GB1581350A

GB1581350A - Electrical motor

Info

Publication number: GB1581350A
Application number: GB1032777A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-03-14
Filing date: 1978-03-14
Publication date: 1980-12-10

Description

(54) ELECTRICAL MOTOR (71) 1, PETER CAMPBELL, a British citizen, of 21 St. Mary's Avenue, Alverstoke, Gosport, Hampshire, do hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an electric motor which is particularly suitable for developing a comparatively high torque at a comparatively low speed.

An electric motor in accordance with the invention comprises a stator, an armature rotatably supported for rotation about its axis relative to the stator, said armature incorporating a plurality of overlapping coils lying substantially in a single plane perpendicular to the axis, said coils being supported upon a ring of magnetic material lying in a plane perpendicular to the axis, a surface of said ring bearing slots to accommodate the sides of said coils which lie substantially radially; said magnetic material comprising synthetic resin mixed with iron powder; a commutator comprising a plurality of segments, brush means carried by the stator and coacting with the commutator for the supply of current to the coils, and a magnetic pole structure carried by the stator and having pole faces closely adjacent said coils to create a magnetic field such that the interaction between said field and a field set up by the coils when current is supplied to said brush means causes torque to be applied to said armature.

In the accompanying drawings, Figure 1 is a section through an electric motor in accordance with the invention; Figure 2 is a section on line 2-2 in Figure 1; Figures 3 and 4 are perspective views showing a few consecutive coils and commutator segments of the armature for lap and wave winding arrangements respectively; Figure 5 is a perspective view showing the ring of magnetic material for supporting the coils; Figure 6 is a perspective view showing an alternative arrangement of magnets to form the pole structure.

The motor shown in the drawings includes a stator 10 comprising two toroidal metal rings 11, 12 one of which is attached to the other. A shaft 13 is integral with the ring 12, and this shaft supports the armature 16 by means of deep-groove ball roller bearings 14, 15.

The armature 16 comprises a metal housing 17 shaped with a recess to accommodate a ring 18 of material comprising synthetic resin mixed with iron powder. The ring 18 (shown in Figure 5) lies in a plane perpendicular to the axis and the surface adjacent to the magnets 39 bears a plurality of slots 45 lying substantially radially. The slots 45 are equispaced to correspond with the positions of the sides of the coils which comprise the winding 19. The two sides of a slot 45 are parallel and the bases of the slots 45 lie in a plane perpendicular to the axis. The width and depth of a slot are just sufficient to accommodate a coil side, such that the outermost part of the coil side lies in the plane of the surface of the ring 18 adjacent to the magnets 39. The advantage of using a ring 18 of the shape described is that the axial distance for magnetic flux to travel from a magnet 39 to the ring 18 is only that required for running clearance between the magnets 39 and the ring 18, whereas a ring without slots would necessitate a much greater axial distance. The ring 18 also provides a former for assembling the winding 19, as will be subsequently described.

The ring 18 has a large diameter compared with its axial length, which makes it very difficult to construct using laminations that must be wound circumferentially then annealed and milled to form the slots. A much simpler technique is to use a magnetic mixture comprising a suitable synthetic re sin, such as a catalytic curing epoxy resin, mixed with iron powder. This magnetic mixture is formed into the ring 18 within the armature housing 17. The method of preparing said magnetic mixture is to use proportions of liquid synthetic resin and iron powder that ensure that substantially all of the particles comprising the iron powder receive a coating of the resin, thus ensuring a higher electrical resistivity and a lower eddy-current power loss for said magnetic mixture than would be found with a laminated structure. Furthermore, such proportions are to ensure that a substantially fluid magnetic mixture results, these proportions being approximately 91 per cent weight of iron powder to approximately 9 per cent weight of epoxy resin, so that the winding 19 may be pressed into the ring 18 thus forming the slots 45. Alternatively, such proportions are approximately 96 per cent weight of iron powder to approximately 4 per cent weight of epoxy resin, so that the ring 18 may be constructed by compacting said magnetic material under pressure either as a whole or in parts comprising a ring with two flat surfaces in planes perpendicular to the axis together with a plurality of wedgeshaped pieces equivalent to the teeth 46 separating the slots 45.

The winding 19 is assembled from a plurality of substantially planar coils in various arrangements which will be described separately. The winding 19 may be assembled as a lap winding (shown in Figure 3) from a plurality of substantially planar coils 21 each consisting of a pair of conductors 22, 23 extending substantially radially from the axis of the winding. The sides 22, 23 are connected at the outer periphery by the end 24, and at the inner periphery the sides 22, 23 are extended to the ends 25, 26 these extensions becoming the commutator segments 27, 28 connecting the coil 21 to the two adjacent coils. The coil 21 is not absolutely planar, since portions of the ends are bent down. This arrangement enables the coils 21 to nest together in an annular array with the ends 26, 30 of each coil lying in a plane underlying the plane of the ends 25, 29 of an adjacent coil but with sides 23 lying in the same plane as the sides 22. The commutator segments 27, 28 are formed as part of the coils 21 and comprise extensions 31 of the ends 25 and extensions 32 of the ends 26. The extensions 31, 32 lie substantially radially and substantially in the same planes as the ends 25, 26 respectively such that the extensions 31 directly overlie the extensions 32. At the extremities of the extension 31 closest to the axis, the conductor turns through 180 degrees to become the extension 32 thus connecting adjacent coils 21. In fact, there are 140 of the coils in a lap winding and these are so arranged that the side 22 of each coil lies directly alongside the side 23 of another coil separated from the first mentioned coil in an annular array by 6 or 7 intervening coils.

Alternatively, the winding 19 may be assembled as a wave winding (shown in Figure 4) from a plurality of substantially planar coils 47 each consisting of a pair of conductors 48, 49 extending substantially radially from the axis of the winding. The sides 48, 49 are interconnected at the outer periphery by the end 50, and at the inner periphery the sides 48, 49 are extended to the ends 51, 52, these extentions becoming the commutator segments 53, 54, connecting the coil 47 to the two coils displaced approximately two poles' pitch anticlockwise and clockwise with respect to the first mentioned coil in an annular array. The coil 47 is not absolutely planar, since portions of the ends may be bent down. This enables the coils 47 to nest together in an annular array with parts of the ends 50, 51, 52 of each coil lying in a plane underlying or overlying the plane of the ends 50, 51, 52 of adjacent coils but with the sides 48, 49 of each coil 47 lying in the same plane as the sides 48, 49 of all other coils 47. The portion of the ends 50, 51, 52, which is bent down out of the plane of the sides 48, 49 of any given coil 47 depends upon where the coil stands in the order of assembly of the coils 47 in the wave winding. Thus, the ends of the first few coils to be assembled will lie beneath the ends of the last few coils to be assembled. The commutator segments 53, 54 are formed as part of the coils 47 and comprise extensions 55 of the ends 51 and extensions 56 of the ends 52. The extensions 55, 56 lie substantially radially. At the extremity of extension 55 closest to the axis, the conductor turns through 180 degrees to become the extension 56 such that the extensions 55 directly overlie the extensions 56. In fact, there are 139 of the coils in a wave winding and these are so arranged that the side 48 of each coil lies directly alongside the side 49 of another coil separated from the first mentioned coil in the order of assembly into the annular array by 68 or 78 intervening coils.

A method of winding the coils 21 for a lap winding or the coils 47 for a wave winding is to use a jig whose cross-section is substantially that of a single coil developed into a plane. The coils are wound continuously along the axial length of the jig, the jig is then removed, and the coils arearranged in an annular array with the ends and extensions bent out of the plane as described above. The bends may be imparted while the winding is on the jig or when it is assembled in an annular array on a former which may be the ring 18. After the full complement of coils have been arranged, the two ends of the conductor are connected together thus forming a continuous winding.

The winding 19 and the commutator 20 are thus supported in the armature housing 17 on the ring 18, and they are fixed in position by encapsulating with a suitable synthetic resin, such as a catalytic curing epoxy resin, which may have iron powders mixed with it and may therefore be the same as the substantially fluid magnetic mixture already described. The positions of the coils 21 or 47 and the commutator 20 are such that they are given only a thin protective and rigidifying coating as the armature surface adjacent to the magnets 39. The commutator 20 is then completed by machining from the armature surface a thin layer across the extensions 31 or 55 such that part of the conductor in the extensions 31 or 55 respectively is removed leaving a planar surface comprising a plurality of conducting segments lying substantially radially, each segment being insulated from adjacent segments by the encapsulating material.

The winding 19 may alternatively be assembled either as a lap winding as already described and shown in Figure 3 or as a wave winding as already described and shown in Figure 4 but from a plurality of substantially planar coils 21 or 47 each consisting of a plurality of turns. If one of said coils 21 or 47 consists of N turns, the sides 22 23 or 48, 49 and their respective end 24 or 50 will consist of N conductors, and there will be N-1 conductors at the inner periphery connecting N-1 of the conductors in side 22 or 48 to M-1 of the conductors in side 23 or 49 respectively. The N turns of each coil are wound consecutively and the ends 25, 26 or 51, 52 are extensions of the side 22 or 48 of the first turn and the side 23 or 49 of the Nth turn respectively, these ends becoming the commutator segments as already described. These coils comprising a plurality of turns may be given temporary rigidity by using wire coated with a thermosetting resin, and they are then assembled as a lap or wave winding with portions bent out of the plane as already described for single turn coils. The commutator segments may be reinforced by soldering to them larger sections of conducting material prior to the addition of the encapsulating material. The method already described by which the whole winding is wound continuously along the axial length of a jig is applicable in the case of coils comprising a plurality of turns.

In this case, removable spacers are located along the length of the jig the distance between adjacent spacers governing the number of layers the turn should occupy in a coil and the shape of the spacers determining the length of the connection between adjacent coils.

When the winding 19 is assembled as a lap winding or a wave winding from a plurality of coils each consisting of a plurality of turns, then any number of said windings 19 may be assembled closely adjacent each other in a plane perpendicular to the axis and may be connected electrically together to form a composite lap or wave windings.

A winding 19 and commutator 20 of any type described above and supported on the ring 18 may be fixed within the armature housing 17 as already described or they may be encapsulated in a mould with a suitable synthetic resin which itself forms the housing 17.

For supplying current to the commutator 20 there are a plurality of brushes 33. These brushes extend axially with respect to the shaft 13 and are held against the commutator 20 by means of springs 44. The brushes 33 are telescopically received by insulative sockets 34 of appropriate cross-section integrally formed in blocks 35 of insulative material. Alternative brushes 33 are connected by pigtails 36 that project through openings in the metal ring 12 to a terminal 37 that is insulated from the ring 12 and is mounted externally on the stator 10 to allow an external connection to be made thereto.

The remaining brushes 33 are connected by pigtails 36 that project through openings in the ring 12 and by screws 38 to the ring 12.

The stator 10 supports a pole structure constituted by a ring of twenty permanent magnets 39 which extend axially with respect to the shaft 13. The magnets 39 have pole faces closely adjacent the winding 19 and are carried on a magnetic ring 11 fixed to the ring 12. The magnets 39 are equispaced circumferentially on the ring 11 and are shaped as segments of a toroid with two edges lying substantially radially. The magnets 39 are magnetised either before assembly onto the ring 11 or in situ in the motor so that alternate magnets present north pole faces to the armature. Each pair of adjacent magnets is therefore part of a magnetic circuit including the rings 11, 18 and the air gap between the winding 19 and the magnets 39. An alternative arrangement of magnets to form the pole structure will be described subsequently.

When current is passed through the motor by applying a d.c. voltage between terminal 37 and the ring 12, the armature 16 is caused to rotate. As a result of the use of a slotted ring of the said magnetic mixture to support the armature winding, a relatively high torque is applied to the armature at a relatively low rotational speed as compared with known motors with disc-type armatures.

For initial magnetisation of the magnets 39 in situ in the motor there are a plurality of magnetising coils 40 on the magnets 39 respectively. The coils 40 each consist of a few turns of wire and are wound alternately in opposite senses to provide alternately reversed magnetising fields. These coils may be formed from a single length of wire so that the coils are in series. One end of the wire is connected to a terminal 41 that is insulated from the ring 12 and is mounted externally on the stator 10. The other end of the wire is connected to the terminal 37. For initial magnetisation of the magnets 39 a d.c. voltage is applied to the terminals 37, 41. Thereafter, the terminal 41 may be employed for energising the motor so that the armature current flows through the coils 40 in series, the terminal 37 being disconnected from the supply. Thus, when the current is high the field set up by the magnetising coils 40 will counteract the demagnetising effect of the armature field and prevent demagnetisation of the permanent magnets 39.

There are certain permanent magnet materials notably the ceramic ferrite type, that will not provide the high field required to develop relatively high torque at low speeds without the use of magnetic pole pieces to focus the flux into the air gap. An advantage of these permanent magnet materials is that they do not require magnetisation in situ in the motor and hence no magnetising coils 40 are required. Part of an alternative pole structure to that already described that is particularly suitable for permanent magnets of the ceramic ferrite type is shown in Figure 6. This alternative pole structure comprises a plurality of magnetic segments 57 each with a face 60 shaped substantially as a segment of a toroid and with each of two edges 58 lying in a plane parallel to that of the neighbouring edge of the adjacent segment 57, and a plurality of permanent magnets 59 magnetised so that the magnets 59 present pole faces of like polarity to the two edges 58.

The pole faces of the magnets 59 are rectangular and they may extend beyond the diameter of the outer periphery of the winding provided that the shape of the segments 57 is substantially that shown in Figure 6. Any section through a segment 57 has such an area as to maintain a constant flux density throughout the segment 57. The segments 57 now have faces 60 closely adjacent the winding 19 such that alternate segments present north pole faces to the armature. The alternative pole structure comprising the segments 57 and permanent magnets 59 is given structural rigidity by an encapsulating mass of synthetic resin material which may be integral with the blocks 35 of insulative material. This pole structure is either fixed directly to the ring 12 without the magnetic ring 11 or the encapsulating mass itself forms the stator 10. One magnet 59 is therefore part of a magnetic circuit including two adjacent segments 57, the ring 18 and the air gap between the winding 19 and the segments 57.

Figure 1 shows the motor as used for the direct driving of a bicycle wheel. The shaft 13 is attached to a spindle 42 which is carried by the front forks or the frame of the bicycle. The armature housing 17 carries two flanges 43 around its periphery in which holes may be drilled to permit the attachment of wheel spokes.

WHAT I CLAIM IS:- 1. An electric motor comprising a stator, an armature rotatably supported for rotation about its axis relative to the stator, said armature incorporating a plurality of overlapping coils lying substantially in a single plane perpendicular to the axis, said coils being supported upon a ring of magnetic material lying in a plane perpendicular to the axis, a surface of said ring bearing slots to accommodate the sides of said coils which lie substantially radially; said magnetic material comprising synthetic resin mixed with iron powder; a commutator comprising plurality of segments, brush means carried by the stator and co-acting with the commutator for the supply of current to the coils, and a magnetic pole structure carried by the stator and having pole faces closely adjacent said coils to create a magnetic field such that the interaction between said field and a field set up by the coils when current is supplied to said brush means causes torque to be applied to said armature.

2. An electric motor as claimed in Claim 1 in which said magnetic material comprises proportions of approximately 91 per cent weight of iron powder to approximately 9 per cent weight of epoxy resin, thus ensuring a substantially fluid mixture; furthermore, said magnetic material is to be prepared in such a way that substantially all of the particles comprising said iron powder receive a coating of said resin, thus ensuring a high electrical resistivity for said mixture.

3. An electric motor as claimed in Claim 1 in which said magnetic material comprises proportions of approximately 96 per cent weight of iron powder to approximately 4 per cent weight of epoxy resin, thus ensuring a substantially powdered mixture; furthermore, said magnetic material is to be prepared in such a way that substantially all of the particles comprising said iron powder receive a coating of said resin, thus ensuring a high electrical resistivity for said mixture when it has been compacted.

4. An electric motor as claimed in any preceding Claim in which each armature coil has a pair of conductors extending substantially radially from the axis, said conductors are interconnected at the outer periphery by an end, part of said end being bent down to enable said coils to nest together in an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. few turns of wire and are wound alternately in opposite senses to provide alternately reversed magnetising fields. These coils may be formed from a single length of wire so that the coils are in series. One end of the wire is connected to a terminal 41 that is insulated from the ring 12 and is mounted externally on the stator 10. The other end of the wire is connected to the terminal 37. For initial magnetisation of the magnets 39 a d.c. voltage is applied to the terminals 37, 41. Thereafter, the terminal 41 may be employed for energising the motor so that the armature current flows through the coils 40 in series, the terminal 37 being disconnected from the supply. Thus, when the current is high the field set up by the magnetising coils 40 will counteract the demagnetising effect of the armature field and prevent demagnetisation of the permanent magnets 39. There are certain permanent magnet materials notably the ceramic ferrite type, that will not provide the high field required to develop relatively high torque at low speeds without the use of magnetic pole pieces to focus the flux into the air gap. An advantage of these permanent magnet materials is that they do not require magnetisation in situ in the motor and hence no magnetising coils 40 are required. Part of an alternative pole structure to that already described that is particularly suitable for permanent magnets of the ceramic ferrite type is shown in Figure 6. This alternative pole structure comprises a plurality of magnetic segments 57 each with a face 60 shaped substantially as a segment of a toroid and with each of two edges 58 lying in a plane parallel to that of the neighbouring edge of the adjacent segment 57, and a plurality of permanent magnets 59 magnetised so that the magnets 59 present pole faces of like polarity to the two edges 58. The pole faces of the magnets 59 are rectangular and they may extend beyond the diameter of the outer periphery of the winding provided that the shape of the segments 57 is substantially that shown in Figure 6. Any section through a segment 57 has such an area as to maintain a constant flux density throughout the segment 57. The segments 57 now have faces 60 closely adjacent the winding 19 such that alternate segments present north pole faces to the armature. The alternative pole structure comprising the segments 57 and permanent magnets 59 is given structural rigidity by an encapsulating mass of synthetic resin material which may be integral with the blocks 35 of insulative material. This pole structure is either fixed directly to the ring 12 without the magnetic ring 11 or the encapsulating mass itself forms the stator 10. One magnet 59 is therefore part of a magnetic circuit including two adjacent segments 57, the ring 18 and the air gap between the winding 19 and the segments 57. Figure 1 shows the motor as used for the direct driving of a bicycle wheel. The shaft 13 is attached to a spindle 42 which is carried by the front forks or the frame of the bicycle. The armature housing 17 carries two flanges 43 around its periphery in which holes may be drilled to permit the attachment of wheel spokes. WHAT I CLAIM IS:-

1. An electric motor comprising a stator, an armature rotatably supported for rotation about its axis relative to the stator, said armature incorporating a plurality of overlapping coils lying substantially in a single plane perpendicular to the axis, said coils being supported upon a ring of magnetic material lying in a plane perpendicular to the axis, a surface of said ring bearing slots to accommodate the sides of said coils which lie substantially radially; said magnetic material comprising synthetic resin mixed with iron powder; a commutator comprising plurality of segments, brush means carried by the stator and co-acting with the commutator for the supply of current to the coils, and a magnetic pole structure carried by the stator and having pole faces closely adjacent said coils to create a magnetic field such that the interaction between said field and a field set up by the coils when current is supplied to said brush means causes torque to be applied to said armature.

annular array with the conductors of all the coils lying in a single plane.

5. An electric motor as claimed in any of Claims 1 to 3 in which each armature coil has a plurality of turns, each of said turns comprise a pair of conductors extending substantially radially from the axis, said conductors are interconnected at the outer periphery by an end, and said turns are interconnected consecutively at the inner periphery by ends; furthermore, part of said ends are bent down to enable said coils to nest together in an annular array with the conductors of all the coils lying in a single plane.

6. An electric motor as claimed in Claim 4 or 5 in which there is a plurality of said annular arrays of coils. and each of said arrays are assembled closely adjacent each other in a plane perpendicular to the axis and are interconnected electrically.

7. An electric motor as claimed in any of Claims 4 to 6 in which each commutator segment is formed by extensions to the conductors on opposite sides of two consecutive coils in an annular array. such that one extension turns through 180 degrees at the inner periphery to become the other extension. such that one said extension directly overlies the other extension in an annular array for a length Ivino substantially radially. the remaining length of the underlying extension being bent down from the plane of the conductors such that the whole of that extension is substantially in one plane. enabling said coils to nest together in an annular array with the conductors of all the coils lying in a single plane: the said commutator is completed by removing a thin layer from the upper laver of said extensions across said lengths to provide a plurality of conducting segments.

8. An electric motor as claimed in Claim 7 in which said commutator segments are reinforced by soldiering to them laroer sections of conducting material.

9. An electric motor as claimed in anv preceding Claim in which said pole structure comprises a plurality of permanent magnets mounted on a magnetic ring on one axial side of the armature. magnetised so that the magnets present pole faces of alternate polarity to the armature. and shaped as segments of a toroid with two edges lying substantially radially.

10. An electric motor as claimed in anv of Claims 1 to S in which said pole structure comprises a plurality of magnetic segments on one axial side of the armature. each shaped substantially as a segment of a toroid with each of two edges lying in a plane parallel to that of the neighbouring edge of the adjacent segment and a plurality of permanent magnets magnetised so thai the magnets present pole faces of like polarity to the two forementioned edges.

11. An electric motor as claimed in Claim 9 in which there are a plurality of magnetising coils on the magnets respectively connected in series with each other and, via said brush means, with the armature coils, whereby the demagnetising effect of the field set up in use by the armature coils is counteracted.

12. An electric motor substantially as hereinbefore described with reference to and as shown in the accompanying drawings.