Brake assembly

Abstract: For a vehicle having a relatively large axle tube (24), a mechanically operated drum brake (25) is provided having a hollow abutment post (53) between adjacent ends of a pair of opposed arcuate brake shoes (29, 30) and having an improved actuating mechanism (55a) for the brake shoes mounted partially within the abutment post. The drum brake is primarily intended for use as a drum-in-hat parking brake assembly for use with a disc brake having a hat-shaped rotor (28) with the drum brake disposed between an inner surface of a body portion (58) of the rotor and the axle tube (24).

Description: BACKGROUND OF THE INVENTION This invention relates to an actuating mechanism for a drum-in-hat parking brake associated with a disc brake rotor for a heavy truck disc brake assembly. The large axle tube on a heavy truck takes up so much space inside the hat of a disc brake that it has been difficult to incorporate a drum-in-hat parking brake in the hat of the disc brake rotor. US-A-3934684 disclosed an arrangement which attempts to overcome this problem by providing an hydraulically operated disc brake caliper with mechanically operated means whereby the caliper can also serve as a parking brake. US-A-3850266 discloses a drum-in-hat parking brake assembly according to the preamble of claim 1 in which a rotary actuator is disposed between adjacent upper ends of the brake shoes. US-A-1913156 discloses an internal hand brake with a composite abutment post which supports brake actuating links. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved form of drum-in-hat parking brake mechanism which can be located in the limited space between the large axle tube of a heavy truck and the hat of a disc brake rotor. Thus according to the present invention, there is provided a drum-in-hat parking brake assembly for an hydraulic disc brake including a backing plate and a caliper supporting structure, a pair of arcuate drum brake shoes supported relative to said backing plate, an abutment post located on said backing plate between a pair of adjacent ends of said brake shoes and actuating means operatively connected to said brake shoes, the assembly being characterised in that said abutment post is of a one-piece hollow construction which defines a chamber and a pair of opposed slots extending from said chamber through opposite ends of said abutment post, in that said actuating means includes a pair of links disposed in the chamber and extending in opposite directions through said slots with each end of each link extending through a respective one of said slots, and in that a lever is coupled to said link to effect lengthwise movement of said links in opposite directions to engage and actuate said brake shoes. The lever may be a pivotable lever with each of the links having an end offset towards the other link and the offset end of one of the links positioned adjacent the non-offset end of the other of said links, whereby intermediate portions of said links are spaced apart for the reception of an outboard end of said lever between said links and adjacent ends of said links are contiguous. The abutment post may be cast integrally with the backing plate. BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an outboard view of a support casting having a drum-in-hat parking brake constructed in accordance with the invention mounted thereon; Figure 1A is an enlarged view of a fastening clip for a right-hand brake shoe of Figure 1; Figure 2 is an inboard view of the support casting of Figure 1; Figure 3 is a sectional view taken along line 3-3 of Figure 1, including a fragmentary section of a disc brake rotor of an associated hydraulic disc brake; Figure 4 is a sectional view taken along the line 4-4 of Figure 1, including the disc brake rotor and showing the actuating mechanism for the parking brake. Figure 5 is an enlarged view of the upper portion of Figure 1, showing the actuating mechanism for the brake shoes of the parking brake; Figure 6 is a fragmentary perspective view of the upper portion of Figure 1, showing the actuating mechanism for the brake shoes of the parking brake; Figure 7 is an exploded perspective view of the actuating mechanism of Figure 6; Figures 8 and 9 are views similar to Figures 3 and 5, respectively, showing the actuating mechanism in an OFF or disengaged condition, and Figures 10 and 11 are views similar to Figures 8 and 9, respectively, showing the actuating mechanism in an ON or engaged condition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawings, Figure 1 shows an anchor plate casting 20 including an annular backing plate 21 and a pair of opposed arms 22 and 23. The casting 20 as shown is adapted for mounting on the left rear axle tube 24 of a heavy truck. The axle tube 24 is best shown in broken lines in Figures 4 and in cross section in Figures 5, 9 and 11. The outboard side of casting 20 is shown in Figure 1. The backing plate 21 has a drum-in-hat parking brake assembly 25 mounted on the outboard side. At their outer ends, arms 22 and 23 respectively include a pair of guide rails 26 and 27 for mounting the caliper (not shown) of a disc brake. The disc brake has a hat-shaped rotor 28 shown in Figures 3, 4, 5, 9 and 11. A body portion 58 of the rotor co-axially surrounds the axle tube 24 and forms a drum for the parking brake assembly and a rim portion 58a of the rotor is engaged by disc brake pads (not shown) carried by the caliper. The drum-in-hat parking brake 25 includes a pair of arcuate brake shoes 29 and 30 of generally T-shaped cross section and including flat arcuate webs 31 and 32 with arcuate tables 33 and 34 secured respectively to outer arcuate edges thereof. Arcuate friction pads 35 and 36 are attached respectively to tables 33 and 34. The annular backing plate 21 typically includes a plurality of raised pads 37 on its outboard side. Tables 33 and 34 are typically held in position against the pads 37 in a manner well-known to the art as by a pair of pins (not fully shown) having enlarged heads 38 (Figure 2) and flattened, T-shaped, outboard ends 39 (Figure 1A). From their heads 38 the pins pass through appropriate holes in backing plate 21 and in both legs of typical U-shaped spring clips 40. The hole in the outboard leg of each spring clip 40 comprises a slot 41 extending across the bottom and up both inclined sides of a transverse groove 42 in the outboard leg. The flattened end 39 of the respective pin is turned ninety degrees into alignment with the groove 42 after being inserted through slot 41. Engagement of the flattened end 39 with the inclined sides of the groove 42 prevents inadvertent turning of the flattened end 39 back into alignment with the slot 41. Backing plate 21 is provided with a plurality of bolt holes 43 for the reception of mounting bolts (not shown) to secure the casting 20 in place with its inboard side against a mounting flange 44 (Figure 4) on a typical axle tube 24. On its outboard face backing plate 21 is machine in a plurality of areas 45 around bolt holes 43 to provide smooth surfaces for engagement by the bolt heads. Adjacent their lower ends as viewed in Figure 1, the brake shoe webs 31 and 32 are provided with suitable openings for the reception respectively of opposite hooked ends of a tension spring 46. A typical duo-servo friction pad wear-adjusting strut 47 is provided between the lower ends of the webs 31 and 32, including a shaft 48, a star wheel 49 threadably mounted on shaft 48, and a sleeve 50. An access hole 51 is provided in the backing plate 21 for external adjustment of star wheel 49. A plug 52 (Figures 2 and 4) typically closes the access hole 51. Between the upper ends of the webs 31 and 32 as viewed in Figure 1, the backing plate 21 is provided with a hollow, rotation-preventing abutment post 53 having a hollow portion 53a (shown best in Figure 7) which prevents rotation of the brake shoes in either direction when the parking brake is actuated and also partially houses the mechanical actuating mechanism for brake shoes 29 and 30. Adjacent their upper ends webs 31 and 32 are provided with suitable openings for the reception respectively of opposite hooked ends of a tension return spring 54 which biases the upper ends of the webs towards each other and into engagement with the post 53. The improved parking brake mechanical actuating mechanism includes an operating lever means 55a having a privotable operating lever 55 mounted between a pair of oppositely reciprocal link members 56 and 57. The return spring 54 biases webs 31 and 32 into engagement with the link members 56 and 57 and acts to configure the mechanism in its non-activated position. Figure 5 shows an enlarged view of an upper portion of Figure 1 and illustrates how the improved actuating mechanism fits between the drum formed by the body portion 58 of disc brake rotor 28 and the axle tube 24. The cavity within abutment post 53 extends through backing plate 21 and is wider on the inboard side as can be seen in Figures 2 and 3, thereby forming a closed chamber with axle tube mounting flange 44 for the pivotable operating lever 55 free from the road environment. A cable 60 has an inner end provided with a stop 61 disposed on one side of a reversely curved inboard end portions 62 of the lever 55. A compression spring 63 encircling cable 60 is disposed on an opposite side of the reversely curved end portion 62. A tab 64 on the reversely curved end portion 62 aids in maintaining spring 63 in place. By this means, cable 60 is secured to the operating lever 55. An elastomeric seal 65 seals the opening in the side wall of backing plate 21 through which cable 60 passes, and a protective sheath 66 is provided on cable 60 outside of the backing plate 21. Figures 6 and 7 more clearly show details of the improved mechanical actuating mechanism and the mounting thereof, particularly links 56 and 57, within abutment post 53. Each of the links 56 and 57 is slotted at opposite ends respectively to receive webs 31 and 32. As shown in Figure 7, the outboard end of the lever 55 opposite the reversely curved inboard end 62 is provided with an oval hole 67 elongated longitudinally of the lever and a circular hole 68 is placed from hole 67 in a direction towards the reversely curved end 62. The upper link 56 is provided, on its lower surface, with a downwardly extending cylindrical stud or boss 69 concentric with an arcuate ear 70 on an inboard edge of the link and received in the hole 68 of lever 55. Similarly the lower link 57 is provided on its upper surface with an upwardly extending cylindrical stud or boss 71 concentric with arcuate ear 72 on the outboard edge of the link and received in hole 67 of the lever 55. A right-hand end 73 of link 55, as viewed in Figure 7, is downwardly offset by one thickness, and the left-hand end 74 of link 57 is upwardly offset by one thickness. When the actuating mechanism is assembled, the offset ends 73 and 74 are aligned with the outboard end of the lever 55, as most clearly shown in Figures 5 and 6. In actual practice, lever 55 and links 56 and 57 are formed from material of the same thickness. As shown in Figure 7, the abutment post 53 is appropriately configured and slotted for reception of the improved mechanical actuating mechanism (lever 55 and links 56 and 57) and the upper portions of webs 31 and 32. Left-hand horizontal slot 75 is upwardly offset from the right-hand horizontal slot 76 for reception of the corresponding assembly of links 56 and 57, as shown in Figures 5 and 6. The left-hand end 74 of the link 57 is supported by slotted shelf 77. An upper portion 78 of the abutment post 53 is slotted on the right-hand side of 79 for reception of brake shoe web 32. A similar slot 80 (Figures 8 and 10) is provided on the left-hand side of the portion 78 for reception of brake shoe web 31. An outboard face 81 on the lower portion 82 of abutment post 53 is recessed inwardly with respect to the outboard face 83 on the upper portion 78, and therefore a right-hand end portion 84 of link 57 is supported from an inboard edge of the link to an outboard edge of slot 85. When assembled, links 56 and 57 are held in slots 75 and 76 by webs 31 and 32, but are free to move longitudinally by action of operating lever 55. Figures 8 and 9 show an OFF or disengaged condition of the mechanical parking brake mechanism. Figure 8 is similar to Figure 3, but in Figure 8 the abutment post 53 is not sectioned and its upper portion 78 is visible. In Figure 8, the operating lever 55 is biased towards the right by action of coil spring 80 and stud 69 is positioned to the right of boss 71. In Figure 9 the friction pads 35 and 36 are spaced from the inner cylindrical surface of the drum formed by the body portion 58 of rotor 28, web portions 31 and 32 are in contact with abutment post 53 and spring 54 is fully contracted. Figures 10 and 11 show the ON or engaged condition of the mechanical parking brake mechanism when the parking brake is applied. In Figure 10 operating lever 55 has been pivoted counter-clockwise from its position in Figure 8 by actuation of cable 60; stud 69 is now substantially vertical above boss 71. Thus.link 56 has moved towards the left from its position in Figures 8 and 9 and link 57 has moved towards the right, thereby urging friction pads 35 and 36 into frictional engagement with the inner cylindrical surface of the drum formed by the body portion 58 of rotor 28, as shown in Figure 11, thereby stretching spring 54. Various modifications may be made in the structure shown and described without departing from the scope of the invention.

Claims: A drum-in-hat parking brake assembly (25) for an hydraulic disc brake including a backing plate (21) and a caliper supporting structure (22, 23), a pair of arcuate drum brake shoes (29, 30) supported relative to said backing plate, an abutment post (53) located on said backing plate between a pair of adjacent ends of said brake shoes and actuating means (55a) operatively connected to said brake shoes, the assembly being characterised in that said abutment post is of a one-piece hollow construction which defines a chamber (53a) and a pair of opposed slots (75, 76) extending from said chamber through opposite ends of said abutment post, in that said actuating means (55a) includes a pair of links (56, 57) disposed in the chamber and extending in opposite directions through said slots with each end of each link extending through a respective one of said slots, and in that a lever (55) is coupled to said link to effect lengthwise movement of said links in opposite directions to engage and actuate said brake shoes. A brake assembly according to claim 1 characterised in that said lever (55) is a privotable lever and that each of said links has an end offset towards the other link and the offset end (73) of one of said links is positioned adjacent the non-offset end of the other of said links, whereby intermediate portions of said links are spaced apart for the reception of an outboard end of said lever (55) between said links and adjacent ends of said links are contiguous. A brake assembly according to claim 2 characterised in that said outboard end of said lever has two holes (67, 68) spaced lengthwise of said lever, at least one of said holes (67) being elongated lengthwise of said lever and each of said links (56, 57) has a cylindrical boss (69, 71) disposed in a respective one of said holes. A brake assembly according to any one of claims 1 to 3 characterised in that each end of said brake shoes (29, 30) includes an arcuate web (31, 32) and each end of each link (56, 57) is slotted to receive an associated web. A brake assembly according to any one of claims 1 to 4 characterised in that said chamber (53a) in said abutment post (53) extends axially of said abutment post from an outboard face (81, 83) thereof to an inboard face of the backing plate (21). A brake assembly according to claim 5 characterised in that said outboard face (81, 83) of said abutment post (53) has slots (75, 76) for reception respectively therein of opposite ends of said elongated links. A brake assembly according to any one of claims 1 to 6 characterised in that said abutment post (53) is cast integrally with said backing plate (21). A brake assembly according to any one of claims 1 to 7 characterised in that said caliper supporting structure includes a pair of spaced arms (22, 23) for mounting a disc brake caliper, said arms being cast integrally with said backing plate to define a one-piece casting.

Inventors: EVANS ANTHONY COLIN, EVANS, ANTHONY COLIN
Applicants: KELSEY HAYES CO, KELSEY-HAYES COMPANY
Application year: 1990
Main classification: B60T1
IPC codes: F16D65, F16D51, B60T1, F16D63