WO2004098022A1

WO2004098022A1 - Improvements in electrical machines

Info

Publication number: WO2004098022A1
Application number: PCT/GB2004/001822
Authority: WO
Inventors: Phillip Raymond Denne
Original assignee: Electro Magnetic Rams Limited
Priority date: 2003-04-28
Filing date: 2004-04-28
Publication date: 2004-11-11
Also published as: GB0309527D0

Abstract

An electromagnetic apparatus is provided comprising an armature arrangement and a stator assembly, the armature arrangement including an armature member arranged to rotate about a central shaft member, the armature including a means for creating a magnetic field and arranged to co-operate with another means for creating a magnetic field provided by the stator assembly. The armature is displaced within a channel formed by the stator assembly without contacting the stator assembly, the channel having a toroidal sectional shape.

Description

IMPROVEMENTS IN ELECTRICAL MACHINES

The present invention relates to the design of linear electric motors, not having a rectilinear motion but being capable of motion in an arc. The invention relates to motors so constructed as to form a torus and which are therefore a new type of rotary motor that is capable of producing a large torque.

It is known to construct linear electric motors in cylindrical form, such as those described in our existing patents and co-pending patent applications under PCT/GB92/01277, PCT/GB98/00495, PCT/GB98/03088 and PCT/GB00/02563. The first three of the above-referenced documents describe machines having a fully-enclosed cylindrical stator and the last reference describes a form of machine in which the stator and the last reference describes a form of machine in which the stator has a slot that is parallel to its central axis. In all of these machines the armature bears directly against a surface that lines the cylindrical assembly of the stator and is sealed to it so that the armature has a dual fluid and electromagnetic action. Usually the armature is comprised of an array of disc magnets and polepieces and the stator is an array of circular coils, but in the alternative the armature may carry an array of coils and the stator may be comprised of a stack of plane ring magnets and polepieces.

Many applications of the cylindrical linear motor require the armature or piston to be connected to an external mechanism, so that the mechanism may be precisely controlled by the combination of electromagnetic and fluid forces acting on the piston or armature of the motor. This is usually contrived by means of a rod or tube attached to the piston and passing through an aperture at one or both ends of the cylindrical stator. It will be understood that the passage of the rod or thrust tube through the end aperture of the stator also requires a bearing. Our patents and co-pending applications under PCT/GB92/01277, PCT/GB98/00495 and PCT/GB98/03088 describe machines having this form of construction. Alternatively, our co-pending applications under PCT/GB00/02563 describe a means by which the piston or armature of a cylindrical linear electric motor may be coupled to an external mechanism by means of a fin that travels in a slot parallel to the axis of the cylinder. In that case the fin requires a guide bearing to prevent it rotating against the sides of the slot in the stator.

Machines with cylindrical symmetry and freely-moving armatures are known, one of which is described in our patents and co-pending applications under PCT/GB98/03092. However, such machines have the disadvantage that the armature or piston moves on bearings that make contact with the lining of the surrounding stator assembly. It will be appreciated that if the armature moves rapidly and continuously back and forth within the machine, the lining will tend to wear quickly. However, as we describe in co-pending applications such as GB204194.5 it is possible to construct a linear motor of cylindrical form in which the armature is supported on bearings of high quality so that it does not otherwise come into contact with the stator. In such designs the factional forces are minimised and the machine is likely to have a long life in operational use.

It is an object of this invention to construct a new and very powerful form of rotary motor by topological modification of a rectilinear motor and to arrange that the surface of the armature does bear against the internal surface of the stator lining.

From a first aspect the present invention provides an electromagnetic apparatus comprising: an armature which includes means for generating a magnetic field and arranged to rotate about a central shaft member; a stator assembly forming a channel including two opposing walls, each provided with at least one magnetic element arranged to emit a magnetic field, the magnetic elements from each wall creating a balanced magnetic field in which the armature is arranged to be displaced through.

In a preferred embodiment of the present invention, the electromagnetic apparatus is a motor comprised of two parts, the armature and the stator, the armature being arranged to move along the circular curved axis of the stator whilst remaining always completely within it, the first part being constructed from a stack of axially-magnetised plane blocks or discs interposed by ferromagnetic plates, the magnets being arranged with like poles opposing and the polepieces acting to produce a high-intensity radial magnetic field of alternating polarity and with a regular spatial period, the second part being constructed from a series of electrical coils having an axial dimension related to the dimensions of the magnets and polepieces of the first part, the coils being arranged to be energized by a current source sensitive to the relative position of the two parts so that there is produced by the interaction of the electrical currents and the magnetic fluxes of an axial force whose magnitude and axial direction may be controlled by the currents in the coils, characterised in that the armature of the motor is curved in at least one dimension and is enclosed within a stator forming a sector of a torus of non-circular section, the armature being supported within, but without touching, the stator by at least one bearing, the bearing or bearings being incorporated within the structure of the stator, the radial magnetic forces between the stator and the armature being balanced within the torus, and the tangential force of the armature being carried out of the stator through extensions to the polepiece plates connecting with a disc or wheel so as to create a torque about the major axis of the torus.

In one arrangement of the invention the motor is characterised such that the magnets and polepieces are rectilinear plates and the two parts of the stator are similarly of rectilinear form, being planar in one dimension on either side of the armature assembly, the major dimension of the armature cross-section being either radial or being parallel to the axis of rotation of the motor.

It is an important feature of the invention that the parameters of the armature and the stator are so designed that the inward and outward radially-attractive forces between the armature and the stator are closely balanced at the periphery of the armature and not at the axis of the machine. That is to say, the net radial forces on the bearings of the machine always remain small although the opposing radial magnetic forces may be very large.

In order that the present invention may be more readily understood, embodiments thereof will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a radial sectional view of a motor according to a basic arrangement useful for the understanding of the present invention;

Figure 2 shows a radial sectional view of a motor according to an alternative arrangement useful for the understanding of the present invention;

Figure 3 shows a radial sectional view of a motor according to a preferred embodiment of the present invention;

Figure 4 shows a detailed view of the connection of coils to the stator in the motor shown in Figure 3. Figure 1 shows a section along a major radius of a motor in which the toroid is rectangular in cross section. In this diagram the plates of the armature 3 are supported by the stout disc 10 that is part of the torque shaft 1. The shaft moves in bearings 7 and thus the armature moves with a clearance 22 within the stator coil assembly 2. The corresponding stator section 4 is u-shaped and it is fitted to discs 20 that carry at their centres the shaft bearings 7. It should be noted that in this design the major dimension of the magnet and polepieces plates is radial and the windings are likewise radial.

The magnetic flux leaving the surface of the magnet can be efficiently diverted outwards to the windings by the use of shaped polepieces, as described in several of our co-pending patent applications. There is no significant flux leakage at the innermost edges of the polepieces.

The above conformation is known as the "disc" form of the machine and the construction has a number of advantages, one of which is that the structure may be sealed by the application of rotary seals 21 at each end of the shaft. The machine has a lower bearing friction that those in which the armature 3 runs on slide bearings within the torus.

It will also be observed that the coil assembly has only half the number of end windings

17 because the complete U-shaped coil system can be wound on a convex former in the same way as previously described and then the stator iron/mild steel casing 4 can be slipped over the whole winding assembly and bonded to it. (The stator iron is prepared in two or more stators having a U-shaped cross-section).

However, the chief disadvantage of the construction described above is that the magnetic attraction forces between the armature and the stator are all additive and aligned in an axial direction, tending to pull the end plates of the motor inwards. For example, in a typical machine that is about 1.5 metres in diameter, the inward force on each of the end plates is in the order of one MegaNewton, which makes the machine very difficult and expensive to construct.

Figure 2 therefore shows an alternative form of the device in which the rectangular armature is arranged with its long axis parallel to the rotational axis of the motor. In the diagram the numerals have the same significance as for Figure 1.

The advantage of the "drum" conformation is that the motor may have a smaller overall diameter at the expense of having a greater height. The attractive forces between the armature and the stator are radial in this design and they are therefore balanced about the axis. Again, the magnetic flux leaving the surface of the magnet can be efficiently diverted outwards to the windings by the use of shaped polepieces, as described in several of our co-pending patent applications.

Nevertheless, the radial forces between the armature and the stator in the "drum" construction are still very large and they have the effect of applying a bursting stress to the armature. In a typical industrial motor about a meter in diameter, the force across any diametric section is likely to be several hundred KN. It will be understood that equal and opposite forces also act on the stator, tending to collapse the casing inwards. Because all the radial magnetic forces are large, any imperfection in the balance of the magnetic forces across a diameter is likely to impose large stresses on the central bearings. Figure 3 shows a preferred embodiment of the present invention in which a moving magnet "drum" armature moves in a channel-shaped stator. It should be noted that the same reference numerals are utilised for corresponding features from Figure 1 and 2. By this means the inward and outward radial forces on the armature are closely balanced at all times near to the periphery of the machine. Thus no large radial forces remain to be conveyed inwards to the central bearings of the torque disc 20a, 20b.

The armature 3 moves between coil units 2 that are bonded to inner 4a and outer 4b sector plates of a circular stator channel 23. The inner 4a and outer 4b sector plates are positioned on opposing walls 23a,23b of the channel 23 and thus the coil units 2 that are bonded to the inner 4a and outer 4b sector plates respectively, provide opposing magnetic fields to the armature which is displaced therethrough. The coil units 2 provide a magnetic field which balances with the magnetic field of the armature so as prevent any resultant radial force being conveyed from the motor. It will be understood that there may be eight inner sector plates and eight outer sector plates making up the complete stator. To withstand the strong magnetic forces drawing them to the armature, the plates are keyed into inner and outer bracing rings 24a and 24b.

The armature is axially constrained by ring bearings 7 that are incorporated into the stator construction and prevent the armature assembly from contacting the peripheral stator wall. In addition a further ring bearing 27 may be provided between the outer edge of the stout disc 10 and the peripheral wall of the stator assembly so as to augment the effect of the ring bearings 7. Further, a supporting bearing 37 is preferably provided under the armature 3, which prevents the lower portion of the armature from contacting the stator assembly. The supporting bearing 37 may be a slide bearing extending along the channel shaped stator. Alternatively, a bearing may be arranged in each sector of the stator or in only some of the sectors of the stator. It should be noted that the magnetic forces within the machine provide a useful benefit in that the armature is strongly attracted to rotate in a plate that is positioned in the centre of the stator in an axial direction. That phenomenon assists the action of the bearings that provide axial constraint and so reduces the consequent wear. The supporting bearing 37 is preferably provided when the motor is configured as shown in Figure 3 such that the stout disc 10 is positioned above the armature 3. However, it will be appreciated that the supporting bearing 37 may not be required if the motor is flipped over such that the stout disc is positioned below the armature 3 as gravitational forces will allow the armature to balance on the stout disc 10. Figure 4 shows a front and side view of how the coils are formed and bonded to the stator backing plates in a three phase version of the arrangement shown in Figure 3. In this embodiment two coils are arranged in sets of three 2a,2b,2c (several sets of three may be bonded to each stator plate). It will be understood that because three coils cover two force units (which each consist of a magnet and two polepieces) the armature must always use an even number of force unit assemblies.

The principal advantages of the invention include the following: 1. The motor can be designed to produce an exceptionally-large torque so that the motor may be directly coupled to the load without the use of gears. 2. The motor can be used to meet the market demand to replace hydraulic rotary mechanisms using cranks to move ship's rudders, for example.

3. There is no requirement for a lining surface of the winding structure that must also act as a bearing and resist hard wear.

4. The armature bearings may be chosen from well-developed, long-life proprietary items.

5. The low friction loading increases the efficiency and the precision of the machine.

6. In the case of an armature having rectangular cross-section, the stator windings are simpler to construct and may be made in segments. 7. The motor may have a sealed construction that allows it to be used in adverse environments or those in which contamination must be prevented. 8. The motor may be designed to be liquid-filled, so that it may be immersed to great depths under the sea in any submarine or oil rig application. It will be appreciated that the armature may be made from a magnetic material or alternatively may be made from a set of coils. Further, the armature may have a continuous structure within the stator or may be formed by one or more separate plates.

Claims

CLAIMS:

1. An electromagnetic apparatus comprising: an armature (3) which includes means for generating a magnetic field and arranged to rotate about a central shaft member; a stator assembly forming a channel (23) including two opposing walls (23a,23b), each provided with at least one magnetic element (2) arranged to emit a magnetic field, the magnetic elements from each wall creating a balanced magnetic field through which the armature is arranged to be displaced.

2. The apparatus of claim 1 wherein the magnetic element is in the form of a coil adapted to provide a magnetic field in response to an electrical control signal.

3. The apparatus of claims 1 or 2 wherein at least one bearing is arranged between the central shaft member and stator assembly thereby preventing the armature from contacting the opposing walls of the channel formed by the stator assembly.

4. The apparatus of claims 1, 2, or 3 wherein a support bearing is arranged between the armature and the channel formed by the stator assembly.

5. The apparatus of any one of the preceding claims wherein the channel is circularly shaped.