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 supplied from the main battery 20; a sub battery 50 for storing direct-current power of which the voltage has been converted by the DC-DC converter 40; and a brake system 60 which is operated by direct-current power supplied from the sub battery 50. The vehicle is so configured as to supply direct-current power to the brake system 60 from the sub battery 50 to operate the brake system 60, and assist brake force of the brake system 60 by brake force caused by regenerative operation of the motor 10 when the DC-DC converter 40 fails.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, electronically controlled brake systems for vehicles are known (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses an electronically controlled brake system for a vehicle to which power is supplied from a main battery or an auxiliary battery. In this electronically controlled brake system, the power supplied from the main battery is stepped down by a DC-DC converter and supplied to the electronically controlled brake system. The power stepped down by the DC-DC converter is stored in the auxiliary battery. The electronically controlled brake system also includes an oil pump and a motor that drives the oil pump. The hydraulic fluid supplied by the oil pump is supplied to the wheel cylinder of the wheel, thereby applying a braking force to the wheel. In Patent Document 1, the motor that drives the oil pump is normally driven by the power supplied from the main battery and stepped down by the DC-DC converter. In addition, when an abnormality occurs in the main battery, the motor that drives the oil pump is driven by the power supplied from the auxiliary battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-227093 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a conventional electronically controlled brake system such as that disclosed in Patent Document 1, if the DC-DC converter fails, it becomes impossible to store power from the main battery via the DC-DC converter in the auxiliary battery, and the auxiliary battery cannot supply a sufficient current to the motor that drives the oil pump. This makes it impossible to operate the electronically controlled brake system properly. Therefore, in order to operate the electronically controlled brake system properly even if the DC-DC converter fails, it is necessary to use an auxiliary battery with a relatively large capacity. However, since a large-capacity auxiliary battery (auxiliary battery) has problems such as its large weight, it is desirable to reduce the capacity of the auxiliary battery. In particular, in a vehicle, the large weight is a major problem in terms of fuel efficiency (electricity cost), and 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 the vehicle body, a main battery for supplying power to the motor, a DC-DC converter for converting the voltage of DC power supplied from the main battery, an auxiliary battery for storing the DC power whose voltage has been converted by the DC-DC converter, and a brake system operated by the DC power supplied from the auxiliary battery, and is configured so that in the event of a failure of the DC-DC converter, DC power is supplied from the auxiliary battery to the brake system to operate the brake system, and the braking force of the brake system is assisted by the braking force generated by the regenerative operation of the motor.

[0008] As described above, a vehicle according to one aspect of the present invention is configured such that, in the event of a failure of the DC-DC converter, DC power is supplied from the auxiliary battery to the brake system to operate the brake system, and the braking force of the brake system is assisted by the braking force generated by the regenerative operation of the motor. As a result, in the event of a failure of the DC-DC converter, the braking force of the brake system is assisted by the braking force generated by the regenerative operation of the motor, so that the power consumption of the auxiliary battery for operating the brake system can be reduced. As a result, there is no need to use an auxiliary battery with a relatively large capacity, so that the capacity of the auxiliary battery can be reduced, and costs can be reduced. Furthermore, because the capacity of the auxiliary battery can be reduced, an increase in weight can be suppressed, and a decrease in fuel efficiency (electricity cost) of the vehicle can be suppressed.

[0009] In the vehicle according to the aforementioned aspect, the vehicle is preferably configured such that, when the DC-DC converter fails, regenerative power generated by the regenerative operation of the motor is not supplied to the brake system but is stored in the main battery.

[0010] With this configuration, the regenerative power can be effectively utilized, unlike the case where the regenerative power is consumed as heat or the like.

[0011] In the vehicle according to the above aspect, the brake system preferably includes a brake system motor that drives the brake system, and is configured such that, in the event of a failure of the DC-DC converter, an amount of current supplied from the auxiliary battery to the brake system motor is smaller than the amount of current supplied to the brake system motor when the DC-DC converter is normal.

[0012] With this configuration, when the DC-DC converter fails, the power required to drive the brake system motor can be reduced, allowing the capacity of the auxiliary battery to be reduced.

[0013] In the vehicle according to the above aspect, the vehicle is preferably configured to perform autonomous driving, and when the DC-DC converter fails during autonomous driving, the vehicle is configured to supply DC power from the auxiliary battery to the brake system to operate the brake system, and to supplement the braking force of the brake system with braking force generated by regenerative operation of the motor.

[0014] With this configuration, even if the DC-DC converter fails during autonomous driving, the vehicle can be stopped by the braking force provided by the brake system and the regenerative operation of the motor.

[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, when the DC-DC converter fails, activates the brake system and controls the brake system to be supplemented by the braking force generated by the regenerative operation of the motor.

[0019] With this configuration, in the event of a failure of the DC-DC converter, the control unit can easily execute control to operate the brake system and control to supplement the braking force of the brake system with braking force generated by the regenerative operation of the motor.

[0020] (Additional note 3) In the vehicle according to supplementary item 2, the control unit preferably includes an ECU (Electronic Control Unit) mounted in the vehicle.

[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 the vehicle configured to perform the above-mentioned automatic driving, the vehicle is preferably configured such that after switching from automatic driving to manual driving, the brake system is manually operated and the braking force of the brake system is assisted by the braking force generated by the regenerative operation of the motor.

[0023] With this configuration, even if the vehicle cannot be stopped by automatic driving when a failure occurs in the DC-DC converter, the vehicle can be stopped manually.

[0024] (Additional note 5) In another aspect of the present invention, a brake control device is a brake control device included in a vehicle which has a motor for driving the vehicle body, a main battery for supplying power to the motor, a DC-DC converter for converting the voltage of 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 which comprises a brake system which operates using DC power supplied from the auxiliary battery, and a control unit which controls the brake system, and which is configured such that in the event of a failure of the DC-DC converter, the control unit supplies DC power from the auxiliary battery to the brake system to operate the brake system, and assists the braking force of the brake system with the braking force generated by the regenerative operation of the motor.

[0025] In another aspect of the present invention, as described above, the brake control device is configured such that, in the event of a failure of the DC-DC converter, the control unit supplies DC power from the auxiliary battery to the brake system to operate the brake system, and supplements the braking force of the brake system with the braking force generated by the regenerative operation of the motor. As a result, in the event of a failure of the DC-DC converter, the braking force of the brake system is supplemented by the braking force generated by the regenerative operation of the motor, so that the power consumption of the auxiliary battery for operating the brake system can be reduced. As a result, there is no need to use an auxiliary battery with a relatively large capacity, so that the capacity of the auxiliary battery can be reduced, and a brake control device that can reduce costs can be provided. In addition, because the capacity of the auxiliary battery can be reduced, an increase in weight can be suppressed, and a brake control device that can suppress a decrease in fuel efficiency (electricity cost) of the vehicle can be provided. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram of a vehicle according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a brake system according to an embodiment. [Diagram 3] FIG. 2 is a diagram for explaining how a braking force of a brake system according to an embodiment works. [Figure 4] FIG. 13 is a diagram for explaining operation of the DC-DC converter when it fails; [Diagram 5] 10 is a diagram for explaining the power consumption (current value) of the secondary battery when the DC-DC converter fails. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0028] A vehicle 100 of the present embodiment will be described with reference to Figures 1 to 5. The vehicle 100 is, for example, an electric vehicle (BEV).

[0029] 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 constitute a brake control device.

[0030] The motor 10 drives a vehicle body 100a of the vehicle 100. 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.

[0031] 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.

[0032] The inverter 30 is provided between the motor 10 and the main battery 20, and converts regenerative power supplied from the motor 10 into DC power. The inverter 30 also converts DC power supplied from the main battery 20 into AC power. Specifically, the inverter 30 includes a converter unit and an inverter unit. That is, the inverter 30 is a bidirectional inverter 30 that can convert DC to AC and AC to DC.

[0033] The DC-DC converter 40 converts the voltage of 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.

[0034] 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 several tens of volts.

[0035] 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. 2, the brake-by-wire system is a system in which a brake pedal 61 and a pressure unit 62 are connected by an electric wire (wire) via a control unit 70, and the pressure unit 62 operates brake pads 64. Specifically, the brake system 60 brakes 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 is a system that transmits a braking force to the brake pads 64 and causes the brake pads 64 to clamp the brake rotor 65 with the transmitted braking force.

[0036] 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.

[0037] 3, 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 control unit 70 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.

[0038] 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, thereby controlling the braking force of the brake pads 64. The pump motor 62b is an example of a "motor for a brake system" in the claims.

[0039] 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.

[0040] In this embodiment, the control unit 70 includes an ECU (Electronic Control Unit) mounted on the vehicle 100. 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 brake system 60 based on a control program stored in the storage unit. The pressurizing unit 62 and the control unit 70 are electrically connected to each other.

[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 to the motor 10 via the inverter 30 from the main battery 20. 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 DC-DC converter fails) Next, an operation when the DC-DC converter 40 fails while the vehicle 100 is performing autonomous driving will be described. A failure in the DC-DC converter 40 is detected, for example, based on the output voltage of the DC-DC converter 40. Whether the DC-DC converter 40 has failed is determined, for example, by the control unit 70. When the control unit 70 determines that the DC-DC converter 40 has failed, the control unit 70 is configured to steer the vehicle 100 to the side of the road by autonomous driving and to stop the vehicle 100.

[0043] Specifically, in this embodiment, the vehicle 100 is configured to supply DC power from the auxiliary battery 50 to the brake system 60 to operate the brake system 60 when the DC-DC converter 40 fails, and to supplement the braking force of the brake system 60 with the braking force due to the regenerative operation of the motor 10. Specifically, when the DC-DC converter 40 fails, 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 with an 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. Furthermore, the control unit 70 rotates the rotor of the motor 10 by 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. As a result, braking force acts on the left front wheel Flb, the right front wheel Frb, the left rear wheel Rlb, and the right rear wheel Rrb.

[0044] Next, referring to FIG. 4, a case where the motor 10 performs a regenerative operation will be described. In FIG. 4, the solid lines indicate the braking force of the brake system 60, the braking force due to the regenerative operation of the motor 10, and the power consumption of the auxiliary battery 50 when the motor 10 performs a regenerative operation. As shown in FIG. 4, it is assumed that the DC-DC converter 40 fails at time t1. The control unit 70 operates the brake system 60 by supplying DC power from the auxiliary battery 50 to the brake system 60. As a result, the braking force of the brake system 60 starts to be applied at time t2. In FIG. 4, the braking force of the brake system 60 has a negative sign, so that the graph moves in the negative direction (downward on the paper) as the braking force increases. In addition, when the DC-DC converter 40 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 after time t1. Then, at time t2, the regenerative operation of the motor 10 starts. As a result, a braking force begins to be applied by the regenerative operation of the motor 10. In FIG. 4, the braking force due to the regenerative operation of the motor 10 has a negative sign, so the graph moves in the negative direction (downward on the paper) as the braking force increases. The speed of the vehicle 100 begins to decelerate at time t2 due to the braking force of the brake system 60 and the braking force due to the regenerative operation of the motor 10. Furthermore, the brake system 60 is operated at time t2, so 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 is completed. Therefore, at time t3, the speed of the vehicle 100 becomes zero. Furthermore, the operation of the brake system 60 is stopped, and the braking force of the brake system 60 becomes zero. Furthermore, the braking force due to the regenerative operation of the motor 10 becomes zero. Furthermore, the power consumption of the auxiliary battery 50 for the brake system 60 becomes zero. Since the power from the auxiliary battery 50 is also supplied to systems other than the brake system 60, the power consumption of the auxiliary battery 50 may not become zero even after time t3.

[0045] Next, referring to FIG. 4, a case where the motor 10 does not perform regenerative operation will be described. In FIG. 4, the dotted lines indicate the braking force of the brake system 60, the braking force due to the regenerative operation of the motor 10, and the power consumption of the auxiliary battery 50 when the motor 10 does not perform regenerative operation. When the motor 10 does not perform regenerative operation, the braking force due to the regenerative operation of the motor 10 after time t2 is zero, so it is necessary to increase the braking force of the brake system 60. Therefore, the power consumption of the auxiliary battery 50 is larger than when the motor 10 performs regenerative operation. Therefore, when the motor 10 does not perform regenerative operation, it is necessary to increase the capacity of the auxiliary battery 50. Therefore, by having the motor 10 perform regenerative operation as in this embodiment, the braking force required by the brake system 60 can be reduced, and the capacity of the auxiliary battery 50 can be reduced.

[0046] Furthermore, in this embodiment, when the DC-DC converter 40 fails, the regenerative power generated by the regenerative operation of the motor 10 is stored in the main battery 20 without being supplied to the brake system 60. Specifically, when the DC-DC converter 40 fails, the control unit 70 controls the inverter 30 to convert the regenerative power from the motor 10 into DC power. The regenerative power converted into DC power is then stored in the main battery 20. Note that when the DC-DC converter 40 fails, power for control is supplied from the auxiliary battery 50 to the inverter 30.

[0047] Next, referring to FIG. 5, the amount of current output from the auxiliary battery 50 when the DC-DC converter 40 fails during automatic driving will be described. In FIG. 5, it is assumed that the DC-DC converter 40 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 a current having a current amount I1 to the pump motor 62b during the period from time t11 to time t12. Here, in this embodiment, when the DC-DC converter 40 fails, the auxiliary battery 50 supplies to the pump motor 62b a current amount I1 that is smaller than the current amount I2 that is supplied to the pump motor 62b when the DC-DC converter 40 is normal. That is, when the brake system 60 is operated when the DC-DC converter 40 is normal, a current having a relatively large current amount I2 is supplied from the auxiliary battery 50 to the pump motor 62b. As a result, the pump 62a is started up quickly, and the braking force of the brake system 60 is generated quickly. On the other hand, when the DC-DC converter 40 fails, in addition to the braking force of the brake system 60, a braking force due to the regenerative operation of the motor 10 also acts. Therefore, when the DC-DC converter 40 fails, even if the pump 62a is started up slowly by supplying the pump motor 62b with the current I1 smaller than the current I2, a sufficient braking force acts on the vehicle 100. Note that, while a relatively large current is required when the pump 62a is started up, once the pump 62a is started up, the power required for the brake system 60 becomes small. Therefore, the current amount from time t12 to time t13 is smaller than the current amount I1.

[0048] 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.

[0049] 5, the amount of current indicated by the dotted line represents the amount of current when no regenerative operation is performed by the motor 10. When no regenerative operation is performed by the motor 10, braking force is applied to the vehicle 100 only by the brake system 60, so the amount of current output from the auxiliary battery 50 is larger than when regenerative operation is performed by the motor 10.

[0050] Furthermore, in this embodiment, the vehicle 100 is configured such that, after switching from automatic driving to manual driving, the brake system 60 is manually operated and the braking force of the brake system 60 is assisted by the braking force due to the regenerative operation of the motor 10. That is, based on the operation of the brake pedal 61 by a human, the brake system 60 is operated and the braking force of the brake system 60 is assisted by the braking force due to the regenerative operation of the motor 10.

[0051] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0052] In this embodiment, as described above, the vehicle 100 is configured to supply DC power from the auxiliary battery 50 to the brake system 60 to operate the brake system 60 when the DC-DC converter 40 fails, and to supplement the braking force of the brake system 60 with the braking force generated by the regenerative operation of the motor 10. As a result, when the DC-DC converter 40 fails, the braking force of the brake system 60 is supplemented by the braking force generated by the regenerative operation of the motor 10, so that the power consumption of the auxiliary battery 50 for operating the brake system 60 can be reduced. As a result, there is no need to use an auxiliary battery 50 with a relatively large capacity, so that the capacity of the auxiliary battery 50 can be reduced and the cost can be reduced. In addition, because the capacity of the auxiliary battery 50 can be reduced, the weight can be prevented from increasing accordingly, and a decrease in fuel efficiency (electricity cost) of the vehicle 100 can be prevented.

[0053] Furthermore, as described above, in this embodiment, when the DC-DC converter 40 fails, the regenerative power generated by the regenerative operation of the motor 10 is stored in the main battery 20 without being supplied to the brake system 60. This allows the regenerative power to be used effectively, unlike when the regenerative power is consumed as heat or the like.

[0054] Furthermore, in this embodiment, as described above, the brake system 60 includes the pump motor 62b that drives the brake system 60. The vehicle 100 is configured so that, when the DC-DC converter 40 fails, an amount of current I1 that is smaller than the amount of current I2 that is supplied to the pump motor 62b when the DC-DC converter 40 is normal is supplied from the auxiliary battery 50 to the pump motor 62b. As a result, when the DC-DC converter 40 fails, the power for driving the pump motor 62b can be reduced, and the capacity of the auxiliary battery 50 can be made smaller.

[0055] Furthermore, in this embodiment, as described above, the vehicle 100 is configured to perform autonomous driving, and is configured to supply DC power from the auxiliary battery 50 to the brake system 60 to operate the brake system 60 when the DC-DC converter 40 fails during autonomous driving, and to supplement the braking force of the brake system 60 with the braking force generated by the regenerative operation of the motor 10. As a result, even if the DC-DC converter 40 fails during autonomous driving, the vehicle 100 can be stopped by the braking force generated by the brake system 60 and the regenerative operation of the motor 10.

[0056] In this embodiment, as described above, the vehicle 100 includes an electric vehicle, and the motor 10 includes 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.

[0057] Furthermore, in this embodiment, as described above, the vehicle 100 further includes a control unit 70 that, when the DC-DC converter 40 fails, operates the brake system 60 and controls the brake system 60 to be supplemented by the braking force generated by the regenerative operation of the motor 10. This allows the control unit 70 to easily execute the control for operating the brake system 60 and the control for supplementing the braking force of the brake system 60 by the braking force generated by the regenerative operation of the motor 10 when the DC-DC converter 40 fails.

[0058] In the present embodiment, as described above, the control unit 70 includes an ECU (Electronic Control Unit) mounted on the vehicle 100. This makes it possible to prevent the configuration of the vehicle 100 from becoming complicated, unlike a case where a control unit separate from the ECU mounted on the vehicle 100 is provided.

[0059] Furthermore, in this embodiment, as described above, after the vehicle 100 is switched from automatic driving to manual driving, the brake system 60 is manually operated and the braking force of the brake system 60 is assisted by the braking force due to the regenerative operation of the motor 10. This allows the vehicle 100 to be stopped manually even if the vehicle 100 cannot be stopped by automatic driving when the DC-DC converter 40 fails. Furthermore, even if the remaining amount of power stored in the auxiliary battery 50 is low, the braking force due to the regenerative operation of the motor 10 is applied, so the vehicle 100 can be stopped.

[0060] [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.

[0061] For example, in the above embodiment, the regenerative power generated by the regenerative operation of the motor 10 is stored in the main battery 20, but the present invention is not limited to this. In the present invention, when the DC-DC converter 40 fails, the regenerative power generated by the regenerative operation of the motor 10 may be consumed as heat by a regenerative resistor.

[0062] 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. For example, the present invention can be applied to a brake system in which the master piston 63a 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.

[0063] In the above embodiment, an example has been described in which, when the DC-DC converter 40 fails, the amount of current I1 that is smaller than the amount of current I2 that is supplied to the pump motor 62b when the DC-DC converter 40 is normal is supplied from the secondary battery 50 to the pump motor 62b, but the present invention is not limited to this. For example, even when the DC-DC converter 40 fails, the same amount of current I2 as when the DC-DC converter 40 is normal may be supplied to the pump motor 62b.

[0064] In the above embodiment, the vehicle 100 is configured to perform automatic driving, but the present invention is not limited to this. For example, the present invention can be applied to a vehicle equipped with a brake-by-wire type brake system 60 that is manually driven.

[0065] In the above embodiment, the vehicle 100 is an electric vehicle, but the present invention is not limited to this. For example, the present invention can be applied to a hybrid vehicle having an engine and a motor.

[0066] In the above embodiment, the control unit 70 controls the brake system 60 and the regenerative operation of the motor 10, but the present invention is not limited to this. For example, the brake system 60 and the regenerative operation of the motor 10 may be controlled by separate control units.

[0067] 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. For example, a control unit separate from the ECU mounted on the vehicle 100 may control the DC-DC converter 40 of the present invention when it fails.

[0068] 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. For example, the present invention can be applied to a brake system other than the brake-by-wire type brake system 60.

[0069] 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. For example, the main battery 20 and the auxiliary battery 50 may be batteries other than lithium ion batteries. [Explanation of symbols]

[0070] 10 Motor 20 Main Battery 40 DC-DC converter 50 Secondary Battery 60 Brake System 62a Pump 62b Pump motor (motor for 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 the DC power supplied from the main battery; a sub-battery that stores the DC power whose voltage is converted by the DC-DC converter; a brake system operated by DC power supplied from the auxiliary battery, The vehicle is configured such that, when the DC-DC converter fails, DC power is supplied from the auxiliary battery to the brake system to operate the brake system, and the braking force of the brake system is assisted by the braking force generated by the regenerative operation of the motor.

2. 2. The vehicle according to claim 1, wherein when the DC-DC converter fails, regenerative power generated by a regenerative operation of the motor is not supplied to the brake system but is stored in the main battery.

3. the brake system includes a brake system motor that drives the brake system, 2. The vehicle according to claim 1, wherein when the DC-DC converter fails, an amount of current supplied from the auxiliary battery to the brake system motor is smaller than an amount of current supplied to the brake system motor when the DC-DC converter is normal.

4. 2. The vehicle according to claim 1, wherein the vehicle is configured to perform autonomous driving, and when the DC-DC converter fails during autonomous driving, the auxiliary battery supplies DC power to the brake system to operate the brake system, and the braking force of the brake system is assisted by the braking force generated by the regenerative operation of the motor.

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