Engine Control Unit

Abstract

To provide a control device of an engine which can effectively prevent a freeze of condensed water contained in a blowby gas, and the formation of an ice block accompanied by the freeze.SOLUTION: In a control device of an engine which is mounted to a vehicle having a transmission, and can switch an operation between a full-cylinder operation at which combustion is performed in all cylinders, and a reduced-cylinder operation at which the combustion is stopped at a specified cylinder out of a plurality of the cylinders, when a fuel cut condition is established during the reduce-cylinder operation, and in a state that a gear stage detected by gear stage detection means is lower than a prescribed reference gear stage, the control device switches an opening / closing mode of a specified intake / exhaust valve to a full-cylinder mode from a reduced-cylinder mode, and when the fuel cut condition is established during the reduced- cylinder operation, and in a state that the gear stage is equal to or higher than the reference gear stage, the control device maintains the opening / closing mode of the specified intake / exhaust valve at the reduced-cylinder mode.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a device for controlling an engine that is mounted on a vehicle equipped with a transmission and has an engine body formed with multiple cylinders, an intake passage, a throttle valve that opens and closes the intake passage, a fuel supply means that supplies fuel to each cylinder, and an ignition means that ignites the mixture in each cylinder, and that can be switched between all-cylinder operation in which combustion is performed in all cylinders and reduced-cylinder operation in which combustion is stopped in specific cylinders among the multiple cylinders. [Background technology]

[0002] It has been known for some time that an engine having multiple cylinders can be switched between full-cylinder operation, in which the intake and exhaust valves (intake valves and exhaust valves) of all cylinders can be opened and closed and combustion takes place in all cylinders, and reduced-cylinder operation, in which the intake and exhaust valves of some cylinders cannot be opened or closed and combustion in those cylinders is stopped.

[0003] Here, there is a risk of torque shock occurring when switching between all cylinder operation and reduced cylinder operation. Specifically, in reduced cylinder operation, the number of cylinders in which combustion is performed is reduced, so it is necessary to increase the opening of the throttle valve provided in the intake passage to increase the amount of intake air into the cylinder compared to when in full cylinder operation. However, there is a delay between changing the opening of the throttle valve and the actual increase in the amount of intake air into the cylinder. Therefore, when switching from all cylinder operation to reduced cylinder operation, if the opening of the throttle valve is increased at the same time as the start of reduced cylinder operation, the amount of intake air into the cylinder will be insufficient, resulting in a decrease in engine torque.

[0004] To address this problem, Patent Document 1 discloses an engine that performs the following control when switching between cylinders. That is, in the engine of Patent Document 1, when switching from all-cylinder operation to reduced-cylinder operation, first, the ignition timing is retarded and the throttle valve opening is increased to increase the intake amount of each cylinder while suppressing fluctuations in engine torque. Then, reduced-cylinder operation is started after the intake amount of each cylinder has increased. By performing this control, a temporary decrease in engine torque when switching from all-cylinder operation to reduced-cylinder operation is suppressed, and the occurrence of torque shock is suppressed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6791360 Summary of the Invention [Problem to be solved by the invention]

[0006] In an engine that switches between full cylinder operation and reduced cylinder operation, fuel may be cut off during reduced cylinder operation, that is, fuel supply to all cylinders may be stopped. Here, as described above, in an engine that is operating with reduced cylinders, the intake and exhaust valves of some cylinders cannot be opened or closed, and the total pumping loss occurring in all cylinders is kept small. Therefore, if fuel supply to each cylinder is stopped in this state, the degree of reduction in engine speed becomes small, and the driver may not feel a sufficient deceleration.

[0007] In response to this, it is possible to switch the engine operation mode to an all-cylinder operation mode during fuel cut, reduce the throttle valve opening (close the throttle valve), and open and close the intake and exhaust valves of all cylinders. However, in this case, when returning to reduced cylinder operation after the fuel cut ends, the engine operation needs to be switched from all-cylinder operation to reduced cylinder operation, and there is a risk of torque shock as described above. Here, this torque shock can be suppressed by implementing the same control as the engine of Patent Document 1, that is, by implementing control to increase the throttle valve opening while retarding the ignition timing. However, when this control is implemented, there is a risk of fuel economy deteriorating due to the retardation of the ignition timing.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to realize an engine control device that can appropriately provide the deceleration feeling desired by the driver while suppressing deterioration of fuel efficiency. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides an engine control device that is mounted on a vehicle equipped with a transmission and has an engine body formed with a plurality of cylinders, an intake passage, a throttle valve that opens and closes the intake passage, a fuel supply means that supplies fuel to each cylinder, and an ignition means that ignites the mixture in each cylinder, and that is switchable between all-cylinder operation in which combustion is performed in all cylinders and reduced-cylinder operation in which combustion is stopped in a specific cylinder among the plurality of cylinders, and that includes gear stage detection means that detects a gear stage of the transmission, a switching mechanism that switches the opening and closing modes of specific intake and exhaust valves, which are the intake valves and exhaust valves of the specific cylinders, between an all-cylinder mode in which opening and closing is permitted and a reduced-cylinder mode in which opening and closing is prohibited, and a control device that controls the throttle valve, fuel supply means, ignition means, and switching mechanism, and controls the opening and closing modes of the specific intake and exhaust valves. and a control means for switching the opening / closing mode of the specific intake / exhaust valve from the all-cylinder mode to the reduced-cylinder mode when the specific intake / exhaust valve is switched from the all-cylinder mode to the reduced-cylinder mode, the control means performing reduced-cylinder switching control for increasing an opening degree of the throttle valve and retarding an ignition timing of the ignition means when switching the opening / closing mode of the specific intake / exhaust valve from the all-cylinder mode to the reduced-cylinder mode, and switching the opening / closing mode after the reduced-cylinder switching control is performed, and a fuel cut control unit for stopping fuel supply from the fuel supply means to all cylinders when a fuel cut condition for stopping fuel supply to all cylinders is established, and when the fuel cut condition is established during reduced-cylinder operation while the gear stage detected by the gear stage detection means is less than a predetermined reference gear stage, the fuel cut control unit switches the opening / closing mode of the specific intake / exhaust valve from the reduced-cylinder mode to the all-cylinder mode. At the same time, the opening of the throttle valve is reduced. During reduced cylinder operation, when the fuel cut condition is satisfied with the gear position being equal to or greater than the reference gear position, the fuel cut control unit maintains the opening / closing mode of the specific intake / exhaust valve in the reduced cylinder mode. When the opening / closing mode is switched from the reduced cylinder mode to the all cylinder mode in response to the fuel cut condition being satisfied, the control means starts all cylinder operation when the fuel cut condition is no longer satisfied. The present invention is characterized by the above (Claim 1).

[0010] In the present invention, when switching from all-cylinder operation in which the opening / closing mode of a specific intake / exhaust valve is the all-cylinder mode to reduced-cylinder operation in which the opening / closing mode of a specific intake / exhaust valve is the reduced-cylinder mode, a reduced-cylinder switching control is implemented to increase the throttle valve opening and retard the ignition timing of the ignition means, thereby suppressing the occurrence of torque shock at the time of the switching.

[0011] Moreover, when the fuel cut condition is satisfied during reduced cylinder operation in a state where the gear stage of the transmission is a low gear stage (lower than the reference gear stage) and the driver is considered to desire a high deceleration feeling, the opening and closing mode of the specific intake and exhaust valves is switched to the all-cylinder mode, and the intake and exhaust valves of all cylinders are switched to a state in which they can be opened and closed. This causes a relatively large pumping loss in all cylinders, and the deceleration of the vehicle can be increased. Therefore, the driver can be given a high deceleration feeling according to his / her request.

[0012] On the other hand, when the fuel cut condition is satisfied during reduced cylinder operation in a state where the gear stage of the transmission is a high gear stage (above the reference gear stage) and the driver is unlikely to desire a strong deceleration feeling, the opening and closing mode of the specific intake and exhaust valve is maintained in the reduced cylinder mode. Therefore, after the fuel cut condition is no longer satisfied, reduced cylinder operation can be started without implementing reduced cylinder switching control, and it is possible to avoid deterioration of fuel efficiency due to the implementation of reduced cylinder switching control, that is, the implementation of control to retard the ignition timing.

[0013] Therefore, according to the present invention, it is possible to suppress deterioration of fuel economy while appropriately providing the driver with the deceleration feeling that the driver desires.

[0014] In the above configuration, preferably, the control means performs reduced cylinder operation when the engine is operating in a predetermined first operating range, and determines that the fuel cut condition is met when the engine is operating in a predetermined second operating range, the second operating range being set to a range in which the engine load is smaller than that of the first operating range and which is adjacent to the first operating range in terms of engine load (claim 2).

[0015] In this configuration, there are many occasions when reduced cylinder operation is performed after fuel cut. Therefore, if the same control as that for the low gear is performed even when the transmission is in the high gear, there is a risk that fuel economy will deteriorate significantly. Therefore, by applying the present invention to this configuration, deterioration of fuel economy can be effectively suppressed. Effect of the Invention

[0016] As described above, according to the engine control device of the present invention, it is possible to appropriately provide the deceleration feeling desired by the driver while suppressing deterioration of fuel economy performance. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of an engine to which an engine control device according to an embodiment of the present invention is applied. [Diagram 2] FIG. 2 is a schematic cross-sectional view of an engine body. [Diagram 3] FIG. 2 is a block diagram showing a control system of the engine. [Figure 4] FIG. 2 is a diagram showing an operating range of the engine. [Diagram 5] 4 is a flowchart showing a control procedure when switching from full cylinder operation to reduced cylinder operation. [Figure 6] 4 is a time chart showing the change over time of each parameter when switching from full cylinder operation to reduced cylinder operation. [Figure 7] 4 is a flowchart showing a control procedure when switching from reduced cylinder operation to full cylinder operation. [Figure 8] 4 is a time chart showing the change over time of each parameter when switching from reduced cylinder operation to full cylinder operation. [Figure 9] 4 is a flowchart showing a control procedure when a fuel cut condition is satisfied. [Figure 10] 4 is a time chart showing the time changes of each parameter when a fuel cut is performed during reduced cylinder operation at a high speed. [Figure 11]4 is a time chart showing the time changes of each parameter when a fuel cut is performed during reduced cylinder operation at a low speed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] (Overall engine configuration) FIG. 1 is a schematic system diagram showing a preferred embodiment of an engine to which an engine control device according to an embodiment of the present invention is applied. The engine includes an engine body 1, an intake passage 30 through which air (intake air) introduced into the engine body 1 flows, and an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows. This engine is mounted in a vehicle such as an automobile as a power source for driving the vehicle. The vehicle on which the engine is mounted is equipped with a transmission 70 (FIG. 3) including a plurality of gear stages, and the output of the engine body 1 is transmitted to the wheels while being shifted by the transmission 70. In this embodiment, the engine body 1 is a gasoline engine that mainly uses gasoline as fuel, and as described later, a mixture of a fuel containing gasoline and air is ignited. In addition, the engine body 1 is a four-stroke engine.

[0019] The engine body 1 has a plurality of cylinders 2. FIG. 2 is a schematic cross-sectional view of the engine body 1. As shown in FIG. 2, the engine body 1 of this embodiment is an in-line four-cylinder engine, and the engine body 1 has four cylinders 2 (2A to 2D) arranged in a row. The engine body 1 includes a cylinder block 3 in which the cylinders 2 are formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the upper end opening of each cylinder 2, and a plurality of pistons 11 accommodated in each cylinder 2 so as to be able to slide back and forth. In this embodiment, the side from the cylinder block 3 toward the cylinder head 4 is treated as the top, and the opposite side is treated as the bottom, but this is for convenience of explanation and is not intended to limit the installation posture of the engine. Above the piston 11 of each cylinder 2, a combustion chamber 5 is defined. Fuel is supplied to the combustion chamber 5 by injection from an injector 12, which will be described later. A mixture of the supplied fuel and air is burned in the combustion chamber 5, and the piston 11 reciprocates in the vertical direction due to the expansion force caused by the combustion.

[0020] A crankshaft 15, which is an output shaft of the engine body 1, is provided at the bottom of the cylinder block 3 (below the pistons 11). The crankshaft 15 is connected to the pistons 11 of each cylinder 2 via connecting rods, and rotates about a central axis in response to the reciprocating motion (up and down movement) of the pistons 11. A crank angle sensor SN1 is attached to the cylinder block 3. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 15, and the engine speed, which is the rotation speed of the crankshaft 15.

[0021] The cylinder head 4 is provided with a pair of an injector 12 and an ignition plug 13 for each cylinder 2. The injector 12 is an injection valve that injects fuel into the combustion chamber 5. In this embodiment, the injector 12 is disposed so that its tip faces the combustion chamber 5 from the inner circumferential surface of the combustion chamber 5, and injects fuel by a side injection method. The ignition plug 13 ignites the mixture of fuel and air by spark discharge. The ignition plug 13 has an electrode for discharging a spark at its tip, and is attached to the cylinder head 4 so as to face the combustion chamber 5 of each cylinder 2 from above. The injector 12 corresponds to the "fuel supply device" in the claims, and the ignition plug 13 corresponds to the "ignition means" in the claims.

[0022] In a four-stroke, four-cylinder engine such as that of this embodiment, combustion occurs at intervals of 180° CA (crank angle) in each cylinder 2 (2A to 2D). Specifically, assuming that the four cylinders 2 are, from the left in FIG. 2, the first cylinder 2 (2A), the second cylinder 2 (2B), the third cylinder 2 (2C), and the fourth cylinder 2 (2D), combustion occurs at intervals of 180° CA in the order of the first cylinder 2 (2A) → the third cylinder 2 (2C) → the fourth cylinder 2 (2D) → the second cylinder 2 (2B). Correspondingly, the timing at which fuel is injected from the injector 12 into each cylinder 2 (2A to 2D) and the timing at which ignition is performed by the spark plug 13 are also shifted in phase by 180° CA.

[0023] In the cylinder head 4, an intake port 6 for introducing air supplied from an intake passage 30 into the combustion chamber 5 and an exhaust port 7 for leading exhaust gas generated in the combustion chamber 5 to an exhaust passage 40 are formed for each cylinder 2. In the cylinder head 4, an intake valve 8 for opening and closing the opening of the intake port 6 on the combustion chamber 5 side and an exhaust valve 9 for opening and closing the opening of the exhaust port 7 on the combustion chamber 5 side are provided for each cylinder 2. As shown in FIG. 2, in this embodiment, two intake valves 8 and two exhaust valves 9 are provided for each cylinder 2.

[0024] The engine of this embodiment is capable of performing all-cylinder operation in which the mixture is burned in all cylinders 2, and reduced-cylinder operation in which the mixture is stopped in some cylinders 2 (i.e., switching between all-cylinder operation and reduced-cylinder operation is possible). During reduced-cylinder operation, fuel injection from the injector 12 is prohibited in cylinders 2 whose combustion order is not consecutive. Hereinafter, the cylinders 2 whose combustion is stopped during reduced-cylinder operation are referred to as specific cylinders 2, and the remaining cylinders 2 are referred to as operating cylinders 2. In this embodiment, the first cylinder 2 (2A) and the fourth cylinder 2 (2D) are set as the specific cylinders 2. Note that the above combustion order is the order during all-cylinder operation, and during reduced-cylinder operation, combustion is performed at 360° intervals in the second cylinder 2 (2B) and the third cylinder 2 (2C), which are the operating cylinders 2.

[0025] The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 6 of each cylinder 2. Specifically, the intake passage 30 is composed of a single intake pipe 33 and a plurality (four) of independent intake passages 31 (arranged in a direction perpendicular to the paper surface of FIG. 1) that individually connect the intake pipe 33 to the intake port 6 of each cylinder 2. A surge tank 32 of a predetermined volume is provided at the downstream end of the intake pipe 33, and the independent intake passages 31 extend from the surge tank 32 to each intake port 6. A throttle valve 34 capable of opening and closing the passage of the intake pipe 33 is provided at a portion of the intake pipe 33 upstream of the surge tank 32. An airflow sensor SN2 for detecting the flow rate of air passing through this portion is provided at a portion of the intake pipe 33 upstream of the throttle valve 34.

[0026] The exhaust passage 40 is connected to one side of the cylinder head 4 (the side opposite to the intake passage 30) so as to communicate with the exhaust ports 7 of each cylinder 2. A catalytic device 90 having a catalyst such as a three-way catalyst built in is provided in the exhaust passage 40. Specifically, the exhaust passage 40 has independent exhaust passages 41 (arranged in a direction perpendicular to the paper surface of FIG. 1 ) that individually communicate with each exhaust port 7, and a single exhaust pipe 43 that communicates with these independent exhaust passages 41, and the catalytic device 90 is disposed in the exhaust pipe 43.

[0027] (Valve train) The intake valve 8 and the exhaust valve 9 are driven to open and close in conjunction with the rotation of the crankshaft 15 by a pair of valve operating mechanisms 28, 29 disposed in the cylinder head 4. The intake valves 8 and the exhaust valves 9 of the second cylinder 2B and the third cylinder 3C, which are the operating cylinders 2, are always driven to open and close in conjunction with the rotation of the crankshaft 15. On the other hand, the intake valves 8 and the exhaust valves 9 of the first cylinder 2A and the fourth cylinder 2D, which are the specific cylinders 2, can be prohibited from opening and closing. That is, the opening and closing modes of the intake and exhaust valves 8, 9 of the specific cylinders 2 (2A, 2D) can be switched between an all-cylinder mode in which opening and closing are permitted and a reduced-cylinder mode in which opening and closing are prohibited. Hereinafter, the intake and exhaust valves 8, 9 of the specific cylinders 2 (2A, 2D) are referred to as specific intake and exhaust valves 8, 9 as appropriate.

[0028] Specifically, each valve mechanism 28, 29 is provided with a known hydraulic lash adjuster (not shown; hereinafter, abbreviated as "HLA," which stands for Hydraulic Lash Adjuster) that automatically adjusts the valve clearance of each cylinder 2 (2A to 2D) to zero. The HLA for a specific cylinder 2 (2A, 2D) has a valve stop mechanism 61 that can prohibit the opening and closing of the intake and exhaust valves 8, 9 (specific intake and exhaust valves 8, 9) of the specific cylinder 2 (2A, 2D).

[0029] The valve stop mechanism 61 is hydraulically driven, and hydraulic oil is supplied to the valve stop mechanism 61 from an oil pump 65. When the hydraulic pressure supplied to the valve stop mechanism 61 reaches or exceeds a predetermined reference hydraulic pressure, the valve stop mechanism 61 disables the specific intake and exhaust valves 8 and 9 from opening or closing. In this embodiment, the valve stop mechanism 61 of each intake valve 8 of the specific cylinder 2 (2A, 2D) is connected to the oil pump 65 via a common oil control valve 62 (hereinafter referred to as OCV 62), and the valve stop mechanism 61 of each exhaust valve 9 of the specific cylinder 2 (2A, 2D) is connected to the oil pump 65 via another common OCV 62. Each OCV 62 is a valve that opens and closes an oil passage between the oil pump 65 and the valve stop mechanism 61 (hereinafter referred to as valve stop mechanism oil passage 66 as appropriate). As a result, the specific intake and exhaust valves 8, 9 are unable to open or close only when each OCV 62 is open to allow the introduction of oil to the valve stop mechanism 61 and the oil pressure in the valve stop mechanism oil passage 66 is increased to a reference oil pressure or higher by the oil pump 65. In this embodiment, the OCV 62 is opened to open the valve stop mechanism oil passage 66 when it is energized and turned ON, and is closed to close the valve stop mechanism oil passage 66 when it is not energized and turned OFF.

[0030] As described above, in this embodiment, the valve stop mechanism 61 and the two OCVs 62 switch the opening and closing mode of the specific intake and exhaust valves 8, 9 between the all-cylinder mode and the reduced-cylinder mode, and the valve stop mechanism 61 and the two OCVs 62 correspond to the "switching mechanism" in the claims.

[0031] (Control system) FIG. 3 is a block diagram showing the control system of the engine. The ECU 100 shown in this figure is a device that controls the engine in an integrated manner, and is composed of a microcomputer including a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses. The ECU 100 functionally has a determination unit 101 that performs various determinations, a fuel cut control unit 103 that performs fuel cut control to stop fuel supply to all cylinders 2, and a basic control unit 102 that performs basic control of the engine, including a first switching control unit 102a that performs all-cylinder switching control described later and a second switching control unit 102b that performs reduced-cylinder switching control described later. The ECU 100 corresponds to the "control means" in the claims, and the second switching control unit 102b corresponds to the "switching control unit" in the claims.

[0032] Information detected by each sensor of the engine is input to the ECU 100. For example, information detected by a crank angle sensor SN1 and an air flow sensor SN2, that is, information on the crank angle, engine speed, and intake amount, is sequentially input to the ECU 100. The vehicle is also provided with an accelerator opening sensor SN3 that detects an accelerator opening, which is the opening of an accelerator pedal 80 provided on the vehicle, and a gear stage sensor SN4 that detects the current gear stage of the transmission 70. Detection signals from these sensors SN3 and SN4 are also sequentially input to the ECU 100. The ECU 100 controls each part of the engine, such as the injector 10, while performing various judgments and calculations based on the input information from each of the sensors SN1 to SN4. The gear stage sensor SN4 corresponds to the "gear stage detection means" in the claims.

[0033] FIG. 4 is a map showing the engine operating region with the engine speed on the horizontal axis and the engine load on the vertical axis. In this embodiment, a cylinder reduction region A2 where the cylinder reduction operation should be performed is set in a medium-speed low-load region where the engine speed is equal to or higher than the first rotation speed N1 and equal to or lower than the second rotation speed N2, and the engine load is equal to or higher than the first load Tq1 and equal to or lower than the second load Tq2. A fuel cut region A3 where the fuel cut should be performed is set adjacent to the cylinder reduction region A2 and in a region where the engine load is lower than the cylinder reduction region A2. Specifically, the fuel cut region A3 is set in a medium-speed very low-load region where the engine speed is equal to or higher than the first rotation speed N1 and equal to or lower than the second rotation speed N2, and the engine load is less than the first load Tq1. The other regions except for the cylinder reduction region A2 and the fuel cut region A3 are set in the all-cylinder region A1 where the all-cylinder operation should be performed. The cylinder reduction region A2 corresponds to the "first operating region" in the claims, and the fuel cut region A3 corresponds to the "second operating region" in the claims.

[0034] The ECU 100 (determination unit 101) determines in which of the regions A1 to A3 the engine is operating based on the engine speed and engine load. The ECU 100 successively calculates the engine load based on the accelerator opening detected by the accelerator sensor SN3 and the engine speed detected by the crank angle sensor SN1, and makes the above determination based on the calculated engine load and the engine speed detected by the crank angle sensor SN1. Here, the fuel cut region A3 is set as a region where the engine load is extremely low, and operation in the fuel cut region A3 is performed when the accelerator opening is 0 (when the accelerator pedal 80 is not depressed).

[0035] (Normal control) Next, control during normal operation, excluding when the fuel is cut off, will be described.

[0036] When the engine is operating in the all-cylinder region A1, the ECU 100 (basic control unit 102) operates the engine in all cylinders. Specifically, the ECU 100 drives all the injectors 12 to inject fuel from the injectors 12 into all the cylinders 2. The ECU 100 also sets the opening / closing mode of the specific intake and exhaust valves 8, 9 to the all-cylinder mode. That is, the ECU 100 turns off each OCV 62 to allow the specific intake and exhaust valves 8, 9 to open and close, thereby enabling the intake and exhaust valves 8, 9 of all the cylinders 2 to open and close.

[0037] (reduced cylinder operation) On the other hand, when the engine is operating in the cylinder reduction region A2, the ECU 100 operates the engine with reduced cylinders. Specifically, the ECU 100 (basic control unit 102) stops the driving of the injector 12 of the specific cylinder 2 (2A, 2D), stops the fuel supply to the specific cylinder 2 (2A, 2D), and injects fuel from the injector 12 only into the operating cylinder 2 (2B, 2C). This stops combustion in the specific cylinder 2 (2A, 2D). In addition, the ECU 100 sets the opening / closing mode of the specific intake and exhaust valves 8, 9 to the reduced cylinder mode. That is, the ECU 100 (basic control unit 102) turns on each OCV 62 to prohibit the opening and closing of the specific intake and exhaust valves 8, 9 by the valve stop mechanism 61, and allows only the intake and exhaust valves 8, 9 of the operating cylinders 2 (2B, 2C) to be opened and closed.

[0038] In this embodiment, all of the spark plugs 13 are driven in both all-cylinder operation and reduced-cylinder operation. However, in reduced-cylinder operation, fuel supply to the specific cylinder 2 (2A, 2D) is stopped as described above, so that combustion in the specific cylinder 2 (2A, 2D) is stopped even if ignition is performed by the spark plug 13.

[0039] (Control when switching from full cylinder operation to reduced cylinder operation) In the reduced cylinder operation, the number of cylinders 2 in which combustion is performed is smaller than that in the full cylinder operation. Therefore, it is necessary to increase the output per cylinder of the operating cylinders 2 (2B, 2C) and the amount of air (intake amount) introduced per cylinder of the operating cylinders 2 (2B, 2C) compared to that in the full cylinder operation. For this reason, the ECU 100 (basic control unit 102) increases the opening of the throttle valve 34 when switching from the full cylinder operation to the reduced cylinder operation. However, since there is a drive delay of the throttle valve 34 and a delay in the intake from the throttle valve 34 to the cylinder 2, the intake amount of the cylinder 2 does not increase immediately even if the opening of the throttle valve 34 is increased. Therefore, if the reduced cylinder operation is started at the same time as the increase in the opening of the throttle valve 34 is started (if the combustion in the specific cylinder 2 (2A, 2D) is stopped), the intake amount of the operating cylinders 2 (2B, 2C) becomes insufficient, and the engine torque decreases, which may cause a torque shock. Therefore, when the reduced cylinder switching condition for switching the engine operation from all cylinder operation to reduced cylinder operation is satisfied, the ECU 100 (basic control unit 102) first performs the reduced cylinder switching control described below while continuing the all cylinder operation, and then starts the reduced cylinder operation. Note that the ECU 100 (determination unit 101) determines that the reduced cylinder switching condition is satisfied when the engine operation point during all cylinder operation becomes a point within the reduced cylinder area A2.

[0040] In the cylinder reduction switching control, the ECU 100 (basic control unit 102) increases the opening of the throttle valve 34 (changes the opening to the open side) to increase the amount of intake air introduced into each cylinder 2. Here, if the amount of intake air into the cylinder 2 is simply increased while continuing all-cylinder operation, the engine torque will become higher than the torque during normal all-cylinder operation, which is the torque requested by the driver, etc. Therefore, in the cylinder reduction switching control, the ECU 100 retards the ignition timing, which is the timing at which the ignition plug 13 ignites, so as to counteract the increase in engine torque.

[0041] In this way, in the reduced cylinder switching control, the opening of the throttle valve 34 is increased and the ignition timing is retarded. The reduced cylinder switching control is terminated when the intake air amount of each cylinder 2 reaches the target intake air amount for reduced cylinder operation (the target value of the intake air amount of the operating cylinders 2 (2B, 2C) set for reduced cylinder operation). The target intake air amount for reduced cylinder operation is set in advance and stored in the ECU 100. For example, it is stored in a map corresponding to the engine speed and the engine load.

[0042] FIG. 5 is a flow chart showing the procedure of control performed by the ECU 100 (the determination unit 101, the basic control unit 102) when switching from all cylinder operation to reduced cylinder operation. FIG. 6 is a time chart showing the time change of each parameter before and after the switching. In FIG. 6, from the top, charts of the reduced cylinder flag, the oil pressure of the valve stop mechanism oil passage 66, the energization state of the OCV 62, the drive state of the injector 12 of the operating cylinder 2 (2B, 2C), the drive state of the injector 12 of the specific cylinder 2 (2A, 2D), the throttle opening (the opening of the throttle valve 34), the intake amount of the operating cylinder 2 (2B, 2C), the intake amount of the specific cylinder 2 (2A, 2D), and the ignition timing are shown. The reduced cylinder flag is a flag that is set to 1 when the engine is operating in the reduced cylinder region A2 and is set to 0 when the engine is operating in the all cylinder region A1. The energization states of the two OCVs 62 are changed almost simultaneously, and Fig. 6 shows the energization states of the two OCVs 62 together. In the following explanation of Fig. 5, the determination unit 101 and the basic control unit 102 will be collectively referred to simply as ECU 100.

[0043] First, in step S1, the ECU 100 determines whether or not the cylinder cut-off switching condition is satisfied. If the determination in step S1 is NO and the cylinder cut-off switching condition is not satisfied, the ECU 100 repeats step S1. On the other hand, if the determination in step S1 is YES and the cylinder cut-off switching condition is satisfied, the ECU 100 increases the oil pressure in the valve stop mechanism oil passage 66 to a predetermined pressure equal to or higher than the reference oil pressure by the oil pump 65. When the oil pressure in the valve stop mechanism oil passage 66 reaches the predetermined pressure, the ECU 100 increases the opening of the throttle valve 34 in step S3 and retards the ignition timing in step S4.

[0044] In the example of Figure 6, at time t1, the cylinder cut-off switching condition is met (the cylinder cut-off flag changes from 0 to 1), and immediately thereafter, the oil pressure in the valve stop mechanism oil passage 66 is increased. Then, at time t2, as the oil pressure reaches a predetermined pressure, the throttle opening is increased and the ignition timing is retarded. As the throttle opening increases, the intake amount of each cylinder 2 increases. In this embodiment, the ignition timing is gradually retarded in accordance with the increase in the intake amount of the cylinder 2.

[0045] Returning to FIG. 5, in step S5 following step S4, the ECU 100 judges whether the intake amount of the operating cylinder 2 (2B, 2C) has increased to or above the target intake amount for reduced cylinder operation. If the judgment in step S5 is NO and the intake amount of the operating cylinder 2 (2B, 2C) has not reached the target intake amount for reduced cylinder operation, the ECU 100 repeats step S4 to continue retarding the ignition timing in accordance with the increase in the intake amount. On the other hand, when the intake amount of the operating cylinder 2 (2B, 2C) reaches the target intake amount for reduced cylinder operation (the judgment in step S5 is YES), the ECU 100 turns on the OCV 62 in step S6 to change the opening / closing mode of the specific intake and exhaust valves 8, 9 from the full-cylinder mode to the reduced-cylinder mode, that is, to disable these valves from opening and closing, and in step S7, stops driving the injector 12 of the specific cylinder 2 (2A, 2D) to start reduced-cylinder operation. In the example of Figure 6, when the intake amount of the operating cylinder 2 (2B, 2C) reaches the target intake amount for reduced-cylinder operation at time t3, immediately thereafter, the OCV 62 is turned on and the drive of the injector 12 of the specific cylinder 2 (2A, 2D) is stopped.

[0046] (Control when switching from reduced cylinder operation to full cylinder operation) The ECU 100 (determination unit 101) determines that the all-cylinder switching condition is satisfied when the engine operating point reaches a point within the all-cylinder region A1 during reduced cylinder operation. Then, the ECU 100 (basic control unit 102) switches from reduced cylinder operation to all-cylinder operation when the all-cylinder switching condition is satisfied. In this switching, unlike the above-mentioned switching from all-cylinder operation to reduced cylinder operation, the ECU 100 (basic control unit 102) starts all-cylinder operation as soon as the all-cylinder switching condition is satisfied. However, when switching from reduced cylinder operation to all-cylinder operation, it is necessary to reduce the intake amount per cylinder, which is the opposite of the switching from all-cylinder operation to reduced cylinder operation. And even if the opening of the throttle valve 34 is reduced to deal with this, the intake amount does not decrease immediately. Therefore, if all-cylinder operation is simply started to start combustion in all cylinders 2 while simultaneously reducing the opening of the throttle valve 34, the amount of intake air in each cylinder 2 will be greater than that during normal all-cylinder operation, causing excessive engine torque and possibly resulting in a torque shock. Therefore, when the all-cylinder switching condition is met, the ECU 100 (basic control unit 102) starts all-cylinder operation and performs all-cylinder switching control to avoid the torque shock.

[0047] In all-cylinder switching control, the ECU 100 (basic control unit 102) reduces the opening of the throttle valve 34 (changes the opening to the closing side) to reduce the amount of intake air introduced into each cylinder 2, and retards the ignition timing to counteract the increase in engine torque that occurs due to the delay in the intake amount.

[0048] Fig. 7 is a flowchart showing the procedure of control performed by the ECU 100 (determination unit 101, basic control unit 102) when switching from reduced cylinder operation to full cylinder operation. Fig. 8 is a time chart showing the time changes of each parameter before and after this switching, and is a chart corresponding to Fig. 6. In the following explanation of Fig. 7, the determination unit 101 and the basic control unit 102 are collectively simply referred to as ECU 100.

[0049] First, in step S11, the ECU 100 judges whether or not the all-cylinder switching condition is satisfied. If the judgment in step S11 is NO and the all-cylinder switching condition is not satisfied, the ECU 100 repeats step S11. On the other hand, if the judgment in step S11 is YES and the all-cylinder switching condition is satisfied, the ECU 100 turns off the OCV 62 in step S12 to set the opening / closing mode of the specific intake and exhaust valves 8, 9 to the all-cylinder mode, that is, makes the specific intake and exhaust valves 8, 9 openable and closable. In addition, in step S13, the ECU 100 drives all the injectors 12 to supply fuel to all the cylinders 2, thereby starting all-cylinder operation. In addition, in step S14, the ECU 100 reduces the opening of the throttle valve 34, and in step S15, retards the ignition timing.

[0050] In the example of FIG. 8, at time t11, the all-cylinder switching condition is satisfied (the cylinder cutoff flag changes from 1 to 0), and accordingly, the OCV 62 is turned off and the injector 12 of the specific cylinder 2 (2A, 2D) is driven (enabled to be driven). Then, at time t12, which is slightly after time t11, the throttle opening is reduced. As the throttle opening is reduced, the intake amount of each cylinder 2 (operated cylinder 2 (2B, 2C) and specific cylinder 2 (2A, 2D)) decreases. Note that the intake amount of the specific cylinder 2 (2A, 2D) increases from 0 to approximately the same as the intake amount of the operating cylinder 2 (2B, 2C) at time t11, as the intake and exhaust valves 8 and 9 (specific intake and exhaust valves 8 and 9) are enabled to open and close at time t11, and then decreases. Also, the ignition timing is retarded at time t11. In this embodiment, the ignition timing is retarded by a relatively large amount at time t11 with respect to the ignition timing during normal all-cylinder operation (all-cylinder operation not switched from reduced-cylinder operation). After time t12, the retard amount of the ignition timing is gradually decreased in accordance with the decrease in the intake amount.

[0051] Returning to FIG. 7, in step S16 following step S15, the ECU 100 judges whether the intake air amount of each cylinder 2 has decreased to or below the target intake air amount for all-cylinder operation (the target value of the intake air amount for the operating cylinders 2 (2B, 2C) set for all-cylinder operation). If the judgment in step S16 is NO and the intake air amount of each cylinder 2 has not reached the target intake air amount for all-cylinder operation, the ECU 100 repeats step S15 and continues retarding the ignition timing with respect to the ignition timing during normal all-cylinder operation (controlling the above-mentioned retard amount to decrease in accordance with the decrease in the intake air amount). On the other hand, if the judgment in step S16 is YES and the intake air amount of each cylinder 2 has become equal to or below the target intake air amount for all-cylinder operation, the ECU 100 stops retarding the ignition timing and starts normal all-cylinder operation. The opening of the throttle valve 34 is reduced so that the intake air amount of each cylinder 2 becomes the target intake air amount for all-cylinder operation, and the reduction of the intake air amount stops when the intake air amount reaches the target intake air amount for all-cylinder operation. In the example of FIG. 8, the intake air amount of each cylinder 2 reaches the target intake air amount for all-cylinder operation at time t13, and the retardation of the ignition timing is stopped at time t13. The target intake air amount for all-cylinder operation is preset and stored in the ECU 100. For example, it is stored as a map corresponding to the engine speed and the engine load.

[0052] (Control when fuel cut conditions are met) Next, the control performed when the fuel cut condition is met will be described with reference to the flowchart of FIG.

[0053] The ECU 100 determines whether or not the fuel cut condition is satisfied in step S21. Whether or not the fuel cut condition is satisfied is determined by the determination unit 101. Specifically, the determination unit 101 determines that the fuel cut condition is satisfied when the engine operation point shifts from the reduced cylinder region A2 or the full cylinder region A1 to the fuel cut region A3.

[0054] When the determination in step S21 is NO and the fuel cut condition is not satisfied, the ECU 100 repeats step S21. On the other hand, when the determination in step S21 is YES and the fuel cut condition is satisfied, the ECU 100 performs a fuel cut in step S22. That is, the ECU 100 stops driving all the injectors 12 to stop the fuel supply to all the cylinders 2. As described above, this step S22 is performed by the fuel cut control unit 103.

[0055] Furthermore, when the fuel cut condition is satisfied, the ECU 100 determines whether or not the engine is in reduced cylinder operation in step S23. In this embodiment, the ECU 100 sets a flag that is set to 1 when reduced cylinder operation is performed (when the injectors 12 of specific cylinders 2 (2A, 2D) are stopped and the injectors 12 of operating cylinders 2 (2B, 2C) are driven) and is set to 0 when all cylinder operation is performed (when the injectors 12 of all cylinders 2 are driven), and performs the determination in step S23 based on the value of this flag.

[0056] If the determination in step S23 is YES and reduced-cylinder operation is in progress, the ECU 100 further determines in step S24 whether the gear stage of the transmission 70 is in a high gear stage. Specifically, the ECU 100 determines that the gear stage is a high gear stage when the current gear stage detected by the gear stage sensor SN4 is equal to or greater than a preset reference gear stage. In this embodiment, the transmission 70 has six gear stages, and the reference gear stage is set to the fifth stage. Thus, if the current gear stage is the fifth or sixth stage, it is determined that the gear stage is a high gear stage.

[0057] If the determination in step S24 is NO and the gear stage is determined to be a low speed stage lower than the reference gear stage, the ECU 100 changes the opening / closing mode of the specific intake and exhaust valves 8, 9 to the all-cylinder mode in step S25 to enable them to be opened and closed. Step S25 is a step that is performed when a fuel cut condition is established during reduced-cylinder operation, and the opening / closing mode of the specific intake and exhaust valves 8, 9 before the execution of step S25 is the reduced-cylinder mode. Thus, in step S25, the opening / closing mode of the specific intake and exhaust valves 8, 9 is switched from the reduced-cylinder mode to the all-cylinder mode, and the specific intake and exhaust valves 8, 9 are changed from an unopenable state to an openable state. In addition, the ECU 100 performs the all-cylinder switching control in step S26. That is, the ECU 100 reduces the opening of the throttle valve 34 and retards the ignition timing.

[0058] By carrying out steps S25 and S26, the opening degree of the throttle valve 34, the ignition timing, and the opening / closing mode of the specific intake and exhaust valves 8 and 9 become the same as those during all-cylinder operation. In other words, when it is determined that the determination in step S24 is NO, the ECU 100 performs the same control as when switching from reduced-cylinder operation to all-cylinder operation, except for the driving state of the injector 12, and makes the opening degree of the throttle valve 34, the ignition timing, and the opening / closing mode of the specific intake and exhaust valves 8 and 9 the same as those during all-cylinder operation. Note that while the fuel cut condition is satisfied, the driving of the spark plug 13 may be stopped, but in this embodiment, the driving of the spark plug 13 continues even while the fuel cut condition is satisfied. However, since the fuel supply to each cylinder 2 is stopped, no combustion occurs in each cylinder 2.

[0059] After step S26, the ECU 100 determines in step S27 whether the fuel cut condition is no longer satisfied, and waits until the determination becomes YES before executing step S28. In step S28, the ECU 100 resumes fuel injection from the injector 12.

[0060] Here, when proceeding to step S28, the opening degree of the throttle valve 34, the ignition timing, and the opening / closing mode of the specific intake and exhaust valves 8 and 9 are set to the same state as in the all-cylinder operation by performing steps S25 and S26. Therefore, it is not possible to start the reduced-cylinder operation immediately after the fuel cut condition is not satisfied. Specifically, since the throttle valve 34 has a response delay, it is not possible to immediately increase the opening degree to a relatively large opening degree for the reduced-cylinder operation. Also, in order to change the opening / closing mode of the specific intake and exhaust valves 8 and 9 from the all-cylinder mode to the reduced-cylinder mode so that they can be opened and closed, it is necessary to open each OCV 62 and increase the hydraulic pressure in the valve stop mechanism oil passage 66 to a reference hydraulic pressure or higher by the oil pump 65. Therefore, it is not possible to immediately switch the opening / closing mode of the specific intake and exhaust valves 8 and 9 from the all-cylinder mode to the reduced-cylinder mode. And, in a state in which the specific intake and exhaust valves 8 and 9 cannot be opened and closed, it is difficult to realize appropriate combustion in the specific cylinder 2. Therefore, in step S28, the ECU 100 performs the all-cylinder operation. That is, in step S28, the driving of all the injectors 12 is resumed with the opening / closing mode of the specific intake and exhaust valves 8, 9 being maintained in the all-cylinder mode, and fuel injection to all the cylinders 2 is resumed.

[0061] On the other hand, when the determination in step S24 is YES and the gear stage of the transmission 70 is a high gear, unlike when the determination in step S24 is NO, i.e., when the gear stage of the transmission 70 is a low gear, the ECU 100 proceeds to step S29 to determine whether or not the fuel cut condition has been satisfied without performing all-cylinder switching control and switching the opening / closing mode of the specific intake and exhaust valves 8, 9 to the all-cylinder mode. In other words, when the gear stage of the transmission 70 is a high gear, the opening degree of the throttle valve 34, the ignition timing, and the opening / closing mode of the specific intake and exhaust valves 8, 9 are maintained in the same state as during reduced-cylinder operation during fuel cut.

[0062] Then, when the determination in step S29 becomes YES and the fuel cut condition is not satisfied, the ECU 100 restores the fuel injection from the injector 12 in step S30. Here, when proceeding to step S30, as described above, the opening degree of the throttle valve 34, the ignition timing, and the opening / closing mode of the specific intake / exhaust valves 8 and 9 are maintained in the same state as during the reduced-cylinder operation. Thus, in step S30, the ECU 100 performs the reduced-cylinder operation. That is, in step S30, while the drive stop of the injector 12 of the specific cylinder 2 (2A, 2D) is maintained, only the drive of the injector 12 of the operating cylinder 2 (2B, 2C) is resumed, and only the fuel supply to the operating cylinder 2 (2B, 2C) is resumed. In addition, the opening / closing mode of the specific intake / exhaust valves 8 and 9 is maintained in the reduced-cylinder mode.

[0063] As described above, in this embodiment, when the fuel cut condition is satisfied during reduced cylinder operation and fuel cut is performed, if the gear stage of the transmission 70 is a low gear stage, control similar to that when switching from reduced cylinder operation to all cylinder operation is performed, except for the control of the injector 12, and all cylinder operation is started when the fuel cut condition is no longer satisfied. On the other hand, when the fuel cut condition is satisfied during reduced cylinder operation and fuel cut is performed, if the gear stage of the transmission 70 is a high gear stage, control similar to that of reduced cylinder operation is continued, except for the control of the injector 12, and reduced cylinder operation is started when the fuel cut condition is no longer satisfied.

[0064] If the determination in step S23 is NO and all-cylinder operation is in progress, the ECU 100 does not perform either all-cylinder switching control or reduced-cylinder switching control, and while maintaining the opening / closing mode of the specific intake and exhaust valves 8, 9 in the all-cylinder mode, when the fuel cut condition is no longer satisfied (when the determination in step S31 becomes YES), the ECU 100 restores fuel injection from all injectors 12 and performs all-cylinder operation (step S32).

[0065] Fig. 10 is a time chart showing an example of the change over time of each parameter before and after the fuel cut condition is satisfied when the engine is in reduced cylinder operation and the transmission gear is in a low gear. From the top, Fig. 10 shows charts of the fuel cut flag, the oil pressure of the valve stop mechanism oil passage 66, the power supply state of the OCV 62, the drive state of the injector 12 of the operating cylinder 2 (2B, 2C), the drive state of the injector 12 of the specific cylinder 2 (2A, 2D), the throttle opening, the intake amount of the operating cylinder 2 (2B, 2C), the intake amount of the specific cylinder 2 (2A, 2D), and the ignition timing. The fuel cut flag is a flag that is set to 1 when the fuel cut condition is satisfied and is set to 0 otherwise.

[0066] In the example of FIG. 10, the fuel cut condition is satisfied at time t21. As a result, fuel cut is executed at time t21 and the drive of all the injectors 12 is stopped. In the example of FIG. 10, since the reduced cylinder operation is performed, the drive of the injectors 12 of the specific cylinders 2 (2A, 2D) has already been stopped, and the drive of the injectors 12 of the operating cylinders 2 (2B, 2C) is stopped at time t12. In addition, since the fuel cut condition is satisfied during deceleration operation and the transmission gear is in a low gear position, the all-cylinder switching control is executed, and the opening / closing mode of the specific intake and exhaust valves 8, 9 is switched from the reduced cylinder mode to the all-cylinder mode at time t21. Specifically, the OCV 62 is turned off at time t21 and the specific intake and exhaust valves 8, 9 are allowed to open and close. In addition, the opening of the throttle valve 34 is reduced and the ignition timing is retarded. As described above, in the all-cylinder switching control, the retard amount of the ignition timing is reduced in accordance with the reduction in the intake amount. In addition, in the all-cylinder switching control performed during fuel cut, when the intake amount of each cylinder 2 reaches a predetermined judgment amount, the retardation of the ignition timing is stopped, and this judgment amount is preset to an amount smaller than the intake amount per cylinder (operating cylinder 2) during reduced cylinder operation and stored in the ECU 100. In the example of Fig. 10, the all-cylinder switching control (retardation of the ignition timing) is stopped at time t22. Then, when the fuel cut condition is not satisfied at the subsequent time t23 (the fuel cut flag becomes 0 from 1), all-cylinder operation is started, and the injectors 12 of all cylinders 2 are started to be driven in a state in which the specific intake and exhaust valves 8, 9 can be opened and closed.

[0067] FIG. 11 is a time chart showing an example of the time change of each parameter before and after the fuel cut condition is satisfied when the reduced cylinder operation is performed and the transmission gear is in a high gear, and corresponds to FIG. 10. In the example of FIG. 11, the fuel cut condition is satisfied at time t31, and the drive of all the injectors 12 is stopped. Here, in the example of FIG. 11, the fuel cut condition is satisfied during deceleration operation and when the transmission gear is in a high gear. Therefore, the switching of the opening / closing mode of the specific intake / exhaust valves 8, 9 and the all-cylinder switching control are not performed. As a result, even during fuel cut, the opening / closing mode of the specific intake / exhaust valves 8, 9 is maintained in the reduced cylinder mode, and the ignition timing is also maintained at the time before time t31. Then, when the fuel cut condition is not satisfied at time 32 (the fuel cut flag is changed from 1 to 0), the reduced cylinder operation is started again, and only the drive of the injector 12 of the specific cylinder 2 is resumed.

[0068] (effect, etc.) As described above, in the above embodiment, when switching from all cylinder operation to reduced cylinder operation, all cylinder switching control is implemented to increase the opening of the throttle valve 34 and retard the ignition timing, and then reduced cylinder operation is started. Also, when switching from reduced cylinder operation to all cylinder operation, reduced cylinder switching control is implemented to decrease the opening of the throttle valve 34 and retard the ignition timing, and all cylinder operation is started. This makes it possible to suppress the occurrence of torque shock when switching between all cylinder operation and reduced cylinder operation, as described above.

[0069] Furthermore, when the fuel cut condition is satisfied during reduced cylinder operation with the vehicle being driven at a low speed (the gear stage of the transmission 70 is lower than the reference gear stage), the opening / closing mode of the specific intake and exhaust valves 8, 9 is switched to the all-cylinder mode, and the intake and exhaust valves 8, 9 of all cylinders 2 are made openable and closable. Furthermore, all-cylinder switching control is implemented to reduce the opening of the throttle valve 34. This allows a relatively large pumping loss to occur in all cylinders 2, thereby increasing the deceleration of the vehicle.

[0070] However, when the fuel cut condition is met during reduced cylinder operation, if the opening / closing mode of the specific intake and exhaust valves 8, 9 is set to the all-cylinder mode and all-cylinder switching control is implemented as described above, there is a risk of fuel efficiency deteriorating.

[0071] Specifically, if the fuel cut condition is satisfied during reduced cylinder operation, that is, when the engine is operating in the reduced cylinder region A2, the operating point when the fuel cut condition is not satisfied is also likely to be within the reduced cylinder region A2. On the other hand, as described above, if the opening / closing mode of the specific intake and exhaust valves 8, 9 is set to the all-cylinder mode and the all-cylinder switching control is performed, reduced cylinder operation cannot be started immediately when the fuel cut condition is not satisfied, and combustion must be resumed with all-cylinder operation. Therefore, if the opening / closing mode of the specific intake and exhaust valves 8, 9 is set to the all-cylinder mode and the all-cylinder switching control is performed in response to the satisfaction of the fuel cut condition during reduced cylinder operation, it is highly likely that the all-cylinder operation must be performed first when the fuel cut condition is not satisfied, and then the all-cylinder operation must be immediately switched to reduced cylinder operation. Then, when switching from the all-cylinder operation to the reduced cylinder operation, the reduced cylinder switching control is performed to suppress the torque shock, and the ignition timing is retarded, which deteriorates the fuel efficiency.

[0072] In contrast, in the above embodiment, when the fuel cut condition is satisfied during reduced cylinder operation while the vehicle is being driven at a high speed (the gear stage of the transmission 70 is equal to or higher than the reference gear stage), the opening / closing mode of the specific intake and exhaust valves 8, 9 is maintained in the reduced cylinder mode and the all-cylinder switching control is not performed. Therefore, in this case, the deceleration of the vehicle is kept low, but deterioration of fuel economy can be avoided.

[0073] Here, it is known that when the driver is driving at a low gear and fuel is cut off, that is, when the accelerator pedal 80 is released, the driver desires a sense of greater deceleration, whereas when the driver is driving at a high gear and the deceleration of the vehicle at fuel cut is small, the driver is less likely to feel uncomfortable.

[0074] Therefore, according to the above embodiment, the vehicle deceleration is increased when driving at low gears, and deterioration of fuel economy is avoided when driving at high gears, thereby suppressing deterioration of fuel economy while providing an appropriate deceleration feeling that meets the driver's needs.

[0075] In particular, in the above embodiment, the fuel cut region A3 where the fuel cut condition is satisfied is set adjacent to the cylinder cut region A2, so that the driving point when the fuel cut condition is no longer satisfied is likely to be a point within the cylinder cut region A2. Therefore, the chance of the fuel economy performance being degraded can be reliably reduced, and the deterioration of the fuel economy performance can be effectively suppressed.

[0076] (Modification) The cylinder reduction region A2 and the fuel cut region A3 are not limited to those described above. In the above embodiment, the fuel cut condition is determined to be satisfied when the engine is operating within the preset fuel cut region A3, but the criteria for determining whether the fuel cut condition is satisfied are not limited to those.

[0077] In addition, the specific configurations of the number of cylinders of the engine, the type of fuel supplied, etc. are not limited to those described above. In addition, the specific configuration for switching the opening / closing modes of the specific intake and exhaust valves 8, 9 is not limited to those described above. [Explanation of symbols]

[0078] 1 Engine body 2-cylinder 8. Intake valve 9 Exhaust valve 12 Injector (fuel supply device) 13 Spark plug (ignition means) 30 Intake passage 34 Throttle valve 61 Valve stop mechanism (switching mechanism) 62 OCV (switching mechanism) 100 ECU (control means) 102b Second switching control unit (switching control unit) 103 Fuel cut control unit A2 Reduced cylinder area (1st operation area) A3 Fuel cut region (second operating region) SN4 Gear step sensor (gear step detection means)

Claims

1. A device for controlling an engine that is mounted on a vehicle equipped with a transmission and has an engine body formed with a plurality of cylinders, an intake passage, a throttle valve that opens and closes the intake passage, a fuel supply means that supplies fuel to each cylinder, and an ignition means that ignites the mixture in each cylinder, and that can be switched between an all-cylinder operation in which combustion is performed in all cylinders and a reduced-cylinder operation in which combustion is stopped in a specific cylinder among the plurality of cylinders, A gear detection means for detecting a gear position of the transmission; A switching mechanism that switches an opening / closing mode of a specific intake / exhaust valve, which is an intake valve and an exhaust valve of the specific cylinder, between an all-cylinder mode in which opening / closing is permitted and a reduced-cylinder mode in which opening / closing is prohibited; a control means for controlling the throttle valve, the fuel supply means, the ignition means and the switching mechanism, and for changing the opening / closing mode of the specific intake / exhaust valve to the all-cylinder mode during all-cylinder operation and to the reduced-cylinder mode during reduced-cylinder operation; The control means a switching control unit that, when switching an opening / closing mode of the specific intake / exhaust valve from the all-cylinder mode to the reduced-cylinder mode, performs reduced-cylinder switching control to increase an opening degree of the throttle valve and retard an ignition timing of the ignition means, and switches the opening / closing mode after the reduced-cylinder switching control is performed; a fuel cut control unit that cuts off the fuel supply from the fuel supply means to all of the cylinders when a fuel cut condition for cutting off the fuel supply to all of the cylinders is satisfied, During reduced cylinder operation, when the fuel cut condition is satisfied in a state in which the gear stage detected by the gear stage detection means is less than a predetermined reference gear stage, the fuel cut control unit switches an opening / closing mode of a specific intake / exhaust valve from the reduced cylinder mode to the all-cylinder mode, and reduces an opening degree of the throttle valve, During reduced cylinder operation, when the fuel cut condition is satisfied with the gear position being equal to or higher than the reference gear position, the fuel cut control unit maintains the opening / closing mode of the specific intake / exhaust valve in the reduced cylinder mode, The control means starts all-cylinder operation when the fuel cut condition is no longer satisfied, when the opening / closing mode is switched from the reduced-cylinder mode to the all-cylinder mode in response to the satisfaction of the fuel cut condition.

2. 2. The engine control device according to claim 1, the control means performs a reduced cylinder operation when the engine is operating in a predetermined first operating range, and determines that the fuel cut condition is satisfied when the engine is operating in a predetermined second operating range, An engine control device, characterized in that the second operating range is set to a range in which an engine load is smaller than that of the first operating range and is adjacent to the first operating range in terms of engine load.

Images