Patent Description:
Aircraft landing gear are arranged to support aircraft when they are on the ground and so typically comprise a wheel or other ground contacting mechanism. The aircraft landing gear are typically movable between an extended position, where the landing gear is arranged to support the aircraft on the ground and a retracted position in which the landing gear is folded so as to be housed within a fuselage or other aircraft location, which may avoid an increase in drag.

When a landing gear is deployed, it is important that it is maintained in the deployed position and cannot be retracted unintentionally. Therefore landing gear are provided with stay assemblies which may support a main strut of the landing gear and the stay assemblies may be locked in place via lock assemblies.

Lock assemblies are formed of lock links which may be placed in an 'over centre' position when the landing gear is deployed such that they cannot be folded without direct actuation and thereby the landing gear may be locked in a deployed position. The lock links cannot be moved into their locked, 'over centre' position via the simple kinematics of the landing gear assembly and the weight of the lock links alone. There is therefore a need for some other force to fully deploy the landing gear.

The force is commonly provided by a helical spring. However, helical springs may be susceptible to vibration due to their shape, may have a high degree of weight, and may also suffer from creep if they are permanently stressed.

<CIT> discloses a linkage arrangement on an aircraft landing gear that uses a secondary shock absorber, which functions independently of a primary shock absorber. <CIT> discloses a landing gear assembly for aircraft having a lost motion assembly which connects a spring assembly to a lower link arm of a lock link while the spring assembly connects to the lower stay arm of a foldable stay.

According to a first aspect of the present invention, there is provided an aircraft landing gear according to claim <NUM>.

The use of elastically deformable washers, as opposed to helical springs, may provide an improved landing gear for at least the reason that the range of materials out of which elastically deformable washers may be formed is greater than the range of materials that out of which helical springs may be formed. Further, by varying the number of washers, the length of the present springs may be more easily customised than those of the prior art. Further still, helical springs travelling in a direction perpendicular to their longitudinal axis may be aerodynamically considered as a bluff body and may therefore suffer from aeroelastically induced vibrations. By comparison, substantially disk shaped washers may have improved aerodynamics and may therefore not suffer from such severe aeroelastic vibrations.

The elastically deformable washers may also have improved robustness in comparison to helical springs and may have improved impact resistance.

When helical springs are used, they will often be fixed such that they are constantly in tension regardless of the condition of the landing gear. However, a constant tensile stress applied for a long time can lead to creep, which lengthens the material in the unstressed state and reduces the elastic tensile force generated at a given length of the material. Springs formed from separable washers may also not suffer from tensile stresses and so creep of the material in the spring may be reduced.

The spring may further comprise a sliding rod coupled to the first and second members, and arranged to slide relative to the first and/or second member, the sliding rod extending through the elastically deformable washers. The sliding rod may provide a structural support to the washers and may thereby prevent the spring from buckling in compression.

The aircraft landing gear may further comprise a disk arranged to slide along the sliding rod and arranged to engage the sliding rod so as to prevent relative rotation between the disk and the sliding rod, the disk being arranged to abut the elastically deformable washers. The disk may prevent any rotational movement from being transferred to the washers and may thereby prevent any torsional stress from being transferred to the washers. The disk may also provide a planar surface for an endmost elastically deformable washer of the spring to abut and may thereby prevent stress concentrations and damage which would occur if the elastically deformable washer were to abut an uneven surface.

The aircraft landing gear may further comprise a guiding shaft disposed parallel to the sliding rod and/or to the spring and a further washer arranged to slide along the guiding shaft and the sliding rod, the further washer being rotationally fixed relative to the sliding rod and arranged to abut at least one of the elastically deformable washers. The further washer may provide a smooth end surface for the spring to abut and may thereby prevent damage to the washers. The further washer may also prevent any torsional forces from being transmitted to the washers. The further washer may also be substantially rigid and not deformable.

The elastically deformable washers may be separable and arranged to abut each other, and the spring may be arranged to generate a compressive biasing force. Since materials suffering tensile forces often suffer from creep, this may reduce the likelihood of the spring suffering from creep.

The elastically deformable washers may be conical washers. Alternatively, hemispherical washers or other shaped washers may be used. The conical washers may also be referred to as coned-disk washers or Belleville washers.

The elastically deformable washers may be formed from an anisotropic material, which may be a composite material, optionally a reinforced fibre thermoplastic composite material. The material used may be carbon fibre in combination with an epoxy or thermoplastic resin such as PEEK, LM-PAEK and PEKK. The use of a thermoplastic may improve the resilience of the elastically deformable washer as well as allowing an improved speed of manufacture.

The landing gear is defined in appended claim <NUM>.

When the main strut is in the retracted condition, the elastically deformable washers are substantially unstressed. This may involve the elastically deformable washers having a minimal compressive stress preventing free movement and vibration of the washers, but no substantial compressive force may be generated to bias a component outside the spring assembly.

Where there is provided a disc arranged to engage a sliding rod, the disc may engage a groove of the sliding rod and a minimum compressive load on the spring may the applied in the substantially unstressed state, due to engagement between the disc and an end point of the groove. The disc and an end stop, the end stop being at an opposite end of the spring from the disc, may determine a maximum length of the spring and thereby a minimum compressive stress.

Where there is a further washer, the further washer may slide along a guiding shaft and may engage an end of the guiding shaft in order to limit movement of the further washer. In conjunction with an end stop, the end stop being at an opposite end of the spring from the further washer, the further washer may limit the maximum length of the spring and may thereby provide a minimum compressive force to the spring.

According to a second aspect of the invention, there is provided an aircraft including an aircraft landing gear according to the first aspect of the invention.

<FIG> is a diagram of an aircraft <NUM>. The aircraft <NUM> includes assemblies such as a nose landing gear <NUM>, one or more main landing gear <NUM> and engines <NUM>. Other aircraft assemblies will be apparent to the skilled person. The term aircraft as used herein includes aeroplanes, helicopters, UAVs and the like.

Referring now to <FIG>, an aircraft landing gear <NUM> is shown. The landing gear assembly <NUM> includes a main strut <NUM>, which may have a shock absorbing function and may comprise a piston slidably coupled within a housing. The main strut <NUM> may also be referred to as a main fitting. The main strut is pivotably coupled to the underside 10a of the aircraft <NUM> at a pivot location <NUM>. At a bottom end of the main strut <NUM>, there is a wheel and brake assembly <NUM>, which may be more generally considered to be a ground-contacting assembly and may be replaced with a skid assembly or the like.

When in a deployed position, as shown in <FIG>, the main strut <NUM> is supported by a foldable stay <NUM>, and the stay <NUM> may be locked in place by a lock assembly <NUM>, which may also be referred to as a lock link assembly. A spring assembly <NUM> is mounted to the stay <NUM> and arranged to urge the lock assembly <NUM> to assume a locked state.

The stay <NUM> has an elongate upper stay arm 112a having a lower end defining a pair of lugs pivotally coupled via a pivot pin <NUM> to a pair of lugs defined at an upper end of an elongate lower stay arm 112b. The stay arms 112a and 112b may therefore be pivotally moveable relative to one another about the pivot pin <NUM>. The upper end of the upper stay arm 112a defines a pair of lugs that are pivotally coupled to a lug of a connector <NUM>, which in turn is pivotally coupled to the underside 10a of the aircraft <NUM>. The lower end of the lower stay arm 112b defines a pair of lugs pivotally coupled to a lug of a connector <NUM> which in turn is pivotally coupled to the main strut <NUM>.

The lock assembly <NUM> is formed of two lock links, also known as link arms: an elongate upper lock link 114a having a lower end pivotally coupled to an upper end of an elongate lower lock link 114b via a pivot pin <NUM>, and the lower lock link 114b. The lock links 114a, 114b may therefore move pivotally relative to one another about the pivot pin <NUM>. An upper end of the upper link arm 114a defines a pair of lugs that are pivotally coupled to a lug of a connector <NUM>, which in turn is pivotally coupled to the main strut <NUM>. A lower end of the lower link arm 114b defines a lug that is pivotally coupled to lugs of the stay arms 112a, 112b via the pivot pin <NUM>. Lugs of the upper stay arm 112a are disposed between the lugs of the lower stay arm 112b and the lugs of the lower link arm 14b.

When the lock assembly <NUM> is in the locked condition, as illustrated in <FIG>, the upper and lower lock links 114a, 114b are generally longitudinally aligned or coaxial, and can be 'over-centre', such that the lock assembly <NUM> is arranged to oppose a force attempting to fold the stay <NUM>, so as to move the landing gear assembly from the deployed condition towards the stowed condition. Generally, when in the locked condition, the lock assembly <NUM> will resist compressive forces applied to it along the length of the lock assembly <NUM> and the central hinge, at the pivot pin <NUM>, of the lock assembly <NUM> is at a limit of its range of movement. In this arrangement, the over-centre condition is where the angle β, measured between the two lock links 114a, 114b on an aircraft side of the joint between the lock links 114a, 114b, is less than <NUM>°.

The aircraft landing gear assembly is movable between a deployed, locked condition shown in <FIG>, for take-off and landing, and a stowed condition for flight. An actuator (not shown) is provided for moving the landing gear between the deployed condition and the stowed condition. This actuator is known in the art as a retraction actuator, and more than one may be provided. A retraction actuator may have one end coupled to the airframe and another end coupled to the main strut such that extension and retraction of the actuator results in movement of the main strut between deployed and stowed conditions.

For the landing gear <NUM> to be retracted, the lock assembly <NUM> must be broken, as shown in <FIG>, to enable the stay <NUM> to be folded, thereby permitting the main strut <NUM> to be moved by the retraction actuator towards the stowed condition. When the lock assembly <NUM> is broken, the angle β is greater than <NUM>°. An unlock actuator, not shown, may also be provided for moving the lock assembly from the locked position shown in <FIG> to the unlocked position shown in <FIG>; changing the angle β from less than <NUM>° to greater than <NUM>°.

The stay <NUM> serves to support the orientation of the main strut <NUM> when the landing gear <NUM> is in the deployed condition. The stay <NUM> generally includes a two bar linkage that can be unfolded to assume a generally straight or aligned condition in which the stay <NUM> inhibits movement of the main fitting, as shown in <FIG>. When the stay is broken, it no longer reacts pivotal movement of the main strut <NUM> and the main strut <NUM> can be moved by the retraction actuator towards the stowed condition, as shown in <FIG> and <FIG>. During flight the stay <NUM> is arranged in the folded condition, while during take-off and landing the stay <NUM> is arranged in the generally straight or aligned condition. Some main landing gear assemblies include a pair of stays coupled to a common shock absorbing strut.

One or more down lock spring assemblies <NUM> are generally provided to assist in moving the landing gear assembly to the deployed condition and locking it in that state by moving the lock assembly <NUM> to the locked condition. Down lock spring assemblies <NUM> also inhibit the lock link accidentally being unlocked. The spring assembly <NUM> is arranged to bias the lock link <NUM> towards the locked condition by way of an elastic restoring force.

The spring assemblies act to increase the angle α between the upper stay arm 112a and the lower lock link 114b. As the angle α increases, the angle β decreases (assuming the geometry of the rest of the landing gear assembly <NUM> remains constant). However, as the landing gear <NUM> retracts and the main strut <NUM> pivots to a retracted position, the angle α increases. As the landing gear <NUM> retracts to the position shown in <FIG>, and further, the angle α becomes sufficiently large that the spring assembly <NUM> may exert no compressive force between the upper stay arm 112a and the lower lock link 114b.

<FIG> shows two spring assemblies <NUM> arranged between the stay assembly <NUM> and the lock assembly <NUM>. The spring assemblies <NUM> may exert an elastic restoring force between an upper stay arm 112a and the lower lock link 114b. As the springs of the spring assemblies <NUM> may be in compression, they will urge the lock assembly <NUM> into a locked condition.

The spring assemblies <NUM> may be coupled to the stay assembly <NUM> and the lock assembly <NUM> at respective connecting lugs 112c, 114c. It can also be seen that two spring assemblies <NUM> may be provided, and that the connecting lugs 112c, 114c may be arranged between the spring assemblies, such that the arrangement is substantially symmetrical and that torsional stresses about respective elongate axes of the stay arm 112a and the lower link arm 114a may be reduced.

<FIG> shows a general view of a spring assembly <NUM>. The spring assembly <NUM> is formed from a sliding rod, shaft or tube <NUM>, which extends along the length of the spring assembly <NUM> between first and second connecting lugs <NUM>, <NUM>, and a spring <NUM> formed of a plurality of elastically deformable washers <NUM>.

The spring <NUM> abuts an end stop <NUM>, which is fixed in place by an end nut <NUM>, which may be screwed onto a thread 216b on the outer surface of the sliding rod <NUM>. The end nut <NUM> and end stop <NUM> may be separate parts arranged in abutment or may be glued together or integrally formed. By rotating the nut <NUM>, the position of the end stop <NUM> may be altered and thereby the minimum compressive stress in the spring <NUM> and the maximum length of the spring <NUM> may be altered. The end stop <NUM> may alternatively be integrally formed with the sliding rod <NUM> or may be glued to the sliding rod <NUM>. However, it is preferable that the end stop <NUM> and nut <NUM> are moveable relative to the sliding rod <NUM> so that a minimum compressive stress preload in the spring <NUM> can be applied and/or adjusted. The end stop <NUM> and nut <NUM> may be fixed to the sliding rod <NUM> after a preload is applied, such as by gluing.

At the opposite end of the spring <NUM>, there is a disc <NUM>, which may provide a substantially flat, planar surface for the spring <NUM> to abut and the disc <NUM> may engage a longitudinal groove 216a of the sliding rod <NUM> such that it remains irrotational relative to the sliding rod <NUM> and is arranged to slide along the shaft <NUM> to translate but not to rotate relative to the shaft <NUM>. Thereby, torsional forces about the shaft <NUM> exerted on the spring <NUM> may be reduced. The groove 216a may extend only part of the way along the rod <NUM> and the disc <NUM> may engage an end of the groove, thereby limiting the range of movement of the disc <NUM> and the maximum length of the spring <NUM>. In contrast to the elastically deformable washers <NUM>, the disc may be substantially planar and may be substantially rigid.

At a first end of the spring assembly <NUM>, there is a first connecting lug <NUM> arranged to be coupled to the stay assembly <NUM>, and in particular to the connecting lug 112c of the stay assembly <NUM>. The first connecting lug <NUM> of the spring assembly <NUM> may be formed separately from the sliding rod <NUM>, as shown in <FIG>, and may be screwed into it or otherwise fixed to it.

At an opposite end of the spring assembly <NUM>, there is a second connecting lug <NUM> arranged to be fixed to the lock assembly <NUM>, and in particular to the connecting lug 114c of the lock assembly <NUM>. The second connecting lug <NUM> comprises a passage for receiving the sliding rod <NUM>, so that the second connecting lug <NUM> may slide relative to the sliding rod <NUM>. Thereby, an end surface of the second connecting lug 214a may abut the disc <NUM> when the spring assembly <NUM> is compressed by relative movement of the lock assembly <NUM> and the stay assembly <NUM> so as to compress the spring <NUM>, which will provide an elastic restoring force in order to bias the lock assembly <NUM> into a locked condition.

As shown in <FIG>, the separate elements of the spring assembly <NUM> may be formed separately and may be threaded onto the shaft <NUM>. The schematic cross section in <FIG> shows how the disc <NUM> may have radially inward protrusions 218a arranged to engage the longitudinal grooves 216a of the shaft <NUM> so as to prevent relative rotation between the disc <NUM> and the central shaft <NUM>. The central shaft <NUM> may be coated with hard anodised aluminium or PTFE in order to reduce friction between the washers <NUM> and the shaft <NUM>. Alternatively, bushings may be inserted between the washers <NUM> and the shaft <NUM>.

<FIG> shows a perspective view of an alternative spring assembly <NUM>. In the alternative spring assembly <NUM>, there is a sliding rod <NUM> integrally formed with an end stop <NUM> and a first connecting lug <NUM>, the first connecting lug <NUM> being arranged to couple to the stay assembly <NUM> in substantially the same manner as the first connecting lug <NUM> of the first-mentioned spring assembly <NUM>. At an opposite end of the sliding rod <NUM>, there is a second connecting lug <NUM>, having a passage through which the sliding rod <NUM> may pass and the second connecting lug <NUM> may be substantially similar to the second connecting lug <NUM> of the first mentioned spring assembly <NUM>, having an end face 314a arranged to abut a further washer <NUM>.

The further washer <NUM> may slide relative to the sliding rod <NUM> and may have a first annular portion 318a surrounding the sliding rod <NUM> and a second annular portion 318b surrounding a guiding shaft <NUM> adjacent to and parallel to the sliding rod <NUM>. In contrast to the elastically deformable washers <NUM>, the further washer <NUM> may be substantially planar and substantially rigid. The further washer <NUM> may also have a figure-of-<NUM> shape.

The sliding rod <NUM> may, in this example, not have a groove. The further washer <NUM>, arranged to slide relative to the central shaft <NUM> and arranged to abut the spring <NUM>, may be rotationally fixed via the guiding shaft <NUM>, which may extend through a second annular portion 318b of the further washer <NUM>. The guiding shaft <NUM> may be fixed via a nut <NUM> and may therefore comprise a thread 330a. The nut <NUM> may limit the range of movement of the further washer <NUM> and may thereby prevent the elastically deformable washers <NUM> of the spring <NUM> from moving freely or vibrating when the spring <NUM> is substantially uncompressed. By rotating the nut <NUM> relative to the guiding shaft <NUM>, the nut <NUM> may move along the guiding shaft and the maximum length of the spring <NUM> may thereby be adjusted. The nut may abut the end stop <NUM>, through which the guiding shaft <NUM> may pass.

The further washer <NUM> may be limited in its range of movement by an enlarged portion 330b of the guiding shaft <NUM>, which may have an outer diameter larger than the inner diameter of the second annular portion 318b.

The spring <NUM> of the alternative spring assembly <NUM> may be substantially similar to the spring <NUM> of the first-mentioned spring assembly <NUM>.

The parts of the spring assembly <NUM> are shown in an exploded plan view in <FIG>. From this view, it can be seen that the guiding shaft <NUM>, when the spring <NUM> is compressed, may extend over the second connecting lug <NUM>. This may allow a more compact arrangement. This function may be allowed by the sizing of the further washer <NUM>, which is shown in cross-section in <FIG>.

In further varied embodiments, spring assemblies may have no sliding rod, and the elastically deformable washers may be joined as a single unit, such as by welding. In particular, resistance welding, induction welding and ultrasonic welding may be suitable for use with thermoplastic materials. Alternatively, resistance to buckling of the spring may be provided by an external tube in which the washers may be placed.

<FIG> shows a schematic cross section of a spring <NUM>, incorporating eight elastically deformable washers <NUM> arranged back to back or alternately facing in opposite directions. However, the washers may alternatively be arranged in nested arrangements, where a convex portion of one washer is received in a concave portion of another. As a further alternative, the elastically deformable washers <NUM> may be arranged where a portion of the washers are nested and a portion are in back to back abutment. Different numbers of washers from eight may also be used.

<FIG> shows a cross section of a single washer <NUM>, the washer being generally conical and annular, having a frusto conical shape with a wide circular base 226b and a smaller central hole 226a, and a sloping side 226c. Such a washer may be referred to as a Belleville washer.

Alternative shapes of washer may be used, such as substantially hemispherical washers or washers with curved sides 226c. The washers may also have non-axisymmetric geometries such as being square or rectangular in plan view. Such washers may have a frusto-pyramidal shape. The washers may and may have portions extending in alternating axial directions, such as biconvex washers formed from flat sheets.

The elastically deformable washers <NUM> may also be formed from composite materials such as carbon fibre, which may be lighter than steel washers or other metallic washers. Such materials may be anisotropic.

<FIG> shows an alternative washer <NUM> which may be used in place of the washers <NUM> described above. The alternative washer <NUM> has a different profile from the earlier-described washers, as shown in <FIG>. The central hole 426a and sloping side 426c is substantially similar to those of the earlier-described washers. However, the base 426b is formed as an edge of the washer <NUM>, with the washer <NUM> not having a flat surface acting as the base 426b.

<FIG> shows how the alternative washers <NUM> may abut to form a spring <NUM>. It can be seen that the contact between washers at their respective bases 426b is a thin, linear contact ring, as opposed to a thicker contact ring where different washers with flat bases are used.

A further alternative washer <NUM> is shown in <FIG>. The further alternative washer <NUM> has two portions: a composite, fibre reinforced portion <NUM> and a resin portion <NUM>. The resin portion <NUM> may be formed of a thermoplastic resin and may be more accurately machined to manage wear and tolerances.

The portions of the washers <NUM> arranged to contact adjacent washers, i.e. the perimeter of the central hole 526a and the base 526b, may therefore have flat surfaces formed of the resin portion <NUM>. This is shown in <FIG>, which shows a spring <NUM> formed of the further alternative washers <NUM> with the resin portions <NUM> in contact.

The outer sloping surface 536c remains as a composite material as it is not arranged to contact adjacent parts. This may also be advantageous for inspecting the condition of the composite material.

While the spring assemblies described above may be used in the landing gear assembly disclosed in <FIG>, other landing gear assemblies may also benefit from the spring assembly. For example, landing gear assemblies may have multiple side stay arrangements, each side stay having a spring assembly as described above. As an illustrative example not falling under the scope of the appended claims, such spring assemblies may also be adapted for use in shock absorbers of landing gear. In all such arrangements, the elastically deformable washers may be stressed only when required and may be otherwise substantially unstressed, in particular when the landing gear is retracted.

Claim 1:
A landing gear for an aircraft (<NUM>) comprising:
a main strut (<NUM>) arranged to be coupled to the aircraft (<NUM>) and movable between a deployed condition and a retracted condition,
a stay (<NUM>) arranged to support the main strut, the stay comprising a first stay arm (112b) coupled to the main strut and a second stay arm (112a) pivotally coupled to the first stay arm and arranged to be coupled to the aircraft,
a lock assembly (<NUM>) arranged to prevent movement of the stay when the lock assembly is in a locked position, the lock assembly comprising a first lock link (114b) pivotally coupled to the stay and a second lock link (114a) pivotally coupled to the first lock link and arranged to be coupled to the aircraft or another component of the landing gear assembly; and
a spring (<NUM>) coupled to a first member and to a second member, the spring being arranged to generate a biasing force between the first member and the second member to bias the first member toward a predetermined orientation relative to the second member, wherein the first member is the first lock link or the second lock link characterised in that the spring (<NUM>) comprises a plurality of elastically deformable washers (<NUM>);
and further characterised in that when the main strut is in the retracted condition, the elastically deformable washers are substantially unstressed.