JP3867725B2 - Negative pressure booster - Google Patents

Description

  The present invention relates to a negative pressure booster for a vehicle, and more particularly to a negative pressure booster for a vehicle that can make up for a lack of brake pedal depression force during emergency braking.

  When an obstacle suddenly appears on the vehicle's track and the driver rushes and depresses the brake pedal, that is, during emergency braking, the pedaling force applied by the driver to the brake pedal is brake fluid that is large enough to lock the wheel. There is a recent analysis result that the brake force of the vehicle is often not sufficiently exhibited because it is considerably smaller than the pedal force that generates pressure. Based on the results of this analysis, it is determined whether the brake is a normal brake or an emergency brake from the brake pedal depression speed and the master cylinder hydraulic pressure rising speed. A device for raising the height is proposed and put into practical use.

  Various devices having various configurations have been proposed as such an apparatus, for example, one described in Japanese Patent Application Laid-Open No. 11-48947. This is configured so that its input-output characteristics can be switched to at least two types (normal brake characteristics and emergency brake characteristics) by an external control signal. By switching the input-output characteristic from the normal brake characteristic to the emergency brake characteristic, the same result as when the driver depresses the brake pedal strongly is obtained.

JP-A-8-318846 JP 11-48947 A

  However, this conventional negative pressure booster has a solenoid for switching to an emergency brake characteristic and a valve seat member driven by the solenoid separately from the annular valve seat for atmospheric inflow control. A solenoid drive signal is output from an electronic control unit that processes a signal from the cylinder hydraulic pressure sensor, and the solenoid is driven based on the signal to separate the valve seat member having the annular valve seat for atmospheric inflow control from the opposing seal member. Thus, the valve mechanism is brought into an output increasing action state, and requires a solenoid, various sensors, an electronic control device, and the like, which is considerably expensive.

  Therefore, the present invention provides a negative pressure booster that does not require a solenoid, various sensors, an electronic control unit, etc., and can achieve an output increasing action state at the time of emergency braking with a simple and inexpensive mechanical configuration. Objective.

  In order to achieve the above object, a housing that forms at least one pressure chamber therein, a housing that can be moved forward and backward relative to the housing inside the housing, and the pressure chamber is a constant pressure chamber and a variable pressure chamber. A movable wall divided into the movable wall, a power piston coupled to the movable wall, an input member installed inside the power piston so as to be able to move forward and backward with respect to the power piston, and the movement wall as the movable wall moves An output member that outputs the propulsion force of the power piston to the outside of the device, an atmospheric outflow control annular valve seat that is disposed on the power piston and faces rearward, and a movable facing the atmospheric outflow control annular valve seat And a valve mechanism having a fixed portion that is airtightly fixed to the power piston, and the annular valve seat for atmospheric outflow control is provided with respect to the power piston. In a negative pressure type booster arranged on a valve seat member capable of moving forward and backward, when the amount of advancement of the input member relative to the power piston by the negative pressure type booster is less than a predetermined value, the valve seat member is Holding means for holding in a predetermined front position; movable means for moving the valve seat member to a rear position by a predetermined amount when the advance amount of the input member relative to the power piston is greater than a predetermined value; and A return means for returning the valve seat member to the predetermined position in front when the valve seat member is in a predetermined position, and one end of the holding means is engaged with the power piston or the power piston side member. And a negative pressure booster characterized in that the other end has a holding member engaged with the valve seat member.

  According to this, when the relative movement amount between the input member and the power piston is larger than a predetermined value, that is, in emergency braking in which the driver rushes and depresses the brake pedal, the locking of the valve seat member by the holding means is released, Since the valve seat member is moved rearward by a predetermined amount by the movable means, and the valve seat member presses the movable portion of the valve mechanism rearward, the variable pressure chamber is rapidly and forcibly communicated with the atmosphere, which is larger than that during normal braking. A propulsive force is applied to the movable wall, the power piston, and thus the output member, so that a sufficiently large brake fluid pressure can be generated. In other words, jumping characteristics (the ratio of output to input is infinite until the input member comes into contact with the reaction member when the brake pedal is depressed and brake operation is performed, which is called jumping) Thus, a larger propulsive force than that during normal braking is applied to the output member. That is, a negative pressure booster having two types of input-output characteristics, that is, a normal brake characteristic and an emergency brake characteristic can be realized with a simple configuration.

  Note that the rear means the brake pedal side or the vehicle rear side with respect to the negative pressure booster, and the front means the master cylinder side or the vehicle front side with respect to the negative pressure booster.

  Preferably, at least one of the input member and the holding member is provided with a tapered portion, and when the advance amount of the input member relative to the power piston is larger than a predetermined value, the holding member is caused by a cam action of the input member or the holding means and the tapered portion. Release the holding. According to this, when the advance amount of the input member relative to the power piston is larger than the predetermined value, the holding action of the holding member can be reliably released by the cam action of the taper portion, and the emergency brake characteristic can be Rapid transition to characteristics is possible.

  An atmospheric outflow control annular valve seat includes a first atmospheric outflow control annular valve seat integral with the power piston, and can be moved forward and backward with respect to the power piston and substantially concentric with the first atmospheric outflow control annular valve seat. 2 An annular valve seat for atmospheric outflow control. According to this, the annular valve seat for the atmospheric air outflow control is arranged so that the first atmospheric outflow control annular valve seat integrated with the power piston and the first atmospheric outflow control annular valve seat are substantially concentric with the second atmospheric outflow control annular valve seat. Therefore, by adding a second atmospheric outflow control annular valve seat to the power piston of an ordinary negative pressure booster having an atmospheric outflow control annular valve seat, the normal brake characteristics and emergency brake characteristics can be obtained. The negative pressure type booster having the two types of input-output characteristics can be configured, and the common use with the parts of the normal negative pressure type booster is achieved, leading to cost reduction.

According to the present invention, a negative pressure booster having two types of input-output characteristics, that is, a normal brake characteristic and an emergency brake characteristic, is required without requiring a solenoid, various sensors, an electronic control unit, or the like. Can be realized.
Other objects and effects of the present invention will become apparent from the description of the embodiments of the present invention described later with reference to the accompanying drawings. In addition, the front means the front direction of the vehicle, and the rear means the rear direction of the vehicle.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 and FIG. 2 are sectional views of a negative pressure booster for a vehicle that is a first embodiment of the present invention, and FIG. 2 is an enlarged view of a part of FIG.

In FIG. 1, a negative pressure booster (brake booster) 10 for a vehicle includes a front shell 11, a rear shell 12, and a movable wall 20, and a constant pressure chamber 23 that communicates with a negative pressure source through the movable wall 20 and the atmosphere. A housing 14 is provided that is divided into a variable pressure chamber 24 that can communicate with the housing. The movable wall 20 in the housing 14 includes a metal plate 18 and a rubber diaphragm 19, and is installed so as to be movable in the front-rear direction with respect to the housing 14.
The bead portion on the outer peripheral edge of the diaphragm 19 is airtightly held between the folded portion provided on the outer peripheral edge of the rear shell 12 and the front shell 11. The bead portion on the inner peripheral edge of the diaphragm 19 is airtightly fixed together with the plate 18 in a groove provided on the outer periphery of the front flange portion of the power piston 22.

  The constant pressure chamber 23 communicates with an engine intake manifold (not shown) which is a negative pressure source, and is always kept at a negative pressure during engine operation. The variable pressure chamber 24 is communicated / blocked with the constant pressure chamber 23 via the passage 60 and the valve mechanism 36, and is also communicated / blocked with the atmosphere via the valve mechanism 36.

  As shown in FIGS. 1 and 2, the power piston 22 has a first space 22a located in the front (leftward in FIGS. 1 and 2) and communicating with the constant pressure chamber, and a rear in the interior. It has the 2nd space 22b which is located (right in FIG.1 and FIG.2) and is connected to air | atmosphere, and the intermediate part 221 interposed between the 1st space 22a and the 2nd space 22b. The intermediate portion 221 communicates the first space 22a and the second space 22b separately from the third space 22c and the third space 22c that communicates the first space 22a and the second space 22b at the center of the intermediate portion 221. And a passage 60 to be connected.

  Inside the power piston 22, the input rod 28 and the plunger 37 constituting the input member 27 penetrate the first space 22 a, the second space 22 b, and the third space 22 c and can move in the front-rear direction with respect to the power piston 22. It is installed as follows. Further, the input rod 28 and the plunger 37 are integrally coupled by a coupling portion 80, and the input rod 28 is coupled to a brake pedal (not shown) at the rear thereof.

An output member 55 is fitted to the front end portion of the power piston 22, and a reaction force member 54 is disposed between the front end portion of the power piston 22 and the output member 55. Further, a contact member 70 is disposed between the reaction force member 54 and the front end portion of the plunger 37, and the contact member 70 is integrated with the power piston 22 so as to be movable in the front-rear direction. Is installed inside the locking member 50.
In order to define the amount of movement of the plunger 37 and the input rod 28 with respect to the power piston 22, the key member 32 is inserted into the radial hole 33 formed in the intermediate portion 221 of the power piston 22. The thickness dimension of the key member 32 in the front-rear direction (left-right direction in FIGS. 1 and 2) is smaller than the front-rear direction dimension of the radial hole 33, and the key member 32 is shown in FIG. It can move in the front-rear direction by the indicated distance C.

  The key member 32 can come into contact with the rear shell 12 at the rear surfaces of both ends protruding to the outer peripheral side of the power piston 22, and the limit of movement of the power piston 22 to the rear with respect to the housing 14 is as shown in FIG. In addition, the front wall of the radial hole 33 is in contact with the front surface of the key member 32, and the rear surfaces of both ends of the key member 32 are in contact with the rear shell 12. The central portion of the key member 32 is disposed between a pair of flange surfaces 34, 35 formed at the central portion of the plunger 37, and the rearward movement limit of the plunger 37 relative to the power piston 22 is determined by the flange surface 34. This is the position where the front surface of the key member 32 abuts and the rear surface of the key member 32 abuts the rear wall of the radial hole 33. The forward movement limit of the plunger 37 with respect to the power piston 22 is such that the flange surface 35 is in contact with the rear surface of the key member 32 and the front surface of the key member 32 is in contact with the front wall of the radial hole 33. is there.

Inside the power piston 22, the variable pressure chamber 24 communicates with the constant pressure chamber 23 in accordance with the longitudinal movement of the plunger 37 relative to the power piston 22, and the variable pressure chamber 24 is connected to the constant pressure chamber 23. In addition, a valve mechanism 36 is provided for switching between an output holding action state that is cut off from the atmosphere and an output increase action state in which the variable pressure chamber 24 is cut off from the constant pressure chamber 23 and communicated with the atmosphere.
The valve mechanism 36 is integrally formed around the rear opening of the third space 22c at the rear portion of the valve seat member 40 and the annular valve seat 37a for atmospheric inflow control formed integrally at the rear end portion of the plunger 37. The movable part 41 and the retainer 42 are provided with a valve 41a, 41b facing the annular valve seat 39 for atmospheric outflow control, the annular valve seat 39 for atmospheric outflow control, and the annular valve seat 37a for atmospheric inflow control formed respectively. A cylindrical member 45 having a fixed portion 43 hermetically fixed to the piston 22 and the movable portion 41 being urged forward by a spring 44 is a main constituent member.

The valve seat member 40 disposed in the third space 22 c of the intermediate portion 221 is movable in the front-rear direction with respect to the power piston 22.
As shown in a perspective view in FIG. 4, the valve seat member 40 includes a slit 40 b in which a contact portion 37 c protruding in the radial direction is inserted on the outer periphery of the plunger 37, and a penetration extending in the front-rear direction of the valve seat member 40. A hole 40e is provided. The key member 32 is inserted through the slit 40b.
By inserting the plunger 37 into the through hole 40e of the valve seat member 40, the contact portion 37c and the slit 40b face each other, and the contact portion 37c protrudes outside the valve seat member 40 through the slit 40b. Will do. When the plunger 37 provided with the valve seat member 40 is disposed in the power piston 22, the outer peripheral surface of the contact portion 37 c comes into sliding contact with the concave portion 221 a of the inner peripheral surface of the intermediate portion 221. It is slidably supported on the inner peripheral portion of the intermediate portion 221, that is, the inner periphery of the power piston 22 via the contact portion 37 c.

On the other hand, the valve seat member 40 is located between the outer peripheral portion of the plunger 37 and the inner peripheral portion of the intermediate portion 221 of the power piston 22 and is intermediate at the rear end portion where the annular valve seat 39 for atmospheric outflow control is formed. It will contact | abut with respect to the internal peripheral surface of the part 221 so that sliding is possible in the front-back direction. That is, the power piston 22 includes the intermediate portion 221 as a holding portion that holds the valve seat member 40 slidably rearward.
An annular seal member 46 that keeps an airtight seal between the rear end portion of the valve seat member 40 and the inner peripheral surface of the intermediate portion 221 is attached to the outer periphery of the rear end portion that contacts the intermediate portion 221 of the valve seat member 40. Yes. Further, the valve seat member 40 is urged rearward by a spring 47 (biasing member) disposed between the valve seat member 40 and a flange portion provided on the inner peripheral surface of the intermediate portion 221.

A spring 59 disposed between a retainer 58 that is locked to the input rod 28 that is integrally connected to the plunger 37 and the coupling portion 80 and a retainer 42 that is locked to the power piston 22 is provided to the input rod 28. When the brake pedal is not depressed, the atmospheric inflow control annular valve seat 37a is brought into contact with the valve 41b of the movable portion 41 of the valve mechanism 36 and the valve 41a of the movable portion 41 is discharged to the atmosphere. It is held in a state separated from the control annular valve seat 39 by a distance A.
The passage 60 formed in the intermediate portion 221 and the first space 22a communicate the valve mechanism 36 and the constant pressure chamber 23, and the third space 22c communicates the valve mechanism 36 and the variable pressure chamber.
A movable means for propelling the valve seat member 40 rearward is disposed inside the front portion of the power piston 22, that is, in the intermediate portion 221. The movable means includes a spring 47 (biasing member) that biases the valve seat member 40 rearward and a key member 32.

  A holding means 48 is disposed inside the front portion of the power piston 22, that is, in the first space 22a. The holding means 48 includes a holding member 52 having an engaging portion 52 b that engages with the engaged portion 40 c of the valve seat member 40, and a ring-shaped elastic body 53 that biases the holding member 52 in a direction of reducing the diameter. As shown in FIG. 5, the holding member 52 has a half hollow truncated cone shape obtained by cutting a hollow truncated cone by a plane passing through the central axis thereof, and two half hollow truncated cones are opposed to each other. The power piston 22 is assembled. The locking portion 52 c of the holding member 52 is fitted in a locking groove 50 a of the locking member 50 fixed to the front portion of the power piston 22. For this reason, the holding member 52 cannot move in the front-rear direction, but is allowed to move in the radial direction around the locking portion 52c.

  FIG. 3 shows a second embodiment of the present invention. In the second embodiment, a first atmospheric outflow control annular valve seat 38 that is integrally formed around the rear side opening of the third space 22c of the intermediate portion 221 of the power piston 22 is provided. A valve seat member 400 including a second atmospheric outflow control annular valve seat 390 facing the movable portion 41 is disposed on the inner diameter side of the control annular valve seat 38 so as to be movable in the front-rear direction with respect to the power piston 22. . The configuration other than that described above is the same as that of the first embodiment shown in FIG.

FIG. 6 shows a third embodiment of the present invention, in which the holding means 148 is different from the first and second embodiments. In the third embodiment, the holding means 148 includes a holding member 152 having an engaging portion 152b that engages with the engaged portion 400c of the valve seat member 400, and a ring that urges the holding member 152 in the direction of reducing the diameter. And an elastic body 53.
The locking portion 152 c of the holding member 152 is provided in a locking member 150 fixed to the front portion of the power piston 22 and is fitted into a locking groove 150 a that extends substantially at right angles to the central axis of the power piston 22. ing. For this reason, the holding member 152 cannot move in the front-rear direction, but is allowed to move in the radial direction around the locking portion 152c. As shown in FIG. 7, the holding member 152 has a three-divided hollow frustum shape obtained by cutting the hollow frustum along three planes passing through its central axis. As shown in FIG. The three divided hollow truncated cones are opposed to each other and assembled to the power piston 22.

  Further, a thin cylindrical regulating member 170 is disposed on the outer periphery of the locking portion 152c of the holding member 152 to prevent the locking portion 152c from coming out of the locking groove 150a. That is, even if an axial component force is applied to the holding member 152 by the cam action caused by the contact between the inclined surface 37b of the plunger 37 and the tapered portion 152a of the holding member 152, the locking portion 152c is lifted from the locking groove 150a. Is prevented. For this reason, there is no loss of the advance amount of the plunger 37 with respect to the power piston 22, and the transition from the normal brake characteristic to the emergency brake characteristic is performed quickly.

Incidentally, as shown in FIG. 6, passes through the rotational center axis _{X 1} in a locking groove 150a of the engaging portion 152c, and the holding member 152 of the tapered portion 37b of the tapered portion 152a and the input member or plunger 37 plane through the center lines X ₃ of the contact surface is, the central axis X ₂ and angle of the power piston 22 is set to 30 ° or less. This is because the distance B between the taper portion 152a of the holding member 152 and the center axis of the power piston 22 is brought closer to the distance A between the rotation center of the locking portion 152c and the center axis of the power piston 22, and this is due to the cam action. The holding member 152 is prevented from rotating in the direction in which the holding member 152 engages with the valve seat member 400 (clockwise in FIG. 6) by the axial component force, and the transition from the normal brake characteristic to the emergency brake characteristic is performed quickly. The purpose is to be.
Therefore, the above angle is not only applied to the third embodiment of the present invention, but also applied to the first embodiment, the second embodiment, and the fourth embodiment described later.

FIG. 9 shows a fourth embodiment of the present invention, and the holding means 248 is different from the first to third embodiments. In the fourth embodiment, the holding means 248 includes a holding member 252 having an engaging portion 252b that engages with the engaged portion 400c of the valve seat member 400, and a ring that urges the holding member 252 in the direction of reducing the diameter. And an elastic body 53.
The locking portion 252c of the holding member 252 is connected to the main body portion of the holding member 252 via the connecting portion 252d and has a substantially cylindrical shape.

  The locking groove 250 a provided in the locking member 250 fixed to the front portion of the power piston 22 and extending substantially perpendicular to the central axis of the power piston 22 is formed by the locking portion 252 c of the holding member 252. It is a cylindrical inner hole to be inserted. Furthermore, the locking groove 250a has a notch 250b extending along the locking groove 250a.

The engaging portion 252c is inserted into the engaging groove 250a from a direction substantially perpendicular to the central axis of the power piston 22, and at this time, the connecting portion 252d connecting the engaging portion 252c and the holding member main body is notched. It will pass through 250b. That is, the locking portion 252c and the locking groove 250a are so-called joint-shaped. As a result, the holding member 250 smoothly rotates with the central axis of the locking groove 250a as the rotation axis, that is, with the axis substantially perpendicular to the central axis of the power piston 22 as the rotation axis. Further, because of the joint-like connection, the locking portion 252c does not come out of the locking groove 250a, and a highly reliable emergency brake function can be realized.
The holding member 252 has the same shape except for the holding member 152 and the locking portion 152C according to the third embodiment shown in FIG. That is, it has a three-part hollow frustum shape that is obtained by cutting the hollow frustum along three planes passing through its central axis, and this three-part hollow frustum is divided into three parts as in the third embodiment shown in FIG. They are assembled to the power piston 22 so as to face each other.

  Next, the operation of the negative pressure type booster of the present invention will be described. Since the operation as a booster in the normal operation state is generally known, the description thereof will be omitted and mainly during emergency braking. Will be described.

  The emergency brake characteristic of the negative pressure booster of the present invention is achieved by changing the jumping characteristic and applying a larger driving force to the output member than during normal braking. In order to change the jumping characteristics, the gap D between the contact member 70 and the reaction force member 54 in FIG. The gap D is increased by the distance between the contact surface 22d of the power piston 22 to the reaction force member 54 and the annular valve seat 39 for controlling air outflow, and the contact surface 22d of the power piston 22 to the reaction force member 54 and the atmosphere. This is the same as increasing the distance from the inflow control annular valve seat 37a. That is, the gap D is enlarged by moving the atmospheric outflow control annular valve seat 39 and the atmospheric inflow control annular valve seat 37a rearward, and the output until the contact member 70 receives the reaction force from the reaction force member 54. The output in the so-called jumping state where the ratio of the output to the input is infinite is made larger than the normal state.

The actual operation will be described below with reference to FIGS.
If the relative movement between the input member 27 and the power piston 22 is greater than a predetermined value B during emergency braking when the driver rushes and depresses the brake pedal, the inclined surface 37b of the plunger 37 contacts the tapered portion 52a of the holding member 52. The holding member 52 urged in the direction of reducing the diameter by the ring-shaped elastic body 53 is expanded in the radial direction.
When the minimum inner diameter portion 52aa of the taper portion 52a rides on the stepped portion 37d of the plunger 37, the engagement between the engaged portion 40c of the valve seat member 40 and the engaging portion 52b of the holding member 52 is released. Since the valve seat member 40 is urged rearward by a spring 47 (biasing member), as soon as the engagement of the engaged portion 40c is released, the urging force of the spring 47 (biasing member) is used. Move backwards.

  When the valve seat member 40 moves rearward, the atmospheric outflow control annular valve seat 39 of the valve seat member 40 comes into contact with the valve 41a constituting the movable portion 41 of the valve mechanism 36, and the constant pressure chamber 23 and the variable pressure chamber 24 are in contact with each other. Block communication. At this time, since the plunger 37 is moving forward integrally with the input rod 28 and the valve seat member 40 pushes back the movable portion 41 of the valve mechanism 36, the annular valve for controlling the air inflow of the plunger 37. The seat 37a and the valve 41b constituting the movable portion 41 of the valve mechanism 36 are rapidly separated, and the variable pressure chamber 24 communicates with the atmosphere. As a result, compared with the normal brake operation, the communication between the constant pressure chamber 23 and the variable pressure chamber 24 is rapidly cut off and the variable pressure chamber 24 is communicated with the atmosphere, and the power piston 22 is substantially connected to the reaction force member 54. The distance between the contact surface 22d and the atmospheric outflow control annular valve seat 38 and the distance between the contact surface 22d of the power piston 22 to the reaction force member 54 and the atmospheric inflow control annular valve seat 37a are increased. The output in the jumping state can be made larger than that in the normal state.

The normal brake characteristics and the emergency brake characteristics are shown in FIG. In FIG. 10, the jumping in the normal brake can only obtain an output having the magnitude of F ₀₁ , but the jumping during emergency braking increases to F ₀₁₁ and can generate a large brake fluid pressure.

  When the brake operation is finished and the brake pedal is returned, the plunger 37 moves rearward while the flange surface 34 is in contact with the key member 32. When the key member 32 comes into contact with the rear shell 12 (fixing member), the key member 32 comes into contact with the front groove wall 40f (see FIG. 4) of the valve seat member 40 and retreats integrally with the power piston 22. The backward movement of the member 40 is restricted. At this time, since the power piston 22 is still retracted, the engaging portion of the holding member 52 that is integrally retracted with the power piston 22 comes into contact with the rear shell 12 (fixing member) via the key member 32 and stops. The holding member 52 and the valve seat member 40, which are disengaged by the emergency brake operation, are engaged with the engaged portion 40c of the valve seat member 40, and the next emergency brake operation is performed. Will be prepared.

It is sectional drawing of the negative pressure type booster of 1st Example of this invention. FIG. 2 is an enlarged partial view of a main part of FIG. 1. It is sectional drawing of the negative pressure type booster of 2nd Example of this invention. It is a perspective view before the assembly of the valve seat member 40. FIG. 6 is a perspective view before the holding member 52 is assembled. It is a partial cross section figure of the negative pressure type booster of 3rd Example of this invention. FIG. 10 is a perspective view before the holding member 152 is assembled. It is XX sectional drawing of FIG. It is a partial cross section figure of the negative pressure type booster of 4th Example of this invention. FIG. 4 is a diagram illustrating a relationship between a force (input) applied to an input rod 28 and a propulsive force (output) of an output member 55.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Brake booster 11, 12 Shell 14 Housing 20 Movable wall 22 Power piston 23 Constant pressure chamber 24 Variable pressure chamber 27 Input member 28 Input rod 32 Key member 36 Valve mechanism 37 Plunger 37a, 39 Valve seat 40 Valve seat member 48 Holding means 50 Locking Member 52 Holding member 53 Ring-shaped elastic body 54 Reaction force member 55 Output member

Claims (12)

A housing that forms at least one pressure chamber therein, a movable wall that is installed inside the housing so as to be capable of moving forward and backward with respect to the housing, and that divides the pressure chamber into a constant pressure chamber and a variable pressure chamber; A power piston coupled to the movable wall, an input member installed inside the power piston so as to be able to move forward and backward with respect to the power piston, and a propulsive force of the power piston accompanying the movement of the movable wall An output member that outputs to the power piston, an annular valve seat for atmospheric outflow control that is disposed on the power piston and faces rearward, a movable portion that faces the annular valve seat for atmospheric outflow control, and the power piston. A valve mechanism having a fixed portion fixed to the valve, and the annular valve seat for atmospheric outflow control is capable of moving forward and backward with respect to the power piston. In the negative pressure type booster arranged, the negative pressure type booster has a holding means for holding the valve seat member at a predetermined position in front when the advance amount of the input member relative to the power piston is not more than a predetermined value. When the advance amount of the input member relative to the power piston is greater than a predetermined value, a movable means for moving the valve seat member to a rear position by a predetermined amount, and when the power piston is at a predetermined position with respect to the housing And a return means for returning the valve seat member to the predetermined position in front. The holding means has one end engaged with the power piston or the power piston side member and the other end with the valve seat member. A negative pressure type booster comprising a holding member engaged with the pressure member. In Claim 1, A taper part is provided in at least one of the holding member which has an engaging part which can be engaged / disengaged with the input member and the valve seat member, and the amount of advance to the power piston of the input member from a predetermined value When it is larger, the negative pressure type booster releases the holding of the holding member by a cam action of the input member or the holding member and the tapered portion. 3. The first atmospheric outflow control device according to claim 1, wherein the annular valve seat for atmospheric outflow control is capable of moving forward and backward relative to the first annular valve seat for atmospheric outflow control integrated with the power piston and the power piston. A negative pressure booster comprising an annular valve seat and a second atmospheric outflow control annular valve seat that is substantially concentric. 2. The negative pressure booster according to claim 1, wherein the movable means includes at least a biasing member that biases the valve seat member rearward. 5. The return means according to claim 1, wherein the return means is capable of moving through the power piston in a radial direction by a predetermined amount in the front-rear direction and backward of the valve seat member with respect to the power piston. A negative pressure doubler, characterized in that it includes a key member for restricting movement of the valve and a fixing member fixed to the housing, and moves forward with respect to the power piston to return the valve seat member to the predetermined position in front. Force device. 2. The negative pressure doubler according to claim 1, wherein the holding member includes a plurality of ring-shaped elastic bodies that press the plurality of holding members inward with a predetermined binding force. Force device. The negative pressure type booster according to claim 6, wherein the holding member includes three pieces. 3. The power piston according to claim 1, wherein the power piston has a locking groove provided so as to extend substantially at right angles to a central axis of the power piston, and the holding member is engaged with the locking groove. A negative pressure type booster characterized by having an engaging portion to be joined. In Claim 1, the locking member which comprises a part of said power piston is fixed to the front-end part of the said power piston, and the said holding member is distribute | arranged between the said power piston and the said locking member. Boost device. 9. The negative pressure booster according to claim 8, wherein a regulating member for regulating outward movement of the locking portion of the holding member is provided. In Claim 8, The said latching | locking part of the said holding member is substantially cylindrical shape, and the said latching groove of the said power piston has a notch for allowing rotation of the said holding member, and the said latching | locking part. A negative pressure type booster characterized by being a cylindrical inner hole that fits with. 3. The power piston according to claim 2, wherein the power piston has a locking groove provided so as to extend substantially at right angles to a central axis of the power piston, and the holding member is engaged with the locking groove. Having a locking part,
A plane passing through the central axis of rotation of the locking portion in the locking groove and passing through the center line of the contact surface between the tapered portion of the holding member and the tapered portion of the input member is the power. A negative pressure booster characterized in that the angle formed with the central axis of the piston is 30 ° or less.

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