The present invention relates generally to conductive devices, and more particularly to high current conduction devices. Still more particularly, the invention pertains to conductive brushes in electric motors.
A basic structure for an electric motor includes a stator and an armature. The stator includes a power supply, magnets and brushes. The magnets can be permanent magnets or electro magnets to provide a magnetic field. The brushes are electrically connected to the power supply. The armature includes a commutator and a coil on a rotatable shaft. The commutator has electrical contacts that interact with the brushes of the stator as the armature rotates to conduct electrical current between the power supply and the coil. The coil is positioned in the magnetic field of the stator magnets. The effect of the magnetic field on the electric current passing through the coil causes the armature to rotate. Since the armature and hence the commutator rotate, the commutator and the brushes are designed to provide moving contact for the flow of electric current therethrough.
It is known to provide the brushes as stationary blocks of carbon. To maintain proper cooperative electrical contact between the carbon block and the commutator surface, a spring element is used to bias the carbon block into contact with the commutator. In some known motor structures the spring is attached to the carbon block, and in other known structures a spring element is attached to a holder for the carbon block. Direct physical contact is provided between the carbon block and the commutator, and the frictional engagement causes wear and periodic need for replacement of the carbon block. Further, the springs can fail and disrupt the desired contact relationship between the brushes and the commutator. Replacement of the brushes, springs or the overall brush assembly can be difficult and time consuming, and necessarily requires the motor to be taken out of service for repair.
What is needed is a high current conduction device that is useful as a brush in an electric motor, and is less subject to wear than known devices for similar purposes.
The present invention provides a high current conduction device including a plurality of microfibers held against or in closely spaced relationship to a surface to which electrical current transfer occurs.
In one aspect of one form thereof, the present invention provides a stator brush assembly for the stator of an electric motor with an electric lead for connecting to the power supply of the motor and microfibers for carrying current between the commutator and power supply.
In another aspect of another form thereof, the present invention provides a stator for an electric motor having a commutator, the stator having an electric power supply; an electric lead electrically connected to the power supply; and microfibers in a brush assembly in sufficient quantity and density to conduct electric current between the power supply and the commutator through electrical connections formed between the commutator and distal end portions of the microfibers.
In a still further aspect of a still further form thereof, the present invention provides an electric motor with an armature having a commutator with electrical contacts, and a stator with a power supply and microfibers in a brush assembly establishing electrical connections to the electrical contacts of the armature.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features.
Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use herein of “including”, “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items and equivalents thereof.
Referring now more specifically to the drawings and to
Referring now to
With reference now to
Each microfiber 60 is a fine, hair-like filament made from conductive material, such as, for example, carbon, stainless steel, conductive plastics such as acrylic or nylon fibers, or any other conductive fiber-type filament or other microfiber such as ceramic that can be coated with conductive materials such as copper, silver, nickel, etc.; and that can be provided with diameters sufficiently small to induce ionization when in the presence of an electrical field. These are fibers with strands generally less than one denier, where one denier equals 1 gram per 900 meters of fiber. In one such embodiment, microfibers 60 generally have diameters less than about 150 microns. In one preferred arrangement, microfibers 60 are conductive filaments having diameters within a range of about 5 microns to about 100 microns. Microfibers of this type are mechanically flexible, high-strength, high stiffness fibers that can maintain physical contact over irregular surfaces. However, in contrast to known brushes for electric motors, individual fibers 60 have ultralow friction and a negligible wear from sliding contact. The individual fibers have sufficient resiliency and stiffness that when flexed against a surface will remain against the surface even if the surface is moving; however due to the light weight of each fiber the pressure of contact is low. Accordingly, wear is minimal. The fibers individually and the brush as a whole are relatively robust against contamination. The very thin fibers will cut through film layers of contamination to maintain contact. Microfibers 60 are provided in sufficient quantity and a density within the rows to carry the current required to complete the circuit through the motor. The highly conductive nature of the microfiber material, and the ability to provide millions of densely packed fibers in a limited area facilitates use of the microfibers as a stator brush to conduct the required current.
Microfibers 60 are held in electric contact with commutator 26. However, electric contact does not necessarily require mechanical contact for all microfibers 60. The manner in which electric contact is established or maintained across gaps of various distances, such as by electric field emission, is well-known to those skilled in the art.
The exposed distal end portions of individual microfibers 60 can flex relative to other microfibers 60, and conditions such as air currents generated by the rotating armature, irregular surface contact of individual microfibers 60 against commutator 26, contact between microfibers and the like can cause some microfibers 60 to move small distances away from direct physical or mechanical contact with commutator 26. Accordingly, some but perhaps not all microfibers 60 are in direct physical contact with commutator 26 at any given time. In the present invention, as individual microfibers 60 move away from direct mechanical contact with commutator 26 electric contact is maintained across such gap distance.
Brush assembly 30 is positioned in motor 20 so that a substantial portion of the thin, lightweight conductive microfibers 60 are in physically contact with commutator 26, for direct current flow between brush assembly 30 and commutator 26 via mechanical and electrical contact between the microfibers commutator contacts 28. However, even if distal ends of some microfibers 60 are not in mechanical contact with commutator 26, the microfibers are in a closely spaced relationship to commutator 26 such that an ionized field is created, allowing current flow between microfibers 60 and commutator 26 across the gap. If mechanical contact exists, a current flows through the microfibers. When any of the microfibers lose electrical contact via mechanical contact, a breakdown due to local field emission will occur, thereby establishing electrical contact even without mechanical contact. Field emission is a function of the diameter of the microfiber. Since the microfiber diameter is very small, the electric field can exceed the field emission voltage even with a low voltage potential. Whereas, theoretically, the same general phenomenon can occur with conventional block carbon brushes, the required voltage potential is dangerously high due to the black nature of the conventional electric motor brush. In the present invention, the very small diameter of each individual microfiber 60 allows electric contact and current flow at low potential with respect to an individual microfiber 60.
Microfiber assemblies 82, 84 and 86 are contained within an enclosure 112, which can be conductive or nonconductive. Within enclosure 112, microfiber holders 92, 94, 96 are separated by electrical conductors in the nature of braided contacts 114 and 116 from electric lead connector 88, and braided contacts 118 and 120 from electric lead connector 90.
Enclosure 112 is of sufficient size to extend past the end edge surfaces 106, 108, 110 of microfiber holders 100, 102, 104 to provide a protective perimeter for the exposed distal end portions of the individual microfibers 98 during handling and installation. Only a small terminal portion of each microfiber 98 extends past an edge 122 of enclosure 112. Accordingly, a substantial extent of the exposed distal ends of microfibers 98 are laterally protected by enclosure 112, as best illustrated in
As shown in
Microfiber assemblies 82, 84, 86 are positioned adjacent each other in brush assembly 80, such that adjacent rows 92, 94, 96 of microfibers are spaced by a distance designated by dimension indicator 128, which is between about 1 to about 4 millimeters, to provide sufficient space for the deflection of microfibers.
The completed assembly can be held together by fasteners, such as rivets screws, bolts or other connectors extended through enclosure 112 and microfiber assemblies 82, 84 and 86. Adhesive, mechanical compression and the like can be used also.
Referring now to
Each microfiber bundle is provided similar to multi-strand wire, with a plurality of microfibers 156 contained within a sheath 158, held in holders 160, 162, 164. Distal end portions of microfibers 156 project outwardly from one end of the sheath 158, and at an opposite end the fibers are connected to electric lead connectors 166, 168. The bundles and microfiber holders are fastened into an enclosure 170 using rivets 172, 174, screws, mechanical compression, adhesive, etc. The rows of bundles are spaced from each other by a distance similar to that spacing described between continuous rows of microfibers. Further, within a row, the individual fiber bundles can be spaced from one another by a similar distance.
Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.
Various features of the invention are set forth in the following claims.
The present regular U.S. patent application claims the benefits of U.S. Provisional Application for patent Ser. No. 60/964,812, filed on Aug. 15, 2007.
Number | Date | Country | |
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60964812 | Aug 2007 | US |