WO1995019063A1

WO1995019063A1 - Rotor slip ring assembly for a homopolar generator

Info

Publication number: WO1995019063A1
Application number: PCT/US1994/000039
Authority: WO
Inventors: Andrew R. Alcon
Original assignee: Alcon Andrew R
Priority date: 1994-01-04
Filing date: 1994-01-04
Publication date: 1995-07-13
Also published as: AU5963394A; IL109694A0; CN1105160A; TW295740B

Abstract

The present invention relates to an improved rotor slip ring design (14) for a homopolar generator which incorporates the concept of channeling the magnetic flux lines (47, 81) and channeling the electric current flow path (36) to separate the flux lines (47, 81) from the current flow path (36) and thereby reduce back emf. The separation is achieved through the principles of an electric current flowing through a path of least electrical resistance and a magnetic field seeking a path of least magnetic reluctance.

Description

ROTOR SLIP RING ASSEMBLY FOR A HOMOPOLAR GENERATOR

Background of the Invention

This invention relates to homopolar dynamoelectric machines? and more particularly it relates to the design and construction of the rotor slip ring assembly for a drum type homopolar dynamoelectric machine.

Homopolar dynamoelectric machines, also referred to as acyclic or unipolar generators are characterized as consisting of a conducting armature in the shape of a disc or cylinder disposed for movement to rotate about a central axis relative to a magnetic field in which the field lines pass through the face of the armature in a direction which is parallel to the axis of rotation and thereby generating a continuous current.

In a classical homopolar disc generator, an electrically conductive disc is rotated about a central axis and a magnetic field is disposed to extend parallel to the disc axis transpiercing the opposed faces of the disc. A pair of brushes are disposed separately to engage the central and peripheral surface portions of the disc providing an electrical connection to an external load.

In a drum type homopolar dynamoelectric machine, the rotor may include a cylindrical shell made of an electrically conductive material such as copper, which would operate as a slip ring. This member is shrunk or pressed onto a solid inner cylindrical core made of a ferromagnetic material which is directly attached to a drive or input shaft. The magnetic field excitation system would include two D.C. electromagnetic field coils or two superconducting magnetic field coils placed at both axial ends of the rotor in a fixed stationary position. The field excitation system would be energized to produce the same magnetic field polarity transpiercing the face of both axial ends of the solid rotor core.

In the case in which permanent magnets are utilized as the field source, the rotor core would consist of a segment made up of ferromagnetic material in the center and in contact with two segments of permanent magnets, with each segment of permanent magnets having the same field polarity facing the ferromagnetic material segment in the center. The permanent magnet segments may also be attached to additional segments of ferromagnetic material which would form the opposite axial ends of the segmented rotor core. All of the segments of the cylindrical rotor core which serve as the main rotor body are attached directly to a drive or input shaft. An external power source is connected to the drive shaft of the rotor around which the rotor is caused to rotate and therefore produces a direct current output voltage along the axial length of the rotor.

These machines incorporate a set of current collection members at either axial end of the rotor which carry the full load current. The brushes are positioned to contact the external shell of the rotor at its axial ends which operate as a slip ring and conducts an electromotive force through one set of brushes to an external circuit and then back onto the rotor shell through the other set of brushes. As electric current is delivered to a load, the interaction between the electric current flow path and the magnetic flux path which transpierces the center of the rotor shell along its peripheral surface, will create a force which decelerates the rotor. The decelerating force of the rotor is due to the classic motor reaction in a generator which is caused by the interaction of the conductor field with the main field of the generator.

Summary of the Invention

The present invention provides for an improved rotor slip ring assembly for a homopolar generator. The invention incorporates the concept of channeling the magnetic flux lines and channeling the electric current flow path to separate the flux lines from the current flow path and thereby reduce back emf. The separation is achieved through the principles of an electric current flowing through a path of least electrical resistance and a magnetic field seeking a path of least magnetic reluctance.

It is therefore an object of the present invention to provide for a homopolar generator having a greater operating efficiency.

It is a further object of the present invention to provide for a homopolar generator with an improved rotor slip ring design.

It is still another object of the present invention to provide for a separate magnetic flux path from the electric current path for the rotor shell slip ring assembly.

Other objects and advantages of the present invention will become apparent from the following preferred embodiments of the invention. Brief Description of the Drawings

Fig. 1 is a side, elevational view, in partial cross section, of a homopolar dynamoelectric machine constructed in accordance with one embodiment of the present invention.

Fig. 2 is a side, elevational view of a segmented internal rotor assembly constructed in accordance with a preferred embodiment of the present invention.

Fig. 3 is a side, elevational view of a solid internal rotor assembly and magnetic field excitation system.

Fig. 4 is a perspective view of a segmented internal rotor and slip ring assembly with current collection members, in accordance with the prior art.

Fig. 5 is a perspective view of a segmented internal rotor and slip ring assembly with current collection members, in accordance with a preferred embodiment of the present invention.

Fig. 6 is a fragmentary cross sectional side view of the slip ring rotor shell of the preferred embodiment.

Detailed Description of the Invention

With reference to Fig. 1, a drum type homopolar dynamoelectric machine of the present invention briefly comprises a cylindrical rotor 10 having an input shaft 12 adapted for connection to a prime mover (not shown). The input shaft 12 having a central axis is mounted for rotation by way of bearings 16 and 18 within a stator structure 20. The stator structure 20 provides for a space 22 in which a plurality of brush assemblies 24 and 26 are located. Tension springs 28 are provided to force brush assemblies 24 and 26 to make contact with the external shell or jacket 14 of rotor 10. The external shell 14 of the rotor 10, which is utilized as a slip ring, is made of a good electrically conductive material such as copper. The external shell 14 has openings 15 located around the circumference of the external shell 14 at the center of the axial length of the rotor 10. The openings 15 may be round, aligned and evenly spaced from each other. Segments of ferromagnetic material 30 are mounted in the openings 15. The segments of ferromagnetic material 30 extend through the thickness of the external shell 14 of the rotor 10. Core 41 (Fig. 2) of rotor 10 is internal to external shell 14. Two segments of permanent magnets 44, 46 (shown in Fig. 2) located in the core 41 of rotor 10, provide for a magnetic field. The magnetic field encounters less reluctance through the segments of ferromagnetic material 30 than through the external shell 14. Therefore, the magnetic field is divaricated or channeled to and transpierces the thickness of the segments of ferromagnetic material 30 and return in a direction as illustrated by flux paths 47. Rotation of the rotor 10 causes an electromotive force to be produced axially along the external shell 14 of the rotor. As sliding electrical contact is made between the brush assemblies 24 and 26 with the external shell 14 of the rotor 10, electric current as illustrated by the dashed arrows referenced as 36 flow axially along the external shell 14 of the rotor 10 and is channeled or divaricated between the segments of ferromagnetic material 30, into brush assembly 26 and out to an external circuit (not shown) by way of conductor 38. The current returns from the external circuit by way of conductor

40 back to the rotor 10 through brush assembly 24.

With reference to Fig. 2, the internal cylindrical rotor core

41 comprises multiple segments in which two segments 44 and 46 are comprised of permanent magnets and are separated by a segment made of ferromagnetic material 42. The segment made of ferromagnetic material 42 is located around the center of the axial length of the internal rotor core assembly 41. The segments of permanent magnets 44 and 46 are aligned such that the same magnetic poles are in contact with the segment of ferromagnetic material 42. The magnetic flux lines 47 converge around the center of the axial length of the segment of ferromagnetic material 42 and flow out of its peripheral surface 43 and along a path as shown by the dotted lines referenced as 47. The internal rotor core 41 may be provided with segments 48 and 50 located at either axial end of the core assembly 41 and in contact with or abutting the segments of permanent magnets 44 and 46. Input shaft 12 passes in the axial direction through the center of the internal rotor segments 42, 44, 46, 48 and 50 and is secured to the segments in a suitable manner.

With reference to Fig. 3, an alternative preferred construction of the magnetic field excitation system and internal rotor core 54 is shown in which the internal rotor core 54 is made of a single piece of ferromagnetic material and is provided with inductor windings 56 and 58 which are secured in a stationary position within the stator structure (not shown), at axial ends 51, 53, but not in contact with the rotor core 54. The inductor windings 56 and 58 are energized to produce the same magnetic field polarity (directed above and shown) transpiercing the face of both axial ends 51, 53 of the solid rotor core 54, as shown by the dotted lines 59. An input shaft 60 is provided and secured to the solid rotor core 54 in a suitable manner.

With reference to Fig. 4, a complete rotor assembly 61 is shown as is common with the prior art in which a cylindrical shell 62, which is made of a good electrically conductive non ferromagnetic material such as copper, is pressed onto and shrunk on the internal rotor core 64. The thermal shrink fit of the cylindrical shell 62 over the internal core 64 is accomplished by heating the cylindrical shell 62 and chilling the internal core 64 and pressing the shell 62 over the core 64 and bringing them both to ambient temperature. The magnetic field path 65 generated within the internal rotor core 64, converges within the center of the axial length of the rotor 61 and transpierces the cylindrical shell 62, creating a ring-shaped area of uniform transpiercing magnetic flux 66 (the area within the dashed lines) on and through the cylindrical shell 62. The magnetic field path 65 shown in fig. 4 only depicts one plane of magnetic flux, whereas, in actuality, the magnetic field path 65 is in all planes containing the central axis of the rotor. As motive power is delivered to the input shaft 68, opposite electric charges are generated at both axial ends of the cylindrical shell 62 and collected by current collection members 70 and 72. When electric current is drawn by an external circuit (not shown), the electric current flow path 74, transpierces the area of the magnetic flux path 66, on the cylindrical shell 62, thereby creating a reaction (back emf) which decelerates the rotor 61.

With reference to Fig. 5, an alternative preferred rotor shell assembly is shown in accordance with the present invention in which a cylindrical shell 76, is provided which is made of a good electrically conductive non-ferromagnetic material such as copper. The cylindrical shell 76 has openings 77 located around the circumference of the shell 76 at the center of the axial length of the shell 76. The openings 77 may be round, aligned and equally spaced apart. Segments of ferromagnetic material 78 are mounted in the openings 77. The segments of ferromagnetic material 78 extend through the thickness of the shell 76. The cylindrical shell 76, may be secured to the internal rotor core 80, through a shrink fit method as described with the prior art referenced in Fig. 4. The magnetic field path referenced as 81 of the rotor core 80, will be divaricated or channeled to and flow through (transpierce) the segments of ferromagnetic material 78, and return to both axial ends 83, 85 of the rotor 74. As motive power is delivered to the input shaft 82, opposite electric charges are generated at both axial ends 83, 85 of the cylindrical shell 76, and collected by current collection members 84 and 86. When electric current is drawn by an external load (not shown), the electric current will be divaricated or channeled to or follow a flow path referenced as 88, between, secluded and/or separate from the segments of ferromagnetic material 78. Because the design of the rotor shell 76 channels and separates (and/or secludes) the magnetic field flow path 81 from the electric current flow path 88, the forces which decelerate the rotor as a result of the magnetic field intersecting the electric current flow path in the prior art design is avoided, thereby greatly improving the overall efficiency of the generator. With reference to Fig. 6, a preferred embodiment of the invention is illustrated in which the components corresponding to those in Fig. 5 are denoted by the same reference numeral with a postscript a. The rotor core shell 76a is formed through a conventional casting means as is suitable for an electrical conducting material such as copper. The casting of the rotor shell 76a provides for openings or cavities 77a located around the center of the axial length of the rotor shell 76a. The cavities 77a extend through the thickness of the rotor shell 76a, to provide for a space in which the segments of ferromagnetic material 78a are pressed into or mounted in the cavities 77a. The segments of ferromagnetic material 78a may be made from iron or steel or alloys which contain ferromagnetic material in combination with other materials and/or materials which exhibit the properties of a low magnetic reluctance,. The shape of the openings 77a and segments 78a should be designed to maximize the diversion of magnetic flux lines through the segments 78a. Although the segments of ferromagnetic material 78a are not limited to a particular geometric» shape, it should be understood that the shape of the segments 78a may determine the means in which it is inserted and secured into the cavities 77a of the rotor shell 76a. For the embodiment shown, segment of ferromagnetic material 78a is internally inserted into cavity 77a. There are numerous means in which the segments of ferromagnetic material 78a may be secured into the cavities 77a.

It is apparent to those skilled in the art that various changes may be made, and various alloys, preferably those having a low magnetic reluctance, may be used without departing from the spirit and scope of the present invention.

Claims

ClaimsWhat is claimed is:

1. A homopolar generator, having a rotor core including a means for providing a magnetic field, the rotor core being jacketed by an improved slip ring where said improved slip ring has electrical contact with a plurality of contact members, said improved slip ring comprising: a shell having a plurality of openings located around the rotor core in a region where the magnetic field means transpierces said shell; and a plurality of segments mounted in the openings, said segments having a magnetic reluctance value less than the magnetic reluctance value of said shell.

2. The homopolar generator according to claim 1 wherein said segments comprise a ferromagnetic material.

3. The homopolar generator according to claim 1 wherein the plurality of openings are spaced evenly apart around the center of the axial length of said shell.

4. The homopolar generator according to claim 1 wherein the openings extend through said shell.

5. A method for improving the overall efficiency of a homopolar generator, comprising: channeling an electric current across a shell jacketing a rotor core of the homopolar generator; channeling a magnetic field provided by the rotor core which transpierces the shell simultaneous with said step of channeling the electric .current; and separating the channeled electric current from the channeled magnetic field whereby the overall efficiency of the homopolar generator is improved.

6. A method for improving the overall efficiency of a homopolar generator comprising: spinning a rotor core having two means for providing a magnetic field which transpierces the center of the axial length of a shell which jackets the rotor core; divaricating the magnetic field means by including a plurality of segments of a material having a lower magnetic reluctance than the shell around the center of the axial length of the shell; divaricating an electric current which flows across the shell by the shell having a lower electrical resistance than the segments; and secluding the magnetic field which transpierces the shell from the electric current which flows across the shell to reduce back emf.

7. A homopolar generator, comprising: a rotor core having two means for providing a magnetic field mounted on the rotor core; an input shaft passing through the rotor core for spinning the rotor core; a shell jacketing the rotor core; a first member in electrical contact with one end of the shell and a second member in electrical contact with the other end of the shell whereby an electric current can flow from an external circuit through the first member across the shell to the second member and back to the external circuit; the shell having a plurality of openings which extend through the shell around the center of the axial length of the shell; and a plurality of segments having a magnetic reluctance value less than the magnetic reluctance value of the shell and an electrical resistance value greater than the electrical resistance value of the shell whereby a magnetic flux provided by the magnetic field means will be channeled through said segments and secluded from the shell and whereby the electric current which flows across the shell will be channeled between and secluded from said segments.

8. The homopolar generator according to claim 7 wherein said segments comprise a ferromagnetic material.

9. The homopolar generator according to claim 7 wherein the openings are spaced evenly apart.