STAKED ADJUSTER SLEEVE

Abstract: The invention relates to an automatic adjusting mechan­ ism for a wedge actuated vehicle brake which includes an extendible plunger assembly (25) having an adjusting bolt (58) threaded internally of a sleeve (54) having one end received within a plunger 26 and includes means for preventing contact between the adjusting bolt 58 and the plunger (26).

Description: STA#ED. ADJUSTER SL SLEEVE Batckgrqund of t¯e Invention The present invention relates to automotive vehicle brakes and more specifically, to an automatic brake adjusting mechanism for a wedge actuated brake for heavy duty service on trucks and coaches. In wedge actuated brakes the brake shoes are moved outwardly into engagement with the friction surface of a surrounding brake drum by forcing a wedge between the adjacent ends of a pair of axially aligned plungers disposed between the ends of a pair of brake shoes. The wedge is mounted in such a manner as to permit it to float slightly with its position between the plungers being partly determined by reaction forces exerted on the wedge by the plungers. Examples of such brake mechanisms are illustrated in United States Patent 3,037,584 issued June 5, 1962, to F. T. Cox et al and United States Patent 3,599,762 issued August 17, 1971, to F. T. Cox Et al. Such brake mechanisms are manufactured in sizes ranging from 15" to 42" in diameter with the larger sizes used primarily for off-highway vehicles. These brakes are subject to tremendous loads due to the size of the vehicles and the loads they carry. This results in relatively rapid wear of the brake shoe linings which may be further compounded by frequent stopping, particularly on other than level terrain as encountered in off-highway and intra-city service. It is therefore customary to equip such brakes with a mechanism that will automatically adjust the brake actuator to accommodate for brake lining wear and to maintain the travel of the actuator plungers and their associated brake shoes relatively constant throughout the normal life of the brake shoe linings. An example of one such automatic adjusting mechanism is described in United States Patent 3,068,964 issued December 18, 1962, to W. J. Williams et al. In such adjusting mechanisms, one of the plungers is comprised of an assembly of parts in which the length of the plunger assembly is automatically increased or extended to compensate for a reduction in the brake shoe lining thickness as the friction lining wears during normal service. Improvements to that type of automatic adjusting mechanism are disclosed in United States Patent 3,570,632 issued March 16, 1971; Patent 3,797,613 issued March 19, 1974; and Patent 3,822,003 issued July 2, 1974. Although such an automatic adjusting mechanism provides satisfactory and reliable service, it has been determined that such service and reliability may be even further enhanced by preventing contact between certain elements of the adjusting plunger assembly. Summary of the Invention The present invention provides an improved self-adjusting mechanism for a wedge type brake actuator which includes an extendible plunger assembly having a plunger mounted for axially slidable movement in a bore provided to the actuator and having an interior cylindrical bore closed at one end and open at the other end. A sleeve is slidably and rotatably received within the plunger bore. The sleeve has a plurality of helical teeth on its external surface and a single thread of predetermined configuration extending helically substantially the entire length of the interior surface of the sleeve. An adjusting bolt longer than the sleeve has a threaded shank engaging the helical internal thread of the sleeve with one end of the adjusting bolt extending through an open end of the sleeve and means are provided to prevent the adjusting bolt from contacting the plunger. In the preferred embodiment, means are provided which prevent the other end of the adjusting bolt from contacting the closed end of the plunger. lhe advantages offered by the present invention will become apparent from the following description of the embodiment shown in the accompanying drawings. Description of the Drawings In the drawings, wherein like reference numerals refer to like parts: Figure 1 is a fragmentary side elevation showing the upper part of a brake assembly incorporating the present invention; Figure 2 is a section taken along line 2-2 of Figure 1; Figure 3 is an enlarged view, partly in section, of the axially extendible plunger assembly of Figure 2; and Figure 4 is a sectional view of one end of one of the elements of Figure 3. Description of the Preferred Embodiment With reference to the drawings, Figure 1 shows a brake assembly comprising a brake drum 10, a pair of brake shoes 12 and 14 and a wedge type brake actuator 20. The brake drum is mounted by conventional means on a ground engaging vehicle wheel (not shown). The actuator 20 is secured by bolts to a support usually referred to as a spider 17 fixed to the vehicle axle beam or housing (not shown). Brake shoes 12 and 14 are supported for movement relative to the spider 17. As shown by Figure 1, the adjacent ends of the webs 18 and 19 of brake shoes 12 and 14 are urged into engagement with the opposite ends of the actuator 20 by means of a return spring 13. In the preferred embodiment, the opposite ends of the brake shoe webs 18 and 19 are similarly urged into engagement with the opposite ends of an actuator by means of still another return spring as disclosed in United States Patent 3,037,584. The brake shoes 12 and 14 are respectively provided with friction linings 15 and 16 adapted to engage the internal friction surface 11 of brake drum 10 upon outward movement of the brake shoes. Figure 2 illustrates details of the wedge type actuator 20 which is comprised of a housing 21 formed with opposed similar coaxial cylindrical end bores 22 and 24 which respectively slidably mount a plunger assembly 25 and a plunger 26 for linear movement therein. One side of housing 21 is provided with an opening 28 coaxial with a hollow boss 29 internally threaded at 30 to mount a tubular support 31 of a fluid motor (not shown) having a reciprocating rod 32 carrying a wedge 34 disposed between rollers 35 and 36 located for rolling movement within the grooved inner ends 38 and 39, respectively, of the plunger assembly 25 and the plunger 26. Rollers 35 and 36 are preferably loosely mounted on the rod 32 by a carrier 40 and, when rod 32 is moved further into the housing 21 to actuate the brake, the rollers 35 and 36 respectively displace the plunger assembly 25 and the plunger 26 outwardly relative to the housing bores 22 and 24 against the force of the return spring 13 to move the linings of the brake shoes 12 and 14 into frictional contact with the internal surface 11 of the brake drum. When the brake is disengaged, the return spring 13, acting through brake shoe webs 18 and 19, moves the plunger assembly 25 and the plunger 26 into the housing bores 22 and 24 as the wedge 34 is retracted with the operative elements of the actuator 20 returning to their respective positions as shown in Figure 2. When the brake is disengaged, the plunger assembly 25 and plunger 26 are each seated against a shoulder provided at the inner end of the housing bores 22 and 24. Plunger 26 has a side slot 41 coacting with the inner end of a cap screw 42 which prevents rotation of the plunger 26 in bore 24. A flexible seal unit 44 is press fit to a counter bore at the outer end of bore 24 to prevent entry of dirt and moisture between the plunger 26 and bore 24. The outer end of plunger 26 is recessed or grooved at 45 to slidably receive the end of the brake shoe web 19. Plunger assembly 25 is comprised of several elements which are movable relative to each other for the purpose of adjusting or extending the length of the plunger assembly to thereby maintain the desired running clearance between the brake shoe friction linings and the brake drum and optimum operation of the brake by assuring relatively constant travel of the wedge 34, the plunger assembly 25 and the plunger 26 within the actuator housing 21. Plunger assembly 25 is thus comprised of an outer member or plunger 48 slidable in housing bore 22. The plunger 48 has an internal cylindrical bore 49 open at the end 50 of the plunger and closed by the surface 51 at the other end of the plunger. An inner sleeve 54, sometimes referred to as an adjusting nut or actuator; is slidably and rotatably mounted internally of the bore 49 and a smaller diameter bore or bearing surface 52 adjacent to the surface 51. The inner sleeve 54 is open at both ends and is formed with an internally threaded bore 55 of uniform diameter defined by a continuous helical thread 56 along substantially the entire length of bore 55. In the preferred embodiment, the thread 56 is a 7/8 14 UNF 2B (Modified) thread with a pitch diameter of about 21.134 cm. The shank 59 of adjusting bolt 58 is provided with a helical thread 60 complimentary to the internal sleeve thread 56. The adjusting bolt 58 is longer than the axial length of the hollow open ended sleeve 54. The threads 56 and 60 are slidably engaged internally of the sleeve 54 with the end 62 of the adjusting bolt 58 extending outward through the open end 64 of the sleeve 54 adjacent the open end 50 of plunger 48. The radially extending surface 65 at the other open end 66 of the sleeve 54 is intended to abut or seat against the surface 51 of plunger 48. The inner sleeve surface 65 is staked at 68 to prevent the inner end 61 of the adjusting bolt 58 from contacting the surface 51 at the closed end of plunger 48. In the preferred embodiment, four stakes 68 are applied by a cone-shaped tool at 900 intervals around the surface 65 to disrupt the configuration of the otherwise continuous helical thread 56 and reduce the internal diameter of the sleeve bore 55 adjacent the end 66 of the sleeve 54. The stakes 68 produce a series of spaced radially inward directed projections or bumps 69 and thereby change the configuration or provide a different configuration in the thread 56 adjacent the open end 66 of the sleeve 54. The depth of the stake 68 preferably provides a space 67 or distance "d" of about .5 to 1.5 mm between the end 61 of adjusting bolt 58 and the end surface 65 of sleeve 54 when the adjusting bolt 58 is manually threaded to the bore 55 of sleeve 54. The outer end 62 of the adjusting bolt 58 comprises an enlarged flange 70 having a toothed periphery 71 to provide a star wheel. A brake shoe retainer 72 having a slot 74, is mounted to the adjusting bolt flange 70 and resiliently held in place by a U-shaped arms 75. The arcuate end of the brake shoe web 18 extends through the slot 74 of retainer 72 and bears against the axially outer end face of the adjusting bolt 58. The slot 74 in the retainer 72 prevents lateral misalignment of the end of brake shoe web 18 and the adjusting bolt 58 while the resilient U-shaped arms 75 each having a detent between adjacent teeth in the toothed periphery 71 of the adjusting bolt flange 70 permit the flange 70 and adjusting bolt 58 to be rotated relative to the retainer 72 and the brake shoe web 18 thereby allowing for manual adjustment by rotating the flange 70 to rotate the adjusting bolt 58 internally of the sleeve 54 until the desired running clearance is obtained. A bellows type expanding flexible seal 76 having its outer end enclosed within a metal case 78 seated In a counter bore provided around the housing bore 22 and its inner periphery snug against the adjusting bolt between the flange 70 and the threaded portion 60 of the shank 59 prevents dirt, moisture and other materials from entering the housing bore 22. The outer periphery of sleeve 54 is formed with a plurality of helical teeth 79. A pawl assembly 80 is provided internally of a bore 81 through actuator housing 21. The bore 81 is substantially normal to the axis of the cylindrical bore 22 and the inner end of the bore 81 intersects cylindrical bore 22. The pawl assembly is comprised of a pawl 82, a compression spring 84 and a hollow cap screw 85 threaded to the outer end of the bore 81. The pawl 82 extends through a side slot 86 provided to plunger 48. The inner end of the pawl 82 is provided with a plurality of buttress teeth 88 which are biased into engagement with the helical teeth 79 provided to the external surface of sleeve 54. The pawl 82 interacts with the side slot 86 of plunger 48 to prevent rotation of the plunger 48 in housing bore 22. During normal operation of the brake, the plunger assembly 25 including the sleeve 54 is displaced axially outwardly in housing bore 22 by the wedge 34 and roller 35. The pawl 82 in bore 81 is in a fixed axial location relative to housing bore 22. If the axially outward movement of the sleeve 54 is greater than the corresponding axial length of the helical teeth 79, the pawl 82 will compress spring 84 and the buttress teeth 88 on the pawl 82 will skip to an adjacent set of helical teeth 79. Then, when the brake is released, the buttress teeth 88 will rotate the helical teeth 79 and sleeve 54 to extend the adjusting bolt 58 which is threaded internally of the sleeve 54 and thereby extend the effective length of the plunger assembly 25 to maintain the desired clearance between the friction linings on the brake shoes and the friction surface of the brake drum. During return movement of the plunger assembly 25, the sleeve 54 is free to rotate internally of the plunger 48 while the retainer 72 prevents rotation of the adjusting bolt 58. Detents in the resilient legs 75 of the retainer 72 are seated between adjacent teeth in the adjusting bolt flange 70 and the end of the brake shoe web 18 extends through the retainer slot 74 to prevent rotation of the retainer 72. The stakes 68 provided to the end surface 65 of sleeve 54 prevent the inner end 66 of adjusting bolt 58 from extending through the inner open end 66 of sieeve 54 and ensure that the end surface 65 of the sleeve contacts the surface 51 at the closed end of the plunger bore 49. This establishes a compressive force or resistance on the threads 56 and 60 in the axial direction of bore 22 and prevents the helical teeth 79 of sleeve 54 from rotating through the buttress teeth 88 of pawl 82 during the brake actuation stroke of wedge 34 and outward movement of the plunger assembly 25. If the end 66 of the adjusting bolt 58 abuts the plunger surface 51, there would be less resistance to rotary movement of the sleeve 54 internally of the plunger bore 49 and the actuator or sleeve 54 would be free to rotate against the pawl buttress teeth b8 during the brake actuation and the brake release stroke of the wedge 34 without extending the effective length of the plunger assembly. 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 to be intended to be embraced thereby.

Claims: What is claimed and desired to be secured by letters patent is: 1. In a wedge actuated brake assembly having a movable brake shoe with friction lining adapted to engage a surrounding brake drum, a self-adjusting brake actuating mechanism comprising a housing having a cylindrical bore therein, a wedge movable substantially normal to the axis of said bore and means for reciprocably moving said wedge, a plunger assembly including a plunger mounted for axially slid able movement in said housing bore and having an interior cylindrical bore closed at one end and open at the other end, an elongate sleeve slidably and rotatably received within said interior bore of said plunger, said sleeve having a plurality of helical teeth on its external surface and a single thread of predetermined configuration extending helically substantially the entire length of the interior surface of said sleeve, an adjusting bolt, said adjusting bolt being of a length greater than the length of said sleeve and having a threaded shank engaging the helical internal thread of said sleeve with one end of said adjusting bolt extending through an open end of said sleeve, a toothed pawl carried by said housing in fixed axial location relative to said housing bore, spring means urging said toothed pawl radially into engagement with said helical teeth, said plunger assembly being movable by said wedge to move said brake shoe toward said drum and being axially extendible by rotation of said sleeve relative to said adjusting bolt to accommodate wear of the friction lining of said brake shoe, and means preventing said adjusting bolt from contacting said plunger. 2. The wedge actuated brake assembly defined by claim 1 wherein said means preventing said adjusting bolt from contacting said plunger comprises means preventing said other end of said adjusting bolt from contacting said closed end of said plunger. 3. The wedge actuated brake assembly defined by claim 2 wherein said sleeve is open at both ends and said means preventing the other end of said adjusting bolt from contacting said plunger comprises means preventing said other end of said adjusting bolt from extending through the open end of said sleeve adjacent the closed end of said plunger. 4. The wedge actuated brake assembly defined by claim 3 wherein the internal diameter of said sleeve is reduced at said open end of said sleeve adjacent said closed end of said plunger to prevent said adjusting bolt from extending through that end of said sleeve. 5. The wedge actuated brake assembly defined by claim 3 including a different configuration of said helical thread provided internally of said sleeve adjacent-said open end of said sleeve to prevent said adjusting bolt from extending through that end of said sleeve. 6. The wedge actuated brake assembly defined by claim 3 wherein said open end of said sleeve is staked to reduce the internal diameter and disrupt the configuration of said thread adjacent said open end of said sleeve.

Inventors: CREWSON, GARY EDWARD, DUBIEL, MARY LYNN
Applicants: ROCKWELL INTERNATIONAL CORPORATION
Application year: 1983
Main classification: F16D65
IPC codes: F16D65, F16D51