KR20150017464A - Pilot valve of brake system - Google Patents

Abstract

Disclosed is a pilot valve of a brake system for a vehicle simplifying an inner composition for an easy movement and manufacturing. According to an embodiment of the present invention, the pilot valve installed in the entrance side of a passage where a fluid flows from a master cylinder into a low pressure accumulator, controls the flow of the fluid. The pilot valve of a brake system for a vehicle includes: a valve seat installed in the entrance side of the passage and having a stepped section making the through-holes, where the inside thereof is penetrated, to be stepped; a cylindrical sleeve pressed and coupled inside the upper side of the valve seat, and having one or more passage in the upper side allowing the fluid to flow in while the sleeve is integrated with filter members filtering the fluid which flows through the passage; a plunger installed to be capable of lifting inside the sleeve, having a center hole which has a first opening and closing passage inside the plunger, and forming a second opening and closing passage with the stepped section in the lower outside; a ball positioned inside the plunger to come in contact with the center hole for opening and closing the first opening and closing passage; a first spring for elastically pressurizing the ball toward the center hole; a second spring which elastically pressurizes the plunger toward the upper side of the sleeve for opening the second opening and closing passage; and a shaft installed in a piston of the low pressure accumulator and coming in contact with the ball.

Description

[0001] The present invention relates to a pilot valve of a brake system for a vehicle,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pilot valve of a vehicle brake system, and more particularly, to a pilot valve applied to a vehicle brake system such as ABS, TCS, ESC, and the like.

Generally, a vehicle includes a plurality of wheel brakes including a caliper device having a disk and a pair of pads for braking front and rear wheels for deceleration or stoppage while the vehicle is running, and a booster And a master cylinder. When the driver depresses the brake pedal, the hydraulic pressure generated by the booster and the master cylinder is transmitted to the pad of the wheel brake, and the pad presses the disk to generate the braking force. However, if the braking pressure is greater than the road surface state while the driver depresses the brake pedal to increase or maintain the braking force, or if the frictional force of the wheel brake generated by the braking pressure is greater than the braking force generated on the tire or the road surface, Slip phenomenon occurs.

In recent years, an anti-lock brake system (ABS: Anti-Lock Brake System) that prevents slippage of the wheel during braking to effectively prevent the slip phenomenon and to exhibit a strong and stable braking force and to facilitate the driving operation, A traction control system (TCS: Traction Control System) that prevents excessive slip of a wheel during a sudden acceleration or a sudden acceleration, and an anti-lock brake system and traction when the vehicle is not adjusted to the driver's will by force externally applied A brake system having a vehicle posture control system (ESC, VDC) function for stably maintaining the running state of the vehicle by controlling the brakes by combining the controls has been developed.

Various conventional vehicle braking systems as described above include a hydraulic unit in which a plurality of valves, an accumulator, a motor and a pump are mounted to control the braking hydraulic pressure transmitted between the master cylinder and the wheel brake, And an electronic control unit (ECU) The electronic control unit senses the vehicle speed through the wheel sensors disposed on the front wheel and the rear wheel, thereby controlling the operation of each valve, the motor, and the pump.

In the vehicle brake system having the above-described structure, a pilot valve is provided for controlling the opening and closing of the passage between the master cylinder and the accumulator during the control of the ABS mode, the TCS mode or the ESC mode. 142346.

Referring to the above-mentioned document, the pilot valve is composed of a ball, a shaft, a valve seat, a spring, and the like. That is, the pilot valve pushes the ball closing the flow path of the valve seat to the shaft and opens it, and presses the ball by the spring to close the flow path of the valve seat, thereby controlling the flow of the fluid.

However, the pilot valve has a problem that it is difficult to secure a required flow rate by controlling the flow of fluid through one flow path in the control of the ABS mode, the TCS mode, the ESC mode, and the like.

In addition, since the end of the shaft for lifting the ball is provided in an inclined shape with a sharp point, it is necessary to precisely process the shaft passing through the valve seat, which makes it difficult to manufacture and assemble the shaft.

Japanese Patent Application Laid-Open No. 2000-142346 (May 23, 2000)

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to simplify the internal structure to facilitate operation and manufacture, and to provide a pilot of a vehicle brake system capable of securing a required flow rate by providing two internal flow paths. The purpose is to provide a valve.

In order to achieve the above object, according to an embodiment of the present invention, there is provided a pilot valve provided at a flow inlet side of a flow path from a master cylinder side to a low pressure accumulator for controlling the flow of fluid, And a stepped portion formed so that a through-hole formed through the inside thereof is stepped; A cylindrical sleeve integrally formed with a filter member which is press-fitted into an upper inner surface of the valve seat and has at least one passage formed therein to allow fluid to flow therethrough, the filter member filtering the fluid flowing through the passage; A plunger which is provided in the sleeve so as to be able to move up and down and has a center hole for forming a first opening / closing flow path therein and forming the stepped portion and the second opening / A ball provided inside the plunger to contact the center hole for opening and closing the first opening and closing passage; A first spring for elastically pressing the ball toward the center hole; A second spring elastically pressing the plunger toward an upper side of the sleeve to open the second opening / closing passage; And a shaft provided on the piston of the low-pressure accumulator and in contact with the ball.

A plurality of protruding pieces are formed on the upper side of the plunger so as to form an outer flow path and are spaced apart along the outer circumferential direction so as to support one end of the second spring, Can be supported by the upper surface.

The elastic force of the first spring may be greater than the elastic force of the second spring.

In addition, a rod for supporting the upper end of the first spring is provided on the upper portion of the sleeve, and the passage may be formed in the radial direction around the rod.

The through hole formed in the valve seat is divided into a large diameter portion and a small diameter portion by the step portion, and a tapered seat surface is provided between the large diameter portion and the small diameter portion. A plunger seat surface that cooperates with the seat surface may be formed.

In addition, the shaft may have a cone shape having the same central axis as the center axis of the ball and symmetrical with respect to the center axis, and the upper surface may have a flat surface.

The low pressure accumulator may include a fluid storage chamber and a piston that ascends and descends in the fluid storage chamber, and the shaft may be installed on the upper side of the piston or integrally.

In addition, the piston may include a spacer protrusion that separates from the upper surface of the fluid storage chamber when the piston is lifted.

The pilot valve of the vehicle brake system according to the embodiment of the present invention is provided with two internal flow passages through which the brake fluid moves and is sequentially opened by the pressure difference so that the brake fluid can be moved quickly according to the braking operation , It is possible to secure a required flow rate.

Further, since the shape of the shaft lifting the ball for opening the flow path is cone shape and the upper surface contacting the ball is formed flat, the shaft is lifted up from the central axis position to facilitate the manufacturing of the shaft, .

In addition, it is possible to provide a protrusion on the upper part of the piston provided in the fluid storage chamber of the low-pressure accumulator, thereby ensuring a sufficient flow rate space to stabilize the flow rate of the fluid flowing into the pump.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in detail with reference to the following drawings, which illustrate preferred embodiments of the present invention, and thus the technical idea of the present invention should not be construed as being limited thereto.
1 is a schematic view of a hydraulic circuit of a vehicle brake system in which a pilot valve according to an embodiment of the present invention is used.
FIG. 2 is a cross-sectional view showing a state in which an inner flow path is closed in a pilot valve of a vehicle brake system according to an embodiment of the present invention. FIG.
3 is a cross-sectional view showing a state in which the first opening and closing passage is open in a pilot valve of a vehicle brake system according to an embodiment of the present invention.
4 is a sectional view showing a state in which the first opening / closing flow path and the second opening / closing flow path are opened in the pilot valve of the vehicular brake system according to the embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

1 is a schematic view of a vehicle brake system in which a pilot valve according to an embodiment of the present invention is used.

1, the vehicle brake system includes a brake pedal 1, a booster 2 for amplifying and outputting the pedal force of the brake pedal 1, and a hydraulic pressure sensor A first hydraulic circuit 10A for connecting the first port 3a of the master cylinder 3 and the two wheel brakes (or wheel cylinders) 4 to control hydraulic pressure transmission; And a second hydraulic circuit 10B for connecting the second port 3b of the master cylinder 3 and the remaining two wheel brakes 4 to control hydraulic pressure transmission. The first hydraulic circuit 10A and the second hydraulic circuit 10B are compactly installed in a modulator block (not shown).

Here, the hydraulic circuits 10A and 10B are capable of controlling an anti-lock brake system (ABS) and a traction control system (TCS) The electronic stability control (ESC) is exemplified as an example, but the present invention is not limited thereto.

Since the configuration of the second hydraulic circuit 10B is substantially the same as the configuration of the first hydraulic circuit 10A, the description will be given below focusing on the first hydraulic circuit 10A and the description of the second hydraulic circuit 10B Repeated explanations are omitted. However, the pumps 13 provided in the first and second hydraulic circuits 10A and 10B are driven together with a phase difference of 180 degrees by one motor 14.

1, the first hydraulic circuit 10A includes a plurality of solenoid valves 11, 12 for controlling the braking hydraulic pressure transmitted to the wheel brake 4 side provided on the two wheels RL, FR A pump 13 for sucking and pumping the fluid from the wheel cylinder 4 or the master cylinder 3 and a low pressure accumulator 16 for temporarily storing the fluid exiting the wheel brake 4 .

A plurality of solenoid valves (11, 12) are connected to the upstream side and the downstream side of the wheel brake (4). The solenoid valve 11 disposed on the upstream side of each wheel brake 4 is a solenoid valve 11 of NO (normally open) type which is kept open in a normal state and a solenoid valve 12 disposed on the downstream side And is an NC (normally closed) type solenoid valve 12 that is maintained in a normally closed state. The opening and closing operations of the solenoid valves 11 and 12 are controlled by an electronic control unit (ECU) (not shown) that senses the vehicle speed through a wheel sensor (not shown) disposed on each wheel side. For example, in the pressure reducing braking, the NO type solenoid valve 11 is closed and the NC type solenoid valve 12 is opened, so that the fluid that has escaped from the wheel brake 4 side is temporarily stored in the low pressure accumulator 16.

The pump 13 is driven by the motor 14 to suck and discharge the fluid stored in the low pressure accumulator 16 to transfer the fluid pressure of the fluid to the wheel brake 4 side or the master cylinder 3 side.

The first hydraulic circuit 10A is provided with an NO solenoid valve 15 (hereinafter referred to as a TC solenoid valve) for controlling the TCS mode in the main flow path between the master cylinder 3 and the outlet side of the pump 13 And an oil suction flow path is provided between the master cylinder 3 and the inlet side of the pump 13 to guide the fluid in the master cylinder 3 to the inlet side of the pump 13 under the TCS mode control.

The TC solenoid valve 15 is kept open during normal operation so that the braking fluid pressure formed in the master cylinder 3 during normal braking through the brake pedal 1 is transmitted to the wheel brake 4 side through the main flow path. Although not shown, a relief passage and a relief valve may be provided between the oil suction passage and the main passage. The relief passage and the relief valve return the brake fluid to the master cylinder 3 when the brake fluid pressure discharged from the pump 13 rises more than necessary in the TCS mode.

The low pressure accumulator 16 is provided with a fluid storage chamber 17 in the form of a cylinder inside as shown in the enlarged view of Figure 2 and the piston 18 is elastically lifted and lowered by the elastic spring 19 . The piston 18 rises when the fluid in the fluid storage chamber 17 exits to the outside and falls when the fluid in the fluid storage chamber 17 flows.

In addition, the piston 18 includes a spacer projection 18a so as to be spaced from the upper surface of the fluid storage chamber 17 when the piston 18 is located at the top dead center. The spacer projection 18a is formed of a plurality of spaced projections to secure a minimum flow rate in the fluid storage chamber 17. [

The pilot valve 100 according to the embodiment of the present invention is provided at the upper portion of the low pressure accumulator 16 so that the fluid only flows to the inlet side of the pump 13 on the oil suction passage.

2, the pilot valve 100 is provided in one of the two flow paths P1 and P2 provided in the modulator block (not shown), and the low pressure accumulator 16 And connects the two flow paths (P1, P2) in cooperation with the pilot valve (100). One side flow path P1 is a flow path connected to the master cylinder 3 side with respect to the low pressure accumulator 16 and the other flow path P2 is a flow path connected to the pump 13 side with respect to the low pressure accumulator 16 .

The pilot valve 100 includes a valve seat 110 coupled to a valve assembly port provided on a flow path inlet side of one flow path P1, a sleeve 120 coupled to an upper portion of the valve seat 110, A plunger 130 provided in the center hole 131 of the plunger 130 and a ball 140 provided in the center hole 131 of the plunger 130 to press the ball 140 toward the center hole 131, A second spring 152 for elastically pressing the plunger 130 upward and a shaft (not shown) for contacting the ball 140 according to the operation of the piston 18 160).

The valve seat 110 is provided at the inlet side of the one flow path P1 and has a bottom surface through which the valve seat 110 penetrates and side walls. That is, the through hole 111 formed in the valve seat 110 is formed to be stepped, and the through hole 111 is divided into the large diameter portion 111a and the small diameter portion 111b by the step portion 113. [ At this time, a tapered valve seat surface 115 is provided between the large-diameter portion 111a and the small-diameter portion 111b on the inner side of the through-hole 111.

The sleeve 120 is provided in a cylindrical shape with its lower side opened and press-fitted into the upper inner surface of the valve seat 110. That is, the lower portion of the sleeve 120 is coupled to the valve seat 110 to form the outer wall of the pilot valve 100. At this time, at least one passage 121 is provided in the upper part of the sleeve 120 so that fluid flows through the one passage P1, and a filter member 122 is integrally provided in the passage 121. [ Accordingly, the fluid introduced through the passage 121 can be filtered by the filter member 122 to pass through the inside of the sleeve 120. The filter member 122 is integrally formed with the sleeve 120, thereby reducing the number of individual components.

A rod 123 for supporting the upper end of the first spring 151 is provided on the upper portion of the sleeve 120. That is, the rod 123 is provided to receive the first spring 151 in the form of a coil spring to support the first spring 151. The rod 123 protrudes downward from the upper center of the sleeve 120 and the passageway 121 can be formed radially about the rod 123.

The plunger 130 is provided in the sleeve 120 so as to be able to move up and down, and a center hole 131 penetrating the plunger 130 in the longitudinal direction is formed therein. A plunger seat surface 135 is provided below the plunger 130 to contact the step portion 113, that is, the valve seat surface 115 of the valve seat 110. The plunger seat surface 135 is formed in a tapered shape to cooperate with the valve seat surface 115 to be in surface contact with the valve seat surface 115. The valve seat surface 115 and the plunger seat surface 135 are selectively in contact with and spaced from each other to form the second opening / closing flow path L2.

Meanwhile, a ball 140 is provided inside the plunger 130. The ball 140 is elastically pressed by the first spring 151 supported at the upper end of the rod 123 and brought into contact with the center hole 131. The center hole 131 selectively contacts and separates from the ball 140 to form the first opening / closing flow path L1. At this time, the diameter of the second opening / closing flow path (L2) is made larger than the diameter of the first opening / closing flow path (L1). In addition, the first opening and closing passage L1 and the second opening and closing passage L2 are sequentially opened and closed, and the operation structure thereof will be described below again.

A projecting piece 133 is provided on the upper outer peripheral surface of the plunger 130, that is, on the opposite side of the plunger seat surface 135. A plurality of protruding pieces 133 are provided in the circumferential direction of the outer periphery of the valve seat 110 so as to be spaced apart from each other. A second spring 152 is provided between the surfaces. That is, the lower end of the projecting piece 133 supports one end of the second spring 152, and the other end of the second spring 152 is supported by the upper surface of the stepped portion 113. At this time, the second spring 152 has an elastic force to separate the plunger 130 from the valve seat surface 115, but normally maintains the closed state by the oil pressure on the master cylinder 3 side.

The shaft 160 is installed on the piston 18 of the low pressure accumulator 16 and protrudes therefrom so that the through hole 111 of the valve seat 110 and the plunger 130 Passes through the center hole 131 and comes into contact with the ball 140. When the shaft 160 rises and the ball 140 is separated from the center hole 131, the one flow path P1 and the other flow path P2 are communicated with each other. The shaft 160 has a central axis that is the same as the center axis of the ball 140, and has a cone shape symmetrical with respect to the center axis. Further, the upper surface of the shaft 160 has a flat surface. This is for the purpose of allowing the shaft 160 lifting the ball 140 to move in and out of the through hole 111 of the valve seat 110 and the center hole 131 of the plunger 130, The ball 140 is quickly separated from the center hole 131 to open the first opening and closing flow path L1 to ensure a rapid fluid flow.

On the other hand, the shaft 160 may be formed on the piston 18 or integrally formed with the piston 18 by injection molding.

The operation and effect of the brake system for a vehicle including the pilot valve according to an embodiment of the present invention will now be described.

2, in the general braking (CBS) mode, the first opening / closing flow path L1 of the pilot valve 100 is closed by the ball 140 pressed by the first spring 151 And the second opening and closing flow path L2 is closed by the oil pressure on the side of the master cylinder (3 'in FIG. 1) which is larger than the second spring 152, the fluid in the master cylinder 3 is supplied to the low pressure accumulator 16 It does not leak.

When a slip phenomenon occurs in a braking operation of a vehicle equipped with this brake system, the electronic control unit performs ABS mode by combining the three modes of the depressurization, the pressure increase, and the pressure maintenance based on the signals inputted from the respective wheel sensors. The respective control modes of the ABS are not controlled to be the same in all of the four wheels FR, FL, RR and RL but can be controlled separately according to the road surface condition and the ABS control state. Each control mode will be described step by step through the first hydraulic circuit 10A.

First, when the braking force is being exerted by the hydraulic pressure generated in the master cylinder 3 by depressing the brake pedal 1 by the user, the braking pressure on the wheel brake 4 associated with the first hydraulic circuit 10A is changed to the road surface condition The solenoid valve 11 is closed and the NC type solenoid valve 12 is opened to perform the ABS depressurization mode so as to lower the pressure to the appropriate pressure (depressurization mode). Then, the hydraulic pressure (fluid) partially escapes from the wheel brake 4 side and is temporarily stored in the low-pressure accumulator 16, so that the braking pressure of the wheel brake 4 mounted on each wheel is lowered to prevent the slip of the road surface.

The electronic control unit drives the motor 14 to increase the hydraulic pressure of the wheel brake 4 to increase the hydraulic pressure of the pump 13 of the first hydraulic circuit 10A, The ABS pressure increasing mode is performed. That is, the fluid stored in the low-pressure accumulator 16 is pressurized through the pump 13 and is transmitted to the wheel brake 4 side through the open-type NO-type solenoid valve 11, thereby increasing the braking pressure. The hydraulic pressure discharged from the pump 13 of the second hydraulic circuit 10B is returned to the master cylinder 3 in accordance with the braking pressure condition, And transmitted to the wheel brake 4 side associated with the hydraulic circuit 10B.

The electronic control unit performs the ABS pressure holding mode when it is necessary to maintain the braking pressure at a constant level in order to reach the state where the braking pressure generates the optimum braking force or to prevent the resonance phenomenon of the vehicle. The ABS pressure holding mode makes the NO brake solenoid valve 11 of the first hydraulic circuit 10A close by blocking the pressure change in the wheel brake 4 and blocks the hydraulic pressure from moving. At this time, the pilot valve 100 is in the open state, and the hydraulic pressure discharged from the pump 13 is transmitted to the master cylinder 3 side, whereby the ABS pressure holding mode is stably performed.

The TCS mode is performed when the electronic control unit senses a slip phenomenon that occurs when the user depresses the accelerator pedal (not shown) when the road surface is slippery and the user depresses the accelerator pedal (not shown). In the TCS mode, the electronic control unit opens the pilot valve 100, closes the TC solenoid valve 15 in the main flow path, and operates the motor 14 and the pump 13 to pump the fluid.

That is, when the TCS mode is performed, the fluid on the master cylinder 3 is sucked into the inlet of the pump 13 through the pilot valve 100 and the low pressure accumulator 16 on the inlet side of the one flow path P1, Is transmitted to the wheel brake 4 through the main flow path and the opened NO-type solenoid valve 11, and acts as a braking pressure. As a result, even if the driver depresses the accelerator pedal for the quick start, the wheel locks on the wheel even if the driver does not step on the brake pedal 1, so that the vehicle slowly and stably starts even under a slip condition in which the road surface condition is poor.

Meanwhile, as described above, the pilot valve 100 selectively opens the flow path between the master cylinder 3 and the low-pressure accumulator 16 in the ABS mode or the TCS mode.

That is, when the pump 13 is operated for braking operation, the fluid in the fluid storage chamber 17 flows out through the flow path P2 and the piston 18 rises. As a result, the shaft 18 160 push the ball 140 to open the first opening and closing flow path L1 between the ball 140 and the center hole 131 of the plunger 130 as shown in FIG. The fluid in the master cylinder 3 flows out from the one flow path P1 to the other flow path P2 through the first opening and closing flow path L1.

When the pressure difference between the two flow paths P1 and P2 is released to some extent as the fluid escapes, the plunger 130 flows (rises) due to the elastic force of the second spring 152, The second open / close flow path L2 between the surfaces 135 is opened as shown in Fig.

Since the pilot valve 100 can secure a sufficient fluid flow rate twice or more than the conventional one through the opened first opening / closing flow path L1 and the second opening / closing flow path L2, the brake control performance greatly increases.

On the other hand, when the fluid of the wheel brake 4 flows into the fluid storage chamber 17 through the fluid passage of the master cylinder 3 or the fluid passage of the other side via the one passage P1, the piston 18 descends As a result, the shaft 160 provided on the upper surface of the piston 18 also descends, and the first opening / closing flow path L1 and the second opening / closing flow path L2 are sequentially closed. If the elastic force of the second spring 152 is greater than the elastic force of the first spring 151, the second opening / closing flow path L2 is not in contact with the first spring 151, The pilot valve 100 may not perform its function without being closed or closed later than the one opening and closing flow path L1. At this time, the spacer protrusion 18a provided on the upper surface of the piston 18 allows the fluid in the fluid storage chamber 17 to secure a certain amount of the flow amount to a minimum, thereby preventing cavitations generated when the oil passage is opened can do.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood that various modifications and changes may be made without departing from the scope of the appended claims.

16: Low pressure accumulator 18: Piston
100: Pilot valve 110: Valve seat
111: Through hole 115: Valve seat surface
120: Sleeve 121: passage
122: filter member 130: plunger
131: center hole 135: plunger seat face
140: ball 151: first spring
152: second spring 160: shaft

Claims (8)

1. A pilot valve provided on an inlet side of a flow path from which a fluid flows from a master cylinder side to a low pressure accumulator,
A valve seat provided on the flow path inlet side and having a stepped portion formed so that a through-hole formed therein is penetrated;
A cylindrical sleeve integrally formed with a filter member which is press-fitted into an upper inner surface of the valve seat and has at least one passage formed therein to allow fluid to flow therethrough, the filter member filtering the fluid flowing through the passage;
A plunger which is provided in the sleeve so as to be able to move up and down and has a center hole for forming a first opening / closing flow path therein and forming the stepped portion and the second opening /
A ball provided inside the plunger to contact the center hole for opening and closing the first opening and closing passage;
A first spring for elastically pressing the ball toward the center hole;
A second spring elastically pressing the plunger toward an upper side of the sleeve to open the second opening / closing passage; And
And a shaft provided in the piston of the low-pressure accumulator and in contact with the ball. The method according to claim 1,
A plurality of projecting pieces spaced apart from each other along the outer circumferential direction so as to support one end of the second spring and having an outer flow path formed on the upper side of the plunger and the other end of the second spring is provided on the upper surface of the step portion Wherein the pilot valve is supported by the pilot valve. The method according to claim 1,
Wherein the elastic force of the first spring is larger than the elastic force of the second spring. The method according to claim 1,
Wherein a top portion of the sleeve is provided with a rod for supporting an upper end of the first spring, the passage being formed radially about the rod. The method according to claim 1,
Wherein the through hole formed in the valve seat is divided into a large diameter portion and a small diameter portion by the step portion and a tapered seat surface is provided between the large diameter portion and the small diameter portion,
And a plunger seat surface formed on the lower outer side of the plunger so as to be in contact with the seat surface so as to be in surface contact with the seat surface. The method according to claim 1,
Wherein the shaft has a cone shape having the same central axis as the center axis of the ball and symmetrical with respect to the center axis, the upper surface having a flat surface. The method according to claim 1,
The low-pressure accumulator includes a fluid storage chamber and a piston that ascends and descends in the fluid storage chamber,
Wherein the shaft is provided on the upper side of the piston or integrally formed with the shaft. 8. The method of claim 7,
Wherein the piston comprises a spacer projection to be spaced apart from an upper surface of the fluid storage chamber when the piston is lifted.

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