JP2002059821A - Master cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conventional master cylinder having good durability, by effectively preventing localized and concentrated damages from being produced, and by intending to extend the life of a seal long. SOLUTION: The inside diameter of the base part 30 of a cup seal 8 is sized so as to form an air gap s1 between the cup seal and the periphery of the shaft part 5a of a piston 5 to be engaged with it, and plural airfoil planes 33 leaning to the axial straight line of the cup seal 8 along its circumferential direction are formed on the back side of the base part 30, as an auxiliary part to induce the rotation of the cup seal 8 relative to a cylinder body 2 or to expedite the rotational allowance of the cup seal 8 by reducing the contact pressure of the piston 5 with the cup seal 8, in keeping with an action to release a hydraulic pressure in a hydraulic pressure generating chamber 7. The back of the base part is inclined so that its internal end side goes away from the flange part 5b of the piston 5, and a shallow ring-shaped groove is also provided on the back of the base part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a brake system for a vehicle or the like, and in particular, a brake system including an anti-skid hydraulic pressure control (ABS) device including a pump for pressurizing and recirculating hydraulic fluid on a wheel cylinder side. The present invention relates to a conventional type master cylinder, which is suitable for:

[0002]

BACKGROUND OF THE INVENTION Conventionally, as one type of master cylinder, a cylinder body having a cylinder hole and a relief port having an opening in an inner peripheral wall of the cylinder hole and connected to a hydraulic fluid reservoir, A piston that is inserted therein to partition a hydraulic pressure generation chamber therein, a base portion whose rear surface is supported by a flange portion of the piston, and an inner peripheral wall of the cylinder hole extending from the front surface toward the hydraulic pressure generation chamber side; An annular cup seal having an outer lip portion slidingly contacting the relief port, wherein the outer lip portion passes through the opening of the relief port in response to the movement of the piston toward the hydraulic pressure generation chamber, thereby forming the relief port. There is well known a so-called conventional type in which communication between the hydraulic pressure generating chamber and the hydraulic fluid reservoir via the hydraulic pressure generating chamber is interrupted. (For example, Japanese Utility Model Publication No. 62-32127,
(See Japanese Utility Model Publication No. 8-8931)

The conventional type master cylinder is structurally simpler than the center valve type master cylinder, but has a disadvantage that the cup seal is easily damaged.

That is, in the conventional master cylinder, when the outer periphery of the outer lip portion or the base portion of the cup seal is in contact with the opening of the relief port at the time of operation, the cup seal is moved toward the hydraulic pressure generating chamber. It has been found that when a high pressure is applied to the cup seal, the outer periphery of the cup seal is locally pushed into the relief port. If such a phenomenon occurs repeatedly, particularly at the same location on the outer periphery of the cup seal, the cup seal suffers damage, such as "bitting", in which a portion of the outer circumference is picked up. It has also been found that this leads to poor sealing.

The above-mentioned damage to the cup seal may be caused by a brake system provided with an anti-skid control device (ABS device) including a pump that pressurizes and returns hydraulic fluid from the wheel cylinder side to the master cylinder side (this system). For example, in JP-A-8-150915), when the ABS device is operated, the cup seal receives a pulsating hydraulic pressure from the pump,
Regardless of the operation of the S device, it tends to be remarkable when the hydraulic pressure in the hydraulic pressure generation chamber rises sharply with the sudden operation of the master cylinder itself.

[0006]

From the above background, as a measure to prevent damage to the cup seal,
It has been considered to rotate the cup seal relative to the cylinder hole so that the same location on the outer periphery of the cup seal is not repeatedly pushed into the opening of the relief port. And
In order to relatively rotate the cup seal, it has been proposed to form a plurality of grooves extending obliquely with respect to the axis on the outer periphery of the cup seal, as viewed in the circumferential direction.

However, when a plurality of grooves are formed on the outer periphery of the cup seal as described above, when a high pressure in the hydraulic pressure generating chamber acts on the cup seal in a state where a part of the groove is over the opening of the relief port, The difference in stress between the outside and inside of the groove occurs at the border of the groove, which increases the deformation that enters the relief port and causes damage to the outer periphery of the cup seal. found.

In view of the above, the present invention has an object to effectively prevent local concentrated damage to a cup seal and extend the life of the seal, and to provide a durable conventional type master. It is intended to provide a cylinder.

[0009]

According to the present invention, in order to achieve the above object, a gap is formed between the inner diameter of the base portion and the outer periphery of the shaft portion of the piston fitted to the cup seal in the master cylinder. The cup seal is rotated with respect to the cylinder main body in accordance with an operation of releasing the hydraulic pressure of the hydraulic pressure generation chamber to a portion other than the outer peripheral portion of the base portion and the outer lip portion, in addition to the size formed. Or an auxiliary part for reducing the contact pressure between the piston and the cup seal and promoting the permissible rotation of the cup seal is formed.

Specifically, as an auxiliary part for inducing the rotation of the cup seal, a wing-shaped surface which is inclined with respect to the axis straight line of the cup seal along the circumferential direction is provided on the back side of the base part. A plurality of recesses or a plurality of recesses having a sloping surface curved or inclined so as to gradually move away from the outer periphery of the shaft portion of the piston along the circumferential direction in the inner peripheral portion of the base portion are provided. I do. In addition, as an auxiliary part for promoting rotation permission, a back surface of the base portion is formed by inclining so that an inner end side thereof is more distant from a flange portion of the piston than an outer end side, or a back surface of the base portion. In addition, a shallow annular groove whose opening is opposed to the flange portion of the piston at a position near the inner end side is provided.

By doing so, the outer lip portion is bent radially inward with respect to the inner peripheral wall of the cylinder hole when the piston returns, without forming any plurality of grooves on the outer periphery of the cup seal. The working force due to the flow of the hydraulic fluid supplied from the back side (the hydraulic fluid reservoir side) of the cup seal toward the hydraulic pressure generating chamber acts to urge the cup seal in the circumferential direction via the auxiliary portion. As a result, relative rotation between the cup seal and the cylinder hole occurs. And
The rotation occurs each time the operation and release of the master cylinder are repeated, and the portion of the outer periphery of the cup seal facing the opening of the relief port changes sequentially.

It is of course possible to form a composite of the above-described specific auxiliary portion so as to have both functions of rotation induction and rotation permission promotion.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a master cylinder according to a first embodiment of the present invention. The master cylinder 1 according to the present embodiment has a primary piston 4 and a secondary piston 5 (hereinafter, referred to as cylinders 3) in a cylinder hole 3 of the cylinder body 2.
These are simply referred to as pistons. ) Is movably inserted into two hydraulic pressure generating chambers 6 and 7, and a tandem brake master in which brake hydraulic pressure is supplied from each of the hydraulic pressure generating chambers 6 and 7 to a wheel cylinder (not shown). Configured as a cylinder.

Annular cup seals 8, 9, 10 and 11 made of a rubber material are mounted on the outer periphery of the pistons 4 and 5, and one hydraulic pressure generating chamber 6 is provided between the pistons 4 and 5.
The other hydraulic pressure generating chambers 7 are defined between the piston 5 and the bottom 3a of the cylinder hole 3, respectively. Each hydraulic pressure generation chamber 6, 7
Is inside of a hydraulic fluid reservoir (only nipples 16 and 17 are shown) connected to bosses 14 and 15 of cylinder body 2 via relief ports 12 and 13 respectively when the illustrated master cylinder is not operated. However, when a brake operation is performed by depressing a brake pedal (not shown), the pistons 4 and 5 move to the left in the figure, and slide in contact with the inner peripheral wall of the cylinder hole 3. The outer lip of the relief port 12
By passing through the opening 13, the fluid communication between the hydraulic pressure generating chambers 6 and 7 and the hydraulic fluid reservoir is shut off. Then, by the further movement of each piston 4, 5, each hydraulic pressure generating chamber 6,
At 7, brake fluid pressure is generated.

In the present embodiment, an anti-skid hydraulic pressure control device (ABS device) is provided between the master cylinder 1 and the wheel cylinder, although not shown, as a brake system. Like
When the ABS device is actuated to prevent the wheels from being locked, the pump included in the ABS device releases the hydraulic fluid discharged from the wheel cylinder by releasing the pressure from the wheel cylinder and returns the hydraulic fluid to the hydraulic pressure generating chambers 6 and 7. It has become.

The hydraulic pressure generating chambers 6 and 7 have springs 18 and 19 respectively.
When the depression operation of the brake pedal is released or weakened, the biasing forces of the springs 18 and 19 move the pistons 4 and 5 toward the inoperative position shown in the drawing. When the hydraulic pressure in the hydraulic pressure generating chambers 6 and 7 temporarily becomes lower than the atmospheric pressure (pressure on the side of the hydraulic fluid reservoir) due to the return operation of the pistons 4 and 5, a cup difference is generated. The outer lip portions of the seals 8 and 10 are
Replenishment chambers 22 and 23 on the outer periphery of the body of the pistons 4 and 5 which are tilted (bent) radially inward away from the inner peripheral wall of the pistons 4 and 5 and always communicate with the hydraulic fluid reservoir via the supply holes 20 and 21.
The hydraulic fluid is supplied to the hydraulic pressure generating chambers 6 and 7 from the hydraulic pressure generating chambers 6 and 7.

Next, the cup seals 8 and 1 according to the present invention will be described.
The details of 0 will be described by taking one cup seal 8 as an example. The configuration and operation of the cup seal 10 are the same as those of the cup seal 8, and a description thereof will be omitted.

FIG. 2 is an enlarged sectional view of the cup seal 8 mounted on the piston 5 and incorporated in the cylinder body 2 (a part of the configuration is not shown). The illustrated state is a state in which no hydraulic pressure is generated in the hydraulic pressure generation chamber 7. The dashed line indicates the free state of the cup seal 8 before being assembled.

The cup seal 8 includes an outer lip portion 31 extending toward the hydraulic pressure generating chamber 7, an inner lip portion 32 also extending toward the hydraulic pressure generating chamber 7, and the outer lip portion 31 and the inner lip portion. Base unit 30 for communicating with 32
Are integrally formed.

The outer peripheral surface of the outer lip portion 31 is
A first inclined surface 31a continuously inclined from the outer peripheral surface toward the radially outward side, and a second inclined surface 31b formed to be bent radially inward from the first inclined surface 31a. In the assembled state shown in the figure, the outer lip portion 31 is elastically deformed radially inward, and the first inclined surface 31a is formed.
And the second inclined surface 31b are in the strongest elastic contact with the inner peripheral wall of the cylinder hole 3.

The inner diameter of the base portion 30 is larger than the diameter of the shaft portion 5a of the piston 5, and the inner peripheral surface 30b of the base portion 30 has a clearance s1 (for example, 0.
(Approximately 1 to 0.2 mm).

The inner peripheral surface 32a of the inner lip portion 32 is formed so as to be bent radially inward from the inner peripheral surface 30b of the base portion 30. In the assembled state shown in the drawing, the inner lip portion 32 It is elastically deformed outward and is in elastic contact with the outer peripheral surface of the shaft portion 5a of the piston 5 at the distal end side of the inner peripheral surface 32a.

FIG. 3 is a rear view of the cup seal 8, and FIG. 4 is a perspective view seen from the rear side. As shown in these figures, the cup seal 8 has an annular surface 30a formed on the rear end side of the base portion 30 at the outer end thereof, and further, on the radially inner side of the annular surface 30a, The wing-like surface 33 which inclines toward the front side of the base portion 30 when viewed around,
A plurality (eight) of auxiliary portions are formed along the circumferential direction and are connected to each other by a step portion as auxiliary portions for inducing rotation of the cup seal 8. Each wing-shaped surface 33 is formed so as to be depressed by about 1/8 to 1/6 with respect to the thickness of the base portion 30 in the axial direction. Further, as shown in FIG. As an auxiliary part for promoting the permissible rotation of the cup seal 8, the inner end side is formed to be inclined so as to be farther from the flange part 5b of the piston 5 than the outer end side. For this reason, in a non-operation state in which the hydraulic pressure generating chamber 7 is at the atmospheric pressure, a gap s is formed between the entire back surface of the base portion 30 including the wing-shaped surface 33 and the flange portion 5b of the piston 5 as shown in FIG.
2, the rear surface of the base portion 30 is supported by the flange portion 5b of the piston 5 only at the outer edge of the annular surface 30a.

Therefore, after the above-mentioned brake fluid pressure is generated, when the piston 5 returns (to the right in FIG. 2) with the release of the brake operation, the cup seal is formed due to the pressure difference between the fluid pressure generating chamber 7 and the supply chamber 23. The outer lip 31 of the cylinder 8 is further tilted radially inward away from the inner peripheral wall of the cylinder hole 3, and the hydraulic fluid from the supply chamber 23 flows between the flange 5 b of the piston 5 and the inner peripheral wall of the cylinder hole 3. Gap s3 between
The hydraulic fluid is supplied to the hydraulic pressure generating chamber 7 through the space between the outer lip portion 31 and the inner peripheral wall of the cylinder hole 3. At this time, a part of the hydraulic fluid from the replenishing chamber 23 is tilted by the outer lip portion 31. Flows through the gap between the annular surface 30a on the back surface of the cup seal 8 and the flange 5b of the piston 5 and flows into the wing-like surface 33 side. Then, the flow of the hydraulic fluid acts on each wing-shaped surface 33 to give a rotating power to the cup seal 8.

At this time, the inner peripheral surface 3 of the base 30 is
0b and the outer peripheral surface of the shaft 5a of the piston 5
The gap s2, which has been eliminated by the elastic deformation of the cup seal 8 against the flange portion 5b side due to the generation of the brake fluid pressure, is removed again by the back surface of the base portion 30 and the flange portion 5b of the piston 5. Is defined between
Since the contact area (contact pressure) between the cup seal 8 and the piston 5 is reduced to a small value, the cup seal 8 can easily move the piston 5 by the acting force acting on each wing surface 33 described above.
Rotate relative to the flange portion 5b.

Such rotation of the cup seal 8 occurs at every return operation of the piston 5 in accordance with the repetition of the operation and release of the operation of the master cylinder 1, and the rotation of the relief port 13 on the outer peripheral surface of the outer lip portion 31. The portion facing the opening changes sequentially. Therefore, the outer lip portion 31
Alternatively, the frequency at which the same portion of the outer periphery of the cup seal 8 of the base portion 30 is pushed into the opening of the relief port 13 by the hydraulic pressure in the hydraulic pressure generating chamber 7 during operation of the master cylinder 1 is reduced. It is possible to prevent intensive damage from occurring at the same location.

Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 5A is a side sectional view of the cup seal 35 in the present embodiment (free state before assembly), and FIG.
Shows a rear view of the cup seal 35. In the present embodiment, the cup seal 35 is used in the master cylinder 1 shown in FIG. 1 instead of the cup seals 8 and 10 in the first embodiment. Therefore, the cup seal 35 is
Similar to the description of the first embodiment, the following description will be made assuming that the piston 5 is mounted.

In the cup seals 8 and 10 of the first embodiment, the wing-shaped surface 33 is formed on the back surface of the base portion as an auxiliary portion for inducing rotation. However, in the cup seal 35 of the present embodiment, the base portion is formed. An auxiliary part that induces rotation is formed on the inner peripheral surface of the.

As shown in FIG. 5, the inner peripheral surface of the base portion 36 of the cup seal 35 has a plurality (six) in the circumferential direction.
Recess 37 is formed. 5B, each recess 37 has a sloping surface that curves gradually away from the outer peripheral surface of the shaft portion 5a of the piston 5 when viewed clockwise in FIG. 5B, and a step portion is interposed between the sloping surfaces. Are connected to each other. The minimum inner diameter of the inner peripheral surface of the base portion 36 in which the recess 37 is formed is the same as that of the cup seal 8 described above.
The gap s1 is set so as to be formed between the piston 5 and the outer peripheral surface of the shaft portion 5a.

In this embodiment, as in the first embodiment, when the piston 5 returns, the supply chamber 23
Part of the working fluid from the base portion 36 of the cup seal 35
When the hydraulic fluid flows into the rear side of the, the flow of the hydraulic fluid reaches the recesses 37, acts on the oblique surfaces of the recesses 37, and gives a rotational power to the cup seal 35. And the base part 3
A gap is formed between the inner peripheral surface of the piston 6 and the outer peripheral surface of the shaft portion 5a of the piston 5, and the contact area between the cup seal 35 and the piston 5 is reduced. It easily rotates with respect to the flange portion 5 b of the piston 5, and the relief port 13 on the outer periphery of the cup seal 35.
Are sequentially changed.

Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 6A is a sectional side view of the cup seal 40 in the present embodiment (free state before assembly), and FIG. 6B.
Shows a rear view of the cup seal 40. Also in this embodiment, since the cup seal 40 is used in the master cylinder 1 shown in FIG. 1 instead of the cup seals 8 and 10 in the first embodiment, the cup seal 40 is attached to the piston 5 below. It will be described as.

In the third embodiment, the cup seal 4
The inner diameter of the base portion 41 of 0 is larger than the diameter of the shaft portion 5a of the piston 5 to form a gap between the inner peripheral surface of the base portion 41 and the outer peripheral surface of the shaft portion 5a of the piston 5, and By inclining the base portion rear surface 41c so that the inner end side 41a is farther from the flange portion 5b of the piston 5 than the outer end side 41b, a gap is formed between the base portion rear surface 41c and the flange portion 5b of the piston 5. (A conical shape) to reduce the contact area with the piston 5.

In this embodiment, since the supply hole 21 is provided at one location on the circumference of the supply chamber 23 formed in an annular shape, when the piston 5 returns, the operation of flowing from the supply chamber 23 is performed. The liquid does not always flow uniformly on the base unit back surface 41c side, but in most cases, the liquid flows in a non-uniform manner. As described above, since the contact surface pressure with the piston 5 is reduced and the cup seal 40 is in a state of being easily rotated, the cup seal 40 receives the liquid flow biased toward the base portion back surface 41c.
The whole is rotated such that a portion of the outer periphery thereof facing the opening of the relief port 13 is displaced.

FIG. 7 shows a cup seal 45 according to a fourth embodiment of the present invention. Based on the same idea as in the above-described third embodiment, the contact area with the piston 5 is reduced and the cup seal 45 is formed. To facilitate rotation, an annular groove 47 is formed in the base rear surface 46 at a position near the inner end thereof, and the inner diameter of the base is larger than the diameter of the shaft 5 a of the piston 5. The annular groove 47 is a shallow groove having a depth of about 1/8 to 1/6 of the axial thickness of the base portion.
The effect of reducing the contact area with b has been sufficiently obtained.

In the third and fourth embodiments, the first and second
Although the rotating power of the cup seal is not as large as that of the embodiment, the rotation for changing the position of the outer periphery of the outer lip portion facing the opening of the relief port can be sufficiently performed.

Further, the cup seal in each of the above-described embodiments may be provided with a hardness of 75 to 85 Hs and a 100% modulus of 1%.
0 MPa or more ethylene-propylene copolymer rubber (EP
When formed using DM), deterioration of physical properties over time is suppressed as much as possible, and the hardness and elastic limit are increased, so it is difficult to be pushed into the relief port, or even if pushed, it can be restored Therefore, the cup seal can be more effectively prevented from being damaged, and the durability of the master cylinder itself can be further improved.
Here, the 100% modulus means the tensile stress of the rubber material when stretched by 100% (when stretched to twice the original length).

The cup seal is placed in the axial direction (FIG. 2).
In the case where the cup seal is obtained by injection molding using a mold that is divided in the left-right direction in FIG.
It is placed in a state where the strength is weak and a crack or the like is liable to occur, such as at a high temperature of a degree or higher. Therefore, it is necessary to take care not to generate cracks or the like when the molded cup seal is removed from the mold (especially when the physical properties are high hardness and high modulus). In the shape with multiple skew grooves for rotation provided on the outer circumference,
These oblique grooves hinder release of the cup seal in the axial direction, resulting in poor releasability. However, the cup seal of each of the above embodiments has a shape that does not have a twist with respect to the mold, including a part for obtaining rotation, so that the cup seal has good releasability, The generation of cracks and the like can be prevented without applying excessive force.

In the first, third and fourth embodiments, the back surface of the base is provided with a dent, a groove, an inclined surface, etc., so that the end face of the cup seal does not become a flat surface extending in the direction perpendicular to the axis. Therefore, when the cup seal is conveyed by vibration with a parts feeder or the like in the automatic assembly line, the cup seal is prevented from sticking to the conveying surface, and can be smoothly supplied to the next process, and the automatic assembly is efficiently performed. Can do well.

Although the embodiments of the present invention have been described above, the present invention is, of course, not limited to these embodiments.
Various modifications are possible based on the technical idea of the present invention.

In the first embodiment, the back surface of the base portion is inclined, but only the wing surface 33 may be formed without inclining, and the number of wing surfaces 33 is not limited to eight. ,
For example, there may be four.

The form of the cup seal is not limited to the above embodiments, but may be a combination of the second and third embodiments, or a combination of the second and fourth embodiments.
It is good also as composition which combined embodiment of this.

[0045]

As described above, according to the present invention, by changing the portion of the outer periphery of the cup seal facing the relief port, it is possible to prevent the occurrence of damage at a specific portion of the outer periphery, and to prevent the cup seal from being damaged. The life of the conventional master cylinder can be greatly extended, and a conventional master cylinder having excellent durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a master cylinder according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part in FIG.

FIG. 3 is a rear view of the cup seal according to the first embodiment of the present invention.

FIG. 4 is a perspective view of the same.

FIG. 5A is a side sectional view of a cup seal according to a second embodiment of the present invention, and FIG. 5B is a rear view of the same.

6A is a side sectional view of a cup seal according to a third embodiment of the present invention, and FIG. 6B is a rear view of the same.

7A is a side sectional view of a cup seal according to a fourth embodiment of the present invention, and FIG. 7B is a rear view of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Master cylinder 2 Cylinder main body 3 Cylinder hole 4 (Primary) piston 5 (Secondary) piston 6 Hydraulic pressure generating chamber 7 Hydraulic pressure generating chamber 8 Cup seal 10 Cup seal 12 Relief port 13 Relief port 20 Supply hole 21 Supply hole 22 Supply chamber Reference Signs List 23 supply chamber 30 base portion 33 wing surface 35 cup seal 37 recess 40 cup seal 45 cup seal 47 annular groove

Claims (7)

[Claims] 1. A cylinder body having a cylinder hole and a relief port having an opening in an inner peripheral wall of the cylinder hole and connected to a hydraulic fluid reservoir, a cylinder body movably inserted into the cylinder hole and having a liquid therein. A piston for partitioning the pressure generating chamber, a base portion supported on the rear surface by the flange portion of the piston, and an outer lip portion extending from the front surface toward the hydraulic pressure generating chamber side and slidingly contacting the inner peripheral wall of the cylinder hole. An annular cup seal, wherein the outer lip portion passes through the opening of the relief port in response to the movement of the piston toward the hydraulic pressure generating chamber side, whereby the hydraulic pressure generating chamber through the relief port is provided. A master cylinder that interrupts communication between the piston and the hydraulic fluid reservoir. The cylinder body has a size such that a gap is formed between the cylinder body and the outer periphery of the base portion and the outer lip portion. A master cylinder having an auxiliary portion for inducing rotation of the cup seal or reducing contact pressure between the piston and the cup seal to facilitate rotation of the cup seal. 2. A plurality of wing-like surfaces which incline with respect to the axis straight line of the cup seal along the circumferential direction thereof are formed on the back side of the base part as auxiliary parts for inducing rotation of the cup seal. The master cylinder according to claim 1. 3. The master cylinder according to claim 2, wherein the wing-like surface is provided by depressing a back surface of the base portion so as to face a flange portion of the piston with a gap. 4. An inner peripheral portion of the base portion is provided with a plurality of recesses having a sloping surface that is curved or inclined so as to gradually move away from the outer periphery of the shaft portion of the piston along the circumferential direction. The master cylinder according to claim 1, wherein an auxiliary portion that induces rotation of the cup seal is formed. 5. The cup seal is formed as an auxiliary part for promoting rotation of the cup seal by inclining a back surface of the base portion in advance so that an inner end side thereof is more distant from a flange portion of the piston than an outer end side. The master cylinder according to claim 1, wherein the master cylinder is provided. 6. An auxiliary part for facilitating rotation of the cup seal by providing a shallow annular groove having an opening facing the flange part of the piston at a position near the inner end side on the back surface of the base part. The master cylinder according to any one of claims 1 to 4, wherein: 7. The hardness of the cup seal is 75 to 85H.
ethylene with a 100% modulus of 10 MPa or more in s
The master cylinder according to any one of claims 1 to 6, wherein the master cylinder is formed using propylene copolymer rubber (EPDM).