JP4385916B2 - In-cylinder direct injection spark ignition internal combustion engine controller - Google Patents

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 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.
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. 7 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 is attenuated as the compression stroke progresses, 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. At the time of cold start of the internal combustion engine, the ignition timing is set after compression top dead center as super retard combustion, and the fuel injection is divided into two times, and the first fuel injection during the intake stroke or the compression stroke The second fuel injection is performed before the ignition timing and during the expansion stroke after the compression top dead center. Further, when the exhaust temperature or the catalyst temperature reaches a predetermined level, the division ratio of the first and second injection amounts is changed so that the second injection amount is reduced.

  That is, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but by the second fuel injection (expansion stroke injection) performed during the expansion stroke after the compression top dead center, In-cylinder turbulence 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.

  Also, prior to the second fuel injection (expansion stroke injection) after compression top dead center, the first fuel injection is performed during the intake stroke or the compression stroke, so that the injected fuel is diffused in advance throughout the combustion chamber. Since this contributes to the promotion of afterburning of HC by ATDC ignition, it is effective in reducing HC and increasing exhaust temperature.

Here, in the above-mentioned super retard combustion, the exhaust temperature can be obtained very high, so that there is a concern that the exhaust pipe and the catalytic converter will rapidly rise in temperature and exceed the breakage temperature locally. Therefore, in the present invention, when the exhaust temperature or the catalyst temperature reaches a predetermined level, the division ratio of the first and second injection amounts is changed so that the second injection amount is reduced, and the exhaust temperature is excessively increased. Suppresses the rise.

  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. Further, by reducing the second injection amount when the exhaust temperature or the catalyst temperature reaches a predetermined level, it is possible to reliably avoid the damage due to the excessive temperature rise of the exhaust system parts and the catalytic converter.

  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 two examples of super retard combustion. In Example 1, the ignition timing is 15 ° to 30 ° ATDC (for example, 20 ° ATDC), and the fuel injection is divided into two times. The injection timing of the first fuel injection (specifically, the fuel injection start timing) is set during the intake stroke, and the injection timing of the second fuel injection (also the fuel injection start timing) is set after the compression top dead center and the ignition timing. Set before. At this time, the air-fuel ratio (the air-fuel ratio obtained by combining the two injections) 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, the turbulence generated in the intake stroke and the compression stroke is attenuated after the compression top dead center. However, in the present invention, the high-pressure fuel injection (during the expansion stroke after the compression top dead center) ( By the second injection), a gas flow is generated, whereby the turbulence in the cylinder can be generated and strengthened. Therefore, flame propagation by ATDC ignition is promoted and stable combustion is possible.

  Further, as described above, when fuel injection (intake stroke injection) is performed during the intake stroke prior to fuel injection after compression top dead center (expansion stroke injection), disturbance due to fuel spray in the intake stroke injection is in the latter half of the compression stroke. Although it is attenuated at the compression top dead center, it hardly affects the gas flow enhancement, but the injected fuel diffuses throughout the combustion chamber and contributes to the promotion of HC afterburning by ATDC ignition. It is effective for HC reduction and exhaust temperature rise.

  In the second embodiment of FIG. 2, the first fuel injection is performed during 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), compared with the intake stroke injection of the first embodiment, the compression stroke injection is performed. 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 2, 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 retard combustion of the first and second embodiments, the turbulence in the cylinder can be generated and strengthened by the fuel spray of the expansion stroke injection immediately before the ignition, and the flame propagation is promoted and stabilized. Combustion can be performed. 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 manner, the second 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 super retarded combustion, the exhaust temperature can be obtained very high, so that there is a concern that the exhaust pipe and the catalytic converter rapidly increase in temperature and locally exceed the breakage temperature. Therefore, in the present invention, when the exhaust temperature or the catalyst temperature reaches a predetermined level, the second injection amount is reduced to suppress an excessive increase in the exhaust temperature. That is, in the above-described super retard combustion, the injection amount of the expansion stroke injection, which is the second fuel injection, and the exhaust temperature have a correlation as shown in FIG. 3, and the exhaust temperature increases as the injection amount of the expansion stroke injection increases. Becomes higher. In other words, when the exhaust temperature and the catalyst temperature are likely to become excessively high, the exhaust temperature can be controlled to an appropriate temperature range by reducing the injection amount of the expansion stroke injection.

  FIG. 4 shows an embodiment in which when the exhaust temperature detected by the exhaust temperature sensor 13 reaches a predetermined temperature close to the exhaust system breakage temperature, the expansion stroke injection amount is controlled to a predetermined amount. The predetermined temperature is set with an appropriate margin for the exhaust system breakage temperature. By reducing the injection amount of the second expansion stroke injection to an appropriate level when the exhaust temperature reaches the predetermined temperature in this way, as shown by the thick solid line, further increase in the exhaust temperature is avoided, It is possible to maintain the temperature just before the exhaust system breakage temperature.

Therefore, early activation of the catalytic converter 10 can be realized while reliably avoiding thermal damage to the exhaust system parts and the catalytic converter 10. Here, since the exhaust temperature gradually rises with a certain time constant after the start, in addition to the direct detection by the exhaust temperature sensor 13, the water temperature at the start, the integrated intake air amount, the engine speed, the load, etc. It is also possible to estimate using these parameters. Furthermore, in order to simplify the control, the exhaust temperature can be simply replaced with the elapsed time from the start. Note that a decrease in the injection amount of the expansion stroke injection is to change the ratio clogging division ratio of the first injection quantity of fuel injection (intake stroke injection or compression stroke injection) and the injection amount of the second expansion stroke injection drunk can be realized.

  Next, FIG. 5 shows an embodiment in which when the catalyst temperature of the catalytic converter 10 reaches a predetermined catalyst activation temperature (more specifically, the catalyst activation start temperature), the expansion stroke injection amount is controlled to be reduced to a predetermined amount. Is shown. As a result, as indicated by the thick solid line, the exhaust temperature does not increase any more, and the catalyst temperature rises more slowly. The catalyst temperature may be detected directly by adding a catalyst temperature sensor (not shown) to the catalytic converter 10, or, like the exhaust temperature described above, gradually after a start with a certain time constant. Can be estimated using parameters such as the water temperature at start-up, the cumulative intake air amount, the engine speed, and the load. Furthermore, in order to simplify the control, the catalyst temperature can be simply replaced with the elapsed time from the start.

  Furthermore, FIG. 6 shows an embodiment in which the injection amount of the expansion stroke injection is reduced stepwise in two steps. In this example, when the exhaust temperature first reaches a predetermined temperature close to the exhaust system breakage temperature, the injection amount of the expansion stroke injection is reduced to the first predetermined amount, and then the catalyst temperature reaches the catalyst activation temperature. Sometimes it is further reduced to the second predetermined amount. As a result, the exhaust temperature and the catalyst temperature change as shown by thick solid lines, and an excessive temperature rise of the exhaust system parts is avoided, and the catalytic converter 10 is excessive after the temperature rises rapidly to the catalyst activation temperature. Temperature rise is suppressed. The second predetermined amount may be set to “0”, that is, the expansion stroke injection may be stopped when the catalyst temperature reaches the catalyst activation temperature.

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 quantity of expansion stroke injection, and exhaust temperature. Explanatory drawing which shows the example which reduces the injection quantity of expansion stroke injection when exhaust temperature reaches predetermined temperature. Explanatory drawing which shows the example which reduces the injection quantity of an expansion stroke injection, when a catalyst temperature reaches a catalyst activation temperature. Explanatory drawing which shows the example which reduces the injection quantity of an expansion stroke injection in two steps based on exhaust gas temperature and catalyst temperature. Explanatory drawing which shows the change of the disturbance in a cylinder in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Combustion chamber 10 ... Catalytic converter 13 ... Exhaust temperature sensor 14 ... Spark plug 15 ... Fuel injection valve 25 ... Control unit

Claims (7)

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 an exhaust system catalytic converter in a control device for a direct ignition spark ignition internal combustion engine At the time of cold start, the ignition timing is set after compression top dead center as super retard combustion, and the fuel injection is divided into two, and the first fuel injection is performed during the intake stroke or the compression stroke, and the ignition is performed. While the second fuel injection is performed before the timing and during the expansion stroke after the compression top dead center, when the exhaust temperature or the catalyst temperature reaches a predetermined level, the first injection is performed so that the second injection amount is reduced. A control device for an in-cylinder direct injection type spark ignition internal combustion engine, characterized in that the split ratio of the second injection amount is changed .   2. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 1, wherein when the exhaust temperature reaches a predetermined temperature close to an exhaust system breakage temperature, the second injection amount is reduced.   The direct injection spark ignition internal combustion engine control device according to claim 1, wherein when the catalyst temperature reaches the catalyst activation temperature, the second injection amount is reduced.   The control device for a direct injection type spark ignition internal combustion engine according to any one of claims 1 to 3, wherein the second injection amount is decreased stepwise in accordance with the exhaust gas temperature or the catalyst temperature.   5. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 1, wherein an elapsed time from the start of the internal combustion engine is used as an alternative to the exhaust gas temperature or the catalyst temperature.   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.   7. 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.

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