whole internal combustion engine which concerns on this invention. The characteristic view which shows the fuel injection timing and ignition timing of the super retard combustion of this invention. The characteristic view which shows the relationship between an engine speed and combustion stability. The characteristic view which shows the relationship between fuel-injection time and combustion stability. Explanatory drawing which shows the change of the disturbance in a cylinder in a prior art.

Explanation of symbols

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

Claims (7)

  In a direct injection type spark ignition internal combustion engine control device having a fuel injection valve for directly injecting fuel into a cylinder and having an ignition plug, the ignition timing is compression top dead center in a predetermined operating state. Set later, and perform super retard combustion that injects fuel before this ignition timing and after compression top dead center, while controlling the fuel pressure in this super retard combustion so that the higher the engine speed, the higher the fuel pressure An in-cylinder direct injection spark ignition internal combustion engine control device.   The control apparatus for an in-cylinder direct injection spark-ignition internal combustion engine according to claim 1, wherein the super retard combustion is executed when a temperature increase of the exhaust gas is required as a predetermined operation state.   The in-cylinder direct injection spark according to claim 2, wherein the temperature of the exhaust gas is required to be raised during a cold start of the internal combustion engine that requires an early temperature increase of the exhaust system catalytic converter. Control device for an ignition internal combustion engine.   3. The control device for a direct injection type spark ignition internal combustion engine according to claim 2, wherein the exhaust gas temperature is required to be raised when performing SOx release processing of the exhaust system catalytic converter.   5. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition timing in the super retard combustion is 15 ° to 30 ° CA after compression top dead center.   6. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the fuel pressure increases in proportion to the square of the engine speed. The in-cylinder direct injection according to any one of claims 1 to 6, wherein the fuel pressure is corrected to be higher as the fuel injection timing before the ignition timing and after the compression top dead center is retarded. Type spark ignition internal combustion engine control device.

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