Patent Publication Number: US-6991468-B1

Title: Folded foil and metal fiber braid electrical current collector brush

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 

   The present invention relates to the transfer of electrical current across a moving surface in an electric current collecting device. 
   BACKGROUND OF THE INVENTION 
   Currently many slip-ring brushes are made from solid carbon. Metal fiber brushes are generally known for providing a much larger number of electrical contact points on the rotor running surface thereby providing a much lower contact voltage drop. However such metal fiber brushes, supported by holders to which they are attached by soldering, are readily deformed by high external forces, which may arise in electrical motor types of environments because of transport current and magnetic field interaction induced forces, which results in excessive brush spreading distortion sometimes called splay. Brushes could be made stronger by using larger fibers, but this would result in fewer contact points and poor following of any imperfections in the rotor surface. It is therefore an important object of the present invention to provide a foil type electrical current collector brush in the aforementioned type of running surface environments to avoid the latter referred to disadvantages associated therewith. 
   SUMMARY OF THE INVENTION 
   Pursuant to the present invention, a single foil sheet is folded into closely spaced layers bonded together and soldered within a base portion of a brush assembly positioned within a holder in spaced relation to a running surface of an electrical current collector type of device, so that one of the folded foil sheet edges on the spaced layers thereof extending from the holder is held under pressure in sliding contact with the running surface. The brush may be fabricated by use of a single piece of folded metal foil, folded in such a way as to keep the free ends near the center, thereby providing the desired mechanical strength and avoiding the requirement for assembling a plurality of stacked foils heretofore associated with prior foil concepts. Other embodiments of the invention involve use of metal fiber braids between each set of adjacent foil folds, thereby providing an increased number of contact points and improved electrical performance similar to that of a fiber brush. The foil and braids are soldered together at the base thereby providing a low resistance path to the brush holder. The folded foil brush may also be well suited for rotor slip ring cleansing when used with other brush types. 

   
     DESCRIPTION OF THE DRAWING 
     A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 
       FIG. 1  is a partial side elevation view illustrating installation of a brush assembly in sliding contact with a running surface within an electric current collecting device; 
       FIG. 2  is a section view taken substantially through a plane indicated by section line  2 — 2  in  FIG. 1 ; 
       FIGS. 2A ,  2 B and  2 C are section views of different hybrid foil layer embodiments of the brush assembly as shown in  FIG. 2 ; 
       FIG. 3  is a partial section view taken substantially through a plane indicated by section line  3 — 3  in  FIG. 2 ; 
       FIG. 3A  is a partial section view corresponding to that of  FIG. 3 , and the embodiment illustrated in  FIG. 2A ; 
       FIG. 4  is a partial perspective view of a partially unfolded electrically conductive foil sheet disassembled from the brush assembly illustrated in  FIGS. 1 ,  2  and  3 ; 
       FIG. 5  is a partial section view taken substantially through a plane indicated by section line  5 — 5  in  FIG. 1 ; and 
       FIG. 6  illustrates a foil component of the brush assembly shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
   Referring now to the drawing in detail,  FIG. 1  illustrates a brush assembly  10  in sliding contact with a running slip ring surface  12  of an electric current collecting type of device  14 , as generally known in the art, with which a fixed support  16  is associated in spaced relation to the slip-ring surface  12 . Pursuant to the present invention, the brush assembly  10  is positioned on the support  16  by a holder  18  to establish sliding contact thereof with the running surface  12  of the device  14 . 
   As shown in  FIGS. 1 ,  2  and  3 , the brush assembly  10  has a base portion  20  that is cross-sectionally rectangular shaped. A folded metal foil  22  is positioned within the base portion  20  and projects therefrom into said sliding contact with the surface  12 . As shown in  FIG. 4 , the foil  22  is a single sheet having opposite parallel spaced edge  24  and  26  that are folded into parallel spaced relation to each other when the foil  22  is fully folded for installation into the brush assembly  10  as shown in  FIG. 2 . When completely folded and installed within an optional container formed within the portion  20 , the brush foil  22  sometimes referred to as a sock, forms a plurality of closely spaced rectangular layers  27  as shown in  FIGS. 2 and 3 . The folded edge  24  of the foil  22  is then in contact with the surface  12  as shown in  FIG. 1 , while the other folded foil edge  26  is soldered throughout to the brush base portion  20  as shown in  FIG. 5 . As to the sides of the folded foil layers  27  extending between the opposite foil edges  24  and  26 , a small portion thereof has a barrier tape  28  or adhesive coating thereon as shown in  FIG. 4  for attachment of the foil  22  to the base portion  20  as shown in  FIG. 3 . Such attachment is effected before soldering of the foil edges  26  to the base  20  so as to prevent wicking after installation of the brush assembly  10  within the electric current collecting device  14 . 
   As shown in  FIGS. 1 and 5 , the brush holder  18  is formed by a housing  30  within which the brush base portion  20  is received and soldered thereto. The holder  18  has an arcuate flange  32  for axial slip ring application as shown in  FIGS. 1 ,  2  and  5 , extending from the housing  30  for releasable attachment by bolts  34  to the support  16 . A coil spring  36  within the holder housing  30 , as shown in  FIG. 5 , exerts brush contact pressure on the brush assembly  10  through the base portion  20 . Such contact pressure is applied to the running surface  12  along parallel spaced sections of the folded contact edge  24  on the foil layers  27 . As shown in  FIG. 2  the folded foil layers  27  of the brush assembly  10  may be made of an electrically conductive metal, such as brass shim stock for example or another suitable metal such as copper, silver or palladium. 
   According to another embodiment as shown in  FIGS. 2A and 3A , a foil  22 ′ is folded into foil layers  27 ′ of a hybrid structure type, having braids  38  positioned between two outer skins  40  of each of the layers  27 ′ to form a container shell or sock. According to yet another embodiment a hybrid foil  22 ″ may be folded to form a closed structure, as shown in  FIG. 2B , without an outer container shell or sock by attachment of the braids  38  to a single folded skin  40 . A still further embodiment is cross-sectionally illustrated in  FIG. 2C , wherein a hybrid foil  22 ′″ is shown in a double jellyroll structural arrangement, having outer skins  40 ′ with an inner braid  38 ′ retained therebetween. 
   In regard to the outer shape of the flange  32  as hereinbefore described with respect to  FIGS. 1 ,  2  and  5 , it would be cylindrical for the brush assembly  10  in a radial installation relative to the slip ring surface  12 . The shape of the foil contact edges  24  may be curved as shown in  FIG. 6 , to a degree dependent on the curvature of the slip ring surface  12 . 
   Obviously, other modifications and variations of the present invention may be possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.