Hybrid vehicle regenerative braking system

Abstract

If a travel battery cannot be charged with electricity regenerated by a travel motor, this hybrid vehicle regenerative braking system causes an engine to rotate by driving an electric generator using electricity regenerated by the travel motor. The hybrid vehicle regenerative braking system comprises: an oil cooling circuit including, in the path thereof, the travel motor and / or the electric generator; an electric oil pump that circulates cooling oil that fills the oil cooling circuit; and a control device that controls the output of the electric oil pump. The control device increases the discharge flow rate of the oil pump if the travel battery cannot be charged with electric power regenerated by the travel motor.

Description

Regenerative braking system for hybrid vehicles

[0001] The present disclosure relates to regenerative braking systems for hybrid vehicles.

[0002] Regenerative braking systems for hybrid vehicles are widely known, including a traction motor that drives drive wheels while regenerating the kinetic energy of the drive wheels into electric power, a generator driven by the engine, and a traction battery that supplies electric power to the traction motor while charging the electric power generated by the generator and the electric power regenerated by the traction motor (see, for example, Patent Documents 1 and 2). In such regenerative braking systems for hybrid vehicles, when the electric power regenerated by the traction motor cannot be used to charge the traction battery, the generator is driven by the electric power regenerated by the traction motor to rotate the engine (hereinafter, rotating the engine by driving the generator with the electric power regenerated by the traction motor will be referred to as "motoring").

[0003] Japanese Patent No. 5510116 Japanese Patent No. 6500368 Japanese Patent Application Laid-Open No. 2021-54331

[0004] However, if the power regenerated by the traction motor cannot be used to charge the traction battery and the amount of power regenerated by the traction motor is large, the engine speed must be increased due to motoring, and the noise generated by the engine also increases.

[0005] However, hybrid vehicles are running as EVs using only a traction motor as a power source, and even when the engine is rotating due to motoring, it is necessary to suppress noise generated by the engine so that it does not become too loud.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide a regenerative braking system for a hybrid vehicle that can suppress engine noise even when the driving battery cannot be charged and the amount of power regenerated by the driving battery is large.

[0007] (1) In at least one embodiment of the present invention, a regenerative braking system for a hybrid vehicle includes a traction motor that drives drive wheels while regenerating kinetic energy from the drive wheels, a generator driven by an engine, and a traction battery that supplies electricity to the traction motor while charging the electricity generated by the generator and the electricity regenerated by the traction motor. When the electricity regenerated by the traction motor cannot be charged to the traction battery, the generator is driven by the electricity regenerated by the traction motor to rotate the engine. The regenerative braking system for a hybrid vehicle includes an oil cooling circuit that includes at least one of the traction motor or the generator in its path, an electric oil pump that circulates cooling oil filled in the oil cooling circuit, and a control device that controls the output of the electric oil pump. When the electricity regenerated by the traction motor cannot be charged to the traction battery, the control device increases the discharge flow rate of the electric oil pump.

[0008] According to the configuration (1) above, when the electric power regenerated by the traction motor cannot charge the traction battery, the discharge flow rate of the electric oil pump is increased, which reduces at least one of the regenerative efficiency of the traction motor and the rotational efficiency of the generator. This increases the power consumption of at least one of the traction motor and the generator, which suppresses the increase in engine speed due to motoring, and also suppresses engine noise.

[0009] Incidentally, Patent Document 3 discloses that when the power generated by regenerative operation is greater than the power consumed by motoring operation, the rotation speed of the water pump is increased. However, the water pump is provided in the cooling system that circulates coolant to the power control unit, and increasing the discharge flow rate of the water pump does not reduce the rotational efficiency of the driving motor or the generator.

[0010] (2) In some embodiments, in the configuration of (1) above, the oil cooling circuit includes at least a traction motor in its path, the drive shaft of the traction motor has a flow path arranged along its central axis, and the cooling oil passes through the flow path.

[0011] According to the above configuration (2), the cooling oil passes through a flow path provided along the central axis of the drive shaft of the traveling motor, so that the traveling motor can be cooled effectively.

[0012] (3) In some embodiments, in the configuration of (1) above, the oil cooling circuit includes both the traction motor and the generator in the path.

[0013] According to the above (3), since the oil cooling circuit includes both the traction motor and the generator in its path, when the power regenerated by the traction motor cannot charge the traction battery, both the regenerative efficiency of the traction motor and the rotational efficiency of the generator decrease. This further increases power consumption, further suppresses the increase in engine speed due to motoring, and further suppresses engine noise.

[0014] According to at least one embodiment of the present invention, an increase in engine speed can be suppressed, and therefore noise generated by the engine can be suppressed from increasing.

[0015] Fig. 1 is a diagram schematically showing the configuration of a hybrid vehicle according to a first embodiment. Fig. 2 is a diagram schematically showing a regenerative braking system of the hybrid vehicle shown in Fig. 1. Fig. 3 is a diagram showing the relationship between the depression amount of the brake pedal (brake pedal stroke) and the deceleration of the hybrid vehicle. Fig. 4 is a diagram schematically showing an electric circuit constituting the regenerative braking system of the hybrid vehicle shown in Fig. 2. Fig. 5 is a diagram schematically showing the configuration of a cooling circuit that cools at least one of the traction motor or the generator shown in Fig. 2. Fig. 6 is a cross-sectional view showing a transverse section of a drive shaft of a traction motor according to a second embodiment.

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative positions, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0017] [Embodiment 1] Fig. 1 is a diagram schematically showing the configuration of a hybrid vehicle according to embodiment 1. Fig. 2 is a diagram schematically showing a regenerative braking system of the hybrid vehicle shown in Fig. 1. Fig. 3 is a diagram showing the relationship between the depression amount of the brake pedal (brake pedal stroke) and the deceleration of the hybrid vehicle.

[0018] As shown in FIG. 1 , a hybrid vehicle 1 according to the first embodiment is powered by an engine 10 and traction motors 12, 14. In addition to the engine 10 and the traction motors 12, 14, the hybrid vehicle 1 also includes a generator 16 driven by the engine 10 and a traction battery 18 that charges with electricity generated by the generator 16. The hybrid vehicle 1 can be operated in one of three modes: an EV driving mode in which the traction motors 12, 14 drive drive wheels 20, 22 using electricity supplied from the traction battery 18; a series driving mode in which the traction motors 12, 14 drive drive wheels 20, 22 using electricity supplied from the generator 16; or a parallel driving mode in which the engine 10 drives drive wheels 20. The hybrid vehicle 1 shown in FIG. 1 is a four-wheel drive hybrid vehicle, but is not limited thereto and may be a two-wheel drive hybrid vehicle. The hybrid vehicle 1 may also be a plug-in hybrid vehicle that can be externally charged by an external power source or externally powered by a battery.

[0019] 2, in the hybrid vehicle 1 according to the first embodiment, a clutch 24 is provided between the engine 10 and the drive wheels 20. A generator 16 is provided between the engine 10 and the clutch 24, and a traction motor 12 is provided between the drive wheels 20 and the clutch 24. As a result, when either the EV drive mode or the series drive mode is selected, the clutch 24 is disconnected, and when the parallel drive mode is selected, the clutch 24 is connected.

[0020] When the hybrid vehicle 1 decelerates, the traction motors 12, 14 regenerate kinetic energy of the drive wheels 20, 22, and the kinetic energy (electric power) is charged to the traction battery 18. In the hybrid vehicle 1 according to the first embodiment, the deceleration of the hybrid vehicle 1 corresponds to the amount of depression of the brake pedal (hereinafter referred to as the "brake pedal stroke"). As shown in FIG. 3 , the deceleration of the hybrid vehicle 1 is classified into, for example, an engine brake regeneration region A1, a pedal regeneration region A2, and a mechanical brake deceleration region A3. The engine brake regeneration region A1 is a regeneration region in which deceleration occurs similar to engine braking. For example, the engine brake regeneration region A1 is entered by releasing the accelerator pedal, and a braking force similar to that of engine braking is applied to the hybrid vehicle 1. The pedal regeneration region A2 is a regeneration region in which deceleration occurs when the brake pedal is lightly depressed. For example, the pedal regeneration region A2 is entered by lightly depressing the brake pedal, and a braking force corresponding to the brake pedal stroke is applied to the hybrid vehicle 1. The mechanical brake deceleration region A3 is a region in which the vehicle slows down due to the mechanical brakes (disc brakes or drum brakes) when the brake pedal is pressed hard. For example, when the brake pedal is pressed hard, the vehicle enters the mechanical brake deceleration region A3, and a braking force corresponding to the brake pedal stroke acts on the hybrid vehicle 1.

[0021] However, when the charging rate (SOC (State of Charge)) of the traction battery reaches or exceeds a predetermined threshold (fully charged), charging of the traction battery 18 is restricted, and even if the traction motor 12 regenerates kinetic energy of the drive wheels 20 when the hybrid vehicle 1 decelerates, the kinetic energy (electric power) cannot be charged to the traction battery 18. When kinetic energy (electric power) cannot be charged to the traction battery 18 in this way, the hybrid vehicle 1 cannot perform regenerative braking even if the driver takes his / her foot off the accelerator pedal or lightly presses the brake pedal. As a result, braking force is only applied when the brake pedal is pressed hard.

[0022] In the regenerative braking system of the hybrid vehicle according to the first embodiment, when the kinetic energy (electric power) regenerated by the traction motors 12, 14 cannot be used to charge the traction battery 18, the generator 16 is driven by the kinetic energy (electric power) regenerated by the traction motors 12, 14, thereby motoring the engine 10. In the hybrid vehicle 1 according to the first embodiment, when the kinetic energy regenerated by the traction motors 12, 14 is large, the rotation speed of the engine 10 rotated by the generator 16 also increases.

[0023] Fig. 4 is a diagram schematically showing the configuration of a cooling circuit including at least one of the traction motor and the generator shown in Fig. 2. Fig. 5 is a diagram schematically showing an electric circuit constituting the regenerative braking system of the hybrid vehicle shown in Fig. 2.

[0024] As shown in FIG. 4 , the regenerative braking system for the hybrid vehicle according to the first embodiment includes an oil cooling circuit 26 including at least one of the traction motor 12 and the generator 16 in its path, an electric oil pump (EOP) 28 that circulates cooling oil filled in the oil cooling circuit 26, and an electronic control unit (ECU) 30 that controls the output of the electric oil pump 28. The oil cooling circuit 26 is provided with an oil cooler 32, and the cooling oil is cooled by heat exchange between the cooling oil flowing through the oil cooler 32 and the outside air. While FIG. 4 shows the oil cooling circuit 26 including both the traction motor 12 and the generator 16 in its path, the oil cooling circuit 26 does not necessarily have to include both of the traction motor 12 and the generator 16 in its path as long as it includes at least one of the traction motor 12 and the generator 16. The electric oil pump 28 is controlled, for example, by pulse width modulation (PWM) control, but is not limited to this.

[0025] When the kinetic energy (electric power) regenerated by the traction motors 12, 14 cannot be used to charge the traction battery 18, the control device 30 increases the discharge flow rate (discharge flow rate per hour) of the electric oil pump 28. This increases the pressure loss of the oil flowing through the oil cooling circuit 26 and reduces the efficiency of at least one of the traction motor 12 or the generator 16, resulting in increased power consumption and allowing the rotation speed of the engine 10 to be reduced when motoring.

[0026] The regenerative braking system for the hybrid vehicle according to the first embodiment includes an inverter 34 that controls the traction motor 12, a coolant cooling circuit 36 ​​that includes the inverter 34 in its path, and an electric water pump (EWP) 38 that circulates the coolant filled in the coolant cooling circuit 36. A radiator 40 is provided in the coolant cooling circuit 36, and the coolant is cooled by heat exchange between the coolant flowing through the radiator 40 and the outside air. The output of the electric water pump 38 is controlled by the control device 30. The electric water pump 38 is controlled, for example, by pulse width modulation (PWM) control, but is not limited to this.

[0027] 5 , in the regenerative braking system of the hybrid system according to the first embodiment, the traction motors 12, 14, the generator 16, the traction battery 18, and the DCDC converter 42 are connected in parallel, and the DCDC converter 42 is connected to the electric oil pump 28 and the electric water pump 38. When the kinetic energy (electricity) regenerated by the traction motors 12, 14 cannot be used to charge the traction battery 18, the kinetic energy (electricity) regenerated by the traction motors 12, 14 is supplied to the DCDC converter 42 and the generator 16, and the electricity supplied to the DCDC converter 42 is supplied to the electric oil pump 28 and the electric water pump 38.

[0028] As shown in Figure 5, if the power received by the drive battery is 0, the kinetic energy (electric power) regenerated by the drive motors 12 and 14 is 10, and the power consumption of the DCDC converter is 2, the power consumption of the generator 16 will be 8 (10 - 2 = 8). Here, if the discharge flow rate of the electric oil pump 28 is increased, the pressure loss of the oil flowing through the oil cooling circuit 26 will increase. As a result, if the efficiency of the drive motor 12 deteriorates, the kinetic energy (electric power) regenerated by the drive motor 12 will decrease from 10 to 9, and the power consumption of the generator will become 7 (9 - 2 = 7). Furthermore, if the efficiency of the generator deteriorates, the power consumption of the generator will increase, and the power consumption of the generator will become 9 (8 + 1 = 9).

[0029] According to the regenerative braking system for a hybrid vehicle according to the first embodiment, when the kinetic energy (electric power) regenerated by the traction motors 12, 14 cannot be used to charge the traction battery 18, the discharge flow rate of the electric oil pump 28 is increased, thereby reducing at least one of the regenerative efficiency of the traction motor 12 and the rotational efficiency of the generator 16. This increases the power consumption of at least one of the traction motor 12 and the generator 16, suppressing an increase in the rotational speed of the engine 10 due to motoring, and also suppressing noise generated by the engine 10.

[0030] If the oil cooling circuit 26 includes both the traction motor 12 and the generator 16 in its path, and the kinetic energy (electric power) regenerated by the traction motors 12, 14 cannot charge the traction battery 18, both the regeneration efficiency of the traction motor 12 and the rotational efficiency of the generator 16 will decrease. This increases the power consumption of both the traction motor 12 and the generator 16, further suppressing the increase in engine speed due to motoring, and further suppressing noise generated by the engine 10.

[0031] Furthermore, when the kinetic energy (electric power) regenerated by the drive motors 12, 14 cannot be used to charge the drive battery 18, the discharge flow rate of the electric oil pump 28 is increased, which increases the power consumption of the electric oil pump 28. This makes it possible to suppress an increase in the rotation speed of the engine 10 due to motoring, which also makes it possible to suppress noise generated by the engine 10 from becoming louder.

[0032] [Embodiment 2] Fig. 6 is a cross-sectional view showing a cross section of a drive shaft of a traction motor according to embodiment 2. The regenerative braking system for a hybrid vehicle according to embodiment 2 is the same as the regenerative braking system for a hybrid vehicle according to embodiment 1, except for the points described below.

[0033] In the regenerative braking system for a hybrid vehicle according to the second embodiment, the oil cooling circuit 26 includes at least the traction motor 12 in its path, the drive shaft 44 of the traction motor 12 has a flow path 46 along the central axis O, and the cooling oil Oil passes through the flow path 46. As shown in Fig. 6 , the drive shaft 44 of the traction motor 12 is a circular pipe having an annular cross section, and the pressure loss ΔP due to friction when the oil (fluid) flows through the flow path 46 (circular pipe) can be expressed by the following Equation 1 (the Darcy-Weisbach equation):

[0034] λ: Pipe friction coefficient d: Pipe diameter (m) l: Pipe length (m) ρ: Fluid density (kg / m ３ ) v: Fluid flow velocity (m / s)

[0035] Increasing the discharge flow rate of the electric oil pump 28 increases the pressure loss ΔP due to the following three factors: (1) As the discharge flow rate of the cooling oil increases, the cooling oil is cooled, the kinetic viscosity of the cooling oil increases, and the pipe friction coefficient λ increases (see Equation 2).

[0036] v: kinematic viscosity (m ２ / s)

[0037] (2) The cooling oil is cooled by the increase in the discharge flow rate of the cooling oil, and the density ρ of the cooling oil increases. (3) The flow rate (flow velocity) of the cooling oil increases (see Equation 3).

[0038] Q: Flow rate (l / min)

[0039] According to the regenerative braking system of the hybrid vehicle of embodiment 2, the cooling oil passes through a flow path 46 arranged along the central axis O of the drive shaft 44 of the traction motor 12, thereby effectively cooling the traction motor 12.

[0040] REFERENCE SIGNS LIST 1 Hybrid vehicle 10 Engine 12, 14 Traction motor 16 Generator 18 Traction battery 20, 22 Drive wheels 24 Clutch 26 Oil cooling circuit 28 Electric oil pump 30 Control unit (ECU) 32 Oil cooler 34 Inverter 36 Coolant cooling circuit 38 Electric water pump 40 Radiator 42 DCDC converter 44 Drive of traction motor 46 Flow path A1 Engine brake regeneration region A2 Pedal regeneration region A3 Mechanical brake deceleration region

Claims

1. a traction motor that drives a drive wheel and regenerates kinetic energy of the drive wheel; A generator driven by the engine; a driving battery that supplies electricity to the driving motor and is charged with electricity generated by the generator and electricity regenerated by the driving motor; Equipped with A regenerative braking system for a hybrid vehicle, which rotates the engine by driving the generator with electricity regenerated by the driving motor when the electricity regenerated by the driving motor cannot be charged to the driving battery, an oil cooling circuit including at least one of the driving motor and the generator in a path; an electric oil pump that circulates the cooling oil filled in the oil cooling circuit; A control device for controlling an output of the electric oil pump; Equipped with The oil cooling circuit includes at least a driving motor in a path thereof, the drive shaft of the travel motor has a flow passage provided along a central axis, The cooling oil passes through the flow path, The control device increases the discharge flow rate of the electric oil pump when the electric power regenerated by the driving motor cannot charge the driving battery.

2. a traction motor that drives a drive wheel and regenerates kinetic energy of the drive wheel; A generator driven by the engine; a driving battery that supplies electricity to the driving motor and is charged with electricity generated by the generator and electricity regenerated by the driving motor; Equipped with A regenerative braking system for a hybrid vehicle, which rotates the engine by driving the generator with electricity regenerated by the driving motor when the electricity regenerated by the driving motor cannot be charged to the driving battery, an oil cooling circuit including at least one of the driving motor and the generator in a path; an electric oil pump that circulates the cooling oil filled in the oil cooling circuit; A control device for controlling an output of the electric oil pump; Equipped with the oil cooling circuit includes both the traction motor and the generator in the path; The control device increases the discharge flow rate of the electric oil pump when the electric power regenerated by the driving motor cannot charge the driving battery.

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