Many types of rotating electrical machinery (e.g., motors and generators) require a means of transferring electrical current from an electrical supply to a rotor. In most cases, the operation of the machine is dependent on the existence of multiple poles on the rotor that must be energized in phase with the rotational position of the rotor. The energizing is normally accomplished through the use of “brushes” that slide on a surface of the rotor and sequentially contact individual poles. Brushes are often made from graphite, despite graphite's relatively poor electrical conductivity, and must be replaced at regular intervals as they wear out.
Homopolar motors do not have multiple poles on the rotor. Therefore, the brushes are energized with the same voltage. As a result, sliding brushes are not necessary for transferring the current to the rotor. The current can also be transferred using conductive rollers, which are similar to ball or roller bearings. However, when current is passed through ball bearings or other roller elements, their life span may be greatly shortened as a result of arc-induced erosion. Arc-induced erosion occurs when individual roller elements lose contact with the rotor or stator and small sparks or arcs occur. Over time, the sparks cause damage to the surfaces of the roller elements, and this damage leads to premature failure of the roller elements.
The contact loss may be avoided if the roller elements were geometrically perfect. However, due to manufacturing tolerances, roller elements cannot be manufactured this way. In addition, because the individual roller elements typically have high stiffness, very large loads are required to bring the roller elements into contact simultaneously, and these large loads cause damage to the roller elements and shorten their life span.
Therefore, there is a need for improved systems and methods for transferring electrical current to a rotor. More specifically, there is a need for systems and methods for preventing the loss of contact of roller elements that leads to arcing.
Various embodiments of the invention provide a rotating electrical machine that includes an electrical supply coupled to a stator, a rotor, and a plurality of brushes adapted for transferring electrical current from the stator to the rotor. Each brush is compressed between the rotor and the stator so that outward forces resulting from expansive properties of each particular brush urge at least a portion of the brush into contact with both the rotor and the stator and maintain the brush in contact with both the rotor and the stator. In a particular embodiment, each brush has a hollow, substantially cylindrical body formed of a conductive material and is elastically deformable in a radial direction to provide at least a portion of the outward forces.
In another embodiment, a rotating electrical machine is provided that includes an electrical supply coupled to a stator, a rotor, and a plurality of brushes adapted for transferring electrical current from the stator to the rotor. Each brush has a shaft having a first end and a second end, a first tapered roller that is mounted adjacent a first end of the shaft, a second tapered roller mounted adjacent a second end of the shaft, and at least one biasing assembly that is adapted to urge at least a portion of the first tapered roller and at least a portion of the second tapered roller into contact with the rotor and stator and maintain the first tapered roller and the second tapered roller in contact with the rotor and stator. In one embodiment, the biasing assembly includes two compression springs that are each disposed within a recessed portion define in each tapered roller.
In another embodiment of the invention, a rotating electrical machine is provided that includes an electrical supply coupled to a stator, a rotor, and a plurality of brushes adapted for transferring electrical current from the stator to the rotor. Each brush includes (1) at least two disk sections that are spaced apart from each other along a central axis extending through the disk sections and (2) at least one flexible element positioned between two of the disk sections. The flexible element is adapted for urging at least a portion of each of the disk sections into contact with the rotor and the stator and maintaining contact of the disk sections with the rotor and the stator.
In various other embodiments, a method of transferring electrical current to a rotor of a rotating electrical machine is provided. The method includes the steps of: (1) providing a stator and a rotor; (2) providing a plurality of roller elements that are adapted for transferring electrical current from the stator to the rotor; (3) compressing the plurality of roller elements; and (4) while the plurality of roller elements are compressed, inserting the plurality of roller elements intermediate the rotor and the stator. The roller elements have a reduced radial stiffness and are biased against a surface of the stator and a surface of the rotor. According to one embodiment, the step of compressing the roller elements includes the steps of (1) providing a plurality of substantially cylindrical bodies; and (2) compressing the substantially cylindrical bodies intermediate the stator and the rotor so that outward forces resulting from expansive properties of each particular substantially cylindrical body (A) urge the particular substantially cylindrical body into contact with the rotor and the stator; and (B) maintain the particular substantially cylindrical body in contact with the rotor and the stator.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
According to various embodiments of the invention, as shown in
Various embodiments of the invention include roller elements 15 that are adapted to transfer large electrical currents (e.g., about 54,000 amperes). In certain embodiments, the roller elements 15 have a longer life span (e.g., about 5 years) than conventional roller elements because they are adapted to prevent the loss of contact that leads to arcing. According to various embodiments, this goal is accomplished by manufacturing individual roller elements that are biased (e.g., through properties and/or mechanical features of the roller elements themselves) into maintaining contact with the rotor 12 and the stator 13. For example, various embodiments of the roller elements 15 are manufactured to have a contact stiffness that allows the roller elements 15 to substantially maintain contact with the rotor 12 and the stator 13 when the roller elements 15 are in a compressed state between the rotor 12 and stator 13.
In particular, in various embodiments, each roller element is manufactured to have a relatively low radial stiffness such that deflections on the order of a few tenths of a millimeter do not cause significant changes in the contact force, e.g., in the range of 10 to 20 N/mm. In particular, according to the embodiment shown in
In a particular embodiment, which is shown in
In regard to one particular embodiment, preliminary tests have been conducted using roller elements described above in a reciprocating tribometer carrying current densities well in excess of the Navy requirements. After 200,000 reciprocation cycles and over 25,000 meters of relative travel, the roller elements showed minimal wear and degradation.
According to another embodiment, such as the embodiment shown in
In various embodiments, the shaft 207 defines a head end and a foot end that is threaded so that a stop, such as a nut can be threaded onto the foot end of the shaft 207.
To assemble the tapered rollers 205 between the stator 13 and rotor 12 according to the embodiment shown in
In a further embodiment, as shown in
In yet another embodiment, shown in
In the embodiment shown in
In this embodiment, the stator 313 may be provided with a central track 314 that extends outwardly toward the rotor 312 between the first and second tracks 315, 316 referenced above. In various embodiments, the central track 314 is adapted to engage the second disk section 321 of the roller brush 305 when the roller brush 305 is in use.
In a particular embodiment, the diameters of the central, first, and second tracks 314, 315, 316 referenced above are selected so that when the roller brush 305 is in use, the roller brush's second disk section 321 is biased slightly toward the rotor 312 and the first and third disk sections 320 and 322 are biased slightly toward the stator 313. This arrangement causes the first and second flexible elements 330, 331 to flex and create a low-stiffness contact force between the roller brush 305 and both the rotor 312 and the stator 313.
Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Accordingly, it should be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended exemplary concepts. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for the purposes of limitation.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US07/18913 | 8/29/2007 | WO | 00 | 11/13/2009 |
Number | Date | Country | |
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60841183 | Aug 2006 | US |