GB2261267A

GB2261267A - Dust cover for a piston and brake cylinder

Info

Publication number: GB2261267A
Application number: GB9123843A
Authority: GB
Inventors: David Pantale
Original assignee: General Motors France SA
Current assignee: General Motors France SA
Priority date: 1991-11-09
Filing date: 1991-11-09
Publication date: 1993-05-12
Also published as: GB9123843D0

Abstract

A dust cover (40) for the sliding surfaces (32, 28) between a piston (22) and a brake cylinder (12) in which the sliding surface of the piston has a circumferentially extending groove (58) therein adjacent its free end (60) and the brake cylinder has a circumferentially extending groove (48) at or adjacent its open end (24), the dust cover being substantially annular and comprising a first annular edge (42) for retention in the circumferentially extending groove in the brake cylinder; a second annular edge (44) for positioning in the circumferentially extending groove in the sliding surface of the piston; and a bellows portion (46) linking the first and second annular edges; the second annular edge having a substantially semi-circular cross-section. Allows extended movement of the piston relative to the brake cylinder. <IMAGE>

Description

DUST COVER FOR A PISTON AND BRAKE CYLINDER This invention relates to a dust cover for the sliding surfaces between a piston and a brake cylinder of a brake of a motor vehicle.

It is known to provide such a dust cover in order to substantially prevent ingress of contaminants (such as dust, water, etc.) between the sliding surfaces which may impair the required smooth sliding action. In these known arrangements, a first annular edge of the dust cover is located in a circumferentially extending groove in the brake cylinder, and a second annular edge of the dust cover is located in an outer circumferentially extending groove in the sliding surface of the piston. A bellows portion extends between, and is integral with, the first and second annular edges. In disc brakes, it is usual for the circumferentially extending groove in the brake cylinder to be in the sliding surface of the brake cylinder adjacent the open end thereof. The second annular edge is shaped to fit tightly in the circumferentially extending groove in the piston.This known arrangement has the disadvantage that the shape and retention of the second annular edge restricts the retracted or extended position of the piston relative to the brake cylinder. Whilst this disadvantage can be overcome by increasing the length of the bellows portion, such an increase in length increases the risk of the bellows portion touching the backing plate of the adjacent brake pad or brake shoe when the piston is partially or fully retracted. Such action can burn a hole in the bellows portion when the backing plate is hot.

It is an object of the present invention to overcome this disadvantage.

To this end, a dust cover in accordance with the present invention is substantially annular and comprises a first annular edge for retention in the circumferentially extending groove in the brake cylinder; a second annular edge for positioning in the circumferentially extending groove in the sliding surface of the piston; and a bellows portion linking the first and second annular edges; the second annular edge having a substantially semi-circular cross-section.

In this arrangement, the semi-circular cross-section provides the second annular edge with a curved surface and a flat surface. The curved surface of the second annular edge allows the second annular edge to rotate in the circumferentially extending groove in the sliding surface of the piston to allow the piston to move further out of the brake cylinder than with previously-known designs.

Further, the flat surface of the second annular edge allows the second annular edge to pass (to a limited extent) into the brake cylinder, thereby allowing the piston to retract further into the brake cylinder than with previously known designs. Such an arrangement can more easily take up the variations in the thickness of friction lining material on brake pads or brake shoes between old and new brake pads or brake shoes.

Where the circumferentially extending groove in the brake cylinder is positioned in the sliding surface thereof adjacent the open end thereof, the first annular edge preferably has an inwardly directed ridge for engaging the piston.

Whilst the present invention has particular application with disc brakes for motor vehicles, it may also be adapted for use with drum brakes.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view, partly in cross-section, of a disc brake including a dust cover in accordance with the present invention; Figure 2 is an enlarged view of the dust cover of Figure 1 with the piston in a fully retracted position; Figure 3 is an enlarged view of the dust cover of Figure 1 with the piston in a fully extended position; and Figure 4 is a cross-sectional view of the dust cover of Figures 1 to 3.

Referring to Figure 1, a disc brake 10 is shown which comprises a brake cylinder 12; a caliper 14; a pair of brake pads 16 having friction lining material 18 thereon for engaging a rotor 20; and a piston 22. The brake cylinder 12 has an open end 24, a closed end 26, and a cylindrical sliding surface 28 therebetween, which define a fluid chamber 30. The piston 22 has a corresponding sliding surface 32 for sliding engagement with the brake cylinder 12. A seal 34 between the sliding surfaces 28,32 provides a fluid seal for the fluid chamber 30. Actuation of the disc brake 10 is achieved by pressurising hydraulic fluid in the fluid chamber 30, which causes the piston 22 to move relative to the brake cylinder 12 to bring the friction lining material into engagement with the rotor 20.The arrangement described thus far is well known to those skilled in the art, and will not be described in greater detail.

A dust cover 40 (Figures 2 to 4) in accordance with the present invention extends between the brake cylinder 12 and the piston 22 at the open end 24 of the brake cylinder. The dust cover 40 substantially prevents contaminants reaching the sliding surfaces 28,32 which can prevent a smooth sliding action. The dust cover 40, which is moulded in one piece from elastomeric material, is substantially annular and comprises a first annular edge 42, a second annular edge 44, and a bellows portion 46 extending between and joining the first and second annular edges. The first annular edge 42 is positioned in an inner circumferentially extending groove 48 in the sliding surface 28 in the brake cylinder 12 adjacent the open end 24 thereof.The first annular edge 42 has an inwardly directed ridge 50 for sliding engagement with the sliding surface 32 of the piston 22, and a ridge 52 directed towards the second annular edge 44, the ridges helping to retain the first annular edge in the circumferentially extending groove 48.

The second annular edge 44 is substantially semi-circular in cross-section and has a curved surface 54 and a flat surface 56. The second annular edge 44 is positioned in an outer circumferentially extending groove 58 in the sliding surface 32 of the piston 22 adjacent the free end 60 thereof. The curved surface 54 allows the second annular edge 44 to rotate in the circumferentially extending groove 58. As can be seen in Figure 3, this allows the piston 22 to extend out of the brake cylinder 12 to a greater extent than the previously known arrangements where the second annular edge is fixed in the circumferentially extending groove in the piston.

The flat surface 56 allows the second annular edge 44 to slide under the first annular edge 42 and move (to a limited extent) inside the brake cylinder 12. As can be seen in Figure 2, this allows the piston 22 to retract further into the brake cylinder 12 than previously known arrangements where the shape of the second annular edge 44 prevents the second annular edge from entering the brake cylinder.

This extra possible movement of the piston 22 relative to the brake cylinder 12 allows the disc brake 10 to accommodate greater variations in thickness of friction lining material 18, especially between old and new brake pads 16. Alternatively, in comparison to previous designs, the length of the bellows portion 46 can be reduced, thereby increasing the gap (L in Figure 1) between the bellows portion and the backing plate of the adjacent brake pad 16 in the retracted (Figure 2) position. This arrangement substantially reduces the risk of the bellows portion 46 touching, and hence burning on, the backing plate.

Alterations may be made to the above embodiment without departing from the scope of the present invention. For example, the circumferentially extending groove in the brake cylinder may be positioned in the outer surface of the brake cylinder at the open end, rather than in the sliding surface, with the first annular edge being adapted to be retained therein. Also, the dust cover may be adapted for use on a drum brake.

As a further alternative, the first annular edge 42 may be secured in a groove in the brake cylinder 12 by way of a steel ring member, a spring member, or other form of insert.

Claims

Claims:

1. A dust cover for the sliding surfaces between a piston and a brake cylinder in which the sliding surface of the piston has a circumferentially extending groove therein adjacent its free end and the brake cylinder has a circumferentially extending groove at or adjacent its open end, the dust cover being substantially annular and comprising a first annular edge for retention in the circumferentially extending groove in the brake cylinder; a second annular edge for positioning in the circumferentially extending groove in the sliding surface of the piston; and a bellows portion linking the first and second annular edges; the second annular edge having a substantially semi-circular cross-section.

2. A dust cover as claimed in claim 1, in which the circumferentially extending groove in the brake cylinder is positioned in the sliding surface thereof adjacent the open end thereof, wherein the first annular edge has an inwardly directed ridge for engaging the piston.

3. A dust cover substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.