Abstract:
A stator for an electric motor includes a yoke and a star disposed in the yoke. The star is configured to receive a rotor therein and has at least one wire coiled thereat. The yoke and the star are configured such that the star is axially insertable into the yoke with reduced interference and reduced insertion force. The star is axially inserted into the yoke in an unlocked position. When the star is inserted into the yoke, the star is rotatable to a locked position, whereby the star is retained at the yoke via an interference fit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the filing benefits of U.S. provisional application, Ser. No. 61/869,195, filed Aug. 23, 2013, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates electrical motors and, more particularly, to stators for electric motors with internal rotors. 
     BACKGROUND OF THE INVENTION 
     Typically, a one-component stator is inexpensive and heavily used in standard inner rotor motors, but has limits in the winding process (copper wire diameter, filling factor, inner diameter, and the like) and as a consequence is limited in reaching high efficiency versus cost and package targets. 
     Two-component stator designs are known. Typically, a two-component stator consists of cutting a ring for a stator yoke and a separate cutting a star which, once separately wound, is then axially pressed into the rotor yoke. Such a stator construction may allow for improved winding with high copper diameter and filling factor but it generates several disadvantages, including (i) high and variable insertion forces required to press the star into the yoke, which makes the process difficult to control, (ii) the necessity to cut the two parts of the stator in different punching stations, in order to have a better dimensional control and for reducing the insertion force issues, which increases the part cost due to process labor and iron scrap, and (iii) iron losses generated by electrical contacts due to interference and not perfect alignment between yoke/star lamination (eddy currents in excess that downgrade the laminations grade). 
     SUMMARY OF THE INVENTION 
     The present invention provides a stator construction for an electric motor that has the star and yoke components of a stator (and rotor) as a single lamination, with the components of the lamination being stamped or punched in “one shot”. This is possible because of the free space between the three components that allows the stamping operation. The stacking of the three elements is also done in the same stamping tool. The star and yoke are laminated and formed via the same stamping operation and then assembled together after the coils are wound onto the star. The present invention provides for more freedom degrees about the winding operation, with less effort for the star insertion into the yoke, and better lamination alignment, thereby reducing the iron losses and increasing the motor efficiency. 
     Therefore, the present invention provides a stator for an electric motor with an internal rotor, with the stator winding with high diameter copper wire, and providing (i) a high copper filling factor, (ii) an easier external winding of the stator star, (iii) needle, flyer, inserted coils, (iv) low or reduced iron losses between yoke/stator star contact areas due to perfect alignment, (v) low assembly forces for yoke/stator interlocking, and (vi) yoke, stator star and rotor lamination stamping in one shot, with process cost reduction because less punches hit and scrapped material reduction. 
     These and other objects, advantages, purposes and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a stator construction in accordance with the present invention; 
         FIG. 2  is an exploded view of a prior art stator construction; 
         FIGS. 3 and 4  are perspective views of a prior art laminated star and prior art laminated yoke as they are pressed together; 
         FIG. 5  is a plan view of the yoke, star and rotor assembly of the stator of the present invention; 
         FIG. 6  is an exploded view of the yoke, star and rotor assembly of  FIG. 5 ; 
         FIG. 7  is a schematic of the punching operation that forms the yoke and star of the stator of the present invention; 
         FIG. 8  is a perspective view of a portion of the punched yoke and star formed from the punching operation of  FIG. 7 ; 
         FIG. 9  is a perspective view of the star and yoke of the stator of the present invention, shown when the star is inserted into the yoke at a portion of the yoke that has a larger inner radius to provide clearance for the star therein; 
         FIG. 10  is a schematic of the assembly of  FIG. 9 , showing the clearance between the star and yoke; 
         FIG. 11  is a perspective and partial sectional view of the stacked or laminated star, with an over molding disposed thereat; 
         FIG. 12  is a plan view of the star of  FIG. 11 ; 
         FIG. 13  is a side elevation of the star of  FIG. 11 ; 
         FIG. 14  is a perspective view of the star of  FIG. 11 , shown with copper wire wound thereat; 
         FIG. 15  is a sectional view of the star of  FIG. 14 ; and 
         FIGS. 16-31  are views of the assembly processes and stator assembly of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and the illustrative embodiments depicted therein, a stator of the present invention comprises a yoke and a star, which are joined together and which rotate about a rotor ( FIGS. 1, 5 and 6 ). The yoke and star are formed so that the star (which may be laminated and comprise a plurality of layers of star elements) may be readily inserted axially into the yoke (which may be laminated and comprise a plurality of layers of yoke elements) and then rotated relative to the yoke to provide a tight interference fit between the yoke and star. The yoke and star elements (and optionally the rotor too) may be punched via a common punching process so that, when the star and yoke are assembled together, the interference fit between the components is tight and consistent. 
     The present invention designs the separation surfaces between the stator yoke and the separate teeth of the star so that they can be assembled, after winding of the wire onto the star, with a zero or near zero force needed for the axial movement of the star into the yoke and then with low force rotational locking. Since both the yoke and star are laminated in a plane perpendicular to the axial direction, they produce a strong reaction force in axial direction, while for a movement parallel to the lamination plane the laminations will naturally tend to slide between them thus minimizing the mechanical and electromagnetic problems. 
     It is known to form a yoke and star for a stator by cutting a ring (having a generally cylindrical inner surface) for stator yoke and a separate stator star, which, once separately wound, is then axially pressed-in into the stator yoke (such as can be seen with reference to  FIGS. 2-4 . Such a construction may allow the winding with high copper diameter and filling factor but it generates several disadvantages, including a high and variable insertion force (to press the star into the yoke) which makes the process difficult to control. Thus, such a construction also has the two parts of the stator cut in different punching steps, in an attempt to provide better dimensional control and for reducing the insertion force issues. The prior art constructions may also have increased iron losses generation, such as by the electrical contacts due to interference and not perfect alignment between the yoke/star lamination (eddy currents in excess that downgrade the material grade). Also, and as can be seen with reference to  FIGS. 3 and 4 , the star (after the winding process) is pressed axially into the yoke and this process may encounter high and variable interferences due to the single lamination blanking process, with the interferences being dependent by the wearing of the blanking punches for the respective parts. 
     The stator (and rotor) components (single lamination) of the present invention include the star and yoke and rotor components of the lamination stamped in “one shot”. This is possible because of the free space (see, for example,  FIG. 10 ) between portions of the three components that allows for the single punching or stamping operation. The stacking of the three elements may also be done with the same stamping tool. 
     As can be seen with reference to  FIGS. 7 and 8 , the process causes a distortion of the lamination&#39;s edges. The distortion may vary and grow with the unavoidable blanking punch wearing. By punching or stamping the parts together (via a single punching operation) the variations that may occur due to wear of the punch occur to all of the punched parts (the star and the yoke and optionally the rotor) such that the effects of the wearing are reduced or minimized. 
     As shown in  FIG. 9 , the stator (and rotor) components are stacked laminations. Optionally, a spacer ( FIGS. 9 and 11 ) lamination may be included between some of the adjacent layers of the star. As shown in  FIG. 10 , there is a clearance dimension between the star and the yoke (before they are interlocked as discussed below) and there is a clearance dimension between the star and the rotor, with the spacings providing a minimum distance for blanking. 
     As shown in  FIGS. 11-13 , the stator star, once stacked and laminated, may be insulated, such as by a plastic over-molding or by two or more plastic shells or the like. The next operation, such as shown in  FIGS. 14 and 15 , in the process workflow is the winding of the copper wire around the respective teeth of the star. Different winding technologies can be used to achieve the highest filling factor required or desired by the particular stator or motor application, thereby enhancing or optimizing the motor dimensions and costs vs. features tradeoffs. As can be seen with reference to  FIG. 15 , the stator of the present invention may have a high or greater or enhanced copper filling factor due to the outer winding operation. 
     To assemble the stator assembly, and with reference to  FIGS. 16-30 , the yoke may be inserted into a gage ( FIGS. 16 and 17 ), and then the wound star is inserted axially into the yoke in the “unlock position”. The unlock position ( FIGS. 18 and 20 ) is when the star is inserted such that its teeth or arms are positioned at portions of the yoke where the inner surface of the yoke has a greater radius to provide additional clearance between the star and the yoke. Thus, the star may be inserted axially into the yoke with little or no axial force required. 
     After the star is inserted into or received in the yoke, the wound star is rotated (such as via a specific tool) relative to the yoke to a “lock position” ( FIGS. 19 and 21 ), where the teeth of the star are moved relative to the yoke to a position at ports of the yoke where the inner surface of the yoke has a reduced or smaller radius to provide no clearance between the star and the yoke and thus to provide an interference between the star and the yoke. 
     As best seen with reference to  FIGS. 20 and 21 , the inner surface of the yoke is formed with different radii, such as a smaller radius portion R 1  and a larger radius portion R 3 , while the outer surface of the star as radius R 3 . R 1  and R 2  are concentric and R 1  is less than or equal to R 2  to ensure the interference between yoke and star stack when in the lock position. The star radius R 3  is concentric to R 1  and R 2 , and R 3  is greater than R 2  to ensure the blanking and to provide the low or zero axial insertion force when in the unlock position. R 3  is connected to R 1  by a profile designed to facilitate the sliding between yoke and star during the rotation from the unlock position to the lock position. 
     The present invention thus provides an assembly process or concept where the star is inserted into the yoke and rotated to achieve the final assembly position. Optionally, and as shown in  FIGS. 22-24 , the star/yoke contact area&#39;s shape may be different than discussed above. 
     Thus, and as can be seen with reference to  FIGS. 25-30 , the yoke is inserted into the gage and the star (with coils and overmolding disposed thereat) is inserted into the yoke with the star ends aligned with or positioned at the larger radius portions of the yoke. A rotation tool is then positioned at the star and yoke and gage to engage portions of the star and to rotate the star from the unlocked position to the locked position. For example, the tool may include one or more keys or elements ( FIGS. 26 and 27 ) that are inserted into the yoke and at the larger radius portion of the yoke to engage the star portion disposed thereat. Rotation of the tool thus imparts a force at the star portions and a torque at the star to rotate the star to the locked position. When in the locked position (such as shown in  FIGS. 28-30 ), a locking pin or safety pin may be inserted between the star portions and the yoke (such as in a passageway formed by corresponding recesses at the inner surface of the yoke and the outer surface of the star when the recesses are aligned when the star is moved to the lock position). 
       FIG. 31  shows the lamination alignment of the stator assembly. The rotation movement (tangential) avoids the stresses on the yoke and the star that may otherwise be typical of the traditional forced insertion techniques (axial), thus providing for enhanced lamination alignment and reducing the iron losses and increasing, as a consequence, the motor efficiency. 
     Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents.