Braking device

Abstract

A braking device 30 comprises: a master cylinder 43 and electric pressurization unit 49; a first solenoid valve 44A, 44B; a second solenoid valve 48A, 48B installed between the first solenoid valve 44A, 44B and a wheel cylinder 211, 212; and a processing circuit 101. The processing circuit 101 executes first valve closing control for closing one among the first solenoid valve 44A, 44B and the second solenoid valve 48A, 48B when liquid pressure is generated, and, during a prescribed period after the fluid pressure in a brake fluid passage between the first solenoid valve 44A, 44B and the second solenoid valve 48A, 48B has exceeded a threshold value subsequent to the execution of the first valve closing control, executes second valve closing control for closing the other among the first solenoid valve 44A, 44B and the second solenoid valve 48A, 48B.

Description

Brake device

[0001] The present disclosure relates to a brake device that controls the braking force of a vehicle by adjusting the hydraulic pressure of a wheel cylinder.

[0002] Patent Document 1 discloses a brake device in which a first electromagnetic valve and a second electromagnetic valve are arranged in series in a brake fluid passage connecting a reservoir and a wheel cylinder. In this brake device, the first electromagnetic valve is located between the second electromagnetic valve and the reservoir, and a master cylinder, which is an example of a pressurizing unit, is arranged between the reservoir and the first electromagnetic valve. In the brake device, when hydraulic pressure is generated by the operation of the master cylinder, the first electromagnetic valve and the second electromagnetic valve are closed almost simultaneously. This suppresses the direct supply of brake fluid from the master cylinder to the wheel cylinder.

[0003] Japanese Patent Application Laid-Open No. 2022-27055

[0004] When the first hydraulic pressure difference, which is the difference between the upstream hydraulic pressure, which is the hydraulic pressure between the master cylinder and the first electromagnetic valve, and the intermediate hydraulic pressure, which is the hydraulic pressure between the first electromagnetic valve and the second electromagnetic valve, becomes large under the condition that the first electromagnetic valve is closed, the valve body of the first electromagnetic valve may be pushed by the first hydraulic pressure difference and the first electromagnetic valve may open. If the first electromagnetic valve opens in this way, the intermediate hydraulic pressure increases because brake fluid flows through the first electromagnetic valve, so the first hydraulic pressure difference becomes small. However, even when the first hydraulic pressure difference becomes small, the first electromagnetic valve does not close immediately due to the hysteresis and responsiveness of the first electromagnetic valve. And while the first electromagnetic valve is open, the intermediate hydraulic pressure increases to be equal to the upstream hydraulic pressure.

[0005] When the intermediate hydraulic pressure thus increases under the condition that the second electromagnetic valve is closed, the second hydraulic pressure difference, which is the difference between the intermediate hydraulic pressure and the downstream hydraulic pressure, which is the hydraulic pressure between the second electromagnetic valve and the wheel cylinder, becomes large. Then, the valve body of the second electromagnetic valve may be pushed by the second hydraulic pressure difference and the second electromagnetic valve may open. That is, if the first electromagnetic valve and the second electromagnetic valve are closed almost simultaneously when hydraulic pressure is generated in the master cylinder, there is a risk that the first electromagnetic valve and the second electromagnetic valve will open in chain as the hydraulic pressure generated by the master cylinder increases.

[0006] The braking device described above includes an electrically operated pressurizing unit as an example of a pressurizing unit, which generates hydraulic pressure between the second solenoid valve and the wheel cylinder. Even when adjusting the hydraulic pressure of the wheel cylinder by operating the electrically operated pressurizing unit, the first and second solenoid valves are closed almost simultaneously. Even in this case, if the difference between the downstream hydraulic pressure and the intermediate hydraulic pressure becomes large, the second solenoid valve may open. When the second solenoid valve opens, the intermediate hydraulic pressure increases, and the difference between the intermediate hydraulic pressure and the upstream hydraulic pressure becomes large. Then, when the difference between the intermediate hydraulic pressure and the upstream hydraulic pressure becomes large enough, the first solenoid valve opens. In other words, even when the electrically operated pressurizing unit is operating, if the first and second solenoid valves are closed almost simultaneously, there is a risk that the first and second solenoid valves will open in a chain reaction.

[0007] The objective of this disclosure is to prevent a solenoid valve from opening when it is closed during the operation of a pressurizing unit such as a master cylinder or an electrically operated pressurizing unit.

[0008] The braking device for solving the above problem is a device that controls the braking force of a vehicle by adjusting the hydraulic pressure of the first wheel cylinder with brake fluid supplied from a pressurizing unit. The braking device comprises a supply fluid passage which is a brake fluid passage connected to the first wheel cylinder; a first solenoid valve installed in the supply fluid passage; a second solenoid valve installed in the portion of the supply fluid passage between the first solenoid valve and the wheel cylinder; a first valve closing control unit which, when generating hydraulic pressure in the first wheel cylinder, performs a first valve closing control to close one of the first solenoid valves and open the other solenoid valve in order to block communication between the first fluid passage, which is the portion of the supply fluid passage on the opposite side of the first wheel cylinder from the first solenoid valve; and a pressure regulating control unit which, after the first valve closing control has been performed and the first solenoid valve has been closed, performs a suppression control to suppress an increase in the differential pressure between the fluid passages on both sides of the first solenoid valve by adjusting the hydraulic pressure in the third fluid passage, which is the portion of the supply fluid passage between the first solenoid valve and the second solenoid valve.

[0009] The above-described braking device has the effect of preventing the solenoid valve from opening when the pressurizing unit is activated and the solenoid valve is closed.

[0010] Figure 1 is a schematic diagram showing the configuration of a vehicle equipped with the braking device of the first embodiment. Figure 2 is a schematic diagram showing the configuration of the first braking unit and the second braking unit equipped with the braking device of Figure 1. Figure 3 is a schematic cross-sectional view showing the configuration of the electric pressurizing section equipped with the braking device of Figure 1. Figure 4 is a block diagram showing the functional configuration of the processing circuit equipped with the braking device of Figure 1. Figure 5 is a flowchart showing a series of processes executed by the processing circuit equipped with the braking device of Figure 1. Figure 6 is a flowchart showing a series of processes executed by the processing circuit equipped with the braking device of Figure 1. Figures 7(a) to 7(e) are timing charts when the driver performs a braking operation. Figures 8(a) to 8(e) are timing charts when the electric pressurizing section is activated. Figures 9(a) to 9(d) are timing charts when the electric pressurizing section is activated in the braking device of the second embodiment. Figure 10 is a schematic diagram showing the configuration of a vehicle equipped with the braking device of the third embodiment. Figure 11 is a schematic diagram showing the first solenoid valve included in the braking device of Figure 10. Figure 12 is a block diagram showing the functional configuration of the processing circuit included in the braking device of Figure 10. Figure 13 is an operation diagram of the braking unit included in the braking device of Figure 10. Figure 14 is an operation diagram of the braking unit included in the braking device of Figure 10. Figure 15 is an operation diagram of the braking unit included in the braking device of Figure 10. Figure 16 is a flowchart showing a series of processes executed by the processing circuit included in the braking device of Figure 10.

[0011] (First Embodiment) A first embodiment of the braking device will be described with reference to Figures 1 to 8. <Vehicle Configuration> Figure 1 shows a vehicle 10 equipped with a braking device 30. The vehicle 10 is equipped with a plurality of wheels and a plurality of friction brakes 20. The plurality of wheels include two first wheels 11 and two second wheels 12. An example of a first wheel 11 is a front wheel. An example of a second wheel 12 is a rear wheel.

[0012] Multiple friction brakes 20 are individually provided for multiple wheels 11 and 12. Each friction brake 20 has a wheel cylinder, a rotating body 22, and a friction part 23. The rotating body 22 rotates integrally with the wheels 11 and 12. Therefore, by pressing the friction part 23 against the rotating body 22, braking force is generated on the wheels 11 and 12. The force pressing the friction part 23 against the rotating body 22 increases with higher hydraulic pressure in the wheel cylinder. Therefore, the friction brake 20 can generate a greater braking force as the hydraulic pressure in the wheel cylinder increases.

[0013] Hereafter, the hydraulic pressure inside the wheel cylinder will be referred to as "braking pressure". 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".

[0014] <Configuration of the braking system> The braking system 30 controls the braking force of the vehicle 10 by adjusting the braking pressure of a plurality of wheel cylinders 211, 212. The braking system 30 comprises a reservoir 31, a first braking unit 40A, a second braking unit 40B, and a control device 100.

[0015] The reservoir 31 stores brake fluid and is open to the atmosphere. The first braking unit 40A adjusts the braking pressure of multiple first wheel cylinders 211. The second braking unit 40B adjusts the braking pressure of multiple second wheel cylinders 212.

[0016] <Configuration of the First Brake Unit> The first brake unit 40A includes a supply fluid passage 41A, which is a brake fluid passage connecting the reservoir 31 and the two first wheel cylinders 211. The supply fluid passage 41A branches into two on its way from the connection point with the reservoir 31 to the first wheel cylinders 211. That is, the supply fluid passage 41A includes one main passage 42a connected to the reservoir 31 and two branch passages 42b and 42c connected to the main passage 42a. Of the two first wheel cylinders 211, one is connected to branch passage 42b and the other is connected to branch passage 42c.

[0017] A master cylinder 43 and a first solenoid valve 44A are installed in the main flow path 42a. The first solenoid valve 44A is positioned between the connection point P1 between the main flow path 42a and the two branch flow paths 42b and 42c and the master cylinder 43.

[0018] A braking operation member 32, operated by the driver of the vehicle 10, is connected to the master cylinder 43. The braking operation member 32 is operated by the driver when adjusting the deceleration of the vehicle 10. An example of a braking operation member 32 is the brake pedal. The act of the driver operating the braking operation member 32 is also called "braking operation". The master cylinder 43 operates to generate hydraulic pressure in response to the driver's braking operation. In other words, the master cylinder 43 is an example of a "pressurizing unit" that operates to generate hydraulic pressure.

[0019] The first solenoid valve 44A is a master cut valve that closes when the communication between the master cylinder 43 and the first wheel cylinder 211 is interrupted. In this embodiment, a normally open type solenoid valve is used as the first solenoid valve 44A. In this case, the first solenoid valve 44A is closed by energizing the solenoid of the first solenoid valve 44A. The greater the amount of current supplied to the solenoid when closing the first solenoid valve 44A, the greater the closing force of the first solenoid valve 44A. Here, "closing force" refers to the magnitude of the force that presses the valve body against the valve seat of the solenoid valve.

[0020] A cut-off passage 45 is connected to the portion of the main passage 42a between the master cylinder 43 and the first solenoid valve 44A. The cut-off passage 45 is a brake fluid passage connecting the main passage 42a and the stroke simulator 46. A simulator cut-off valve 47, which is a normally closed solenoid valve, is installed in the cut-off passage 45. When the braking system 30 is functioning normally, the simulator cut-off valve 47 opens when the vehicle is braking.

[0021] A second solenoid valve 48A is installed in each of the multiple branch passages 42b and 42c. The multiple second solenoid valves 48A are cut-off valves that are closed when the communication between the corresponding first wheel cylinder 211 and the master cylinder 43 is interrupted. In this embodiment, a normally open type solenoid valve is used as the second solenoid valve 48A. In this case, the second solenoid valve 48A is closed by energizing the solenoid of the second solenoid valve 48A. Therefore, the greater the amount of current supplied to the solenoid when closing the second solenoid valve 48A, the greater the closing force of the second solenoid valve 48A.

[0022] An electric pressurizing unit 49 is connected to each of the multiple branch passages 42b and 42c. Specifically, the electric pressurizing unit 49 is connected to the portion of the branch passages 42b and 42c between the second solenoid valve 48A and the first wheel cylinder 211. The two electric pressurizing units 49 of the first braking unit 40A adjust the braking pressure of the wheel cylinder 211 by supplying brake fluid to the branch passages 42b and 42c driven by an electric motor 63. In other words, the electric pressurizing unit 49 is an example of a "pressurizing unit". Details of the configuration of the electric pressurizing unit 49 will be described later.

[0023] In this embodiment, as shown in Figure 2, the portion of the supply fluid passage 41A between the first solenoid valve 44A and the reservoir 31 corresponds to the "first fluid passage 71A". The portion of the supply fluid passage 41A between the second solenoid valve 48A and the wheel cylinder 211 corresponds to the "second fluid passage 72A". The portion of the supply fluid passage 41A between the first solenoid valve 44A and the second solenoid valve 48A corresponds to the "third fluid passage 73A". Hereafter, the fluid pressure of the first fluid passage 71A will be referred to as "upstream fluid pressure PupA". The fluid pressure of the second fluid passage 72A will be referred to as "downstream fluid pressure PdwA". The fluid pressure of the third fluid passage 73A will be referred to as "intermediate fluid pressure PmdA".

[0024] As shown in Figure 1, the first braking unit 40A has a plurality of sensors that output detection signals to the control device 100. The plurality of sensors include a brake sensor 51, a first pressure sensor 52, and two second pressure sensors 53A.

[0025] The brake sensor 51 detects the amount of operation performed by the driver on the braking control member 32. The first pressure sensor 52 is connected to the portion of the supply fluid passage 41A between the master cylinder 43 and the first solenoid valve 44A. In other words, the first pressure sensor 52 can detect the upstream fluid pressure PupA.

[0026] Multiple second pressure sensors 53A are connected to the portion of the supply fluid passage 41A between the second solenoid valve 48A and the wheel cylinder 211. In other words, multiple second pressure sensors 53A can detect the downstream fluid pressure PdwA.

[0027] <Configuration of the Second Braking Unit> As shown in Figure 1, the second braking unit 40B is equipped with a supply fluid passage 41B, which is a brake fluid passage connecting the reservoir 31 and the two second wheel cylinders 212. The supply fluid passage 41B branches into two on its way from the connection point with the reservoir 31 to the second wheel cylinders 212. That is, the supply fluid passage 41B includes one second main passage 42d connected to the reservoir 31 and two branch passages 42e and 42f connected to the second main passage 42d. Of the two second wheel cylinders 212, one is connected to branch passage 42e and the other is connected to branch passage 42f.

[0028] A first solenoid valve 44B is installed in the second main flow path 42d. The first solenoid valve 44B is a cut-off valve that closes when the communication between the reservoir 31 and the second wheel cylinder 212 is interrupted. In this embodiment, a normally open type solenoid valve is used as the first solenoid valve 44B. In this case, the first solenoid valve 44B is closed by energizing the solenoid of the first solenoid valve 44B. The greater the amount of current supplied to the solenoid when closing the first solenoid valve 44B, the greater the closing force of the first solenoid valve 44B.

[0029] A second solenoid valve 48B is installed in each of the multiple branch passages 42e and 42f. The multiple second solenoid valves 48B are cut-off valves that are closed when the communication between the corresponding second wheel cylinder 212 and the reservoir 31 is interrupted. In this embodiment, a normally open type solenoid valve is used as the second solenoid valve 48B. In this case, the second solenoid valve 48B is closed by energizing the solenoid of the second solenoid valve 48B. The greater the amount of current supplied to the solenoid when closing the second solenoid valve 48B, the greater the closing force of the second solenoid valve 48B.

[0030] An electric pressurizing unit 49 is connected to each of the multiple branch passages 42e and 42f. Specifically, the electric pressurizing unit 49 is connected to the portion of the branch passages 42e and 42f between the second solenoid valve 48B and the second wheel cylinder 212. The electric pressurizing unit 49 of the second braking unit 40B adjusts the braking pressure of the second wheel cylinder 212 by supplying brake fluid to the branch passages 42e and 42f through the drive of an electric motor 63.

[0031] In this embodiment, as shown in Figure 2, the portion of the supply fluid passage 41B between the first solenoid valve 44B and the reservoir 31 corresponds to the "first fluid passage 71B". The portion of the supply fluid passage 41B between the second solenoid valve 48B and the second wheel cylinder 212 corresponds to the "second fluid passage 72B". The portion of the supply fluid passage 41B between the first solenoid valve 44B and the second solenoid valve 48B corresponds to the "third fluid passage 73B". Hereafter, the fluid pressure of the first fluid passage 71B will be referred to as "upstream fluid pressure PupB". The fluid pressure of the second fluid passage 72B will be referred to as "downstream fluid pressure PdwB". The fluid pressure of the third fluid passage 73B will be referred to as "intermediate fluid pressure PmdB".

[0032] As shown in Figure 1, the second braking unit 40B has multiple sensors that output detection signals to the control device 100. The multiple sensors include two second pressure sensors 53B. The multiple second pressure sensors 53B are connected to the portion of the supply fluid passage 41B between the second solenoid valve 48B and the second wheel cylinder 212. In other words, the multiple second pressure sensors 53B can detect the downstream fluid pressure PdwB.

[0033] <Operation of the braking unit> When a braking request is received from the vehicle 10, multiple first solenoid valves 44A, 44B and multiple second solenoid valves 48A, 48B are closed. As a result, in the first braking unit 40A, communication between the reservoir 31 and the master cylinder 43 and the first wheel cylinder 211 is cut off. In the second braking unit 40B, communication between the reservoir 31 and the second wheel cylinder 212 is cut off.

[0034] Furthermore, in the first braking unit 40A, the simulator cut-off valve 47 is opened. As a result, when the driver performs a braking operation, brake fluid output from the master cylinder 43 is supplied to the stroke simulator 46. Consequently, an operating reaction force is input to the braking operation member 32.

[0035] When multiple electric pressurizing units 49 are activated in this state, brake fluid is supplied to the corresponding wheel cylinders 211 and 212, generating braking pressure. This generates braking force in the vehicle 10.

[0036] <Electric Pressure Unit> Referring to Figure 3, an example of the electric pressure unit 49 will be described in detail. An example of the electric pressure unit 49 is an electric cylinder. In this case, the electric pressure unit 49 has a cylinder 61, a piston 62, an electric motor 63, a conversion mechanism 64, and a motor angle sensor 65. The piston 62 is provided in a slidable state within the cylinder 61. The conversion mechanism 64 converts the rotation of the output shaft of the electric motor 63 into the linear movement of the piston 62.

[0037] Inside the cylinder 61, a hydraulic chamber Re for storing brake fluid is partitioned by the peripheral wall of the cylinder 61 and the piston 62. The position of the piston 62 inside the cylinder 61 can be changed by driving the electric motor 63. Hereafter, the direction of linear movement of the piston 62 when reducing the volume of the hydraulic chamber Re will be referred to as the "forward direction Za". The opposite direction of the forward direction Za will be referred to as the "reverse direction Zb". The reverse direction Zb is also the direction of linear movement of the piston 62 when increasing the volume of the hydraulic chamber Re.

[0038] The cylinder 61 has an output port 61P that connects the hydraulic chamber Re to the outside. The output port 61P is always open. Supply fluid passages 41A and 41B are connected to the output port 61P.

[0039] The motor angle sensor 65 outputs a detection signal to the control device 100 corresponding to the change in the rotation angle of the electric motor 63. Hereafter, the rotation angle of the electric motor 63 based on the detection signal of the motor angle sensor 65 will be referred to as "motor rotation angle θmt".

[0040] When the motor rotation angle θmt increases due to the drive of the electric motor 63, the piston 62 moves in the forward direction Za. As a result, the brake fluid in the hydraulic chamber Re is discharged to the supply fluid passages 41A and 41B via the output port 61P. This supplies brake fluid to the wheel cylinders 211 and 212, increasing the braking pressure. On the other hand, when the motor rotation angle θmt decreases due to the drive of the electric motor 63, the piston 62 moves in the backward direction Zb. As a result, the brake fluid in the supply fluid passages 41A and 41B flows into the hydraulic chamber Re via the output port 61P. In this case, brake fluid flows out of the wheel cylinders 211 and 212, decreasing the braking pressure.

[0041] <Control Device> The control device 100 will be described with reference to Figure 1. The control device 100 includes a processing circuit 101. An example of a processing circuit 101 is an electronic control device. In this case, the processing circuit 101 has a CPU 102, a first memory 103, and a second memory 104. The first memory 103 stores a control program executed by the CPU 102. The second memory 104 stores the calculation results of the CPU 102, etc. When the CPU 102 executes the control program in the first memory 103, the processing circuit 101 activates the first braking unit 40A and the second braking unit 40B.

[0042] <Function Configuration of Processing Circuit>Referring to FIG. 4, the function configuration of the processing circuit 101 will be described. The processing circuit 101 functions as a plurality of functional units when the CPU 102 executes the control program in the first memory 103. The plurality of functional units includes a pressure control unit M10 and a solenoid valve control unit M20. The pressure control unit M10 controls a plurality of electric pressure boosting units 49. The solenoid valve control unit M20 controls a plurality of first solenoid valves 44A, 44B, a plurality of second solenoid valves 48A, 48B, and a simulator cut-off valve 47. The solenoid valve control unit M20 includes a first valve closing control unit M21, a second valve closing control unit M22, a first hydraulic pressure estimation unit M23, and a second hydraulic pressure estimation unit M24.

[0043] <Pressure Control Unit>The pressure control unit M10 acquires a target braking pressure PwTr which is the target of the braking pressure of a plurality of wheel cylinders 211, 212. The pressure control unit M10 derives a target rotation angle which is the target of the motor rotation angle θmt based on the target braking pressure PwTr. Then, the pressure control unit M10 operates the electric pressure boosting unit 49 by driving the electric motor 63 so that the motor rotation angle θmt becomes the target rotation angle. Thereby, the pressure control unit M10 can generate a braking pressure corresponding to the target braking pressure PwTr in the wheel cylinders 211, 212.

[0044] <First Valve Closing Control Unit>During braking of the vehicle 10, the first valve closing control unit M21 performs first valve closing control to close one of the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B to block the communication between the first liquid paths 71A, 71B and the second liquid paths 72A, 72B.

[0045] <First Valve Closing Control in the First Brake Unit 40A> The first brake unit 40A includes a master cylinder 43. When the master cylinder 43 is operated by the driver's braking operation, the master cylinder 43 generates hydraulic pressure. When hydraulic pressure is generated in the master cylinder 43, the first valve closing control unit M21 closes the plurality of second solenoid valves 48A in the first brake unit 40A by performing the first valve closing control. Thereby, the first valve closing control unit M21 can block the first liquid path 71A and the second liquid path 72A in the first brake unit 40A.

[0046] The first braking unit 40A may generate a braking pressure of the first wheel cylinder 211 even when the driver is not performing a braking operation, upon a request from another in-vehicle computer. In this case, in the first braking unit 40A, the electric pressure boosting unit 49 operates to generate a hydraulic pressure. When a hydraulic pressure is generated by the operation of at least one of the plurality of electric pressure boosting units 49 of the first braking unit 40A, the first valve closing control unit M21 closes the first solenoid valve 44A by performing the first valve closing control.

[0047] In addition, the electric pressure boosting unit 49 of the first braking unit 40A may operate to increase the braking pressure of the first wheel cylinder 211 by the driver's braking operation. In such a case, the first valve closing control unit M21 closes the plurality of second solenoid valves 48A by performing the first valve closing control.

[0048] [First Valve Closing Control in the Second Braking Unit 40B] When the second braking unit 40B generates a braking force at the second wheel 12 in accordance with a braking request, the second braking unit 40B operates the electric pressure boosting unit 49 to generate a braking pressure of the second wheel cylinder 212. When the braking pressure is increased by the operation of at least one of the plurality of electric pressure boosting units 49 of the second braking unit 40B, the first valve closing control unit M21 closes the first solenoid valve 44B by performing the first valve closing control.

[0049] <Second Valve Closing Control Unit> After one of the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B is closed by the implementation of the first valve closing control, the second valve closing control unit M22 performs the second valve closing control within a predetermined period TM after the intermediate hydraulic pressure exceeds a threshold value based on a hydraulic pressure capable of maintaining the closing of the one solenoid valve. In the second valve closing control, the second valve closing control unit M22 closes the other solenoid valve among the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B. The predetermined period TM is set, for example, in accordance with the response speed of the solenoid valve closed by the second valve closing control. The threshold value is a criterion for determining whether or not the above-described valve opening force is slightly smaller than the valve closing force. Therefore, the larger the valve closing force of the solenoid valve closed by the first valve closing control, the larger the value is set as the threshold value.

[0050] In other words, the second valve closing control unit M22 can adjust the intermediate liquid pressure PmdA, which is the liquid pressure in the third liquid passage 73A, by controlling the opening and closing of the other solenoid valve among the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B. To put it another way, the second valve closing control unit M22 can suppress the increase in differential pressure in the liquid passages on both sides of one of the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B by controlling the other solenoid valve. In short, the second valve closing control unit M22 is an example of a "pressure regulating control unit".

[0051] [Second valve closing control performed after the second solenoid valve 48A is closed by the first valve closing control] When hydraulic pressure is generated by the operation of the master cylinder 43, the upstream hydraulic pressure PupA increases in the first braking unit 40A. When the second solenoid valve 48A is closed by the first valve closing control when hydraulic pressure is generated by the operation of the master cylinder 43, if the first solenoid valve 44A is open, the intermediate hydraulic pressure PmdA also increases in proportion to the increase in the upstream hydraulic pressure PupA. If the second solenoid valve 48A is closed, the intermediate hydraulic pressure PmdA acts as a force to open the second solenoid valve 48A. Since the second solenoid valve 48A is a normally open type solenoid valve, the greater the amount of current supplied to the second solenoid valve 48A, the greater the closing force of the second solenoid valve 48A. On the other hand, the greater the difference between the intermediate hydraulic pressure PmdA and the downstream hydraulic pressure PdwA, the greater the opening force, which is the force that tries to open the second solenoid valve 48A. If the closing force is greater than or equal to the opening force, the second solenoid valve 48A can be kept closed. However, if the intermediate hydraulic pressure PmdA increases and the opening force becomes greater than the closing force, the second solenoid valve 48A will be forcibly opened due to the hydraulic pressure difference. Therefore, when the communication between the first liquid passage 71A and the second liquid passage 72A is blocked by the first solenoid valve 44A and the second solenoid valve 48A, it is preferable to close the first solenoid valve 44A to restrict a further increase in the intermediate hydraulic pressure PmdA before the opening force becomes greater than the closing force.

[0052] Therefore, the second valve closing control unit M22 determines whether the intermediate hydraulic pressure PmdA is higher than the threshold Pth1, which is based on the intermediate hydraulic pressure that can maintain the closing of the second solenoid valve 48A. For example, the second valve closing control unit M22 determines whether the first estimated intermediate hydraulic pressure PmdE1, which is an estimated value of the intermediate hydraulic pressure PmdA, exceeds the threshold Pth1. As will be described in detail later, the first estimated intermediate hydraulic pressure PmdE1 is derived by the first hydraulic pressure estimation unit M23. If the first estimated intermediate hydraulic pressure PmdE1 exceeds the threshold Pth1, the second valve closing control unit M22 performs second valve closing control during a predetermined period TM after the first estimated intermediate hydraulic pressure PmdE1 exceeds the threshold Pth1. In the second valve closing control, the second valve closing control unit M22 closes the first solenoid valve 44A.

[0053] [Second valve closing control performed after the first solenoid valve 44A is closed by the first valve closing control] In the first braking unit 40A, even when the master cylinder 43 is not operating, the braking pressure of the first wheel cylinder 211 may increase due to the operation of the electric pressurizing unit 49. In this case, the downstream hydraulic pressure PdwA increases in the first braking unit 40A. When hydraulic pressure is generated in the first braking unit 40A by the operation of the electric pressurizing unit 49, if the first solenoid valve 44A is closed by the first valve closing control, and the second solenoid valve 48A is open, the intermediate hydraulic pressure PmdA also increases in proportion to the increase in the downstream hydraulic pressure PdwA. When the first solenoid valve 44A is closed, the intermediate hydraulic pressure PmdA acts as an opening force on the first solenoid valve 44A. Since the first solenoid valve 44A is a normally open type solenoid valve, the greater the amount of current supplied to the first solenoid valve 44A, the greater the closing force of the first solenoid valve 44A. On the other hand, the greater the difference between the intermediate hydraulic pressure PmdA and the upstream hydraulic pressure PupA, the greater the opening force acting on the first solenoid valve 44A. If the closing force is greater than or equal to the opening force, the first solenoid valve 44A can be kept closed. However, if the intermediate hydraulic pressure PmdA increases and the opening force becomes greater than the closing force, the first solenoid valve 44A will be forcibly opened due to the hydraulic pressure difference. Therefore, when the communication between the first liquid passage 71A and the second liquid passage 72A is blocked by the first solenoid valve 44A and the second solenoid valve 48A, it is preferable to close the second solenoid valve 48A to restrict a further increase in the intermediate hydraulic pressure PmdA before the opening force becomes greater than the closing force.

[0054] Therefore, the second valve closing control unit M22 determines whether the intermediate hydraulic pressure PmdA is higher than the threshold Pth2, which is based on the intermediate hydraulic pressure that can maintain the closing of the first solenoid valve 44A. For example, the second valve closing control unit M22 determines whether the second estimated intermediate hydraulic pressure PmdE2A, which is an estimated value of the intermediate hydraulic pressure PmdA, exceeds the threshold Pth2. As will be described in detail later, the second estimated intermediate hydraulic pressure PmdE2A is derived by the second hydraulic pressure estimation unit M24. If the second estimated intermediate hydraulic pressure PmdE2A exceeds the threshold Pth2, the second valve closing control unit M22 performs second valve closing control during a predetermined period TM after the second estimated intermediate hydraulic pressure PmdE2A exceeds the threshold Pth2. In the second valve closing control, the second valve closing control unit M22 closes a plurality of second solenoid valves 48A.

[0055] [Second valve closing control performed after the first solenoid valve 44B is closed by the first valve closing control] In the second braking unit 40B, the braking pressure of the second wheel cylinder 212 is increased by the operation of the electric pressurizing unit 49. In this case, the downstream hydraulic pressure PdwB increases in the second braking unit 40B. When the braking pressure of the second wheel cylinder 212 is generated by the operation of the electric pressurizing unit 49, if the first solenoid valve 44B is closed by the first valve closing control, and the second solenoid valve 48B is open, the intermediate hydraulic pressure PmdB also increases in accordance with the increase in the downstream hydraulic pressure PdwB. When the first solenoid valve 44B is closed, the intermediate hydraulic pressure PmdB acts as an opening force on the first solenoid valve 44B. Since the first solenoid valve 44B is a normally open type solenoid valve, the greater the amount of current supplied to the first solenoid valve 44B, the greater the closing force of the first solenoid valve 44B. On the other hand, the greater the difference between the intermediate hydraulic pressure PmdB and the upstream hydraulic pressure PupB, the greater the opening force acting on the first solenoid valve 44B. If the closing force is greater than or equal to the opening force, the first solenoid valve 44B can be kept closed. However, if the intermediate hydraulic pressure PmdB increases and the opening force becomes greater than the closing force, the first solenoid valve 44B will be forcibly opened due to the hydraulic pressure difference. Therefore, when the communication between the first liquid passage 71B and the second liquid passage 72B is blocked by the first solenoid valve 44B and the second solenoid valve 48B, it is preferable to close the second solenoid valve 48B to restrict a further increase in the intermediate hydraulic pressure PmdB before the opening force becomes greater than the closing force.

[0056] Therefore, the second valve closing control unit M22 determines whether the intermediate hydraulic pressure PmdB is higher than the threshold Pth2, which is based on the intermediate hydraulic pressure that can maintain the closing of the first solenoid valve 44B. For example, the second valve closing control unit M22 determines whether the second estimated intermediate hydraulic pressure PmdE2B, which is an estimated value of the intermediate hydraulic pressure PmdB, exceeds the threshold Pth2. As will be described in detail later, the second estimated intermediate hydraulic pressure PmdE2B is derived by the second hydraulic pressure estimation unit M24. If the second estimated intermediate hydraulic pressure PmdE2B exceeds the threshold Pth2, the second valve closing control unit M22 performs second valve closing control for a predetermined period TM after the second estimated intermediate hydraulic pressure PmdE2B exceeds the threshold Pth2. In the second valve closing control, the second valve closing control unit M22 closes multiple second solenoid valves 48B.

[0057] <First Hydraulic Pressure Estimation Unit> The first hydraulic pressure estimation unit M23 derives a first estimated intermediate hydraulic pressure PmdE1, which is an estimated value of the intermediate hydraulic pressure PmdA, based on the detected value of the first pressure sensor 52. For example, the first hydraulic pressure estimation unit M23 derives the first estimated intermediate hydraulic pressure PmdE1 when the second solenoid valve 48A of the first braking unit 40A is closed by the first valve closing control. When the second solenoid valve 48A is closed while the first solenoid valve 44A is open, the first hydraulic pressure estimation unit M23 derives the first estimated intermediate hydraulic pressure PmdE1 based on the detected value of the first pressure sensor 52 of the first braking unit 40A. Since the first solenoid valve 44A is open, for example, the first hydraulic pressure estimation unit M23 may derive the detected value of the first pressure sensor 52 as the first estimated intermediate hydraulic pressure PmdE1. Furthermore, the first hydraulic pressure estimation unit M23 may derive an estimated value of the intermediate hydraulic pressure PmdA based on the value detected by the brake sensor 51 as the first estimated intermediate hydraulic pressure PmdE1.

[0058] The first hydraulic pressure estimation unit M23 corrects at least one of the first estimated intermediate hydraulic pressure PmdE1 and the threshold Pth1 based on at least one of the operating speed of the master cylinder 43, the temperature of the brake fluid in the supply fluid passage 41A, and the hydraulic pressure in the second fluid passage 72A.

[0059] When the second solenoid valve 48A is closed and the first solenoid valve 44A is open in the first braking unit 40A, brake fluid flows into the third fluid passage 73A from the first fluid passage 71A. Therefore, the flow velocity and temperature of the brake fluid in the first fluid passage 71A can affect the intermediate fluid pressure PmdA. The higher the operating speed of the master cylinder 43, the greater the rate of increase in the intermediate fluid pressure PmdA tends to be. Also, the higher the temperature of the brake fluid, the lower the viscosity of the brake fluid, which also tends to increase the rate of increase in the intermediate fluid pressure PmdA.

[0060] Furthermore, when the second solenoid valve 48A is closed, the higher the braking pressure of the first wheel cylinder 211, the less likely it is that the hydraulic pressure difference on both sides of the second solenoid valve 48A will increase. In other words, even if the intermediate hydraulic pressure PmdA increases, the second solenoid valve 48A is less likely to be forcibly opened.

[0061] Therefore, the first hydraulic pressure estimation unit M23 corrects the first estimated intermediate hydraulic pressure PmdE1 so that the higher the operating speed of the master cylinder 43, the larger the first estimated intermediate hydraulic pressure PmdE1 becomes. The first hydraulic pressure estimation unit M23 corrects the first estimated intermediate hydraulic pressure PmdE1 so that the higher the temperature of the brake fluid, the larger the first estimated intermediate hydraulic pressure PmdE1 becomes. Also, when the magnitude of the difference between the hydraulic pressure corresponding to the closing force of the second solenoid valve 48A and the detected value of the second pressure sensor 53A is derived as the first estimated intermediate hydraulic pressure PmdE1, the first hydraulic pressure estimation unit M23 corrects the first estimated intermediate hydraulic pressure PmdE1 so that the higher the hydraulic pressure of the second fluid passage 72A, the smaller the first estimated intermediate hydraulic pressure PmdE1 becomes.

[0062] On the other hand, the first hydraulic pressure estimation unit M23 corrects the threshold Pth1 so that the threshold Pth1 decreases as the operating speed of the master cylinder 43 increases. The first hydraulic pressure estimation unit M23 corrects the threshold Pth1 so that the threshold Pth1 decreases as the temperature of the brake fluid increases. Furthermore, when the magnitude of the difference between the hydraulic pressure corresponding to the closing force of the second solenoid valve 48A and the detected value of the second pressure sensor 53A is derived as the first estimated intermediate hydraulic pressure PmdE1, the first hydraulic pressure estimation unit M23 corrects the threshold Pth1 so that the threshold Pth1 increases as the hydraulic pressure of the second fluid passage 72A increases.

[0063] <Second Hydraulic Pressure Estimation Unit> The second hydraulic pressure estimation unit M24 derives a second estimated intermediate hydraulic pressure PmdE2A, which is an estimated value of the intermediate hydraulic pressure PmdA, based on the detected value of the second pressure sensor 53A of the first braking unit 40A. The second hydraulic pressure estimation unit M24 derives a second estimated intermediate hydraulic pressure PmdE2B, which is an estimated value of the intermediate hydraulic pressure PmdB, based on the detected value of the second pressure sensor 53B of the second braking unit 40B.

[0064] When the first solenoid valve 44A of the first braking unit 40A is closed by the first valve closing control, if the second solenoid valve 48A is open, the second liquid passage 72A and the third liquid passage 73A are in communication. Therefore, the intermediate liquid pressure PmdA and the downstream liquid pressure PdwA can be considered to be approximately equal. For this reason, the second liquid pressure estimation unit M24 derives the second estimated intermediate liquid pressure PmdE2A based on the detected value of the second pressure sensor 53A. In this case, the second liquid pressure estimation unit M24 may derive the average value of the detected values ​​of multiple second pressure sensors 53A as the second estimated intermediate liquid pressure PmdE2A. Alternatively, the second liquid pressure estimation unit M24 may derive one of the detected values ​​of multiple second pressure sensors 53A as the second estimated intermediate liquid pressure PmdE2A.

[0065] The configuration of the second braking unit 40B is substantially the same as that of the first braking unit 40A, except that it does not have a master cylinder 43. Therefore, the second hydraulic pressure estimation unit M24 can derive the second estimated intermediate hydraulic pressure PmdE2B using the same method as the second estimated intermediate hydraulic pressure PmdE2A.

[0066] The second hydraulic pressure estimation unit M24 corrects at least one of the second estimated intermediate hydraulic pressure PmdE2A and the threshold Pth2 for the second estimated intermediate hydraulic pressure PmdE2A based on at least one of the operating speed of the electric pressurizing unit 49 of the first braking unit 40A, the temperature of the brake fluid in the supply fluid passage 41A, and the hydraulic pressure in the first fluid passage 71A.

[0067] The case in which the second estimated intermediate hydraulic pressure PmdE2A and the threshold Pth2 for the second estimated intermediate hydraulic pressure PmdE2A are corrected will be explained. When the first solenoid valve 44A is closed and the second solenoid valve 48A is open in the first braking unit 40A, brake fluid flows into the third fluid passage 73A from the second fluid passage 72A. Therefore, the temperature of the brake fluid in the second fluid passage 72A may affect the intermediate hydraulic pressure PmdA.

[0068] Therefore, the second hydraulic pressure estimation unit M24 corrects the second estimated intermediate hydraulic pressure PmdE2A and the threshold Pth2 based on the temperature of the brake fluid in the supply fluid passage 41A. The higher the temperature of the brake fluid, the lower the viscosity of the brake fluid, so the rate of increase of the intermediate hydraulic pressure PmdA tends to be greater. The higher the operating speed of the electric pressurizing unit 49, the higher the rate of increase of the intermediate hydraulic pressure PmdA tends to be. A high operating speed of the electric pressurizing unit 49 means that the rate of increase of the discharge pressure of the brake fluid from the electric pressurizing unit 49 is high. When the first solenoid valve 44A is closed, the higher the hydraulic pressure in the first fluid passage 71A, the less likely the hydraulic pressure difference on both sides of the first solenoid valve 44A is to become high. In other words, even if the intermediate hydraulic pressure PmdA becomes high, the second solenoid valve 48A is less likely to be forcibly opened.

[0069] Therefore, the second hydraulic pressure estimation unit M24 corrects the second estimated intermediate hydraulic pressure PmdE2A so that the higher the temperature of the brake fluid, the larger the second estimated intermediate hydraulic pressure PmdE2A becomes. The second hydraulic pressure estimation unit M24 corrects the second estimated intermediate hydraulic pressure PmdE2A so that the higher the operating speed of the electric pressurizing unit 49, the larger the second estimated intermediate hydraulic pressure PmdE2A becomes. Also, when the magnitude of the difference between the hydraulic pressure corresponding to the closing force of the first solenoid valve 44A and the detected value of the first pressure sensor 52 is derived as the second estimated intermediate hydraulic pressure PmdE2A, the second hydraulic pressure estimation unit M24 corrects the second estimated intermediate hydraulic pressure PmdE2A so that the higher the hydraulic pressure of the first fluid passage 71A, the smaller the second estimated intermediate hydraulic pressure PmdE2A becomes.

[0070] The second hydraulic pressure estimation unit M24 corrects the threshold Pth2 so that the threshold Pth2 decreases as the brake fluid temperature increases. The second hydraulic pressure estimation unit M24 corrects the threshold Pth2 so that the threshold Pth2 decreases as the operating speed of the electric pressurizing unit 49 increases. Furthermore, when the magnitude of the difference between the hydraulic pressure corresponding to the closing force of the first solenoid valve 44A and the detected value of the first pressure sensor 52 is derived as the second estimated intermediate hydraulic pressure PmdE2A, the second hydraulic pressure estimation unit M24 corrects the threshold Pth2 so that the threshold Pth2 increases as the hydraulic pressure in the first fluid passage 71A increases.

[0071] The second hydraulic pressure estimation unit M24 corrects at least one of the second estimated intermediate hydraulic pressure PmdE2B and the threshold Pth2 for the second estimated intermediate hydraulic pressure PmdE2B based on at least one of the operating speed of the electric pressurizing unit 49 of the second braking unit 40B and the temperature of the brake fluid in the supply fluid passage 41A. The correction method for the second estimated intermediate hydraulic pressure PmdE2B and the threshold Pth2 for the second estimated intermediate hydraulic pressure PmdE2B in this case is substantially the same as the correction method for the second estimated intermediate hydraulic pressure PmdE2A and the threshold Pth2 for the second estimated intermediate hydraulic pressure PmdE2A described above.

[0072] <Solenoid valve control when braking operation is performed> Referring to Figure 5, a series of processes for operating the first solenoid valve 44A and the second solenoid valve 48A of the first braking unit 40A when braking operation is performed by the driver will be explained. When the first solenoid valve 44A and the second solenoid valve 48A are open, the processing circuit 101 repeatedly executes the series of processes.

[0073] In step S11, the processing circuit 101 determines whether or not hydraulic pressure has been generated in the master cylinder 43. For example, the processing circuit 101 determines that hydraulic pressure has been generated in the master cylinder 43 if it can determine that the driver has started braking based on the detection signal from the brake sensor 51. If the processing circuit 101 determines that hydraulic pressure has been generated in the master cylinder 43 (S11: YES), the processing circuit 101 proceeds to step S13. On the other hand, if the processing circuit 101 determines that hydraulic pressure has not been generated in the master cylinder 43 (S11: NO), the processing circuit 101 terminates the series of processes shown in Figure 5.

[0074] In step S13, the processing circuit 101 performs first valve closing control by functioning as the first valve closing control unit M21. In the first valve closing control, the processing circuit 101 shuts off communication between the first liquid passage 71A and the second liquid passage 72A by closing the multiple second solenoid valves 48A of the first braking unit 40A. Then, the processing circuit 101 proceeds to step S15.

[0075] In step S15, the processing circuit 101 corrects the threshold Pth1 by functioning as the first hydraulic pressure estimation unit M23. In this embodiment, the processing circuit 101 corrects the threshold Pth1 based on the operating speed of the master cylinder 43, the temperature of the brake fluid in the first fluid passage 71A, and the braking pressure of the first wheel cylinder 211. At this time, the processing circuit 101 corrects the threshold Pth1 based on the operating speed of the master cylinder 43, the temperature of the brake fluid in the first fluid passage 71A, and the braking pressure of the first wheel cylinder 211 at the time the first valve closing control is started.

[0076] In the following step S17, the processing circuit 101 functions as a first hydraulic pressure estimation unit M23 to derive a first estimated intermediate hydraulic pressure PmdE1. The processing circuit 101 derives the first estimated intermediate hydraulic pressure PmdE1 based on the detected value of the first pressure sensor 52.

[0077] In the next step S19, the processing circuit 101 corrects the first estimated intermediate hydraulic pressure PmdE1 derived in step S17 by functioning as the first hydraulic pressure estimation unit M23. In the following step S21, the processing circuit 101 determines whether the first estimated intermediate hydraulic pressure PmdE1 is greater than the threshold Pth1. If the first estimated intermediate hydraulic pressure PmdE1 is less than or equal to the threshold Pth1 (S21: NO), the processing circuit 101 proceeds to step S17. On the other hand, if the first estimated intermediate hydraulic pressure PmdE1 is greater than the threshold Pth1 (S21: YES), the processing circuit 101 proceeds to step S23.

[0078] In step S23, the processing circuit 101 performs a second valve closing control by functioning as a second valve closing control unit M22. In the second valve closing control, the processing circuit 101 closes the first solenoid valve 44A of the first braking unit 40A, thereby blocking communication between the first liquid passage 71A and the third liquid passage 73A. The processing circuit 101 then completes the series of processes shown in Figure 5.

[0079] <Solenoid valve control when the electric pressurizing unit is activated> Referring to Figure 6, a series of processes for activating the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B when the braking pressure is increased by the operation of the electric pressurizing unit 49 will be explained. When the first solenoid valves 44A, 44B and the second solenoid valves 48A, 48B are open, the processing circuit 101 repeatedly executes the series of processes. When the processing circuit 101 generates braking pressure for the first wheel cylinder 211 under conditions where the driver is not performing braking operations, it closes the first solenoid valves 44A and the second solenoid valves 48A by executing the series of processes shown in Figure 6.

[0080] In step S41, the processing circuit 101 determines whether there is a request to increase the braking pressure of the wheel cylinders 211 and 212. If there is a request (S41: YES), the processing circuit 101 proceeds to step S43. On the other hand, if there is no request (S41: NO), the processing circuit 101 terminates the series of processes shown in Figure 6.

[0081] In step S43, the processing circuit 101 performs first valve closing control by functioning as the first valve closing control unit M21. If there is a request to increase the braking pressure of the first wheel cylinder 211, the processing circuit 101 cuts off communication between the first fluid passage 71A and the second fluid passage 72A by closing the first solenoid valve 44A of the first braking unit 40A in the first valve closing control. If there is a request to increase the braking pressure of the second wheel cylinder 212, the processing circuit 101 cuts off communication between the first fluid passage 71B and the second fluid passage 72B by closing the first solenoid valve 44B of the second braking unit 40B in the first valve closing control. Then, the processing circuit 101 proceeds to step S45.

[0082] In step S45, the processing circuit 101 corrects the threshold Pth2 by functioning as a second hydraulic pressure estimation unit M24. In the following step S47, the processing circuit 101 derives the second estimated intermediate hydraulic pressures PmdE2A and PmdE2B by functioning as a second hydraulic pressure estimation unit M24. When the first solenoid valve 44A is closed by the first valve closing control, the processing circuit 101 derives the second estimated intermediate hydraulic pressure PmdE2A based on the detected value of the second pressure sensor 53A. When the first solenoid valve 44B is closed by the first valve closing control, the processing circuit 101 derives the second estimated intermediate hydraulic pressure PmdE2B based on the detected value of the second pressure sensor 53B.

[0083] In the next step S49, the processing circuit 101 functions as a second hydraulic pressure estimation unit M24 to correct the second estimated intermediate hydraulic pressures PmdE2A and PmdE2B derived in step S47.

[0084] In the following step S51, the processing circuit 101 determines whether the conditions for performing the second valve closing control are met. If the first solenoid valve 44A is closed by the first valve closing control, the processing circuit 101 determines whether the second estimated intermediate hydraulic pressure PmdE2A is greater than the threshold Pth2. The processing circuit 101 determines that the conditions for performing the control are met if the second estimated intermediate hydraulic pressure PmdE2A is greater than the threshold Pth2. The processing circuit 101 determines that the conditions for performing the control are not met if the second estimated intermediate hydraulic pressure PmdE2A is less than or equal to the threshold Pth2. Also, if the first solenoid valve 44B is closed by the first valve closing control, the processing circuit 101 determines whether the second estimated intermediate hydraulic pressure PmdE2B is greater than the threshold Pth2. The processing circuit 101 determines that the conditions for performing the control are met if the second estimated intermediate hydraulic pressure PmdE2B is greater than the threshold Pth2. The processing circuit 101 determines that the implementation conditions are not met if the second estimated intermediate hydraulic pressure PmdE2B is less than or equal to the threshold Pth2.

[0085] If the processing circuit 101 determines that the implementation conditions are not met (S51: NO), the processing circuit 101 proceeds to step S47. On the other hand, if the processing circuit 101 determines that the implementation conditions are met (S51: YES), the processing circuit 101 proceeds to step S53.

[0086] In step S53, the processing circuit 101 performs second valve closing control by functioning as a second valve closing control unit M22. If there is a request to increase the braking pressure of the first wheel cylinder 211, the processing circuit 101 cuts off communication between the second fluid passage 72A and the third fluid passage 73A by closing a plurality of second solenoid valves 48A of the first braking unit 40A in the second valve closing control. If there is a request to increase the braking pressure of the second wheel cylinder 212, the processing circuit 101 cuts off communication between the second fluid passage 72B and the third fluid passage 73B by closing a plurality of second solenoid valves 48B of the second braking unit 40B in the second valve closing control. After that, the processing circuit 101 completes the series of processes shown in Figure 6.

[0087] <Operation and Effects When the Driver Performs Braking Operation> Referring to Figure 7, the operation and effects when the driver performs braking operation will be explained. As shown in Figures 7(a) to (e), the driver starts braking at timing t11. Then, due to the operation of the master cylinder 43, the upstream hydraulic pressure PupA of the first fluid passage 71A in the first braking unit 40A begins to increase. As a result, the first valve closing control is implemented, and multiple second solenoid valves 48A are closed. This blocks communication between the first fluid passage 71A and the second fluid passage 72A. On the other hand, at this point the first solenoid valve 44A remains open, so the first fluid passage 71A and the third fluid passage 73A are in communication. As a result, as shown in Figures 7(a) and (b), the intermediate hydraulic pressure PmdA, which is the hydraulic pressure of the third fluid passage 73A, increases in accordance with the increase in the upstream hydraulic pressure PupA.

[0088] The processing circuit 101 determines whether the first estimated intermediate hydraulic pressure PmdE1, which is an estimated value of the intermediate hydraulic pressure PmdA, is greater than the threshold Pth1. In the example shown in Figure 7, at timing t12, the processing circuit 101 determines that the first estimated intermediate hydraulic pressure PmdE1 is greater than the threshold Pth1. Therefore, the second valve closing control is performed for a predetermined period TM between timing t12 and timing t14. For example, at timing t13 between timing t12 and timing t14, the first solenoid valve 44A of the first braking unit 40A is closed by the second valve closing control. Therefore, from timing t13 onward, both the first solenoid valve 44A and the second solenoid valve 48A are closed, and the intermediate hydraulic pressure PmdA is maintained.

[0089] When hydraulic pressure is generated in the master cylinder 43, the second solenoid valve 48A is closed while the first solenoid valve 44A remains open. As a result, the downstream hydraulic pressure PdwA does not increase, but the intermediate hydraulic pressure PmdA increases. If the difference between the intermediate hydraulic pressure PmdA and the downstream hydraulic pressure PdwA becomes large, this difference may cause the second solenoid valve 48A to be forcibly opened.

[0090] Therefore, in the braking device 30, the first solenoid valve 44A is closed during a predetermined period TM after the first estimated intermediate hydraulic pressure PmdE1 exceeds a threshold Pth1 based on the intermediate hydraulic pressure that can maintain the closure of the second solenoid valve 48A. For this reason, the processing circuit 101 closes the first solenoid valve 44A before the second solenoid valve 48A is forcibly opened due to the difference between the intermediate hydraulic pressure PmdA and the downstream hydraulic pressure PdwA, and after the intermediate hydraulic pressure PmdA has risen to a certain level.

[0091] Here, let's consider a first comparative example in which the first solenoid valve 44A is closed at approximately the same time as the second solenoid valve 48A is closed. In the first comparative example, when the hydraulic pressure of the master cylinder 43 increases, the difference between the upstream hydraulic pressure PupA and the intermediate hydraulic pressure PmdA increases. If this difference becomes too large, the first solenoid valve 44A may be forcibly opened due to this difference. If the first solenoid valve 44A is forcibly opened while the driver is performing a braking operation, brake fluid will flow from the first fluid passage 71A to the third fluid passage 73A via the first solenoid valve 44A. As a result, even if the driver's operating force of the braking operation member 32 is constant, the amount of operation of the braking operation member 32 will increase. When this occurs, the driver performing the braking operation will feel something is wrong.

[0092] When the first solenoid valve 44A is forcibly opened, brake fluid flows from the first fluid passage 71A to the third fluid passage 73A via the first solenoid valve 44A, increasing the intermediate fluid pressure PmdA. As a result, the first fluid pressure difference, which is the difference between the intermediate fluid pressure PmdA and the upstream fluid pressure PupA, decreases. However, even though the first fluid pressure difference decreases, the first solenoid valve 44A does not close immediately due to its hysteresis and responsiveness. While the first solenoid valve 44A remains open, the intermediate fluid pressure PmdA increases to the same level as the upstream fluid pressure PupA.

[0093] In this regard, in the braking device 30, the closing of the first solenoid valve 44A is delayed compared to the closing of the second solenoid valve 48A. As a result, the first solenoid valve 44A is closed only after the intermediate hydraulic pressure PmdA has risen to a certain extent. Consequently, even if the hydraulic pressure of the master cylinder 43 rises, the difference between the upstream hydraulic pressure PupA and the intermediate hydraulic pressure PmdA is prevented from becoming excessive, making it less likely for the first solenoid valve 44A to be forcibly closed. Furthermore, the fact that the first solenoid valve 44A is not forcibly closed means that the intermediate hydraulic pressure PmdA does not become excessive. Therefore, the forcible opening of the second solenoid valve 48A due to an excessive difference between the intermediate hydraulic pressure PmdA and the downstream hydraulic pressure PdwA is prevented.

[0094] Therefore, when the braking device 30 closes the first solenoid valve 44A and the second solenoid valve 48A in response to the generation of hydraulic pressure in the master cylinder 43, the first solenoid valve 44A and the second solenoid valve 48A can be prevented from opening in a chain reaction. As a result, the above-mentioned events do not occur, and the braking device 30 can prevent the driver performing the braking operation from feeling any discomfort.

[0095] Furthermore, the electric pressurizing unit 49 is designed to operate under the assumption that communication between the first fluid passage 71A and the second fluid passage 72A is blocked. If the first solenoid valve 44A and the second solenoid valve 48A are forcibly opened, causing communication between the first fluid passage 71A and the second fluid passage 72A, the relationship between the position of the piston 62 of the electric pressurizing unit 49 and the braking pressure of the first wheel cylinder 211 will be disrupted. As a result, the controllability of the braking pressure of the first wheel cylinder 211 when the electric pressurizing unit 49 is operated will decrease.

[0096] In this regard, the braking device 30 prevents the first solenoid valve 44A and the second solenoid valve 48A from being forcibly opened when hydraulic pressure is generated in the master cylinder 43. In other words, the state in which communication between the first fluid passage 71A and the second fluid passage 72A is blocked can be maintained. Therefore, it is possible to prevent a change in the relationship between the position of the piston 62 of the electric pressurizing unit 49 and the braking pressure of the first wheel cylinder 211 due to the driver's braking operation. Consequently, the braking device 30 can prevent a decrease in the controllability of the braking pressure of the first wheel cylinder 211 when the electric pressurizing unit 49 is activated.

[0097] In particular, after the first solenoid valve 44A and the second solenoid valve 48A are closed, if the system configuration maintains the closed state of the first solenoid valve 44A and the second solenoid valve 48A, a change in the relationship between the position of the piston 62 of the electric pressurizing unit 49 and the braking pressure of the first wheel cylinder 211 can cause various problems. For example, even if the electric pressurizing unit 49 is operated to create a non-braking state, the braking pressure may not become 0 (zero), potentially causing a dragging sensation due to braking. Also, in the non-braking state, the piston 62 may move too far in the reversing direction Zb, potentially causing a delay in the generation of braking force when a braking request is made. In such a system configuration, closing the first solenoid valve 44A and the second solenoid valve 48A in sequence as described above makes these problems less likely to occur.

[0098] The braking device 30 can further achieve the following effects: (1-1) The greater the operating speed of the master cylinder 43, the greater the rate of increase of the upstream hydraulic pressure PupA. Therefore, when the first solenoid valve 44A is not yet closed, the greater the operating speed of the master cylinder 43, the greater the rate of increase of the intermediate hydraulic pressure PmdA. In order to prevent the second solenoid valve 48A from being forcibly opened due to an excessive difference between the intermediate hydraulic pressure PmdA and the downstream hydraulic pressure PdwA, it is preferable that the first solenoid valve 44A is closed earlier when the operating speed of the master cylinder 43 is greater.

[0099] In this regard, the braking device 30 corrects the first estimated intermediate hydraulic pressure PmdE1 so that its value increases as the operating speed of the master cylinder 43 increases. As a result, the processing circuit 101 can close the first solenoid valve 44A earlier as the operating speed of the master cylinder 43 increases. Consequently, the processing circuit 101 can prevent the second solenoid valve 48A from being forcibly opened due to an excessive intermediate hydraulic pressure PmdA caused by a delay in closing the first solenoid valve 44A.

[0100] (1-2) In the braking device 30, the threshold Pth1 is corrected so that the value decreases as the operating speed of the master cylinder 43 increases. As a result, the processing circuit 101 can close the first solenoid valve 44A earlier as the operating speed of the master cylinder 43 increases. Consequently, the processing circuit 101 can prevent the second solenoid valve 48A from being forcibly opened due to an excessive intermediate hydraulic pressure PmdA caused by a delay in closing the first solenoid valve 44A.

[0101] (1-3) The higher the temperature of the brake fluid, the lower its viscosity. The lower the viscosity of the brake fluid, the easier it is for the brake fluid to pass through the closed solenoid valve. In other words, even if the intermediate hydraulic pressure PmdA is not very high when the second solenoid valve 48A is closed, the brake fluid can easily pass through the second solenoid valve 48A and flow into the second fluid passage 72A.

[0102] Therefore, in the braking device 30, the first estimated intermediate fluid pressure PmdE1 is corrected so that the value increases as the brake fluid temperature increases. As a result, the processing circuit 101 can close the first solenoid valve 44A earlier as the brake fluid temperature increases. Consequently, the braking device 30 can suppress the outflow of brake fluid from the first fluid passage 71A and the third fluid passage 73A into the second fluid passage 72A due to the low viscosity of the brake fluid.

[0103] (1-4) In the braking device 30, the threshold Pth1 is corrected so that the value decreases as the temperature of the brake fluid increases. As a result, the processing circuit 101 can close the first solenoid valve 44A earlier as the temperature of the brake fluid increases. Consequently, the braking device 30 can prevent the brake fluid from flowing out of the first fluid passage 71A and the third fluid passage 73A into the second fluid passage 72A due to the low viscosity of the brake fluid.

[0104] (1-5) When the second solenoid valve 48A is closed and the braking pressure of the first wheel cylinder 211 is high, even if the hydraulic pressure of the master cylinder 43 increases, the difference between the intermediate hydraulic pressure PmdA and the downstream hydraulic pressure PdwA does not tend to increase.

[0105] Therefore, in the braking device 30, the first estimated intermediate fluid pressure PmdE1 is corrected so that the higher the fluid pressure in the second fluid passage 72A, the smaller the first estimated intermediate fluid pressure PmdE1 becomes. As a result, the processing circuit 101 can delay the closing of the first solenoid valve 44A as the fluid pressure in the second fluid passage 72A increases. Consequently, the braking device 30 can optimize the closing timing of the first solenoid valve 44A.

[0106] (1-6) In the braking device 30, the threshold Pth1 is corrected so that the threshold Pth1 increases as the hydraulic pressure in the second liquid passage 72A increases. As a result, the processing circuit 101 can delay the closing of the first solenoid valve 44A as the hydraulic pressure in the second liquid passage 72A increases. Consequently, the braking device 30 can optimize the closing timing of the first solenoid valve 44A.

[0107] <Effects and Actions of Generating Braking Pressure> Referring to Figure 8, the effects and actions of increasing braking pressure in accordance with braking requirements will be explained.

[0108] As shown in Figures 8(a) to 8(e), a braking request is generated at timing t21, so the electric pressurizing unit 49 starts operating to increase the braking pressure of the wheel cylinders 211 and 212. Then, the first valve closing control is performed, and the first solenoid valves 44A and 44B in the first braking unit 40A and the second braking unit 40B are closed. As a result, communication between the first fluid passages 71A and 71B and the second fluid passages 72A and 72B is cut off. In this state, multiple second solenoid valves 48A and 48B are open. Therefore, when the downstream fluid pressures PdwA and PdwB increase due to the operation of multiple electric pressurizing units 49, the intermediate fluid pressures PmdA and PmdB also increase in accordance with the increase in the downstream fluid pressures PdwA and PdwB.

[0109] The processing circuit 101 determines whether the second estimated intermediate hydraulic pressures PmdE2A and PmdE2B, which are estimated intermediate hydraulic pressures, are greater than the threshold Pth2. In the example shown in Figure 8, at timing t22, the processing circuit 101 determines that the second estimated intermediate hydraulic pressures PmdE2A and PmdE2B are greater than the threshold Pth2. Therefore, the second valve closing control is performed for a predetermined period TM between timing t22 and timing t24. For example, at timing t23 between timing t22 and timing t24, the second valve closing control closes the multiple second solenoid valves 48A and 48B of the first braking unit 40A and the second braking unit 40B. Therefore, from timing t23 onward, all of the first solenoid valves 44A and 44B and the second solenoid valves 48A and 48B are closed, and the intermediate hydraulic pressures PmdA and PmdB are maintained.

[0110] When hydraulic pressure is generated in the electrically pressurized section 49, the first solenoid valves 44A and 44B are closed while the second solenoid valves 48A and 48B remain open. As a result, the upstream hydraulic pressures PupA and PupB do not increase, but the intermediate hydraulic pressures PmdA and PmdB increase. If the difference between the intermediate hydraulic pressures PmdA and PmdB and the upstream hydraulic pressures PupA and PupB becomes excessive, the first solenoid valves 44A and 44B may be forcibly opened due to this difference.

[0111] Therefore, in the braking device 30, the second solenoid valve 48A is closed during a predetermined period TM after the second estimated intermediate hydraulic pressure PmdE2A exceeds a threshold Pth2 based on the intermediate hydraulic pressure that can maintain the closure of the first solenoid valve 44A. For this reason, the processing circuit 101 closes the second solenoid valve 48A before the first solenoid valve 44A is forcibly opened due to the difference between the intermediate hydraulic pressure PmdA and the upstream hydraulic pressure PupA, and after the intermediate hydraulic pressure PmdA has risen to a certain level.

[0112] Furthermore, in the braking device 30, the second solenoid valve 48B is closed after a predetermined period TM following the second estimated intermediate hydraulic pressure PmdE2B exceeding a threshold Pth2 based on the intermediate hydraulic pressure that can maintain the closure of the first solenoid valve 44B. Therefore, the processing circuit 101 closes the second solenoid valve 48B before the first solenoid valve 44B is forcibly opened due to the difference between the intermediate hydraulic pressure PmdB and the upstream hydraulic pressure PupB, and after the intermediate hydraulic pressure PmdB has risen to a certain level.

[0113] Here, we consider a second comparative example in which the second solenoid valves 48A and 48B are closed at approximately the same time as the first solenoid valves 44A and 44B are closed. In the second comparative example, as the braking pressure of the wheel cylinders 211 and 212 increases, the difference between the downstream hydraulic pressures PdwA and PdwB and the intermediate hydraulic pressures PmdA and PmdB increases. If this difference becomes excessive, the second solenoid valves 48A and 48B may be forcibly opened due to this difference. When the second solenoid valves 48A and 48B are forcibly opened while the electric pressurizing unit 49 is operating, some of the brake fluid supplied from the electric pressurizing unit 49 flows into the third fluid passages 73A and 73B. If the difference between the intermediate hydraulic pressures PmdA and PmdB and the upstream hydraulic pressures PupA and PupB becomes excessive due to the increase in intermediate hydraulic pressures PmdA and PmdB, there is a risk that the first solenoid valves 44A and 44B will be forcibly opened. When the second solenoid valves 48A, 48B and the first solenoid valves 44A, 44B open in this manner, a portion of the brake fluid supplied from the electric pressurizing unit 49 flows to the first fluid passages 71A, 71B via the third fluid passages 73A, 73B. In this case, the rate of increase in braking pressure becomes smaller compared to when the second solenoid valves 48A, 48B and the first solenoid valves 44A, 44B can be kept closed.

[0114] When the second solenoid valves 48A and 48B are forcibly opened, brake fluid flows from the second fluid passages 72A and 72B to the third fluid passages 73A and 73B via the second solenoid valves 48A and 48B, causing the intermediate fluid pressures PmdA and PmdB to increase. As a result, the second fluid pressure difference, which is the difference between the intermediate fluid pressures PmdA and PmdB and the downstream fluid pressures PdwA and PdwB, decreases. However, even though the second fluid pressure difference decreases, the second solenoid valves 48A and 48B do not close immediately due to their hysteresis and responsiveness. While the second solenoid valves 48A and 48B remain open, the intermediate fluid pressures PmdA and PmdB increase to the same level as the downstream fluid pressures PdwA and PdwB.

[0115] In this regard, in the braking device 30, the closing of the second solenoid valves 48A and 48B is delayed compared to the closing of the first solenoid valves 44A and 44B. As a result, the second solenoid valves 48A and 48B are closed only after the intermediate hydraulic pressures PmdA and PmdB have risen to a certain extent. Consequently, even if the braking pressure of the wheel cylinders 211 and 212 increases, the difference between the downstream hydraulic pressures PdwA and PdwB and the intermediate hydraulic pressures PmdA and PmdB is prevented from becoming excessively large, making it less likely for the second solenoid valves 48A and 48B to be forcibly closed. Furthermore, the fact that the second solenoid valves 48A and 48B are not forcibly closed means that the intermediate hydraulic pressures PmdA and PmdB do not become too high. Therefore, the forcible opening of the first solenoid valves 44A and 44B is suppressed.

[0116] Therefore, the braking device 30 can prevent the first solenoid valve 44A and the second solenoid valve 48A from opening in a chain reaction when the first solenoid valve 44A and the second solenoid valve 48A are closed due to the generation of hydraulic pressure in the electrically pressurized section 49.

[0117] As described above, the electric pressurizing unit 49 is designed to operate under the premise that communication between the first fluid passages 71A, 71B and the second fluid passages 72A, 72B is interrupted. In the braking device 30, the first solenoid valve 44A and the second solenoid valve 48A are prevented from being forcibly opened when the braking pressure is adjusted by the operation of the electric pressurizing unit 49. In other words, the state in which communication between the first fluid passages 71A, 71B and the second fluid passages 72A, 72B is interrupted can be maintained. Therefore, it is possible to prevent a change in the relationship between the position of the piston 62 of the electric pressurizing unit 49 and the braking pressure of the wheel cylinders 211, 212 during the operation of the electric pressurizing unit 49. Consequently, the braking device 30 can prevent a decrease in the controllability of the braking pressure when the electric pressurizing unit 49 is operated.

[0118] The braking device 30 can further achieve the following effects: (2-1) The higher the temperature of the brake fluid, the lower the viscosity of the brake fluid. The lower the viscosity of the brake fluid, the easier it is for the brake fluid to flow between the valve seat and valve body of the open solenoid valve. In other words, the lower the viscosity of the brake fluid, the greater the flow rate through the solenoid valve.

[0119] Therefore, in the braking device 30, the second estimated intermediate fluid pressures PmdE2A and PmdE2B are corrected so that their values ​​increase as the brake fluid temperature rises. As a result, the processing circuit 101 can close the second solenoid valves 48A and 48B earlier as the brake fluid temperature rises.

[0120] (2-2) In the braking device 30, the threshold Pth2 is corrected so that the value decreases as the temperature of the brake fluid increases. As a result, the processing circuit 101 can close the second solenoid valves 48A and 48B earlier as the temperature of the brake fluid increases. Consequently, the braking device 30 can prevent the brake fluid from flowing out of the second fluid passages 72A and 72B and the third fluid passages 73A and 73B into the first fluid passages 71A and 71B due to the low viscosity of the brake fluid.

[0121] (2-3) The faster the operating speed of the electric pressurizing unit 49, the faster the rate of increase of the downstream hydraulic pressures PdwA and PdwB. Therefore, when the second solenoid valves 48A and 48B are not yet closed, the faster the operating speed of the electric pressurizing unit 49, the faster the rate of increase of the intermediate hydraulic pressures PmdA and PmdB. In order to prevent the first solenoid valves 44A and 44B from being forcibly opened due to an excessive difference between the intermediate hydraulic pressures PmdA and PmdB and the upstream hydraulic pressures PupA and PupB, it is preferable that the faster the operating speed of the electric pressurizing unit 49, the earlier the second solenoid valves 48A and 48B are closed.

[0122] In this regard, the braking device 30 corrects the second estimated intermediate hydraulic pressures PmdE2A and PmdE2B so that their values ​​increase as the operating speed of the electric pressurizing unit 49 increases. As a result, the processing circuit 101 can close the second solenoid valves 48A and 48B earlier as the operating speed of the electric pressurizing unit 49 increases. Consequently, the processing circuit 101 can prevent the first solenoid valves 44A and 44B from being forcibly opened due to excessive intermediate hydraulic pressures PmdA and PmdB caused by a delay in closing the second solenoid valves 48A and 48B.

[0123] (2-4) In the braking device 30, the threshold Pth2 is corrected so that the value decreases as the operating speed of the electric pressurizing unit 49 increases. As a result, the processing circuit 101 can close the second solenoid valves 48A and 48B earlier as the operating speed of the electric pressurizing unit 49 increases. Consequently, the processing circuit 101 can prevent the first solenoid valves 44A and 44B from being forcibly opened due to the intermediate hydraulic pressures PmdA and PmdB becoming excessive because the closing of the second solenoid valves 48A and 48B was delayed.

[0124] (2-5) In the first braking unit 40A, when the first solenoid valve 44A is closed and the upstream hydraulic pressure PupA is high, even if the downstream hydraulic pressure PdwA increases, the difference between the intermediate hydraulic pressure PmdA and the upstream hydraulic pressure PupA does not tend to increase.

[0125] Therefore, in the braking device 30, the second estimated intermediate fluid pressure PmdE2A is corrected so that the higher the fluid pressure in the first fluid passage 71A, the smaller the second estimated intermediate fluid pressure PmdE2A becomes. As a result, the processing circuit 101 can delay the closing of the second solenoid valve 48A as the fluid pressure in the first fluid passage 71A increases. Consequently, the braking device 30 can optimize the closing timing of the second solenoid valve 48A.

[0126] (2-6) In the braking device 30, the threshold Pth2 is corrected so that the threshold Pth2 increases as the hydraulic pressure in the first fluid passage 71A increases. As a result, the processing circuit 101 can delay the closing of the second solenoid valve 48A as the hydraulic pressure in the first fluid passage 71A increases. Consequently, the braking device 30 can optimize the closing timing of the second solenoid valve 48A.

[0127] (Second Embodiment) A second embodiment of the braking device will be described with reference to Figure 9. Note that the second embodiment differs from the first embodiment in the content of the first valve closing 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.

[0128] The processing circuit 101 of the braking device 30 in this embodiment functions as a first valve closing control unit M21, a second valve closing control unit M22, a first hydraulic pressure estimation unit M23, and a second hydraulic pressure estimation unit M24. The first valve closing control unit M21 performs first valve closing control when hydraulic pressure is generated in the master cylinder 43. In the first valve closing control, the first valve closing control unit M21 closes the second solenoid valve 48A of the first braking unit 40A and operates the first solenoid valve 44A so that the valve closing force Fc of the first solenoid valve 44A becomes the first valve closing force Fc1. The first valve closing force Fc1 at this time is smaller than the valve closing force generated in the second solenoid valve 48A by the implementation of the first valve closing control.

[0129] The second valve closing control unit M22 performs a second valve closing control during a predetermined period TM after the first estimated intermediate hydraulic pressure PmdE1 exceeds the threshold Pth1, following the closing of the second solenoid valve 48A of the first braking unit 40A by the first valve closing control. In the second valve closing control, the second valve closing control unit M22 operates the first solenoid valve 44A so that the closing force Fc of the first solenoid valve 44A becomes the second closing force Fc2. The second closing force Fc2 is greater than the first closing force Fc1. For example, the second closing force Fc2 is equal to or greater than the opening force of the second solenoid valve 48A.

[0130] <Operation and Effects of this Embodiment> Referring to Figure 9, the operation and effects when the driver performs a braking operation will be explained. As shown in Figures 9(a) to (d), the driver starts the braking operation at timing t31. Then, due to the operation of the master cylinder 43, the upstream hydraulic pressure PupA of the first fluid passage 71A in the first braking unit 40A begins to increase. As a result, the first valve closing control is performed, and multiple second solenoid valves 48A are closed. Furthermore, the first solenoid valve 44A operates so that the valve closing force Fc of the first solenoid valve 44A becomes the first valve closing force Fc1.

[0131] In this case, the flow of a portion of the brake fluid discharged from the master cylinder 43 into the third fluid passage 73A is suppressed. Therefore, even if the upstream fluid pressure PupA increases, the intermediate fluid pressure PmdA does not increase. As a result, a sufficient amount of brake fluid is ensured to flow from the master cylinder 43 to the stroke simulator 46 in the initial stages of braking when the driver initiates braking. Consequently, the braking device 30 of this embodiment can transmit the reaction force to the operation of the braking operating member 32 to the braking operating member 32 in the initial stages of braking.

[0132] In the example shown in Figure 9, at timing t32, the opening force acting on the first solenoid valve 44A due to the hydraulic pressure difference between the upstream hydraulic pressure PupA and the intermediate hydraulic pressure PmdA becomes greater than the first closing force Fc1. Therefore, the first solenoid valve 44A is forcibly opened. Consequently, the intermediate hydraulic pressure PmdA increases after timing t32.

[0133] At the subsequent timing t33, an indicator related to the driver's braking operation exceeds a threshold. Examples of such indicators include the amount of braking operation, the operating speed of the braking operation member 32, the upstream hydraulic pressure PupA, and the rate of increase of the upstream hydraulic pressure PupA.

[0134] Then, during a predetermined period TM between timing t33 ​​and timing t35, the second valve closing control is performed. For example, at timing t34 between timing t33 ​​and timing t35, the first solenoid valve 44A is operated by the second valve closing control so that the closing force Fc of the first solenoid valve 44A becomes the second closing force Fc2. As a result, the first solenoid valve 44A is closed again. Therefore, after timing t34, the closing force Fc of the first solenoid valve 44A becomes larger, so the intermediate hydraulic pressure PmdA is maintained even if the upstream hydraulic pressure PupA increases.

[0135] Similar to the first embodiment, the braking device 30 of this embodiment can prevent the first solenoid valve 44A and the second solenoid valve 48A from opening in a chain reaction when the first solenoid valve 44A and the second solenoid valve 48A are closed due to the generation of hydraulic pressure in the master cylinder 43.

[0136] (Third Embodiment) A third embodiment of the braking device will be described with reference to Figures 10 to 16. In the following description, the differences 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.

[0137] Figure 10 shows a vehicle 10C to which the braking system 30C is applied. The vehicle 10C comprises a first wheel 11C and a second wheel 12C, and a plurality of friction brakes 20 provided for each of the plurality of wheels 11C and 12C. The wheel cylinder of the friction brake 20 corresponding to the first wheel 11C is referred to as the "first wheel cylinder 211C". The wheel cylinder of the friction brake 20 corresponding to the second wheel 12C is referred to as the "second wheel cylinder 212C".

[0138] <Configuration of the braking system> The braking system 30C controls the braking force of the vehicle 10C by adjusting the braking pressure of multiple wheel cylinders 211C, 212C. The braking system 30C comprises a reservoir 31, a braking unit 80, and a control device 100C.

[0139] <Configuration of the braking unit> The braking unit 80 includes a supply fluid passage 81 connected to the first wheel cylinder 211C and the second wheel cylinder 212C, a first solenoid valve 83, and a second solenoid valve 84. Of the two ends of the supply fluid passage 81, the first end is connected to the first wheel cylinder 211C and the second end is connected to the second wheel cylinder 212C. The first solenoid valve 83 is installed in the supply fluid passage 81. The second solenoid valve 84 is installed in the supply fluid passage 81 between the first solenoid valve 83 and the first wheel cylinder 211C.

[0140] Of the supply fluid passage 81, the portion between the first solenoid valve 83 and the second wheel cylinder 212C corresponds to the "first fluid passage 81A". Of the supply fluid passage 81, the portion between the second solenoid valve 84 and the first wheel cylinder 211C corresponds to the "second fluid passage 81B". Of the supply fluid passage 81, the portion between the first solenoid valve 83 and the second solenoid valve 84 corresponds to the "third fluid passage 81C".

[0141] Figure 11 is a schematic diagram of the first solenoid valve 83. The first solenoid valve 83 has a valve seat 301, a valve body 302, a spring 303, and a solenoid 304. The first solenoid valve 83 is a normally open type solenoid valve. Therefore, the spring 303 applies a biasing force to the valve body 302 in the direction of separating it from the valve seat 301. When the power supply to the solenoid 304 is stopped, the biasing force of the spring 303 separates the valve body 302 from the valve seat 301. As a result, brake fluid flows between the second fluid passage 81B and the third fluid passage 81C. On the other hand, when the solenoid 304 is energized, the electromagnetic force generated by the solenoid 304 presses the valve body 302 against the valve seat 301. As a result, the flow of brake fluid between the second fluid passage 81B and the third fluid passage 81C is restricted.

[0142] As shown by the white arrow Y1 in Figure 11, the first solenoid valve 83 is configured to utilize the hydraulic pressure of the first liquid passage 81A as the closing force, which is the force that presses the valve seat 301 against the valve body 302. In other words, the first solenoid valve 83 is configured such that when the hydraulic pressure of the first liquid passage 81A is higher than the hydraulic pressure of the third liquid passage 81C, the closing force increases as the differential pressure between the first liquid passage 81A and the third liquid passage 81C increases.

[0143] The configuration of the second solenoid valve 84 is the same as that of the first solenoid valve 83. In other words, the second solenoid valve 84 is a normally open type solenoid valve and has a valve seat 301, a valve body 302, a spring 303, and a solenoid 304. Furthermore, the second solenoid valve 84 is configured to utilize the hydraulic pressure of the second liquid passage 81B as the closing force. Therefore, the second solenoid valve 84 is configured such that when the hydraulic pressure of the second liquid passage 81B is higher than the hydraulic pressure of the third liquid passage 81C, the closing force increases as the differential pressure between the second liquid passage 81B and the third liquid passage 81C increases.

[0144] Returning to Figure 10, the braking unit 80 includes a pressurizing unit configured to supply brake fluid to the first wheel cylinder 211C and the second wheel cylinder 212C, and a reservoir shut-off mechanism 90. The pressurizing unit includes a first electric pressurizing unit 85 connected to the second fluid passage 81B and a second electric pressurizing unit 86 connected to the first fluid passage 81A.

[0145] The first electric pressurizing unit 85 is configured to adjust the hydraulic pressure in the second fluid passage 81B, i.e., the braking pressure of the first wheel cylinder 211C, by supplying brake fluid to the second fluid passage 81B by driving the electric motor 63. The second electric pressurizing unit 86 is configured to adjust the hydraulic pressure in the first fluid passage 81A, i.e., the braking pressure of the second wheel cylinder 212C, by supplying brake fluid to the first fluid passage 81A by driving the electric motor 63. Hereafter, the braking pressure of the first wheel cylinder 211C will be referred to as "first braking pressure Pw1," and the braking pressure of the second wheel cylinder 212C will be referred to as "second braking pressure Pw2."

[0146] An example of the first electric pressurizing unit 85 and the second electric pressurizing unit 86 is an electric cylinder. Each of the first electric pressurizing unit 85 and the second electric pressurizing unit 86, like the electric pressurizing unit 49, has a cylinder 61, a piston 62, an electric motor 63, a conversion mechanism 64, and a motor angle sensor 65. The position Zb furthest back in the movable range of the piston 62 is the "last retracted position".

[0147] The cylinder 61 is provided with an output port 61P and an input port 61Pi, which are ports that connect the hydraulic chamber Re to the outside. The output port 61P of the first electric pressurizing unit 85 is connected to the second liquid passage 81B. The output port 61P of the second electric pressurizing unit 86 is connected to the first liquid passage 81A.

[0148] The input port 61Pi is positioned to communicate with the hydraulic chamber Re when the piston 62 is in its rearmost position. In the example shown in Figure 10, the piston 62 is provided with a through hole 62a. When the piston 62 is in its rearmost position, the input port 61Pi communicates with the hydraulic chamber Re through the through hole 62a. When the piston 62 moves from its rearmost position to the forward direction Za, the piston 62 blocks the communication between the hydraulic chamber Re and the input port 61Pi. As a result, the hydraulic pressure in the hydraulic chamber Re increases, and the brake fluid in the hydraulic chamber Re is discharged to the outside through the output port 61P.

[0149] The reservoir shut-off mechanism 90 includes a first reservoir communication passage 91 that connects the input port 61Pi of the first electric pressurizing unit 85 to the reservoir 31, and a second reservoir communication passage 92 that connects the input port 61Pi of the second electric pressurizing unit 86 to the reservoir 31. A first reservoir shut-off valve 93 is installed in the first reservoir communication passage 91. A second reservoir shut-off valve 94 is installed in the second reservoir communication passage 92. An example of the first reservoir shut-off valve 93 and the second reservoir shut-off valve 94 is a normally open type solenoid valve.

[0150] When the first reservoir shut-off valve 93 is open, the input port 61Pi of the first electric pressurizing unit 85 communicates with the reservoir 31 via the first reservoir communication passage 91. When the first reservoir shut-off valve 93 is closed, communication between the input port 61Pi of the first electric pressurizing unit 85 and the reservoir 31 via the first reservoir communication passage 91 is blocked. Similarly, when the second reservoir shut-off valve 94 is open, the input port 61Pi of the second electric pressurizing unit 86 communicates with the reservoir 31 via the second reservoir communication passage 92. When the second reservoir shut-off valve 94 is closed, communication between the input port 61Pi of the second electric pressurizing unit 86 and the reservoir 31 via the second reservoir communication passage 92 is blocked.

[0151] The braking unit 80 has multiple sensors that output detection signals to the control device 100C. The multiple sensors include a first pressure sensor 87 and a second pressure sensor 88. The first pressure sensor 87 is connected to the second fluid passage 81B. The second pressure sensor 88 is connected to the first fluid passage 81A. Therefore, the first pressure sensor 87 can detect the fluid pressure in the second fluid passage 81B, i.e., the first braking pressure Pw1. The second pressure sensor 88 can detect the fluid pressure in the first fluid passage 81A, i.e., the second braking pressure Pw2.

[0152] <Control device> The control device 100C receives detection signals from multiple sensors other than the sensors provided by the braking unit 80. The multiple sensors include a brake sensor 51 and a state detection sensor that detects the driving state of the vehicle 10C. Examples of the state detection sensor include a yaw rate sensor 111 that detects the yaw rate of the vehicle 10C and a lateral acceleration sensor 112 that detects the lateral acceleration of the vehicle 10C.

[0153] The control device 100C includes a processing circuit 101 that controls the braking unit 80. An example of the processing circuit 101 is an electronic control device. In this case, the processing circuit 101 includes a CPU 102, a first memory 103, and a second memory 104.

[0154] <Functional Configuration of the Processing Circuit> Referring to Figures 12 to 15, the functional configuration of the processing circuit 101 in the braking device 30C of this embodiment will be described.

[0155] As shown in Figure 12, the processing circuit 101 functions as a plurality of functional units when the CPU 102 executes the control program for the first memory 103. The plurality of functional units include a first valve closing control unit M121, a hydraulic pressure adjustment unit M122, a hydraulic pressure acquisition unit M123, and a third valve closing control unit M124, which are functional units related to the operation of the first solenoid valve 83 and the second solenoid valve 84.

[0156] <First valve closing control unit> When the vehicle 10C is being braked, the first valve closing control unit M121 performs a first valve closing control by closing only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, in order to block communication between the first fluid passage 81A and the second fluid passage 81B. For example, when the first valve closing control unit M121 generates braking pressure for the first wheel cylinder 211C and the second wheel cylinder 212C, in the first valve closing control, as shown in Figure 13, the first solenoid valve 83 is closed while the second solenoid valve 84 is not closed. As a result, the first valve closing control unit M121 can block communication between the first fluid passage 81A and the second fluid passage 81B.

[0157] When a braking request is received and the first valve closing control unit M121 performs the first valve closing control, only the first solenoid valve 83 of the two solenoid valves 84 closes. As a result, brake fluid supplied from the first electric pressurizing unit 85 flows into the third fluid passage 81C, increasing the fluid pressure in the third fluid passage 81C.

[0158] <Hydraulic Pressure Adjustment Unit> Returning to Figure 12, the hydraulic pressure adjustment unit M122 performs suppression control after only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, has been closed by the first valve closing control. In suppression control, the hydraulic pressure adjustment unit M122 adjusts the hydraulic pressure in the third liquid passage 81C by operating the first electric pressurizing unit 85 or the second electric pressurizing unit 86, thereby suppressing an increase in the differential pressure between the liquid passages on both sides of the one solenoid valve. For example, if the first solenoid valve 83 is closed by the first valve closing control, in suppression control, the hydraulic pressure adjustment unit M122 maintains the state in which the second solenoid valve 84 is open and adjusts the hydraulic pressure in the third liquid passage 81C by operating the first electric pressurizing unit 85, thereby suppressing an increase in the differential pressure between the third liquid passage 81C and the first liquid passage 81A (see Figure 13). For example, if the second solenoid valve 84 is closed by the first valve closing control, in the suppression control, the hydraulic pressure adjustment unit M122 maintains the state in which the first solenoid valve 83 is open and suppresses the increase in differential pressure between the third liquid passage 81C and the second liquid passage 81B by adjusting the hydraulic pressure in the third liquid passage 81C through the operation of the second electric pressurizing unit 86. In other words, the first electric pressurizing unit 85 and the second electric pressurizing unit 86, which are operated by the hydraulic pressure adjustment unit M122, are an example of a "pressure regulating control unit".

[0159] <Hydraulic Pressure Acquisition Unit> The hydraulic pressure acquisition unit M123 acquires the intermediate hydraulic pressure Pmd1, which is the hydraulic pressure in the third fluid passage 81C. For example, when only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, is closed by the first valve closing control and suppression control, the hydraulic pressure acquisition unit M123 acquires the intermediate hydraulic pressure Pmd1. When only the first solenoid valve 83 of the two solenoid valves 84 is closed, the hydraulic pressure acquisition unit M123 acquires the intermediate hydraulic pressure Pmd1 based on the detection signal of the first pressure sensor 87. When the second solenoid valve 84 is open, the hydraulic pressure in the third fluid passage 81C and the hydraulic pressure in the second fluid passage 81B can be considered to be approximately equal. Therefore, the hydraulic pressure acquisition unit M123 may acquire the first braking pressure Pw1 as the intermediate hydraulic pressure Pmd1. Furthermore, the hydraulic pressure acquisition unit M123 may acquire the intermediate hydraulic pressure Pmd1 as a value obtained by correcting the first braking pressure Pw1 based on the temperature of the brake fluid, the rate of increase of the first braking pressure Pw1, etc.

[0160] Conversely, if only the second solenoid valve 84 of the first solenoid valve 83 and the second solenoid valve 84 is closed, the hydraulic pressure acquisition unit M123 acquires the intermediate hydraulic pressure Pmd1 based on the detection signal of the second pressure sensor 88. When the first solenoid valve 83 is open, the hydraulic pressure in the third fluid passage 81C and the hydraulic pressure in the first fluid passage 81A can be considered to be approximately equal. Therefore, the hydraulic pressure acquisition unit M123 may acquire the second braking pressure Pw2 as the intermediate hydraulic pressure Pmd1. Alternatively, the hydraulic pressure acquisition unit M123 may acquire the first braking pressure Pw1 as the intermediate hydraulic pressure Pmd1, after correcting it for factors such as the temperature of the brake fluid and the rate of increase of the first braking pressure Pw1.

[0161] <Third valve closing control unit> The third valve closing control unit M124 performs a third valve closing control when a predetermined valve closing condition is met during suppression control after one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, has been closed by the first valve closing control. In the third valve closing control, the third valve closing control unit M124 adjusts the liquid pressure in the third liquid passage 81C by closing the other solenoid valve. The third valve closing control unit M124 determines that the valve closing condition has been met when the intermediate liquid pressure Pmd1 exceeds a threshold Pmd1th based on the liquid pressure that can maintain the closure of the closed solenoid valve, and this period TM is within a predetermined time. The threshold Pmd1th is a criterion for determining whether the opening force is slightly less than the closing force. Therefore, it is preferable that the greater the closing force of the solenoid valve closed by the first valve closing control, the larger the value of the threshold Pmd1th. In other words, the third valve closing control unit M124 is an example of a "pressure regulating control unit".

[0162] When the third valve closing control unit M124 performs the third valve closing control, both the first solenoid valve 83 and the second solenoid valve 84 are closed, as shown in Figure 14. In this state, braking control that individually controls the first braking pressure Pw1 and the second braking pressure Pw2, such as anti-lock brake control, may be performed. During the performance of such braking control, by setting the intermediate hydraulic pressure Pmd1 to the lower of the first braking pressure Pw1 and the second braking pressure Pw2, or a hydraulic pressure close to that braking pressure, it is less likely that the solenoid valve will open unintentionally.

[0163] Therefore, when both the first solenoid valve 83 and the second solenoid valve 84 are closed, and the first braking pressure Pw1, which is substantially equal to the liquid pressure in the second liquid passage 81B, is lower than the second braking pressure Pw2, which is substantially equal to the liquid pressure in the first liquid passage 81A, the third valve closing control unit M124 opens only the second solenoid valve 84 (not shown). On the other hand, when both the first solenoid valve 83 and the second solenoid valve 84 are closed, and the second braking pressure Pw2 is lower than the first braking pressure Pw1, the third valve closing control unit M124 opens only the first solenoid valve 83 (see Figure 15).

[0164] When the above valve closing condition is met while only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, is open, the third valve closing control unit M124 closes that one solenoid valve.

[0165] By the way, when the braking control described above is implemented, the solenoid valve to be closed may be switched repeatedly. Frequent changes in the solenoid valve to be closed can cause problems such as an increase in the operating noise of the braking unit 80 during braking control and an increase in the number of times the solenoid valve is operated. Therefore, the third valve closing control unit M124 maintains both the first solenoid valve 83 and the second solenoid valve 84 in a closed state if the number of times the solenoid valve to be closed is switched within a predetermined determination time exceeds a specified number.

[0166] Furthermore, it is preferable that the third valve closing control unit M124 maintains a closed state for both the first solenoid valve 83 and the second solenoid valve 84, even if it is determined that the vehicle 10C is traveling on a rough road or if the vehicle 10C is stopped.

[0167] <Solenoid Valve Control During Vehicle Braking> Referring to Figure 16, a series of processes for operating the first solenoid valve 83 and the second solenoid valve 84 when braking force is generated in the vehicle 10C by the operation of multiple electric pressurizing units 85 and 86 will be explained.

[0168] In step S101, the processing circuit 101 determines whether or not there is a braking request for the vehicle 10C. If there is no braking request (S101: NO), the processing circuit 101 repeatedly performs the determination in step S101 until a braking request is made. On the other hand, if there is a braking request (step S101: YES), the processing circuit 101 proceeds to step S103.

[0169] In step S103, the processing circuit 101 functions as a first valve closing control unit M121 and performs a first valve closing control to close only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84. The solenoid valve that is closed in the first valve closing control may be predetermined or changed depending on the situation. When changing the solenoid valve to be closed depending on the situation, for example, the solenoid valve that has been operated fewer times may be closed. Once the first valve closing control is performed, the processing circuit 101 proceeds to step S107.

[0170] In step S107, the processing circuit 101 acquires the intermediate hydraulic pressure Pmd1 by functioning as a hydraulic pressure acquisition unit M123. In the following step S109, the processing circuit 101 may compare the hydraulic pressure difference ΔPw1 or hydraulic pressure difference ΔPw2 with a threshold value Pmd1th to make a determination. The hydraulic pressure difference ΔPw1 is the hydraulic pressure difference between the intermediate hydraulic pressure Pmd1, which is the hydraulic pressure in the third fluid passage 81C, and the first damping pressure Pw1, which is the hydraulic pressure in the second fluid passage 81B. The hydraulic pressure difference ΔPw2 is the hydraulic pressure difference between the intermediate hydraulic pressure Pmd1, which is the hydraulic pressure in the third fluid passage 81C, and the second damping pressure Pw2, which is the hydraulic pressure in the first fluid passage 81A. An example of the threshold value Pmd1th in this case is a criterion for determining whether the hydraulic pressure difference between the fluid passages on both sides of a closed solenoid valve is large or not.

[0171] For example, when the first solenoid valve 83 is closed by the first valve closing control, the processing circuit 101 compares the hydraulic pressure difference ΔPw2 with the threshold Pmd1th. If the hydraulic pressure difference ΔPw2 is less than or equal to the threshold Pmd1th (S109: NO), the processing circuit 101 proceeds to step S111. On the other hand, if the hydraulic pressure difference ΔPw2 is greater than the threshold Pmd1th (S109: YES), the processing circuit 101 proceeds to step S121.

[0172] For example, when the second solenoid valve 84 is closed by the first valve closing control, the processing circuit 101 compares the hydraulic pressure difference ΔPw1 with the threshold Pmd1th. If the hydraulic pressure difference ΔPw1 is less than or equal to the threshold Pmd1th (S109: NO), the processing circuit 101 proceeds to step S111. On the other hand, if the hydraulic pressure difference ΔPw1 is greater than the threshold Pmd1th (S109: YES), the processing circuit 101 proceeds to step S121.

[0173] The determination in step S109 may be changed to the following modified example. That is, the processing circuit 101 may make a determination by comparing the intermediate hydraulic pressure Pmd1 with the threshold Pmd1th. In this case, if the intermediate hydraulic pressure Pmd1 is less than or equal to the threshold Pmd1th (S109: NO), the processing circuit 101 may proceed to step S111. On the other hand, if the intermediate hydraulic pressure Pmd1 is higher than the threshold Pmd1th (S109: YES), the processing circuit 101 may proceed to step S121.

[0174] In step S111, the processing circuit 101 determines whether or not there is still a braking request. If there is still a braking request (S111: YES), the processing circuit 101 proceeds to step S107. On the other hand, if there is no braking request (S111: NO), the processing circuit 101 proceeds to step S113.

[0175] In step S113, the processing circuit 101 performs a valve opening process to open both the first solenoid valve 83 and the second solenoid valve 84. After that, the processing circuit 101 completes the series of processes shown in Figure 16.

[0176] In step S121, the processing circuit 101 functions as a third valve closing control unit M124 and performs a third valve closing control to close the solenoid valve that was open among the first solenoid valve 83 and the second solenoid valve 84. Once both the first solenoid valve 83 and the second solenoid valve 84 are closed as a result of the third valve closing control, the processing circuit 101 proceeds to step S123.

[0177] In step S123, the processing circuit 101 determines whether there is still a braking request. If there is still a braking request (S123: YES), the processing circuit 101 proceeds to step S125. On the other hand, if there is no braking request (S123: NO), the processing circuit 101 proceeds to step S113.

[0178] In step S125, the processing circuit 101, functioning as the third valve closing control unit M124, determines whether the prohibition condition for switching the open solenoid valve is met. For example, the processing circuit 101 determines that the prohibition condition is met if at least one of the following conditions is met.

[0179] - The number of times the solenoid valve to be closed was switched during the above-mentioned judgment time in this braking operation is equal to or greater than the specified number. - It can be determined that vehicle 10C is traveling on rough roads.

[0180] If the prohibition condition is met (S125: YES), the processing circuit 101 proceeds to step S123. This allows the processing circuit 101 to maintain the state in which both the first solenoid valve 83 and the second solenoid valve 84 are closed. On the other hand, if the prohibition condition is not met (S125: NO), the processing circuit 101 proceeds to step S127.

[0181] In step S127, the processing circuit 101 determines whether the deviation amount ΔPw, which is the absolute value of the difference between the first damping pressure Pw1 and the second damping pressure Pw2, is greater than or equal to the determination deviation amount ΔPwth. The determination criterion for determining whether the deviation between the first damping pressure Pw1 and the second damping pressure Pw2 is large is set as the determination deviation amount ΔPwth. If the deviation amount ΔPw is greater than or equal to the determination deviation amount ΔPwth (S127: YES), the processing circuit 101 proceeds to step S129. On the other hand, if the deviation amount ΔPw is less than the determination deviation amount ΔPwth (S127: NO), the processing circuit 101 proceeds to step S123. That is, the processing circuit 101 maintains the state in which both the first solenoid valve 83 and the second solenoid valve 84 are closed.

[0182] In step S129, the processing circuit 101 determines whether the first damping pressure Pw1 is higher than the second damping pressure Pw2. If the first damping pressure Pw1 is higher than the second damping pressure Pw2 (S129: YES), the processing circuit 101 proceeds to step S131. On the other hand, if the first damping pressure Pw1 is lower than the second damping pressure Pw2 (S129: NO), the processing circuit 101 proceeds to step S133 because the second damping pressure Pw2 is higher than the first damping pressure Pw1.

[0183] In step S131, the processing circuit 101 functions as a third valve closing control unit M124, causing only the first solenoid valve 83 out of the two solenoid valves 84. After that, the processing circuit 101 proceeds to step S107.

[0184] In step S133, the processing circuit 101 functions as a third valve closing control unit M124, causing only the second solenoid valve 84 out of the first solenoid valve 83 and the second solenoid valve 84 to open. After that, the processing circuit 101 proceeds to step S107.

[0185] <Operation and Effects of this Embodiment> (3-1) In the braking device 30C of this embodiment, when only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, is closed, the processing circuit 101 closes the open solenoid valve of the first solenoid valve 83 and the second solenoid valve 84 for a predetermined period TM after the intermediate liquid pressure Pmd1 exceeds the threshold Pmd1th. By closing both the first solenoid valve 83 and the second solenoid valve 84 in this way, the intermediate liquid pressure Pmd1, which is the liquid pressure in the third liquid passage 81C, is maintained. As a result, the processing circuit 101 can contain the liquid pressure in the third liquid passage 81C. Therefore, the processing circuit 101 can suppress the differential pressure between the liquid passages on both sides of the first solenoid valve 83 from increasing, and can also suppress the differential pressure between the liquid passages on both sides of the second solenoid valve 84 from increasing.

[0186] (3-2) When both the first solenoid valve 83 and the second solenoid valve 84 are closed, the differential pressure between the first braking pressure Pw1, which is substantially equal to the hydraulic pressure of the second liquid passage 81B, and the second braking pressure Pw2, which is substantially equal to the hydraulic pressure of the first liquid passage 81A, may become large.

[0187] In the braking device 30C of this embodiment, the first solenoid valve 83 is configured such that when the hydraulic pressure in the first fluid passage 81A is higher than the hydraulic pressure in the third fluid passage 81C, the greater the pressure difference between the first fluid passage 81A and the third fluid passage 81C, the greater the force with which it presses the valve body against the valve seat. The second solenoid valve 84 is configured such that when the hydraulic pressure in the second fluid passage 81B is higher than the hydraulic pressure in the third fluid passage 81C, the greater the pressure difference between the second fluid passage 81B and the third fluid passage 81C, the greater the force with which it presses the valve body against the valve seat. The processing circuit 101 then closes both the first solenoid valve 83 and the second solenoid valve 84 by performing a third valve closing control. In this state, if the hydraulic pressure in the second fluid passage 81B is higher than the hydraulic pressure in the first fluid passage 81A, the processing circuit 101 opens the first solenoid valve 83. On the other hand, if the hydraulic pressure in the first liquid passage 81A is higher than the hydraulic pressure in the second liquid passage 81B, the processing circuit 101 opens the second solenoid valve 84. As a result, even if the hydraulic pressure difference between the first liquid passage 81A and the second liquid passage 81B becomes large and one of the solenoid valves that was closed by the first valve closing control is about to open, the processing circuit 101 can prevent the one solenoid valve that was closed by the first valve closing control from unintentionally opening by switching the solenoid valve being operated.

[0188] (3-3) In the braking device 30C of this embodiment, when generating braking pressure for the first wheel cylinder 211C and the second wheel cylinder 212C, the processing circuit 101 closes only one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84. After the one solenoid valve is closed, the processing circuit 101 adjusts the liquid pressure in the third liquid passage 81C using the first electric pressurizing unit 85 or the second electric pressurizing unit 86, which functions as a pressure regulating control unit, thereby suppressing an increase in the differential pressure between the liquid passages on both sides of the one solenoid valve. As a result, the processing circuit 101 can prevent the one solenoid valve from opening when adjusting the first braking pressure Pw1.

[0189] (Examples of modifications) The above multiple embodiments can be implemented with the following modifications. The above multiple embodiments and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0190] In the first and second embodiments, the processing circuit 101 (i.e., the first valve closing control unit M21) may correct only one of the first estimated intermediate hydraulic pressure PmdE1 and the threshold Pth1. The correction of the first estimated intermediate hydraulic pressure PmdE1 and the threshold Pth1 may be performed based on one of the operating speed of the master cylinder 43, the temperature of the brake fluid, and the braking pressure of the first wheel cylinder 211.

[0191] The above examples of modifications are also applicable to the correction of the second estimated intermediate hydraulic pressures PmdE2A, PmdE2B and the threshold Pth2. In the second embodiment, the processing circuit 101 (i.e., the first valve closing control unit M21) may derive the first estimated intermediate hydraulic pressure PmdE1 based on the detected value of the first pressure sensor 52 and the first valve closing force Fc1. In this case, the processing circuit 101 may derive the magnitude of the difference between the hydraulic pressure corresponding to the first valve closing force Fc1 and the detected value as the first estimated intermediate hydraulic pressure PmdE1. When the first estimated intermediate hydraulic pressure PmdE1 exceeds the threshold Pth1, the processing circuit 101 (i.e., the second valve closing control unit M22) can operate the first solenoid valve 44A so that the valve closing force Fc of the first solenoid valve 44A becomes the second valve closing force Fc2.

[0192] In the first and second embodiments, the first braking unit may be configured without a master cylinder 43. In this case, the first braking unit may have a configuration substantially equivalent to that of the second braking unit 40B.

[0193] In the first and second embodiments, the electric pressurizing unit may have a configuration different from the electric pressurizing unit 49 shown in Figure 3, as long as it is capable of supplying brake fluid to the second fluid passages 72A and 72B by driving an electric motor. For example, the electric pressurizing unit may include a pump powered by an electric motor, or it may include an accumulator in which brake fluid is pressurized by driving an electric motor.

[0194] In the first and second embodiments, the first solenoid valves 44A and 44B may be normally closed solenoid valves. In this case, the processing circuit 101 can close the first solenoid valves 44A and 44B by reducing the amount of current supplied to the solenoids of the first solenoid valves 44A and 44B or by stopping the supply of current to the solenoids. Furthermore, when the first solenoid valves 44A and 44B are closed, the processing circuit 101 can increase the closing force of the first solenoid valves 44A and 44B as the amount of current supplied to the solenoids decreases.

[0195] In the first and second embodiments, the second solenoid valves 48A and 48B may be normally closed solenoid valves. In this case, the processing circuit 101 can close the second solenoid valves 48A and 48B by reducing the amount of current supplied to the solenoids of the second solenoid valves 48A and 48B or by stopping the supply of current to the solenoids. Furthermore, when the second solenoid valves 48A and 48B are closed, the processing circuit 101 can increase the closing force of the second solenoid valves 48A and 48B as the amount of current supplied to the solenoids decreases.

[0196] In the third embodiment, after both solenoid valves 83 and 84 were closed, the processing circuit 101 determined which solenoid valve to open based on the relative magnitudes of the first damping pressure Pw1 and the second damping pressure Pw2, but it is not limited to this. For example, the processing circuit 101 may open the solenoid valve corresponding to the electric pressurizing unit with the smaller output torque of the electric motor 63 among the two electric pressurizing units 85 and 86. The solenoid valve corresponding to the electric pressurizing unit 86 is the first solenoid valve 83, and the solenoid valve corresponding to the electric pressurizing unit 85 is the second solenoid valve 84.

[0197] For example, the processing circuit 101 may determine which solenoid valve to open based on the yaw rate and lateral acceleration of the vehicle 10C. Alternatively, the processing circuit 101 may determine which solenoid valve to open based on the target value of the braking force generated by the first wheel 11C and the target value of the braking force generated by the second wheel 12C.

[0198] In the third embodiment, it is preferable that the processing circuit 101 maintains a closed state of the two solenoid valves 83 and 84 if any abnormality is detected in at least one of the two pressure sensors 87 and 88, the two electric pressurizing units 85 and 86, and the two solenoid valves 83 and 84.

[0199] In step S125 shown in Figure 16 of the third embodiment, the processing circuit 101 may determine whether the prohibition condition is met by comparing the magnitude of the difference between the target value of the first damping pressure Pw1 and the target value of the second damping pressure Pw2 with a predetermined value based on the error. In this case, if the magnitude of the difference is smaller than the predetermined value, the processing circuit 101 preferably determines that the prohibition condition is met (i.e., S125: YES) and maintains the state in which the two solenoid valves 83 and 84 are closed.

[0200] In the third embodiment, the processing circuit 101 closes one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, in response to a braking request, but is not limited to this. For example, after startup, the processing circuit 101 may keep one of the solenoid valves, the first solenoid valve 83 and the second solenoid valve 84, closed at all times, regardless of whether or not there is a braking request.

[0201] In the third embodiment, the processing circuit 101 may close one of the first solenoid valves 83 and the second solenoid valve 84, and then close the other solenoid valve, and maintain both the first solenoid valve 83 and the second solenoid valve 84 in a closed state until the current braking request is no longer needed.

[0202] In the third embodiment, the first solenoid valve 83 and the second solenoid valve 84 may be solenoid valves that can utilize the hydraulic pressure of the third liquid passage 81C as the closing force. That is, the first solenoid valve 83 may be configured such that, when the hydraulic pressure of the third liquid passage 81C is higher than the hydraulic pressure of the first liquid passage 81A, the greater the differential pressure between the third liquid passage 81C and the first liquid passage 81A, the greater the force that presses the valve body 302 against the valve seat 301. The second solenoid valve 84 may be configured such that, when the hydraulic pressure of the third liquid passage 81C is higher than the hydraulic pressure of the second liquid passage 81B, the greater the differential pressure between the third liquid passage 81C and the second liquid passage 81B, the greater the force that presses the valve body 302 against the valve seat 301.

[0203] When such solenoid valves are used as the first solenoid valve 83 and the second solenoid valve 84, increasing the liquid pressure in the third liquid passage 81C makes it easier to maintain the closed state of the first solenoid valve 83 and the second solenoid valve 84. For this reason, when both the first solenoid valve 83 and the second solenoid valve 84 are closed, it is preferable for the processing circuit 101 to close the second solenoid valve 84 and then open the first solenoid valve 83 if the liquid pressure in the first liquid passage 81A is higher than the liquid pressure in the second liquid passage 81B. It is also preferable for the processing circuit 101 to close the first solenoid valve 83 and then open the second solenoid valve 84 if the liquid pressure in the second liquid passage 81B is higher than the liquid pressure in the first liquid passage 81A.

[0204] The control device 100 may be configured to include multiple processing circuits. For example, the multiple processing circuits may include a processing circuit for controlling the first braking unit 40A and a processing circuit for controlling the second braking unit 40B.

[0205] For example, the multiple processing circuits may include a processing circuit that functions as a first valve closing control unit M21 and a processing circuit that functions as a second valve closing control unit M22. The processing circuit 101 may be configured as a circuit including one or more processors that operate according to a computer program, one or more dedicated hardware circuits such as 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 processing. Memory, i.e., storage medium, includes any available medium that can be accessed by a general-purpose or dedicated computer.

[0206] <Other Technical Concepts> The technical concepts that can be understood from the above multiple embodiments and modifications are described below. [Note 1] A braking device that controls the braking force of a vehicle by adjusting the hydraulic pressure of a wheel cylinder with brake fluid supplied from a pressurizing unit, comprising: a supply fluid passage which is a brake fluid passage connecting a reservoir for storing brake fluid and the wheel cylinder; a first solenoid valve installed in the supply fluid passage; a second solenoid valve installed in the portion of the supply fluid passage between the first solenoid valve and the wheel cylinder; and a first valve closing control unit that performs a first valve closing control to close one of the solenoid valves, the first fluid passage which is the portion of the supply fluid passage between the first solenoid valve and the reservoir, and the second fluid passage which is the portion of the supply fluid passage between the second solenoid valve and the wheel cylinder, when hydraulic pressure is generated by the operation of the pressurizing unit. A braking device comprising: a second valve closing control unit that, after the first valve closing control has been performed and the solenoid valve has been closed, performs a second valve closing control for a predetermined period after the liquid pressure in the third liquid passage, which is the portion of the supply liquid passage between the first solenoid valve and the second solenoid valve, has exceeded a threshold value based on the liquid pressure that can maintain the closure of the first solenoid valve; and closes the other solenoid valve of the first and second solenoid valves.

[0207] [Note 2] The first valve closing control unit preferably performs a first valve closing control to close the second solenoid valve when hydraulic pressure is generated in the master cylinder, and the second valve closing control unit preferably performs a second valve closing control to close the first solenoid valve after the second solenoid valve has been closed by the first valve closing control, when the hydraulic pressure in the third fluid passage exceeds a threshold value based on the hydraulic pressure at which the second solenoid valve can maintain its closed position.

[0208] [Note 3] The threshold is preferably a hydraulic pressure lower than the hydraulic pressure at which the second solenoid valve can maintain its closed position.

[0209] [Note 4] The first valve closing control unit performs a first valve closing control to close the second solenoid valve when hydraulic pressure is generated in the master cylinder, and to operate the first solenoid valve so that the closing force, which is the force that maintains the closing of the first solenoid valve, becomes the first valve closing force. The second valve closing control unit performs a second valve closing control to operate the first solenoid valve so that, after the second solenoid valve has been closed by the first valve closing control, the closing force of the first solenoid valve becomes a second valve closing force greater than the first valve closing force, when the hydraulic pressure in the third fluid passage exceeds a threshold based on the hydraulic pressure at which the second solenoid valve can maintain its closing.

[0210] [Note 5] The threshold is preferably a hydraulic pressure lower than the hydraulic pressure at which the second solenoid valve can maintain its closed position, and higher than the hydraulic pressure corresponding to the first valve closing force.

[0211] [Note 6] The first valve closing control unit preferably performs a first valve closing control to close the first solenoid valve when the hydraulic pressure in the second liquid passage increases due to the operation of the electric pressurizing unit, and the second valve closing control unit preferably performs a second valve closing control to close the second solenoid valve after the first solenoid valve has been closed by the first valve closing control, when the hydraulic pressure in the third liquid passage exceeds a threshold value based on the hydraulic pressure at which the first solenoid valve can maintain its closed position.

[0212] [Note 7] The threshold is preferably a hydraulic pressure lower than the hydraulic pressure at which the first solenoid valve can maintain its closed position.

[0213] [Note 8] A braking device that controls the braking force of a vehicle by adjusting the hydraulic pressure of a first wheel cylinder and a second wheel cylinder with brake fluid supplied from a pressurizing unit, comprising: a supply fluid passage which is a brake fluid passage connected to the first wheel cylinder and the second wheel cylinder; a first solenoid valve installed between the first wheel cylinder and the second wheel cylinder in the supply fluid passage; and a second solenoid valve installed in the portion of the supply fluid passage between the first solenoid valve and the first wheel cylinder, wherein the supply fluid passage has a first fluid passage which is the portion between the second wheel cylinder and the first solenoid valve, a second fluid passage which is the portion between the first wheel cylinder and the second solenoid valve, and a third fluid passage which is the portion between the first solenoid valve and the second solenoid valve, and the braking device is A braking device comprising: a first valve closing control unit that performs a first valve closing control to close one of the first and second solenoid valves and open the other solenoid valve in order to block communication between the first and second fluid passages when generating hydraulic pressure in at least one of the first wheel cylinder and the second wheel cylinder; and a third valve closing control unit that performs a third valve closing control to close the other solenoid valve of the first and second solenoid valves for a predetermined period after the one solenoid valve has been closed by the implementation of the first valve closing control, during which time the hydraulic pressure in the third fluid passage exceeds a threshold value based on the hydraulic pressure that can maintain the closure of the one solenoid valve.

[0214] [Note 9] The third valve closing control unit, with both the first and second solenoid valves closed by the third valve closing control, preferably opens the second solenoid valve while maintaining the closure of the first solenoid valve, provided that the hydraulic pressure in the first fluid passage is higher than the hydraulic pressure in the second fluid passage, and preferably opens the first solenoid valve while maintaining the closure of the second solenoid valve, provided that the hydraulic pressure in the second fluid passage is higher than the hydraulic pressure in the first fluid passage.

[0215] [Note 10] It is preferable that the third valve closing control unit maintains the state in which both the first and second solenoid valves are closed if the number of times the solenoid valve to be closed is switched within a predetermined determination time exceeds a specified number.

[0216] [Note 11] When the second valve closing control unit determines that the pressurizing unit and at least one of the first solenoid valve and the second solenoid valve are malfunctioning, it is preferable to maintain a state in which both the first solenoid valve and the second solenoid valve are closed.

[0217] 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."

Claims

1. A braking device that controls the braking force of a vehicle by adjusting the hydraulic pressure of a first wheel cylinder with brake fluid supplied from a pressurizing unit, comprising: a supply fluid passage which is a brake fluid passage connected to the first wheel cylinder; a first solenoid valve installed in the supply fluid passage; a second solenoid valve installed in the portion of the supply fluid passage between the first solenoid valve and the first wheel cylinder; and a first valve closing control unit that performs a first valve closing control to block communication between the first fluid passage, which is the portion of the supply fluid passage opposite the first wheel cylinder with the first solenoid valve in between, and the second fluid passage, which is the portion of the supply fluid passage between the first wheel cylinder and the second solenoid valve, by closing one of the first solenoid valves and opening the other solenoid valve when generating hydraulic pressure in the first wheel cylinder. A braking device comprising: a pressure regulating control unit that, after the first valve closing control has been performed and the solenoid valve has been closed, performs suppression control to suppress an increase in the differential pressure between the liquid passages on either side of the solenoid valve by adjusting the liquid pressure of the third liquid passage, which is the portion of the supply liquid passage between the first solenoid valve and the second solenoid valve.

2. The braking device according to claim 1, wherein, when generating hydraulic pressure in the first wheel cylinder, after the first valve closing control has closed one of the solenoid valves, the brake device further comprises a second valve closing control unit which, by operating the pressurizing unit, performs a second valve closing control to close the other solenoid valve of the first and second solenoid valves for a predetermined period after the hydraulic pressure in the third fluid passage exceeds a threshold value based on the hydraulic pressure that can maintain the closure of the one of the solenoid valves, and the second valve closing control unit operates as the pressure regulating control unit to adjust the hydraulic pressure in the third fluid passage.

3. The braking device according to claim 2, wherein the pressurizing unit includes a master cylinder provided in the first fluid passage that generates hydraulic pressure in response to the braking operation of the driver of the vehicle, the braking device includes a first hydraulic pressure estimation unit that derives an estimated value of the hydraulic pressure in the third fluid passage based on the detection value of a first pressure sensor that detects the hydraulic pressure in the portion of the first fluid passage between the master cylinder and the first solenoid valve, the first valve closing control unit closes the second solenoid valve by performing the first valve closing control when hydraulic pressure is generated in the master cylinder, the second valve closing control unit closes the first solenoid valve by performing the second valve closing control during a predetermined period after the estimated value of the hydraulic pressure in the third fluid passage exceeds the threshold when hydraulic pressure is generated in the master cylinder, and the first hydraulic pressure estimation unit corrects at least one of the estimated value of the hydraulic pressure in the third fluid passage and the threshold based on at least one of the operating speed of the master cylinder, the temperature of the brake fluid in the supply fluid passage, and the hydraulic pressure in the second fluid passage.

4. The braking device according to claim 2, wherein the pressurizing unit includes an electric pressurizing unit that adjusts the hydraulic pressure of the second fluid passage by supplying brake fluid to the second fluid passage by driving an electric motor, the braking device includes a second hydraulic pressure estimation unit that derives an estimated value of the hydraulic pressure of the third fluid passage based on the detection value of a second pressure sensor that detects the hydraulic pressure of the second fluid passage, the first valve closing control unit closes the first solenoid valve by performing the first valve closing control when the hydraulic pressure of the second fluid passage is increased by the electric pressurizing unit, the second valve closing control unit closes the second solenoid valve by performing the second valve closing control during the predetermined period after the estimated value of the hydraulic pressure of the third fluid passage exceeds the threshold when the hydraulic pressure of the second fluid passage is increased by the electric pressurizing unit, and the second hydraulic pressure estimation unit corrects at least one of the estimated value of the hydraulic pressure of the third fluid passage and the threshold based on at least one of the operating speed of the electric pressurizing unit, the temperature of the brake fluid in the supply fluid passage, and the hydraulic pressure of the first fluid passage.

5. The vehicle has a second wheel cylinder connected to the first fluid passage, and the pressurizing unit includes a first electric pressurizing unit connected to the second fluid passage and adjusting the fluid pressure of the second fluid passage by supplying brake fluid to the second fluid passage by driving an electric motor, and a second electric pressurizing unit connected to the first fluid passage and adjusting the fluid pressure of the first fluid passage by supplying brake fluid to the first fluid passage by driving an electric motor, and the braking device further includes a third valve closing control unit that performs a third valve closing control to close the other solenoid valve of the first and second solenoid valves for a predetermined period after the fluid pressure of the third fluid passage exceeds a threshold value based on the fluid pressure that can maintain the closing of one of the solenoid valves, The braking device according to claim 1, wherein the first solenoid valve is closed by the first valve closing control and the liquid pressure in the third liquid passage changes due to the operation of the first electric pressurizing unit, or the second solenoid valve is closed by the first valve closing control and the liquid pressure in the third liquid passage changes due to the operation of the second electric pressurizing unit, and the third valve closing control unit operates as the pressure regulating control unit to adjust the liquid pressure in the third liquid passage.

6. The braking device according to claim 5, wherein the first solenoid valve is configured such that when the hydraulic pressure in the first fluid passage is higher than the hydraulic pressure in the third fluid passage, the greater the differential pressure between the first fluid passage and the third fluid passage, the greater the force with which it presses the valve body against the valve seat; the second solenoid valve is configured such that when the hydraulic pressure in the second fluid passage is higher than the hydraulic pressure in the third fluid passage, the greater the differential pressure between the second fluid passage and the third fluid passage, the greater the force with which it presses the valve body against the valve seat; and the third valve closing control unit, in a state where both the first and second solenoid valves are closed due to the implementation of the third valve closing control, opens the first solenoid valve when the hydraulic pressure in the second fluid passage is higher than the hydraulic pressure in the first fluid passage, and opens the second solenoid valve when the hydraulic pressure in the first fluid passage is higher than the hydraulic pressure in the second fluid passage.

7. The braking device according to claim 1, wherein the vehicle has a second wheel cylinder connected to the first fluid passage, and the pressurizing unit includes a first electric pressurizing unit connected to the second fluid passage and adjusting the fluid pressure of the second fluid passage by supplying brake fluid to the second fluid passage by driving an electric motor, and a second electric pressurizing unit connected to the first fluid passage and adjusting the fluid pressure of the first fluid passage by supplying brake fluid to the first fluid passage by driving an electric motor, wherein when the first solenoid valve is closed by the first valve closing control, the first electric pressurizing unit operates as the pressure regulating control unit to adjust the fluid pressure of the third fluid passage, and when the second solenoid valve is closed by the first valve closing control, the second electric pressurizing unit operates as the pressure regulating control unit to adjust the fluid pressure of the third fluid passage, thereby suppressing an increase in the differential pressure of the fluid passages on both sides of the one solenoid valve that has been closed by the first valve closing control.

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