Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-07-30
2001-12-04
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S072500, C188S362000
Reexamination Certificate
active
06325181
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to vehicle drum brake assemblies and in particular to an improved structure for a piston assembly adapted for use in a wheel cylinder of such a vehicle drum brake assembly.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies can be actuated by hydraulic, pneumatic, or mechanical pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like. The structure and operation of both drum brake assemblies and disc brake assemblies, as well as the actuators therefor, are well known in the art.
A typical drum brake assembly includes a backing plate which is secured to a fixed, non-rotatable component of the vehicle, such as the vehicle axle housing. A pair of opposed arcuate brake shoes are supported on the backing plate for selective movement relative thereto. Each of the brake shoes has a friction pad secured thereto. The drum brake assembly further includes a cylindrical brake drum which is secured to the vehicle wheel for rotation therewith. The interior of the brake drum is hollow, defining an inner cylindrical braking surface. The brake drum is disposed adjacent to the backing plate such that the brake shoes extend within the inner cylindrical braking surface. To effect braking action, the brake shoes are moved outwardly apart from one another such that the friction pads frictionally engage the inner cylindrical braking surface of the brake drum. Such frictional engagement causes slowing or stopping of the rotational movement of the brake drum and, therefore, the wheel of the vehicle in a controlled manner.
One or more actuating mechanisms are provided in the drum brake assembly for selectively moving the brake shoes outwardly apart from one another into frictional engagement with the cylindrical braking surface of the brake drum. Usually, a hydraulically or pneumatically actuated service brake mechanism is provided for selectively actuating the drum brake assembly under normal operating conditions. Such a service brake mechanism can include a hydraulically actuated wheel cylinder having a pair of opposed pistons which abut and move the brake shoes apart from one another into frictional engagement with the cylindrical braking surface of the brake drum.
A mechanically actuated parking and emergency brake mechanism is also usually provided for selectively actuating the drum brake assembly. The parking and service brake mechanism can include an actuating lever pivotally supported on one of the brake shoes. The actuating lever is connected to a cable which, when pulled, moves the brake shoes apart from one another into frictional engagement with the cylindrical braking surface of the brake drum.
SUMMARY OF THE INVENTION
This invention relates to an improved structure for a piston assembly adapted for use in a wheel cylinder of drum brake assembly having a pair of brake shoes which are adapted to be urged into frictional engagement with a brake drum. The piston assembly includes a piston body formed from a plastic material and a piston insert formed from metal. In accordance with one embodiment of this invention, the piston insert is molded in situ with the piston body and the piston insert includes a radially outwardly extending first flange and a radially outwardly extending second flange. The first flange defines a first flange outer diameter, and the second flange defines a second flange outer diameter which is less than the first flange outer diameter. The first flange of the piston insert is operative to distribute the pressure across the associated outer face of the piston body during brake application, and the second flange of the piston insert is operative to assist in securing the piston insert to the piston body during the molding process.
Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.
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Burch Melody M.
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
Oberleitner Robert J.
LandOfFree
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