Braking device

Abstract

To suppress vehicle deflection when controlling the braking pressure of the first and second wheel cylinders by performing connection control. [Solution] The braking device 100 includes a first fluid passage 32 and a second fluid passage 34, a first supply source 50A and a second supply source 50B, a switching unit 40, and a first control unit 60. In connection control, the first control unit 60 sets an upper limit based on an index that takes into account at least one of the fluid volume per unit time of brake fluid passing through the system shut-off valves 42 and 43 of the switching unit 40 and the viscosity of the brake fluid, and operates the normal supply source, which is one of the first supply source 50A and the second supply source 50B, so that at least one of the discharge rate and suction rate of brake fluid per unit time of the normal supply source does not exceed the upper limit.

Description

Technical Field

[0001] The present invention relates to a brake device that applies braking force to a vehicle by adjusting the brake pressures of a first wheel cylinder and a second wheel cylinder.

Background Art

[0002] Patent Document 1 discloses a brake device including a first supply source connected to a first wheel cylinder via a first fluid passage, and a second supply source connected to a second wheel cylinder via a second fluid passage. The brake device further includes a communication passage that connects the first fluid passage and the second fluid passage, and a switching valve installed in the communication passage.

[0003] When a braking request is generated in a situation where all of the plurality of supply sources operate normally, the switching valve is closed to block communication between the first fluid passage and the second fluid passage. In this state, brake fluid is supplied from the first supply source to the first wheel cylinder via the first fluid passage, whereby the first brake pressure, which is the brake pressure of the first wheel cylinder, is adjusted. In addition, brake fluid is supplied from the second supply source to the second wheel cylinder via the second fluid passage, whereby the second brake pressure, which is the brake pressure of the second wheel cylinder, is adjusted.

[0004] On the other hand, when an abnormality occurs only in one of the plurality of supply sources, the switching valve is opened to communicate the first fluid passage and the second fluid passage. In this state, the other supply source is operated. In this case, brake fluid is supplied from the other supply source to the plurality of wheel cylinders. That is, the first brake pressure and the second brake pressure are adjusted by the operation of one supply source. Such brake control is referred to as "communication control".

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of Invention

[0006] In connection control when an abnormality occurs in the first supply source, a portion of the brake fluid discharged from the second supply source passes through a switching valve installed in the communication passage and flows into the first wheel cylinder via the first fluid passage. In this case, because the switching valve functions as an orifice, it is difficult for the brake fluid discharged from the second supply source to reach the first wheel cylinder. As a result, the first braking pressure does not increase as easily as the second braking pressure, which may lead to a large discrepancy between the first and second braking pressures. These problems also occur in connection control when an abnormality occurs in the second supply source. [Means for solving the problem]

[0007] The braking device for solving the above problems is applied to a vehicle comprising a first wheel and a second wheel arranged at different positions in the vehicle width direction, a first wheel cylinder corresponding to the first wheel, and a second wheel cylinder corresponding to the second wheel. The braking device comprises a first fluid passage which is a brake fluid passage connected to the first wheel cylinder, a second fluid passage which is a brake fluid passage connected to the second wheel cylinder, a first supply source connected to the first fluid passage and discharging brake fluid into the first fluid passage, a second supply source connected to the second fluid passage and discharging brake fluid into the second fluid passage, a switching unit having a connecting passage connecting the first fluid passage and the second fluid passage and a switching valve installed in the connecting passage, which connects the first fluid passage and the second fluid passage when the switching valve is open and blocks communication between the first fluid passage and the second fluid passage when the switching valve is closed, and a control unit which performs connection control to control the braking pressure of the multiple wheel cylinders by operating only one of the multiple supply sources, which is a normal supply source, while the first fluid passage and the second fluid passage are connected by opening the switching valve. In the connection control, the control unit sets an upper limit for at least one of the discharge rate and suction rate of the brake fluid per unit time of the normal supply source based on an index that takes into account at least one of the amount of brake fluid passing through the switching valve per unit time and the viscosity of the brake fluid, and operates the normal supply source so that at least one of the discharge rate and suction rate of the brake fluid per unit time of the normal supply source does not exceed the upper limit. [Effects of the Invention]

[0008] The above braking device has the effect of suppressing vehicle deviation when the braking pressure of the first wheel cylinder and the second wheel cylinder is controlled by the execution of connection control. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing a vehicle equipped with a braking system according to the first embodiment. [Figure 2]Figure 2 is a flowchart showing the processing flow when the first control unit of the braking device in Figure 1 performs shutoff control. [Figure 3] Figure 3 is a flowchart showing the processing flow when the first control unit of the braking device in Figure 1 performs connection control. [Figure 4] Figure 4 is a flowchart showing the operation process of the normal supply source as shown in Figure 3. [Figure 5] Figures 5(a) to 5(d) are timing charts showing examples of the transitions of various parameters when connection control is performed. [Figure 6] Figure 6 is a flowchart showing a portion of the processing flow when the control switches from interruption control to connection control during the execution of interruption control in the braking device of the second embodiment. [Figure 7] Figures 7(a) to 7(c) are timing charts showing an example of the change in braking pressure when the control switches from interruption control to connection control during the execution of interruption control. [Figure 8] Figure 8 is a flowchart showing a portion of the operation process of a normal supply source in the braking device of the third embodiment. [Figure 9] Figure 9 is a flowchart showing a series of processes for predicting the change in the braking pressure difference between the first wheel cylinder and the second wheel cylinder that occurs when connection control is performed in the braking device of the fourth embodiment. [Figure 10] Figure 10 is a flowchart showing a series of processes for adjusting the braking force of the third and fourth wheels in the braking device of the fourth embodiment, where the braking pressure of the first wheel cylinder and the second wheel cylinder is controlled by connection control. [Modes for carrying out the invention]

[0010] (First Embodiment) A first embodiment of the braking device will be described with reference to Figures 1 to 5. <Overall vehicle configuration> Figure 1 illustrates a vehicle 10 equipped with a braking system 100. The vehicle 10 comprises a plurality of wheels, a plurality of friction brakes 20 provided for each of the plurality of wheels, and a plurality of sensors. The plurality of wheels include a first wheel 11 and a second wheel 12, and a third wheel 13 and a fourth wheel 14 positioned at different locations in the vehicle's longitudinal direction from the first wheel 11 and the second wheel 12. For example, the first wheel 11 and the second wheel 12 are the front wheels of the vehicle 10, positioned at different locations in the vehicle width direction. The third wheel 13 and the fourth wheel 14 are the rear wheels of the vehicle 10, positioned at different locations in the vehicle width direction.

[0011] Each of the multiple friction brakes 20 comprises a wheel cylinder, a rotating body 22, and a friction part 23. The hydraulic pressure in the wheel cylinder is the braking pressure. The rotating body 22 rotates integrally with the corresponding wheels 11-14. The friction brake 20 can apply braking force to the corresponding wheels 11-14 by pressing the friction part 23 against the rotating body 22. The force pressing the friction part 23 against the rotating body 22 increases with increasing braking pressure in the wheel cylinder. In other words, the friction brake 20 can apply greater braking force to the corresponding wheels 11-14 as the braking pressure in the wheel cylinder increases.

[0012] Hereafter, the wheel cylinder corresponding to the first wheel 11 will be referred to as "first wheel cylinder 211". The wheel cylinder corresponding to the second wheel 12 will be referred to as "second wheel cylinder 212". The wheel cylinder corresponding to the third wheel 13 will be referred to as "third wheel cylinder 213". The wheel cylinder corresponding to the fourth wheel 14 will be referred to as "fourth wheel cylinder 214". The braking pressure of the first wheel cylinder 211 will be referred to as "first braking pressure Pw1". The braking pressure of the second wheel cylinder 212 will be referred to as "second braking pressure Pw2". The braking pressure of the third wheel cylinder 213 will be referred to as "third braking pressure Pw3". The braking pressure of the fourth wheel cylinder 214 will be referred to as "fourth braking pressure Pw4".

[0013] The multiple sensors include, for example, a brake sensor 16, a wheel speed sensor 17, and a yaw rate sensor 18. The brake sensor 16 detects operation-related information, which is information related to the driver's operation of the brake pedal. An example of the brake sensor 16 is a stroke sensor that detects the operation amount of the driver's brake pedal as the operation-related information. The operation amount based on the detection signal of the brake sensor 16 is referred to as "braking operation amount Ba".

[0014] The wheel speed sensors 17 are provided for each of the plurality of wheels 11 to 14. Each of the plurality of wheel speed sensors 17 detects the rotational speed of the corresponding wheel 11 to 14. The rotational speed of the wheels 11 to 14 based on the detection signal of the wheel speed sensor 17 is referred to as "wheel speed VW". The traveling speed of the vehicle 10 calculated based on the wheel speeds VW of the plurality of wheels 11 to 14 is the vehicle body speed VS of the vehicle 10.

[0015] The yaw rate sensor 18 detects the yaw rate of the vehicle 10. The yaw rate of the vehicle 10 based on the detection signal of the yaw rate sensor 18 is referred to as "yaw rate YR". <Configuration of Braking Device> The braking device 100 includes a first braking unit 30 and a second braking unit 80. The first braking unit 30 is configured to be able to apply a braking force to the vehicle 10 by adjusting the first braking pressure Pw1 and the second braking pressure Pw2. The second braking unit 80 is configured to be able to apply a braking force to the vehicle 10 by adjusting the third braking pressure Pw3 and the fourth braking pressure Pw4.

[0016] <Configuration of First Braking Unit> The first braking unit 30 includes a reservoir 31, a first hydraulic passage 32, a second hydraulic passage 34, a switching portion 40, a reservoir blocking portion 45, a first supply source 50A, a second supply source 50B, and a first control portion 60.

[0017] The reservoir 31 stores brake fluid and is open to the atmosphere. The first fluid passage 32 and the second fluid passage 34 are brake fluid passages through which brake fluid flows. The first fluid passage 32 is connected to the first wheel cylinder 211. The second fluid passage 34 is connected to the second wheel cylinder 212. A first hydraulic pressure sensor 33, which detects the brake fluid pressure in the first fluid passage 32, is connected to the first fluid passage 32. A second hydraulic pressure sensor 35, which detects the brake fluid pressure in the second fluid passage 34, is connected to the second fluid passage 34. Each of the first hydraulic pressure sensor 33 and the second hydraulic pressure sensor 35 outputs a detection signal to the first control unit 60 according to the detection result. For example, the detection signal from the first hydraulic pressure sensor 33 is input to the second controller 62 of the first control unit 60, which will be described later. The detection signal from the second hydraulic pressure sensor 35 is input to the first controller 61 of the first control unit 60, which will be described later. Hereafter, the detected value of the first braking pressure Pw1 based on the detection signal from the first hydraulic pressure sensor 33 will be referred to as the "first braking pressure detection value Pw1S". The detected value of the second braking pressure Pw2 based on the detection signal of the second hydraulic pressure sensor 35 is referred to as the "second braking pressure detection value Pw2S". Furthermore, the first hydraulic pressure sensor 33 may be referred to as the "first braking pressure detection unit" that inputs the detection result to the second controller 62, and the second hydraulic pressure sensor 35 may be referred to as the "second braking pressure detection unit" that inputs the detection result to the first controller 61.

[0018] The switching unit 40 is configured to switch between a connected state, which connects the first fluid passage 32 and the second fluid passage 34, and a blocked state, which blocks the connection between the first fluid passage 32 and the second fluid passage 34. For example, the switching unit 40 has a connecting passage 41, a first system shut-off valve 42, and a second system shut-off valve 43. The connecting passage 41 is a brake fluid passage that connects the first fluid passage 32 and the second fluid passage 34. Of the two ends of the connecting passage 41, the first end is connected to the first fluid passage 32, and the second end is connected to the second fluid passage 34.

[0019] The first system shut-off valve 42 and the second system shut-off valve 43 are switching valves installed in the communication passage 41. Of the two system shut-off valves 42 and 43, the one located near the first hydraulic pressure sensor 33 is the first system shut-off valve 42, while the one located near the second hydraulic pressure sensor 35 is the second system shut-off valve 43. Each of the first system shut-off valve 42 and the second system shut-off valve 43 is a normally open solenoid valve. Therefore, when the power supply to the system shut-off valves 42 and 43 is stopped, the system shut-off valves 42 and 43 open. As a result, the first liquid passage 32 and the second liquid passage 34 communicate via the communication passage 41. On the other hand, when power is supplied to the system shut-off valves 42 and 43, the system shut-off valves 42 and 43 close. As a result, communication between the first liquid passage 32 and the second liquid passage 34 via the communication passage 41 is interrupted. Therefore, the state of the switching unit 40 when both of the multiple system shut-off valves 42 and 43 are open is the "connected state". On the other hand, the state of the switching unit 40 when all of the multiple system shut-off valves 42 and 43 are closed is the "shut-off state".

[0020] The reservoir shutoff unit 45 includes an atmospheric vent passage 46, which is a brake fluid passage connecting the communication passage 41 and the reservoir 31, and a reservoir shutoff valve 47 installed in the atmospheric vent passage 46. The atmospheric vent passage 46 is connected to the portion of the communication passage 41 between the first system shutoff valve 42 and the second system shutoff valve 43. The reservoir shutoff valve 47 is a normally open solenoid valve. For example, the reservoir shutoff valve 47 has a first solenoid and a second solenoid. When power is supplied to at least one of the first solenoid and the second solenoid, the reservoir shutoff valve 47 is closed. This shuts off communication between the portion of the communication passage 41 between the first system shutoff valve 42 and the second system shutoff valve 43 and the reservoir 31. On the other hand, when the power supply to both the first solenoid and the second solenoid is stopped, the reservoir shutoff valve 47 is opened. As a result, the portion of the communication passage 41 between the first system shut-off valve 42 and the second system shut-off valve 43 is in communication with the reservoir 31.

[0021] The first supply source 50A is connected to the first fluid passage 32 and discharges brake fluid into the first fluid passage 32. Therefore, the first supply source 50A can supply brake fluid to the first wheel cylinder 211 via the first fluid passage 32. The second supply source 50B is connected to the second fluid passage 34 and discharges brake fluid into the second fluid passage 34. Therefore, the second supply source 50B can supply brake fluid to the second wheel cylinder 212 via the second fluid passage 34.

[0022] Each of the first supply source 50A and the second supply source 50B has, for example, an electric cylinder 51. The electric cylinder 51 has a cylinder 52, a piston 53, an electric motor 54, and a conversion mechanism 55. The piston 53 is provided to be reciprocating within the cylinder 52. The conversion mechanism 55 converts the rotation of the output shaft of the electric motor 54 into the linear movement of the piston 53.

[0023] Inside cylinder 52, a hydraulic chamber Re for storing brake fluid is partitioned by the peripheral wall of cylinder 52 and piston 53. The position of piston 53 inside cylinder 52 can be changed by driving electric motor 54. Hereafter, the movement of piston 53 when decreasing the volume of hydraulic chamber Re will be described as "forward." The movement of piston 53 when increasing the volume of hydraulic chamber Re will be described as "reverse." Reverse is the movement of piston 53 in the opposite direction to forward.

[0024] When the piston 53 moves forward due to the drive of the electric motor 54 of the first power source 50A, the brake fluid in the hydraulic chamber Re is discharged to the first fluid passage 32 via the output port 52p. As a result, brake fluid is supplied to the first wheel cylinder 211, and the first braking pressure Pw1 increases. When the piston 53 moves forward due to the drive of the electric motor 54 of the second power source 50B, the brake fluid in the hydraulic chamber Re is discharged to the second fluid passage 34 via the output port 52p. As a result, brake fluid is supplied to the second wheel cylinder 212, and the second braking pressure Pw2 increases.

[0025] On the other hand, when the piston 53 retracts due to the drive of the electric motor 54 of the first power source 50A, the brake fluid in the first fluid passage 32 flows into the hydraulic chamber Re via the output port 52p. As a result, the brake fluid from the first wheel cylinder 211 flows out into the first fluid passage 32, and the first braking pressure Pw1 decreases. When the piston 53 retracts due to the drive of the electric motor 54 of the second power source 50B, the brake fluid in the second fluid passage 34 flows into the hydraulic chamber Re via the output port 52p. As a result, the brake fluid from the second wheel cylinder 212 flows out into the second fluid passage 34, and the second braking pressure Pw2 decreases.

[0026] The electric motor 54 has a motor angle sensor 54s. The motor angle sensor 54s outputs a detection signal to the first control unit 60 in accordance with the change in the rotation angle of the output shaft of the electric motor 54. Specifically, the motor angle sensor 54s of the first power source 50A outputs a detection signal to the first controller 61 of the first control unit 60, which will be described later. The motor angle sensor 54s of the second power source 50B outputs a detection signal to the second controller 62 of the first control unit 60, which will be described later. Hereafter, the rotation angle of the electric motor 54 based on the detection signal of the motor angle sensor 54s will be referred to as "motor rotation angle θmt".

[0027] When the motor rotation angle θmt increases due to the drive of the electric motor 54, the piston 53 moves forward. Conversely, when the motor rotation angle θmt decreases due to the drive of the electric motor 54, the piston 53 moves backward.

[0028] The first control unit 60 controls the switching unit 40, the reservoir shut-off unit 45, the first power source 50A, and the second power source 50B. For example, the first control unit 60 includes a first controller 61 and a second controller 62 that can send and receive information from each other. The first controller 61 is a processing circuit that controls the energization of the first solenoid of the first power source 50A, the first system shut-off valve 42, and the reservoir shut-off valve 47. The second controller 62 is a processing circuit that controls the energization of the second solenoid of the second power source 50B, the second system shut-off valve 43, and the reservoir shut-off valve 47. An example of a processing circuit is an electronic control device. In this case, each of the multiple controllers 61, 62 has a CPU 71 and a memory 72 that stores a control program executed by the CPU 71. Each of the multiple controllers 61, 62 controls its controlled object by having the CPU 71 execute the control program in the memory 72.

[0029] The detection signal from the second hydraulic pressure sensor 35 is input to the first controller 61. Therefore, the first controller 61 can derive the second damping pressure detection value Pw2S. The first controller 61 also transmits the second damping pressure detection value Pw2S to the second controller 62 at predetermined communication cycles. The detection signal from the first hydraulic pressure sensor 33 is input to the second controller 62. Therefore, the second controller 62 can derive the first damping pressure detection value Pw1S. The second controller 62 also transmits the first damping pressure detection value Pw1S to the first controller 61 at predetermined communication cycles. Thus, multiple controllers 61 and 62 can acquire either the first damping pressure detection value Pw1S or the second damping pressure detection value Pw2S.

[0030] <Configuration of the second braking unit> The second braking unit 80 comprises a braking actuator 81 and a second control unit 90. The braking actuator 81 is configured to allow individual adjustment of the braking force applied to the third wheel 13 and the fourth wheel 14. In the example shown in Figure 1, the braking actuator 81 applies braking force to the third wheel 13 by adjusting the third braking pressure Pw3. The braking actuator 81 also applies braking force to the fourth wheel 14 by adjusting the fourth braking pressure Pw4.

[0031] The second control unit 90 is a processing circuit that controls the braking actuator 81. An example of such a processing circuit is an electronic control unit. In this case, the second control unit 90 includes a CPU 91 and a memory 92 that stores a control program executed by the CPU 91. The second control unit 90 controls the braking actuator 81 by having the CPU 91 execute the control program stored in the memory 92.

[0032] The second control unit 90 is configured to send and receive information and commands to and from the first control unit 60 via the in-vehicle network 200. An example of the in-vehicle network 200 is a CAN bus. "CAN" is an abbreviation for "Controller Area Network". Therefore, the second control unit 90 can adjust the braking force applied to the third wheel 13 and the fourth wheel 14 in cooperation with the first control unit 60.

[0033] <Shutdown control> The first control unit 60 adjusts the first braking pressure Pw1 and the second braking pressure Pw2 by executing shutoff control when a braking request is issued to the vehicle 10 under conditions in which it has determined that predetermined normal determination conditions have been met. The first control unit 60 determines that the normal determination conditions have been met if all of the following conditions (A1), (A2), and (A3) are met. On the other hand, the first control unit 60 determines that the normal determination conditions have not been met if at least one of the conditions (A1) to (A3) is not met.

[0034] (A1) Both the first supply source 50A and the second supply source 50B must be functioning normally. (A2) Both the first controller 61 and the second controller 62 must be functioning correctly.

[0035] (A3) Communication between the first controller 61 and the second controller 62 is normal. In addition to the above conditions (A1) to (A3), the following conditions may be added to the criteria for determining normality.

[0036] • The switching unit 40 must be functioning correctly. • The first hydraulic pressure sensor 33 and the second hydraulic pressure sensor 35 are functioning correctly. The relationship between the drive amount of power sources 50A and 50B and the resulting braking pressure does not deviate significantly from the standard relationship.

[0037] Referring to Figure 2, the shutdown control performed by the first control unit 60 will be described. In step S11, the first control unit 60 sets the state of the switching unit 40 to the shut-off state. The first controller 61 closes the first system shut-off valve 42. The second controller 62 closes the second system shut-off valve 43. As a result, the first control unit 60 can shut off communication between the first liquid passage 32 and the second liquid passage 34.

[0038] In the next step S13, the first control unit 60 sets the requested braking force FbRq, which is the required value of the braking force applied to the vehicle 10. For example, the first controller 61 sets the requested braking force FbRq. For example, if the driver is operating the brake pedal, the first controller 61 sets the requested braking force FbRq to be larger the larger the braking operation amount Ba is. If another onboard control device requests deceleration of the vehicle 10, the first controller 61 sets the requested braking force FbRq to be the braking force corresponding to the request of the other control device.

[0039] In the subsequent step S15, the first control unit 60 sets the first target braking pressure Pw1Tr and the second target braking pressure Pw2Tr based on the requested braking force FbRq. The first target braking pressure Pw1Tr is the target value for the first braking pressure Pw1. The second target braking pressure Pw2Tr is the target value for the second braking pressure Pw2. For example, the first controller 61 sets the first target braking pressure Pw1Tr and the second target braking pressure Pw2Tr. Then, the first controller 61 transmits information regarding the second target braking pressure Pw2Tr to the second controller 62.

[0040] In the next step S17, the first controller 61 of the first control unit 60 activates the first supply source 50A based on the first target braking pressure Pw1Tr. The second controller 62 of the first control unit 60 activates the second supply source 50B based on the second target braking pressure Pw2Tr.

[0041] An example of the operation process of the electric cylinders 51 of the supply sources 50A and 50B in shutoff control is described below. In the electric cylinder 51, the rearmost end of the piston 53's range of motion is the rearmost position. The amount of forward movement of the piston 53 from the rearmost position is the stroke of the piston 53. In the electric cylinder 51, there is a correspondence between the stroke of the piston 53 and the amount of brake fluid supplied from the electric cylinder 51 to the wheel cylinders 211 and 212, which is the consumption amount. There is also a correspondence between the braking pressure of the wheel cylinders 211 and 212 and the consumption amount. Furthermore, there is a correspondence between the stroke of the piston 53 and the motor rotation angle θmt. Therefore, it can be said that there is a correspondence between the motor rotation angle θmt and the braking pressure.

[0042] Therefore, the first controller 61 uses a map showing the correspondence between the motor rotation angle θmt and the first braking pressure Pw1 to obtain the motor rotation angle corresponding to the first target braking pressure Pw1Tr, and sets this motor rotation angle as the target motor rotation angle θmtTr1. Then, the first controller 61 operates the electric cylinder 51 of the first power source 50A by performing feedback control to make the motor rotation angle θmt of the electric motor 54 of the first power source 50A follow the target motor rotation angle θmtTr1.

[0043] Similarly, the second controller 62 uses a map showing the correspondence between the motor rotation angle θmt and the second braking pressure Pw2 to obtain the motor rotation angle corresponding to the second target braking pressure Pw2Tr, and sets this motor rotation angle as the target motor rotation angle θmtTr2. The second controller 62 then operates the electric cylinder 51 of the second power source 50B by performing feedback control to make the motor rotation angle θmt of the electric motor 54 of the second power source 50B follow the target motor rotation angle θmtTr2.

[0044] In the next step S19, the first control unit 60 determines whether or not a braking request has occurred. If a braking request has occurred (S19: YES), the first control unit 60 proceeds to step S13. That is, the first control unit 60 continues to adjust the first braking pressure Pw1 and the second braking pressure Pw2 by shut-off control. On the other hand, if no braking request has occurred (S19: NO), the first control unit 60 terminates the shut-off control and ends the series of processes shown in Figure 2.

[0045] <Connection Control> If the first control unit 60 determines that the above-mentioned normal determination conditions are not met and a braking request is issued to the vehicle 10, it adjusts the first braking pressure Pw1 and the second braking pressure Pw2 by performing connection control.

[0046] Referring to Figures 3 and 4, the connection control performed by the first control unit 60 will be described. In step S31, the first control unit 60 sets the state of the switching unit 40 to a connected state. The first controller 61 opens the first system shut-off valve 42. The second controller 62 opens the second system shut-off valve 43. If a malfunction occurs in the first controller 61, the first controller 61 cannot control the first system shut-off valve 42, so the power supply to the first system shut-off valve 42 is stopped. As a result, the first system shut-off valve 42 opens. If a malfunction occurs in the second controller 62, the second controller 62 cannot control the second system shut-off valve 43, so the power supply to the second system shut-off valve 43 is stopped. As a result, the second system shut-off valve 43 opens. Therefore, even if a malfunction occurs in at least one of the multiple controllers 61, 62, the first control unit 60 can set the state of the switching unit 40 to a connected state.

[0047] In the next step S33, the first control unit 60 sets the requested braking force FbRq. If the first controller 61 is functioning normally, the first controller 61 sets the requested braking force FbRq. If all of the multiple controllers 61 and 62 are functioning normally, but communication between the multiple controllers 61 and 62 is poor, the first controller 61 sets the requested braking force FbRq. On the other hand, if an abnormality occurs in the first controller 61, the second controller 62 sets the requested braking force FbRq. In connection control, among the multiple controllers 61 and 62, the controller that sets the requested braking force FbRq is referred to as the "main controller".

[0048] In the subsequent step S35, the main controller of the first control unit 60 sets the target braking pressure PwTr based on the requested braking force FbRq. The target braking pressure PwTr is a common target value for the first braking pressure Pw1 and the second braking pressure Pw2.

[0049] Then, in step S37, the main controller of the first control unit 60 executes an operation process to activate the electric cylinder 51 of the normal supply source based on the target braking pressure PwTr. A normal supply source is one of the multiple supply sources 50A, 50B that operates to discharge brake fluid when connection control is executed. In other words, among the multiple supply sources 50A, 50B, the one controlled by the main controller is the normal supply source. Therefore, if the first controller 61 is the main controller, the first supply source 50A becomes the normal supply source. If the second controller 62 is the main controller, the second supply source 50B becomes the normal supply source. Details of the operation process in step S37 will be described later with reference to Figure 4.

[0050] In the next step S39, the first control unit 60 determines whether or not a braking request has occurred. If a braking request has occurred (S39: YES), the first control unit 60 proceeds to step S33. That is, the first control unit 60 continues to adjust the first braking pressure Pw1 and the second braking pressure Pw2 by connection control. On the other hand, if no braking request has occurred (S39: NO), the first control unit 60 terminates the connection control and ends the series of processes shown in Figure 3.

[0051] Referring to Figure 4, the operation process of the normal supply source in step S37 described above will be explained. In step S51, the main controller acquires the acquired braking pressure detection value PwN. The acquired braking pressure detection value PwN is the braking pressure detection value of the wheel cylinder corresponding to the non-normal supply source among the first braking pressure detection value Pw1S and the second braking pressure detection value Pw2S. Therefore, if the first controller 61 is the main controller, the main controller acquires the second braking pressure detection value Pw2S as the acquired braking pressure detection value PwN. If the second controller 62 is the main controller, the main controller acquires the first braking pressure detection value Pw1S as the acquired braking pressure detection value PwN. Note that among the first braking pressure detection value Pw1S and the second braking pressure detection value Pw2S, the braking pressure detection value of the wheel cylinder corresponding to the normal supply source is sometimes referred to as the "opposite braking pressure detection value PwR".

[0052] Here, due to the rigidity relationship between the wheel cylinders 211 and 212, the lower the braking pressure, the smaller the gradient of increase in braking pressure, which is the amount of increase in braking pressure relative to the amount of brake fluid flowing into the wheel cylinders 211 and 212. Therefore, the lower the braking pressure of the wheel cylinder corresponding to the non-normal supply source, the less likely it is that the braking pressure of that wheel cylinder will increase even if brake fluid is supplied to it.

[0053] In the next step S53, the main controller obtains an index that takes into account at least one of the fluid volume per unit time of brake fluid passing through the multiple system shut-off valves 42, 43 and the viscosity of the brake fluid. For example, the main controller obtains the fluid temperature TMP, which is the temperature of the brake fluid, and the braking pressure difference ΔPw as indicators.

[0054] If the main controller can obtain the counter-braking pressure detection value PwR, it obtains the absolute value of the difference between the first braking pressure detection value Pw1S and the second braking pressure detection value Pw2S as the braking pressure difference ΔPw. On the other hand, if the main controller cannot obtain the counter-braking pressure detection value PwR, it derives the counter-braking pressure estimate value PwRe, which is an estimated value of the braking pressure of the wheel cylinder corresponding to the normal power source. For example, the main controller derives the target braking pressure PwTr as the counter-braking pressure estimate value PwRe. Alternatively, the main controller may derive the braking pressure corresponding to the motor rotation angle θmt of the electric motor 54 of the normal power source as the counter-braking pressure estimate value PwRe. In this case, it is preferable that the main controller derives the counter-braking pressure estimate value PwRe using a map showing the relationship between the motor rotation angle θmt and the braking pressure when the switching unit 40 is in a connected state. The main controller then obtains the absolute value of the difference between the acquired braking pressure detection value PwN and the counter-braking pressure estimate value PwRe as the braking pressure difference ΔPw.

[0055] Here, the lower the fluid temperature TMP, the higher the viscosity of the brake fluid. And the higher the viscosity of the brake fluid, the more difficult it is for the brake fluid to pass through the multiple system shut-off valves 42 and 43. For example, if the first supply source 50A is a normal supply source, the lower the fluid temperature TMP, the less likely the brake fluid discharged from the first supply source 50A is to flow into the second fluid passage 34 via the switching section 40. As a result, the second braking pressure Pw2 is less likely to increase, and the fluid pressure difference between the first braking pressure Pw1 and the second braking pressure Pw2 is more likely to increase.

[0056] The greater the hydraulic pressure difference between the first fluid passage 32 and the second fluid passage 34, the greater the hydraulic pressure difference between the first braking pressure Pw1 and the second braking pressure Pw2. In other words, the difference in braking force between the left and right sides of the vehicle 10 is large. In the subsequent step S55, the main controller sets the upper limit QbL of the discharge rate per unit time of brake fluid from a normal supply source based on the acquired braking pressure detection value PwN obtained in step S51 and the index obtained in step S53.

[0057] The main controller sets the upper limit QbL based on the above indicators. For example, the main controller sets the upper limit QbL such that the value decreases as the liquid temperature TMP decreases. Alternatively, the main controller sets the upper limit QbL such that the value decreases as the braking pressure difference ΔPw increases.

[0058] The main controller corrects the upper limit QbL, which is set based on the above indicators, using the acquired braking pressure detection value PwN. For example, the main controller reduces the upper limit QbL when the acquired braking pressure detection value PwN is less than the judgment braking pressure Pwth. On the other hand, the main controller does not correct the upper limit QbL based on the acquired braking pressure detection value PwN when the acquired braking pressure detection value PwN is equal to or greater than the judgment braking pressure Pwth. As a result, the main controller can set the upper limit QbL lower when the acquired braking pressure detection value PwN is less than the judgment braking pressure Pwth than when the acquired braking pressure detection value PwN is equal to or greater than the judgment braking pressure Pwth. The judgment braking pressure Pwth is a criterion for determining whether or not the braking pressure is unlikely to increase due to the inflow of brake fluid into the wheel cylinder.

[0059] When the main controller sets the upper limit QbL in this way, it proceeds to step S57. In step S57, the main controller acquires various vehicle information that can be used to correct the upper limit value QbL. For example, the main controller acquires at least one of the following as vehicle information: the required braking force FbRq, the vehicle speed VS of the vehicle 10, the yaw rate YR of the vehicle 10, and the range information of the shift device.

[0060] Here, the greater the braking force applied to the vehicle 10, the larger the difference in left-right braking force, which is the difference between the braking force applied to the first wheel 11 and the braking force applied to the second wheel 12. In other words, the smaller the required braking force FbRq, which corresponds to the braking force applied to the vehicle 10, the less likely the difference in left-right braking force is to be large.

[0061] When the above-mentioned difference in left-right braking force occurs while vehicle 10 is in motion, a yaw moment may be generated in vehicle 10. In this case, the greater the vehicle speed VS, the greater the degree of vehicle 10's deflection tends to be. In other words, the smaller the vehicle speed VS, the less likely vehicle 10 is to deflect even if a difference in left-right braking force occurs.

[0062] If the above-mentioned difference in left-right braking force occurs while vehicle 10 is turning, the actual turning behavior of vehicle 10 may deviate from the turning behavior desired by the driver. Whether or not vehicle 10 is turning can be determined from the magnitude of the yaw rate YR. Alternatively, whether or not vehicle 10 is turning can also be determined using the lateral acceleration of vehicle 10 and the steering angle of the steering wheel.

[0063] If the shift mechanism is in the parking or neutral range, it can be inferred that vehicle 10 is not moving. If vehicle 10 is not moving, the above-mentioned difference in left-right braking force does not pose a problem.

[0064] In the subsequent step S59, the main controller performs a correction process to correct the upper limit value QbL set in step S55 based on the vehicle information acquired in step S57.

[0065] When the main controller corrects the upper limit QbL based on the required braking force FbRq, it corrects the upper limit QbL such that the smaller the required braking force FbRq, the larger the amount of correction for increasing the upper limit QbL.

[0066] When the main controller corrects the upper limit QbL based on the vehicle speed VS, it corrects the upper limit QbL such that the smaller the vehicle speed VS, the larger the amount of correction for increasing the upper limit QbL.

[0067] When the main controller corrects the upper limit QbL based on the shift device's range information, it increases the upper limit QbL when the shift device's range is the parking range or the neutral range. On the other hand, when the shift device's range is the driving range, the main controller does not correct the upper limit QbL based on the range information.

[0068] When the main controller corrects the upper limit QbL based on the yaw rate YR, it corrects the upper limit QbL such that the larger the absolute value of the yaw rate YR, the larger the reduction correction amount for the upper limit QbL.

[0069] In the following step S61, the main controller derives the target motor current ImtTr by performing feedback control (i.e., hydraulic feedback control) that causes the acquired braking pressure detection value PwN to follow the target braking pressure PwTr. The target motor current ImtTr is the target value of the motor current Imt, which is the current flowing through the electric motor 54. Here, the target motor torque may also be derived by hydraulic feedback control. The target motor torque is the target value of the motor torque, which is the output torque of the electric motor 54.

[0070] In the next step, S63, the main controller performs a correction process using the values ​​derived from the hydraulic feedback control in step S61 (e.g., target motor current ImtTr, target motor torque) to ensure that the discharge rate of brake fluid per unit time from the normal supply source does not exceed the upper limit QbL. For example, the main controller derives a rotational speed limit for the electric motor 54 by dividing the upper limit QbL by the cross-sectional area of ​​the piston 53 of the normal supply source. The rotational speed limit for the electric motor 54 is sometimes referred to as the "speed limit value". The main controller then performs a correction process on the target motor current ImtTr, which is a value derived from hydraulic feedback, to ensure that the electric motor 54 does not drive at a speed exceeding this limit value.

[0071] Then, in step S65, the main controller drives the electric motor 54 of the normal power source based on the value derived from the hydraulic feedback corrected by the correction process in step S63. If the derived value is the target motor current ImtTr, the main controller operates the electric cylinder 51 of the normal power source by performing feedback control (i.e., current feedback control) to make the motor current Imt follow the target motor current ImtTr. After that, the main controller completes the series of processes shown in Figure 4.

[0072] In this example, the case in step S61 above is shown as an example of performing hydraulic feedback control, but this is not the only example. For example, in step S61 above, the target motor current ImtTr and target motor torque may be derived by performing position feedback control.

[0073] <Operation and Effects of This Embodiment> Referring to Figure 5, the operation and effects of increasing the first braking pressure Pw1 and the second braking pressure Pw2 by connection control will be explained. The example shown in Figure 5 is an embodiment of connection control when the first supply source 50A is a normal supply source. Figure 5(c) shows the changes in the first braking pressure Pw1 and the second braking pressure Pw2 in this embodiment. Figure 5(d) shows the changes in the first braking pressure Pw1 and the second braking pressure Pw2 in a comparative example. In this comparative example, no upper limit QbL is set for the discharge rate of brake fluid per unit time in a normal supply source.

[0074] As shown in Figure 5(a), the required braking force FbRq gradually increases. In the above comparative example, the first supply source 50A (normal supply source) is activated by feedback control that causes the acquired braking pressure detection value PwN to follow the target braking pressure PwTr based on the required braking force FbRq. In this case, if the rate of increase of the target braking pressure PwTr is relatively large, the first braking pressure Pw1 follows the target braking pressure PwTr, as shown in Figure 5(d). However, a differential pressure corresponding to the flow resistance of the multiple open system shut-off valves 42 and 43 is generated between the first braking pressure Pw1 and the second braking pressure Pw2. The flow resistance of the system shut-off valves 42 and 43, that is, the effect of the orifices inside the system shut-off valves 42 and 43, increases as the amount of brake fluid per unit time flowing from the first fluid passage 32 to the second fluid passage 34 via the communication passage 41 increases.

[0075] In contrast, in this embodiment, an upper limit QbL is set for the discharge rate of brake fluid per unit time in the first supply source 50A (normal supply source). As shown in Figures 5(a) and (b), when the required braking force FbRq is relatively small, the acquired braking pressure detection value PwN is low, so the upper limit QbL is set to a small value. The first supply source 50A is then operated so that the discharge rate of brake fluid per unit time does not exceed the upper limit QbL. As a result, compared to the comparative example above, the amount of brake fluid per unit time flowing from the first fluid passage 32 to the second fluid passage 34 via the communication passage 41 is less likely to be large. Consequently, as shown in Figure 5(c), a discrepancy is less likely to occur between the first braking pressure Pw1 and the second braking pressure Pw2 when connection control is performed.

[0076] Therefore, the braking device 100 of this embodiment can suppress the vehicle 10 from deviating when the first braking pressure Pw1 and the second braking pressure Pw2 are controlled by the execution of connection control. The connection control when the first supply source 50A is a normal supply source is referred to as the first connection control. The connection control when the second supply source 50B is a normal supply source is referred to as the second connection control. The content of the second connection control is almost the same as that of the first connection control, except that the supply source that discharges the brake fluid is the second supply source 50B. Therefore, a detailed explanation of the second connection control is omitted.

[0077] The braking device 100 of this embodiment can further provide the following effects. (1-1) When brake fluid has difficulty passing through the system shut-off valves 42 and 43, if the discharge rate of brake fluid per unit time from the normal supply source is large, the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 tends to become large. Therefore, in connection control, the first control unit 60 sets an upper limit QbL based on an index that takes into account at least one of the amount of brake fluid per unit time passing through the system shut-off valves 42 and 43 and the viscosity of the brake fluid. The first control unit 60 then operates the normal supply source so that the discharge rate of brake fluid per unit time does not exceed the upper limit QbL. As a result, when the braking device 100 performs connection control, it is possible to suppress the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 from becoming large.

[0078] (1-2) For example, the first control unit 60 sets the upper limit QbL lower as the fluid temperature TMP decreases. The first control unit 60 then operates the normal supply source so that the discharge amount of brake fluid per unit time does not exceed the upper limit QbL. As a result, when the braking device 100 performs connection control under conditions where the fluid temperature TMP is low and the viscosity of the brake fluid is high, it is possible to suppress a large discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2.

[0079] (1-3) The first control unit 60 sets the upper limit value QbL lower as the braking pressure difference ΔPw is larger. The first control unit 60 then operates the normal supply source so that the discharge amount of brake fluid per unit time does not exceed the upper limit value QbL. As a result, when the braking device 100 performs connection control under conditions where the differential pressure on both sides of the switching unit 40 is large, it is possible to suppress a further widening of the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2.

[0080] (1-4) When adjusting the first braking pressure Pw1 and the second braking pressure Pw2 by connection control, if the braking pressure of the wheel cylinder is low relative to the non-normal supply source, the increase gradient, which is the increase in braking pressure relative to the amount of brake fluid flowing into the wheel cylinder, is smaller compared to when the braking pressure is high. Therefore, the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 tends to be large.

[0081] Therefore, in connection control, the first control unit 60 sets the upper limit QbL lower than when the acquired braking pressure detection value PwN is equal to or greater than the determined braking pressure Pwth, if the acquired braking pressure detection value PwN is less than the determined braking pressure Pwth. The first control unit 60 then operates the normal supply source so that the discharge amount of brake fluid per unit time does not exceed the upper limit QbL. As a result, the braking device 100 can suppress a large discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 when connection control is started under conditions where the braking pressure of the wheel cylinder corresponding to the non-normal supply source is low.

[0082] (1-5) When the required braking force FbRq is small, neither the first braking pressure Pw1 nor the second braking pressure Pw2 will be very high. Under these circumstances, even if a discrepancy occurs between the first braking pressure Pw1 and the second braking pressure Pw2, the discrepancy will not be very large.

[0083] Therefore, in connection control, the first control unit 60 corrects the upper limit QbL so that the lower the required braking force FbRq, the larger the upper limit QbL becomes. The first control unit 60 then operates the normal supply source so that the discharge amount of brake fluid per unit time does not exceed the upper limit QbL. As a result, when the required braking force FbRq is relatively small, the braking device 100 can ensure braking responsiveness while keeping the degree of vehicle 10's deviation within an acceptable range.

[0084] (1-6) In the braking device 100, the detection signal from the first hydraulic pressure sensor 33 is input to the second controller 62, while the detection signal from the second hydraulic pressure sensor 35 is input to the first controller 61. Therefore, even if there is a malfunction in the second controller 62 or if communication between the multiple controllers 61 and 62 is poor, the first controller 61 can still obtain the second braking pressure detection value Pw2S. Since the first controller 61 can estimate the first braking pressure, it can estimate and calculate the braking pressure difference ΔPw, which is the hydraulic pressure difference between the first braking pressure Pw1 and the second braking pressure Pw2.

[0085] Furthermore, even if there is a malfunction in the first controller 61 or if communication between the multiple controllers 61 and 62 is poor, the second controller 62 can still obtain the first braking pressure detection value Pw1S. The second controller 62 can then estimate the second braking pressure based on the motor current Imt of the electric motor 54, and therefore can estimate the braking pressure difference ΔPw.

[0086] (Second Embodiment) A second embodiment of the braking device will be described with reference to Figures 6 and 7. The second embodiment differs from the first embodiment in that it assumes a case where the control transitions from interruption control to connection control during the adjustment of the first and second braking pressures by interruption control. In the following description, the parts that differ from the first embodiment will be mainly described, and the same reference numerals will be used for components identical to those in the first embodiment to avoid redundant explanations.

[0087] Figure 6 illustrates a part of the process that occurs when a braking request is generated under conditions where the above-mentioned normal judgment conditions are determined to be met. The process flow from step S11 to step S17 is the same as in the first embodiment described above, so a detailed explanation is omitted here.

[0088] When the first control unit 60 activates the multiple supply sources 50A and 50B in step S17, it proceeds to step S101. In step S101, the first control unit 60 determines whether or not an abnormality has occurred. The first control unit 60 determines that an abnormality has occurred if at least one of the following conditions (B1) and (B2) is met. On the other hand, the first control unit 60 determines that no abnormality has occurred if neither of the following conditions (B1) and (B2) is met.

[0089] (B1) An abnormality occurs in the first supply source 50A or the second supply source 50B. (B2) An abnormality occurs in the first controller 61 or the second controller 62. For example, if an abnormality occurs in at least one of the first supply source 50A and the first controller 61, the first supply source 50A will be unable to regulate the first braking pressure Pw1, causing brake fluid to leak from the first wheel cylinder 211 into the first fluid passage 32. As a result, the first braking pressure Pw1 decreases, and the piston 53 in the electric cylinder 51 of the first supply source 50A retracts.

[0090] If the first control unit 60 determines that an abnormality has occurred in step S101 (S101: YES), the first control unit 60 proceeds to step S103. On the other hand, if the first control unit 60 determines that no abnormality has occurred (S101: NO), the first control unit 60 proceeds to step S19. In this case, the adjustment of the first damping pressure Pw1 and the second damping pressure Pw2 by shut-off control continues.

[0091] In step S103, the first control unit 60 is set as the main controller. For example, if an abnormality occurs in at least one of the second power source 50B and the second controller 62, and the first controller 61 is functioning normally, the first controller 61 is set as the main controller. On the other hand, if an abnormality occurs in at least one of the first power source 50A and the first controller 61, and the second controller 62 is functioning normally, the second controller 62 is set as the main controller.

[0092] In the following step S105, the main controller instructs the second control unit 90 to increase the braking force applied to the third wheel 13 and the fourth wheel 14. When the second control unit 90 receives the instruction, the second control unit 90 activates the braking actuator 81 to increase the braking force applied to the third wheel 13 and the fourth wheel 14.

[0093] When the main controller instructs the second control unit 90 to increase the braking force applied to the third wheel 13 and the fourth wheel 14, it terminates the shutoff control and executes the transition control. Specifically, in step S107, the main controller starts reducing the braking pressure of the wheel cylinder corresponding to it by activating the power source that it controls. That is, the main controller reduces the braking pressure by reducing the motor rotation angle θmt of the electric motor 54. If the main controller is the second controller 62, the power source that the main controller controls is the second power source 50B. Also, the wheel cylinder corresponding to the main controller is the second wheel cylinder 212. Therefore, if the main controller is the second controller 62, the second controller 62 reduces the second braking pressure Pw2 by driving the electric motor 54 of the second power source 50B.

[0094] In the following step S109, the main controller sets the state of the switching unit 40 to the connected state. Then, in step S111, the main controller determines whether the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 falls within an acceptable range. For example, the main controller determines that the discrepancy is within an acceptable range when the absolute value of the difference between the acquired braking pressure detection value PwN and the opposite braking pressure estimate value PwRe equals the difference determination value ΔPwth. Alternatively, the main controller may determine that the discrepancy is within an acceptable range when the elapsed time from the time the state of the switching unit 40 was set to the communication state reaches the determination time. If the main controller determines that the discrepancy is not within an acceptable range (S111: NO), the main controller repeatedly performs the determination in step S111 until it can determine that the discrepancy is within an acceptable range. On the other hand, if the main controller determines that the discrepancy is within an acceptable range (S111: YES), the main controller terminates the transfer control and performs the connection control shown in Figure 3.

[0095] <Operation and Effects of This Embodiment> Referring to Figure 7, the operation and effects of the transition from shut-off control to connection control during the process of adjusting the first damping pressure Pw1 and the second damping pressure Pw2 by shut-off control will be explained.

[0096] As shown in Figures 7(a) to 7(c), while the first damping pressure Pw1 and the second damping pressure Pw2 are being adjusted by the shut-off control, an abnormality may occur in only one of the multiple controllers 61, 62. Here, we will explain assuming that an abnormality has occurred in the first controller 61.

[0097] In the example shown in Figure 7, at timing t11, the first controller 61 loses control of the first power source 50A. As a result, the power supply from the first power source 50A to the electric motor 54 is stopped. Consequently, the electric cylinder 51 of the first power source 50A no longer receives torque from the electric motor 54, causing the piston 53 to retract. As a result, brake fluid flows out of the first wheel cylinder 211 into the first fluid passage 32, reducing the first braking pressure Pw1. Note that at timing t11, since shut-off control is performed, the second braking pressure Pw2 is controlled by the second target braking pressure Pw2Tr.

[0098] At the subsequent timing t12, the second controller 62 determines that an abnormality has occurred in the first controller 61. Therefore, from timing t12 onward, the second controller 62 functions as the primary controller. Then, the second controller 62 terminates the shutdown control and executes the transition control.

[0099] In transition control, the second controller 62 operates the second power source 50B so that the second braking pressure Pw2 decreases. The second controller 62 also changes the state of the switching unit 40 to a connected state. As a result, the second braking pressure Pw2 decreases, and the gap between the first braking pressure Pw1 and the second braking pressure Pw2 becomes smaller.

[0100] At timing t13, the second controller 62 determines that the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 has fallen within the acceptable range. Therefore, the second controller 62 terminates the transfer control and starts the connection control. In the connection control, the second controller 62 adjusts the first braking pressure Pw1 and the second braking pressure Pw2 by operating only the second supply source 50B (i.e., the normal supply source) among the multiple supply sources 50A and 50B. At this time, similar to the first embodiment described above, the second controller 62 sets an upper limit QbL for the discharge rate of brake fluid per unit time at the second supply source 50B. The second controller 62 then operates the second supply source 50B so that the discharge rate of brake fluid per unit time does not exceed the upper limit QbL.

[0101] Therefore, even if the braking device 100 of this embodiment switches the control from interruption control to connection control while adjusting the first braking pressure Pw1 and the second braking pressure Pw2 by interruption control, it can reduce the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2.

[0102] As described above, during the period when the control is switched from disconnection control to connection control, the sum of the braking force applied to the first wheel 11 and the braking force applied to the second wheel 12 temporarily decreases. However, during this period, the sum of the braking force applied to the third wheel 13 and the braking force applied to the fourth wheel 14 increases. Therefore, the braking device 100 can suppress a decrease in the deceleration of the vehicle 10 during the process of switching the control from disconnection control to connection control.

[0103] (Third embodiment) A third embodiment of the braking device will be described with reference to Figure 8. The third embodiment differs from the above-described embodiments in the method for adjusting the braking force of the third and fourth wheels. In the following description, the parts that differ from the above-described embodiments will be mainly described, and the same reference numerals will be used for components identical to those in the above-described embodiments to avoid redundant explanations.

[0104] Figure 8 illustrates a part of the normal supply source operation process in step S37 described above. When the main controller of the first control unit 60 performs the correction process for the upper limit value QbL in step S59 of Figure 4, the process moves to step S301. In step S301, the main controller determines whether or not to generate a braking force difference between the third wheel 13 and the fourth wheel 14. For example, when the vehicle 10 is traveling in a straight line, it may be determined that a braking force difference is generated between the third wheel 13 and the fourth wheel 14. If the main controller determines that a braking force difference is generated between the third wheel 13 and the fourth wheel 14 (S301: YES), the main controller moves the process to step S303. On the other hand, if the main controller determines that no braking force difference is generated between the third wheel 13 and the fourth wheel 14 (S301: NO), the main controller moves the process to step S61.

[0105] Here, when a braking force difference is generated between the third wheel 13 and the fourth wheel 14, the second control unit 90 adjusts the braking force difference between the third wheel 13 and the fourth wheel 14 by operating the braking actuator 81 so as to reduce the discrepancy between the yaw rate YR and the target yaw rate YRTr. This type of braking control is described as "amplification suppression control". The target yaw rate YRTr is the target value of the yaw rate YR. For example, the yaw rate that can be calculated using the steering angle of the steering wheel of the vehicle 10 may be set as the target yaw rate YRTr.

[0106] In step S303, the main controller increases the upper limit value QbL. In other words, when the second control unit 90 performs expansion suppression control, even if a braking force difference occurs between the first wheel 11 and the second wheel 12, the vehicle 10 is less likely to deviate. Therefore, the main controller sets the upper limit value QbL to be larger than when the second control unit 90 does not perform expansion suppression control. After that, the main controller proceeds to step S61.

[0107] <Operation and Effects of This Embodiment> In this embodiment, when the braking force between the first wheel 11 and the second wheel 12 is adjusted by connection control, the braking force difference between the third wheel 13 and the fourth wheel 14 can be adjusted by expansion suppression control. For this reason, the first control unit 60 sets a large upper limit QbL. The first control unit 60 then operates the normal supply source so that the discharge amount of brake fluid per unit time does not exceed the upper limit QbL. Thus, when the braking pressure of the first wheel cylinder and the second wheel cylinder is controlled by the execution of connection control, the braking device 100 can suppress the vehicle 10 from deviating while suppressing a decrease in the deceleration of the vehicle 10.

[0108] (Fourth Embodiment) A fourth embodiment of the braking device will be described with reference to Figures 9 and 10. The fourth embodiment differs from the third embodiment in that it includes a method for adjusting the braking force of the third and fourth wheels when connection control is being performed. In the following description, the parts that differ from the above embodiments will be mainly described, and the same reference numerals will be used for components identical to those in the above embodiments to avoid redundant explanations.

[0109] In the braking device 100 of this embodiment, the first control unit 60 adjusts the first braking pressure Pw1 and the second braking pressure Pw2 by performing connection control when a braking request is made to the vehicle 10 under circumstances where the above-mentioned normal conditions are not met.

[0110] In the initial stages of connection control, a hydraulic pressure difference occurs between the first braking pressure Pw1 and the second braking pressure Pw2, as shown in Figure 5. The occurrence of a hydraulic pressure difference between the first braking pressure Pw1 and the second braking pressure Pw2 means that a braking force difference occurs between the first wheel 11 and the second wheel 12. If the braking force difference between the first wheel 11 and the second wheel 12 is relatively large, a yaw moment corresponding to the braking force difference is generated in the vehicle 10.

[0111] The first control unit 60 performs a prediction process to predict the future trend of the braking pressure difference ΔPw, which is the difference between the first braking pressure Pw1 and the second braking pressure Pw2, when connection control is performed. In the prediction process, the first control unit 60 predicts the future trend of the braking pressure difference ΔPw based on an index that takes into account at least one of the amount of brake fluid per unit time passing through the multiple system shut-off valves 42, 43 and the viscosity of the brake fluid. Details of the prediction process will be described later.

[0112] The second control unit 90 performs yaw moment cancellation processing when the first control unit 60 performs connection control while the vehicle 10 is in motion. In yaw moment cancellation processing, the second control unit 90 estimates the change in the braking force difference between the third wheel 13 and the fourth wheel 14, which can cancel out the yaw moment caused by the occurrence of the braking pressure difference ΔPw, based on the results of the prediction processing performed by the first control unit 60, i.e., the prediction results of the future change in the braking pressure difference ΔPw. Then, the second control unit 90 operates the braking actuator 81 based on the change in the braking force difference. Details of the yaw moment cancellation processing will be described later.

[0113] <Predictive Processing> Referring to Figure 9, the prediction process will be explained. The main controller of the first control unit 60 repeatedly performs the prediction process at predetermined control cycles when connection control is executed.

[0114] In step S401, the main controller obtains the above metrics. For example, the main controller obtains the following parameters as metrics. • The fluid temperature (TMP) is the temperature of the brake fluid.

[0115] The braking pressure difference ΔPw at the start of connection control, or at the time when the switching unit 40 enters a communication state. The elapsed time from the start of connection control, or from the time when the switching unit 40 enters a connected state.

[0116] • The motor rotation angle θmt of the normal electric cylinder 51. The lower the fluid temperature TMP, the higher the viscosity of the brake fluid, which tends to reduce the amount of brake fluid passing through the multiple system shut-off valves 42 and 43 per unit time. In other words, in the initial stages of connection control, the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12 tends to be large.

[0117] In the subsequent step S403, the main controller predicts the change in the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12 based on the indicators obtained in step S401. An example of predicting the change in the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12 when the electric cylinder 51 of the first supply source 50A is a normal electric cylinder 51 is described below. The main controller predicts the change in the braking pressure difference ΔPw based on the fluid volume per unit time of brake fluid supplied by the normal electric cylinder 51, the upper limit value QbL, the braking pressure difference ΔPw at the start of connection control, the orifice of the switching unit 40, the fluid volume characteristics of the first wheel cylinder 211, and the fluid volume characteristics of the second wheel cylinder 212. For example, the main controller estimates the fluid volume per unit time of brake fluid passing through the switching unit 40 based on the orifice of the switching unit 40 and the braking pressure difference ΔPw at the start of connection control. The main controller then predicts the trend of the first braking pressure Pw1, which is the braking pressure of the first wheel cylinder 211, based on the estimated fluid volume per unit time of brake fluid passing through the switching unit 40, the fluid volume per unit time of brake fluid supplied by the normal electric cylinder 51, and the fluid volume characteristics of the first wheel cylinder 211. Furthermore, the main controller predicts the trend of the second braking pressure Pw2, which is the braking pressure of the second wheel cylinder 212, based on the estimated fluid volume per unit time of brake fluid passing through the switching unit 40 and the fluid volume characteristics of the second wheel cylinder 212. The fluid volume characteristics of the wheel cylinders are, for example, a map showing the relationship between the amount of brake fluid flowing into the wheel cylinders and the braking pressure.

[0118] The main controller then predicts the change in the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12 based on the predicted changes in the first braking pressure Pw1 and the predicted changes in the second braking pressure Pw2. Furthermore, based on the braking pressure difference ΔPw obtained in this way, the main controller updates the amount of brake fluid per unit time passing through the switching unit 40 and updates the predicted changes in the first braking pressure Pw1 and the second braking pressure Pw2. In this way, the main controller can derive the difference between the predicted changes in the first braking pressure Pw1 and the predicted changes in the second braking pressure Pw2 as the change in the braking pressure difference ΔPw.

[0119] Furthermore, in order to improve the accuracy of predicting the changes in the braking pressure difference ΔPw, if the piston 53 of the malfunctioning supply source is moving forward, the main controller may predict the changes in the second braking pressure Pw2 by considering that the piston 53 of the malfunctioning supply source is pushed back by the hydraulic pressure that rises due to the amount of brake fluid per unit time passing through the switching section 40, which has been calculated by estimation.

[0120] In the next step, S405, the main controller transmits information regarding the predicted change in the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12 to the second control unit 90 via the in-vehicle network 200. The main controller then terminates the connection process.

[0121] <Yaw moment cancellation process> Referring to Figure 10, the yaw moment cancellation process will be explained. The second control unit 90 repeatedly performs the yaw moment cancellation process at predetermined control cycles when connection control is executed.

[0122] In step S421, the second control unit 90 determines whether or not it has received information from the first control unit 60 regarding the predicted change in the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12. If the second control unit 90 has not received this information (S421: NO), the second control unit 90 terminates the yaw moment cancellation process. On the other hand, if the second control unit 90 has received this information (S421: YES), the second control unit 90 proceeds to step S423.

[0123] In step S423, the second control unit 90 predicts the change in the braking force difference between the first wheel 11 and the second wheel 12 based on the predicted result of the change in the braking pressure difference ΔPw between the first wheel 11 and the second wheel 12, which is indicated by the received information.

[0124] In the subsequent step S425, the second control unit 90 derives the amount of yaw moment cancellation. For example, based on the change in the braking force difference between the first wheel 11 and the second wheel 12 predicted in step S423, the second control unit 90 predicts a specified yaw moment, which is the yaw moment generated by the braking force difference. Then, the second control unit 90 derives the amount of yaw moment cancellation by reversing the direction of the specified yaw moment.

[0125] In the next step S427, the second control unit 90 derives a target braking force difference, which is the braking force difference to be generated between the third wheel 13 and the fourth wheel 14, based on the amount of yaw moment cancellation. At this time, the second control unit 90 derives the target braking force difference as the braking force difference that can generate the amount of yaw moment cancellation.

[0126] In the subsequent step S429, the second control unit 90 sets the target braking force of the third wheel 13 and the target braking force of the fourth wheel 14 based on the target braking force difference. Here, the second control unit 90 sets the target braking force of the third wheel 13 and the target braking force of the fourth wheel 14 such that the difference between the target braking force of the third wheel 13 and the target braking force of the fourth wheel 14 is equal to the target braking force difference.

[0127] In this embodiment of the braking device 100, the second control unit 90 performs the processing in steps S423 to S429, but this is not limited to this. For example, the first control unit 60 may perform at least one of the processing in steps S423 to S429.

[0128] Then, in step S431, the second control unit 90 activates the braking actuator 81 based on the target braking force of the third wheel 13 and the target braking force of the fourth wheel 14. This allows the second control unit 90 to individually adjust the braking force applied to the third wheel 13 and the braking force applied to the fourth wheel 14. After that, the second control unit 90 temporarily terminates the yaw moment cancellation process.

[0129] <Operation and Effects of This Embodiment> In the braking device 100 of this embodiment, when adjusting the braking force between the first wheel 11 and the second wheel 12 by connection control, the change in the braking pressure difference ΔPw between the first braking pressure Pw1 and the second braking pressure Pw2 is predicted. Then, the braking actuator 81 operates so that the braking force difference between the third wheel 13 and the fourth wheel 14 changes according to the predicted result. As a result, the braking force difference between the third wheel 13 and the fourth wheel 14 is adjusted before the yaw rate YR caused by the braking pressure difference ΔPw is generated. In other words, the braking force difference between the third wheel 13 and the fourth wheel 14 is adjusted feedforward. Therefore, the braking device 100 of this embodiment can achieve a higher deflection suppression effect of the vehicle 10 when the braking pressure of the first wheel cylinder 211 and the second wheel cylinder 212 is controlled by the execution of connection control.

[0130] (Example of change) The above embodiments can be implemented with the following modifications. The above embodiments and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0131] In the above embodiments, the main controller set an upper limit QbL for the discharge rate of brake fluid per unit time, but it is not limited to this. For example, the main controller may set an upper limit for the suction rate of brake fluid per unit time.

[0132] Consider the case where braking pressure is generated in multiple wheel cylinders 211, 212 under connection control, and brake fluid is drawn from wheel cylinders 211, 212 using a normal supply source. Of the multiple wheel cylinders 211, 212, the brake fluid from the wheel cylinder corresponding to the non-normal supply source is drawn through the system shut-off valves 42, 43, i.e., the orifice, making it more difficult to draw compared to the brake fluid from the wheel cylinder corresponding to the normal supply source. As a result, there is a risk of a braking pressure difference occurring among the multiple wheel cylinders 211, 212. With the braking device of this modified example, an upper limit is set for the amount of brake fluid drawn per unit time from the normal supply source under the above circumstances, so when connection control is performed, it is possible to suppress a large discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2.

[0133] - During the adjustment of the braking pressures Pw1 and Pw2 of multiple wheel cylinders 211 and 212 using shut-off control, an abnormality may occur in only one of the multiple supply sources 50A and 50B. In this case, the braking pressure of the wheel cylinder corresponding to the abnormal supply source decreases, and this braking pressure becomes lower than the braking pressure of the wheel cylinder corresponding to the normal supply source. In this situation, the control is switched from shut-off control to connection control as described above. Furthermore, if the target braking force decreases in this situation, the normal supply source performs control to draw brake fluid from the wheel cylinder. In this case, although a braking pressure difference occurs among the multiple wheel cylinders 211 and 212, it is preferable to increase the upper limit of the amount of brake fluid drawn per unit time from the normal supply source. In this situation, a discrepancy occurs between the first braking pressure Pw1 and the second braking pressure Pw2 because the braking pressure of the wheel cylinder corresponding to the normal supply source is higher than the braking pressure of the wheel cylinder corresponding to the abnormal supply source. Therefore, by increasing the upper limit of the amount of brake fluid drawn per unit time from a normal supply source, the discrepancy between the first braking pressure Pw1 and the second braking pressure Pw2 can be suppressed at an early stage.

[0134] The detection signal from the first hydraulic pressure sensor 33 may be input to both the first controller 61 and the second controller 62. Similarly, the detection signal from the second hydraulic pressure sensor 35 may be input to both the first controller 61 and the second controller 62. Alternatively, the detection signal from the first hydraulic pressure sensor 33 may be input only to the first controller 61, and the detection signal from the second hydraulic pressure sensor 35 may be input only to the second controller 62.

[0135] In the third embodiment, when the second control unit 90 performs amplification suppression control, the first control unit 60 does not need to increase the upper limit value QbL. The first control unit 60 does not need to correct the upper limit value QbL based on the required braking force FbRq.

[0136] The first control unit 60 does not need to correct the upper limit value QbL based on the vehicle speed VS. The first control unit 60 does not need to correct the upper limit QbL based on the yaw rate YR, lateral acceleration, and steering angle of the steering wheel.

[0137] The first control unit 60 does not need to vary the upper limit QbL depending on whether the braking pressure of the wheel cylinder corresponding to the non-normal supply source is less than the determination braking pressure Pwth.

[0138] If the first control unit 60 varies the upper limit QbL based on the liquid temperature TMP, it is not necessary to vary the upper limit QbL based on the braking pressure difference ΔPw. If the first control unit 60 varies the upper limit QbL based on the braking pressure difference ΔPw, it is not necessary to vary the upper limit QbL based on the liquid temperature TMP.

[0139] In the fourth embodiment, when the second control unit 90 performs yaw moment cancellation processing, the first control unit 60 does not need to set an upper limit value QbL. In transfer control, if the main controller changes the state of the switching unit 40 to a connected state, it does not need to perform the process of activating the power source of its controlled object in order to reduce the braking pressure of the wheel cylinder corresponding to itself.

[0140] If the first braking unit 30 does not have a reservoir shutoff unit 45, the switching unit 40 may have only one system shutoff valve. In this case, it is preferable that the system shutoff valve has a configuration comprising a first solenoid whose energization can be controlled by the first controller 61 and a second solenoid whose energization can be controlled by the second controller 62. As a result, the system shutoff valve is closed when power is supplied to at least one of the first solenoid and the second solenoid. On the other hand, the system shutoff valve is opened when power is not supplied to either the first solenoid or the second solenoid.

[0141] The electric cylinder 51 may or may not have a return spring that biases the piston 53 in the direction of retraction. The first braking unit 30 may be configured such that the first supply source 50A can supply brake fluid to the two wheel cylinders even when the switching unit 40 is in a shut-off state. In this case, the two wheel cylinders are connected to the first fluid passage 32. In this respect, the two wheel cylinders correspond to the "first wheel cylinder".

[0142] The first braking unit 30 may be configured such that the second supply source 50B can supply brake fluid to the two wheel cylinders even when the switching unit 40 is in a shut-off state. In this case, the two wheel cylinders are connected to the second fluid passage 34. In this respect, the two wheel cylinders correspond to the "second wheel cylinders".

[0143] The first control unit 60 may have only one controller, as long as it can control the first braking unit 30. The first and second supply sources may be configured to include pressurizing sources other than the electric cylinder 51, as long as they can supply brake fluid to the wheel cylinder. For example, the first and second supply sources may be configured to include electric pumps.

[0144] The first wheel 11 and the second wheel 12 may be rear wheels, and the third wheel 13 and the fourth wheel 14 may be front wheels. That is, the first braking unit 30 may be a unit that adjusts the braking force of the front wheels, and the second braking unit 80 may be a unit that adjusts the braking force of the rear wheels.

[0145] The braking actuator 81 may have any configuration as long as the braking force applied to the third wheel 13 and the braking force applied to the fourth wheel 14 can be adjusted individually. For example, the braking actuator 81 may be configured to include an electric braking device for the third wheel 13 and an electric braking device for the fourth wheel 14. An example of an electric braking device is disclosed in "Japanese Patent Application Publication No. 2024-143525". In the case where the braking actuator 81 is equipped with two electric braking devices, the second control unit 90 may have a third controller that controls one of the two electric braking devices and a fourth controller that controls the other.

[0146] The first control unit 60 may be configured as a circuit including one or more dedicated hardware circuits, such as one or more processors that operate according to a computer program, and dedicated hardware that performs at least some of the various processes, or a combination thereof. Examples of dedicated hardware include application-specific integrated circuits (ASICs). The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., storage medium, includes any available medium that can be accessed by a general-purpose or dedicated computer.

[0147] <Other technological ideas> This section describes the technical concepts that can be understood from the above-mentioned multiple embodiments and modifications. [Note 1] A first braking pressure detection unit for detecting the braking pressure of the first wheel cylinder, It comprises a second braking pressure detection unit for detecting the braking pressure of the second wheel cylinder, The control unit includes a first controller for controlling the first supply source, and a second controller that is communicative with the first controller and controls the second supply source. Preferably, the detection result of the second damping pressure detection unit is input to the first controller, and the detection result of the first damping pressure detection unit is input to the second controller.

[0148] [Note 2] This invention is applied to a vehicle comprising: first wheels and second wheels positioned at different locations relative to each other in the vehicle width direction; third wheels and fourth wheels positioned at different locations relative to the first and second wheels in the vehicle longitudinal direction and at different locations relative to each other in the vehicle width direction; a first wheel cylinder corresponding to the first wheel; and a second wheel cylinder corresponding to the second wheel. A first fluid passage, which is a brake fluid passage connected to the first wheel cylinder, A second fluid passage, which is a brake fluid passage connected to the second wheel cylinder, A first supply source connected to the first fluid passage and discharging brake fluid into the first fluid passage, A second supply source connected to the second fluid passage and discharging brake fluid into the second fluid passage, A switching unit having a connecting passage between the first liquid passage and the second liquid passage and a switching valve installed in the connecting passage, wherein when the switching valve is open, the first liquid passage and the second liquid passage are connected, and when the switching valve is closed, the connection between the first liquid passage and the second liquid passage is blocked, A braking actuator configured to allow individual adjustment of the braking force applied to the third wheel and the braking force applied to the fourth wheel, The system includes a control unit that performs connection control to control the braking pressure of multiple wheel cylinders by opening the switching valve to connect the first fluid passage and the second fluid passage, and then activating only one of the multiple supply sources, which is the normal supply source, The control unit, During the execution of the connection control, a prediction process is performed to predict the future trend of the braking pressure difference between the first wheel cylinder and the second wheel cylinder, based on an index that takes into account at least one of the amount of brake fluid per unit time passing through the switching valve and the viscosity of the brake fluid. A braking device that, when the connection control is executed, operates the braking actuator so that the difference in braking force between the third wheel and the fourth wheel changes according to the result of the prediction process.

[0149] [Note 3] Preferably, when the connection control is executed, the control unit estimates the change in the braking force difference between the third wheel and the fourth wheel, which can cancel out the yaw moment caused by the generation of the braking pressure difference, based on the result of the prediction process, and operates the braking actuator based on the change in the braking force difference.

[0150] In this specification, the expression "at least one" means "one or more" of the desired options. For example, if there are two options, the expression "at least one" means "only one option" or "both of the two options." As another example, if there are three or more options, the expression "at least one" means "only one option" or "a combination of two or more arbitrary options." [Explanation of Symbols]

[0151] 10... Vehicles 11...1st wheel 12…Second wheel 13...Third wheel 14…4th wheel 211…First wheel cylinder 212... Second wheel cylinder 32...1st liquid path 33…First hydraulic pressure sensor (an example of the first damping pressure detection unit) 34…Second liquid path 35…Second hydraulic pressure sensor (an example of a second damping pressure detection unit) 40…Switching section 41...Communication path 42, 43… System shut-off valve (an example of a switching valve) 50A…1st supply source 50B…Second supply source 60...First Control Unit 61…First controller 62...Second controller 81... Brake Actuator 90...Second Control Unit 100...braking device

Claims

1. This is applied to a vehicle comprising a first wheel and a second wheel positioned at different locations in the vehicle width direction, a first wheel cylinder corresponding to the first wheel, and a second wheel cylinder corresponding to the second wheel. A first fluid passage, which is a brake fluid passage connected to the first wheel cylinder, The second fluid passage, which is a brake fluid passage connected to the second wheel cylinder, A first supply source connected to the first fluid passage and discharging brake fluid into the first fluid passage, A second supply source connected to the second fluid passage and discharging brake fluid into the second fluid passage, A switching unit having a connecting passage between the first liquid passage and the second liquid passage and a switching valve installed in the connecting passage, wherein when the switching valve is open, the first liquid passage and the second liquid passage are connected, and when the switching valve is closed, the connection between the first liquid passage and the second liquid passage is blocked, The system includes a control unit that performs connection control to control the braking pressure of multiple wheel cylinders by opening the switching valve to connect the first fluid passage and the second fluid passage, and then activating only one of the multiple supply sources, which is the normal supply source, The control unit, in the connection control, Based on an index that takes into account at least one of the fluid volume per unit time of the brake fluid passing through the switching valve and the viscosity of the brake fluid, an upper limit is set for at least one of the discharge rate and suction rate per unit time of the brake fluid from the normal supply source. The normal supply source is operated such that at least one of the discharge rate and suction rate of brake fluid per unit time does not exceed the upper limit. Braking device.

2. The control unit, in the connection control, As the aforementioned indicator, the fluid temperature, which is the temperature of the brake fluid, is obtained. The lower the liquid temperature, the smaller the upper limit is set. The braking device according to claim 1.

3. The control unit, in the connection control, As the aforementioned indicator, the braking pressure difference, which is the difference between the braking pressure of the first wheel cylinder and the braking pressure of the second wheel cylinder, is obtained. The larger the braking pressure difference, the smaller the upper limit is set. The braking device according to claim 1.

4. The control unit, in the connection control, In the case where, among the plurality of wheel cylinders, the braking pressure of the wheel cylinder corresponding to the supply source that is not the normal supply source among the plurality of supply sources is less than the determination braking pressure, and the braking pressure of the plurality of wheel cylinders is increased by the normal supply source, the upper limit is set to be smaller than when the braking pressure is equal to or greater than the determination braking pressure. The braking device according to claim 1.

5. The first wheel and the second wheel are the front wheels of the vehicle. The vehicle has two rear wheels positioned at different locations in the vehicle width direction, The control unit is the first control unit, The braking device comprises a braking actuator capable of individually adjusting the braking force applied to the two rear wheels, and a second control unit that controls the braking actuator. The second control unit is capable of performing expansion suppression control, which involves operating the braking actuator to adjust the braking force difference between the two rear wheels in order to suppress the deviation between the yaw rate of the vehicle and the target value of the yaw rate when the first control unit performs the connection control. The first control unit corrects the upper limit so that, when the expansion suppression control is performed, the upper limit is greater than when the expansion suppression control is not performed. The braking device according to claim 1.

6. The control unit is capable of performing shut-off control, which involves shutting off communication between the first fluid passage and the second fluid passage by closing the switching valve, then controlling the braking pressure of the first wheel cylinder by activating the first supply source, and controlling the braking pressure of the second wheel cylinder by activating the second supply source. The control unit, In the situation where the braking pressure of the multiple wheel cylinders is controlled by the execution of the shut-off control, if an abnormality occurs in only one of the first and second supply sources, After performing transition control, which includes activating the other supply source to reduce the braking pressure of the wheel cylinder corresponding to the other supply source among the plurality of wheel cylinders, and opening the switching valve to connect the first fluid passage and the second fluid passage, the connection control is started. A braking device according to any one of claims 1 to 5.

7. The control unit, The upper limit is adjusted so that the lower the required braking force, which is the required value of braking force for the vehicle, the larger the upper limit becomes. A braking device according to any one of claims 1 to 5.

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