Vacuum brake power booster with metal cup supporting reaction disk

A metal cup accommodating a reaction disc and the end of a push rod is fixed with respect to a control valve housing of a vacuum brake power booster. The manner of fixation is of simple design, allowing the parts to be manufactured at low cost and offering ease of mounting. According to the invention a metal cup is supported in axial direction at the front side of the control valve housing and is retained by a retaining clip in a positive locking fit with the control valve housing.

BACKGROUND OF THE INVENTION 
The invention relates to a vacuum brake power booster for automotive 
vehicles, with a housing which is sealingly subdivided into at least one 
vacuum chamber and at least one power chamber by at least one axially 
movable wall. The axially movable wall is prestressed by means of a return 
spring, and has a mechanically actuatable control valve serving to connect 
the power chamber to the vacuum chamber, and to the atmosphere. An axially 
movable control valve housing is made of thermoplastic material and is 
furnished with a metal cup that accommodates a reaction disc of 
high-elasticity material and a push rod abutted against the reaction disc. 
The push rod transmits the brake power to an actuating piston of a master 
cylinder that is positioned on the vacuum side of the housing of the brake 
power booster. 
A vacuum brake power booster of this kind is known from German Patent 
Application No. 29 18 907, which was published without examination. In 
German Application No. 29 18 907, the metal cup is screwed into the 
control valve housing with a sealing ring interposed and is furnished with 
a radial flange. A diaphragm disc, forming the movable wall, is retained 
at the control valve housing in axial direction by the radial flange. 
In the aforementioned vacuum brake power booster, the screwed union 
provided between the metal cup and the control valve housing, and the kind 
of sealing used involves elevated manufacturing and assembly costs, that 
have to be considered less advantageous. 
SUMMARY OF THE INVENTION 
It is, therefore, the object of the present invention to provide, in a 
vacuum brake power booster, a simple design for fixing the metal cup in 
the control valve housing. The design allows the parts to be manufactured 
at low cost and offers ease of assembly, while maintaining simultaneously 
the reliable operation of the brake power booster. 
According to the invention, this object is achieved by axially supporting 
the metal cup at the front side of the control valve housing and retaining 
the metal cup by means of a retaining clip which is in a positive locking 
fit with the control valve housing. 
In one embodiment of the invention, the retaining clip is formed by a 
U-shaped bracket with a central through opening for the push rod and with 
arms connecting at their ends behind two projections disposed radially 
opposite each other on the control valve housing. This configuration 
achieves an effective guidance of the push rod and protects against its 
falling out. 
A considerable simplification of the control assembly of the vacuum brake 
power booster is obtained in that, adjacent the metal cup, the control 
valve housing is provided with an annular collar whose height or axial 
length is slightly larger than the material thickness of the metal cup to 
form a sealing surface that interacts with the reaction disc. 
According to another advantageous feature of the invention, the reliability 
of operation is increased in that the ends of the retaining clip are 
radially secured by a diaphragm disc that forms the movable wall and is 
fixed to the control valve housing. 
In particular, in a brake power booster of tandem design whose second 
movable wall is connected to the control valve housing by means of a guide 
tube, a major improvement of the guidance of the control valve housing, 
and a reduction of the risk of buckling out of the push rod, is attained 
in that the outside diameter of the metal cup corresponds to the inside 
diameter of the guide tube. The metal cup is also formed with radial 
cutouts and, in the range of fixation of the guide tube at the control 
valve housing, the retaining clip is secured in radial direction by the 
guide tube. 
In accordance with another version of the vacuum brake power booster, in 
which the metal cup is positioned within a cylindrical recess in the 
control valve housing, the object of the invention is attained in that the 
bottom of the recess is furnished with an annular collar whose height or 
axial length is slightly larger than the material thickness of the metal 
cup to form a sealing surface that interacts with the reaction disc. In 
this configuration, the metal cup is secured in the axial direction by 
means of a retaining member that is slidable into the control valve 
housing in the radial direction. As a result of this configuration, the 
push rod is protected from falling out. 
In an advantageous development of the subject matter of the present 
invention, the retaining member has a U-shaped configuration. The 
retaining member has arms engaging within grooves provided in the control 
valve housing bounded by two annular segment-shaped retaining elements 
positioned radially opposite each other at the control valve housing. In 
this context, the control valve housing is furnished, in the range between 
the retaining elements, with axial cutouts extending to the bottom of the 
recess and into air guide ducts formed in the control valve housing. These 
provisions allow large cross-sectional areas for the air flow, and the 
release times of the brake power booster are thereby reduced to a 
considerable extent. 
An improved guidance of the control valve housing in a tandem design of the 
brake power booster is achieved in that the retaining member is formed 
with guide edges which interact with the inside wall of the guide tube. 
A simplified design of the vacuum brake power booster is attained by a 
further feature of the present invention wherein the metal cup is provided 
at its edge with at least two locking apparatuses arranged opposite each 
other which interact with the retaining elements that are formed on the 
control valve housing. 
Finally, in order to obtain protection against the push rod falling out, it 
is contemplated that one embodiment the metal cup may be formed with 
radial depressions in its edge ranges positioned between the locking 
apparatuses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The housing of the vacuum brake power booster shown in FIG. 1 is comprised 
of two parts which are coupled together at a point of connection. Only the 
brake pedal-side housing 2 is partly illustrated for clarity. The interior 
space of the housing is subdivided by a movable wall 3 into a vacuum 
chamber 20 which is connected through a connecting bore to a vacuum source 
(not shown in more detail in the drawing), and a power chamber 23. The 
movable wall 3 is formed by a diaphragm disc 19 and by a rolling diaphragm 
18 adhering to it in the power chamber 23. The movable wall 3 is fastened 
to a control valve housing 10, shown as a two-part assembly in the example 
illustrated in the drawing, so that the rolling diaphragm 18 straddles 
with its inner portion the internal edge of the diaphragm disc 19 and 
seals it with respect to the control valve housing 10. With its 
cylindrical guide section 4, the control valve housing 10 projects from 
the booster housing 2 and is protected by means of a boot 52 against 
soiling of its surface. The control valve housing 10 seals off the power 
chamber 23 toward the atmosphere by means of a slip guide ring 5. 
A control rod, including a piston rod 13 and a valve piston 16, is axially 
slidably positioned within the interior space of the control valve housing 
10. The control rod is connectable through a clevis (not shown in detail 
in the drawing) to the brake pedal of an automotive vehicle. The control 
valve housing 10, furthermore, contains a control valve arrangement 9 
which is actuated by the valve piston 16 and which controls through ducts 
the pressure differential between the vacuum chamber 20 and the power 
chamber 23. The front section 7 of the control valve housing 10 is 
positioned in the vacuum chamber 20 and is formed with a stepped bore 12 
which accommodates a transmission disc 6 and the valve piston 16. At the 
front face of the front section 7, a metal cup 11 is axially retained by 
means of a retaining clip 8. A high-elasticity reaction disc 14 and a 
thrust plate 17 are arranged in metal cup 11. A push rod 21 is abutted 
against thrust plate 17 for actuating a master brake cylinder fixed to the 
front face of the booster housing. 
In this configuration, the metal cup 11 is preferably provided with an 
opening in its bottom whose diameter corresponds to that of an annular 
collar 15 at the front section 7, such that the annular collar 15 projects 
into the metal cup 11. The axial length of the collar 15 is slightly 
greater than the material thickness of the bottom of the metal cup 11 
surrounding it, so that upon actuation the front surface of the collar 15 
interacts with the reaction disc 14 as a sealing surface. The retaining 
clip 8 is formed in the shape of a steel bracket whose arms 22 make 
contact with their ends behind two projections 24, 25 which are formed 
radially opposite each other at the front section 7. In this context, the 
diaphragm disc 19 has such a configuration that in its range of fixation 
at the front section 7 of the control valve housing 10 it radially secures 
the arms 22 of the steel bracket 8 which make contact behind the 
projections 24, 25. 
In addition to that, the steel bracket 8 is formed in its center with an 
opening 26 (FIG. 3) accommodating the push rod 21 which passes into an 
axially extending guide attachment 27. 
The vacuum brake power booster of tandem design shown in FIG. 2 provides in 
its housing a partition wall 46 which divides two booster chambers 47, 48 
from each other. A second movable wall 51 subdivides the second booster 
chamber 48 into a second vacuum chamber 49 and a second power chamber 50. 
The second movable wall 51 is in power-transmitting connection with the 
control valve housing 10 by means of a guide tube 28 which is sealedly 
guided in the partition wall 46. The metal cup 11 is axially abutted 
against the control valve housing 10 and is guided in tube 28. The steel 
bracket 8, having arms 22 retaining the metal cup 11, is radially secured 
in the range of fixation of the guide tube 28 to the control valve housing 
10 by a radial abutment of the inside wall of the guide tube 28. The metal 
cup 11 has cutouts 29 formed at its edge. In order to render possible an 
evacuation of the power chambers 23, 50, the control valve housing 10 is 
furnished with two radially opposed vacuum ducts 44 (FIG. 3, lower half) 
in its ranges positioned between the projections 24, 25. 
In another embodiment of the vacuum brake power booster illustrated in 
FIGS. 4, 5 and 6, the metal cup 11 is positioned in a recess 30 disposed 
in the front section 7 of the control valve housing 10. The bottom of the 
recess 30 presents a projected ring-shaped collar 31. The collar 31, whose 
axial length is slightly larger than the material thickness of the metal 
cup 11, interacts with the reaction disc 14 and safely seals off the 
vacuum chamber 20 with respect to the power chamber 23. Axial fixation of 
the metal cup 11, which is inserted in the control valve housing 10, is 
provided by a retaining member 32. The retaining member 32 is slidable 
into the control valve housing 10 in radial direction and preferably has a 
U-shaped configuration with two arms 33 extending parallel to each other 
that in the assembled condition engage, with a prestress in radial 
direction, grooves 34 formed in the control valve housing. 
The grooves 34 are bounded by two retaining elements 35 which are formed in 
an annular segment shape radially opposite each other at the front section 
7. If and when the U-shaped retaining member 32 is intended for use in a 
tandem brake power booster which is furnished with the guide tube 28 
mentioned above, then it will be appropriate to furnish the retaining 
member 32, in its range positioned outside the two arms 33, with guide 
edges 36 whose contour corresponds to the inside wall of guide tube 28. 
Finally, the metal cup 11 is furnished at its edge with two opposed locking 
apparatuses 37, 38 that interact in the assembled condition with the 
retaining elements 35 which are formed on the control valve housing 10 
which is partially illustrated in FIG. 7. Each locking apparatus 37, 38 is 
provided with a straight locking section 39 extending radially toward the 
outside which, upon incorporation of the metal cup 11 in the control valve 
housing 10, is introduced into the groove 34 defined by the retaining 
element 35 by rotating the control valve housing 10. The locking section 
39 is preferably positioned between two antirotating means 40, 41 which 
may, for example, be configurated in the shape of spring notches (right 
hand half of the metal cup 11) which, in the event of a rotating motion of 
the metal cup 11, are urged down by their engaging the retaining elements 
35, and which project on either side of the associated retaining element 
35 upon the introduction of the locking section 39 into the groove 34. The 
distance of the two notches preferably corresponds approximately to the 
width of the retaining element 35. 
The left hand half of the metal cup 11, when viewing the drawing, shows a 
slightly modified design of the locking apparatus 38 in which the one 
antirotating means 40 is formed by a spring notch, while the other 
antirotating means 41 is formed in the shape of an axially extending 
supporting area 42 that is positioned at right angles with the locking 
section 39 and which forms one part with the locking section 39. 
In order to be able to effectively secure the push rod (not illustrated in 
this Figure) against falling out, radial depressions 43 are provided in 
the edge ranges of the metal cup 11 positioned between the locking 
apparatuses 37 and 38, one of which is illustrated diagrammatically in 
FIG. 7. 
In order to create favorable flow conditions, in particular during 
evacuation of the power chamber 23, axial cutouts 45 are provided in the 
control valve housing 10 in the range between the retaining elements 35. 
The axial cutouts extend down to the bottom of the recess 30 into the 
range of the mouth of the air guide ducts 44. 
While certain embodiments of the invention have been described in detail 
above in relation to a vacuum brake power booster, it will be apparent to 
those skilled in the art that the disclosed embodiments may be modified. 
Therefore, the foregoing description is to be considered exemplary rather 
than limiting, and the true scope of the invention is that defined in the 
following claims.