Abstract:
A power tool is provided including a tool housing in which an electric motor is disposed. The electric motor includes a stator and an armature rotatably received within the stator. The armature has an armature shaft on which a commutator is mounted. The power tool further includes at least one brush assembly disposed around the commutator, the brush assembly including: a brush having two grooves on opposites surfaces therein; a brush holder comprising two support plates arranged defining guiderails that extend into the grooves of the brush to facilitate movement of the brush along a single axis; and a spring contacting the brush that urges the brush radially inwardly along the axis.

Description:
FIELD OF THE INVENTION 
     The present invention relates to power tools, and more particularly to a brush system for a power tool motor. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Known portable power tools typically have an electric motor received within a housing. One common type of electric motor used in power tools has a rotor, a stator, and brushes. The rotor includes a rotor shaft, laminations mounted on the rotor shaft, armature windings wound in slots in the lamination stack, and a commutator mounted on the rotor shaft and electrically connected to the armature windings. The stator may have field windings wound in laminations, or may have permanent magnets. The brushes are mounted in brush housings, often known as brush boxes, surrounding the commutator. Electric current is supplied from a power source through the brushes to the commutator and then to the armature windings. 
     The brushes and brush boxes are typically part of a brush assembly(ies). The brush boxes and brushes are disposed diametrically opposite to each other with the commutator disposed therebetween. The brush assembly(ies) includes springs that urge the brushes against the commutator. 
       FIG. 1  illustrates a half piece  102  of a conventional brush assembly  100 . Each piece  102  in this design includes a base member  103  on which a brush box  104  is mounted. The base member  103  has a semi-annular periphery  106 . Brush box  104  includes a mounting portion  116 , an arm  118  connected to the mounting portion  116  and extending perpendicularly from the base member  103 , and a metallic brush box  120 . Brush box  104  receives a brush therein. The mounting portion  116  includes a plurality of legs  122  for crimping to corresponding cutout portions  124  in the base member  103  to secure the mounting portion  116  to the base member  103 . The spring  101  includes one end connected to the arm  118  and the other end having a contact portion  132 . The contact portion  132  is disposed adjacent to the second open end  128  of the brush box  120 . When the brush is received in the brush box  120 , the contact portion  132  of the spring  101  contacts the brush and urges the brush radially inwardly against the motor commutator. 
       FIG. 2  depicts the conventional brush assembly  100  including two half pieces  102  inside a power tool. As can be shown in this figure, the brush half pieces  102  are inserted inside a groove  103  of the tool housing. The brush box  120  are arranged around the commutator  34  of the motor  14 . Bosses  134  are used to mate the two housing halves together after assembling the half pieces  102  is complete. 
     The brush assembly  100  depicted herein is for a direct current (DC) cordless power tools. However, similar brush assemblies may be used in alternating current (AC) corded power tools. Further, also the brush box  120  depicted in  FIG. 1  mounted on a brush card  102 , similar brush boxes are mounted directly into the tool housing around the commutator. 
     The conventional brush assembly described herein has several disadvantages. First, brush box  120  includes a large amount of metal, which is both expensive and requires a great degree of accuracy in performing procedures such as stamping, bending and crimping the metal components. In addition, the gap between the brush box  120  and the brush is prone to collecting dust and debris over time. This increases the wear on the brush over time and may even cause the brush to jam inside the brush box. A jammed or “hung” brush results in the tool failing during runtime and may even damage the motor commutator. Moreover, since the brush box  120  encloses all four sides of the brush, it limits direct brush exposure to airflow. This can raise the brush box  102  temperature to fairly high levels, particularly in high power applications such as power tools, which can potentially damage the tool housing. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a conventional brush assembly with a brush box. 
         FIG. 2  illustrates the arrangement of the brush assembly of  FIG. 1  inside a power tool. 
         FIG. 3A  illustrates a perspective view of a brush assembly according to an embodiment of the invention. 
         FIG. 3B  illustrates a rear view of the brush assembly of  FIG. 3A , according to an embodiment. 
         FIG. 4  illustrates a perspective view of a portion of an exemplary power tool, in this case a small angle grinder, incorporating the brush assembly of  FIG. 3A , according to an embodiment. 
         FIG. 5A  illustrates a perspective view of a brush assembly according to an alternative embodiment of the invention. 
         FIG. 5B  illustrates a rear view of the brush assembly of  FIG. 5A , according to an embodiment. 
         FIG. 6  illustrates a perspective view of a portion of an exemplary power tool, in this case a small angle grinder, incorporating the brush assembly of  FIG. 5A , according to an embodiment. 
         FIG. 7  illustrates the same perspective view of  FIG. 6 , without the brush assembly assembled into the housing, according to an embodiment. 
         FIG. 8  illustrates a similar perspective view to  FIG. 6 , with half of the tool housing removed to show the motor components, according to an embodiment. 
         FIG. 9  illustrates a perspective view of a brush assembly according to yet another embodiment of the invention. 
     
    
    
     The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     SUMMARY 
     According to an embodiment of the invention, a power tool is provided. The power tool includes a tool housing in which an electric motor is disposed. The electric motor includes a stator and an armature rotatably received within the stator. The armature has an armature shaft on which a commutator is mounted. The power tool further includes at least one brush assembly disposed around the commutator, the brush assembly including: a brush having two grooves on opposites surfaces therein; a brush holder comprising two support plates arranged defining guiderails that extend into the grooves of the brush to facilitate movement of the brush along a single axis; and a spring contacting the brush that urges the brush radially inwardly along the axis. 
     According to an embodiment, the brush holder is supported by the tool housing. In an embodiment, the tool housing includes at least one openings around the commutator in which the brush assembly is arranged, the tool housing including retaining features for retaining the brush holder in the opening. In an embodiment, the brush holder comprises conductive material. 
     According to an embodiment, the two support plates are arranged along a single plane and the brush holder further comprises at least one side plate extending angularly from the two support plates to provide an opening for the axial movement of the brush. In an embodiment, the side plate includes a terminal pin extending therefrom adapted to couple to a motor terminal. In an embodiment, the side plate is supported by the tool housing. 
     According to an embodiment, the tool housing includes a spring post formed therein adjacent the brush assembly to support the spring in the proximity of the brush. 
     According to an embodiment, the brush holder includes a spring post extending therefrom to support the spring in the proximity of the brush. The brush holder may include at least one side plate extending angularly from the support plates to provide an opening for the axial movement of the brush, and the spring post extends from the side plate perpendicularly to the axis of the brush. 
     According to an embodiment, a shunt wire is provided attaching the brush to a motor terminal. In an embodiment, a brush card is provided on which the brush holder is mounted, the brush card being supported by the tool housing. 
     According to an embodiment, the grooves extend through the entire length of the brush. Alternatively, the grooves extend through only one end of the brush and close-ended at an opposite end. 
     DESCRIPTION 
     Referring to  FIGS. 3A and 3B , a perspective view and a rear view of a brush assembly  300  is illustrated, according to an exemplary embodiment of the invention. In this embodiment, a brush  302  is illustratively shown with two grooves  304  on two opposing surfaces. The brush is supported by a brush holder  306  that includes two guide rails  308  engaging oppositely-arranged grooves  304  in the opposing surfaces the brush  302 . In an embodiment, the guide rails  308  may be open-ended to allow for easy removal of the brush  302  (e.g., when the brush need be replaced during a routine power tool service). The grooves  304  on the brush  302  may be similarly be open-ended on one or both sides. Alternatively, the grooves  304  may extend only through a portion of the brush  302  and be close-ended on one or both sides. 
     The brush holder  306  may be formed in different shapes to accommodate the back and forth (axial) movement of the brush  302 . For example, the brush holder  306  may include support plates  306   a  arranged on a first plane and extended on two sides of the brush  302  to form the guides  308 , and one or more legs  306   b  (also referred to as side plates  306   b ) that support the support plates  306   a  and engage a portion of the tool housing. The legs  306   b  may protrude on one or more sides of the support plates  306   a  at an angle (typically 90 degrees). It is possible for one of the legs  306   b  to be on the same plane as the support plates  306   a . Size and angular arrangement of the support plates  306   a  and legs  306   b  may vary from one tool to another depending on the tool housing and motor design requirements. The brush holder  306  may be mounted on a portion of the tool housing via the legs  306   b , the support plates  306   a , or a combination of the two. The brush holder  306  may alternatively be mounted on a brush card, which is in turn secured to the tool housing. 
     A spring mechanism  310  is mounted adjacent the brush  302 . A first leg  310   a  of the spring engages a post (described later) and a second leg  310   b  extends from the spring  310  to engage a back portion of the brush  302  and apply a biasing force to the brush towards the motor armature commutator. In one embodiment, the brush holder  306  includes no legs  306   b  and the plates  306   a  is provided as two separate parts embedded in the tool housing. In yet another embodiment, the support plates  306   a  (or lets  306   b ) may be embedded into additional components, which are them supported or embedded into the tool housing 
       FIG. 4  illustrates a perspective view of a portion of a power tool  400 , in this case a small angle grinder, incorporating the brush assembly  300  described above, according to an embodiment of the invention. The full operation of a grinder is beyond the scope of this disclosure. Reference is made to U.S. Pat. No. 8,087,977 assigned to Black &amp; Decker Inc., which is incorporated herein in its entirety by reference, for an example of a grinder. An outer shell of the grinder  400  that houses the brush assembly  300  has been removed for illustration purposes, although the main housing  402  that houses the motor (not shown) and supports the brush assembly  300  has been depicted. The tool housing  402  includes two opening  404  on the two sides of the commutator for arranging the brush assembly  300 . The openings  404  include retaining features  406 , which may be ribs, slots, snapping features, etc., to securely maintain the brush holder  306  in the tool housing  402 . The tool housing  402  further includes a post  408  arranged adjacent the opening  404  to accommodate the spring  310 . The post  408  may be an integral part of the tool housing  402 . The post  408  includes a slot that receives the first leg  310   a  of the spring  310 . A flexible shunt wire  312 , made of braided copper or similar material, is welded at one end to the brush  302 . The other end of the shut wire  312  may be connected to a motor terminal, as disclosed in U.S. Pat. No. 7,059,038 assigned to Black &amp; Decker Inc., which is incorporated herein by reference in its entirety. 
     During assembly, according to an exemplary embodiment, the brush  302  is inserted through the guide rails  308  of the brush holder  306  adjacent the motor commutator. The spring  310  is then inserted into the post  408  and the second leg  310   b  of the spring  310  is manually pulled to engage the back of the brush  302 . 
       FIGS. 5A and 5B  depict perspective front and rear views of a brush assembly  500 , according to an alternative embodiment of the invention. In this embodiment, similarly to the fist embodiment, a brush  502  is illustratively shown with two grooves  504  on two opposite surfaces. The brush is supported by a brush holder  506  that includes two guide rails  508  engaging oppositely-arranged grooves  504  in the opposite surfaces the brush  502 . As in the first embodiment, the guide rails  508  may be open-ended to allow for easy removal of the brush  502 . 
     The brush holder  506  may be formed in different shapes to accommodate the back and forth (axial) movement of the brush  502 . In the illustrated example, the brush holder  506  includes support plates  506   a  arranged on a first plane and extended on two sides of the brush  502  to form the guides  508 , and one or more side plates  506   b ,  506   c  that support the support plates  506   a  and engage a portion of the tool housing. In this embodiment, side plates  506   b  and  506   c  protrude angularly (typically 90 degrees) from the support plates  506   a  in opposite directions, although it is envisioned that other arrangements of the side plates  506   b ,  506   c  are within the scope of this invention. It is possible for one of the side plates  506   b ,  506   c  to be on the same plane as the support plates  506   a . The brush holder  506  may be mounted on a portion of the tool housing via the side plates  506   b  and/or  506   c , the support plates  506   a , or a combination of the two. Additionally, according to this embodiment, a spring post  516  extends from the side plate  506   c  to support a spring  510  of the brush assembly  500 . Also depicted in these figures is shut wire  512  connected to a terminal  514 . 
       FIG. 6  illustrates a perspective view of a portion of a power tool  600 , in this case a small angle grinder, incorporating the brush assembly  500  described above, according to an embodiment of the invention.  FIG. 7  depicts the same perspective view of the grinder  600  without components of the brush assembly  500 . An outer shell of the grinder  600  tool housing that houses the brush assembly  500  has been removed for illustration purposes, although the main housing  602  that houses the motor (not shown) and supports the brush assembly  500  has been depicted. The tool housing  602  includes two opening  604  on the two sides of the commutator for arranging the brush assembly  500 . Arranged in the periphery of the openings  604  are retaining features such as slots  606 , arranged to receive end portions of the support plate  506   a , and side portions  508  arranged to accommodate side plate  506   b . In addition, a screw receptacle  610  may be arranged in alignment with a hole  518  in the side plate  506   b  to receive a screw in order to secure the brush holder  506  in the tool housing  602 . In the periphery of the opening  604  may further be provided a gap  612  through which the spring  510  is supported by the spring post  516 . Tool housing  602  further includes a support post  614  arranged adjacent the gap  612  to support an end of the spring post  516 . A flexible shunt wire  512 , made of braided copper or similar material, is welded at one end to the brush  502 . The other end of the shut wire  512  may be connected to a motor terminal. 
       FIG. 8  illustrates a similar perspective view to  FIG. 6 , with half of the tool housing  602  removed to show the motor components, including a stator (i.e., field) lamination stack (or field can)  802 , field windings  804 , an armature (not shown) arranged within the stator, a commutator  806  attached to the armature, and an armature shaft end bearing  808 . Details of the operation of the motor in a grinder are outside the scope of this disclosure, and can be found in U.S. Patent Publication No. 2012/0077424 filed by Black &amp; Decker, Inc., which is incorporated herein by reference in its entirety. This figure is provided to illustrate the arrangement of the brush assembly  500  with respect to the armature commutator  806 . 
       FIG. 9  illustrates a brush assembly  900  according to yet another exemplary embodiment of the invention. This embodiment is different from the previous two embodiments in two ways. First, the brush holder  906  is mounted on a brush card  912  rather than be the tool housing. The brush holder  906  is secured on the brush card  912  via two pins  922 . The spring mechanism  910  is also mounted on a post  920  of the brush card  912 . The brush card  912  may be attached to the tool housing using any known method. For example, the brush card  912 , although shown as a rectangular piece herein, may be a one or two piece brush card with a circular inner aperture that can be received within the tool housing around the armature commutator. Second, in this embodiment, a side plate  906   b  of the brush holder  906  is provided with a pin terminal  914  provided to receive electric power for the brush  902 . This arrangement therefore eliminates the need for a separate shunt wire connection to the brush  902 . In an embodiment, a shunt wire (not shown) may be used to connect the brush  902  to the brush holder  906 . It must be understood that these two features may be combined with any of the features and/or designed described in the previous embodiments. 
     It should be noted that although the illustrated power tool described above is a small angle grinder, the brush assemblies according to embodiments of the invention may be used in any other power tool, either corded or cordless, including, but not limited to, drills, impact drivers, circular saw, miter saw, chop saw, recip saw, router, power screw gun, sandom orbital sander, large angle grinders, impact wrench, etc. U.S. Pat. No. 7,893,583, assigned to Black &amp; Decker Inc., which is incorporated herein by reference in its entirety, describes examples of different types of power tools that can incorporate the brush assemblies of this invention. 
     The term “tool housing” or “motor housing” in this disclosure has been used to refer to a single piece of insulating material housing the motor components including the stator, commutator, brushes, etc. It must be understood that the term “tool housing” or “motor housing” may include any type of housing, including, but not limited to, a motor frame (for framed motors), a multi-piece housing, a inner motor housing inside a separate outer housing, and outer housing containing a separate inner housing, etc. 
     The spring mechanisms depicted in the  FIGS. 3A through 8  of this disclosure are commonly known as “clock springs.” It must be understood that any type of spring may alternatively be used. For example, a conventional wound spring may be placed directly behind the brush. Also, instead of a spring post, it is envisioned that the spring may be supported by a hole in the housing. 
     The brush holders discussed in embodiments of this disclosure are made of conductive material. It is envisioned, however, that the brush holder may be made of either fully non-conductive material, or a combination of conductive and non-conductive material. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the scope of the invention.