JP4073583B2 - Negative pressure booster - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative pressure booster used for boosting a brake master cylinder of an automobile, and in particular, to a booster shell, a front negative pressure chamber connected to a negative pressure source and a rear working chamber. The booster piston to be partitioned is accommodated, and a valve cylinder slidably supported on the rear wall of the booster shell is connected to the booster piston, and the valve cylinder is slidable in the front-rear direction in the valve cylinder. A valve piston to be fitted, an input rod that connects the front end to the valve piston, an input return spring that is mounted between the input rod and the valve cylinder and biases the input rod in the backward direction, and the valve piston A control valve that switches the working chamber to a negative pressure chamber and the atmosphere in response to the longitudinal movement, and this control valve is an annular and rearward air introduction valve seat formed at the rear end of the valve piston; And formed in the valve cylinder to surround the air introduction valve seat An annular and rearward negative pressure introduction valve seat, and a common valve portion that is spring-biased to be seated on the air introduction valve seat and the negative pressure introduction valve seat at the front end thereof on the inner peripheral surface of the valve cylinder A cylindrical valve body attached to the valve cylinder, a first port that communicates with the negative pressure chamber and opens between the negative pressure introduction valve seat and the valve body, and communicates with the working chamber. The present invention relates to an improvement in the provision of a second port that opens between the atmosphere introduction valve seat and the negative pressure introduction valve seat, while the inside of the valve body communicates with the atmosphere.
[0002]
[Prior art]
Conventionally, such a negative pressure booster is already known as disclosed in, for example, Japanese Patent Application Laid-Open No. 10-278772.
[0003]
[Problems to be solved by the invention]
Conventionally, in such a negative pressure booster, when the input rod is retracted, the valve body of the control valve is seated on the air introduction valve seat, while being separated from the negative pressure introduction valve seat, the working chamber is shut off from the atmosphere. By communicating with the negative pressure chamber, the booster piston is placed in a negative pressure state before and after the booster piston so that the booster piston can be retracted by the biasing force of the valve barrel return spring.
[0004]
By the way, while the valve body of the control valve is seated on the atmosphere introduction valve seat as described above, the negative pressure chamber is negatively placed on the front side of the atmosphere introduction valve seat and the valve body in a state of being separated from the negative pressure introduction valve seat. Since the pressure acts and the atmospheric pressure in the valve cylinder acts on the rear side, a forward thrust is applied to the valve piston due to the pressure difference between them, which prevents the input rod connected to the valve piston from moving backward. Become. Therefore, conventionally, the set load of the input return spring for urging the input rod in the backward direction is set to be large so that the input rod is reliably retracted against the forward thrust.
[0005]
However, setting a large set load of the input return spring causes an increase in initial load of the input rod that raises the output of the negative pressure booster, which is not preferable in terms of operational feeling.
[0006]
The present invention has been made in view of such circumstances, so that even if the set load of the input return spring is set to a small value, the input rod can be accurately retracted, the initial load of the input rod is reduced, and the operation is performed. It aims at providing the said negative pressure booster which can contribute to the improvement of a feeling.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention accommodates a booster piston that divides the interior of a booster shell into a front negative pressure chamber and a rear working chamber connected to a negative pressure source. A valve cylinder that is slidably supported on the rear wall of the booster shell is connected, and a valve piston that is slidably fitted in the valve cylinder in the front-rear direction, and a front end of the valve piston. An input rod that connects the parts, an input return spring that is mounted between the input rod and the valve cylinder and urges the input rod in the backward direction, and the working chamber is moved to the negative pressure chamber and the atmosphere according to the back-and-forth movement of the valve piston. And a control valve for switching the communication between the valve piston, an annular rear-facing air introduction valve seat formed at the rear end of the valve piston, and the air introduction valve seat formed in the valve cylinder. An annular, backward-facing negative pressure introduction valve seat that surrounds the air introduction valve seat, A cylindrical valve body that has a common valve portion that is spring-biased to be seated on the pressure introducing valve seat and that is attached to the inner peripheral surface of the valve cylinder. A first port that communicates with the pressure chamber and opens between the negative pressure introduction valve seat and the valve body; and a second port that communicates with the working chamber and opens between the atmosphere introduction valve seat and the negative pressure introduction valve seat. On the other hand, in the negative pressure booster in which the inside of the valve body is communicated with the atmosphere, the valve piston is connected to the front end portion of the input rod, and the connecting cylinder portion is connected radially outward from the rear end of the connecting cylinder portion. A flange portion that protrudes and the atmosphere introduction valve seat is formed on the rear surface, and protrudes radially outward from the front end of the connecting tube portion, and the outer peripheral surface is slidably fitted to the inner peripheral surface of the valve tube via a seal member. A piston portion having a diameter larger than that of the flange portion, and at the front end of the valve piston, Than Stone section diameter piston slidably fitted into the valve cylinder at the front side are integrally formed, in order to effect the rearward thrust by the atmospheric pressure to said piston part, between the valve cylinder and piston unit, A first feature is that an annular atmosphere chamber surrounding the small-diameter piston and communicating with the atmosphere is provided, and the front surface of the piston portion is a forward pressure receiving surface facing the atmosphere chamber.
[0008]
Thus, when the input rod is retracted, the valve body of the control valve is seated on the air introduction valve seat, while being separated from the negative pressure introduction valve seat, the working chamber is shut off from the atmosphere and communicated with the negative pressure chamber. Then, the negative pressure of the negative pressure chamber acts on the air introduction valve seat and the front side of the valve body, and the atmospheric pressure inside the valve body acts on the rear side of the valve piston. However, according to the first feature of the present invention, since the forward pressure receiving surface of the valve piston faces the atmospheric chamber between the valve cylinder and the valve piston, a backward thrust due to atmospheric pressure is applied to the pressure receiving surface. In addition, this balances with the forward thrust, or significantly reduces the effect of the thrust, and the input rod can be accurately retracted even if the set load of the input return spring is reduced. Thus, the set load of the input return spring can be reduced, and the initial moving load of the input rod can be reduced, thereby improving the operational feeling.
[0009]
In addition to the above feature, the present invention has a second feature that the valve piston is provided with a vent hole communicating the atmosphere chamber with the inside of the valve body.
[0010]
According to the second feature, communication between the atmosphere chamber and the atmosphere can be easily and reliably performed using the inside of the valve body that communicates with the atmosphere.
[0011]
[Embodiment]
Embodiments of the present invention will be described based on examples of the present invention shown in the accompanying drawings.
[0012]
1 is a longitudinal sectional view showing a tandem negative pressure booster according to an embodiment of the present invention in a resting state of an input rod, FIG. 2 is an enlarged view of a part 2 in FIG. 1, and FIG. 3 shows a retracted state of the input rod. FIG. 4 is a diagram illustrating the boosting characteristics of the negative pressure booster.
[0013]
1 and 2, a booster shell 1 of a negative pressure booster B is sandwiched between a pair of front and rear shell halves 1a and 1b that connect opposite ends to each other and both shell halves 1a and 1b. 1 includes a partition plate 1c that divides the interior into a front shell chamber 2 and a rear shell chamber 3, and a rear shell half 1b is fixed to and supported by a vehicle front wall F of a vehicle with a bolt 8. A cylinder body Ma of a brake master cylinder M operated by the booster B is fixed to the shell half body 1a by bolts 9.
[0014]
The front shell chamber 2 has a front booster piston 4 accommodated therein so as to be capable of reciprocating back and forth, and a front shell chamber 2 which is stacked on the rear surface of the front shell chamber 2 and is sandwiched between the front shell half 1a and the partition plate 1c. The front diaphragm 5 is partitioned into a front negative pressure chamber 2a on the front side and a front working chamber 2b on the rear side. The front negative pressure chamber 2a is connected to a negative pressure source V (for example, inside the intake manifold of the internal combustion engine) via a negative pressure introduction pipe.
[0015]
The rear shell chamber 3 has a rear booster piston 6 accommodated therein so as to be capable of reciprocating back and forth, and a rear diaphragm which is bonded to the rear surface of the rear booster piston 6 and is fixed between the shell halves 1a and 1b together with the partition plate 1c. 7 is divided into a front rear negative pressure chamber 3a and a rear rear working chamber 3b.
[0016]
The front and rear booster pistons 4 and 6 are each formed in an annular shape from a steel plate, and these are integrally connected via a synthetic resin valve cylinder 10 fixed to the center. The valve cylinder 10 is slidably supported on the partition plate 1c via the seal member 11 and on the rear extension cylinder 12 formed at the center of the rear shell half 1b via the seal member 13. The retreat limit of both booster pistons 4 and 6 is defined by the protrusions 7a that are raised on the rear surface of the rear diaphragm 7 abutting against the rear wall of the booster shell 1.
[0017]
In the valve cylinder 10, the working chambers 2 b and 3 b are switched to the negative pressure chambers 2 a and 3 a and the atmosphere according to the valve piston 18, the input rod 20 connected to the valve piston 18, and the back and forth movement of the input rod 20. A control valve 38 is disposed. The valve piston 18, a connecting tube portion 18a, a flange portion 18c which the piston portion 18 b projecting from the front end of the connecting cylinder portion 18a radially outwardly projecting from the rear end of the connecting tube portion 18a outward in the radial direction The piston portion 18b has a forward pressure receiving surface 45, and the flange portion 18c has a substantially conical and rearward air introduction valve seat 31 formed therein. The piston portion 18 b is fitted on the inner peripheral surface of the valve cylinder 10 through a seal member 44 so as to be slidable in the front-rear direction. A spherical front end portion 20a of the input rod 20 is fitted inside the connecting cylinder portion 18a, and a part 19 of the connecting cylinder portion 18a is caulked to prevent the input rod 20 from coming off. It is connected to the head so that it can swing.
[0018]
The valve cylinder 10, the negative pressure chamber 2a of the front and rear portions, a first communication passage 28 ₁ which communicates between 3a, working chamber 2b of the front and rear portions, a ₂ second communication passage 28 which communicates between 3b, the first communication a first port 29 ₁ which opens into inner peripheral surface of the valve cylinder 10 continues to the passage 28 _1, the continuous _two second communication passage 28, the opening to the inner peripheral surface of the valve cylinder 10 in front of the first port 29 ₁ 2 ports 29 ₂ are formed. An annular negative pressure introducing valve seat 30 is formed on the inner peripheral surface of the valve cylinder 10 in the middle in the front-rear direction of the first and second ports 29 ₁ and 29 ₂ . The cylindrical valve piston 18 to the front inner peripheral surface of the valve cylinder 10 is fitted slidably in the rear end of the valve piston 18, a negative pressure across the annular passage 32 leading to ₂ second port 29 An annular atmosphere introduction valve seat 31 surrounded by the introduction valve seat 30 is formed, and a common valve body 34 facing the negative pressure introduction valve seat 30 and the atmosphere introduction valve seat 31 is disposed in the valve cylinder 10. The The valve body 34 has an annular valve portion 34a facing the negative pressure introduction valve seat 30 and the atmospheric introduction valve seat 31 so as to be seatable, and an annular mounting bead portion 34b at the rear end, and both portions 34a, 34b. In the middle part, a diaphragm part 34c is connected to each other so as to be axially displaceable. The mounting bead part 34b is a cylindrical valve holder 35 fitted to the inner peripheral surface of the rear part of the valve cylinder 10. The front end is attached to the inner peripheral surface of the valve cylinder 10. And the valve spring 36 which urges | biases the valve part 34a to both the valve seats 30 and 31 in the seating direction is retracted between the valve part 34a and the input rod 20.
[0019]
In the above, the valve seats 30 and 31, the valve body 34 and the valve spring 36 constitute a control valve 38.
[0020]
Between the valve cylinder 10 and the valve piston 18, an annular atmospheric chamber 46 facing the forward pressure receiving surface 45 of the piston portion 18 b is provided so as to surround the small-diameter piston 17 described later . The atmosphere chamber 46 is always in communication with the inside of the valve body 34, that is, the atmosphere, through a vent hole 47 formed in the valve piston 18.
[0021]
An inward flange 12a having an air introduction port 39 opened at the center is integrally formed at the rear end of the rear extension cylinder 12, and defines the retreat limit of the input rod 20 by contacting the inner surface of the flange 12a. The stopper plate 40 is fixed to the input rod 20 so as to be adjustable in the front-rear direction, and the input rod 20 is urged by the input return spring 41 supported by the valve holder 35 toward the retreat limit.
[0022]
An air filter 42 is attached to the inner periphery of the rear end of the valve cylinder 10, and the inner periphery of the negative pressure introduction valve seat 30 is always in communication with the atmosphere introduction port 39 through the air filter 42. The air filter 42 has flexibility so as not to hinder the forward / backward movement of the input rod 20 relative to the valve cylinder 10.
[0023]
The front end portion of the valve cylinder 10 is formed in a large-diameter piston 15, and is formed in the center portion of the large-diameter piston 15. A reduced-diameter small-diameter piston 17 is slidably fitted. In the illustrated example, the small-diameter piston 17 is continuously provided integrally with the front end of the valve piston 18. A cup body 21 is slidably fitted on the outer periphery of the large-diameter piston 15, and the cup body 21 is filled with a flat elastic piston 22 facing the large-diameter and small-diameter pistons 15, 17. In the above, the large-diameter piston 15, the small-diameter piston 17, the elastic piston 22, and the cup body 21 constitute a reaction force mechanism 24 that transmits the resultant force of the input to the input rod 20 and the thrust of the booster pistons 4, 6 to the output rod 25. To do.
[0024]
An output rod 25 projects from the front surface of the cup body 21, and this output rod 25 is connected to the piston Mb of the brake master cylinder M. A retainer 26 that contacts the cup body 21 and the front end surface of the valve cylinder 10 is disposed, and a valve cylinder return spring 27 is contracted between the retainer 26 and the front wall of the booster shell 1.
[0025]
Next, the operation of this embodiment will be described.
[0026]
In the resting state of the negative pressure booster B, as shown in FIG. 1, the input rod 20 is positioned in the backward limit, and the control valve 38 seats the valve body 34 on the atmosphere introduction valve seat 31 and the negative pressure introduction valve seat 30. The front and rear working chambers 2b and 3b are in a neutral state in which both the negative pressure chambers 2a and 3a and the air introduction port 39 are not in communication with each other. The negative pressure of the negative pressure source supplied through the negative pressure introduction pipe 14 is stored, and the negative pressure appropriately diluted by the atmosphere is held in both working chambers 2b and 3b. Thus, a small forward force is given to the front and rear booster pistons 4 and 6 by a slight pressure difference generated 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. However, the forward force and the force of the valve return spring 27 are balanced, and the booster pistons 4 and 6 are stopped when they are slightly advanced from the backward limit.
[0027]
Now, when the brake pedal P is depressed to brake the vehicle and the input rod 20 is advanced, the valve piston 18 also advances. Initially, since both booster pistons 4 and 6 are immobile, the air introduction valve seat 31 is separated from the valve body 34 by the advancement of the valve piston 18, and the atmosphere is introduced through the _second passage 292 and the inside of the valve body 34. Communicate with the mouth 39. As a result, the atmosphere flowing into the valve cylinder 10 from the atmosphere introduction port 39 passes through the atmosphere introduction valve seat 31 and is quickly introduced into both the working chambers 2b and 3b via the second port 29 _2. Since both the negative pressure chambers 2a and 3a have a higher pressure than that of the negative pressure chambers 2a and 3a, both the booster pistons 4 and 6 obtain the large forward thrust based on the pressure difference therebetween, Since it moves forward so as to follow the movement of the input rod 20 against the force, the large-diameter piston 15 pushes the cup body 21, that is, the output rod 25 forward via the elastic piston 22, and the brake master cylinder M The piston Mb is driven. Thus, the brake master cylinder M can be operated without delay to the depression of the brake pedal P, and the vehicle can be braked.
[0028]
By the way, during such braking, the thrust of the booster pistons 4 and 6 applied to the large-diameter piston 15 and the pedaling force of the operator applied to the small-diameter piston 17 from the input rod 20 act on the rear end surface of the elastic piston 22. In addition, the reaction force of the output rod 25 acts on the front end surface of the front end surface, whereby the elastic piston 22 is compressed back and forth. As a result, a part of the reaction force of the output rod 25 is transmitted to the input rod 20 via the elastic piston 22, and the driver senses the output of the output rod 25, that is, the magnitude of the braking force. Can do.
[0029]
Thus, until the output of the output rod 25 reaches the boost limit (see line ab in FIG. 4), the valve cylinder 10 integrated with the booster pistons 4 and 6 moves forward by the advance amount of the input rod 20. Therefore, when the input rod 20 stops moving forward, the valve element 34 that has moved forward together with the valve cylinder 10 is seated again on the air introduction valve seat 31 to prevent further introduction of air into the working chambers 2b and 3b. Therefore, the forward movement of the booster pistons 4 and 6 is also stopped, and a boost output corresponding to the input is obtained.
[0030]
When the output of the output rod 25 exceeds the boost limit, the thrust due to the pressure difference between the booster pistons 4 and 6 becomes maximum, and the atmosphere introduction valve seat 31 remains separated from the valve body 34. Is the sum of the maximum thrust due to the pressure difference between the booster pistons 4 and 6 and the thrust of the input rod 20 due to the depression force applied to the brake pedal P (see line bc in FIG. 4).
[0031]
When the pedaling force is released from the brake pedal P to release the braking state of the vehicle, the input rod 20 and the valve piston 18 are first moved backward by the force of the input return spring 41. Accordingly, as shown in FIG. 3, the valve piston 18 largely separates the valve body 34 from the negative pressure introduction valve seat 30 while seating the air introduction valve seat 31 on the valve body 34. 2b and 3b communicate with both the negative pressure chambers 2a and 3a through the second port 29 ₂ , the annular passage 32 and the first port 29 ₁ . As a result, the introduction of the atmosphere into both working chambers 2b and 3b is prevented, while the air in both working chambers 2b and 3b is sucked into the negative pressure limit V through both negative pressure chambers 2a and 3a, and the pressure difference between them. Therefore, the booster pistons 4 and 6 are also moved backward by the force of the valve barrel return spring 27 to release the operation of the master cylinder M.
[0032]
By the way, when the valve body 34 is seated on the atmosphere introduction valve seat 31 and is separated from the negative pressure introduction valve seat 30 as the input rod 20 moves backward as described above, the atmosphere introduction valve seat 31 and the valve The negative pressure of the negative pressure chambers 2a and 3a acts on the front surface side of the body 34, and the atmospheric pressure in the valve body 34 acts on the rear surface side, and forward thrust is applied to the valve piston 18 due to the pressure difference therebetween. However, since the forward pressure receiving surface 45 of the valve piston 18 faces the atmospheric chamber 46 that is always in communication with the atmosphere between the valve cylinder 10 and the valve piston 18, the pressure receiving surface 45 faces backward due to atmospheric pressure. This thrust is balanced with the forward thrust or greatly reduces the action of the thrust, and the input rod 20 can be retracted accurately even if the set load of the input return spring is reduced. Accordingly, the set load of the input return spring can be reduced, and the initial load of the input rod 20 is reduced accordingly. Therefore, as shown in FIG. 4, the output rise time is advanced and the operational feeling is improved. Can do.
[0033]
In addition, since the atmospheric chamber 46 communicates with the inside of the valve body 34 in the atmospheric pressure state through the vent hole 47 formed in the valve piston 18, a relatively short vent hole is obtained by using the valve body 34. The atmosphere chamber 46 can be communicated with the atmosphere at 47.
[0034]
Thereafter, when the input rod 20 is retracted to the retreat limit in which the stopper plate 40 is brought into contact with the inward flange 12a of the rear extension cylinder 12, the rear booster piston 6 temporarily moves the protrusion 7a of the rear diaphragm 7 to the rear wall of the booster shell 1. Since the negative pressure introduction valve seat 30 is seated on the valve body 34 and the valve body 34 is separated from the atmosphere introduction valve seat 31, the atmosphere again enters the working chambers 2 b and 3 b. When the booster pistons 4 and 6 are slightly moved forward by the pressure difference caused by the pressure difference, the valve body 34 is also seated on the negative pressure introducing valve seat 30 to bring the control valve 38 into the initial neutral state. Thus, the negative pressure diluted to the atmosphere is maintained in both working chambers 2b and 3b, and the negative pressure booster B is in a resting state as shown in FIGS.
[0035]
The present invention is not limited to the above embodiments, and various design changes can be made without departing from the scope of the invention. For example, the negative pressure booster B can be configured as a single type having a single booster piston. Further, the stopper plate 40 of the input rod 20 and the inward flange 12a of the rear extension cylinder 12 are abolished, and when the negative pressure booster B is stopped, the negative pressure introduction valve seat 30 is left open and the working chambers 2b and 3b are formed. You may make it hold | maintain in the communication state with the negative pressure chambers 2a and 3a.
[0036]
【The invention's effect】
As described above, according to the first feature of the present invention, the valve piston is connected to the connecting cylinder part to which the front end part of the input rod is connected, and protrudes radially outward from the rear end of the connecting cylinder part to the atmosphere introduction valve. A flange portion formed on the rear surface of the seat, and a radially outer side projecting from a front end of the connecting tube portion, and an outer peripheral surface is slidably fitted to an inner peripheral surface of the valve tube via a seal member ; the flange portion have a piston section of larger diameter, the front end of the valve piston, the small-diameter piston being slidably fitted into the valve cylinder in front of the piston portion is integrally formed with the piston portion An annular atmospheric chamber surrounding the small-diameter piston and communicating with the atmosphere is provided between the valve cylinder and the piston portion so that a backward thrust due to atmospheric pressure is applied to the piston, and the front surface of the piston portion faces the atmospheric chamber. Since it is a pressure-receiving surface facing forward, the negative pressure chamber is installed in the air introduction valve seat and valve body. Even if a forward thrust due to the pressure difference between the negative pressure and the atmospheric pressure in the valve body is applied, a backward thrust due to the atmospheric pressure is applied to the pressure-receiving surface, thereby greatly balancing the forward thrust and the effect of the thrust. Therefore, it is possible to greatly reduce the set load of the input return spring that urges the input rod in the backward direction without impairing the reverse performance of the input rod, reducing the initial load of the input rod, As a result, the operational feeling can be improved.
[0037]
Further, according to the second feature of the present invention, the valve piston is provided with a vent hole that communicates the atmosphere chamber with the inside of the valve body. It can be done easily and reliably.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a tandem negative pressure booster according to an embodiment of the present invention in a resting state of an input rod. FIG. 2 is an enlarged view of a part 2 in FIG. FIG. 4 is a diagram for explaining the operation corresponding to FIG. 2. FIG. 4 is a diagram showing the boost characteristic of the negative pressure booster.
B ... Negative pressure booster V ... Negative pressure source 1 ... Booster shell 2a ... Negative pressure chamber (front negative pressure chamber)
3a ... Negative pressure chamber (rear negative pressure chamber)
2b ... Working chamber (front working chamber)
3b ... Working chamber (rear working chamber)
4 .... Booster piston (front booster piston)
6. Booster piston (rear booster piston)
10 ... Valve 17 ... Small-diameter piston 18 ... Valve piston 18a ... Connecting cylinder 18b ... Piston 18c ... Flange 20 ... Input rod 29 ₁ ... First port 29 ₂ ... Second port 30 ... Negative pressure introduction valve seat 31 ... Air introduction valve seat 34 ... Valve body 34a ... Valve part 41 ... Input return spring
44 ... Sealing member 45 ... Pressure receiving surface 46 ... Air chamber 47 ... Vent

Claims (2)

A booster piston (4, 6) having a booster shell (1) divided into a front negative pressure chamber (2a, 3a) and a rear working chamber (2b, 3b) connected to the negative pressure source (V). The booster piston (4, 6) is connected to a valve cylinder (10) that is slidably supported on the rear wall of the booster shell (1). In the valve cylinder (10), A valve piston (18) fitted to the valve cylinder (10) so as to be slidable in the front-rear direction, an input rod (20) connecting the front end to the valve piston (18), the input rod (20) and An input return spring (41) mounted between the valve cylinders (10) and urging the input rod (20) in the backward direction, and a working chamber (2b, 3b) according to the back-and-forth movement of the valve piston (18). A negative pressure chamber (2a, 3a) and a control valve (38) for switching between the atmosphere and the atmosphere are arranged, and the control valve (38) An annular and rearward air introduction valve seat (31) formed at the rear end of the valve piston (18), and an annular and rearward formation formed on the valve cylinder (10) and surrounding the air introduction valve seat (31) Negative pressure introducing valve seat (30) and a common valve portion (34a) spring-biased to be seated on the atmospheric introducing valve seat (31) and the negative pressure introducing valve seat (30) at the front end. And a cylindrical valve body (34) attached to the inner peripheral surface of the valve cylinder (10). The negative pressure is communicated with the negative pressure chamber (2a, 3a) to the valve cylinder (10). A first port (29 ₁ ) opened between the introduction valve seat (30) and the valve body (34), and the atmosphere introduction valve seat (31) and the negative pressure introduction valve communicated with the working chamber (2b, 3b). seat (30) while providing a second port for opening (29 ₂₎ between the negative pressure booth communicating the interior of said valve body (34) to the atmosphere In,
The valve piston (18) has a connecting cylinder part (18a) to which a front end part of the input rod (20) is connected, and projects outward from the rear end of the connecting cylinder part (18a) in the radial direction. (31) is a flange portion formed on the rear surface (18c), the linking tube sealing member on the inner peripheral surface of the outer peripheral surface valve cylinder protrudes radially outwardly from the front end (10) of (18a) (44 ) And a piston portion (18b) having a diameter larger than that of the flange portion (18c). The piston portion (18b) is provided at the front end of the valve piston (18). A small-diameter piston (17) slidably fitted to the valve cylinder (10) in front of 18b),
Between the valve cylinder (10) and the piston portion (18b), an annular ring surrounding the small-diameter piston (17) and communicating with the atmosphere is provided in order to apply a backward thrust by atmospheric pressure to the piston portion (18b). An atmospheric pressure chamber (46) is provided, and the front surface of the piston part (18b) is a forward pressure receiving surface (45) facing the atmospheric chamber (46). The negative pressure booster according to claim 1,
A negative pressure booster, wherein the valve piston (18) is provided with a vent hole (47) for communicating the atmospheric chamber (46) with the inside of the valve body (34).

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