JP2006144609A - Control device for cylinder direct injection spark ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid smoke caused by delay of completion of injection while activating a catalyst early and reducing HC caused by after-burning, by significantly retarding ignition timing. <P>SOLUTION: In the cold-start of an internal combustion engine requiring quick temperature rise of a catalytic converter, the ignition timing is set after a compression top dead center, and a very retarded combustion accompanying expansion stroke injection in which fuel start timing is before the ignition timing and after a compression top dead center is performed. Since high-pressure fuel injection immediately before the ignition timing intensifies disturbance in a cylinder to promote flame propagation, resulting in stable combustion. If a fuel injection period (crank angle) is elongated for some reason and an injection completion timing is delayed from a smoke tolerance after the ignition timing, the fuel injection is forcibly stopped before the end of the injection period. Therefore, degradation in smoke is prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct-injection spark ignition internal combustion engine that directly injects fuel into a cylinder, and in particular, injection at a cold start in which early temperature rise (early activation) of an exhaust system catalytic converter is required. It relates to the control of 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 combustion stability in ATDC ignition for early activation of the catalyst and HC reduction based on such a situation.

  The present invention requires an early temperature rise of an exhaust system catalytic converter in 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 the cylinder and includes an ignition plug. When the internal combustion engine is cold started, the ignition timing is set after the compression top dead center, and the super retard combustion is performed with the expansion stroke injection in which the fuel injection start timing is set before the ignition timing and after the compression top dead center. It is what I did. Further, when the fuel injection end timing of the expansion stroke injection is delayed from a predetermined allowable range after the ignition timing, the expansion stroke injection is forcibly ended in the middle of the injection period.

  That is, 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 caused by the fuel injection, that is, the expansion stroke injection performed during the expansion stroke after the compression top dead center. Can be generated and strengthened, and flame propagation in ATDC ignition is promoted. Therefore, super retard combustion with the ignition timing after the compression top dead center is established stably.

  Here, in the above-described super retard combustion, since fuel injection is performed after compression top dead center close to the ignition timing, the engine speed increases or the fuel pressure decreases, and the injection period at the crank angle is relatively long. Then, the fuel injection end timing may be delayed from the ignition timing. In such a case, since the fuel is injected at the point where combustion has already started, the fuel injected late is exposed to a high temperature without being sufficiently mixed with oxygen, and smoke is likely to deteriorate. Note that fuel supplied later than the ignition timing set after compression top dead center contributes to an increase in exhaust temperature, but hardly contributes to torque generation of the internal combustion engine.

  Therefore, in the present invention, when the fuel injection end timing of the expansion stroke injection is delayed from a predetermined allowable range after the ignition timing, the expansion stroke injection is forcibly ended in the middle of the injection period. Thereby, the deterioration of smoke is avoided.

  In one aspect of the present invention, during the super retard combustion, fuel injection is further performed during the intake stroke or the compression stroke prior to the expansion stroke injection, and the intake stroke injection or the compression stroke injection is performed as an injection. There is no forcible termination in the middle of the period.

  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 by the expansion stroke injection. HC reduction by burning can be achieved. If the fuel injection end timing is greatly delayed from the ignition timing for some reason, the expansion stroke injection is forcibly ended in the middle of the injection period, so that the deterioration of smoke is 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.

  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.

  By the way, in the above-mentioned super retard combustion, since the fuel injection is started after the compression top dead center just before the ignition as the expansion stroke injection, the crank angle is increased by the crank angle due to some cause (for example, increase in engine speed, decrease in fuel pressure, etc.). When the indicated fuel injection period becomes relatively long, the fuel injection end timing may be later than the ignition timing. In such a case, the fuel is injected at the point where combustion has already started. Therefore, the fuel injected late is exposed to a high temperature without being sufficiently mixed with oxygen, causing smoke. FIG. 3 shows, for example, the relationship between the injection end timing of the expansion stroke injection and the smoke when performing the intake stroke injection and the expansion stroke injection as in Example 2 described above. The smoke is the least when the fuel injection ends just before the ignition timing, and if the injection end timing becomes later than a certain allowable range after the ignition timing, the smoke deteriorates rapidly. That is, as shown in the figure, it is desirable that the injection end timing is within a predetermined smoke allowable range including the ignition timing.

  Therefore, in the present embodiment, for the expansion stroke injection, the fuel injection end timing is obtained from the fuel injection start timing and the required fuel injection amount, and the original fuel injection end timing is the above smoke allowable range including the ignition timing. It is judged whether it becomes the late side. If the original fuel injection end timing is behind the smoke allowable range, the expansion stroke injection is forcibly ended in the middle of the injection period so as to be within the smoke allowable range. In other words, even if the fuel injection period (crank angle) becomes longer for some reason, the fuel injection always ends at the most retarded angle position within the smoke allowable range in FIG. Thereby, the deterioration of smoke is avoided.

  Incidentally, with respect to the stability of the super retard combustion, as shown in FIG. 4, the relationship between the injection end timing of the expansion stroke injection and the combustion stability is such that the injection end timing is later than a certain allowable range after the ignition timing. Although the combustion stability deteriorates, the allowable range of the combustion stability is far wider than the smoke allowable range. Therefore, if the fuel injection end timing is controlled so as not to be behind the smoke allowable range, the combustion stability does not deteriorate.

  In addition, as described above, the fuel supplied later than the ignition timing after the compression top dead center contributes to the increase in exhaust temperature, but hardly contributes to the torque generation of the internal combustion engine. Even if the expansion stroke injection is forcibly terminated in the middle of the injection period, the torque fluctuation of the internal combustion engine is very small.

  When the suction stroke injection or the compression stroke injection is performed prior to the expansion stroke injection as in the second embodiment or the third embodiment, naturally, the suction stroke injection or the compression stroke injection is forced on the way. The target injection amount is always injected.

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 the injection completion time of expansion stroke injection, and smoke. The characteristic view which shows the relationship between the injection completion time of expansion stroke injection, 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 25 ... Control unit

Claims (4)

  An internal combustion engine that is provided with a fuel injection valve that directly injects fuel into a cylinder and that is provided with an ignition plug, and that requires an early temperature rise of a catalytic converter in an exhaust system in a control device for an in-cylinder direct injection spark ignition internal combustion engine During the cold start, the ignition timing is set after the compression top dead center, and the super retard combustion is performed with the expansion stroke injection in which the fuel injection start timing is set before the ignition timing and after the compression top dead center. In-cylinder direct injection spark ignition internal combustion engine characterized in that, when the fuel injection end timing of the stroke injection is delayed from a predetermined allowable range after the ignition timing, the expansion stroke injection is forcibly ended in the middle of the injection period. Engine control device.   2. In-cylinder direct injection spark ignition according to claim 1, wherein in super retard combustion, fuel injection is further performed during an intake stroke or a compression stroke prior to an expansion stroke injection after compression top dead center. Control device for internal combustion engine.   3. 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. The in-cylinder direct injection spark ignition internal combustion engine control device according to any one of claims 1 to 3, wherein the permissible range is determined by a smoke limit.

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