Braking control device

Abstract

To enable a piston to be retuned to a reference position, even if an electric motor cannot be driven, so that the piston is not returned to the reference position.SOLUTION: A braking control device 10 comprises an electric cylinder device 23 using an electric motor 233 as a power source, a rear wheel-side assisting device 32 having a differential pressure control valve 301 and a pump 304, and a downstream control device 35 that controls the rear wheel-side assisting device 32. The downstream control device 35, when sensing that a vehicle is stopped and the electric motor 233 cannot be driven, activates the pump 304 while making the differential pressure control valve 301 open, so as to make pressure at wheel cylinders 12L and 12R sides higher than pressure at the differential pressure control valve 301 and make pressure at a slave cylinder 230 side higher than pressure at the differential pressure control valve 301, and then executes a stop-time process in which brake liquid is caused to flow from the wheel cylinders 12L and 12R into a liquid chamber 232 of the slave cylinder 230 by making the differential pressure control valve 301 open.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a brake control device that generates braking force on vehicle wheels by adjusting hydraulic pressure in wheel cylinders. [Background technology]

[0002] The braking control device disclosed in Patent Document 1 includes an electric cylinder device and a control unit. The electric cylinder device includes a slave cylinder and an electric motor that is the power source for the slave cylinder. No return spring is disposed inside the slave cylinder of this electric cylinder device. When the electric motor is driven by the control unit, a piston in the slave cylinder moves from a reference position. 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 a braking force corresponding to this hydraulic pressure is generated on the wheel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5946544 Summary of the Invention [Problem to be solved by the invention]

[0004] Consider a situation where hydraulic pressure in a wheel cylinder is adjusted by the operation of an electric cylinder device, and an abnormality occurs in at least one of the control unit and the electric motor, rendering the electric motor unable to operate. In this case, brake fluid returns from the wheel cylinder to the slave cylinder, causing the piston in the slave cylinder to attempt to move toward its reference position. However, sliding resistance occurs in the electric cylinder device that prevents the piston from moving, so the piston may not be able to return to its reference position. If the piston does not return to its reference position, hydraulic pressure may remain in the wheel cylinder.

[0005] This problem can occur even if a return spring with a relatively small force is disposed in the slave cylinder to bias the piston toward the reference position. [Means for solving the problem]

[0006] One aspect of a brake control device that solves the above problems is a device that generates braking force on vehicle wheels by adjusting hydraulic pressure in wheel cylinders. This brake control device includes an electric cylinder device that has a slave cylinder, a piston slidable within the slave cylinder, and an electric motor that is capable of generating driving force to slide the piston, and that supplies brake fluid from the fluid chamber through a fluid passage to the wheel cylinder by moving the piston so as to reduce the volume of a fluid chamber formed in the slave cylinder, a pressure unit that has a solenoid valve arranged in the fluid passage and a pressure device that can supply brake fluid to a portion of the fluid passage that is closer to the wheel cylinder than the solenoid valve, and a control unit that controls the pressure unit. When the control unit detects that the vehicle is stopped and that the electric motor cannot be driven, it controls the pressurizing unit to supply brake fluid to the pressurizing device with the solenoid valve closed, so that the pressure in the part of the fluid path closer to the wheel cylinder than the solenoid valve is higher than the pressure in the part of the fluid path closer to the slave cylinder than the solenoid valve, and then opens the solenoid valve to perform a vehicle-stop process that causes brake fluid to flow from the wheel cylinder to the fluid chamber of the slave cylinder.

[0007] In the above configuration, when the vehicle-stopping process is executed, the pressurizing unit operates to increase the pressure in the portion of the fluid path 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. This increases the pressure differential before the solenoid valve opens, allowing brake fluid to flow from the wheel cylinder to the slave cylinder. This applies pressure to the slave cylinder, allowing the piston in the electric cylinder device to move toward the reference position against the sliding resistance that prevents the piston from moving.

[0008] One aspect of a brake control device for solving the above problem is a device that generates braking force at vehicle wheels by adjusting hydraulic pressure in wheel cylinders. The brake control device includes an electric cylinder device that has a slave cylinder, a piston slidable within the slave cylinder, and an electric motor that is capable of generating a driving force to slide the piston, and that supplies brake fluid from the hydraulic chamber formed in the slave cylinder through a hydraulic passage by moving the piston so as to reduce the volume of the hydraulic chamber formed in the slave cylinder. A pressurizing unit includes a holding valve disposed in the hydraulic passage, a pressure-reducing valve that reduces the hydraulic pressure in the wheel cylinder when open, and a pressurizing device that, when the pressure-reducing valve is open, draws brake fluid from the wheel cylinder through the pressure-reducing valve and supplies it to a portion of the hydraulic passage closer to the slave cylinder than the holding valve. The control unit also includes a control unit that controls the pressurizing unit. When the control unit detects that the electric motor has become inoperable while the vehicle is running and there is no braking request, the control unit executes a driving process that opens the pressure-reducing valve, closes the holding valve, and activates the pressurizing device.

[0009] In the above configuration, when the driving process is executed, the brake fluid in the wheel cylinder is sucked by the pressure device and supplied to the portion of the fluid path closer to the slave cylinder than the pressure device, so that the brake fluid flows from the pressure device to the wheel cylinder. This applies pressure to the slave cylinder, moving the piston toward the reference position against the sliding resistance that prevents the piston from moving in the electric cylinder device.

[0010] Therefore, even if the electric motor cannot be driven and the piston has not returned to the reference position, the braking control device can return the piston to the reference position. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a braking control device according to an embodiment. [Figure 2] FIG. 2 is a flowchart showing a processing routine executed to detect the state of the upstream pressurizing portion of the brake control device. [Figure 3] FIG. 3 is a flowchart showing a processing routine executed when the vehicle is running. [Figure 4] FIG. 4 is a time chart when the driving process is executed. [Figure 5] FIG. 5 is a flowchart showing a processing routine executed when the vehicle is stopped. [Figure 6] FIG. 6 is a time chart when the vehicle stop processing is executed. [Figure 7] FIG. 7 is a schematic diagram showing the configuration of an upstream pressurizing unit according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, one embodiment of a brake control device will be described with reference to FIGS. 1, the braking control device 10 generates braking force at the wheels by adjusting the hydraulic pressure in wheel cylinders 11L, 11R of the left and right front wheels and wheel cylinders 12L, 12R of the left and right rear wheels. The braking control device 10 includes an upstream pressure section 20 and a downstream pressure section 30.

[0013] <Configuration of the upstream pressurizing unit 20> The upstream pressurizing unit 20 is connected to the wheel cylinders 11L, 11R of the left and right front wheels through a first fluid passage 13. The upstream pressurizing unit 20 is connected to the wheel cylinders 12L, 12R of the left and right rear wheels through a second fluid passage 14. The upstream pressurizing unit 20 includes a reserve tank 21, a master cylinder 22, an electric cylinder device 23, a master cut valve 24, a system shutoff 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 pressurizing device that generates hydraulic pressure electrically. The master cut valve 24 and the system shutoff valve 25 constitute a switching mechanism that switches the state of the upstream pressurizing unit 20. The master cut valve 24 is a normally open solenoid valve, and the system shutoff valve 25 is a normally closed solenoid valve. The simulator cut valve 26 is a normally closed solenoid 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 connection is cut off. The upstream control device 28 is an electronic control device that controls the electric cylinder device 23, the master cut valve 24, the system shutoff valve 25, and the simulator cut valve 26.

[0014] <Configuration of master cylinder 22> A master piston 221 is slidably provided inside the master cylinder 22. The master piston 221 defines a pressure chamber 222 into which brake fluid is introduced. The 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 the 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 that increases the volume of the pressure chamber 222.

[0015] The master cylinder 22 also has two ports, an input port 224 and an output port 225, which connect the pressure chamber 222 to 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 or not. The output port 225 of the master cylinder 22 is connected to a stroke simulator 27 via a simulator cut valve 26. The stroke simulator 27 is a device that generates a reaction force in response to the operation of the brake pedal 15. The output port 225 of the master cylinder 22 is also connected to the first fluid path 13 via a master cut valve 24.

[0016] <Configuration of electric cylinder device 23> The electric cylinder device 23 includes a slave cylinder 230, a piston 231 slidable within the slave cylinder 230, an electric motor 233, and a linear motion conversion mechanism 234 that converts the rotation of the electric motor 233 into linear motion of the piston 231. A fluid chamber 232 into which brake fluid is introduced is defined by the piston 231 within the slave cylinder 230. The operating position of the piston 231 within the slave cylinder 230 is changed by the electric motor 233. That is, the electric motor 233 is capable of generating a driving force that causes the piston 231 to slide within the slave cylinder 230. The volume of the fluid chamber 232 changes in response to changes in the operating position of the piston 231. The moving direction of the piston 231 that reduces the volume of the fluid 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." The operating position of the piston 231 at which the volume of the fluid chamber 232 is maximized is referred to as the "reference position."

[0017] The slave cylinder 230 has two ports, an input port 236 and an output port 237, which communicate between the fluid chamber 232 and the outside. The fluid chamber 232 of the slave cylinder 230 is connected to the reserve tank 21 via the input port 236. The input port 236 is open when the piston 231 is at its 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. The output port 237 of the slave cylinder 230 is connected to the second fluid path 14. Furthermore, the output port 237 of the slave cylinder 230 is connected to the first fluid path 13 via the system shut-off valve 25. When the system shut-off valve 25 is open, the first fluid path 13 and the second fluid path 14 are in communication with each other.

[0018] A cup seal 238 is provided further in the braking direction Za than the input port 236, filling the gap between the inner wall of the slave cylinder 230 and the piston 231. A cup seal 239 is provided further in the releasing direction Zb than the input port 236, filling the gap between the inner wall of the slave cylinder 230 and the piston 231. The two cup seals 238, 239 are made of an elastic material.

[0019] <Configuration of the upstream control device 28> The upstream control device 28 is an electronic control device including 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 shutoff 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 detects a pedal stroke S, which is the amount of depression of the brake pedal 15 by the driver. The master pressure sensor 281 detects a master pressure P0, which is the hydraulic pressure output from the output port 225 of the master cylinder 22. The output pressure sensor 282 detects a slave pressure P2, which is the hydraulic pressure output from the output port 237 of the slave cylinder 230. The upstream control device 28 can communicate with a downstream control device 35 provided in the upstream pressurizing unit 20.

[0020] The upstream control device 28 controls the electric cylinder device 23, the master cut valve 24, the system shutoff valve 25, and the simulator cut valve 26 based on the detection results of the stroke sensor 280, the master pressure sensor 281, the output pressure sensor 282, and the like.

[0021] <Configuration of downstream pressurizing unit 30> The downstream pressurizing section 30 is a unit capable of individually adjusting the pressures in the plurality of wheel cylinders 11L, 11R, 12L, and 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 assisting device 32 generates braking force at the rear wheels by adjusting the hydraulic pressure in the wheel cylinders 12L and 12R of the left and right rear wheels. The front-wheel-side assisting device 31 generates braking force at the front wheels by adjusting the hydraulic pressure in the wheel cylinders 11L and 11R of the left and right front wheels. The hydraulic pressure sensor 33 detects the hydraulic pressure P1 supplied to the first hydraulic path 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 this embodiment, the rear-wheel-side assisting device 32 corresponds to the "pressurizing unit," and the downstream control device 35 corresponds to the "control section."

[0022] When the rear wheel assisting device 32 is defined as a "first pressurizing unit" and the wheel cylinder whose hydraulic pressure is adjusted by the first pressurizing unit is defined as a "first wheel cylinder," in this embodiment, the wheel cylinders 12L, 12R of the rear wheels correspond to the first wheel cylinder. When the front wheel assisting device 31 is defined as a "second pressurizing unit" and the wheel cylinder whose hydraulic pressure is adjusted by the second pressurizing unit is defined as a "second wheel cylinder," in this embodiment, the wheel cylinders 11L, 11R of the front wheels correspond to the second wheel cylinder.

[0023] <Configuration of the front wheel side assisting device 31 and the rear wheel side assisting device 32> First, a description will be given of the configuration of the hydraulic circuit for the wheel cylinder 12L in the rear wheel assisting device 32. This hydraulic circuit includes a differential pressure control valve 301, a holding valve 302, a pressure reducing valve 303, a pump 304, a pressure adjusting reservoir 306, and a return fluid path 307.

[0024] The second fluid line 14 is connected to the fluid line 308 via a 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 of the differential pressure control valve 301 and the wheel cylinder 12L side. The differential pressure here refers to the value obtained by subtracting the pressure in the portion of the fluid line closer to the slave cylinder 230 than the differential pressure control valve 301 from the pressure in the portion of the fluid line closer to the wheel cylinder than the differential pressure control valve 301.

[0025] Fluid path 308 is connected to wheel cylinder 12L via retention valve 302. Fluid path 310 connects retention valve 302 to wheel cylinder 11L. Retention valve 302 is a normally open solenoid valve that closes when energized and opens when de-energized. For example, retention valve 302 is closed to restrict an increase in hydraulic pressure in wheel cylinder 12L. Fluid path 310 is connected to pressure regulating reservoir 306 via pressure reducing valve 303. Pressure reducing valve 303 is a normally closed solenoid valve that opens when energized and closes when de-energized. For example, pressure reducing valve 303 is opened to allow brake fluid to flow from wheel cylinder 12L. Pressure reducing valve 303 and pressure regulating reservoir 306 are connected via fluid path 312.

[0026] Fluid path 312 is connected to fluid path 308 through pump fluid path 313. Pump 304 is installed in pump fluid path 313. Pump 304 is operated by the rotation of pump motor 305. Pump 304 corresponds to the "pressurizing device." In response to its operation, pump 304 sucks brake fluid from pressure regulating reservoir 306 and discharges it into fluid path 308. Pump 304 discharges brake fluid to a portion of the fluid path connecting slave cylinder 230 and wheel cylinder 12L, between differential pressure control valve 301 and holding valve 302.

[0027] The pressure regulating reservoir 306 is connected to the second fluid path 14 through the return fluid path 307. When a certain amount of brake fluid is present inside the pressure regulating reservoir 306, the pressure regulating reservoir 306 is disconnected from the return fluid path 307. In this state, the pump 304 sucks the brake fluid from the pressure regulating reservoir 306. On the other hand, when the brake fluid inside the pressure regulating reservoir 306 decreases due to suction by the pump 304, the pressure regulating reservoir 306 is connected to the return fluid path 307. As a result, when the pump 304 is operated with the pressure reducing valve 303 closed, the pump 304 sucks the brake fluid from the second fluid path 14 through the return fluid path 307. On the other hand, when the pump 304 is operated with the pressure reducing valve 303 open, the pump 304 sucks the brake fluid from the wheel cylinder 12L through the pressure reducing valve 303.

[0028] The hydraulic circuit for wheel cylinder 12R in rear-wheel assisting device 32 has the same configuration as the hydraulic circuit for wheel cylinder 12L. The hydraulic circuits for wheel cylinder 12L and wheel cylinder 12R share differential pressure control valve 301, pump 304, pressure regulating reservoir 306, return fluid line 307, fluid line 308, fluid line 312, and pump fluid line 313. The hydraulic circuit for wheel cylinder 12L and the hydraulic circuit for wheel cylinder 12R each have separate holding valve 302, pressure reducing valve 303, and fluid line 310.

[0029] On the other hand, the hydraulic circuits for the wheel cylinders 11L and 11R in the front wheel assisting device 31 have the same configuration as the hydraulic circuits for the wheel cylinders 12L and 12R in the rear wheel assisting device 32. The front wheel assisting device 31 and the rear wheel assisting device 32 share a pump motor 305.

[0030] <Downstream control device 35> Like the upstream control device 28, the downstream control device 35 is also configured as an electronic control device. The downstream control device 35 controls the front wheel assisting device 31 and the rear wheel assisting device 32. In addition, detection signals from a stroke sensor 350 and a hydraulic pressure sensor 33 are input to the downstream control device 35. The stroke sensor 350 is a sensor for detecting the pedal stroke S, separate from the above-mentioned stroke sensor 280. In addition, although not shown, detection signals from wheel speed sensors provided on each wheel are also input to the downstream control device 35.

[0031] <Normal braking force control> Braking force control when the upstream pressurizing unit 20 is normal will be described. Under normal conditions, the upstream control device 28 closes the master cut valve 24 and opens the system shutoff valve 25 and simulator cut valve 26. This causes the output port 237 of the slave cylinder 230 to be connected to both the first fluid line 13 and the second fluid line 14. Meanwhile, 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 line 13 or the second fluid line 14. In other words, in this state, the brake control device 10 connects both the front wheel assisting device 31 and the rear wheel assisting device 32 to the reserve tank 21 via the slave cylinder 230. In this state, brake fluid discharged from the slave cylinder 230 is sent to the wheel cylinders 11L, 11R, 12L, and 12R.

[0032] Under normal conditions, the upstream control device 28 controls the braking force of the vehicle by adjusting the hydraulic pressure in the wheel cylinders 11L, 11R, 12L, and 12R through 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, the upstream control device 28 acquires the required braking force transmitted from another control device. Then, 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.

[0033] In the following description, the hydraulic pressure in the left and right front wheel cylinders 11L, 11R will be referred to as "front wheel pressure Pf," and the hydraulic pressure in the left and right rear wheel cylinders 12L, 12R will be referred to as "rear wheel pressure Pr."

[0034] <Braking force control during abnormal conditions> A description will be given of braking force control when an abnormality occurs in the upstream pressurizing unit 20. Here, "abnormality in the upstream pressurizing unit 20" refers to a state in which at least one of the following conditions (A1) and (A2) is satisfied. (A1) When the supply of power to the upstream pressurizing unit 20 is stopped unintentionally. (A2) When an abnormality such as a breakdown occurs in the electric motor 233 of the electric cylinder device 23.

[0035] When the condition (A1) occurs, it becomes impossible to drive the electric motor 233, the master cut valve 24, the system shutoff valve 25, and the simulator cut valve 26. 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.

[0036] When the 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.

[0037] When the downstream control device 35 detects such an abnormality in the upstream pressurizing section 20, the downstream control device 35 adjusts the wheel pressure Pf of the front wheels by operating the master cylinder 22 due to the driver's operation of the brake pedal 15, and controls the braking force of the vehicle by adjusting the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels through control of the front wheel assisting device 31 and the rear wheel assisting device 32.

[0038] <Control of the downstream control device 35> 2, a processing routine executed by the downstream control device 35 when determining whether or not an abnormality has occurred in the upstream pressurizing unit 20 will be described. This processing routine is repeatedly executed by the downstream control device 35 at predetermined control cycles.

[0039] In step S11 of this processing routine, the downstream control device 35 determines whether 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 pressurizing unit 20, and is set to OFF when the downstream control device 35 does not detect that an abnormality has occurred. If the abnormality detection flag FLG1 is set to OFF (S11: YES), the downstream control device 35 proceeds to step S13.

[0040] In step S13, the downstream control device 35 executes upstream abnormality detection processing. The upstream abnormality detection processing is processing for detecting the occurrence of an abnormality in the upstream pressurizing unit 20. As described above, the downstream control device 35 and the upstream control device 28 communicate with each other. When the downstream control device 35 receives from the upstream control device 28 a message 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 unit 20. The downstream control device 35 may also determine that an abnormality has occurred in the upstream pressurizing unit 20 when it cannot communicate with the upstream control device 28. In this way, when a communication abnormality occurs between the upstream control device 28 and the downstream control device 35, the upstream control device 28 may stop control of the electric motor 233. On the other hand, when the downstream control device 35 receives from the upstream control device 28 a message that the upstream pressurizing unit 20 is normal, the downstream control device 35 determines that no abnormality has occurred in the upstream pressurizing unit 20. Then, when the downstream control device 35 determines that an abnormality has occurred in the upstream pressurizing unit 20, the downstream control device 35 detects that the electric motor 233 of the electric cylinder device 23 cannot be driven.

[0041] After executing the upstream abnormality detection process, the downstream control device 35 proceeds to step S15. If the downstream control device 35 detects that an abnormality has occurred in the upstream pressurizing unit 20 in step S15 (YES), the downstream control device 35 sets the abnormality detection flag FLG1 to ON in step S17, and then temporarily ends this process routine. On the other hand, if the downstream control device 35 does not detect that an abnormality has occurred in the upstream pressurizing unit 20 in step S15 (NO), the downstream control device 35 temporarily ends this process routine. That is, the abnormality detection flag FLG1 remains set to OFF.

[0042] On the other hand, if the abnormality detection flag FLG1 is set to ON in step S11 (NO), the downstream control device 35 proceeds to step S21. In step S21, the downstream control device 35 executes upstream return detection processing. The upstream return detection processing is processing for detecting that the upstream pressurizing unit 20 has returned to normal. When the downstream control device 35 receives from the upstream control device 28 information that the upstream pressurizing unit 20 is normal, the downstream control device 35 determines that the abnormality in the upstream pressurizing unit 20 has been resolved and that the upstream pressurizing unit 20 has returned to normal. In other words, the downstream control device 35 determines that it has become possible to drive the electric motor 233 of the electric cylinder device 23. On the other hand, when the downstream control device 35 receives from the upstream control device 28 information that it is not possible to drive the electric motor 233 of the electric cylinder device 23 or when it is unable to communicate with the upstream control device 28, the downstream control device 35 determines that the upstream pressurizing unit 20 has not returned to normal.

[0043] After executing the upstream return detection process, the downstream control device 35 proceeds to step S23. If the downstream control device 35 detects in step S23 that the upstream pressurizing unit 20 has returned to normal (YES), the downstream control device 35 sets the abnormality detection flag FLG1 to OFF in step S25, and then temporarily ends this process routine. On the other hand, if the downstream control device 35 does not detect in step S23 that the upstream pressurizing unit 20 has returned to normal (NO), the downstream control device 35 temporarily ends this process routine. That is, the abnormality detection flag FLG1 remains set to ON.

[0044] Next, a processing routine executed by the downstream control device 35 when the vehicle is traveling will be described with reference to Fig. 3. This processing routine is repeatedly executed at predetermined control cycles when the vehicle is traveling.

[0045] In this processing routine, in step S31, the downstream control device 35 determines whether 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 temporarily ends this processing routine. On the other hand, if the abnormality detection flag FLG1 is set to ON (S31: YES), the downstream control device 35 proceeds to step S33.

[0046] 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, we will explain what happens when residual pressure occurs in the rear wheel cylinders 12L, 12R. If an abnormality occurs in the upstream pressurizing unit 20 while the electric cylinder device 23 is operating to adjust the wheel pressure Pf of the front wheels and the wheel pressure Pr of the rear wheels, the electric motor 233 will no longer be driven. For example, if an abnormality occurs in the electric motor 233 while the piston 231 is moving from the reference position in the braking direction Za, the drive torque of the electric motor 233 acting on the piston 231 in the braking direction Za will no longer be generated. Therefore, brake fluid flows from the wheel cylinders 12L, 12R to the slave cylinder 230. As a result, the brake fluid pressure flowing from the output port 237 into the fluid chamber 232 in the slave cylinder 230 will attempt to return the piston 231 to the reference position. Furthermore, if an abnormality occurs in the upstream pressurizing unit 20, the system shutoff valve 25 will close and the master cutoff valve 24 will open. As a result, the wheel cylinders 11L, 11R of the front wheels are disconnected from the slave cylinder 230 and then connected to the master cylinder 22. As a result, the brake fluid in the wheel cylinders 11L, 11R of 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 significantly. In addition, in this embodiment, the slave cylinder 230 is not provided with a return spring. Furthermore, when the piston 231 returns to its reference position due to the brake fluid pressure flowing into the slave cylinder 230, a sliding resistance that prevents the piston 231 from moving in the release direction Zb is generated in the electric cylinder device 23. Therefore, if 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 in the slave cylinder 230 may not return to its reference position. If the piston 231 does not return to the reference position, residual pressure will be generated in the wheel cylinders 12L, 12R of the rear wheels. When the brake pedal 15 is not operated, such as when the vehicle is moving, the brake fluid in the wheel cylinders 11L, 11R of the front wheels is returned to the reserve tank 21 via the master cylinder 22.Therefore, even 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, no residual pressure will be generated in the wheel cylinders 11L, 11R of the front wheels.

[0047] Therefore, if the abnormality detection flag FLG1 is switched from OFF to ON while the front wheel pressure Pf and the rear wheel pressure Pr are being adjusted by the operation of the electric cylinder device 23, it can be assumed that there is a possibility of residual pressure in the wheel cylinders 12L, 12R of the rear wheels. If it is determined in step S33 that there is a possibility of residual pressure in the wheel cylinders 12L, 12R of the rear wheels (YES), the downstream control device 35 proceeds to step S35. On the other hand, if it is not determined that there is a possibility of residual pressure in the wheel cylinders 12L, 12R of the rear wheels (NO in S33), the downstream control device 35 temporarily ends this processing routine.

[0048] In step S35, the downstream control device 35 determines whether the execution conditions for the in-travel processing are met. In this embodiment, the downstream control device 35 determines that the execution conditions for the in-travel processing are met when both of the following conditions (B1) and (B2) are met. (B1) The wheel speed sensor value indicates that the cumulative elapsed time during which the vehicle is not stopped since the last execution of the in-motion process has reached a predetermined first interval time TM1. (B2) There is no requirement for the vehicle to slow down.

[0049] Although details will be described later, the in-travel process is a process for reducing the wheel pressure Pr of the rear wheels. Even if the in-travel process is executed to reduce the wheel pressure Pr, if the rear wheels are rotating with the friction material in contact with the frictioned portion of the rear wheel friction brake that rotates integrally with the rear wheels, the temperature of the brake fluid in the wheel cylinders 12L, 12R rises due to frictional heat, causing the brake fluid to expand. At this time, if the piston 231 of the electric cylinder device 23 has not returned to its reference position, the fluid passage connecting the wheel cylinders 12L, 12R and the electric cylinder device 23 is sealed, which may increase the wheel pressure Pr. Therefore, if the above condition (B1) is met, the downstream control device 35 considers that the wheel pressure Pr has increased due to the influence of the above frictional heat.

[0050] When the vehicle is required to decelerate, an increase in wheel pressure Pr due to the influence of the frictional heat is not considered to be a major problem. A case where the vehicle is required to decelerate can be referred to as a case where a braking request is made to the vehicle. On the other hand, a case where the vehicle is not required to decelerate can be referred to as a case where no braking request is made to the vehicle.

[0051] Therefore, if both the above conditions (B1) and (B2) are satisfied, the downstream control device 35 determines that the execution condition is satisfied. On the other hand, if at least one of the above conditions (B1) and (B2) is not satisfied, the downstream control device 35 determines that the execution condition is not satisfied.

[0052] The downstream control device 35 varies the predetermined first interval time TM1 depending on the rotation speed of the rear wheels. Specifically, the downstream control device 35 sets a shorter predetermined first interval time TM1 as the rotation speed of the rear wheels increases. This is because the amount of frictional heat generated by the rear wheel friction brake increases as the rotation speed of the rear wheels increases.

[0053] If it is determined in step S35 that the execution conditions for the travel-time processing are met (YES), the downstream control device 35 proceeds to step S37. On the other hand, if it is determined that the execution conditions are not met (S35: NO), the downstream control device 35 temporarily ends this processing routine without executing the travel-time processing.

[0054] In step S37, the downstream control device 35 executes the running-time processing. That is, the downstream control device 35 executes the running-time processing when the vehicle is running, the downstream control device 35 detects that the electric motor 233 has become unable to be driven, and there is no braking request. When the execution of the running-time processing is completed, the downstream control device 35 temporarily ends this processing routine.

[0055] The running process will now be described in detail with reference to FIG. In the example shown in Fig. 4, the execution conditions for the running-time processing are met at timings t11, t13, and t15. In the running-time processing, the downstream control device 35 operates the rear-wheel-side assisting device 32 as shown in Fig. 4(A) to (D), thereby reducing the wheel pressure Pr of the rear wheels as shown in Fig. 4(E). In the running-time processing, 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.

[0056] When the rear-wheel assisting device 32 is operated in this manner, the pump 304 sucks in the brake fluid in the wheel cylinders 12L, 12R of the rear wheels and discharges the brake fluid into the fluid passage 308 between the differential pressure control valve 301 and the holding valve 302. Because 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, a pressure corresponding to the discharge pressure of the pump 304 acts on the piston 231 of the slave cylinder 230, causing the piston 231 to move toward the reference position as shown in FIG. 4(F).

[0057] 4, the execution of the running-time processing ends at timings t12, t14, and t16. Then, the downstream control device 35 stops the operation of the rear wheel-side assisting device 32. That is, the downstream control device 35 stops the driving of 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.

[0058] A processing routine executed by the downstream control device 35 when the vehicle is stopped will be described with reference to Fig. 5. This processing routine is repeatedly executed at predetermined control cycles when the vehicle is stopped.

[0059] In this processing routine, in step S41, the downstream control device 35 determines whether 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 temporarily ends this processing routine. On the other hand, if the abnormality detection flag FLG1 is set to ON (S41: YES), the downstream control device 35 proceeds to step S43.

[0060] In step S43, the downstream control device 35 determines whether there is a possibility of residual pressure in the wheel cylinders 12L, 12R of the rear wheels, similar to the processing of step S33 shown in Fig. 3. If it is determined that there is a possibility of residual pressure in the wheel cylinders 12L, 12R of the rear wheels (S43: YES), the downstream control device 35 proceeds to step S45. On the other hand, if it is not determined that there is a possibility of residual pressure in the wheel cylinders 12L, 12R (S43: NO), the downstream control device 35 temporarily ends this processing routine.

[0061] In step S45, the downstream control device 35 determines whether the execution condition for the stationary-vehicle processing is met. In this embodiment, the downstream control device 35 determines that the execution condition is met if the time elapsed since the stationary-vehicle processing was last executed reaches a predetermined second interval time TM2. On the other hand, the downstream control device 35 determines that the execution condition is not met if the time elapsed since the stationary-vehicle processing was last executed does not reach the predetermined second 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.

[0062] If it is determined in step S45 that the execution condition for the stationary vehicle processing is met (YES), the downstream control device 35 proceeds to step S47. On the other hand, if it is determined that the execution condition is not met (S45: NO), the downstream control device 35 temporarily ends this processing routine without executing the stationary vehicle processing.

[0063] In step S47, the downstream control device 35 executes the vehicle stoppage process. That is, the downstream control device 35 executes the vehicle stoppage process when it detects that the vehicle is stopped and that driving of the electric motor 233 has become impossible. When the execution of the vehicle stoppage process ends, the downstream control device 35 temporarily ends this processing routine.

[0064] The process when the vehicle is stopped will be described in detail with reference to FIG. In the example shown in FIG. 6, the conditions for executing the stationary-state processing are met at timings t21, t23, and t25. In the stationary-state processing, the downstream control device 35 operates the rear-wheel-side assisting device 32 as shown in (A) to (D) of FIG. 6, thereby increasing the pressure in the portion of the hydraulic passage closer to the wheel cylinders 12L and 12R than the differential pressure control valve 301 to be higher than the pressure in the portion of the hydraulic passage closer to the slave cylinder 230 than the differential pressure control valve 301. That is, the downstream control device 35 increases the wheel pressure Pr of the rear wheels as shown in (E) of FIG. 6. Specifically, the downstream control device 35 operates the pump 304 of the rear-wheel-side assisting device 32 to reduce the instructed opening 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.

[0065] When the rear wheel assisting device 32 is operated in this manner, the pump 304 sucks brake fluid from the slave cylinder 230. When the pressure in the fluid chamber 232 of the slave cylinder 230 decreases 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 brake fluid from the reserve tank 21 through this gap. The pump 304 discharges brake fluid into a fluid passage 308 that is closer to the wheel cylinders 12L, 12R than the differential pressure control valve 301. As a result, the brake fluid discharged from the pump 304 flows into the wheel cylinders 12L, 12R, and the wheel pressure Pr of the rear wheels increases.

[0066] Then, at timings t22, t24, and t26, the downstream control device 35 stops the operation of the rear-wheel assisting device 32, thereby ending the vehicle-stop processing. That is, the downstream control device 35 stops the pump 304, sets the instructed opening of the differential pressure control valve 301 to 100%, and opens the differential pressure control valve 301. When the differential pressure control valve 301 is opened while the differential pressure between the wheel cylinders 12L, 12R and the slave cylinder 230 is increased in this manner, brake fluid flows from the wheel cylinders 12L, 12R into the slave cylinder 230. That is, in the vehicle-stop processing, the rear-wheel assisting device 32 is operated to increase the differential pressure, and then the increase in the differential pressure is stopped and the differential pressure control valve 301 is opened, thereby allowing brake fluid to flow from the wheel cylinders 12L, 12R to the slave cylinder 230. As a result, as shown in FIG. 6(F), in the slave cylinder 230, the piston 231 moves toward the reference position due to the brake fluid pressure that has flowed into the slave cylinder 230 from the output port 237.

[0067] If the wheel pressure Pr of the rear wheels is increased or decreased by operating the rear wheel assisting device 32 in this way, there is a possibility that the braking force required to keep the vehicle stopped will be insufficient. Therefore, in this embodiment, it is possible to ensure the wheel pressure Pr of the front wheels by the master cylinder 22, which is caused by the driver's operation of the brake pedal 15. Furthermore, if the vehicle can be kept stopped by a shift gear, EPB, or the like, a process equivalent to the process during stopping may also be performed on the front wheels to return the piston 231 to the reference position.

[0068] <Actions and Effects of This Embodiment> When the vehicle is stopped and it is detected that the electric motor 233 of the electric cylinder device 23 is no longer drivable, a vehicle stoppage process is executed. When the vehicle stoppage process is executed, the rear wheel assisting device 32 is activated to increase the pressure difference between the rear wheel cylinders 12L, 12R and the slave cylinder 230, i.e., the wheel pressure Pr of the rear wheels is increased. In this state, the rear wheel assisting device 32 is deactivated and the differential pressure control valve 301 is opened. This causes a large amount of brake fluid to flow from the wheel cylinders 12L, 12R toward the slave cylinder 230. As a result, within the slave cylinder 230, the hydraulic pressure of the brake fluid flowing in via the output port 237 moves the piston 231 toward the reference position. Therefore, even if the electric motor 233 cannot be driven and the piston 231 has not yet returned to the reference position, the vehicle stoppage process can be executed to return the piston 231 to the reference position.

[0069] As shown in Fig. 6, it may not be possible to return piston 231 to the reference position by executing the vehicle-stop processing only once. In this regard, in this embodiment, the vehicle-stop processing is executed intermittently while the vehicle is stopped. By executing the vehicle-stop processing multiple times in this manner, piston 231 can be caused to gradually approach the reference position within slave cylinder 230, as shown in Fig. 6(F). In the example shown in Fig. 6, piston 231 returns to the reference position by executing the vehicle-stop processing three times.

[0070] Incidentally, if residual pressure occurs in the wheel cylinders 12L, 12R of the rear wheels while the vehicle is traveling, the driver of the vehicle may feel a dragging sensation. Therefore, in this embodiment, when the vehicle is traveling and it is detected that the electric motor 233 of the electric cylinder device 23 has become unable to be driven, a traveling process is executed. When the traveling process is executed, the rear wheel assisting device 32 is activated to return the brake fluid in the wheel cylinders 12L, 12R of the rear wheels to the slave cylinder 230. 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 a dragging sensation while the vehicle is traveling.

[0071] Furthermore, execution of the running process causes brake fluid to flow into slave cylinder 230 from output port 237. As a result, as shown in FIG. 4(F), piston 231 can be moved toward the reference position in slave cylinder 230.

[0072] Even if the vehicle is running and the brake fluid in the wheel cylinders 12L, 12R is reduced by executing the in-vehicle process, the rear wheel friction brakes may continue to have their frictional parts in contact with the frictioned parts that rotate together with the rear wheels. In this case, frictional heat is generated in the friction brakes, causing the temperature of the brake fluid in the wheel cylinders 12L, 12R to rise, and the wheel pressure Pr of the rear wheels to rise again.

[0073] In this embodiment, the driving process is executed intermittently and repeatedly while the vehicle is driving, as shown in Figure 4. This can enhance the effect of suppressing the driver from feeling a dragging sensation while the vehicle is driving.

[0074] If the vehicle's traveling speed remains low, the temperature of the friction material of the friction brake will not rise significantly. Therefore, the interval between execution of the traveling process may be lengthened. In other words, the higher the traveling speed, the shorter the interval between execution of the traveling process. For example, the interval between execution of the traveling process can be adjusted by varying the above-mentioned predetermined first interval time TM1.

[0075] Incidentally, even while the vehicle is traveling, a request to decelerate the vehicle may be made by operating the brake pedal 15, for example. In other words, a braking request may be made. In this embodiment, if a braking request is made while the vehicle is traveling, the traveling process is not executed. This makes it possible to prevent the rear wheel assisting device 32 from operating too frequently.

[0076] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0077] The upstream pressurizing unit may have a different configuration from the upstream pressurizing unit 20 shown in FIG. 1, as long as it is configured to include the electric cylinder device 23. 7 shows a modified upstream pressurizing section 20A. The upstream pressurizing section 20A includes a master cylinder 22A, a stroke simulator 27, and an electric cylinder device .

[0078] The configuration of the master cylinder 22A is described in, for example, Japanese Patent Application Laid-Open 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. The brake pedal 15 is connected to the input piston 44. Within the main cylinder 41, a master chamber 411, a first hydraulic pressure chamber 412, and a servo chamber 413 are defined by the master piston 43. Within the cover cylinder 42, a second hydraulic pressure chamber 421 and a third hydraulic pressure chamber 422 are defined. Within the main cylinder 41, a master spring 45 is provided that urges the master piston 43 in a direction that increases the volume of the master chamber 411. Within the cover cylinder 42, an input spring 46 is provided that urges the input piston 44 in a direction that increases the volume of the second hydraulic pressure chamber 421.

[0079] In the upstream pressurizing section 20A, the slave cylinder 230 of the electric cylinder device 23 is connected to the servo chamber 413. That is, the electric cylinder device 23 can supply brake fluid to the wheel cylinders 12L, 12R of the rear wheels and the servo chamber 413. In addition, the upstream pressurizing section 20A has a plurality of control valves 52, 53.

[0080] When the upstream pressurizing unit 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 hydraulically disconnected from the reserve tank 21. When the brake pedal 15 is operated in this state, the stroke simulator 27 provides a pedal feeling to the brake pedal 15. With the control valve 52 open and the control valve 53 closed, the electric cylinder device 23 outputs brake fluid from the output port 237 in accordance with the amount of operation of the brake pedal 15. The output brake fluid is supplied to the second hydraulic line 14 and the servo chamber 413. As the brake fluid is supplied to the servo chamber 413, the master piston 43 slides in a direction that reduces the volume of the master chamber 411. As the master piston 43 slides in this manner, brake fluid is supplied from the master chamber 411 to the first hydraulic line 13. In this way, during normal operation, the upstream pressurizing section 20A controls the electric cylinder device 23 and the control valves 52, 53 to supply brake fluid to the first fluid path 13 and the second fluid path 14, respectively.

[0081] If an abnormality occurs in the upstream pressurizing unit 20A, the control valves 52 and 53 are de-energized. This causes the control valve 52 to close and the control valve 53 to open. As a result, the reserve tank 21 is connected to the first hydraulic pressure chamber 412 and the stroke simulator 27. The reserve tank 21 is also isolated from the second hydraulic pressure chamber 421. This seals the second hydraulic pressure chamber 421, and the depression force applied to the brake pedal 15 is transmitted to the master piston 43 via the input piston 44 and the brake fluid sealed in the second hydraulic pressure chamber 421. At this time, the first hydraulic line 13 is connected to the master chamber 411 of the master cylinder 22A. Therefore, in the braking control device 10, the front wheel assisting device 31 increases the pressure of the brake fluid output from the master cylinder 22A and sends it to the front wheel cylinders 11L and 11R, thereby generating braking force for the front wheels. At this time, the brake control device 10 generates braking force for the rear wheels by causing the rear wheel assisting device 32 to send brake fluid to the wheel cylinders 12L, 12R of the rear wheels independently of the master cylinder 22A.

[0082] As described above, under the circumstances where the upstream pressurizing unit 20A is normal and the wheel pressure Pr of the rear wheels is adjusted by the operation of the electric cylinder device 23, an abnormality may occur in the upstream pressurizing unit 20A, and the electric motor 233 may become unable to be driven. In this case, as described above, the control valve 52 is closed and the control valve 53 is opened. At this time, the downstream control device 35 executes the vehicle-stopped process and the vehicle-traveled process, thereby achieving the same functions and effects as those of the above embodiment.

[0083] In the modified example shown in FIG. 7, if the electric motor 233 becomes inoperable, the piston 231 of the slave cylinder 230 may not return to its reference position. In this case, hydraulic pressure may remain in the servo chamber 413 of the master cylinder 22A. If hydraulic pressure remains in the servo chamber 413 and the master piston 43 does not return to its reference position, hydraulic pressure may be generated in the front wheel cylinders 11L, 11R. Therefore, in the modified example shown in FIG. 7, the front wheel assisting device 31 may be controlled to perform processing equivalent to the vehicle-stopping processing or the vehicle-driving processing on the front wheel cylinders 11L, 11R. For example, the front wheel assisting device 31 may be controlled so that brake fluid flows from the front wheel assisting device 31 to the master chamber 411.

[0084] When the vehicle-stop processing is being executed, the front wheel pressure Pf may be increased by operating the front wheel assisting device 31. In the above embodiment, the predetermined first interval time TM1 that defines the execution interval of the driving process is varied according to the rear wheel rotation speed. However, the first interval time TM1 may be varied based on parameters other than the rear wheel rotation speed. For example, the higher the brake fluid temperature or the outside air temperature, the shorter the first interval time TM1 may be set. Furthermore, the first interval time TM1 may be set according to the estimated temperature of the friction material of the friction brake, taking into account not only the vehicle's driving speed but also heat generated by braking during deceleration.

[0085] It can be assumed that the more frequently the vehicle is braked, the more opportunities there are for residual pressure to occur in the rear wheel cylinders 12L, 12R. Therefore, the more frequently the vehicle is braked while in motion, the more preferably the in-motion processing should be executed intermittently at shorter intervals.

[0086] The first interval time TM1 does not need to be variable. The execution conditions for the running process do not necessarily have to include a requirement for the vehicle to decelerate, i.e., no braking requirement.

[0087] · It is not necessary to repeatedly execute driving processing intermittently while the vehicle is moving. If the vehicle is running and it has been detected that the electric motor 233 is no longer able to be driven, and there is a possibility that residual pressure is present in the wheel cylinders 12L, 12R of the rear wheels, the running processing may continue to be executed while the vehicle is running.

[0088] The downstream control device 35 does not need to execute the vehicle-traveling process while the vehicle is traveling, as long as the vehicle-traveling process is executed when the vehicle is stopped. The downstream control device 35 does not need to execute the vehicle-stop processing if it executes the vehicle-travel processing while the vehicle is traveling. In this case, the rear wheel assisting device 32 may not have a differential pressure control valve 301.

[0089] In the above embodiment, the vehicle stop processing is executed intermittently and repeatedly while the vehicle is stopped. However, this is not limiting. For example, the vehicle stop processing may be executed only once during one vehicle stop period.

[0090] In the above embodiment, if it is determined in step S43 of Fig. 5 that there is a possibility of residual pressure, the process proceeds to step S45, but the determination in step S43 may be omitted. In this case, if the abnormality detection flag FLG1 is set to ON, the process proceeds to step S45 to determine whether the execution condition for the stationary-vehicle processing is met.

[0091] The brake control device may be configured such that the front wheel cylinders 11L, 11R are the first wheel cylinders, the rear wheel cylinders 12L, 12R are the second wheel cylinders, the front wheel assisting device 31 is the first pressurizing unit, and the rear wheel assisting device 32 is the second pressurizing unit. In other words, the brake control device may be applied to individual wheels or any combination thereof.

[0092] The rear wheel assisting device may have a configuration in which a device other than the pump 304 is provided as a pressurizing device capable of supplying brake fluid to the fluid passage between the differential pressure control valve 301 and the holding valve 302 . The electric cylinder device 23 may be configured such that 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 biasing force of the return spring alone cannot return the piston 231 to the reference position. In the brake control device 10 equipped with such an electric cylinder device 23, effects equivalent to those of the above embodiment can be obtained by executing the vehicle-stopping process and the vehicle-traveling process.

[0093] The downstream control device 35 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for performing at least some of the various processes, or a combination thereof. Examples of dedicated hardware include an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, which stores program code or instructions configured to cause the CPU to perform the processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer. [Explanation of symbols]

[0094] 10...Brake control device 11L, 11R, 12L, 12R...Wheel cylinder 13...1st liquid path 14…Second liquid path 23...Electric cylinder device 230...Slave cylinder 231...Piston 232…liquid chamber 233...Electric motor 301... Differential pressure control valve (an example of a solenoid valve) 302...Retention valve 303...Reducing valve 304...Pump (an example of a pressure device) 31... Front wheel assist device (an example of a pressure unit) 32... Rear wheel assist device (an example of a pressure unit) 35...Downstream control device (an example of a control unit)

Claims

1. A braking control device that generates braking force on a vehicle wheel by adjusting hydraulic pressure in a wheel cylinder, an electric cylinder device having a slave cylinder, a piston slidable within the slave cylinder, and an electric motor capable of generating a driving force to slide the piston, and supplying brake fluid from the fluid chamber through a fluid passage to the wheel cylinder by moving the piston so as to reduce the volume of a fluid chamber formed within the slave cylinder; a pressure applying unit including a solenoid valve disposed in the fluid passage and a pressure applying device capable of supplying brake fluid to a portion of the fluid passage closer to the wheel cylinder than the solenoid valve; a control unit that controls the pressurizing unit, The control unit When the vehicle is stopped and it is detected that the electric motor is no longer operable, By supplying brake fluid to the pressurizing device with the solenoid valve closed, the pressurizing unit is controlled so that the pressure in the portion of the fluid path closer to the wheel cylinder than the solenoid valve becomes higher than the pressure in the portion of the fluid path closer to the slave cylinder than the solenoid valve, and then the solenoid valve is opened to execute a vehicle-stopping process in which brake fluid flows from the wheel cylinder to the fluid chamber of the slave cylinder. Braking control device.

2. A braking control device that generates braking force on a vehicle wheel by adjusting hydraulic pressure in a wheel cylinder, an electric cylinder device having a slave cylinder, a piston slidable within the slave cylinder, and an electric motor capable of generating a driving force to slide the piston, and supplying brake fluid from the fluid chamber through a fluid passage to the wheel cylinder by moving the piston so as to reduce the volume of a fluid chamber formed within the slave cylinder; a pressure-reducing valve that reduces the hydraulic pressure in the wheel cylinder when the valve is open, and a pressure-reducing device that, when the valve is open, draws brake fluid from the wheel cylinder through the pressure-reducing valve and supplies the fluid to a portion of the hydraulic path closer to the slave cylinder than the pressure-reducing valve; a control unit that controls the pressurizing unit, The control unit When the vehicle is running, it is detected that the electric motor has become unable to be driven, and there is no braking request, A running process is executed in which the pressure reducing valve is opened while the holding valve is closed and the pressurizing device is activated. Braking control device.

3. the solenoid valve is a differential pressure control valve, The pressurizing unit is a pressure holding valve, which is an electromagnetic valve disposed in a portion of the fluid passage 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 opens when the brake fluid is to be discharged from the wheel cylinder; the pressurizing device is a pump that, when the pressure reducing valve is open, sucks brake fluid from the wheel cylinder through the pressure reducing valve and discharges the brake fluid to a portion of the fluid path 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 is unable to be driven, A running process is executed in which the pressure reducing valve and the differential pressure control valve are opened, while the holding valve is closed, and the pressurizing device is operated. The braking control device according to claim 1.

4. The control unit intermittently executes the running process at shorter intervals while the vehicle is running, as the running speed of the vehicle increases or the braking frequency of the vehicle increases. The braking control device according to claim 2 or 3.

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