Field coil insulation shield

A field coil insulation shield for a motor or generator is made of a single sheet of insulating material, and defines portions which substitute for the paper insulator conventionally disposed around a field pole and between a field coil and a motor frame, and portions which substitute for individual wrappings with tape to form the field coil and to protect it from the structure of the field pole which holds it in position. The portions which substitute for a wrapping of tape are provided with elongated projections which are latchingly received around the edge of a central aperture, through which the field pole passes.

The instant application relates to the field of dynamoelectric machines. In 
particular, the application relates to a shield or insulator for 
protecting a wound field coil of a dynamoelectric machine. 
BACKGROUND OF THE INVENTION 
In dynamoelectric machines such as motors and generators, the stationary 
field which interacts with the rotatable armature to convert electrical 
energy to mechanical energy, or to convert mechanical energy to electrical 
energy, is provided by coils of wire, known as field coils, which are 
disposed about field poles, for concentrating and directing the magnetic 
flux produced by the field coils. Field poles are generally configured as 
including a pole shoe, which has a concave contour matching the contour of 
the exterior of the armature, and overhangs the field coil, for trapping 
the field coil between the pole shoe and the motor frame to retain it in 
place. It has long been conventional to place a piece of insulating 
material having a generally rectangular outer periphery around the pole 
piece and against the motor frame, to protect the field coil from abrasion 
against the motor frame, and also to provide protection for the sides of 
the generally-rectangular field coils, to protect them from abrasion 
against the shoe portion of the pole piece and the sides of the pole 
piece. This is conventionally done by wrapping the coil with tape, even 
though one-piece insulators for field coils have long been known, such as 
that described in U.S. Pat. No. 1,797,768, issued to L. C. Goad on Mar. 
24, 1931. Although functional, such structures have been difficult to 
produce properly and repeatedly, or have been inconvenient to use, and so 
have not found commercial acceptance. 
The instant invention overcomes these and other deficiencies of the prior 
art. 
SUMMARY OF THE INVENTION 
The instant invention provides a field coil insulation shield which is easy 
to fabricate and use, and which may be used to properly form or shape 
fine-wire coils, as well as to insulate and protect field coils made of 
larger wire sizes, and which may be applied to a field coil either before 
or after it is deformed to conform to the inner surface of a motor frame. 
Thus, it is an object of the invention to provide a simplified unitary 
replacement for the prior art technique which utilized tape to form and 
protect the coil wires and a paper member to shield and insulate the coil 
from the motor frame. 
It is a feature of the invention that an insulation shield is comprised of 
a sheet of insulative material having a shield body of generally 
rectangular geometry with rounded corners and with a centrally located 
generally rectangular aperture. Four arms or the like with locking tabs 
extend from the four sides of the shield body, the locking tabs being 
adapted to engage slots in the shield body adjacent the rectangular 
aperture when the shield is wrapped around the field coil. 
It is an advantage of the invention that a single, easy-to-make and 
easy-to-use insulating member may be quickly installed by hand, or with 
the use of simple hand tools. Thus, as will be apparent, the preferred 
embodiment of the instant invention provides a field coil shield made of a 
sheet of insulating material, the sheet of insulating material defining a 
central generally rectangular aperture having rounded corners and four 
inwardly-facing edge portions, each including a centrally-disposed 
inwardly-facing projection defining a slot, and having a profile defined 
by a rectangular portion extending outward from each edge of the central 
aperture, each rectangular portion having first and second side portions, 
a base portion adjacent the central aperture, and an end portion, each end 
portion having a centrally-located outwardly-extending elongated 
projection having a pointed tip portion and a base portion including a 
transverse latching projection, defining a notch adjacent the end portion, 
the rectangular portions having their base portions connected by arcuate 
portions, such that the base portions and the arcuate portions are adapted 
to insulate the field coil from a mounting surface, and each elongated 
projection is adapted to latchingly engage the slots adjacent the central 
aperture and thus cover respective portions of the field coil and insulate 
each portion from a pole piece retaining it in place. 
Other objectives, features and advantages of the invention will become 
apparent from the detailed description which follows.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, it can be seen that a field coil insulation 
shield 10 according to the preferred embodiment of the invention is 
composed of a sheet of insulating material defining a central generally 
rectangular aperture 12 having four rounded corners 14 and four 
inwardly-facing edge portions 16, each edge portion 16 including a 
centrally-disposed inwardly-facing projection 18, and each projection 18 
defining a slot 20 therein extending parallel to edge portion 16. A 
generally rectangular portion 21 extends outwardly from each said edge 
portion 16, each rectangular portion having first and second side portions 
22, 24, a base portion 26 and an end portion 28. Each end portion 28 
includes a centrally-located, outwardly-extending elongated projection 30, 
each having a pointed tip portion 32 and a base portion 34 including a 
transverse projection portion 36 defining a notch 38 adjacent each end 
portion 28. As will be apparent, each elongated projection 30 may be made 
as long as desired, and, preferably, transverse projection 36 has 
outwardly tapered leading edges 40. 
As illustrated, each rectangular portion is connected to an adjacent 
rectangular portion by an integral arcuate portion 42. 
As can be seen, insulation shield 10 includes a portion composed of base 
portions 26 and arcuate portions 42 similar in shape to the paper 
insulating member commonly placed around a field pole, to shield and 
protect it from contact with the motor or generator frame or housing, and, 
when each elongated projection 30 is inserted into and pulled through its 
respective slot 20 over a field coil disposed on base portions 26 and 
arcuate portions 42, the part of the rectangular portion bounded by first 
and second side portions 22, 24, serves the function presently served by a 
wrapping of tape in forming the coil, and insulating the coil from the 
metallic field pole structure. 
As will be apparent, the illustrated embodiment of the invention is 
suitable for use with rectangular pole pieces. However, it is believed 
that some large dynamoelectric machines are made with circular pole 
pieces. The invention illustrated may easily be modified for use in such 
machines, if desired. 
Turning now to FIG. 2, a field coil insulation shield 10 according to the 
preferred embodiment of the invention may be seen disposed about a field 
coil composed of a plurality of turns of wire. As conventional, field coil 
44 has a first end 46, and a second end 48, covered with a tubular piece 
of insulation 50, since it extends from the inside or start of the 
winding. 
In FIG. 3, first and second ends 46 and 48 have been omitted for clarity. 
As can be seen in FIG. 3, elongated projections 30 have been pulled 
through slots 20, and severed at line 52, the remainder of elongated 
projections 30 being illustrated in phantom lines. Severing the elongated 
projections at line 52, adjacent transverse projection portion 36, is 
desirable, but is not necessary, provided that elongated portions 30 are 
not permitted to interfere with the mechanical contact between the motor 
frame and pole pieces, since any spacing between the motor frame and pole 
piece increases the magnetic reluctance of the magnetic path through the 
poles of the motor or generator. 
Turning now to FIG. 4, the assembly of field coil 44 and insulation shield 
10 is shown formed in a shape appropriate for insertion in a motor frame 
or housing. 
In FIG. 5, a pair of assemblies such as shown in FIG. 4 are shown installed 
in a motor or generator frame 54, as appropriate for a series-connected 
two pole dynamoelectric machine. The connections necessary for a shunt, 
compound, split-series or balanced series configuration will be obvious to 
one skilled in the art. As can be seen, each field coil 44 is retained in 
place by a field pole 56 including a pole shoe portion 58 which serves to 
hold each field coil 44, protected by field coil insulation shield 10 in 
position. The field poles themselves are held within motor frame 54 by 
fastening means shown as screws 60 passing through frame 54 and engaging 
threaded bores 62 in field poles 56. As shown in FIG. 5, second ends 48 of 
each of the two illustrated field coils 44 are joined at a splice 64 to a 
wire 66, provided with a section of insulation 68. Wire 66 is intended to 
be connected to a brush or slip ring of a motor or generator. First end 46 
of one field winding 44 is shown joined at a splice 70 to a jumper wire 
72, which joins an end 46 of the second field coil 44 at a splice 74, 
which connects both first ends 46 to a lead wire 76, passing through frame 
54 at grommet 78 in aperture 80. A second lead wire 82 also passes through 
grommet 78, and has an end, not shown, for connection to a second brush or 
slip ring contact, not shown, in a motor or generator. 
Numerous modifications and variations of the invention, including various 
nonsymmetries in the illustrated embodiment of the invention and various 
modifications to the precise structure of the elongated projections and 
the slots into which they are received will be apparent to one skilled in 
the art, and may be easily made without departing from the spirit and 
scope of the invention.