JP4529832B2 - In-cylinder direct injection spark ignition internal combustion engine controller - Google Patents

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 after the middle of the compression stroke, for example, at 120 ° BTDC to 45 ° BTDC.
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. 6 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.

  Therefore, ATDC ignition is more advantageous for exhaust temperature rise and HC reduction, 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 is provided with a fuel injection valve for injecting fuel directly into the cylinder, the control apparatus for a cylinder direct injection spark ignition internal combustion engine comprising comprises a spark plug, such as during cold catalytic converter if example embodiment the exhaust the Atsushi Nobori if required for the gas temperature, and sets after the compression top dead center of the ignition timing, is characterized by performing the super-retard combustion for injecting fuel after and compression top dead center before the ignition timing. 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, the engine speed at idling is maintained at the target idling speed by feedback control of the ignition timing. In particular, the engine speed during the idling operation in the super retard combustion is particularly high. When it decreases, the super retard combustion is canceled.

  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.

  On the other hand, in the idle state, when the idling engine speed greatly decreases due to an auxiliary load (for example, a compressor of an air conditioner) or a range position change of the automatic transmission, ignition is performed by ignition timing feedback control to maintain the target idling engine speed. The timing will be corrected to approach the MBT point, but if the ignition timing is advanced toward the MBT point while continuing the super retard combustion that injects fuel after the compression top dead center, the exhaust gas temperature decreases. As a result, smoke in the exhaust gas increases.

Therefore, in the present invention, when the engine speed is relatively lowered during the idling operation in the super retard combustion, the super retard combustion is canceled. This avoids an increase in smoke.

  In one aspect of the present invention, the super retard combustion is released when the actual engine speed falls below a predetermined lower limit speed. Desirably, the lower limit engine speed is set higher as the engine speed decreases. As a result, even when the engine speed rapidly decreases, the engine does not stop.

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. Then, when the rotational speed is greatly reduced during the idling operation in the super retard combustion, the super retard combustion is canceled, so that an increase in smoke due to the feedback control of the ignition timing can be avoided.

  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.

  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, 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 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.

  Thus, if fuel injection (intake stroke injection) is performed during the intake stroke prior to fuel injection after compression top dead center (expansion stroke injection), the 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, when the depression amount of the accelerator pedal or the opening amount of the electronically controlled throttle valve 7 is ON, the normal homogeneous combustion operation, the stratified combustion operation or the super retard combustion is performed. Regardless, known idle speed control by feedback control of ignition timing is executed. In other words, the ignition timing is corrected so that the torque increases or decreases according to the rotational speed deviation between the target idle speed and the actual rotational speed, but under super retard combustion, the ignition timing is after the compression top dead center. Therefore, the ignition timing is corrected to advance so as to approach the MBT point when the rotational speed decreases, and conversely, the ignition timing is retarded when the rotational speed increases. The idle switch signal is not necessarily a physical switch, and is generated from a detection signal of the accelerator opening sensor 23, for example.

  Here, during the idling operation by the super retard combustion, the idling speed is increased by switching the auxiliary machine load (for example, the compressor of the air conditioner) or the range position of the automatic transmission (switching from the N range to the D range). In the case of a decrease, the ignition timing is advanced to correct the target idle speed by the idle speed control described above, but as shown in FIG. 3, although the torque increases with the advance of the ignition timing, As the exhaust gas temperature decreases, the smoke in the exhaust increases.

  Therefore, in the present invention, when the engine speed falls below the predetermined lower limit speed NL during idling operation with super retard combustion, super retard combustion is canceled. In particular, in this embodiment, the lower limit rotational speed NL is set based on the rotational speed decrease speed ΔNe when the rotational speed is decreased. That is, as shown in FIG. 4, considering the response delay, the lower limit rotational speed NL is set higher as the rotational speed decrease speed ΔNe is larger. Therefore, if the engine speed is rapidly decreased, the super retard combustion is released at a higher engine speed.

  FIG. 5 is a flowchart showing the above-described processing flow. When a decrease in the rotation speed is detected during the idling operation in the super retard combustion, the lower limit rotation speed NL is determined from the rotation speed decrease speed ΔNe in step 1. In step 2, the engine speed Ne at that time is compared with the lower limit speed NL. If the engine speed Ne is equal to or higher than the lower limit speed NL, the routine proceeds to step 3 where the super retard combustion is continued. On the other hand, if it is below the lower limit rotational speed NL, the routine proceeds to step 4 where super retard combustion is canceled and normal combustion, that is, normal stratified combustion operation or homogeneous combustion operation described above is performed. Thereby, the torque can be increased without increasing the smoke, and the engine stop due to the excessive decrease in the engine speed Ne is avoided.

  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 change of a torque, exhaust temperature, and smoke with respect to ignition timing. The characteristic view which shows the characteristic of the minimum rotation speed NL with respect to rotation speed fall speed (DELTA) Ne. The flowchart which shows the flow of a process. 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 25 ... Control unit

Claims (8)

In-cylinder direct injection spark-ignition internal combustion engine having a fuel injection valve that directly injects fuel into the cylinder, an ignition plug, and maintaining the engine speed during idling at the target idle speed by feedback control of ignition timing In this control device, when the temperature of the exhaust gas is required to be raised , the ignition timing is set after the compression top dead center, and super retard combustion is performed in which fuel is injected before the ignition timing and after the compression top dead center. On the other hand, a control device for a direct injection spark ignition internal combustion engine, characterized in that the super retard combustion is canceled when the engine speed decreases during idling in the super retard combustion.   2. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the super retard combustion is canceled when the engine speed falls below a predetermined lower limit rotational speed.   3. The control device for a direct injection type spark ignition internal combustion engine according to claim 2, wherein the lower limit rotational speed is set higher as the decrease speed of the engine rotational speed is larger.   The control device for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 3, wherein the ignition timing in the super retard combustion is 15 ° to 30 ° CA after compression top dead center.   The in-cylinder direct injection according to any one of claims 1 to 4, wherein in super retard combustion, fuel injection is further performed during an intake stroke or a compression stroke prior to fuel injection after compression top dead center. A control device for an injection spark ignition internal combustion engine.   The control device for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 5, wherein the air-fuel ratio in the super retard combustion is a stoichiometric air-fuel ratio or slightly lean. The cylinder according to any one of claims 1 to 6, 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 internal direct injection spark ignition internal combustion engine. When performing the SOx release process of a catalytic converter in the exhaust system, cylinder direct injection spark ignition internal combustion according to any one of claims 1 to 6, characterized in that heating of the exhaust gas temperature is required Engine control device.

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