Vehicle drive systems

Abstract

To improve acceleration responsiveness while reducing a vehicle shock when switching to an engine travel mode.SOLUTION: A vehicular driving apparatus includes: an engine including a fuel injection valve; a motor; a hydraulic clutch which connects the engine and the motor in a disconnectable manner; a hydraulic pressure detector which detects a hydraulic pressure of the clutch; and a controller. When starting the engine with switching from a motor travel mode to an engine travel mode, the controller determines an engagement state of the clutch on the basis of the hydraulic pressure detected by the hydraulic pressure detector while causing the clutch to transition from a disengagement state to an engagement state. At a point in time when it is confirmed that the clutch is in a predetermined engagement initial state as a result of the determination, the controller causes the fuel injection valve to inject fuel.SELECTED DRAWING: Figure 7

Description

Technical Field

[0004] , , , , , , ,

[0005] , , ,

[0001] The present invention relates to a vehicle drive device that uses both an engine and a motor.

Background Art

[0002] Vehicles that use both an internal combustion engine and an electric motor as power sources, that is, hybrid vehicles, are known. As a type of hybrid vehicle, there is a vehicle that can be switched between an engine driving mode in which at least part of the power is provided by the engine and a motor driving mode in which all of the power is provided by the motor. In such a hybrid vehicle, control to stop the engine or control to restart the stopped engine is executed as the driving mode is switched.

[0003] For example, Patent Document 1 below discloses that when switching from a motor driving mode (EV driving mode) to an engine driving mode (HV mode), while starting the engine, the engine and the motor (motor generator) are connected via a clutch. Specifically, in Patent Document 1, when switching to the engine driving mode, control to ignite the air-fuel mixture to increase the engine speed and control to fill the clutch with hydraulic oil to engage the clutch are performed in this order.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] This invention has been made in view of the above circumstances, and aims to provide a vehicle drive system that can reduce vehicle shock when switching to engine driving mode while improving acceleration response. [Means for solving the problem]

[0007] To solve the above problems, the vehicle drive system of the present invention comprises an engine including a fuel injector, an electric motor connected to a wheel, a hydraulic clutch that connects the engine and the motor so as to be able to disconnect and reconnect, a hydraulic pressure detector that detects the hydraulic pressure of the clutch, and a controller capable of selectively executing either a motor driving mode in which the motor is driven and the engine is stopped, or an engine driving mode in which at least the engine is driven, wherein when the engine is started due to switching from the motor driving mode to the engine driving mode, the controller transitions the clutch from a disengaged state to an engaged state, determines the engaged state of the clutch based on the hydraulic pressure detected by the hydraulic pressure detector, and when it is confirmed as a result of the determination that the clutch is in a predetermined initial engaged state, fuel is injected into the fuel injector. The initial engagement state is a state in which the clearance between the clutch plates of the clutch is virtually zero. The present invention is characterized by the following (Claim 1).

[0008] There is a delay between the injection of fuel and the actual combustion of the fuel causing the engine to rotate, and also a delay between the initial engagement state of the clutch and its full engagement. Taking this into consideration, in this invention, fuel is injected as soon as the initial engagement state of the clutch is confirmed, making it possible to fully engage the clutch within the period when the engine is rotating due to combustion energy. As a result, the rotational force transmitted from the motor to the engine via the clutch can be superimposed on the rotational force due to combustion energy, allowing the engine speed to increase rapidly. Consequently, the time required until the engine is fully started (complete combustion) can be shortened, and the acceleration response when switching to engine driving mode can be improved. Furthermore, by fully engaging the clutch while the engine is rotating, it is possible to suppress the large vehicle shock that occurs when the clutch is fully engaged.

[0010] Moreover, in this invention, The clutch plates stroked until the clearance between them was virtually zero. When the state is confirmed as the initial state of the agreement described above, Fuel can be injected at that point. This allows the timing of the subsequent increase in clutch hydraulic pressure and the full engagement of the clutch to be suitably contained within the period during which the engine is rotating due to combustion energy.

[0011] Preferably, the engine further comprises a spark plug that ignites a fuel-air mixture injected from the fuel injector, and the controller causes the spark plug to ignite after a predetermined period of time has elapsed since the fuel injection from the fuel injector when the engine is started. Claim 2 ).

[0012] In this embodiment, the fuel-air mixture can be ignited at the moment when the injected fuel and air are sufficiently mixed, allowing the mixture to burn properly.

[0013] Preferably, the engine includes a plurality of cylinders, each equipped with a fuel injector and a spark plug, and the controller, when starting the engine, causes the fuel injector to inject fuel and the spark plug to ignite first in the cylinders that were stopped in the expansion stroke, which are the cylinders in the stopped expansion stroke. Claim 3 ).

[0014] In this embodiment, the engine can be quickly given rotational force by causing the initial combustion to occur in the cylinder undergoing the expansion stroke while the engine is stationary, thereby pushing down the piston of that cylinder.

[0015] Preferably, the controller performs multiple fuel injections to the cylinder in the expansion stroke while stopped, and then performs multiple ignitions. Claim 4 ).

[0016] In this embodiment, the uncompressed fuel-air mixture formed in the cylinder during the expansion stroke while the engine is stationary can be burned without any problems. That is, multiple fuel injections repeatedly stir the air in the combustion chamber, promoting the mixing of fuel and air. As a result, a well-mixed fuel-air mixture is formed in the combustion chamber. Then, multiple ignitions of the formed mixture improve its ignition properties, allowing most of the mixture to be burned effectively. [Effects of the Invention]

[0017] As described above, the vehicle drive system of the present invention makes it possible to reduce vehicle shock when switching to engine driving mode while improving acceleration responsiveness. [Brief explanation of the drawing]

[0018] [Figure 1] This is a system diagram showing the schematic configuration of a vehicle to which a drive system according to one embodiment of the present invention is applied. [Figure 2] This is a schematic cross-sectional view showing the structure of the engine. [Figure 3] This is a functional block diagram showing the vehicle's control system. [Figure 4] It is a flowchart showing the content of automatic stop control of an engine performed in accordance with the switching from an engine running mode to a motor running mode. [Figure 5] It is a diagram showing a preferred example of the piston position when the engine has completely stopped. [Figure 6] It is a flowchart showing the content of engine restart control performed in accordance with the switching from a motor running mode to an engine running mode. [Figure 7] It is a time chart showing an example of the time-series change of various state quantities accompanying the engine restart control.

Mode for Carrying Out the Invention

[0019] [Overall Configuration of Vehicle] FIG. 1 is a system diagram showing a schematic configuration of a vehicle V to which a drive device according to an embodiment of the present invention is applied. As shown in this figure, the vehicle V includes an engine 1, a clutch 30, a motor 31, an inverter 32, a battery 33, a transmission 35, a differential device 36, drive wheels 37, and a PCM 50. Both the engine 1 and the motor 31 can drive the drive wheels 37 (wheels) as power sources for running. That is, the vehicle V in the present embodiment is a hybrid vehicle that uses both the engine 1 and the motor 31 as power sources.

[0020] The engine 1 is an internal combustion engine that generates output by burning fuel. In the present embodiment, a four-cycle gasoline engine using fuel mainly composed of gasoline (gasoline fuel) is used as the engine 1. Details of the engine 1 will be described later.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Battery 33 is equipped with a battery sensor SN4 that detects the input and output current to and from the battery 33. The current value detected by the battery sensor SN4 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 SN4 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 SN4, and calculates the battery SOC by integrating these values.

[0025] The clutch 30 is a clutch that connects the engine 1 and the motor 31 in a way that allows them to be connected and disconnected. In other words, the clutch 30 connects the output shaft of the engine 1 (crankshaft 7, which will be described later) and the rotating shaft (rotor shaft) of the motor 31 in series, or disconnects them.

[0026] The clutch 30 includes a pair of clutch plates 30a that are opposed to each other in the axial direction. That is, the clutch 30 is displaceable between a engaged state in which the clutch plates 30a are pressed against each other and a disengaged state in which the clutch plates 30a are separated. When the clutch 30 is engaged and the engine 1 and motor 31 are connected, the torques of both the engine 1 and the motor 31 are 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.

[0027] The clutch 30 is engaged and disengaged through control of hydraulic pressure supplied from a hydraulic supply device (not shown). Specifically, when the clutch 30 is engaged, the hydraulic pressure acting on the clutch plates 30a, i.e., the clutch hydraulic pressure, is increased, causing the clutch plates 30a to press against each other. When the clutch 30 is disengaged, the clutch hydraulic pressure is reduced, releasing the pressure between the clutch plates 30a. The clutch 30 is also equipped with a hydraulic pressure sensor SN3 for detecting the clutch hydraulic pressure. The hydraulic pressure sensor SN3 corresponds to the "hydraulic pressure detector" in this invention.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] [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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] A crank angle sensor SN5 is attached to the cylinder block 3. The crank angle sensor SN5 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.

[0037] The cylinder head 4 is fitted with an injector 8 and a spark plug 9. The injector 8 is a fuel 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.

[0038] 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.

[0039] The cylinder head 4 is equipped with an intake valve mechanism 15 and an exhaust valve mechanism 16. 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 on the combustion chamber C side of the intake port 11 in response to the drive of the intake valve mechanism 15, and the exhaust valve 14 periodically opens and closes the opening on the combustion chamber C side of the exhaust port 12 in response to the drive of the exhaust valve mechanism 16.

[0040] 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 connecting each intake port 11 of the plurality of (six) cylinders 2a to the surge tank 22. 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 flowing through the intake passage 20.

[0041] 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.

[0042] [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, hydraulic pressure sensor SN3, battery sensor SN4, and crank angle sensor SN5 mentioned above. The PCM50 receives sequential input of information detected by each of these sensors, namely vehicle speed, accelerator opening, clutch hydraulic pressure, battery SOC, crank angle, and engine speed.

[0043] 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, 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.

[0044] 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 SN4, 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).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] [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 flowchart in Figure 4. The control shown in this figure is executed while driving in engine-driven mode. In other words, the premise for this control to be executed is that the driving mode of vehicle V is engine-driven mode.

[0049] When the control shown in Figure 4 starts, the PCM50 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 PCM50 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 SN4. Then, when these condition parameters change to conditions that are suitable for motor driving mode, the PCM50 determines that a request to switch from engine driving mode to motor driving mode has been made.

[0050] If step S1 is determined to be NO and it is confirmed that there is no request to switch to motor driving mode, the PCM50 maintains the driving mode of vehicle V in engine driving mode (step S7).

[0051] On the other hand, if step S1 is determined to be YES and it is confirmed that there is a request to switch to motor driving mode, the automatic stop control unit 51 of the PCM 50 releases the clutch 30 and disconnects the engine 1 and the motor 31 (step S2).

[0052] 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.

[0053] Next, the automatic stop control unit 51 controls the throttle opening, which is the opening degree of the throttle valve 24, based on the engine speed (step S4). For example, for a while after fuel cut, the automatic stop control unit 51 reduces the throttle opening to a relatively small opening (near fully closed) in order to suppress vibration of the engine 1. Then, when the engine speed drops to a predetermined specified speed (for example, 160 rpm), the throttle opening is increased. In this way, by increasing the throttle opening just before the engine 1 comes to a complete stop, the pumping loss of the engine 1 is reduced, and the piston 5 of the cylinder that will reach the last compression top dead center before coming to a complete stop is more likely to pass the compression top dead center. This makes it possible to stop the piston 5 of the cylinder that is in the expansion stroke when stopped and the piston 5 of the cylinder that is in the compression stroke when stopped at positions approximately the same distance from the compression top dead center.

[0054] For example, in the case of a 6-cylinder engine like the one in this embodiment, as a result of controlling the throttle valve 24 as described above, it is easy to obtain a stopping position pattern for the pistons 5 of each cylinder 2a as shown in Figure 5. That is, the piston 5 of the cylinder in the expansion stroke when stopped stops near ATDC60°CA, 60° retarded from the compression top dead center, and the piston 5 of the cylinder in the compression stroke when stopped stops near BTDC60°CA, 60° advanced from the compression top dead center. The pistons 5 of the other cylinders 2a will stop either near ATDC60°CA, which is in phase with the expansion stroke cylinder when stopped, near BTDC60°CA, which is in phase with the compression stroke cylinder when stopped, or near bottom dead center (BDC).

[0055] 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 S5).

[0056] If step S5 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 S4.

[0057] On the other hand, if step S4 determines that YES and it is confirmed that engine 1 has completely stopped, the automatic stop control unit 51 sets the throttle opening to the required value for stopping (step S6). The required value for stopping is predetermined, for example, taking into consideration the restart of engine 1. That is, in step S6, the automatic stop control unit 51 sets the throttle opening to an opening suitable for restarting engine 1.

[0058] [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 6. The control shown in this figure is executed while the vehicle is running in motor-driven mode. In other words, the premise for this control to be executed is that the vehicle V is in motor-driven mode.

[0059] When the control shown in Figure 6 starts, the PCM50 determines whether a request has been made to switch the vehicle V's driving mode from motor driving mode to engine driving mode (step S11). That is, while driving in motor driving mode, the PCM50 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 SN4. Then, when these condition parameters change to conditions that are suitable for engine driving mode, the PCM50 determines that a request to switch from motor driving mode to engine driving mode has been made.

[0060] If step S11 is determined to be NO and it is confirmed that there is no request to switch to engine driving mode, the PCM50 maintains the vehicle V's driving mode in motor driving mode (step S23). As a result, the engine 1 remains stopped.

[0061] On the other hand, if step S11 is determined to be YES and it is confirmed that there is a request to switch to engine driving mode, the restart control unit 52 of the PCM 50 supplies hydraulic pressure to the clutch 30 which is in the disengaged state, causing the clutch plate 30a to stroke in the engagement direction (step S12). In step S12, the hydraulic pressure supplied to the clutch 30, i.e., the clutch hydraulic pressure, only needs to be a pressure that can stroke the clutch plate 30a, and is set to a value smaller than the pressure that causes the clutch 30 to engage (engagement hydraulic pressure).

[0062] Next, the restart control unit 52 determines whether the clutch 30 has entered a zero clearance state (step S13). A zero clearance state is a state in which the clearance between the clutch plates 30a is virtually zero, or in other words, a state in which the clutch plates 30a have been stroked to a position where they are just touching each other.

[0063] The determination of the zero clearance state described above is made based on the detection value of the hydraulic sensor SN3 provided on the clutch 30. For example, when the clutch plates 30a come into contact with each other, the clutch hydraulic pressure rises accordingly. That is, the clutch hydraulic pressure remains approximately constant while the clutch plates 30a are in stroke, but rises instantaneously when the clutch plates 30a come into contact with each other. The restart control unit 52 determines that the clutch 30 has entered the zero clearance state when it confirms this hydraulic pressure behavior based on the detection value of the hydraulic sensor SN3.

[0064] If step S13 determines NO and it is confirmed that the stroke of the clutch plate 30a has not yet been completed, the restart control unit 52 repeats the control in step S12.

[0065] On the other hand, if step S13 determines that the clutch 30 is in a zero clearance state, the restart control unit 52 gradually increases the clutch hydraulic pressure toward a predetermined target hydraulic pressure (step S14). The target hydraulic pressure is set to a value somewhat lower than the engagement hydraulic pressure, which is the hydraulic pressure required to fully engage the clutch 30. This gradual increase in clutch hydraulic pressure toward the target hydraulic pressure causes the clutch 30 to transition to a partially engaged state. The partially engaged state is a state in which the clutch 30 is engaged with a relatively weak force that allows torque to be transmitted while allowing relative rotation (slip) between the clutch plates 30a.

[0066] In conjunction with step S14 above, the restart control unit 52 injects fuel into the injector 8 of the cylinder in the expansion stroke at the time of stopping (step S15). As mentioned earlier, the cylinder in the expansion stroke at the time of stopping is the cylinder that was in the expansion stroke when the engine 1 stopped due to the automatic stop control (Figure 4). The restart control unit 52 injects fuel into the injector 8 of this cylinder in the expansion stroke at the time of stopping 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 at the time of stopping.

[0067] In this embodiment, the fuel injection in step S15 is performed as a split injection. That is, in step S15, the restart control unit 52 injects the required amount of fuel from the injector 8 of the cylinder undergoing expansion stroke during cessation in multiple portions. For example, three portions are preferred.

[0068] 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 S16). Ignition occurs after a predetermined period of time has elapsed since the fuel injection in step S22. The predetermined period is set in advance as the time required for the injected fuel to mix with air and form an air-fuel mixture. 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. This imparts rotational force to the engine 1, causing the engine speed to begin to increase.

[0069] In this embodiment, the ignition in step S16 is multi-ignition. That is, in step S16, the restart control unit 52 causes the spark plug 9 of the cylinder in the expansion stroke during stop to ignite multiple times. The number of ignitions is preferably three, for example. In this case, the first ignition occurs after the predetermined period has elapsed since the last of the multiple fuel injections in step S15, and then the second and subsequent ignitions occur in quick succession.

[0070] Next, the restart control unit 52 determines whether the difference in rotational speed between the output shaft (crankshaft 7) of the engine 1 and the rotating shaft of the motor 31 has fallen below a predetermined value (step S17).

[0071] If the above step S17 is determined to be YES and it is confirmed that the above rotational speed difference is less than the specified value, the restart control unit 52 fully engages the clutch 30 (step S18). That is, the restart control unit 52 fully engages the clutch 30 by increasing the clutch hydraulic pressure to a predetermined engagement hydraulic pressure that is high enough so that slippage of the clutch plate 30a is not permitted.

[0072] 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 S19). 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 when the engine 1 stops, 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.

[0073] Next, the restart control unit 52 determines whether or not engine 1 has fully ignited (step S20). 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.

[0074] If step S20 determines NO and it is confirmed that engine 1 has not yet fully combusted, the restart control unit 52 repeats the control in step S19.

[0075] On the other hand, if step S20 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 S21). That is, the restart control unit 52 controls the combustion of engine 1 so that the torque output from engine 1 is the torque obtained by subtracting the output torque of motor 31 from the torque requested by vehicle V.

[0076] [Example of operation] Figure 7 is a time chart showing an example of the time-series changes of various state variables associated with the restart 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 command to restart engine 1 is issued. From this time t0, hydraulic pressure is applied to the clutch 30 to stroke the clutch plate 30a. As a result, the state of the clutch 30 transitions from the disengaged state to a state in which the clutch plate 30a strokes in the engagement direction.

[0077] Due to the stroke of the clutch plate 30a, at time t1, which is delayed from time t0, the clutch 30 reaches a zero clearance state, and the clearance between the clutch plates 30a becomes virtually zero. In response to this, from time t1, multiple fuel injections (three in this case) are performed on the cylinders in the expansion stroke while stationary, and then multiple ignitions (three) are performed on the same cylinders in the expansion stroke while stationary. In addition, the clutch hydraulic pressure is controlled to gradually increase from time t1.

[0078] As a result of the fuel injection and ignition described above, the fuel-air mixture burns in the cylinder during the stationary expansion stroke. The expansion force from this combustion pushes down the piston 5 in the stationary expansion stroke cylinder, thereby imparting rotational force to the engine 1. As a result, the engine speed begins to increase from time t2 onward.

[0079] Furthermore, after the clutch 30 reaches a zero clearance state at point t1, the clutch 30 transitions to a partially engaged state. In the partially engaged state, the clutch 30 transmits torque from the motor 31 to the engine 1, thereby imparting rotational force to the engine 1. The increase in engine speed from point t2 as described above includes this increase in rotation due to the torque transmitted from the motor 31.

[0080] As engine 1 begins to rotate, shortly thereafter, piston 5 of the cylinder in the compression stroke at rest, which is the first cylinder to reach top dead center after starting, passes over top dead center. Due to the increase in rotational resistance associated with passing over top dead center, the engine speed begins to decrease at time t3.

[0081] Meanwhile, at time t4, slightly later than time t3, the clutch hydraulic pressure is increased to the engagement hydraulic pressure, and the clutch 30 fully engages. As a result, the engine 1 and the motor 31 are fully connected, and the torque of the motor 31 is transmitted to the engine 1 in earnest. Then, the engine speed, which had begun to decrease, starts to rise again. The engine speed continues to rise thereafter, and after some time, reaches the full combustion speed.

[0082] [Effects and Effects] As described above, in this embodiment, when the engine 1 starts up in conjunction with switching from motor driving mode to engine driving mode, the clutch hydraulic pressure is increased to engage the clutch 30, and the engagement state of the clutch 30 is determined based on the detected value of the clutch hydraulic pressure. When it is confirmed as a result of the determination that the clutch 30 is in a zero clearance state, fuel is injected into the cylinder during the expansion stroke while stopped. With this configuration, there is an advantage in that acceleration response can be improved while reducing vehicle shock when switching to engine driving mode.

[0083] In other words, in this embodiment, when the clutch 30 reaches a zero clearance state, that is, when the clearance between the clutch plates 30a becomes virtually zero, fuel is injected into the cylinder undergoing the expansion stroke while the engine is stopped. As a result, the energy from the combustion of the injected fuel can fully engage the clutch 30 within the period that the engine 1 is rotating, and the engine speed can be rapidly increased.

[0084] Specifically, when fuel is injected into the cylinder in the expansion stroke while stationary, the injected fuel burns upon subsequent ignition, and the expansion force (combustion energy) from this combustion pushes down the piston of the cylinder in the expansion stroke while stationary, increasing the engine speed. On the other hand, the clutch 30 in the zero-clearance state remains partially engaged for a while before becoming fully engaged. In other words, there is a delay between the injection of fuel and the actual combustion of the fuel causing the engine 1 to rotate, and there is also a delay between the clutch 30 entering the zero-clearance state and becoming fully engaged. Taking this into consideration, in this embodiment, fuel is injected as soon as the zero-clearance state is confirmed, making it possible to fully engage the clutch 30 within the period when the engine 1 is rotating due to combustion energy. As a result, the rotational force transmitted from the motor 31 to the engine 1 via the clutch 30 can be superimposed on the rotational force due to combustion energy, and the engine speed can be rapidly increased, as shown by the solid waveform in the bottom chart of Figure 7. As a result, the time required for engine 1 to fully start (combust) can be shortened, and acceleration responsiveness when switching to engine driving mode can be improved. In addition, since clutch 30 is fully engaged while engine 1 is rotating, it is possible to suppress the large vehicle shock that occurs when the clutch is fully engaged.

[0085] For example, if the timing of fuel injection were determined independently of the state of the clutch 30, the timing of fuel injection and the timing of clutch engagement would be significantly out of sync. As a result, as shown by the dashed-dotted waveform in the bottom chart of Figure 7, the increase in engine speed due to combustion energy and the increase in engine speed due to torque transmission via the engaged clutch 30 would occur separately with a time lag. In other words, torque transmission via the clutch 30 would only occur after the engine, which had started rotating after receiving combustion energy, had stopped again. In this case, since the engine speed is increased again by the motor 31 after it has dropped to zero, not only would the time until the engine 1 is fully started (combusted) be prolonged, but there is also concern that the vehicle shock when the clutch 30 is engaged would increase. In contrast, in this embodiment, the clutch 30 is fully engaged while the engine 1 is rotating after receiving combustion energy, so the above situation can be effectively avoided, and acceleration responsiveness can be improved while reducing vehicle shock.

[0086] Furthermore, in this embodiment, since fuel injection and ignition are performed multiple times each in the cylinder during the expansion stroke while the engine is stationary, the uncompressed fuel-air mixture formed in the cylinder during the expansion stroke while the engine is stationary can be burned without any problems. In other words, multiple fuel injections repeatedly stir the air in the combustion chamber C, promoting the mixing of fuel and air. As a result, a well-mixed fuel-air mixture is formed in the combustion chamber C. Then, by igniting the formed mixture multiple times, the ignition properties of the mixture are improved, and most of the mixture can be burned accurately.

[0087] [Differentiation] In the above embodiment, fuel is injected into the cylinder undergoing the expansion stroke during cessation when the clutch 30 reaches a zero clearance state, that is, when the clearance between the clutch plates 30a becomes virtually zero. However, the timing of fuel injection is not limited to the zero clearance state; it can be performed during the initial engagement state, which is the initial stage of the control for engaging the clutch 30. For example, the initial engagement state may be defined as a state in which the clearance between the clutch plates 30a has decreased to a predetermined value greater than zero, and fuel injection may be performed when this state is confirmed.

[0088] In the above embodiment, an example of applying the present invention to a hybrid vehicle V equipped with a 6-cylinder engine 1 and a motor 31, the present invention is not limited to such a vehicle, but is broadly applicable to vehicles equipped with an engine and motor that are engaged and disengaged via a clutch. For example, the engine equipped in a vehicle to which the present invention can be applied is not limited to a 6-cylinder type, but can be an engine with various numbers of cylinders, such as a 4-cylinder type or a 3-cylinder type. [Explanation of Symbols]

[0089] 1 Engine 2a cylinder 8. Injector (fuel injection valve) 9 Spark plugs 30 Clutch 30a Clutch plate 31 Motor 37. Drive wheels 50 PCM (Controller) SN3 Hydraulic Sensor (Hydraulic Detector)

Claims

1. The engine, including the fuel injectors, An electric motor connected to the wheels, A hydraulic clutch that connects the engine and the motor in a way that allows them to be disconnected and reconnected, A hydraulic pressure detector for detecting the hydraulic pressure of the clutch, The system includes a controller capable of selectively executing either a motor-driven mode in which the motor is driven and the engine is stopped, or an engine-driven mode in which at least the engine is driven. The controller, when switching from the motor driving mode to the engine driving mode and starting the engine, transitions the clutch from the disengaged state to the engaged state, determines the clutch's engaged state based on the hydraulic pressure detected by the hydraulic pressure detector, and when it is confirmed that the clutch is in a predetermined initial engaged state as a result of the determination, injects fuel into the fuel injector. The vehicle drive system is characterized in that the initial engagement state is a state in which the clearance between the clutch plates of the clutch is substantially zero.

2. In the vehicle drive system according to Claim 1, The engine further comprises a spark plug that ignites the fuel-air mixture injected from the fuel injection valve, The control unit is characterized in that, when the engine is started, it causes the spark plug to ignite after a predetermined period of time has elapsed since the fuel injection by the fuel injector.

3. In the vehicle drive system according to Claim 2, The engine includes a plurality of cylinders, each equipped with a fuel injector and a spark plug. The control unit is characterized in that, when the engine is started, it causes the fuel injection valve to first inject fuel and the spark plug to ignite the cylinder that was stopped during the expansion stroke, which is the cylinder that was stopped during the expansion stroke.

4. In the vehicle drive system according to claim 3, The control unit is characterized by performing multiple fuel injections to the cylinder undergoing the expansion stroke while stopped, and then performing multiple ignitions.

Images