GB1580963A

GB1580963A - Brake shoe and brake assembly

Info

Publication number: GB1580963A
Application number: GB13540/77A
Authority: GB
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1976-05-17
Filing date: 1977-03-31
Publication date: 1980-12-10
Also published as: DE2721707C2; JPS6157501B2; SE7705710L; DE2721707A1; AU520585B2; MX144779A; SE8100845L; FR2352218A1; AU2385677A; JPS52140774A; SE448254B; BR7703183A; CA1076494A

Description

(54) BRAKE SHOE AND BRAKE ASSEMBLY (71) We, ROCKWELL INTER NATIONAL CORPORATION, a corporation of the State of Delaware, U.S.A., having a place of business at 600 Grant Street, itt- sburgh, Pennsylvania, U.S.A., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a brake shoe for a vehicle brake assembly, and to such an assembly.

The brake shoe of the invention is useful in a brake assembly which includes a pair of brake shoes acting within a brake drum and having adjacent ends pivotally located by 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 radially outwardly of the drum axis about a 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 adjacent the actuating cam. The opposite adjacent ends of the brake shoes may be mounted for pivoting movement about a common single anchor pin as disclosed in United States Patent No.

3,398,814 or each shoe may be pivotally mounted for movement about a respective one of a pair of spaced anchor pins as disclosed in United States Patent No.

3,114,437.

Dual web brake shoes for brake assemblies are known employing a pair of spaced anchor pins 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 a base plate or spider of the brake support and inserting a pm axially through said bore and the coaxial brake shoe bores. The pin, generally referred to as an anchor pin, may be a press fit in 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 to 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.

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 anchor 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 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 fre gently 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 sur faces, less than 1800 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 disassembly from the anchor pin without moving the anchor pin relative to the spider.

Although this arrangement provides for ease of assembly and disassembly 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 acnhor 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 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 direction 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 com aliment 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. However, 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 selfactuating movement of the brake shoe causes unnecessarily rapid wear of the lining on the brake shoe most often subject to "sell-actuation" and uneven wear of the friction linings provided to the brake assembly. The movement also causes undesirable noise and chatter.

According to one aspect of the invention there is provided a shoe for a vehicle brake assembly of the kind including a drum and shoes acting within the drum, said shoe comprising a web carrying an arcuate table to the outer periphery of which is secured a friction lining pad, said web being formed at one end for engagement by an actuating element of said assembly and having at its other end a recess for pivotal engagement on a cylindrical portion of an achor pin of the assembly about which portion the shoe pivots in use; said recess being an openended slot having an arcuate bearing surface complementary to the periphery of said pin portion and a mouth of sufficient width to enable said surface to be seated on said periphery by radially directed movement relative to the pin the recess being so oriented in said web end that a portion of the bearing surface intersects and extends on both sides of a datum plane containing the axis of rotation of the drum for which the shoe is adapted to be used and the axis of curvature of the bearing surface, said intersection of said portion with said plane lying on the side of the latter axis remote from said axis of rotation, that part of said portion of the bearing surface which lies on the opposite side of said lane to the major part of the web extending not more than 30 beyond said plane, whereby displacement of said shoe from said pin portion in the circumferential direction of the actuating element as when the shoe operates in a trailing mode is operatively resisted while permitting slideable disengagement radially of said pin portion when said drum is removed from the assembly.

According to another aspect of the invention there is provided a brake assembly for a vehicle comprising a drum, a support, a pair of brake shoes acting within the drum and having webs carrying respective arcuate friction pads, an actuator disposed between adjacent one ends of the brake shoe webs, and a recess formed in the other end of each shoe web, each recess being in pivotal engagement with a cylindrical portion of a respective pivot pin carried by said support, each said recess having an arcuate bearing surface engaging the periphery of the associated pin portion and an opening enabling the shoe to be slideably disengaged radially from said pin portion after the drum is removed, a portion of said arcuate bearing surface extending on both sides of a datum plane containing the axis of the respective pin portion and the axis of rotation of the drum, said portion intersecting said plane on the side of said pin portion axis remote from said axis of rotation, that part of said portion of the bearing surface which lies on the opposite side of said plane to the major part of the respective web extending not more than 30 beyond said plane whereby displacement of said shoe from said pin portion when the shoe operates in a trailing mode during rotation of said drum is operatively resisted while permitting slideable disengagement radially of said pin portion with said drum removed from the assembly.

A preferred embodiment of the invention is now particularly described with reference to the accompanying drawings, wherein: Figure 1 is a side elevation, partly in section, of a brake assembly; Figure 2 is a view, partly in section, taken along line 2-2 of Figure 1; and Figure 3 is a fragmentary view showing part of the brake shoe and brake spider of the brake assembly shown by Figure 1.

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 which is pivotally mounted at one end to a respective cylindrical anchor pin 15 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 14.

An actuating cam 19 is mounted for rotary movement between the adjacent ends of the brake shoes 14 opposite from the anchor pins 15. Webs of the brake shoes 14 are each provided at one end 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 (as viewed in Fig. 1) through an arc in the range of 10 to 300. 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 to the outer periphery of table 32.

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 an open-ended slot which includes an inner arcuate bearing surface 35 and a mouth formed by integral brake shoe web portions 36, 38 which extend 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 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 portions 37 and 39 of the bearing surface 35 are disposed to enrage the complementary arcuate surface 17 on both sides of a radial datum plane including the axis of anchor pin portion 13 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 axis of anchor pin 15 (equivalent to the axis of curvature of bearing surface 35 as assembled) and the longitudinal 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 (e(luivalent to the axis of curvature of the actmg peripheral surface of the respective pad 24 when applied to the drum).

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 brake shoe 31 shown to the left 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 arrow 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 14 in a clockwise direction. The circumferentially directed force between the brake drum 25 and the friction linings 24 secured to the brake shoe 14 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 brake actuating force applied by cam 19. The circumferentially directed force developed between the brake drum 25 and the friction linings 24 secured to the brake shoe 14 shown to the left in Figure 1 (which is operating in a trailing mode) 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 show 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 14 prevents such movement. A portion of the complementary arcuate surface 17 of pin 15 bears against the lower portion 39 to the right of the plane rep resented by line A i.e. on the side of that plane remote from the major parts of the webs and prevents the brake shoe from becoming disassociated from the anchor pin.

The width D of the mouth portion of recess 34 and the diameter of the arcuate bearing surface 35 are selected so as to permit the brake shoes to be slidably engaged in a generally radial direction with the portions 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 major part of the web prevents the brake shoes from becoming self-actuating.

Although for ease of manufacture and assembly it is preferred to utilize a semicircular inner arcuate bearing surface 35, the bearing surface of recess 34 may be less than 1800 of arc from end to end. The recess 34 or slotted ends of the brake shoes 31 are canted at an angle of not more than 30 and preferably at least about 5 relative to the plane represented by the line A in Figure 3 so as to dispose 5 to 300 of the arcuate bearing surface 35 at the lower end portion 39 on the right or remote side of the datum plane represented by the line A as shown in Figure 3.

Although the web material at recesses 34 may be of the same thickness as the main part of brake show webs 31 it is preferred to provide a greater surface area for 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 fitted in bores 16 of the spider bosses 18. The brake shoes 14 are mounted to the spider by sliding the recesses 34 in a generally radially direction onto the cylindrical end portions 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 inserted through the laterally aligned holes 41 of each brake shoe 14 and the opposite ends of a retention spring 44 are hooked around each respective pin 42. The retention spring 44 helps spring 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 15 to 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 mounted in conventional manner.

The brake shoes as described 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 self-actuating.

WHAT WE CLAIM IS:- 1. A shoe for a vehicle brake assembly of the kind including a drum and shoes acting within the drum, said shoe comprising a web carrying an arcuate table to the outer periphery of which is secured a friction lining pad, said web being formed at one end for engagement by an actuating element of said assembly and having at its other end a recess for pivotal engagement on a cylindrical portion of an anchor pin of the assembly about which portion the shoe pivots in use; said recess being an open-ended slot having an arcuate bearing surface complementary to the periphery of said pin portion and a mouth of sufficient width to enable said surface to the seated on said periphery by radially directed movement relative to the pin, the recess being so oriented in said web end that a portion of the bearing surface intersects and extends on both sides of a datum plane containing the axis of rotation of the drum for which the shoe is adapted to be used and the axis of curvature of the bearing surface, said intersection of said portion with said plane lying on the side of the latter axis remote from said axis of rotation, that part of said portion of the bearing surface which lies on the opposite side of said plane to the major part of the web extending not more than 30 beyond said plane, whereby displacement of said shoe from said pin portion in the circumferential direction of the actuating element as when the shoe operates in a trailing mode is operatively resisted while permitting slideable disengagement radially of said pin portion when said drum is removed from the assembly.

2. A shoe as in Claim 1 wherein said part of said portion of the bearing surface extends at least about 5 beyond the datum plane.

3. A shoe as in Claim 1 or 2 wherein said arcuate bearing surface extends through an arc no greater than 1800 from end to end.

4. A shoe as in Claim 1, 2, or 3 including a pair of said webs in parallel spaced relationship and provided with similar laterally aligned said recesses for pivotal engagement on cylindrical portions of a common said anchor pin.

5. A shoe as in any one preceding claim including a shoulder around the recess to increase the effective area of the arcuate

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. resented by line A i.e. on the side of that plane remote from the major parts of the webs and prevents the brake shoe from becoming disassociated from the anchor pin. The width D of the mouth portion of recess 34 and the diameter of the arcuate bearing surface 35 are selected so as to permit the brake shoes to be slidably engaged in a generally radial direction with the portions 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 major part of the web prevents the brake shoes from becoming self-actuating. Although for ease of manufacture and assembly it is preferred to utilize a semicircular inner arcuate bearing surface 35, the bearing surface of recess 34 may be less than 1800 of arc from end to end. The recess 34 or slotted ends of the brake shoes 31 are canted at an angle of not more than 30 and preferably at least about 5 relative to the plane represented by the line A in Figure 3 so as to dispose 5 to 300 of the arcuate bearing surface 35 at the lower end portion 39 on the right or remote side of the datum plane represented by the line A as shown in Figure 3. Although the web material at recesses 34 may be of the same thickness as the main part of brake show webs 31 it is preferred to provide a greater surface area for 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 fitted in bores 16 of the spider bosses 18. The brake shoes 14 are mounted to the spider by sliding the recesses 34 in a generally radially direction onto the cylindrical end portions 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 inserted through the laterally aligned holes 41 of each brake shoe 14 and the opposite ends of a retention spring 44 are hooked around each respective pin 42. The retention spring 44 helps spring 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 15 to 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 mounted in conventional manner. The brake shoes as described 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 self-actuating. WHAT WE CLAIM IS:-

1. A shoe for a vehicle brake assembly of the kind including a drum and shoes acting within the drum, said shoe comprising a web carrying an arcuate table to the outer periphery of which is secured a friction lining pad, said web being formed at one end for engagement by an actuating element of said assembly and having at its other end a recess for pivotal engagement on a cylindrical portion of an anchor pin of the assembly about which portion the shoe pivots in use; said recess being an open-ended slot having an arcuate bearing surface complementary to the periphery of said pin portion and a mouth of sufficient width to enable said surface to the seated on said periphery by radially directed movement relative to the pin, the recess being so oriented in said web end that a portion of the bearing surface intersects and extends on both sides of a datum plane containing the axis of rotation of the drum for which the shoe is adapted to be used and the axis of curvature of the bearing surface, said intersection of said portion with said plane lying on the side of the latter axis remote from said axis of rotation, that part of said portion of the bearing surface which lies on the opposite side of said plane to the major part of the web extending not more than 30 beyond said plane, whereby displacement of said shoe from said pin portion in the circumferential direction of the actuating element as when the shoe operates in a trailing mode is operatively resisted while permitting slideable disengagement radially of said pin portion when said drum is removed from the assembly.

beaing surface.

6. A brake shoe substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

7. A vehicle brake assembly including a drum, a pair of shoes according to any one of the preceding claims, an actuating element acting between the adjacent one ends of the webs of said shoes, and a respective anchor pin on which the recess at the other end of the web of each shoe is pivotally engaged in use.

8. An assembly as in Claim 7 wherein said actuating element is a rotatable cam disposed between said adjacent one ends.

9. A brake assembly for a vehicle comprising a drum, a support, a pair of brake shoes acting within the drum and having webs carrying respective arcuate friction pads, an actuator disposed between adjacent one ends of the brake shoe webs, and a recess formed in the other end of each shoe web, each recess being in pivotal engagement with a cylindrical portion of a respective pivot pin carried by said support, each said recess having an arcuate bearing surface engaging the periphery of the associated pin portion and an opening enabling the shoe to be slideably disengaged radially from said pin portion after the drum is removed, a portion of said arcuate bearing surface extending on both sides of a datum plane containing the axis of the respective pin portion and the axis of rotation of the drum, said portion intersecting said plane on the side of said pin portion axis remote from said axis of rotation, that part of said portion of the bearing surface which lies on the opposite side of said plane to the major part of the respective web extending not more than 30C beyond said plane whereby displacement of said shoe from said pin portion when the shoe operates in a trailing mode during rotation of said drum is operatively resisted while permitting slideable disengagement radially of said pin portion with said drum removed from the assembly.

10. The brake assembly defined by Claim 9 wherein each of said recesses is a slot comprising the respective arcuate bearing surface and a mouth defined by portions of the brake shoe at the opposite ends of said arcuate bearing surface, said slot being so orientated as to extend at least about 5 beyond the datum plane.