Aircraft landing gear struts coated with a zinc-nickel alloy

Abstract

Aircraft landing gear strut (1) comprising a main part (1a) extending along a main axis (X-X) of the strut and comprising an axle shaft (1b) extending in a plane (P) perpendicular to the main shaft (1a) of the strut, this axle shaft (1b) being designed to support at least one landing gear when (2a, 2b) equipped with brakes (3a, 3b) for braking the wheel, said axle shaft (1b) being made of steel. The axle shaft (1b) bears at least one layer of zinc-nickel alloy coating (C), this zinc-nickel alloy comprising, as a mass percent of the alloy, between 12% and 18% or nickel, at most 0.5% of elements other than nickel and zinc, the rest being zinc.

Claims

1. An aircraft landing gear strut (1) comprising: a main part (1a) extending along a main axis (X X) of the strut and comprising an axle shaft (1b) extending in a plane (P) perpendicular to the main shaft (1a) of the strut, the axle shaft (1b) being designed to support at least one landing gear wheel (2a, 2b) equipped with brakes (3a, 3b) for braking the wheel, said axle shaft (1b) being made of steel, wherein the axle shaft (1b) has at least one layer of zinc nickel alloy coating (C), the zinc nickel alloy comprising, as a mass percent of the alloy, between 12% and 18% of nickel, at most 0.5% of elements other than nickel and zinc, the rest being zinc, wherein the axle shaft (1b) comprises at least one bearing seat (5a, 5b) designed to accept at least one wheel bearing ring, each said at least one bearing seat (5a, 5b) being formed by an annular layer of chrome formed on an external surface made of steel of the axle shaft (1b), the at least one layer of zinc nickel alloy coating extending at least over all the steel surfaces of the axle shaft that are situated outside of the said at least one bearing seat made of chrome (5a, 5b), and wherein each at least one bearing seat (5a, 5b) made of chrome extends between two chrome annular edges specific to it, the at least one layer of zinc nickel alloy coating extending over the annular edges made of chrome of each at least one bearing seat.

2. The aircraft landing gear strut according to claim 1, in which the said at least one layer (C) of zinc nickel alloy coating extends exclusively over external surfaces of the axle shaft which are chosen to be kept at a temperature of below 300 C. when the strut is used for performing a normal aircraft braking cycle.

3. The aircraft landing gear strut according to claim 1, in which the axle shaft (1b) extends through a bore (6) that passes through the main part of the landing gear strut, this axle shaft being tightly fitted into this bore (6), and a continuous annular portion of the layer of zinc nickel alloy coating (C) borne by the axle shaft (1b) forms an interface between the internal annular surface of the said bore (6) and a longitudinal portion of the axle shaft which extends into the bore (6).

4. The aircraft landing gear strut according to claim 3, in which the said internal annular surface of the bore bears an annular layer internal to the bore (6), this annular layer internal to the bore (6) being made of the same zinc nickel alloy.

5. The aircraft landing gear strut according to claim 1, in which the main strut and the axle shaft are formed as a single piece.

6. The aircraft landing gear strut according to claim 1, in which the zinc nickel alloy contains, as a mass percentage of the alloy, between 12% and 16% nickel.

7. An aircraft landing gear comprising: at least one landing gear strut (1) according to claim 1; at least one wheel (2a, 2b) equipped with brakes (3a, 3b) and supported by the axle (1b) of the said at least one landing gear strut (1).

8. A method of manufacturing a landing gear strut (1) for an aircraft according to claim 1, characterized in that it comprises: a step of forming an axle shaft (1b) made of steel; followed by a step of applying the said at least one layer of zinc nickel alloy coating (C) to this steel axle shaft (1b), this application step being performed by immersing the said at least one axle shaft in an alkaline bath containing zinc and nickel in the form of ions and by applying an electrical potential between an electrode immersed in the bath and the steel axle shaft.

9. The method of manufacturing a landing gear strut according to claim 8, in which prior to the step of applying the coating to this steel axle shaft, a step of preparing a steel surface of the strut, comprising chemical or mechanical surface activation, is carried out.

10. Method of manufacturing a landing gear strut according to claim 8, in which, after the coating step, a passivation step is carried out which consists in immersing the portions of the strut that are coated with the layer of zinc nickel alloy coating in an acid solution.

11. The method of manufacturing a landing gear strut according to claim 8, further comprising a step of degassing any hydrogen potentially occluded in the steel, this degassing step involving placing the strut in a furnace for at least 12 hours, keeping the furnace at a temperature of 190 C. plus or minus 14 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from reading the following description of some nonlimiting embodiments, with reference to the figures of the attached drawings among which:

(2) FIGS. 1 and 2 depict the aforementioned tests;

(3) FIGS. 3a and 3b show the successive steps that make it possible to obtain an aircraft landing gear strut according to the invention, the axle shaft 1b here being incorporated into the main part 1a of the strut;

(4) FIGS. 4a, 4b, 4c, 4d depict the successive steps making it possible to obtain an aircraft landing gear strut according to the invention, in an embodiment in which the axle shaft 1b is assembled by force fitting into a complementary bore formed through the main part 1a of the strut 1.

DETAILED DESCRIPTION OF THE INVENTION

(5) As can be seen in FIGS. 3b and 4d, the invention relates to an aircraft landing gear strut 1 comprising a main part 1a extending along a main axis X-X of the strut 1 and comprising an axle shaft 1b extending in a plane P perpendicular to the main axis 1a of the strut 1.

(6) This axle shaft 1b is designed to support at least one landing gear wheel fitted with brakes. In this particular instance, in FIGS. 3b and 4d, the axle shaft 1b bears two wheels 2a, 2b respectively fitted with brakes 3a, 3b to brake the wheels so equipped.

(7) The axle shaft 1b is made of steel bearing at least one layer of zinc-nickel alloy coating C, this zinc-nickel alloy containing, as a mass percent of the alloy, between 12% and 18% nickel, preferably between 12% and 16% nickel, preferably 15% nickel, to within + or 1%.

(8) The alloy contains at most 0.5 mass percent of elements other than nickel and zinc, it being possible for these other elements to be elements that have been added deliberately or impurities. The rest of the alloy consists of zinc. Ideally, the alloy contains no alloy element other than the zinc and the nickel. In all the embodiments of the alloy, the alloy always contains at least 81.5% zinc.

(9) The landing gear strut 1 comprises means 4a, 4b of attachment of brakes 3a, 3b designed to arrange the brakes around the axle shaft 1b so as to brake the wheels 2a, 2b of the landing gear which are fitted with brakes.

(10) In FIGS. 1a and 1b, the attachment means 4a, 4b comprise two annular bands of the axle shaft. Each of these bands extends radially from the axle shaft 1b towards the periphery of the axle shaft. Each of these bands is perforated with holes parallel to the plane P in which the axle extends. Each brake with which a wheel is fitted comprises a rotor secured to the wheel and a stator secured to one of the bands corresponding to it. The stator comprises discs pressed selectively by cylinders to clamp other discs belonging to the rotor. Ideally, the layer of zinc-nickel alloy covers the bands and a non-chrome-plated portion of the main part of the strut. The main part of the strut has a chrome-plated portion intended to slide inside a landing gear assembly designed to be fixed to the structure of the aircraft. This chrome-plated portion forms lands for hydraulic seals.

(11) In FIGS. 4a and 4b, the attachment means 4a, 4b comprise protuberances extending from the sides of the main part of the landing gear strut. As in the embodiment of FIGS. 1a and 1b, each brake with which a wheel is fitted comprises a rotor secured to the wheel and a stator secured to a protuberance of the main part which corresponds to it. The stator comprises discs selectively pressed by cylinders to clamp other discs belonging to the rotor.

(12) For preference, the layer of zinc-nickel alloy coating C extends exclusively over external surfaces of the axle shaft which are chosen to be kept at a temperature of below 300 C. when the strut is used for implementing a normal aircraft braking cycle.

(13) Ideally, the layer of zinc-nickel alloy covers the protruberances used as attachment means 4a, 4b and all or part of the main part of the strut.

(14) A normal aircraft braking cycle includes all the usual braking of the aircraft which takes place during aircraft taxiing, take off and landing.

(15) A normal braking cycle does not include emergency braking likely to give rise to significant damage to the landing gear strut 1 that would require the strut to be removed and replaced or reconditioned.

(16) As can be seen in FIGS. 3a, 3b, 4b, 4c, 4d, the axle shaft 1b comprises at least one antifriction bearing land, in this instance two lands 5a, 5b. Each land 5a, 5b is designed to accept at least one wheel antifriction bearing ring to orient the wheel about the axle shaft.

(17) According to a first embodiment of the lands 5a, 5b, each land is formed by an annular layer of chrome formed on a steel external surface of the axle shaft 1b. The layer of zinc-nickel alloy coating extends at least over all the steel surfaces of the axle shaft that are outside of the chrome antifriction bearing lands 5a, 5b.

(18) This embodiment makes it possible to have antifriction bearing lands that are extremely hard because they are made of chrome but at the same time have anticorrosion protection compatible with high-temperature axle operation.

(19) According to this embodiment, each antifriction bearing land 5a, 5b made of chrome extends between two annular edges made of chrome specific to it. The layer C of zinc-nickel alloy coating which extends outside of the lands 5a and 5b also extends over the annular edges made of chrome of each of these lands 5a, 5b.

(20) The fact that the layer C of zinc-nickel alloy coating covers all the edges of the chrome lands makes it possible to limit the risk of seeing corrosion at the annular edges of the annular lands made of chrome.

(21) Ideally, the main part 1a of the landing gear strut 1 is made of steel and the layer of zinc-nickel alloy coating extends over at least a portion of this main part 1a, this layer being formed against the steel of the landing gear strut. This then avoids the risk of corrosion at the interface between the axle 1b and the main part 1a.

(22) Finally, whereas in FIGS. 3a and 3b the main strut 1a and the axle shaft 1b form one and the same component, in FIGS. 4a, 4b, 4c and 4d it may be seen that the axle shaft 1b and the main strut 1a form two distinct components assembled by force fitting.

(23) FIGS. 4a to 4d illustrate the method of manufacturing the landing gear strut in two parts.

(24) In FIG. 4a, the shaft 1b is bare and does not yet have its antifriction bearing lands.

(25) In FIG. 4b, the antifriction bearing lands 5a, 5b are formed.

(26) FIG. 4c shows the axle shaft 1b and the main part 1a of the strut before these components are assembled. A bore 6 is formed through the main part 1a. The layer C of ZnNi alloy is formed on the axle shaft 1 and on the main part 1a, including on the inside of the bore 6 before the axle shaft 1b is assembled with the main part 1a of the strut 1.

(27) FIG. 4d shows the axle shaft 1b assembled with the main part 1a of the strut.

(28) In this case, the axle shaft extends through the bore 6 that passes through the main part of the landing gear strut. This axle shaft 1b is tightly fitted into this bore 6 and a continuous annular portion of the layer C of zinc-nickel alloy coating borne by the axle shaft forms an interface between the internal annular surface of the said bore 6 and a longitudinal portion of the axle shaft 1b extending into the bore.

(29) Thus, the continuous annular portion of the layer C which extends into the bore 6 forms an interface between the bore and the steel of the axle shaft. This interface provides anticorrosion protection for the axle shaft while at the same time allowing the layer C to deform during the force-fitting of the axle shaft 1b into the bore 6. This then limits the risk of empty spaces appearing between the internal annular surface of the bore and the axle shaft. The fact that the formation of such empty spaces is limited limits the clearances and vibrations between the main part 1a and the axle shaft 1b and the risk of peening and oxidation when the landing gear strut is in service. The causes of weakening and embrittlement of the landing gear strut are thus minimized.

(30) Finally, as can be seen in FIG. 4c, the internal annular surface of the bore 6 may bear an annular layer inside the bore, this annular layer inside the bore being made of the same zinc-nickel alloy.