JP2003025986A - Negative pressure type booster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative pressure type booster capable of surely regulating detachment of an output member from a power piston without generating deformation and damage of a second end part of a rod retainer, even when the power piston moves forward in a full stroke. SOLUTION: The output member 55 is repulsively pressed on the power piston 22 by a tongue piece 15b of the rod retainer 15. A front end face of the tongue piece 15b of the rod retainer 15 arranges a tongue piece 15b1 on a rear side of a front end face 22f of the power piston 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative pressure type booster for a vehicle.

[0002]

2. Description of the Related Art Generally, in a negative pressure type booster, a housing having at least one pressure chamber formed therein, a housing provided inside the housing so as to be able to move forward and backward with respect to the housing, and the pressure chamber is a constant pressure chamber. A movable wall that is divided into a variable pressure chamber and a power piston that is coupled to the movable wall,
An input member that is installed inside the power piston so as to be able to move forward and backward with respect to the power piston, an output member that outputs the propulsive force of the power piston due to the movement of the movable wall to the outside of the device, and a power piston that is provided inside the housing. And a rod retainer that has a first end pressed against the power piston by the biasing member and a second end that restricts separation of the output member from the power piston. Has been. An example of such a conventional negative pressure type booster is disclosed in Japanese Patent Laid-Open No. 8-67239.

In this system, the atmosphere is introduced into the variable pressure chamber in accordance with the brake operation, the movable wall and the power piston connected to the movable wall move forward, and the propulsive force of the power piston is output to the external device such as the master cylinder. Is output to and the braking force is generated. Then, when the brake operation is completed, the reaction force from the external device such as the master cylinder causes
The output member and the power piston are returned to the rear side, but at this time, the rod retainer is provided so that the output member fitted at the front end portion of the power piston does not fall off from the power piston. The rod retainer has a first end pressed by the biasing member against the power piston, and a second end restricting separation of the output member from the power piston.

[0004]

However, in this conventional negative pressure type booster, when the power piston fully strokes forward, the rod retainer is provided between the front end face of the power piston and the front inward protruding portion of the housing. The second end of the rod retainer may be caught and the second end of the rod retainer may be deformed or damaged.

According to the present invention, even when the power piston makes a full stroke forward, the second end portion of the rod retainer is not deformed or damaged, and the separation of the output member from the power piston can be reliably regulated. It is an object of the present invention to provide a negative pressure type booster that can be used.

[0006]

In order to achieve the above object, according to claim 1, a housing having at least one pressure chamber formed therein, and an inside of the housing, which is advanced with respect to the housing. And a movable wall that is installed so as to be retractable and divides the pressure chamber into a constant pressure chamber and a variable pressure chamber, a power piston that is coupled to the movable wall, and a forward direction with respect to the power piston inside the power piston. An input member that is installed so as to be retractable, an output member that outputs the propulsive force of the power piston accompanying the movement of the movable wall to the outside of the device, a first end portion fixed to the power piston, and the output member A negative pressure type booster including a rod retainer provided with a second end portion for restricting separation from the power piston, the front end of the second end portion of the rod retainer. There have configured the vacuum booster, characterized in that in the rear than the front end surface of the power piston.

The rear means the brake pedal side or the vehicle rear side of the negative pressure type booster, and the front side means the master cylinder side or the vehicle front side of the negative pressure type booster.

According to the first aspect of the present invention, the front end surface of the second end portion of the rod retainer is arranged rearward of the front end surface of the power piston, so that the power piston can be operated even during a full forward stroke. The second end of the rod retainer is not sandwiched between the front end face of the piston and the front inward projection of the housing, and the second end of the rod retainer is securely prevented from being deformed or damaged.

Next, as set forth in claim 2, the second end of the rod retainer is composed of a plurality of tongues extending inward in the radial direction, and the rod piston is circumferentially formed on the front end face of the power piston. A negative pressure type booster characterized in that the tongue is engaged with a plurality of grooves provided is preferable.

According to the second aspect of the present invention, since the second end portion of the rod retainer is formed as a plurality of tongue pieces, an appropriate elastic force for pressing the output member against the power piston can be obtained, and The tongue piece is easily formed during press forming of the rod retainer. Further, since the tongue pieces are engaged with the plurality of grooves provided in the front end surface of the power piston in the circumferential direction, the rod retainer can be easily and surely assembled.

Next, as set forth in claim 3, a plurality of tongue-shaped rim portions in which the second end portion of the rod retainer extends inward in the radial direction and a ring for circumferentially connecting the rim portions. The negative pressure type booster is characterized in that the rim portion is engaged with a plurality of grooves circumferentially provided on the front end face of the power piston.

According to the third aspect of the invention, since the second end of the rod retainer is formed of a plurality of tongue-shaped rim portions extending inward in the radial direction, an appropriate elastic force can be obtained. Since the rim portion and the ring portion are integrally formed, the strength is high. Further, since the rim portion is engaged with the plurality of grooves provided in the front end surface of the power piston in the circumferential direction, the rod retainer can be easily and surely assembled.

Next, as set forth in claim 4, a negative pressure type booster characterized in that the second end portion of the rod retainer elastically presses the output member toward the power piston. A device is preferred.

According to the invention of claim 4, the second end portion of the rod retainer elastically presses the output member against the power piston, so that the separation of the output member from the power piston can be reliably regulated. it can.

Next, as set forth in claim 5, a reaction force corresponding to the output of the negative pressure valve seat disposed on the power piston and facing rearward and the output member is transmitted to the input member. A negative pressure valve seat is provided with a reaction member, and a valve mechanism having a movable portion facing the negative pressure valve seat and a fixed portion fixed to the power piston in an airtight manner. The first negative pressure valve seat is integral with the power piston, and the second negative pressure valve seat is provided on a valve seat member that can move forward and backward with respect to the power piston and is substantially concentric with the first negative pressure valve seat. Holding means for holding the valve seat member at a predetermined front position when the amount of advance with respect to the power piston is less than or equal to a predetermined value, and the valve seat member when the amount of advance of the input member with respect to the power piston is greater than a predetermined value. To A movable means for moving a predetermined amount towards,
It is preferable that the negative pressure type booster includes a returning means for returning the valve seat member to a predetermined front position when the power piston comes to a predetermined position with respect to the housing.

According to the fifth aspect of the invention, when the relative movement amount between the input member and the power piston is equal to or greater than a predetermined value, that is, during emergency braking in which the driver hurriedly depresses the brake pedal, the valve seat member by the holding means is provided. Is released, the valve seat member is moved rearward by a predetermined amount by the movable means, and the second negative pressure valve seat provided on the valve seat member presses the movable portion of the valve mechanism rearward. Rapid and forced communication with the atmosphere.

As a result, a larger propulsive force than that during normal braking is applied to the movable wall, the power piston, and the output member, so that a sufficient amount of brake fluid pressure can be generated. In other words, jumping characteristics (the ratio of output to input becomes infinite until the input member comes into contact with the reaction member when the brake pedal is depressed and the brake is operated, which is called jumping). Is changed to apply a larger propulsive force to the output member than during normal braking. That is, a negative pressure type booster having two types of input-output characteristics, that is, a characteristic for normal braking and a characteristic for emergency braking, that is, a negative pressure type booster with a B / A (brake assist) function can be realized with a simple configuration.

Moreover, since the second end portion of the rod retainer elastically presses the output member against the power piston, when the brake pedal is returned and the valve seat member moves forward, the reaction force member and the output member are moved. The reaction force from the valve seat member is
It is positively supported by the second end of the rod retainer.
Therefore, there is no gap in the axial direction between the reaction member and the output member, and the power piston, and the re-engagement of the valve seat member with the holding means is ensured.

Further, since the front end face of the second end portion of the rod retainer is arranged rearward of the front end face of the power piston, the front end face of the power piston and the housing are not separated even when the power piston is fully stroked forward. The second end of the rod retainer is not pinched between the front retainer and the inward projection, and the second end of the rod retainer is securely prevented from being deformed or damaged.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are sectional views of a negative pressure type booster for a vehicle according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view of FIG.

Referring to FIG. 1, a negative pressure type booster 1 for a vehicle.
0 is the front shell 11, the rear shell 12, and the movable wall 20.
The interior of the constant pressure chamber 23 is composed of
And a housing 14 that is divided into a transformer chamber 24.
The movable wall 20 in the housing 14 is a metal plate 1
8 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
The folded-back portion provided on the outer peripheral edge of the rear shell 12 and the front shell 11 are hermetically sandwiched. 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 is connected to an engine intake manifold (not shown) which is a negative pressure source, and is always kept at a negative pressure during engine operation. The transformer room 24 has a passage 60.
The valve mechanism 36 communicates with and blocks the constant pressure chamber 23, and the valve mechanism 36 communicates with and blocks the atmosphere.

As shown in FIGS. 1 and 2, the power piston 22 has a front portion (left side in FIGS. 1 and 2) inside thereof.
The first space 22a located at the position communicating with the constant pressure chamber, the second space 22b located inside (the right side in FIGS. 1 and 2) located inside thereof and communicating with the atmosphere, the first space 22a 2 space 22
It has an intermediate portion 221 that is interposed between b and b. The middle part 221 communicates the first space 22a and the second space 22b separately from the third space 22c, which communicates the first space 22a and the second space 22b at the center of the middle part 221. And a passage 60 that operates.

Inside the power piston 22, an input rod 28 and a plunger 37 forming an input member 27 are provided.
The first space 22a, the second space 22b, and the third space 22c are penetrated, and the power piston 22 is installed so as to be movable in the front-rear direction. In addition, the input rod 28 and the plunger 37 are integrally connected by a connecting portion 80, and the input rod 28 is connected to a brake pedal (not shown) behind the input rod 28.

As shown in FIGS. 1, 2 and 5, the tongue piece 15b and the base portion 1 are provided on the outer periphery of the front end portion of the power piston 22.
5a and a rod retainer 15 integrally connected to each other by a connecting portion 15c are provided, and the base portion 15a is pressed by the power piston 22 by the spring 57 and the tongue engaged with the groove 22e of the front end face 22f of the power piston 22. The piece 15b elastically presses the flange portion of the output member 55 to restrict the output member 55 from being detached forward.

The front end surface 15b1 of the tongue piece 15b is
The power piston 22 is located rearward of the front end face 22f, and even when the power piston 22 makes a full stroke forward, the front end face 22f of the power piston 22 comes into contact with the front inward protruding portion 14a of the housing 14. Since the tongue piece 15b of the rod retainer 15 is not sandwiched between the front end surface 22f of the power piston 22 and the front inward protruding portion 14a of the housing 14, the tongue piece 15b is securely prevented from being deformed or damaged. .

As shown in FIG. 6, the rod retainer includes a plurality of tongue-shaped rim portions 11 extending inward in the radial direction.
Alternatively, the rod retainer 115 may be formed by connecting and integrally forming the ring portion 115d and the base portion 115a with the 5b and the connecting portion 115c. In this case, an appropriate elastic force for pressing the output member 55 against the power piston 22 is obtained, and since the rim portion 115b and the ring portion 115d are integrally formed, the strength is high. Further, since the rim portion 115b is engaged with the plurality of grooves 22e provided in the front end surface of the power piston 22 in the circumferential direction, the rod retainer 115 can be easily and surely assembled.

In the present embodiment, considering that the rod retainer is applied to a negative pressure type booster having an emergency braking function, which will be described later, the tongue piece 15b is the output member 5.
Although it is configured to elastically press the flange portion of No. 5, it is not necessarily limited to this. That is, in a normal negative pressure type booster having no emergency braking function, the tongue piece 15b does not need to elastically press the flange portion of the output member 55, and a slight gap may be set. .

An output member 55 is fitted on the front end of the power piston 22, and a reaction member 54 is disposed between the front end of the power piston 22 and the output member 55. Further, the 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 provided.
Transmits a part of the reaction force corresponding to the output of the output member 55 transmitted via the reaction force member 54 to the plunger 37.

Plunger 3 for power piston 22
The key member 32 is inserted into a radial hole 33 formed in the intermediate portion 221 of the power piston 22 in order to regulate the movement amount of the input rod 28 and the input rod 28. The thickness dimension of the key member 32 in the front-rear direction (the left-right direction in FIGS. 1 and 2) is smaller than the front-rear dimension of the radial hole 33.
2 can move forward and backward with respect to the power piston 22 by a distance C shown in FIG.

The key member 32 is capable of contacting the rear shell 12 at the rear surfaces of both ends projecting to the outer peripheral side of the power piston 22, and the rearward movement limit of the power piston 22 with respect to the housing 14 is as shown in FIG. 3, 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 has a pair of flange surfaces 34, 35 formed in the central portion of the plunger 37.
The rearward movement limit of the plunger 37 with respect to the power piston 22 is that the flange surface 34 abuts the front surface of the key member 32 and the rear surface of the key member 32 is the rear wall of the radial hole 33. This is the position where it touches. Further, the limit of the forward movement of the plunger 37 with respect to the power piston 22 is that the flange surface 35 contacts the rear surface of the key member 32 and the front surface of the key member 32 has a radial hole 33.
This is the position where it comes into contact with the front wall of the.

Inside the power piston 22, the variable pressure chamber 24 is communicated with the constant pressure chamber 23 in response to the front-rear movement of the plunger 37 with respect to the power piston 22, and the variable pressure chamber 23 is shut off from the atmosphere. Is the constant pressure chamber 2
3 and a valve mechanism 36 for switching between an output holding action state in which the variable pressure chamber 24 is shut off from the atmosphere and an output increasing action state in which the variable pressure chamber 24 is shut off from the constant pressure chamber 23 and communicates with the atmosphere.

The valve mechanism 36 is formed integrally with the atmosphere valve seat 37a formed at the rear end of the plunger 37 and the power piston 22 around the rear side opening of the third space 22c. The negative pressure valve seat 38, and the negative pressure valve seat 41 facing the first negative pressure valve seat 38 and the atmosphere valve seat 37a, respectively.
a and an atmosphere valve seat 41b, a movable portion 41, and a fixed portion 43 that is hermetically fixed to the power piston 22 by a retainer 42, and the movable portion 41 is urged forward by a spring 44. The tubular member 45 present is the main constituent member.

In the third space 22c of the intermediate portion 221, a valve seat member 40 having a second negative pressure valve seat 39 is arranged concentrically with the first negative pressure valve seat 38 and the power piston 22 is provided.
It is possible to move in the front-back direction.

As shown in a perspective view in FIG. 3, the valve seat member 40
Is provided with a slit 40b into which an abutting portion 37c protruding in the radial direction is inserted on the outer periphery of the plunger 37, and a through hole 40e penetrating the valve seat member 40 in the front-rear direction. In addition, the key member 32 is inserted across the connecting portion 40a.

By inserting the plunger 37 into the through hole 40e of the valve seat member 40, the abutting portion 37c and the slit 40b face each other, and the abutting portion 37c of the valve seat member 40 is inserted through the slit 40b. It will be projected to the outside. When the plunger 37 having the valve seat member 40 is disposed in the power piston 22, the contact portion 37c comes into contact with the recess 221a on the inner peripheral surface of the intermediate portion 221.
The plunger 37 is connected to the intermediate portion 221 via the contact portion 37c.
Will be slidably supported on the inner periphery of the power piston 22, that is, on the inner periphery of the power piston 22.

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 at the rear end portion where the first negative pressure valve seat 38 is formed. It comes into contact with the inner peripheral surface of the intermediate portion 221 so as to be slidable in the front-rear direction. That is, the power piston 2
2 includes an intermediate portion 221 as a holding portion that holds the valve seat member 40 slidably in the front-rear direction.

The rear end portion of the valve seat member 40 and the intermediate portion 2 are provided on the outer periphery of the rear end portion of the valve seat member 40 which abuts on the intermediate portion 221.
An annular seal member 46 for keeping airtightness with the inner peripheral surface of 21 is attached. Further, the valve seat member 40 is the valve seat member 40.
And a flange portion provided on the inner peripheral surface of the intermediate portion 221 urges the spring portion 47 rearward.

The spring 59 disposed between the retainer 58 locked to the input rod 28 and the retainer 42 locked to the power piston 22, which are integrally connected to the plunger 37 by the connecting portion 80, is When the rod 28 is biased rearward and the brake pedal is not depressed, the atmosphere valve seat 37a is brought into contact with the movable portion 41 of the valve mechanism 36 and the movable portion 41 is separated from the first negative pressure valve seat 38 by a distance A. Hold them apart.

The passage 60 formed in the intermediate portion 221 and the first
The space 22a connects the valve mechanism 36 and the constant pressure chamber 23,
The third space 22c connects the valve mechanism 36 and the variable pressure chamber.

Inside the front portion of the power piston 22, that is, in the intermediate portion 221, movable means for propelling the valve seat member 40 rearward is provided. This movable means includes a spring 47 for biasing the valve seat member 40 rearward and a key member 32.
It consists of

A holding means 48 is provided 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 a first engaging portion 52b that engages with the engaged portion 40c of the valve seat member 40, and the ring-shaped elastic body 5 that urges the holding member 52 in a direction of reducing the diameter.
The second engaging portion 52c of the holding member 52 is fitted in the locking groove 50a of the auxiliary holding 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 second engagement portion 52c. As shown in FIG. 4, the holding member 52 has a three-section hollow truncated cone shape obtained by cutting a hollow truncated cone along three planes passing through the central axis thereof. And is assembled to the power piston 22 via the auxiliary holding member 50.

The auxiliary holding member 50 also functions as a guide member for guiding the movement of the contact member 70 in the front-rear direction.

A cam is constituted by a slant surface portion 52a provided on the inward flange portion of the holding member 52 and a slant surface portion 37b provided on the front outward bulge portion of the plunger 37,
When the plunger 37 moves forward relative to the power piston 22 by a predetermined amount, the holding member 5 is moved by the cam action.
2 is moved in the radial direction to release the engagement between the engaging portion 52b and the engaged portion 40c of the valve seat member 40.

Next, the operation of the negative pressure type booster of the present embodiment will be described, but the operation as the negative pressure type booster during normal braking is generally known, and the description thereof is omitted. , Mainly the operation during emergency braking will be described.

The emergency braking characteristic of the negative pressure type booster of this embodiment is achieved by changing the jumping characteristic so that a larger propulsive force than that during normal braking is applied to the output member. In order to change the jumping characteristic, the gap D between the contact member 70 and the reaction member 54 in FIG. 2 may be increased. The expansion of the gap D depends on the distance between the contact surface 22d of the power piston 22 against the reaction force member 54 and the negative pressure valve seat 38, and the power piston 2
This is the same as expanding the distance between the contact surface 22d of the second reaction member 54 and the atmosphere valve seat 37a. That is, by moving the negative pressure valve seat 38 and the atmosphere valve seat 37a rearward, the gap D is enlarged, the output until the contact member 70 receives the reaction force from the reaction force member 54 is increased, and the output to the input is increased. The output in the so-called jumping state where the ratio of is infinite is larger than that in the normal state.

During an emergency brake in which the driver hurriedly depresses the brake pedal, if the relative movement amount between the input rod 28 and the power piston 22 becomes larger than the predetermined value B,
The inclined surface portion 37b of the plunger 37 abuts on the tapered portion 52a of the holding member 52, and radially expands the holding member 52 which is urged by the ring-shaped elastic body 53 in the direction of reducing the diameter.

When the minimum inner diameter portion 52aa of the inclined surface portion 52a rides on the step portion 37d of the plunger 37, the valve seat member 40
The engagement between the engaged portion 40c and the engaging portion 52b of the holding member 52 is released. Since the valve seat member 40 is biased rearward by the spring 47, immediately after the engagement of the engaged portion 40c is released, the valve seat member 40 is moved rearward by the biasing force of the spring 47.

When the valve seat member 40 moves rearward, the second negative pressure valve seat 39 of the valve seat member 40 moves the movable portion 41 of the valve mechanism 36.
Of the constant pressure chamber 23 and the variable pressure chamber 24.
Cut off communication with. At this time, the plunger 37 is moving forward together with the input rod 28, and the valve seat member 4
Since 0 pushes back the movable portion 41 of the valve mechanism 36 to the rear, the atmosphere valve seat 37a of the plunger 37 and the valve 41b constituting the movable portion 41 of the valve mechanism 36 are rapidly separated, and the variable pressure chamber 24 is exposed to the atmosphere. Communicate with. As a result, compared with the normal braking operation, the communication between the constant pressure chamber 23 and the variable pressure chamber 24 is interrupted and the variable pressure chamber 24 is rapidly communicated with the atmosphere, and substantially, the reaction force member 54 of the power piston 22 to the reaction force member 54 is substantially reduced. Abutment surface 22
d and the distance between the first negative pressure valve seat 38 and the power piston 2
The distance between the contact surface 22d of the second reaction member 54 and the atmosphere valve seat 37a is increased, so that the output in the jumping state can be made larger than in the normal state.

FIG. 7 shows the normal brake characteristic and the emergency brake characteristic. In FIG. 7, the jumping in the normal brake can obtain only the output of F ₀₁ , but the jumping in the emergency braking is increased to F ₀₁₁ and the brake fluid pressure of a sufficient magnitude can be obtained with a small pedal effort. Can be generated.

When the brake operation is completed and the brake pedal is returned, the plunger 37 moves rearward while the flange surface 34 of the plunger 37 contacts the key member 32.
When the key member 32 comes into contact with the rear shell 12, the key member 32 comes into contact with the front groove wall 40f of the valve seat member 40 and restricts the rearward movement of the valve seat member 40 that has retracted integrally with the power piston 22. To do. At this time, since the power piston 22 still retracts, the engaging portion of the holding member 52 that retracts integrally with the power piston 22 abuts the rear shell 12 via the key member 32 and is stationary. Member 40
The engaged member 40c is engaged, and the holding member 52 disengaged by the emergency braking operation and the valve seat member 40 are re-engaged to prepare for the next emergency braking operation.

[0054]

According to the present invention, even when the power piston makes a full stroke forward, the second end of the rod retainer is not deformed or damaged, and the output member is reliably separated from the power piston. It is possible to provide a negative pressure type booster that can be regulated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a negative pressure type booster according to an embodiment of the present invention.

FIG. 2 is an enlarged partial view of a main part of FIG.

FIG. 3 is a perspective view of the valve seat member 40 before assembly.

FIG. 4 is a perspective view of a holding member 52 before assembly.

5 is a view from A in FIG. 1 showing a mounted state of a rod retainer 15. FIG.

6 is an A view in FIG. 1 showing a mounted state of a rod retainer 115. FIG.

7 is a diagram showing a relationship between a force (input) applied to the input rod 28 and a propulsive force (output) of the output member 55. FIG.

[Explanation of symbols]

10 Negative pressure type booster 12 Rear shell (return means) 14 housing 15 Rod retainer 15a Base (first end) 15b Tongue piece (second end) 15b1 Front end face of tongue 20 movable walls 22 Power Piston 22e groove 22f Power piston front end face 23 Constant pressure chamber 24 transformer room 27 Input member 28 Input rod (input member) 32 key members (movable means, return means) 37 Plunger (input member) 38 First negative pressure valve seat 39 Second negative pressure valve seat 47 spring (movable means) 48 holding means 50 Auxiliary holding member (holding means) 52 holding member (holding means) 53 Ring-shaped elastic body (holding means) 54 Reaction member 55 Output member 57 Spring (biasing member) 115 Rod retainer 115a Base (first end) 115b Rim portion (second end portion) 115d ring portion (second end portion)

Claims (5)

[Claims] 1. A housing in which at least one pressure chamber is formed, and a housing which is installed inside the housing so as to be able to move forward and backward with respect to the housing and divides the pressure chamber into a constant pressure chamber and a variable pressure chamber. A 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 power piston associated with the movement of the movable wall. An output member for outputting a propulsive force to the outside of the apparatus, a rod retainer provided with a first end portion that abuts the power piston, and a second end portion that restricts separation of the output member from the power piston. In the negative pressure type booster, the front end surface of the second end portion of the rod retainer is behind the front end surface of the power piston. Type booster. 2. The plurality of tongues according to claim 1, wherein the second end of the rod retainer comprises a plurality of tongues extending inward in the radial direction, and a plurality of tongues circumferentially provided on the front end face of the power piston. A negative pressure type booster, wherein the tongue is engaged with the groove. 3. The rod retainer according to claim 1, wherein the second end portion of the rod retainer comprises a plurality of tongue-shaped rim portions extending radially inward and a ring portion connecting the rim portions in a circumferential direction. The negative pressure type booster characterized in that the rim portion engages with a plurality of grooves circumferentially provided on the front end face of the power piston. 4. The rod retainer according to claim 1, wherein the second end portion of the rod retainer elastically presses the output member toward the power piston. Negative pressure type booster. 5. The reaction force according to any one of claims 1 to 4, wherein the reaction force corresponding to the output of the negative pressure valve seat disposed on the power piston and facing rearward and the output member is input. A negative pressure valve seat is provided, which includes a reaction member that transmits to a member, and a valve mechanism that includes a movable portion facing the negative pressure valve seat and a fixed portion that is airtightly fixed to the power piston. A first negative pressure valve seat that is integral with the power piston; and a second negative pressure valve seat that is provided on a valve seat member that can move forward and backward with respect to the power piston and that is substantially concentric with the first negative pressure valve seat. When the amount of advance of the input member with respect to the power piston is less than or equal to a predetermined value, holding means for holding the valve seat member at a predetermined front position, and when the amount of advance of the input member with respect to the power piston is greater than a predetermined value Previous And a return means for returning the valve seat member to a predetermined front position when the power piston comes to a predetermined position with respect to the housing. Negative pressure type booster.