Braking device

Abstract

To make it possible to determine whether or not brake fluid leakage occurs in a braking device during braking, while suppressing excessive heat generation in a partial coil of multiple phase coils constituting an electric motor.SOLUTION: A braking device 100 includes: an electric cylinder 51 having a first electric motor 513 as a power source; a fifth flow path 55 through which brake fluid flows when the brake fluid is discharged from the electric cylinder 51; a servo pressure sensor 58; and a control device 200. The control device 200 increases a motor rotation angle until a detection value of the servo pressure sensor 58 becomes equal to or greater than a determination hydraulic pressure, and executes determination processing to determine whether or not brake fluid leakage occurs in the braking device 100 during braking, on the basis of a position of a piston 512 of the electric cylinder 51 or a correlation value thereof at that time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a braking device that adjusts hydraulic pressure in a wheel cylinder by operating an electric cylinder. [Background technology]

[0002] Patent Document 1 discloses an example of a braking device equipped with an electric cylinder powered by an electric motor. A control unit of the braking device executes a diagnostic process to determine whether or not a brake fluid leak occurs within the braking device during braking.

[0003] In the diagnostic process, the control unit drives the electric motor until the hydraulic pressure in the brake flow path through which brake fluid discharged from the electric cylinder flows reaches a predetermined pressure. When the hydraulic pressure reaches the predetermined pressure, the control unit holds the position of the piston of the electric cylinder for a predetermined time. Based on the results of monitoring the hydraulic pressure in the brake flow path during the period in which the piston position is held, the control unit diagnoses whether or not a brake fluid leak will occur within the braking device during braking. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2020 / 339096 Summary of the Invention [Problem to be solved by the invention]

[0005] During the diagnostic process, while the piston position is maintained, the rotation angle of the electric motor is maintained. During this period, there is a risk that the amount of current flowing through some of the coils of the multiple phases of the electric motor will be greater than the amount of current flowing through the other coils. If this situation continues, there is a risk that the amount of heat generated by the coils in the electric motor will be excessive. [Means for solving the problem]

[0006] A braking device for solving the above problem is a device applied to a vehicle in which a braking force corresponding to wheel pressure, which is hydraulic pressure in a wheel cylinder, is generated at a wheel. The braking device includes an electric cylinder configured to discharge brake fluid from the cylinder when a piston moves forward in the cylinder in response to an increase in a motor rotation angle, which is the rotation angle of the electric motor, a supply flow path through which brake fluid flows in a direction to increase the wheel pressure when brake fluid is discharged from the electric cylinder, a hydraulic pressure sensor that detects the hydraulic pressure in the supply flow path, and a control device that controls the electric motor, and is configured to increase the wheel pressure by discharging brake fluid from the electric cylinder. The control device increases the motor rotation angle so that a hydraulic pressure detection value, which is the hydraulic pressure detected by the hydraulic pressure sensor, gradually increases until the detected hydraulic pressure value becomes equal to or exceeds a threshold hydraulic pressure, and performs a determination process to determine whether brake fluid leakage will occur within the braking device during braking based on the position of the piston at that time or a correlation value thereof. [Effects of the Invention]

[0007] The braking device has the advantage of being able to determine whether or not a brake fluid leak will occur within the braking device during braking, while preventing excessive heat generation in some of the coils among the multiple phase coils that make up the electric motor. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a braking device according to an embodiment. [Figure 2] FIG. 2 is a flowchart showing a series of processes for diagnosing whether or not a brake fluid leak occurs in the braking system of FIG. [Figure 3] FIG. 3 is a timing chart showing the execution of the determination process. [Figure 4] FIG. 4 is a timing chart showing the execution of the leakage diagnosis process. [Figure 5]FIG. 5 is a graph showing the relationship between the stroke of the piston of the electric cylinder provided in the braking device of FIG. 1 and the servo pressure. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a braking device mounted on a vehicle will be described below with reference to FIGS. 1 shows a vehicle equipped with a braking device 100. The vehicle has two front wheels 11fl, 11fr and two rear wheels 11rl, 11rr as wheels. The vehicle also has friction brakes 15 in the same number as the wheels.

[0010] <Friction brake configuration> The multiple friction brakes 15 each generate a braking force at a corresponding wheel. The friction brakes 15 have a wheel cylinder 16, a rotating body 17, and a friction portion 18. Because the rotating body 17 rotates together with the wheel, braking force is generated at the wheel by pressing the friction portion 18 against the rotating body 17. The force pressing the friction portion 18 against the rotating body 17 increases as the wheel pressure Pw, which is the hydraulic pressure in the wheel cylinder 16, increases. Therefore, the friction brakes 15 can generate a greater braking force at the wheel as the wheel pressure Pw increases.

[0011] As shown in FIG. 1, the vehicle has a plurality of wheel cylinders 16. In this embodiment, of the plurality of wheel cylinders 16, the wheel cylinder 16 corresponding to the left front wheel 11fl and the wheel cylinder 16 corresponding to the left rear wheel 11rl correspond to the "first wheel cylinder." Of the plurality of wheel cylinders 16, the wheel cylinder 16 corresponding to the right front wheel 11fr and the wheel cylinder 16 corresponding to the right rear wheel 11rr correspond to the "second wheel cylinder." In this case, of the plurality of rear wheels 11rl, 11rr, the left rear wheel 11rl corresponds to the "first rear wheel," and the right rear wheel 11rr corresponds to the "second rear wheel." Of the plurality of front wheels 11fl, 11fr, the left front wheel 11fl corresponds to the "first front wheel," and the right front wheel 11fr corresponds to the "second front wheel."

[0012] <Braking system configuration> The braking device 100 adjusts the braking force of the vehicle by controlling the wheel pressure Pw of the multiple wheel cylinders 16. The braking device 100 includes a hydraulic pressure generating device 20, a brake actuator 70, and a control device 200. The hydraulic pressure generating device 20 and the brake actuator 70 are each configured to be able to control the wheel pressure Pw of the multiple wheel cylinders 16. The control device 200 controls the operation of the hydraulic pressure generating device 20 and the brake actuator 70.

[0013] <Liquid pressure generator> The hydraulic pressure generating device 20 has a reservoir tank 21, a brake operating member 22, a master device 30, and an electric pressurizing unit 50. The reservoir tank 21 stores brake fluid and is open to the atmosphere.

[0014] The brake operating member 22 is a member that is operated by the driver of the vehicle when decelerating the vehicle. An example of the brake operating member 22 is a brake pedal. The driver's operation of the brake operating member 22 is referred to as a "braking operation." When a braking operation is being performed, the hydraulic pressure generating device 20 can generate wheel pressure Pw in the multiple wheel cylinders 16 according to the amount of operation of the brake operating member 22.

[0015] <Master device> The master unit 30 includes a master cylinder 31, a stroke simulator 32, multiple flow paths 331, 332, and 333 connected to the master cylinder 31, and multiple control valves 341 and 342 that control the flow of brake fluid. The master unit 30 includes a hydraulic pressure sensor 351 that detects the hydraulic pressure of the brake fluid. A detection signal from the hydraulic pressure sensor 351 is input to the control device 200.

[0016] The stroke simulator 32 is capable of generating a reaction force according to the amount of operation of the brake operating member 22 . The master cylinder 31 includes a main cylinder 41, a cover cylinder 42, a master piston 43, and an input piston 44. The master piston 43 and the input piston 44 can move relative to the main cylinder 41 and the cover cylinder 42. The master cylinder 31 includes a master spring 45 that biases the master piston 43, and an input spring 46 that biases the input piston 44.

[0017] The main cylinder 41 has a plate-shaped bottom wall 411, a cylindrical peripheral wall 412 extending from the bottom wall 411 along the axis of the bottom wall 411, and a first annular wall 413 extending from the rear end of the peripheral wall 412 toward the axis of the peripheral wall 412. A hole is formed in the first annular wall 413, into which the rear end of a master piston 43 (described later) is inserted.

[0018] Within the main cylinder 41, a master chamber Rm is defined by a bottom wall 411, a peripheral wall 412, and a master piston 43. Hereinafter, in the master cylinder 31, the movement direction of the master piston 43, which is to the left in FIG. 1 and which reduces the volume of the master chamber Rm, will be referred to as the "forward" direction. On the other hand, the opposite direction to the forward direction will be referred to as the "rearward" direction. The rearward direction is also the direction which increases the volume of the master chamber Rm.

[0019] A first fluid chamber R1 is defined behind the master chamber Rm within the main cylinder 41 by the peripheral wall 412 and the master piston 43. A servo chamber Rs is defined behind the first fluid chamber R1 within the main cylinder 41 by the peripheral wall 412, the first annular wall 413, and the master piston 43. Inside the main cylinder 41, the master chamber Rm, the first fluid chamber R1, and the servo chamber Rs are not connected to one another.

[0020] The cover cylinder 42 has a cylindrical peripheral wall 421 and a second annular wall 422 extending from the rear end of the peripheral wall 421 toward the axis of the peripheral wall 421. The peripheral wall 421 is attached to the first annular wall 413 so that its axis coincides with that of the peripheral wall 412 of the main cylinder 41. The second annular wall 422 has a hole into which the rear end of the input piston 44 (described later) is inserted.

[0021] Within the cover cylinder 42, a second fluid chamber R2 is defined by the peripheral wall 421, the second annular wall 422, and the first annular wall 413 of the main cylinder 41. In the master cylinder 31, the second fluid chamber R2 is located rearward of the servo chamber Rs.

[0022] The master piston 43 is housed in the master cylinder 31 in surface contact with the inner circumferential surface of the peripheral wall 412 of the main cylinder 41 and the inner circumferential surface of the first annular wall 413. Therefore, when the master piston 43 moves in the axial direction, the master piston 43 slides on the inner circumferential surface of the peripheral wall 412 and the inner circumferential surface of the first annular wall 413. The rear end of the master piston 43 protrudes rearward beyond the first annular wall 413 and is located in the second fluid chamber R2.

[0023] The input piston 44 is housed in the master cylinder 31 in surface contact with the inner circumferential surface of the second annular wall 422 of the cover cylinder 42. Therefore, when the input piston 44 moves in the axial direction, the input piston 44 slides on the inner circumferential surface of the second annular wall 422. The rear end of the input piston 44 protrudes rearward beyond the second annular wall 422. The brake operating member 22 is connected to the rear end of the input piston 44. In the second fluid chamber R2, a gap is formed between the input piston 44 and the master piston 43. When the brake operating member 22 is operated, the input piston 44 moves in a direction approaching the master piston 43.

[0024] The master spring 45 is disposed between the bottom wall 411 of the main cylinder 41 and the master piston 43. The master spring 45 biases the master piston 43 rearward, so when the master piston 43 moves forward, the master spring 45 is elastically compressed.

[0025] The input spring 46 is disposed between the first annular wall 413 of the main cylinder 41 and the input piston 44. The input spring 46 biases the input piston 44 rearward, so that when the input piston 44 moves forward, the input spring 46 is elastically compressed.

[0026] In the master cylinder 31, the master chamber Rm is connected to the reservoir tank 21. More specifically, a portion of the master chamber Rm near the rear end is connected to the reservoir tank 21 via a port formed in the peripheral wall 412 of the main cylinder 41. Therefore, when the master piston 43 moves forward from the initial position shown in FIG. 1, the connection between the master chamber Rm and the reservoir tank 21 is released. After this, the hydraulic pressure in the master chamber Rm increases as the master piston 43 moves forward. For example, when the hydraulic pressure in the servo chamber Rs increases, the hydraulic pressure in the servo chamber Rs moves the master piston 43 forward. This increases the hydraulic pressure in the master chamber Rm.

[0027] The first flow path 331 connects a second hydraulic circuit 712 of the brake actuator 70 (described later) to the master chamber Rm. The second flow path 332 connects the first fluid chamber R1 to a third flow path 333. The stroke simulator 32 is also connected to the second flow path 332. The third flow path 333 connects the second fluid chamber R2 to the reservoir tank 21.

[0028] 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 provided in a portion of the third flow path 333 closer to the second liquid chamber R2 than the connection point with the second flow path 332. The second control valve 342 is provided in a portion of the third flow path 333 on the opposite side of the connection point with the second flow path 332 from the first control valve 341. When the control device 200 is operating, the first control valve 341 is opened and the second control valve 342 is closed.

[0029] The hydraulic pressure sensor 351 detects the hydraulic pressure in the second hydraulic chamber R2. For example, the hydraulic pressure sensor 351 is provided in a portion of the third flow path 333 between the connection point with the second hydraulic chamber R2 and the first control valve 341. In the following description, the hydraulic pressure based on the detection signal of the hydraulic pressure sensor 351 will be referred to as the "input hydraulic pressure Pgs."

[0030] <Pressure unit> 1, the pressurizing unit 50 includes an electric cylinder 51. The pressurizing unit 50 can adjust the wheel pressure Pw of the plurality of wheel cylinders 16 by operating the electric cylinder 51.

[0031] The pressurizing unit 50 has a fourth flow path 54, a fifth flow path 55, and a sixth flow path 56 as flow paths for brake fluid. The fourth flow path 54 is connected to an input port 515 of the electric cylinder 51 and the reservoir tank 21. The fifth flow path 55 is connected to a servo chamber Rs of the master cylinder 31 and an output port 516 of the electric cylinder 51. The sixth flow path 56 is connected to a first hydraulic pressure circuit 711 of the brake actuator 70 (described later) and the fifth flow path 55. Therefore, the electric cylinder 51 can supply brake fluid discharged from the output port 516 to both the servo chamber Rs and the first hydraulic pressure circuit 711.

[0032] The pressurizing unit 50 includes a differential pressure adjustment valve 551 installed in the fifth flow path 55. The differential pressure adjustment valve 551 is a normally open linear solenoid valve that adjusts the differential pressure between a portion of the fifth flow path 55 that is closer to the servo chamber Rs than the differential pressure adjustment valve 551 and a portion of the fifth flow path 55 that is closer to the electric cylinder 51 than the differential pressure adjustment valve 551. The pressurizing unit 50 can adjust the amount of brake fluid supplied to the servo chamber Rs, i.e., the hydraulic pressure in the servo chamber Rs, by adjusting the command opening of the differential pressure adjustment valve 551.

[0033] A check valve 552 is provided in parallel with the differential pressure adjustment valve 551 in the fifth flow path 55. The check valve 552 allows the flow of brake fluid through the check valve 552 from the servo chamber Rs toward the electric cylinder 51. On the other hand, the check valve 552 restricts the flow of brake fluid through the check valve 552 in the direction from the electric cylinder 51 to the servo chamber Rs.

[0034] The electric cylinder 51 includes a cylinder 511, a piston 512, a first electric motor 513, and a conversion mechanism 514. The piston 512 is slidably provided within the cylinder 511. The first electric motor 513 is a power source for the electric cylinder 51. The conversion mechanism 514 converts the rotation of the output shaft of the first electric motor 513 into linear movement of the piston 512.

[0035] The first electric motor 513 is a servo motor having multi-phase coils and a rotor that can rotate in both forward and reverse directions. When the rotor rotates in the forward direction of the forward and reverse rotation directions, it is referred to as "the first electric motor 513 rotating in the forward direction." When the rotor rotates in the reverse direction of the forward and reverse rotation directions, it is referred to as "the first electric motor 513 rotating in the reverse direction." The forward direction is the rotation direction when the electric cylinder 51 increases the hydraulic pressure of the brake fluid. The reverse direction is the rotation direction when the electric cylinder 51 reduces the hydraulic pressure of the brake fluid. When the first electric motor 513 rotates in the forward direction, the motor rotation angle θ increases. Furthermore, when the first electric motor 513 rotates in the forward direction, the motor rotation speed Nmt, which is the rotational speed of the first electric motor 513, is a positive value. On the other hand, when the first electric motor 513 rotates in the reverse direction, the motor rotation angle θ decreases. When the first electric motor 513 rotates in the reverse direction, the motor rotation speed Nmt becomes a negative value.

[0036] A hydraulic pressure chamber Re into which brake fluid is introduced is defined inside the cylinder 511 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 first electric motor 513. Hereinafter, the direction of linear movement of the piston 512 when reducing the volume of the hydraulic pressure chamber Re will be referred to as the "forward direction Za," and the direction opposite to the forward direction Za will be referred to as the "rearward direction Zb." The rearward direction Zb is also the direction of linear movement of the piston 512 when increasing the volume of the hydraulic pressure chamber Re.

[0037] An input port 515 and an output port 516 are formed in the peripheral wall of the cylinder 511 as ports connecting the hydraulic pressure chamber Re with the outside. A through hole 517 is formed in the piston 512. The through hole 517 is positioned so that the input port 515 and the hydraulic pressure chamber Re can communicate with each other when the piston 512 is in the most retracted position. As a result, when the piston 512 is in the most retracted position, the hydraulic pressure chamber Re of the cylinder 511 communicates with the reservoir tank 21 via the through hole 517, the input port 515, and the fourth flow path 54. The input port 515 is open when the piston 512 is in the most retracted position, and is closed by the piston 512 when the piston 512 moves forward in the forward direction Za from the most retracted position. Even after the input port 515 is closed by the piston 512, the hydraulic pressure in the hydraulic pressure chamber Re increases when the piston 512 moves forward in the forward direction Za.

[0038] The output port 516 is connected to the master cylinder 31 and the sixth flow path 56 via the fifth flow path 55. The output port 516 is always open regardless of the position of the piston 512. Therefore, when the input port 515 is blocked by the piston 512, the piston 512 moves in the forward direction Za within the cylinder 511 in response to the driving of the first electric motor 513, causing the brake fluid in the hydraulic chamber Re to be discharged from the output port 516 to the fifth flow path 55. On the other hand, the piston 512 moves in the backward direction Zb within the cylinder 511 in response to the driving of the first electric motor 513, causing the brake fluid in the fifth flow path 55 to be drawn into the hydraulic chamber Re through the output port 516.

[0039] In the hydraulic pressure generator 20, when brake fluid is discharged from the output port 516 of the electric cylinder 51, the brake fluid flows through the fifth flow path 55. A portion of the brake fluid flowing through the fifth flow path 55 flows toward the wheel cylinders 16 for the rear wheels 11rl, 11rr via the sixth flow path 56. The remaining brake fluid flows into the servo chamber Rs of the master unit 30. As a result, the hydraulic pressure in the servo chamber Rs increases, causing the master piston 43 to move forward, thereby increasing the hydraulic pressure in the master chamber Rm. As a result, the brake fluid in the master chamber Rm flows through the first flow path 331 toward the wheel cylinders 16 for the front wheels 11fl, 11fr.

[0040] On the other hand, when the electric cylinder 51 is sucking brake fluid through the output port 516, brake fluid flows out from each of the wheel cylinders 16 for the rear wheels 11rl, 11rr and the wheel cylinders 16 for the front wheels 11fl, 11fr. Then, the brake fluid flows through the sixth flow path 56 toward the fifth flow path 55. Also, the brake fluid flows through the first flow path 331 toward the master chamber Rm. Then, the hydraulic pressure in the master chamber Rm increases, and the master piston 43 moves in the backward direction Zb. As a result, the brake fluid in the servo chamber Rs flows out to the fifth flow path 55. As a result, the brake fluid flows through the fifth flow path 55 toward the electric cylinder 51.

[0041] Hereinafter, among the flow directions of the brake fluid in the fifth flow path 55, the flow direction of the brake fluid for increasing the wheel pressure Pw will be referred to as the "pressure increase direction Ya," and the direction opposite to the pressure increase direction Ya will be referred to as the "pressure decrease direction Yb." In this case, the pressure decrease direction Yb is the flow direction of the brake fluid for decreasing the wheel pressure Pw.

[0042] The pressurizing unit 50 is equipped with a servo pressure sensor 58 as a hydraulic pressure sensor that detects the hydraulic pressure of a supply flow path through which brake fluid flows in the pressurizing direction Ya when brake fluid is discharged from the electric cylinder 51. The servo pressure sensor 58 is connected to, for example, the fifth flow path 55. In other words, the fifth flow path 55 corresponds to the "supply flow path." The pressure of the brake fluid discharged from the electric cylinder 51 via the output port 516 is referred to as the "servo pressure." At this time, the servo pressure sensor 58 detects the servo pressure. Hereinafter, the servo pressure based on the detection signal of the servo pressure sensor 58 is referred to as the "servo pressure detection value PscE."

[0043] The pressurizing unit 50 is equipped with a rotation angle sensor 59. The rotation angle sensor 59 detects a motor rotation angle θ, which is the rotation angle of the output shaft of the first electric motor 513. Hereinafter, the motor rotation angle θ based on the detection signal of the rotation angle sensor 59 will be referred to as the "detected rotation angle value θE."

[0044] <Braking actuator> The brake actuator 70 is configured to be able to individually adjust the wheel pressures Pw of the multiple wheel cylinders 16, independent of the pressurizing unit 50. The brake actuator 70 has a first hydraulic pressure circuit 711 and a second hydraulic pressure circuit 712. The first hydraulic pressure circuit 711 is connected to the sixth flow path 56 and is connected to the two wheel cylinders 16 for the rear wheels 11rl, 11rr. The second hydraulic pressure circuit 712 is connected to the first flow path 331 and is connected to the two wheel cylinders 16 for the front wheels 11fl, 11fr.

[0045] The first hydraulic pressure circuit 711 has a connection flow path 721 connected to the sixth flow path 56. The second hydraulic pressure circuit 712 has a connection flow path 722 connected to the first flow path 331. The connection flow path 721 is a brake fluid path connecting the two wheel cylinders 16 for the rear wheels 11rl and 11rr to the sixth flow path 56. The connection flow path 722 is a brake fluid path connecting the two wheel cylinders 16 for the front wheels 11fl and 11fr to the first flow path 331. A differential pressure control valve is provided in each of the multiple connection flow paths 721, 722. The differential pressure control valve in the connection flow path 721 is the differential pressure control valve 731, and the differential pressure control valve in the connection flow path 722 is the differential pressure control valve 732. The differential pressure control valves 731, 732 are normally open linear solenoid valves. The differential pressure control valve 731 can adjust the differential pressure between the portion of the connection flow path 721 on the sixth flow path 56 side and the portion on the wheel cylinder 16 side. The differential pressure control valve 732 can adjust the differential pressure between the portion of the connecting flow path 722 on the first flow path 331 side and the portion on the wheel cylinder 16 side. For example, the differential pressure control valves 731, 732 can generate a larger differential pressure as the current flowing through their solenoids increases.

[0046] A portion of the connecting flow path 721 closer to the wheel cylinder 16 than the differential pressure control valve 731 branches into two paths 72a and 72b. The path 72a is connected to the wheel cylinder 16 for the left rear wheel 11rl, while the path 72b is connected to the wheel cylinder 16 for the right rear wheel 11rr. A portion of the connecting flow path 722 closer to the wheel cylinder 16 than the differential pressure control valve 732 branches into two paths 72c and 72d. The path 72c is connected to the wheel cylinder 16 for the left front wheel 11fl, while the path 72d is connected to the wheel cylinder 16 for the right front wheel 11fr.

[0047] A retention valve, which is a normally open solenoid valve, is provided in each of the multiple paths 72a to 72d. The retention valve in path 72a is retention valve 74a, and the retention valve in path 72b is retention valve 74b. The retention valve in path 72c is retention valve 74c, and the retention valve in path 72d is retention valve 74d. These retention valves 74a to 74d are provided for each of the multiple wheel cylinders 16, and correspond to the "solenoid valves" that are closed to restrict the supply of brake fluid to the corresponding wheel cylinder 16.

[0048] The first hydraulic pressure circuit 711 has a reduced pressure reservoir 751 that stores brake fluid and a reduced pressure fluid passage 761 connected to the reduced pressure reservoir 751. The second hydraulic pressure circuit 712 has a reduced pressure reservoir 752 that stores brake fluid and a reduced pressure fluid passage 762 that is connected to the reduced pressure reservoir 752. The reduced pressure fluid passage 761 is a brake fluid passage that connects the reduced pressure reservoir 751 to portions of the paths 72a and 72b that are closer to the wheel cylinder 16 than the retention valves 74a and 74b. The reduced pressure fluid passage 762 is a brake fluid passage that connects the reduced pressure reservoir 752 to portions of the paths 72c and 72d that are closer to the wheel cylinder 16 than the retention valves 74c and 74d. Pressure reducing valves are provided in the pressure reducing fluid passage 761 at a portion connected to passage 72a, the portion connected to passage 72b, the portion connected to passage 72c, and the portion connected to passage 72d. The pressure reducing valve in the portion of pressure reducing fluid passage 761 connected to passage 72a is pressure reducing valve 77a. The pressure reducing valve in the portion of pressure reducing fluid passage 761 connected to passage 72b is pressure reducing valve 77b. The pressure reducing valve in the portion of pressure reducing fluid passage 762 connected to passage 72c is pressure reducing valve 77c. The pressure reducing valve in the portion of pressure reducing fluid passage 762 connected to passage 72d is pressure reducing valve 77d. The pressure reducing valves 77a to 77d are normally closed solenoid valves. When the pressure reducing valves 77a to 77d open, the brake fluid in the wheel cylinder 16 flows into the pressure reducing reservoirs 751 and 752 via the pressure reducing fluid passages 761 and 762.

[0049] The first hydraulic pressure circuit 711 has a pump 791. The second hydraulic pressure circuit 712 has a pump 792. The multiple pumps 791, 792 are electric pumps powered by a second electric motor 78. The pump 791 pumps up the brake fluid in the reduced pressure reservoir 751 and discharges the brake fluid into a portion of the connecting flow path 721 between the differential pressure control valve 731 and the holding valves 74a, 74b. The pump 792 pumps up the brake fluid in the reduced pressure reservoir 752 and discharges the brake fluid into a portion of the connecting flow path 722 between the differential pressure control valve 732 and the holding valves 74c, 74d.

[0050] The first hydraulic pressure circuit 711 has a return flow path 801 and a valve mechanism 811. The second hydraulic pressure circuit 712 has a return flow path 802 and a valve mechanism 812. The return flow path 801 is a brake fluid path that connects a portion of the connecting flow path 721 that is closer to the sixth flow path 56 than the differential pressure control valve 731 and a reduced-pressure reservoir 751. The valve mechanism 811 is integrated with the reduced-pressure reservoir 751. The valve mechanism 811 allows the flow of brake fluid from the return flow path 801 to the sixth flow path 56, while restricting the flow of brake fluid from the sixth flow path 56 to the reduced-pressure reservoir 751. However, when the pump 791 operates while the reduced-pressure reservoir 751 is empty, the valve mechanism 811 allows the flow of brake fluid from the sixth flow path 56 through the return flow path 801.

[0051] The reflux flow path 802 is a brake fluid path that is connected to a portion of the connecting flow path 722 that is closer to the first flow path 331 than the differential pressure control valve 732 and to the reduced-pressure reservoir 752. The valve mechanism 812 is integrated with the reduced-pressure reservoir 752. The valve mechanism 812 allows the brake fluid to flow from the reduced-pressure reservoir 752 to the first flow path 331 in the reflux flow path 802, while restricting the flow of brake fluid from the first flow path 331 to the reduced-pressure reservoir 752. However, when the pump 792 operates while the reduced-pressure reservoir 752 is empty, the valve mechanism 812 allows the brake fluid to flow from the first flow path 331 in the reflux flow path 802.

[0052] The second hydraulic circuit 712 is provided with a hydraulic pressure sensor 83 that detects the hydraulic pressure of the brake fluid that has flowed into the second hydraulic circuit 712 from the first flow path 331. The hydraulic pressure sensor 83 is connected to a portion of the connecting flow path 722 that is closer to the first flow path 331 than the differential pressure control valve 732. The first flow path 331 is connected to the master chamber Rm of the master device 30. Therefore, it can be said that the hydraulic pressure sensor 83 detects the hydraulic pressure of the brake fluid discharged from the master chamber Rm. Hereinafter, the hydraulic pressure based on the detection signal of the hydraulic pressure sensor 83 will be referred to as the "master pressure detection value PmcE."

[0053] <Control device> The control device 200 operates the hydraulic pressure generating device 20 and the brake actuator 70 based on detection signals from the plurality of sensors 351, 58, 59, and 83. The control device 200 includes a plurality of processing circuits. Of the plurality of processing circuits, a first processing circuit 210 operates the hydraulic pressure generating device 20, and a second processing circuit 220 operates the hydraulic pressure generating device 20.

[0054] An example of the processing circuits 210, 220 is an electronic control device. In this case, each of the multiple processing circuits 210, 220 has a CPU and a memory that stores a control program executed by the CPU. The first processing circuit 210 operates the hydraulic pressure generating device 20 by the CPU executing the control program stored in the memory. The second processing circuit 220 operates the brake actuator 70 by the CPU executing the control program stored in the memory.

[0055] The processing circuits 210, 220 are configured to be able to transmit and receive various information and commands to and from each other via the in-vehicle network, so that the control device 200 can adjust the braking force of the vehicle by coordinating the hydraulic pressure generating device 20 and the brake actuator 70.

[0056] The first processing circuit 210 has a function of diagnosing whether a brake fluid leak occurs within the braking device 100 during vehicle braking. For example, the first processing circuit 210 rotates the first electric motor 513 of the electric cylinder 51 in the forward direction to increase the servo pressure. When increasing the servo pressure, the servo pressure increases as the motor rotation angle θ of the first electric motor 513 increases. If no brake fluid leak occurs within the braking device 100, the servo pressure starts to increase immediately when the motor rotation angle θ begins to increase. Furthermore, the servo pressure increases at a rate corresponding to the rate at which the motor rotation angle θ increases. On the other hand, if a brake fluid leak occurs within the braking device 100, the timing at which the servo pressure starts to increase may be significantly delayed compared to the start of the increase in the motor rotation angle θ. Furthermore, even if the servo pressure starts to increase as the motor rotation angle θ increases, the rate at which the servo pressure increases may be slower than the rate corresponding to the rate at which the motor rotation angle θ increases.

[0057] Therefore, the first processing circuit 210 determines whether or not leakage of brake fluid will occur within the braking device 100 during vehicle braking, based on the relationship between the detected servo pressure value PscE and the detected rotation angle value θE when the servo pressure is increased by driving the first electric motor 513. For example, the relationship between the detected servo pressure value PscE and the detected rotation angle value θE when no brake fluid leakage occurs within the braking device 100 is set as the reference relationship. In this case, the first processing circuit 210 determines whether or not leakage of brake fluid will occur within the braking device 100 during vehicle braking, based on the reference relationship and the actual relationship, which is the relationship between the detected servo pressure value PscE and the detected rotation angle value θE when the servo pressure is increased by driving the first electric motor 513.

[0058] <Diagnostic function> 2 to 4, a series of processes executed by the first processing circuit 210 when implementing the diagnostic function will be described. The diagnostic function is a function for diagnosing whether or not a brake fluid leak occurs within the braking device 100 when the vehicle is braked.

[0059] The first processing circuit 210 executes the series of processes when predetermined execution conditions are met. The predetermined execution conditions include, for example, that the vehicle can be kept stopped even when the electric cylinder 51 is operated, and that the driver is not performing a braking operation.

[0060] When a predetermined execution condition is met, the first processing circuit 210 executes the process of step S10. In step S10, the first processing circuit 210 executes a determination process. In this embodiment, the determination process includes a first determination process and a second determination process. First, the first processing circuit 210 executes the first determination process in step S11.

[0061] The first determination process will be described with reference to FIG. 3. In the first determination process, the first processing circuit 210 opens the pressure-reducing valve corresponding to the first wheel cylinder and closes the pressure-reducing valve corresponding to the second wheel cylinder. At this time, the first processing circuit 210 keeps all pressure-reducing valves 77a to 77d closed. In this embodiment, the wheel cylinder 16 corresponding to the left front wheel 11fl and the wheel cylinder 16 corresponding to the left rear wheel 11rl correspond to the first wheel cylinder. The wheel cylinder 16 corresponding to the right front wheel 11fr and the wheel cylinder 16 corresponding to the right rear wheel 11rr correspond to the second wheel cylinder. Therefore, as shown in FIGS. 3C and 3D, the first processing circuit 210 instructs the second processing circuit 220 to close the pressure-reducing valve 74d for the right front wheel 11fr and the pressure-reducing valve 74b for the right rear wheel 11rr. Upon receiving this instruction, the second processing circuit 220 closes the pressure-reducing valves 74b and 74d. This allows the first processing circuit 210 to restrict the supply of brake fluid to the wheel cylinder 16 for the right front wheel 11fr and the wheel cylinder 16 for the right rear wheel 11rr. On the other hand, as shown in Figures 3(E) and 3(F), the first processing circuit 210 does not close the retention valve 74c for the left front wheel 11fl and the retention valve 74a for the left rear wheel 11rl, thereby allowing the supply of brake fluid to the wheel cylinder 16 for the left front wheel 11fl and the wheel cylinder 16 for the left rear wheel 11rl, which correspond to the first wheel cylinder.

[0062] 3A and 3B, the first processing circuit 210 rotates the first electric motor 513 in the forward direction to increase the detected rotation angle θE, thereby gradually increasing the detected servo pressure value PscE. The first processing circuit 210 increases the detected rotation angle θE so that the detected servo pressure value PscE becomes equal to or greater than the threshold hydraulic pressure Pscth. At this time, the first processing circuit 210 preferably drives the first electric motor 513 so that the detected rotation angle θE increases at a predetermined increasing speed.

[0063] In this embodiment, the first processing circuit 210 determines that the termination condition is met if both of the following two conditions (A1) and (A2) are met while the servo pressure detection value PscE is being increased.

[0064] (A1) The detected servo pressure value PscE is equal to or greater than the judgment hydraulic pressure Pscth. (A2) The time elapsed since the start of driving the first electric motor 513 reaches the determination time TMth.

[0065] The determination hydraulic pressure Pscth is set so that the motor rotation angle θ, i.e., the position of the piston 512, at the time when the detected servo pressure value PscE reaches the determination hydraulic pressure Pscth will be significantly different between when a brake fluid leak occurs and when no leakage occurs. In addition, the determination time TMth is set so that the detected servo pressure value PscE can be increased to the determination hydraulic pressure Pscth by driving the first electric motor 513 even if a leak occurs.

[0066] When the first processing circuit 210 determines that the termination condition is met, it reverses the rotation direction of the first electric motor 513. That is, the first processing circuit 210 rotates the first electric motor 513 in the reverse direction, thereby reducing the rotation angle detection value θE until the servo pressure detection value PscE becomes equal to or less than a predetermined pressure. The predetermined pressure is a criterion for determining whether the servo pressure has become sufficiently low, and is sufficiently lower than the determination hydraulic pressure Pscth. An example of the predetermined pressure is 0 (zero).

[0067] The first processing circuit 210 acquires the rotation angle detected value θE at the time when the servo pressure detected value PscE reaches the judgment hydraulic pressure Pscth due to an increase in the rotation angle detected value θE as a correlation value of the position of the piston 512 of the electric cylinder 51 at that time. The time when the servo pressure detected value PscE reaches the judgment hydraulic pressure Pscth refers to the time when the servo pressure detected value PscE switches from a state where it is less than the judgment hydraulic pressure Pscth to a state where it is equal to or greater than the judgment hydraulic pressure Pscth.

[0068] If the rotation angle detection value θE at the time point is within a predetermined normal range Rθ, the first processing circuit 210 determines that brake fluid leakage will not occur within the braking device 100 when the vehicle is braked. On the other hand, if the rotation angle detection value θE at the time point is not within the normal range Rθ, the first processing circuit 210 determines that brake fluid leakage may occur within the braking device 100 when the vehicle is braked. The normal range Rθ is a range that includes the motor rotation angle θ corresponding to the determination hydraulic pressure Pscth that can be estimated from the reference relationship. The normal range Rθ is set so that if brake fluid leakage occurs within the braking device 100, the rotation angle detection value θE at the time point is sufficiently larger than the upper limit of the normal range Rθ.

[0069] After the servo pressure detection value PscE becomes equal to or lower than the predetermined pressure, the first processing circuit 210 transmits an instruction to the second processing circuit 220 to open the two holding valves 74b, 74d. Upon receiving the instruction, the second processing circuit 220 opens the two holding valves 74b, 74d. After confirming that the two holding valves 74b, 74d have opened, the first processing circuit 210 ends the first determination process. The first processing circuit 210 then proceeds to the next step S13.

[0070] 2, in step S13, if the first processing circuit 210 determines through execution of the first determination process that brake fluid leakage will not occur within the braking device 100 (S13: YES), the first processing circuit 210 proceeds to step S15. On the other hand, if the first processing circuit 210 determines through execution of the first determination process that there is a possibility that brake fluid leakage will occur within the braking device 100 (S13: NO), the first processing circuit 210 proceeds to step S17.

[0071] In step S15, the first processing circuit 210 sets the first determination flag FLG1 to OFF. The first determination flag FLG1 is a flag that indicates the determination result in the first determination process. After that, the first processing circuit 210 proceeds to step S19.

[0072] In step S17, the first processing circuit 210 sets the first determination flag FLG1 to ON, and then the first processing circuit 210 proceeds to step S19. In step S19, the first processing circuit 210 executes the second determination process.

[0073] The second determination process will be described with reference to FIG. 3. In the second determination process, the first processing circuit 210 opens the pressure-reducing valve corresponding to the second wheel cylinder and closes the pressure-reducing valve corresponding to the first wheel cylinder. At this time, the first processing circuit 210 keeps all pressure-reducing valves 77a to 77d closed. In this embodiment, the wheel cylinder 16 corresponding to the right front wheel 11fr and the wheel cylinder 16 corresponding to the right rear wheel 11rr correspond to the second wheel cylinder. The wheel cylinder 16 corresponding to the left front wheel 11fl and the wheel cylinder 16 corresponding to the left rear wheel 11rl correspond to the first wheel cylinder. Therefore, as shown in FIGS. 3(E) and 3(F), the first processing circuit 210 instructs the second processing circuit 220 to close the pressure-reducing valve 74c for the left front wheel 11fl and the pressure-reducing valve 74a for the left rear wheel 11rl. Upon receiving this instruction, the second processing circuit 220 closes the pressure-reducing valves 74a and 74c. This allows the first processing circuit 210 to restrict the supply of brake fluid to the wheel cylinder 16 for the left front wheel 11fl and the wheel cylinder 16 for the left rear wheel 11rl. On the other hand, as shown in Figures 3C and 3D, the first processing circuit 210 does not close the retention valve 74d for the right front wheel 11fr and the retention valve 74b for the right rear wheel 11rr, thereby allowing the supply of brake fluid to the wheel cylinder 16 for the right front wheel 11fr and the wheel cylinder 16 for the right rear wheel 11rr, which correspond to the second wheel cylinder.

[0074] Next, as shown in FIGS. 3A and 3B, the first processing circuit 210 drives the first electric motor 513 in the same manner as in the first determination process. That is, the first processing circuit 210 rotates the first electric motor 513 in the forward direction to increase the rotation angle detection value θE, thereby gradually increasing the servo pressure detection value PscE. The first processing circuit 210 determines that the termination condition is met when both of the above two conditions (A1) and (A2) are met. If the first processing circuit 210 determines that the termination condition is met, the first processing circuit 210 reverses the rotation direction of the first electric motor 513, thereby decreasing the rotation angle detection value θE until the servo pressure detection value PscE becomes equal to or less than the predetermined pressure.

[0075] The first processing circuit 210 acquires the rotation angle detected value θE at the time when the servo pressure detected value PscE reaches the determination hydraulic pressure Pscth due to an increase in the rotation angle detected value θE as a correlation value of the position of the piston 512 of the electric cylinder 51 at that time. If the rotation angle detected value θE at that time is within a predetermined normal range Rθ, the first processing circuit 210 determines that brake fluid leakage will not occur within the braking device 100 when the vehicle is braked. On the other hand, if the rotation angle detected value θE at that time is not within the normal range Rθ, the first processing circuit 210 determines that there is a possibility of brake fluid leakage occurring within the braking device 100 when the vehicle is braked.

[0076] After the servo pressure detection value PscE becomes equal to or lower than the predetermined pressure, the first processing circuit 210 transmits an instruction to the second processing circuit 220 to open the two holding valves 74a, 74c. Upon receiving the instruction, the second processing circuit 220 opens the two holding valves 74a, 74c. After confirming that the two holding valves 74a, 74c have opened, the first processing circuit 210 terminates the second determination process. Thereafter, the first processing circuit 210 proceeds to the next step S21.

[0077] 2, in step S21, if the first processing circuit 210 determines through execution of the second determination process that brake fluid leakage will not occur within the braking device 100 (S21: YES), the process proceeds to step S23. On the other hand, if the first processing circuit 210 determines through execution of the second determination process that there is a possibility that brake fluid leakage will occur within the braking device 100 (S21: NO), the process proceeds to step S25.

[0078] In step S23, the first processing circuit 210 sets the second determination flag FLG2 to OFF. The second determination flag FLG2 is a flag that indicates the determination result in the second determination process. Then, the first processing circuit 210 ends the determination process of step S10 and proceeds to the next step S31.

[0079] In step S25, the first processing circuit 210 sets the second determination flag FLG2 to ON. Then, the first processing circuit 210 ends the determination process of step S10 and proceeds to the next step S31.

[0080] In step S31, the first processing circuit 210 determines whether at least one of the first determination flag FLG1 and the second determination flag FLG2 is set to ON. If at least one of the two flags FLG1, FLG2 is set to ON (S31: YES), the first processing circuit 210 proceeds to step S33. On the other hand, if neither of the two flags FLG1, FLG2 is set to ON (S31: NO), the first processing circuit 210 proceeds to step S39.

[0081] In step S33, the first processing circuit 210 executes the leakage diagnosis process. The leak diagnosis process will be described with reference to FIG. 4. In the leak diagnosis process, the first processing circuit 210, for example, opens all of the holding valves 74a to 74d and closes all of the pressure-reducing valves 77a to 77d, and drives the first electric motor 513 to increase the rotation angle detected value θE until the servo pressure detected value PscE reaches the reference hydraulic pressure PscA. The reference hydraulic pressure PscA may be the same as the determination hydraulic pressure Pscth, or may be a different hydraulic pressure from the determination hydraulic pressure Pscth. As shown in FIGS. 4A and 4B, the first processing circuit 210 feedback-controls the first electric motor 513 so that the servo pressure detected value PscE is maintained at the reference hydraulic pressure PscA for a predetermined diagnosis time TMth1.

[0082] The solid line in Fig. 4(B) shows the transition of the detected rotation angle value θE when no brake fluid leakage occurs in the braking device 100. The two-dot chain line in Fig. 4(B) shows the transition of the detected rotation angle value θE when brake fluid leakage occurs in the braking device 100. As shown in Fig. 4(B), when brake fluid leakage occurs, the detected rotation angle value θE increases in order to maintain the detected servo pressure value PscE.

[0083] When the diagnosis time TMth1 has elapsed, the first processing circuit 210 drives the first electric motor 513 to reduce the rotation angle detected value θE until the servo pressure detected value PscE becomes equal to or less than the predetermined pressure. When the first processing circuit 210 stops driving the first electric motor 513, it ends the leak diagnosis process. Then, the first processing circuit 210 proceeds to step S35.

[0084] Returning to FIG. 2, in step S35, the first processing circuit 210 determines whether or not a brake fluid leak will occur within the braking device 100, based on the transition of the rotation angle detection value θE during execution of the leakage diagnosis process. If the first processing circuit 210 determines that a leak will occur (S35: YES), the process proceeds to step S37. On the other hand, if the first processing circuit 210 determines that a leak will not occur (S35: NO), the process proceeds to step S39.

[0085] In step S37, the first processing circuit 210 determines that a brake fluid leak has occurred in the braking system 100. Then, the first processing circuit 210 ends the leakage diagnosis control. In step S39, the first processing circuit 210 diagnoses that no brake fluid leakage has occurred within the braking system 100. Then, the first processing circuit 210 ends the leakage diagnosis control.

[0086] <Actions and Effects of This Embodiment> When a predetermined execution condition is met, the control device 200 starts the determination process. Then, the control device 200 rotates the first electric motor 513 in the forward direction. In the electric cylinder 51, the motor rotation angle θ increases, and the piston 512 moves in the forward direction Za. This causes brake fluid to be discharged from the electric cylinder 51 to the fifth flow path 55. As a result, brake fluid is supplied to the wheel cylinder 16, and the wheel pressure Pw in the wheel cylinder 16 increases.

[0087] Here, pressure-reducing valves 77a to 77d are provided in the hydraulic circuits 711 and 712. The pressure-reducing valves 77a to 77d are normally closed. However, if the valve discs of the pressure-reducing valves 77a to 77d are not properly seated on the valve seats, the brake fluid flowing through the paths 72a to 72d will flow into the pressure-reducing reservoirs 751 and 752 via the pressure-reducing valves 77a to 77d. In this case, the brake fluid continues to flow into the pressure-reducing reservoirs 751 and 752 via the pressure-reducing valves 77a to 77d until the pressure-reducing reservoirs 751 and 752 are full. Therefore, during this period, almost no brake fluid is supplied to the wheel cylinders 16, and the wheel pressure Pw does not increase. In this case, when the pressure-reducing reservoirs 751 and 752 are full, further flow of brake fluid into the pressure-reducing reservoirs 751 and 752 is prevented, and brake fluid begins to be supplied to the wheel cylinders 16. That is, there is a relatively large time lag between when the electric cylinder 51 starts discharging the brake fluid and when the wheel pressure Pw starts to increase.

[0088] Valve mechanisms 811, 812 are integrated with the reduced-pressure reservoirs 751, 752. The valve mechanisms 811, 812 regulate the flow of brake fluid through the return flow paths 801, 802 toward the reduced-pressure reservoirs 751, 752. However, if the valve mechanisms 811, 812 do not operate normally, the valve mechanisms 811, 812 may be unable to regulate the flow of brake fluid through the return flow paths 801, 802 toward the reduced-pressure reservoirs 751, 752. In this case, the brake fluid supplied from the hydraulic pressure generator 20 to the hydraulic pressure circuits 711, 712 by the electric cylinder 51 flows into the reduced-pressure reservoirs 751, 752 via the return flow paths 801, 802. While the brake fluid is flowing into the reduced-pressure reservoirs 751, 752 in this way, almost no brake fluid is supplied to the wheel cylinders 16, and therefore the wheel pressure Pw does not increase. In this case, when the reduced-pressure reservoirs 751, 752 become full, brake fluid cannot further flow into the reduced-pressure reservoirs 751, 752, and brake fluid begins to be supplied to the wheel cylinders 16. In other words, there is a relatively large time lag from when the electric cylinder 51 starts discharging brake fluid to when the wheel pressure Pw starts to increase.

[0089] Therefore, the control device 200 rotates the first electric motor 513 in the forward direction so that the servo pressure detection value PscE increases until the servo pressure detection value PscE becomes equal to or greater than the threshold hydraulic pressure Pscth. Then, the control device 200 determines whether or not a brake fluid leak will occur within the braking device 100 when the vehicle is braked, based on the position of the piston 512 at that time or a correlation value thereof.

[0090] At this time, the control device 200 does not maintain the motor rotation angle θ of the first electric motor 513. Therefore, the control device 200 can prevent a state in which the amount of current supplied to some of the coils of the multiple phases of the first electric motor 513 is greater than the amount of current supplied to the other coils from continuing. This allows the control device 200 to determine whether a leak will occur while preventing the amount of heat generated by some of the coils of the multiple phases that make up the first electric motor 513 from becoming excessive.

[0091] Furthermore, since the control device 200 can prevent current from continuing to flow through some of the coils, it can also prevent excessive heat generation from the electronic components in the driver circuit for the first electric motor 513 that control the amount of current flowing through those coils.

[0092] In this embodiment, the following effects can be further obtained. (1) If the rotation angle detected value θE at the time when the servo pressure detected value PscE becomes the determination hydraulic pressure Pscth is within the normal range Rθ, the control device 200 determines that no brake fluid leakage will occur within the braking device 100. On the other hand, if the rotation angle detected value θE at that time is not within the normal range Rθ, the control device 200 determines that there is a possibility of leakage. This allows the control device 200 to determine whether there is a possibility of leakage occurring.

[0093] (2) The control device 200 executes a first determination process and a second determination process as the determination process. In the first determination process, the control device 200 discharges brake fluid from the electric cylinder 51 while closing only some of the retention valves 74a to 74d. Then, the control device 200 determines whether or not a brake fluid leak will occur within the braking device 100 based on the position of the piston 512 at that time or a correlation value thereof.

[0094] Furthermore, in the second determination process, the control device 200 discharges brake fluid from the electric cylinder 51 while closing only the remaining retention valves among the plurality of retention valves 74a to 74d. Then, the control device 200 determines whether or not leakage of brake fluid will occur within the braking device 100 based on the position of the piston 512 at that time or a correlation value thereof.

[0095] As a result, the control device 200 can reduce the number of wheel cylinders 16 to which brake fluid is supplied, and therefore the amount of brake fluid discharged from the electric cylinder 51 during the determination process, compared to when brake fluid is discharged from the electric cylinder 51 without closing any of the plurality of retention valves 74a to 74d. In other words, the control device 200 can determine whether or not a brake fluid leak has occurred within the braking device 100 while reducing the amount of brake fluid discharged from the electric cylinder 51.

[0096] (3) Generally, the volume of the wheel cylinders 16 for the front wheels 11fl, 11fr is larger than the volume of the wheel cylinders 16 for the rear wheels 11rl, 11rr. Therefore, consider a comparative example in which the brake fluid is supplied to the wheel cylinders 16 for the two front wheels by closing the retention valves 74a, 74b for the two rear wheels in the first determination process. In this comparative example, the brake fluid is supplied to the wheel cylinders 16 for the two rear wheels by closing the retention valves 74c, 74d for the two front wheels in the second determination process.

[0097] FIG. 5 shows the relationship between the stroke of the piston 512, i.e., the motor rotational angle θ and the servo pressure Psc, when the determination process is performed in the comparative example. Specifically, the dashed line L11 in FIG. 5 shows the relationship between the motor rotational angle θ and the servo pressure Psc when no brake fluid leakage occurs during the first determination process, which closes the two rear wheel retention valves 74a and 74b. The two-dot chain line L12 in FIG. 5 shows the relationship between the motor rotational angle θ and the servo pressure Psc when a brake fluid leakage occurs during the first determination process. The solid line L21 in FIG. 5 shows the relationship between the motor rotational angle θ and the servo pressure Psc when no brake fluid leakage occurs during the second determination process, which closes the two front wheel retention valves 74c and 74d. The dashed line L22 in FIG. 5 shows the relationship between the motor rotational angle θ and the servo pressure Psc when a brake fluid leakage occurs during the second determination process.

[0098] Compare the dashed line L11 and the dashed-dotted line L22 in FIG. 5. When the stroke of the piston 512 is relatively small, the servo pressure Psc when no brake fluid leakage occurs during the first determination process is higher than the servo pressure Psc when brake fluid leakage occurs during the second determination process. However, when the stroke of the piston 512 exceeds a certain value, the servo pressure Psc when no brake fluid leakage occurs during the first determination process becomes lower than the servo pressure Psc when brake fluid leakage occurs during the second determination process. This is because the volume of the wheel cylinder 16 for the rear wheels is smaller than the volume of the wheel cylinder 16 for the front wheels. As a result, when brake fluid begins to flow into the wheel cylinder 16 for the rear wheels, the wheel pressure Pw in the wheel cylinder 16 for the rear wheels tends to increase at a faster rate.

[0099] Therefore, if the same value is set as the determination hydraulic pressure Pscth in the first determination process and the second determination process, there is a risk that the determination accuracy of either the first determination process or the second determination process will be reduced.

[0100] In this regard, in the braking system 100, in the first determination process, the retention valve 74b for the right rear wheel 11rr and the retention valve 74d for the right front wheel 11fr are closed before the electric cylinder 51 is actuated. In the second determination process, the retention valve 74a for the left rear wheel 11rl and the retention valve 74c for the left front wheel 11fl are closed before the electric cylinder 51 is actuated. In this case, a first total, which is the sum of the volumes of the wheel cylinders 16 for the left rear wheel 11rl and the left front wheel 11fl corresponding to the first wheel cylinder, is smaller than the sum of the volumes of the wheel cylinders 16 for the two front wheels 11fl and 11fr. A second total, which is the sum of the volumes of the wheel cylinders 16 for the right rear wheel 11rr and the right front wheel 11fr corresponding to the second wheel cylinder, is smaller than the sum of the volumes of the wheel cylinders 16 for the two front wheels 11fl and 11fr. Furthermore, the first total and the second total are equal to each other. Therefore, in both the first determination process and the second determination process, the magnitude relationship between the servo pressure Psc when the stroke of the piston 512 is increased when no brake fluid leakage occurs and the servo pressure Psc when the stroke of the piston 512 is increased when brake fluid leakage occurs is unlikely to change. Therefore, even if the same value is set as the determination fluid pressure Pscth in both the first determination process and the second determination process, a decrease in determination accuracy can be suppressed in both the first determination process and the second determination process.

[0101] (4) The control device 200 executes the leak diagnosis process only when it determines, through the execution of the determination process, that there is a possibility of brake fluid leakage within the braking device 100. This allows the control device 200 to prevent an increase in the number of times that the leak diagnosis process is executed.

[0102] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0103] 2 does not necessarily include the leakage diagnosis process of step S33. In this case, the first processing circuit 210 may diagnose that a brake fluid leak has occurred in the braking system 100 when the vehicle is braked if at least one of the first determination flag FLG1 and the second determination flag FLG2 is set to ON.

[0104] The first wheel cylinder may include a wheel cylinder 16 corresponding to the right front wheel 11fr and a wheel cylinder 16 corresponding to the left rear wheel 11rl. In this case, the second wheel cylinder includes a wheel cylinder 16 corresponding to the left front wheel 11fl and a wheel cylinder 16 corresponding to the right rear wheel 11rr.

[0105] As the first determination process, the first processing circuit 210 may determine whether or not a brake fluid leak will occur in the braking device 100 by operating the electric cylinder 51 while the retention valves 74c, 74d for the two front wheels 11fl, 11fr are open and the retention valves 74a, 74b for the two rear wheels 11rl, 11rr are closed. Furthermore, as the second determination process, the first processing circuit 210 may determine whether or not a brake fluid leak will occur in the braking device 100 by operating the electric cylinder 51 while the retention valves 74a, 74b for the two rear wheels 11rl, 11rr are open and the retention valves 74c, 74d for the two front wheels 11fl, 11fr are closed. In this case, the determination fluid pressure Pscth used in the first determination process may be different from the determination fluid pressure Pscth used in the second determination process.

[0106] The first processing circuit 210 may execute the first determination process after executing the second determination process. The first processing circuit 210 may not execute the second determination process if it executes the first determination process. Conversely, the first processing circuit 210 may not execute the first determination process if it executes the second determination process.

[0107] The first processing circuit 210 may be configured to execute a first determination process, a second determination process, a third determination process, and a fourth determination process as the determination process. In this case, the first determination process is a process of discharging brake fluid from the electric cylinder 51 while closing all of the plurality of retention valves 74a to 74d except for retention valve 74a. The second determination process is a process of discharging brake fluid from the electric cylinder 51 while closing all of the plurality of retention valves 74a to 74d except for retention valve 74b. The third determination process is a process of discharging brake fluid from the electric cylinder 51 while closing all of the plurality of retention valves 74a to 74d except for retention valve 74c. The fourth determination process is a process of discharging brake fluid from the electric cylinder 51 while closing all of the plurality of retention valves 74a to 74d except for retention valve 74d.

[0108] In the determination process, the first processing circuit 210 may discharge brake fluid from the electric cylinder 51 without closing any of the plurality of retention valves 74a to 74d, and then determine whether or not a brake fluid leak will occur within the braking device 100.

[0109] The first processing circuit 210 may derive the position of the piston 512 based on the rotation angle detection value θE. In this case, the first processing circuit 210 may determine whether or not a brake fluid leak will occur in the braking device 100 based on the derived value of the position of the piston 512 in the determination process.

[0110] The first processing circuit 210 may determine whether or not a brake fluid leak will occur within the braking device 100 using a method different from the method described in the above embodiment. If a brake fluid leak occurs in the braking device 100, a time lag occurs between the start of an increase in the detected rotational angle value θE and the start of an increase in the detected servo pressure value PscE. Therefore, when increasing the detected rotational angle value θE, the first processing circuit 210 may determine whether a brake fluid leak will occur based on the length of time from the start of an increase in the detected rotational angle value θE to the start of an increase in the detected servo pressure value PscE.

[0111] In addition, the first processing circuit 210 may determine whether a brake fluid leak will occur based on the length of time from when the rotation angle detection value θE starts to increase to when the servo pressure detection value PscE reaches the judgment fluid pressure Pscth.

[0112] In addition, the first processing circuit 210 may determine whether a brake fluid leak will occur by using the position of the piston 512 or a correlation value thereof at the time of switching from a state in which the rotation angle detection value θE is increased to a state in which the rotation angle detection value θE is decreased.

[0113] The first processing circuit 210 also moves the piston 512 in the forward direction Za until the piston 512 reaches a position where a predetermined target servo pressure is achieved under normal conditions. The first processing circuit 210 may then determine whether a brake fluid leak will occur based on whether the detected servo pressure value PscE is equal to or less than a predetermined threshold value that is smaller than the target servo pressure when the piston 512 reaches that position.

[0114] In the leak diagnosis process described in the above embodiment, the presence or absence of brake fluid leakage is detected based on an increase in the rotational angle detected value θE while pressure is maintained, but leak detection may be performed in a different manner. For example, the first processing circuit 210 may close all of the retention valves 74a-74d and pressure-reducing valves 77a-77d, and then perform feedback control of the first electric motor 513 so that the servo pressure detected value PscE is maintained at the reference hydraulic pressure PscA for a predetermined diagnosis time TMth1. Then, when the pressure-reducing valve of the wheel for which the first determination process was performed is opened, the first processing circuit 210 may determine the presence or absence of leakage by determining whether the servo pressure detected value PscE has decreased by a predetermined value or more, or whether the rotational angle detected value θE has increased by a predetermined value or more. If there is a leak in the valve mechanisms 811, 812 of the pressure-reducing reservoirs 751, 752, brake fluid flows into the pressure-reducing reservoirs 751, 752 through the leaking valve mechanism while the pressure is maintained until the pressure-reducing reservoirs 751, 752 are filled, and by opening the pressure-reducing valve, the brake fluid stored in the pressure-reducing reservoirs 751, 752 flows into the wheel cylinders 16, and the flow of brake fluid from the valve mechanisms 811, 812 into the pressure-reducing reservoirs 751, 752 resumes. Therefore, when a drop in servo pressure or a change in motor rotation angle occurs in synchronization with the opening of the pressure-reducing valve as described above, the first processing circuit 210 can determine that there is a brake fluid leak in the valve mechanisms 811, 812.

[0115] Alternatively, as another leak diagnosis process, the first processing circuit 210 may open all the holding valves 74a-74d and close the pressure-reducing valves 77a-77d, then feedback-control the first electric motor 513 so that the detected servo pressure value PscE is maintained at the reference hydraulic pressure PscA for a predetermined diagnosis time TMth1. Then, when the pressure-reducing valve for the wheel to be diagnosed is opened, the first processing circuit 210 may determine whether the detected servo pressure value PscE decreases by a predetermined amount or whether the detected rotation angle value θE increases by a predetermined amount to determine whether a leak exists. If a pressure-reducing valve 77a-77d leaks, brake fluid flows into the pressure-reducing reservoirs 751, 752 through the leaking pressure-reducing valve while the pressure is maintained until the pressure-reducing reservoirs 751, 752 are filled. Even if the pressure-reducing valve is subsequently opened, brake fluid does not flow into the pressure-reducing reservoirs 751, 752 because brake fluid is already stored in the pressure-reducing reservoirs 751, 752, and the servo pressure does not change. Therefore, if no change in servo pressure or motor rotation angle occurs in synchronization with the opening of the pressure reducing valve as described above, the first processing circuit 210 can determine that there is a leak in either the pressure reducing valve that has opened or the pressure reducing valve connected to the pressure reducing reservoir.

[0116] The first processing circuit 210 may be configured to execute the leakage diagnosis process after turning on and off the pressure reducing valves 77a to 77d a predetermined number of times. During the leak diagnosis process, the first processing circuit 210 may alternate between opening the wheel cylinder holding valve and closing the wheel cylinder holding valve, and each time increase the rotation angle detection value θE until the servo pressure detection value PscE reaches the reference hydraulic pressure PscA, thereby determining whether or not there is a leak in multiple iterations.

[0117] The hydraulic pressure generating device may have a different configuration from the hydraulic pressure generating device 20 shown in Fig. 1 as long as it includes the electric cylinder 51. For example, the hydraulic pressure generating device may have a configuration in which the fifth flow path 55 is connected to the second hydraulic pressure circuit 712.

[0118] The control device 200 is not limited to a device that includes a CPU and ROM and executes software processing. In other words, the control device 200 may have any one of the following configurations (a), (b), and (c):

[0119] (a) The control device 200 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 that 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.

[0120] (b) The control device 200 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."

[0121] (c) The control device 200 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 among the various processes.

[0122] <Other technical ideas> The technical ideas that can be understood from the above-described embodiment and modified examples will be described. [Appendix 1] In the determination process, it is preferable that the control device determines that a brake fluid leak has occurred in the braking device if the position of the piston or its correlation value at the time the hydraulic pressure detection value reaches the determination hydraulic pressure is not within the normal range.

[0123] [Appendix 2] In the determination process, it is preferable that the control device increases the motor rotation angle so that the hydraulic pressure detection value gradually increases until the hydraulic pressure detection value becomes equal to or greater than the determined hydraulic pressure, and then decreases the motor rotation angle so that the hydraulic pressure detection value gradually decreases.

[0124] [Appendix 3] It is preferable that the control device increases the motor rotation angle so that the hydraulic pressure detection value, which is the hydraulic pressure detected by the hydraulic pressure sensor, gradually increases, and executes a determination process to determine whether or not a brake fluid leak will occur within the braking device based on the relationship between the motor rotation angle and the hydraulic pressure detection value at that time.

[0125] The expression "at least one" used herein means "one or more" of the desired options. As an example, the expression "at least one" used herein 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 herein means "only one option" or "any combination of two or more options" if the number of options is three or more. [Explanation of symbols]

[0126] 11fl,11fr…Front wheel 11rl,11rr…Rear wheel 15...Friction brake 16...Wheel cylinder 51...Electric cylinder 511...Cylinder 512...Piston 513...First electric motor 55...fifth flow path (an example of a supply flow path) 58...Servo pressure sensor (hydraulic pressure sensor) 74a to 74d... Holding valve (an example of a solenoid valve) 751,752...Decompression reservoir 77a~77d...Reducing valve 100...braking device 200...Control device 210, 220...Processing circuit

Claims

1. A braking device applied to a vehicle in which a braking force corresponding to a wheel pressure, which is a hydraulic pressure in a wheel cylinder, is generated at a wheel, an electric cylinder configured such that brake fluid is discharged from inside the cylinder when a piston moves forward in the cylinder in response to an increase in a motor rotation angle, which is a rotation angle of the electric motor; a supply flow path through which brake fluid flows in a direction to increase the wheel pressure when the brake fluid is discharged from the electric cylinder; a hydraulic pressure sensor for detecting the hydraulic pressure in the supply flow path; a control device for controlling the electric motor; The wheel pressure can be increased by discharging brake fluid from the electric cylinder, The control device increases the motor rotation angle so that the hydraulic pressure detection value, which is the hydraulic pressure detected by the hydraulic pressure sensor, gradually increases until the hydraulic pressure detection value becomes equal to or greater than a reference hydraulic pressure, and performs a determination process to determine whether or not a brake fluid leak will occur within the braking device during braking based on the position of the piston at that time or a correlation value thereof. Braking device.

2. In the determination process, the control device determines that no brake fluid leakage will occur in the braking device during braking if the position of the piston or its correlation value at the time the hydraulic pressure detection value reaches the determination hydraulic pressure is within a predetermined normal range.

2. The braking device of claim 1.

3. The vehicle includes a first wheel cylinder and a second wheel cylinder as the wheel cylinders, the braking device includes a plurality of electromagnetic valves provided for the plurality of wheel cylinders, the electromagnetic valves being closed when restricting the supply of brake fluid to the corresponding wheel cylinders; The control device performs the determination process by: a first determination process that is executed in a state in which the supply of brake fluid to the second wheel cylinder is restricted by closing the electromagnetic valve corresponding to the second wheel cylinder among the plurality of electromagnetic valves, while allowing the supply of brake fluid to the first wheel cylinder; a second determination process that is executed in a state in which the supply of brake fluid to the first wheel cylinder is restricted by closing the electromagnetic valve corresponding to the first wheel cylinder among the plurality of electromagnetic valves, while allowing the supply of brake fluid to the second wheel cylinder. The braking device according to claim 1 or 2.

4. The vehicle has two front wheels and two rear wheels as the wheels, the first wheel cylinder includes the wheel cylinder corresponding to a first front wheel of the two front wheels and the wheel cylinder corresponding to a first rear wheel of the two rear wheels, The second wheel cylinder includes the wheel cylinder corresponding to a second front wheel of the two front wheels, and the wheel cylinder corresponding to a second rear wheel of the two rear wheels.

4. The braking device according to claim 3.

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