Abstract:
A shaft seal assembly is disclosed having a stator including a main body and axial and radial projections therefrom. The rotor is radially extended and encompasses the axial and radial projections from said stator. A passageway formed between the radial projection of stator and rotor results in an axial passageway having its opening facing rearwardly from the rotor and away from the source of impinging coolant and/or contaminant. A concentric circumferential receptor groove in the stator facing the housing allows insertion of conductive means for transmission of electrostatic charge away from the shaft through the shaft seal assembly to the housing and ground. The receptor groove is opposite the axial passageway and provides for both a substantially lower contaminant environment and improved engagement with conductive means. The dimension of interface gap between the rotor and the radial projection from the stator, which the access to the shaft of any impinging material is fixed at a predetermined value and does not vary with the relative movement between the rotor and the stator. The shaft seal assembly provides improved rejection or warding off of contaminants from ingress into the labyrinths and ultimately restrains attack of the bearing environment as well as substantial elimination of bearing current and attendant bearing fluting or frosting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefits of U.S. Provisional Application Ser. No. 60/693,548, filed Jun. 25, 2005. Applicant herein claims priority from and incorporates herein by reference in its entirety provisional patent application No. 60/693,548. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an improved bearing isolator sealing device, and more particularly, to a bearing isolator for directing electrostatic charge to ground while retaining lubrication solution and repelling contamination such as water, dust, dirt, sand and paper stock from the bearing environment and away from the shaft grounding ring, within the bearing cavity of a hub assembly such as an electrical motor bearing for engagement with a rotatable shaft. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     No federal funds were used to develop or create the invention disclosed and described in the patent application. 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to shaft sealing devices for use with rotating equipment. Adequate maintenance of rotating equipment is difficult to obtain because of extreme equipment duty cycles, the lessening of service factors, design and the lack of spare rotating equipment in many processing plants. This is especially true of machine tool spindles, wet end paper machine rolls, aluminum rolling mills and steam quench pumps and other equipment utilizing extreme contamination affecting lubrication. Various forms of shaft sealing devices have been utilized to try to protect the integrity of the bearing environment, including rubber lip seals, clearance labyrinth seals, and attraction magnetic seals. Lip seals or O-ring shaft seals can quickly wear out and fail and are also known to permit excessive amounts of moisture and other contaminants to immigrate into the oil reservoir of the operating equipment even before failure had exposed the interface between the rotor and the stator to the contaminants or lubricants at the radial extremity of the seal. The problem of seal wear and damage as applied to electrical motors using variable frequency drives is compounded because of the very nature of the control of electricity connected to variable frequency drive (hereinafter referred to as VFD) controlled motors. 
     VFDs regulate the speed of a motor by converting sinusoidal line alternating current (AC) voltage to direct current (DC) voltage, then back to a pulse width modulated (PWM) AC voltage of variable frequency. The switching frequency of these pulses ranges from 1 kHz up to 20 kHz and is referred to as the “carrier frequency.” The ratio of change in voltage to the change in time (ΔV/ΔT) creates what has been described as a parasitic capacitance between the motor stator and the rotor, which induces a voltage on the rotor shaft. If the voltage induced on the shaft, which is referred to as “common mode voltage” or “shaft voltage,” builds up to a sufficient level, it can discharge to ground through the bearings. 
     Current that finds its way to ground through the motor bearings in this manner is called “bearing current.” 1  http://www.greenheck.com/technical/tech_detail.php?display=files/Product_guide/fa 117 — 03 
     There are many causes of bearing current including voltage pulse overshoot in the VFD, non-symmetry of the motor&#39;s magnetic circuit, supply unbalances, transient conditions, and others. Any of these conditions can occur independently or simultaneously to create bearing currents. 2  http://www.greenheck.com/technical/tech_detail.php?display=files/Product_guide/fa 117 — 03 
     Shaft voltage accumulates on the rotor until it exceeds the dielectric capacity of the motor bearing lubricant, then the voltage discharges in a short pulse to ground through the bearing. After discharge, the voltage again accumulates on the shaft and the cycle repeats itself. This random and frequent discharging has an electric discharge machining (EDM) effect, causing pitting of the bearing&#39;s rolling elements and raceways. Initially, these discharges create a “frosted” or “sandblasted” effect. Over time, this deterioration causes a groove pattern in the bearing race called “fluting” which is a sign that the bearing has sustained severe damage. Eventually, the deterioration will lead to complete bearing failure. 3  See www.Greenheck.com 
     The prior art teaches numerous methods of handling shaft voltages including using a shielded cable, grounding the shaft, insulated bearings and installation of a Faraday shield. For example, see published U.S. Patent Applications 2004/0233592 and 2004/0185215 filed by Oh et al., which are incorporated herein by reference. Most external applications add to costs, complexity and exposure to external environmental factors. Insulated bearings provide an internal solution by eliminating the path to ground through the bearing for current to flow. But, installing insulated bearings does not eliminate the shaft voltage, which will still find the lowest impedance path to ground. Thus, insulated bearings are not effective if the impedance path is through the driven load. Therefore, the prior art does not teach an internal, low wearing method or apparatus to efficaciously ground shaft voltage and avoid electric discharge machining of bearings leading to premature bearing failure. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide an improvement to seals or bearing isolators to prevent leakage of lubricant and entry of contaminants by encompassing the stator within the rotor to create an axial directed interface at the radial extremity of the rotor. It is also an objective of the present invention to disclose and claim a seal or bearing isolator for rotating equipment that retains lubricants, prevents contamination and conducts and transmits and directs bearing current to ground. 
     Prior art seals traditionally had the interface between the rotor and the stator exposed radially to the contaminants or lubricants at the radial extremity of the seal. The projection of an axial portion of the stator into the rotor has been expanded radially. This projection or protruding member of the stator into the rotor has been expanded radially beyond the diameter of the major portion or body of the stator. 
     The rotor and the recess rotor, which previously surrounded the stator projection or insertion, is also extended radially beyond the major portion of the stator. The rotor now encompasses the stator, or a substantial portion of the stator radial projection, in such a manner that the interface presented to the ingress of the lubricant or contaminates is facing axially and rearwardly. The axial facing interface presents limited access to the internal of the seal and a constant dimensional interface between the rotor and the stator regardless of any axial movement of the rotor with respect to the stator. 
     A groove may be machined into the stator to accentuate the novel radial extension of the rotor and the stator. This groove improves the ability of the seal to prevent contaminants from entering the axial interface gap between the rotor and the stator. This novel improvement, i.e., the encapsulation of the radial extension stator by the rotor, enables the interface gap between the accessible portions of the stator and the rotor to be of a predetermined dimension. The improvement also means that there is no fluctuation or variation in the interface gap resulting from any relative axial movement between the rotor and the stator. 
     This novel seal or bearing isolator will operate to vastly improve the rejection or ingress of contaminants into the interface gap between the rotor and stator. The entrance to the interface gap is facing or directed away from the normal flow of contaminants, i.e., along the axis of the shaft toward the housing. The interface gap can be machined to extremely close tolerances because there is no movement radially between the rotor and the stator and any axial movement does not affect the interface. 
     The increased rejection of contaminants also provides an opportunity to reduce shaft voltage and attendant bearing wear caused by electrostatic discharge machining. Placement of a receptor groove in the stator of the above described shaft seal assembly allows insertion of a conductive insert. This insert can be a metallic or non-metallic solid, machined or molded. The insert can also be a metallic ring having conductive filament brushes affixed therein. Although any type of metal compatible with operating conditions and metallurgy may be selected, bronze or aluminum are believed to be preferred metals because of increased conductivity, strength, corrosion and wear resistance. Combining the receptor groove and conduction means with the benefits of the improved bearing isolator reduces the environmental exposure of the conduction means. 
     It has been found that a bearing isolator assembly having a rotor and stator manufactured from bronze has improved charge dissipation qualities. The preferred bronze metallurgy is that meeting specification 932 (also referred to as 932000 or “bearing bronze”). This bronze is preferred for bearings and bearing isolators because it has excellent load capacity and antifriction qualities. This bearing bronze alloy also has good machining characteristics and resists many chemicals. It is believed that the specified bronze offers increased shaft voltage collection properties comparable to the ubiquitous lighting rod due to the relatively low electrical resistivity (85.9 ohms-cmil/ft @ 68 F or 14.29 microhm-cm @ 20 C.) and high electrical conductivity (12% IACS @ 68 F or 0.07 MegaSiemens/cm @ 20 C.) of the material selected. 
     This embodiment improves upon shaft brushes typically mounted external of the motor housing. Previous tests of a combination shaft seal assembly with a concentric inserted conductive brush engaged with the shaft have shown substantial reduction in shaft voltage and attendant electrostatic discharge machining. Direct seating between the conduction ring means and the bearing isolator portion of the motor ground seal improves the conduction to ground over a simple housing in combination with a conduction means as taught by the prior art. Those practiced in the arts will understand that this improvement requires the electric motor base to be grounded, as is the norm. 
     It is therefore an objective of the present invention to disclose and claim an electric motor for rotating equipment having bearing isolator means that retains lubricants, prevents contamination and conducts and transmits and directs bearing current to ground. 
     It is another objective of the present invention to disclose and claim a bearing isolator for rotating equipment that retains lubricants, prevents contamination and conducts electrostatic discharge (shaft voltage) to improve bearing operating life. 
     It is another objective of the present invention to disclose and claim a bearing isolator for rotating equipment that retains lubricants, prevents contamination and provides adequate grounding. 
     It is another objective of the present invention to disclose and claim a bearing isolator for rotating equipment that retains lubricants, prevents contamination and provides a low impedance ground path for the voltage to flow to earth ground without passing through the motor bearings or other components. 
     Other objects, advantages and embodiments of the invention will become apparent upon the reading the following detailed description and upon reference to drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective exterior view of motor ground seal assembly mounted to a motor housing. 
         FIG. 2  is a sectional view of the present invention as shown in  FIG. 1 . 
         FIG. 3  is a sectional view of another embodiment of the present invention as shown in  FIG. 2  wherein a conduction ring is shown with a plurality of conductive brushes. 
         FIG. 4  is a sectional view of another embodiment of the present invention wherein a metallic conduction ring is shown with an insert having conductive properties. 
         FIG. 5  is a sectional view of another embodiment as shown in  FIG. 2  wherein the conductive ring is solid. 
         FIG. 6  is another embodiment of the present invention as shown in  FIG. 2 . 
         FIG. 7  is a side view of the present invention illustrating the concentric nature of the invention. 
         FIG. 8  is a perspective view of the motor ground seal assembly. 
     
    
    
     DETAILED DESCRIPTION—ELEMENT LISTING 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Description 
                 Element No. 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Drive bearing 
                 2 
               
               
                   
                 Conductive brushes 
                 3 
               
               
                   
                 Receptor groove 
                 4 
               
               
                   
                 Brush ring 
                 5 
               
               
                   
                 Metallic insert with solid conductor ring 
                 6 
               
               
                   
                 Conductive insert ring 
                 7 
               
               
                   
                 First O-ring 
                 8 
               
               
                   
                 Solid conductive ring 
                 9 
               
               
                   
                 Rotatable shaft 
                 10 
               
               
                   
                 Housing 
                 11 
               
               
                   
                 Rotatable shaft center 
                 12 
               
               
                   
                 Rotor 
                 13 
               
               
                   
                 Stator 
                 14 
               
               
                   
                 Second O-ring 
                 15 
               
               
                   
                 Brush ring frame 
                 16 
               
               
                   
                 Third O-ring 
                 17 
               
               
                   
                 Motor ground seal assembly 
                 18 
               
               
                   
                 First axial interface gap 
                 20 
               
               
                   
                 Second axial interface gap 
                 22 
               
               
                   
                 Third axial interface gap 
                 24 
               
               
                   
                 Fourth axial interface gap 
                 26 
               
               
                   
                 First radial interface gap 
                 30 
               
               
                   
                 Second radial interface gap 
                 32 
               
               
                   
                 Third radial interface gap 
                 34 
               
               
                   
                 Stator main body 
                 40 
               
               
                   
                 Stator axial projection 
                 42 
               
               
                   
                 Stator radial projection 
                 44 
               
               
                   
                 Stator exterior groove 
                 45 
               
               
                   
                 Stator first O-ring groove 
                 46 
               
               
                   
                 Interior annular groove 
                 48 
               
               
                   
                 Rotor main body 
                 50 
               
               
                   
                 Rotor axial projection 
                 52 
               
               
                   
                 Rotor radial projection 
                 54 
               
               
                   
                 Rotor first O-ring groove 
                 56 
               
               
                   
                 Labyrinth passage 
                 60 
               
               
                   
                   
               
             
          
         
       
     
     Before the various embodiments of the present invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that phraseology and terminology used herein with reference to device or element orientation (such as, for example, terms like “front”, “back”, “up”, “down”, “top”, “bottom”, and the like) are only used to simplify description of the present invention, and do not alone indicate or imply that the device or element referred to must have a particular orientation. In addition, terms such as “first”, “second”, and “third” are used herein and in the appended claims for purposes of description and are not intended to indicate or imply relative importance or significance. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a perspective view of the present invention applied to a rotatable shaft  10  of an electrical motor controller having a variable frequency drive (VFD). (Motor not shown) The motor ground seal™ assembly  18  shown in  FIG. 1  may be mounted to rotatable shaft  10  on either one or both sides of the housing  11 . As depicted herein, the housing  11  may be a pump housing, compressor housing, motor housing, or any other housing  11  that may be employed with rotating equipment of any type. The motor ground seal™ assembly  18  may be flange-mounted or press-fit or attached by other means to a housing  11 . The present invention will also function with a rotating housing and stationary shaft. (Not shown) 
     As shown in  FIGS. 2-6 , the rotor  13  faces outboard and is engaged with an inboard facing stator  14 . The receptor groove  4  allows placement of one of the following conduction means with the motor ground seal assembly  18 : a solid conductive ring having conductive filament brushes  3  attached therein, a solid conductive ring having conductive filament brushes  3  attached therein and a metallic annular frame surrounding the conductive ring, a metallic insert with solid conductor ring  6 , or a conductive insert ring  7 . The receptor groove  4  as shown can also be utilized on other shaft seal assemblies and bearing isolators or combinations therein which use only labyrinths. 
     As shown in  FIGS. 2-6 , the location of the gap with respect to the rotor  13  and stator  14  surfaces and the direction of the opening interface gaps  20  and  21  are both important elements of one embodiment of the motor ground seal assembly  18 . The rotor  13  extends radially well beyond the major diameter of the stator  14 . This permits the rotor  13  to encompass the stator radial projection  44 . It is important that the rotor radial projection  54  extends beyond the basic radial dimension of stator  14 . See U.S. Pat. No. 6,419,233 issued to Orlowski and incorporated by reference herein. This requires a departure from the prior art wherein the rotor  13  was radially co-extensive with the major diameter of the stator  14 . 
     As shown in  FIGS. 2-6 , the stator  14  and rotor  13  may be configured to create a labyrinth passage  60  from the exterior of the housing  11  (generally depicted toward the right in  FIGS. 2-6 ) and the interior of the housing  11  (generally depicted toward the left in  FIGS. 2-6 ) through the motor ground seal assembly  18 . The rotor  13  is generally affixed to the rotatable shaft  11  (and rotatable therewith) using a second O-ring  15 , but may be affixed thereto using other structures, such as set screws, keys with corresponding grooves, or any other means known to those skilled in the art. In the exemplary embodiment, the labyrinth passage  60  includes (in order from the exterior of the housing  11  to the interior thereof) a first axial interface gap  20 , a first radial interface gap  30 , a second axial interface gap  22 , an interior annular groove  48 , a third axial interface gap  24 , a second radial interface gap  32 , a fourth axial interface gap  26 , a first O-ring  8 , and a third radial interface gap  34 . The first O-ring  8  may be a unitizing ring, as is well known to those skilled in the art, which helps to isolate the third radial interface gap  34  from the fourth axial interface gap  26 . In the exemplary embodiment, the first O -ring  8  is positioned partially in a stator first O-ring groove  46  and a rotor first O-ring groove  56 . In other embodiments not pictured herein, no first O-ring  8  is used in the motor ground seal assembly  18 . 
     The stator  14  and rotor  13  each include a stator main body  40  and a rotor main body  50 , respectively. The stator main body  40  is generally the portion of the stator  14  that abuts the housing  11 . The rotor main body  50  is generally the portion of the rotor  13  that abuts the rotatable shaft  10 . In the exemplary embodiment, a stator axial projection  42  and a stator radial projection  44  protrude from the stator main body  40 , and a rotor axial projection  52  and rotor radial projection  54  protrude from the rotor main body  50 . As shown in  FIGS. 2-6 , these projections  42 ,  44 ,  52 ,  54  cooperate with the geometry of the stator  14  and rotor  13  to form the various interface gaps  20 ,  22 ,  24 ,  26 ,  30 ,  32 ,  34 , which in turn form the labyrinth passage  60 . More or fewer projections  42 ,  44 ,  52 ,  54  from the stator main body  40  and/or rotor main body  50  may be employed in embodiments not pictured herein without departing from the spirit and scope of the present invention. 
     The first axial interface gap  20  between the rotor  13  and stator  14  that is exposed to the contamination or lubricants is now fixed in dimension and independent of any relative axial movement between the rotor  13  and the stator  14 . The first radial interface gap  30  is still subject to variation in dimension by any relative axial movement between the rotor  13  and the stator  14 . This relative movement is not significant to the operation in as much as only a small amount of contaminants have been able to enter the labyrinth passage  60  because of the size and location of the first radial interface gap  30 . The removal of the first axial interface gap  20  from variations is more important in seals where the rotor  13  and the stator  14  are not restrained from relative movement. 
     The orientation of the opening of the first axial interface gap  20  is important regardless of relative movement between the stator  14  and rotor  13 . The axial orientation of the first axial interface gap  20  controls entrance of contaminants. Reduction or elimination of contaminants improves both the life and performance of the conductive means. The opening of the first axial interface gap  20  is now facing rearwardly toward the housing  11  and away from the contaminant stream. The contaminant or cooling stream, if present, will normally be directed along the axis of the shaft  10  and toward the housing  11 . 
     A stator exterior groove  45  may be cut in the stator  14 . This stator exterior groove  45  enhances and accentuates the benefits of the rotor radial and axial projections  54 , 52  and the stator radial and axial projections  44 ,  42  with the resultant orientation and independence of the first axial and first radial interface gaps  20 ,  30 . The motor ground seal assembly may be made from any machinable metal such as stainless steel or having low resistivity including bronze, aluminum, copper, gold and combinations thereof. 
     The precise number of projections in either the axial or radial direction of either the stator  14  or rotor  13  may vary depending on the specific embodiment of the motor ground seal assembly  18 , and therefore the number and orientation of the specific interfaces between the stator  14  and rotor  13  may also vary depending on the specific embodiment. Accordingly, the specific orientation, angles, and/or number of interfaces between the stator  14  and rotor  13  may vary in an infinite number of ways without departing from the spirit and scope of the present invention. Furthermore, the presence or absence of the interior annular groove  48  or dimensions thereof in no way limit the scope of the motor ground seal assembly  18 . 
     As is well known to those skilled in the art, in other embodiments not pictured herein the motor ground seal assembly  18  may be configured with a drain (not shown) to allow for the removal of contaminants from the labyrinth  50 . In a similar embodiment not pictured herein, such a drain (not shown) may be used to provide a passage for injected coolant to exit the motor ground seal assembly  18 , as is apparent to those skilled in the art in light of the present disclosure. Furthermore, in still other embodiments, the motor ground seal assembly  18  could be configured to return lubricant captured in the labyrinth  50  to a lubricant sump (not shown). 
     A receptor groove  4  may be cut into the stator  14  on the inboard side facing away from the rotor  13  and into the housing  11 . This receptor groove  4  allows insertion of a circumferential ring-like structure within the stator  14 . The embodiment illustrated in  FIG. 2  shows a solid conductive ring  9  having conductive filaments or brushes  3  in contact with said shaft  10 . The concentric solid conduction ring  9  may be flange-mounted, press-fit or attached by other means to and or within receptor groove  4 . 
       FIG. 3  describes another embodiment of the present invention wherein the conductive insert is a brush ring  5  having a metallic base or frame  16 , preferably made from a low resistivity material such as bronze, copper, gold or aluminum, having a plurality of fibrous conductive brushes  3  engaged with rotatable shaft  10  for transmission of bearing currents to ground. In this embodiment, the circumference of the brush ring  5  is force-fitted into the receptor groove  4  in the motor ground seal assembly  18 , by means of a slightly tapered bore in said receptor groove  4  (not shown) to accommodate imperfections and dimensional tolerance of the brush ring  5  surrounding the filament brushes  3 . In the preferred embodiment, the brush ring  5  would be as described in published U.S. Patent Applications 2004/0233592 and 2004/0185215 filed by Oh et al. The brush ring  5  incorporates technology sold as an “AEGIS SGRTM Conductive MicroFiber™ brush” by Electro Static Technology—an Illinois Tool Works Company. 
     The motor ground seal assembly  18  improves conduction and reduces the effects of “bearing current” by enhancing and increasing the rigidity of circumferential brush ring  5 , thereby increasing the resistance to deformation of the brush ring frame  16  during operation. Deformation of the brush ring  5  and frame  16  during operation is a problem because it destabilizes the spatial relationship between the tip of the brushes, or the shaft facing surfaces of other conductive means, and the rotating shaft  10 . The resulting change in spatial relationship, which although small and within normal machine operating tolerances, negatively affects the conduction of the electrostatic discharge (shaft voltage) from the rotating shaft to ground, thus resulting in the decreased performance of prior art grounding devices. 
     The performance of the motor ground seal assembly  18  disclosed and claimed herein is further improved by aggressive interference between the conduction means and receptor groove  4  of the motor ground seal assembly  18 . The outside diameter of the brush ring  5  means may be up to 0.004 inches (0.102 mm) greater than the inside diameter of the receptor groove  4 . The performance of the motor ground seal assembly  18  is further improved by aggressive interference between the motor grounding seal assembly  18  and the housing  11  of the motor. The outside diameter of the stator may be up to 0.004 inches (0.102 mm) greater than the inside diameter of the motor housing  11 . 
       FIG. 4  describes another embodiment of the present invention wherein the metallic insert with solid conductor ring  6  has a metallic base, preferably a low resistivity material such as bronze, copper, gold or aluminum, and forms a circumferential conductive ring around the rotating shaft when inserted into the receptor groove  4  of the stator  14  for engagement with rotatable shaft  10  for transmission of bearing currents to ground. (Not shown) 
       FIG. 5  describes another embodiment of the present invention wherein the conductive insert ring  7  is a concentric circumferential ring affixed within the receptor groove  4  of said stator  14  therein for engagement with shaft  10  for transmission of bearing currents to ground. (Not shown). Reduction of deformity aggressive interference between conduction means/receptor groove  4  and motor ground seal  18 /housing  11  rotating is contemplated for the embodiments shown and described at  FIGS. 4 and 5 . 
     The motor ground seal assembly  18  may be used with a third o-ring  17  between stator  14  and motor housing  11  as shown in preceding  FIGS. 1-5 . Performance of the motor ground seal assembly  18 , however, may be further improved by eliminating third o-ring  17  and its companion groove as shown in  FIG. 6 . The non-conductive nature of third o-ring  17  may impede conductivity between the motor grounding seal assembly  18  and housing  11  thereby decreasing the overall charge dissipation performance of the motor ground seal assembly  18 . 
     As shown in  FIG. 7 , the motor ground seal assembly  18  in combination with the motor housing  11  creates a stable concentric system with the rotating shaft as its center point  12 . Inserting the combination of conductive brushes  3 , brush rings  5  or conductive inserts ( 6 ,  7  or  9 ) into the motor ground seal assembly  18  within the motor housing  10 , and press or force fitting the various conducting elements (conduction means, stator  14  and housing  11 ) together, forms a relatively fixed and stable spatial relationship between the conducting elements, thereby improving the collection and conduction of electrostatic discharge (shaft voltage) from the rotating shaft  10  to ground, through the conducting elements of the motor ground seal assembly  18 . This improved motor ground sealing system directly seats major elements together which compensates for motor shafts, which are not necessarily perfectly round, and ensures the variation or change in distance from the brush tips  3  to the shaft  10  surface caused by external forces acting on the motor ground sealing system are minimal, thus promoting effective ionization of the air surrounding the brushes  3  and conduction of shaft voltage. 
       FIG. 8  is a perspective view of a circumferential filament brush ring  5  having an annular brush ring frame  16 . The brush ring  5  includes a brush ring frame  16  configured with an annular channel having a plurality of electrically conductive filament brushes  3  positioned therein. The conductive filament brushes  3  are sufficiently small to induce ionization in the presence of an electrical field. The conductive filament brushes  3  are retained by the brush ring frame  16  and have distal end portions disposed in the annular channel formed therein. As shown, the circumference of the brush ring  5  was force-fitted into the receptor groove  4  in the motor ground seal assembly  18 . 
     Having described the preferred embodiment, other features of the present invention will undoubtedly occur to those versed in the art, as will numerous modifications and alterations in the embodiments of the invention illustrated, all of which may be achieved without departing from the spirit and scope of the invention.