GB2391602A

GB2391602A - Shaft coupling using concentric tie rod

Info

Publication number: GB2391602A
Application number: GB0214967A
Authority: GB
Inventors: Phil Ewart; Renza Aini
Original assignee: Turbo Genset Co Ltd
Current assignee: Turbo Genset Co Ltd
Priority date: 2002-06-27
Filing date: 2002-06-27
Publication date: 2004-02-11
Also published as: GB0214967D0

Abstract

A shaft coupling 1 for connecting two rotary machines comprises connection portions 10, 11 connected to each of the machines, with torque transferring surfaces 14 where they meet. A tie shaft 12 is screwed into a bore 111 in one of the shafts 11, and is then tensioned, for example by a hydraulic tensioner, before being held in place in a bore in the mating shaft 10 by lock screws 13. The screws may butt against a shoulder 124 in the tie shaft. The tensioning device may be attached to the tie shaft 12 using a thread 123.

Description

239 1 602

Coupling The present invention relates to mechanical couplings, more particularly to couplings between rotary machines.

There are many well-known difficulties in coupling rotary machines together to provide a reliable and efficient connection for carrying torque from one machine to another. In addition, it is desirable to make such couplings and the machines they connect as easy as possible to maintain. Often couplings between machines are provided by welding together the rotor shafts to form a permanent correction. This provides good torque handling capability and a reliable link but it is not practical to separate the machines subsequently, without cutting the shafts apart.

Other techniques include using fasteners to join together the ends of the respective rotors. This is easier than welding and it is easier to separate the machines subsequently for servicing and repair. However, such fasteners are placed under considerable strain or many are required making the coupling complex. Friction couplings can be used but at high speed and under high torques, these couplings need to have a high tensioning force to hold the friction surfaces in contact.

Consequently, there is a need for a relatively simple coupling which is capable of operating at high speed and high torques reliably and which is capable of being separated to allow the machines which are coupled to be separated.

Turbo generator sets which use a gas turbine coupled to an electrical generator, such as an axial flux type generator, to produce electrical power often operate at high speeds and powers. This particular application puts considerable constraints on the design of

( coupling between the two machines. In addition these units are often used in distributed power generation and may be located in remote locations. Therefore, it is important to make maintenance as easy as possible without the need for complex and heavy machinery. It is therefore important to be able to remove and if necessary replace either of the two main components, i.e. the generator and the turbine, separately.

Although such a generator would normally only provide torque in one direction, under extreme conditions such as a fault, a reverse torque may be experienced. Consequently, to avoid damage or failure of the coupling, it should be able to handle bi-directional torque. Therefore, according to the present invention there is provided a coupling arrangement comprising a tie shaft for coupling a first connection means to a second connection means, the tie shaft comprising first engaging means for engaging said first connection means to resist relative axial movement; second engaging means for engaging said I second connection means to resist relative axial movement; and attachment means for removably connecting a tensioning device to said tie shaft for tensioning said tie shaft.

The present invention provides a coupling which provides bi-directional torque handling and which is easily assembled and disassembled to allow each of the rotary machines to be serviced or replaced independently.

The coupling arrangement is preferably arranged so that the tie shaft can be tensioned whilst the connection means are in place by using the tensioning device. Once the tie; shaft has been tensioned, the second engaging means can be utilised to engage the tie shaft with the second connection means to prevent relative axial movement between them. The first and second connection means are in this way caused to bear the load applied to the tie shaft. This load is borne by the interface between the two connection means to prevent slipping under load conditions.

The second engaging means is preferably manually engageable so that the tie shaft can be tensioned and then locked off. Separate engaging members are preferably used. I This may be in the form of lock screws extending from the second connection means

against the tie shaft. The tie shaft may be provided with a stepped portion against which the locking members can engage. By angling the engaging members between the radial and axial directions, for example at 45 degrees, the end of the lock screws can be brought up into engagement with the stepped portion.

The first and second connection means are preferably extensions of the rotors of the rotary machines. However, they may be formed as separate assemblies which are attached to the rotor.

The tie shaft is preferably provided with a recess in which the attachment means can be provided. This allows the tensioning device or extension bar to be passed through the centre of the second connection means to tension the tie shah prior to engaging it with the second connection means. Prior to engagement, the tie shaft is preferably formed so that it is slideable within the second connection means to allow the second connection means to be brought into position by sliding it along the tie shaft and also to allow the tie shaft to be extended during tensioning.

The first and second connection means preferably have an engaging surface for transferring torque. The surface is more preferably provided with a face type coupling (e.g. a Hirth type coupling) which is provided with engaging teeth to transfer torque without slipping and also to centre the first and second connection means properly.

The tie shaft preferable engages the first connection means by being threaded and screwed into a corresponding recess in the first connection means.

The present invention will now be described in more detail by reference to the following drawings in which: Figure 1 shows a schematic representation of a coupling according to the present invention between two rotary machines; Figure 2 shows a cut away view through the coupling of figure 1; and

Figure 3 shows a cut away perspective view of the coupling of figure 1.

Figure I shows a coupling I according to an embodiment of the present invention. The coupling of this embodiment is used to connect a gasturbine 2 or the like to an electrical generator 3.

The coupling 1 is formed from three main parts 10,11,12. The generator connection 10 is connected to or is an extension of the rotor of the electrical generator. The turbine connection 11 is similarly connected to or is an extension of the rotor of the turbine. The generator connection and the turbine connection have end faces which engage each other to form a torque transferring interface 14 as described in more detail below.

In order to hold the engaging faces of the interface together, a tie shaft 12 is provided.

The tie shaft 12 is held under tension between the generator connection and the turbine connection. The tension is the tie shaft is supported across the end faces of the generator connection and the turbine connection forcing them against each other.

The arrangement of the coupling will now be described with reference to figures 2 and 3. Initially, the turbine is positioned with the turbine connection 11 projecting from the turbine. The turbine connection has a cylindrical hollow 1 12 extending down the turbine connection from its end. At the end of the hollow portion, a further cylindrical hollow 111 is provided which extends further along the turbine connection. The further cylindrical hollow 111 is provided with an internal thread.

The tie shaft 12 is an elongate generally cylindrical body with a larger diameter portion 122 at one end. Within the larger diameter portion a cylindrical hollow 123 is provided.

The internal surface of the hollow portion 123 is threaded. At its opposite end, the tie shaft has an externally threaded portion 121.

The externally threaded end 121 of the tie shaft is screwed into the threaded portion 1 1 1 of the turbine connection. As the tie shaft is progressively screwed in, the end face of the tie shaft eventually buts up against the mating face 113 of the turbine connection.

The turbine assembly, including the turbine connection and the tie shaft, is mated to the generator. The end of the generator connection is mated to the end of the turbine shaft by a face coupling 14 to act as the torque transferring interface. A face coupling provides optimum concentricity and runout alignment and also provides the necessary bi- directional torque transmission properties.

The larger diameter portion 122 of the tie shaft is arranged to be tight sliding but not an interference fit within the hollow centre of the generator connection. This allows the end 122 of the tie shaft to be slid into the hollow core of the generator connection but I the face coupling ensures that alignment of the generator and turbine connections takes place. Once the connections are engaged, an extension bar 4 is inserted into the hollow core of I the rotor of the generator, as shown in figure 1. The extension bar is provided with a I threaded portion 41 at its end. The extension bar is passed through the rotor of the generator to engage the tie shad. The extension bar 4 is then screwed into the internal thread 123 of the tie shaft. The extension bar is provided with an engagement means 42 such as a hex nut at the opposite end to allow tightening of the bar. Once the extension bar is completely inserted into the tie shaft, the end bottoms out on the end of the hollow portion.

Once the extension bar is engaged with the tie shaft, tension is applied to the end, for example using a hydraulic puller. The extension bar is tensioned to a predetermined load level. The load is selected to provide a minimum pre-load on the tie shaft once the puller and extension bar are removed. Once the extension bar is loaded, the tie shaft is locked in place with lock screws 13. In the embodiment shown in the figures, three lock screws are screwed into partially threaded bores 101 in the generator connection 10. As the lock screws are screwed into place, they engage the stepped portion 124 provided between the portions of different diameter on the tie shaft. Once in place, the lock screws prevent the tie shaft from relaxing back to its unstressed length and thus maintain the pre-load on the shaft.

Once the lock screws are in position, the load can be removed from the extension bar.

The lock screws will then support the load in the tie shaft. The extension bar can then be removed by unscrewing it from the tie shaft and withdrawing it from the interior of the generator rotor. By removing the extension bar, rather than having a permanent tensioning device, the hollow core of the rotor can used for the passage of cooling fluid therethrough. The pre-load applied to the tie shah is borne through the lock screws which in turn brings the load to bear on the engaging faces of the face coupling 14 to provide the operational force required for this type of coupling. The lock nuts are then locked to the I generator connection to prevent them unscrewing in use and allowing loss of the preload. If subsequently, it is necessary to separate the two machines, the whole process can be I reversed. The extension bar would be inserted and then tensioned to carry the preload I on the tie shaft. The load would thus be removed from the lock screws which can then be removed. The tension can then be removed from the extension bar and it can then be unscrewed and withdrawn. The generator can then be retracted from its engagement with the turbine connection and slid along the tie shaft to release it.

The connection means referred to above are provided by an extension of the rotor shafts in the above embodiment. However, the connection means may be formed by a separate; assembly which is connected to the rotor of the respective machine.

The above embodiment is described is relation to a tie shaft being mounted onto a turbine and then the generator mounted to the tie shaft. It will be apparent that the generator and turbine could be reversed where desirable.

The embodiment of the present invention described above relates to a coupling between a gas-turbine and an electrical generator. However, the present invention is not limited to these specific kinds of machines and is more generally applicable to any kind of rotary machine.

Claims

( CLAIMS:

1. A coupling arrangement comprising a tie shaft for coupling a first connection means to a second connection means, the tie shaft comprising: first engaging means for engaging said first connection means to resist relative axial movement; second engaging means for engaging said second connection means to resist relative axial movement; and attachment means for removably connecting a tensioning device to said tie shaft for tensioning said tie shaft.

2. A coupling arrangement according to claim 1, further comprising: a first connection means for connection to a first rotary machine; and a second connection means for connection to a second rotary machine.

3. A coupling arrangement according to claim 1 wherein the second connection means has a tie shaft engaging means interoperable with the second engaging means for engaging the tie shaft, after tensioning by the tensioning device, to resist axial movement of the tie shaft.

4. A coupling arrangement according to claim 3 wherein the tie shaft engaging means is selectively engageable.

5. A coupling arrangement according to claim 3 or 4 wherein the tie shaft engaging means comprises one or more movable engagement members.

(

6. A coupling arrangement according to claim 5 wherein the engagement members are generally angled relative to the radial and axial directions.

7. A coupling arrangement according to any one of claims 3 to 6 wherein the tie shaft includes a stepped portion against which said tie shaft engaging means can engage.;

8. A coupling arrangement according to any one of claims I to 7 wherein said first connection means is a rotor of said first rotary machine.;

9. A coupling arrangement according to any one of claims l to 7 wherein said first connection means is connected to a rotor of said first rotary machine. I

10. A coupling arrangement according to any one of claims 1 to 9 wherein the second connection means is a rotor of said second rotary machine.

11. A coupling arrangement according to any one of claims l to 9 wherein a second connection means is connected to a rotor of said second rotary machine.

12. A coupling arrangement according to claim 10 or l l wherein the second rotary machine has a hollow shaft through which said tensioning device is insertable to engage said attachment means.

13. A coupling arrangement according to any one of claims 2 to 12 wherein the first I and second connection means have respective interengaging surfaces for engaging each other.

l 4. A coupling arrangement according to claim 13 wherein said interengaging surfaces engage each other via a face type coupling.

15. A coupling arrangement according to any one of the preceding claims wherein the tie shaR is slideable relative to the second connection means prior to engagement therewith.

16. A coupling arrangement according to any one of the preceding claims wherein the first engaging means is a threaded portion for engaging a corresponding thread on the first connection means.

17. A coupling arrangement according to any one of the preceding claims wherein the attachment means is provided in a hollow portion formed in the tie shaft.

18. A coupling arrangement according to claim 17 wherein the attachment means is a thread for engaging a corresponding thread on said tensioning device.

19. A coupling arrangement substantially as described herein with reference to the accompanying drawings.

20. A turbo-generator including a turbine and a generator coupled by a coupling arrangement according to any one of the preceding claims.

21. A tie shaft substantially as described herein with reference to the accompanying drawings.