JPH0543543B2 - - Google Patents

Description

[Detailed Description of the Invention] A. Object of the Invention (1) Industrial Application Field The present invention provides a booster shell with a partition plate fixed thereto that partitions the inside of the booster shell into a front shell chamber and a rear shell chamber, A front booster piston that divides the shell chamber into a front negative pressure chamber on the front side and a front working chamber on the rear side; A rear booster piston partitioned into a rear working chamber and a rear diaphragm superimposed on its rear surface are hermetically fixed to the front and rear parts of a piston boss that passes through the partition plate and is connected to the output rod, and the piston boss Inside the valve cylinder, which is connected to the rear end and is slidably supported on the rear wall of the booster shell, there is an input rod that can move forward and backward. The present invention relates to a tandem negative pressure booster that is provided with a control valve that switches communication with a negative pressure chamber.

(2) Prior Art Such a tandem-type negative pressure booster has already been proposed by the present applicant, for example, in JP-A No.
It is known from the publication No. 122766.

The tandem type negative pressure booster is a means for connecting the front and rear booster pistons and the front and rear diaphragms to the piston boss. Three members, the bulkhead plate of the cylinder and the presser plate superimposed on the rear end of the piston boss, are connected with multiple through bolts, so that the front booster piston is connected between the bulkhead plate and the front end of the piston boss. and the front diaphragm, and the rear booster piston and the rear diaphragm are fixed between the presser plate and the rear end of the piston boss.

(3) Problems to be Solved by the Invention By the way, the conventional tandem-type negative pressure booster described above has a large number of parts because it is necessary to pass a plurality of through bolts through the piston boss, bulkhead plate, and retaining plate and tighten them. There is a problem that not only does the number increase, but also that the assembly work requires a lot of effort and time.

In order to solve the above problem, a sleeve is fitted around the outer periphery of the piston boss and locked with a set ring, and the front and rear booster pistons and the front and rear diaphragms are connected to the front and rear parts of the piston boss, respectively, through the sleeve. It is conceivable that the conventional through-bolts could be eliminated and ease of assembly could be improved. However, with the above method, if the setting ring were to fall off, the sleeve would move in the axial direction, and as a result, the front and rear booster pistons and the front and rear diaphragms would separate from the piston boss, and the negative pressure booster There is a risk that functionality may be impaired.

The present invention has been made in view of the above, and even if the settling ring for locking the sleeve that connects the front and rear booster pistons and the front and rear diaphragm to the piston boss falls off, the function of the set ring is maintained. It is an object of the present invention to provide a tandem type negative pressure booster that can be maintained.

B. Structure of the Invention (1) Means for Solving the Problems In order to achieve the above object, the tandem negative pressure booster of the present invention has a claw formed at the inner peripheral end of the front booster piston and a front end of the piston boss. The booster piston and the piston boss are bayonetly connected by the formed notch, and the sleeve is engaged with both the booster piston and the piston boss in a convex-concave manner in a manner that prevents relative rotation, and the front end of the sleeve and the front booster piston are connected to the front. Press the inner bead of the diaphragm and fix it to the front of the piston boss.
Further, the stopper member and the rear end of the sleeve clamp the inner peripheral end of the rear booster piston and the inner peripheral bead of the rear diaphragm to fix them to the rear part of the piston boss.

(2) Effect According to the above configuration, first, the claw formed at the inner peripheral end of the front booster piston is fitted into the notch formed at the front end of the piston boss, and then the piston is rotated by relatively rotating the two. Connect the boss and front booster piston together with a bayonet. Next, a sleeve is fitted to the outer periphery of the piston boss, and this sleeve engages both the piston boss and the front booster piston in a concave and convex manner, thereby regulating the relative rotation between the piston boss and the front booster piston, and connecting the bayonet together. prevent it from coming off. At this time, the inner peripheral bead of the front diaphragm is clamped and fixed between the front end of the sleeve and the front booster piston. Next, by attaching the stopper member to the piston boss, the inner peripheral end of the rear booster piston and the inner peripheral bead of the rear diaphragm are clamped and fixed between the stopper member and the rear end of the sleeve, and at the same time they are fitted into the piston boss. This prevents the sleeve from falling off.

Now, if the stopper member falls off from the piston boss for some reason, the rear booster piston and rear diaphragm separate from the piston boss, the rear negative pressure chamber and the rear working chamber communicate with each other, and the booster function of that part is lost. However, because the front booster piston and the front diaphragm are bayonet-coupled, and the relative rotation between the two is restricted by the uneven engagement with the sleeve, the front booster piston and the front diaphragm immediately fall off the piston boss. As a result, the booster function of the front negative pressure chamber and the front working chamber remains and the effectiveness of the brake is maintained.

(3) Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a brake master cylinder M operated by the booster B is attached to the front surface of a booster shell 1 of a tandem negative pressure booster B. As shown in FIG.

The booster shell 1 includes a pair of front and rear shell halves 1a, 1b whose opposite ends are connected to each other, and is sandwiched between the two shell halves 1a, 1b so that the inside of the booster shell 1 is divided into a front shell chamber 2 and a rear shell chamber. 3, and a partition wall plate 1c that partitions the rear shell half body 1b into
is supported by a vehicle body (not shown).

The front shell chamber 2 includes a front booster piston 4 accommodated therein so as to be able to reciprocate back and forth, and a front booster piston 4 which is superposed and bonded to the rear surface and sandwiched between the front shell half 1a and the partition wall plate 1c. The diaphragm 5 creates a front negative pressure chamber 2a on the front side and a front working chamber 2 on the rear side.
It is divided into b. The rear shell chamber 3 also includes a rear booster piston 6 housed therein so as to be able to reciprocate back and forth, and a rear diaphragm 7 which is superimposed on the rear surface and fixed between the shell halves 1a and 1b together with the partition wall plate 1c. Accordingly, it is divided into a rear negative pressure chamber 3a on the front side and a rear working chamber 3b on the rear side.

The front and rear booster pistons 4 and 6 are annularly formed from steel plates and have a piston boss 10 made of synthetic resin.
A sleeve 12 that fits around the outer periphery of the piston boss 10 is connected to the partition wall plate 1c via the bush 8 and the seal member 9 so as to be connected to the front and rear ends of the booster pistons 4 and 6, respectively, and to be located between the booster pistons 4 and 6. Slidably supported.

That is, as is clear from FIG. 3 and FIG. 4, the piston boss 10 has a circular recess 11 formed in its front end surface with a depth reaching approximately half the length of the boss 10. A flange 10a is provided protruding from the periphery of the opening of the circular recess 11. Flange 1
0a has four notches 10b at equal intervals in the circumferential direction.
is formed, and one stopper 10c is provided protruding from the front surface of the flange 10a. on the other hand,
A flange 4a that comes into contact with the rear surface of the flange 10a of the piston boss 10 is formed at the inner peripheral end of the front booster piston 4 that is fixed to the piston boss 10. Four claws 4b having substantially the same shape as the notch 10b are formed by cutting and raising. When the front booster piston 4 is fixed to the front end of the piston boss 10, the flange 10a of the piston boss 10 is connected to the flange 4a of the front booster piston 4 and the claw 4b, as will be described in detail later. They are sandwiched from the front and back and connected by bayonet.

Sleeve 1 that fits around the outer periphery of piston boss 10
A groove 12a is formed in the axial direction on the inner circumference of the front end of the front booster piston 2, and a protrusion 4c that can be engaged with this groove 12a is formed in the axial direction on the inner circumference of the front booster piston 4 (see FIGS. 1 and 2). (See Figure 3). Further, in another groove 12b formed in the axial direction on the inner circumference of the sleeve 12, a protrusion 10 formed in the axial direction on the outer circumference of the piston boss 10 is provided.
d is engaged (see Figures 1 and 2). Therefore,
When the sleeve 12 is fitted onto the outer circumference of the piston boss 10, the front booster piston 4 and the piston boss 10 are both attached to the sleeve 1 due to the engagement between the groove 12a and the protrusion 4c and the engagement between the groove 12b and the protrusion 10d.
2, and as a result, the front booster piston 4 and the piston boss 10 are also coupled so as not to rotate relative to each other.

When the sleeve 12 is fitted onto the outer periphery of the piston boss 10 in this manner, the inner bead 5a of the front diaphragm 5 is compressed between the front end of the sleeve 12 and the inner peripheral end of the front booster piston 4. and is firmly fixed to the front part of the piston boss 10. Further, the inner circumferential end of the rear booster piston 6 and the inner circumferential bead 7a of the rear diaphragm 7 are engaged with the rear end of the sleeve 12 in a superposed state, and the inner circumferential bead 7
Settling ring 1 with the rear surface of a as a stopper member
It is locked by 3. That is, settling 13
is locked in an annular groove 10e formed at the rear end of the piston boss 10 by a large number of pawls 13a protruding from its inner periphery. The sleeve 12 is firmly fixed to the piston boss 10, and movement of the sleeve 12 in the axial direction is restricted.

Note that the rear working chambers 2b and 3b are connected to a control valve 32, which will be described later.
In order to communicate with the atmosphere through the piston boss 1
A first port 14 is formed at 0. As is clear when referring to FIG. 2 and FIG.
The port 14 includes a passage 14a that passes through the rear end of the piston boss 10 in the radial direction and communicates between the rear working chamber 3b and the control valve 32, and a passage 14b that is formed in the axial direction inside the piston boss 10 and has an arcuate cross section. , a passage 14c rising radially outward from the front end of the passage 14b to the inside of the sleeve 12, and a passage 14d formed axially inside the sleeve 12 and communicating with the front working chamber 2b. Further, the front and rear working chambers 2b and 3b are connected to the front and rear negative pressure chambers 2 through the first port 14 and the control valve 32.
The second port 15 communicated with the control valve 32 extends through the piston boss 10 in the axial direction.
A passage 1 having an arcuate cross section connecting the front negative pressure chamber 2a and the front negative pressure chamber 2a.
5a, a passage 15b rising radially outward from the middle of this passage 15a to the inside of the sleeve 12;
and a passage 15c extending rearward in the axial direction from the passage 15b and communicating with the rearmost part of the rear negative pressure chamber 3a. At that time, in order to align the passages 14c and 15b formed across the piston boss 10 and the sleeve 12, the protrusion 10d and the groove 12b are aligned.
Thus, the piston boss 10 and sleeve 12 are positioned in the rotational direction. And the passage 14
The contact surface between the outer periphery of the piston boss 10 and the inner periphery of the sleeve 12 is sealed by the O-rings 16 installed in two seal grooves 10e formed on the outer periphery of the piston boss 10 so as to be located before and after c. Thus, the first port 14 communicating with the front working chamber 2b
is blocked by the O-ring 16 from communicating between the front negative pressure chamber 2a and the rear negative pressure chamber 3a, and both negative pressure chambers 2
The second port 15 communicating with the rear working chambers 3b and 3a is blocked by the inner bead 7a of the rear diaphragm 7 and the O-ring 16 from communicating with the rear working chamber 3b and the front working chamber 2b.

A circular recess 1 formed at the front end of the piston boss 10
A return spring 23 is compressed between the outer periphery of the piston 1 and the front shell half 1a, and the spring force of the return spring 23 always urges the piston boss 10, that is, both booster pistons 4 and 6 in the backward direction. Ru. The retraction limit of both booster pistons 4 and 6 is determined by the rear diaphragm 6.
A large number of protrusions 24 on the rear surface abut against the rear wall of the booster shell 1, thereby regulating the booster shell 1.

The front negative pressure chamber 2a is connected to a negative pressure source (not shown, for example, inside the intake manifold of an internal combustion engine) via a negative pressure introduction pipe 29, and is also connected to the piston boss 1.
The second port 15 is connected to the rear negative pressure chamber 3a through a second port 15 formed at the rear negative pressure chamber 3a. Also, the front and rear working chambers 2b,
3b communicate with each other via a first port 14 formed in the piston boss 10, and the control valve 32
The end wall 26 of the rear extension tube 26 is connected to the front and rear negative pressure chambers 2a, 3a and the rear end of the booster shell 1.
Communication is alternately switched to the atmospheric air inlet 33 which opens to a.

In the valve cylinder 25 connected to the rear of the piston boss 10, there is an input rod 35 connected to the brake pedal 34.
The control valve 32 controlled thereby is provided as follows. That is, a valve piston 38 is slid into the front part of the inside of the valve cylinder 25, and this valve piston 38
, there is an input rod 35 passing through the air inlet 33.
The front ends of the two are connected to each other so as to be swingable. Also, the valve cylinder 25
An annular first valve seat 39 is protruded from the inner peripheral surface of the valve piston 38, and an annular second valve seat 40 surrounded by the annular first valve seat 39 is formed on the rear end surface of the valve piston 38.
A valve body 41 cooperating with the valve body 25 is arranged in the valve barrel 25 .
The valve body 41 is made of rubber and has a cylindrical shape with both front and rear ends open, with a rear end, that is, a base end 41a.
is held in close contact with the inner circumferential surface of the valve tube 25 by the holding tube 42 fitted onto the inner circumferential surface of the valve tube 25 . The valve body 41 includes a thin flexible portion 41b bent radially inward from the base end 41a, and a thick valve portion 41c continuous to the front end of the flexible portion 41b.
The valve portion 41c is arranged to face the first and second valve seats 39 and 40. Thus, the valve part 41c can be moved back and forth by deforming the flexible part 41b, and is seated on the first and second valve seats 39, 40 when moving forward, and is received at the front end of the holding cylinder 42 when moving backward. .

An annular reinforcing plate 43 is embedded in the valve portion 41c,
A valve spring 44 is compressed between this and the input rod 35 and urges the valve portion 41c toward both valve seats 39 and 40. On the inner surface of the valve cylinder 25, one end of the second port 15 is located outside the first valve seat 39, and one end of the second port 15 is located outside the first valve seat 39.
One end of each of the first ports 14 opens inside the first port 9 . Further, the inside of the second valve seat 40 communicates with the atmosphere inlet 33 through the hollow part of the valve body 41 and the holding cylinder 42 . Thus, the valve body 41, the valve spring 44, the first
The control valve 32 is configured by the valve seat 39 and the second valve seat 40.

Between the input rod 35 and the holding cylinder 42, the input rod 35
A return spring 45 is provided that urges the return spring 45 toward its retraction limit. The backward limit of the input rod 35 is regulated by a stopper plate 46 that is screwed into the input rod 35 so as to be adjustable in forward and backward movement and comes into contact with the inner surface of the end wall 26a of the rear extension tube 26 via a washer 48. Therefore,
By turning the stopper plate 46, the screwing position between the stopper plate 46 and the input rod 35 changes, so that the retraction limit of the input rod 35 can be adjusted back and forth. After this adjustment, the stopper plate 46 is fixed using the input rod 35.
This is done by tightening a lock nut 47 that is screwed into the lock nut 47. The above washer 48 has this air inlet port 3.
A ventilation hole 48a is provided so as not to block the air hole 3.

The valve cylinder 25 is provided with an air filter 4 for filtering air taken into the valve cylinder 25 from the atmosphere inlet 33.
9 is attached to surround the input rod 35. This air filter 49 has appropriate flexibility so as not to impede relative displacement between the input rod 35 and the valve cylinder 25.

The piston boss 10 is provided with a piston portion 37 protruding from the center of its front surface, and a cylinder hole 36 that opens at both ends into the front surface of the piston portion 37 and into the valve cylinder 25. A reaction piston 52 that is integral with or in contact with the valve piston 38 is slid into the cylinder hole 36, and the piston portion 37 has an output that holds an elastic piston 50 facing the reaction piston 52 inside. The cylinder 51 is slid together. An output rod 53 is protruded from the front surface of the output cylinder 51, and the output rod 53 is connected to the piston 55 of the brake master cylinder M.

Next, the operation of this embodiment will be explained. First, when the negative pressure booster B is at rest, as shown in Fig. 1,
The input rod 35 is located at the backward limit, and the control valve 32 has the valve portion 41c seated on the first and second valve seats 39, 40, and the front and rear working chambers 2b, 3b are connected to both the negative pressure chambers 2.
The control valve 32 is in a neutral state where it is disconnected from both the negative pressure chambers 2a and 3a and the atmospheric air inlet 33. Negative pressure is stored, and the negative pressure appropriately diluted with the atmosphere is maintained in both working chambers 2b and 3b. In this way, a slight forward force is applied to the front and rear booster pistons 4 and 6 due to the pressure difference generated between the negative pressure chamber 2a and the working chamber 2b at the front, and between the negative pressure chamber 3a and the working chamber 3b at the rear. ,
These forward forces are balanced with the elastic force of the return spring 23, so that both booster pistons 4 and 6 are stopped when they have advanced slightly from the retraction limit.

Now, when the brake pedal 34 is depressed to brake the vehicle and the input rod 35 and the valve piston 38 are moved forward, since both the booster pistons 4 and 6 are initially stationary, the second valve seat 40 moves away from the valve portion 41c. The two working chambers 2b and 3b are immediately separated and communicated with the atmosphere inlet 33. As a result, the atmosphere is quickly introduced from the atmosphere inlet 33 through the second valve seat 40 and the first port 14 into the working chambers 2b, 3b.
Since b is made to have a higher pressure than both negative pressure chambers 2a and 3a, as shown in FIG. It moves forward with good response, and the output rod 5
3, the piston 55 of the brake master cylinder M is driven forward. In this way, the brake master cylinder M can be operated without delay when the brake pedal 34 is depressed, and the vehicle can be braked. At this time, since the passage 15c of the second port 15 formed in the piston boss 10 opens at the rear end of the rear negative pressure chamber 3a, it is possible to ensure a sufficient stroke of the piston boss 10, that is, the stroke of the piston 55. can.

During such braking, the valve piston 38 also advances together with the input rod 35 and comes into contact with the elastic piston 50 via the reaction piston 52.
0 bulges and deforms toward the cylinder hole 36 side in response to the actuation reaction force of both booster pistons 4 and 6, and a part of the reaction force acts on the reaction force piston 52, so that force is transferred to the valve piston 38 and the input Feedback is provided to the brake pedal 34 via the rod 35. Due to such a reaction force, the driver can sense the output of the output rod 53, that is, the magnitude of the braking force.

When the output of the output rod 53 exceeds the boosting limit point due to an increase in the pedal force on the brake pedal 34, that is, the input to the input rod 35, the front surface of the valve piston 38 comes into contact with the piston boss 10, so that the entire input is applied to the valve piston. 38, the output rod 53 via the piston boss 10, the elastic piston 50 and the output cylinder 51
As a result, the sum of the forward force due to the pressure difference between the booster pistons 4 and 6 and the forward force due to the input is output from the output rod 53.

Next, when the pedal force on the brake pedal 34 is released, the input rod 35 moves back together with the valve piston 38 due to the elastic force of the return spring 45, and the second valve seat 4
0 is seated on the valve portion 41c of the valve body 41, and the valve portion 41c is separated from the first valve seat 39 by a large distance. , 6 immediately disappears, and therefore both booster pistons 4 and 6 move back with the elastic force of the return spring 23, and the operation of the brake master cylinder M is released. Then, when the input rod 35 returns to the backward limit where the stopper plate 46 contacts the partition wall 26a of the extension tube 26, the rear booster piston 6 temporarily brings the protrusion 24 of the rear diaphragm 7 into contact with the rear wall of the booster shell 1. Return to the retraction limit and this time move to the first valve seat 3
9 is seated on the valve seat 41c, and the valve portion 41c is slightly spaced from the second valve seat 402, so that the atmosphere is again introduced into both working chambers _2b and 3b, but due to the resulting pressure difference, both booster pistons 4 and 6 move forward a little, the small gap between the second valve seat 40 and the valve portion 41c disappears, and the control valve 32 is brought to its initial neutral state. In this way both working chambers 2b, 3b
The negative pressure diluted with the atmosphere is maintained, and the negative pressure booster B enters the rest state as shown in FIG.

In such a tandem type negative pressure booster B, in order to fix the front and rear booster pistons 4 and 6 and the front and rear diaphragms 5 and 7 to the piston boss 10, first, the piston boss 10 is attached to the inside of the front booster plate 4. Insert the piston boss 1 into the circumference from the master cylinder M side as shown in Fig. 4.
Four notches 10 formed in the flange 10a of 0
The four pawls 4b of the front booster piston 4 are fitted into the parts b. From this state, the booster piston 10 is further pushed forward, and the front booster piston 4 is rotated in the direction of arrow A at a position where the rear surface of the flange 10a abuts the front surface of the flange 4a of the front booster piston 4. Then, as shown in FIG. 3, the four pawls 4b of the front booster plate 4 wrap around the front surface of the flange 10a of the piston boss 10, and one pawl 4b comes into contact with a stopper 10c formed on the piston boss 10. At this position, the front booster piston 10 stops rotating. In this state, the flange 10a of the piston boss 10 is sandwiched from the front and back by the flange 4a of the front booster plate 4 and the pawl 4b, and are joined together by a so-called bayonet connection.

When the inner peripheral end of the front booster piston 4 is fixed to the piston boss 10 as described above, the sleeve 12 is inserted from the rear end side of the piston boss 10 toward the front. Sleeve 12 is piston boss 1
0, the front booster piston is completely fitted to the outer periphery of the piston boss 10 by the engagement of the groove 12a of the sleeve 12 with the protrusion 4c of the front booster plate 4, and the engagement of the groove 12b of the sleeve 12 with the protrusion 10d of the piston boss 10. 4 and piston boss 10 are both sleeve 12
It is coupled so that it cannot rotate relative to it. As a result, the relative rotation between the piston boss 10 and the front booster piston 4 is also restricted via the sleeve 12, and separation of the piston boss 10 and the front booster piston 4, which are integrated by the bayonet connection, is prevented. be done. And sleeve 12
In the state where is fitted into the piston boss 10,
The inner peripheral bead 5a of the front diaphragm 5 is located between the front end of the sleeve 12 and the front booster plate 4.
is clamped and fixed. At this time, the front end of the sleeve 12 inserted from the rear causes the partition plate 1c to
Since the sealing member 9 provided in
pressure leakage is effectively prevented. Next, the inner peripheral end of the rear booster piston 6 and the inner peripheral bead 7a of the rear diaphragm 7 are fitted to the rear end of the sleeve 12 from behind, and then the setting ring 1 is fitted to the rear end of the sleeve 12.
3, the rear booster piston 6 and rear diaphragm 7 are clamped and fixed between the rear end of the sleeve 12 and the settling ring 13.

Now, if the settling ring 13 falls off from the annular groove 10e of the piston boss 10 for some reason, the rear booster plate 6 and the rear diaphragm 7 will separate from the piston boss 10, so that the rear negative pressure chamber 3a and the rear working chamber 3b will be mutually connected. The booster function will be impaired. However, the front booster piston 4 and the front diaphragm 5 are bayonet connected to each other, and both members are connected to the sleeve 12.
Since the relative rotation is restricted through the bayonet, the bayonet connection is immediately separated and the front negative pressure chamber 2a and the front working chamber 2b are prevented from communicating with each other. As a result, the rear negative pressure chamber 3a and the rear working chamber 3b
Even if the booster function of the front negative pressure chamber 2a is impaired,
The booster function of the front working chamber 2b remains, and the reliability of the brake device can be improved.

C. Effects of the Invention As described above, according to the present invention, even if the stopper member that fixes the sleeve to the piston boss falls off for some reason, the front booster piston and the piston boss are bayonet-coupled, and the relative relationship between the two Since the rotation is restricted by the uneven engagement with the sleeve, the front booster piston and the front diaphragm are prevented from immediately falling off from the piston boss. As a result, even after the stopper member falls off, the booster function of the front negative pressure chamber and the front working chamber remains, improving the reliability of the brake system.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a longitudinal sectional side view of a tandem negative pressure booster in a rest state, and FIGS. 2 and 3 are sectional views taken along lines - and - in FIG. 1. , FIG. 4 is the same sectional view as FIG. 3, showing the procedure for connecting the piston boss and the front booster piston, and FIG. 5 is a partial longitudinal sectional side view showing the operating state of the negative pressure booster. 1... Booster shell, 1c... Partition plate, 2... Front shell chamber, 2a... Front negative pressure chamber, 2b... Front working chamber, 3... Rear shell chamber, 3a... Rear negative pressure chamber, 3b
...Rear working chamber, 4...Front booster piston, 4b
...Claw, 5...Front diaphragm, 5a...Inner bead, 6...Rear booster piston, 7...Rear diaphragm, 7a...Inner circumference bead, 10...Piston boss, 10b...Notch, 12...Sleeve, 13...Settling (stopper member), 25...valve cylinder, 32
...Control valve, 35...Input rod, 53...Output rod.

Claims (1)

[Claims] 1. A partition plate 1c is fixed to the booster shell 1 to partition the inside thereof into a front shell chamber 2 and a rear shell chamber 3, and the front shell chamber 2 is connected to a front negative pressure chamber 2a on the front side. A front booster piston 4 that divides the rear shell chamber 3 into a rear negative pressure chamber 3a and a rear rear working chamber 2b, a front diaphragm 5 superimposed on the rear surface thereof, and a front rear negative pressure chamber 3a and a rear rear working chamber 2b. A rear booster piston 6 divided into 3b and a rear diaphragm 7 superimposed on its rear surface are attached to the front and rear portions of the piston boss 10 that passes through the partition wall plate 1c and is connected to the output rod 53. A sleeve 1 that fits around the outer periphery and is locked at the rear end by a stopper member 13
2, and the piston boss 10
In the valve cylinder 25 that is connected to the rear end and is slidably supported on the rear wall of the booster shell 1, there is an input rod 35 that can move back and forth, and both working chambers are opened in response to the back and forth movement of the input rod 35. 2b, 3b to the atmosphere and both negative pressure chambers 2a, 3a
It is a tandem type negative pressure booster equipped with a control valve 32 that switches communication between the front booster piston 4 and the front booster piston 4. The front booster piston 4 and the piston boss 10 are bayonet-coupled, and the sleeve 12 is engaged with both the booster piston 4 and the piston boss 10 in a concave-convex manner so that the front end of the sleeve 12 and the front booster piston 4 are connected together. The inner peripheral bead 5a of the front diaphragm 5 is clamped and fixed to the front part of the piston boss 10, and the rear ends of the stopper member 13 and sleeve 12 are connected to the inner peripheral end of the rear booster piston 6 and the inner periphery of the rear diaphragm 7. A tandem type negative pressure booster characterized in that a bead 7a is compressed and fixed to the rear part of a piston boss 10.