JP3148157B2 - Center valve structure of master cylinder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a center valve in a master cylinder used for a hydraulic brake or a clutch system of a vehicle or the like, and more particularly, to a method in which a rubber valve material is swollen by contact with a hydraulic fluid. Regarding countermeasure technology.

[0002]

BACKGROUND OF THE INVENTION In this type of master cylinder, a valve for communicating and shutting off between a hydraulic chamber inside a cylinder body and an external hydraulic fluid reservoir is indispensable. As a form of the valve, a conventional type having a valve on the outer periphery of the piston and a center valve type located at the center of the piston are representative. Among them, in the center valve type, a rubber member having a sealing function is hardly damaged.

However, even in such a center valve, when a fluid flow from the hydraulic pressure chamber side to the hydraulic fluid reservoir side occurs with the valve body slightly separated from the valve seat, the tip of the rubber member is attached to the piston. Sucked into the central hole,
The so-called biting phenomenon easily occurs. In a vehicle equipped with an anti-lock brake device, this phenomenon is exacerbated because excess pumping liquid flows into the hydraulic pressure chamber from the pump until immediately before the piston returns to the inoperative position.

Accordingly, the present applicant has proposed a technique for improving the center valve by holding the inner peripheral side of a rubber member having a sealing function by a cylindrical retainer member made of a material having higher rigidity than the rubber. A technique for preventing suction into the center hole at the tip was previously proposed (Japanese Patent Application No. 7-3).
No. 32738). This technique itself can be applied to the case where the rubber ring member is disposed on both the valve body side and the valve seat side. However, from the viewpoint of preventing the biting phenomenon, it is better to arrange the rubber ring member on the valve seat side. This is because the arrangement is less susceptible to the liquid flow that causes the bite.

[0005] However, further investigations have been continued thereafter, and it has been found that the rubber ring member disposed on the valve seat side often suffers from erosion, although it is inherently difficult to produce erosion. The fundamental cause seems to be that the rubber material swells on contact with the hydraulic fluid. This point will be described briefly with reference to FIG. The rubber ring member 98 'located on the valve seat side is restrained from both the inner and outer circumferences and the axial direction to ensure the support. That is, the ring member 98 ′ is connected to the retainer member 9.
The rear end in the axial direction is restrained by a flange 94'f at the rear end of 4 ', the front end is restrained by a cylindrical stopper member 92', and the retainer member 94 'in the radial direction.
And the inner wall of the recess 300 'of the piston 202' is held in a compressed state. Such a ring member 98 ′
Only the inner peripheral portion of the front end where the seat is located is open. The rubber ring member 98 'in this state is in a form shown by a two-dot chain line at the beginning of assembly. However, when it comes into contact with the hydraulic fluid filled in the hydraulic chamber 42 ', it swells and projects forward. In particular, the ring member 9
Because the rear end of 8 'is kept in a shrimp state
It can be considered that the front side serves as a shelter, and the forward projection becomes prominent.

[0006] When the head portion 72'h of the valve body 72 'tries to seat on the projecting portion of the ring member 98', the projecting portion tends to fall inward due to the flow of the hydraulic fluid. . As a result, the valve member 72 'is sandwiched between the head portion 72'h and the retainer member 94' (that is, a biting phenomenon occurs), and the protruding portion 98't of the ring member 98 'is easily damaged. In particular, when the anti-lock brake device is mounted, the ring member 98 'is damaged due to pulsation accompanying the operation of the device, and the damage is accelerated. Further, when the hydraulic pressure inside the hydraulic pressure chamber 42 'increases and a strong liquid flow from the hydraulic pressure chamber 42' to the hydraulic fluid reservoir side occurs, the biting phenomenon is inevitable.

Therefore, the present invention provides a center valve of a master cylinder, in which a rubber ring member having a sealing function is arranged on a valve seat side, and even if the ring member swells, It is an object of the present invention to provide a technique capable of effectively preventing damage caused by us.

[0008]

The center valve structure according to the present invention has the following features. A. The rubber ring member has its inner peripheral side fitted to the outer periphery of the cylindrical retainer member, and the outer peripheral side of the ring member fitted to the inner wall of the recess of the piston, whereby the inner and outer peripheral surfaces are restrained. ing. B. The rubber ring member has its rear end face separated from the hydraulic chamber restricted. C. The rubber ring member includes a seating portion in which the outer peripheral portion of the front end surface near the hydraulic chamber is restrained by the stopper member, and the head portion of the valve body sits on the inner peripheral portion of the front end surface. D. The front end surface of the rubber ring member forms a smooth and continuous surface from the portion constrained by the stopper member to the unrestricted inner peripheral portion.

The features A, B, and C are for securely holding the ring member, and the feature D corresponds to the absence of abnormal projection. In order to more reliably prevent the occurrence of biting, Japanese Patent Application No. 7-3327, which is a prior application of the present applicant, is used.
As described in No. 38, it is preferable that after the head portion of the valve body is seated on the ring member, it is also seated on the retainer member.

The smooth continuous surface in the feature D means a substantially flat surface without a bent portion. These features A to D need only be satisfied at least by the time the piston of the master cylinder operates. For example, a ring member having a small expansion coefficient is selected and the characteristics A to D are always satisfied before filling with the hydraulic fluid. In addition, in consideration of the swelling amount in advance, the rubber ring member before filling is selected. The holding may be provided with a clearance so as to satisfy the characteristics A to D in a state where the working fluid is filled and swollen. However, in order to ensure the original function of the center valve, the rubber ring member should be provided with a sealing function in conjunction with the poppet valve body regardless of before or after swelling or not. .

The present invention can be applied to various master cylinders including a center valve. The master cylinder may be of a clutch type, a brake type, a single type or a tandem type. In particular, the present invention
Take measures against swelling of the ring member by hydraulic fluid,
This is to reliably prevent erosion by the liquid flow.
Therefore, if the present invention is applied to a center valve in which such a liquid flow is more likely to occur, the effect is large. For example, a brake device having an anti-lock brake function is a preferred application of the present invention. Further, the present invention is particularly effective for a configuration in which the end opposite to the side serving as the valve seat is partially supported in a shrunk state. This is because, in such a form, abnormal protrusion is likely to occur on the side serving as the valve seat due to swelling.

[0012]

FIG. 1 is an overall sectional view showing a tandem type brake master cylinder to which the present invention is applied. First, referring to FIG. 1, a specific application point of the present invention will be clarified, and thereafter, an embodiment of the present invention, and further,
The modified example will be described.

The tandem type master cylinder 10 has a primary portion 100 including a conventional type valve and a secondary portion 200 including a center valve along the axial direction. The primary part 100 is for the front wheel brake device and the secondary part 20
0 is for a rear wheel brake device having an anti-lock brake function. Master cylinder 10 includes a cylinder body 14 having a cylinder hole 12 with a uniform inner diameter. The front end 14f of the cylinder body 14 is closed, and a return spring 162 for a secondary piston, a secondary piston 202, a return spring 161 for a primary piston, and a primary piston 201 are sequentially arranged from the closed side. , A push rod (not shown) is arranged.

The primary and secondary pistons 201, 202 have lip seal members 31a, 31b; 32a, 32b at locations separated in the front-rear direction. Each of these lip seal members is connected to the cylinder body 14.
Is sealed between the inner peripheral surface of each of the pistons 201 and 202, whereby the second hydraulic chamber 42 is provided in front of the secondary piston 202, and the first hydraulic chamber 42 is provided between the secondary piston 202 and the primary piston 201. A hydraulic chamber 41 is defined. The primary-side valve 50 and the secondary-side valve 70 are different from the conventional type or the center valve type, but are provided with the first or second hydraulic chambers 41 and 42 and the hydraulic fluid at the upper part of the cylinder body 14. It communicates with and blocks the reservoir 80.

FIG. 2 is an enlarged view of a portion of the secondary side center valve. There is a recess 300 at the end of the secondary piston 202 facing the second hydraulic chamber 42. The recess 300 extends along the axis of the cylinder body 14 and has a substantially uniform inner diameter. The bottom of the recess 300 is
Through the center hole 302 and the guide hole 304 following the center hole 302, and further through the side peripheral hole 306 on the outer periphery of the piston 202, to the inside of the hydraulic fluid reservoir 80. The guide hole 3
Reference numeral 04 denotes a hole for receiving a stopper bolt 308 as a valve opening means, and itself penetrates the piston 202. The stopper bolt 308 is connected to the cylinder body 14
It is fixed to.

Each part of the center valve 70 is
Located in 0. The poppet type valve body 72 includes a head portion 72h and a rod portion 7 extending from the head portion 72h.
2r, the rod portion 72r is fitted in the center hole 302 of the piston 202, and is movable in a direction along the axis. A valve spring 73 is provided on the head portion 72h of the valve body 72,
Is pressed toward the stopper bolt 308. The portion surrounding the opening of the center hole 302 of the piston 202 constitutes a valve seat 90, and the valve body 72 is seated here.

The valve seat 90 includes a rubber ring member 98,
A retainer member 94 for supporting the ring member 98 is mainly used. The inner peripheral side of the ring member 98 is a cylindrical retainer member 9 made of a material (for example, metal) having higher rigidity than rubber.
4 and fit it into the recess 30 of the piston 202.
0 at the bottom. Therefore, the outer peripheral side of the ring member 98 is supported by the inner wall of the recess 300 of the piston 202.
One end of the retainer member 94 has an outward flange 94f, and near the other end is another flange 94e lower than the flange 94f. Recess 98 of ring member 98
e is unevenly coupled to the flange 94e,
It is integrated with the retainer member 94. The ring member 9
The seating portion 8 is at a position inclined by 43 to 45 degrees with respect to the movement axis of the valve body 72 as shown in the figure. Such a range is a preferable angle range based on the structural analysis, and
This is a range in which the inner peripheral portion of the front end face 98y of the ring member 98 can be prevented from falling inward in the radial direction when seated. This range will be described in more detail later.

In this case, the valve seat 90 has a double structure, and the head portion 7 of the valve body 72 is also provided at the tip of the retainer member 94.
2h sits down. The distance from the head 72h of the valve body 72 to the seating portion of the retainer member 94 is slightly longer than the distance from the head 72h of the valve body 72 to the seating portion of the ring member 98. The lengthened portion is smaller than the size of the ring member 98 at which the rubber is deformed. Thus, the valve body 72 is seated on the retainer member 94 after being seated on the ring member 98. Also, the valve element 7
The second head portion 72h has a tapered shape such that a portion facing the retainer member 94 protrudes toward the valve seat 90 more than a portion facing the ring member 98. This tapered shape, together with the seating portion of the retainer member 94, more reliably prevents the ring member 98 from being sucked into the center hole 302.

In the recess 300 of the piston 202,
After assembling the valve seat 90, a cylindrical stopper member 92 is further inserted. The stopper member 92 is provided in the recess 3
00 has an inward flange 92f at the opening end thereof, and the flange portion 92f functions as a spring receiver for the valve spring 73. In addition, the outer peripheral side and the inner peripheral side of the end of the stopper member 92 facing the valve seat 90 are chamfered to reduce the supporting area of the front end face 98y of the ring member 98, and to the front end face 98y of the ring member 98. It does not give too much restraint. This is also effective in preventing abnormal deformation due to swelling of the front end of the ring member 98.
The stopper member 92 itself is prevented from coming off by a C-ring 93.

Incidentally, a rubber member having a sealing function (the ring member 98 in this case) is normally held in a compressed state from the beginning from the viewpoint of preventing displacement and detachment. However, here, as described below, before filling with the hydraulic fluid,
Some clearance is provided. FIG. 3 (or a two-dot chain line in FIG. 2) shows a state of the ring member 98 before filling with the hydraulic fluid. The outer circumference of the retainer member 94 is about 0.2 mm wider than the inner circumference of the ring member 98 in this state.
mm is set small. On the other hand, an end (rear end, second side) 98 of the ring member 98 on the rear side of the concave portion 98e.
2 is bulged radially outward as shown by a chain line before assembling. Accordingly, the flange 9 of the retainer member 94
When the concave portion 4e and the concave portion 98e of the ring member 98 are integrated by a concave and convex connection, and this is arranged in the concave portion 300 of the piston 202, the rear end portion 982 of the ring member 98 is formed by a portion 982a bulging to the outer periphery as an interference. The inner wall of the recess 300 of the piston 202 and the outer periphery of the retainer member 94 are tightly held in a shrinking state. On the other hand, the end (front end, first end) of the ring member 98 on the front side with respect to the concave portion 98e.
Side) 981 does not have a bulge like the rear end portion 982, so that the outer periphery of the retainer member 94 and the recess 3 of the piston 202
A clearance occurs in the radial support of the front end 981 of the ring member 98 by the inner wall of the ring member 98. The stopper member 92 is for supporting the outer peripheral portion of the front end face 98y of the ring member 98, and has a clearance of about 0.5 mm in the same manner as described above before filling with the hydraulic fluid. That is, the end of the stopper member 92 is slightly separated from the front end face 98y of the ring member 98 before filling with the working fluid. The degree of clearance mentioned here can be appropriately adjusted by the expansion rate of the rubber material. In addition, the clearances at each location may be provided independently, or the clearances at a plurality of locations may be provided in combination.

Now, the hydraulic fluid is filled from the hydraulic fluid reservoir 80 into each of the hydraulic chambers 41 and 42 inside the cylinder body 14 of the master cylinder 10. Then, the ring member 98 in contact with the hydraulic fluid undergoes a volume expansion (swelling) of, for example, about 3% over time. In this case, since the rear end of the ring member 98 is in the shrinking state, the front end with the clearance swells preferentially. The swelling is performed in the radial direction and in a direction to eliminate the clearance of the front end face 98y, and finally the state shown by the two-dot chain line in FIG. 3 (or the solid line in FIG. 2) is obtained. The contact is supported. The front end of the retainer member 94 is inclined so as to open from the outside in the radial direction to the inside so as not to restrict the swelling of the front end of the ring member 98 toward the hydraulic chamber. It should be particularly noted here that the front end face 98y of the ring member 98 is
2 swells evenly because it is not restricted by 2. As a result, a smooth continuous surface is formed from the inner peripheral portion to the outer peripheral portion. Therefore, when the head portion 72 of the valve body 72 is seated on the ring member 98, the inner peripheral portion of the front end face 98y of the ring member 98 does not fall down toward the retainer member 94, and the hydraulic fluid reservoir 42 The liquid flow toward the side does not cause the tip to be sucked.

Here, the position where the head part 72 of the valve body 72 is seated on the swollen ring member 98 is, as shown in FIG.
The angle is set to 5 degrees. By setting such an angle, the head portion 72h of the valve body 72, when seated, exerts not only a force acting on the ring member 98 in the direction of the movement axis but also a force acting on the radially outer periphery substantially equivalent thereto. And give it. This acting force is applied to the valve body 7
This is sufficient to prevent the inner peripheral portion of the front end face 98y of the ring member 98 from falling inward in the radial direction when the seat 2 is seated. Such an angle range can be effectively set by, for example, balancing the volume of rubber swelling and the volume of clearance. If the angle is less than 43 degrees, the force in the moving axis direction becomes too large, and the inner peripheral portion of the front end face 98y may fall down inward in the radial direction. When the angle is 45 degrees or less, the characteristics of shutting off and communicating with the center valve 70 are best exhibited. The seating portion 9 of the ring member 98
The angle of the 8x with respect to the valve body 72 depends on the distance from the bottom of the recess 300 of the piston 202, the inclination angle of the end of the retainer member 94 that supports the front end of the ring member 98, and the tapered shape of the head of the valve body. Adjust together.

When the brakes are not operated and the pistons 201 and 202 are in the non-operated position, as shown in FIG. 1, the end of the rod portion 72r hits the stopper bolt 308, and the center valve 70 is opened. ing. On the other hand, with the operation of the brake, first, the primary piston 201 advances, and the lip seal member 31 a on the outer periphery of the primary piston 201 closes the relief port 61 communicating with the hydraulic fluid reservoir 80. Then, the first hydraulic chamber 41
Hydraulic pressure is generated in the secondary piston 20
2 moves forward. Accordingly, the end of the rod portion 72r is separated from the stopper bolt 308, and the valve body 72 is seated on the inner peripheral portion of the front end face 98y of the ring member 98 by the force of the valve spring 73. At this time, the front end surface 98y of the ring member 98 forms a smooth and continuous surface from the inner peripheral portion to the outer peripheral portion, and the valve body 72 is seated at a predetermined angle thereat. Do not fall inside. Therefore, when the valve body 72 is subsequently seated on the retainer member 94, the inner peripheral portion of the front end face 98y of the ring member 98 is not sandwiched between the retainer member 94 and the valve body 72. Therefore, in this state, even if the pulsation is caused by the operation of the antilock brake device, the ring member is not eroded. Also, slight elastic deformation of the ring member 98 toward the inner peripheral side is suppressed by the head portion 72h sitting on the retainer member 94, and is directed toward the outer peripheral side. From this state, when the valve is opened by releasing the brake, even if a strong liquid flow from the hydraulic pressure chamber 42 toward the hydraulic fluid reservoir 80 is generated, the inner peripheral portion of the front end face 98y of the ring member 98 has the center hole of the piston. It is not sucked into 302 or into the gap between the head 72h and the retainer member 94. Further, when the control of the antilock brake device is released, a stronger liquid flow is generated due to the addition of the liquid discharged from the pump.

In the above-described embodiments, the rubber ring member is provided with a seal forming portion at the radially inner peripheral portion at the end near the hydraulic chamber before being assembled to the retainer member. I have. However, as shown in FIG. 4, before assembling to the retainer member 94 (a), the ring member 498 does not have a seal forming part, but by assembling to the retainer member 94, (b) the seal forming part 498 s is formed. It can also be configured to form.

[0025]

[Modified example in which prevention of bite is further ensured] In the above-described embodiments, the outer peripheral shape of the portion near the front end of the retainer member 94 has a smaller outer diameter toward the front facing the hydraulic chamber 42. It has a tapered shape. Such a shape is advantageous in facilitating the assembly of the rubber ring member 98. However, focusing on the outer shape of the retainer member 94, the outer diameter of the portion of the first outer peripheral surface 941 between the front end side and another flange 94e is the second diameter between the outward flange 94f and another flange 94e. Is smaller than the outer diameter of the outer peripheral surface 942. Therefore, there is no major problem in assembling the elastically deformable rubber ring member 98 to the retainer member 94. Therefore, in the example shown in FIG. 6, both the first and second outer peripheral surfaces 941 and 942 of the retainer member 94 are formed substantially parallel to the axis. Thereby, the valve body 7 of the rubber ring member 98 is
The distance between the seating portion 98s for the second member 2 and the seating portion 94s for the valve body 72 of the retainer member 94 can be increased, so that the rubber ring member 98 can be more reliably prevented from being bitten. Two seating portions 94s,
It is preferable that the distance between 98 s is larger than the thickness of the portion of the first outer peripheral surface 941. To do so, the seating portion 94s of the retainer member 94
Should be located as far as possible in the radial direction.

The rubber ring member 98 is obtained by molding, but in order to form the inner peripheral side of the ring member 98,
It is necessary to prepare two molds, one to pull forward and one to pull backward. Therefore, at the stage where the molding has been completed, burrs are formed on the ring member 98 at positions corresponding to the joining portions of the two molds. It is necessary to remove the burrs after molding. Here, in order to facilitate the removal of burrs, the burrs are generated (that is, the joining positions of the two molds).
Is arranged at a specific position as described below. The ring member 98 has a first side 981 that fits into the first outer peripheral surface 941 of the retainer member 94 and a second outer peripheral surface 942 with a recess 98e halfway in the axial direction as a boundary.
And a second side 982 that fits the portion. The inner diameter of the first side 981 is smaller than the inner diameter of the second side 982 and is the smallest among the ring members 98. In order to facilitate the removal of burrs, it is preferable to provide a position where burrs are generated at the portion having the smallest inner diameter (the first side 981). This is because burrs can be removed without damaging other parts. The burr is
If it is disposed too close to the seating portion 98s, it may be damaged during operation. Therefore, the burr generation position should be set to a position closer to the recess 98e than the front end of the seating portion 98s. In addition, the second including the recess 98e
Since the material of the ring member 98 is elastically deformable rubber, the mold that forms the side 982 can be pulled out while forcibly deforming the ring member.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a master cylinder including a center valve according to the present invention.

FIG. 2 is a partially enlarged sectional view of FIG. 1;

FIG. 3 is a partial cross-sectional view showing a state of a valve at the time of assembly.

FIG. 4 is a sectional view showing another embodiment of the present invention.

FIG. 5 is a partial cross-sectional view showing an example of an embodiment of the prior application on which the present invention is based.

FIG. 6 is a partial sectional view showing a preferred modification of the present invention.

[Explanation of symbols]

 Reference Signs List 10 master cylinder 12 cylinder hole 14 cylinder body 201 primary piston 202 secondary piston 300 recess 302 center hole 308 stopper bolt (valve opening means) 42 second hydraulic chamber 70 center valve 72 valve body 72h head portion 73 valve spring 80 operation Liquid reservoir 90 Valve seat 92 Stopper member 94 Retainer member 94s Seating portion 98 Ring member 98s Seating portion

──────────────────────────────────────────────────の Continuation of the front page (56) References JP-A-63-142251 (JP, U) Special table Hei 7-500298 (JP, A) Special table Hei 5-502645 (JP, A) German patent application published 4425403 (DE, A1) German Patent Application Publication 3932248 (DE, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60T 11/16

Claims (11)

(57) [Claims] 1. A cylinder body having an axis and having a cylinder hole therein along the axis, a piston defining a hydraulic chamber inside the cylinder hole, and a piston moving in the axial direction. A master cylinder provided with a valve that communicates with and shuts off the hydraulic chamber and the hydraulic fluid reservoir, wherein the valve is a center valve located at the center of the piston, and a recess provided at an end of the piston. A valve body that includes a head portion located in the location, a rod portion extending from the head portion and fitted in a center hole following the recess, the valve body being movable in a direction along the axis, and being located in the recess. A valve seat that produces a valve function in cooperation with the valve body, a valve spring that urges the head portion of the valve body to be seated toward the valve seat, and a biasing force of the valve spring, Non-piston A master which comprises valve opening means for separating the valve body and a valve seat in an operating position, wherein the valve seat is disposed at one end of a rubber ring member, and the ring member is supported as follows. Center valve structure of cylinder. A. The inner peripheral side of the rubber ring member is fitted on the outer periphery of the cylindrical retainer member, and the outer peripheral side of the ring member is fitted on the inner wall of the recess of the piston. Have been. B. The rubber ring member has a rear end face separated from the hydraulic chamber restricted. C. The rubber ring member includes a seating portion in which an outer peripheral portion of a front end surface near the hydraulic chamber is restrained by a stopper member, and a head portion of the valve body sits on an inner peripheral portion of the front end surface. D. The front end surface of the rubber ring member forms a smooth and continuous surface from a portion constrained by the stopper member to an unrestricted inner peripheral portion. 2. The rubber ring member according to claim 1, wherein one end in the axial direction has a seating portion for the valve body, and the other end opposite to the one end is supported in a compressed state. Center valve structure of master cylinder. 3. The master according to claim 1, wherein a front end surface of the rubber ring member is in contact with a hydraulic fluid filled in the hydraulic chamber, and swells the ring member to satisfy the characteristic D. Center valve structure of cylinder. 4. In a state where the cylindrical retainer member, the rubber ring member and the stopper member are assembled in the recess of the piston, a clearance is provided between the stopper member and a front end surface of the rubber ring member. 2. The center valve structure of the master cylinder according to claim 1, wherein the characteristic C is satisfied when the rubber ring member comes into contact with the hydraulic fluid and swells. 5. The position where the head of the valve body is seated on the valve seat is 43 to 4 with respect to the axis of movement of the valve body.
The center valve structure of a master cylinder according to any one of claims 1 to 4, wherein the master cylinder is located at an angle of 5 degrees. 6. The master according to claim 1, wherein the cylindrical retainer member has an outward flange on a rear end side, and the flange restrains a rear end surface of the rubber ring member. Center valve structure of cylinder. 7. The center valve structure of a master cylinder according to claim 1, wherein a rear end surface of said stopper member is chamfered at an inner peripheral end portion and an outer peripheral end portion thereof. 8. The rubber ring member, wherein a front end of the cylindrical retainer member is seated on a head portion of the valve body, and a distance required for the retainer member to be seated on the head portion is set by the rubber ring member. The center valve structure of a master cylinder according to any one of claims 1 to 7, wherein the distance is larger than a distance required for sitting on the head portion. 9. The cylindrical retainer member has a seating portion on which a head portion of the valve element is seated at a front end side near the hydraulic chamber, and a rearward portion facing away from the hydraulic chamber at a rear end side. A flange further provided on an outer peripheral portion between a rear end side having the outward flange and a front end side having the seating portion, each of the flanges being shorter than the outward flange, and the retainer member; The center valve structure of a master cylinder according to claim 1, wherein a first outer peripheral surface between said front end side and said another flange is substantially parallel to an axis of said retainer member. 10. The cylindrical retainer member includes a second outer peripheral surface between the outward flange and the another flange, the second outer peripheral surface being substantially parallel to an axis thereof. The center valve structure of a master cylinder according to claim 9, wherein an outer diameter is larger than an outer diameter of the first outer peripheral surface. 11. The rubber ring member includes a recess at an intermediate portion in the axial direction thereof, the recess being fitted to the another flange, and the first ring fitted to the first outer peripheral surface at the recess. And a second side which fits into the second outer peripheral surface, and a burr generation position due to molding is located on an inner periphery of the first side having a small inner diameter. 10
The center valve structure of the master cylinder.