Note: Descriptions are shown in the official language in which they were submitted.
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This is a divisional patent application based upon
Canadian application Serial Number 325,584, filed April 17, 1979.
This in~ention relates to a disc brake for an auto-
motive vehicle.
More specifically, the invention concerns an improved
hydraulic seal for hydraulically sealing the brake actuating
piston within the cylinder. Conventional sealing means of the
prior art are designed to not only provide a hydraulic seal be-
tween the piston and cylinder but also to exert a resisting force
tending to prevent full retraction of the piston upon release of
the brakes. Such a seal design is illustrated in U.S. Patent
3,998,466.
Although effective, such sealing means may at times
create too much resistance thereby causing the friction pads to
excessively drag.
It is therefore an object of the present invention to
provide a piston seal with mitigates this disadvantage of the
prior art.
It is another object of the invention to provide a
piston seal arrangement whereby the force resisting piston re-
tractlon may be varied or tailored to the particular brake
structure.
The present invention provides a seal for a piston of
a hydraulic vehicle braking system, the seal comprises an elasto-
meric annular ring having a cylindrical outer peripheral surface
portion and a frusto-conical outer peripheral surface portion
sloping outwardly to the cylindrical outer peripheral surface
portion.
The invention further provides a seal for a piston of
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a hydraulic vehicle braking system, the seal comprising an
elastomeric annular ring having a cylindrical outer peripheral
surface portion and a frusto-conical outer peripheral surface
portion sloping outwardly to the cylindrical outer peripheral
surface portion.
The invention will be more readily apparent from the
following description of an embodiment shown in the drawings,
in which:-
Figure 1 is a perspective view ofadiscbrake asviewed
from the outboard side;
Figure 2 is a perspective view of the disc brake shownin Figure 1 as viewed from the inboard side;
Figure 3 is a rear elevational view of the brake shown
in Figure 1 as viewed from the inboard side;
Figure 4 is a front elevational view of the disc brake
shown in Figure 1 as viewed from the outboard side;
Figure 5 is a top plan view of the disc brake shown
in Figure l;
Figure 6 is an exploded perspective view, partly
broken away and partly in diagrammatic form, of the disc brake
shown in Figure l;
Figure 7 is a longitudinal cross-sectional view taken
along line 7-7 of Figure l;
Figure 7A is an enlarged view of the circled portion
of Figure 7 showing details of the piston hydraulic seal con-
struction;
Figure 7B is a plot of force resisting piston return
versus return travel of the piston;
Figure 8 is an enlarged cross-sectional view taken
along line 8-8 of Figure 5;
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Figure 9 is an exploded perspective view showing the
pin bushing and sleeve assembly and details;
Figure 10 is a cross-sectional view taken along line
10-10 of Figure 5 showing the assembled position of the anti-
rattle clip shown in Figures 12 and 13;
Figure 11 is a cross-sectional view taken along line
11-11 of Figure 5 showing the assembled position of the anti-
rattle clip shown in Figures 12 and 13;
Figure 12 is an elevational view of an anti-rattle
clip used in the disc brake as shown in Figure l;
Figure 13 is a plan view of an anti-rattle clip used
in the disc brake as shown in Figure l;
Figure 14 is an enlarged cross-sectional view of the
piston dust boot used in the disc brake as shown in Figure l;
Figure 15 is a cross-sectional view taken along line
15-15 of Figure 3;
Figure 16 is a front elevational view of the inboard
brake shoe assembly used in the disc brake shown in Figure l;
Figure 17 is a bottom view of the brake shoe assembly
shown in Figure 16;
Figure 18 is an end view of the brake shoe assembly
shown in Figure 16;
Figure 19 is a cross-sectional view taken along line
19-19 of Figure 16;
Figure 20 is an elevational view looking outboard at
the outboard brake shoe assembly used in the disc brake shown
in Figure l;
Figure 21 is a bottom view of the brake shoe assembly
shown in Figure 20; and
Figure 22 is a cross-sectional view taken along line
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22-22 of Figure 20.
The disc brake shown in Figures 1 to 7 comprise a
generally C-shaped caliper 10 slidably supported on pins 15L
and 15R secured to anchor plate 11 which is secured to a fixed
part of the vehicle. Caliper 10 has a front or outboard leg
13 and a rear or inboard leg 12 interconnected by a bridge por-
tion 14. The inboard caliper leg 12 contains the hydraulic
actuation means comprising a piston 16 slidable in cylinder 17
and engaging back plate 18 of the inboard friction pad 20. An
indirectly actuated outboard friction pad 21 has its back plate
22 engaged by the outboard caliper leg 13. When hydraulic
fluid is forced into the actuator cylinder through inlet port
23, inboard pad 20 is urged into frictional engagement with
the inboard side of rotor 24 whereupon caliper 10 is caused to
slide on pins 15L and 15R thereby applying an inwardly directed
force to outboard backing plate 22 causing frictional engage-
ment of outboard friction pad 21 with the outboard surface of
rotor 24.
Anchor plate 11 has two axially and outward extending
arms 26L and 26R which extend over the periphery of the rotor
and slidably support both the inboard friction pad backing plate
18 and the outboard friction pad backing plate 22 upon rail
guides 30L and 30R by engagement of inboard backing plate guide
grooves 32L and 32R and ou~board backing plate guide grooves
33L and 33R. By this construction all braking friction torque
is transferred directly to anchor plate support 11 and hence to
the vehicle frame (not shown). The caliper 10 serves primarily
as means for applying the necessary clamping forces to the
brake shoe assemblies without having im~arted thereto the
braking torque.
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Pins 15L and 15R are secured to anchor plate 11 by
threaded engagement and are each received in a bushing assembly,
as shown in Figure 9, which extends through bores appropriately
positioned and configured in the caliper inboard leg 12.
Referring now to Figures 8 and 9, in which reference
numeral 15 is used to indicate either of pins 15L and 15R, bush-
ing 40 is made of an elastomeric material, such as rubber, and
comprises two zones. Zone A, extending between outboard flange
45 and inboard flange 46 extends through bore 34 in the caliper
inboard leg 12 as shown in Figure 8. Flanges 45 and 46 posi-
tion, lock and retain bushing 40 within bore 34 and prevent
axial movement of the bushing with respect to the caliper in-
board leg. Positioned inside zone A of bushing 40 is sleeve
50, made of any suitable plastic or other low friction material
such as "Teflon"*. Sleeve 50 functions as a low friction bear-
ing within bushing 40 and is retained axially between radially
extending portion 49 of Flange 45 and annular recess 43. The
inside cylindrical surface of zone A of bushing 40 may be pro-
vided with annular grooves 42 to allow for radial displacement
of material upon insertion of pin 15 into sleeve 50. Sleeve 50
is preferably provided with a longitudinal gap 51 permitting
ease of insertion into bushing 40. Zone B of bushing 40, ex-
tending inboard of caliper leg 12, is provided with a multiple
number of annular ribs 41 generally having a circular cross-
section; a preferable number being three as shown in Figures 8
and 9.
During assembly of the caliper brake, pin 15 is in-
serted into bushing 40 from the inboard side, first passing
through zone B, then through sleeve 50 and threaded into or
otherwise fastened to anchor plate 11. Annular recess 43 is
* Registered Trade Mark
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thus provided to permit radial deflection of sleeve 50 into
recess 43 thereby allowing passage of the pin leading edge
through sleeve 50 without pushing the sleeve through the bush-
ing ahead of the pin thusly dislodging sleeve 50 from its
desired position within zone A. Further, upon insertion of pin
15 into bushing 40 ribs 41 in zone B slidingly engage pin 15,
and are slightly compressed or deformed as shown in Figure 8.
Once assembled and during brake actuation the caliper
is free to slide axially upon pins 15L and 15R. Lip 44 of
flange 45 acts as a seal preventing entrance of dirt or other
contaminants into the bushing assembly of each pin. Annular
ribs 48, because of their seal like engagement of the pin, form
annular contamination chambers 4 7 and 4 8 thereby preventing
dirt or other contaminants from entering the bushing from the
inboard side. Thus a reasonably dirt free environment is
assured between each pin and its sleeve 50.
Caliper 10, supported upon pins 15L and 15R extending
inboard from anchor plate 11 has no other principal means of
support. Outboard leg 13 extends laterally between and abut-
tingly engages anchor plate rails 30L and 30R through verticalabutment surfaces 35 and 36 respectively. Caliper 10 is
principally restrained from circumferential movement resulting
from any possible brake shoe frictional drag forces, which may
be imparted to caliper 10, by the interaction of abutment sur-
faces 35 and 36 with anchor plate rails 30L and 30R respect-
fully. The caliper is further restrained from possible radial
or vertical movement by the interference of horizontal abut-
ment surface 37 with anchor plate rail 30R.
Thus caliper 10 is supported and free to move in an
30 axial direction upon pins 15L and 15R passing through the
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caliper inboard leg 12 and restrained from circumferential or
vertical movement through interference abutments on the outboard
leg. Movements of or forces imparted to caliper 10 as a result
of brake activation are transmitted directly to anchor plate 11
without passing through supporting pins 15L and 15R.
Figure 15 presents a cross-sectional view taken along
line 15-15 of Figure 3 showing details of the rear portion of
the hydraulic cylinder in claiper inboard leg 12. The cylinder
rear wall 52 is provided with boss-like port 23 protruding there-
from and allows for cavity 53 to the rear of cylinder wall 17.Thus, the cylinder inlet 54 may be bored directly into cavity
53 requiring no interior machining of the cylinder rear wall 52.
Figures 16 to 19 show the preferred structure of the
inboard brake shoe assembly 19. Friction pad 20 is bonded,
using any suitable bonding technique known to the industry, or
may be integrally molded upon backing plate 18 using readily
known methods. Backing plate 18 has a multiplicity of recesses
or apertures such as the double step bore 27 shown in Figure 19
extending through the backing plate. During molding of friction
pad 20 upon backing plate 18, friction material is forced into
and through the apertures and after curing serves to resist
shear forces be~ween the pad 20 and backing plate 18 during
brake application.
Friction pad 20 is further provided with double cham-
fered leading and trailing edges 28 and 29, respectively. When
new, or so long as the frictional surface of pad 20 wears evenly,
the centroid thereof will coincide with the center of pressure
P, which is fixed by the hydraulic piston geometry. Thus a
uniform loading is applied to the rotor by pad 20 cver its
friction surface. Should, for example, the leading portion of
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pad 20 wear unevenly or at a faster rate than the trailing por-
tion, the frictional surface area increases by reason of cham-
fer 28 thus causing the centroid of the friction surface area
to translate to C' or C", depending upon the particular wear
pattern experienced. However, the center of pressure P remains
fixed and coincident with the piston axial center-line, causing
an increased surface pressure loading over the trailing portion
of the pad friction surface and a decrease in surface loading
over the leading portion of pad 20. Thus the pad tends to cor-
rect its wear pattern and return the centroid to the center ofpressure P thereby restoring uniform loading and pad wear. By
reason of the double chamfer, friction pad 20 will tend to cor-
rect for uneven wear in both the circumferential and radial
directions.
Figures 20 to 22 show the preferred configuration of
the outboard brake shoe assembly 25. Similar to the inboard
brake shoe assembly 19 described above, friction pad 21 is
molded onto backing plate 22 which also has double step bore
apertures therein receiving friction material therein to resist
shear forces between pad 21 and backing plate 22. Although the
outboard friction pad 21 may be provided with double chamfered
leading and trailing edges, it is not believed necessary be-
cause of the uniform force applied to backing plate 22 by the
caliper outboard leg 13.
As an alternative and upon reuse of backing plates 18
and 22, the double step bore apertures 27 may serve to accommo-
date the application of riveted frictional material thereto.
One merely applies the friction pad to the reverse side of the
backing plate and the double step bore 27 accommodates the rivet
fastener therein.
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Outboard brake shoe assembly 25 is configured so as
to prevent its inadvertent installation on the inboard side of
rotor 24. Therefore the width W of friction pad 21 is such
that pad 21 interferes with anchor plate arms 26L and 26R pre-
venting insertion of brake pad assembly 25 on the inboard side
of the rotor. As a further prevention against installing the
outboard brake shoe upon the inboard side of the rotor when the
pad 21 is worn thin the backing plate width is such that it
abuts against anchor plate ledges 38L and 38R (Figure 6), thus
preventing sliding of guide grooves 33L and 33R along guide
rails 30L and 30R.
Figures 12 and 13 show anit-rattle clip 60 which is
preferably constructed of spring steel wire comprising two
longitudinally extending segments 61 and 62 (see also Figure 5)
projecting oppositely away from looped hook 63. Inboard seg-
ment 61 terminates in looped projection 64 which serves as a
finger hold for insertion or removal of clip 60. Clip 60 is
positioned as shown in Figures 5, 10 and 11 such that inboard
segment 61 and outboard segment 62 lie axially along rail guide
30R and are respectively disposed within notches 31 and 39 of
inboard backing plate 18 and outboard backing plate 22. Looped
hook 63 extends under and engages the bottom surface of caliper
bridge 14 thereby providing a torsional spring force in clip
segments 61 and 62 tending to force backing plates 18 and 22
into frictional engagement with rail guides 30L and 30R thereby
preventing rattling of the backing plates upon rail guides 30L
and 3OR.
To further assist in applying a positive force upon
backing plates 18 and 22, it is preferred to preload the spring
clip legs 61 and 62 as shown by the broken line extensions of
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Figure 13. Alternatively the legs 61 and 62 may be preloaded
as shown by the broken line extensions shown in Figure 12 or
preloaded in both directions. However it has been found that
preloading as shown in Figure 13 alone proves satisfactory.
Figure 14 presents an enlarged cross-sectional view
of piston dust boot 70. Dust boot 70 comprises an integral
one piece molding of an elastomeric material, such as rubber,
having an annular bead 71 suitably received in annular groove
38 of piston 17, and flexible bellows portion 72, which radially
extends to and terminates at annular flange 73. Annular flange
73 has molded therein a rigid annular ring 74 and is fixedly
received in annular groove 75 cut into caliper inboard leg 12
about the hydraulic cylinder bore 17.
By encapsulating ring 74 within elastomeric material,
a compression fit is thereby obtained within groove 75 assuring
retention of dust boot 70. Further, ring 74 and groove 75 are
sealed from moisture and other contaminants which would tend to
cause corrosion making it difficult to remove boot 70, and to
require groove maintenance prior to replacing boot 70 upon
brake servicing.
Sealing piston 16 hydraulically within cylinder 17
is accomplished by use of annular seal means 55 in the form of
an elastomeric ring positioned within annular groove 56 in the
wall of cylinder 17 as shown in Figure 7A. The floor of groove
56 has a cylindrical portion thereof 57 axially paralleling
cylinder 17 and a frusto-conical portion 58 sloped at angle x
of 7 to 2~. Preferably angle x is fifteen degrees (15) and
the ratio of portion 57 to portion 58 is within the range of 1:1
and 4:1 and preferably three to one (3:1).
Seal means 55 has cylindrical and frusto-conical outer
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surface portions corresponding in orientation and axial length
to groove portions 57 and 58.
It has been common practice in the industry to pro-
vide a groove floor sloped at approximately 7 so as to cause
the seal to compressingly grip the piston thereby resisting in-
board movement of the piston upon deactivation of the brake.
However, it has been noticed that many times too much resistance
is experienced causing the brake shoe assemblies to slightly
drag. By varying the ratio of floor portion 57 to portion 58
various piston resistance forces may be obtained thereby per-
mitting one to tailor such resistance to the particular brake
assembly without need for specially engineered elastomeric
seals. In addition to varying the ratio of floor portion 57 to
58 the slope or angle x may also be varied, thus adding another
variable to consider. The seal 55 may be either of rectangular
cross-section or may be shaped to conform to the floor con-
figuration.
Figure 7B presents a typical plot of seal compressive
force against piston ~ravel. The curve identified as "Standard
Groove" represents the force distribution for a groove floor
sloped at a constant 7 as known in the prior art. The curve
identified as "Improved Groove" represents the force distri-
bution for a groove floor as shown in Figure 7A having a ratio
of portion 57 to portion 58 of 3:1 and x being 15.
The foregoing description presents the preferred em-
bodiment of this invention. Modifications and alterations may
occur to those skilled in the art which will come within the
scope of the following claims.
