WO2023140280A1

WO2023140280A1 - Braking control device

Info

Publication number: WO2023140280A1
Application number: PCT/JP2023/001302
Authority: WO
Inventors: 和俊余語; 康典坂田; 翔太加藤
Original assignee: 株式会社アドヴィックス
Priority date: 2022-01-20
Filing date: 2023-01-18
Publication date: 2023-07-27
Also published as: JP2023106046A

Abstract

A braking control device 10 comprises: an electric cylinder device 23, the power source of which is an electric motor 233; a rear-wheel-side assist device 32 which has a differential pressure control valve 301 and a pump 304; and a downstream control device 35 which controls the rear-wheel-side assist device 32. When a vehicle is stopped and it has been detected that driving of the electric motor 233 is impossible, the downstream control device 35 performs a during-stop process for operating the pump 304 in a state where the differential pressure control valve 301 is closed, such that pressure in a fluid passage on a side further toward wheel cylinders 12L, 12R than the differential pressure control valve 301 becomes higher than pressure on a side further toward a slave cylinder 230 than the differential pressure control valve 301, and thereafter opening the differential pressure control valve 301 to cause brake fluid to flow from the wheel cylinders 12L, 12R to a fluid chamber 232 of the slave cylinder 230.

Description

Braking control device

The present invention relates to a braking control device that generates braking force at the wheels of a vehicle by adjusting the hydraulic pressure in the wheel cylinders.

The braking control device disclosed in Patent Document 1 includes an electric cylinder device and a control section. The electric cylinder device includes a slave cylinder and an electric motor that is a power source for the slave cylinder. No return spring is arranged in the slave cylinder of the electric cylinder device. When the electric motor is driven by the controller, the piston moves from the reference position in the slave cylinder. Then, an amount of brake fluid corresponding to the amount of movement of the piston from the reference position is supplied from the slave cylinder to the wheel cylinder. As a result, the hydraulic pressure in the wheel cylinder increases, and braking force corresponding to the hydraulic pressure is generated at the wheels.

Japanese Patent No. 5946544

Consider the case where the electric motor cannot be driven due to an abnormality occurring in at least one of the control unit and the electric motor while the hydraulic pressure in the wheel cylinder is being adjusted by the operation of the electric cylinder device. In this case, since the brake fluid returns from the wheel cylinder to the slave cylinder, the piston in the slave cylinder tries to move toward the reference position. However, since the electric cylinder device generates sliding resistance that hinders the movement of the piston, there is a possibility that the piston cannot be returned to the reference position. If the piston does not return to the reference position, hydraulic pressure may remain in the wheel cylinder.

These problems can arise even if a return spring with a relatively small force that urges the piston toward the reference position is arranged in the slave cylinder.

One aspect of the braking control device for solving the above problems is a device that generates braking force at the wheels of the vehicle by adjusting the hydraulic pressure in the wheel cylinder. This braking control device has a slave cylinder, a piston slidable in the slave cylinder, and an electric motor capable of generating a driving force for sliding the piston. An electric cylinder device that supplies brake fluid from the fluid chamber through a fluid passage to the wheel cylinder by moving the piston so that the volume of the fluid chamber formed in the slave cylinder is reduced, an electromagnetic valve arranged in the fluid passage, and a pressurization device capable of supplying the brake fluid to a portion of the fluid passage closer to the wheel cylinder than the electromagnetic valve. A pressurizing unit and a controller for controlling the pressurizing unit are provided. When the control unit detects that the electric motor cannot be driven while the vehicle is stopped, the control unit supplies brake fluid to the pressurizing device with the electromagnetic valve closed, thereby controlling the pressurizing unit so that the pressure in the portion of the fluid path closer to the wheel cylinder than the electromagnetic valve becomes higher than the pressure in the portion closer to the slave cylinder than the electromagnetic valve. Execute stop time processing to flow.

With the above configuration, when the vehicle stop process is executed, the pressurizing unit is operated to make the pressure in the portion of the liquid passage closer to the wheel cylinder than the solenoid valve higher than the pressure in the portion closer to the slave cylinder than the solenoid valve. Since the electromagnetic valve is opened after the differential pressure is increased in this manner, the brake fluid flows from the wheel cylinder to the slave cylinder. As a result, the pressure is applied to the slave cylinder, and the piston can be moved toward the reference position against the sliding resistance that hinders the movement of the piston in the electric cylinder device.

One aspect of the braking control device for solving the above problems is a device that generates braking force at the wheels of the vehicle by adjusting the hydraulic pressure of the wheel cylinders. This braking control device includes a slave cylinder, a piston slidable in the slave cylinder, and an electric motor capable of generating a driving force for sliding the piston. An electric cylinder device that supplies brake fluid from the fluid chamber to the wheel cylinder through a fluid passage by moving the piston so that the volume of the fluid chamber formed in the slave cylinder is reduced, a holding valve arranged in the fluid passage, a pressure reducing valve that reduces the hydraulic pressure of the wheel cylinder in an open state, and the pressure reducing valve that is open. In some cases, a pressurizing unit having a pressurizing device capable of supplying brake fluid sucked from the wheel cylinder via the pressure reducing valve to a portion of the fluid passage closer to the slave cylinder than the holding valve, and a control unit for controlling the pressurizing unit. When the vehicle is running, the control unit detects that the electric motor has become undrivable, and there is no braking request, the control unit opens the pressure reducing valve, closes the holding valve, and operates the pressurizing device.

In the above configuration, when the running process is executed, the holding valve is closed and the pressure reducing valve is opened, so the brake fluid in the wheel cylinder is sucked by the pressurizing device and supplied to the part of the fluid path closer to the slave cylinder than the holding valve. That is, the brake fluid flows from the pressure device toward the wheel cylinder. As a result, the pressure is applied to the slave cylinder, and the piston can be moved toward the reference position against the sliding resistance that hinders the movement of the piston in the electric cylinder device.

Therefore, the braking control device described above can return the piston to the reference position even if the electric motor cannot be driven and the piston has not returned to the reference position.

FIG. 1 is a configuration diagram showing an outline of a braking control device according to an embodiment. FIG. 2 is a flow chart showing a processing routine executed to detect the state of the upstream pressurizing section of the braking control device. FIG. 3 is a flowchart showing a processing routine that is executed while the vehicle is running. FIG. 4 is a time chart when running processing is executed. FIG. 5 is a flow chart showing a processing routine executed when the vehicle is stopped. FIG. 6 is a time chart when the vehicle stop process is executed. FIG. 7 is a configuration diagram showing an outline of an upstream pressurizing section of a modification.

An embodiment embodying a braking control device will be described below with reference to FIGS. 1 to 6. FIG.
As shown in FIG. 1, the braking control device 10 is a device that generates braking force at the wheels by adjusting the hydraulic pressures of

wheel cylinders

11L and 11R for the left and right front wheels and

wheel cylinders

12L and 12R for the left and right rear wheels. The braking control device 10 includes an upstream pressurizing section 20 and a downstream pressurizing section 30 .

<Structure of Upstream Pressure Unit 20>
The upstream pressure unit 20 is connected through the first fluid passage 13 to the

wheel cylinders

11L and 11R for the left and right front wheels. The upstream pressurizing section 20 is connected to the

wheel cylinders

12L and 12R for the left and right rear wheels via the second fluid passage 14 . The upstream pressurization section 20 includes a reserve tank 21 , a master cylinder 22 , an electric cylinder device 23 , a master cut valve 24 , a system cutoff valve 25 , a simulator cut valve 26 , a stroke simulator 27 and an upstream control device 28 . The reserve tank 21 is a tank that stores brake fluid. The master cylinder 22 is a mechanical pressurizing device that generates hydraulic pressure in response to depression of the brake pedal 15 . The electric cylinder device 23 is an electric pressure device that electrically generates hydraulic pressure. The master cut valve 24 and the system cutoff valve 25 constitute a switching mechanism for switching the state of the upstream pressurizing section 20 . The master cut valve 24 is a normally open solenoid valve, and the system cutoff valve 25 is a normally closed solenoid valve. The simulator cut valve 26 is a normally closed electromagnetic valve that switches between a state in which the master cylinder 22 and the stroke simulator 27 are hydraulically connected and a state in which the communication is blocked. The upstream control device 28 is an electronic control device that controls the electric cylinder device 23 , the master cut valve 24 , the system cutoff valve 25 and the simulator cut valve 26 .

<Configuration of Master Cylinder 22>
A master piston 221 is slidably provided inside the master cylinder 22 . A pressure chamber 222 into which brake fluid is introduced is defined inside the master cylinder 22 by the master piston 221 . A brake pedal 15 is mechanically connected to the master piston 221 . The operating position of the master piston 221 in the master cylinder 22 changes in conjunction with depression of the brake pedal 15 . The operating position is the position of the master piston 221 within the range in which the master piston 221 can slide within the master cylinder 22 . The volume of the pressure chamber 222 changes depending on the operating position of the master piston 221 . The master cylinder 22 also has a biasing member 223 that biases the master piston 221 in a direction to increase the volume of the pressure chamber 222 .

In addition, the master cylinder 22 has two ports, an input port 224 and an output port 225, as ports for communicating the pressure chamber 222 with the outside. The pressure chamber 222 is connected to the reserve tank 21 via the input port 224 . The input port 224 is open when the brake pedal 15 is not operated, but is closed by the master piston 221 when the brake pedal 15 is operated and the amount of operation exceeds a certain amount. On the other hand, the output port 225 of the master cylinder 22 is always open regardless of whether the brake pedal 15 is operated. An output port 225 of the master cylinder 22 is connected to the stroke simulator 27 via the simulator cut valve 26 . The stroke simulator 27 is a device that generates reaction force to the operation of the brake pedal 15 . Also, the output port 225 of the master cylinder 22 is connected to the first fluid passage 13 via the master cut valve 24 .

<Configuration of electric cylinder device 23>
The electric cylinder device 23 has a slave cylinder 230 , a piston 231 slidable in the slave cylinder 230 , an electric motor 233 , and a linear motion conversion mechanism 234 that converts rotation of the electric motor 233 into linear motion of the piston 231 . Inside the slave cylinder 230 , a fluid chamber 232 into which brake fluid is introduced is defined by a piston 231 . The operating position of the piston 231 inside the slave cylinder 230 is changed by an electric motor 233 . That is, the electric motor 233 can generate driving force for sliding the piston 231 within the slave cylinder 230 . The volume of the liquid chamber 232 changes according to the change in the operating position of the piston 231 . The moving direction of the piston 231 that reduces the volume of the liquid chamber 232 is referred to as the "braking direction Za", and the direction opposite to the braking direction Za is referred to as the "releasing direction Zb". Further, the operating position of the piston 231 at which the volume of the liquid chamber 232 is maximized is referred to as a "reference position".

Two ports, an input port 236 and an output port 237, are formed in the slave cylinder 230 as ports for communicating the fluid chamber 232 with the outside. A fluid chamber 232 of the slave cylinder 230 is connected to the reserve tank 21 via an input port 236 . The input port 236 is open when the piston 231 is positioned at the reference position, and is closed by the piston 231 when the piston 231 moves from the reference position in the braking direction Za. On the other hand, the output port 237 of the slave cylinder 230 is always open regardless of the position of the piston 231 . An output port 237 of the slave cylinder 230 is connected to the second fluid passage 14 . Furthermore, the output port 237 of the slave cylinder 230 is connected to the first liquid passage 13 via the system cutoff valve 25 . When the system cutoff valve 25 is open, the first fluid path 13 and the second fluid path 14 are in communication with each other.

A cup seal 238 that fills the gap between the inner wall of the slave cylinder 230 and the piston 231 is provided in the braking direction Za from the input port 236 . A cup seal 239 that fills the gap between the inner wall of the slave cylinder 230 and the piston 231 is provided in the release direction Zb from the input port 236 . The two

cup seals

238, 239 are made of elastic material.

<Configuration of upstream control device 28>
The upstream control device 28 is an electronic control device that includes one or more processors that execute various controls and a memory that stores control programs and data. The upstream control device 28 controls the electric cylinder device 23 , the master cut valve 24 , the system cutoff valve 25 and the simulator cut valve 26 . Detection signals from various sensors such as a stroke sensor 280 , a master pressure sensor 281 and an output pressure sensor 282 are input to the upstream control device 28 . The stroke sensor 280 is a sensor that detects a pedal stroke S, which is the amount of depression of the brake pedal 15 by the driver. The master pressure sensor 281 is a sensor that detects the master pressure P0, which is the hydraulic pressure that the master cylinder 22 outputs from the output port 225 . The output pressure sensor 282 is a sensor that detects a slave pressure P<b>2 that is the hydraulic pressure that the slave cylinder 230 outputs from the output port 237 . Further, the upstream control device 28 can communicate with a downstream control device 35 provided in the upstream pressure section 20 .

The upstream control device 28 controls the electric cylinder device 23, the master cut valve 24, the system cutoff valve 25 and the simulator cut valve 26 based on the detection results of the stroke sensor 280, master pressure sensor 281, output pressure sensor 282, and the like.

<Structure of Downstream Pressure Unit 30>
The downstream pressurizing section 30 is a unit capable of individually adjusting the pressure of the plurality of

wheel cylinders

11L, 11R, 12L, 12R. The downstream pressurizing section 30 includes a front wheel side assisting device 31 , a rear wheel side assisting device 32 , a hydraulic pressure sensor 33 and a downstream control device 35 . The rear wheel side assist device 32 is a device that generates a braking force on the rear wheels by adjusting the hydraulic pressures of the

wheel cylinders

12L and 12R for the left and right rear wheels. The front wheel side assist device 31 is a device that generates a braking force on the front wheels by adjusting the hydraulic pressures of the

wheel cylinders

11L and 11R of the left and right front wheels. The hydraulic pressure sensor 33 is a sensor that detects the hydraulic pressure P<b>1 supplied to the first liquid passage 13 by the upstream pressurizing section 20 . The downstream control device 35 is an electronic control device that controls the front wheel side assisting device 31 and the rear wheel side assisting device 32 . In the present embodiment, the rear wheel side assisting device 32 corresponds to the "pressure unit", and the downstream control device 35 corresponds to the "control section".

When the rear wheel side assisting device 32 is referred to as the "first pressure unit" and the wheel cylinder whose hydraulic pressure is adjusted by the first pressure unit is referred to as the "first wheel cylinder", the

wheel cylinders

12L and 12R of the rear wheels correspond to the first wheel cylinder in this embodiment. Further, when the front wheel side assisting device 31 is referred to as a "second pressure unit" and the wheel cylinder whose hydraulic pressure is adjusted by the second pressure unit is referred to as a "second wheel cylinder", the

wheel cylinders

11L and 11R of the front wheels correspond to the second wheel cylinder in this embodiment.

<Structures of Front Wheel Side Assisting Device 31 and Rear Wheel Side Assisting Device 32>
Here, first, the configuration of the hydraulic circuit for the wheel cylinder 12L in the rear wheel side assisting device 32 will be described. This hydraulic circuit includes a differential pressure control valve 301 , a holding valve 302 , a pressure reducing valve 303 , a pump 304 , a pressure regulating reservoir 306 and a reflux fluid path 307 .

The second fluid path 14 is connected to the fluid path 308 via the differential pressure control valve 301 . The differential pressure control valve 301 is a normally open linear solenoid valve. The differential pressure control valve 301 operates to adjust the differential pressure between the slave cylinder 230 side and the wheel cylinder 12L side of the differential pressure control valve 301 . The differential pressure referred to here is a value obtained by subtracting the pressure of a portion closer to the slave cylinder 230 than the differential pressure control valve 301 from the pressure of the portion closer to the wheel cylinder than the differential pressure control valve 301 in the fluid passage.

The liquid passage 308 is connected to the wheel cylinder 12L via the holding valve 302. A liquid passage 310 connects the holding valve 302 and the wheel cylinder 11L. The holding valve 302 is a normally open electromagnetic valve that closes when energized and opens when energized. For example, the holding valve 302 is closed when restricting an increase in hydraulic pressure in the wheel cylinder 12L. The liquid path 310 is connected to the pressure regulation reservoir 306 via the pressure reducing valve 303 . The pressure reducing valve 303 is a normally closed electromagnetic valve that opens when energized and closes when energized. For example, the pressure reducing valve 303 is opened when the brake fluid is discharged from the wheel cylinder 12L. The pressure reducing valve 303 and the pressure regulating reservoir 306 are connected through a liquid passage 312 .

The liquid path 312 is connected to the liquid path 308 through the pump liquid path 313 . A pump 304 is installed in the pump fluid path 313 . The pump 304 operates by receiving the rotation of the pump motor 305 . The pump 304 corresponds to the "pressurizing device". The pump 304 sucks the brake fluid in the pressure regulating reservoir 306 and discharges it to the fluid passage 308 according to its operation. The pump 304 discharges the brake fluid to a portion between the differential pressure control valve 301 and the holding valve 302 in the fluid passage connecting the slave cylinder 230 and the wheel cylinder 12L.

The pressure regulating reservoir 306 is connected to the second liquid path 14 through the reflux liquid path 307 . The pressure regulating reservoir 306 is in a state of blocking communication with the return fluid passage 307 when there is more brake fluid than a certain amount inside. The pump 304 at this time sucks the brake fluid in the pressure regulation reservoir 306 . On the other hand, the pressure regulating reservoir 306 communicates with the return fluid passage 307 when the brake fluid inside is reduced due to the suction of the pump 304 . As a result, when the pump 304 is operated while the pressure reducing valve 303 is closed, the pump 304 sucks brake fluid from the second fluid path 14 via the reflux fluid path 307 . On the other hand, when the pump 304 is operated while the pressure reducing valve 303 is open, the pump 304 sucks the brake fluid from the wheel cylinder 12L through the pressure reducing valve 303 .

The hydraulic circuit for the wheel cylinder 12R in the rear wheel side assisting device 32 has the same configuration as the hydraulic circuit for the wheel cylinder 12L. The hydraulic circuits for the wheel cylinder 12L and the wheel cylinder 12R share the differential pressure control valve 301, the pump 304, the pressure regulating reservoir 306, the reflux liquid passage 307, the liquid passage 308, the liquid passage 312, and the pump liquid passage 313. As for the holding valve 302, the pressure reducing valve 303, and the fluid passage 310, the fluid pressure circuit for the wheel cylinder 12L and the fluid pressure circuit for the wheel cylinder 12R are separate.

On the other hand, the hydraulic circuits for the

wheel cylinders

11L and 11R in the front wheel side assisting device 31 have the same configuration as the hydraulic circuits for the

wheel cylinders

12L and 12R in the rear wheel side assisting device 32. Note that the front wheel side assisting device 31 and the rear wheel side assisting device 32 share the pump motor 305 .

<Downstream control device 35>
Like the upstream controller 28, the downstream controller 35 is also configured as an electronic controller. The downstream control device 35 controls the front wheel side assisting device 31 and the rear wheel side assisting device 32 . Detection signals from the stroke sensor 350 and the hydraulic pressure sensor 33 are input to the downstream control device 35 . Stroke sensor 350 is a sensor for detecting pedal stroke S, which is different from stroke sensor 280 described above. Although not shown, detection signals from wheel speed sensors provided for each wheel are also input to the downstream control device 35 .

<Normal braking force control>
Braking force control when the upstream pressure unit 20 is normal will be described. During normal operation, the upstream control device 28 closes the master cut valve 24 and opens the system cutoff valve 25 and the simulator cut valve 26 . As a result, the output port 237 of the slave cylinder 230 is connected to both the first fluid path 13 and the second fluid path 14 . On the other hand, the output port 225 of the master cylinder 22 is connected only to the stroke simulator 27 without being connected to either the first fluid path 13 or the second fluid path 14 . In other words, the braking control device 10 at this time is in a state in which both the front-wheel-side force-assisting device 31 and the rear-wheel-side force-assisting device 32 are connected to the reserve tank 21 via the slave cylinder 230 . In this state, the brake fluid discharged by the slave cylinder 230 is sent to the

wheel cylinders

11L, 11R, 12L, 12R.

During normal operation, the upstream control device 28 controls the braking force of the vehicle by adjusting the hydraulic pressure in the

wheel cylinders

11L, 11R, 12L, 12R through the control of the electric cylinder device 23. Specifically, when the driver operates the brake pedal 15, the upstream control device 28 derives the required braking force based on at least one of the pedal stroke S detected by the stroke sensor 280 and the master pressure P0 detected by the master pressure sensor 281. In the case of automatic braking, upstream controller 28 obtains the requested braking force transmitted from other controllers. The upstream control device 28 drives the electric motor 233 so that the hydraulic pressure in the slave cylinder 230 increases as the required braking force increases.

In the following description, the hydraulic pressure of the left and right

front wheel cylinders

11L and 11R is referred to as "front wheel pressure Pf", and the hydraulic pressure of the left and right

rear wheel cylinders

12L and 12R is referred to as "rear wheel pressure Pr".

<Braking force control at abnormal time>
Braking force control when an abnormality occurs in the upstream pressurizing section 20 will be described. The "abnormality of the upstream pressure unit 20" here means a state in which at least one of the following conditions (A1) and (A2) is satisfied.
(A1) When power supply to the upstream pressure unit 20 is unintentionally stopped.
(A2) When an abnormality such as a failure occurs in the electric motor 233 of the electric cylinder device 23 .

When condition (A1) occurs, the electric motor 233, the master cut valve 24, the system cutoff valve 25, and the simulator cut valve 26 cannot be driven. Therefore, the upstream control device 28 cannot adjust the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels by operating the electric cylinder device 23 .

When condition (A2) occurs, the upstream control device 28 cannot operate the electric cylinder device 23. Therefore, the upstream control device 28 closes the system shutoff valve 25 and the simulator cut valve 26 and opens the master cut valve 24 .

When the downstream control device 35 detects such an abnormality in the upstream pressurizing unit 20, the downstream control device 35 adjusts the wheel pressure Pf of the front wheels by operating the master cylinder 22 caused by the operation of the brake pedal 15 by the driver, and controls the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels through the control of the front wheel side assist device 31 and the rear wheel side assist device 32, thereby controlling the braking force of the vehicle.

<Control of downstream control device 35>
A processing routine executed by the downstream control device 35 when determining whether or not an abnormality has occurred in the upstream pressurizing section 20 will be described with reference to FIG. 2 . This processing routine is repeatedly executed by the downstream control device 35 for each predetermined control cycle.

At step S11 in this processing routine, the downstream control device 35 determines whether or not the abnormality detection flag FLG1 is set to OFF. The abnormality detection flag FLG1 is set to ON when the downstream control device 35 detects that an abnormality has occurred in the upstream pressure unit 20, and is set to OFF when the downstream control device 35 has not detected that an abnormality has occurred. When the abnormality detection flag FLG1 is set to OFF (S11: YES), the downstream control device 35 shifts the process to step S13.

In step S13, the downstream control device 35 executes upstream abnormality detection processing. The upstream abnormality detection process is a process for detecting the occurrence of abnormality in the upstream pressure unit 20 . As described above, the downstream controller 35 and the upstream controller 28 communicate with each other. When the downstream control device 35 receives from the upstream control device 28 that the electric motor 233 of the electric cylinder device 23 cannot be driven, the downstream control device 35 determines that an abnormality has occurred in the upstream pressurizing section 20 . The downstream control device 35 may determine that an abnormality has occurred in the upstream pressurizing section 20 even when communication with the upstream control device 28 is not possible. When a communication error occurs between the upstream control device 28 and the downstream control device 35 in this way, the upstream control device 28 may stop controlling the electric motor 233 . On the other hand, when the downstream control device 35 receives from the upstream control device 28 that the upstream pressurizing unit 20 is normal, it determines that the upstream pressurizing unit 20 is not abnormal. Then, when the downstream control device 35 determines that the upstream pressure unit 20 is abnormal, it detects that the electric motor 233 of the electric cylinder device 23 cannot be driven.

After executing the upstream abnormality detection process, the downstream control device 35 shifts the process to step S15. When downstream control device 35 detects that an abnormality has occurred in upstream pressure unit 20 in step S15 (YES), it sets an abnormality detection flag FLG1 to ON in step S17, and then terminates this processing routine. On the other hand, if the downstream control device 35 does not detect that the upstream pressure unit 20 is abnormal in step S15 (NO), the processing routine is once terminated. That is, the abnormality detection flag FLG1 remains off.

On the other hand, if the abnormality detection flag FLG1 is set to ON in step S11 (NO), the downstream control device 35 shifts the process to step S21. In step S21, the downstream control device 35 executes upstream return detection processing. The upstream return detection process is a process for detecting that the upstream pressure unit 20 has returned to normal. When receiving from the upstream control device 28 that the upstream pressurizing unit 20 is normal, the downstream control device 35 determines that the upstream pressurizing unit 20 is no longer abnormal and the upstream pressurizing unit 20 returns to normal. That is, the downstream control device 35 determines that the electric motor 233 of the electric cylinder device 23 can be driven. On the other hand, when the downstream control device 35 receives from the upstream control device 28 that the electric motor 233 of the electric cylinder device 23 cannot be driven or cannot communicate with the upstream control device 28, it determines that the upstream pressure unit 20 has not returned to normal.

After executing the upstream return detection process, the downstream control device 35 shifts the process to step S23. When the downstream control device 35 detects that the upstream pressure unit 20 has returned to normal in step S23 (YES), it sets the abnormality detection flag FLG1 to OFF in step S25, and then terminates this processing routine. On the other hand, if the downstream control device 35 does not detect that the upstream pressurizing section 20 has returned to normal in step S23 (NO), the processing routine is once terminated. That is, the abnormality detection flag FLG1 remains set to ON.

Next, with reference to FIG. 3, a processing routine executed by the downstream control device 35 when the vehicle is running will be described. This processing routine is repeatedly executed for each predetermined control cycle while the vehicle is running.

In step S31 of this processing routine, the downstream control device 35 determines whether or not the abnormality detection flag FLG1 is set to ON. If the abnormality detection flag FLG1 is set to OFF (S31: NO), the downstream control device 35 once terminates this processing routine. On the other hand, when the abnormality detection flag FLG1 is set to ON (S31: YES), the downstream control device 35 shifts the process to step S33.

In step S33, the downstream control device 35 determines whether there is a possibility that residual pressure is generated in the

wheel cylinders

12L, 12R of the rear wheels.
Here, a case where residual pressure is generated in the

wheel cylinders

12L and 12R of the rear wheels will be described. If an abnormality occurs in the upstream pressurizing section 20 while the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels are being adjusted by the operation of the electric cylinder device 23, the electric motor 233 will not be driven. For example, if an abnormality occurs in the electric motor 233 while the piston 231 is moving in the braking direction Za from the reference position, the driving torque of the electric motor 233 acting on the piston 231 in the braking direction Za ceases to be generated. Therefore, the brake fluid flows from the

wheel cylinders

12L, 12R toward the slave cylinder 230. As shown in FIG. As a result, the piston 231 of the slave cylinder 230 tries to return to the reference position due to the brake fluid pressure flowing into the fluid chamber 232 from the output port 237 . Further, when an abnormality occurs in the upstream pressurizing section 20, the system cutoff valve 25 is closed and the master cut valve 24 is opened. As a result, the

wheel cylinders

11L and 11R of the front wheels communicate with the master cylinder 22 after communication with the slave cylinder 230 is cut off. As a result, the brake fluid in the

wheel cylinders

11L and 11R for the front wheels is not returned to the slave cylinder 230. Therefore, the brake fluid pressure flowing from the output port 237 into the slave cylinder 230 does not increase so much. Further, in this embodiment, the slave cylinder 230 is not provided with a return spring. Furthermore, when the brake fluid pressure flowing into the slave cylinder 230 causes the piston 231 to return to the reference position, the electric cylinder device 23 generates sliding resistance that prevents the piston 231 from moving in the release direction Zb. Therefore, when an abnormality occurs in the upstream pressurizing unit 20 while the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels are being adjusted by the operation of the electric cylinder device 23, the piston 231 may not return to the reference position in the slave cylinder 230. If the piston 231 does not return to the reference position, residual pressure will be generated in the

wheel cylinders

12L and 12R of the rear wheels. When the brake pedal 15 is not operated such as when the vehicle is running, the brake fluid in the

wheel cylinders

11L and 11R of the front wheels is returned to the reserve tank 21 through the master cylinder 22. Therefore, even if an abnormality occurs in the upstream pressurizing part 20 while the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels are being adjusted by the operation of the electric cylinder device 23, residual pressure is not generated in the

wheel cylinders

11L and 11R of the front wheels.

Therefore, if the abnormality detection flag FLG1 is switched from OFF to ON while the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels are being adjusted by operating the electric cylinder device 23, it can be considered that residual pressure may be generated in the

wheel cylinders

12L and 12R of the rear wheels. If it is determined in step S33 that the

wheel cylinders

12L and 12R of the rear wheels may have residual pressure (YES), the downstream control device 35 proceeds to step S35. On the other hand, if it is not determined that the

wheel cylinders

12L and 12R of the rear wheels may have residual pressure (S33: NO), the downstream control device 35 temporarily terminates this processing routine.

In step S35, the downstream control device 35 determines whether or not the conditions for executing the processing during running are satisfied. In the present embodiment, the downstream control device 35 determines that the execution conditions for the running process are satisfied when both of the following conditions (B1) and (B2) are satisfied.
(B1) The accumulated elapsed time of the vehicle not stopped from the wheel speed sensor values after the previous execution of the running process has reached a predetermined first interval time TM1.
(B2) Vehicle deceleration is not requested.

Although the details will be described later, the running process is a process of reducing the wheel pressure Pr of the rear wheels. Even if the wheel pressure Pr is reduced by executing the running process, when the rear wheels are rotating in a state where the friction material is in contact with the part to be rubbed that rotates integrally with the rear wheels in the friction brake for the rear wheels, the temperature of the brake fluid in the

wheel cylinders

12L and 12R rises due to the heat of friction, and the brake fluid expands. At this time, if the piston 231 of the electric cylinder device 23 does not return to the reference position, the wheel pressure Pr may increase because the fluid paths connecting the

wheel cylinders

12L, 12R and the electric cylinder device 23 are sealed. Therefore, when the condition (B1) is satisfied, the downstream control device 35 considers that the wheel pressure Pr has increased due to the effect of the frictional heat.

When the vehicle is required to decelerate, it is considered that there will be no major problem even if the wheel pressure Pr increases due to the above frictional heat. The case where the vehicle is requested to decelerate can be said to be the case where the vehicle is requested to brake. On the other hand, when the vehicle is not required to decelerate, it can be said that the vehicle is not required to brake.

Therefore, the downstream control device 35 determines that the execution condition is satisfied when both the conditions (B1) and (B2) are satisfied. On the other hand, the downstream control device 35 determines that the execution condition is not satisfied when at least one of the conditions (B1) and (B2) is not satisfied.

Note that the downstream control device 35 varies the predetermined first interval time TM1 according to the rotational speed of the rear wheels. Specifically, the downstream control device 35 sets a shorter time as the predetermined first interval time TM1 as the rotational speed of the rear wheels increases. This is because the greater the rotational speed of the rear wheels, the greater the amount of frictional heat generated by the rear wheel friction brakes.

When it is determined in step S35 that the conditions for executing the process during running are satisfied (YES), the downstream control device 35 shifts the process to step S37. On the other hand, if it is determined that the execution condition is not satisfied (S35: NO), the downstream control device 35 once terminates this processing routine without executing the processing during running.

In step S37, the downstream control device 35 executes running processing. That is, the downstream control device 35 executes the running process when the vehicle is running, it is detected that the electric motor 233 cannot be driven, and there is no braking request. After completing the running process, the downstream control device 35 once ends this process routine.

Referring to FIG. 4, the processing during running will be described in detail.
In the example shown in FIG. 4, the execution conditions for the running process are established at timings t11, t13, and t15. In the running process, the downstream control device 35 operates the rear wheel side assist device 32 as shown in (A) to (D) of FIG. 4 to reduce the wheel pressure Pr of the rear wheels as shown in (E) of FIG. In the running process, the downstream control device 35 operates the pump 304 of the rear wheel side assisting device 32, opens the differential pressure control valve 301 of the rear wheel side assisting device 32, closes the holding valve 302 of the rear wheel side assisting device 32, and opens the pressure reducing valve 303 of the rear wheel side assisting device 32.

When the rear wheel assisting device 32 is operated in this way, the pump 304 sucks the brake fluid in the

wheel cylinders

12L and 12R of the rear wheels, and the pump 304 discharges the brake fluid to the fluid passage 308 between the differential pressure control valve 301 and the holding valve 302. Since the holding valve 302 is closed and the differential pressure control valve 301 is open, the brake fluid discharged from the pump 304 passes through the differential pressure control valve 301 and flows into the slave cylinder 230 . As a result, the wheel pressure Pr of the rear wheels is reduced. Furthermore, since the pressure corresponding to the discharge pressure of the pump 304 acts on the piston 231 of the slave cylinder 230, the piston 231 can be moved toward the reference position as shown in FIG. 4(F).

In the example shown in FIG. 4, execution of the running process ends at timings t12, t14, and t16. Then, the downstream control device 35 stops the operation of the rear wheel side assist device 32 . That is, the downstream control device 35 stops driving the pump 304 , the differential pressure control valve 301 , the holding valve 302 and the pressure reducing valve 303 of the rear wheel side assisting device 32 .

A processing routine executed by the downstream control device 35 when the vehicle is stopped will be described with reference to FIG. This processing routine is repeatedly executed for each predetermined control cycle when the vehicle is stopped.

At step S41 in this processing routine, the downstream control device 35 determines whether or not the abnormality detection flag FLG1 is set to ON. If the abnormality detection flag FLG1 is set to OFF (S41: NO), the downstream control device 35 once terminates this processing routine. On the other hand, when the abnormality detection flag FLG1 is set to ON (S41: YES), the downstream control device 35 shifts the process to step S43.

In step S43, the downstream control device 35 determines whether there is a possibility that residual pressure is generated in the

wheel cylinders

12L and 12R of the rear wheels, similar to the process of step S33 shown in FIG. When determining that there is a possibility that residual pressure is generated in the

wheel cylinders

12L and 12R of the rear wheels (S43: YES), the downstream control device 35 shifts the process to step S45. On the other hand, if it is not determined that there is a possibility that residual pressure is generated in the

wheel cylinders

12L, 12R (S43: NO), the downstream control device 35 once terminates this processing routine.

In step S45, the downstream control device 35 determines whether or not the conditions for executing the vehicle stop processing are satisfied. In the present embodiment, the downstream control device 35 determines that the execution condition is met when the elapsed time since the last execution of the vehicle stop process reaches the predetermined second interval time TM2. On the other hand, the downstream control device 35 determines that the execution condition is not met when the elapsed time since the last execution of the vehicle stop process has not reached the second predetermined interval time TM2. A time longer than the execution cycle of the processing routine shown in FIG. 5 is set as the second interval time TM2.

When it is determined in step S45 that the conditions for executing the process when the vehicle is stopped are satisfied (YES), the downstream control device 35 shifts the process to step S47. On the other hand, if it is determined that the execution condition is not satisfied (S45: NO), the downstream control device 35 temporarily terminates this processing routine without executing the vehicle stop processing.

In step S47, the downstream control device 35 executes the vehicle stopping process. That is, when the downstream control device 35 detects that the vehicle is stopped and the electric motor 233 cannot be driven, the downstream control device 35 executes the vehicle stop processing. After completing the execution of the vehicle stop processing, the downstream control device 35 temporarily ends this processing routine.

With reference to FIG. 6, the processing at the time of stop will be described in detail.
In the example shown in FIG. 6, the conditions for executing the stop processing are established at timings t21, t23, and t25. In the vehicle stop processing, the downstream control device 35 operates the rear wheel side assisting device 32 as shown in FIGS. That is, the downstream control device 35 increases the wheel pressure Pr of the rear wheels as shown in FIG. 6(E). Specifically, the downstream control device 35 operates the pump 304 of the rear wheel side assisting device 32 to reduce the indicated opening degree of the differential pressure control valve 301 of the rear wheel side assisting device 32 . At this time, the downstream control device 35 keeps the holding valve 302 of the rear wheel side assisting device 32 open and the pressure reducing valve 303 of the rear wheel side assisting device 32 closed.

When the rear wheel side assist device 32 is operated in this way, the pump 304 sucks the brake fluid in the slave cylinder 230 . When the pressure in the liquid chamber 232 of the slave cylinder 230 is reduced due to the suction of the pump 304, the cup seal 238 is deformed. As a result, a gap is created between the inner wall of the slave cylinder 230 and the piston 231, and the pump 304 sucks the brake fluid from the reserve tank 21 through the gap. A pump 304 discharges brake fluid to a fluid passage 308 closer to the

wheel cylinders

12L and 12R than the differential pressure control valve 301 is. As a result, the brake fluid discharged from the pump 304 flows into the

wheel cylinders

12L, 12R, increasing the wheel pressure Pr of the rear wheels.

Then, at timings t22, t24, and t26, the downstream control device 35 stops the operation of the rear wheel side assisting device 32 and ends the vehicle stop processing. That is, the downstream control device 35 stops the pump 304 and sets the indicated degree of opening of the differential pressure control valve 301 to 100% to open the differential pressure control valve 301 . When the differential pressure control valve 301 is opened with the differential pressure between the

wheel cylinders

12L, 12R and the slave cylinder 230 thus increased, brake fluid flows into the slave cylinder 230 from the

wheel cylinders

12L, 12R. That is, in the stop processing, after the rear wheel side assist device 32 is operated to increase the differential pressure, the increase in the differential pressure is stopped and the differential pressure control valve 301 is opened, thereby causing the brake fluid to flow from the

wheel cylinders

12L, 12R to the slave cylinder 230. As a result, as shown in (F) of FIG. 6 , in slave cylinder 230 , piston 231 moves toward the reference position due to the brake fluid pressure that has flowed into slave cylinder 230 from output port 237 .

If the wheel pressure Pr of the rear wheels is increased or decreased by operating the rear wheel side assist device 32, there is a possibility that the braking force required to keep the vehicle stopped will be insufficient. Therefore, in the present embodiment, it is possible to ensure the wheel pressure Pr of the front wheels by the master cylinder 22 resulting from the operation of the brake pedal 15 by the driver. Further, if the vehicle can be kept stopped by shift gear, EPB, or the like, the same process as the vehicle stop process may be performed on the front wheels to return the piston 231 to the reference position.

<Actions and effects of the present embodiment>
When the vehicle is stopped and it is detected that the electric motor 233 of the electric cylinder device 23 cannot be driven, the vehicle stop processing is executed. When the vehicle stop process is executed, the rear wheel assist device 32 is actuated to increase the differential pressure between the

rear wheel cylinders

12L, 12R and the slave cylinder 230, that is, the wheel pressure Pr of the rear wheels is increased. In this state, the operation of the rear wheel side assist device 32 is stopped, and the differential pressure control valve 301 is opened. Then, a large amount of brake fluid flows from the

wheel cylinders

12L, 12R toward the slave cylinder 230. As shown in FIG. As a result, in the slave cylinder 230, the hydraulic pressure of the brake fluid flowing through the output port 237 can move the piston 231 toward the reference position. Therefore, even if the electric motor 233 cannot be driven and the piston 231 has not returned to the reference position, it is possible to return the piston 231 to the reference position by executing the vehicle stop processing.

As shown in FIG. 6, it may not be possible to return the piston 231 to the reference position by executing the vehicle stop processing only once. In this respect, in the present embodiment, the vehicle stop processing is intermittently executed while the vehicle is stopped. By repeatedly executing the vehicle stop processing in this manner, the piston 231 in the slave cylinder 230 can be gradually brought closer to the reference position, as shown in FIG. 6(F). In the example shown in FIG. 6, the piston 231 returns to the reference position by executing the vehicle stop processing three times.

By the way, if residual pressure is generated in the

wheel cylinders

12L and 12R of the rear wheels while the vehicle is running, the driver of the vehicle will feel dragged. Therefore, in this embodiment, when the vehicle is running and it is detected that the electric motor 233 of the electric cylinder device 23 is disabled, the running process is executed. When the running process is executed, the brake fluid in the

wheel cylinders

12L and 12R of the rear wheels is returned to the slave cylinder 230 by the operation of the rear wheel side assisting device 32 . As a result, the wheel pressure Pr of the rear wheels can be reduced as shown in FIG. 4(E). Therefore, it is possible to prevent the driver from feeling dragged while the vehicle is running.

Furthermore, the execution of the running process causes the brake fluid to flow into the slave cylinder 230 from the output port 237 . As a result, the piston 231 in the slave cylinder 230 can be moved toward the reference position, as shown in FIG. 4(F).

Even if the brake fluid in the

wheel cylinders

12L and 12R is reduced by executing the running process while the vehicle is running, the friction brake for the rear wheels may continue to contact the friction part that rotates integrally with the rear wheel. In this case, frictional heat is generated in the friction brakes, the temperature of the brake fluid in the

wheel cylinders

12L, 12R rises, and the wheel pressure Pr of the rear wheels rises again.

In this embodiment, as shown in FIG. 4, while the vehicle is running, the running process is intermittently and repeatedly executed. As a result, it is possible to enhance the effect of suppressing the driver from feeling dragged while the vehicle is running.

Note that if the vehicle continues to travel at low speed, the temperature of the friction material of the friction brake will not rise that much. Therefore, the execution interval of the running process may be lengthened. In other words, the higher the running speed, the shorter the interval at which the running process is executed. For example, by varying the predetermined first interval time TM1, it is possible to adjust the execution interval of the running process.

By the way, even while the vehicle is running, it may be necessary to decelerate the vehicle by operating the brake pedal 15 or the like. That is, there may be a braking request. In this embodiment, the running process is not executed when there is a braking request while the vehicle is running. As a result, it is possible to suppress an increase in the frequency of operation of the rear wheel side assist device 32 .

<Change example>
The above embodiment can be implemented with the following modifications. The above embodiments and the following modifications can be combined with each other within a technically consistent range.

The upstream pressurizing section may have a configuration different from that of the upstream pressurizing section 20 shown in FIG.
FIG. 7 shows an upstream pressurizing section 20A of a modified example. The upstream pressurizing section 20A includes a master cylinder 22A, a stroke simulator 27, and an electric cylinder device 23. As shown in FIG.

The configuration of the master cylinder 22A is described, for example, in "Japanese Unexamined Patent Application Publication No. 2021-49935". The master cylinder 22A includes a main cylinder 41, a cover cylinder 42, a master piston 43 and an input piston 44. A brake pedal 15 is connected to the input piston 44 . A master chamber 411 , a first hydraulic chamber 412 and a servo chamber 413 are defined in the main cylinder 41 by the master piston 43 . A second hydraulic chamber 421 and a third hydraulic chamber 422 are defined in the cover cylinder 42 . A master spring 45 is provided in the main cylinder 41 to bias the master piston 43 in a direction to increase the volume of the master chamber 411 . An input spring 46 is provided in the cover cylinder 42 to bias the input piston 44 in a direction to increase the volume of the second hydraulic pressure chamber 421 .

The slave cylinder 230 of the electric cylinder device 23 is connected to the servo chamber 413 in the upstream pressure section 20A. That is, the electric cylinder device 23 can supply the brake fluid to the

wheel cylinders

12L and 12R of the rear wheels and the servo chamber 413 . In addition, the upstream pressurization section 20A has a plurality of control valves 52,53.

When the upstream pressurizing section 20A is normal, the control valve 52 is opened and the control valve 53 is closed. In this state, the second hydraulic chamber 421 is hydraulically connected to the stroke simulator 27 and is hydraulically disconnected from the reserve tank 21 . When the brake pedal 15 is operated in this state, the pedal feeling is supplied to the brake pedal 15 by the stroke simulator 27 . With the control valve 52 opened and the control valve 53 closed, the electric cylinder device 23 outputs brake fluid from the output port 237 according to the amount of operation of the brake pedal 15 . The output brake fluid is supplied to the second fluid passage 14 and the servo chamber 413 . By supplying the brake fluid to the servo chamber 413 , the master piston 43 slides in the direction of decreasing the volume of the master chamber 411 . Brake fluid is supplied from the master chamber 411 to the first fluid passage 13 as the master piston 43 slides in this manner. Thus, in normal operation, the upstream pressurizing section 20A controls the electric cylinder device 23 and the control valves 52 and 53 to supply brake fluid to the first fluid passage 13 and the second fluid passage 14, respectively.

When an abnormality occurs in the upstream pressurizing section 20A, the control valves 52 and 53 are de-energized. Then, the control valve 52 is closed and the control valve 53 is opened. As a result, the reserve tank 21 is connected to the first hydraulic pressure chamber 412 and the stroke simulator 27 . Also, the reserve tank 21 is isolated from the second hydraulic pressure chamber 421 . As a result, the second hydraulic chamber 421 is closed, and the pedal force applied to the brake pedal 15 is transmitted to the master piston 43 via the brake fluid sealed in the input piston 44 and the second hydraulic chamber 421 . The first fluid passage 13 at this time is connected to the master chamber 411 of the master cylinder 22A. Therefore, in the brake control device 10 at this time, the front wheel side assist device 31 increases the pressure of the brake fluid output from the master cylinder 22A and sends it to the

wheel cylinders

11L and 11R of the front wheels, thereby generating braking force for the front wheels. Also, in the braking control device 10 at this time, the rear wheel side assist device 32 sends brake fluid to the

wheel cylinders

12L and 12R of the rear wheels independently of the master cylinder 22A, thereby generating braking force for the rear wheels.

Under the circumstances where the upstream pressurizing section 20A is normal and the wheel pressure Pr of the rear wheel is adjusted by the operation of the electric cylinder device 23 as described above, an abnormality may occur in the upstream pressurizing section 20A and the electric motor 233 may become inoperable. In this case, the control valve 52 is closed and the control valve 53 is opened as described above. At this time, the downstream control device 35 executes the processing when the vehicle is stopped and the processing when the vehicle is running, so that the same functions and effects as those of the above-described embodiment can be obtained.

Also, in the modification shown in FIG. 7, there is a possibility that the piston 231 of the slave cylinder 230 will not return to the reference position due to the electric motor 233 not being driven. In this case, hydraulic pressure may remain in the servo chamber 413 of the master cylinder 22A. If the hydraulic pressure remains in the servo chamber 413 and the master piston 43 does not return to the reference position, hydraulic pressure may be generated in the

wheel cylinders

11L and 11R of the front wheels. Therefore, in the modification shown in FIG. 7, the front-wheel-side assisting device 31 may be controlled to perform processing corresponding to the stop processing and the running processing for the

wheel cylinders

11L and 11R of the front wheels. For example, the front wheel side assisting device 31 may be controlled so that the brake fluid flows from the front wheel side assisting device 31 to the master chamber 411 .

When the vehicle stop processing is being executed, the wheel pressure Pf of the front wheels may be increased by operating the front wheel side assist device 31 .
In the above embodiment, the predetermined first time interval TM1 that defines the execution interval of the running process is varied according to the rotational speed of the rear wheels, but the first time interval TM1 may be varied based on parameters other than the rotational speed of the rear wheels. For example, the higher the brake fluid temperature or the outside air temperature, the shorter the first interval time TM1 may be set. Further, the first time interval TM1 may be set according to the estimated temperature of the friction material of the friction brake, which takes into account not only the running of the vehicle but also the heat generated by braking during deceleration.

· It can be inferred that the higher the braking frequency of the vehicle, the more opportunities there are for residual pressure to occur in the

wheel cylinders

12L and 12R of the rear wheels. Therefore, it is preferable to intermittently execute the running process at shorter intervals as the braking frequency increases while the vehicle is running.

- It is not necessary to change the first interval time TM1.
- The condition for executing the process during running does not have to include the fact that deceleration of the vehicle is requested, that is, there is no braking request.

- It is not necessary to intermittently repeat the running process while the vehicle is running.
When the vehicle is running, it is detected that the electric motor 233 has become undrivable, and there is a possibility that residual pressure is generated in the

wheel cylinders

12L and 12R of the rear wheels, the running process may continue to be executed while the vehicle is running.

The downstream control device 35 does not have to execute the running process while the vehicle is running, as long as the vehicle stopping process is executed when the vehicle is stopped.
- The downstream control device 35 does not have to execute the process when the vehicle is stopped if the process when the vehicle is running is to be executed while the vehicle is running. In this case, the rear wheel side assist device 32 may be configured without the differential pressure control valve 301 .

· In the above embodiment, the stop processing is intermittently repeated while the vehicle is stopped, but the present invention is not limited to this. For example, during one stop period, the stop process may be executed only once.

· In the above embodiment, when it is determined in step S43 of FIG. 5 that there is a possibility that residual pressure is generated, the process proceeds to step S45, but the determination in step S43 may be omitted. In this case, when the abnormality detection flag FLG1 is set to ON, it is preferable to shift to the process of step S45 and determine whether or not the conditions for executing the process when the vehicle is stopped are satisfied.

The braking control device may be configured so that the

wheel cylinders

11L and 11R for the front wheels are the first wheel cylinders, the

wheel cylinders

12L and 12R for the rear wheels are the second wheel cylinders, the front wheel side force device 31 is the first pressure unit, and the rear wheel side force force device 32 is the second pressure unit. That is, the applicable wheels may be applied individually or in any combination.

The rear-wheel-side assisting device may have a pressurizing device other than the pump 304 that can supply the brake fluid to the fluid passage between the differential pressure control valve 301 and the holding valve 302 .
The electric cylinder device 23 may have a configuration in which a return spring is provided in the slave cylinder 230 to bias the piston 231 in the release direction Zb. If the biasing force of this return spring is relatively small, the piston 231 cannot be returned to the reference position only by the biasing force of the return spring. In the braking control device 10 having such an electric cylinder device 23, the effects equivalent to those of the above-described embodiment can be obtained by executing the stop-time processing and the running-time processing.

- The downstream control device 35 can be configured as a circuit that includes one or more dedicated hardware circuits such as one or more processors that operate according to a computer program, dedicated hardware that executes at least part of various types of processing, or a combination thereof. Dedicated hardware may include, for example, an ASIC, which is an application specific integrated circuit. A processor includes a CPU and memory, such as RAM and ROM, which stores program code or instructions configured to cause the CPU to perform processes. Memory or storage media includes any available media that can be accessed by a general purpose or special purpose computer.

Claims

A braking control device that generates a braking force at a vehicle wheel by adjusting hydraulic pressure in a wheel cylinder,
an electric cylinder device comprising a slave cylinder, a piston slidable within the slave cylinder, and an electric motor capable of generating a driving force for sliding the piston, the electric cylinder device supplying brake fluid from the fluid chamber to the wheel cylinder through a fluid path by moving the piston so as to reduce the volume of a fluid chamber formed in the slave cylinder;
a pressurizing unit having an electromagnetic valve arranged in the fluid path and a pressurizing device capable of supplying brake fluid to a portion of the fluid path closer to the wheel cylinder than the electromagnetic valve;
A control unit that controls the pressure unit,
The control unit
When the vehicle is stopped and it is detected that the electric motor has become inoperable,
A braking control device for executing stop-time processing for causing brake fluid to flow from the wheel cylinder to the fluid chamber of the slave cylinder by opening the electromagnetic valve after controlling the pressurizing unit so that the pressure in a portion of the fluid passage closer to the wheel cylinder than the electromagnetic valve is higher than the pressure in a portion closer to the slave cylinder than the electromagnetic valve by supplying brake fluid to the pressurizing device while the electromagnetic valve is closed.
A braking control device that generates a braking force at a vehicle wheel by adjusting the hydraulic pressure of a wheel cylinder,
an electric cylinder device comprising a slave cylinder, a piston slidable within the slave cylinder, and an electric motor capable of generating a driving force for sliding the piston, the electric cylinder device supplying brake fluid from the fluid chamber to the wheel cylinder through a fluid path by moving the piston so as to reduce the volume of a fluid chamber formed in the slave cylinder;
a pressurization unit having a holding valve disposed in the fluid path, a pressure reducing valve that reduces the hydraulic pressure of the wheel cylinder when the valve is open, and a pressurizing device that can supply brake fluid sucked from the wheel cylinder via the pressure reducing valve when the pressure reducing valve is open to a portion of the fluid path closer to the slave cylinder than the holding valve;
A control unit that controls the pressure unit,
The control unit
When the vehicle is running, it is detected that the electric motor has become inoperable, and there is no braking request,
A braking control device that executes a running process of opening the pressure reducing valve, closing the holding valve, and operating the pressurization device.
The solenoid valve is a differential pressure control valve,
The pressure unit is
a holding valve, which is an electromagnetic valve disposed in a portion of the fluid path between the differential pressure control valve and the wheel cylinder and which is closed when restricting an increase in fluid pressure in the wheel cylinder;
a pressure reducing valve, which is an electromagnetic valve that is opened when brake fluid flows out from the wheel cylinder,
The pressurizing device is a pump that sucks the brake fluid in the wheel cylinder via the pressure reducing valve when the pressure reducing valve is open and discharges the brake fluid to a portion of the fluid passage between the differential pressure control valve and the holding valve,
The control unit
When the vehicle is running and it is detected that the electric motor has become inoperable,
2. The braking control device according to claim 1, wherein running processing is executed to open the pressure reducing valve and the differential pressure control valve, close the holding valve, and operate the pressurizing device.
4. The braking control device according to claim 2, wherein the control unit intermittently executes the running process at shorter intervals as the running speed of the vehicle increases or as the braking frequency of the vehicle increases during running of the vehicle.