System of variable-height wedges for oleo-pneumatic shock absorber

Abstract

The invention relates to a maintenance system (1) of an oleo-pneumatic shock absorber (2), comprising wedges arranged to be assembled so as to form a plurality of wedge devices of different heights and each associated with a separate temperature range, each wedge device being arranged to be installed on the shock absorber by being positioned between one end (8) of the cylinder (4) through which the rod (5) is inserted and one end (9) of the rod located outside the cylinder, such that, when the shock absorber is compressed so that the end of the cylinder or the end of the rod abuts against the wedge device, an oil volume in the chamber (10), when the latter is maximally filled, is equal to an optimised volume for an oil temperature comprised in the temperature range associated with the wedge device.

Description

[0001]VARIABLE HEIGHT SHIM SYSTEM FOR OLEOPNEUMATIC SHOCK ABSORBER The invention relates to oleopneumatic shock absorbers, and in particular those of aircraft landing gears. BACKGROUND OF THE INVENTION An aircraft landing gear is very conventionally equipped with a shock absorber. This shock absorber is generally an oleopneumatic shock absorber, which comprises a cylinder and a rod. The rod slides in a sealed manner in the cylinder which contains a pressurized gas and a hydraulic damping fluid (hereinafter referred to as "oil"). The cylinder can be constituted by the landing gear box. In this case, the rod carries an axle on which the landing gear wheels are mounted. The shock absorber can also be produced independently of the box. When the aircraft lands, the volume of oil in the shock absorber depends on the oil temperature, which poses the following problem. When the plane lands in a cold region (e.g. Canada, Russia, etc.), theoil temperature is low and the oil volume is less. There is therefore a risk, when the wheels of the landing gear touch the ground at the time of landing, that the cylinder of the shock absorber will come into abutment against the end of the rod, which causes a shock that can be felt by the passengers of the aircraft. This problem mainly concerns the main landing gear of the aircraft, whose wheels are the first to touch the ground, and which absorb the most energy at the time of impact during landing. OBJECT OF THE INVENTION The object of the invention is to improve the comfort of the passengers of an aircraft, in a simple and inexpensive manner. SUMMARY OF THE INVENTION In order to achieve this object, a system for maintaining an oleopneumatic shock absorber is proposed which comprises a cylinder comprising a chamber containing oil and a rod sliding in the cylinder, the maintenance system comprising a plurality of shims arranged to beassembled so as to form a plurality of shim devices of different heights and each associated with a distinct temperature range, each shim device being arranged to be installed on the shock absorber by being positioned between an end of the cylinder through which the rod is inserted and an end of the rod located outside the cylinder, so that, when the shock absorber is compressed so that said end of the cylinder or said end of the rod abuts against said shim device, a volume of oil in the chamber, when the latter is filled to the maximum, is equal to a volume optimized for an oil temperature included in the temperature range associated with said shim device. The maintenance system therefore comprises a plurality of shim devices having different heights, and which are each associated with a distinct temperature range. At the time of maintenance of the shock absorber and moreParticularly in the oil filling operation, the operator measures the oil temperature, selects the shim device whose temperature range includes the measured temperature, positions it on the shock absorber between the end of the cylinder and the end of the rod, and compresses the shock absorber to the maximum. Under these conditions, when the chamber is filled to the maximum, the volume of oil in the chamber is an optimized volume compared to the measured temperature. The maintenance system allows, very precisely, to adjust the volume according to the oil temperature. The higher the temperature, the greater the volume of oil. This prevents, during landings at low temperatures, the end of the cylinder from hitting the end of the rod due to a reduction in the volume of oil in the shock absorber due to the temperature. The maintenance system is very inexpensive and very simple and quick to use for the operator:each shim device includes an indication of the associated temperature range. The operator simply has to measure the oil temperature and select the appropriate shim device. The maintenance system is also lightweight, reusable and robust. When the shock absorber is a shock absorber of an aircraft landing gear, the downtime of the aircraft is reduced during the maintenance operation, which is very advantageous for the operator of the aircraft. It is noted that the invention also makes it possible to extend the service life of the shock absorbers (and also of the landing gears), by facilitating the maintenance and mechanical repair of the shock absorbers (and therefore of the landing gears). A maintenance system as previously described is further proposed, in which the shim devices comprise a primary shim device and at least one secondary shim device, the primary shim device being associated with the lowest temperature range and comprisinga single primary shim, each secondary shim device comprising said primary shim device and at least one secondary shim stacked on the primary shim. A maintenance system is further provided as previously described, in which each secondary shim device comprises the primary shim device and a single secondary shim. A maintenance system is further provided as previously described, in which the primary shim comprises a first bearing surface arranged to be applied to a receiving surface of the shock absorber located near said end of the cylinder or said end of the rod, and a second bearing surface on which a secondary shim can be placed, the primary shim further comprising first holding means arranged to position and hold the secondary shim on the second bearing surface. A maintenance system is further provided as previously described, in which said shimsecondary shim comprises second holding means arranged to cooperate with the first holding means to position and hold said secondary shim on the second bearing surface of the primary shim. A maintenance system is further provided as previously described, in which the first holding means comprise holes and the second holding means comprise pins, or conversely, the pins being intended to be positioned in the holes. A maintenance system is further provided as previously described, in which at least one secondary shim comprises third holding means arranged to position and hold another secondary shim on said secondary shim. A maintenance system is further provided as previously described, in which the primary shim device further comprises a strap and a loop through which the strap passes, the strap being arranged to surround the rod or the cylinder, andthe loop being arranged to tighten the strap so as to fix the primary shim device to the rod or cylinder. A maintenance system is further provided as previously described, in which the primary shim device comprises a first protective element arranged to be applied against the rod or cylinder, and to be positioned between the rod or cylinder and the primary shim when the primary shim device is installed on the shock absorber. A maintenance system is further provided as previously described, in which the primary shim device comprises a second protective element arranged to be applied against the rod or cylinder, and to be positioned between the rod or cylinder and the loop when the primary shim device is mounted on the landing gear. A maintenance system is further provided as previously described, in which the first protective element and / or the second protective element aremade of polyoxymethylene. A maintenance system is further provided as previously described, in which the shock absorber is a shock absorber of an aircraft landing gear. A maintenance system is further provided as previously described, in which the cylinder is a box of the landing gear and in which the rod carries at least one wheel of the landing gear, the primary shim device being arranged to be fixed to the rod, the receiving surface being an upper surface of a radial protrusion of the rod. A maintenance system is further provided as previously described, in which the radial protrusion has a perforation through which a connecting pin passes, the landing gear comprising a compass, a lower branch of which is pivotally mounted relative to the rod by means of the connecting pin. A maintenance system is further provided as previously described, in which the primary shim device comprises two stopslaterals arranged so that, when the primary shim device is installed, the radial protrusion is positioned between the two lateral stops. A method of maintaining an oleopneumatic shock absorber is further proposed, using the maintenance system as previously described and comprising the steps of: - measuring an oil temperature; - selecting the shim device associated with a temperature range in which the oil temperature is included, and installing said shim device on the shock absorber; - compressing the shock absorber so that said end of the cylinder or said end of the rod abuts against said shim device; - ensuring that the shock absorber is filled with oil to the maximum. A method of maintenance is further proposed as previously described, further comprising the preliminary steps of fully compressing the shock absorber and draining all the oil contained in the shock absorber chamber, thento completely fill the chamber with new oil, then to relax the shock absorber. A maintenance method is further proposed as previously described, in which the compression of the shock absorber is carried out with a jack making it possible to bring said end of the rod closer to said end of the cylinder. A maintenance method is further proposed as previously described, in which, when said end of the cylinder or said end of the rod comes into abutment against said shim device, excess oil is evacuated, which ensures that the shock absorber is filled with oil to the maximum. A maintenance method is further proposed as previously described, the oleopneumatic shock absorber being a shock absorber of an aircraft landing gear. A landing gear assembly is further proposed, comprising an aircraft landing gear and a maintenance system as previously described, the maintenance method as previously described being implemented inthe landing gear using the maintenance system. The invention will be better understood in light of the following description of a particular non-limiting embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Reference will be made to the appended drawings, among which: [Fig. 1] Figure 1 is a schematic view of an aircraft landing gear, on which the maintenance system is mounted; [Fig. 2] Figure 2 represents a perspective and front view of a primary chock device (comprising a primary chock), and three secondary chocks; [Fig. 3] Figure 3 represents a perspective and bottom view of the primary chock device; [Fig. 4] Figure 4 represents a perspective and top view of the primary chock device; [Fig. 5] Figure 5 represents a perspective view of the shock absorber, compressed to the maximum, on which the primary chock device is mounted; [Fig. 6] Figure 6 is a view similar to that of Figure 5, with thefirst secondary shim device; [Fig. 7] Figure 7 is a view similar to that of Figure 5, but oriented differently, with the second secondary shim device; [Fig. 8] Figure 8 is a view similar to that of Figure 5, with the third secondary shim device. DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 1, a particular and non-limiting embodiment of the invention is described, in which the maintenance system 1 is used to fill an oleopneumatic damper 2 of a main landing gear 3 of an aircraft with oil. The oleopneumatic damper 2 is a conventional damper, which does not have any particularity compared to the dampers known to those skilled in the art. The shock absorber 2 comprises a cylinder 4, which is here the box of the landing gear 3, and a rod 5 sliding in the cylinder 4. The rod 5 carries an axle 6 on which the wheels 7 of the landing gear 3 are mounted. The cylinder 4 comprises a firstend attached to the wing (not shown), and a second end 8 through which the rod 5 is inserted into the cylinder 4. The rod 5 has a first end located inside the cylinder 4 (not shown), and a second end 9 located outside the cylinder 4. Here, only the second end 8 of the cylinder 4 and the second end 9 of the rod 5 will be referred to, and these second ends 8, 9 will simply be called "ends". The shock absorber 2 has a chamber 10 and a filling valve 11, shown schematically in Figure 1. The chamber 10 contains oil. The chamber 10 is filled with oil and emptied via the filling valve 11. As seen, the volume of oil in the chamber 10 depends on the temperature of the oil, which can cause discomfort for passengers during landings in cold regions. Maintenance system 1 is intended to ensure that, following the oil filling operation of thechamber 10 of the shock absorber 2, which takes place when the aircraft is on the ground, the chamber 10 is filled with a volume of oil which is an optimized volume with respect to the temperature of the oil at the time of filling. The optimized volume is a predefined volume as a function of the temperature and ensures that, whatever the temperature of the oil at landing, and even for a landing in a cold region, the volume of oil in the chamber 10 of the shock absorber 2 is sufficient so that, during landing, the stroke of the rod 5 in the cylinder 4 is stopped by the internal action of the shock absorber 2, without the end 8 of the cylinder 4 coming into abutment against the end 9 of the rod 5. The chamber 10 of the shock absorber 2 is therefore filled with an additional margin of oil when the oil temperature is high. Thus, during a landing at low temperature, the volume of oil in shock absorber 2 will be sufficient to avoid the shock just mentioned, despitethe decrease in the volume of oil in the shock absorber 2 due to the drop in temperature between the time when filling takes place and the time when landing takes place. With reference to Figures 2 to 8, the maintenance system 1 comprises a plurality of shims 12. The shims 12 can be assembled so as to form a plurality of shim devices 13 of different heights and each associated with a distinct temperature range. Each shim device 13 may be installed on the shock absorber 2 by being positioned between the end 8 of the cylinder 4 and the end 9 of the rod 5 and so that, when the shock absorber 2 is compressed so that the end 8 of the cylinder 4 abuts against said shim device 13, the volume of oil in the chamber 10 of the shock absorber 2, when the latter is filled to the maximum, is equal to a volume optimized for an oil temperature included in the temperature range associated with said shim device 13. At the time of fillingof the shock absorber 2, the oil temperature is therefore measured, and the shim device 13 associated with the temperature range which includes the oil temperature is used. When the shock absorber 2 is compressed so that the end 8 of the cylinder 4 abuts against said shim device 13, and the shock absorber 2 is filled to the maximum, the volume of oil contained in the shock absorber 2 is the optimized volume. The shim devices 13 here comprise a primary shim device 13a and at least one secondary shim device, in this case three secondary shim devices: a first secondary shim device 13b, a second secondary shim device 13c, and a third secondary shim device 13d. The primary shim device 13a is associated with the lowest temperature range and comprises a single primary shim 12a. The shims 12 comprise the primary shim 12a and at least one secondary shim, in this case a first shimsecondary shim 12b, a second secondary shim 12c, and a third secondary shim 12d. Each secondary shim device 13b, 13c, 13d comprises the primary shim device 13a and at least one secondary shim 12b, 12c, 12d stacked on the primary shim 12a. Here, each secondary shim device 13b, 13c, 13d comprises the primary shim device 13a and a single secondary shim 12b, 12c, 12d. There are therefore four separate shim devices here: 13a, 13b, 13c, 13d. The primary shim device 13a (visible in Figures 2 to 5) comprises only the primary shim 12a, and is associated here with the temperature range [-20°C; -5°C]. Note that this temperature range is inscribed (here engraved) on the front face of the primary shim 12a. The first secondary shim device 13b (visible in Figure 6) comprises the primary shim device 13a (and therefore the primary shim 12a) and the first secondary shim 12b. The first secondary shim 12b is stacked on the shimprimary 12a. The first secondary shim device 13b is associated with the temperature range [-5°C; +15°C]. Note that this temperature range is inscribed (here engraved) on the front face of the first secondary shim 12b. The second secondary shim device 13c (visible in Figure 7) comprises the primary shim device 13a (and therefore the primary shim 12a) and the second secondary shim 12c. The second secondary shim 12c is stacked on the primary shim 12a. The second secondary shim device 13c is associated with the temperature range [+15°C; +25°C]. Note that this temperature range is inscribed (here engraved) on the front face of the second secondary shim 12c. The third secondary wedge device 13d (visible in Figure 8) comprises the primary wedge device 13a (and thus the primary wedge 12a) and the third secondary wedge 12d. The third secondary wedge 12d is stacked on the primary wedge 12a. The third wedge devicesecondary 13d is associated with the temperature range [+25°C; +40°C]. Note that this temperature range is inscribed (here engraved) on the front face of the third secondary shim 12d. It can be seen that the height of the first secondary shim 12b is lower than that of the second secondary shim 12c which is lower than that of the third secondary shim 12d. The higher the temperature range, the greater the height of the shim device 13. Thus, the higher the oil temperature at the time of filling, the greater the height of the shim device 13 used, and the greater the volume of oil in the shock absorber 2, when the chamber 10 is filled to the maximum. Note that the total temperature range covered extends between -20°C and +40°C, because beyond these temperatures, maintenance operations on the shock absorber 2 are not permitted. The primary wedge device 13a therefore comprises the primary wedge 12a. The primary wedge 12acomprises a central portion 22a and two lateral portions 22b. The central portion 22a comprises two lateral fingers 22c which each extend on either side of the central portion 22a and from a lower part thereof. Each lateral portion 22b is fixed to one of the lateral fingers 22c via two screws, and is positioned behind said lateral finger 22c when the primary wedge 12a is viewed from the front. The primary shim 12a comprises a first bearing surface 14 arranged to be applied against a receiving surface 15 (visible in FIGS. 5 and 7) of the shock absorber located near the end of the rod 5. The first bearing surface 14 is here located on a first face 16 of the primary shim 12a, which is the lower face of the primary shim 12a when the latter is installed on the shock absorber 2. The first bearing surface 14 comprises two flat surfaces 14a, 14b. The lateral portions 22b project downwards relative to the lower part of thecentral portion 22a, so that a recess 17 is formed between the two flat surfaces 14a, 14b. This recess 17 allows access to screw heads when the primary wedge 12a is positioned on the receiving surface 15. Here, the receiving surface 15 is an upper surface of a radial protrusion 18 of the rod 5, which extends from the end 9 of the rod 5. The radial protrusion 18 is here in the shape of an ear. The radial protrusion 18 has a perforation 19 (visible in Figures 6 and 8) in which a connecting pin 20 passes. The longitudinal direction of the connecting pin 20 is parallel to a plane perpendicular to the sliding direction of the rod 5 in the cylinder 4. The landing gear 2 comprises a compass comprising an upper branch (not shown) and a lower branch 21 (visible in Figures 6 and 8). The compass thus allows the rod 5 to slide in the cylinder 4 in the sliding direction, while preventing thepivoting of the rod 5 in the cylinder 4. The lower branch 21 of the compass is pivotally mounted relative to the rod 5 by means of the connecting axis 20. Each lateral portion 22b of the primary wedge 12a comprises a lateral stop 23. The two lateral stops 23 are thus arranged at the ends of the primary wedge 12a, on either side of the flat surfaces 14a, 14b of the first bearing surface 14, and extend vertically from the first face 16 of the primary wedge 12a. To install the primary shim device 13a on the shock absorber, the first bearing surface 14 of the primary shim 12a is therefore placed on the receiving surface 15 located on the radial protrusion 18, so that the two lateral stops 23 are positioned on either side of the radial protrusion 18. The lateral stops 23 form guides which assist in the positioning of the primary shim 12a. The lateral stops 23 also oppose the pivoting of the primary shim 12a.relative to the rod 5. The shape of the primary wedge 12a ensures that each wedge device 13, when installed, remains in position without risk of tipping. The primary wedge 12a further comprises a second bearing surface 24. The second bearing surface 24 is located on a second face 25 of the primary wedge 12a, opposite the first face 16, which is the upper face of the primary wedge 12a when the primary wedge device 13a is installed on the shock absorber 2. The second bearing surface 24 comprises the upper faces of the central portion 22a and the lateral portions 22b of the primary wedge 12a. When the primary shim device 13a, which comprises only the primary shim 12a, is used, the second bearing surface 24 is the surface which bears against the end 8 of the cylinder 4 when the shock absorber 2 is compressed to the maximum. When a secondary shim device 13b, 13c or 13d is used, one of the secondary shims12b, 12c or 12d is placed on the second bearing surface 24. Each secondary wedge 12b, 12c, 12d comprises a first bearing surface 26, which is a first face of said secondary wedge (lower face), and a second bearing surface 27, which is formed on a second face of said secondary wedge (upper face). The second bearing surface 27 of each secondary wedge comprises a first surface 27a and a second surface 27b. The upper and central portion of each secondary wedge is hollowed out, and the surfaces 27a and 27b extend on either side of this hollowing. The first bearing surface 26 of one of the secondary shims 12b, 12c or 12d is therefore placed on the second bearing surface 24 of the primary shim 12a when these are assembled to form a secondary shim device 13b, 13c or 13d. When a secondary shim device 13b, 13c or 13d is used, the second bearing surface 27 of the secondary shim used 12b, 12c or 12d is thesurface which bears against the end 8 of the cylinder 4 when the shock absorber 2 is compressed to the maximum. The primary shim 12a further comprises first holding means arranged to position and hold on the second bearing surface 24 a secondary shim 12b, 12c or 12d. Similarly, each secondary shim 12b, 12c, 12d comprises second holding means arranged to cooperate with the first holding means to position and hold said secondary shim 12b, 12c or 12d on the second bearing surface 24 of the primary shim 12a. The first holding means comprise holes and the second holding means comprise pins, or vice versa, the pins being intended to be positioned in the holes. Here, the first means for holding the primary wedge 12a comprise two holes 28 positioned along the length of the upper face of the central portion 22a of the primary wedge 12a (forming part of the second bearing surface24), and the second means for holding each secondary shim comprise two pins 29 positioned along the length of a central portion of the first bearing surface 26 of said secondary shim. Of course, the number of pins and holes could be different. For a given oil temperature, the operator in charge of maintenance selects the shim device 13 whose associated temperature range includes said given temperature, and assembles said shim device 13 by positioning the appropriate secondary shim 12b, 12c, 12d on the primary shim 12a – unless the oil temperature belongs to the lowest range, in which case the primary shim device 13a is used directly and without additional shim. The shims 12 are for example made of steel, and for example of 35NCD16-THR type steel. The shims 12 could be made of any other suitable material, having the same properties depending on the intended application.The primary shim device 13a further comprises a first protective element 30 arranged to be applied against the rod 5, and to be positioned between the rod 5 and the primary shim 12a when the primary shim device 13a is installed on the shock absorber 2. This prevents the steel shims 12 from damaging the coating of the various parts of the landing gear 3 (in particular the chrome-plated parts). The first protective element 30 is here made of plastic, and for example polyoxymethylene. This material has the property of not swelling and not deforming in the presence of humidity and high temperatures, which are conditions that can be found for example in the climates of Asian countries. Another material, having these properties, could be used. Nylon, for example, does not have these properties and swells in the presence of humidity. The first protective element 30 comprises a concave surface 31 complementary to the cylindrical shape of therod 5 and intended to be applied against the rod 5 during the installation of the primary wedge device 13a. The primary wedge device 13a further comprises a strap 32 and a loop 33 through which the strap 32 passes. The strap 32 makes it possible to hold the primary wedge device 13a (and the secondary wedge devices 13b, 13c, 13d which all comprise the primary wedge device 13a) in position. The strap 32 surrounds the rod 5, and the loop 33 allows the strap 32 to be tightened around the rod 5 so as to fix the shim device 13 used to the rod 5. The primary shim device 13a comprises a second protective element 34 arranged to be applied against the rod 5, and to be positioned between the rod 5 and the loop 32 when the shim device 13 is mounted on the shock absorber 1. The second protective element 34 prevents the loop from damaging the coating of the rod 5 and is, for example, again made of polyoxymethylene (butnot necessarily). The second protective element 34 comprises a concave surface 35 complementary to the cylindrical shape of the rod 5 and intended to be applied against the rod 5 during the installation of the primary shim device 13a. It is noted that the maintenance system 1 is very simple to use, and can be transported by hand very easily (possibly in a suitcase). As has been seen, each shim 12 includes an indication making it possible to identify the temperature range associated with the shim device 13 comprising said shim 12. To further facilitate the selection made by the operator, the shims 12 are painted over their entire surface, except on the functional surfaces (in particular the support surfaces). The higher the temperature range, the warmer the paint color used. Thus, the primary shim 12a is for example painted dark blue, and the secondary shim 12d is for example painted red. A “REMOVE BEFORE FLIGHT” flame(not shown) is attached to the front face of the primary wedge 12a and ensures that the operator does not forget the tools on the aircraft following the maintenance operation of the shock absorber 2. A first embodiment of the method for maintaining the oleopneumatic shock absorber 2 is now described. The aircraft is placed on the ground, on its wheels. The aircraft could also be on stands. The method firstly comprises the following preliminary steps. The operator opens the filling valve 11 and connects a hose to the filling valve. The operator places a jack under the rod 5 and, using the jack, he gives the rod 5 an upward movement to completely compress the shock absorber 2 so as to drain all the oil contained in the chamber 10 of the shock absorber 2. He then completely fills the chamber 10 of the shock absorber 2 with new oil. To perform this operation, he connects the hose to an oil supply source. The operatorthen releases the jack, which has the effect of relaxing the rod 5, which falls back by gravity. The oil is sucked into the shock absorber 2 in the same way as a syringe. The chamber 10 is then completely filled with oil. Once the leg is completely relaxed, the operator measures the temperature of the oil. For this, he uses, for example, an infrared thermometer. The operator then selects the shim device 13 associated with the temperature range in which the oil temperature is included, and assembles said shim device 13 (if it is a secondary shim device 13b, 13c or 13d). He therefore chooses the correct stack of shims 12 corresponding to the temperature recorded. For example, if the operator records 35° in oil temperature, he will choose the third secondary shim device 13d which covers the temperature range [+25°C; +40°C]. The operator then installs said shim device 13 on the shock absorber 2. He places the primary shim 12a on the surfacereception 15 by correctly positioning the lateral stops 23 on either side of the radial protrusion 18, and he surrounds the strap 32 with the rod 5, then he tightens the strap 32 using the loop 33. The operator again compresses the shock absorber 2 with the jack until the end 8 of the cylinder 4 comes into abutment against the wedge device 13. The excess oil is then evacuated via the filling valve 11. The operator removes the pipe, closes the filling valve 11, and releases the jack. The rod 5 falls back by gravity. A second embodiment of the maintenance method for the oleopneumatic shock absorber 2 is now described. The aircraft is placed on the ground, on its wheels. The aircraft could also be on stands. The operator measures the temperature of the oil. He uses for example an infrared thermometer for this. The operator then selects and assembles the shim device 13 associated with the temperature range in which the oil temperature is included.The operator then installs said shim device 13 on the shock absorber 2. He places the primary shim 12a on the receiving surface 15 by correctly positioning the lateral stops 23 on either side of the radial protrusion 18, and he surrounds the rod 5 with the strap 32, then he tightens the strap 32 using the loop 33. The operator places a jack under the rod 5. He drains the shock absorber 2 by compressing it as much as possible using a jack. All the oil is then evacuated. The chamber 10 is empty. He slowly lowers the jack. The rod 5 therefore also descends. The shock absorber 2 collapses. The cylinder 4 therefore comes into abutment against the shim device 13. The operator then fills the chamber 10 of the shock absorber 2 with new oil. The operator ensures that the chamber 10 is completely filled with oil. It should be noted that, in this second embodiment of the maintenance method, the shim device 13 supports the mass of the aircraft and must therefore be extremely robust.shims 13 are designed to have the maximum surface area in contact with the rod 5 and the cylinder 4. In the example shown in the figures, each shim device 13 can support a mass of 51 tonnes. Each flat surface 14a, 14b of the first bearing surface 14 has an area of ​​729 mm2. The second bearing surface 24 of the primary shim 12a has an area of ​​2772 mm 2, so that the applied load is equal to: F / S = 510000 / 2772= 183 MPa. 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. The maintenance system, and therefore the shim device used, is not necessarily mounted on the shock absorber rod, but could be mounted on the cylinder. In this case, when the shock absorber is compressed to the maximum, it is the end of the rod which abuts against the shim device. In the case where the shim device is mounted on the rod, it is not necessarily positioned on an ear-shaped radial protrusion through which a connecting axis of the compass passes; it can be positioned on a different element of the rod and in particular on a radial protrusion of a different shape.It has been indicated here that the primary shim device comprises a single shim (the primary shim), and that each secondary shim device comprises a single secondary shim (in addition to the primary shim). This configuration is not mandatory. It is possible, for example, to provide that one or more secondary shim devices comprise the primary shim device and several secondary shims. In this case, at least one secondary shim comprises third holding means arranged to position and hold another secondary shim on said secondary shim. The third holding means are, for example, holes, into which pins of the other secondary shim are inserted (or vice versa).The maintenance system can be implemented in any type of oleopneumatic shock absorber: main or auxiliary landing gear shock absorber, shock absorber integrated into the landing gear box or independent of it, shock absorber equipping an aircraft other than an airplane, shock absorber used in another vehicle, etc.

Claims

CLAIMS 1. Maintenance system (1) for an oleopneumatic shock absorber (2) which comprises a cylinder (4) comprising a chamber (10) containing oil and a rod (5) sliding in the cylinder, the maintenance system comprising a plurality of shims (12) arranged to be assembled so as to form a plurality of shim devices (13) of different heights and each associated with a distinct temperature range, each shim device being arranged to be installed on the shock absorber by being positioned between an end (8) of the cylinder through which the rod is inserted and an end (9) of the rod located outside the cylinder, so that, when the shock absorber (2) is compressed so that said end of the cylinder or said end of the rod abuts against said shim device (13), a volume of oil in the chamber (10), when the latter is filled to the maximum,is equal to a volume optimized for an oil temperature within the temperature range associated with said shim device (13).

2. Maintenance system according to claim 1, wherein the shim devices (13) comprise a primary shim device (13a) and at least one secondary shim device (13b, 13c, 13d), the primary shim device being associated with the lowest temperature range and comprising a single primary shim (12a), each secondary shim device comprising said primary shim device and at least one secondary shim (12b, 12c, 12d) stacked on the primary shim., 3. Maintenance system according to claim 2, wherein each secondary shim device (13b, 13c, 13d) comprises the primary shim device (13a) and a single secondary shim (12b, 12c, 12d).

4. Maintenance system according to one of claims 2 or 3, wherein the primary shim (12a) comprises a first bearing surface (14) arranged to be applied to a receiving surface (15) of the shock absorber (2) located near said end (8) of the cylinder (4) or said end (9) of the rod (5), and a second bearing surface (24) on which a secondary shim (12b, 12c, 12d) can be placed, the primary shim further comprising first holding means (28) arranged to position and hold the secondary shim on the second bearing surface. 5.Maintenance system according to claim 4, wherein said secondary wedge comprises second holding means (29) arranged to cooperate with the first holding means (28) to position and hold said secondary wedge on the second bearing surface of the primary wedge.

6. Maintenance system according to claim 5, wherein the first holding means comprise holes (28) and the second holding means comprise pins (29), or vice versa, the pins being intended to be positioned in the holes.

7. Maintenance system according to one of claims 5 or 6, wherein at least one secondary wedge (12b, 12c, 12d) comprises third holding means arranged to. position and maintain on said secondary wedge another secondary wedge.

8. Maintenance system according to claim 4, in which the cylinder (4) is a box of an aircraft landing gear and in which the rod (5) carries at least one wheel (7) of the landing gear, the primary wedge device (13a) being arranged to be fixed to the rod, the receiving surface (15) being an upper surface of a radial protrusion (18) of the rod.

9. Maintenance system according to claim 8, in which the radial protrusion (18) has a perforation (19) in which a connecting pin (20) passes, the landing gear comprising a compass of which a lower branch (21) is pivotally mounted relative to the rod (5) by means of the connecting pin. 10.Maintenance system according to one of claims 8 or 9, wherein the primary shim device (13a) comprises two lateral stops (23) arranged so that, when the primary shim device is installed, the radial protrusion (18) is positioned between the two lateral stops.

11. Method for maintaining an oleopneumatic shock absorber (2), using the maintenance system (1) according to one of the preceding claims and comprising the steps of: - measuring an oil temperature; - selecting the shim device (13) associated with a temperature range in which the oil temperature is included, and installing said shim device on. the shock absorber; - compressing the shock absorber so that said end of the cylinder or said end of the rod abuts against said shim device; - ensuring that the shock absorber is filled with oil to the maximum.

12. Maintenance method according to claim 11, further comprising the preliminary steps of completely compressing the shock absorber (2) and draining all the oil contained in the chamber (10) of the shock absorber, then completely filling the chamber with new oil, then relaxing the shock absorber.

13. Maintenance method according to claim 12, wherein, when said end of the cylinder or said end of the rod abuts against said shim device, excess oil is evacuated, which ensures that the shock absorber is filled with oil to the maximum.

14. Maintenance method according to one of claims 11 to 13, the oleopneumatic shock absorber (2) being a shock absorber of a landing gear of an aircraft. 15.Landing gear assembly, comprising an aircraft landing gear and a maintenance system (1) according to one of claims 1 to 10, the maintenance method according to claim 14 being implemented in the landing gear using the maintenance system.

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