Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-01-22
2001-09-04
Hall, Carl E. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S736000
Reexamination Certificate
active
06282775
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to stators for dynamoelectric machines and, more particularly, to methods and apparatus for injecting stator winding coil groups into the slots of a magnetic core.
BACKGROUND OF THE INVENTION
The stator of a dynamoelectric machine such as an electric motor or generator typically includes a core of magnetic material having an axially extending bore for receiving a rotor. The core typically is formed from a plurality of identical laminations which are aligned and arranged in a stack held together by clips. Each lamination includes a plurality of teeth which extend radially into the bore. Slots between each of the teeth extend radially outwardly from the bore. The ends of the teeth and the open ends of the slots define the periphery of the bore.
A plurality of coils formed from insulated conductive wire are inserted into selected core slots with portions of the coils at the ends of the core forming end turn regions. The coils are interconnected to form coil groups or poles. The conductive wires which form the coils, sometimes referred to as stator windings, typically are coated with a varnish or an enamel so that a tough protective coating is formed around each wire. The coating is required so that each wire is well insulated from the other wires. Improvements to or reduction of damage to such coating facilitates improved motor performance by, for example, reducing field failures.
To insert the coils into the stator core slots, it is known to form coil groups with coil forms, locate the coil groups on coil insertion (or injection) tooling, and then move the coil groups from the coil insertion tooling to a stator with portions thereof located in stator slots. Coil injection apparatus for inserting the coils into the stator slots is described, for example, in U.S. Pat. No. 3,949,464. Known tooling for such apparatus typically include a base having a plurality of radially arranged and spaced blades extending from an upper surface of the base. The blades are arranged in a circular array.
With known apparatus, a “stripper” having fins is placed within the bore defined by the circular array of blades. The stripper fins are aligned with and extend into the gaps between adjacent blades. One stripper fin extends into each such gap. The stripper includes an upper, or operative, surface configured to contact segments of the coils which lie within the gaps between adjacent blades and extend into the interior, or bore, established by the circular array of blades. A lower surface of the stripper is connected to an axially movable ram, or pusher rod, which extends through the apparatus base and moves the stripper axially along the bore of the circular array of blades. The stripper typically is constructed of a material such as brass.
A single speed motor typically includes coil groups which establish at least one main winding and an auxiliary or start winding. The coil groups are formed with a winding machine and located on the tooling of coil insertion tooling so that the coil groups are located in gaps between the blades at a location between the stripper and the free ends of the blades. Portions of each coil extend through gaps between the blades and segments of each coil span an interior region of the bore established by the circular array of blades. A stator core is then aligned with and placed on the tooling of the coil injection apparatus or device so that at the open end of the circular array of blades, each blade registers with a stator tooth and so that gaps between adjacent blades register with stator slot openings. The pusher rod then moves the stripper within the circular array of blades and from a retracted position toward the stator core. The fins of the stripper contact the portions of the coils which lie in the gaps between adjacent blades. Also, the surface of the stripper facing the core contacts the segments of the coils which span along the interior of the circular array of blades. Once the stripper contacts the coLls as described above, and as the stripper moves toward the stator core, the stripper forces the coils to move along the blades toward the stator core.
As the stripper begins to move through the bore of the stator core, each fin of the stripper which contacts a coil portion in the blade gaps forces such coil portion into respective aligned stator slots. When the upper surface of the stripper has fully moved through the stator bore, each such coil portion is fully injected into the stator core slots. The stripper is then retracted to a retracted position and the “injected” stator core is removed from the insertion device.
When injecting two coil groups, e.g., main and auxiliary (or start) coil groups, into a stator core, at least a portion of at least the lowermost coil group on the blades directly contacts the fins of the stripper. Typically, some portions of the uppermost coil group also are in direct contact with some of the fins. During the injection process, the stripper fins exert sufficient forces against such coil portions to move the coils axially along the blades and to inject side turn portions thereof into the stator slots. Such forces generally have a sufficient magnitude to not only move the coils along the blades and into the stator slots, but also are sufficient to cause stretching and abrading of the magnet wire which forms the coils.
Such deformations sometimes are referred to as pressure marks. Pressure marks are particularly troublesome because over time, as the wire insulation wears, the insulation may fail and conductor material may be exposed. Such exposure may lead to a field failure of the motor. Also, if the magnetic wire is sufficiently deformed or stretched, there may be reduced operational efficiency for the motor due, for example, to increased resistance of the magnet wire and possibly even short circuiting of the wire.
With respect to known strippers, such strippers generally are constructed from a soft metal such as brass in an attempt to limit the damage to insulation and pressure marks on the coils caused during the coil injection process. Manufacturing brass strippers is, of course, expensive in terms of both the material and labor. In addition, the brass fins of the stripper usually must be polished at regular intervals to remove nicks and prevent sharp insulation piercing edges from forming. Polishing such strippers, of course, is time consuming and expensive. Further, the fins of a stripper are susceptible to damage if, for example, the stripper is dropped. If a stripper is dropped, a fin may chip or even break-off. Such a damaged stripper may have to be discarded.
In addition, with known strippers, as the number of windings forming the coil groups being injected increases, the likelihood of coil binding, or “lock-up”, also increases. Also, the windings which form the coils may be twisted during the injection process or may get caught between the stripper and one or more of the circular array of blades. When this occurs, the stripper may become locked and axial movement of the stripper may be prevented. Usually, the chance of lock-up is reduced by limiting the number of coils injected in one-pass of the stripper through the rotor bore. Thus, the likelihood of occurrence of a lock-up condition with known strippers can be reduced with this technique.
When using the stripper and one-pass process described above to inject three or more coil groups into a stator core, the forces exerted by the stripper against the coil wires are very high. As a result, the coil wires may be significantly damaged. In addition, although it is highly desirable in some motor applications, e.g., when the effect of inductive reactance is significant, to have the start winding coil group as close as possible to the stator bore to facilitate magnetic coupling between the fields generated by the start winding and rotor, the start winding coil wire and insulation usually cannot withstand the direct high forces which must be exerted against the start winding by the stripper fins in such one-pass injecti
Armstrong Teasdale LLP
General Electric Company
Hall Carl E.
Horton Esq. Carl B.
Wasserbauer Esq. Damian
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