Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BRAKE ASSEMBLY
Background of the Invention
The present invention is directed to an improvement in vehicle
brake mechanisms and more specifically to a brake shoe for a vehicle brake
assembly.
The invention is particularly useful in a brake assembly which
includes a pair of brake shoes having adjacent ends pivotally mounted to
a support and a rotatable actuating cam disposed between the other ends of
the brake shoes. Rotary movement of the cam causes each of the brake shoes
to pivot outwardly about its pivot or anchor pin to contact the inwardly
facing friction surface of the brake drum. This type of brake assembly is
used for heavy duty brake applications which may employ a dual or a single
web brake shoe. The brake shoes may be cast or fabricated. The brake
shoes may also carry a roller type cam follower on the ends adiacent the
actuating cam. The opposite adjacent ends of the brake shoes may be mounted
for pivoting movement about a single anchor pin as disclosed in United States
Patent No. 3,398,814 or each shoe may be pivotally mounted for movement
about one of a pair of spaced anchor pins a$ disclosed in Patent No.
3,114,437.
Dual web brake shoes for the brake assemblies employing a pair
of spaced anchor pins are provided with axially aligned, laterally extending
bores in each of the webs at the end of the shoe to be pivotally mounted
to the support. The brake shoes are mounted to the assembly by aligning the
web bores on opposite sides of a bore through a boss formed on the brake spider
and inserting a pin axially through the spider bore and the coaxial brake
shoe bores. The pin, generally referred to as an anchor pin, may be press fit
to the boss and snap rings may be provided to the axially extending ends
of the pin to prevent axial displacement of the brake shoe relative ~o the
pin. This arrangement fixes the brake shoe against all movement relative to
the support except for the desired pivoting movement about the anchor pin.
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Some difficulties have been encountered with the foregoing
arrangement when it becomes necessary to remove the brake shoes for the
purpose of replacing or relining the same. Although the brake assemblies
are partly enclosed to protect the parts against road dirt and inclement
weather conditions, the parts are nevertheless subjected to dampness and
fluctuations in temperature which cause corrosion. The pins frequently
become seized in the spider bore and/or the brake shoe. This makes it
difficult to disassemble the brake mechanism since the pin must be
removed from its relatively tight fit in the spider bore. The anchor
pins are often driven from the assembly to free the brake shoes and
depending upon the degree of difficulty encountered this may cause
deformation of the spider or damage to the spider boss mounting the
anchor pin. If the spider is severely damaged, it may be necessary to
replace the spider on the axle housing or replace the entire axle assembly.
The foregoing difficulties are not frequently encountered in
brake assemblies of the type where the brake shoes are mounted for
pivoting movement about a single anchor pin. In that type of assembly
the adjacent ends of the brake shoe webs are each recessed to provide
arcuate bearing surfaces, less than 180 in arc, which are seated on
opposite sides of the anchor pin by a radially directed movement relative
to the pin. The open ended recesses provided to the brake shoe ends
permit assembly to and dlsassembly from the anchor pin without moving
the anchor pin relative to the spider. Although this arrangement provides
for ease of assembly and d~sassembly the brake shoes are not positively
secured to the anchor pin and may become self-actuating. That is, when
the brake assembly is actuated, the cam causes the brake shoes to pivot
about the anchor pin to bring the friction lining pads into contact with
the brake drum and thereby inhibit rotation of the brake drum and the
wheel to which it is attached. The friction force between the brake
drum and the linings secured to the brake shoes tends to draw the linings
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into further contact with the brake drum and thereby increase the magnitude
of the friction force. The effect the friction force will have on the
linings depends upon the direc~ion of rotation of the brake drum.
The friction force between the drum and the lining secured to one
of the brake shoes will be in the same direction as the force applied by
the cam actuator and will compliment the brake actuating force. The
friction force between the drum and the lining secured to the other brake
shoe will be opposite to the direction of the force applied by the rotatable
cam actuator. The friction force at the circumference of that brake shoe
will tend to move the brake shoe away from the anchor pin and toward the
actuating cam at the other end of the shoe. ~lowever, since there is no
space for movement toward the other end of the brake shoe, the brake drum
and the brake shoe will distort and the recessed end of the brake shoe
will move away from the anchor pin. This self-actuating movement of the
brake shoe causes unnecessarily rapid wear of the lining on the brake shoe ;
most often subject to "self-actuation" and uneven wear of the friction
- linings provided to the brake assembly. The movement also causes undesir- ;
able noise and chatter.
Summary of the Invention
The present invention provides a brake shoe including at least one
continuous rigid web having an open ended recess at one end, said recess
being of a width to radially, slidably engage a cylindrical bearing surface
of an anchor pin mounted to a support on a vehicle axle housing and being
oriented to pivot about said cylindrical bearing surface of said pin in
response to an outwardly directed force applied at the other end of said ~;
brake shoe and to abut said cylindrical bearing surface and prevent movement ;
of said brake shoe in response ~o a force tending to move said brake shoe
away from said anchor pin.
The invention and the advantages offered thereby will become
apparent from the following detailed description of the embodiment shown
by the accompany drawings.
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Description of the Drawings
In the drawings wherein like reFerence numerals refer to like
parts:
Figure 1 is a side elevation, partly in section, of a brake
assembly according to the present invention;
Figure 2 is a view, partly in section, taken along line 2-2
of Figure l; and
Figure 3 is a fragmentary view showing part of the brake shoe
and brake spider of the brake assembly shown by Figure 1.
Description of the Invention
With reference to the drawings there is shown a cam actuated ::
brake assembly generally designated by the numeral 10. The brake assembly
10 is supported by a spider 11 rigid with a vehicle axle housing 12. The
brake assembly 10 includes a pair of brake shoes 14 each of wh;ch is
pivotally mounted at one end to an anchor pin lS carried by the spider
11. The anchor pins 15 are each carried in a cylindrical bore 16 provided
through bosses 18. As best shown by Figure 2 the bosses 18 are formed as
depending integral parts of the spider 11 and are axially offset from the
upper portion of the spider 11. The offset permits the bosses 18 to be
located between the dual webs of the brake shoes 1~.
A cam 19 is mounted for rotary movement between the adjacent ends ~
of the brake shoes 1~ opposite from the anchor pins 15. The brake shoes .
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14 are each provided with a roller type cam follower 22. The cam is
nonrotatably secured to a cam shaft 20 mounted to the spider for rotary
movement in a bearing 21. The cam shaft is rotated by means not shown
to rock the cam 19 in a clockwise direction through an arc in the range of
10 to 30 degrees. The cam 19 provides an outwardly directed force to
the rollers 22 and the brake shoes 14 which cause the brake shoes to pivot
about the anchor pins 15. This movement forces the friction lining pads 24
into contact with the inwardly facing friction surface 26 of a brake
drum 25 secured by conventional means to a wheel rotatably mounted to a
spindle at the outer end of axle housing 12. When the brakes are released
the brake shoes 14 and the friction lining pads 24 are withdrawn from
contact with the brake drum surface 26 by a return spring 28 secured at
its opposite ends to the brake shoe webs.
The brake shoes 14 are dual web fabricated brake shoes. That
is, each brake shoe includes a pair of axially spaced webs 31 secured
to a table 32. The webs 31 are flat in a radial direction and curved in a
longitudinal or circumferential direction. The brake shoe table 32 is curved
in the circumferential direction and the webs 31 are welded in parallel
relation along the interior curved portion of the table. This provides a
generally rigid assembly of component parts to which the friction lining
pads 24 may be secured by rivets or by chemical bonding.
Each of the brake shoe webs 31 is provided with an open recess
34 at the end opposite the cam follower 22. The recess 34 is in the form
of a slot which includes an inner arcuate bearing surface 35 and a mouth
formed by integral brake shoe portions 36, 38 which extend tangentially
outward from the opposite ends of the arcuate bearing surface 35. The
bearing surface 35 is a semi-circular bearing surface adapted to engage a
complementary arcuate surface 17 of the generally cylindrical end portion 13
of anchor pin 15. The bearing surface 35 is comprised of an upper portion 37
and a lower portion 39. The recess 34 is canted so the upper and lower
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portions 37 and 39 of the bearing surface 35 are disposed to engage the
complementary arcuate surface 17 on both sides of a radial plane passing
through the center of anchor pin 17 and the axis of rotation of the wheel
carried by axle housing 12. The plane is represented by the line A in
Figure 3 which passes through the center of anchor pin 15 and the longitud~nal
center of axle housing 12 which is coaxial with the axis of rotation of
brake drum 25 and the wheel to which the brake drum is secured.
With reference to Figures 1 and 3, the outer end of the lower
portion 39 of arcuate bearing surface 35 and the web portion 38 of the
10 brake shoe 31 shown to the lef~ in the drawings are disposed to bear against
a portion of the complementary arcuate surface 17 to the right of the plane
represented by line A. When the brake assembly 10 is actuated with the
wheel and brake drum 25 rotating in a clockwise direction as indicated by
the arro\" in Figure 1, the friction developed between the pads 24 and surface
26 of brake drum 25 will develop a circumferentially directed force tending
to move both of the brake shoes 31 in a clockwise direction. The circumferentially
directed force between the brake drum 25 and the friction linings 24 secured
to the brake shoe 31 shown to the right in Figure 1 will tend to move that
brake shoe in the direction of its anchor pin 15 and thus compliment the
20 brake actuating force applied by cam 19. The circumferentially directed forcedeveloped between the brake drum 25 and the friction linings 24 secured to the
brake shoe 31 shown to the left in Figure 1 will be opposite to the force
applied by the cam 19 and, if that brake shoe were not restrained, the
circumferentially directed force would move the brake shoe away from the
anchor pin 15 in a clockwise direction toward the other end, that is, the
cam follower end of the brake shoe. The canted, recess 34 of the brake shoe
31 prevents such movement. A portion of the complementary arcuate surface 17
of pin 15 bears against the lower end surface 35 to the right of the plane
represented by line A and prevents the brake shoe from becoming disassociated
30 with the anchor pin.
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The width D of the mouth portion of recess 34 and the diameter
of the inner arcuate bearing surface 35 are selected so as to pcrmit the
brake shoes to be slidably engaged with the ends of the anchor pin 15
projecting from opposite sides of the spider boss 18. This arrangement
provides for ease of assembly and disassembly while the lower portion 39
of the recess 34 being hooked around a portion of the anchor pin 15
remote from the prinlary bearing portion prevents the brake shoes from
becoming self-actuat;ng.
Although for ease of manufacture and assembly it is preferred
10 to utilize a semi-circular inner arcuate bearing surface 35, the bearing
z surface of recess 34 may be less than 180 of arc from end to end. The
recess 34 or slotted ends of the brake shoes 31 are preferably canted at
an angle between about 5 and 30 relative to the plane represented by
the line A in Figure 3. With an inner arcuate bearing surface of 180
a! this disposes 5 to 30 of the arcuate bearing surface 35 at the lower
c~ end portion 39 on the right or remote side of the plane represented by
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the line A as shown in Figure 3.
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Although the recesses 34 may be of the same thickness as the ~ .
brake shoe webs 31 it is preferred to provide a greater surface area for
20 bearing against the anchor pin 15. The area of the arcuate bearing
surface 35 may be increased by providing a shoulder 40 around the recess
34. This may be accommodated by welding a U-shaped element to the
surface of the web 31.
During assembly the anchor pins 15 are preferably press fit,
to the bores 16 of the spider bosses 18. The brake shoes 31 are mounted
to the spider by sliding the recesses 84 in a generally radially direction
over the cylindrical ends 13 of the anchor pins 15 extending from the
opposite sides of the spider bosses 18. The webs 31 of each brake shoe
may be through punched with laterally aligned holes 41. A pin 42 is
30 inserted through the laterally aligned holes 41 of each brake shoe 14
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and the opposite ends of a retention spring 44 are hooked around each
respective pin 42. The retention spring 44 helps sprlng 28 urge the
arcuate bearing surfaces 35 provided at the recessed ends of the brake
shoes 14 into contact with the anchor pins 15.
A pair of snap rings 45 are seated in grooves 46 provided
adjacent the opposite ends of the anchor pins 151to prevent axial
movement of the brake shoe webs 31 relative to each anchor pin 15.
The remaining components of the brake assembly 10 as shown by
Figure 1 and the brake drum 25 are added in conventional manner.
The brake shoes of the invention thus, through the anchor pin
recesses and their particular orientation relative to the anchor pins
supported by the spider, provide for ease of assembly and disassembly
while avoiding the self-actuating feature associated with prior art
brake assemblies utilizing brake shoes having open ended anchor pin
recesses.
The invention may also be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
foregoing description is therefore to be considered as illustrative and
not restrictive, the scope of the invention being defined by the
appended claims, and all changes which come within the meaning and range
of equivalency of the claims are therefore intended to be embraced
thereby.
