Aircraft landing gear assembly

Abstract

An aircraft landing gear assembly comprising a first structural member coupled to a second structural member via a joint, the joint comprising a bearing, the bearing comprising a tubular body formed from: a metal matrix composite (MMC) comprising a metal, a carbide compound and tungsten disulphide.

Description

[0001] Aircraft Landing Gear Assembly

[0002] Background

[0003] An aircraft landing gear assembly can include structural members movably coupled via a joint which includes one or more bearings. For example, structural members can be movably coupled via a pin joint. A pin joint can include a one or more bearings, each being located between the pin and one of the structural members to provide a load bearing counter-face for the pin. One example of a bearing is known in the art as a 'bush', having a hollow, tubular body which can be inserted and retained within a bore of the structural member and the pin received within a bore of the tubular body such that the bush defines the bearing surface for the pin.

[0004] Aluminium-Bronze (Al-Br) bushes are often used for their ratio of load capacity and coefficient of friction at high temperatures, but they require periodically greasing in order to maintain a low friction coefficient at the bearing surface to control the amount of wear, and to flush out contaminants. Integral grease channels can be provided to enable grease to be introduced to the bearing surface during maintenance operations.

[0005] Self-lubricating bushes are known which include a Polytetrafluoroethylene (PTFE) inner liner, which can reduce maintenance requirements relative to Al-Br bushes. However, such bushes can be inferior to Al-Br bushes in terms of load capacity, working temperature and electrical conductivity, which can limit their applicability.

[0006] The present inventors have devised a new type of aircraft landing gear bearing which can exhibit one of more of the following advantages relative to known aircraft landing gear bearings:

[0007] • Improved thermal behaviour

[0008] • Reduced weight

[0009] • Reduced friction

[0010] • Improved coupling to a self-lubricating liner

[0011] Summary

[0012] In accordance with a first aspect of the present invention there is provided an aircraft landing gear assembly comprising a first structural member coupled to a second structural member via a joint, the joint comprising a bearing, the bearing comprising a tubular body formed from: a metal matrix composite (MMC) comprising a metal, a carbide compound and tungsten disulphide.

[0013] As used herein the term "metal" encompasses metals as well as metal alloys.

[0014] The metal may be selected from any metal, metal alloy or combination thereof. Preferably, the metal may be selected from magnesium, magnesium alloys, aluminium, aluminium alloys, titanium, titanium alloys, copper, copper alloys and combinations thereof. More preferably, the metal is selected from magnesium, magnesium alloys, aluminium or aluminium alloys.

[0015] The metal may be present in the MMC in an amount of about 50% to about 90%, or about 60% to about 80%, about 65% to about 75%, or about 65% to about 70% or about 70 to about 75% based on the total weight of the MMC. The metal may be present in the MMC in an amount of about 60% or about 61% or about 62% or about 63% or about 64% or about 65% or about 66% or about 67% or about 68% or about 69% or about 70% or about 71% or about 72% or about 73% or about 74% or about 75% based on the total weight of the MMC.

[0016] Preferably, when the metal is magnesium, it is present in the MMC in an amount of about 65% to about 80%, more preferably about 70% to about 75% based on the total weight of the MMC.

[0017] Preferably when the metal is aluminium it is present in the MMC in an amount of about 60% to about 80%, more preferably about 65% to about 75% based on the total weight of the MMC.

[0018] The carbide compound may be selected from silicon carbide, boron carbide, titanium carbide, tungsten carbide, calcium carbide, lanthanum carbide, vanadium carbide, chromium carbide, aluminium carbide, zirconium carbide, hafnium carbide, molybdenum carbide, niobium carbide, tantalum carbide, yttrium carbide and combinations thereof. Preferably the carbide compound is silicon carbide, boron carbide or titanium carbide. More preferably, the carbide compound is silicon carbide.

[0019] The carbide compound may be present in the MMC in an amount of about 5% to about 30%, or about 10% to about 25%, or about 10% to about 15%, or about 15% to about 20%, or about 15% to about 25% based on the total weight of the MMC. The carbide compound may be present in the MMC is an amount of about 10%, or about 11%, or about 12%, or about 13%, or about 14%, or about 15%, or about 16%, or about 17%, or about 18%, or about 19%, or about 20%, or about 21%, or about 22%, or about 23%, or about 24%, or about 25% based on the total weight of the MMC.

[0020] An amount of about 5% to about 30%, preferably about 10% to about 25% carbide compound based on the total weight of the MMC compound provides a balance between good load-bearing capacity and economic cost.

[0021] The tungsten disulphide may be present in the MMC in an amount of about 5% to about 20%, or about 5% to about 15%, or about 10% to about 20%, or preferably about 10% to about 15%.

[0022] The tungsten disulphide may be present in the MMC in an amount of about 5%, or about 6%, or about 7%, or about 8%, or about 9%, or about 10%, or about 11%, or about 12%, or about 13%, or about 14%, or about 15%, or about 16%, or about 17%, or about 18%, or about 19%, or about 20% based on the total weight of the MMC. Preferably the tungsten disulphide is present in the MMC in an amount of about 10% based on the total weight of the MMC.

[0023] Tungsten disulphide advantageously helps to reduce friction of the aircraft landing gear bearing.

[0024] A preferred MMC is a magnesium MMC (Mg MMC) comprising about 70 to about 75% magnesium, about 10 to about 15% silicon carbide and about 10% tungsten disulphide based on the total weight of the Mg MMC.

[0025] Another preferred MMC is an aluminium MMC (Al MMC) comprising about 65% to about 75% aluminium, about 15 to about 25% silicon carbide and about 10% to about 15% tungsten disulphide based on the total weight of the Al MMC.

[0026] Mg MMCs and Al MMCs have densities close to thermoplastic materials (p = 2-3.5 g / cm3). In comparison, Al-Br has a density of 7.8 g / cm3. Therefore, Mg MMCs and Al MMCs are >50% lighter than Al-Br and commercially available copper nickel tin alloys such as ToughMet®. ToughMet® is currently the optimum material for demanding applications due to its wear rate, load capacity and coefficient of friction. However, Toughmet® is heavy like Al-Br. Therefore Mg MMCs and Al MMCs provide lighter alternatives to Al-Br and copper nickel tin alloys such as ToughMet®, yet with good wear rate, load capacity and coefficient of friction properties. Mg MMCs and Al MMCs also maintain good electrical conductivity compared to Al-Br and copper nickel tin alloys such as ToughMet®.

[0027] The joint can comprise a pin mounted within holes formed through the first and second structural members so as to define a pin joint, the bearing being provided between the pin on the one hand and one of the first and second structural members on the other hand.

[0028] The first structural member can be a bogie beam, and the second structural member can be a shock absorbing strut.

[0029] The joint can further comprise one or more further bearings, each further bearing comprising a tubular body formed from: a metal matrix composite (MMC) comprising a metal, silicon carbide and tungsten disulphide. Optional features set out above for the bearing can be applied to any of the further bearings in an analogous manner.

[0030] The aircraft landing gear assembly can further comprise a mounting formation, via which the landing gear assembly is arranged to be coupled to an aircraft, and a ground contacting assembly, arranged to support the weight of the aircraft on the ground.

[0031] The mounting formation can be arranged to movably couple the landing gear assembly to the aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing.

[0032] According to a second aspect of the present invention, there is provided an aircraft including one or more aircraft landing gear assemblies according to the first aspect.

[0033] Brief Description of the Drawings

[0034] By way of example only, certain embodiments of the invention will now be described by reference to the accompanying drawings, in which:

[0035] Figure 1 is a diagram of an aircraft;

[0036] Figures 2 and 3 are diagrams of a known aircraft landing gear assembly; Figure 4 is a cross sectional view through a pin joint of a landing gear assembly according to an embodiment of the invention; and

[0037] Figure 5 is a cross sectional view through a bearing of a landing gear assembly according to an embodiment of the invention.

[0038] Detailed Description

[0039] Figure 1 is a diagram of an aircraft 2. The aircraft includes assemblies such as a nose landing gear 4 and a pair of main landing gear 6. The landing gear 4, 6 each includes a shock absorber strut for damping landing loads and supporting the weight of the aircraft 2 when it is on the ground. The term aircraft as used herein can include aeroplanes, helicopters and the like having mass in excess of 450Kg.

[0040] Figure 2 is an example of an aircraft landing gear assembly 6 which can include a bearing according to an embodiment of the invention. It will however be appreciated that bearings according to embodiments of the invention can be used in a range of types of aircraft landing gear including main landing gear and nose landing gear, with one more axles and include wheels or other ground contacting means.

[0041] The aircraft landing gear assembly 6 is movable between a deployed condition, for take-off and landing, and a stowed condition for flight. The landing gear assembly includes a main shock absorber strut 8, comprising an outer cylinder and a sliding tube, a foldable stay 14, a lock link 20. An upper end of the strut 8 is provided with a bearing 9 via which the strut 8 is pivotally coupled to the airframe of the aircraft 2. A lower end of the strut 8 is provided with a wheel and brake assembly 30. A retraction actuator 12 is provided for moving the landing gear between the deployed condition and the stowed condition. The retraction actuator can have one end coupled to the airframe 11 and another end coupled to the strut 8.

[0042] The stay 16 serves to support the orientation of the strut 8 when the landing gear is in the deployed condition. The stay 18 generally includes a two-bar linkage 16, 18 that can be unfolded to assume a generally straight or aligned, over centre condition in which the stay 18 is locked to inhibit movement of the outer cylinder, as shown in Figure 2. When the stay is broken, it no longer inhibits pivotal movement of the strut 8 about the mounting bearing and strut 8 can be moved by the retraction actuator 12 towards the stowed condition. The lock link 20 has an elongate upper link arm having a lower end pivotally coupled to an upper end of an elongate lower link arm via a pivot pin. The link arms can therefore pivotally move relative to one another about the pivot pin. The lock link is pivotally coupled to the strut 8 and one of the stay arms 16. When the lock link 20 is in the locked condition, as shown in Figure 2, the upper and lower link arms are generally longitudinally aligned or coaxial, and can be 'over-centre', such that the lock link 20 is arranged to oppose a force attempting to break or fold the stay 14. The lock link 20 must be broken to enable the stay 14 to be broken and folded, thereby permitting the strut 6 to be moved by the retraction actuator 12 towards the stowed condition.

[0043] The down lock assist in moving the landing gear assembly to the deployed condition and locking it in that state by making the lock link 20. Down lock springs also inhibit the lock link 20 accidentally being broken / unlocked.

[0044] A lock stay actuator 22 is coupled between the stay 14 and lock link 20 and arranged to pivotally move the link arms so as to make and break the lock link 20. The lock stay actuator 22 can break the lock link 20 against the down lock spring bias, allowing the landing gear assembly to be folded and stowed as described previously.

[0045] Referring additionally to Figure 3, the outer cylinder 24 and sliding tube 26 of the strut 8 can be coupled via a set of torque links 28 which permit relative axial movement but inhibit relative rotational movement between the outer cylinder 24 and sliding tube 26.

[0046] Wheel and brake assemblies 10 can be mounted on axles 30 which in turn are mounted at end regions of a bogie beam 32. The bogie beam 32 is pivotally coupled near its centre to the sliding tube 26 via a bogie pivot pin 34. Brake rods 36 can be provided to anchor the brake packs to the sliding tube 26 to react brake torque.

[0047] Figure 4 shows part of a landing gear assembly according to an embodiment of the invention, in which a first structural member 40 is pivotally coupled to a second structural member 42 via a pin joint. The first structural member 40 terminates in a lug having a pair of arms which define a space between them that is sized to receive first and second arms of a lug defined at the end of the second structural member 42. Each arm includes a hole such that when the lugs are aligned, a pin 44 can be received by each hole in order to pivotally couple the first structural member 40 to the second structural member 42. The first and second structural members 40, 42 can for example be main fitting attachment lugs, by which the main fitting is pivotally coupled to the airframe, links of a side stay, torque links, lock links, shortening links, bogie pivot pin, actuator attachments or the like.

[0048] Each lug hole is provided with a plane, tubular bearing 46, also known in the art as a bush.

[0049] Referring additionally to Figure 5, the tubular bearings 46 each have a generally cylindrical tubular body 46a and optionally a radial flange 46b. In other embodiments the tubular body 46 can have a different cross-sectional profile; for example, rectangular.

[0050] The tubular bearings 46 are situated within the lug holes such their bodies 46a extends generally parallel with respect to the longitudinal axis A of the pin 44 so as to be situated between the lug and pin 44 to support the pin 44 in use.

[0051] In the illustrated embodiment, the inner, bore defining face of the tubular body 46a defines a first bearing surface Bl which in use is arranged to support the pin 44. The outer cylindrical face of the tubular body 46a defines a second bearing surface B2 which in use is arranged to be statically engaged with a lug bore surface so that the bearing 46 is retained within the lug bore; for example, by way of an interference fit. The bearing surfaces Bl and B2 are parallel; however, in other embodiments the bearing can includes non-parallel sides, such as a tapered or spherical bearing. The distance between the bearing surfaces Bl, B2 defines the thickness TB of the tubular body 46a. The bearing thickness TB can be, for example, between 4mm and 25mm.

[0052] The tubular body 46a has a main body layer 48 formed from a metal matrix composite (MMC) comprising a metal, a carbide compound and tungsten disulphide. Optional features of the MMC are set out in the Summary section.

[0053] An optional self-lubricating liner 50 can be provided. Using MMC bushes in selflubricating applications can improve bonding between the body and liner in comparison with Al-Br bushes with PTFE liners.

[0054] The optional radial flange 46b is also formed from an MMC comprising a metal, a carbide compound and tungsten disulphide and has a first axial surface that defines a third bearing surface B3, and a second axial surface that defines a fourth bearing surface B4. The bearing surfaces B3 and B4 are parallel in this example, but this need not be the case. The radial flange 46b and be integrally formed with the main body layer 48, or can be formed separately and bonded or mechanically coupled.

[0055] Thus, the body 46a of each bearing 46 defines a bearing surface which in use cooperates with a bearing counter-face of the pin 44. The length of each bearing body 46a can be defined by the width of the lug arms at the lug holes; examples of typical body lengths are between 20mm and 100mm.

[0056] The optional radial flange 46b can react lateral loads, serve to limit axial travel of the bearing 46 through the lug hole and be used to attach the bearing 46 to the lug.

[0057] The pin joint is designed to withstand operational loads resulting in static pressure across each bearing body 46a of at least about lOMPa, and in some cases pressures up to about 50 MPa. The joint can also be designed to withstand dynamic pressure of approximately 200 MPa as the landing gear structural members move between operational conditions.

[0058] Grease channels (not shown) can be provided within at least some of the structural members and / or bearings to enable grease lubricant or the like to be introduced to the bearing surface during maintenance operations.

[0059] As will be apparent from Figure 4, aircraft landing gear assemblies according to embodiments of the invention can have a plurality of bearings as defined herein, each bearing having one or more respective bearing surfaces each arranged in dynamic or static contact with a respective counter-face of the coupling. Counter-faces of the coupling can be provided by surfaces of the structural elements, a pin or other coupling member, or by other bearings or bearing parts such as races of roller bearings.

[0060] Blocks of MMC can be machined to bearings through Electrical Discharge Machining (EDM) for example.

[0061] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parenthesis shall not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. Parts of the invention can be implemented by means of hardware comprising several distinct elements. In a device claim enumerating several parts, several of these parts can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

Claims1. An aircraft landing gear assembly comprising a first structural member coupled to a second structural member via a joint, the joint comprising a bearing, the bearing comprising a tubular body formed from: a metal matrix composite (MMC) comprising a metal, a carbide compound and tungsten disulphide.

2. The aircraft landing gear assembly of claim 1, wherein the MMC comprises a metal selected from magnesium, magnesium alloys, aluminium, aluminium alloys or combinations thereof3. The aircraft landing gear assembly of claim 2, wherein the MMC comprises a magnesium alloy.

4. The aircraft landing gear assembly of claim 2, wherein the MMC comprises an aluminium alloy.

5. The aircraft landing gear assembly of any preceding claim, wherein the MMC comprises about 60% to about 80% metal based on the total weight of the MMC.

6. The aircraft landing gear assembly of any preceding claim, wherein the carbide compound is selected from silicon carbide, boron carbide or titanium carbide.

7. The aircraft landing gear assembly of any preceding claim, wherein the carbide compound is silicon carbide.

8. The aircraft landing gear assembly of any preceding claim, wherein the MMC comprises about 5% to about 30% carbide compound based on the total weight of the MMC.

9. The aircraft landing gear assembly of any preceding claim, wherein the MMC comprises about 5% to about 20% tungsten disulphide based on the total weight of the MMC.

10. The aircraft landing gear assembly of claim 1, wherein the MMC is a magnesium MMC (Mg MMC) comprising about 70 to about 75% magnesium, about 10 to about 15% silicon carbide and about 10% tungsten disulphide based on the total weight of the Mg MMC.

11. The aircraft landing gear assembly of claim 1, wherein the MMC is an aluminium MMC (Al MMC) comprising about 65% to about 75% aluminium, about 15 to about 25% silicon carbide and about 10% to about 15% tungsten disulphide based on the total weight of the Al MMC.

12. The aircraft landing gear assembly of any preceding claim, wherein the joint comprises a pin mounted within holes formed through the first and second structural members so as to define a pin joint, the bearing being provided between the pin on the one hand and one of the first and second structural members on the other hand.

13. The aircraft landing gear assembly of any preceding claim, wherein the first structural member is a bogie beam, and the second structural member is a shock absorbing strut.

14. The aircraft landing gear assembly of any preceding claim, wherein the joint further comprises one or more further bearings, each further bearing comprising a tubular body formed from: a metal matrix composite (MMC) comprising a metal, a carbide compound and tungsten disulphide.

15. The aircraft landing gear assembly of any preceding claim, further comprising a mounting formation, via which the landing gear assembly is arranged to be coupled to an aircraft, and a ground contacting assembly, arranged to support the weight of the aircraft on the ground.

16. The aircraft landing gear assembly of claim 15, wherein the mounting formation is arranged to movably couple the landing gear assembly to the aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing.

17. An aircraft including one or more aircraft landing gear assemblies according to any preceding claim.

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