Electric powered vehicle performing regenerative braking

A regeneration control portion sets a torque command value (in general, a negative value) of a motor generator at a time of regenerative braking. A braking cooperative control portion calculates a total braking force (power) required for the entire vehicle based on a brake depression force BK of a driver and also controls the shares of the output of the total braking force between a hydraulic brake and the motor generator. An MG-ECU drives and controls the motor generator so that a regenerative torque is generated according to a torque command value. The regeneration control portion puts a limitation such that the absolute value of the regenerative torque is smaller at a time of downhill travel than at a time of flat-road travel, for the same brake operation.

This nonprovisional application is based on Japanese Patent Application No. 2006-356816 filed with the Japan Patent Office on Dec. 29, 2006, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric powered vehicle, and more particularly to an electric powered vehicle equipped with a motor generator performing generation of a vehicle driving force and regenerative power generation at a time of regenerative braking.

2. Description of the Background Art

Hybrid vehicles have recently received attention as environmentally-friendly automobiles. A hybrid vehicle is an automobile that can generate a vehicle traveling power using an electric motor for driving the vehicle in addition to the conventional engine. In particular, in order to recover energy by regenerative power generation at a time of regenerative braking of the vehicle, a motor generator having both the functions of an electric motor and an electric generator is generally employed as an electric motor for the vehicle.

As for regenerative control of electric powered vehicles, Japanese Patent Laying-Open No. 2002-262411 (Patent Document 1) discloses a configuration of a speed control device for an electric powered vehicle such as an electrically operated golf car for avoiding the likelihood of skids. As the slope angle is larger in downhill traveling, the braking force of regenerative braking is increased, and the proportion applied to the drive wheels of the entire braking force including an electrical braking force and a mechanical braking force is increased, so that the drive wheel is locked, causing a skid. Specifically, the speed control device of the electric powered vehicle disclosed in Patent Document 1 is intended to improve traveling stability by limiting the wheel braking force by regenerative braking of the main motor when the gradient of a road is larger than a preset threshold value, thereby preventing a skid of the wheel due to locking.

Furthermore, International Publication WO97/10966 (Patent Document 2) also discloses a regenerative braking control device of an electric vehicle configured such that a regenerative braking force of an electric motor is controlled according to a gradient state, in order to avoid a wheel lock at a time of downhill travel and maintain vehicle traveling stability. In particular, Patent Document 2 discloses that a wheel lock is avoided by keeping the regenerative braking force on a down slope at the similar state as on a flat road, and thus traveling stability can be kept.

In addition, Japanese Patent Laying-Open No. 2000-32602 (Patent Document 3), Japanese Patent Laying-Open No. 2002-369578 (Patent Document 4), and Japanese Patent Laying-Open No. 2005-263061 (Patent Document 5) disclose a control configuration to limit regenerative power generation at a time of a temperature increase of an electric motor, in an electric powered vehicle such as an electric vehicle or a hybrid vehicle.

In electric powered vehicles, generally, regenerative power generation is performed by a motor generator in response to a brake operation by a driver to generate a regenerative braking force. However, not only power running of generating a vehicle driving force but also regenerative power generation at a time of regeneration causes the temperature of the motor generator (also referred to as a motor temperature hereinafter) to be increased by heat generated mainly in a coil winding. When the motor temperature rises, it becomes necessary to limit the current amount, that is, the output torque, so that the vehicle driving force that can be generated by the motor generator is limited.

Therefore, even with the regeneration limitation as disclosed in Patent Documents 1, 2, when a downhill with a relatively gentle gradient continues, the motor temperature is increased by the continuous regenerative power generation, and the output (power running) torque of the motor generator is limited at a time of uphill travel or flat-road travel after downhill travel, so that the motive power performance may not be fully exerted. This problem is expected, in particular, in a travel pattern in which downhill travel and uphill travel are alternately performed, as in a mountain road.

Furthermore, in the control configuration that limits the regenerative power generation at a time of temperature increase of an electric motor (motor generator) that generates a vehicle driving force, as disclosed in Patent Documents 3-5, an excessive increase of the motor temperature can be prevented. However, this configuration is not enough as regeneration control that can cope with aforementioned problem and can secure a vehicle driving force sufficient for flat-road travel or uphill travel after downhill travel.

If the aforementioned problem is addressed in view of specification design, the size of the motor generator is increased, for the increased thermal capacity and the enforced cooling structure are required to suppress a temperature increase of the motor generator. In addition, in order to secure traveling performance at a time of temperature increase, torque has to be secured by shifting to low gear for the entire vehicle, leading to a poor fuel efficiency at a time of high-speed travel.

SUMMARY OF THE INVENTION

An object of the present invention is to perform regenerative power generation control of a motor generator at a time of downhill travel of an electric powered vehicle, with consideration for achieving sufficient motive power performance in flat-road travel or uphill travel following downhill travel.

An electric powered vehicle in accordance with the present invention includes a motor generator, a power conversion unit, a gradient sensing portion sensing a gradient of a road, and a regeneration control portion configured to generate a torque command value of the motor generator in a regenerative braking operation, at least according to a brake operation by a driver. The motor generator is configured to be able to receive/transmit a rotational force from/to a wheel. The power conversion unit is configured to perform bidirectional electric power conversion between a chargeable power supply and the motor generator so that the motor generator outputs a torque according to a torque command value. For the torque command value in the regenerative braking operation at a time of downhill travel and at a time of flat-road travel corresponding to the same brake operation, the regeneration control portion continuously puts a limitation such that an absolute value of the torque command value is smaller at a time of the downhill travel than at a time of the flat-road travel, based on a road gradient sensed by the gradient sensing portion.

According to the above-noted electric powered vehicle, heat generation in the motor generator can be suppressed by limiting regenerative power generation at a time of downhill travel as compared with at a time of flat-road travel. As a result, the output torque of the motor generator in flat-road travel or uphill travel after the end of downhill travel is secured thereby achieving sufficient motive power performance. In particular, it is possible to avoid a large temperature increase followed by the regenerative power generation at a time of downhill travel in which the requested braking force by a brake operation of a driver is increased, so that the size of the motor generator can be reduced because of the simplified cooling structure of the motor generator, or the fuel efficiency at a time of high-speed travel can be improved by shifting to high gear while avoiding shifting to low gear for the entire vehicle for ensuring the traveling performance at a time of temperature increase. Thus, the specification design related to the motor generator can be made efficient.

Preferably, the regeneration control portion includes a braking cooperative control portion and a regenerative torque setting portion. The braking cooperative control portion calculates a requested braking power in the entire vehicle according to a state of the electric powered vehicle and the brake operation and also sets a regenerative braking power shared by the motor generator, of the requested braking power. The regenerative torque setting portion generates the torque command value in the regenerative braking operation according to the regenerative braking power set by the braking cooperative control portion. Then, the braking cooperative control portion limits the regenerative braking power set corresponding to the same brake operation to be lower at a time of the downhill travel than at a time of the flat-road travel, based on the road gradient.

Further preferably, the regeneration control portion further includes a charging control portion setting requested charging power of the power supply according to a charge state of the power supply. The braking cooperative control portion sets the regenerative braking power within a range of the requested charging power or lower. Then, the charging control portion limits the requested charging power set corresponding to the same charge state to be lower at a time of the downhill travel than at a time of the flat-road travel, based on the road gradient.

According to such a configuration, a temperature increase of the motor generator at a time of downhill travel can be suppressed by the braking cooperative control at a time of downhill travel and the adjustment of the requested charging power.

Preferably, the electric powered vehicle further includes a temperature obtaining portion obtaining a temperature of the motor generator. Then, the regeneration control portion sets a limitation degree of the torque command value in the regenerative braking operation at a time of the downhill travel with respect to at a time of the flat-road travel, according to the temperature of the motor generator.

Preferably, the regeneration control portion sets a limitation degree of the torque command value in the regenerative braking operation at a time of the downhill travel with respect to at a time of the flat-road travel, according to the road gradient. Alternatively, preferably, the regeneration control portion sets a limitation degree of the torque command value in the regenerative braking operation at a time of the downhill travel with respect to at a time of the flat-road travel, according to the brake operation.

According to such a configuration, the regenerative power generation by the motor generator can be limited by a proper degree, corresponding to the temperature state of the motor generator, the gradient of a road, or the brake operation of the driver. As a result, while energy is recovered by regenerative power generation within a possible extent, a temperature increase of the motor generator can be prevented.

Preferably, in the electric powered vehicle according to the present invention, the regeneration control portion sets the torque command value of the motor generator to approximately zero, at a time of the downhill travel.

According to such a configuration, regenerative power generation by the motor generator is stopped at a time of downhill travel, so that a temperature increase of the motor generator can be prevented reliably.

An electric powered vehicle in accordance with another aspect of the present invention includes a motor generator, a power conversion unit, a gradient sensing portion sensing a gradient of a road, a temperature obtaining portion obtaining a temperature of the motor generator, and a regeneration control portion configured to generate a torque command value of the motor generator in a regenerative braking operation, at least according to a brake operation by a driver. The motor generator is configured to be able to receive/transmit a rotational force from/to a wheel. The power conversion unit is configured to perform bidirectional electric power conversion between a chargeable power supply and the motor generator so that the motor generator outputs a torque according to a torque command value. Then, for the torque command value in the regenerative braking operation at a time of downhill travel and at a time of flat-road travel corresponding to the same brake operation, the regeneration control portion puts a limitation such that an absolute value of the torque command value is smaller at a time of the downhill travel than at a time of the flat-road travel, based on a road gradient sensed by the gradient sensing portion, according to a limitation degree corresponding to the temperature of the motor generator and the road gradient.

According to the above-noted electric powered vehicle, the regenerative power generation at a time of downhill travel can be limited by a proper degree in accordance with the limitation degree corresponding to the temperature of the motor generator and the gradient of a road. Therefore, while energy is recovered by regenerative power generation within a possible extent, a temperature increase of the motor generator can be prevented at a time of downhill travel.

Therefore, the main advantage of the present invention is in that regenerative power generation control of a motor generator can be performed at a time of downhill travel of an electric powered vehicle, with consideration for achieving sufficient motive power performance in flat-road travel or uphill travel following downhill travel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an embodiment of the present invention will be described in detail with reference to the figures. It is noted that in the following, the same or corresponding parts will be denoted with the same reference characters and description thereof will not basically be repeated.

Referring toFIG. 1, an electric powered vehicle100in accordance with an embodiment of the present invention includes a DC voltage generation portion10#, a smoothing capacitor C0, an inverter20, a control circuit50and a control device80typically formed of an ECU (Electronic Control Unit), a motor generator MG, a driving shaft62, and a wheel65rotatably driven with rotation of driving shaft62. Driving shaft62is configured to be able to receive/transmit a rotational force from/to the output shaft of motor generator MG, generally, through a transmission mechanism such as a not-shown speed reducer. In addition, wheel65is provided with a braking mechanism, typically, a hydraulic brake90mechanically applying a braking force by hydraulic pressure supply. Such a braking mechanism is generally provided for each wheel.

Motor generator MG is mounted on an electric powered vehicle such as a hybrid vehicle or an electric vehicle to generate driving torque for wheels at a time of power running and to generate regenerative torque in the opposite direction to the rotational direction of drive wheels65at a time of regeneration thereby performing regenerative power generation by generation of an electrical braking force (regenerative braking force). In other words, motor generator MG is configured as a “motor generator” for vehicle driving, including both functions of an electric motor and an electric generator. In a hybrid vehicle, another motor generator may be further provided which is configured to have a function of an electric generator driven by an engine. It is noted that in a case where electric powered vehicle100is a hybrid vehicle, a vehicle driving system is configured such that driving shaft62can also be rotated by an output of an engine (not shown).

DC voltage generation portion10# includes a DC power supply B, system relays SR1, SR2, a smoothing capacitor C1, and a step-up/down converter12. As DC power supply B, a secondary battery such as a nickel metal hydride or lithium ion battery, or an electricity storage device such as an electric double layer capacitor can be applied. DC voltage Vb output by DC power supply B is sensed by a voltage sensor10. Voltage sensor10outputs the detected DC voltage Vb to control circuit50.

System relay SR1is connected between the positive electrode terminal of DC power supply B and a power supply line6, and system relay SR2is connected between the negative electrode terminal of DC power supply B and a ground line5. System relays SR1, SR2are turned on/off by a signal SE from control circuit50. More specifically, system relays SR1, SR2are turned on by signal SE at H (logic high) level from control circuit50and turned off by signal SE at L (logic low) level from control circuit50. Smoothing capacitor C1is connected between power supply line6and ground line5.

Step-up/down converter12includes a reactor L1and power semiconductor switching elements Q1, Q2. Power semiconductor switching elements Q1and Q2are connected in series between a power supply line7and ground line5. The on/off of power semiconductor switching elements Q1and Q2is controlled by switching control signals S1and S2from control circuit50.

In the embodiment of the present invention, an IGBT (Insulated Gate Bipolar Transistor), a power MOS (Metal Oxide Semiconductor) transistor, a power bipolar transistor, or the like may be used as the power semiconductor switching element (simply referred to as “switching element” hereinafter). Anti-parallel diodes D1, D2are arranged for switching elements Q1, Q2.

Reactor L1is connected between the connection node of switching elements Q1and Q2and power supply line6. In addition, smoothing capacitor C0is connected between power supply line7and ground line5.

Inverter20includes a U-phase arm22, a V-phase arm24and a W-phase arm26provided in parallel between power supply line7and ground line5. Each phase arm is formed of switching elements connected in series between power supply line7and ground line5. For example, U-phase arm22is formed of switching elements Q11, Q12, V-phase arm24is formed of switching elements Q13, Q14, and W-phase arm26is formed of switching elements Q15, Q16. Anti-parallel diodes D11-D16are respectively connected to switching elements Q11-Q16. The on/off of switching elements Q11-Q16is controlled by switching control signals S11-S16from control circuit50.

The intermediate point of each phase arm is connected to each phase end of each phase coil of motor generator MG. In other words, motor generator MG is a three-phase permanent magnet motor and is configured such that one end of each phase coil winding of U, V, W phases is connected in common to a neutral point N. Furthermore, the other end of each phase coil winding is connected to the intermediate point of the switching elements of each phase arm22,24,26.

In a step-up operation (voltage increasing operation), step-up/down converter12supplies DC voltage VH (which corresponds to an input voltage to inverter20) produced by increasing DC voltage Vb supplied from DC power supply B to inverter20. More specifically, in response to switching control signals S1, S2from control circuit50, the duty ratio (on-period ratio) of switching elements Q1, Q2is set, so that the step-up ratio corresponds to the duty ratio.

On the other hand, in a step-down operation (voltage decreasing operation), step-up/down converter12charges DC power supply B by decreasing the DC voltage supplied from inverter20through smoothing capacitor C0. More specifically, in response to switching control signals S1, S2from control circuit50, a period during which only switching element Q1is turned on and a period during which both switching elements Q1, Q2are turned off are alternately provided, so that the step-down ratio corresponds to the duty ratio of the on-period described above.

Smoothing capacitor C0smoothes DC voltage from step-up/down converter12and supplies the smoothed DC voltage to inverter20. A voltage sensor13detects the voltage (namely, an inverter input voltage) between the opposite ends of smoothing capacitor C0and outputs the detected value VH to control circuit50.

When a torque command value of motor generator MG is positive (Tqcom>0), inverter20drives motor generator MG to output a positive torque by converting the DC voltage supplied from smoothing capacitor C0into AC voltage by the switching operation of switching elements Q11-Q16responsive to switching control signals S11-S16from control circuit50. In addition, when a torque command value of motor generator MG is zero (Tqcom=0), inverter20drives motor generator MG to attain a zero torque by converting DC voltage into AC voltage by the switching operation responsive to switching control signals S11-S16. Thus, motor generator MG is driven to generate a zero or positive torque designated by torque command value Tqcom.

In addition, at a time of regenerative braking of electric powered vehicle100, torque command value Tqcom of motor generator MG is set negative (Tqcom<0). In this case, inverter20converts the AC voltage generated by motor generator MG into DC voltage and supplies the converted DC voltage (system voltage) to step-up/down converter12through smoothing capacitor C0, by the switching operation responsive to switching control signals S11-S16.

It is noted that the regenerative braking referred to herein includes braking involving regenerative power generation with a foot brake (brake pedal) operation by the driver of a hybrid vehicle or an electric vehicle, and decelerating (or stopping acceleration) the vehicle while regenerative power generation is performed by lifting off the accelerator pedal during travel without operating a foot brake. In other words, “a regenerative braking operation” of the electric powered vehicle in the present invention is defined to at least include a brake pedal operation by the driver or include both the brake pedal operation and the accelerator pedal off.

A current sensor27detects motor current MCRT flowing in motor generator MG and outputs the detected motor current to control circuit50. It is noted that since the sum of instantaneous values of three phase current iu, iv, iw is zero, current sensor27may be arranged such that the motor current of only two phases (for example, V-phase current iv and W-phase current iw) is detected as shown inFIG. 1.

A rotational angle sensor (resolver)28detects a rotational angle θ of a not-shown rotor of motor generator MG and sends the detected rotational angle θ to control circuit50. In control circuit50, rotational speed Nmt (rotational angular speed ω) of motor generator MG can be calculated based on rotational angle θ.

In addition, motor generator MG is further provided with a temperature sensor29. In general, temperature sensor29is provided to measure the temperature of the coil winding part where insulating coating destruction or the like may be caused by a temperature increase, and then output the measured temperature at least to control device80. In the following, a temperature measured by temperature sensor29is called motor temperature Tmg.

Control device80receives battery information indicating the charge state and the input/output power limitation of DC power supply (battery) B and various vehicle sensor signals (for example, a sensor detection value indicating a vehicle state such as a vehicle speed or a road condition, and a sensor detection value indicating an operational state of a variety of equipment in the vehicle). Typically, a brake pedal70operated by the driver is provided with a depression force sensor75, and depression force sensor75senses a brake depression force BK indicating a brake operation by the driver and transmits the same to control device80.

A signal indicating a gradient GR of a road on which electric powered vehicle100travels is input from a gradient sensor95formed of a G sensor or the like to control device80. Alternatively, control device80may receive altitude data of each point (the current location and the direction of travel) on a map from a navigation system98to sense or predict the gradient of a road. In other words, gradient sensor95and/or navigation system98corresponds to “gradient sensing portion” in the present invention.

Control device80generates torque command value Tqcom of motor generator MG and a regeneration instruction signal RGE based on the vehicle state, the accelerator/brake operation by the driver, and the like. It is noted that control device80generates torque command value Tqcom and regeneration instruction signal RGE in a range in which overcharging or overdischarging of DC power supply B does not occur, based on information concerning DC power supply B such as State of Charge (SOC) which is 100% at a time of full charge, inputtable electric power Pin indicating a charging limit, and outputtable electric power Pout indicating a discharging limit.

The control circuit for electric motor control (MG-ECU)50generates switching control signals S1, S2, S11-S16controlling the operations of step-up/down converter12and inverter20so that motor generator MG outputs a torque according to torque command value Tqcom, based on torque command value Tqcom input from control device80, battery voltage Vb detected by voltage sensor10, system voltage VH detected by voltage sensor13and motor current MCRT from current sensor27, and rotational angle θ from rotational angle sensor28. In other words, control device80corresponds to an upper-level ECU of control circuit (MG-ECU)50. It is noted that although in the example inFIG. 1, control circuit50and control device80are configured with separate ECUs, the functions of both of them may be integrated in a single ECU.

In this manner, in the configuration shown inFIG. 1, step-up/down converter12, inverter20and control circuit50constitute “power conversion unit (PCU)” which performs bidirectional electric power conversion between DC power supply B and motor generator MG so that motor generator MG outputs a torque (positive torque, negative torque or zero torque) according to torque command value Tqcom.

At a time of step-up operation of step-up/down converter12, control circuit50calculates a command value of system voltage VH depending on the operational state of motor generator MG and generates switching controls signals S1, S2, based on this command value and the detected value of system voltage VH by voltage sensor13, so that output voltage VH attains a voltage command value.

Furthermore, when receiving control signal RGE indicating that electric powered vehicle100enters the regenerative braking mode from control device80, control circuit50generates and outputs switching control signals S11-S16to inverter20so that AC voltage generated in motor generator MG by the output of regenerative torque according to torque command value Tqcom is converted into DC voltage. Accordingly, inverter20converts regenerative electric power from motor generator MG into DC voltage, which is then supplied to step-up/down converter12.

In addition, control circuit50generates and outputs switching control signals S1, S2to step-up/down converter12in response to control signal RGE so that the DC voltage supplied from inverter20is decreased to the charging voltage of DC power supply B as necessary. In this manner, regenerative electric power from motor generator MG is used to charge DC power supply B.

In addition, control circuit50generates signal SE for turning on/off system relays SR1, SR2and outputs the same to system relays SR1, SR2, at a time of start/stop of the driving system of electric powered vehicle100.

FIG. 2is a schematic block diagram illustrating regenerative torque setting of motor generator MG at a time of regenerative braking in the electric powered vehicle in accordance with the embodiment of the present invention.

Referring toFIG. 2, a regeneration control portion110for setting a torque command value of regenerative torque at a time of regenerative braking of the hybrid vehicle has a braking cooperative control portion150and a charging control portion200.

Charging control portion200sets requested charging power Pch indicating electric power received by DC power supply B, based on battery information (SOC, Pin, and the like). Braking cooperative control portion150calculates a total barking force (power) required in the entire vehicle based on brake depression force BK of the driver and also controls the shares of the output of this total braking force between hydraulic brake90and motor generator MG.

Here, referring toFIG. 3andFIGS. 4A-4D, an example of braking cooperative control will be described in a case where electric powered vehicle100is a hybrid vehicle.

As shown inFIG. 3, in electric powered vehicle (hybrid vehicle)100, the total braking force power is cooperatively secured by a combination of a mechanical braking force (power) generated by hydraulic brake90and an electrical braking force (power) generated as regenerative braking force (power) by the regenerative torque of motor generator MG. Thus, generation of charging power of DC power supply B recovered from the vehicle energy at a time of deceleration and securing of the braking force are set so as not to degrade the vehicle driving performance.

InFIGS. 4A-4D, an example of cooperative control of hydraulic braking and regenerative braking in each vehicle speed region in the hybrid vehicle is shown. As shown inFIG. 4A-4Din common, basically, a total braking power Pt requested in the entire vehicle increases proportionately with an increase of brake depression force BK.

At the times of high-speed and low/mid-speed with the engine driven as shown inFIGS. 4A and 4B, total braking power Pt is secured by the sum of braking power Peg by engine braking, regenerative braking power Pmg by motor generator MG, and hydraulic braking power Pol generated by the hydraulic brake. Specifically, while braking power Peg by engine braking is secured constantly, regenerative braking power Pmg is increased to a prescribed level with the increasing braking depression force. Then, the shortage of the total braking power by engine braking and regenerative braking is made up for by hydraulic brake90.

Furthermore, at the time of low/mid-speed with the engine stopped as shown inFIG. 4C, regenerative braking power Pmg is set similarly as inFIG. 4B, and in addition, the shortage of the total braking power by regenerative braking is made up for by hydraulic brake90. In addition, at the time of extremely low-speed when the vehicle driving force is generated only by motor generator MG as shown inFIG. 4D, basically, the total braking power is secured only by hydraulic brake90.

InFIGS. 4A-4D, when the brake depression force=0, the regenerative braking power Pmg=0. However, even when brake depression force=0, the vehicle may be decelerated or be stopped accelerating by generating a prescribed amount of regenerative braking power in an engine braking manner with the accelerator pedal off.

Referring toFIG. 2again, regeneration control portion110sets regenerative torque command value Tqcom (generally, a negative value) so that regenerative power generation (regenerative braking) by motor generator MG at a time of regenerative braking is properly controlled. In particular, braking cooperative control portion150limits the regenerative electric power by regenerative braking within a range of requested charging power Pch set by charging control portion200or lower and determines the share of braking power (regenerative braking power) by motor generator MG. Regenerative control portion110sets torque command value Tqcom at a time of regenerative braking according to regenerative torque required for the output of the regenerative braking power. Torque command value Tqcom is transmitted to control circuit (MG-ECU)50, and MG-ECU50controls the switching operation of converter12and inverter20so that motor generator MG generates regenerative torque according to torque command value Tqcom, in accordance with the control configuration illustrated inFIG. 1.

In addition, regeneration control portion110instructs a hydraulic control portion120of a hydraulic braking power requested for hydraulic brake90, which corresponds to the difference between the total braking power and the regenerative braking power, so that the total braking power is secured in electric powered vehicle100as a whole. Hydraulic control portion120controls hydraulic pressure supply to each hydraulic brake90so that hydraulic brake90generates the requested hydraulic braking power. Then, each hydraulic brake90outputs a braking force according to the hydraulic pressure set by hydraulic control portion120. It is noted that the braking force of hydraulic brake90provided for each wheel can be controlled independently as appropriate so that the comfortable vehicle traveling performance can be maintained at a time of deceleration.

FIG. 5is a block diagram showing the configuration of the regeneration control portion in accordance with the embodiment of the present invention in more detail. Each block shown inFIG. 5is realized by software or hardware by control device80.

Referring toFIG. 5, regeneration control portion110includes braking cooperative control portion150, charging control portion200, a downhill determination portion250, and a regenerative torque setting portion260.

Downhill determination portion250determines whether electric powered vehicle100is on downhill or not based on gradient GR of a road sensed by gradient sensor95and/or map information from navigation system98. A downhill travel flag Fds indicating the determination result by downhill determination portion250is continuously turned on during downhill travel of electric powered vehicle100and is turned off in other cases.

Charging control portion200sets requested charging power Pch according to charging power that can be received by DC current supply B, according to battery information (SOC, Pin). It is noted that if DC power supply B is fully charged or in a high temperature state and charging is thus prohibited, Pch=0 is set.

Braking cooperative control portion150includes a required braking power calculation portion160and a braking power distribution portion170. Required braking power calculation portion160calculates total braking power Pt required in the entire electric powered vehicle100, based on outputs of various sensors indicating braking depression force BK and a vehicle speed and the like. Braking power distribution portion170sets regenerative braking power Pmg within a range of requested charging power Pch set by charging control portion200or lower, for example, in accordance with the cooperative control method according to a vehicle speed as illustrated inFIGS. 4A-4D, and also sets hydraulic braking power Pol in accordance with the remaining braking power (Pt−Pmg−Peg). As shown inFIG. 2, hydraulic pressure supply to each hydraulic brake90is controlled by hydraulic control portion120according to hydraulic braking power Pol, as shown inFIG. 2.

Here, braking power distribution portion170limits the regenerative braking power during the on of downhill travel flag Fds in comparison with during the off of downhill travel flag Fds, including at a time of flat-road travel. In other words, with the same total braking power Pt and vehicle condition (vehicle speed and the like) and so on, regenerative braking power Pmg# set during the on of downhill travel flag Fds is set at a value lower than regenerative braking power Pmg set during the off of downhill travel flag Fds (specifically, Pmg#<Pmg).

It is noted that regenerative braking power Pmg at a time of downhill travel can also be limited by charging control portion200by limiting the requested charging power during the on of downhill travel flag Fds in comparison with at a time of flat-road travel. In other words, charging control portion200is configured such that requested charging power Pch# set at a time of downhill travel is set at a value lower than requested charging power Pch in other cases including at a time of flat-road travel (specifically, Pch#<Pch), for the similar state (the same SOC or Pin) of DC power supply B, so that Pmg#=Pch# is set by braking power distribution portion170. Therefore, regenerative braking power Pmg# set during the on of downhill travel flag Fds can be limited to a value lower than regenerative braking power Pmg set during the off of downhill travel flag Fds (Pmg#<Pmg).

Regenerative torque setting portion260sets torque command value Tqcom of motor generator MG according to regenerative braking power Pmg or Pmg# set by braking power distribution portion170. Accordingly, the regenerative torque of motor generator MG is set so that the regenerative braking force corresponding to regenerative braking power Pmg or Pmg# is obtained. In other words, while the regenerative torque is set according to regenerative braking power Pmg# during the on of downhill travel flag Fds, regenerative torque Tqcom is set according to regenerative braking power Pmg during the off of downhill travel flag Fds.

It is noted that heat generation of motor generator MG at a time of downhill travel can be suppressed reliably by continuously prohibiting generation of regenerative torque at a time of downhill travel, namely, by setting regenerative braking power Pmg#=0.

Alternatively, as shown inFIG. 6-FIG.8, a limitation degree, of regenerative braking power (a limitation value of Pmg−Pmg#, or a limitation rate indicated by (Pmg−Pmg#)/Pmg), that is, the limitation degree of regenerative torque at a time of downhill travel, may be set variably based on the conditions during downhill travel.

FIG. 6shows a control example in which the limitation degree of regenerative torque is increased with the increase of motor temperature Tmg. In this case, regeneration is prohibited, that is, limited as Tqcom=0, by maximizing the limitation degree at least in motor temperature Tmg=Tlmt (temperature limit), preferably, at a temperature range lower than temperature limit Tlmt.

Furthermore, in a condition in which the regenerative braking power is highly requested and without limiting regenerative torque, a large regenerative torque is generated causing a temperature increase of motor generator MG, a temperature increase of motor generator MG can be suppressed by increasing the limitation degree of regenerative torque with the increasing brake depression force BK as shown inFIG. 7or with the increasing road gradient (downhill) as shown inFIG. 8.

FIG. 9is a flowchart illustrating the procedure of regenerative torque setting of motor generator MG in the electric powered vehicle in accordance with the embodiment of the present invention. The control process procedure shown inFIG. 9is realized, for example, by executing a program stored beforehand in control device (ECU)80at prescribed intervals.

Referring toFIG. 9, control device80calculates total braking power Pt required in the entire electric powered vehicle100based on the brake depression force, the vehicle conditions and the like, in step S100. Specifically, the processing in step S100corresponds to the function of required braking power calculation portion160inFIG. 5.

Furthermore, control device80determines whether electric powered vehicle100is during downhill travel or not based on the output of gradient sensor95and/or map information from navigation system98, in step S120. Specifically, the processing in step S120corresponds to the function of downhill determination portion250shown inFIG. 5.

If not during downhill travel (if No in S120), control device80sets requested charging power Pch at normal times according to battery information or the like, in step S140, and sets regenerative braking power Pmg that is to be shared by motor generator MG, of total braking power Pt, according to a vehicle speed, requested charging power Pch, and the like, in step S160. Here, regenerative braking power Pmg is set within a range of Pmg<Pch. Then, control device80sets torque command value Tqcom (namely, the regenerative torque command) according to regenerative braking power Pmg set in step S160, in step S180.

On the other hand, during downhill travel (if YES in step S120), control device80sets requested charging power Pch# at the time of downhill limitation according to battery information and the like, in step S200. In other words, for the same battery information, requested charging power Pch# set in step S200is lower than requested charging power Pch set in step S140(Pch#<Pch).

In addition, control device80sets regenerative braking power Pmg# at the time of downhill limitation, according to a vehicle speed, requested charging power, and the like, in step S220. In other words, as for the regenerative braking power set under the same condition, regenerative braking power Pmg# set in step S220is lower than regenerative braking power Pmg set in step S160(Pmg#<Pmg).

Here, as illustrated inFIG. 6-FIG.8, the limitation degree (limitation amount or limitation rate) of requested charging power and regenerative braking power is variably set according to the motor temperature, the downhill gradient, and the brake depression force. Alternatively, Pch#=0 may be set in order to avoid an increase of the motor temperature reliably by prohibiting generation of regenerative torque.

In addition, control device80sets torque command value Tqcom (regenerative torque command) according to regenerative braking power Pmg# set in step S220, in step S240.

Specifically, the processing in steps S140and S200corresponds to the function of charging control portion200shown inFIG. 5, the processing in step S160and step S220corresponds to the function of braking power distribution portion170shown inFIG. 5, and the processing in steps S180and S240corresponds to the function of regenerative torque setting portion260shown inFIG. 5. Here, even if the limitation of requested charging power in step S200(Pch# is set in place of Pch) is not executed, the regenerative braking power at a time of downhill travel may be limited (Pmg# is set in place of Pmg) in step S200.

FIG. 10is a waveform diagram showing an example of torque command value setting in the electric powered vehicle in accordance with the embodiment of the present invention.

Referring toFIG. 10, in accordance with the travel pattern RPT in which flat-road travel—uphill travel—flat-road travel—downhill travel—flat-road travel are successively executed, torque command value Tqcom of motor generator MG is timely set. In the example inFIG. 10, for simplification of the explanation, the torque command value Tqcom=0 at a time of flat-road travel.

Torque command value Tqcom increases in the positive direction at a time of uphill travel to generate a vehicle driving force. Temperature Tmg of motor generator MG rises accordingly. Then, during downhill travel, according to the normal setting in which regenerative torque is set according to a brake operation, similarly as in flat-road travel, without provision of any particular limitation, torque command value Tqcom increases in the negative direction so that regenerative torque is output for generating regenerative braking force. Because of the following regenerative torque generation, motor temperature Tmg rises. At the end of downhill travel, torque command value Tqcom=0 is set again.

It is assumed that a toque output (positive direction) is additionally requested for uphill travel after downhill travel. In such a situation, due to a motor temperature Tmg increase at a time of downhill travel, motor temperature Tmg reaches the region in which torque limitation is required, so that power running torque cannot be generated enough, which may make it difficult to secure the vehicle driving force by motor generator MG. In such a circumstance, in a hybrid vehicle, engine drive in a low-efficiency region becomes necessary and fuel efficiency becomes poor. In an electric vehicle, it becomes difficult to secure a vehicle driving force.

Then, according to the regenerative torque setting in accordance with the embodiment of the present invention, torque command value Tqcom# during downhill travel is continuously limited so that the absolute value of the regenerative torque is smaller than at normal times, for a brake operation by the driver. Therefore, the increase of motor temperature Tmg# is gentler. As a result, a motor temperature increase at the end of downhill travel can be prevented, and in the following travel, such a circumstance can be prevented in that the torque limitation of motor generator MG makes it difficult to secure the vehicle driving force by motor generator MG.

In this way, in the electric powered vehicle in accordance with the embodiment of the present invention, an increase of motor temperature at a time of downhill travel can be suppressed by limiting or prohibiting (Tqcom#=0) an output of regenerative torque at a time of downhill travel. As a result, the output torque of motor generator MG in flat-road travel or uphill travel after the end of downhill travel is secured, thereby achieving the full motive power performance.

In addition, as for the limitation of regenerative torque at a time of downhill travel, the limitation degree is variably set according to the motor temperature, the downhill gradient, or the brake operation, so that the regenerative power generation at a time of downhill travel can be limited at an appropriate degree. As a result, while energy is recovered by regenerative power generation within a possible extent, a temperature increase of motor generator MG at a time of downhill travel can be prevented.

In particular, the regenerative power generation is designed to be focused on deceleration energy recovery at a time of flat-road travel, by suppressing or stopping regenerative power generation at a time of downhill travel in which the requested braking force by the driver's brake operation tends to increase and regenerative electric power is high, that is, a motor temperature increase is significant. Then, the specifications for suppressing a temperature increase of motor generator MG are relaxed. As a result, the size reduction can be achieved because of the simplified cooling structure of motor generator MG. Moreover, shifting to low gear in the entire vehicle for securing the traveling performance at a time of temperature increase can be avoided, so that fuel efficiency can be improved at a time of high-speed travel by shifting to high gear. In this manner, in the electric powered vehicle in accordance with the embodiment of the present invention, the specification design related to motor generator MG can be made efficient.

It is noted that the application of the prevent invention is not limited only to hybrid vehicles and electric vehicles, and the present invention is applicable in common to an electric powered vehicle equipped with a motor generator configured to generate a vehicle driving force by generation of power running torque and to perform regenerative power generation by generation of regenerative torque.