Reaction mechanism for booster

According to the invention, the booster is not provided with a brake reaction transmission mechanism, and hence a reaction cannot be transmitted to a brake pedal. On the other hand, a pseudo-reaction imparting means is provided to impart a pseudo-reaction of suitable magnitude which depends on the degree of depression of the brake pedal. The pseudo-reaction imparting means is arranged so that when the brake pedal is depressed relatively rapidly, a relatively smaller braking reaction is imparted than during a usual depression. With this arrangement, the transmission of an abnormally high braking reaction to a driver which is experienced in a conventional booster during a quick braking operation due to an operational rag of the booster is avoided. The pseudo-reaction imparting means allows a reaction of a suitable magnitude which depends on the rate of depression of the brake pedal by a driver to be imparted, thus permitting a high output to be obtained with a reduced force of depression during a quick braking operation.

FIELD OF THE INVENTION 
The invention relates to a booster as may be used in a brake of an 
automobile, and more particularly, to a reaction mechanism for booster 
which imparts reaction force to an operating rod which actuates the 
booster. 
DESCRIPTION OF THE PRIOR ART 
A brake booster is known in the art which comprises a valve body slidably 
disposed within a shell, a power piston mounted on the valve body, a 
constant and a variable pressure chamber defined across the power piston, 
a valve mechanism disposed in the valve body, an input shaft connected to 
an operating rod and adapted to drive a valve plunger, which forms part of 
the valve mechanism, back and forth to thereby switch a flow path in the 
valve mechanism, and an output shaft driven forward as the valve body is 
driven forward. 
A conventional reaction mechanism is provided with a reaction disc formed 
of rubber and disposed between the output shaft and the valve plunger so 
that when the brake booster is actuated, both the valve body and the valve 
plunger are brought into contact with the reaction disc simultaneously, 
part of a braking force applied to the output shaft being transmitted to 
the valve body while the remainder thereof is transmitted to the valve 
plunger, the braking reaction force transmitted to the valve plunger being 
sensed by a driver through the input shaft and the brake pedal. 
A serve ratio of the brake booster can be changed by changing the ratio of 
the reaction force transmitted to the valve body and the reaction force 
transmitted to the valve plunger, and more specifically, the ratio of 
pressure-responsive areas of the both members. 
A high serve ratio is generally established in the brake booster so that a 
braking liquid pressure of an increased magnitude can be developed with a 
depression of the brake pedal with a reduced force. However, it is found 
that during a quick braking operation, a serve ratio of a predetermined 
magnitude cannot be obtained as a result of an operational lag of the 
brake booster, and it is difficult for a powerless driver such as an aged 
person or woman to perform a quick braking operation. 
More specifically describing the reason, when the brake pedal is depressed, 
a flow path in the valve mechanism is switched through the input shaft, 
whereby a pressure fluid is introduced into the variable pressure chamber 
to drive the power piston and the valve body forward. As the valve body is 
driven forward, the output shaft is also driven forward through the 
reaction disc, the forward movement of the output shaft developing a 
breaking pressure. A reaction therefrom is applied to the output shaft, 
and the brake reaction applied to the output shaft is distributed between 
the valve body and the valve plunger in a manner mentioned above. 
However, the valve plunger which is connected to the brake pedal through 
the input shaft will be driven forward before the power piston and the 
valve body are driven forward by the pressure fluid which is introduced 
into the variable pressure chamber during a quick braking operation, and 
as a consequence, a major portion of the braking reaction which is applied 
to the output shaft will be transmitted to the valve plunger. This results 
in a braking reaction of an abnormally high magnitude being transmitted to 
the driver. 
Consequently, when a quick braking operation is to be performed, the brake 
pedal must be depressed by overcoming the abnormally high braking reaction 
which is transmitted. As compared with a normal braking operation in which 
the brake pedal is gradually depressed to achieve a high braking force, a 
braking force of increased magnitude which is required for a quick braking 
operation cannot be obtained unless the brake pedal is depressed with a 
force which is much greater than in a normal braking operation. 
SUMMARY OF THE INVENTION 
In view of the foregoing, the invention provides a reaction mechanism for 
booster which enables a high output to be obtained with a reduced force of 
depression during a quick braking operation. 
Thus, the invention relates to a booster including a valve body slidably 
disposed within a shell, a power piston mounted on the valve body, a 
constant and a variable pressure chamber defined across the power piston, 
a valve mechanism disposed in the valve body, an input shaft connected to 
an operating rod for driving a valve plunger, which forms a valve 
mechanism, back and forth to switch a flow path in the vale mechanism, and 
an output shaft which is driven forward as the valve body is driven 
forward. In accordance with the invention, there is provided 
pseudo-reaction imparting means which prevents the reaction applied to the 
output shaft during the operation of the booster from being transmitted to 
the valve plunger and which imparts a pseudo-reaction which depends on a 
travel of the operating rod to the operating rod. 
The pseudo-reaction imparting means comprises a reaction piston slidably 
mounted on either the power piston or the valve body and which partitions 
between a second constant pressure, to the rear side of which a pressure 
from the constant pressure chamber is introduced, and a second variable 
pressure chamber, to the front side of which a pressure from the variable 
pressure chamber is introduced. A pressure differential between the second 
constant pressure chamber and the second variable pressure chamber urges 
the reaction piston rearward, and the force which urges the rear piston is 
transmitted, as a pseudo-reaction, to the valve plunger. 
If required, an orifice passage may provide a communication between the 
variable pressure chamber and the second variable pressure chamber. 
The described arrangement provides for a mechanism which prevents a 
reaction applied to the output shaft from being transmitted to the valve 
plunger when the booster is actuated. Accordingly, during a quick breaking 
operation, if the valve plunger which is coupled to the operating rod 
through the input shaft is driven forward before the power piston and the 
valve body are driven forward by the pressure fluid which is introduced 
into the valuable pressure chamber during a quick breaking operation, the 
transmission of a reaction applied to the output shaft through the valve 
plunger, the input shaft and the operating rod to a driver is prevented. 
On the other hand, the pseudo-reaction imparting means is provided with a 
reaction piston which is subject to a pressure differential between the 
second constant pressure chamber into which the pressure from the constant 
pressure chamber is introduced and the second variable pressure chamber 
into which the pressure from the variable pressure chamber is introduced. 
The reaction piston is urged rearward by the pressure differential, and 
the force from the reaction piston is transmitted to the valve plunger as 
a pseudo-reaction. In this manner, an increase of the reaction to an 
abnormally high value during a quick breaking operation, as occurs in the 
prior art, is prevented. By choosing a suitable value of 
pressure-responsive area of the reaction piston, a high output can be 
obtained with a reduced force of depression during a quick breaking 
operation. 
In particular, when the second variable pressure chamber is made to 
communicate with the variable pressure chamber through an orifice passage, 
the pressure in the second variable pressure chamber rises in delayed 
relationship with respect to a pressure rise in the variable pressure 
chamber. Accordingly, the power piston is driven forward in response to a 
pressure rise in the variable pressure chamber while the pseudo-reaction 
produced by the reaction piston rises in delayed relationship thereto, 
thus allowing a high output to be obtained with a more reduced force of 
depression during a quick breaking operation. 
Above an other objects, features an advantages of the invention will become 
apparent from the following description with reference to the attached 
drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
Referring to the drawings, an embodiment of the invention which is applied 
to a brake booster will now be described. Referring to FIG. 1, a front 
shell 1 and a rear shell 2 constitute together an enclosed vessel, in 
which a power piston 3 is slidably disposed. The power piston 3 includes a 
stepped cylinder member 3A having a closed bottom which is disposed in its 
axial portion and a dish-shaped plate member 3B secured to the cylinder 
member 3A. 
A piston assembly 4a formed at the front end of a valve body 4 is slidably 
fitted into the cylinder member 3A of the power piston 3 from the rear 
side in which the cylinder member has its opening, and is capable of 
sliding motion between a step 3a formed forwardly on the cylinder member 
3A and a retainer 3b mounted rearwardly on the cylinder member 3A. 
A diaphragm 5 is applied to the rear side of the plate member 3B which 
constitutes the power piston 3, thus partitioning the interior of the 
enclosed vessel into a forwardly located constant pressure chamber 6 and a 
rearwardly located variable pressure chamber 7. It should be understood 
that a pressure within the constant pressure chamber 6 acts upon the front 
end face of the plate member 3B which constitutes the power piston 3, and 
also acts upon the front end face of the piston assembly 4a which forms 
the valve body 4 through a passage 3c formed in the cylinder member 3A. A 
pressure within the variable pressure chamber 7 acts upon the rear end 
face of the plate member 3B and the rear end face of the piston assembly 
4a. 
The valve body 4 contains a valve mechanism 9 which switches a fluid 
circuit. Specifically, the valve mechanism 9 comprises an annular first 
valve seat 10 formed around the inner periphery of the valve body 4, an 
annular second valve seat 12 formed on the right end of a valve plunger 11 
which is slidably fitted into the valve body 4, and a valve element 14 
which is urged from the right, as viewed in FIG. 1, to be seated upon 
either valve seat 10 or 12 under the influence of a poppet return spring 
13. 
A space located radially outward of the first valve seat 10 communicates 
with the constant pressure chamber 6 through an axial constant pressure 
passage 15 formed in the valve body 4 and a passage 3c formed in the 
cylinder member 3A, and the constant pressure chamber 6 communicates with 
an intake manifold of an engine through a tubing 16 mounted on the front 
shell 1 for introducing a negative pressure. In this manner, a negative 
pressure is normally introduced into the chamber 6. A space located 
intermediate the first valve seat 10 and the second valve seat 12 
communicates with the variable pressure chamber 7 through a radial 
variable pressure passage 17 formed in the valve body 4. Finally, a space 
located radially inward of the second valve seat 12 communicates with the 
atmosphere through a pressure passage 18 formed in the valve body 4. 
The right end of the valve plunger 11 is pivotally connected with a distal 
end of an input shaft 19, and a valve return spring 20 having a greater 
resilience than the poppet return spring 13 is disposed between the input 
shaft 19 and the valve body 4, thus normally maintaining the valve element 
14 seated upon the second valve seat 12 of the valve plunger 11 while 
maintaining the valve element 14 away from the first valve seat 10 on the 
valve body 4. The other end of the input shaft 19 is coupled to a brake 
pedal, not shown. 
The valve plunger 11 is prevented from being disengaged from the valve body 
4 by means of a key member 22. While not shown, the key member 22 is 
forked in a region from its center toward the distal end thereof, and the 
key member 22 is inserted into a receiving hole 23 which is diametrically 
formed in the valve body 4, with the end from which the forked portion 
extends being engaged with a portion 11a of the valve plunger 11 which has 
a reduced diameter. 
The receiving hole 23 and the variable pressure passage 17 are formed 
adjacent to each other axially of the valve body 4 so as to be integral, 
but the width of the receiving hole 23, or the width as measured in a 
direction which is perpendicular to the axial direction of the valve body 
4 and which is orthogonal to the direction in which the key member 22 is 
inserted into the hole 23, is chosen to be greater than the width of the 
variable pressure passage 17 measured in the same direction, whereby the 
key member 22 is displaceable axially of the valve body 4 only within the 
receiving hole 23. 
The key member 22 and the valve plunger 11 are displaceable axially of the 
valve body 4 within an extent of the axial length of the portion 11a 
having a reduced diameter. By maintaining the key member 22 in abutment 
against the inner surface of the rear shell 2 when the brake booster is 
inoperative to thereby maintain the key member 22 and the valve plunger 11 
at an advanced position relative to the valve body 4, a lost motion of the 
input shaft 19 at the commencement of operation of the brake booster can 
be reduced. 
The left end of an output shaft 26 disposed forwardly of the valve plunger 
11 projects externally of the front shell 1 while maintaining a hermitic 
seal by means of a seal member 27, with the distal end of the output shaft 
being coupled to a piston of a master cylinder, not shown, which is 
connected to the front shell 1. 
On the other hand, the right end of the output shaft 26 is connected to an 
axial portion of the cylinder member 3A, whereby a braking reaction which 
is transmitted from the output shaft 26 during the operation of the brake 
booster is received by the cylinder member 3A or the power piston 3, and 
no braking reaction is transmitted to the valve body 4 while also 
preventing it from being transmitted to the brake pedal through the valve 
plunger 11. 
The power piston 3 is urged to the right by a return spring 28, and is 
normally maintained in its inoperative position shown where it abuts 
against the key member 22 which is maintained in abutment against the 
inner surface of the rear shell 2. At this time, the right end of the 
cylinder member 3A is substantially in abutment against the inner wall 
surface of the rear shell 2. 
Since the braking reaction is not transmitted to the brake pedal as 
mentioned previously, a driver cannot obtain a brake operating feeling 
with the described arrangement alone. Accordingly, pseudo-reaction 
imparting means 31 is provided to enable a pseudo-reaction which depends 
on the amount of depression of the brake pedal to be imparted to a driver. 
The pseudo-reaction imparting means 31 comprises a reaction piston 32 
disposed forwardly of the valve body 4 and which is slidably fitted into 
the cylinder member 3A. The reaction piston 32 defines a second constant 
pressure chamber 33 rearwardly of the cylinder member 3A and a second 
variable pressure chamber 34 forwardly of the cylinder member 3A. The 
second constant pressure chamber 33 is maintained in communication with 
the constant pressure chamber 6 through the passage 3c which is formed in 
the cylinder member 3A, and also communicates with the constant pressure 
passage 15 formed in the valve body 4. On the other hand, the second 
variable pressure chamber 34 communicates with the variable pressure 
passage 17 through an orifice passage 32a formed in the reaction piston 
32, and thence to the variable pressure chamber 7. 
The reaction piston 32 is formed with a portion 32b of a reduced diameter 
rearwardly, and such portion 32b is slidably fitted into the valve body 4 
while maintaining a hermitic seal, while urging the reaction piston 32 
rearward by a spring 35 which is disposed in the second variable pressure 
chamber 34. The rear end face of the portion 32b having a reduced diameter 
is formed with a recess 32c, in which the front end of the valve plunger 
11 is slidably fitted, whereby the front end face of the valve plunger 11 
is disposed in opposing relationship with the bottom of the recess 32c. 
The depth or the axial size of the recess 32c is chosen to a given value, 
and in the inoperative condition shown, the rear end of the portion 32b of 
a reduced diameter in which the recess 32c is formed abuts against the 
inner wall surface of the rear shell 2, and hence abuts against the key 
member 22 which is maintained at an advanced position relative to the 
valve body 4. In the inoperative condition, a clearance is maintained 
between the bottom of the recess 32c and the front end face of its 
opposing valve plunger 11. 
By contrast, in the operative condition in which the valve body 4 is driven 
forward and the key member 22 moves away from the inner wall surface of 
the rear shell 2, the key member 22, and hence the reaction piston 32, is 
allowed to retract relative to the valve body 4 to permit an abutment 
between the bottom of the recess 32c and the front end face of the 
opposing valve plunger 11 to occur, whereby the force acting from the 
reaction piston 32 can be transmitted to the brake pedal through the valve 
plunger 11 and the input shaft 19 as a pseudo-reaction. 
Thus, in the present embodiment, the key member 22 constitutes separating 
means which abuts against the rear shell to separate the reaction piston 
32 and its opposing valve plunger 11 from each other during the 
inoperative condition of the booster. 
A return spring 36 is disposed between the reaction piston 32 and the valve 
body 4 to urge the valve body 4 rearward. 
With the described arrangement, when the brake pedal is depressed to drive 
the input shaft 19 and the valve plunger 11 forward, a flow path in the 
valve mechanism 9 is switched to introduce the atmosphere into the 
variable pressure chamber 7, whereby a pressure differential between the 
constant pressure chamber 6 and the variable pressure chamber 7 drives the 
power piston 3 forward. The output shaft 26 is then driven forward in 
integral manner with the power piston 3, whereby a braking liquid pressure 
is developed in the master cylinder. A braking reaction which results from 
the braking liquid pressure is transmitted through the output shaft 26 to 
be received entirely by the power piston 3, and no reaction is transmitted 
to the valve plunger 11. 
On the other hand, when the atmosphere is introduced into the variable 
pressure chamber 7, the atmosphere is introduced into the second variable 
pressure chamber 34 through the variable pressure passage 17 and through 
the orifice passage 32a, whereby the reaction piston 32 is urged rearward 
by a pressure differential between the second constant pressure chamber 33 
and the second variable pressure chamber 34. As mentioned previously, a 
clearance is maintained between the bottom of the recess 32c and the front 
end face of the opposing valve plunger 11 in the inoperative condition 
shown in which the key member 22 abuts against the inner wall surface of 
the rear shell 2, and hence any pseudo-reaction which is acting upon the 
reaction piston 32 cannot be transmitted to the valve plunger 11. 
By contrast, the pressure differential between the constant pressure 
chamber 6 and the variable pressure chamber 7 also acts upon the valve 
body 4, and accordingly, the valve body 4 is driven forward as the power 
piston 3 is driven forward. As the valve body 4 is driven forward, when 
the key member 22 moves away from the inner wall surface of the rear shell 
2, the key member 22 and the reaction piston 32 are allowed to retract 
relative to the valve body 4, whereby an abutment occurs between the 
bottom of the recess 32c and the front end face of the opposing valve 
plunger 11 to cause a pseudo-reaction which is acting upon the reaction 
piston 32 to be transmitted to the brake pedal through the valve plunger 
11 and the input shaft 19. 
FIG. 2 shows a servo balance condition of the brake booster in an 
intermediate load region. Under this condition, there is achieved a 
balance in the power piston 3 between a retracting force caused by a 
braking reaction from the output shaft 26 and the resilience of the return 
spring 28 and a forward driving force which results from the pressure 
differential between the constant pressure chamber 6 and the variable 
pressure chamber 7. 
In the valve body 4, a balance is also achieved between the retracting 
force caused by the resilience of the return spring 36 and the forward 
driving force which results from the pressure differential between the 
second constant pressure chamber 33 and the variable pressure chamber 7. 
In the reaction piston 32, a balance is also achieved between the 
retracting force which is caused by the resilience of the spring 35 and 
the pressure differential between the second constant pressure chamber 33 
and the second variable pressure chamber 34 and the force to depress the 
brake pedal by a driver or the forward driving force from the valve 
plunger 11. 
It will be seen from this servo balance condition that the forward travel 
of the power piston 3 and the forward travel of the valve body 4 can be 
separately determined depending on the resilience of the return springs 
28, 36 and their pressure-responsive areas. In the present embodiment, the 
forward travel of the valve body 4 is chosen to be smaller than the 
forward travel of the power piston 3. 
More specifically, a relatively large forward travel is required for the 
output shaft 26 to which the braking reaction is applied in order to 
compensate for a lost motion or stroke for the piston of the master 
cylinder, not shown, or a lost motion or a stroke from the commencement of 
forward movement of the piston of the master cylinder until the braking 
liquid pressure rises substantially. By contrast, the forward travel of 
the valve body can be determined in accordance with the resilience of the 
return spring 36 and the pressure-responsive area of the piston assembly 
4a independently from the magnitude of the braking reaction. As mentioned 
previously, the forward travel of the valve body 4 is chosen to be smaller 
than the forward travel of the power piston 3. As a consequence, the 
stroke of the input shaft 19 which is driven forward as the valve body 4 
is driven forward or the stroke of its associated brake pedal can be made 
relatively small, permitting an improvement in the brake feeling. 
FIG. 3 graphically shows a relationship between a force of depressing the 
brake pedal and a pseudo-reaction transmitted to a driver. A point P shown 
in FIG. 3 indicates the time when the rear end face of the portion 32b of 
the reaction piston 32 which has a reduced diameter abuts against the 
front end face of the valve plunger 11. 
Thus, in the present embodiment, at the commencement of depression of the 
brake pedal, the portion 32b of the reaction piston 32 which has a reduced 
diameter is spaced from the valve plunger 11, and a pseudo-reaction is 
transmitted to a driver from the time on after the brake booster is 
actuated and the portion 32b abuts against the valve plunger 11. 
As mentioned previously, a balance is achieved in the reaction piston 32 
between the retracting force caused by the resilience of the spring 35 and 
the pressure differential between the second constant pressure chamber 33 
and the second variable pressure chamber 34 and the forward driving force 
caused by the resilience of the return spring 36 and the force of 
depressing the brake pedal by the driver or from the valve plunger 11. 
Accordingly, a retracting force which is caused by the pressure 
differential between the second constant pressure chamber 33 and the 
second variable pressure chamber 34 is principally transmitted to the 
brake pedal as a pseudo-reaction. Clearly, the pseudo-reaction depends on 
the pressure differential between the second constant pressure chamber 33 
and the second variable pressure chamber 34, and this pressure 
differential is equal to the pressure differential between the constant 
pressure chamber 6 and the variable pressure chamber 7, and the latter 
pressure differential is controlled in accordance with the magnitude of 
depression of the brake pedal. Thus, the magnitude of the pseudo-reaction 
is eventually dependent upon the travel of the brake pedal. 
As a consequence, even though a reaction disc which is usually provided in 
a conventional booster is omitted, a jumping characteristic similar to 
that occurring in a conventional booster can be obtained at the time the 
portion 32b of the reaction piston 32 which has a reduced diameter abuts 
against the valve plunger 11. Subsequently, a pseudo-reaction which is 
dependent on the degree of depression of the brake pedal is transmitted to 
a driver. This improves a brake feeling experienced by a driver as 
compared with an arrangement in which a pseudo-reaction is immediately 
imparted to a driver upon commencement of depression of the brake pedal. 
While a quick braking operation is basically identical to a normal 
operation, it will be noted that in the present embodiment, the second 
variable pressure chamber 34 and the variable pressure passage 17 
communicate with each other through the orifice passage 32a, and hence, if 
a pressure in the variable pressure passage 17 and the variable pressure 
chamber 7 increases rapidly during a quick braking operation, the pressure 
in the second variable pressure chamber 34 will rise in delayed 
relationship to the pressure rise in the variable pressure chamber 7. 
Consequently, the pseudo-reaction which the pseudo-reaction imparting means 
31 imparts to the brake pedal will be smaller during the quick braking 
operation than during the normal braking operation. In addition, since the 
occurrence of an abnormally high braking reaction which is experienced in 
a conventional arrangement during a quick braking operation is avoided, a 
high braking force can be obtained with a relatively reduced force of 
depression during a quick braking operation. In this manner, a powerless 
driver such as an aged person or woman is enabled to perform a quick 
braking operation in a reliable manner. 
In the described embodiment, the valve body 4 is slidably disposed in the 
power piston, but they may be integral. In such instance, the reaction 
piston 32 may be slidably disposed in the valve body. 
In the described embodiment, a brake pedal is used as an operating rod, 
which however may be a manual brake lever used by a physically handicapped 
person. It is also to be understood that the invention is also applicable 
to a clutch booster, and in this instance, a clutch pedal can be used as 
an operating rod. 
While the invention has been described above in connection with an 
embodiment thereof, it should be understood that a number of changes, 
modifications and substitutions therein are possible by one skilled in the 
art from the above disclosure without departing from the scope and the 
spirit of the invention defined by the appended claims.