JP2510869B2 - Tandem negative pressure booster - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Field of Industrial Application The present invention relates to a tandem-type negative pressure booster used for vehicle brake operation and the like, and more particularly to a booster shell,
A partition plate is fixedly installed to partition the interior into a front shell chamber and a rear shell chamber, and a front booster piston that divides the front shell chamber into a front negative pressure chamber on the front side and a front working chamber on the rear side is provided. , A rear booster piston that partitions the rear shell chamber into a front rear negative pressure chamber and a rear rear working chamber is connected via a piston boss slidably supported by the partition plate and connected to an output rod. A first valve cylinder is integrally formed with the piston boss and projects from the rear end thereof and is slidably supported by the rear wall of the booster shell, and communicates with both negative pressure chambers in the first cylinder.
A port and a second port that communicates with both working chambers in the same valve cylinder are provided, and this second port connects the axial port that communicates between the front and rear working chambers and the rear working chamber and the valve cylinder. A radial port, and an input rod that can be moved back and forth inside the valve cylinder; and a second port that is provided with a first port according to the forward and backward movement of the input rod.
The present invention relates to a tandem type negative pressure booster provided with a control valve for switching communication between a port and the atmosphere.

(2) Prior Art Such a negative pressure booster is already known, as disclosed in, for example, Japanese Utility Model Laid-Open No. 62-121160.

(3) Problems to be Solved by the Invention Conventionally, the axial port and the radial port of the second port provided in the piston boss are arranged so as to be separated from each other in the circumferential direction of the piston boss, and between the ports. A step portion of the piston boss, a stopper member, and the like are interposed in this. Therefore, when the control valve is switched, the flow of air between the axial port and the radial port is resisted, the responsiveness of the booster piston is reduced, and the wind noise is emitted by the present inventors. It was investigated.

Therefore, according to the present invention, when the control valve is switched, the response of the booster piston is good, no wind noise is generated, and the piston boss and the valve cylinder are integrally formed.
It is an object of the present invention to provide a tandem-type negative pressure booster whose ports can be easily processed.

B. Configuration of the Invention (1) Means for Solving the Problems According to the present invention in order to achieve the above object, according to the present invention, the axial port and the radial port of the second port are respectively shafts opening to the rear working chamber. The rear end of the directional port and the outer end of the radial port are arranged at the same position in the circumferential direction of the piston boss, and the opening to the rear working chamber of the rear end of the axial port is the radial port. The outer end is expanded in the radial direction of the piston boss more than the front portion of the axial port so as to be close to the opening to the rear working chamber, and the openings are located on the outer surface of the piston boss between them. It is formed and connected to the inner surface of each opening through a smoothly continuous curved surface.

(2) Action The position of the opening of the second port in the axial direction and the radial port to the rear working chamber is the same in the circumferential direction of the boss, and the rear end opening of the axial port in order to bring the two openings close to each other. The parts are expanded in the radial direction of the piston boss, and the inner surfaces of both openings are connected by the curved surface on the outer peripheral surface of the piston boss. In addition to shortening the section, the air flow between the openings can be made smooth.

Therefore, when air flows between the axial port and the radial port due to the switching of the control valve, the air smoothly and quickly passes through the extremely short curved surface corresponding section in the rear working chamber.

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

First, in FIG. 1, a brake master cylinder M operated by the booster B is mounted on the front surface of the booster shell 1 of the tandem type negative pressure booster B.

The booster shell 1 includes a pair of front and rear shell halves 1a and 1b for connecting opposing ends to each other, and is sandwiched between the two shell halves 1a and 1b to divide the inside of the booster shell 1 into a front shell chamber 2 and a rear shell chamber. The rear shell half 1b is supported by a vehicle body (not shown).

The front shell chamber 2 is a steel-made front booster piston 4 accommodated therein so as to be able to reciprocate back and forth, and is superposed and bonded to the rear surface thereof and is sandwiched between the front shell half 1a and the partition plate 1c. The front diaphragm 5 made of rubber is partitioned into a front negative pressure chamber 2a on the front side and a front working chamber 2b on the rear side. The rear shell chamber 3 has a rear booster piston 6 made of a steel plate accommodated therein so as to be able to reciprocate back and forth, and is bonded to the rear surface by polymerization and fixed between the two shell halves 1a and 1b together with the partition plate 1c. The rear diaphragm 7 made of rubber is divided into a front 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 each formed into an annular shape by a steel plate, and these are attached to both ends of a piston boss 10 made of synthetic resin slidably supported on the partition plate 1c via a push 8 and a seal member 9. It is bound as follows.

That is, the piston boss 10 is formed with a circular recess 11 whose depth reaches approximately half the length of the boss 10 at the front end face, and a flange 12 at a position slightly forward from the rear end of the outer peripheral face.
The circular concave portion 11 has a connecting tube 1 with an end wall plate 13a connected to the inner peripheral end of the front booster piston 4.
3 is fitted, and a holding plate 14 for holding the rear booster piston 6 in cooperation with the flange 12 is overlapped on the rear end face of the piston boss 10. The holding plate 14, the piston boss 10, and the end wall plate 13a are mutually connected by a plurality of (three in the figure) through bolts 15 surrounding the axis of the piston boss 10 and a nut 16 screwed to them. To be fixed.

At this time, between the front booster piston 4 and the front end face of the piston boss 10, the inner peripheral bead 5a of the front diaphragm 5 is provided.
And an annular retainer 17 made of metal covering the outer peripheral surface and the rear surface of the inner peripheral bead 5a.
14, an inner bead 7a of the rear diaphragm 7 surrounding the inner peripheral end of the rear booster piston 6 is inserted. Therefore, the front and rear booster pistons 4, 6 and the piston boss 1
Each of the three diaphragms is bound together and each diaphragm
Booster pistons 4,6 corresponding to inner peripheral beads 5a, 7a of 5,7
To be fixed.

Furthermore, to insert the through bolt 15, the piston boss 10
A seal member 19 is attached to the bolt hole 18 provided in the
As a result, communication between the front negative pressure chamber 2a and the rear working chamber 3b by the bolt hole 18 is prevented. Further, a seal member 20 surrounding the plurality of through bolts 15 is interposed between the end wall plate 13a and the piston boss 10, whereby the end wall plate 13a
Further, communication between the first and second ports 30 and 31 described below due to the contact surface gap of the piston boss 10 is prevented.

Each through-bolt 15 is disposed with its square head 15a facing the rear working chamber 3b, and a recess 21 (see FIG. 2) of the same shape into which the square head 15a fits in a non-rotatable manner is provided on the holding plate 14. It is formed. Therefore, when the nut 16 is screwed into the bolt 15 on the front negative pressure chamber 2a side, the rotation of the bolt 15 is prevented, so that the nut 16 can be securely tightened.

Using the through bolt 15 and the nut 16, the connecting cylinder 13
The seat plate 22 is superposed and bonded to the end wall plate 13a. This seat plate 22
Is provided with a plurality of seats 22a (see FIG. 3) raised above the height of the nut 16 between the plurality of nuts 16, and a piston boss is provided between the seat 22a and the front shell half 1a. A return spring 23 for urging the lever 10 in the backward direction is contracted. In this way, the return spring 23 together with the connecting cylinder 13 is a recess on the front surface of the piston boss 10.
Accepted by 11.

The retreat limit of both booster pistons 4 and 6 is defined by a large number of protrusions 24, which are raised on the rear surface of the rear diaphragm 6, contacting the rear wall of the booster shell 1.

The front negative pressure chamber 2a is connected to a negative pressure source (not shown) (for example, the inside of an intake manifold of an internal combustion engine) via a negative pressure introducing pipe 29. The front and rear negative pressure chambers 2a and 3a are
The boss 1 through the bifurcated first port 30 drilled in 0
It communicates with the inside of the valve cylinder 25 integrally formed at the rear end of 0,
Both rear working chambers 2b and 3b communicate with the inside of the valve cylinder 25 via a pair of second ports 31 and 31 that are also formed in the piston boss 10. Then, the second ports 31, 31 are alternately connected and switched by the control valve 32 in the valve cylinder 25 to the first port 30 and the atmosphere introduction port 33 opening to the end wall 26a of the rear extension cylinder 26.

An input rod 35 connected to the brake pedal 34 is provided in the valve cylinder 25.
The control valve 32 controlled thereby is provided as follows. That is, a valve piston 38 is slidably fitted to a front portion in the valve cylinder 25, and a front end of an input rod 35 penetrating through the air introduction port 33 is swingably connected to the valve piston 38. Also on the inner peripheral surface of the valve cylinder 25 first valve seat 40 _first annular is projected, the second valve seat 40 _second annular, surrounded thereto is formed on the rear end face of the valve piston 38, these valve seats Valve element 41 cooperating with 40 ₁ , 40 ₂
Is disposed in the valve cylinder 25. The valve body 41 is made of rubber and has a cylindrical shape with both front and rear ends open.The rear end, that is, the base end 41a, is opened by a holding cylinder 42 fitted on the inner peripheral surface of the valve cylinder 25. It is held in close contact with the inner peripheral surface of the cylinder 25. This valve body
41 includes a thin flexible portion 41b bent inward in the radial direction from the base end portion 41a, and a thick valve portion 41c connected to the front end of the flexible portion 41b. First and second
It is arranged so as to face the valve seats 40 ₁ and 40 ₂ .

And Thus, the valve portion 41c be capable of moving back and forth by the deformation of the flexible portion 41b, it is seated on the first and second valve seat 40 _1, 40 ₂ at the time of forward movement, received at the front end of the holding cylinder 42 during retraction Can be stopped.

The valve portion 41c is embedded annular reinforcement plate 43, between the input rod 35 and this, a valve spring 44 which biases the valve portion 41c to both valve seat 40 _1, 40 ₂ are compressed state You.

The inner surface of the valve cylinder 25, one end of the first port 30 on the outside of the first valve seat 40 _1, One end of the second port 31 on the inside of the valve seat 40 ₁ is opened, respectively.

The inside of the second valve seat 40 ₂ communicates with the atmosphere introduction port 33 through the hollow portion of the valve body 41 and the holding cylinder 42.

And Thus, the valve element 41, the control valve 32 is constituted by a valve spring 44, first valve seat 40 ₁ and the second valve seat 40 _2.

Between the input rod 35 and the holding cylinder 42, a return spring 45 for urging the input rod 35 toward the backward limit thereof is contracted.

The retraction limit of the input rod 35 is regulated by the stopper plate 46 screwed to the input rod 35 so as to be able to advance and retreat, in contact with the inner surface of the end wall 26a of the rear extension cylinder 26. Therefore, the stopper plate 46
By turning, 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 the adjustment, the stopper plate 46 is fixed by the input
This is performed by tightening a lock nut 47 screwed to 35. A vent hole 48 is formed in the stopper plate 46 so that the stopper plate 46 does not block the air inlet 33.

An air filter 49 for filtering air taken into the valve cylinder 25 from the air inlet 33 is attached to the valve cylinder 25 around the input rod 35. The air filter 49 includes the input rod 35 and the valve cylinder 25.
It has appropriate flexibility so as not to interfere with relative displacement with.

The piston boss 10 is provided with a large cylinder hole 37 opening at the center of the front surface thereof, and a small cylinder hole 36 opening at both ends in the large cylinder hole 37 and the valve cylinder 25. A reaction piston 52 integral with or in contact with the valve piston 38 is slid into the small cylinder 36, and an elastic piston 50 opposed to the reaction piston 52 is fitted into the large cylinder hole 37.
Further, the output piston 51 which is superposed on the front surface of the elastic piston 50 is slidably fitted. Large cylinder hole of this output piston 51
The inner peripheral edge of the end wall plate 13a extends to the opening of the large cylinder hole 37 in order to prevent the end wall plate 13a from being pulled out.

An output rod 53 projects from the front surface of the output piston 51. The output rod 53 is a piston 55 of the brake master cylinder M.
Will be serialized.

In FIGS. 1, 4 and 5, each of the second ports 31 is an axial port 31A communicating between the two working chambers 2b and 3b.
And a radial port 31R communicating between the rear working chamber 3b and the valve cylinder 25. The axial port 31A and the radial port 31R have the rear end of the axial port 31A and the outer end of the radial port 31R both of which directly open to the rear working chamber 3b and are identical to each other in the circumferential direction of the piston boss 10. The openings of the rear end of the axial port 31A and the outer end of the radial port 31R to the rear working chamber 3b are formed on the outer peripheral surface of the piston boss 10 between them. A curved surface r that smoothly continues to the inner surface of each opening of the lever
Connected via

The axial port 31A includes a rear elongated hole c extending from the rear end of the piston boss 10 to the vicinity of the recess 11 and a piston boss.
A front elongated hole a extending from the front end of 10 to near the rear elongated hole c;
It is composed of a taper hole b that continuously connects the two elongated holes a and c. Although the long holes a and c are arranged with their long diameters oriented in the circumferential direction of the piston boss 10, the front long hole a is formed flatter and has a larger long diameter than the rear long hole c. Thus, the opening to the rear working chamber 3b of the rear end of the axial port 31A (that is, the opening to the rear working chamber 3b of the rear elongated hole c) extends to the rear working chamber 3b of the outer end of the radial port 31R. Axial port 31A as shown in FIGS. 1 and 5 so that it is close to the opening.
Is expanded in the radial direction of the piston boss 10 from the front side portion (that is, the taper hole b, the front elongated hole a).

Further, the front elongated hole a is formed by covering the axial groove 56 formed on the inner peripheral surface of the recess 11 of the piston boss 10 with the outer peripheral surface of the connecting cylinder 13, and the front end of the front elongated hole a has the piston boss 10 at its front end. Is a notch 57 that opens to the front end surface and the outer peripheral surface of the.
With this configuration, when the piston boss 10 is molded, the front long hole a having a large degree of flatness can be easily formed by the mold.

Next, the operation of this embodiment will be described. First, in the rest state of the negative pressure booster B, as shown in FIG. 1, the input rod 35 is located at the retreat limit, and the control valve 32 moves the valve portion 41c to the first and second valve seats 40 ₁ and 40 ₂ . It is in a neutral state in which the front and rear working chambers 2b, 3b are disconnected from both the negative pressure chambers 2a, 3a and the air introduction port 33 after being seated, and the negative pressure chambers 2a, 2a, Three
The negative pressure of the negative pressure source supplied through the negative pressure introducing pipe 29 is stored in b, and the negative pressure appropriately diluted by the atmosphere is held in both working chambers 2b and 3b. Thus, a slight forward force is applied to the front and rear booster pistons 4 and 6 by the pressure difference between the front negative pressure chamber 2a and the working chamber 2b and between the rear negative pressure chamber 3a and the working chamber 3b. When these forward forces and the resilient force of the return spring 23 are balanced, the booster pistons 4 and 6 stop when they slightly advance from the retreat limit.

Now, depress the brake pedal 34 to brake the vehicle,
If caused to advance the input rod 35 and the valve piston 38, initially, since both booster pistons 4 and 6 are stationary, the second valve seat 40 ₂ immediately away both working chambers 2b from the valve portion 41c, the 3b atmosphere introduction Connect to mouth 33. As a result, the atmosphere is both operating chambers 2b through the second valve seat 40 ₂ and the second port 31 from the air inlet 33, is quickly introduced into 3b, the chamber 2b, 3b and Ryomake chamber 2a, to a high pressure from 3a Therefore, the booster pistons 4, 6 move forward with good response against the force of the return spring 23 by obtaining a large forward force based on the pressure difference between them, and move the piston 55 of the brake master cylinder M forward through the output rod 53. Drive to In this way, the brake master cylinder M can be operated without delay when the brake pedal 34 is depressed to brake the vehicle.

During such braking, the valve piston 38 moves forward together with the input rod 35 and abuts on the elastic piston 50 via the reaction force piston 52.
Receiving the operation reaction force, swells and deforms toward the small cylinder hole 36 to cause a part of the reaction force to act on the reaction force piston 52, and the force is applied to the brake pedal via the valve piston 38 and the input rod 35.
Feedback to the 34 side. The operator can sense the output of the output rod 53, that is, the magnitude of the braking force by the reaction force.

When the output of the output rod 53 exceeds the boosting limit point due to the increase in the input force of the input rod 35, the pedaling force on the brake pedal 34,
Since the front surface of the valve piston 38 is in contact with the piston boss 10, the entire input is transmitted to the output rod 53 via the valve piston 38, the piston boss 10, the elastic piston 50, and the output piston 51. 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 the output rod 53.
Output from

Next, when the pedaling force on the brake pedal 34 is released,
First, the input rod 35 is moved by the spring force of the return spring 45 to the valve piston 38.
With this, the second valve seat 40 ₂ is seated on the valve portion 41c of the valve body 41, and the valve portion 41c is largely separated from the first valve portion 40 _1, so that both working chambers 2b and 3b have the first and second working chambers 2b and 3b. By communicating with both negative pressure chambers 2a and 3a via ports 30 and 31, the pressure difference between the booster pistons 4 and 6 immediately disappears, so that both booster pistons 4 and 6 are retracted by the elastic force of the return spring 23. , The operation of the brake master cylinder M is released. When the input rod 35 returns to the retreat limit where the stopper plate 46 contacts the partition 26a of the extension cylinder 26, the rear booster piston 6 moves to the sixth position.
As shown, once return the protrusion 24 of the rear diaphragm 7 to the retracted limit to abut the rear wall of the booster shell 1, the valve portion 41c with turn to seat the first valve seat 40 ₁ in the valve seat 41c
Since slightly moved away from the second valve seat 40 _2, the second port 3
Both working chambers 2b again through 1, but the air is introduced into 3b, it small clearance between the second valve seat 40 ₂ and the valve portion 41c when the forward both booster pistons 4 and 6 Sukoshiku by pressure difference caused by the eliminated Then, the control valve 32 is returned to the initial neutral state. In this way, the working chambers 2b and 3b hold the negative pressure diluted with the atmosphere,
The negative pressure booster B enters the rest state shown in FIG.

In such a tandem type negative pressure booster B, the connecting cylinder 13 connected to the piston boss 10 and the front booster piston 4
A plurality of through bolts 15 arranged around the axis of the piston boss 10 by pressing the three end plates 13a and the holding plate 14 which sandwiches the rear booster piston 6 in cooperation with the piston boss 10;
The nut is screwed to these, and the nut is screwed together. Further, an inner circumferential bead 5a of the front diaphragm 5 is provided between the front booster piston 4 and the piston boss 10, and a rear diaphragm 7 is provided between the rear booster piston 6 and the holding plate 14. Inner bead 7a
Since the piston bosses 10 are respectively inserted, the front and rear pistons 4 and 6 and the front and rear diaphragms 5 and 7 can be bonded thereto without dividing the piston boss 10, and the end wall plate 13a of the connecting cylinder 13 is connected. Since the pressing plate 14 is restrained from rotating by a plurality of through bolts 15, it does not rotate even when the nut 16 is tightened, which prevents the front and rear diaphragms 5 and 7 from being twisted.

Further, the positions of the openings of the axial port 31A and the radial port 31R that form the second port 31 in the rear working chamber 3b are the same in the boss circumferential direction, and that both openings are axially close to each other. The rear end opening of the port 31A expands in the radial direction of the boss, and the inner surfaces of both openings are connected to each other by the curved surface r on the outer peripheral surface of the piston boss 10. It is possible to achieve a great reduction in the section between both openings and to make the flow of air between both openings smooth. As a result, control valves
Axial port 31A and radial port 31R with switching of 32
When air flows through the space, the air can smoothly and quickly pass through the extremely short curved surface corresponding section in the rear working chamber 3b, and therefore the responsiveness of the front and rear booster pistons 4 and 6 becomes good. The generation of wind noise is suppressed as much as possible.

Further, the axial port 31A of the second port 31 has a rear elongated hole c extending from the rear end of the piston boss 10 to the vicinity of the concave portion 11 with its major axis oriented in the circumferential direction of the piston boss 10, and the rear elongated hole c. Since it is flat and has a large major diameter and extends from the front end of the piston boss 10 to a position close to the rear elongated hole c, it is composed of a front elongated hole a and a tapered hole b continuously following between the front and rear elongated holes a and c. , The cross-sectional area of the axial port 31A can be made sufficiently large over the entire length without being restricted by the recessed portion 11, and therefore, when the control valve 32 is switched, a large amount of air smoothly flows in the axial port 31A. Is possible.

C. Effects of the Invention As described above, according to the present invention, the axial port and the radial port of the second port have the rear end of the axial port and the outer end of the radial port that open to the rear working chamber, respectively. The piston bosses are arranged at the same position in the circumferential direction, and the opening to the rear working chamber of the rear end of the axial port is close to the opening to the rear working chamber of the outer end of the radial port. The opening is expanded in the piston boss radial direction from the front side portion of the axial port, and the two opening portions are formed on the outer surface of the piston boss between them so as to form a smoothly continuous curved surface on the inner surface of the opening portion. Since it is connected via the axial port and the radial port, it is possible to achieve a great reduction in the section between the openings of the axial port and the radial port to the rear working chamber, and to smooth the air flow between the openings. Can be Therefore, when air flows between the axial port and the radial port due to the switching of the control valve, it can pass smoothly through the short curved surface corresponding section in the rear working chamber, and the response of the booster piston This can contribute to improvement and prevention of wind noise.

Further, since the rear end of the axial port and the outer end of the radial port of the second port both open directly to the rear working chamber, the piston boss and the valve cylinder are integrally formed, but Processing can be performed without difficulty.

[Brief description of drawings]

The drawings show one embodiment of the present invention. FIG. 1 is a vertical sectional side view of a tandem type negative pressure booster in a resting state, and FIGS. 2 and 3 are lines II-II and III- of FIG. III line sectional view, FIG. 4 is a plan view of the piston boss, FIG. 5 is VV of FIG.
FIG. 6 is a partial vertical sectional side view showing a state immediately before the negative pressure booster finishes its operation and returns to the rest state. B ... Negative pressure booster, r ... Curved surface, 1 ... Booster shell, 1a, 1b ... Shell half, 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,
5 …… front diaphragm, 5a …… inner bead, 6 …… rear booster piston, 7 …… rear diaphragm, 10 ……
Piston boss, 13 ... Connection tube, 13a ... End wall plate, 14 ...
Holding plate, 15 ... through bolt, 16 ... nut, 25 ... valve cylinder, 30 ... first port, 31 ... second port, 31A ... axial port, 31R ... radial port, 32 ... … Control valves, 3
3 ... Atmosphere inlet, 35 ... Input rod, 53 ... Output rod

Front page continuation (72) Inventor Go Hatada Ueda City, Nagano Prefecture 840 Kokubu, Niishin Kogyo Co., Ltd. (72) Inventor Takahiro Yasato 1-4-1 Chuo, Wako-shi, Saitama, Ltd. Inside the Honda R & D Co., Ltd. (56) References: 53-95091 (JP, U) JP47-47077 ) Japanese Patent Publication Sho 50-5787 (JP, B1)

Claims (1)

(57) [Claims] A partition plate (1c) for partitioning the interior of the booster shell (1) into a front shell chamber (2) and a rear shell chamber (3) is fixed to the front shell chamber (2). The front booster piston (4) that divides the front front negative pressure chamber (2a) and the rear front working chamber (2b) and the rear shell chamber (3) into the front rear negative pressure chamber (3a). And a rear booster piston (6) which is partitioned into a rear working chamber (3b) on the rear side and the partition plate (1c).
Is connected to the output rod (53) through a piston boss (10) which is slidably supported by the piston boss (10).
In addition, a valve cylinder (25) that projects rearward from the rear end face thereof and is slidably supported by the rear wall of the booster shell (1) is integrally formed, and the inside of the valve cylinder (25) has both negative pressure chambers ( 2a, 3
A first port (30) communicating with a) and a second port (31) communicating with both working chambers (2b, 3b) in the valve cylinder (25) are provided, and the second port (31) is Front and rear working chambers (2b, 3b)
Axial port (31A) for communication between the
b) and the radial port (31
R) and an input rod (35) that can move back and forth in the valve cylinder (25), and a second rod according to the forward and backward movement of the input rod (35).
A tandem-type negative pressure booster provided with a control valve (32) for switching the port (31) to the first port (30) and the atmosphere, wherein the axial port (31A) of the second port (31) and The radial port (31R) is connected to the rear end of the axial port (31A) and the radial port (3R) that open to the rear working chamber (3b).
1R) and the outer end thereof are arranged at the same position in the circumferential direction of the piston boss (10), and the axial port (31
A) The opening to the rear working chamber (3b) at the rear end is close to the opening to the rear working chamber (3b) at the outer end of the radial port (31R) so that the axial port (31A) Of the piston boss (10) in the radial direction of the piston boss (10), and the openings are formed on the outer peripheral surface of the piston boss (10) so as to be smoothly continuous with the inner surface of the opening. Tandem negative pressure booster characterized in that it is connected via a curved surface (r).