JPH11348763A - Brake booster device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve braking feeling in the zone where a spring is extended/ compressed than a brake booster device provided with a conventional reaction transmitting means. SOLUTION: A reaction disk 36 of a brake booster device provided with a reaction transmitting means 34 is provided with a first member 51 with low hardness arranged on the rear side and a second member 52 with high hardness arranged on the front side. A stepped recess part 51A curved on the rear side is formed on the front end face of the first member, while a stepped projecting part 52A to be fitted in the stepped recess part is formed on the rear side end face of the second member, and the stepped projecting part is constituted so that it prevents elastic deformation of the stepped recess part inward in the radial direction when compressed and does not prevent elastic restoration of the stepped recess part outward in the radial direction when the compression is released.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake booster, and more particularly, to a brake booster having a reaction force transmitting means having a reaction disk and a spring.

[0002]

2. Description of the Related Art Conventionally, as a brake booster, there has been known a brake booster in which a servo ratio is reduced at an early stage of braking and increased at a late stage of braking. In this type of brake booster, a first retainer and a second retainer are provided between the reaction disc and the valve plunger so as to be relatively displaceable from each other, and a predetermined retainer is provided between the first retainer and the second retainer. Reaction force transmitting means comprising a spring which is elastically loaded with a set load and normally holds both retainers in a separated state, and a stopper member which prevents the first retainer and the second retainer from being separated from each other by a predetermined distance or more. (Japanese Patent Application Laid-Open No. 8-85442). According to such a configuration, as shown in FIG. 10, even if the brake pedal is depressed and the brake booster is operated, the reaction force transmission means is simply a reaction disk until the spring of the reaction force transmission means is compressed. Is transmitted only to the valve plunger via the first retainer, the spring, and the second retainer, so that the servo ratio at this time can be set to a small value. The operability in is improved. On the other hand, when the spring of the reaction force transmitting means is compressed, the second retainer and the valve plunger are advanced relative to the first retainer and the plate plunger, so that the brake pedal is consequently moved by the spring. As a result, the servo ratio at this time can be set to be large, so that a large braking force can be obtained by a light pedaling force.

[0003]

In the brake booster using the above-mentioned reaction disk, the reaction disk is made of an elastic member such as rubber, so that the brake pedal is released when the brake pedal is depressed and released. It is known that there is a hysteresis in which the output of the brake booster is different even when the pedaling force of the brake booster is the same, that is, the output when released is higher than when the pedal is depressed. With the above-mentioned hysteresis, the same braking force can be obtained even if the driver stops the increase in the depression force of the brake pedal and then slightly reduces the depression force unconsciously. There is an advantage that it becomes. However, in the brake booster provided with the reaction force transmitting means, as shown in FIG. 10, in the region where the spring of the reaction force transmitting means is not compressed, the hysteresis can be obtained as in the related art. It has been found that in the region where the spring of the means expands and contracts, the output at the time of release is smaller than the output at the time of stepping, and it is impossible to obtain hysteresis. In other words, the reaction disk has a relatively small amount of elastic deformation in a region where the spring of the reaction force transmitting means is not compressed. Therefore, when the compression is released from this state, the reaction disk can quickly return elastically. Since the amount of elastic deformation is relatively large in the region where the spring of the means is compressed, even if the compression is released from this state, it initially returns very slowly and slowly, and the amount of elastic deformation eventually decreases Will return promptly. As a result, in a region where the spring of the reaction force transmission means expands and contracts, even if the brake force is reduced by loosening the depression force of the brake pedal, the spring of the reaction force transmission means is not released for a while without being released while the spring of the reaction force transmission means is compressed. Since the power is transmitted, when the pedaling force is the same at the time of stepping and at the time of releasing, the output at the time of releasing is smaller than at the time of stepping. Therefore, in the brake booster provided with the reaction force transmitting means, in the region where the spring expands and contracts, the output of the booster greatly decreases in response to the reduction in the depression force of the brake pedal, and the brake feeling is impaired. was there. The present invention has been made in view of such circumstances, and provides a brake booster capable of improving a brake feeling in a region where a spring of a reaction force transmitting unit expands and contracts as compared with the related art.

[0004]

According to the first aspect of the present invention, a valve body slidably provided in a shell, a valve mechanism provided in the valve body, and a valve plunger constituting the valve mechanism are moved forward and backward. An input shaft for switching the flow path of the valve mechanism, an output shaft slidably provided on the valve body, a reaction disk interposed between the output shaft and the valve body, and a reaction disk and a valve plunger. A reaction force transmitting means interposed between the reaction disk and the reaction force transmitting means for transmitting a brake reaction force from the reaction disk to the valve plunger. It is configured so that it can be elastically restored without being inhibited when the compression is released. According to the fourth aspect of the present invention, the valve body slidably provided in the shell, the valve mechanism provided in the valve body, and the valve plunger constituting the valve mechanism are moved forward and backward to switch the flow path of the valve mechanism. An input shaft, an output shaft slidably provided on the valve body, a reaction disk interposed between the output shaft and the valve body, and a reaction disk interposed between the reaction disk and the valve plunger. And a reaction force transmitting means for transmitting the reaction force of the brake to the valve plunger, the end surface of the valve body contacting the rear end surface of the reaction disk being moved when the reaction disk is compressed. The disk is configured to inhibit elastic deformation, and when the compression is released, It is obtained by constituting so as not to interfere with the elastic return of the action disc.

[0005]

According to the structure of the first aspect, when the brake pedal is depressed and compressed, the reaction disc inhibits its own compression deformation, but the depression of the brake pedal is loosened and the compression is released. In this case, the reaction disk does not hinder its own elastic recovery, so that when the depression force of the brake pedal is the same at the time of depression and at the time of release, the output at the time of release is relatively higher than at the time of depression. As a result, hysteresis can be obtained in the region where the spring of the reaction force transmitting means expands and contracts, so that the brake feeling in the region where the spring expands and contracts is better as compared with a conventional brake booster including the reaction force transmitting means. Can be According to the configuration of claim 4, when the brake pedal is depressed and compressed, the end face of the valve body inhibits the elastic deformation of the reaction disk, but the depression of the brake pedal is loosened and the compression is released. In this case, the end face of the valve body does not hinder the elastic recovery of the reaction disk, so that when the pedaling force of the brake pedal is the same between when the pedal is depressed and when the pedal is released, the output when released is relatively higher than when depressed. Become higher. As a result, hysteresis can be obtained in the region where the spring of the reaction force transmitting means expands and contracts, so that the brake feeling in the region where the spring expands and contracts is better as compared with a conventional brake booster including the reaction force transmitting means. Can be

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiment. In FIG. 1, a shell 2 of a tandem brake booster 1 defines a front chamber 4 and a rear chamber 5 in front and rear by a center plate 3. . Then, a cylindrical valve body 6 is slidably penetrated through the rear side of the shell 2 and the center plate 3 by sealing means 7 and 8 while maintaining airtightness. Front power piston 10 and rear power piston 1 are provided on the outer peripheral portions of valve body 6 located in front chamber 4 and rear chamber 5, respectively.
1 and each power piston 10, 11
A front diaphragm 12 and a rear diaphragm 13 are respectively stretched on the back of the vehicle. And the front room 4
A constant-pressure chamber A before and after the front diaphragm 12
A constant pressure chamber C and a variable pressure chamber D are formed before and after the rear diaphragm 13 in the rear chamber 5.

In the valve body 6, the constant pressure chamber A,
A valve mechanism 15 for switching the communication state between C and the transformation chambers B and D is provided. As shown in FIG. 2, the valve mechanism 15 includes an annular first valve seat 16 formed in the valve body 6 and a valve plunger 17 slidably provided on the valve body 6 inside the first valve seat 16. An annular second valve seat 18 is formed on the rear side of the vehicle, and a valve body 20 is further seated on both valve seats 16 and 18 from the right side of the drawing by the resilience of a poppet return spring 19. The space outside the first valve seat 16 is communicated with a constant pressure chamber A through an axial constant pressure passage 22 formed in the valve body 6, and the variable pressure chamber A is connected to another axial direction formed in the valve body 6. Constant pressure passage 2
3 is connected to the constant pressure chamber C. The constant-pressure chamber A is connected to an intake manifold of an engine (not shown) via a negative-pressure introducing pipe 24 provided in the shell 2, whereby a constant negative pressure is introduced into the constant-pressure chamber A and the constant-pressure chamber C. ing. The space between the first valve seat 16 and the second valve seat 18 communicates with a variable pressure chamber D via a radial variable pressure passage 26 formed in the valve body 6, and the variable pressure chamber D is connected to the valve body 6. It communicates with the transformation chamber B via the formed axial transformation path 27. Further, the space inside the second valve seat 18 is communicated with the atmosphere through a pressure passage 28 provided in the end cylindrical portion 6A, and a filter 29 is provided in the pressure passage 28.

The right end of the valve plunger 17 has an input shaft 3
The input shaft 30 is urged rearward by a valve return spring 31 having an elastic force larger than that of the poppet return spring 19, and the input shaft 30 is normally connected to the rear end. The valve body 20 is seated on the second valve seat 18 of the plunger 17, and the valve body 20 is separated from the first valve seat 16 of the valve body 6. The end of the input shaft 30 is linked to a brake pedal (not shown). Further, the valve plunger 17 is prevented from coming out of the valve body 6 by the key member 32. The key member 32 can move forward and backward in the axial direction of the valve body 6, and abuts on the inner surface of the shell 2 when the brake booster 1 is not operated to hold the valve plunger 17 in the forward position with respect to the valve body 6. Input shaft 3 at the start of operation of brake booster 1
The loss stroke of 0 can be reduced. Further, on the front side of the valve plunger 17, a reaction force transmitting means 34, a plate plunger 35, and a reaction disk 36, which will be described in detail later, are sequentially disposed. The plate plunger 35 is slidably fitted in a holder 37 fixed to the front end face of the valve body 6 while maintaining airtightness. The reaction disk 36 is housed in a recess formed at the base of the output shaft 38, and the recess of the output shaft 38 is fitted on the outer peripheral surface of a holder 37 as a front end of the valve body 6. The tip of the output shaft 38 is
9 to keep the airtight and project out of the shell 2,
It is linked to a master cylinder piston (not shown). Therefore, the brake reaction force transmitted from the piston of the master cylinder is transmitted to the reaction disk 36 via the output shaft 38 and received by the valve body 6 via the holder 37 from the reaction disk 36 and the plate plunger 35 , And is transmitted to a brake pedal (not shown) via the reaction force transmitting means 34, the valve plunger 17 and the input shaft 30. The valve body 6 and the power pistons 10, 1
1 is normally held at a non-operating position in the figure by a return spring 40 mounted between the shell 2 and the valve body 6. In this non-operating state, a gap is formed between the plate plunger 35 and the reaction disc 36, whereby a brake reaction force is generated until the reaction disc 36 contacts the plate plunger 35 when the brake booster starts operating. The output rises (jumps) without it.

Next, as shown in FIG. 2, the reaction force transmitting means 34 includes a first retainer 42 and a second retainer 43.
And a coil spring 44 elastically mounted between the retainers 42 and 43, and a stopper 45 for preventing the first retainer 42 from being pulled out of the second retainer 43. The front side first retainer 42 is slidably fitted to the inner peripheral surface of the holder 37, and extends radially inward from the front end of the outer cylindrical portion 42a. At the same time, a radial portion 42b abutting on the rear end surface of the plate plunger 35, and an inner cylindrical portion extending from the inner peripheral side of the radial portion 42b to the rear side and through which the projecting portion 17A of the valve plunger 17 is loosely inserted. 42c. On the other hand, the second retainer 43 on the rear side
An outer cylindrical portion 43a housed in the outer cylindrical portion 42a of the retainer 42, and extends radially inward from a rear end of the outer cylindrical portion 43a and abuts on a step end surface of the valve plunger 17. A radial portion 43b and an inner cylindrical portion 43c extending from the inner peripheral side of the radial direction portion 43b to the axial front side and penetrating the projecting portion 17A of the valve plunger 17 are provided. The coil spring 44 is elastically mounted between the radial portion 42b of the first retainer 42 and the radial portion 43b of the second retainer 43, and the first coil spring 44 is compressed by a predetermined amount. The ring-shaped stopper 45 fixed to the outer tubular portion 42a of the retainer 42 is brought into contact with the rear side of the second retainer 43, so that the first retainer 42, the second retainer 43,
The coil spring 44 and the stopper 45 are integrally assembled. Therefore, the brake reaction force from the plate plunger 35 is transmitted to the valve plunger 17 via the first retainer 42, the coil spring 44, and the second retainer 43.

In the brake booster provided with the above-described reaction force transmitting means, when the brake pedal is depressed to advance the input shaft 30 and the valve plunger 17, the pedaling force exceeds the set load of the coil spring 44. In other words, the reaction force transmitting means 34 is integrally advanced while maintaining the state of FIG. 1, whereby the plate plunger 35 is also advanced. When the valve plunger 17 is advanced, the valve body 20 seated on the second valve seat 18 formed on the valve plunger 17
Is moved forward, seated on the first valve seat 16 of the valve body 6 stopped forward, and then separated from the second valve seat 18. As a result, the atmosphere is introduced into the variable pressure chambers B and D, and a pressure difference is generated between the constant pressure chambers A and C and the variable pressure chambers B and D. The pressure difference causes the power pistons 10 and 11 and the valve body 6 to move forward. As a result, the output shaft 38 moves forward, and brake fluid pressure is generated in the master cylinder. Then, when the brake pedal continues to be depressed and the brake reaction force exceeds the set load of the coil spring 40 of the reaction force transmission means 34, as shown in FIG. 2, the second retainer 43 and the valve plunger 17 are moved relative to the valve body. Since the vehicle is relatively advanced, the output of the brake booster 1 is
It rises at a servo ratio larger than the previous servo ratio (see FIG. 10).

By the way, the reaction disk 36
When an outer portion is compressed between the holder 37 and the output shaft 38 due to a brake reaction force, the inner portion swells and deforms into the holder 37 and comes into contact with the plate plunger 35. Thereby, a part of the brake reaction force acting on the reaction disk 36 is transmitted to the driver via the plate plunger 35, the valve plunger 17, and the input shaft 30. When the brake pedal is continuously depressed and the brake reaction force transmitted from the reaction disk 36 to the plate plunger 35 exceeds the set load of the coil spring 44 of the reaction force transmission means 34, the holder 37 and the output shaft 38, reaction disk 3 compressed between plate plunger 35
6 is a plate plunger 35 and a second retainer 43
Is retracted relatively to the valve body 6. However, in the brake booster provided with the above-described reaction force transmission means, in a region where the coil spring is not compressed, hysteresis can be obtained as in the related art,
It has been found that in the region where the coil spring expands and contracts, when the pedaling force is the same, the output at the time of release is smaller than the output at the time of depression, so that hysteresis cannot be obtained. That is, since the reaction disk has a relatively small amount of elastic deformation in a region where the coil spring is not compressed, the reaction disk can quickly return elastically when the compression is released from this state, but in a region where the coil spring is compressed. In this case, since the elastic deformation is relatively large, even if the compression is released from this state, it returns very slowly at first, and then returns promptly after the elastic deformation decreases. As a result, in the region where the coil spring expands and contracts, even if the brake pedal depressing force is loosened and the brake reaction force is reduced,
For a while, the brake reaction force is transmitted without being released while the coil spring is compressed, so that the output when released is smaller than the output when depressed. Therefore, in the brake booster provided with the reaction force transmission means, in the region where the coil spring expands and contracts, the output of the booster greatly decreases with respect to the reduction in the pedaling force of the brake pedal, so that the brake feeling is impaired. There were drawbacks.

In this embodiment, the reaction disk 36 is prevented from being compressed and deformed during compression in order to improve the brake feeling in the region where the coil spring 44 of the reaction force transmitting means 34 expands and contracts. And when the compression is released, it can be elastically restored without being hindered. That is, the reaction disk 36 is disposed on the rear side, and has a relatively low hardness first member 51 abutting on the holder 37 as the front end surface of the valve body 6 and the plate plunger 35; A second member 52 having a relatively high hardness is disposed on the front side and abuts against the base bottom of the output shaft 38. The front end surface of the first member 51 that contacts the rear end surface of the second member 52 has a stepped recess 51A that is gradually recessed rearward from the outer side toward the inner side. On the other hand, a stepped projection 52A is formed on the rear end face of the second member 52 so as to gradually project rearward from the outer side to the inner side.
The stepped projection 52A of the second member 52 is fitted into the stepped recess 51A of the first member 51 without any gap. As shown in FIG. 3 in an enlarged manner, in this embodiment, the step 51a of the stepped recess 51A of the first member 51 and the second member 5 are formed.
The stepped portion 52a of the second stepped projection 52A is formed in parallel with the center line O of the brake booster 1 (solid line in FIG. 3). Accordingly, when the brake pedal is depressed and compressed, each step 51a of the stepped recess 51A and the stepped protrusion 52
The step 52a of A will interfere with each other, but the two steps 51a and 52a will not interfere when released. Therefore, according to the reaction disk 36 having the above-described configuration, the brake pedal is depressed and the holder 37 is depressed.
When compressed by the output shaft 38, as shown by the imaginary line in FIG. 3, the stepped concave portion 51A of the first member 51 is elastically deformed radially inward by the stepped convex portion 52A of the second member 52. 4 is hindered, so that the output at the time of stepping on becomes relatively small as shown in FIG. On the other hand, when the depression force is released from the state where the brake pedal is depressed and the compression is released, the stepped projection 5 of the second member 52 is released.
Since 2A does not prevent the stepped concave portion 51A of the first member 51 from elastically returning outward in the radial direction, the output at the time of release is relatively large as shown in FIG. As can be understood from the above results, the output at the time of release is larger than at the time of stepping on, and the hysteresis can be obtained, so that it is compared with the conventional brake booster having the reaction force transmission means. The brake feeling in the region where the spring expands and contracts can be improved. In this embodiment, the step 51a of the first member 51 and the step 5 of the second member 52
2a is formed so as to be parallel to the center line O, but the present invention is not limited to this, and it may be formed so as to be inclined to the left with respect to the center line O.

Next, FIG. 5 shows a second embodiment of the present invention.
6 is composed of the first member 51 and the second member 52,
In the second embodiment, a thin resin plate 160 having a higher hardness than the reaction disk 136 is embedded in the reaction disk 136. As shown in FIG. 6, the resin plate 160 has a central portion and a slit 161 extending radially outward from the central portion.
One side of the reaction disk 136 located on the rear side of the resin plate 160 and the other side located on the front side are connected via the slit 161. Accordingly, when the outer peripheral portion of the reaction disk 136 is compressed, the elastic deformation of the outer portion is transmitted to the inner portion through the portion communicating from between the slits 161. Similarly, the inner side portion swells and deforms into the holder 137. The configuration other than that described above is the same as that of the first embodiment, and the same members as those of the first embodiment are denoted by reference numerals obtained by adding “100”. According to the above-described configuration, when the reaction pedal 138 is compressed by depressing the brake pedal, the inner side portion of the reaction disk 136 swells and deforms into the holder 137 as shown in FIG. However, at this time, since the compression deformation of the reaction disk 136 is impeded by the elastic deformation of the resin plate 160, the output when the brake pedal is depressed becomes relatively small as in the first embodiment. On the other hand, when the depression force is released from the state where the brake pedal is depressed and the compression force between the holder 137 and the output shaft 138 is released, the resin plate 1 is moved from the state shown in FIG.
Since the wheel 60 returns by its own elasticity, the elastic recovery of the reaction disk 136 is not hindered, so that the output when the brake pedal is released becomes relatively large as in the first embodiment. As can be understood from the above results, in the second embodiment as well, as in the first embodiment, it is possible to obtain a hysteresis by increasing the output at the time of release from that at the time of stepping on, and to obtain the hysteresis. Brake feeling in a region where the spring expands and contracts can be improved as compared with a brake booster including the reaction force transmitting means.

FIG. 8 shows a third embodiment of the present invention. In the first and second embodiments, the reaction disks 36 and 136 themselves are improved. In the embodiment, the reaction disk 236 is the same as the conventional one, and the holder
7 is provided with a plurality of annular projections 270 protruding on the front side around the shaft part on the front end surface of the front side. As shown in an enlarged manner in FIG.
Has an outer peripheral surface 270a formed in parallel with a center line (not shown) of the brake booster, and an inner peripheral surface 270b formed by inclining rightward and downward with respect to the center line.
The distal end portions of the outer peripheral surface 270a and the inner peripheral surface 270b are brought into contact with the rear end surface of the reaction disk 236. The configuration other than the above-described holder 237 and the reaction disk 236 is the same as that of the first embodiment, and the same members as those of the first embodiment are denoted by reference numerals obtained by adding “200”. According to the above-described configuration, when the reaction disk 236 is compressed by depressing the brake pedal, the outer peripheral portion 270a of each annular projection 270 causes the outer side portion of the reaction disk 236 to bulge radially inward. Since the deformation is hindered, the output when the brake pedal is depressed becomes relatively small as in the first embodiment. On the other hand, when the depression force is released from the state in which the brake pedal is depressed and the compression is released, the inner peripheral surface 270b of each annular projection 270 has the outer portion of the reaction disc 236 radially outward. Since the elastic return is not prevented, the output when the brake pedal is released becomes relatively large as in the first embodiment. As can be understood from the above results, in the third embodiment as well, as in the first embodiment, it is possible to obtain a hysteresis by increasing the output at the time of release compared to the time of stepping on, and obtain the hysteresis. Brake feeling in a region where the spring expands and contracts can be improved as compared with a brake booster including the reaction force transmitting means.

In the third embodiment, the outer peripheral surface 270a is formed parallel to the center line. However, the present invention is not limited to this. It may be formed so as to be inclined downward.

[0016]

As described above, according to the present invention, in the region where the coil spring of the reaction force transmitting means is compressed, the output when the brake pedal is released is greater than when the brake pedal is depressed, so that hysteresis can be obtained. Therefore, an effect is obtained that the brake feeling in a region where the coil spring expands and contracts can be improved as compared with a conventional brake booster including a reaction force transmitting means.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing an essential part of FIG. 1 during operation.

FIG. 3 is an enlarged sectional view showing a step portion 51a of a first member 51 and a step portion 52a of a second member 52.

FIG. 4 is a characteristic diagram of the brake booster 1 of the present invention.

FIG. 5 is an enlarged sectional view of a main part showing a second embodiment of the present invention.

FIG. 6 is a front view of a resin plate 160.

FIG. 7 is an enlarged cross-sectional view of a main part showing a state when the reaction disk 136 is compressed.

FIG. 8 is an enlarged sectional view of a main part showing a third embodiment of the present invention.

FIG. 9 is an enlarged sectional view of an annular projection 270.

FIG. 10 is a characteristic diagram of a conventional brake booster including a reaction force transmitting unit.

[Explanation of symbols]

 6, 106, 206 ... valve body 15, 115, 215 ... valve mechanism 17, 117, 217 ... valve plunger 30, 130, 230 ... input shaft 34, 134, 234 ... reaction force transmitting means 35, 135, 235 ... plate plunger 36 Reference numerals 136, 236: Reaction disks 37, 137, 237: Holders 38, 138, 238: Output shafts 44, 144, 244: Coil springs 51: First member 52: Second member 51a: Step 52b: Step 160 Resin plate 270: annular protrusion 270a: outer peripheral surface 270b: inner peripheral surface

Claims (6)

[Claims] 1. A valve body slidably provided in a shell, a valve mechanism provided in the valve body, and an input shaft for switching a flow path of the valve mechanism by moving a valve plunger constituting the valve mechanism forward and backward. An output shaft slidably provided on the valve body, a reaction disk interposed between the output shaft and the valve body, and a brake countermeasure interposed between the reaction disk and the valve plunger and from the reaction disk. In a brake booster provided with a reaction force transmitting means for transmitting a force to a valve plunger, when the reaction disk is compressed, its own compression deformation is inhibited, and when the compression is released, A brake booster configured to be able to return elastically without being hindered. 2. The reaction disk according to claim 1, wherein the reaction disk is disposed at a rear side and has a relatively low hardness at least in contact with a valve body and a reaction force transmitting means. A second member having a relatively high hardness that is in contact with the first member, and a stepped concave portion that is gradually recessed rearward from the outer side toward the inner side at the front end surface of the first member. Forming a stepped projection on the rear end face of the second member from the outside to the inside in a stepwise manner toward the rear side, and fitted into the stepped recess of the first member. The stepped projection of the second member prevents the stepped recess of the first member from elastically deforming inward in the radial direction when the reaction disc is compressed, and when the compression is released, Do not prevent the stepped recess of the first member from elastically returning radially outward. It has Tsu brake booster according to claim 1, wherein the. 3. A plate member having elasticity is embedded in the reaction disk, and when the reaction disk is compressed, the plate member is elastically deformed toward the rear side in the axial direction to reduce the compression deformation of the reaction disk. 2. The brake booster according to claim 1, wherein when the compression is released, the reaction booster returns by its own elasticity and does not hinder the elastic recovery of the reaction disk. 4. A valve body slidably provided in a shell, a valve mechanism provided in the valve body, and an input shaft for moving a valve plunger constituting the valve mechanism forward and backward to switch a flow path of the valve mechanism. An output shaft slidably provided on the valve body, a reaction disk interposed between the output shaft and the valve body, and a brake disk interposed between the reaction disk and the valve plunger to prevent a reaction from the reaction disk. A brake booster having a reaction force transmitting means for transmitting a force to a valve plunger, wherein the end surface of the valve body contacting the rear end surface of the reaction disk is elastically deformed when the reaction disk is compressed. In order to prevent deformation, when the compression is released, the reaction Brake booster, characterized by being configured so as not to interfere with the elastic return of the disc. 5. A front end of the valve body,
A plurality of annular projections are provided around the shaft portion and protruding toward the front side, and each of the annular projections has an outer peripheral surface facing radially outward and an inner peripheral surface facing radially inward. , And at least one of the inner peripheral surfaces thereof is formed so as to be tapered with respect to the center line of the booster, and the inclination angle of the inner peripheral surface with respect to the center line of the booster is set with respect to the center line of the outer peripheral surface. The annular projection having the outer peripheral surface and the inner peripheral surface is formed so as to be larger than the inclination angle, and when the reaction disk is compressed, the outer portion of the reaction disk expands and deforms radially inward. 5. The method according to claim 4, wherein when the compression is released, the bulging-out deformed outer portion does not prevent the outer portion from elastically returning radially outward. 4. The brake booster according to 4. 6. The brake booster according to claim 1, wherein a plate plunger is provided between the reaction disk and the reaction force transmitting means.