Armature for an electric motor having a core face insulation disc
TECHNICAL FIELD 
     The invention relates to the field of electric motors and, in particular, to an armature for an electric motor having an insulator disc swagged against the end face of the laminated armature core to reduce electrical breakdown between the armature windings and the armature core. 
     BACKGROUND ART 
     Various techniques are currently being used to provide electrical insulation between the winding of the armature coil and the armature core. Perkins, in U.S. Pat. No. 2,831,991 teaches the lamination of the ends of the armature core with insulating laminates which are fabricated separately and require individual handling during assembly. 
     Studer, in U.S. Pat. No. 2,232,812, discloses an armature insulating arrangement in which layers of insulating material covering each end of the armature core are formed integral with the core slot insulation. This layer of insulating material may be molded separately or molded directly onto the faces of the armature core. 
     Robison et al, in U.S. Pat. No. 3,917,967, discloses an armature insulation arrangement in which a molded insulating material is applied between the shaft the armature core and against the end faces of the armature coil to a diameter which is approximately equal to the root diameter of the slots in which the coil is wound, while Caillier, Sr., U.S. Pat. No. 4,663,835 teaches applying the insulation along the arms which extend radially on opposite sides of these slots. 
     As is evidenced by the prior art, a continuous effort is being exerted to improve the electrical insulation between the coil windings and the core on which these coils are wound. 
     SUMMARY OF THE INVENTION 
     An armature for an electric motor having a shaft and a laminate core circumscribing the shaft is disclosed. The laminated core having a plurality of radial arms defining a plurality of longitudinal coil slots therebetween. The coil slots have a root end and an open end. A sleeve made of a dielectric material circumscribes the shaft in the region between the shaft and the laminated core and extends a predetermined distance beyond the laminated core on both sides thereof. The sleeve secures the laminated core to the shaft and provides electrical insulation therebetween. 
     A slot liner made of an insulating material is disposed in each of the coil slots and at least one insulating disc is attached to the sleeve adjacent to one end face of the laminated core. The insulating disc engages each slot liner in the region of the root end of the coil slots prohibiting their longitudinal displacement in one direction. 
     A commutator is attached to the shaft on the side of the laminated core opposite the insulating disc and a plurality of coil windings connected to the commutator are wound in selected coil slots of the laminated core. 
     In the preferred embodiment, peripheral regions of the insulating disc are slightly indented into the end openings of the coil slots when the insulating disc is swagged onto the sleeve. 
     The advantage of the armature assembly is that during the winding of the coils, the occurrence of electrical shorts between the coil and the laminated coil are significantly reduced. 
     Another advantage is that the addition of the insulating disc on the end face of the laminated core significantly inhibits the displacement of the slot liners during the winding of the laminated core. 
     These and other improvements will become more apparent from the reading of the specification in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional perspective view of a partially assembled armature; 
     FIG. 2 is a perspective view of the armature showing the addition of the slot liners and the insulating disc; 
     FIG. 3 is a perspective view showing the insulating disc swagged against the end face of the laminated core; 
     FIG. 4 is a top view of the insulating disc; and 
     FIG. 5 is a perspective view of a completed armature. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the structure of a partially assembled armature for an electric motor. The armature is of the type taught by Caillier, Sr. in U.S. Pat. No. 4,663,835 having a shaft 10, a laminated core assembly 12 and an injected molded sleeve 14 which electrically insulates the core assembly 12 from the shaft 10 and secures it thereto. The core assembly 12 has a plurality of radially extending arms 16 defining therebetween a plurality of coil slots 18 which extend through the core assembly parallel to the axis of the shaft 10. The free ends of the radially extending arms 16 may be provided with enlarged heads 20 partially enclosing the open end of the coil slots 18 as shown. 
     The injection molded sleeve 14 has a pair of radially extended spider flange 22 which engage opposite end faces of the core assembly 12 to lock the core assembly 12 axially relative to the shaft 10. The spider flanges 22 have a radially extending finger 24 secured to the end face of each radial arm 16 as shown. A commutator 26 is attached to the shaft 10 at a location displaced from the core assembly. 
     The laminated core assembly 12 is constructed of a plurality of individual annular discs 28 made from a soft iron or any other low magnetic reluctance material in a conventional manner. The discs 28 have a central aperture larger than the diameter of shaft 10 and are insulated from each other to reduce the formation of eddy currents as is known in the art. The sleeve 14 is injection molded between the shaft 10 and the core assembly 12 using a thermosetting dielectric material such as a glass-filled polyester and extends beyond the core assembly 12 in both directions along the shaft 10. 
     As shown in FIG. 2, the assembly of the armature proceeds with the insertion of a slot liner 30 made from a sheet of insulating material in each of the coil slots 18. The contour of the slot liners 30 are shaped to mate with the internal contour of the coil slots 18 including the contours of the enlarged heads 20. To prevent displacement of the slot liners 30 in an axial direction during the winding of the coils on the core assembly, an insulating disc 32 is swagged on the sleeve 12 as shown in FIG. 3. The insulating disc 32 is preferably made from a thin sheet of insulating material such as a sheet of paper having a high fiber content, called rag paper, and may be impregnated or coated with mylar or other plastic material. The insulating disc 32 preferably has an outside diameter selected to engage the edges of the slot liners 40 as shown in FIG. 3. A plurality of arcuate tabs 34 define the internal diameter of the insulating disc 32 which is selected to be less than the diameter of the sleeve 14 adjacent to the core assembly 12 so that the arcuate tabs 34 are deformed when it is swagged against the radial end surface of the laminated core 12. This deformation of the arcuate tabs 34 lock the insulating disc 32 onto the sleeve 14 abutting the radial end surface of the core assembly 12. The insulating disc 32 prevents the longitudinal displacement of the slot liners 30 while the electrical coils are being wound in the slots 18. 
     The peripheral edge of the swagging tool engaging the insulating disc 32 preferably has a plurality of forming bosses aligned with the slots 18 so that during the swagging process, the edges of the insulating disc 32 in the vicinity of the longitudinal slots 18 are indented a small distance into the slots 18 producing a wavy contour as shown in FIG. 3. 
     It has been found that the use of the insulating disc 32 at the end of the core assembly 12 opposite the commutator 26 significantly reduces the production failure rate caused by the longitudinal displacement of slot liners 30 during the winding of the core. The longitudinal displacement of one or more of the slot liners 30 during the winding of the core is believed to be a primary cause of the shorting of the wire to the core assembly 12 and other electrical breakdowns. 
     Although only a single insulating disc 32, swagged to the end of the core assembly 12 on the side opposite the commutator 26 has resulted in a satisfactory solution to the electrical breakdown problem and has reduced the failure rate in the manufacture of armatures, it is recognized that a second insulating disc 32 may also be swagged into the end of the core assembly 12 facing the commutator 26. 
     A complete armature having electrical coils 36 wound in the slots 18 of the core assembly 12 is shown in FIG. 5. 
     Having described the invention with reference to the preferred embodiment shown in the figures, it is recognized that those skilled in the art may make certain changes or improvements within the scope of the appended claims.