JP7552344B2 - Vehicle Brake Device - Google Patents

Description

The present invention relates to a vehicle braking system.

For example, the brake system disclosed in Japanese Patent No. 6202741 includes a reservoir, an electric cylinder, and a wheel cylinder. In this system, the reservoir and the wheel cylinder are connected via the electric cylinder.

Patent No. 6202741

In the above system, for example, if an electrical failure occurs in the electric cylinder, it is possible to prohibit control of the electric cylinder, de-energize the switching valve, connect the master cylinder to the wheel cylinder of the first system, and cut off the master cylinder from the wheel cylinder of the second system. For example, in this state, by operating the ESC device (actuator) in response to the operation of the brake pedal, it is possible to supply fluid drawn from the master cylinder to the wheel cylinder of the first system, and to supply fluid drawn from the reservoir via the electric cylinder to the wheel cylinder of the second system. In this way, it is possible to increase the braking force even if a failure occurs in the electric cylinder.

However, in the above system, if the failure of the electric cylinder is not an electrical failure, but for example, if the piston is locked in a position that blocks communication between the hydraulic chamber and the reservoir due to a locked reduction gear, it is possible to increase pressure in the wheel cylinder of the second system but not to reduce pressure. Specifically, when the above system detects a piston lock and prohibits pressure adjustment by the electric cylinder and attempts to perform assist control using the ESC device, the wheel cylinder of the second system is supplied with fluid sucked from the reservoir via the sealing member (rubber cup) of the electric cylinder. However, even if an attempt is made to reduce pressure in the wheel cylinder of the second system, the sealing member of the electric cylinder blocks the flow of fluid from the hydraulic chamber to the reservoir, making it impossible to reduce pressure in that wheel cylinder.

The object of the present invention is to provide a vehicle braking device that allows auxiliary control by a downstream unit even if a piston lock failure occurs in an electric cylinder.

The vehicle braking device of the present invention includes a first hydraulic pressure output unit that is provided in a first hydraulic passage connecting a reservoir and a first wheel cylinder and is capable of selectively outputting hydraulic pressure to the reservoir side and the first wheel cylinder side, a master cylinder that is provided between the reservoir and the first hydraulic pressure output unit in the first hydraulic passage, a second hydraulic pressure output unit that is provided in a second hydraulic passage connecting the reservoir and a second wheel cylinder and is capable of selectively outputting hydraulic pressure to the reservoir side and the second wheel cylinder side, and an electric brake system that is provided between the reservoir and the second hydraulic pressure output unit in the second hydraulic passage and has a cylinder and a piston that slides within the cylinder, hydraulically connects or disconnects the reservoir and the second hydraulic pressure output unit depending on the position of the piston and outputs fluid depending on the sliding of the piston. A fluid path to which the fluid output from the electric cylinder is supplied includes a communication control valve provided in a communication path connected to a portion of the first fluid path between the master cylinder and the first hydraulic pressure output unit, a failure determination unit that determines whether the piston position of the electric cylinder is in an uncontrollable state, and a control unit that controls the first hydraulic pressure output unit, the second hydraulic pressure output unit, and the communication control valve. When the failure determination unit determines that the piston position of the electric cylinder is in an uncontrollable state, the control unit executes a specific assist control to increase the braking force by causing the first hydraulic pressure output unit to output fluid toward the first wheel cylinder with the communication control valve closed and not causing the second hydraulic pressure output unit to output fluid toward the second wheel cylinder.

According to the present invention, when a piston lock failure occurs and the piston position cannot be controlled, the first wheel cylinder that can be hydraulically connected to the reservoir via the master cylinder is pressurized by the first hydraulic output unit, and the second wheel cylinder that may not be hydraulically connected to the reservoir because the piston position of the electric cylinder is uncontrollable is not pressurized. Pressurization of the first wheel cylinder increases the braking force.

The reservoir and the master cylinder can be hydraulically connected, and the first hydraulic output unit can return the fluid in the first wheel cylinder to the master cylinder and the reservoir. In other words, the first hydraulic output unit can be operated to reduce the pressure in the first wheel cylinder (reduce the braking force). The second wheel cylinder may not be hydraulically connected to the reservoir via the electric cylinder because the piston position of the electric cylinder is uncontrollable, but if the piston position is uncontrollable, the second wheel cylinder is not pressurized and therefore reduction in pressure is not necessary. Therefore, even if a piston lock failure occurs in the electric cylinder, braking force can be obtained by the first hydraulic output unit, which is one of the downstream units, performing auxiliary control (braking force adjustment) on the first wheel cylinder, which can be reduced pressure later.

1 is a configuration diagram of a vehicle braking device according to an embodiment of the present invention; FIG. 2 is a configuration diagram of an electric cylinder according to the present embodiment. FIG. 2 is a configuration diagram of a downstream unit according to the present embodiment. 4 is a flowchart illustrating a control flow of the present embodiment. 10 is a flowchart illustrating another example of control according to the present embodiment. FIG. 11 is a configuration diagram of another example of the downstream unit of the embodiment.

The following describes an embodiment of the present invention with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings. As shown in FIG. 1, the vehicle braking device 1 of this embodiment includes an upstream unit 11, a downstream unit 3, a first brake ECU 901, and a second brake ECU 902. The vehicle braking device 1 is a device capable of supplying fluid to first wheel cylinders 81, 82 and second wheel cylinders 83, 84 provided on the wheels of the vehicle. For example, the first wheel cylinders 81, 82 are provided on the front wheels, and the second wheel cylinders 83, 84 are provided on the rear wheels. The first brake ECU 901 controls at least the upstream unit 11. The second brake ECU 902 controls at least the downstream unit 3.

(Upstream unit)
The upstream unit 11 includes a master cylinder device 4, a stroke simulator 43, a simulator cut valve 44, a reservoir 45, a first fluid path 51, the electric cylinder 2, a second fluid path 52, a communication path 53, a master cut valve 62, a communication control valve 61, a stroke sensor 71, pressure sensors 72, 73, and a level switch 74. Fig. 1 shows a de-energized state of the vehicle braking device 1.

The master cylinder device 4 is a device capable of generating hydraulic pressure in response to driver operation. The master cylinder device 4 includes a master cylinder 41, a master piston 42, a master chamber 41a, and a biasing member 41b. The master cylinder 41 is a cylindrical member or part with a bottom. An input port 411 and an output port 412 are formed in the master cylinder 41. The input port 411 and the output port 412 will be described later.

The master piston 42 is a piston member disposed in the master cylinder 41 and is mechanically connected to the brake pedal Z. The master piston 42 slides in the master cylinder 41 in response to the operation of the brake pedal Z. A through hole 421 is formed in the master piston 42. The master piston 42 is biased toward the initial position by a biasing member 41b, which will be described later. The initial position is the position of the master piston 42 when the volume of the master chamber 41a is maximum. When the master piston 42 is located in the initial position, the through hole 421 and the input port 411 are in communication.

The master chamber 41a is formed in the master cylinder 41 by the master cylinder 41 and the master piston 42. In this embodiment, the number of master chambers 41a formed in the master cylinder 41 is one. The volume of the master chamber 41a changes according to the movement of the master piston 42. When the master piston 42 moves to one side in the axial direction, the volume of the master chamber 41a decreases, and the hydraulic pressure in the master chamber 41a (hereinafter referred to as "master pressure") increases.

The biasing member 41b is a spring member provided in the master chamber 41a. When no force is acting on the master piston 42, the master piston 42 is located in the initial position. The stroke simulator 43 is connected to the master cylinder device 4 via a simulator cut valve 44. The stroke simulator 43 is a device that generates a reaction force (load) against the operation of the brake pedal Z. The stroke simulator 43 includes a cylinder, a piston, and a biasing member. The stroke simulator 43 is connected to the output port 412 of the master cylinder 41 via a fluid path 43a.

The simulator cut valve 44 is a normally closed solenoid valve provided in the fluid passage 43a. When the brake pedal Z is operated with the master cut valve 62 (described later) closed and the simulator cut valve 44 open, a pedal reaction force is generated by the stroke simulator 43.

The reservoir 45 stores fluid. The pressure inside the reservoir 45 is kept at atmospheric pressure. Inside the reservoir 45, two storage chambers 451 and 452 are formed, each of which stores fluid.

The reservoir chamber 451 is connected to the master cylinder device 4. More specifically, the reservoir chamber 451 is connected to the input port 411 of the master cylinder 41. When the master piston 42 is in the initial position, the reservoir chamber 451 is hydraulically connected to the master chamber 41a via the input port 411 and the through hole 421. When the master piston 42 slides a predetermined amount, the input port 411 and the through hole 421 are hydraulically disconnected. In this case, the master chamber 41a and the reservoir 45 are hydraulically blocked. The reservoir chamber 452 is connected to the electric cylinder 2 via the second fluid path 52 (reservoir fluid path 522 described later). The reservoir 45 may be composed of two separate reservoirs instead of two reservoirs.

The first fluid path 51 is a fluid path that connects the reservoir 45 (storage chamber 451) and the first wheel cylinders 81, 82 via the master cylinder device 4 and the downstream unit 3 (first hydraulic pressure output section 31). Hereinafter, the portion of the first fluid path 51 that connects the master cylinder device 4 and the downstream unit 3 is referred to as the "first connecting fluid path 511," and the portion that connects the downstream unit 3 and the first wheel cylinders 81, 82 is referred to as the "first downstream fluid path 512." When the master piston 42 slides to reduce the size of the master chamber 41a while the master chamber 41a and the reservoir 45 are hydraulically disconnected, fluid is supplied from the master chamber 41a to the first connecting fluid path 511 via the output port 412, and hydraulic pressure is generated in the first connecting fluid path 511. The hydraulic pressure generated in the master chamber 41a is supplied to the downstream unit 3 via the first connecting fluid path 511. The first connecting fluid path 511 includes a connecting portion 50 that is connected to a communication passage 53 described below. The first connecting fluid path 511 is provided with a master cut valve 62 and a pressure sensor 72.

The master cut valve 62 is a normally open solenoid valve provided in the first fluid passage 51 between the connection part 50 and the master cylinder 41. When the master cut valve 62 is closed, the master cylinder device 4 and the downstream unit 3 are hydraulically isolated.

The pressure sensor 72 is provided in the first fluid path 51 between the master cut valve 62 and the master cylinder 41. The pressure sensor 72 detects the pressure in the first connecting fluid path 511. When the master cut valve 62 is closed, the pressure detected by the pressure sensor 72 corresponds to the master pressure, which is the pressure generated in the master chamber 41a.

The electric cylinder 2 has a cylinder 21, an electric motor 22, a piston 23, a hydraulic chamber 24, and a biasing member 25. The electric cylinder 2 is a single-type electric cylinder in which a single hydraulic chamber 24 is formed inside the cylinder 21. In the following description of the electric cylinder 2, the movement direction of the piston 23 in which the volume of the hydraulic chamber 24 becomes smaller is referred to as the forward direction, and the opposite direction is referred to as the rearward direction.

The cylinder 21 is a bottomed cylindrical member or part. The cylinder 21 is formed, for example, by using a part of a housing (metal block). An input port 211 and an output port 212 are formed in the cylinder 21. As shown in FIG. 2, the input port 211 is an opening and is formed between the seal member X1 and the seal member X2 provided in the cylinder 21. The seal member X1 and the seal member X2 are annular seal members, and their cross sections are concave and open forward (in other words, convex arc shapes bulging backward). Therefore, when the hydraulic chamber 24 becomes negative pressure, the seal member X1 allows the flow of fluid from the input port 211 to the hydraulic chamber 24, and when the pressure of the hydraulic chamber 24 is equal to or higher than atmospheric pressure, the seal member X1 prohibits the flow of fluid from the hydraulic chamber 24 to the input port 211. The seal members X1 and X2 are arranged in annular grooves formed on the inner peripheral surface of the cylinder 21. The output port 212 is an opening and is formed forward of the input port 211. At least one input port 211 and at least one output port 212 must be formed.

The electric motor 22 is connected to the piston 23 via a linear motion mechanism 22a that converts rotational motion into linear motion. The piston 23 is a cylindrical member with a bottom, and slides inside the cylinder 21 when driven by the electric motor 22. A through hole 231 is formed in the piston 23. When the piston 23 is in the initial position, the through hole 231 communicates with the input port 211.

The hydraulic chamber 24 is defined by the cylinder 21 and the piston 23, and its volume changes according to the movement of the piston 23. The initial position of the piston 23 is the position where the volume of the hydraulic chamber 24 is maximum (see Figure 2).

The hydraulic chamber 24 can communicate with the reservoir 45 through the input port 211. In detail, when the piston 23 is in the initial position, it is hydraulically connected to the reservoir 45 through the through hole 231 and the input port 211. When the through hole 231 and the input port 211 are not in communication, the hydraulic chamber 24 and the reservoir 45 are hydraulically blocked. In detail, even if the communication between the input port 211 and the through hole 231 is blocked as a result of the piston 23 moving forward by a predetermined amount, if the hydraulic pressure in the hydraulic chamber 24 is negative pressure, the flow of fluid from the reservoir 45 to the hydraulic chamber 24 is permitted through the seal member X1. However, in order to make the explanation easier to understand, in this embodiment, an example in which negative pressure is not generated in the hydraulic chamber 24 will be explained. The hydraulic chamber 24 is connected to the second hydraulic path 52 (the second connecting hydraulic path 521 described later) through the output port 212.

The biasing member 25 is a spring disposed in the hydraulic chamber 24 and biases the piston 23 toward the initial position. When the electric motor 22 is not driven, the biasing force of the biasing member 25 causes the piston 23 to be located in the initial position.

When the piston 23 is in the initial position, the hydraulic chamber 24 is connected to the reservoir 45 via the input port 211, the through hole 231, and the second hydraulic passage 52 (reservoir hydraulic passage 522 described later). When the piston 23 moves a predetermined amount forward from the initial position by driving the electric motor 22, the communication between the input port 211 and the through hole 231 is blocked. In this case, the hydraulic chamber 24 is hydraulically blocked from the reservoir 45. When the piston 23 slides to reduce the hydraulic chamber 24 while the hydraulic chamber 24 and the reservoir 45 are hydraulically blocked, fluid is output from the hydraulic chamber 24 through the output port 212. The output fluid is supplied to the second hydraulic passage 52 (second connecting hydraulic passage 521) and the communicating passage 53 (described later). As a result, hydraulic pressure is generated in each of the second hydraulic passage 52 (second connecting hydraulic passage 521) and the communicating passage 53.

The electric cylinder 2 is configured such that the input port 211 is opened by the piston 23 when the relative position of the piston 23 to the cylinder 21 is a predetermined open position, and the input port 211 is closed by the piston 23 when the relative position of the piston 23 to the cylinder 21 is a predetermined closed position. In other words, when the piston 23 is located in the "communication area" in the cylinder 21, the reservoir 45 and the hydraulic chamber 24 are in communication, and when the piston 23 is located in the "blocking area" in the cylinder 21, the connection between the reservoir 45 and the hydraulic chamber 24 is blocked. Of the movable area of the piston 23, the communication area is the area (including the initial position) between the initial position of the piston 23 and a position (switching position) a predetermined amount forward from the initial position, and the blocking area is the area between the switching position and the front end face of the cylinder 21.

The second fluid path 52 is a fluid path that connects the reservoir 45 (storage chamber 452) and the second wheel cylinders 83, 84 via the electric cylinder 2 and the downstream unit 3 (second hydraulic pressure output section 32). Hereinafter, the portion of the second fluid path 52 that connects the electric cylinder 2 and the downstream unit 3 is referred to as the "second connecting fluid path 521", the portion of the second fluid path 52 that connects the electric cylinder 2 and the reservoir 45 is referred to as the "reservoir fluid path 522", and the portion that connects the downstream unit 3 and the second wheel cylinders 83, 84 is referred to as the "second downstream fluid path 523". The hydraulic pressure generated in the hydraulic chamber 24 is supplied to the downstream unit 3 via the second connecting fluid path 521. A hydraulic pressure sensor 73 is provided in the second connecting fluid path 521.

The hydraulic pressure sensor 73 is a sensor that detects the pressure in the second connecting hydraulic line 521. When the control mode of the vehicle braking device 1 is a brake-by-wire mode (hereinafter referred to as the "by-wire mode") described below, the hydraulic pressure detected by the hydraulic pressure sensor 73 corresponds to the output pressure of the electric cylinder 2.

The communication passage 53 is a liquid path that connects the first connection liquid path 511 and the second connection liquid path 521. The communication passage 53 is connected to the first liquid path 51 at the connection part 50. A communication control valve 61 is provided in the communication passage 53. The communication control valve 61 is a normally closed type solenoid valve.

The stroke sensor 71 detects the stroke of the brake pedal Z. In this embodiment, two stroke sensors 71 are provided. Data detected by the two stroke sensors 71 is transmitted to each of the brake ECUs 901 and 902. The brake ECUs 901 and 902 each obtain stroke information from the corresponding stroke sensor 71.

The level switch 74 is provided in the reservoir 45 and detects when the fluid level in the reservoir 45 falls below a predetermined level. When the fluid level in the reservoir 45 falls below a predetermined value, the level switch 74 transmits data indicating that the fluid level has dropped to the first brake ECU 901.

(Downstream unit)
Next, the downstream unit 3 will be described with reference to Fig. 3. The downstream unit 3 is a so-called ESC actuator (ESC device) and can independently adjust the hydraulic pressure of each of the wheel cylinders 81 to 84. In detail, the downstream unit 3 includes a first hydraulic pressure output unit 31 configured to be able to adjust the pressure of the first wheel cylinders 81, 82, and a second hydraulic pressure output unit 32 configured to be able to adjust the pressure of the second wheel cylinders 83, 84. Hereinafter, in the description of the downstream unit 3, the position of the upstream unit 11 relative to the downstream unit 3 will be referred to as the upstream, and the positions of the wheel cylinders 81 to 84 relative to the downstream unit 3 will be referred to as the downstream.

The first hydraulic pressure output unit 31 is connected to the first connecting fluid path 511 on the upstream side and to the first wheel cylinders 81, 82 on the downstream side. The second hydraulic pressure output unit 32 is connected to the second connecting fluid path 521 on the upstream side and to the second wheel cylinders 83, 84 on the downstream side. The first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32 are independent of each other in the hydraulic circuit within the downstream unit 3.

The first hydraulic pressure output unit 31 is supplied with fluid from the upstream unit 11 via the first connecting fluid path 511. The first hydraulic pressure output unit 31 is configured to be able to increase the hydraulic pressure in the first wheel cylinders 81, 82 based on the base hydraulic pressure generated by the upstream unit 11. The first hydraulic pressure output unit 31 is configured to pressurize the first wheel cylinders 81, 82 by generating a pressure difference between the input hydraulic pressure and the hydraulic pressure in the first wheel cylinders 81, 82.

The first hydraulic pressure output section 31 includes a hydraulic path 311, a pump hydraulic path 315a, a pressure sensor 75, a differential pressure control valve 312, a check valve 312a, a holding valve 313, a check valve 313a, a pressure reducing hydraulic path 314a, a pressure reducing valve 314, a pump 315, an electric motor 316, a reservoir 317, and a return hydraulic path 317a.

Fluid path 311 is a fluid path that connects first connecting fluid path 511 and first downstream fluid path 512. Fluid path 311 includes a branching section X that is connected to pump fluid path 315a. Fluid path 311 branches at branching section X into a fluid path that connects to one first wheel cylinder 81 and a fluid path that connects to the other first wheel cylinder 82. Since the configurations on the two fluid paths of fluid path 311 are similar, only the fluid path that connects to first wheel cylinder 81 will be described (as fluid path 311).

The pressure sensor 75 is provided on the upstream unit 11 side of the differential pressure control valve 312 in the fluid path 311. The pressure sensor 75 detects the pressure in the fluid path 311. The pressure detected by the pressure sensor 75 corresponds to the fluid pressure input from the first connecting fluid path 511 to the first fluid pressure output section 31. The data detected by the pressure sensor 75 is transmitted to the second brake ECU 902.

The differential pressure control valve 312 is a normally open linear solenoid valve provided in the fluid path 311 between the branch point X and the pressure sensor 75. By controlling the opening degree of the differential pressure control valve 312, a pressure difference can be generated between the upstream and downstream sides of the differential pressure control valve 312. The check valve 312a is provided in parallel with the differential pressure control valve 312. The check valve 312a is configured to only allow the flow of fluid from the upstream side to the downstream side.

The retention valve 313 is a normally open solenoid valve provided in the fluid path 311 between the branch point X and the first wheel cylinder 81. The check valve 313a is provided in parallel to the retention valve 313. The check valve 313a is configured to only allow the flow of fluid from the downstream side to the upstream side.

The pressure reducing fluid path 314a is a fluid path that connects the portion of the fluid path 311 between the retention valve 313 and the first wheel cylinder 81 to the reservoir 317. The pressure reducing fluid path 314a is provided with a pressure reducing valve 314.

The pressure reducing valve 314 is a normally closed solenoid valve provided in the pressure reducing fluid passage 314a. When the pressure reducing valve 314 is open, the fluid in the first wheel cylinder 81 can flow into the reservoir 317 via the pressure reducing fluid passage 314a. Therefore, by opening the pressure reducing valve 314, the pressure in the first wheel cylinder 81 can be reduced.

The reservoir 317 is a known pressure regulating reservoir that stores fluid, and is connected to the reduced pressure fluid path 314a and the return fluid path 317a. The return fluid path 317a is a fluid path that connects the portion of the fluid path 311 between the pressure sensor 75 and the differential pressure control valve 312 to the reservoir 317. The fluid in the reservoir 317 is sucked in by the operation of the pump 315. When the amount of fluid in the reservoir 317 decreases, the valve in the reservoir 317 opens, and fluid is supplied to the reservoir 317 from the first connecting fluid path 511 via the return fluid path 317a.

The pump fluid path 315a is a fluid path that connects the portion of the pressure reducing fluid path 314a between the pressure reducing valve 314 and the reservoir 317 to the branch point X of the fluid path 311. The pump fluid path 315a is provided with a pump 315.

Pump 315 is a pump that operates in response to the drive of electric motor 316, and is, for example, a well-known piston pump or gear pump. The suction side of pump 315 is connected to reservoir 317, and the discharge side of pump 315 is connected to branch section X. When pump 315 operates, it sucks in the fluid in reservoir 317 and supplies the fluid to branch section X.

The first hydraulic pressure output unit 31 is configured to be able to pressurize the first wheel cylinders 81, 82 based on hydraulic pressure input from the upstream side by operating various solenoid valves and pumps. The second hydraulic pressure output unit 32 has the same configuration as the first hydraulic pressure output unit 31 except that it is not provided with a pressure sensor 75, so a description thereof will be omitted. Like the first hydraulic pressure output unit 31, the second hydraulic pressure output unit 32 is also configured to be able to pressurize the second wheel cylinders 83, 84 based on the basal hydraulic pressure.

(Summary of the configuration)
The vehicle braking device 1 of this embodiment includes a first hydraulic pressure output unit 31, a master cylinder 41, a second hydraulic pressure output unit 32, an electric cylinder 2, a communication control valve 61, a first brake ECU 901, and a second brake ECU 902. The first hydraulic pressure output unit 31 is provided in a first hydraulic passage 51 that connects the reservoir 45 and the first wheel cylinders 81, 82, and is a device that can selectively output hydraulic pressure to the reservoir 45 side or the first wheel cylinders 81, 82 side. The master cylinder 41 is provided between the reservoir 45 and the first hydraulic pressure output unit 31 in the first hydraulic passage 51. The reservoir 45 and the first hydraulic pressure output unit 31 can be hydraulically connected via the master cylinder 41. The second hydraulic pressure output unit 32 is provided in the second hydraulic path 52 connecting the reservoir 45 and the second wheel cylinders 83, 84, and is a device capable of selectively outputting hydraulic pressure to the reservoir 45 side or the second wheel cylinders 83, 84 side. The electric cylinder 2 is provided between the reservoir 45 and the second hydraulic pressure output unit 32 in the second hydraulic path 52, has a cylinder 21 and a piston 23 that slides within the cylinder 21, and hydraulically connects or disconnects the reservoir 45 and the second hydraulic pressure output unit 32 depending on the position of the piston 23, and outputs fluid depending on the sliding of the piston 23. The communication control valve 61 is provided in a communication path 53 that is a hydraulic path to which the fluid output from the electric cylinder 2 is supplied and is connected to a portion of the first hydraulic path 51 between the master cylinder 41 and the first hydraulic pressure output unit 31. More specifically, the communication control valve 61 is provided in a communication passage 53 that connects the portion in the first fluid path 51 between the master cylinder 41 and the first hydraulic pressure output section 31 (i.e., the first connecting fluid path 511) and the portion in the second fluid path 52 between the electric cylinder 2 and the second hydraulic pressure output section 32 (i.e., the second connecting fluid path 521).

(Brake ECU)
The first brake ECU 901 and the second brake ECU 902 (hereinafter also referred to as "brake ECUs 901, 902") are electronic control units each including a CPU and a memory. Each of the brake ECUs 901, 902 includes one or more processors that execute various types of control. The first brake ECU 901 and the second brake ECU 902 are separate ECUs and are connected to each other so that they can communicate information (control information, etc.) with each other.

The first brake ECU 901 is configured to be able to control the upstream unit 11. In detail, the first brake ECU 901 can control the electric cylinder 2 and each solenoid valve 61, 62, 44 based on data detected by multiple sensors 71, 72, 73, 74 of the upstream unit. The first brake ECU 901 can calculate each wheel pressure based on the detection results of the pressure sensors 72, 73 and the control state of the downstream unit 3.

The second brake ECU 902 is configured to be able to control the downstream unit 3 based on data detected by the stroke sensor 71 and the pressure sensor 75. The second brake ECU 902 also receives data detected by a wheel speed sensor (not shown) and an acceleration sensor (not shown) provided on the vehicle. When the second brake ECU 902 pressurizes the first wheel cylinder 81 using the downstream unit 3, the second brake ECU 902 applies a control current to the differential pressure control valve 312 according to a target differential pressure (hydraulic pressure of the first wheel cylinder 81>hydraulic pressure of the first connecting fluid passage 511) to close the differential pressure control valve 312. At this time, the holding valve 313 is open and the pressure reducing valve 314 is closed. In addition, by operating the pump 315, fluid is supplied from the first connecting fluid passage 511 to the branch section X via the reservoir 317. This causes the first wheel cylinder 81 to be pressurized.

When the second brake ECU 902 reduces the wheel pressure by the downstream unit 3 for anti-skid control or the like, it operates the pump 315 with the pressure reducing valve 314 open and the holding valve 313 closed to pump back the fluid in the first wheel cylinder 81. When the second brake ECU 902 maintains the wheel pressure by the downstream unit 3, it closes the holding valve 313 and the pressure reducing valve 314. When the wheel pressure is increased or decreased only by the operation of the electric cylinder 2 or the master cylinder device 4, the second brake ECU 902 opens the differential pressure control valve 312 and the holding valve 313 and closes the pressure reducing valve 314.

The second brake ECU 902 can calculate each wheel pressure based on the control state of the pressure sensor 75 and the downstream unit 3. The detection values of the various sensors may be sent to both brake ECUs 901 and 902.

The vehicle braking device 1 is configured to be able to execute normal control. Normal control is also called by-wire mode. In normal control, the output pressure of the upstream unit 11 is the hydraulic pressure output by the electric cylinder 2. The downstream unit 3 is capable of outputting hydraulic pressure to the wheel cylinders 81 to 84 based on the output pressure of the upstream unit 11. The normal control will be described below.

(Normal control)
The first brake ECU 901 includes a normal control unit 91 that controls the upstream unit 11 including the electric motor 22 etc., and a failure determination unit 92. The normal control unit 91 is configured to be able to execute normal control. The normal control is a control in which the master cylinder device 4 and the wheel cylinders 81 to 84 are hydraulically isolated, and the wheel cylinders 81 to 84 are pressurized by at least one of the electric cylinder 2 and the downstream unit 3. The normal control includes a preparation control and a normal pressurization control.

The preparatory control is a control that forms a so-called by-wire mode. In the preparatory control, the normal control unit 91 closes the master cut valve 62 and opens the communication control valve 61 and the simulator cut valve 44. The preparatory control is executed when the vehicle in which the vehicle braking device 1 is provided is ready to start. Examples of when the vehicle is ready to start include when the vehicle ignition is turned on or when an electric vehicle is started. More specifically, the preparatory control in the first embodiment is executed when the first brake ECU 901 is started (power is turned on).

The preparatory control may be executed when the brake pedal is operated, rather than when the vehicle ignition is turned on or the electric vehicle is started. In this case, the by-wire mode may be established when the brake pedal is operated, and the by-wire mode may not be established when the brake pedal is not operated.

Normal pressurization control is a control that pressurizes the wheel cylinders 81 to 84 in the by-wire mode (a state in which preparation control is completed). In normal pressurization control, the normal control unit 91 sets a target output pressure based on data detected by the stroke sensor 71 and the pressure sensor 72. Based on the set target output pressure, the electric cylinder 2 is controlled. The second brake ECU 902 operates the downstream unit 3 when performing anti-skid control or the like. In this way, in normal control, the electric cylinder 2, the first hydraulic pressure output unit 31, and the second hydraulic pressure output unit 32 are controlled based on the set target value, making it possible to adjust the hydraulic pressure of the wheel cylinders 81 to 84.

(Fault detection of electric cylinders)
The failure determination unit 92 determines whether or not the position of the piston 23 of the electric cylinder 2 (also referred to as the "piston position") is in an uncontrollable state. Furthermore, the failure determination unit 92 of the present embodiment determines whether or not the reservoir 45 and the second hydraulic pressure output unit 32 are hydraulically connected via the electric cylinder 2 based on the determination result. The failure determination unit 92 estimates the position of the piston 23 when it determines that at least the piston position is in an uncontrollable state.

More specifically, the failure determination unit 92 determines whether the piston 23 of the electric cylinder 2 is locked (or stuck) based on the detection result of the rotation angle sensor 22b provided for the electric motor 22. The rotation angle sensor 22b is a sensor that detects the rotation angle (rotation position) of the electric motor 22. If the piston 23 is mechanically locked (i.e., the piston 23 cannot be physically moved relative to the cylinder 21) due to the reduction gear that constitutes part of the linear motion mechanism 22a being locked, the electric motor 22 does not rotate even if an operation command (control current) is output to the electric motor 22, and the detection value of the rotation angle sensor 22b does not change. Using this principle, the failure determination unit 92 can determine whether the piston 23 is locked based on the control command content to the electric motor 22 and the detection result of the rotation angle sensor 22b. In the following description, the mechanical locking of the piston 23 is also referred to as "piston lock".

The failure determination unit 92 can also estimate where the piston 23 is located in the cylinder 21 based on the detection result of the rotation angle sensor 22b. That is, the failure determination unit 92 can estimate whether the piston 23 is located in the communication area or the cut-off area in the cylinder 21 based on the detection result of the rotation angle sensor 22b. Therefore, when the failure determination unit 92 detects a piston lock, it can also estimate at what position the piston 23 is locked. However, when it is difficult to estimate which area the piston 23 is located, for example, when the detection result of the rotation angle sensor 22b indicates the vicinity of the boundary (switching position) between the communication area and the cut-off area, the determination result of the failure determination unit 92 is "unknown (position cannot be determined)". In this way, the failure determination unit 92 selects one of "communication", "cut-off", and "unknown" for the lock position of the piston 23.

(Assistance control when piston is locked)
The brake ECUs 901, 902 each include a control unit 93 that controls the first hydraulic pressure output unit 31, the second hydraulic pressure output unit 32, and the communication control valve 61. In assist control during piston lock, for example, the control unit 93 of the first brake ECU 901 controls the communication control valve 61, and the control unit 93 of the second brake ECU 902 controls the downstream unit 3. Both brake ECUs 901, 902 cooperate to execute various controls.

When the brake operation is started (the brake pedal Z is depressed) and the failure determination unit 92 detects a piston lock, the control unit 93 sets the control mode to the assist mode. The assist mode is a mode in which the downstream unit 3 executes assist control when the piston locks. The assist control is a control in which the downstream unit 3 adjusts the wheel pressure according to the required braking force. In the assist modes (each of the assist controls described below), the master cut valve 62 is open and the simulator cut valve 44 is closed.

(Assistance control when the judgment result is "unknown")
When the failure determination unit 92 determines that the piston position of the electric cylinder 2 is in an uncontrollable state and when it is not determined that the reservoir 45 and the second hydraulic pressure output unit 32 are hydraulically connected via the electric cylinder 2 (only when the determination result is “unknown” in this embodiment), the control unit 93 causes the first hydraulic pressure output unit 31 to output hydraulic pressure toward the first wheel cylinders 81, 82 with the communication control valve 61 closed, and does not cause the second hydraulic pressure output unit 32 to output hydraulic pressure toward the second wheel cylinders 83, 84, in order to increase the braking force. In other words, when the failure determination unit 92 determines that the lock position of the piston 23 is unknown, the control unit 93 operates the first hydraulic pressure output unit 31 with the communication control valve 61 closed, and does not operate the second hydraulic pressure output unit 32, in order to increase the braking force.

In this assist control, the first hydraulic pressure output unit 31 operates to supply fluid from the master cylinder 41 to the first wheel cylinders 81 and 82, pressurizing only the first wheel cylinders 81 and 82. The first hydraulic pressure output unit 31 pressurizes the first wheel cylinders 81 and 82 using the master pressure generated by the driver's brake operation as the base hydraulic pressure.

The reservoir 45 (storage chamber 451) and the master cylinder 41 can communicate with each other, and the first hydraulic pressure output unit 31 can return the fluid in the first wheel cylinders 81, 82 to the master cylinder 41 and the reservoir 45. In other words, the control unit 93 can operate the first hydraulic pressure output unit 31 to reduce the pressure in the first wheel cylinders 81, 82 (to reduce the braking force). Hereinafter, the assist control when the determination result is "unknown" is referred to as "unknown assist control (corresponding to "specific assist control")."

(Assistance control when the judgement result is "blocked")
When the failure determination unit 92 determines that the piston position of the electric cylinder 2 is in an uncontrollable state and that the reservoir 45 and the second hydraulic pressure output unit 32 are hydraulically blocked, the control unit 93 causes the first hydraulic pressure output unit 31 to output hydraulic pressure toward the first wheel cylinders 81, 82 and the second hydraulic pressure output unit 32 to output hydraulic pressure toward the second wheel cylinders 83, 84 with the communication control valve 61 open in order to increase the braking force. In other words, when the failure determination unit 92 determines that the locked position of the piston 23 is in the block region, the control unit 93 operates both the first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32 with the communication control valve 61 open in order to increase the braking force.

In this assist control, the first hydraulic pressure output unit 31 operates to supply fluid from the master cylinder 41 to the first wheel cylinders 81, 82, and the second hydraulic pressure output unit 32 operates to supply fluid from the master cylinder 41 to the second wheel cylinders 83, 84 via the communication control valve 61. The first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32 each pressurize the target wheel cylinders 81-84 using the master pressure generated by the driver's brake operation as the base hydraulic pressure. This causes all wheel cylinders 81-84 to be pressurized.

The control unit 93 can reduce the pressure in the first wheel cylinders 81 and 82 by operating the first hydraulic pressure output unit 31 to return the fluid in the first wheel cylinders 81 and 82 to the master cylinder 41 and the reservoir 45 (storage chamber 451). When reducing the pressure in the second wheel cylinders 83 and 84, the control unit 93 can return the fluid in the second wheel cylinders 83 and 84 to the master cylinder 41 and the reservoir 45 (storage chamber 451) through the communication control valve 61 by opening the communication control valve 61. In this way, when the control unit 93 causes the second hydraulic pressure output unit 32 to output hydraulic pressure toward the reservoir 45, the control unit 93 opens the communication control valve 61. This allows the second wheel cylinders 83 and 84 to be reduced in pressure as well. In this way, in the boost control when the determination result is "shut off" (hereinafter referred to as "shut off boost control"), all wheel cylinders 81 to 84 can be boosted or depressurized.

In this embodiment, the conditions for executing the boost control during cutoff include the failure determination unit 92 not determining "connected" (first condition) and the failure determination unit 92 determining "cutoff" (second condition). When these two conditions are satisfied, the boost control during cutoff is executed. When the failure determination unit 92 has not determined "connected" or "cutoff", that is, when only the first condition is satisfied, the boost control when determination is impossible is executed.

(Assistance control when the judgement result is "connected")
When the failure determination unit 92 determines that the piston position of the electric cylinder 2 is in an uncontrollable state and that the reservoir 45 and the second hydraulic pressure output unit 32 are hydraulically connected via the electric cylinder 2, the control unit 93 causes the first hydraulic pressure output unit 31 to output hydraulic pressure toward the first wheel cylinders 81, 82 and the second hydraulic pressure output unit 32 to output hydraulic pressure toward the second wheel cylinders 83, 84 with the communication control valve 61 closed to increase the braking force. In other words, when the failure determination unit 92 determines that the locked position of the piston 23 is in the communication region, the control unit 93 operates both the first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32 with the communication control valve 61 closed to increase the braking force.

In this assist control, the first hydraulic pressure output unit 31 is operated to supply fluid from the master cylinder 41 to the first wheel cylinders 81 and 82, and the second hydraulic pressure output unit 32 is operated to supply fluid from the reservoir 45 (storage chamber 452) to the second wheel cylinders 83 and 84 via the electric cylinder 2. Because the communication control valve 61 is closed, the first fluid path 51 and the second fluid path 52 are independent of each other.

The first hydraulic pressure output unit 31 pressurizes the first wheel cylinders 81, 82 using the master pressure generated by the driver's brake operation as the base hydraulic pressure. The second hydraulic pressure output unit 32 pressurizes the second wheel cylinders 83, 84 using the fluid in the reservoir 45 (storage chamber 452). This causes all wheel cylinders 81 to 84 to be pressurized.

As in the unknown state assist control, the control unit 93 can reduce the pressure in the first wheel cylinders 81, 82 by operating the first hydraulic pressure output unit 31 with the communication control valve 61 closed to return the fluid in the first wheel cylinders 81, 82 to the master cylinder 41 and the reservoir 45 (storage chamber 451). When reducing the pressure in the second wheel cylinders 83, 84, the control unit 93 can operate the second hydraulic pressure output unit 32 with the communication control valve 61 closed to return the fluid in the second wheel cylinders 83, 84 to the reservoir 45 (storage chamber 452) via the electric cylinder 2. When the control unit 93 causes at least one of the first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32 to output hydraulic pressure toward the reservoir 45, it closes the communication control valve 61. In this way, even when the boost control is performed when the determination result is "connected" (hereinafter referred to as "connected boost control"), pressure can be increased or decreased in all wheel cylinders 81 to 84.

(Flow of Control)
The flow of control of this embodiment will be described with reference to Fig. 4. As shown in Fig. 4, a brake operation is started, and the malfunction determination unit 92 determines whether or not a piston lock has been detected (S100). If a piston lock has been detected (S100: Yes), the assist mode is started (S101). The control unit 93 checks whether or not the malfunction determination unit 92 can determine (estimate) the position of the piston 23 (S102). If the malfunction determination unit 92 determines that the position is "unknown (position cannot be determined)" (S102: No), the control unit 93 executes unknown assist control (S103).

When the failure determination unit 92 determines that the state is "connected" (S102: Yes, S104: Yes), the control unit 93 executes the connected assist control (S105). When the failure determination unit 92 determines that the state is "cut off" (S102: Yes, S104: No), the control unit 93 executes the cut off assist control (S106). In this way, when the determination result is "connected", the control unit 93 executes the connected assist control instead of the unknown assist control, and when the determination result is "cut off", the control unit 93 executes the cut off assist control instead of the unknown assist control.

(Effects of this embodiment)
According to this embodiment, when a locking failure occurs in piston 23 and the determination result of failure determination unit 92 is not "reservoir 45 and second hydraulic pressure output unit 32 are in communication" (in this embodiment, only when the determination result is "unknown"), only first wheel cylinders 81, 82 are pressurized by the assist control, and second wheel cylinders 83, 84 which are not in communication with reservoir 45 are not pressurized. Pressurization of first wheel cylinders 81, 82 increases the braking force (front wheel braking force in this embodiment).

The first hydraulic pressure output unit 31 can also return the fluid in the first wheel cylinders 81, 82 to the master cylinder 41 and the reservoir 45. In other words, the operation of the first hydraulic pressure output unit 31 can also reduce the pressure in the first wheel cylinders 81, 82 (reduce the braking force). There is no need to reduce the pressure in the second wheel cylinders 83, 84, which are not pressurized. Therefore, even if a locking failure occurs in the piston 23 in the electric cylinder 2, the first hydraulic pressure output unit 31, which is one of the downstream units 3, can provide assist control (adjust the braking force).

In addition, in the case of the disconnected assist control and the connected assist control, the control unit 93 can increase or decrease the pressure of the wheel cylinders 81 to 84 as described above. Thus, according to this embodiment, even if a locking failure occurs in the piston 23 of the electric cylinder 2, the downstream unit 3 can perform assist control (adjust the braking force).

(others)
The present invention is not limited to the above embodiment. For example, the shut-off assist control may have the same control content as the unknown assist control. Examples of cases in which the determination result of the failure determination unit 92 is not "communication between the reservoir 45 and the second hydraulic pressure output unit 32" include "unknown" and "shut-off". In the above embodiment, different assist controls are executed for the "unknown" and "shut-off" cases, but the unknown assist control may be executed regardless of the determination result. For example, as shown in FIG. 5, when the failure determination unit 92 determines "unknown" (S202: No) or "shut-off" (S203: No), the control unit 93 executes the unknown assist control and pressurizes only the first wheel cylinders 81, 82 (S204). When the failure determination unit 92 determines "communication" (S203: Yes), the control unit 93 executes the connected assist control (S205). This also enables the downstream unit 3 to perform the assist control (braking force adjustment) even when a locking failure of the piston 23 occurs. In addition, for example, if the failure determination unit 92 is configured not to estimate the locked position of the piston 23, the control unit 93 may execute the unknown assist control when the failure determination unit 92 detects a piston lock. In this configuration, the assist control is only the unknown assist control (specific assist control). In other words, when the failure determination unit 92 determines that the piston position of the electric cylinder 2 is in an uncontrollable state, the control unit 93 executes the specific assist control to increase the braking force by making the first hydraulic pressure output unit 31 output fluid toward the first wheel cylinders 81, 82 with the communication control valve 61 closed and not making the second hydraulic pressure output unit 32 output fluid toward the second wheel cylinders 83, 84.

The downstream unit 3 may also be configured as shown in FIG. 6 (the check valve symbol is omitted). The parts that differ from the above embodiment will be briefly described below using the first hydraulic pressure output unit 31 as an example. The return liquid path 317a is a liquid path connected to the first connecting liquid path 511 at one end and connected to the suction port of the pump 315 without going through the reservoir 317 at the other end. A normally closed type solenoid valve 318 is arranged in the return liquid path 317a. The reservoir 317 does not have a valve function like a pressure regulating reservoir, and is a reservoir equipped with a cylinder, a piston, and a biasing member. In this downstream unit 3, the upstream unit 11 and the suction port of the pump 315 can be communicated by opening the solenoid valve 318. When the pump 315 operates with the solenoid valve 318 open, the pump 315 sucks in fluid from the upstream unit 11 and discharges it to the branch section X. The second hydraulic pressure output section 32 has the same configuration as the first hydraulic pressure output section 31.

In such a downstream unit 3, when the control unit 93 executes the unknown assist control, it opens the solenoid valve 318 of the first hydraulic pressure output unit 31 and does not open the solenoid valve 318 of the second hydraulic pressure output unit 32. This allows only the first hydraulic pressure output unit 31, which is capable of pressure reduction control, to draw fluid from the master cylinder 41 and supply it to the first wheel cylinders 81, 82. Furthermore, when the control unit 93 executes the cutoff assist control or the connected assist control, it opens the solenoid valves 318 of both the first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32. This allows both the first hydraulic pressure output unit 31 and the second hydraulic pressure output unit 32 to draw fluid from the upstream unit 11.

In addition, instead of the electric cylinder 2, an electric cylinder not including the biasing member 25 may be used. In this case, it is preferable that the current supply configuration to the electric motor 22 is redundant. In addition, the downstream unit 3 may include an electric cylinder instead of the pump 315. The present invention can also be applied to vehicles including a regenerative braking device (hybrid vehicles and electric vehicles), vehicles that perform automatic brake control, or autonomous vehicles, for example.

In the above embodiment, the first wheel cylinders 81 and 82 are provided on the front wheels, and the second wheel cylinders 83 and 84 are provided on the rear wheels. However, the first wheel cylinders 81 and 82 may be provided on the right front wheel and the left rear wheel, and the second wheel cylinders 83 and 84 may be provided on the left front wheel and the right rear wheel. The communication passage 53 may be, for example, a fluid passage that connects the first fluid passage 51 and the electric cylinder 2. In this case, the communication passage 53 can be said to connect the first fluid passage 51 and the second fluid passage 52 via the electric cylinder 2. The communication passage 53 can be said to be a fluid passage to which the fluid output from the electric cylinder 2 is supplied directly or via the second fluid passage 52.

1...vehicle braking device, 2...electric cylinder, 21...cylinder, 22...electric motor, 23...piston, 24...hydraulic pressure chamber, 31...first hydraulic pressure output section, 32...second hydraulic pressure output section, 41...master cylinder, 45...reservoir, 51...first hydraulic path, 52...second hydraulic path, 53...communication passage, 61...communication control valve, 81, 82...first wheel cylinder, 83, 84...second wheel cylinder, 92...failure determination section, 93...control section.

Claims (4)

a first hydraulic pressure output unit provided in a first hydraulic passage connecting a reservoir and a first wheel cylinder, the first hydraulic pressure output unit being capable of selectively outputting hydraulic pressure to the reservoir side and the first wheel cylinder side;
a master cylinder provided in the first fluid passage between the reservoir and the first fluid pressure output portion;
a second hydraulic pressure output unit provided in a second hydraulic passage connecting the reservoir and a second wheel cylinder, the second hydraulic pressure output unit being capable of selectively outputting hydraulic pressure to the reservoir side and the second wheel cylinder side;
an electric cylinder provided in the second fluid passage between the reservoir and the second hydraulic pressure output portion, the electric cylinder having a cylinder and a piston that slides within the cylinder, hydraulically connecting or disconnecting the reservoir and the second hydraulic pressure output portion according to a position of the piston, and outputting fluid according to the sliding of the piston;
a communication control valve provided in a communication passage connected to a portion of the first fluid passage between the master cylinder and the first hydraulic pressure output portion, the communication control valve being a fluid passage to which the fluid output from the electric cylinder is supplied, the communication control valve being provided in a communication passage connected to a portion of the first fluid passage between the master cylinder and the first hydraulic pressure output portion;
a failure determination unit that determines whether a piston position of the electric cylinder is in an uncontrollable state;
a control unit that controls the first hydraulic pressure output unit, the second hydraulic pressure output unit, and the communication control valve;
Equipped with
When the failure determination unit determines that the piston position of the electric cylinder is in an uncontrollable state, the control unit executes a specific assist control to increase the braking force by causing the first hydraulic pressure output unit to output fluid toward the first wheel cylinder with the communication control valve closed and not causing the second hydraulic pressure output unit to output fluid toward the second wheel cylinder. the failure determination unit determines whether the reservoir and the second hydraulic pressure output unit are hydraulically connected via the electric cylinder,
The control unit is
When the failure determination unit determines that the piston position of the electric cylinder is in an uncontrollable state and that the reservoir and the second hydraulic pressure output unit are hydraulically blocked,
When increasing the braking force, a cut-off assist control is executed instead of the specific assist control, in which the first hydraulic pressure output portion outputs hydraulic pressure toward the first wheel cylinder and the second hydraulic pressure output portion outputs hydraulic pressure toward the second wheel cylinder with the communication control valve open.
2. The vehicle brake system according to claim 1, wherein, in the cut-off assist control, when the second hydraulic pressure output section is caused to output hydraulic pressure toward the reservoir, the communication control valve is opened. the failure determination unit determines whether the reservoir and the second hydraulic pressure output unit are hydraulically connected via the electric cylinder,
The control unit is
When the failure determination unit determines that the piston position of the electric cylinder is in an uncontrollable state and that the reservoir and the second hydraulic pressure output unit are hydraulically connected via the electric cylinder,
When increasing the braking force, a communication assisting control is executed instead of the specific assisting control, in which the communication control valve is closed and the first hydraulic pressure output portion is caused to output hydraulic pressure toward the first wheel cylinder and the second hydraulic pressure output portion is caused to output hydraulic pressure toward the second wheel cylinder,
3. The vehicle brake device according to claim 1, wherein, in the communication assist control, when at least one of the first hydraulic pressure output portion and the second hydraulic pressure output portion is caused to output hydraulic pressure toward the reservoir, the communication control valve is closed. the failure determination unit determines whether the reservoir and the second hydraulic pressure output unit are hydraulically connected via the electric cylinder,
4. The vehicle brake device according to claim 1, wherein the control unit executes the specific assist control when increasing the braking force if the failure determination unit determines that the piston position of the electric cylinder is in an uncontrollable state and it cannot be determined whether the reservoir and the second hydraulic pressure output unit are hydraulically connected via the electric cylinder.

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