Brake device

Abstract

A brake device (20) is provided with: an electric cylinder (51) for discharging, from an output port (516), brake fluid having a hydraulic pressure corresponding to the driving of an electric motor (513); a master cylinder (31) configured so that the brake fluid flows out of the main chamber (Rm) by the movement of the master piston (43) as the hydraulic pressure of the servo chamber (Rs) increases, and so that the brake fluid flows into the main chamber (Rm) by the movement of the master piston (43) as the hydraulic pressure of the servo chamber (Rs) decreases; a first flow path (331) connecting the main chamber (Rm) and a wheel cylinder (11) for a front wheel; a sixth flow path (58) connecting the output port (516) and a wheel cylinder (11) for a rear wheel; a fifth flow path (55) that connects the sixth flow path (58) and the servo chamber (Rs); and a differential pressure adjustment valve (551) that is provided in the fifth flow path (55) and adjusts the differential pressure between a first hydraulic pressure, which is the hydraulic pressure in the sixth flow path (58), and a second hydraulic pressure, which is the hydraulic pressure in the servo chamber (Rs).

Description

Technical Field

[0001] The present invention relates to a braking device. Background Art

[0002] Conventionally, there has been known a braking device that generates different magnitudes of frictional braking forces on the front wheels and the rear wheels by adjusting the hydraulic pressure of the brake fluid supplied to the wheel cylinders for the front wheels and the wheel cylinders for the rear wheels. For example, the braking device described in Patent Document 1 includes a main unit that supplies brake fluid to the wheel cylinders for the front wheels, and a pressure regulating unit that supplies brake fluid to the wheel cylinders for the rear wheels and the main unit.

[0003] The main unit has a main piston that divides a servo chamber and a master chamber. In the main unit, when brake fluid is supplied to the servo chamber, the main piston moves in a direction to reduce the volume of the master chamber. As a result, brake fluid is supplied from the master chamber to the wheel cylinders for the front wheels.

[0004] The pressure regulating unit includes an electric pump that discharges brake fluid, a first electromagnetic valve that adjusts the brake fluid discharged from the electric pump to a first hydraulic pressure, and a second electromagnetic valve that adjusts the brake fluid discharged from the electric pump to a second hydraulic pressure. The pressure regulating unit supplies the brake fluid adjusted to the first hydraulic pressure to the wheel cylinders for the rear wheels, and supplies the brake fluid adjusted to the second hydraulic pressure to the servo chamber. The pressure regulating unit makes the frictional braking force generated on the front wheels smaller than the frictional braking force generated on the rear wheels by making the second hydraulic pressure smaller than the first hydraulic pressure.

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-137202

[0006] When generating frictional braking forces on the front wheels and the rear wheels, the braking device as described above needs to control the electric pump, the first electromagnetic valve, and the second electromagnetic valve. In other words, when generating frictional braking forces on the front wheels and the rear wheels, the braking device as described above needs to control many control objects. Summary of the Invention

[0007] Hereinafter, means for solving the above problems and their effects are described.

[0008] The braking device for solving the above problems is a braking device for a vehicle that is applied to a vehicle having a first wheel cylinder and a second wheel cylinder, a first wheel that generates a frictional braking force corresponding to the hydraulic pressure of the first wheel cylinder, and a second wheel that generates a frictional braking force corresponding to the hydraulic pressure of the second wheel cylinder, and includes: an electric cylinder having an electric motor as a power source and an output port that discharges brake fluid corresponding to the drive of the electric motor; a master cylinder having a master piston that divides a servo chamber and a master chamber, configured such that brake fluid flows out of the master chamber as the master piston moves as the hydraulic pressure in the servo chamber increases, and on the other hand, brake fluid flows into the master chamber as the master piston moves as the hydraulic pressure in the servo chamber decreases; a first liquid passage that connects the master chamber to the first wheel cylinder; a second liquid passage that connects the output port to the second wheel cylinder; a third liquid passage that connects the second liquid passage to the servo chamber; and a differential pressure adjustment valve provided in the third liquid passage that adjusts the differential pressure between a first hydraulic pressure, which is the hydraulic pressure in the second liquid passage, and a second hydraulic pressure, which is the hydraulic pressure in the servo chamber.

[0009] When the braking device generates frictional braking forces on the first wheel and the second wheel, it controls the electric cylinder and the differential pressure adjustment valve. Specifically, the braking device supplies the brake fluid adjusted to the first hydraulic pressure by the electric cylinder to the second wheel cylinder via the second liquid passage. In addition, the braking device supplies the brake fluid adjusted to the second hydraulic pressure by the differential pressure adjustment valve to the servo chamber of the master cylinder via the third liquid passage. In this case, in the first wheel cylinder, brake fluid corresponding to the hydraulic pressure in the servo chamber is supplied from the master chamber of the master cylinder via the first liquid passage. In this way, by controlling the electric cylinder and the differential pressure adjustment valve, the braking device can generate different magnitudes of frictional braking forces on the first wheel and the second wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of a vehicle equipped with a braking device.

[0011] Figure 2 is a flowchart showing the process implemented by the control device.

[0012] Figure 3 (a) to (c) thereof are timing charts showing the changes in the required braking force, the regenerative braking force, and the wheel cylinder pressure when the vehicle has a braking requirement.

[0013] Figure 4 is a diagram showing the relationship between the front wheel braking force and the rear wheel braking force. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] Hereinafter, an embodiment of the braking device will be described with reference to the drawings.

[0015] Figure 1The figure shows multiple wheels FL, FR, RL, RR, multiple friction braking mechanisms 10, a braking device 20, and a regenerative braking device 60. The multiple wheels FL, FR, RL, RR include two front wheels FL, FR, and two rear wheels RL, RR. In the present embodiment, the two front wheels FL, FR correspond to the "first wheels", and the two rear wheels RL, RR correspond to the "second wheels".

[0016] <Constitution of Friction Braking Mechanism>

[0017] One friction braking mechanism 10 is provided for one wheel. The multiple friction braking mechanisms 10 each have a wheel cylinder 11 to which brake fluid is supplied, a rotating plate 12 that rotates integrally with one wheel, and a friction material 13 that is pressed against the rotating plate 12. The friction braking mechanism 10 is configured such that the greater the hydraulic pressure in the wheel cylinder 11, the stronger the friction material 13 can be pressed against the rotating plate 12. The friction braking mechanism 10 generates a friction braking force corresponding to the hydraulic pressure in the wheel cylinder 11.

[0018] The vehicle has multiple wheel cylinders 11. In the present embodiment, among the multiple wheel cylinders 11, the wheel cylinders 11 for the front wheels FL, FR correspond to the "first wheel cylinders", and the wheel cylinders 11 for the rear wheels RL, RR correspond to the "second wheel cylinders".

[0019] <Constitution of Braking Device>

[0020] The braking device 20 adjusts the friction braking force generated in the vehicle by supplying brake fluid to the wheel cylinders 11 of the multiple friction braking mechanisms 10. The braking device 20 includes a braking operation member 21, a hydraulic pressure generating device 22, a brake actuator 23, and a storage tank 24.

[0021] The braking operation member 21 can be operated by the driver of the vehicle. An example of the braking operation member 21 is a brake pedal. The storage tank 24 stores brake fluid. The inside of the storage tank 24 is open to the atmosphere.

[0022] The hydraulic pressure generating device 22 is configured to be able to generate hydraulic pressure according to the operation amount of the braking operation member 21. The hydraulic pressure generating device 22 includes a main device 30 and a friction braking portion 50. The main device 30 can supply brake fluid to the brake actuator 23. The friction braking portion 50 can supply brake fluid to both the main device 30 and the brake actuator 23.

[0023] <Main Device>

[0024] The main device 30 includes a master cylinder 31, a stroke simulator 32, multiple flow paths 331, 332, 333 connected to the master cylinder 31, and multiple control valves 341, 342 that control the flow of brake fluid. The stroke simulator 32 can generate a reaction force corresponding to the operation amount of the braking operation member 21.

[0025] The master cylinder 31 includes a cylinder main body 41 and a cylinder head 42. The master cylinder 31 includes a main piston 43 and an input piston 44. The master cylinder 31 includes a main spring 45 that presses the main piston 43 and an input spring 46 that presses the input piston 44. The main piston 43 and the input piston 44 are capable of relative movement with respect to the cylinder main body 41 and the cylinder head 42.

[0026] The cylinder main body 41 of the master cylinder 31 has a plate-shaped bottom wall 411 and a first peripheral wall 412 that extends along the axis of the bottom wall 411. And, the cylinder main body 41 has a second peripheral wall 413 that extends along the axis of the first peripheral wall 412 from the rear end of the first peripheral wall 412 and a first annular wall 414 that extends toward the axis of the second peripheral wall 413 from the rear end of the second peripheral wall 413. The first peripheral wall 412 and the second peripheral wall 413 are each cylindrical. A hole for inserting the rear end portion of the main piston 43 described later is formed in the first annular wall 414. The inner diameter of the first peripheral wall 412 is smaller than the inner diameter of the second peripheral wall 413.

[0027] In the cylinder main body 41, a master chamber Rm is defined by the bottom wall 411, the first peripheral wall 412, and the main piston 43. Hereinafter, in the master cylinder 31, Figure 1 the left side in, that is, the moving direction of the main piston 43 that reduces the volume of the master chamber Rm is referred to as "front", and on the other hand, the opposite direction of the front is referred to as "rear". The rear is also the direction in which the volume of the master chamber Rm increases.

[0028] In the cylinder main body 41, a first fluid chamber R1 is defined by the second peripheral wall 413 and the main piston 43, and a servo chamber Rs is defined by the second peripheral wall 413, the first annular wall 414, and the main piston 43. The master chamber Rm is formed at a position near the front end of the master cylinder 31. The first fluid chamber R1 is formed rearward compared to the master chamber Rm. The servo chamber Rs is formed rearward compared to the first fluid chamber R1. Inside the cylinder main body 41, the master chamber Rm, the first fluid chamber R1, and the servo chamber Rs are not connected to each other. In addition, the cross-sectional area of the master chamber Rm is equal to the cross-sectional area of the servo chamber Rs. Here, the cross-sectional area of the servo chamber Rs refers to the cross-sectional area of the servo chamber Rs in a state where the main piston 43 is accommodated.

[0029] The cylinder head 42 of the master cylinder 31 has a cylindrical third peripheral wall 421 and a second annular wall 422 that extends toward the axis of the third peripheral wall 421 from the rear end of the third peripheral wall 421. The third peripheral wall 421 is installed on the first annular wall 414 such that the axis thereof coincides with the second peripheral wall 413 of the cylinder main body 41. A hole for inserting the rear end portion of the input piston 44 described later is provided in the second annular wall 422.

[0030] In the cylinder head 42, a second fluid chamber R2 is defined by a third peripheral wall 421, a second annular wall 422, and a first annular wall 414 of the cylinder body 41. In the master cylinder 31, the second fluid chamber R2 is formed behind the servo chamber Rs.

[0031] The master piston 43 is received in the master cylinder 31 in a state of surface contact with the inner peripheral surface of the first peripheral wall 412, the inner peripheral surface of the second peripheral wall 413, and the inner peripheral surface of the first annular wall 414 of the cylinder body 41. Therefore, when the master piston 43 moves axially, the master piston 43 slides on the inner peripheral surfaces of the first peripheral wall 412, the second peripheral wall 413, and the first annular wall 414. The rear end portion of the master piston 43 protrudes rearward compared to the first annular wall 414 and is located within the second fluid chamber R2. The area of the rear end portion of the master piston 43 (the area that is axially forced by the hydraulic pressure in the second fluid chamber R2) is equal to the sectional area of the first fluid chamber R1. Here, the sectional area of the first fluid chamber R1 refers to the sectional area of the first fluid chamber R1 in a state where the master piston 43 is received.

[0032] The input piston 44 is received in the master cylinder 31 in a state of surface contact with the inner peripheral surface of the second annular wall 422 of the cylinder head 42. Therefore, when the input piston 44 moves axially, the input piston 44 slides on the inner peripheral surface of the second annular wall 422. The rear end portion of the input piston 44 protrudes rearward compared to the second annular wall 422. The area of the front end portion of the input piston 44 is equal to the area of the rear end portion of the master piston 43. Moreover, a brake operating member 21 is connected to the rear end portion of the input piston 44. Therefore, the input piston 44 moves in a direction approaching the master piston 43 according to the operation amount of the brake operating member 21. In addition, a gap is formed between the input piston 44 and the master piston 43 in the second fluid chamber R2.

[0033] The master spring 45 is disposed in the master chamber Rm of the cylinder body 41. The master spring 45 presses the master piston 43 rearward. Therefore, if the master piston 43 moves forward, the master spring 45 is elastically compressed.

[0034] The input spring 46 is disposed in the second fluid chamber R2 of the cylinder head 42. The input spring 46 presses the input piston 44 rearward. Therefore, if the input piston 44 moves forward, the input spring 46 is elastically compressed.

[0035] In the master cylinder 31, the master chamber Rm is connected to the reservoir 24. Specifically, a portion of the master chamber Rm near the rear end is connected to the reservoir 24 via a port formed in the first peripheral wall 412 of the cylinder body 41. Therefore, when the master piston 43 moves from Figure 1When moving forward from the shown initial position, the main chamber Rm is not connected to the storage tank 24. As a result, as the main piston 43 moves forward, the hydraulic pressure in the main chamber Rm increases. For example, if the hydraulic pressure in the servo chamber Rs becomes high, the main piston 43 moves forward by the hydraulic pressure in the servo chamber Rs. Thereby, the hydraulic pressure in the main chamber Rm increases.

[0036] The first flow path 331 connects the main chamber Rm to the brake actuator 23. Specifically, the first flow path 331 connects the main chamber Rm to the wheel cylinders 11 for the front wheels FL and FR. In this regard, the first flow path 331 corresponds to the "first liquid path". The second flow path 332 connects the first liquid chamber R1 to the second liquid chamber R2. The third flow path 333 connects the storage tank 24 to the second flow path 332.

[0037] The first control valve 341 is a normally closed solenoid valve. The second control valve 342 is a normally open solenoid valve. The first control valve 341 is arranged between the connection point with the third flow path 333 on the second flow path 332 and the second liquid chamber R2. The second control valve 342 is provided on the third flow path 333. When the control device 80 of the braking device 20 operates, the first control valve 341 opens and the second control valve 342 closes.

[0038] The stroke simulator 32 is arranged between the first liquid chamber R1 and the first control valve 341 on the second flow path 332. For example, the stroke simulator 32 has a piston (not shown) pressed from the back by a spring inside. In this case, if the piston inside the stroke simulator 32 displaces against the pressure of the spring due to the inflow of the brake fluid from the second flow path 332, the brake fluid generates pressure according to the displacement of the piston. Specifically, if, in a state where the first control valve 341 is open and the second control valve 342 is closed, the input piston 44 moves forward by the operation of the brake operation member 21, the volume of the second liquid chamber R2 decreases by the volume of the input piston 44 entering the second liquid chamber R2. Thereby, the brake fluid flowing out from the second liquid chamber R2 to the second flow path 332 flows into the stroke simulator 32. As a result, the same pressure is generated in the second liquid chamber R2 and the first liquid chamber R1 connected by the second flow path 332 through the stroke simulator 32. Since the area of the rear end portion of the main piston 43 protruding into the second liquid chamber R2 is equal to the sectional area of the first liquid chamber R1, in a state where the same pressure is generated in the second liquid chamber R2 and the first liquid chamber R1, the main piston 43 does not move axially due to this pressure.

[0039] <Friction braking portion>

[0040] The friction braking portion 50 includes an electric cylinder 51. The friction braking portion 50 can operate through the electric cylinder 51 to adjust the hydraulic pressure in the plurality of wheel cylinders 11.

[0041] The friction braking unit 50 includes a fourth flow path 54, a fifth flow path 55, and a sixth flow path 58. The fourth flow path 54 connects the electric cylinder 51 and the storage tank 24. The fifth flow path 55 connects the servo chamber Rs of the master cylinder 31 and the sixth flow path 58. The sixth flow path 58 connects the brake actuator 23 and the electric cylinder 51. Specifically, the sixth flow path 58 connects the wheel cylinders 11 for the rear wheels RL and RR and the electric cylinder 51. In this regard, the sixth flow path 58 corresponds to the "second liquid path", and the fifth flow path 55 corresponds to the "third liquid path".

[0042] The electric cylinder 51 is provided between the fourth flow path 54 and the sixth flow path 58. The fourth flow path 54 is connected to the input port 515 of the electric cylinder 51. The sixth flow path 58 is connected to the output port 516 of the electric cylinder 51. Moreover, a differential pressure regulating valve 551 and a check valve 552 are provided in the fifth flow path 55. The differential pressure regulating valve 551 is an electromagnetic valve that adjusts the differential pressure between the part of the fifth flow path 55 on the servo chamber Rs side compared with the differential pressure regulating valve 551 and the part of the fifth flow path 55 on the electric cylinder 51 side compared with the differential pressure regulating valve 551. That is, the differential pressure regulating valve 551 can adjust the supply amount of the brake fluid to the servo chamber Rs.

[0043] Hereinafter, the hydraulic pressure of the part of the fifth flow path 55 on the electric cylinder 51 side compared with the differential pressure regulating valve 551 is referred to as "first hydraulic pressure", and the hydraulic pressure of the part of the fifth flow path 55 on the servo chamber Rs side compared with the differential pressure regulating valve 551 is referred to as "second hydraulic pressure". The first hydraulic pressure is the hydraulic pressure of the sixth flow path 58, and the second hydraulic pressure is also the hydraulic pressure of the servo chamber Rs.

[0044] The check valve 552 is provided in the fifth flow path 55 in parallel with the differential pressure regulating valve 551. The check valve 552 allows the flow of the brake fluid from the servo chamber Rs toward the sixth flow path 58 and restricts the flow of the brake fluid from the sixth flow path 58 toward the servo chamber Rs. Specifically, the check valve 552 allows the brake fluid to flow toward the sixth flow path 58 when the second hydraulic pressure is greater than the first hydraulic pressure. On the other hand, the check valve 552 restricts the flow of the brake fluid toward the servo chamber Rs when the second hydraulic pressure is less than the first hydraulic pressure.

[0045] <Configuration of the Electric Cylinder>

[0046] The electric cylinder 51 includes a cylinder 511, a piston 512, an electric motor 513, and a conversion mechanism 514. The piston 512 is provided in the cylinder 511 in a slidable state. The electric motor 513 is the power source of the electric cylinder 51. The conversion mechanism 514 converts the rotational motion of the output shaft of the electric motor 513 into the linear motion of the piston 512.

[0047] Inside the cylinder 511, a hydraulic chamber Re into which brake fluid is introduced is defined by the peripheral wall of the cylinder 511 and the piston 512. The position of the piston 512 inside the cylinder 511 can be changed by driving the electric motor 513. Hereinafter, the moving direction of the piston 512 that reduces the volume of the hydraulic chamber Re is referred to as the "forward direction Za", and the direction opposite to the forward direction Za is referred to as the "backward direction Zb". The backward direction Zb is also the moving direction of the piston 512 that increases the volume of the hydraulic chamber Re.

[0048] An input port 515 and an output port 516 are formed in the peripheral wall of the cylinder 511 as ports for connecting the hydraulic chamber Re to the outside. A through hole 517 is formed in the piston 512. When the position of the piston 512 in a situation where there is no braking requirement for the vehicle is set as the standby position, when the piston 512 is at the standby position or in the backward direction Zb compared to the standby position, the through hole 517 connects the input port 515 to the hydraulic chamber Re. Thus, when the piston 512 is at the standby position, the hydraulic chamber Re of the cylinder 511 is connected to the fourth flow path 54 via the input port 515 and the through hole 517. That is, the hydraulic chamber Re of the cylinder 511 is connected to the storage tank 24 via the input port 515 and the through hole 517. The input port 515 is configured to be open when the piston 512 is at the standby position and is closed by the piston 512 if the piston 512 moves from the standby position in the forward direction Za. If the piston 512 moves in the forward direction Za even though the input port 515 is closed by the piston 512 like this, the hydraulic pressure in the hydraulic chamber Re increases.

[0049] The output port 516 of the cylinder 511 is connected to the brake actuator 23 and the fifth flow path 55 via the sixth flow path 58. The output port 516 is always open regardless of the position of the piston 512. Therefore, when the input port 515 is closed by the piston 512, if the piston 512 moves in the forward direction Za, the brake fluid in the hydraulic chamber Re is discharged from the output port 516 to the outside of the cylinder 511.

[0050] In addition, the electric cylinder 51 provided in the braking device 20 does not have a spring that presses the piston 512 in the backward direction Zb. The electric cylinder 51 may have a spring that presses the piston 512 in the backward direction Zb.

[0051] The friction braking portion 50 includes a release flow path 56 and a release valve 57 disposed in the release flow path 56. The release flow path 56 is a flow path that connects the storage tank 24 and the wheel cylinder 11 so as to bypass the electric cylinder 51. The first end portion of the release flow path 56 is connected to the fourth flow path 54, and on the other hand, the second end portion of the release flow path 56 is connected to the sixth flow path 58. Specifically, the release flow path 56 connects between the storage tank 24 on the fourth flow path 54 and the input port 515, and between the output port 516 on the sixth flow path 58 and the brake actuator 23.

[0052] The release valve 57 is a normally closed solenoid valve. Therefore, the release flow path 56 is closed when the control for opening the release valve 57 is not performed.

[0053] <Brake Actuator>

[0054] The brake actuator 23 is configured to be able to independently adjust the hydraulic pressure of a plurality of wheel cylinders 11. The brake actuator 23 includes a front wheel side pressure regulating unit 231 and a rear wheel side pressure regulating unit 232. The front wheel side pressure regulating unit 231 generates frictional braking forces on the front wheels FL and FR by adjusting the hydraulic pressure of the wheel cylinders 11 for the front wheels FL and FR. The rear wheel side pressure regulating unit 232 generates frictional braking forces on the rear wheels RL and RR by adjusting the hydraulic pressure of the wheel cylinders 11 for the rear wheels RL and RR. Hereinafter, the hydraulic pressure of the wheel cylinders 11 for the front wheels FL and FR will also be referred to as the front wheel cylinder pressure, and the hydraulic pressure of the wheel cylinders 11 for the rear wheels RL and RR will also be referred to as the rear wheel cylinder pressure.

[0055] <Detection System of Brake Device>

[0056] As Figure 1 and Figure 2 shown, the detection system of the brake device 20 has a plurality of sensors. The detection signals of the sensors are input to the control device 80 of the brake device 20. The plurality of sensors include a plurality of hydraulic pressure sensors 351, 352, 353, and a stroke sensor SE1.

[0057] The main hydraulic pressure sensor 351 detects the hydraulic pressure in the master chamber Rm. For example, the main hydraulic pressure sensor 351 is disposed in the first flow path 331. The input hydraulic pressure sensor 352 detects the hydraulic pressure in the second hydraulic chamber R2. For example, the input hydraulic pressure sensor 352 is connected at a position between the first control valve 341 on the second flow path 332 and the second hydraulic chamber R2. The control pressure sensor 353 is a pressure sensor that detects the hydraulic pressure of the brake fluid discharged from the electric cylinder 51. For example, the control pressure sensor 353 is disposed near the output port 516 in the electric cylinder 51. As an example, in Figure 1 it shows a configuration in which the control pressure sensor 353 is connected between the release valve 57 and the output port 516 in the release flow path 56. The stroke sensor SE1 detects the operation amount of the brake operation member 21.

[0058] <Control Device of Braking Device>

[0059] The braking device 20 is provided with a control device 80. For example, the control device 80 is an electronic control device having a CPU and a memory. The memory stores a control program executed by the CPU. The control device 80 operates the hydraulic pressure generating device 22 and the brake actuator 23 by executing this control program by the CPU. That is, the control device 80 controls various solenoid valves 341, 342, 551, 57 of the hydraulic pressure generating device 22, the electric motors 513, and the front wheel side pressure regulating unit 231 and the rear wheel side pressure regulating unit 232 of the brake actuator 23. In addition, the control device 80 conducts various information communications with the regenerative braking device 60.

[0060] The control device 80 functions as a required braking force deriving unit 81, a frictional braking force deriving unit 82, and a friction control unit 83 by executing a control program by the CPU. The required braking force deriving unit 81, the frictional braking force deriving unit 82, and the friction control unit 83 are functional units for operating the hydraulic pressure generating device 22.

[0061] The required braking force deriving unit 81 derives the braking force required for the vehicle, that is, the required braking force. That is, when the braking operation member 21 is operated, the required braking force deriving unit 81 derives a value corresponding to the operation amount of the braking operation member 21 as the required braking force. For example, the more the operation amount is, the more the required braking force deriving unit 81 increases the required braking force. In addition, when deceleration is required for the vehicle in a state where no braking operation is performed, the required braking force deriving unit 81 also derives the required braking force. Moreover, the required braking force deriving unit 81 sends the required braking force to the regenerative braking device 60. The required braking force deriving unit 81 receives the actual regenerative braking force actually generated by the regenerative braking device 60 on the front wheels FL, FR. The actual regenerative braking force received here is the regenerative braking force generated by the regenerative braking device 60 on the front wheels FL, FR.

[0062] The frictional braking force derivation unit 82 derives a target value for the frictional braking force of the vehicle, that is, the target frictional braking force, based on the required braking force and the actual regenerative braking force. The target frictional braking force is the sum of the target values of the frictional braking forces generated by the front wheels FL and FR and the target values of the frictional braking forces generated by the rear wheels RL and RR. Specifically, when the actual regenerative braking force is greater than or equal to the required braking force, it is not necessary to generate a frictional braking force, so the frictional braking force derivation unit 82 sets the target frictional braking force to "0". On the other hand, when the actual regenerative braking force is less than the required braking force, it is necessary to generate a frictional braking force, so the frictional braking force derivation unit 82 derives a value greater than "0" as the target frictional braking force. For example, when the actual regenerative braking force is less than the required braking force, the greater the difference between the required braking force and the actual regenerative braking force, the greater the value derived as the target frictional braking force.

[0063] The friction control unit 83 controls the electric cylinder 51 and the differential pressure adjustment valve 551 based on the target frictional braking force. That is, the friction control unit 83 calculates the target first hydraulic pressure generated by the electric cylinder 51 based on the command value corresponding to the target frictional braking force. Then, the friction control unit 83 drives the electric motor 513 of the electric cylinder 51. At this time, the friction control unit 83 drives the electric motor 513 in such a way that the greater the target frictional braking force, the greater the amount of movement of the piston 512 from the standby position in the forward direction Za.

[0064] In addition, when the target first hydraulic pressure is "0", the friction control unit 83 sets "0" as the command value for the differential pressure between the first hydraulic pressure and the second hydraulic pressure, that is, the differential pressure command value. On the other hand, when the target first hydraulic pressure is greater than "0", the friction control unit 83 sets "0" or a value greater than "0" as the differential pressure command value. For example, when the target first hydraulic pressure is greater than "0", the friction control unit 83 sets a specified differential pressure as the differential pressure command value. In addition, the specified differential pressure can be either a preset fixed value or a variable value. When the specified differential pressure is a variable value, the μ value of the road surface on which the vehicle is traveling can also be used as a parameter to make the specified differential pressure variable.

[0065] The friction control unit 83 adjusts the energization amount of the solenoid of the differential pressure adjustment valve 551 so that the differential pressure adjustment valve 551 generates an electromagnetic force corresponding to the set differential pressure command value. If the second hydraulic pressure changes due to the operation of the differential pressure adjustment valve 551 in this way, the hydraulic pressure in the servo chamber Rs changes. Therefore, in the master cylinder 31, the master piston 43 moves according to the change in the hydraulic pressure in the servo chamber Rs. As a result, the hydraulic pressure in the master chamber Rm connected to the wheel cylinders 11 for the front wheels FL and FR changes. Here, the hydraulic pressure in the master chamber Rm is equal to the hydraulic pressure in the servo chamber Rs, that is, the second hydraulic pressure. In this way, the friction control unit 83 generates a frictional braking force for the front wheels FL and FR according to the second hydraulic pressure.

[0066] <Regenerative Braking Device>

[0067] The regenerative braking device 60 includes an electric generator 61 for the front wheels FL and FR, and a regenerative control unit 62 that controls the electric generator 61. By causing the electric generator 61 to function as an electric motor, driving force is transmitted from the electric generator 61 to the front wheels FL and FR. On the other hand, by causing the electric generator 61 to function as a generator, a regenerative braking force corresponding to the power generation amount of the electric generator 61 is generated in the front wheels FL and FR.

[0068] The regenerative control unit 62 controls the electric generator 61. The regenerative control unit 62 derives the maximum regenerative braking force, which is the maximum value of the regenerative braking force that the electric generator 61 can generate in the front wheels FL and FR at the current moment. For example, the regenerative control unit 62 derives the maximum regenerative braking force based on the rotational speeds of the front wheels FL and FR, the power storage amount and temperature of the in-vehicle battery that supplies power to the electric generator 61, and the like. Moreover, when the regenerative control unit 62 receives information related to the required braking force from the control device 80 of the braking device 20, it compares the required braking force with the maximum regenerative braking force. When the required braking force is less than or equal to the maximum regenerative braking force, the regenerative control unit 62 controls the power generation amount of the electric generator 61 so that the regenerative braking force is equal to the required braking force. On the other hand, when the required braking force is greater than the maximum regenerative braking force, the regenerative control unit 62 controls the power generation amount of the electric generator 61 so that the regenerative braking force is equal to the maximum regenerative braking force. The regenerative control unit 62 sends information related to the actual regenerative braking force actually generated in the front wheels FL and FR to the control device 80.

[0069] <Braking Process>

[0070] Refer to Figure 2 , and the process flow of the processing performed by the control device 80 during braking of the vehicle will be described.

[0071] As Figure 2 shown, the control device 80 determines whether there is a braking requirement (S11) based on the detection signal of the stroke sensor SE1 and the like. When deceleration of the vehicle is required from another control device, the control device 80 determines that there is a braking requirement even if the braking operation member 21 is not operated. When there is no braking requirement (S11: No), the control device 80 ends this processing. On the other hand, when there is a braking requirement (S11: Yes), the control device 80 derives the required braking force (S12). For example, when the braking operation member 21 is operated, the control device 80 derives the required braking force based on the detection signal of the stroke sensor SE1 and the like. In addition, when deceleration of the vehicle is required from another control device, the control device 80 derives a value corresponding to the required deceleration value as the required braking force.

[0072] Then, the control device 80 sends the required braking force to the regenerative control unit 62 (S13), and receives the actual regenerative braking force from the regenerative control unit 62 (S14).

[0073] When the regenerative control unit 62 receives the required braking force sent by the control device 80 in step S13, the regenerative control unit 62 derives the actual regenerative braking force that can be generated at the front wheels FL and FR by comparing the maximum regenerative braking force with the required braking force. Then, the regenerative control unit 62 controls the electric generator 61 to generate the actual regenerative braking force at the front wheels FL and FR. And, the regenerative control unit 62 sends the actual regenerative braking force to the control device 80. Thus, the control device 80 receives the actual regenerative braking force sent by the regenerative control unit 62 in step S14.

[0074] Next, the control device 80 determines whether the actual regenerative braking force is equal to the required braking force (S15). When the actual regenerative braking force is equal to the required braking force (S15: Yes), in other words, when the required braking force can be satisfied only by the regenerative braking force, the target frictional braking force is made "0" (S16). Thereafter, the control device 80 moves the process to step S18 described later. On the other hand, when the actual regenerative braking force is not equal to the required braking force (S15: No), in other words, when the required braking force cannot be satisfied only by the regenerative braking force, the target frictional braking force is derived based on the difference between the required braking force and the actual regenerative braking force (S17).

[0075] The control device 80 derives the target first hydraulic pressure and the target second hydraulic pressure based on the target frictional braking force set in steps S16 and S17, and controls the operation of the frictional braking unit 50 (S18). In other words, the control device 80 adjusts the first hydraulic pressure and the second hydraulic pressure by controlling the electric cylinder 51 and the differential pressure regulating valve 551. Thereafter, the control device 80 ends this process.

[0076] <Function and Effect>

[0077] Refer to Figure 3 (a) to (c) of Figure 4 and Figure 3 to describe the transition of the regenerative braking force, the front wheel cylinder pressure, and the rear wheel cylinder pressure with respect to the change in the required braking force. The front wheel cylinder pressure is related to the second hydraulic pressure, and the rear wheel cylinder pressure is related to the first hydraulic pressure. Therefore, in Figure 3 the transition of the front wheel cylinder pressure corresponds to the transition of the second hydraulic pressure, and the transition of the rear wheel cylinder pressure corresponds to the transition of the first hydraulic pressure. In addition, Figure 4 the multiple moments shown in

[0078] As in Figure 3As shown, at the first moment t11, if there is a braking requirement, the braking force is required to start increasing. In the case where the required braking force is small, specifically, in the case where the required braking force is below the maximum regenerative braking force, the required braking force can be satisfied only by the regenerative braking force. Therefore, during the period from the first moment t11 to the next second moment t12, the regenerative braking force increases in the same manner as the required braking force, and the front-wheel frictional braking force and the rear-wheel frictional braking force are maintained at "0". The regenerative braking force is the braking force generated only at the front wheels FL and FR. Therefore, as Figure 4 shown, during the period from the first moment t11 to the second moment t12, only the front-wheel braking force among the front-wheel braking force and the rear-wheel braking force increases.

[0079] When the second moment t12 is reached, as the required braking force increases, the required braking force becomes equal to the maximum regenerative braking force. In the Figure 3 example shown, the required braking force also increases after the second moment t12. Therefore, during the period after the second moment t12, the required braking force cannot be satisfied only by the regenerative braking force. As a result, during the period after the second moment t12, as the required braking force increases, the rear-wheel wheel cylinder pressure increases to increase the frictional braking force.

[0080] Specifically, based on the difference between the required braking force and the actual regenerative braking force, the target frictional braking force is derived. In this way, based on the target frictional braking force, the electric cylinder 51 and the differential pressure control valve 551 can be controlled. In the electric cylinder 51, the piston 512 moves in the forward direction Za by the drive of the electric motor 513. In this way, the brake fluid is discharged from the output port 516 of the electric cylinder 51, so the first hydraulic pressure increases. As a result, since the rear-wheel wheel cylinder pressure increases, the rear-wheel frictional braking force increases.

[0081] In the frictional braking portion 50, in a state where the above-mentioned specified differential pressure is set as the differential pressure command value for the differential pressure control valve 551, the hydraulic pressure of the brake fluid discharged from the electric cylinder 51 increases. Therefore, when the magnitude of the differential pressure between the first hydraulic pressure and the second hydraulic pressure is below the specified differential pressure, the differential pressure control valve 551 restricts the supply of the brake fluid discharged from the output port 516 of the electric cylinder 51 to the servo chamber Rs in the master cylinder 31. In other words, the second hydraulic pressure does not increase. In this case, the hydraulic pressure in the master chamber Rm in the master cylinder 31 does not increase, so the front-wheel wheel cylinder 11 pressure does not increase. As a result, the front-wheel frictional braking force does not increase. For example, the above-mentioned specified differential pressure is set according to the front-wheel wheel cylinder pressure for generating the braking force of the regenerative braking force as the frictional braking force of the front wheels FL and FR.

[0082] In this way, when the magnitude of the differential pressure between the first hydraulic pressure and the second hydraulic pressure is below the specified differential pressure, only the first hydraulic pressure among the second hydraulic pressure and the first hydraulic pressure increases. As a result, as Figure 4As shown, after the second moment t12, the rear-wheel braking force increases while the front-wheel braking force is maintained.

[0083] In Figure 3 the example shown, the target frictional braking force also increases after the second moment t12. Moreover, when the third moment t13 is reached, the magnitude of the differential pressure between the first hydraulic pressure and the second hydraulic pressure reaches a specified differential pressure. In this way, in order to maintain the magnitude of the differential pressure between the first hydraulic pressure and the second hydraulic pressure at the specified differential pressure, a part of the brake fluid discharged from the output port 516 of the electric cylinder 51 is supplied to the servo chamber Rs via the differential pressure adjustment valve 551. As a result, the second hydraulic pressure also increases. After the third moment t13, if the piston 512 in the electric cylinder 51 moves in the forward direction Za, the first hydraulic pressure and the second hydraulic pressure increase together while maintaining the differential pressure between the first hydraulic pressure and the second hydraulic pressure.

[0084] If the second hydraulic pressure, i.e., the hydraulic pressure in the servo chamber Rs, increases, in the master cylinder 31, the hydraulic pressure in the master chamber Rm increases by driving the master piston 43 corresponding to the increase in the hydraulic pressure in the servo chamber Rs. In this way, since the brake fluid is supplied from the master chamber Rm to the wheel cylinders 11 for the front wheels FL and FR, the pressure in the front-wheel wheel cylinders 11 increases. As a result, the front-wheel frictional braking force increases.

[0085] In Figure 3 the example shown, the target frictional braking force increases until the subsequent fourth moment t14. Therefore, during the period from the third moment t13 to the fourth moment t14, the rear-wheel wheel cylinder pressure and the front-wheel wheel cylinder pressure increase together while maintaining the pressure difference between the rear-wheel wheel cylinder pressure and the front-wheel wheel cylinder pressure. As a result, while maintaining the braking force difference between the rear-wheel frictional braking force and the front-wheel frictional braking force, the rear-wheel frictional braking force and the front-wheel frictional braking force increase together.

[0086] In this way, the braking device 20 can adjust the magnitudes of the front-wheel frictional braking force and the rear-wheel frictional braking force by controlling the electric cylinder 51 and the differential pressure adjustment valve 551. In addition, when an electric pump is used instead of the electric cylinder 51 as the hydraulic pressure generation source, it is necessary to use an expensive pump such as a gear pump as the electric pump, or multiple solenoid valves are used for hydraulic pressure adjustment. In other words, the braking device 20 is easy to construct the system at low cost in that it uses the inexpensive electric cylinder 51 compared with the electric pump and only one solenoid valve is required for hydraulic pressure adjustment.

[0087] During the period from the fourth moment t14 to the next fifth moment t15, a constant braking force is required. Therefore, if the maximum regenerative braking force is constant, the front-wheel frictional braking force and the rear-wheel frictional braking force are also constant. In the friction braking portion 50, the position of the piston 512 of the electric cylinder 51 is maintained.

[0088] When the fifth time t15 is reached, the required braking force is required to start decreasing. Therefore, the target frictional braking force decreases while maintaining the regenerative braking force. In this way, in the friction braking unit 50, the piston 512 of the electric cylinder 51 moves in the backward direction Zb while maintaining the differential pressure command value for the differential pressure adjustment valve 551. Due to the operation of the electric cylinder 51 in this way, the first hydraulic pressure decreases. Here, when the first hydraulic pressure is greater than the second hydraulic pressure, the brake fluid does not flow from the servo chamber Rs toward the sixth flow path 58 via the check valve 552. Therefore, only the first hydraulic pressure among the first hydraulic pressure and the second hydraulic pressure decreases. As a result, during the period from the fifth time t15 to the next sixth time t16, the front wheel wheel cylinder pressure does not decrease, while the rear wheel wheel cylinder pressure decreases. In other words, only the rear wheel braking force decreases.

[0089] When the sixth time t16 is reached, the front wheel wheel cylinder pressure and the rear wheel wheel cylinder pressure become equal. Therefore, during the period after the sixth time t16, if the first hydraulic pressure decreases according to the movement of the piston 512 of the electric cylinder 51 in the backward direction Zb, the second hydraulic pressure is slightly higher than the first hydraulic pressure. Therefore, the brake fluid flows from the servo chamber Rs toward the sixth flow path 58 via the check valve 552, and thus the second hydraulic pressure also decreases according to the decrease in the first hydraulic pressure. As a result, during the period after the sixth time t16, the front wheel wheel cylinder pressure and the rear wheel wheel cylinder pressure decrease together. As a result, the front wheel frictional braking force and the rear wheel frictional braking force decrease together.

[0090] When the seventh time t17 is reached, both the front wheel wheel cylinder pressure and the rear wheel wheel cylinder pressure are "0". Therefore, during the period after the seventh time t17, the required braking force can be satisfied only by the regenerative braking force. In other words, during the period after the seventh time t17, the regenerative braking force decreases in the same manner as the required braking force.

[0091] When the eighth time t18 is reached, the required braking force is "0". Therefore, the regenerative braking force is also "0".

[0092] In Figure 3 In the example shown, the period during which the vehicle generates braking force is set as the braking period, the period during which the vehicle generates regenerative braking force is set as the regenerative braking period, and the period during which the vehicle generates frictional braking force is set as the frictional braking period. In this case, both the braking period and the regenerative braking period are the period from the first time t11 to the eighth time t18. In other words, the braking period and the regenerative braking period are equal periods. In contrast, the frictional braking period is the period from the second time t12 to the seventh time t17. In other words, the frictional braking period is a period shorter than the braking period.

[0093] During frictional braking, there is a first increasing period in which only the rear-wheel frictional braking force increases, and a second increasing period in which the front-wheel frictional braking force and the rear-wheel frictional braking force increase together after the first increasing period. In addition, during frictional braking, there is a first decreasing period in which only the rear-wheel frictional braking force decreases, and a second decreasing period in which the front-wheel frictional braking force and the rear-wheel frictional braking force decrease together after the first decreasing period.

[0094] The first increasing period is a period that includes the start time of the frictional braking period and is a period in which only the first hydraulic pressure increases. On the other hand, the second increasing period is a period in which the first hydraulic pressure and the second hydraulic pressure increase together. The length of the second increasing period may be "0" depending on the magnitude of the required braking force. For example, when the required braking force can be satisfied by the regenerative braking force and the rear-wheel frictional braking force, the length of the second increasing period is "0".

[0095] The first decreasing period is a period in which only the first hydraulic pressure decreases until the differential pressure between the first hydraulic pressure and the second hydraulic pressure is eliminated. When the front-wheel frictional braking force is "0", in other words, when the first hydraulic pressure is atmospheric pressure, it decreases until the first hydraulic pressure becomes atmospheric pressure. In this case, the length of the subsequent second decreasing period is "0". The second decreasing period is a period in which the first hydraulic pressure and the second hydraulic pressure decrease together.

[0096] In Figure 3 In the example shown, the first increasing period is the period from the second time t12 to the third time t13, and the second increasing period is the period from the third time t13 to the fourth time t14. In addition, the first decreasing period is the period from the fifth time t15 to the sixth time t16, and the second decreasing period is the period from the sixth time t16 to the seventh time t17.

[0097] The present embodiment can also obtain the following effects.

[0098] (1) Consider a comparative example that does not have the check valve 552. In this comparative example, when the piston 512 of the electric cylinder 51 is driven in the backward direction Zb as the frictional braking force decreases, the second hydraulic pressure may be greater than the first hydraulic pressure. Therefore, in order to reduce the second hydraulic pressure, the differential pressure command value for the differential pressure control valve 551 is decreased, but there is a concern that the opening of the differential pressure control valve 551 may be delayed depending on the structure of the differential pressure control valve 551 and the hydraulic pressure difference between the first hydraulic pressure and the second hydraulic pressure. In this regard, in the braking device 20 of the present embodiment, when the second hydraulic pressure is greater than the first hydraulic pressure, the brake fluid flows from the servo chamber Rs toward the sixth flow path 58 through the check valve 552. Thus, the braking device 20 can avoid a delay in the decrease of the second hydraulic pressure when the frictional braking force decreases.

[0099] (2) When the required braking force increases, the braking device 20 can adjust the second hydraulic pressure to be smaller than the first hydraulic pressure, but cannot adjust the second hydraulic pressure to be larger than the first hydraulic pressure. In other words, the braking device 20 can make the front wheel cylinder pressure smaller than the rear wheel cylinder pressure, but cannot make the front wheel cylinder pressure larger than the rear wheel cylinder pressure. However, the vehicle is equipped with a regenerative braking device 60 that can generate regenerative braking force on the front wheels FL and FR. Therefore, the braking device 20 can make the front wheel braking force larger than the rear wheel braking force.

[0100] <Change Example>

[0101] This embodiment can be implemented with the following changes. This embodiment and the following change examples can be implemented in combination with each other within the range where there is no technical contradiction.

[0102] · The distribution ratio of the regenerative braking force and the frictional braking force can be appropriately changed. For example, when there is a braking requirement, not only the regenerative braking force can be increased, but both the regenerative braking force and the frictional braking force can be increased.

[0103] · The friction braking part 50 may not be provided with the check valve 552. In this case, it is preferable that the control device 80 changes the differential pressure command value for the differential pressure adjustment valve 551 in order to avoid a state where the second hydraulic pressure is too large compared to the first hydraulic pressure when reducing the frictional braking force.

[0104] · In the above embodiment, the first flow path 331 is connected to the wheel cylinders 11 for the front wheels FL and FR, and the sixth flow path 58 is connected to the wheel cylinders 11 for the rear wheels RL and RR. In the change example, the first flow path 331 may be connected to the wheel cylinders 11 for the rear wheels RL and RR, and the sixth flow path 58 may be connected to the wheel cylinders 11 for the front wheels FL and FR. In this case, the control device 80 can adjust the wheel cylinder pressure so that the front wheel cylinder pressure is larger than the rear wheel cylinder pressure. Therefore, the control device 80 can adjust the frictional braking force so that the front wheel frictional braking force is larger than the rear wheel frictional braking force.

[0105] · The vehicle may be equipped with a regenerative braking device 60 for the rear wheels RL and RR that can generate regenerative braking force on the rear wheels RL and RR.

[0106] · The vehicle may not be equipped with the regenerative braking device 60. Even in this case, the braking device 20 can also adjust the front wheel frictional braking force and the rear wheel frictional braking force by controlling the electric cylinder 51 and the differential pressure adjustment valve 551.

[0107] · The control device 80 is not limited to a device that includes a CPU and a ROM and executes software processing. That is, the control device 80 may have any of the following configurations (a) to (c).

[0108] (a) The control device 80 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU, and memories such as a RAM and a ROM. The memory stores program codes or instructions configured to cause the CPU to execute processes. The memory, that is, the computer-readable medium includes all available media that can be accessed by a general-purpose or special-purpose computer.

[0109] (b) The control device 80 includes one or more dedicated hardware circuits that execute various processes. As the dedicated hardware circuit, for example, an application specific integrated circuit, that is, an ASIC or an FPGA can be cited. Further, ASIC is an abbreviation for "Application Specific Integrated Circuit", and FPGA is an abbreviation for "Field Programmable Gate Array".

[0110] (c) The control device 80 includes a processor that executes a part of various processes according to a computer program, and a dedicated hardware circuit that executes the remaining processes among the various processes.

Claims

1. A braking device is applied to a vehicle having a first wheel cylinder and a second wheel cylinder, a first wheel that generates a frictional braking force corresponding to the hydraulic pressure of the first wheel cylinder, and a second wheel that generates a frictional braking force corresponding to the hydraulic pressure of the second wheel cylinder. The braking device includes: An electric cylinder having an electric motor as a power source and an output port that discharges brake fluid with a hydraulic pressure corresponding to the drive of the electric motor; A master cylinder having a master piston that divides a servo chamber and a master chamber, configured such that brake fluid flows out of the master chamber as the master piston moves with an increase in the hydraulic pressure of the servo chamber, and on the other hand, brake fluid flows into the master chamber as the master piston moves with a decrease in the hydraulic pressure of the servo chamber; A first hydraulic circuit that connects the master chamber to the first wheel cylinder; A second hydraulic circuit that connects the output port to the second wheel cylinder; A third hydraulic circuit that connects the second hydraulic circuit to the servo chamber; and A differential pressure regulating valve provided in the third hydraulic circuit that adjusts the differential pressure between a first hydraulic pressure and a second hydraulic pressure, where the first hydraulic pressure is the hydraulic pressure of the second hydraulic circuit and the second hydraulic pressure is the hydraulic pressure of the servo chamber.

2. The braking device according to claim 1, wherein: A check valve is provided in parallel with the differential pressure regulating valve, The check valve allows the flow of brake fluid from the servo chamber toward the second hydraulic circuit and restricts the flow of brake fluid from the second hydraulic circuit toward the servo chamber.

3. The braking device according to claim 1 or 2, wherein: A control device for controlling the electric cylinder and the differential pressure regulating valve is provided, The control device adjusts the first hydraulic pressure by controlling the electric cylinder and adjusts the second hydraulic pressure to be below the first hydraulic pressure by controlling the differential pressure regulating valve.

4. The braking device according to claim 3, wherein: The first wheel is a front wheel, the first wheel cylinder is a wheel cylinder for the front wheel, the second wheel is a rear wheel, and the second wheel cylinder is a wheel cylinder for the rear wheel, The control device adjusts the frictional braking force generated at the rear wheel by adjusting the first hydraulic pressure and adjusts the frictional braking force generated at the front wheel by adjusting the second hydraulic pressure.

5. The braking device according to claim 4, wherein: The vehicle is equipped with a regenerative braking device that generates a regenerative braking force at the front wheel, The control device adjusts the second hydraulic pressure to be below the first hydraulic pressure when the regenerative braking force is generated at the front wheel.

6. The braking device according to claim 3, wherein: In a situation where the target frictional braking force increases, the control device increases the first hydraulic pressure while maintaining the state where the second hydraulic pressure is less than the first hydraulic pressure, and the target frictional braking force is the target value of the frictional braking force of the vehicle.

7. The braking device according to claim 5, wherein: When the differential pressure between the first hydraulic pressure and the second hydraulic pressure is below a specified differential pressure and the control device increases the frictional braking force, only the first hydraulic pressure among the first hydraulic pressure and the second hydraulic pressure is increased. When the differential pressure is greater than the specified differential pressure and the control device increases the frictional braking force, the first hydraulic pressure and the second hydraulic pressure are increased together.

8. The braking device according to claim 3, wherein when the target frictional braking force decreases, when the first hydraulic pressure is greater than the second hydraulic pressure, only the first hydraulic pressure among the first hydraulic pressure and the second hydraulic pressure is decreased. When the first hydraulic pressure is less than or equal to the second hydraulic pressure, the first hydraulic pressure and the second hydraulic pressure are decreased together. The target frictional braking force is the target value of the frictional braking force of the vehicle.

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