Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-08-24
2001-05-22
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S1960BA, C192S111400
Reexamination Certificate
active
06234279
ABSTRACT:
BRIEF SUMMARY OF THE INVENTION
The present invention relates generally to methods and apparatus for adjusting hydraulic brake pistons, for example, to compensate for brake friction surfaces wear, and more especially to an internal automatic adjuster for such brake pistons. The preferred embodiment of the present invention relates to an internally disposed mechanical brake piston adjuster assembly for an aircraft brake.
It is common knowledge that vehicle braking over a period of time causes wear of the brake pads or other friction surfaces resulting in increased clearance between the braking surfaces and requiring a longer stroke of the brake actuator piston to effect braking. At one time this problem was alleviated by periodic manual adjustment of the brake. Automatic adjustment schemes have largely eliminated the need for such periodic manual adjustments.
Many automatic brake piston adjustment arrangements are external to the brake actuator, however, in some applications this is undesirable, for example, due to space considerations. Another application where such external adjustment arrangements may be undesirable is multi-disk brakes employed, for example, on aircraft.
Internally disposed brake piston adjusters are also known and frequently employ an adjuster tube which may be periodically deformed radially outwardly (U.S. Pat. Nos. 4,751,985 and 5,154,262) or inwardly (copending Berwanger USSN 081905,246, assigned to the assignee of the present application and entitled Pinless Automatic Adjuster for Brake Piston now U.S. Pat. No. 6,016,892) to compensate for braking surface wear by re-establishing the rest or quiescent retracted position of the brake piston.
Briefly, in the U.S. Pat. No. 4,751,985 patented system, the brake piston adjuster mechanism includes a radially outwardly expandable or deformable adjuster tube which is attached to the brake piston and engaged by a fixed deforming member comprising a cantilevered adjuster pin having a threaded free end receiving thereon a nut and tube expander. As braking surfaces wear, the piston stroke during brake actuation increases and becomes sufficient to move the adjuster tube axially along the tube expander deforming the tube and establishing a new retracted or rest position for the piston. This system had excessive stress regions in the area of the pin threaded end. The U.S. Pat. No. 5,154,262 patented system alleviated the stress regions while retaining the deforming member structure of a pin having a threaded end receiving a nut and tube expander, with the nut biasing the tube expander against a chamfered pin shoulder. The tube expander had at least one inner diameter chamfer which engaged the chamfered pin shoulder in order to impose preload forces upon the chamfered pin shoulder and reduce stresses at a smaller diameter portion of the pin. The nut could be a castellated nut which received a locking wire or pin extending through an opening in the threaded end of the pin. Alternatively, the tube expander and nut could comprise a one-piece expander nut having an enlarged radially extending end portion and the nut, when advanced along the threads of the pin, caused a chamfer of the end portion to advance along the chamfered pin shoulder and caused the end portion to deform elastically, improving the preload retention of the connection. In some implementations of these patented systems, the adjuster pin fixed end was square so as to not rotate about its axis when the nut was unthreaded. While this arrangement allowed removal of the adjuster tube without the need for removing the entire brake bushing portion of the housing, the square end was also susceptible to high stress region failure. In other implementations, the fixed end was conical and not susceptible to such failures, however, the conical fixed end configuration, which was provided with an Allen wrench socket, required removal of the entire piston bushing from the remaining portion of the brake piston housing to gain access to the conical end to effect removal of the nut and replacement of the adjuster tube.
While these prior patented arrangements generally achieved their desired goals, some shortcomings remain. Elimination of the square fixed end stress regions required the undesirable removal of the brake piston bushing during maintenance and adjustment tube replacement. The threaded free end of the adjuster pin still experienced undesirably high stress regions near the base of the threads and where the castellated nut locking wire or cotter pin hole passed transversely through the pin. Due to the limited number (typically six) of discrete angular positions for the castellated nut, appropriate torquing of the nut was difficult and sometimes inaccurate. This torquing establishes the initial location and preload of the tube expander within the adjuster tube.
It is highly desirable to provide an easily serviced brake piston adjuster assembly which automatically adjusts the return position of the brake piston as the brake friction surfaces wear. It is also highly desirable to provide a brake piston adjuster assembly which eliminates the adjuster pin high stress points and possibility of fatigue induced failures. It is further highly desirable to provide a compact, economical internal adjustment arrangement for a brake piston which does not experience fatigue induced failures and which does not require excessive disassembly during maintenance.
The present invention provides solutions to the above problems by providing a brake piston adjuster assembly including a housing with a cylindrical bore and a relatively fixed return spring anchor location within the housing. A piston is disposed slidably in the housing bore and may be extended therefrom in response to the application of hydraulic pressure to one piston end. A helical piston return spring resides within the piston and has one end engaging the piston and another end engaging the relatively fixed anchor location. The spring compresses as the piston is extended from the housing and urges the piston further back into the housing upon the reduction of hydraulic pressure on the piston end. The anchor location of the return spring may be modified by radially expanding an adjuster tube to establish a new relatively fixed location within the housing in response to piston translation which exceeds a predetermined distance to change the location to which the spring returns the piston. This effectively restores a predetermined clearance spacing between the piston and a braking mechanism each time the piston stroke becomes excessive. Periodically, the adjuster tube requires replacement which is accomplished by compressing the spring and moving the adjuster tube thereby exposing a split ring tube expander for removal preparatory to removing the adjuster tube. The split ring tube expander normally resides in a complementarily contoured groove in a fixed cantilevered adjuster pin.
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patent: 6016892 (2000-01-01), Berwanger
Jankowski Richard B.
Zigler Chad N.
Allied-Signal Inc.
Butler Douglas C.
Palguta Larry J.
Pezzlo Benjamin A.
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