SE419366B - FLUID BEARING DEVICE - Google Patents

Description

'7710297-8 brushing for the shoulder movements. The films may be as thin as about 0.025 mm in accordance with US PS 3,434,762 or have a thickness of about 0.006 x the bearing diameter in accordance with US PS 3,215,480.

We have found that the thinness of the foils sets a limit to the function of this type of layer. The maximum pressure in the fluid film, which supports the bearing, is built up in the area with a minimum thickness of the gap.

As soon as the pressure begins to build up between the shaft and the foil, the foil bends away from the shaft except in the immediate vicinity of the supports. The load-bearing capacity of the bearing is a function of the product of the generated pressures and the area over which these pressures act. Because the pressure can only act in the immediate vicinity of the supports. they act only on a small part of the area of the layer foils. High pressures are therefore required to withstand the relatively high working loads at a heavily loaded bearing, for example in a gas turbine engine, and this necessitates very small gaps, which limits the bearing capacity due to premature contact with the shaft or too strong heat generation.

The problem therefore lies in how to prevent deflections, which reduce the bearing's capacity, and at the same time provide sufficient suspension in the bearing to accommodate circular movements of the shaft and compensate for different thermal expansions of the various components.

This problem is solved according to the present invention by replacing the thin foils resp. the rigid bearing blocks in known bearings with relatively thick but still resilient cups and the introduction of controlled bending of the bowls under the operating conditions of the bearing in order to optimize the load-bearing capacity of the bearing.

In the present description, the term "resilient cup" means a plate, a block or the like, which may be curved or flat and whose thickness in relation to its other dimensions is such that it can be bent in substantially the same way as a rigid beam under impact. of gas pressure loads and the concentrated support or reaction loads, but which is rigid enough to withstand local elevations due to the high fluid pressure loads generated during operation during its unsupported length between load reaction points, so that it is able to maintain a substantially uniform fluid film thickness over the unsupported length between the load reaction points. 7710297-8 In this respect, the bearing acts in a completely different way than a film gas bearing. Comparison between such a foil and a bowl shows that the bowl can be of the order of 10 x the thickness of a foil for a corresponding layer for heavy operation and thus of the order of one thousand times the rigidity.

A further advantage of the bowl bearing is that the bowls, which are relatively thick, can be coated with friction-reducing high-temperature coatings, such as cobalt or chromium oxides, by plasma spraying, which was not possible with the thin foils.

According to the present-ugmänn fl¶; a fluid storage device is provided, which comprises a pair of elements movably mounted relative to each other on a fluid film, which is formed as a result of the relative movement between a bearing surface on one of the elements and bearing surfaces on a plurality of resilient cups, which are supported in places along the same between the elements, it being particularly characteristic of the invention that each resilient bowl has a thickness which, in relation to its other dimensions, is such that the bowl is incapable of locally deflecting in unsupported places as a result. of increases in the pressure of the fluid film, and that load loading means are mounted between each bowl and the element on which the bowls are mounted, each load reaction means being arranged to abut against the element on which the bowls are mounted, at a fixed support point, located between midpoints the bottom of the bowl and a trailing edge thereof, and depending on increases in the fluid film pressure to produce at least two reactions forces, of which a first is applied to the trailing edge of the bowl and a second is applied to a point which lies between the center of the bowl and the leading edge thereof and which also lies on the side of the resultant of the pressure in the fluid film opposite the first reaction force, to bend each bowl like a rigid beam and change the shapes of the bowls so that the bearing surfaces of the bowls adhere more closely to the bearing surface of one of the elements in zones of minimal fluid film thickness to increase the bearing capacity of the bearing.

The bowl bearing according to the invention described above can be used as a shaft bearing, both for radial loads and compressive loads on the shafts, or can be used with a linear bearing.

The fluid film produced in the bearing may be a liquid or gas film, however, in most applications the fluid film consists of an air film which is generated during relative movement between the two elements.

In an embodiment of the invention, the two elements consist of a housing and a shaft, the shaft being rotatably mounted in the housing.

The load reaction means may be a resilient mechanism, for example springs or their pneumatic or hydraulic equivalents or lever mechanisms.

Further features of the bearing device according to the invention appear from the following claims.

Examples of the present invention will now be described in more detail with reference to the accompanying drawing. Fig. 1 is a schematic sectional view of a bearing constructed in accordance with the principles of the present invention; Figs. 2a, 2b and 2c show curves illustrating the gap profiles at the unloaded state and the loaded state of a bearing. typical stock according to the invention resp. the air pressure in the gap during operation. Fig. 3 is an exploded perspective view of a shell bearing according to the invention. Fig. 4-is a cross-sectional view of the bearing according to Fig. 3 with the bearing in assembled condition. Fig. S is a sectional view showing the bearing housing and part of the shaft. Fig. 6 is a cross-sectional view of a portion of an alternative bearing construction, showing the shell bearing formed equivalent to a rocker block bearing.

Fig. 1 schematically shows a shaft bearing in which a shaft 10 supports for rotation in a housing 12 by means of a fluid film formed during operation between the surface of the shaft and the surfaces of four bowls 14. The leading edge of each bowl is supported on the rear edge of the preceding bowl to form a ledge, so that a gap 16 is formed between the surfaces of the shaft and the cups, which gap tapers towards the rear edge of each bowl.

During operation with the shaft 10 rotating in the direction of the arrow R, air is drawn into the tapered slots, and as the rotational speed increases, the pressure in the air film increases until it lifts the bowl free from the shaft and the shaft runs completely supported on the air film.

In order to optimize the load bearing capacity of the bearing, load reaction means are provided in the form of resilient levers 18, which act between the shells and the housing to transfer air pressure loads on the shells to the housing and thereby give rise to reaction loads back on the shells to modify the shape of the bowls in relation to their shape in the unloaded state. The positions of the load reaction points are calculated to give rise to a shape of each steel, which shape more accurately corresponds to the shape of the shaft in order to maintain an optimal gap profile under the bowl for an intended operating speed and an intended load on the shaft.

Regarding the loads on a bowl, the air pressure in the gap gives rise to a distributed load on the underside of the bowl, which load varies with the thickness of the gap, whereby the maximum pressure is generated where the gap thickness is least. For analytical purposes, this load can be considered suuem.enda resultüæn fl ast (A) on the bowl, which load acts near the pressure spike.

This load A is transmitted to the housing via the spring levers 18, which abut the shells at reaction points B, C and the housing at D. The effect of the reactions on the shells at B, C is to bend the shells in the same way as a beam, so that its curvature more closely adheres to it at the shaft than it did in the unloaded state of the bowl.

A further reaction, which complements the bowl equilibrium, takes place at E, where the two bowls overlap.

The effect of the combined gas pressure loads and the different reactions on the bowl can, by appropriate placement of points B and D, be formed to generate an optimal gap profile under the bowl for a intended operating speed and a intended load on the shaft. This in turn gives rise to a greater load-bearing capacity for a given maximum pressure. 1 Since the trays act as elastic beams and the values of the air pressures generated for each given gap profile can be calculated, the dimensions of the springs and the positions and values of the reactions can be calculated to optimize the load bearing capacity of the bearing by appropriate bending of the trays.

Of course, many variations can be made in the design of the shell bearing to optimize its performance. For example, the mini gap thickness' can be arranged to be located at the rear edge of each bowl, when the bowl bearing is out of operation, so that it is retained near the rear edge during operation. Furthermore, the bowls do not have to overlap at the ends and apart from the reaction point at B, which must be located between the ends of the bowls, other reaction points can be arranged at a distance from or at the ends of the bowl.

Figs. 2a, 2b, 2c show curves for the special bearing construction described in the following with reference to Figs. 3-5. Fig. 2a shows the gap profile under a bowl at zero load and no rotation of the shaft. It appears that the gap is reduced to zero at the rear edge of the bowl. Fig. 2b shows the gap profile at the intended load and it can be seen that the gap thickness due to the bowl-bending reaction loads at B, C and E is maintained substantially uniformly over a substantial part of the length of the bowl in front of the rear edge. Fig. 2c shows the flat pressure profile of the air film under the bowl, which enables considerably increased loads to be supported by the bowl bearing according to the present invention in comparison with conventional bearings under corresponding conditions.

The bearing construction, from which the curves described above are obtained, is shown in Figs. 3-5. These figures show a shaft 20 mounted for rotation in a housing 22 and supported for such rotation in four cups 24 (only three shown), each of which extends 90 ° around the circumference of the shaft.

Each bowl has a fixed radius of curvature which with a small measured AR exceeds the radius R of the shaft, and at each end each bowl is provided with a cut-out to form a ledge 26, so that at the assembly adjacent ends of the bowls overlap each other. The ledge heights h1 and h2 of the radially inner portions of the ledges are different at the opposite ends of each bowl. Thus, in the composite bearing, the leading edge of each bowl is supported free of the shaft to give rise to a fixed gap g at this end between the radially inner surface of the bowl and the radially outer surface of the shaft. Since the rear edge of each bowl is in contact with the shaft or during the operation of the bearing has a very small distance to the shaft, a tapered gap is defined between the bowl and the shaft. The tapered gap is arranged to converge in the direction of the rotation of the shaft, i.e. in the direction of the rear edge of the bowl, so that rotation of the shaft causes air to be compressed under the bowls and generates a lifting force to support the shaft on a film of air during shaft rotation. In this particular example, the radius R of the shaft is 47.015 mm and the AR is equal to 0.102 mm. The landing height g at the front edge without load on the shaft (other than an initial preload) and without rotation of the shaft is thus 0.102 mm.

The cups themselves are in turn supported in the housing 22 by means of curved spring levers 28. Each of the spring levers is located relative to a bowl, and the entire assembly of cups and spring levers in the housing is prevented from rotating by means of four pins 30, which extend through the housing and the spring levers and are received in holes 32 in the bowls. Each spring lever 28 has radially inwardly directed ribs 34, 36, one at each end, which extend axially along the lever. The ribs abut the outer surfaces of the bowls, and the levers are arranged so that one of the ribs abuts a bowl adjacent the overlapping ends and the other rib abuts the adjacent bowl at a location between the ends of the bowl. Each spring lever also has a similar rib 38 on its radially outer surface, which rib is arranged to be in contact with the outer housing. The spring levers can thus apply the required preload to the shells to locate the shaft in its rest position.

In operation, the air pressure under each of the bowls is built up in the manner described above and results in a pressure distribution which has a maximum at a short distance from the rear edge of each bowl, where the gap has a minimum thickness.

As soon as sufficient pressure has been built up to overcome the preload on the bowls, the bowls are lifted away from the shaft at the trailing edges to give rise to a thin film of air under the bowls on which the rotating shaft is supported, as described above.

When a radial load is applied to the shaft during bearing operation, the spring levers act as follows: Each radial movement of the shaft initially tends to change the small gap thickness between the cups and the shaft, which directly changes the pressure in the air film under the cups. The movement of the shaft is therefore transmitted to the bowl via the air pressure, and the bowl tends to move radially. Due to the overlapping arrangement of the bowls, movement of the rear edge of a bowl causes a corresponding movement of the leading edge of the adjacent bowl, which is supported thereon, and the ledge height g of the bowls cannot be changed. The cups will therefore strive to move together in the direction of the shaft movement while increasing the spring load on one side of the bearing and decreasing the spring load on the other side. Since the bowls are affected by the rib 34 on each spring lever, which rib abuts directly against the bowl, and by the rib 36, which abuts the bowl via the adjacent bowl, movement of the bowls will cause movement of the reaction points of the spring levers, i.e. the ribs 34 and 36. This in turn causes bending of the lever arms between the ribs 34, 36 and the pivot points 38 of the levers relative to the housing. The bending moment thus generated in the spring gives rise to reactions on the cup via the ribs 34, 36. Since these reactions are located on opposite sides of the resulting air pressure load, they bend the cup to make it more accurately form fit to the shaft close to the rear edge.

By selecting the lengths of the lever arms between the ribs 34, 36 and the rib 38 and the stiffness of the shells and springs appropriately, the reaction loads on the shells can be caused to change the curvature of the shells relative to the axis radius and thereby the slit profile to optimize it. 2b, to produce a flattened pressure distribution, as shown in Fig. 2c, which may have a maximum pressure which is less than the peak pressure which would be generated at the unmodified gap profile. This pressure over a considerable length of the bowl surfaces greatly increases the load-bearing capacity of the bearing.

It thus appears that the cups at the bearing in question are not subject to the strong local distortion or deformation which occurs with very thin foils in foil layers, since their rigidity is such that they can withstand the fluid pressure loads between the reaction points on the springs, and thus a more general deformation. of the dish is achieved.

As shown in Fig. 5, the assembly of the cups in the housing is completed by means of rings 40, which engage with circumferentially extending projections 42 at the axial ends of each bowl, and the rings are retained in the housing by means of locking rings 44. , the cups and the spring levers thus form a complete bearing element, in which the shaft can be fitted. 7710297-8 The theory shows that greater lifting force can be achieved by using a small number of bowls of greater length, and although any number of bowls between, for example, 3 and 12 can be selected, it has been found that a suitable number is four. With four sub-cylindrical bowls, if in the unloaded state of the bearing the radius difference AR between the inner surface of the bowl and the outer surface of the shaft is equal to the ledge height at the front edges of the bowls, the tangent points where the bowls touch the shaft will be located at the rear edges of the bowls. unloaded condition.

Although the bowls have been described as having a constant radius of curvature, they can of course in their free state be elevated according to any suitable law, for example a cubic law, and the height of the ledge would then choose accordingly.

In the example described above, the bowl thickness is 3.56 mm and the shaft speed for which the bearing is constructed is only 10,000 rpm. For higher speeds and higher loads, the bowl thickness is of the order of 0.060 cm per cm shaft diameter.

In alternative embodiments, the load reaction means may have different shapes. For example, the spring levers can be replaced by resilient load reacting elements with different resilience, which are not connected to each other, to produce proportional reactions at the different places, when the cups move radially, to achieve the appropriate bending of the bowl. Alternatively, the spring levers can be replaced by rigid levers, the proportional loads being produced by the different torques of the lever arms due to different lengths of these.

However, an elastic spring lever system, such as the one described above, is preferred because the stiffness of the cups can then be calculated on the basis that the spring levers will give rise to the required suspension to compensate for shaft deflections and vibrations, while the suspension of the bowl will contribute little to this function. Of course, the rigidity of the bowls and the levers must be adjusted one after the other, but greater design flexibility is achieved.

Fig. 6 shows an alternative embodiment of the invention, in which the trays are mounted independently of each other and do not overlap each other. In this respect, the bearing is more like a rocker block bearing than a foil bearing, but the difference is that the bowls have a certain elasticity and the supports exert a controlled bending stress on the bowls to optimize the load-bearing capacity. Components corresponding to those shown in Figs. 3-5 are assigned the same reference numerals.

The bowls 24 are supported in resilient locating levers 54, which are laid around the ends of the bowls. Ribs 34 and 36 are provided on each of the resilient locating levers to be in direct contact with the cups, and a further rib 38 is provided on the rear of the spring lever to communicate with the housing 22. The rib 38 is located opposite the resultant of the gas pressure loads and, as described above, the ribs 34 and 36 move radially as the cup moves under the action of gas pressure loads, exerting bending stresses in the lever arms between them and the rib 38. The rib 38 transfers the pressure loads to the housing, and the reactions of the bowls at the ribs 34 and 36, which are located on either side of the rib 38, bend the bowl into a shape with greater load-bearing capacity. In this example, a further reaction is generated by the spring being in contact with the bowl below the leading edge, and this results in the application of a clockwise moment on the bowl in addition to the other reactions to facilitate the attainment of the optimal deformation of the bowl.

Further advantages of the invention are that with a suitable thickness of the bowl, which can be about 3.8 mm at a bearing of about 75 mm, a metal oxide can be sprayed on the bowls to reduce the friction between the bowls and the shaft. Suitable oxides for work at elevated temperatures, for example 500 ° C, are chromium oxide, cobalt oxide or a combination of nickel and chromium oxides, and the oxide layer may have a thickness of about 0.05 - 0.15 mm. An oxide coating can also be applied to the shaft surface, if desired. For use of the bearing at lower temperatures, other suitable, known friction-reducing coatings may be used.

Claims (10)

a 7710297-8 ll Patent Claim A fluid bearing device, comprising a pair of elements movably mounted relative to each other on a fluid film, which is formed as a result of the relative movement between a bearing surface on one of the elements and bearing surfaces on a plurality of resilient cups (1U; 2ü), which are supported in places along the same between the elements, characterized in that each resilient bowl (1H; 2N) has a thickness which, in relation to its other dimensions, is such that the bowl is unable to deflect locally in unsupported places due to increases in the pressure of the fluid film, and that load loading means (18; 28) are mounted between each cup and the element on which the bowls are mounted, each load reaction means being arranged to abut against the element on which the bowls are mounted, at a fixed support point (D), located between the center of the bowl and a trailing edge thereof, and depending on increases in the fluid film pressure produce at least two reaction forces (B, C) p on the bowl, a first (C) of which is applied to the trailing edge of the bowl and a second (B) is applied to a point which lies between the center of the bowl and the leading edge thereof and which also lies on the side of the resultant (A) for the pressure in the fluid film opposite to the first reaction force (C), to bend each bowl like a rigid beam and change the shapes of the bowls so that the bearing surfaces of the bowls adhere more closely to the bearing surface of one of the elements in zones of minimal fluid film thickness to increase the bearing load capacity. Fluid bearing device according to claim 1, characterized in that the pair of elements comprises a shaft (10; 20) and a cylindrical housing (12; 22), inside which the shaft is rotatably mounted, the bowls (1U; 2U ) are mounted on the house. Fluid storage device according to claim 2, characterized in that a third reaction load position is arranged on each bowl. 4. A fluid storage device according to claim 2, characterized in that the load reaction means are in the form of resilient levers (18; 28), arranged between each bowl and the housing, the levers (28) abutting against the cups. at the places of said reaction forces and abuts against the housing at a place between these places to generate the reaction forces. S. Fluid bearing device according to claim U, characterized in that the levers (28) extend in the circumferential direction of the housing (22), each lever having an axial projection (38) facing radially outwardly in contact with the housing and two axial projections (3ü, 36), which extend radially inwards in contact with the cups (24) to produce said reaction forces, the radially outwardly facing projection being located in the circumferential direction between the inwardly facing projections 1 Fluid storage device according to one of Claims 2 to 5, characterized in that the leading and trailing edges of the cups (1U; 2ü) are cut away to form ledges (21), whereby the cups are mounted in excess position at each other at the leading and trailing edges, the heights of the ledges (hl and hg) at the leading and trailing edges differing to a predetermined degree, so that the leading edge of each bowl is kept free from the shaft to a predetermined degree, whereby each bowl delimits a gap (9) with the surface of the shaft with a profile which tapers towards the rear edge of the bowl. 7. A fluid bearing device according to any one of claims 2-6, characterized in that the cups are cylindrical and have a slightly larger radius than the shaft. Fluid storage device according to claim 4, characterized in that the cups (2U) and the levers (28) are locked against rotation inside the housing by means of pins (30) which lock the housing and the cups and which extend through the levers. Fluid storage device according to claim 4, characterized in that the levers (54) are resilient and provided with hooks at their ends, which are arranged to grip the ends of the cups (ZÄ). 10. Fluid storage device according to any one of claims 1-9, characterized in that the fluid is constituted by air. PROMISED PUBLICATIONS: US 3,711,169 (308-73)