JP2006112329A - Control device of cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid the transitional deterioration in HC in a stage of the low cylinder temperature, by realizing early activation of a catalyst and HC reduction by after burning by a large ignition timing delay of the ignition timing. <P>SOLUTION: In a cold start of an internal combustion engine for requiring an early temperature rise in a catalytic converter, the ignition timing is set after the compression upper dead center, and super retard combustion for injecting fuel before the ignition timing and after the compression upper dead center is performed. Turbulence in a cylinder is improved by high pressure fuel injection just before the ignition timing, and since propagation of a flame is promoted, stable combustion can be realized. While, since an HC generating quantity increases to the contrary without securing vaporization of atomization in a stage just after starting of the low cylinder temperature, an interval T up to the ignition timing from the fuel injection timing is set large as the cylinder temperature becomes low, and a temporary HC increase is avoided just after the cold start. <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. 10 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, it is characterized in that the interval from the fuel injection start timing after the compression top dead center to the ignition timing in this super retard combustion is set larger as the in-cylinder temperature is lower.

  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-mentioned super retard combustion, since fuel injection is performed after compression top dead center, the period from fuel injection to ignition and hence the fuel vaporization time is shortened. For this reason, immediately after the cold start where the in-cylinder temperature (in other words, the combustion chamber wall temperature) is very low, the amount of unburned HC generated tends to increase conversely due to insufficient fuel vaporization. Moreover, immediately after such a cold start, the exhaust system temperature is also low, so that 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. .

  On the other hand, if the period from fuel injection to ignition, which is the fuel vaporization time, is excessively long, the degree of fuel stratification in the combustion chamber deteriorates, so HC also increases.

  Therefore, in the present invention, the interval from the fuel injection start timing to the ignition timing is changed according to the increase in the in-cylinder temperature immediately after the start. That is, the interval is set larger as the in-cylinder temperature is lower. Thereby, sufficient vaporization time is obtained at a stage where the in-cylinder temperature is low, and an increase in HC is suppressed. Since the in-cylinder temperature gradually increases with a certain time constant after starting, the in-cylinder temperature can be estimated using parameters such as the water temperature at the time of starting, the integrated intake air amount, the engine speed, and the load. Further, in order to simplify the control, the in-cylinder temperature can be simply replaced with the elapsed time from the start.

  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, immediately after the cold start with a very low in-cylinder temperature, the fuel spray in the cylinder is insufficiently vaporized by giving a large interval from the fuel injection start timing to the ignition timing according to the in-cylinder temperature. Therefore, it is possible to avoid a temporary increase in HC.

  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-described super retard combustion, since fuel injection is performed after compression top dead center, the period from fuel injection to ignition and thus the fuel vaporization time is shortened. Therefore, immediately after the cold start (for example, about several seconds to several tens of seconds) in which the in-cylinder temperature (in other words, the temperature of the combustion chamber wall) is very low, conversely, the unburned HC The production amount tends to increase. Moreover, immediately after such a cold start, the exhaust system temperature is also low, so that 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 amount of HC generated when the above-described super retard combustion is started immediately after the cold start. As shown in FIG. 3, in the super retard combustion in which the ignition timing is retarded to the maximum, The HC generation amount becomes large for a short time immediately after the cold start when the in-cylinder temperature is very low, and then rapidly decreases when the in-cylinder temperature warms to some extent.

  Therefore, in the present invention, the in-cylinder temperature that gradually rises after the cold start is estimated, and the interval from fuel injection to ignition, which is the fuel vaporization time, is variably set according to the in-cylinder temperature. FIG. 4 shows an example of setting of the fuel injection timing and the ignition timing. Characteristic A shows a setting in which the interval T from the fuel injection start timing to the ignition timing is the smallest, and characteristic B has the largest interval T. Indicates settings. In this example, the ignition timing does not change, and only the fuel injection timing changes. Then, as shown in FIG. 5, the interval T continuously changes between the characteristics A and B according to the in-cylinder temperature. In other words, the interval T is controlled to increase as the in-cylinder temperature decreases. As described above, the in-cylinder temperature gradually rises with a certain time constant after starting, and is thus estimated using parameters such as the water temperature at the time of starting, the total intake air amount, the engine speed, and the load. be able to. Further, in order to simplify the control, the in-cylinder temperature can be simply replaced with the elapsed time from the start.

  FIG. 6 shows the relationship between the in-cylinder temperature change and the HC generation amount (so-called engine-out HC measured at the exhaust port) for the above-mentioned characteristics A and B. The in-cylinder temperature is low. In the case of the characteristic B having a longer interval T, the amount of HC produced is smaller. Conversely, in the state where the in-cylinder temperature is somewhat warm, the characteristic A having a shorter interval T has a smaller amount of HC production. In the present embodiment, since the in-cylinder temperature and the interval T have the relationship shown in FIG. 5, the optimum interval T is obtained regardless of the in-cylinder temperature, and the amount of HC generation is suppressed.

  The reduction of HC involves the fuel vaporization and the stratification degree associated with the interval T. FIG. 7 shows the relationship between the interval T, the in-cylinder temperature, and the vaporization quality. The longer the interval T corresponding to the vaporization time, the better the vaporization of the fuel. The higher the internal temperature, the better the vaporization. This improvement in vaporization reduces HC. On the other hand, as shown in FIG. 8, when the interval T becomes longer, the stratification degree of the fuel in the combustion chamber 3 decreases, and accordingly, HC tends to increase. Therefore, according to the present embodiment, by setting the interval T according to the in-cylinder temperature, it is possible to suppress an increase in HC due to insufficient vaporization while minimizing a decrease in the degree of stratification.

  FIG. 9 shows an example in which the settings of the fuel injection timing and the ignition timing are different. Characteristic A shows a setting in which the interval T from the fuel injection start timing to the ignition timing is the smallest, and characteristic B has the smallest interval T. Indicates a large setting. In this example, the ignition timing also changes at the same time, with the characteristic A being the most retarded and the characteristic B being the most advanced. The interval T and the ignition timing continuously change between the characteristics A and B according to the in-cylinder temperature. That is, the lower the in-cylinder temperature is, the longer the interval T is, and the ignition timing is advanced. Thus, when the in-cylinder temperature is low, by increasing the interval T and at the same time the ignition timing is advanced, the combustion efficiency is increased, and the intake air amount necessary for obtaining the same torque is relatively reduced. The amount of HC produced is smaller.

  In the setting examples of FIGS. 4 and 9, only the fuel injection after the compression top dead center has been described. However, as in the second and third embodiments, the intake stroke is performed prior to the fuel injection after the compression top dead center. The same applies to the case where the first fuel injection is performed during the middle or compression stroke. In this case, the first injection timing may be changed in accordance with the change of the second fuel injection timing, or the first injection timing may not be changed.

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 the HC production | generation amount immediately after the cold start by super retard combustion. The characteristic view which shows the example of a setting from which the space | interval T from injection timing to ignition is the minimum and the maximum. The characteristic view which shows the relationship between cylinder temperature and the space | interval T. FIG. The characteristic view which shows the relationship between the in-cylinder temperature change and HC production | generation amount about the setting example of FIG. The characteristic view which shows the relationship between the space | interval T, in-cylinder temperature, and the quality of vaporization. The characteristic view which shows the relationship between the space | interval T and the degree of stratification. The characteristic view which shows the example from which the setting of fuel injection timing and ignition timing differs. 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 (5)

  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 During the cold start, the ignition timing is set after the compression top dead center, and the super retard combustion is performed before the ignition timing and after the compression top dead center, while the interval from the fuel injection start timing to the ignition timing is performed. Is set larger as the in-cylinder temperature is lower, the control device for the in-cylinder direct injection spark ignition internal combustion engine.   2. The direct injection spark ignition internal combustion engine according to claim 1, wherein in the 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. Engine control device.   The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1 or 2, wherein the air-fuel ratio in the super retard combustion is a stoichiometric air-fuel ratio or slightly lean.   4. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 1, wherein an elapsed time since the start of the internal combustion engine is regarded as an in-cylinder temperature. The control apparatus for a direct injection spark ignition internal combustion engine according to any one of claims 1 to 4, wherein the ignition timing is set to an advance side as the in-cylinder temperature is lower.

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