JP2009041540A - Control device of gasoline engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase an internal EGR amount and to suppress a decrease of a temperature in a cylinder, while controlling an air flow in the cylinder when fuel is cut off. <P>SOLUTION: A control device of a gasoline engine includes: a valve timing control means for opening both an intake valve and an exhaust valve around an exhaust top dead point in an operation region in which an air-fuel mixture in the cylinder self-ignites; and a fuel cut determination means for determining whether a predetermined fuel cut condition for stopping a supply of fuel into the cylinder is met. The valve timing control means changes a time period of opening the exhaust valve so as to cover the exhaust top dead point and so as not to overlap a time period of opening the intake valve, if the fuel cut determination means determines that the predetermined fuel cut condition is met in the operation region. <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 JP 2006-83737 A

  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 for preventing a decrease in the in-cylinder temperature, there is an increase in the amount of internal EGR, that is, an increase in the amount of burned gas remaining in the cylinder. As a technique related to the increase in the internal EGR amount, Patent Document 2 discloses a positive overlap period in which both the exhaust valve and the intake valve are opened in order to prevent the intake system from becoming negative pressure when the fuel is cut. Proposed to be longer. However, if the positive overlap period is lengthened, the air flow in the cylinder is promoted, which is not desirable from the viewpoint of preventing a decrease in the cylinder temperature.

  Accordingly, an object of the present invention is to increase the internal EGR amount and suppress the decrease in the cylinder temperature while suppressing the flow of air in the cylinder at the time of 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. When the means determines that the fuel cut condition is satisfied, the valve opening period of the exhaust valve is changed so as to straddle the exhaust top dead center and not overlap the valve opening period of the intake valve. A gasoline engine control device is provided.

  In the present invention, the recirculation amount of the burned gas from the exhaust passage into the cylinder is increased by changing the valve opening period of the exhaust valve so as to cross the exhaust top dead center at the time of fuel cut. Further, by changing the opening period of the exhaust valve so as not to overlap the opening period of the intake valve, both the exhaust valve and the intake valve are prevented from opening, and the air in the cylinder Suppresses flow. In this way, when the fuel is cut, the internal EGR amount can be increased while suppressing the flow of air in the cylinder, and the decrease in the cylinder temperature can be suppressed.

  In the present invention, the valve timing control means determines the timing at which the exhaust valve reaches the maximum lift amount when the fuel cut determination means determines that the fuel cut condition is satisfied in the operating region. You may make it be after a dead point.

  According to this configuration, the recirculation amount of the burned gas from the exhaust passage into the cylinder can be further increased, and a decrease in the cylinder temperature can be suppressed.

  Further, in the present invention, when the fuel cut determination unit determines that the fuel cut condition is satisfied in the operating region, the valve timing control unit performs the exhaust valve after a predetermined period after the determination. The valve opening period may be changed.

  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.

  The present invention further includes an EGR valve control means for controlling an EGR valve that opens and closes a recirculation path for recirculating exhaust gas from the exhaust passage to the intake passage, and the EGR valve control means is configured to control the fuel cut in the operating region. When the determination means determines that the fuel cut condition is satisfied, the EGR valve may be opened.

  According to this configuration, the recirculation amount of the burned gas from the exhaust passage into the cylinder can be further increased by using the external EGR, and the decrease in the cylinder temperature can be suppressed.

  As described above, according to the present invention, it is possible to increase the internal EGR amount and suppress the decrease in the cylinder temperature while suppressing the flow of air in the cylinder at the time of 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. First, in S7, it is determined whether or not a later-described valve timing setting has been changed. If the setting has been changed, the process of one unit is terminated. If the setting has not been changed, the process proceeds to S8. In S8, 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 S9, it is determined whether or not the count value added in S8 has reached a specified value. If applicable, the process proceeds to S10, and if not applicable, 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 exhaust valve 35 is opened three times after the fuel cut condition is satisfied, the valve timing is changed by a process described later.

  In S10, the valve timing is set and a control signal is output to the variable valve gears 341 and 351. In S11, the counter is reset and one unit of processing is terminated. In S10, the opening period of the exhaust valve 35 is changed so as to straddle the exhaust top dead center and not overlap the opening period of the intake valve 34. In the present embodiment, the opening timing of the intake valve 34 is not changed, and the opening period of the exhaust valve 35 is retarded. FIG.3 (c) is a figure which shows the valve timing at the time of fuel cut.

  In FIG. 3C, the opening timing of the intake valve 34 is the same as that in FIG. 3B, but the opening period of the exhaust valve 35 is the solid line from the timing indicated by the broken line (same as in FIG. 3B). Delay angle correction is performed at the timing shown. Since the exhaust valve 35 is also opened in the intake stroke, the burned gas exhausted from the cylinder 22 to the exhaust port 33 or the exhaust passage 7 in the exhaust stroke is sucked into the cylinder 22 again, and the burned gas The amount of reflux into the cylinder 22 increases. At that time, since the intake valve 34 is not closed, the flow of air in the cylinder 22 is suppressed. Thus, in the present embodiment, it is possible to increase the internal EGR amount and suppress a decrease in the cylinder temperature while suppressing the flow of air in the cylinder 22 at the time of fuel cut.

  In addition, it is preferable that the timing when the exhaust valve 35 reaches the maximum lift amount is after the exhaust top dead center during the opening period of the exhaust valve 35. FIG. 4 is a diagram showing another example of valve timing at the time of fuel cut. In FIG. 4, the opening period of the exhaust valve 35 is delayed from the timing indicated by the broken line (same as FIG. 3B) to the timing indicated by the solid line, and the timing T at which the maximum lift amount is reached is the exhaust top dead center. It is set after. Also in this case, the valve opening period of the exhaust valve 35 and the valve opening period of the intake valve 34 are not overlapped. Thus, by setting the timing T at which the maximum lift amount is reached after the exhaust top dead center, the internal EGR amount can be further increased, and the temperature drop in the cylinder 22 can be suppressed.

  If the internal EGR amount is increased, the ratio of burned gas in the cylinder 22 is high and oxygen is low, and when the fuel injection is restarted and compression self-ignition is performed, the ignitability may deteriorate. Concerned. In this respect, in the present embodiment, the scavenging performance in the cylinder 22 immediately after the fuel cut condition is satisfied is improved by changing the valve opening period of the exhaust valve 35 after a predetermined period has elapsed since it is determined that the fuel cut condition is satisfied. Thus, the amount of oxygen in the cylinder 22 can be ensured, and the self-ignitability when the fuel supply is resumed can be improved. Since the scavenging performance is improved immediately after the fuel cut, the temperature drop in the cylinder 22 can be minimized.

Second Embodiment
In the first embodiment, the temperature drop in the cylinder 22 is prevented by increasing the internal EGR amount. However, in this embodiment, the recirculation amount of the burned gas into the cylinder 22 is further increased by utilizing the external EGR. It increases more and suppresses the fall of the temperature. FIG. 5 is a control system diagram of the engine 1 ′ to which a control device B according to another embodiment of the present invention is applied. The same components as those in the control system diagram of FIG. 1 are denoted by the same reference numerals, the description thereof is omitted, and only different components are described.

  In the present embodiment, the engine 1 ′ includes a recirculation passage 8 that recirculates exhaust gas from the exhaust passage 7 to the intake passage 6, and an EGR valve 81 that opens and closes the recirculation passage 8. ECU 100 sends a control signal to EGR valve 81 to control its opening and closing. In the case of the present embodiment, the EGR valve 81 has an operation region of the engine 1 ′ that is a spark ignition region, and opens in a region of relatively low load and low engine rotation, and other spark ignition regions, and It is assumed that the valve is closed during the combustion operation in the self-ignition region.

  FIG. 6 is a flowchart showing processing executed by the CPU 101 in this embodiment. The same processes as those in the flowchart of FIG. 2 are denoted by the same reference numerals, the description thereof is omitted, and only different processes are described.

  In this embodiment, when it is determined that the self-ignition region is determined in S2 and the fuel cut condition is not satisfied in S4, the EGR valve 81 is closed in S21 after the valve timing is set in S5. To do.

  Further, if it is determined in S2 that the self-ignition region is determined, and if it is determined in S4 that the fuel cut condition is satisfied, the valve timing is set and changed in S10 after a predetermined period has elapsed (S8, S9) ( 3 (c) or FIG. 4), then, in S22, the EGR valve 81 is opened. Thus, burned gas existing in the exhaust passage 7 is introduced into the cylinder 22 via the intake passage 6 and the intake port 32 during the opening period of the intake valve 34 in the intake stroke, and burned gas into the cylinder 22 is introduced. Increase the amount.

  Thus, in the present embodiment, by increasing the internal EGR amount and utilizing the external EGR, the amount of burned gas in the cylinder 22 can be increased, and the temperature drop in the cylinder 22 during fuel cut can be suppressed. In this embodiment, since the EGR valve 81 is opened after a predetermined period of time has elapsed since the fuel cut condition is established, the scavenging performance in the cylinder 22 immediately after the fuel cut condition is established is improved and the amount of oxygen in the cylinder 22 is secured. In addition, self-ignitability at the time of resumption of fuel supply can be improved. Since the scavenging performance is improved immediately after the fuel cut, the temperature drop in the cylinder 22 can be minimized.

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 figure which shows the other example of the valve timing at the time of fuel cut. It is a control system figure of engine 1 'to which control device B concerning other embodiments of the present invention is applied. It is a flowchart which shows the other example of the process which CPU101 performs.

Explanation of symbols

A, B Control device 8 Return passage 100 ECU
34 Intake valve 35 Exhaust valve 81 EGR valves 341 and 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 operating region, when the fuel cut determination means determines that the fuel cut condition is satisfied, the exhaust valve opening period spans the exhaust top dead center and the intake valve opening period. A gasoline engine control device that is modified so that it does not overlap. The valve timing control means includes
2. The timing when the exhaust valve reaches a maximum lift amount after the exhaust top dead center when the fuel cut determination unit determines that the fuel cut condition is satisfied in the operation region. 1. A gasoline engine control device according to 1. The valve timing control means includes
When the fuel cut determination unit determines that the fuel cut condition is satisfied in the operation region, the valve opening period of the exhaust valve is changed after a predetermined period after the determination. The gasoline engine control device according to 1 or 2. EGR valve control means for controlling an EGR valve that opens and closes a recirculation passage for recirculating exhaust gas from the exhaust passage to the intake passage;
The EGR valve control means includes
4. The gasoline according to claim 1, wherein the EGR valve is opened when the fuel cut determination unit determines that the fuel cut condition is satisfied in the operation region. 5. Engine control device.

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