Bearing unit for an aircraft wheel

Abstract

A packaged bearing unit is disclosed including an outer surface for receiving an aircraft landing gear wheel and an inner surface for receiving an axle. The unit may include first and second spaced-apart sets of tapered roller bearings, held between inner and outer raceways. There may be a bearing setting spacer which can be used when setting and pre-loading the bearings. The bearing unit may be a sealed unit which includes a pre-set amount of lubricant (grease) for lubricating the bearings. One or more sensors may be retained in a void between the sets of bearings.

Claims

1. An aircraft landing gear wheel packaged bearing unit, comprising: an outer surface, an inner surface, an inner raceway, an outer raceway, wherein the outer surface receives an aircraft wheel and the inner surface receives an axle, a first set of tapered roller bearings, and a second set of tapered roller bearings, spaced apart in an axial direction, each set of first and second tapered roller bearings being held between the inner raceway and the outer raceway, a bearing setting spacer attached to the axle which when clamped in position dictates the separation in the axial direction of the first set of tapered roller bearings from the second set of tapered roller bearings, thus enabling the roller bearings of the bearing unit to be configured in a set position and pre-loaded, a pre-set amount of lubricant for lubricating the first and second set of tapered roller bearings, the lubricant being retained within the bearing unit by one or more seals, wherein the bearing setting spacer forms part of a clamping arrangement for clamping and preloading the first set of tapered roller bearings and the second set of tapered roller bearing in the set position, and a fixing, separate from the clamping arrangement, comprising a first nut that secures the outer raceway to the inner surface of the wheel.

2. The packaged bearing unit according to claim 1, wherein the clamping arrangement further includes a second nut configured for retaining preloading and/or setting the first and second set of tapered roller bearings, and for securing the bearing unit to the axle.

3. The packaged bearing unit according to claim 1, wherein the bearing unit includes a void between the first set of tapered roller bearings and the second set of tapered roller bearings.

4. The packaged bearing unit according to claim 1, wherein the bearing unit includes one or more sensors.

5. The packaged bearing unit according to claim 1, further comprising one or more thermal barriers arranged to reduce the flow of heat energy from brakes associated with the wheel to one or more of the first and second set of tapered roller bearings.

6. The packaged bearing unit according to claim 1, with the first and second set of tapered roller bearings are seated and under pre-load position.

7. The packaged bearing unit according to claim 1, wherein the amount of pre-loading of the tapered roller bearings can be controlled independently of the mounting of the wheel on the axle of an aircraft landing gear.

8. An aircraft including a landing gear on the axle of which is mounted the bearing unit according to claim 1.

Description

DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

(2) FIG. 1 shows in cross-section an aircraft wheel of the prior art;

(3) FIG. 2 is a front view of an aircraft according to a first embodiment of the invention, the aircraft including a wheel and associated bearing unit;

(4) FIG. 3 is a side view of the aircraft shown in FIG. 1;

(5) FIG. 4 shows in cross-section the aircraft wheel and associated bearing unit of the first embodiment;

(6) FIG. 5 shows an enlarged portion of FIG. 4,

(7) FIG. 6 shows in cross-section the aircraft wheel and associated bearing unit of the first embodiment;

(8) FIG. 7 shows an enlarged portion of FIG. 6,

(9) FIGS. 8 to 12 illustrate a method of installing a bearing unit and wheel of the first embodiment.

(10) FIG. 13 shows in cross-section an aircraft wheel and associated bearing unit according to a second embodiment;

(11) FIG. 14 is a flowchart illustrating the steps of a method of manufacturing a sealed bearing unit in accordance with a third embodiment; and

(12) FIG. 15 is a flowchart illustrating the steps of servicing of an aircraft wheel in accordance with a fourth embodiment.

DETAILED DESCRIPTION

(13) The embodiments generally relate to an aircraft wheel for a landing gear (LG) and an associated bearing unit, which is provided separately from the wheel, for providing the rotational bearing interface between LG axle and wheel. The bearing unit is provided as a packaged unit and once set up, with correctly seated bearings with the correct pre-load, can remain on the axlepossibly for the lifetime of the LGbut at least for the duration of a significant part of the lifetime of the LG during which the wheel and/or associated brakes may be serviced, maintained and/or replaced multiple times. Any wheel can then be removed, with or without its associated brake pack, leaving the bearing unit in place on the LG axle. The bearing unit will not need assessing or servicing unless a sufficiently significant event has happened, such as a very hard landing for example, warranting a precautionary inspection. The bearing unit is thus treated both technically and commercially as an independent product, as compared to the wheels with which it is designed to be used. As a result of packaging the bearings in this manner, it may also be possible to enable higher loads within a smaller space envelope. It may also provide an improved load path (from the tyre through the bearing system architecture to the axle) for transferring static and dynamic loads. It may also reduce static and rotational un-sprung weight imbalance and/or reduce the chance of misalignment of the bearing system architecture and/or reduce system stress, and/or reduce tyre wear.

(14) FIGS. 2 and 3 show an aircraft in accordance with a first example embodiment. The aircraft 2 comprises a fuselage 4 and wings 6. A nose landing gear (NLG) 12 is mounted on the fuselage 4 and a main landing gear (MLG) 10 is mounted to each wing 6. Both NLG and MLG are retractable into respective landing gear bays on the aircraft. All LG on the aircraft could utilise the benefits of the present embodiment, but the description that follows will refer by way of example only to a MLG and its associated axle, wheel, bearing and brakes.

(15) FIG. 4 shows a wheel 10 of MLG of FIGS. 2 and 3 including a bearing unit 12 according to the first embodiment. The bearing unit 12 is mounted to an axle 14 via a sleeve 13. The bearing unit 12 allows the wheel to rotate relative to the axle 14, the axis of which being shown by broken line 16. The split rim wheel has two halves 10a, 10b, which define a rim which carries a tyre (not shown). The bearing unit 12 is secured to the sleeve by means of a bearing nut 40. The wheel is held on the bearing unit by a wheel nut 42. The wheel 10 is associated with a removable brake pack 28 operated by a brake calliper 30.

(16) The bearing unit 12 is provided as a single sealed unit integrating two sets of tapered roller bearings. The roller bearings thus comprise a first set 18a at a first location along the axis 16 and a second set 18b spaced along the axis at a second location. Each set of roller bearings is held between an inner raceway and an outer raceway. The rollers are silicon nitride bearings and therefore extremely hard-wearing. FIG. 5 shows an enlarged view of the second set 18b of rollers (enlarging the area shown by dashed oval 19 in FIG. 4). The rollers 18 are held between an inner raceway (or cone) 20 and an outer raceway (or cup) 22. The rollers are held in spaced apart position circumferentially around the axis 16 by a cage 44. Two seals 46, 48 are attached to and rotate with the outer raceway 22, in sealing engagement with the inner (fixed) raceway 20. A precise amount of grease 50 is provided which is sealed in by the seals 46, 48. A spacer 52 sets the axial separation of the sets 18 of bearings and assists in setting the preload as will be described in further detail below. A void 54 is provided between the innermost seals 46.

(17) FIG. 7 shows an enlarged view of the void 54 and the surrounding structure (enlarging the area shown by dashed oval 49 in FIG. 6, which shows the same wheel 10 and bearing unit 12 as shown in FIG. 4). Inside the void 54 are provided multiple sensors, including one sensor set 25 including a rotation detector 56 and an associated target device 58. The rotation detector 56 is fixed to the spacer 52 and therefore fixed relative to the axle. The target device 58 is fixed to the outer raceway structure 22 and therefore rotates with the wheel. The rotation detector 56 is arranged to detect the passing of the target device 58 so that a 360 degree rotation of the wheel can be reliably detected. The void is sealed from the outside environment and therefore sensors in the void are protected from brake debris, moisture and/or other elements that might otherwise affect the operation of such sensors.

(18) The mounting and preloading of the bearing unit and wheel of the first embodiment will now be described with reference to FIGS. 8 to 12. In the step shown by FIG. 8, the sleeve 13 is mounted and secured to the axle 14. The sleeve 13 keys into the axle (the keying-in structure not being shown in the Figures), forms a close fit with the axle 14 and is bolted into place (fixings not shown). FIG. 8 shows schematically the presence of the brake calliper 30, which is already attached to the MLG.

(19) In the step shown by FIG. 9, the bearing unit 12 is supplied and pushed onto the sleeve 52, until it abuts a flange 13f on the sleeveas shown in FIG. 10. Then the bearing nut 40 is tightened. The geometry of the roller bearings, the inner and outer raceways and the spacer 52 is such that the correct amount of preload is supplied at the point at which the spacer 52 starts to undergo compression as a result of the axial forces exerted by the bearing sets 18a, 18b at each end. Further tightening of the nut 40 loads the spacer 52 rather than the bearings, so it is relatively straightforward to tighten the nut to a torque that applies the correct preload to the bearings, with a reduced risk of excessive load on the bearing rollers. Once the nut 40 is so tightened, both sets of bearing rollers are corrected seated and correctly loaded. The spacer 52 thus dictates accuratelywith the required precisionthe separation in the axial direction of the first set of tapered roller bearings from the second set of tapered roller bearings, thus enabling the roller bearings of the unit to be accurately and precisely configured in a correctly set position (correctly seated) and correctly pre-loaded, independently and separately from the fitting of the wheel on the axle. This may enable any variation in setting to be reduced or minimised and may also enable improving or optimising location and load path.

(20) The bearing unit is provided as a packaged and sealed unit, with the correct amount of grease provided for each bearing set. The seating of the bearings and the preload on the bearings is known to be correct and unlikely to change. Wear of the bearings can thus be reliably predicted and the bearings can be designed to have a servicing interval many times longer than wheel/brake servicing intervals. The bearing unit need not be removed or serviced, barring exceptional events, any more frequently that the landing gear structure.

(21) A wheel 10 and associated brake pack 28 may then be mounted on the bearing unit 12 as shown in FIG. 11, and fixed in place with a wheel nut 42 as shown in FIG. 12. Tolerances between the halves of the wheel 10 and/or resulting from the torque applied to the nut 42 will have little or no influence on the performance of the bearings of the bearing unit 12.

(22) The bearing unit is designed such that the variation in bearing performance is reduced because setting and pre-loading is better controlled, the correct quantity of lubricant is guaranteed and a protected environment is provided by the seals.

(23) FIG. 13 shows a wheel 210 and bearing unit 212 according to a second embodiment which is similar to that of the first embodiment. Only the main differences will now be described. Firstly, there is no sleeve on the axle 214. Instead the axle includes an integrally formed flange 214f for receiving the bearing unit 212, which is shown abutting the flange 214f in FIG. 13. The axle has a series of hydraulic lines 260 formed within it, which exit the axle 214 at various locations 262 spaced around the exterior surface of the axle that, in use, is in contact with the inner diameter of the bearing unit 212. The hydraulic lines 260 are pressurised to assist in the releasing of the bearing unit from the axle.

(24) FIG. 14 shows a flowchart illustrating a method 300 (according to a third embodiment) of manufacturing and mounting a sealed bearing unit being in accordance with the unit shown in FIG. 4. The method starts (represented by box 301) with arranging a first set of tapered roller bearings between inner and outer raceway structure and a second set of tapered roller bearings between the same inner and outer raceway structure. The roller bearings are in an unloaded position, there being endplay. The roller bearings are spaced apart from each other along the rotational axis by a spacer. As a subsequent step (although it could be performed at a different time), the step being represented by box 302, a predetermined amount of grease is added to the first set of tapered roller bearings and a predetermined amount of grease is added to the second set of tapered roller bearings. Then as a later step (represented by box 303) each set of tapered roller bearings is sealed with a pair of seals so that the predetermined amount of grease is retained within the bearing unit. It could of course be the case that the seals are in situ before the grease is added via one or more dedicated channels for that purpose.

(25) The spacer is sized such that when the first set of tapered roller bearings and second set of tapered roller bearings are urged together, the spacing structure is under axial compression when the correct axial preload for the tapered roller bearings is applied. Thus as a subsequent step (although again the step could be performed at a different stage in the process)represented by box 304, the first set of tapered roller bearings are urged towards the second set of tapered roller bearings until the spacing structure undergoes axial compression. At this point, it is assumed (correctly) that the tapered roller bearings are correctly seated and preloaded. A wheel may then be mounted on the axle, with the rotation of the wheel about the axle being facilitated by the bearing unit. Thus, there is a step (represented by box 305) of moving the wheel into position over the bearing unit and then fixing it in place with a wheel nut. As part of this step (box 305) it may also be that a brake pack assembly is mounted on the axle in advance of, but immediately before, the wheel.

(26) FIG. 15 shows a flowchart illustrating a method 400 (according to a fourth embodiment) of servicing an aircraft landing gear assembly having a wheel, bearing unit and brake pack in accordance with the unit shown in FIG. 4. The method starts (represented by box 401) with removing the wheel and brake pack (but not the brake calliper) from the landing gear axle, leaving the associated bearing unit in situ, then (represented by box 402) servicing them (i.e. checking, maintaining and if necessary repairing the wheel and brake pack), then (represented by box 403) securing to the axle a serviced/replacement wheel and brake pack (which may include new or replacement parts, or which may be the same wheel and brake pack as removed by step 401) using the same bearing assembly, which has remained in situ during step 402. Thus, the bearings need not be inspected or maintained at the same time as the wheel and/or brake pack. The bearing unit may be designed to be serviced fewer than one in ten service intervals for servicing the wheel/brake packs. If and when the bearing unit is serviced it may be subjected to cleaning, an NDT inspection, an overhaul, a bearing reset, re-greasing, replacement of seals, and/or replacement of other parts (for example being returned to a bearing manufacturer for that purpose).

(27) Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

(28) The spacer between the bearing sets could be formed as part of one or both of the inner raceways.

(29) The wheel need not be formed as a split rim wheel.

(30) Other sensors could be provided in the bearing unit, such as one or more temperature sensors, inertial sensors, orientation sensors, load sensors, vibration sensors, other active health monitoring sensor(s), or the like. Such sensors could be active or reactive and could provide information that can be used for brake controls. A sensor in the void could be combined with a load sensor to enable improvements to the braking system, possibly on a wheel by wheel basis.

(31) The bearing unit has an outer surface for receiving a wheel. That same outer surface may optionally be configured to engage with part of the brake pack.

(32) The bearing unit may include one or more thermal barriers. For example, the outer raceway may include a thermally insulating material. The thermal barriers may be provided to prevent or minimise heat transfer from the brake through the wheel. The thermal barriers may be provided as one or more coatings, for example comprising a bonding coat, an insulating layer (which may be in the form of a thermal barrier coating, for example having a metallic bond coat [for bonding to the metal substrate], a thermally-grown oxide layer, and a ceramic topcoat).

(33) Other embodiments of the bearing unit could be used on a Body LG (BLG) and/or a Wing LG (WLG).

(34) The bearing rollers could, instead of being made from silicon nitride, be made from advanced bearing steel material or be coated with industrial diamond.

(35) In some embodiments, the bearings may be set up with a pre-load but also have endplay in operation.

(36) The bearing unit may be a single component that is for example provided and/or manufactured separately from of the wheel and axle. The bearing unit may be provided as a single line-replaceable unit (LRU).

(37) Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

(38) The term or shall be interpreted as and/or unless the context requires otherwise.