Patent Publication Number: US-6701606-B2

Title: Method for forming an AC electromagnet lamination assembly incorporating shading coil

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a divisional of, claims priority to, and incorporates by reference herein in its entirety the non-provisional patent application Ser. No. 09/957,140, filed Sept. 20, 2001. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to electromagnetically actuable devices and, more particularly, to an electromagnet incorporating a shading coil. 
     BACKGROUND OF THE INVENTION 
     A typical electromagnetically actuable device has a magnetic core proximate an armature. A coil is selectively energized to draw the armature to the magnetic core. The device may be a solenoid, a contactor, a motor starter, or the like. The armature is operatively associated with a movable device such as movable contacts or an actuator. In many instances the coil is selectively energized from an AC power source. With AC-operated electromagnets, elimination or control of noise is a prime concern. To minimize noise the surface interface of the magnetic core and armature of each device must be matched to provide minimal magnetic “air gap” and a stable interface surface. The minimal air gap assures sufficient force to prevent movement and the stable surface interface prevents movements due to the widely changing forces in the AC-operated device. Particularly, a spring provides a constant force between the magnetic core and the armature. Energization of the coil counteracts the spring force to draw the armature toward the magnetic core. However, with an AC power source operating at, for example, 60 Hz, there are 120 zero crossings each second during energization. At each zero crossing the spring force may overcome the magnetic force causing the armature to be pushed away and then drawn back again. This can produce a noisy electromagnet. 
     Conventional shading coils have been used without success to address this problem. A conventional shading coil drives the formation of a small shaded magnetic pole formed on the interface or mating surface of the core or armature. The conventional shading coil is typically a conductive alloy in a stamped ring that is attached to the laminations of the AC electromagnet. These conventional coils routinely break and therefore are costly to produce and assemble. Also, the laminations of conventional coils are often held together with rivets that add costs to producing the electromagnets. The rivets provide points of failure. Accordingly, the inherent weakness of the rivets and the conventional shading coils typically limit the mechanical life of the electromagnet. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a shading coil is formed in an electromagnet by welding or brazing or the like. 
     Broadly, there is disclosed herein an electromagnetically actuable device having a magnetic core proximate an armature and a coil selectively energized to draw the armature to the magnetic core. The device comprises the armature and magnetic core being of laminated magnetic steel and having mating surfaces. At least one of the armature and magnetic core includes means for integrally securing laminations together to define a conductive path proximate the mating surface to provide a shading coil. 
     It is a feature of the invention that the securing means comprises weld connections between adjacent laminations of the at least one of the armature and magnetic core. 
     It is another feature of the invention that the securing means comprises braze connections between adjacent laminations of the at least one of the armature and magnetic core. The braze connections may use a conductive alloy such as copper. 
     It is still another feature of the invention that the securing means comprises the sole means for securing the laminations together. 
     It is a further feature of the invention that a single conductive line is provided on the mating surface transverse to the laminations and a plurality of conductive lines are provided below the mating surface transverse to the laminations. It is a further feature of the invention that the single conductive line is of greater depth than the plurality of conductive lines. 
     There is disclosed in accordance with another aspect of the invention an electromagnetically actuable device having a magnetic core proximate an armature and a coil selectively energized to draw the armature to the magnetic core. The device comprises the armature and magnetic core including laminations of magnetic steel and having mating surfaces and at least one of the armature and one of the magnetic core including conductive areas formed integrally with the laminations to define a conductive path proximate the mating surface to provide a shading coil. 
     There is disclosed in accordance with still another aspect of the invention the method of forming an electromagnet having a magnetic core and an armature. The method comprises providing an armature and magnetic core formed of lamination of magnetic steel and having a mating surface and integrally securing the laminations together to define a conductive path proximate the mating surface to provide a shading coil. 
     Further features and advantages of the invention will be readily apparent from the specification and from the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded, perspective view of an electromagnetically actuable device in the form of a contactor including an electromagnet in accordance with the invention; 
     FIG. 2 is a perspective view of an armature or magnetic core of an electromagnet in accordance with the invention during an initial stage of assembly; 
     FIG. 3 is a view similar to FIG. 2 of the electromagnet after conductive areas are formed therein; 
     FIG. 4 is a view similar to FIGS. 2 and 3 of the electromagnet after grinding a mating surface; and 
     FIG. 5 is a side elevation view of the electromagnet of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1, an electromagnetically actuable device in the form of an electrical contactor  18  is illustrated in exploded form. The contactor  18  includes a base  20 , a housing  22 , an electromagnet  24 , a coil  26  an actuator assembly  28  and a cover plate  30 . The electromagnet  24  includes an armature  48  and a magnetic core  50 . The housing  22  is mounted to the base  20  and encloses the coil  26  and the magnetic core  50 . The magnetic core  50  is fixedly mounted in the housing  22 . The magnetic core  50  is made of laminated magnetic steel, as is well known. The coil  26  includes a conventional bobbin, winding and terminal assembly and is located within the housing  22  and on the magnetic core  40 . The armature  48  is also of laminated magnetic steel and is associated with movable contacts  32  carried on a contact carrier  34  moveable mounted in the housing  22 . Particularly, the contact carrier  34  moves with the armature  48 . The housing  22  also supports stationary contacts  36  positioned in proximity with the moveable contacts  32 . 
     When the coil  26  is energized, the movable armature  48  is drawn toward the magnetic core  50  in a conventional manner. The movement of the armature  48  toward the magnetic core  50  causes the moveable contacts  32  to selectively open or close an electrical circuit with the stationary contacts  36 , as is known. 
     While this application illustrates an electromagnetically actuable device in the form of a contactor, the teachings of the invention can similarly be applied to other electromagnetically actuable devices such as AC solenoids, electromagnetic actuators, motor starters, or the like. 
     In accordance with the invention, the electromagnet  24  uses weld penetration areas as conductive sections to replace conventional shading coils and structurally hold the laminations together as an assembly. Conductive alloys may optionally be added to the weld or braze areas to improve the conductivity of the resulting shading coil zone, as the resistivity of the lamination material is not extremely low. 
     FIGS. 2-4 illustrate an assembly sequence for the magnetic core  50  in accordance with the invention. Additionally, the method described can be used to produce the armature  48  with a shading coil, or both an armature and magnetic core for use in an electromagnet, as will be apparent to those skilled in the art. 
     Referring initially to FIG. 2, a plurality of “E-shaped” laminations  52  are stacked with each lamination  52  being aligned with the other laminations  52 . The laminations  52  are temporarily held together by any known means, represented by a bracket  54 , during initial stages of the assembly process. The laminations  52  are typically formed of a material such as silicon steel having approximately 6% silicon. However, the laminations  52  could be cold rolled steel or most other types of steel, except annealed stainless steel. The use of laminations is intended to prevent electrical currents from being conducted between laminations. The assembled laminations  52  define interface first and second opposite end mating surfaces  56  and  57  and a center mating surface  58  to be associated with corresponding mating surfaces of an associated armature, or magnetic core, as the case may be, as with the contactor  18  of FIG.  1 . 
     Referring to FIGS. 3 and 5, the laminations  52  are integrally secured together by welding a plurality of weld lines across or transverse to the stack of laminations  52 . Owing to conductivity of the lamination material and/or an alloy used for welding, the weld lines comprise conductive lines that define conductive paths between laminations  52 . Particularly, a single conductive line  60  is provided on the first end mating surface  56 . Three parallel conductive lines  62  are provided just below the first end mating surface  56 . The use of three conductive weld lines  62  provides as much conductivity as possible between the laminations  52 . However, there may be room for only a single conductive weld line  60  on the mating surface  56  itself. In accordance with the invention, the depth of the single conductive weld line  60  may be greater than the three conductive weld lines  62 . As is apparent, the conductive weld lines  60  and  62  in combination with the outermost laminations  52  form a continuous conductive path. This conductive path provides the function of a shading coil. Additionally, the weld lines  60  and  62  provide structural connections between the laminations  52 . 
     Similarly, a single conductive weld line  64  is provided on the second end mating surface  57 , while three conductive weld lines  66  are provided below the second end mating surface  57 . The conductive lines  64  and  66  along with the outermost laminations  52  again form a shading coil. In accordance with the invention, the conductive weld lines  60 ,  62 ,  64  and  66  may comprise the sole means for securing the laminations  52  together. Additionally, a structural weld line  68  can be provided transversely in the central mating surface  58 , with a similar structural weld line  70  opposite thereto. 
     Referring to FIG. 4, as a final manufacturing step, the mating surfaces  56 ,  57  and  58  may be subjected to a grinding operation to provide relatively smooth surfaces for a minimal magnetic air gap. In so doing, the single conductive weld lines  60 ,  64  and  68  may not be readily visible, but are still present as represented by the dashed lines. 
     As described above, conductive weld lines are used to define shading coils and to provide structural connections. Alternatively, conductive lines may be provided by conventional brazing techniques rather than welding. Moreover, conductive alloys may be added to the weld or braze lines to improve the conductivity of the shading coil. Copper would be a suitable alloy. As described, a shading coil is formed from either the base material of the laminations or an alternative welding material that is holding the laminations together. This avoids the addition of parts to the magnetic core or armature in order to hold it together and provide a shading coil. More particularly, the described solution replaces the separate pieces with conductive areas that are formed by weld or braze operations. These conductive areas may be structurally superior to rivet connections and also less expensive. 
     It can therefore be appreciated that a new and novel system and method for forming a shading coil within an electromagnet has been described. It will be appreciated by those skilled in the art that, given the teaching herein, numerous alternatives and equivalent will be seen to exist which incorporate the disclosed invention. As a result, the invention is not to be limited by the foregoing exemplary embodiments, but only by the following claims.