Electrically powered vehicle

A MG-ECU includes, as a regeneration limiting value, a limited value set according to a state of a battery, and an unlimited value enabling generation of braking force greater than the limited value. In a state in which regenerative braking is being limited, the MG-ECU causes frictional braking force to be generated based on a difference between the unlimited value and the drive force demand of a driver. In cases in which the frictional braking force is also limited in a state of the regenerative braking, the MG-ECU switches the regeneration limiting value from the limited value to the unlimited value, and requests a motor-generator to generate regenerative braking based on the limited value.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2015-155293, filed Aug. 5, 2015, entitled “Electrically Powered Vehicle.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present embodiment relates to an electrically powered vehicle provided with a traction motor.

2. Description of the Related Art

Japanese Unexamined Patent Application Publication No. 10-271605 describes technology for switching from regenerative braking force to frictional braking force in an electric vehicle when a battery that stores electricity, such as regenerated electrical power, has reached full charge.

For example, in a vehicle such as an electric vehicle, switching is made from regenerative braking force to frictional braking force when a battery for storing electricity, such as regenerated electrical power, reaches full charge, such as in the technology described in Japanese Unexamined Patent Application Publication No. 10-271605.

In particular, in order to realize braking like that of engine braking in an ordinary gasoline car or diesel car, braking force equivalent to engine braking and arising from regenerative braking force can also be realized in an electric vehicle. In such cases, when the amount of charging of the battery approaches a reference value acting as the limit for charging, conceivably a unit for implementing braking force equivalent to engine braking might make a smooth transition from regenerative braking force to frictional braking force by gradually reducing the regenerative braking force, and gradually increasing the frictional braking force. Generating frictional braking force is also conceivable in cases in which, relative to the braking force demanded by a driver, there is insufficient battery charge, or insufficient braking force due to regenerative braking force being limited in order to protect the battery.

The technology of Japanese Unexamined Patent Application Publication No. 10-271605 is technology to switch from regenerative braking to frictional braking in cases in which regeneration is limited due to a battery reaching full charge, or the like. Hitherto, when regeneration is limited, deficiencies in drive force demanded by a driver (drive force demand) have been supplemented by frictional braking force; however, fractional braking force cannot foe generated in cases in which there has been a breakdown in frictional braking force, or cases in which a rise in the temperature of brake components (brake pads or rotors) has occurred.

However, there is no mention in Japanese Unexamined Patent Application Publication No. 10-271605 regarding how braking force will be generated in cases in which frictional braking force cannot be generated under regeneration limiting.

SUMMARY

The present application describes generation of braking force in cases in which frictional braking force cannot be generated under regeneration limiting.

A first aspect of technology disclosed herein is an electrically powered vehicle including a regenerative braking force generator that generates regenerative braking force in a vehicle, a battery that stores electrical power regenerated with the regenerative braking force, a frictional braking force generator that generates frictional braking force in a vehicle, and a controller that controls generation of the regenerative braking force and the frictional braking force, thereby controlling a total breaking force applied to the vehicle according to a drive force (deceleration and/or acceleration) demand from a driver. The controller includes as a limit threshold value of the regenerative braking force, a first regeneration limit threshold value set according to a state of the battery, and a second regeneration limit threshold value enabling generation of braking force greater than the first regeneration limit. The controller, in a state in which regenerative braking is being limited, causes frictional braking force to be generated based on a difference between the second regeneration limit threshold value and the drive force demand of a driver, in cases in which the frictional braking force is also limited in a state of the regenerative braking, switches the limit threshold value from the second regeneration limit threshold value to the first regeneration limit threshold value, and requests the regenerative braking force generator to generate regenerative braking based on the first regeneration limit threshold value.

The first aspect of technology disclosed herein enables braking force to be generated under regeneration limiting, even in cases in which frictional braking is limited.

A second aspect of technology disclosed herein may be the electrically powered vehicle of the first aspect, wherein the controller switches from the first regeneration limit threshold value to the second regeneration limit threshold value when the driver has actuated acceleration.

The application according to the second aspect enables surprise, arising from braking force from the frictional braking component suddenly disappearing while frictional braking is being performed, to be prevented from occurring, due to frictional braking being switched in a not-in-use state.

A third aspect of technology disclosed herein may be the electrically powered vehicle of the first aspect or the second aspect, wherein the first regeneration limit threshold value is based on regenerative braking force the regenerative braking force generator is capable of outputting when the battery is in a regenerative braking state.

The application according to the third aspect enables limited regenerative braking force to be generated, even in a state in which frictional braking is being limited.

A fourth aspect of technology disclosed herein may be the electrically powered vehicle of any one of the first aspect to the third aspect, wherein the first regeneration limit threshold value is based on regenerative braking force the regenerative braking force generator is capable of outputting when the battery is in a non-regenerative braking state.

The application according to the fourth aspect enables all the demanded braking force to be output in a state in which frictional braking is not being limited.

A fifth aspect of technology disclosed herein may be the electrically powered vehicle of any one of the first aspect to the fourth aspect, wherein the controller smoothes and outputs regenerative braking generated based on the first regeneration limit threshold value.

The application according to the fifth aspect enables the elimination of abrupt change in the braking force arising when the braking force demand is limited to the first regeneration limit threshold value. This thereby enables the elimination of a feeling of unease being imparted to the driver, and enables an improvement in feel.

A sixth aspect of technology disclosed herein may be the electrically powered vehicle of any one of the first aspect to the fifth aspect, wherein the controller gradually reduces the frictional braking force when limiting the frictional braking.

The application according to the sixth aspect enables a sharp reduction in braking force to be prevented.

The present application describes being able to generate braking force in cases in which frictional braking force cannot be generated under regeneration limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed explanation follows regarding a mode (an “embodiment”) for implementing the present application, with reference to the drawings as appropriate.

Overall Configuration

FIG. 1is a system diagram of relevant portions of a vehicle according to the present embodiment.

This vehicle100is, for example, an electric vehicle, and includes a left and right pair of front wheels2aR,2aL provided at the front side of the vehicle100, and a left and right pair of rear wheels2bR,2bL provided at the rear side of the vehicle100. A motor-generator (MG)3is coupled through a torque transmission mechanism to a front axle4coupling the left and right front wheels2aR,2aL together. The vehicle100may be configured with four wheel drive, rear wheel drive, or as a hybrid vehicle provided with the motor-generator3. The operating mechanism provided to the front axle4is omitted from illustration.

The motor-generator3doubles as both an electric motor for driving the vehicle100, and as an electric generator used in regeneration. A battery5, configured by a rechargeable cell, supplies electrical power to the motor-generator3by using an inverter6as the power source for the motor-generator3. Deceleration energy is converted by the motor-generator3into electrical power by the motor-generator3when the vehicle100decelerates, and the battery5stores this regenerated electrical power. Regenerative braking force is generated by the motor-generator3during regeneration. Namely, a regenerative braking force generator is implemented by the motor-generator3, etc.

A charged amount detection sensor8(voltage sensor or current sensor) is provided in the battery5for detecting the amount of charging (state of charge (SOC)) of the battery5. The battery5is controlled by a battery ECU; however, the battery ECU is omitted from illustration in the present embodiment.

A management-electronic control unit (MG-ECU7) is provided with a microcomputer, and is a device to centrally control each section (described in detail later).

An electric servo brake-electronic control unit (ESB-ECU)13controls a non-illustrated electric motor in a frictional braking device10by sending control signals through signal lines according to the frictional braking force demand that has been output from the MG-ECU7(described in detail later).

The frictional braking device10serves as a frictional braking force generator. Namely, the frictional braking device10is a device that is connected to each of the wheel cylinders of disc brake mechanisms30ato30dof the respective wheels2aR,2aL,2bR,2bL, for hydraulically driving the wheel cylinders and for generating frictional braking force by pressing brake pads against brake rotors.

Various sorts of device may be applied as the frictional braking device10, as long as it is a braking device for generating frictional braking force. For example, what is referred to as a by-wire braking system may be applied therefor. A by-wire braking system is a device that is provided with an electric motor and, under control of the electric motor, drives the disc brake mechanisms30ato30dof the respective wheels2aR,2aL,2bR,2bL by actuation of a hydraulic mechanism, and imparts frictional braking force to the respective wheels2aR,2aL,2bR,2bL.

Control System Configuration

FIG. 2is a block diagram illustrating a control system configuration of a vehicle. A brake pedal stroke sensor21that detects the operation amount of the brake pedal, an accelerator opening sensor22that detects the accelerator opening, and the charged amount detection sensor8are connected through a specific interface to the MG-ECU7by signal lines. The motor-generator3, the inverter6, and the battery5are connected through a specific interface to the MG-ECU7by signal lines. A detection signal of a wheel speed sensor11(wheel speed signal) is input to the MG-ECU7. The wheel speed sensor11is a sensor that detects the rotation speed of a wheel. The wheel speed signal is a pulse wave with a specific number of pulses generated for each revolution of the wheel. The MG-ECU7computes the vehicle speed of the vehicle100based on the wheel speed signal input from the wheel speed sensor11. Thus, the wheel speed sensor11serves as a vehicle speed sensor to detect vehicle speed.

A pad temperature sensor12that measures the temperature of the brake pads provided to the respective wheels2aR,2aL,2bR,2bL is connected through a specific interface to the ESB-ECU13by signal lines. The MG-ECU7and the frictional braking device10are also connected to the ESB-ECU13by signal lines.

Detailed explanations regarding the MG-ECU7and the ESB-ECU13are given below.

Timing Chart

FIG. 3AtoFIG. 3Dare timing charts for operations in the MG-ECU and the ESB-ECU according to the present embodiment; operations in the ESB-ECU13are illustrated atFIG. 3AandFIG. 3D, and operations in the MG-ECU7are illustrated atFIG. 3BandFIG. 3C.

Reference numeral201inFIG. 3Aindicates a change with time in temperature of a brake pad (referred to below as pad temperature). Reference numeral202indicates a flag to suspend frictional braking control, which is sent by the ESB-ECU13to the MG-ECU7and adopts either an ON state or an OFF state.

The reference numeral211inFIG. 3Bindicates ON or OFF of frictional braking control in the MG-ECU7.

The reference numeral221inFIG. 3Cis the demanded drive force that has been subjected to smoothing processing (smoothed), reference numeral222indicates a limited value of a regeneration limiting value, and reference numeral223indicates an unlimited value of the regeneration limiting value.

In the present embodiment, drive force includes braking force. Namely, drive force that is drive force in the direction of travel (referred to as the + direction as appropriate) of the vehicle100is “drive force”, and drive force in the opposite direction to the direction of travel (referred to as the—direction as appropriate) is “braking force”. Thus, the drive force demand221includes braking force demand. When it is clearly braking force that is being referred to, then it is called “braking force”.

The limited value (the first regeneration limit threshold value)222of the regeneration limiting value is a limit threshold value for the regenerative braking force. The limited value222is set according to the state of the battery5, and is a limited value used when motor torque in the motor-generator3is limited and storage of power in the battery5is limited. Namely, the limited value222is the regenerative braking force the motor-generator3is capable of outputting when regeneration is being limited. Adopting such a configuration enables the regenerative braking force that is being subjected to limiting to still be generated in a state in which frictional braking is being limited.

The limited value222may be a value of regeneration capability even in a fully charged state, albeit though this might have a somewhat detrimental effect on the life of the battery5.

The unlimited value (second regeneration limit threshold value)223of the regeneration limiting value is a limited value the battery5is capable of outputting according to specification, without motor torque in the motor-generator3being limited or storage of power in the battery5being limited. Namely, the unlimited value223is the regenerative braking force the motor-generator3is capable of outputting when regeneration is not being limited (during unlimited regeneration), and enables generation of braking force greater than the limited value222. This thereby enables all the demanded braking force to be output in a state in which frictional braking is not being limited.

The reference numeral231inFIG. 3Dindicates the frictional braking force the frictional braking device10outputs.

Whether or not the battery5is in a regeneration limited state is determined by the SOC detected by the charged amount detection sensor8(seeFIG. 1).

In this interval, the driver is OFF the accelerator pedal and there is a regenerative braking state (equivalent to an engine braking state in a gasoline engine); however, since regeneration limiting is in place, any deficiency in braking force is supplemented by the frictional braking force231.

During this interval, the regeneration limiting value is set to the unlimited value223. Thus, since braking force up to the unlimited value223is demanded and regeneration limiting is in place, the MG-ECU7demands braking force up to the unlimited value223as braking force by regeneration from the motor-generator3. The MG-ECU7also demands a braking force of a difference F1between the drive force demand221and the unlimited value223as frictional braking force. The ESB-ECU13outputs the frictional braking force231demanded by the MG-ECU7.

At time t1, if the pad temperature201exceeds a first threshold value Th1for suspending frictional braking control (limiting frictional braking), the ESB-ECU13raises the frictional braking control suspend flag202(switches the suspend flag202from an OFF state to an ON state).

On receipt of the suspend flag201in an ON state, the MG-ECU7demands braking force up to the unlimited value223as illustrated inFIG. 3C; however, as illustrated inFIG. 3D, the ESB-ECU13gradually releases hydraulic pressure for each of the sections in the frictional braking device10so as to gradually reduce the frictional braking force231. This thereby enables a sharp reduction in braking force to be prevented.

At time t2, the frictional braking force231inFIG. 3Dbecomes 0; however, the MG-ECU7leaves the frictional braking state211as the ON state, and leaves the regeneration limiting value at the unlimited value223.

At time t3, the driver depresses the accelerator pedal (actuates acceleration) and the drive force demand224moves to the + side (the direction of travel), the MG-ECU7places the frictional braking state211in the OFF state, and switches the regeneration limiting value to the limited value222. Depression of the accelerator pedal is determined by the MG-ECU7being input with an input from the accelerator opening sensor22(seeFIG. 1) or the like. From this point in time onwards, the braking force demandable by the MG-ECU7is a value up to the limited value222. This thereby enables braking force to be generated even in cases in which frictional braking has been limited while under regeneration limiting.

Thus, the MG-ECU7does not immediately switch the regeneration limiting value although the frictional braking control has adopted an OFF state. The MG-ECU7switches the initial frictional braking state211to OFF and switches the regeneration limiting value only when the driver has depressed the accelerator pedal and the drive force demand224has moved to the + side (the direction of travel). Thus, by switching the regeneration limiting value in a state in which braking force is not being demanded (a state in which the accelerator pedal has been depressed, and the drive force demand224has moved to the + side (the direction of travel)), surprise, arising from braking force from the frictional braking component suddenly disappearing while frictional braking is being performed, can be prevented due to frictional braking being switched when in a not-in-use state.

At time t4, a regenerative braking state (equivalent to engine braking in a gasoline engine) is adopted due to the driver again lifting OFF the accelerator pedal. When this occurs, the MG-ECU7would normally demand the braking force as indicated by the dash line225; however, due to the regeneration limiting value being limited to the limited value222as described above, as illustrated inFIG. 3C, the MG-ECU7performs a transient processing (smoothing) on the drive force demand input by the driver to adjust the bottom part of the drive force demand which goes outside the limited threshold value222(the dash line225) so as to output the adjusted drive force demand221(the solid line above the dash line225) which meets the limited threshold value222, such as by cutting the bottom of the drive force demand225and making the drive force to smoothly and continuously transit above the limited threshold value222. Doing so enables the elimination of abrupt change in the braking force arising when the braking force demand is limited to the first regeneration limit threshold value. This thereby enables the elimination of a feeling of unease being imparted to the driver, and enables an improvement in feel.

Note that at time t5, as illustrated inFIG. 3A, the pad temperature201has fallen as far as a temperature Th2where frictional braking control is possible, and the ESB-ECU13switches the suspend flag of the frictional braking control to OFF. However, the MG-ECU7keeps the frictional braking state ON as illustrated inFIG. 3B, and also leaves the regeneration limiting value at the limited value222.

At time t6, when the driver depresses the accelerator pedal and the drive force demand224has moved to the + side (the direction of travel), as illustrated inFIG. 3B, the MG-ECU7switches the frictional braking state211to the ON state, and, as illustrated inFIG. 3C, switches the regeneration limiting value to the unlimited value223. From then onwards, the braking force demandable by the MG-ECU7is braking force up to the unlimited value223, enabling braking force to be supplemented by the frictional braking force231.

Thus, even in a state in which the frictional braking control is ON, the MG-ECU7does not immediately switch the regeneration limiting value. Thus, the MG-ECU7switches the frictional braking state211to the ON state, and switches the regeneration limiting value only when the driver has depressed the accelerator pedal, and the drive force demand224has moved to the + side (direction of travel). Thereby, by switching the regeneration limiting value in a state other than a state in which regenerative braking force is demanded (in a state when the accelerator pedal has been depressed and the drive force demand224has moved to the + side (direction of travel), the surprise, arising from braking force from the frictional braking component suddenly disappearing while frictional braking is being performed, can be prevented due to frictional braking being switched when in a not-in-use state.

Time t7Onwards

At time t7, the regenerative braking state (equivalent to engine braking in a gasoline engine) is adopted due to the driver again lifting OFF the accelerator pedal. As illustrated inFIG. 3C, the drive force demand221is the limited value222or greater up till the time t8, and so supplementation by the frictional braking force231is not required.

When the drive force demand221falls below the limited value222at the time t8, the ESB-ECU13outputs the frictional braking force231corresponding to the difference between the drive force demand221and the limited value222.

COMPARATIVE EXAMPLE

FIG. 4is a graph illustrating change with time in the drive force demand and the regeneration limiting value in a comparative example.

FIG. 4corresponds toFIG. 3C, and, other than at time t11, is similar toFIG. 3C, so explanation thereof will be omitted.

The reference numerals222to224are similar to those ofFIG. 3C, and so explanation thereof will be omitted.

As illustrated inFIG. 4, drive force demand251in the comparative example changes abruptly at time t4and time t11, as illustrated by the intermittent line circles. This results in a feeling of unease being imparted to the driver.

In the present embodiment, as illustrated in the interval from time t4to time t6inFIG. 3C, due to smoothing processing being performed on the drive force demand221even in the interval of output up to limited value222, abrupt change in the drive force demand221is eliminated, enabling elimination of a feeling of unease from being imparted to the driver.

Configuration of MG-ECU7and ESB-ECU13

FIG. 5is a block diagram illustrating a configuration of the MG-ECU and the ESB-ECU. The processing performed by each section illustrated inFIG. 5will be explained later.

Configuration of MG-ECU7

The MG-ECU7includes a switching section301, a first limit processing section302, a smoothing processing section303, a second limit processing section304, and a frictional braking controller305.

The switching section301switches the regeneration limiting value to the limited value222(FIG. 3C) or to the unlimited value223(FIG. 3C) based on the suspend flag and the drive force demand sent from the ESB-ECU13.

The first limit processing section302performs limit processing on the drive force demand at the current regeneration limiting value switched to by the switching section301.

The smoothing processing section303performs smoothing processing on the output result of the first limit processing section302(the drive force demand after limiting) so as to achieve a smooth change in the drive force demand with time.

The second limit processing section304limits the output result of the smoothing processing section303(the drive force demand after smoothing processing) to the limited value222. If the current regeneration limiting value (the regeneration limiting value after switching) is the limited value222, then the output of the second limit processing section304is the same as the output of the smoothing processing section303. If the current regeneration limiting value is the unlimited value223, then the output of the second limit processing section304is the drive force demand limited to the unlimited value223. The second limit processing section304outputs its own output result to the motor-generator3, as a regenerative braking force demand, and also to the frictional braking controller305.

The frictional braking controller305computes the difference between the output of the smoothing processing section303, and the output of the second limit processing section304, and outputs the computed difference value as a frictional braking force demand to the ESB-ECU13. When this is performed, if the current regeneration limiting value (regeneration limiting value after switching) is the limited value222, then, as described above, the output of the second limit processing section304and the output of the smoothing processing section303are the same value as each other, and so the frictional braking controller305outputs 0 as the frictional braking force demand. Namely, the MG-ECU7does not generate frictional braking force if the current regeneration limiting value is the limited value222. If the current regeneration limiting value is the unlimited value223, then the difference value between the output of the smoothing processing section303and the output of the limited value222is output as the frictional braking force demand.

Configuration of ESB-ECU13

The ESB-ECU13includes an operation determination section311and a hydraulic pressure controller312.

Based on the pad temperature input from the pad temperature sensor12, the operation determination section311outputs a frictional braking control suspend flag, as ON or OFF, to the MG-ECU7and the hydraulic pressure controller312.

The hydraulic pressure controller312controls the hydraulic pressure in each of the sections of the frictional braking device10and generates frictional braking force according to the frictional braking force demand output by the frictional braking controller305of the MG-ECU7. The hydraulic pressure controller312performs processing to gradually release the hydraulic pressure of the frictional braking device10according to the ON or OFF state of the suspend flag output by the operation determination section311.

Operation of Operation Determination Section311of ESB-ECU13

FIG. 6is a flowchart illustrating an operational sequence in an operation determination section of an ESB-ECU. Reference is also made toFIG. 3AandFIG. 5, as appropriate. InFIG. 6toFIG. 8, whether or not the battery5is in a regeneration limited state is determined using the SOC detected based on the charged amount detection sensor8(seeFIG. 1).

First, the operation determination section311receives input of the pad temperature201from the pad temperature sensor12(FIG. 1) (S101).

The operation determination section311determines whether or not the pad temperature is a threshold value Th1to suspend frictional braking control, or greater (S102).

In cases in which the result of102is that the pad temperature is the threshold value Th1or greater (S102, Yes), the operation determination section311sends the frictional braking control suspend flag as ON to the MG-ECU7(S103). The processing of step S103corresponds to the time t1inFIG. 3A. Note that the suspend flag is OFF in the initial state (when the ignition switch is switched ON).

In cases in which the result of102is that the pad temperature is less than the threshold value Th1(S102, No), the operation determination section311determines whether or not the pad temperature is a threshold value Th2to restart frictional braking control, or lower (S111).

In cases in which the result of S111is that the pad temperature is less than the threshold value Th2(S111, Yes), the operation determination section311sends the suspend flag as OFF to the MG-ECU7and the hydraulic pressure controller312(S112). The processing of step S103corresponds to the time t5ofFIG. 3A.

In cases in which the result of step S111is that the pad temperature is greater than the threshold value Th2(S111, No), the operation determination section311maintains the current suspend flag state (S121).

Operation of MG-ECU7

FIG. 7is a flowchart illustrating an operational sequence in the MG-ECU according to the present embodiment. Reference is also made toFIGS. 3A to 3DandFIG. 5, as appropriate.

First, the switching section301determines whether or not the state of the suspend flag sent from the operation determination section311of the ESB-ECU13is the same as the frictional braking state (S201). For example, when, as in the interval from time t1to time t3inFIG. 3AandFIG. 3Bthe suspend flag202and the frictional braking state211are both ON, then the switching section301determines that the suspend flag state is the same as the frictional braking state. When, as in the interval from time t5to time t6, the suspend flag202and the frictional braking state211are both OFF, then the switching section301determines that the suspend flag state is the same as the frictional braking state. When, as in the intervals from time t0to t1, from time t3to t5, and from time t6onwardsFIG. 3AandFIG. 3B, one out of the suspend flag202or the frictional braking state211is ON, and the other is OFF, then the switching section301determines that the suspend flag state is not the same as the frictional braking state.

In cases in which the result of step S201is that the suspend flag state is not the same state as the frictional braking state (S201, No), the MG-ECU7proceeds to the processing of step S221. Namely, the MG-ECU7employs the current regeneration limiting value to compute and output the regenerative braking force and the frictional braking force.

In cases in which the result of step S201is that the suspend flag state is the same state as the frictional braking state (S201, Yes), the switching section301determines whether or not the drive force demand on the drive (Dr) side has moved to the + side (S202). “Drive force demand on the drive (Dr) side moving to the + side” is what happens when the driver depresses the accelerator pedal (actuates acceleration).

In cases in which the result of step S202is that the drive force demand on the drive side has moved to the + side (S202, Yes), the switching section301switches the frictional braking state (S211), and switches the regeneration limiting value (S212). This processing corresponds to time t3and to time t6inFIG. 3BandFIG. 3C.

After step S212, the MG-ECU7proceeds to the processing of step S221.

In cases in which the result, of step S202is that the drive force demand on the drive side has not moved to the + side (S202, No), then the MG-ECU7proceeds to the processing of step S221.

At step S221, the first limit processing section302performs first limit processing of processing to limit the drive force demand using the current regeneration limiting value switched to by the switching section301.

Next, the smoothing processing section303performs smoothing processing (S222) on the output result of the first limit processing section302such that the drive force demand changes smoothly with time.

Then, the second limit processing section304performs the second limit processing to limit the output result of the smoothing processing section303to the limited value222(S223). The second limit processing section304outputs its own output result to the motor-generator3, as a regenerative braking force demand, and also to the frictional braking controller305.

The frictional braking controller305then computes a difference between the output of the smoothing processing section303and the output of the second limit processing section304, and outputs the computed difference value as the frictional braking force demand to the ESB-ECU13(S224). After step S224, the MG-ECU7returns to the processing of step S201.

Operation of Hydraulic Pressure Controller312of ESB-ECU13

FIG. 8is a flowchart illustrating an operational sequence in a hydraulic pressure controller of the ESB-ECU. Reference is also made toFIG. 3DandFIG. 5, as appropriate.

First, the hydraulic pressure controller312determines whether or not the frictional braking control suspend flag is currently in the ON state (S301).

In cases in which the result of step S301is that the suspend flag is not currently in the ON state (S301, No), then the hydraulic pressure controller312performs hydraulic pressure control according to the frictional braking force demand sent from the MG-ECU7(S311). After step S311, the hydraulic pressure controller312returns to the processing of step S301.

In cases in which the result of step S301is that the suspend flag is currently in the ON state (S301, Yes), the hydraulic pressure controller312then determines whether or not the frictional braking force currently being output is greater than zero (S302).

In cases in which the result of step S302is that the frictional braking force currently being output is zero (S302, No), the hydraulic pressure controller312returns to the processing of step S301. Namely, the hydraulic pressure controller312maintains the frictional braking force at a state of zero.

In cases in which the result, of step S302is that the frictional braking force currently being output is greater than zero (S302, Yes), then the hydraulic pressure controller312releases hydraulic pressure in the frictional braking device10(S303). Only a small amount of hydraulic pressure is released when this is performed. Thus, the frictional braking force is gradually reduced. After step S303, the hydraulic pressure controller312returns to the processing of step S301. The processing of step S303corresponds to time t1to time t2inFIG. 3D.

According to the present exemplary embodiment, in cases in which the frictional braking force is being limited, braking force can be generated even when frictional braking is in a limited state by switching the regeneration limiting value from the limited value to the unlimited value, and by generating regenerative braking force of the amount of the limited value.

Moreover, due to switching the regeneration limiting value when the driver has actuated acceleration by depressing the accelerator pedal, surprise, arising from braking force from the frictional braking component suddenly disappearing while frictional braking is being performed, can be prevented due to frictional braking being switched when in a not-in-use state.

Moreover, according to the present embodiment, due to performing smoothing processing to smooth the value of the drive force demand limited to the limited value before output, abrupt change in the braking force arising when the braking force demand is limited to the first regeneration limit threshold value can be eliminated. This thereby enables the elimination of a feeling of unease being imparted to the driver, and enables an improvement in feel.

Explanation has been given of application to a case in the present embodiment where the temperature of the brake pads was a specific temperature or greater; however, application may also be made in cases in which there is insufficient frictional braking, such as due to a servo malfunction, or the like.