Power supply device for vehicle and method of controlling the same

This nonprovisional application is based on Japanese Patent Application No. 2005-229849 filed with the Japan Patent Office on Aug. 8, 2005, the entire contents of which are hereby incorporated by reference.

1. Field of the Invention

The present invention relates to a power supply device for a vehicle, and particularly to a power supply device for a vehicle, the power supply device having two electric storage devices.

2. Description of the Background Art

In recent years, attention has been focused on an electric vehicle and a fuel-cell vehicle that use a motor in driving a wheel, and a hybrid vehicle that uses a motor and an engine in combination, and other vehicles, as an environmental-friendly vehicle.

For example, an electric vehicle requires a charging device for charging a battery. The charging device may be mounted on a vehicle, or provided at a certain location in a fixed manner.

In the case where the charging device is provided at a certain location in a fixed manner, it is necessary to move the electric vehicle to that place for charging. In other words, the charging device being provided in a fixed manner is disadvantageous in that the battery cannot be charged at a place other than the place where the charging device is provided in a fixed manner.

In contrast, if the charging device is mounted on the vehicle, there exists a problem of increase in vehicle weight. In order to solve the problem, there has been proposed a device that charges a battery from a commercial power supply at home by using a coil of a drive motor as a reactor, and by controlling a circuit element of an inverter that controls the motor. As to this device, the existing part is utilized so that the number of parts to be newly mounted is reduced, and weight increase is avoided.

Japanese Patent Laying-Open No. 08-126121 discloses a technique of preventing rotation of a rotor in an electric vehicle by allowing magnetic fields generated by three-phase coils to cancel each other out, in order to prevent movement of the vehicle caused by the rotor rotation, when the coils of the drive motor are used as a reactor to charge a battery.

If a battery in an electric vehicle as well as a hybrid vehicle can be charged from a commercial power supply at home, there may be a merit in that the frequency with which one has to go to the gas station for refueling is decreased, or may be an economical merit in a country where commercial electric power is inexpensive.

However, the Japanese Patent Laying-Open No. 08-126121 relates to an electric vehicle having two drive motors mounted on the left and right sides or the front and rear sides thereof, and hence the disclosure cannot be applied as it is to the hybrid vehicle.

Furthermore, a hybrid vehicle commercially available at present has a storage battery with small capacity, and hence even if the battery can be charged at home, an amount of energy to be supplied at that time is small. Accordingly, just after the vehicle runs for a while, a state of charge (SOC) of the storage battery decreases and the engine is required to start for activating an electric generator to generate electric power. Therefore, refueling with petrol is frequently required.

Furthermore, the hybrid vehicle performs regenerative braking in a downslope and recaptures electric power at that time to charge the storage battery. However, the capacity of the storage battery is so small that, when a running route includes a long downslope, power generated by regenerative braking is discarded as heat, once a state of charge of the storage battery reaches a prescribed value.

FIG. 14 is a diagram for describing electric power discarded as heat during regenerative braking.

Referring to FIG. 14 , the storage battery is controlled such that it is used within 40-80% of the SOC range, for example, so as not to shorten its life. When the SOC of the storage battery is 60% at time t 0 , chargeable capacity is only 20%.

In the case of a long downslope, the storage battery is charged with regenerative electric power generated at times t 0 -t 1 . As a result, the SOC of the storage battery increases from 60% to 80%.

If the storage battery is further charged during a period from time t 1 to time t 2 at which the slope ends, the life of the storage battery may be shortened. The regenerative electric power generated is therefore discarded as heat. If even a part of electric power to be discarded can be recaptured, it is possible to implement a hybrid vehicle with higher energy efficiency.

An object of the present invention is to provide a power supply device for a vehicle that has an electric storage device mounted thereon, that has improved energy efficiency, and that can be driven for a long time without the need of refueling.

To summarize, the present invention is a power supply device for a vehicle, includes: a first electric storage device; a second electric storage device; a first rotating electric machine driving a wheel; a selection switch selecting one of the first and second electric storage devices and connecting the selected electric storage device to the first rotating electric machine; and a control device controlling switching of the selection switch in accordance with a state of charge of each of the first and second electric storage devices. In a case where the selection switch selects the first electric storage device, when charging is performed so that the state of charge of the first electric storage device becomes higher than a first prescribed level, the control device instructs the selection switch to select the second electric storage device.

Preferably, the charging in the case where the selection switch selects the first electric storage device is performed with regenerative electric power generated during a regenerative braking operation of the first rotating electric machine during running of the vehicle.

Preferably, in a case where the selection switch selects the second electric storage device, when the state of charge of the second electric storage device becomes lower than a second prescribed level, the control device instructs the selection switch to select the first electric storage device.

Preferably, the second electric storage device has larger electricity storage capacity than the first electric storage device has.

Preferably, the first electric storage device has larger maximum chargeable electric power than the second electric storage device has.

Preferably, the power supply device for the vehicle further includes an input unit for receiving electric power supplied from outside of the vehicle and charging at least the second electric storage device.

More preferably, the power supply device for the vehicle further includes: a first inverter provided corresponding to the first rotating electric machine; a second rotating electric machine; and a second inverter provided corresponding to the second rotating electric machine. The input unit includes a first terminal connected to the first rotating electric machine, and a second terminal connected to the second rotating electric machine. The control device controls the first and second inverters such that an alternating-current electric power supplied to the first and second terminals is converted into a direct-current electric power and supplied to the second electric storage device.

More preferably, a rotary shaft of the first rotating electric machine is mechanically coupled to a rotary shaft of the wheel. The power supply device for the vehicle further includes an internal combustion engine having a crankshaft mechanically coupled to a rotary shaft of the second rotating electric machine.

A power supply device for a vehicle according to another aspect of the present invention includes: a first electric storage device; a second electric storage device; a first rotating electric machine receiving electric power from the first electric storage device and driving a wheel; a voltage converting unit provided between the first and second electric storage devices, for receiving and transferring electric power between the first and second electric storage devices; and a control device controlling the voltage converting unit in accordance with a state of charge of each of the first and second electric storage devices. In a case where charging of the first electric storage device is performed, when the state of charge of the first electric storage device becomes higher than a first prescribed level, the control device instructs the voltage converting unit to perform a voltage converting operation such that the second electric storage device is charged from the first electric storage device.

Preferably, the charging of the first electric storage device is performed with regenerative electric power generated during a regenerative braking operation of the first rotating electric machine during running of the vehicle.

Preferably, when energy in the first electric storage device is consumed and the state of charge of the first electric storage device becomes lower than a second prescribed level, the control device instructs the voltage converting unit to perform the voltage converting operation such that the first electric storage device is charged from the second electric storage device.

Preferably, the second electric storage device has larger electricity storage capacity than the first electric storage device has.

Preferably, the first electric storage device has larger maximum chargeable electric power than the second electric storage device has.

Preferably, the power supply device for a vehicle further includes an input unit for receiving electric power supplied from outside of the vehicle and charging at least the second electric storage device.

More preferably, the power supply device for a vehicle further includes: a first inverter provided corresponding to the first rotating electric machine; a second rotating electric machine; and a second inverter provided corresponding to the second rotating electric machine. The input unit includes a first terminal connected to the first rotating electric machine, and a second terminal connected to the second rotating electric machine. The control device controls the first and second inverters and the voltage converting unit such that an alternating-current electric power supplied to the first and second terminals is converted into a direct-current electric power, and supplied to the second electric storage device.

More preferably, a rotary shaft of the first rotating electric machine is mechanically coupled to a rotary shaft of a wheel. The power supply device for the vehicle further includes an internal combustion engine having a crankshaft mechanically coupled to a rotary shaft of the second rotating electric machine.

A method according to still another aspect of the present invention is a method of controlling a power supply device for a vehicle, the power supply device including first and second electric storage devices, a first rotating electric machine driving a wheel, and a selection switch selecting one of the first and second electric storage devices and connecting the selected electric storage device to the first rotating electric machine, includes the steps of: determining whether or not charging is performed when the selection switch selects the first electric storage device; determining whether or not a state of charge of the first electric storage device is higher than a first prescribed level; and instructing the selection switch to select the second electric storage device when the state of charge of the first electric storage device becomes higher than the first prescribed level.

Preferably, the charging when the selection switch selects the first electric storage device is performed with regenerative electric power generated during a regenerative braking operation of the first rotating electric machine during running of the vehicle.

A method according to a further aspect of the present invention is a method of controlling a power supply device for a vehicle, the power supply device including first and second electric storage devices, a first rotating electric machine receiving electric power from the first electric storage device and driving a wheel, and a voltage converting unit provided between the first and second electric storage devices and receiving and transferring electric power between the first and second electric storage devices, includes the steps of: determining whether or not charging of the first electric storage device is performed; determining whether or not a state of charge of the first electric storage device becomes higher than a first prescribed level; and instructing the voltage converting unit to perform a voltage converting operation such that the second electric storage device is charged from the first electric storage device when the state of charge of the first electric storage device becomes higher than the first prescribed level.

Preferably, the charging of the first electric storage device is performed with regenerative electric power generated during a regenerative braking operation of the first rotating electric machine during running of the vehicle.

According to the present invention, by mounting two batteries on a vehicle and charging these batteries, it is possible to prolong a distance the vehicle can run or a period of time the vehicle can run for without the need of refueling, and to decrease the frequency of refueling.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic block diagram of a vehicle according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram of a control device 60 shown in FIG. 1 .

FIG. 3 is a functional block diagram of a converter control unit 61 shown in FIG. 2 .

FIG. 4 is a functional block diagram of first and second inverter control units 62 , 63 shown in FIG. 2 .

FIG. 5 is a diagram of the circuit diagram in FIG. 1 , which circuit diagram is simplified to focus on a portion relating to charging.

FIG. 6 is a diagram showing a control state of a transistor during charging.

FIG. 7 is a flowchart showing a control structure of a program relating to a determination as to the start of charging, which determination is made by control device 60 shown in FIG. 1 .

FIG. 8 is a conceptual diagram for describing a difference in characteristic between batteries B 1 , B 2 in FIG. 1 .

FIG. 9 is a flowchart showing a control structure of a program relating to battery selection in recapturing regenerative electric power, which battery selection is made by control device 60 in FIG. 1 .

FIG. 10 is a diagram for describing recapture of regenerative electric power in the first embodiment.

FIG. 11 is a circuit diagram showing a configuration of a battery unit BU 1 used in a second embodiment.

FIG. 12 is a flowchart showing a control structure of a program relating to battery selection in recapturing regenerative electric power, which battery selection is made by control device 60 in the second embodiment.

FIG. 13 is a diagram for describing recapture of regenerative electric power in the second embodiment.

FIG. 14 is a diagram for describing electric power discarded as heat during regenerative braking.

The embodiments of the present invention will hereinafter be described in detail with reference to the drawings. The same or corresponding portions are denoted by the same reference characters, and the description thereof will not be described.

First Embodiment

FIG. 1 is a schematic block diagram of a vehicle according to a first embodiment of the present invention.

Referring to FIG. 1 , vehicle 100 includes a battery unit BU, a voltage step up converter 10 , inverters 20 , 30 , power supply lines PL 1 , PL 2 , a ground line SL, U-phase lines UL 1 , UL 2 , V-phase lines VL 1 , VL 2 , W-phase lines WL 1 , WL 2 , motor generators MG 1 , MG 2 , an engine 4 , a power split device 3 , and a wheel 2 .

Vehicle 100 is a hybrid vehicle that uses a motor and an engine in combination for driving the wheel.

Power split device 3 is a mechanism connected to engine 4 and motor generators MG 1 , MG 2 for distributing motive power among them. For example, a planetary gear mechanism having three rotary shafts of a sun gear, a planetary carrier, and a ring gear may be used for the power split device. The three rotary shafts are connected to rotary shafts of engine 4 , motor generators MG 1 , MG 2 , respectively. For example, engine 4 and motor generators MG 1 , MG 2 can mechanically be connected to power split device 3 by allowing a crankshaft of engine 4 to extend through the center of a hollow space in a rotor of motor generator MG 1 .

A rotary shaft of motor generator MG 2 is coupled to wheel 2 through a reduction gear, a running gear, and the like not shown. A speed reducer for the rotary shaft of motor generator MG 2 may further be incorporated inside power split device 3 .

Motor generator MG 1 is incorporated in the hybrid vehicle for operating as an electric generator driven by the engine and operating as an electric motor capable of starting the engine, while motor generator MG 2 is incorporated in the hybrid vehicle for serving as an electric motor that drives a driving wheel of the hybrid vehicle.

Each of motor generators MG 1 , MG 2 is, for example, a three-phase alternating synchronous electric motor. Motor generator MG 1 includes three-phase coils composed of a U-phase coil U 1 , a V-phase coil V 1 , and a W-phase coil W 1 , as a stator coil. Motor generator MG 2 includes three-phase coils composed of a U-phase coil U 2 , a V-phase coil V 2 , and a W-phase coil W 2 , as a stator coil.

Motor generator MG 1 uses an engine output to thereby generate a three-phase alternating voltage, and outputs the generated three-phase alternating voltage to inverter 20 . Furthermore, motor generator MG 1 generates driving force by three-phase alternating voltage received from inverter 20 to thereby start the engine.

Motor generator MG 2 generates driving torque for the vehicle by three-phase alternating voltage received from inverter 30 . Furthermore, motor generator MG 2 generates a three-phase alternating voltage during regenerative braking of the vehicle and outputs the same to inverter 30 .

Battery unit BU includes batteries B 1 , B 2 serving as electric storage devices whose negative electrodes are both connected to a ground line SL, a selection switch RY 0 that selects one of batteries B 1 , B 2 and connects the selected battery to a vehicle load, voltage sensors 70 , 71 that measure voltages of batteries B 1 , B 2 , respectively, and current sensors 84 , 83 that measure currents of batteries B 1 , B 2 , respectively. The vehicle load includes motor generators MG 1 , MG 2 , inverters 20 , 30 , and voltage step up converter 10 that supplies a stepped-up voltage to inverters 20 , 30 .

In battery unit BU, a combination of batteries B 1 , B 2 is selected such that battery B 2 has larger electricity storage capacity than battery B 1 has, and instead that battery B 1 has larger maximum allowed output electric power than battery B 2 has. In this case, battery B 1 usually has larger maximum chargeable electric power than battery B 2 has. For example, battery B 1 can store electric power of up to 20 kW, while battery B 2 can store electric power of up to 5 kW.

A secondary battery such as a nickel metal hydride battery or a lithium-ion battery may be used for battery B 1 . In this case, an inexpensive, high-capacity, lead-acid battery may be used for battery B 2 .

Alternatively, a high-capacity electric double layer capacitor may be substituted for battery B 1 . In this case, a battery that has smaller maximum allowed output electric power and larger electricity storage capacity, when compared with the high-capacity electric double layer capacitor, may be used for battery B 2 . In this case, a secondary battery such as a nickel metal hydride battery or a lithium-ion battery may be used for battery B 2 .

In other words, as the performance of an electric storage device improves, a combination of battery B 1 and battery B 2 may widely be varied for use. By combining and using two electric storage devices having different characteristics, it is possible to implement the power supply device for the vehicle, which power supply device can store a large amount of electric power and has high output performance.

Battery unit BU outputs a direct voltage output from battery B 1 or B 2 to voltage step up converter 10 . Furthermore, battery B 1 or B 2 inside battery unit BU are charged with a direct voltage output from voltage step up converter 10 .

Selection switch RY 0 is configured to assure that, when one of batteries B 1 and B 2 is connected to power supply line PL 1 , the other of batteries B 1 and B 2 is disconnected from power supply line PL 1 , in order to prevent a short-circuit between a positive electrode of battery B 1 and a positive electrode of battery B 2 . This is because batteries B 1 , B 2 are different in characteristic and sometimes in state of charge (SOC), and hence it is necessary to avoid directly connecting the positive electrodes thereof to each other, so as to prevent an excessive current flowing from one to the other of the batteries.

Voltage step up converter 10 includes a reactor L, NPN-type transistors Q 1 , Q 2 , and diodes D 1 , D 2 . Reactor L has one end connected to power supply line PL 1 , and the other end connected to a connection point of NPN-type transistors Q 1 , Q 2 . NPN-type transistors Q 1 , Q 2 are connected in series between power supply line PL 2 and ground line SL, and each receives a signal PWC from a control device 60 at its base. Diodes D 1 , D 2 are connected between the collectors and the emitters of NPN-type transistors Q 1 , Q 2 , respectively, so that a current flows from the emitter side to the collector side.

For the above-described NPN-type transistor and the NPN-type transistor described herein, an insulated gate bipolar transistor (IGBT) may be used. Furthermore, an electric power switching element such as a power metal oxide semiconductor field-effect transistor (MOSFET) may be substituted for the NPN-type transistor.

Inverter 20 includes a U-phase arm 22 , a V-phase arm 24 , and a W-phase arm 26 . U-phase arm 22 , V-phase arm 24 , and W-phase arm 26 are connected in parallel between power supply line PL 2 and ground line SL.

U-phase arm 22 includes NPN-type transistors Q 11 , Q 12 connected in series. V-phase arm 24 includes NPN-type transistors Q 13 , Q 14 connected in series. W-phase arm 26 includes NPN-type transistors Q 15 , Q 16 connected in series. Diodes D 11 -D 16 are connected between the collectors and the emitters of the NPN-type transistors Q 11 -Q 16 , respectively, for allowing a current to flow from the emitter side to the collector side. The connection points of the NPN-type transistors in the U, V, and W-phase arms are connected to coil ends different from a neutral point N 1 of the U, V, and W-phase coils of motor generator MG 1 through U, V, and W-phase lines UL 1 , VL 1 , and WL 1 , respectively.

Inverter 30 includes a U-phase arm 32 , a V-phase arm 34 , and a W-phase arm 36 . U-phase arm 32 , V-phase arm 34 , and W-phase arm 36 are connected in parallel between power supply line PL 2 and ground line SL.

U-phase arm 32 includes NPN-type transistors Q 21 , Q 22 connected in series. V-phase arm 34 includes NPN-type transistors Q 23 , Q 24 connected in series. W-phase arm 36 includes NPN-type transistors Q 25 , Q 26 connected in series. Diodes D 21 -D 26 are connected between the collectors and the emitters of NPN-type transistors Q 21 -Q 26 , respectively, for allowing a current to flow from the emitter side to the collector side. In inverter 30 , the connection points of the NPN-type transistors in the U, V, and W-phase arms are also connected to coil ends different from a neutral point N 2 of the U, V, and W-phase coils of motor generator MG 2 through U, V, and W-phase lines UL 2 , VL 2 , and WL 2 , respectively.

Vehicle 100 further includes capacitors C 1 , C 2 , a relay circuit 40 , a connector 50 , an EV priority switch 52 , a control device 60 , AC lines ACL 1 , ACL 2 , voltage sensors 72 - 74 , and current sensors 80 , 82 .

Capacitor C 1 is connected between power supply line PL 1 and ground line SL, to reduce the effect caused by voltage fluctuations on battery B 1 and voltage step up converter 10 . A voltage VL between power supply line PL 1 and ground line SL is measured by voltage sensor 73 .

Capacitor C 2 is connected between power supply line PL 2 and ground line SL, to reduce the effect caused by voltage fluctuations on inverters 20 , 30 and voltage step up converter 10 . A voltage VH between power supply line PL 2 and ground line SL is measured by voltage sensor 72 .

Voltage step up converter 10 steps up a direct voltage supplied from battery unit BU through power supply line PL 1 and outputs the same to power supply line PL 2 . More specifically, based on signal PWC from control device 60 , voltage step up converter 10 performs a voltage step up operation by storing in reactor L a current flowing in accordance with a switching operation of NPN-type transistor Q 2 , as magnetic field energy, and by releasing the stored energy by allowing a current to flow to power supply line PL 2 through diode D 1 in synchronization with a timing at which NPN-type transistor Q 2 is turned off.

Furthermore, based on signal PWC from control device 60 , voltage step up converter 10 steps down a direct voltage received from either of, or both of inverters 20 and 30 through power supply line PL 2 to a voltage level of battery unit BU, and charges the batteries inside battery unit BU.

Based on a signal PWM 1 from control device 60 , inverter 20 converts a direct voltage supplied from power supply line PL 2 into a three-phase alternating voltage, and drives motor generator MG 1 .

Motor generator MG 1 is thereby driven to generate torque specified by a torque control value TR 1 . Furthermore, based on signal PWM 1 from control device 60 , inverter 20 converts the three-phase alternating voltage, which is generated by motor generator MG 1 that receives an output from the engine, into a direct voltage, and outputs the obtained direct voltage to power supply line PL 2 .

Based on a signal PWM 2 from control device 60 , inverter 30 converts the direct voltage supplied from power supply line PL 2 into a three-phase alternating voltage, and drives motor generator MG 2 .

Motor generator MG 2 is thereby driven to generate torque specified by a torque control value TR 2 . Furthermore, during regenerative braking of vehicle 100 , namely, the hybrid vehicle, based on signal PWM 2 from control device 60 , inverter 30 converts the three-phase alternating voltage, which is generated by motor generator MG 2 that receives a turning force from a drive shaft, into a direct voltage, and outputs the obtained direct voltage to power supply line PL 2 .

The regenerative braking referred to herein includes braking with regenerative power generation when a driver that drives the hybrid vehicle operates a foot brake, and deceleration (or termination of acceleration) of the vehicle with regenerative power generation by lifting the driver's foot off from an accelerator pedal during running of the vehicle, without operating a foot brake.

Relay circuit 40 includes relays RY 1 , RY 2 . For relays RY 1 , RY 2 , a mechanical contact relay may be used, for example, or alternatively, a semiconductor relay may also be used. Relay RY 1 is provided between AC line ACL 1 and connector 50 , and is turned on/off in accordance with a control signal CNTL from control device 60 . Relay RY 2 is provided between AC line ACL 2 and connector 50 , and is turned on/off in accordance with control signal CNTL from control device 60 .

Relay circuit 40 connects AC lines ACL 1 , ACL 2 to/disconnects AC lines ACL 1 , ACL 2 from connector 50 in accordance with control signal CNTL from control device 60 . In other words, when receiving control signal CNTL at an H (logic high) level from control device 60 , relay circuit 40 electrically connects AC lines ACL 1 , ACL 2 to connector 50 . When receiving control signal CNTL at an L (logic low) level from control device 60 , relay circuit 40 electrically disconnects AC lines ACL 1 , ACL 2 from connector 50 .

Connector 50 is a terminal for inputting an alternating voltage from outside to neutral points N 1 , N 2 of motor generators MG 1 , MG 2 . For the alternating voltage, an alternating current of 100V, for example, can be input from a commercial power line at home. A voltage VAC between AC lines ACL 1 and ACL 2 is measured by voltage sensor 74 , and the measured value is transmitted to control device 60 .

Voltage sensor 70 detects a battery voltage VB 1 of battery B 1 , and outputs the detected battery voltage VB 1 to control device 60 . Voltage sensor 71 detects a battery voltage VB 2 of battery B 2 , and outputs the detected battery voltage VB 2 to control device 60 . Voltage sensor 73 detects a voltage across capacitor C 1 , namely, input voltage VL to voltage step up converter 10 , and outputs the detected voltage VL to control device 60 . Voltage sensor 72 detects a voltage across capacitor C 2 , namely, output voltage VH from voltage step up converter 10 (which output voltage VH corresponds to input voltages to inverters 20 , 30 ; the same applies to the following), and outputs the detected voltage VH to control device 60 .

Current sensor 80 detects a motor current MCRT 1 flowing through motor generator MG 1 , and outputs the detected motor current MCRT 1 to control device 60 . Current sensor 82 detects a motor current MCRT 2 flowing through motor generator MG 2 , and outputs the detected motor current MCRT 2 to control device 60 .

Based on torque control values TR 1 , TR 2 and motor rotation speeds MRN 1 , MRN 2 of motor generators MG 1 , MG 2 output from an electronic control unit (ECU) externally provided, voltage VL from voltage sensor 73 , and voltage VH from voltage sensor 72 , control device 60 generates signal PWC for driving voltage step up converter 10 , and outputs the generated signal PWC to voltage step up converter 10 .

Furthermore, based on voltage VH, and motor current MCRT 1 and torque control value TR 1 of motor generator MG 1 , control device 60 generates signal PWM 1 for driving motor generator MG 1 , and outputs the generated signal PWM 1 to inverter 20 . Furthermore, based on voltage VH, and motor current MCRT 2 and torque control value TR 2 of motor generator MG 2 , control device 60 generates signal PWM 2 for driving motor generator MG 2 , and outputs the generated signal PWM 2 to inverter 30 .

Based on a signal IG from an ignition switch (or an ignition key) and state of charge of battery B 2 (SOC 2 ), control device 60 generates signals PWM 1 , PWM 2 for controlling inverters 20 , 30 such that battery B 2 is charged with an alternating voltage for a commercial power supply, which alternating voltage is supplied to neutral points N 1 , N 2 of motor generators MG 1 , MG 2 .

Furthermore, based on state of charge of battery B 2 (SOC 2 ), control device 60 determines whether or not battery B 2 can be charged from outside. When control device 60 determines that battery B 2 can be charged, it outputs control signal CNTL at an H level to relay circuit 40 . In contrast, when control device 60 determines that battery B 2 is approximately fully charged and cannot be charged, it outputs control signal CNTL at an L level to relay circuit 40 . When signal IG shows a stopped state of the vehicle, control device 60 stops inverters 20 , 30 .

In accordance with an instruction provided through EV priority switch 52 by a driver, control device 60 switches between a hybrid running mode in which consumption of petrol in a normal manner is a prerequisite and an EV priority running mode in which the vehicle runs only by a motor with the maximum torque made smaller than in the case of the hybrid running, and electric power in the battery is used as much as possible.

FIG. 2 is a functional block diagram of control device 60 shown in FIG. 1 .

Referring to FIG. 2 , control device 60 includes a converter control unit 61 , a first inverter control unit 62 , a second inverter control unit 63 , and an AC input control unit 64 . Based on battery voltages VB 1 , VB 2 , voltage VH, torque control values TR 1 , TR 2 , and motor rotation speeds MRN 1 , MRN 2 , converter control unit 61 generates signal PWC for turning on/off NPN-type transistors Q 1 , Q 2 in voltage step up converter 10 , and outputs the generated signal PWC to voltage step up converter 10 .

Based on torque control value TR 1 and motor current MCRT 1 of motor generator MG 1 and voltage VH, first inverter control unit 62 generates signal PWM 1 for turning on/off NPN-type transistors Q 11 -Q 16 in inverter 20 , and outputs the generated signal PWM 1 to inverter 20 .

Based on torque control value TR 2 and motor current MCRT 2 of motor generator MG 2 and voltage VH, second inverter control unit 63 generates signal PWM 2 for turning on/off NPN-type transistors Q 21 -Q 26 in inverter 30 , and outputs the generated signal PWM 2 to inverter 30 .

Based on torque control values TR 1 , TR 2 and motor rotation speeds MRN 1 , MRN 2 , AC input control unit 64 determines a driving state of each of motor generators MG 1 , MG 2 , and in accordance with signal IG and the SOC of each of batteries B 1 , B 2 , controls the two inverters in a coordinated manner to convert the alternating voltage supplied from outside into a DC voltage and steps up the voltage, so as to charge the battery.

Here, signal IG at an H level is a signal indicating that vehicle 100 , namely, the hybrid vehicle is activated, while signal IG at an L level is a signal indicating that the hybrid vehicle is stopped.

In the case where a driving state of each of motor generators MG 1 , MG 2 is a stopped state, and where signal IG also indicates that the hybrid vehicle is stopped, AC input control unit 64 permits a charging operation if the SOC of each of batteries B 1 , B 2 is lower than a prescribed level. Specifically, AC input control unit 64 brings relays RY 1 , RY 2 into conduction by signal CNTL, and if there is an input of voltage VAC, generates a control signal CTL 1 in accordance with the input, controls inverters 20 , 30 in a coordinated manner, converts the alternating voltage supplied from outside into a DC voltage and steps up the voltage as well, so as to permit charging of the battery.

In contrast, in the case where a driving state of each of motor generators MG 1 , MG 2 is a running state or signal IG indicates that the hybrid vehicle is driven, when the SOC of each of batteries B 1 , B 2 is higher than a prescribed level, AC input control unit 64 does not permit a charging operation. Specifically, AC input control unit 64 causes relays RY 1 , RY 2 to be released by signal CNTL, generates a control signal CTL 0 , and causes voltage step up converter 10 and inverters 20 , 30 to perform a normal operation observed during driving of the vehicle.

FIG. 3 is a functional block diagram of converter control unit 61 shown in FIG. 2 .

Referring to FIG. 3 , converter control unit 61 includes an inverter input voltage command calculating unit 112 , a feedback voltage command calculating unit 114 , a duty ratio calculating unit 116 , and a PWM signal converting unit 118 .

Based on torque control values TR 1 , TR 2 and motor rotation speeds MRN 1 , MRN 2 , inverter input voltage command calculating unit 112 calculates an optimal value (target value), namely, a voltage command VH_com, of an inverter input voltage, and outputs the calculated voltage command VH_com to feedback voltage command calculating unit 114 .

Based on output voltage VH of voltage step up converter 10 detected by voltage sensor 72 and voltage command VH_com from inverter input voltage command calculating unit 112 , feedback voltage command calculating unit 114 calculates a feedback voltage command VH_com_fb for controlling output voltage VH to be voltage command VH_com, and outputs the calculated feedback voltage command VH_com_fb to duty ratio calculating unit 116 .

Based on battery voltages VB 1 , VB 2 from voltage sensor 70 and feedback voltage command VH_com_fb from feedback voltage command calculating unit 114 , duty ratio calculating unit 116 calculates a duty ratio for controlling output voltage VH of voltage step up converter 10 to be a voltage command VH_corn, and outputs the calculated duty ratio to PWM signal converting unit 118 .

Based on the duty ratio received from duty ratio calculating unit 116 , PWM signal converting unit 118 generates a pulse width modulation (PWM) signal for turning on/off NPN-type transistors Q 1 , Q 2 in voltage step up converter 10 , and outputs the generated PWM signal to NPN-type transistors Q 1 , Q 2 of voltage step up converter 10 as signal PWC.

By allowing NPN-type transistor Q 2 in the lower arm of voltage step up converter 10 to have a longer on-time in the duty ratio, an amount of electric power to be stored in reactor L is increased, and hence it is possible to obtain an output at a higher voltage. In contrast, by allowing NPN-type transistor Q 1 in the upper arm to have a longer on-time in the duty ratio, the voltage on power supply line PL 2 is lowered. Accordingly, by controlling the duty ratio of each of NPN-type transistors Q 1 , Q 2 , it is possible to control the voltage on power supply line PL 2 to be an arbitrary voltage equal to or higher than the output voltage of battery B 1 .

Furthermore, when control signal CTL 1 is activated, PWM signal converting unit 118 brings NPN-type transistor Q 1 into a conduction state, and brings NPN-type transistor Q 2 into a non-conduction state, regardless of an output of duty ratio calculating unit 116 . It is thereby possible to allow a charging current to flow from power supply line PL 2 to power supply line PL 1 .

FIG. 4 is a functional block diagram of first and second inverter control units 62 , 63 shown in FIG. 2 .

Referring to FIG. 4 , each of first and second inverter control units 62 , 63 includes a phase voltage calculating unit 120 for motor control, and a PWM signal converting unit 122 .

Phase voltage calculating unit 120 for motor control receives input voltage VH of inverters 20 , 30 from voltage sensor 72 , receives from current sensor 80 (or 82 ) motor current MCRT 1 (or MCRT 2 ) flowing through the coil of each of the phases in motor generator MG 1 (or MG 2 ), and receives torque control value TR 1 (or TR 2 ) from the ECU. Based on these input values, phase voltage calculating unit 120 for motor control calculates a voltage to be applied to the coil of each of the phases in motor generator MG 1 (or MG 2 ), and outputs the calculated voltage to be applied to the coil of each of the phases to PWM signal converting unit 122 .

When PWM signal converting unit 122 receives a control signal CTL 0 from AC input control unit 64 , it generates a signal PWM 1 _ 0 (a type of signal PWM 1 ) (or PWM 2 _ 0 (a type of signal PWM 2 )) that actually turns on/off each of NPN-type transistors Q 11 -Q 16 (or Q 21 -Q 26 ) in inverter 20 (or 30 ), based on the voltage command for the coil of each of the phases received from phase voltage calculating unit 120 for motor control, and outputs the generated signal PWM 1 _ 0 (or PWM 2 _ 0 ) to each of NPN-type transistors Q 11 -Q 16 (or Q 21 -Q 26 ) in inverter 20 (or 30 ).

As such, switching control is performed on each of NPN-type transistors Q 11 -Q 16 (or Q 21 -Q 26 ), and a current to flow through the coil of each of the phases in motor generator MG 1 (or MG 2 ) is controlled such that motor generator MG 1 (or MG 2 ) outputs the commanded torque. As a result, motor torque in accordance with torque control value TR 1 (or TR 2 ) is output.

Furthermore, when PWM signal converting unit 122 receives control signal CTL 1 from AC input control unit 64 , it generates signal PWM 1 _ 1 (a type of signal PWM 1 ) (or PWM 2 _ 1 (a type of signal PWM 2 )) that turns on/off NPN-type transistors Q 11 -Q 16 (or Q 21 -Q 26 ) such that an in-phase alternating current flows through U-phase arm 22 (or 32 ), V-phase arm 24 (or 34 ), and W-phase arm 26 (or 36 ) of inverter 20 (or 30 ), regardless of an output of phase voltage calculating unit 120 for motor control, and outputs the generated signal PWM 1 _ 1 (or PWM 2 _ 1 ) to NPN-type transistors Q 11 -Q 16 (or Q 21 -Q 26 ) in inverter 20 (or 30 ).

When an in-phase alternating current flows through the U, V, and W-phase coils, no rotational torque is generated in motor generators MG 1 , MG 2 . By controlling inverters 20 , 30 in a coordinated manner, alternating voltage VAC is converted into a direct charging voltage.

A method of generating a direct charging voltage in vehicle 100 from alternating voltage VAC for a commercial power supply will now be described.

FIG. 5 is a diagram of the circuit diagram in FIG. 1 , which circuit diagram is simplified to focus on a portion relating to charging.

In FIG. 5 , the U-phase arm in each of inverters 20 , 30 in FIG. 1 is shown as a representative example. Furthermore, the U-phase coil out of three-phase coils in each of the motor generators is shown as a representative example. If a description of the U-phase is made as a representative example, the description of other phases will not be required because an in-phase current flows through the coils of each of the phases, and hence the circuits of other two phases operate similarly to that of the U-phase. As seen from FIG. 5 , each of a set of U-phase coil U 1 and U-phase arm 22 and a set of U-phase coil U 2 and U-phase arm 32 has a configuration similar to that of voltage step up converter 10 . Accordingly, it is possible not only to convert an alternating voltage of 100V, for example, into a direct voltage, but also to step up the direct voltage to a battery charging voltage of approximately 200V.

FIG. 6 is a diagram showing a control state of the transistor during charging.

Referring to FIGS. 5 and 6 , initially, if voltage VAC>0, in other words, a voltage V 1 on line ACL 1 is higher than a voltage V 2 on line ACL 2 , transistor Q 1 in the voltage step up converter is brought into an on state, while a transistor Q 2 in the voltage step up converter is brought into an off state. Voltage step up converter 10 can thereby allow a charging current to flow from power supply line PL 2 to power supply line PL 1 .

In the first inverter, transistor Q 12 is switched in a cycle and at a duty ratio in accordance with voltage VAC, while transistor Q 11 is controlled to be in an off state or in a switching state in which transistor Q 11 is brought into conduction in synchronization with the conduction of diode D 11 . At that time, in the second inverter, transistor Q 21 is brought into an off state, while transistor Q 22 is controlled to be in an on state.

If voltage VAC>0, a current flows through a path from coil U 1 through transistor Q 12 and diode D 22 to coil U 2 , with transistor Q 12 being in an on state. The energy stored in coils U 1 , U 2 at that time is released when transistor Q 12 is brought into an off state, and a current flows through diode D 11 to power supply line PL 2 . In order to reduce loss due to diode D 11 , transistor Q 11 may be brought into conduction in synchronization with the conduction period of diode D 11 . Based on the values of voltage VAC and voltage VH, a voltage step up ratio is determined, so that a switching cycle and a duty ratio of transistor Q 12 are determined.

Next, if voltage VAC<0, in other words, voltage V 1 on line ACL 1 is lower than voltage V 2 on line ACL 2 , transistor Q 1 in the voltage step up converter is brought into an on state, while transistor Q 2 in the voltage step up converter is brought into an off state. Voltage step up converter 10 can thereby allow a charging current to flow from power supply line PL 2 to power supply line PL 1 .

In the second inverter, transistor Q 22 is switched in a cycle and at a duty ratio in accordance with voltage VAC, while transistor Q 21 is controlled to be in an off state or in a switching state in which transistor Q 21 is brought into conduction in synchronization with the conduction of diode D 21 . At that time, in the first inverter, transistor Q 11 is brought into an off state, while transistor Q 12 is controlled to be in an on state.

If voltage VAC<0, a current flows through a path from coil U 2 through transistor Q 22 and diode D 12 to coil U 1 , with transistor Q 22 being in an on state. The energy stored in coils U 1 , U 2 at that time is released when transistor Q 22 is brought into an off state, and a current flows through diode D 21 to power supply line PL 2 . In order to reduce loss due to diode D 21 , transistor Q 21 may be brought into conduction in synchronization with the conduction period of diode D 21 . At that time, based on the values of voltage VAC and voltage VH, a voltage step up ratio is also determined, so that a switching cycle and a duty ratio of transistor Q 22 are determined.

FIG. 7 is a flowchart showing a control structure of a program relating to a determination as to the start of charging, which determination is made by control device 60 shown in FIG. 1 . The process in the flowchart is invoked from a main routine whenever a certain time has passed or a prescribed condition is established, for execution.

Referring to FIGS. 1 and 7 , initially in step S 1 , control device 60 determines whether or not signal IG is in an off state. If signal IG is not in an off state in step S 1 , the present state is not suitable for connecting a charging cable to the vehicle for charging. Accordingly, the process proceeds to step S 6 , and the control is returned to the main routine.

In step S 1 , if signal IG is in an off state, it is determined that the present state is suitable for charging, and the process proceeds to step S 2 . In step S 2 , relays RY 1 and RY 2 are controlled to be in a conduction state from a non-conduction state, and voltage VAC is measured by voltage sensor 74 . If an alternating voltage is not observed, it is assumed that the charging cable is not connected to a socket of connector 50 , and hence charging is not performed and the process proceeds to step S 6 . The control is returned to the main routine.

In contrast, if an alternating voltage is observed as voltage VAC in step S 2 , the process proceeds to step S 3 . In step 3 , it is determined whether or not the state of charge of battery B 2 SOC(B 2 ) is lower than a threshold value Sth(F) indicative of a fully-charged state.

If SOC (B 2 )<Sth(F) is established, battery B 2 is in a chargeable state, and hence the process proceeds to step S 4 . In step S 4 , control device 60 controls the two inverters in a coordinated manner to charge battery B 2 .

In step S 3 , if SOC (B 2 )<Sth(F) is not established, battery B 2 is in a fully-charged state, and requires no charging. The process therefore proceeds to step S 5 . In step S 5 , charging is terminated. Specifically, inverters 20 and 30 are stopped and relays RY 1 , RY 2 are released, so that an input of the alternating-current electric power to vehicle 100 is shut off. The process proceeds to step S 6 , and the control is returned to the main routine.

FIG. 8 is a conceptual diagram for describing a difference in characteristic between batteries B 1 , B 2 in FIG. 1 .

As described above, in battery unit BU, a combination of batteries B 1 , B 2 is selected such that battery B 2 has larger electricity storage capacity than battery B 1 has, and instead that battery B 1 has larger maximum allowed output electric power than battery B 2 has.

When a secondary battery such as a nickel metal hydride battery or a lithium-ion battery is used for battery B 1 and an inexpensive, high-capacity, lead-acid battery is used for battery B 2 , a range for use is set in each of the batteries as shown in FIG. 8 .

The range for use of battery B 1 is controlled to fall within the range having the lower limit of Sth (E 1 ) and the upper limit of Sth (F 1 ), while a state where SOC is at Sth (C) is set as a standard condition. For example, Sth (C)=60%, Sth (E 1 )=40%, and Sth (F 1 )=80%. As to the secondary battery such as a nickel metal hydride battery or the lithium-ion battery, if the SOC is controlled to be such an intermediate value, it can achieve improved charging performance for a long period of time.

In contrast, the range for use of battery B 2 is controlled to fall within the range having the lower limit of Sth (E 2 ) and the upper limit of Sth (F 2 ). Here, Sth (E 2 )<Sth (E 1 ) and Sth (F 2 )>Sth (F 1 ). For example, Sth (E 2 )=10%, and Sth (F 2 )=90%.

FIG. 9 is a flowchart showing a control structure of a program relating to battery selection in recapturing regenerative electric power, which battery selection is made by control device 60 in FIG. 1 . The process in the flowchart is invoked from the main routine whenever a certain time has passed, or a prescribed condition is established, for execution.

Referring to FIGS. 1 and 9 , the power supply device of vehicle 100 has a battery B 1 serving as a first electric storage device, a battery B 2 serving as a second electric storage device, a motor generator MG 2 driving a wheel, selection switch RY 0 selecting one of the first and second electric storage devices and connecting the selected electric storage device to motor generator MG 2 , and control device 60 controlling switching of selection switch RY 0 in accordance with the state of charge of each of the first and second electric storage devices. In the case where the selection switch RY 0 selects battery B 1 , when the state of charge of battery B 1 becomes higher than a first prescribed level by charging, control device 60 instructs the selection switch to select the second electric storage device.

At that time, the charging in the case where selection switch RY 0 selects battery B 1 is preferably performed with regenerative electric power generated during a regenerative braking operation of motor generator MG 2 during running of the vehicle.

Preferably, in the case where the selection switch selects battery B 2 , when the state of charge of battery B 2 becomes lower than a second prescribed level, control device 60 instructs the selection switch to select the first electric storage device. The second prescribed level may be set to be equal to the first prescribed level, namely, set to Sth (C), or alternatively, both of the first and second prescribed levels may be set to different values.

The charging operation above will now be described in detail. Initially, when the process starts, control device 60 determines in step S 11 whether or not there is regenerative electric power. For example, in the case of deceleration from high-speed running, or in the case of braking to prevent acceleration in a downslope, the vehicle generates electric power by means of motor generator MG 2 mechanically coupled to the wheel, and recaptures the electric power. Such a case corresponds to the case where there is regenerative electric power.

In step S 11 , if there is no regenerative electric power, the process proceeds to step S 17 , and the control is returned to the main routine. In contrast, if there is regenerative electric power in step S 11 , the process proceeds to step S 12 . In step S 12 , it is determined whether or not the state of charge of battery B 1 SOC (B 1 ) is lower than prescribed threshold value Sth (F 1 ) in FIG. 8 .

If SOC (B 1 )<Sth (F 1 ) is established in step S 12 , the process proceeds to step S 13 , and battery B 1 is selected as a place where the recaptured electric power is to be stored. An electric power recapture limit value at that time is set to, for example, 20 kW. If regenerative electric power is generated beyond the limit value, excess electric power is discarded as heat.

In contrast, if SOC (B 1 )<Sth (F 1 ) is not established in step S 12 , the process proceeds to step S 14 . In step S 14 , it is determined whether or not the state of charge of battery B 2 SOC (B 2 ) is lower than prescribed threshold value Sth (F 2 ) in FIG. 8 .

If SOC (B 2 )<Sth (F 2 ) is established in step S 14 , the process proceeds to step S 15 , and battery B 2 is selected as a place where the recaptured electric power is to be stored. An electric power recapture limit value at that time is set to, for example, 5 kW. If regenerative electric power is generated beyond the limit value, excess electric power is discarded as heat.

In contrast, if SOC (B 2 )<Sth (F 2 ) is not established in step S 14 , it is determined that additional electric power cannot be recaptured in the batteries, and hence the process proceeds to step S 16 . In step S 16 , the regenerative electric power is discarded as heat.

If any of the steps in steps S 13 , S 15 , and S 16 is terminated, the process proceeds to step S 17 , and the control is returned to the main routine.

FIG. 10 is a diagram for describing recapture of regenerative electric power in the first embodiment.

Referring to FIG. 10 , battery B 1 is charged at times t 0 -t 1 , and thereby a recaptured amount 1 of regenerative electric power is recaptured. At time t 1 , when the SOC of battery B 1 reaches Sth (F 1 ) indicative of a fully-charged state, control device 60 allows the process to proceed from step S 12 to step S 14 in FIG. 9 . Since the SOC of battery B 2 is at Sth (E 2 ) indicative of an almost empty state, battery B 2 is selected as a place where regenerative electric power is stored, and the process in step S 15 proceeds.

A recaptured amount 2 of electric power is stored at times t 1 -t 2 , resulting in that the SOC of battery B 2 gradually increases. In other words, an additional amount of electric power, which corresponds to recaptured amount 2 of electric power, is recaptured, when compared with the case in FIG. 14 , and hence energy efficiency is improved.

As described above, in the first embodiment, an additional amount of regenerative electric power can be recaptured in battery B 2 , when compared with the common hybrid vehicle. Accordingly, if a commuting route includes a mountain pass, it is possible to increase the mileage per charge. The frequency with which the fuel is thereby consumed is decreased, and the frequency of refueling is further decreased.

Second Embodiment

In the second embodiment, battery unit BU is replaced with a battery unit BU 1 , in the configuration of FIG. 1 . Other configurations are similar to those in the first embodiment, and hence the description thereof will not be repeated.

FIG. 11 is a circuit diagram showing a configuration of battery unit BU 1 used in the second embodiment.

Referring to FIG. 11 , battery unit BU 1 includes batteries B 1 , B 2 serving as electric storage devices whose negative electrodes are connected to each other, system main relays SMR 1 -SMR 3 connecting battery B 1 to the vehicle load, voltage sensors 70 , 71 measuring voltages of batteries B 1 , B 2 , respectively, current sensors 84 , 83 measuring currents of batteries B 1 , B 2 , respectively, and a DC/DC converter 200 connected between battery B 1 and battery B 2 , and capable of transferring electric power bidirectionally. The combination of batteries B 1 , B 2 is similar to that described in the first embodiment, and hence the description thereof will not be repeated.

System main relay SMR 1 is connected in series with a limiting resistor R 1 between a positive electrode of battery B 1 and power supply line PL 1 . System main relay SMR 2 is connected between the positive electrode of battery B 1 and power supply line PL 1 . System main relay SMR 3 is connected between negative electrodes of batteries B 1 , B 2 , and ground line SL. System main relays SMR 1 -SMR 3 are controlled to be in a conduction/non-conduction state, in accordance with a control signal SE supplied from control device 60 .

DC/DC converter 200 includes a first arm connected between the terminals of battery B 2 , a second arm connected between the power supply terminals of battery B 1 , and a reactor L 2 connected between the first and second arms.

The first arm includes NPN-type transistors Q 3 , Q 4 connected in series between a positive electrode and a negative electrode of battery B 2 , a diode D 3 connected in parallel with NPN-type transistor Q 3 , and a diode D 4 connected in parallel with NPN-type transistor Q 4 .

NPN-type transistor Q 3 has a collector connected to the positive electrode of battery B 2 , and an emitter connected to one end of reactor L 2 . Diode D 3 is connected such that a direction from the emitter to the collector of NPN-type transistor Q 3 is set as its forward direction.

NPN-type transistor Q 4 has a collector connected to one end of reactor L 2 , and an emitter connected to the negative electrode of battery B 2 . Diode D 4 is connected such that a direction from the emitter to the collector of NPN-type transistor Q 4 is set as its forward direction.

The second arm includes NPN-type transistors Q 5 , Q 6 connected in series between the positive electrode and the negative electrode of battery B 1 , a diode D 5 connected in parallel with NPN-type transistor Q 5 , and a diode D 6 connected in parallel with NPN-type transistor Q 6 .

NPN-type transistor Q 5 has a collector connected to the positive electrode of battery B 1 , and an emitter connected to the other end of reactor L 2 . Diode D 5 is connected such that a direction from the emitter to the collector of NPN-type transistor Q 5 is set as its forward direction.

NPN-type transistor Q 6 has a collector connected to the other end of reactor L 2 , and an emitter connected to the negative electrode of battery B 1 . Diode D 6 is connected such that a direction from the emitter to the collector of NPN-type transistor Q 6 is set as its forward direction.

The ranges that can be covered by voltage VB 2 of battery B 2 and voltage VB 1 of battery B 1 overlap partially. For example, when a nickel metal hydride battery or the like is used for battery B 1 , the power supply voltage thereof varies within a range of, for example, 200 V-300 V. Alternatively, when a lead-acid battery or the like is used for battery B 1 , the output voltage thereof also varies within a range of, for example, 200 V-300 V. Accordingly, if battery B 2 is in a fully-charged state and battery B 1 is empty, it is assumed that the voltage of battery B 2 is higher than that of battery B 1 . In contrast, if battery B 1 is in a fully-charged state and battery B 2 is empty, it is assumed that the voltage of battery B 1 is higher than that of battery B 2 .

In such cases, in order to charge battery B 2 , or to allow electric power in battery B 2 to be used preferentially, DC/DC converter 200 has a configuration having the first and second arms as described above. With this configuration, it is possible to step up and step down the voltage from the battery B 2 side to the battery B 1 side, and it is also possible to step up and step down the voltage from the battery B 1 side to the battery B 2 side.

FIG. 12 is a flowchart showing a control structure of a program relating to battery selection in recapturing regenerative electric power, which battery selection is made by control device 60 in the second embodiment. The process in the flowchart is invoked from the main routine whenever a certain time has passed, or a prescribed condition is established, for execution.

Referring to FIGS. 11 , 12 , in the second embodiment, the power supply device for a vehicle includes a battery B 1 serving as a first electric storage device, a battery B 2 serving as a second electric storage device, a motor generator MG 2 receiving electric power from battery B 1 to drive a wheel, DC/DC converter 200 provided between batteries B 1 , B 2 and serving as a voltage converting unit receiving and transferring electric power between batteries B 1 , B 2 , and control device 60 controlling DC/DC converter 200 in accordance with the state of charge of each of batteries B 1 , B 2 . When the state of charge of battery B 1 becomes higher than the first prescribed level by charging, control device 60 instructs DC/DC converter 200 to perform a voltage converting operation such that battery B 2 is charged from battery B 1 .

Charging of battery B 1 at that time is performed with regenerative electric power generated during a regenerative braking operation of the first rotating electric machine during running of the vehicle. Of course, in the case where charging is performed by externally receiving an alternating-current electric power at a neutral point of the motor generator, control device 60 may similarly instruct DC/DC converter 200 to perform a voltage converting operation such that battery B 2 is charged from battery B 1 .

Preferably, control device 60 instructs DC/DC converter 200 to perform a voltage converting operation such that battery B 1 is charged from battery B 2 , when the energy in battery B 1 is consumed through running, for example, and the state of charge of battery B 1 becomes lower than the second prescribed level.

In the following, the process during charging will further be described in detail. Initially, when the process starts, control device 60 determines in step S 21 whether or not there is regenerative electric power. For example, in the case of deceleration from high-speed running, or in the case of braking to prevent acceleration in a downslope, the vehicle generates electric power by means of motor generator MG 2 mechanically coupled to the wheel, and recaptures the electric power. Such a case corresponds to the case where there is regenerative electric power.

In step S 21 , if there is no regenerative electric power, the process proceeds to step S 28 , and the control is returned to the main routine. In contrast, if there is regenerative electric power in step S 21 , the process proceeds to step S 22 . In step S 22 , it is determined whether or not the state of charge of battery B 1 SOC (B 1 ) is lower than prescribed threshold value Sth (F 1 ) in FIG. 8 .

In step S 22 , if SOC (B 1 )<Sth (F 1 ) is established, the process proceeds to step S 23 , and battery B 1 is selected as a place where recaptured electric power is stored. The electric power recapture limit value at that time is set to, for example, 20 kW. If regenerative electric power is generated beyond the limit value, excess electric power is discarded as heat.

In contrast, if SOC (B 1 )<Sth (F 1 ) is not established in step S 22 , the process proceeds to step S 27 . In such a case, battery B 1 , which is to receive regenerative electric power, is in a fully-charged state, and hence regenerative electric power is discarded as heat.

If battery B 1 is charged in step S 23 , it is determined in step S 24 whether or not the state of charge of battery B 1 exceeds Sth (C) indicative of the standard condition in FIG. 8 .

If SOC (B 1 )>Sth (C) is established in step S 24 , the process proceeds to step S 25 . If SOC (B 11 )>Sth (C) is not established in step S 24 , the process proceeds to step S 28 .

In step S 25 , it is determined whether or not the state of charge of battery B 2 SOC (B 2 ) is smaller than Sth (F 2 ) in FIG. 8 . If SOC (B 2 )<Sth (F 2 ) is established, battery B 2 is in a chargeable state, and hence the process proceeds to step S 26 . In contrast, if SOC (B 2 )<Sth (F 2 ) is not established, battery B 2 has already been in a fully-charged state and cannot be charged, and hence the process proceeds to step S 28 .

In step S 26 , DC/DC converter 200 is driven to transfer electric power from battery B 1 to battery B 2 . The electric power charge limit value is set to, for example, 5 kW. The process proceeds to step S 28 .

When the process proceeds to step S 28 , the control is returned to the main routine.

FIG. 13 is a diagram for describing recapture of regenerative electric power in the second embodiment.

Referring to FIG. 13 , battery B 1 is charged at times t 0 -t 1 , and thereby regenerative electric power is recaptured. At the same time, SOC (B 1 ) of battery B 1 is larger than standard condition Sth (C), and hence DC/DC converter 200 is driven to transfer electric power from battery B 1 to battery B 2 . As a result, SOC (B 1 ) and SOC (B 2 ) at times t 0 -t 1 gradually increase. The rate of increase in SOC (B 1 ) is lower than that at times t 0 -t 1 in FIG. 10 , because electric power is transferred to battery B 2 . Accordingly, it is possible to recapture regenerative electric power of 20 kW until time t 1 A.

At time t 1 A, SOC (B 1 ) reaches Sth (F 1 ) indicative of a fully-charged state, and hence electric power of 20 kW can no longer be recaptured. Accordingly, the amount of recapture is reduced to 5 kW, and remaining regenerative electric power is discarded as heat. During that time, SOC (B 2 ) continues to increase by a recaptured amount of 5 kW.

When the downslope ends at time t 2 , regenerative electric power is turned to 0. Even after that, electric power is transferred from battery B 1 to battery B 2 , and at time t 3 , the state of charge of battery B 1 reaches Sth (C) indicative of the standard condition, and the state of charge of battery B 2 reaches the maximum.

As described above, in the second embodiment, it is possible to recapture much more regenerative electric power into battery B 2 , when compared with the case of the first embodiment. Accordingly, if a commuting route includes a mountain pass, it is possible to further increase the mileage per charge. Accordingly, the frequency with which the fuel is consumed is decreased, and the frequency of refueling is further decreased.

As to the control in charging at home or the like when the vehicle is stopped, electric power may also be received and transferred between batteries B 1 , B 2 in a similar manner. In this case, the determination as to whether or not there is regenerative electric power in step S 21 in the flowchart of FIG. 12 may be replaced with a determination as to whether or not there is an AC input, and a step of terminating charging may be performed instead of step S 27 .

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.