Braking device

Abstract

This braking device 100 comprises: a second supply liquid path 722 connected to a wheel cylinder 16 for a rear wheel 11r; a holding valve 74 provided in the second supply liquid path 722; a pressure device 50; and a control device 90. A processing circuit 91 of the control device 90, when an increase regulation control is implemented in a situation where the holding valve 74 is open and a regenerative braking force is being generated in the rear wheel 11r, activates a regeneration device 200 and the pressurizing device 50 so that the regenerative braking force is reduced and the friction braking force is increased by increasing in supply pressure. When the regenerative braking force reaches a prescribed value or less, the processing circuit 91 regulates an increase in wheel pressure by closing the holding valve 74.

Description

braking device

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

[0002] Japanese Patent Application Laid-Open No. 2006-129999 discloses a braking device for a vehicle capable of generating both regenerative braking force and friction braking force at the rear wheels. The control device of the braking device may perform front / rear braking force distribution control to adjust the distribution of braking force between the front and rear wheels even when regenerative braking force is being generated at the rear wheels. However, even when performing front / rear braking force distribution control, if the vehicle speed is equal to or greater than a threshold speed, the control device cancels the state in which regenerative braking force is being generated at the rear wheels.

[0003] JP 2013-183502 A

[0004] A known vehicle includes a friction brake that generates a friction braking force on a wheel corresponding to the wheel pressure, which is the hydraulic pressure in the wheel cylinder, and a hydraulic circuit that controls the wheel pressure. For example, the hydraulic circuit includes a holding valve that closes to restrict the supply of brake fluid to the wheel cylinder. When the holding valve is closed, brake fluid is no longer supplied to the wheel cylinder, and wheel pressure cannot be increased. In other words, when the holding valve is closed, the friction braking force cannot be increased.

[0005] When a braking system includes the hydraulic circuit, the control device of the braking system maintains wheel pressure by closing the holding valve to maintain the frictional braking force generated at the rear wheels during front / rear braking force distribution control. At this time, to release the regenerative braking force generated at the rear wheels, the control device reduces the regenerative braking force to zero or a value close to zero. However, because the holding valve is closed, the control device cannot increase the wheel pressure. In other words, the control device cannot compensate for the decrease in regenerative braking force by increasing the frictional braking force. As a result, the vehicle deceleration decreases in accordance with the decrease in regenerative braking force.

[0006] The braking control for closing the hold valve may be other than the front / rear brake force distribution control. If the regenerative braking force is reduced to a predetermined value while such other control is being performed, the same problem as described above may occur.

[0007] A braking device for solving the above problems is applied to a vehicle that includes a regenerative wheel capable of generating both regenerative braking force and friction braking force, a regenerative device configured to adjust the regenerative braking force generated by the regenerative wheel, and a wheel cylinder, and that generates friction braking force at the regenerative wheel according to wheel pressure, which is hydraulic pressure in the wheel cylinder. The braking device includes a flow path through which brake fluid flows, a supply fluid line connected to the wheel cylinder, a holding valve that is an electromagnetic valve provided in the supply fluid line and closes to regulate an increase in the wheel pressure, an electric pressure device configured to adjust the supply pressure, which is hydraulic pressure in a portion of the supply fluid line opposite the wheel cylinder across the holding valve, and a control device that performs increase regulation control to regulate an increase in total braking force, which is the sum of the regenerative braking force and friction braking force generated by the regenerative wheel. When the control device performs the increase restriction control under the condition that the holding valve is open and regenerative braking force is being generated at the regenerative wheel, the control device executes a regenerative switching process that activates the regenerative device and the pressurizing device so that the regenerative braking force decreases and the frictional braking force increases by increasing the supply pressure, and when the regenerative switching process causes the regenerative braking force to fall below a predetermined value, a valve closing process that restricts the increase in the wheel pressure by closing the holding valve.

[0008] The braking device has the effect of being able to reduce the regenerative braking force generated at the regenerative wheels to a predetermined value or less while suppressing a decrease in the deceleration of the vehicle when the increase restriction control is implemented.

[0009] Fig. 1 is a schematic diagram showing a vehicle equipped with a braking device of an embodiment. Fig. 2 is a flowchart showing a series of processes executed by a first processing circuit of a control device equipped in the braking device of Fig. 1. Fig. 3 is a flowchart showing a series of processes executed by a second processing circuit of a control device equipped in the braking device of Fig. 1. Fig. 4 is a timing chart when the vehicle braking force request value is not increased during execution of regenerative substitution processing. Fig. 5 is a timing chart when the vehicle braking force request value is increased during execution of regenerative substitution processing.

[0010] An embodiment of a braking device will be described below with reference to FIGS. 1 to 5. FIG. 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 also has friction brakes 15, the same number as the number of wheels, and a regenerative device 200 configured to be able to adjust the regenerative braking force FxRR generated at the two rear wheels 11r. In this embodiment, the rear wheels 11r correspond to "regenerative wheels" that are capable of generating both regenerative braking force and friction braking force. On the other hand, since the front wheels 11f do not generate regenerative braking force, the front wheels 11f are sometimes referred to as "non-regenerative wheels."

[0011] When the total braking force generated at the rear wheels 11r is defined as "rear wheel braking force FxR," the sum of the regenerative braking force FxRR and the friction braking force FxRF generated at the rear wheels 11r becomes the rear wheel braking force FxR. When the total braking force generated at the front wheels 11f is defined as "front wheel braking force FxF," the front wheel braking force FxF is equal to the friction braking force FxFF generated at the front wheels 11f. When the braking force of the vehicle is defined as "vehicle braking force Fx," the sum of the rear wheel braking force FxR and the front wheel braking force FxF becomes the vehicle braking force Fx.

[0012] <Regenerative Device> The regenerative device 200 includes a motor generator 201 and a regenerative control unit 202 that controls the motor generator 201. When the motor generator 201 functions as an electric motor, a driving force is transmitted from the motor generator 201 to the multiple rear wheels 11r. On the other hand, when the motor generator 201 functions as a generator, a regenerative braking force FxRR corresponding to the amount of power generated by the motor generator 201 is generated at the multiple rear wheels 11r.

[0013] An example of the regeneration control unit 202 is an electronic control device. In this case, the regeneration control unit 202 has a CPU and a memory. The memory stores a control program to be executed by the CPU. The regeneration control unit 202 operates the motor generator 201 by the CPU executing the control program.

[0014] The regenerative control unit 202 is configured to be able to send and receive various information to and from a control device 90 of the braking system 100, which will be described later, via an in-vehicle network. As will be described in detail later, when braking the vehicle, the regenerative control unit 202 adjusts the regenerative braking force FxRR by sending and receiving information to and from the control device 90.

[0015] <Friction Brake> The plurality of friction brakes 15 each generate a friction braking force at the corresponding wheels 11f, 11r. 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.

[0016] <Brake Device> The brake device 100 adjusts the vehicle braking force Fx by controlling the wheel pressure Pw of the plurality of wheel cylinders 16. The brake device 100 includes a hydraulic pressure generating device 20, a brake actuator 70, and a control device 90. 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 plurality of wheel cylinders 16. In this embodiment, the hydraulic pressure generating device 20 corresponds to a "first brake unit," and the brake actuator 70 corresponds to a "second brake unit" disposed between the first brake unit and the wheel cylinders 16. The control device 90 controls the operation of the hydraulic pressure generating device 20 and the brake actuator 70.

[0017] <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 device 50. The reservoir tank 21 stores brake fluid and is open to the atmosphere.

[0018] The brake operating member 22 is a member that is operated by the driver of the vehicle to decelerate 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.

[0019] <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 also includes an input hydraulic pressure sensor 353 as a sensor for detecting hydraulic pressure. A detection signal from the input hydraulic pressure sensor 353 is input to the control device 90.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The first flow path 331 connects a first hydraulic circuit 711 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.

[0032] 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 90 is operating, the first control valve 341 is opened and the second control valve 342 is closed.

[0033] The input hydraulic pressure sensor 353 detects the hydraulic pressure in the second hydraulic chamber R2. For example, the input hydraulic pressure sensor 353 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 input hydraulic pressure sensor 353 will be referred to as the "input hydraulic pressure Pgs."

[0034] <Pressurizing Device> The pressurizing device 50 includes a pump 51, a supply flow path 54, and a return flow path 55. The pump 51 is an electric pump powered by a first electric motor 52. The pump 51 pressurizes brake fluid pumped up from an input port 51a and discharges it from an output port 51b. The supply flow path 54 connects the reservoir tank 21 to the input port 51a. The return flow path 55 is connected to the output port 51b and returns the brake fluid discharged from the output port 51b to the reservoir tank 21. For example, one end of the return flow path 55 is connected to the reservoir tank 21. A check valve 56 is provided in the return flow path 55. The check valve 56 prevents brake fluid from flowing in the return flow path 55 toward the output port 51b.

[0035] The pressurizing device 50 includes a hydraulic pressure adjustment unit 60, a first servo pressure sensor 65, and a second servo pressure sensor 66. The hydraulic pressure adjustment unit 60 is installed in the return flow path 55 on the opposite side of the check valve 56 from the output port 51b. The hydraulic pressure adjustment unit 60 has a first pressure adjustment valve 61 and a second pressure adjustment valve 62. The first pressure adjustment valve 61 and the second pressure adjustment valve 62 are normally-open linear solenoid valves. The second pressure adjustment valve 62 is installed in the return flow path 55 on the opposite side of the check valve 56 from the first pressure adjustment valve 61.

[0036] Therefore, when brake fluid is being discharged from the output port 51b of the pump 51, the first pressure regulating valve 61 can adjust the pressure difference between a portion of the return flow path 55 between the first pressure regulating valve 61 and the check valve 56 and a portion of the return flow path 55 between the first pressure regulating valve 61 and the second pressure regulating valve 62. The second pressure regulating valve 62 can adjust the pressure difference between a portion of the return flow path 55 between the first pressure regulating valve 61 and the second pressure regulating valve 62 and a portion of the return flow path 55 between the second pressure regulating valve 62 and the end of the return flow path 55 on the reservoir tank 21 side. In other words, by operating the first pressure regulating valve 61, the upstream supply pressure, which is the hydraulic pressure in the portion of the return flow path 55 between the first pressure regulating valve 61 and the check valve 56, is adjusted. In addition, by operating the first pressure regulating valve 61 and the second pressure regulating valve 62, the downstream supply pressure, which is the hydraulic pressure in the portion of the return flow path 55 between the first pressure regulating valve 61 and the second pressure regulating valve 62, is adjusted.

[0037] The first servo pressure sensor 65 detects the discharge pressure of the brake fluid from the pump 51. For example, the first servo pressure sensor 65 is provided in a portion of the return flow path 55 between the check valve 56 and the first pressure regulating valve 61. In this case, it can also be said that the first servo pressure sensor 65 detects the upstream supply pressure. In the following description, the fluid pressure based on the detection signal of the first servo pressure sensor 65 will be referred to as the "first servo pressure Pp."

[0038] The second servo pressure sensor 66 is provided in a portion of the return flow path 55 between the first pressure regulating valve 61 and the second pressure regulating valve 62. Therefore, it can be said that the second servo pressure sensor 66 detects the downstream supply pressure. In the following description, the hydraulic pressure based on the detection signal of the second servo pressure sensor 66 will be referred to as the "second servo pressure Po."

[0039] The portion of the return flow path 55 between the check valve 56 and the first pressure regulating valve 61 is connected to the servo chamber Rs of the master unit 30 via a first connecting flow path 67. The portion of the return flow path 55 between the first pressure regulating valve 61 and the second pressure regulating valve 62 is connected to a second hydraulic circuit 712 of the brake actuator 70 (described later) via a second connecting flow path 68.

[0040] The pressurizing device 50 operates the hydraulic pressure adjusting unit 60 while the pump 51 is discharging brake fluid, thereby supplying brake fluid at a regulated pressure to the brake actuator 70 and the master cylinder 31. Specifically, the brake fluid adjusted by the first pressure adjusting valve 61 of the hydraulic pressure adjusting unit 60 is supplied from the first connecting flow path 67 to the servo chamber Rs of the master device 30. This increases the hydraulic pressure in the servo chamber Rs, causing the master piston 43 to move forward. This increases the hydraulic pressure in the master chamber Rm, causing brake fluid to be supplied from the master chamber Rm to the first hydraulic pressure circuit 711 of the brake actuator 70. As a result, brake fluid is supplied to two of the multiple wheel cylinders 16 connected to the first hydraulic pressure circuit 711. This increases the wheel pressure Pw in the two wheel cylinders 16, thereby increasing the front wheel frictional braking force FxFF generated at the front wheels 11f. Hereinafter, the wheel pressure Pw of the wheel cylinder 16 for the front wheel 11f may also be referred to as "front wheel pressure Pwf."

[0041] Furthermore, the brake fluid whose pressure is adjusted by the second pressure adjusting valve 62 of the fluid pressure adjusting unit 60 is supplied from the second connecting flow path 68 to the second fluid pressure circuit 712 of the brake actuator 70. Then, of the multiple wheel cylinders 16, brake fluid is supplied to two wheel cylinders 16 connected to the second fluid pressure circuit 712. This increases the wheel pressure Pw of those two wheel cylinders 16, thereby increasing the rear wheel friction braking force FxRF, which is the friction braking force generated at the rear wheel 11r. Hereinafter, the wheel pressure Pw of the wheel cylinder 16 for the rear wheel 11r may also be referred to as the "rear wheel pressure Pwr."

[0042] <Brake Actuator> The brake actuator 70 has a first hydraulic pressure circuit 711 and a second hydraulic pressure circuit 712. The two wheel cylinders 16 for the front wheels 11f are connected to the first hydraulic pressure circuit 711. The two wheel cylinders 16 for the rear wheels 11r are connected to the second hydraulic pressure circuit 712.

[0043] The first hydraulic circuit 711 includes a first supply fluid line 721 and a first differential pressure control valve 731 provided in the first supply fluid line 721. The first supply fluid line 721 is a brake fluid line connecting the two wheel cylinders 16 for the front wheels 11f to the first flow path 331. The first differential pressure control valve 731 is a normally open linear solenoid valve. The first differential pressure control valve 731 can adjust the differential pressure between the portion of the first supply fluid line 721 on the first flow path 331 side and the portion on the wheel cylinder 16 side. For example, the first differential pressure control valve 731 can generate a larger differential pressure as the current flowing through its solenoid increases.

[0044] The first hydraulic pressure circuit 711 is provided with a master pressure sensor 85 as a sensor for detecting the hydraulic pressure of the brake fluid. The master pressure sensor 85 is connected to a portion of the first supply hydraulic line 721 that is closer to the first flow path 331 than the first differential pressure control valve 731. As described above, the first flow path 331 is connected to the master chamber Rm of the master device 30. Therefore, it can be said that the master pressure sensor 85 detects the hydraulic pressure of the master chamber Rm. Hereinafter, the hydraulic pressure based on the detection signal of the master pressure sensor 85 will be referred to as the "master pressure Pmc."

[0045] The first supply fluid line 721, at a portion closer to the wheel cylinders 16 than the first differential pressure control valve 731, branches into two paths 72a and 72b. The path 72a is connected to one of the wheel cylinders 16 for the two front wheels 11f, while the path 72b is connected to the other of the wheel cylinders 16 for the two front wheels 11f. A holding valve 74 is installed in each of the two paths 72a and 72b. That is, the holding valve 74 is installed in a portion of the first supply fluid line 721 closer to the wheel cylinders 16 than the first differential pressure control valve 731. The holding valve 74 is a normally open solenoid valve. When the holding valve 74 is closed, it restricts the supply of brake fluid to the wheel cylinders 16. As a result, an increase in the front wheel pressure Pwf is restricted. That is, the holding valve 74 is an solenoid valve installed in the first supply fluid line 721 that is closed to restrict an increase in the front wheel pressure Pwf.

[0046] The first hydraulic circuit 711 has a first pressure-reducing reservoir 751 that stores brake fluid, and a first pressure-reducing fluid passage 761 that is connected to the first pressure-reducing reservoir 751. The first pressure-reducing fluid passage 761 is a brake fluid passage that connects the first pressure-reducing reservoir 751 to the portions of the passages 72a and 72b that are closer to the wheel cylinder 16 than the holding valve 74. Pressure-reducing valves 77, which are normally-closed solenoid valves, are installed in the portions of the first pressure-reducing fluid passage 761 that are connected to the passage 72a and the passage 72b, respectively.

[0047] The first hydraulic circuit 711 has a first pump 791 powered by the second electric motor 78, and a first return fluid path 801. The first pump 791 pumps up brake fluid from the first reduced-pressure reservoir 751 and discharges the brake fluid to a portion of the first supply fluid path 721 between the first differential pressure control valve 731 and the holding valve 74. The first return fluid path 801 is a brake fluid path that is connected to the first reduced-pressure reservoir 751 and a portion of the first supply fluid path 721 that is closer to the first flow path 331 than the first differential pressure control valve 731.

[0048] The second hydraulic circuit 712 includes a second supply fluid line 722 and a second differential pressure control valve 732 provided in the second supply fluid line 722. The second supply fluid line 722 is a brake fluid line connecting the two wheel cylinders 16 for the rear wheels 11r to the second connecting flow path 68. The second differential pressure control valve 732 is a normally open linear solenoid valve. The second differential pressure control valve 732 can adjust the differential pressure between the portion of the second supply fluid line 722 on the second connecting flow path 68 side and the portion on the wheel cylinder 16 side. For example, the second differential pressure control valve 732 can generate a larger differential pressure as the current flowing through its solenoid increases.

[0049] The portion of the second supply fluid path 722 closer to the wheel cylinder 16 than the second differential pressure control valve 732 branches into two paths 72c and 72d. Path 72c is connected to one of the two wheel cylinders 16 for the rear wheel 11r, while path 72d is connected to the other of the two wheel cylinders 16 for the rear wheel 11r. A holding valve 74 is installed in each of the two paths 72c and 72d. The holding valve 74 is a normally open solenoid valve. When the holding valve 74 is closed, an increase in the rear wheel pressure Pwr is restricted. In other words, the holding valve 74 is installed in the second supply fluid path 722 and is a solenoid valve that is closed to restrict an increase in the rear wheel pressure Pwr, which is the wheel pressure Pw in the wheel cylinder 16 for the regenerative wheel, the rear wheel 11r.

[0050] The second hydraulic circuit 712 has a second pressure-reducing reservoir 752 that stores brake fluid, and a second pressure-reducing fluid path 762 that is connected to the second pressure-reducing reservoir 752. The second pressure-reducing fluid path 762 is a brake fluid path that connects the second pressure-reducing reservoir 752 to the portions of paths 72c and 72d that are closer to the wheel cylinder 16 than the holding valve 74. Pressure-reducing valves 77 are installed in the portions of the second pressure-reducing fluid path 762 that are connected to path 72c and the portions of the second pressure-reducing fluid path 762 that are connected to path 72d.

[0051] The second hydraulic circuit 712 has a second pump 792 powered by the second electric motor 78, and a second return fluid line 802. The second pump 792 pumps up brake fluid from the second reduced-pressure reservoir 752 and discharges the brake fluid to a portion of the second supply fluid line 722 between the second differential pressure control valve 732 and the holding valve 74. The second return fluid line 802 is a brake fluid line that is connected to the second reduced-pressure reservoir 752 and a portion of the second supply fluid line 722 that is closer to the second connecting flow line 68 than the second differential pressure control valve 732.

[0052] <Control Device> The control device 90 includes a plurality of processing circuits. Of the plurality of processing circuits, a first processing circuit 91 operates the hydraulic pressure generating device 20, and a second processing circuit 92 operates the brake actuator 70. These plurality of processing circuits 91, 92 are each configured to be able to send and receive various types of information via the in-vehicle network.

[0053] An example of the processing circuits 91, 92 is an electronic control device. In this case, each of the multiple processing circuits 91, 92 has a CPU and a memory that stores a control program executed by the CPU. The first processing circuit 91 operates the hydraulic pressure generating device 20 by the CPU executing the control program stored in the memory. The second processing circuit 92 operates the brake actuator 70 by the CPU executing the control program stored in the memory.

[0054] The control device 90 receives detection signals from a plurality of sensors provided in the hydraulic pressure generating device 20 and the brake actuator 70. The plurality of sensors includes the above-mentioned plurality of hydraulic pressure sensors 353, 65, 66, 85 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."

[0055] <Regenerative Cooperative Control> The control device 90 performs regenerative cooperative control when braking the vehicle. Regenerative cooperative control is braking control that generates both regenerative braking force and friction braking force in the vehicle. For example, the control device 90 derives a vehicle braking force request value FxRq that increases as the braking operation amount X increases. The vehicle braking force request value FxRq is a request value for the vehicle braking force Fx. Next, the control device 90 derives a target regenerative braking force FxRRTr, a target front wheel braking force FxFTr, and a target rear wheel friction braking force FxRFTr based on the vehicle braking force request value FxRq. The target regenerative braking force FxRRTr is a target value for the regenerative braking force FxRR to be generated at the rear wheels 11r. The target rear wheel friction braking force FxRFTr is a target value for the rear wheel friction braking force FxRF, which is a friction braking force to be generated at the rear wheels 11r. The target front wheel braking force FxFTr is a target value of the front wheel braking force FxF. In this embodiment, the front wheels 11f are non-regenerative wheels. Therefore, the target front wheel braking force FxFTr can also be said to be a target value of the front wheel friction braking force FxFF, which is the friction braking force generated at the front wheels 11f.

[0056] The first processing circuit 91 of the control device 90 then operates the pressurizing device 50 of the hydraulic pressure generating device 20 based on the target front wheel braking force FxFTr and the target rear wheel friction braking force FxRFTr. The second processing circuit 92 of the control device 90 also transmits the target regenerative braking force FxRRTr to the regenerative control unit 202.

[0057] When the regenerative control unit 202 receives the target regenerative braking force FxRRTr from the control device 90, it controls the amount of power generated by the motor generator 201 so that the regenerative braking force FxRR becomes the target regenerative braking force FxRRTr. The regenerative control unit 202 also transmits the regenerative braking force FxRR to the control device 90 as the effective value of the regenerative braking force. The first processing circuit 91 then acquires the regenerative braking force FxRR transmitted by the regenerative control unit 202.

[0058] <Front / rear braking force distribution control> The control device 90 may perform front / rear braking force distribution control when braking the vehicle. Hereinafter, the front / rear braking force distribution control will be referred to as "EBD control." The control device 90 starts EBD control when it determines that the rear wheels 11r are showing a tendency to lock before the front wheels 11f when braking the vehicle. In EBD control, the control device 90 allows an increase in the front wheel braking force FxF, but restricts an increase in the rear wheel braking force FxR. In other words, the EBD control is an example of "increase restriction control" that restricts an increase in the rear wheel braking force FxR, which is the total braking force generated by the regenerative wheels.

[0059] Regardless of whether regenerative braking force FxRR is being generated at the rear wheels 11r, the control device 90 starts EBD control when the execution conditions for EBD control are met. In EBD control when regenerative braking force FxRR is not being generated at the rear wheels 11r, the control device 90 closes the retention valves 74 for the rear wheels 11r, i.e., the two retention valves 74 provided in the second hydraulic circuit 712. This restricts the increase in the rear wheel pressure Pwr, thereby restricting the increase in the rear wheel friction braking force FxRF, i.e., the rear wheel braking force FxR. If the vehicle braking force request value FxRq increases during EBD control, the control device 90 activates the pressurizing device 50 to increase the first servo pressure Pp and the second servo pressure Po. This causes the control device 90 to increase the front wheel pressure Pwf, i.e., the front wheel friction braking force FxFF. At this time, since the holding valve 74 for the rear wheel 11r is closed, even if the second servo pressure Po increases, the rear wheel pressure Pwr does not increase, so the rear wheel friction braking force FxRF is held.

[0060] During EBD control when a regenerative braking force FxRR is generated at the rear wheel 11r, the control device 90 executes a regenerative substitution process to substitute the regenerative braking force FxRR for a rear wheel friction braking force FxRF. Specifically, during the regenerative substitution process, the control device 90 operates the pressurizing device 50 to increase the second servo pressure Po. At this time, the control device 90 increases the second servo pressure Po at a rate that corresponds to the rate at which the regenerative braking force FxRR decreases. Because the pressure retention valve 74 for the rear wheel 11r is open, the rear wheel pressure Pwr increases in accordance with the increase in the second servo pressure Po. As a result, the control device 90 can substitute the regenerative braking force FxRR for the rear wheel friction braking force FxRF.

[0061] When the regenerative braking force FxRR becomes equal to or less than a predetermined value due to the regenerative switching process, the control device 90 executes a valve closing process to restrict an increase in the rear wheel pressure Pwr. In the valve closing process, the control device 90 restricts an increase in the rear wheel pressure Pwr by closing the holding valve 74 for the rear wheel 11r. In other words, when the termination condition for the regenerative switching process is met, the control device 90 terminates the regenerative switching process and starts the opening / closing process.

[0062] In this embodiment, 0 (zero) is set as the predetermined value. Note that the predetermined value may be greater than 0 (zero) as long as it is a value close to 0 (zero). <Series of Processing Executed by First Processing Circuit During EBD Control> A series of processing executed by the first processing circuit 91 when EBD control is being performed will be described with reference to FIG. 2. The first processing circuit 91 repeatedly executes this series of processing at every predetermined control cycle.

[0063] In step S11, the first processing circuit 91 derives a vehicle braking force request value FxRq. When the driver is performing a braking operation, the first processing circuit 91 derives a vehicle braking force request value FxRq that increases as the braking operation amount X increases. When another control device requests the control device 90 to decelerate, the first processing circuit 91 derives a braking force corresponding to the request from the other control device as the vehicle braking force request value FxRq.

[0064] In the next step S13, the first processing circuit 91 derives the target rear wheel braking force FxRTr and the target front wheel braking force FxFTr. For example, the first processing circuit 91 derives the target rear wheel braking force FxRTr and the target front wheel braking force FxFTr based on the vehicle braking force request value FxRq and the distribution rate α. The distribution rate α is a target value for the proportion of the front wheel braking force FxF in the vehicle braking force Fx. In this case, the first processing circuit 91 derives the target front wheel braking force FxFTr as the product of the vehicle braking force request value FxRq and the distribution rate α. The first processing circuit 91 derives the target rear wheel braking force FxRTr by subtracting the target front wheel braking force FxFTr from the vehicle braking force request value FxRq. Note that the distribution rate α is a value that varies depending on the vehicle state, road surface conditions, etc.

[0065] In the next step S15, the first processing circuit 91 derives the target rear wheel friction braking force FxRFTr. The first processing circuit 91 acquires the regenerative braking force FxRR as the effective value of the regenerative braking force from the regenerative control unit 202 at every predetermined communication cycle. Therefore, the first processing circuit 91 subtracts the latest value of the regenerative braking force FxRR from the target rear wheel braking force FxRTr, and derives the result as the target rear wheel friction braking force FxRFTr.

[0066] Then, in step S17, the first processing circuit 91 operates the pressurizing device 50 based on the target front wheel braking force FxFTr and the target rear wheel friction braking force FxRFTr. For example, the processing circuit 91 operates the pressurizing device 50 so that the first servo pressure Pp becomes a hydraulic pressure corresponding to the target front wheel braking force FxFTr and the second servo pressure Po becomes a hydraulic pressure corresponding to the target rear wheel friction braking force FxRFTr. Thereafter, the first processing circuit 91 temporarily ends the series of processes shown in FIG. 2.

[0067] <Series of processes executed by the second processing circuit during EBD control> A series of processes executed by the second processing circuit 92 when EBD control is being performed will be described with reference to Fig. 3. The second processing circuit 92 repeatedly executes this series of processes at predetermined control cycles.

[0068] In step S31, the second processing circuit 92 determines whether the execution conditions for EBD control are met. If the second processing circuit 92 determines that the execution conditions are met (S31: YES), the process proceeds to step S33. On the other hand, if the second processing circuit 92 determines that the execution conditions are not met (S31: NO), the process temporarily ends.

[0069] In step S33, the second processing circuit 92 determines whether regenerative cooperative control is being performed. For example, if the target regenerative braking force FxRRTr is greater than 0 (zero), it is determined that regenerative cooperative control is being performed. If the target regenerative braking force FxRRTr is 0 (zero), it is determined that regenerative cooperative control is not being performed. If the second processing circuit 92 can acquire the regenerative braking force FxRR, the second processing circuit 92 may determine whether regenerative cooperative control is being performed based on the acquired regenerative braking force FxRR. If the second processing circuit 92 determines that regenerative cooperative control is being performed (S33: YES), it proceeds to step S35. On the other hand, if the second processing circuit 92 determines that regenerative cooperative control is not being performed (S33: NO), it proceeds to step S45.

[0070] In step S35, the second processing circuit 92 derives the increase rate ΔFxR of the target rear wheel braking force FxRTr. The second processing circuit 92 acquires the target rear wheel braking force FxRTr from the first processing circuit 91 at predetermined communication intervals. In this case, the second processing circuit 92 derives the increase rate ΔFxR of the target rear wheel braking force FxRTr per unit time based on the change in the target rear wheel braking force FxRTr acquired from the first processing circuit 91. In this case, if the target rear wheel braking force FxRTr is increasing, the increase rate ΔFxR will be a positive value. If the target rear wheel braking force FxRTr is maintained, the increase rate ΔFxR will be 0 (zero). If the target rear wheel braking force FxRTr is decreasing, the increase rate ΔFxR will be a negative value.

[0071] In the following step S37, the second processing circuit 92 derives the decrease amount ΔFx. The decrease amount ΔFx is a parameter that defines the decrease rate of the regenerative braking force FxRR. The second processing circuit 92 derives the decrease amount ΔFx based on the increase rate ΔFxR. For example, the second processing circuit 92 determines whether the target rear wheel braking force FxRTr is increasing based on the increase rate ΔFxR. If the second processing circuit 92 determines that the target rear wheel braking force FxRTr is not increasing, it derives the first decrease amount ΔFx1 as the decrease amount ΔFx. If the second processing circuit 92 determines that the target rear wheel braking force FxRTr is increasing, it derives a value greater than the first decrease amount ΔFx1 as the decrease amount ΔFx. Specifically, the greater the increase rate ΔFxR, the greater the value of the decrease amount ΔFx that the second processing circuit 92 derives. For example, when the second processing circuit 92 determines that the target rear wheel braking force FxRTr is increasing, it may derive the decrease amount ΔFx by referring to the following relational expression (D1): In this case, the correction amount dFx in the relational expression (D1) increases as the increase rate ΔFxR increases.

[0072] ΔFx = ΔFx + dFx (D1) In the next step S39, the second processing circuit 92 sets the target regenerative braking force FxRRTr to the larger of a target candidate value, which is a value obtained by subtracting the decrease amount ΔFx from the target regenerative braking force FxRRTr, or 0 (zero). Then, in step S41, the second processing circuit 92 transmits the target regenerative braking force FxRRTr to the regenerative control unit 202 of the regenerative device 200.

[0073] When the regenerative control unit 202 receives the target regenerative braking force FxRRTr from the second processing circuit 92, it controls the amount of power generated by the motor generator 201 based on the target regenerative braking force FxRRTr. This allows the regenerative control unit 202 to reduce the regenerative braking force FxRR at a speed corresponding to the reduction amount ΔFx.

[0074] In the next step S43, the second processing circuit 92 determines whether the target regenerative braking force FxRRTr transmitted to the regenerative control unit 202 in step S41 is 0 (zero). If the target regenerative braking force FxRRTr is 0 (zero), it can be assumed that the regenerative braking force FxRR will quickly become 0 (zero), even if the regenerative braking force FxRR has not yet become 0 (zero) or less. Therefore, if the target regenerative braking force FxRRTr is 0 (zero), it can be assumed that the regenerative braking force FxRR will become 0 (zero). Therefore, if the target regenerative braking force FxRRTr is 0 (zero) (S43: YES), the second processing circuit 92 proceeds to step S45. On the other hand, if the target regenerative braking force FxRRTr is greater than 0 (zero) (S43: NO), the second processing circuit 92 proceeds to step S35. That is, the second processing circuit 92 continues to reduce the regenerative braking force FxRR.

[0075] In step S45, the second processing circuit 92 closes the holding valve 74 for the rear wheel 11r. In the following step S47, the second processing circuit 92 determines whether or not the termination condition for EBD control is satisfied. For example, the second processing circuit 92 can determine that the termination condition is satisfied when the vehicle stops or the driver stops braking. If the second processing circuit 92 determines that the termination condition is not satisfied (S47: NO), it continues the EBD control by shifting the processing to step S33. On the other hand, if the second processing circuit 92 determines that the termination condition is satisfied (S47: YES), it shifts the processing to step S49.

[0076] In step S49, the second processing circuit 92 ends the EBD control by opening the holding valve 74 for the rear wheel 11r. After that, the second processing circuit 92 temporarily ends the series of processes shown in FIG.

[0077] In this embodiment, when the second processing circuit 92 repeatedly executes the processes from steps S35 to S41 shown in Fig. 3, the regenerative braking force FxRR decreases. Then, while the second processing circuit 92 repeatedly executes the processes from steps S35 to S41 shown in Fig. 3, the first processing circuit 91 executes the series of processes shown in Fig. 2, thereby executing a "regenerative substitution process" that substitutes the regenerative braking force FxRR for the rear wheel friction braking force FxRF. Then, when it is determined that the regenerative substitution process has resulted in the regenerative braking force FxRR becoming 0 (zero), step S45 is executed, thereby closing the holding valve 74 for the rear wheel 11r. The process of step S45 corresponds to the "valve closing process."

[0078] <Operations and Effects of the Present Embodiment> Operations and effects when EBD control is started under the condition that a regenerative braking force FxRR is generated at the rear wheels 11r will be described.

[0079] First, referring to Figure 4, a case will be described in which the vehicle braking force request value FxRq does not increase during execution of the regenerative switching process. As shown in Figure 4A, 4B, 4C, and 4D, braking force is generated at both the front wheels 11f and the rear wheels 11r by regenerative cooperative control based on the vehicle braking force request value FxRq. Under these circumstances, at timing t11, the control device 90 determines that the execution condition for EBD control is met.

[0080] As shown in (C) and (D) of FIG. 4 , at timing t11, the holding valve 74 for the rear wheel 11r is open, and the regenerative braking force FxRR is generated at the rear wheel 11r, which is a regenerative wheel. Therefore, the control device 90 starts a regenerative switching process at timing t11. In the regenerative switching process, the second processing circuit 92 of the control device 90 operates the regenerative device 200 to reduce the target regenerative braking force FxRRTr toward 0 (zero). In the example shown in FIG. 4 , because the vehicle braking force request value FxRq, i.e., the target rear wheel braking force FxRTr, does not increase during the regenerative switching process, the second processing circuit 92 reduces the target regenerative braking force FxRRTr at a rate corresponding to the first decrease amount ΔFx1. Therefore, the regenerative braking force FxRR decreases at a rate corresponding to the first decrease amount ΔFx1.

[0081] During the regenerative switching process, the regenerative braking force FxRR decreases. Therefore, the first processing circuit 91 of the control device 90 operates the pressurizing device 50 to increase the second servo pressure Po, which is the pressure supplied to the pressurizing device 50, as shown in FIG. 4B. In the example shown in FIG. 4, the vehicle braking force request value FxRq is held. In this case, the target front wheel braking force FxFTr is also held. Therefore, the first processing circuit 91 operates the pressurizing device 50 to hold the first servo pressure Pp and increase the second servo pressure Po.

[0082] Because the holding valve 74 for the rear wheel 11r is open, when the second servo pressure Po increases in this way, the rear wheel pressure Pwr also increases. The rate at which the second servo pressure Po increases corresponds to the rate at which the regenerative braking force FxRR decreases. Therefore, the rate at which the rear wheel friction braking force FxRF increases is approximately the same as the rate at which the regenerative braking force FxRR decreases.

[0083] As a result, the control device 90 can reduce the regenerative braking force FxRR to 0 (zero) while suppressing a decrease in the rear wheel braking force FxR during execution of the regenerative switching process. In other words, when EBD control is being performed, the control device 90 can reduce the regenerative braking force FxRR to 0 (zero) while suppressing a decrease in the deceleration of the vehicle.

[0084] At timing t12, the target regenerative braking force FxRRTr becomes 0 (zero) due to the regenerative switching process. The control device 90 then determines that the regenerative braking force FxRR becomes 0 (zero), and terminates the regenerative switching process and starts the valve closing process. In the valve closing process, the second processing circuit 92 of the control device 90 closes the holding valve 74 for the rear wheel 11r. This allows the second processing circuit 92 to restrict an increase in the rear wheel pressure Pwr, thereby restricting an increase in the rear wheel friction braking force FxRF.

[0085] At a subsequent timing t13, due to an increase in the braking operation amount X, the vehicle braking force request value FxRq increases as shown in FIG. 4A. At this time, the first processing circuit 91 of the control device 90 increases the target front wheel braking force FxFTr and the target rear wheel braking force FxRTr in accordance with the increase in the vehicle braking force request value FxRq. After timing t12, because the regenerative braking force FxRR is zero, the first processing circuit 91 derives the target rear wheel braking force FxRTr as the target rear wheel friction braking force FxRFTr. Therefore, as shown in FIG. 4B, the first processing circuit 91 operates the pressurizing device 50 so that the first servo pressure Pp increases in accordance with the increase in the target front wheel braking force FxFTr and the second servo pressure Po increases in accordance with the increase in the target rear wheel braking force FxRTr.

[0086] In this case, the holding valve 74 for the rear wheel 11r is closed, so the rear wheel pressure Pwr does not increase. As a result, the rear wheel braking force FxR is maintained. On the other hand, the holding valve 74 for the front wheel 11f is open, so the front wheel pressure Pwf increases in response to the increase in the first servo pressure Pp. As a result, the front wheel friction braking force FxFF increases.

[0087] Next, a case where the vehicle braking force request value FxRq increases during execution of the regenerative switching process will be described with reference to Figure 5. As shown in Figure 5A, 5B, 5C, and 5D, braking force is generated at both the front wheels 11f and the rear wheels 11r by regenerative cooperative control based on the vehicle braking force request value FxRq. Under these circumstances, at timing t21, the control device 90 determines that the conditions for executing EBD control are met.

[0088] As shown in (C) and (D) of Figure 5, at timing t21, the holding valve 74 for the rear wheel 11r is open, and the regenerative braking force FxRR is generated at the rear wheel 11r, which is a regenerative wheel. Therefore, the control device 90 starts the regenerative switching process at timing t21. In the regenerative switching process, the second processing circuit 92 of the control device 90 operates the regenerative device 200 to decrease the target regenerative braking force FxRRTr toward 0 (zero). During the period in which the vehicle braking force request value FxRq is not increasing, the target rear wheel braking force FxRTr is not increasing, so the second processing circuit 92 decreases the target regenerative braking force FxRRTr at a rate corresponding to the first decrease amount ΔFx1. Therefore, the regenerative braking force FxRR decreases at a rate corresponding to the first decrease amount ΔFx1.

[0089] During the regenerative switching process, the regenerative braking force FxRR decreases. Therefore, the first processing circuit 91 of the control device 90 operates the pressurizing device 50 to increase the second servo pressure Po, which is the pressure supplied to the pressurizing device 50, as shown in FIG. 5B . Since the target front wheel braking force FxFTr is maintained during the period in which the vehicle braking force request value FxRq is maintained, the first processing circuit 91 operates the pressurizing device 50 to increase the second servo pressure Po while maintaining the first servo pressure Pp. The rate at which the second servo pressure Po increases corresponds to the rate at which the regenerative braking force FxRR decreases.

[0090] At timing t22, the regenerative braking force FxRR is still being generated at the rear wheels 11r. In the example shown in FIG. 5 , from timing t22, the vehicle braking force request value FxRq begins to increase, for example, by increasing the braking operation amount X. Then, the first processing circuit 91 of the control device 90 increases the target front wheel braking force FxFTr and the target rear wheel braking force FxRTr in accordance with the increase in the vehicle braking force request value FxRq. When the target rear wheel braking force FxRTr increases in this manner, the increase rate ΔFxR of the target rear wheel friction braking force FxRFTr becomes greater than when the target rear wheel braking force FxRTr is maintained.

[0091] When the rate of increase ΔFxR of the target rear wheel braking force FxRTr increases, the second processing circuit 92 of the control device 90 increases the rate of decrease of the target regenerative braking force FxRRTr compared to when the vehicle braking force request value FxRq is not increased, as was the case before timing t22. In other words, the second processing circuit 92 decreases the target regenerative braking force FxRRTr by an amount of decrease ΔFx that corresponds to the rate of increase ΔFxR of the target rear wheel braking force FxRTr.

[0092] As a result, the regenerative braking force FxRR decreases at a rate corresponding to the rate of increase ΔFxR of the target rear wheel braking force FxRTr. As a result, the rate of increase of the target rear wheel friction braking force FxRFTr becomes greater than before timing t22. The first processing circuit 91 operates the pressurizing device 50 to increase the first servo pressure Pp while increasing the second servo pressure Po so as to increase the rate of increase of the second servo pressure Po. Therefore, the control device 90 can maintain the rear wheel braking force FxR even if the vehicle braking force request value FxRq is increased during execution of the regenerative substitution process.

[0093] When the vehicle braking force requirement value FxRq increases, as shown by the solid line in FIG. 5B , the first processing circuit 91 of the control device 90 operates the pressurizing device 50 to increase the first servo pressure Pp. This increases the front wheel pressure Pwf, and therefore the front wheel friction braking force FxFF. Therefore, the control device 90 can increase the vehicle deceleration even when the vehicle braking force requirement value FxRq increases during EBD control.

[0094] In the example shown in Figure 5, at timing t23, the target regenerative braking force FxRRTr becomes 0 (zero) due to the regenerative switching process. The control device 90 then determines that the regenerative braking force FxRR becomes 0 (zero), and terminates the regenerative switching process and starts the valve closing process. In the valve closing process, the second processing circuit 92 of the control device 90 closes the holding valve 74 for the rear wheel 11r. This allows the second processing circuit 92 to restrict an increase in the rear wheel pressure Pwr, thereby restricting an increase in the rear wheel friction braking force FxRF.

[0095] The present embodiment can further achieve the following effects. (1) Consider a case where the rate of decrease of the regenerative braking force FxRR is not changed even when the vehicle braking force request value FxRq starts to increase while the regenerative braking force FxRR is still being applied to the rear wheels 11r. When the vehicle braking force request value FxRq increases, the first processing circuit 91 of the control device 90 increases the target front wheel braking force FxFTr and the target rear wheel braking force FxRTr in accordance with the increase in the vehicle braking force request value FxRq. Furthermore, the first processing circuit 91 increases the target rear wheel friction braking force FxRFTr taking into account the increase in the target rear wheel braking force FxRTr and the decrease in the regenerative braking force FxRR. In this case, the rate of increase of the target rear wheel braking force FxRTr is faster than before the increase in the vehicle braking force request value FxRq began, while the rate of decrease of the regenerative braking force FxRR remains unchanged. Therefore, the rate of increase of the target rear wheel friction braking force FxRFTr, i.e., the rate of increase of the second servo pressure Po, becomes greater than before the vehicle braking force request value FxRq began to increase. However, because the rate of decrease of the regenerative braking force FxRR is slower than the rate corresponding to the increase of the second servo pressure Po, even when the second servo pressure Po reaches a hydraulic pressure corresponding to the target rear wheel braking force FxRTr, the regenerative braking force FxRR does not fall below a predetermined value. As a result, the closing of the holding valve 74 for the rear wheel 11r is delayed, and the rear wheel braking force FxR, which is the sum of the regenerative braking force FxRR and the rear wheel friction braking force FxRF, increases during the regenerative switching process. In this case, the driver may feel that the brakes are too strong. Furthermore, an increase in the rear wheel braking force FxR during EBD control may result in a decrease in the stability of the vehicle's behavior.

[0096] In this regard, in the control device 90, when the vehicle braking force request value FxRq increases while the regenerative braking force FxRR is still being applied to the rear wheels 11r, the control device 90 increases the rate of decrease of the target regenerative braking force FxRRTr compared to when the vehicle braking force request value FxRq is not increased. This allows the control device 90 to suppress an increase in the rear wheel braking force FxR during execution of the regenerative switching process compared to when the rate of decrease of the regenerative braking force FxRR is not increased when the vehicle braking force request value FxRq increases. As a result, the control device 90 can suppress the driver from feeling that the brakes are being applied too effectively. Furthermore, because the control device 90 can suppress an increase in the rear wheel braking force FxR during execution of EBD control, it can suppress a decrease in the stability of the vehicle's behavior.

[0097] (2) In the brake actuator 70, the rear wheel pressure Pwr can be increased by operating the pump 792 and the differential pressure adjustment valve 732. In other words, the pump 792 and the differential pressure adjustment valve 732 can constitute an example of a pressurizing device. However, the hydraulic pressure generating device 20 is provided with the first servo pressure sensor 65 and the second servo pressure sensor 66 as hydraulic pressure sensors that detect the hydraulic pressure generated by the pressurizing device 50. On the other hand, the brake actuator 70 does not have a hydraulic pressure sensor that detects the hydraulic pressure in the wheel cylinder 16 for the rear wheel 11r. Therefore, if supply pressure is generated using the pump 792 and the differential pressure adjustment valve 732, the supply pressure may not be adjusted accurately. Poor controllability of the supply pressure may result in variations in the rear wheel braking force FxR during regenerative switching processing.

[0098] In contrast, in the braking system 100, the pressurizing device 50 of the hydraulic pressure generating device 20 can adjust the second servo pressure Po as the supply pressure based on the detection signal of the second servo pressure sensor 66. In this case, the control device 90 can accurately adjust the second servo pressure Po and the rear wheel pressure Pwr during execution of the regenerative switching process. Therefore, the control device 90 can suppress variations in the rear wheel braking force FxR during execution of the regenerative switching process.

[0099] <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.

[0100] The first brake unit may be a device having a configuration different from the hydraulic pressure generating device 20 shown in Fig. 1 as long as it is equipped with an electric pressurizing device. For example, the first brake unit may be a device that can supply the supply pressure generated by the pressurizing device 50 to the first hydraulic pressure circuit 711 of the brake actuator 70 without going through the master device 30.

[0101] The fluid pressure adjusting unit 60 of the pressurizing device may not include the first pressure adjusting valve 61 as long as it includes the second pressure adjusting valve 62. The pressurizing device may include a pressurizing means other than the pump 51 as long as it can pressurize the brake fluid. For example, the pressurizing device may include an electric cylinder as the pressurizing means, or may include an accumulator that can accumulate high-pressure brake fluid as the pressurizing means.

[0102] The braking system may be configured such that the pressurizing device is provided in the second braking unit. For example, the pumps 791, 792 and the differential pressure adjustment valves 731, 732 of the brake actuator 70 may constitute an example of the pressurizing device. This pressurizing device can control the supply pressure by adjusting the commanded openings of the differential pressure adjustment valves 731, 732 while operating the pumps 791, 792. In this case, the brake actuator 70 may be provided with a sensor that can detect the hydraulic pressure in the hydraulic path between the differential pressure adjustment valves 731, 732 and the pressure retention valve 74.

[0103] In the above embodiment, the case where EBD control, an example of increase restriction control, is performed has been described. Braking control that closes the holding valve 74 is not limited to EBD control. Another example of braking control is anti-lock brake control, which suppresses deceleration slip of a wheel. Even when anti-lock brake control is initiated while regenerative braking force is being applied to a regenerative wheel, the control device 90 may execute regenerative switching processing and close the holding valve 74 for the regenerative wheel after the regenerative braking force generated by the regenerative wheel becomes zero through the regenerative switching processing. When anti-lock brake control is implemented, the control device 90 may set the target rear wheel friction braking force FxRFTr during the regenerative switching processing to a braking force that is lower than the target rear wheel braking force FxRTr at the time when the start condition for anti-lock brake control is satisfied. Even in this case, the rear wheel braking force FxR does not become less than the target rear wheel braking force FxRTr during the implementation of anti-lock brake control, thereby preventing the vehicle deceleration from becoming excessively small.

[0104] In this case, the vehicle equipped with the braking device 100 may be a vehicle equipped with a regenerative device that can control the regenerative braking force generated in the front wheels 11f. In this case, the front wheels 11f correspond to the "regenerative wheels."

[0105] The decrease ΔFx may be increased beyond the first decrease ΔFx1 because the vehicle braking force request value FxRq starts to increase during execution of the regenerative replacement process. In this case, the control device 90 does not need to decrease the decrease ΔFx even if the vehicle braking force request value FxRq subsequently decreases during execution of the regenerative replacement process.

[0106] The control device 90 does not need to increase the rate of decrease of the regenerative braking force FxRR when the vehicle braking force request value FxRq increases during regenerative switching processing. When regenerative switching processing of EBD control is being performed, deceleration slippage may occur at the rear wheels 11r. In such cases, the control device 90 may reduce the target rear wheel braking force FxRTr during regenerative switching processing to eliminate deceleration slippage at the rear wheels 11r. For example, the second processing circuit 92 of the control device 90 may reduce the rear wheel pressure Pwr and the rear wheel braking force FxR by opening the pressure reducing valve 77 for the rear wheels 11r provided in the second hydraulic circuit 712 of the brake actuator 70. Alternatively, for example, the control device 90 may reduce the rear wheel braking force FxR by increasing the rate of decrease of the regenerative braking force FxRR compared to before deceleration slippage occurred.

[0107] Furthermore, during execution of the regenerative switching process, if deceleration slip occurs on the rear wheel 11r, the deceleration slip of the rear wheel 11r may be resolved by reducing the rear wheel braking force FxR. In this case, the control device 90 may return the target rear wheel braking force FxRTr to the magnitude before the occurrence of deceleration slip of the rear wheel 11r.

[0108] The control device 90 is not limited to a device that includes a CPU and a ROM and executes software processing. In other words, the control device 90 may have any one of the following configurations (a), (b), and (c):

[0109] (a) The control device 90 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.

[0110] (b) The control device 90 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."

[0111] (c) The control device 90 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.

[0112] <Other Technical Ideas> The following describes technical ideas that can be understood from the above embodiment and modified examples. [Supplementary Note 1] When the control device performs the increase restriction control under the condition that the holding valve is open and regenerative braking force is being generated at the regenerative wheel, it is preferable that the control device derives a required value of the total braking force of the regenerative wheel based on a vehicle braking force required value that is a required value of the braking force of the vehicle, derives a target frictional braking force that is a target value of the frictional braking force to be generated at the regenerative wheel by subtracting the regenerative braking force generated at the regenerative wheel from the required value of the total braking force of the regenerative wheel, operates the pressurizing device to generate the supply pressure corresponding to the target frictional braking force, and instructs the regenerative device to increase the rate of decrease of the regenerative braking force as the rate of increase of the supply pressure increases.

[0113] [Note 2] It is preferable that the regenerative wheels are rear wheels of the vehicle, and the increase restriction control is front / rear braking force distribution control that restricts the increase in total braking force generated at the rear wheels while allowing an increase in total braking force generated at the front wheels of the vehicle.

[0114] [Appendix 3] The increase restriction control includes anti-lock brake control that suppresses deceleration slip of the regenerative wheels, and it is preferable that, in the anti-lock brake control, the control device sets a braking force that is smaller than the total braking force generated at the regenerative wheels at the start of the anti-lock brake control as the target value of the total braking force generated at the regenerative wheels.

[0115] It should be noted that the expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

Claims

1. Applied to a vehicle equipped with a regenerative wheel capable of generating both regenerative braking force and friction braking force, and equipped with a regenerative device configured to be able to adjust the regenerative braking force generated by the regenerative wheel, and a wheel cylinder, in which the regenerative wheel generates a friction braking force corresponding to the wheel pressure, which is the hydraulic pressure in the wheel cylinder; a supply fluid line, which is a flow path through which brake fluid flows, connected to the wheel cylinder; a holding valve, which is an electromagnetic valve provided in the supply fluid line and closes when restricting an increase in the wheel pressure; an electric pressure device configured to be able to adjust the supply pressure, which is the hydraulic pressure in the portion of the supply fluid line opposite the wheel cylinder across the holding valve; and a control device that performs increase restriction control to restrict an increase in the total braking force, which is the sum of the regenerative braking force and friction braking force generated by the regenerative wheel; and when the control device performs the increase restriction control under conditions in which the holding valve is open and regenerative braking force is being generated by the regenerative wheel, A braking device that executes a regenerative switching process that operates the regenerative device and the pressurizing device so that the regenerative braking force decreases and the frictional braking force increases by increasing the supply pressure, and a valve closing process that restricts an increase in the wheel pressure by closing the holding valve when the regenerative braking force becomes equal to or less than a predetermined value due to the regenerative switching process.

2. The braking device according to claim 1, wherein, when a vehicle braking force requirement value, which is a required value for the braking force of the vehicle, increases during execution of the regenerative switching process, the control device increases the rate at which the regenerative braking force decreases and the rate at which the supply pressure increases compared to when the vehicle braking force requirement value does not increase.

3. A braking device as described in claim 1 or claim 2, comprising a first braking unit and a second braking unit arranged between the first braking unit and the wheel cylinder, wherein the first braking unit comprises the pressurizing device and a hydraulic pressure sensor that detects the supply pressure adjusted by the pressurizing device, and the second braking unit comprises the retention valve.

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