Armature winding structure for electric motors

An armature winding structure for use in an electric motor includes a web-shaped strand bundle composed of a plurality of parallel strands. The strand bundle has a plurality of longitudinally spaced bends and a plurality of straight strand bundle segments. Adjacent ones of the strand bundle segments are positioned one on each side of one of the bends. The strand bundle segments are transversely staggered on one side of the strand bundle successively from one end to the other of the strand bundle, by intervals each substantially equal to the width of the strand bundle. The strand bundle segments thus staggered are longitudinally folded over along fold lines extending respectively across or near the bends transversely of the strand bundle, thereby providing a plate-like winding in which the strand bundle segments lie adjacent to one another.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an armature winding structure for use in 
an electric motor. 
2. Description of the Prior Art 
One conventional winding structure for use on the armature of an electric 
motor is shown in FIG. 22 of the accompanying drawings. 
The winding structure comprises a winding D generally known as a helical 
winding. The winding D is composed of three parallel web-shaped strand 
bundles 50, 51, 52 each comprising a plurality of parallel strands, the 
strand bundles 50, 51, 52 being allotted respectively to U-, V-, and 
W-phase currents. The strand bundles 50, 51, 52 are folded over on 
themselves at certain intervals into a flat configuration. The folded flat 
winding structure has a plurality of folded edges 53, 54 on its opposite 
sides and a plurality of straight conducting regions 55, extending between 
the folded edges 53, 54, where currents flow in a straight direction. 
These straight conducting regions 55 are disposed adjacent to one another, 
and jointly make up a flat strand plate 56 in which the strand bundles 50, 
51, 52 extend transversely. Since the winding D can easily be 
manufactured, it is widely used as armature windings. 
In the U-phase, however, the folded strand bundle 50 overlaps itself in 
each of folds e at the folded edges 53, 54. The overlapping strand bundle 
50 causes the current to flow in opposite directions through the face and 
back areas of each fold e. Since the magnetic fields generated by the 
current flowing in the opposite directions cancel out each other in each 
fold e, the winding D brings about a loss when used as a motor armature 
winding. In view of the fact that the currents of one set of phases, such 
as V- and W-phases, among the U-, V-, and W-phases, flow in one direction, 
the strand bundles 51, 52 for the V- and W-phases as well as the strand 
bundle 50 for the U-phase also overlap themselves at the folded edges 53, 
54, as shown hatched in FIG. 22. The overlapping regions of these strand 
bundles 50, 51, 52 total 33 through 56% of the entire area of the flat 
strand plate 56. Therefore, the winding D is responsible for a very large 
torque loss. 
With the overlapping strand bundles 50, 51, 52, the winding D as it is 
incorporated in an electric motor requires a relatively large number of 
strands in order to produce a desired torque. Therefore, the winding D is 
relatively heavy, and so is the electric motor. In the electric motor, the 
winding D is positioned between a core and a rotor. Inasmuch as the 
winding D is rendered thick by the overlapping strand bundles 50, 51, 52, 
the core and the rotor are spaced from each other by a large distance, and 
the flux density between the core and the rotor is relatively low, also 
resulting in a torque loss. 
Furthermore, the directions in which the currents flow through the strand 
bundles 50, 51, 52 extend obliquely to the axis of the electric motor. 
Consequently, the magnetic field generated by the winding D and the 
magnetic field generated by a magnet (not shown) have different 
directions. As a consequence, the electric motor produces electromagnetic 
forces with low efficiency, causing a torque loss. 
SUMMARY OF THE INVENTION 
In view of the foregoing drawbacks of the conventional armature winding 
structure, it is an object of the present invention to provide an armature 
winding structure for use in an electric motor, which can easily be 
manufactured, is able to produce a desired torque when incorporated in the 
electric motor, and is light in weight and small in size. 
To achieve the above object, there is provided in accordance with a first 
aspect of the present invention an armature winding structure for use in 
an electric motor, comprising a web-shaped strand bundle composed of a 
plurality of parallel strands, the strand bundle having a plurality of 
longitudinally spaced bends and a plurality of straight strand bundle, 
segments, adjacent strand bundle segments being positioned one on each 
side of one of the bends, the strand bundle segments being transversely 
staggered on one side of the strand bundle successively from one end to 
the other of the strand bundle, by intervals each substantially equal to 
the width of the strand bundle, the strand bundle being longitudinally 
folded over along fold lines extending respectively across or near the 
bends transversely of the strand bundle, thereby providing a plate-like 
winding in which the strand bundle segments lie adjacent to one another. 
Overlapping regions of the strand bundle are positioned only in the 
vicinity of the fold lines and have a relatively small area. Almost no 
regions of the strand bundle segments themselves overlap each other. 
Therefore, the winding is effective to produce a magnetic field necessary 
to rotate the electric motor. 
The strand bundle segments extend parallel to each other before the strand 
bundle is folded over. Preferably, each of the bends has a pair of 
opposite arcuate edges extending along the respective arcs of a pair of 
quadrants whose radii are the same as the width of the strand bundle and 
whose centers are spaced from each other by the width of the strand 
bundle. The bends can easily be formed, and occupy a relatively small area 
in the strand bundle. The overlapping regions of the strand bundle are 
minimized. 
In the case where the strand bundle segments extend parallel to each other 
before the strand bundle is folded over, the fold lines preferably extend 
substantially perpendicularly to the longitudinal direction of the strand 
bundle, and are positioned centrally in the bends, respectively, in the 
longitudinal direction of the strand bundle. More preferably, the bends 
have equal lengths in the longitudinal direction of the strand bundle, and 
the strand bundle segments between the bends have equal lengths in the 
longitudinal direction of the strand bundle. Such an arrangement makes it 
possible to fold over the strand bundle with ease. The overlapping regions 
of the strand bundle are positioned only at the bends, preventing the 
strand bundle segments from overlapping each other and also allowing them 
to lie parallel to each other. The winding structure is further effective 
in producing a magnetic field necessary to rotate the electric motor. 
Preferably, the strand bundle which is longitudinally folded over has 
portions extending between the fold lines, the portions having equal 
lengths. The armature winding structure is thus made compact, and magnetic 
fields produced by those portions between the fold lines are uniformly 
standardized for efficiently rotating the electric motor. 
When the armature winding structure is incorporated in the electric motor, 
the strand bundle which is longitudinally folded over has overlapping 
regions near the fold lines, respectively, the overlapping regions being 
positioned axially outwardly of a core of an armature of the electric 
motor, so that the magnetic fields produced by the overlapping regions 
will not affect the operation of the motor. Alternatively, the strand 
bundle which is longitudinally folded over has portions extending between 
the fold lines, the portions having lengths equal to the length of the 
core or a magnet of the electric motor, so that the magnetic fields 
produced by the overlapping regions will be employed to rotate the 
electric motor. 
Before the strand bundle is folded over, odd-numbered ones of the strand 
bundle segments as counted from a reference strand bundle segment at one 
end of the strand bundle may extend parallel to each other, and 
even-numbered ones of the strand bundle segments as counted from the 
reference strand bundle segment may extend parallel to each other and 
obliquely to the odd-numbered strand bundle segments, the fold lines being 
positioned such that the strand bundle segments lie parallel to each other 
after the strand bundle is folded over. 
Alternatively, before the strand bundle is folded over, odd-numbered ones 
of the strand bundle segments as counted from a reference strand bundle 
segment at one end of the strand bundle may extend parallel to each other, 
and even-numbered ones of the strand bundle segments as counted from the 
reference strand bundle segment may extend parallel to each other, the 
fold lines being positioned such that adjacent ones of the strand bundle 
segments are inclined at an angle to each other after the strand bundle is 
folded over. With the strand bundle segments being inclined to each other, 
the magnetic field produced by the winding and the magnetic field produced 
by the magnet of the motor are oriented in different directions with a 
suitable angle therebetween, resulting in a skew effect for smooth motor 
rotation. 
Each of the bends may be formed when the strand bundle segments positioned 
one on each side thereof are displaced relatively to each other in 
substantially transverse opposite directions, respectively. Alternatively, 
each of the bends may be formed when the strand bundle segments positioned 
one on each side thereof are folded over in substantially perpendicular 
directions, providing an overlapping region thereof, and then one of the 
strand bundle segments is folded over in a direction substantially 
parallel to the other of the strand bundle segments outside of the 
overlapping region. 
According to a second aspect of the present invention, there is also 
provided an armature winding structure for use in an electric motor, 
comprising a web-shaped strand bundle composed of a plurality of parallel 
strands, the strand bundle having a plurality of longitudinally spaced 
bends and a plurality of straight strand bundle segments, adjacent two of 
the strand bundle segments being positioned one on each side of one of the 
bends, the strand bundle segments being transversely staggered on one side 
of the strand bundle such that odd-numbered ones of the strand bundle 
segments as counted from a reference strand bundle segment at one end of 
the strand bundle are staggered from the strand bundle by different 
intervals which are equal to multiples of the width of the strand bundle 
by respective odd numbers, and that even-numbered ones of the strand 
bundle segments as counted from the reference strand bundle segment are 
staggered from the strand bundle by different intervals which are equal to 
multiples of the width of the strand bundle by respective even numbers, 
the strand bundle being longitudinally folded over along folds extending 
respectively across or near the bends transversely of the strand bundle, 
thereby providing a plate-like winding in which the strand bundle segments 
lie adjacent to one another. In this arrangement, overlapping regions of 
the strand bundle are positioned only in the vicinity of the fold lines 
and have a relatively small area. Almost no regions of the strand bundle 
segments themselves overlap each other. Therefore, the winding is 
effective to produce a magnetic field necessary to rotate the electric 
motor. The additional features, as described above, of the armature 
winding structure according to the first aspect of the present invention 
may also be added to the armature winding structure according to the 
second aspect of the present invention. 
The armature winding structure according to the second aspect of the 
invention is equivalent to the armature winding structure according to the 
first aspect of the invention in that the intervals by which the strand 
bundle segments are transversely staggered from the reference strand 
bundle segment are equal to the products of the width of the strand bundle 
and the counts of the strand bundle segments from the reference strand 
bundle. 
According to a third aspect of the present invention, there is provided an 
armature winding structure for use in an electric motor, comprising a 
web-shaped strand bundle composed of a plurality of parallel strands, the 
strand bundle having a plurality of longitudinally spaced bends and a 
plurality of straight strand bundle segments, adjacent strand bundle, 
segments being positioned one on each side of one of the bends, the strand 
bundle segments being transversely staggered on one side of the strand 
bundle successively from one end to the other of the strand bundle, the 
strand bundle being longitudinally folded over at the bends obliquely to 
the longitudinal direction of the strand bundle, thereby providing a 
plate-like winding in which the strand bundle segments lie adjacent to one 
another and extend obliquely to each other in a successively overlapping 
relationship. 
Since adjacent strand bundle segments are transversely staggered at the 
bend therebetween, any overlapping regions of the strand segments have a 
smaller area than the conventional helical winding structure. The strand 
bundle segments are capable of effectively producing magnetic fields. 
Preferably, before the strand bundle is folded over, the strand bundle 
segments lie parallel to each other and spaced at substantially equal 
intervals transversely of the strand bundle, the strand bundle being 
folded over along fold lines at the respective bends, the fold lines being 
inclined at an angle to the transverse direction of the strand bundle. 
This structure permits the armature winding to be manufactured easily. 
The above and other objects, features, and advantages of the present 
invention will become apparent from the following description when taken 
in conjunction with the accompanying drawings which illustrate preferred 
embodiments of the present invention by way of example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 through 7 show a winding according a first embodiment of the 
present invention. 
In FIG. 1, the winding, shown unfolded, comprises a unitary strand bundle 1 
composed of three parallel web-shaped strand bundles 1.sub.u, 1.sub.v, 
1.sub.w each comprising a plurality of parallel strands, the strand 
bundles 1.sub.u, 1.sub.v, 1.sub.w being allotted respectively to U-, V-, 
and W-phase currents. The unitary strand bundle 1 includes a plurality of 
(seven in this embodiment) bends 2 longitudinally spaced at predetermined 
intervals q. The unitary strand bundles 1 is divided into a plurality of 
straight strand bundle segments 1a by the bends 2, each bend 2 being 
disposed between two of the strand bundle segments 1a. The strand bundle 
segments 1a are successively staggered transversely on one side of the 
strand bundle 1 from one end to the other of the strand bundle 1, and 
extend parallel to each other. The unitary strand bundle 1 has a width s. 
Any adjacent two of the strand bundle segments 1a are transversely 
staggered relative to each other by an interval r that is the same as the 
width s of the unitary strand bundle 1. Each of the bends 2 has a length t 
that is the same as the width s. As shown in FIG. 2 at an enlarged scale, 
each of the bends 2 has opposite arcuate edges extending along the 
respective arcs of quadrants 2a, 2b whose radii are the same as the width 
s and whose centers are spaced from each other by the width s. Each bend 2 
and adjoining portions of the two strand bundle segments 1a are 
substantially S-shaped. As shown in FIG. 1, a fold line 3 extending 
perpendicularly to the longitudinal direction of the strand bundle 1 lies 
centrally across each bend 2. 
The strand bundle 1 with the bends 2 is manufactured as follows: As shown 
in FIG. 3, before the strand bundle 1 is bent into the staggered shape, a 
plurality of sets of jigs A.sub.1, A.sub.2 are positioned at certain 
spaced intervals y longitudinally along the strand bundle 1. The jigs 
A.sub.1, A.sub.2 in each set grip the portion of the strand bundle 1 which 
corresponds to one of the strand bundle segments 1a, and have a length 
which is the same as the interval q, i.e., the length of each strand 
bundle segment la between two bends 2. The distance y between two adjacent 
sets of the jigs A.sub.1, A.sub.2 is 1/2 of the circumferential dimension 
of a circle whose diameter is the same as the width s. 
While the opposite sides of the strand bundle 1 are being gripped by the 
jigs A.sub.1, A.sub.2, the sets of the jigs A.sub.1, A.sub.2, except the 
one at the lefthand end of the strand bundle 1, are displaced 
substantially transversely of the strand bundle 1 and at the same time are 
pressed toward each other in the longitudinal direction of the strand 
bundle 1, as shown in FIG. 4. The portions of the strand bundle 1 between 
the sets of the jigs A.sub.1, A.sub.2 are arcuately bent about-ends 
B.sub.1, B.sub.2 of the jigs A.sub.1, A.sub.2 into the respective bends 2. 
The strand bundle 1 thus staggered is then folded over on itself 
successively along the fold lines 3 so that the strand bundle segments la 
lie parallel and adjacent to each other, jointly making up a flat 
plate-shaped winding 4 as shown in FIG. 5. The winding 4 is of an elongate 
shape extending transversely of the strand bundles 1.sub.u, 1.sub.v, 
1.sub.w, which remain unchanged in the order in which they are arranged in 
the winding 4. The folded strand bundle 1 overlaps itself only in the 
bends 2 which are folded over on themselves along the fold lines 3, 
resulting in overlapping regions 5 which are shown hatched in FIG. 5,. In 
the other areas of the strand bundle 1 than the overlapping regions 5, the 
strand bundles 1.sub.u, 1.sub.v, 1.sub.w are positioned adjacent to one 
another without overlapping. The strand bundles 1.sub.u, 1.sub.v, 1.sub.w 
have portions of equal length between the fold lines 3. 
The overlapping regions 5 of the winding 4 are smaller in area than the 
overlapping regions of the strand bundles of the conventional helical 
winding shown in FIG. 22. Consequently, the amount of material of the 
winding 4 is reduced, and so is the electric resistance of the winding 4 
to electric currents flowing therethrough. The winding 4 is also reduced 
in thickness and hence weight. 
When an electric current flows in one direction through the U-phase strand 
bundle 1.sub.u, and electric currents flow in an opposite direction 
through the V- and W-phase strand bundles 1.sub.v, 1.sub.w, the magnetic 
fields generated by the respective strand bundles 1.sub.u, 1.sub.v, 
1.sub.w are directed as shown in FIG. 5. More specifically, because the 
strand bundles 1.sub.u, 1.sub.v, 1.sub.w are bent over successively in 
opposite directions, the magnetic fields generated thereby are directed in 
successively opposite directions, providing a regularly arranged array of 
N- and S-poles, i.e., alternate sets of three N-poles and three S-poles, 
along the winding 4. Inasmuch as the portions of the strand bundles 
1.sub.u, 1.sub.v, 1.sub.w between the fold lines 3 are of equal length and 
extend parallel to each other , and the overlapping regions 5 are of a 
small area, uniform magnetic fields can efficiently be generated by the 
strand bundle segments 1a. 
The winding 4 is assembled in an electric motor as follows: The winding 4 
is curved into a tubular form with opposite edges 4a, 4b (FIG. 5) held 
against each other. Then, as shown in FIG. 6, the tubular winding 4 is 
placed against the inner surface of a tubular core 9 of an armature 8 on a 
housing 7 of the stator of an electric motor 6 in a radially spaced 
relationship to a magnet 11 of a rotor 10. The overlapping regions 5 of 
the winding 4 are positioned axially outwardly of the core 9. Since the 
overlapping regions 5 are not radially placed on the core 9, the distance 
from the inner surface of the core 9 to the radially outer surface of the 
magnet 11 is minimized. As a consequence, the flux density in the gap 
between the core 9 and the magnet 11 is relatively large. The relatively 
large flux density and the uniform magnetic fields produced by the strand 
bundle segments 1a are effective to produce a desired motor torque 
efficiently. 
As shown in FIG. 7, the strand bundle segments 1a disposed in the tubular 
core 9 extend parallel to each other in the axial direction of the stator 
without overlapping each other. Accordingly, the magnetic field produced 
by the winding 4 and the magnetic field produced by the magnet 11 are 
oriented in the same direction for efficient generation of a motor torque. 
As indicated by the imaginary lines in FIG. 6, either the length of the 
magnet 11 or the length of the core 9 may be equalized to the axial length 
of the winding 4 including the overlapping regions 5, so that the 
overlapping regions 5 may be positioned axially outwardly of the magnet 11 
or the core 9 for effectively utilizing magnetic fields produced by 
non-overlapping portions of the strand bundle 1 that are located in the 
vicinity of opposite sides of the overlapping regions 5, for increased 
motor efficiency. 
In the above first embodiment, the fold lines 3 are positioned centrally 
across the respective bends 2 of the strand bundles 1. However, as shown 
in FIG. 1, fold lines 3x may be positioned on respective strand bundle 
segments 1a near the respective bends 2. Overlapping regions which are 
formed when the strand bundle 1 is folded over on itself along the fold 
lines 3x are also relatively small in area. The resultant winding also has 
parallel strand bundles 1a for generating magnetic fields efficiently with 
a relatively small loss. 
FIG. 8 shows a winding according to a second embodiment of the present 
invention. 
As shown in FIG. 8, a unitary strand bundle 12 comprises parallel strand 
bundles 12.sub.u, 12.sub.v, 12.sub.2 assigned respectively to U-, V-, and 
W-phases, and has a plurality of longitudinally spaced bends 13. The 
strand bundle 12 also has a plurality of strand bundle segments 12a each 
positioned one on each side of one of the bends 13. The strand bundle 
segments 12a are successively staggered transversely on one side of the 
strand bundle 12 from one end to the other of the strand bundle 12, and 
adjacent ones of the strand bundle segments 12a extend obliquely to each 
other. More specifically, odd-numbered strand bundle segments 12a as 
counted from a reference strand bundle segment 12as on one end of the 
strand bundle 12 are oriented parallel to each other, and even-numbered 
strand bundle segments 12a including the reference strand bundle segment 
12as are oriented parallel to each other and obliquely to the odd-numbered 
strand bundle segments 12a. 
The strand bundle segments 12a between the bends 13 have equal lengths q, 
and the bends 13 have equal lengths t. The strand bundle segments 12a 
positioned one on each side of each of the bends 13 are transversely 
staggered by an interval r which is the same as the width s of the strand 
bundle 12. 
The strand bundle 12 has a plurality of transverse fold lines 14 extending 
centrally across the respective bends 13. Angles .theta..sub.1 formed 
between the fold lines 14 and the odd-numbered strand bundle segments 12a 
and angles .theta..sub.2 formed between the fold lines 14 and the 
even-numbered strand bundle segments 12a are equal to each other. 
The strand bundle 12 is folded over on itself successively along the fold 
lines 14 in the longitudinal direction of the strand bundle 12, forming a 
plate-like winding 15 indicated by the imaginary lines. In the winding 15, 
the strand bundle segments 12a lie adjacent to one another in their 
transverse direction and extend parallel to each other. The folded strand 
bundle 12 overlaps itself in overlapping regions 16 which are positioned 
only in the respective bends 13. Accordingly, the winding 15 is effective 
to produce uniform magnetic fields efficiently for rotating an electric 
motor. 
For assembling the winding 15 in an electric motor, the winding 15 is 
curved into a tubular form with opposite edges 15a, 15b abutting against 
each other. The strand bundle segments 12a are inclined at an angle to the 
axis of the tubular winding 15. 
FIG. 9 shows a winding according to a third embodiment of the present 
invention. 
As shown in FIG. 9, a unitary strand bundle 17 comprises parallel strand 
bundles 17.sub.u, 17.sub.v, 17.sub.w assigned respectively to U-, V-, and 
W-phases, and has a plurality of longitudinally spaced bends 18. The 
strand bundle 17 also has a plurality of strand bundle segments 17a 
adjacent two of which are positioned one on each side of one of the bends 
18. The strand bundle segments 17a are successively staggered transversely 
on one side of the strand bundle 17 from one end to the other of the 
strand bundle 17, and extend parallel to each other. The shape of and the 
distance between the bends 18 and the length of the strand bundle segments 
17a are the same as those of the bends 2 and the strand bundle segments 1a 
according to the first embodiment. 
The strand bundle 17 has a plurality of transverse fold lines 19 extending 
centrally across the respective bends 18, the fold lines 19 being inclined 
at an angle .theta..sub.3 to the transverse direction of the strand bundle 
17. The strand bundle 17 is folded over on itself successively along the 
fold lines 19, thus forming a plate-like winding 20 as indicated by the 
imaginary lines in FIG. 9. 
In the winding 20, adjacent ones of the strand bundle segments 17a are 
angularly spaced from each other by the angle .theta..sub.3 without 
overlapping each other, with overlapping regions 21 present only at the 
respective fold lines 18. 
Since the strand bundle segments 17a do not overlap each other and the 
overlapping regions 21 are relatively small in area, the winding 20 can 
produce magnetic fields efficiently. As adjacent ones of the strand bundle 
segments 17a are inclined to each other by the angle .sub.74.sub.3, the 
magnetic field produced by the winding 20 and the magnetic field produced 
by the magnet of an electric motor are oriented in different directions 
with a suitable angle therebetween, resulting in a skew effect for smooth 
motor rotation. 
FIG. 10 shows a winding according to a fourth embodiment of the present 
invention. 
As shown in FIG. 10, a unitary web-shaped strand bundle 22 composed of a 
plurality of parallel strands has five longitudinally spaced bends 23a, 
23b, 23c, 23d, 23e which divide the strand bundle 22 into a plurality of 
strand bundle segments 22a, 22b , 22c, 22d, 22e, 22f. Adjacent two of the 
strand bundle segments 22a, 22b , 22c, 22d, 22e, 22f are positioned one on 
each side of one of the bends 23a, 23b, 23c, 23d, 23e. The strand bundle 
segments 22a, 22b , 22c, 22d, 22e, 22f are staggered transversely of the 
strand bundle 22, and extend parallel to each other. The strand bundle 
segments 22b , 22c, 22d, 22e between the bends 23a.about.23e have equal 
lengths q, and the bends 23a.about.23e have equal lengths t in the 
longitudinal direction of the strand bundle 22. 
The strand bundle segments 22b , 22d, 22f joined to odd-numbered bends 23a, 
23c, 23e as counted from a reference strand bundle segment 22aon one end 
of the strand bundle 22 are transversely staggered from the reference 
strand bundle segment 22a by respective distances that are multiples of 
the width s of the strand bundle 22 by odd numbers. The strand bundle 
segments 22c, 22e joined to even-numbered bends 23b, 23d as counted from 
the reference strand bundle segment 22a are transversely staggered from 
the reference strand bundle segment 22a by respective distances that are 
multiples of the width s of the strand bundle 22 by even numbers. More 
specifically, the first, third, and fifth strand bundle segments 22b , 
22d, 22f from the reference strand bundle segment 22a are transversely 
staggered from the reference strand bundle segment 22a by one, three, and 
five times the width s of the strand bundle 22, and the second and fourth 
strand bundle segments 22c, 22e from the reference strand bundle segment 
22a are transversely staggered from the reference strand bundle segment 
22a by two and four times the width s of the strand bundle 22. The strand 
bundle segments 22b through 22f can thus be transversely staggered from 
the reference strand bundle segments 22a by suitably adjusting the lengths 
and directions of the bends 23a.about.23e in the transverse direction of 
the strand bundle 22. 
The strand bundle 22 has a plurality of fold lines 24 extending 
perpendicularly to the longitudinal direction thereof and lying centrally 
across the respective bends 23a.about.23e. 
The strand bundle 22 is folded over on itself successively along the fold 
lines 24, thus forming a plate-like winding 25 as indicated by the 
imaginary lines in FIG. 10. The strand bundle segments 22a through 22f lie 
parallel to each other in the winding 25. The folded strand bundle 22 
overlaps itself only in overlapping regions 26 at the respective bends 
23a.about.23e. The overlapping regions 26 are smaller in area than the 
overlapping regions of the conventional helical winding shown in FIG. 22. 
Consequently, the amount of material of the winding 25 is reduced, and so 
is the electric resistance of the winding 25 to electric currents flowing 
therethrough. The winding 25 is also reduced in thickness and hence 
weight. The winding 25 can produce uniform magnetic fields efficiently for 
rotating an electric motor. 
FIG. 11 shows a winding according to a fifth embodiment of the present 
invention. 
In FIG. 11, a strand bundle 27 has a plurality of bends 28a.about.28e and a 
plurality of strand bundle segments 27a.about.27f similar to those of the 
strand bundle 22 shown in FIG. 10, and the strand bundle segments 
27a.about.27f are inclined similarly to those of the strand bundle 12 
shown in FIG. 8. 
More specifically, odd-numbered strand bundle segments 27b, 27d, 27f as 
counted from a reference strand bundle segment 27a on one end of the 
strand bundle 27 are substantially transversely staggered from the 
reference strand bundle segment 27a by respective distances that are 
multiples of the width of the strand bundle 27 by odd numbers, and are 
oriented parallel to each other. Even-numbered strand bundle segments 27c, 
27e are substantially transversely staggered from the reference strand 
bundle segment 27a by respective distances that are multiples of the width 
of the strand bundle 27 by even numbers, and are oriented parallel to each 
other and obliquely to the odd-numbered strand bundle segments 27b, 27d, 
27f. The strand bundle 27 has a plurality of fold lines 29 extending 
transversely thereof centrally across the respective bends 28a.about.28e. 
When the strand bundle 27 is folded over on itself successively along the 
fold lines 29, a plate-like winding 30 is produced which is of the same 
shape as the winding 15 shown in FIG. 8. The winding 30 is also effective 
to produce uniform magnetic fields efficiently for rotating an electric 
motor. 
A winding according to a sixth embodiment of the present invention, and a 
process of manufacturing the winding according to the sixth embodiment 
will be described below with reference to FIGS. 12 through 15. 
As shown in FIG. 12, a flat web-shaped strand bundle 31 comprises three 
parallel strand bundles assigned respectively to U-, V-, and W-phases and 
each composed of enameled wires. The strand bundles are bonded to each 
other except for longitudinally spaced regions 32 where the strand bundles 
or enameled wires are separate from each other. The strand bundle 31 
therefore includes a plurality of strand bundle segments 31a, 31b divided 
by the regions 32 where the strand bundles are bonded together. 
As shown in FIG. 13, one bonded strand bundle segment 31a is turned 
upwardly about an adjacent region 32 with respect to an adjacent bonded 
strand bundle segment 31b. Then, as indicated by the arrow in FIG. 13, the 
erected strand bundle segment 31a is horizontally displaced in the 
transverse direction of the strand bundle segment 31b until the strand 
bundle segment 31a is transversely shifted as shown in FIG. 14. Such 
transverse displacement of the strand bundle segment 31a is allowed by the 
region 32 because the enameled wires are not bonded in the region 32. At 
this time, as shown in FIG. 14, the enameled wires in the region 32 cross 
each other, forming a bend 33. The strand bundle segment 31a is 
transversely displaced over an interval which is the same as the width of 
the strand bundle 31. Then, as indicated by the arrow in FIG. 14, the 
transversely displaced strand bundle segment 31a is turned downwardly 
about the region 32 into a position adjacent to the strand bundle segment 
31b. Now, the strand bundle segments 31a, 31b are juxtaposed parallel to 
each other as shown in FIG. 15. The above process is repeated to fold over 
the strand bundle 31 successively, forming a flat plate-like winding which 
is of essentially the same shape as the winding 4 according to the first 
embodiment. The winding thus formed has overlapping regions which are very 
small in area. The winding is small in size and can be manufactured with 
ease. The winding according to the sixth embodiment is also effective to 
produce uniform magnetic fields efficiently for rotating an electric 
motor. 
A winding according to a seventh embodiment of the present invention, and a 
process of manufacturing the winding according to the seventh embodiment 
will be described below with reference to FIGS. 16 through 19. 
As shown in FIG. 16, a flat web-shaped strand bundle 34 comprises three 
parallel strand bundles assigned respectively to U-, V-, and W-phases and 
each composed of enameled wires. The strand bundle 34 has a pair of fold 
lines 35a, 35b for forming a bend which will be described later on. The 
strand bundle 34 also has strand bundle segments 34a, 34b disposed one on 
each side of the pair of fold lines 35a, 35b. The fold lines 35a, 35b 
extend parallel to each other and are inclined at 45.degree. to the 
longitudinal direction of the strand bundle 34. The fold lines 35a, 35b 
are spaced from each other by a distance which is the same as the width of 
the strand bundle 34, in the longitudinal direction of the strand bundle 
34. 
As shown in FIG. 17, the strand bundle segment 34a is folded over along the 
fold line 35a in the direction of a fold line 36 that extend centrally 
across the fold line 35a in the transverse direction of the strand bundle 
34, thus overlapping the strand bundle 35b. At this time, half of the area 
between the fold lines 35a, 35b is superimposed on the surface of the 
strand bundle 35b, and hence the fold line 35b is positioned outside of 
the overlapping region. The reverse side of the strand bundle 34 is shown 
hatched in FIG. 17. 
Then, as shown in FIG. 18, the folded strand bundle segment 34a is further 
folded over along the fold line 35b in the longitudinal direction of the 
strand bundle 34. The strand bundle segments 34a, 34b are therefore 
displaced a distance equal to the width of the strand bundle 34 in the 
transverse direction of the strand bundle 34, with a bend 37 formed 
therebetween. The bend 37 is constituted by the area between the fold 
lines 35a, 35b, only shown upside down. 
Thereafter, as shown in FIG. 19, the strand bundle 34a is folded over along 
the fold line 36 into a position adjacent to the strand bundle 34b. the 
strand bundles 34a, 34b now being positioned parallel to each other. The 
above process is repeated to fold over the strand bundle 34 successively 
along the fold lines 36, forming a flat plate-like winding which is of 
essentially the same shape as the winding 4 according to the first 
embodiment. The winding thus formed has overlapping regions which are very 
small in area, and can be manufactured with ease. The winding according to 
the seventh embodiment is also effective to produce uniform magnetic 
fields efficiently for rotating an electric motor. 
The angle at which the fold lines 35a, 35b are inclined in the longitudinal 
direction of the strand bundle 34 and the distance by which the fold lines 
35a, 35b are spaced from each other may be suitably selected to form 
windings which are similar to the windings according to the second through 
fifth embodiments described above. 
A winding according to an eighth embodiment of the present invention will 
be described with reference to FIGS. 20 and 21. 
As shown in FIG. 20, a unitary strand bundle 38 is composed of three 
parallel web-shaped strand bundles 38.sub.u, 38.sub.v, 38.sub.w each 
comprising a plurality of parallel strands, the strand bundles 38.sub.u, 
38.sub.v, 38.sub.w being allotted respectively to U-, V-, and W-phase 
currents. The unitary strand bundle 38 includes a plurality of bends 39 
longitudinally spaced at predetermined intervals g. The unitary strand 
bundle 38 is divided into a plurality of straight strand bundle segments 
38a by the bends 39, each bend 38 being disposed between two of the strand 
bundle segments 38a. The strand bundle segments 38a are successively 
staggered transversely on one side of the strand bundle 38 from one end to 
the other of the strand bundle 38, and extend parallel to each other. 
Any adjacent two of the strand bundle segments 38a are transversely 
staggered relatively to each other by an interval that is the same as the 
width h of the strand bundle 38.sub.u, for example. The strand bundle 38 
has a plurality of fold lines 40 extending across the respective bends 39 
and inclined at a certain angle to the transverse direction of the strand 
bundle 38. The bends 39 have equal lengths in the longitudinal direction 
of the strand bundle 38. 
The strand bundle 38 thus staggered is then folded over on itself 
successively along the fold lines 40 so that the strand bundle segments 
38a overlap for the distances g, jointly making up a flat plate-shaped 
winding 41 as shown in FIG. 21. The winding 41 is of an elongate shape 
extending transversely of the strand bundles 38.sub.u, 38.sub.v, 38.sub.w, 
which remain unchanged in the order in which they are arranged in the 
winding 41. The strand bundle segments 38a are inclined to each other at 
an angle which is equal to the angle at which the fold lines 40 are 
inclined. The folded strand bundle 38 overlaps itself in overlapping 
regions 42, shown hatched, in the bends 40 where electric currents flow in 
opposite directions. Since the strand bundle segments 38a are transversely 
displaced from each other, the overlapping regions 42 are smaller in area 
than the overlapping regions of the conventional helical winding shown in 
FIG. 22. Any canceling out of produced magnetic fields caused by the 
overlapping regions of the strand bundle 38 is therefore relatively small. 
The strand bundle 38 can efficiently produce magnetic fields that are 
required to rotate an electric motor. As the magnetic field produced by 
the strand bundle segments 38a and the magnetic field produced by the 
magnet of an electric motor are oriented in different directions with a 
suitable angle therebetween, the winding 41 provides a skew effect for 
smooth motor rotation. The winding 41 as it is assembled in an electric 
motor allows the motor to rotate smoothly with a reduced torque loss. 
The winding according to any of the above embodiments of the present 
invention can easily be manufactured simply by folding the strand bundle 
successively along the fold lines. As the overlapping regions of the 
strand bundle where electric currents flow in opposite directions are 
relatively small in area, the winding enables the electric motor to 
produce a desired torque efficiently. The relatively small area of the 
overlapping regions of the strand bundle allows the winding to be reduced 
in thickness and weight, and also to have a low electric resistance for 
efficient generation of a desired motor torque. Since the winding has a 
reduced thickness, the distance between the core and the magnet of the 
electric motor which incorporates the winding is made relatively small. As 
a result, the flux density between the core and the magnet is increased 
for efficient motor torque generation. 
Since the strand bundle is folded over on itself along the fold lines 
across the bends, the strand bundle segments of the folded strand bundle, 
and hence the directions in which electric currents flow through the 
strand bundle are substantially parallel to the rotatable shaft of the 
electric motor. Therefore, the direction of the magnetic field produced by 
the winding and the direction of the magnetic field produced by the magnet 
of the motor are substantially the same as each other for generating 
electromagnetic forces highly efficiently. 
The direction of the magnetic field produced by the winding and the 
direction of the magnetic field produced by the magnet of the motor may be 
determined as desired depending on the angle of the fold lines. Thus, the 
winding is effective to both generate a motor torque efficiently and cause 
the motor to rotate smoothly. 
The winding according to the present invention can easily be manufactured, 
allows an electric motor to produce a desired torque when incorporated in 
the motor, and makes the electric motor light in weight and small in size. 
While the present invention has been described above with respect to 
windings for the passage of three-phase currents, the principles of the 
present invention are also applicable to windings for the passage of a 
single-phase current or a polyphase current. 
Although certain preferred embodiments of the present invention have been 
shown and described in detail, it should be understood that various 
changes and modifications may be made therein without departing from the 
scope of the appended claims.