Stator winding structure for gap winding type electric rotary machine

In a gap winding type electric rotary machine, a stator winding consisting of a plurality of stator coils is mounted on the inner surface of a stator core within the air gap defined by the clearance between the stator core and the rotor core, in such a manner that the stator coils are grouped together in a plurality of stator coil units and each stator coil unit is encapsulated in a solid casing comprising an outer cover fixed to the inner surface of the stator core through an elastic sheet and an inner cover closing the outer cover. The inner clearance within the solid casing is also provided with an elastic sheet.

BACKGROUND OF THE INVENTION 
The present invention relates to improvements in a stator winding structure 
for a gap wwinding type electric rotary machine, in which the stator 
winding is disposed within a gap defined between the stator core and the 
rotor core thereof. 
In general, the stator winding for a gap winding type electric rotary 
machine is disposed in a gap between the stator core and the rotor core, 
and is mounted on the inner surface of the stator core by coil supporting 
members which project from the inner surface of the stator core in the 
radial direction. As a result, the stator winding such as provided in the 
gap winding type electric rotary machine is much more directly influenced 
by the main magnetic flux of the machine than the stator winding for a 
slot winding type electric rotary machine in which the stator winding is 
wound within slots provided on the inner surface of the stator core. 
Therefore, in the gap winding type electric rotary machine, fine wires of 
about 1.0 mm in diameter are usually formed as a strand and bundled 
together to form one stator conductor. Each stator conductor has a 
covering insulation over the outer periphery of the stator conductor. 
Further, a plurality of such stator conductors are gathered and an earth 
insulation is provided on all of the surfaces to form one stator coil. 
Every stator coil, or a plurality of such stator coils thus formed, is 
then mounted on the inner surface of the stator core by means of coil 
supporting members. 
U.S. Pat. No. 3,405,297 to K. D. Madsen shows one example of this kind of 
stator winding structure, in which the stator winding comprises a 
plurality of stator coils, each of which is composed of a plurality of 
conductors respectively surrounded by a suitable insulating material and 
bundled together to form one stator coil. The stator coil is further 
solidified by a suitable insulating material surrounding the stator coil 
and then mounted on the inner surface of the stator core with the 
assistance of a plurality of coil supporting members projecting from the 
inner surface of the stator core. 
In another embodiment of the prior art, for example, as disclosed in U.S. 
Pat. No. 3,082,337 to W. D. Horsley, a stator winding comprising a 
plurality of stator coils is embedded in a detachable cylinder composed of 
a suitable casting resin, for example, an epoxy-resin, and fixed to the 
inner surface of the stator core. 
However, as described before, the electromagnetic forces generated in the 
stator coils of a gap winding type electric rotary machine become very 
large with the aid of the main flux in the air gap. Further, these 
electromagnetic forces are directly applied to the respective stator coils 
adjacently disposed in the air gap, which tends to cause various vibration 
modes in the respective stator coils. The magnitudes, phases and 
directions of the vibration produced in the respective stator coils are 
different from each other; therefore, each stator coil oscillates with 
vibrations different in magnitude, phase and direction from the other 
stator coils. The electromagnetic forces thus produced with respectively 
different magnitudes, phase, and directions are exerted on the stator core 
as individual vibration sources in the electric rotary machine. 
Consequently, the stator core suffers from vibrating stresses, local 
abnormal oscillations and noises. Also, the electrical insulations 
surrounding the respective stator coils are conspicuously degraded by the 
vibrating stresses, and local losses and temperature rises are induced in 
the coils. 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide a stator winding 
structure for a gap winding type electric rotary machine, in which 
vibrations produced by electromagnetic forces are reduced. 
Another object of the present invention is to provide a durable stator 
winding structure for a gap winding type electric rotary machine. 
Still another object of the present invention is to provide a stator 
winding structure for a gap winding type electric rotary machine which is 
easy to fabricate. 
According to features of the present invention, a stator winding for a gap 
winding type electric rotary machine, which is disposed within a gap 
defined between a stator core and a rotor core, is divided into a 
plurality of coil unit groups, and each or a plurality of the coil unit 
groups grouped together is or are encapsulated in enveloping means. Each 
enveloping means is fixed to the inner surface of the stator core by 
supporting means. Thereby, vibrations thus produced with respectively 
different magnitudes, phase, and directions are exerted on the stator core 
as individual vibration sources in the electric rotary machine. 
Consequently, the stator core suffers from vibrating stresses, local 
abnormal oscillations and noises. Also, the electrical insulations 
surrounding the respective stator coils are conspicuously degraded by the 
vibrating stresses, and local losses and temperature rises are induced in 
the coils. 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide a stator winding 
structure for a gap winding type electric rotary machine, in which 
vibrations produced by electromagnetic forces are reduced. 
Another object of the present invention is to provide a durable stator 
winding structure for a gap winding type electric rotary machine. 
Still another object of the present invention is to provide a stator 
winding structure for a gap winding type electric rotary machine which is 
easy to fabricate. 
According to features of the present invention, a stator winding for a gap 
winding type electric rotary machine, which is disposed within a gap 
defined between a stator core and a rotor core, is divided into a 
plurality of coil unit groups, and each or a plurality of the coil unit 
groups grouped together is or are encapsulated in enveloping means. Each 
enveloping means is fixed to the inner surface of the stator core by 
supporting means. Thereby, vibrations produced by electromagnetic forces 
in the enveloping means are reduced and made more uniform.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 of the drawings, there is illustrated one 
embodiment of the stator winding structure of the present invention, 
applied to a single-layer winding of a gap winding type electric rotary 
machine, in which a stator coil 100 and adjacently disposed stator coils, 
which are partly shown, are mounted on the inner surface of a stator core 
10 within an air gap defined by the stator core 10 and a rotor core (not 
shown). 
Each stator conductor 11 to 16 is formed of a bundle of fine wires 17 as a 
strand and a covering insulation 18 on the outer periphery of the strand. 
A cooling pipe 19 is respectively provided through the stator conductors 
11 to 16 along the fine wires 17 for coil cooling purposes. Six stator 
conductors 11 to 16 thus formed are grouped together to form one stator 
coil 100 with an earth insulation layer 20 surrounding the outer periphery 
of the grouped stator conductors 11 to 16. On the outer periphery of the 
stator coil 100, there is further provided an elastic sheet 21 for 
absorbing vibrations of the stator coil 100. The stator coil 100 covered 
with the earth insulation 20 and the elastic sheet 21 is integrally held 
and fixed in a solid casing 30. The solid casing 30 is attached and fixed 
to the inner surface of the stator 10 by supporting sticks 22 and 23 which 
are fixed at one end in key slots in the stator core and project in the 
radial direction into the air gap. 
The solid casing 30 in this embodiment is formed of two components, that 
is, an outer cover 301 contacting the inner surface of the stator core 10 
and an inner cover 302 for covering the outer cover 301. The details of 
the solid casing 30 will be later described with reference to FIG. 2. In 
the clearance between the outer cover 301 and the stator core 10, there is 
also provided an elastic sheet 24 for absorbing the vibrations of the 
stator coil 100. The end portions of the outer and inner cover 301, 302 
are fit in grooves 25, 26 provided on the coil supporting sticks 22, 23 
and fixed therein. 
By the employment of the solid casing 30, the electromagnetic forces 
produced in the respective stator coils in one solid casing 30, which have 
respectively different magnitudes, phases and directions, are combined 
into a single vibrating source and the magnitudes, phases, and directions 
are made uniform. Also, the use of the elastic sheets 21, 24 inside and/or 
outside of the solid casing 30 enables the electromagnetic forces to be 
absorbed, and as a result, to reduce the magnitudes of the electromagnetic 
forces. 
Consequently, the individual electromagnetic forces produced in the 
respective stator conductors 11 to 16 are not exerted directly on the 
stator core 10, but they are exerted on the stator core 10 in such a 
manner that the vibrating sources are combined into one source and that 
the magnitudes of the vibrations are reduced and made uniform. 
FIG. 2 shows an enlarged view of a unit component of the solid casing 30 of 
FIG. 1, in which the solid casing 30 is divided into two covers 301, 302 
in the radial direction to facilitate the insertion of the stator coil 
100. The stator coil 100 provided with the elastic sheet 21 is inserted in 
the interior of the outer cover 301. Thereafter, the inner cover 302 is 
secured to the outer cover 301 at joint surfaces 51, 52 in a suitable 
manner, and the resultant structure 30 is inserted and fixed in grooves 
25, 26 provided in the supporting sticks 22, 23, with the elastic sheet 24 
provided at the outer surface of the outer cover 301. 
The solid casing 30 can also be fabricated in such a way, as illustrated in 
FIG. 2, that the solid casing 30 is divided into two or more covers in the 
axial direction, thereby to further facilitate the insertion of the stator 
coil 100. The outer covers 301, 303 and the inner covers 302, 304 are 
bonded after installation of the stator coil 100 at the joint surfaces 51, 
52, and 53. 
As the solid casing 30 performs a function to make uniform the various 
vibrations of the stator coil, it is preferable that the solid casing has 
significant mechanical strength against the electromagnetic forces and 
heat degradations. Also, the material for the solid casing preferably has 
a nonmagnetic character and a good workability. For example, it may be 
formed of a reinforced plastic material, such as fiber-reinforced plastic 
(which is commonly referred to as FRP). 
Also, since the elastic sheets 21, 24 perform the function absorbing and 
reducing vibrations, it is preferable that the elastic sheets have 
elasticities and durabilities against repeated fatigues and insulations. 
For example, it may be formed of non-woven synthetic resin fabrics such as 
those sold by E. I. du Pont Company under the trademark "TEFLON" 
impregnated with synthetic resin or varnish, or glass based polyester 
laminations formed into wave-like plates. 
FIG. 3 shows another embodiment of the present invention applied to a 
double layer winding. Where the winding factor is smaller than 1.0, the 
vibration modes of an overlying and underlying coil may be different from 
each other, and the vibration modes to which the stator core is subjected 
become complicated. The present embodiment illustrates a case where an 
overlying stator coil 101 and an underlying stator coil 102, and an 
overlying stator coil 103, and an underlying stator coil 104 are 
respectively grouped together and enclosed in solid casings 31, 32. 
Hereafter, the description will be made with reference to the stator coils 
101, 102 and the solid casing 31 of FIG. 3. The overlying stator coil 101 
and the underlying stator coil 102 are grouped together by the solid 
casing 31 which is composed of a pair of covers including an outer cover 
311 and an inner cover 312. The clearance defined within the solid casing 
31 is filled with an elastic sheet 41 to absorb the vibrations produced in 
the stator coils 101 and 102. Also, the outer periphery of the solid 
casing 31 is covered with an elastic sheet 42 to absorb the vibrations 
transmitted to the stator core 10. The solid casing 31 thus covered with 
the elastic sheet 42 is attached and fixed to the inner surface of the 
stator core 10 with the aid of coil supporting sticks 27, 28 projecting 
radially from the surface of the stator core 10. The solid casing 31 is 
fixed to the inner surface of the stator core 10 by a supporting plate 43 
fixed in respective grooves provided on the coil supporting sticks 27, 28. 
As described above, in the case of the double layer winding, the overlying 
and underlying stator coils usually have electrically different phases. 
However, according to the present invention, the vibration sources in the 
respective stator coil 101, 102 are made integral into a single vibration 
source by the solid casing 31. It is also preferable to choose stator 
coils to be enclosed in a solid casing, such that an overlying stator coil 
and an underlying stator coil in the solid casing have the same electrical 
phase to minimize the magnitudes and to unify the phases and directions of 
the vibrations. 
In the present embodiment for the double-layer winding, the overlying and 
underlying stator coils are grouped together and enclosed in a single 
solid casing contacting each other. However, it is also preferable to 
insert a suitable elastic layer or sheet between the contacting surfaces 
of the stator coils further to reduce the friction between the two stator 
coils within the solid casing. It is also preferable to enclose the 
respective stator coils in respective solid casings. In this case, an 
elastic sheet may be inserted between the two solid casings. 
Although, in the present embodiment, the elastic sheets 41, 42 for 
absorbing vibrations are provided both on the outer periphery of the solid 
casing 31 and outer periphery of the earth insulation 44 surrounding the 
stator conductors, almost the same effects can be obtained even when one 
of the elastic sheets 41, 42 is eliminated. The inside elastic sheet 41 
surrounding the outer periphery of the earth insulation 44 can be provided 
within the earth insulation 44, in which case, the earth insulation 44 may 
be provided on the outer periphery of the inside elastic sheet 41. Each 
elastic sheet 41, 42 provided inside and outside of the solid casing 31 
may be split and inserted in the form of a plurality of pieces or layers 
without being made integral. Further, the respective elastic sheets 41, 42 
can enhance the effects in such a way that the materials which have 
respectively different elastic modulus are employed in conformity with the 
vibration modes of the stator coils. The shape of the solid casing alters 
in dependence on the shape of the stator coils, the arrangement of the 
supporting sticks, the number of phases and layers of the stator coils, 
and the size of the rotary machine. 
As described herein in detail, according to the present invention, the 
various vibration sources having different magnitudes, phases, and 
directions which are distributed all over the stator coil or coils are 
combined into a single vibration source within the respective solid 
casings, and the vibrations are reduced and made uniform. Further, 
according to the present invention, due to the reduction of the 
vibrations, the degradations of the electrical insulating layers and the 
stator core by the vibration stresses are significantly reduced or 
eliminated and a durable stator winding structure is obtained. Still more, 
according to the present invention, a simplified stator winding structure 
convenient for fabrications can be obtained.