Abstract:
Round keyed brushes for electric motors. The brushes are formed from sintered material and the protruding key runs the length of the brush. The brush material is preferably carbon combined with copper and/or silver. Brush guides (or hoods) are screwed into an end bell, and keyways are then broached in the brush guides to properly align the round brushes. A braided copper shunt wire is centered in the round brush (i.e., co-axial) and runs substantially the length of the brush. The commutator contact surfaces are arced to match the commutator, and may be grooved to improve motor break-in.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to brushes for electric motors, and more particularly to round brushes, each having a key to rotationally align the brushes with a commutator.  
         [0002]     Electric motors are used in many industrial, home, and recreational activities. In some applications, achieving high power from a small light motor is important, for example in radio control car racing. Many motors have been developed, sold, and raced, and several factors determine the value of such motors. These factors include performance, reliability, initial cost, and maintenance cost among others.  
         [0003]     In order to achieve a high, or competitive, level of performance, a motor must include brush to commutator contact capable of conducting the greatest possible amount of current. The amount of current conducted is inversely proportional to the resistance between the brushes and the commutator, so reducing this resistance is very important. Known motors often experience undesirable motion and vibration of the brushes, which motion increases the resistance between the brushes and the commutator.  
         [0004]     The result of increased resistance is an immediate loss of power, but also creates heat. Such heat reduces brush life, and may result in motor failure. For example, when the commutator reaches sufficient temperature, armature wire may come un-soldered from the commutator.  
         [0005]     Various attempts have been made to improve the brushes, for example the Revolution (V2) motor made by Team Orion Performance Racing Products. The Revolution motor includes cylindrical brushes which are positioned at an angle other than 90 degrees away from the commutator, and claim a resulting performance advantage. Unfortunately, while some advantage may exist in this design, the result is costly to manufacture and difficult to maintain. For example, the motor is assembled by first loading the brushes into the end cap from the inside, and then assembling the motor, which is an awkward process.  
         [0006]     Excess heat created by resistance between the brushes and the commutator may result in a need to replace brushes early or often, and as noted above, may in extreme cases, melt the solder attaching the armature windings to the commutator. Thus, maintenance and associated costs are increased when brush to commutator resistance increases.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The present invention addresses the above and other needs by providing round keyed brushes for electric motors. The brushes are formed from sintered material and the protruding key runs the length of the brush. The brush material is preferably carbon combined with copper and/or silver. Brush guides (or hoods) are screwed into an end bell, and keyways are then broached in the brush guides to properly align the round brushes. A braided copper shunt wire is centered in the round brush (i.e., co-axial) and runs substantially the length of the brush. The commutator contact surfaces are arced to match the commutator, and may be grooved to improve motor break-in.  
         [0008]     In accordance with one aspect of the invention, there is provided an electric motor having a case, magnets residing in the case, an armature inside the case, and an end bell on one end of the case. The motor includes an improvement comprising round brush guides and round brushes adapted to slide axially within the brush guides and to be rotationally positioned by cooperation of keys with keyways. In one embodiment, the brushes include keys and the brush guides are screwed into the end bell, and after the brush guides are fixed in place, the keyways are formed in the brush guides by broaching, thereby establishing the proper orientation of the brushes. The brushes are preferably sintered and made from a combination of carbon combined with copper and/or silver. In another embodiment, the keys resides in the brush guides, and a keyway is formed on the brushes.  
         [0009]     In accordance with another aspect of the present invention, there is provided a method for manufacturing a round keyed brush electric motor. The method comprising installing brush guides in a motor end bell, which brush guides include round brush holes, forming keyways in the brush holes, providing brushes having keys, and inserting the keyed brushes into the brush guides so that the keys cooperate with the keyways to align the brushes. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0010]     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:  
         [0011]      FIG. 1  is an electric motor having round keyed brushes.  
         [0012]      FIG. 2A  is a perspective view of a round keyed brush.  
         [0013]      FIG. 2B  is a perspective view of a second round brush having a keyway.  
         [0014]      FIG. 3A  is a side view of the round keyed brush.  
         [0015]      FIG. 3B  is a top view of the round keyed brush.  
         [0016]      FIG. 3C  is a face view of the round keyed brush.  
         [0017]      FIG. 4  is a cross-sectional view of the round keyed brush taken along line  44  of  FIG. 3A .  
         [0018]      FIG. 5A  is an end view of a brush guide having a keyway.  
         [0019]      FIG. 5B  is an end view of a brush guide having a key.  
         [0020]      FIG. 6  is a detailed view of an end bell with brush guides, and with the brushes shown removed from the brush guides.  
         [0021]      FIG. 7  is a method for constructing a motor with round keyed brushes. 
     
    
       [0022]     Corresponding reference characters indicate corresponding components throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims.  
         [0024]     An electric motor  10  having round keyed brushes is shown in  FIG. 1 . The motor  10  includes a case  12 , an end bell  14 , brush guides  16 , brush caps  17 , and shunt wire  18 . The brush caps  17  hold a spring against brushes  20  (see  FIG. 2 ) to maintain force on the brushes  20 .  
         [0025]     A perspective view of a round keyed brush  20  for use with the motor  10 , is shown in  FIG. 2A . The round brush  20  includes a key  22  for cooperating with a keyway  30  in the brush guide  16  (see  FIG. 5 ) to rotationally positioning the round brush. An arced face  24  cooperates with a motor commutator, and includes a plurality of grooves to facilitate break-in. The shunt wire  18  is electrically connected to the round brush  20  to carry electricity to the round brush  20 . While the key  22  is shown running the length of the brush  20 , the key  22  may also run a portion of the brush length, or be broken into segments. There also may be two or more keys  22  on each brush  20 .  
         [0026]     The round brush may also be embodied in a second round brush  20   a  as shown in  FIG. 2B . The round brush  20   a  includes a second keyway  30   a  which cooperates with a second key  22   a  (see  FIG. 5B ). While rounded (or semi-circular) keys and keyways have been described above, the present invention may be exercised using any shape key and keyway, and any electric motor with round brushes, which motor includes cooperating keys and keyways to rotationally position the round brushes, is intended to come within the scope of the present invention.  
         [0027]     A side view of the round keyed brush  20  is shown in  FIG. 3A , a top view of the round keyed brush  20  in  FIG. 3B , and a face view of the round keyed brush  20  in  FIG. 3C . The face  24  is curved to match the curvature of the motor commutator. The grooves  28  run in the direction of rotation of the commutator. A step  26  is formed on the end of the brush  20  opposite the face  24 , which step  26  may aid in positioning the spring  19  (see  FIG. 6 ) behind the brush  20 . The key  22  runs parallel with the main axis of the brush  20 , and preferably runs the entire length of the brush  20 , or substantially the entire length of the brush  20 . The brush  20  is preferably a sintered brush and is preferably made from a combination of carbon and copper and/or silver.  
         [0028]     A preferred application of the present invention is in a motor used in Remote Control (RC) cars, and more particularly in RC racing cars. A brush  20  suitable for RC race cars preferably has a brush length Lb of approximately 0.325 inches and a brush diameter Db of approximately 0.174 inches to approximately 0.176 inches. The brush face  24  preferably has a curvature with a 0.31 inch radius. The key  22  preferably has an approximately semi-circular cross-section, and preferably has a radius of approximately 0.015 inches, or preferably extends approximately 0.015 inches from the round brush  20 . The grooves  28  are preferably approximately 0.10 inches deep and are spaced approximately 0.023 inches apart on the face  24 . The step  26  has a diameter Ds which is preferably approximately 0.103 inches, and a depth which is preferably approximately 0.025 inches.  
         [0029]     While an RC race car motor is a preferred use, the present invention is suitable for a variety of electric motors, and any electric motor with round brushes and a cooperation of a key with a keyway to rotationally position the brushes, is intended to come within the scope of the present invention.  
         [0030]     A cross-sectional view of the round keyed brush taken along line  4 - 4  of  FIG. 3A  is shown in  FIG. 4 . The shunt wire  18  is axially centered in the brush  20  and runs substantially the entire length of the brush  20 .  
         [0031]     An end view of the brush guide  16 , brush hole  32 , and keyway  30  is shown in  FIG. 5A . The brush hole  32  diameter Dh is preferably approximately 0.176 inches to approximately 0.179 inches. The brush diameter and brush hole diameter may vary, but preferably, the brush hole diameter Dh is approximately 0.002 inches to approximately 0.003 inches greater than the brush diameter Db.  
         [0032]     A second brush guide  16   a  is shown in  FIG. 5B . The brush guide  16   a  includes a second key  22   a  which cooperates with the second keyway  30   a  (see  FIG. 2B ).  
         [0033]     A detailed view of the end bell  14  with brush guides  16  and with the brushes  20  removed from the brush guides  16  is shown in  FIG. 6 . The brush guides  16  are on opposite sides of the end bell  14 , and are approximately co-axial (i.e., within reasonable manufacturing tolerances). In a preferred embodiment the keys  22  are to the rear (i.e., pointed toward the case  12 ). The brush guides  16  are preferably made from copper or aluminum, and more preferably from copper. The brush guides preferably screw into the end bell  14  which is preferably made from aluminum, and anodized to electrically insulate the brush guides  16  from each other. The brushes  20  are held against the commutator by springs  19  which are held in place by brush caps  17 . The brush caps  17  preferably screw onto the brush guides  16 .  
         [0034]     Alternatively, the end cap may be plastic. The brush guides may be formed in the end cap, or threaded holes may be cast into the plastic end cap to attach the brush guides. In a preferred embodiment, threads are formed half way through the end cap, leaving an un-threaded region having a diameter to create interference with a brush guide, thereby holding the brush guide in place.  
         [0035]     While the embodiment described in  FIG. 6  includes brush guides which are separate parts which are attached to an end bell, in other embodiments, the brush guides may be machined, cast, or in some other way formed directly as part of the end bell. Any motor having round keyed brushes and brush holes with keyways, wherein the keys cooperate with the keyways to rotationally position the brushes in the brush holes, is intended to come within the scope of the present invention, regardless of the of how the brush holes and keyways are formed, and regardless of what structure of the motor defines the brush holes and keyways.  
         [0036]      FIG. 7  is a method for constructing the motor with round keyed brushes. The method comprises attaching brush guides to a motor end bell, where in the brush guides have brush holes, broaching keyways in the brush holes, obtaining round sintered brushes having keys, and inserting the keyed brushes into the brush holes so that the keys cooperate with the keyways to rotationally position the brushes. Attaching the pair brush guides in a motor end bell preferably comprises screwing the brush guides into the end cap and using a high temperature locking material to hold the brush guides in place, and forming sintered brushes having keys preferably comprises forming sintered brushes from carbon combined with at least one material selected from the group consisting of copper and silver.  
         [0037]     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.