Apparatus for inserting coils into stator core slots

A method of and apparatus for inserting coils into slots formed in the stator core of a dynamoelectric machine such as an electric motor, with the stator core having open type slots each of which cooperates with blades of the apparatus for guiding the coil and a stripper for forcing the coil out of the blades. A closed space has a volume sufficient to avoid any disorder of coil wire layers when the coil is received by the closed space. After placing the coils in the closed spaces, the coils are pushed into the respective slots and, as desired, the coils are further compressed until the coil wires assume a non-circular cross-section. By so doing, it is possible to remarkably increase the space factor of each slot.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of and apparatus for inserting 
coils into slots formed in the stator core of a dynamoelectric machine and 
more particularly, to a method of and apparatus for inserting coils into 
the slots in the stator core of a small-sized dynamoelectric machine such 
as, for example an electric motor. 
In a dynamoelectric machine such as an electric motor, the space factor of 
the slots in the stator or armature, i.e. the ratio of the sum of the 
cross-sectional areas of the coil wires received by the slots to the 
cross-sectional area of the slots, is a very significant factor which 
affects the performance, e.g. the ratio of the output energy to the input 
energy, as well as the size of the machine. 
For instance, in a large-size electric motor operating with large high 
voltage electric current such as a current for driving an electric car, it 
is necessary to employ coil wires having a large diameter and to ensure 
insulation between adjacent coil wires. In the production of a large-size 
motor, therefore, the wires are pre-shaped to have the desired 
cross-section are subjected to an insulating treatment. The pre-treated 
wires are then put into each slot in the stator core in a one-by-one 
fashion. To this end, each slot in the stator core is an open type slot 
having a substantially constant circumferential width over entire radial 
length thereof. The assembling of such a large-size electric motor, 
therefore, requires considerable manual labor resulting in a low 
production efficiency, although a high space factor on the order of 70 to 
80% is achieved. 
On the other hand, small-sized electric motors such as industrial general 
purpose motors, operating with comparatively small low voltage electric 
current, are designed and produced making much of the productivity. 
Generally, a small-sized electric motor having a space factor of about 60% 
exhibits an efficiency generally ranging between 60% and 70%, although 
more strictly the efficiency depends on the type of the motor. It is also 
known that about 10% increase of the efficiency is attained by an increase 
of the space factor to 90%. 
However, there has been no effective measures for increasing the space 
factor so that the users have been obliged to use electric motors having 
rather low efficiency. 
Accordingly, an object of the invention is to provide method of and 
apparatus for inserting coils, which provides a large value of the space 
factor in the stator without a reduction in the production efficiency, 
thereby overcoming the problems of the prior art. 
Another object of the invention is to provide method of and apparatus for 
inserting coils, which enables a reduction in the size of the motor 
thereby contributing to the saving of natural resources. 
To these ends, according to the invention, a method of inserting coils is 
proposed wherein the coils have a coil wire wound regularly in wire layers 
automatically inserted into slots in the stator core of a dynamoelectric 
machine by a coil inserting apparatus, with the method including supplying 
the coils into the spaces formed between respective adjacent blades of the 
inserting apparatus, pushing up, by a stripper of the apparatus, the 
portions of the coils located in an area inside the blades until the coil 
portions are moved out of an area beyond the ends of the blades so as to 
insert the coils into closed spaces defined by the walls of the respective 
slots, blades of the apparatus and the stripper. The coils are forced in 
the closed spaces into the slots in the stator core, and the coils, 
received by the slots, are compressed as desired until each coil wire 
assumes a non-circular cross-section. 
According to another feature of the invention, an apparatus for inserting 
coils into slots in a stator core of a dynamoelectric machine is proposed 
which includes a plurality of blades disposed along a circle at a 
predetermined circumferential pitch so as to oppose the ends of the 
partition walls separating adjacent slots from each other, with a 
plurality of projections being provided which are capable of projecting 
into the spaces formed between respective adjacent blades. A stripper is 
disposed at the center of the circle of the blades and is adapted to push 
up the coils supported by the blades into corresponding slots of the core 
fitting around the upper ends of the blades. At least the portions of the 
projections opposed to the slots in the stator core when the stripper is 
in the end of its upward stroke, are constituted by pushers which are 
disposed radially around the stripper for sliding movement in the radial 
direction. The coil inserting apparatus includes a conical or pyramidal 
cam disposed at the center of the stripper and contacting one end of the 
pushers, with a means being provided for moving the cam up and down. 
These and other objects, features and advantages of the invention will 
become more apparent from the following description of the preferred 
embodiments taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION 
Preferred embodiments of the invention will be described hereinunder with 
reference to the accompanying drawings. 
Referring now to the drawings wherein like reference numerals are used 
throughout the various views to designate like parts and, more 
particularly, to FIG. 1, according to this figure, a small sized electric 
motor is provided with semi-closed slots in a stator core, with the slots 
including an open end 5 in the stator core 1 which is partially closed by 
radial ends 4 of adjacent teeth 3 the insertion of the coils into the 
slots 2 is automatically carried out by a coil inserting machine generally 
designated by the reference numeral 6 such as, for example, of the type 
illustrated in FIGS. 2 and 3. 
More particularly, as shown in FIGS. 2 and 3, the coil insertion machine 6 
has a holder 8 fixed to the base 7, with a plurality of wedge-shaped 
guides 9 being fixed to the holder 8 along a circle at a constant 
circumferential pitch. An inner surface of each wedge-shaped guide 9 
supports a blade 11, with the blades 11 being located by an inner guide 10 
which is disposed at a center of the holder 8. A hydraulic cylinder 13 is 
supported by the lower face of the base 7 through a bracket 12, with the 
cylinder 13 including a cooperating rod 14, the upper end of which carries 
a stripper 15 located above the inner guide 10 at a center of the circle 
of the blades 11. The stripper 15 has projections 16 projecting into the 
spaces between adjacent blades 11. 
For inserting the coils 17 into the slots 2, the coils 17 are first 
positioned in the spaces between adjacent blades 11 and then the stator 
core 1 is fitted around the upper ends of the blades 11. In this state, 
the cylinder 13 operates to lift the stripper 15, so that the stripper 
pushes up the coils 17 received by the spaces between adjacent blades 11 
to insert the same into the slots 2. 
By employing the coil inserting machine 6 of FIG. 2, it is possible to 
simultaneously mount the required number of coils in the stator core 1 so 
as to attain a high productivity. A disadvantage of this proposed 
arrangement resides in the fact that the coils 17, inserted into the slots 
2 through the openings of the slots 2, are relieved from stresses which 
have been incurred during winding and insertion, so that the wires of the 
coils 17 in each slot 2 are free to take an irregular position. 
Consequently, the space factor of each slot is unfavorably decreased in 
the order of 60% to 67%. If the coil 17 is forcibly compacted to increase 
the space factor, the irregularly arranged and lapping coil wires are 
partially collapsed or damaged often resulting in serious problems such 
as, for example, an insulation failure, cutting of the conductor, an 
increase in resistance, and so forth. 
In accordance with the present invention, as shown in FIG. 4, a stator core 
18 has a plurality of substantially trapezoidal teeth 19 projected towards 
the center thereof, such that substantially rectangular slots 20 are 
formed between adjacent teeth 19, with an opening 21 of each slot 20 
having substantially the same circumferential width as the bottom of the 
same slot 20. The ends of the teeth 19 of the stator core 18 may be cut to 
fit the outer surfaces of blades of a coil inserting apparatus of the 
invention which will be explained more fully hereinbelow. 
A coil inserting apparatus in accordance with the invention, as shown in 
FIGS. 5-8, includes a bracket 12 fixed to the lower side of the base 7. A 
pair of guide bars 22, spaced by a suitable distance from each other are 
disposed between the base 7 and the bracket 12, with a movable plate 23 
slidably engaging the guide bars 22. A hydraulic cylinder 24 is fixed to 
the lower side of the movable plate 23, with a rod 14 of a cylinder 13 
being connected to the lower end of the cylinder 24. A hollow shaft 25, 
slidably received by bores formed in the base 7 and an inner guide 10, are 
fixed to the upper side of the movable plate 23. A stripper 26 is 
supported by the upper end of the shaft 25, with the stripper 26 including 
a main body 27 disposed at the inner side of the blades 11, and a 
plurality of pushers 28 each of which being so shaped and sized so as to 
be slidingly engageable in the spaces between adjacent blades 11 and also 
by the slot 20 in the stator core 18. The pushers 28 are mounted on the 
main body 27 so as to be radially slidable along the main body 27. 
Although not shown, grooves are formed in the upper and lower surfaces of 
the pushers 28, as well as corresponding portions of the main body 27. 
Annular rubber or spring members are received by these grooves so as to 
bias the pushers 28 towards the center of the main body 27. A rod 29 of 
the cylinder 24 is disposed at the center of the shaft 25. A 
frusto-conical or pyramidal cam 30 is fixed to the upper end of the rod 
29, with a conical surface of the cam 30 slidably contacting the radially 
inner surfaces of the pushers 28 so that the pushers are urged radially 
outwardly, i.e. from the position adjacent to the main body 27 towards the 
stator core 18, as the cam 30 is moved upwardly. 
In operation, the required number of coils 17, are placed in the spaces 
between respective adjacent blades 11 in such a manner so as to avoid any 
disorder of the layers of the wound wire. Then, the stator core 18 is 
fitted to the outside of the upper ends of the blades 11. The cylinder 13 
operates in this state to push up the stripper 26 which, in turn, pushes 
up the coils 17 received by the spaces between adjacent blades 11. 
Consequently, the coils 17 move together with the stripper 26 and are 
driven toward the slots 20 in the stator core 18. 
Then, the stripper 26 is projected from the upper end of the blade 11 by a 
further operation of the cylinder 13 to force the portions of the coils 17 
located in an area inside the blades 11, thereby moving the latter coil 
portions out from the latter area beyond the upper ends of the blades 11. 
In this state, the coils 17 are received by closed spaces which are 
defined by the walls of respective slots 20 in the stator core, blades 11 
and the pushers 28. The space factor of the closed space, i.e. the ratio 
of the volume occupied by the coil to the volume of the closed space, is 
selected so as not to allow the coil 17 to move freely due to the stresses 
generated in the coil wire. For example, the size of the cross-section of 
the space is so selected that when the coil wire is wound in wire layers 
in close contact with one another from the bottom towards the opening of 
the slot 20, the gap formed between the pusher 28 and the uppermost wire 
layer is smaller than the diameter of the coil wire, preferably less than 
a half of the wire diameter. 
Then, the cylinder 24 operates to push the cam 30 upwardly as shown in FIG. 
7, so that the pushers 28 are outwardly radially driven by the cam 30. 
Consequently, the pushers 28 are projected towards corresponding slots 20 
in the stator core 18 so that the coils 17 in the aforementioned spaces 
are pressed by the pushers 28 into the slots 20 as shown in FIG. 8 and are 
compressed and shaped by further radial movement of the pushers 28. 
Although not essential, the compression of the coils 17 is carried out 
until each coil wire, which originally has a circular cross-section, 
assumes a non-circular cross-section. 
After the insertion of the coils 17 into the slots 20, the cylinder 24 is 
reversed to lower the cam 30 so that the pushers 28 are allowed to move 
out of corresponding slots 20 to the original position. Subsequently, the 
cylinder 13 operates to extract the stripper 26 downwardly from the stator 
core 18 and then the stator core 18, now receiving the coils, is 
dismounted or removed from the blades 11. According to the invention, the 
coils 17 are inserted into the slots 20 in the stator in the manner 
explained hereinabove. 
In the embodiment of the invention described hereinabove, the coil 17 in 
each slot is compressed until the cross-sectional shape of each coil wire 
becomes non-circular. Such a deformation of the coil wires, however, is 
not essential and, in some cases, the coils 17 are merely inserted into 
the slots 20 without being followed by compression. 
An experiment was conducted to examine the relationship between the rate of 
compression of the coil and the space factor of each slot into which the 
coil has been inserted by the inserting apparatus of the invention 
described hereinbefore, the result of which is shown in Table 1 below. 
TABLE 1 
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Compression rate 
Space factor 
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1 0% 84% 
2 6% 90% 
3 11% 95% 
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The experiment showed that no damage of the insulation coating on the coil 
wire is caused by the compression of the coil in the slot 20. 
Additionally, no cutting of the coil wires was caused due to the uniform 
distribution of the compression force resulting from the regular 
arrangement of the coil wires. 
As will be apparent seen from the foregoing description, according to the 
invention, the coils 17 are first placed in the closed spaces each defined 
by a slot in the stator core 18, blades 11 of an inserting apparatus and a 
stripper of the apparatus, and are then forced into the slots by the 
operation of the apparatus. It is, therefore, possible to attain a large 
value of space factor of 84% or higher which is more than 25% higher than 
that of the conventionally attained maximum value 67%. 
According to the invention, therefore, the stator core of the same 
thickness can have a reduced size of the slots for receiving a given 
number coil wires, which, in turn, affords a reduction in the outside 
diameter of the stator core, contributing to a reduction in the size of 
the electric motor, as well as to a saving of material. The close contact 
of the coil wires which are compacted in accordance with the invention can 
provide a greater heat transfer between adjacent coil wires, so that the 
heat radiating characteristics of the electric motor can be remarkably 
increased.