JP4380481B2 - 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 more particularly to control of the injection timing and ignition timing.

Patent Document 1 discloses that when an exhaust purification catalytic converter is in an unwarmed state lower than an 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, the fuel injection is performed as the top dead center injection operation mode so that 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. In particular, the top dead center injection operation mode is prohibited while the catalytic converter provided in the exhaust system is in a predetermined low temperature state.

  FIG. 1 illustrates the fuel injection period and ignition timing in the top dead center injection operation mode of the present invention together with the change in the in-cylinder pressure. The injection start timing ITS is before the compression top dead center (TDC), and the injection end timing ITE is After 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.

  Here, in the top dead center injection operation mode in which the ignition timing is significantly retarded as described above, the exhaust gas temperature is extremely higher than that of the conventional technique such as Patent Document 1, and so on. Is in a completely cold state (close to the outside air temperature), and if the engine is shifted to the top dead center injection operation mode immediately after the engine is started, the temperature gradient inside the catalytic converter becomes very steep. That is, there is a concern that only the upstream portion such as the monolithic ceramic catalyst carrier rapidly becomes high in temperature and the thermal strain increases.

  Therefore, in the present invention, the top dead center injection operation mode is prohibited while the catalytic converter provided in the exhaust system is in a predetermined low temperature state.

That is, in this onset bright, until the catalyst outlet temperature at the outlet side of the catalytic converter reaches the first set temperature prohibits the TDC injection operation mode, the catalyst outlet temperature is the first predetermined temperature or higher and The top dead center injection operation mode is performed until the catalyst temperature of the catalytic converter reaches a second set temperature higher than the first set temperature.
If the catalytic activity starts even slightly, the catalytic converter tries to increase the temperature from the inside due to the exothermic reaction, so even if the temperature of the exhaust gas flowing from the upstream to the catalytic converter becomes very high, the temperature gradient of the catalytic converter is It will be moderate.

Since the temperature change at the outlet of the catalytic converter occurs later than the temperature change of the carrier of the catalytic converter, it can be considered that the temperature of the entire catalytic converter has risen uniformly to some extent when it becomes high to some extent. Therefore, even if the exhaust temperature rises rapidly in the top dead center injection operation mode, excessive thermal distortion is not caused.

  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. Then, since the exhaust gas temperature starts to rise rapidly from a state where the catalytic converter is warmed to some extent, thermal deterioration due to an extreme temperature gradient of the catalytic converter can be avoided.

  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 disposed at the center in the longitudinal direction of the monolithic ceramic catalyst carrier of the catalytic converter 22, and an outlet portion of the catalytic converter 22 And a catalyst outlet temperature sensor 39.

  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, 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). Fuel injection is performed across the dead center. The ignition timing ADV is after compression top dead center (TDC), and is ignited at a timing delayed by 10 ° CA to 25 ° CA from the injection start timing ITS. 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 is controlled so that the average air-fuel ratio becomes the stoichiometric air-fuel ratio.

  In this embodiment, the fuel injection timing is controlled so 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.

  Here, in the above-described top dead center injection operation mode, the exhaust gas temperature can be obtained extremely high. Therefore, when the top dead center injection operation mode is executed immediately after the start when the catalytic converter 22 is in a completely cold state, There is a concern about thermal distortion of the converter 22. Therefore, in this embodiment, the mode is switched by monitoring the temperature state of the catalytic converter 22 by the process as shown in FIG.

  First, in step 1, the outlet temperature TC of the catalytic converter 22 detected by the catalyst outlet temperature sensor 39 is compared with a predetermined first reference temperature T1, and if it is lower than the first reference temperature T1, the process proceeds to step 2. Perform normal control when cold. The first reference temperature T1 substantially corresponds to the activation start temperature of the catalyst, and is set to about 150 ° C. to 200 ° C., for example. The normal control when the engine is cold is not for the extreme exhaust temperature rise as in the top dead center injection operation mode, but for a certain degree of exhaust temperature rise. For example, fuel injection is performed during the intake stroke and compression is performed. Ignition is performed at a time later than the MBT point before the top dead center. Alternatively, the compression stroke injection may be performed in addition to the intake stroke injection. When the catalytic converter 22 is in a completely cold state when the engine is started, the temperature of the catalytic converter 22 is gradually increased by the normal control during the cold state.

  If the outlet temperature TC is equal to or higher than the first reference temperature T1, it is determined in step 3 whether the catalyst temperature TB is lower than the second reference temperature T2. The second reference temperature T2 is a temperature substantially corresponding to the complete activity of the catalyst, and is set to about 250 ° C. to 300 ° C., for example. If the engine is started from a cold state, when the outlet temperature TC reaches the first reference temperature T1, the catalyst temperature TB is usually lower than the second reference temperature T2. The dead center injection operation mode is executed. Thereby, the exhaust gas temperature rises rapidly, and the catalytic converter 22 quickly rises in temperature. This top dead center injection operation mode is continued until the catalyst temperature TB becomes equal to or higher than the second reference temperature T2 in Step 5. If the catalyst temperature TB is equal to or higher than the second reference temperature T2, the routine proceeds to step 6 where normal control after warm-up, that is, the above-described homogeneous combustion operation mode or stratified combustion operation mode after warm-up is executed.

  Thus, in this embodiment, the top dead center injection operation mode is prohibited until the outlet temperature TC reaches the first reference temperature T1, and the time required until the catalyst is fully activated in the top dead center injection operation mode. Thus, thermal degradation of the catalytic converter 22 is avoided.

  FIGS. 9 and 10 show the temperature change of the catalytic converter 22 when the internal combustion engine including the catalytic converter 22 is completely cooled, when the exhaust temperature is very high (FIG. 9) and relatively exhausted. This shows the case where the temperature is low (FIG. 10). Specifically, as shown in FIG. 11, the temperature TA at the inlet (point A) of the catalytic converter 22, the temperature TB1 near the upstream end (point B1) of the monolith catalyst carrier, and the monolith catalyst carrier. 4 shows temperature changes at four locations, a temperature TB2 near the downstream end (point B2) and a temperature TC at the outlet (point C) of the catalytic converter 22.

  When a high exhaust temperature is given as the top dead center injection operation mode immediately after starting, as shown in FIG. 9, the catalyst carrier upstream end temperature TB1 rises rapidly together with the inlet temperature TA, so The temperature difference ΔT becomes very large. That is, a large thermal distortion occurs.

  On the other hand, when the exhaust temperature is relatively low, the temperature difference ΔT before and after the catalyst carrier is sufficiently small as shown in FIG. When the outlet temperature TC reaches the predetermined first reference temperature T1, if the mode is switched to the top dead center injection operation mode, the temperature of each part rapidly increases as shown by the broken line in FIG. The required time to reach the catalyst complete activity, which is a target, is not much different from that in FIG. Note that, at the stage of switching to the top dead center injection operation mode, reaction heat begins to be generated inside the catalyst carrier, and thereafter, a large temperature difference ΔT does not occur.

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 flowchart which shows the mode switching process at the time of a start. The time chart which shows the temperature change of each part of a catalytic converter when exhaust gas temperature is high. The time chart which shows the temperature change of each part of a catalytic converter when exhaust gas temperature is low. Explanatory drawing which shows the temperature-measurement point of FIG. 9 and FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Combustion chamber 10 ... Spark plug 15 ... Fuel injection valve 38 ... Catalyst temperature sensor 39 ... Catalyst exit temperature sensor

Claims (4)

In a control device for a direct injection type spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug,
After starting the engine cold , the fuel injection is performed as a top dead center injection operation mode in a period across the compression top dead center so that the injection start timing is before the compression top dead center and the injection end timing is after the compression top dead center. And is configured to perform ignition after compression top dead center delayed from the injection start timing,
The top dead center injection operation mode is prohibited until the catalyst outlet temperature on the outlet side of the catalytic converter provided in the exhaust system reaches the first set temperature, and the catalyst outlet temperature becomes equal to or higher than the first set temperature. Until the catalyst temperature of the catalytic converter reaches a second set temperature higher than the first set temperature, the top dead center injection operation mode is performed. Engine control device.   2. The control apparatus for a direct injection type spark ignition internal combustion engine according to claim 1, wherein the ignition timing is a time delayed by 10 [deg.] CA to 25 [deg.] CA from the injection start timing. The control device for a direct injection type spark ignition internal combustion engine according to claim 1 or 2, wherein the first set temperature substantially corresponds to an activation start temperature of the catalyst . The control device for a direct injection type spark ignition internal combustion engine according to any one of claims 1 to 3, wherein the second set temperature substantially corresponds to a complete activation temperature of the catalyst .

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