Controller of hybrid vehicle

A controller of a hybrid vehicle includes: a control unit configured to activate a starter device for starting any one of a drive motor and an engine by stepping up electric power from a battery by a voltage transformer. The control unit includes a limitation part that limits passing power of the voltage transformer when the temperature of the voltage transformer rises, and a calculation part that obtains a maximum electric power that can be supplied to the drive motor when the starter device is activated, by subtracting a consumed power of the starter device from limited power during limitation of passing power by the limitation part. The control unit activates the starter device and starts the engine, when required power of the drive motor reaches the maximum electric power calculated by the calculation part during limitation of passing power by the limitation part.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a controller of a hybrid vehicle, and specifically to a controller of a hybrid vehicle equipped with a voltage transformer (boost converter) that steps up electric power of a drive battery, and supplies it to a drive motor.

Description of the Related Art

For example, a hybrid vehicle whose drive mode is switchable between EV mode and parallel mode is constructed with a drive motor connected to a drive wheel and an engine also connected to the drive wheel through a clutch. In EV mode, the vehicle travels by disconnecting the clutch to drive the drive motor by power supply from the drive battery. When the total required output for travel is increased by pressing of an accelerator, for example, and cannot be achieved by the drive motor alone, the drive mode is switched to parallel mode. In parallel mode, the clutch is connected after the engine is started by a starter device such that driving force of the engine is transmitted to the drive wheel in addition to the driving force of the drive motor, to achieve travel corresponding to the operation of the accelerator.

Incidentally, as described in Japanese Patent Laid-Open No. 2007-325352 (Patent Document 1), for example, in hybrid vehicles brought into actual use in recent years, electric power of a drive battery is not only converted from DC to AC by an inverter, but is also stepped up by a boost converter to improve efficiency of a drive motor, an inverter, and the like.

However, the hybrid vehicle described in Patent Document 1 suffers from a problem such that a power limit, which is imposed to prevent the boost converter from being heated, temporarily reduces the driving force of the drive wheel when switching from EV mode to parallel mode.

For example, an increase in electric power stepped up or stepped down through the boost converter (hereinafter referred to as passing power), or operation and the like in high temperature environment increases the temperature of the boost converter and may cause malfunction due to overheating. Hence, to protect parts, a countermeasure is taken to limit passing power in a certain high temperature range.

As mentioned above, the switching from EV mode to parallel mode is performed when the total required output is increased by pressing of the accelerator or the like, and cannot be achieved by the drive motor alone. Hence, at this time, the required power of the drive motor often exceeds the limited power of the boost converter. When the electric power to the drive motor is limited to the limited power, the entire passing power of the boost converter is supplied to the drive motor.

However, when switching from EV mode to parallel mode is performed during power limitation of the boost converter, the starter device is activated to start the engine. Since power supply to the drive motor is reduced by the power consumption amount of the starter device, the driving force transmitted to the drive wheel is also reduced. Although the driving force recovers when the starter device stops after completion of startup of the engine, even a temporary reduction of the driving force causes acceleration failure or pitching, for example, which leads to deterioration in drivability.

For example, in the case of a hybrid vehicle in which a drive wheel (e.g., rear wheel) other than the drive wheel (e.g., front wheel) driven by the drive motor is driven by another drive motor that directly receives electric power from a drive battery (i.e., unaffected by power limit), it is possible to prevent reduction of driving force of the vehicle as a whole, by temporarily increasing the driving force of this drive motor in synchronization with the activation of the starter device. However, this is hardly a practical measure, since a change in driving force that occurs momentarily between the front wheel and the rear wheel may disturb the behavior of the vehicle.

An objective of the present invention is to provide a controller of a hybrid vehicle that can prevent a temporary reduction of driving force due to activation of a starter device for starting an engine when the drive mode is switched from EV mode to parallel mode during power limitation of a boost converter, and can thereby ensure satisfactory drivability of the vehicle.

SUMMARY OF THE INVENTION

To achieve the above objective, a controller of a hybrid vehicle of the present invention includes: a control unit configured to activate a starter device for starting any one of a drive motor and an engine by stepping up electric power from a battery by a voltage transformer, wherein: the control unit includes a limitation part that limits passing power of the voltage transformer when the temperature of the voltage transformer rises, and a calculation part that obtains a maximum electric power that can be supplied to the drive motor when the starter device is activated, by subtracting a consumed power of the starter device from limited power during limitation of passing power by the limitation part; and the control unit activates the starter device and starts the engine, when required power of the drive motor reaches the maximum electric power calculated by the calculation part during limitation of passing power by the limitation part.

According to the controller of a hybrid vehicle configured in this manner, the control unit activates the starter device to start the engine, when required power of the drive motor reaches the maximum electric power during limitation of passing power by the limitation part. The passing power of the voltage transformer at this point is still allowed to increase by the amount of the consumed power of the starter device before reaching the limited power of the limitation part. Even if the power consumed by activation of the starter device is added to the required power of the drive motor, electric power supplied to the drive motor is not reduced, and is maintained at the required power level. Hence, it is possible to prevent acceleration failure or pitching, for example, caused by a temporary reduction of driving force, and satisfactory drivability can be ensured.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a description will be given of an embodiment in which the present invention is embodied as a controller of a plug-in hybrid vehicle (hereinafter referred to as vehicle1).

FIG. 1is an overall configuration diagram of the plug-in hybrid vehicle to which the controller of the embodiment is applied.

The vehicle1of the embodiment is a four-wheel drive vehicle configured to drive front wheels4by an output of a front motor2(drive motor) or outputs of the front motor2and an engine3, and drive rear wheels6by an output of a rear motor5.

An output shaft of the front motor2is connected to a drive shaft7of the front wheels4, and the engine3is also connected to the drive shaft7through a clutch8. Moreover, the front wheels4are connected to the drive shaft7through a front differential9and right and left drive shafts10. Driving force of the front motor2and driving force of the engine3when the clutch8is connected are transmitted to the front wheels4through the drive shaft7, the front differential9, and the right and left drive shafts10, to generate driving force for the vehicle to run, in the front wheels4. A motor generator (starter device)11is connected to an output shaft of the engine3. The motor generator11can arbitrarily generate electric power by being driven by the engine3regardless of whether or not the clutch8is connected, and also functions as a starter for starting the engine3from a stopped state when the clutch8is disconnected.

Meanwhile, an output shaft of the rear motor5is connected to a drive shaft12of the rear wheels6, and the rear wheels6are connected to the drive shaft12through a rear differential13and right and left drive shafts14. Driving force of the rear motor5is transmitted to the rear wheels6through the drive shaft12, the rear differential13, and the right and left drive shafts14, and generates driving force for the vehicle to run, in the rear wheels6.

Inverters16,17are connected to the front motor2and the motor generator11, respectively, and the inverters16,17are connected to a boost converter (voltage transformer)18. An inverter19is connected to the rear motor5, and the inverter19and a drive battery20are connected to the boost converter18. The drive battery20is formed of a secondary battery such as a lithium ion battery, and includes a battery monitoring unit20athat calculates its SOC (state of charge), and detects its temperature TBAT.

The operating voltage differs between rear and front sides of the boost converter18. The rear motor5and the inverter19are designed to operate at a voltage (e.g., 300V) of the drive battery20and form a low voltage circuit21with the drive battery20, while the front motor2, the motor generator11, and their inverters16,17are designed to operate at a higher voltage (e.g., 600V) to improve efficiency, and form a high voltage circuit22.

The boost converter18has a function of stepping up and down the voltage when electric power is exchanged between the circuits21,22. For example, the boost converter18steps up the low voltage-side DC power discharged from the drive battery20and supplies it to the inverter16, so that the three-phase AC power converted by the inverter16drives the front motor2, and the three-phase AC power similarly converted by the inverter17causes the motor generator11to function as a starter. Additionally, the three-phase AC power generated by the motor generator11is converted into high voltage-side DC power by the inverter17, and the boost converter18steps down the DC power to charge the drive battery20. The DC power stepped down by the boost converter18is also converted into three-phase AC power by the inverter19, and is supplied to drive the rear motor5.

Note that electric power is exchanged in each of the circuits21,22without passing through the boost converter18. For example, on the low voltage circuit21side, DC power discharged from the drive battery20is converted into three-phase AC power by the inverter19and supplied to the rear motor5. Conversely, three-phase AC power regenerated by the rear motor5is converted into DC power by the inverter19, and is used to charge the drive battery20. In addition, three-phase AC power generated by the motor generator11on the high voltage circuit22side is converted into DC power by the inverter17, and is then converted back into three-phase AC power by the inverter16to be supplied to the front motor2.

A front motor ECU24is connected to each of the inverters16,17on the high voltage circuit22side, and the front motor ECU24switches the inverters16,17to control the above-mentioned operation of the front motor2and the motor generator11. Meanwhile, a rear motor ECU25is connected to the inverter19on the low voltage circuit21side, and the rear motor ECU25switches the inverter19to control the above-mentioned operation of the rear motor5.

An engine ECU26is connected to the engine3, and the engine ECU26controls the throttle position, fuel injection amount, ignition timing, and the like of the engine3, to operate the engine3.

Note that although not shown inFIG. 1, the drive battery20includes a charger, and the charger can be used to arbitrarily charge the drive battery20with electric power supplied from an external power source.

The front motor ECU24, rear motor ECU25, and engine ECU26described above are connected to a vehicle ECU27which is a higher-level unit. Each of The ECUs24to27includes an input/output device, a storage device (e.g., ROM, RAM, or nonvolatile RAM), a central processing unit (CPU), and the like. Note that the nonvolatile RAM of each storage device stores instructions for various later-mentioned control performed by each CPU.

The vehicle ECU27is a control unit for performing general control of the vehicle1, and lower-level ECUs24to26having received instructions from the vehicle ECU27control the aforementioned operation of the front motor2, motor generator11, rear motor5, and engine3. Hence, the battery monitoring unit20aof the drive battery20, a temperature sensor28for detecting a temperature Tcvtrof the boost converter18, and unillustrated sensors such as an accelerator pedal position sensor for detecting the accelerator pedal position and a speed sensor for detecting a vehicle speed V are connected to the input side of the vehicle ECU27. Additionally, operation states of the front motor2, motor generator11, rear motor5, and engine3are input to the input side of the vehicle ECU27through the ECUs24to26.

In addition to the aforementioned front motor ECU24, rear motor ECU25, and engine ECU26, the clutch8and boost converter18are connected to the output side of the vehicle ECU27.

The vehicle ECU27switches the drive mode of the vehicle1among EV mode, series mode and parallel mode, on the basis of the aforementioned various detection amounts and operation information of the accelerator pedal position sensor and the like. For example, the drive mode is set to parallel mode in ranges such as a high speed range where efficiency of the engine3is high. In medium to low speed ranges, the drive mode is switched between EV mode and series mode depending on the SOC and the like of the drive battery20.

In EV mode, the clutch8is disconnected and the engine3is stopped, so that electric power from the drive battery20drives the front wheels4through the front motor2, and drives the rear wheels6through the rear motor5to drive the vehicle1. In series mode, the clutch8is disconnected to separate the engine3from the front wheels4side, and the engine3is operated to drive the motor generator11. The generated electric power drives the front wheels4through the front motor2and drives the rear wheels6through the rear motor5to drive the vehicle1, and also charges the drive battery20with surplus power.

In parallel mode, the engine3is operated after connecting the clutch8, to transmit driving force to the front wheels4. When the engine driving force is insufficient, battery power is used to drive the front motor2and the rear motor5. In addition, when the SOC of the drive battery20is low and charging is required, the engine3drives the motor generator11, and the generated electric power is used to charge the drive battery20.

When electric power is thus exchanged between the high and low voltage circuits21,22, the boost converter18steps up and down the voltage in the aforementioned manner, as a matter of course.

Additionally, the vehicle ECU27calculates a total required output for travel of the vehicle1, on the basis of the aforementioned various detection amounts and operation information. The vehicle ECU27distributes the total required output to the front motor2side and the rear motor5side in EV mode and series mode, and to the front motor2side, the engine3side, and the rear motor5side in parallel mode. Then, the vehicle ECU27sets a required torque for each of the front motor2, the rear motor5, and the engine3on the basis of the distributed required output and the like, and outputs an instruction signal to the front motor ECU24, rear motor ECU25, and engine ECU26, so that the respective required torques can be achieved.

According to the instruction signal from the vehicle ECU27, the front motor ECU24and the rear motor ECU25calculate a target current value to apply to a coil of each phase of the front motor2and the rear motor5to achieve the required torque. Thereafter, the front motor ECU24and the rear motor ECU25switch the respective inverters16,19according to the target current values, and achieve the required torque. Note that a similar operation is performed when the motor generator11generates electric power. Here, the front motor ECU24switches the inverter17according to the target current value calculated from the required torque on the negative side, and achieves the required torque.

According to the instruction signal from the vehicle ECU27, the engine ECU26calculates target values of the throttle position, fuel injection amount, ignition timing and the like for achieving the required torque, and controls operation of the engine3on the basis of the target values to achieve the required torque.

Meanwhile, the vehicle ECU27controls the boost converter18to step up and down the voltage of electric power exchanged between the low and high voltage circuits21,22. Although stepping up and down the voltage improves efficiency of the front motor2and the motor generator11as well as their inverters16,17, for example, the boost converter18consumes power with its operation. For this reason, the boost converter18is activated in a high speed-heavy load range of the front motor2or the motor generator11where particularly high efficiency can be achieved, and the boost converter18is stopped in other operation ranges.

Also, since an increase in passing power of the boost converter18or operation and the like in high temperature environment increases the temperature of the boost converter18and may cause malfunction, the vehicle ECU27limits passing power (limitation part) according to the temperature of the boost converter18.

FIG. 2is a characteristics diagram showing how a power limit value Wlimitof the boost converter18and the maximum electric power of the front motor2are set.

As indicated by a thin solid line inFIG. 2, the vehicle ECU27calculates the power limit value Wlimit(hereinafter referred to as power limit value) of passing power on the basis of the temperature Tcvtrof the boost converter18detected by the temperature sensor28, and causes the boost converter18to step up and down the voltage by using the power limit value Wlimitas an upper limit. Hereinafter, for convenience of the description, passing power limited according to the power limit value Wlimitis referred to as limited power.

As can be seen fromFIG. 2, the power limit value Wlimitis set to a constant value in a temperature range of a certain temperature or lower. In a higher temperature range, temperature rise is suppressed by setting a lower power limit value Wlimitfor a higher temperature Tcvtr. However, as has been mentioned in Description of the Related Art, there is a problem that when the drive mode is switched from EV mode to parallel mode during power limitation of the boost converter18, the driving force of the front wheels4is temporarily reduced, whereby drivability is deteriorated.

This situation will be described below. When the driving mode is switched to parallel mode after an increase in the total required output due to pressing of the accelerator or the like during travel in EV mode, first, the engine3is started by the motor generator11, and then the clutch8is connected to transmit, in addition to the driving force of the front motor2, the driving force of the engine3to the front wheels4. Then, if electric power to the front motor2is limited by the boost converter18immediately before start of the engine, part of passing power of the boost converter18(i.e., power supply to the front motor2) is consumed to activate the motor generator11. Hence, power supply to the front motor2is reduced by this consumption amount. For this reason, the driving force of the front wheels4is reduced until the motor generator11stops after completion of engine startup. This deteriorates drivability.

In view of the above problem, the inventors of the present invention focused on the following points. The switching to parallel mode at this time is performed when the required power of the front motor2exceeds the limited power of the boost converter18. However, if the switching to parallel mode is performed before the required power exceeds the limited power, the required power of the front motor2can be ensured even if part of the limited power is consumed to activate the motor generator11.

Additionally, since reduction of power supply to the front motor2is caused by activation of the motor generator11, by switching to parallel mode at a timing hastened by the power consumption amount, that is, at a timing when the required power of the front motor2reaches a value (maximum electric power to be described below) obtained by subtracting the power consumption amount of the motor generator11from the limited power of the boost converter18, the switching to parallel mode can be done while ensuring the required power of the front motor2. According to this observation, drive mode switching control from EV mode to parallel mode performed by the vehicle ECU27will be described below as first and second embodiments.

First Embodiment

In the first embodiment, the maximum electric power is calculated according to the following expression (1) (calculation part).
Maximum electric power=Wlimit−Wstart(1)

As shown inFIG. 2, the maximum electric power is set as a value obtained by subtracting a consumed power Wstartof the motor generator11from the power limit value Wlimit, over the entire temperature range of the boost converter18. Hence, the maximum electric power refers to the maximum electric power that can be supplied to the front motor2when the motor generator11is activated for engine startup, during limitation of passing power of the boost converter18.

Accordingly, when the total required output necessary for the vehicle1to run increases by pressing of the accelerator or the like during travel in EV mode, and the required power (required output) of the front motor2also increases, switching to parallel mode is performed when the required power reaches the maximum electric power.

FIG. 3is a time chart showing the switch timing to parallel mode when the required power of the front motor2increases. As shown inFIG. 3, in the technique of Japanese Patent Laid-Open No. 2007-325352, switching from EV mode to parallel mode is performed when the required power of the front motor reaches the power limit value Wlimit. Meanwhile, in the first embodiment, switching to parallel mode is performed at a timing hastened by the consumed power Wstartof the motor generator11.

Hence, the passing power of the boost converter18at this point is still allowed to increase by the amount of the consumed power Wstartbefore reaching the power limit value Wlimit. Even if the consumed power Wstartfrom activation of the motor generator11is added to the required power of the front motor2, electric power supplied to the front motor2is not reduced, and is maintained at the required power level. Thus, it is possible to prevent acceleration failure or pitching, for example, caused by a temporary reduction of the driving force of the front wheels4, and satisfactory drivability of the vehicle can be ensured.

Additionally, as shown inFIG. 2, electric power supplied to the front motor2is limited to the maximum electric power lower than the power limit value Wlimitof the boost converter18. However, since the driving force of the engine3is added by switching to parallel mode when the required power reaches the maximum electric power, transition of the driving force of the front wheels4in the course of switching from EV mode to parallel mode is smooth and no different from the technique of Japanese Patent Laid-Open No. 2007-325352, for example. In this regard, too, satisfactory drivability can be ensured.

Moreover, since limitation of passing power according to the maximum electric power reduces thermal load on the boost converter18in EV mode, the temperature of the boost converter18is lowered. For this reason, the power limit value Wlimitset on the basis of the temperature Tcvtrincreases promptly. This also achieves an advantage that limitation imposed on power supply to the front motor2can be cancelled promptly.

Second Embodiment

In the second embodiment, the maximum electric power is calculated according to the following expression (2) (calculation part).
Maximum electric power=Wlimit−Wstart−Wα(2)

Here, Wα is an allowance amount, and is calculated according to the following expression (3).
Wα=Wα1+Wα2  (3)

Here, Wα1is a temperature correlation amount, and Wα2is an SOC correlation amount.

FIG. 4is a characteristics diagram showing a relation among the consumed power Wstart, the allowance amount Wα, the temperature correlation amount Wα1, and the SOC correlation amount Wα2.

As shown inFIG. 4, while the consumed power Wstartof the motor generator11is constant regardless of the temperature Tcvtr of the boost converter18, the temperature correlation amount Wα1is set to 0 in a temperature range of a certain temperature or lower, and, in a higher temperature range, is set larger for a higher temperature Tcvtr. Similarly, the SOC correlation amount Wα2is set to 0 in a temperature range of a certain temperature or lower, and, in a higher temperature range, is set larger for a higher temperature Tcvtr. Here, the inclination of the SOC correlation amount relative to the temperature Tcvtris steeper, that is, set larger, for a lower SOC (remaining battery level) of the drive battery20.

Note that the characteristics set inFIG. 4are an example, and can be changed arbitrarily as long as they vary the temperature correlation amount Wα1and the SOC correlation amount Wα2in the above-mentioned direction according to variation in the temperature Tcvtrof the boost converter18.

As a result, the allowance amount Wα is set to a larger value for a higher temperature Tcvtrof the boost converter18, and a lower SOC of the drive battery20, in a temperature range of a certain temperature or higher. As shown inFIG. 2, since the allowance amount Wα is subtracted from the power limit value Wlimit, the maximum electric power is set even lower than the first embodiment.

The reason of reflecting the temperature Tcvtrand the SOC on the maximum electric power is because these are requirements that affect thermal load on the boost converter18. That is, the temperature Tcvtrdirectly affects thermal load on the boost converter18, and the higher the temperature Tcvtr, the greater the necessity to reduce the passing power of the boost converter18. Also, the lower the SOC of the drive battery, the larger the loss when the boost converter18steps up and down the passing power, and a larger loss is more likely to raise the temperature of the boost converter18. Accordingly, the SOC can be regarded as a requirement that indirectly affects thermal load on the boost converter18, and the lower the SOC, the greater the necessity to reduce the passing power of the boost converter18.

Since the maximum electric power is set in this manner, when the required power of the front motor2increases, switching to parallel mode is performed at an earlier timing than the first embodiment, as shown inFIG. 3. Hence, power supply to the front motor2can be more reliably ensured, and a temporary reduction of the driving force of the front wheels4can be more reliably prevented.

What is more, the higher the temperature Tcvtrof the boost converter18and the lower the SOC of the drive battery, the earlier the switch timing to parallel mode becomes. As a result, since switching to parallel mode is performed earlier when the necessity of reducing passing power of the boost converter18with respect to the temperature Tcvtr and the SOC is greater, the passing power of the boost converter18is limited according to a lower maximum electric power, and thermal load can be reduced even more. Accordingly, the temperature of the boost converter18is lowered, the power limit value Wlimitincreases promptly, and limitation imposed on power supply to the front motor2can be cancelled promptly.

Also, naturally, as in the case of the first embodiment, even if the motor generator11is activated after switching to parallel mode, power supply to the front motor2is maintained at the required power level. Hence, it is possible to prevent deterioration in drivability due to a temporary reduction in the driving force of the front wheels4. Furthermore, although power supply to the front motor2is limited to the maximum electric power, at this point, the driving force of the engine3is added by switching to parallel mode. Hence, the driving force of the front wheels4transitions smoothly, and satisfactory drivability can be ensured.

Note that although the SOC correlation amount Wα2is set on the basis of the SOC of the drive battery20in the second embodiment, any index may be used as long as it represents electric allowance of the drive battery20. For example, instead of the SOC correlation amount Wα2, a larger voltage correlation amount Wα3may be set for a lower voltage (remaining battery level) of the drive battery20, and an allowance amount Wα may be calculated according to the following expression (4).
Wα=Wα1+Wα3  (4)

Although this is the end of the description of the embodiment, the form of the present invention is not limited to the embodiment. For example, although the above embodiments prevent deterioration in the driving force of the front wheels4caused by engine startup when switching from EV mode to parallel mode, the invention is not limited to this. For example, in a hybrid vehicle that can select, as a drive mode, engine mode where the vehicle travels by driving force of the engine alone, a similar reduction in driving force occurs when switching from EV mode to engine mode. Hence, measures similar to those of the above embodiments may be taken to prevent reduction in driving force, when switching between such drive modes.