GB2228626A

GB2228626A - Induction motor having effectively DC current in the rotor

Info

Publication number: GB2228626A
Application number: GB8818716A
Authority: GB
Inventors: Richard James Warner
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-08-05
Filing date: 1988-08-05
Publication date: 1990-08-29
Also published as: GB8818716D0

Abstract

The motor comprises at least one ring shaped Stator (1, 2) made with spirally wound and slotted steel strip wound on a core 3, 4, the rotor 5 including a homogeneous iron ring 15 which may include conductive rings 14, 16 of copper or aluminium the rotor running on bearings 8 around shaft 9. The Stator windings produce rotating or pulsating magnetic flux which passes axially through the Stator and air gaps and induces effectively DC current in the rotor. At a constant air gap flux density the Rotors produce a torque approximately proportional to the Rotor slip, thus creating a starting torque several times greater than full load torque. Alternatively the rotor may comprise an iron or mild steel ring cast around with aluminium which also forms cooling fins. Multiple stator/rotor arrangements and power output configurations are disclosed. <IMAGE>

Description

DC HOTOR INDUCTION MOTOR This invention relates to an alternating current electric induction motor which uses axial air gaps and a solid metal disc Rotor.

Most industrial electric motors are of the induction type, using either single or three phase alternating electric current. Such motors comprise of a Stator and Rotor. The most common form comprises a cylindrical Stator made up of many stamped out laminations and wound with copper wire, and a drum shaped Rotor, made up of many stamped out laminations slotted at the periphery and cast around with aluminium to form bars in the slots and two disc shaped end rings. The whole assembly is mounted in an outer case.

This form of motor produces a near constant speed, but suffers from a relatively low starting torque. Another form is the repulsion motor which uses a similar Stator but whose Rotor is wire wound and has a commutator with brushes, this motor is capable of producing a large starting torque but with the penalty of greater complexity and higher production costs.

Another form is the slip ring induction motor, using a wire wound Rotor with slip rings and brushes1 which can also produce a high starting torque, but also with the penalty of greater complexity and high production costs.

Small alternating current motors which are required to give a thigh starting torque are usually the universal type, which is similar to a DC series motor and has a wire wound Stator and Rotor with a commutator and brushes, again resulting in complexity and high production costs.

According to the present invention there is provided an axial air gap induction motor comprising two ring shaped Stators and one disc shaped Rotor; a small air gap is provided between each Stator and the Rotor.

The Stators are made of spirally wound steel strip to form laminations, with slots at the air gaps which are wound with conductive wire for three phase alternating current. The Rotor is made of three rings to form a disc, the inner and outer are made of copper or aluminium and the middle ring is made of steel or iron. The outer and inner diameters of tEle two .Stators are the same as those of the middle steel or iron Rotor ring.

The three phase Stator windings produce rotating magnetic flux. At a particular instant a pattern of poles is set up in the Stators such that like poles face each other across the Rotor. Flux flows out of the north poles of the Stators into the Rotor middle ring and emerges to flow back -into the adjacent Stator south poles. Such that flux flows axially into the Rotor from both sides, diverges into circumferential flow and diverges again to flow axially out from both sides of the Rotor into the Stators.

With the Rotor slipping in relation to the rotating magnetic flux, currents are induced in the Rotor which flow in all three rings and form a pattern when viewed from the rotating flux. The Rotor current behaves like direct current in that there is no noticeable frequency dependent reactance or skin effect resistance. Nevertheless there is a certain depth of penetration of the flux into the Rotor which is proportional to the strength of that flux. Rotor electromagnetic force increases with slip, flux and depth of penetration of that flux. At a constant strength of flux, torque is approximately directly proportional to Rotor slip, being a maximum at stall.Other forms of the motor comprise two Stators and a one piece solid steel or iron disc Rotor; one Stator sandwiched between two Rotors of solid steel or iron or using a middle ring of steel or iron surrounded by conductive metal such as copper or aluminium; one Rotor of solid steel or iron or using a middle ring of steel or iron surrounded by conductive metal such as copper or aluminium and one Stator; in all cases steel or iron must be used where magnetic flux flows, but more conductive metals may be used where only current flows to reduce electrical resistance; all forms of the motor may have Stator or Stators fixed in an outer case with Rotor or Rotors fixed to a revolving shaft, or Stators or Stator mounted on a stationary shaft on which revolves the Rotor or Rotors with no outer case, or Stators or Stator mounted on a stationary shaft on which revolves the Rotor or Rotors with an outer case, the Stator windings may be single phase or poly phase.

A specific embodiment of the invention will now be described by way of example with reference to accompanying Drawing 1 in which: Figure 3 shows in perspective and section the machine as a fan motor excluding fan blades and support frame.

Referring to Figure 3, the Stators 1 and 2 are made of mild steel strip laminations interleaved with insulation and spirally wound onto aluminium hubs 3 and 4. The Stators are slotted adjacent the Rotor 5, and wire wound 6 and 7 for three phase alternating current electrical supply; there are two poles per Stator. The Rotor 5 has bearings 8 fitted at its centre providing axial and radial support. The shaft 9, thrust collars 10 and 11 and Stators are fixed together by way of nuts 12 and 13, such that components 1,2t3,4,6,7,9,10,11,12 and 13 are stationary, whereas components 5 and 8 are free to rotate. There are two threaded holes 17 at the periphery of the Rotor in which two fan blades (not shown) are fitted. The whole machine is supported by a frame (not shown) attached at 12 and 13.The air gaps between the Rotor 5 and the Stators 1 and 2 are of unequal length, such that an axial force due to magnetic flux is produced nearly equal and opposite to the axial reactance force of the fan blades, so as to minimise axial load on the bearings. The three phase windings 6 and 7 are arranged in a similar fashion as those of a conventional radial field three phase induction motor, so as to produce rotating magnetic flux which passes axially through each air gap into and out of the Rotor. The Rotor is made of three metal rings, an inner ring 14 of copper, a middle ring 15 of mild steel and an outer ring 16 of copper, these three rings are shrink fitted together.

A specific embodiment of the invention will now be described by way of example with reference to accompanying Drawing 2 in which : Figure 1 shows in cross section the motor using two Rotors, one Stator and shaft drive.

Referring to Figure 1 each Rotor 19 is formed of a middle steel or iron ring cast around with aluminium which also forms the cooling fins 18, the Rotors are fixed to the shaft 20 running in bearings mounted in two end castings 21, these castings are fixed into an outer case 23, and this outer case supports the Stator 22, the Stator is single or poly phase wound producing rotating magnetic flux which flows axially through the Stator and air gaps.

A specific embodiment of the invention will now be described by way of example with reference to accompanying Drawing 2 in which: Figure 2 shows in cross section the motor using one Rotor, one Stator and shaft drive.

Referring to Figure 2 the Rotor 24 is formed of a middle steel or iron ring cast around with aluminium which also forms the cooling fins 28, the Rotor is fixed to the shaft 25 running in bearings mounted in two end castings, the two castings are mounted in an outer case, the Stator 27 is fixed to the end casting 26, the Stator is single or poly phase wound producing rotating magnetic flux which flows axially through the air gap.

Claims

' LAI.iS

1 A rotating axial air gap induction rotor comprising of two Stators and one homogenous iron Rotor. The Stators take the form of laminated iron rings, being made of spirally wound iron strip, one or each of these Stators is slotted at its axially inner surface adjacent to the Rotor and wound with electrically conductive wire, so as to produce rotating magnetic flux under the influence of three phase alternating current electrical supply. The Rotor takes the form of an homogenous iron ring acting both as magnetic permeator and electrical conductor.

2 A rotating axial air gap induction motor as claimed in Claim 1, wherein the Rotor takes the form of an homogenous iron ring with attached inner and outer homogenous rings of high electrically conductive metal.

3 A rotating axial air gap induction rotor as claimed in any preceding claim, wherein several Stators and several Rotors are mounted along a shaft.

4 h rotating axial air gap induction motor as claimed in any preceding claim, wherein the alternating current electrical supply is single phase.

5 A rotating axial air gap induction motor as claimed in any preceding claim, wherein the alternating current electrical supply has any number of phases.

6 A rotating axial air gap induction motor as claimed in any preceding claim, wherein the Rotor speed is changed by turning one or more Stators through an arc.

7 A rotating axial air gap induction motor as claimed in any preceding claim, wherein the shaft is fixed to one or more Rotors and the aforementioned shaft is free to rotate in the Stators.

CLAIilS

8 A rotating axial air gap induction motor as claimed in any preceding claim, wherein the shaft is fixed in the Stators and one or more Rotors is free to rotate on the aforementioned shaft.

9 A rotating axial air gap induction motor substantially as described herein with reference to Figures 1-3 of the accompanying Drawings 1-2.