GB2275744A

GB2275744A - Bearing assembly

Info

Publication number: GB2275744A
Application number: GB9406456A
Authority: GB
Inventors: S Robert Ahlman; William E Dunn; Harry Magazian
Original assignee: Torrington Co
Current assignee: Timken US LLC
Priority date: 1990-10-04
Filing date: 1991-10-02
Publication date: 1994-09-07
Anticipated expiration: 2011-10-02
Also published as: GB9406456D0; GB2275744B

Abstract

A track roller bearing comprises a floating sleeve (50) between an inner bearing member (10) and an outer bearing member (20). The floating sleeve has a self-lubricating bearing material (52) on its outer surface. The coefficient of friction of the self-lubricating bearing material increases as the material is worn. When the self-lubricating bearing material coefficient of friction exceeds the coefficient of friction of the floating sleeve inner surface, the floating sleeve will rotate with the outer bearing member until a new unworn surface of self-lubricating bearing material is presented to the load area of the outer bearing member. This precessing of the floating sleeve will continue until the entire surface area of the self-lubricating bearing material is worn, thus extending the track roller bearing life. The material (52) may comprise ptfe threads interwoven with peek backing threads. <IMAGE>

Description

BEARING ASSEMBLY This invention relates generally to bearing assemblies and more particularly to track roller bearings with a sleeve or liner to which a self-lubricating bearing material is bonded.

Conventional track roller bearings are constructed of rolling elements positioned between inner and outer bearing surfaces, lubricated by grease. Periodic lubrication is required to maintain operational performance with added resistance to corrosion. The performance of these conventional track roller bearings also depends on the effectiveness of the bearing seals which not only ensures that the grease lubrication is maintained within the bearing but also that contamination from external sources is avoided.

Newer aircraft designs require that moving parts shall be able to operate for long periods of time with relatively little or no maintenance. For example, bearings provided for the operation of ailerons on aircraft should be able to operate through tens of thousands of revolutions without any maintenance. Conventional roller bearings may have to be greased after 5,000 revolutions.

In one approach to this periodic maintenance requirement, a bearing liner is attached to the outer bearing surface.

The bearing liner contains a self-lubricating bearing material such as polytetrafluorethylene. As an alternative, the self-lubricating bearing material has been attached to the inner bearing surface.

Neither alternative using an attached bearing liner has been satisfactory. The bearing liner attached to the outer bearing surface frequently fails to achieve desired lifetimes due to fatigue failure. The liner is subject to a ploughing action by induced liner deflection when loaded by the inner bearing surface during rotation of the outer bearing surface. Self-lubricating bearing liners attached to the inner bearing surface are subject to premature wear.

In typical aircraft applications, the inner bearing surface is fixed and does not rotate. The outer bearing surface will bear against a limited portion of the inner bearing liner, that portion which is in line with the applied load.

In this instance, all the wear is to a small portion of the bearing liner which will prematurely wear out.

Another alternative adds a sleeve of self-lubricating bearing material between the inner and the outer bearing surfaces. The sleeve is free to float between the bearing surfaces. The bearing sleeve periodically and randomly sticks to one bearing surface or the other.

This random sticking can cause uneven wear and premature failure of the bearing.

According to the present invention, there is provided a bearing assembly, comprising a first bearing member, a second bearing member and lubricating means between the first and second members for exposing a lubricating surface to the second member, said lubricating means having a varying coefficient of friction which increases upon wearing away of the lubricating surface, and in response to said wearing away, said lubricating means is movable by the second member for incrementally presenting to the second member an unworn portion of the lubricating surface.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing in which Figure 1 is a partial cross-section illustrating an embodiment of a bearing assembly; and Figure 2 is a cross-section of a typical known track roller bearing.

Figure 1 illustrates a bearing assembly in the form of a track roller bearing having an inner bearing member 10 and an outer bearing member 20 with a floating bearing sleeve 50 located between the inner member 10 and the outer member 20.

The bearing members 10, 20 are typically formed from a corrosion resistant metal. Bearing surfaces 30, 40 are formed on opposing surfaces of the inner member 10 and the outer member 20. The outer bearing surface 40 has been polished to remove any residual marks from metal forming.

This polishing is sometimes referred to as superfinishing.

A floating bearing sleeve 50, with self-lubricating bearing material 52 bonded to its outer radial surface slidingly engages bearing surfaces 30, 40.

The floating bearing sleeve 50 is of steel. Other materials can be used so long as the material has sufficient stiffness to prevent undue flexing of the selflubricating bearing material 52 on the floating bearing sleeve 50 outer radial surface. The self-lubricating bearing material 52 is a calendared fabric containing solid lubricant threads made of polytetrafluorethylene, known under the Registered Trade Mark "Teflon". A fabric such as the one disclosed in U.S. Patent No. 4,358,167 is the preferred fabric for the self-lubricating bearing material 52.

The fabric is a weave of solid lubricant threads, polytetrafluorethylene, interwoven with backing or support threads, polyetheretherketone. Polyetheretherketone is used for the backing threads because it has adequate resistance to contaminants and cleansing solutions typically used by the airline industry. A weave such as the weave disclosed in U.S. Patent 4,358,167 is used. The upper surface of this weave is ' predominantly solid lubricant threads and the lower surface is predominantly backing threads. This weave gives the desired characteristic of an increasing coefficient of friction as the fabric is worn away. Typically, the self-lubricating bearing material 52 is bonded to the floating bearing sleeve 50 using a phenolic adhesive, modified phenolic adhesive or a vinyl phenolic.

A lubricant is used between the inner bearing surface 30 and the floating bearing sleeve 50. The key characteristic of the lubricant is that the coefficient of friction must be higher than the coefficient of friction of the upper surface of the self-lubricating bearing material 52.

Normally, the floating bearing sleeve 50 does not rotate since the coefficient of friction between the floating bearing sleeve 50 and the outer bearing surface 40 is substantially less than the coefficient of friction between the floating bearing sleeve 50 and the inner bearing surface 30. The preferred lubricant is a dry film lubricant such as molybdenum disulphide or Dycronite, by Lubrication Services, Inc. Other lubricants such as a solid self-lubricating material may be used between the inner bearing surface 30 and the floating bearing sleeve 50.

Figure 2 (prior art) depicts a cross-section of a typical track roller bearing with self-lubricating material 66 bonded to the inner bearing member 64. The inner bearing member 64 is attached to a shaft or securing fastener 62 such that the inner bearing member 64 does not rotate. In a typical mode of operation, the applied bearing load is directed vertically as indicated by the arrow, thus causing the outer bearing member 60 to bear against a portion 66a of the self-lubricating bearing material 66 of the inner bearing member 64 in the illustrated wear zone. Thus, if the inner bearing member 64 is fixed in position, only the portion 66a of bearing material 66 in the wear zone will be subjected to wear. The floating bearing sleeve 50 of the present invention is designed periodically to rotate, thus presenting a new surface of the self-lubricating bearing material 52 to the wear zone.

As the outer bearing surface 40 wears against the selflubricating bearing material 52, the self-lubricating bearing material 52 is worn away. The area of wear is only a fraction of the complete surface area of the floating bearing sleeve 50, that area which is in line with the applied load. As the self-lubricating bearing material 52 is worn, its coefficient of friction increases until its coefficient of friction exceeds the coefficient of friction between the floating bearing sleeve 50 and the inner bearing surface 30. At this time, the floating bearing sleeve 50 will begin to turn with the outer bearing surface 40. As the floating bearing sleeve 50 turns, a new, unworn area of the self-lubricating bearing material will precess under the wear zone of the outer bearing surface 40. Once the coefficient of friction of the self-lubricating bearing material 52 has again become less than the coefficient of friction between the floating bearing sleeve 50 and the inner bearing surface 30, the floating bearing sleeve 50 stops turning.

The new area of self-lubricating material under the wear zone of the outer bearing surface 40 begins to wear away increasing the coefficient of friction repeating the process described above. The repeated precessing of the floating bearing sleeve 50 results in even and complete wear of the self-lubricating bearing material 52. A track roller bearing with the floating bearing sleeve described above has a lifetime of several times the lifetime of a conventional track roller bearing with self-lubricated bearing material bonded to a bearing member.

Figure 1 shows the preferred embodiment with the outer bearing member 20 being rotatable. For applications where the inner bearing member 10 rotates, the self-lubricating bearing material 52 is bonded to the inner radial surface of the sleeve 50.

The present bearing assembly is also shown and described in co-pending Application No. 9120956.9 (Serial No. 2 248 894 A), to which reference is accordingly directed. In that application, the invention is directed to a bearing assembly comprising a first bearing member having a first peripheral bearing surface; a coaxial second bearing member rotatable relative to said first member, the second member having a second peripheral bearing surface; and a sleeve member having an outer radial surface and an inner radial surface. The sleeve member is disposed between and in sliding engagement with the first and second bearing surfaces and has a self-lubricating bearing material bonded to the radial surface adjacent the second bearing surface and being incrementally movable by the second bearing surface in response to wearing away of the material.

Claims

CLAIMS:

1. A bearing assembly, comprising a first bearing member, a second bearing member and lubricating means between the first and second members for exposing a lubricating surface to the second member, said lubricating means having a varying coefficient of friction which increases upon wearing away of the lubricating surface, and in response to said wearing away, said lubricating means is movable by the second member for incrementally presenting to the second member an unworn portion of the lubricating surface.

2. A bearing assembly according to claim 1, wherein said first bearing member is an inner bearing surface and said second bearing member is an outer bearing surface.

3. A bearing assembly according to claim 1, wherein said first bearing member is an outer bearing surface and said second bearing member is an inner bearing surface.

4. A bearing assembly according to any one of the preceding claims, wherein said lubricating means comprises a fabric of interwoven solid lubricant threads and support threads; and one surface of said fabric being predominantly solid lubricant threads and another surface of said fabric being predominantly support threads, whereby the coefficient of friction of said fabric is less at said one surface than at said other surface.

5. A bearing assembly according to claim 4, wherein said solid lubricant threads are polytetrafluorethylene.

6. A bearing assembly according to claim 4 or 5, wherein said support threads are polyetheretherketone.