EP0290503A4 - Electric machine and method of increasing operating efficiency of electric machines. - Google Patents
Electric machine and method of increasing operating efficiency of electric machines.Info
- Publication number
- EP0290503A4 EP0290503A4 EP19870907056 EP87907056A EP0290503A4 EP 0290503 A4 EP0290503 A4 EP 0290503A4 EP 19870907056 EP19870907056 EP 19870907056 EP 87907056 A EP87907056 A EP 87907056A EP 0290503 A4 EP0290503 A4 EP 0290503A4
- Authority
- EP
- European Patent Office
- Prior art keywords
- grooves
- rotor
- eddy currents
- reducing losses
- electric machine
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
- H02K1/22—Rotating parts of the magnetic circuit
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
Abstract
In order to improve the efficiency of electric machines, by reducing losses caused by eddy currents induced by high frequency fluxes, the outer surface (12) of the rotor (10), including the rotor pole face, has a plurality of circumferential grooves (14). The grooves are provided in axially spaced relation along the rotor. Preferably, the method of reducing losses includes the step of forming the grooves by laser cutting (16), which permits the width and spacing of the grooves to be minimized so as to maximize loss reduction by increasing resistance to eddy currents.
Description
ELECTRIC MACHINE AND METHOD OF INCREASING OPERATING EFFICIENCY OF ELECTRIC MACHINES
Field of the Invention
The present invention relates to electric machines and, more particularly, to increasing the operating efficiency of electric machines.
Background of the Invention
Electric machines such as motors and generators are known to suffer from eddy current losses generally due to the fact that eddy currents are generated in the pole face of rotors. This occurs by reason of high frequency fluxes in the air gap between rotors and stators. VThile the losses depend on the frequencies generated and materials utilized for rotor fabrication, they can be very high, particularly in high speed electric machines, which reduces operating efficiency considerably.
2 Generally, it is recognized that eddy current loss = ~ , where V is voltage induced in the surface of the rotor and R is the resistance to eddy current. In order to reduce losses caused by eddy currents induced by fluxes in the air gap between rotors and stators, laminated rotors consisting of alternating layers of conductive material and insulation are conventionally utilized since the insulation layers break up eddy currents and, therefore, tend to reduce eddy current loss. Unfortunately, it is impractical to use laminated rotors with high speed and large rotor diameter electric machines, i.e., electric machines operating in excess of 40,000 RPM with 3.5 inch rotor diameter.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objective by providing an electric machine and method of improving efficiency of electric machines.
Summary of the Invention
Accordingly, the present invention is directed to a method of reducing losses caused by eddy currents induced by high frequency fluxes. The method includes the steps of providing a rotor having an outer surface formed exclusively of a conductive material and machining the outer surface to provide a plurality of circumferential grooves in axially spaced relation. Preferably, the machining step includes forming the grooves by laser cutting which permits the width and spacing of the grooves to be minimized to maximize loss reduction by increasing resistance to eddy currents.
More specifically, the rotor is preferably a solid rotor and the grooves are equally spaced and disposed along the entire length of the rotor. Then, depending upon the particular operating characteristics of a given electric machine, the width, depth and spacing of the grooves can be selected to maximize loss reduction by increasing resistance to eddy currents. Moreover, the grooves are each defined by a pair of parallel side walls terminating in a circum- ferential bottom surface radially inward of the outer surface of the rotor.
In an exemplary embodiment, the electric machine is of a type in which high frequency fluxes are generated which induce eddy currents in a rotor pole face. The inven- tion includes the improvement in such an electric machine including a rotor having an outer surface formed of a conductive material wherein the outer surface of the rotor is provided with a plurality of circumferential grooves in axially spaced relation. With this construction, the operating efficiency of the electric machine is signifi¬ cantly increased by reducing losses caused by induced eddy currents.
Other objects, advantages and features of the present invention will become apparent from the following specification taken in conjunction with the accompanying drawing.
Brief Description of the Drawing
The drawing is a partially schematic cross- sectional view illustrating a rotor being machined for an electric machine utilizing a method all in accordance with the present invention.
Detailed Description of the Preferred Embodiment
An exemplary embodiment of a grooved rotor for an electric machine in accordance with the invention is illustrated in the drawing. The rotor 10 is particularly well suited for use with an electric machine such as a motor or generator in which high frequency fluxes are generated which induce eddy currents in a rotor pole face. As shown, the rotor 10 has an outer surface 12 formed exclusively of a conductive material such as .magnetic steel or a magnetic alloy.
With regard to the rotor 10, it will be seen that the outer surface 12 has a plurality of circumferential grooves 14 in axially spaced relation. The grooves 14, as will be described in greater detail hereinafter, increase the operating efficiency of the electric machine by reducing losses caused by induced eddy currents. Preferably, the grooves 14 are formed by machining the outer surface 12 of the rotor 10 by means of laser cutting with a laser generating device 16. The present invention is also directed to a method of reducing losses caused by eddy currents induced by high frequency fluxes. The method includes the steps of
providing a rotor 10 having an outer surface 12 formed exclusively of a conductive material and, thereafter, machining the outer surface 12 to.provide a plurality of circumferential grooves 14 in axially spaced relation. Moreover, the method preferably includes the step of selecting the width, depth and spacing of the grooves 14 to maximize loss reduction by increasing resistance to eddy currents.
As shown, the rotor 10 is preferably a solid rotor and the grooves 14 are preferably equally spaced and disposed along the entire length of the rotor 10. The grooves 14 are each defined by a pair of parallel side walls IS and 20 terminating in a circumferential bottom surface 22 radially inwardly of the outer surface 12 of the rotor 10. With this construction, the side walls IS and 20 are preferably transverse to the axis of the rotor 10 and the bottom surfaces 22 are preferably generally concentric with the outer surface 12 of the rotor 10.
By utilizing laser cutting with the laser generating device 16, the width and spacing of the grooves
14 can be minimized to maximize loss reduction by increasing resistance to eddy currents. It is also then possible to select the depth of the grooves to maximize loss reduction in the same fashion. While it might be possible to utilize conventional machining techniques for forming the grooves 14, it is advantageous to employ laser cutting due to the enhanced operating efficiencies, this can be achieved.
As will be appreciated, laser cutting by means of the laser generating device 16 permits creation of very thin grooves 14. For instance, the grooves 14 can be formed on the order of 0.006 inches wide by 1/8 inch deep and can be spaced apart by a distance on the order of 0.030-0.040
inches. In order to minimize losses caused by eddy currents induced by high frequency fluxes, the width and spacing of the grooves 14 is minimized to the extent possible.
In this connection, minimizing the width and spacing of the grooves 14 increases the length of eddy current path. This, in turn, increases the resistance and, hence, losses are reduced considerably by reason of the fact that eddy current loss - -v-— , where V is voltage induced in the outer surface 12 of the rotor 10 and R is the resistance to eddy current. The width, depth and spacing of the grooves 14 can be controlled and optimized for given performance parameters.
By providing the thinnest air gap possible between the respective pairs of side walls 18 and 20, the high frequency fluxes which extend perpendicular to the axis of the rotor 10 are broken. This increases the resistance to eddy current at the gaps and, therefore, decreases losses. While useful in any high speed electric machine, it is particularly advantageous for use in organic Rankine cycle engines of the type that may. be utilized in the Space Station.
While in the foregoing there has been set forth a preferred embodiment of the invention, it is to be under¬ stood that the invention is only to be limited by the spirit and scope of the appended claims.
Claims
We Claim:
1. A method of reducing losses in electric machines caused by eddy currents in rotors induced by high frequency fluxes, comprising the steps of: providing a rotor having an outer surface formed exclusively of a conductive material; and machining said outer surface to provide a plurality of circumferential grooves in axially spaced relation.
2. The method of reducing losses as defined by claim 1 wherein said rotor is a solid rotor.
3. The method of reducing losses as defined by claim 1 wherein said grooves are equally spaced.
4. The method of reducing losses as defined by claim 1 wherein said grooves are disposed along substantially the entire length of said rotor.
5. The method of reducing losses as defined by claim 1 including the step of selecting the width, depth and spacing of said grooves to maximize loss reduction by increasing resistance to eddy currents.
6. The method of reducing losses as defined by claim 1 wherein said grooves each extend radially inwardly of said outer surface of said rotor.
7. The method of reducing losses as defined by claim 6 wherein said grooves are each defined by a pair of parallel side walls terminating in a circumferential bottom surf ce.
8. The method of reducing losses as defined by claim 7 wherein said side walls are transverse to the axis of said rotor and said bottom surfaces are generally concentric with said outer surface of said rotor.
9. The method of reducing losses as defined by claim 1 wherein said machining step includes forming said grooves by laser cutting.
10. The method of reducing losses as defined by claim 9 including the step of minimizing the width and spacing of said grooves to maximize loss reduction by increasing resistance to eddy currents.
11. The method of reducing losses as defined by claim 10 including the step of selecting the depth of said grooves to maximize loss reduction by increasing resistance to eddy currents.
12. A method of increasing operating efficiency of high speed electric machines by reducing losses caused by eddy currents, comprising the steps of: providing a solid rotor having an outer surface formed of a conductive material; and laser cutting said outer surface to provide a plurality of circumferential grooves in axially spaced relation, said grooves 14 being equally spaced along substantially the entire length of said rotor, said
grooves each being defined by a pair of parallel side walls extending radially inwardly of said outer surface to a circumferential bottom surface.
13. The method of increasing operating efficiency as defined by claim 12 including the step of selecting the width, depth and spacing of said grooves to maximize loss reduction by increasing resistance to eddy currents.
14. The method of increasing operating efficiency as defined by claim 12 wherein said side walls are trans¬ verse to the axis of said rotor and said bottom surfaces are generally concentric with said outer surface of said rotor.
15. The method of increasing operating efficiency as defined by claim 12 including the step of minimizing the width and spacing of said grooves to maximize loss reduction by increasing resistance to eddy currents.
16. The method of increasing operating efficiency as defined by claim 12 including the step of selecting the depth of said grooves to maximize loss reduction by increasing resistance to eddy currents.
17. In an electric machine in which high frequency fluxes are generated which induce eddy currents in a rotor pole face, the improvement comprising: a rotor having an outer surface formed exclusively of a conductive material, said outer surface having a plurality of circumferential grooves in axially spaced relation;
whereby operating efficiency is increased by reducing losses caused by induced eddy currents.
18. The electric machine as defined by claim 17 wherein said rotor is a solid rotor.
19. The electric machine as defined by claim 17 wherein said grooves are equally spaced.
20. The electric machine as defined by claim 17 wherein said grooves are disposed along substantially the entire length of said rotor.
21. The electric machine as defined by claim 17 wherein said grooves each extend radially inwardly of said outer surface of said rotor.
22. The electric machine as defined by claim 21 wherein said grooves are each defined by a pair of parallel side walls terminating in a -circumferential bottom surface.
23. The electric machine as defined by claim 22 wherein said side walls are transverse to the axis of said rotor and said bottom surfaces are generally concentric with said outer surface of said rotor.
24. The electric machine as defined by claim 17 wherein said grooves are formed by laser cutting.
25. The electric machine as defined by claim 24 wherein the width and spacing of said grooves are minimized and the depth of said grooves is selected to maximize loss reduction by increasing resistance to eddy currents.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US91537586A | 1986-10-06 | 1986-10-06 | |
US915375 | 1986-10-06 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0290503A1 EP0290503A1 (en) | 1988-11-17 |
EP0290503A4 true EP0290503A4 (en) | 1989-01-26 |
Family
ID=25435641
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19870907056 Withdrawn EP0290503A4 (en) | 1986-10-06 | 1987-09-28 | Electric machine and method of increasing operating efficiency of electric machines. |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0290503A4 (en) |
JP (1) | JPH01500956A (en) |
WO (1) | WO1988002569A1 (en) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE411326C (en) * | 1921-04-16 | 1925-03-27 | Pour I Expl Des Procedes Mauri | AC motor or dynamo with cage armature for high speed and frequency |
US3504153A (en) * | 1965-10-11 | 1970-03-31 | Lloyd Dynamowerke Gmbh | Method of spark machining stator or rotor having lamination simulating characteristics |
US4187441A (en) * | 1977-03-23 | 1980-02-05 | General Electric Company | High power density brushless dc motor |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3530573A (en) * | 1967-02-24 | 1970-09-29 | Sprague Electric Co | Machined circuit element process |
US4339655A (en) * | 1979-01-17 | 1982-07-13 | General Electric Company | Laser undercutting system |
LU84687A1 (en) * | 1983-03-11 | 1984-11-14 | Centre Rech Metallurgique | PROCESS FOR IMPROVING THE SURFACE CONDITION OF A CYLINDER |
DE3336229A1 (en) * | 1983-10-05 | 1985-04-25 | Resista Fabrik elektrischer Widerstände GmbH, 8300 Landshut | METHOD FOR ADJUSTING THE VALUE OF RESISTORS |
US4644210A (en) * | 1985-12-12 | 1987-02-17 | Rockwell International Corporation | High speed induction motor with squirrel cage rotor |
-
1987
- 1987-09-28 JP JP50652387A patent/JPH01500956A/en active Pending
- 1987-09-28 WO PCT/US1987/002500 patent/WO1988002569A1/en not_active Application Discontinuation
- 1987-09-28 EP EP19870907056 patent/EP0290503A4/en not_active Withdrawn
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE411326C (en) * | 1921-04-16 | 1925-03-27 | Pour I Expl Des Procedes Mauri | AC motor or dynamo with cage armature for high speed and frequency |
US3504153A (en) * | 1965-10-11 | 1970-03-31 | Lloyd Dynamowerke Gmbh | Method of spark machining stator or rotor having lamination simulating characteristics |
US4187441A (en) * | 1977-03-23 | 1980-02-05 | General Electric Company | High power density brushless dc motor |
Non-Patent Citations (1)
Title |
---|
See also references of WO8802569A1 * |
Also Published As
Publication number | Publication date |
---|---|
JPH01500956A (en) | 1989-03-30 |
WO1988002569A1 (en) | 1988-04-07 |
EP0290503A1 (en) | 1988-11-17 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US6879075B2 (en) | Trapezoidal shaped magnet flux intensifier motor pole arrangement for improved motor torque density | |
CA2231123C (en) | Alternator for an automotive vehicle | |
EP0726638B1 (en) | Electromagnetic rotary machine comprising an electromagnetic bearing | |
Chalmers et al. | Design and field-weakening performance of a synchronous reluctance motor with axially laminated rotor | |
US3428840A (en) | Axial air gap generator with cooling arrangement | |
US4843271A (en) | Conductive metal inserts in rotor dynamoelectric machine | |
US4751417A (en) | Method of increasing operating efficiency of electric machines | |
US4464596A (en) | Multi-section permanent magnet rotor | |
US2795714A (en) | Laminated end-shield for turbine generators | |
US10749385B2 (en) | Dual magnetic phase material rings for AC electric machines | |
JPH11146615A (en) | Reluctance motor | |
Petrov et al. | Fault-tolerant modular stator concentrated winding permanent magnet machine | |
US4409506A (en) | Induction motor | |
CN111682668A (en) | Fractional slot brushless permanent magnet motor rotor yoke with inclined slots and slot size determining method | |
US20090195113A1 (en) | Induction machine stator apparatus and method | |
CN111555493B (en) | Symmetrical rotor structure of double-end axial magnetic circuit hybrid excitation motor | |
Hebala et al. | PM Halbach arrays in motors: loss reduction and performance improvements | |
JPH03159531A (en) | Reluctance rotating machinery | |
EP0290503A4 (en) | Electric machine and method of increasing operating efficiency of electric machines. | |
US3513342A (en) | Rotor for alternating-current machines | |
CN202111543U (en) | Salient pole type rotor iron core of three-phase brushless alternating-current generator | |
Evans et al. | Disc-geometry homopolar synchronous machine | |
RU2246167C1 (en) | Face-type electrical machine | |
JP3303674B2 (en) | Rotating electric machine and its cylindrical rotor | |
US3182216A (en) | Electric alternators including basket windings located in the air gap |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
17P | Request for examination filed |
Effective date: 19880625 |
|
AK | Designated contracting states |
Kind code of ref document: A1 Designated state(s): FR GB IT |
|
A4 | Supplementary search report drawn up and despatched |
Effective date: 19890126 |
|
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE APPLICATION HAS BEEN WITHDRAWN |
|
18W | Application withdrawn |
Withdrawal date: 19900716 |