Control device for hybrid vehicle

Abstract

The present invention relates to a control device for a hybrid vehicle. The control device for a hybrid vehicle includes an internal combustion engine, a motor, and a clutch disposed between the internal combustion engine and the motor. The control device includes a first starting control unit that starts the internal combustion engine by cranking the motor, a second starting control unit that starts the internal combustion engine without cranking the motor, and a setting unit that sets a threshold value for the rotational speed of the internal combustion engine based on the vehicle speed of the hybrid vehicle. The first starting control unit starts the internal combustion engine when the rotational speed of the internal combustion engine is less than the threshold value. The second starting control unit starts the internal combustion engine when the rotational speed of the internal combustion engine is equal to or greater than the threshold value.

Description

Technical Field

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

[0002] Some hybrid vehicles are equipped with an internal combustion engine (engine), a motor in the power transmission path between the engine and the wheels, and a clutch in the power transmission path between the engine and the motor. When an engine start request is made, the clutch slips, and the engine is cranked by the motor. Then, the clutch is engaged, and the engine is started (for example, Japanese Unexamined Patent Application Publication No. 2020-111276 (JP 2020-111276 A)). Summary of the Invention

[0003] As described above, an internal combustion engine can be started by cranking. An internal combustion engine can also be started by supplying and burning fuel without cranking. Air is introduced into the internal combustion engine for combustion. However, before air is introduced, there is a possibility that the rotational speed of the internal combustion engine will decrease and the engine will stall (engine stall). Therefore, the present invention provides a control device for a hybrid vehicle that is capable of preventing engine stall and starting the internal combustion engine.

[0004] One aspect of the present disclosure is a control device for a hybrid vehicle, the hybrid vehicle including an internal combustion engine, a motor, and a clutch disposed between the internal combustion engine and the motor. The control device includes: a first starting control unit configured to start the internal combustion engine by causing the motor to perform a crank start; a second starting control unit configured to start the internal combustion engine without causing the motor to perform a crank start; and a setting unit configured to set a threshold value for the rotational speed of the internal combustion engine according to the vehicle speed of the hybrid vehicle. The first starting control unit is configured to start the internal combustion engine when the rotational speed of the internal combustion engine is less than the threshold value. The second starting control unit is configured to start the internal combustion engine when the rotational speed of the internal combustion engine is equal to or higher than the threshold value.

[0005] In this aspect, the control device may include a throttle control unit configured to control a throttle of the internal combustion engine. The throttle control unit may open the throttle when the vehicle speed of the hybrid vehicle is equal to or higher than a predetermined speed. When the vehicle speed of the hybrid vehicle is equal to or higher than the predetermined speed, the setting unit may set the threshold value to a first value. When the vehicle speed of the hybrid vehicle is lower than the predetermined speed, the setting unit may set the threshold value to a second value that is greater than the first value.

[0006] A control device for a hybrid vehicle can be provided that can prevent engine stall and start an internal combustion engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like symbols represent like elements, and in which:

[0008] Figure 1 is a schematic diagram illustrating a hybrid vehicle;

[0009] Figure 2 is a diagram of the approximate configuration of the engine; and

[0010] Figure 3 is a flowchart illustrating processing executed by the ECU. DETAILED DESCRIPTION

[0011] hybrid vehicles

[0012] Figure 1 1 is a schematic diagram illustrating a hybrid vehicle 1. The hybrid vehicle 1 is equipped with an engine 10 (internal combustion engine) and a motor 15 as a driving source. The hybrid vehicle 1 is provided with a K0 clutch 14, a motor 15, a torque converter 18 and an automatic transmission 19 in the following order along the power transmission path from the engine 10 to the wheels 13. The engine 10 can be, for example, a V6 engine having six cylinders #1 to #6. The engine 10 can be, for example, a V-type engine or an inline engine. The engine 10 can be a gasoline engine or a diesel engine. The number of cylinders of the engine 10 can be multiple, for example, four or six, or can be one. The K0 clutch 14, the motor 15, the torque converter 18 and the automatic transmission 19 are provided in a speed change unit 11. The speed change unit 11 and the left and right wheels 13 are drivingly connected via a differential gear 12.

[0013] The K0 clutch 14 is positioned between the engine 10 and the motor 15 on the same power transmission path. The state of the K0 clutch 14 switches to one of a released state, a slipping state, and an engaged state depending on the supply of hydraulic pressure. Specifically, when the K0 clutch 14 is in the released state, the hydraulic pressure causes it to slip or engage, and power transmission between the engine 10 and the motor 15 is connected. Furthermore, when the hydraulic pressure stops, the K0 clutch 14 switches to the released state, disconnecting power transmission between the engine 10 and the motor 15. The slipping state is a state in which the engaging element on the engine 10 side of the K0 clutch 14 and the engaging element on the motor 15 side are in sliding contact with each other at a predetermined rotational speed difference. The engaged state is a state in which the two engaging elements of the K0 clutch 14 are connected and the engine 10 and the motor 15 have the same rotational speed. The released state is a state in which the two engaging elements of the K0 clutch 14 are separated from each other.

[0014] The motor 15 is connected to the battery 16 via the inverter 17. The motor 15 functions as a motor that generates driving force for the vehicle in response to electric power supplied from the battery 16, and also functions as a generator that generates electric power for charging the battery 16 in response to power transmission from the engine 10 and the wheels 13. The electric power transferred between the motor 15 and the battery 16 is regulated by the inverter 17.

[0015] The inverter 17 is controlled by the ECU 50 described below, and the inverter 17 either 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 operation in which the motor 15 outputs torque, the inverter 17 converts the DC voltage of the battery 16 into an AC voltage to adjust the power supplied to the motor 15. In the case of regenerative operation in which the motor 15 generates power, the inverter 17 converts the AC voltage from the motor 15 into a DC voltage to adjust the power supplied to the battery 16.

[0016] The torque converter 18 is a fluid coupling with a torque-amplifying function. The automatic transmission 19 is a stepped automatic transmission that switches gear ratios in multiple steps by switching gear stages. The automatic transmission 19 is provided between the motor 15 and the wheels 13 in the power transmission path. The motor 15 and the automatic transmission 19 are connected via the torque converter 18. The torque converter 18 is equipped with a lockup clutch 20, which receives hydraulic pressure and, when engaged, directly connects the motor 15 and the automatic transmission 19.

[0017] The speed change 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, respectively, via the hydraulic control mechanism 22. The hydraulic control mechanism 22 is provided with a hydraulic circuit for each of the K0 clutch 14, the torque converter 18, the automatic transmission 19, and the lock-up clutch 20, and various hydraulic control valves for controlling their hydraulic pressures.

[0018] Hybrid vehicle 1 is equipped with an electronic control unit (ECU) 50 as a control device. ECU 50 is an electronic control unit that includes an arithmetic processing circuit that performs various arithmetic processes related to vehicle travel control, and a memory that stores programs and data used for control. ECU 50 is an example of a control device for a hybrid vehicle. ECU 50 functionally serves as a first and second starting control unit for starting engine 10, a setting unit for setting a threshold value for the rotational speed of engine 10, and a throttle control unit for controlling the opening of throttle valve 40.

[0019] The ECU 50 controls the driving of the engine 10 and the motor 15. For example, the ECU 50 controls the torque and rotational speed of the engine 10 by controlling the throttle opening, ignition timing, and fuel injection amount of the engine 10. Furthermore, the ECU 50 controls the driving of the K0 clutch 14, the lockup clutch 20, and the automatic transmission 19 by controlling the hydraulic control mechanism 22. The ECU 50 controls the hydraulic pressure applied to the K0 clutch 14 by using the hydraulic control mechanism 22, and changes the state of the K0 clutch 14 to control the cranking torque transmitted from the motor 15 to the engine 10.

[0020] The ECU 50 controls the rotational speed and torque of the motor 15 by controlling the inverter 17 to adjust the amount of electric power exchanged between the motor 15 and the battery 16. Furthermore, as will be described in detail below, the ECU 50 controls the electric power supplied from the motor 15 to the battery 16 via the inverter 17 so that the motor braking torque during regenerative operation becomes a target value.

[0021] Signals from an ignition switch 71, a crank angle sensor 72, a motor rotational speed sensor 73, an air flow meter 74, an accelerator opening sensor 75, and a vehicle speed sensor 76 are input to the ECU 50. The crank angle sensor 72 detects the rotational speed of the crankshaft 33 of the engine 10. The motor rotational speed sensor 73 detects the rotational speed of the output shaft of the motor 15. The air flow meter 74 detects the amount of intake air entering the engine 10. The accelerator opening sensor 75 detects the opening of the accelerator pedal, which is the amount by which the driver has depressed the accelerator pedal. The vehicle speed sensor 76 detects the speed of the hybrid vehicle 1 (vehicle speed).

[0022] The ECU 50 drives the hybrid vehicle in either motor mode or hybrid mode. In motor mode, the ECU 50 releases the K0 clutch 14 and drives the hybrid vehicle using the power of the motor 15. In hybrid mode, the ECU 50 engages the K0 clutch 14 and drives the hybrid vehicle using at least the power of the engine 10. The hybrid mode includes a mode in which the hybrid vehicle travels using only the power of the engine 10, and a mode in which the motor 15 is driven by power operation and the hybrid vehicle travels using both the engine 10 and the motor 15 as power sources.

[0023] The travel mode is switched based on the required driving force of the vehicle obtained from the vehicle speed and the accelerator opening, the state of charge of the battery 16, and the like. For example, when the required driving force is relatively low and the state of charge (SOC) indicating the remaining amount of power in the battery 16 is relatively high, the motor mode in which the engine 10 is stopped is selected to improve fuel efficiency. When the required driving force is relatively high or the SOC of the battery 16 is relatively low, the hybrid mode in which at least the engine 10 is driven is selected.

[0024] In hybrid mode, the ECU 50 performs intermittent operation control to automatically stop the engine 10 when predetermined stop conditions are met and restart the automatically stopped engine 10 when predetermined restart conditions are met. For example, when the accelerator opening reaches zero in hybrid mode, the ECU 50 deems the automatic stop condition satisfied and automatically stops the engine 10. Furthermore, when the accelerator opening exceeds zero, the ECU 50 deems the restart condition satisfied and automatically restarts the engine 10. When the engine 10 automatically stops, the ECU 50 releases the K0 clutch 14 to stop fuel injection. When the engine 10 automatically restarts, the ECU 50 cranks the engine 10 via the K0 clutch 14 and the motor 15 to initiate fuel injection and ignition, and then engages the K0 clutch 14. Furthermore, the ECU 50 can also start the engine 10 without performing cranking. Fuel is supplied to the cylinders of the engine 10, and a mixture of fuel and air is combusted to start the engine 10.

[0025] During the period of inertial rotation after combustion stops in the engine 10, the ECU 50 temporarily increases the opening of the throttle valve 40 and then decreases the opening (stop position control). By opening the throttle valve 40 during the inertial rotation, air is introduced into the cylinder. By increasing the compression torque, the stop position of the engine 10 is set to the desired position. Stop position control can reduce the cranking torque required of the motor 15 when the engine 10 is restarted.

[0026] engine

[0027] Figure 2 1 is a schematic diagram of the configuration of engine 10, illustrating cylinder #1, one of the multiple cylinders of engine 10. Engine 10 includes a piston 31, a connecting rod 32, a crankshaft 33, an intake passage 35, an intake valve 36, an exhaust passage 37, and an exhaust valve 38. An air-fuel mixture is combusted within the cylinder. Piston 31 is housed in cylinder #1, reciprocating therein, and is connected to crankshaft 33, 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.

[0028] Intake passage 35 is connected to intake port 35p of cylinder #1 via intake valve 36. Exhaust passage 37 is connected to exhaust port 37p of cylinder #1 via exhaust valve 38. Intake passage 35 is provided with air flow meter 74 described above and throttle valve 40 for adjusting the amount of intake air. Exhaust passage 37 is provided with catalyst 43 to purify exhaust gas.

[0029] Cylinder #1 is provided with an in-cylinder injection valve 41. In-cylinder injection valve 41 injects fuel directly into cylinder #1. In addition to or in place of in-cylinder injection valve 41, a port injection valve that injects fuel into an intake port may be provided. Cylinder #1 is provided with an ignition device 42 that ignites a mixture of intake air introduced through intake passage 35 and fuel injected by in-cylinder injection valve 41 through spark discharge. The other cylinders of engine 10 have similar configurations.

[0030] The ECU 50 starts the engine 10 by cranking, or starts the engine 10 without cranking. When cranking is not performed, the engine 10 is started by supplying fuel to the engine 10 and burning the fuel. In order to burn the fuel, it is important that air is introduced into the cylinders. Introducing air after the engine 10 stops takes time. Even during this period, the rotational speed continues to decrease.

[0031] When the engine is requested to start, if the rotational speed is low, engine 10 may stall due to the reduced rotational speed. To prevent engine stalling, cranking is performed and engine 10 is started. On the other hand, when the rotational speed is high, the time until engine 10 stalls becomes longer. At this time, air can be introduced, and engine 10 can be started without cranking.

[0032] Figure 31 is a flowchart illustrating the processing executed by ECU 50. Engine 10 is in a fuel cut (F / C) state. ECU 50 determines whether engine 10's rotational speed Ne is less than a predetermined value Neth1 (step S10). If the determination is negative (No), ECU 50 returns engine 10 from fuel cut (F / C return, step S12). After step S12, the processing ends.

[0033] If the answer is yes in step S10, ECU 50 determines whether the vehicle speed V of hybrid vehicle 1 is equal to or greater than a predetermined value Vth (step S14). If the answer is no, ECU 50 sets the threshold value Neth2 for the rotational speed to Neth2A (the second value) (step S16). Stop position control, described below, is not performed. If the answer is yes in step S14, ECU 50 sets the threshold value Neth2 to Neth2B (the first value) (step S18). Neth2B is smaller than Neth2A. ECU 50 also executes starting position control and temporarily opens throttle valve 40 (step S19).

[0034] After step S16 or S19, the ECU 50 determines whether the rotational speed Ne is equal to or higher than the threshold value Neth2 (step S20). If the determination is negative, the ECU 50 starts the engine 10 by cranking (step S22). If the determination is positive, the ECU 50 starts the engine 10 without cranking (step S24). After step S22 or S24, the process ends.

[0035] According to this embodiment, ECU 50 starts engine 10. Air is introduced into engine 10 to start engine 10. While air is being introduced into engine 10, the rotational speed decreases. ECU 50 sets a threshold value, Neth2, based on the vehicle speed. When rotational speed Ne is less than Neth2, ECU 50 starts engine 10 by cranking (step S22). On the other hand, when rotational speed Ne is equal to or greater than Neth2, ECU 50 starts engine 10 without cranking. When rotational speed Ne is as high as or greater than Neth2, engine stall is less likely to occur while air is being introduced. Therefore, engine stall can be prevented and engine 10 can be started.

[0036] When the vehicle speed V is less than the predetermined speed Vth, the ECU 50 sets the threshold value Neth2 to Neth2A (step S16). When the rotational speed Ne is equal to or greater than Neth2A, the ECU 50 starts the engine 10 without cranking. Due to the high rotational speed, engine stall is less likely to occur before a sufficient amount of air is introduced for combustion. Therefore, the engine 10 can be started without cranking. When the rotational speed Ne is less than Neth2A, the ECU 50 performs cranking and starts the engine 10. Cranking can prevent engine stall.

[0037] When vehicle speed V is equal to or greater than Vth, ECU 50 opens throttle valve 40 (step S19), allowing air to be introduced into engine 10 before the start request. This allows for a sufficient amount of air for combustion to be quickly secured. In this case, ECU 50 sets threshold value Neth2 to Neth2B, which is less than Neth2A. Even when threshold value Neth2B is set to less than Neth2A, the time required for air to be introduced is short, making engine stall less likely. This prevents engine stall and allows engine 10 to be started without cranking (step S24). When rotational speed Ne decreases to, for example, less than Neth2B, cranking can be performed to start engine 10 (step S22).

[0038] In the example described above, the hybrid vehicle 1 is controlled by a single ECU 50. The embodiment is not limited thereto, and the control described above may be performed by a plurality of ECUs such as an engine ECU for controlling the engine 10, a motor ECU for controlling the motor 15, and a clutch ECU for controlling the K0 clutch 14.

[0039] The preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to this specific embodiment, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

Claims

1. A control device for a hybrid vehicle, the hybrid vehicle comprising an internal combustion engine, a motor, and a clutch disposed between the internal combustion engine and the motor, the control device comprising: a first starting control unit configured to start the internal combustion engine by causing the motor to perform cranking; a second starting control unit configured to start the internal combustion engine without causing the motor to perform cranking; and a setting unit configured to set a threshold value for the rotational speed of the internal combustion engine according to a vehicle speed of the hybrid vehicle, wherein: The first starting control unit is configured to start the internal combustion engine when the rotation speed of the internal combustion engine is less than the threshold value; and The second starting control unit is configured to start the internal combustion engine when the rotation speed of the internal combustion engine is equal to or higher than the threshold value, And the control device further includes a throttle control unit, which is configured to control a throttle of the internal combustion engine, wherein: the throttle control unit being configured to open the throttle valve when a vehicle speed of the hybrid vehicle is equal to or higher than a predetermined speed; The setting unit is configured to set the threshold value to a first value when a vehicle speed of the hybrid vehicle is equal to or higher than the predetermined speed; and The setting unit is configured to set the threshold value to a second value that is greater than the first value when a vehicle speed of the hybrid vehicle is less than the predetermined speed.

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