Motor armature having distributed windings for reducing arcing

Abstract

An armature for a brush commutated electric motor having a distributed coil winding arrangement for reducing brush arcing and electro-magnetic interference (EMI). The winding pattern involves winding a first coil into a first pair of slots of the armature. A second coil having a first subcoil portion is then wound into the same slots as the first coil, while a second subcoil portion of the second coil is wound into a pair of slots that is offset by one slot position from the first pair of slots. The two subcoil portions have the same number of turns, and the total turns of the two subcoil portions equals the number of turns of the first coil. A third coil is then wound in the same slots as the second subcoil portion of the second coil. The third coil has the same number of turns as the first coil. This pattern is repeated around the armature. In a two coil per slot armature, this pattern enables the magnetic axis of each coil to be maintained at a constant angular position relative to the commutator bars to which it is coupled without the need for using uneven numbers of turns for the two subcoil portions of each segmented coil.

1 . A method for forming a power tool, comprising: 
 forming a stator having at least a pair of field coils separated by a gap, said gap defining a commutation zone;    locating the stator within a tool housing;    locating an armature coaxially relative to the stator, and within the housing;    forming the armature with a plurality of circumferentially arranged winding slots;    winding a first coil into a first pair of said winding slots;    forming a second coil with first and second serially coupled subcoil portions, and winding said first subcoil portion into said first pair of slots, and winding said second subcoil portion into a second pair of slots that are offset by one slot position from said first pair of slots;    winding a third coil in said second pair of slots; and    forming a fourth coil with first and second subcoil portions, and winding said first subcoil portion of said fourth coil in said second pair of slots, and winding said second subcoil portion of said fourth coil in a third pair of slots that are offset by one slot position from said second pair of slots; and    wherein each of said coils at least substantially completes commutation within said commutation zone.    
   
   
       2 . The method of  claim 1 , further comprising winding each of said subcoil portions with approximately half the number of winding turns as said first coil.  
   
   
       3 . The method of  claim 1 , further comprising winding each of said subcoil portions with the same number of winding turns.  
   
   
       4 . The method of  claim 1 , further comprising winding each of said first and third coils with an identical number of winding turns.  
   
   
       5 . The method of  claim 1 , further comprising winding each of said first and third coils with identical numbers of winding turns; and 
 winding each of said subcoil portions with identical numbers of winding turns.    
   
   
       6 . A method for forming an electric motor, comprising: 
 forming a stator having a pair of field coils defining a gap therebetween, the gap defining a commutation zone;    forming an armature and locating the armature coaxially relative to said stator;    forming said armature with a plurality of parallel, circumferentially arranged slots;    winding a first coil in a first pair of said slots;    forming a second coil in first and second subcoil portions connected serially with one another;    winding said second coil such that said first subcoil portion is wound in said first pair of slots, and said second subcoil portion is wound in a second pair of slots offset by one slot position from said first pair of slots;    winding a third coil in said second pair of slots;    forming a fourth coil having first and second subcoil portions serially connected with one another, and winding said first subcoil portion of said fourth coil in said second pair of slots, and winding said second subcoil portion of said fourth coil in a third pair of slots offset by one slot position from said second pair of slots; and    wherein each of said coils substantially complete commutation while a magnetic axis of each said coil passes through said commutation zone.    
   
   
       7 . The method of  claim 6 , wherein said electric motor forms an electric motor with twice the number of commutator bars as armature slots.  
   
   
       8 . A method for reducing brush arcing in an electric motor, comprising: 
 forming a stator having at least a pair of field coils separated by a gap, the gap defining a commutation zone;    forming an armature with a plurality of circumferentially arranged slots, a second plurality of commutator bars, and locating the armature coaxially adjacent said stator;    winding a first coil in a first pair of said slots;    segmenting a second coil into first and second subcoil portions and winding said first subcoil portion in said first pair of slots, and said second subcoil portion in a second pair of slots offset by one slot position from said first pair of slots;    winding a third coil in said second pair of slots;    segmenting a fourth coil into first and second subcoil portions, and winding said first subcoil portion of said fourth coil into said second pair of slots and winding said second subcoil portion of said fourth coil into a third pair of slots that are offset by one slot position from said second pair of slots; and    further arranging said first and second subcoil portions of each of said second and fourth coils such that a magnetic axis of said first subcoil portions are advanced, relative to a pair of commutator bars with which it is associated, and that said second subcoil portions each have a magnetic axis that is retarded, relative to its associated pair of commutator bars; and    wherein each of said coils substantially completes commutation with said commutation zone.    
   
   
       9 . The method of  claim 8 , wherein said subcoil portions of said third coil each have a magnetic axis, with one of said magnetic axes being retarded, relative to a pair of commutator bars to which said third coil is coupled, and the other of said subcoil portions being advanced, relative to said commutator bars.  
   
   
       10 . A method for controlling commutation in an electric motor to reduce brush arcing, the method comprising: 
 winding a plurality of slots of an armature with a plurality of first coils and a plurality of second coils;    forming each of said second coils with first and second subcoil portions;    winding each of said first coils about a single pair of slots;    winding said second coils about two spaced apart pairs of slots, and further such that said first subcoil portion thereof is wound in a common pair of slots with one of said first coils, and the second subcoil portion is wound in a pair of slots that is spaced apart, by one slot position, from the first subcoil portion; and    further winding said subcoil portions such that one of said portions is advanced, relative to a pair of commutator bars with which it is coupled, while the other one of the pair is retarded relative to the same pair of commutator bars.    
   
   
       11 . The method of  claim 10 , further comprising winding each of said subcoil portions with the same number of winding turns.  
   
   
       12 . The method of  claim 10 , further comprising winding each subcoil portion with a lesser number of turns that each said first coil.  
   
   
       13 . A method of controlling commutation of an electric motor, comprising: 
 forming an armature with a plurality of circumferentially arranged winding slots;    forming the armature with a circumferentially arranged plurality of commutator bars;    winding a first coil around a first pair of said slots and coupling said coil to a first pair of adjacent ones of said commutator bars such that a magnetic axis of said first coil is centered over the first pair of commutator bars;    forming a second coil into first and second subcoil portions, winding said first subcoil portion in the same pair of slots as the first coil and winding said second subcoil portion in a pair of winding slots that is offset by one slot position from said slots in which said first coil is wound in, and coupling ends of said second coil to a second pair of commutator bars that is offset by one said commutator bar from said first pair of commutator bars,    winding each of said first and subcoil portions with a number of turns such that said a magnetic axis of said first subcoil portion is advanced, relative to said second pair of commutator bars, and a magnetic axis of said second subcoil portion is retarded, relative to said second pair of commutator bars, and further such that a resultant magnetic axis of said second coil is centered over said second pair of commutator bars; and    each of said first and second coils at least substantially completing commutation with a predetermined, fixed commutation zone.    
   
   
       14 . The method of  claim 13 , further comprising alternating winding said first and second coils around said slots such that one of said subcoil portions is wound in an overlapping pair of slots with one of said first coils.  
   
   
       15 . A method for forming an electrically powered power tool, comprising: 
 providing a tool housing;    forming a motor having a stator and an armature disposed coaxially within said stator, and locating the motor within the tool housing;    forming said stator to have at least a pair of field coils separated by a gap, said gap defining a commutation zone;    forming the armature with a plurality of circumferentially arranged winding slots;    forming a first plurality of coils and a second plurality of coils, with each of said second plurality of coils being comprised of first and second serially connected subcoil portions;    alternately winding ones of said first plurality of coils and ones of said second plurality of coils in slots around said armature such that said first subcoil portion of each coil of said second plurality of coils fully overlaps a previously wound one of said first plurality of coils, while said second one of said subcoils is wound in a pair of slots that is offset from by one slot pitch from said previously wound coil of said first plurality of coils; and    wherein each one of said first and second pluralities of coils is aligned relative to said gap such that each one of said first and second pluralities of coils substantially completes commutation within said commutation zone.    
   
   
       16 . A method for forming an electrically powered power tool, comprising: 
 providing a tool housing;    forming a two-coil-per-slot motor having a stator and an armature disposed coaxially within said stator, and locating the motor within the tool housing;    forming said stator to have at least a pair of field coils separated by a gap, said gap defining a commutation zone;    forming the armature with a plurality of circumferentially arranged winding slots;    forming a first plurality of coils and a second plurality of coils, with each of said second plurality of coils being comprised of first and second serially connected subcoil portions;    alternately winding ones of said first plurality of coils and ones of said second plurality of coils in said slots around said armature;    further winding said first and second pluralities of coils such that each one of said second coils has one of its subcoil portions overlapping a previously wound one of said coils of said first plurality of coils; and    wherein each one of said first and second pluralities of coils is aligned relative to said gap such that each one of said first and second pluralities of coils substantially completes commutation within said commutation zone as said armature rotates.