CA1076494A

CA1076494A - Brake assembly

Info

Publication number: CA1076494A
Application number: CA275,145A
Authority: CA
Inventors: William J. Williams
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1976-05-17
Filing date: 1977-03-30
Publication date: 1980-04-29
Also published as: AU520585B2; GB1580963A; AU2385677A; MX144779A; JPS6157501B2; FR2352218A1; BR7703183A; DE2721707C2; SE7705710L; JPS52140774A; SE8100845L; SE448254B; DE2721707A1

Abstract

BRAKE ASSEMBLY

Abstract of the Disclosure A brake assembly including 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. The brake shoe webs are recessed at one end to engage a fixed pin. The recess provides an arcuate bearing surface adapted to bear against a portion of the pin and permit pivoting movement of thebrake shoe about the pin as the brake is actuated and released. The recess is so oriented relative to the pin that the pin will engage an end portion of the arcuate bearing surface and prevent the recessed end of the brake shoe from moving away from the pin when the brake assembly is actuated.

Description

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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 ' .:

10'~ 4 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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~0'7~;4~4 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 u~ .
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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1076~94 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 to a force tending to move said brake shoe away from said anchor pin.

2. The brake shoe defined by claim 1 wherein said recess is comprised of an inner arcuate bearing surface and a portion of said web extending tangentially from said arcuate bearing surface at one end thereof.

3. The brake shoe defined by claim 2 wherein said arcuate bearing surface extends through an arc no greater than 180° from end to end.

4. The brake shoe defined by claim 2 wherein said one end of said arcuate bearing surface is disposed to abut said cylindrical surface of said anchor pin in response to a force tending to move said brake shoe away from said anchor pin.

5. The brake shoe defined by claim 2 wherein said portion of said web extending tangentially from said arcuate bearing surface is disposed to abut said cylindrical bearing surface of said anchor pin in response to a force tending to move said brake shoe away from said anchor pin.

6. The brake shoe defined by claim 2 wherein said one end of said arcuate bearing surface and said tangentially extending portion of said brake shoe web comprise a portion of said brake shoe web formed to be hooked around and abut said anchor pin in response to a force tending to move said brake shoe away from said anchor pin.

7. The brake shoe defined by claim 1 wherein said recess is in the form of a slot comprised of an inner arcuatc bearing surface having oppositely disposed ends and a mouth portion formed by integral web portions at the opposite ends of said arcuate bearing surface and said slot is so oriented that the web portion at one end of said arcuate bearing surface will abut said anchor pin in response to a force tending to move said brake shoe away from said anchor pin.

8. A rigid brake shoe having a dual continuous web structure includ-ing an open recess formed at one end of each web, each said recess being laterally aligned with the other recess and comprised of an inner arcuate bearing surface having opposite ends and a mouth portion formed by integral shoe portions at the opposite ends of said arcuate bearing surface, said mouth portions being of a width to slidably engage said arcuate bearing surfaces with a fixed pin and said arcuate bearing surfaces being so oriented as to bear against a complementary arcuate surface of said pin in response to an outwardly directed force applied at the other end of said brake shoe with said pin abutting against a portion of said recesses disposed relative to said pin to prevent substantial movement of said brake shoe in response to a force tending to move said brake shoe away from said pin.

9. In a brake assembly for a vehicle wheel, a support, a pair of rigid brake shoes, a rotary cam actuator disposed between adjacent ends of said brake shoes, an open ended recess formed in the web at the end of each of said brake shoes opposite from said adjacent ends, each said recess being adapted to be radially, slidably mounted to a pin carried by said support, each said recess having an inner arcuate bearing surface disposed to engage a surface portion of said pin on both sides of a plane passing through the center of said pin and parallel to a major axis of said brake assembly which axis passes through the center of said rotary cam with the lower portion of the arcuate bearing surface extending at least 5° on the remote side of said pin and adapted to abut said pin and prevent further movement of said brake shoe in response to a force tending to move said brake shoe away from said pin.

10. The brake assembly defined by claim 9 wherein each of said recesses is a slot comprised of an inner arcuate bearing surface and a mouth portion formed by integral brake shoe portions at the opposite ends of said arcuate bearing surfaces and said slot is so oriented that said arcuate bearing sur-faces are disposed to engage said pin on both sides of said plane.

11. In a brake assembly for a vehicle wheel, a support, a pair of rigid brake shoes, a rotary cam disposed between adjacent ends of said brake shoes, an open ended recess formed in the end of the web of each brake shoe opposite from said adjacent ends, each said recess being adapted to be radially, slid-ably mounted to a pin carried by said support, each of said recess having an inner arcuate bearing surface disposed to engage a surface portion of said pin and a brake shoe portion extending tangentially outward from at least one end of said arcuate bearing surface, said brake shoe portion extending sub-stantially beyond a radial plane passing through the center of said pin and the axis of rotation of said wheel on the side of said plane remote from a major portion of said arcuate bearing surface, and adapted to abut said pin and prevent further movement of said brake shoe in response to a force tend-ing to move said brake shoe away from said pin.