Engine control device

Abstract

To secure ignitability in restart of an engine while suppressing vibration during automatic stop of the engine.SOLUTION: A control device of an engine includes a phase variable device which can vary a phase of an intake valve, an automatic stop control unit for automatically stopping the engine by performing fuel cut when a prescribed automatic stop condition is established, and a restart control unit for injecting first fuel to a stop-time expansion stroke cylinder which is stopped at an expansion stroke so as to perform combustion when a prescribed restart condition is established. The automatic stop control unit controls the phase variable device so that intake valve closing timing becomes first timing IV1 on an advance side when engine speed after fuel cut is in a prescribed first engine speed region I, and the intake valve closing timing becomes second timing IV2 on a retard side when the engine speed after the fuel cut is in a second engine speed region II lower than the first engine speed region I.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a control device capable of automatically stopping and restarting an engine. Background Art

[0002] As a technology related to automatic stop and restart of an engine, the following Patent Document 1 is known. Specifically, the engine stop control device disclosed in Patent Document 1 includes: a valve timing changing means capable of changing the opening and closing timing of an intake valve; and a valve timing control means for controlling the valve timing changing means such that the opening and closing timing of the intake valve is corrected to the most advanced angle timing when an automatic engine stop condition is satisfied. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2008-95519 Summary of the Invention Problems to be Solved by the Invention

[0004] In the above-mentioned Patent Document 1, when the automatic stop condition is satisfied, the closing timing of the intake valve is corrected to the most advanced angle timing. As a result, the period during which the intake valve opens during the compression stroke is shortened, which reduces the amount of intake air blown back from the combustion chamber to the intake port. This has the effect of increasing the amount of intake air actually compressed in the cylinder, that is, the intake charge amount, compared to the case where the above-mentioned advance angle correction is not performed. When the intake charge amount increases, the compression reaction force acting on the piston increases, which may increase engine vibration during the stop operation.

[0005] Furthermore, ensuring the ignition of the fuel-air mixture is necessary to properly restart an engine that has automatically stopped. For example, in order to reduce the torque required for the motor that cranks the engine, the initial combustion may occur in the cylinder that has stopped during the expansion stroke. In such cases, the ignition of the fuel-air mixture is particularly problematic. That is, since the fuel-air mixture in the cylinder that has stopped during the expansion stroke is at near atmospheric pressure, ignition may not be possible unless sufficient scavenging is performed to reduce the amount of already burned gas in the combustion chamber as much as possible.

[0006] This invention has been made in view of the above circumstances, and aims to provide an engine control device that can suppress vibrations during automatic stopping while ensuring ignition performance during restart. [Means for solving the problem]

[0007] To solve the above problems, the engine control device of the present invention comprises a phase variable device capable of changing the phase of the intake valve, a throttle valve provided in the intake passage so as to be openable and closable, an automatic stop control unit that automatically stops the engine by performing a fuel cut to stop the fuel supply to the engine when predetermined automatic stop conditions are met, and controls the phase variable device and the throttle valve based on the engine speed after the fuel cut, and a restart control unit that injects the first fuel into the expansion stroke cylinder that stopped during the expansion stroke and burns it when restart conditions for restarting the automatically stopped engine are met, and the range of engine speed from the engine speed at the time of execution of the fuel cut to a lower first reference engine speed is defined as the first engine speed range, and from the first reference engine speed... Reyo The range up to the second reference rotational speed is the second rotational speed range, and the range from the second reference rotational speed to zero rotational speed is the third rotational speed range. regionIn this case, the automatic stop control unit controls the variable phase device so that when the engine speed after the fuel cut is in the first rotational speed range, the intake valve closes at a first timing that is advanced to the side of the most retarded timing, which is the closing timing of the intake valve when the variable phase device is operated to the most retarded side, and increases the opening degree of the throttle valve compared to before the fuel cut, and controls the variable phase device so that when the engine speed after the fuel cut is in the second rotational speed range, the intake valve closes at a second timing that is retarded to the side of either the first timing or the intake bottom dead center (Claim 1).

[0008] According to the present invention, since the intake valve closing timing in the first rotational speed region is set to a first timing that is advanced more than the timing that is retarded, the period during which the intake valve is open during the compression stroke is shortened, and the amount of burnt gas present in the combustion chamber that is blown back into the intake port is reduced. This has the effect of reducing the amount of burnt gas that is reintroduced into the combustion chamber from the intake port, i.e., the amount of internal EGR, and improves the scavenging performance of the combustion chamber. As a result, the ignition performance of the air-fuel mixture during restart is improved, and the engine can be restarted smoothly.

[0009] In particular, in this invention, the initial combustion occurs in the cylinder during the expansion stroke while the engine is stopped when the engine is restarted, so the ignition quality of the air-fuel mixture tends to be a problem. That is, since the air-fuel mixture in the cylinder during the expansion stroke while the engine is stopped is not substantially compressed, if the amount of internal EGR increases, there is a high possibility that the necessary ignition quality cannot be secured. In contrast, in this invention, the intake valve closing timing is set to be closer to the advanced ignition timing in the first rotational speed range, so an improvement in ignition quality can be expected due to a reduction in the amount of internal EGR, allowing the initial combustion in the cylinder during the expansion stroke while the engine is stopped to occur without problems, and the engine to restart smoothly. Furthermore, since the throttle valve opening (hereinafter also referred to as throttle opening) is increased in the first rotational speed range, the amount of fresh air introduced into the combustion chamber can be increased, further improving scavenging performance. As a result, the initial combustion in the cylinders undergoing the expansion stroke during engine restart can be performed without hindrance, enabling a smooth restart.

[0010] Furthermore, in this invention, the intake valve closing timing in the second rotational speed region, which is lower than the first rotational speed region, is set to a second timing that is retarded more than either the first timing or the intake bottom dead center. As a result, the period during which the intake valve is open during the compression stroke is lengthened, and the amount of backflow from the combustion chamber to the intake port increases. This reduces the compression reaction force acting on the piston of each cylinder, thereby reducing the fluctuation range of the engine's shaft torque and suppressing engine vibration.

[0011] The second period is preferably the same as the period of maximum angle retardation (Claim 2).

[0012] In this embodiment, the intake valve closing timing in the second rotational speed region is set to the retarded timing, which maximizes the aforementioned effect of reducing the compression reaction force of each cylinder and effectively suppresses engine vibration.

[0015] Preferably, the automatic stop control unit reduces the opening degree of the throttle valve in the second rotational speed region compared to the first rotational speed region. Claim 3 ).

[0016] In this embodiment, the intake pressure in the second rotational speed region can be reduced to a desired pressure near that which is advantageous for reducing engine vibration, thereby suppressing engine vibration.

[0017] More specifically, When the range from the first reference rotational speed to the third reference rotational speed, which is intermediate between the first and second reference rotational speeds, is defined as the first half of the second rotational speed range, The automatic stop control unit preferably sets the opening of the throttle valve variably based on the intake pressure in the first half of the second rotational speed range to a range smaller than the opening in the first rotational speed range and larger than fully closed, and in the latter half of the second rotational speed range, it is preferable to fully close the throttle valve. Claim 4 ).

[0018] In this aspect, the throttle opening is adjusted based on intake pressure in the first half of the second rotation speed region, so that the intake pressure can be stabilized when subsequently transitioning to the second half of the second rotation speed region. If the intake pressure is stabilized during this transition, by fully closing the throttle uniformly in the second half of the second rotation speed region, the intake pressure can be reduced in accordance with the target pattern, and engine vibration can be effectively suppressed.

[0019] Preferably, the automatic stop control unit, in the third Record number rotation speed region, increases the opening degree of the throttle valve more than that in the second rotation speed region ( Claim 5 ).

[0020] In this way, when the throttle opening in the third rotation speed region is increased, engine pumping loss can be reduced shortly before the engine comes to a complete stop. This makes it easier for the piston of the cylinder that reaches the last compression top dead center before the complete stop to pass the compression top dead center, and allows the engine crankshaft to advance further in the normal rotation direction. This enables the piston of the expansion stroke cylinder at stop and the piston of the compression stroke cylinder at stop to stop at positions equally spaced from the compression top dead center. As a result, the air amounts of the two cylinders on either side of the compression top dead center are balanced, so the restart performance of the engine can be improved.

[0021] The engine may be connectable to and disconnectable from an electric motor capable of rotationally driving wheels ( Claim 6 ).

[0022] In this aspect, for a hybrid vehicle using both an engine and an electric motor, engine vibration can be suppressed when the engine automatically stops accompanying switching of driving modes, and the ignitability of the air-fuel mixture can be ensured when the engine is subsequently restarted. Effect of the Invention

[0023] As described above, according to the engine control device of the present invention, it is possible to ensure ignitability at the time of restart while suppressing vibration during automatic stop. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0024] [Figure 1] FIG. 1 is a system diagram showing a schematic configuration of an engine to which a control device according to an embodiment of the present invention is applied and a vehicle equipped with the same. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the structure of the engine. [Figure 3] FIG. 3 is a functional block diagram showing a control system of the vehicle. [Figure 4] FIG. 4 is a flowchart showing a first half of automatic stop control of an engine performed when switching from an engine travel mode to a motor travel mode. [Figure 5] FIG. 5 is a flowchart showing a second half of the above automatic stop control. [Figure 6] FIG. 6 is a diagram showing intake valve closing timing set during the above automatic stop control. [Figure 7] FIG. 7 is a flowchart showing the content of engine restart control performed when switching from a motor travel mode to an engine travel mode. [Figure 8] FIG. 8 is a time chart showing an example of time-series changes of various state quantities associated with automatic stop control of an engine. [Figure 9] FIG. 9 is a diagram showing a preferred example of piston positions when the engine is completely stopped. [EMBODIMENTS FOR CARRYING OUT THE INVENTION]

[0025] [Overall Configuration of Vehicle] Figure 1 is a system diagram showing the schematic configuration of an engine 1 to which a control device according to one embodiment of the present invention is applied, and a vehicle V equipped with the same. As shown in this figure, the vehicle V comprises an engine 1, a clutch 30, a motor 31, an inverter 32, a battery 33, a transmission 35, a differential 36, drive wheels 37, and a PCM 50. Both the engine 1 and the motor 31 are capable of driving the drive wheels 37 (wheels) as power sources for driving. In other words, the vehicle V in this embodiment is a hybrid vehicle that uses both the engine 1 and the motor 31 as power sources.

[0026] Engine 1 is an internal combustion engine that generates power through the combustion of fuel. In this embodiment, a four-stroke gasoline engine using gasoline as the main component fuel (gasoline fuel) is used as Engine 1. Details of Engine 1 will be described later.

[0027] Motor 31 is a motor generator that combines the functions of both a motor and a generator. For example, motor 31 consists of a three-phase AC synchronous electric motor. Motor 31 operates as a motor when the vehicle V is accelerating, generating driving force to rotate the drive wheels 37. Motor 31 also operates as a generator when the vehicle V is decelerating, generating electricity by receiving rotational force transmitted from the drive wheels 37.

[0028] The inverter 32 is a converter that converts AC power to DC power and vice versa. When the motor 31 operates as a generator, the inverter 32 converts the AC power generated by the motor 31 into DC power and supplies it to the battery 33. On the other hand, when the motor 31 operates as a motor, the inverter 32 converts the DC power stored in the battery 33 into AC power and supplies it to the motor 31. The inverter 32 also has a function to adjust the output or power generation amount of the motor 31 through power transfer control between the motor 31 and the battery 33.

[0029] The battery 33 is a rechargeable secondary battery. For example, the battery 33 is a lithium-ion battery or a nickel-metal hydride battery. The battery 33 supplies driving power to the motor 31 via the inverter 32, and also receives and stores the power generated by the motor 31 via the inverter 32.

[0030] Battery 33 is equipped with a battery sensor SN3 that detects the input and output current to and from the battery 33. The current value detected by the battery sensor SN3 is used to determine the battery state of charge (SOC), that is, the ratio of the current charge to the charge level when the battery 33 is fully charged. In other words, the battery sensor SN3 is a sensor for detecting the battery SOC. Specifically, the PCM 50 calculates the charge and discharge rates of the battery 33 per unit time based on the values ​​detected by the battery sensor SN3, and calculates the battery SOC by integrating these values.

[0031] The clutch 30 is a clutch that connects the engine 1 and the motor 31 in a way that allows them to be disconnected and reconnected. That is, the clutch 30 connects the output shaft of the engine 1 (crankshaft 7, described later) and the rotating shaft (rotor shaft) of the motor 31 in series, or disconnects them. When the clutch 30 is engaged and the engine 1 and motor 31 are connected, the torque of both the engine 1 and the motor 31 is transmitted to the drive wheels 37 via the transmission 35 and the differential 36. On the other hand, when the clutch 30 is disengaged, the motor 31 and the engine 1 are disconnected, and only the torque of the motor 31 is transmitted to the drive wheels 37.

[0032] The transmission 35 changes the rotation input from the engine 1 and motor 31 and outputs it to the differential 36. In this embodiment, the transmission 35 is an automatic transmission, and the gear ratio is automatically changed according to the vehicle speed and engine speed. The differential 36 distributes the rotation input from the transmission 35 to the left and right drive wheels 37.

[0033] The transmission 35 is equipped with a vehicle speed sensor SN1 for determining the vehicle speed of the vehicle V. Specifically, the vehicle speed sensor SN1 detects the rotational speed of the output shaft 43 of the transmission 35, and the vehicle speed is determined based on this detected value.

[0034] Vehicle V is equipped with an accelerator pedal 39 that is operated by the driver. An accelerator sensor SN2 is attached to the accelerator pedal 39 to detect the accelerator opening degree, which represents the degree to which the pedal is pressed.

[0035] The PCM50 is a controller whose main component is a microcomputer, which includes a processor (CPU) for calculations, memory such as ROM and RAM, and various input / output buses. The PCM50 comprehensively controls the engine 1, motor 31, and transmission 35. Specifically, the PCM50 controls the output of the engine 1 so that appropriate driving force is transmitted to the drive wheels 37 according to the driving conditions of the vehicle V, controls the output of the motor 31 through the inverter 32, and further controls the gear shift of the transmission 35.

[0036] [Engine structure] Figure 2 is a schematic cross-sectional view showing the structure of engine 1. Engine 1 comprises an engine body 2, an intake passage 20, and an exhaust passage 27.

[0037] The engine body 2 is a multi-cylinder type having multiple cylinders 2a. In this embodiment, the engine body 2 is an inline 6-cylinder type. That is, the engine body 2 has six cylinders 2a arranged in a direction perpendicular to the plane of the paper in Figure 2. The engine body 2 comprises a cylinder block 3 and a cylinder head 4 that define the six cylinders 2a inside, and six pistons 5 that are reciprocally housed in each cylinder 2a.

[0038] A combustion chamber C is formed above the piston 5 of each cylinder 2a. Each combustion chamber C is a space defined by the lower surface of the cylinder head 4, the side surface of the cylinder 2a (cylinder liner), and the upper surface (crown surface) of the piston 5. Injected fuel from the injector 8, which will be described later, is supplied to the combustion chamber C. The piston 5 reciprocates vertically in response to the expansion energy (combustion energy) from the combustion of the fuel supplied to the combustion chamber C.

[0039] Below the piston 5 is the crankshaft 7. The crankshaft 7 is the output shaft of the engine 1 and is rotatably supported at the bottom of the cylinder block 3. The crankshaft 7 is connected to the piston 5 of each cylinder 2a via a crank mechanism including a connecting rod 6 and rotates around its central axis in accordance with the reciprocating motion (up and down motion) of the piston 5.

[0040] A crank angle sensor SN4 is mounted on the cylinder block 3. The crank angle sensor SN4 is a sensor that detects the crank angle, which is the rotation angle of the crankshaft 7, and the engine speed, which is the rotational speed of the crankshaft 7.

[0041] The cylinder head 4 is fitted with an injector 8 and a spark plug 9. The injector 8 is an injection valve that injects fuel into the combustion chamber C of each cylinder 2a. The spark plug 9 is a plug that ignites the fuel-air mixture injected from the injector 8 into the combustion chamber C. One set of injector 8 and spark plug 9 is provided for each cylinder 2a.

[0042] The cylinder head 4 has intake ports 11 and exhaust ports 12. The intake ports 11 connect the combustion chamber C of each cylinder 2a to the intake passage 20. The exhaust ports 12 connect the combustion chamber C of each cylinder 2a to the exhaust passage 27. Each intake port 11 of each cylinder 2a is provided with an intake valve 13, and each exhaust port 12 of each cylinder 2a is provided with an exhaust valve 14.

[0043] The cylinder head 4 is equipped with an intake valve mechanism 15 and an exhaust valve mechanism 16. The intake valve mechanism 15 includes an intake camshaft 15a located above the intake valve 13, and the exhaust valve mechanism 16 includes an exhaust camshaft 16a located above the exhaust valve 14. The intake camshaft 15a, the exhaust camshaft 16a, and the crankshaft 7 are connected to each other via a power transmission mechanism, for example, a chain. That is, the intake valve mechanism 15 and the exhaust valve mechanism 16 open and close the intake valve 13 and exhaust valve 14 of each cylinder 2a in conjunction with the rotation of the crankshaft 7. The intake valve 13 periodically opens and closes the opening of the intake port 11 on the combustion chamber C side in response to the drive of the intake valve mechanism 15, and the exhaust valve 14 periodically opens and closes the opening of the exhaust port 12 on the combustion chamber C side in response to the drive of the exhaust valve mechanism 16.

[0044] The intake valve mechanism 15 is equipped with an intake SVT 17. The intake SVT 17 is a device that changes the phase (opening / closing timing) of the intake valve 13 by changing the rotational phase of the intake camshaft 15a relative to the rotational phase of the crankshaft 7. The intake SVT 17 corresponds to the "phase variable device" in this invention.

[0045] In this embodiment, the intake SVT 17 is a variable device that changes the phase while maintaining a constant lift amount and opening period of the intake valve 13; in other words, it changes the opening and closing timings of the intake valve 13 by the same amount. The intake camshaft 15a, whose phase is changed by the intake SVT 17, is a camshaft shared by all cylinders 2a. In other words, the intake SVT 17 changes the phase (opening and closing timing) of the intake valve 13 of each cylinder 2a collectively by changing the rotational phase of the intake camshaft 15a.

[0046] The intake passage 20 is a passage for introducing intake air into the combustion chamber C of each cylinder 2a. The intake passage 20 is connected to the engine body 2 so as to communicate with the combustion chamber C of each cylinder 2a via the intake port 11. Specifically, the intake passage 20 has a single-tube common intake pipe 23, a surge tank 22 connected to the downstream end of the common intake pipe 23, and a plurality of (six) independent intake pipes 21 that connect each intake port 11 of the plurality of (six) cylinders 2a to the surge tank 22.

[0047] A throttle valve 24 is provided in the common intake pipe 23 so as to be openable and closable. The throttle valve 24 is driven to open and close in order to adjust the flow rate of intake air circulating through the intake passage 20.

[0048] The surge tank 22 is equipped with an intake pressure sensor SN5. The intake pressure sensor SN5 is a sensor that detects the pressure of the intake air introduced into the engine body 2 (cylinder 2a), i.e., the intake pressure, and detects the internal pressure of the surge tank 22 as the intake pressure.

[0049] The exhaust passage 27 is a passage for discharging exhaust gas discharged from the combustion chamber C of each cylinder 2a to the outside. The exhaust passage 27 is connected to the engine body 2 so as to communicate with the combustion chamber C of each cylinder 2a via the exhaust port 12. The exhaust passage 27 is equipped with a catalytic converter 28 for purifying harmful components in the exhaust gas.

[0050] [Control System] Figure 3 is a functional block diagram showing the control system of vehicle V. As shown in this figure, the PCM50 is electrically connected to the vehicle speed sensor SN1, accelerator sensor SN2, battery sensor SN3, crank angle sensor SN4, and intake pressure sensor SN5 mentioned above. The PCM50 receives sequential input of information detected by each of these sensors, namely vehicle speed, accelerator opening, battery SOC, crank angle, engine speed, and intake pressure.

[0051] The PCM50 controls the movement of the vehicle V based on the input information from each of the sensors SN1 to SN5. Specifically, the PCM50 is electrically connected to the injector 8, spark plug 9, intake SVT 17, and throttle valve 24 of the engine 1, as well as to the clutch 30, motor 31, and inverter 32. The PCM50 outputs control signals to these devices, generated through calculations based on the input information from each of the sensors SN1 to SN5.

[0052] For example, the PCM50 calculates the required torque of the vehicle V, which is the torque to be transmitted to the drive wheels 37, based on the vehicle speed detected by the vehicle speed sensor SN1 and the accelerator opening detected by the accelerator sensor SN2. Based on the calculated required torque and the battery SOC detected by the battery sensor SN3, it determines the driving mode of the vehicle V. Then, according to the determined driving mode, it controls the engine 1, clutch 30, and motor 31 (inverter 32).

[0053] Specifically, when the required torque for vehicle V is relatively small and the battery SOC is relatively high, the motor-driven mode is selected. In this case, the PCM 50 stops engine 1 and releases clutch 30. The PCM 50 also outputs torque from motor 31 equivalent to the required torque for vehicle V, thereby driving vehicle V using only motor 31.

[0054] If the required torque of vehicle V is relatively high or the battery SOC is relatively low, the engine driving mode is selected. In this case, the PCM 50 drives the engine 1 (combustion) and engages the clutch 30. Furthermore, if, for example, the output torque of engine 1 is insufficient for the required torque of vehicle V, the PCM 50 drives the motor 31 and outputs an assist torque from the motor 31 equivalent to the torque deficit. In this case, the PCM 50 controls engine 1 and motor 31 so that the combined torque of engine 1 and motor 31 corresponds to the required torque of vehicle V. On the other hand, if motor 31 is not driven, the engine 1 outputs a torque equivalent to the required torque of vehicle V, thereby driving vehicle V using only engine 1.

[0055] As part of the functional elements for realizing the above-described control, the PCM50 includes an automatic stop control unit 51 and a restart control unit 52. The automatic stop control unit 51 is a module that automatically stops the engine 1 when switching from engine driving mode to motor driving mode. The restart control unit 52 is a module that restarts the stopped engine 1 when switching from motor driving mode to engine driving mode.

[0056] [Automatic stop control] Next, the control during the switch from the engine-driven mode to the motor-driven mode, and in particular the control that automatically stops engine 1 in conjunction with this switch (automatic stop control), will be explained in detail using the flowcharts in Figures 4 and 5. The control shown in these figures is executed while the vehicle is running in engine-driven mode. In other words, the premise for this control to be executed is that the vehicle V is in engine-driven mode.

[0057] When the control shown in Figure 4 starts, the PCM 50 determines whether a request has been made to switch the vehicle V's driving mode from engine driving mode to motor driving mode (step S1). That is, while driving in engine driving mode, the PCM 50 checks the condition parameters that determine the vehicle V's driving mode (e.g., required torque, battery SOC, etc.) based on the detected values ​​of the vehicle speed sensor SN1, accelerator sensor SN2, and battery sensor SN3. Then, when these condition parameters change to conditions that are suitable for motor driving mode, the PCM 50 determines that a request to switch from engine driving mode to motor driving mode has been made. Note that switching from engine driving mode to motor driving mode involves control to automatically stop engine 1 (automatic stop control), so determining whether a switching request has been made here is equivalent to determining whether the automatic stop condition for engine 1 has been met.

[0058] If step S1 is determined to be NO and there is no request to switch to motor driving mode, in other words, if it is confirmed that the automatic stop condition for engine 1 is not met, the PCM 50 maintains the vehicle V's driving mode in engine driving mode (step S17). At this time, the opening degree of the throttle valve 24 and the operating angle of the intake SVT 17 are controlled to appropriate values ​​according to the required torque of the vehicle V.

[0059] On the other hand, if the above step S1 is determined to be YES and the request to switch to motor driving mode is confirmed, that is, if the conditions for automatic stopping of engine 1 are met, the automatic stop control unit 51 of PCM 50 releases the clutch 30 and disconnects engine 1 and motor 31 (step S2).

[0060] Next, the automatic stop control unit 51 performs a fuel cut, which stops the fuel supply (fuel injection) from the injector 8 to the combustion chamber C (step S3). As combustion stops due to this fuel cut, the engine speed begins to decrease.

[0061] Next, the automatic stop control unit 51 controls the intake SVT 17 so that the intake valve closing timing, which is the timing when the intake valve 13 closes, becomes a predetermined first period IV1 (step S4). As shown in Figure 6, the first period IV1 is a timing that is retarded from intake bottom dead center (BDC) and advanced from the second period IV2 (retarded timing) which is set in step S7 later. For example, the first period IV1 can be ABDC70°CA, which is 70° retarded in crank angle from intake bottom dead center. Note that the intake valve closing timing when the automatic stop condition is met is often retarded from the first period IV1, depending on the conditions. In this case, the automatic stop control unit 51 changes the intake valve closing timing to the first period IV1 by advancing the operating angle of the intake SVT 17 from the operating angle immediately before fuel cut.

[0062] In conjunction with step S4 described above, the automatic stop control unit 51 sets the throttle opening, which is the opening degree of the throttle valve 24, to a predetermined first opening degree TV1 (step S5). The first opening degree TV1 can be, for example, about 25%. Note that the switch to motor driving mode occurs when the required torque of the vehicle V is relatively small, so the throttle opening when the automatic stop condition is met is relatively small. For this reason, in step S5, the automatic stop control unit 51 drives the throttle valve 24 to increase its opening degree compared to just before fuel cut, thereby changing the throttle opening degree to the first opening degree TV1.

[0063] Next, the automatic stop control unit 51 determines, based on the value detected by the crank angle sensor SN4, whether the engine speed has decreased to a predetermined first rotational speed NE1 or not (step S6). The first rotational speed NE1 can be, for example, around 780 rpm.

[0064] If step S6 is determined to be NO and it is confirmed that the engine speed is equal to or greater than the first rotational speed NE1, the automatic stop control unit 51 repeats the control in steps S4 and S5.

[0065] On the other hand, if step S6 determines that the result is YES and it is confirmed that the engine speed has decreased to less than the first rotational speed NE1, the automatic stop control unit 51 controls the intake SVT 17 so that the intake valve closing timing becomes a predetermined second period IV2 (step S7). As shown in Figure 6, the second period IV2 is a timing that is retarded compared to both the first period IV1 and the intake bottom dead center (BDC). In other words, in step S7, the automatic stop control unit 51 retards the intake valve closing timing from the first period IV1 to the second period IV2. In this embodiment, the second period IV2 is the same as the retarded timing, which is the intake valve closing timing when the operating angle of the intake SVT 17 is shifted to the retarded side as much as possible. For example, the second period IV2 can be approximately ABDC100°CA, which is 100° retarded in crank angle from the intake bottom dead center.

[0066] In conjunction with step S7 described above, the automatic stop control unit 51 sets the throttle opening to the second opening TV2 (step S8). The second opening TV2 is smaller than the first opening TV1 described above, and larger than fully closed (0%). In other words, in step S8, the automatic stop control unit 51 reduces the throttle opening from the first opening TV1 to the second opening TV2.

[0067] Furthermore, the second opening degree TV2 is variably set based on the intake pressure detected by the intake pressure sensor SN5. In other words, the second opening degree TV2 is the opening degree that fluctuates between the first opening degree TV1 and fully closed (0%) depending on the intake pressure. For example, the second opening degree TV2 can be set to approximately 3% when the intake pressure is at a standard value. In this case, the second opening degree TV2 is set to less than 3% when the intake pressure is higher than the standard value, and the second opening degree TV2 is set to more than 3% when the intake pressure is lower than the standard value.

[0068] Next, the automatic stop control unit 51 determines whether the engine speed has decreased to a predetermined second rotational speed NE2 (step S9). The second rotational speed NE2 can be, for example, around 500 rpm.

[0069] If step S9 determines NO and it is confirmed that the engine speed is 2nd rotational speed NE2 or higher, the automatic stop control unit 51 repeats the control in steps S7 and S8.

[0070] On the other hand, if step S9 determines that the result is YES and it is confirmed that the engine speed has decreased to less than the second rotational speed NE2, the automatic stop control unit 51 reduces the throttle opening to fully closed (0%) (S11). The intake valve closing timing is not changed and is maintained at the second timing IV2 (latest timing) set in step S7.

[0071] Next, the automatic stop control unit 51 determines whether the engine speed has decreased to a predetermined third rotational speed NE3 (step S12). The third rotational speed NE3 can be, for example, around 160 rpm.

[0072] If step S12 determines NO and it is confirmed that the engine speed is 3rd rotational speed NE3 or higher, the automatic stop control unit 51 repeats the control in step S11.

[0073] On the other hand, if step S12 determines that the result is YES and it is confirmed that the engine speed has decreased to less than the third rotational speed NE3, the automatic stop control unit 51 increases the throttle opening to full open (100%) (S13). The intake valve closing timing is not changed and is maintained at the second timing IV2 (latest timing) set in step S7.

[0074] Next, the automatic stop control unit 51 determines whether the engine 1 has come to a complete stop, that is, whether the engine speed has decreased to virtually zero (step S14).

[0075] If step S14 determines NO and it is confirmed that engine 1 has not yet completely stopped, the automatic stop control unit 51 repeats the control in step S13.

[0076] On the other hand, if step S14 determines that YES and it is confirmed that engine 1 has completely stopped, the automatic stop control unit 51 sets the intake valve closing timing and throttle opening to the required values ​​for stopping (step S15). The required values ​​for stopping are predetermined with consideration for restarting engine 1. That is, in step S15, the automatic stop control unit 51 sets the intake valve closing timing and throttle opening to a timing and opening suitable for restarting engine 1, respectively.

[0077] [Restart control] Next, the details of the control during the switch from motor-driven mode to engine-driven mode, particularly the control to restart engine 1 (restart control) associated with this switch, will be explained using the flowchart in Figure 7. The control shown in this figure is executed while driving in motor-driven mode. In other words, the premise for this control to be executed is that the driving mode of vehicle V is motor-driven mode.

[0078] When the control shown in Figure 7 starts, the PCM 50 determines whether or not a request has been made to switch the vehicle V's driving mode from motor driving mode to engine driving mode (step S21). That is, while driving in motor driving mode, the PCM 50 checks the condition parameters that determine the vehicle V's driving mode (e.g., required torque, battery SOC, etc.) based on the detected values ​​of the vehicle speed sensor SN1, accelerator sensor SN2, and battery sensor SN3. Then, when these condition parameters change to conditions that are suitable for engine driving mode, the PCM 50 determines that a request to switch from motor driving mode to engine driving mode has been made. Note that switching from motor driving mode to engine driving mode involves control to restart engine 1 (restart control), so determining whether or not a switching request has been made here is equivalent to determining whether or not the restart conditions for engine 1 have been met.

[0079] If step S21 is determined to be NO and there is no request to switch to engine driving mode, in other words, if it is confirmed that the conditions for restarting engine 1 are not met, the PCM 50 maintains the vehicle V's driving mode in motor driving mode (step S30). As a result, the engine 1 remains stopped.

[0080] On the other hand, if the above step S21 is determined to be YES and the request to switch to engine driving mode is confirmed, that is, if the conditions for restarting engine 1 are confirmed to be met, the restart control unit 52 of the PCM 50 injects fuel into the injector 8 of the cylinder in the expansion stroke while stopped (step S22). The cylinder in the expansion stroke while stopped is the cylinder that was in the expansion stroke when engine 1 stopped due to the automatic stop control described above. The restart control unit 52 injects fuel into the injector 8 of this cylinder in the expansion stroke while stopped in order to perform the first combustion for restarting. This fuel injection forms a mixture of fuel and air in the combustion chamber C of the cylinder in the expansion stroke while stopped.

[0081] Next, the restart control unit 52 generates a spark at the spark plug 9 of the cylinder in the expansion stroke while stopped, igniting the air-fuel mixture formed in the combustion chamber C of that cylinder (step S23). Ignition occurs shortly after the fuel injection in step S22. This ignition triggers combustion of the air-fuel mixture in the compression stroke cylinder while stopped, and the expansion force from this combustion pushes down the piston 5 of the expansion stroke cylinder while stopped, imparting rotational force to the engine 1.

[0082] Next, the restart control unit 52 engages the clutch 30 (step S24) and starts cranking the engine 1 (step S25). That is, the restart control unit 52 engages the clutch 30 to connect the engine 1 and the motor 31, and transmits the torque of the motor 31 to the engine 1 via the engaged clutch 30, thereby imparting rotational force to the engine 1. The applied rotational force is added to the rotational force due to combustion in the cylinder during the compression stroke while stopped, as described above. This accelerates the piston 5 of the cylinder that first reaches top dead center after starting (the cylinder during the compression stroke while stopped), enabling the piston 5 to move beyond top dead center. In order to avoid shock due to the sudden transmission of torque, the engagement of the clutch 30, at least in the initial stages of cranking, is performed with a relatively weak engagement force (partial engagement) that allows relative rotation between the output shaft (crankshaft 7) of the engine 1 and the rotation shaft of the motor 31.

[0083] Next, the restart control unit 52 sequentially initiates combustion in cylinders other than the cylinder in the expansion stroke at the time of stopping (step S26). Combustion is performed in the order of the cylinders that reach top dead center. Specifically, the restart control unit 52 initiates combustion in the cylinder in the compression stroke at the time of stopping, which was in the compression stroke when the engine 1 stopped, around the time it reaches top dead center, and then similarly initiates combustion in the other cylinders around the time they reach top dead center.

[0084] Next, the restart control unit 52 determines whether or not engine 1 has fully ignited (step S27). For example, when the engine speed exceeds a predetermined specified speed, the restart control unit 52 determines that engine 1 has fully ignited, that is, that the restart of engine 1 is complete.

[0085] If step S27 determines NO and it is confirmed that engine 1 has not yet fully combusted, the restart control unit 52 repeats the control in step S26.

[0086] On the other hand, if step S27 determines that YES and it is confirmed that engine 1 has fully combusted, the restart control unit 52 controls the combustion of engine 1 according to the torque requested by vehicle V (step S28). That is, the restart control unit 52 controls the combustion of engine 1 so that the torque output from engine 1 is the torque requested by vehicle V minus the output torque of motor 31.

[0087] [Example of operation] Figure 8 is a time chart showing an example of the time-series changes of various state variables associated with the automatic stop control of engine 1. In this figure, time t0 is defined as the moment when the vehicle V's driving mode switches from engine driving mode to motor driving mode, in other words, the moment when the automatic stop condition for engine 1 is met. At time t1, slightly delayed from time t0, the clutch 30 is released, and at time t2, slightly delayed from time t1, a fuel cut (F / C) is performed to stop fuel injection. In conjunction with this fuel cut, the intake valve closing timing is advanced toward the first period IV1 (e.g., ABDC70°CA), and the throttle opening is increased toward the first opening TV1 (e.g., 25%). This control, which includes an increase in the throttle opening, results in an increase in intake pressure. This is why the intake pressure increases from time t2 onward.

[0088] At time t3, which is delayed from time t2, the engine speed decreases to the first rotational speed NE1 (e.g., 780 rpm). In response to this decrease in rotational speed, the intake valve closing timing is retarded towards the second timing IV2 (e.g., ABDC100°CA), which is the retardedest angle, and the throttle opening is reduced towards the second opening TV2 (e.g., around 3%). The second opening TV2 is increased or decreased as appropriate depending on the engine speed value from time t3 onward.

[0089] At time t4, which is delayed from time t3, the engine speed decreases to the second rotational speed NE2 (for example, 500 rpm). In response to this decrease in rotational speed, the throttle opening is reduced towards fully closed (0%).

[0090] At time t6, which is delayed from time t4, the engine speed decreases to the third rotational speed NE3 (for example, 160 rpm). In response to this decrease in rotational speed, the throttle opening is increased toward full opening (100%). This state continues until time t7, when engine 1 comes to a complete stop, that is, when the engine speed becomes zero.

[0091] As described above, in this embodiment, the intake valve closing timing and throttle opening are controlled in different ways depending on the engine speed after fuel cut. Here, the engine speed after the fuel cut is executed at time t2 is divided into three regions based on the differences in the control of the intake valve closing timing and throttle opening, and these are defined as the first rotational speed region I, the second rotational speed region II, and the third rotational speed region III. The first rotational speed region I is the region from the rotational speed at time t2 when the fuel cut is executed to the rotational speed at time t3 (first rotational speed NE1). The second rotational speed region II is the region from the rotational speed at time t3 (first rotational speed NE1) to the rotational speed at time t6 (third rotational speed NE3). The third rotational speed region III is the region from the rotational speed at time t6 (third rotational speed NE3) to the rotational speed at time t7 (zero). In this case, the first rotational speed NE1 corresponds to the "first reference rotational speed" in the present invention, and the third rotational speed NE3 corresponds to the "second reference rotational speed" in the present invention.

[0092] Furthermore, the second rotational speed region II is divided into two parts, defined as the first half of the second rotational speed region II-1 and the second half of the second rotational speed region II-2. The first half of the second rotational speed region II-1 is the region from the rotational speed at time t3 (first rotational speed NE1) to the rotational speed at time t4 (second rotational speed NE2), and the second half of the second rotational speed region II-2 is the region from the rotational speed at time t4 (second rotational speed NE2) to the rotational speed at time t6 (third rotational speed NE3). The first half of the second rotational speed region II-1 corresponds to the "first half of the second rotational speed region" in this invention, and the second half of the second rotational speed region II-2 corresponds to the "second half of the second rotational speed region" in this invention. Furthermore, the second rotational speed NE2 corresponds to the "third reference rotational speed" in this invention.

[0093] Based on the control details shown in Figure 8 and Figures 4 and 5, in this embodiment, the control of the intake valve closing timing and throttle opening for each rotational speed range can be summarized as follows.

[0094] (First rotational speed region) In the first rotational speed region I, the intake valve closing timing is set to the first period IV1, which is advanced compared to the retarded timing (second period IV2). The throttle opening is set to the first opening TV1, which is larger than the opening before fuel cut.

[0095] (Second rotational speed domain) In the second rotational speed region II, which is lower than the first rotational speed region I, the intake valve closing timing is set to the second timing IV2, which is the latest angle. The throttle opening is set to a value smaller than the first opening TV1. Specifically, in the first half of the second rotational speed region II-1, the throttle opening is variably set based on the intake pressure, within a range that is smaller than the first opening TV1 and larger than fully closed. In the second half of the second rotational speed region II-2, the throttle opening is fully closed.

[0096] (Third rotational speed domain) In the third rotational speed region III, which has a lower rotational speed than the second rotational speed region II, the intake valve closing timing is set to the second stage IV2, which is the latest angle, and the throttle opening is fully open.

[0097] [Effects and Effects] As described above, in this embodiment, when the automatic stop condition for engine 1 (request to switch from engine driving mode to motor driving mode) is met, a fuel cut is performed to stop the fuel supply to engine 1, and control is performed to advance or retard the intake valve closing timing based on the engine speed after the fuel cut. Specifically, when the engine speed is in the first rotational speed region I, the intake SVT 17 is controlled so that the intake valve 13 closes at a first period IV1 which is advanced to its most retarded timing, and when the engine speed is in the second rotational speed region II which is lower than the first rotational speed region I, the intake SVT 17 is controlled so that the intake valve 13 closes at a second period IV2 which is set to be retarded to either the first period IV1 or the intake bottom dead center. With this configuration, there is an advantage in that vibration of engine 1 during automatic stop can be suppressed while ensuring ignition performance during restart.

[0098] In other words, in this embodiment, the intake valve closing timing in the first rotational speed region I is set to the first timing IV1, which is on the advanced side of the timing compared to the retarded timing. As a result, the period during which the intake valve 13 is open during the compression stroke is shortened, and the amount of burnt gas present in the combustion chamber C that is blown back into the intake port 11 is reduced. This reduces the amount of burnt gas that is reintroduced into the combustion chamber C from the intake port 11, i.e., the amount of internal EGR, and improves the scavenging performance of the combustion chamber C. This improves the ignition performance of the air-fuel mixture during restart, enabling a smooth restart of the engine 1.

[0099] In particular, in this embodiment, the initial combustion occurs in the cylinder during the expansion stroke while stopped when the engine 1 is restarted, making the ignition of the air-fuel mixture a potential problem. That is, since the air-fuel mixture in the cylinder during the expansion stroke while stopped is not substantially compressed, a large amount of internal EGR increases the likelihood that the necessary ignition cannot be secured. In contrast, in this embodiment, where the intake valve closing timing is set to be advanced in the first rotational speed region I, an improvement in ignition can be expected due to a reduction in the amount of internal EGR. This allows the initial combustion in the cylinder during the expansion stroke while stopped to proceed without problems, enabling a smooth restart of the engine 1. Furthermore, performing the initial combustion in the cylinder during the expansion stroke while stopped reduces the torque required by the motor 31 that cranks the engine 1, leading to a decrease in the power consumption of the motor 31. This increases the opportunities to select the motor-driven mode, thereby improving overall energy efficiency.

[0100] Furthermore, in this embodiment, the intake valve closing timing in the second rotational speed region II, which has a lower rotational speed than the first rotational speed region I, is set to the second period IV2, which is retarded more than both the first period IV1 and the intake bottom dead center. As a result, the period during which the intake valve 13 is open during the compression stroke is extended, and the amount of backflow from the combustion chamber C to the intake port 11 increases. This reduces the compression reaction force acting on the piston 5 of each cylinder 2a, thereby reducing the fluctuation range of the engine 1's shaft torque and suppressing engine 1 vibration.

[0101] In particular, in this embodiment, the intake valve closing timing in the second rotational speed region II is set to the most retarded timing, which is the intake valve closing timing when the operating angle of the intake SVT 17 is shifted to the most retarded side. This maximizes the aforementioned effect of reducing the compression reaction force of each cylinder 2a, and effectively suppresses vibrations of the engine 1.

[0102] Furthermore, in this embodiment, the throttle opening in the first rotational speed region I is set to a first opening TV1 which is larger than the opening before fuel cut-off. This increases the amount of fresh air introduced into the combustion chamber C, thereby improving scavenging performance. As a result, the initial combustion in the cylinders undergoing the expansion stroke during engine restart can be performed without hindrance, enabling a smooth restart.

[0103] Furthermore, in this embodiment, since the throttle opening in the second rotational speed region II is lower than the throttle opening in the first rotational speed region I, the intake pressure in the second rotational speed region II can be reduced to near the desired pressure, thereby suppressing vibration of the engine 1.

[0104] In other words, according to the inventors' findings, the vibration of engine 1 during a stopped operation is greatly influenced by the intake pressure at time t5 when the engine speed drops to a predetermined speed NEx (Figure 8). The predetermined speed NEx is the speed corresponding to the engine's resonant frequency (e.g., 300 rpm) and is included in the second speed region II. Keeping the intake pressure at this predetermined speed NEx (time t5) near a certain target value is important for suppressing the vibration of engine 1. The reduction in throttle opening in the second speed region II described above has the effect of lowering the intake pressure at the predetermined speed NEx to near the above target value, and as a result, the vibration of engine 1 can be suppressed.

[0105] In particular, in this embodiment, in the first half of the second rotational speed region II-1, where the rotational speed is relatively high within the second rotational speed region II, the throttle opening is variably set based on the intake pressure within a range that is smaller than the first opening TV1 and larger than fully closed. In the second half of the second rotational speed region II-2, where the rotational speed is relatively low within the second rotational speed region II, the throttle opening is fully closed. As a result, the intake pressure at the predetermined rotational speed NEx can be accurately brought close to the target value.

[0106] In other words, by adjusting the throttle opening based on the intake pressure in the first half of the second rotation speed region II-1, the intake pressure can be stabilized when transitioning to the second half of the second rotation speed region II-2. For example, as shown by the dashed-dotted waveform in the intake pressure graph of Figure 8, if the intake pressure after fuel cut is relatively high, the rate of decrease in intake pressure can be accelerated by reducing the throttle opening (bringing it closer to fully closed) in the first half of the second rotation speed region II-1. As a result, the intake pressure when transitioning to the second half of the second rotation speed region II-2 becomes equivalent to the pressure when the intake pressure is standard (solid waveform). In this way, if the intake pressure when transitioning to the second half of the second rotation speed region II-2 is stable, the intake pressure can be reduced according to the desired pattern by uniformly closing the throttle opening completely in the second half of the second rotation speed region II-2. As a result, the intake pressure at the predetermined rotation speed NEx included in the second half of the second rotation speed region II-2 can be accurately brought near the target value, and vibration of the engine 1 can be effectively suppressed.

[0107] Furthermore, in this embodiment, since the throttle opening is fully opened in the third rotational speed region III, which has a lower rotational speed than the second rotational speed region II, the piston stopping position, which is the position of the piston 5 when the engine 1 has completely stopped, can be made suitable for restarting, thereby improving the restartability of the engine 1. In other words, by fully opening the throttle in the third rotational speed region III, the pumping loss of the engine 1 can be sufficiently reduced shortly before the engine 1 comes to a complete stop. As a result, the piston 5 of the cylinder that is about to reach the last compression top dead center before complete stop can easily pass the compression top dead center, allowing the crankshaft 7 of the engine 1 to advance further in the forward direction. This makes it possible to stop the piston 5 of the cylinder in the expansion stroke and the piston 5 of the cylinder in the compression stroke at the time of stopping at positions approximately the same distance from the compression top dead center. As a result, the amount of air in the two cylinders 2a on either side of the compression top dead center is balanced, thereby improving the restartability of the engine 1.

[0108] For example, in the case of a 6-cylinder engine like the one in this embodiment, as shown in Figure 9, the piston 5 of the cylinder in the expansion stroke when stopped can be stopped around ATDC60°CA, 60° retarded from the compression top dead center, and the piston 5 of the cylinder in the compression stroke when stopped can be stopped around BTDC60°CA, 60° advanced from the compression top dead center. In this case, the pistons 5 of the other cylinders 2a will be stopped either around ATDC60°CA, which is in phase with the cylinder in the expansion stroke when stopped, or around BTDC60°CA, which is in phase with the cylinder in the compression stroke when stopped, or near bottom dead center (BDC). By stopping the pistons 5 in this positional relationship, the amount of air in each cylinder 2a is balanced, making it easier to restart the engine 1.

[0109] [Differentiation] In the above embodiment, as part of the automatic stop control of the engine 1, the intake valve closing timing when the engine speed after fuel cut is in the second rotational speed region II is set to the same second period IV2 as the most retarded timing, which is the intake valve closing timing when the operating angle of the intake SVT 17 is shifted to the most retarded side. However, the intake valve closing timing in the second rotational speed region II (second period IV2) does not necessarily have to be the most retarded timing; it just needs to be a timing that is sufficiently retarded from the intake bottom dead center, in other words, a timing that significantly reduces the compression reaction force acting on the piston 5. For example, the second period IV2 may be a timing that is slightly advanced from the most retarded timing.

[0110] In the above embodiment, the throttle opening in the third rotational speed region III, where the rotational speed is lower than in the second rotational speed region II, was set to fully open (100%). However, the throttle opening in the third rotational speed region III only needs to be somewhat larger than the throttle opening in the second rotational speed region II, and does not necessarily need to be fully open.

[0111] In the above embodiment, an intake SVT17, which is a type of variable phase device that changes the phase while keeping the lift amount and opening period of the intake valve 13 constant, was used as a variable phase device to change the phase of the intake valve 13. However, instead, a variable phase device that changes the lift amount or opening period in conjunction with the valve phase may be used.

[0112] In the above embodiment, an example of applying the present invention to a hybrid vehicle V that uses both an engine 1 consisting of a gasoline engine and an electric motor 31 was described. However, the present invention can also be applied to engine-powered vehicles that use only an engine as a power source for driving. That is, engine-powered vehicles often employ an idle stop system that automatically stops the engine when the vehicle is stopped, and the present invention can be suitably applied to such idle stop type vehicles as well.

[0113] Furthermore, the engines to which the present invention can be applied are not limited to the 6-cylinder type engine as in the above embodiment. The present invention can be applied to engines with various numbers of cylinders, such as 4-cylinder and 3-cylinder types. [Explanation of Symbols]

[0114] 1 Engine 2a cylinder 17. Intake SVT (Variable Phase Device) 24 Throttle valve 31. Motor (Electric Motor) 37. Drive wheels 51 Automatic Stop Control Unit 52 Restart Control Unit IV1 1st period IV2 2nd period I. First rotational speed region II. Second rotational region II-1 First half of the second rotational speed region (first half of the second rotational speed region) II-2 Second half of the second rotational speed region (the latter half of the second rotational speed region) III. Third Rotational Domain

Claims

1. An engine control device, A phase-variable device capable of changing the phase of the intake valve, A throttle valve is provided in the intake passage so as to be openable and closable, When predetermined automatic stop conditions are met, the system performs a fuel cut to stop the fuel supply to the engine and automatically stops the engine, and also controls the variable phase device and the throttle valve based on the engine speed after the fuel cut, The system includes a restart control unit that, when the restart conditions for restarting the automatically stopped engine are met, injects the first fuel into the cylinder that stopped during the expansion stroke and burns it, With respect to engine speed, when the range from the engine speed at the time of fuel cut-off to a lower first reference engine speed is defined as the first rotational speed region, the range from the first reference engine speed to a lower second reference engine speed is defined as the second rotational speed region, and the range from the second reference engine speed to zero rotational speed is defined as the third rotational speed region, the automatic stop control unit shall: When the engine speed after the fuel cut is in the first rotational speed range, the variable phase device is controlled so that the intake valve closes at a first timing that is advanced more than the maximum timing, which is the closing timing of the intake valve when the variable phase device is operated to the maximum retarded side, and the opening degree of the throttle valve is increased compared to before the fuel cut. An engine control device characterized by controlling the variable phase device so that, when the engine speed after the fuel cut is in the second rotational speed range, the intake valve closes at a second timing set to be retarded more than either the first timing or the intake bottom dead center.

2. In the engine control device according to claim 1, An engine control device characterized in that the second period is the same as the most retarded period.

3. In the engine control device according to claim 1, The automatic stop control unit is characterized in that, in the second rotational speed region, it reduces the opening degree of the throttle valve compared to that in the first rotational speed region.

4. In the engine control device according to claim 3, When the second rotational speed range is divided into two parts, the first part being the range from the first reference rotational speed to the third reference rotational speed which is intermediate between the first and second reference rotational speeds, and the second part being the range from the third reference rotational speed to the second reference rotational speed, the automatic stop control unit shall In the first half of the second rotational speed region, the opening degree of the throttle valve is variably set based on the intake pressure within a range that is smaller than the opening degree in the first rotational speed region and larger than fully closed. An engine control device characterized by closing the throttle valve completely in the latter half of the second rotational speed range.

5. In the engine control device according to claim 3, The automatic stop control unit is characterized in that, in the third rotational speed region, it increases the opening degree of the throttle valve compared to the second rotational speed region.

6. In the engine control device according to any one of claims 1 to 5, The control device for an engine is characterized in that the engine is disconnectably connected to an electric motor capable of rotating a wheel.

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