GB2070156A

GB2070156A - Hydrostatic Bearing

Info

Publication number: GB2070156A
Application number: GB8106161A
Authority: GB
Original assignee: Escher Wyss AG
Current assignee: Sulzer Escher Wyss AG
Priority date: 1980-02-26
Filing date: 1981-02-26
Publication date: 1981-09-03
Also published as: ES8205964A1; SE8100717L; BR8100588A; JPS56131891A; AR222279A1; FR2476773A1; FI810581L; IT1135484B; ES499779A0; IT8119779A0; NL8100913A

Abstract

The invention relates to hydrostatic bearings and seeks to provide a bearing design which affords a reduced consumption of pressure medium without increased risk of bearing breakdown as a result of inlet path blockage. According to the invention an hydrostatic bearing comprises a bearing portion (1) provided with bearing pockets (6), and a mounted portion (2) with a bearing surface (3). Pressure medium is supplied through an inlet duct (7), which extends towards the bearing surface (3) of the mounted portion (2). The end faces (10) of the inlet duct (7) and the corresponding surface (3<1>) of the mounted portion (2) form an annular throttle gap (11). A choke valve (12) may be mounted in series with the throttle gap (11) in the inlet duct (7). Because of the throttle gap (11), the effective cross section of the inlet duct (7) or choke valve (12) if used, can be made larger, thus reducing the risk of blockage of the inlet path. The annular throttle gap (11) is self-cleaning, since it consists of two parts (1) and (2) moving relative to each other. <IMAGE>

Description

SPECIFICATION Hydrostatic Bearing This invention relates to a hydrostatic bearing in which a bearing portion and a mounted portion define juxtaposed bearing surfaces the portions being movable relative to each other, and the bearing portion defining at least one hydrostatic bearing pocket at its bearing surface for receiving a medium under pressure through an inlet duct.

A bearing of this kind is known, for example, from Swiss Patent Specification No. 541 088.

The bearing portion of the hydrostatic bearing shown in Figure 2 of the drawings accompanying this specification comprises a single bearing pocket to which the pressure medium is supplied through a throttling inlet duct. The throttling effect is achieved by the narrow cross section of the inlet duct.

Since hydrostatic bearings became known, designers have been at great pains to minimize the throughflow of pressure medium required for satisfactory functioning of the bearing, which is major component of the energy requirement of the bearing. The throughflow of pressure medium can be reduced by increasing the throttling effect of the inlet duct for pressure medium to the bearing pocket. Attempts to achieve this goal by progressively reducing the cross section of the inlet duct and/or by increasing the length of the inlet duct run into major problems because of the small cross-sections and/or duct lengths that are required. On the one hand, the production of fine ducts of this kind leads to a complex form of construction, and the required accuracy is extremely difficult, sometimes virtually impossible to achieve, particularly in mass production.On the other hand, as the duct is made increasingly fine, the hydrostatic bearing becomes more prone to breakdown as a result of blockage. This risk of blockage is substantially independent of the choice of pressure medium, since blockage is usually caused by very fine particles formed by erosion during the circulation of the pressure medium. As soon as the duct leading to the bearing pocket becomes blocked, the pressure in the bearing pocket collapses and this invariably leads to breakdown of the bearing.

The aim of the present invention is to provide an hydrostatic bearing with a throttling inlet duct for the pressure medium, which can satisfactorily be produced mechanically with the throttling effect required for a minimum throughflow of pressure medium and which is also more reliable, as the abovementioned danger of blockage is substantially reduced. To this end, the invention provides a bearing portion and a mounted portion defining juxtaposed bearing surfaces, the portions being movable relative to each other, and the bearing portion defining at least one hydrostatic bearing pocket at its bearing surface for receiving a medium under pressure through an inlet duct which extends to its bearing surface, the end of the inlet duct and the bearing surface of the mounted portion forming an annular throttle gap through which a said medium unit into said at least one bearing pocket.The housing may include a choke valve in the inlet flow path for pressure medium to the annular throttle gap.

Such a choke valve may be located in the inlet duct, or upstream thereof. Because the annular throttle gap is formed by two parts moving relative to one another, the gap may be made as narrow as desired, without risk of causing a blockage of the supply of pressure medium to the bearing pocket. As a consequence of this relative movement, any impurities located in the throttle gap can be immediately eliminated. Further, because of the throttle gap, the effective cross section of the inlet duct, or choke valve when used, can be made larger, thus reducing the risk of blockage of the choke valve or inlet duct.

In one embodiment of the invention, the inlet duct passes through the base of the bearing pocket. In this construction, all the pressure medium supplied flows first into the bearing pocket from the throttle gap, and only afterwards does it flow away over the end faces of the pocket walls.

In a number of applications, the bearing portior of a bearing according to this invention can comprise a base part and a support part which are displaceable relative to each other in the direction of support and together define a pressure chamber which is acted upon by the pressure medium via a pump. The inlet duct may extend from this chamber, the chamber being the source of pressure medium for the bearing pocket.

The inlet duct may comprise a separate component which is removably mounted in the bearing portion. Typically, such a component has a screw thread mateable with a complementary screw thread in the bearing portion. This feature can further simplify mass production.

If a plurality of bearing pockets are provided, the manufacturing process can be simplified in two ways by the fact that only choke valve need be provided in the inlet flow path of pressure medium thereto. Firstly, a smaller total number of choke valves need be produced, and secondly, the cross section of such choke valves can be made larger than it would be in a bearing of the same size in which each bearing pocket has its own individual choke valve associated with it.

Embodiments of the invention will now be described by way of example, and with reference to the accompanying simplified drawings wherein: Figure 1 is a cross section through a first bearing according to the invention, Figure 2 shows a plan view of the bearing portion of the bearing of Figure 1, on a smaller scale, Figure 3 is a cross section through a second bearing according to the invention, Figure 4 shows a plan view of the support member of the bearing of Figure 4, on a smaller scale, Figure 5 is a cross section through a third embodiment of the invention, Figure 6 is a cross section through a fourth embodiment of the invention, and Figure 7 is a plan view of the support member of the bearing of Figure 5 or Figure 6 on a smaller scale.

In the embodiments which follow, like parts have been given the same reference numerals.

The hydrostatic bearing shown in Figure 1 comprises a bearing portion 1 and a mounted portion 2 with a bearing surface 3. The arrows 4, 5 show, by way of example, the directions in which the bearing portion 1 and the mounted portion 2 of the hydrostatic bearing illustrated move relative to each other. The hydrostatic bearing shown is also equally suitable for cases wherein either the bearing portion 1 or the mounted portion 2 moves whilst the other part is stationary As can be seen from Figures 1 and 2, the bearing portion 1 comprises, on its side facing the bearing surface 3 of the mounted portion 2, a plurality of hydrostatic bearing pockets 6. A pressure medium is supplied to each bearing pocket 6 through an inlet duct 7.

In order to obtain an automatically adjusted bearing gap between the end faces 8 of the bearing pocket walls 9 and the corresponding bearing surfaces 3 of the mounted portion 2 when a plurality of bearing pockets 6 are supplied by one pump, the pressure medium is fed to the bearing pockets 6 in throttled manner. The more the pressure medium is throttled, the thinner the hydrostatic bearing gap which is formed, and the lower the unavoidable throughflow of pressure medium which can be obtained. On the other hand, the throttling must be such that there is no contact between the parts 1 and 2 moving relative to each other.

In order to fulfill all these criteria without any restrictions, whilst avoiding throttle cross section which are so small that, on the one hand, they can be almost impossible to manufacture and, on the other hand, fail during operation of the hydrostatic bearing owing to blockage, the inlet duct 7 extends as far as the bearing surface 3 of the mounted portion 2. The end face 10 of the inlet duct 7 and the bearing surface 3' of the mounted portion 2 corresponding to the end face 10 form an annular throttle gap 11 for the pressure medium flowing out of the inlet duct 7 and into the bearing pocket 6.

To ensure that there is a defined throughflow of pressure medium and hence a defined bearing gap between the end faces 8 of the bearing pocket walls 9 and the corresponding bearing surface 3 of the mounted portion 2, the inlet duct 7 includes at least one point, a choke valve 12 which is mounted in series with the throttle gap 1 or else the inlet duct 7 could itself act as a choke valve of this kind, on account of its dimensions. The choke valve 12, which may thereafter be formed by the dimensions of the inlet duct 7 or by a constrictcon formed in the inlet duct 7 especially for this purpose, thus contributes to the stablilsation and reliability of the hydrostatic bearing.

The main advantage of this invention is that the contribution to the throttling effect to be made by the choke valve 12 is greatly reduced, since additional throttling is effected by an annular throttle gap 1 The throttling effect of the throttle gap 11 can be varied within wide limits by the choice of the ratio of the diameter of the inner boundary line of the end face 10 to the diameter of the outer boundary line of the end face 10. The contributions of the choke valve 12 and throttle gap 11 to the throttling of the pressure medium supplied to the bearing pockets 6 can thus be matched to the particular application of the hydrostatic bearing, both in terms of the correlation between the contributions to throttling and also in terms of the throttling action as a whole.

As can also be seen from Figures 1 and 2 the inlet duct 7 passes centrally through the base of the bearing pockets 6. This ensures that the pressure medium supplied to a bearing pocket first flows into the pocket and only then flows outwards over the end faces 8 of the walls 9 of the bearing pockets.

Figures 3 and 4 show an hydrostatic bearing which is suitable, for example, for internally supporting a hollow cylindrical part 2 rotating substantially in the direction of the arrow 4. The bearing portion 1, shown as a non-rotating part, consists of a base member 11 comprising groove 13 in which a support member 12 displaceable relative to the mounted portion 2 is guided in sealed manner. The base member 11 and support member 12 together define a pressure chamber 14 which is acted upon by the pressure medium by means of a pump (not shown). In this arrangement, the support member 12 can adapt to one-sided stresses on the mounted portion 2 within certain limits, by being inclined towards the base member 1'.By varying action of the pressure medium on the pressure chamber 14, the force to be exerted by the mounted portion 2 in the direction of the arrow 1 5 can be increased or reduced. The pressure chamber 14 permits movement of the mounted portion 2 in the direction of the arrow 1 5.

As can be seen from Figures 3 and 4 together the support member 12 has a total of four bearing pockets 6. Only one inlet duct 7 is provided for supplying these four bearing pockets 6. Webs 16 divide the individual bearing pockets 6 from one another. The inlet duct 7 passes through the webs 1 6 at the point where they intersect. Thus, a plurality of bearing pockets can be supplied at the same time with a single bore. A number of bearing pockets increase the reliability of the hydrostatic bearing.

The embodiments shown in Figures 5 to 7 also comprise four bearing pockets 6. In Figure 6, each bearing pocket 6 is connected by a separate inlet duct 7 to the pressure chamber 14. In Figure 5, each of these inlet ducts 7 has its own choke valve 12. The end of each inlet duct 7 extending up to the mounted portion 2 is made from a part which can be screwed in. Thus, these parts can be mass-produced in a rationalised manner and can easily be replaced, if necessary.

In the alternative embodiment shown in Figure 6, only one choke valve 12 is provided for all four inlet ducts 7 together. With the hydrostatic bearing having the same construction in Figures 5 and 6, the choke valve 12 in Figure 6 has to let through four times as much pressure medium.

Obviously, a choke of this kind is considerably less exacting both in its manufacture and in its operational reliability.

As can be seen from Figure 7, in particular, the inlet ducts 7 do not open into the central region of the bearing pockets 6. Instead, the inlet ducts 7 are mounted so that the ends, extending right up to the mounted portion 2, are displaced towards the centre of the entire bearing portion 12. This central arrangement of the inlet ducts 7 results in an increase in the self stabilising properties of the hydrostatic bearing in many instances.

Claims

1. An hydrostatic bearing comprising a bearing portion and a mounted portion defining juxtaposed bearing surfaces, the portions being movable relative to each other, and the bearing portion defining at least one hydrostatic bearing pocket at its bearing surface for receiving a medium under pressure through an inlet duct which extends to its bearing surface, the end of the inlet duct and the bearing surface of the mounted portion forming an annular throttle gap through which a said medium unit flow into said at least one bearing pocket.

2. A bearing according to Claim 1 wherein the inlet duct passes through the base of the bearing pocket.

3. A bearing according to Claim 1 or Claim 2 wherein the bearing portion comprises a base member and a support member which are displaceable relative to each other and together define a pressure chamber from which the inlet duct extends.

4. A bearing according to any preceding Claim wherein the inlet duct comprises a separate component which is movably mounted in the bearing portion.

5. A bearing according to Claim 4 wherein the component has a screw thread mateable with a complimentary screw.

6. A bearing according to any preceding Claim including a choke valve in the inlet flow path for pressure medium to the chamber throttle gap.

7. A bearing according to Claim 6 wherein the bearing portion defines a plurality of bearing pockets, and wherein a single choke valve is provided in a single inlet duct which divides to direct a said medium to said plurality of inlet ducts.

8. An hydrostatic bearing substantially as described herein with reference to Figures 1 and 2; Figures 3 and 4; Figure 5 or Figure 6 of the accompanying drawings.