Hybrid vehicle and control method therefor

An HV-ECU executes refresh-discharging of a battery before the battery is charged from a commercial power source using an AC/DC converter. After the battery is refresh-discharged, the HV-ECU outputs a control signal to the AC/DC converter such that the battery is charged from the commercial power source by the drive of the AC/DC converter.

TECHNICAL FIELD

The present invention relates to a hybrid vehicle and a control method therefor, particularly to refresh control of a battery incorporated in a hybrid vehicle.

BACKGROUND ART

In view of the recent increasing concern about energy saving and environmental problems, great attention is focused on hybrid vehicles. A hybrid vehicle employs a battery, an inverter, and a motor driven by the inverter, as well as a conventional engine, as the motive power source. In addition to obtaining motive energy by driving the engine, the voltage from the battery is converted into alternating voltage by the inverter, and the motor is rotated by the converted alternating voltage to obtain further motive energy.

In such a hybrid vehicle, the charge and discharge of a battery is controlled such that the amount of charge indicating the state of charge (SOC) of the battery (hereinafter, also simply referred to as “SOC”; represented by 0 to 100%) falls within a predetermined range.

It is known that such battery charging and discharging within a predetermined range will cause an error between the SOC estimated value and the actual SOC, reduction in the charging/discharging capacitance by the so-called memory effect, degradation by sulfation, and the like. These problems can be solved by carrying out the so-called refresh on the battery. In other words, these problems can be eliminated by achieving substantially a fully-charged or fully-discharged state of the battery. It is known that the refresh effect is increased by charging or discharging the battery such that the SOC greatly deviates from the control range.

Japanese Patent Laying-Open No. 2004-328906 discloses a charging control apparatus for a hybrid vehicle that carries out such battery refresh. In this charging control apparatus, the continuous operating time of the engine is calculated based on the vehicle state. Furthermore, the time required for refresh-charging the battery is calculated. Refresh-charging of the battery is effected when determination is made that the engine continuous operation time is longer than said time required for charging.

Since refresh charging is completed before or simultaneous to the elapse of the engine continuous operation time by the charging control apparatus, the engine will not be driven just for the purpose of refresh-charge. As a result, reduction in mileage can be suppressed.

However, the charging control apparatus disclosed in Japanese Patent Laying-Open No. 2004-328906 is disadvantageous in that fuel consumption by the engine is encountered since the generator is driven by the engine to carry out refresh-charging of the battery.

Particularly in a hybrid vehicle that can have the battery charged by means of a power source external to the vehicle, the SOC control range will become higher than that of a hybrid vehicle absent of an external charging function. There is a possibility that sufficient refresh effect cannot be achieved even if refresh-charging is carried out.

DISCLOSURE OF THE INVENTION

In view of the foregoing, an object of the present invention is to provide a hybrid vehicle that can have a battery refreshed reliably and efficiently.

Another object of the present invention is to provide a control method for a hybrid vehicle that can have a battery refreshed reliably and efficiently.

According to the present invention, a hybrid vehicle includes an internal combustion engine, a first electric motor, a battery that can be charged and discharged, a power generation device, an electrical power conversion device, and a control device. The internal combustion engine and the first electric motor are incorporated as the motive energy source for the vehicle. The battery constitutes the power source for the first electric motor. The power generation device generates electrical power using the motive energy from the internal combustion engine and can charge the battery. The electrical power conversion device conducts electrical power conversion such that electrical power can be transmitted and received between a power source external to the vehicle and the battery. The control device controls the electrical power conversion device such that refresh-discharging of the battery is executed prior to charging the battery from an external power source using the electrical power conversion device, and that the battery is charged from the external power source after the battery has been refresh-discharged.

Preferably, the power generation device includes a second electric motor. The second electric motor has a rotational shaft mechanically coupled to a crankshaft of the internal combustion engine, and can start the internal combustion engine using the electrical power from the battery. The control device determines that refresh-discharging is to be executed when the remaining amount of fuel in the internal combustion engine exceeds a prescribed amount. As used herein, the prescribed amount is the amount that allows the internal combustion engine to be operated continuously during the period when a state of charge indicating the battery charge state is lower than a required amount required to start the internal combustion engine by the second electric motor in accordance with refresh-discharging.

Further preferably, the control device controls the second electric motor such that the internal combustion engine is started before the state of charge becomes lower than the required amount in accordance with refresh-discharging, and controls the internal combustion engine such that the internal combustion engine is continuously operated during the period when the state of charge is lower than the required amount.

Preferably, the control device determines whether the external power source is stable or not, and determines that refresh-discharging is to be executed when determination is made that the external power source is stable.

Preferably, the power generation device includes a second electric motor. The second electric motor has a rotational shaft mechanically coupled to a crankshaft of the internal combustion engine, and can start the internal combustion engine using the electrical power from the battery. The control device determines whether the external power source is stable or not, and controls the second electric motor such that the internal combustion engine is started when determination is made that the external power source is unstable.

Preferably, the hybrid vehicle further includes an input device. The input device allows the user to designate execution of refresh-discharging. The control device determines that refresh-discharging is to be executed when execution of refresh-discharging is designated through the input device.

Further preferably, the hybrid vehicle further includes an input device. The input device allows the user to designate whether the internal combustion engine is to be operated or not in accordance with refresh-discharging. The power generation device includes a second electric motor. The second electric motor has a rotational shaft mechanically coupled to a crankshaft of the internal combustion engine, and can start the internal combustion engine using electrical power from the battery. The control device controls the second electric motor such that the internal combustion engine is started in accordance with refresh-discharging when operation of the internal combustion engine is designated through the input device.

Preferably, the control device controls the electrical power conversion device such that the electrical power discharged from the battery is supplied to the external power source.

Preferably, the hybrid vehicle further includes a notification device. The notification device notifies the user that the battery is currently charging/discharging in accordance with refresh-discharging.

Further preferably, the hybrid vehicle further includes a notification device. The notification device notifies the user that the internal combustion engine is currently operating in accordance with refresh-discharging.

According to the present invention, a control method is directed to a control method for a hybrid vehicle. The hybrid vehicle includes an internal combustion engine, a first electric motor, a battery that can be charged and discharged, a power generation device, and an electrical power conversion device. The internal combustion engine and the first electric motor are incorporated as the motive energy source for the vehicle. The battery constitutes the power source for the first electric motor. The power generation device generates electrical power using the motive energy from the internal combustion engine, and can charge the battery. The electrical power conversion device conducts electrical power conversion such that electrical power can be transmitted and received between a power source external to the vehicle and the battery. The control method includes first and second steps. In the first step, refresh-discharging of the battery is executed before the battery is charged from an external power source using the electrical power conversion device. In the second step, the battery is charged from an external power source by controlling the electrical power conversion device, after the battery is refresh-discharged.

Preferably, the power generation device includes a second electric motor. The second electric motor has a rotational shaft mechanically coupled to a crankshaft of the internal combustion engine, and can start the internal combustion engine using the electrical power from the battery. The control method further includes a third step. In the third step, determination is made as to whether refresh-discharging is to be executed or not based on a remaining amount of fuel in the internal combustion engine. When determination is made that the remaining amount of fuel in the internal combustion engine exceeds a prescribed amount and refresh-discharging is to be executed in the third step, refresh-discharging of the battery is executed in the first step. As used herein, the prescribed amount is the amount that allows the internal combustion engine to be operated continuously during the period when a state of charge indicating the battery charge state is lower than a required amount required to start the internal combustion engine by the second electric motor in accordance with refresh-discharging.

Preferably, the control method further includes fourth and fifth steps. In the fourth step, the internal combustion engine is started before the state of charge becomes lower than the required amount in accordance with refresh-discharging. In the fifth step, the internal combustion engine is shut down when the state of charge exceeds the required amount in the event of the battery being charged by an external power source in the second step.

Preferably, the control method further includes a sixth step. In the sixth step, determination is made as to whether refresh-discharging is to be executed or not based on the external power source. When determination is made that the external power source is stable and refresh-discharging is to be executed in the sixth step, the refresh-discharging of the battery is executed at the first step.

Preferably, the power generation device includes a second electric motor. The second electric motor has a rotational shaft mechanically coupled to a crankshaft of the internal combustion engine, and can start the internal combustion engine using the electrical power from the battery. The control method further includes seventh and eighth steps. In the seventh step, determination is made as to whether the external power source is stable or not. In the eighth step, the internal combustion engine is started when determination is made that the external power source is unstable.

In the present invention, the control device executes refresh-discharging of the battery before the battery is charged from an external power source using the electrical power conversion device. Therefore, the battery can be refreshed reliably even in the case where the SOC control range is high. Since the control device controls the electrical power conversion device such that the battery is charged from the external power source after the battery is refresh-discharged, the battery can be charged efficiently as compared to the case where the internal combustion engine is operated to charge the battery.

According to the present invention, the battery can be refreshed reliably and efficiently.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinafter with reference to the drawings. In the drawings, the same or corresponding elements have the same reference characters allotted, and description thereof will not be repeated.

First Embodiment

FIG. 1is an entire block diagram of a hybrid vehicle according to a first embodiment of the present invention. Referring toFIG. 1, a hybrid vehicle10includes a battery B, a power supply line PL, a ground line SL, a capacitor C, inverters12and14, motor generators MG1and MG2, an engine16, a fuel tank18, a driving wheel20, an MG-ECU (Electronic Control Unit)22, an engine ECU24, and an HV-ECU26, a voltage sensor36, and a current sensor37. Hybrid vehicle10further includes an AC/DC converter28, a voltage sensor38, terminals40,42, an auxiliary device30, an input device32, and a notification device34.

Battery B is a battery that can be charged and discharged, formed of a secondary battery such as of nickel hydroxide, lithium ions, or the like. Battery B supplies direct current power to inverters12and14via power supply line PL and ground line SL. Battery B is charged by the electrical power generated by motor generator MG1using the output of engine16, and also the electrical power generated by motor generator MG2at the time of regenerative braking of the vehicle. Battery B is also charged by the electrical power supplied from a commercial power source44external to the vehicle.

Voltage sensor36detects battery voltage VB of battery B, and provides the detected battery voltage VB to MG-ECU22and HV-ECU26. Current sensor37detects battery current IB that is input to or output from battery B, and provides detected battery current IB to MG-ECU22and HV-ECU26. Capacitor C smoothes the voltage variation between power supply line PL and ground line SL.

Inverters12and14are provided corresponding to motor generators MG1and MG2, respectively. Inverter12converts the 3-phase alternating current power generated by motor generator MG1upon receiving the motive energy of engine16into direct current power based on a signal PWM1from MG-ECU22, and supplies the converted direct current power onto power supply line PL. At the startup of engine16, inverter12converts the direct current power supplied from power supply line PL into 3-phase alternating current power to drive motor generator MG1, based on signal PWM1from MG-ECU22.

Inverter14responds to a signal PWM2from MG-ECU22to convert the direct current power supplied from power supply line PL into 3-phase alternating current power to drive motor generator MG2. Accordingly, motor generator MG2is driven to generate the designated torque. In the regenerative braking mode of the vehicle, inverter14converts the 3-phase alternating current power generated by motor generator MG2using the rotational force received from driving wheel20into direct current power based on signal PWM2from MG-ECU22, and provides the converted direct current power onto power supply line PL.

Motor generators MG1and MG2are 3-phase alternating current electric motors, formed of a 3-phase alternating current synchronous electric motor, for example. Motor generator MG1generates 3-phase alternating current power using the motive energy of engine16, and provides the generated 3-phase alternating current power to inverter12. Motor generator MG1generates motive power by the 3-phase alternating current power from inverter12to start engine16. Motor generator MG2generates the driving torque of driving wheel20by the 3-phase alternating current power received from inverter14. In a vehicle regenerative braking mode, motor generator MG2generates 3-phase alternating current power using the rotational force from driving wheel20, and provides the generated 3-phase alternating current power to inverter14.

Engine16is cranked by motor generator MG1to be started. The throttle valve provided at the intake pipe, ignition device, injection device, and the like (all not shown) are operated to allow engine16to generate motive energy, based on a control signal CTL1from engine ECU24. Fuel tank18stores the fuel for engine16. Fuel tank18has the fuel remaining amount FUEL detected by a sensor not shown. The detected fuel remaining amount FUEL is provided to HV-ECU26.

AC/DC converter28is provided between battery B and terminals40and42. AC/DC converter28responds to a control signal CTL2from HV-ECU26to convert the electrical power from commercial power source44applied to terminals40and42to the voltage level of battery B for output thereto. Moreover, AC/DC converter28responds to control signal CTL2from HV-ECU26to convert the electrical power from battery B to the voltage level of commercial power source44for output thereto.

Terminals40and42serve to connect commercial power source44to AC/DC converter28. When battery B is charged from commercial power source44, the commercial voltage of commercial power source44is applied to terminals40and42. Voltage sensor38detects voltage VAC across terminals40and42to provide the detected voltage VAC to HV-ECU26.

Auxiliary device30is connected to power supply line PL and ground line SL. Auxiliary device30receives the electrical power from power supply line PL to be driven based on a control signal CTL3from HV-ECU26. Auxiliary device30includes, for example, an electric air conditioner, a DC/DC converter, and the like. Power consumption PC of auxiliary device30is detected, which is provided to HV-ECU26.

MG-ECU22receives from HV-ECU26a control command COMEG required to drive-control motor generators MG1and MG2. MG-ECU22receives battery voltage VB and battery current IB from voltage sensor36and current sensor37, respectively, and receives the detected value of motor current of motor generators MG1and MG2from a current sensor not shown. MG-ECU22generates a control signal PWM1directed to drive inverter12and a control signal PWM2directed to drive inverter14, based on control command COMEG from HV-ECU26and respective detected values set forth above. Generated control signals PWM1and PWM2are provided to inverters12and14, respectively.

Engine ECU24receives from HV-ECU26a control command COMEG required to drive-control engine16. Engine ECU24generates a control signal CTL1directed to drive engine16, based on control command COMEG from HV-ECU26. Generated control signal CTL1is provided to engine16.

HV-ECU26generates a control command COMEG required to drive-control motor generators MG1and MG2. Generated control command COMEG is provided to MG-ECU22. For example, HV-ECU26calculates the torque command of motor generators MG1and MG2based on the running state of the vehicle or the SOC of battery B to provide the calculated torque command to MG-ECU22as control command COMEG. HV-ECU26generates control command COMEG required to drive-control engine16. Generated control command COMEG is output to engine ECU24. For example, HV-ECU26calculates the rotational speed command of engine16based on the vehicle running state or the SOC of battery B to provide the calculated rotational speed command to engine ECU24as control command COMEG.

HV-ECU26receives battery voltage VB and battery current IB from voltage sensor36and current sensor37, respectively, to calculate the SOC of battery B based on the received battery voltage VB and battery current IB. For example, the SOC can be calculated by accumulating battery current IB. Alternatively, the SOC can be calculated based on battery voltage VB using a map indicating the relationship between the open circuit voltage (OCV) of battery B and SOC. HV-ECU26controls the charge/discharge of battery B such that the calculated SOC is adjusted to be within a predetermined range (for example, in the range of ±20% about 60%).

When battery B is charged by commercial power source44, HV-ECU26generates control signal CTL2directed to drive AC/DC converter28. Generated control signal CTL2is output to AC/DC converter28. The charging of battery B by means of commercial power source44can be designated, for example, by a user through input device32, or executed at the time of refresh control of battery B, as will be described afterwards.

When determination is made that refresh of battery B is required and allowed, HV-ECU26executes refresh control by a method that will be described afterwards such that battery B is refresh-discharged, and then charged from commercial power source44using AC/DC converter28after execution of refresh-discharging.

Input device32is provided to allow the user to designate execution of refresh control, or allow the user to designate whether engine16is to be set in a backup operation mode as a preparation for electrical outage at commercial power source44during refresh control, as will be described afterwards. Input device32is formed of a touch panel, a button, or the like. Upon manipulation made by the user through input device32, a signal corresponding to the manipulation is output to HV-ECU26.

Notification device34notifies the user that battery B is currently charging/discharging in accordance with refresh control, or that engine16is currently in a backup operation mode as a preparation for electrical outage at commercial power source44during refresh control, as will be described afterwards. Notification device34may be a display device allowing visual confirmation by the user, or an audio device for notification by sound.

FIG. 2is a diagram to describe the concept of refresh control of battery B by HV-ECU26ofFIG. 1. Referring toFIG. 2, the vertical axis represents the SOC (%) of battery B. An upper limit SU and a lower limit SL define the control range of SOC. HV-ECU26controls SOC such that the SOC value is within this range. High upper limit SH represents the charge termination level when battery B is charged from commercial power source44using AC/DC converter28.

In hybrid vehicle10, the SOC will exceed upper limit SU since battery B can be charged from commercial power source44using AC/DC converter28. In other words, hybrid vehicle10has a SOC control range higher than that of a hybrid vehicle absent of an external charging function.

Battery refresh is effective by the deviation of SOC from the general control range as much as possible. In hybrid vehicle10that has a high SOC control range, there is a possibility that battery B cannot be refreshed sufficiently by just setting battery B at a fully-charged state in the refresh operation of battery B. In this context, battery B is refreshed by discharging battery B, and then battery B is charged from commercial power source44by means of AC/DC converter28in the first embodiment.

In the charging operation of battery B, charging is executed, not by the electrical power generated by motor generator MG1upon the drive of engine16, but by means of commercial power source44. Therefore, battery B is charged efficiently without degradation in mileage.

FIG. 3is a flowchart of the control configuration of refresh control of battery B by HV-ECU26ofFIG. 1. The process in this flowchart is invoked from the main routine at a constant interval or every time a predetermined condition is satisfied to be executed.

Referring toFIG. 3, HV-ECU26first identifies the state of battery B (step S10). Specifically, HV-ECU26drives auxiliary device30at a predetermined standard state using the electrical power from battery B to estimate the actual SOC, by a method that will be described afterwards, and calculates the amount of deviation from the SOC, employed in SOC control, calculated based on battery voltage VB and battery current IB. HV-ECU26estimates the status of occurrence of memory effect at battery B based on the elapsed time from execution of the previous refresh control.

FIG. 4is a diagram to describe a method of calculating the SOC deviation amount using auxiliary device30. Referring toFIG. 4, the horizontal axis represents the SOC of battery B, and the vertical axis represents the power consumption of auxiliary device30. Line k1represents the relationship between the power consumption of auxiliary device30and SOC when auxiliary device30is driven at a predetermined standard state using the electrical power from battery B. The relationship is established in a map based on data taken in advance.

The reason why power consumption of auxiliary device30increases as SOC becomes lower is due to the fact that the battery voltage becomes lower in proportion to a lower SOC, which in turn increases the current supplied to auxiliary device30.

By measuring the power consumption of auxiliary device30when auxiliary device30is driven at a predetermined standard state using the electrical power from battery B, the actual SOC is estimated using the map. Specifically, P1is taken as the power consumption of auxiliary device30when auxiliary device30is driven at a predetermined standard state using the electrical power from battery B, and S1is taken as the actual SOC that is estimated. Further, S2is taken as the SOC calculated based on battery voltage VB and battery current IB, employed in SOC control. HV-ECU26calculates the difference AS between S1and S2as the SOC deviation amount.

Referring toFIG. 3again, HV-ECU26determines whether refresh of battery B is required or not based on the identified state of battery B (step S20). Specifically, HV-ECU26determines that battery B must be refreshed in the case where the SOC deviation amount exceeds a threshold value that is set in advance, or in the case where the elapsed time from execution of the previous refresh control exceeds a prescribed time that is set in advance, leading to the presumption that memory effect has occurred.

When HV-ECU26determines that refresh of battery B is not required (NO at step S20), control returns to the main routine without carrying out the subsequent series of processes. In contrast, when HV-ECU26determines that refresh of battery B is required (YES at step S20), fuel remaining amount FUEL of engine16detected at fuel tank18is obtained (step S30). Then, HV-ECU26determines whether execution of refresh control of battery B is allowed or not based on the obtained fuel remaining amount FUEL (step S40). Specifically, HV-ECU26determines that refresh control of battery B is not to be executed when fuel remaining amount FUEL is lower than a threshold value set in advance. This threshold value corresponds to the remaining amount of fuel that allows engine16to be operated continuously during the period when SOC is lower than the lowest amount that can ensure the electrical power required to start engine16by motor generator MG1in a refresh control operation.

FIG. 5represents the change in SOC in a refresh control operation. Referring toFIG. 5, the vertical axis represents the SOC of battery B, and the horizontal axis represents the elapsed time. Prior to time t1, refresh control of battery B is initiated, and refresh-discharging is completed at time t1. The SOC calculated-value (SOC calculated value used in SOC control) is reset during the period of time t1to t2. Charging of battery B is initiated at time t2.

As used herein, value SE represents the lowest level that allows engine16to be started based on the drive of motor generator MG1using the electrical power from battery B. Specifically, if SOC is lower than value SE, engine16cannot be started by the drive of motor generator MG1. Therefore, if commercial power source44fails in a period ΔT during which SOC is lower than value SE, engine16, if stopped, cannot be started. Moreover, the vehicle cannot be made to move since the SOC is low.

In the first embodiment, engine16is set in a backup operation mode as a preparation for electrical outage at commercial power source44in period ΔT during which SOC is lower than value SE. Thus, the remaining amount of fuel that allows engine16to be operated continuously during this period ΔT is set as the threshold value, and refresh control of battery B is not to be executed when fuel remaining amount FUEL is lower than this threshold value.

Referring toFIG. 3again, when determination is made that execution of refresh control is allowed at step S40(YES at step S40), HV-ECU26actually executes refresh control (step S50). The details of this refresh control will be described afterwards. HV-ECU26outputs to notification device34a signal indicating that refresh control is currently executed. The user is notified that battery B is currently charging/discharging in accordance with refresh control by notification device34(step S60).

When determination is made that execution of refresh control is not allowed at step S40(NO at step S40), HV-ECU26proceeds to step S60. HV-ECU26outputs to notification device34a signal indicating that determination has been made that execution of refresh control is not allowed. The user is notified accordingly through notification device34.

FIG. 6is a flowchart of the details of the process of step S50shown inFIG. 5. Referring toFIG. 6, HV-ECU26initiates the discharge of battery B (step S110). Specifically, HV-ECU26provides a control signal CTL3to auxiliary device30. In response, auxiliary device30is driven such that the electrical power stored in battery B is consumed by auxiliary device30.

When discharging of battery B is initiated, HV-ECU26provides a control command COMEG directed to drive motor generator MG1to MG-ECU22. In response, inverter12is driven by MG-ECU22, and startup of engine16is effected by motor generator MG1(step S120). Startup of engine16is effected at least before SOC becomes lower than the aforementioned value SE that allows startup of engine16by the drive of motor generator MG1using the electrical power from battery B.

When engine16is started, HV-ECU26outputs to notification device34a signal indicating that engine16has been started. Notification device34notifies the user that engine16is in a backup operation mode in accordance with refresh control (step S130).

During the discharge of battery B, HV-ECU26monitors battery current IB from current sensor37to determine whether battery current IB becomes lower than a threshold value δ (step S140). This threshold value δ is set to a sufficiently low value. Determination is made that battery B has been discharged sufficiently when battery current IB becomes lower than threshold value δ. When HV-ECU26determines that battery current IB has become lower than threshold value δ (YES at step S140), auxiliary device30is shut down and discharging of battery B ends (step S150). Then, HV-ECU26resets the SOC calculated value (SOC calculated value employed in SOC control) to a prescribed value (step160). This prescribed value may be 0%, or an offset value corresponding to threshold value δ.

Upon reset of the SOC calculated value, HV-ECU26outputs control signal CTL2to AC/DC converter28to drive the same. Battery B is charged by commercial power source44(step S170). Then, HV-ECU26determines whether the SOC of battery B exceeds the aforementioned value SE (step S180). When HV-ECU26determines that the SOC exceeds value SE (YES at step S180), engine16is shut down (step S190) since an SOC level that allows startup of engine16even in the event of electrical outage at commercial power source44is ensured. When the SOC is equal to or lower than value SE (NO at step S180), HV-ECU26proceeds to step S200.

Then, HV-ECU26determines whether battery B has attained a fully-charged state or not (step S200) based on whether SOC has exceeded the high upper limit SH indicating the charge termination level of battery B. When HV-ECU26determines that battery B has not yet attained a fully-charged state (NO at step S200), control returns to step S170to continue charging of battery B.

When determination is made that battery B has attained a fully-charged state at step S200(YES at step S200), HV-ECU26stops AC/DC converter28, and charging of battery B ends (step S210).

The backup operation of engine16during refresh control is restricted to be carried out only in the period during which the SOC is low. Moreover, power generation load is not exerted. Therefore, the fuel consumption is lower as compared to the case where engine16is driven to charge battery B.

The above description is based on a configuration in which battery B is discharged by driving auxiliary device30such that electrical power of battery B is consumed at auxiliary device30. Alternatively, battery B may be discharged by power consumption of the coil of motor generator MG1(or MG2) or discharge resistor (not shown).

Moreover, HV-ECU26may drive AC/DC converter28to provide the electrical power of battery B to commercial power source44for the purpose of discharging battery B. This allows battery B to be discharged without wasting electrical power. In this case, the advantage in cost is increased by executing refresh control during the midnight power time zone.

Although the above embodiment has been described in which determination is made as to whether refresh control is to be executed or not based on fuel remaining amount FUEL of engine16, this determination may be made based on a signal from input device32. Namely, the user can designate whether execution of refresh control is allowed or not through input device32. Accordingly, the convenience for the user is improved.

The above description is based on a configuration in which engine16is started upon initiation of the discharge of battery B. Determination of whether engine16can be started or nor may be made based on a signal from input device32. Namely, the user can designate through input device32whether engine16is to be set in a backup operation mode during the discharge of battery B. Accordingly, the convenience for the user is improved.

Since battery B can be charged from commercial power source44using AC/DC converter28in the first embodiment, the SOC control region is higher than that of a hybrid vehicle absent of an external charging function. In view of the possibility that a sufficient refresh effect cannot be achieved by simply carrying out refresh-charging, refresh-discharging of battery B is executed prior to the charge of battery B from commercial power source44using AC/DC converter28in the first embodiment. Thus, battery B can be refreshed reliably. Since HV-ECU26drives AC/DC converter28such that battery B is charged from commercial power source44after battery B has been subjected to refresh-discharge, battery B can be charged more efficiently than in the case where battery B is charged upon driving engine16. According to the first embodiment, battery B can be refreshed reliably and efficiently.

Since engine16is set in a backup operation mode during refresh control, the event of the vehicle being disabled in movement can be prevented even if commercial power source44fails when the SOC is low in accordance with refresh-discharging.

Furthermore, since determination is made as to whether refresh control is to be executed or not based on the remaining amount of fuel at engine16, engine16will not be brought to a stall as a result of running out of gas during refresh control. Therefore, standstill of the vehicle can be reliably prevented even when commercial power source44fails when the SOC is low in accordance with refresh-discharging.

Further, the safety during refresh control can be ensured since the user is notified, by means of notification device34, of battery B being currently charged/discharged in accordance with refresh-discharging, and of a backup operation mode of engine16.

Since battery B can be charged from commercial power source44using AC/DC converter28in the first embodiment, there will be more occasions of running by motor generator MG2alone using the electrical power from battery B with engine16stopped. In view of the possibility of the engine being degraded if left for a long period of time immobilized, engine16is operated in accordance with refresh control. Therefore, degradation of engine16can be prevented in the first embodiment.

Second Embodiment

In the first embodiment, determination is made as to whether refresh control is to be executed or not based on the remaining amount of fuel of engine16. This is in view of the possibility that commercial power source44may fail during refresh control. In the present second embodiment, determination is made as to whether refresh control is to be executed or not based on the stability of commercial power source44. Namely, refresh control is executed upon determination that commercial power source44will not fail during refresh-discharge if commercial power source44is stable.

The entire configuration of a hybrid vehicle10A according to the second embodiment is similar to that of hybrid vehicle10according to the first embodiment shown inFIG. 1.

FIG. 7is a flowchart of the control configuration of refresh control of battery B by an HV-ECU26A according to the second embodiment. The process of this flowchart is invoked from the main routine to be executed at a predetermined time interval or every time a predetermined condition is satisfied.

The flowchart ofFIG. 7includes steps S35, S45and S55instead of steps S30, S40, and S50, respectively, in the flowchart ofFIG. 3. Specifically, when determination is made that refresh is required for battery B at step S20(YES at step S20), HV-ECU26A obtains voltage VAC of commercial power source44detected by voltage sensor38(step S35).

HV-ECU26A determines whether execution of refresh control of battery B is allowed or not based on the obtained voltage VAC (step S45). Specifically, HV-ECU26A determines the stability of commercial power source44based on the level of voltage VAC, the frequency, and the like. For example, when voltage VAC is reduced or frequency variation observed, HV-ECU26A determines that commercial power source44is unstable. HV-ECU26A determines that refresh control of battery B is not to be executed upon determination of commercial power source44being unstable.

When determination is made that refresh control can be executed at step S45(YES at step S45), HV-ECU26A actually executes refresh control (step S55). When determination is made that refresh control cannot be executed at step S45(NO at step S45), HV-ECU26A proceeds to the process of step S60.

The process of refresh control at step S55corresponds to the process of the flowchart ofFIG. 6, absent of steps S120, S130, S180and S190. In other words, the refresh control process is constituted of the series of processes with the process related to startup and stop of engine16removed in the flowchart ofFIG. 6.

Since determination is made as to whether refresh control is to be executed or not based on the stability of commercial power source44in the second embodiment, the possibility of commercial power source44failing during refresh control is low. Therefore, the risk of the vehicle being disabled in movement as a result of failure of commercial power source44when the SOC is low in accordance with refresh-discharging can be reduced.

Modification of Second Embodiment

The second embodiment has been described based on a configuration in which determination of whether refresh control is to be executed out or not is made based on the stability of commercial power source44. In the present modification, determination as to whether engine16is to be set in a backup operation mode during refresh control is made based on the stability of commercial power source44.

When determination is made that refresh is required of battery B in the modification of the second embodiment, refresh control is executed independent of the stability of commercial power source44.

FIG. 8is a flowchart of refresh control according to the modification of the second embodiment. The flowchart ofFIG. 8further includes an addition step S115in the flowchart ofFIG. 6. Specifically, when discharge of batter B is initiated at step S110, HV-ECU26A determines the stability of commercial power source44based on voltage VAC from voltage sensor38(step S115). Determination of the stability of commercial power source44is made in a manner similar to that of step S45ofFIG. 7.

When determination is made that commercial power source44is unstable (NO at step S115), HV-ECU26A proceeds to step S120to start engine16(step S120). In other words, engine16is operated for backup as a preparation for failure at commercial power source44when commercial power source44is unstable.

When determination is made that commercial power source44is stable at step S115(YES at step S115), HV-ECU26A proceeds to step S140. Specifically, determination is made that commercial power source44will not fail, and backup operation of engine16is not executed when commercial power source44is stable.

The steps subsequent to step S150are similar to those of the flowchart ofFIG. 6.

Since determination is made as to whether engine16is to be set in a backup operation mode during refresh control based on the stability of commercial power source44in the modification of the second embodiment, engine16will not be driven in a backup operation mode when the possibility of failure of commercial power source44is low. Therefore, an unnecessary operation of engine16for backup can be obviated.

In the second embodiment and modification thereof set forth above, determination of whether refresh control is to be executed or not and determination of whether backup operation is to be executed or not are made based on the stability of commercial power source44. Alternatively, such determinations can be made based on predetermined date information. For example, at the summer season or at noon time, execution of refresh control may be suppressed since the possibility of electrical outage is high in view of the power peak. Moreover, execution of backup operation of engine16can be suppressed during nighttime hours in view of the problem of noise.

In each of the embodiments set forth above, hybrid vehicles10and10A may be based on a series/parallel type configuration that allows the motive energy of engine16to be divided to the axle and motor generator MG1by a power split mechanism for transmission, or a series type configuration in which engine16is used only for the purpose of driving motor generator MG1, and the driving force of axle is developed by motor generator MG2alone using the electrical power generated by motor generator MG1.

The above description is based on a configuration in which battery B is charged from commercial power source44. Alternatively, battery B may be charged by another power source, for example a solar cell, instead of commercial power source44.

Although the above embodiments have been described in which AC/DC converter28is installed in the vehicle, AC/DC converter28may be installed outside the vehicle.

The above description is based on a configuration in which battery B is charged from commercial power source44using AC/DC converter28. Alternatively, the electrical power from commercial power source44may be supplied to the neutral point of each of the 3-phase coils of motor generators MG1and MG2to charge battery B under switching control such that inverters10and20are operated as respective phase arms of single-phase PWM converters. By employing this method, AC/DC converter28is dispensable.

In the description set forth above, engine16corresponds to “internal combustion engine” of the present invention, and motor generator MG2corresponds to “first electric motor” of the present invention. Battery B corresponds to “battery” in the present invention. Motor generator MG1corresponds to “power generation device” and “second electric motor” of the present invention. Further, AC/DC converter28corresponds to “electrical power conversion device” of the present invention. HV-ECUs26and26A correspond to “control device” of the present invention.

It will be understood that the embodiments disclosed herein are by way of example only, and is not to be taken by way of limitation in all aspects. The scope of the present invention is defined, not by the description set forth above, but by the appended claims, and all changes that fall within limits and bounds of the claims, or equivalence thereof are intended to be embraced by the claims.