Brake device

Abstract

To inhibit dragging of a brake unit with a simple structure.SOLUTION: A brake device includes: a housing which has a replenishment port communicating with a reservoir tank and is closed at one end; a piston which is formed with a through hole penetrating through an outer peripheral surface and an inner peripheral surface and is moved to one end side in the housing to block the through hole from the replenishment port and thereby generate a fluid pressure in a fluid pressure chamber in the housing; and a seal member which is provided at a portion, which is located closer to the one end side than the through hole, of the piston over a circumferential direction and seals a space between an inner peripheral surface of the housing and the outer peripheral surface of the piston.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to the technical field of braking devices provided in vehicles.

Background Art

[0002] As described in Patent Document 1, a braking device generates brake hydraulic pressure in a master cylinder in response to an operation of a brake pedal. Then, the braking device operates a wheel cylinder by the brake hydraulic pressure generated in the master cylinder to brake the vehicle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above braking device, an on-off valve and a slave cylinder are provided between the master cylinder and the wheel cylinder, and a negative pressure is generated in the wheel cylinder by operating the slave cylinder after closing the on-off valve. Thereby, the above braking device prevents the dragging of the braking force by the wheel cylinder.

[0005] However, in the above braking device, there is a problem that it is necessary to provide an on-off valve and a slave cylinder, and the configuration becomes complicated.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to suppress the dragging of the brake unit with a simple configuration.

Means for Solving the Problems

[0007] The brake device according to an embodiment of the present invention includes a supply port communicated with a reservoir tank, a housing having one end closed, a through hole formed through an outer peripheral surface and an inner peripheral surface, and by being moved to the one end side inside the housing, a piston that closes the through hole with respect to the supply port and generates hydraulic pressure in a hydraulic chamber inside the housing, and a seal member provided over a circumferential direction on the one end side of the piston with respect to the through hole, and sealing between an inner peripheral surface of the housing and an outer peripheral surface of the piston.

Effect of the Invention

[0008] According to the present invention, dragging of the brake unit can be suppressed with a simple configuration.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] <1. Configuration of Brake Device 10> FIG. 1 is a diagram for explaining the configuration of the brake device 10. As shown in FIG. 1, the vehicle 1 includes the brake device 10.

[0011] The braking device 10 includes a brake pedal 11 and a brake sensor 12. The brake pedal 11 is connected to a brake booster 14. The brake sensor 12 detects the depression amount (stroke) of the brake pedal 11 and outputs information indicating the detected depression amount to the control device 13.

[0012] The control device 13 is a processor including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control device 13 controls the entire braking device 10 by expanding and executing a program stored in the ROM or a storage unit (not shown) on the RAM.

[0013] The brake booster (power assist device) 14 is, for example, an electric brake booster, and moves the primary piston 43 (see FIG. 2) of the master cylinder 15 based on the control of the control device 13. For example, the brake booster 14 moves the primary piston 43 by an amount corresponding to the depression amount of the brake pedal 11.

[0014] The master cylinder 15 is of a tandem type, is connected to a reservoir tank 16, and is connected to the brake unit 20 via a hydraulic circuit 30. The master cylinder 15 generates a brake hydraulic pressure and applies the brake hydraulic pressure to the brake unit 20 via the hydraulic circuit 30, as will be described in detail later.

[0015] The brake unit 20 is, for example, a disc brake unit and is provided on each wheel (RL, FR, FL, RR). The brake unit 20 includes a brake caliper 21, a brake piston 22, a brake pad 23, and a brake rotor 24. Brake hydraulic pressure is applied to the brake caliper 21 via the hydraulic circuit 30. The brake piston 22 is slidably housed in the brake caliper 21 and moves (slides) inside the brake caliper 21 by the brake hydraulic pressure applied to the brake caliper 21.

[0016] The brake pad 23 is connected to the tip of the brake piston 22. When the brake piston 22 moves by brake hydraulic pressure, it is pressed against a brake rotor 24 that rotates integrally with the wheel. Thereby, the brake unit 20 brakes the vehicle 1 (wheel).

[0017] The hydraulic circuit 30 is composed of two systems, a first hydraulic circuit 30a and a second hydraulic circuit 30b. The hydraulic circuit 30 is a cross pipe or a front-rear pipe. The first hydraulic circuit 30a is connected to the brake unit 20 provided on the wheels (RL, FR), and the second hydraulic circuit 30b is connected to the brake unit 20 provided on the wheels (FL, RR).

[0018] Since the first hydraulic circuit 30a and the second hydraulic circuit 30b have the same configuration, the same reference numerals will be used hereinafter for simplicity of explanation. Also, in the hydraulic circuit 30, the master cylinder 15 side will be described as the upstream and the brake unit 20 side as the downstream.

[0019] The master cylinder 15 is provided with a supply / discharge port 15a and a supply / discharge port 15b. First liquid paths L1 are respectively connected to the supply / discharge port 15a and the supply / discharge port 15b. The first liquid path L1 has its upstream end connected to the master cylinder 15 and its downstream end connected to a second liquid path L2.

[0020] The second hydraulic line L2 has its downstream end branched and connected to a third hydraulic line L3 and a fourth hydraulic line L4. The downstream end of the third hydraulic line L3 is connected to the brake unit 20 (brake caliper 21) of the wheels (RL, RR). The downstream end of the fourth hydraulic line L4 is connected to the brake unit 20 (brake caliper 21) of the wheels (FL, FR). Note that the third hydraulic line L3 and the fourth hydraulic line L4 may be connected to the brake unit 20 of any wheel. For example, the third hydraulic line L3 of the first hydraulic circuit 30a may be connected to the wheel (RL), the fourth hydraulic line L4 may be connected to the wheel (RR), the third hydraulic line L3 of the second hydraulic circuit 30b may be connected to the wheel (FR), and the fourth hydraulic line L4 may be connected to the wheel (FL) of the brake unit 20, respectively. Also, the third hydraulic line L3 of the first hydraulic circuit 30a may be connected to the wheel (RR), the fourth hydraulic line L4 may be connected to the wheel (FR), the third hydraulic line L3 of the second hydraulic circuit 30b may be connected to the wheel (RL), and the fourth hydraulic line L4 may be connected to the wheel (FL) of the brake unit 20, respectively.

[0021] The upstream end of a fifth hydraulic line L5 is connected in the middle of the third hydraulic line L3. The upstream end of a sixth hydraulic line L6 is connected in the middle of the fourth hydraulic line L4. A seventh hydraulic line L7 is connected to the downstream ends of the fifth hydraulic line L5 and the sixth hydraulic line L6. The downstream end of the seventh hydraulic line L7 is connected to a position downstream of the gate inlet valve 31 in the first hydraulic line L1 and upstream of the hydraulic pump 32 in the second hydraulic line L2.

[0022] A gate inlet valve 31 is provided in the first hydraulic line L1. Also, a hydraulic pump 32 is provided in the second hydraulic line L2. Furthermore, the hydraulic pumps 32 of the first hydraulic circuit 30a and the second hydraulic circuit 30b are connected to a common electric motor 33.

[0023] A pulsation pressure reducing mechanism 34 is provided downstream of the hydraulic pump 32 in the second hydraulic line L2. The pulsation pressure reducing mechanism 34 attenuates the pulsation of the brake fluid discharged from the hydraulic pump 32.

[0024] The upstream side of the gate-in valve 31 in the first liquid path L1 and the downstream side of the pulsation pressure reducing mechanism 34 in the second liquid path L2 are bypass-connected via the eighth liquid path L8. A bypass valve 35 is provided in the eighth liquid path L8.

[0025] A pressure increasing valve 36 is provided in the third liquid path L3. A pressure increasing valve 37 is provided in the fourth liquid path L4. A pressure reducing valve 38 is provided in the fifth liquid path L5. A pressure reducing valve 39 is provided in the sixth liquid path L6.

[0026] Also, a low-pressure chamber 40 is provided in the seventh liquid path L7. The low-pressure chamber 40 temporarily stores the brake fluid.

[0027] The gate-in valve 31, the pressure reducing valve 38, and the pressure reducing valve 39 are electromagnetic solenoid valves that close when de-energized (non-controlled) and open when energized (controlled). The bypass valve 35, the pressure increasing valve 36, and the pressure increasing valve 37 are electromagnetic solenoid valves that open when de-energized (non-controlled) and close when energized (controlled).

[0028] The gate-in valve 31, the electric motor 33, the bypass valve 35, the pressure increasing valve 36, the pressure increasing valve 37, the pressure reducing valve 38, and the pressure reducing valve 39 are controlled by the control device 13.

[0029] When not controlled by the control device 13, as described above, the gate-in valve 31, the pressure reducing valve 38, and the pressure reducing valve 39 are closed, and the bypass valve 35, the pressure increasing valve 36, and the pressure increasing valve 37 are open. Also, the electric motor 33 is not driven and the hydraulic pump 32 is also stopped.

[0030] Therefore, when not controlled, when the driver depresses the brake pedal 11, the brake hydraulic pressure generated in the master cylinder 15 is branched into the third liquid path L3 and the fourth liquid path L4 via the first liquid path L1, the eighth liquid path L8, and the second liquid path L2 and supplied to the brake unit 20. Then, the brake unit 20 brakes the wheels by this brake hydraulic pressure.

[0031] Incidentally, the control device 13 performs hydraulic control such as antilock braking system (ABS) control operation and electronic stability program (ESP) control operation. During such control, the control device 13 opens the gate inlet valve 31, the pressure reducing valves 38 and 39, and closes the bypass valve 35, the pressure increasing valves 36 and 37. Further, the control device 13 drives the electric motor 33.

[0032] Then, the driving of the electric motor 33 causes the hydraulic pump 32 to rotate, and the brake fluid stored in the reservoir tank 16 via the master cylinder 15 is sucked into the first liquid passage L1 independently of the operation of the brake pedal 11.

[0033] Then, the brake fluid sucked into the first liquid passage L1 is branched into the third liquid passage L3 and the fourth liquid passage L4 via the second liquid passage L2 through the gate inlet valve 31, and is supplied to the brake unit 20. Then, the brake unit 20 brakes the wheels by this brake fluid pressure. When braking a specific wheel, only the corresponding pressure increasing valves 36 and 37 may be opened.

[0034] <2. Configuration of Master Cylinder 15> FIG. 2 is a diagram for explaining the configuration of the master cylinder 15. As shown in FIG. 2, the reservoir tank 16 stores the brake fluid at atmospheric pressure, and is provided with two replenishing liquid passages 41.

[0035] The master cylinder 15 includes a housing 42, a primary piston 43, a secondary piston 44, a coil spring 45, and a coil spring 46.

[0036] The housing 42 is formed in a cylindrical shape with one end (the left end in the figure) closed and the other end (the right end in the figure) open. Inside the housing 42, a primary piston 43, a coil spring 45, a secondary piston 44, and a coil spring 46 are accommodated in order from the other end side.

[0037] In addition, supply ports 42a and 42b and supply / discharge ports 15a and 15b are formed in the housing 42. The supply ports 42a and 42b are connected to the supply liquid passage 41 of the reservoir tank 16. The supply / discharge ports 15a and 15b are respectively connected to the first liquid passage L1 (see FIG. 1) of the first hydraulic circuit 30a and the second hydraulic circuit 30b.

[0038] In the master cylinder 15, a space surrounded by the inner peripheral surface of the housing 42, the primary piston 43, and the secondary piston 44 is formed as the primary chamber 47. Also, in the master cylinder 15, a space surrounded by the inner peripheral surface on one end side of the housing 42 and the secondary piston 44 is formed as the secondary chamber 48. Note that the primary chamber 47 and the secondary chamber 48 may be collectively referred to as a hydraulic chamber.

[0039] The coil spring 45 is interposed between the primary piston 43 and the secondary piston 44. The coil spring 46 is interposed between one end of the housing 42 and the secondary piston 44.

[0040] The primary piston 43 is disposed on the other end side inside the housing 42 and is moved to one end side (tip side) and the other end side (end side) by the brake booster 14 based on the control of the control device 13. Note that the movement of the primary piston 43 to the one end side may be expressed as the primary piston 43 being pushed. Also, the movement of the primary piston 43 to the other end side may be expressed as the primary piston 43 being pulled.

[0041] The primary piston 43 is formed such that the inside on the secondary piston 44 side is recessed, and a through-hole 43a penetrating the outer peripheral surface and the inner peripheral surface is formed. When the through-hole 43a moves to a position facing the supply port 42a, the primary piston 43 communicates the primary chamber 47 with the reservoir tank 16.

[0042] Also, a seal member 50 is provided on the primary piston 43 in the circumferential direction on one end side rather than the through-hole 43a. The seal member 50 is made of an elastic body such as rubber, for example, and is fixed to the outer peripheral surface of the primary piston 43. When the primary piston 43 is pulled and the seal member 50 moves to a position facing the supply port 42a, the seal member 50 closes the supply port 42a. As a result, the primary chamber 47 and the reservoir tank 16 are blocked.

[0043] The secondary piston 44 is disposed in the housing 42 so as to be sandwiched between the coil spring 45 and the coil spring 46, and is moved to one end side (tip side) and the other end side (end side) as the primary piston 43 moves. Note that the movement of the secondary piston 44 to the one end side may be described as the secondary piston 44 being pushed. Also, the movement of the secondary piston 44 to the other end side may be described as the secondary piston 44 being pulled.

[0044] The secondary piston 44 is formed such that the inside on one end side is recessed, and a through-hole 44a penetrating the outer peripheral surface and the inner peripheral surface is formed. When the through-hole 44a moves to a position facing the supply port 42b, the secondary piston 44 communicates the secondary chamber 48 with the reservoir tank 16.

[0045] Also, a seal member 51 is provided on the secondary piston 44 in the circumferential direction on one end side rather than the through-hole 44a. The seal member 51 is made of an elastic body such as rubber, for example, and is fixed to the outer peripheral surface of the secondary piston 44. Then, when the secondary piston 44 is pulled and the seal member 51 moves to a position facing the supply port 42a, the seal member 51 closes the supply port 42a. As a result, the primary chamber 47 and the reservoir tank 16 are blocked from each other.

[0046] Also, on the inner peripheral surface of the housing 42, annular piston seals 60, 61, 62, 63 that contact the primary piston 43 and the secondary piston 44 are arranged at predetermined intervals in the moving direction of the primary piston 43 and the secondary piston 44.

[0047] The piston seals 60, 61 are arranged so as to sandwich the supply port 42a. The piston seals 62, 63 are arranged so as to sandwich the supply port 42b.

[0048] <3. Origin position of the primary piston 43> In the master cylinder 15 configured as described above, the primary piston 43 and the secondary piston 44 are moved based on the control of the control device 13. Hereinafter, the non-braking state in which the brake pedal 11 is not depressed and no brake hydraulic pressure is applied to the brake unit 20 will be described.

[0049] In the master cylinder 15, in the non-braking state where no brake hydraulic pressure is applied to the brake unit 20, the primary piston 43 and the secondary piston 44 are moved to either the first origin position or the third origin position based on the control of the control device 13. Since the primary piston 43 and the secondary piston 44 are moved to the same origin position in the non-braking state, the primary piston 43 will be described here, and the description of the secondary piston 44 will be omitted.

[0050] During non-braking, the control device 13 normally moves the primary piston 43 to the first origin position. Also, during non-braking, for example, when driving at a high speed of 80 km / h or more or during ACC (Adaptive Cruise Control) when the driver does not operate the brake pedal 11 much, the control device 13 moves the primary piston 43 to the third origin position.

[0051] The first origin position is a position where the through-hole 43a of the primary piston 43 faces the supply port 42a, and the reservoir tank 16 and the primary chamber 47 communicate with each other.

[0052] When the primary piston 43 is at the first origin position, the primary chamber 47 communicates with the reservoir tank 16 through the through-hole 43a.

[0053] And since the reservoir tank 16 stores the brake fluid at atmospheric pressure, the primary chamber 47 communicated with the reservoir tank 16 also becomes atmospheric pressure, and the hydraulic pressure circuit 30 and the brake unit 20 connected to the primary chamber 47 also become atmospheric pressure. Therefore, the inside of the brake caliper 21 of the brake unit 20 also becomes atmospheric pressure, and the brake pad 23 is no longer pressed against the brake rotor 24.

[0054] When the brake pedal 11 is operated and the primary piston 43 is pushed from the first origin position, the through-hole 43a deviates from the position facing the supply port 42a, and the primary chamber 47 is blocked from the reservoir tank 16. Then, when the primary piston 43 is further pushed, brake fluid pressure (positive pressure) is generated in the primary chamber 47. In this way, when brake fluid pressure is generated in the primary chamber 47, the brake fluid pressure is applied to the brake unit 20 through the hydraulic pressure circuit 30, and the brake unit 20 brakes the wheels.

[0055] FIG. 3 is a diagram for explaining the second origin position. The second origin position is on the other end side with respect to the first origin position, and is a position where the supply port 42a and the seal member 50 face each other (the position immediately after facing each other). When the primary piston 43 is further pulled from the first origin position and moves to the second origin position, the supply port 42a and the seal member 50 face each other, the seal member 50 closes the supply port 42a, and the primary chamber 47 and the reservoir tank 16 are blocked.

[0056] Thus, in the braking device 10, by moving the primary piston 43 from the first origin position to the second origin position, the reservoir tank 16 and the primary chamber 47 are blocked. While the primary piston 43 is moving from the first origin position to the second origin position, since the reservoir tank 16 and the primary chamber 47 are in communication, the hydraulic circuit 30 and the brake unit 20 are maintained at atmospheric pressure.

[0057] FIG. 4 is a diagram for explaining the third origin position. FIG. 5 is a diagram for explaining the relationship between the seal member 50 and the supply port 42a when the primary piston 43 moves to the third origin position.

[0058] As shown in FIGS. 4 and 5, the third origin position is a position where the primary piston 43 is further pulled than the second origin position. More specifically, the third origin position is a position when the end portion on one end side of the seal member 50 is in close contact with the edge of the supply port 42a.

[0059] In the braking device 10, by moving the primary piston 43 from the second origin position to the third origin position, the inside of the primary chamber 47 can be made into a negative pressure. Further, in the braking device 10, along with the negative pressure in the primary chamber 47, the hydraulic circuit 30 and the brake unit 20 can also be made into a negative pressure. Thereby, in the brake unit 20, the brake piston 22 is pulled by the negative pressure, and the brake pad 23 is moved so as to be separated from the brake rotor 24. Therefore, the braking device 10 can prevent the brake pad 23 from being dragged while in contact with the brake rotor 24 by moving the primary piston 43 from the second origin position to the third origin position.

[0060] FIG. 6 is a diagram for explaining the seal member 50 when positive pressure is generated at the third origin position. By the way, in the braking device 10, as described above, when hydraulic pressure control such as ABS control operation and ESP control operation is performed, the brake fluid pressure is applied to the brake unit 20 independently of the operation of the brake pedal 11, that is, independently of the operation of the master cylinder 15.

[0061] When such hydraulic pressure control is performed, if the primary piston 43 is moved to the third origin position due to some cause such as a failure, and the brake fluid pressure in the hydraulic circuit 30 remains at positive pressure, the brake fluid pressure (positive pressure) will be applied to the brake unit 20. In such a situation, the brake pad 23 will be dragged while in contact with the brake rotor 24. That is, the state in which braking force is applied to the wheel will be maintained.

[0062] Therefore, in the braking device 10, when positive pressure is applied to the primary chamber 47 due to the positive pressure in the hydraulic circuit 30, as shown in FIG. 6, the seal member 50, which is an elastic body, is deformed by the positive pressure, and the replenishing port 42a and the primary chamber 47 are communicated with each other.

[0063] Thereby, the braking device 10 can eliminate the irregular positive pressure applied to the primary chamber 47, the hydraulic circuit 30, and the brake unit 20. Therefore, the braking device 10 can prevent the brake pad 23 from being dragged while in contact with the brake rotor 24, and can prevent the state in which braking force is applied to the wheel from being maintained.

[0064] <4. Summary> The brake device 10 in the above-described embodiment has supply ports 42a and 42b communicating with the reservoir tank 16, a housing 42 with one end closed, through holes 43a and 44a formed through the outer peripheral surface and the inner peripheral surface, and pistons (primary piston 43, secondary piston 44) that generate hydraulic pressure (brake hydraulic pressure) in the hydraulic chambers (primary chamber 47, secondary chamber 48) inside the housing 42 by moving to one end side inside the housing 42, and seal members 50 and 51 provided over the circumferential direction on one end side of the pistons with respect to the through holes 43a and 44a, and sealing between the inner peripheral surface of the housing 42 and the outer peripheral surface of the pistons. Thereby, when the pistons are pulled, the supply ports 42a and 42b are blocked by the seal members 50 and 51, and a negative pressure can be generated in the hydraulic chambers. Therefore, the brake device 10 can suppress the dragging of the brake unit 20 with a simple configuration.

[0065] The pistons are movable to a first origin position where the through holes and the supply ports face each other and the reservoir tank and the hydraulic chambers communicate, a second origin position on the other end side of the first origin position where the supply ports and the seal members face each other, and a third origin position on the other end side of the second origin position. Thereby, by the pistons moving to the first origin position, the second origin position, and the third origin position, a negative pressure can be generated in the hydraulic chambers. Therefore, the brake device 10 can suppress the dragging of the brake unit 20 with a simple configuration.

[0066] By the pistons moving from the second origin position to the third origin position, a negative pressure is generated in the hydraulic chambers. Thereby, the hydraulic circuit 30 and the brake unit 20 can also be made negative pressure. Therefore, the brake device 10 can suppress the brake pads 23 from being dragged while in contact with the brake rotor 24.

[0067] When the piston is at the third origin position, one end of the seal member is in close contact with the edge of the supply port. Thus, when a positive pressure is applied to the hydraulic chamber due to the positive pressure in the hydraulic circuit 30, the seal member 50 is deformed by the positive pressure, and the supply port 42a and the hydraulic chamber are brought into communication. Therefore, in the braking device 10, it is possible to eliminate the irregular positive pressure applied to the hydraulic chamber, the hydraulic circuit 30, and the brake unit 20.

[0068] A control unit for controlling the movement of the piston is provided, and the control unit moves the piston to either the first origin or the third origin according to the running state of the vehicle. Thereby, when the brake pedal 11 is not operated much, it is possible to suppress the brake pad 23 from being dragged by the brake rotor 24, and the responsiveness of the brake can be enhanced under the situation where the brake pedal 11 is operated.

[0069] <5. Modification Example> As described above, the embodiments according to the present invention have been described. However, the present invention is not limited to the above-described specific examples and can adopt various configurations.

[0070] For example, in the above embodiment, the primary piston 43 and the secondary piston 44 are provided as the pistons. However, the number of pistons may be one or plural.

[0071] Also, in the above embodiment, the brake booster 14 is an electric brake booster, and the primary piston 43 is moved based on the control of the control device 13. However, the brake booster 14 may be, for example, a negative pressure type brake booster. In this case, for example, the primary piston 43 and the secondary piston 44 may be moved to the third origin position during non-braking.

Explanation of Reference Numerals

[0072] 1 Vehicle 10 Brake device 15 Master cylinder 42 Housing 43 Primary piston 44 Secondary piston 50 Seal member 51 Seal member

Claims

1. A housing having a supply port communicating with a reservoir tank and having one end closed, a piston in which a through-hole penetrating an outer peripheral surface and an inner peripheral surface is formed, and by being moved to the one end side inside the housing, hydraulic pressure is generated in a hydraulic chamber in the housing, a seal member provided over a circumferential direction on the one end side of the piston with respect to the through-hole, sealing between the inner peripheral surface of the housing and the outer peripheral surface of the piston and being made capable of facing the supply port when the piston is moved to the other end side of the housing, comprising: the piston is a first origin position where the through-hole and the supply port face each other and the reservoir tank and the hydraulic chamber communicate with each other, a second origin position on the other end side of the first origin position, where the supply port and the seal member face each other and an end portion on the other end side of the seal member is in close contact with an edge of the supply port, a third origin position on the other end side of the second origin position, where the supply port and the seal member face each other, is movable to, and by moving from the second origin position to the third origin position, a negative pressure is generated in the hydraulic chamber a braking device.

2. When the piston is at the third origin position, an end portion on the one end side of the seal member is in close contact with an edge of the supply port, and the reservoir tank and the hydraulic chamber are made communicable by the seal member being deformed by a positive pressure in the hydraulic chamber The braking device according to claim 1.

3. comprising a control unit that controls movement of the piston, wherein the control unit moves the piston to either the first origin position or the third origin position according to a traveling state of a vehicle The braking device according to claim 1 or claim 2.

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