JPH049251Y2 - - Google Patents

Description

[Detailed description of the invention] A. Purpose of the invention (1) Industrial application field The present invention is a negative pressure booster mainly used to operate the brake master cylinder of an automobile, especially the inside of a booster shell. A negative pressure source is created by a booster piston that is housed so as to be able to reciprocate back and forth, and a diaphragm that overlaps the rear surface of the booster piston and connects the inner peripheral bead to the booster piston and the outer peripheral bead to the peripheral wall of the booster shell. a first working chamber at the front connected to the input rod, and a second working chamber at the rear selectively communicated with the first working chamber or the atmosphere via a control valve interlocked with an input rod, the control valve being A valve cylinder for accommodating the booster piston is provided protruding from the rear surface of the booster piston, and the control valve is configured to
A valve piston is slidably fitted to the front inner circumference of the valve cylinder via a guide protrusion and is connected to the front end of the input rod, and faces a valve seat provided at the rear end of the valve piston. The present invention relates to a type including a valve body supported by the valve cylinder.

(2) Prior Art Conventionally, the valve piston is caulked to the front end of the input rod by plastically deforming its peripheral wall portion radially inward. In this case, since the caulking joint is arranged between the valve seat and the guide protrusion on the peripheral wall, there is a risk that the stress or distortion generated in the peripheral wall during caulking may affect the shape of the valve seat and the guide protrusion. .

Therefore, conventionally, in order to eliminate the above-mentioned influence, the distance between the valve seat and the guide protrusion is set wide.

(3) Problems to be solved by the invention However, with the above structure, not only does the overall length of the valve piston become longer, but also the valve piston becomes shorter due to the sliding gap between the guide protrusion and the inner peripheral surface of the valve cylinder. When the valve seat tilts, the position of the valve seat increases, and as a result, there is a problem that the sealing performance between the valve seat and the valve body deteriorates.

An object of the present invention is to provide the negative pressure booster which can solve the above problems.

B. Structure of the invention (1) Means for solving the problem In order to achieve the above object, according to the invention, in the negative pressure booster of the type described above, the valve piston is connected to the front end of the input rod. an outer cylinder whose front inner periphery is fitted onto the inner cylinder at a position in front of the input rod joint,
The rear part of the outer cylindrical body surrounds the input rod coupling part of the inner cylindrical body through an annular gap, and is provided with the guide protrusion on the outer peripheral surface of the door and the valve seat on the rear end surface.

(2) Function The valve piston can be configured by being divided into an inner cylinder body having an input rod coupling part and an outer cylinder body having a guide protrusion and a valve seat. By interposing an annular gap between the valve seat and the rear part of the outer cylindrical body having the valve seat, it is possible to prevent the stress and strain generated in the joint part when the input rod is connected to be transmitted to the valve seat and the guide protrusion as much as possible. The influence of stress and strain on the input rod coupling portion on the shape of the valve seat and guide protrusion is suppressed.

Further, since the input rod coupling portion of the inner cylinder can be arranged concentrically with the rear part of the outer cylinder having the valve seat and the guide protrusion, the overall length of the valve piston can be shortened. Moreover, since the guide protrusion and the valve seat can be arranged close to each other at the rear of the outer cylinder, even if the valve piston tilts to some extent due to the sliding gap between the guide protrusion and the inner periphery of the valve cylinder, The amount of displacement of the valve seat due to the tilting is small.

(3) Embodiment In FIG. 1, W is a support wall constituting the rear wall of the engine room of an automobile, and a negative pressure booster S having a brake master cylinder M coupled to the front end is attached to the front of the support wall.

The booster shell 1 of the booster S has a pair of front and rear parts made of lightweight thin steel plate or synthetic resin.
Consisting of rear shells 1F and 1R, a plurality of claw pieces 1a protruding from the opening of the rear shell 1R at equal intervals on the circumference are formed at the opening of the front shell 1F at equal intervals on the circumference. The two shells 1F, 1R are engaged with the notch 1b to position the shells 1F, 1R relative to each other, and the two shells 1F, 1R are connected via two tie rods 30 passing through their front and rear opposing walls. The connection structure between the booster shell 1 and the tie rod 30 will be described later.

A booster piston 2 is housed inside the booster shell 1 so as to be able to freely reciprocate back and forth, and an annular groove 61 is formed in the rear surface of the booster piston 2.

The outer peripheral bead 3a of the diaphragm 3 has two positioning protrusions 3c (only one shown in the figure) protruding from the end face thereof at equal intervals on the circumference, and each positioning hole is formed on the outer peripheral part of the rear shell 1R. 1c and settle with both shells 1F and 1R. In addition, the inner bead 3b of the diaphragm 3 is connected to the annular groove 61 of the booster piston 2, and the diaphragm 3 and the booster piston 2 divide the inside of the booster shell 1 into the first working chamber A at the front and the first working chamber A at the rear. It is divided into a second working chamber B.

The pressure receiving portion 3d of the diaphragm 3 is overlapped with the rear surface of the booster piston 2, and is bent into a U-shape so as to protrude toward the first working chamber A between the outer circumferential surface of the booster piston 2 and the inner circumferential surface of the front shell 1F. The rolling movement of this U-shaped bent portion allows the booster piston 2 to move forward and backward.

As clearly shown in FIGS. 2 and 3, a notch 6 is formed in the rear wall 61a of the annular groove 61 of the booster piston 2.
5 is provided, and a portion of the inner circumferential bead 3b of the diaphragm 3 facing the above-mentioned notch 65 is formed into a thin wall portion 63, which is tightly attached to the rear surface of the booster piston 2 so as to be freely separated. Further, a channel-shaped positioning projecting wall 64 is integrally raised from the peripheral edge of the thin portion 63, and this projecting wall 64 is engaged with the notch 65. This engagement restricts relative rotation between the booster piston 2 and the diaphragm 3. A vent hole 66 is formed in the booster piston 2 so as to face the thin wall portion 63 of the diaphragm 3.

The first working chamber A is always in communication with the intake manifold (not shown) of the internal combustion engine, which is a negative pressure source, through a negative pressure introduction pipe 4, and the second working chamber B is connected to a control valve 5, which will be described later.
The air inlet 6 is selectively connected to the first working chamber A or the atmosphere inlet 6 which is opened in the end wall 1e of the rear extension tube 1d of the booster shell 1 through the opening.

The booster piston 2 is always pushed in the backward direction, that is, toward the second working chamber B by a return spring 7 contracted in the first working chamber A, and its backward limit is set by a protrusion 3e formed protrudingly on the back surface of the diaphragm 3 in the booster shell. 1
It is regulated by coming into contact with the inner surface of the rear wall.

The booster piston 2 is integrally formed with a valve cylinder 8 projecting in the axial direction from the rear surface of its central part, and is slidably supported on a flat bearing 9 provided in the extension cylinder 1d, and its rear end is introduced into the atmosphere. Open toward mouth 6.

As clearly shown in FIGS. 4 to 6, the control valve 5 is constructed in the valve cylinder 8 as follows.

That is, a cylinder hole 67 is formed in the front inner wall of the valve cylinder 8, and has a large diameter portion 67a at the rear and a small diameter portion 67b at the front. 2. Constantly communicates with working chamber B. In addition, a through hole 1 is provided in the valve cylinder 8 at the rear of the large diameter portion 67a.
It constantly communicates with the first working chamber A via 7.

An annular first valve seat 10 ₁ is formed on the edge of the rear opening in the large diameter portion 67 a, and the cylinder hole 67 includes:
The valve piston 12, which is caulked to the spherical front end 11a of the input rod 11, is slid onto the valve piston 12.
An annular second valve seat 10 ₂ surrounded by the first valve seat 10 ₁ is formed at the rear end.

A cylindrical valve body 1 with both ends open is mounted on the inner wall of the valve cylinder 8.
The base end portion 13a of the valve body 3 is clamped via the valve body holding cylinder 14 which is fitted into the valve cylinder 8. This valve body 13 is made of an elastic material such as rubber, and its base end 13
A thin-walled diaphragm 13b extends radially inward from a, and a thick-walled valve portion 13c is connected to the inner peripheral end of the thin-walled diaphragm 13b. ₁ , and the inner peripheral portion of the seating surface 13d is made to face the second valve seat ₁₀₂ . Therefore, valve part 1
3c can move back and forth by deforming the diaphragm 13b, and can also come into contact with the front end surface of the valve body holding cylinder 14. The inside of the valve body 13 is the atmosphere inlet 6
Communicate at all times.

An annular reinforcing plate 15 is embedded in the valve portion 13c, and a valve spring 16 acts on the annular reinforcing plate 15 to bias the valve portion 13c toward both valve seats 10 ₁ and 10 ₂ .

The valve piston 12 includes an inner cylindrical body 122 to which the front end of the input rod 11 is caulked, and an inner cylindrical body ₁₂ .
₂ An outer cylindrical body 1 whose front inner periphery is screwed to the front side of the input rod coupling part Ca through a tap screw 68.
2 ₁ , this outer cylinder body 12 ₁ consists of a large diameter cylinder 12 _a at the rear and a small diameter cylinder 12 b at the front, and the second valve seat 10 ₂ is arranged on the rear end surface of the large diameter cylinder 12 a. Furthermore, on the outer surface of the peripheral wall of the large diameter cylinder 12a, there are four guide protrusions 6 continuous from the vicinity of the second valve seat _102.
9 are arranged at intervals on the circumference.

The small diameter tube _12b of the outer cylinder 121 is connected to the small diameter portion 67b of the cylinder hole 67, and the tip of each guide protrusion 69 is connected to the inner peripheral surface of the large diameter portion 67a of the cylinder hole 67, extending in the axial direction. It is slidably fitted into the groove 70. The engagement between the guide protrusion 69 and the guide groove 70 prevents the outer cylinder 12 ₁ from rotating, and the pair of adjacent guide protrusions 69, the outer surface of the peripheral wall of the large diameter cylinder 12a existing between them, and the adjacent A space s surrounded by a land between a pair of guide grooves 70
into the second working chamber B through the communicating hole 18, and into the valve cylinder 8.
They communicate within each other.

When processing the input rod coupling portion Ca in the inner cylinder 12 ₂ , three points on the rear end of the peripheral wall of the inner cylinder 12 ₂ are bulged and deformed inward in the radial direction, and each protrusion 71 connects the input rod 11 . The spherical front end 11a of the holder is held in place. In this state, the inner cylinder 12 ₂
The rear end surface is located inside the outer cylinder 12 ₁ , and the caulking joint Ca as the input rod joint is located inside the outer cylinder 12 ₁ .
It is surrounded by the rear part of, that is, the large-diameter cylinder 12a via an annular gap C.

The booster piston 2 is provided with a large diameter hole 19 that opens at the center of its front surface and a small diameter hole 20 that opens at the inner end face of the large diameter hole 19, and the large diameter hole 19 is made of rubber or the like from the back. The elastic piston 21 and the output piston 22 having the same diameter are sequentially slid together. Further, a reaction piston 23 integral with the inner cylinder body 12 ₂ is slidably fitted into the small diameter hole 22 . The output piston 22 integrally has an output rod 22a that projects forward.

In this case, since the inner cylinder 12 ₂ is fitted to the outer cylinder 12 ₁ via the tap screw 68, a tool is engaged with the tool engagement groove 23a of the reaction piston 23 to move the inner cylinder 12 ₂ . By doing so, it is possible to accurately determine the jumping distance l between the elastic piston 21 and the reaction piston 23, and thereby the valve piston 12
the second valve seat 10 before it comes into contact with the elastic piston 21
₂ can be spaced apart from the valve body 13.

In addition, the reaction piston 23 and the rear end wall 2 of the small diameter hole 20
Since the input rod 11 is prevented from coming off by cooperation with the input rod 0a, there is no need for a member such as a circlip or a key to prevent the input rod 11 from coming off.

The input rod 11 is always pushed in the backward direction by the return spring 24, and its retraction limit is set by the movable stopper plate 25 screwed onto the input rod 11 coming into contact with the inside of the end wall 1e of the rear extension tube 1d. regulate.
When the movable stopper plate 25 is rotated, the screwing position between it and the input rod 11 changes, so the input rod 11 is rotated.
The retraction limit can be adjusted back and forth. After the adjustment, the movable stopper plate 25 is fixed by tightening a lock nut 26 which is also screwed onto the input rod 11. A ventilation hole 27 is bored in the movable stopper plate 25 so as not to block the air inlet 6.

Filters 28 and 29 are attached to the outer end opening of the valve cylinder 8 to purify the air introduced from the atmosphere inlet 6 and to be deformable so as not to interfere with the operation of the input rod 11.

Next, the connection structure between the tie rod 30 and the booster shell 1 will be explained.

A mounting bolt 33 that penetrates the front wall of the booster shell 1 and projects forward thereof is integrally formed on the tie rod 30, and a spring receiving plate 34 that comes into contact with the inner surface of the front wall of the booster shell 1 is fixed. Then, the mounting bolt 33 is passed through the mounting flange 36 of the brake master cylinder M stacked on the front surface of the booster shell 1, and the nut 35 is screwed onto the tip of the bolt 33 and tightened. and the mounting flange 36 are connected together. At that time, an annular groove 37 formed on the front surface of the spring receiving plate 34 so as to surround the bolt 33
An annular seal member 38 is fitted to seal the tie rod through hole in the front wall of the booster shell 1. The spring support plate 34 supports the fixed end of the return spring 7, and allows the tie rod 30 to bear the elastic force of the return spring 7, thereby removing the load on the booster shell 1.

Furthermore, the tie rod 30 is integrally formed with a mounting bolt 39 that penetrates through the rear wall of the booster shell 1 and projects rearward thereof, and a stepped flange 41 that abuts the inner surface of the rear wall of the booster shell 1. The stepped flange 41 is fitted into the support tube 43 that is welded and fixed to the inner surface of the rear wall, and its retaining ring 42 is locked to the support tube 43, thereby integrating the tie rod 30 and the rear wall of the booster shell 1. Connect to. At that time, the small diameter part of the stepped flange 41 and the support tube 4
An annular seal member 45 for sealing the tie rod through hole in the rear wall of the booster shell 1 is fitted into the annular groove 44 between the booster shells 1 and 3.

The mounting bolt 39 passes through the support wall W of the automobile, and the tie rod 30 is fixed to the support wall W by screwing and tightening a nut 40 at its tip.

Thus, the booster shell 1 is attached to the support wall W via the tie rod 30, and the brake master cylinder M is connected to the booster shell 1 via the tie rod 30.

Two tie rods 30 are arranged at one diagonal vertex of the rectangle, and two bolts exclusively for mounting to the support wall W are attached to the booster shell 1 at the other diagonal vertex.
It is welded to the rear wall of the building, but these are omitted from the drawing.

Booster piston 2 penetrated by tie rod 30
A sealing means is provided between the booster piston 2 and the tie rod 30 in order to seal the through hole 31 so as not to interfere with the operation of the piston 2. The sealing means is composed of a bellows-shaped telescopic boot 46 made of an elastic material such as rubber, and the boot 46 surrounds the tie rod 30 in the first working chamber A, and its front end 46a is attached to the outer peripheral surface of the tie rod 30. In the formed annular groove 47, also at the rear end 46b
are fitted into the through holes 31, respectively.

In the vehicle interior, a brake pedal 52, which is pivoted 51 on a fixed bracket 50, is connected to the rear end of the input rod 11 of the booster S via a connecting fitting 53. 54 is a return spring that biases the brake pedal 52 rearward.

Cylinder body 55 of brake master cylinder M
The rear end penetrates the front wall of the booster shell 1 and plunges into the first working chamber A, and the cylinder body 5
The output rod 22a of the booster S is opposed to the rear end of the operating piston 56 in the booster S.

Next, to explain the operation of this embodiment, the illustrated state shows the non-operating state of the booster.
The valve piston 12, the input rod 11, and the brake pedal 52, which are connected to each other, are returned to a predetermined retracted position where the movable stopper plate 25 abuts the fixed end wall 1e, and are held by the spring force of the spring 24, and the valve piston 12 is held by the spring force of the spring 24. 2. Press the seating surface 13d of the valve portion 13c through the valve seat 10 ₂ to hold it against the valve body holding cylinder 14.
The first valve seat 101 is moved back until it lightly contacts the front surface of the valve portion 13c, thereby forming a small gap g between the first valve seat ₁₀₁ and the valve portion 13c. Such a state can be easily obtained by adjusting the movable stopper plate 25 described above.

As described above, the first working chamber A, which constantly stores negative pressure during engine operation, has a penetration 17, a gap g, and a space s.
The second working chamber B communicates with the second working chamber B through the through hole 18, and is closed by the second valve seat ₁₀₂ , which is the seating surface opening of the valve portion 13c. Negative pressure is transmitted and the air pressures in both working chambers A and B are balanced. Therefore, the booster piston 2 also occupies the illustrated retracted position by the elastic force of the return spring 7.
In this case, since the guide protrusion 69 and the second valve seat 10 ₂ are close to each other, even if the valve piston 12 swings due to the sliding gap between the guide protrusion 69 of the valve piston 12 and the guide groove 70 of the cylinder hole 67. Second valve seat 10
As a result, the sealing performance between the _second valve seat 10 ₂ and the valve body 13 is good.

Now, if the brake pedal 52 is depressed to brake the vehicle and the input rod 11 and the valve piston 12 are moved forward, the valve portion 13c, which is urged forward by the valve spring 16, will move forward following the valve piston 12. Since the gap g between the first valve seat 10 ₁ and the valve part 13c is extremely narrow as described above, the valve part 13c immediately seats on the first valve seat 10 ₁ to establish communication between the working chambers A and B. At the same time, the second valve seat ₁₀₂ is closed to the valve part 13.
The second working chamber B is communicated with the atmosphere inlet 6 through the hole 18, the space s, and the inside of the valve body 13, apart from the second working chamber B. Therefore, the atmosphere is quickly introduced into the second working chamber B, and the pressure in this chamber B becomes higher than that in the first working chamber A, and the pressure difference between the two chambers A and B causes the booster piston 2 to resist the return spring 7. Since the output rod 22a is moved forward via the elastic piston 21, the operating piston 5 of the brake master cylinder M
6 is driven forward, and the vehicle is braked. In this case, due to the pressure difference between the working chambers A and B, the thin walled portion 63 of the inner peripheral bead 3b tightly adheres to the booster piston 2 and blocks the ventilation hole 66. is definitely blocked.

When the actuating piston 56 is driven, a thrust load is applied forward to the cylinder body 55, and this load is transmitted to the vehicle body, ie, the support wall W, through the tie rod 30 and supported. Therefore, the above-mentioned load does not act on the booster shell 1.

On the other hand, when the valve piston 12 comes into contact with the elastic piston 21 via the reaction piston 23 due to its advancement, the elastic piston 21 bulges and deforms toward the reaction piston 23 side due to the actuation reaction force of the output rod 22a, thereby reducing the reaction force. A portion is fed back to the brake pedal 52 side via the valve piston 12, so that the driver can sense the output of the output rod 22a, that is, the braking force.

Next, when the depressing force of the brake pedal 52 is released, the input rod 11 is moved backward due to the reaction force applied to the valve piston 12 and the elastic force of the return spring 24, which causes the second valve seat 10 ₂ to move toward the valve portion 13c. and seat the valve portion 13c in the valve body holding cylinder 14.
The valve part 13c is brought into contact with the front surface of the input rod 1.
Compressive deformation occurs in the axial direction due to the retreating force of 1.
As a result, a gap larger than the initial gap g is formed between the first valve seat ₁₀₁ and the valve part 13c, so that the air pressures in both working chambers A and B are quickly balanced with each other through this gap, and When the pressure difference disappears, the booster piston 2 moves backward by the elastic force of the return spring 7, and the protrusion 3e of the diaphragm 3 comes into contact with the inner surface of the rear wall of the booster shell 1 and stops. Then, when the input rod 11 comes into contact with the end wall 1e, the valve part 13c is released from the retreating force of the input rod 11 and returns to its original shape, so that the gap with the first valve seat ₁₀₁ is reduced to the small gap g again. It can be sandwiched.

When manually operating the booster piston 2 with no negative pressure stored in the first working chamber A, depress the brake pedal 52 and press the booster piston 2.
, the second working chamber B is disconnected from the first working chamber A and communicated with the atmosphere by the control valve 5, so that the air in the first working chamber A is compressed and the negative pressure introduction pipe 4 However, the air in the first working chamber A is compressed by the discharge resistance, and if the air pressure in the first working chamber A becomes higher than that in the second working chamber B, the air in the first working chamber A becomes higher than that in the second working chamber B. 1 A part of the air in the working chamber A is distributed between the rear surface of the booster piston 2 and the diaphragm pressure receiving part 3d.
When it enters between the front surface and the front surface, it passes through the ventilation hole 66 and presses the thin part 63 rearward. This creates a gap between the booster piston 2 and the thin wall portion 63,
Since the air in the first working chamber A is easily discharged through the gap into the second working chamber B under atmospheric pressure, there is almost no resistance to discharging the air in the first working chamber A, and the booster piston 2 can be moved easily. Can be operated manually.

When the booster piston 2 retreats, the pressure in the first working chamber A becomes lower than that in the second working chamber B, so the diaphragm pressure receiving part 3d
Air that is in close contact with the rear surface and exists between the pressure receiving portion 3d and the rear surface of the booster piston 2 is immediately discharged to the first working chamber A side through the ventilation hole 66. Therefore, when performing a braking operation with negative pressure stored in the first working chamber A, the booster pressure generated due to the buffering effect of the air trapped between the rear surface of the booster piston 2 and the diaphragm pressure receiving portion 3d. Operation loss of the piston 2 can be avoided.

Note that when connecting the valve piston 12 to the input rod 11, it is also possible to employ means other than caulking connection.

C. Effects of the invention According to the invention, the valve piston includes an inner cylindrical body to which the front end of the input rod is connected, and a front inner periphery fitted into the inner cylindrical body on the front side of the input rod joint. The rear part of the outer cylinder surrounds the input rod coupling part of the inner cylinder through an annular gap, and has a guide protrusion on its outer peripheral surface and a valve seat on its rear end surface. Since it is equipped with a valve piston,
The inner cylindrical body has an input rod coupling portion, and the outer cylindrical body has a guide protrusion and a valve seat. By interposing an annular gap between the input rod and the rear part, it is possible to prevent the stress and strain generated in the input rod connection from being transmitted to the valve seat and the guide protrusion as much as possible, thereby reducing the stress in the input rod connection. This is advantageous in that the influence of distortion on the shape of the valve seat and the guide protrusion can be minimized, which is advantageous in improving the sealing performance between the valve seat and the valve body and the slidability of the valve piston. Moreover, since the input rod coupling portion of the inner cylinder can be arranged concentrically with the rear portion of the cylinder having the valve seat and the guide protrusion, this is advantageous in reducing the overall length of the valve piston. Furthermore, since the guide protrusion and the valve seat can be arranged close to each other at the rear of the outer cylinder, even if the valve piston tilts to some extent due to the sliding gap between the guide protrusion and the inner circumference of the valve cylinder. , the amount of displacement of the valve seat due to its tilting can be reduced, and therefore the sealing performance between the valve seat and the valve body can be further improved.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, in which FIG. 1 is a longitudinal sectional view, FIG. 2 is a view taken along the line indicated by the arrow in FIG.
3 is a partial perspective view of the diaphragm, FIG. 4 is an enlarged view of the main part of FIG. 1, FIG. 5 is a sectional view taken along line V-V in FIG. 4, and FIG. 6 is an enlarged perspective view of the bent piston. S... Negative pressure booster, A... First working chamber, B
...Second working chamber, Ca...Caulking joint as input rod joint, C...Gap, 1...Booster shell, 2...Booster piston, 3...Diaphragm, 3a...Outer bead, 3b... ...Inner circumferential bead,
5... Control valve, 8... Valve cylinder, 11... Input rod, 1
2... Valve piston, 12 ₁ ... Outer cylinder body, 12 ₂ ...
Inner cylinder body, 13... Valve body, 13d... Seating surface, 67
...Cylinder hole, 69...Guide protrusion.

Claims (1)

[Scope of utility model registration request] A booster piston 2 is housed inside the booster shell 1 so as to be able to reciprocate back and forth, and the booster piston 2 overlaps the rear surface of the booster piston 2 to bond the inner peripheral bead 3b to the booster piston 2 and connect the outer peripheral bead 3a to the booster piston 2. A diaphragm 3 connected to the peripheral wall of the shell 1 creates a first working chamber A at the front connected to a negative pressure source, and a control valve 5 linked to the input rod 11.
The booster piston 2 is partitioned into the first working chamber A or a second working chamber B at the rear which is selectively communicated with the atmosphere through The control valve 5 includes a valve piston 12 that is slidably fitted to the front inner circumference of the valve cylinder 8 via a guide protrusion 69 and connected to the front end of the input rod 11, and the valve piston 12. In the negative pressure booster, the valve piston 12 is provided with a valve body 13 supported by the valve cylinder 8 so as to face a valve seat 10 ₂ disposed at the rear end of the valve piston 12 . an inner cylindrical body 12 ₂ to which the front end of 11 is coupled;
This inner cylinder body 12 ₂ is composed of an outer cylinder body 12 1 whose front inner periphery is fitted on the front side of the input rod coupling part Ca, and the rear part of the outer cylinder body 12 ₁ is connected to the inner cylinder body 12 ₂ . The input rod coupling portion Ca of 12 ₂ is surrounded through an annular gap C, and the guide protrusion 69 is provided on the outer peripheral surface.
A negative pressure booster, further comprising the valve seat 10 ₂ on the rear end surface.