JP4207866B2 - 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.

Patent Document 2 discloses an example of a variable injection rate fuel injection valve that can variably control the fuel injection rate (injection amount per unit time).
JP 2001-336467 A JP 2000-274331 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. Further, in order to make the length of the fuel injection period more appropriate, a variable injection rate fuel injection valve capable of variably controlling the fuel injection rate is used as the fuel injection valve.

Therefore, by controlling the fuel injection rate lower than the fuel injection rate in the normal stratified combustion operation mode in which ignition is performed before the compression top dead center in the top dead center injection operation mode, the compression top dead center is reduced. It is possible to secure a longer fuel injection period.

  In one aspect of the present invention, a homogeneous combustion operation mode in which fuel is injected during the intake stroke is provided, and the fuel injection rate in the top dead center injection operation mode is relative to the fuel injection rate in the homogeneous combustion operation mode. It is designed to be controlled low.

  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 order to inject fuel against a high in-cylinder pressure near the compression top dead center as described above, it is necessary to set the fuel pressure of the fuel injection system to be relatively high. If so, the fuel injection period tends to be shorter. However, if the fuel injection period in which the fuel is injected over the compression top dead center is short, the timing at which the combustible air-fuel mixture is formed in the vicinity of the spark plug becomes subtle and tends to become unstable. In other words, the optimum ignition timing can be obtained only within a narrow range, and if the timing at which the combustible air-fuel mixture is actually formed deviates for some reason, the ignition becomes unstable. On the other hand, if a fuel injection valve having a low fuel injection rate is used to lengthen the fuel injection period, the fuel injection period may become excessively long in a mode other than the top dead center injection operation mode.

  In the present invention, by using the variable injection rate fuel injection valve, the fuel injection rate can be set in the top dead center injection operation mode without excessively extending the fuel injection period in a mode other than the top dead center injection operation mode. By making it low, the fuel injection period that is injected across the compression top dead center can be made sufficiently long. As a result, in a stable field where there is no large flow as described above, the time for the appropriate combustible mixture to remain in the vicinity of the spark plug becomes longer, and the optimal ignition timing can be obtained in a relatively wide range. . That is, for example, more reliable ignition combustion can be obtained with respect to fluctuations in each cycle.

  Further, for example, in the homogeneous combustion operation mode in a high load region, by increasing the fuel injection rate, the fuel injection can be completed in a short period of time, and deterioration of combustion due to the prolonged fuel injection period can be avoided. Is possible.

  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 lowering the fuel injection rate during this top dead center injection operation mode, it is possible to ensure a sufficiently long fuel injection period that is injected across the compression top dead center. More reliable ignition is possible.

  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.

  Here, a variable injection rate fuel injection valve capable of variably controlling the fuel injection rate (injection amount per unit time) is used as the fuel injection valve 15. In the above-mentioned Patent Document 2, the fuel injection rate is changed by changing the fuel pressure. However, the variable injection rate fuel injection valve 15 of this embodiment has a fuel injection rate that is independent of the fuel pressure. The configuration can be variably controlled.

  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.

  In the internal combustion engine configured as described above, when the warm-up is completed, for example, when the cooling water temperature exceeds 80 ° C., normal stratified combustion operation and homogeneous combustion operation are performed.

  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. At this time, the injection rate of the fuel injection valve 15 is controlled to an intermediate injection rate.

  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. The injection rate of the fuel injection valve 15 is controlled to a high injection rate. Therefore, even during a high load with a large amount of fuel injection, the fuel injection period is relatively short, and the fuel is mixed well in a short period of time, thus ensuring good combustion.

  On the other hand, when the cooling water temperature of the internal combustion engine is 80 ° C. or lower, that is, when the warm-up is not completed, the top dead center is used to activate the catalytic converter 22, that is, promote the temperature rise and reduce the HC emissions. It becomes the injection operation mode. In this top dead center injection operation mode, the injection rate is controlled to be low so that the fuel injection period is sufficiently long. Then, 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). Is done. 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. In particular, by reducing the injection rate during the top dead center injection operation mode and sufficiently lengthening the fuel injection period that is injected across the compression top dead center, a stable field where there is no large flow such as tumble exists. Among these, the time during which an appropriate combustible mixture remains in the vicinity of the spark plug 10 can be made longer, and the optimal ignition timing can be obtained in a relatively wide range. Thereby, for example, more reliable ignition combustion can be obtained with respect to fluctuation or the like for each cycle.

  FIG. 8 is a characteristic diagram schematically showing the relationship between the local air-fuel ratio in the vicinity of the spark plug 10 and the ignition timing in the top dead center injection operation mode, and the air-fuel ratio in the vicinity of the spark plug 10 is After a slight delay from the start of fuel injection, it gradually increases and reaches an air-fuel ratio range that can be ignited. After that, when the fuel injection is completed, after a slight delay, the fuel gradually becomes thinner and deviates from the ignitable air-fuel ratio range. Therefore, in the present embodiment, the period Δ1 in the figure is a timing at which ignition is possible. For example, if the ignition timing is set with an appropriate margin within the period Δ1, the actual air-fuel ratio is caused by various factors such as cycle fluctuations. Even if the timing of the change slightly deviates, reliable ignition is possible.

  On the other hand, if fuel injection is performed with a high injection rate, the fuel injection period set across the compression top dead center is shortened, and the change in the air-fuel ratio in the vicinity of the spark plug 10 is shown as a comparative example. It looks like a dashed line. That is, the period during which the air-fuel ratio can be ignited is shortened as the fuel injection period is shortened, and the ignition timing is limited within the period Δ2. Accordingly, it becomes difficult to set an appropriate ignition timing, and if the actual air-fuel ratio change timing slightly shifts due to some factor such as cycle fluctuation, the ignition tends to become unstable.

  In the above-described embodiment, the fuel injection valve 15 is disposed on the side of the combustion chamber 5 and is configured to inject fuel in a direction close to horizontal. Instead, the fuel injection valve 15 includes a pair of fuel injection valves 15. Of the combustion chamber 5 surrounded by the intake valve 6 and the pair of exhaust valves 8 in the center of the ceiling surface of the combustion chamber 5 so as to inject fuel toward the top surface of the piston 3 at an angle close to vertical. A configuration is also possible.

  In the above embodiment, the fuel pressure is always maintained constant. However, the fuel pressure increases as the load increases so that the fuel injection period does not become excessively long with respect to the increase in load (that is, increase in fuel injection amount). Alternatively, fuel pressure control may be performed.

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 relationship between the local air fuel ratio in the vicinity of a spark plug, and ignition timing.

Explanation of symbols

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

Claims (4)

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 that includes an ignition plug, when the exhaust gas temperature is required to rise, As the point injection operation mode, fuel injection is performed in a period spanning the compression top dead center so that the injection start time is before the compression top dead center and the injection end time is after the compression top dead center, and from the injection start time The ignition is performed after the delayed compression top dead center, and the variable injection rate fuel injection valve capable of variably controlling the fuel injection rate is used as the fuel injection valve. A control device for an in-cylinder direct injection spark ignition internal combustion engine, wherein the fuel injection rate is controlled to be lower than the fuel injection rate in a normal stratified combustion operation mode in which ignition is performed .   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. A homogeneous combustion operation mode in which fuel is injected during an intake stroke is provided, and the fuel injection rate in the top dead center injection operation mode is relatively lower than the fuel injection rate in the homogeneous combustion operation mode. 3. A control apparatus for an in-cylinder direct injection spark ignition internal combustion engine according to 1 or 2 . 4. The control device for a direct injection spark ignition internal combustion engine according to claim 3 , wherein the fuel pressure does not change between the homogeneous combustion operation mode and the top dead center injection operation mode.

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