Abstract:
A method may be used to retroactively install a grounding ring on an electrical motor used with an inverter to reduce the likelihood that shaft currents affect motor bearings. The method includes securing a ring of conductive material to an endplate of an electrical motor at a position that enables a shaft extending through the endplate to pass through the ring, the ring of conductive material includes conductive material that extends from the ring to contact the shaft when the ring is secured to the endplate, and covering the ring of conductive material with a bearing cap that has an opening that enables the shaft to pass through the bearing cap.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to electrical motors and, more particularly, to electrical motors in which shaft currents may be induced. 
     BACKGROUND 
     Electrical motors are used in a number of applications including condenser fans. Under some conditions, electrical currents may be induced in the shaft of the electrical motor. For example, to make condenser motors more electrically efficient, inverters are frequently incorporated in the motors. One issue that arises from the use of inverters is the occurrence of currents in the shafts of the motors that are caused by the inverters. These currents may flow to bearings that are mounted about the motor shaft within the motor housing. These currents may result in arcing between bearings and bearing races. Such arcing over a period of time may pit the bearings and degrade the life of the bearings. 
     To deal with the generation of currents in motor shafts caused by inverters, grounding rings have been developed. These grounding rings include a ring of conductive material that is typically formed with a toroidal shape. In the central bore of the toroid, brushes made of conductive material extend from the inside diameter of the ring into the central bore. By mounting the grounding ring about the motor shaft to enable the brushes to contact the motor shaft, any currents in the shaft can be conducted through the brushes and the grounding ring into the housing of the motor, which is electrically grounded. In the past, these grounding rings have sometimes been installed by tapping two or more holes in an endplate of the motor housing at positions that would be outside the diameter of a grounding ring concentrically mounted about a motor shaft. Brackets having a hole in one end are secured to the endplate by passing a threaded fastener through the hole and rotating the threaded fastener in the threaded hole. The outboard end of the bracket is positioned over the grounding ring before the threaded fastener is firmly tightened to secure the bracket against the grounding ring and hold the grounding ring in place about the shaft. Unfortunately, the bracket disrupts the continuous nature of the outside diameter of the grounding ring and adversely impacts the ability to mount barriers, such as bearing caps and water slingers, over the grounding ring. In other installations, the grounding rings were installed on an endplate without a bearing cap or water slinger. These components help reduce the amount of particulate and other debris from entering the motor housing. Consequently, a way of installing grounding rings without interfering with the placement of environmental debris barriers is desirable. 
     SUMMARY 
     A method may be used to retroactively install a grounding ring on an electrical motor without interfering with the placement of environmental debris barriers has been developed. The method includes securing a ring of conductive material to an endplate of an electrical motor at a position that enables a shaft extending through the endplate to pass through the ring, the ring of conductive material includes conductive material that extends from the ring to contact the shaft when the ring is secured to the endplate, and covering the ring of conductive material with a bearing cap that has an opening that enables the shaft to pass through the bearing cap. 
     A kit has been developed that enables implementation of the method for retroactively installing a grounding ring about a motor shaft. The kit includes a ring of conductive material having a central bore and at least one hole through the ring to enable a threaded fastener to be inserted through the hole and engage a threaded opening in an endplate of an electrical motor, the central bore having at least one electrical conductor extending from the ring into the central bore to enable the electrical conductor to be coupled electrically to a motor shaft, at least one threaded member having a head and a threaded shaft, the threaded shaft being received within a threaded bore in the endplate to secure the ring of conductive material to the endplate, and a cap that is configured to engage the endplate and secure the cap over the ring, the cap having a central bore to enable the motor shaft to pass through the cap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of a kit and method for retroactively installing a grounding ring in an electrical motor are explained in the following description, taken in connection with the accompanying drawings. 
         FIG. 1  depicts a perspective view of the grounding ring kit assembled onto the motor endplate, according to an exemplary embodiment of the present disclosure. 
         FIG. 2  depicts a cross sectional view of the grounding ring kit of  FIG. 1  along the line  2 - 2  in the direction of the arrows. 
         FIG. 3  depicts a partial perspective view of the motor endplate of  FIG. 1  showing the threaded holes for receiving fasteners to secure the kit of  FIG. 1  onto the motor endplate of  FIG. 1 . 
         FIG. 4  depicts a partial perspective view of the motor endplate of  FIG. 1  showing a grounding ring of the grounding ring kit of  FIG. 1  in position on the motor endplate with fasteners fitted into the threaded holes of  FIG. 3 . 
         FIG. 5  depicts a partial perspective view of the motor endplate of  FIG. 1  showing a bearing cap of the grounding ring kit of  FIG. 1  in position on the grounding ring of  FIG. 4 . 
         FIG. 6  depicts a flow diagram for a method of retroactively installing a grounding ring on an electrical motor used with an inverter according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     According to the present disclosure and referring to  FIG. 1 , a grounding ring kit  10  is shown after installation on an endplate  16  of a motor  18 . The only visible component after installation is the water slinger  22 . The water slinger  22  and the bearing cap  20  (see  FIG. 2 ) to which the slinger  22  is mounted help form a barrier to debris that may be in the operating environment for the motor  18 . Prior to installation of the grounding ring as discussed more fully below, the water slinger  22  and bearing cap  20 , if present, are removed from a motor  18  being retroactively fitted with a grounding ring. Such removal is not necessary during the manufacture of an electrical motor as the bearing cap  20  and water slinger  22  are mounted after the grounding ring has been installed. 
     As shown in more detail in  FIG. 2 , the kit  10  includes a grounding ring  12 , a bearing cap  20 , and a water slinger  22 . The grounding ring  12  is fitted over motor shaft  14  and threadably secured by threaded fasteners  36  to endplate  16  of electric motor  18 . The bearing cap  20  is also fitted over motor shaft  14  and frictionally fitted to a hub  34  between the outside edge of the grounding ring  12  and the inside wall of a recessed well  32  of the endplate  16 , which is centered about the shaft  14 . The water slinger  22  is positioned over the motor shaft  14  and frictionally fitted to the shaft  14  to secure the water slinger to the motor shaft  14 . 
     Referring now to  FIG. 3 , the recessed well  32  is exposed following the removal of the water slinger  22  and the bearing cap  20 . The endplate  16  in  FIG. 3  is shown separately from the motor to facilitate the discussion of the grounding ring installation. Retroactive installations in operational environments occur with the endplate  16  remaining attached to the motor housing. Within the recessed well  32  of the hub  34  is a pair of spaced-apart openings  28 . Each opening  28  includes internal threads  30  for receiving threaded fasteners  36  that secure the grounding ring  12  to the motor endplate  16 . In another embodiment, openings may not be threaded, but suitably sized to receive thread forming screws. In another embodiment, the ring may be secured to the endplate  16  using conductive epoxy or the like. Other attachment devices are also contemplated as being within the scope of the present invention. 
     Referring now to  FIG. 4 , the grounding ring  12  is shown secured to the endplate  16  by external fasteners in the form of socket headed cap screws  36 . A lock washer  38  is fitted to each screw  36  to help securely lock the ring  12  to the endplate  16 . The grounding ring  12  has a generally cylindrical shape with opposed parallel planar ends  40  ( FIG. 2 ) and a cylindrical bore  42  fitted to receive the motor shaft  14  of the motor  18 . The grounding ring  12  fits into recess  32  of the hub  34 . The grounding ring  12  is made of an electrically conductive material and includes electrically conductive brushes  44  that extend inwardly from the bore  42  of the ring  12  to contact the motor shaft  14 . Thus, the brushes  44  provide an electrically conductive path from the shaft  14  to the ring  12 . One of the parallel planar ends  40  of the grounding ring  12  contacts the endplate  16  to provide an electrical path from the grounding ring  12  to the endplate  16 . The screws  36  are typically made of an electrically conductive material and provide a further electrical path from the ring  12  to the endplate  16 . Other components (not shown) are electrically connected to the endplate  16  to complete the grounding of the shaft  14  through the grounding ring  12 . 
     The grounding ring  12  and the brushes  44  may be made of any electrically conductive material. As shown, the grounding ring  12  and the brushes  44  are made of an electrically conductive carbon graphite material. The brushes may be integral with the ring  12  with some of the bonding material removed at the brushes  44  to expose carbon fibers that provide contact with the shaft  14 . Alternatively, the grounding ring  12  and the brushes  44  may be made of an electrically conductive metal, such as aluminum, copper or a ferrous material. 
     Referring now to  FIG. 5 , the bearing cap  20  is shown in position on the endplate  16  of the motor  18 . The bearing cap  20  includes an end face  46  having an opening  48  for clearance passage of the motor shaft  14 . The cap  20  also includes a generally cylindrical wall  50  that extends from the end face  46 . An end  54  of the wall  50  includes a rim  52  that extends from a cylindrical flange  56  (see also  FIG. 2 ). The flange  56  is generally concentric with the cylindrical wall  50 . The cylindrical flange  56  is interference fitted to inner periphery  58  of the hub  34  to secure the cap to the hub  34  of the endplate  16  of the motor  18 . Other configurations of the cap may be used having an opening for the motor shaft  14  and a feature, for example, other interfering surfaces (not shown) or fasteners (not shown) to secure the cap  20  to the hub  34 . The cap  20  may be made of any durable suitable material such as a metal, a composite, or a polymer. For example, the cap may be stamped from a ferrous metal. 
     Referring again to  FIG. 1 , the water slinger  22  is shown in position on motor shaft  14 . The water slinger  22  includes a central opening  60  and, at the opening  60  has an interference fit with the shaft  14 . Alternatively, fasteners (not shown) may secure the slinger  22  onto the shaft  14 . The slinger  22  rotates with the shaft  14  to sling moisture from the slinger  22  and away from the grounding ring  12  and the motor bearing  26  ( FIG. 2 ). Inner face  62  of the slinger  22  is spaced slightly from end shield  16 . The slinger  22  has a smooth continuous periphery  64  extending from the central opening  60  to the inner face  62 . The periphery  64  extends slightly past hub  34  of endplate  16  to direct moisture away from hub  34 . The smooth continuous periphery  64  assists in the flinging of the moisture. The slinger  22  is made of a suitable durable material, for example, a molded plastic. 
     The grounding ring kit  10  may be used with a new motor  18  to provide an electrical grounding and a moisture barrier to the bearing or may be used to retrofit an existing motor (not shown) that was not originally equipped with either electrical grounding or a moisture barrier, or both. When used to retrofit an existing motor, the existing slinger (not shown), if any, and the existing bearing cap (not shown), if any, need to be removed from the motor. The endplate (not shown) of the existing motor needs to have the threaded openings (not shown) prepared, if not already provided. Grounding ring  12  of the grounding ring kit  10  is then fitted over the shaft (not shown) and secured to the endplate by screws  36  of the grounding ring kit  10 . The bearing cap of the grounding ring kit  10  is interference fitted into the hub  34 . Water slinger  22  is then securely fitted over shaft and positioned slightly spaced from the endplate. 
     Referring again to  FIG. 2 , when used on a new motor, the grounding ring  12  of the grounding ring kit  10  is fitted over shaft  14  and secured to the endplate  16  by screws  36  of the grounding ring kit  10 . The bearing cap of the grounding ring kit  10  is interference fitted into the hub  34  and the water slinger  22  of the grounding ring kit  10  is then securely fitted over shaft  14  and positioned slightly spaced from the endplate  16 . 
     Referring now to  FIG. 6 , a method for retroactively installing a grounding ring on an electrical motor is shown. The method includes aligning at least one hole in a ring of conductive material with a hole within an endplate of an electrical motor, as depicted in block  66 . The ring of conductive material has an opening that is sized to enable a motor shaft to pass through the ring. The method also includes securing the ring to the endplate with a fastener that passes through the hole in the ring and is received within the hole, as depicted in block  68 . The fastener may be, for example, a threaded fastener that fits into a threaded opening in the endplate, or, the fastener may be a self-threading fastener that produces threaded engagement with the endplate. The ring of conductive material includes additional conductive material that extends from the ring and contacts the motor shaft when the ring is secured to the endplate. In an alternative embodiment, the method may be performed by securing the ring of conductive material to the endplate of the motor with conductive epoxy rather than with fasteners received in holes in the ring. 
     Those skilled in the art will recognize that numerous modifications can be made to the specific implementations described above. Therefore, the following claims are not to be limited to the specific embodiments illustrated and described above. The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.