This disclosure pertains to the construction of and the method of constructing an enhanced thermally conductive pivot bushing. More particularly, this disclosure pertains to an aircraft main landing gear pivot joint bushing having an increased heat sink material construction.
Many transport category aircraft have truck beams on their main landing gear assemblies. In a typical landing gear assembly at least two pairs of wheels are attached to the fore and aft ends of the truck beam. A pivot pin connects an intermediate portion of the truck beam to an inner cylinder fork for pivoting movement of the truck beam relative to the fork. Cylindrical bushings are provided between the pivot pin and the truck beam and inner cylinder fork.
On take off and landing, as the aircraft rolls along a runway, the truck beam pitches in a fore and aft plane about the pivot pin. This pivoting movement generates localized friction heating at the interfaces of the moving parts. The amount of heating varies with factors such as runway roughness, joint friction, truck beam pitch velocity, and aircraft weight. The localized friction heating creates hot spots within the landing gear truck beam and the inner cylinder fork. If the generated friction heating reaches too high a level in the landing gear components, the metallic structure of the landing gear components can be adversely affected in various ways. This occurrence is generally referred to as “friction-induced heat damage.” The friction-induced heat damage can lead to fractures of the landing gear components where the damage occurs and possible loss of control of the aircraft.
Two basic approaches have been employed to resolve the problem of friction-induced heat damage of landing gear components. One has been to reduce frictional heating in the joint (e.g., improved lubrication systems, better greases, more frequent lubrication, active lubrication systems, use of polymer-lined bushings, metallic bushings with lower coefficients of friction, or use of truck beam-pitch dampers). The second has been to use structural components in the truck beam that are less susceptible to friction-induced heat damage (e.g., metal alloys).
However, these solutions have several drawbacks. Truck dampers and active lubrication systems are prone to failure and cannot be easily retrofitted to existing designs of landing gear assemblies. Improved greases and bushing materials often do not provide enough friction reduction to prevent heat damage. Polymer-lined bushings have not survived in extreme operating conditions. Increased lubrication frequency is burdensome and costly to aircraft maintenance programs. Special structural alloys are very expensive.
The enhanced thermally conductive pivot bushing of this disclosure overcomes the problem of localized friction-induced heat damage in landing gear components. The bushing distributes heat more equally to the landing gear components than previous solutions by increasing the thermal dissipating capacity of the bushing within the pivot joint, thus decreasing the amount of localized friction-induced heat transferred to the truck beam and the inner cylinder fork.
The aircraft pivot joint bushing has an inner cylindrical portion and an outer cylindrical portion. The inner cylindrical portion is constructed of a first material having a first thermal dissipating capacity. The first material also has a low coefficient of friction. The outer cylindrical portion is constructed of a second material having a second thermal dissipating capacity. The outer cylindrical portion engages around the inner cylindrical portion. The first material of the inner cylindrical portion is more thermally conductive than the second material of the outer cylindrical portion. Therefore, the inner cylindrical portion of the bearing has a more thermal dissipating capacity than the material of the outer cylindrical portion of the bearing.
In use, the inner cylindrical portion of the bearing is mounted inside the outer cylindrical portion, and the outer cylindrical portion of the bearing is mounted in pivot joint bores of the inner cylinder fork and the truck beam of the landing gear assembly.
Instead of reducing friction heat in the pivot joint or using different alloy materials in the truck beam or inner cylinder fork, the bushing simply adds a less thermally conductive material to the outer cylindrical portion of the bushing. Adding a less thermally conductive layer to the outer cylindrical portion of the bushing increases the thermal dissipating capacity of the inner cylindrical portion of the bushing. This construction forces heat in the inner cylindrical portion of the bushing to spread circumferentially through the inner cylindrical portion of the bushing before transferring radially to the outer cylindrical portion of the bushing. This distributes bushing heat more evenly and thus inhibits or prevents localized hot spots from forming on the landing gear truck beam and the inner cylinder fork connected to the pivot pin, thus inhibiting or preventing localized friction-induced heat damage to the truck beam and inner cylinder fork.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings.
Further features of the enhanced thermally conductive pivot bushing of this disclosure are set forth in the following detailed description and the drawing figures.
Referring to
The inner cylinder fork 10 has a pair of bore holes through the fork arms. The bore holes are surrounded by cylindrical interior surfaces 18, 22. The fork cylindrical interior surfaces 18, 22 are aligned with the truck beam cylindrical interior surface 16.
The pivot pin 14 has a cylindrical exterior surface 24 with a center axis 26. The pivot pin 14 is inserted through the aligned cylindrical interior surface 18 of the inner cylinder fork 10, the truck beam bore cylindrical interior surface 16 and the other inner cylinder fork cylindrical interior surface 22, completing the pivot connection between the inner cylinder fork 10 and the truck beam 12.
Also represented in
Referring to
The inner cylindrical portions 46, 48, 52 and their respective outer cylindrical portions 54, 56, 58 could be separate cylinders with the outer cylindrical portions 54, 56, 58 press fit or shrunk fit over the respective inner cylindrical portions 46, 48, 52. Alternatively, the inner cylindrical portions 46, 48, 52 and their respective outer cylindrical portions 54, 56, 58 could be formed as monolithic cylinders with the materials of the concentric and coaxial cylinders being fused together where the inner cylindrical portion exterior surfaces 68, 72, 74 meet with the outer cylindrical portion interior surfaces 76, 78, 82.
As represented in
As represented in
Each of the inner cylindrical portions 46, 48, 52 is constructed of a first material having a first thermal dissipating capacity. Each of the outer cylindrical portions 54, 56, 58 is constructed of a second material having a second thermal dissipating capacity. The first material of the inner cylindrical portions 46, 48, 52 has a lower coefficient of friction and better wear characteristics than the second material of the outer cylindrical portions 54, 56, 58. The first material of the inner cylindrical portions 46, 48, 52 is more thermally conductive than the second material of the outer cylindrical portions 54, 56, 58. Stated differently, the first material of the inner cylindrical portions 46, 48, 52 has more thermal dissipating capacity than the second material of the outer cylindrical portions 54, 56, 58, or the second material of the outer cylindrical portions 54, 56, 58 has less thermal dissipating capacity than the first material of the inner cylindrical portions 46, 48, 52. With the material of the inner cylindrical portions 46, 48, 52 of the bushings 32, 34, 36 being more thermally conductive, friction-induced heat created by the rotation of the bushings around the pivot pin exterior surface 24 is spread circumferentially through the inner cylindrical portions 46, 48, 52 of the bushings 32, 34, 36 before transferring radially to the respective outer cylindrical portions 54, 56, 58 of the bushings. This distributes the friction-induced heat more evenly through the bushings 32, 34, 36 and inhibits or prevents localized hot spots from forming on the truck beam bore cylindrical interior surface 16 and the inner cylinder fork cylindrical interior surface 18, thus inhibiting or preventing localized friction-induced heat damage to the truck beam 12 and the inner cylinder fork 10.
Represented in
Referring to
The inner cylindrical portions 116, 118, 122 and their respective middle cylindrical portions 124, 126, 128 and outer cylindrical portions 132, 134, 136 could be separate cylinders with the middle cylindrical portions 124, 126, 128 fit over the respective inner cylindrical portions 116, 118, 122 and the outer cylindrical portions 132, 134, 136 fit over the respective middle cylindrical portions 124, 126, 128. Alternatively, the inner cylindrical portions 116, 118, 122 and their respective middle cylindrical portions 124, 126, 128 and outer cylindrical portions 132, 134, 136 could be formed as monolithic cylinders with the materials of the concentric and coaxial cylinders being fused together where the inner cylindrical portion exterior surfaces 146, 148, 152 meet with the middle cylindrical portion interior surfaces 154, 156, 158 and the middle cylindrical portion exterior surfaces 162, 164, 166 meet with the outer cylindrical portion interior surfaces 168, 172, 174.
The inner cylindrical portions 116, 118, 122, the middle cylindrical portions 124, 126, 128 and the outer cylindrical portions 132, 134, 136 could have substantially the same radial thicknesses, or different radial thicknesses.
Additionally, the inner cylindrical portions 116, 118, 122, the middle cylindrical portions 124, 126, 128 and the outer cylindrical portions 132, 134, 136 could have the same axial lengths, or different axial lengths.
Each of the inner cylindrical portions 116, 118, 122 is constructed of a first material. Each of the middle cylindrical portions 124, 126, 128 is constructed of a second material. Each of the outer cylindrical portions 132, 134, 136 is constructed of a third material.
The first material is optimized for wear resistance and low friction coefficient. The first material has a greater wear resistance and a lower friction coefficient than the second material and the third material.
The second material is optimized for high thermal conductivity. The second material has a greater thermal conductivity than the first material and the third material.
The third material is optimized for low thermal conductivity. The third material has a lower thermal conductivity than the first material and the second material.
The second material of the middle cylindrical portions 124, 126, 128 has more thermal dissipating capacity than the first material of the inner cylindrical portions 116, 118, 122 and the third material of the outer cylindrical portions 132, 134, 136.
With the second material of the middle cylindrical portions 124, 126, 128 of the bushings 102, 104, 106 being more thermally conductive and having more thermal dissipating capacity than the first material of the inner cylindrical portions 116, 118, 122 and the third material of the outer cylindrical portions 132, 134, 136, friction induced heat created in the bushing inner cylindrical portions 116, 118, 122 is spread circumferentially around the bushings 102, 104, 106 through the respective middle cylindrical portions 124, 126, 128 before transferring radially to the respective outer cylindrical portions 132, 134, 136 of the bushings. This distributes the friction induced heat more evenly through the bushings 102, 104, 106 and inhibits or prevents localized hotspots from forming on the truck beam bore interior surface 16 and the inner cylinder fork cylindrical interior surface 18, thus inhibiting or preventing localized friction induced heat damage to the truck beam 12 and the inner cylinder fork 10.
As various modifications could be made in the construction of the apparatus and its method of operation herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.