GB2194603A - Fluid bearings - Google Patents

Abstract

A hydrostatically gas-lubricated plain bearing arrangement has as bearing elements, which accommodate a wheel body in a rotatable manner, two bearing cones (2) which are rigidly fixed on a fixed axle (1) made up of two halves (1a, 1b). Lubricating-air pockets (7) with counterbores (9) and air-supply bores (8) are provided on the external conical surfaces of the bearing cones. The lubricating air is supplied into the air-supply bores (8) through the hollow axle (1) via air-distribution channels (28). For setting the bearing gaps, the mutual distance of the two bearing cones (2) can be changed by a threaded sleeve (18) inside one axle half (1b) in interaction with a threaded spigot (17) of the other axle half (1a). <IMAGE>

Description

SPECIFICATION Hydrostatically gas-lubricated plain bearing arrangement The present invention relates to a hydrostatically gas-lubricated plain bearing arrangement according to the preamble of Patent Claim 1.

Gas-lubricated plain bearings are preferably used for the bearing arrangement of shafts rotating at high speed under relatively low transverse loads. Air is usually used as the lubricating gas. The air, which forms the lubricating film between the sliding surfaces of the bearing and the shaft, can come from a compressed-air source located outside the bearing, for example from a compressor, in which case this is referred to as hydrostatic air lubrication, or the lubricating air, as a result of its viscosity, can form, in accordance with the hydrodynamic theory of bearing lubrication, a separating wedge-shaped gap between the shaft and the bearing shell. These are then hydrodynamically gas-lubricated bearings. The present plain bearing according to the invention belongs to the first-mentioned generic type.

Prior art In principle, the design of air-lubricated bearings, in both generic types mentioned above, has to ensure that the separating air cushion between the shaft and the bearing is retained under all operating conditions. Under constant loading of the shaft this is no problem, but on the other hand, under shock-like loads, e.g.

during rough handling of turbo-milling and turbodrilling tools and also, in particular, in the case of air-cushioned compressor impellers in aircraft air-conditioning systems and air-cushioned gyroscopic devices, such contact, caused by acceleration forces as a result of changes in flight altitude, can occur during which the sliding surfaces of the shaft and the bearing shell can be damaged on account of the extremely high rotational speeds.

A further cause of such damage is unbalance-type vibrations which are absorbed only within certain amplitudes of air film. In order to avoid such larger -damaging shaft displacements, it has been proposed, for example in the GB Patent Specifications no. 1,018,300 and no. 1,146,422, to accommodate the bearing shells and sealing elements at the end faces at the shaft outlet in a sleeve or bush which, in turn, sit in the machine part under the interposition of elastic elements which are intended to dampen the said vibration amplitudes. In the last mentioned patent specification, the toroidal sealing rings which are known by the abbreviated designation Orings are proposed as elastic elements, which toroidal sealing rings sit in annular grooves on the outer periphery of the said bush.The bush itself sits with considerable clearance in the bore of the machine part accommodating it so that an adequately large damping distance is available to the O-rings so that even larger oscillation amplitudes can be absorbed.

The deciding factor for the operating costs, in particular of larger air bearings, is the air consumption, which depends on the gap losses at the bearing end faces. In order to keep the air consumption as low as possible, it is attempted to realise running clearances between the shaft and the bearing shell which are as small as possible so as to do without contact seals, which would lead to friction losses, at the bearing end faces. According to the above, however, limits are imposed on the running clearance, so that it is not possible in this way to keep the air consumption as low as desired.As a further measure, it is known from the abovementioned Patent Specification GB 1,146,422 to provide at one shaft end or both shaft ends narrow discs which are of large diameter in relation to the shaft, run in annular grooves of the bearing body and form labyrinths which choke the lateral escape of the air and thereby reduce the air consumption.

However, this solution results in relatively large radial diameters of the bearing and therefore requires a large installation space.

Above all, however, this solution and other known solutions have the disadvantage that automatic axial stabilization is not ensured. But such stabilization is important when axial positioning of a rotor, shaft collar, gear or the like is required while very close tolerances are maintained.

Description of the invention The aforementioned disadvantages of known plain bearings are avoided with the hydrostatically gas-lubricated plain bearing arrangement according to the invention for a rotating machine part. Long lubricating gap surfaces and a very precise axial fixing are obtained by double-conical shaft running surfaces and bearing running surfaces.In the hydrostatically gas-lubricated plain bearing arrangement according to the invention for a rotating machine part, a fixed bearing has bearing sliding surfaces with shaped elements for forming lubricating-gas films and the rotating machine part has smooth running surfaces; moreover, the bearing arrangement has means for supplying a lubricating gas into the bearing gaps defined by the bearing sliding surfaces and the smooth running surfaces of the rotating machine part, and means for changing the size of the bearing gaps for the purpose of adapting them to predetermined operating conditions, and also a compressed-gas source, and is characterized in that the bearing sliding surfaces are two truncated-cone surfaces arranged symmetrically to one another, in that the shaped elements for forming the lubricating-gas films consist of lubricating-gas pockets arranged in uniformly distributed manner over the periphery of the truncated-cone surfaces, gas-supply bores provided in the centre of the lubricated-gas pockets, and counterbores which are coaxial to the gas-supply bores, and in that the smooth running surfaces of the rotating machine part are truncated-cone surfaces which form a running combination with the truncated-cone surfaces of the fixed bearing.

Brief description of the drawings The invention is described below in greater detail with reference to an embodiment shown in the drawings. In the drawings: Fig. 1 shows an axial longitudinal section through the bearing arrangement of a rotating wheel-shaped body, with the plain bearing accommodating this body being mounted on a spatially fixed axle, and Figs. 2 and 3 show details of this bearing arrangement.

Ways of embodying the invention The bearing arrangement shown in Fig. 1 is such in which a wheel, a disc, roller or the like is rotatably mounted on a bearing sliding surface consisting of two external conical surfaces. In this arrangement, the elements accommodating or containing the bearing sliding surface are rigidly mounted on an axle 1 mounted in fixed manner on the machine. In the present case, these elements are essentially two bearing cones 2 of the same configuration which are clamped-in place on the axle 1. Since this axle, apart from its task as a supporting element, also has the function of supplying the lubricating air and it accommodates elements for fixing and adjusting the bearing cones, it is made up of several parts.

The element rotating on the bearing sliding surface is a wheel body 3, the outer part of which, which can be, a blade ring, a gyroscope or the like, is not shown. The hub part of the wheel body has two truncated-cone bores 4 which point inwards from its side flanks and which, in the hub centre, lead into a short cylindrical bore 5.

A bearing cone 2 is shown separately in Fig. 2. Its external conical surface 6 has a number of lubricating film pockets 7 which are uniformly distributed over its periphery and are fed with compressed air during operating through air-supply bores 8 which, between the external conical surfaces 6 and the truncatedcone bores 4, form a lubricating-air film which separates the external the lower part of Fig.

1, the lubricating-air films are emphasized in thick black lines. The bores 8, in front of the lubricating-film pockets 7, lead into cylindrical counterbores 9.

An annular cylinder 10 with a chamfer 11 inside its free end adjoins the-truncated-coneshaped part of the bearing cones 2 having the external conical surfaces 6-see Fig. 2. The truncated-cone-shaped part of the bearing cone 2 has a cylindrical bore 12 with an annular groove 13 for accommodating a sealing ring 14. The latter is preferably a toroidal sealing ring.

The elements for fixing and adjusting the bearing cones 2 on the axle 1 and for supplying the lubricating film to the bearing points can be seen from Fig. 1. Since a mutual axial adjustment of both bearing cones 2 must be possible for accurately setting the bearing play, the axle 1 is made in two pieces. The two axle halves la and Ib are centred relative to one another and are longitudinally displa cable relative to one another. For this purpose, the right-hand axle half 1a, at its lefthand end, has a centring spigot 15 which is accommodated by a centring bore 16 of the left-hand axle half 1 b. For the mutual displaceability of the two axle halves, the left-hand end of the right-hand axle half la is designed as a threaded spigot 17 on which a threaded sleeve 18 can be screwed.This threaded sleeve 18 is widened at its left-hand end and is provided there with an external thread 19 with which it can be screwed in a corresponding internal thread 20 in a bore in the lefthand axle half 1b. The latter, at its left hand end, is also provided with an external thread 21 for a ring nut 23 which is used for fastening the left-hand bearing cone 2 via a thrust ring 24 against a collar 25b at the right-hand end of the left-hand axle half 1b. In the same way, the right-hand bearing cone 2 is fastened by the right-hand ring nut 23 against a collar 25a at the left-hand end of the axle half 1a.

The left-hand, free end of the axle half 1 b, with its external thread 21, is mounted in a smooth bore of an axle bracket 22, whereby the axle 1, the right-hand half 1a of which, as described below, is axially fixed in a second axle bracket 30, can freely extend axially to the left. A threaded ring 31 which presses the right-hand end face of the ring nut 23 against the left-hand flank of the axle bracket 30 is used for fixing the axle 1 in the right-hand axle bracket 30. At the ieft-hand end of the left-hand axle bracket 22, an identical threaded ring (not shown) can likewise be provided for the external thread 21 of the left-hand axle half 1 b in order to obtain a rigid axle bearing arrangement.

An inner and an outer sealing ring 26 and 27 respectively are provided in the left-hand thrust ring 24, just as in the thrust ring sitting on the right-hand axle half 1a and provided with the same reference numeral, whereby, in conjunction with the sealing ring 14 mentioned previously inside the conical part of the bearing cone 2, an air-distribution channel 28 is sealed against the atmosphere. A narrow axial annular gap is to be maintained between the two collars 25a and 25b in order to ensure that the bearing gap adjustment down to the minimum values is not blocked.

In the right-hand axle half la, an air-supply channel 32 in conductive connection with a compressed-air source (not shown) extends to the left into the area of the left-hand bearing cone 2. Here, at least one oblique connecting bore 33 in the right-hand axle half 1a and at least one connecting bore 34 located in the axle half 1 b at right angles to the same make a conductive connection between the air-supply channel 32 and the air-distribution channel 28. The compressed air passes from the latter via the capillary air-supply bores 8, the counterbores 9 and the lubricating-film pockets 7 on the left-hand bearing cone 2 into the bearing gap between the external conical surface 6 of the bearing cone and the truncated-cone bore 4, acting as a bearing sliding surface of the wheel body 3, where it forms the separating lubricating-air film.The compressed air passes into the air-distribution channel 28 of the right-hand bearing cone 2 directly from the air-supply channel 32 via at least one connecting bore 35 located in the axle half 1a at right angles to the latter and further, in the same manner as on the left-hand side, into the right-hand bearing gap for forming a lubricating-air film. The flow arrows show the course of the influx of the compressed air to the bearing points.

In a practically embodied bearing of this type, the lubricating-air pockets are about 0.15 mm deep and the capillary air-supply bores 8 have a diameter of 0.4mm. In the counterbores 9, in the aper-ture area of the bores 8, a supersonic expansion takes place, and the air discharges sonically out of the lubricating-air pockets into the bearing gap via a choke gap of about 0.03 mm. At a bearing width of 20 mm, the air consumption is only about 1 I/s at the high load-carrying capacity of 10 kp in the axial direction and of 4 kp in the radial direction. Even when there is a slight positive pressure without sonic choking of, e.g. 200 mbar, the bearing is already stable, with a radial load of 300 p already being absorbed.

By changing the distances between the two bearing cones 2 by the adjusting means described above, namely the threaded sleeve 18 in interaction with the threaded spigot 17, the bearing gaps and the choke gaps after the lubricating-air pockets can be changed and thus the sensitivity and the load-carrying capacity of the bearing can be adapted to the particular application. In order to prevent the two axle halves from turning relative to one another when the threaded sleeve 18 of the left-hand axle half 1 b is screwed onto the threaded spigot 17 of the right-hand axle half 1a, the right-hand axle half 1a, between the centring spigot 15 and the threaded spigot 17, has a guide spigot 36 with a guide groove 37 into which a guide pin 39 engages which is tightly fitted in a bore 38 of the lefthand axle half 1 b.

In the present exemplary embodiment, a wheel-shaped machine part runs on a fixed axle. But the same principle, without a fundamental change, can also be applied to the bearing arrangement of a shaft in one or more bearings. Apart from the adjusting means for the bearing gap, the difference is that the compressed air has to be supplied via the bearings, and the lubricating-air pockets 7, the counterbores 9 in the same and the capillary air-supply bores 8 have to be provided in two bearing running surfaces corresponding to the truncated-cone bores 4 of the wheel body 3.

The bearing gap can be adapted either by axially adjusting the bearing cones sitting on the shaft or by axially adjusting the bearing elements having the truncated-cone bores.

The bearing gaps can be changed not only by screwing the threaded sleeve 18 on the threaded spigot 17 but also by spacer discs which are inserted either in the gap between the collars 25a and 25b of the two axle halves la and Ib or also between one or both of the annular end faces of the two bearing cones 2 resting against the said collars.

Claims (4)

1. Hydrostatically gas-lubricated plain bearing arrangement of a rotating machine part, with a fixed bearing having bearing sliding surfaces with shaped elements for forming lubricating-gas films and the rotating machine part having smooth running surfaces, with means for supplying a lubricating gas into the bearing gap defined by the bearing sliding surfaces and the smooth running surfaces of the rotating machine part, with means for changing the size of the bearing gaps for the purpose of adapting them to predetermined operating conditions, and also with a compressed-gas source, characterized in that the bearing sliding surfaces are two truncated-cone surfaces, arranged symmetrically to one another, in that the shaped elements for forming the lubricating-gas films consist of lubricating-gas pockets arranged in uniformly distributed manner over the periphery of the truncated-cone surfaces, gas-supply bores provided in the centre of the lubricating-gas pockets, and counterbores which are coaxial to the gas-supply bores, and in that the smooth running surfaces of the rotating machine part are truncated-cone surfaces which form a running combination with the truncated-cone surfaces of the fixed bearing.

2. Plain bearing arrangement according to Claim 1, characterized in that the longitudinal centre lines of the lubricating-gas pockets lie on generating lines of their truncated-cone surfaces, in that the gas-supply bores and the counterbores are provided at the central point of the lubricating-gas pockets, in that the means of supplying the lubricating gas from the compressed-gas source into the bearing gaps consist of a gassupply channel and gasdistribution channels which communicate therewith and are conductively connected to the gas-supply bores, and in that the means for changing the size of the bearing gaps consist of screw means which enable the axial distance of the bearing parts to be changed on which the truncated-cone surfaces acting as bearing sliding surfaces are provided.

3. Plain bearing arrangement according to Claims 1 and 2, characterized in that the fixed bearing is fixed on a two-piece axle fixed on the machine, the two axle halves of which are centred in aligned manner relative to one another by a centring spigot in the one axle half and one centring bore of the second axle half and are fastened axially relative to one another by a threaded spigot on one axle half and a threaded sleeve guided in the second axle half, with the bearing sliding surfaces being formed by external conical surfaces located on two bearing cones which are fixed on the axle, in that the rotating machine part is a wheel body, the running surfaces of which, interacting with the bearing sliding surfaces, consist of two truncated-cone bores, in that the compressed-gas source is an air compressor, in that the air-supply channel is provided in the axle, in that the air-distribution channels are provided inside the bearing cones and are sealed against the atmosphere by thrust rings sealed relative to the axle, in that the bearing cones are fastened by ring nuts via the thrust rings against one collar each of the two axle halves, and in that the means for changing the bearing gaps consist of the mentioned threaded spigot of one axle half and the threaded sleeve which can be screwed thereon and is guided in the second axle half, and also of a guide groove in a guide spigot of one axle half and a guide pin sitting in the second axle half and engaging into the guide groove.

4. A gas-lubricated bearing, substantially as herein described with reference to the accompanying drawings.