Hybrid vehicle control device

Abstract

To provide a control device of a hybrid vehicle which can restart an engine at an early stage while securing the drivability.SOLUTION: A control device of a hybrid vehicle including an engine having a plurality of cylinders, a motor provided in a power transmission path between the engine and wheels, and a clutch provided between the engine and the motor in the power transmission path comprises: a cranking control unit which starts cranking of the engine by the motor by turning the clutch into a slip state in a case where combustion stops when the clutch is in the release state and there is a restart request for the engine that is inertially rotating; and a combustion control unit which starts combustion from a cylinder in which a cranking angle is scheduled to exceed the compression top dead center after a cylinder in which the cranking angle exceeds the compression top dead center for the first time after cranking start.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device for a hybrid vehicle. [Background technology]

[0002] After the engine automatically stops, it may be restarted by cranking. If reverse rotation of the engine is detected during this restart, there is a technology that prohibits ignition of fuel to prevent further reverse rotation (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-185444 Summary of the Invention [Problem to be solved by the invention]

[0004] Because the above-mentioned technologies do not prevent reverse engine rotation, restarting the engine when reverse rotation occurs takes time. Another possible approach to preventing reverse engine rotation is to rapidly increase the torque required to crank the engine. For example, in hybrid vehicles, the engine is sometimes cranked using a motor, which is a driving source for the vehicle. In this case, if the cranking torque is rapidly increased, the proportion of the cranking torque in the motor's output torque increases during motor-driven driving. This reduces the torque required for driving, potentially affecting drivability.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a control device for a hybrid vehicle that can quickly restart the engine while ensuring drivability. [Means for solving the problem]

[0006] The object of the present invention is to provide a control device for a hybrid vehicle that includes an engine having a plurality of cylinders, a motor provided in a power transmission path between the engine and wheels, and a clutch provided between the engine and the motor in the power transmission path, wherein the clutch is in a disengaged state and combustion is stopped. Ta When there is a request to restart the engine, the clutch is put into a slip state and the motor starts cranking the engine. When a restart request is made for the engine in which the clutch is released, combustion has stopped, and the engine is rotating by inertia at a predetermined rotation speed or less, or when a restart request is made for the engine in which the clutch is released, combustion has stopped, and rotation has stopped and the elapsed time since the engine stopped is less than a predetermined time, After the cranking starts, combustion begins in the cylinder whose crank angle is about to pass the compression top dead center, after which the cylinder whose crank angle is about to pass the compression top dead center begins combustion. when a restart request is made for the engine that is rotating by inertia at a speed higher than the predetermined speed with the clutch disengaged and combustion stopped, or when a restart request is made for the engine that is rotating by inertia at a speed higher than the predetermined speed with the clutch disengaged and the time that has elapsed since combustion stopped and rotation stopped is longer than the predetermined time, combustion starts from the cylinder whose crank angle is expected to exceed compression top dead center for the first time after cranking starts, and the predetermined speed is set to a maximum engine speed at which the engine may rotate in reverse if combustion starts from the cylinder whose crank angle is expected to reach compression top dead center for the first time after cranking starts, and the predetermined time is set to a time required for the internal pressure of all of the plurality of cylinders to return to atmospheric pressure after the engine rotation stops. This can be achieved by a control device for a hybrid vehicle. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a control device for a hybrid vehicle that can quickly restart the engine while ensuring drivability. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a hybrid vehicle. [Figure 2] FIG. 2 is a schematic diagram of the engine. [Figure 3] FIG. 3 is a timing chart showing an example of engine restart control. [Figure 4] FIG. 4 is a flowchart showing an example of engine restart control executed by the ECU. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Hybrid vehicle configuration] FIG. 1 is a schematic diagram of a hybrid vehicle 1. In the hybrid vehicle 1, a K0 clutch 14, a motor 15, a torque converter 18, and an automatic transmission 19 are provided in this order in a power transmission path from an engine 10 to wheels 13. The engine 10 and the motor 15 are mounted as a driving source for running the hybrid vehicle 1. The engine 10 is, for example, a V6 gasoline engine having cylinders #1 to #6, but is not limited to this. The engine 10 may be an in-line gasoline engine or a diesel engine as long as it has multiple cylinders. The K0 clutch 14, the motor 15, the torque converter 18, and the automatic transmission 19 are provided in a transmission unit 11. The transmission unit 11 and the left and right wheels 13 are drivingly connected via a differential 12.

[0010] The K0 clutch 14 is provided between the engine 10 and the motor 15 on the power transmission path. The K0 clutch 14 is switched between a released state, a slip state, and an engaged state depending on the supply of hydraulic pressure. Specifically, when the K0 clutch 14 is in the released state, the supply of hydraulic pressure switches it to a slip state or an engaged state, thereby connecting the power transmission between the engine 10 and the motor 15. Furthermore, when the hydraulic pressure supply is stopped, the K0 clutch 14 switches to a released state, thereby disconnecting the power transmission between the engine 10 and the motor 15. The slip state is a state in which the engagement element of the K0 clutch 14 on the engine 10 side and the engagement element on the motor 15 side are in sliding contact with each other with a predetermined difference in rotation speed. The engaged state is a state in which both engagement elements of the K0 clutch 14 are connected and the engine 10 and the motor 15 are at the same rotation speed. The released state is a state in which both engagement elements of the K0 clutch 14 are separated.

[0011] The motor 15 is connected to the battery 16 via an inverter 17. The motor 15 functions as a motor that generates driving force for the hybrid vehicle 1 in response to power supplied from the battery 16, and also functions as a generator that generates electric power to charge the battery 16 in response to power transmitted from the engine 10 and the wheels 13. The electric power exchanged between the motor 15 and the battery 16 is adjusted by the inverter 17.

[0012] The inverter 17 is controlled by the ECU 100, which will be described later, and converts the DC voltage from the battery 16 into an AC voltage, or converts the AC voltage from the motor 15 into a DC voltage. In the case of power running in which the motor 15 outputs torque, the inverter 17 converts the DC voltage from the battery 16 into an AC voltage and adjusts the power supplied to the motor 15. In the case of regenerative running in which the motor 15 generates power, the inverter 17 converts the AC voltage from the motor 15 into a DC voltage and adjusts the power supplied to the battery 16.

[0013] The torque converter 18 is a fluid coupling with a torque amplification function. The automatic transmission 19 is a stepped automatic transmission that changes the gear ratio in multiple stages by changing gear positions. The automatic transmission 19 is provided between the motor 15 and the wheels 13 on the power transmission path. The motor 15 and the automatic transmission 19 are connected via the torque converter 18. The torque converter 18 is provided with a lock-up clutch 20 that is supplied with hydraulic pressure and enters an engaged state, directly connecting the motor 15 and the automatic transmission 19.

[0014] The transmission unit 11 is further provided with an oil pump 21 and a hydraulic control mechanism 22. The hydraulic pressure generated by the oil pump 21 is supplied to the K0 clutch 14, the torque converter 18, the automatic transmission 19, and the lock-up clutch 20 via the hydraulic control mechanism 22. The hydraulic control mechanism 22 is provided with hydraulic circuits for each of the K0 clutch 14, the torque converter 18, the automatic transmission 19, and the lock-up clutch 20, as well as various hydraulic control valves for controlling the operating hydraulic pressures thereof.

[0015] The hybrid vehicle 1 is provided with an ECU (Electronic Control Unit) 100 as a control device for the hybrid vehicle. The ECU 100 is an electronic control unit that includes a processing circuit that performs various arithmetic processes related to vehicle driving control, and a memory that stores control programs and data. The ECU 100 is an example of a control device for a hybrid vehicle, and functionally realizes a cranking control unit and a combustion control unit, which will be described in detail later.

[0016] The ECU 100 controls the operation of the engine 10 and the motor 15. Specifically, the ECU 100 controls the throttle opening, ignition timing, and fuel injection amount of the engine 10 to control the rotation speed and torque of the engine 10. The ECU 100 controls the inverter 17 to adjust the amount of power exchanged between the motor 15 and the battery 16, thereby controlling the rotation speed and torque of the motor 15. The ECU 100 also controls the operation of the K0 clutch 14, the lock-up clutch 20, and the automatic transmission 19 through control of the hydraulic control mechanism 22.

[0017] The ECU 100 receives signals from an ignition switch 71, a crank angle sensor 72, a motor rotation speed sensor 73, and an air flow meter 74. The crank angle sensor 72 detects the rotation speed of the crankshaft of the engine 10. The motor rotation speed sensor 73 detects the rotation speed of the output shaft of the motor 15. The air flow meter 74 detects the amount of intake air into the engine 10.

[0018] The ECU 100 causes the hybrid vehicle 1 to run in either a motor mode or a hybrid mode. In the motor mode, the ECU 100 disengages the K0 clutch 14 and runs the vehicle using power from the motor 15. In the hybrid mode, the ECU 100 switches the K0 clutch 14 to an engaged state and runs the vehicle using power from at least the engine 10. The hybrid mode includes a mode in which the vehicle runs using power from the engine 10 alone, and a mode in which the motor 15 is powered and the vehicle runs using both the engine 10 and the motor 15 as power sources.

[0019] The driving mode is switched based on the vehicle's required driving force, which is calculated from the vehicle speed and accelerator pedal position, and the state of charge of the battery 16. For example, when the required driving force is relatively small and the SOC (State of Charge), which indicates the remaining charge level of the battery 16, is relatively high, the motor mode, in which the engine 10 is stopped, is selected to improve fuel economy. When the required driving force is relatively large or the SOC of the battery 16 is relatively low, the hybrid mode, in which at least the engine 10 is driven, is selected.

[0020] The ECU 100 executes intermittent operation control in hybrid mode or engine mode, automatically stopping the engine 10 when a predetermined stop condition is met, and restarting the automatically stopped engine 10 when a predetermined restart condition is met. For example, when the accelerator pedal position becomes zero in hybrid mode or engine mode, the ECU 10 automatically stops the engine 10, assuming that the automatic stop condition is met. Furthermore, when the accelerator pedal position becomes greater than zero, the ECU 10 automatically restarts the engine 10, assuming that the restart condition is met. When automatically stopping the engine 10, the ECU 100 disengages the K0 clutch 14 to stop fuel injection. When automatically restarting the engine 10, the ECU 100 cranks the engine 10 using the motor 15 via the K0 clutch 14 to start fuel injection and ignition, and then engages the K0 clutch 14.

[0021] [Engine outline] FIG. 2 is a schematic diagram of engine 10. Engine 10 has cylinder #1, piston 31, connecting rod 32, crankshaft 33, intake passage 35, intake valve 36, exhaust passage 37, and exhaust valve 38. FIG. 2 shows only cylinder #1 of the multiple cylinders #1 to #6 of engine 10. Combustion of an air-fuel mixture occurs in cylinder #1. Piston 31 is accommodated in cylinder #1 so as to be able to reciprocate, and is connected to crankshaft 33, which is the output shaft of engine 10, via connecting rod 32. Connecting rod 32 and crankshaft 33 convert the reciprocating motion of piston 31 into rotational motion of crankshaft 33.

[0022] The intake passage 35 is connected to an intake port 35p of cylinder #1 via an intake valve 36. The exhaust passage 37 is connected to an exhaust port 37p of cylinder #1 via an exhaust valve 38. The intake passage 35 is provided with the air flow meter 74 described above and a throttle valve 40 that adjusts the amount of intake air. The exhaust passage 37 is provided with a catalyst 43 for purifying exhaust gas.

[0023] Cylinder #1 is provided with an in-cylinder injection valve 41. The in-cylinder injection valve 41 injects fuel directly into cylinder #1. Note that in addition to or instead of the in-cylinder injection valve 41, a port injection valve that injects fuel toward the intake port may be provided. Each cylinder #1 is provided with an ignition device 42 that ignites, by spark discharge, an air-fuel mixture of intake air introduced through the intake passage 35 and fuel injected by the in-cylinder injection valve 41.

[0024] [Engine restart control] As described above, during execution of intermittent operation control, immediately after the accelerator opening becomes zero and the engine 10 automatically stops, the accelerator opening may increase again, requesting a restart of the engine 10. Furthermore, a request to restart the engine 10 may be made after the engine 10 has failed to start. At the time of such a restart request, the engine 10 may be rotating by inertia, even though combustion has stopped. In this case, cranking is initiated by the motor 15 via the K0 clutch 14 while the engine 10 is rotating by inertia, and the engine 10 is restarted.

[0025] When the engine 10 is restarted, torque in the forward rotation direction and torque in the reverse rotation direction act on the engine 10. The torque in the forward rotation direction is mainly due to the inertial torque during coasting rotation just before cranking starts, the cranking torque by the motor 15, and the combustion torque generated by the start of combustion. The inertial torque increases as the engine speed during coasting rotation increases. The cranking torque by the motor 15 also gradually increases from zero just before cranking starts.

[0026] The torque in the reverse rotation direction is mainly due to the repulsive force of the air compressed by the piston 31 inside the cylinder. This is because, even during inertial rotation before combustion starts, the reciprocating movement of the piston 31 and the opening and closing of the intake valve 36 and exhaust valve 38 repeatedly introduce, compress, and exhaust air into the cylinder. This repulsive force of the compressed air increases as the crank angle approaches compression top dead center from compression bottom dead center, and reaches a maximum at compression top dead center. Therefore, when restarting the engine 10, if the torque in the forward rotation direction is greater than the torque in the reverse rotation direction, reverse rotation of the engine 10 can be suppressed and the engine 10 can be restarted.

[0027] If combustion starts when the engine speed is low and the cranking torque is small during coasting, the torque in the reverse direction may be greater than the torque in the forward direction, potentially causing the engine 10 to rotate in reverse. Therefore, it may be possible to rapidly increase the cranking torque of the motor 15 immediately after cranking begins so that the torque in the forward direction is always greater than the torque in the reverse direction. However, when the hybrid vehicle 1 is running on the motor 15, the cranking torque accounts for a larger proportion of the output torque of the motor 15. This may result in a decrease in the torque required for running, potentially affecting drivability.

[0028] In this embodiment, the ECU 100 starts combustion in the cylinder whose crank angle is scheduled to exceed the compression top dead center after the cylinder whose crank angle exceeds the compression top dead center for the first time after cranking of the engine 10 starts. In other words, combustion is stopped in the cylinder whose crank angle exceeds the compression top dead center first after cranking starts, and combustion is started in the cylinder whose crank angle is scheduled to exceed the compression top dead center second. Even if the cranking torque is gradually increased after cranking starts, the cranking torque has increased sufficiently after the crank angle exceeds the compression top dead center for the first time after cranking starts. Therefore, reverse rotation of the engine 10 can be suppressed by starting combustion in the cylinder whose crank angle is scheduled to exceed the compression top dead center next. Note that because the engine 10 is a V6 gasoline engine, the crank angles at which the compression top dead center of each of cylinders #1 to #6 occurs are, for example, 0 degrees, 120 degrees, 240 degrees, 360 degrees, 480 degrees, and 600 degrees.

[0029] Figure 3 is a timing chart showing an example of engine start control. Figure 3 shows the engine speed [rpm], motor speed [rpm], the state of the K0 clutch 14, the elapsed crank angle [deg], and the combustion state of the engine 10. The elapsed crank angle is the crank angle elapsed since cranking of the engine 10 started. The motor speed is shown by a dashed line, and the others are shown by solid lines.

[0030] At time t0, the K0 clutch 14 is in a disengaged state and the vehicle is running using the motor 15, combustion has stopped in the engine 10 and the engine speed is gradually decreasing. If a restart request for the engine 10 is made when the engine speed is equal to or lower than a predetermined speed α, the K0 clutch 14 is switched from the disengaged state to the slip state at time t1, and cranking of the engine 10 is initiated. The predetermined speed α is set to the maximum engine speed at which the engine 10 may rotate in reverse if combustion first starts in the cylinder whose crank angle is at compression top dead center after cranking begins. The predetermined speed α is obtained in advance by experiment and stored in the memory of the ECU 100.

[0031] Combustion stops when the elapsed crank angle is equal to or less than a predetermined angle θ, and starts after time t2 when the elapsed crank angle exceeds the predetermined angle θ. Here, the predetermined angle θ is the crank angle from the crank angle at the start of cranking to the first compression top dead center. Therefore, the predetermined angle θ is a variable value that varies depending on the crank angle at the start of cranking. The predetermined angle θ is calculated by subtracting the crank angle at the start of cranking from the crank angle at which the compression top dead center first occurs after the start of cranking.

[0032] When combustion in the engine 10 begins, the engine speed increases to the motor speed, and at time t3, the K0 clutch 14 is switched from the slip state to the engaged state, thus restarting the engine 10.

[0033] [Engine restart control executed by ECU] 4 is a flowchart showing an example of engine restart control executed by the ECU 100. This control is repeatedly executed at predetermined intervals while the ignition is on. The ECU 100 determines whether or not there is a request to restart the engine 10 (step S1). If the answer is No in step S1, this control is terminated.

[0034] If the answer is Yes in step S1, the ECU 100 determines whether the engine speed is equal to or lower than a predetermined speed α (step S2). If the answer is No in step S2, that is, if the engine speed at the time of the request to restart the engine 10 is relatively high, the ECU 10 starts cranking the engine 10 (step S3) and starts combustion (step S4). This is because if the engine speed is higher than the predetermined speed α, the inertia torque in the forward rotation direction is still large, and there is little risk of reverse rotation even if combustion starts in the cylinder where the crank angle is at the compression top dead center for the first time after cranking starts.

[0035] If the answer is Yes in step S2, the ECU 100 determines whether the engine speed is greater than 0, in other words, whether the engine 10 is stopped (step S5). If the answer is No in step S5, i.e., if the engine 10 is stopped, the ECU 100 determines whether the rotation stop time is equal to or less than a predetermined time T (step S6). The predetermined time T is set to the time required for the in-cylinder pressure to return to atmospheric pressure after the rotation stops. If the answer is No in step S6, i.e., if the predetermined time T has passed since the rotation of the engine 10 stopped, the ECU 100 starts cranking the engine 10 (step S3) and starts combustion (step S4). Because the in-cylinder pressure has returned to atmospheric pressure after the predetermined time T has passed since the rotation stopped, the repulsive force of the compressed air in the cylinder whose crank angle is at the compression top dead center for the first time after cranking starts is weak, and there is little risk of reverse rotation even if combustion starts in this cylinder.

[0036] If the answer is Yes in step S5 or S6, the ECU 100 starts cranking the engine 10 by the motor 15 (step S7) and determines whether the elapsed crank angle is equal to or less than a predetermined angle θ (step S8). The processing in step S7 is an example of processing executed by a cranking control unit. If the answer is Yes in step S8, the ECU 100 executes the processing in step S8 again. If the answer is No in step S8, the ECU 100 starts combustion from the cylinder whose crank angle is next scheduled to be at compression top dead center after the crank angle exceeds the predetermined angle θ (step S4). The processing in steps S4 and S8 is an example of processing executed by a combustion control unit.

[0037] In this way, combustion is stopped in the cylinder where the crank angle passes the compression top dead center for the first time after cranking starts, and combustion is started in the cylinder where the crank angle is scheduled to pass the compression top dead center next. This prevents reverse rotation of the engine 10, enabling early restart. Furthermore, because the engine 10 can be restarted without a sudden increase in cranking torque, the engine 10 can be restarted without affecting drivability, even while the vehicle is running using the motor 15.

[0038] In the above embodiment, combustion is initiated in the cylinder whose crank angle exceeds the compression top dead center second after the start of cranking, but this is not limited to this. For example, combustion may be initiated in the cylinder whose crank angle exceeds the compression top dead center third or later after the start of cranking. This is suitable, for example, when the cranking torque generated by the motor 15 increases slowly and the cranking torque is insufficient even when the crank angle reaches the compression top dead center second after the start of cranking. However, combustion must be initiated before the engine speed reaches a level at which it can operate autonomously. Furthermore, from the viewpoint of quickly restarting the engine 10, it is preferable to initiate combustion as early as possible, as in the above embodiment.

[0039] In the above embodiment, combustion is stopped in the cylinder where the crank angle exceeds the compression top dead center for the first time after cranking starts when the engine speed is equal to or lower than a predetermined speed α. However, this is not limited to this. That is, combustion may always be stopped in the cylinder where the crank angle exceeds the compression top dead center for the first time after cranking starts, regardless of the engine speed during coasting. This is because the inertial torque in the forward rotation direction during coasting decreases quickly if the friction loss of the engine 10 is large. Therefore, even if the engine speed during coasting is high, starting combustion immediately after cranking may result in reverse rotation.

[0040] In the above embodiment, a hybrid vehicle is controlled by a single ECU 100, but this is not limited to this. The above-mentioned control may be performed by multiple ECUs, such as an engine ECU that controls the engine 10, a motor ECU that controls the motor 15, and a clutch ECU that controls the K0 clutch 14.

[0041] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0042] 10 Engine 14 K0 clutch 15 motor 100 ECU (control unit, cranking control unit, combustion start unit)

Claims

[Claim 1] A control device for a hybrid vehicle including an engine having a plurality of cylinders, a motor provided in a power transmission path between the engine and wheels, and a clutch provided between the engine and the motor in the power transmission path, When there is a request to restart the engine in which combustion has stopped while the clutch is in a disengaged state, the clutch is put into a slip state and cranking of the engine is started by the motor; When a restart request is made for the engine that is rotating by inertia at a predetermined rotation speed or less with combustion stopped while the clutch is in a released state, or when a restart request is made for the engine that has been in an released state with combustion stopped and rotation stopped for a predetermined time or less, combustion is started in the cylinder whose crank angle is expected to pass the compression top dead center after the cylinder whose crank angle has passed the compression top dead center for the first time since cranking started, When a restart request is made for the engine that is rotating by inertia at a rotation speed higher than the predetermined rotation speed with combustion stopped while the clutch is in a released state, or when a restart request is made for the engine that has been rotating by inertia at a rotation speed higher than the predetermined rotation speed with the clutch in a released state for a period longer than the predetermined time since combustion stopped, combustion is started in the cylinder where the crank angle is expected to exceed the compression top dead center for the first time after cranking starts, the predetermined rotation speed is set to a maximum value of the engine rotation speed at which the engine may rotate in reverse when combustion starts in a cylinder whose crank angle is first at compression top dead center after cranking starts, A control device for a hybrid vehicle, wherein the predetermined time is set to a time required for the internal pressure of all of the plurality of cylinders to return to atmospheric pressure after the rotation of the engine has stopped.

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