KR20120047463A

KR20120047463A - Piston for master cylinder and master cylinder having the same

Info

Publication number: KR20120047463A
Application number: KR1020100109029A
Authority: KR
Inventors: 강동구
Original assignee: 주식회사 만도
Priority date: 2010-11-04
Filing date: 2010-11-04
Publication date: 2012-05-14

Abstract

The present invention relates to a master cylinder in which a communication port of a piston and a flow path of an oil tank are rapidly communicated when releasing braking, and in the master cylinder of the present invention, the diameter of a communication flow path of an oil port provided in a piston is changed, so that the communication of a piston is released. The flow passage between the oil passage and the oil tank side can be quickly communicated to minimize the insignificant retraction of the piston and the brake release delay.

Description

Piston for master cylinder and master cylinder with same {PISTON FOR MASTER CYLINDER AND MASTER CYLINDER HAVING THE SAME}

The present invention relates to a piston for a master cylinder and a master cylinder having the same, and more particularly, to a master cylinder piston and a master cylinder having the same, in which the communication hole of the piston for the master cylinder and the oil tank side are quickly communicated when the brake is released.

The master cylinder is a device for generating hydraulic pressure in the hydraulic brake system. 1 exemplarily illustrates a general tandem master cylinder and an oil tank applied to a vehicle.

As shown in FIG. 1, the master cylinder includes a cylinder body 1 and a first piston 3 and a second piston 4 which are installed to be retractable in the bore 2 of the cylinder body 1. do.

In the first piston 3 and the second piston 4, oil flows into the first hydraulic chamber 7 and the second hydraulic chamber 8 through the oil ports 6 communicating with the oil tank 5. Each of the plurality of communication holes (9) to be provided.

When the first piston 3 and the second piston 4 are advanced, the oil ports 6 and the plurality of communication holes 9 are blocked by the sealing members 11 and the first hydraulic chamber 7 ) And the second hydraulic chamber 8 rise.

On the contrary, when the first piston 3 and the second piston 4 retreat, the plurality of communication holes 9 are respectively moved behind the sealing members 11 to communicate with the oil ports 6. Accordingly, the oil in the first hydraulic chamber 7 and the second hydraulic chamber 8 returns to the oil tank 5, and the hydraulic pressure in the first hydraulic chamber 7 and the second hydraulic chamber 8 drops. , The braking pressure is released.

As shown in Figure 2a, the sealing member 11 is provided in a ring shape and is installed in the receiving groove (1a) of the cylinder body (1). Since the sealing members 11 have an inner blade portion 11a in contact with the outer surface of the piston 4 and an outer wing portion 11b in contact with the inner surface of the receiving groove 1a and have a cup-shaped cross-sectional structure, it is also called a cup chamber. do.

As shown in FIG. 2B, since the pressure of the hydraulic chamber 8 acts on the inner surface of the sealing members 11 when the piston 4 moves forward, the inner wing portion 11a and the outer wing portion 11b are formed. The pressure of the hydraulic chamber 8 is increased by being in close contact with the outer surface of the piston 4 and the inner surface of the receiving groove 1a to block the flow of oil. As the pressure in the hydraulic chamber 8 rises, the deformation of the inner and outer blade portions 11a and 11b also increases, and the adhesion force also increases.

However, as shown in FIG. 2C, even when the piston 4 is retracted, the deformation state of the sealing member 11 is maintained by the hydraulic pressure so that the inner blade portion 11a blocks the communication hole 9 so as to return the oil. It happens when you block it. Accordingly, there is a problem that the piston (3) causes the operation (Lost travel) to retreat irrelevantly a predetermined section, and delay the release of braking. This phenomenon is exacerbated when the temperature of the oil rises in the summer and the pressure in the hydraulic chamber 8 increases.

One aspect of the present invention is to provide a master cylinder piston and a master cylinder having the same to ensure that the communication hole of the piston and the oil tank side flow in rapid communication when the brake is released to minimize the meaningless retraction and braking release delay of the piston will be.

The master cylinder piston according to the spirit of the present invention is a piston for a master cylinder including at least one piston installed inside the cylinder body, the piston having a groove to reduce the overall length, and the inner side of the piston A plurality of communication flow paths formed to communicate the inside and the outside outside, and the communication flow path is characterized in that it comprises a stepped communication flow path is expanded diameter so as to shorten the passage time of oil.

One step of the piston is formed between the first groove and the second slope and the first slope and the second inclined surface of the piston groove is formed in the communication groove is formed on both sides of the piston groove, the inclined surface on both sides of the piston groove A communication flow path, a step outside communication hole extending stepwise to the oil port side in the step communication flow path, and a step inside communication hole formed to face the step outside communication hole, and the step communication flow path has a large flow rate of oil passing therethrough. The stepped outer communication hole is characterized in that the diameter is expanded than the other outer communication hole to be formed.

On the other hand, the master cylinder according to the spirit of the present invention, a cylinder body having an oil port and a hydraulic chamber, at least one piston for retreating from the bore of the cylinder body to raise the pressure in the hydraulic chamber, and the cylinder body and A sealing member for selectively blocking the flow of oil between the pistons, a plurality of communication passages for communicating the oil port and the hydraulic chamber in the pistons, and a step having an expanded diameter so as to shorten the passage time of the oil in the communication passages; Characterized in that the communication flow path is included.

The sealing member includes an outer wing portion in contact with the cylinder body and an inner wing portion in contact with the outer surface of the piston, and a deformation surface generated by deformation in the master cylinder is generated on the outer circumferential surface of the inner wing portion. The surface includes a strain plane start point and a strain plane end point, and the plurality of communication passages include an outer communication hole and an inner communication hole, and the plurality of outer communication holes have stepped outer communication holes formed larger than other outer communication holes in diameter. The first step is formed in the rear side of the master cylinder, the second side is formed in the front side of the master cylinder, the first port is in communication with the oil in the step outside communication hole It characterized in that the circumference of the deformation surface and the circumference of the step outer communication hole so as to be spaced apart.

The piston for the master cylinder according to the present invention and the master cylinder having the same change the shape of the communication hole so that the pressure of the hydraulic chamber can be effectively discharged through the communication holes when the brake is released, thereby reducing the adhesion between the sealing member and the piston to communicate. By facilitating the opening of the ball, there is an effect that the braking release is performed quickly.

Accordingly, the insignificant retraction operation and the brake release delay of the piston are minimized.

In addition, the piston for the master cylinder and the master cylinder having the same according to the present invention has the effect of preventing the brake lock phenomenon because the oil in the hydraulic chamber can communicate with the oil port when the sealing member is deformed when the brake is released. There is.

In addition, the piston for the master cylinder and the master cylinder having the same according to the present invention is provided with a space formed in the step communication passage further stepped, so that the diameter of the step communication outer communication hole is larger than the other communication flow path, the hydraulic chambers and oil ports A large amount of oil passes between them, the passage time of the oil is short, and the oil can move in the shortest distance.

1 is a cross-sectional view showing a conventional master cylinder.
FIG. 2A is an enlarged cross-sectional view of part A of FIG. 1.
FIG. 2B is a cross-sectional view corresponding to FIG. 2A, illustrating the advanced state of the piston. FIG.
FIG. 2C is a cross-sectional view corresponding to FIG. 2A, illustrating a retracted state of the piston. FIG.
3 is a cross-sectional view showing a master cylinder piston and a master cylinder having the same according to an embodiment of the present invention.
4A is an enlarged cross-sectional view of part B of FIG. 3.
FIG. 4B is a cross-sectional view corresponding to FIG. 4A, illustrating the advanced state of the piston. FIG.
4C is a cross-sectional view corresponding to FIG. 4A, illustrating a retracted state of the piston.
5 is a perspective view of a piston according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings a preferred embodiment according to the present invention will be described in detail.

The piston for the master cylinder according to the present invention and the master cylinder having the same are coupled to the upper end of the master cylinder by coupling with the cylinder body 20 and the cylinder body 20, the bore 21 is formed as shown in FIG. The oil tank 60, the first and second pistons 30 and 40 installed in the bore 21 of the cylinder body 20 so as to be retracted, respectively, and the inner side and the first and the first body of the cylinder body 20. It comprises a sealing member 51 for sealing the outside of the two pistons (30, 40).

As shown in FIG. 3, the cylinder body 20 includes a first hydraulic chamber 23, a second piston 40, and a bore 21 formed between the first piston 30 and the second piston 40. The second hydraulic chamber 24 is formed between the inner surface of the terminal.

First and second oil ports 27 and 28 connected to the oil tank 60 are provided at an upper portion of the cylinder body 20, and the oil ports 27 and 28 are provided to the first and second oil ports. 27 and 28 communicate with the first and second hydraulic chambers 23 and 24, respectively. To this end, the first and second oil ports 27 and 28 are formed between the sealing member 51 and the packing member 52. In addition, the first and second pistons 30 and 40 have inner surfaces such that oil flowing through the first and second oil ports 27 and 28 can flow into the first and second hydraulic chambers 23 and 24. A plurality of communication passages 81 communicating with the outer surface are formed.

Inside the cylinder body 20, the first and second hydraulic chambers 23 and 24 are pressurized by the first and second pistons 30 and 40, respectively. The first oil outlet 25 is formed at the first hydraulic chamber 23 so that the oil is discharged, and the second oil outlet 26 is formed at the second hydraulic chamber 24. The oil in the first and second hydraulic chambers 23 and 24 is discharged to the first and second oil outlets 25 and 26 and supplied to a wheel cylinder (not shown) on the wheel side.

As shown in FIGS. 3 to 5, the first and second pistons 30 and 40 are installed in the bore 21 to generate braking hydraulic pressure in the first and second hydraulic chambers 23 and 24. do. The first piston 30 and the second piston 40 are connected in series with a predetermined distance apart.

The first and second pistons 30 and 40 advance and retreat inside the bore 21 of the cylinder body 20. Accordingly, the first and second pistons 30 and 40 advance the inside of the bore 21 of the cylinder body 20 and increase the pressure of the first and second hydraulic chambers 23 and 24 at the time of braking. Form. The first and second pistons 30 and 40 may be installed at least one in order to reduce the overall length.

As shown in FIGS. 3 and 4B, the sealing member 51 and the packing member 52 are disposed between the inner circumferential surface of the bore 21 of the cylinder body 20 and the outer circumferential surfaces of the first and second pistons 30 and 40. To prevent the leakage of oil and to create a high pressure hydraulic pressure. Each of the sealing member 51 and the packing member 52 is installed in the receiving groove 22 formed on the inner surface of the bore 21 so as not to move even when the first and second pistons 30 and 40 move forward and backward.

3 and 4b, the first chamfer 22a, the second chamfer 22b, and the third chamfer 22 are disposed at the lower end of the accommodation groove 22 so as to alleviate stress concentration. 22c) is formed. The first chamfer 22a is disposed in the front lower accommodating groove 22 of the master cylinder, and the second chamfer 22b is disposed in the rear lower accommodating groove 22 of the master cylinder, respectively. The third chamfer 22c is disposed in the rear upper receiving groove 22 of the master cylinder. The chamfer of the accommodation groove 22 may also be formed in the front upper end of the master cylinder.

As shown in FIGS. 3 and 4B, the sealing member 51 has an inner wing portion 53 in contact with the outer surfaces of the first and second pistons 30 and 40 and an outer wing portion in contact with the inner surface of the receiving groove 22. It has 54 and has a cup-shaped cross-sectional structure. By such a configuration, the internal space of the bore 21 is defined between the first hydraulic chamber 23 between the first piston 30 and the second piston 40 and the distal inner surface of the second piston 40 and the bore 21. Is divided into a second hydraulic chamber 24.

At this time, the sealing member 51 selectively blocks the flow of oil through the communication holes 82 and 83 which will be described later in accordance with the advancing and retracting operations of the first and second pistons 30 and 40, whereby the first and second pistons The hydraulic pressure in the second hydraulic chambers 23 and 24 rises.

When the hydraulic pressure of the first and second hydraulic chambers 23 and 24 rises as described above, as shown in FIG. 4C, the cross-sectional structure of the sealing member 51 is deformed. For example, when the first piston 30 and the second piston 40 move forward, the sealing member 51 acts on the pressures of the first and second hydraulic chambers 23 and 24 on the inner surface thereof. This pressure acts on the outer surface of the sealing member 51 and the first and second pistons 30 and 40 and the inner surface of the receiving groove 22. When the pressure is applied in this way, the cross section of the sealing member 51 is deformed.

Therefore, the sealing member 51 is the lower chamfered portion 55 of the outer peripheral surface 56 of the inner blade portion is deformed into a round deformation surface 57. The deformation surface 57 is formed at the lower end of the outer circumferential surface 56 of the inner blade portion and is divided into the deformation surface starting point 58 and the deformation surface end point 58.

The first and second restoration springs 71 and 72 are for restoring the first and second pistons 30 and 40 after the braking operation is completed in the first hydraulic chamber 23 and the second hydraulic chamber 24. . In addition, the first and second pistons 30 and 40 have spring receiving grooves 31 and 41 in front so that the first and second restoring springs 71 and 72 can enter each of them in order to reduce the electric field. Is formed. Therefore, the first and second pistons 30 and 40 are not provided with the first and second restoration springs 71 and 72 on the outer side of the first and second pistons 30 and 40, and the first and second pistons ( Since it is installed inside the 30, 40, the overall length can be reduced.

In addition, the support parts 32 and 42 are provided inside the first and second pistons 30 and 40 so that the retainers 33 and 43 described later are installed. Each of the supporting parts 32 and 42 is fitted such that the retainers 33 and 43 supporting the first and second restoring springs 71 and 72 are retractable. Reference numerals 35 and 45 represent steprings 35 and 45 fitted to the support parts 32 and 42 to prevent the retainers 33 and 43 from being separated. As a result, one end of the first and second restoring springs 71 and 72 is supported inside the spring receiving grooves 31 and 41 and the other end of the flanged ends 34 and 44 of the respective retainers 33 and 43. Is supported.

On the other hand, Figure 3 is a cross-sectional view showing a master cylinder piston and a master cylinder having the same according to an embodiment of the present invention. 4A is an enlarged cross-sectional view of part B of FIG. 3, and FIG. 4B is a cross-sectional view corresponding to FIG. 4A, showing a forward state of the piston, and FIG. 4C is a cross-sectional view corresponding to FIG. 4A, showing a retracted state of the piston. Indicates. 5 is a perspective view of a piston according to an embodiment of the present invention.

As shown in FIGS. 3 to 5, the piston grooves 80 are included in the first and second pistons 30 and 40 to act as the sealing member 51 and the first and second pistons 30 and 40. This helps to move the oil flowing in and out of the first and second hydraulic chamber (23, 24). The piston groove 80 is in the form of a groove recessed in the outer circumferential surfaces of the first and second pistons 30 and 40. In detail, the piston groove 80 includes a first inclined surface 84 and a second inclined surface 85. The first inclined plane 84 and the second inclined plane 85 are formed to be inclined at a predetermined angle, and the angle of the second inclined plane is formed to be gentler than that of the first inclined plane. The second inclined surface 85 comes into contact with the outer circumferential surface 56 of the inner blade portion of the sealing member 51 when the first and second pistons 30 and 40 are advanced.

4 and 5, hydraulic chambers 23 and 24 and oil ports 27 and 28 are disposed between the first inclined surface 84 and the second inclined surface 85 of the piston groove 80. A plurality of communication passages 81 are further included to communicate with each other. The upper ends of the communication passages 81 include an outer communication hole 82, and the lower end of the communication passages 81 include an inner communication hole 83. The diameter of the outer communication hole 82 and the inner communication hole 83 is formed the same. Therefore, the piston for the master cylinder and the master cylinder having the same according to the present invention includes a communication passage 81 having an outer communication hole 82 and an inner communication hole 83 to allow oil to communicate with the hydraulic chambers ( 23 and 24 and oil ports 27 and 28 may be in communication.

As shown in FIGS. 4C and 5, the communication path 81 has a step communication path 90 formed by extending a step toward the first and second oil ports 27 and 28, unlike the other communication path 81. ) Is included. The step communication passage 90 is spaced apart from each other with the communication passage 81 on both sides. The step communication passage 90 includes a step part 97, and the step part 97 has a horizontal step surface 97a and a vertical step surface 97b. The horizontal step surface 97a extends horizontally to the rear side of the master cylinder. The vertical step surface 97b vertically extends in the direction in which the master cylinder first and second oil ports 27 and 28 are installed.

Accordingly, the piston for the master cylinder and the master cylinder having the same according to the present invention have a stepped portion 97 in which the stepped outer communication hole 91 is stepped so that the diameter of the oil ports 27 and the other outer communication holes 82 is increased. Since it expands to the side 28, a large amount of oil can pass between the first and second hydraulic chambers 23 and 24 and the oil ports 27 and 28.

In addition, since the master cylinder according to the present invention and the master cylinder having the same extend in diameter toward the oil ports 27 and 28 than other outer communication holes 82, the oil is connected to the hydraulic chambers 23 and 24 and the oil port. It is possible to move the shortest distance between the fields 27 and 28, thereby shortening the passage time of the oil.

As shown in FIG. 5, the diameters of the stepped outer communication holes 91 and the inner communication holes 92 included in the step communication passage 90 are larger than those of the other outer communication holes 82. This is to prevent the case in which the outer communication hole 82 is closed when the sealing member 51 is deformed.

As shown in FIG. 4C, the first port 95 and the second port 96 are formed in the step-outside communication hole 91 to allow oil to flow in and out. The first port 95 is formed on the rear side with respect to the deformation surface time point 58. The second port 96 is formed on the front side with respect to the deformation surface time point 58. The formation space of the first port 95 and the second port 96 may be generated or disappeared as the first and second pistons 30 and 40 move forward or backward. In addition, the first port 95 is formed so that the circumference of the deformation surface time point 58 and the stepped outer communication hole 91 so that oil can communicate. That is, the deformation surface 57 may be spaced apart from the horizontal step surface 97a and the vertical step surface 97b so that oil in the hydraulic chambers 23 and 24 may communicate with the oil ports 27 and 28. .

For example, when the first and second pistons 30 and 40 advance, the space of the first port 95 is reduced and the space of the second port 96 is enlarged. Finally, when the first and second pistons 30 and 40 are advanced, the space of the first port 95 disappears and only the space of the second port 96 remains. On the other hand, when the first and second pistons 30 and 40 retreat, the space of the first port 95 is enlarged and the space of the second port 96 is reduced.

Hereinafter will be described the operation and operation effects of the master cylinder piston and the master cylinder having the same configured as described above.

When the first piston 30 is pressurized by the braking operation, as shown in FIGS. 3 to 4B, as the first piston 30 moves forward, the first hydraulic chamber 23 is pressed, and the first hydraulic chamber 23 is pressed. Is pressed, the second piston 40 is pushed forward by this pressure. As a result, the second hydraulic chamber 24 is pressurized. At this time, the sealing member 51 blocks the communication between the first and second hydraulic chambers 23 and 24 and the first and second oil ports 27 and 28, and thus the first and second hydraulic chambers 23 24, the pressure rises. The oil in the first and second hydraulic chambers 23 and 24 is supplied to a wheel cylinder (not shown) on the wheel side through the first and second oil discharge ports 25 and 26 to brake.

3 and 4C, the first and second pistons 30 and 40 are pushed backward by the restoring force of the first and second restoring springs 71 and 72 when the brake is released. The second pistons 30 and 40 return to their original states. As the first and second pistons 30 and 40 retreat, a first port 95 is created between the outer circumferential surface 56 of the inner wing portion of the sealing member 51 and the circumference of the step outer communication hole 91. The oil in the first and second hydraulic chambers 23 and 24 communicates with the first and second oil ports 27 and 28 through the first port 95, so that the brake is released quickly.

3 to 5, the master cylinder according to the present invention has a first port (when the brake is released, that is, when the first and second pistons 30 and 40 finally retreat). 95) space should be created. This is because the high pressure oil generated by the pressure generated in the first and second hydraulic chambers 23 and 24 of the master cylinder during normal and abnormal braking should return to the oil tank 60 after braking, otherwise the brake is locked. This happens. This keeps the brakes in a locked state, which cannot guarantee driver safety and shorten the life of the vehicle components.

In order to prevent such a brake lock phenomenon, the master cylinder according to the present invention includes the first and second hydraulic chambers 23 and 24 and the first and second oil when the sealing member 51 is deformed when the brake is released. A configuration is provided in which the ports 27 and 28 can communicate at the shortest distance. That is, the step communication passage 90 is provided to be stepwise extended to the first and second oil ports 27 and 28. In addition, the step communication path 90 is formed with a step outside communication hole 91 having a larger diameter than the other communication paths 81. The step outside communication hole 91 may form the first port 95 between the deformation surface time point 58 of the sealing member 51 when the brake is in a released state.

Accordingly, the master cylinder piston and the master cylinder having the same according to the present invention provide a step communication passage 90 formed stepwise toward the first and second oil ports 27 and 28 to release the first and second brakes. The high pressure oil formed by the pressures in the hydraulic chambers 23 and 24 is effectively discharged through the step communication passage 90.

In addition, the master cylinder piston and the master cylinder having the same according to the present invention includes a stepped outer communication hole 91 having a diameter larger than the other outer communication hole 82, so that when the brake is in the released state of the sealing member 51 Since the first port 95 is formed between the deformed surface points 58, the braking is quickly released.

In addition, in the master cylinder according to the present invention, when the brake member is released, the oil in the first and second hydraulic chambers 23 and 24 is changed to the first and second oil ports 27 when the sealing member 51 is deformed. And 28), the brake lock phenomenon can be prevented.

Accordingly, the meaningless retraction and braking release delay of the pistons 30 and 40 are minimized.

In addition, the master cylinder according to the present invention is provided with a step portion 97 formed to be stepped in addition to the step communication passage, the diameter of the step outside communication hole 91 is formed larger than the other outside communication hole 82, the hydraulic chamber A large amount of oil passes between the fields 23 and 24 and the oil ports 27 and 28, the passage time of the oil is short, and the oil can move in the shortest distance.

20: cylinder body 21: bore
22: receiving groove 23: the first hydraulic chamber
24: 2nd hydraulic chamber 27: 1st oil port
28: 2nd oil pot 30: 1st piston
40: second piston 51: sealing member
52: packing member 53: inner blade portion
54: outer wing portion 56: outer peripheral surface of the inner wing portion
57: deformation surface 58: deformation surface viewpoint
59: end face of deformation surface 80: piston groove
81: communication flow path 82: outside communication hole
83: inside communication hole 90: step communication flow path
91: step outside communication hole 92: step inside communication hole
95: first port 96: second port
97: stepped part 97a: horizontal stepped surface
97b: vertical step surface

Claims

In the piston for the master cylinder comprising at least one piston installed inside the cylinder body,
The piston having a groove formed so as to reduce the overall length;
A plurality of communication passages formed to communicate the inner inner side and the outer outer side of the piston,
The communication cylinder piston is a master cylinder piston, characterized in that the stepped communication passage is expanded diameter so that the passage time of the oil is shortened.

The method of claim 1,
A piston groove in which the communication flow path is formed at one outer peripheral surface of the piston;
A first communicating surface and a second inclined surface having inclined surfaces formed on both sides of the piston groove, and the step communication passage provided between the first inclined surface and the second inclined surface;
A stepped outer communication hole extending stepwise to the oil port side in the step communicating flow path, and a stepped inner communication hole formed to face the stepped outer communication hole,
The stepped communication passage is a master cylinder piston, characterized in that for forming the stepped outer communication hole is expanded diameter than the other outer communication hole so as to increase the flow rate of the oil passing through.

A cylinder body having an oil port and a hydraulic chamber,
At least one piston that retracts from the bore of the cylinder body and raises and lowers the pressure in the hydraulic chamber;
Sealing member for selectively blocking the flow of oil between the cylinder body and the piston,
A plurality of communication passages for communicating the oil port and the hydraulic chamber in the piston;
The communication cylinder has a master cylinder characterized in that it comprises a stepped communication passage is expanded diameter so that the passage time of the oil is shortened.

The method of claim 3,
A piston groove in which the communication flow path is formed at one outer peripheral surface of the piston;
A first communicating surface and a second inclined surface having inclined surfaces formed on both sides of the piston groove, and the step communication passage provided between the first inclined surface and the second inclined surface;
A stepped outer communication hole extending stepwise to the oil port side in the step communicating flow path, and a stepped inner communication hole formed to face the stepped outer communication hole,
And the stepped outer communication hole is formed in the stepped communication path, the stepped outer communication hole having a diameter larger than that of the other outer communication holes so as to increase the flow rate of the oil passing therethrough.

The method of claim 3,
The sealing member includes an outer wing portion in contact with the cylinder body, and an inner wing portion in contact with the outer surface of the piston,
The outer circumferential surface of the inner blade portion is generated by the deformation surface generated by the pressure in the master cylinder, the deformation surface includes a deformation surface start point and the deformation surface end point,
The plurality of communication passages include an outer communication hole and an inner communication hole,
The plurality of outer communication holes include a stepped outer communication hole formed larger than the other outer communication holes in diameter,
In the stepped outer communication hole, a first port is formed at the rear side of the master cylinder based on the point of time of the deformation surface, and a second port is formed at the front side of the master cylinder.
The first port is a master cylinder, characterized in that the circumference of the step surface and the outer circumferential communication hole spaced apart so that oil can communicate.