Aircraft landing gear shock absorber assembly

Abstract

An aircraft landing gear shock absorber assembly includes: an outer cylinder (14) having a bore extending into the outer cylinder, the bore defining an opening in the outer cylinder; a slide tube (12) including a first end region and a second end region, the first end region being slidably coupled within the bore and the second end region protruding from the opening; a ground fitting (28, 54) distinct from the slide tube; and a mechanical fastener (30, 52) arranged to mechanically couple the ground fitting to the second end region of the slide tube, wherein the slide tube includes a tubular body portion formed from a ceramic-coated fiber composite tube.

Description

Technical Field

[0001] The invention relates to a shock absorber assembly for an aircraft landing gear. Background Art

[0002] A known aircraft landing gear shock absorber assembly includes an outer cylinder having a bore extending partially therethrough and a slide tube slidably coupled within the bore such that an upper end of the slide tube is retained in the bore and a lower end of the slide tube protrudes from the bore.

[0003] In a single axle landing gear assembly, the lower end of the slide tube is provided with an axle to carry one or a pair of wheels and brake assemblies. In a multi-axle landing gear assembly, the lower end of the slide tube may include a fork yoke or other end fitting arranged to be attached to a component of the wheel assembly, such as a bogie beam. For simplicity, such end fittings as described above will be collectively referred to as "ground fittings".

[0004] It is known to manufacture the slide tube and the ground fitting separately from one another and then couple them together using one or more mechanical fasteners such as nuts and bolts. Such mechanical fasteners may include brackets, collars and the like to facilitate the mechanical coupling between the slide tube on the one hand and the ground fitting on the other hand. Although such a two-part assembly may result in a cost-effective assembly that is easy to manufacture, the weight of the mechanical fasteners increases the overall weight of the landing gear assembly.

[0005] Therefore, it is known to form the slide tube and the ground fitting as a single piece; for example, machining the slide tube and the axle from a single metal billet. Although this can reduce the weight of the landing gear assembly compared to the multi-part arrangement described above, it can increase the cost and complexity of manufacturing.

[0006] The present inventors have recognised that an aircraft landing gear shock absorber slide tube may be improved in terms of weight, cost and manufacturing complexity compared to known assemblies. Summary of the invention

[0007] According to a first aspect of the present invention, there is provided an aircraft landing gear shock absorber assembly according to claim 1 .

[0008] Thus, a shock absorber assembly according to a first aspect comprises a multi-component sliding tube and ground fitting assembly, wherein the tubular member of the sliding tube is formed from a fiber composite tube having a ceramic coating defining an outer surface. The inventors have recognized that the ceramic coating of such a tubular member can provide a suitable opposing surface for a lower bearing member of an outer cylinder of an aircraft landing gear shock strut. Advantageously, the weight savings provided by the fiber composite element of the sliding tube can be greater than the weight added by the overlapping portions and additional fixings required to enable the ground fitting to be separately formed and mechanically coupled to the sliding tube. Thus, a landing gear assembly according to an embodiment of the present invention possesses the advantages of a multi-piece design while having the ability to be at least as light as an assembly in which the sliding tube and the ground fitting are integrally formed from a single piece of metal. The lightweight nature of the sliding tube can also reduce unsprung mass compared to known assemblies.

[0009] Optional features of the shock absorber assembly are set out in the dependent claims.

[0010] According to a second aspect of the present invention, there is provided an aircraft landing gear assembly comprising a shock absorber assembly according to the first aspect.

[0011] According to a third aspect of the present invention, there is provided an aircraft comprising one or more aircraft landing gear assemblies according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0013] Figure 1 is a schematic diagram of an aircraft according to an embodiment of the present invention;

[0014] Figure 2 is a schematic cross-sectional view of a landing gear assembly according to an embodiment of the present invention.

[0015] Figure 3 yes Figure 1 Schematic diagram of the components of the slide tube and ground fittings of the landing gear assembly.

[0016] Figure 4 yes Figure 1 A schematic cross-sectional view of components of a slide tube and a ground fitting of a landing gear assembly; and

[0017] Figure 5 is a schematic diagram of components of a sliding tube, a mechanical and a fixed ground fitting of a shock absorber according to another embodiment of the present invention. DETAILED DESCRIPTION

[0018] Reference Figure 1, an aircraft according to an embodiment of the present invention is generally shown at 100. The aircraft 100 includes a plurality of main landing gear assemblies 10 according to an embodiment of the present invention and a nose landing gear assembly 50 according to an embodiment of the present invention.

[0019] Figure 2 is a schematic cross-sectional view of a main landing gear assembly 10 according to an embodiment of the present invention.

[0020] The landing gear assembly 10 includes an "oil-gas" shock absorber, which defines a shock strut of the landing gear. An oil-gas shock absorber includes a hydraulic fluid, such as oil, and a gas, such as nitrogen, which provide spring and damping characteristics.

[0021] The shock absorber comprises an inner housing portion 12 having an inner end region slidably coupled and housed within an outer housing portion 14. The inner housing portion 12 is referred to in the art as a "slider", "sliding tube", "inner cylinder" or "piston", and the outer housing portion 14 is referred to as an "outer cylinder" or "main fitting", which comprises a main pivot bearing lug 16 via which the shock absorber is arranged to be pivotally coupled to the aircraft 100 to pivot between a deployed condition for take-off and landing and a stowed condition for flight. However, in other embodiments, the main struts may be rigidly fixed to the aircraft, i.e., not forming a retractable landing gear.

[0022] The slide tube 12 and the outer cylinder 14 together define an inner cavity or chamber OC, GC that contains the shock absorber fluid. In the illustrated embodiment, the chambers OC, GC are divided into an oil chamber OC that is primarily defined by the outer cylinder 14 and contains oil, and a gas chamber GC that is primarily defined by a bore extending along the slide tube 12 and contains a gas such as nitrogen. A separator piston 18 is slidably received within the bore of the slide tube 12 to slide along the longitudinal axis L of the shock absorber. In other embodiments, the oil and gas may not be separated.

[0023] The area where the slide tube 12 and the outer cylinder 14 overlap defines an annulus A between adjacent surfaces of the slide tube 12 and the outer cylinder 14. The size of the annulus A varies depending on the extended state of the shock absorber. The term "annulus" may mean an annular space having a cylindrical or non-cylindrical cross-sectional profile.

[0024] An annular ring 20 is housed within the annular portion A adjacent the open end of the outer barrel 14. The annular ring 20 defines a lower bearing member of the shock absorber that carries one or more dynamic seals (not shown) acting on the outer surface of the sliding tube 12 to confine the shock absorber fluid to the oil chamber OC. For example, a pair of dynamic seals may be mounted on the inner cylindrical surface of the annular ring 20 and arranged so that as the shock absorber extends and retracts, one or both of them press against the sliding tube 12, thereby blocking the passage of the shock absorber fluid from the chamber OC to the external environment. A pair of static seals may be mounted on the outer cylindrical surface of the annular ring 20 to bear against the corresponding inner surface of the outer barrel 14 to block the passage of the shock absorber fluid from the chamber OC to the external environment. The annular ring 20 may be locked in place within the annular portion A between the shoulder of the outer barrel 14 and a compression nut 22 that is threaded into engagement with the threaded end portion of the inner surface of the outer barrel 14. To prevent dust and other contaminants from entering the annular portion A, an external environmental seal known in the art, such as a scraper seal or an extruder seal, may be provided. The scraper seal may be mounted in a groove formed in the inner surface of the compression nut 22 between the outer flange and the inner flange so that its position is fixed relative to the outer cylinder 14.

[0025] An upper end region of the slide tube 12 housed within the outer cylinder 14 is radially enlarged to define a piston-shaped upper bearing 24 arranged to act in sliding engagement with the inner surface of the outer cylinder 14 as the shock absorber extends and retracts. The upper bearing 24 may include one or more conventional apertures 26 or damping holes arranged to provide damping as oil passes through them between the oil chamber OC and the annular portion A as the shock absorber extends and retracts. Alternatively, the upper bearing may be defined by the inner side wall of the outer cylinder and arranged to act on an upper portion of the slide tube.

[0026] Therefore, the shock absorber assembly can be extended and retracted between the maximum and minimum extension states, and the shock absorber includes a first carrier 20 and a second carrier 24 axially spaced from each other along the longitudinal axis L of the shock absorber, and each carrier 20, 24 is arranged to move into sliding engagement with the corresponding first and second opposing surface portions CFL, CFU of the sliding tube or the outer cylinder as the shock absorber assembly extends and retracts between the maximum and minimum extension states.

[0027] See also Figure 3, the lower end region of the slide tube 12 held outside the outer cylinder 14 is coupled to a ground fitting. In this embodiment, the ground fitting is a fork yoke 28. The fork yoke 28 is arranged to be mechanically coupled to the lower end of the slide tube 12 via a mechanical fastener comprising a nut and bolt assembly 30 extending through holes H in the slide tube 12 and the fork yoke 28 to maintain the fork yoke 28 in a substantially fixed orientation and position relative to the slide tube 12. The upper surface of the fork yoke 28 is provided with holes for receiving the end of the slide tube 12 so that the yoke 28 and the tube 12 overlap and the holes can be axially aligned to receive the mechanical fastener. The fork yoke, in turn, pivotally mounts a truck beam 32 via a truck pivot pin 34. As will be appreciated, the truck beam 32 is an elongated beam arranged to carry a plurality of axles (not shown), each axle carrying a pair of wheels and brake assemblies. In other embodiments, the mechanical fastener may include a truck pivot pin 34 .

[0028] In other embodiments, the ground fitting may be any suitable component arranged to enable the slide tube to be mechanically coupled to a ground contacting assembly, such as a wheel or brake assembly.

[0029] In other embodiments, the shock absorber may form part of a "capsule" type shock absorber, wherein the shock absorber is inverted and housed within a different primary fitting to which the inner housing portion is coupled, such that the outer housing portion acts as a sliding tube.

[0030] Furthermore, in other embodiments any suitable dampener may be provided, such as magnetic.

[0031] The landing gear assembly according to an embodiment of the present invention differs from known landing gear assemblies in that the slide tube 12 is formed of a fiber composite tube having a ceramic coating. The inventors have discovered that the ceramic coating of such a tubular member can provide a suitable opposing surface for the lower bearing member 20 of the aircraft landing gear. The ceramic coating can thus provide a load bearing surface for one or more bearing members and a sealing surface for a dynamic seal to act against to confine the shock absorber fluid to the shock absorber. Advantageously, the weight savings provided by the fiber composite element of the slide tube 12 can be greater than the weight added by the overlap and additional fixings required to enable the ground fitting 28 to be separately formed and mechanically connected to the slide tube 12. Therefore, the landing gear assembly according to an embodiment of the present invention has the advantages of a multi-piece design while having the ability to be at least as light as an assembly in which the slide tube and the ground fitting are formed from a single piece of metal.

[0032] Figure 4Components of the slide tube 12 are shown in cross-section along the longitudinal axis L. The slide tube 12 includes a cylindrical body portion 36. The body portion 36 is primarily formed of a tubular substrate 36a of a composite material such as a fiber reinforced plastic in which reinforcing fibers are embedded in a cured plastic matrix. The substrate 36 may include or be formed around a metal tube or a plastic tube, although such an arrangement may increase the weight of the assembly. An outer coating 36b of a ceramic material is applied to a component of the slide tube 12 that will serve as the opposing face of the lower bearing 20 in use, and in some embodiments, also as the opposing face of the upper bearing, as the shock absorber extends and retracts. Some or all of the outer surface of the tubular substrate 36a is coated with a ceramic material. Thus, the first opposing face portion CFL is defined by the ceramic coated portion of the slide tube 12. Optionally, some or all of the inner surface of the tubular substrate 36a may be coated with a ceramic material; for example, in an embodiment including a separator piston 18, an area of ​​the inner surface along which the separator piston 18 moves in use. The fiber composite tubular substrate may, for example, have a thickness T1 in the range of 3 mm-75 mm. The outer ceramic coating may, for example, have a thickness T2 of 0.0025 mm-0.5 mm. Similarly, the optional inner ceramic coating may, for example, have a thickness T2 of 0.0025 mm-0.5 mm. The thickness of either coating or both coatings may be uniform along the length of the coating. One or more ceramic coatings may, for example, include an oxide ceramic coating, such as titanium dioxide, chromium oxide, or aluminum oxide. With the benefit of the present disclosure, those skilled in the art will be able to produce suitable sliding tubes; US2016 / 0153080A1 provides an example of how to form a fiber composite tube with a ceramic coating.

[0033] Figure 5 A portion of a single axle landing gear assembly 50, such as a nose landing gear assembly, is shown. The slide tube 12 may be connected to the reference Figures 2 to 4 The sliding tube 12 described above is the same or similar. Figures 2 to 4 The difference of the embodiment of is that the ground fitting 54 is an axle, and the mechanical fastener 52 includes a collar and a nut / bolt assembly (not shown). The axle 54 is inserted through the collar 52 and the hole H in the sliding tube 12, and the nut / bolt assembly is tightened to hold the axle 54 in place.

[0034] The floor fittings and mechanical fasteners used in embodiments of the present invention may be conventional in shape and material.

[0035] It should be noted that the above embodiments illustrate rather than limit the present invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the present invention as defined by the appended claims. In the claims, any reference numerals placed in brackets should not be understood as limiting the claims. The word "comprise" does not exclude the presence of components or steps other than those listed in any claim or specification as a whole. The singular reference to a component does not exclude the plural reference to these components, and vice versa. The various components of the present invention may be implemented by means of hardware comprising several different elements. The fact that specific measures are described in mutually different dependent claims does not mean that a combination of these measures cannot be used to produce good results.

Claims

1. An aircraft landing gear shock absorber assembly, comprising: an outer cylinder having a bore extending into the outer cylinder, the bore defining an opening in the outer cylinder; as well as a sliding tube including a first end region slidably coupled within the bore and a second end region protruding from the opening; wherein the shock absorber assembly includes an end stop that limits the amount of relative sliding movement between the sliding tube and the outer cylinder so that the shock absorber assembly can be extended and retracted between maximum and minimum extended states, the shock absorber assembly includes an upper bearing and a lower bearing axially spaced from each other along a longitudinal axis of the shock absorber assembly, each bearing being arranged to move into sliding engagement with a respective upper opposing face portion and a lower opposing face portion as the shock absorber assembly is extended and retracted between the maximum and minimum extended states, wherein the second end region of the outer cylinder or the sliding tube is configured to be mechanically coupled to a ground fitting different from the sliding tube using a mechanical fastener, The sliding tube includes a tubular body portion formed by a ceramic fiber composite tube, and Wherein, the lower opposing surface portion is defined by a ceramic-coated portion of the sliding tube.

2. The aircraft landing gear shock absorber assembly according to claim 1, characterized in that: The upper opposing surface portion is defined by a ceramic-coated portion of the slide tube.

3. The aircraft landing gear shock absorber assembly according to claim 1, characterized in that: The ceramic coated fiber composite tube includes a fiber composite tubular substrate having a first ceramic coating applied to some or all of an outer cylindrical sidewall of the fiber composite tubular substrate.

4. The aircraft landing gear shock absorber assembly according to claim 3, characterized in that: The fiber composite tubular substrate has a thickness of at least 3 mm, and / or wherein the first ceramic coating has a thickness of at least 0.0025 mm.

5. The aircraft landing gear shock absorber assembly according to claim 3, characterized in that: The ceramic coated fiber composite tube includes a second ceramic coating applied to some or all of the inner cylindrical sidewall of the fiber composite tubular substrate.

6. The aircraft landing gear shock absorber assembly according to claim 5, characterized in that: The second ceramic coating has a thickness of at least 0.0025 mm.

7. The aircraft landing gear shock absorber assembly according to claim 3, characterized in that: The ceramic coated fiber composite tube includes a plurality of reinforced fibers embedded in a cured plastic matrix.

8. The aircraft landing gear shock absorber assembly according to claim 5, characterized in that: The first ceramic coating and / or the second ceramic coating each include an oxide ceramic.

9. An aircraft landing gear assembly, comprising: Aircraft landing gear shock absorber assembly according to any one of claims 1 to 8 a primary pivot bearing configuration via which the shock absorber assembly is arranged to be pivotally coupled to the aircraft for movement between a deployed condition and a stowed condition; a ground contact structure coupled to the ground fitting, and a mechanical fastener arranged to mechanically couple the floor fitting to the second end region of the sliding tube, The aircraft landing gear assembly is enabled to absorb landing loads and support the weight of the aircraft when the aircraft is on the ground.

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

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