The present invention relates to a housing to support a ball bearing or like rolling-element bearing, and/or a shaft passing through such a roller-element bearing.

Rolling element bearings are conventionally mounted between a shaft and a housing to allow low friction relative rotation with limited axial and radial movement of these parts. Either the shaft or housing may be the rotating part while the other remains fixed to a static local structure. Such machine elements rely on effective lubrication in order to function over a long life. In some cases the operational life may be reduced due to insufficient lubricant near to the tribological contact surfaces. This may be due to loss of the lubricating medium, typically oil, to the external environment through creep or evaporation, or it may be the result of degradation of the constituents of the lubricant through use. This is particularly problematic in applications where opportunities for maintenance are limited or impossible.

According to the present invention there is provided a housing for at least one bearing, the housing defining a location for each bearing, and/or a shaft adapted to extend through such a bearing, so the bearing would be at a predetermined location on the shaft, wherein the housing and/or the shaft also defines an internal reservoir cavity and a communication path to enable a lubricant from the internal reservoir cavity to reach the or each bearing, and being produced as a single integral item using an additive manufacturing process.

If such an internal reservoir cavity is provided in the housing, the housing acts as a conventional housing in that it bears against each bearing, but it contains an internal cavity which can act as a reservoir for a lubricant, which is then available to maintain appropriate quantities of lubricant within each bearing. This replaces lubricant that is either lost or degraded within each bearing.

If such an internal reservoir cavity is provided in the shaft, the shaft acts as a conventional shaft, and bears against each bearing, but it contains an internal cavity which can act as a reservoir for a lubricant, which is then available to maintain appropriate quantities of lubricant within each bearing. This replaces lubricant that is either lost or degraded within each bearing.

In either case the internal reservoir may include internal structures to inhibit rapid redistribution of the liquid lubricant.

The present invention enables more effective lubrication of bearing components to be provided over an extended duration, and is particularly useful in demanding environments such as in space satellites, where there may also be additional constraints on mass and/or structural integrity. It is clearly particularly useful in situations where there are restrictions on performing maintenance, for example where maintenance can only be performed at very long intervals, or is not possible. Preferably, the housing is designed so that it is structurally efficient. It may define a variety of features such as precision bearing-mounting seats, in addition to the lubricating cavity, within a single item. Preferably, it also provides fastening features for the retention of the bearings in the housing, or for fixing the housing to adjacent components so that it fulfils its role as a structural component within a wider system. The housing preferably is arranged to define an inlet means such that any powder trapped within the structure as a result of the manufacturing process can be flushed out, and this inlet means could also provide a means of filling the reservoir cavity prior to use. In a preferred embodiment, the housing defines a plurality of integral feet for fastening the housing to an adjacent structure. These integral feet may be defined at one end of the housing, or at an intermediate position along the length of the housing. For example there may be three or four such integral feet. The internal structures within the reservoir cavity may be in the form of a mesh or labyrinthine structure or other porous structure, such that it provides a large surface area. The porosity and the size of pores may vary between different portions of the porous structure, to passively prevent rapid loss of lubricant from the reservoir cavity. Preferably, if there are a plurality of bearings, the housing defines separate reservoir cavities for each bearing, so that a predetermined volume of lubricant may be provided independently for each bearing. Preferably, the housing is also arranged to inhibit migration of oil away from the bearings due to capillary action and, as such, the desired properties in these respects may be optimised for the particular environment in which the bearings are being employed. The invention may also be employed within a pumped system, whereby an additional quantity of oil may be introduced periodically for gradual distribution within the bearing system over a period of time.

In one embodiment the housing defines a cylindrical duct with a bore through which a shaft may freely extend, and defines two seats to locate bearings to support the shaft, one such seat at each end of the cylindrical duct, and at least one reservoir cavity is defined within the wall of the cylindrical duct between the bearing-locating seats. Preferably the porous structures within the cavity extend to an aperture at the inner surface of the cylindrical duct, so lubricant can migrate over the surface of the porous structure to reach the inner surface of the cylindrical duct. By way of example there may be two reservoir cavities, each being intended in use to provide lubricant to one of the bearings. Each such reservoir cavity may be of annular form within the wall of the cylindrical duct, so it surrounds the bore.

Alternatively there may be a plurality of reservoir cavities which provide lubricant to one and the same bearing, each of which may for example be in the form of a segment of an annulus, or any other convenient shape that can fit within the wall of the cylindrical duct. Each such reservoir cavity communicates with an aperture at the inner surface of the cylindrical duct, and preferably arranged to distribute lubricant all around the cylindrical surface of the bore. For example in the case of a single reservoir cavity of annular form, the cavity may communicate with a single aperture extending right round the cylindrical surface of the bore.

The size of the pores within the porous material in the reservoir cavity may for example be larger in a portion closer to the aperture, and smaller in a portion further from the aperture. The pores may vary in size between for example 10 μιη and 2 mm, more preferably between 40 μιη and 1 mm. During operation oil or other fluid lubricant creeps over the surfaces of the porous material, and then creeps over the surfaces within the bore, to reach the surfaces within a bearing. The housing may be provided with a coating on at least part of the surface of the bore, the coating altering the surface energy so as to repel oil, so the coating can act as an anti-creep barrier to inhibit creep of lubricant over that part of the surface of the bore. For example such an anti-creep barrier may be arranged right around the cylindrical surface of the bore between apertures communicating with different reservoir cavities, the anti-creep barrier hence ensuring that each aperture and so each reservoir cavity communicates with only one end of the cylindrical duct, and so with only one bearing.

In the case that at least one internal reservoir cavity is provided in the shaft, the operation is substantially the same. Each such reservoir cavity communicates with an aperture at the outer surface of the shaft, and preferably arranged to distribute lubricant all around the cylindrical surface of the shaft. For example in the case of a single reservoir cavity of annular form, the cavity may communicate with a single aperture extending right round the cylindrical surface of the shaft, or with multiple apertures spaced around the shaft. And at least part of the surface of the shaft may be provided with a coating to alter the surface energy and so act as an anti-creep barrier.

The size of the pores within the porous material in the reservoir cavity may for example be larger in a portion closer to the aperture, and smaller in a portion further from the aperture. The pores may vary in size between for example 10 μιη and 2 mm, more preferably between 40 μιη and 1 mm. During operation oil or other fluid lubricant creeps over the surfaces of the porous material, and then creeps over the surface of the shaft, to reach the surfaces within a bearing.

The shaft may be provided with a coating on at least part of the surface of the shaft, the coating altering the surface energy so as to repel oil, so the coating can act as an anti-creep barrier to inhibit creep of lubricant over that part of the surface of the shaft. For example such an anti-creep barrier may be arranged right around the cylindrical surface of the shaft between apertures communicating with different reservoir cavities, the anti-creep barrier hence ensuring that each aperture and so each reservoir cavity communicates with only one bearing.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 shows a perspective view of a housing of the invention;

Figure 2 shows a view in the direction of arrow A of figure 1;

Figure 3 shows a longitudinal sectional view on the line X-X of figure 2; and

Figure 4 shows a view equivalent to that of figure 3, showing also a shaft.

Referring to the drawings, a housing 10 comprises a cylindrical tubular structure 12 to house two rolling-element bearings 13 (shown in broken lines in figure 3), and three structural abutments 14 for attaching the housing 10 to a local structure. The cylindrical tubular structure 12 defines at each end precision machined axial seating faces 16 and precision bores 18 for locating the two rolling- element bearings 13, and these axial seating faces 16 and precision bores 18 constrain the bearing 13 in the axial and radial directions. Each end face of the housing 10 incorporates six screw holes 20 for attachment of a retaining ring 15 (shown in broken lines in figure 3) to secure the bearing 13 against the seating face 16. The three abutments 14, which form an external mounting interface of the housing 10, incorporate a recess 22 for fitting a fastener, and there are apertures 24 in the thin wall of these abutments 14 to achieve weight savings for mass-critical applications. I nternal to the cylindrical tubular structure 12 (see in particular figure 3) are two cavities 30 occupied by a porous or mesh structure 32, which have been created using an additive layer (or "3-D printing") manufacturing process. These cavities 30, which in use act as reservoirs for a lubricating fluid, are enclosed within the solid wall of the structure 12, except for filling holes 26 at the outside surface and an aperture 33 at the inner surface of the tubular structure 12, and the porous or mesh structure 32 extends to the inner surface of the tubular structure 12.

The production process may be described as a three-dimensional printing process from a powder. The powder may be a metal powder. In one example the housing 10 is produced by direct metal laser sintering. This process involves fusing together of very fine layers of metal powder using a focused laser beam. The powder may be deposited in layers of between 20 and 60 μιη, and each layer is then scanned with a high intensity laser beam so that the particles within the layer fuse together, and the layer fuses to the layer below. This direct metal laser sintering process involves gradually and repeatedly lowering a piston or support plate on which is repeatedly placed a thin layer of a powder of material, and scanning with a laser those portions of the layer of powder which are to be sintered together. After scanning the selected parts of each layer, the powder bed is lowered by one layer thickness, and the process repeated. Preferably the entire bed of powder is warmed up to slightly below the temperature required for sintering, so that the power required by the laser is reduced. This process is substantially identical to those referred to as selective laser metal sintering, or selective laser metal melting. An equivalent process, which may also be suitable, is electron beam melting. After performing the sintering as described above, the housing is separated from the remaining powder. The resulting housing 10 is single integral structure, with no joints.

All the components of the housing 10, that is to say the cylindrical tubular structure 12, the abutments 14, and the porous or mesh structure 32 in the cavities 30, are integral, having been made as a single near net shape component of metal (such as titanium) using an additive manufacturing process as described above. This would typically be followed by a finishing machining step to achieve the necessary dimensional tolerances and surface finishes for the bearing-fitting or bolted interfaces. Prior to this finishing machining step, it may also be appropriate to perform heat treatment, to achieve the required material properties. It may also be advantageous additionally to incorporate in the near net shape component temporary features for the purposes of the finishing machining step, which are subsequently removed before use of the housing 10.

During the manufacturing process, the filling holes 26 allow any powder left over from the manufacturing process to be flushed out. The filling holes 26 in this embodiment are arranged such that both reservoir cavities 30 can be filled during the same operation; once the cavities 30 have been filled with a fluid lubricant they are then sealed by inserting sealing screws (not shown) into each of the filling holes

26. Thus, in use, the only exit path for lubricant from the reservoir cavities 30 is into the bore of the cylindrical tubular structure 12 and so into the bearings 13.

The density of the mesh or porous structure 32 within the cavities 30 can be controlled during the manufacturing process to achieve a density and pore size appropriate to the application. The structure 32 may define labyrinthine paths.

The bore of the cylindrical tubular structure 12 may be provided with anti- creep barrier, by coating the surface with a material which changes the surface energy, so as to provide further control of the lubricant migration over the surfaces of the housing 10. Such an anti-creep barrier may for example be provided all around the portion of the bore between the two apertures 33.

The housing 10 as shown would typically be assembled with a pair of angular contact bearings 13 clamped in place and with a rotary shaft (not shown) mounted within the bearings 13. The shaft may then have other rotating parts fastened to it.

It will be appreciated that the housing 10 described above is by way of example only, and that it may be modified in many ways while remaining within the scope of the present invention, which is defined by the claims. For example there may be a different internal fluid retaining structure within the cavities 30 or a different number of flushing and filling holes 26. I n a further modification, instead of the annular reservoir chambers 30, a housing may instead define a number of discrete cavities spaced around the bore, although this would mean that each such cavity would need to be filled with lubricant separately. As described above the housing 10 incorporates three structural abutments 14 at one end for attaching the housing 10 to a local structure, but instead the housing 10 might incorporate a different number of such structural abutments 14, and the abutments might be in a different position, for example halfway along the cylindrical tubular structure 12.

Referring now to figure 4, this shows a shaft 38 extending through the housing 10. Although the housing 10 can be used with a conventional shaft, in this example the shaft 38 also defines an internal annular cavity 40 which communicates at each end with fifteen radial apertures 43 equally spaced around the

circumference of the shaft 38. The space within the annular cavity 40 and the radial apertures 43 is occupied by a porous or mesh structure 42 which has been created by an additive layer (or "3-D printing") manufacturing process, so the porous or mesh structure 42 extends to the surface of the shaft 38. The cavity 40 in use acts as a reservoir for a lubricating fluid, which gradually creeps out through the apertures 43 to the surface of the shaft 38, and so to the bearings 13. It will be appreciated that the shaft 38 may be made in substantially the same way as described above. In this case the flushing out of any particular material can be achieved by passing air into the apertures 43 at one end, to emerge through the apertures 43 at the opposite end; and subsequently the lubricant can be introduced in a similar fashion. The shaft 38 may be of a suitable metal material such as steel or titanium; and it will be appreciated that it may be connected to a conventional shaft by means of flanges (not shown). Although the shaft 38 may, as shown in figure 4, be used in conjunction with a housing 10 that incorporates an internal reservoir for lubricant, it will be appreciated that instead the shaft 38 might be used with a more conventional housing that does not include any lubricant reservoir. The housing 10 and the shaft 38 as described above may be used as part of a spacecraft bearing assembly, where lubricant management is required over a long duration. It should be appreciated that it may alternatively be used in a wide range of different applications, in particular applications in which long life of bearings is required, or where environmental or operational constraints demand that supplementary lubricant may be required over a period of time.