JP2008075533A - Control device and control method for cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize HC reduction by early stage activation of a catalyst and after burn by great retardation of ignition timing and to avoid deterioration of HC in ultra retard combustion in a stage where oil and water temperature is low. <P>SOLUTION: The ultra retard combustion in which ignition timing ADV is retarded to 10°-50° ATDC, first fuel injection I1 is performed in compression stroke, and second fuel injection I2 is performed in an expansion stroke at timing advanced from ignition timing ADV by 10°-20° CA is carried out in cold start of an internal combustion engine during which early stage temperature rise of a catalytic converter is demanded. Compact air fuel mixture lump is formed at a part of combustion chamber near a spark plug by the first injection, rich air fuel mixture lump is locally formed in a part near the spark plug inside thereof by the second injection, and ignition is done under these conditions. However, ultra retard combustion is inhibited when engine oil water temperature is lower than predetermined oil water temperature tolerance. <P>COPYRIGHT: (C)2008,JPO&INPIT

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, for example, at 120 ° BTDC to 45 ° BTDC after the middle of the compression stroke. A similar technique is also described in Patent Document 2.

Further, Patent Document 3 was previously proposed by the present applicant, and uses combustion in the cylinder due to the spray energy of high-pressure fuel injection to retard the ignition timing until after compression top dead center. As an example, it is disclosed that the first fuel injection is performed in the latter half of the compression stroke, and the second fuel injection is performed immediately before the ignition of the expansion stroke. ing.
Japanese Patent No. 3325230 JP 2001-336467 A Japanese Patent Laid-Open No. 2005-214039

  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. Therefore, combustion stability is low, and especially in the no-load region, the ignition timing is set to before compression top dead center (BTDC ignition), so that exhaust temperature rise and retarded HC can be sufficiently achieved by retarding the ignition timing. I can't. In addition, if the first injection is performed during the intake stroke, the fuel enters the quench region and the clevis in the combustion chamber and becomes a source of HC generation.

  On the other hand, in Patent Document 2, the first fuel injection is performed in the latter half of the compression stroke, and the second fuel injection is performed immediately before the ignition of the expansion stroke. However, depending on the in-cylinder turbulence due to the second fuel injection, Since combustion is established, a high fuel pressure is required. As a result, combustion is relatively fast (compared to the case where the fuel pressure is low), and there is still room for improvement in terms of an increase in exhaust temperature and a reduction in HC associated therewith.

  The present invention includes a fuel injection valve that directly injects fuel into a cylinder and a spark plug, and in a predetermined operating state, for example, when the temperature of the exhaust (gas) temperature needs to be increased, such as when the catalytic converter is cold. In addition, in a direct injection spark ignition internal combustion engine that performs super retard combustion with the ignition timing set after compression top dead center, during super retard combustion, the first fuel injection is performed during the compression stroke, and combustion in the vicinity of the spark plug is performed. A rich air-fuel mixture is formed in a part of the chamber, and a second time during the expansion stroke at a timing preceding the ignition timing by a predetermined period so that the locally rich air-fuel mixture reaches the ignition plug at the ignition timing. Fuel injection is performed, and ignition is performed with a two-stage stratified mixture formed in a part of the combustion chamber near the spark plug.

  That is, in the present invention, a compact stratified mixture is formed in the combustion chamber by two fuel injections at a relatively low fuel pressure without depending on the spray energy of the fuel injection. In particular, at the ignition timing, a locally rich air-fuel mixture is present in the vicinity of the spark plug due to the spray of the second fuel injection, and surrounds the periphery of the spark plug rather than the stoichiometric air-fuel ratio by the first fuel injection. A rich and lean air-fuel mixture exists near the spark plug. That is, a compact stratified mixture having two different concentrations is formed, and ignition is performed in this state. It is desirable that the air-fuel mixture produced by the first fuel injection does not diffuse throughout the combustion chamber.

  According to such a combustion method, stable combustion is possible with respect to a minute change in rotational speed or a minute load change for each cycle. Since both fuel injections are performed at a relatively low fuel pressure in a place where the in-cylinder pressure is high, the spray becomes compact and hardly enters the quench region or the clevis, thus suppressing the generation of HC. In addition, since a relatively low fuel pressure can be used, the combustion speed can be suppressed, which is advantageous in increasing the exhaust temperature and reducing HC.

  Here, in the above-described super retard combustion, fuel injection is performed in a state where the cylinder in the vicinity of the compression top dead center is relatively narrow, so that the engine oil water temperature (engine temperature) is low just after a cold start of the internal combustion engine. Then, the wall flow increases due to insufficient vaporization of the fuel, and conversely, the amount of unburned HC generated 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. .

  Therefore, in the present invention, the engine temperature such as engine water temperature or engine oil temperature (hereinafter also referred to as engine oil water temperature) is set to a predetermined permitted temperature (hereinafter also referred to as permitted oil water temperature) as in a predetermined period immediately after the cold start of the internal combustion engine. The above-mentioned super retard combustion is prohibited. This predetermined period corresponds to a period until the in-cylinder temperature (combustion chamber wall temperature) reaches a predetermined temperature, or a period until the exhaust system temperature reaches a predetermined temperature. It is determined based on the detection or estimation of this, or simply the passage of a predetermined time.

  According to the present invention, the combustion stability of the super retard combustion in which the ignition timing is set after the compression top dead center is improved. For example, at the time of cold start, early activation of the catalyst and reduction of HC are achieved by increasing the exhaust temperature. can do. When the engine temperature has not reached the predetermined allowable temperature, such as during a short period immediately after the cold start, the super-retard combustion is prohibited, and the vaporization of the fuel spray in the cylinder becomes insufficient. A transient increase in HC due to can be avoided.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a system configuration of a direct injection type spark ignition internal combustion engine according to an embodiment of the present invention. 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.

  The internal combustion engine 1 includes a water temperature sensor 21 for detecting the engine cooling water temperature and an oil temperature sensor 24 for detecting the engine oil temperature as means for detecting the engine oil temperature as the engine temperature and the engine oil water temperature. , Is provided. Furthermore, a crank angle sensor 22 that detects the crank angle and an accelerator opening sensor 23 that detects the amount of depression of the accelerator pedal by the driver are provided.

  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, normal control such as normal stratified combustion operation or homogeneous combustion operation is performed. For example, 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 at a time before the compression top dead center. The fuel spray is collected in a layered manner in the vicinity of the spark plug 14, thereby realizing, for example, stratified combustion with a lean air-fuel ratio. 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.

  In this embodiment, the super retard combustion is performed 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. This super retard combustion will be described below. The fuel injection timing and ignition timing will be described with reference to FIG. FIG. 2 shows an example of the fuel injection timing and ignition timing during super retard combustion, and the ignition timing ADV is set to 10 ° to 50 ° ATDC in order to obtain a sufficiently high exhaust temperature. . That is, the period B is 10 ° to 50 ° CA. Further, the first fuel injection I1 is performed during the compression stroke, and the second fuel injection I2 is performed during the expansion stroke. The first fuel injection I1 is for forming a rich air-fuel mixture that spreads in a part of the combustion chamber 3 in the vicinity of the spark plug 14, and from the fuel injection timing (specifically, the fuel injection start timing) to the ignition timing. The period C until ADV is set to 50 ° to 140 ° CA, for example. In other words, the fuel injection timing is set so that the fuel spray by the first fuel injection I1 diffuses in the combustion chamber 3 to some extent but does not diffuse excessively. When the period C is excessively long, the fuel spray is excessively diffused, and the fuel component enters the quench region or the clevis.

  Then, the second fuel injection I2 during the expansion stroke is performed at a timing preceding the ignition timing ADV by a predetermined period A so that a locally richer air-fuel mixture reaches the ignition plug 14 at the ignition timing ADV. Done. The period A from the fuel injection timing (specifically, the fuel injection start timing) to the ignition timing ADV basically correlates with the distance from the fuel injection valve 15 to the spark plug 14, for example, 10 ° to 20 ° CA. is there. At this time, the air-fuel ratio (the average air-fuel ratio of the entire combustion chamber by two injections) is set to the stoichiometric air-fuel ratio or slightly lean (about 16 to 17). Thereby, a sufficient amount of oxygen necessary for afterburning of HC is secured.

  Further, since combustion is performed without depending on the disturbance due to the energy of the fuel spray, a relatively low fuel pressure is used as the fuel pressure within a range where combustion is established as will be described later.

  By performing the fuel injection as described above, at the ignition timing ADV, as shown in FIG. 3, a compact stratified air-fuel mixture having a two-stage concentration surrounding the spark plug 14 is formed. That is, by the first fuel injection I1, a first air-fuel mixture richer than the stoichiometric air-fuel ratio is formed in a part of the combustion chamber 3 in the vicinity of the spark plug 14 as indicated by reference numeral 31, and 2 A richer second air-fuel mixture resulting from the second fuel injection I2 is locally formed in the vicinity of the spark plug 14 as indicated by reference numeral 32. Both fuel injections are performed toward a field where the in-cylinder pressure in the vicinity of the top dead center is high and the fuel pressure is relatively low. The outside is basically a fresh air layer where fuel is not diffused. Then, in this state of stratification, the second air-fuel mixture 32 is ignited by the spark plug 14 and combustion is performed relatively slowly.

  In the retarded combustion of the system of this embodiment, the injection timing of the first fuel injection I1 hardly affects the combustion stability, that is, the misfire rate and torque fluctuation, and the fluctuation of the injection timing of the second fuel injection I2 is misfired. The effect on the rate and torque fluctuation is small.

  FIG. 4 shows the change in misfire rate and torque fluctuation when the expansion stroke injection, that is, the injection timing of the second fuel injection I2 is changed from the optimal injection timing. In the characteristics of the embodiment, the injection timing slightly changes. However, the misfire rate and torque fluctuation do not deteriorate rapidly. On the other hand, in the characteristics of the comparative example in which the entire amount is injected at a time during the expansion stroke, if the injection timing changes even slightly from the optimal injection timing, the misfire rate and torque fluctuation are rapidly deteriorated. Therefore, in the present embodiment, even if the optimum value of the injection timing of the second fuel injection I2 changes due to a minute change in the rotational speed or a minute load for each cycle, the misfire rate and the torque fluctuation are not detected. Without increasing, stable combustion can be obtained. In other words, the robustness against cycle changes is high. Further, in this embodiment, the air-fuel mixture becomes compact and the fuel component does not enter the quench region or the clevis, so that HC generated from these locations is reduced.

  Further, as shown in FIG. 5 (a), in the combustion system of this embodiment, even if the fuel pressure is lowered, the deterioration of combustion (for example, torque fluctuation) is small, and on the other hand, by reducing the fuel pressure, (b) As shown in (c), the exhaust gas temperature is obtained higher, and accordingly, as shown in (c), the HC emission amount is reduced. This is because by lowering the fuel pressure, the combustion becomes slower and the combustion is performed later. Therefore, in the present invention, it is desirable to reduce the fuel pressure within a range where combustion is established. As a result, the exhaust temperature can be increased and HC can be further reduced.

  6 and 7 show the catalyst temperature (exhaust temperature), engine oil water temperature, HC emission amount E.E. O. It is a characteristic view which shows the mode of a change with HC. In the above-described super retard combustion, fuel injection is performed in a state where the cylinder in the vicinity of the compression top dead center is relatively narrow, and fuel injection is performed after the compression top dead center, so the period from fuel injection to ignition and hence the fuel vaporization time. Therefore, the oil water temperature does not reach the predetermined permitted oil water temperature sTeng during a predetermined period Δα (for example, between several seconds to several tens of seconds) immediately after the cold start, and the in-cylinder temperature (in other words, For example, when the temperature of the combustion chamber wall is very low, the amount of fuel adhering to the wall increases due to insufficient vaporization of the fuel, and the amount of unburned HC produced 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. .

  Therefore, in this embodiment, as shown in FIG. 6 (A), this super retard combustion is prohibited until a predetermined period Δα immediately after the start, specifically, until the oil water temperature reaches a predetermined permitted oil water temperature sTeng. For example, BTDC ignition of so-called compression stroke injection is performed in which fuel is injected during the compression stroke and ignition is performed before the compression top dead center after the fuel injection. As a result, as shown in FIG. 6 (B), the unburned HC emission amount E.E. is compared with the reference example in which the super retard combustion is started immediately after the engine is started. O. HC can be greatly reduced.

  In other words, in this embodiment, the catalyst temperature (or exhaust temperature) does not reach the predetermined catalyst activation temperature sTcat just after the cold start, and the exhaust oil temperature is required to be raised. The super retard combustion is performed when the water temperature is equal to or higher than a predetermined permitted oil water temperature sTeng. Therefore, for example, as shown in FIG. 7, when the catalyst temperature reaches the catalyst activation temperature sTcat before the engine oil water temperature reaches the permitted oil water temperature sTeng, super retard combustion is not performed.

  FIG. 8 is a flowchart schematically showing the flow of control at the time of starting the engine of this embodiment, and this routine is repeatedly executed by the control unit 25 immediately after the engine is started. In step S1, the exhaust temperature detected by the exhaust temperature sensor 13 is read. Alternatively, the catalyst temperature may be directly detected and read by an appropriate sensor. In step S2, it is determined whether the catalytic converter 10 is inactive based on the exhaust temperature. Specifically, it is determined whether the exhaust gas temperature (or catalyst temperature) is lower than the catalyst activation temperature sTcat. If it is determined that the temperature is equal to or higher than the catalyst activation temperature sTcat, the process proceeds to step S3, and the normal control after the completion of warm-up described above is performed.

  If it is determined that the catalyst is inactive, the process proceeds to step S4, and the engine oil water temperature is read. As the engine oil water temperature, either the engine cooling water temperature detected by the water temperature sensor 21 or the engine oil temperature detected by the oil temperature sensor 24 may be used, or an average value of the both may be used.

  In step S5, it is determined whether the engine oil water temperature is equal to or higher than the permitted oil water temperature sTeng. If the engine oil water temperature is equal to or higher than the permitted oil water temperature sTeng, super retard combustion is performed (step S6). BTDC ignition is performed (step S7).

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, the combustion form of step S7 may be any of general homogeneous combustion, general stratified combustion, or BTDC ignition that performs intake stroke injection and compression stroke injection.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the system structure of the whole internal combustion engine which concerns on one Example of this invention. The characteristic view which shows the fuel injection timing and ignition timing of the super retard combustion of a present Example. Explanatory drawing which shows the state of the stratified mixture formed in a combustion chamber. The characteristic view which shows the relationship between the injection timing of expansion stroke injection, (a) torque fluctuation, and (b) misfire rate. The characteristic view which shows the relationship between a fuel pressure, (a) torque fluctuation, (b) exhaust temperature, (c) HC discharge | emission amount. The characteristic view which shows the mode of the change of the catalyst temperature at the time of engine starting, oil-water temperature, and HC discharge | emission amount in a present Example (A) and a reference example (B). The characteristic view which shows the relationship between the catalyst temperature and oil-water temperature in case super retard combustion is not performed at the time of the engine start which concerns on a present Example. The flowchart which shows the flow of control at the time of the engine starting which concerns on a present Example.

Explanation of symbols

3 ... Combustion chamber 10 ... Catalytic converter 14 ... Spark plug 15 ... Fuel injection valve 25 ... Control unit

Claims (6)

An in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and an ignition plug, and performs super retard combustion with ignition timing set after compression top dead center in a predetermined operating state ,
During super retard combustion, the first fuel injection is performed during the compression stroke to form a rich air-fuel mixture in a part of the combustion chamber near the spark plug, and a locally richer air-fuel mixture is sparked at the ignition timing. The fuel is injected for the second time during the expansion stroke at a timing that precedes the ignition timing so as to reach the ignition timing, and ignition is performed with a two-stage stratified mixture formed in a part of the combustion chamber near the spark plug. Done
In addition, when the engine temperature is lower than a predetermined allowable temperature, the super retard combustion is prohibited.   The in-cylinder direct injection spark-ignition internal combustion engine according to claim 1, wherein when the exhaust gas temperature is required to be raised and the engine temperature is equal to or higher than a predetermined allowable temperature, the super retard combustion is performed. Engine control device.   3. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition timing in the super retard combustion is 10 ° to 50 ° CA after compression top dead center.   The in-cylinder direct injection spark ignition internal combustion engine according to any one of claims 1 to 3, wherein a period from an injection start timing of the second fuel injection to an ignition timing is 10 ° to 20 ° CA. Control device.   The in-cylinder direct injection spark ignition internal combustion engine according to any one of claims 1 to 4, wherein a period from an injection start timing of the first fuel injection to an ignition timing is 50 ° to 140 ° CA. Control device. An in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and an ignition plug, and performs super retard combustion with ignition timing set after compression top dead center in a predetermined operating state ,
During super retard combustion, the first fuel injection is performed during the compression stroke to form a rich air-fuel mixture in a part of the combustion chamber near the spark plug, and a locally richer air-fuel mixture is sparked at the ignition timing. The fuel is injected for the second time during the expansion stroke at a timing that precedes the ignition timing so as to reach the ignition timing, and ignition is performed with a two-stage stratified mixture formed in a part of the combustion chamber near the spark plug. Done
In addition, the control method for a direct injection spark ignition internal combustion engine, wherein the super retard combustion is prohibited within a predetermined period immediately after the engine is started.

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