VEHICLE

Abstract

Vehicle that features: a first energy storage device (26); a second energy storage device (30) having a lower rated voltage than a rated voltage of the first energy storage device (26); a DC-DC converter (32, 34) designed to step down a voltage of electrical power from a high-voltage-side power line (PH) to which the first energy storage device (26) is connected, and to supply the electrical power of the step-down voltage to a low-voltage-side power line (PL) to which the second energy storage device (30) is connected; a first auxiliary device (36) which is connected to the low-voltage power line (PL) and is designed such that it must be operated in a system shutdown state; a second auxiliary device (38) which is connected to the low-voltage power line (PL) and is designed such that it does not need to be operated in the system shutdown state; and a switch (40) designed to disconnect the second auxiliary device (38) from the low-voltage power line (PL), characterized by a second switch (42) designed to disconnect the second energy storage device (30) from the low-voltage power line (PL), and a control device designed to control the switch (40) in the system shutdown state to disconnect the second auxiliary device (38) from the low-voltage power line (PL) when a charge state or voltage of the second energy storage device (30) becomes equal to or less than a first reference value in a state in which the second auxiliary device (38) and the second energy storage device (30) are connected to the low-voltage power line (PL), wherein If the charge state or voltage of the second energy storage device (30) subsequently becomes equal to or less than a second reference value that is less than the first reference value, the control device controls the DC-DC converter to step down the voltage of the electrical power of the high-voltage-side power line (PH) and supply the electrical power of the step-down voltage to the low-voltage-side power line (PL), while controlling the second switch (42) to disconnect the second energy storage device (30) from the low-voltage-side power line (PL).

Description

Technical area

[0001] The present invention relates to a vehicle. background

[0002] A proposed configuration of a vehicle includes: a main energy storage device, an auxiliary equipment battery, a DC-DC converter configured to step down the voltage of electric power on a high-voltage side power line to which the main energy storage device is connected, and supply the step-down voltage electric power to a low-voltage side power line to which the auxiliary equipment battery is connected; and an auxiliary equipment connected to the low-voltage side power line (as described, for example, in JP 2014-143868 A). When a parking time of this vehicle reaches or exceeds a predetermined period of time, the vehicle with this configuration controls the DC-DC converter to supply the electric power to the auxiliary equipment battery.To supply power from the main energy storage device and thereby charge the auxiliary equipment battery with the supplied electrical power.

[0003] In the vehicle with the above configuration, not only the auxiliary equipment battery but also the auxiliary equipment is connected to the low-voltage side power line. Accordingly, dark current is supplied to the auxiliary equipment when the system is off. This reduces the state of charge or voltage of the auxiliary equipment battery. This configuration causes dark current to be supplied to all the auxiliary equipment, even though the auxiliary equipment only includes a few auxiliary devices or machines that must be operated when the system is off. This leads to an excessive reduction in the state of charge or voltage of the auxiliary equipment battery.

[0004] US 2012 / 0 123 625 A1 and US 5 334 926 A each disclose a vehicle comprising: a first energy storage device; a second energy storage device having a lower rated voltage than a rated voltage of the first energy storage device; a DC-DC converter configured to down-convert a voltage of electric power of a high-voltage side power line to which the first energy storage device is connected, and supply the down-converted voltage electric power to a low-voltage side power line to which the second energy storage device is connected; a first auxiliary device connected to the low-voltage side power line and configured to be operated in a system-off state;a second auxiliary device connected to the low-voltage side power line and configured such that it does not need to be operated in the system off state; and a switch configured to disconnect the second auxiliary device from the low-voltage side power line.

[0005] DE 11 2016 004 681 T5 discloses a power supply device in which first to third series-connected switches are inserted in a supply path through which a supply current flows for first and second electrical loads. A first point is provided at a first end of the first switch, and the second switch is provided at a second end of the first switch. A second point is provided between the first and second switches. A third point is provided between the second and third switches. A fourth point is provided at a first end of the third switch, and the second switch is provided at a second end of the third switch. A first battery, a second battery, the first electrical load, and the second electrical load are each connected to a corresponding one of the first, second, third, and fourth points.A control unit controls on and off switching operations of each of the first to third switches.

[0006] It is an object of the present invention to provide a vehicle that reduces an amount of reduction in a state of charge or a voltage of an auxiliary equipment battery.

[0007] The object is achieved by a vehicle having the features of claim 1. The dependent claims are directed to advantageous developments of the invention.

[0008] According to the present invention, there is provided a vehicle including: a first energy storage device; a second energy storage device having a lower rated voltage than a rated voltage of the first energy storage device; a DC-DC converter configured to down-convert a voltage of electric power of a high-voltage side power line to which the first energy storage device is connected, and supply the down-converted voltage electric power to a low-voltage side power line to which the second energy storage device is connected; first auxiliary equipment connected to the low-voltage side power line and configured to be operated in a system-off state;a second auxiliary equipment connected to the low-voltage side power line and configured such that it does not need to be operated in the system off state; and a switch configured to disconnect the second auxiliary equipment from the low-voltage side power line.

[0009] The vehicle according to the present invention includes: the first energy storage device; the second energy storage device having a lower rated voltage than the rated voltage of the first energy storage device; the DC-DC converter configured to down-convert the voltage of the electric power of the high-voltage side power line to which the first energy storage device is connected and supply the down-converted voltage electric power to the low-voltage side power line to which the second energy storage device is connected; the first auxiliary equipment connected to the low-voltage side power line and configured to be operated in the system off state; the second auxiliary equipment connected to the low-voltage side power line and configured to be non-operated in the system off state.and the switch configured to disconnect the second auxiliary equipment from the low-voltage side power line. This configuration disconnects the second auxiliary equipment from the low-voltage side power line in the system off state by means of the switch. As a result, dark current is prevented from being supplied to the second auxiliary equipment, and an amount of decrease in the state of charge or voltage of the second energy storage device is reduced or restricted.

[0010] The "first accessory equipment" referred to here refers to auxiliary equipment that must be operated when the system is off, and includes, for example, auxiliary equipment used for vehicle theft prevention or security purposes (e.g., a horn and emergency flashers or hazard warning lights). The second accessory equipment refers to auxiliary equipment that does not need to be operated when the system is off, and is additional equipment not included in the first accessory equipment (e.g., a vehicle audio system or a power window).

[0011] In the vehicle, the vehicle may further include a control device configured to control the switch such that the second auxiliary equipment is disconnected from the low-voltage side power line when, in the system off state, a state of charge or voltage of the second energy storage device becomes equal to or less than a first reference value in a state where the second auxiliary equipment is connected to the low-voltage side power line. This configuration limits the amount of decrease in the state of charge or voltage of the second energy storage device after the state of charge or voltage of the second energy storage device becomes equal to or less than the first reference value.

[0012] In this case, the control device may control the DC-DC converter to step down the voltage of the electric power of the high-voltage side power line in the system off state and supply the electric power of the step-down voltage to the low-voltage side power line when the second auxiliary equipment is disconnected from the low-voltage side power line. This configuration restricts a further decrease in the state of charge or voltage of the second energy storage device after the state of charge or voltage of the second energy storage device becomes equal to or less than the second reference value.

[0013] The vehicle according to the present invention includes a second switch configured to disconnect the second energy storage device from the low-voltage side power line. The vehicle according to the invention further includes a control device configured to control the switch in the system-off state such that the second auxiliary equipment is disconnected from the low-voltage side power line when a charge level or voltage of the second energy storage device becomes equal to or less than a first reference value in a state where the second auxiliary equipment and the second energy storage device are connected to the low-voltage side power line, and when the charge level or voltage of the second energy storage device subsequently becomes equal to or less than a second reference value that is less than the first reference value, wherein the control device controls the DC-DC converter such thatthat the voltage of the electric power of the high-voltage side power line is down-converted, and the electric power of the down-converted voltage is supplied to the low-voltage side power line, while the second switch is controlled such that the second energy storage device is disconnected from the low-voltage side power line. This configuration allows the dark current to be supplied from the high-voltage side power line (first energy storage device) via the DC-DC converter and the low-voltage side power line to the first auxiliary equipment and restricts a further reduction in the state of charge or voltage of the second energy storage device after the state of charge or voltage of the second energy storage device becomes equal to or lower than the second reference value.

[0014] In the vehicle according to the present invention, the vehicle may further include a relay arranged in the high-voltage side power line and configured to connect a driving device for travel to the first energy storage device. The DC-DC converter may be connected to the first energy storage device side of the relay in the high-voltage side power line and to the low-voltage side power line. This configuration enables the dark current to be supplied from the first energy storage device to the first auxiliary equipment via the DC-DC converter and the low-voltage side power line without turning on the relay, that is, without electrically connecting the driving device to the first energy storage device in the system off state. Short description of the drawings Fig. 1 is a configuration diagram showing the schematic configuration of an electric vehicle according to a first embodiment of the present invention; Fig. 2 is a flowchart showing an example of a system power-off state processing routine performed by the electronic control unit; Fig. 3 is a diagram showing an example of a state in which the electric vehicle is left in the system off state; Fig. 4 is a diagram showing the schematic configuration of an electric vehicle according to a second embodiment not according to the invention; Fig. 5 is a flowchart showing an example of a system power-off state processing routine according to the second embodiment; and Fig. 6 is a diagram showing an example of a state in which the electric vehicle according to the second embodiment is left in the system off state. Description of the embodiments

[0015] Some aspects of the present invention are described below. First embodiment

[0016] Fig. Figure 1 is a configuration diagram illustrating the schematic configuration of an electric vehicle 20 according to a first embodiment of the present invention. As illustrated, the electric vehicle 20 of the first embodiment includes an electric motor 22, an inverter 24, a main battery 26 serving as a first energy storage device, a system main relay 28, an auxiliary equipment battery 30 serving as a second energy storage device, a main DC-DC converter 32, a sub-DC-DC converter 34, a first auxiliary equipment 36, a second auxiliary equipment 38, switches 40 and 42, and an electronic control unit 50.

[0017] The electric motor 22 is configured, for example, as a synchronous generator motor and serves to output power for propulsion or drive power. The inverter 24 is used to drive the electric motor 22. The main battery 26 is configured, for example, as a rechargeable lithium-ion battery or a nickel-metal hydride battery with a nominal voltage of approximately several hundred volts and is connected to the inverter 24 via high-voltage side power lines PH. The system main relay 28 is arranged in the high-voltage side power lines PH and serves to connect and disconnect the inverter 24 side to and from the main battery 26 side.

[0018] The auxiliary equipment battery 30 is configured, for example, as a lead-acid battery with a rated voltage of 12 V. The main DC-DC converter 32 is configured, for example, as a converter with a rated current of approximately several tens of amperes and is connected to the inverter 24 side of the system main relay 28 in the high-voltage side power lines PH and to a low-voltage side power line PL. This main DC-DC converter 32 serves to step down the voltage of the electric power of the high-voltage side power lines PH and supply the step-down electric power to the low-voltage side power line PL.

[0019] The sub-DC-DC converter 34 is configured, for example, as a converter with a rated current of approximately several tens of mA (for supplying a dark current), and is arranged on the main battery 26 side of the system main relay 28 in the high-voltage side power lines PH and connected to the low-voltage side power line PL. This sub-DC-DC converter 34 serves to step down the voltage of the electric power of the high-voltage side power lines PH and supply the step-down electric power to the low-voltage side power line PL.

[0020] The first auxiliary equipment 36 denotes auxiliary devices or machines that must be operated in a system-off state, and includes, for example, auxiliary machines used in vehicle theft prevention and security (e.g., a horn and an emergency flasher or hazard warning light). The second auxiliary equipment 38 denotes auxiliary devices or machines that do not need to be operated in the system-off state and are auxiliary machines not included in the first auxiliary equipment 36 (e.g., a vehicle audio system or power windows).

[0021] The switch 40 is configured as a normally closed switch and has one side connected to the low-voltage side power line PL and another side connected to the second auxiliary equipment 38. The switch 42 is configured as a normally closed switch and has one side connected to the low-voltage side power line PL and another side connected to the auxiliary equipment battery 30.

[0022] The electronic control unit 50 is implemented as a CPU-based microprocessor and includes, in addition to the CPU, a ROM configured to store processing programs, a RAM configured to temporarily store data, and input / output ports, although these are not shown. Signals from various sensors are input to the electronic control unit 50 via the input port. The signals input to the electronic control unit 50 include, for example, a rotational position from a rotational position sensor (not shown) configured to detect a rotational position of a rotor of the electric motor 22, and phase currents from current sensors (not shown) configured to detect electric currents flowing through respective phases of the electric motor 22.The input signals also include a voltage Vmb of the main battery 26 from a voltage sensor 26a disposed between terminals of the main battery 26, an electric current Imb of the main battery 26 from a current sensor 26b mounted on an output terminal of the main battery 26, a voltage Vab of the auxiliary equipment battery 30 from a voltage sensor 30a disposed between terminals of the auxiliary equipment battery 30, and an electric current lab of the auxiliary equipment battery 30 from a current sensor 30b mounted on an output terminal of the auxiliary equipment battery 30.

[0023] Various control signals are output from the electronic control unit 50 through the output port. The signals output from the electronic control unit 50 through the output port include, for example, control signals for the inverter 24, control signals for the system main relay 28, control signals for the main DC-DC converter 32, control signals for the sub DC-DC converter 34, control signals for the first auxiliary equipment 36, and control signals for the second auxiliary equipment 38. The electronic control unit 50 calculates a state of charge SOCmb of the main battery 26 based on an integrated value of the electric current Imb of the main battery 26 input from the current sensor 26b.The electronic control unit 50 also calculates a state of charge SOCab of the auxiliary equipment battery 30 based on an integrated value of the electric current lab of the auxiliary equipment battery 30 input from the current sensor 30b.

[0024] Next, operations of the electric vehicle 20 of the first embodiment configured as described above, or more specifically, a sequence of operations when the electric vehicle 20 is left in the system-off state for a relatively long period of time, will be described. Fig. Fig. 2 is a flowchart showing an example of a system shutdown processing routine executed by the electronic control unit 50. This routine is triggered by a start of the system shutdown state.

[0025] If the system power-off processing routine of the Fig. 2 is triggered, the electronic control unit 50 first receives the input of the state of charge SOCab of the auxiliary equipment battery 30 from the current sensor 30b (step S100) and compares the input state of charge SOCab of the auxiliary equipment battery 30 with a reference value Sabref1 (step S110). The reference value Sabref1 used here denotes a threshold value used to determine whether it is permissible to supply a dark current from the auxiliary equipment battery 30 to the second auxiliary equipment 38, and is, for example, 38%, 40%, or 42%. If the state of charge SOCab of the auxiliary equipment battery 30 is greater than the reference value Sabref1, the processing routine of the electronic control unit 50 returns to step S100.

[0026] On the other hand, if the state of charge SOCab of the auxiliary equipment battery 30 is equal to or less than the reference value Sabref1 in step S110, the electronic control unit 50 turns off the switch 40 (step S120). Turning off the switch 40 disconnects the second auxiliary equipment 38 from the low-voltage side power line PL, thereby preventing the dark current from the auxiliary equipment battery 30 from being supplied to the second auxiliary equipment 38. This accordingly limits a discharge amount of the auxiliary equipment battery 30 and therefore limits a decrease in the state of charge SOCab of the auxiliary equipment battery 30. Even in this state, a dark current is supplied from the auxiliary equipment battery 30 to the first auxiliary equipment 36.

[0027] The electronic control unit 50 then receives the input of the SOCab of the auxiliary equipment battery 30 from the current sensor 30b (step S130) and compares the input SOCab of the auxiliary equipment battery 30 with a reference value Sabref2 that is lower than the reference value Sabref1 (step S140). If the SOCab of the auxiliary equipment battery 30 is greater than the reference value Sabref2, the processing routine of the electronic control unit 50 returns to step S130. The reference value Sabref2 used here is determined as a value of the SOCab required for a next system startup or as a slightly higher value than this SOCab, and is, for example, 28%, 30%, or 32%.

[0028] On the other hand, when the state of charge SOCab of the auxiliary equipment battery 30 is equal to or less than the reference value Sabref2 in step S140, the electronic control unit 50 starts driving the auxiliary DC-DC converter 34 to step down the voltage of the electric power of the high-voltage side power lines PH (i.e., the electric power of the main battery 26) and supply the step-down voltage electric power to the low-voltage side power line PL (step S150), and then turns off the switch 42 (step S160). Turning off the switch 42 disconnects the auxiliary equipment battery 30 from the low-voltage side power line PL. This restricts subsequent discharge of the auxiliary equipment battery 30 and thereby maintains the state of charge SOCab required for subsequent system startup in the auxiliary equipment battery 30.Control of the auxiliary DC-DC converter 34 enables the supply of dark current from the main battery 26 via the auxiliary DC-DC converter 34 to the first auxiliary equipment 36 without turning on the system main relay 28, that is, without connecting the inverter 24 to the main battery 26. Furthermore, turning off the switch 42 after starting control of the auxiliary DC-DC converter 34 prevents an interruption in the supply of dark current to the first auxiliary equipment 36.

[0029] The electronic control unit 50 then waits for receipt of a system start command (step S170). The system start command is received when the user operates a start switch (not shown). Upon receiving the system start command, the electronic control unit 50 turns on the switches 40 and 42 to connect the second auxiliary equipment 38 and the auxiliary equipment battery 30 to the low-voltage side power line PL (step S180), stops driving the auxiliary DC-DC converter 34 (step S190), starts the system (step S200), and then terminates this processing routine. According to an exemplary procedure for starting the system, the electronic control unit 50 turns on the system main relay 28 to connect the main battery 26 to the inverter 24 (to make the electric motor 22 drivable).

[0030] During this processing routine, the electronic control unit 50 likely receives the system start instruction before the switch 42 is turned off (that is, before the processing in step S160 is performed). In this state, the auxiliary equipment battery 30 is connected to the low-voltage side power line PL, so the electronic control unit 50 turns on the switch 40 when the switch 40 is off, and then starts the system.

[0031] Fig. 3 is a diagram illustrating an example of the state in which the electric vehicle 20 is left in the system-off state. As illustrated, in the system-off state, when the supply of dark current from the auxiliary equipment battery 30 to the first auxiliary equipment 36 and the second auxiliary equipment 38 reduces the state of charge SOCab of the auxiliary equipment battery 30 to be equal to or less than the reference value Sabref1 (at time t11), the electric vehicle 20 turns off the switch 40 to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. This limits the amount of discharge of the auxiliary equipment battery 30 and thereby limits the amount of reduction in the state of charge SOCab of the auxiliary equipment battery 30.When subsequent supply of dark current from the auxiliary equipment battery 30 to the first auxiliary equipment 36 reduces the state of charge SOCab of the auxiliary equipment battery 30 to be equal to or less than the reference value Sabref2 (at time t12), the electric vehicle 20 starts driving the sub-DC-DC converter 34 and then turns off the switch 42. This allows supply of dark current from the main battery 26 to the first auxiliary equipment 36 via the sub-DC-DC converter 34 while preventing interruption of the supply of dark current to the first auxiliary equipment 36. This also limits subsequent discharge of the auxiliary equipment battery 30 and causes the auxiliary equipment battery 30 to maintain the state of charge SOCab required for subsequent system startup.

[0032] As described above, the electric vehicle 20 of the first embodiment includes the switch 40 configured to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. In the system off state, when the state of charge SOCab of the auxiliary equipment battery 30 becomes equal to or less than the reference value Sabref1, the electric vehicle 20 turns off the switch 40 to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. This limits the amount of discharge of the auxiliary equipment battery 30 and thereby limits the amount of decrease in the state of charge SOCab of the auxiliary equipment battery 30.

[0033] The electric vehicle 20 of the first embodiment also includes the switch 42 configured to disconnect the auxiliary equipment battery 30 from the low-voltage side power line PL. In the system off state, when the state of charge SOCab of the auxiliary equipment battery 30 becomes equal to or less than the reference value Sabref2 after the switch 40 is turned off, the electric vehicle 20 starts driving the sub-DC-DC converter 34 and then turns off the switch 42. This allows the dark current to be supplied from the main battery 26 to the first auxiliary equipment 36 via the sub-DC-DC converter 34, while preventing the dark current from being supplied to the first auxiliary equipment 36. This also restricts subsequent discharge of the auxiliary equipment battery 30 and causes the state of charge SOCab required for subsequent system startup to be maintained in the auxiliary equipment battery 30. Second embodiment

[0034] Fig. Fig. 4 is a diagram illustrating the schematic configuration of an electric vehicle 120 according to a second embodiment not according to the invention. The electric vehicle 120 of the second embodiment has a similar configuration to the electric vehicle 20 of the first embodiment shown in Fig. 1, except that the electric vehicle 120 does not include the sub-DC-DC converter 34 or the switch 42, and the auxiliary equipment battery 30 is directly connected to the low-voltage side power line PL. Similar hardware components in the electric vehicle 120 of the second embodiment to those in the electric vehicle 20 of the first embodiment are denoted by the same reference numerals, and their detailed descriptions will not be repeated.

[0035] In the electric vehicle 120 of the second embodiment, the electronic control unit 50 executes a system off-state processing routine according to Fig. 5 instead of the system shutdown processing routine of the Fig. 2. The system shutdown processing routine of the Fig. 5 is similar to the system power-off state processing routine of the Fig. 2, except that the processing in steps S150 to S200 is replaced by the processing in steps S300 to S360. The same processing steps are designated by the same step numbers, and their detailed descriptions will not be repeated.

[0036] In the system shutdown processing routine of the Fig. 5, the electronic control unit 50 determines whether the system start command is received (step S300) when the state of charge SOCab of the auxiliary equipment battery 30 is equal to or less than the reference value Sabref2 in step S140. If it is determined that no system start command is received, the electronic control unit 50 controls the main DC-DC converter 32 to step down the voltage of the electric power of the high-voltage side power lines PH (i.e., the electric power of the main battery 26) and supply the step-down voltage electric power to the low-voltage side power line PL (step S310). Controlling the main DC-DC converter 32 enables dark current to be supplied from the main battery 26 to the auxiliary equipment battery 30 and the first auxiliary equipment 36 via the main DC-DC converter 32.This limits further discharging of the auxiliary equipment battery 30 and ensures that the state of charge SOCab required for subsequent system startup is maintained in the auxiliary equipment battery 30. The main DC-DC converter 32 has a higher rated current than the auxiliary DC-DC converter 34 and, accordingly, has lower controllability with respect to a small electrical current. However, the auxiliary equipment battery 30 serves as a buffer and allows the dark current to be supplied to the first auxiliary equipment 36.

[0037] The electronic control unit 50 then receives the input of the state of charge SOCab of the auxiliary equipment battery 30 from the current sensor 30b (step S320) and compares the input state of charge SOCab of the auxiliary equipment battery 30 with a reference value Sabref3, which is lower than the reference value Sabref1 but higher than the reference value Sabref2 (step S330). The reference value Sabref3 used here denotes a threshold value used to determine whether the state of charge SOCab of the auxiliary equipment battery 30 has recovered to a certain extent, and is, for example, 34%, 35%, or 36%. If the state of charge SOCab of the auxiliary equipment battery 30 is equal to or less than the reference value Sabref3, the processing routine of the electronic control unit 50 returns to step S300.On the other hand, when the state of charge SOCab of the auxiliary equipment battery 30 is greater than the reference value Sabref3, the electronic control unit 50 stops driving the main DC-DC converter 32 (step S340), and then the processing routine returns to step S130.

[0038] When it is determined in step S300 that the system start instruction is received, the electronic control unit 50 turns on the switch 40 (step S350), starts the system (step S360), and then ends this processing routine.

[0039] During this processing routine, the electronic control unit 50 likely receives the system start instruction during execution of the processing in steps S100 to S140. In this state, the electronic control unit 50 turns on the switch 40 if the switch 40 is off, and then starts the system.

[0040] Fig.6 is a diagram illustrating an example of a state in which the electric vehicle 100 is left in the system-off state. As illustrated, in the system-off state, when the supply of a dark current from the auxiliary equipment battery 30 to the first auxiliary equipment 36 and the second auxiliary equipment 38 reduces the state of charge SOCab of the auxiliary equipment battery 30 to become equal to or less than the reference value Sabref1 (at time t21), the electric vehicle 120 turns off the switch 40 to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. This limits the amount of discharge of the auxiliary equipment battery 30 and thereby limits the amount of reduction in the state of charge SOCab of the auxiliary equipment battery 30.When subsequent supply of a dark current from the auxiliary equipment battery 30 to the first auxiliary equipment 36 reduces the state of charge SOCab of the auxiliary equipment battery 30 to be equal to or less than the reference value Sabref2 (at a time t22), the electric vehicle 120 starts driving the main DC-DC converter 32. This enables supply of an electric current from the main battery 26 via the main DC-DC converter 32 to the auxiliary equipment battery 30 and to the first auxiliary equipment 36. As a result, further discharge of the auxiliary equipment battery 30 is restricted and results in the auxiliary equipment battery 30 maintaining the state of charge SOCab required for subsequent system startup.After the auxiliary equipment battery 30 is charged to increase the state of charge SOCab of the auxiliary equipment battery 30 to greater than the reference value Sabref3 (at a time t23), the electric vehicle 120 stops driving the main DC-DC converter 32.

[0041] As described above, similar to the electric vehicle 20 of the first embodiment, the electric vehicle 120 includes the switch 40 configured to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. When the state of charge SOCab of the auxiliary equipment battery 30 becomes equal to or less than the reference value Sabref1 in the system off state, the electric vehicle 120 turns off the switch 40 to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. This limits the amount of discharge of the auxiliary equipment battery 30 and thereby limits the amount of decrease in the state of charge SOCab of the auxiliary equipment battery 30.

[0042] After turning off the switch 40 in the system-off state, when the state of charge SOCab of the auxiliary equipment battery 30 becomes equal to or less than the reference value Sabref2, the electric vehicle 120 of the second embodiment drives the main DC-DC converter 32. This enables supply of electric power from the main battery 26 via the main DC-DC converter 32 to the auxiliary equipment battery 30 and to the first auxiliary equipment 36. This limits further discharge of the auxiliary equipment battery 30 and causes the auxiliary equipment battery 30 to maintain the state of charge SOCab required for subsequent system startup.

[0043] In the system off state, when the charge level SOCab of the auxiliary equipment battery 30 becomes equal to or less than the reference value Sabref1, the electric vehicle 20 of the first embodiment or the electric vehicle 120 of the second embodiment turns off the switch 40 to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL. A modification may turn off the switch 40 in the system off state, regardless of the charge level SOCab of the auxiliary equipment battery 30, in response to a user's instruction to turn off the switch 40, to disconnect the second auxiliary equipment 38 from the low-voltage side power line PL.

[0044] The electric vehicle 20 of the first embodiment or the electric vehicle 120 of the second embodiment compares the state of charge SOCab of the auxiliary equipment battery 30 with the reference value Sabref1 and / or the reference value Sabref2. A modification may compare the voltage Vab of the auxiliary equipment battery 30 with a reference value Vabref1 and / or a reference value Vabref2. The reference value Vabref1 and the reference value Vabref2 are determined as voltages corresponding to the reference value Sabref1 and the reference value Sabref2, respectively.

[0045] The electric vehicle 20 of the first embodiment or the electric vehicle 120 of the second embodiment uses the main battery 26 as the first energy storage device. According to a modification, a capacitor may be used as the first energy storage device.

[0046] According to the above embodiments, the present invention is implemented as configurations of the electric vehicles 20 and 120 including the electric motor 22. According to a modification, the present invention may be implemented as a configuration of a hybrid vehicle equipped with both an electric motor and an internal combustion engine.

[0047] The following describes the correspondence between the primary components of the embodiment and the primary components of the invention described in the above summary. The main battery 26 of the embodiment corresponds to the "first energy storage device," the auxiliary equipment battery 30 corresponds to the "second energy storage device," and the sub-DC-DC converter 34 corresponds to the "DC-DC converter" in the above aspect of the present invention.

[0048] However, the correspondence relationship between the primary elements of the above embodiment and the primary elements in the above aspects of the present invention described in the above summary does not limit the elements in the aspects of the present invention described in the above summary, since the embodiment is only a concrete example of the invention described in the above summary. Industrial applicability

[0049] The present invention is applicable to the manufacturing industry of vehicles, etc.

Claims

[1] Vehicle that has: a first energy storage device (26); a second energy storage device (30) having a lower rated voltage than a rated voltage of the first energy storage device (26); a DC-DC converter (32, 34) configured to down-convert a voltage of an electric power of a high-voltage side power line (PH) to which the first energy storage device (26) is connected, and to supply the down-converted electric power voltage to a low-voltage side power line (PL) to which the second energy storage device (30) is connected; a first auxiliary device (36) connected to the low-voltage side power line (PL) and designed to be operated in a system off state; a second auxiliary device (38) connected to the low-voltage side power line (PL) and designed such that it need not be operated in the system off state; and a switch (40) designed to disconnect the second additional device (38) from the low-voltage power line (PL), characterized by a second switch (42) designed to disconnect the second energy storage device (30) from the low-voltage side power line (PL), and a control device configured to control the switch (40) in the system off state to disconnect the second auxiliary device (38) from the low-voltage side power line (PL) when a charge state or a voltage of the second energy storage device (30) becomes equal to or less than a first reference value in a state in which the second auxiliary device (38) and the second energy storage device (30) are connected to the low-voltage side power line (PL), wherein when the state of charge or the voltage of the second energy storage device (30) subsequently becomes equal to or less than a second reference value which is less than the first reference value, the control device controls the DC-DC converter to step down the voltage of the electric power of the high-voltage side power line (PH) and supply the electric power of the step-down voltage to the low-voltage side power line (PL), while controlling the second switch (42) to disconnect the second energy storage device (30) from the low-voltage side power line (PL). [2] A vehicle according to claim 1, further comprising: a control device (50) configured to control the switch (40) in the system off state to disconnect the second auxiliary device (38) from the low-voltage side power line (PL) when a charge state or a voltage of the second energy storage device (30) becomes equal to or less than a first reference value in a state in which the second auxiliary device (38) is connected to the low-voltage side power line (PL). [3] The vehicle according to claim 2, wherein the control device (50) controls the DC-DC converter (32) in the system off state in a state where the second auxiliary device (38) is disconnected from the low-voltage side power line (PL) to down-convert the voltage of the electric power of the high-voltage side power line (PH) and supply the down-converted voltage electric power to the low-voltage side power line (PL) when the state of charge or the voltage of the second energy storage device (30) becomes equal to or less than a second reference value which is less than the first reference value. [4] A vehicle according to claim 1, further comprising: a relay (28) arranged in the high-voltage side power line (PH) and designed to connect a drive device (22, 24) for travel to the first energy storage device (26), wherein the DC-DC converter (34) is connected to the side of the first energy storage device (26) of the relay in the high-voltage side power line (PH) and to the low-voltage side power line (PL).

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