Two circuit vacuum brake booster

A two-circuit vacuum brake booster in which two pressure chambers are disposed in tandem with respect to each other, are atmospherically separated from each other and are controlled by its own valve arrangement. The two valve arrangements are arranged in a single control hub one behind the other and are simultantously controlled since their pistons are mechanically rigidly connected with one another.

BACKGROUND OF THE INVENTION 
The present invention relates to a two-circuit vacuum brake booster which 
includes two vacuum housings arranged axially behind each other and each 
provided with at least one wall which is movably arranged therein. The 
movable walls act on a force-transmitting member and subdivide each of the 
vacuum housings into a vacuum chamber and a working chamber. 
Such a two-circuit vacuum brake booster has come to knowledge from German 
Pat. No. DE-OS 2,314,792. Each of the movable walls is fastened on a 
different control hub each of which contains a valve arrangement including 
a valve piston and a plate valve. The control hubs are designed such that 
they will penetrate the vacuum and working chambers and will slidingly 
project from the vacuum housings in an axially sealed manner. The first 
control hub serves as the air supply to the first valve arrangement and 
houses the pedal-actuated piston rod which is mechanically connected with 
the first valve piston. A reaction mechanism adding up the pedal force and 
the boosting force, which acts on the movable wall, in a predetermined 
ratio will operate a control rod arranged in the control hub, the control 
rod acting on the second valve piston in the second control hub. The first 
control hub slides in a sealed manner in the first vacuum chamber in the 
second control hub and, thus, a separation of the two vacuum circuits is 
ensured. A further reaction mechanism will ensure that the boosting force 
of the second working chamber, together with the force transmitted onto 
the second valve piston, will act on the force-transmitting member sliding 
in the second control hub. The support for the reception of the 
force-transmitting member has a bore which ensures the supply of 
atmospheric air to the second valve arrangement. Upon actuation of the 
brake pedal, the axial displacement of the valve piston will provide for 
the supply of atmospheric air to the first working chamber, the forces 
that result from the pressure difference moving the first movable wall 
with the first control hub in the direction of the force-transmitting 
member. After overcoming of a first dead travel of the first vacuum 
booster, a piston rod which axially slides in the first control hub will 
move the second valve piston, atmospheric air also entering the second 
working chamber due to the air supply from the side of the 
force-transmitting member. After overcoming of the dead travel of the 
second vacuum booster, the second movable wall will transmit the forces by 
which it is acted upon to the force-transmitting member. In this 
arrangement, the costs are enormous because of the multitude of 
components. A multitude of seals and springs consume unnecessary energies, 
while the at times narrow air supply lines tend to rapidly become dirty if 
the operational surroundings are unfavorable which will result in a 
derogation of the operation of the vacuum booster. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a two-circuit vacuum 
brake booster which will feature a simple design and have a small number 
of components, thus offering a manufacture at favorable costs, ensuring a 
high degree of operational reliability, and quickly and safely responding 
without high energy losses and pedal travels thanks to the reduced number 
of seals, springs, and dead travels. 
A feature of the present invention is the provision of a two-circuit vacuum 
brake booster comprising a housing having a longitudinal axis; two 
pressure chambers disposed one behind the other coaxial of the axis within 
the housing; at least one movable wall disposed in each of the two 
chambers to divide each of the two chambers into a vacuum chamber and a 
working chamber, each of the movable walls acting on a force-transmitting 
member; and a control hub disposed in the housing coaxial of the axis 
supporting the force-transmitting member and to which each of the movable 
walls are fastened, the hub having disposed therein a valve and duct 
system for separate evacuation of and joint supply of atmospheric pressure 
to the working chamber of each of the two chambers. 
Because of the fact that the control hub has but one means of air supply 
for the pressurizing of the working chambers with air, several filter 
systems can be eliminated and a cheaper manufacture and service of the 
booster thus becomes possible. 
The fact that in a two-circuit vacuum booster provided with valve 
arrangements, each coordinated with a working chamber and known per se and 
including a valve piston, a plate valve and a valve spring, the valve 
piston being directly operable by the piston rod, which are arranged 
axially behind each other and the fact that the two valve pistons are 
rigidly connected with each other by means of a rod will provide for a 
simultaneous action of the boosting forces of the two vacuum circuits. The 
operating condition of the vacuum booster corresponding to the pedal 
position will rapidly and safely be reached since both valves will 
simultaneously adopt their operationally indicated positions. The direct 
mechanical force transmission from the pedal to the force-transmitting 
member will ensure that only one dead travel will have to be overcome. 
By providing the first valve piston, which is directly connected with the 
piston rod, with ducts in its guidance for the passage of air to the 
second valve arrangement a simple air supply will be ensured to the second 
valve arrangement. 
The structural design of the vacuum booster where the vacuum chambers are 
arranged in one housing and are separated by an atmospheric intermediate 
chamber will ensure that the housing of the vacuum booster is of a simple 
one-piece manufacture and the separation of the two vacuum circuits will 
be maintained. 
The assembly of the control hub from two components will enable a simple 
mounting of the second valve arrangement. The two components can be put 
together at the point of separation by threads, clamp fittings or similar 
means.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A cup-shaped housing 1 is closed by means of a cover 2. Two rigid walls 12 
and 13 fastened in housing 1 provide two pressure chambers 3 and 4 and a 
separating chamber 5. Separating chamber 5 communicates with the 
atmosphere via an opening 6. Pressure chambers 3 and 4 are each connected 
with non-illustrated vacuum pumps by means of connections 7 and 8, 
respectively, vacuum pumps being separately-working and serving as energy 
sources. A control hub 11 rigidly assembled from two components 9 and 10 
penetrates cover 2 as well as rigid walls 12 and 13. Walls 12 and 13 are 
rigidly connected with each other around the circumference of control hub 
11. This rigid connection also embraces control hub 11 with radial play. 
Atmospheric air penetrates through bores 20 until it reaches the 
circumference of control hub 11. Packing rings 14 and 15 which are 
positively arranged to the right and to the left of bores 20 in the walls 
seal pressure chambers 3 and 4 from the atmosphere around the 
circumference of control hub 11. The two components 9 and 10 join each 
other in pressure chamber 3. At this joint they are each provided with a 
circumferential collar 16, 17, the front faces of collars 16, 17 being 
firmly pressed together by a clamp fitting 19. A seal 18 is inserted 
between collars 16 and 17. A seal 59 inserted between cover 2 and 
component 9 seals pressure chamber 3 from the atmosphere. Component 10 of 
control hub 11 positively embraces a force-transmitting member 24 which is 
supported at the control hub via a reaction disk 25. The reaction disk 25 
at the same time is used as a seal between pressure chamber 4 and the 
hollow inner chambers 33 and 34 of control hub 11. Force-transmitting 
member 24 is sealingly led out of housing 1 and axially acts on a 
non-illustrated master cylinder of a hydraulic brake system. Two further 
walls 21 and 22 are spaced axially along and fastened to control hub 11. 
Wall 21 is disposed in pressure chamber 3 and wall 22 is disposed in 
pressure chamber 4. Wall 21 is positively resting in the direction of 
force transmission at a surrounding collar 23 of component 9 of control 
hub 11, while it is held against the direction of force transmission by 
the inside edge 60 of a rubber diaphragm 26 which is fixed around the 
circumference of control hub 11, outside edge 61 of diaphragm 26 being 
clamped between housing 1 and cover 2 and thus dividing pressure chamber 3 
into a vacuum chamber 27 and a working chamber 28. Wall 22 disposed in 
pressure chamber 4 is positively resting in a groove 64 at the head of 
component 10 in the direction of force transmission as well as against 
said direction. Pressure chamber 4 is likewise divided by a rubber 
diaphragm 29 into a working chamber 30 and a vacuum chamber 31. The inside 
edge 62 of rubber diaphragm 29 firmly embraces the control hub's 
circumference in working chamber 30, the outside edge being clamped 
between partition wall 12 and housing 1. Vacuum connections 7 and 8 each 
are coordinated with vacuum chambers 27 and 31. In vacuum chamber 31 a 
spring 32 acts against the direction of force transmission and keeps 
control hub 11 in its illustrated rest position. 
The interior of control hub 11 is hollow and is essentially divided by a 
step 35 into two chambers 33 and 34. Chamber 33 is axially open towards 
the atmosphere, the chamber 34 being axially confined by the head of the 
control hub. In the head of control hub 11 as well as in step 35, two 
supports are provided for two valve pistons 36 and 37, these supports 
being coaxial with respect to each other. Around the support, in a 
circular manner, the head of control hub 11 has a projection 55 which 
projects into chamber 34, the step 35 having a projection 54 which 
projects into chamber 33. The support of valve piston 37 has a radial 
groove 39 which is open towards chamber 34 and which communicates with 
working chamber 30 via a bore 40. Chamber 34 further communicates with 
vacuum chamber 31 via a bore 41 which is radially arranged outside and 
above projection 55. Moreover, valve piston 37 lies directly opposite 
reaction disk 25 of force-transmitting member 24 with a small play x. 
Besides a radial groove 42 which is open towards chamber 33, the support 
of valve piston 36 also has axial grooves 45 which provide an atmospheric 
connection between chambers 34 and 33. Groove 42 communicates with working 
chamber 28 via a bore 43 and vacuum chamber 27 communicates with chamber 
33 via the bore 44 radially arranged outside and above projection 54. 
Valve piston 36 is mechanically connected with a non-illustrated pedal by 
means of a stepped piston rod 46 coaxially projecting from control hub 11. 
Valve piston 37 is mechanically connected in a rigid manner with valve 
piston 36 by means of a piston rod 38. Further, chambers 33 and 34 each 
house plate valves 47 and 48, respectively, which are radially and axially 
bearing in a sealing manner against steps 49 and 50, respectively, in the 
housing of control hub 11. Valve plates 57 and 58 reinforced by an insert 
51 are penetrated by the piston rods 46 and 38, respectively, with radial 
play and are sealingly held in abutment against valve pistons 36 and 37 by 
means of springs 52 and 53, respectively. Spring 52 supports itself at a 
step of piston rod 46 and spring 53 supports itself at step 35 in the 
housing of control hub 11. Piston rod 46 is also embraced by a filter 56 
which is positively inserted in the housing of control hub 11, thus 
closing chamber 33 so as to ensure permeability with respect to air. 
For the sake of better understanding of the mode of operation of the 
booster assume that vacuum chamber 27 is coordinated with a vacuum circuit 
I and that vacuum chamber 31 is coordinated with a vacuum circuit II. 
In the illustrated rest position of the vacuum brake booster valve plate 57 
rests sealingly against valve piston 36 and valve plate 58 rests sealingly 
against valve piston 37. Both valve plates then will be at a distance y 
with respect to projections 54 and 55, respectively. Thus, it is ensured 
that--with the exception of that portion of chamber 33 which is separated 
by plate valve 47 and valve piston 36 and which is filled with atmospheric 
air--all other chambers are evacuated by the two vacuum circuits. Working 
chamber 30 communicates with vacuum chamber 31 and, hence, with the vacuum 
circuit II via bore 40, groove 39, projection 55 and bore 41. Working 
chamber 28 communicates with vacuum chanber 27 and, hence, with the vacuum 
circuit I via bore 43, groove 42, projection 54 and bore 44. Also, chamber 
34 is evacuated by the vacuum circuit I via axial grooves 45. If now the 
non-illustrated pedal is actuated, piston rod 46 will move axially and, 
thus, carry along valve pistons 36 and 37 in its movement. Thereby, valve 
plate 57 will come to rest against projection 54 and valve plate 58 will 
come to rest against projection 55. Thus, the vacuum circuits I and II 
will have been separated from the other chambers by means of plate valves 
57 and 58. The vacuum booster is now ready for operation. 
If valve pistons 36 and 37 are further axially displaced in the direction 
of force transmission they will lift off valve plates 57 and 58. Thus, the 
atmospheric pressure may flow from chamber 33 via groove 42 and bore 43 
into working chamber 28 and via axial groove 45, chamber 34, groove 39 and 
bore 40 into working chamber 30. Thereby, a pressure difference will be 
brought about between working chamber 28 and vacuum chamber 27 as well as 
between working chamber 30 and vacuum chamber 31. This results in forces 
acting on walls 21 and 22 in the direction of vacuum chambers 27 and 31. 
These forces will be transmitted to force-transmitting member 27 via 
control hub 11 and reaction disk 25. If the booster is fully actuated, all 
further forces that are applied to the piston rod 46 will directly be 
passed on to the force-transmitting member 24 via valve piston 36, piston 
rod 38, valve piston 37 and reaction disk 25. If piston rod 46 returns 
into the rest position, the valve pistons 36 and 37 will again come to 
sealingly rest at valve plates 47 and 48, respectively, and the direct 
communication between the vacuum and working chambers is, thus, restored. 
The vacuum circuit I will evacuate working chamber 28 as well as chamber 
34 and the vacuum circuit II will evacuate working chamber 30. Return 
spring 32 will return control hub 11 into its initial position. 
It should be pointed out that during the assembly of the two components 9 
and 10 of control hub 11 means will have to be used that will have no 
unfavorable influence on the stroke of the vacuum booster. Advantageous 
embodiments would be, e.g. stepped interlocking components that would be 
connected by means of a thread or that could be assembled by means of 
elements which may not be loosened again. 
While I have described above the principles of my invention in connection 
with specific apparatus it is to be clearly understood that this 
description is made only by way of example and not as a limitation to the 
scope of my invention as set forth in the objects thereof and in the 
accompanying claims.