Braking device

Abstract

A braking device 100 comprises an electric cylinder 51 and a control device 200 that controls the electric cylinder 51. A first processing circuit 211 of the control device 200 executes heat generation suppression control that alternately repeats increasing a motor rotation angle from a reference rotation angle to an upper limit rotation angle which is the sum of the reference rotation angle and a prescribed angle, and decreasing the motor rotation angle from the upper limit rotation angle to the reference rotation angle, when a required braking force is maintained. The first processing circuit 211 sets the prescribed angle, when the vehicle is traveling, to be smaller than the prescribed angle when the vehicle is stopped.

Description

Brake device

[0001] The present invention relates to a brake device that generates braking force on the wheels of a vehicle by adjusting the hydraulic pressure of a wheel cylinder.

[0002] Patent Document 1 discloses a brake device that generates braking force by adjusting the wheel pressure, which is the hydraulic pressure of the wheel cylinder, by supplying brake fluid from an electric cylinder to the wheel cylinder. When the required braking force, which is the required value of the braking force, is held, the control device of the brake device holds the motor rotation angle, which is the rotation angle of the electric motor provided in the electric cylinder. When the motor rotation angle is held, some of the coils of the plurality of phases of the electric motor may enter an overheated state. Therefore, when the required braking force is held under the condition that the vehicle is stopped, the control device periodically vibrates the motor rotation angle within a predetermined range to suppress some of the coils of the plurality of phases from entering an overheated state.

[0003] German Patent Application Publication No. 102019215313

[0004] In recent years, even when the vehicle is running, the required braking force may be held for a relatively long period. Even in such a case, the control device can suppress some of the coils of the plurality of phases from entering an overheated state by periodically vibrating the motor rotation angle as described above. However, when the wheel pressure vibrates with the vibration of the motor rotation angle, the braking force generated in the vehicle also vibrates. When the vehicle is running and the braking force vibrates, the deceleration of the vehicle also vibrates. Due to the vibration of the deceleration of the vehicle when the vehicle is running, there is a risk that the passengers of the vehicle will feel uncomfortable. In particular, when the variation range of the deceleration generated by the vibration of the deceleration is large, the passengers are likely to feel uncomfortable.

[0005] A braking device for solving the above problems is a device that generates braking force at the wheels of a vehicle by adjusting the hydraulic pressure of a wheel cylinder. The braking device comprises an electric cylinder configured such that when the piston moves forward in the cylinder in accordance with an increase in the motor rotation angle, which is the rotation angle of an electric motor, brake fluid is discharged from the cylinder through an output port; a supply passage that guides brake fluid to the wheel cylinder when brake fluid is discharged from the output port of the electric cylinder; and a control device that drives the electric motor. When the required braking force, which is the required value of the braking force, is maintained, the control device performs heat suppression control that alternately repeats the following: increasing the motor rotation angle at a first speed from a reference rotation angle, which is the motor rotation angle corresponding to the required braking force, to an upper limit rotation angle, which is the sum of the reference rotation angle and a specified angle, and decreasing the motor rotation angle at a second speed from the upper limit rotation angle to the reference rotation angle. When the vehicle is moving, the control device makes the specified angle smaller compared to when the vehicle is stopped.

[0006] The above braking system has the effect of simultaneously suppressing the overheating of only some of the multiple coils in the electric motor of the electric cylinder, and suppressing the discomfort caused to the occupants due to fluctuations in the vehicle's deceleration.

[0007] Figure 1 is a schematic diagram showing the configuration of a braking device according to an embodiment. Figure 2 is a schematic diagram showing a part of the braking actuator provided in the braking device of Figure 1. Figure 3 is a flowchart showing a series of processes executed by the control device provided in the braking device of Figure 1. Figure 4 is a flowchart showing the condition setting process that constitutes the series of processes shown in Figure 3. Figure 5 is a flowchart showing a series of processes that realize heat suppression control, which constitutes the series of processes shown in Figure 3. Figure 6 is a flowchart showing a series of processes that realize correction control, which constitutes the series of processes shown in Figure 3. Figures 7(a) and 7(b) are timing charts when heat suppression control is executed. Figures 8(a) to 8(d) are timing charts when heat suppression control is interrupted and correction control is executed. Figures 9(a) and 9(b) are timing charts when heat suppression control is executed in the modified braking device.

[0008] An embodiment of the braking device will be described with reference to Figures 1 to 8. Figure 1 shows a vehicle 10 equipped with the braking device 100. The vehicle 10 has two first wheels 11 and two second wheels 12 as its wheels. An example of the first wheels 11 is the front wheels, and an example of the second wheels 12 is the rear wheels. The vehicle 10 is also equipped with the same number of friction brakes 15 as the number of wheels.

[0009] <Configuration of Friction Brakes> Multiple friction brakes 15 each generate braking force on their corresponding wheels. Each friction brake 15 has a wheel cylinder 16, a rotating body 17, and a friction part 18. Since the rotating body 17 rotates with the wheel, braking force is generated on the wheel by pressing the friction part 18 against the rotating body 17. The force pressing the friction part 18 against the rotating body 17 increases with increasing wheel pressure, which is the hydraulic pressure inside the wheel cylinder 16. Therefore, the friction brake 15 can generate a greater braking force on the wheel as the wheel pressure increases.

[0010] <Configuration of the braking system> The braking system 100 adjusts the braking force generated in the vehicle 10 by controlling the wheel pressure of a plurality of wheel cylinders 16. The braking system 100 comprises an upstream unit 110 and a downstream unit 120. Each of the upstream unit 110 and the downstream unit 120 is configured to control the wheel pressure of a plurality of wheel cylinders 16.

[0011] <Configuration of the upstream unit> The upstream unit 110 includes a hydraulic pressure generator 20 and a first controller 210 that controls the hydraulic pressure generator 20. The first controller 210 will be described later.

[0012] The hydraulic pressure generator 20 includes a reservoir tank 21, a braking operating member 22, a brake sensor 23, a master device 30, and an electrically operated pressurized unit 50. The reservoir tank 21 stores brake fluid and is open to the atmosphere.

[0013] The braking operation member 22 is a member operated by the driver of the vehicle 10 when adjusting the deceleration of the vehicle 10. An example of the braking operation member 22 is the brake pedal. The act of the driver operating the braking operation member 22 is called "braking operation". When braking operation is being performed, the hydraulic pressure generator 20 can generate wheel pressure in multiple wheel cylinders 16 according to the amount of operation of the braking operation member 22.

[0014] The brake sensor 23 detects information regarding the driver's operation of the braking control member 22. For example, the brake sensor 23 detects the amount of operation of the braking control member 22 by the driver as information regarding the operation of the braking control member 22. Hereafter, the amount of operation based on the detection signal of the brake sensor 23 will be referred to as "braking operation amount Ba".

[0015] <Master Device> The master device 30 includes a master cylinder 31, a stroke simulator 32, a plurality of flow paths 331, 332, 333 connected to the master cylinder 31, and a plurality of control valves 341, 342 for controlling the flow of brake fluid. The master device 30 is equipped with a hydraulic pressure sensor 351 for detecting the hydraulic pressure of the brake fluid.

[0016] The stroke simulator 32 can generate a reaction force corresponding to the amount of operation of the braking operating member 22. The master cylinder 31 comprises 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, respectively. The master cylinder 31 comprises 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 circumferential 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 circumferential wall 412 toward the axis of the circumferential wall 412. The first annular wall 413 has a hole into which the rear end of the master piston 43, which will be described later, is inserted.

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

[0019] Rearward of the master chamber Rm within the main cylinder 41, the first fluid chamber R1 is partitioned by the peripheral wall 412 and the master piston 43. Rearward of the first fluid chamber R1 within the main cylinder 41, the servo chamber Rs is partitioned 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 each other.

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

[0021] Within the cover cylinder 42, the second fluid chamber R2 is partitioned 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 behind the servo chamber Rs.

[0022] The master piston 43 is housed in the master cylinder 31, in contact with the inner surface of the circumferential wall 412 of the main cylinder 41 and the inner surface of the first annular wall 413 via seals. Therefore, when the master piston 43 moves axially, it slides against the inner surface of the circumferential wall 412 and the inner surface of the first annular wall 413 via seals. The rear end of the master piston 43 protrudes rearward from the first annular wall 413 and is located within the second fluid chamber R2.

[0023] The input piston 44 is housed in the master cylinder 31, in contact with the inner circumferential surface of the second annular wall 422 of the cover cylinder 42 via a seal. Therefore, when the input piston 44 moves axially, it slides against the inner circumferential surface of the second annular wall 422 via the seal. The rear end of the input piston 44 protrudes behind the second annular wall 422. A braking 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 braking operating member 22 is operated, the input piston 44 moves in a direction toward the master piston 43.

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

[0025] The input spring 46 is positioned 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 backward, so 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, the rear end portion of the master chamber Rm 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 Figure 1, the connection between the master chamber Rm and the reservoir tank 21 is released. From this point onward, the hydraulic pressure in the master chamber Rm increases as the master piston 43 moves forward. For example, if the hydraulic pressure in the servo chamber Rs increases, the hydraulic pressure in the servo chamber Rs will move the master piston 43 forward. This will increase the hydraulic pressure in the master chamber Rm.

[0027] The first flow path 331 connects the first hydraulic circuit 711 of the braking actuator 70 (described later) to the master chamber Rm. The second flow path 332 connects the first liquid 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 liquid 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 located in the portion of the third flow path 333 between the connection point with the second flow path 332 and the second liquid chamber R2. The second control valve 342 is located in the portion of the third flow path 333 opposite to the first control valve 341, with the connection point with the second flow path 332 in between. 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 liquid chamber R2. For example, the hydraulic pressure sensor 351 is installed in the portion of the third flow path 333 between the connection point with the second liquid chamber R2 and the first control valve 341. In the following description, the hydraulic pressure based on the detection signal from the hydraulic pressure sensor 351 will be referred to as the "input hydraulic pressure Pgs".

[0030] <Pressurization Unit> The pressurization unit 50 is equipped with an electric cylinder 51. The pressurization unit 50 can adjust the wheel pressure of multiple wheel cylinders 16 by operating the electric cylinder 51.

[0031] The pressurizing unit 50 is equipped with a fourth passage 54, a fifth passage 55, and a sixth passage 56 as brake fluid passages. The fourth passage 54 is connected to the input port 515 of the electric cylinder 51 and the reservoir tank 21. The fifth passage 55 is connected to the servo chamber Rs of the master cylinder 31 and the output port 516 of the electric cylinder 51. The sixth passage 56 is connected to the second hydraulic circuit 712 of the brake actuator 70 (described later) and the fifth passage 55. Therefore, the electric cylinder 51 can supply brake fluid discharged from the output port 516 to both the servo chamber Rs and the second hydraulic circuit 712.

[0032] The pressurizing unit 50 includes a differential pressure regulating valve 551 installed in the portion of the fifth flow path 55 between the connection point with the sixth flow path 56 and the servo chamber Rs. The differential pressure regulating valve 551 is a normally open linear solenoid valve that adjusts the differential pressure between the portion of the fifth flow path 55 between the differential pressure regulating valve 551 and the servo chamber Rs and between the portion of the fifth flow path 55 between the differential pressure regulating valve 551 and the electric cylinder 51. 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 indicated opening degree of the differential pressure regulating valve 551.

[0033] Furthermore, a check valve 552 is provided in parallel with the differential pressure regulating 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 toward the servo chamber Rs toward the electric cylinder 51.

[0034] The electric cylinder 51 comprises a cylinder 511, a piston 512, a first electric motor 513, and a conversion mechanism 514. The piston 512 is slidably mounted within the cylinder 511. The first electric motor 513 functions as the 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 the linear movement of the piston 512.

[0035] An example of the first electric motor 513 is a brushless motor having multiple phase coils. In this case, the motor rotation angle can be adjusted by adjusting the current flowing through the multiple phase coils. The motor rotation angle is the rotation angle of the output shaft of the first electric motor 513.

[0036] Inside the cylinder 511, a hydraulic chamber Re into which brake fluid is introduced is partitioned 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. Hereafter, the direction of linear movement of the piston 512 when reducing the volume of the hydraulic chamber Re will be referred to as the "forward direction Za," while the opposite direction to the forward direction Za will be referred to as the "reverse direction Zb." The reverse direction Zb is also the direction of linear movement of the piston 512 when increasing the volume of the hydraulic chamber Re.

[0037] An input port 515 and an output port 516 are formed on the peripheral wall of the cylinder 511 as ports connecting the hydraulic chamber Re to 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 when the piston 512 is in its rearmost position. As a result, when the piston 512 is in its rearmost 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 its rearmost position, and is configured to be closed by the piston 512 when the piston 512 moves forward in the Za direction from the rearmost position. Even after the input port 515 is closed by the piston 512, if the piston 512 moves forward in the Za direction, the hydraulic pressure in the hydraulic chamber Re increases.

[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, when the piston 512 moves in the forward direction Za within the cylinder 511 in response to the drive of the first electric motor 513, brake fluid from the hydraulic chamber Re is discharged from the output port 516 into the fifth flow path 55. On the other hand, when the piston 512 moves in the backward direction Zb within the cylinder 511 in response to the drive of the first electric motor 513, brake fluid from the fifth flow path 55 is drawn into the hydraulic chamber Re from 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 passage 55. A portion of the brake fluid flowing through the fifth passage 55 flows towards the wheel cylinder 16 for the second wheel 12 via the sixth passage 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 and increasing the hydraulic pressure in the master chamber Rm. This causes the brake fluid in the master chamber Rm to flow through the first passage 331 towards the wheel cylinder 16 for the first wheel 11. In other words, the first passage 331 and the sixth passage 56 correspond to "supply passages" that guide the brake fluid to the wheel cylinder 16 when it is discharged from the output port 516 of the electric cylinder 51.

[0040] 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 cylinders 16 for the multiple wheels 11 and 12. As a result, in the sixth passage 56, the brake fluid flows toward the fifth passage 55. Also, in the first passage 331, the brake fluid flows 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. Consequently, the brake fluid in the servo chamber Rs flows out into the fifth passage 55. This causes the brake fluid in the fifth passage 55 to flow toward the electric cylinder 51.

[0041] The pressurizing unit 50 is equipped with a servo pressure sensor 58 and a rotation angle sensor 59. The servo pressure sensor 58 detects the servo pressure, which is the discharge pressure of the brake fluid from the electric cylinder 51. The rotation angle sensor 59 detects the motor rotation angle of the first electric motor 513. Hereafter, the servo pressure based on the detection signal of the servo pressure sensor 58 will be referred to as the "servo pressure detection value Psb". The motor rotation angle based on the detection signal of the rotation angle sensor 59 will be referred to as the "rotation angle detection value θ".

[0042] <Downstream Unit> The downstream unit 120 includes a braking actuator 70 and a second controller 220 that controls the braking actuator 70. The second controller 220 will be described later.

[0043] As shown in FIGS. 1 and 2, the braking actuator 70 is configured to adjust the differential pressure between the servo pressure and the wheel pressure. The braking actuator 70 is connected to the first flow path 331 and the sixth flow path 56. Specifically, the braking actuator 70 has a first hydraulic circuit 711 and a second hydraulic circuit 712. The first hydraulic circuit 711 is connected to the first flow path 331 and is also connected to two wheel cylinders 16 for the first wheel 11. The second hydraulic circuit 712 is connected to the sixth flow path 56 and is also connected to two wheel cylinders 16 for the second wheel 12.

[0044] FIG. 2 shows a schematic configuration of the second hydraulic circuit 712. The second hydraulic circuit 712 has a connection flow path 72 connected to the sixth flow path 56. The connection flow path 72 is a brake liquid path that connects two wheel cylinders 16 for the second wheel 12 and the sixth flow path 56.

[0045] A differential pressure control valve 73, which is a normally open linear solenoid valve, is provided in the connection flow path 72. The differential pressure control valve 73 can adjust the differential pressure between the portion between the connection point of the differential pressure control valve 73 and the sixth flow path 56 in the connection flow path 72 and the portion between the differential pressure control valve 73 and the wheel cylinder 16 in the connection flow path 72. For example, the differential pressure control valve 73 can generate a greater differential pressure as the current flowing through its solenoid increases.

[0046] In the connection flow path 72, the portion between the differential pressure control valve 73 and the wheel cylinder 16 branches into two paths 72a and 72b. Path 72a is connected to one of the two wheel cylinders 16, while path 72b is connected to the remaining wheel cylinder 16.

[0047] A holding valve 74 is installed in each of the plurality of paths 72a and 72b. The holding valve 74 is a normally open solenoid valve. When the holding valve 74 is closed, the supply of the brake fluid to the wheel cylinder 16 corresponding to the holding valve 74 is restricted. That is, the increase in the wheel pressure is restricted. A bypass fluid passage 85 that bypasses the holding valve 74 is connected to each of the plurality of paths 72a and 72b. A check valve 86 that restricts the flow of the brake fluid in the bypass fluid passage 85 from the differential pressure control valve 73 side toward the wheel cylinder 16 is installed in each of the plurality of bypass fluid passages 85.

[0048] The first hydraulic circuit 711 has a pressure reducing reservoir 75 that stores the brake fluid, and a pressure reducing fluid passage 76 that is connected to the pressure reducing reservoir 75. The pressure reducing fluid passage 76 is a brake fluid passage that connects a portion of the paths 72a and 72b on the wheel cylinder 16 side with respect to the holding valve 74 and the pressure reducing reservoir 75. A pressure reducing valve 77 is installed in a portion of the pressure reducing fluid passage 76 that is connected to the path 72a and a portion of the pressure reducing fluid passage 76 that is connected to the path 72b, respectively. The pressure reducing valve 77 is a normally closed solenoid valve. When the pressure reducing valve 77 is opened, the brake fluid in the wheel cylinder 16 flows into the pressure reducing reservoir 75 through the pressure reducing fluid passage 76.

[0049] The first hydraulic circuit 711 has a pump 79. The pump 79 is an electric pump that uses the second electric motor 78 as a power source. The pump 79 pumps up the brake fluid in the pressure reducing reservoir 75 and discharges the brake fluid to a portion between the differential pressure control valve 73 and the holding valve 74 in the connection flow path 72.

[0050] The first hydraulic circuit 711 has a reflux flow path 80. The reflux flow path 80 is a brake fluid passage that is connected to a portion between the connection point with the sixth flow path 56 and the differential pressure control valve 73 in the connection flow path 72 and the pressure reducing reservoir 75. Therefore, when the pressure reducing reservoir 75 is empty, the pump 79 can suck the brake fluid through the reflux flow path 80 and the sixth flow path 56.

[0051] The configuration of the first hydraulic circuit 711 is substantially the same as that of the second hydraulic circuit 712 described above. Specifically, the first hydraulic circuit 711 is equipped with a differential pressure control valve 73, a plurality of holding valves 74, a plurality of pressure reducing valves 77, a pressure reducing reservoir 75, and a pump 79 powered by a second electric motor 78.

[0052] <Configuration of the control device> As shown in Figure 1, the control device 200 of the braking device 100 can operate the hydraulic pressure generator 20 and the braking actuator 70 based on detection signals from a plurality of sensors 351, 58, and 59. For example, the control device 200 adjusts the discharge of brake fluid from the output port 516 by adjusting the motor rotation angle of the first electric motor 513. This allows the control device 200 to control the servo pressure. In this state, the control device 200 adjusts the wheel pressure of the plurality of wheel cylinders 16 by operating the braking actuator 70. This allows the control device 200 to adjust the braking force generated by the plurality of wheels 11 and 12.

[0053] Furthermore, the control device 200 can adjust the wheel pressure of multiple wheel cylinders 16 by operating the pump 79 of the braking actuator 70 and controlling the differential pressure control valve 73. In this case, the control device 200 can also adjust the wheel pressure of multiple wheel cylinders 16 individually by operating the retaining valve 74.

[0054] The control device 200 includes the first controller 210 and the second controller 220 described above. The multiple controllers 210 and 220 can send and receive various information and commands from each other via the in-vehicle network 230.

[0055] The first controller 210 has a first processing circuit 211. The second controller 220 has a second processing circuit 221. An example of the processing circuits 211 and 221 is an electronic control device. In this case, each of the multiple processing circuits 211 and 221 has a CPU and a memory that stores a control program executed by the CPU. The first processing circuit 211 operates the hydraulic pressure generator 20 by having the CPU execute the control program in the memory. The second processing circuit 221 operates the braking actuator 70 by having the CPU execute the control program in the memory.

[0056] <Overview of control of hydraulic pressure generator by the first controller> When a braking request is generated, such as when the braking operation member 22 is operated, the first processing circuit 211 of the first controller 210 derives a requested braking force FxRq, which is the requested value of the braking force of the vehicle 10. Based on the requested braking force FxRq, the first processing circuit 211 operates the electric cylinder 51 of the hydraulic pressure generator 20. For example, the first processing circuit 211 sets the servo pressure corresponding to the requested braking force FxRq to the target servo pressure PsbTr.

[0057] The first processing circuit 211 adjusts the discharge amount of brake fluid from the electric cylinder 51 based on the target servo pressure PsbTr. For example, the first processing circuit 211 corrects the target servo pressure PsbTr by feedback control, which uses the difference between the target servo pressure PsbTr and the detected servo pressure Psb as the basis. The corrected target servo pressure is referred to as "target servo pressure PsbTra".

[0058] The first processing circuit 211 sets the target rotation angle θTr based on the target servo pressure PsbTra. The target rotation angle θTr is the target value of the motor rotation angle of the first electric motor 513. In this case, the first processing circuit 211 sets the target rotation angle θTr to the value obtained by converting the target servo pressure PsbTra into a motor rotation angle.

[0059] The first processing circuit 211 drives the first electric motor 513 based on the target rotation angle θTr. For example, the first processing circuit 211 derives a command value Imt for the motor current, which is the current supplied to the first electric motor 513, by feedback control that takes the deviation between the target rotation angle θTr and the detected rotation angle θ as input. Then, the first processing circuit 211 activates the driver circuit for the first electric motor 513 according to the drive signal based on the command value Imt. As a result, the first processing circuit 211 can drive the first electric motor 513 based on the target rotation angle θTr.

[0060] <Heat Generation of the First Electric Motor> When the required braking force FxRq is maintained, the wheel pressure is maintained. When the electric cylinder 51 is operated to maintain the wheel pressure, the motor rotation angle of the first electric motor 513 of the electric cylinder 51 is maintained. When the motor rotation angle is maintained in this way, a large current may continue to flow through some of the coils of the multi-phase coils of the first electric motor 513. If this condition continues, the temperature of the coils in question and the components of the driver circuit that adjust the magnitude of the current flowing through those coils may become too high.

[0061] Therefore, the first controller 210 of the control device 200 performs processing to suppress overheating of the first electric motor 513 and a part of the driver circuit. The first processing circuit 211 performs heat suppression control when the required braking force FxRq is maintained. In heat suppression control, the first processing circuit 211 sets the motor rotation angle corresponding to the required braking force FxRq as the reference rotation angle θB. For example, the rotation angle detection value θ at the start of the heat suppression control can be considered as the motor rotation angle corresponding to the required braking force FxRq at that time. The first processing circuit 211 sets the sum of the reference rotation angle θB and the specified angle θA as the upper limit rotation angle θL. Then, the first processing circuit 211 alternately repeats increasing the rotation angle detection value θ from the reference rotation angle θB to the upper limit rotation angle θL at the first speed SPA, and decreasing the rotation angle detection value θ from the upper limit rotation angle θL to the reference rotation angle θB at the second speed SPB. During the execution of heat suppression control, the period during which the detected rotation angle θ is increased from the reference rotation angle θB to the upper limit rotation angle θL is described as the "increase period." During the execution of heat suppression control, the period during which the detected rotation angle θ is decreased from the upper limit rotation angle θL to the reference rotation angle θB is described as the "decrease period."

[0062] When the motor rotation angle fluctuates, the wheel pressure also fluctuates. Therefore, if the above heat suppression control is executed while the vehicle 10 is in motion, the deceleration of the vehicle 10 will fluctuate. Accordingly, in the braking device 100, the first processing circuit 211 reduces the above specified angle θA when the vehicle 10 is in motion compared to when the vehicle 10 is stopped.

[0063] Furthermore, when the motor rotation angle is vibrated by the execution of heat suppression control, the larger the absolute value of the first speed SPA, which is the rate of increase in the motor rotation angle, the larger the rate of increase in the wheel pressure. Also, the larger the absolute value of the second speed SPB, which is the rate of decrease in the motor rotation angle, the larger the rate of decrease in the wheel pressure. In particular, when the vehicle 10 is in motion, if the rate of increase or decrease in the wheel pressure is large, the rate of change in the deceleration of the vehicle 10 that accompanies the execution of heat suppression control will be large.

[0064] Therefore, in the braking device 100, the first processing circuit 211 makes the maximum speed while the vehicle 10 is moving, which is the larger of the absolute value of the first speed SPA and the absolute value of the second speed SPB, smaller than the maximum speed while the vehicle 10 is stopped, which is the larger of the absolute value of the first speed SPA and the absolute value of the second speed SPB when the vehicle 10 is stopped.

[0065] For example, the first processing circuit 211 makes the difference between the absolute value of the first speed SPA and the absolute value of the second speed SPB when the vehicle 10 is moving smaller than the difference between the absolute value of the first speed SPA and the absolute value of the second speed SPB when the vehicle 10 is stopped. In this embodiment, the first processing circuit 211 makes the difference between the absolute value of the first speed SPA and the absolute value of the second speed SPB when the vehicle 10 is moving 0 (zero).

[0066] When heat suppression control is in operation, the servo pressure may become excessively high compared to the target servo pressure PsbTra. This can occur when the wheel pressure is increased by the braking actuator 70 while the electric cylinder 51 is operating. When the braking actuator 70 is activated, the pump 79 draws brake fluid from the sixth passage 56 and discharges it into the brake fluid passage between the differential pressure control valve 73 and the retaining valve 74. Some of this brake fluid flows back into the sixth passage 56. As a result, the servo pressure, which is the fluid pressure in the sixth passage 56, increases. A large discrepancy between the detected servo pressure Psb and the target servo pressure PsbTra is undesirable for controlling the electric cylinder 51.

[0067] Therefore, the first processing circuit 211 sets the sum of the target servo pressure PsbTra and the allowable fluid pressure PsbA as the correction start servo pressure Perr. If the servo pressure detection value Psb becomes higher than the correction start servo pressure Perr while the first processing circuit 211 is executing the heat suppression control, it interrupts the heat suppression control. Then, the first processing circuit 211 executes the correction control. The correction control is a control that drives the first electric motor 513 so that the servo pressure detection value Psb returns to the target servo pressure PsbTra.

[0068] For example, in correction control, the first processing circuit 211 decreases the servo pressure detection value Psb by driving the first electric motor 513 so that the rotation angle detection value θ decreases at a speed higher than the second speed SPB. When the servo pressure detection value Psb falls below the target servo pressure PsbTra due to the decrease in the rotation angle detection value θ, the first processing circuit 211 increases the servo pressure detection value Psb by driving the first electric motor 513 so that the rotation angle detection value θ increases at a speed higher than the first speed SPA.

[0069] When the servo pressure detection value Psb reaches the target servo pressure PsbTra through the execution of this correction control, the first processing circuit 211 terminates the correction control. Then, the first processing circuit 211 resumes the heat suppression control.

[0070] When the vehicle 10 is moving, it is preferable that the controllability of the electric cylinder 51 is higher compared to when the vehicle 10 is stopped. Therefore, when the vehicle 10 is moving, the first processing circuit 211 lowers the allowable hydraulic pressure PsbA compared to when the vehicle 10 is stopped. As a result, when the vehicle 10 is moving, the first processing circuit 211 can perform correction control earlier compared to when the vehicle 10 is stopped.

[0071] <Motor Protection Processing> Referring to Figure 3, a series of processes performed by the first processing circuit 211 of the control device 200 to prevent the first electric motor 513 and a part of the driver circuit from becoming overheated will be described. This series of processes constitutes motor protection processing. The first processing circuit 211 repeatedly performs motor protection processing.

[0072] As shown in Figure 3, in step S11, the first processing circuit 211 determines whether or not a braking request has occurred. If the braking operating member 22 is being operated or if another control device has requested deceleration of the vehicle 10, it can be considered that a braking request has occurred. If the first processing circuit 211 determines that a braking request has occurred (S11: YES), the first processing circuit 211 proceeds to step S13. On the other hand, if the first processing circuit 211 determines that no braking request has occurred (S11: NO), the first processing circuit 211 terminates the motor protection process.

[0073] In step S13, the first processing circuit 211 determines whether the required braking force FxRq is maintained. For example, the first processing circuit 211 determines that the required braking force FxRq is maintained if the state in which the required braking force FxRq is substantially constant continues for a predetermined determination time TMth or longer. The condition that the required braking force FxRq is substantially constant means that the amount of change in the required braking force FxRq per unit time is within the error range.

[0074] If the first processing circuit 211 determines that the required braking force FxRq is maintained (S13: YES), the first processing circuit 211 proceeds to step S15. On the other hand, if the first processing circuit 211 determines that the required braking force FxRq is not maintained (S13: NO), the first processing circuit 211 terminates the motor protection process.

[0075] In step S15, the first processing circuit 211 determines whether the motor temperature TMP is higher than the determination temperature TMPth. An example of the motor temperature TMP is the estimated temperature of the first electric motor 513. For example, the first processing circuit 211 estimates the temperatures of multiple coils based on the energizing time of the first electric motor 513 and the changes in the current flowing through the multiple coils. The first electric motor 513 then obtains the highest estimated value among the estimated temperatures of the multiple coils as the motor temperature TMP. The determination temperature TMPth is the criterion for determining whether the motor temperature TMP is about to become too hot. If the motor temperature TMP is higher than the determination temperature TMPth (S15: YES), the first processing circuit 211 proceeds to step S17. On the other hand, if the motor temperature TMP is less than the determination temperature TMPth (S15: NO), the first processing circuit 211 terminates the motor protection process.

[0076] In step S17, the first processing circuit 211 sets the correction start servo pressure Perr. For example, the first processing circuit 211 sets the correction start servo pressure Perr to the sum of the target servo pressure PsbTra and the allowable fluid pressure PsbA. The allowable fluid pressure PsbA is the allowable deviation between the servo pressure detection value Psb and the target servo pressure PsbTra during the execution of the heat generation suppression control described later.

[0077] In this embodiment, the first processing circuit 211 varies the allowable hydraulic pressure PsbA depending on the driving state of the vehicle 10. For example, when the vehicle 10 is stopped, the first processing circuit 211 sets the allowable hydraulic pressure PsbA to a first allowable value P1. When the vehicle 10 is moving, the first processing circuit 211 sets the allowable hydraulic pressure PsbA to a second allowable value P2. The second allowable value P2 is smaller than the first allowable value P1. Therefore, when the vehicle 10 is moving, the first processing circuit 211 can set the allowable hydraulic pressure PsbA lower than when the vehicle 10 is stopped.

[0078] When the first processing circuit 211 sets the correction start servo pressure Perr, it proceeds to step S19. In step S19, the first processing circuit 211 determines whether the servo pressure detection value Psb is higher than the correction start servo pressure Perr. If the servo pressure detection value Psb is higher than the correction start servo pressure Perr (S19: YES), the first processing circuit 211 proceeds to step S25. On the other hand, if the servo pressure detection value Psb is less than or equal to the correction start servo pressure Perr (S19: NO), the first processing circuit 211 proceeds to step S21.

[0079] In step S21, the first processing circuit 211 executes a condition setting process. The condition setting process is a process for setting various conditions used when executing the heat suppression control described later. The condition setting process will be described later with reference to Figure 4. After executing the condition setting process, the first processing circuit 211 moves the process to step S23.

[0080] In step S23, the first processing circuit 211 performs heat suppression control. Heat suppression control is a control that prevents the first electric motor 513 from becoming overheated by causing the motor rotation angle to vibrate. Heat suppression control will be described later with reference to Figure 5. After that, the first processing circuit 211 temporarily terminates the motor protection process.

[0081] In step S25, the first processing circuit 211 performs correction control. Correction control is performed to resolve the discrepancy between the servo pressure detection value Psb and the target servo pressure PsbTra that occurred during the execution of heat suppression control. The correction control will be described later with reference to Figure 6. After performing the correction control, the first processing circuit 211 terminates the motor protection process.

[0082] <Condition Setting Process> Referring to Figure 4, an example of the condition setting process in step S21 described above will be explained in detail. In step S101, the first processing circuit 211 determines whether or not the vehicle 10 is in motion. If the first processing circuit 211 determines that the vehicle 10 is in motion (S101: YES), the first processing circuit 211 proceeds to step S107. On the other hand, if the first processing circuit 211 determines that the vehicle 10 is stopped (S101: NO), the first processing circuit 211 proceeds to step S103.

[0083] In step S103, the first processing circuit 211 sets the first rotation angle θ1 to a specified angle θA. When the detected rotation angle value θ is an electrical angle, an example of the first rotation angle θ1 is "180° × n", where "n" is a positive number greater than or equal to 1.

[0084] In the following step S105, the first processing circuit 211 sets the control mode MD for heat suppression control to stop mode. After that, the first processing circuit 211 finishes the condition setting process. In step S107, the first processing circuit 211 sets the second rotation angle θ2 to a specified angle θA. The second rotation angle θ2 is set to an electrical angle smaller than the first rotation angle θ1. For example, the second rotation angle θ2 is set to an electrical angle corresponding to the fluctuation period of the cogging torque generated when the first electric motor 513 is driven, or an electrical angle slightly larger than that electrical angle.

[0085] In the subsequent step S109, the first processing circuit 211 sets the driving mode to the heat suppression control mode MD. After that, the first processing circuit 211 completes the series of processes shown in Figure 4.

[0086] <Heat generation suppression control> Referring to Figure 5, an example of the heat generation suppression control in step S23 described above will be explained in detail. In step S201, the first processing circuit 211 determines whether the current time is an increasing period or not. If the current time is an increasing period (S201: YES), the first processing circuit 211 proceeds to step S203. On the other hand, if the current time is not an increasing period (S201: NO), the current time is a decreasing period, and therefore the first processing circuit 211 proceeds to step S221.

[0087] In step S203, the first processing circuit 211 determines whether the driving mode is set to control mode MD. If the driving mode is set to control mode MD (S203: YES), the first processing circuit 211 proceeds to step S207. On the other hand, if the stopping mode is not set to control mode MD (S203: NO), the first processing circuit 211 proceeds to step S205.

[0088] In step S205, the first processing circuit 211 sets the first increasing speed SPA1 to the first speed SPA. Then, the first processing circuit 211 proceeds to step S209. In step S207, the first processing circuit 211 sets the second increasing speed SPA2 to the first speed SPA. The second increasing speed SPA2 is smaller than the first increasing speed SPA1. Then, the first processing circuit 211 proceeds to step S209.

[0089] In step S209, the first processing circuit 211 increases the target rotation angle θTr at the first speed SPA set in step S205 or step S207, and performs motor rotation angle increase control to drive the first electric motor 513 based on the target rotation angle θTr. After that, the first processing circuit 211 completes the series of processes shown in Figure 5.

[0090] In step S221, the first processing circuit 211 determines whether the driving mode is set to control mode MD. If the driving mode is set to control mode MD (S221: YES), the first processing circuit 211 proceeds to step S225. On the other hand, if the stopping mode is not set to control mode MD (S221: NO), the first processing circuit 211 proceeds to step S223.

[0091] In step S223, the first processing circuit 211 sets the first decreasing speed SPB1 to the second speed SPB. The first decreasing speed SPB1 is smaller than the first increasing speed SPA1. Then, the first processing circuit 211 proceeds to step S227.

[0092] In step S225, the first processing circuit 211 sets the second decreasing speed SPB2 to the second speed SPB. The second decreasing speed SPB2 is greater than the first decreasing speed SPB1 and equal to the second increasing speed SPA2. Then, the first processing circuit 211 proceeds to step S227.

[0093] In step S227, the first processing circuit 211 reduces the target rotation angle θTr by the second speed SPB set in step S223 or step S225, and performs motor rotation angle reduction control to drive the first electric motor 513 based on the target rotation angle θTr. After that, the first processing circuit 211 completes the series of processes shown in Figure 5.

[0094] <Correction Control> Referring to Figure 6, an example of the correction control in step S25 described above will be explained in detail. In step S301, the first processing circuit 211 sets the sum of the second speed SPB and the first correction speed ΔSP1 to the third speed SPC. In the following step S303, the first processing circuit 211 sets the sum of the first speed SPA and the second correction speed ΔSP2 to the fourth speed SPD. For example, the second correction speed ΔSP2 is greater than the first correction speed ΔSP1.

[0095] Then, in step S305, the first processing circuit 211 performs a servo pressure reduction process to reduce the servo pressure based on the third speed SPC set in step S301. In the servo pressure reduction process, the first processing circuit 211 reduces the target rotation angle θTr of the first electric motor 513 by the third speed SPC and drives the first electric motor 513 based on the target rotation angle θTr.

[0096] In the following step S307, the first processing circuit 211 determines whether the detected servo pressure Psb is less than or equal to the target servo pressure PsbTra. If the detected servo pressure Psb is greater than or equal to the target servo pressure PsbTra (S307: NO), the first processing circuit 211 proceeds to step S305. That is, the first processing circuit 211 continues the servo pressure reduction process. On the other hand, if the detected servo pressure Psb is less than or equal to the target servo pressure PsbTra (S307: YES), the first processing circuit 211 proceeds to step S309. That is, the first processing circuit 211 performs the servo pressure reduction process until the detected servo pressure Psb becomes less than or equal to the target servo pressure PsbTra.

[0097] In step S309, the first processing circuit 211 performs a servo pressure increase process to increase the servo pressure based on the fourth speed SPD set in step S303. In the servo pressure increase process, the first processing circuit 211 increases the target rotation angle θTr of the first electric motor 513 by the fourth speed SPD and drives the first electric motor 513 based on the target rotation angle θTr.

[0098] In the following step S311, the first processing circuit 211 determines whether the detected servo pressure Psb has become equal to or greater than the target servo pressure PsbTra. If the detected servo pressure Psb is less than the target servo pressure PsbTra (S311: NO), the first processing circuit 211 proceeds to step S309. That is, the first processing circuit 211 continues the servo pressure increase process. On the other hand, if the detected servo pressure Psb has become equal to or greater than the target servo pressure PsbTra (S311: YES), the first processing circuit 211 terminates the servo pressure increase process and ends the series of processes shown in Figure 6.

[0099] <Operation and Effects of this Embodiment> Referring to Figure 7, the operation and effects when heat suppression control is performed will be described. (1) As shown in Figures 7(a) and (b), when the required braking force FxRq is maintained, the rotation angle detection value θ and the servo pressure detection value Psb of the first electric motor 513 of the electric cylinder 51 are substantially maintained. At timing t11, the duration of this state reaches the determination time TMth. Therefore, the first processing circuit 211 starts heat suppression control from timing t11.

[0100] In Figure 7(a), the change in the rotation angle detection value θ when heat suppression control is performed while the vehicle 10 is stopped is shown by a dashed line. On the other hand, in Figure 7(a), the change in the rotation angle detection value θ when heat suppression control is performed while the vehicle 10 is moving is shown by a solid line. In Figure 7(b), the change in the servo pressure detection value Psb when heat suppression control is performed while the vehicle 10 is stopped is shown by a dashed line. On the other hand, in Figure 7(b), the change in the servo pressure detection value Psb when heat suppression control is performed while the vehicle 10 is moving is shown by a solid line.

[0101] In the heat generation suppression control, the first processing circuit 211 alternately increases the detected rotation angle θ from the reference rotation angle θB to the upper limit rotation angle θL, and decreases the detected rotation angle θ from the upper limit rotation angle θL to the reference rotation angle θB.

[0102] As a result, the current flowing through the coils of the multiphase coils of the first electric motor 513 fluctuates. Therefore, it is suppressed that a large current continues to flow through only some of the coils of the multiphase coils of the first electric motor 513. Consequently, the first processing circuit 211 can suppress the temperature of some of the coils of the multiphase coils, and the electronic components in the driver circuit that regulate the current flowing through those coils, from becoming excessively high.

[0103] The upper limit rotation angle θL is the sum of the reference rotation angle θB and the specified angle θA. When the vehicle 10 is moving, the first processing circuit 211 reduces the specified angle θA compared to when the vehicle 10 is stopped. As a result, when heat suppression control is performed while the vehicle 10 is moving, the first processing circuit 211 can suppress large fluctuations in the deceleration of the vehicle 10.

[0104] Therefore, the braking device 100 can suppress the overheating of only some of the coils among the multiple phase coils of the first electric motor 513, and suppress the discomfort caused to the occupants due to fluctuations in the deceleration of the vehicle 10.

[0105] (2) During the increasing period while the heat suppression control is being executed, the rotation angle detected value θ is increased at the first speed SPA. During the decreasing period while the heat suppression control is being executed, the rotation angle detected value θ is decreased at the second speed SPB. The larger the first speed SPA, the greater the rate of increase in the deceleration of the vehicle 10 during the increasing period. The larger the second speed SPB, the greater the rate of decrease in the deceleration of the vehicle 10 during the decreasing period. And the larger the rate of change in deceleration, the greater the discomfort caused to the occupants of the vehicle 10 while the heat suppression control is being executed.

[0106] In this regard, in the braking system 100, the maximum speed while the vehicle 10 is moving, which is the larger of the first speed SPA and the second speed SPB, is smaller than the maximum speed while the vehicle 10 is stopped, which is the larger of the first speed SPA and the second speed SPB when the vehicle 10 is stopped. As a result, when the first processing circuit 211 performs heat suppression control while the vehicle 10 is moving, the rate of change in the deceleration of the vehicle 10 is less likely to become large. Therefore, even when the braking system 100 performs heat suppression control while the vehicle 10 is moving, it is possible to suppress causing discomfort to the occupants due to fluctuations in the deceleration of the vehicle 10.

[0107] (3) In the braking device 100, the difference between the first speed SPA and the second speed SPB when the vehicle 10 is moving is smaller than the difference between the first speed SPA and the second speed SPB when the vehicle 10 is stopped. As a result, the first processing circuit 211 can reduce the difference between the rate of increase in the deceleration of the vehicle 10 during the increase period and the rate of decrease in the deceleration of the vehicle 10 during the decrease period in the heat generation suppression control while the vehicle 10 is moving.

[0108] Next, referring to Figure 8, we will explain the operation and effects when correction control is performed because the servo pressure detection value Psb becomes too large while heat suppression control is being performed during vehicle 10 operation. The "rocking speed" shown in Figure 8(c) is the speed of the motor rotation angle when heat suppression control and correction control are performed. Here, increasing the wheel pressure by operating the braking actuator 70 is also called "downstream pressurization".

[0109] (4) As shown in Figures 8(a) to (d), the first processing circuit 211 starts heat suppression control at timing t21 while the vehicle 10 is in motion. At timing t22 while the heat suppression control is being executed, the required braking force FxRq increases. Therefore, the first processing circuit 211 terminates the heat suppression control. Then, the first processing circuit 211 drives the first electric motor 513 based on the required braking force FxRq. As a result, the servo pressure detection value Psb increases, and the wheel pressure increases. Consequently, the deceleration of the vehicle 10 increases.

[0110] In the example shown in Figure 8, the second processing circuit 221 activates the braking actuator 70 between timing t22 and timing t24. As a result, the wheel pressure becomes higher than the servo pressure detection value Psb.

[0111] Furthermore, in the example shown in Figure 8, the required braking force FxRq is again maintained at timing t23, which is between timing t22 and timing t24. Then, at timing t24, the conditions for executing the heat suppression control are met, and the first processing circuit 211 starts the heat suppression control.

[0112] When heat suppression control is performed in this manner, the servo pressure detection value Psb may increase sharply even though the rotation angle detection value θ is fluctuating between the reference rotation angle θB and the upper limit rotation angle θL. In the example shown in Figure 8, at timing t25, the servo pressure detection value Psb becomes higher than the correction start servo pressure Perr.

[0113] Then, the first processing circuit 211 interrupts the heat suppression control and executes correction control. In the correction control, the first processing circuit 211 drives the first electric motor 513 so that the servo pressure detection value Psb returns to the target servo pressure PsbTra as soon as possible. When the servo pressure detection value Psb returns to the target servo pressure PsbTra at timing t27, the first processing circuit 211 resumes the heat suppression control. As a result, the braking device 100 can suppress the deterioration of servo pressure controllability while preventing the first electric motor 513 from overheating.

[0114] (5) For example, in correction control, the first processing circuit 211 reduces the rotation angle detection value θ at a third speed SPC that is higher than the second speed SPB, thereby creating a state in which the servo pressure detection value Psb is less than the target servo pressure PsbTra. When the servo pressure detection value Psb falls below the target servo pressure PsbTra at timing t26, the first processing circuit 211 increases the rotation angle detection value θ at a fourth speed SPD that is higher than the first speed SPA. As a result, the first processing circuit 211 can quickly return the servo pressure detection value Psb to the target servo pressure PsbTra, and consequently restart the heat suppression control at an early stage.

[0115] (6) When the vehicle 10 is moving, it is preferable that the controllability of the servo pressure is higher than when the vehicle 10 is stopped. For this reason, the first processing circuit 211 lowers the allowable hydraulic pressure PsbA when the vehicle 10 is moving compared to when the vehicle 10 is stopped. As a result, when the vehicle 10 is moving, the first processing circuit 211 can perform correction control earlier.

[0116] <Examples of Modifications> The above embodiment can be implemented with the following modifications. The above embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0117] - The allowable hydraulic pressure PsbA when the vehicle 10 is in motion does not have to be lower than the allowable hydraulic pressure PsbA when the vehicle 10 is stopped. For example, the allowable hydraulic pressure PsbA when the vehicle 10 is in motion may be equal to the allowable hydraulic pressure PsbA when the vehicle 10 is stopped. Also, for example, the allowable hydraulic pressure PsbA when the vehicle 10 is in motion may be higher than the allowable hydraulic pressure PsbA when the vehicle 10 is stopped.

[0118] - The first processing circuit 211 executes correction control if the servo pressure detection value Psb becomes higher than the correction start servo pressure Perr during the execution of heat suppression control. The content of the correction control at this time may differ from that described in the above embodiment, as long as it can return the servo pressure detection value Psb to the target servo pressure PsbTra. For example, in the correction control, the first processing circuit 211 may drive the first electric motor 513 by feedback control that takes the deviation between the servo pressure detection value Psb and the target servo pressure PsbTra as input.

[0119] - In the heat suppression control, when the first electric motor 513 is driven at the second speed SPB so that the rotation angle detected value θ decreases, the servo pressure detected value Psb may fall below the target servo pressure PsbTra. In such cases, for example as shown in Figure 9, the first processing circuit 211 should perform a recovery process to quickly increase the rotation angle detected value θ of the first electric motor 513 until the servo pressure detected value Psb is equal to or greater than the target servo pressure PsbTra. As shown in Figures 9(a) and (b), at timing t31, while the rotation angle detected value θ is decelerating at the second speed SPB, the servo pressure detected value Psb falls below the target servo pressure PsbTra. Then, the first processing circuit 211 starts the recovery process from timing t32. In the recovery process, the first processing circuit 211 increases the servo pressure detection value Psb toward the target servo pressure PsbTra by driving the first electric motor 513 so that the rotation angle detection value θ increases at a speed higher than the first speed SPA, for example.

[0120] In the example shown in Figure 9, at timing t33, the servo pressure detection value Psb becomes equal to or greater than the target servo pressure PsbTra. Then, the first processing circuit 211 terminates the recovery process and starts the increase period during the execution of heat suppression control, thereby increasing the rotation angle detection value θ up to the upper limit rotation angle θL at the first speed SPA.

[0121] - The first processing circuit 211 does not need to set the first difference to 0 (zero) if it can make the first difference, which is the difference between the first speed SPA and the second speed SPB when the vehicle 10 is moving, smaller than the second difference, which is the difference between the first speed SPA and the second speed SPB when the vehicle 10 is stopped.

[0122] The first processing circuit 211 may configure the fluctuation period of the rotation angle detection value θ for heat suppression control when the vehicle 10 is running to be longer than the fluctuation period of the rotation angle detection value θ for heat suppression control when the vehicle 10 is stopped.

[0123] - In the heat suppression control when the vehicle 10 is running, the first processing circuit 211 does not have to make the first speed SPA equal to the second speed SPB. For example, the first processing circuit 211 may make the first speed SPA greater than the second speed SPB, or it may make the first speed SPA less than the second speed SPB.

[0124] - In the heat suppression control when the vehicle 10 is stopped, the first processing circuit 211 does not have to make the first speed SPA greater than the second speed SPB. For example, the first processing circuit 211 may make the first speed SPA equal to the second speed SPB, or it may make the first speed SPA less than the second speed SPB.

[0125] - If a temperature sensor is provided to detect the temperature of the first electric motor 513, the first processing circuit 211 may acquire the detected value of the temperature sensor as the motor temperature TMP. - The first processing circuit 211 may acquire the temperature of the driver circuit of the first electric motor 513 as the motor temperature TMP. The temperature of the driver circuit may be a value derived based on the detected value of a temperature sensor provided in or around the driver circuit. Alternatively, the temperature of the driver circuit may be a value derived based on the energizing time of the first electric motor 513 and the change in the current flowing through multiple coils.

[0126] - The first processing circuit 211 does not need to make the maximum speed while driving less than the maximum speed while stopped, as long as it can make the amplitude of the rotation angle detection value θ for heat suppression control when the vehicle 10 is moving less than the amplitude of the rotation angle detection value θ for heat suppression control when the vehicle 10 is stopped.

[0127] - The hydraulic pressure generator may have a different configuration from the hydraulic pressure generator 20 shown in Figure 1, as long as it is equipped with an electric cylinder 51. - The braking actuator may have a different configuration from the one shown in Figure 2, as long as it can pressurize the wheel pressure independently of the operation of the electric cylinder 51.

[0128] The control device 200 is not limited to one that includes a CPU and ROM and executes software processing. In other words, the control device 200 may have any of the following configurations: (a), (b), and (c).

[0129] (a) The control device 200 includes one or more processors that perform various processes according to a computer program. The processors include a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to perform the processes. The memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or dedicated computer.

[0130] (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, i.e., ASICs or FPGAs. ASIC is an abbreviation for "Application Specific Integrated Circuit". FPGA is an abbreviation for "Field Programmable Gate Array".

[0131] (c) The control device 200 comprises one or more processors that execute a part of the various processes according to a computer program, and one or more dedicated hardware circuits that execute the remaining processes of the various processes.

Claims

1. A braking device that generates braking force at the wheels of a vehicle by adjusting the hydraulic pressure of a wheel cylinder, comprising: an electric cylinder configured such that when a piston moves forward within the cylinder in accordance with an increase in the motor rotation angle, which is the rotation angle of an electric motor, brake fluid is discharged from the cylinder through an output port; a supply passage that guides brake fluid to the wheel cylinder when brake fluid is discharged from the output port of the electric cylinder; and a control device that drives the electric motor, wherein the control device performs heat suppression control that, when a required braking force is maintained, alternately increases the motor rotation angle at a first speed from a reference rotation angle, which is the motor rotation angle corresponding to the required braking force, to an upper limit rotation angle, which is the sum of the reference rotation angle and a specified angle, and decreases the motor rotation angle at a second speed from the upper limit rotation angle to the reference rotation angle, and when the vehicle is running, the specified angle is smaller than when the vehicle is stopped.

2. The braking device according to claim 1, wherein the control device makes the maximum speed while the vehicle is in motion, which is the larger of the absolute value of the first speed and the absolute value of the second speed, less than the maximum speed while the vehicle is stopped, which is the larger of the absolute value of the first speed and the absolute value of the second speed when the vehicle is stopped.

3. The braking device according to claim 1, wherein the control device makes the difference between the absolute value of the first speed and the absolute value of the second speed when the vehicle is moving smaller than the difference between the absolute value of the first speed and the absolute value of the second speed when the vehicle is stopped.

4. The braking device according to any one of claims 1 to 3, wherein the discharge pressure of the brake fluid of the electric cylinder is the servo pressure, the servo pressure corresponding to the required braking force is the target servo pressure, the sum of the target servo pressure and the allowable fluid pressure is the correction start servo pressure, and the control device interrupts the heat suppression control and performs correction control to drive the electric motor so that the servo pressure returns to the target servo pressure when the servo pressure becomes higher than the correction start servo pressure while the heat suppression control is being performed.

5. The braking device according to claim 4, wherein the control device, in the correction control, reduces the motor rotation angle at a speed higher than the second speed, and when the servo pressure falls below the target servo pressure due to the reduction in the motor rotation angle, increases the motor rotation angle at a speed higher than the first speed, and when the servo pressure reaches the target servo pressure due to the execution of the correction control, terminates the correction control and resumes the heat suppression control.

6. The braking device according to claim 4, wherein the control device lowers the allowable hydraulic pressure when the vehicle is moving compared to when the vehicle is stopped.

7. The braking device according to claim 1, wherein the discharge pressure of the brake fluid of the electric cylinder is the servo pressure, and the servo pressure corresponding to the required braking force is the target servo pressure, and the control device, in the heat suppression control, reduces the motor rotation angle at the second speed, and when the servo pressure falls below the target servo pressure due to the reduction in the motor rotation angle, performs a recovery process to temporarily increase the motor rotation angle at a speed higher than the first speed, and thereafter, when the servo pressure reaches the target servo pressure, terminates the recovery process, restarts the heat suppression control, and increases the motor rotation angle at the first speed up to the upper limit rotation angle.

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