Vacuum-type brake booster device having improved ease of mounting

A vacuum-type brake booster device for automotive use having a shape such that the mounting of the booster device and surrounding components inside the engine compartment of the vehicle is markedly eased. The shell of the booster device, and hence the diaphragm contained therein, has the shape in the plane of the diaphragm of a circle having a peripheral segment thereof removed. This causes the effective center of the diaphragm to be shifted from the center of the circle. The input and output shafts and the master cylinder are mounted on the shell aligned with the offset effective center of the diaphragm.

BACKGROUND OF THE INVENTION 
The present invention relates to a vacuum-type brake booster device for 
automotive use. More particularly, the invention relates to such a 
vacuum-type brake booster device which can easily be mounted, such as 
during the manufacture and repair of the vehicle, and which provides 
reduced interference with the mounting of other components of the vehicle. 
A vacuum-type brake booster device is generally mounted on the front 
surface of the fire wall of the vehicle, behind the wheel well and 
adjacent the rear end of the engine. The brake master cylinder is mounted 
on the forward end of the booster. Conventionally, it has been difficult 
to mount the booster device and master cylinder due to interference with 
other components of the vehicle, such as suspension components which are 
mounted at the adjacent wheel well. 
To overcome this difficulty, vacuum-type brake boosters have been proposed 
in which the shell or housing of the booster is made noncircular in cross 
section to thereby prevent side portions of the shell from interfering 
with the mounting of the device and the mounting of other components. 
Examples of such devices are shown in U.S. Pat. No. 2,896,586, issued July 
28, 1959 to Ayers, Jr., and U.S. Pat. No. 4,434,707, issued Mar. 6, 1984 
to Takeuchi et al. Although some advantages may be attained using such an 
approach, nevertheless, such vacuum-type brake boosters suffer from a 
drawback in that the effective pressure receiving area of the booster is 
excessively great. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a 
vacuum-type brake booster device for automotive use in which the 
above-discussed disadvantages have been eliminated. 
Specifically, it is an object of the present invention to provide a 
vacuum-type brake booster device having easier mounting, which does not 
interfere with the mounting of adjacent components, and which does not 
have an overly large pressure receiving area. 
In accordance with the above and other objects, the invention provides a 
vacuum-type brake booster device for automotive use in which the shell of 
the device, and hence the diaphragm of the device, are formed with a 
cross-sectional configuration which has symmetry in at most one axis in 
the plane of the diaphragm. Specifically, it is preferred that the 
cross-sectional shape of the shell and diaphragm be that of a circle 
having a cut-out segment. In this case, the effective center of the 
pressure receiving surface of the diaphragm of the booster device is 
offset from the center of the circle. The operating rods of the booster 
device and the master cylinder are centered on an axis extending through 
this offset center. Accordingly, interference with adjacent engine and 
vehicle body components is reduced, and the ease of mounting of the brake 
booster device itself is improved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, the mounting of a brake booster in an 
automotive vehicle will be described The brake booster device 1 is mounted 
on the front surface of the fire wall 3 of the engine compartment of the 
vehicle 2. The brake booster device 1 is mounted rearwardly of the cover 6 
of, for instance, the front right wheel well 4, the latter including 
strut-type front suspension components 5. As seen in FIG. 2, the cover 6 
has a concave portion 7 to the rear of the area where the suspension 
components 5 join the upper surface of the wheel well 4. 
In accordance with the invention, the shell 9 of the vacuum-type brake 
booster device has a generally circular shape in cross section, but with 
the circular shape being interrupted by an indented portion 8. The brake 
booster device 1 is mounted by bolts 10 on the fire wall 3 so that the 
indented portion 8 is adjacent the side of the wheel well 4. As is usual, 
an input shaft 15 and a valve body 16 extend rearwardly from the booster 
device 1 through a hole in the fire wall 3. The input shaft 15, of course, 
connects with a brake pedal. 
Referring now to FIG. 3, the construction of the vacuum-type brake booster 
device of the invention will be described in more detail. The input shaft 
15 extends through the valve body 16 and connects with a valve mechanism 
17. When a force is applied to the input shaft 15 by pressing on the brake 
pedal, the input shaft 15 is moved to control the fluid pressure 
introduced into a chamber 18 defined at the rear of the diaphragm 20 of a 
power piston assembly 21, as is well known. The effect is to amplify the 
force applied to the input rod 15, and to transmit the amplified force via 
an output shaft 22 to a master cylinder 23, the latter being mounted at 
the front end of the shell 9 in this embodiment. 
As shown in FIG. 4, the shell 9 of the vacuum-type brake booster device 1 
is generally circular but has an indented portion 8 where the line 
defining the edge of the shell 9, and hence the diaphragm 20, extends 
along a chord offset from the edge of the circle defined by the other 
portions of the shell 9 by a distance l. That is, the shell 9 and 
diaphragm 20 have symmetry along only one axis in the plane parallel to 
the surface of the diaphragm This causes the effective center of the 
diaphragm 20 (the center of the area where the pressure acts) to be 
offset, as shown in FIG. 4, from the center B of the aforementioned circle 
to a position A displaced by a distance .delta.. In accordance with one 
important aspect of the invention, the axes of the input and output shafts 
15 and 22, respectively, are aligned with the effective pressure center 
point . Accordingly, the master cylinder 23 is offset from the center B of 
the circle by the distance .delta.. 
As an example, if the outer diameter of the circular portion of the shell 9 
is 205 mm and the distance l is 40 mm, the offset .delta. from the center 
B of the circle is 12 mm. As may be appreciated from the diagram of FIG. 
2, this means that the master cylinder is moved 12 mm further away from 
the edge of the cover 6 of the wheel well 4 and the suspension components 
5 than was possible using a conventional brake booster device 
Additionally, in the example given, it is necessary to reduce the pressure 
receiving surface area of the diaphragm by only 13%, which is one half 
that required in the case where the shell of the booster device is made 
elliptical or oval, as in the prior art approaches described above. 
FIGS. 5 and 6 show an alternative embodiment of the invention. In this 
embodiment, the master cylinder 30 is provided on the side of the fire 
wall 3, that is, on the side opposite that employed in the first-described 
embodiment. In this case, the vacuum-type brake booster device 31 is 
mounted to the fire wall 3 by a bolt 32 extending through a flange of the 
master cylinder 30. An input shaft 33 of the brake booster device 31 
extends rearwardly, in substantially the same manner as in the 
first-described embodiment The input shaft 33 cooperates with a valve 
mechanism 35 disposed in a valve body 34 through which the shaft of the 
master cylinder 30 slidably passes. 
When the brake pedal is depressed, the input shaft 33 is moved to operate 
the valve mechanism 35 to control the amount of communication between a 
chamber 38, located to the rear of the pressure receptive surface 40 of a 
diaphragm 39, through a filter 36 to the atmosphere Accordingly, a power 
piston 41 is moved, transmitting its force to a reaction disc 42, a plate 
member 43 and output shaft 44. 
As seen in FIG. 6, the shell 37 of this embodiment of the brake booster 
device has a shape similar to that of the first-described embodiment. That 
is, the shell 37 has an indented portion 46 having an edge falling along a 
chord offset by a distance l from the edge of the circle defined by the 
other portions of the shell 37. This results in an offset .delta. of the 
effective center of the pressure receiving surface of the diaphragm of the 
device from the center B of the circle to a position A As in the 
first-described embodiment, this permits the master cylinder 30 to be 
mounted offset from the center of the circle. Accordingly, the ease of 
mounting of the device is improved and interference with the mounting of 
other components inside the engine compartment is reduced.