WO1995025903A1

WO1995025903A1 - Bearings

Info

Publication number: WO1995025903A1
Application number: PCT/GB1995/000635
Authority: WO
Inventors: Robert Topping Knox
Original assignee: Vickers Plc
Priority date: 1994-03-23
Filing date: 1995-03-22
Publication date: 1995-09-28
Also published as: GB9405754D0

Abstract

The invention relates to a so-called self-contained bearing assembly capable of continuous running with the minimum of maintenance procedure, said bearing using a minimal amount of lubricant. A shaft (2) rotates in bush members (6a, 6b) suitably supported in a housing (14) which encloses a two-part sump (16, 18). A lubricant settling chamber (26) is contained within the upper portio (22) of the housing (14). Lubricant passes from an inlet (30) to an outlet (32) of the housing to an air-cooled heat exchanger (36) and is returned via the inlet (30). The lubricant system is dual-action having an entrainment means (20) capable of supplying adequate lubricant in a first mode at low, start-up, speeds and a second, normal, mode. The means (20) comprises a tray member (44) rotatable within the shaft (4) and having a flanged wall (46) which dips into the lubricant in the sump (16). Stationary scoop means (52) entrains and directs lubricant onto the bearing components and also into the settling chamber (26) for de-aeration. The shaft (2) may be the output shaft of a motor (35) having a cooling fan (37) arranged to provide an air-cooling effect on the heat-exchanger (36).

Description

BEARINGS

The invention is concerned with improvements in or relating to bearings, particularly but not exclusively so-called self-contained bearings, i.e. of the kind which are capable of maintaining self-supplied lubrication without the involvement or support of external lubricating units.

Problems encountered with such bearings arise from a variety of circumstances. For example, a bearing may be required to operate at a high speed thereby generating heat in the bearing surfaces at such a level that the casing that contains the bearing is incapable of dissipating this heat even with air forcibly drawn over it. Solutions which require water-cooling of the lubricant may be impracticable in environments where water is a scarce commodity.

Additional problems may also be encountered at high operational speeds where the rotational rate is such as to cause excessive foaming of the lubricant resulting in short lubricant life and poor bearing durability.

The present invention provides, in one of its several aspects, a bearing assembly adapted to support a shaft for rotation about an at least substantially horizontal axis, said bearing assembly comprising a housing, bush supports, bush members mounted within said bush supports and adapted to surround said shaft in use, sump means adapted to contain liquid lubricant, annular, dual-action lubricant entrainment means mounted in use upon the shaft for rotation with respect to the bush members, said entrainment means being adapted to entrain a first quantity of lubricant from said sump means at a first speed of rotation and to entrain at a second, higher, speed of rotation a second quantity of lubricant to be circulated in a continuous path around faces of said bush members, a heat-exchange apparatus adjacent said housing and conduit means to carry lubricant leaving said faces to said heat-exchange apparatus and to return said lubricant to an inlet of the housing for re-circulation in said path, said conduit means comprising a main portion and a branch portion including at least one orifice through which lubricant passes, said orifice(s) leading to a settling chamber provided within the housing for de-aerating lubricant prior to return to the main portion of the conduit means.

The invention further provides, in another of its features, a bearing assembly as described above in combination with a rotatable shaft, said shaft comprising the output shaft of a motor having a cooling fan, said heat exchanger being air-cooled and positioned adjacent said cooling fan of said motor.

Advantageously, said settling chamber is provided with overflow means to regulate the quantity of de- aerated lubricant retained therein, said chamber further acting to provide a secondary supply of lubricant during a period of slow-running of the shaft.

Preferably, said dual-action lubricant entrainment means may comprise an annular tray member adapted to extend in use radially of the shaft to which it is securable, said tray member being provided with a cylindrical wall extending axially from the periphery thereof, said cylindrical wall having at an annular free edge thereof an inturned annular flange defining a circular aperture facing said bush members, and a stationary gathering means mounted within the housing so as to enter a recess in the entrainment means formed by the flanged cylindrical wall so as to deflect lubricant therefrom in use into said continuous path so as to provide propulsion to the lubricant present in said path.

Advantageously, said wall of said annular tray member may be arranged to dip into lubricant provided, in use, within said sump means so as to entrain lubricant on an external surface of the wall as the tray member rotates so as to provide a supply of lubricant at start-up speeds of the assembly.

Conveniently, valve means may be provided which are normally biassed in an open position at rest and at start-up or slow-running speeds but which are closed by the pressure of lubricant travelling in said continuous path at full operating speeds.

Other features of the invention will become apparent from the following description of an example of an assembly according to the invention which is intended to be read with reference to the drawings. It will be understood that the description, which for the sake of convenience includes reference to parts associated with said means in use, is given by way of example only and not by way of limitation.

In the drawings:-

Figure 1 is a view in longitudinal section of an assembly according to the invention;

Figure 2 is a diagram illustrating the position of the assembly in use in relation to an arrangement for transferring lubricant to a heat exchanger;

Figure 3 is a composite cross-sectional view of the assembly of Figure 1 in a start-up mode, taken on lines X-X (left hand side) and Y-Y (right hand side) ;

Figure 4 is a composite view similar to Figure 3 showing the assembly in operational mode; and

Figure 5 is a fragmentary view of a branch portion of conduit means for transferring the lubricant in the bearing.

A shaft 2 is plain-journalled at 4 for rotation in bush members 6a, 6b about a horizontal axis. The bush members are supported in bush support members 8a, 8b and are provided with location faces 10 adapted to limit axial movement of the shaft 2 by contact with shaft flanges 12 thereof, although it will be understood that a suitable bearing arrangement may be devoid of such surfaces or may incorporate thrust bearing surfaces if necessary. The bush members 6a, 6b and the bush support members 8a, 8b are mounted in a housing 14 which encloses a two part sump 16, 18, and a dual action lubricant entrainment means indicated generally at 20 in Figure l and to be partially received in the sump path 16.

The housing 14 comprises an upper portion 22 and a lower portion 24 which encloses the sump portions 16, 18. A lubricant settling chamber 26 is contained within the upper housing portion 22.

Labyrinth seals 28 surround apertures in the housing through which the shaft 2 passes, the seals serving effectively to prevent any loss of lubricant at these positions. Lubricant passes through the assembly from an inlet 30 through a path as will be described in detail below to and outlet 32 and, as illustrated diagrammatically in Figure 2 is circulated via a line 34 to a heat exchanger 36, which in the present example is an air-cooled heat exchanger, the cooled lubricant then returning to the housing 14 via said inlet 30.

It will be appreciated that the labyrinth seals 28 are dimensioned so that when the shaft 2 is rotating there is a minimum clearance provided between the seals and the shaft. This prevents wear and avoids failure of the seals. Since the efficient provision of lubricant to the bush members 6a, 6b as herein described prevents metal-to-metal contact with the shaft when it is rotated, it is apparent that the arrangement is virtually maintenance free and may be allowed to run unattended for very long periods of time. In the present example, the bearing assembly is supporting an output shaft (shaft 2) of an air-cooled electric motor 35 and may conveniently be secured to a motor casing thereof adjacent stator and armature means of the motor 35 . The motor is provided with an electric fan 37 the air current from which is arranged to impinge upon surfaces of the heat exchanger 36 . The proximity of this cooling fan, however, may cause a suction effect on the lubricant circulating in the bearing assembly and therefore the housing 14 is provided with a baffle 38 which although not in contact with the shaft, prevents the unwanted suction effect on the lubricant. An air passage 40 provided in the lower casing portion 24 allows air to be preferentially drawn through.

The construction of the dual-action lubricant entrainment means 20 will now be described. Secured to the shaft 2 by means of a locking screw 42, is an annular tray member 44 having a cylindrical wall 46 at the peripheral edge thereof.

The wall 46 has an inturned flange 48 at its free edge so as to define a circular opening facing to the right as viewed in Figure 1, i.e. towards the bush members 6a and 6b. At the lowest portion of its periphery, the tray member 44 enters the sump portion 16. The sump 16 is provided with an arcuate weir 50 positioned between the sump portions 16 and 18, the weir partially overhanging the flange 48. Turning to Figures 3 and 4, it will be seen that the outline of the tray member wall 46 is indicated at a position in proximity to a stationary lubricant gathering means 52 arranged to enter the recess of the tray member formed by the flanged wall 46 and to scoop up lubricant from the sump portion 16 as will be explained below. The means 52 comprises an open-ended hollow cylindrical scoop communicating with the outlet 32. The scoop 52 is mounted in the housing 14 so as to lie at an angle to the wall 46 so that the open end faces against the direction of rotation of the tray 44 (see in particular Figure 4) .

Lubricant returning to the housing 14 through the inlet 30 passes inwardly of the bearing assembly to a channel 54 formed in the bush support member 8b. The bush members 6a, 6b are insulated from the bush support members 8a, 8b respectively by means of a portion of sheet insulating material 56, 58. An insulated pin 60 prevents rotation between the bush member 6a and its support member 8a which is formed integrally with the housing 14. Relevant rotation between the bush member 6b and its support member 8b is therefore also prevented.

A passage 62 leads from the channel 54 to the faces of the bush members 6a and 6b that confront the rotational shaft. Lubricant in this portion of the circulating path to be described below then returns to the sump portions 16, 18. Lubricant (oil) returning to the housing 14 from the heat exchanger 36 passes, as mentioned above, along a path through the inlet 30. A branch portion of the path is formed by a vertical pipe 64 (Figure 5) provided with orifices 66 through which the lubricant passes into the interior of the upper portion of the housing 14, to the settling tank 26, this action tending to enhance the reduction of air entrained in the oil which results in a tendency for the oil to foam. De-aerated oil then accumulates in the tank from which it overflows a lip of a down-tube 68, which is in communication with the sump 16, 18.

The operation of the bearing assembly will now be described.

It will be appreciated that in an arrangement where surfaces are in contact during high speed rotational operation, the rotational rate of lower speed for example during start-up may not be adequate to ensure proper levels of lubrication at those lower speeds. There are therefore two available modes of lubrication within the assembly, described below with principal reference to Figure 3 (low speeds) and Figure 4 (higher speeds) respectively.

At the start of operation the sump portions 16, 18 contain lubricant (oil) to a level indicated at A in Figures 1 and 3. As the shaft 2, supported on the bush member 6b, starts to rotate in the direction of arrow R, together with the entrainment means 20, oil from the sump portion 16 is taken up on the outside surface of the wall 46 due to viscosity (see arrow B in Figure 3, in which the position of the wall 46 is shown superimposed upon the sump portion 18) .

Oil is thus carried upwards into the interior of the upper housing portion 22.

It is then at least partially removed from the wall 46 by the action of a deflector/scraper member 70 provided on the portion 22 which deflects the oil rightwardly and downwardly as shown in Figure 1 by arrows C through an aperture 72 in a flange of the bush support member 8a. The oil then flows downwardly over the bush support 8a (arrows D) and through an aperture 76 of a flange of the casing portion 22. The aperture 76 is adapted to be closed, as will be explained below, by a pivotally mounted valve member 78 which is normally in an open position due to gravity.

Oil then travels into the channel 54 and, importantly, into the passage 62 to the faces of the bush members 6a, 6b in contact with the rotating shaft. Referring to Figure 1, the oil then leaves the faces of the bush members in axial directions and drains down (arrows E) to the sump.

Thus the faces of the bush members are protected from undue wear in the build-up to full operational speeds which may be example by in the region of 3600 r.p.m. with a shaft journal diameter of 140 mm.

During operation at normal running speed, the following oil circulation path builds up and effectively takes over from the circulation path described above.

Thus as the shaft 2 and the entrainment means 20 gather rotational speed, oil is also being entrained in the recess formed by the flanged wall 46 of the tray member 44, initially to the level A. Oil is thus forced into the open end of the scoop of the lubricant gathering means 52 as shown in Figure 4 at arrow F this force producing a pump action causing the oil to take the path indicated by arrows G to enter the outlet 32 and the line 34 as explained earlier in this specification. When cooled by the heat exchanger 36, the oil returns to the assembly through inlet 30 (arrows H) to enter the channel 54 and the passage 62 for lubrication of the bush member faces and return downwards (arrows E) to the sump portions 16, 18.

At this time, it will be appreciated that the pressure of oil in the circulating path is high enough that the oil present at the junction of the channel 54 and the passage 62 is sufficient to force the valve member 78 to close the aperture 76.

It will be appreciated that the operation of the scoop acts to reduce the quantity of oil entrained in the recess so that although this is constantly renewed by the action of the tray member dipped into the oil in the sump portion 16, the level falls from the start-up level A to the normal running level J.

This lower oil level J is maintained by the position of the weir 50 over which the oil runs from the sump 18 as shown in Figure 1 at arrow K back into the recess to be picked up again by the scoop 52.

If the shaft loses rotational speed the scoop will not act so effectively as a pump and oil will tend to build up in the sump portions 16, 18. During such period of slow running, the pick-up of oil by the external surface of the wall 46 will again return to an effective level and will prevent the bush surfaces becoming starved of oil.

At high rotational speeds of operation, there is a tendency for air within the housing to be taken up by the oil causing it to foam. The problem has been minimised by previously suggested lay-outs by drawing off oil from the housing and allowing it to remain in a settling or de-aerating tank. This is rendered unnecessary by the arrangement of the assembly of the present invention in which as the oil enters the housing through inlet 30, a proportion of the oil is forced into a branch portion of the course of the main circulation path indicated by arrows H.

The branch portion is formed by the vertical pipe 64 and the down tube 68, the oil being forced to pass through the orifices 66 and in doing so to release much of its air. The oil then remains as a reserve of oil in the settling chamber 26 at a level between the maximum level L and the minimum level M. However, oil will travel down the tube 68 to return to the sump portions 16, 18 until the oil falls to the minimum level M permitted by the height of the tube 68. Oil then remains at this height during the period of high speed running, since the aperture 76 is closed.

It will be understood that in operation more than one bearing normally supports the rotating shaft of an electric motor. It is therefore not always necessary to provide for example each of two bearing assemblies with the passageways and conduits associated with the lubricant pathway through the heat exchanger 36. Where one bearing assembly is fully provided as illustrated in the example described above, the second bearing assembly may be less complex in construction, not requiring the system of conduits 34 from the heating exchanger but instead receiving cooled lubricant from the first assembly.

Various modifications may be made within the scope of the invention as defined in the following claims.

Claims

CLAIMS :

1. A bearing assembly adapted to support a shaft for rotation about an at least substantially horizontal axis, said bearing assembly comprising a housing, bush supports, bush members mounted within said bush supports and adapted to surround said shaft in use, sump means adapted to contain liquid lubricant, annular, dual-action lubricant entrainment means mounted in use upon the shaft for rotation with respect to the bush members, said entrainment means being adapted to entrain a first quantity of lubricant from said sump means at a first speed of rotation and to entrain at a second, higher, speed of rotation a second quantity of lubricant to be circulated in a continuous path around faces of said bush members, a heat-exchange apparatus adjacent said housing and conduit means to carry lubricant leaving said faces to said heat- exchange apparatus and to return said lubricant to an inlet of the housing for re-circulation in said path, said conduit means comprising a main portion and a branch portion including at least one orifice through which lubricant passes, said orifice(s) leading to a settling chamber provided within the housing for de-aerating lubricant prior to return to the main portion of the conduit means.

2. A bearing assembly as claimed in claim 1, in combination with a rotatable shaft, said shaft comprising the output shaft of a motor having a . cooling fan, said heat exchanger being air-cooled and positioned adjacent said cooling fan of said motor.

3. A bearing assembly as claimed in either one of claims 1 and 2, wherein said settling chamber is provided with overflow means to regulate the quantity of de-aerated lubricant retained therein, said chamber further acting to provide a secondary supply of lubricant to said sumps during a period of slow-running of the shaft.

4. A bearing assembly as claimed in any one of the preceding claims wherein said dual-action lubrication means comprises an annular tray member adapted to extend in use radially of the shaft to which it is securable, said tray member being provided with a cylindrical wall extending axially from the periphery thereof, said cylindrical wall having at an annular free edge thereof an inturned annular flange defining a circular aperture facing said bush members, and a stationary gathering means mounted within the housing so as to enter a recess in the entrainment means formed by the flanged cylindrical wall so as to deflect lubricant therefrom in use into said continuous path so as to provide propulsion to the lubricant present in said path.

5. A bearing assembly as claimed in claim 4, wherein said wall of said annular tray member is arranged to dip into lubricant provided, in use, within said sump means so as to entrain lubricant on an external surface of the wall as the tray member rotates so as to provide a supply of lubricant to the bearing surfaces at start-up or slow-running speeds of the assembly.

6. A bearing assembly as claimed in claim 5 wherein the level of lubricant is maintained at a higher level in said sumps at low or start-up speeds through a passage controlled by valve means which are normally biassed in an open position at rest and at start-up or slow-running speeds but which are closed by the pressure of lubricant travelling in said continuous path at full operating speeds.

7. A bearing assembly as claimed in claim 6, wherein said sump means comprises a first sump into which said tray member is arranged to dip into lubricant contained therein, and a second sump adapted to receive lubricant flowing through said valve means when in the open position, there being provided between said sumps a weir means adapted to control the flow of lubricant thereover.

8. A bearing assembly as claimed in any one of the preceding claims, wherein there is provided in said bearing support members a channel arrangement adapted to receive lubricant from said lubricant path inlet.

9. A bearing assembly as claimed in either one of claims 1 and 2, wherein said branch portion of said lubricant conduit means comprises a plurality of said orifices.

10. A bearing assembly as claimed in claim 9, wherein said orifices are provided in a branch pipe wall portion, said settling chamber being provided with an outlet weir arrangement at a higher level relative to the orifices of said branch pipe wall portion.