Abstract:
An adjustable spring grounding pin for grounding separate parts of an electrical device, for example end shields and a stator of an electric motor, automatically adjusts its circumferential dimension to provide a tight grounding fit between aligned holes of different interior diameters in the end shields and the stator of the device as the grounding pin is driven into the aligned holes.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to an adjustable spring grounding pin for grounding three separate parts of an electrical device, for example two end shields and a stator of an electric motor. In particular, the invention pertains to a grounding pin that automatically adjusts its circumferential dimension to provide a tight grounding fit between aligned holes of different interior diameters in end shields and a stator of an electrical device as the grounding pin is driven into the aligned holes. 
     (2) Description of the Related Art 
     An electrical device such as an electric motor typically includes the basic component parts of a stator, a pair of end shields mounted over axially opposite ends of the stator, and a rotor. The rotor is positioned in a center bore of the stator with opposite ends of the rotor shaft being mounted for rotation in bearings or bushings in the opposite end shields of the motor. 
       FIG. 1  shows the basic construction of an electric motor of the type commonly used in household appliances. The motor is comprised of the pair of end shields  12 ,  14  containing the stator  16 . The rotor (not shown) is positioned inside the stator  16  and the end shields  12 ,  14  support the opposite ends of the rotor shaft  18 . On the particular motor shown, each of the end shields  12 ,  14  has four legs  22 ,  24  that extend over the peripheral edges of the stator laminations. The distal ends of the legs are secured together by adhesive or by other equivalent means. 
     Where motors of the type shown in  FIG. 1  are employed in household appliances such as dishwashers, clothes washers and clothes dryers, it is very important that the electric motor be properly grounded to protect users of the appliance. One of the motor end shields  12 ,  14  is usually provided with a ground terminal that is electrically connected to a ground connection of the appliance. The ground connection of the appliance in turn is grounded through a three-prong outlet plug or through a separate ground, for example a ground connection to a cold water pipe of the household. 
     Component parts of the motor, i.e., the end shields  12 ,  14  and the stator  16  are often ground connected together by a ground pin  26  that is received in aligned holes in the stator and the end shields. The prior art ground pin  26  is a conductive pin of solid metal having a cylindrical exterior surface and flat circular end surfaces. The pin is usually constructed of a harder metal than that of the end shields and stator laminations to enable the pin to be driven into the stator hole without bending the pin. The ground pin  26  is often installed by first drilling or reaming holes through the soft metal of the end shield legs  22 ,  24  and into the harder metal of the laminations of the stator  16 . To provide grounding contact with both end shields, the grounding pin hole  28  is usually drilled between mating surfaces of the legs, as shown in  FIG. 1 . The pin  26  would then be manually pressed or hammered into the aligned holes. 
     This prior art method of grounding motor parts was found to be disadvantaged in that, because the metal of the end shields, and in particular the end shield legs  22 ,  24 , is usually softer than the metal of the laminations of the stator  16 , when the hole is formed through the end shield legs and into the stator it would often result in the hole  28  through the end shield legs being slightly larger than the hole  32  formed in the stator. This would occur due to the material of the end shield legs being softer than the material of the stator laminations, and also due to the positioning of the ground pin hole, the hole being drilled through the two mating surfaces of the end shield legs and then into the stator. The dimension of the hole  32  drilled into the stator would be chosen to provide a tight friction fit of the ground pin  26  in the stator hole. If the hole  28  through the end shield legs is larger than the stator hole  32  by 0.006 of an inch, with the ground pin outer diameter being sized to fit tightly into the interior diameter of the stator hole, it is possible that the ground pin would not make contact with the end shield legs or would only make sufficient grounding contact with one of the end shield legs, resulting in the motor not being grounded or only one end shield of the motor being grounded with the possibility of the opposite end shield being live. In order for the motor to have a proper ground, the ground pin  26  must make contact with the stator and both end shields at all times. 
     SUMMARY OF THE INVENTION 
     The ground pin of the present invention overcomes the disadvantages associated with the prior art ground pin by providing an adjustable spring ground pin that is designed to fit in tight friction engagement in both the stator hole and the hole of the end shields, even when these holes are of different diameters. This is accomplished by the novel construction of the subject ground pin. 
     The pin has a cylindrical exterior surface that extends longitudinally between opposite first and second end faces of the pin, and a hollow interior bore extending through the center of the pin from the first end face to the second end face. The exterior surface of the pin has an outer diameter that is dimensioned to fit in tight friction engagement with the hole drilled through the end shields of the motor, even when that hole is slightly larger than the hole drilled into the stator of the motor. The construction of the pin center bore allows the opposite ends of the pin to contract or collapse radially inwardly independently of each other. With this construction, when the stator hole is smaller than the hole of the end shields, the end of the pin driven into the stator hole will collapse to a greater extent than the end of the pin that remains in the hole of the end shields. In this manner, both ends of the pin of the invention engage in a tight friction engagement with the stator hole and the hole of the end shields, and the pin provides a proper ground between the separate component parts of the motor. 
     The exterior surface of the pin is provided with a plurality of protrusions. The protrusions are formed as either longitudinally extending splines extending over the exterior of the pin, or pairs of longitudinally spaced bumps on the exterior surface of the pin. The protrusions insure a proper grounding connection of the pin with the stator and the end shields when the pin is installed in the stator and end shield holes. 
     A longitudinally extending slot is formed in the pin from its exterior surface through to the pin center bore. The slot intersects the opposite end faces of the pin. The slot gives the pin a cross section resembling a c-spring. The slot, together with the hollow center bore of the pin enables the pin to collapse on itself as it is driven through the hole of the end shields and into the hole of the stator. 
     In the preferred embodiment, a transverse notch is also formed into the exterior surface of the pin intermediate the opposite end faces of the pin. The notch extends across the longitudinal slot of the pin and intersects the pin center bore. The notch isolates the longitudinally opposite ends of the pin and prevents the collapsing of the pin end driven into the stator hole from influencing the collapsing of the pin end driven into the hole of the end shields. 
     By constructing the adjustable spring grounding pin of the invention in the manner described above, the pin insures a proper grounding connection between the stator and the end shields of the motor when the pin is driven through the hole of the end shields and into a smaller stator hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further objects and features of the invention are revealed in the following detailed description of the preferred embodiment of the invention and in the drawing figures wherein: 
         FIG. 1  is a side view of a prior art electric motor showing a grounding pin driven through the end shield legs of the motor and into the stator of the motor; 
         FIG. 2  is a side elevation view of the grounding pin of the invention; 
         FIG. 3  is a top plane view of the grounding pin; 
         FIG. 4  is an end view of the grounding pin; 
         FIG. 5  is a cross section of the grounding pin in the plane of line  5 — 5  of  FIG. 3 ; and, 
         FIG. 6  is a partial cross section of the grounding pin length. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 2 and 3  show respective side and top views of the grounding pin  34  of the invention. In the preferred embodiment, the pin is constructed of a metal having a hardness that is greater than that of the laminations of the stator into which the pin is to be driven. The metal of the grounding pin is also harder than the metal employed in forming the end shields of the motor. Preferably, the metal is spring steel. 
     The grounding pin  34  is constructed with a cylindrical exterior surface  36  that extends longitudinally between axially opposite first  38  and second  42  end faces of the pin. The exterior diameter of the pin is determined to provide a tight friction engagement with the hole to be drilled into the end shields and stator laminations of the motor (not shown) with which the pin is used. The pin is formed with tapered portions  44 ,  46  adjacent the opposite end faces  38 ,  42  of the pin. The tapered portions are provided to assist in aligning the pin with the holes of the end shields and the stator, and in initially driving the pin into the aligned holes. 
     A hollow center bore  48  passes longitudinally through the interior of the pin and intersects the first end face  38  and the second end face  42 . The center bore  48  is defined by a cylindrical interior surface  52  and has a center axis  54 . 
     A longitudinal slot  56  is formed into the exterior surface  36  of the pin and passes completely through the pin to its interior surface  52 . The slot  56 , by intersecting the pin interior bore  48 , effectively extends to the center axis  54  of the pin. A variant embodiment of the pin could include a center bore that does not have a cylindrical interior surface, but is defined by the parallel, opposed side walls of the slot. The slot  56  extends the entire longitudinal length of the pin and intersects the first end face  38  and the second end face  42 . As seen in  FIG. 3 , the slot  56  is comprised of two sections that are slightly, axially misaligned. The pin center bore  48  and the slot  56  give the length of the pin a cross section resembling that of a c-spring. The presence of the slot  56  through the pin enables the axially opposite ends of the pin to contract or collapse radially inwardly. 
     A transverse notch  58  is also formed into the pin exterior surface  36  and extends through to the pin interior surface  52  intersecting the pin center bore  48 . As seen in  FIG. 2 , the notch  58  is positioned in the pin intermediate the first end face  38  and second end face  42 , and partially bisects the pin to the extent that it intersects the center axis  54  of the pin center bore. The extent to which the notch  58  extends across the pin isolates the opposite ends of the pins from each other. This enables the contraction or collapsing of a first end of the pin adjacent the first end face  38  to occur without influencing the contraction or collapsing of the second end of the pin adjacent the second end face  42 , and vice versa. If the transverse notch  58  were not present in the pin, when the first end of the pin adjacent the first end face  38  is driven through the hole of the end shields and into the stator hole, the contraction or collapsing of the pin first end radially inwardly would have a tendency to contract or collapse the opposite second end of the pin to a certain extent. However, with the presence of the transverse notch  58 , the extent to which the first end of the pin adjacent the first end face  38  contracts or collapses as it is driven into the stator hole will have no influence on the second end of the pin adjacent the second end face  42 . Thus, with the exterior surface  36  of the pin being dimensioned to be sufficiently large to provide a tight friction fit in the larger hole of the end shields, the first end of the pin adjacent the first end face  38  can be contracted and collapsed radially inwardly to a greater extent as it is driven into the stator hole than the second end of the pin adjacent the second end face  42 , which remains in a tight friction fit in the hole of the end shields. 
     A plurality of projections are provided on the exterior surface of the pin  34 . The projections  62 ,  64  enhance the tight friction fit of the opposite ends of the pin in the aligned holes of the motor end shields and stator when the pin is driven into the aligned holes. A plurality of the projections are formed as circular bumps  62  and a plurality of the projections are formed as axially tapered splines  64 . The tapered splines  64  provide a temporary fixturing of the pin  34  in the drilled hole of the motor end shields prior to driving the pin completely into the hole. Without the splines  64  the pin  34  would have a tendency to fall out of the end shield&#39;s hole before it can be driven into the hole. This is because the base diameter of the pin  34  is often smaller than the interior diameter of the drilled hole. As seen in  FIGS. 2 through 3 , pairs of longitudinally spaced bumps  62  and pairs of longitudinally spaced spline  64  are axially misaligned with each other on the exterior surface  36  of the pin. Looking at  FIG. 3 , the bumps  62  and splines  64  adjacent the first end face  38  of the pin are moved slightly to the right relative to the bumps  62  and splines  64  adjacent the second end face  42  of the pin. Looking at  FIG. 4 , the bumps  62  and splines  64  adjacent the pin first end face  38  are spaced circumferentially around the exterior surface  36  of the pin from the bumps  62  and splines  64  adjacent the pin second end face  42 . This particular arrangement of the pairs of longitudinally spaced bumps  62  and splines  64  enhances the ability of the pin to fit in a tight friction engagement in the aligned holes of the motor end shields and the stator when the pin is driven into the aligned holes. With the first end face  38  being first driven into the holes  28  through the end shield legs  22 ,  24 , the bumps  62  and splines  64  adjacent the first end face  38  would have a tendency to form grooves through the softer material of the end shield legs as the bumps  62  and splines  64  pass through the end shields hole  28 . If the bumps  62  and splines  64  were axially aligned on the exterior surface  36 , the bumps  62  and splines  64  adjacent the second end face  42  of the pin would then be received in the same grooves in the end shields hole  28  formed by the bumps  62  and splines  64  adjacent the first end face  38  of the pin that passed through the hole previously. However, by circumferentially skewing the bumps  62  and splines  64  relative to each other, as the bumps  62  and splines  64  adjacent the second end face  42  of the pin pass into the end shields hole  28  they form their own grooves in the material of the end shield legs, thereby insuring a tight friction fit of the pin in the end shields hole  28 . In a like manner, the bumps  62  and splines  64  adjacent the first end face  38  of the pin cut grooves into the material of the stator laminations  16  as they are pressed into the hole  32  of the stator, thus insuring a tight friction fit of the pin in the stator hole. 
     The partial cross section of  FIG. 6  shows recesses  66  formed into the pin interior surface  52  behind each of the projections  62 ,  64 . The recesses  66  allow the projections  62 ,  64  to easily compress or crush as the pin  34  is driven into the motor stator hole  32  and end shield hole  28 . 
     The grounding pin of the invention described above is employed in basically the same manner as the prior art grounding pin. However, as explained earlier, because the opposite ends of the grounding pin of the invention are capable of contracting or collapsing radially inwardly independently of each other, the grounding pin provides a tight friction engagement of the pin with aligned holes of the end shields and the stator when the hole of the end shields is larger than that of the stator. 
     While the present invention has been described by reference a specific embodiment, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.