Aircraft landing gear with a spring that opposes the rotation between the upper and lower elements of the landing gear

Description

[0001] The present invention relates to the field of landing gear which includes an upper element intended to be connected with an aircraft structure and a lower element carrying an axle, this lower element being mounted in translation relative to the upper element along a longitudinal axis, a damper being arranged to dampen translational displacements of the lower element relative to the upper element. BACKGROUND OF THE INVENTION

[0002] It is known, for example from document EP1786669_A1, that a lander comprises an upper element (here the upper element is a main lander box) intended to be connected with an aircraft structure and a lower element carrying an axle of the aircraft (here the lower element is a sliding rod of the lander which slides inside the box).

[0003] This lower element is mounted in translation relative to the upper element along a longitudinal axis of the upper element, and a damper is arranged to dampen translational displacements of the lower element relative to the upper element.

[0004] In order to oppose the rotation of the lower element relative to the upper element while allowing translation between these elements along the longitudinal axis, the lander includes a compass.

[0005] This compass has an upper arm and a lower arm, these arms being articulated to each other around a main axis of the compass extending in a plane perpendicular to the longitudinal axis of the upper element.

[0006] The upper arm of the compass is pivotally mounted relative to the upper element about a first connecting axis that is parallel to the compass's main axis. The lower arm of the compass is pivotally mounted relative to the lower element about a second connecting axis that is parallel to the compass's main axis. When a significant rotational torque is applied to the lower element relative to the upper element about this longitudinal axis, the compass's main axis can deform, potentially damaging the compass under repeated loading and reducing its lifespan. Patent documents CN108820191A and US4172570A also describe prior art landers, these documents disclosing a helical spring. SUBJECT OF THE INVENTION

[0007] One object of the present invention is to provide a lander minimizing all or part of the aforementioned disadvantages. SUMMARY OF THE INVENTION

[0008] To this end, the invention relates to an aircraft landing gear comprising an upper element intended to be connected with an aircraft structure, a lower element carrying an axle, said lower element being mounted in translation relative to the upper element along a longitudinal axis of symmetry of the upper element, a damper being arranged to dampen translational displacements of the lower element relative to the upper element.

[0009] This lander is essentially characterized in that it comprises a spring having first and second parts which are far from said longitudinal axis, the first part of the spring being attached to the upper element and the second part of the spring being attached to the lower element so that during the translational displacement of the lower element relative to the upper element, this spring opposes any rotation of the lower element with respect to the upper element around said longitudinal axis.

[0010] Thus the spring allows the translation of the lower element of the lander relative to the upper element along the longitudinal axis of symmetry of the upper element while achieving a rotational mechanical coupling between the lower and upper elements around this same longitudinal axis.

[0011] The lander according to the invention can be: in the first case, a non-steerable axle landing gear (during the aircraft's ground roll) along the longitudinal axis relative to the aircraft structure; or in the second case, a landing gear with a steerable axle (during the ground roll) along the longitudinal axis relative to the aircraft structure (in this second case, during the ground roll, the wheels carried by the axle can be steered around the longitudinal axis to define a direction of roll).

[0012] In each of these first and second cases, the spring creates a mechanical coupling between the upper element and the lower element such that: on the one hand it exerts along the longitudinal axis of the upper element, an elastic return torque of the lower element towards a given orientation position relative to the upper element; and on the other hand it exerts an elastic force tending to oppose the approach of the lower element relative to the upper element along the longitudinal axis of the element.

[0013] In the first case, during taxiing, the spring maintains a fixed orientation of the axle relative to the aircraft structure while allowing the lower element to slide relative to the upper element (the shock absorber's function being to dampen this sliding movement).

[0014] In the second case, the orientation of the lower element and its axle is achieved by orienting the upper element relative to the aircraft structure. The spring here creates a rotational mechanical coupling between the upper and lower elements, such that these elements are rotationally linked around the longitudinal axis and are oriented together.

[0015] In each of these cases, the spring performs the essential functions normally performed by a compass while simplifying the connection between the upper and lower elements.

[0016] The invention also relates to an aircraft equipped with at least one landing gear according to the invention conforming to any one of the landing gear embodiments described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying drawings, in which: there figure 1 is a schematic perspective view of a lander according to the invention in an extended configuration in which it has a maximum length (the shock absorber 20 and the spring 17 are here slightly compressed along the longitudinal axis ZZ); the figure 2 is a view of the lander of the figure 1 while it is in a compressed configuration in which it has a reduced length relative to said maximum length (the shock absorber 20 and the spring 17 are here strongly compressed along the longitudinal axis ZZ and the axle 16 is here brought closer to the aircraft structure 2 by translation / sliding along a direction parallel to the longitudinal axis ZZ); the figure 3is a side view of the lander of the figure 1 while it is in its extended configuration, this figure 3 illustrates the relative positions of the first and second parts 17a, 17b of the spring 17 with respect to the longitudinal axis ZZ, these first and second parts 17a, 17b being arranged to limit the risk of generating a parasitic torque of rotation of the lower element with respect to the upper element during the compression of the spring. DETAILED DESCRIPTION OF THE INVENTION

[0018] Typically, an aircraft has several primary landing gear, each located closer to the aircraft's wing than to its cockpit, and a secondary landing gear located closer to the cockpit than to the wing.

[0019] Each main landing gear generally includes at least one axle whose orientation during aircraft taxiing is generally fixed with respect to a longitudinal plane of symmetry of the aircraft, this axle being substantially perpendicular to this longitudinal plane of symmetry of the aircraft.

[0020] A secondary landing gear typically includes at least one steering actuator and a steerable axle controlled by that steering actuator. Steering the axle allows the aircraft's taxiing direction to be changed.

[0021] Preferably, the main landing gear is arranged to be able to support a load greater than the maximum load permissible by a secondary landing gear, the main landing gear having the main function of carrying the aircraft while the secondary landing gear has the function of carrying the aircraft and orienting the axle during taxiing.

[0022] The aircraft landing gear 0 shown on the figures 1 to 3 is a main lander, having an upper element 11 which is a main box and a lower element 15 which is a rod mounted sliding inside the box.

[0023] As illustrated on the figures 1 to 3 , the upper element 11 is intended to be, directly or indirectly, connected to an aircraft structure 2 and the lower element 15, supported by the upper element 11, carries an axle 16.

[0024] Axle 16 is arranged to be equipped with at least one wheel (not shown) mounted to rotate on it, the plane of the wheel being perpendicular to a principal axis of symmetry of the axle.

[0025] The structure of aircraft 2 is represented here in a simplified manner by two zones of structure 2 which together form an attachment of the upper element 11.

[0026] The upper element 11 which is supported by the aircraft structure is here mounted pivotally relative to these areas of the structure 2 via a simple pivot joint with axis X'.

[0027] Like most known landers, the lander according to the invention may include a main strut (not shown in the figures).

[0028] Such a strut typically comprises upper and lower arms joined by a bend. These upper and lower arms are either aligned to hold the landing gear in a deployed position outside the aircraft structure, or folded towards each other when the landing gear is retracted inside the aircraft structure. Such a strut may be equipped with a locking mechanism to secure it in position when the upper and lower arms are aligned.

[0029] An orthonormal coordinate system formed by normalized vectors X, Y, and Z is represented on each of the figures 1 to 3 .

[0030] The vector Y is parallel to the direction of the longitudinal axis of axle 16.

[0031] The vector Z coincides with a direction of the longitudinal axis ZZ of the upper element 11.

[0032] The vector X which is perpendicular to the vectors Y and Z and is oriented in a direction of rolling of the wheel or wheels which equip axle 16.

[0033] The said axis X' forming the pivot link of the lander 0 vis-à-vis the structure 2 of the aircraft has a direction which is here substantially parallel to the direction of the vector X but it could be oriented differently depending on the mode of linkage chosen between the lander 0 and the structure 2.

[0034] The lower element 15 is mounted to slide relative to the upper element 11 along the longitudinal axis ZZ of symmetry of the upper element 11.

[0035] In this case, the lower element 15 is here mounted sliding inside the upper element 11.

[0036] A damper 20 is arranged to dampen translational displacements of the lower element 15 relative to the upper element 11 along the axis ZZ.

[0037] This damper 20 exerts elastic return forces on the lower element 15 towards a stable position of this lower element 15 relative to the upper element 11 and damping forces on the translational movement of the lower element 15 relative to the upper element 11.

[0038] Lander 0 is thus deformable between a compressed configuration illustrated in the figure 2 in which it has a reduced length (compared to a maximum length) and an extended configuration illustrated in Figures 1 And 3 in which it exhibits a maximum length.

[0039] During the passage of the lander 0 between its extended configuration and its compressed configuration, the lower element 15 passes through said stable position with respect to the upper element.

[0040] The lander according to the invention also includes at least one spring 17 comprising first and second parts 17a, 17b which are away from said longitudinal axis ZZ.

[0041] These first and second parts 17a, 17b of the spring are here terminal ends of the spring 17.

[0042] The first part 17a of the spring is attached to the upper element 11 (i.e., the first part 17a of the spring is mechanically coupled to move with this upper element 11) and the second part 17b of the spring 17 is attached to the lower element 15 (i.e., the second part 17b of the spring is mechanically coupled to move with the lower element 15) so that when the lower element 15 moves in translation relative to the upper element 11, this spring 17 opposes any rotation of the lower element 15 relative to the upper element 11 around said longitudinal axis ZZ.

[0043] This spring 7 creates a rotational mechanical coupling between the upper element 11 and the lower element 15, this coupling being elastic.

[0044] Thus, the spring 17 constitutes an elastically deformable link between the upper element 11 and the lower element 15.

[0045] The lower element 15 and the second part of the spring 17b move together relative to the upper element 11, both in translation along a direction of translation parallel to the axis ZZ and in rotation around this direction parallel to the axis ZZ.

[0046] This spring 7 is a helical spring extending along a longitudinal axis of the spring which is parallel to the longitudinal axis ZZ of the upper element 11.

[0047] This longitudinal axis of the spring is preferably coincident with the longitudinal axis ZZ of the upper element.

[0048] This spring is compressible along this longitudinal axis of the spring 17 by bringing the first part 17a closer to the second part 17b and it has an elastic stiffness in compression along said longitudinal axis ZZ which is identical to its elastic stiffness in tension along said longitudinal axis ZZ.

[0049] In other words, over the operating range of the spring, when the lander moves from its extended configuration to its compressed configuration, the elastic stiffness of the spring subjected to a tension tending to separate the first and second parts 17a, 17b from each other in a direction parallel to the longitudinal axis of the spring is similar, within a variation depending on the characteristics of the lander, or is more particularly identical, within plus or minus 10%, to the elastic stiffness of this spring subjected to a compression tending to bring these first and second parts of the spring closer together in this same direction.

[0050] This helical spring 17 has several turns extending between the said first and second parts 17a, 17b, some of the turns extending around the upper element 11 and the others of these turns extending around the lower element 15.

[0051] Thus, the elastic forces returning the lander to its extended configuration are essentially generated by the shock absorber 20 and to a lesser extent by the spring 17.

[0052] According to a direction of observation of the lander which is parallel to the longitudinal axis ZZ of the upper element, the said first and second parts 17a, 17b of the spring 17 appear on either side of this longitudinal axis ZZ of the upper element 11.

[0053] In other words, the first and second parts 17a and 17b of the spring are preferably in the same first plane in which said longitudinal axis ZZ extends, while being on either side of a second plane in which said longitudinal axis ZZ also extends, this second plane being perpendicular to said first plane.

[0054] During rolling, the lower element 15 slides along the longitudinal axis ZZ of the upper element 11 and the particular arrangement of the first and second parts of the spring 17 with respect to the longitudinal axis ZZ prevents the generation of a parasitic torque of rotation of the lower element with respect to the upper element.

[0055] Preferably, as illustrated on the figures 1 to 3 , the upper element 11 comprises two portions 11a, 11b which extend radially with respect to the longitudinal axis ZZ outwards from this upper element 15.

[0056] These two portions 11a, 11b of the upper element 11 constitute a clevis usually used for the clevis mounting of a first compass arm.

[0057] Similarly, the lower element 15 comprises two portions 15a, 15b which extend radially with respect to the longitudinal axis ZZ outwards from this lower element 15.

[0058] These two portions 15a, 15b of the lower element 15 constitute a clevis usually used for the clevis mounting of a second compass arm.

[0059] The first part 17a of the spring is subjected to the upper element 11 via at least one of these portions 11a, 11b of the upper element 11.

[0060] Similarly, the second part 17b of the spring 17 is preferentially subjected to the lower element 15 via at least one of these portions 15a, 15b of the lower element 15.

[0061] By assembling a spring 17 to the clevises usually used to connect a compass, it is therefore possible to obtain, in an economical way, a lander according to the invention.

[0062] More specifically, the first part 17a of the spring is attached to the upper element via a first ball joint and the second part 17b of the spring is attached to the lower element via a second ball joint.

[0063] In this case, the first ball joint comprises first and second parts forming a first ball joint. The first part of the first ball joint is fixed to the first part 17a of the spring, and the second part of the first ball joint is fixed to the upper element 11.

[0064] Similarly, the second ball joint comprises third and fourth parts forming a second ball joint. The third part of the second ball joint is fixed to the second part 17b of the spring, and the fourth part of the second ball joint is fixed to the lower element 15.

[0065] These ball-and-socket type connections help to eliminate torques / moments that could cause the lower element 15 to rotate relative to the upper element 11 during axial movement of the lower element 15 along the axis ZZ.

[0066] The spring is arranged to generate, around the longitudinal axis, an elastic restoring torque of the lower element towards a predetermined angular rest position relative to the upper element.

[0067] For this reason, the spring has a first elastic stiffness opposing the rotation of the lower element relative to the upper element around the longitudinal axis.

[0068] This initial elastic stiffness is such that, as long as the torque transmitted between the upper element 11 and the lower element 15 remains below a predetermined maximum torque value, the spring 17 ensures that the rotation of the lower element 15 relative to the upper element 11 remains below a predetermined maximum orientation angle. This predetermined maximum orientation angle is determined in such a way as to guarantee stability of the rolling direction during movement.

[0069] In the event of exceeding the said predetermined maximum torque value, a temporary pivoting of the lower element 15 relative to the upper element 11 may be observed beyond the predetermined maximum orientation angle without risk of damage to the lander.

[0070] The spring then forces the lower element back to its predetermined angular rest position.

[0071] For this purpose, said spring 17 preferably has a minimum elastic stiffness in torsion Jmin opposing a pivoting of the lower element 15 relative to the upper element 11 around said longitudinal axis ZZ which is given by the equation: Jmin = Cmax / θ 1 - θ 2 max , in which Cmax is the standard of the maximum permissible pivoting torque of the lower element 15 with respect to the upper element 11 around said longitudinal axis ZZ (Cmax is a predetermined maximum torque value that the lander must be able to withstand during its use); and in which |θ1-θ2 |max is a maximum permissible angular rotation angle of the lower element 15 with respect to the upper element 11 around said longitudinal axis ZZ expressed in absolute value.

[0072] This value |θ1-θ2|max is a predetermined value based on the expected behavior of the lander during its use. For example, |θ1-θ2|max could be chosen to be less than 3°, preferably less than or equal to 1°.

[0073] This minimum elastic stiffness in torsion Jmin is chosen to maintain the angular orientation of the axle relative to the aircraft structure within a range of forces compatible with stable taxiing, including in the event of an impact on the lower element 15 of the landing gear 0.

[0074] Preferably, the shock absorber 20 has an elastic stiffness opposing the deformation of the shock absorber along said longitudinal axis ZZ which is several times greater than an elastic stiffness of the spring 17 opposing the deformation of the spring along this same longitudinal axis ZZ.

[0075] The invention makes it possible to eliminate the compass which normally connects the upper element to the lower element and replace it with a spring, which allows a reduction in mass, an elimination of undesirable side moment effects and an elastic return effect parallel to that exerted by the shock absorber 20.

[0076] The invention is not limited to the examples described above and encompasses any variant falling within the scope defined by the claims.

[0077] In particular, the invention encompasses all variants in which the spring stiffness, the geometry of its coils, its diameter and its unstretched length would be determined according to the type of lander, its architecture and the expected performance.

[0078] It should be noted that the lander according to the invention could be a secondary lander and in this case the upper element 11 would be a tube mounted pivoting, preferably about the axis ZZ, relative to a lander shaft, this secondary lander shaft extending at least partly inside this rotating tube.

[0079] The secondary landing gear strut is hinged to the aircraft structure, allowing it to move from a deployed position outside the aircraft structure to a retracted position within it. The upper element, in this case the tube, would then be connected to the aircraft structure via the strut. An actuator would be used to rotate the upper element relative to the strut, thereby maneuvering the orientation of the lower element and its axle during taxiing.

Claims

1. An aircraft undercarriage (0) comprising an upper element (11) arranged to be connected to an aircraft structure (2), a lower element (15) carrying an axle (16), said lower element being mounted to be movable in translation relative to the upper element along a longitudinal axis (Z-Z) of the upper element (11), and a shock absorber (20) arranged to damp movements in translation of the lower element (15) relative to the upper element (11), the undercarriage includes a spring (17) having first and second portions (17a, 17b) that are spaced apart from said longitudinal axis (Z-Z), the spring is a helical spring that is compressible along a longitudinal axis of the spring by moving the first portion (17a) closer to the second portion (17b), the first portion (17a) of the spring being secured to the upper element (11), characterized in that the second portion (17b) of the spring (17) being secured to the lower element (15) in such a manner that during movement in translation of the lower element (15) relative to the upper element (11) the spring (17) opposes any turning of the lower element (15) relative to the upper element (11) about the longitudinal axis (Z-Z), the helical spring extending partially about the upper element (11) and partially about the lower element (15), the first portion of the spring being secured to the upper element via a first ball-joint connection and the second portion of the spring being secured to the lower element via a second ball-joint connection.

2. An aircraft undercarriage according to claim 1, wherein said spring (17) presents elastic stiffness in compression along said longitudinal axis (Z-Z).

3. An aircraft undercarriage according to claim 2, wherein said spring also presents elastic stiffness in traction along said longitudinal axis (Z-Z), said elastic stiffness in compression of the spring being identical to said elastic stiffness in traction of the spring.

4. An aircraft undercarriage according to claim 2 or claim 3, wherein the shock absorber (20) presents elastic stiffness opposing deformation of the shock absorber along said longitudinal axis (Z-Z) that is several times greater than said elastic stiffness in compression of the spring along said longitudinal axis (Z-Z).

5. An aircraft undercarriage according to any one of claims 1 to 4, wherein said helical spring presents a plurality of turns extending between said first and second portions of the spring, and wherein, when the undercarriage is observed in an observation direction that is parallel to the longitudinal axis (Z-Z) of the upper element, said first and second portions of the spring appear on opposite sides of the longitudinal axis (Z-Z) of the upper element (11).

6. An aircraft undercarriage according to any one of claims 1 to 5, wherein the first and second portions of the spring are terminal ends of the spring.

7. An aircraft undercarriage according to any one of claims 1 to 6, wherein the first portion of the spring is secured to the upper element via a portion of the upper element that projects outwards from the upper element, radially relative to the longitudinal axis (Z-Z) of the upper element, and wherein the second portion of the spring is secured to the lower element via a portion of the lower element that projects outwards from the lower element, radially relative to the longitudinal axis (Z-Z) of the upper element.

8. An aircraft undercarriage according to any one of claims 1 to 7, wherein: · the first ball joint connection comprises first and second parts forming a first ball joint, the first part of the first ball joint connection being fixedly connected to the first portion (17a) of the spring, and the second part of the first ball joint connection being fixedly connected to the upper element (11); and · the second ball joint connection comprises third and fourth parts forming a second ball joint, the third part of the second ball joint connection being fixedly connected to the second portion (17b) of the spring, and the fourth part of the second ball joint connection being fixedly connected to the lower element (15).

9. An aircraft undercarriage according to any one of claims 1 to 8, wherein said spring presents a minimum value Jmin of elastic stiffness in twisting opposing pivoting of the lower element (15) relative to the upper element (11) about said longitudinal axis (Z-Z), the minimum elastic stiffness in twisting being given by the following equation: Jmin = Cmax / θ 1 - θ 2 max , · in which Cmax is the magnitude of a maximum authorized pivoting torque for the lower element (15) relative to the upper element (11) about said longitudinal axis (Z-Z), Cmax being a predetermined value; and · in which |θ1-θ2|max is a maximum authorized angle of rotation for the lower element (15) relative to the upper element (11) about said longitudinal axis (Z-Z) expressed as its absolute value.

10. An aircraft undercarriage according to any one of claims 1 to 9, wherein the undercarriage is an aircraft main undercarriage, the upper element being a main strut leg of the undercarriage and the lower element being an undercarriage rod slidably mounted to slide inside the strut leg.

11. An aircraft undercarriage according to any one of claims 1 to 9, wherein the undercarriage is an aircraft nose undercarriage, the upper element being a tube that is pivotally mounted relative to a shaft of the undercarriage, the shaft of the undercarriage extending at least in part inside the turnable tube.

12. An aircraft including at least one undercarriage according to any one of claims 1 to 11.