JP2009041539A - Control device for gasoline engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit a drop in cylinder pressure while inhibiting excessive pumping loss during fuel cut. <P>SOLUTION: A control device for a gasoline engine is provided with a valve timing control means closing both of an intake valve and an exhaust valve at a period before and after exhaust top dead center in an operation zone making air-fuel mixture in a cylinder spontaneously ignite, and a fuel cut determination means for determining whether predetermined fuel cut conditions for stopping fuel supply to the cylinder are satisfied or not. The valve timing control means sets a period from exhaust top dead center to valve open start timing of the intake valve shorter than a period from valve close start timing of the exhaust valve to exhaust top dead center when the fuel cut determination means determines that the fuel cut conditions are satisfied in the operation zone. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a gasoline engine that compresses an air-fuel mixture in a cylinder and burns it by self-ignition.

  In order to improve the fuel efficiency and clean the exhaust gas of a gasoline engine, a combustion method has been proposed in which an air-fuel mixture in a cylinder is compressed and burned by self-ignition. In this combustion method, in general, in order to increase the temperature in the cylinder and promote self-ignition, a negative overlap period is set in which both the intake valve and the exhaust valve are closed before and after exhaust top dead center, More burnt gas remains (for example, Patent Document 1).

Japanese Patent Laying-Open No. 2005-220839

  Here, when the fuel supply to the cylinder is cut and the combustion is not temporarily performed when the vehicle is decelerated or when idling is stopped, the temperature in the cylinder is lowered. Therefore, auto-ignition combustion may not occur when fuel supply and combustion are restarted. As a method of preventing the temperature in the cylinder from decreasing, it is conceivable to close both the intake valve and the exhaust valve during fuel cut. However, in this case, the pumping loss becomes excessive and the engine brake works strongly, so that the riding comfort deteriorates.

  Accordingly, an object of the present invention is to suppress a decrease in the in-cylinder temperature while suppressing an excessive pumping loss during fuel cut.

  According to the present invention, in the operation region in which the air-fuel mixture in the cylinder is self-ignited, the valve timing control means for closing both the intake valve and the exhaust valve before and after the exhaust top dead center, and the fuel supply to the cylinder And a fuel cut determination means for determining whether or not a predetermined fuel cut condition is satisfied, wherein the valve timing control means is configured to determine the fuel cut determination in the operation region. If the means determines that the fuel cut condition is satisfied, the period from the exhaust top dead center to the start of opening of the intake valve is longer than the period from the start of closing of the exhaust valve to the exhaust top dead center. There is provided a control device for a gasoline engine characterized by shortening.

  In the present invention, at the time of fuel cut, by shortening the period from the exhaust top dead center to the start of valve opening of the intake valve than the period from the start of closing the exhaust valve to the exhaust top dead center, Accelerate the introduction of fresh air into the cylinder. In the intake stroke, the temperature in the cylinder gradually decreases as the cylinder expands, but by introducing new air, new air is introduced when the temperature in the cylinder is relatively high. The decrease can be suppressed. In addition, since intake and exhaust are performed even when the fuel is cut, an excessive pumping loss can be suppressed.

  In the present invention, the valve timing control means includes a period from the start of closing of the exhaust valve to an exhaust top dead center and a period from the exhaust top dead center to the start of opening of the intake valve in the operation region. If the fuel cut determination means determines that the fuel cut condition is satisfied, the opening timing of the intake valve may be corrected to advance.

  According to this configuration, at the time of fuel supply, the period from the start of closing the exhaust valve to the exhaust top dead center is equal to the period from the exhaust top dead center to the start of opening of the intake valve. Thus, the compression energy of the air-fuel mixture can be effectively used for the propulsive force of the piston, and the pumping loss is suppressed, and at the time of fuel cut, the opening angle of the intake valve is corrected to advance the pumping loss. It is possible to suppress a decrease in the in-cylinder temperature while suppressing an excessive increase in the number of cylinders.

  The present invention further includes a lift amount control means for controlling the lift amount of the intake valve, wherein the lift amount control means determines that the fuel cut condition is satisfied in the operating region. In this case, the lift amount of the intake valve may be reduced.

  According to this configuration, the amount of fresh air introduced into the cylinder at the time of fuel cut can be suppressed, and the decrease in the cylinder temperature can be further suppressed.

  In the present invention, when the fuel cut determination unit determines that the fuel cut condition is satisfied in the operating region, the lift amount control unit is configured to control the intake valve after a predetermined period after the determination. The lift amount may be reduced.

  According to this configuration, scavenging performance in the cylinder at the time of fuel cut can be improved, and self-ignitability at the time of resumption of fuel supply can be improved.

  As described above, according to the present invention, it is possible to suppress a decrease in the cylinder temperature while suppressing an excessive pumping loss during fuel cut.

<First Embodiment>
FIG. 1 is a control system diagram of an engine 1 to which a control device A according to an embodiment of the present invention is applied. The engine 1 is a 4-cycle gasoline engine and includes a cylinder block 2, a cylinder head 3, and a crankcase 4. A cylinder (cylinder) 22 in which the piston 21 slides is formed in the cylinder block 2, and the reciprocating motion of the piston 21 is converted into the rotational motion of the crankshaft 41.

  A combustion chamber 31 is formed between the cylinder block 2 and the cylinder head 3. A water jacket through which cooling water passes is provided in the cylinder block 2, and a water temperature sensor 201 for detecting the temperature of the cooling water passing through the water jacket is provided in the cylinder block 2.

  The cylinder head 3 includes an intake port 32 and an exhaust port 33 communicating with the combustion chamber 31. The intake port 32 is opened and closed by an intake valve 34, and the exhaust port 33 is opened and closed by an exhaust valve 35. The cylinder head 3 is provided with a variable valve device 341 that changes the opening / closing timing and the shift amount of the intake valve 34 and a variable valve device 351 that changes the opening / closing timing (valve timing) and the shift amount of the exhaust valve 35. It has been. The cylinder head 3 is further provided with a spark plug 36 facing the electrode at the tip of the combustion chamber 31, and spark-ignites an air-fuel mixture supplied into the combustion chamber 31.

  The cylinder head 3 is also provided with an electronically controlled fuel injection valve 37. In the case of this embodiment, the fuel injection valve 37 is disposed in the cylinder 22 so as to supply fuel by direct injection (in-cylinder injection). The fuel supply into the cylinder 22 may be port injection.

The crankcase 4 is provided with a crank angle sensor 401 that detects the rotation angle of the crankshaft 41. An intake passage 6 communicates with the intake port 32. An air filter 61, an air flow meter (intake air amount sensor) 601, an electronically controlled throttle valve 602, and a surge tank 63 are arranged in the intake passage 6 from the upstream side. An exhaust passage 7 communicates with the exhaust port 33. An air-fuel ratio sensor (O ₂ sensor) 701 and catalytic converters 71 and 72 are provided in the exhaust passage 7 from the upstream side.

  The ECU 100 includes a CPU 101, a ROM 102, a RAM 103, and an I / F (interface) 104. The CPU 101 controls the engine 1 by executing a control program stored in the ROM 102. In addition to the program executed by the CPU 101, the ROM 102 stores information in which ignition timing, fuel injection timing, fuel injection amount, intake valve 34 and exhaust valve 35 opening / closing timing, shift amount, and the like are set according to the operating state of the engine 1. Remember. The RAM 103 stores temporary data. The ROM 102 and RAM 103 may be other storage means.

  The I / F 104 includes a water temperature sensor 201, a crank angle sensor 401, an air flow meter 601, an air-fuel ratio sensor 701, an accelerator pedal sensor 10 a that detects an operation amount with respect to the accelerator pedal 10, and a brake pedal that detects a driver's operation with respect to the brake pedal 11. Detection results of the sensor 11a and the vehicle speed sensor 12 for detecting the vehicle speed are input, and the CPU 101 can read them. A control command from the CPU 101 is output to the ignition plug 36, the fuel injection valve 37, the throttle valve 602, and the actuators (solenoid, motor, etc.) of the variable valve gears 341 and 351 via the I / F 104.

  FIG. 2 is a flowchart illustrating an example of processing executed by the CPU 101. In S1, the detection result of each sensor is acquired. In S2, based on the detection result in S1, it is determined whether the operation region of the engine 1 is a self-ignition region or a spark ignition region. FIG. 3A is a diagram showing a difference in combustion method depending on the operation region. In the example of the figure, on the assumption that the engine 1 is warm, a region with a relatively low load and a low engine frequency is set as a self-ignition region, and the other region is set as a spark ignition region. The load is based on the detection result of the air flow meter 601, for example, and the engine speed is based on the detection result of the crank angle sensor 401.

  When the operation region of the engine 1 is not the self-ignition region in S2 (in the case of the spark ignition region), the process proceeds to S3 and the operation control of the engine 1 by spark ignition is performed. That is, the air-fuel mixture in the cylinder 22 is ignited by the spark plug 36 and burned to obtain a driving force. After the processing of S3, one unit of processing is terminated.

  When the operation region of the engine 1 is the self-ignition region in S2, a process for obtaining a driving force by performing self-ignition by burning the air-fuel mixture in the cylinder 22 and performing combustion is performed. First, in S4, based on the detection result of S1, it is determined whether or not a predetermined fuel cut condition for stopping the fuel supply into the cylinder 22 is satisfied. If not established, the process proceeds to S5, and if established, the process proceeds to S7. Examples of the fuel cut condition include a case where idling stop is executed when deceleration of the vehicle is required. As a case where deceleration of the vehicle is required, for example, when the brake pedal sensor 11a detects an operation on the brake pedal 11, or the vehicle speed based on the detection result of the vehicle speed sensor 12 tends to be reduced, and the accelerator pedal The case where operation with respect to the accelerator pedal 10 based on the detection result of the sensor 10a is not detected is mentioned. Moreover, as a case where idling stop is performed, the case where the vehicle speed based on the detection result of the vehicle speed sensor 12 is substantially 0 and the brake pedal sensor 11a detects the operation with respect to the brake pedal 11 is mentioned, for example.

  In S5, the valve timings of the intake valve 34 and the exhaust valve 35 are set, and control signals are output to the variable valve gears 341 and 351. In setting the valve timing, a period (negative overlap period) in which both the intake valve 34 and the exhaust valve 35 are closed before and after the exhaust top dead center is provided. FIG. 3B is a diagram showing valve timing at the time of self-ignition.

  In FIG. 3B, a negative overlap period P in which both the intake valve 34 and the exhaust valve 35 are closed is set before and after the exhaust top dead center. By providing the negative overlap period P, the temperature in the cylinder 22 can be maintained at a higher temperature by the burned gas remaining in the cylinder 22, and the compression self-ignition of the air-fuel mixture can be promoted in the compression stroke.

  In the present embodiment, the period P1 from the start of closing of the exhaust valve 35 to the exhaust top dead center and the period P2 from the exhaust top dead center to the start of opening of the intake valve 34 are set equal. Yes. Thereby, the compressed energy of the burned gas in the period P1 can be effectively used as the driving force for moving the piston 21 in the period P2, and the pumping loss of the engine 1 can be suppressed.

  Returning to FIG. 2, in S <b> 6, fuel is injected into the cylinder 22 by the fuel injection valve 37, and the air-fuel mixture is combusted in the combustion chamber 31. If it is determined in S4 that the fuel cut condition is satisfied, the fuel is not injected into the cylinder 22 and the combustion in the combustion chamber 31 is not performed. In S7, the valve timing is set, and a control signal is output to the variable valve gears 341 and 351. Here, the period from the exhaust top dead center to the start of opening of the intake valve 34 is made shorter than the period from the start of closing the exhaust valve 35 to the exhaust top dead center. In the present embodiment, the period from the start of closing of the exhaust valve 35 to the exhaust top dead center is not changed, and the opening timing of the intake valve 34 is corrected to advance. FIG.3 (c) is a figure which shows the valve timing at the time of fuel cut.

  In FIG. 3C, the period P1 from the start of closing of the exhaust valve 35 to the exhaust top dead center is the same as in FIG. 3B, but the opening timing of the intake valve 34 is the timing indicated by the broken line (FIG. 3). 3 (same as (b)), the advance angle is corrected to the timing indicated by the solid line, and the period from the exhaust top dead center to the start of opening of the intake valve 34 changes to P2 ′, and therefore the negative overlap period is It has changed to P ′.

  Here, the temperature drop in the cylinder 22 is caused by the fact that the burned gas in the cylinder 22 expands due to the piston 21 moving toward the bottom dead center in the intake stroke, and the intake valve 34 is opened to open the cylinder 22. This is due to the introduction of fresh air. In the present embodiment, by opening the opening timing of the intake valve 34, fresh air is introduced when the temperature in the cylinder 22 is relatively high before the temperature in the cylinder 22 decreases due to the expansion of burned gas. By doing so, the temperature drop in the cylinder 22 is suppressed. As a result, the temperature drop in the cylinder 22 is suppressed during the fuel cut, the fuel cut condition is not satisfied, and the ignitability can be improved when the fuel injection is restarted and the compression self-ignition is performed. Moreover, since intake and exhaust are performed during fuel cut, it is possible to suppress an excessive pumping loss.

Second Embodiment
In the present embodiment, when the fuel is cut, the lift amount of the intake valve 34 is further reduced, so that the amount of fresh air introduced into the cylinder 22 is suppressed, and the temperature drop in the cylinder 22 is suppressed. However, if the amount of fresh air introduced into the cylinder 22 is suppressed, the ratio of burned gas in the cylinder 22 is high, the oxygen is low, and ignition is performed when compression self-ignition is performed by restarting fuel injection. There is concern about the deterioration of sex. Therefore, in the present embodiment, the oxygen amount in the cylinder 22 is ensured by reducing the lift amount of the intake valve 34 after a predetermined period has elapsed after determining that the fuel cut condition is satisfied.

  FIG. 4 is a flowchart showing processing executed by the CPU 101 in this embodiment. In the figure, the processing from S1 to S7 is the same as the processing from S1 to S7 in FIG. In the present embodiment, the processes of S8 to S11 are performed following the process of S7.

  In S8, it is determined whether or not the lift amount of the intake valve 34 has already been reduced. If applicable, the process of one unit is terminated. If not, the process proceeds to S9. In S9, a counter for measuring a period after it is determined that the fuel cut condition is satisfied is added. The counter may be a software counter that stores a count value in a partial storage area of the RAM 103.

  In S10, it is determined whether or not the count value added in S9 has reached a specified value. If applicable, the process proceeds to S11. If not, one unit of processing is terminated. The prescribed value is set based on the period measured by the counter, and may be based on the number of cycles of the engine 1 or may be based on time. When the number of cycles of the engine 1 is used as a reference, for example, the specified value can be three times with the expansion stroke, the exhaust stroke, the intake stroke, and the compression stroke as one unit. In this case, after the fuel cut condition is satisfied, the lift amount is controlled to be small after the intake valve 34 is opened three times.

  In S 11, the lift amount of the intake valve 34 is corrected to be small, and a control signal is output to the variable valve operating apparatus 341. Also, the counter is reset. Thus, one unit of processing is completed.

  FIG. 5A is a diagram showing the valve timing at the time of fuel cut in this embodiment, and FIG. 5B is a diagram showing the change in the lift amount of the intake valve 34 at the time of fuel cut. The valve timing of FIG. 5A is the same as that of FIG. 3B, and shows a state in which the valve opening timing of the intake valve 34 has been advanced in S7 of FIG. FIG. 5B shows a state in which the lift amount of the intake valve 34 is controlled to be small in the process of S11 of FIG. 4, and the broken line shows before correction and the solid line shows after correction.

  As described above, in this embodiment, the amount of fresh air introduced into the cylinder 22 can be suppressed by reducing the lift amount of the intake valve 34, and the temperature drop in the cylinder 22 can be suppressed. Further, since the lift amount of the intake valve 34 is reduced after a predetermined period after the fuel cut condition is satisfied, the oxygen amount in the cylinder 22 can be secured and the compression self-ignitability when the fuel injection is resumed can be maintained. Also, when the temperature in the cylinder 22 is relatively high immediately after the fuel cut condition is established, the amount of fresh air introduced is relatively large, and the temperature in the cylinder 22 is relatively low after a predetermined period of time. In addition, since the amount of fresh air introduced is relatively small, it contributes to the suppression of the temperature drop in the cylinder 22.

It is a control system figure of engine 1 to which control device A concerning one embodiment of the present invention is applied. It is a flowchart which shows the example of the process which CPU101 performs. (A) is a figure which shows the difference in the combustion system by an operation area | region, (b) is a figure which shows the valve timing at the time of self-ignition, (c) is a figure which shows the valve timing at the time of fuel cut. It is a flowchart which shows the other example of the process which CPU101 performs. (A) is a figure which shows the valve timing at the time of fuel cut, (b) is a figure which shows the change of the lift amount of the intake valve at the time of fuel cut.

Explanation of symbols

A Control device 100 ECU
34 Intake valve 35 Exhaust valve 341, 351 Variable valve mechanism

Claims (4)

Valve timing control means for closing both the intake valve and the exhaust valve before and after exhaust top dead center in an operation region in which the air-fuel mixture in the cylinder self-ignites.
Fuel cut determination means for determining whether or not a predetermined fuel cut condition is satisfied, stopping supply of fuel into the cylinder;
In a gasoline engine control device equipped with
The valve timing control means includes
In the operation region, when the fuel cut determination means determines that the fuel cut condition is satisfied, the intake air from the exhaust top dead center is longer than the period from the start of closing of the exhaust valve to the exhaust top dead center. A control device for a gasoline engine, characterized by shortening the period until the start of valve opening. The valve timing control means includes
In the operating region, the period from the start of closing of the exhaust valve to the exhaust top dead center is made equal to the period from the exhaust top dead center to the start of opening of the intake valve, while the fuel cut determination 2. The gasoline engine control device according to claim 1, wherein when the means determines that the fuel cut condition is satisfied, the opening timing of the intake valve is advanced. Further comprising lift amount control means for controlling the lift amount of the intake valve;
The lift amount control means includes:
The gasoline engine control according to claim 1 or 2, wherein when the fuel cut determination means determines that a fuel cut condition is satisfied in the operating region, the lift amount of the intake valve is reduced. apparatus. The lift amount control means includes:
4. The lift amount of the intake valve is reduced after a predetermined period after the determination, when the fuel cut determination unit determines that the fuel cut condition is satisfied in the operation region. The gasoline engine control device described.

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