Braking system

Abstract

A braking system 200 is applied to a vehicle comprising a front wheel cylinder 31F and a rear wheel cylinder 31R of smaller volume than the front wheel cylinder 31F. The braking system 200 comprises: an electric cylinder 60; a system separation cylinder 70; a connecting channel 551 joining a first output port 62b of the electric cylinder 60 and a first chamber R1 of the system separation cylinder 70; a front wheel supply channel 552 which is connected to the connecting channel 551 and which supplies brake fluid discharged from the first output port 62b to the front wheel cylinder 31F; and a rear wheel supply channel 553 that supplies brake fluid discharged from the second chamber R2 of the system separation cylinder 70 to the rear wheel cylinder 31R.

Description

Braking system

[0001] The present invention relates to a braking system that adjusts the braking force generated by a vehicle.

[0002] Patent Document 1 discloses an example of a braking system including an electric cylinder and a system separation cylinder. In this system, a portion of the brake fluid discharged from the electric cylinder is supplied to a first wheel cylinder via a first supply line, while the remaining brake fluid is supplied to the system separation cylinder. The system separation cylinder includes a cylinder and a piston that divides the cylinder into a first chamber and a second chamber. In this system separation cylinder, brake fluid discharged from the electric cylinder flows into the first chamber, increasing the hydraulic pressure in the first chamber. This moves the piston in a direction that reduces the volume of the second chamber, thereby supplying brake fluid from the second chamber to the second wheel cylinder via the second supply line. In other words, in this system, the system separation cylinder fluidically separates the first system for adjusting the hydraulic pressure in the first wheel cylinder from the second system for adjusting the hydraulic pressure in the second wheel cylinder.

[0003] International Publication No. 2023 / 066587

[0004] In a braking system equipped with a system separation cylinder as described above, it is required to suppress an increase in the size of the entire system.

[0005] A braking system for solving the above problem is applied to a vehicle having front and rear wheels, a front wheel cylinder corresponding to the front wheels, and a rear wheel cylinder corresponding to the rear wheels and having a smaller volume than the front wheel cylinder. The braking system includes a supply device having an electric motor and configured to be able to discharge brake fluid from an output port when driven by the electric motor; a system separation cylinder having a cylinder and a piston that divides the interior of the cylinder into a first chamber and a second chamber, and configured so that when the hydraulic pressure in the first chamber increases, the piston moves in a first movement direction that reduces the volume of the second chamber, thereby discharging brake fluid from the second chamber, and when the hydraulic pressure in the first chamber decreases, the piston moves in a second movement direction that is opposite to the first movement direction, thereby drawing brake fluid into the second chamber; a connecting flow path that is a brake flow path connecting the output port and the first chamber; a front wheel supply flow path that is connected to the connecting flow path and supplies brake fluid discharged from the output port to the front wheel cylinder; and a rear wheel supply flow path that is a brake flow path that supplies brake fluid discharged from the second chamber to the rear wheel cylinder.

[0006] The braking system described above has the advantage of being able to suppress an increase in the size of the entire system.

[0007] Fig. 1 is a schematic diagram showing a vehicle equipped with a braking system according to an embodiment. Fig. 2 is a schematic diagram showing a state in which brake fluid is supplied from an electric cylinder to a system separation cylinder in the braking system of Fig. 1. Fig. 3 is a schematic diagram showing a brake actuator equipped in the braking system of Fig. 1. Fig. 4 is a flowchart showing a series of processes for finding a standby position of a first piston in an electric cylinder equipped in the braking system of Fig. 1. Fig. 5 is a timing chart when regenerative cooperative control is performed in the braking system of Fig. 1.

[0008] An embodiment of a braking system will be described with reference to Figures 1 to 5. Figure 1 shows a vehicle equipped with a braking system 200. The vehicle includes a plurality of wheels, a regenerative device 20, and a plurality of friction brakes. The plurality of wheels includes two front wheels 11F and two rear wheels 11R.

[0009] <Regenerative Device> The regenerative device 20 includes a motor generator 21 for the front wheels 11F and a regenerative control unit 22 that controls the motor generator 21. When the motor generator 21 functions as an electric motor, driving force is transmitted from the motor generator 21 to the plurality of front wheels 11F. On the other hand, when the motor generator 21 functions as a generator, a regenerative braking force FxR corresponding to the amount of power generated by the motor generator 21 is generated at the axles of the plurality of front wheels 11F.

[0010] An example of the regeneration control unit 22 is an electronic control device. In this case, the regeneration control unit 22 has a CPU and a memory. The memory stores a control program executed by the CPU. The CPU executes the control program, allowing the regeneration control unit 22 to control the motor generator 21.

[0011] The regenerative control unit 22 is configured to be able to transmit and receive various information to and from a control device 210 of the braking system 200, which will be described later in detail. As will be described later in detail, when braking the vehicle, the regenerative control unit 22 adjusts the regenerative braking force FxR by transmitting and receiving information to and from the control device 210.

[0012] <Friction Brake> One friction brake is provided for each wheel. Of the multiple friction brakes, the friction brake provided for the front wheel 11F is the front wheel friction brake 30F, and the friction brake provided for the rear wheel 11R is the rear wheel friction brake 30R. Each of the front wheel friction brake 30F and the rear wheel friction brake 30R has a wheel cylinder to which brake fluid is supplied, a rotor 32 that rotates integrally with the wheel, and a friction material 33 that is pressed against the rotor 32. The wheel cylinder of the front wheel friction brake 30F is the front wheel wheel cylinder 31F. The wheel cylinder of the rear wheel friction brake 30R is the rear wheel wheel cylinder 31R. In a friction brake, the higher the hydraulic pressure in the wheel cylinder, the stronger the friction material 33 is pressed against the rotor 32. This generates a frictional braking force at the wheel. Specifically, the higher the hydraulic pressure in the wheel cylinder, the greater the frictional braking force generated.

[0013] The hydraulic pressure in the front wheel cylinder 31F is referred to as the "front wheel hydraulic pressure PwcF." The hydraulic pressure in the rear wheel cylinder 31R is referred to as the "rear wheel hydraulic pressure PwcR." A frictional braking force corresponding to the front wheel hydraulic pressure PwcF is generated in the front wheel 11F. A frictional braking force corresponding to the rear wheel hydraulic pressure PwcR is generated in the rear wheel 11R. The frictional braking force generated in the front wheel 11F is referred to as the "front wheel frictional braking force FxMF." The frictional braking force generated in the rear wheel 11R is referred to as the "rear wheel frictional braking force FxMR."

[0014] <Brake System> The brake system 200 generates a front wheel friction braking force FxMF and a rear wheel friction braking force FxMR by adjusting the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR. The brake system 200 includes an operation mechanism 40, an upstream unit 50, and a downstream unit 90. The upstream unit 50 and the downstream unit 90 are each configured to adjust the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0015] <Configuration of Operation Mechanism> The operation mechanism 40 has a brake operation member 41 and a reaction force generating unit 42. The brake operation member 41 is operated by the driver of the vehicle when adjusting the deceleration of the vehicle. An example of the brake operation member 41 is a brake pedal. The reaction force generating unit 42 generates a reaction force in response to the driver's operation of the brake operation member 41. In the braking system 200, the operation mechanism 40 is structurally connected to neither the upstream unit 50 nor the downstream unit 90. Therefore, if neither the upstream unit 50 nor the downstream unit 90 is activated, the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR do not increase even if the brake operation member 41 is operated.

[0016] The operation mechanism 40 has a first brake sensor 81 and a second brake sensor 111. Each of the plurality of brake sensors 81, 111 detects information related to the operation of the brake operation member 41 by the driver of the vehicle. For example, the plurality of brake sensors 81, 111 detect the amount of operation of the brake operation member 41 by the driver as the information. For example, the same type of sensor as the first brake sensor 81 is adopted as the second brake sensor 111. A detection signal from the first brake sensor 81 is input to a first controller 220, which will be described later. A detection signal from the second brake sensor 111 is input to a second controller 230, which will be described later. Note that the plurality of brake sensors 81, 111 may be sensors that detect the operating force of the brake operation member 41 by the driver, as information related to the operation of the brake operation member 41.

[0017] <Configuration of Upstream Unit> The upstream unit 50 includes a reservoir tank 51, an electric cylinder 60, a system separation cylinder 70, a differential pressure adjustment valve 52, a reservoir shutoff valve 53, and a first controller 220. The first controller 220 will be described later.

[0018] The reservoir tank 51 stores brake fluid and is open to the atmosphere. The reservoir tank 51 is divided into a first reservoir chamber 513 and a second reservoir chamber 514 by an internal partition wall 511. For example, when the amount of brake fluid stored in the reservoir tank 51 is sufficiently large, the first reservoir chamber 513 and the second reservoir chamber 514 are connected to each other. On the other hand, when the amount of brake fluid stored in the reservoir tank 51 decreases below a predetermined amount, the internal partition wall 511 separates the first reservoir chamber 513 and the second reservoir chamber 514. Therefore, brake fluid can be supplied to both the first reservoir chamber 513 and the second reservoir chamber 514 from a single supply port.

[0019] The differential pressure adjustment valve 52 is a normally open linear solenoid valve. The reservoir shutoff valve 53 is a normally open solenoid valve. <Brake Flow Channel> The upstream unit 50 has multiple brake flow channels. The multiple brake flow channels include a connection flow channel 551, a front wheel supply flow channel 552, a rear wheel supply flow channel 553, a release flow channel 554, a reservoir flow channel 555, a first input flow channel 556, and a second input flow channel 557.

[0020] The connection flow path 551 connects the electric cylinder 60 and the system separation cylinder 70. Specifically, the connection flow path 551 connects a first output port 62b of the electric cylinder 60 (described later) to a first chamber R1 of the system separation cylinder 70 (described later).

[0021] The front wheel supply flow path 552 is connected to the connecting flow path 551. The front wheel supply flow path 552 supplies brake fluid to the front wheel cylinder 31F. For example, the front wheel supply flow path 552 connects the connecting flow path 551 to a first hydraulic circuit 93F of the downstream unit 90, which will be described later. A differential pressure adjustment valve 52 is installed in the front wheel supply flow path 552.

[0022] A bypass flow path 521 that bypasses the differential pressure adjustment valve 52 is connected to the front wheel supply flow path 552. A check valve 522 is installed in the bypass flow path 521. The check valve 522 allows the flow of brake fluid from the front wheel cylinder 31F toward the electric cylinder 60, while restricting the flow of brake fluid from the electric cylinder 60 toward the front wheel cylinder 31F.

[0023] The rear wheel supply passage 553 is connected to the system separation cylinder 70. The rear wheel supply passage 553 supplies brake fluid to the rear wheel cylinder 31R. For example, the rear wheel supply passage 553 connects a second output port 71b of the system separation cylinder 70 (described later) to a second hydraulic circuit 93R of the downstream unit 90 (described later).

[0024] The release flow path 554 connects the reservoir tank 51 and the connection flow path 551. A reservoir shutoff valve 53 is installed in the release flow path 554. The reservoir flow path 555 guides the brake fluid in the reservoir tank 51 to an intermediate portion 552a of the front-wheel supply flow path 552. When the connection point of the front-wheel supply flow path 552 with the connection flow path 551 is defined as connection point P1, the portion of the front-wheel supply flow path 552 on the opposite side of connection point P1 across the differential pressure adjustment valve 52 is the intermediate portion 552a. For example, the reservoir flow path 555 connects a portion of the release flow path 554 between the reservoir shutoff valve 53 and the reservoir tank 51 to the intermediate portion 552a of the front-wheel supply flow path 552.

[0025] A check valve 56, which is an example of a valve mechanism, is installed in the reservoir flow path 555. The check valve 56 regulates the flow of brake fluid in the reservoir flow path 555 from the intermediate portion 552a toward the reservoir tank 51. On the other hand, the check valve 56 allows the flow of brake fluid in the reservoir flow path 555 from the reservoir tank 51 toward the intermediate portion 552a.

[0026] The first input flow path 556 connects the portion of the reservoir flow path 555 between the connection point P2 with the release flow path 554 and the check valve 56 to a first input port 62a of the electric cylinder 60 described below.

[0027] The second input flow path 557 connects the reservoir tank 51 with a second input port 71a of the system separation cylinder 70 (described later). The second input port 71a is a port that connects a second chamber R2 in the system separation cylinder 70 (described later) with the outside.

[0028] For example, the second input flow path 557 is connected to a second reservoir chamber 514 in the reservoir tank 51. The second input flow path 557 also communicates with a second chamber R2 in a system separation cylinder 70 (described later) via a second input port 71 a. On the other hand, the release flow path 554 is connected to a first reservoir chamber 513 in the reservoir tank 51. The release flow path 554 also communicates with a first chamber R1 in a system separation cylinder 70 (described later) via a connection flow path 551. That is, the first chamber R1 and the second chamber R2 of the system separation cylinder 70 (described later) are fluidly separated by a second piston 72 of the system separation cylinder 70 (described later), and are also separated by an internal partition wall 511 in the reservoir tank 51 to which the first chamber R1 and the second chamber R2 of the system separation cylinder 70 (described later) are connected.

[0029] <Electric Cylinder> The electric cylinder 60 has a first electric motor 61. The electric cylinder 60 is configured to be able to discharge brake fluid from a first output port 62b when driven by the first electric motor 61. The electric cylinder 60 corresponds to the "supply device."

[0030] For example, the electric cylinder 60 has a first cylinder 62, a first piston 63, and a conversion mechanism 64. The first piston 63 is slidably provided within the first cylinder 62. The conversion mechanism 64 converts the rotation of the output shaft of the first electric motor 61 into linear movement of the first piston 63. An example of the conversion mechanism 64 is a ball screw.

[0031] A hydraulic pressure chamber Re, into which brake fluid is introduced, is defined inside the first cylinder 62 by the peripheral wall of the first cylinder 62 and the first piston 63. The position of the first piston 63 inside the first cylinder 62 can be changed by driving the first electric motor 61. The direction in which the first piston 63 moves when reducing the volume of the hydraulic pressure chamber Re is referred to as the "forward direction Za," while the direction opposite to the forward direction Za is referred to as the "reverse direction Zb." The reverse direction Zb is also the direction in which the first piston 63 moves when increasing the volume of the hydraulic pressure chamber Re.

[0032] A first input port 62a and a first output port 62b are formed on the peripheral wall of the first cylinder 62 as ports connecting the hydraulic pressure chamber Re with the outside. A first input flow path 556 is connected to the first input port 62a. A connection flow path 551 is connected to the first output port 62b.

[0033] A first through-hole 63a is formed in the first piston 63. The first through-hole 63a is positioned so that the first input port 62a and the hydraulic chamber Re can communicate with each other when the first piston 63 is in its most retracted position. As a result, when the first piston 63 is in its most retracted position, the hydraulic chamber Re of the first cylinder 62 communicates with the reservoir tank 51 via the first through-hole 63a, the first input port 62a, the first input flow path 556, and the release flow path 554. The first input port 62a is open when the first piston 63 is in its most retracted position, and is closed by the first piston 63 when the first piston 63 moves forward in the Za from the most retracted position. Even after the first input port 62a is closed by the first piston 63, the hydraulic pressure in the hydraulic chamber Re increases when the first piston 63 moves forward in the Za.

[0034] The first output port 62b is always open regardless of the position of the first piston 63. Therefore, when the first input port 62a is closed by the first piston 63, the first piston 63 moves in the forward direction Za within the first cylinder 62 in response to the driving of the first electric motor 61, causing the brake fluid in the hydraulic chamber Re to be discharged from the first output port 62b to the connecting flow path 551. On the other hand, the first piston 63 moves in the backward direction Zb within the first cylinder 62 in response to the driving of the first electric motor 61, causing the brake fluid in the connecting flow path 551 to be drawn into the hydraulic chamber Re from the first output port 62b.

[0035] <System Separation Cylinder> The system separation cylinder 70 includes a second cylinder 71 and a second piston 72 and spring 73 provided within the second cylinder 71. The interior of the second cylinder 71 is partitioned into a first chamber R1 and a second chamber R2 by the circumferential wall of the second cylinder 71 and the second piston 72. Brake fluid is introduced into each of the first chamber R1 and the second chamber R2. The second piston 72 is configured to be movable along the circumferential wall of the second cylinder 71 in a direction to decrease the volume of the second chamber R2 and a direction to increase the volume of the second chamber R2 along the circumferential wall of the second cylinder 71. The movement direction of the second piston 72 to decrease the volume of the second chamber R2 is referred to as the "first movement direction Ya." The movement direction of the second piston 72 to increase the volume of the second chamber R2 is referred to as the "second movement direction Yb." The second movement direction Yb is opposite to the first movement direction Ya. The position of the second piston 72 that minimizes the volume of the first chamber R1 is referred to as the "most retracted position of the second piston 72."

[0036] The spring 73 applies a biasing force to the second piston 72 in the second movement direction Yb. For example, the spring 73 is disposed in the second chamber R2. The position of the second piston 72 inside the second cylinder 71 can be changed by the hydraulic pressure in the first chamber R1. When the hydraulic pressure in the first chamber R1 increases, the second piston 72 moves in the first movement direction Ya against the biasing force of the spring 73. On the other hand, when the hydraulic pressure in the first chamber R1 decreases, the second piston 72 moves in the second movement direction Yb due to the biasing force of the spring 73.

[0037] A connecting flow path 551 is connected to the first chamber R1. As a result, brake fluid discharged from the first output port 62b of the electric cylinder 60 is supplied to the first chamber R1. A rear wheel supply flow path 553 is connected to the second chamber R2. Therefore, when the second piston 72 moves in the first movement direction Ya due to an increase in hydraulic pressure in the first chamber R1, brake fluid in the second chamber R2 is discharged into the rear wheel supply flow path 553. As a result, brake fluid is supplied to the rear wheel cylinder 31R via the rear wheel supply flow path 553.

[0038] A second input port 71a and a second output port 71b are formed on the peripheral wall of the second cylinder 71 as ports connecting the second chamber R2 with the outside. A second input flow path 557 is connected to the second input port 71a. A rear wheel supply flow path 553 is connected to the first output port 62b.

[0039] A second through-hole 72a is formed in the second piston 72. The second through-hole 72a is positioned to allow communication between the second input port 71a and the second chamber R2 when the second piston 72 is in the most retracted position. As a result, when the second piston 72 is in the most retracted position, the second chamber R2 is in communication with the reservoir tank 51 via the second through-hole 72a, the second input port 71a, and the second input flow path 557. The second input port 71a is open when the second piston 72 is in the most retracted position and is closed by the second piston 72 when the second piston 72 moves from the most retracted position in the first movement direction Ya. Even after the second input port 71a is closed by the second piston 72, the hydraulic pressure in the second chamber R2 increases when the second piston 72 moves in the first movement direction Ya.

[0040] The second output port 71b is always open regardless of the position of the second piston 72. Therefore, when the second input port 71a is blocked by the second piston 72, if the second piston 72 moves in the first movement direction Ya due to an increase in the hydraulic pressure in the first chamber R1, the brake fluid in the second chamber R2 is discharged from the second output port 71b into the rear wheel supply flow path 553. On the other hand, if the second piston 72 moves in the second movement direction Yb due to a decrease in the hydraulic pressure in the first chamber R1, the brake fluid in the rear wheel supply flow path 553 is sucked into the second chamber R2 through the second output port 71b.

[0041] <Sensors of Upstream Unit> The upstream unit 50 includes a plurality of sensors that output signals according to detection results to the first controller 220. The plurality of sensors include a rotation angle sensor 82, a servo pressure sensor 83, and a supply pressure sensor 84.

[0042] The rotation angle sensor 82 detects the rotation angle of the output shaft of the first electric motor 61. The rotation angle based on the detection signal of the rotation angle sensor 82 is referred to as the "motor rotation angle θm." The servo pressure sensor 83 is a fluid pressure sensor that detects the discharge pressure of the brake fluid from the electric cylinder 60. For example, the servo pressure sensor 83 is connected to a portion of the front wheel supply flow path 552 between the connection point P1 and the differential pressure adjustment valve 52. The discharge pressure of the electric cylinder 60 based on the detection signal of the servo pressure sensor 83 is referred to as the "servo pressure Psv."

[0043] The supply pressure sensor 84 detects the pressure of the brake fluid discharged from the second output port 71b of the system separation cylinder 70. For example, the supply pressure sensor 84 is connected to the rear wheel supply flow path 553. The discharge pressure of the system separation cylinder 70 based on the detection signal of the supply pressure sensor 84 is referred to as the "supply pressure Psp."

[0044] A detection signal from the above-described first brake sensor 81 is input to the first controller 220. The operation amount of the brake operating member 41 based on the detection signal from the first brake sensor 81 is referred to as a "first braking operation amount BS1."

[0045] 1 and 2, the operation of the upstream unit 50 will be described. When the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are adjusted by operating the electric cylinder 60, the reservoir shutoff valve 53 is closed. When the first electric motor 61 is driven in this state, the first piston 63 of the electric cylinder 60 moves in the forward direction Za. As a result, the brake fluid in the hydraulic chamber Re is discharged from the first output port 62b to the connecting flow path 551.

[0046] A portion of the brake fluid discharged from the electric cylinder 60 flows through the front wheel supply flow path 552 and is supplied to the front wheel cylinder 31F. The remaining brake fluid is introduced into the first chamber R1 of the system separation cylinder 70 through the connecting flow path 551. This increases the hydraulic pressure in the first chamber R1. As the hydraulic pressure in the first chamber R1 increases, the second piston 72 in the second cylinder 71 moves in the first movement direction Ya. As a result, the second piston 72 closes the second input port 71a, as shown in FIG. 2 . If the second piston 72 continues to move in the first movement direction Ya, the brake fluid in the second chamber R2 is discharged into the rear wheel supply flow path 553 through the second output port 71b. As a result, the brake fluid discharged from the second output port 71b of the system separation cylinder 70 flows through the rear wheel supply flow path 553 and is supplied to the rear wheel cylinder 31R.

[0047] The hydraulic pressure supplied to a first hydraulic circuit 93F (described later) of the downstream unit 90 via the front wheel supply flow path 552 is referred to as the "front wheel supply hydraulic pressure." The hydraulic pressure supplied to a second hydraulic circuit 93R (described later) of the downstream unit 90 via the rear wheel supply flow path 553 is referred to as the "rear wheel supply hydraulic pressure."

[0048] When brake fluid is being discharged from the electric cylinder 60 with the differential pressure adjustment valve 52 open, the front wheel supply fluid pressure and the rear wheel supply fluid pressure are substantially equal to the servo pressure. However, when the differential pressure adjustment valve 52 is actuated when brake fluid is being discharged from the electric cylinder 60, the front wheel supply fluid pressure becomes lower than the servo pressure. Specifically, the differential pressure between the servo pressure and the front wheel supply fluid pressure can be adjusted by controlling the command valve closing force of the differential pressure adjustment valve 52. The valve closing force is the force that pushes the valve body in the direction that closes the solenoid valve. The command value of this valve closing force is the command valve closing force. Even when the differential pressure adjustment valve 52 is actuated in this way, the rear wheel supply fluid pressure is substantially equal to the servo pressure. Therefore, the differential pressure between the front wheel supply fluid pressure and the rear wheel supply fluid pressure can be adjusted by controlling the command valve closing force of the differential pressure adjustment valve 52.

[0049] When the first piston 63 of the electric cylinder 60 moves in the backward direction Zb, the servo pressure decreases. As a result, the hydraulic pressure in the first chamber R1 of the system separation cylinder 70 decreases. Then, the second piston 72 moves in the second movement direction Yb due to the biasing force of the spring 73 and the hydraulic pressure supplied to the rear wheels. As a result, both the hydraulic pressure supplied to the front wheels and the hydraulic pressure supplied to the rear wheels decrease.

[0050] <Downstream Unit> The downstream unit 90 includes a braking actuator 91 and a second controller 230 that controls the braking actuator 91. The second controller 230 will be described later.

[0051] 1 and 3, the brake actuator 91 includes a front wheel pressure device 92F and a rear wheel pressure device 92R. The front wheel pressure device 92F is connected to the front wheel supply flow path 552 and is configured to be able to supply brake fluid to the front wheel cylinder 31F independently of the electric cylinder 60. The rear wheel pressure device 92R is connected to the rear wheel supply flow path 553 and is configured to be able to supply brake fluid to the rear wheel cylinder 31R independently of the electric cylinder 60.

[0052] 3, the front wheel pressurizing device 92F has a first hydraulic circuit 93F, and the rear wheel pressurizing device 92R has a second hydraulic circuit 93R. The first hydraulic circuit 93F is connected to the front wheel supply flow path 552 and to the two front wheel cylinders 31F. The second hydraulic circuit 93R is connected to the rear wheel supply flow path 553 and to the two rear wheel cylinders 31R.

[0053] The configuration of the first hydraulic pressure circuit 93F will be described. The first hydraulic pressure circuit 93F has an inlet flow path 94, which is a brake flow path connected to the front wheel supply flow path 552. The inlet flow path 94 is provided with a differential pressure control valve 95, which is a normally-open linear solenoid valve. The differential pressure control valve 95 is disposed between the upstream unit 50 and a holding valve 96, which will be described later. The brake flow path between the differential pressure control valve 95 and the upstream unit 50 is referred to as the upstream portion of the differential pressure control valve 95. The brake flow path between the differential pressure control valve 95 and the holding valve 96 is referred to as the downstream portion of the differential pressure control valve 95. The differential pressure difference between the upstream portion and the downstream portion of the differential pressure control valve 95 can be adjusted by adjusting the valve closing force commanded to the differential pressure control valve 95. Therefore, by adjusting the valve closing force commanded to the differential pressure control valve 95, the differential pressure control valve 95 can increase the front wheel hydraulic pressure PwcF, which is the pressure downstream of the differential pressure control valve 95, higher than the front wheel supply hydraulic pressure, which is the pressure upstream of the differential pressure control valve 95. This allows the differential pressure control valve 95 to adjust the differential pressure between the front wheel supply fluid pressure and the front wheel fluid pressure PwcF.

[0054] The portion of the intake passage 94 between the differential pressure control valve 95 and the front wheel cylinder 31F branches into two passages 94a and 94b. One of the two front wheel cylinders 31F is connected to passage 94a, and the other of the two front wheel cylinders 31F is connected to passage 94b.

[0055] A retention valve 96 is provided in each of the multiple paths 94a, 94b. When the retention valve 96 is closed, the supply of brake fluid to the front wheel cylinder 31F corresponding to the retention valve 96 is restricted. In other words, an increase in the front wheel hydraulic pressure PwcF is restricted. The retention valve 96 is a normally-open linear solenoid valve. The brake flow path between the retention valve 96 and the differential pressure control valve 95 is referred to as the upstream portion of the retention valve 96. The brake flow path between the retention valve 96 and the front wheel cylinder 31F is referred to as the downstream portion of the retention valve 96. The differential pressure between the upstream and downstream portions of the retention valve 96 can be adjusted by adjusting the command valve closing force of the retention valve 96. Therefore, by adjusting the command valve closing force of the retention valve 96 while front wheel hydraulic pressure is generated, the front wheel hydraulic pressure PwcF can be made lower than the front wheel hydraulic pressure. In other words, the retention valve 96 can adjust the differential pressure between the front wheel hydraulic pressure and the front wheel hydraulic pressure PwcF. The range of differential pressure that can be generated by the pressure retention valve 96 is wider than the range of differential pressure that can be generated by the differential pressure adjustment valve 52 of the upstream unit 50 .

[0056] The first hydraulic circuit 93F has a pressure-reducing reservoir 97 that stores brake fluid and a pressure-reducing flow path 98 that is connected to the pressure-reducing reservoir 97. The pressure-reducing flow path 98 is a brake flow path that connects the portions of the paths 94a, 94b downstream of the pressure-reducing valve 96 to the pressure-reducing reservoir 97. The pressure-reducing flow path 98 is provided with a plurality of pressure-reducing valves 99 that individually correspond to the plurality of front wheel cylinders 31F. The pressure-reducing valves 99 are normally-closed solenoid valves. When a pressure-reducing valve 99 opens, the brake fluid in the front wheel cylinder 31F corresponding to that pressure-reducing valve 99 flows into the pressure-reducing reservoir 97 via the pressure-reducing flow path 98.

[0057] The first hydraulic circuit 93F has a pump 100. The pump 100 is an electric pump operated by a second electric motor 101. The pump 100 pumps up the brake fluid in the reduced-pressure reservoir 97 and discharges the brake fluid into a portion of the inlet flow path 94 between the differential pressure control valve 95 and the holding valve 96.

[0058] The first hydraulic circuit 93F has a return flow path 102 and a valve device 103. The return flow path 102 is a brake flow path that is connected to a portion of the inlet flow path 94 between the differential pressure control valve 95 and the upstream unit 50 and to a reduced-pressure reservoir 97. The valve device 103 is integrated with the reduced-pressure reservoir 97. The valve device 103 allows the flow of brake fluid from the return flow path 102 to the upstream unit 50, while restricting the flow of brake fluid from the upstream unit 50 to the reduced-pressure reservoir 97. However, when the pump 100 operates while the reduced-pressure reservoir 97 is empty, the valve device 103 allows the flow of brake fluid from the upstream unit 50 through the return flow path 102.

[0059] The second hydraulic circuit 93R has the same configuration as the first hydraulic circuit 93F, that is, the second hydraulic circuit 93R includes a differential pressure control valve 95, two holding valves 96, two pressure reducing valves 99, a pressure reducing reservoir 97, a pump 100 operated by a second electric motor 101, and a valve device 103.

[0060] 1 and 3, the downstream unit 90 includes a hydraulic pressure sensor 112 that outputs a signal corresponding to the detection result to the second controller 230. The hydraulic pressure sensor 112 is connected to the inlet flow path 94 of the first hydraulic pressure circuit 93F. Specifically, the hydraulic pressure sensor 112 is connected to a portion of the inlet flow path 94 between the differential pressure control valve 95 and the front wheel supply flow path 552. Therefore, the hydraulic pressure sensor 112 can detect the hydraulic pressure supplied from the upstream unit 50 to the first hydraulic pressure circuit 93F. The hydraulic pressure based on the detection signal of the hydraulic pressure sensor 112 is referred to as the "front wheel supply hydraulic pressure PkF."

[0061] The detection signal of the above-mentioned second brake sensor 111 is input to the second controller 230. The operation amount of the brake operating member 41 based on the detection signal of the second brake sensor 111 is referred to as a "second braking operation amount BS2."

[0062] 1, the control device 210 of the braking system 200 controls the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR by operating the electric cylinder 60, the differential pressure adjustment valve 52, the reservoir shutoff valve 53, and the brake actuator 91. In this way, the control device 210 can adjust the front wheel friction braking force FxMF and the rear wheel friction braking force FxMR.

[0063] The control device 210 includes the above-described first controller 220 and second controller 230. The multiple controllers 220, 230 can transmit and receive various information and commands to and from each other via an in-vehicle network 240.

[0064] The first controller 220 has a first processing circuit 221. The second controller 230 has a second processing circuit 231. An example of the processing circuits 221, 231 is an electronic control device. In this case, each of the multiple processing circuits 221, 231 has a CPU and a memory that stores a control program executed by the CPU. The first processing circuit 221 operates the electric cylinder 60, the differential pressure adjustment valve 52, and the reservoir shutoff valve 53 by the CPU executing the control program in the memory. The second processing circuit 231 operates the brake actuator 91 by the CPU executing the control program in the memory.

[0065] <Start-up Process> A series of processes executed by the first processing circuit 221 of the first controller 220 when the braking system 200 is started will be described with reference to Fig. 4. This series of processes is the startup process. The startup process is a process for searching for a standby position for the first piston 63 of the electric cylinder 60 and then causing the first piston 63 to wait at the standby position. The standby position is the position of the first piston 63 when no braking request is made.

[0066] In step S11, the first processing circuit 221 closes both the reservoir shutoff valve 53 and the differential pressure adjustment valve 52. In the following step S13, the first processing circuit 221 drives the first electric motor 61 so that the first piston 63 moves in the retraction direction Zb to the most retracted position of the first piston 63. When the first processing circuit 221 determines that the first piston 63 has reached the most retracted position, it stops driving the first electric motor 61.

[0067] For example, the electric cylinder 60 is provided with a restricting member that restricts further movement of the first piston 63 in the backward direction Zb. When the first piston 63 comes into contact with the restricting member, the first piston 63 cannot move in the backward direction Zb. This increases the motor current that flows through the first electric motor 61. Therefore, the first processing circuit 221 can determine whether the first piston 63 has reached the most backward position based on the progression of the motor current.

[0068] In the next step S15, the first processing circuit 221 drives the first electric motor 61 so as to move the first piston 63 forward in the Za direction. In this state, the first processing circuit 221 monitors the servo pressure Psv. The first processing circuit 221 then determines whether the servo pressure Psv has reached or exceeded the servo pressure determination value Psvth.

[0069] When the first piston 63 is in the most retracted position, the first input port 62a is not blocked by the first piston 63. In other words, the hydraulic chamber Re is in communication with the reservoir tank 51. However, when the first piston 63 moves forward in the Za direction from the most retracted position, the first input port 62a is blocked by the first piston 63. If the first piston 63 continues to move forward in the Za direction in this state, the servo pressure Psv increases because the reservoir shutoff valve 53 and the differential pressure control valve 52 are closed. Therefore, a criterion for determining whether the first input port 62a is blocked by the movement of the first piston 63 is set to the servo pressure determination value Psvth. If possible, it is desirable to set the servo pressure determination value Psvth to a value lower than the pressure when the second piston 72 of the system separation cylinder 70 starts to move from the most retracted position against the sliding resistance and the biasing force of the spring 73.

[0070] When the servo pressure Psv becomes equal to or greater than the servo pressure determination value Psvth, the first processing circuit 221 stops driving the first electric motor 61. Then, the first processing circuit 221 proceeds to step S17.

[0071] In step S17, the first processing circuit 221 stores, as the standby position of the first piston 63, a position in the backward direction Zb that is slightly lower than the position of the first piston 63 at the time when the servo pressure Psv becomes equal to or higher than the servo pressure determination value Psvth. The standby position is the position of the first piston 63 when the first input port 62a is not blocked and the hydraulic chamber Re is connected to the reservoir tank 51.

[0072] In the next step S18, the first processing circuit 221 drives the first electric motor 61 to move the first piston 63 to the standby position. Then, the first processing circuit 221 stops driving the first electric motor 61. Thereafter, the first processing circuit 221 ends the startup process.

[0073] By setting the standby position of the first piston 63 near the position where the first input port 62a is closed, the time required for the first piston 63 to close the first input port 62a when a braking request is generated is shortened, thereby improving the responsiveness of increasing the servo pressure Psv.

[0074] <Regenerative Cooperative Control> The regenerative cooperative control performed by the braking system 200 will be described with reference to Figure 5. As shown in Figures 5A, 5B, and 5C, when a braking request is generated at timing t11, for example, when the brake operating member 41 begins to be operated, the first processing circuit 221 of the first controller 220 derives a required braking force FxRq, which is a required value of braking force for the vehicle. For example, when the brake operating member 41 is being operated, the first processing circuit 221 derives the required braking force FxRq such that the required braking force FxRq increases as the first braking operation amount BS1 increases. The first processing circuit 221 transmits information related to the required braking force FxRq to the regenerative control unit 22 of the regenerative device 20.

[0075] The regenerative control unit 22 sets a regenerative braking force command value FxR*, which is a command value for the regenerative braking force FxR, based on the required braking force FxRq indicated by the information. The limit value of the regenerative braking force FxR that the regenerative device 20 can generate is set as the regenerative braking force limit value FxRL. At this time, if the required braking force FxRq is equal to or less than the regenerative braking force limit value FxRL, the regenerative control unit 22 sets the required braking force FxRq to the regenerative braking force command value FxR*. On the other hand, if the required braking force FxRq is greater than the regenerative braking force limit value FxRL, the regenerative control unit 22 sets the regenerative braking force limit value FxRL to the regenerative braking force command value FxR*.

[0076] 5, the required braking force FxRq is equal to or less than the regenerative braking force limit value FxRL during the period from timing t11 to timing t12, whereas the required braking force FxRq is greater than the regenerative braking force limit value FxRL during the period from timing t12 to timing t17.

[0077] The regenerative control unit 22 operates the motor generator 21 based on the regenerative braking force command value FxR*, thereby causing the regenerative device 20 to generate a regenerative braking force FxR corresponding to the regenerative braking force command value FxR* at the front wheels 11F.

[0078] After timing t12, the required braking force FxRq becomes greater than the regenerative braking force limit value FxRL. Therefore, the first processing circuit 221 of the first controller 220 sets the frictional braking force command value FxM* to the value obtained by subtracting the regenerative braking force FxR from the required braking force FxRq. The frictional braking force command value FxM* is a command value for the sum of the front wheel frictional braking force FxMF and the rear wheel frictional braking force FxMR. The first processing circuit 221 then sets the front wheel frictional braking force command value FxMF* and the rear wheel frictional braking force command value FxMR* based on the frictional braking force command value FxM* and the regenerative braking force FxR. The front wheel frictional braking force command value FxMF* is a command value for the front wheel frictional braking force FxMF. The rear wheel frictional braking force command value FxMR* is a command value for the rear wheel frictional braking force FxMR.

[0079] Before timing t12, braking force is generated on the front wheel 11F, but no braking force is generated on the rear wheel 11R. Therefore, during the period from timing t12 to timing t13, the first processing circuit 221 sets the friction braking force command value FxM* to the rear wheel friction braking force command value FxMR*. The first processing circuit 221 also sets the front wheel friction braking force command value FxMF* to 0 (zero).

[0080] The first processing circuit 221 converts the rear wheel friction braking force command value FxMR* into a rear wheel hydraulic pressure command value PwcR*. The rear wheel hydraulic pressure command value PwcR* is a command value for the rear wheel hydraulic pressure PwcR. Similarly, the first processing circuit 221 converts the front wheel friction braking force command value FxMF* into a front wheel hydraulic pressure command value PwcF*. The front wheel hydraulic pressure command value PwcF* is a command value for the front wheel hydraulic pressure PwcF.

[0081] Then, with the reservoir shutoff valve 53 closed, the first processing circuit 221 operates the electric cylinder 60 and the differential pressure adjustment valve 52 based on the front wheel hydraulic pressure command value PwcF* and the rear wheel hydraulic pressure command value PwcR*. For example, the first processing circuit 221 sets the rear wheel hydraulic pressure command value PwcR* to the target servo pressure Psvtr. The target servo pressure Psvtr is a target value for the servo pressure Psv. The first processing circuit 221 drives the first electric motor 61 so that the servo pressure Psv becomes the target servo pressure Psvtr.

[0082] Furthermore, the first processing circuit 221 sets the command valve closing force of the differential pressure control valve 52 based on the difference between the rear wheel hydraulic pressure command value PwcR* and the front wheel hydraulic pressure command value PwcF*. For example, the first processing circuit 221 sets the command valve closing force of the differential pressure control valve 52 so that the difference between the servo pressure Psv and the front wheel hydraulic pressure PkF is equal to the difference between the rear wheel hydraulic pressure command value PwcR* and the front wheel hydraulic pressure command value PwcF*.

[0083] As a result, the first processing circuit 221 can make the rear wheel hydraulic pressure PwcR substantially equal to the rear wheel hydraulic pressure command value PwcR*. Also, the first processing circuit 221 can make the front wheel hydraulic pressure PwcF substantially equal to the front wheel hydraulic pressure command value PwcF*.

[0084] 5, at timing t13, the ratio between the braking force generated at the front wheel 11F and the braking force generated at the rear wheel 11R reaches a predetermined distribution ratio. Therefore, after timing t13, the first processing circuit 221 increases both the rear wheel friction braking force command value FxMR* and the front wheel friction braking force command value FxMF* so as to satisfy the following two conditions. In other words, the first processing circuit 221 increases both the rear wheel hydraulic pressure command value PwcR* and the front wheel hydraulic pressure command value PwcF*.

[0085] The sum of the rear wheel friction braking force command value FxMR* and the front wheel friction braking force command value FxMF* is equal to the friction braking force command value FxM*. The ratio between the braking force generated at the front wheel 11F and the braking force generated at the rear wheel 11R is maintained at a predetermined distribution ratio.

[0086] As a result, both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR increase, as shown in FIG. 5C. During the period from time t14 to time t15, the required braking force FxRq is maintained. Therefore, both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are maintained.

[0087] From time t15, the required braking force FxRq is reduced. Then, the first processing circuit 221 of the first controller 220 reduces the rear wheel friction braking force command value FxMR* in accordance with the reduction in the required braking force FxRq while maintaining the front wheel friction braking force command value FxMF*. In other words, the first processing circuit 221 reduces the rear wheel fluid pressure command value PwcR* while maintaining the front wheel fluid pressure command value PwcF*.

[0088] As described above, the first processing circuit 221 sets the rear wheel hydraulic pressure command value PwcR* to the target servo pressure Psvtr. Therefore, the first processing circuit 221 moves the first piston 63 in the reverse direction Zb by reducing the target servo pressure Psvtr. This reduces the servo pressure Psv and the rear wheel hydraulic pressure PwcR. At this time, the first processing circuit 221 maintains the command valve closing force for the differential pressure control valve 52 at the value at timing t15. Then, because the servo pressure Psv is higher than the front wheel hydraulic pressure PwcF, the rear wheel hydraulic pressure PwcR is reduced, but the front wheel hydraulic pressure PwcF is maintained.

[0089] At timing t16, the rear wheel hydraulic pressure PwcR becomes equal to the front wheel hydraulic pressure PwcF. The required braking force FxRq continues to decrease even after timing t16. Therefore, the first processing circuit 221 continues to decrease the target servo pressure Psvtr. In other words, the first processing circuit 221 continues to move the first piston 63 in the reverse direction Zb and maintains the command valve closing force for the differential pressure control valve 52 at the value at timing t15.

[0090] As a result, the servo pressure Psv and the rear wheel hydraulic pressure PwcR decrease. When the servo pressure Psv decreases, the servo pressure Psv temporarily becomes lower than the hydraulic pressure supplied to the front wheels, i.e., the front wheel hydraulic pressure PwcF. As a result, brake fluid in the first hydraulic pressure circuit 93F flows toward the electric cylinder 60 via the check valve 522 arranged in parallel with the differential pressure adjustment valve 52. This also decreases the front wheel hydraulic pressure PwcF.

[0091] At timing t17, both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR become 0 (zero). That is, both the front wheel friction braking force FxMF and the rear wheel friction braking force FxMR become 0 (zero). Therefore, from timing t17 onwards, the regenerative control unit 22 of the regenerative device 20 sets the required braking force FxRq to the regenerative braking force command value FxR*. Then, the motor generator 21 is operated based on the regenerative braking force command value FxR*, so the regenerative braking force FxR decreases. Then, when the required braking force FxRq becomes 0 (zero) at timing t18, the regenerative braking force FxR also becomes 0 (zero).

[0092] The first processing circuit 221 of the first controller 220 can determine that the braking request has disappeared at timing t18. Therefore, the first processing circuit 221 may set the command valve closing force of the differential pressure control valve 52 to 0 (zero) at timing t18 or any timing after timing t18.

[0093] <Fail-safe processing when an abnormality occurs in the upstream unit> If an abnormality occurs in the electric cylinder 60 or if power to the upstream unit 50 is cut off, the upstream unit 50 will no longer be able to adjust the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0094] When the first processing circuit 221 of the first controller 220 detects an abnormality in the upstream unit 50, it stops the supply of electricity to the first electric motor 61, the reservoir shutoff valve 53, and the differential pressure adjustment valve 52. Furthermore, when the supply of electricity to the upstream unit 50 is stopped, the supply of electricity to the reservoir shutoff valve 53 and the differential pressure adjustment valve 52 is also stopped. Then, both the reservoir shutoff valve 53 and the differential pressure adjustment valve 52 are opened, and the connection flow path 551 communicates with the reservoir tank 51 via the release flow path 554. As a result, the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR decrease to 0 (zero). Therefore, if an abnormality occurs in the upstream unit 50 while the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are being adjusted by the operation of the electric cylinder 60, the braking system 200 can suppress the continued generation of frictional braking force at the front wheels 11F and the rear wheels 11R.

[0095] A braking request may be issued even if an abnormality occurs in the upstream unit 50. In this case, in the braking system 200, the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are adjusted by the downstream unit 90. That is, the second processing circuit 231 of the second controller 230 derives the required braking force FxRq based on the second braking operation amount BS2. The second processing circuit 231 derives a front wheel friction braking force command value FxMF* and a rear wheel friction braking force command value FxMR* based on the required braking force FxRq. The second processing circuit 231 derives the front wheel hydraulic pressure command value PwcF* based on the front wheel friction braking force command value FxMF*, and derives the rear wheel hydraulic pressure command value PwcR* based on the rear wheel friction braking force command value FxMR*.

[0096] The second processing circuit 231 then drives the second electric motor 101 to operate the two pumps 100. At this time, in the front wheel pressurizing device 92F, the pump 100 pumps brake fluid from the front wheel supply passage 552. When both the reservoir shutoff valve 53 and the differential pressure control valve 52 are open, the front wheel supply passage 552 is in communication with the reservoir tank 51 via the release passage 554. Therefore, the brake fluid in the reservoir tank 51 is pumped to the pump 100 via the release passage 554, the front wheel supply passage 552, and the return passage 102. Furthermore, when the first piston 63 is positioned to open the first input port 62a, the brake fluid in the reservoir tank 51 is pumped to the pump 100 via the first input passage 556, the front wheel supply passage 552, and the return passage 102. The brake fluid in the reservoir tank 51 is also pumped up by the pump 100 via the reservoir flow path 555 and the check valve 56 .

[0097] The second processing circuit 231 can adjust the amount of brake fluid supplied to the two front wheel cylinders 31F by adjusting the command valve closing force of the differential pressure control valve 95 of the front wheel pressurizing device 92F, thereby controlling the front wheel hydraulic pressure PwcF.

[0098] On the other hand, in the rear wheel pressurizing device 92R, the pump 100 pumps brake fluid from the rear wheel supply flow path 553. When the reservoir shutoff valve 53 of the upstream unit 50 is open or when the first piston 63 is positioned to open the first input port 62a, the servo pressure is 0 (zero), and the second piston 72 of the system separation cylinder 70 is positioned in the most retracted position. Therefore, the second chamber R2 is in communication with the reservoir tank 51. Even when the reservoir shutoff valve 53 is not open and the first piston 63 is positioned to close the first input port 62a, the servo pressure becomes 0 (zero) when the pump 100 is operated, and the second piston 72 of the system separation cylinder 70 retracts to the most retracted position. Therefore, the second chamber R2 is in communication with the reservoir tank 51. As a result, the brake fluid in the reservoir tank 51 is pumped up to the pump 100 via the second input flow path 557, the second chamber R2, the rear wheel supply flow path 553 and the return flow path 102.

[0099] The second processing circuit 231 can adjust the amount of brake fluid supplied to the two rear wheel cylinders 31R by adjusting the command valve closing force of the differential pressure control valve 95 of the rear wheel pressurizing device 92R, thereby controlling the rear wheel hydraulic pressure PwcR.

[0100] <Advantages of this embodiment> (1) The upstream unit 50 includes an electric cylinder 60 and a system separation cylinder 70. The second chamber R2 of the system separation cylinder 70 is connected to the rear wheel cylinder 31R via the rear wheel supply passage 553. As described above, the volume of the rear wheel cylinder 31R is smaller than the volume of the front wheel cylinder 31F. Therefore, the upstream unit 50 can generate the rear wheel hydraulic pressure PwcR even when the amount of brake fluid supplied from the system separation cylinder 70 to the rear wheel cylinder 31R is small. Therefore, the volume of the second chamber R2 can be smaller than in a configuration in which brake fluid is supplied from the second chamber R2 to the front wheel cylinder 31F. Reducing the volume of the second chamber R2 enables the system separation cylinder 70 to be made smaller. Therefore, the brake system 200 can prevent the overall system from becoming larger.

[0101] (2) In the upstream unit 50, a differential pressure adjustment valve 52 is installed in the front wheel supply flow path 552. Therefore, the upstream unit 50 can control the differential pressure between the rear wheel hydraulic pressure PwcR and the front wheel hydraulic pressure PwcF by adjusting the command valve closing force of the differential pressure adjustment valve 52. Therefore, in a vehicle that can generate regenerative braking force FxR at the axle of the front wheels 11F, the braking system 200 can perform regenerative cooperative control that appropriately adjusts the distribution ratio between the front wheel braking force and the rear wheel braking force.

[0102] (3) The range of differential pressure that can be generated by the differential pressure adjustment valve 52 is narrower than the range of differential pressure that can be generated by the holding valve 96 of the downstream unit 90. In other words, within the range of differential pressure that can be generated by the differential pressure adjustment valve 52, the accuracy of adjustment of the differential pressure by the differential pressure adjustment valve 52 is higher than the accuracy of adjustment of the differential pressure by the holding valve 96. Therefore, the braking system 200 can accurately adjust the differential pressure by using the differential pressure adjustment valve 52 to control the differential pressure between the rear wheel hydraulic pressure PwcR and the front wheel hydraulic pressure PwcF.

[0103] (4) In the upstream unit 50, a check valve 56 is installed in the reservoir flow path 555. The check valve 56 restricts the flow of brake fluid from the intermediate portion 552a of the front wheel supply flow path 552 toward the reservoir tank 51, while allowing the flow of brake fluid from the reservoir tank 51 toward the intermediate portion 552a. Therefore, the front wheel pressurizing device 92F can supply brake fluid from the reservoir tank 51 to the front wheel cylinder 31F by operating the pump 100. Therefore, the braking system 200 can adjust the front wheel hydraulic pressure PwcF by operating the front wheel pressurizing device 92F without operating the electric cylinder 60. For example, even if the differential pressure control valve 52 remains closed, the braking system 200 can adjust the front wheel hydraulic pressure PwcF by operating the front wheel pressurizing device 92F.

[0104] (5) In the upstream unit 50, a reservoir shutoff valve 53 is installed in the release flow path 554 connecting the connection flow path 551 and the reservoir tank 51. Therefore, the first processing circuit 221 can increase the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR by operating the electric cylinder 60 with the reservoir shutoff valve 53 closed. Furthermore, if an abnormality occurs in the upstream unit 50, the first processing circuit 221 can open the reservoir shutoff valve 53 to set the system separation cylinder 70 to a state in which the second input port 71a is open. This allows both the front wheel cylinder 31F and the rear wheel cylinder 31R to communicate with the reservoir tank 51. As a result, if an abnormality occurs in the upstream unit 50 while the electric cylinder 60 is operating, the braking system 200 can reduce the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR to 0 (zero).

[0105] (6) The upstream unit 50 is equipped with a servo pressure sensor 83 that detects the discharge pressure of the brake fluid from the electric cylinder 60. Therefore, the first processing circuit 221 can control the electric cylinder 60 using the servo pressure Psv based on the detection signal of the servo pressure sensor 83. In other words, the first processing circuit 221 can appropriately control the hydraulic pressure supplied to the front wheels and the hydraulic pressure supplied to the rear wheels.

[0106] <Modifications> 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.

[0107] The servo pressure sensor 83 may be disposed at a position different from the position shown in Fig. 1 as long as it can detect the discharge pressure of the brake fluid from the electric cylinder 60. For example, the servo pressure sensor 83 may be connected to the connection flow path 551.

[0108] The upstream unit 50 does not need to include the servo pressure sensor 83. The upstream unit 50 may be provided with a normally open solenoid valve instead of the check valve 56 as the valve mechanism of the reservoir flow path 555.

[0109] The upstream unit 50 does not need to include the release flow path 554. Even in this case, when the power supply to the first electric motor 61 is stopped, the servo pressure causes the first piston 63 to retract to a position where it opens the first input port 62 a.

[0110] The upstream unit 50 does not have to include the reservoir flow path 555. The upstream unit 50 does not have to include the differential pressure adjustment valve 52. In this case, the regenerative cooperative control is performed while the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are at the same pressure.

[0111] The supply device may be configured to include a pressure source other than the electric cylinder 60 as long as it is capable of generating servo pressure in the connection flow path 551. For example, the supply device may be configured to include an electric pump.

[0112] The first controller 220 is not limited to a controller having a CPU and ROM and executing software processing. In other words, the first controller 220 may have any one of the following configurations (a), (b), and (c):

[0113] (a) The first controller 220 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer.

[0114] (b) The first controller 220 includes one or more dedicated hardware circuits that perform various processes. Examples of dedicated hardware circuits include application-specific integrated circuits (ASICs) or FPGAs. ASIC is an abbreviation for "Application Specific Integrated Circuit." FPGA is an abbreviation for "Field Programmable Gate Array."

[0115] (c) The first controller 220 includes one or more processors that execute some of the various processes in accordance with a computer program, and one or more dedicated hardware circuits that execute the remaining processes of the various processes.

[0116] The second controller 230 is not limited to a controller having a CPU and ROM and executing software processing. In other words, the second controller 230 may have any of the configurations (a), (b), and (c) above.

[0117] It should be noted that the expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

Claims

1. Applicable to a vehicle equipped with front and rear wheels, a front wheel cylinder corresponding to the front wheels, and a rear wheel cylinder corresponding to the rear wheels and having a smaller volume than the front wheel cylinder, the supply device having an electric motor and configured to be able to discharge brake fluid from an output port when driven by the electric motor; a system separation cylinder having a cylinder and a piston dividing the interior of the cylinder into a first chamber and a second chamber, configured so that when fluid pressure in the first chamber increases, the piston moves in a first moving direction which is a direction that reduces the volume of the second chamber, thereby discharging brake fluid from the second chamber, and when fluid pressure in the first chamber decreases, the piston moves in a second moving direction which is the opposite direction to the first moving direction, thereby drawing brake fluid into the second chamber; a connecting flow path which is a brake flow path connecting the output port and the first chamber; a front wheel supply flow path which is connected to the connecting flow path and is a brake flow path that supplies brake fluid discharged from the output port to the front wheel cylinder; a rear wheel supply passage that is a brake passage that supplies the brake fluid discharged from the second chamber to the rear wheel cylinder.

2. The braking system according to claim 1, further comprising a differential pressure regulating valve which is a linear solenoid valve installed in the front wheel supply flow path.

3. A braking system as described in claim 2, comprising: a reservoir tank for storing brake fluid; a front wheel pressurizing device connected to the front wheel supply flow path and configured to be able to supply brake fluid to the front wheel cylinder independently of the supply device; a reservoir flow path that is connected to an intermediate portion of the front wheel supply flow path between the differential pressure control valve and the front wheel pressurizing device and is a brake flow path that directs the brake fluid from the reservoir tank to said intermediate portion; and a valve mechanism installed in the reservoir flow path that regulates the flow of brake fluid in the reservoir flow path from the intermediate portion toward the reservoir tank.

4. A braking system as described in claim 1 or claim 2, comprising: a reservoir tank for storing brake fluid; a release flow path which is a brake flow path connecting the connecting flow path and the reservoir tank; a reservoir shut-off valve which is a normally open solenoid valve installed in the release flow path; and a processing circuit which controls the electric motor and the reservoir shut-off valve, wherein the processing circuit closes the reservoir shut-off valve when driving the electric motor to adjust the hydraulic pressure in the front wheel cylinder and the rear wheel cylinder.

5. A braking system according to claim 1 or 2, further comprising a hydraulic pressure sensor for detecting the discharge pressure of the brake fluid from the supply device.

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