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EP-4565487-B1 - AIRCRAFT LANDING GEAR SHOCK ABSORBER STRUT

EP4565487B1EP 4565487 B1EP4565487 B1EP 4565487B1EP-4565487-B1

Inventors

  • BENNETT, IAN

Dates

Publication Date
20260506
Application Date
20230725

Claims (15)

  1. An aircraft landing gear shock absorber strut (50, 70, 90, 100, 120) comprising: an outer cylinder (52) having an inner surface defining a cylinder bore extending into the outer cylinder from a first axial face of the outer cylinder, the cylinder bore defining an oleo chamber for containing pressurised oleo-pneumatic shock absorber fluid; a sliding tube (54) including a hollow tube member coupled to first piston head (56), the hollow tube member defining a tube bore, the first piston head being movably mounted within the cylinder bore so as to be movable along an axis of the cylinder bore between: a compressed position in which a free end portion of the hollow tube member disposed outside of the cylinder bore is relatively close to the first axial face of the outer cylinder; and an extended position in which the free end portion of the hollow tube member is relatively far from the first axial face of the outer cylinder, wherein the first piston head includes a first axial surface upon which pressurised oleo-pneumatic shock absorber fluid within the oleo chamber acts to force the sliding tube to move from the compressed position to the extended position, the first axial surface having a first surface area; a second piston comprising a second piston head (60, 80, 110) slidably mounted within the tube bore in sealing engagement to inhibit pressurised oleo-pneumatic shock absorber fluid passing from the oleo chamber beyond the second piston head, wherein the second piston head includes a second axial surface upon which pressurised oleo-pneumatic shock absorber fluid within the oleo chamber acts to force the sliding tube to move from the compressed position to the extended position, the second axial surface having a second surface area; a piston restraining arrangement (62,82) configured to limit axial separation between the second piston and the outer cylinder to retain the second piston within the tube bore at a first position as oleo-pneumatic shock absorber fluid within the oleo chamber forces the sliding tube to move from the compressed position to the extended position; and a first abutment (68, 72) within the tube bore on the opposite side of the second piston head with respect to the oleo chamber, the first abutment being spaced from the second piston head by a first distance when the second piston head is in the first position and the sliding tube is in the extended position, the first abutment being arranged to engage the second piston head as the sliding tube moves from the extended position to the compressed position.
  2. The aircraft landing gear shock absorber strut according to claim 1, wherein the piston restraining arrangement comprises an elongate, hollow tube located at the axis of the bore, the tube having a first axial end coupled to outer cylinder, and a tether pin having a first end coupled to the second piston head and a second end region which extends into the hollow tube through an opening in the second axial end of the hollow tube, the second end region of the tether element including a second abutment arranged to retain the second piston within the tube bore at the first position as oleo-pneumatic shock absorber fluid within the oleo chamber forces the sliding tube to move from the compressed position to the extended position.
  3. The aircraft landing gear shock absorber strut according to claim 2, wherein the hollow tube is a diaphragm support tube or office support tube and the second piston head is mounted on the tether element.
  4. The aircraft landing gear shock absorber strut according to claim 2 or 3, wherein the second abutment comprises a radially enlarged portion of the tether elementthat is slidably mounted within the hollow tube, wherein the opening has a smaller diameter than the radially enlarged portion such that the radially enlarged portion engages the second axial end of the hollow tube to prevent movement of the second piston head so as to retain the second piston within the tube bore at the first position as oleo-pneumatic shock absorber fluid within the oleo chamber forces the sliding tube to move from the compressed position to the extended position.
  5. The aircraft landing gear shock absorber strut according to claim 4, wherein the radially enlarged portion is distinct from the tether element and is arranged to be coupled to the tether element.
  6. The aircraft landing gear shock absorber strut according any of claims 2 to 5, further comprising an elongate rod located at the axis of the bore, the rod having a first end coupled to outer cylinder or the hollow tube, the tether element being slidably mounted on the rod, wherein second abutment comprises a radially enlarged portion of one of the elongate rod and the tether element which is arranged to engage the other one of the elongate rod and the tether element to limit axial separation between them so as to retain the second piston within the tube bore at the first position as oleo-pneumatic shock absorber fluid within the oleo chamber forces the sliding tube to move from the compressed position to the extended position.
  7. The aircraft landing gear shock absorber strut according to any of claims 2 to 6, wherein the opening comprises a damping orifice.
  8. The aircraft landing gear shock absorber strut according to any preceding claim, wherein the sliding tube comprises a baffle plate on an opposite side of the second piston head with respect to the first abutment, the baffle plate having a second opening sized to permit passage of fluid within the oleo chamber.
  9. The aircraft landing gear shock absorber strut according to claim 1, wherein the piston restraining arrangement comprises an elongate rod located at the axis of the bore, the rod having a first end coupled to outer cylinder, the second piston head being slidably mounted on the rod, the rod including a second abutment on an opposite side of the second piston head with respect to the first end of the rod, the second abutment being sized to prevent movement of the second piston head so as to retain the second piston within the tube bore at the first position as oleo-pneumatic shock absorber fluid within the oleo chamber forces the sliding tube to move from the compressed position to the extended position.
  10. The aircraft landing gear shock absorber strut according to any preceding claim, wherein the sliding tube is vented to atmosphere on an opposite side of the first abutment with respect of the second piston head.
  11. The aircraft landing gear shock absorber strut according to any preceding claim, wherein the first abutment is arranged to travel a distance of at least 20 mm before contacting the second piston.
  12. An aircraft landing gear assembly comprising: the aircraft landing gear shock absorber strut according to any preceding claim; and a wheel assembly or other ground contacting assembly coupled to the shock absorber strut.
  13. The aircraft landing gear assembly according to claim 12, comprising a side stay, drag stay or plunger lock arrangement coupled to the shock absorber strut and arranged to enable the shock absorber strut to be maintained in a deployed condition relative to an aircraft to which the landing gear assembly is movably coupled.
  14. The aircraft landing gear assembly according to claim 12 or 13, further comprising a main landing gear assembly.
  15. An aircraft comprising one or more aircraft landing gear assemblies according to any of claims 12 to 14.

Description

Background to the Invention It is common for an aircraft landing gear assembly to include a main hydraulic shock absorber strut having an upper end arranged to be pivotally coupled to the underside of the aircraft and a lower end coupled to a wheel and brake assembly. Such shock absorber struts can comprise an outer cylinder and a sliding tube arranged to telescope relative to the outer cylinder. The shock absorber strut can be compressed and extended as the sliding tube moves relative to the outer cylinder. The two portions are coupled together to define a chamber containing oil and in some cases a gas. As the shock absorber is compressed, oil within the chamber is forced through damping orifices and, where gas is also provided, the gas is compressed, in order to absorb landing loads. The compressed gas serves as a spring to lengthen the shock absorber as applied external load decreases. Recoil damping orifices can be provided to restrict the flow of oil to the annulus as the shock absorber extends. Such telescopic landing gear can be provided with an elongate metering pin mounted on the sliding tube to move with it, inside the chamber. A mating damping orifice is provided within the chamber, often supported on an orifice support tube. As the sliding tube moves relative to the outer cylinder, a control portion of the metering pin moves through the damping orifice. Variation in the diameter of the metering pin along the control portion varies the free space of the damping orifice through which oil can flow. Thus, the profile of the metering pin affects damping properties of the shock absorber based on shock absorber extension. "Weight-on-wheels" is a term used in the art to refer to an operational phase of an aircraft when the weight of the aircraft is being support by its landing gear. Weight-on-wheels switches or sensors, also known in the art as "squat switches", are commonly used to indicate to aircraft systems via an electronic signal that the aircraft has transitioned from air to ground mode or vice-versa. This signal, which will be referred to as a "weight-on-wheels signal", can be used to enable lift dumpers or brakes to operate on fixed wing aircraft or can be used in the case of rotorcraft to indicate a change of control laws once in ground contact. It is desirable to transmit the weight-on-wheels signal as soon as possible (consistent with reliability) so that lift dumpers for example can be deployed as early as possible to shorten landing distance. A weight-on-wheels signal is typically triggered by proximity sensors or proximity switches, or by microswitches on older aircraft, driven by a mechanism related to strut closure i.e. extension state. Various mechanisms exist for the operation of the switch, but it is common to sense an initial angular movement of the upper torque link i.e. the upper link of the pivotable linkage which inhibits axial rotation of the lower cylinder or "sliding tube" of the shock absorber strut relative to the outer cylinder of the shock absorber strut. Microswitches can be set to trigger at consistent movement but have several disadvantages. As such, microswitches largely been replaced by proximity sensors. However, proximity sensors have a tolerance range on their sensing i.e. variation in position between guaranteed activation and guaranteed deactivation. For commercial wide body aircraft it is common for the weight-on-wheels switch to not be guaranteed to trigger before about 25 to 30 mm of shock absorber closure has occurred. Due to the inflation pressure of a shock absorber there is a minimum "breakout load" below which the shock absorber will not move. Thus, a weight-on-wheels transition can occur before it is sensed and the weight-on-wheels signal is transmitted to the aircraft systems. EP3069994B1 and WO2021/019422 describe aircraft landing gear shock absorber struts. US2015344131A1 describes a shock strut having multiple pistons and multiple chambers. In this manner, the shock strut may compress different lengths for different applied forces at different points during its stroke. EP0341021A2 describes a hydraulic shock absorber suitable for use with an aircraft landing gear which includes a first casing member telescopically and sealingly engaged with a second casing member, the second casing member having a first section of reduced diameter in comparison to a second section and an oil reservoir defined by the first and second casing members, which is divided into two distinct volumes by a one way restrictor means attached to the second casing member. Further, the volume of the oil reservoir defined by the first casing member and the first section of the second casing member is further divided into two sections by a two way restrictor means. US3265163A describes a shock absorber for a vehicle comprising: a support structure affixed to the vehicle; a first cylinder operatively connected to the support structure; second cylinder arranged to reciprocate in the fi