JPH0412849Y2 - - 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 that is used, for example, to operate the brake master cylinder of a vehicle, in particular,
a booster shell; the interior of the booster shell is divided into a first working chamber connected to a negative pressure source and a second working chamber selectively communicated with the first working chamber or the atmosphere via a control valve; a booster piston made of a metal plate that is housed in a booster shell so as to be able to reciprocate back and forth; an outer peripheral bead that is superposed on the rear surface of the booster piston and is bonded to the peripheral wall of the booster shell;
a diaphragm having an inner peripheral bead attached to the rim of the valve cylinder fitting hole located at the center of the booster piston;
a valve barrel for a control valve that is fitted onto the inner circumferential surface of the inner peripheral bead and has a retaining flange in contact with the front surface of the booster piston; and a stop plate that rotates around the center line of the retaining flange and engages with a plurality of locking pawls of the booster piston.

(2) Prior art The present applicant previously developed a device of this type in Japanese Patent Application Laid-open No. 1983
-We are proposing what is disclosed in Publication No. 67251.

(3) Problems to be solved by the invention When the clamping plate is engaged with the locking pawl, when the valve cylinder rotates relative to the booster piston, the inner bead of the diaphragm is twisted, and as a result, the inner bead is twisted. This causes problems such as it coming off the rim of the valve barrel fitting hole and impairing its durability.

Therefore, in the above device, the notch portion of the retaining flange is engaged with the outer peripheral surface of the attachment cylinder of the tie rod seal member attached to the booster piston, thereby preventing the valve cylinder from rotating relative to the booster piston.

An object of the present invention is to provide a negative pressure booster in which the above-mentioned valve cylinder rotation prevention structure can be simplified without impairing the operating characteristics of the booster.

B. Structure of the invention (1) Means for solving the problems In order to achieve the above object, the present invention forms a notch-like recess on the outer periphery of the retaining flange, and a cutout-like recess is formed on the front surface of the booster piston. A protrusion that bulges forward is molded so as to be engaged in a relatively non-rotatable manner with the booster piston, and a diaphragm covers the rear end opening of the recess that is formed on the rear surface of the booster piston as the protrusion bulges out. It is characterized by

(2) Effect Since the engagement of the concave portion and convex portion described above ensures that the valve cylinder is prevented from rotating relative to the booster piston, the inner peripheral bead of the diaphragm must not be forcibly twisted when the retaining plate is engaged with the retaining pawl. There will be no fear.

Moreover, the above-mentioned convex portion can be easily formed into a bulge by simply pressing the booster piston made of a metal plate. Furthermore, since the rear end opening of the recess formed on the rear surface of the booster piston due to the bulge molding of the convex portion is covered with a diaphragm that overlaps with the rear surface of the booster piston, the formation of the recess also causes the second There is no risk that the effective volume of the working chamber (if this volume is large, the responsiveness of the piston will be reduced when atmospheric air is introduced into the chamber and the booster piston is advanced) will be expanded more than necessary, and therefore, The response characteristics of the booster piston when introducing atmospheric air into the second working chamber are not impaired by the recess.

(3) Embodiment In FIGS. 1 and 2, a booster piston 2 is housed in a booster shell 1 so as to be able to reciprocate back and forth. and a second working chamber B.

A diaphragm 3 is superimposed on the rear surface of the booster piston 2, and its outer peripheral bead 3a is an annular groove defined in the peripheral wall of the booster shell 1, and thus in the abutting portion of the front and rear shells 1a and 1b that constitute the booster shell 1. 4, and the inner circumference bead 3b is attached to the inner circumference of the booster piston 2. The binding structure of this inner peripheral bead 3b will be described later.

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 5, and the second working chamber B is connected to a control valve 6, which will be described later.
It is configured to selectively communicate with the first working chamber A or an atmosphere inlet 9 opened in the end wall 8 of the rear extension tube 7 of the booster shell 1 through the opening.

The booster piston 2 is always urged in the backward direction, that is, toward the second working chamber B, by a return spring 10 contracted in the first working chamber A, and its backward limit is reached by a protrusion 11 formed protrudingly formed on the back surface of the diaphragm 3. It is regulated by coming into contact with the inner surface of the rear wall of the shell 1.

The booster piston 2 is provided with a valve cylinder 12 for a control valve that protrudes rearward from its center, and the valve cylinder 12 is slidably supported on a flat bearing 13 provided in the rear extension cylinder 7, and its rear end is The air inlet 9
It will be opened towards.

The control valve 6 is configured in the valve cylinder 12 as follows. That is, an annular first valve seat 14 ₁ is formed on the front inner wall of the valve cylinder 12 , and an input rod 1 is formed on the front part of the valve cylinder 12 .
A valve piston 16 is connected to the valve piston 16 and forms a front end thereof, and an annular second valve seat 14 ₂ surrounded by the first valve seat 14 ₁ is attached to the rear end of the valve piston 16 .
is formed.

A base end portion 18 of a cylindrical valve body 17 with both ends open is clamped on the inner wall of the valve cylinder 12 via a valve body holding cylinder 19 that is fitted into the valve cylinder 12 . The valve body 17 is made of an elastic material such as rubber, and a thin diaphragm 20 extends radially inward from its base end 18, and a thick valve portion 21 is connected to the inner peripheral end thereof. The valve portion 21 faces the first and second valve seats 14 ₁ and 14 ₂ . Thus, the valve portion 21 can move back and forth by deforming the diaphragm 20, and can also come into contact with the front end surface of the valve body holding cylinder 19.

An annular reinforcing plate 22 is embedded in the valve portion 21, and a valve spring 60 is connected to this to bias the valve portion 21 toward both valve seats 14 ₁ and 14 ₂ .

The outer part of the first valve seat ₁₄₁ is the through hole 23 of the valve cylinder 12.
The intermediate portion of the first and second valve seats 14 ₁ , 14 ₂ is connected to the second working chamber B through another through hole 24 , and the second valve seat 14 2 is connected to the first working chamber A through the second valve seat 14 ₂ . The inner portions are always in communication with the atmosphere inlet 9 through the inside of the valve body 17 .

The valve cylinder 12 is provided with a large-diameter cylinder hole 25 that opens at the center of the front surface thereof, and a small-diameter cylinder hole 26 that opens at the inner end surface of the cylinder hole 25.
An elastic piston 27 made of rubber or the like and an output piston 28 of the same diameter are sequentially slid into the large-diameter cylinder hole 25 from the back thereof, and a reaction piston 29 with a smaller diameter than the elastic piston 27 is slid into the small-diameter cylinder hole 26. Ru. Further, a small shaft 30 protruding from the front end surface of the valve piston 16 enters the small diameter cylinder hole 26 and opposes the rear end surface of the reaction piston 29 . An output rod 31 is installed in front of the output piston 28.
is provided in a protruding manner, and its output rod 31 is connected to an operating piston of a brake master cylinder (not shown).

The input rod 15 is always urged in the backward direction by the return spring 32, and its retreat limit is reached when the movable stopper plate 33 screwed onto the input rod 15 comes into contact with the inside of the end wall 8 of the rear extension tube 7. regulated by.
When the movable stopper plate 33 is rotated, the screwing position between it and the input rod 15 changes, so the input rod 15 is rotated.
The retraction limit can be adjusted back and forth. After the adjustment, the movable stopper plate 33 is fixed by tightening a lock nut 34 which is also threaded onto the input rod 15. A ventilation hole 35 is formed in the movable stopper plate 33 so as not to block the air inlet 9.

Filters 36 and 37 are attached to the outer end opening of the valve cylinder 12 to purify the air introduced from the atmospheric air inlet 9 and to be deformable so as not to interfere with the operation of the input rod 15.

Next, the assembly structure of the valve cylinder 12 to the booster piston 2 will be explained.
In order to reduce its price, it is formed into a substantially disk shape from a thin steel plate, and a valve barrel fitting hole 38 is formed in the center, and the inner circumferential bead 3b of the diaphragm 3 is formed at the mouth edge of the valve barrel fitting hole 38. It will be installed.

The valve cylinder 12 is molded from a synthetic resin such as phenolic resin, and fits into the valve cylinder fitting hole 38, and therefore the cylinder body 3 is fitted onto the inner peripheral surface of the inner peripheral bead 3b.
9, and a retaining flange 40 which is protruded from the outer peripheral surface of the front end of the cylindrical body 39 and whose rear surface a overlaps the front surface b of the booster piston 2.

A pair of notch-like recesses 41 are formed on the outer circumference of the retaining flange 40 so as to be point symmetrical with respect to the center of the retaining flange 40.
A pair of convex portions 42 that respectively engage with the booster piston 2 are bulged on the front surface b of the booster piston 2, and the engagement of these concave portions 41 and the convex portions 42 ensures that the valve cylinder 12 is prevented from rotating relative to the booster piston 2. It will be done. Further, on the rear surface of the booster piston 2, a recess 42a is formed corresponding to the projection 42 as the projection 42 is expanded. Since the recess 42a is covered by the thick wall portion, the effective volume of the second working chamber B (if this volume is large, when the atmosphere is introduced into the chamber B to advance the booster piston 2), the effective volume of the second working chamber B is reduced. (responsivity of the piston 2 decreases)
There is no risk that the second
The response characteristics of the booster piston 2 when the atmosphere is introduced into the working chamber B are not impaired.

As clearly shown in FIG. 2, the booster piston 2
A pair of hook-shaped first and second hook-shaped locking claws 43 ₁ , 4 are provided around the retaining flange 40 .
3 ₂ are formed adjacently by cutting and raising.

Both first locking claws 4 existing on both sides of the straight line XX
_3.1 and both second locking claws _43.2 are point symmetrical with respect to the center of the booster piston 2, with the first locking claw _43.1 on one side and the second locking claw on the other side across the straight line XX. Both tips 44 ₁ , 44 ₂ of the 2 locking claws 43 ₂
are now facing each other.

The flat portion 4 of the booster piston 2 is connected to each of the first and second locking claws 43 ₁ 43 ₂ from its tip portions 44 ₁ , 44 ₂ .
Reinforcing ribs 46 ₁ and 46 ₂ are bulge-molded so as to extend to 5 .

The clamping plate 46 is formed from a steel plate, and is assembled to the booster piston 2 by rotating clockwise in FIG. It clamps the flange 40, and the retaining flange 4
0, and a pair of arcuate bent portions 48 that are formed to face each other on the outer circumference of the stopper plate body 47 and loosely fit into the outer circumferential surface of the retaining flange 40. First and second locking claws 43 ₁ , 43 ₂ are provided to protrude outward in the radial direction of the retaining flange 40 from the outer peripheral edge of the tip of each bent portion 48 .
It has a pair of first and second engaging pieces 49 ₁ and 49 ₂ that elastically engage the inner surfaces of the tip portions 44 ₁ and 44 ₂ .

As clearly shown in FIG. 3, each first engaging piece 49 ₁
is on the rear side edge of the clamping plate in the rotating direction, and each second
The engagement piece 49 ₂ has a side edge on the front side in the direction of rotation of the clamping plate,
Retainers 50 ₁ and ₅₀ 2 bent inward to approach the flat portion 45 of the booster piston 2, respectively.
has. The flat portion 45 of the booster piston 2 has cut-and-raised holes 51 ₁ for the first and second locking claws 43 ₁ , 43 ₂ extending so as to intersect with the rotational direction of the locking plate 46 .
Each pair of reinforcing ribs 52 _{1 ,} 5 2 sandwiching 5 ₂ are bulging molded, and the tip of each first engagement piece 49 ₁ to prevent it from coming off 50 ₁ is connected to one of the reinforcing ribs 5 located on the rear side in the direction of rotation of the clamping plate.
2 ₁ , and the tips of the retainers 50 ₂ of each second engaging piece 49 ₂ connect between the front side edge of the second retaining pawl 43 ₂ in the direction of rotation of the retaining plate and the flat portion 45 of the booster piston 2. It abuts against the connecting side wall 53. This side wall 53 is formed at the same time as the second locking pawl 43 ₂ is cut and raised.

As described above, due to the cooperation of both retainers 50 ₁ and 50 ₂ , one of the reinforcing ribs 52 ₁ , and the side wall 53, the retainer plate 46 moves in the detachment direction around the center line of the retainer flange 40, that is, in the clockwise and counterclockwise directions in FIG. Clockwise rotation is prevented.

Each pair of reinforcing ribs 52 ₁ , 52 ₂ has cut holes 51
₁ , 51 ₂ , and each reinforcing rib 52 ₁ existing on the rear side in the direction of rotation of the clamping plate 46
It also serves as a stopper.

Further, the inner peripheral bead 3b of the diaphragm 3 is bonded between the mouth edge of the valve sleeve fitting hole 38 and the outer surface of the valve sleeve 12, thereby sealing the valve sleeve fitting hole 38. A pair of windows 54 are formed in the blocking plate main body 47 , one of which faces the opening of the through hole 23 in the valve barrel 12 .

The clamping plate 46 is assembled to the booster piston 2 as follows.

That is, as shown by the chain lines in FIGS. 2 and 3, the retaining plate main body 47 is overlapped with the front surface c of the retaining flange 40, and each bent portion 48 is loosely fitted to the outer peripheral surface of the retaining flange 40, and each first The engaging piece 49 ₁ is placed above each reinforcing rib 52 ₁ on the rear side in the direction of rotation of the clamping plate, and each second engaging piece 49 ₂ is placed above the adjacent first and second locking claws 43 ₁ , 43 .
They are placed between _{the two} . And the clamping plate 46,
As a result, while pressing the retaining flange 40 and compressing the inner peripheral bead 3b of the diaphragm 3, the respective first and second engaging pieces 49 ₁ rotate clockwise in FIG.
49 ₂ are forcibly slid onto the inner surfaces of the tip portions 44 ₁ , 44 ₂ of the respective first and second locking claws 43 ₁ , 43 ₂ .

In this case, since each concave portion 41 of the retaining flange 40 engages with each convex portion 42 of the booster piston 2 and the valve cylinder 12 is reliably prevented from rotating relative to the booster piston 2, each of the first and second Engagement piece 49 ₁ ,
49 ₂ to the respective first and second locking claws 43 ₁ and 43 ₂ , the inner peripheral bead 3b of the diaphragm 3 is not twisted.

Further, the retainer 50 ₁ of each first engagement piece 49 ₁ easily overcomes each reinforcing rib 52 ₁ due to its elasticity, and therefore each reinforcing rib 52 ₁ allows rotation of the clamping plate 46 in the engagement direction. Moreover, a guide 55 is provided on the rear side edge of each of the first and second locking claws 43 ₁ , 43 ₂ in the direction of rotation of the clamping plate, and is bent outward so as to move away from the flat portion 45 of the booster piston 2 . ₁ , 55 ₂ are formed, and a flat portion 45 of the booster piston 2 is formed on the front side edge of each first engaging piece 49 ₁ in the rotational direction of the blocking plate.
A guide 56 is formed that bends inward so as to be close to the second engagement piece 492, and a guide 56 is formed to prevent the second engagement piece ₄₉₂ from coming off.
0 ₂ acts as a guide, each of the first and second engaging pieces 49 for each of the first and second locking claws 43 ₁ and 43 _2
1 , 49 ₂ sliding is carried out smoothly.

As shown in FIG. 4a, the retaining flange 40
The outer periphery of the front surface c is formed into a tapered surface 57 that widens from the front surface c toward the rear surface a, and the tapered surface 57 and the rear surface of the engaging piece connecting portion 46a of the clamping plate 46 that opposes the tapered surface 57. An arcuate space S is defined between them. By this space S, each of the first and second engaging pieces 49
₁ and 49 ₂ becomes the front edge of the tapered surface ₅₇ , and the distance between the fulcrum f ₁ and each of the first and second engaging pieces 49 ₁ and 49 ₂ becomes longer. The spring action of the first and second engaging pieces 49 ₁ and 49 ₂ increases,
This facilitates sliding of each of the first and second engaging pieces 49 ₁ and 49 ₂ on each of the first and second locking claws 43 ₁ and 43 ₂ , and also allows each of the first and second engaging pieces 49 1 and 49 ₂ to slide together easily. 49 ₂
The elastic engagement force of is increased.

Furthermore, as clearly shown in FIG.
The booster piston 2 has an abutment surface 58a located at a portion other than 1 and spaced apart from the front surface b of the booster piston 2. A pair of semi-annular reinforcing ribs 59 whose ends are connected to both convex portions 42 are bulge-molded on the flat portion 45 of the booster piston 2 so as to face the contact surface 58a. Each reinforcing rib 59 has an arcuate cross section.

A predetermined interval d is provided between the abutting surface 58a and the reinforcing rib 59, so that the fulcrum _f2 of the deflection of the booster piston 2 becomes the rear edge of the connecting surface 58b between the abutting surface 58a and the rear surface a, Therefore its fulcrum
Since the distance between f ₂ and each of the first and second locking claws 43 ₁ , 43 ₂ becomes longer, each of the first and second locking claws 43 ₁ , 43 ₂
This increases the spring action of each of the first and second engaging pieces 49 for each of the first and second locking claws 43 ₁ , 43 ₂ .
_1,492 can be easily slid together _.

When the amount of forward deflection of the booster piston 2 increases, both annular reinforcing ribs 59 come into contact with the contact surface 58a to regulate the amount of deflection. The elastic engagement forces of the first and second engagement pieces 49 ₁ and 49 ₂ are set so that the engagement pieces 49 ₁ and 49 ₂ do not come off the respective first and second locking claws 43 ₁ and 43 ₂ . .

Next, to explain the operation of this embodiment, the state shown in FIG. 1 shows a non-operating state, in which the valve piston 16 and the input rod 15 are connected to each other, and the movable stopper plate 33 is in contact with the fixed end wall 8. The valve piston 16 is returned to the predetermined retracted position and held by the spring force of the spring 32, and the valve piston 16 presses the front surface of the valve portion 21 through the second valve seat ₁₄₂ to lightly contact the front surface of the valve body holding cylinder 19. By this, a small gap g is formed between the first valve seat 14 ₁ and the valve portion 21 . Such a state can be easily obtained by adjusting the movable stopper plate 33 described above.

As described above, during engine operation, the first working chamber A, which always stores negative pressure, communicates with the second working chamber B through the through hole 23, the gap g, and the through hole 24, and also through the front opening of the valve part 21. is closed by the second valve seat ₁₄₂ , the negative pressure in the first working chamber A is transmitted to the second working chamber B, and the air pressures in both working chambers A and B are balanced. Therefore, the booster piston 2 also returns the spring 1.
It assumes the retracted position shown with a spring force of zero.

Now, in order to brake the vehicle, the brake pedal (not shown) is depressed, and the input rod 15 and valve piston 16 are pressed down.
When the valve spring 60 moves forward, the valve part 21, which is urged forward by the valve spring 60, moves forward following the valve piston 16, but the gap g between the first valve seat ₁₄₁ and the valve part 21 is Since the valve portion 21 is extremely narrow, the valve portion 21 immediately seats on the first valve seat 14 ₁ to cut off communication between the two working chambers A and B, and at the same time, the second valve seat 14 ₂ separates from the valve portion 21 and enters the second working chamber. Chamber B through hole 24 and valve body 17
It communicates with the atmosphere inlet 9 through the inside. Therefore, the atmosphere is quickly introduced into the second working chamber B, and the pressure in the second working chamber B becomes higher than that in the first working chamber A.
Due to the pressure difference between B and B, the booster piston 2 moves forward against the return spring 10, and the elastic piston 27
Since the output rod 31 is advanced through the brake master cylinder, the operating piston of the brake master cylinder is driven forward
Braking is applied to the vehicle.

When the small shaft 30 of the valve piston 16 comes into contact with the elastic piston 27 via the reaction piston 29 due to its advancement, the elastic piston 27 bulges and deforms toward the reaction piston 29 side due to the actuation reaction force of the output rod 31, thereby absorbing the reaction force. A portion of the braking force is fed back to the brake pedal side via the valve piston 16, so that the driver can sense the output of the output rod 31, that is, the braking force.

When the booster piston 2 moves forward, both working chambers A and B
The booster piston 2 is bent forward due to the pressure difference between the booster pistons 2 and 4.
It is supported by the fulcrum _f2 on the rear surface.

On the other hand, the pressure difference generated between the working chambers A and B becomes excessive, and the amount of forward deflection of the booster piston 2 increases, and as shown in FIG. When it comes into contact with the contact surface 58a, the amount of deflection of the booster piston 2 is restricted, and the first and second locking claws 43 ₁ and 43 ₂ do not move forward any more, and in this state, each Each of the first and second locking claws 43 ₁ and 43 ₂
Since the elastic engagement force of the second engagement pieces 49 ₁ , 49 ₂ is maintained, the respective first and second engagement pieces 49 ₁ , 49 ₂ are connected to the respective first and second locking claws 43 ₁ , 43 _{2 .} It will never come off.

In addition, the deflection of the booster piston 2 is determined by the reinforcing rib 5.
The fulcrums f 2 and f ₃ support the deflection of the booster piston ₂ depending on the magnitude of the pressure difference generated between the working _chambers A and B. Since this changes, the stress caused by the deflection does not act concentratedly on one location of the booster piston 2, and thereby the durability of the booster piston 2 can be improved.

Next, when the depression force of the brake pedal is released, the input rod 15 is moved backward due to the reaction force applied to the valve piston 16 and the elastic force of the return spring 32, and this causes the second valve seat ₁₄₂ to be pressed against the valve portion 21. Since the valve portion 21 is seated and brought into contact with the front surface of the valve body holding cylinder 19, the valve portion 21 receives the retreating force of the input rod 15 and undergoes compressive deformation in the axial direction. As a result, a gap larger than the initial gap g is formed between the first valve seat 14 ₁ and the valve part 21, so that the air pressures in both working chambers A and B are quickly balanced with each other through this large gap. When the pressure difference between them disappears, the booster piston 2 moves back due to the elastic force of the return spring 10, and the projection 11 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 15 comes into contact with the end wall 8, the valve part 21 is released from the retreating force of the input rod 15 and returns to its original shape, so that the gap with the first valve seat ₁₄₁ is reduced to the small gap g again. Can be narrowed.

C. Effects of the invention As described above, according to the invention, a notch-like recess is formed on the outer periphery of the retaining flange, and the front surface of the booster piston made of a metal plate is engaged with the recess in a relatively non-rotatable manner. Since the convex portion that bulges forward is formed, the engagement between the concave portion and the convex portion ensures that the valve cylinder is prevented from rotating relative to the booster piston, and therefore, when the retaining plate is engaged with the retaining pawl, There is no risk of forcibly twisting the inner peripheral bead of the diaphragm, which can contribute to improving its durability. Moreover, the above-mentioned convex portion is
Since the booster piston made of a metal plate can be easily bulged and molded by simple press processing, the molding process is easy and contributes to cost reduction, and the rotation prevention structure itself for the valve cylinder is simplified.

In addition, a recess is formed on the rear surface of the booster piston due to the bulging of the convex portion, and the rear end opening of the recess is covered with a diaphragm that overlaps with the rear surface of the booster piston. There is no risk that the effective volume of the second working chamber will be expanded more than necessary by forming the convex portion of the booster piston. The response characteristics of the booster piston 2 at the time of introduction do not deteriorate.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a longitudinal cross-sectional view of the whole, which corresponds to a cross-sectional view taken along the line in FIG. 2, FIG. −
The line sectional view and FIG. 4 are enlarged longitudinal sectional views of the part where the valve cylinder is assembled to the booster piston, where a shows the state before the booster piston is bent, and b shows the state where the booster piston is bent. A, B...First and second working chambers, b...Front, 1
...Booster Ciel, 2...Booster Piston,
3...Diaphragm, 3a...Outer bead, 3b
...Inner peripheral bead, 6...Control valve, 12...Valve cylinder,
38... Valve cylinder fitting hole, 40... Removal prevention flange,
41... recessed part, 42... convex part, 42a... recessed part,
43 ₁ , 43 ₂ ... first and second locking claws, 46 ... clamping plate.

Claims (1)

[Scope of utility model registration request] A booster shell 1; a first working chamber A connected to a negative pressure source within the booster shell 1; and a second working chamber B selectively communicated with the first working chamber A or the atmosphere via a control valve 6. a booster piston 2 made of a metal plate and housed in the booster shell 1 so as to be able to reciprocate back and forth;
The outer peripheral bead 3a is bonded to the peripheral wall of the booster shell 1, and the inner peripheral bead 3b is polymerized on the rear surface.
A diaphragm 3 is attached to the rim of the valve cylinder fitting hole 38 located at the center of the booster piston 2; and a diaphragm 3 is fitted to the inner circumferential surface of the inner circumferential bead 3b to bring the retaining flange 40 into contact with the front surface of the booster piston 2. the control valve valve cylinder 12; the retaining flange 40;
The plurality of locking pawls 43 ₁ ,
In the negative pressure booster equipped with a clamping plate 46 that engages with the booster piston ₂ , a notch-like recess 41 is formed on the outer circumference of the retaining flange 40, and a notch-like recess 41 is formed on the front surface b of the booster piston 2. A convex portion 42 that bulges forward is molded so as to engage with the concave portion 41 in a relatively non-rotatable manner, and a rear end of a concave portion 42a is formed on the rear surface of the booster piston 2 as the convex portion 42 is bulged. A negative pressure booster characterized in that an opening is covered with the diaphragm 3.