Inductive torque transmitter with stationary field winding

An electromagnetic torque transmission structure for transmitting torque from one shaft to a second aligned shaft, the structure including an excitation-rotor attached to a first shaft, an induction-rotor attached to a second shaft, and a magnetic field-exciter. An inner pole, an outer pole and a pole-connecter of the excitation-rotor surround the inner and outer surfaces and one end of the hollow induction-rotor cylinder. At least an inner or outer pole includes field concentrators. A stationary winding with magnetic circuitry provides an excitation field associated with the excitation-rotor. Magnetic fields from induced currents in the induction-rotor react with fields from the excitation-rotor to provide torque transmission between shafts.

RELATED APPLICATIONS 
This application is realted to U.S. Patent Application Ser. No. 128,716, 
Brushless Alternator and Synchronous Motor With optional Stationary Field 
Winding; to U.S. Patent Application Ser. No. 128,719, Dual-Rotor Induction 
Motor With Stationary Field Winding; and to U.S. Patent Application Ser. 
No. 128,718, Transformer and Synchronous Machine With Stationary Field 
Winding; all of which were filed by the same inventor on the same date as 
this application. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is in the field of torque transmission and, in particular, 
the field of electromagnetic coupling of torque from one shaft to a second 
shaft aligned with the first shaft. 
2. Description of the Prior Art 
Commercially successful prior-art devices for transmission of torque from 
one shaft to a second aligned shaft primarily use mechanical or fluid 
means for transmission of rotational forces. The use of electrical torque 
transmission methods, such as generator-motor combinations, has been 
generally limited to applications in which torque is transmitted to a 
remote location. The additional construction expense, the size and the 
weight associated with use of traditional generator-motor devices 
generally precludes use where torque is transmitted from one shaft to a 
second aligned shaft. 
BRIEF SUMMARY OF THE INVENTION 
This invention discloses an electromagnetic torque transmitter that 
includes a double-rotor structure having an excitation-rotor attached to a 
first shaft, a hollow cylindrical induction-rotor attached to a second 
shaft, and a stationary field-excitation means. The cylindrical 
excitation-rotor includes inner- and outer-pole members concentrically 
attached to one side of a pole-connecting means. The outer-pole member, 
inner-pole member and pole-connecting means surround the outer and the 
inner surfaces of and one end of the hollow cylindrical induction-rotor. 
At least one of the inner-and outer-pole members includes field 
concentrator members. A stationary field winding with associated magnetic 
circuitry is used to provide field excitation to the excitation-rotor. The 
field-excitation means combines with the excitation-rotor to provide 
time-and space-varying magnetic fields that induce currents in the 
induction-rotor during operation. The induced currents produce magnetic 
fields which react with the excitation-rotor fields to provide torque 
transmission between shafts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1, 2, 3 and 4, excitation-rotor 1 includes a cylindrical 
inner-pole member 2 and a cylindrical outer-pole member 3, both pole 
members 2 and 3 being concentrically attached to, or formed with, annular 
pole-connecting means 4 such that poles 2 and 3 extend from the same side 
of connector 4. Connector 4 is illustrated in FIGS. 1 and 2 as including 
annular excitation-rotor disc member 5 with concentrically attached inner 
and outer extensions 6 and 7 which are attached to, or formed with, pole 
members 2 and 3. Pole members 2 and 3 and inner and outer extensions 6 and 
7 are fabricated using material having relatively high magnetic 
permeability. Excitation-rotor positioning means 8 includes a first shaft 
concentrically attached to, or formed with, members 2 and 3 and connector 
4. Field concentrator members 9 are illustrated as forming inner pole 2. 
Excitation-rotor disc 5, as illustrated in FIGS. 1 and 2, is fabricated 
using material having relatively high magnetic permeability. As 
illustrated in FIGS. 3 and 4, excitation-rotor disc 5 is fabricated using 
material having relatively low magnetic permeability in at least a 
circumferential portion between extensions 6 and 7. In FIGS. 3 and 4, 
extensions 6 and 7 extend radially and axially a distance from 
excitation-rotor disc 5 in the direction opposite pole members 2 and 3. 
Induction-rotor 10 includes inductive-means 11 which is illustrated in the 
Figures as a hollow cylinder 11. Cylinder 11 is fabricated using 
electrically conductive material and has a relatively short radial 
thickness. Inductive-means 11 may, in the alternative, include a hollow, 
cylindrical, laminated, magnetic core on which squirrel-cage windings are 
formed. Cylinder 11 is attached to, or formed with, induction-rotor 
positioning means 12, which includes a second shaft 12a and a third shaft 
12b. Induction-rotor positioning means 12 and excitation-rotor positioning 
means 8 position inductive-means 11 and poles 2 and 3 such that an air gap 
exists between each outer surface of inner pole 2 and the 
inner-cylindrical surface of inductive-means 11 and such that at least one 
air gap exists between the inner surface of outer-pole 3 and the 
outer-cylindrical surface of inductive-means 11. 
Hollow cylindrical stator 13, as illustrated in FIGS. 1 and 2, is 
concentrically attached to stator positioning means 14. Stator 13 is 
positioned concentrically by stator positioning means 14, by 
induction-rotor positioning means 12, and by excitation-rotor positioning 
means 8 such that an air gap exists between the inner-cylindrical surface 
of stator 13 and the outer-cylindrical surface of inductive-means 11 and 
such that an air gap exists between the outer-cylindrical surface of 
stator 13 and the inner surface of outer pole 3. Stator 13 is illustrated 
in FIGS. 1 and 2 as a high-magnetic-permeability configuration including 
commonly used layers of sheet steel or other magnetically permeable 
material separated by material having high electrical resistivity. The 
laminations should preferably be planar in planes defined by the structure 
cylindrical-coordinate, radial-angular directions, where the axial 
coordinate of the structure is defined to coincide with the centers of the 
first and second shafts. 
Stator 13, as illustrated in FIGS. 3 and 4, is positioned concentrically by 
stator positioning means 14 and by excitation-rotor positioning means 8 
such that a short air gap exists between the end of the outer-cylindrical 
surface of inner extension 6 opposite inner pole 2 and the cylindrical 
surface of stator 13 and such that a short air gap exists between the 
cylindrical surface of stator 13 and the end of the inner-cylindrical 
surface of outer extension 7 of connector 4 opposite outer pole 3. 
Excitation-rotor means 1 and induction-rotor means 10 are positioned 
concentrically by excitation-rotor positioning means 8 and inductive-rotor 
positioning means 12 such that only one air gap exists between the 
outer-cylindrical surface of inductive-means 11 and the inner surface of 
outer pole 3. The axial length of stator 13 defines the axial length of 
poles 2 and 3 for the purposes of this description 
Field winding 15 is illustrated in the Figures as including an insulated 
conductor 16 attached to the end of cylindrical stator 13 adjacent to disc 
5 of connector 4. The ends of conductor 16 should usually extend through 
the stator 13 of FIGS. 1 and 2 in close proximity to each other, to 
prevent alternating voltages and currents from being induced in winding 
15. Attaching means 17 attaches stator 13 and field winding 15 to a 
reference structure, not shown. 
During operation, a source of preferably direct current energy is connected 
to conductor 16 of field winding 15. For most applications the source 
should provide a variable magnitude direct current to winding 15. The 
currents in field winding 15 and in inductive-means 11 produce magnetic 
fields that extend through paths consisting of stator 13, inner and outer 
poles 2 and 3, inductive-means 11 and, in Figures 1 and 2, connector 4 
including disc 5. In FIGS. 3 and 4, the field path includes extensions 6 
and 7 but does not include disc 5 of connector 4. If there is a relative 
torque difference between the first shaft of excitation-rotor positioning 
means 8 and the second shaft of induction-rotor positioning means 12, 
inductive-means 11 will rotate at a speed less than, or grater than, the 
rotational speed of poles 2 and 3. The concentration of magnetic fields 
caused by concentrators 9 induces currents in inductive-means 11. The 
reaction of the fields associated with concentrators 9 with the fields 
associated with the currents induced in inductive-means 11 causes torque 
to be transmitted between the first shaft and the second shaft of 
positioning means 8 and 12. The torque transmitted varies with the 
magnitude of current in field winding 15 and with the slippage between 
rotors 1 and 10. 
Winding 15 may be energized by alternating current windings, not 
illustrated, mounted on stator 13 of FIGS. 1 and 2 and with appropriate 
circuitry to convert the alternating current to direct current. Use of 
such circuitry requires that poles 2 and 3 have sufficient residual 
magnetism to initiate current flow during onset of operation. 
Field concentrators 9 of excitation-rotor 1 are indicate in FIGS. 1 and 2 
as being shaped with non-uniform-length air gaps between the outer 
surfaces of each concentrator 9 and inner-cylindrical surface of 
inductive-means 11. The shapes of concentrators 9 may be, for example, 
sinusoidal or half-sinusoidal with uniform-length air gaps, although those 
configurations are better suited for use with a squirrel-cage version of 
inductive-means 11 rather than with a conductive cylinder version of 
inductive-means 11 because of resulting concentrations of current in a 
conductive cylinder and the possibly excessive heat generated thereby. The 
shape and number of concentrators 9 should be chosen to avoid unnecessary 
concentrations of current in a conductive cylinder version of 
inductive-cylinder 11. Concentrators 9 may be formed to have increased 
thickness at the ends near connector 4 to provide improved structural 
integrity and to provide more uniform magnetic flux density throughout 
each such concentrator 9. 
Concentrators 9 may be included in either or both inner and outer poles 2 
and 3 of excitation-rotor 1. If concentrators 9 are used for both inner 
and outer poles 2 and 3, concentrators 9 should be paired along the same 
radii as illustrated in FIG. 1A. Outer pole 3, if including concentrators 
9, should preferably include concentrators 9 fabricated in an enclosed 
cylinder having non-uniform air gaps if the application requires 
minimization of radiation of energy at frequencies that may cause 
interference with operation of any nearby electronic equipment. 
In the embodiment of FIGS. 3 and 4, extensions 6 and 7 of connector 4 must 
be of sufficient length that the magnetic flux density in the air gaps 
between extensions 6 and 7 and stator disc 16 is uniform throughout the 
circumference of those air gaps. A non-uniform magnetic flux density in 
those air gaps will cause eddy currents to be induced in stator 13. Those 
currents will cause a friction-like torque that will degrade performance 
of the device and may cause the temperature of the metal near the air gap 
to rise to excessive levels. 
Operation of the device will cause positively and negatively charged 
regions in inner and outer portions of excitation-rotor 1 because the 
magnetic field associated with field winding 15 does not rotate. For 
applications at usual rotational speeds, the electric fields associated 
with those charges may be ignored. 
If a conductive cylinder is included in inductive-means 11, that cylinder 
should have a relatively short radial thickness to minimize the effective 
length of the air gap between inner and outer poles. Use of a 
squirrel-cage winding mounted on a laminated steel core, or use of a 
cylinder 11 composed of a material that is both conductive and has a high 
magnetic permeability, will result in decrease of the effective length of 
the air gap. 
The means for inducing field excitation for FIGS. 1, 2, 3 and 4 includes 
field winding 15, a magnetic circuit means including stator 13, and stator 
positioning means 14. The magnetic circuit means completes the closed 
magnetic field path which includes magnetically permeable poles 2 and 3, 
extensions 6 and 7 and the radial thickness of inductive-means 11. The 
closed magnetic field follows a path that passes through the circle formed 
by field winding 15. 
In FIGS. 1 and 2, the magnetic circuit means includes stator 13 and 
magnetically permeable excitation-rotor disc 5. Stator 13 extends into the 
air gap between inductive-means 11 and outer pole 3, causing the closed 
magnetic field path to have a third air gap. 
In FIGS. 3 and 4, the magnetic circuit means includes stator 13 and 
elongated magnetically permeable extensions 6 and 7. Excitation-rotor disc 
5 must be composed of material with low magnetic permeability. The air 
gaps between stator 13 and extensions 6 and 7 result in a total of four 
air gaps in the closed magnetic field path. 
Excitation-rotor positioning means 8, induction-rotor positioning means 12 
and stator positioning means 14 may be of sleeve, ball, roller or other 
configurations known in the art. As is well-known, positioning means 8, 12 
and 14 may each take any of several configurations that accomplish the 
purpose of maintaining the relative rotary positions of excitation-rotor 
means 1, induction-rotor means 10 and stator 13. Such configurations 
include shafts and journals attached to or formed with any or all of 
excitation-rotor means 1, induction-rotor means 10 and stator 13. Torque 
may be transmitted to or from any part of excitation-rotor 1 or 
induction-rotor 10. For example, belt pulleys may be attached to either or 
both rotor first and second shafts, or may be formed with rotor 
positioning means 8 and 12. 
Field winding 15 should be attached to stator 13 such that conductor 16 is 
at least a short distance from any magnetically permeable part, including 
stator 13 to which it is attached. 
Stator positioning means 14 should be formed from nonmagnetic material in 
at least the region extending between inner pole 2 and outer pole 3 or 
should be constructed such that its nearest surface is distanced from 
either pole 2 or 3 by a relatively long air gap. 
Attaching means 17 attaches field winding 15, stator 13 and stator 
positioning means 14 to a reference structure, not shown. Attaching means 
17 may include bolts extending through the length of stator 13. In the 
configuration of FIGS. 1 and 2, bolts 17 should preferably be composed of 
material having a very high electrical resistivity. If the bolts 17 are 
electrically conductive, they should be insulated from electrically 
conductive parts to prevent undesired current flow from voltages induced 
along their lengths by time-varying fields that pass through the stator. 
To minimize the possibility of undesired current flow, the number of bolts 
17 should be equal to the number of concentrators 9 and the bolts 17 
should be spaced uniformly around an end circumference of stator 13. Each 
of the insulated bolts 17 may be electrically grounded at one end, for 
example, to a reference structure. The same considerations apply to use of 
clamps or other devices for attaching means 17. 
The embodiments described above and indicated in drawings are illustrative 
and are not to be interpreted in a limiting sense. Many variations, 
modifications and substitutions may be made without departing from the 
scope of the claimed invention. Certain of those variations, modifications 
and improvements may be patentable, yet fall within the claims of this 
invention.