JP2007032378A - Control device for cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize rise of exhaust gas temperature and reduction of HC emission at a time of cold engine by compatibly establishing large delay of ignition timing and combustion stability. <P>SOLUTION: Normal stratified combustion operation and homogeneous combustion operation are performed under warm up completion condition. Main fuel injection I1 is performed over top dead center to make injection start timing ITS before compression top dead center and injection end timing ITE after top dead center as a top dead center injection operation mode is performed for accelerating activation of a catalytic converter and HC emission reduction under a cold engine condition. Ignition timing ADV is after top dead center. Since swirl and tumble are attenuated at compression top dead center and minute turbulence is activated and position change of a piston is small at compression top dead center, stable combustion can be materialized. Part of fuel is injected as expansion stroke injection I2 for raise exhaust gas temperature further. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an in-cylinder direct injection spark ignition internal combustion engine that directly injects fuel into a cylinder, and more particularly to control of the injection timing and ignition timing.

In Patent Document 1, when the exhaust gas-purifying catalytic converter is in an unwarmed state lower than the activation temperature, fuel is injected during the compression stroke, and the ignition timing is retarded from the compression top dead center. Technology is disclosed.
JP 2001-336467 A

  In order to raise the exhaust gas temperature and reduce HC in order to achieve early activation of the catalyst when the internal combustion engine is cold, it is desirable to retard the ignition timing as much as possible, but if the ignition timing is significantly retarded Since the combustion stability deteriorates, it cannot be retarded from a certain limit determined from the viewpoint of combustion stability. In the conventional technique such as Patent Document 1, it is difficult to ensure stable combustion, particularly under conditions such as cold, and the retard limit of the ignition timing determined from the combustion stability is relatively advanced, which is sufficient. The ignition timing delay cannot be realized.

  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 it is necessary to raise the exhaust gas temperature, such as when the engine is cold, the fuel injection is performed as the top dead center injection operation mode. The injection start timing is before the compression top dead center and the injection end timing is after the compression top dead center. The ignition is performed in a period straddling the compression top dead center, and ignition is performed after the compression top dead center delayed from the injection start timing, and the ignition is performed after the main injection in the period straddling the compression top dead center. A feature is that a part of the fuel is injected later as an expansion stroke injection. The expansion stroke injection is desirably performed immediately after the combustion by the main injection is completed. For example, the injection start timing of the expansion stroke injection is delayed by about 50 ° CA to 100 ° CA from the ignition timing.

  FIG. 1 exemplifies the fuel injection period and ignition timing in the top dead center injection operation mode of the present invention. As shown in FIG. 1, the main injection I1 straddling the compression top dead center and the expansion stroke injection I2 delayed from the main injection I1 However, in the present invention, combustion is basically established by the main injection I1. In the main injection I1, the injection start timing ITS is before the compression top dead center (TDC), and the injection end timing ITE is after the compression top dead center (TDC). The length of the injection period T during that time corresponds to the injection amount. The ignition timing ADV is after compression top dead center (TDC), and is a timing delayed by a predetermined crank angle (for example, 10 ° CA to 25 ° CA) from the injection start timing ITS. This delay period D generally correlates with the distance from the fuel injection valve to the spark plug.

  The injection start timing ITS and the injection end timing ITE are controlled so that the period before the compression top dead center in the first half and the period after the compression top dead center in the second half are substantially equal with the compression top dead center (TDC) as the center. You may make it do.

  FIG. 2 shows the piston position change amount and the combustion chamber volume change amount due to the piston stroke in one cycle of the internal combustion engine. As shown in the figure, the amount of change per unit crank angle is the largest near the middle position of the stroke, and is very small near the bottom dead center (BDC) and near the top dead center (TDC). Therefore, in the vicinity of the compression top dead center where the fuel injection is performed in the present invention, the piston position change and volume change are very small, and a stable field that is not affected by the piston movement or the like can be formed.

  In the cylinder, a relatively large gas flow such as a swirl flow or a tumble flow is generated in the intake stroke and remains in the compression stroke. However, a large flow such as a swirl flow or a tumble flow is When the piston reaches near the compression top dead center and the combustion chamber becomes narrow, it collapses rapidly. FIG. 3 shows a change in flow velocity of a large flow in the combustion chamber under various engine speeds. As shown in the figure, a swirl flow or a tumble flow having a strength corresponding to the rotation speed is generated. Collapses rapidly before reaching compression top dead center (360 ° CA). Therefore, in the present invention, the fuel spray injected near the compression top dead center is not moved by a large flow such as a swirl flow or a tumble flow, and always forms a spray in a stable manner on the spark plug. Is possible.

  On the other hand, the energy of a relatively large flow such as the swirl flow or the tumble flow described above transitions to minute turbulence as the flow collapses. Therefore, the minute disturbance in the combustion chamber increases rapidly just before the compression top dead center. FIG. 4 shows the intensity of the minute turbulence caused by the collapse of the flow shown in FIG. 3 as a so-called turbulent flow rate converted to a flow velocity, and as shown in the figure, immediately before the compression top dead center. , Disturbances increase greatly. Such minute disturbances contribute to the activation of the combustion field, and a combustion improving action is obtained.

  In other words, the field in the combustion chamber near the compression top dead center where the fuel is injected does not have a large flow that moves the spray, and there are many minute disturbances that activate the combustion, It is a very stable place against the movement of the piston. Therefore, stable combustion is possible with the ignition timing retarded from the compression top dead center, and the retard limit of the ignition timing that is limited in terms of combustion stability is on the retard side. For this reason, the exhaust gas temperature can be raised significantly by a large retardation of the ignition timing, and the HC emission amount is reduced.

  In the present invention, in order to further raise the exhaust gas temperature, a part of the fuel is injected as the expansion stroke injection I2 in the expansion stroke after ignition of the fuel by the main injection. The fuel by the expansion stroke injection is self-ignited by the temperature in the cylinder, and further increases the exhaust gas temperature. In addition, if the fuel of the next expansion stroke injection is injected during the combustion of the main injection, it becomes diffusion combustion and the smoke increases. Therefore, it is desirable to carry out immediately after the completion of the combustion by the main injection. In the present invention, since the combustion by the main injection is performed after the top dead center, the combustion of the fuel by the expansion stroke injection becomes very late, and the exhaust gas temperature effectively rises.

  According to the present invention, stable combustion can be obtained in a state where the ignition timing is significantly retarded from the compression top dead center. For example, when the internal combustion engine is cold, the exhaust gas temperature is raised and the catalyst is accelerated. Activation can be achieved and HC emissions can be reduced. In particular, by injecting a part of the fuel as an expansion stroke injection after ignition of the main injection, the exhaust gas temperature can be maximized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  5 to 7 show an embodiment of a direct injection type spark ignition internal combustion engine to which the present invention is applied. In particular, FIGS. 5 and 6 show the configuration of one cylinder. Indicates the system configuration of the entire organization.

  As shown in FIGS. 5 and 6, a piston 3 is slidably disposed in a cylinder 2 formed in the cylinder block 1, and a cylinder head 4 fixed to the upper surface of the cylinder block 1 and the piston 3 A combustion chamber 5 is formed between them. The cylinder head 4 is formed with an intake port 7 that is opened and closed by an intake valve 6 and an exhaust port 9 that is opened and closed by an exhaust valve 8. A pair of intake valves 6 and a pair of exhaust valves 8 are provided for one cylinder, and an ignition plug 10 is disposed at the center of the ceiling surface of the combustion chamber 5 surrounded by these four valves. . Further, in this embodiment, the intake port 7 is provided with a partition wall 11 that divides the intake port 7 into two upper and lower flow paths so that the tumble flow can be strengthened depending on the operating state. A tumble control valve 12 that opens and closes the lower flow path at the upstream end is provided. As can be easily understood by those skilled in the art, the tumble flow is strengthened when the lower flow path is closed by the tumble control valve 12, and the tumble flow is weakened when the tumble control valve 12 is opened. The tumble control valve 12 is not necessarily essential in the present invention, and can be omitted. Alternatively, a known swirl control valve may be provided.

  A fuel injection valve 15 for directly injecting fuel into the cylinder is disposed below the intake port 7 of the cylinder head 4, more specifically at a position between the pair of intake ports 7. That is, the fuel injection valve 15 is located on the side of the combustion chamber 5 on the intake valve 6 side, and is disposed so as to inject fuel along a direction orthogonal to a piston pin (not shown) on the plan view. In the cross-sectional view of FIG. However, the downward inclination angle is relatively small, that is, the fuel is injected in a direction close to the horizontal.

  On the other hand, the top of the piston 3 has a convex shape along the inclination of the ceiling surface of the combustion chamber 5 that forms a pent roof type, and a concave portion 16 having a substantially rectangular shape in plan view is formed at the center. Yes. The bottom surface of the recess 16 forms an arc surface having a predetermined radius of curvature or a curved surface approximating an arc so as to follow the tumble flow.

  As shown in FIG. 7, the internal combustion engine of this embodiment is, for example, an in-line four-cylinder engine, and a catalytic converter 22 for purifying exhaust gas is provided in an exhaust passage 21 to which an exhaust port 9 of each cylinder is connected. An air-fuel ratio sensor 23 such as an oxygen sensor is disposed on the upstream side. The intake passage 24 to which the intake port 7 of each cylinder is connected is provided with an electronically controlled throttle valve 25 that is opened and closed by a control signal on the inlet side. An exhaust gas recirculation passage 26 is provided between the exhaust passage 21 and the intake air passage 24, and an exhaust gas recirculation control valve 27 is interposed in the middle. Further, the tumble control valves 12 of the respective cylinders are configured to be simultaneously opened and closed by a negative pressure type tumble control actuator 29 that is operated by a suction negative pressure introduced via a solenoid valve 28.

  The fuel injection valve 15 is supplied with the fuel adjusted to a predetermined pressure by the fuel pump 31 and the pressure regulator 32 via the fuel gallery 33. 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. In this embodiment, the fuel pressure is always kept constant. The ignition plug 10 of each cylinder is connected to an ignition coil 34.

  The fuel injection timing, injection amount, injection rate, ignition timing, etc. of the internal combustion engine are controlled by the control unit 35. The control unit 35 includes a detection signal of an accelerator opening sensor 30 that detects the amount of depression of an accelerator pedal, a detection signal of a crank angle sensor 36, a detection signal of an air-fuel ratio sensor 23, and a detection of a water temperature sensor 37 that detects a cooling water temperature. Signals, etc. are input. Furthermore, in this embodiment, in order to detect the temperature state of the catalytic converter 22, a catalyst temperature sensor 38 is provided at the center in the longitudinal direction of the monolith ceramic catalyst carrier of the catalytic converter 22.

  In the internal combustion engine configured as described above, normal stratified combustion operation and homogeneous combustion operation are performed after the warm-up is completed.

  That is, in a predetermined region on the low speed and low load side, as a normal stratified combustion operation mode, fuel injection is performed at an appropriate time in the compression stroke, with the tumble control valve 12 basically closed. Ignition is performed before the top dead center. In this operation mode, fuel injection always ends before compression top dead center. The fuel injected toward the piston 3 during the compression stroke is collected in the vicinity of the spark plug 10 using a tumble flow swirling along the recess 16 and ignited there. Therefore, stratified combustion with an average air-fuel ratio lean is realized.

  Further, in a predetermined region on the high speed and high load side after the warm-up is completed, fuel injection is performed during the intake stroke under the condition that the tumble control valve 12 is basically opened as a normal homogeneous combustion operation mode. And ignition is performed at the MBT point before the compression top dead center. In this case, the fuel becomes a homogeneous air-fuel mixture in the cylinder and is basically operated near the stoichiometric air-fuel ratio.

  On the other hand, in the state where the warm-up of the internal combustion engine is not completed, the top dead center injection operation mode is basically set in order to activate the catalytic converter 22, that is, promote the temperature rise and reduce the HC emission amount. . In this top dead center injection operation mode, as shown in FIG. 1 described above, main injection I1 and expansion stroke injection I2 are performed. In main injection I1, the injection start timing ITS is before compression top dead center (TDC). The injection end timing ITE is after the compression top dead center (TDC), and fuel injection is performed across the compression top dead center. The ignition timing ADV is after the compression top dead center (TDC), and is ignited at a timing delayed by 10 ° CA to 25 ° CA from the injection start timing ITS of the main injection I1. During this delay period, the fuel spray just reaches the vicinity of the spark plug 10 and forms a combustible air-fuel mixture in the vicinity of the spark plug 10, so that ignition combustion is surely performed and stratified combustion is performed. At this time, the fuel injection amount of the main injection I1 is set so that the average air-fuel ratio is around 30. The expansion stroke injection I2 is injected at a time immediately after the combustion by the main injection I1 is completed. For example, the expansion stroke injection I2 is started at a time delayed by about 50 ° CA to 100 ° CA from the ignition timing ADV. The injection amount of the expansion stroke injection I2 is set so that the average air-fuel ratio based on the total fuel amount of the main injection I1 and the expansion stroke injection I2 is slightly leaner than the theoretical air-fuel ratio, for example, about 16 to 17.

  In the present embodiment, the fuel injection timing of the main injection I1 is controlled such that the injection start timing ITS becomes a predetermined crank angle, and the injection end timing ITE is determined by the injection start timing ITS and the fuel injection amount ( Injection time). The injection start timing ITS and the injection end timing ITE are obtained based on the fuel injection amount so that the period before the compression top dead center and the period after the compression top dead center in the fuel injection period are equal. Is also possible.

  As described above, the field in the combustion chamber near the compression top dead center where fuel is injected in this top dead center injection operation mode does not have a large flow that causes the spray to move due to the collapse of the large flow, Along with the collapse of the large flow, there are many minute disturbances that activate the combustion, and the field becomes very stable against the movement of the piston. Therefore, stable combustion is possible with the ignition timing retarded from the compression top dead center, and the retard limit of the ignition timing that is limited in terms of combustion stability is on the retard side. For this reason, the exhaust gas temperature can be raised significantly by a large retardation of the ignition timing, and the HC emission amount is reduced.

  Further, the fuel of the expansion stroke injection I2 injected immediately after the end of the combustion of the main injection I1 is self-ignited by the temperature in the cylinder, and most of the energy becomes heat and contributes to the increase of the exhaust gas temperature. In particular, the combustion by the main injection I1 is performed later than the top dead center TDC, and the combustion by the expansion stroke injection is performed after the end of the combustion, so that it becomes a very late time and the exhaust gas temperature effectively increases. Further, since the temperature change in the cylinder at the timing when the expansion stroke injection I2 is performed is relatively gradual, the self-ignition of the fuel in the expansion stroke injection I2 is stably performed.

  FIG. 8 shows the amount of heat generated by the combustion of the main injection I1 (a1) and the in-cylinder temperature (b1) in the above-described top dead center injection operation mode of the present invention. ) And the amount of heat generated by combustion (a2) and the in-cylinder temperature (b2). Although the combustion period is represented by a change in the amount of generated heat, in the present invention, the expansion stroke injection I2 is performed immediately after the end of the combustion, and the in-cylinder temperature at this time is in the vicinity indicated by the symbol t1. On the other hand, if the additional injection I102 is added immediately after the end of the combustion of the general compression stroke injection, the in-cylinder temperature at this time is in the vicinity indicated by reference numeral t2. Although the temperature itself does not change much between the temperature near t1 and the temperature near t2, the temperature decrease per unit crank angle is sharper near t2 and relatively gentle near t1. Therefore, the expansion stroke injection I2 of the present invention leads to self-ignition more reliably. Further, since the expansion stroke injection I2 of the present invention burns at a much later time than the additional injection I102 in the figure, it is advantageous in increasing the exhaust gas temperature.

  Next, FIG. 9 and FIG. 10 show an example of more specific operation mode changes immediately after the start of the internal combustion engine of the above embodiment. In this example, after the start, the three phases of the first phase, the second phase, and the third phase are sequentially shifted with time. That is, as shown in the flowchart of FIG. 9, the first phase is set until a predetermined time (for example, about several seconds) elapses after starting (steps 1 and 2). After a predetermined time has elapsed, the rate of change ΔTcat of the catalyst temperature Tcat detected by the catalyst temperature sensor 38 is monitored, and the first phase is continued during a rapid temperature rise above a certain rate of change a. If it becomes, it will transfer to a 2nd phase (step 3, 4, 5). In the second phase, the catalyst temperature Tcat is monitored, and when it exceeds the predetermined temperature b, the process proceeds to the third phase (steps 6 and 7).

  The above-described top dead center injection operation mode in FIG. 1 corresponds to the second phase. The normal homogeneous combustion operation mode corresponds to the third phase. On the other hand, the first phase corresponds to the combustion of only the main injection I1 in the top dead center injection operation mode, and as shown in the time chart of FIG. 10, the injection start timing is the compression top dead center (TDC). ) The entire amount of fuel is injected during one fuel injection period that is performed across the compression top dead center so that the injection end timing is after the compression top dead center (TDC). The ignition timing ADV is after compression top dead center (TDC), and is also ignited at a timing delayed by 10 ° CA to 25 ° CA from the injection start timing. The air-fuel ratio is maintained at about 16 to 17 as in the second phase.

  In this first phase combustion mode, the exhaust gas temperature is lower than that in the second phase top dead center injection operation mode, but a sufficiently high exhaust gas temperature is obtained compared to the normal stratified combustion operation and homogeneous fuel operation. And the amount of HC generated is smaller than that in the second phase top dead center injection operation mode. That is, immediately after start-up where the catalyst temperature Tcat is very low, the expansion stroke injection I2 is not performed so that HC is minimized without depending on the catalytic action, and the entire amount of fuel is straddled over the top dead center. To spray. In the illustrated example, the injection period before top dead center is equal to the injection period after top dead center.

  When shifting from the first phase to the second phase according to the flowchart described above, a part of the fuel is injected as the expansion stroke injection I2, and the above-described top dead center injection operation mode is set. In this top dead center injection operation mode, the combustion efficiency is lower than that of the combustion mode of the first phase. Therefore, in order to maintain the same torque, the opening degree of the electronic control throttle valve 25 is controlled to be larger, and the intake air amount Qa is increased. . Accordingly, the total amount of fuel also increases correspondingly, and the average air-fuel ratio does not change from the first phase. Actually, the change in the intake air amount Qa is accompanied by a response delay with respect to the change in the opening degree of the electronic control throttle valve 25. However, in FIG. It is shown in

  Thereafter, when the third phase is entered, air-fuel ratio control based on the detection of the air-fuel ratio sensor 23 is started, so that the air-fuel ratio is maintained at the stoichiometric air-fuel ratio. In the third phase, since the ignition timing approaches the MBT point and the combustion efficiency increases, the opening degree of the electronically controlled throttle valve 25 decreases to maintain the same torque, and the intake air amount Qa decreases. In this way, by changing in stages from the first to third phases at the time of cold start, the catalyst can be activated quickly and the discharge of HC or the like to the outside can be minimized.

  Note that the first phase is not necessarily essential and can be omitted.

The characteristic view which showed an example of the fuel-injection period and ignition timing of this invention. The characteristic figure of the piston position change amount and volume change amount during a cycle. The characteristic figure which shows the change in the cycle of a big flow. The characteristic view which shows the change in the cycle of a minute disturbance. Sectional drawing which shows one Example of a direct injection type spark ignition internal combustion engine. FIG. FIG. 2 is a configuration explanatory view showing the system configuration of the entire internal combustion engine. The characteristic view which shows the amount of heat generated by combustion of the main injection I1 and the change in the in-cylinder temperature in comparison with general compression stroke injection. The flowchart which shows the flow of control at the time of cold start. The time chart which shows the change of the phase at the time of cold start.

Explanation of symbols

3 ... Piston 5 ... Combustion chamber 10 ... Spark plug 15 ... Fuel injection valve

Claims (8)

  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 includes an ignition plug, the fuel injection is performed at an injection start timing in a predetermined operating state. Is performed in a period straddling the compression top dead center so that the injection end timing is after the compression top dead center before the compression top dead center, and ignition is performed after the compression top dead center delayed from the injection start timing. A control apparatus for an in-cylinder direct injection spark ignition internal combustion engine, characterized in that a part of the fuel is injected as an expansion stroke injection after the ignition, delayed from the main injection in a period over the compression top dead center.   2. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the expansion stroke injection is performed immediately after the combustion by the main injection is completed.   The control device for a direct injection spark ignition internal combustion engine according to claim 1 or 2, wherein an average air-fuel ratio according to a total fuel amount of the main injection and the expansion stroke injection is about 16 to 17.   4. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 3, wherein an average air-fuel ratio according to the amount of fuel of the main injection is about 30.   The in-cylinder direct injection type according to any one of claims 1 to 4, wherein the ignition timing is a timing delayed by 10 ° CA to 25 ° CA from an injection start timing of main injection straddling the compression top dead center. Control device for spark ignition internal combustion engine.   The in-cylinder according to any one of claims 1 to 5, wherein a period before the compression top dead center and a period after the compression top dead center in the fuel injection period of the main injection straddling the compression top dead center are substantially equal. Control device for a direct injection spark ignition internal combustion engine.   6. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 5, wherein an injection start timing of the expansion stroke injection is a timing delayed by 50 [deg.] CA to 100 [deg.] CA from the ignition timing. The in-cylinder direct injection spark ignition according to any one of claims 1 to 7, wherein the injection / ignition is performed when a temperature increase of the exhaust gas is required as a predetermined operation state. Control device for internal combustion engine.

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