Abstract:
A driven seal assembly is provided for a shaft rotated by a motor disposed in a motor housing and having a seal housing adjacent to the motor housing through which the shaft extends. A first rotary seal is frictionally fit on the shaft adjacent the first stationary seal seat. A second rotary seal is frictionally fit on the shaft adjacent a second stationary seal seat. A spring surrounds the shaft and provides bi-directional axial forces on the first and second rotary seals against the first and second stationary seal seats. A positive drive mechanism is mounted on the shaft between the first and second rotary seals in a driving, mating relationship therewith and includes a first driving element in driving engagement with the first rotary seal and a second driving element in driving engagement with the second rotary seal.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a driven seal assembly for preventing leakage of fluid along a rotary shaft of a motor and into a housing associated with the motor. 
   BACKGROUND OF THE INVENTION 
   A mechanical seal assembly is commonly used on a rotating shaft of a motor enclosed in a motor housing, and projecting through a seal housing adjacent the motor housing to prevent water or other fluid from migrating along the shaft and entering the seal and motor housings. One such known application involves a driven seal assembly mounted in a seal housing about the rotating shaft of an electric motor drivingly connected to an impeller of a fountain aerator having its motor housing disposed in a body of water. 
   Such prior art driven seal assemblies include a pair of stationary seal seats, a pair of rotary seals and a coil spring, all of which are mounted on a shaft driven by the motor. Typically, one stationary seal seat is fixedly mounted in a bore of the seal housing and cooperates with one of the rotary seals. The other stationary seal seat is fixed in a bore of the motor housing and cooperates with the other of the rotary seals. Both rotary seals have internal rubber surfaces that are frictionally fit upon the outer diameter of the shaft so that the rotary seals will rotate with the shaft and provide inner seals along the shaft to prevent water from migration therealong. To maintain a seal between the opposed seal faces of the rotary seals and the stationary seat seals and thus seal the bores in the seal and motor housings, the coil spring is placed under compression between the two rotary seals. 
   Certain problems may arise with using this type of driven seal assembly on a driven motor shaft. For example during motor operation, the rotary seals are driven by friction of rubber against the shaft. If the friction fit begins to slip, heat is generated and a groove will begin to be worn into the shaft. The rubber surfaces of the rotary seals become glazed, locking of the stationary seal seats and rotary seals may occur, the supple fit of the rotary seals is lost and wear on the shaft will enable water to enter the motor housing and destroy the motor. 
   Accordingly, there is a need to provide a driven seal assembly that overcomes the problems of the prior art and ensures proper sealing of a rotating shaft relative to seal and motor housings is maintained for prolonged operation of the motor. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a driven seal assembly for a shaft rotated by a motor disposed in a motor housing and having a seal housing adjacent to the motor housing through which the shaft extends. A first stationary seal seat is mounted on the shaft and secured in the bore of the seal housing. A first rotary seal is frictionally fit on the shaft adjacent the first stationary seal seat. A second stationary seal seat is mounted on the shaft and secured in the bore of the motor housing. A second rotary seal is frictionally fit on the shaft adjacent the second stationary seal seat. A spring surrounds the shaft and provides bidirectional axial forces on the first and second rotary seals against the first and second stationary seals seats. The invention is improved by a positive drive mechanism mounted on the shaft between the first and second seals in a driving, mating relationship therewith and including a first driving element in driving engagement with the first rotary seal and a second driving element in driving engagement with the second rotary seal. The spring is placed in compression between the first and second driving elements. 
   The positive drive mechanism includes a third driving element fixed to the shaft between the first and second driving elements and encircled by the spring. The third driving element is connected by pins to the first and second driving elements. The spring encircles axially extending portions of the first and second driving elements. The spring has opposite ends engaged against portions of the first and second driving elements extending radially from the axially extending portions. The first and second driving elements are formed with non-circular cavities for receiving mating non-circular portions of the first and second rotary seals. The shaft passes freely through the cavities of the first and second driving elements. 
   In another aspect of the invention, a driven seal assembly is provided for a shaft rotated by a motor disposed in a motor housing and having a seal housing adjacent the motor housing through which the shaft extends. The driven seal assembly includes a first stationary seal seat mounted on the shaft and secured in a bore of the seal housing. A first rotary seal is frictionally fit on the shaft adjacent the first stationary seal seat. A first rotor driver is mounted on the shaft in mating relationship with the first rotary seal. A second stationary seal seat is mounted to the shaft and is secured in a bore of the motor housing. A second rotary seal is frictionally fit on the shaft adjacent to the second stationary seal seat. A second rotor driver is mounted on the shaft in mating relationship with the second rotary seal. A set collar is attached to the shaft between the first and second rotor drivers and is drivingly connected thereto. A spring surrounds the set collar and is placed in compression between the first and second rotor drivers. The spring exerts bidirectional forces causing the first and second rotary seals to constantly engage the first and second stationary seal seats respectively, and seal the bores of the seal housing and the motor housing. The set collar, the first and second rotor drivers and the first and second rotary seals define a positive drive mechanism for constantly urging the first and second rotary seals against the first and second stationary seal seats upon rotation of the shaft regardless of the fit between the first and second rotary seals on the shaft. 
   The first and second stationary seal seats are press fit and non-rotatably mounted in the bores of the seal and motor housings, respectively. The first and second rotary seals are aligned with rubber surfaces that seal against an outer periphery of the shaft. The first and second rotary seals include hexagonally-shaped bosses. The first and second rotor drivers have hexagonally-shaped wall structure matingly engagable with the bosses on the first and second rotary seals. Each of the first and second rotor drivers has a circular crown integrally formed with an annular neck having a diameter less than a diameter of the crown. Each rotor driver is formed with a pair of axially extending apertures spaced substantially 180 degrees apart. The set collar is attached to the shaft by at least one set screw. The set collar is provided with a pair of axially extending pins that are received in the rotor driver apertures. The spring surrounds the necks of the first and second rotor drivers and has opposite ends engaged against inner faces of the circular crowns of the first and second rotor drivers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
       FIG. 1  is a perspective view of a housing for a motor having a driven shaft provided with a driven seal assembly embodying the present invention; 
       FIG. 2  is an exploded elevational view of the seal assembly; 
       FIG. 3  is an exploded perspective view of the seal assembly; and 
       FIG. 4  is a cross-sectional view taken on line  4 - 4  of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Referring to the drawings,  FIG. 1  depicts a generally cylindrical motor housing  10  for protectively enclosing an electric motor  12  having a rotary drive shaft  14  projecting from one end thereof. Although not illustrated, the shaft  14  may be drivingly connected to an impeller of a fountain aerator having motor housing  10  disposed in a body of water. On one end, the motor housing  10  has a bottom plate  16  provided with an electrical enclosure  18  for establishing the necessary electrical connections for the motor  12 . On an opposite end, the motor housing  10  has a top plate  20  as well as a seal housing  22  through which the rotary drive shaft  14  passes. The top plate  20  is formed with certain holes  24  to permit the attachment of the motor  12  inside motor housing  10  using fasteners  26 . The motor housing  10  is reinforced by a series of elongated rods  28  having bolt heads  30  engaged adjacent bottom plates  16  and threaded ends received in nuts  32  drawn against the top plate  20 . 
   As seen best in  FIG. 4 , seal housing  22  is defined by a cylindrical sidewall or cartridge tube  34  and a circular seal top plate  36 . A bottom end of the cartridge tube  34  is received along with an O-ring  38  in a circular groove  40  formed in an outside surface of motor housing top plate  20 . A top end of the cartridge tube  34  is received along with another O-ring  42  in an annular channel  44  formed on an inside surface of the seal top plate  36 . The motor housing top plate  20  is formed with a central opening  46  for receiving the drive shaft  14  therethrough. The motor housing top plate  20  is also configured with a number of threaded blind holes  48  lying between the groove  38  and the central opening  46 . The seal top plate  36  is constructed with a central recess  50  that is aligned with the central opening  46  in the motor housing top plate  20  for receiving the drive shaft  14  therethrough. The seas top plate  36  is designed with a plurality of bores  52  aligned with the threaded blind holes  48 . Bolts  54  are passed through the bores  52  and threaded into the threaded blind holes  48  to attach the seal housing  22  to the motor housing top plate  20 . Although not shown, it is preferable to include an O-ring and a washer around bolt  54  adjacent the head thereof. 
   A driven seal assembly  56  forming the present invention is mounted on the drive shaft  14  and enclosed in the seal housing  22  for preventing leakage of water along the drive shaft  14  and into the seal housing  22  and the motor housing  10 . Referring now to  FIGS. 2 and 3 , the driven seal assembly  56  includes a pair of identical stationary seal seats  58 ,  60 , a pair of identical rotary seals  62 ,  64 , a pair of identical rotor drivers,  66 ,  68 , a set collar  70 , and a coil spring  72 , all of which encircle shaft  14 . The stationary seal seats  58 ,  60  and the rotary seals  62 ,  64  are commercially purchased components available from Flowserve Corporation of Irving, Tex. as assembly part 31-125-273. 
   The stationary seal seats  58 ,  60  have inner diameters that are slightly larger than the outside diameter of shaft  14  so that shaft  14  will pass freely through the stationary seal seats  58 ,  60 . Both of the stationary seal seats  58 ,  60  also commonly have an O-ring  74  interposed in an external groove  76  between an inner face  78  and an outer face  80 , and are designed to be press fit and non-rotatably mounted to the motor housing top plate  20  and the seal housing top plate  36 . More particularly, as seen in  FIG. 4 , inboard stationary seal seat  58  is frictionally retained in a bore  82  formed in top plate  20  that opens from central opening  46  into a larger diameter than central opening. The seal seat  58  is prevented from rotating by means of a screw  84  that is inserted into the top plate  20  and engaged with a notch  86  on an outer face  80 . Similarly, outboard stationary seal seat  60  is frictionally retained in a bore  88  formed in a seal housing top plate  36  that communicates with central recess  50 . The seal seat  60  is restrained against rotation by a screw  90  which extends into the top plate  36  and engages a notch  86  on outer face  80 . 
   The rotary seals  62 ,  64  have inner rings  91  lined with rubber surfaces  92  ( FIG. 3 ) than snugly engage the outer diameter of shaft  14  in a tight frictional fit to support rotation of the rotary seals upon rotation of the driven shaft  14 . The rotary seals  62 ,  64  further have tapered portions  94  with outer planar faces  96  for contacting the inner planar faces  78  of stationary seal seats  58 ,  60 . and inner hexagonally-shaped bosses  98  which are matingly received by walls  100  of hexagonally-shaped cavities formed in the rotor drivers  66 ,  68 . That is, inboard rotary seal  62  is positioned adjacent inboard stationary seal seat  58  so that a flat sealing surface is created between outer face  96  and inner face  78 . Inboard rotary seal boss  98  is drivingly engaged with the walls  100  of the cavity in inboard rotor driver  66 . Outboard rotary seal  64  is juxtaposed against outboard stationary seal seat  60  so that a flat sealing surface is defined between outer face  96  and inner face  78 . Outboard rotary seal boss  98  is keyed into the walls  100  of cavity of outboard rotor driver  68 . 
   The rotor drivers  66 ,  68  have commonly shaped outer circular crowns  102  integrally formed with inner step down, annular necks  104  with the shaft  14  passing through the hexagonal cavities formed therein. The rotor drivers  66 ,  68  are provided with a pair of axially extending pin apertures  106 ,  108  formed completely through the crowns  102  and necks  104  of the rotor drivers  66 ,  68  and spaced substantially  180  degrees apart. 
   The set collar  70  surrounds shaft  14  and is interposed between the necks  104  of rotor drivers  66 ,  68 . The set collar  70  includes a pair of radially extending holes (one being seen at  110 ) through which set screws (such as  112 ) are inserted to secure the set collar  70  around shaft  14 . A pair of axially extending pin holes  114 ,  116  is formed through the set collar  70  for frictionally retaining a pair of drive pins  118 ,  120  spaced substantially 180 degrees apart. The drive pins  118 ,  120  project bi-directionally beyond planar faces of the set collar  70  with end portions being inserted into registering apertures  106 ,  108  on the rotor drivers  66 ,  68  flanking the set collars  70 . 
   Coil spring  72  surrounds the set collar  70  and the necks  104  of the rotor drivers  66 ,  68  and is compressed between inner faces  122  of the crowns  102  which extend radially beyond the necks  104  of the rotor drivers  66 ,  68 . The spring  72  creates constant bidirectional axial forces against the rotor drivers  66 ,  68  which, in turn, constantly urge the rotary seals  62 ,  64  keyed thereto outwardly against the stationary seal seats  58 ,  60  so that water is kept outside seal housing  22  and motor housing  10 . 
   In use, when motor  12  drives shaft  14 , it can be understood that the constant bi-directional axial forces acting on rotary seals  62 ,  64  against stationary seal seats  58 ,  60  create tight sealing of bore  82  in motor housing top plate  20  and bore  88  in seal housing top plate  36 . Leakage along shaft  14  is prevented by the tight fit of rotor seal rubber surfaces  92  acting on the outer diameter of shaft  14 . In addition, as shaft  14  is driven, the set collar  70  rotates causing pins  118 ,  120  to drive rotor drivers  66 ,  68  and rotary seals  62 ,  64  keyed thereto so that sealing is maintained between the planar faces  78 ,  96  of the rotary seals  62 ,  64  and stationary seal seats  58 ,  60 . That is, the set collar  70 , pins  118 ,  120 , rotary drivers  66 ,  68  and rotary seals  62 ,  64  form a positive drive mechanism for the seal assembly  56 . This positive drive mechanism prevents slippage of the shaft  14  relative to the rotary seals  56 ,  58  which formerly occurred during motor shaft rotation. Such slippage would be accompanied by heat generation causing a groove to wear in the shaft  14 , possible locking between the rotary seals and the stationary seal seats, loss of the supple fit of the rotary seals and eventual leakage of water along the shaft  14  and into the seal and motor housings  22  and  10  respectively. The present invention uses the positive drive mechanism in combination with the bi-directional axial forces exerted by the spring  72  upon the rotor drivers  66 ,  68  and rotary seals  62 ,  64  to alleviate slippage and wear problems, and prevent water from migrating along the shaft  14  into the motor housing  10 . 
   While the invention has been described with reference to a preferred embodiment, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made without departing from the spirit thereof. Accordingly, the foregoing description is meant to be exemplary only and should not be deemed limitative on the scope of the invention set forth with the following claims.