GB1596024A - Wedge-type actuating means for vehicle brakes - Google Patents

Description

(54) IMPROVEMENTS IN WEDGE-TYPE ACTUATING MEANS FOR VEHICLE BRAKES (71) We, GIRLING LIMITED, a British Company of Kings Road, Tyseley. Birmingham, 11, 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: This invention relates to improvements in wedge-type actuating means for vehicle brakes of the kind in which opposed tappets guided to slide in a housing are movable away from each other to apply a brake by operation of a wedge expander assembly which includes a wedge member and which is movable in the housing in a generally transverse direction with respect to the direction of movement of the tappets, at least one roller interposed between each inclined surface of the wedge member and a complementary inclined surface on the adjacent tappet, and a cage in which the rollers are retained and guided and in which the wedge member is received, one of the tappets being provided with an axially extending extension comprising spaced arms between which the cage is slidably received to retain the cage and the wedge member against lateral movement as they move transversely with respect to the direction of movement of the tappets in operation.

In known wedge-type actuating means of the kind set forth the faces of the arms with which the cage engages slidably are flat and parallel. There is a tendency due to angular movement of the arms relative to the cage in operation for these surfaces to score the sides of the cage which may impede subsequent brake application.

According to our invention in a wedgetype actuating means of the kind set forth opposed portions of the faces of the arms with which the cage engages slidably diverge from aligned intermediate axially extending fulcrum regions so that angular movement of the arms relative to the cage can be accommodated by a rocking engagement between the cage and fulcrum regions.

Normally the tappet provided with the extension is keyed substantially against rotation in the bore in which it works, and the divergence of the faces is chosen to accommodate the theoretical maximum rotational movement of the tappet which can occur, for example up to 3.5 degrees in each direction.

One embodiment of our invention is illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section of a wedge-type actuating means for an internal shoe-drum brake; Figure 2 is an end view of the nonadjustable tappet incorporated in the actuating means of Figure 1; and Figure 3 is a transverse section through the actuating means with the wedge omitted for clarity.

The actuating means illustrated in the drawings is adapted to be mounted on the back-plate of an internal shoe-drum brake between adjacent ends of a pair of arcuate shoes carrying friction linings for engagement with the rotatable drum.

The actuating means comprises a housing 1 formed with a pair of opposed bores 2, each extending outwardly from a central chamber 3 and containing a respective tappet 4, 5 for engagement with a shoe end.

The tappets 4, 5 are guided to slide in the housing, and are movable away from each other to apply the brake. The tappet 4 incorporates an automatic adjuster assembly for maintaining a substantially constant shoe-drum clearance irrespective of wear of the friction linings. The other tappet 5 is non-adjustable in length and is held substantially against rotation with respect to the bore 2 in which it works by means of a pin 6 which is tangential to the bore and which is received in a chordal recess 7 in the tappet 5. A small sliding clearance exists between the pin 6 and the base 8 of the recess 7 to facilitate sliding movement of the tappet and thus permits the tappet 5 to rotate through a small angle, not exceeding say 3.5 degrees in each direction i.e. 7 degrees in total.

The housing 1 is provided with a further bore 9 of which the axis is normal to that of the bore 2. At its inner end the bore 9 leads into the chamber 3. The bore 9 accommodates a wedge expander assembly having an actuating shaft 10 for connection to an actuator preferably of the air-operated type (not shown) and a wedge member 11. The wedge assembly is displaceable by the actuator in a direction generally longitudinally of the bore 9, and transversely with respect to the direction of movement of the tappets against the action of a compression return spring 12 which is adapted to urge the wedge member outwardly away from the tappets 4, 5 into the "off" or "rest" position.

A roller 13 is disposed between each inclined face 14 of the wedge member 11 and a respective adjacent complementary inclined face 15, 16 on an adjacent tappet 4, 5 the faces 14 and 15 and 14 and 16 of each pair being parallel with each other. A brake actuating force from the actuator is thus transmitted from the wedge member 11, through the rollers 13 to the tappets 4, 5 and thence to the shoe ends when the wedge assembly is moved longitudinally of the bore 9, inwardly towards the bores 2.

A cage 17 of generally U-shaped outline conveniently formed as a metal pressing is located within the chamber 3. The cage 17 includes a pair of upwardly directed arms 18 of which one arm is provided adjacent to its upper end with a pair of apertures 19 and superimposed upon a pair of complementary apertures 20 in the other arm. Each roller 13 has a pair of oppositely extending axially aligned spindles 21 which are received in apertures 19 and 20 in the arms 18 so that the rollers 13 are retained and guided in the cage 17.

The arms 18 extend upwardly from an enlarged base 22 by means of which the cage 17 is slidably guided in the bore 9. The wedge member 11 is axially movable relative to the cage 17 in which it is received through an opening 23 in the base 22. The inoperative or rest position of the cage 17 and thus of the wedge member, is defined by the engagement of the base 22 with an abutment 24 comprising a circlip or the like housed within the bore 9.

In operation of the actuator with tappets 4, 5 acting between adjacent ends of the shoes of a drum brake of the two-leading shoe type, in the normal forward direction of drum rotation, the non-adjustable tappet 5 normally remains stationary and the adjustable tappet 4 moves outwardly in its bore away from the tappet 5. During this movement the cage 17 is adapted to tilt to follow the movement of the wedge member 11 and the spindles 21 of the roller 13 which contacts the stationary tappet 5, tend to ride along the upper edges of the apertures 19, 20 with the other roller 13 moving in its apertures in a linear path.

The non-adjustable tappet 5 has an extension extending axially and inwardly of the housing 1 so that, in an inoperative retracted position, its inner end 25 lies on the opposite side of the wedge-member 11. The axially extending extension of this tappet is bifurcated so that the extension comprises spaced arms 26, between which the cage 17 is slidably received with the arms 26 straddling and embracing the arms 18. This guides the wedge member 11 and the cage 17 against lateral movement as they move inwardly and transversely of the housing in the application of the brake.

Limited rotational movement of the tappet 5 with respect to the bore 2 is accommodated by the clearance between the pin 6 and the base 8 of the recess. Opposed portions 27 and 28 of the faces of the arms 26 with which the cage engages slidably diverge from aligned intermediate axially extending fulcrum regions 29 so that angular movement of the arms relative to the cage can be accommodated by a rocking engagement between the cage and the fulcrum regions. Each portion 27 and 28 diverges from the axis of the bore 9 by an angle not exceeding 3.5 degrees, thus providing a total angle of divergence between opposed faces 27 and 28 of not more than 7 degrees. This substantially eliminates or reduces any tendency for the cage 17 to score the inner faces of the arms 26 when the actuator is operated.

WHAT WE CLAIM IS: 1. A wedge-type actuating means of the kind set forth, in which opposed portions of the faces of the arms with which the cage engages slidably diverge from aligned intermediate axially extending fulcrum regions so that angular movement of the arms relative to the cage can be accommodated by a rocking engagement between the cage and the fulcrum regions.

2. A wedge-type actuating means as claimed in Claim 1, in which the tappet provided with the extension is keyed substantially against rotation in the bore in which it works, and the divergence of the faces is chosen to accommodate the theoretical maximum rotation of the tappet.

3. A wedge-type actuating means as claimed in Claim 1 or Claim 2 in which the divergence between the opposed portions of the faces is not more that 7 degrees.

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

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. 5. A small sliding clearance exists between the pin 6 and the base 8 of the recess 7 to facilitate sliding movement of the tappet and thus permits the tappet 5 to rotate through a small angle, not exceeding say 3.5 degrees in each direction i.e. 7 degrees in total. The housing 1 is provided with a further bore 9 of which the axis is normal to that of the bore 2. At its inner end the bore 9 leads into the chamber 3. The bore 9 accommodates a wedge expander assembly having an actuating shaft 10 for connection to an actuator preferably of the air-operated type (not shown) and a wedge member 11. The wedge assembly is displaceable by the actuator in a direction generally longitudinally of the bore 9, and transversely with respect to the direction of movement of the tappets against the action of a compression return spring 12 which is adapted to urge the wedge member outwardly away from the tappets 4, 5 into the "off" or "rest" position. A roller 13 is disposed between each inclined face 14 of the wedge member 11 and a respective adjacent complementary inclined face 15, 16 on an adjacent tappet 4, 5 the faces 14 and 15 and 14 and 16 of each pair being parallel with each other. A brake actuating force from the actuator is thus transmitted from the wedge member 11, through the rollers 13 to the tappets 4, 5 and thence to the shoe ends when the wedge assembly is moved longitudinally of the bore 9, inwardly towards the bores 2. A cage 17 of generally U-shaped outline conveniently formed as a metal pressing is located within the chamber 3. The cage 17 includes a pair of upwardly directed arms 18 of which one arm is provided adjacent to its upper end with a pair of apertures 19 and superimposed upon a pair of complementary apertures 20 in the other arm. Each roller 13 has a pair of oppositely extending axially aligned spindles 21 which are received in apertures 19 and 20 in the arms 18 so that the rollers 13 are retained and guided in the cage 17. The arms 18 extend upwardly from an enlarged base 22 by means of which the cage 17 is slidably guided in the bore 9. The wedge member 11 is axially movable relative to the cage 17 in which it is received through an opening 23 in the base 22. The inoperative or rest position of the cage 17 and thus of the wedge member, is defined by the engagement of the base 22 with an abutment 24 comprising a circlip or the like housed within the bore 9. In operation of the actuator with tappets 4, 5 acting between adjacent ends of the shoes of a drum brake of the two-leading shoe type, in the normal forward direction of drum rotation, the non-adjustable tappet 5 normally remains stationary and the adjustable tappet 4 moves outwardly in its bore away from the tappet 5. During this movement the cage 17 is adapted to tilt to follow the movement of the wedge member 11 and the spindles 21 of the roller 13 which contacts the stationary tappet 5, tend to ride along the upper edges of the apertures 19, 20 with the other roller 13 moving in its apertures in a linear path. The non-adjustable tappet 5 has an extension extending axially and inwardly of the housing 1 so that, in an inoperative retracted position, its inner end 25 lies on the opposite side of the wedge-member 11. The axially extending extension of this tappet is bifurcated so that the extension comprises spaced arms 26, between which the cage 17 is slidably received with the arms 26 straddling and embracing the arms 18. This guides the wedge member 11 and the cage 17 against lateral movement as they move inwardly and transversely of the housing in the application of the brake. Limited rotational movement of the tappet 5 with respect to the bore 2 is accommodated by the clearance between the pin 6 and the base 8 of the recess. Opposed portions 27 and 28 of the faces of the arms 26 with which the cage engages slidably diverge from aligned intermediate axially extending fulcrum regions 29 so that angular movement of the arms relative to the cage can be accommodated by a rocking engagement between the cage and the fulcrum regions. Each portion 27 and 28 diverges from the axis of the bore 9 by an angle not exceeding 3.5 degrees, thus providing a total angle of divergence between opposed faces 27 and 28 of not more than 7 degrees. This substantially eliminates or reduces any tendency for the cage 17 to score the inner faces of the arms 26 when the actuator is operated. WHAT WE CLAIM IS:

1. A wedge-type actuating means of the kind set forth, in which opposed portions of the faces of the arms with which the cage engages slidably diverge from aligned intermediate axially extending fulcrum regions so that angular movement of the arms relative to the cage can be accommodated by a rocking engagement between the cage and the fulcrum regions.

2. A wedge-type actuating means as claimed in Claim 1, in which the tappet provided with the extension is keyed substantially against rotation in the bore in which it works, and the divergence of the faces is chosen to accommodate the theoretical maximum rotation of the tappet.

3. A wedge-type actuating means as claimed in Claim 1 or Claim 2 in which the divergence between the opposed portions of the faces is not more that 7 degrees.

4. A wedge-type actuating means sub

stantially as herein described with reference to and as illustrated in the accompanying drawings -