Apparatus for clearance adjustment in brake booster

For use in a brake booster of the type having a master cylinder disposed rearwardly of a booster mechanism having a power piston and in which a braking reaction force produced on an output shaft is transmitted therefrom to an input shaft through a reaction disc and a reaction transmitting member, an apparatus is provided for adjusting the magnitude of a clearance defined between the reaction disc and the reaction transmitting member. In this apparatus, the input shaft comprises a first section associated with the reaction transmitting member and a second section on which a valve seat is formed. The valve seat forms a valve mechanism disposed within a valve body for controlling the opening or closing of a passage for hydraulic fluid. The first and the second section of the input shaft are formed by separate members, both of which project toward the front shell and are connected together in a manner to permit their relative position to be adjusted. The relative position of the both members can be adjusted through an opening formed in the front shell, thus facilitating the adjustment of the clearance.

FIELD OF THE INVENTION 
The invention relates to a brake booster, and more particularly, to a brake 
booster of the type including a master cylinder disposed rearwardly of a 
booster mechanism having a power piston. 
DESCRIPTION OF THE PRIOR ART 
In a usual brake booster, namely, in a brake booster having a master 
cylinder connected forwardly of a booster mechanism, it is a common 
practice to transmit a brake reaction produced on an output shaft to an 
input shaft through a reaction disc and a valve plunger which forms a 
valve mechanism during the operation of the broke booster. In order to 
establish the timing when the transmission of a reaction force is to be 
initiated during the initial phase of operation of the brake booster, it 
is necessary to define a given clearance between the reaction disk and the 
valve plunger in the reaction transmission mechanism of the type including 
the reaction disk. Where such clearance must be provided within a given 
range with a high precision, it has been the practice in the prior art to 
provide an apparatus for clearance adjustment which can be adjusted to 
achieve a desired clearance with a high precision. 
However, it should be understood that the conventional apparatus for 
clearance adjustment is adapted to be incorporated into a usual brake 
booster as mentioned above, and while such apparatus may be directly 
incorporated into a brake booster of the type contemplated in the present 
invention, namely, of the type including a master cylinder disposed 
rearwardly of a booster mechanism, such arrangement does not always 
represent an optimum arrangement. 
SUMMARY OF THE INVENTION 
It is an object of the invention to enable a clearance adjustment in a 
facilitated and accurate manner through a front shell side, based upon the 
finding that a free space is available outside the front shell in a brake 
booster of the type having a master cylinder disposed rearwardly of a 
booster mechanism, with the free space being provided when the master 
cylinder is connected. 
Specifically, on accordance with the invention, an input shaft includes a 
first and a second section which are formed by separate members. The first 
section of the input shaft is mechanically coupled with a reaction 
transmitting member which is disposed in opposing relationship with a 
reaction disc with a given clearance therebetween for transmitting a 
reaction force to the input shaft upon abutment thereof against the 
reaction disc. The second section of the input shaft is formed with a 
valve seat disposed within a valve body to define a valve mechanism which 
controls to open or close a passage for hydraulic fluid. The both members 
which form the first and the second section project into a front shell and 
are interconnected in a manner so that their relative position can be 
adjusted. The front shell is formed with an opening through which the 
relative position of the both members can be adjusted. In this manner, a 
clearance adjustment can be performed in a facilitated and accurate manner 
through the front shell even when the master cylinder is connected. 
Above and other objects, features and advantages of the invention will 
become apparent from the following description with reference to the 
attached drawing.

DETAILED DESCRIPTION OF EMBODIMENT 
Referring to the drawing, there is shown a shell including a front shell 1a 
and a rear shell 1b. The rear shell 1b has a shank portion, to which the 
free end of a master cylinder 2 is connected. The other end of the master 
cylinder 2 is secured to a carrosserie 3. A valve body 5 having a power 
piston 4 integrally formed therewith is disposed within the shell 1 so as 
to be reciprocable in the axial direction thereof. The interior of the 
shell 1 is divided into a constant pressure chamber 7 located toward the 
front shell 1a and a variable pressure chamber 8 located toward the rear 
shell 1b, by the combination of the valve body 5, the power piston 4 and a 
diaphragm 6. 
The valve body 5 is generally cylindrical in configuration and is slidable 
while maintaining a hermetic seal of the shell by means of a seal member 
10 which cooperates with the free end of the valve body and with a 
cylindrical portion 9 defined by a shank portion of the front shell 1a. 
The seal member 10 includes a front end 10a which is connected to the edge 
of an opening 9a, formed in the front end of the cylindrical portion 9, by 
means of a retainer 11. Intermediate its length, the seal member is folded 
back inwardly, with its other end 10b being connected to the free end of 
the valve body 5 so as to maintain the constant pressure chamber 7 
hermetically sealed. A return spring 12 is interposed between the front 
shell 1a and the valve body 5 for normally urging the valve body into its 
non-operative position shown where it bears against the housing 13 of the 
master cylinder 2. 
A valve mechanism 15 which switches a fluid circuit is disposed within the 
valve body 5, and comprises an annular first valve seat 16 formed around 
the inner periphery of the valve body 5, a second valve seat 18 disposed 
inside the first valve seat 16 and connected to the free end of an input 
shaft 17, and a valve element 19 which is adapted to be seated upon each 
of the valve seats 16, 18 from the front side of the power piston 4 or 
from the left side, as viewed in the drawing. In the non-operative 
position shown, a spring 21 interposed between the valve element 19 and a 
closure member 20, which closes the axial opening within the valve body 5, 
causes the valve element to be seated upon the first valve seat 16. 
Another spring 22 causes the second valve seat 18 formed on the input 
shaft 17 to be disengaged from the valve element 19 when the latter is 
seated upon the first valve seat 16. 
In the embodiment shown, the member in which the second valve seat 18 is 
defined is substantially dish-shaped in order to cover a reaction disc 34, 
to be described in detail later, and the spring 22 is interposed between 
the valve body 5 and the member defining the second valve seat adjacent to 
the outer periphery of the reaction disc 34. Disposing the spring 22 
around the outer periphery of the reaction disc 34 dispenses with the 
provision of a devoted space between the valve body 5 and the second valve 
seat 18 for accommodating such spring, thus allowing the axial length of 
the valve mechanism 15 to be reduced. Alternatively, this avoids the need 
to secure the closure member 20 firmly upon the valve body 5 which may be 
required as when the spring 22 is interposed between the closure member 20 
and the second valve sheet 18. 
Around its inner periphery, the valve element 19 includes a cylindrical 
seal 19a which is connected to the closure member 20, whereby the 
combination of the outer periphery of the cylindrical seal 19a, the 
closure member 20 and the seal formed between the valve element 19 and the 
first valve seat 16 defines a space which communicates with the atmosphere 
through a plurality of axial passages 23 formed in the closure member 20 
and through a filter 24 disposed between the closure member 20 and the 
other end 10b of the seal member 10. On the other hand, the combination of 
the inner periphery of the cylindrical seal 19a, the closure member 20, 
the input shaft 17 and the seal formed between the second valve seat 18 on 
the input shaft and the valve element 19 defines another space which 
communicates with the constant pressure chamber 7 through a plurality of 
radial passages 25 formed in the closure member 20 in a manner to avoid 
their communication with the axial passages 23 also formed therein, and 
through a passage 26 formed in the valve body 5. Finally, a space located 
intermediate the seal formed between the valve element 19 and the first 
valve seat 16 and the seal formed between the valve element 19 and the 
second valve seat 18 communicates with the variable pressure chamber 8 
through an axial passage 27 formed in the valve body 5 and through a 
passage 28 formed in the power piston 4. 
The input shaft 17 comprises a first section 17a and a second section 17b, 
with the second valve seat 18 being formed on the first section 17a of the 
input shaft. The first section 17a of the input shaft slidably extends 
through a shank portion of the housing 13 of the master cylinder 2 and 
carries on its end opposite from the second valve seat 18, an 
interconnecting member 30 which is adapted to mount pivotally a sphere 
portion formed on the free end of the second section 17b of the input 
shaft. The other end of the second section 17b is mechanically coupled to 
a brake pedal, not shown. An output shaft 32 is slidably fitted around the 
first section 17a of the input shaft in surrounding relationship therewith 
for transmitting a thrust from the power piston 4 to a piston 31 received 
within the master cylinder 2. In the embodiment shown, the combination of 
the output shaft 32 and the piston 31 is formed by an integral stepped 
hollow shaft. 
The free end of the output shaft 32 extends close to the second valve seat 
18 on the input shaft 17, and threadably carries a cylindrical member 33 
within which the reaction disc 34 is received. In this manner, the thrust 
from the power piston 4 and the valve body 5 can be transmitted through 
the reaction disc 34 and the cylindrical member 33. A resulting reaction 
force is transmitted from the reaction disc 34 to the brake pedal through 
a reaction transmitting member 35 which is slidably disposed around the 
output shaft 32, a pin 37 secured to the input shaft 17 and freely 
extending through an axial slot 36 formed in the output shaft 32 and 
responsive to the reaction transmitting member 35, and through the input 
shaft 17. 
The output shaft 32 slidably extends through the shank portion of the 
housing 13 while maintaining liquid tightness by means of seal members 40, 
41 mounted on the housing 13 and a sleeve 39, respectively. In the 
embodiment shown, the master cylinder is illustrated as a two circuit type 
including the piston 31 integral with the output shaft 32 and serving as a 
primary piston and also including a secondary piston 42 which is slidably 
fitted between the output shaft 32 and the sleeve 13 while maintaining 
liquid tightness. A spring 43 interposed between the both pistons 31, 42 
normally maintains the piston 42 in abutment against a stop ring 44 formed 
on the output shaft 32. 
Except for the specialized construction of the pistons 31, 42, the master 
cylinder 2 of two circuit type is similar to a corresponding master 
cylinder of two circuit type which is well known on the art, and therefore 
will not be described in detail. In the drawing, numeral 45 represents the 
pressure chamber of one circuit, 46 the pressure chamber of the other 
circuit and 47 a reservoir. 
It will be noted that a given clearance .delta. is defined between the 
reaction disc 34 and the reaction transmitting member 35, and an apparatus 
50 for adjusting the clearance .delta. is mounted on the free end of the 
input shaft 17. Specifically, the apparatus 50 comprises a shaft-like 
member 51 forming part of the input shaft section 17a and responsive to 
the reaction transmitting member 35, and a hollow shaft-like member 52 
forming a portion of the input shaft section 17a on which the second valve 
seat 18 forming the valve mechanism 15 is defined. The shaft-like member 
51 extends through and threadably engages the hollow shaft-like member 52 
so as to achieve an interconnection which permits their relative position 
to be adjusted in the axial direction. Normally, the both members are 
connected together integrally by a nut 53. The both members 51, 52 
slidably extend through the closure member 20 into the front shell 1a 
while maintaining hermetic seal, thereby permitting the relative position 
of the both members 51, 52 to be adjusted through the opening 9a formed in 
the front shell. It will be noted that a pair of slits 54, 55 are formed 
in the free end of the respective members 51, 52 to permit a tool, not 
shown, to be engaged therewith. 
With the described arrangement in its non-operative position shown, the 
valve element 19 is seated upon the first valve seat 16 to interrupt the 
communication between the variable pressure chamber 8 and the atmosphere 
while the valve element 19 is removed from the second valve seat 18 to 
permit a communication between the constant pressure and the variable 
pressure chamber 7, 8. Accordingly, a negative pressure which is 
introduced into the constant pressure chamber 7 through a corresponding 
inlet, not shown, which is formed in the front shell 1a, is also 
introduced into the variable pressure chamber 8 through the passages 26, 
25 through the clearance between the valve element 19 and the second valve 
seat 18 and through the passages 27, 28, producing no pressure 
differential across the power piston 4. 
When a brake pedal, not shown, is then depressed to move the input shaft 17 
to the left, the valve element 19 is seated upon the second valve seat 18 
to interrupt the communication between the constant pressure chamber 7 and 
the variable pressure chamber 8, and a continued movement of the input 
shaft 17 to the left causes the valve element 19 to be disengaged from the 
first valve seat 16. Thereupon, the atmosphere is introduced into the 
variable pressure chamber 8 through the filter 24 and the passage 27, 
producing a pressure differential across the power piston 4 and the valve 
body 5, thus causing them to move to the left against the resilience of 
the return spring 12. 
As the valve body 5 moves to the left, the thrust therefrom is transmitted 
to the primary piston 31 within the master cylinder 2 through the reaction 
disc 34, the cylindrical member 33 and the output shaft 32, supplying a 
braking liquid pressure to wheel cylinders of respective circuits, not 
shown, in the similar manner as with a master cylinder of two circuit type 
known in the art. In the meantime, a reaction force from the brake is 
transmitted to the brake pedal from the reaction disc 34 through the 
reaction transmitting member 35, the pin 37 and the input shaft 17. 
When the brake pedal is then released, the valve mechanism 15 switches to 
the condition shown, thus returning the arrangement to its non-operative 
position. 
The adjustment of the clearance .delta. between the reaction disc 34 and 
the reaction transmitting member 35 can be accomplished by inserting a 
tool through the opening 9a, formed in the front shell 1a, to loosen the 
nut 53, and then engaging a suitable tool with the respective slits 54, 55 
to rotate the both members 51, 52 relative to each other, thereby causing 
a relative axial displacement of the members. It will be noted that the 
adjustment of the clearance .delta. is facilitated in this manner. In 
addition, it should be noted that such adjustment can be implemented while 
the master cylinder 2 is integrally connected to the shell 1 to allow the 
actual braking liquid pressure prevailing within the master cylinder 2 to 
be determined, thus allowing an accurate clearance adjustment. When a 
proper clearance .delta. is established, the nut 53 may be tightened to 
complete the adjustment. 
It should be understood that the reaction transmitting member 35 may be 
formed integrally with the input shaft 17. Also, it is unnecessary that 
both members 51, 52, which form the apparatus for clearance adjustment, 
project through the closure member 20 into the front shell 1a. 
While the invention has been shown and illustrated above in terms of an 
embodiment thereof, it should be understood that a number of changes, 
modifications and substitutions will readily occur to one skilled in the 
art without departing from the scope and spirit of the invention and that 
the invention is therefore solely defined by the appended claims.