JPH0437020Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a reaction force transmission mechanism for a brake booster, and more specifically, the invention relates to a reaction force transmission mechanism for a brake booster. The present invention relates to a reaction force transmission mechanism of a brake booster that transmits force.

[Prior art] Generally, brake boosters (for example, November 1982)
26th, page 2-22 of “New Automotive Engineering Handbook (Part 5)” published by the Society of Automotive Engineers of Japan
(shown in Fig. 86), the input and output in the intermediate load state have a proportional relationship called the servo ratio. Conventionally, it is known that there is a slight difference in output due to hysteresis when the input is set to a predetermined value when the brake is applied and when the input is set to the same predetermined value when the brake is released. Even if there is a difference in the output during operation, it is small, and moreover, from the proportional relationship of the servo ratio mentioned above, both are essentially the same, and the servo ratio can be changed freely between when the brake is applied and when the brake is released. could not be changed.

[Problem to be solved by the invention] However, from the perspective of the brake feeling, especially when the brake pedal is depressed and then stopped at an intermediate load state, the output increases in a proportional relationship, and when the pedal is stopped being depressed. At the servo balance point, it is desirable that the output increases further than the output obtained by the proportional relationship. Such an automatic brake pedal depression effect gives the driver the impression that the brakes are working well, thereby providing a good brake feeling that gives the driver a sense of security.

In consideration of such circumstances, the present invention has been developed to further increase the output in intermediate load conditions than would be obtained with a normal proportional relationship, thereby providing a good brake feeling that gives the driver a sense of security. It is something.

[Means for Solving the Problems] In other words, the present invention consists of a power piston that is slidably disposed within a shell, a valve body that is provided on the shaft of the power piston, and a constant pressure that is formed on the front side of the power piston. a variable pressure chamber formed on the rear side of the power piston, a valve plunger slidably fitted in the valve body, an annular first valve seat formed in the valve body, and a variable pressure chamber formed in the valve plunger. an annular second valve seat located inside the first valve seat; a valve body urged toward the first valve seat and the second valve seat by a spring and seated on the valve seats; an input shaft that is loosely fitted through the shaft portion of the valve body so as to be freely retractable and interlocked with the valve plunger; a constant pressure passage that communicates the space on the outer peripheral side of the first valve seat with the constant pressure chamber; A variable pressure passage that communicates the space between the valve seat and the second valve seat with the variable pressure chamber, and an inner circumferential surface of the valve body and the outer peripheral surface of the input shaft through which the valve body is loosely fitted. a pressure passage formed and communicating with a space on the inner peripheral side of the second valve seat; an output shaft having a base slidably fitted in the valve body and facing the valve plunger; and a base of the output shaft. and a reaction disk interposed between the valve plunger and the brake booster, the brake booster is configured to transmit the reaction force of the output applied to the output shaft to the input shaft via the reaction disk and the valve plunger. , the valve body and the second part of the valve plunger on which it is seated.
At least one of the valve seats is made of an elastic body, and the variable pressure passage and the pressure passage are communicated with each other, and when the valve body is pressed against the second valve seat, the elastic body is elastically deformed. The valve plunger forms an orifice passage in which the passage is blocked, and is capable of moving forward and backward with respect to the valve body between the reaction disk and the valve plunger, and comes into contact with the valve body at a predetermined retreat position to restrict its retreat. A reaction force transmission member is provided, and when the input shaft moves forward relative to the valve body,
The valve body is seated on the first valve seat to cut off communication between the constant pressure passage and the variable pressure passage, and from the state where the valve body is pressed against the second valve seat, the orifice passage is connected to the variable pressure passage and the pressure passage. Before starting communication between the valve plunger and the reaction force transmission member, the reaction force is transmitted from the reaction disk to the input shaft via the valve plunger and the reaction force transmission member, and the input shaft When the valve body is retracted from the valve body, the valve body seats on the first valve seat to cut off communication between the constant pressure passage and the variable pressure passage, and the valve body contacts the second valve seat so that only the orifice passage is operated. The reaction force transmitting member and the valve plunger are disengaged from each other before the orifice passage is closed and the communication between the variable pressure passage and the pressure passage is interrupted. The reaction force is transmitted from the reaction disk to the input shaft via the valve plunger without passing through the reaction force transmission member.

[Operation] According to the above configuration, when the input shaft is moved forward by depressing the brake pedal from a non-operating state, that is, when the input shaft moves forward relative to the valve body, the valve body is seated on the first valve seat. The first valve seat is sealed, and the valve body is separated from the second valve seat to open the second valve seat and open the orifice passage. Since the valve plunger and the reaction force transmitting member are interlocked with each other before this state is reached, that is, before the orifice passage starts to open, the reaction force applied to the output shaft cannot be transmitted from the reaction disk to the valve plunger alone. Instead, the force is transmitted to the input shaft via the reaction force transmission member, and therefore the servo ratio at that time can be kept small, that is, the output relative to the input can be kept relatively small.

Next, when the input shaft is moved forward and the increase in the input load is stopped and maintained, the valve body moves forward with respect to the input shaft, so the input shaft moves relative to the valve body. Starts to retreat. As a result, when the second valve seat of the valve plunger comes into contact with the valve body, the variable pressure passage and the pressure passage are brought into communication only through the orifice passage. In this state, pressure fluid is gradually supplied into the variable pressure chamber through the orifice passage, so
The valve body continues to move forward relative to the input shaft,
Therefore, the valve plunger continues to move relatively backward relative to the valve body, and eventually stops when the orifice passage is closed by the elastic deformation of the elastic body.

Then, from a state in which the valve body contacts the second valve seat and the variable pressure passage and the pressure passage are communicated only through the orifice passage, the orifice passage is closed and the communication between the variable pressure passage and the pressure passage is interrupted. Since the communication between the reaction force transmission member and the valve plunger is released before the reaction is shut off, the reaction force transmitted from the reaction disk to the valve plunger via the reaction force transmission member can be received by the valve body.
As a result, the reaction force from the reaction disk is transmitted to the valve plunger without going through the reaction force transmission member, thereby increasing the servo ratio and therefore increasing the output relative to the input. I can do it.

In this way, when the input shaft depression force is stopped and maintained in an intermediate load state, the output can be further increased compared to the output at the moment when the depression stopped, providing peace of mind to the driver. It can provide a good brake feeling with a good feel.

[Example] The present invention will be explained below with reference to the illustrated example.
In FIG. 1, 1 is a front shell, 2 is a rear shell, and a power piston 3 and a diaphragm 4 stretched on the back side of the power piston 3 are provided in a sealed container composed of both shells 1 and 2.
The power piston 3 and the diaphragm 4 partition the inside of the shells 1 and 2 into a constant pressure chamber 5 at the front and a variable pressure chamber 6 at the rear.

A valve body 7 is integrally provided on the shaft portion of the power piston 3, and a valve mechanism 8 for switching the fluid circuit is housed within the valve body 7, and the base of the output shaft 9 is slidably fitted and held. There is. The power piston 3, valve body 7, etc. are normally held in the non-operating position shown in the figure by a return spring 10.

The valve mechanism 8 includes a first annular valve seat 15 provided on the valve body 7 and a second annular valve seat 17 formed on the valve plunger 16 inside the first valve seat 15.
and an elastic valve body 18 that seats on both valve seats 15 and 17 from the right side in the figure. The space on the outer peripheral side of the first valve seat 15 is communicated with the constant pressure chamber 5 through a constant pressure passage 19 formed in the valve body 7, and the constant pressure chamber 5 is connected to the front shell 1.
It communicates with a negative pressure source such as an engine intake manifold (not shown) through a negative pressure introduction pipe 20 provided in the engine.

Further, the space between the first valve seat 15 and the second valve seat 17 is communicated with the variable pressure chamber 6 via a variable pressure passage 21 formed in the valve body 7, and
The space on the inner peripheral side of the valve seat 17 is communicated with the atmosphere via a pressure passage 22 and a filter 22'.

The valve plunger 16 is prevented from being pulled out from the valve body 7 by a key member 23, and an input shaft 2 is connected to the brake pedal (not shown).
4, and the distal end surface of the valve plunger 16 faces the other end surface of a reaction disk 25, which is disposed with one end surface facing the base end surface of the push rod 9. The input shaft 24 is loosely fitted through the shaft portion of the valve body 18 so that it can move forward and backward, and is interlocked with the valve plunger 16, and between the outer circumferential surface of the input shaft 24 and the inner circumferential surface of the valve body 18. The pressure passage 22 is formed to communicate with the space on the inner peripheral side of the second valve seat 17.

As shown in an enlarged view in FIG. 2, a reaction force transmitting member 26 is interposed between the valve body 7, the valve plunger 16, and the reaction disk 25, and as shown in FIG.
A plurality of radial slits are formed in the annular convex portion 18a formed at 8, and the slits serve as orifice passages 27. In the illustrated non-operating state, the valve body 1
8 is a spring 28 loaded between this and the input shaft 24.
is seated in pressure contact with the second valve seat 17, and in this pressed state, the seat portion 18b formed on the inner circumferential side of the annular projection 18a due to elastic deformation of the annular projection 18a is seated on the second valve seat 17. 17, and the orifice passage 27 is also closed. Also, at this time, the valve body 18 is provided with a required gap l ₁ to the first valve seat 15.
They are facing each other with a

On the other hand, the reaction force transmitting member 26 is formed into a ring shape with an L-shaped cross section, and the cylindrical portion 26
The valve plunger 16 is slidably fitted onto the shaft portion of the valve body a, and the outer peripheral portion of the flange-shaped portion 26b is located between the valve body 7 and the reaction disk 25. And the reaction force transmission member 26
In the illustrated non-operating state, the right end surface of the cylindrical portion 26a is connected to the stepped portion 16a of the valve plunger 16 which is slidably fitted to the shaft portion of the cylindrical portion 26a.
facing each other with a required gap l ₂ larger than l ₁ ,
Further, the distal end surface of the reaction force transmitting member 26 is opposed to the end surface of the reaction disk 25 with a required gap δ.

In the above configuration, in the illustrated non-operating state, the valve body 18 and the second valve seat 17 are in contact with each other at the seat portion 18b and close the orifice passage 27, thus completely blocking the atmosphere at that portion. .
Also, there is a required gap between the valve body 18 and the first valve seat 15.
A gap l ₁ is formed between the valve plunger 16 and the reaction force transmitting member 26, and a gap _{l 2 larger} than the gap l 1 is also formed between the valve plunger 16 and the reaction force transmitting member 26.

In this state, when the brake pedal (not shown) is depressed and an input is applied to the input shaft 24, the input shaft 24 and the valve plunger 16 are connected to the valve body 7.
1, move to the left, close the gap l ₁ above, and remove the valve body 1.
8 seats on the first valve seat 15 to cut off communication between the constant pressure chamber 5 and variable pressure chamber 6, and then when the valve plunger 16 further moves to the left, the valve body 18 and the second valve seat 17 are separated. Atmospheric pressure is now supplied to the variable pressure chamber 6.

As a result, a pressure difference is generated before and after the power piston 3 due to the atmospheric pressure supplied to the variable pressure chamber 6 and the vacuum in the constant pressure chamber 5, and this pressure difference causes the power piston to
moves forward against the repulsive force of the return spring 10. In this state, the orifice passage 27 is of course open, and the valve plunger 16 closes the gap _l2 so that its stepped portion 16a abuts against the cylindrical portion 26a of the reaction force transmitting member 26. Furthermore, the flange-shaped portion 26b of the reaction force transmitting member 26 is separated from the valve body 7.

5a and 5b, the valve body 18 is located at the first valve seat 1.
5 to cut off communication between the constant pressure chamber 5 and variable pressure chamber 6, and separate the annular convex portion 18a of the valve body 18 from the second valve seat 17 to open the space between them and the orifice passage 27; Furthermore, the valve plunger 16
and the reaction force transmission member 26 are interlocked, and the flange-shaped portion 26b of the reaction force transmission member 26 is connected to the valve body 7.
It shows a state of being far away from.

When an output is generated on the output shaft 9 due to the forward movement of the power piston 3, the reaction disk 25 is elastically deformed by the reaction force, and the gap between the reaction disk 25 and the distal end surface of the reaction force transmitting member 26 is closed, and the reaction disk 25 is turned into a valve. Plunger 16 and reaction force transmission member 26
come into contact with. At this time, even if there is a slight difference in level between the left end surface of the valve plunger 16 and the left end surface of the reaction force transmission member 26, the reaction disk 25 has sufficient flexibility, so that the valve plunger 16 substantially simultaneously and the reaction force transmitting member 26.

In this way, when the input shaft 24 is moved forward by depressing the brake pedal from a non-operating state, that is, when the input shaft 24 moves forward relative to the valve body 7, the valve plunger 16 and the reaction force transmission member 26 are interlocked. Therefore, the reaction force applied to the output shaft 9 is transmitted not only from the reaction disk 25 to the valve plunger 16 but also from the reaction force transmission member 2.
6 to the input shaft 24.

As a result, since the contact area where the reaction disk 25 contacts the valve plunger 16 and the reaction force transmitting member 26 is obtained by the relatively large diameter D shown in FIG. In a state where the servo ratio is small, that is, the output relative to the input is relatively small, and therefore the input increases, the output increases at a small servo ratio, as shown by straight line A in Figure 4. Become.

Next, in an intermediate load state, for example, if the input to the input shaft 24 is held constant at point B in FIG. 5b, the valve body 7 continues to move forward relative to the input shaft 24, so that the input shaft 24 moves backward relative to the valve body 7.

When the input shaft 24 retreats relative to the valve body 7, first the second valve seat 17 of the valve plunger 16 comes into contact with the annular convex portion 18a of the valve body 18, so that the pressure is transformed only by the orifice passage 27. The passage 21 and the pressure passage 22 are brought into communication. At this time, it goes without saying that the seat portion 18b of the valve body 18 is separated from the second valve seat 17.

Therefore, atmospheric pressure is gradually supplied to the variable pressure chamber 6 through the orifice passage 27, and the power piston 3
As the pressure difference between the front and rear increases, the power piston 3
is gradually advanced, so the output of the output shaft 9 continues to rise gradually (see straight line C in FIG. 4). As the power piston 3 is gradually advanced, the valve plunger 16 is gradually retreated relative to the valve body 7, so that it comes into contact with the second valve seat 17 due to the elastic force of the spring 28. The amount of elastic deformation of the annular convex portion 18a that comes into contact gradually increases, and the orifice passage 27 is gradually closed, and eventually the seat portion 18b of the valve body 18 comes into contact with the second valve seat 17, and the second valve seat 17 is closed. The valve seat 17 is closed and the orifice passage 27 is closed. As a result, the supply of atmospheric pressure is completely cut off, and at that point the increase in output also stops, resulting in a servo balance state (position D in FIG. 4).

During this period, the annular convex portion 18a of the valve body 18 comes into contact with the second valve seat 17 of the valve plunger 16, and the variable pressure passage 21 and the pressure passage 22 are brought into communication only through the orifice passage 27. Before the seat portion 18b of the valve body 18 contacts the second valve seat 17 and closes that portion, that is, the second valve seat 17
Before closing the orifice passage 27, the flange-shaped portion 26b of the reaction force transmitting member 26 comes into contact with the valve body 7 at a predetermined retreat position and its retreat is restricted, so that the valve body 18 closes the orifice passage 27. When it is closed and the servo balance state is reached, the reaction force transmission member 26 and the valve plunger 16
The connection with has been canceled.

6a and 6b, the valve body 18 is located at the first valve seat 1.
5 to cut off communication between the constant pressure chamber 5 and variable pressure chamber 6, and the second valve seat 17 of the valve plunger 16 comes into contact with the annular convex portion 18a of the valve body 18 so that the valve is closed only by the orifice passage 27. A state is shown in which the variable pressure passage 21 and the pressure passage 22 are communicated with each other, and the seat portion 18b of the valve body 18 is open. Before the second valve seat 17 closes the orifice passage 27 (the state shown in FIG. 6b), the valve plunger 16
From the state in which the and reaction force transmission member 26 are interlocked,
This shows that the flange-shaped portion 26b of the reaction force transmission member 26 is in contact with the valve body 7.

The valve body 18 closes the orifice passage 27 and enters the servo balance state, and the reaction force transmission member 26
In the state where the interlock between the valve plunger 16 and the valve plunger 16 is released, the reaction force that was being transmitted from the reaction disk 25 to the valve plunger 16 via the reaction force transmission member 26 can be received by the valve body 7, so that the reaction force is transferred to the valve plunger 16. The reaction force from the Yon disk 25 is transmitted to the valve plunger 16 without passing through the reaction force transmission member 26.

As a result, the contact area where the reaction disk 25 contacts the valve plunger 16 is obtained by the relatively small diameter d in FIG. output can be made relatively large.

In this way, in an intermediate load state, the input shaft 24
When the increase in the depressing force is stopped and maintained, the output can be further increased compared to the output at the moment when the depressing is stopped (output at point B in Fig. 4). The output at point D) can give the driver the impression that the brakes work better than when using a conventional brake booster that does not increase the output, thereby giving the driver a sense of security. It can provide a good brake feel.

Note that the seat portion 18b can be omitted, and in that case, the annular convex portion 18a of the valve body 18
After contacting the second valve seat 17 of the valve plunger 16 and establishing communication between the pressure transformation passage 21 and the pressure passage 22 only through the orifice passage 27, the valve body 18 and the second valve seat 17 are connected to each other. The interlock between the reaction force transmitting member 26 and the valve plunger 16 may be released before the orifice passage 27 is closed by the elastic deformation of the elastic body due to pressure contact.

Next, when the input is decreased from the above point D, the valve plunger 16 further retreats with respect to the valve body 7, and the first valve seat 15 and the valve body 18 are separated from each other, so that the atmospheric pressure in the variable pressure chamber 6 increases. First valve seat 15 and valve body 1
8 and is discharged to the constant pressure chamber 5 side, the pressure difference before and after the power piston 3 decreases, and the output of the output shaft 9 decreases.

At this time, the output decreases while the reaction force of the reaction disk 25 and the input are balanced, but the cylindrical portion 26a of the reaction force transmission member 26 is separated from the stepped portion 16a of the valve plunger 16, and the flange-shaped portion 26b is in contact with the valve body 7, the reaction force to the reaction force transmission member 26 is transferred to the valve plunger 1.
Therefore, as shown by straight line F in FIG. 4, the output decreases at a large servo ratio.

On the other hand, from the servo balance state at point D, that is, the valve body 18 and the second valve seat 17 are pressed against each other, the orifice passage 27 is closed, and the valve body 18 and the first valve seat 15 are also pressed against each other. When the input is increased from the closed state, the seat portion 18b of the valve body 18 and the second valve seat 17 separate, the orifice passage 27 begins to open, and the atmosphere flows into the variable pressure chamber 6.
The output rises in a 1:1 relationship with the input until the voltage is introduced (line E in Figure 4).

Eventually, the orifice passage 27 begins to open at point G in FIG. 4, but at this time,
Before the orifice passage 27 begins to open, the valve plunger 16 and the reaction force transmitting member 26 begin to interlock. More specifically, the valve body 18 is seated on the first valve seat 15 to cut off communication between the constant pressure passage 19 and the variable pressure passage 21, and the valve body 18 is pressed against the second valve seat 17. From this state, before the orifice passage 27 starts communicating the variable pressure passage 21 and the pressure passage 22, the valve plunger 16 and the reaction force transmission member 26 come to interlock with each other. Therefore, in this state, the output increases along the aforementioned straight line A of the small servo ratio.

6a and 6c, the valve body 18 is located at the first valve seat 1.
5 and cuts off communication between the constant pressure chamber 5 and variable pressure chamber 6, and the second valve seat 17 of the valve plunger 16 comes into contact with the seat portion 18b of the valve body 18 to
A state in which the gap between the valve seat 17 and the valve body 18 and the orifice passage 27 are closed is shown. Then, before the second valve seat 17 and the seat portion 18b are separated and the orifice passage 27 begins to open (the state shown in FIG. 6c), the flange-like portion 26 of the reaction force transmitting member 26
b indicates that the valve plunger 16 and the reaction force transmitting member 26 have changed from being in contact with the valve body 7 to being in contact with each other.

After this, when the pressure inside the variable pressure chamber 6 becomes the same as the atmospheric pressure, the pressure inside the variable pressure chamber 6 will not increase any further, so from this point on, the output will increase while maintaining a 1:1 relationship with the input. (straight line H in Figure 4).

By the way, as understood from the above explanation,
The valve plunger 16 and the reaction force transmission member 26 are interlocked when the input shaft 24 advances relative to the valve body 7, and the timing is such that the valve body 18 is seated on the first valve seat 15 and the constant pressure passage 19 and the variable pressure passage are connected to each other. 21, and the valve body 18 is connected to the second
This is done before the orifice passage 27 starts to communicate with the pressure changing passage 21 and the pressure passage 22 from the state in which it is pressed against the valve seat 17 (Fig. 6a, Fig. 6).
(see figure b).

On the other hand, the interlock between the valve plunger 16 and the reaction force transmission member 26 is released when the input shaft 24 retreats with respect to the valve body 7, and the timing is such that the valve body 18 contacts the second valve seat 17 and the This is performed from a state where the variable pressure passage 21 and the pressure passage 22 are communicated only through the orifice passage 27, and before the orifice passage 27 is closed and the communication between the variable pressure passage 21 and the pressure passage 22 is cut off. 6a and 6c).

In other words, from the perspective of opening and closing the orifice passage 27, the valve plunger 16 and the reaction force transmitting member 2
6 is performed before the orifice passage 27 begins to open, and the valve plunger 16 and the reaction force transmission member 2
6 is released before the orifice passage 27 is closed. Such a timing shift can be obtained from the characteristics of the valve mechanism 8 that uses an elastic body.

Specifically, taking as an example a conventional valve mechanism of this type that does not include the orifice passage 27, the valve body made of an elastic body is connected to the second valve body made of a rigid body.
When the valve element leaves the second valve seat, a seal can be maintained between the two until the moment when the valve element almost leaves the second valve seat.On the other hand, when the valve element seats on the second valve seat, the seal between the two can be maintained. It is not possible to seal the gap between the body and the second valve seat by just making light contact with the second valve seat, but it is possible to seal the gap between the two only when the valve body and the second valve seat are in stronger contact with each other. In other words, even if the state where the valve body is able to maintain the seal between the two when the valve body leaves the second valve seat is reproduced when the valve body is seated on the second valve seat, It is not possible to seal between the two. As a result, a timing difference occurs between opening and closing of the valve body when the valve body leaves the second valve seat and when the valve body seats on the second valve seat.

Such a phenomenon has been known as a cause of hysteresis, and the present invention utilizes such a timing difference to transfer the valve plunger 16 and the reaction force transmitting member 26 at the above-mentioned timing.
It is set to link and release the link.

In the above embodiment, a slit is formed in the valve body 18 to serve as the orifice passage 27.
In addition, for example, it is also possible to form a slit in the second valve seat 17 and use this as the orifice passage 27.

[Effects of the invention] As described above, according to the invention, when the increase in input is stopped and maintained in an intermediate load state, the output can be further increased than that obtained with a normal proportional relationship. Therefore, it is possible to provide a good brake feeling that gives the driver a sense of security.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention;
The figure is an enlarged sectional view of the main part of Figure 1, and Figure 3 is the valve body 1.
8 is a front view, FIG. 4 is a characteristic diagram obtained by the present invention, FIG. 5a is a sectional view showing the operating state when the input shaft is advanced, and FIG. 5b is a main part of FIG. 5a. FIG. 6a is an enlarged sectional view showing a different operating state from FIG. 5a, FIG. 6b is an enlarged sectional view of a main part of FIG.
It is an enlarged sectional view of the main part showing the 2nd operating state of figure a. 1, 2...Ciel, 3...Power Piston, 5
... Constant pressure chamber, 6 ... Variable pressure chamber, 7 ... Valve body, 8 ... Valve mechanism, 9 ... Output shaft, 15 ... First
Valve seat, 16... Valve plunger, 17... Second valve seat, 18... Valve body, 18a... Annular convex portion, 18b
... Seat part, 19 ... Constant pressure passage, 21 ... Variable pressure passage, 22 ... Pressure passage, 24 ... Input shaft, 26
... Reaction force transmission member, 25 ... Reaction disk, 27 ... Orifice passage, 28 ... Spring,
l ₁ , l ₂ , δ...gap, D, d... diameter.

Claims (1)

[Scope of Claim for Utility Model Registration] A power piston slidably disposed within a shell, a valve body provided on the shaft of the power piston, a constant pressure chamber formed on the front side of the power piston, and the power piston. a variable pressure chamber formed on the rear side of the valve body, a valve plunger slidably fitted in the valve body, an annular first valve seat formed in the valve body, and a first valve seat formed in the valve plunger; an annular second valve seat located inside; a valve body that is urged toward the first valve seat and the second valve seat by a spring and is seated on the valve seats; and a shaft portion of the valve body. an input shaft that is loosely fitted through the valve plunger so that it can move forward and backward; a constant pressure passage that communicates the space on the outer peripheral side of the first valve seat with the constant pressure chamber; and the first valve seat and the second valve. a pressure-changing passage communicating between the space between the seat and the pressure-changing chamber; and the second pressure-changing passage formed between the outer circumferential surface of the input shaft through which the valve body is loosely fitted and the inner circumferential surface of the valve body; a pressure passage communicating with the space on the inner peripheral side of the valve seat; an output shaft having a base slidably fitted in the valve body and facing the valve plunger; and a connection between the base of the output shaft and the valve plunger. A brake booster is provided with a reaction disk interposed between the brake booster and the brake booster, which transmits the reaction force of the output applied to the output shaft to the input shaft via the reaction disk and the valve plunger. The second seated valve plunger
At least one of the valve seats is made of an elastic body, and the variable pressure passage and the pressure passage are communicated with each other, and when the valve body is pressed against the second valve seat, the elastic body is elastically deformed. The valve plunger forms an orifice passage in which the passage is blocked, and is capable of moving forward and backward with respect to the valve body between the reaction disk and the valve plunger, and comes into contact with the valve body at a predetermined retreat position to restrict its retreat. A reaction force transmission member is provided, and when the input shaft moves forward relative to the valve body,
The valve body is seated on the first valve seat to cut off communication between the constant pressure passage and the variable pressure passage, and from the state where the valve body is pressed against the second valve seat, the orifice passage is connected to the variable pressure passage and the pressure passage. Before starting communication between the valve plunger and the reaction force transmission member, the reaction force is transmitted from the reaction disk to the input shaft via the valve plunger and the reaction force transmission member, and the input shaft When the valve body is retracted from the valve body, the valve body seats on the first valve seat to cut off communication between the constant pressure passage and the variable pressure passage, and the valve body contacts the second valve seat to allow only the orifice passage to flow. The reaction force transmitting member and the valve plunger are disengaged from each other before the orifice passage is closed and the communication between the variable pressure passage and the pressure passage is interrupted. A reaction force transmission mechanism for a brake booster, characterized in that reaction force is transmitted from a reaction disk to an input shaft via a valve plunger without passing through a reaction force transmission member.