vehicle

Abstract

To provide a vehicle that can reduce capacity of a sub battery.SOLUTION: A vehicle 100 comprises: a motor 10 for driving a vehicle body 100a; a main battery 20 for supplying electric power to the motor 10; a DC-DC converter 40 for converting a voltage of direct-current power; and a sub battery 50 for storing direct-current power of which the voltage has been converted by the DC-DC converter 40. The vehicle 100 is so configured as to supply direct-current power such that counter electromotive force from the motor 10 has been converted to the sub battery 50 via the DC-DC converter 40 when the main battery 20 fails.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a vehicle. [Background technology]

[0002] 2. Description of the Related Art Electric brake devices for vehicles are known in the art (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 describes a brake device mounted on a vehicle. This brake device operates the brakes by driving an electric motor with a direct current from a power supply device. The brake device described in the above-mentioned Patent Document 1 also includes a power storage means, and drives the electric motor with the power stored in the power storage means when the power supply capacity determined by either or both of the voltage and current of the power supply device decreases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-122123 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in a vehicle in which a motor is driven by power supplied from a main battery to drive the vehicle body, it is conceivable to provide an auxiliary battery as a power storage means as in Patent Document 1, so that when the main battery as a power supply device fails, the auxiliary battery can supply power to a brake system or a steering system for operating the vehicle. However, when power is supplied to a brake system or a steering system for operating the vehicle by the auxiliary battery when the main battery fails as in Patent Document 1, it is necessary to use an auxiliary battery with a relatively large capacity. In this case, a large-capacity auxiliary battery has problems such as an increase in weight or an increase in cost, so it is desirable to reduce the capacity of the auxiliary battery. In particular, in a vehicle, an increase in weight is a major problem in terms of fuel efficiency (electricity cost), so it is desirable to reduce the capacity of the auxiliary battery.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a vehicle in which the capacity of the auxiliary battery can be reduced. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, a vehicle in one aspect of the present invention comprises a motor for driving a vehicle body, a main battery for supplying power to the motor, a DC-DC converter for converting DC power converted from the back electromotive force from the motor and the voltage of the DC power supplied from the main battery, and an auxiliary battery for storing the DC power whose voltage has been converted by the DC-DC converter, and is configured to supply the DC power converted from the back electromotive force from the motor to the auxiliary battery via the DC-DC converter in the event of a failure of the main battery.

[0008] As described above, a vehicle according to one aspect of the present invention is configured to supply DC power converted from the back electromotive force from the motor to the auxiliary battery via a DC-DC converter when the main battery fails. This allows the auxiliary battery to be charged by the back electromotive force from the motor, so that even when the main battery fails, the auxiliary battery can supply sufficient power. As a result, there is no need to use an auxiliary battery with a relatively large capacity, so the capacity of the auxiliary battery can be reduced. Furthermore, because the capacity of the auxiliary battery can be reduced, it is possible to prevent the weight from increasing accordingly, and to prevent a decrease in the fuel efficiency (electricity cost) of the vehicle.

[0009] In the vehicle according to the above aspect, preferably, the vehicle further comprises a brake system that is operated by DC power supplied from the auxiliary battery, and is configured to operate the brake system by supplying DC power converted from the back electromotive force from the motor to the auxiliary battery via a DC-DC converter in the event of a failure of the main battery.

[0010] With this configuration, when the main battery fails, the auxiliary battery can be charged by the back electromotive force from the motor, so that the auxiliary battery can supply power to the brake system without increasing the capacity of the auxiliary battery. As a result, when the main battery fails, the vehicle can be stopped without increasing the capacity of the auxiliary battery.

[0011] The vehicle according to the above aspect preferably further comprises an inverter that converts DC power from the main battery into AC power and supplies it to the motor, and converts back electromotive force from the motor into DC power and supplies it to the main battery and the DC-DC converter, and is configured such that, in the event of a failure of the main battery, the back electromotive force from the motor is converted by the inverter into DC power of a predetermined voltage or higher and supplied to the DC-DC converter.

[0012] With this configuration, even if the back electromotive force in the motor decreases due to a decrease in the vehicle's traveling speed, the inverter can operate to supply DC power of a predetermined voltage or higher to the DC-DC converter, allowing stable power supply from the DC-DC converter to the auxiliary battery. Therefore, even if the main battery fails and the vehicle's traveling speed is low, the auxiliary battery can be charged, allowing a sufficient supply of power from the auxiliary battery.

[0013] In the vehicle according to the above aspect, the vehicle is preferably configured to perform autonomous driving, and when the main battery fails during autonomous driving, the vehicle is configured to supply direct current power converted from the back electromotive force from the motor to the auxiliary battery via a DC-DC converter.

[0014] With this configuration, even if the main battery fails during automatic driving, the auxiliary battery can be charged by the back electromotive force from the motor, so that the auxiliary battery can supply sufficient power to the brake system, steering system, and other systems used to operate the vehicle without increasing the capacity of the auxiliary battery. As a result, if the main battery fails during automatic driving, the vehicle can be stopped without increasing the capacity of the auxiliary battery.

[0015] In the vehicle according to the above aspect, the following configuration is also possible.

[0016] (Additional note 1) In the vehicle according to the aforementioned aspect, the vehicle preferably includes an electric vehicle, and the motor preferably includes a motor for driving the electric vehicle.

[0017] With this configuration, the capacity of the auxiliary battery in the electric vehicle can be reduced, which in turn prevents an increase in the weight of the electric vehicle and thus prevents a decrease in the power efficiency of the electric vehicle.

[0018] (Additional note 2) The vehicle according to the aforementioned aspect preferably further includes a control unit that performs control so that, when the main battery fails, DC power converted from the back electromotive force from the motor is supplied to the auxiliary battery via the DC-DC converter.

[0019] With this configuration, when the main battery fails, the control unit can easily execute control for supplying the back electromotive force from the motor to the auxiliary battery.

[0020] (Additional note 3) In the vehicle according to supplementary item 2 above, the control unit preferably includes an ECU (Electronic Control Unit) that is mounted on the vehicle and controls the vehicle body.

[0021] With this configuration, unlike the case where a control unit separate from the ECU mounted on the vehicle is provided, it is possible to prevent the vehicle configuration from becoming complicated.

[0022] (Additional note 4) In another aspect of the present invention, a brake control system is included in a vehicle which has a motor for driving a vehicle body, a main battery for supplying power to the motor, a DC-DC converter for converting DC power converted from the back electromotive force from the motor and the voltage of the DC power supplied from the main battery, and an auxiliary battery for storing the DC power whose voltage has been converted by the DC-DC converter, and the brake control system comprises a brake system which operates using DC power supplied from the auxiliary battery, and a control unit which controls the DC power supplied to the auxiliary battery, and the control unit is configured to operate the brake system by supplying the DC power converted from the back electromotive force from the motor to the auxiliary battery via the DC-DC converter in the event of a failure of the main battery.

[0023] In another aspect of the brake control system of the present invention, as described above, the control unit is configured to operate the brake system by supplying DC power converted from the back electromotive force from the motor to the auxiliary battery via the DC-DC converter when the main battery fails. This allows the auxiliary battery to be charged by the back electromotive force from the motor, so that even when the main battery fails, the auxiliary battery can supply sufficient power. As a result, it is not necessary to use an auxiliary battery with a relatively large capacity, so a brake control system can be provided that allows the capacity of the auxiliary battery to be reduced. In addition, because the capacity of the auxiliary battery can be reduced, it is possible to prevent the weight from increasing accordingly, and it is possible to provide a brake control system that can prevent a decrease in fuel efficiency (electricity cost) of the vehicle. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram of a vehicle according to an embodiment. [Diagram 2] FIG. 2 is a circuit diagram showing a schematic configuration of an inverter. [Diagram 3] FIG. 1 is a schematic diagram of a brake system according to an embodiment. [Figure 4] FIG. 2 is a diagram for explaining how a braking force of a brake system according to an embodiment works. [Diagram 5] FIG. 4 is a diagram for explaining operation when the main battery fails. [Figure 6] 10 is a diagram for explaining the power consumption (current value) of the secondary battery when the main battery fails. FIG. [Figure 7] FIG. 4 is a diagram showing the relationship between the vehicle speed and the back electromotive voltage in the motor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0026] A vehicle 100 of this embodiment will be described with reference to Figures 1 to 7. The vehicle 100 is, for example, an electric vehicle (BEV).

[0027] 1, a vehicle 100 includes a motor 10, a main battery 20, an inverter 30, a DC-DC converter 40, an auxiliary battery 50, a brake system 60, and a control unit 70. The brake system 60 and the control unit 70 form a brake control system.

[0028] The motor 10 drives the vehicle body 100a of the vehicle 100. In other words, the motor 10 is a motor for driving an electric vehicle. The motor 10 converts power supplied from a main battery 20 into driving force for the vehicle 100. The motor 10 is composed of a rotor and a stator, and the rotor rotates due to magnetic force generated in the stator. DC power supplied from the main battery 20 is converted to AC power by an inverter 30 and supplied to the motor 10. The motor 10 is, for example, a brushless motor driven by three-phase AC.

[0029] The main battery 20 supplies power to the motor 10. The main battery 20 is, for example, a lithium ion battery. The main battery 20 outputs a relatively high voltage. For example, the main battery 20 outputs a voltage of several hundred volts.

[0030] The inverter 30 is provided between the motor 10 and the main battery 20, and converts the back electromotive force (regenerative power) supplied from the motor 10 into DC power. The inverter 30 also converts the DC power supplied from the main battery 20 into AC power. The inverter 30 is a bidirectional inverter capable of converting DC to AC and AC to DC. Specifically, the inverter 30 converts the DC power from the main battery 20 into AC power and supplies it to the motor 10, and also converts the back electromotive force, which is AC power from the motor 10, into DC power and supplies it to the main battery 20 and the DC-DC converter 40. The inverter 30 operates by switching between converting the back electromotive force from the motor 10 and converting the DC power from the main battery 20.

[0031] For example, as shown in Fig. 2, the inverter 30 has a conversion circuit section 30a that converts between DC and AC in both directions. In the conversion circuit section 30a, for example, a plurality of switching elements Sw, such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), are bridge-connected. In the inverter 30, bidirectional conversion between AC power and DC power is performed by controlling the switching operations of the plurality of switching elements Sw. Note that the inverter 30 may have an insulated DC-DC conversion circuit having a transformer, a chopper circuit that boosts or lowers the DC power, a filter circuit having a reactor, or a capacitor that suppresses harmonics.

[0032] 1, the DC-DC converter 40 converts the voltage of the DC power converted from the back electromotive force from the motor 10 and the DC power supplied from the main battery 20. The DC-DC converter 40 is a step-down DC-DC converter 40. For example, the DC-DC converter 40 steps down a voltage of several hundred volts supplied from the main battery 20 to a dozen volts or several tens of volts.

[0033] The auxiliary battery 50 stores DC power whose voltage has been converted by the DC-DC converter 40. The auxiliary battery 50 is, for example, a lithium ion battery. The auxiliary battery 50 outputs a relatively low voltage. For example, the auxiliary battery 50 outputs a voltage of a dozen volts or several tens of volts.

[0034] The brake system 60 operates by DC power supplied from the auxiliary battery 50. The brake system 60 is a brake-by-wire type brake system 60. As shown in FIG. 3, the brake-by-wire system is a system in which a brake pedal 61 and a pressure applying unit 62 are connected by an electric wire via an ECU 60a (Electronic Control Unit) that controls the operation of the brake system 60, and the pressure applying unit 62 applies brake pads 64. Specifically, the brake system 60 applies brakes to each of the left front wheel Flb, the right front wheel Frb, the left rear wheel Rlb, and the right rear wheel Rrb based on the brake operation by the driver. That is, the brake system 60 transmits a braking force to the brake pads 64, and causes the brake pads 64 to clamp a brake rotor 65 with the transmitted braking force.

[0035] The brake system 60 includes a brake pedal 61, a pressure applying unit 62, and a master cylinder 63. The brake pedal 61 is an operating member that is depressed by the driver when braking the vehicle 100. The pressure applying unit 62 has a function of increasing the brake fluid pressure of the brake fluid based on the driver's depressing force. The master cylinder 63 is configured to supply brake fluid of appropriate brake fluid pressure to each of the left front wheel Flb, the right front wheel Frb, the left rear wheel Rlb, and the right rear wheel Rrb.

[0036] 4, the brake system 60 includes a brake caliper 66, a wheel cylinder 67, and a wheel piston 68 in addition to the brake pads 64 and the brake rotor 65. The wheel cylinder 67 is provided in the brake caliper 66. The wheel piston 68 is disposed in the wheel cylinder 67. The master cylinder 63 is connected to the wheel cylinder 67 by a fluid path 69. In the brake system 60, the ECU 60a controls the pressure unit 62 based on the depression amount of the brake pedal 61, whereby a braking force is transmitted to the brake pads 64 via the master cylinder 63.

[0037] The pressurizing unit 62 includes a pump 62a and a pump motor 62b. The pump 62a increases the pressure of the brake fluid in a fluid path 69 that connects the wheel cylinder 67 and the master cylinder 63. The pump motor 62b drives the pump 62a. The pump motor 62b is driven by power supplied from the auxiliary battery 50. The pump motor 62b is, for example, a DC motor. A master piston 63a is inserted in the master cylinder 63, and by controlling the pump motor 62b, the master piston 63a moves in the master cylinder 63, and the braking force of the brake pads 64 is controlled.

[0038] In addition to the brake system 60, the vehicle 100 also includes an electric power steering (EPS), an anti-lock brake system (ABS), an automatic driving system, and the like, which are driven by power from the auxiliary battery 50.

[0039] In this embodiment, the control unit 70 includes an ECU (Electronic Control Unit) mounted on the vehicle 100. The control unit 70 controls the vehicle body 100a. The control unit 70 also includes a CPU (Central Processing Unit) and a storage unit such as a memory. The control unit 70 is configured to control the operation of the vehicle 100 based on a control program stored in the storage unit.

[0040] For example, the control unit 70 is arranged separately from the ECU 60a that controls the operation of the brake system 60. In the vehicle 100, ECUs that control the operation of the motor 10, the main battery 20, the inverter 30, the DC-DC converter 40, the auxiliary battery 50, and the brake system 60 are provided separately for each of the motor 10, the main battery 20, the inverter 30, the DC-DC converter 40, the auxiliary battery 50, and the brake system 60. The control unit 70 is configured to control the operation of the vehicle 100 by transmitting and receiving signals to and from each of the ECUs of the motor 10, the main battery 20, the inverter 30, the DC-DC converter 40, the auxiliary battery 50, and the brake system 60. The auxiliary battery 50 outputs DC power to each ECU as a power source for control. Each ECU has a calculation device such as a CPU and a storage device such as a memory.

[0041] (Normal operation) The normal operation of the vehicle 100 will be described. In this embodiment, the vehicle 100 normally performs automatic driving. Automatic driving is a method in which a system performs driving operations such as acceleration, steering, and braking, which are normally performed by a driver (human), instead of a human. Furthermore, during normal driving, power is supplied from the main battery 20 to the motor 10 via the inverter 30. This allows the vehicle 100 to run. Furthermore, the power of the main battery 20 is stepped down by the DC-DC converter 40 and stored in the auxiliary battery 50. The brake system 60, electric power steering (EPS), anti-lock brake system (ABS), automatic driving system, and the like are driven by the power supplied from the auxiliary battery 50. Furthermore, the headlights, wipers, and the like of the vehicle 100 are also driven by the power supplied from the auxiliary battery 50.

[0042] (Operation when main battery fails) Next, an operation when the main battery 20 fails while the vehicle 100 is traveling by automatic driving will be described. The failure of the main battery 20 is detected by an ECU provided in the main battery 20, for example, based on the output voltage, output current, or temperature of the main battery 20, and a signal indicating that the main battery 20 has failed is output to the control unit 70. When the control unit 70 receives a signal indicating that the main battery 20 has failed, the control unit 70 is configured to steer the vehicle 100 to the side of the road by automatic driving and to stop the vehicle 100. When a failure in the main battery 20 is detected, an electric circuit for inputting and outputting power to and from the main battery 20 is opened by a relay.

[0043] In this embodiment, the vehicle 100 is configured to supply DC power converted from the back electromotive force from the motor 10 to the auxiliary battery 50 via the DC-DC converter 40 when the main battery 20 fails during automatic driving, under the control of the control unit 70. When the main battery 20 fails, the brake system 60 is activated by supplying the back electromotive force from the motor 10 to the auxiliary battery 50. Specifically, while traveling, the rotor of the motor 10 rotates due to the rotational forces of the left front wheel Flb, the right front wheel Frb, the left rear wheel Rlb, and the right rear wheel Rrb, causing the motor 10 to function as a generator. In other words, the rotation of the rotor of the motor 10 generates a back electromotive force (back electromotive voltage) in the motor 10. When the main battery 20 fails while the vehicle 10 is traveling, the control unit 70 converts the AC power, which is the back electromotive force from the motor 10, into DC power by the inverter 30, and supplies the DC power from the inverter 30 to the auxiliary battery 50 via the DC-DC converter 40. In the event of a failure of the main battery 20, the control unit 70 supplies DC power from the auxiliary battery 50 to the pump motor 62b of the brake system 60 to operate the pump 62a, thereby supplying brake fluid at an appropriate brake fluid pressure to each of the left front wheel Flb, right front wheel Frb, left rear wheel Rlb, and right rear wheel Rrb. Note that in the motor 10, a regenerative operation is performed in which the rotational energy of the rotor is converted into regenerative energy as electric power, and a braking force is applied to the left front wheel Flb, right front wheel Frb, left rear wheel Rlb, and right rear wheel Rrb due to the energy conversion.

[0044] Next, referring to FIG. 5, the details of the operation when the main battery 20 fails will be described. In FIG. 5, the solid lines indicate the braking force of the brake system 60, the driving force of the motor 10, and the power consumption of the auxiliary battery 50 in the operation when the main battery 20 fails. As shown in FIG. 5, it is assumed that the main battery 20 fails at time t1. The control unit 70 supplies DC power from the auxiliary battery 50 to the brake system 60 to operate the brake system 60. As a result, the braking force of the brake system 60 starts to be applied at time t2. In FIG. 5, the braking force of the brake system 60 has a negative sign, so that the larger the braking force, the more negative the graph moves (downward on the paper). In addition, when the main battery 20 fails, the control unit 70 stops the supply of power from the main battery 20 to the motor 10. As a result, the driving force of the motor 10 decreases to zero after time t1. Then, at time t2, the back electromotive force from the motor 10 is converted by the inverter 30 and supplied to the secondary battery 50 via the DC-DC converter 40. In this case, the back electromotive force caused by the rotation of the motor 10 is consumed, and a braking force is generated by the regenerative operation so as to suppress the rotation of the motor 10. Note that in Fig. 5, the braking force of the motor 10 is shown as the negative of the driving force, so that the larger the braking force, the more the graph moves in the negative direction (downward on the page).

[0045] Due to the braking force of the brake system 60 and the braking force of the motor 10, the speed of the vehicle 100 starts to decelerate at time t2. Furthermore, since the brake system 60 is operated at time t2, the power consumption of the auxiliary battery 50 increases at time t2. After that, at time t3, the stopping operation of the vehicle 100 by the autonomous driving ends. At time t3, the operation of the brake system 60 is stopped and the braking force of the brake system 60 becomes zero. Furthermore, the braking force by the motor 10 becomes zero. Furthermore, the power consumption of the auxiliary battery 50 for the brake system 60 becomes zero. Note that since the power from the auxiliary battery 50 is also supplied to other than the brake system 60, the power consumption of the auxiliary battery 50 may not become zero even after time t3. Furthermore, if the power supplied to the auxiliary battery 50 by the back electromotive force from the motor 10 is sufficiently large, the power consumption of the auxiliary battery 50 in the period from time t2 to time t3 may be equal to or smaller than the power consumption in the period before time t2 when the operation of the brake system 60 started.

[0046] Also, referring to FIG. 5, a case where the counter electromotive force from the motor 10 is not supplied to the auxiliary battery 50 will be described. In FIG. 5, the dotted lines indicate the braking force of the brake system 60, the driving force by the motor 10, and the power consumption of the auxiliary battery 50 when the counter electromotive force is not supplied from the motor 10. When the counter electromotive force is not supplied from the motor 10, the regenerative operation of the motor 10 is not performed after time t2, so that the braking force is not generated in the motor 10. Therefore, it is necessary to increase the braking force of the brake system 60. Also, since the counter electromotive force from the motor 10 is not converted and supplied to the auxiliary battery 50, the power consumption of the auxiliary battery 50 increases. Therefore, when the counter electromotive force from the motor 10 is not supplied to the auxiliary battery 50, it is necessary to increase the capacity of the auxiliary battery 50. Therefore, by supplying the counter electromotive force from the motor 10 to the auxiliary battery 50 as in this embodiment, it is possible to reduce the capacity of the auxiliary battery 50.

[0047] Next, the amount of current output from the auxiliary battery 50 when the main battery 20 fails during automatic driving will be described with reference to Fig. 6. In Fig. 6, the amount of current indicated by a solid line represents the amount of current when the counter electromotive force from the motor 10 is supplied to the auxiliary battery 50 during operation when the main battery 20 fails. In Fig. 6, the amount of current indicated by a dotted line represents the amount of current when the counter electromotive force from the motor 10 is not supplied to the auxiliary battery 50.

[0048] 6, it is assumed that the main battery 20 fails at time t11. The control unit 70 supplies DC power from the auxiliary battery 50 to the brake system 60 to operate the brake system 60. Specifically, the control unit 70 controls the auxiliary battery 50 to supply current to the pump motor 62b from time t11 to time t12. In this case, in this embodiment, the counter electromotive force from the motor 10 is supplied to the auxiliary battery 50 during operation when the main battery 20 fails, so the amount of current (power consumption) output from the auxiliary battery 50 is smaller than when the counter electromotive force is not supplied from the motor 10. For example, the amount of current I1 when the counter electromotive force from the motor 10 is supplied to the auxiliary battery 50 from time t11 to time t12 is smaller than the amount of current I2 when the counter electromotive force is not supplied to the auxiliary battery 50.

[0049] At the start of operation of the brake system 60, a current having a relatively large amount of current is supplied to the pump motor 62b. This allows the pump 62a to be started quickly, and the braking force of the brake system 60 is generated quickly. At the start of operation of the pump 62a, a relatively large amount of current is required, but once the pump 62a is started, the power required for the brake system 60 becomes small. Therefore, the amount of current from time t12 to time t13 is smaller than the amount of current I1 from time t11 to time t12. For example, the control unit 70 supplies the counter electromotive force from the motor 10 to the auxiliary battery 50 so that the amount of current output from the auxiliary battery 50 to the brake system 60 during the time from time t11 to time t12 is compensated for by the amount of current output from the auxiliary battery 50 when the main battery 20 fails. That is, the control unit 70 controls the operation of the inverter 30 so that the power equivalent to the relatively large amount of current at the start of operation of the brake system 60 is supplied to the auxiliary battery 50. In addition, between times t12 and t13, the control unit 70 supplies the back electromotive force from the motor 10 to the auxiliary battery 50 so as to compensate for the power equivalent to a value greater than the amount of current output to the brake system 60 in the event of a failure of the main battery 20.

[0050] Between time t11 and time t13, power is supplied from the auxiliary battery 50 to the electric power steering (EPS), the automatic driving system, headlights, wipers, and the like in addition to the brake system 60. Between time t11 and time t13, the amount of current for the electric power steering (EPS) is relatively large in order to move the vehicle 100 away from the vehicle 100, but the amount of current decreases after time t13. Then, at time t14, the control unit 70 ends the automatic driving. Thereafter, the control unit 70 controls the vehicle 100 so that it is manually driven.

[0051] Furthermore, in this embodiment, if the main battery 20 fails during automatic driving and the vehicle 100 continues to travel after switching from automatic driving to manual driving, the brake system 60 is manually operated. Even in this case, the counter electromotive force from the motor 10 is converted to DC power by the inverter 30 and supplied to the auxiliary battery 50 via the DC-DC converter 40. That is, the brake system 60 is operated based on the operation of the brake pedal 61 by a human, and the counter electromotive force from the motor 10 is supplied to the auxiliary battery 50, thereby charging the auxiliary battery 50 to compensate for the power consumption of the auxiliary battery 50. Therefore, even when switching to manual driving, the counter electromotive force from the motor 10 is supplied to the auxiliary battery 50 to compensate for the power consumption of the auxiliary battery 50.

[0052] (Regenerative braking control switching) As shown in FIG. 7, the speed of the vehicle 100 and the magnitude of the back electromotive force from the motor 10 are in a proportional relationship. When the speed (vehicle speed) of the vehicle 100 decreases, the rotation speed of the motor 10 decreases, and the voltage value of the back electromotive force (value of the back electromotive voltage) in the motor 10 decreases. Here, in order to operate stably, the DC-DC converter 40 receives DC power having a value equal to or higher than a predetermined voltage. In other words, the DC-DC converter 40 outputs DC power of a constant voltage to the auxiliary battery 50 by receiving DC power of a predetermined voltage or higher. The value of the predetermined voltage is, for example, a preset value between 150V and 200V. In this embodiment, the vehicle 100 is configured such that, when the main battery 20 fails, the back electromotive force from the motor 10 is converted by the inverter 30 into DC power of a predetermined voltage or higher and supplied to the DC-DC converter 40. That is, the control unit 70 controls the operation of the inverter 30 so that the voltage value of the DC voltage supplied (output) from the DC-DC converter 40 to the secondary battery 50 is constant, and so that the voltage value of the DC power from the inverter 30 input to the DC-DC converter 40 is equal to or greater than a predetermined voltage.

[0053] Specifically, the control unit 70 acquires the speed of the vehicle 100 from an ECU that controls the operation of the motor 10. When the speed of the vehicle 100 is greater than a preset threshold value S, the control unit 70 controls the operation of the inverter 30 so that in the conversion of the back electromotive force from the motor 10 to DC power in the inverter 30, the energy conversion in the regenerative operation is relatively small and the braking force generated in the motor 10 is relatively small. When the speed of the vehicle 100 is equal to or less than the preset threshold value S, the control unit 70 controls the operation of the inverter 30 so that the energy conversion in the regenerative operation is relatively large and the braking force generated in the motor 10 is relatively large. That is, the control unit 70 switches the control of the regenerative operation according to the speed of the vehicle 100 so that DC power of a predetermined voltage or more is output from the inverter 30.

[0054] For example, the control unit 70 switches regenerative braking control ON and OFF in which the braking force in the motor 10 is large and the voltage of the DC power output from the inverter 30 is large according to the speed of the vehicle 100. When the speed of the vehicle 100 is equal to or lower than a threshold value S, the control unit 70 switches the DUTY ratio in the switching operation of the switching element Sw of the inverter 30 to relatively increase the amount of energy converted in the regenerative operation, relatively increase the braking force of the motor 10, and turn on the regenerative braking control so that the voltage of the DC power output from the inverter 30 is large. The DUTY ratio represents the ratio of switching ON and OFF of the switching operation of the switching element Sw in the conversion circuit unit 30a of the inverter 30. When the regenerative braking control is ON, a large braking force is generated in the motor 10 and the amount of conversion to regenerative energy is large. On the other hand, when the speed of the vehicle 100 is higher than the threshold value S, the control unit 70 turns off the regenerative braking control to relatively reduce the amount of energy converted in the regenerative operation and relatively reduce the braking force of the motor 10. When the regenerative braking control is off, the consumption of regenerative energy is relatively small, and the braking force of the motor 10 is also relatively small. When the speed of the vehicle 100 is high and the back electromotive force of the motor 10 is sufficiently large, the amount of energy converted in the regenerative operation is made relatively small, thereby preventing excessive power supply to the auxiliary battery 50. In other words, in this embodiment, when the speed of the vehicle 100 is relatively high, the conversion to regenerative energy is limited to a relatively small amount so that the power supplied to the auxiliary battery 50 does not become too large when the main battery 20 fails. On the other hand, when the speed of the vehicle 100 is relatively low, the conversion to regenerative energy is made relatively large, allowing the DC-DC converter 40 to operate stably.

[0055] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0056] In this embodiment, as described above, the vehicle 100 is configured to supply DC power converted from the counter electromotive force from the motor 10 to the auxiliary battery 50 via the DC-DC converter 40 when the main battery 20 fails. This allows the auxiliary battery 50 to be charged by the counter electromotive force from the motor 10, so that even when the main battery 20 fails, the auxiliary battery 50 can supply sufficient power. As a result, it is not necessary to use the auxiliary battery 50 with a relatively large capacity, so the capacity of the auxiliary battery 50 can be reduced. In addition, since the capacity of the auxiliary battery 50 can be reduced, it is possible to prevent the weight from increasing accordingly, and it is possible to prevent a decrease in fuel efficiency (electricity cost) of the vehicle 100. In addition, since the capacity of the auxiliary battery 50 can be reduced, it is possible to reduce costs.

[0057] Furthermore, in this embodiment, as described above, the vehicle 100 includes the brake system 60 that operates with DC power supplied from the auxiliary battery 50. The vehicle 100 is configured to operate the brake system 60 by supplying DC power converted from the back electromotive force from the motor 10 to the auxiliary battery 50 via the DC-DC converter 40 when the main battery 20 fails. As a result, by charging the auxiliary battery 50 with the back electromotive force from the motor 10 when the main battery 20 fails, it is possible to supply power to the brake system 60 from the auxiliary battery 50 without increasing the capacity of the auxiliary battery 50. As a result, it is possible to stop the vehicle 100 when the main battery 20 fails without increasing the capacity of the auxiliary battery 50.

[0058] In this embodiment, as described above, the vehicle 100 includes the inverter 30 that converts DC power from the main battery 20 into AC power and supplies it to the motor 10, and also converts the back electromotive force from the motor 10 into DC power and supplies it to the main battery 20 and the DC-DC converter 40. The vehicle 100 is configured such that, when the main battery 20 fails, the back electromotive force from the motor 10 is converted by the inverter 30 into DC power of a predetermined voltage or higher and supplied to the DC-DC converter 40. As a result, even if the back electromotive force in the motor 10 falls due to a decrease in the running speed of the vehicle 100, the inverter 30 can operate to supply DC power of a predetermined voltage or higher to the DC-DC converter 40, so that power can be stably supplied from the DC-DC converter 40 to the auxiliary battery 50. Therefore, even if the running speed of the vehicle 100 is low when the main battery 20 fails, the auxiliary battery 50 can be charged, so that sufficient power can be supplied from the auxiliary battery 50.

[0059] Furthermore, in this embodiment, as described above, the vehicle 100 is configured to perform autonomous driving, and is configured to supply DC power converted from the back electromotive force from the motor 10 to the auxiliary battery 50 via the DC-DC converter 40 when the main battery 20 fails during autonomous driving. As a result, even if the main battery 20 fails during autonomous driving, the auxiliary battery 50 can be charged with the back electromotive force from the motor 10, thereby allowing the auxiliary battery 50 to supply sufficient power to the brake system 60 or the steering system (electric power steering) for operating the vehicle 100 without increasing the capacity of the auxiliary battery 50. As a result, the vehicle 100 can be stopped when the main battery 20 fails during autonomous driving, without increasing the capacity of the auxiliary battery 50.

[0060] (Additional note 1) In this embodiment, as described above, the vehicle 100 includes an electric vehicle and the motor 10 for driving the electric vehicle. This allows the capacity of the auxiliary battery 50 in the electric vehicle to be reduced. Also, since an increase in the weight of the electric vehicle can be suppressed, a decrease in the power consumption of the electric vehicle can be suppressed.

[0061] (Additional note 2) Furthermore, in this embodiment, as described above, the vehicle 100 includes a control unit 70 that performs control so that, when the main battery 20 fails, DC power converted from the back electromotive force from the motor 10 is supplied to the auxiliary battery 50 via the DC-DC converter 40. This allows the control unit 70 to easily execute control so that, when the main battery 20 fails, the back electromotive force from the motor 10 is supplied to the auxiliary battery 50.

[0062] (Additional note 3) In the present embodiment, as described above, the control unit 70 includes an ECU (Electronic Control Unit) that is mounted on the vehicle 100 and controls the vehicle body 100a. This makes it possible to prevent the configuration of the vehicle 100 from becoming complicated, unlike a case where a control unit 70 separate from an ECU mounted on the vehicle 100 is provided.

[0063] [Variations] The above-described embodiments disclosed herein should be considered as illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the above-described embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0064] For example, in the above embodiment, in the vehicle 100 equipped with the brake system 60, when the main battery 20 fails, the brake system 60 is operated by supplying the counter electromotive force from the motor 10 to the auxiliary battery 50 via the DC-DC converter 40, but the present invention is not limited to this. In the present invention, when the main battery fails, the counter electromotive force from the motor may be supplied to the auxiliary battery, so that power may be supplied from the auxiliary battery to systems other than the brake system, such as an electric power steering (EPS), an antilock braking system (ABS), or an automatic driving system.

[0065] In the above embodiment, when the main battery 20 fails, the back electromotive force from the motor 10 is converted by the inverter 30 into DC power of a predetermined voltage or more and supplied to the DC-DC converter 40, but the present invention is not limited to this. In the present invention, when the main battery fails, the inverter does not need to output DC power of a predetermined voltage or more. For example, when the vehicle speed decreases and the back electromotive force from the motor decreases, the voltage of the DC power output from the inverter becomes smaller than a predetermined voltage, the operation of the DC-DC converter may be stopped.

[0066] In the above embodiment, the regenerative braking control is switched on and off depending on the speed of the vehicle 100 so that the inverter 30 outputs DC power equal to or higher than a predetermined voltage, but the present invention is not limited to this. In the present invention, the regenerative braking control may not be switched on even when the vehicle speed decreases. For example, the control of the inverter may be constant regardless of the vehicle speed. Also, the regenerative braking control may be switched on and off by acquiring the output voltage value of the back electromotive force from the motor, the voltage value of the DC voltage output from the inverter, or the rotation speed of the motor, instead of the vehicle speed.

[0067] In the above embodiment, the vehicle 100 is configured to perform automatic driving, but the present invention is not limited to this. The present invention can also be applied to a vehicle that is manually driven. That is, even if the main battery fails while the vehicle is being manually driven, the counter electromotive force from the motor may be supplied to the auxiliary battery.

[0068] In the above embodiment, the vehicle 100 is an electric vehicle, but the present invention is not limited to this. The present invention can also be applied to a hybrid vehicle having an engine and a motor.

[0069] In the above embodiment, the brake system 60 includes the pump 62a that boosts the brake fluid pressure and the pump motor 62b that drives the pump 62a, but the present invention is not limited to this. The present invention can also be applied to a brake system in which a master piston is directly driven by a motor. The present invention can also be applied to a brake system that does not use a pump. For example, a brake system that does not use a pump is an EMB (electromechanical brake) that has a reducer that amplifies the torque generated by the motor and a linear converter that converts rotational motion into linear motion.

[0070] In the above embodiment, the brake system 60 is a brake-by-wire type brake system 60, but the present invention is not limited to this. The present invention can also be applied to brake systems other than the brake-by-wire type brake system.

[0071] In the above embodiment, the main battery 20 and the auxiliary battery 50 are lithium ion batteries, but the present invention is not limited to this. In the present invention, the main battery and the auxiliary battery may be batteries other than lithium ion batteries, such as lead-acid batteries or solid-state batteries.

[0072] In the above embodiment, the control unit 70 is an ECU mounted on the vehicle 100, but the present invention is not limited to this. In the present invention, a control unit separate from the ECU mounted on the vehicle may perform control when the main battery of the present invention fails. For example, a computer separate from the ECU may be used as the control unit that executes the control process of the present invention.

[0073] In the above embodiment, the vehicle 100 has been described as an example in which the control unit 70, which is arranged separately from the ECUs provided for the motor 10, the main battery 20, the inverter 30, the DC-DC converter 40, the auxiliary battery 50, and the brake system 60, controls the supply of counter electromotive force from the motor 10 to the auxiliary battery 50 when the main battery 20 fails, but the present invention is not limited to this. In the present invention, the control when the main battery fails in the present invention may be performed by an ECU (control unit) that controls the operation of any of the motor, the main battery, the inverter, the DC-DC converter, the auxiliary battery, and the brake system. For example, the ECU (control unit) that controls the brake system may control the supply of counter electromotive force from the motor to the auxiliary battery when the main battery fails, or the ECU that controls the inverter or the ECU that controls the DC-DC converter may control the supply of counter electromotive force from the motor to the auxiliary battery when the main battery fails. Furthermore, the ECUs that control the operation of the motor, main battery, inverter, DC-DC converter, auxiliary battery, and brake system may transmit and receive signals to each other to perform control when the main battery fails. Also, the control unit that controls the supply of counter electromotive force from the motor to the auxiliary battery when the main battery fails may be another ECU (control unit) mounted on the vehicle. [Explanation of symbols]

[0074] 10 Motor 20 Main Battery 40 DC-DC converter 50 Secondary Battery 60 Brake System 70 Control section 100 vehicles 100a Vehicle body

Claims

1. A motor that drives the vehicle body; a main battery for powering the motor; a DC-DC converter that converts the voltage of DC power obtained by converting the back electromotive force from the motor and the voltage of DC power supplied from the main battery; a sub-battery that stores the DC power whose voltage is converted by the DC-DC converter, The vehicle is configured to supply DC power obtained by converting back electromotive force from the motor to the auxiliary battery via the DC-DC converter when the main battery fails.

2. a brake system operated by DC power supplied from the auxiliary battery, 2. The vehicle according to claim 1, wherein the brake system is operated by supplying DC power converted from a back electromotive force from the motor to the auxiliary battery via the DC-DC converter when the main battery fails.

3. an inverter that converts DC power from the main battery into AC power and supplies the AC power to the motor, and converts back electromotive force from the motor into DC power and supplies the DC power to the main battery and the DC-DC converter; 2. The vehicle according to claim 1, wherein, when the main battery fails, a back electromotive force from the motor is converted by the inverter into DC power having a predetermined voltage or higher and supplied to the DC-DC converter.

4. The vehicle according to claim 1, wherein the vehicle is configured to perform autonomous driving, and when the main battery fails during autonomous driving, the vehicle is configured to supply DC power converted from the back electromotive force from the motor to the auxiliary battery via the DC-DC converter.

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