JP2001213303A - Negative pressure booster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower a set load of an input return spring for energizing an input rod backward by reducing the forward pulling force of a valve piston and a valve element to be generated by an air pressure difference. SOLUTION: The valve element 34 of a control valve 38 is formed of an annular valve part 34a facing to a negative pressure lead-in valve seat 30 and an atmospheric air lead-in valve seat 31 freely to be seated thereon, an annular fitting bead parts 34b held for fixation by the inner peripheral surface of a valve cylinder 10, an annular first flexible film part 34c extended inward in the radial direction from the fitting bead part 34b, and an annular second flexible film 34d extended in the axial direction from the inner peripheral end of the first flexible film part 34c and connected to the valve part 34a. In this booster with above structure, a support plate 43 abutting on a front surface of the first flexible film part 34c while surrounding the second flexible film part 34d is fixed to the valve cylinder 10. The forward pulling force to be generated by a pressure difference and to be applied to the first flexible film part 34c is supported by the support plate 43 so as to prevent the transmission thereof to an input rod 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative pressure booster used for boosting operation of a brake master cylinder of an automobile, and more particularly, to a booster shell having a front negative pressure chamber connected to a negative pressure source. A booster piston partitioned into a rear working chamber is housed therein. A valve piston connected to the booster piston is fitted to the valve cylinder so as to be slidable in the front-rear direction. A control valve for switching the working chamber between the negative pressure chamber and the atmosphere in accordance with the forward and backward movement of the input rod between the valve piston and the valve cylinder; And an input return spring for biasing the control valve. The control valve is provided between an annular negative pressure introducing valve seat formed on the valve cylinder and the negative pressure introducing valve seat formed on the valve piston. The air introduction valve seat to be arranged and the negative pressure An annular valve portion that is seatably opposed to the inlet valve seat and the air introduction valve seat, an annular mounting bead portion fixedly held on the inner peripheral surface of the valve cylinder, and extends radially inward from the mounting bead portion; A valve body comprising an annular first flexible film portion, an annular second flexible film portion axially extending from an inner peripheral end of the first flexible film portion and coupled to the valve portion; And a valve spring for biasing the negative pressure introducing valve seat and the air introducing valve seat in the seating direction, and communicating with the negative pressure chamber on the inner peripheral surface of the valve cylinder between the negative pressure introducing valve seat and the valve body. A second port communicating with the working chamber is opened on the inner peripheral surface of the valve cylinder between the negative pressure introducing valve seat and the atmosphere introducing valve seat, and the inner peripheral side of the valve portion is exposed to the atmosphere. It relates to improvement of a connected negative pressure booster.

[0002]

2. Description of the Related Art Such a negative pressure booster is disclosed in, for example,
It is already known as disclosed in JP-A-8-48923.

FIG. 6 shows the vicinity of a control valve of a negative pressure booster disclosed in the above publication. As is apparent from FIG. 1, the control valve 38 of the conventional negative pressure booster is formed by an annular negative pressure introduction valve seat 30 formed on the valve cylinder 10 and a valve piston 18 formed on the valve piston 18 connected to the input rod 20. An air introduction valve seat 31 disposed inside the pressure introduction valve seat 30 and a negative pressure introduction valve seat 30
And an annular valve portion 34a opposed to the air introduction valve seat 31 so as to be seated, an annular mounting bead portion 34b fixedly held on the inner peripheral surface of the valve cylinder 10, and a radially inward direction from the mounting bead portion 34b. A valve body 34 that includes an annular first flexible film portion 34c that extends and an annular second flexible film portion 34d that extends axially from the inner peripheral end of the first flexible film portion 34c and is coupled to the valve portion 34a. And a valve spring 36 for urging the valve portion 34a in the seating direction of the negative pressure introducing valve seat 30 and the atmosphere introducing valve seat 31.
It is composed of Then, the negative pressure introduction valve seat 30 and the valve body 3
A first port 28 communicating with the negative pressure chamber 2 is opened on the inner peripheral surface of the valve cylinder 10 between the valve cylinders 4. 2nd communicating with 3
The port 29 is opened, and an air introduction port 39 connected to the inner peripheral side of the valve portion 34a is provided at the rear end of the valve cylinder 10. Valve cylinder 1
An input return spring 41 for urging the input rod 20 in the backward direction is contracted between 0 and the input rod 20. Reference numeral 4 denotes a booster piston to which the valve cylinder 10 is integrally connected.

[0004]

Generally, in such a negative pressure booster, since the initial operation input of the input rod is determined by the set load of the input return spring, the set load of the input return spring is set as small as possible. It is desirable to reduce operating force.

When the input load of the input return spring 41 is released, the operation input from the input rod 20 is released, the air introduction valve seat 31 is seated on the valve portion 34a of the valve body 34, and the valve portion 34a is placed under negative pressure. When it is separated from the introduction valve seat 30, the valve piston 18 and the valve body 34 move forward due to the pressure difference between the negative pressure of the negative pressure chamber 2 acting inside and outside of the valve body 34 and the atmospheric pressure. It is necessary that the input rod 20 be large enough to hold the input rod 20 at the backward limit against the retraction force.

However, in the conventional negative pressure booster,
Since the negative pressure of the negative pressure chamber 2 acts on the front surface of the first flexible film portion 34c of the valve body 34, the force of drawing the valve piston 18 and the valve body 34 forward due to the pressure difference is small. Has a relatively large value obtained by multiplying the pressure difference by the effective diameter D of the first flexible membrane portion 34c.
There is a limit in reducing the set load of No. 1.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and reduces a set force of an input return spring by reducing a retraction force of a valve piston and a valve body caused by the pressure difference. It is an object of the present invention to provide a negative pressure booster capable of reducing initial operation input of the above.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a booster piston having a booster shell, the interior of which is divided into a front negative pressure chamber connected to a negative pressure source and a rear working chamber. A valve piston connected to the booster piston, the valve piston being slidably fitted in the valve cylinder in the front-rear direction, and an input rod connecting a front end to the valve piston.
A control valve for switching the working chamber between the negative pressure chamber and the atmosphere in accordance with the forward and backward movement of the input rod between the valve piston and the valve cylinder; and an input return spring for urging the input rod in a backward direction. The control valve is provided with an annular negative pressure introduction valve seat formed in the valve cylinder, and an air introduction valve seat formed in the valve piston and arranged inside the negative pressure introduction valve seat. An annular valve portion which faces the valve cylinder so as to be seated on the negative pressure introduction valve seat and the air introduction valve seat, an annular mounting bead portion fixedly held on an inner peripheral surface of the valve cylinder, An annular first flexible membrane portion extending radially inward from the bead portion;
A valve body comprising an annular second flexible film portion extending in the axial direction from the inner peripheral end of the flexible film portion and coupled to the valve portion; and the valve portion having the negative pressure introduction valve seat and the atmosphere introduction valve seat. A first port communicating with the negative pressure chamber is opened on the inner peripheral surface of the valve cylinder between the negative pressure introducing valve seat and the valve body, and the negative pressure introducing valve is provided. In a negative pressure booster in which a second port communicating with the working chamber is opened on an inner peripheral surface of a valve cylinder between a valve seat and an atmosphere introduction valve seat, and the inner peripheral side of the valve portion communicates with the atmosphere, the second flexible membrane is provided. A support plate surrounding the portion and abutting on the front surface of the first flexible membrane portion is fixed to the valve cylinder.

According to this feature, even if the pull-in force due to the pressure difference is applied to the first flexible membrane portion, the pull-in force to the first flexible membrane portion is received by the support plate fixed to the valve cylinder. Therefore, the pulling force due to the pressure difference acting on the input rod from the valve piston and the valve body decreases accordingly.
Therefore, the set load of the input return spring can be reduced, and the initial operation input to the input rod can be reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments of the present invention shown in the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing a single type negative pressure booster according to an embodiment of the present invention in a state where an input rod is at rest, and FIG.
2 is an enlarged view of part 2 of FIG. 1, and FIG. 3 shows a boost operation state.
FIG. 4 is an operation explanatory diagram corresponding to FIG. 2, and FIG. 5 is a boost characteristic diagram of the negative pressure booster.

First, in FIGS. 1 and 2, the booster shell 1 of the negative pressure booster B is composed of a pair of front and rear shell halves 1a and 1b whose opposite ends are connected to each other. A cylinder body Ma of a brake master cylinder M, which is operated by the booster B, is fixed to the front shell half 1a by bolts 9 and is fixedly supported on the front wall F of the vehicle cabin by the bolts 8.

The interior of the booster shell 1 includes a booster piston 4 accommodated therein so as to be able to reciprocate back and forth, and a diaphragm 5 which is bonded to and overlapped with a rear surface thereof and is sandwiched between the two shell halves 1a and 1b. Thereby, it is divided into a negative pressure chamber 2 on the front side and a working chamber 3 on the rear side. The negative pressure chamber 2 is connected to a negative pressure source V (for example, inside an intake manifold of an internal combustion engine) via a negative pressure introducing pipe 14.

The booster piston 4 is formed in an annular shape from a steel plate, and a synthetic resin valve cylinder 10 is integrally connected to the center of the booster piston 4 and the center of the diaphragm 5. The valve cylinder 10 is slidably supported via a bearing member 13 with a seal lip on a support cylinder 12 projecting rearward from the center of the rear shell half 1b.

A valve piston 18, an input rod 20 connected to the valve piston 18, and an input rod 2
A control valve 38 for switching the working chamber 3 to communicate with the negative pressure chamber 2 and the atmosphere in accordance with the zero back and forth movement is provided.

The valve piston 18 is slidably fitted in a guide hole 11 provided in the valve cylinder 10, and has a reaction force piston 17 at a front end via a neck 18a and a rear end at a rear end. Are formed with respective annular air introduction valve seats 31. An annular negative pressure introduction valve seat 30 is formed in the valve cylinder 10 so as to surround the atmosphere introduction valve seat 31.

The valve piston 18 is provided with a connection hole 18a which is opened at the rear end surface of the air introduction valve seat 31, and the spherical front end 20a of the input rod 20 is fitted into the connection hole 18a and the stopper is prevented from coming off. For this purpose, a part of the valve piston 18 is swaged, so that the input rod 20 is swingably connected to the valve piston 18.

The negative pressure introducing valve seat 30 is provided in the valve cylinder 10.
One common valve body 34 facing the air introduction valve seat 31 is provided. The valve body 34 has an annular valve portion 34a which is opposed to the negative pressure introduction valve seat 30 and the atmosphere introduction valve seat 31 so as to be seated.
An annular mounting bead portion 34b fixed to the inner peripheral surface of the valve cylinder 10, an annular first flexible film portion 34c extending radially inward from the mounting bead portion 34b, and the first flexible film portion The valve portion 34a extends axially forward from the inner peripheral end of the portion 34c.
And a ring-shaped second flexible film portion 34d coupled to
A valve spring 36 for urging the valve portion 34a in the seating direction between the valve seats 30 and 31 is contracted between the valve portion 34a and the input rod 20. The control valve 38 is constituted by the negative pressure introduction valve seat 30, the atmosphere introduction valve seat 31, the valve body 34 and the valve spring 36.

An annular support plate 43 surrounding the second flexible film portion 34d is disposed in front of the mounting bead portion 34b of the valve body 34 and the front surface of the first flexible film portion 34c so as to abut.
The bearing plate 43 abuts against an annular step portion 44 formed on the inner peripheral surface of the valve cylinder 10 and is prevented from moving forward. The mounting bead portion 34b is engaged with an outer peripheral groove 35a of a cylindrical valve holder 35 fitted to the inner peripheral surface of the valve cylinder 10, and
The valve holder 35 is held between the support plate 43 and the valve holder 35. In order to hold the valve holder 35 at its clamping position, a locking claw 47 protruding from the outer periphery of the rear end of the valve holder 35 is provided with a valve cylinder 10.
It is engaged with an annular groove 46 formed on the inner peripheral surface. Thus, the mounting bead portion 34b is fixed to the inner peripheral surface of the valve cylinder 10 together with the support plate 43.

An input return spring 41 for urging the input rod 20 in the backward direction is provided between the valve holder 35 and the input rod 20.
Is contracted.

Further, the valve cylinder 10 has first and second ports 2.
8, 29 are provided. The first port 28 communicates with the negative pressure chamber 2 and opens on the inner peripheral surface of the valve cylinder 10 between the negative pressure introducing valve seat 30 and the mounting bead portion 34b.
Is connected to the working chamber 3 and opens on the inner peripheral surface of the valve cylinder 10 between the negative pressure introducing valve seat 30 and the atmosphere introducing valve seat 31.

At the rear end of the support cylinder portion 12 of the rear shell half 1b and the input rod 20, both ends of an extendable boot 40 covering the valve cylinder 10 are attached. An air inlet 39 communicating with the inside of the valve body 34 is provided. A filter 42 for filtering air flowing into the air inlet 39 is interposed between the outer peripheral surface of the input rod 20 and the inner peripheral surface of the valve cylinder 10. The filter 42 has flexibility so as not to hinder the relative movement of the input rod 20 and the valve cylinder 10.

Further, a key 32 for limiting the retraction limit of the booster piston 4 and the valve piston 18 is attached to the valve cylinder 10 so as to be movable in the axial direction within a certain distance. The key 32 is used for the valve piston 18 and the reaction force piston 17.
A fork portion 32a straddling the neck portion 18b is provided at the inner end, and the outer end 32b is disposed so as to face the front surface of the stopper wall 19 provided on the support tube portion 12 of the rear shell half 1b. . Thus, the key 32 is connected to the stopper wall 1.
9, the booster piston 4 and the valve cylinder 1
A retraction limit of 0 is defined, and the retraction limit of the valve piston 18 and the input rod 20 is defined by the rear end face of the reaction force piston 17 abutting on the key 32. The axial length of the neck portion 18b is set to be larger than the thickness of the key 32, so that the valve piston 18 and the key 32 can slightly move relative to each other.

Further, the valve cylinder 10 is provided with a working piston 15 protruding forward and a small-diameter cylinder hole 16 penetrating through the center of the working piston 15. Are slidably fitted. A cup body 21 is slidably fitted around the outer periphery of the working piston 15, and the cup body 21 is filled with a flat elastic piston 22 facing the working piston 15 and the reaction force piston 17. At this time, a certain gap is formed between the reaction force piston 17 and the elastic piston 22 when the negative pressure booster B is not operated.

An output rod 25 projects from the front surface of the cup body 21. The output rod 25 is connected to the brake master cylinder M.
Of the piston Mb.

In the above, the working piston 15, the reaction piston 17, the elastic piston 22 and the cup 21 constitute a reaction mechanism 24 for feeding back a part of the output of the output rod 25 to the input rod 20.

A retainer 26 is disposed so as to contact the front end surfaces of the cup body 21 and the valve cylinder 10.
Between the booster piston 4 and the front wall of the booster shell 1
And a booster return spring 2 for urging the valve cylinder 10 in the backward direction.
7 is contracted.

Next, the operation of this embodiment will be described.

When the negative pressure booster B is at rest, the key 32 attached to the valve cylinder 10 contacts the front surface of the stopper wall 19 of the rear shell half 1b, as shown in FIGS. When the rear end face of the reaction force piston 17 abuts, the booster piston 4 and the input rod 20 are located at the retreat limit. At this time, the air introduction valve seat 31 is
While closely contacting the valve portion 34a, the valve portion 34a is pressed to be slightly separated from the negative pressure introducing valve seat 30. As a result, communication between the air inlet 39 and the second port 29 is cut off, while communication between the first and second ports 28, 29 is established, and thus the negative pressure in the negative pressure chamber 2 is reduced.
The booster piston 4 and the valve cylinder 10 are held in the retracted position by the urging force of the booster return spring 27 because the pressures in the two chambers 2 and 3 are the same.

The negative pressure in the negative pressure chamber 2 also acts on the front surfaces of the valve piston 18 and the air introduction valve seat 31, and also on the front surfaces of the valve portion 34a and the first flexible film portion 34c of the valve body 34. Due to the pressure difference between the negative pressure and the atmospheric pressure outside the air introduction valve seat 31, a forward retraction force acts on the valve piston 18 and the valve body 34, but the forward retraction force acting on the first flexible membrane portion 34c is , Received by the support plate 43 fixed to the valve cylinder 10, the forward retraction force transmitted from the valve piston 18 and the valve body 34 to the input rod 20 is obtained by multiplying the inner diameter d of the annular support plate 43 by the pressure difference. Value. Thus, the input rod 20 of the front retraction force acting on the first flexible film portion 34c of the valve body 34
To the input return spring 4
1, the valve piston 18 and the valve body 3
The input rod 20 can be held at a predetermined retreat limit against the front retraction force of No. 4. This means that the initial operation input to the input rod 20 by the brake pedal P can be reduced.

Therefore, even if the brake pedal P is lightly depressed to brake the vehicle, the input rod 20 can be advanced together with the valve piston 18 against the set load of the input return spring 41. Then, as shown in FIG.
With the advance of the valve piston 18, the urging force of the valve spring 36 causes the valve portion 34a to be seated on the negative pressure introducing valve seat 30 while extending the second flexible film portion 34d, and at the same time, the atmosphere introducing valve seat 31 becomes the valve body 34. From the first and second ports 28,
The communication between the second and third ports 29 is cut off, and the second port 29 is communicated with the atmosphere inlet 39 through the inside of the valve body 34. As a result, the air flowing into the valve cylinder 10 from the air inlet 39 passes through the air inlet valve seat 31, is introduced into the working chamber 3 through the second port 29, and the working chamber 3 is set to a higher pressure than the negative pressure chamber 2. Therefore, the forward thrust based on the pressure difference is obtained, and the booster piston 4 resists the force of the booster return spring 27 together with the valve cylinder 10, the working piston 15, the elastic piston 22, the cup body 21 and the output rod 25. , The piston Mb of the brake master cylinder M is driven by the output rod 25. The elastic piston 22 is compressed by the reaction force generated by this driving, and a part of the elastic piston 22 swells into the small-diameter cylinder hole 16.
Since the above-mentioned reaction force is not transmitted to the input rod 20 until it comes into contact with the front surface of 7, the output of the output rod 25 shows a jumping characteristic that rises rapidly as shown by a line ab in FIG.
As described above, since the jumping characteristic is obtained by the relatively small initial operation input, the ineffective stroke of the brake master cylinder M and each wheel brake can be quickly eliminated, and the responsiveness of each wheel brake can be improved.

After the elastic piston 22 comes into contact with the reaction force piston 17, a part of the operation reaction force of the output rod 25 is fed back to the input rod 20 via the elastic piston 22. The magnitude of the output of the output rod 25 can be sensed. Then, the output of the output rod 25 increases as shown by a line bc in FIG. 5 with a boosting ratio determined by the ratio of the pressure receiving areas of the working piston 15 and the reaction force piston 17 that abut on the elastic piston 22.

After reaching the boosting limit point c at which the pressure difference between the negative pressure chamber 2 and the working chamber 3 is maximized, the output of the output rod 25 is changed to the booster piston 4 as shown by the line cd. The sum of the maximum thrust due to the pressure difference and the operation input to the input rod 20 is obtained.

When the pedaling force is released from the brake pedal P in order to release the braking state of the vehicle, first, the input rod 20 and the valve piston 18 are retracted by the force of the input return spring 41.
Accordingly, as shown in FIG. 4, the valve piston 18 causes the valve body 34 to be largely separated from the negative pressure introduction valve seat 30 while the air introduction valve seat 31 is seated on the valve body 34. Communicates with the negative pressure chamber 2 via the second port 29 and the first port 28. As a result, the introduction of air into the working chamber 3 is prevented, while the air in the working chamber 3 is sucked into the negative pressure limit V through the negative pressure chamber 2 and the pressure difference between them is eliminated. With the resilience of the booster return spring 27, it retreats and releases the operation of the master cylinder M. Then, the booster piston 4 and the input rod 20 return to the rest state of FIGS. 1 and 2 again.

The present invention is not limited to the above embodiment, and various design changes can be made without departing from the gist of the present invention. For example, the negative pressure booster B may be configured as a tandem type in which a pair of front and rear booster pistons are connected to the same valve cylinder.

[0036]

As described above, according to the present invention, the booster shell houses the booster piston partitioning the interior into a front negative pressure chamber connected to a negative pressure source and a rear working chamber. A valve piston slidably fitted to the valve cylinder in a front-rear direction with a valve cylinder connected to the piston, an input rod connecting a front end of the valve piston to the valve piston; A control valve for switching the working chamber between the negative pressure chamber and the atmosphere in accordance with the forward and backward movement of the input rod, and an input return spring for urging the input rod in a backward direction are provided. An annular negative pressure introducing valve seat formed on the valve cylinder, an atmosphere introducing valve seat formed on the valve piston and disposed inside the negative pressure introducing valve seat, and introducing the negative pressure into the valve cylinder. An annular valve portion which is seatably opposed to the valve seat and the air introduction valve seat, and which is fixed to the inner peripheral surface of the valve cylinder; An annular mounting bead portion, which is held in a fixed manner, an annular first flexible film portion extending radially inward from the mounting bead portion, and an axially extending one extending from an inner peripheral end of the first flexible film portion. A valve body composed of an annular second flexible membrane portion coupled to the valve portion, and a valve spring for urging the valve portion in a seating direction of the negative pressure introduction valve seat and the atmosphere introduction valve seat, A first port communicating with the negative pressure chamber is opened on the inner peripheral surface of the valve cylinder between the negative pressure introducing valve seat and the valve body. In a negative pressure booster in which a second port communicating with the working chamber is opened and an inner peripheral side of the valve portion communicates with the atmosphere, the negative pressure booster surrounds the second flexible film portion and contacts a front surface of the first flexible film portion. Since the contacting support plate is fixed to the valve cylinder, even if the drawing force due to the pressure difference is applied to the first flexible film portion of the valve body, the first flexible film portion is prevented. By receiving the retracting force on the support plate, the retracting force due to the pressure difference acting on the input rod from the valve piston and the valve body can be reduced accordingly, so that the set load of the input return spring can be reduced. This makes it possible to reduce the initial operation input to the input rod.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a single type negative pressure booster according to an embodiment of the present invention in a state where an input rod is at rest.

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

FIG. 3 is an operation explanatory view corresponding to FIG. 2 and showing a boost operation state.

FIG. 4 is an operation explanatory view corresponding to FIG. 2, showing a boost cancellation process;

FIG. 5 is a boosting characteristic diagram of the negative pressure booster.

FIG. 6 is a sectional view of a control valve section in a conventional negative pressure booster.

[Explanation of symbols]

 B: Negative pressure booster V: Negative pressure source 1 Booster shell 2 Negative pressure chamber 3 Working chamber 4 Booster piston 10 Valve Cylinder 18 ... Valve piston 20 ... Input rod 28 ... First port 29 ... Second port 30 ... Negative pressure introduction valve seat 31 ... Atmospheric introduction valve seat 34 ... Valve element 34a ··· Valve part 34b ··· Mounting bead part 34c ··· First flexible film part 34d ··· Second flexible film part 36 ... Valve spring 38 ... Control valve 43 ... Bearing plate

Claims (1)

[Claims] 1. A booster shell (1) having a booster piston (4) for partitioning a booster shell (1) into a front negative pressure chamber (2) connected to a negative pressure source (V) and a rear working chamber (3). Contain
A valve cylinder (10) connected to the booster piston (4)
A valve piston (18) fitted to the valve cylinder (10) so as to be slidable in the front-rear direction, an input rod (20) connecting a front end to the valve piston (18), and the valve piston (18). A control valve (38) for switching the working chamber (3) between the negative pressure chamber (2) and the atmosphere in accordance with the forward and backward movement of the input rod (20) between the valve cylinders (10); An input return spring (41) for urging the input rod (20) in the backward direction is provided, and the control valve (38) is connected to an annular negative pressure introducing valve seat (10) formed in the valve cylinder (10). 30) and the valve piston (18)
And an air introduction valve seat (31) arranged inside the negative pressure introduction valve seat (30), and the negative pressure introduction valve seat (30) and the air introduction valve seat ( 31), an annular valve portion (34a) which is seatably opposed to the valve cylinder (1).
0), an annular mounting bead portion (34b) fixedly held on the inner peripheral surface, an annular first flexible film portion (34c) extending radially inward from the mounting bead portion (34b), and A valve body (34) comprising an annular second flexible film portion (34d) extending in an axial direction from an inner peripheral end of the first flexible film portion (34c) and coupled to the valve portion (34a); Part (34
a) is replaced with the negative pressure introduction valve seat (30) and the atmosphere introduction valve seat (3).
1) and a valve spring (36) for urging in the seating direction. The negative pressure chamber is provided on the inner peripheral surface of the valve cylinder (10) between the negative pressure introducing valve seat (30) and the valve element (34). The first port (28) communicating with (2) is opened, and the negative pressure introduction valve seat (30) is opened.
A second port (29) communicating with the working chamber (3) is opened in the inner peripheral surface of the valve cylinder (10) between the air introduction valve seat (31) and the inner peripheral side of the valve portion (34a). A support plate (43) surrounding the second flexible membrane (34d) and abutting against the front surface of the first flexible membrane (34c) is fixed to the valve cylinder (10). Negative pressure booster characterized by doing.