Abstract:
A gas turbine engine ( 10 ) has a compressor ( 14 ) which includes a rotary stage ( 16 ) supported for rotation by a plurality of wire wound stators ( 34 ). When the stators ( 34 ) are electrically energised, they exert Maxwell type magnetic forces on a magnetically permeable ring ( 18 ) joining the tips of compressor blades ( 21 ) in the stage ( 16 ), and lift it into a position in space where it can rotate on a common axis with the turbine of the engine ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to fluid displacement apparatus of the kind comprising relatively rotatable parts which, on relative rotation occurring, causes fluid to move. 
     2. Description of Related Art 
     The invention is particularly concerned with the suspension of the rotatable parts especially in a gas turbine engine compressor. Present day gas turbine engine technology includes shafts which rotate within fixed structure, and are supported therefrom via ball and roller bearings. The support mode necessitates the use of oil pumps, galleries, scavenge pumps, oil coolers and reservoirs, which adds considerably to design complexity, weight and cost. Consequently, the present invention seeks to provide gas turbine engine fluid displacement apparatus, which obviates that need in toto. 
     SUMMARY OF THE INVENTION 
     According to the present invention, gas turbine engine fluid displacement apparatus comprises a ring and a drum, the ring being held co-axially with and around the drum by a circular array of blades, the ring being magnetically permeable, and In turn surrounded by a casing, through which a circular array of electromagnetic stators comprising wire wound poles protrude, a stator power supply, and sensors for sensing the magnitude of any gap between the stators and ring, and generating signals therefrom, and control means connected between said sensors and said stator power supply, so as to receive any said signals and so cause said power supply to power one or more stator windings in a manner which will result in one or more stator poles generating sufficient magnetism across appropriate gaps as to cause the fluid displacement apparatus to adapt a position wherein said ring is equidistant from all said stator poles. 
     The invention will now be described, by way of example and with reference to the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, part axial cross sectional view of a gas turbine engine incorporating an example of the present invention, 
     FIG. 2 is an enlarged part view of the engine of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 a gas turbine engine  10  is enclosed in a streamlined casing  12 . A multi-stage compressor  14  is fitted to the upstream end of the engine  10  in known manner. In the present example, a first, rotary stage of compressor blades  16 , comprises a ring  18  and a drum  20  which is held in co-axial, radially spaced relationship within ring  18 , by a plurality of blades  21 . The ring  18  is of short axial length, the ring may or may not be fibre reinforced to increase its strength. The drum  20  however, extends downstream, bypassing the combustion equipment  22 , and terminates at a connection (not shown) with a turbine stage (not shown). 
     Referring now to FIG. 2 the material, from which ring  18  is made, contains sufficient iron as to be magnetically permeable. The drum  20  is made from any material which will withstand the stresses imposed upon it, during operation of engine  10 . 
     An outer casing  24  surrounds all of the rotor and stator blades of the compressor  14  In known manner. However, the casing  24  has a thickened band  26  around it, in the plane of the blade stage  16 . The band  26  has an annular recess  28  formed internally thereof, and a plurality of flats  30  formed on Its outer diameter, the flats  30  being spaced apart equidistantly around the circumference of casing  24  and band  26 . The band  26  is drilled through the flats  30 , into the annulus  28  at a plurality of locations to receive the ends of pole pieces  32  of a stator  34  fitted in each resulting hole. Each pole piece end is dimensioned such that its radially inner face protrudes Into the annulus  28 . Interdigitated with pole pieces  32  are a plurality of sensors  33  which are sensitive to the radial gap between the rotary ring  18  and the stationary pole pieces  32  belonging to stator  34 . Each sensor  33  generates an output signal in response to the magnitude of its associated radial gap. 
     The radial position of the outer magnetically permeable ring  18  in its running position also places It within the annulus  28  at an even, close radial spacing. 
     In order to achieve the assembly as described hereinbefore, it may be necessary to form the compressor casing  24  in two parts  24   a  and  24   b , and then, having fitted the blade stage  16 , along with its associated ring  18  and drum  20 , in casing portion  24   b , to clamp parts  24   a  and  24   b  together by any suitable means. The stat or pole pieces  32  may then be inserted in respective drilled holes. 
     When the blade stage  16  is stationary the ring  18  will rest on the pole pieces  32  in the lowest quadrant of the casing  24 . In order to achieve rotation of the stage  16 , it must first be levitated and centralised with respect to the ends of all of the pole pieces  32 , so that it is co-axial with the rotational axis of engine  10 . To this end, the wire windings of the upper pole pieces  32  are electrically energised by a power source (not shown) such that magnetic forces, of the kind known as Maxwell forces, are generated across the Saps between the ring  18  and the ends of the upper pole pieces  32 . These Maxwell forces magnetically repel the ring  18  so as to levitate and support it. The sensors  33  respond to the reducing gaps between the ring  18  and the upper pole pieces  32 , and the correspondingly increasing gaps between the ring  18  and the lower pole pieces  32 . When the sensor output signals indicate that all of the gaps are equal in magnitude or substantially equal rotation may be commenced. A power source controller (not shown) of any suitable type continues to receive sensor output signals to monitor all of the gaps during engine operation and to exercise control over the power source (not shown) to maintain the gaps equal around the stage circumference. Any attempt by the stage  16  to rotate eccentrically will be sensed, and appropriate signals sent via the controller (not shown) to the power source (not shown) to vary current through the pole piece windings to maintain Maxwell forces of appropriate magnitudes across the gaps, so as to restore the rotation of stage  16  on the desired axis. 
     When the gas turbine engine is de-activated by cutting off the fuel supply, the rotary machinery continues to windmill at a reducing rate, until air resistance and friction dissipates its momentum. During this time, the sensors  33  continue to monitor the gaps, and to cause the power source to maintain the stage  16  in suspension. When windmilling has ceased output from the power source is reduced at a rate which ensures that the stage  16  is lowered gently onto the lowest stator poles  32  without Incurring damage. 
     In the present example, the stage  16  is depicted as the first rotary stage of a multi-stage compressor. However, any rotary stage in such a compressor may be utilised as described herein. The drum  20 , which as described hereinbefore, extends downstream (with respect to the direction of gas flow through the engine  10 ) may also be supported by electrically powered stators (not shown) spaced apart along its length, in a manner similar to that described hereinbefore with respect to stage  16 , thus ensuring the co-axial rotation of the engine rotary system.