Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-02-09
2001-10-02
Graham, Matthew C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S073360
Reexamination Certificate
active
06296084
ABSTRACT:
The present invention relates to a torque transmission device such as a brake or clutch. It relates in particular, though not exclusively, to a torque transmission device in the form of a multi-disc brake assembly for an aircraft wheel and to a wheel and brake assembly comprising said torque transmission device.
An aircraft brake assembly typically comprises a torque tube having a splined outer surface on which is mounted a series of stator type friction discs of a material such as steel or carbon. The stator discs are interleaved with rotor discs carried by the aircraft wheel and the interleaved assembly of discs is axially compressible between a series of circumferentially spaced actuation pistons secured to one axial end region of the torque tube and a thrust reaction member at the other end region of the torque tube.
The torque tube is coaxial with a wheel axle relative to which a wheel is rotatably mounted by means of bearings secured to the axle, usually in an annular space between the radially outer surface of the axle and the inner surface of the torque tube.
The torque tube commonly includes a so-called pedestal which extends radially inwards to a foot portion that is supported by the radially outer surface of the axle.
In the aforedescribed construction of a typical aircraft brake assembly the torque tube locates the stator discs, provides a thermal barrier between the brake friction discs and the axle, increases whirl stability and enhances vibration damping in addition to the structural function of transmitting torque during a braking operation.
During a braking operation the torque transmitted by the torque tube can result in a change in the annular configuration of that tube. The torque tube can experience some consequential whirl instability and torsional movement and can also experience squeal vibrations. It is recognised by brake designers that it would be preferable to achieve an improvement in the precision with which the configuration of the torque tube is maintained during braking operations so as to improve whirl stability, increase torsional damping and reduce squeal vibrations.
One proposal for endeavouring to improve the maintenance of the torque tube configuration during braking operations is described in the specification of U.S. Pat. No. 5,485,898. That proposal comprises provision of a spacer member located radially between the torque tube and axle, at a position axially outwards of the conventional pedestal, so as to lie axially between the pedestal and wheel bearings.
The pedestal typically is integral with the torque tube and extends radially inwardly for support by bushing means associated with the axle. The spacer member is located axially between a radially inner region of that pedestal and the wheel bearings. The pedestal also may have a tubular extension which extends outwards towards the axial position of the wheel bearings to lie radially interposed between the spacer member and torque tube.
A cylindrical outer surface of the spacer member is provided with a coating such as aluminium bronze which uniformly contacts and supports the inner diameter surface of the torque tube or a component part associated with the torque tube. The coating may serve to provide improved frictional contact between the spacer member and inner diameter surface of the torque tube. Additionally a support ring may be disposed between the inner diameter surface of the spacer member and the outer diameter surface of the axle, the support ring and spacer member each then including respective splines to effect a splined interconnection which prevents relative rotation of the ring and spacer member. In this construction it is claimed by the prior art teaching that the provision of the spacer member leads to improved torque tube configuration stability and support.
It has now been found that, notwithstanding the alleged benefits of a spacer member and coated surface, there are problems due to fretting and/or galling wear at the contact areas between the spacer member and adjacent surfaces, and including at that interface between the cylindrical radially outer surface of the spacer member and the confronting surface of the torque tube or other component part such as a pedestal extension against which that outer surface lies in contact. Small movements at those interfaces lead to wear and in consequence yet further interface movement during braking operations. As that wear, and hence relative movement, increases there is a progressive reduction in the beneficial effects which the spacer member might otherwise provide.
An object of the present invention is to provide means by which the effectiveness of the spacer member of a torque transmission device such as an aircraft brake assembly may be preserved better during the working life of the device, or at least during the period between normal service operations.
According to the present invention it is taught that the spacer member has a radially outer portion which at least in part defines a non-rigid, non-cylindrical outer surface region that is deformable to bear resiliently against the inner diameter surface of the torque tube, or component part associated with the torque tube.
Said radially outer portion may comprise said deformable region and a substantially non-deformable region. The non-deformable region may have a substantially cylindrical outer surface to confront and optionally also to bear against a confronting surface of the torque tube or component part associated with the torque tube. Alternatively all of said radially outer portion may be non-rigid, with all or at least a part of said outer portion being non-cylindrical. Any said non-deformable region may be at that end region of the radially outer portion which first enters the torque tube on assembly of the spacer member into the torque tube.
The non-rigid, non-cylindrical outer surface region may comprise an outer surface which, in the absence of applied radial force such as that due to a surrounding torque tube, flares outwardly in a direction away from that end region which first enters the torque tube during assembly. Said outer surface may be of a frusto-conical shape, or as considered in axial cross-section it may be concave.
Preferably the deformable portion flares outwardly at an angle in the range 0.1° to 7°, more preferably between 0.2° and 2°.
The non-cylindrical outer surface region may be circumferentially continuous, or it may be discontinuous. It may, for example, comprise a plurality of narrow, axially extending and circumferentially spaced slits which will tend to close as the spacer member is fitted into a torque tube. Thus the discontinuous region may comprise a plurality of resiliently outwardly biassed finger sections which in the assembled condition bear resiliently against an inner surface of the torque tube or component part associated with the torque tube.
The outer surface of said radially outer portion optionally may include a coating or sleeve, which may be of a kind known per se.
The radially outer portion of the spacer member typically is formed of a metallic material such as spring steel, e.g. a spring type stainless steel.
Additionally spring means may be employed to provide an axial force that resiliently loads the interfaces between the torque tube pedestal and the spacer member, and/or between the spacer member and other structure of the torque transmission device, such as wheel bearing means.
The spring means preferably is subject normally to compression load when in use. Preferably the resiliency of the spring means enables it to prevent or at least substantially eliminate relative movement at said interface(s) during normal use.
Examples of suitable spring means include a metal spring, such as a frusto-conical disc spring (known generally as a Belleville washer), or a wave type disc spring or other type of metallic annular spring washer. Alternatively the spring means may be an element, such as a ring-shaped member, of a resilient polymeric or other non-metallic material provided that the temperatures attained in use o
Dunlop Limited
Graham Matthew C.
Young & Thompson
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