JP4577091B2 - 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. 9 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, it rapidly attenuates as indicated by reference symbol C, 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 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 that 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. Note that in a NOx trap catalyst that adsorbs NOx, the sulfur component (SOx) adheres to the catalyst, so that the NOx adsorption performance deteriorates. Therefore, the SOx release treatment (sulfur coating) that forcibly raises the temperature of the catalyst and releases SOx. 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, when the load increases during the operation in the super retard combustion, 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.

  Here, in the super retard combustion in which the ignition timing is greatly retarded as described above, the exhaust temperature becomes very high as compared with the conventional technique such as Patent Document 1, so that the vehicle starts or the auxiliary load There is a concern that when the load is slightly increased due to fluctuations in the temperature, the temperature of the catalytic converter becomes excessively high, causing thermal damage or deterioration. In particular, even if the catalyst temperature reaches the activation temperature and cancels the super retard combustion, the internal temperature of the catalytic converter continues to increase due to the heat capacity of the exhaust system components upstream of the catalytic converter, the reaction heat of the catalyst itself, etc. There is a risk of overshooting.

  Therefore, in the present invention, when the load increases during the operation in the super retard combustion, the super retard combustion is canceled.

  The load change can be detected based on, for example, accelerator opening change. Or it can detect based on an auxiliary machine operating state. Alternatively, the super retard combustion may be canceled when the idle state shifts to the non-idle state.

  When the load decreases after canceling the super retard combustion, the super retard combustion may be resumed.

In the present invention, the super retard combustion is prohibited until the catalyst outlet temperature on the outlet side of the catalytic converter reaches the activation start temperature of the catalyst. In other words, in the super retard combustion, the exhaust temperature becomes very high. Therefore, if the catalytic converter is in a completely cold state (a state close to the outside air temperature), it is assumed that the engine has shifted to the super retard combustion immediately after the engine is started. Then, the temperature gradient inside the catalytic converter becomes very steep. That is, there is a concern that only the upstream portion such as the monolithic ceramic catalyst carrier rapidly becomes high in temperature and the thermal strain increases. Therefore, after the internal combustion engine is started, thermal damage to the catalytic converter can be avoided more reliably by starting super retard combustion from a state in which the catalytic converter has reached the activation start temperature of the catalyst.

  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. When the load increases due to the start of the vehicle or the like during operation in super retard combustion, the super retard combustion is canceled, so that the catalyst temperature becomes excessively high, causing catalyst deterioration or catalyst support damage. 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. Further, in the present embodiment, in order to detect the temperature state of the catalytic converter 10, a catalyst temperature sensor 31 disposed at the center in the longitudinal direction of the monolithic ceramic catalyst carrier of the catalytic converter 10 and an outlet portion of the catalytic converter 10 And a catalyst outlet temperature sensor 32.

  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.

  Here, in the above-described super retard combustion, the exhaust gas temperature can be obtained extremely high, so the catalytic converter 10 is rapidly heated from the upstream side, and there is a concern of thermal distortion of the catalytic converter 10 or excessive temperature rise. . Therefore, in this embodiment, the operation mode is switched while monitoring the temperature state of the catalytic converter 10 by the processing as shown in FIG.

  First, in step 1, the outlet temperature TC of the catalytic converter 10 detected by the catalyst outlet temperature sensor 32 is compared with a predetermined first reference temperature T1, and if it is lower than the first reference temperature T1, the process proceeds to step 2. Perform normal control when cold. The first reference temperature T1 substantially corresponds to the activation start temperature of the catalyst, and is set to about 150 ° C. to 200 ° C., for example. Also, the normal control when the engine is cold is not for an extreme exhaust temperature increase such as super retard combustion, but for a certain amount of exhaust temperature increase.For example, while performing fuel injection during the intake stroke, compression top dead center Ignition is performed at a time later than the previous MBT point. Alternatively, in addition to or instead of the intake stroke injection, the compression stroke injection may be performed. When the catalytic converter 10 is in a completely cold state when the engine is started, the temperature of the catalytic converter 10 is gradually increased by the normal control during the cold state.

  If the outlet temperature TC is equal to or higher than the first reference temperature T1, it is determined in step 3 whether the catalyst temperature TB detected by the catalyst temperature sensor 31 is lower than the second reference temperature T2. The second reference temperature T2 is a temperature substantially corresponding to the complete activity of the catalyst (more specifically, a temperature slightly lower than the complete activation temperature), and is set to about 250 ° C. to 300 ° C., for example. If starting from the cold state, when the outlet temperature TC reaches the first reference temperature T1, the catalyst temperature TB is usually lower than the second reference temperature T2. Perform retarded combustion. As a result, the exhaust gas temperature rises rapidly, and the catalytic converter 10 quickly rises in temperature. This super retard combustion is basically continued in step 6 until the catalyst temperature TB becomes equal to or higher than the second reference temperature T2. If the catalyst temperature TB is equal to or higher than the second reference temperature T2, the routine proceeds to step 7, where the normal control after warm-up, that is, the above-described homogeneous combustion operation or stratified combustion operation after warm-up is executed.

  During super retard combustion, it is repeatedly determined in step 5 whether the throttle opening Th of the electronically controlled throttle valve 7 exceeds a predetermined upper limit value Th1, and if the upper limit value Th1 is exceeded, the catalyst Without waiting for the temperature TB to reach the second reference temperature T2, the routine proceeds to step 7 where the super retard combustion is immediately canceled. When the super retard combustion is canceled in this way, the normal control after the warming-up (step 7) is not performed, but the normal control during the cold-cooling described above is performed, for example, the catalyst temperature TB is the second reference temperature T2. You may make it carry out until it becomes the above.

  As described above, in this embodiment, the super retard combustion is prohibited until the outlet temperature TC reaches the first reference temperature T1, and the catalytic converter reduces the time required until the catalyst is fully activated by the super retard combustion. 10 thermal degradation is avoided.

  FIGS. 4 and 5 show the temperature change of the catalytic converter 10 when the internal combustion engine including the catalytic converter 10 is completely cooled. When the exhaust temperature is very high (FIG. 4), the exhaust gas is relatively exhausted. This shows the case where the temperature is low (FIG. 5). Specifically, as shown in FIG. 6, the temperature TA at the inlet portion (point A) of the catalytic converter 10, the temperature TB1 near the upstream end (point B1) of the monolith catalyst carrier, and the monolith catalyst carrier. 4 shows temperature changes at four locations, a temperature TB2 in the vicinity of the downstream end (point B2) and a temperature TC at the outlet portion (point C) of the catalytic converter 10.

  When a high exhaust temperature is applied as super retard combustion immediately after start-up, as shown in FIG. 4, the catalyst carrier upstream end temperature TB1 rises rapidly with the inlet temperature TA, so the temperature difference ΔT before and after the catalyst carrier Becomes very large. That is, a large thermal distortion occurs.

  On the other hand, when the exhaust temperature is relatively low, as shown in FIG. 5, the temperature difference ΔT before and after the catalyst carrier is sufficiently small. When the outlet temperature TC reaches the predetermined first reference temperature T1, when switching to super retarded combustion, as shown by the broken lines in FIG. The time required to reach a certain catalyst complete activity is not much different from the case of FIG. Note that, at the stage of switching to super retarded combustion, reaction heat begins to be generated inside the catalyst carrier, so that a large temperature difference ΔT does not occur thereafter.

  In addition, when the throttle opening Th increases during the super retard combustion and the fuel injection amount increases, the inlet temperature TA (in other words, the exhaust gas temperature) becomes excessively high (not shown), and accordingly, the catalyst carrier Since the upstream end temperature TB1 further increases, the temperature difference ΔT of the catalyst carrier, that is, the thermal strain becomes large. Moreover, even after the catalyst temperature TB reaches the second reference temperature T2 and the super retard combustion is stopped, the internal temperature of the catalytic converter 10 rises due to the heat capacity of the exhaust system components upstream of the catalytic converter 10 and the reaction heat of the catalyst itself. There is a risk of overshooting to the catalyst deterioration temperature. On the other hand, in the above embodiment, the super retard combustion is stopped immediately when the throttle opening degree Th exceeds the predetermined upper limit value Th1, so that the excessive temperature rise and thermal distortion as described above can be avoided. .

  If the throttle opening Th becomes equal to or lower than the predetermined opening Th1 before the catalyst temperature TB reaches the second reference temperature T2 after the throttle opening Th becomes large and the super retard combustion is stopped, the super retard combustion is performed. Is resumed.

  7 and 8 show a modification of the flowchart of FIG. In the example of FIG. 7, during the execution of super retard combustion, in step 5A, it is repeatedly determined whether or not a predetermined auxiliary load such as an air conditioner compressor has been turned ON, and the auxiliary load is turned ON. In this case, the super retard combustion is immediately canceled without waiting for the catalyst temperature TB to reach the second reference temperature T2. The super retard combustion may be canceled when the sum of the loads of the plurality of auxiliary machines reaches a predetermined level.

  In the example of FIG. 8, whether or not the idle switch signal indicating that the accelerator pedal depression amount or the opening degree of the electronically controlled throttle valve 7 is 0 is ON in step 5B during the execution of the super retard combustion. When the idle switch signal is turned OFF, the super retard combustion is immediately canceled without waiting for the catalyst temperature TB to reach the second reference temperature T2. 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. Accordingly, when the vehicle shifts from the idle state to the non-idle state due to the start of the vehicle or the like, the super retard combustion is stopped.

  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 flowchart which shows the mode switching process at the time of a start. The time chart which shows the temperature change of each part of a catalytic converter when exhaust gas temperature is high. The time chart which shows the temperature change of each part of a catalytic converter when exhaust gas temperature is low. Explanatory drawing which shows the temperature measuring point of FIG. 4 and FIG. The flowchart which shows the modification of a detection of load change. The flowchart which shows the modification of a detection of load change. Explanatory view showing a change in turbulence in the cylinder in accordance coming technology.

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 31 ... Catalyst temperature sensor 32 ... Catalyst outlet temperature sensor

Claims (9)

In a control device for a direct injection type spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug,
At the time of cold start of the engine, the ignition timing is set after the compression top dead center, and the super retard combustion is performed so that fuel is injected before the ignition timing and after the compression top dead center.
The super retard combustion is prohibited until the catalyst outlet temperature on the outlet side of the catalytic converter provided in the exhaust system reaches the activation start temperature of the catalyst, and the super retard combustion is performed after the catalyst exit temperature reaches the activation start temperature. While starting
A control apparatus for an in-cylinder direct injection spark ignition internal combustion engine, wherein the super retard combustion is canceled when a load increases during operation in the super retard combustion. The in-cylinder direct injection spark according to claim 1 , wherein the super retard combustion is terminated when the temperature of the catalyst carrier of the catalytic converter reaches a second set temperature higher than the set temperature. Control device for an ignition internal combustion engine. 3. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1 or 2 , wherein after the cancellation of the super retard combustion, the super retard combustion is resumed when the load decreases. The control device for a direct injection type spark ignition internal combustion engine according to any one of claims 1 to 3 , wherein the load change is detected based on an accelerator opening change. The control apparatus for a direct injection type spark ignition internal combustion engine according to any one of claims 1 to 3 , wherein the load change is detected based on an operating state of an auxiliary machine. The control apparatus for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 5 , wherein the super retard combustion is canceled when the idle state is shifted to the non-idle state. The in-cylinder direct injection spark ignition internal combustion engine control device according to any one of claims 1 to 6 , 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 7 , 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 8 , wherein the air-fuel ratio in super retarded combustion is a stoichiometric air-fuel ratio or slightly lean.

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