GB2214993A - Fluid seals and bearings - Google Patents

Abstract

A shaft seal or bearing comprises an annular reaction member 16 and a co-operating deflectable member 18 wherein the deflectable member 18 deflects under the influence of fluid pressure in order to develop a convergent surface slope adjacent the shaft. The seal or bearing may be used in a pressure range from 10 to 10,000 p.s.i. depending upon the material from which the reaction member and annular member are made. <IMAGE>

Description

Fluid Seals and Bearings The present invention relates to a seal and/or bearing for a rotatable shaft and where the operation of such depends upon a deflectable member or members contained in the seal and/or bearing.

Seals and bearings having a deflectable member either for the reduction of seal to shaft clearance or the generation of a convergent hydrodynamic oil film are -known. Heretofore the axial convergence of a bearing or seal surface has been developed by hoop strains in a radially thin member.

According to the present invention a shaft seal or bearing comprises an annular reaction member and a co-operating deflectable member wherein the deflectable member deflects under the influence of fluid pressure principally by toroidal rotation in order to develop a convergent surface slope.

In a bearing the reaction member may be a rigid part of the bearing housing, the deflectable bearing member deforming under the influence of the supplied fluid pressure and further deforming locally due to fluctuations in the applied load on the shaft.

The reaction member of a seal moves with the deflectable member and is itself sealed against a rigid seal housing member.

Preferably the reaction member and deflectable member may be metal.

A seal used maybe used in the pressure range from 10 to 10,000 psi.

At the lower end of the operating pressure range plastics or elastomeric materials may in some circumstances be used for the deflectable member.

In order that the present invention may be more fully understood examples will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a section through a seal according to the present invention; Figure 2 shows in operation the upper half of the seal in Figure 1; Figure 3 shows a section through half of a pair of bearings according to the present invention; and Figure 4 which shows the bearing of the left hand side of Figure 3 in operation.

Referring now to Figure 1 and where a shaft 10 is shown having a seal assembly indicated generally at 12. The seal assembly comprises a housing member 14, a reaction member 16, a deflectable seal member 18 and spring biassing means 20. The seal assembly is retaining fluid at a pressure PS in the region 22 from escaping to the outside of the assembly designated generally at 24 and at ambient pressure PA. The seal is shown in Figure 1 in a static condition, i.e. where PS approaches PA and the deflectable element 18 is in its relaxed condition. It should also be noted that the various gaps, clearances and angular deflections are shown greatly exaggerated.

The housing member 14 includes a first annular face 26 substantially normal to the axis 28 and a second annular face 30 having a groove 32 for an "0" ring seal 34. A third annular face 36 is also included. The reaction member 16 has a first annular face 38 substantially normal to the axis 28 and which co-operates with the face 30 and seal 34. The reaction member also has a second annular face 40 having a groove 42 and "0" ring seal 44. The reaction member has an annular nosepiece 46 which is urged against the face 26 by the springs 20 via the deflectable member 18. The nosepiece 46 has a series of holes 48 therein in the radial direction the purpose of which-holes are to vent the annular space 50 to ambient pressure PA. The member 16 also has an inner annular edge 52 which provides a pivot for the deflectable seal member 18 during operation.A series of holes 54 vent the annular space 56 between the reaction member 16 and the deflectable members 18 to ambient pressure PA. The reaction member further includes an axially extending annular face 58. The deflectable seal member 18 has an angled annular face 60 which co-operates with, by pivotal and sliding movement, the edge 52 of the reaction member. A radial face 62 co-operates with the "0" ring seal 44. The member 18 has a bore 64 which is machined to a close clearance fit with the shaft 10. The member 18 has a second radial face 66 and an axially extending annular face 68. The seal face 60 is urged against the edge 52 by the spring 20 which themselves react against the third radially extending face 36 of the housing 14.

The housing is, or course, split in any convenient manner, for example, radially between faces 30 and 36 (not shown) to allow assembly of the components.

As indicated in Figure 2 operation of the seal is caused by the pressure PS in the region 22 rising above the ambient pressure PA in the region 24. As pressure PS rises toroidal rotation of the seal member 18 occurs due to the net hydraulic moments caused by pressures acting on faces 68,66,64 and 58, the latter transferred through the contact at edge 52. The member 18 rotates mainly about its cross section centroid and slides with respect to the edge 52. The effect of this is to bring the leading edge 70 of the member 18 into closest proximity to the shaft surface 72 and move the trailing edge 74 away from the shaft so forming a convergent hydrostatic film 76.

The deflectable seal member 18 is able to move with the shaft 10 by movement of the reaction member 16 relative to the housing member 14 so as to allow the whole assembly to follow shaft radial movements.

The net forces acting on the annular faces 58 and 68 are balanced by the load in the fluid film 76. The load on face 58 however is reacted on the edge 52 which, as a result of those equivalent forces in the film 76 cause a net rotational couple on the member 18 in an anti-clockwise direction. Thus a convergent film is formed.

If the shaft moves radially, the convergence of the film is such as to generate a net force on the assembly to overcome the frictional forces resisting radial movement and the whole floating assembly tends to follow the shaft, thus maintaining close clearances all around the shaft.

Figure 3 shows a bearing having two deflectable members 100. Each member has an inner annular bearing surface 102, on outer annular face 104, an inner radial face 106, an outer radial face 108, a leading edge 110, a trailing edge 112 and an angled, annular face 114. The members 100 are contained within a housing 116 which has a supply of pressurised fluid via a conduit 118 into the region 120. The housing further comprises a radial face 122 having a groove 124 and "0" ring seal 126 for each member 100. A reaction endge 128 co-operates with the face 114. The face 108 co-operates with the "0" ring seal 126 to prevent escape of fluid to the outside of the housing between the faces 108.and 122. A shaft -130 is supported by an oil film 132 between the surface 102 and the shaft surface 134. The annular space 136 is vented to ambient pressure in any suitable manner.

In operation fluid, for example, oil is supplied under pressure to the region 120 via the conduit 118. As in the case of the seal fluid pressure in the region 120 causes the elements 100 to rotate toroidally and produce a covergent hydrostatic oil film as shown in Figure 4.

The leading edge 110 approaches the shaft surface 134 whilst the trailing edge 112, depending upon the geometry may remain substantially stationary or move away from the shaft surface. The load imposed on the bearing via the shaft also affects the film and bearing geometry. If the shaft load increases upwardly as indicated by the arrows 138 further toroidal rotation of the bearing member 100 occurs thus increasing the load in the oil film 132. Similarly the half (not shown) of the bearing will undergo a corresponding decrease in the oil film load resulting in less toroidal deflection in the lower half.

The deflectable members 100 may not necessarily be accommodated in a single housing member as shown but may be combined singly with a seal member of the type shown in Figure 1, for example.

Claims (7)

1. A shaft seal or bearing comprising an annular reaction member and a co-operating deflectable member wherein the deflectable member deflects under the influence of fluid pressure principally by toroidal rotation in order to develop a convergent surface slope.

2. A bearing according to Claim l wherein the reaction member is a part of the bearing housing.

3. A bearing or seal according to either Claim 1 or Claim 2 wherein the reaction member and deflectable member are made of metal.

4. A bearing or seal according to either Claim 1 or Claim 2 wherein the deflectable member is made of a plastics or elastomeric material.

5. A bearing or seal according to any one preceeding claim wherein the deflectable member is held in contact with the reaction member by resilient biasing means.

6. A bearing substantially as hereinbefore described with reference to the accompanying specification and Figures 3 and 4 of the drawings.

7. A seal substantially as hereinbefore described with reference to the accompanying specification and Figures 1 and 2 of the drawings.