Braking system

Abstract

The brake system (20) is provided with: a pressure regulating unit (50) that generates a reference hydraulic pressure and generates a rear wheel hydraulic pressure corresponding to the reference hydraulic pressure; a front wheel hydraulic pressure adjusting section (74) configured to be able to make the front wheel hydraulic pressure smaller than the rear wheel hydraulic pressure in the case where the reference hydraulic pressure is generated; and a control device (80) that controls the regenerative device (90), the pressure regulating unit (50), and the front wheel hydraulic pressure adjusting section (74). When the vehicle brake force request value is reduced in a state where the vehicle brake force request value is a first brake force or more, the control device (80) executes first reduction processing of reducing the regenerative brake force applied to the front wheels (FL, FR) and reducing the rear wheel hydraulic pressure by reducing the reference hydraulic pressure while maintaining the front wheel hydraulic pressure.

Description

Technical Field

[0001] The present invention relates to a braking system for use in a vehicle, the vehicle having a regenerative device that applies regenerative braking force to the front wheels. Background Technology

[0002] Patent Document 1 discloses a braking system applied to a vehicle, the vehicle having a regenerative device capable of applying regenerative braking force to the front wheels. This braking system includes: a pressure regulating unit that generates a reference hydraulic pressure; and a front wheel hydraulic pressure adjusting unit that, when the reference hydraulic pressure is generated, adjusts the hydraulic pressure of the front wheel cylinders, i.e., the front wheel hydraulic pressure. When the hydraulic pressure of the rear wheel cylinders is set to the rear wheel hydraulic pressure, this braking system can generate rear wheel hydraulic pressure corresponding to the reference hydraulic pressure. Furthermore, by activating the front wheel hydraulic pressure adjusting unit while the reference hydraulic pressure is generated, this braking system can make the front wheel hydraulic pressure lower than the rear wheel hydraulic pressure.

[0003] When the braking system control device fails to achieve a regenerative braking force exceeding the vehicle's required braking force value during vehicle braking, it implements regenerative coordination control by activating the pressure regulating unit to increase at least the rear wheel hydraulic pressure. The required vehicle braking force value is the required braking force applied to the vehicle.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2019-182278

[0005] In the aforementioned braking system, when regenerative braking force is applied to the front wheels and friction braking force is applied to both the front and rear wheels, the hydraulic pressure in the rear wheels is higher than that in the front wheels. If the required braking force is reduced in this state, the control device reduces the aforementioned reference hydraulic pressure. However, due to the configuration of the pressure regulating unit, when the reference hydraulic pressure is reduced while the rear wheel hydraulic pressure is higher than the front wheel hydraulic pressure, sometimes the front wheel hydraulic pressure does not decrease. In this case, while maintaining the total braking force applied to the front wheels, the braking force applied to the rear wheels decreases. Thus, if only the braking force applied to the rear wheels decreases, the vehicle may exhibit a greater tendency to understeer. Summary of the Invention

[0006] A braking system for solving the above-mentioned problems is applied to a vehicle to control the braking force applied to the vehicle, i.e., the vehicle braking force. The vehicle includes: front wheel cylinders and rear wheel cylinders; a front wheel to which a frictional braking force corresponding to the hydraulic pressure of the front wheel cylinders is applied; a rear wheel to which a frictional braking force corresponding to the hydraulic pressure of the rear wheel cylinders is applied; and a regenerative braking device to apply regenerative braking force to the front wheels. The braking system includes: a pressure regulating unit that generates a reference hydraulic pressure and generates the rear wheel hydraulic pressure corresponding to the reference hydraulic pressure; a front wheel hydraulic pressure adjusting unit configured to make the front wheel hydraulic pressure less than the rear wheel hydraulic pressure when the reference hydraulic pressure is generated; and a control device that controls the regenerative braking device, the pressure regulating unit, and the front wheel hydraulic pressure adjusting unit based on the required value of the vehicle braking force, i.e., the vehicle braking force requirement value. When the required vehicle braking force is greater than or equal to the first braking force, the control device controls the regenerative device, the pressure regulating unit, and the front wheel hydraulic adjustment unit to apply regenerative braking force to the front wheels and apply friction braking force to both the front and rear wheels. When the required vehicle braking force is greater than or equal to the first braking force, and the required vehicle braking force is reduced, the control device performs a first reduction process: reducing the regenerative braking force applied to the front wheels, reducing the hydraulic pressure of the rear wheels by reducing the reference hydraulic pressure, and maintaining the hydraulic pressure of the front wheels.

[0007] The aforementioned braking system can suppress a large tendency for understeer when reducing the vehicle's braking force while applying regenerative braking force to the front wheels. Attached Figure Description

[0008] Figure 1 This is a schematic diagram showing the configuration of a vehicle equipped with the braking system of the first embodiment.

[0009] Figure 2 This is a schematic diagram showing the configuration of the brake actuator included in the braking system of the first embodiment.

[0010] Figure 3 This is a flowchart illustrating the first half of the regenerative coordination control performed by the control device included in the braking system of the first embodiment.

[0011] Figure 4 This is a flowchart illustrating the latter half of the regenerative coordination control performed by the control device included in the braking system of the first embodiment.

[0012] Figure 5 This is a timing diagram of the vehicle braking in the braking system of the first embodiment.

[0013] Figure 6It is a graph showing the shift of state points represented by the front wheel braking force and the rear wheel braking force in the braking system of the first embodiment.

[0014] Figure 7 This is a flowchart illustrating a portion of the regenerative coordination control performed by the control device included in the braking system of the second embodiment.

[0015] Figure 8 This is a timing diagram of vehicle braking in the braking system of the second embodiment.

[0016] Figure 9 It is a graph showing the shift of state points represented by the front wheel braking force and the rear wheel braking force in the braking system of the second embodiment. Detailed Implementation

[0017] (First Implementation)

[0018] The following is based on Figures 1 to 6 The first embodiment of the braking system mounted on a vehicle will be described.

[0019] Figure 1 The diagram illustrates multiple wheels, multiple friction brakes 10, a regenerative device 90, and a braking system 20. The multiple wheels include two front wheels FL and FR and two rear wheels RL and RR.

[0020] <Friction Brake>

[0021] One friction brake 10 is provided for each wheel. Each friction brake 10 includes: a wheel cylinder 11 supplied with brake fluid; a rotating body 12 that rotates integrally with the wheel; and friction material 13 pressed against the rotating body 12. The friction brake 10 is configured such that the greater the hydraulic pressure on the wheel cylinder 11, the more forcefully the friction material 13 can be pressed against the rotating body 12. The friction brake 10 applies a friction braking force to the wheel corresponding to the hydraulic pressure of the wheel cylinder 11.

[0022] The wheel cylinder 11 of the friction brake 10 used for the front wheels FL and FR corresponds to the "front wheel cylinder". The wheel cylinder 11 of the friction brake 10 used for the rear wheels RL and RR corresponds to the "rear wheel cylinder". The hydraulic pressure of the wheel cylinder 11 corresponding to the front wheel cylinder is called "front wheel hydraulic pressure PwcF". The hydraulic pressure of the wheel cylinder 11 corresponding to the rear wheel cylinder is called "rear wheel hydraulic pressure PwcR". A friction braking force corresponding to the front wheel hydraulic pressure PwcF is applied to the front wheels FL and FR. A friction braking force corresponding to the rear wheel hydraulic pressure PwcR is applied to the rear wheels RL and RR. The friction braking force applied to the front wheels FL and FR is called "front wheel friction braking force FxMF". The friction braking force applied to the rear wheels RL and RR is called "rear wheel friction braking force FxMR".

[0023] <Regeneration Device>

[0024] The regenerative braking device 90 includes: an electric generator 91 for the front wheels FL and FR; and a regenerative control unit 92 for controlling the electric generator 91. When the electric generator 91 functions as an electric motor, driving force is transmitted from the electric generator 91 to the front wheels FL and FR. On the other hand, when the electric generator 91 functions as a generator, a regenerative braking force FxR corresponding to the power generation of the electric generator 91 is applied to the front wheels FL and FR.

[0025] An example of a regenerative control unit 92 is an electronic control device. In this case, the regenerative control unit 92 has a CPU and a memory. The memory stores a control program executed by the CPU. By executing this control program by the CPU, the regenerative control unit 92 can control the electric generator 91.

[0026] The regenerative control unit 92 is configured to transmit and receive various information with the control device 80 of the braking system 20, which will be described later. Although detailed descriptions follow, during vehicle braking, the regenerative control unit 92 adjusts the regenerative braking force FxR by transmitting and receiving information with the control device 80.

[0027] Furthermore, when the braking force applied to the vehicle is defined as "vehicle braking force Fx", the sum of the regenerative braking force FxR, the front wheel friction braking force FxMF, and the rear wheel friction braking force FxMR is equivalent to the vehicle braking force Fx. That is, the sum of the braking forces applied to multiple wheels FL, FR, RL, and RR is the vehicle braking force Fx.

[0028] <Braking System>

[0029] The braking system 20 applies friction braking force to multiple wheels FL, FR, RL, and RR by adjusting the hydraulic pressure of multiple wheel cylinders 11. The braking system 20 includes: a brake operating component 21, a hydraulic generating device 22, a brake actuator 23, and an atmospheric pressure reservoir 24. The brake operating component 21 is a component operable by the vehicle's driver. An example of the brake operating component 21 is the brake pedal. The atmospheric pressure reservoir 24 stores brake fluid and is open to the atmosphere.

[0030] The hydraulic generating device 22 is configured to generate hydraulic pressure corresponding to the operating amount of the brake operating component 21. The hydraulic generating device 22 includes a main unit 30 and a pressure regulating unit 50. The main unit 30 can supply brake fluid to the brake actuator 23. The pressure regulating unit 50 can supply brake fluid to both the main unit 30 and the brake actuator 23.

[0031] <Main Device>

[0032] The main unit 30 includes: a master cylinder 31; a stroke simulator 32; multiple flow paths 331, 332, and 333 connected to the master cylinder 31; and multiple control valves 341 and 342 for controlling the flow of brake fluid. The stroke simulator 32 is capable of generating a reaction force corresponding to the amount of operation of the brake operating component 21.

[0033] The master cylinder 31 includes a master cylinder body 41 and a cover cylinder 42. The master cylinder 31 includes a master piston 43 and an input piston 44. The master cylinder 31 includes a master spring 45 that applies force to the master piston 43 and an input spring 46 that applies force to the input piston 44. The master piston 43 and the input piston 44 are movable relative to the master cylinder body 41 and the cover cylinder 42.

[0034] The main cylinder body 41 of the master cylinder 31 has: a plate-shaped bottom wall 411; and a first peripheral wall 412 extending from the bottom wall 411 along its axis. Furthermore, the main cylinder body 41 has: a second peripheral wall 413 extending from the rear end of the first peripheral wall 412 along its axis; and a first annular wall 414 extending from the rear end of the second peripheral wall 413 toward its axis. The first peripheral wall 412 and the second peripheral wall 413 are each cylindrical. A hole is formed in the first annular wall 414 for insertion of the rear end of the main piston 43, described later. The inner diameter of the first peripheral wall 412 is smaller than the inner diameter of the second peripheral wall 413.

[0035] Within the main cylinder 31, the main chamber Rm is defined by the bottom wall 411, the first peripheral wall 412, and the main piston 43. Hereinafter, within the main cylinder 31, [the following will be described...] Figure 1 The direction of movement of the main piston 43, which is to the left and decreases the volume of the main chamber Rm, is called "forward". On the other hand, the opposite direction of forward is called "rearward". Rearward is also the direction of movement of the main piston 43, which increases the volume of the main chamber Rm.

[0036] Within the main cylinder 31, a first liquid chamber R1 is defined by a second peripheral wall 413 and a main piston 43, and a servo chamber Rs is defined by the second peripheral wall 413, a first annular wall 414, and the main piston 43. The main chamber Rm is formed at the front end of the main cylinder 31. The first liquid chamber R1 is formed further rearward than the main chamber Rm. The servo chamber Rs is formed further rearward than the first liquid chamber R1. Inside the main cylinder 31, the main chamber Rm, the first liquid chamber R1, and the servo chamber Rs are not connected to each other.

[0037] The main cylinder 31's casing 42 has: a cylindrical third peripheral wall 421; and a second annular wall 422 extending from the rear end of the third peripheral wall 421 toward its axis. The third peripheral wall 421 is mounted to the first annular wall 414 such that its axis coincides with the axis of the second peripheral wall 413 of the main cylinder body 41. The second annular wall 422 is provided with a hole for insertion of the rear end of the input piston 44, which will be described later.

[0038] Within the cover cylinder 42, the second liquid chamber R2 is divided by the first annular wall 414, the third circumferential wall 421, and the second annular wall 422 of the main cylinder body 41. In the main cylinder 31, the second liquid chamber R2 is formed at a position further rear than the servo chamber Rs.

[0039] The main piston 43 is housed within the main cylinder 31. When the main piston 43 moves axially, it moves forward and backward along the inner circumferential surfaces of the first circumferential wall 412, the second circumferential wall 413, and the first annular wall 414 of the main cylinder 41. The rear end of the main piston 43 protrudes rearward beyond the first annular wall 414 and is located within the second liquid chamber R2.

[0040] The input piston 44 is positioned rearward within the master cylinder 31, relative to the master piston 43. The input piston 44 moves forward and backward along the inner circumferential surfaces of the third circumferential wall 421 and the second annular wall 422 of the cover cylinder 42. A brake operating member 21 is connected to the rear end of the input piston 44. Therefore, the input piston 44 moves forward, closer to the master piston 43, according to the amount of operation of the brake operating member 21. Furthermore, a gap is formed between the input piston 44 and the master piston 43 in the second fluid chamber R2.

[0041] The main spring 45 is disposed in the main chamber Rm of the main cylinder 41. The main spring 45 exerts a force on the main piston 43 rearward. Therefore, if the main piston 43 moves forward, the main spring 45 is elastically compressed.

[0042] An input spring 46 is disposed in the second liquid chamber R2 of the cylinder 42. The input spring 46 exerts a force on the input piston 44 backward. Therefore, if the input piston 44 moves forward, the input spring 46 is elastically compressed.

[0043] In the master cylinder 31, the main chamber Rm is connected to the atmospheric pressure reservoir 24. Specifically, the rearward portion of the main chamber Rm is connected to the atmospheric pressure reservoir 24 via a port formed in the first circumferential wall 412 of the master cylinder body 41. Therefore, when the main piston 43 moves from... Figure 1 When the initial position is moved forward, the connection between the main chamber Rm and the atmospheric pressure reservoir 24 is severed. As a result, the hydraulic pressure in the main chamber Rm increases as the main piston 43 moves forward. For example, if the hydraulic pressure in the servo chamber Rs increases, the main piston 43 moves forward due to the hydraulic pressure in the servo chamber Rs. This causes brake fluid to flow out of the main chamber Rm, thus increasing the hydraulic pressure in the main chamber Rm. On the other hand, if the hydraulic pressure in the servo chamber Rs decreases, the main piston 43 moves backward due to the hydraulic pressure in the main chamber Rm. This causes brake fluid to flow into the main chamber Rm, thus decreasing the hydraulic pressure in the main chamber Rm.

[0044] The first flow path 331 connects the main chamber Rm to the brake actuator 23. Specifically, the first flow path 331 connects the second hydraulic circuit 612 of the brake actuator 23 (described later) and the main chamber Rm. The second flow path 332 connects the first liquid chamber R1 to the second liquid chamber R2. The third flow path 333 connects the atmospheric pressure reservoir 24 to the second flow path 332.

[0045] 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 second flow path 332, between the connection point with the third flow path 333 and the second liquid chamber R2. The second control valve 342 is located in the third flow path 333. When the control device 80 of the braking system 20 is operating, the first control valve 341 is open, and the second control valve 342 is closed.

[0046] The stroke simulator 32 is configured between the first liquid chamber R1 and the first control valve 341 in the second flow path 332.

[0047] <Voltage Regulating Unit>

[0048] The pressure regulating unit 50 includes an electric cylinder 51. By operating the electric cylinder 51, the pressure regulating unit 50 can adjust the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0049] The pressure regulating unit 50, serving as the brake fluid flow path, includes a fourth flow path 54, a fifth flow path 55, and a sixth flow path 58. The fourth flow path 54 is connected to the input port 515 of the electric cylinder 51 and the atmospheric pressure reservoir 24. The fifth flow path 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 flow path 58 is connected to the first hydraulic circuit 611 of the brake actuator 23 (described later) and the fifth flow path 55. Therefore, the electric cylinder 51 can supply brake fluid discharged from the output port 516 to both the servo chamber Rs and the first hydraulic circuit 611 of the brake actuator 23.

[0050] Furthermore, when the hydraulic pressure of the fifth flow path 55 is set to "servo pressure," this servo pressure corresponds to the "reference hydraulic pressure" generated by the pressure regulating unit 50. The flow path connecting the pressure regulating unit 50 to the servo chamber Rs is designated as the "first supply fluid path," and the flow path branching from the first supply fluid path is designated as the "second supply fluid path." In this case, the fifth flow path 55 corresponds to the first supply fluid path, and the sixth flow path 58 corresponds to the second supply fluid path.

[0051] The electric cylinder 51 includes a cylinder 511, a piston 512, a first electric motor 513, and a conversion mechanism 514. The piston 512 is slidably disposed within the cylinder 511. The first electric motor 513 is the power source for the electric cylinder 51. The conversion mechanism 514 converts the rotational motion of the output shaft of the first electric motor 513 into the linear motion of the piston 512.

[0052] Inside cylinder 511, a hydraulic chamber Re for brake fluid introduction is defined by the peripheral wall of cylinder 511 and piston 512. The position of piston 512 inside cylinder 511 can be changed by driving the first electric motor 513. Hereinafter, the direction of movement of piston 512 that reduces the volume of hydraulic chamber Re will be referred to as the "forward direction Za", and the opposite direction of forward direction Za will be referred to as the "reverse direction Zb". Reverse direction Zb is also the direction of movement of piston 512 that increases the volume of hydraulic chamber Re.

[0053] An input port 515 and an output port 516 are formed on the peripheral wall of cylinder 511 to connect the hydraulic chamber Re to the outside. A through hole 517 is formed in piston 512. The position on the farthest retracting direction Zb that piston 512 can move is defined as the final retracting position. At this time, the through hole 517 is formed at a position that allows the input port 515 to communicate with the hydraulic chamber Re when piston 512 is in the final retracting position. Thus, when piston 512 is in the final retracting position, the hydraulic chamber Re of cylinder 511 is connected to the atmospheric pressure reservoir 24 via the through hole 517, the input port 515, and the fourth flow path 54. The input port 515 is configured such that it is open when piston 512 is in the final retracting position, and is blocked by piston 512 if piston 512 moves forward in the forward direction Za from the final retracting position. If piston 512 moves further forward in the forward direction Za after the input port 515 is blocked by piston 512, the hydraulic pressure in hydraulic chamber Re increases.

[0054] Output port 516 is connected to master cylinder 31 and sixth flow path 58 via fifth flow path 55. Output port 516 is always open regardless of the position of piston 512. Therefore, if piston 512 moves in the forward direction Za when input port 515 is blocked by piston 512, brake fluid in hydraulic chamber Re is discharged from output port 516 to fifth flow path 55.

[0055] <Brake Actuator>

[0056] like Figure 2 As shown, the brake actuator 23 is configured to individually adjust the hydraulic pressure PwcF and PwcR of multiple wheel cylinders 11. The brake actuator 23 can increase the hydraulic pressure PwcF and PwcR of the wheel cylinders 11 without increasing the hydraulic pressure after it has been adjusted by the pressure regulating unit 50. That is, the braking system 20 has a redundant configuration with the pressure regulating unit 50 as the upstream side and the brake actuator 23 as the downstream side.

[0057] The brake actuator 23 has a first hydraulic circuit 611 and a second hydraulic circuit 612. The first hydraulic circuit 611 is connected to two wheel cylinders 11 for the rear wheels RL and RR. The second hydraulic circuit 612 is connected to two wheel cylinders 11 for the front wheels FL and FR.

[0058] The first hydraulic circuit 611 includes: a first connecting fluid passage 621; and a first differential pressure control valve 631 disposed in the first connecting fluid passage 621. The first connecting fluid passage 621 is a brake fluid passage connecting the two wheel cylinders 11 for the rear wheels RL and RR to the sixth flow passage 58. The first differential pressure control valve 631 is a normally open linear solenoid valve. The first differential pressure control valve 631 can adjust the differential pressure between the portion of the first connecting fluid passage 621 on the sixth flow passage 58 side and the portion on the wheel cylinder 11 side. For example, the greater the current flowing in the solenoid of the first differential pressure control valve 631, the greater the differential pressure that the first differential pressure control valve 631 can generate.

[0059] The portion of the first connecting fluid circuit 621 closer to the wheel cylinder 11 than the first differential pressure control valve 631 branches into two paths 62a and 62b. Path 62a connects to the wheel cylinder 11 for the left rear wheel RL, and path 62b connects to the wheel cylinder 11 for the right rear wheel RR. A holding valve 641 is provided in each of the two paths 62a and 62b. That is, the holding valve 641 is located in the portion of the first connecting fluid circuit 621 closer to the wheel cylinder 11 than the first differential pressure control valve 631. The holding valve 641 is a normally open linear solenoid valve that adjusts the differential pressure between the portion of the path 62a and 62b on the side of the first differential pressure control valve 631 and the portion on the side of the wheel cylinder 11. The greater the current flowing in the solenoid of the holding valve 641, the greater the differential pressure that the holding valve 641 can generate.

[0060] Multiple paths 62a and 62b are connected to bypass flow paths 721 that bypass the holding valve 641. The first end of the bypass flow path 721 is connected to the portion of path 62a or 62b that is closer to the first differential pressure control valve 631 than the holding valve 641. The second end of the bypass flow path 721 is connected to the portion of path 62a or 62b that is closer to the wheel cylinder 11 than the holding valve 641. A check valve 731 is provided in each of the multiple bypass flow paths 721. That is, the check valve 731 is arranged side-by-side with the holding valve 641.

[0061] An example of the check valve 731 is a one-way valve. When the hydraulic pressure on the side of the holding valve 641 closest to the first differential pressure control valve 631 is greater than the rear wheel hydraulic pressure PwcR, the check valve 731 closes. Conversely, when the hydraulic pressure on the side of the holding valve 641 closest to the first differential pressure control valve 631 is less than the rear wheel hydraulic pressure PwcR, the check valve 731 opens. If the check valve 731 opens in this way, it allows brake fluid to flow from the wheel cylinder 11 to the side of the first differential pressure control valve 631.

[0062] The first hydraulic circuit 611 includes: a first pressure-reducing reservoir 651 for storing brake fluid; and a first pressure-reducing fluid passage 661 connected to the first pressure-reducing reservoir 651. The first pressure-reducing fluid passage 661 is a brake fluid passage that connects the portion of paths 62a and 62b on the side of the retaining valve 641 near the wheel cylinder 11 to the first pressure-reducing reservoir 651. A first pressure-reducing valve 671, which is a normally closed solenoid valve, is provided in the portion of the first pressure-reducing fluid passage 661 connected to path 62a and the portion connected to path 62b, respectively.

[0063] The first hydraulic circuit 611 includes: a first pump 681 powered by a second electric motor 69; a first return fluid passage 701; and a first flow control unit 711. The first pump 681 draws brake fluid from the first pressure-reducing reservoir 651 and discharges the brake fluid into the portion of the first connecting fluid passage 621 between the first differential pressure control valve 631 and the holding valve 641. The first return fluid passage 701 is the brake fluid passage connected to the portion of the first connecting fluid passage 621 that is closer to the sixth flow path 58 than the first differential pressure control valve 631 and the first pressure-reducing reservoir 651.

[0064] The first flow control unit 711 controls the flow of brake fluid in the first return fluid path 701. An example of the first flow control unit 711 is a check valve.

[0065] The second hydraulic circuit 612 includes: a second connecting fluid passage 622; and a second differential pressure control valve 632 disposed in the second connecting fluid passage 622. The second connecting fluid passage 622 is a brake fluid passage connecting the two wheel cylinders 11 for the front wheels (FL and FR) to the first flow path 331. The second differential pressure control valve 632 is a normally open linear solenoid valve. The second differential pressure control valve 632 can adjust the differential pressure between the portion of the second connecting fluid passage 622 on the first flow path 331 side and the portion on the wheel cylinder 11 side. For example, the greater the current flowing in the solenoid of the second differential pressure control valve 632, the greater the differential pressure that the second differential pressure control valve 632 can generate.

[0066] The portion of the second connecting fluid circuit 622 closer to the wheel cylinder 11 than the second differential pressure control valve 632 branches into two paths 62c and 62d. Path 62c connects to the wheel cylinder 11 for the left front wheel (FL), and path 62d connects to the wheel cylinder 11 for the right front wheel (FR). A holding valve 642 is provided in each of the two paths 62c and 62d. The holding valve 642 is a normally open linear solenoid valve that adjusts the differential pressure between the portion of paths 62c and 62d on the side of the second differential pressure control valve 632 and the portion on the side of the wheel cylinder 11. The greater the current flowing in the solenoid of the holding valve 642, the greater the differential pressure that the holding valve 642 can generate.

[0067] Multiple paths 62c and 62d are connected to bypass flow paths 722, which bypass the holding valve 642. The first end of the bypass flow path 722 is connected to the portion of path 62c or 62d that is closer to the second differential pressure control valve 632 than the holding valve 642. The second end of the bypass flow path 722 is connected to the portion of path 62c or 62d that is closer to the wheel cylinder 11 than the holding valve 642. A check valve 732 is provided in each of the multiple bypass flow paths 722. That is, the check valve 732 is configured side-by-side with the holding valve 642.

[0068] An example of the check valve 732 is a one-way valve. When the hydraulic pressure on the side of the holding valve 642 closest to the second differential pressure control valve 632 is greater than the front wheel hydraulic pressure PwcF, the check valve 732 closes. Conversely, when the hydraulic pressure on the side of the holding valve 642 closest to the second differential pressure control valve 632 is less than the front wheel hydraulic pressure PwcF, the check valve 732 opens. If the check valve 732 is open, it allows brake fluid to flow from the wheel cylinder 11 to the side of the second differential pressure control valve 632.

[0069] As described above, the multiple holding valves 642 are normally open linear solenoid valves. Furthermore, the second hydraulic circuit 612 is connected to the main chamber Rm of the main unit 30 via the first flow path 331. Therefore, by adjusting the magnitude of the current flowing in the solenoids of the multiple holding valves 642, the front wheel hydraulic pressure PwcF is made lower than the servo pressure of the fifth flow path 55, more specifically, the hydraulic pressure of the main chamber Rm. Although detailed later, the servo pressure corresponds to the rear wheel hydraulic pressure PwcR. Therefore, by operating the holding valves 642 when the servo pressure is generated, the front wheel hydraulic pressure PwcF is made less than the rear wheel hydraulic pressure PwcR. Thus, an example of a "front wheel hydraulic adjustment unit 74" consisting of multiple holding valves 642 and multiple check valves 732 is provided, which is configured to make the front wheel hydraulic pressure PwcF less than the rear wheel hydraulic pressure PwcR when the servo pressure is generated.

[0070] The second hydraulic circuit 612 includes: a second pressure-reducing reservoir 652 for storing brake fluid; and a second pressure-reducing fluid passage 662 connected to the second pressure-reducing reservoir 652. The second pressure-reducing fluid passage 662 is a brake fluid passage that connects the portion of paths 62c and 62d on the side of the retaining valve 642 near the wheel cylinder 11 to the second pressure-reducing reservoir 652. A second pressure-reducing valve 672, which is a normally closed solenoid valve, is provided in the portion of the second pressure-reducing fluid passage 662 connected to path 62c and the portion of the second pressure-reducing fluid passage 662 connected to path 62d.

[0071] The second hydraulic circuit 612 includes: a second pump 682 powered by a second electric motor 69; a second return fluid passage 702; and a second flow control unit 712. The second pump 682 draws brake fluid from the second pressure-reducing reservoir 652 and discharges the brake fluid into the portion of the second connecting fluid passage 622 between the second differential pressure control valve 632 and the holding valve 642. The second return fluid passage 702 is the brake fluid passage connected to the portion of the second connecting fluid passage 622 that is closer to the first flow path 331 than the second differential pressure control valve 632, and to the second pressure-reducing reservoir 652.

[0072] The second flow control unit 712 controls the flow of brake fluid in the second return fluid circuit 702. An example of the second flow control unit 712 is a check valve.

[0073] <Brake System Testing System>

[0074] like Figure 1 As shown, the braking system's detection system has multiple sensors, which output signals corresponding to the detection results to the control device 80. These multiple sensors include multiple hydraulic sensors and a stroke sensor SE1. The multiple hydraulic sensors include a main pressure sensor 351, an input pressure sensor 352, and a servo pressure sensor 353.

[0075] The main pressure sensor 351 detects the hydraulic pressure within the main chamber Rm. For example, the main pressure sensor 351 is located in the first flow path 331. The hydraulic pressure within the main chamber Rm based on the detection signal from the main pressure sensor 351 is referred to as the "main pressure".

[0076] Input pressure sensor 352 detects the hydraulic pressure in the second liquid chamber R2. For example, input pressure sensor 352 is connected in the second flow path 332 between the first control valve 341 and the second liquid chamber R2. The hydraulic pressure in the second liquid chamber R2 based on the detection signal of input pressure sensor 352 is called "input hydraulic pressure".

[0077] The servo pressure sensor 353 detects the hydraulic pressure, or servo pressure, of the brake fluid discharged from the electric cylinder 51 to the sixth flow path 58. For example, the servo pressure sensor 353 is located in the fifth flow path 55, between the connection point with the sixth flow path 58 and the output port 516. The hydraulic pressure discharged from the electric cylinder 51 based on the detection signal of the servo pressure sensor 353 is called the "servo pressure Psc".

[0078] The stroke sensor SE1 detects the amount of operation of the braking operation component 21.

[0079] <Control Device>

[0080] like Figure 1As shown, the control device 80 is configured to communicate with the regeneration control unit 92 via an in-vehicle network. The control device 80 includes a processing circuit 81. An example of the processing circuit 81 is an electronic control device. In this case, the processing circuit 81 has a CPU 82 and a memory 83. The memory 83 stores the control program executed by the CPU 82. By executing the control program by the CPU 82, the processing circuit 81 causes the braking system 20 to operate.

[0081] <Regeneration Coordination Control>

[0082] Reference Figure 3 as well as Figure 4 The regenerative coordination control performed by the processing circuit 81 of the control device 80 during vehicle braking will be described. The regenerative coordination control is the braking control that adjusts the regenerative braking force FxR, the front wheel friction braking force FxMF, and the rear wheel friction braking force FxMR. The processing circuit 81 repeatedly executes the regenerative coordination control according to each predetermined control cycle when braking is required.

[0083] In step S11, the processing circuit 81 derives the required value of the vehicle braking force Fx, i.e., the vehicle braking force requirement value FxTr. For example, when the driver operates the brake operating component 21, the processing circuit 81 derives the vehicle braking force requirement value FxTr in such a way that the greater the amount of operation of the brake operating component 21, the greater the value of the vehicle braking force requirement value FxTr. Furthermore, when a deceleration request is received from other onboard control devices, the processing circuit 81 sets the value corresponding to that deceleration request as the vehicle braking force requirement value FxTr.

[0084] In the next step S13, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr has increased. For example, if the latest value of the vehicle braking force requirement value FxTr is greater than the previous value, it can be considered that the vehicle braking force requirement value FxTr has increased. Conversely, if the latest value of the vehicle braking force requirement value FxTr is less than the previous value, it can be considered that the vehicle braking force requirement value FxTr has not increased. The latest value of the vehicle braking force requirement value FxTr is the vehicle braking force requirement value FxTr derived in the current control cycle. The previous value of the vehicle braking force requirement value FxTr is the vehicle braking force requirement value FxTr derived in the previous control cycle. If the processing circuit 81 determines that the vehicle braking force requirement value FxTr has increased (S13: Yes), the processing proceeds to step S15. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr has not increased (S13: No), the processing proceeds to step S31.

[0085] In step S15, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is less than the regenerative braking force upper limit value FxRL. The regenerative braking force upper limit value FxRL is the upper limit of the regenerative braking force FxR that the regenerative device 90 can apply to the vehicle. If the vehicle braking force requirement value FxTr is less than the regenerative braking force upper limit value FxRL (S15: Yes), the processing circuit 81 proceeds to step S17. On the other hand, if the vehicle braking force requirement value FxTr is greater than or equal to the regenerative braking force upper limit value FxRL (S15: No), the processing circuit 81 proceeds to step S19.

[0086] In step S17, the processing circuit 81 performs a first increase process. In the first increase process, the processing circuit 81 increases the regenerative braking force FxR according to the increase of the vehicle braking force requirement value FxTr, while not increasing the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0087] Specifically, in step S171, the processing circuit 81 sets the vehicle braking force requirement value FxTr to the regenerative braking force target value FxRTr. The regenerative braking force target value FxRTr is the target value of the regenerative braking force FxR applied to the front wheels FL and FR. In the next step S173, the processing circuit 81 sends the regenerative braking force target value FxRTr to the regeneration control unit 92 of the regeneration device 90.

[0088] If the regenerative braking force target value FxRTr is received, the regenerative control unit 92 will generate electricity from the electric generator 91 based on the regenerative braking force target value FxRTr. As a result, the regenerative control unit 92 can increase the regenerative braking force FxR applied to the front wheels FL and FR according to the increase of the regenerative braking force target value FxRTr.

[0089] In the next step S175, the processing circuit 81 sets the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr to 0 (zero). The front wheel hydraulic target value PwcFTr is the target value of the front wheel hydraulic PwcF. The rear wheel hydraulic target value PwcRTr is the target value of the rear wheel hydraulic PwcR.

[0090] In step S177, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. Specifically, the processing circuit 81 activates the electric cylinder 51 of the pressure regulating unit 50 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. In this case, the processing circuit 81 activates the electric cylinder 51 in a manner that makes the servo pressure Psc 0 (zero). Then, the processing circuit 81 terminates the first increase process. Afterward, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0091] In step S19, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is less than the first braking force Fx1. The braking force that is greater than the regenerative braking force target value FxRTr is set as the first braking force Fx1.

[0092] Here, refer to Figure 6 This indicates that the first braking force is Fx1. Figure 6 The horizontal axis represents the sum of the braking forces applied to the front wheels FL and FR, i.e., the front wheel braking force FxAF. Figure 6 The vertical axis represents the sum of the braking forces applied to the rear wheels RL and RR, i.e., the rear wheel braking force FxAR. In this example, the sum of the front wheel friction braking force FxMF and the regenerative braking force FxR is equal to the front wheel braking force FxAF. The rear wheel braking force FxAR is equal to the rear wheel friction braking force FxMR. Figure 6 The single-dot dashed line is the ideal braking force distribution line L1. The ideal braking force distribution line L1 is a line that represents the relationship between the front wheel braking force FxAF and the rear wheel braking force FxAR when the front wheels FL and FR and the rear wheels RL and RR lock up simultaneously during vehicle braking. Figure 6 The dashed line is the braking force distribution line L2 under equal pressure. The braking force distribution line L2 under equal pressure is a line that shows the relationship between the front wheel braking force FxAF and the rear wheel braking force FxAR when the hydraulic pressure is increased while maintaining the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR at the same pressure.

[0093] For example, the first braking force Fx1 is set to satisfy the following conditions (A1) and (A2).

[0094] (A1) The front wheel braking force FxAF is equal to the regenerative braking force target value FxRTr at the moment of switching from the first increase process to the second increase process.

[0095] (A2) in Figure 6 In the diagram shown, the point P representing the front wheel braking force FxAF and the rear wheel braking force FxAR, i.e., the state point, is a point on the braking force distribution line L2 when the pressure is the same.

[0096] return Figure 3 In step S19, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr is less than the first braking force Fx1 (S19: Yes), the processing will proceed to step S21. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1 (S19: No), the processing will proceed to step S23.

[0097] In step S21, the processing circuit 81 performs a second increase process. In the second increase process, the processing circuit 81 increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR, while maintaining the front wheel hydraulic pressure PwcF, and maintaining the regenerative braking force FxR.

[0098] In detail, in step S211, the processing circuit 81 sends an instruction to maintain the regeneration braking force FxR to the regeneration control unit 92 of the regeneration device 90.

[0099] If the regeneration control unit 92 receives the instruction, it will activate the electric generator 91 to maintain the regenerative braking force FxR.

[0100] In the next step S213, the processing circuit 81 increases the target value of the rear wheel hydraulic pressure PwcRTr and keeps the target value of the front wheel hydraulic pressure PwcFTr at 0 (zero). The processing circuit 81 sets the target value of the rear wheel hydraulic pressure PwcR as the value when the rear wheel friction braking force FxMR is equal to the value obtained by subtracting the regenerative braking force FxR from the vehicle braking force requirement value FxTr.

[0101] In step S215, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. Specifically, the processing circuit 81 sets the hydraulic pressure based on the rear wheel hydraulic target value PwcRTr as the target value of the servo pressure Psc, i.e., the servo pressure target value PscTr. For example, the processing circuit 81 sets the servo pressure Psc used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. Thus, the processing circuit 81 increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0102] Furthermore, the processing circuit 81 activates the front wheel hydraulic adjustment unit 74 so that the front wheel hydraulic pressure PwcF does not increase even if the servo pressure Psc increases. For example, the processing circuit 81 maintains the front wheel hydraulic pressure PwcF by closing multiple holding valves 642 of the front wheel hydraulic adjustment unit 74. In this case, the greater the differential pressure between the servo pressure Psc and the target front wheel hydraulic pressure value PwcFTr, the greater the current flowing in the solenoid of the holding valve 642 caused by the processing circuit 81. Furthermore, if the processing circuit 81 terminates the second increase process, it temporarily terminates the regenerative coordination control.

[0103] In step S23, the processing circuit 81 performs a third increase process. In the third increase process, the processing circuit 81 increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR, while maintaining the regenerative braking force FxR.

[0104] In detail, in step S231, similar to step S211 above, the processing circuit 81 sends an instruction to maintain the regeneration braking force FxR to the regeneration control unit 92 of the regeneration device 90.

[0105] In the next step S233, the processing circuit 81 increases the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. At this time, the processing circuit 81 increases the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr in a manner that satisfies the following conditions (B1) and (B2).

[0106] (B1) Maintain the difference between the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR at the start of the third increase process.

[0107] (B2) The sum of the front wheel friction braking force FxMF, the rear wheel friction braking force FxMR, and the regenerative braking force FxR is equal to the vehicle braking force requirement value FxTr.

[0108] In addition, the difference between the rear wheel hydraulic pressure PwcR and the front wheel hydraulic pressure PwcF at the start of the third additional processing is also called the "reference hydraulic pressure difference ΔPwcB".

[0109] In step S235, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. For example, the processing circuit 81 sets the servo pressure Psc, which is used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr, as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. Thus, the processing circuit 81 increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0110] Furthermore, the processing circuit 81 activates the front wheel hydraulic adjustment unit 74 so that the front wheel hydraulic pressure PwcF increases in response to the increase in servo pressure Psc. For example, the processing circuit 81 sets the magnitude of the current flowing in the solenoids of the multiple holding valves 642 to a value corresponding to the aforementioned reference hydraulic pressure difference ΔPwcB. Thus, the processing circuit 81 can increase the front wheel hydraulic pressure PwcF and the front wheel friction braking force FxMF in response to the increase in servo pressure Psc. Then, the processing circuit 81 terminates the third increase process. Afterward, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0111] In step S31, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr has decreased. For example, if the latest value of the vehicle braking force requirement value FxTr is less than the previous value, it can be considered that the vehicle braking force requirement value FxTr has decreased. Conversely, if the latest value of the vehicle braking force requirement value FxTr is greater than or equal to the previous value, it can be considered that the vehicle braking force requirement value FxTr has not decreased. If the processing circuit 81 determines that the vehicle braking force requirement value FxTr has decreased (S31: Yes), it transfers the processing to... Figure 4 Step S41. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr does not decrease (S31: No), it can determine that the vehicle braking force requirement value FxTr should be maintained, and therefore transfers the processing to step S33.

[0112] In step S33, similar to step S211 above, the processing circuit 81 sends an instruction to maintain the regenerative braking force FxR to the regeneration control unit 92 of the regeneration device 90. In the next step S35, the processing circuit 81 maintains the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. In the next step S37, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. Specifically, the processing circuit 81 activates the electric cylinder 51 to maintain the servo pressure Psc. The processing circuit 81 activates the front wheel hydraulic adjustment unit 74 to maintain the difference between the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR at the aforementioned reference hydraulic pressure difference ΔPwcB. Furthermore, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0113] In step S41, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1. If the processing circuit 81 determines that the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1 (S41: Yes), the processing proceeds to step S43. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr is less than the first braking force Fx1 (S41: No), the processing proceeds to step S45.

[0114] In step S43, the processing circuit 81 performs a first reduction process. In the first reduction process, the processing circuit 81 reduces the regenerative braking force FxR, and reduces the rear wheel hydraulic pressure PwcR by reducing the servo pressure Psc, while maintaining the front wheel hydraulic pressure PwcF.

[0115] In detail, in step S431, the processing circuit 81 reduces the target value of the regenerative braking force FxRTr. The processing circuit 81 reduces the target value of the regenerative braking force FxRTr in a manner that satisfies the following conditions (C1) and (C2).

[0116] (C1) The sum of the regenerative braking force FxR, the front wheel friction braking force FxMF, and the rear wheel friction braking force FxMR is equal to the vehicle's required braking force value FxTr.

[0117] (C2) Maintain the front wheel braking force FxAF and the rear wheel braking force FxAR as the baseline front-rear distribution ratio.

[0118] The pre- and post-benchmark allocation ratio refers to the ratio before and after the benchmark. Figure 6 The distribution ratio of the front wheel braking force FxAF to the rear wheel braking force FxAR when the state point P is located on the braking force distribution line L2 under the same pressure. That is, when the distribution ratio of the front wheel braking force FxAF to the rear wheel braking force FxAR is the baseline front-rear distribution ratio, the state point P is located on the braking force distribution line L2 under the same pressure.

[0119] In the next step S433, the processing circuit 81 sends the regenerative braking force target value FxRTr to the regenerative control unit 92.

[0120] If the regenerative control unit 92 receives a target value for regenerative braking force FxRTr, it causes the electric generator 91 to generate electricity based on the target value FxRTr. Thus, the regenerative control unit 92 reduces the regenerative braking force FxR as the target value FxRTr decreases.

[0121] In step S435, the processing circuit 81 reduces the target hydraulic value PwcRTr for the rear wheels while maintaining the target hydraulic value PwcFTr for the front wheels. The processing circuit 81 reduces the target hydraulic value PwcFTr for the front wheels in a manner that satisfies the following condition (D1).

[0122] (D1) The target value of the rear wheel friction braking force FxMRTr is equal to the value obtained by subtracting the front wheel braking force FxAF from the vehicle braking force requirement value FxTr. The target value of the rear wheel friction braking force FxMRTr is the target value of the rear wheel friction braking force FxMR.

[0123] In step S437, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. For example, the processing circuit 81 sets the servo pressure Psc, which is used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr, as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. As a result, the processing circuit 81 reduces the servo pressure Psc according to the decrease in the vehicle braking force requirement value FxTr, thereby reducing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0124] Furthermore, the processing circuit 81 activates the front wheel hydraulic adjustment unit 74 so that the front wheel hydraulic pressure PwcF does not decrease as the servo pressure Psc decreases, as described above. For example, the processing circuit 81 maintains the magnitude of the current flowing in the solenoids of the multiple holding valves 642. Therefore, by maintaining the multiple holding valves 642 in a closed state, the processing circuit 81 can maintain the front wheel hydraulic pressure PwcF and the front wheel friction braking force FxMF even when the servo pressure Psc decreases. Then, the processing circuit 81 terminates the first reduction process. Afterwards, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0125] In step S45, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is greater than or equal to the second braking force Fx2. A braking force smaller than the first braking force Fx1 is set as the second braking force Fx2. For example, among the front wheel friction braking force FxMF, the rear wheel friction braking force FxMR, and the regenerative braking force FxR, when only the rear wheel friction braking force FxMR is reduced, the vehicle braking force Fx when the rear wheel hydraulic pressure PwcR is equal to the front wheel hydraulic pressure PwcF is set as the second braking force Fx2. That is, the second braking force Fx2 is the vehicle braking force Fx when the rear wheel hydraulic pressure PwcR is reduced by the execution of the second reduction process described later, and the rear wheel hydraulic pressure PwcR is equal to the front wheel hydraulic pressure PwcF. If the vehicle braking force requirement value FxTr is greater than or equal to the second braking force Fx2 (S45: Yes), the processing circuit 81 proceeds to step S47. On the other hand, if the vehicle braking force requirement value FxTr is less than the second braking force Fx2 (S45: No), the processing circuit 81 will transfer the processing to step S49.

[0126] In step S47, the processing circuit 81 performs a second reduction process. In the second reduction process, the processing circuit 81 maintains the regenerative braking force FxR and reduces the rear wheel hydraulic pressure PwcR by reducing the servo pressure Psc, while maintaining the front wheel hydraulic pressure PwcF.

[0127] In detail, in step S471, similar to step S211 above, the processing circuit 81 sends an instruction to maintain the regeneration braking force FxR to the regeneration control unit 92 of the regeneration device 90.

[0128] In the next step S473, the processing circuit 81 reduces the target hydraulic value PwcRTr for the rear wheels while maintaining the target hydraulic value PwcFTr for the front wheels. At this time, the processing circuit 81 reduces the target hydraulic value PwcRTr for the rear wheels in a manner that satisfies the following condition (E1).

[0129] (E1) The target value of the rear wheel friction braking force FxMRTr is equal to the value obtained by subtracting the front wheel braking force FxAF from the vehicle braking force requirement value FxTr.

[0130] In step S475, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. For example, the processing circuit 81 sets the servo pressure Psc, which is used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr, as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. As a result, the processing circuit 81 reduces the servo pressure Psc according to the decrease in the vehicle braking force requirement value FxTr, thereby reducing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0131] Furthermore, the processing circuit 81 activates the front wheel hydraulic adjustment unit 74 so that the front wheel hydraulic pressure PwcF does not decrease despite the reduction in servo pressure Psc. For example, the processing circuit 81 maintains the magnitude of the current flowing in the solenoids of the multiple holding valves 642. Thus, by maintaining the closed state of the multiple holding valves 642, the processing circuit 81 is able to maintain the front wheel hydraulic pressure PwcF and the front wheel friction braking force FxMF even when the servo pressure Psc decreases. Then, the processing circuit 81 terminates the second reduction process. Afterwards, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0132] In step S49, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is greater than or equal to the third braking force Fx3. A vehicle braking force Fx smaller than the second braking force Fx2 is set as the third braking force Fx3. For example, the vehicle braking force Fx when the vehicle braking force requirement value FxTr is equal to the upper limit value of the regenerative braking force FxRL is set as the third braking force Fx3. That is, the third braking force Fx3 is the vehicle braking force Fx when the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are both 0 (zero) after the execution of the third reduction process described later. If the vehicle braking force requirement value FxTr is greater than or equal to the third braking force Fx3 (S49: Yes), the processing circuit 81 proceeds to step S51. On the other hand, if the vehicle braking force requirement value FxTr is less than the third braking force Fx3 (S49: No), the processing circuit 81 proceeds to step S53.

[0133] In step S51, the processing circuit 81 performs a third reduction process. In the third reduction process, the processing circuit 81 maintains the regenerative braking force FxR and reduces both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR by reducing the servo pressure Psc.

[0134] In detail, in step S511, similar to step S211 above, the processing circuit 81 sends an instruction to maintain the regeneration braking force FxR to the regeneration control unit 92 of the regeneration device 90.

[0135] In the next step S513, the processing circuit 81 reduces the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. At this time, the processing circuit 81 reduces the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr in a manner that satisfies the following conditions (F1) and (F2).

[0136] (F1) The target hydraulic value of the rear wheel, PwcRTr, is equal to the target hydraulic value of the front wheel, PwcFTr.

[0137] (F2) The sum of the front wheel friction braking force FxMF and the rear wheel friction braking force FxMR is equal to the value obtained by subtracting the regenerative braking force FxR from the vehicle braking force requirement value FxTr.

[0138] In step S515, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. For example, the processing circuit 81 sets the servo pressure Psc, which is used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr, as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. As a result, the processing circuit 81 reduces the servo pressure Psc according to the decrease in the vehicle braking force requirement value FxTr, thereby reducing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0139] Furthermore, the front wheel hydraulic adjustment unit 74 has a check valve 732 arranged in parallel with the holding valve 642. Therefore, if the hydraulic pressure in the hydraulic circuit between the holding valve 642 and the second differential pressure control valve 632 is less than the front wheel hydraulic pressure PwcF due to the reduction of the servo pressure Psc, the check valve 732 opens. As a result, the brake fluid in the wheel cylinder 11 corresponding to the front wheel cylinder flows out through the check valve 732. As a result, the processing circuit 81 can reduce the front wheel hydraulic pressure PwcF and the front wheel friction braking force FxMF by reducing the servo pressure Psc, even without changing the magnitude of the current flowing in the solenoid of the holding valve 642.

[0140] If the processing circuit 81 reduces the servo pressure Psc via the electric cylinder 51, it terminates the third reduction process. Afterward, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0141] In step S53, the processing circuit 81 performs a fourth reduction process to decrease the regenerative braking force FxR. Specifically, in step S531, the processing circuit 81 reduces the target regenerative braking force FxRTr based on the decrease in the vehicle braking force requirement value FxTr. In the following step S533, similarly to step S173 above, the processing circuit 81 sends the target regenerative braking force value FxRTr to the regeneration control unit 92. The processing circuit 81 then ends the fourth reduction process. Afterwards, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0142] If the regenerative control unit 92 receives a target value for regenerative braking force FxRTr, it causes the electric generator 91 to generate electricity based on the target value FxRTr. Thus, the regenerative control unit 92 reduces the regenerative braking force FxR as the target value FxRTr decreases.

[0143] <The function and effects of this implementation method>

[0144] Reference Figure 5 as well as Figure 6 This explains the function and effect of the braking system 20 when the vehicle is braking. Figure 5(A) represents the vehicle braking force requirement value FxTr and the shift of the vehicle braking force Fx. Figure 5 (B) represents the target value of regenerative braking force FxRTr and the shift of regenerative braking force FxR. Figure 5 (C) represents the shift of the front wheel hydraulic target value PwcFTr, the rear wheel hydraulic target value PwcRTr, the front wheel hydraulic PwcF, and the rear wheel hydraulic PwcR.

[0145] Since a vehicle braking requirement arises from time T0, the processing circuit 81 of the control device 80 increases the vehicle braking force requirement value FxTr. During the period from time T0 to time T1, the vehicle braking force requirement value FxTr is below the upper limit value of regenerative braking force FxRL. When the vehicle braking force requirement value FxTr is increased while it is below the upper limit value of regenerative braking force FxRL, the processing circuit 81 performs a first increase process. The first increase process increases the regenerative braking force FxR based on the increase in the vehicle braking force requirement value FxTr, but does not increase the front wheel hydraulic pressure PwcF or the rear wheel hydraulic pressure PwcR. Therefore, in the first increase process, the processing circuit 81 increases the regenerative braking force target value FxRTr in a manner that keeps the regenerative braking force target value FxRTr equal to the vehicle braking force requirement value FxTr. If the control device 80 sends the regenerative braking force target value FxRTr to the regenerative control unit 92, the regenerative device 90 applies the regenerative braking force FxR corresponding to the regenerative braking force target value FxRTr to the front wheels FL and FR.

[0146] Furthermore, during the period from time T0 to time T1, although the front wheel braking force FxAF is increased, the rear wheel braking force FxAR is not increased. The state point P where no vehicle braking requirement arises is called the "initial state point P0". During the period from time T0 to time T1, such as... Figure 6 As shown, state point P moves from the initial state point P0 in the direction of the first arrow Y1. The first arrow Y1 indicates the direction along... Figure 6 The direction of the horizontal axis, which increases the front wheel braking force FxAF.

[0147] During the period from time T0 to time T1, although braking force is applied only to the front wheels FL and FR and the rear wheels RL and RR, the vehicle's braking force Fx is not very large. Therefore, even if only the front wheel braking force FxAF increases between the front wheel braking force FxAF and the rear wheel braking force FxAR, the vehicle will not exhibit a significant tendency to understeer.

[0148] return Figure 5Even after time T1, the processing circuit 81 increases the vehicle braking force requirement value FxTr. At time T1, the regenerative braking force target value FxRTr is equal to the regenerative braking force upper limit value FxRL. Therefore, at time T1, the processing circuit 81 switches the processing from the first increase processing to the second increase processing. That is, when the vehicle braking force requirement value FxTr is increased while the regenerative braking force FxR has reached the regenerative braking force upper limit value FxRL, the processing circuit 81 performs the second increase processing. The second increase processing increases the servo pressure Psc according to the increase in the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR, while maintaining the front wheel hydraulic pressure PwcF and the regenerative braking force FxR.

[0149] If the rear wheel hydraulic pressure PwcR increases, the rear wheel friction braking force FxMR increases. On the other hand, the front wheel hydraulic pressure PwcF is kept at 0 (zero), and the regenerative braking force FxR is maintained. Therefore, the rear wheel braking force FxAR increases, while the front wheel braking force FxAF is maintained.

[0150] exist Figure 6 In this context, the state point P at the end of the first incremental process is referred to as the "first state point PA". In this case, if the second incremental process begins, state point P moves from the first state point PA towards the direction of the second arrow Y2. The second arrow Y2 represents the direction along... Figure 6 The direction of the longitudinal axis, which increases the rear wheel braking force FxAR. For example... Figure 6 As shown, if the state point P moves in the direction of the second arrow Y2 as the vehicle braking force requirement value FxTr increases, then the state point P approaches the braking force distribution line L2 under the same pressure. Therefore, the braking system 20 can suppress the tendency of the vehicle to exhibit significant understeer due to the increase in vehicle braking force Fx.

[0151] return Figure 5 Even after time T2, the processing circuit 81 increases the vehicle braking force requirement value FxTr. At time T2, the vehicle braking force requirement value FxTr is equal to the first braking force Fx1. Therefore, at time T2, the processing circuit 81 switches the processing from the second increase processing to the third increase processing. That is, when the regenerative braking force FxR reaches the upper limit value of the regenerative braking force FxRL and the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1, the processing circuit 81 performs the third increase processing when increasing the vehicle braking force requirement value FxTr. The third increase processing increases the servo pressure Psc according to the increase in the vehicle braking force requirement value FxTr, thereby increasing the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR, while maintaining the regenerative braking force FxR.

[0152] If the rear wheel hydraulic pressure PwcR increases, the rear wheel friction braking force FxMR increases. If the front wheel hydraulic pressure PwcF increases, the front wheel friction braking force FxMF increases. Therefore, even if the regenerative braking force FxR remains constant, both the front wheel braking force FxAF and the rear wheel braking force FxAR increase.

[0153] exist Figure 6 In this context, the state point P at the end of the second increase process is referred to as the "second state point PB". The second state point PB is the action point on the brake force distribution line L2 under the same pressure. If the third increase process begins, the state point P moves from the second state point PB in the direction of the third arrow Y3. The third arrow Y3 is the direction along the brake force distribution line L2 under the same pressure that increases the rear wheel braking force FxAR. Therefore, when the state point P moves in the direction of the third arrow Y3 according to the increase of the vehicle's required braking force value FxTr, the state point P moves on the brake force distribution line L2 under the same pressure.

[0154] return Figure 5 At time T3, the processing circuit 81 begins to maintain the vehicle braking force requirement value FxTr. Therefore, the processing circuit 81 maintains the front wheel friction braking force FxMF, the rear wheel friction braking force FxMR, and the regenerative braking force FxR.

[0155] After timing T4, the processing circuit 81 reduces the vehicle braking force requirement value FxTr. During the period from timing T4 to timing T5, the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1. Therefore, the processing circuit 81 performs a first reduction process. That is, when reducing the vehicle braking force requirement value FxTr while it is greater than or equal to the first braking force Fx1, the processing circuit 81 performs a first reduction process. The first reduction process reduces the regenerative braking force FxR and reduces the rear wheel hydraulic pressure PwcR by reducing the servo pressure Psc, while maintaining the front wheel hydraulic pressure PwcF.

[0156] If the rear wheel hydraulic pressure PwcR decreases, the rear wheel friction braking force FxMR decreases. If the front wheel hydraulic pressure PwcF is maintained, the front wheel friction braking force FxMF is also maintained. However, because the regenerative braking force FxR decreases, both the front wheel braking force FxAF and the rear wheel braking force FxAR decrease.

[0157] Here, we consider the case where, starting from time T4, a reduction process is performed that maintains the regenerative braking force FxR while reducing the rear wheel braking force FxAR. In this case, since the regenerative braking force FxR does not decrease, the regenerative energy recovery efficiency is higher compared to the case where the first increase process is performed. However, because the proportion of the front wheel braking force FxAF in the vehicle's braking force Fx increases, the vehicle may exhibit a greater tendency to understeer.

[0158] That is, in Figure 6 In this context, the state point P immediately preceding the reduction of the vehicle's required braking force FxTr is designated as the "third state point PC". In this state, while maintaining the regenerative braking force FxR and the front wheel friction braking force FxMF, and reducing the rear wheel friction braking force FxMR, state point P moves from the third state point PC towards the direction of the dashed arrow YA. The dashed arrow YA represents the direction along... Figure 6 The direction of the longitudinal axis, which reduces the rear wheel braking force FxAR. Therefore, as... Figure 6 As shown, when the vehicle's braking force Fx is relatively large, the state point P deviates significantly from the braking force distribution line L2 under the same pressure towards the direction of increasing the braking force distribution to the front wheels FL and FR. Therefore, as the vehicle's braking force Fx decreases, the vehicle may exhibit a greater tendency to understeer. This understeer tendency occurs when the vehicle is turning, for example, when the driver increases the steering input to maintain the vehicle's trajectory.

[0159] In this regard, in the braking system 20, the processing circuit 81 begins a first reduction process starting from timing T4. If the first reduction process is executed, as described above, both the front wheel braking force FxAF and the rear wheel braking force FxAR are reduced.

[0160] That is, in Figure 6 In this process, state point P moves from the third state point PC towards the direction of the fourth arrow Y4. The fourth arrow Y4 is the direction of reducing the rear wheel braking force FxAR along the braking force distribution line L2 under the same pressure. Therefore, if state point P moves towards the direction of the fourth arrow Y4 according to the reduction of the vehicle braking force requirement value FxTr, then state point P moves on the braking force distribution line L2 under the same pressure. That is, it suppresses the state point P from deviating from the braking force distribution line L2 under the same pressure when the vehicle braking force Fx is relatively large. Therefore, when reducing the vehicle braking force Fx while applying regenerative braking force FxR to the front wheels FL and FR, the braking system 20 can suppress the vehicle from exhibiting a large tendency for understeer.

[0161] return Figure 5 Even after time T5, the processing circuit 81 reduces the vehicle braking force requirement value FxTr. At time T5, the vehicle braking force requirement value FxTr is equal to the first braking force Fx1. Therefore, at time T5, the processing circuit 81 switches the processing from the first reduction processing to the second reduction processing. That is, when reducing the vehicle braking force requirement value FxTr while it is less than the first braking force Fx1 and greater than the second braking force Fx2, the processing circuit 81 performs the second reduction processing. The second reduction processing maintains the regenerative braking force FxR and reduces the rear wheel hydraulic pressure PwcR by reducing the servo pressure Psc, while maintaining the front wheel hydraulic pressure PwcF.

[0162] If the rear wheel hydraulic pressure PwcR decreases, the rear wheel friction braking force FxMR decreases. If the front wheel hydraulic pressure PwcF is maintained, the front wheel friction braking force FxMF is maintained. In this case, since the regenerative braking force FxR is also maintained, the rear wheel braking force FxAR decreases while the front wheel braking force FxAF is maintained.

[0163] The vehicle braking force requirement value FxTr at the end of the first reduction process is equal to the first braking force Fx1. Therefore, in Figure 6 In the diagram, the state point P at the end of the first reduction process is the second state point PB. Furthermore, if the second reduction process begins, state point P moves from the second state point PB towards the direction of the fifth arrow Y5. The fifth arrow Y5 represents moving along... Figure 6 The direction of the longitudinal axis, which reduces the rear wheel braking force FxAR.

[0164] Here, if the state point P moves in the direction of the fifth arrow Y5 as the vehicle braking force demand value FxTr decreases, then the state point P deviates from the braking force distribution line L2 under the same pressure. However, at this moment, the vehicle braking force Fx is relatively small. Therefore, even if the state point P deviates from the braking force distribution line L2 under the same pressure, the vehicle's understeer tendency will not be as great. That is, the braking system 20 can suppress the increase of the vehicle's understeer tendency and reduce the vehicle braking force Fx.

[0165] return Figure 5 Even after time T6, the processing circuit 81 reduces the vehicle braking force requirement value FxTr. At time T6, the vehicle braking force requirement value FxTr is equal to the second braking force Fx2. Furthermore, at time T6, if... Figure 5 As shown in (C), the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are equal. Therefore, at timing T6, the processing circuit 81 switches the processing from the second reduction processing to the third reduction processing. That is, when the vehicle braking force requirement value FxTr is reduced while the second braking force Fx2 is less than or equal to the third braking force Fx3, the processing circuit 81 performs the third reduction processing. The third reduction processing maintains the regenerative braking force FxR and reduces both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR by reducing the servo pressure Psc.

[0166] If the rear wheel hydraulic pressure PwcR decreases, the rear wheel friction braking force FxMR decreases. If the front wheel hydraulic pressure PwcF decreases, the front wheel friction braking force FxMF decreases. Therefore, even if the regenerative braking force FxR is maintained, both the front wheel braking force FxAF and the rear wheel braking force FxAR decrease.

[0167] The front wheel hydraulic adjustment unit 74 of the braking system 20 has a holding valve 642 and a check valve 732 arranged in parallel with the holding valve 642. The check valve 732 opens when the hydraulic pressure on the side closer to the main unit 30 than the holding valve 642 is less than the front wheel hydraulic pressure PwcF. When the check valve 732 is open, brake fluid flows from the wheel cylinders 11 of the front wheels FL and FR towards the main unit 30 via the check valve 732. Therefore, in the braking system 20, the servo pressure Psc is reduced by the operation of the pressure regulating unit 50, resulting in a reduction in both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR. Therefore, control is simpler compared to the case where the front wheel hydraulic pressure PwcF is reduced by decreasing the current flowing in the solenoid of the holding valve 642.

[0168] exist Figure 6 In the diagram, the state point P at the end of the second reduction process is the fourth state point PE. Therefore, if the third reduction process begins, state point P moves from the fourth state point PE in the direction of the sixth arrow Y6. The sixth arrow Y6 represents the direction that reduces both the front wheel braking force FxAF and the rear wheel braking force FxAR.

[0169] return Figure 5 Even after timer T7, the processing circuit 81 reduces the vehicle braking force requirement value FxTr. At timer T7, the vehicle braking force requirement value FxTr is equal to the third braking force Fx3. In this case, if... Figure 5 As shown in (C), both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR are 0 (zero). That is, since both the front wheel friction braking force FxMF and the rear wheel friction braking force FxMR are 0 (zero), the regenerative braking force FxR is equal to the vehicle braking force requirement value FxTr. Therefore, at time T7, the processing circuit 81 switches the processing from the third reduction processing to the fourth reduction processing. That is, when reducing the vehicle braking force requirement value FxTr when it is less than the third braking force Fx3, the processing circuit 81 performs the fourth reduction processing. The fourth reduction processing is the process of reducing the regenerative braking force FxR. Figure 5 In the example shown, at time T8, the vehicle braking force requirement value FxTr is 0 (zero).

[0170] exist Figure 6 In the process, the state point P at the end of the third reduction process is the fifth state point PF. The fifth state point PF is a point on the horizontal axis. Therefore, by reducing the target value of the regenerative braking force FxRTr, the state point P moves from the fifth state point PF in the direction of the seventh arrow Y7. The seventh arrow Y7 represents the direction of reducing the front wheel braking force FxAF along the horizontal axis. And, the state point P returns to the initial state point P0.

[0171] (Second Implementation)

[0172] according to Figures 7 to 9 This section describes a second embodiment of the braking system. Furthermore, in the second embodiment, since the upper limit of the regenerative power that the regenerative device can apply to the front wheels is larger, a portion of the regenerative coordination control differs from that of the first embodiment. In the following description, the parts that differ from the first embodiment will be primarily explained; for components identical to those in the first embodiment, the same symbols will be used, and repeated descriptions will be omitted.

[0173] <Regeneration Device>

[0174] The vehicle's regenerative braking device 90 can apply a regenerative braking force FxR to the front wheels FL and FR that is greater than the first braking force Fx1. That is, the upper limit of the regenerative braking force FxRL is greater than the first braking force Fx1.

[0175] <Regeneration Coordination Control>

[0176] Reference Figure 7 This explains the regeneration coordination control performed in this embodiment.

[0177] In step S11, the processing circuit 81 derives the vehicle braking force requirement value FxTr. In the next step S13, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr has increased. If the processing circuit 81 determines that the vehicle braking force requirement value FxTr has increased (S13: Yes), the processing proceeds to step S16. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr has not increased (S13: No), the processing proceeds to step S31. The processing flow after step S31 is the same as in the first embodiment, so the description is omitted.

[0178] In step S16, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is less than the switching regenerative braking force FxRA. The braking force that is smaller than the upper limit value of the regenerative braking force FxRL and the first braking force Fx1 is set as the switching regenerative braking force FxRA.

[0179] In a vehicle equipped with braking system 20, regenerative braking force FxR is applied only to the front wheels FL and FR and the rear wheels RL and RR. Therefore, if the regenerative braking force FxR applied to the front wheels FL and FR is increased to the upper limit of regenerative braking force FxRL through the first increase process described later, the vehicle's understeer tendency may increase. Therefore, the braking force that reduces the vehicle's understeer tendency to an acceptable level even when regenerative braking force FxR is applied to the front wheels FL and FR through the execution of the first increase process is set to switch the regenerative braking force FxRA.

[0180] If the processing circuit 81 determines that the vehicle braking force requirement value FxTr is less than the switching regenerative braking force FxRA (S16: Yes), the processing will proceed to step S17. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr is greater than or equal to the switching regenerative braking force FxRA (S16: No), the processing will proceed to step S19.

[0181] In step S17, the processing circuit 81 performs a first addition process. The content of the first addition process is the same as that of the first addition process performed in the first embodiment described above, so the description of the first addition process is omitted.

[0182] In step S19, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is less than the first braking force Fx1. If the processing circuit 81 determines that the vehicle braking force requirement value FxTr is less than the first braking force Fx1 (S19: Yes), the processing proceeds to step S21. On the other hand, if the processing circuit 81 determines that the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1 (S19: No), the processing proceeds to step S25.

[0183] In step S21, the processing circuit 81 performs a second addition process. The content of the second addition process is the same as that of the second addition process performed in the first embodiment described above, therefore the description of the second addition process is omitted.

[0184] In step S25, the processing circuit 81 determines whether the vehicle braking force requirement value FxTr is less than the regenerative braking force upper limit value FxRL. If the vehicle braking force requirement value is less than the regenerative braking force upper limit value FxRL (S25: Yes), the processing circuit 81 proceeds to step S27. On the other hand, if the vehicle braking force requirement value is greater than or equal to the regenerative braking force upper limit value FxRL (S25: No), the processing circuit 81 proceeds to step S29.

[0185] In step S27, the processing circuit 81 performs a third increase process. This third increase process differs from the third increase process described in the first embodiment. In this third increase process, the processing circuit 81 increases the regenerative braking force FxR based on the increase in the vehicle braking force requirement value FxTr, and increases the servo pressure Psc based on the increase in the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR while maintaining the front wheel hydraulic pressure PwcF.

[0186] Specifically, in step S271, the processing circuit 81 increases the regenerative braking force target value FxRTr. For example, the processing circuit 81 sets a value that maintains the distribution ratio of the front wheel braking force FxAF to the rear wheel braking force FxAR at the aforementioned reference front-rear distribution ratio as the regenerative braking force target value FxRTr. In the next step S273, the processing circuit 81 sends the regenerative braking force target value FxRTr to the regenerative control unit 92.

[0187] If the regenerative control unit 92 receives a target value for regenerative braking force FxRTr, it causes the electric generator 91 to generate electricity based on the target value FxRTr. Thus, the regenerative control unit 92 can increase the regenerative braking force FxR as the target value FxRTr increases.

[0188] In the next step S275, the processing circuit 81 increases the rear wheel hydraulic target value PwcRTr and keeps the front wheel hydraulic target value PwcFTr at 0 (zero). The processing circuit 81 derives a value that maintains the distribution ratio of the front wheel braking force FxAF to the rear wheel braking force FxAR at the aforementioned reference front-rear distribution ratio, and uses this value as the rear wheel friction braking force target value FxMRTr. Furthermore, the processing circuit 81 sets the value obtained by converting the rear wheel friction braking force target value FxMRTr into rear wheel hydraulic pressure, and uses this value as the rear wheel hydraulic pressure target value PwcRTr.

[0189] In step S277, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. For example, the processing circuit 81 sets the servo pressure Psc, which is used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr, as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. Thus, the processing circuit 81 increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0190] Furthermore, the processing circuit 81 activates the front wheel hydraulic adjustment unit 74 so that, as described above, even if the servo pressure Psc is increased, the front wheel hydraulic pressure PwcF does not increase. For example, the processing circuit 81 maintains the front wheel hydraulic pressure PwcF by closing the multiple holding valves 642 of the front wheel hydraulic adjustment unit 74. At this time, the greater the differential pressure between the servo pressure Psc and the target front wheel hydraulic pressure value PwcFTr, the greater the current flowing in the solenoid of the holding valve 642 caused by the processing circuit 81. Then, the processing circuit 81 terminates the third increase process. Afterwards, the processing circuit 81 temporarily terminates the regeneration coordination control.

[0191] In step S29, the processing circuit 81 performs a fourth increase process. In the fourth increase process, the processing circuit 81 maintains the regenerative braking force FxR and increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0192] In detail, in step S291, similar to step S211 above, the processing circuit 81 sends an instruction to maintain the regeneration braking force FxR to the regeneration control unit 92 of the regeneration device 90.

[0193] In the next step S293, the processing circuit 81 increases the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. At this time, the processing circuit 81 increases the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr in a manner that satisfies the following conditions (G1), (G2) and (G3).

[0194] (G1) Maintain the difference between the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR at the start of the fourth increase process.

[0195] (G2) The sum of the front wheel friction braking force FxMF, the rear wheel friction braking force FxMR, and the regenerative braking force FxR is equal to the vehicle braking force requirement value FxTr.

[0196] (G3) The distribution ratio of front wheel braking force FxAF to rear wheel braking force FxAR is the same as the above-mentioned front-rear distribution ratio.

[0197] In addition, the difference between the rear wheel hydraulic pressure PwcR and the front wheel hydraulic pressure PwcF at the start of the fourth additional processing is also called the "reference hydraulic pressure difference ΔPwcB1".

[0198] In step S295, the processing circuit 81 activates the braking system 20 based on the front wheel hydraulic target value PwcFTr and the rear wheel hydraulic target value PwcRTr. For example, the processing circuit 81 sets the servo pressure Psc, which is used to make the rear wheel hydraulic pressure PwcR equal to the rear wheel hydraulic target value PwcRTr, as the servo pressure target value PscTr. The processing circuit 81 activates the electric cylinder 51 based on this servo pressure target value PscTr. Thus, the processing circuit 81 increases the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR and the rear wheel friction braking force FxMR.

[0199] Furthermore, the processing circuit 81 activates the front wheel hydraulic adjustment unit 74 to increase the front wheel hydraulic pressure PwcF as described above, based on the increase in servo pressure Psc. For example, the processing circuit 81 sets the magnitude of the current flowing in the solenoids of the multiple holding valves 642 to a value corresponding to the aforementioned reference hydraulic pressure difference ΔPwcB1. Thus, the processing circuit 81 increases the servo pressure Psc based on the increase in the vehicle braking force requirement value FxTr, thereby increasing the front wheel hydraulic pressure PwcF and the front wheel friction braking force FxMF. Then, the processing circuit 81 terminates the fourth increase process. Afterward, the processing circuit 81 temporarily terminates the regenerative coordination control.

[0200] <The function and effects of this implementation method>

[0201] Reference Figure 8 as well as Figure 9 The explanation will focus on the parts of the braking system 20 that differ from the first embodiment in terms of its function and effect when the vehicle is braking. Figure 8 (A) represents the vehicle braking force requirement value FxTr and the shift of the vehicle braking force Fx. Figure 8 (B) represents the target value of regenerative braking force FxRTr and the shift of regenerative braking force FxR. Figure 8 (C) represents the shift of the front wheel hydraulic target value PwcFTr, the rear wheel hydraulic target value PwcRTr, the front wheel hydraulic PwcF, and the rear wheel hydraulic PwcR.

[0202] Starting from time T10, a vehicle braking requirement is generated, therefore the processing circuit 81 of the control device 80 increases the vehicle braking force requirement value FxTr. During the period from time T10 to time T11, the vehicle braking force requirement value FxTr is below the switching regenerative braking force FxRA. When the vehicle braking force requirement value FxTr is increased while it is less than the switching regenerative braking force FxRA, the processing circuit 81 performs a first increase process. The first increase process increases the regenerative braking force FxR based on the increase in the vehicle braking force requirement value FxTr, but does not increase the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0203] Furthermore, during the period from time T10 to time T11, although the front wheel braking force FxAF increases, the rear wheel braking force FxAR does not increase. Therefore, during the period from time T10 to time T11, if... Figure 9 As shown, state point P moves from the initial state point P0 in the direction of the first arrow Y11. The first arrow Y11 indicates the direction along... Figure 9 The direction of the horizontal axis, which increases the front wheel braking force FxAF.

[0204] During the period from time T10 to time T11, Figure 9The mid-state point P deviates from the braking force distribution line L2 under the same pressure. However, during this period, the vehicle's braking force Fx is not that large. Therefore, even if only the front wheel braking force FxAF increases among the front wheel braking force FxAF and the rear wheel braking force FxAR, as shown by the first arrow Y11, the vehicle's understeer tendency is not likely to increase significantly.

[0205] return Figure 8 Even after time T11, the processing circuit 81 increases the vehicle braking force requirement value FxTr. At time T11, the regenerative braking force target value FxRTr is equal to the switching regenerative braking force FxRA. Therefore, at time T11, the processing circuit 81 switches the processing from the first increase processing to the second increase processing. That is, when the regenerative braking force FxR reaches the switching regenerative braking force FxRA and the vehicle braking force requirement value FxTr is less than the first braking force Fx1, the processing circuit 81 performs the second increase processing when increasing the vehicle braking force requirement value FxTr. The second increase processing is the process of increasing the servo pressure Psc according to the increase of the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR, while maintaining the front wheel hydraulic pressure PwcF, and maintaining the regenerative braking force FxR.

[0206] If the rear wheel hydraulic pressure PwcR increases, the rear wheel friction braking force FxMR increases. On the other hand, the front wheel hydraulic pressure PwcF is kept at 0 (zero), and the regenerative braking force FxR is maintained. Therefore, the rear wheel braking force FxAR increases, while the front wheel braking force FxAF is maintained.

[0207] exist Figure 9 In this context, the state point P at the end of the first increment process is referred to as "first state point PA1". In this case, if the second increment process begins, state point P moves from first state point PA1 in the direction of the second arrow Y12. The second arrow Y12 represents the direction along... Figure 9 The direction of the longitudinal axis, which increases the rear wheel braking force FxAR. For example... Figure 9 As shown, if the state point P moves in the direction of the second arrow Y12 as the vehicle braking force requirement value FxTr increases, then the state point P approaches the braking force distribution line L2 under the same pressure. Therefore, the braking system 20 can suppress the increased tendency of the vehicle to understeer due to the increase in the vehicle braking force Fx.

[0208] return Figure 8Even after time T12, the processing circuit 81 increases the vehicle braking force requirement value FxTr. At time T12, the vehicle braking force requirement value FxTr is greater than the first braking force Fx1. Furthermore, the regenerative braking force FxR is equal to the switching regenerative braking force FxRA. Therefore, at time T12, the processing circuit 81 switches the processing from the second increase processing to the third increase processing. That is, when the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1, and on the other hand, the regenerative braking force FxR is greater than or equal to the switching regenerative braking force FxRA but less than the upper limit value of the regenerative braking force FxRL, and the vehicle braking force requirement value FxTr is increased, the processing circuit 81 performs the third increase processing. The third increase processing increases the regenerative braking force FxR based on the increase in the vehicle braking force requirement value FxTr, and increases the servo pressure Psc based on the increase in the vehicle braking force requirement value FxTr, thereby increasing the rear wheel hydraulic pressure PwcR while maintaining the front wheel hydraulic pressure PwcF.

[0209] If the rear wheel hydraulic pressure PwcR increases, the rear wheel friction braking force FxMR increases, and the regenerative braking force FxR also increases. Therefore, even if the front wheel hydraulic pressure PwcF does not increase, both the front wheel braking force FxAF and the rear wheel braking force FxAR will increase.

[0210] exist Figure 9 In this context, the state point P at the end of the second increase process is referred to as "second state point PB1". In this case, if the third increase process begins, state point P moves from second state point PB1 towards the direction of the third arrow Y13. The third arrow Y13 is the direction along the brake force distribution line L2 under equal pressure, which increases the rear wheel braking force FxAR. Therefore, when state point P moves towards the direction of the third arrow Y13 according to the increase in the vehicle's required braking force value FxTr, state point P moves along the brake force distribution line L2 under equal pressure.

[0211] return Figure 8 Even after time T13, the processing circuit 81 increases the vehicle braking force requirement value FxTr. At time T13, the regenerative braking force FxR is equal to the upper limit value of the regenerative braking force FxRL. Therefore, at time T13, the processing circuit 81 switches the processing from the third increase processing to the fourth increase processing. That is, when the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1, and on the other hand, the regenerative braking force FxR reaches the upper limit value of the regenerative braking force FxRL, the processing circuit 81 performs the fourth increase processing when increasing the vehicle braking force requirement value FxTr. The fourth increase processing maintains the regenerative braking force FxR and increases the servo pressure Psc according to the increase in the vehicle braking force requirement value FxTr, thereby increasing both the front wheel hydraulic pressure PwcF and the rear wheel hydraulic pressure PwcR.

[0212] If the front wheel hydraulic pressure PwcF increases, the front wheel friction braking force FxMF increases. If the rear wheel hydraulic pressure PwcR increases, the rear wheel friction braking force FxMR increases. Therefore, even if the regenerative braking force FxR remains constant, both the front wheel braking force FxAF and the rear wheel braking force FxAR increase.

[0213] exist Figure 9 In this context, the state point P at the end of the third additional process is referred to as the "third state point PC1". In this case, if the fourth additional process begins, state point P moves from the third state point PC1 in the direction of the third arrow Y13. That is, state point P moves along the braking force distribution line L2 under the same pressure.

[0214] return Figure 8 If the timer is T14, the processing circuit 81 maintains the vehicle braking force requirement value FxTr. Therefore, the processing circuit 81 maintains the front wheel friction braking force FxMF, the rear wheel friction braking force FxMR, and the regenerative braking force FxR.

[0215] After timing T15, processing circuit 81 reduces the vehicle braking force requirement value FxTr. During the period from timing T15 to timing T16, processing circuit 81 performs a first reduction process. During the period from timing T16 to timing T17, processing circuit 81 performs a second reduction process. During the period from timing T17 to timing T18, processing circuit 81 performs a third reduction process. Furthermore, during the period from timing T18 to timing T19, processing circuit 81 reduces the regenerative braking force target value FxRTr towards 0 (zero).

[0216] exist Figure 9 In the above, the state point P at the end of the fourth increase process is the fourth state point PD1 on the braking force distribution line L2 under the same pressure. Furthermore, if the first decrease process is performed, state point P moves from the fourth state point PD1 in the direction of the fourth arrow Y14. The fourth arrow Y14 is the direction along the braking force distribution line L2 under the same pressure, which reduces the rear wheel braking force FxAR. Furthermore, if state point P reaches the second state point PB1, the second decrease process is performed. Therefore, state point P moves from the second state point PB1 in the direction of the fifth arrow Y15. The fifth arrow Y15 represents the direction along... Figure 9 The direction of the longitudinal axis is the direction that reduces the rear wheel braking force FxAR. Then, if the third reduction process is performed, the state point P moves in the direction of the sixth arrow Y16. The sixth arrow Y16 indicates the direction that reduces both the front wheel braking force FxAF and the rear wheel braking force FxAR. If the fourth reduction process is finally performed, the state point P moves in the direction of the seventh arrow Y17. The seventh arrow Y17 indicates the direction along the longitudinal axis. Figure 9The direction of the horizontal axis is the direction of reducing the front wheel braking force FxAF. Furthermore, state point P returns to the initial state point P0.

[0217] (Example of amendment)

[0218] The above-described embodiments can be modified as follows. The above-described embodiments and the following modifications can be combined and implemented within the scope of technical inconsistency.

[0219] • In the second embodiment described above, when the vehicle braking force requirement value FxTr is greater than or equal to the first braking force Fx1, and on the other hand, the regenerative braking force FxR is greater than or equal to the switching regenerative braking force FxRA and less than the upper limit value of the regenerative braking force FxRL, the processing circuit 81 performs the fourth increase process when the vehicle braking force requirement value FxTr is increased.

[0220] • When the vehicle's regenerative braking device 90 is able to apply a regenerative braking force FxR greater than the first braking force Fx1 to the front wheels FL and FR, the braking system 20 implements the second embodiment described above, but is not limited thereto. Alternatively, even when the braking system 20 is able to apply a regenerative braking force FxR greater than the first braking force Fx1 to the front wheels FL and FR, it may perform the same regenerative coordination control as the first embodiment described above when predetermined conditions are met.

[0221] • In the third reduction process, the processing circuit 81 can also gradually reduce the magnitude of the current flowing in the solenoid of the holding valve 642 of the front wheel hydraulic adjustment unit 74, thereby reducing the front wheel FL and FR according to the reduction of the servo pressure Psc.

[0222] • If the rear wheel hydraulic pressure PwcR is reduced by the execution of the second reduction process, thereby making the rear wheel hydraulic pressure PwcR equal to the front wheel hydraulic pressure PwcF, the processing circuit 81 may not execute the third reduction process. For example, the processing circuit 81 may also execute a process in which the front wheel hydraulic pressure PwcF, the rear wheel hydraulic pressure PwcR, and the regenerative braking force FxR are all reduced based on the reduction of the vehicle braking force requirement value FxTr.

[0223] • As a pressure regulating unit, a unit other than the pressure regulating unit 50, which has an electric cylinder 51 as a pressure source, may also be used. For example, the pressure regulating unit may also be a unit that has an electric pump as a pressure source. An example of such a pressure regulating unit is disclosed in Japanese Patent Application Publication No. 2019-182278.

[0224] • As a hydraulic generating device, it can also be used with Figure 1The hydraulic generating device 22 shown is configured in different ways. In the hydraulic generating device 22, brake fluid output from the pressure regulating unit 50 is supplied to the servo chamber Rs of the master cylinder 31. Furthermore, as the hydraulic pressure in the servo chamber Rs increases, brake fluid is supplied from the master cylinder 31 to the wheel cylinders 11 for the front wheels FL and FR. However, the hydraulic generating device may also be configured to supply brake fluid output from the pressure regulating unit to the wheel cylinders 11 for the front wheels FL and FR without passing through the master cylinder 31.

[0225] • The processing circuit 81 is not limited to a circuit that performs software processing by having a CPU and ROM. That is, the processing circuit 81 can be configured as any one of the following (a), (b) and (c).

[0226] (a) The processing circuit 81 includes one or more processors that perform various processes according to a computer program. The processor includes a CPU and memories such as RAM and ROM. The memories store program code or instructions configured to cause the CPU to perform processes. Memory, i.e., computer-readable media, includes all available media that can be accessed by a general-purpose or special-purpose computer.

[0227] (b) The processing circuit 81 has one or more dedicated hardware circuits for performing 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," and FPGA is an abbreviation for "Field Programmable Gate Array."

[0228] (c) The processing circuit 81 includes: a processor that performs a portion of various processes according to a computer program, and dedicated hardware circuitry that performs the remaining processes in the various processes.

[0229] Other Technological Ideas

[0230] The document records the technical ideas that can be grasped from the above-mentioned multiple implementation methods and variations.

[0231] [Note 1] Preferably, the above braking system includes:

[0232] The master cylinder is configured to have a main piston that divides the servo chamber and the main chamber. The main piston moves as the hydraulic pressure in the servo chamber increases, causing brake fluid to flow out of the main chamber. On the other hand, the main piston moves as the hydraulic pressure in the servo chamber decreases, causing brake fluid to flow into the main chamber.

[0233] The first fluid supply path connects the pressure regulating unit to the servo chamber; and

[0234] The second fluid supply path branches off from the first fluid supply path.

[0235] Furthermore, brake fluid flowing from the first supply fluid passage into the second supply fluid passage is supplied to the rear wheel cylinder, and brake fluid flowing out of the main chamber is supplied to the front wheel cylinder.

[0236] Furthermore, the term "at least one" as used in this specification means "more than one" of the desired options. As an example, regarding the use of "at least one" in this specification, if the number of options is two, it means "only one option" or "both options". As another example, regarding the use of "at least one" in this specification, if the number of options is three or more, it means "only one option" or "a combination of any two or more options".

Claims

1. A braking system applied to a vehicle, controlling the braking force applied to the vehicle, the vehicle comprising: front wheel cylinders and rear wheel cylinders; a front wheel subjected to a frictional braking force corresponding to the hydraulic pressure of the front wheel cylinders, i.e., front wheel hydraulic pressure; a rear wheel subjected to a frictional braking force corresponding to the hydraulic pressure of the rear wheel cylinders, i.e., rear wheel hydraulic pressure; and a regenerative device for applying a regenerative braking force to the front wheel, wherein... This braking system has the following features: The pressure regulating unit generates a reference hydraulic pressure and generates the aforementioned rear wheel hydraulic pressure corresponding to the reference hydraulic pressure; The front wheel hydraulic adjustment unit is configured to, when the aforementioned reference hydraulic pressure is generated, make the front wheel hydraulic pressure less than the rear wheel hydraulic pressure; and The control device controls the regenerative device, the pressure regulating unit, and the front wheel hydraulic adjustment unit based on the required vehicle braking force value. When the required braking force for the vehicle is greater than or equal to the first braking force, the control device controls the regenerative braking device, the pressure regulating unit, and the front wheel hydraulic adjustment unit to apply regenerative braking force to the front wheels and friction braking force to both the front and rear wheels. When the required braking force of the vehicle is greater than or equal to the first braking force, and the required braking force of the vehicle is reduced, the control device performs the following first reduction process: reducing the regenerative braking force applied to the front wheels, reducing the hydraulic pressure of the rear wheels by reducing the reference hydraulic pressure, and maintaining the hydraulic pressure of the front wheels.

2. The braking system according to claim 1, wherein, When the required braking force value of the vehicle is less than the first braking force and is greater than or equal to the second braking force which is less than the first braking force, and the required braking force value of the vehicle is reduced, the control device performs the following second reduction process: maintaining the regenerative braking force applied to the front wheels, reducing the hydraulic pressure of the rear wheels by reducing the reference hydraulic pressure, and maintaining the hydraulic pressure of the front wheels.

3. The braking system according to claim 2, wherein, When the required braking force value of the vehicle is less than the second braking force and is greater than or equal to the third braking force which is less than the second braking force, and the required braking force value of the vehicle is reduced, the control device performs the following third reduction process: maintaining the regenerative braking force applied to the front wheels, and reducing the hydraulic pressure of both the front wheels and the rear wheels by reducing the reference hydraulic pressure.

4. The braking system according to claim 3, wherein, The aforementioned second braking force is the vehicle braking force when the rear wheel hydraulic pressure is reduced to be equal to the front wheel hydraulic pressure by the execution of the aforementioned second reduction process.

5. The braking system according to claim 4, wherein, The aforementioned third braking force is the vehicle braking force when the hydraulic pressure of both the front wheels and the rear wheels is zero due to the execution of the aforementioned third reduction process. When the required braking force of the vehicle is less than the third braking force, and the required braking force of the vehicle is reduced, the control device performs the fourth reduction process as follows: reducing the regenerative braking force applied to the front wheels.

6. The braking system according to claim 3 or 4, wherein, It is equipped with a main device that generates the aforementioned front wheel hydraulic pressure corresponding to the aforementioned reference hydraulic pressure. The aforementioned front wheel hydraulic adjustment unit has: As a holding valve of the linear solenoid valve, it is provided in the hydraulic circuit connecting the main device and the front wheel cylinder, adjusting the differential pressure between the portion on the main device side and the portion on the front wheel cylinder side; and The inspection valve is configured in parallel with the holding valve. The aforementioned inspection valve is configured such that it closes when the hydraulic pressure on the main unit side, which is greater than or equal to the front wheel hydraulic pressure, and opens when the hydraulic pressure on the main unit side, which is less than or equal to the front wheel hydraulic pressure, allowing brake fluid to flow from the front wheel cylinders to the main unit. In the third reduction process, the control device activates the pressure regulating unit to reduce the hydraulic pressure of both the front and rear wheels, thereby reducing the hydraulic pressure generated by the main device (i.e., the main pressure) to the level of the front wheels.

7. The braking system according to claim 1, wherein, The above control device performs the following processing: The first increase process is as follows: when the required vehicle braking force is less than the upper limit of the regenerative braking force that can be applied to the front wheels, i.e., the upper limit of the regenerative braking force, and the required vehicle braking force is increased, the regenerative braking force applied to the front wheels is increased according to the increase in the required vehicle braking force, while the hydraulic pressure of the front wheels and the hydraulic pressure of the rear wheels are not increased. The second additional process involves increasing the vehicle's braking force requirement when the regenerative braking force applied to the front wheels reaches the upper limit of the regenerative braking force. This is achieved by increasing the reference hydraulic pressure based on the increase in the vehicle's braking force requirement, thereby increasing the hydraulic pressure of the rear wheels while maintaining the hydraulic pressure of the front wheels and maintaining the regenerative braking force applied to the front wheels. as well as The third additional process involves increasing the vehicle braking force requirement when the regenerative braking force applied to the front wheels reaches the upper limit of the regenerative braking force and the vehicle braking force requirement is greater than or equal to the first braking force. In this case, the reference hydraulic pressure is increased according to the increase in the vehicle braking force requirement, thereby increasing both the hydraulic pressure of the front wheels and the hydraulic pressure of the rear wheels, while maintaining the regenerative braking force applied to the front wheels.

8. The braking system according to claim 1, wherein, As a braking force smaller than the upper limit of the regenerative braking force, a switching regenerative braking force is set. The upper limit of the regenerative braking force is the upper limit of the regenerative braking force that the regenerative device can apply to the front wheels. The above control device performs the following processing: The first increase process involves increasing the vehicle braking force requirement value when the vehicle braking force requirement value is smaller than the regenerative braking force required for switching. In this case, the regenerative braking force applied to the front wheels is increased according to the increase in the vehicle braking force requirement value. On the other hand, the hydraulic pressure of the front wheels and the hydraulic pressure of the rear wheels are not increased. The second additional process involves increasing the vehicle braking force requirement when the regenerative braking force applied to the front wheels reaches the switching regenerative braking force and the vehicle braking force requirement value is less than the first braking force. In this case, the reference hydraulic pressure is increased according to the increase in the vehicle braking force requirement value, thereby increasing the hydraulic pressure of the rear wheels, while maintaining the hydraulic pressure of the front wheels and maintaining the regenerative braking force applied to the front wheels. The third additional processing involves increasing the vehicle braking force requirement value when, on the other hand, the regenerative braking force applied to the front wheels is greater than or equal to the switching regenerative braking force but less than the upper limit of the regenerative braking force. In this case, the regenerative braking force applied to the front wheels is increased according to the increase in the vehicle braking force requirement value, and the rear wheel hydraulic pressure is increased by increasing the reference hydraulic pressure according to the increase in the vehicle braking force requirement value, while maintaining the front wheel hydraulic pressure. The fourth additional process involves increasing the vehicle braking force requirement value when the vehicle braking force requirement value is greater than or equal to the first braking force, and the regenerative braking force applied to the front wheels reaches the upper limit of the regenerative braking force. In this case, the regenerative braking force applied to the front wheels is maintained, and the reference hydraulic pressure is increased according to the increase in the vehicle braking force requirement value, thereby increasing both the hydraulic pressure of the front wheels and the hydraulic pressure of the rear wheels.

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