WO2018185525A1

WO2018185525A1 - An electric rotary machine having magnetically isolated pairs of magnetic poles

Info

Publication number: WO2018185525A1
Application number: PCT/IB2017/051976
Authority: WO
Inventors: Geoffrey Kwananga MKANDAWIRE
Original assignee: Van Der Walt, Louis, Stephanus
Priority date: 2017-04-06
Filing date: 2017-04-06
Publication date: 2018-10-11

Abstract

A rotor or stator (100) for an electric rotary machine has magnetically isolated pairs of magnetic poles (120). The rotor or stator (100) has a magnet-carrying member (110) of a magnetically non-conductive material and at least two magnet components (120) with each magnet component defining a pair of opposite magnetic poles. The magnet components (120) are mounted to the magnet-carrying member (110) in a circumferentially spaced relationship such that there is a clearance space between adjacent pairs of magnet components (120) such that the magnetically non-conducting magnet-carrying member (110) inhibits conduction of magnetic flux generated in one of the magnet components (120) through the magnet-carrying member (110) to any other magnet component.

Description

An electric rotary machine having magnetically isolated pairs of magnetic poles

FIELD OF INVENTION

This invention relates broadly to electric rotary machines (e.g., motors and generators) and specifically to an electric rotary machine having magnetically isolated pairs of magnetic poles.

BACKGROUND OF INVENTION

A conventional rotary machine typically has a magnetising layer configured to generate a magnetic field and a coiled layer (or generating layer) comprising a plurality of coils operable to pass through the magnetic field, either to generate motion (in the case of a motor) or to generate electricity (in the case of a generator). The magnets could be permanent magnets or electromagnets.

The conventional electric rotary machine comprises a rotor and a stator. Usually, but not always, the rotor is provided on a central axle and carries a plurality of magnets to provide the magnetising layer, while the stator is provided concentrically around the rotor and houses the plurality of coils. The rotor (or other magnet-carrying member) is usually of a magnetically conductive material, like a ferromagnetic material, like iron or steel, to permit magnetic flux generated by the magnets to flow freely there-through. In fact, conventional wisdom dictates that it is desirable to have the magnetically conductive material to permit formation and completion of magnetic flux paths. The Applicant desires an electric rotary machine which does not have a magnetically conductive magnet carrying member which may thereby allow for different magnetic flux configurations.

SUMMARY OF INVENTION

Accordingly, the invention provides a rotor or stator as well as an electric rotary machine as disclosed in the claims.

Disclosed is an electric rotary machine having magnetically isolated pairs of magnetic poles, the electric rotary machine including a magnet-carrying member and a coil- carrying member which are relatively rotatable about an axis of rotation, wherein: the magnet-carrying member is of a magnetically non-conductive material; the electric rotary machine includes at least two magnet components with each magnet component defining a pair of opposite magnetic poles; and the magnet components are mounted to the magnet-carrying member in a circumferentially spaced relationship such that there is a clearance space between adjacent pairs of magnet components such that the magnetically nonconducting magnet-carrying member inhibits conduction of the magnetic flux generated in one of the magnet components through the magnet-carrying member to any other magnet component.

The invention extends to a magnet-carrying member and a plurality of magnet components for use in an electric rotary machine as defined above. The magnet- carrying member may be a rotor or a stator.

The electric rotary machine may be a motor or a generator. The electric rotary machine may be AC or DC. There may be a minimum of two magnet components. In such case, the magnetic components may be spaced 180° apart and the electric rotary machine may be a four pole machine. There may be three magnet members. In such case, magnetic components may be spaced 120° apart and the electric rotary machine may be a six pole machine. There may be n magnetic components. In such case, the magnetic components may be spaced 360° / n apart and the electric rotary machine may be a 2 x n pole machine.

The poles defined by the magnet component may be elongate in an axial direction and arcuate in a circumferential direction. The poles defined by the magnet component may be circumferentially spaced.

A rotor of the machine may comprise the magnet-carrying member and the magnet components. In such case, a stator of the machine may comprise the coil-carrying member. The rotor may be accommodated inside the stator.

A stator of the machine may comprise the magnet-carrying member and the magnet components. In such case, a rotor of the machine may comprise the coil-carrying member.

Each magnet component may be a single element. Each magnet component may include two radially inner or outer ridges, each ridge corresponding to one of the magnetic poles. Inner or outer surfaces of the ridges may be arcuate, the surfaces being aligned in a circle about the axis of rotation.

The magnet component may comprise a permanent magnet. In such case, the magnet component may be a single fixed magnet. The magnet component may comprise an electromagnet. In such case, the magnet component may comprise a body of ferromagnetic material (e.g., iron or steel) and windings. The body may include slots or channels to accommodate the windings. The magnet-carrying member and the magnet component may include complemental mounting formations. For example, the magnet-carrying member may include a groove or slot and the magnet component may include a complemental flange or tongue. The magnet component may be slidably accommodated by the magnet- carrying member.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying diagrammatic drawings.

In the drawings:

FIG. 1 shows a three-dimensional view of a magnet-carrying member and a plurality of magnet components, in accordance with the invention;

FIG. 2 shows a side view of the magnet-carrying member and a plurality of magnet components of FIG. 1 ;

FIG. 3 shows an exploded view of the magnet-carrying member and a plurality of magnet components;

FIG. 4 shows a three-dimensional view of the magnet-carrying member of FIG. 1 ;

FIG. 5 shows a side view of the magnet-carrying member of FIG. 4;

FIG. 6 shows a three-dimensional view of the magnet component of FIG. 1 ;

FIG. 7 shows a side view of the magnet component of FIG. 6;

FIG. 8 shows a side view of the magnet component of FIG. 7, with flux lines; and

FIG. 9 shows a side view of the magnet-carrying member and a plurality of magnet components of FIG. 2, with flux lines; and FIG. 10 shows a side view of an electric rotary machine, in accordance with the invention, comprising the magnet-carrying member and a plurality of magnet components of FIG. 9 in the form of a rotor located within a stator.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

The following description of the invention is provided as an enabling teaching of the invention. Those skilled in the relevant art will recognise that many changes can be made to the embodiment described, while still attaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances, and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not a limitation thereof.

FIGS 1 -3 illustrate various views of a magnet-carrying member 1 10 and a plurality of magnet components 120, in accordance with the invention. In this example, the magnet-carrying member 1 10 and a plurality of magnet components 120 together comprise a rotor 100 of an electric machine (with a remainder of the electric machine not illustrated), which may be a DC or AC motor or generator.

The rotor 100 comprises three magnet components 120 mounted to the magnet- carrying member 1 10. Each magnet component 120 provides a pair of opposite (N-S) poles, the rotor 100 thus being a 6-pole rotor.

FIGS 4-5 illustrate the magnet-carrying member 1 10 in more detail. The magnet- carrying member 1 10 is made of a non-magnetic and non-ferrous material. It may be of a hard polymer or composite material which does not conduct magnetic fields well. The magnet-carrying member 1 10 has a tubular body 130 which defines a central circular channel 132 for accommodating a shaft or axle to which the magnet-carrying member 1 10 can be mounted. The magnet-carrying member 1 10 has three small equi-angularly spaced axially-extending ridges 134 which have a T-shaped cross- sectional profile. Adjacent ridges 134 define there-between a mounting formation in the form of an axially-extending slot 136. In this example, there are three slots 136 spaced 120° apart. The slots 136 extend a full length of the body 130.

FIGS 6-7 illustrate the magnet components 120 which complement the magnet- carrying member 1 10. Each magnet component 120 includes an arcuate base 140 portion and a pair of large ridges 142, also with a T-shaped profile. Each ridge 142 serves as a magnetic pole (see FIGS 8-9). The arcuate base 140 has a flange 144 at each side. Outer surfaces of the large ridges 142 are arcuate and curved along a common circular outline, co-axial with an axis of rotation of the rotor 100.

The arcuate base 140 is a mounting formation complemental to the slot 136 of the magnet-carrying member 1 10. The arcuate base 144 can be slid axially into the slot 136 but cannot be moved radially or circumferentially. The flange 144 is fitted snugly with a frictional fit within corresponding channels define by the ridges 134. (In a different embodiment, a space 146 between the large ridges 142 may accommodate windings of the magnet component 140 to form an electromagnet.)

FIGS 8-9 illustrate magnetic aspects of the rotor 100. Each of the large ridges 142 defines a magnetic pole, either north (N) or south (S). In this example, the magnetic component 120 is a permanent magnet. FIG. 8 illustrates the magnet component 120 in isolation. Magnetic flux lines 150, 152 extend from the N pole to the S pole, both through the arcuate base 140 of the magnetic component 120 itself and through the surrounding space. FIG. 9 illustrates an important aspect of the rotor 100. The N-S poles of a single magnetic component 120 couple magnetically via the arcuate base 140 and external space as illustrated by flux lines 150, 152. However, opposite poles (S-N) of adjacent magnetic components 120 may couple magnetically in external space as illustrated by flux lines 154, but do not couple (or couple comparatively insignificantly) via the magnet-carrying member 1 10, as illustrated by the absence of flux lines 156.

In a different embodiment (not illustrated), the axially-extending ridges 134 (in FIGS 4- 5) could be shaped different, for example narrower at their base and broader at their top with tapered sides. Correspondingly, the flanges 144 (in FIG. 7) could be broader at their bottom with the areas of contact having tapering sides so as to match the axially-extending ridges 134. The magnet components 120 (in FIGS 6-7) could be one piece of metal or it could be a stack of laminations of magnetic material.

FIG. 10 illustrates an electric rotary machine 200 comprising the rotor 100 provided concentrically within a stator 202. The stator 202 comprises 18 stator teeth 203 with adjacent pairs of teeth 203 defining there-between stator slots 204. An air gap 205 is defined between the rotor 100 and the stator 202. The stator 202 is constituted by a plurality of annular laminations.

FIG. 10 illustrates magnetic flux paths (represented by numeral 208) within the stator 202 due to the effect of the magnetically isolated pairs of magnetic poles from the respective magnetic components 120. A concentric magnetic flux 210 may also form around and within the stator 202.

Accordingly, the example embodiment of the invention provides a way of isolating pairs of magnetic poles to enhance coupling within the same magnet component but isolate or inhibit coupling via the magnet-carrying member in poles of adjacent magnet components. By way of example, the Applicant submits that, in a conventional rotary electric machine, if the magnetic flux density developed in the rotor core is 2 Tesla, in an eight pole machine each pole would experience only 0.25 Tesla. In the present invention, the magnetic flux density is not shared with the adjacent pole pairs. This is to say if each pole pair develops the magnetic flux density of 2.0 Tesla, it remains confined to this pole pair. So in a four pole pair (which is an eight pole machine of the present invention) there is 8 Tesla of flux density available to the motor.

There are two ways to exploit this benefit. There can be one unit of motor or generator in the machine frame or there can be several units utilising the axial scaling presented in invention PCT/18215/054833.

The back electromotive force (EMF) of a motor depends on: the surface area; the magnetic flux density; and the length of the conductor only for DC and the length of the conductor and the frequency of power supply for AC = impedance.

These factors also govern the speed of the machine. Reducing the surface area and the length of the wire in a given DC machine for the same flux density and same voltage results in increased speed. In AC reducing the surface area and length of the wire reduces the impedance in the machine and hence the frequency of the power supply has to be increased to an optimal level resulting in increased speed is increased the or conductor length can be adjusted to maintain same speed but higher torque and optimal current currying or both frequency and conductor length can be adjusted. In brief, changing any of the three factors for a given voltage and number of poles will affect the speed of the electric motor. For example, a 0.3 metre rotor length with a given number of poles and stator teeth if each pole pitch takes 30 metres of 5 mm copper wire. If this motor is divided into three segments mounted on the same shaft and connect the wirings in parallel arrangement: this could relate to slot pitches or individual machines and speeds power carrying capacities are higher when each slot pitch is connected to power supply in parallel arrangement we will have the following factors changed:

The speed of the machine will be higher because the surface area and the copper wire length have been reduced. This is to say the machine segments will have to run at higher speed to produce enough back EMF for the safe running of the machine.

The reduction in the length of the wire results in the ability of each segment to carry more current due to reduced resistance due to wire length reduction; and

Depending on the desired results the current carrying capacity of the machine can be mitigated to lower losses.

In total for the same effective machine length and voltage, the current carrying ability of the machine, in accordance with the invention, is increased and the speed of the machine is also increased. It should be seen that rotor shaft experiences total torque of the three magnet components (being the sum because these units are on the same shaft. It should be born in mind that the input power has changed because of the current carrying ability of the machine has improved due to resistance reduction.

Further implication of this invention is the machine size reduction that results from better current carrying capacity and increased flux density or the machine of the same size or volume having higher power capacity.

Claims

1. A rotor or stator for an electric rotary machine having magnetically isolated pairs of magnetic poles, wherein: the rotor or stator includes a magnet-carrying member of a magnetically non-conductive material; the rotor or stator includes at least two magnet components with each magnet component defining a pair of opposite magnetic poles; and the magnet components are mounted to the magnet-carrying member in a circumferentially spaced relationship such that there is a clearance space between adjacent pairs of magnet components such that the magnetically non-conducting magnet-carrying member inhibits conduction of magnetic flux generated in one of the magnet components through the magnet- carrying member to any other magnet component.

2. The rotor or stator of claim 1 , in which the magnet component is elongate in an axial direction and arcuate in a circumferential direction.

3. The rotor or stator of any one of claims 1 -2, in which the poles defined by the magnet component are circumferentially spaced.

4. The rotor or stator of any one of claims 1 -3, in which the magnet component comprises one of: a single, unity element; or a plurality of laminations.

5. The rotor or stator of any one of claims 1 -4, in which each magnet component includes two radially inner or outer ridges, each ridge corresponding to one of the magnetic poles.

6. The rotor or stator of claim 5, in which inner or outer surfaces of the ridges are arcuate, the surfaces being aligned in a circle about the axis of rotation.

7. The rotor or stator of any one of claims 1 -6, in which the magnet-carrying member and the magnet component include complemental mounting formations.

8. The rotor or stator of claim 7, in which the magnet component is slidably accommodated by the magnet-carrying member.

9. The rotor or stator of claim 8, in which the magnet-carrying member includes a groove or slot and the magnet component includes a complemental flange or tongue.

10. The rotor or stator of any one of claims 1 -9, in which the magnet component includes at least one of: a permanent magnet; or an electromagnet.

11. An electric rotary machine which includes the rotor or stator as claimed in claim 1.

12. The electric rotary machine of claim 1 1 , in which there are n magnetic components spaced 360° / n apart and in which the electric rotary machine is a 2 x n pole machine.

13. The electric rotary machine of any one of claims 1 1 -12, which includes a coil- carrying member which rotatable relative to the magnet-carrying member about an axis of rotation.

14. The electric rotary machine of claim 12, in which the rotor comprises the magnet- carrying member and the magnet components and the stator comprises the coil- carrying member.

The electric rotary machine of claim 12, in which the stator comprises the magnet carrying member and the magnet components and the rotor comprises the coil carrying member.