LANDING GEAR EQUIPPED WITH A SHAPE SENSOR

Description

[0001] The present invention relates to the field of landing gear and more particularly to the means for detecting the positions of a landing gear. BACKGROUND OF THE INVENTION

[0002] Aircraft landing gears are known comprising a leg movably mounted on the structure of an aircraft between a deployed position (for takeoff and landing) and a retracted position (for flight) under the action of a maneuvering actuator.

[0003] Some of these landing gears, and in particular the auxiliary landing gears, have a lower part that can move in translation and rotation, in particular to allow the aircraft to be damped and steered on the ground. For this purpose, the leg generally consists of a box in which a rod carrying the wheels of the landing gear is slidably mounted, and a rotating sleeve surrounding a lower part of the box or a rotating tube inserted between the box and the sliding rod. The sleeve (or rotating tube) is connected to the rod by an articulated compass. Actuators allow the sleeve (or rotating tube) to pivot, and therefore the wheels, in response to an orientation command generated for example by means of a control wheel in the cockpit.

[0004] For safety reasons, such landing gear must send information about the status of the landing gear back to the aircraft systems, for example to allow the retraction or change of orientation of the leg depending on the different operating modes of the aircraft (taxiing, takeoff, landing, flight, etc.).

[0005] To provide such information, it is known to use contactless switches or position sensors.

[0006] The upper arm of the compass is, for example, equipped with a magnetic target arranged to be opposite a Hall effect sensor fixed to the housing when the rod is in an extremely relaxed position. In operation, the presence of the magnetic target in front of the Hall effect sensor makes it possible to generate a signal indicating that the wheels are not in contact with the ground and therefore that the aircraft is in flight.

[0007] It is also common to equip the leg with a potentiometer or an RVDT (Rotary Variable Differential Transformer) type sensor to copy an angular position of the sleeve, and therefore of the rod carrying the wheels, via a gear reduction system.

[0008] However, such a copying system does not allow the exact angular position of the rod to be captured, the position measured by the system accumulating inaccuracies linked to the mechanical play of the leg's operation (rod, compass, sleeve, gears) and to the electrical measurement errors of the sensor.

[0009] Furthermore, the integration of contactless switches or position sensors tends to increase the mass of the lander and requires the routing of cables that are often shielded with bending radii that are difficult to integrate.

[0010] Moreover, adjusting such sensors can be complicated, especially when installing or replacing them.

[0011] Document US 7,274,310 B1 discloses a prior art landing gear. SUBJECT OF THE INVENTION

[0012] The invention therefore aims to propose an aircraft landing gear making it possible to at least partially overcome the aforementioned drawbacks. SUMMARY OF THE INVENTION

[0013] To this end, an aircraft landing gear is provided comprising a fixed element and at least one movable element which can move relative to the fixed element between a first position and a second position, and detection means arranged to detect when the movable element is in at least one of its positions.

[0014] According to the invention, the detection means comprise at least one shape sensor, filiform and flexible, connected to an electronic processing unit arranged to deduce the position of the mobile element from the shape of the shape sensor. The shape sensor comprises a first section secured to the fixed element and a second section secured to the mobile element so that the first section and the second section are stationary with respect to the fixed element and the mobile element respectively, and are movable relative to each other.

[0015] Thus, the movement of the mobile element between the first and second positions causes a deformation of the sensor (with the exception of at least the first and second sections) representative of a position of the mobile element relative to the fixed element, and therefore of a state of the landing gear. The electronic processing unit makes it possible to determine the shape of the shape sensor and to deduce the state of the landing gear. Learning during installation or replacement of the sensor may be necessary, but it is "software" and does not depend on complex mechanical adjustments.

[0016] Furthermore, such a sensor can provide several pieces of information on the state of the lander and therefore replace several sensors, which makes it possible to limit the mass of said lander and simplify its integration.

[0017] According to a particular embodiment of the invention, the shape sensor is a fiber optic shape sensor. This type of sensor is particularly light and easy to install.

[0018] In particular, the shape sensor includes a Bragg grating optical fiber.

[0019] In particular, the shape sensor includes a WDM type wavelength division multiplexed optical fiber.

[0020] In particular, the shape sensor includes an OFDR type frequency reflectometry optical fiber.

[0021] According to a particular embodiment of the invention, the landing gear comprises a leg consisting of a box in which a rod is slidably mounted along a Z axis, a lower end of which carries wheels, and a sleeve rotating around the Z axis and surrounding a lower part of the box. The sleeve is connected by an articulated compass to the sliding rod. The first section and the second section of the shape sensor are respectively secured to the box and the rod.

[0022] According to another particular embodiment of the invention, the landing gear comprises a leg consisting of a box in which a rod is slidably mounted along a Z axis, a lower end of which carries wheels, and a rotating sleeve surrounding a lower part of the box and connected by a compass articulated to the sliding rod. The first section and the second section of the deformation sensor are respectively integral with the box and the compass.

[0023] The invention also relates to a method for measuring at a time t a stroke of the landing gear rod of such a landing gear, in which the electronic processing unit carries out the following steps: when said rod is in an extreme relaxed position, determining and recording from a light signal introduced into the shape sensor a reference position along the Z axis of a measuring point of the second section of the shape sensor; at the instant t , determine the position of the measuring point from the light signal introduced into the shape sensor; calculate the difference between the reference position and the position at the instant t ; and deduce from this difference the stroke of the rod at the instant t .

[0024] The invention also relates to a method for measuring at a time t a stroke of the rod of such a landing gear, in which the compass comprises an upper branch articulated on the sleeve and a lower branch articulated on the upper branch and on the rod, the upper branch and the lower branch defining an opening angle of the compass. The electronic processing unit carries out the following steps: when said rod is in an extreme relaxed position, determining and recording from a light signal introduced into the shape sensor a reference opening angle of the compass; at time t, determining the opening angle of the compass from the light signal introduced into the shape sensor; calculating the difference between the reference opening angle and the opening angle at time t ; and deduce from this difference the race at the moment t of the stem by trigonometry.

[0025] The invention further relates to a method for measuring at a time t an angular position of the rod of such a landing gear, in which the electronic processing unit performs the following steps: when the wheels are oriented along a longitudinal axis of the aircraft, determine and record from a light signal introduced into the shape sensor a reference position of a measurement point of the second section of the shape sensor; at the instant t , determine the position of the measuring point from the light signal introduced into the shape sensor; calculate the angle formed by the reference position and the position at the instant t with respect to the Z axis of sliding and rotation of the rod; and deduce from this angle the angular position of the rod at the instant t .

[0026] The invention further relates to a method for measuring at a time t an angular position of the rod of such a landing gear, in which the electronic processing unit carries out the following steps: when the wheels are oriented along a longitudinal axis of the aircraft, determine and record from a light signal introduced into the shape sensor the reference positions of at least two measurement points of the second section of the shape sensor arranged in an XY plane orthogonal to the Z axis of sliding and rotation of the rod; at the instant t , determine the positions of the measuring points from the light signal introduced into the shape sensor; and calculate the angle formed by the straight line defined by the reference positions and the straight line defined by the positions at time t; and deduce from this angle the angular position of the rod at time t . BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will be better understood in light of the following description, which is purely illustrative and non-limiting, and must be read in conjunction with the appended figures, among which: [ Fig.1 ] there figure 1 is a view of a landing gear according to a particular embodiment of the invention; [ Fig.2 ] there figure 2 is a schematic view of a method for determining at a time t an angular position of the rod of the landing gear illustrated in figure 1 ; [ Fig.3 ] there figure 3 is a schematic view of a variant of the method illustrated in figure 2 . DETAILED DESCRIPTION OF THE INVENTION

[0028] In reference to the figure 1 , an aircraft landing gear 1 comprises, in a manner known per se, a leg 2 carrying wheels R in the lower part. The leg 2 comprises a box 3 mounted articulated on a structure of the aircraft. In the box 3 slides a rod 4, along a longitudinal axis Z of the rod 4, between a first extreme position called relaxed (illustrated here) and a second extreme position called compressed. A lower end of the rod 4 carries an axle 5 receiving wheels R mounted to move in rotation around an axis X1 which is substantially horizontal in service.

[0029] A sleeve 6 is mounted rotating about the Z axis on a lower part of the box 3 to be oriented in a controlled manner by an orientation member, known per se, such as jacks mounted in "push-pull", a rack arrangement or a rotary actuator. The sleeve 6 and the rod 4 are linked in rotation by a compass 7, so that the orientation of the sleeve 6 causes the orientation of the rod 4 and therefore of the wheels R. The compass 7 comprises an upper branch 7a articulated on the sleeve 6 along an axis X2 of articulation, and a lower branch 7b articulated on the upper branch 7a and the rod 4 along respective axes X3 and X4 of articulation. The axes X2, X3, X4 of articulation of the compass are substantially parallel to the axis X1 of rotation of the wheels R.

[0030] All this is well known and is only mentioned for information purposes to provide context for the invention.

[0031] According to the invention, one side of the landing gear 1 is equipped with a sensor of shape 10, filiform and flexible, comprising an optical fiber 11 secured both to the box 3, to the upper and lower branches 7a, 7b of the compass 7 and to the rod 4 as will be explained below.

[0032] The optical fiber 11 comprises a first section 11.1 fixed to an external surface of the box 3 to extend along the sliding axis Z of the rod 4, a third section 11.3 fixed to an external surface of the upper branch 7a of the compass 7 to extend along a longitudinal axis of said upper branch 7a, a fifth section 11.5 fixed to an external surface of the lower branch 7b of the compass 7 to extend along a longitudinal axis of said lower branch 7b, and a seventh section 11.7 fixed to the rod 4 to extend along the articulation axis X4. The first, third, fifth and seventh sections 11.1, 11.3, 11.5, 11.7 are substantially rectilinear and are immobile with respect to the box 3, the upper branch 7a, the lower branch 7b and the rod 4 respectively.

[0033] The optical fiber 11 also comprises a second section 11.2 connecting the first section 11.1 and third section 11.3, a fourth section 11.4 connecting the third section 11.3 and the fifth section 11.5, and a sixth section 11.6 connecting the fifth section 11.5 and the seventh section 11.7. The second, fourth and sixth sections 11.2, 11.4, 11.6 are free of any attachment except at their ends and thus form ease loops whose path is essentially given by the stiffness of the optical fiber 11 and the relative positions of the first, third, fifth and seventh sections 11.1, 11.3, 11.5, 11.7 with respect to each other. If necessary, the path of the ease loops can also be defined by mechanical guide elements fixed to the landing gear.

[0034] A free end of the first section 11.1 is connected to an electronic processing unit 12, also called an interrogator, which is adapted to the technology of the optical fiber 11 of the shape sensor 10.

[0035] In a manner known per se, the interrogator 12 introduces a light signal at a free end of the first section 11.1. The light signal propagates through the optical fiber 11 to a free end of the seventh section 11.7 and is partially reflected by the core of the optical fiber 11 at different measurement points distributed over all of the sections 11.1-11.7. Any deformation of the optical fiber 11 causes a variation in the spectrum of the part of the signal reflected at each measurement point. This variation is analyzed by the interrogator 12 to deduce the shape modifications applied to the optical fiber 11 between the different measurement points by determining in particular the coordinates of said measurement points.

[0036] A method for determining at a time t a stroke C of the rod 4 via the shape sensor 10 will now be detailed.

[0037] While the rod is in the extreme relaxed position (shown in figure 1 ), the interrogator 12 determines and records, via a light signal introduced into the optical fiber 11, a reference position T z_ref along the Z axis of a measurement point T of the seventh section 11.7. This step could, for example, be carried out in the factory when the landing gear 1 is in a relaxed state in which the wheels R do not touch the ground.

[0038] On landing, the contact of the wheels R with the ground causes the rod 4 to slide towards the inside of the box 1, which simultaneously causes a translation of the seventh section 11.7 along the Z axis and a rotation of the upper and lower branches 7a, 7b of the compass 7 around the articulation axes X2, X3, X4, and therefore a deformation of the second, fourth and sixth sections 11.2, 11.4, 11.6.

[0039] Interrogator 12 determines, at each moment t , a position T z (t) along the Z axis of the measuring point T then deduces the stroke C of the rod by comparing the reference position T z_ref and the position T z (t) according to the following formula: C ( t ) = T z_réf - T z ( t ) .

[0040] When the stroke C exceeds a predetermined threshold (here of the order of a few millimeters), it is considered that the wheels R are in contact with the ground.

[0041] The application of this method to several measuring points T of the seventh section 11.7 makes it possible to improve the precision but also the robustness with which the stroke C of the rod 4 is determined.

[0042] It is also possible to trigonometry link the stroke C of the rod 4 to the opening angle α of the compass 7 defined by the longitudinal axes of the upper and lower branches 7a, 7b. Another method therefore consists of comparing the opening angle α ref of the compass 7 when the rod 4 is in the extreme relaxed position with that α(t) at time t. These opening angles α ref , α(t) can be deduced from positions determined by the interrogator 12 of at least two measurement points on each of the third and fifth sections 11.3, 11.5.

[0043] Using these two methods together allows for C-stroke redundancy without adding additional sensors.

[0044] The addition of a second shape sensor 10 similarly equipping the other side of the lander also makes it possible to significantly improve the robustness of the stroke C determined by the implementation of at least one of the two methods.

[0045] In reference to the figure 2 , a method for determining at a time t an angular position Ø of the rod 4, and therefore an orientation of the wheels R, via the shape sensor 10 will now be detailed.

[0046] While the wheels R are oriented along a longitudinal axis of the aircraft, the interrogator 12 determines and records, via a light signal introduced into the optical fiber 11, a reference position T' ref of a measurement point T' of the seventh section 11.7. This step could for example be carried out in the factory once the landing gear 1 is mounted on the structure of the aircraft.

[0047] When the aircraft moves on the ground, the orientation cylinders are caused to control a rotation of the sleeve 6, which causes a rotation of the third, fifth and seventh sections 11.3, 11.5, 11.7 around the Z axis, and therefore a deformation of the second section 11.2.

[0048] The interrogator 12 determines, at each instant t, a position T' (t) of the measuring point T' to deduce therefrom the angular position Ø of the rod 4 defined by the angle Ø(t) formed by the positions T' ref, T' of the measuring points T with respect to the Z axis.

[0049] The application of this method to several measuring points T' of the seventh section 11.7 makes it possible to improve the precision but also the robustness with which the angular position Ø of the rod 4 is determined.

[0050] Another method consists in determining and recording via the interrogator 12, when the wheels R are oriented along the longitudinal axis of the aircraft, the positions T1' ref , T2' ref of at least two measurement points T1', T2' of the seventh section 11.7. The interrogator 12 then determines at time t the positions T1' (t), T2' (t) of the measurement points T1', T2' to deduce therefrom the angular position Ø of the rod 4 defined by the angle Ø(t) formed by the straight lines (T1' ref , T2' ref ) and (T1'(t), T2'(t)).

[0051] It will be noted that a single shape sensor 10 here makes it possible to obtain several distinct pieces of information on the state of the lander 1, namely the orientation of the wheels R and their contact with the ground.

[0052] The application of this method to several pairs of measuring points T1', T2' of the seventh section 11.7 makes it possible to improve the precision but also the robustness with which the angular position Ø of the rod 4 is determined.

[0053] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0054] Several fiber optic technologies can be used: Bragg grating (Fiber Bragg Grating), WDM (Wavelength Division Multiplexing), OFDR (Optical Frequency Domain Reflectometry)...

[0055] Although the shape sensor here is a fiber optic based sensor, the principle applies to any shape sensor.

[0056] In the case where the leg 2 is mounted movably on the structure of the aircraft between a deployed position (for takeoff and landing) and a retracted position (for flight), the leg 2 is generally held in the deployed position by a breaker strut which is coupled to the leg 2 and to the structure of the aircraft, and which comprises two connecting rods articulated together. The connecting rods are held in an aligned position by a stabilizing member comprising two connecting rods articulated together. It is possible to equip the connecting rods and / or the connecting rods with a shape sensor 10 such as that described here to determine the position of the leg and / or to ensure the correct locking of the stabilizing member.

[0057] Although the seventh section 11.7 is here collinear with the axis X4 of articulation of the compass 7 on the rod 4, it can also extend in an XY plane substantially orthogonal to the Z axis. Preferably then, the measurement points T1', T2' will form a straight line intersecting the Z axis.

Claims

1. Aircraft landing gear (1) comprising a stationary element (3) and at least one movable element (4, 6, 7) which can move relative to the stationary element between a first position and a second position, and detection means arranged to detect when the movable element is in at least one of its positions, characterised in that the detection means comprise at least one threadlike and flexible shape sensor (10), connected to an electronic processing unit (12) arranged to deduce the position of the movable element of the shape of the shape sensor, the shape sensor comprising a first section (11.1) rigidly connected to the stationary element and a second section (11.3, 11.5, 11.7) rigidly connected to the movable element so that the first section and the second section are immobile with respect to the stationary element and the movable element respectively, and are movable relative to one another.

2. Landing gear (1) according to claim 1, wherein the shape sensor is an optical fibre shape sensor.

3. Landing gear (1) according to claim 2, wherein the shape sensor (10) comprises a Bragg grated optical fibre (11).

4. Landing gear (1) according to claim 1, wherein the shape sensor (10) comprises a WDM-type wavelength multiplexing optical fibre (11).

5. Landing gear (1) according to claim 1, wherein the shape sensor (10) comprises an OFDR-type frequency domain reflectometry optical fibre (11).

6. Landing gear according to any one of the preceding claims, comprising a strut (2) constituted of a box (3) wherein a rod (4) is slidingly mounted about an axis (Z), a lower end of which carries wheels (R), and a rotating sleeve (6) surrounding a lower part of the box and connected by a compass (7) articulated to the sliding rod, the first section (11.1) and the second section (11.7) of the shape sensor (11) being respectively rigidly connected to the box and to the rod.

7. Landing gear (1) according to any one of claims 1 to 5, comprising a strut (2) constituted of a box (3) wherein a rod (4) is slidingly mounted about an axis (Z), a lower end of which carries wheels (R), and a rotating sleeve (6) surrounding a lower part of the box and connected by a compass (7) articulated to the sliding rod, the first section (11.1) and the second section (11.3, 11.5) of the shape sensor (10) being respectively rigidly connected to the box and to the compass.

8. Method for measuring at an instant t a stroke (C) of the rod (4) of the landing gear (1) according to claims 2 and 6, wherein the electronic processing unit (12) carries out the following steps: . when said rod is in a relaxed extreme position, determining and recording from a light signal introduced in the shape sensor (10) a reference position (Tz_ref) about the axis (Z) of a measuring point (T) of the second section (11.7) of the shape sensor; . at the instant t, determining the position (Tz(t)) of the measuring point (T) from the light signal introduced in the shape sensor; . calculating the difference between the reference position (Tz_ref) and the position at the instant t (Tz(t)); and . deducing from this difference, the stroke C(t) of the rod (4) at the instant t.

9. Method for measuring at an instant t, a stroke (C) of the rod (4) of the landing gear (1) according to claim 7, wherein the compass (7) comprises an upper branch (7a) articulated on the sleeve (6) and a lower branch (7b) articulated on the upper branch and on the rod, the upper branch and the lower branch defining an opening angle (α) of the compass and the electronic processing unit (12) carrying out the following steps: . when said rod is in a relaxed extreme position, determining and recording from a light signal introduced in the shape sensor (10) a reference opening angle (αref) of the compass; . at the instant t, determining the opening angle (α(t)) of the compass from the light signal introduced in the shape sensor; . calculating the difference between the reference opening angle (αref) and the opening angle (α(t)) at the instant t; and . deducing from this difference the stroke C(t) at the instant t of the rod by trigonometry.

10. Method for measuring at an instant t, an angular position (Ø) of the rod (4) of the landing gear (1) according to claim 6, wherein the electronic processing unit (12) carries out the following steps: . when the wheels are oriented about a longitudinal axis of the aircraft, determining and recording from a light signal introduced in the shape sensor (10) a reference position (T'ref) of a measuring point (T') of the second section (11.7) of the shape sensor; . at the instant t, determining the position (T'(t)) of the measuring point (T') from the light signal introduced in the shape sensor; . calculating the angle (Ø(t)) formed by the reference position (T'ref) and the position at the instant t (T' (t)) with respect to the sliding axis (Z) of the rod; and . deducing from this angle the angular position (Ø) of the rod at the instant t.

11. Method for measuring at an instant t, an angular position (Ø) of the rod (4) of the landing gear (1) according to claim 6, wherein the electronic processing unit (12) carried out the following steps: . when the wheels are oriented about a longitudinal axis of the aircraft, determining and recording from a light signal introduced in the shape sensor (10) reference positions (T1'ref, T2'ref) of at least two measuring points (T1', T2') of the second section (11.7) of the shape sensor arranged in a plane (XY) orthogonal to the sliding axis (Z) of the rod; . at the instant t, determining positions (T1'(t), T2'(t)) of the measuring points (T1', T2') from the light signal introduced in the shape sensor; and . calculating the angle (Ø(t)) formed by the straight line defined by the reference positions (T1'ref, T2'ref) and the straight line defined by the positions at the instant t (T1'(t), T2'(t)); and . deducing from this angle, the angular position (Ø) of the rod at the instant t.