GB2357321A

GB2357321A - Electromagnetic-pneumatic positioning device.

Info

Publication number: GB2357321A
Application number: GB9929481A
Authority: GB
Inventors: David Malcolm Ham
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1999-12-14
Filing date: 1999-12-14
Publication date: 2001-06-20
Also published as: GB9929481D0

Abstract

A rotatable shaft 10 of a gas turbine engine (65, Figure 4) is provided with a flange 14, positioned between the compressor and turbine (68, 70, Figure 4) of the engine. Flange 14 rotates in close proximity to a stator device 26 comprising poles 28, which exert an electromagnetic force to attract the flange. Additional axial forcing is provided by high pressure air from compressor 68, which is directed through a valve 44 onto a disk 16 on the opposite side of flange 14. Thus, axial movement of shaft 10 due pressure imbalances in the engine is opposed by a combination of electromagnetic and pneumatic means. Cooling air from compressor 68 is also directed into space 48 above shaft 10 via valve 50. Further embodiments (Figures 2 and 3) use dual arrangements of stators and pneumatic pressure forcing.

Description

ELECTRO MAGNETIC-PNEUMATIC POSITIONING DEVICE The present invention

relates to structures held in positional relationship by magnetic

fields.

The invention has efficacy in the field of rotating power transfer shafts, which require holding against axial movement relative to fixed structure which supports them.

It is known to provide a rotatable shaft with a flange, and to provide fixed structure within which the shaft rotates during operation, and to fix an annular electrical stator to the fixed structure so that it surrounds the shaft in coaxial relationship.

In the known arrangement the stator has a plurality of axially aligned poles spaced around a radial face, which their end extremities closely adjacent a radial face of the shaft flange. During operation if the shaft attempts to move axially away from the pole end extremities, wire windings around the poles are energised, thus generating an electro-magnetic field which acts upon the flange to pull it and its associated shaft back to their original position, and hold them there until the cause of the movement has been obviated.

In the same known device, it is further known to provide a flow of cool air between the stator and flange, primarily to provide an air bearing which will prevent collision and resultant friction between stator and flange. The drawback to the known device, is that it is not possible to use high pressure air to achieve any desired functions, without serious risk of damaging the stator device, where the creation of high pressure results in high temperatures.

A further drawback to the known device, is that use of a stator-rotor device alone to achieve the required force can result in the need for bulky, heavy stators, which immediately restricts their range of application. The present invention seeks to provide a shaft mounted in fixed structure for rotation therein, and including improved means for retaining said shaft in or returning it to, a desired axial positional relationship with the fixed structure.

According to the present invention an electro magnetic-pneumatic positioning device comprises a flanged shaft rotatably mounted in fixed structure, an electrical stator fixed to said fixed structure coaxially with said shaft, the poles of said stator being equi angularly spaced about said stator and shaft with their end extremities adjacent one face of said flange in close spaced relationship, and means in partial engagement with the other face of said flange, which means are connectable for use to a pressurised fluid supply wherefrom, during rotation of said shaft, said means receives pressurised fluid and transmits the resulting force via said engaging parts, to counter axial movement of said shaft away from said stator poles.

The invention will now be described, by way of example, and with reference to the accompanying drawings in which:

Figure 1 is an axial cross sectional part view of a shaft and fixed structure incorporating a first example of the present invention, Figure 2 is as Figure I but incorporating a second example of the present invention, Figure 3 is as Figure 1 but incorporating a third example of the present invention, and Figure 4 is a diagrammatic cross sectional view of a gas turbine engine incorporating the example of Figure 1.

Referring to Figure 1 a shaft 10 is mounted for rotation in fixed structure U, by any suitable means eg ball and/or roller bearings (not shown) or forms the rotor of a rotor/stator device (not shown) in known manner.

An annular flange 14 is fixed to shaft 10 for coaxial rotation therewith, and an annular disk 16, having an annular relieved portion 18 is clamped, again by any suitable means (not shown) to a radial face of the flange 14, coaxially with the shaft 10.

The radial face of the disk 16 remote from the flange 14, has seals 20,22 formed around its radially inner and outer peripheries respectively.

The fixed structure 12, in the present example, is a cylinder around the outer surface of which gas turbine engine combustion equipment 64 (Figure 4) is arranged. Cylinder 12 has an internal flange 24, to which an annular electrical stator 26 is fastened, coaxially with the shaft 10. Wire wound poles 28, of which only one is shown, are equi-angularly spaced about the stator 26, with their end extremities closely adjacent face 30 of flange 14.

A ring 32 traps a dished, annular member 34 against a shoulder 35 internally of cylinder 12, so that radially inner and outer flanges portions of the dished, annular member 34 are positioned adjacent brush seals 20,22 respectively when the shaft 10 is in its axial operative position.

Cylinder 12 has a further internal shoulder 36 to which an annular plate 38 is fastened by suitable means (not shown). Plate 38 has a bore 40 which is clear of shaft 10, the resulting gap being effectively substantially closed by an annular seal 42 mounted on shaft 10.

Shaft 10, cylinder 12, flange 14, the radially outer portion of dished member 35 and plate 38 together define a space 48.

During operation of the gas turbine engine 65 (Figure 4) a pressure imbalance may develop between the compressor 68 and turbine 70, the result being a movement of shaft 10 in a downstream direction ie to the right as viewed in Figure 4. The movement will be sensed by any suitable means (not shown) eg a capacitance probe (not shown) to cause signals to be generated, which will be utilised to bring about powering of the wire wound poles 28 of the stator 26, to generate an electro magnetic pull on the flange 14, and simultaneously to open valve 44 to allow high pressure air from point 49 on compressor 68 to flow to the interior 45 of dished member 35. The resulting increase in pressure in the interior 45 of member 35 will act, via the rims of disk 16, on flange 14 in an upstream direction to the left as viewed in Figures 1 and 4. The electro magnetic pull being exerted on flange 14, will thus be assisted and shaft 10 will return to its original position.

A further tapping point 49 is provided in compressor 68, at its upstream, low pressure, low temperature end. Air is taken from this point and passed via valve 50 to space 48, where it cools stator 26. This operation can be effected during the whole of the operating time of the engine 65. Alternatively it can be effected simultaneously with introduction of hot, high pressure air into the interior 45 of member 35. Either way the cool low pressure air, along with any high pressure air which has leaked through seal 22 as a result of shaft 10 returning to its required position, will be sucked out of space 48, via valve 56.

A further function effected by the cool low pressure air is to flow via passages 52, only one of which is shown, in flange 14, relieved portion 18 in disk 16 and radial slots 54 in the outer peripheral portion of disk 16, back into space 48, thus cooling that side of flange 14 nearest the interior 45 of member 35.

Referring now to Figure 2, in this example the arrangement on the righthand side of Figure 2 is identical with that shown Figure 1. The lefthand side of Figure 2 is a mirror image of Figure 1 and therefore a mirror image of its own righthand side. Thus, stator 26 has further equi-angularly arranged wire wound poles 28a in its other radial face and shaft 10 has a further flange 14a, and includes a relieved disk 16a, a dished member 35a and hot high pressure air supply from compressor 68 via valve 44a.

Brush seals 20a,22a on relieved disk 15a separate it from dished member 35a.

Cooling air passes, via valve 50, radially inward through the body of stator 2a to spread laterally thereof and turn radially outwardly, mostly between the opposing faces of respective flanges 14 and 14a and stator 26. A portion of the cooling air passes through passages 52 and 52a in the flanges 14,14a to respective relieved portions 18 and 18a to exit via slots 54 and 54a, into the suction area of space 48. Suction is via valve 50.

The arrangement of Figure 2 enables simultaneous electro magnetic pulling and pneumatic pushing of shaft 10 in either axial direction.

Referring now to Figure 3 which reverts to a single flange. The stator 26b has an internal groove 72, and poles 28b,28c are provided in the inner radial surfaces thereof.

The outer peripheral portion of the single flange 14c, in operation, rotates within the groove 72 with its radial faces closely adjacent the end extremities of the respective poles 28b and 28c.

Cooling air from point 49 on the compressor 68 (Figure 4) enters space 48 via valve 50 and divided conduits 51,53 to be sucked therefrom via valve 56. It should be noted that in the arrangement depicted in Figure 3, cooling air does not pass through the relieved portion 18 of disk 16, or relieved portion 18b of disk 16b, but is directed only to the groove 72 where, prior to passing radially outwards over the ends of poles 28b,28c, it mixes with the high pressure air which has leaked through seals 62 and the resultant mixed flow is of a sufficiently low temperature, as to avoid damage to the poles 28b,28c.

The arrangement depicted in Figure 3, like that of Figure 2, enables simultaneous electro magnetic pulling, and pneumatic pushing forces to be exerted on a rotating shaft, so as to retain or return the shaft in or to a desired position.

Referring to Figure 4 the arrangement depicted in Figure 1 is shown installed therein.

The Figure 2 arrangement is also appropriate for installation in the same space. The Figure 3 arrangement however, by virtue of its need for more space radially of the engine, would be more easily accommodated (not shown) within the engine exhaust bullet 74. This would be achieved by extending shaft 10 with flange 14c and its associated structure downstream of turbine 70 and fix stator 16b to the inner surface of the bullet 74, in the same positional relationship with respect to the shaft flange as is depicted in Figure 3.

Whilst the present invention has been described only in connection with gas turbine engines, it has efficacy in many power field, wherein rotating shafts are subjected to undesirable axial displacement over small, say to 0.040" (1 mm) distances, and where stator/rotor devices per se are not appropriate.

In all of the examples of the present invention described herein, the brush seals 20,22 may be substituted by labyrinth seals, or any other seals of appropriate shape and capability of the desired performance.

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Claims

An electro magnetic-pneumatic positioning device comprising a flanged shaft rotatably mounted in fixed structure, an electrical stator fixed to said fixed structure coaxially with said shaft, the poles of said stator being equi angularly spaced about said stator and shaft with their end extremities adjacent one face of said flange in close spaced relationship, and means in partial engagement with the other face of said flange which means are connectable for use, to a pressurised fluid supply wherefrom during rotation of said shaft, said means receives pressurised fluid and transmits the resulting force to said other flange face via said engaging parts to counter axial movement of said shaft away from said stator poles.
2 The device of claim 1 wherein said means on said flange other face comprises an annular disk having an annular relieved portion which faces said flange other face, the disk engaging said flange other face via peripheral rims formed by said relieved portion.
3 The device as claimed in claim 1 or claim 2 wherein said means is connectable to a said pressurised fluid supply via an annular plenum chamber fixed to said fixed structure and spaced from said disk by leaking seal members.
4 The device as claimed in claim 3 wherein said pressurised fluid leaks via said seals into a space containing said stator and flange, and is extracted therefrom by suction.
The device as claimed in any previous claim and including a further reduced pressure fluid supply, which is directable to both sides of said flange.
6 The device as claimed in any previous claim wherein said stator has a further array of poles on its other radial face, said shaft has a further flange thereon in opposition to the poles of said further stator, said further flange including an annular disk having an annular relieved portion facing that face of said further flange remote from said further poles and engaging said face via rims, and a further plenum chamber fixed in said fixed structure and connectable to a pressurised fluid supply and spaced from said annular disk by leaking seal means.
7 The device as claimed in any of claims 1 to 5 wherein said stator has an annular groove therein, each opposing wall of which contains an equi angular array of poles the outer radial portion of said flange lies within said groove in close spaced relationship with said array of poles, and the inner radial portion of said flange is sandwiched between opposing disk means which has respective relieved portions and engage said flange via respective rims and are connectable, via respective dished plenum chambers, to receive a pressurised fluid flow which in operation exerts a force on a selected disk member which via its rim transmits said force to that side of said flange which will assist one or other of said pole arrays to move said shaft in a desired direction.
8 The device as claimed in any preceding claim including conduits and valves for connecting and directing a pressurised fluid to said the or each disk means.
9 The device as claimed in any previous claim, including conduits and valves for connecting and directing a cooling fluid to the stator poles and the or each flange.
The device as claimed in any previous claim including a conduit and valve for connecting the space occupied by the stator and the or each flange, to fluid extraction means.
11 The device as claimed in any previous claim wherein the cooling and pressurised fluid are air.
12 A gas turbine engine including an electro magnetic-pneumatic device as claimed in any preceding claim.
13 An electro magnetic-pneumatic positioning device substantially as described in this specification with reference to Figure 1 of the drawings.
14 An electro magnetic-pneumatic positioning device substantially as described in this specification with reference to Figure 2 of the drawings.
An electro magnetic-pneumatic positioning device substantially as described in this specification with reference to Figure 3 of the drawings.
16 A gas turbine engine including an electro magnetic-pneumatic device substantially as described in this specification, and with reference to any of Figures 1 to 3 of the drawings.