Self-lubricating bushing assembly

Abstract

To provide an improved self-lubricating bush assembly.SOLUTION: A bush assembly configured to be disposed between a first component and a second component movably coupled to the first component comprises: a first bush portion comprising a self-lubricating material; and a second bush portion, the second bush portion having greater electrical conductivity than the first bush portion, where the second bush portion provides a conductive path between the first component and the second component.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a self-lubricating bushing assembly. [Background technology]

[0002] An aircraft landing gear assembly may include several structural components that are movably connected via couplings or joints. For example, a forward stay has first and second components that are pivotally connected to each other using a pin joint to allow the stay to fold. Bushings are commonly used in the joints to reduce wear on these structural components as they move relative to each other.

[0003] It is desirable for landing gear to provide a conductive path between the aircraft wheels and the landing gear attachment points to allow for the discharge of static electricity and ensure protection against lighting strikes. In pin joints, for example, the conductive path is formed by a number of structural parts electrically connected with a conductive path between a metallic bush and the joint pin.

[0004] Recently, low friction materials, commonly known as self-lubricating materials, have been used in joint bushings to reduce the need for periodic greasing of the joints. These self-lubricating materials are generally poor conductors and therefore the guaranteed electrical bond is lost from the metal-to-metal contact between the joint bushings and the components and pins.

[0005] Bonding straps are one method for providing a current path between multiple joined parts. However, bonding straps require attachment points and fasteners and can cause snagging of other equipment. Additionally, bonding straps can cause excessive noise and increase the complexity of the joint leading to higher maintenance levels. It is therefore desirable to mitigate these issues. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a bushing assembly configured to be disposed between a first part and a second part movably connected to the first part, the bushing assembly comprising a first bushing portion having a self-lubricating material and a second bushing portion having a greater electrical conductivity than the first bushing portion, the second bushing portion providing a conductive path between the first part and the second part.

[0007] The second bushing portion of the bushing assembly may comprise a metallic material, a conductive elastomer, or graphite.

[0008] The bushing assembly may include a third bushing portion comprising a self-lubricating material, the second bushing portion being located between the first bushing portion and the third bushing portion.

[0009] The bushing assembly may include a flange.

[0010] The second bushing portion of the bushing assembly may be configured to apply a force to at least one of the first component and the second component.

[0011] The second bushing portion of the bushing assembly may be configured to apply a force to at least one of the first bushing portion and the third bushing portion.

[0012] According to a further aspect of the present invention there is provided a joint assembly comprising a first part, a second part movably connected to the first part, and a bush assembly according to the above aspect arranged between the first part and the second part, wherein the first part of the joint assembly is a joint pin and the second part can be rotatably connected to the joint pin.

[0013] According to yet another aspect of the present invention, there is provided a joint assembly comprising a first part, a second part movably connected to the first part, and a bush assembly according to the above aspect disposed between the first part and the second part, wherein the first part is a shaft connected to the second part such that the shaft can move along a longitudinal axis of the shaft.

[0014] According to a further aspect of the present invention there is provided a landing gear assembly for an aircraft comprising one or more of the above mentioned joint assemblies.

[0015] According to a further aspect of the present invention there is provided an aircraft comprising one or more aircraft landing gear assemblies comprising one or more of the joint assemblies described above.

[0016] Some embodiments of the present invention will now be described, by way of illustrative examples only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 shows a known joint assembly including a binding strap. [Diagram 2] FIG. 2 is a cross-sectional view of a bushing assembly according to one embodiment of the present invention. [Figure 3a] FIG. 3a is a cross-sectional view of a bushing assembly according to another embodiment of the present invention. [Figure 3b] FIG. 3b is a schematic diagram of a possible alternative arrangement of the second bushing portion of the bushing assembly of the present invention. [Figure 3c] FIG. 3c is a schematic diagram of a possible alternative arrangement of the second bushing portion of the bushing assembly of the present invention. [Figure 3d] FIG. 3d is a schematic diagram of a possible alternative arrangement of the second bushing portion of the bushing assembly of the present invention. [Figure 3e]FIG. 3e is a schematic diagram of a possible alternative arrangement of a second bushing portion of a bushing assembly of the present invention. [Figure 4a] FIG. 4a is a diagram of a bushing assembly according to a third embodiment of the present invention. [Figure 4b] FIG. 4b is a diagram of a bushing assembly according to a third embodiment of the present invention. [Figure 4c] FIG. 4c is a diagram of a bushing assembly according to a third embodiment of the present invention. [Diagram 5] FIG. 5 is a partial view of an aircraft including a landing gear assembly according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] FIG. 1 shows a known pin joint 100 and two pivotally connected parts 104, 106. The pin joint 100 comprises a joint pin 108 and a self-lubricating bushing (not visible in FIG. 1). The longitudinal axis of the joint pin 108 defines an axis A. The pin joint movably connects the first part 104 and the second part 106 such that the first part 104 can pivot about the axis A relative to the second part 106. The first part 104 and the second part 106 can be, for example, side stay links, torque links, lock links, bogie pivot pins, actuator attachments or other similar parts commonly found in landing gear. The self-lubricating bushings are disposed between the joint pins and the first part 104 and the second part 106. The self-lubricating bushings are made of a low friction material, reducing or eliminating the need for periodic lubrication of the bushings. In another known pin joint arrangement, one of the first and second parts 104 and 106 may be cross-bolted to the joint pin 108 such that only the other part is allowed to move relative to the joint pin 108 .

[0019] The low friction material of the self-lubricating bushings may be poor conductors. To ensure that there is a conductive path through which electrostatic discharge or current resulting from a lighting strike can flow from the first part 104 to the second part 106, the binding strap 110 is coupled to the first part 104 via a first strap attachment point 112a and to the second part 106 via a second strap attachment point 112b. The binding strap comprises a conductive material. The attachment points 112a and 112b are configured to allow current to flow from the first part 104 through the binding strap 110 to the second part 106.

[0020] Tie-down straps have many disadvantages. For example, they can cause snagging of other equipment and can cause the landing gear to "hang up" during deployment. Additionally, tie-down straps can generate excessive noise and the attachment points 112 can require bolts and fasteners that can be detrimental to the structural integrity of the components 104, 106. Tie-down straps also increase the complexity of the joint assembly, resulting in higher maintenance.

[0021] FIG. 2 shows a cross section of a pin joint assembly including a bushing assembly 200 according to a first embodiment of the invention. The bushing assembly 200 is arranged between a first part 206 and a second part 208 movably connected to the first part 206. The first part 206 may be a joint pin. The second part 208 is pivotally connected to the joint pin and may be a side stay, a torque link, a lock link, a shortening link, an actuator attachment, or the like. The bushing assembly 200 includes a first bushing part 202 and a second bushing part 204. The bushing assembly 200 surrounds the joint pin. The second bushing part 204 may be a relatively thin ring of conductive material. As illustrated in FIG. 2, the conductive second bushing part 204 may be arranged to be removable and replaceable (when the pin joint is disassembled) by simply sliding it off the joint pin. This may be advantageous if the second bushing part needs to be replaced due to wear.

[0022] The first bushing portion 202 comprises a self-lubricating material, as described later in this specification. In a preferred embodiment, the self-lubricating material may be an electrical insulator. In other embodiments, the self-lubricating material is electrically conductive, but less conductive than the second bushing portion 204.

[0023] The second bushing portion 204 has a greater electrical conductivity than the first bushing portion 202 and is positioned to provide a conductive path between the first component 206 and the second component 208. In a preferred embodiment, the second bushing portion 204 comprises a conductive elastomer or graphite and completely or partially surrounds the first component 206. In some embodiments, the second bushing portion 204 may comprise a metallic material. Thus, the second bushing portion 204 electrically couples the first component 206 to the second component 208. In some embodiments, the second bushing portion 204 may be sized to withstand a current of at least 200 kA.

[0024] 2, the first bushing portion 202 and the second bushing portion 204 contact each other and fit together with no gap between them. In other embodiments of the invention, the first bushing portion 202 and the second bushing portion 204 may be separated by a gap. This gap may facilitate removal and replacement of the second bushing portion, as previously described.

[0025] In use, a joint assembly including bushing assembly 200 allows the second part 208 to move relative to the first part 206 while always providing a conductive path for electrical current to flow between the first part 206 and the second part 208 through the second bushing portion 204.

[0026] Figure 3a shows a cross section of a part of a joint assembly comprising a bushing assembly 300 according to a second embodiment of the invention. The joint assembly of Figure 3a forms a pin joint in a similar manner to the joint shown in Figure 2. The bushing assembly 300 comprises a first bushing part 202 of a self-lubricating material, a second bushing part 204 of an electrically conductive material and a further third bushing part 312, which also comprises a self-lubricating material and is arranged such that the second bushing part 204 is located between the first bushing part 202 and the third bushing part 312.

[0027] In a preferred embodiment, the second bushing portion 204 surrounds the first part 206 (the joint pin) and is in direct contact with the first bushing portion 202 and the third bushing portion 312 such that the first bushing portion 202, the second bushing portion 204 and the third bushing portion 312 form a substantially tubular bushing disposed between the first part 206 and the second part 208 of the pin joint.

[0028] The bushing assembly 300 further includes a flange 314 on one or both ends of the first bushing portion 202 and the third bushing portion 312. The flange 314 includes a radially extending layer and is positioned to limit axial movement of the bushing assembly 300 relative to the first component 206 or the second component 208.

[0029] Advantageously, bushing assembly 300 allows for a compact, self-lubricating joint assembly that ensures electrical connection between multiple structural components of the landing gear, thus reducing the need for external coupling straps and fasteners, resulting in a joint assembly that is quieter, has greater structural integrity, and is lighter in weight than known assemblies.

[0030] 3b-3e show close-up views of the second bushing portion 204. FIG. 3b shows an axially offset view of the second bushing portion 204 configured to surround the first component 206. The second bushing portion 204 may have a split to allow the second bushing portion 204 to be adjusted to fit the joint pin 206, as shown in FIG. 3b. The circumferential cross-sectional shape of the second bushing portion 204 may be such that in use the second bushing portion 204 is compressed to fit between the first bushing portion 202 and the third bushing portion 312.

[0031] 3c-3e illustrate some possible alternative cross-sectional shapes that the second bushing portion 204 may have in embodiments of the present invention. The second bushing portion 204 may have a circumferential cross-sectional shape having an "N" shape as shown in FIG. 3c or a "U" shape as shown in FIG. 3e, such that when the second bushing portion 204 is compressed, it exerts a force on at least one of the first and second parts 206 and 208 due to inherent elastic deformation caused by the shape. In other embodiments of the present invention, the second bushing portion 204 may have a cross-sectional shape having a "Z" or "C" shape, such that the second bushing portion 204 is configured to exert a force on at least one of the adjacent first and third bushing portions 202 and 312 due to elastic deformation as described above. Another embodiment may have a graphite packing washer compressed between the first and third bushing portions 202 and 312 and the first and second parts 206 and 208, as shown in FIG. 3d.

[0032] Fig. 4a shows a further embodiment of the invention in which the joint assembly is a sliding joint. The first part 406 is a shaft and is connected to the second part 408 so that the shaft can move along the longitudinal axis of the shaft. In Fig. 4a, the shaft is shown as being tubular and having a circular cross section, but in other embodiments, the shaft may be a geometric prism and may have a rectangular, triangular or other polygonal cross-sectional shape. In Figs. 4a, 4b and 4c, the axis Y is parallel to the longitudinal axis of the shaft, and the axes X and Z define a plane perpendicular to the axis Y as shown. In a manner similar to the preceding elements, the bushing assembly 400 comprises at least a first bushing part 402 and a second bushing part 404, which are provided with a self-lubricating material.

[0033] Figure 4b illustrates one possible arrangement of the bushing assembly 400, where the first bushing portion and the second bushing portion are axially aligned and positioned to surround the shaft 406. Preferably, but not necessarily, the bushing assembly 400 of Figure 4b further comprises a third bushing portion 412 positioned such that the second bushing portion 404 is between the first and third bushing portions. The second bushing portion 404 may have any of the alternative circumferential cross-sectional shapes shown in Figures 3b-3e.

[0034] Figure 4c shows another possible arrangement of the bushing assembly 400, in which the first and second bushing portions are not axially aligned. Instead, the second bushing portion extends longitudinally parallel to the shaft along the Y axis of Figure 4c. The second bushing portion 404 and the first bushing portion 402 together form a substantially tubular bushing and are disposed between a first component 406 and a second component 408.

[0035] FIG. 5 shows a partial schematic diagram of an aircraft 520 having a landing gear assembly 500 comprising a main landing strut 540, wheels 530 and at least one joint assembly comprising a bushing assembly according to an embodiment of the present invention.

[0036] The self-lubricating material discussed above may be a polymer reinforced with synthetic fibers, which may include long fibers such as carbon, aramid, glass, PTFE, polyester, or combinations thereof. The self-lubricating material may also comprise an epoxy containing particles of a dry lubricant such as graphite, and a continuously woven mixture of PTFE and carbon fibers. Those skilled in the art will recognize that the above are merely examples and that any material having low friction characteristics may be used in its place. The self-lubricating material may be a liner injected into the surface of the first bushing part and / or the third bushing part, or the first bushing part and / or the third bushing part may be directly machined out of the material. The self-lubricating material may be bonded onto the surface of the first bushing part and / or the third bushing part. The present disclosure also includes the following inventions. The first aspect is 1. A bushing assembly adapted to be disposed between a first part and a second part movably coupled to the first part, comprising: The bushing assembly includes a first bushing portion having a self-lubricating material and a second bushing portion having greater electrical conductivity than the first bushing portion, the second bushing portion providing a conductive path between the first and second components. The second aspect is 2. The bushing assembly of claim 1, wherein the second bushing portion comprises any of a conductive elastomer, graphite, or metallic material. The third aspect is The bush assembly is the bush assembly of the first or second aspect, further comprising a third bush portion having the self-lubricating material, and the second bush portion is positioned between the first bush portion and the third bush portion. The fourth aspect is The bush assembly according to any one of the first to third aspects, further comprising a flange. The fifth aspect is The bushing assembly according to any one of the first to fourth aspects, wherein the second bushing portion is configured to apply a force to at least one of the first component and the second component. The sixth aspect is The bushing assembly according to any one of the first to fifth aspects, wherein the second bushing portion is configured to apply a force to at least one of the first bushing portion and the third bushing portion. The seventh aspect is A first part; A second part movably connected to the first part; a bush assembly according to any one of the first to sixth aspects, disposed between the first part and the second part. The eighth aspect is A seventh aspect of the joint assembly, wherein the first part is a joint pin and the second part is pivotally connected to the joint pin. The ninth aspect is A seventh aspect of the joint assembly, wherein the first part is a shaft, the first part being connected to the second part such that the shaft can move along a longitudinal axis of the shaft. A tenth aspect is A landing gear assembly for an aircraft, comprising one or more joint assemblies according to any one of the seventh to ninth aspects. An eleventh aspect is A tenth aspect is an aircraft comprising one or more aircraft landing gear assemblies.

Claims

1. 1. A bushing assembly adapted to be disposed between a first part and a second part movably coupled to the first part, comprising: The bushing assembly comprises a first bushing portion configured to contact both the first and second components, the first bushing portion comprising a self-lubricating material, and a second bushing portion configured to contact both the first and second components, the second bushing portion having a greater electrical conductivity than the first bushing portion, the second bushing portion providing a conductive path between the first and second components, a cross-sectional shape of the second bushing portion allowing elastic deformation of the second bushing portion, and the second bushing portion configured to apply a force to at least one of the first and second components.

2. The bushing assembly of claim 1 , wherein the second bushing portion comprises one of a conductive elastomer, a graphite, or a metallic material.

3. The bushing assembly of claim 1 or 2, further comprising a flange.

4. The bushing assembly according to any one of claims 1 to 3, further comprising a third bushing portion comprising the self-lubricating material, the second bushing portion being located between the first bushing portion and the third bushing portion.

5. The bushing assembly of claim 4 , wherein the second bushing portion is configured to apply a force to at least one of the first bushing portion and the third bushing portion.

6. A first part; A second part movably coupled to the first part; A joint assembly comprising: a bushing assembly according to any one of claims 1 to 5, disposed between the first part and the second part.

7. 7. The joint assembly of claim 6, wherein said first part is a joint pin and said second part is pivotally connected to said joint pin.

8. 7. The joint assembly of claim 6, wherein said first part is a shaft, said first part being connected to said second part such that said shaft can move along a longitudinal axis of said shaft.

9. An aircraft landing gear assembly comprising one or more joint assemblies according to any one of claims 6 to 8.

10. 10. An aircraft comprising one or more aircraft landing gear assemblies according to claim 9.

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