JPH11255106A - Reaction force mechanism of booster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent any obstruction of a brake pedal feeling by alleviating impact of a reaction force piston in abutting to a valve plunger by a cushioning member. SOLUTION: A reaction force mechanism of a booster is constructed not to transmit a reaction force acting on an output shaft 35 to a valve plunger 19 at the operation of the booster, but to apply a pseudo-reaction force by a pseudo-reaction force applying means 37 instead. The pseudo-reaction force applying means 37 is constructed of a reaction force piston 38 slidably provided in a valve body 3, a first constant pressure chamber 39 formed at the rear side of the reaction force piston and introducing the pressure of a constant pressure chamber (A), a second constant pressure chamber 40 formed at the front side of the reaction force piston and introducing the pressure of the variable pressure chamber (B), a cushioning member 46 provided on the front side end surface of the valve plunger 19 and absorbing the impact resulting from the abutting of the reaction force piston.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a booster used for a brake or the like of an automobile, and more particularly to a reaction mechanism of the booster.

[0002]

2. Description of the Related Art Conventionally, a brake booster generally includes a valve body slidably provided in a shell, a power piston provided in the valve body, a constant pressure chamber and a variable pressure chamber formed before and after the power piston. A valve mechanism provided in the valve body for switching and controlling a flow path, a valve plunger slidably provided in the valve body to constitute a part of the valve mechanism, and a valve for moving the valve plunger forward and backward. An input shaft for switching the flow path of the mechanism and an output shaft which is advanced by the advance of the power piston are provided. The conventional general reaction mechanism has a rubber reaction disk disposed between the output shaft and the valve plunger.When the brake booster operates, the valve body and the valve plunger come into contact with the reaction disk simultaneously. A part of the brake reaction force applied to the output shaft is received by the valve body, and the remainder is transmitted to the valve plunger so that the driver can sense the brake reaction force applied to the valve plunger via the input shaft and the brake pedal. ing. At this time, the servo ratio of the brake booster can be changed by changing the ratio between the reaction force received by the valve body and the reaction force received by the valve plunger, more specifically, by changing the ratio of the pressure receiving areas of both. .

[0003]

The servo ratio of the conventional brake booster is generally set to a large value so that a large brake fluid pressure can be generated with a small brake pedal depression force. The expected large output was not obtained due to the operation delay of the booster, and it was found that it was difficult for a weak driver such as an elderly person or a woman to perform sudden braking. That is, when the brake pedal is depressed, the flow path of the valve mechanism is switched via the input shaft, whereby pressure fluid is introduced into the variable pressure chamber, and the power piston and the valve body are advanced. When the valve body advances, the output shaft advances through the reaction disk. When the output shaft advances, a brake fluid pressure is generated and the reaction force is applied to the output shaft. As described above, the brake reaction force applied to the output shaft is increased. Is distributed to the valve body and the valve plunger. However, at the time of sudden braking, before the power piston and the valve body are advanced by the pressure fluid introduced into the variable pressure chamber,
Since the valve plunger interlocked with the brake pedal via the input shaft is advanced, most of the brake reaction force applied to the output shaft is transmitted to the valve plunger,
As a result, the brake reaction force transmitted to the driver becomes abnormally large. As a result, when performing sudden braking, the brake pedal must be depressed by overcoming the abnormally large brake reaction force, and in the case of normal brake operation in which the brake pedal is gradually depressed and a large braking force is obtained. In comparison, the brake force required for sudden braking could not be obtained unless the brake pedal was depressed with a much larger force. The present invention has been made in view of such circumstances, and provides a reaction force mechanism of a booster in which a large output can be obtained with a light pedaling force even at the time of sudden braking.

[0004]

That is, the present invention provides the above-described booster in which the reaction force applied to the output shaft when the booster is operated is not transmitted to the valve plunger. And a buffer member provided between the reaction force piston and the valve plunger so as to be slidable, and urged by a pressure difference between the variable pressure chamber and the constant pressure chamber acting on the reaction force piston. A pseudo reaction force applying means for transmitting the urging force as a pseudo reaction force to the valve plunger via the buffer member.

[0005]

According to the above construction, the reaction force applied to the output shaft during operation of the booster is prevented from being transmitted to the valve plunger. Even if the valve plunger interlocked via the input shaft is largely advanced before the valve body is advanced, the reaction force applied to the output shaft is not transmitted to the driver via the valve plunger and the input shaft. Absent. On the other hand, the pseudo reaction force applying means includes a reaction force piston in which a pressure difference between the second constant pressure chamber into which the pressure of the constant pressure chamber is introduced and the second variable pressure chamber into which the pressure of the variable pressure chamber is introduced acts. During normal depression, a pseudo reaction force corresponding to the pressure difference can be transmitted to the valve plunger. At the time of sudden braking, since the pressure in the variable pressure chamber does not increase at that moment due to the operation delay of the booster, the pressure in the second variable pressure chamber does not increase, and therefore a large differential pressure is not applied to the reaction force piston. The valve plunger can be advanced greatly by force, and a large output can be obtained with a small operating force. Further, since the reaction force piston abuts on the valve plunger via the buffer member, the input shaft is pushed back at the moment the reaction force piston abuts on the valve plunger as in the case where the buffer member is omitted. Such an impact does not occur, and the operation feeling can be improved.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an illustrated embodiment. A valve body 3 is slidably provided in a front shell 1 and a rear shell 2. Valve body 3 of the present embodiment
Comprises an input member 4 slidably provided in the cylindrical portion 2A of the rear shell 2 and an output member 5 fitted to the front end of the input member 4 so as to be relatively displaceable. I have.
The input side member 4 is fitted and fixed to a cylindrical member 6 slidably penetrating into a cylindrical portion 2A of the rear shell 2 and to an outer peripheral surface of a front end portion of the cylindrical member 6. It comprises an outer member 7 having a substantially U-shaped cross section with an open side end, and a cylindrical inner member 8 fitted and fixed to the inner peripheral surface of the front end of the cylindrical member 6. On the other hand, the output-side member 5 is disposed on the rear side, and has a substantially U-shaped cross-section.
And a bottomed cylindrical front side member 11 whose rear side is open. And
The rear side member 10 of the output side member 5 is slidably fitted to the outer side member 7 of the input side member 4 from the front side where the output side member 5 is opened.
And a stopper 12 attached to the rear member 10. A spring 13 is mounted between the rear member 10 and the outer member 7, and the output member 5 and the input member 4 are
Are urged in a direction away from each other in the axial direction. A power piston 1 is provided on an outer peripheral portion of the output side member 5.
4 and a diaphragm 15 attached to the rear side of the power piston 14. The inside of the sealed container is partitioned into a constant pressure chamber A on the front side and a variable pressure chamber B on the rear side by the diaphragm 15.

Next, the valve mechanism 17 for switching the fluid circuit between the constant pressure chamber A and the variable pressure chamber B will be described. The valve mechanism 17 has an annular first valve seat 18 formed on the cylindrical member 6 of the input side member 4 and an annular first valve seat 18 formed on the right end of a valve plunger 19 slidably fitted in the cylindrical member 6. 1 and a valve element 22 which is seated on both of the valve seats 18 and 20 from the right side in FIG. 1 by a poppet return spring 21. A constant pressure chamber A is provided on the outer peripheral side of the first valve seat 18 via a shaft portion of the cylindrical member 6 and a constant pressure passage 23 formed between the outer member 7 and the inner member 8.
The constant pressure chamber A is connected to an intake manifold of an engine (not shown) through a negative pressure introducing pipe 24 connected to the front shell 1 to constantly introduce a negative pressure. Further, an intermediate portion between the first valve seat 18 and the second valve seat 20 is communicated with the variable pressure chamber B via a radial variable pressure passage 25 formed in the cylindrical member 6. Further, an inner peripheral side of the second valve seat 20 is communicated with the atmosphere through a pressure passage 26 formed in the input side member 4.

An input shaft 30 is provided at the right end of a valve plunger 19 slidably provided in the input member 4 of the valve body 3.
A spring 31 having an elastic force greater than the elastic force of the poppet return spring 21 is elastically mounted between the input shaft 30 and the input side member 4 of the valve body 3. When the brake pedal is not depressed by the resilience of the spring 31, the valve body 22 is seated on the second valve seat 20 of the valve plunger 19 when the brake pedal is not depressed. 1st valve seat 1
8 away from you. The distal end of the input shaft 30 is linked to a brake pedal (not shown) as an operating rod. Further, the valve plunger 19 is prevented from being pulled out of the cylindrical member 6 of the input side member 4 of the valve body 3 by the key member 32. The key member 32
Although not shown, the key member 32 is formed in a bifurcated shape from the center portion to the distal end portion thereof, and the key member 32 is inserted into an insertion hole 33 formed in the diameter direction of the cylindrical member 6 of the input side member 4,
The base of the bifurcated portion is connected to the small diameter portion 19 of the valve plunger
a. At this time, the insertion hole 33 and the variable pressure passage 25 are integrally formed adjacent to each other in the axial direction of the input member 4, but are orthogonal to the width of the insertion hole 33, that is, orthogonal to the axial direction of the input member 4, The width of the key member 32 in the direction perpendicular to the direction of insertion into the insertion hole 33 is set to be wider than the width of the variable pressure passage 25 in the same direction. The member 4 can be displaced in the axial direction. Further, the key member 32 and the valve plunger 19 can be displaced in the axial direction with respect to the key member 32 within the range of the axial length of the small-diameter portion 19a, thereby disabling the brake booster. Sometimes rear shell 2
The input-side member 4 and the valve plunger 19 abut against the key member 32 abutting on the inner surface thereof, and are stopped. In this state, the valve plunger 19 is held at a position relatively advanced with respect to the valve body 3, so that the loss stroke of the input shaft 30 at the start of operation of the brake booster can be reduced. I have. When the brake booster is not operating, the rear member 10 of the output member 5 is moved by the return spring 34 elastically mounted between the inner surface of the front shell 1 and the front member 11 of the output member 5. It is retracted against the elastic force of the spring 13 and held at the non-operating position shown in the state in which it comes into contact with the outer member 7 of the input-side member 4.

Next, the tip of the output shaft 35 of this embodiment is
It protrudes outside from the shaft portion of the front shell 1 and is linked to a piston of a master cylinder (not shown). On the other hand, the base 35A of the output shaft 35 is fitted into a recess 11A formed in the front side member 11 of the output side member 5 and is integrally connected to the output side member 5. Thus, in this embodiment, when the brake booster is operated, all the brake reaction force acting on the output shaft 35 via the master cylinder is received by the output side member 5 of the valve body 3 and the input side member 4 and It is not transmitted to the valve plunger 19. By the way, if the brake reaction force is configured not to be transmitted to the valve plunger 19,
The driver cannot get the brake operation feeling. For this reason, in this embodiment, the provision of the pseudo reaction force applying means 37 applies the pseudo reaction force to the driver according to the amount of depression of the brake pedal. That is, the pseudo-reaction-force applying means 37 is configured to output the front-side member 1 of the output-side member 5.
1, a reaction force piston 38 is slidably fitted in the first member 11, and a second constant pressure chamber 39 is provided on the rear side of the front side member 11 by the reaction force piston 38, and a second constant pressure chamber 39 is provided on the front side of the front side member 11. The two variable pressure chambers 40 are formed separately. A ring-shaped seal member 41 is provided on an outer peripheral portion of the reaction force piston 38, and the seal member 41 maintains airtightness between an outer peripheral surface of the reaction force piston 38 and an inner peripheral surface of the front-side member 11. . The second constant pressure chamber 39 communicates with the constant pressure chamber A via a communication hole 41 formed at the front end of the front member 11 on the rear side, and also communicates with the constant pressure passage 23. On the other hand, the second transformer chamber 40 is
The passage 42A formed in the shaft of the protruding portion 38A protruding rearward from the shaft of the reaction force piston 38, the inner peripheral surface of the inner member 8 of the input side member 4, and the large diameter portion 19b of the valve plunger 19 The second variable pressure chamber 40 is communicated with the variable pressure passage 25 via a reaction force passage 43 composed of a passage 42B formed between the reaction force passage 43 and the partially cut-out portion. It is communicated with the variable pressure chamber B via the variable pressure passage 25 and also with the constant pressure chamber A via the reaction force passage 43 and the constant pressure passage 23. The flow passage area of the passage 42A of the reaction force piston 38 constituting the reaction force passage 43 is:
Passage 42 composed of inner member 8 and valve plunger 19
B and the passage area of the variable pressure passage 25 are set smaller than the passage area, and the passage 42A substantially corresponds to an orifice passage. Projection 38 of the reaction force piston 38
A is slidably fitted inside the inner member 8 of the input side member 4 while maintaining airtightness. The large-diameter portion 19b of the valve plunger 19 fitted into the inner member 8 from the front side. It is facing. A spring 44 is elastically mounted between the reaction force piston 38 and the inner member 8 of the input member 4, and the spring 44 causes the reaction force piston 38 to be connected to the output member 5 when the brake booster is not operated. It is brought into contact with the front side member 11 and held at the forward end position. In this state, the projecting portion 38A of the reaction force piston 38 and the large-diameter portion 1 of the valve plunger 19
9b is formed with a gap. A passage 42A formed in the shaft of the protruding portion 38A of the reaction piston 38
Is opened in a radial groove 45 formed in the rear end face of the projection 38A, so that when the projection 38A comes into contact with the large diameter portion 19b of the valve plunger 19, the passage is formed through the groove 45. 42A and the passage 42B are communicated with each other. By the way, the reaction force piston 38 is separated from the valve plunger 19 by the resilient force of the spring 44 when it is not operated. Therefore, the impact at the moment when the reaction force piston 38 retreats and comes into contact with the valve plunger 19 from this separated state This may give the driver a feeling that the brake pedal is pushed back momentarily. Therefore, in this embodiment, a thin disk-shaped buffer member 46 made of an elastic material is provided on the front end surface of the large diameter portion 19b of the valve plunger 19. The buffer member 46 is partially cut off at the same position as the large diameter portion 19b of the valve plunger 19 so as not to close the reaction passage 43. The cushioning member 4
6 is not limited to an elastic material, but may be a disc spring or a coil spring.

In the present embodiment, a reaction force passage 43 is formed in the outer peripheral portion of the large diameter portion 19b of the valve plunger 19 so that a large braking force can be obtained with a smaller pressing force at the time of sudden braking than at the time of normal depression. A sealing member 48 is provided as closing means for closing. The input side member 4 which forms the reaction force passage 43 at the time of non-operation or normal operation is provided.
Is located in a large-diameter portion 49 (see FIG. 2) formed by cutting out the inner peripheral surface of the inner member 8 of this embodiment, and in this state, the pressure is changed through the space between the seal member 48 and the large-diameter portion 49. Passage 2
5 and the second transformer chamber 40 are communicated with each other.
On the other hand, when the valve plunger 19 advances by a predetermined amount or more with respect to the input-side member 4, the seal member 48 escapes from the large-diameter portion 49 and has a small-diameter portion 50 formed on the front side. In this state, the seal member 48 comes into close contact with the small diameter portion 50 to seal this portion. As can be understood from this, when the brake pedal is suddenly depressed, the valve plunger 19 is greatly advanced with respect to the input side member 4 as shown in FIG. The communication between the passage 25 and the second variable pressure chamber 40 is interrupted. Further, even when the brake booster is gradually depressed and the brake booster is fully loaded, as shown in FIG.
9 is advanced greatly with respect to the input-side member 4, and the variable pressure passage 25 and the second
The communication of 0 is interrupted.

In the above configuration, when the brake pedal is depressed relatively slowly from the above-mentioned non-operating state, the first valve seat 18 formed on the input side member 4
2 is seated to cut off the communication between the constant pressure passage 23 and the variable pressure passage 25 which have been connected so far, and the valve plunger 19.
The valve body 22 is spaced apart from the second valve seat 20 formed in the first valve seat 20 to connect the variable pressure passage 25 and the pressure passage 26 to each other. As a result, the atmosphere is introduced into the variable pressure chamber B via the variable pressure passage 25, so that a pressure difference occurs between the constant pressure chamber A and the variable pressure chamber B, and the pressure difference causes the output side member 5 of the valve body 3 and the power piston 1 to move.
4 will be advanced. On the other hand, the input side member 4
Is smaller than the amount of advance of the output-side member 5 and the power piston 14. That is,
Negative pressure acts on a portion of the input-side member 4 located in the transformation chamber B, and atmospheric pressure acts on a portion protruding outside the transformation chamber B. Immediately after the valve mechanism 17 is switched, a differential pressure greater than the set load of the springs 13A and 13B acts on the input member 4 so that the input member 4 comes into contact with the output member 5 and However, the differential pressure decreases as the negative pressure in the variable pressure chamber B decreases, and when the differential pressure falls below the set load of the springs 13A and 13B, the input-side member 4 becomes the output-side member 5 It gradually becomes separated from. As can be understood from this, in the present embodiment, the advance amount of the input side member 4 containing the valve mechanism 17 is set smaller than the advance amount of the output side member 5.
Since the stroke of the input shaft 30 and the brake pedal interlocked with the input shaft 30 which are advanced with the advance of the input side member 4 can be relatively reduced, the output side member 5 and the input side member 4 are fixed to output. Brake feeling can be improved as compared with the case where the amount of advance of the side member 5 and the input side member 4 is the same. Also, the reaction force piston 38
Since the atmosphere is introduced into the second variable pressure chamber 40 formed on the front side of the second variable pressure chamber 40 through the reaction force passage 43, a differential pressure is generated between the second variable pressure chamber 40 and the second constant pressure chamber 39, and the differential pressure The reaction force piston 38 is biased rearward. As a result, the reaction force piston 38 compresses the spring 44 and retreats, and the protruding portion 38A abuts against the end face of the large-diameter portion 19b of the valve plunger 19 which opposes. Since it is transmitted to the brake pedal via the input shaft 19 and the input shaft 30, the driver can sense the operation feeling of the brake. The shock when the reaction force piston 38 comes into contact with the large diameter portion 19b of the valve plunger 19 is effectively absorbed by the buffer member 46, so that the shock transmitted to the valve plunger 19 can be reduced. As a result, it is possible to prevent the operation feeling from being hindered. The input side member 4
Can be adjusted by the set load of the spring 13 and the spring constant.

Next, the operation when the brake pedal is depressed slightly faster than the above-mentioned gentle operation will be described. In such an operation, the valve plunger 19 interlocked with the brake pedal via the input shaft 30 is normally used. Of the input side member 4 as compared with the time of stepping on. As a result, the valve element 22 is separated from the second valve seat 20 formed on the valve plunger 19 more greatly than when the valve element 22 is gently operated, so that a large amount of air is introduced into the variable pressure chamber B through the variable pressure passage 25, As a result, the output side member 5 of the valve body 3 and the power piston 14 advance relatively quickly. On the other hand, only the same amount of air is introduced into the second variable pressure chamber 40 on the front side of the reaction force piston 38 through the reaction force passage 43 as in the gentle operation.
The reaction force rises with a delay with respect to the increase in output.
In other words, the speed at which the reaction force piston 38 retreats is the second
Even if the opening amounts of the valve seat 20 and the valve body 22 are large, there is not much change. Therefore, even when the brake pedal is operated relatively quickly, the reaction piston 38 comes into contact with the valve plunger 19. The magnitude of the impact at that time hardly increases, so that the operation feeling is not hindered. Accordingly, the reaction force applied to the brake pedal by the fluid pressure reaction force mechanism 37 can operate the brake booster with a relatively small force when the operation speed of the brake pedal is high as compared with a gradual operation. .

Next, the operation when the brake pedal is suddenly operated will be described. In such a sudden operation, the valve plunger 19 interlocking with the brake pedal via the input shaft 30 advances at a stroke to the forward end position with respect to the input side member 4. As a result, the valve element 22 is largely separated from the second valve seat 20 formed in the valve plunger 19, so that a large amount of air is introduced into the variable pressure chamber B via the variable pressure passage 25. As a result, the differential pressure acting on the output side member 5 and the power piston 14 sharply increases, and the output side member 5 and the power piston 14 are rapidly advanced to perform rapid braking. In the second variable pressure chamber 40 on the front side of the reaction force piston 38, the reaction force passage 4
3. More specifically, the atmosphere has been introduced through the space between the seal member 48 and the large diameter portion 49. In such a rapid operation, the seal member 48 is switched immediately after the valve mechanism 17 is switched.
Is in close contact with the small diameter portion 50 beyond the large diameter portion 49 and the reaction force passage 4
Since the valve 3 is closed, the reaction force piston 38 is urged rearward by a slight differential pressure and seats on the valve plunger 19. As a result, a small reaction force is transmitted to the brake pedal by the fluid pressure reaction mechanism 37 during a rapid operation in which the valve plunger 19 is advanced to the forward end position with respect to the valve body 3. During a sudden operation, the brake booster can be suddenly operated with a lighter pedaling force than during a normal operation.

By the way, even when the brake pedal is gently depressed and fully loaded, the sealing member 48 is in close contact with the small diameter portion 50 of the inner member 8 so that the reaction force passage 43 is formed.
Is closed (see FIG. 3). That is, in the present embodiment, as described above, the advance amount of the input side member 4 is relatively smaller than the advance amount of the output side member 5, so that the brake booster shifts from the full load state to the brake state. When an attempt is made to obtain a larger braking force by depressing the pedal, the output and reaction force do not increase even if the brake pedal is depressed until the input side member 4 comes into contact with the output side member 5 that is moving forward. Sections occur. However, when the brake booster is in a full load state, the sealing member 48 closes the reaction force passage 43 and seals the second transformer chamber 40 as described above.
The input side member 4 depends on the atmosphere introduced into the transformation chamber 40.
And the output side member 5 can be integrally advanced, so that the operation feeling can be prevented from being hindered.

In the above embodiment, the input side member 4 and the output side member 5 constituting the valve body 3 are slidably provided. However, the present invention is not limited to this. Of course, the present invention can be applied to a normal booster in which the member 5 is integrated. In the above-described embodiment, the seal member 48 is provided to reduce the reaction force at the time of sudden operation. However, the present invention is not limited to this, and may be omitted as appropriate.

[0016]

As described above, according to the present invention, the pseudo reaction force according to the treading force is transmitted by the pseudo reaction force applying means at the time of normal depression, and the reaction force by the pseudo reaction force applying means is not transmitted at the time of sudden braking. Therefore, an effect that a large braking force can be obtained with a light pedaling force is obtained. Furthermore, since the reaction force piston comes into contact with the valve plunger via the buffer member, as in the case where the buffer member is omitted, an impact such that the input shaft is pushed back at the moment when the reaction force piston comes into contact with the valve plunger. This does not occur, thereby providing an effect that the operation feeling can be improved.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view of a main part showing a state at the time of sudden braking.

FIG. 3 is an enlarged sectional view showing a full load state of the brake booster.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 3 ... Valve body 4 ... Input side member 5 ... Output side member 6 ... Cylindrical member 7 ... Outer member 8 ... Inner member 10 ... Rear side member 11 ... Front side member 17 ... Valve mechanism 25 ... Variable pressure passage 30 ... Input shaft 35 ... Output shaft 37 ... Pseudo reaction force applying means 38 ... Reaction force piston 39 ... Second constant pressure chamber 40 ... Second variable pressure chamber 42A ... Pathway (orifice path) 43 ... Reaction force path 46 ... Buffer member 48 ... Seal member A ... Constant pressure chamber B… Transformer room

Continuation of the front page (72) Inventor Yuzo Imoto 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation

Claims (4)

[Claims] 1. A valve body slidably provided in a shell, a power piston provided on the valve body, a constant pressure chamber and a variable pressure chamber formed before and after the power piston.
A valve mechanism provided in the valve body for switching and controlling a flow path, a valve plunger slidably provided in the valve body to constitute a part of the valve mechanism, and a valve for moving the valve plunger forward and backward. In a booster including an input shaft for switching a flow path of a mechanism and an output shaft advanced by the advance of the power piston, a reaction force applied to the output shaft when the booster is operated is applied to a valve plunger. While being configured not to be transmitted, a reaction force piston slidably provided on the valve body and a buffer member provided between the reaction force piston and the valve plunger,
A pseudo reaction force applying means for transmitting an urging force urged by a pressure difference between the variable pressure chamber and the constant pressure chamber acting on the reaction piston to the valve plunger via the buffer member as a pseudo reaction force is provided. Characteristic reaction mechanism of booster. 2. The quasi-reaction applying means, when the valve plunger advances by a predetermined amount or more with respect to the valve body,
The reaction mechanism of the booster according to claim 1, further comprising a closing means for closing a flow of the fluid in the variable pressure chamber acting on the reaction force piston. 3. The booster according to claim 1, wherein the pseudo reaction force applying means has an orifice for restricting a flow of a fluid in the variable pressure chamber acting on the reaction force piston. Reaction force mechanism. 4. The booster according to claim 1, wherein said reaction force piston is slidably fitted to said valve body, and a seal member is provided on an outer peripheral portion of said reaction force piston. The reaction mechanism of the device.