Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a means for separating
a first piston from a second piston in a tAndem master
cylinder.
U.S. P~tent No. 3,818,706 dlscloses a brakin~ system
with a tandem ~ast~er cyllnder having a piston positioned in
a bore by first and second springs to establish first and
second pressuri~ing chambers therein. The volumetric size
of the first and second pressurizing chamber are matched to
the actuation fluid requirement of drum brakes and disc
brakes located in the braking system. If the first and second
springs are not matched, a delay in actuation between the
drum brakes and disc brakes can result.
To prevent such a delay, it was found that by caging
one of the springs, the size of the first and secondary
chambers could be positively established.
U.S. Patent No. 3,686,8b4 discloses a tandem master
cylinder with`a typical caged spring for establishing the
position of a first piston relative to a second piston. The
caged spring has a retainer which is threadedly attached to
a second piston by a long bolt. However, under some con-
ditions of operation the threaded connection has failed and
allowed the second piston to shift ln the bore and thereby
change the operating characterlstics o the tandem master
cyllnder.
The present invention resides in a master cylinder
having a housing defining a bore therein with a pair of
plstons slldably mounted in the bore, the pistons cooperating
wlth one another and the housing to create a first pressure
chamber between corresponding ends of the pistons and a
second pressure chamber between the other end of one of the
pistons and the end of ~he bore. Cage means is provided
in the first chamber yieldably-maintaining each of the
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pistons a predetermlned distance from the other piston, the
cage means havlng a first retainer with a conlcal body
extending from a base, the base engaging one of the pair
o~ pistons. The conical body has an inwardly pro;ecting
lip for establishing an axial opening. The cage means has
a disc for engaging the other of the pair of pistons, the
disc having a first contour and a concentric second contour
with a first diameter opening located adjaceat the first
contour and a second diamater opening located in the axial
center of the second contour. The first diameter opening
is connected to the second diameter opening by a slot. The
cage means has a spring that surrounds the conical body.
One end of the spring engages the first contour of the disc,
the spring moving the first retainer and the disc away from
each other, The first contour malntains the spring ln a
substantially radlal position in the bore, and the cage
means has ~ stem w:Lth a first head and a second head, the
first head being larger than the axial opening 9 and the
second head being larger than the second diameter opening
in the disc. The first head engages the lip on the first
retainer and the second head is located in the second diameter
opening in the axial center of the second contour ln the disc
after passing through the first diameter opening and free~y
moving radlally ln the slot, l`lle second head en8~ges the
secolld conto~r when the pair of pistons move relative to
each other within the bore to hold the stem in the axial
ccnter o~ the bore.
It is therefore the ob~ect of this invention to
provide a master cylinder with a caging means which separates
a first plston from a second piston to establish the volume
of first and second pressurizing chambers located in the
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master cylin~er.
It is another obJect of this lnvention to provide
a means for fastening a stem between a first retainer and
n second retalner to hold a 3prLng in a caged position.
It ls a still urther object of this invention for
providing a fastener means having an opening with a first
diameter section offset from a second diameter section to
permit a head on a stem to pass through the first diameter
section and thereafter be shifted to the second diameter
section to retain a resilient means in a caged condition.
These and other objects will be apparent from
reading this specification and viewing the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illustration of a braking
system including a sectional view of a master cylinder
incorporating the teachings of my invent:lon; and
Figure 2 is a sectional view taken along lines 2-2
of Figure 1.
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DETAILED DESCRIPTION OF THE DRAWINGS
The braking system lO has a master cylinder 12 connected to
front wheel brake~ 14 ani rear wheel brakes 16 by conduits 18 and 20
respectively. A push rod 22 and a pedal 24 provide a linear input for
moving a first piston 26 and a second piston 28 in bore 30 of the m~ster
cylinder 12 .o create the energizing force. The position of the second
piston 28 in bore 30 is established by a ca~lng means 32. The position of
the second ptston 28 determJnes thc slze of a fTrst pressurizin~ chamber 34
and a second pressurtzlng chamber 36 1n bore 30. The size of the first
pressurizing chamber 34 and the second pressurizing chamber 36 determines
the volume of fluid capable of betng supplied to the front wheel disc brakes
14 and the rear wheel drum brakes 16 through the conduits 18 and 20.
Thc first piston 26 has a bearing surface 38 with a diameter
which substant;ally f~lls the bore 30 and separates a compensator port 40
from a relief port 42. The fTrst piston 26 has a shoulder 4fl which cooper-
ates with bearing surface 38 to hold the seal 44 in a fixed position wTthin
bore 30. A seal 44 prevents communlcation of fluid between the first
pressurizing chamber 34 and the relief chamber 46.
The second piston 28 has a cylindrical body 50 with a bearing
surface 52. The bearing surface 52 has a diameter substantTally equal to
bore 30 and separates a compensator port 54 from a relief port 56.
shoulder 58 on the cyllndrlcal body 50 forms a g~roove 60 with bearing
surface 52. A seal 62 located In ~roove 60 prevents fluld communlcation
between the second pressurlzlng chamber 36 and the rellef chamber 64. A
return spring 66 located between the bottom 61 oF bore 30 and shoulder 58
holds thc second plston 28 agalnst the caglng means 32 and the ft rst piston
26 agalnst stop 68
The caging means 32 Includes a ~Irst retalner 70 connected to a
second retainer 72 by a stem 74 for holding a spring or resilient means 76
In a caged condltinn.
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The first retainer 70 has a base 78 which abuts shoulder
48 on the first piston 26 and a conical or cylindrical body 80
which extends into the first pressurizing chamber 3~. The cylindri-
cal body 80 has an inwardly projecting lip 82 -Eor forming an axial
opening 84.
The second retainer 72 includes a disc 86, see Figure
2, with an opening having a first diameter section 88 offset from
a second smaller diameter section 90 by an interconnecting slot
89. A first contour 92 on disc 86 forms a guide for holding one
end of spring 76 in substantially a fixed position in bore 30.
A second annular contour 94 on disc 86 provides a barrier for
holding the stem 74 in an axial position with respect to bore 96
in the second piston 28.
The stem 74 has a first head 98 located on a first
end 97 of a cylindrical body 75 and a second head 100 located
on a second end 99 of the cylindrical body 75. The first head
98 has a larger diameter than the second head 100. l'he diameter
of the second head 100 is substantially equal to axial opening
84 in the first retainer 70 and -the first diameter section 88
in disc 86.
MODE OF ASSEMBLY OF THE CAGING MEANS
. . _ .
The spring 76 is located on base 78 of -the first re-
tainer 70. The second head 100 on stem 74 is passed through open-
ing 84 and the first head 98 brought into engagement w.ith lip 82.
The disa ~6 1~ loc~ted on th~ end o~ ~the sprin~ 76 by contour 92.
A compressive force is applied to the first retainer 70 and the
second retainer 72 to compress spring 76. When a sufficient
compr~iv~ force is applied, the second head 100 passes through
the first diameter section 88. Thereafter, the second head 100
is shifted through slot 89 to the axial section 90 and the compressive
force is released. The second contour 94 holds the stem 74 in the
center of the disc 86. The length of stem 74 determines the length
of the caging means 32 and the volumetric size oE the pressurizing
chambers in a master cylinder. In order to change the size relation-
ship between a first chamber and second chamber in a master cylinde.r
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all that is required is -to change the stem 74 in the caging means
32.
MODE OF OPERATION OF THE EMBODIM~NT
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When an operator applies an input force to pedal 24,
push rod 22 moves the first piston 26 in bore 30 and produces a
- firs-t pressurizing ~orce in chamber 34. Movement of the ~irst
piston 26 is transmitted through caging means 32 into the second
piston 28. When the second piston 28 moves pas-t compensator port
54, a second pressurizing force develops in the second chamber 36.
As the first and second pressurizing forces increase, spring 76
is comp~essed to allow the first piston 26 to move toward the
second piston 28 at a different rate than the movement of the
second piston 28 toward the end 61 of bore 30. Relative movement
between the first piston 26 and the second piston 28, eliminates
the restraining forces on the stem 74. At this point, s-tem 7~ is
free to move axially with the confines of bore 30. However, bore
96 engages head 98 to prevent any lateral movement and maintain
the stem in a fixed axial position with respect to bore 30. When
the spring 76 is completely collapsed, end 102 on the ~irst piston
20 26 engages head 98 and moves the second head 100 on stem 7~ against
the bottom of bore 96 to manually move the second piston 28 in the
second chamber 36 and further pressurize the fluid contained therein.
Upon termination o~ the input ~'orce, spring 76 ~oves the
~irst pisto~n 26 and the second piston 28 away from each other and
return spring 66 again seats the first piston 26 in stop 68.
Thus, the caging means 32 makes it possible to provide
a means of establishing the size o~ the ~irst pressurizing chamber
without physically connecting the first piston 26 to the second
piston 28.
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