Landing-gear assembly for an aircraft, the landing-gear assembly including a secondary shimmy damper

Abstract

A landing-gear assembly (1) for an aircraft, the landing-gear assembly comprising: an axle shaft (2); a leg (3) presenting a first portion (3a) carrying said axle shaft (2) and a second portion (3b) connected to a carrier structure of the aircraft; a main damper (5); and a first secondary damper (6a) distinct from the main damper (5). The first secondary damper (6a) is carried by the axle shaft (2) and comprises: an inertial mass (M); and connection means (7a) between the inertial mass (M) and the axle shaft (2) damping movements of the inertial mass (M) along a first axis (X1) of movement of the inertial mass (M) relative to the axle shaft (2), said first axis of movement (X1) extending in a plane (P) perpendicular to said steering axis (Z).

Claims

1. A landing-gear assembly (1) for an aircraft, the landing-gear assembly comprising: an axle shaft (2) arranged to carry wheels for enabling the aircraft to run on the ground; a leg (3) presenting a first portion (3a) carrying said axle shaft (2) and a second portion (3b) adapted to be connected to a carrier structure of the aircraft, said leg extending along a main axis of the leg passing via said first and second leg portions; a main damper (5) arranged to damp axial movements of the first leg portion (3a) relative to the second leg portion (3b); a first secondary damper (6a) distinct from the main damper (5), characterized in that said first secondary damper (6a) is carried by said axle shaft (2), said first secondary damper (6a) comprising: an inertial mass (M); and first connector (7a) connecting said inertial mass (M) to said axle shaft (2) in order to enable said inertial mass (M) to move about at least one first axis of movement (X1) of said inertial mass (M) relative to the axle shaft (2) and in order to enable said inertial mass (M) to oscillate along said at least one first axis of movement (X1) on either side of a stationary rest position relative to the axle shaft (2), said first connector (7a) being adapted to damp said movements of said inertial mass (M) relative to said axle shaft (2) about said at least one first axis of movement (X1), said first axis of movement (X1) extending in a plane (P) perpendicular to said main axis (Z).

2. The landing-gear assembly according to claim 1, wherein said first axis of movement (X1) of the inertial mass (M) of the first secondary damper lies at a distance from the main leg axis.

3. The landing-gear assembly according to claim 1, further comprising a steering mechanism (4) adapted to steering the first portion (3a) of the leg relative to the second portion (3b) of the leg by turning the first leg portion about a steering axis that is parallel to said main leg axis (Z).

4. The landing-gear assembly according to claim 1, wherein said first connector (7a) connecting said inertial mass (M) to said axle shaft (2) comprise: resilient return means (8a) for returning the inertial mass (M) towards said stationary rest position of the inertial mass relative to the axle shaft (2); and a damper (9a) that present a damping coefficient of predetermined value.

5. The landing-gear assembly according to claim 4, wherein said resilient return means (8a) present a stiffness constant value along the first axis of movement (X1) of the inertial mass (M) relative to the axle shaft (2).

6. The landing-gear assembly according to claim 1, wherein said first axis of movement (X1) of the inertial mass (M) of the first secondary damper (7a) extends along the axle shaft (2).

7. The landing-gear assembly according to claim 6, wherein said axle shaft (2) is tubular, the first secondary damper (6a) being placed inside said tubular axle (2).

8. The landing-gear assembly, according to claim 1, wherein said axle shaft (2) carries a second secondary damper (6b) comprising: a second inertial mass (M); and second connector connecting said second inertial mass to said axle in order to enable said second inertial mass to move along at least one second axis of movement (X2) of said second inertial mass (M) relative to the axle shaft (2) and in order to enable said second inertial mass to oscillate along said at least one second axis of movement (X2) on either side of a stationary rest position of said second inertial mass (M) relative to the axle shaft (2), said second connector being adapted to damp said movements of said second inertial mass (M) relative to said axle along said at least one second axis of movement (X2), said second axis of movement (X2) extending in a plane perpendicular to said main leg axis (Z) and at a distance from said main axis (Z), the axle shaft extending between first and second ends (2a, 2b) of the axle shaft (2), the first secondary damper (6a) being carried by the first end (2a) of the axle shaft (2) and the second secondary damper (6b) being carried by the second end (2b) of the axle shaft (2).

9. The landing-gear assembly according to claim 8, wherein the first and second dampers (6a, 6b) are linear dampers, the first axis of movement (X1) of the inertial mass (M) of the first secondary damper (6a) being parallel to the second axis of movement (X2) of the second inertial mass (M) of the second secondary damper (6b).

10. The landing-gear assembly according to claim 8, further comprising a first rim (10) for supporting a first wheel for enabling the aircraft to run on the ground and a second rim for supporting a second wheel for enabling the aircraft to run on the ground, said first and second rims being mounted to rotate about the axle shaft (2), the first secondary damper (6a) being arranged at least in part inside a hollow zone (10a) of the first rim (10) and the second secondary damper (6b) being arranged at least in part inside a hollow zone of the second rim.

11. The landing-gear assembly, according to claim 10, wherein the inertial mass (M) of the first secondary damper (6a) is in the form of a ring (11) and extends around the first end (2a) of said axle shaft, the second inertial mass of the second secondary damper (6b) also being in the form of a ring (14) and extending around the second end (2b) of said axle shaft (2).

12. The landing-gear assembly according to claim 11, wherein said connection means (7a) adapted to connect said inertial mass (M) of said first secondary damper (6a) to said axle shaft (2) comprise a first fastener ring (12) fastened to the axle shaft (2) and a resilient annular sleeve (13) coaxial with the inertial mass (M) of said first secondary damper (6a), said resilient annular sleeve (13) being placed between the first fastener ring (12) and the inertial mass (M) of the first secondary damper (6a).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be better understood in the light of the following description of particular non-limiting embodiments of the invention, given with reference to the figures of the accompanying drawings, in which:

(2) FIG. 1a shows a first embodiment of the landing-gear assembly of the invention in which the first secondary damper is located in a longitudinal opening inside the axle shaft;

(3) FIG. 1b is a diagrammatic view corresponding to the first secondary damper shown in FIG. 1a;

(4) FIG. 2a shows a second embodiment of the landing-gear assembly of the invention in which there are two secondary dampers, each placed at a corresponding end of the axle shaft, if possible each secondary damper is positioned at least in part inside the corresponding wheel rim and is preferably positioned in full inside the corresponding wheel rim;

(5) FIG. 2b is a diagram of a secondary damper corresponding to the first and second secondary dampers in the landing-gear assembly of FIG. 2a, in this embodiment, the secondary damper is of annular shape with an annular inertial mass carried on the outside of a damper ring that is itself carried by a fastener ring for engaging around the axle shaft;

(6) FIG. 3 shows, the behavior of two landing-gear assemblies in terms of free angular oscillations about their steering axes, in response to typical angular torsion, one of said landing-gear assemblies not including a secondary damper and the other including one secondary damper as shown in FIG. 1a or two secondary dampers as shown in FIG. 2a or as shown in FIG. 4a;

(7) FIG. 4a shows a third embodiment of the landing-gear assembly of the invention in which there are two secondary dampers each placed at a respective end of the axle shaft, in this embodiment said dampers are linear dampers that, where possible, extend inside one of the wheel rims of the landing-gear assembly; and

(8) FIG. 4b is a diagram of a secondary damper corresponding to the first and second secondary dampers used in the landing-gear assembly of FIG. 4a, in this embodiment the secondary damper is of cylindrical shape with an inertial mass that can be moved along a mass movement axis X1 with connection means connecting said inertial mass M to the shaft, said connection means damping the movements of said inertial mass relative to the shaft about the axis X1.

DETAILED DESCRIPTION OF THE INVENTION

(9) As described above, and shown in FIGS. 1a, 2a, and 4a, the invention relates to an aircraft landing-gear assembly 1 comprising an axle shaft 2 arranged to carry wheels for enabling the aircraft to run on the ground.

(10) The landing-gear assembly 1 includes a leg 3 extending along a main leg axis Z and presenting a first portion 3a carrying said axle shaft 2 and a second portion 3b suitable for being connected to a carrier structure belonging to the aircraft. The main axis Z passes via the first and second leg portions 3a, 3b.

(11) A main damper 5 of the landing-gear assembly 1 is arranged to damp axial movements of the first leg portion 3a relative to the second leg portion 3b along a main axial axis of movement of the first leg portion 3a relative to the second leg portion 3b. In this embodiment, said main axis of movement coincides with the main leg axis Z.

(12) The second leg portion 3b may comprise a strut box in which the first leg portion 3a slides, the main damper 5 being located at least partly inside said box.

(13) In certain embodiments of the invention, such as those shown in FIGS. 1a, 2a, and 4a, the landing-gear assembly 1 may include a steering mechanism 4 for steering it that is suitable for steering the first portion 3a of the leg relative to the second portion 3b of the leg by turning the first leg portion about/relative to a steering axis that extends along the leg 3. This steering axis may coincide with the main leg axis Z. A landing-gear assembly provided with such a steering mechanism is generally used as a nose wheel assembly for an aircraft.

(14) As described above, the invention may also concern landing-gear assemblies not including a steering mechanism. Such assemblies are generally used for the main landing-gear in aircraft.

(15) It should be observed that the axial movement of the first leg portion 3a relative to the second leg portion 3b is movement of the first leg portion 3a in translation along a main axis of movement that is preferably parallel to and possibly coincides with said main leg axis Z and with the steering axis of the aircraft.

(16) In order to limit oscillation phenomena of the landing-gear assembly about the main leg axis Z (shimmy phenomena), a first secondary damper 6a is adapted to damp the oscillating motion of the first leg portion 3a relative to the second leg portion 3b. This first secondary damper 6a that is carried by the axle shaft 2 comprises: an inertial mass M; and connection means 7a connecting said inertial mass M to said axle shaft 2.

(17) Said connection means 7a are adapted to damp movements of said inertial mass M relative to the axle shaft 2 about at least one first axis of movement X1 of said inertial mass M relative to the axle shaft 2.

(18) As can be seen in the various FIGS. 1a to 2b, and 4a, 4b, this first axis of movement X1 extends in a plane P that is perpendicular to the main leg axis Z and that is located at a distance from said axis Z. It should be observed that the inertial mass M is carried only by the connection means 7a, which are themselves attached to the axle shaft 2.

(19) Since the inertial mass M of the first secondary damper 6a is connected to the axle shaft 2 via connection means 7a that provide damping of the motion of the inertial mass M relative to the axle shaft 2 along at least the first axis of movement X1, which itself extends in a plane P that is perpendicular to the main axis Z, the motion of the inertial mass M relative to the axle shaft 2 gives rise to damping of oscillation about the axis Z.

(20) This damping of oscillation about the main axis Z serves to damp the oscillating motion of the first portion 3a of the leg relative to the second portion 3b of the leg. The greater the distance between the first axis of movement X1 of the inertial mass M and the main axis Z, the more effective the device.

(21) In the embodiment shown in FIG. 1a, the first axis of movement X1 coincides with the axle shaft 2 since the inertial mass M is inside the axle shaft, the axis of movement X1 extending along the axle shaft. In this embodiment, the distance between the axis X1 and the main leg axis Z is equal to the distance between the axle shaft 2 and the main axis Z. The first secondary damper 6a thus has an effect of reducing the shimmy phenomenon. In the embodiment of FIG. 1a, the inertial mass M serves to damp motion of the first leg portion relative to the second leg portion that presents at least one movement component in movement along the axis X1. By way of example, damping may be performed on a movement of the first portion 3a in turning about the axis Z or in translation radially relative to the axis Z, or on complex movements combining both angular oscillations and oscillations in translation.

(22) Ideally, the inertial mass M is carried only by the connection means 7a, which implies that it is subjected only to inertia forces and to mechanical forces transmitted via the connection means 7a.

(23) Damping of the movements of the inertial mass M relative to the axle shaft 2 is thus easily controllable via the connection means 7a alone, without having to modify the rest of the landing-gear assembly 1.

(24) Preferably, the connection means 7a are not only adapted to damping movement of the inertial mass M relative to said axle 2 along the first axis of movement X1, but they are also adapted to guide movements of the inertial mass M relative to the axle 2 along the first axis of movement X1 of the inertial mass M relative to the axle shaft 2. The connection means 7a thus perform the functions both of guiding and of damping movements of the inertial mass M along the first axis of movement X1.

(25) As shown in FIGS. 1b, 2b, and 4b, the connection means 7a of the first secondary damper 6a that connect the inertial mass M to the axle shaft 2 comprise: resilient return means 8a for returning the inertial mass M towards said stationary rest position of the inertial mass relative to the axle shaft 2; and damper means 9a that present a damping coefficient of predetermined value c.

(26) As shown in FIGS. 1b and 4b, the resilient means 8a may be implemented by means of one or more springs that are stressed to a greater or lesser extent as a function of the position of the inertial mass M relative to the axle shaft. In these figures, the resilient means 8a of a secondary damper comprise two springs mounted in opposition at opposite ends of the inertial mass M. Ideally, these springs are prestressed in order to bring the mass towards a predetermined rest position. Naturally, other types of resilient means 8a may be envisaged in place of a spring: use may be made of one or more parts made of a resilient polymer material.

(27) The damper means 9a may be made by associating: one or more chambers of internal volume that varies as a function of the movement of the inertial mass M relative to the axle shaft 2; with one or more constrictions for the flow of fluid between the inside and outside of said chamber(s). A constriction makes it possible to limit the flow of fluid towards the chamber or out from the chamber, thereby generating damping.

(28) Although, in this example, the resilient return means 8a and the damper means 9a are shown in the form of separate mechanical means, it is nonetheless possible to implement said resilient means 8a and said damper means 9a as at least one part made of a material, such as an elastomer, that presents both resilient characteristics (elastic stiffness) and damping characteristics (damping coefficient).

(29) The value of the damping coefficient c is predetermined so that the connection means 7a of the first secondary damper 6a are adapted to damp the movement of the inertial mass M relative to the axle shaft 2 and along the first axis of movement X1.

(30) The resilient return means 8a present a stiffness constant of value k along the first axis of movement X1 of the inertial mass M relative to the axle shaft 2.

(31) In FIG. 3: the fine line shows the angular oscillating motion about the main leg axis Z of a landing-gear assembly not including a secondary damper carried by the axle shaft; and the thick line shows the angular oscillating motion about the main axis Z of a landing-gear assembly fitted with a secondary damper carried by the axle.

(32) For each of these curves, the angular oscillating motion is obtained by mechanically exciting the landing-gear assembly under predetermined and constant exciting conditions. By way of example, the applied excitation could be typical angular twisting of the leg about the main axis Z.

(33) When the landing-gear assembly does not include a secondary damper, the free angular oscillation about the axis Z presents an amplitude of oscillation that is sustained and substantially constant over time.

(34) In contrast, with a landing-gear assembly of the invention, i.e. fitted with at least one secondary damper for the axle shaft, the angular amplitude of oscillation is observed to be damped strongly during the first second after the start of free oscillation (see thick line curves).

(35) In a particular embodiment of the invention, the damping coefficient and stiffness constant values c and k of each secondary damper may be adjustable and selected within predetermined ranges of values. This makes it possible to adapt the damping characteristics of the secondary dampers to the type of landing-gear assembly that is concerned.

(36) The value of the inertial mass M also acts on the efficiency of the system. Typically, the inertial mass M value of each secondary damper is selected as a function of the amount of damping of the shimmy phenomenon that is desired from each damper.

(37) As can be understood from FIGS. 1a, 2a, and 4a, three main embodiments of the invention are envisaged.

(38) In the first of said three embodiments (see FIGS. 1a and 1b), the first axis of movement X1 of the inertial mass M of the first secondary damper 7a extends along the axle shaft 2.

(39) For this purpose, the axle shaft 2 may be made to be tubular and the first secondary damper 6a may be placed inside said tubular axle shaft 2.

(40) In this embodiment, the axle shaft 2 is hollow along its entire length, the first secondary damper 6a being arranged entirely inside the axle shaft 2. The first axis of movement X1 of the inertial mass M relative to the axle 2 extends along the axle shaft and inside said axle shaft 2.

(41) In this embodiment, the first secondary damper 6a may include a guide 15 extending along the inertial mass M, between said inertial mass and an inside face of the axle shaft. The inertial mass M may thus slide inside and along the guide 15 in the form of a tube, without coming into contact against the axle shaft. This avoids any risk of wear on the axle shaft as a result of the oscillations of the inertial mass M.

(42) In alternative embodiments of the invention, as shown in FIGS. 2a and 4a, the axle shaft 2 carries a second secondary damper 6b.

(43) Said second secondary damper 6b comprises: a second inertial mass M; and second connection means connecting said second inertial mass M to said axle 2 in order to enable it to move along at least one second movement axis X2 of said second inertial mass M relative to the axle shaft 2 and in order to enable it to oscillate along said at least one second axis of movement X2 on either side of a stationary rest position of said second inertial mass M relative to the axle shaft 2, said second connection means being suitable for damping said movements of said second inertial mass M relative to said axle along said at least one second axis of movement X2.

(44) This second axis of movement X2 extends in a plane P that is perpendicular to said main leg axis Z (in this embodiment coinciding with the steering axis) and at a distance from said axis Z. The axle shaft 2 extends between first and second ends 2a, 2b of the axle shaft 2. The first secondary damper 6a is carried by the first end 2a of the axle shaft 2 while the second secondary damper 6b is carried by the second end 2b of the axle shaft 2.

(45) This second inertial mass M is thus arranged to be able to move relative to the axle shaft 2 along said second axis of movement X2. The second connection means enable said second inertial mass M to oscillate on either side of a rest position that is specific thereto, said oscillation being performed along said second axis of movement X2. These same second connection means damp said oscillatory movement of the second inertial mass M relative to the axle shaft X2. Said damping of the oscillating motion of the second inertial mass leads to damping of the relative movements between the first and second portions of the leg 3.

(46) In the embodiments of the landing-gear assembly where there are a plurality of secondary dampers: the inertial mass of said first secondary damper may be referred to as the first inertial mass; the inertial mass of the second secondary damper is referred to as the second inertial mass; and the connection means of the first secondary damper may be referred to as the first connection means.

(47) Ideally, the first connection means of the inertial mass of the first secondary damper and the second connection means of the inertial mass of the second secondary damper, present a single damping coefficient value c. In addition, in the embodiments in which the landing-gear assembly includes first and second dampers 6a, 6b, the first axis of movement of the first inertial mass of the first secondary damper is preferably parallel to the second axis of movement X2 of the second inertial mass M of the second secondary damper 6b. This enables the two secondary dampers to behave symmetrically.

(48) FIGS. 2a, 2b, 4a, 4b show two particular embodiments of the invention in which there are first and second secondary dampers assembled at the ends 2a, 2b of the axle shaft. In these embodiments, the axle shaft 2 has the first secondary damper 6a fitted at its first end and the second secondary damper 6b fitted at its second end 2b.

(49) It can be seen that the landing-gear assembly includes a first rim 10 for supporting a first wheel for enabling the aircraft to run on the ground and a second rim (not shown for reasons of clarity) for supporting a second wheel for enabling the aircraft to run on the ground. Said first and second rims are mounted to rotate about the axle shaft 2 and around said shaft. In each of these embodiments, the first secondary damper 6a is arranged at least in part inside a hollow zone 10a of the first rim 10 and the second secondary damper 6b is arranged at least in part inside a hollow zone of the second rim. In order to limit overall size, it is preferable for each first and second secondary damper to be arranged in full inside the hollow zone of the corresponding rim.

(50) In the embodiment of FIGS. 2a and 2b, the inertial mass M of the first secondary damper 6a is in the form of a ring 11 and extends around the first end 2a of said axle shaft. The second inertial mass of the second secondary damper 6b is also in the form of a ring 14 and extends around the second end 2b of said axle shaft 2.

(51) The connection means 7a that connect the inertial mass M of the first secondary damper 6a to the axle shaft 2 comprise: a first fastener ring 12 fastened to the axle shaft 2; and a resilient annular sleeve 13 coaxial with the inertial mass M of the first secondary damper 6a.

(52) Said resilient annular sleeve 13 is placed between the first fastener ring 12 and the inertial mass M of the first secondary damper 6a.

(53) Ideally, in this embodiment, the connection means of the second secondary damper 6b also include a fastener ring, referred to as the second fastener ring. This second fastener ring is fastened to the axle shaft 2. The second secondary damper 6b also includes a resilient annular sleeve coaxial with the second inertial mass. Said resilient annular sleeve is placed between the second fastener ring and the second inertial mass, in the form of a ring 14.

(54) In this embodiment: firstly, the resilient annular sleeve 13 of the first secondary damper 6a extends between the fastener ring 12 and the inertial mass M of the first secondary damper 6a; and secondly, the resilient annular sleeve of the second secondary damper 6b extends between the fastener ring and the inertial mass of the second secondary damper 6b.

(55) Each resilient annular sleeve can be made of a polymer material that is suitable for dissipating energy that enables movement between the inertial mass and the axle shaft to be damped.

(56) The first and second secondary dampers 6a, 6b are similar to each other and each has an inertial mass M in the form of a ring of the same given weight, a fastener ring and a resilient sleeve connecting the inertial mass to the fastener ring, the sleeve having the same damping coefficient value c and the same resilient stiffness value k. The advantage of this type of secondary damper provided with an inertial mass in the form of a ring is being able to damp oscillations about a plurality of axes of movement that are radial or axial relative to the axis of revolution of the ring.

(57) In the embodiment in FIGS. 4a and 4b, the first and second secondary dampers 6a, 6b are linear dampers. The term linear damper makes reference to the fact that the damper has an inertial mass moving along a single given axis of the damper.

(58) The first axis of movement X1 of the inertial mass M of the first secondary damper 6a is parallel to the second axis of movement X2 of the second inertial mass M of the second secondary damper 6b.

(59) Said first and second axes of movement X1, X2 of the inertial masses M of the first and second secondary dampers 6a, 6b are preferably perpendicular to the axle shaft 2 and preferably parallel to each other.

(60) This type of linear damper serves to damp only angular oscillations about the axis Z.

(61) The invention is not limited to the above description, in particular it is possible for a single landing-gear assembly to include a plurality of secondary dampers such as those of FIGS. 1a, 2a, 4a, each of said secondary dampers being carried in full in the axle shaft.