JP4333548B2 - 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. 11 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. When the internal combustion engine is cold-started, 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. Further, immediately after the cold start, the temperature raising phase is executed prior to the execution of the super retard combustion . The heating phase, the fuel is injected during the compression stroke, the interval between the ignition timing is set after the advance side and the compression top dead center than when the super-retard combustion Rutotomoni, the fuel injection start timing to the ignition timing However, it is set to be larger than the super retard combustion, and a predetermined period immediately after the cold start in which the HC emission amount by the super retard combustion becomes larger than the HC emission amount by the temperature raising phase is the super retard combustion. Combustion is prohibited and the temperature is raised .

  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 above-described super retard combustion, the amount of unburned HC generated tends to increase due to an increase in gas volume accompanying an increase in combustion efficiency (that is, an increase in intake air amount necessary to obtain the same torque). There is. Since the exhaust system temperature is low immediately after the cold start, oxidation of HC in the exhaust passage is not sufficiently promoted, and unburned HC generated in the cylinder is easily discharged to the outside as it is. That is, if the super retard combustion is performed immediately after the cold start, HC discharged from the exhaust system to the outside temporarily increases.

Therefore, in the present invention, within a very short period immediately after start-up, as the temperature rising phase, the ignition timing is set to a slightly advanced angle than in the case of super retard combustion even after the same compression top dead center , and The compression stroke injection is used. That is, after this temperature rising phase, the shift to super retarded combustion is made. In this heating phase, although the exhaust temperature is slightly lower than in the super retard combustion, the combustion efficiency is higher than in the super retard combustion by setting the ignition timing to the advanced side, and the gas volume becomes relatively small. The total amount of HC is reduced. Further, the interval from the fuel injection start timing to the ignition timing, that is, the fuel vaporization time becomes longer. Therefore, the exhaust system temperature can be raised while suppressing a temporary increase in the amount of HC emission when the exhaust system temperature is low.

  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, and at the time of cold start, early activation of the catalyst and reduction of HC due to afterburning. Can be achieved. Then, during a short period immediately after the cold start, a transient increase in the HC emission amount can be avoided by executing the temperature rising phase with the ignition timing slightly advanced.

  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 fuel injection is performed after compression top dead center, the combustion efficiency is reduced, and the intake amount necessary to obtain the same torque is increased. On the contrary, the amount of HC produced tends to increase. In addition, in super retard combustion in which fuel injection is performed after compression top dead center, the time from fuel injection to ignition and thus the fuel vaporization time is shortened, so that fuel vaporization is insufficient immediately after a cold start with a very low in-cylinder temperature. As a result, an increase in unburned HC may occur. Since the exhaust system temperature is low immediately after the cold start, oxidation of HC in the exhaust passage is not sufficiently promoted, and unburned HC generated in the cylinder is easily discharged to the outside as it is.

  FIG. 3 shows the characteristics of the HC generation amount and exhaust temperature immediately after such cold start, and the super retard combustion shown in FIG. 4A (this is the same as that of the first embodiment described above). ) Is indicated by a broken line A when it is started immediately after a cold start. As shown in the figure, in the super retard combustion, immediately after the cold start with a very low in-cylinder temperature, the amount of HC generated becomes large due to an increase in gas volume or insufficient vaporization, and then the in-cylinder temperature reaches a certain level. When warmed, the amount of HC produced becomes very small.

  Therefore, in the present invention, during a predetermined period immediately after start-up (for example, until t1 in FIG. 3 where the amount of HC generation is large), the temperature rising phase is set so as to suppress the increase in gas volume. After that, it shifts to super retard combustion.

  FIG. 4B shows an example of setting of the temperature rising phase executed prior to the super retarded combustion of FIG. 4A. Here, fuel injection is performed before compression top dead center, and compression is performed. Ignition after top dead center. However, this ignition timing is set to an advance side with respect to the ignition timing at the time of super retard combustion shown in (A). In other words, the ignition timing at the time of super retard combustion is set to the retard side to the limit at which combustion can be established, whereas the ignition timing in the temperature rising phase is after the compression top dead center. In order to relatively increase the combustion efficiency, the angle is set to the more advanced side without delaying to the combustion limit. As a result, for example, the intake air amount (more strictly speaking, the intake air amount and the fuel amount) required to maintain the same idle speed becomes relatively smaller than that in the super retard combustion, and the increase in gas volume is suppressed. . Therefore, the total amount of HC generation at the initial stage when the exhaust gas temperature is low is reduced. Further, the interval T2 from the fuel injection start timing to the ignition timing in the temperature raising phase is relatively larger than the interval T1 in the super retard combustion. Thereby, in the temperature rising phase, the fuel vaporization time becomes longer, and the generation of HC in the cold state is suppressed.

  A solid line B in FIG. 3 shows the characteristics of the HC generation amount and the exhaust temperature when the above temperature rising phase is executed from the start to t1 and the shift to the super retarded combustion is performed at the time t1. As shown in the figure, a temporary increase in HC can be avoided by setting the temperature rising phase with a small gas volume immediately after the cold start. Further, focusing on the characteristics of the exhaust temperature, the solid line B has a slow initial temperature rise compared to the broken line A, which has been super retarded from the beginning, but the exhaust temperature is relatively high due to ATDC ignition in the temperature rising phase, Moreover, after switching to the super retard combustion at the time point t1, the temperature rapidly rises due to the super retard combustion, so the time required for the activation of the final target catalyst is the case of the super retard combustion from the beginning. There will be almost no difference. Incidentally, the period up to t1 as the temperature rising phase is, for example, about several seconds to several tens of seconds. As is apparent from FIG. 3, the period t1 during which the temperature raising phase is executed is basically HC emission amount in the characteristic B in the temperature raising phase rather than the characteristic A in the case of super retard combustion from the beginning. It is desirable that the values coincide with each other in a relatively small period.

  FIG. 5 shows different setting examples of the temperature rising phase. In this example, the fuel injection is divided into two times, and each is injected during the compression stroke. The interval T3 from the start timing of the second fuel injection to the ignition timing is relatively larger than the interval T1 in the super retard combustion. As in the example of FIG. 4B, the ignition timing is set to an advance side after the compression top dead center and with respect to the ignition timing at the time of super retard combustion.

  FIG. 6 is a flowchart showing the combustion control process of the present invention executed at the cold start. When it is detected in step 1 that the internal combustion engine 1 is started, the process proceeds to step 2 to estimate the in-cylinder temperature. In step 3, it is determined whether or not the estimated in-cylinder temperature has reached a predetermined temperature (temperature necessary for fuel vaporization). As shown in FIG. 7, the in-cylinder temperature is assumed to gradually increase with a certain time constant after starting, and is estimated using parameters such as water temperature at startup, integrated intake air amount, engine speed, load, and the like. can do. Furthermore, in order to simplify the control, it may be determined whether or not the predetermined temperature has been reached simply by the elapsed time from the start.

  If it is determined in step 3 that the predetermined temperature has not been reached, the process proceeds to step 4 until the predetermined temperature is reached, and the above-described temperature increase phase is executed. When the predetermined temperature is reached, the process proceeds to step 5 to perform super retard combustion. The super retarded combustion can be divided injection as in the second and third embodiments in addition to the above-described first embodiment. Further, the temperature raising phase in step 4 is not limited to the setting shown in FIG. 4B or FIG. 5, and various settings are possible.

  Next, FIG. 8 shows an embodiment in which the period of the temperature raising phase is determined based on the exhaust gas temperature. That is, immediately after the cold start when the exhaust system temperature is low, the oxidation of HC in the exhaust passage is not sufficiently promoted, and unburned HC generated in the cylinder is easily discharged to the outside as it is, but the exhaust temperature is somewhat If it becomes high, unburned HC is oxidized in the exhaust passage. This flowchart is similar to the embodiment of FIG. 6. When it is detected in step 1 that the internal combustion engine 1 has been started, the process proceeds to step 2 where the exhaust temperature detected by the exhaust temperature sensor 13 is read. In step 3, it is determined whether or not the detected exhaust gas temperature has reached a predetermined temperature (temperature necessary for HC oxidation). As shown in FIG. 9, the exhaust temperature gradually rises with a certain time constant after the start, so that instead of direct detection by the exhaust temperature sensor 13, the water temperature at the start, the integrated intake air amount, the engine speed It can also be estimated using parameters such as number, load, etc. Furthermore, in order to simplify the control, it may be determined whether or not the predetermined temperature has been reached simply by the elapsed time from the start.

  If it is determined in step 3 that the predetermined temperature has not been reached, the process proceeds to step 4 until the predetermined temperature is reached, and the above-described temperature increase phase is executed. When the predetermined temperature is reached, the process proceeds to step 5 to perform super retard combustion.

  Next, FIG. 10 shows an embodiment in which the period of the temperature raising phase is determined in consideration of both the in-cylinder temperature and the exhaust gas temperature. Here, it is assumed that the in-cylinder temperature is simply indicated by the elapsed time from the start, and the exhaust temperature is directly detected by the exhaust temperature sensor 13. It is also possible to estimate from parameters. If it is detected in step 1 that the internal combustion engine 1 has been started, the process proceeds to step 2 where the elapsed time since the start is read, and in step 3, the exhaust temperature detected by the exhaust temperature sensor 13 is read. Next, in step 4, it is determined whether or not the elapsed time from the start has reached a predetermined time (a time during which the in-cylinder temperature necessary for fuel vaporization can be reached), and in step 5, the detected exhaust temperature is determined to be It is determined whether or not the temperature (temperature necessary for HC oxidation) has been reached.

  If it is determined in step 4 or step 5 that the predetermined time or temperature has not been reached, the process proceeds to step 6 to execute the above-described temperature raising phase. Then, when a predetermined time from the start elapses and the exhaust gas temperature reaches the predetermined temperature, the routine proceeds to step 7 where super retard combustion is performed.

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 characteristic of HC production | generation amount and exhaust temperature immediately after the cold start by this invention. The characteristic view which shows the example of a setting of super retarded combustion (A) and a temperature rising phase (B). The characteristic view which shows the example of a setting from which a temperature rising phase differs. The flowchart which shows one Example of the combustion control of this invention. Explanatory drawing of estimation of in-cylinder temperature. The flowchart which shows the Example from which the combustion control of this invention differs. Explanatory drawing of estimation of exhaust gas temperature. The flowchart which shows the further another Example of the combustion control of this invention. 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)

In addition to a fuel injection valve that directly injects fuel into the cylinder, an ignition plug is provided , and the ignition timing is set after compression top dead center at the time of cold start of an internal combustion engine that requires early temperature rise of the exhaust system catalytic converter In addition, in the control device for a direct injection type spark ignition internal combustion engine that performs super retard combustion that injects fuel before the ignition timing and after compression top dead center ,
Immediately after the cold start, the temperature rising phase is executed prior to the execution of the super retard combustion , and this temperature increasing phase injects fuel during the compression stroke, and the ignition timing is more advanced than that in the case of the super retard combustion. Rutotomoni is set after compression top dead center, distance from the fuel injection start timing to the ignition timing, it is set larger than the super-retard combustion,
An in-cylinder characterized in that the super retard combustion is prohibited and the temperature rising phase is set for a predetermined period immediately after the cold start in which the HC emission amount due to the super retard combustion is larger than the HC emission amount due to the temperature rising phase. Control device for a direct injection spark ignition internal combustion engine.   2. 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 according to claim 1 or 2, 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. Control device for an ignition internal combustion engine.   The control apparatus for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 3, wherein the air-fuel ratio in super retarded combustion is a stoichiometric air-fuel ratio or slightly lean.

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