GB2524266A

GB2524266A - Reducing oil leakage

Info

Publication number: GB2524266A
Application number: GB1404829.2A
Authority: GB
Inventors: Stephen Barnes; Dominic Arulsamy Mariajoseph; Andreas Kellerer
Original assignee: Cummins Generator Technologies Ltd
Current assignee: Cummins Generator Technologies Ltd
Priority date: 2014-03-18
Filing date: 2014-03-18
Publication date: 2015-09-23
Also published as: GB201404829D0

Abstract

A baffle 30 for a rotating electrical machine is provided. The machine comprises: a shaft 10; a bearing 16 for supporting the shaft; a rotor 12 mounted on the shaft on one side of the bearing; and a rotating component 24 mounted on the shaft on the other side of the bearing. The baffle 30 is arranged to be mounted between the bearing 16 and the rotating component 24 for restricting air flow between the bearing 16 and the rotating component. The baffle 30 can reduce a pressure differential across the bearing 16 caused by the rotating component 24, which can help to reduce oil leakage from the bearing 16.

Description

REDUCING OIL LEAKAGE

The present invention relates to techniques for reducing oil leakage from a bearing of a rotating electrical machine. The present invention has particular, but not exclusive, application in a rotating electrical machine with a journal bearing and an additional rotating component mounted on the shaft.

Rotating electrical machines such as generators and motors generally require some form of bearing for the shaft. One type of bearing which is used particularly in larger machines is a journal bearing. In a journal bearing the shaft runs on a wedge of oil, which is picked up from a tank. Seals are provided to retain the oil within the bearing. Journal bearings can provide a number of advantages, such as damping, noise reduction, long life, and heat extraction.

In some electrical machine designs an additional rotating component may be mounted on the shaft of the machine in proximity to the bearing. For example, in the case of a generator, a rectifier plate may be located on the shaft in proximity to the bearing. In other examples, a fly wheel, fan, or drive coupling may be located on the shaft. In some cases the rotating component may have fins to assist with cooling.

Rotating components positioned on a shaft close to a journal bearing may generate a draft of air which could lead to oil being drawn out of the bearing.

Conventional techniques for overcoming this problem involve upgrading the bearing seals, providing additional seals, or locating the rotating component further away from the machine. However upgraded seals may result in increased cost and complexity and reduced efficiency. Locating the rotating component further away from the bearing may require a longer shaft, thereby increasing the size and cost of the machine.

According to a first aspect of tho present invention thero is provided a baffle for a rotating electrical machine, the machine comprising a shaft, a bearing for supporting the shaft, a rotor mounted on the shaft on one side of the bearing, and a rotating component mounted on the shaft on the other side of the bearing, wherein the baffle is arranged to be mounted between the bearing and the rotating component for restricting air flow between the bearing and the rotating corn ponent.

The present invention may provide the advantage that, by providing a baffle mounted between the bearing and the rotating component for restricting air flow between the two, it may be possible to reduce a pressure differential across the bearing caused by the rotating component. Thus the present invention may help to reduce oil flow out of the bearing.

Preferably the baffle comprises a through-hole for the shaft. This can allow the baffle to surround the shaft and thus help to restrict air flow between the bearing and the rotating component.

Preferably the through-hole is arranged to clear the shaft. This may allow the shaft to rotate without coming into contact with the baffle. This may avoid loss of efficiency due to friction, and avoid the need to provide a seal between the baffle and the shaft.

The baffle may comprise mounting holes for mounting the baffle to the machine.

The baffle may be attachable to the machine using any suitable fixing means such as bolts, screws, rivets, clamps, adhesive or any other suitable fixing means.

In a preferred embodiment the baffle is disk-shaped, although any other suitable shape may be used. The baffle is preferably constructed from a thin sheet of material. The material may be a metal such as steel, or any other suitable material.

In one embodiment the baffle is divided into two or more parts. For example, the baffle may be provided as two half disks, or as two or more segments of any appropriate sizo or shape. This may allow the baffle to bo assomblod around the shaft without the need to remove other components. Thus this arrangement may facilitate retro-fitting of the baffle to an existing machine.

The baffle may be arranged to be mounted to the machine by means of an adaptor ring. Thus there may be provided a baffle assembly comprising a baffle in any of the forms described above, and an adaptor ring for mounting the baffle to the machine. Providing a separate adaptor ring may facilitate mounting of the baffle to the machine. Furthermore overall costs may be reduced since it may be easier to manufacture the adaptor ring separately from the baffle.

The adaptor ring may have an inside radius which is larger than the radius of the rotating component. This can allow the adaptor ring to clear the rotating component as it is being assembled onto the machine. Thus this arrangement may allow the adaptor ring to be assembled onto the machine without the need to remove the rotating component.

The adaptor ring is preferably provided as a single piece. In one embodiment, the adaptor ring is provided as a single piece, while the baffle is divided into two or more parts. In this case, the two or more parts of the baffle may be assembled around the shaft, and the adaptor ring used to hold the assembled parts together.

This arrangement may therefore facilitate assembly of the baffle around the shaft without the need to remove the rotating component. However, if desired, the adaptor ring could also be provided in two or more parts.

The adaptor ring may be arranged to space the baffle from the bearing. This can help to ensure the correct spacing between the bearing and the baffle.

The adaptor ring may comprise means for ventilating a space between the bearing and the baffle. For example, the adaptor ring may have ventilation holes, which may connect the space between the bearing and the baffle with the atmosphere. The ventilation holes may be substantially radial. This may help to provide a path for air flow through an air gap between the shaft and the baffle.

The ventilation holes may be provided, for example, by drilling holes through the adaptor ring. This may be facilitated by providing a separate adaptor ring.

In an alternative arrangement, rather than providing the adaptor ring as a separate component, it may be integrated with the baffle. In this case the baffle and the adaptor ring may be provided as one piece.

According to a second aspect of the present invention there is provided a rotating electrical machine comprising: a shaft; a bearing for supporting the shaft; a rotor mounted on the shaft on one side of the bearing; a rotating component mounted on the shaft on the other side of the bearing; and a baffle between the bearing and the rotating component, wherein the baffle is arranged to restrict air flow between the bearing and the rotating com ponent.

The baffle in the second aspect of the invention may be in any of the forms described above in the first aspect of the invention.

Preferably the baffle is stationary, preferably with respect to the bearing and/or a main part of the machine. This may help to provide a low cost solution which is easy to fit to an existing machine.

The baffle may comprise a through-hole for the shaft, and the through-hole may clear the shaft. Thus there may be a small air gap between the shaft and the through-hole. This may allow the shaft to rotate without contacting the baffle.

In a preferred embodiment of the invention, air flow between the bearing and the rotating component is restricted, but a small amount of air flow is still allowed through an air gap between the shaft and the baffle. Thus, in operation, air may be allowed to pass through an air gap between the shaft and the baffle. This can allow a baffle to be provided which does not touch the shaft. By accepting a restricted amount of air flow through the air gap, a low cost, low maintenance solution may be provided which is sufficient to reduce or to prevent oil from being drawn out of the bearing.

Preferably air passing through the air gap is drawn at least partially from a space between the bearing and the baffle. This can help to avoid air and/or oil from being drawn out of the bearing.

Preferably a space between the bearing and the baffle is ventilated. This can allow a path of least resistance for the air flow to be provided through the space between the bearing and the baffle. For example, the space between the bearing and the baffle may be connected to the atmosphere, for example, by means of holes. Thus in operation air may be drawn from the atmosphere, through the space between the bearing and the baffle, and through the air gap between the shaft and the baffle. This arrangement may provide an air flow path which substantially bypasses a seal of the bearing, and thus may help to reduce or to prevent air and/or oil from being drawn out of the bearing.

The machine may further comprise an adaptor ring which mounts the baffle to the machine. The adaptor ring is preferably located between the bearing and the baffle. The adaptor ring may space the baffle from the bearing. The adaptor ring may be in any of the forms described above in the first aspect of the invention.

Preferably the adaptor ring comprises holes for ventilating a space between the bearing and the baffle. This may provide a convenient way of ventilating the space, without the need to provide holes in the machine itself. Thus this arrangement may facilitate retro-fitting of the baffle to an existing machine.

In operation, air may be drawn through the holes in the adaptor ring into the space between the bearing and the baffle. This may provide a path of least resistance for any air flow in the air gap between the shaft and the baffle, and thus may help to avoid air and/or oil from being drawn from the bearing.

The rotating component may be any type of component such as a rectifier plate, a fly wheel, a fan, a drive coupling, or anything else which is attached to the shaft.

The rotating component and/or bearing may be located at the drive end or the non-drive end of the machine. The rotating component may or may not have fins.

In operation the rotating component may produce a draft of air, which might otherwise cause air and/or oil to be drawn from the bearing.

The machine may further comprise a housing for the rotating component. The housing may be removable, and the baffle and/or an adaptor ring may be mountable to the machine by removing the housing. For example, the housing may be removed, the baffle and/or adaptor ring assembled on the machine, and the housing then refitted to the machine. This may provide a convenient way of mounting the baffle, in particular to an existing machine.

The baffle and/or adaptor ring may be attachable to the machine using fixing means which are also used to attach the housing. For example, the baffle and/or adaptor ring may be provided with mounting holes which are substantially aligned with mounting holes in the housing, and these holes may all be aligned with screw holes in the machine. This may allow the baffle and/or adaptor ring to be mounted to the machine without the need to provide separate fixing means.

In order to facilitate fitting of the baffle to the machine, the baffle may be divided into two or more parts which are assembled around the shaft. This may facilitate fitting of the baffle, in particular to an existing machine.

In a preferred embodiment the bearing is a journal bearing, and may comprise one or more seal. However the present invention may be used with any other type of bearing such as roller-type bearings.

According to a third aspect of the present invention there is provided a method of adapting a rotating electrical machine to reduce leakage from a bearing, the machine comprising a shaft, a bearing for supporting the shaft, a rotor mounted on the shaft on one side of the bearing, and a rotating component mounted on the shaft on the other side of the bearing, the method comprising mounting a baffle between the bearing and the rotating component to restrict air flow between the bearing and the rotating component.

Features of one aspect may be provided with any other aspect. Apparatus features may be provided with the method aspect and vice versa.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a cross section through the non-drive end of a rotating electrical machine; Figure 2 shows an embodiment of a baffle; Figure 3 shows parts of a machine with a baffle in place; Figures 4(a) and 4(b) show schematically air flows in a machine without and with a baffle; Figures 5(a) and 5(b) show how a pressure differential across a bearing may vary with spacing between the bearing and a rotating component.

Figure 1 shows a cross section through part of a rotating electrical machine, which in this example is a generator. In Figure 1, part of the non-drive end (NDE) of the generator is shown. The generator includes a shaft 10, on which is mounted a rotor 12. In operation, the rotor rotates inside a stator (not shown).

An exciter (not shown) is also mounted on the shaft to provide excitation for the rotor.

The shaft 10 is supported at the non-drive end by a journal bearing 16. A shaft seal 14 separates the rotor 12 from the bearing 16. The journal bearing 16 includes a tank 18 which contains oil for lubrication. As the shaft 10 rotates inside the bearing 16, oil is drawn into the bearing, lifting the shaft and forming an oil "wedge". This oil wedge supports the shaft as it rotates. Shaft seals 20, 22 are provided in order to contain the oil within the bearing.

In the arrangement shown in Figure 1, a rectifier plate 24 is located at the far end of the shaft 10. The rectifier plate 24 contains rotating diodes which are connected to the exciter and the rotor through the shaft. The rotating diodes convert the AC output of the exciter to DC for supply to the rotor. In this design, the rectifier plate is located on the end of the shaft in order to provide easy access for servicing, and to help with cooling. Fins 28 are provided on the back of the rectifier plate 24 in order to circulate air for cooling. The rectifier plate 24 is housed within rectifier housing 26, which is removable to allow access.

It has been found that rotating components positioned on the shaft close to the journal bearing can generate a draft of air which can lead to air and oil being drawn out of the bearing. For example, the seals supplied as standard on a typical journal bearing may seal up to 5OPa of pressure differential, whereas pressures of up to 8OPa have been observed in some circumstances. In the arrangement shown in Figure 1 the fins on the rectifier plate act as a fan and may draw air and oil out of the bearing causing a slow leakage of oil.

A possible solution to this problem would be to upgrade the seals to withstand a greater pressure differential. However shaft seals can be expensive, particularly in larger sizes, and may be difficult to retro-fit to an existing machine.

Furthermore, seals which are able to withstand a greater pressure differential may also reduce efficiency due to increased friction with the shaft.

Alternatively it would be possible to locate the rotating component further away from the journal bearing. However this would increase the length of the shaft, resulting in a larger and more expensive machine.

In an embodiment of the invention, a stationary baffle is placed between the bearing 16 and the rotating rectifier plate 24. The baffle interrupts the flow of air between the rotating rectifier plate and the bearing, and thus reduces the likelihood of oil being drawn out of the bearing.

Figure 2 shows one embodiment of a baffle. Referring to Figure 2, the baffle 30 is disc-shaped, and is made of a thin sheet of material such as steel or other metal. Alternatively another suitable material such as a high density plastic could be used. A central hole 34 is provided through the baffle for the shaft. Mounting holes 36 are provided for mounting the baffle to the bearing.

Figure 3 shows parts of the machine with the baffle in place. Referring to Figure 3, the baffle 30 is located in the space between the bearing 16 and the rectifier plate 24. The periphery of the baffle is sandwiched between an adaptor ring 32 and the rectifier housing 26. Bolts (not shown) are used to secure the rectifier housing 26, baffle 30 and adaptor ring 32 to the bearing 16 or other part of the machine. &

The shaft 10 of the machine passes through the central hole 34 in the baffle. The central hole 34 clears the shaft 10 with a small air gap 38. This ensures that the shaft does not rub against the baffle, and allows for any misalignment.

The adapter ring 32 is used to ensure the correct spacing between the bearing and the baffle. The adaptor ring 32 is also provided with radial ventilation holes 40. The ventilation holes can be drilled through the adaptor ring prior to assembly. The ventilation holes 40 allow the space 42 between the bearing 16 and the baffle 30 to be ventilated and maintained at atmospheric pressure.

In operation, the baffle 30 acts as a barrier to restrict the flow of air between the bearing 16 and the rectifier plate 24. Some air is still drawn through the gap 38 between the shaft and the baffle, but the amount of air flow is considerably less than without the baffle. Furthermore, the space 42 between the bearing and the baffle is well ventilated to the atmosphere through the radial holes 40 in the adaptor ring 32. As a consequence, the air is drawn from the easiest flow path, which is through the radial holes 40 in the adaptor rather than through the bearing. Thus this arrangement can avoid oil and air being drawn out of the bearing due to the fan effect of the rectifier plate.

Operation of the present design is shown schematically in Figures 4(a) and 4(b).

Figure 4(a) shows air flow in a generator without a baffle. The shaft 10 is supported by a journal bearing 16. A rotating component 26 is located at the end of the shaft. Due to the fan effect of the rotating component, air and oil is drawn through the bearing as shown by the arrows. This causes a slow leakage of oil.

Figure 4(b) shows air flow in a generator with a baffle as described above. The total amount of airflow between the bearing 16 and the rotating component 26 is significantly reduced by the baffle 30. Although some air does flow through the gap between the shaft and the baffle, this air is drawn through the gap 42 between the bearing and the baffle. This alternative path for air flow can prevent air and oil from being drawn out of the bearing.

An advantage of the present design is that it does not require a seal between the baffle and the shaft. This reduces the cost of the baffle, and avoids any loss of efficiency due to friction between a seal and the shaft. Furthermore long term maintenance requirements are reduced, since if a seal were provided against the rotating shaft the seal would ultimately need replacing.

In a preferred embodiment it has been found that a suitable value for the air gap between the baffle and the shaft is around 1mm, although of course other values could be used. The size of the air gap is chosen depending on one hand on the amount of clearance which is necessary to prevent rubbing, and on the other hand on the extent to which it is desired to restrict air flow.

It has been found that a suitable spacing between the bearing and the baffle is around 6mm, although any other appropriate value could be used. The size of the air gap between the bearing and the baffle is chosen to ensure sufficient air flow between the two, while avoiding unnecessarily large gaps which could add to the size of the machine.

The spacing between the bearing and the rotating component can be chosen in order to minimise the length of the machine, without causing air and oil be drawn out of the bearing.

Figures 5(a) and 5(b) show how the pressure differential across the bearing may vary as the spacing between the bearing and the rotating component varies.

Figure 5(a) shows bearing pressure against spacing for a design with no baffle.

As the gap between the rotating component and the bearing decreases, the pressure differential across the bearing increases. If the bearing can seal, for example, up to 5OPa of pressure differential (approximately 5.1 mm H20), then the spacing between the bearing and the rotating component needs to be at least 33mm, and possibly more to ensure a sufficient margin of error. This may require the shaft to be lengthened, increasing the cost of the machine as well as its overall size.

Figure 5(b) shows bearing pressure against spacing for a design with a baffle as described above. In this case the pressure differential across the bearing can be kept at less than 15 Pa (1.5mm H20) even for spacings of less than 20mm. This can allow the length of the shaft to be reduced, thus reducing the cost of the machine as well as its overall size.

Another advantage of the present design is that it can be easily retro-fitted to an existing machine. Referring to Figures 1 and 3, this can be achieved by removing the rectifier housing 26, inserting the baffle 30 and adaptor ring 32, and replacing the housing.

In this example the rectifier housing 26 is attached to the machine using bolts 44.

The bolts 44 pass through mounting holes in the housing, and screw into threaded holes in the machine. The baffle 30 and the adaptor ring 32 are both provided with mounting holes which are aligned with the mounting holes in the rectifier housing. This can allow the baffle 30 and the adaptor ring 32 to be attached to the machine using the same bolts as are used to secure the housing.

Thus this arrangement avoids the need to drill additional holes in the machine.

In order to facilitate retro-fitting to existing machine, the baffle can be made in two or more pieces and assembled over the shaft. This can avoid the need to remove any components that are mounted to the shaft. For example, the baffle can be provided as two half discs, with the appropriate holes, which when brought together form a whole disc as shown in Figure 2. Alternatively any other number and size of segments could be used, as appropriate.

Easy retro-fitting is also facilitated through use of the separate adaptor ring 32 as described above. In this example the adaptor ring 32 is sized so that it can pass over the rectifier plate 24. This can allow the adaptor ring to be provided as a single piece, which can help to hold the baffle together if it is provided in two or more parts. However if required the adaptor ring could also be provided in two or more parts and/or as an integral part of the baffle.

The adapter ring 32 helps to ensure the correct spacing between the bearing and the baffle. The adapter ring also provides the radial ventilation holes 40 which allow the space 42 between the bearing and the baffle to be ventilation. These holes can conveniently be drilled through the adaptor ring prior to assembly on the machine. However, if desired, ventilation holes could be provided through part of the machine and/or bearing as well or instead.

The embodiments described above may provide a low cost solution to leaking journal bearings that can easily be retro-fitted in the field to leaking machines.

The baffle requires no maintenance, will not wear and is cheap to make.

Although the above embodiments have been described with reference to a generator with a rectifier plate on the non-drive end of the machine, the present invention is applicable to any type of rotating electrical machine with a rotating component at either the drive end, or the non-drive end, or both. For example, the present invention is applicable to motors or generators with a rotating component such as a fly wheel, a fan, or drive coupling located at either or both ends of the shaft.

Thus it will be appreciated that, while embodiments of the invention have been described with reference to particular examples, the invention is not limited to these embodiments, and variations in detail may be made within the scope of the appended claims.

Claims

CLAIMS1. A baffle for a rotating electrical machine, the machine comprising a shaft, a bearing for supporting the shaft, a rotor mounted on the shaft on one side of the bearing, and a rotating component mounted on the shaft on the other side of the bearing, wherein the baffle is arranged to be mounted between the bearing and the rotating component for restricting air flow between the bearing and the rotating component.
2. A baffle according to claim 1, wherein the baffle comprises a through-hole for the shaft.
3. A baffle according to claim 2, wherein the through-hole is arranged to clear the shaft.
4. A baffle according to any of the preceding claims, the baffle comprising mounting holes for mounting the baffle to the machine.
5. A baffle according to any of the preceding claims, wherein the baffle is disk-shaped.
6. A baffle according to any of the preceding claims, wherein the baffle is divided into two or more parts.
7. A baffle according to any of the preceding claims, wherein the baffle is arranged to be mounted to the machine by means of an adaptor ring.
8. A baffle assembly comprising a baffle according to any of the preceding claims and an adaptor ring for mounting the baffle to the machine.
9. A baffle assembly according to claim 8, wherein the adaptor ring is arranged to space the baffle from the bearing.
10. A baffle assembly according to claim 8 or 9, wherein the adaptor ring comprises means for ventilating a space between the bearing and the baffle.
11. A rotating electrical machine comprising: a shaft; a bearing for supporting the shaft; a rotor mounted on the shaft on one side of the bearing; a rotating component mounted on the shaft on the other side of the bearing; and a baffle between the bearing and the rotating component, wherein the baffle is arranged to restrict air flow between the bearing and the rotating component.
12. A machine according to claim 11, wherein the baffle is stationary.
13. A machine according to claim 11 or 12, wherein the baffle comprises a through-hole for the shaft.
14. A machine according to claim 13, wherein the through-hole clears the shaft.
15. A machine according to claim 13 or 14, wherein in operation air is allowed to pass through an air gap between the shaft and the baffle.
16. A machine according to claim 15, wherein air passing through the through-hole is drawn at least partially from a space between the bearing and the baffle.
17. A machine according to any of claims 11 to 16, wherein a space between the bearing and the baffle is ventilated.
18. A machine according to any of claims 11 to 17, wherein a space between the bearing and the baffle is connected to the atmosphere.
19. A machine according to any of claims 11 to 18, wherein in operation air is drawn from the atmosphere, through a space between the bearing and the baffle, and through an air gap between the shaft and the baffle.
20. A machine according to any of claims 11 to 19, further comprising an adaptor ring which mounts the baffle to the machine.
21. A machine according to claim 20, wherein the adaptor ring is located between the bearing and the baffle.
22. A machine according to claim 20 or 21, wherein the adaptor ring spaces the baffle from the bearing.
23. A machine according to any of claims 20 to 22, wherein the adaptor ring comprises holes for ventilating a space between the bearing and the baffle.
24. A machine according to claim 23, wherein in operation air is drawn through the holes in the adaptor ring into the space between the bearing and the baffle.
25. A machine according to any of claims 11 to 24, wherein in operation the rotating component produces a draft of air.
26. A machine according to any of claims 11 to 25, further comprising a housing for the rotating component.
27. A machine according to claim 26, wherein the housing is removable, and the baffle and/or an adaptor ring can be mounted to the machine by removing the housing.
28. A machine according to claim 27, wherein the baffle and/or adaptor ring are attachable to the machine using fixing means which are also used to attach the housing.
29. A machine according to any of claims 11 to 28, wherein the baffle is divided into two or more parts which are assembled around the shaft.
30. A machine according to any of claims 11 to 29, wherein the bearing is a journal bearing.
31. A method of adapting a rotating electrical machine to reduce leakage from a bearing, the machine comprising a shaft, a bearing for supporting the shaft, a rotor mounted on the shaft on one side of the bearing, and a rotating component mounted on the shaft on the other side of the bearing, the method comprising mounting a baffle between the bearing and the rotating component to restrict air flow between the bearing and the rotating component.
32. A baffle, a baffle assembly or a rotating electrical machine substantially as described herein with reference to and as illustrated in the accompanying drawings.
33. A method of adapting a rotating electrical machine to reduce leakage from a bearing substantially as described herein with reference to the accompanying drawings.