Note: Descriptions are shown in the official language in which they were submitted.
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BRA~E SHOE
Background of the Invention
This application is a division of application Serial No.
310,237 filed August 29, 1978.
This invention relates to a brake mechanism for an automotive
vehicle and more specifically to an improved fabricated brake shoe
which is particularly useful in a brake mechanism employing
floating brake shoes.
For purposes of this invention, floating brake shoes shall
mean those brake shoes which when^assembled in a brake mechanism
are actuated at one end and, although anchored at the other end to
resist the brake torque, they are not fixedly anchored to the brake
mechanism support, but are free to move or float relative to an
abutment serving as the anchoring surface. The improved brake
shoe of this invention is particuIarly useful in dual actuated
brake mechanisms in which both brake shoes become leading brake
shoes. One such brake mechanism is disclosed in U.S. Patent
3,269,492, which issued to F.T. Cox, et al, on August 30, 1966.
The fabricated brake shoes employed in that as well as other
brake mechanisms are comprised of an elongate curved table which
supports the friction lining and a web extending along a sub-
stantial length of the inner surface of the table to reinforce
the brake shoe table and provide means for mounting and moving
the brake shoe. By the term "fabricated brake shoe," we mean a
brake shoe in which the web is formed as a separate element and
welded to the inner surface of the table. The brake shoe webs
have commonly been dimensioned to extend from edge to edge across
; the full arcuate length of the table. This reinforces the
arcuate length of the brake shoe and provides maximum support to
the longitudinally spaced edges of the brake shoe table at the
relatively high temperature and pressure generated under dynamic
braking conditions.
The structure of the fabricated brake shoe of the present in-
vention deviates from this practice and improves performance under
dynamic braking conditions.
Summary of the Invention
The present invention consists of a fabricated brake shoe
comprising an elongate curved table having longitudinally spaced
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edges and a web secured to the radially inner surface of said
table between said edges, and at least one of said edges being
bent to form a lip extending laterally across said table and
inward adjacent one end of said web.
In a preferred embodiment of the invention, the end of the
web at the trailing edge of the brake shoe is spaced inward from
the radially inner surface of the table to provide a relief space.
The provision of this relief space is a feature claimed ~ se in
- the parent application referred to above.
In the improved brake shoe structure described herein the lip
distributes the load laterally across the trailing edge of the
table and, since the lip extends longitudinally beyond the trailing
edge of the web, it also provides additional strength extending
circumferentially in both directions away from the trailing edge
of the web. The lip thus enhances both the circumferential and
lateral strength of the brake shoe table adjacent the trailing
edge of the web.
The invention also provides a brake assembly comprising a
support, a pair of fabricated floating brake shoes slidably carried
by said support, each brake shoe comprising an elongate curved
table having longitudinally spaced edges and a web secured to the
radially inner surface of said table between said edges, a brake
drum mounted for rotation about said brake shoes, means for moving
each brake shoe outward into frictional contact with said brake
drum, means abutting one end of each said brake shoe web and pre-
venting rotary movement of its respective brake shoe in response to
friction contact with said brake drum, and a iip bent inwardly at
said one end of each said brake shoe, each said lip being formed
from a portion of its respective brake shoe table extending beyond
said brake shoe web and t-raversing its respective brake table.
The above and other features and advantages of an embodiment
of the invention will be apparent from the following description
of such ernbodiment.
Brief D~s ription of t~he~Drawings
In the drawings, wherein like reference numerals denote like
parts;
Figure 1 is a side elevation of a brake assembly incorporating
the present invention;
Figure 2 is a fragmentary view, partly in section and enlarged
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showing portions of the brake assembly in Figure li
Figure 3 is a ~iew taken along the line 3-3 of Figure 2.
- Descript`io~ `of t~e`Prefe`rr-d Embodiment
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With reference to the drawings, there is shown a wedge
actuated brake assembly generally designated by the numeral 10.
The brake assembly is supported on a spider 11 secured by a
plurality of bolts 12 to a flange 14 which may be formed
integrally with or welded to the axle housing 15. The brake
actuating mechanisms are contained within and supported by the
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actuator housings 16 and 18 formed integrally with the spider
11 .
As best shown in Figure 3, the actuator housing 16, which
is identical to actuator housing 18, is provided with aligned
cylindrical bores 19 and 20 which slidably support tappet
assemblies 21 and 22 and an opening on the reverse side of the
spider through which a brake actuating plunger extends. The
inner end of the brake actuating plunger is formed as a wedge
24 and carries a roller mechanism 25. The roller mechanism 25
engages the inner ends of the tappet assemblies 21 and 22 and
moves the tappet assemblies axially outward in the bores 19
and 20 in response to inward movement of the wedge 24. The
tappet assembly 21 is comprised of an inner screw 26, a nut 28
and a ratchet mechanism for rotating the nut 28 relative to
the screw 26 to automatically adjust the brake running
clearance in response to wear. A star wheel 29 is integrally
formed on the end of screw 26 and provides means for manually
adjusting the brake clearance. The tappet assembly 22 may
comprise a plunger fitted with a dust shield 23.
Corresponding components of the actuator housing 18 are
identified by the same reference numerals as used in
describing the components of actuator housing 16.
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The brake assembly 10 includes a pair of fabricated brake
shoes 30 slidably carried by the spider 11. Each brake shoe is
comprised of an elongate curved table 31 and a web 3~ secured
to the radially inner surface 32 of the table 31. A
substantial length of the radially outer edge 35 of the web is
in abutment with and secured by welding to the inner surface
32 of the brake shoe table 31 and an end portion 36 of the web
is spaced radially inward from the surface 32 of the table 31
to provide a relief 38 at the trailing edge 39 of the brake
; shoe. The web end portion 37 at the leading edge ~3 of the
brake shoe may also be spaced inward from the table 31.
However, it is not considered necessary to provide a relief at
the leading edge of the brake shoe since, as soon will become
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apparent, the longitudinally spaced edges 39 and 43 of the
brake shoe 30 are subject to different effects when the brake
assembly is actuated.
The brake shoe tables 31 support friction lining 40 and
are formed as a lip 41 at the trailing edge 39 of each brake
shoe 30. The lip 41 of each brake shoe 30 extends inward
adjacent the end portion 36 of the brake shoe web and, as best
shown by Figure 3, extends laterally across the full width of
the brake shoe table 31.
The brake shoe webs 34 are slidably guided by spring
clips 42 secured to the spider 11. The opposite ends of the
brake shoe webs are biased into contact with the ends of the
tappet assemblies extending from the actuator housings 15 and
18 by a pair of return springs 44. The actuator housings 16
and 18 are each disposed bet~een adjacent ends of the brake
shoe webs 34 and, when the brake assembly is actuated, the
wedges 24 move into the actuator housings 16 and 18 and drive
the tappet assemblies 21 and 22 outward in their respective
bores. The tappet assemblies move the brake shoes 30 outward
2~ until the friction lining 40 contacts a cylindrical friction
surface of a brake drum 45 secured to a wheel, not shown, but
mounted for rotation about the brake shoes 30 and axle housing
15 .
As the friction lining contacts the friction surface of
the brake drum, the torque tends to move the brake shoes 30 in
the same direction the drum is rotating. Thus, if the brake
drum 45 is rotating counterclockwise, as indicated by the
arrow in Figure 1, frictional contact between the friction
~; lining 40 and the brake drum 45 tends to move each of the brake
shoes 30 in a counterclockwise direction and the tappet
assemblies 22 serve as abutments anchoring that end, i.e., the
trailing edges 39 of each brake shoe, to resist the friction
induced torque.
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Aithough the tappet assemblies 22 anchor the trailing
edges 39 of the brake shoes 30, as best shown by Figure 3, the
trailing edges of the brake shoes are not fixedly anchored to
the tappet assemblies 22. The ends 3O of the brake shoe webs
34 at the trailing edges of the brake shoes are free to slide
outward on the inclined abutting sur~aces of the tappet
assemblies 22.
The trailing edges of the brake shoes 30 are slidably
anchored in areas of the brake assembly where the brake drum
is subject to significant distortion under dynamic braking
conditions. Although the brake drum 45 is shown in Figure 1 to
be circular and concentric with tbe brake shoe tables 31, when
the brake assembly is actuated, the Qressure applied by the
tappet assemblies 21 and 22 and the temperature generated by
frictional contact with the brake lining 40 causes the brake
drum 45 to distend in the vertical direction relative to the
orientation of Figure 1. The brake drum 45 contracts in the
horizontal direction and, as represented by phantom lines in
Figure 3, moves toward the actuator housings. Thus the
configuration of the brake assembly 10, as shown by Figures 1
- and 3, undergoes significant dimensional changes under dynamic
braking as the anchor ends 36 of the brake shoe webs slide
outward toward a contracting section of the brake drum 45.
The relief 38 provided between the end portion 3~ of the ``
brake shoe web 34 and the brake shoe table 41 permits the
` trailing edge 39 of the brake shoe table to move inward toward
the ~eb and accommodate the dimensionally changing
configuration of the brake assembly under dynamic braking
` conditions. This reduces the pressure level at the trailing
edge of the brake shoe. The lip transversing the brake shoe
table 31 structurally reinforces the unsupported trailing edge
of the brake shoe and distributes the remaining pressure
across the width of the brake shoe table to prevent lateral
distortion under dynamic braking conditions.
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The brake shoe structure of the present invention
provides for more uniform wear of the friction lining material
and minimizes undesirable vibration by avoiding the hish
localized pressure previously encountered at the trailing edge
of the brake shoe.
The relief may be provided to conventional brake shoes by
cutting or sawing a portion of the web away at the trailing
edge of the brake shoe. However, it is preferred to form a
major portion of the outer edge of the brake shoe web to the
same radius of curvature as the inner surface of the brake
shoe table and to blend that radius into a smaller radius of
curvature at the trailing edge of the brake shoe web. The
smaller radius is preferably selected to enable the end
portion of the brake shoe web to support the trailing edge of
the brake shoe table after the trailing edge has been
deflected inward under synamic braking conditions.
Significantly improved performance has been achieved in
tests conducted on a 15-1/2 inch nominal diameter brake
assembly of the type shown in Figure 1 by utilizing brake
shoes having tables formed from a highly ductile, .179 inch
thick by 8 inches wide by 16 inches long SAE No. 1020 steel
sheet. The inner surface of the brake shoe tables and the
outer edge of the brake shoe webs formed to a radius of about
7-1/4 inches and a radius of about 7 inches was blended for an
arcuate distance of about one inch at the trailing edge of
each brake shoe web. The radii forming the outer edge of the
brake shoe webs were off-set to provide a wedge-shaped relief
about one inch long and increasing from a gap of zero to about
- .075 inches at the trailing edge of the brake shoe.
The invention may be embodied in other forms without
departing from the spirit or essential characteristics
thereof. The foregoing description is, therefore, to be
considered as illustrative and non-restrictive, the scope of
the invention being defined by the appended claims and all
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changes to the described embodiment which co~e within the
meaning and range of equivalency of the claims are therefore
intended to be embraced thereby.
