Electromagnetic interference (emi) suppression in a power tool

Abstract

A power tool is provided including a housing and an electric motor including a stator and an armature rotatably received within the stator. The armature includes an armature shaft on which a commutator is mounted. The power tool includes a rear bearing mounted on the armature shaft adjacent the armature, and a brush assembly disposed around the commutator. The brush assembly includes a brush card, at least two brushes secured to the brush card around and in contact with the commutator, and a bridge cap extending from the brush card via legs and forming a bearing support for supporting the rearing bearing. At least one electromagnetic interference (EMI) suppression component is provided having a first terminal electrically coupled to the brush(es) and a second terminal electrically coupled to the rear bearing through the bridge cap so as to substantially ground the second terminal of the EMI suppression component.

1 . A power tool comprising:
 a housing;   an electric motor disposed within the housing, the electric motor including a stator and an armature rotatably received within the stator, the armature having an armature shaft on which a commutator is mounted;   a brush assembly disposed around the commutator, the brush assembly including at least two brushes in contact with the commutator;   a bearing retainer assembly disposed adjacent the brush assembly to retain an end bearing of the armature shaft; and   at least one electromagnetic interference (EMI) suppression component secured to the bearing retainer assembly and electrically coupled to at least one of the brushes.   
     
     
         2 . The power tool of  claim 1 , wherein the bearing retainer assembly comprises metal routings thereon for connecting the EMI suppression component to at least one of the brushes. 
     
     
         3 . The power tool of  claim 2 , wherein the brush assembly includes two brush holders housing the two brushes and the bearing retainer assembly comprises two walls extending along the brush holders, wherein the metal routings extend from a first side of the wall, where they are in contact with the brush holders, to a second side of the wall, where they are connected to one or more EMI suppression component. 
     
     
         4 . The power tool of  claim 2 , wherein the brush assembly includes two brush holders housing the two brushes and two brush holder mounts on which the brush holders are mounted, wherein the metal routings extend from one or more EMI suppression component to the brush holder mounts. 
     
     
         5 . The power tool of  claim 1 , wherein the at least one EMI suppression component comprises an X capacitor having terminals electrically coupled to the two brushes and two Y capacitors having first terminals electrically coupled to the two brushes and second terminals electrically coupled to a point of substantially zero potential. 
     
     
         6 . The power tool of  claim 5 , wherein the bearing retainer assembly comprises metal routings thereon for connecting the X capacitor to the brushes, the first terminal of the Y capacitor to the brushes, and second terminal of the Y capacitors to the end bearing of the armature shaft. 
     
     
         7 . A power tool comprising:
 a housing;   an electric motor disposed within the housing, the electric motor including a stator and an armature rotatably received within the stator, the armature having an armature shaft on which a commutator is mounted;   a rear bearing mounted on the armature shaft adjacent the armature;   a brush assembly disposed around the commutator, the brush assembly including a brush card defining an opening for receiving the commutator, at least two brushes secured to the brush card around and in contact with the commutator, and a bridge cap extending from the brush card via a plurality of legs and forming a bearing support for supporting the rearing bearing; and   at least one electromagnetic interference (EMI) suppression component having a first terminal electrically coupled to at least one of the brushes and a second terminal electrically coupled to the rear bearing through the bridge cap so as to substantially ground the second terminal of the EMI suppression component.   
     
     
         8 . The power tool of  claim 7 , wherein the at least one EMI suppression component comprises two Y capacitors coupled between the brushes and the armature and an X capacitor electrically coupled between the two brushes. 
     
     
         9 . The power tool of  claim 7 , wherein the at least one EMI suppression component is mounted on the bridge cap. 
     
     
         10 . The power tool of  claim 9 , further comprising metal routings supported by the bridge portion for electrically connecting the at least one EMI suppression component to at least one of the brushes. 
     
     
         11 . The power tool of  claim 7 , wherein the at least two brushes comprise four brushes arranged around the commutator. 
     
     
         12 . The power tool of  claim 11 , further comprising metal routings supported on the bridge cap electrically connecting opposing brushes. 
     
     
         13 . The power tool of  claim 7 , further comprising a conductive pin disposed through the bridge cap to electrically connect the at least one EMI suppression component to the rear bearing. 
     
     
         14 . A motor assembly comprising:
 an electric motor including a stator and an armature rotatably received within the stator, the armature having an armature shaft on which a commutator is mounted;   a rear bearing mounted on the armature shaft adjacent the armature;   a brush assembly disposed around the commutator, the brush assembly including a brush card defining an opening for receiving the commutator, at least two brushes secured to the brush card around and in contact with the commutator, and a bridge cap extending from the brush card via a plurality of legs and forming a bearing support for supporting the rearing bearing; and   at least one electromagnetic interference (EMI) suppression component having a first terminal electrically coupled to at least one of the brushes and a second terminal electrically coupled to the rear bearing through the bridge cap so as to substantially ground the second terminal of the EMI suppression component.   
     
     
         15 . The motor assembly of  claim 14 , wherein the at least one EMI suppression component comprises two Y capacitors coupled between the brushes and the armature and an X capacitor electrically coupled between the two brushes. 
     
     
         16 . The motor assembly of  claim 14 , wherein the at least one EMI suppression component is mounted on the bridge cap. 
     
     
         17 . The motor assembly of  claim 16 , further comprising metal routings supported by the bridge portion for electrically connecting the at least one EMI suppression component to at least one of the brushes. 
     
     
         18 . The motor assembly of  claim 14 , wherein the at least two brushes comprise four brushes arranged around the commutator. 
     
     
         19 . The motor assembly of  claim 18 , further comprising metal routings supported on the bridge cap electrically connecting opposing brushes. 
     
     
         20 . The motor assembly of  claim 14 , further comprising a conductive pin disposed through the bridge cap to electrically connect the at least one EMI suppression component to the rear bearing.