Metal working – Means to assemble or disassemble – Spreading parts apart or separating them from face to face...
Reexamination Certificate
2000-04-06
2001-03-06
Scherbel, David A. (Department: 3723)
Metal working
Means to assemble or disassemble
Spreading parts apart or separating them from face to face...
C029S266000
Reexamination Certificate
active
06195863
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disc brake assembly and disassembly apparatus and, in particular, to a tool for positioning and installing a piston into the piston cylinder of disc brake caliper housing.
2. Prior Art
Disc brake assemblies in automobiles and trucks typically include a rotor disc mounted on the axle of the vehicle and a caliper assembly including one or more hydraulically operated pistons which control the movement of brake pads on each side of the disc causing them to contact the disc and prevent or inhibit the rotation thereof. The caliper typically includes an outer support bracket. After a period of use, parts of the caliper assembly, especially the brake pads and pistons may require replacement. As the brake pads wear due to friction against the disc, they become thinner and the piston assumes an extended position and must be retracted into the piston bore to allow room for new (thicker) pads to replace them. Considerable force may be necessary to retract the pistons into the bore and allow room for the new pads to be mounted.
One of the more common techniques for the retraction of pistons into the bore of a disc brake assembly involves the use of a C-clamp to apply pressure to the piston. The use of a C-clamp (as well as some other tools that have been used for this purpose) often involves difficulty with respect to the alignment of the piston during retraction. The clamp may tend to shift during the procedure, causing the piston to shift from the axial alignment within the piston bore. This may result in the jamming of the piston in the bore or cause damage to the seals and may, as a consequence, require a more complete rebuilding of the assembly.
Various tools and methods have been developed for the retraction of pistons or the installation of new pistons in disc brake assemblies, release of frozen pistons as well as various other problems associated with disc brake assemblies in general and disc brake pistons in particular.
U.S. Pat. No. 3,654,689 to Schwarz discloses a method and apparatus for releasing frozen pistons through the use of an hydraulic system to force the piston(s) against a spacer block. The piston can then be drawn back into the piston bore with the aid of a vacuum line.
U.S. Pat. No. 5,018,261 to Markous and U.S. Pat. No. 5,850,680 to Verrier et al. describes a disc brake assembly tools wherein the piston is forced back into the piston bore by pressure from a threadably adjustable arm positioned in the channel of a caliper body.
It will be appreciated that, although a variety of disc brake caliper tools are known, there is a continuing need for improved tools and methods, especially for use in the retraction of pistons or the installation of new pistons in disc brake assemblies.
It is an object of the present invention to provide a new and improved tool for the retraction of a piston into the piston bore of a disc brake caliper assembly.
It is a further object to provide a piston installation tool for the repair of disc brake caliper assemblies that will exert an even pressure on the edges of a piston and thus maintain the proper axial orientation of the piston during installation.
It is a still further object to provide a disc brake piston installation tool that is easy to use and is powered by pneumatic pressure.
It is a still further object to provide such a tool that may be adapted to fit a variety of disc brake calipers and that may be used to determine the resistance of a piston to retraction.
SUMMARY OF THE INVENTION
The above and other objects are achieved in accordance with the present invention, which provides a pneumatically operated piston installation tool for use with disc brake caliper assemblies having a piston movably disposed in a piston bore at one side of a caliper housing and an outer support bracket at the opposite side. The piston installation tool comprises:
a first plate, positionable within the disc brake caliper housing in contact with an outer edge of an extended piston;
a second plate in alignment with, and spaced apart from, the first plate and positionable against an inside surface of the outer support bracket;
a piston shaft attached at one end to the first plate at a central point thereof and extending perpendicularly therefrom passing slidably through a central opening in the second plate into a surrounding cylinder attached to the second plate; and
pneumatic means for moving the piston shaft out of the cylinder and pushing the first plate against the outer edge of the piston in a direction away from the second plate, forcing the piston to retract into the piston bore.
Compressed air for the operation of hand-held pneumatic tools is generally available in garages and maintenance shops where repair work on disc brake assemblies is commonly carried out. The piston installation tool of the present invention includes a hose that can be plugged into the compressed air system in the same manner as other common pneumatic tools, such as pneumatic drills, impact guns, and the like to supply pneumatic pressure to the cylinder.
In a preferred embodiment, the piston installation tool of this invention includes a pressure gauge that displays the pressure being applied. By observing the pressure gauge, the amount of pressure necessary to move the piston can be determined. Thus, the gauge can be used to determine the resistance of the piston to retraction and also can be used as an indicator of a frozen piston. Furthermore, the resistance of a piston to retraction can be compared with the resistance of a piston in the disc brake assembly on the opposite wheel and thus determine whether the brakes are stopping evenly or not.
In a further preferred embodiment, the cylinder attached to the second plate includes a return mechanism that operates when the pneumatic pressure is withdrawn. Thus, for example the cylinder may be a single acting cylinder with a spring return, that is, incorporating a built-in spring which returns the piston shaft to its starting position.
In use, the disc brake caliper assembly is removed from a vehicle, generally with the hydraulic brake lines remaining in place and the brake pads are removed. The installation tool is then placed in the caliper with the first plate positioned against the outer edge of the brake piston and the second plate brace against the inside surface of the disc brake outer support bracket. Pneumatic pressure is then applied to move the piston shaft out of the cylinder and move the first plate against the brake piston, and push it back into the piston bore of the caliper housing.
One embodiment of the disc brake installation tool of the invention is suitable for installing two pistons simultaneously in a dual piston disc brake caliper assembly. For this purpose, two of the installation tools that would be used for the installation of single piston disc brake assemblies can be yoked in a side by side relationship. The first plate may be wide enough to position across two side by side pistons in a dual piston caliper, or may be separate plates. The second plate may comprise two separate plates, each attached to one of the yoked cylinders. Preferably, in this embodiment, the second plate is a single plate, wide enough for attachment to both cylinders. In this manner it may also serve as the yoke to hold the two cylinders together.
REFERENCES:
patent: 3654689 (1972-04-01), Schwarz
patent: 3786551 (1974-01-01), Gregg et al.
patent: 4903391 (1990-02-01), Franks
patent: 5018261 (1991-05-01), Markous
patent: 5269053 (1993-12-01), Hicks
patent: 5850680 (1998-12-01), Verrier et al.
patent: 6085398 (2000-07-01), Arch
Cookfair Arthur S.
Scherbel David A.
Shanley Daniel
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