WO2005086323A1

WO2005086323A1 - Dc excited field transverse flux motor

Info

Publication number: WO2005086323A1
Application number: PCT/US2004/003232
Authority: WO
Inventors: Robin Miller; Paul Wagner; Zbigniew Piech; Jacek Gieras; Kitty Liu
Original assignee: Otis Elevator Company
Priority date: 2004-02-04
Filing date: 2004-02-04
Publication date: 2005-09-15

Abstract

A three-phase transverse flux motor (20) has three stator assemblies (38-40) with hollow annular soft magnetic bases (36) containing ac coils (43). The rotor comprises four soft magnetic bases (68, 50-52, 69) and a plurality of interdigitated pairs of magnetic segment rings (59, 53; 54, 55; 56, 57; 58, 60) each secured to a pair of said bases centered on isolation ring (76) between the bases. Instead of permanent magnets, the rotor magnetic fields are provided by dc excitation coils (63, 46-48, 64). The flux from the dc excitation coils is applied to the stator annuli in an alternating north/ south fashion due to the interdigitated magnetic segments, thereby eliminating the need for expensive, rare earth permanent magnets on the rotor.

Description

DC EXCITED FIELD TRANSVERSE FLUX MOTOR

Background of the invention Technical Field This invention relates to a transverse flux motor having dc excited fields distributed by claw-type rotor segments to eliminate permanent magnets on the armature.

Background Art It is known that transverse flux motors have a number of advantages over conventional electric motors. The TFM has no stator end-turns, and each stator module is completely self-contained, there are no flux path connections or interaction necessary to other stator modules, so it can be combined in any number of units to assemble a motor in a modular fashion. An exemplary utilization is elevator motors, which operate at slow rotating speeds. For decades of maintenance-free, smooth operation and low noise, gearing is to be avoided if possible. The deciding factor on motor requirements is the torque output per unit of active material volume - core steel, copper wire and permanent magnets. Unlike conventional electric motors, TFMs do not have their phases integrated into one monolithic core structure; instead, each phase has its own separate magnetic path, though some designs may have shared sections between poles. TFM motors can be assembled, in a modular fashion, by integrating separate rotor/stator drive modules, either one or a multiple per phase, depending on the desired load and torque capabilities. A major problem with the preferred, synchronous TFMs is that the stator has heretofore required expensive, rare earth permanent magnets on the rotor. This causes a TFM, to be considerably more expensive than conventional motors per load/torque size. Thus, obtaining the advantages of a TFM, particularly the modular motor integration capability, is far offset by the excessive cost. Disclosure of Invention Objects of the invention include: a low cost TFM; eliminating permanent magnets in a TFM; and an improved motor having all the characteristics of the TFM without the need for expensive rare earth permanent magnets on the rotor.

According to the present invention, dc excitation coils mounted on the stator provide magnetic fields which are distributed in an alternative north/south fashion by interdigitated magnetic segments disposed on the rotor of the TFM. In one embodiment, a three-phase motor having one stator/rotor segment per phase, there are five dc excitation coils, three are fixed to each stator coil, with two on either end. There are four pairs of interdigitated segment rings, one on either side of each stator assembly, the interdigitated segments distributing flux to the two sides of the stator soft magnetic material alternatively from one or the other of two dc excitation coils disposed on opposite sides of each leg of the stator soft magnetic material. The present invention totally eliminates permanent magnets from a TFM, thereby reducing its cost substantially.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.

Brief Description of the Drawings Fig. 1 is a partially sectioned, side elevation view of a three-phase TFM according to the invention. Fig. 2 is an exploded perspective view of a three-phase TFM according to the invention. Fig. 3 is a partial, partially sectioned, stylized simplified perspective view of the three- phase TFM of Fig. 1. Fig. 4 is a partial, sectioned side elevation view of the three-phase TFM of Fig. 1 , after the rotor moves by the amount of one segment. Fig. 5 is an exploded perspective detail view of interdigitated segment rings. Fig. 6 is an exploded perspective view of segments of the interdigitated segment rings. Fig. 7 is a perspective view of a pair of interdigitated segment rings when interlaced together.

Mode(s) for Carrying Out the Invention Referring to Figs. 1 and 2, a transverse flux motor (TFM) 20 which requires no permanent magnets on the rotor in accordance with the invention, includes an axial shaft 23 journaled in bearings 24, 25 which are set within respective end caps 28, 29 that are fastened to an enclosure 30, such as by means of screws 27. The enclosure 30 is disposed on a mounting base 31. The enclosure 30 has a slot 34 which engages pins 35 set within hollow annular bases of soft magnetic material 36 of three stator assemblies 38-40, each relating to a corresponding one of three phases of the three phase TFM 20.

Fig. 3 is a simplified schematic that is offered to help in visualizing the invention. Each stator assembly 38-40, also shown in Fig. 3, includes an annular coil 43 with annular, non-magnetic gaps, such as provided by spacers 44, disposed on either side thereof. The wire loops of the coil windings are coaxial with the shaft and respond respectively to three phase drive currents, as in prior art TFMs.

According to the invention, each of the stator assemblies 38-40 also has an annular dc rotor excitation coil 46-48 adhered to the respective annular coils 43 and separated galvanically from the stator coils 43, such as by epoxy resin 49 (Fig. 4). The coils 46-48, when energized with a dc current, which can be varied to suit the load on the motor as needed, provide the dc magnetic field for the armature, thereby eliminating the necessity for expensive, rare earth magnets, as has heretofore been required in TFMs of the prior art.

In the prior art, the magnets on the armature are staggered with north poles interspersed between south poles. To provide the same effect in a TFM of the invention, the rotor assembly includes a plurality of soft magnetic bases 50-52, 68, 69, between which there are interdigitated pairs of magnetic segment rings 59, 53; 54, 55; 56, 57; 58, 60. These are shown in more detail in Figs. 5-7. The interdigitated segments are sometimes referred to as

"claw-type" or "Lundell" tooth systems. With respect to the center phase assembly 39, at an exemplary point of rotation where the cross section is taken in Fig 1 , as illustrated by the direction of cross-hatching, the left side of the soft magnetic annulus 36 will respond to flux equivalent to a south pole provided by the field of the dc excitation coil 46 through the segment 54, while the right side of the soft magnetic annulus will respond to magnetic flux equivalent to a north pole provided by the segment 56 in response to the field of the dc excitation coil 47 As illustrated in Fig 4, after the rotor rotates l/2n of a revolution, where n is the number of segments on each ring 53-60, the left side of the soft magnetic annulus 36 will receive magnetic flux equivalent to a south pole through the segment 55 m response to the dc excitation coil 47, and the right side of the soft magnetic annulus 36 will respond to magnetic flux equivalent to a north pole provided by the segment 57 in response to the dc excitation winding 48 Thus, there is alternating north, south, north, south, etc , magnetic flux provided to the two sides of the magnetic annulus 36 of the center phase stator assembly 39 as the rotor rotates The same is true of the other stator assemblies 38, 40 due to the additional pair of dc excitation windings 63, 64 which are also disposed on the soft magnetic annuluses of the stator assemblies 38, 40, by electric insulation such as epoxy resin 65 The rings of segments 59, 60 cause the magnetic fields of the dc excitation windings 63, 64 to alternatively be provided, or not, to the left and right sides, respectively, of the soft magnetic annuluses of the stator assemblies 38, 40, in the same fashion as described with respect to the stator assembly 39, hereinbefore

The rings 59, 60 are disposed on respective soft magnetic bases 68, 69 Each of the soft magnetic bases 50-52, 68, 69 has a key 72 (Fig 2) that fits within a key slot 73 on the shaft 23 to cause the segment rings, which are press fit or otherwise secured to the soft magnetic bases, to remain properly aligned with one another Each of the soft magnetic bases 50-52, 68, 69 is separated from adjacent bases by gaps, such as provided by magnetic isolation rings 76 The stator assembly 39 is separated from the stator assemblies 38, 40 by magnetic isolation rings 78, 79

The dc excitation coils 63, 64 are of a larger diameter than the coils 46-48 in the embodiment shown herein The coils 63, 64 could be of the same diameter as the coils 46-48, but that would unnecessarily extend the length of the motor, making it heavier and more expensive. The effect is the same, so long as the coils 63, 64 are in flux communication with the corresponding interdigitated segment rings 59, 53 and 58, 60 respectively. A feature of the invention is that the dc excitation level can be adjusted; for example, to attenuate noise and temperature rise under low torque demand, the dc excitation level may be reduced; for greater torque, it may be increased.

The segment rings must be properly spaced from each other. One way to achieve thiso is to coat the segment rings with non-magnetic material, such as epoxy, prior to assembly. A method for assembling the embodiment of the TFM disclosed herein may first preassemble a number of parts, and thereafter move these parts into position on the shaft 2 . For instance, various parts may be "potted" together into subassemblies, such as by means of epoxy resin or other strong, durable adhesive. The end cap 28 will be fastened to the enclosure 30, with thes bearing 24 inserted therein. Then the shaft 23 may be inserted into the bearing 24. A first subassembly to be disposed on the shaft 23 might be the soft magnetic base 68, and the tooth rings 59, 53. Next to be assembled, by being inserted into the enclosure 30 might be a subassembly comprising the soft magnetic annulus 36 of the stator assembly 38 with its pin 35, the coil 63 with its spacer 65, the coil 43 with the spacers 44 and the magnetic isolation ring o 78, together with the dc excitation coil 46 and its spacer 49.

The third subassembly that may be inserted onto the shaft 23 may comprise the soft magnetic base 50, the interdigitated segment rings 54, 55, the spacer 76, and the soft magnetic base 51 , all of which may be adhered together, such as by epoxy, prior to being inserted on the5 shaft 23.

A fourth subassembly which may be inserted into the enclosure 30 may comprise the soft magnetic annulus 36 of the stator assembly 39 together with its pin 35, the corresponding annular coil 43 with its spacers 44, the magnetic isolation ring 79, and the dc excitation coil 47o and its spacer 49. A fifth subassembly which may be inserted onto the shaft 23 may comprise the soft magnetic base 52 with a magnetic isolation ring 76 to the left thereof as seen in Fig. 1, and the segmented rings 56, 57, all of which may be adhered together such as by epoxy. A sixth subassembly which may be inserted into the enclosure 30 may consist of the soft magnetic annulus 36 of the stator assembly 40, together with its pin 35, the corresponding annular coil 43 and non-magnetic spacers 44 on either side thereof, the dc excitation winding 48 together with its spacer 49, the dc excitation winding 64 and its non-magnetic spacer 65. A seventh subassembly which may be inserted onto the shaft 23 after being preassembled with an appropriate adhesive such as epoxy, may comprise the soft magnetic base 69, together with the last magnetic isolation ring 76, and the interdigitated segment rings 58, 60. Then the bearing 25 can be mounted on the shaft 23 and the end cap 29 can be fastened to the enclosure 30.

Claims

1. A rotary transverse flux motor (20) having one or more phases, comprising: an axial shaft (23); a stator assembly (38, 40) for each of said phases, each comprising a hollow soft magnetic annulus (36) surrounding a stator coil (43); characterized by: a dc excitation coil (46-48) disposed on each said stator coil but magnetically isolated (49) therefrom, each of said stator assemblies (38, 40) which is not disposed between additional ones of said stator assemblies having an additional dc excitation coil (63, 64) disposed thereon but magnetically isolated (65) therefrom; a rotor comprising a plurality of soft magnetic bases (50-52, 68, 69) disposed on said shaft there being one for each of said phases plus two more, said bases being magnetically isolated from each other by magnetic isolation gaps (76); and said rotor also comprising a plurality of interdigitated pairs of magnetic segment rings (59, 53; 54, 55; 56, 57; 58, 60), each secured to a pair of said bases centered on a corresponding one of said isolation rings.

2. A motor according to claim 1 wherein: there are three phases.

3. A motor according to claim 1 wherein: there are three stator assemblies (38-40).

4. A motor according to claim 3 wherein: one of said stator assemblies (39) is separated from the other two of said stator assemblies by magnetic isolation gaps (78, 79).

5. A motor according to claim 1 wherein: there are four pairs of rings (59, 53; 54, 55; 56, 57; 58, 60).

6. A motor according to claim 1 wherein: there are five dc excitation coils (46-48, 63, 64).

7. A motor according to claim 1 wherein: there are five soft magnetic bases (50-52, 68, 69).