Patent Application
20080061651
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
Referring to
Referring to
The end caps 18, 20 are made from different materials than is used to make the bobbin 14, such as a laminate sheet structure consisting of a combination of Mylar™ and Nomex™ materials, for example. However, a number of other laminates are also acceptable, such as paper laminates or single layer sheets of Mylar or other materials, for example. In addition, stamped or molded polymer end caps may also be used. The laminate structure is preferred because of its ability to resist tearing and puncture. That is, laminates can be designed to exhibit higher tear strength than its plastic polymer counterparts. This allows the field coil 10 to be “crushed” between pole pieces with greater force, increasing the heat transfer by virtue of increased contact area and contact force. Additionally, more wire 22 can be wound into the field coil 10, since the field coil 10 decreases in size when it is sandwiched or crushed between pole pieces.
The thin, in the range of 0.1 to 0.5 mm, flexible nature of the end caps 18, 20, however, prevents using the end caps 18, 20 as anchor points to which the wire 22 may be fastened to maintain tension in the winding 24. In an embodiment of the present invention, therefore, the bobbin 14 includes a tie-off 54 that extends both axially and radially from the first flange 28. By extending axially the tie-off 54 does not encroach into the volume that the winding 24 occupies and it allows the tie-off 54 to fit through an opening, not shown, in the second end cap 20. By extending radially, the tie-off 54 forms a protrusion around which a wire end 56 can be wound upon completion of the winding process. The rigidity of the bobbin 14 provides adequate stability for the tie-off 54 to maintain tension in the winding 24 after completion of the winding operation. The tie-off 54 has a head 58, which has a larger cross sectional area than a central portion 62 to prevent the wire 22, wound around the tie-off 54, from inadvertently slipping off of the tie-off 54.
The tie-off 54 can be injection molded as an integral part of the bobbin 14 itself or may be a separate component that is attached by means of welding, adhesive bonding, etc. Integrally molding the tie-off 54 as part of the bobbin 14 eliminates additional processing steps for forming and attaching a separate tie-off 54 component and may therefore be advantageous for economic reasons.
The presence of the tie-off 54 permits the automatic conventional winding machine to wrap an end of the wire 22 around the tie-off 54 for a few rotations prior to the wire 22 being cut. The elasticity and memory of the wire 22 prevents the end from unwrapping from the tie-off 54 and thereby maintains the tension of the winding 24 around the hub 26 of the bobbin 14.
A first end 66 of the wire 22 is automatically positioned, by the winding machine, in an axial orientation relative to the bobbin 14, through a slit 70 and into a hole 74 formed in the second end cap 20, prior to the beginning of the winding process. The hole 74 is located radially in line with an outer diameter 78 of the second flange 30 to properly position the wire 22 for initiation of the winding process. The winding machine holds the first end 66 fixed relative to the first end cap 20 and hub 26 throughout the winding process. Upon completion of the winding process the first end 66 is sandwiched between the hub 26 and the outer layers of the winding 24 thereby frictionally locking the first end 66 to the bobbin 14.
Alternately, the first end 66 could be wrapped around a second tie-off, not shown, that could be attached to either of the end caps 18, 20, to maintain tension in the winding 24 from the beginning of the winding process while not deviating from the spirit and scope of the present invention.
After the wire 22 has been wound onto the bobbin 14 and anchored around the tie-off 54, the flaps 34, 38 of the end caps 18, 20 can be folded down over the field coil 10, and then held in place with tape, not shown. By connecting the end caps 18, 20 together via the flaps 34, 38, by way of the tape, the winding 24 is prevented from overcoming the thin end cap sidewalls causing bulging or sagging of the coil 10. Alternatively, the tape could be replaced with an adhesive, mechanically interlocking flaps 34, 38 or other fastening means to secure the flaps 34, 38 of opposing end caps 18, 20 together. The tape, however, could also be eliminated in applications that can afford to allow the coil to sag before assembly.
While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims.
