Patent Publication Number: US-2005121988-A1

Title: Alternator and method of manufacture

Description:
This application division of U.S. continuation application Ser. No. 10/794,908, filed Mar. 5, 2004 which claims priority to U.S. application Ser. No. 10/098,782, filed Mar. 14, 2002 which claims priority to U.S. provisional patent application Ser. No. 60/276,723, filed Mar. 16, 2001. 
    
    
     TECHNICAL FIELD  
      This invention relates generally to alternators for internal combustion engine applications and the like and to methods of manufacturing such alternators, and further to the manufacture of molded plastic housings for electrical devices generally having a bearing for supporting a rotating shaft.  
     RELATED ART  
      Alternators, particularly those for automotive engine applications, are fabricated with drive-end (D.E.) and a stator-regulator-end (S.R.E.) frames which house a stator and rotor and support the other components that make up the alternator. The stator is normally fitted in the D.E. frame. Both frames are typically cast from aluminum and have several surfaces that require secondary machining to prepare the surfaces to support a corresponding component of the alternator. One of those surfaces is the stator bore of the D.E. frame which supports the stator. Once machined, the D.E. frame is heated to expand the stator bore at which point the stator is inserted into the D.E. frame and the frame then cooled to shrink the D.E. frame about the stator to retain the stator in place. The machining and heating operations add to the cost of manufacturing such alternators.  
      Aluminum is typically employed for the D.E. frame for its ability to provide a ground path for the stator and for its strength and dimensional stability at elevated operating temperatures of the stator.  
      Included among the other machined surfaces of such aluminum D.E. frames is a bearing well whose inner surface is machined to receive a sealed D.E. roller bearing with a press fit. The well includes a lip of aluminum material extending about the opening of the bearing well which, after installation of the bearing, is spun over onto the outer race to capture the bearing axially within the well. The secondary machining and lip deformation operations further add to the cost of alternators.  
      Moreover, when it is desired to rebuild a spent alternator, the spun-over lip must be ground off and the D.E. frame modified with a retro-fit metal retainer fastened to the bearing well in position of the former spun-overlip. Such process involves remachining of the bearing well wall, removal of the spun-overlip and machining of the frame to receive the retainer ring, and the provision and fastening of the retainer ring to make use of the otherwise spent, aluminum D.E. frame. Such adds cost to the rebuilding of spent alternators.  
      Other surfaces that require machining are the mating surfaces of the D.E. and S.R.E. frames, which are brought together and then secured by fasteners. Also machined are several bores which are fitted with pressed steel bushings for mounting the alternator in service. Such dissimilar metal materials (i.e., steel against aluminum) present issues of corrosion which must be contended with.  
      U.S. Pat. No. 4,705,983 discloses an alternator having, as part of its structure, an end shield fabricated of insulating plastics material and formed with a central molded hub that, after forming, is provided to seat a roller bearing.  
      U.S. Pat. No. 5,982,057 discloses molding a plastics housing in place about a stator of an electric motor along with a molded-in bearing bush. Following molding, a roller bearing is installed in the bearing bush. Provision of the molded-in bearing bush adds cost and complexity to the structure.  
      It is an object of the invention to overcome or greatly minimize the foregoing limitations in connection with alternators and other electrical devices employing a plastic housing to support a bearing of the art.  
     SUMMARY OF THE INVENTION AND ADVANTAGES  
      According to one aspect of the invention, an alternator is provided comprising a D.E. frame having an electrical grounding portion; a stator secured to the D.E. frame remote from the grounding portion; a D.E. bearing secured to the D.E. frame; a S.R.E. frame secured to the D.E. frame, a S.R.E. bearing secured to the S.R.E. frame, a rotor housed within the D.E. and S.R.E. frames and journaled by the D.E. and S.R.E. bearings for rotation relative to the rotor, and wherein the D.E. frame is fabricated of plastics material and includes an electrically conductive ground circuit coupling the stator electrically to the ground portion. This aspect of the invention has the advantage of providing a plastics D.E. housing which is less costly and lighter weight than the aluminum counterparts and yet is provided with a ground path for the stator.  
      According to a further aspect of the invention, a housing assembly, such as the D.E. or S.R.E. frame of an alternator, includes a sealed roller bearing having inner and outer races and roller elements therebetween, and a molded plastics housing having a bearing well within which the sealed roller bearing is molded in place. The bearing well includes an inner wall surface engaging an outer surface of the outer race, and axial restraining portions which extend radially inwardly from the inner wall of the well in overlying relation to axially opposite end faces of the outer face for restraining the bearing axially against removal from the bearing well. According to a related method of the invention, during molding, the bearing is maintained at a temperature in the mold below that which would cause heat damage to the bearing.  
      This aspect of the invention has the advantage of providing a simple, effective way of securing a sealed, heat-sensitive roller bearing within a housing, such as an alternator frame, which avoids machining or pressing operations or provision of a premolded bearing bush. The same technique and features are applicable to other plastics housings of electrical devices in which the bearing is molded in place in the housing.  
      According to yet another aspect of the invention, an alternator is formed according to a method in which the D.E. frame is molded from plastics material and is removed from the mold. While still hot, the stator is installed in the D.E. frame and the plastics material allowed to cool to constrict about the stator to secure the stator in place in the D.E. frame.  
      According to still a further aspect of the invention, a ground path is molded in place in a plastic housing of an electrical component to establish a defined electrical path through the plastics housing. 
    
    
     THE DRAWINGS  
      A presently preferred embodiment of the invention is disclosed in the following description and in the accompanying drawings, wherein:  
       FIG. 1  is an exploded perspective view of an alternator constructed according to a presently preferred embodiment of the invention;  
       FIG. 2  is an enlarged elevation view looking into the D.E. frame;  
       FIG. 3  is an enlarged, exploded perspective view of the D.E. frame and stator prior to their assembly;  
       FIG. 4  is a view like  FIG. 3  following assembly of the stator in the D.E. frame;  
       FIG. 5  is an enlarged fragmentary cross-sectional view taken generally along lines  5 - 5  of  FIG. 2 ; and  
       FIG. 6  is an enlarged perspective view of a bearing whose outer race is formed with retaining grooves shown interlocked with retaining ribs of the housing. 
    
    
     DETAILED DESCRIPTION  
      Referring initially to  FIG. 1 , an exploded perspective view of an alternator  10  is shown constructing according to a presently preferred embodiment of the invention. The alternator  10  includes a housing assembly  12  comprised of a drive-end (D.E.) frame  14 , and a stator-regulator-end (S.R.E.) frame  16  which are joined at mating flanges  18 ,  20  and secured by bolts  22  to house therein a stator  24  and a rotor  26 .  
      The D.E. frame  14  is molded of plastics material and mounts a D.E. bearing  28 . The S.R.E. frame  16  is likewise preferably fabricated of plastics material and mounts a corresponding S.R.E. bearing  30 . The bearings  28 ,  30  are double sealed roller bearings of the type schematically illustrated in  FIG. 5  including an outer race  32 , an inner race  34  and a plurality of rolling elements, such as the illustrated bearing balls  36 , captured between the outer and inner races  32 ,  34  to enable the inner race  34  to rotate relative to the outer race  32 . Annular seals  38  span the gap between the inner and outer race to provide a sealed environment to the roller elements  36 , which are lubricated with grease  40 . Such sealed roller bearings  28 ,  30  are heat-sensitive, in that if the bearings  28 ,  30  are heated above a critical upper operational limit temperature, either the seals  38  overheat and fail and/or the grease  40  within the bearings  28 ,  30  liquefies and leaks out of the bearings past the seals  38  and the bearing fails. The critical upper limit operating temperature will vary depending on the type of grease and seals employed in a given bearing, and an understanding of the operating limits are known by those of ordinary skill in the art of alternators and bearings. The bearings  28 ,  30  surround openings in the frames  14 ,  16  through which a shaft of the rotor  26  extends and is journaled by the bearings.  
      According to one aspect of the invention, at least the D.E. bearing  28  is molded in-place with the formation of the D.E. frame  14  and preferably the S.R.E. frame  16 . As shown best in  FIG. 5 , the bearing  28  is inserted in a mold (not shown) configured to form the D.E. frame  14  into which hot, flowable plastics material is introduced which, as shown, flows around the bearing  28  to capture the bearing  28  within a bearing well  42  of the D.E. frame  14 . More specifically, the bearing well  42  is comprised of a cylindrical hub or bearing well ball portion  44  projecting axially inwardly from an end wall  46  of the D.E. frame  14 . The hub  44  has an inner wall surface  48  which engages an outer peripheral surface  50  of the outer race  32 . An annular retaining portion or flange  52  molded as one piece with the D.E. frame  14  projects radially inwardly from the inner wall surface  48  on opposite axial sides of the D.E. bearing  28  in overlying relationship to axially opposite end faces  54 ,  56  and in radially outer spaced relation to the inner race  34  for restraining the D.E. bearing within the bearing well  42  in both axial directions via upper and lower retaining portions  52 ,  53  and radially via the inner wall surface  48 . In this way, the bearing  28  is captured in place during molding by the structure of the D.E. frame alone. The lower retaining portion  53  forms part of the end wall  46  of the frame and extends from the opening  55  in the end wall  46  to the bearing well wall or hub  44 .  
      As shown in  FIG. 6 , the outer surface  50  of the outer race  32  may be formed with a series of retaining grooves  58  which are recessed into the outer surface  50 . During molding, the grooves  58  are filled with the plastics material of the D.E. frame  14  to provide interlocking retaining ribs  60  of the D.E. frame  14 . The grooves  58  and ribs  60  are preferably transverse to the longitudinal axis and lateral plane of the outer race  32 , such that the interlocking grooves  58  and ribs  60  crisscross one another and constrain the outer race  32  against longitudinal movement along the axis as well as rotational movement about the axis of the outer race  32 . The grooves  58  may be ground into the outer surface  50  or provided by other suitable means. The grooves preferably have a depth of about 0.020-0.030 inches and a width of about 0.060 inches. The same technique for molding in place a bearing in a plastic housing is equally applicable to other housing components such as electric starters and the like.  
      Turning now to  FIGS. 2 and 3 , the D.E. frame  14  has a stator hub  62  provided by an outer peripheral wall of the frame  14  formed with an inner stator bearing surface  64  which, in its as-molded state without machining, is sized to engage an outer surface  66  of the stator  24  with sufficient frictional interference to secure the stator  24  within the D.E. frame  14 .  
      According to the invention, the D.E. frame  14  is molded such that the stator bearing surface  64  has a size in relation to the outer surface  66  of the stator  24  that, when the D.E. frame  14  is cooled to ambient temperature, tightly constricts about and grips the outer surface  66  of the stator  24  to secure the stator  24  in place within the D.E. frame  14 . According to a preferred aspect of the invention, the D.E. frame  14  is molded initially without the stator  24 . Upon solidification of the plastics material of the D.E. frame  14 , but while the D.E. frame  14  is still hot from molding, the D.E. frame  14  is removed from the mold and, while still hot, the stator  24  is inserted into the stator hub  62  of the D.E. frame  14 . The temperature, of course, will vary depending upon the material used to form the D.E. frame  14 . However, at the temperature of removal from the mold, the heat of the D.E. frame  14  causes the stator bearing surface  64  to be in an expanded state whereby the stator  24  can be inserted into the stator hub  62  with very little effort due to the radial clearance between the stator  24  and stator hub  62 . Once installed, the D.E. frame  14  is allowed to cool, which causes the stator bearing surface  64  to constrict tightly about the outer surface  66  of the stator  24 , securing the stator  24  both axially and rotatably against movement relative to the D.E. frame  14  and preventing its removal from the frame  14 .  
      Preferably, the inner cylindrical stator bearing surface  64  is formed with an alignment rib  68  which projects radially inwardly from the surface  64 . The alignment rib  68  extends axially along the surface  64  of the stator hub  62 . The alignment rib  68  is thus fixed relative to the frame  14  and projects inwardly from the stator bearing surface  64 . The outer surface  66  of the stator  24  is formed with a plurality of axial grooves  70 , any one of which can receive the rib  68 . In most cases, the stator  24  will have a preferred angular orientation relative to the D.E. frame  14 . As illustrated in  FIGS. 3 and 4 , the stator  24  can be marked with a visible alignment indicator  72  positioned such that when aligned with the alignment rib  68  the stator  24  is in the proper angular orientation relative to the D.E. frame  14 . As shown in  FIG. 4 , during installation of the stator  24  when the D.E. frame  14  is still hot from the mold, the appropriate groove  70  associated with the alignment indicator  72  is guided into position over the alignment rib  68  to quickly, easily and positively orient the stator  24  precisely relative to the D.E. frame so as to eliminate variation between components.  
      The stator  24  preferably includes a stack of metal laminates  74  and copper windings  76 .  
      The D.E. frame  14  is preferably formed with at least one and, as illustrated here, a pair of electrically grounding portions  78  in the form of ears which have molded-in metal bushings or sleeves  80  defining lined bolt holes for received bolts (not shown) which mount the alternator  10  to the frame or other structure of a vehicle or the like and provides, by that connection, a grounding vehicle. The sleeves  80  are preferably aluminum.  
      The plastics molded D.E. frame  14  includes an electrically conductive ground circuit which couples the stator  24  electrically to the grounding portion  78 . According to one aspect of the invention, the D.E. frame  14  is molded from an electrically conductive plastics composite material which renders the entire D.E. frame  14  conductive and thus establishing the ground path. Suitable materials are those which can withstand the operating temperature of an alternator while maintaining adequate strength and stability to provide the needed support of the D.E. frame  14 . Among the candidate materials are high temperature, heat stabilized polyamide resins having a carbon fiber fill of about 35 to 50 vol % which renders the composite electrically conductive to provide the electrically conductive path from the rotor  26  to the grounding portion  78 . One such material is manufactured by E.I. du Pont de Nemours (DuPont) under the Zytel® family. Alternatively, or in addition to conduction by the composite material per se, the ground path  82  may be provided by an embedded wire  84  leading to the sleeve  80  and molded in place during the molding of the D.E. frame  14 , or an external wire  86  added after molding the D.E. frame  14 . The same technique for providing a molded-in ground path is applicable to housings of other electrical devices, such as starters and the like.  
      According to a further aspect of the invention, the S.R.E. frame  16  is fabricated of a plastics material that is relatively non-conductive in relation to the conductivity of the D.E. frame  14 . In other words, the S.R.E. frame  16  is more insulating than electrically conductive in relation to the properties of the D.E. frame  14 . The S.R.E. frame  16  may be fabricated of a substantially non-conductive plastics material. A suitable material may comprise 35-50 vol % glass fiber- filled polyamide resin of the Zytel® family. Making the S.R.E. frame  16  from non-electrically conductive plastics material has the advantage of insulating many of the component parts mounted on the S.R.E. frame which normally require special insulating shields and the like to prevent conductive between the components and the usual aluminum S.R.E. frame. Mounted on the backside of the S.R.E. frame  16  is a regulator  88 , a rectifier  90 , and a brush holder assembly  92 . When installed, these components are concealed by an end cover  94  which likewise may be plastic. With the non-conductive plastic S.R.E. frame  16 , there is no need to electrically insulate the regulator  88  and rectifier  90  from the S.R.E. frame  16 , which greatly simplifies and reduces the cost of manufacturing alternators.  
      The invention further contemplates methods in remanufacturing spent alternators both of the traditional metal frame construction and those of the plastic frame variety of the invention. In either case, the rotor and bearing, along with any other inserts, are removed from the D.E. frame and a new D.E. frame  14  molded from the plastics material as previously described, preferably including the molded-end bearing  28 . The spent plastic D.E. frame  14  can be ground and recycled. The stator  24  is installed by the same process of inserting it into the frame  14  when the frame  14  is hot out of the mold.  
      The disclosed embodiment is representative of a presently preferred form of the invention, but is intended to be illustrative rather than definitive thereof. The invention is defined in the claims.