Braking device

Abstract

A braking device 100 comprises: a pressurization unit 50 using a first electric motor 513 as a power source; differential pressure control valves 731, 732; and a control device 200. The control device 200 executes: heat generation suppression processing for operating the pressurization unit 50 so that a servo pressure becomes lower than a required servo pressure after restricting a reduction in wheel pressure by increasing an instructed differential pressure; and degeneration processing, including operating the pressurization unit 50 so that the servo pressure reaches the required servo pressure, if a required braking force has been changed in a situation where the servo pressure became lower than the required servo pressure due to the execution of the heat generation suppression processing.

Description

braking device

[0001] The present invention relates to a braking device that generates braking force at a wheel by controlling hydraulic pressure in a wheel cylinder.

[0002] Japanese Patent Application Laid-Open No. 2006-129999 discloses an example of a braking system equipped with a pressurizing unit powered by an electric motor. The pressurizing unit is configured to pressurize brake fluid and supply it to wheel cylinders. The hydraulic pressure of the brake fluid supplied from the pressurizing unit is referred to as servo pressure. A control device for the braking system adjusts wheel pressure, which is the hydraulic pressure in the wheel cylinders, by operating the pressurizing unit to generate servo pressure corresponding to the required braking force, which is the required value of braking force.

[0003] Japanese Patent Application Laid-Open No. 2023-103614

[0004] In the pressure applying unit described above, the amount of current supplied to the electric motor is increased in order to increase the servo pressure, and therefore, if the servo pressure remains high for a long period of time, the electric motor may overheat due to the current supplied to the electric motor.

[0005] The object of the present application is to appropriately adjust wheel pressure while preventing the electric motor from overheating.

[0006] A braking device for solving the above problems is applied to a vehicle in which a braking force is generated at a wheel according to wheel pressure, which is hydraulic pressure in a wheel cylinder. The braking device is equipped with an electric motor as a power source, a pressurizing unit that adjusts the pressure of brake fluid and supplies it, a supply flow path through which brake fluid flows toward the wheel cylinder when the pressurizing unit supplies brake fluid, a differential pressure adjustment valve that is a linear solenoid valve installed in the supply flow path and adjusts the differential pressure between a portion of the supply flow path opposite the wheel cylinder and a portion of the supply flow path on the wheel cylinder side, and a control device that controls the pressurizing unit and the differential pressure adjustment valve to control the wheel pressure. The control device executes a normal pressure adjustment process that adjusts the wheel pressure by operating the pressurizing unit so that the servo pressure, which is the hydraulic pressure of the brake fluid supplied by the pressurizing unit, becomes a required servo pressure, which is a servo pressure corresponding to the required value of the braking force; a heat generation suppression process that, after executing the normal pressure adjustment process, regulates a decrease in the wheel pressure by increasing an indicated differential pressure, which is an indicated value of the differential pressure for the differential pressure control valve, and then operates the pressurizing unit so that the servo pressure becomes lower than the required servo pressure; and a degeneration process that includes operating the pressurizing unit so that the servo pressure becomes the required servo pressure when the required value of the braking force is changed under a situation where the servo pressure becomes lower than the required servo pressure due to the execution of the heat generation suppression process.

[0007] The braking device has the advantage of being able to appropriately adjust the wheel pressure while preventing the electric motor from overheating.

[0008] Fig. 1 is a schematic diagram showing a braking system of an embodiment. Fig. 2 is a flowchart showing the first half of a series of processes executed by a control device provided in the braking system of Fig. 1. Fig. 3 is a flowchart showing the second half of a series of processes executed by a control device provided in the braking system of Fig. 1. Fig. 4 is a timing chart when the required frictional braking force is reduced during execution of heat generation suppression processing. Fig. 5 is a timing chart when the required frictional braking force is increased during execution of heat generation suppression processing.

[0009] An embodiment of a braking device mounted on a vehicle will be described below with reference to Figures 1 to 5. Figure 1 shows a vehicle equipped with a braking device 100. The vehicle has two front wheels 11f and two rear wheels 11r as wheels. The vehicle has the same number of friction brakes 15 as the number of wheels.

[0010] <Configuration of Friction Brake> The multiple friction brakes 15 each generate a braking force at the corresponding wheel. The braking force generated at the wheel by the operation of the friction brake 15 is called the "friction braking force." The friction brake 15 has a wheel cylinder 16, a rotating body 17, and a friction portion 18. Because the rotating body 17 rotates together with the wheel, the friction portion 18 presses against the rotating body 17, generating a friction braking force at the wheel. 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 brake 15 can generate a greater friction braking force at the wheel as the wheel pressure Pw increases.

[0011] <Configuration of Brake Device> The brake device 100 adjusts the friction braking force generated by the vehicle by controlling the wheel pressure Pw of the multiple wheel cylinders 16. The brake 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.

[0012] <Hydraulic Pressure Generator> The hydraulic pressure generator 20 includes a reservoir tank 21, a brake operating member 22, a master device 30, and an electric pressure unit 50. The reservoir tank 21 stores brake fluid and is open to the atmosphere.

[0013] The brake operating member 22 is a member that is operated by the driver of the vehicle when adjusting the deceleration of 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 pressures Pw in the multiple wheel cylinders 16 according to the amount of operation of the brake operating member 22.

[0014] <Master Device> The master device 30 includes a master cylinder 31, a stroke simulator 32, a plurality of flow paths 331, 332, and 333 connected to the master cylinder 31, and a plurality of control valves 341 and 342 that control the flow of brake fluid. The master device 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.

[0015] The stroke simulator 32 is capable of generating a reaction force corresponding 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 each 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.

[0016] 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.

[0017] 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.

[0018] 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. Within the main cylinder 41, the master chamber Rm, the first fluid chamber R1, and the servo chamber Rs are not connected to one another.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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. From this point on, 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.

[0026] 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 the 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.

[0027] 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.

[0028] 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."

[0029] <Pressurizing Unit> 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.

[0030] 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.

[0031] 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.

[0032] The first electric motor 513 is a servo motor having a multi-phase coil and a rotor that can rotate in both forward and reverse directions. When the rotor rotates in the forward direction of the two rotation directions, the motor rotation angle θ increases. When the rotor rotates in the reverse direction, which is the opposite direction of the forward rotation of the two rotation directions, the motor rotation angle θ decreases.

[0033] 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.

[0034] An input port 515 and an output port 516 are formed in the peripheral wall of the cylinder 511 as ports connecting the hydraulic 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 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 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 chamber Re increases when the piston 512 moves forward in the forward direction Za.

[0035] 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 drive 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 drive 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.

[0036] In the hydraulic pressure generating device 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 cylinder 16 for the rear wheel 11r via the sixth flow path 56. The remaining brake fluid flows into the servo chamber Rs of the master device 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 cylinder 16 for the front wheel 11f.

[0037] On the other hand, when the electric cylinder 51 is drawing brake fluid through the output port 516, brake fluid flows out from each of the wheel cylinder 16 for the rear wheel 11r and the wheel cylinder 16 for the front wheel 11f. As a result, brake fluid flows through the sixth flow path 56 toward the fifth flow path 55. Also, brake fluid flows through the first flow path 331 toward the master chamber Rm. As a result, the hydraulic pressure in the master chamber Rm increases, causing the master piston 43 to move in the backward direction Zb. As a result, brake fluid in the servo chamber Rs flows out into the fifth flow path 55. As a result, brake fluid flows through the fifth flow path 55 toward the electric cylinder 51.

[0038] The pressurizing unit 50 includes a servo pressure sensor 58 as a hydraulic pressure sensor that detects the servo pressure, which is the pressure of the brake fluid discharged from the electric cylinder 51 to the fifth flow path 55. The servo pressure sensor 58 is connected to the fifth flow path 55, for example. Hereinafter, the hydraulic pressure based on the detection signal of the servo pressure sensor 58 will be referred to as the "servo pressure detection value Psv."

[0039] 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. <Brake 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 11r. 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 11f.

[0040] The first hydraulic pressure circuit 711 has a supply flow path 721 connected to the sixth flow path 56. The second hydraulic pressure circuit 712 has a supply flow path 722 connected to the first flow path 331. The supply flow path 721 is a brake fluid path connecting the two wheel cylinders 16 for the rear wheels 11r to the sixth flow path 56. The supply flow path 722 is a brake fluid path connecting the two wheel cylinders 16 for the front wheels 11f to the first flow path 331. A differential pressure adjustment valve 731 is provided in the supply flow path 721, and a differential pressure adjustment valve 732 is provided in the supply flow path 722. The differential pressure adjustment valves 731 and 732 are normally-open, linear solenoid valves. The differential pressure adjustment valve 731 can adjust the differential pressure between the portion of the supply flow path 721 on the sixth flow path 56 side and the portion on the wheel cylinder 16 side. The differential pressure adjustment valve 732 can adjust the differential pressure between the portion of the supply flow path 722 on the first flow path 331 side and the portion on the wheel cylinder 16 side. For example, the differential pressure adjustment valves 731, 732 can generate a larger differential pressure as the current flowing through their solenoids increases.

[0041] The first hydraulic pressure circuit 711 has a bypass flow path 811, which is a flow path for brake fluid that bypasses the differential pressure adjustment valve 731, and a check valve 821 installed in the bypass flow path 811. The second hydraulic pressure circuit 712 has a bypass flow path 812, which is a flow path for brake fluid that bypasses the differential pressure adjustment valve 732, and a check valve 822 installed in the bypass flow path 812.

[0042] A first end of the bypass flow path 811 is connected to a portion of the supply flow path 721 that is closer to the wheel cylinder 16 than the differential pressure adjustment valve 731. A second end of the bypass flow path 811 is connected to a portion of the supply flow path 721 that is on the opposite side of the wheel cylinder 16 from the differential pressure adjustment valve 731. Similarly, a first end of the bypass flow path 812 is connected to a portion of the supply flow path 722 that is closer to the wheel cylinder 16 than the differential pressure adjustment valve 732. A second end of the bypass flow path 812 is connected to a portion of the supply flow path 722 that is on the opposite side of the wheel cylinder 16 from the differential pressure adjustment valve 732.

[0043] The check valve 821 restricts the flow of brake fluid from the wheel cylinder 16 side toward the sixth flow path 56. On the other hand, the check valve 821 allows the flow of brake fluid from the sixth flow path 56 side toward the wheel cylinder 16. The check valve 822 restricts the flow of brake fluid from the wheel cylinder 16 side toward the first flow path 331. On the other hand, the check valve 822 allows the flow of brake fluid from the first flow path 331 side toward the wheel cylinder 16.

[0044] The portion of the supply flow path 721 closer to the wheel cylinder 16 than the differential pressure adjustment valve 731 branches into two paths 72a and 72b. Path 72a is connected to one of the two wheel cylinders 16 for the rear wheel 11r, while path 72b is connected to the other of the two wheel cylinders 16 for the rear wheel 11r. The portion of the supply flow path 722 closer to the wheel cylinder 16 than the differential pressure adjustment valve 732 branches into two paths 72c and 72d. Path 72c is connected to one of the two wheel cylinders 16 for the front wheel 11f, while path 72d is connected to the other of the two wheel cylinders 16 for the front wheel 11f. A holding valve 74, which is a normally open solenoid valve, is provided in each of the multiple paths 72a to 72d.

[0045] The first hydraulic circuit 711 has a reduced-pressure reservoir 751 that stores brake fluid and a reduced-pressure fluid path 761 that is connected to the reduced-pressure reservoir 751. The second hydraulic circuit 712 has a reduced-pressure reservoir 752 that stores brake fluid and a reduced-pressure fluid path 762 that is connected to the reduced-pressure reservoir 752. The reduced-pressure fluid path 761 is a brake fluid path that connects the reduced-pressure reservoir 751 to the portions of the paths 72a and 72b that are closer to the wheel cylinder 16 than the holding valve 74. The reduced-pressure fluid path 762 is a brake fluid path that connects the reduced-pressure reservoir 752 to the portions of the paths 72c and 72d that are closer to the wheel cylinder 16 than the holding valve 74. A pressure reducing valve 77, which is a normally closed solenoid valve, is provided in each of the portion of the pressure reducing fluid passage 761 connected to passage 72a, the portion of the pressure reducing fluid passage 761 connected to passage 72b, the portion of the pressure reducing fluid passage 762 connected to passage 72c, and the portion of the pressure reducing fluid passage 762 connected to passage 72d. When the pressure reducing valve 77 opens, 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.

[0046] 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 the second electric motor 78. The pump 791 pumps up the brake fluid in the reduced pressure reservoir 751 and discharges the brake fluid to a portion of the supply flow path 721 between the differential pressure adjustment valve 731 and the holding valve 74. The pump 792 pumps up the brake fluid in the reduced pressure reservoir 752 and discharges the brake fluid to a portion of the supply flow path 722 between the differential pressure adjustment valve 732 and the holding valve 74.

[0047] The first hydraulic pressure circuit 711 has a return flow path 801. The second hydraulic pressure circuit 712 has a return flow path 802. The return flow path 801 is a brake fluid path that is connected to a portion of the supply flow path 721 that is closer to the sixth flow path 56 than the differential pressure adjustment valve 731 and to the reduced-pressure reservoir 751. The return flow path 802 is a brake fluid path that is connected to a portion of the supply flow path 722 that is closer to the first flow path 331 than the differential pressure adjustment valve 732 and to the reduced-pressure reservoir 752.

[0048] The second hydraulic pressure 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 pressure circuit 712 from the first flow path 331. The hydraulic pressure sensor 83 is connected to a portion of the supply flow path 722 that is closer to the first flow path 331 than the differential pressure adjustment valve 732. The first flow path 331 is connected to the master chamber Rm of the master unit 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.

[0049] <Control Device> Detection signals from a plurality of sensors are input to the control device 200. The plurality of sensors include the above-mentioned plurality of sensors 351, 58, 59, 83 and an operation amount sensor 221. The operation amount sensor 221 detects the amount of operation of the brake operating member 22 by the driver. The operation amount based on the detection signal of the operation amount sensor 221 is referred to as the "braking operation amount Ba." The control device 200 operates the hydraulic pressure generating device 20 and the brake actuator 70 based on the detection signals from these sensors.

[0050] 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. An example of the processing circuits 210, 220 is an electronic control device. In this case, each of the plurality of processing circuits 210, 220 includes 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.

[0051] 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. Therefore, the control device 200 can adjust the friction braking force generated in the vehicle by coordinating the hydraulic pressure generating device 20 and the brake actuator 70.

[0052] During vehicle braking, the control device 200 executes a normal pressure adjustment process, a heat generation suppression process, and a degeneration process. <Normal Pressure Adjustment Process> In the normal pressure adjustment process, the control device 200 activates the pressurizing unit 50 based on a required braking force FxRq, which is a required value of the braking force of the vehicle. The braking force of the vehicle is the sum of the friction braking force generated by the vehicle and the regenerative braking force generated by the vehicle.

[0053] For example, the first processing circuit 210 derives a required frictional braking force FxMRq, which is a required value of the frictional braking force to be generated in the vehicle, based on the required braking force FxRq. When regenerative braking force is generated in the vehicle, the first processing circuit 210 derives the required frictional braking force FxMRq by subtracting the regenerative braking force from the required braking force FxRq. When no regenerative braking force is generated in the vehicle, the first processing circuit 210 derives the required frictional braking force FxMRq from the required braking force FxRq. The first processing circuit 210 derives a required servo pressure PsvRq by converting the required frictional braking force FxMRq into a servo pressure. In other words, the required servo pressure PsvRq corresponds to a servo pressure according to the required frictional braking force FxMRq.

[0054] The first processing circuit 210 then operates the electric cylinders 51 of the pressure unit 50 so that the servo pressure becomes equal to the required servo pressure PsvRq, thereby increasing the wheel pressure Pw of the multiple wheel cylinders 16. For example, the first processing circuit 210 sets the required servo pressure PsvRq to a target servo pressure PsvTr. The target servo pressure PsvTr is a target value for the servo pressure. The first processing circuit 210 then drives the first electric motors 513 of the electric cylinders 51 so that the detected servo pressure Psv becomes equal to the target servo pressure PsvTr. For example, the first processing circuit 210 drives the first electric motors 513 using feedback control that uses the deviation between the target servo pressure PsvTr and the detected servo pressure Psv as an input. This allows the control device 200 to generate wheel pressures Pw in the multiple wheel cylinders 16 that correspond to the detected servo pressure Psv, i.e., the required frictional braking force FxMRq.

[0055] <Heat generation suppression process> The control device 200 executes the heat generation suppression process after executing the normal pressure adjustment process. In the heat generation suppression process, the control device 200 regulates the decrease in the wheel pressure Pw by increasing the indicated differential pressure DPTr, which is the indicated value of the differential pressure DP for the differential pressure adjustment valves 731, 732 of the brake actuator 70. Then, the control device 200 operates the electric cylinder 51 to make the detected servo pressure value Psv lower than the required servo pressure PsvRq.

[0056] For example, when a transition condition from the normal pressure adjustment process to the heat generation suppression process is satisfied, the first processing circuit 210 of the control device 200 sets the target servo pressure PsvTr at the time the transition condition is satisfied to the specified servo pressure PTr. The first processing circuit 210 derives the indicated differential pressure DPTr based on a reference differential pressure DPB, which is the difference between the specified servo pressure PTr and a reference pressure PsvB. The reference pressure PsvB is a servo pressure lower than the specified servo pressure PTr. It is preferable that the reference pressure PsvB be higher than 0 (zero). For example, the first processing circuit 210 derives the indicated differential pressure DPTr as the sum of the reference differential pressure DPB and the offset hydraulic pressure αDP. The offset hydraulic pressure αDP is greater than 0 (zero). The first processing circuit 210 then transmits information regarding the derived indicated differential pressure DPTr to the second processing circuit 220.

[0057] When the second processing circuit 220 receives the above information from the first processing circuit 210, it supplies a current corresponding to the indicated differential pressure DPTr to the solenoids of the differential pressure regulating valves 731, 732. The larger the indicated differential pressure DPTr, the larger the current supplied to the solenoids of the differential pressure regulating valves 731, 732.

[0058] When the first processing circuit 210 confirms that the second processing circuit 220 is operating the differential pressure regulating valves 731, 732 based on the indicated differential pressure DPTr, it sets the reference pressure PsvB to the target servo pressure PsvTr.The first processing circuit 210 then drives the first electric motor 513 based on the target servo pressure PsvTr.This allows the control device 200 to reduce the detected servo pressure value Psv to the reference pressure PsvB while maintaining the wheel pressure Pw.

[0059] When the first processing circuit 210 determines that the detected servo pressure value Psv has decreased to the reference pressure PsvB, it executes a motor vibration process that oscillates the motor rotation angle θ of the first electric motor 513. When the motor rotation angle θ oscillates, the detected servo pressure value Psv also oscillates in response to the oscillation of the motor rotation angle θ. In this instance, in one example of the motor vibration process, the first processing circuit 210 oscillates the motor rotation angle θ within a range in which the amplitude of the detected servo pressure value Psv does not exceed the offset hydraulic pressure αDP. Note that when the first processing circuit 210 ends the heat generation suppression process, it stops oscillating the motor rotation angle θ of the first electric motor 513.

[0060] <Degeneration Processing> The control device 200 executes the degeneration processing when the required braking force FxRq is changed under the condition that the detected servo pressure value Psv becomes lower than the required servo pressure PsvRq due to the execution of the heat generation suppression processing. In the degeneration processing, the control device 200 operates the electric cylinder 51 so that the detected servo pressure value Psv becomes equal to the required servo pressure PsvRq. Specifically, the first processing circuit 210 changes the target servo pressure PsvTr so that it approaches the required servo pressure PsvRq. Then, the first processing circuit 210 drives the first electric motor 513 based on the target servo pressure PsvTr.

[0061] After the heat generation suppression process is performed, the control device 200 performs the degeneration process both when the required braking force FxRq decreases and when the required braking force FxRq increases. The degeneration process when the required braking force FxRq decreases is referred to as the "first degeneration process." The degeneration process when the required braking force FxRq increases is referred to as the "second degeneration process."

[0062] <First Degeneration Process> In the first degeneration process, the first processing circuit 210 reduces the indicated differential pressure DPTr at a rate corresponding to the rate at which the required braking force FxRq is reduced. The second processing circuit 220 drives the differential pressure control valves 731, 732 based on the indicated differential pressure DPTr. Therefore, when the first processing circuit 210 reduces the indicated differential pressure DPTr, the second processing circuit 220 reduces the current flowing through the solenoids of the differential pressure control valves 731, 732 at a rate corresponding to the rate at which the required braking force FxRq is reduced.

[0063] When the indicated differential pressure DPTr is greater than a predetermined value DP1, the first processing circuit 210 maintains the target servo pressure PsvTr equal to the reference pressure PsvB. That is, the first processing circuit 210 maintains the detected servo pressure value Psv. The predetermined value DP1 is set to a value that allows the differential pressure DP to be regarded as substantially 0 (zero). An example of the predetermined value DP1 is 0 (zero).

[0064] When the command differential pressure DPTr reaches the predetermined value DP1, the required servo pressure PsvRq becomes substantially equal to the reference pressure PsvB. That is, from this point onward, the required servo pressure PsvRq becomes lower than the reference pressure PsvB as the required braking force FxRq decreases. Therefore, when the command differential pressure DPTr falls below the predetermined value DP1, the first processing circuit 210 reduces the target servo pressure PsvTr from the reference pressure PsvB. For example, the first processing circuit 210 sets the required servo pressure PsvRq to the target servo pressure PsvTr. This allows the first processing circuit 210 to reduce the target servo pressure PsvTr at a rate that corresponds to the rate at which the required braking force FxRq decreases. The first processing circuit 210 then drives the first electric motor 513 so that the detected servo pressure value Psv decreases as the target servo pressure PsvTr decreases. When the reduction of the required braking force FxRq is stopped, the control device 200 ends the first degeneration process.

[0065] <Second Degeneration Process> In the second degeneration process, the first processing circuit 210 increases the target servo pressure PsvTr to the required servo pressure PsvRq. The required servo pressure PsvRq increases in response to an increase in the required braking force FxRq. Furthermore, at the start of the degeneration process, the target servo pressure PsvTr is lower than the required servo pressure PsvRq. Therefore, the first processing circuit 210 increases the target servo pressure PsvTr at a rate faster than the rate at which the required servo pressure PsvRq increases. After the target servo pressure PsvTr reaches the required servo pressure PsvRq, the first processing circuit 210 sets the required servo pressure PsvRq to the target servo pressure PsvTr. Then, the first processing circuit 210 drives the first electric motor 513 so that the detected servo pressure value Psv increases in response to an increase in the target servo pressure PsvTr. When the increase in the required braking force FxRq is stopped, the control device 200 ends the second degeneration process.

[0066] 2 and 3, a series of processes executed by the first processing circuit 210 of the control device 200 when a braking request is issued to the vehicle will be described.

[0067] When a braking request is issued to the vehicle, the first processing circuit 210 starts the process of step S10. In step S10, the first processing circuit 210 executes normal pressure adjustment processing. Specifically, in step S11, the first processing circuit 210 derives a required braking force FxRq and a required frictional braking force FxMRq. When the driver is performing a braking operation, the first processing circuit 210 derives a required braking force FxRq such that the required braking force FxRq increases as the braking operation amount Ba increases. Furthermore, when deceleration of the vehicle is requested by another control device, the first processing circuit 210 derives a braking force corresponding to the deceleration request as the required braking force FxRq. The first processing circuit 210 then derives the required frictional braking force FxMRq based on the required braking force FxRq.

[0068] In the next step S13, the first processing circuit 210 derives a target servo pressure PsvTr. That is, the first processing circuit 210 derives a servo pressure corresponding to the required frictional braking force FxMRq as a required servo pressure PsvRq. Then, the first processing circuit 210 sets the required servo pressure PsvRq as the target servo pressure PsvTr.

[0069] In the following step S15, the first processing circuit 210 operates the electric cylinder 51 based on the target servo pressure PsvTr. For example, the first processing circuit 210 drives the first electric motor 513 of the electric cylinder 51 by feedback control using the deviation between the target servo pressure PsvTr and the detected servo pressure value Psv as an input.

[0070] In the next step S17, the first processing circuit 210 determines whether the required frictional braking force FxMRq has changed. If either the required frictional braking force FxMRq has increased or the required frictional braking force FxMRq has decreased, the first processing circuit 210 determines that the required frictional braking force FxMRq has changed (S17: YES). In this case, the first processing circuit 210 proceeds to step S11. On the other hand, if neither the required frictional braking force FxMRq has increased nor the required frictional braking force FxMRq has decreased, the first processing circuit 210 determines that the required frictional braking force FxMRq has not changed (S17: NO). In this case, the first processing circuit 210 proceeds to step S19.

[0071] In step S19, the first processing circuit 210 determines whether a transition condition from the normal voltage adjustment process to the heat generation suppression process is met. For example, the first processing circuit 210 determines that the transition condition is met when the following condition (A1) is met:

[0072] (A1) The duration of the state in which it is determined that the required frictional braking force FxMRq has not changed is equal to or longer than the first determination time TMth. The first determination time TMth is set as the criterion for determining whether the required frictional braking force FxMRq is being reliably maintained.

[0073] If the first processing circuit 210 determines that the transition condition is not met (S19: NO), the process proceeds to step S11. That is, the first processing circuit 210 continues the normal pressure adjustment process. On the other hand, if the first processing circuit 210 determines that the transition condition is met (S19: YES), the first processing circuit 210 ends the normal pressure adjustment process and proceeds to step S30.

[0074] In step S30, the first processing circuit 210 executes heat generation suppression processing. Specifically, in step S31, the first processing circuit 210 derives the indicated differential pressure DPTr based on the specified servo pressure PTr and the reference pressure PsvB. Then, in step S33, the first processing circuit 210 transmits information about the indicated differential pressure DPTr to the second processing circuit 220.

[0075] Upon receiving this information, the second processing circuit 220 drives the multiple differential pressure control valves 731, 732 based on the indicated differential pressure DPTr indicated by the information. That is, the larger the indicated differential pressure DPTr, the larger the current that the second processing circuit 220 passes through the solenoids of the differential pressure control valves 731, 732. Then, when the multiple differential pressure control valves 731, 732 begin to be driven based on the indicated differential pressure DPTr, the second processing circuit 220 transmits a confirmation signal indicating this to the first processing circuit 210.

[0076] In the next step S35, the first processing circuit 210 determines whether it has confirmed that the multiple differential pressure control valves 731, 732 are being operated based on the indicated differential pressure DPTr. If the first processing circuit 210 has not received the confirmation signal from the second processing circuit 220, it determines that it has not confirmed that the multiple differential pressure control valves 731, 732 are being operated based on the indicated differential pressure DPTr (S35: NO). In this case, the first processing circuit 210 repeatedly executes the determination in step S35 until it receives the confirmation signal. On the other hand, if the first processing circuit 210 has received the confirmation signal from the second processing circuit 220, it determines that it has confirmed that the multiple differential pressure control valves 731, 732 are being operated based on the indicated differential pressure DPTr (S35: YES). In this case, the first processing circuit 210 proceeds to step S37.

[0077] In step S37, the first processing circuit 210 decreases the target servo pressure PsvTr toward the reference pressure PsvB. For example, if the target servo pressure PsvTr is higher than the reference pressure PsvB, the first processing circuit 210 decreases the target servo pressure PsvTr. On the other hand, if the target servo pressure PsvTr is equal to or lower than the reference pressure PsvB, the first processing circuit 210 maintains the target servo pressure PsvTr.

[0078] In the following step S39, the first processing circuit 210 operates the electric cylinder 51 based on the target servo pressure PsvTr, as in step S15. Then, in step S41, the first processing circuit 210 determines whether the detected servo pressure value Psv has decreased to the reference pressure PsvB. For example, if both of the following conditions (B1) and (B2) are met, the first processing circuit 210 determines that the detected servo pressure value Psv has decreased to the reference pressure PsvB.

[0079] (B1) The target servo pressure PsvTr is equal to the reference pressure PsvB. (B2) The difference between the servo pressure detection value Psv and the reference pressure PsvB is within the error range. If the first processing circuit 210 determines that the servo pressure detection value Psv has not decreased to the target servo pressure PsvTr (S41: NO), the process proceeds to step S37. On the other hand, if the first processing circuit 210 determines that the servo pressure detection value Psv has decreased to the target servo pressure PsvTr (S41: YES), the process proceeds to step S43.

[0080] In step S43, the first processing circuit 210 executes the motor vibration processing. In the following step S45, the first processing circuit 210 derives the required braking force FxRq and the required frictional braking force FxMRq, similar to step S11.

[0081] In the next step S47, the first processing circuit 210 determines whether the required frictional braking force FxMRq has changed during the execution of the heat generation suppression process. For example, the first processing circuit 210 determines whether the required frictional braking force FxMRq has changed by comparing the required frictional braking force FxMRq at the start of the heat generation suppression process with the latest value of the required frictional braking force FxMRq. In this case, the first processing circuit 210 may determine that the required frictional braking force FxMRq has changed if the absolute value of the difference between the required frictional braking force FxMRq at the start of the heat generation suppression process and the latest value of the required frictional braking force FxMRq is equal to or greater than the determination difference. On the other hand, the first processing circuit 210 may determine that the required frictional braking force FxMRq has not changed if the absolute value of the difference is less than the determination difference. The determination difference is a criterion for determining whether the required frictional braking force FxMRq has changed.

[0082] If the first processing circuit 210 determines that the required frictional braking force FxMRq has not been changed (S47: NO), the process proceeds to step S43 and continues executing the motor vibration process. On the other hand, if the first processing circuit 210 determines that the required frictional braking force FxMRq has been changed (S47: YES), the motor vibration process ends. Then, the first processing circuit 210 ends the heat generation suppression process. Thereafter, the first processing circuit 210 proceeds to step S51.

[0083] In step S51, the first processing circuit 210 determines whether the required frictional braking force FxMRq is decreasing. If the latest value of the required frictional braking force FxMRq is smaller than the required frictional braking force FxMRq at the start of the heat generation suppression processing, the required frictional braking force FxMRq is considered to be decreasing. On the other hand, if the latest value of the required frictional braking force FxMRq is greater than the required frictional braking force FxMRq at the start of the heat generation suppression processing, the required frictional braking force FxMRq is considered to be increasing. If the first processing circuit 210 determines that the required frictional braking force FxMRq is decreasing (S51: YES), the process proceeds to step S60. On the other hand, if the first processing circuit 210 determines that the required frictional braking force FxMRq is not decreasing (S51: NO), the process proceeds to step S80.

[0084] In step S60, the first processing circuit 210 executes a first degeneration process, which is one of the degeneration processes. Specifically, in step S61, the first processing circuit 210 derives the required braking force FxRq and the required frictional braking force FxMRq, as in step S11. The first processing circuit 210 also derives a servo pressure corresponding to the required frictional braking force FxMRq as the required servo pressure PsvRq.

[0085] In the next step S63, the first processing circuit 210 derives the command differential pressure DPTr based on the required servo pressure PsvRq and the target servo pressure PsvTr. For example, the first processing circuit 210 derives the command differential pressure DPTr by subtracting the target servo pressure PsvTr from the required servo pressure PsvRq. The target servo pressure PsvTr is maintained at the value at the end of the heat generation suppression process. Therefore, the target servo pressure PsvTr is lower than the required servo pressure PsvRq. Therefore, at the start of the first degeneration process, the first processing circuit 210 can derive a positive value as the command differential pressure DPTr.

[0086] In the following step S65, the first processing circuit 210 transmits information related to the indicated differential pressure DPTr derived in step S63 to the second processing circuit 220. Upon receiving this information, the second processing circuit 220 drives the multiple differential pressure regulating valves 731, 732 based on the indicated differential pressure DPTr indicated by this information. If the indicated differential pressure DPTr gradually decreases in response to a decrease in the required frictional braking force FxMRq, the second processing circuit 220 reduces the current flowing through the solenoids of the differential pressure regulating valves 731, 732 in response to the decrease in the indicated differential pressure DPTr.

[0087] In the next step S67, the first processing circuit 210 determines whether the indicated differential pressure DPTr has become equal to or less than a predetermined value DP1. If the indicated differential pressure DPTr is greater than the predetermined value DP1 (S67: NO), the first processing circuit 210 proceeds to step S61. In this case, the first processing circuit 210 continues to reduce the indicated differential pressure DPTr in accordance with the decrease in the required frictional braking force FxMRq. On the other hand, if the indicated differential pressure DPTr is equal to or less than the predetermined value DP1 (S67: YES), the first processing circuit 210 proceeds to step S69.

[0088] In step S69, the first processing circuit 210 derives the required braking force FxRq, the required frictional braking force FxMRq, and the required servo pressure PsvRq, similar to step S61. In the following step S71, the first processing circuit 210 sets the required servo pressure PsvRq derived in step S69 as the target servo pressure PsvTr. If the required frictional braking force FxMRq is decreasing, the required servo pressure PsvRq is decreasing in accordance with the decrease in the required frictional braking force FxMRq. Therefore, the first processing circuit 210 decreases the target servo pressure PsvTr. Then, in step S73, the first processing circuit 210 operates the electric cylinder 51 based on the target servo pressure PsvTr, similar to step S15.

[0089] In the following step S75, the first processing circuit 210 determines whether the target servo pressure PsvTr is decreasing. If the target servo pressure PsvTr is decreasing (S75: YES), the first processing circuit 210 proceeds to step S69. On the other hand, if the target servo pressure PsvTr is not decreasing (S75: NO), the first processing circuit 210 ends the first degeneration process. Then, the first processing circuit 210 proceeds to step S77.

[0090] In step S77, the first processing circuit 210 determines whether or not a braking request is made to the vehicle. If the required braking force FxRq is greater than 0 (zero), the first processing circuit 210 determines that a braking request is made (S77: YES). Then, the first processing circuit 210 proceeds to step S10. That is, the first processing circuit 210 starts the normal pressure adjustment process. On the other hand, if the required braking force FxRq is 0 (zero), the first processing circuit 210 determines that a braking request is not made (S77: NO). Then, the first processing circuit 210 ends the series of processes shown in FIGS. 2 and 3.

[0091] In step S80, the first processing circuit 210 executes a second degeneration process, which is one of the degeneration processes. Specifically, in step S81, the first processing circuit 210 derives the required braking force FxRq, the required frictional braking force FxMRq, and the required servo pressure PsvRq, similar to step S61. In the following step S83, the first processing circuit 210 increases the target servo pressure PsvTr. At this time, the first processing circuit 210 sets the target servo pressure PsvTr so that the target servo pressure PsvTr approaches the required servo pressure PsvRq at a speed commensurate with the discharge capacity of the electric cylinder 51. When the maximum value of the rate of increase in the servo pressure due to operation of the electric cylinder 51 is defined as the maximum increase rate, it is preferable that the first processing circuit 210 increase the target servo pressure PsvTr at an increase rate slightly slower than the maximum increase rate. However, if the target servo pressure PsvTr has already reached the required servo pressure PsvRq, the first processing circuit 210 sets the required servo pressure PsvRq to the target servo pressure PsvTr.

[0092] In the next step S85, the first processing circuit 210 operates the electric cylinder 51 based on the target servo pressure PsvTr, as in step S15. In the following step S87, the first processing circuit 210 determines whether the target servo pressure PsvTr has become equal to or greater than the required servo pressure PsvRq. If the target servo pressure PsvTr has become less than the required servo pressure PsvRq (S87: NO), the first processing circuit 210 proceeds to step S81. On the other hand, if the target servo pressure PsvTr has become equal to or greater than the required servo pressure PsvRq (S87: YES), the first processing circuit 210 proceeds to step S89.

[0093] In step S89, the first processing circuit 210 determines whether the target servo pressure PsvTr is being held. If the target servo pressure PsvTr is not being held (S89: NO), the first processing circuit 210 proceeds to step S81. That is, the first processing circuit 210 continues executing the second degeneration process. On the other hand, if the target servo pressure PsvTr is being held (S89: YES), the first processing circuit 210 terminates the second degeneration process. Then, the first processing circuit 210 proceeds to step S10 and starts the normal pressure adjustment process.

[0094] <Functions and Effects of the Present Embodiment> The functions and effects when the first degeneration process is executed after the heat generation suppression process will be described with reference to Fig. 4. For ease of understanding, the description will be given assuming that no regenerative braking force is generated in the vehicle.

[0095] As shown in (A) of FIG. 4, a braking request is generated at timing T11, for example, when a braking operation is initiated. The control device 200 then derives a required braking force FxRq and a required frictional braking force FxMRq. In the example shown in FIG. 4, the required frictional braking force FxMRq increases. Therefore, the first processing circuit 210 of the control device 200 executes normal pressure adjustment processing to increase the wheel pressure Pw in the multiple wheel cylinders 16. In other words, the control device 200 increases the frictional braking force FxM generated by the vehicle.

[0096] When the normal pressure adjustment process is being executed, the requested servo pressure PsvRq is set to the target servo pressure PsvTr. Then, the first electric motor 513 of the electric cylinder 51 is driven based on the target servo pressure PsvTr, thereby increasing the detected servo pressure value Psv. That is, the detected servo pressure value Psv increases in accordance with the increase in the requested servo pressure PsvRq. Then, the wheel pressure Pw increases in accordance with the increase in the detected servo pressure value Psv.

[0097] In the example shown in FIG. 4 , the required frictional braking force FxMRq and the required servo pressure PsvRq are maintained at timing T12. Then, at subsequent timing T13, it is determined that the conditions for transitioning from the normal pressure adjustment process to the heat generation suppression process are met, and the first processing circuit 210 transitions from the normal pressure adjustment process to the heat generation suppression process. In the heat generation suppression process, as shown in FIGS. 4B and 4C , the first processing circuit 210 sets the indicated differential pressure DPTr based on the specified servo pressure PTr, which is the target servo pressure PsvTr at timing T13, and the reference pressure PsvB. The first processing circuit 210 then transmits information regarding the indicated differential pressure DPTr to the second processing circuit 220.

[0098] The second processing circuit 220 drives the differential pressure regulating valves 731, 732 based on the indicated differential pressure DPTr indicated by the received information, thereby enabling the control device 200 to regulate the decrease in the wheel pressure Pw in the plurality of wheel cylinders 16.

[0099] Then, the first processing circuit 210 sets a servo pressure lower than the requested servo pressure PsvRq as the target servo pressure PsvTr, and drives the first electric motor 513 of the electric cylinder 51 based on the target servo pressure PsvTr.

[0100] As a result, the detected servo pressure value Psv gradually decreases as the target servo pressure PsvTr decreases. Because the differential pressure regulating valves 731, 732 are driven in response to the command differential pressure DPTr, the differential pressure DP increases as the detected servo pressure value Psv decreases, as shown in FIG. 4B. This maintains the wheel pressure Pw as shown in FIG. 4C. In other words, the control device 200 can maintain the wheel pressure Pw even if the amount of current supplied to the first electric motor 513 is reduced. Therefore, the control device 200 can prevent the first electric motor 513 from overheating.

[0101] Here, the first electric motor 513 has coils of multiple phases. The motor rotation angle θ of the first electric motor 513 is controlled by adjusting the current flowing through the coils of the multiple phases. Therefore, if the motor rotation angle θ is maintained, there is a possibility that the current flowing through some of the coils of the multiple phases will continue to be greater than the current flowing through the other coils. In this case, there is a possibility that some of the coils will become overheated.

[0102] Therefore, the control device 200 executes a motor vibration process from timing T14 to timing T15. Timing T15 is the timing when the required frictional braking force FxMRq and the required servo pressure PsvRq begin to decrease. When the first processing circuit 210 executes the motor vibration process, the motor rotation angle θ oscillates, and the detected servo pressure value Psv also oscillates, as shown in FIG. 4C . This prevents a large current from continuing to flow through some of the coils of the multiple phases of the first electric motor 513.

[0103] The required frictional braking force FxMRq may be changed in a situation where the detected servo pressure value Psv becomes lower than the required servo pressure PsvRq due to the execution of the heat generation suppression process. In the example shown in FIG. 4, the required frictional braking force FxMRq is reduced from timing T15. Then, the required servo pressure PsvRq is reduced in accordance with the reduction in the required frictional braking force FxMRq. Therefore, the control device 200 transitions from the heat generation suppression process to the first degeneration process.

[0104] When the heat generation suppression process ends, the first processing circuit 210 ends the motor vibration process. Therefore, the detected servo pressure value Psv is maintained from timing T15 onward. In the first degeneration process, the first processing circuit 210 maintains the target servo pressure PsvTr and then reduces the indicated differential pressure DPTr in accordance with the reduction in the required frictional braking force FxMRq and the required servo pressure PsvRq. The first processing circuit 210 then transmits information related to the indicated differential pressure DPTr to the second processing circuit 220.

[0105] The second processing circuit 220 drives the differential pressure regulating valves 731, 732 based on the indicated differential pressure DPTr indicated by the received information. As a result, as shown in FIG. 4B, the second processing circuit 220 can reduce the wheel pressures Pw in the multiple wheel cylinders 16 at a rate that corresponds to the required servo pressure PsvRq. In other words, the control device 200 can reduce the frictional braking force FxM in accordance with the reduction in the required frictional braking force FxMRq.

[0106] At timing T16, the command differential pressure DPTr becomes equal to or less than the predetermined value DP1. In this case, the first processing circuit 210 can determine that the differential pressure DP has become 0 (zero). Therefore, the first processing circuit 210 sets the required servo pressure PsvRq to the target servo pressure PsvTr. Since the required frictional braking force FxMRq continues to decrease after timing T16, the required servo pressure PsvRq also decreases. Therefore, the first processing circuit 210 can decrease the target servo pressure PsvTr in accordance with the decrease in the required frictional braking force FxMRq. The first processing circuit 210 drives the first electric motor 513 of the electric cylinder 51 based on this target servo pressure PsvTr. As a result, the control device 200 can decrease the wheel pressure Pw and the frictional braking force FxM of the multiple wheel cylinders 16 in accordance with the decrease in the required frictional braking force FxMRq, even after the command differential pressure DPTr becomes equal to or less than the predetermined value DP1. Therefore, even when the wheel pressure Pw is reduced after the heat generation suppression process is completed, the control device 200 can appropriately adjust the wheel pressure Pw.

[0107] 4, the required friction braking force FxMRq becomes 0 (zero) at timing T17, and the braking request is cancelled, so the control device 200 ends the first degeneration process.

[0108] The operation and effect of the second degeneration process when the second degeneration process is executed after the heat generation suppression process will be described with reference to Fig. 5. For ease of understanding, the description will be made assuming that no regenerative braking force is generated in the vehicle.

[0109] As shown in (A) of FIG. 5, a braking request is generated at timing T21, for example, when a braking operation is initiated. The control device 200 then derives a required braking force FxRq and a required frictional braking force FxMRq. In the example shown in FIG. 5, the required frictional braking force FxMRq increases. Therefore, the first processing circuit 210 of the control device 200 executes normal pressure adjustment processing to increase the wheel pressure Pw in the multiple wheel cylinders 16. In other words, the control device 200 increases the frictional braking force FxM generated by the vehicle.

[0110] At a subsequent timing T22, when it is determined that the condition for transitioning from the normal voltage adjustment process to the heat generation suppression process is met, the first processing circuit 210 transitions the process from the normal voltage adjustment process to the heat generation suppression process.

[0111] The required frictional braking force FxMRq may be changed in a situation where the detected servo pressure value Psv becomes lower than the required servo pressure PsvRq due to the execution of the heat generation suppression process. In the example shown in FIG. 5, the required frictional braking force FxMRq is increased from timing T23. Then, the required servo pressure PsvRq is increased in accordance with the increase in the required frictional braking force FxMRq. Therefore, the control device 200 transitions from the heat generation suppression process to the second degeneration process.

[0112] In the second degeneration process, the first processing circuit 210 increases the target servo pressure PsvTr in response to an increase in the required servo pressure PsvRq, thereby causing the detected servo pressure value Psv to approach the required servo pressure PsvRq.

[0113] Here, the first hydraulic pressure circuit 711 and the second hydraulic pressure circuit 712 of the brake actuator 70 are equipped with check valves 821, 822 arranged in parallel with the differential pressure adjustment valves 731, 732. The check valves 821, 822 restrict the flow of brake fluid from the wheel cylinders 16 while allowing the flow of brake fluid from the hydraulic pressure generator 20 toward the wheel cylinders 16. Therefore, when the servo pressure increases due to the operation of the electric cylinder 51 based on the target servo pressure PsvTr, the brake fluid supplied from the hydraulic pressure generator 20 is supplied to the multiple wheel cylinders 16 via the check valves 821, 822. Specifically, the detected servo pressure value Psv increases as the target servo pressure PsvTr increases. If the detected servo pressure value Psv is equal to or less than the wheel pressure Pw, the wheel pressure Pw does not increase. However, even if the indicated differential pressure DPTr remains at the value at time T23, the differential pressure DP decreases as the detected servo pressure value Psv increases, as shown in (B) and (C) of Figure 5. Eventually, the differential pressure DP becomes 0 (zero) at time T24. Then, from time T24 onwards, the wheel pressure Pw increases as the detected servo pressure value Psv increases. In other words, the control device 200 can increase the wheel pressure Pw to the wheel pressure corresponding to the requested servo pressure PsvRq. Therefore, the control device 200 can appropriately adjust the wheel pressure Pw even when increasing the wheel pressure Pw after the heat generation suppression process is completed.

[0114] 5, the required frictional braking force FxMRq is maintained from timing T25. Therefore, the first processing circuit 210 shifts the processing from the second degeneration processing to the normal pressure adjustment processing. Then, at subsequent timing T26, it is determined that the condition for shifting from the normal pressure adjustment processing to the heat generation suppression processing is met, so the first processing circuit 210 shifts the processing from the normal pressure adjustment processing to the heat generation suppression processing.

[0115] <Modifications> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0116] In the above embodiment, the first processing circuit 210 maintained the indicated differential pressure DPTr even when the process shifted from the second degeneration process to the normal pressure adjustment process. However, this is not limited to this. For example, when the process shifts from the second degeneration process to the normal pressure adjustment process, the first processing circuit 210 may set the indicated differential pressure DPTr to 0 (zero). This allows the control device 200 to shorten the time that current is applied to the differential pressure adjustment valves 731, 732.

[0117] In the second degeneration process, the first processing circuit 210 may decrease the indicated differential pressure DPTr as the target servo pressure PsvTr increases. For example, the first processing circuit 210 may decrease the indicated differential pressure DPTr as the difference between the requested servo pressure PsvRq and the target servo pressure PsvTr decreases.

[0118] In the first degeneration process, the first processing circuit 210 may decrease the target servo pressure PsvTr while decreasing the indicated differential pressure DPTr. The reference pressure PsvB may be maintained at a preset value, or may be varied depending on the situation. For example, the first processing circuit 210 may set the reference pressure PsvB to increase as the required frictional braking force FxMRq at the end of the normal pressure adjustment process increases.

[0119] The reference pressure PsvB may be 0 (zero). In this case, the first processing circuit 210 controls the first electric motor 513 in the heat generation suppression process so that the detected servo pressure value Psv becomes 0 (zero). In this case, the heat generation suppression process does not need to include the motor vibration process.

[0120] In the above embodiment, the brake fluid is supplied to the second hydraulic pressure circuit 712 of the brake actuator 70 via the master unit 30, but this is not limited to this. For example, the hydraulic pressure generating device may be configured to directly supply the brake fluid discharged from the electric cylinder 51 to the second hydraulic pressure circuit 712.

[0121] If the pressurizing unit has an electric motor as its power source, it does not need to have the electric cylinder 51. For example, the pressurizing unit may have a pump powered by an electric motor. Even in this case, as the amount of current supplied to the electric motor increases, the servo pressure, which is the discharge pressure of the brake fluid from the pump, increases.

[0122] The control device 200 is not limited to a device that includes a CPU and a ROM and executes software processing. That is, the control device 200 may have any one of the following configurations (a), (b), and (c):

[0123] (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 configured to cause the CPU to execute processes. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer.

[0124] (b) The control device 200 includes one or more dedicated hardware circuits that execute 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."

[0125] (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 of the various processes.

[0126] Other Technical Ideas The following describes technical ideas that can be understood from the above-described embodiment and modified examples. [Supplementary Note 1] In the heat generation suppression process, it is preferable that the control device oscillates the rotation angle of the electric motor after reducing the servo pressure to the reference pressure.

[0127] [Supplementary Note 2] In the heat generation suppression process, the control device preferably sets the indicated differential pressure to a value corresponding to the pressure difference between the servo pressure and the reference pressure before the start of the heat generation suppression process.

Claims

1. A vehicle adapted to a vehicle in which braking force is generated at a wheel according to wheel pressure, which is hydraulic pressure in a wheel cylinder, comprising: a pressurizing unit having an electric motor as a power source and adjusting and supplying the pressure of brake fluid; a supply flow path through which brake fluid flows toward the wheel cylinder when the pressurizing unit supplies brake fluid; a differential pressure adjustment valve, which is a linear electromagnetic valve installed in the supply flow path, adjusting the differential pressure between a portion of the supply flow path opposite the wheel cylinder and a portion of the supply flow path on the wheel cylinder side; and a control device that controls the wheel pressure by controlling the pressurizing unit and the differential pressure adjustment valve, wherein the control device performs a normal pressure adjustment process that adjusts the wheel pressure by operating the pressurizing unit so that the servo pressure, which is the hydraulic pressure of the brake fluid supplied by the pressurizing unit, becomes a required servo pressure, which is a servo pressure according to the required value of the braking force; and a heat generation suppression process that, after the normal pressure adjustment process has been performed, operates the pressurizing unit so that the servo pressure becomes lower than the required servo pressure by increasing an indicated differential pressure, which is an indicated value of the differential pressure for the differential pressure adjustment valve, thereby restricting a decrease in the wheel pressure. and a degeneration process that, when the required value of the braking force is changed under the condition that the servo pressure becomes lower than the required servo pressure due to the execution of the heat generation suppression process, operates the pressurizing unit so that the servo pressure becomes the required servo pressure.

2. The braking device of claim 1, wherein, in the degeneration process when the required value of the braking force is reduced under the condition that the servo pressure becomes lower than the required servo pressure due to the execution of the heat generation suppression process, the control device reduces the wheel pressure by reducing the indicated differential pressure in accordance with the reduction in the required value, and when the indicated differential pressure becomes equal to or less than a predetermined value, reduces the wheel pressure by operating the pressure unit so that the servo pressure decreases in accordance with the reduction in the required servo pressure.

3. A brake fluid flow path that bypasses the differential pressure adjustment valve, the first end of which is connected to a portion of the supply flow path closer to the wheel cylinder than the differential pressure adjustment valve, and the second end of which is connected to a portion of the supply flow path on the opposite side of the differential pressure adjustment valve from the wheel cylinder, and a check valve installed in the bypass flow path that regulates the flow of brake fluid from the wheel cylinder side, wherein the control device increases the wheel pressure by operating the pressurizing unit so that the servo pressure approaches the requested servo pressure during the degeneration process when the requested value of braking force is increased under circumstances where the servo pressure has become lower than the requested servo pressure due to the execution of the heat generation suppression process.

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