AU631809B2 - Electric motor - Google Patents

Description

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631809 COMPLETE SPECIF ICATION FOR OFFICE USE Application Number: Lodged: Class Int. Class Complete Specification Priority: Lodged: Accepted: Published: 4 9 4

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9 4 S S Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: FRAMU DEVELOPMENTS (UK) LIMITED 108 Coombe Lane, London SW20 0AY, England FRANK MOHN SMITH SHELSTON BEADLE 207 Riversdale Road Box 410) Hawthorn, Victoria, Australia Complete Specification for the invention entitled: EICTRIC MOTOR 4 The following statement is a full description of this invention, including the best method of performing it known to me,' Page 1 Our Ref: #4013 PS:CD 39fra LeZ-=ApCUL Ui Lile saiq invention.

4. The basic application referred to in paragraph 2 of this Declaration was the first application made in a Convention country in respect of the invention the subect of the application.

Declared at London this 23rd day of August 19 89 Signature of Declarant lopAI" i lP -IIn .1 1A- The invention relates to an electric motor and more specifically to an electric motor capable of providing a high torque at a relatively low speed, as is required in some applications for example in drilling and fluid extraction systems.

A rotary drive having high torque at a relatively low speed can be obtained from a conventional electric motor, which provides low torque at high speed, by use of appropriate gearing, but this represents an undesirable complication. Alternatively, a high torque, low speed drive can be obtained by a special design of the motor, but this tends to require the motor to be of very large size. The present invention is concerned with the provision of an electric motor which provides high torque at low speeds without the use of gearing and which can be nevertheless of compact construction.

The invention accordingly provides an electric motor comprisin,. a housing having a shaft mounted therein for rotation about its axis and for movement along the axis, electrical drive means carried by one of the shaft and the housing and co-operp' -g 15 driven means carried by the other of the shaft and housing, the drive and driven means having co-operating faces extending laterally of the shaft axis, and energizing means selectively operable to energize the drive means to act on the driven means to effect the rotation and/or the axial movement of the shaft.

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00 S 00 00 005 0000 0 0'o 50 5 5005 0@ 55 5 S 1' -2- The drive means may comprise windings wound in the manner of linear electric motor windings but extending around the shaft. axis in a circular path so as to carry the driven means, which can comprise magnetic material, around the axis. A high torque can be obtained because the motor structure of the invention allows a large effective "motor area" between the motor elements, that is, the drive windings and the co-operating driven element.

For most purposes, the invention can be embodied o• in a motor having a housing of circular cylindrical shape with the shaft journalled along its axis by suitable bearings, so as to function as an output or o 15 drive shaft. The driven means is conveniently carried by the shaft and preferably comprises a plurality of axially spaced rotor discs elements of magnetic material, which may be selected to maximise the drive effect of the energization of the drive means. The e20 drive means then comprises a plurality of annular 0 stator windings carried by the housing so that each is located adjacent at least one side of a respective .i ~rotor disc. Each rotor disc can advantageously be received between two of the annular stator windings which are energized in common.

A motor embodying the invention can be energized asynchronously, in simple, robust applications, when S" the driven means can comprise laminated or solid material, or synchronously to obtain greater efficiency, when the driven means can comprise permanent magnets. Effective cooling may be required, as by forced circulation of a cooling fluid, for example, an oil which may function additionally as a lubricant for the motor bearings. The circulation can be effected by an external pump or by an impeller on i li-l iii "1; -3-

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the motor shaft.

The shaft and the frame or housing can be journalled together for relative rotation by conventional bearings located between them.

Alternatively such bearings can be located between the shaft motor elements and the housing. Hydrodynamic and hydrostatic bearings can be integrated with the motor elements and housing, and the motor elements can be arranged and energized so as to provide an electromagnetic bearing effect.

The configuration of the drive elements of the motor of the invention provides the advantage over that of conventional electric motors that the stator means does not have to surround the rotor means, but need 15 exceed it in diameter essentially by no more than the thickness of the supporting housing wall. A plurality of the co-operating rotor and stator means can be stacked along the shaft to provide a motor which provides a desired high output torque at a readily controllable speed. The motor can be extremely compact, particv'arly in its transverse dimension, and is consequently very suitable for incorporation in pipe stacks used in drilling and fluid extraction systems.

It can thus be employed for driving drill bits and low speed borehole pumps, for example, screw pumps. The motor can be readily incorporated in pump systems such as are described in EP 0 063 444.

A further improvement in compactness can be obtained by employing a hollow motor shaft which can be used for example, for passage of a fluid being pumped or for supply of drilling mud.

Although axial spacing between the drive windings and the driven elements is desirably small to maximize efficiency, clearance can be provided in a motor according to the invention so that desired axially

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a elec embol or h cros exte prot: 35 at e -4directed forces between the windings and the driven elements can be generated by selective energization of the former. The resulting relative axial movement of the housing and the shaft can be controlled as to direction and timing so as to be employed for example to effect braking of shaft rotation, or as a hammering action as may be advantageous when the motor is driving a drill bit.

Where a plurality of drive windings are provided, the translational relative movement of the shaft and housing can be electrically powered in both directions, but the powered stroke can be resisted by a suitable form of spring providing energy for the return stroke.

0@cS The invention thus also provides an electric motor o. 15 comprising a housing having a silaft received therein SO,.for relative movement of the shaft and housing along ~O e the shaft axis, and co-operating electrical drive an driven elements on the shaft and housing or on the housing and shaft respectively, the drive and driven 20 elements being such that energization of the drive element effects the relative movement in at least one direction.

The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional schematic front view of an electric motor embodying the invention; and Figure 2 is a like view of a second electric motor embodying the invention incorporated in a pump unit.

The illustrated electric motor comprises a frame or housing having a wall 2 of circular cylindrical cross-section, and a motor drive or output shaft 4 extending along the axis 5 of the housing and protruding beyond its ends. The drive shaft 4 carries at equally spaced intervals along it a selected number ren of like rotor elements 6, each in the f orm of a coof axial circular disc of magnetic material secured to the

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of shaft. Each rotor element 6 is received axially 1 to between two annular stator elements 7 which are :)le 5 concentric with the shaft 4 and secured at their outer igperipheries to the housing wall. The two outer stator ang ing elements 7 form end walls to the housing 2 and the inner stator elements are stacked together in pairs in r acontact, with each pair between each adjacent spaced o and 10 pair of the rotor elements 6.10u -is, The housing wall 2 and shaft 4 are journalled* together for relative rotation about the'ir common axis *c 64, and, as shown at the upper only of Figure 1, the *se a 0 1. f b .rhousing wall supports bearing means 9 operative between el ~in 15 it and the peripheral outer edges of the rotor elements 1 )ng j Additionally or instead, such bearings could extend el an between the stator elements 7 and the shaft 4.

hThe stator elements 7 each comprise windings as 7en employed in linear electric motors but with the cc.

Lye 20 windings arranged to extend not linearly but in a g 0c Lve~4 20c n ,circular conf iguration, so as to ef fect rotation in a selected direction of the elements 6 and thus of the ,7a shaft 4 when energized. The stator elements 7 are chc .genergised asynchronously, or preferably synchronously, ci by an AC and/or DC power supply derived, from an 25 mc ane external power source 10 by way of a frtequency g~.hy converter 11. **ah The illustrated electric motor is shown with axial ac spacing between the rotor elements 6 and the stator elements 7 and this spacing permits operation of the 30 es motor so that the rotational movement of the drive in ,al shaft 4 is replaced or supplemented by an axial rc :4 nd reciprocating movement, as when the shaft or the N housing is driving a drill bit. To achieve such r Les r operation, the energisation of the stator elements 7 is 35 m :)er c i 1 cothe ally are uter ator the s in aced lied axis the ween ents tend 3 as the Ln a in a the are sly, 1 an ncy xial ator the cive .al the such 7 is o

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go•O appropriately controlled by means of a control unit 12.

The bearing means 9 are such to permit the resulting limited axial movement of the shaft 4.

Thus by appropriately energising, for example, 5 only the lower of each pair of the stator elements 7, as shown in Figure 1, the rotor elements 5 and the shaft 4 are moved downwardly, with or without a rotational movement, and by energising only the upper one of each pair of stator elements 7, the shaft is urged upwardly. A hammer action of the shaft 4 can thus be obtained. The axial movement of the shaft 4 can be limited by appropriate stop means, for example, abutments 15 provided on the radial faces of the stator element 7 as shown at the lower part of Figure to 15 avoid physical contact between the rotor and stator elements. The stop means can be arranged to have a braking effect on shaft rotation if required.

To remove the heat developed by energization of the windings of the stator elements 6, forced 20 circulation of cooling fluid through the housing can be provided. The cooling fluid can be a lubricant, to lubricate the bearing means 9. The shaft 4 can be hollow to provide a path for inclusion in the fluid circulation circuit. A fluid circulated through the 25 motor can have a bearing function by providing hydrodynamic and/or hydrostatic bearing, and it can absorb or distribute shocks resulting from the hammer action of the shaft.

The electric motor 20 of Figure 2 corresponds in 30 essential particulars to the motor of Figure 1, but is incorporated in a borehole pump unit for which only a rotational output is required and the facility for axial, translational, movement is accordingly not required, although it can be provided if braking of the 35 motor should be required.

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g -7- The pump unit of Figure 2 comprises a Moineau-type displacement element 21 coupled to the lower end of the t 12.

motor drive shaft 24 so as to be rotated by the motor g within tubing 25 of which the motor housing 26 forms a 5 part. The tubing 25 is received within production mple, Scasing 27. At least the portion of tubing 25 above the ts 7, Shousing 26 conveniently comprises electric conductor i the means providing power for the motor 20. The conductor Dut a means can comprise concentric tubular conductors upper separated by solid insulating sleeving or by dielectric ft is S* or barrier fluid circulated through passages in which 4 can Sc the motor housing may be included. Reference may be aft 4 S- made to EP 0 063 444 for further particulars of such mple, l I conductor and fluid arrangements.

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tator15 The motor shaft 24 can be tubular so as to provide 1, to a passage for a fluid being pumped, as indicated by tator arrows 29,through into the tubing 25, with a fuither ave a Simprovement in compactness.

The invention can be embodied in other ways than S 20 as specifically described and illustrated.

)rced r ed The claims form part of the disclosure of this specification.

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Claims (12)

1. An electric motor comprising a housing having a shaft mounted therein for rotation about its axis and for movement along the axis, electrical drive means carried by one of the shaft and the housing and co-operating driven means carried by the other of the shaft and housing, the drive and driven means having co-operating faces extending laterally of the shaft axis, and energizing means selectively operable to energize the drive means to act on the driven means to effect the rotation and/or the axial movement of the shaft.

2. An electric motor as claimed in claim 1 wherein the drive means comprises a 10 plurality of axially spaced annular windings.

3. An electric motor as claimed in claim 2 wherein the windings comprise linear motor type windings orientated around the axis.

4. An electric mraotor as claimed in claim 2 or 3 wherein the driven means comprises a plurality of axially spaced discs of magnetic material.

5. An electric motor as claimed in any one of claims 1, 2, 3 or 4 having braking or abutment means on at least one face of the co-operating facer of the drive means and the driven means.

6. An electric motor as claimed in any one of the preceding claims wherein the housing comprises a circular cylindrical housing wall having the shaft joumalled along its axis, the drive means being mounted on the housing wall and the driven means being mounted on the shaft.

7. An electric motor as claimed in any one of the preceding claims wherein the or each driven means is located between a respective associated pair of the drive means. I -9-

8. An electric motor as claimed in any one of the preceding claims arranged for synchronous operation. therein for

9. An electric motor as claimed in any one of the preceding claims wherein the ans carried shaft is journalled in the housing by bearings carried by the drive means and/or the ied by the 5 driven means. ating faces iperable to

10. An electric motor as claimed in any one of the preceding claims wherein the and/or the shaft is tubular to provide a fluid passage therethrough.

11. An electric motor as claimed in any one of the preceding claims having means :mprises a circulating fluid through the housing or providing at least one of cooling, lubrication, SI.? 10 hydrodynamic bearing, hydrostatic bearing and shock absorption. >rise linear

12. An electric motor as hereinbefore described with reference to the accompanying drawings. ten means DATED this 23rd day of March, 1992 CARTER SMITH BEADLE *1 ng braking 5 Qantas House, 2 Railway Parade, ive means Camberwell, Victoria 3124, Australia. 'herein the died along ren means herein the the drive fr