Braking control apparatus for hybrid vehicle

A braking control apparatus includes a braking force control unit, a first abnormality detecting unit, a regenerative brake stopping unit, and a braking force compensating unit. The braking force control unit is configured to perform a braking force control by causing an engine brake, a regenerative brake, and a friction brake to operate in cooperation with each other. The regenerative brake stopping unit is configured to disconnect the regenerative brake from the braking force control, when an abnormality of the regenerative brake is detected by the first abnormality detecting unit. The braking force compensating unit is configured to perform a braking force compensation that utilizes the friction brake, from the detection of the abnormality of the regenerative brake until the regenerative brake is disconnected from the braking force control, by performing a feedback control on a deceleration rate at a time when the abnormality of the regenerative brake is detected.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent Application No. 2021-089979 filed on May 28, 2021, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The technology relates to a braking control apparatus for a hybrid vehicle.

A vehicle such as a hybrid vehicle includes a braking control apparatus that uses a friction brake and a regenerative brake in combination to achieve a desired braking force. The friction brake generates a braking force at a wheel by operating a friction engagement member by means of a pressure such as a hydraulic pressure. The regenerative brake generates the braking force at the wheel by activating a motor generator as an electrical generator.

For example, Japanese Patent (JP-B) No. 6064762 discloses a technique that stabilizes a vehicle behavior in a case where an abnormality occurs in the regenerative brake of the braking control apparatus, or a vehicle control apparatus, for the hybrid vehicle. The technique disclosed in JP-B No. 6064762 performs the following operation when the abnormality of the regenerative brake is detected, in a case where a difference between a target behavior of the vehicle, calculated on the basis of an operation amount of a brake pedal or an operation amount of an accelerator pedal, and a deceleration rate detected by an accelerometer exceeds a predetermined range. Namely, a torque to be generated at the vehicle as a whole is distributed to normal devices other than the abnormal regenerative brake, i.e., to the friction brake, an engine, and a transmission to cover a torque decreased by the abnormal regenerative brake and thereby to achieve the target behavior, until the motor generator is electrically disconnected from the vehicle.

SUMMARY

An aspect of the technology provides a braking control apparatus for a hybrid vehicle. The hybrid vehicle includes a power unit, an engine, and a motor generator. The engine and the motor generator serve as drive sources of the power unit. The braking control apparatus includes a braking force control unit, a first abnormality detecting unit, a regenerative brake stopping unit, and a braking force compensating unit. The braking force control unit is configured to perform a braking force control by causing an engine brake that is based on the engine, a regenerative brake that is based on the motor generator, and a friction brake that is based on a friction engagement member to operate in cooperation with each other. The first abnormality detecting unit is configured to detect an abnormality of the regenerative brake. The regenerative brake stopping unit is configured to disconnect the regenerative brake from the braking force control and stop an activation of the regenerative brake, in a case where the abnormality of the regenerative brake is detected by the first abnormality detecting unit. The braking force compensating unit is configured to perform a braking force compensation that utilizes the friction brake, during a time period from when the detection of the abnormality of the regenerative brake is detected by the first abnormality detecting unit to when the regenerative brake is disconnected from the braking force control by the regenerative brake stopping unit. The braking force compensating unit is configured to perform the braking force compensation by performing a feedback control on a deceleration rate at a time when the abnormality of the regenerative brake is detected by the first abnormality detecting unit.

An aspect of the technology provides a braking control apparatus for a hybrid vehicle. The hybrid vehicle includes a power unit, an engine, and a motor generator. The engine and the motor generator serve as drive sources of the power unit. The braking control apparatus includes circuitry configured to perform a braking force control by causing an engine brake that is based on the engine, a regenerative brake that is based on the motor generator, and a friction brake that is based on a friction engagement member to operate in cooperation with each other, detect an abnormality of the regenerative brake, disconnect the regenerative brake from the braking force control and stop an activation of the regenerative brake, in a case where the abnormality of the regenerative brake is detected, and perform a braking force compensation that utilizes the friction brake, during a time period from when the abnormality of the regenerative brake is detected to when the regenerative brake is disconnected from the braking force control, by performing a feedback control on a deceleration rate at a time when the abnormality of the regenerative brake is detected.

DETAILED DESCRIPTION

A technique disclosed in JP-B No. 6064762 can no longer able to perform appropriate braking in a case where complex abnormalities are occurred. For example, it is not possible to perform the appropriate braking in a case where an abnormality occurs in various sensors in addition to cutoff of a regenerative brake.

It is desirable to provide a braking control apparatus for a hybrid vehicle which makes it possible to perform appropriate braking even in a case where complex abnormalities are occurred upon a braking control.

Referring toFIG.1, a vehicle1is a hybrid vehicle that includes a power unit PU. The power unit PU may include an engine2and a motor generator (M/G)4that is coupled to an output shaft of the engine2via an automatic transmission (T/M)3.

The vehicle1illustrated inFIG.1according to an example embodiment may be a four-wheel drive. The output shaft of the automatic transmission3may be coupled to a left front wheel5fl, a right front wheel5fr, a left rear wheel5r1, and a right rear wheel5rr(hereinafter collectively referred to as “wheels5”). The wheels5may be provided with wheel cylinders8fl,8fr,8r1, and8rr(hereinafter collectively referred to as “wheel cylinders8”) each having a friction engagement member such as a disc brake. The vehicle1illustrated inFIG.1may also include a center differential device Dc, a front differential device Df, and a rear differential device Dr.

The vehicle1may include a control system that performs a traveling control. The control system may include: a hybrid control unit (HEV_CU)10; an engine control unit (ECU)11; a transmission control unit (TCU)12; a power control unit (PCU)13that includes an inverter (INV)13a; and a brake control unit (BCU)14. The hybrid control unit10, the engine control unit11, the transmission control unit12, the power control unit13, and the brake control unit14may be so coupled to each other as to communicate with each other via an in-vehicle network such as controller area network (CAN).

The hybrid control unit10may be coupled to various sensors including, for example, an accelerator sensor15and a brake sensor16. The accelerator sensor15may be coupled to an input side of the hybrid control unit10, and may detect a state of operation of an accelerator pedal15aperformed by a driver. In one embodiment, the accelerator sensor15may serve as an “accelerator operation detector”. The brake sensor16may be coupled to the input side of the hybrid control unit10, and may detect a state of brake operation of a brake pedal16aperformed by the driver. In one embodiment, the brake sensor16may serve as a “brake operation detector”.

The accelerator sensor15may detect factors including, for example, a speed of operation performed on the accelerator pedal15aand a fully-released state or a fully-pressed state of the accelerator pedal15a. The brake sensor16may detect factors including, for example, a speed of operation performed on the brake pedal16aand a fully-released state or a fully-pressed state of the brake pedal16a.

The hybrid control unit10may calculate, for example, a request torque requested for the engine2and the motor generator4on the basis of signals supplied from the various sensors, and may perform a comprehensive drive control of the engine2and the motor generator4.

The hybrid control unit10may also perform a switching control of a traveling mode by controlling various unillustrated clutches provided in the automatic transmission4. In an example embodiment, the hybrid control unit10may switch the traveling mode to any of an EG mode in which the vehicle1travels solely by the engine2, an HEV mode in which the vehicle1travels by a combined use of the engine2and the motor generator4, and an EV mode in which the vehicle1travels solely by the motor generator4.

The hybrid control unit10performs, for example, a braking force control on the basis of an engine brake that utilizes the engine2, a regenerative brake that is based on the motor generator4, a friction brake that is based on activation of respective wheel cylinders8, or a cooperative operation thereof.

The hybrid control unit10may acquire a target deceleration rate upon performing the braking force control. For example, upon coast traveling, the hybrid control unit10may calculate the target deceleration rate on the basis of a signal (e.g., an accelerator position) supplied from the accelerator sensor15. The hybrid control unit10may calculate the target deceleration rate on the basis of signals received from devices including, for example, later-described first and second brake fluid pressure sensors59aand59b, in a case where pressing of the brake pedal16aperformed by the driver is detected on the basis of a signal supplied from the brake sensor16. The hybrid control unit10may acquire the target acceleration rate to be used for, for example, an automatic brake control calculated by an unillustrated driving assist device, in a case where the vehicle1is mounted with the driving assist device.

The hybrid control unit10may calculate a necessary brake torque on the basis of the acquired target deceleration rate, for example. Further, the hybrid control unit10may calculate respective distribution values on the basis of a factor such as a traveling state of the vehicle1, and may output control signals that are based on the calculated respective distribution values to the respective engine control unit11, transmission control unit12, power control unit13, and brake control unit14. The distribution values, i.e., an engine brake torque, a regenerative brake torque, and a friction brake torque, may be used to distribute the calculated necessary brake torque to the engine brake, the regenerative brake, and the friction brake.

The engine control unit11may receive control data such as the request torque from the hybrid control unit10, and may receive detection data supplied from unillustrated various sensors including, for example, a crank angle sensor provided in the engine2. The engine control unit11may drive the engine2by controlling a fuel injection amount, an ignition timing, and various devices including, for example, an electronically controlled throttle value, on the basis of the received pieces of data.

The transmission control unit12may receive control data from the hybrid control unit10, and may receive detection data supplied from unillustrated various sensors including, for example, a shift position sensor provided on a shift lever and a vehicle speed sensor. The transmission control unit12may perform, for example, a hydraulic pressure control to be performed on respective elements, such as clutches, configuring the automatic transmission3on the basis of the received pieces of data, and may thereby control a gear ratio of the automatic transmission3.

The transmission control unit12may perform a predetermined shift control upon braking in cooperation with the engine control unit11to thereby generate a braking force, or the engine brake torque, that is based on the engine brake.

The power control unit13may receive control data such as the request torque from the hybrid control unit10, and may acquire, from the inverter13a, factors including, for example, a value of a current that flows in the motor generator4and a voltage value thereof and signals supplied from various sensors. The power control unit13may convert a direct-current electric power supplied from a battery (BATT)7into an alternating-current electric power by controlling the inverter13a, and may thereby drive the motor generator4.

The power control unit13may cause the motor generator4to function as an electrical generator by controlling the inverter13aupon deceleration traveling, and may convert an alternating-current electric power generated by the motor generator4on the basis of the regenerative brake into a direct-current electric power to thereby charge the battery7. Causing the motor generator4to function as the electrical generator may apply a regenerative braking force based on the regenerative brake to the wheels5. It should be noted that the regenerative braking force may be applied to drive wheels, and that the regenerative braking force, or the regenerative brake torque, may be applied to all of the wheels5in an example embodiment where the vehicle1is the four-wheel drive.

The brake control unit14may receive control data from the hybrid control unit10, and may receive detection data supplied from various sensors including, for example, wheel speed sensors17fl,17fr,17r1, and17rr(hereinafter collectively referred to as “wheel speed sensors17”) that detect wheel speeds of the respective wheels5and a longitudinal acceleration sensor18. The brake control unit14may control driving of the wheel cylinders8by performing a brake fluid pressure control on a brake actuator (B/A)6on the basis of the received pieces of data, and may thereby generate a friction braking force, or the friction brake torque, at the wheels5.

Referring toFIG.2, for example, the brake actuator6may include a brake fluid pressure circuit42coupled to a brake fluid pressure generator41.

The brake fluid pressure generator41may include: a master cylinder44; a reservoir tank45attached to the master cylinder44; and a brake booster46provided between the brake pedal16aand the master cylinder44. The reservoir tank45may contain a pressuring medium such as an oil. The brake pedal16amay be coupled to the brake booster46via an operating rod48.

The master cylinder44of the brake fluid pressure generator41may be coupled, via the brake fluid pressure circuit42, to the wheel cylinders8fl,8fr,8r1, and8rrthat are provided at the respective left front wheel5fl, right front wheel5fr, left rear wheel5r1, and right rear wheel5rrof the vehicle1.

The brake fluid pressure circuit42may have two fluid pressure lines including a first fluid pressure circuit52and a second fluid pressure circuit53. In an example embodiment, the brake fluid pressure circuit42may be of a cross piping type, or an X-piping type in which the first fluid pressure circuit52and the second fluid pressure circuit53are so installed as to intersect in diagonal directions of the vehicle1. For example, the first fluid pressure circuit52of the brake fluid pressure circuit42in an example embodiment may be coupled to the wheel cylinders8fland8rrof the left front wheel5fland the right rear wheel5rrdisposed in one of the diagonal directions of the vehicle1. For example, the second fluid pressure circuit53of the brake fluid pressure circuit42in an example embodiment may be coupled to the wheel cylinders8frand8r1of the right front wheel5frand the left rear wheel5r1disposed in the other of the diagonal directions of the vehicle1.

It should be noted that the first fluid pressure circuit52and the second fluid pressure circuit53have the same configuration as each other, and that elements having substantially the same function and configuration are denoted with the same reference numerals in the following as appropriate to simplify the description. Further, for convenience of description, the description is given by referring to a side on which the master cylinder44is provided as an upstream side and a side on which the wheel cylinders8fl,8fr,8r1, and8rrare provided as a downstream side, on the basis of a flow from the master cylinder44to the side on which the wheel cylinders8fl,8fr,8r1, and8rrof brake calipers are provided.

The master cylinder44may be provided with first and second feed/discharge ports44aand44b. The first and the second feed/discharge ports44aand44bmay be coupled to the respective upstream sides of first fluid paths L1configuring the respective first and second fluid pressure circuits52and53. The downstream side of the first fluid path L1may be coupled to a mid-stream part of the second fluid path L2. The upstream side of the second fluid path L2may be coupled to a low-pressure accumulator54. In one embodiment, the low-pressure accumulator54may serve as a “pressure-accumulating device”.

The downstream side of the second fluid path L2may be so branched as to be coupled to a third fluid path L3and a fourth fluid path L4. The downstream side of the third fluid path L3or the fourth fluid path L4may be coupled to the wheel cylinders8fland8rr(or8frand8r1). The wheel cylinders8fland8rr(or8frand8r1) may operate the brake calipers provided at the respective wheels5fland5rr(or5frand5r1) to thereby generate a braking force, i.e., the friction braking force, at the respective wheels5fland5rr(or5frand5r1).

The mid-stream parts of the respective third and fourth fluid paths L3and L4may be coupled to the upstream sides of fifth and sixth fluid paths L5and L6. The downstream sides of the respective fifth and sixth fluid paths L5and L6may be coupled to respective seventh fluid paths L7. The downstream side of the seventh fluid path L7may be coupled to the low-pressure accumulator54.

The first fluid path L1may be provided with a gate-in valve55. A fluid pressure pump56is provided at the second fluid path L2at a location downstream of the first fluid path L1. The fluid pressure pumps56of the respective first and second fluid pressure circuits52and53may be coupled to a common electric motor57.

The fluid pressure pumps56may have their respective drive shafts that are so coupled to the electric motor57that the pulsations of fluid pressures to be generated by the respective fluid pressure pumps56have opposite phases to each other. The electric motor57may be driven and controlled on the basis of a control signal, or a brake fluid pressure indication value, to be supplied from the brake control unit14. The electric motor57may be basically driven at a high speed upon braking during high-speed traveling where the large braking force, or a large brake fluid pressure, is necessary. The electric motor57may be basically driven at a low speed upon braking during low-speed traveling where the large braking force, or the large brake fluid pressure, is not so necessary.

The first fluid path L1on the upstream side of the gate-in valve55and the second fluid path L2on the downstream side of the fluid pressure pump56may be bypass coupled via an eighth fluid path L8. The eighth fluid path L8may be provided with a bypass valve58. The first brake fluid pressure sensor59a(or the second brake fluid pressure sensor59b) may be provided at the second fluid path L2at a location downstream of the eighth fluid path L8. The first brake fluid pressure sensor59a(or the second brake fluid pressure sensor59b) may detect a fluid pressure of a brake fluid that acts on the second fluid path L2, for example. The third and the fourth fluid paths L3and L4may be provided with respective pressuring valves60and61. The fifth and the sixth fluid paths L5and L6may be provided with respective decompression valves62and63.

The gate-in valve55, the bypass valve58, the pressuring valves60and61, and the decompression valves62and63each may be, for example, an electromagnetic solenoid valve, and may be switched in response to a drive signal supplied from the brake control unit14. In an example embodiment, the bypass valve58and the pressuring valves60and61each may be a normally-open electromagnetic solenoid valve, and the gate-in valve55and the decompression valves62and63each may be a normally-closed electromagnetic solenoid valve, for example.

The brake control unit14may perform various braking control on the brake actuator6by controlling devices including, for example, the electric motor57and each of the gate-in valve55, the bypass valve58, the pressuring valves60and61, and the decompression valves62and63.

For example, the brake control unit14may basically stop the electric motor57, close the gate-in valve55, and open the bypass valve58. Thus, the brake fluid pressure generated by the master cylinder44in response to an amount of pressing performed on the brake pedal16aby the driver may be fed as it is to each of the wheel cylinders8.

The brake control unit14may drive the electric motor57when the target deceleration rate for a control such as the automatic brake control is set by the driving assist device, in a case where the vehicle1is mounted with the unillustrated driving assist device. Further, the brake control unit14may open the gate-in valve55and close the bypass valve58. Thus, the pressuring medium pressurized by the master cylinder44or the pressuring medium fed as it is from the reservoir tank45may be pressurized to a predetermined brake fluid pressure as a result of traveling through the fluid pressure pump56, following which the thus-pressurized pressuring medium may be fed to from the second fluid path L2to the third and the fourth fluid paths L3and L4.

The brake control unit14may drive and control the pressuring valves60and61and the decompression valves62and63to perform a distribution control and a depressurizing control of the brake fluid pressure to be supplied to each of the wheel cylinders8, thereby achieving controls including, for example, an anti-lock brake system (ABS) and an antiskid brake control.

The brake control unit14may decrease the brake fluid pressure by driving and controlling devices including, for example, the decompression valves62and63and the electric motor57, upon the braking force control that causes the friction brake to operate in cooperation with a brake such as the regenerative brake or the engine brake. Thus, the friction braking force may be control to a braking force corresponding to a torque distribution value of the necessary brake torque calculated by the hybrid control unit10.

In an example embodiment, the brake control unit14performs a braking force compensation that utilizes the friction brake until the regenerative brake is disconnected from the braking force control by the power control unit13in a case where an abnormality occurs in the regenerative brake, upon the braking force control that causes the engine brake, the regenerative brake, and the friction brake to operate in cooperation with each other.

For example, the brake control unit14may perform a first braking force compensation control in a case where an abnormality is detected only for the regenerative brake, or in a case where: the abnormality is detected for the regenerative brake; and an abnormality is detected for a control system of the power unit PU. Upon the first braking force compensation control, the brake control unit14may compensate for the braking force by setting, as the target deceleration rate, an acceleration rate that is at the time when the abnormality of the regenerative brake is detected (in some embodiments, at the time immediately prior to the detection of the abnormality of the regenerative brake) and by performing a feedback control that utilizes the friction brake on the thus-set target deceleration rate.

The abnormality of the regenerative brake may refer to, for example, a case where the regenerative brake is cutoff, or in a case where the braking force based on the regenerative brake is no longer generated. The abnormality of the regenerative brake may be determined, for example, by the power control unit13. For example, the power control unit13may determine the abnormality of the regenerative brake in a case where a predetermined regenerative electric power generation is not achieved by the motor generator4even through the regenerative brake control is carried out.

The abnormality of the control system of the power unit PU may refer to, for example, a case where an abnormality of a sensor system of the power unit PU or an abnormality of an actuator system is detected on the basis of a known abnormality diagnosis performed by a device such as the engine control unit11or the transmission control unit12.

In some embodiments, the brake control unit14may perform a second braking force compensation control at least in a case where: an abnormality is detected for the regenerative brake; and an abnormality of a sensor is detected for a braking system. Upon the second braking force compensation control, the brake control unit14may compensate for the braking force by means of the braking force that is based on a preset brake fluid pressure. The case where the abnormality is detected for the regenerative brake and where the abnormality of the sensor is detected for the braking system may encompass, for example, a case where: the abnormality is detected for the regenerative brake; the abnormality is detected for the control system of the power unit PU; and the abnormality of the sensor is detected for the braking system.

The abnormality of the sensor of the braking system may refer to, for example, a case where a sensor value is not outputted or an abnormal sensor value is outputted by a device such as each wheel sensor17or the longitudinal acceleration sensor18, on the basis of a known abnormality diagnosis performed by a device such as the brake control unit14.

In one embodiment, the hybrid control unit10may serve, together with the engine control unit11, the transmission control unit12, the power control unit13, and the brake control unit14, as a “braking force control unit”. In one embodiment, devices including, for example, the engine control unit11and the transmission control unit12may serve as a “power unit abnormality detecting unit” or a “third abnormality detecting unit”. In one embodiment, the power control unit13may serve as a “regenerative brake abnormality detecting unit” or a “first abnormality detecting unit”. In one embodiment, the power control unit13may serve as a “regenerative brake stopping unit”. In one embodiment, the brake control unit14may serve as a “braking force compensating unit”. In one embodiment, the brake control unit14may serve as a “braking system sensor abnormality detecting unit” or a “second abnormality detecting unit”.

Next, a description is given, with reference toFIG.3, of a brake torque distribution control to be performed on each brake, i.e., the regenerative brake, the engine brake, and the friction brake.FIG.3is a flowchart illustrating an example of a routine of the brake torque distribution control. The hybrid control unit10may repeatedly execute the routine of the brake torque distribution control for each set time.

After the start of the routine, in step S101, the hybrid control unit10may determine whether a deceleration request is made. For example, the hybrid control unit10may determine that the deceleration request that is based on the coast traveling is made, in a case where a released state of the accelerator pedal15ais detected on the basis of a signal supplied from the accelerator sensor15. Alternatively, for example, the hybrid control unit10may determine that the deceleration request is made, in a case where a pressing state of the brake pedal16ais detected on the basis of a signal supplied from the brake sensor16. Alternatively, for example, the hybrid control unit10may determine that the deceleration request is made, in a case where the target deceleration rate is supplied from the unillustrated driving assist device.

If the hybrid control unit10determines in step S101that the deceleration request is not made (step S101: NO), the hybrid control unit10may end the routine.

The routine may proceed to step S102from step S101. In step S102, the hybrid control unit10may acquire the target deceleration rate. For example, upon the coast traveling, the hybrid control unit10may calculate the target deceleration rate on the basis of a factor such as a signal (e.g., the accelerator position) supplied from the accelerator sensor15or a vehicle speed. The hybrid control unit10may calculate the target deceleration rate on the basis of signals received from devices including, for example, the first and the second brake fluid pressure sensors59aand59b, in a case where pressing of the brake pedal16aperformed by the driver is detected on the basis of a signal supplied from the brake sensor16. The hybrid control unit10may acquire the target acceleration rate to be used for, for example, the automatic brake control calculated by the unillustrated driving assist device, in a case where the vehicle1is mounted with the driving assist device.

Thereafter, in step S103, the hybrid control unit10may calculate the necessary brake torque on the basis of the current target deceleration rate. Further, the hybrid control unit10may calculate the respective brake torque distribution values to be used to distribute the calculated necessary brake torque to the regenerative brake, the engine brake, and the friction brake on the basis of a factor such as a traveling state of the vehicle1.

The routine may proceed to step S104from step S103. In step S104, the hybrid control unit10may output, as the control data, the calculated brake torque distribution values to the respective corresponding control units, following which the hybrid control unit10may end the routine.

For example, in a case where the brake toque distribution value for the regenerative brake is calculated, the hybrid control unit10may output, as the control data, the calculated brake toque distribution value to the power control unit13. Thus, a control such as a magnetic field control for the regenerative electric power generation may be performed on the motor generator4, and the regenerative braking force corresponding to the brake torque distribution value may be generated accordingly. It should be noted that the regenerative brake may be prohibited in a case where a later-described regenerative brake prohibition flag F is set to “1”. Accordingly, the regenerative brake may be excluded from a target of the calculation of the brake torque distribution values in step S103described above, in a case where the regenerative brake prohibition flag F is set to “1”.

Further, for example, in a case where the brake toque distribution value for the engine brake is calculated, the hybrid control unit10may output, as the control data, the calculated brake toque distribution value to the engine control unit11and the transmission control unit12. Thus, an output torque of the engine2and the gear ratio of the automatic transmission3may be controlled, and the engine braking force corresponding to the brake torque distribution value may be generated accordingly.

Further, for example, in a case where the brake toque distribution value for the friction brake is calculated, the hybrid control unit10may output, as the control data, the calculated brake toque distribution value to the brake control unit14. Thus, the brake fluid pressure control may be performed on the brake actuator6, and the friction braking force corresponding to the brake torque distribution value may be generated accordingly.

Next, a description is given, with reference toFIG.4, of a regenerative brake disconnection control upon an abnormality of the regenerative brake.FIG.4is a flowchart illustrating an example of a routine of the regenerative brake disconnection control. The regenerative brake disconnection control may disconnect the regenerative brake from the braking control in a case where an abnormality of the regenerative brake is detected upon the above-described braking control, i.e., the brake torque distribution control. The power control unit13may repeatedly execute the routine of the regenerative brake disconnection control for each set time.

After the start of the routine, in step S201, the power control unit13may determine whether the regenerative brake prohibition flag F is set to “1”. If the power control unit13determines in step S201that the regenerative brake prohibition flag F is set to “1” (step S201: YES), the power control unit13may end the routine.

If the power control unit13determines in step S201that the regenerative brake prohibition flag F is cleared and set to “0” (step S201: NO), the routine may proceed to step S202. In step S202, the power control unit13may determine whether an abnormality of the regenerative brake is detected.

If the power control unit13determines in step S202that the abnormality of the regenerative brake is not detected (step S202: NO), the power control unit13may end the routine.

If the power control unit13determines in step S202that the abnormality of the regenerative brake is detected (step S202: YES), the routine may proceed to step S203. In step S203, the power control unit13may determine whether the regenerative brake is currently controlled.

If the power control unit13determines in step S203that the regenerative brake is not currently controlled (step S203: NO), the routine may proceed to step S206.

If the power control unit13determines in step S203that the regenerative brake is currently controlled (step S203: YES), the routine may proceed to step S204. In step S204, the power control unit13may execute the disconnection of the regenerative brake from the braking force control. For example, the power control unit13may cancel the magnetic field control for the regenerative electric power generation performed on the motor generator4, and may release the coupling of the output shaft of the automatic transmission3to the motor generator4by controlling the unillustrated clutches.

The routine may proceed to step S205from step S204. In step S205, the power control unit13may determine whether the disconnection of the regenerative brake is completed.

If the power control unit13determines in step S205that the disconnection of the regenerative brake is not completed (step S205: NO), the routine may return to step S204.

If the power control unit13determines in step S205that the disconnection of the regenerative brake is completed (step S205: YES), the routine may proceed to step S206.

The routine may proceed to step S206from step S203or from step S205. In step S206, the power control unit13may set the regenerative brake prohibition flag F that prohibits the regenerative brake to “1”. Thereafter, the power control unit13may end the routine.

Next, a description is given, with reference toFIG.5, of the braking force compensation control upon an abnormality of the regenerative brake.FIG.5is a flowchart illustrating an example of a routine of the braking force compensation control upon the abnormality of the regenerative brake. The brake control unit14may repeatedly execute the routine of the braking force compensation control for each set time.

After the start of the routine, in step S301, the brake control unit14may determine whether the regenerative brake prohibition flag F is set to “1”.

If the brake control unit14determines in step S301that the regenerative brake prohibition flag F is set to “1” (step S301: YES), the brake control unit14may end the routine.

If the brake control unit14determines in step S301that the regenerative brake prohibition flag F is cleared and set to “0” (step S301: NO), the routine may proceed to step S302. In step S302, the brake control unit14may determine whether an abnormality of the regenerative brake is detected by the power control unit13.

If the brake control unit14determines in step S302that the abnormality of the regenerative brake is not detected (step S302: NO), the brake control unit14may end the routine.

If the brake control unit14determines in step S302that the abnormality of the regenerative brake is detected (step S302: YES), the routine may proceed to step S303. In step S303, the brake control unit14may determine whether an abnormality is detected for a sensor of a control system.

If the brake control unit14determines in step S303that the abnormality is detected for the sensor of the control system (step S303: YES), the routine may proceed to step S305.

If the brake control unit14determines in step S303that the abnormality is not detected for the sensor of the control system (step S303: NO), the routine may proceed to step S304. In step S304, the brake control unit14may execute the first braking force compensation control.

The brake control unit14may execute the first braking force compensation control on the basis of a subroutine of the first braking force compensation control illustrated by way of example inFIG.6.FIG.6is a flowchart illustrating an example of the subroutine of the first braking force compensation control.

After the start of the subroutine, in step S401, the brake control unit14may determine whether the current state is immediately after the disconnection of the regenerative brake due to the abnormality.

If the brake control unit14determines in step S401that the current state is not immediately after the disconnection of the regenerative brake (step S401: NO), the routine may proceed to step S404.

If the brake control unit14determines in step S401that the current state is immediately after the disconnection of the regenerative brake (step S401: YES), the routine may proceed to step S402. In step S402, the brake control unit14may store, as the target deceleration rate, a deceleration rate that is at the time of the generation of the abnormality of the regenerative brake. For example, the brake control unit14may store, as the target deceleration rate, the deceleration rate that is at the time immediately before the disconnection of the regenerative brake.

Thereafter, in step S403, the brake control unit14may calculate the target brake fluid pressure. For example, the brake control unit14may calculate, as the target brake fluid pressure, the brake fluid pressure that is necessary for generating the target deceleration rate by the friction brake, on the basis of the target deceleration rate and a current deceleration rate of the vehicle1. For example, the current deceleration rate of the vehicle1may be a deceleration rate detected by the longitudinal acceleration sensor18. Thereafter, the routine may proceed to step S406.

The routine may proceed to step S404from step S401. In step S404, the brake control unit14may calculate a feedback correction amount for a correction of the target brake fluid pressure, on the basis of the target deceleration rate set in step S402and the current deceleration rate of the vehicle1. For example, the current deceleration rate of the vehicle1may be the deceleration rate detected by the longitudinal acceleration sensor18.

Thereafter, in step S405, the brake control unit14may correct the target brake fluid pressure on the basis of the feedback correction amount. Thereafter, the routine may proceed to step S406.

The routine may proceed to step S406from step S403or from step S405. In step S406, the brake control unit14may perform the brake fluid pressure control on the brake actuator6by means of the target brake fluid pressure. Thereafter, the brake control unit14may end the routine.

The routine may proceed to step S305from step S303of the main routine illustrated inFIG.5. In step S305, the brake control unit14may execute the second braking force compensation control, following which the routine may proceed to step S306.

The brake control unit14may execute the second braking force compensation control on the basis of a subroutine of the second braking force compensation control illustrated by way of example inFIG.7.FIG.7is a flowchart illustrating an example of the subroutine of the second braking force compensation control.

After the start of the subroutine, in step S501, the brake control unit14may determine whether the brake fluid pressure that is at the time of the generation of the abnormality of the regenerative brake is equal to or greater than a preset threshold. For example, the brake control unit14may determine whether the brake fluid pressure that is at the time immediately before the disconnection of the regenerative brake is equal to or greater than the preset threshold.

If the brake control unit14determines in step S501that the brake fluid pressure at the time of the generation of the abnormality of the regenerative brake is less than the threshold (step S501: NO), the brake control unit14may end the routine.

If the brake control unit14determines in step S501that the brake fluid pressure at the time of the generation of the abnormality of the regenerative brake is equal to or greater than the threshold (step S501: YES), the routine may proceed to step S502. In step S502, the brake control unit14may perform the brake fluid pressure control on the brake actuator6by means of a preset constant brake fluid pressure. Thereafter, the brake control unit14may end the routine.

The routine may proceed to step S306from step S304or from step S305of the main routine illustrated inFIG.5. In step S306, the brake control unit14may determine whether the disconnection of the regenerative brake from the braking force control is completed.

If the brake control unit14determines in step S306that the disconnection of the regenerative brake is not completed (step S306: NO), the routine may return to step S302.

If the brake control unit14determines in step S306that the disconnection of the regenerative brake is completed (step S306: YES), the brake control unit14may end the routine.

In an example embodiment described above, the brake control unit14sets, as the target deceleration rate, the deceleration rate that is at the time when the abnormality of the regenerative brake is detected and performs the braking force compensation that is based on the friction brake by performing the feedback control on the target deceleration rate in a case where the abnormality of the regenerative brake is detected, upon the braking force control that causes the engine brake, the regenerative brake, and the friction brake to operate in cooperation with each other. This helps to perform appropriate braking even in a case where complex abnormalities are occurred upon the braking control.

For example, the brake control unit14may perform the braking force compensation that is based on the feedback control that utilizes only sensor data acquirable by the brake control unit14, even in a case where an abnormality occurs in the regenerative brake, or even in a case where the abnormality occurs in the regenerative brake and where it is not possible to use the control data of the control system of the power unit PU for the braking control. Thus, it helps to prevent a temporal decrease in the braking force of the vehicle1as a whole until the regenerative brake is disconnected from the braking force control. Hence, it helps to accurately prevent, for example, an increase in a braking distance and to secure a safety. In addition, the feedback control is performed on the deceleration rate that is at the time when the abnormality of the regenerative brake is detected until the regenerative brake is disconnected from the braking force control, which also helps to prevent a sense of discomfort to be given to an occupant due to a rapid increase in the deceleration rate.

In some embodiments, the brake control unit14may perform the braking force compensation control that is based on the preset constant brake fluid pressure in place of the braking force compensation that is based on the feedback control, at least in a case where: an abnormality of the regenerative brake is detected; and an abnormality of a sensor of the braking system is detected. Thus, it helps to perform the braking force compensation even for further complex abnormalities.

In some embodiments, the brake control unit14may refrain from performing the braking force compensation that is based on the constant brake fluid pressure, in a case where the brake fluid pressure that is at the time when the abnormality of the regenerative brake is detected is less than the preset threshold. Thus, it helps to prevent the generation of excessive braking force.

In some embodiments, one or more of the devices including the hybrid control unit10, the engine control unit11, the transmission control unit12, the power control unit13, and the brake control unit14may include a known microprocessor and its peripheral devices. The microprocessor may have devices including, for example, a central processing unit (CPU), a random-access memory (RAM), a read-only memory (ROM), and a rewritable non-volatile storage. The ROM may contain, in advance, a program to be executed by the CPU and fixed data such as a data table, for example. All or a part of functions of the processor may be achieved by a logic circuit or an analog circuit, and processes based on various programs may be achieved by an electronic circuit such as field programmable gate array (FPGA).

Although some example embodiments of the technology have been described in the foregoing by way of example with reference to the accompanying drawings, the technology is by no means limited to the embodiments described above. It should be appreciated that modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. The technology is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof.

For example, in a case where it is possible to solve a problem mentioned above and any of effects mentioned above is achievable even if at least one element is removed from all of the elements described in at least one embodiment described above, a configuration in which the at least one element is removed may be extracted as one embodiment of the technology.