Rotor of a superconductive rotary electric machine

The rotor of a superconductive rotary electric machine has a coil-carrying shaft carrying superconductive field coils. A plurality of axially running parallel grooves and a pair of annular circumferentially running indentations, each of which is connected to one end of each of the grooves, are formed on the outer surface of the coil-carrying shaft. The axially and circumferentially running portions of the field coils are accommodated in the grooves and indentations respectively, and the spaces left by the circumferentially running portions of the field coils in the indentations are filled by electrically insulating fillers. Further, a plurality of wedges are fitted into the grooves above the axially running portions of the field coils, while a pair of sleeves are fitted around the coil-carrying shaft over the indentations, each of the sleeves being fitted around the coil-carrying shaft only at one end thereof which is situated farther from the central portion of the coil-carrying shaft than the other end thereof. Rings for preventing the slippage of the sleeves are interposed between the portions of the surfaces of the sleeves and the coil-carrying shaft which are fitted together.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a rotor of a superconductive rotary electric 
machine, and more particularly to the mounting structure of the 
superconductive field coils on the coil-carrying shaft of such a rotor. 
2. Description of the Prior Art 
The electrical resistance of certain metals, such as lead, tin, and 
vanadium, and alloys, such as niobium-tin and niobium-titanium, become 
vanishingly small, i.e. they become superconductive, when the temperature 
thereof falls below the transition temperatures thereof which are in the 
neighbourhood of a few degrees above absolute zero. Thus, when the field 
windings of an alternating current generator, for example, are formed of 
such a superconductive material and cooled below the transition 
temperature thereof, then a large magnetic field can be established 
without the expenditure of appreciable amounts of electrical energy. 
Alternating current generators having rotors which carry superconductive 
field windings have already been constructed. In such superconductive 
rotors, however, secure and reliable mounting of the superconductive field 
coils on the coil-carrying shaft of the rotor is of paramount importance, 
because when the field coils are displaced by the vibrations due to the 
rotational movement of the rotor, the resulting frictional heat may 
destroy the superconductivity of the field coils. Further, as the field 
coils much be covered many times by a complicated covering structure for 
the purpose of preventing outside heat from entering thereinto, the 
checking and repairing thereof are difficult to perform. 
Thus, it has already been proposed to wind the superconductive field coils 
around bobbins and then to mount the bobbins on the outer surface of the 
coil-carrying shaft. This makes it possible to wind the field coils 
separately from the coil-carrying shaft at a place where the winding 
operation can be performed effectively and reliably. The bobbins, however, 
make the dimension of the rotor larger and increase the production cost 
and production time thereof. 
Thus, another mounting structure for mounting the field coils on the 
coil-carrying shaft has been proposed to solve the above-mentioned problem 
caused by using bobbins. Namely, grooves having forms corresponding to the 
rectangular-loop-shaped field coils are formed on the outer surface of the 
coil-carrying shaft, and the field coils are accommodated in these 
grooves. A plurality of wedges are then fitted into recesses formed in the 
side surfaces of the grooves above the portions thereof which accommodate 
the field coils, thereby keeping the field coils situated thereunder 
securely in the proper positions thereof. The portions of the grooves 
running in the circumferential direction of the coil-carrying shaft, 
however, have the form of circular arcs and wedges of this shape for use 
according to this method are difficult to machine. The wedges and the 
recesses corresponding to these circumferentially running portions of the 
grooves are also curved. The complicated forms of the circumferentially 
running portions of the grooves and wedges result not only in increased 
production time and cost, but also in difficulty in the precise and 
reliable machining thereof. 
SUMMARY OF THE INVENTION 
Thus, an object of the present invention is to provide a rotor of a 
superconductive rotary electric machine in which the superconductive field 
coils are securely and reliably mounted on the coil-carrying shaft of the 
rotor, while the mounting operation of the field coils on the 
coil-carrying shaft can be performed at less cost, in less time and with 
more precision. 
The rotor of a rotary electric machine according to the present invention 
comprises a coil-carrying shaft having a cylindrical outer surface, and at 
least one winding formed of electrically conductive linear material. A 
plurality of parallel grooves running in the axial direction of the 
coil-carrying shaft and a pair of annular indentations running in the 
circumferential direction of the coil-carrying shaft are formed on the 
outer surfaces of the coil-carrying shaft. Each of the indentations is 
connected to one end of each of the grooves. The axially running portions 
of the winding are disposed in the grooves corresponding thereto, while 
the end portions, i.e., the circumferentially running portions thereof are 
disposed in the pair of indentations. The spaces left by the end portions 
of the field coils in the indentations are filled by electrically 
insulating filler which is tightly fitted thereinto. A pair of hollow 
cylindrical sleeves are then fitted around the coil-carrying shaft over 
the pair of indentations, thereby keeping the end portions of the field 
coils securely in the proper positions thereof in the indentations. 
Preferably, each of the sleeves is fitted around the coil-carrying shaft 
only at one end thereof which is situated farther from the central portion 
of the coil-carrying cylinder than the other end thereof, thereby avoiding 
the problem of frictional abrasion between the surfaces of the sleeves and 
the coil-carrying shaft and of making the dimensions of the rotor 
unnecessarily large. It is also preferred that rings for preventing the 
slippage of the sleeves with respect to the coil-carrying shaft are 
inserted between the portions of the inner surfaces of the sleeves and the 
outer surface of the coil-carrying shaft which are fitted together.

In the drawing, like reference numerals and characters represent like or 
corresponding parts. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1 to 4 of the drawings, a rotor structure of a 
superconductive rotary electric machine according to the present invention 
will be described. 
FIG. 1 shows an overall view of a rotor of an alternating current generator 
having superconductive field windings. The outer housing of the rotor is 
formed by a normal temperature damper 4, the disk-shaped portion 8A of the 
driving end shaft 8, and the outwardly turning annular flange portion 9A 
of the non-driving end shaft 9 having a central bore 9B therein, the 
driving and the non-driving end shafts 8 and 9 being rotatably supported 
by bearings 10. A coil-carrying shaft 2 having the form of a thick hollow 
cylinder is disposed coaxially within the normal temperature damper 4, the 
two ends of the coil-carrying shaft 2 being fixedly secured to a pair of 
torque tubes 1 having the form of thin hollow cylinders, which in their 
turn are fixedly mounted on the disk-shaped portion 8A and the annular 
flange portion 9A of the driving and the non-driving end shafts 8 and 9. 
Field coils 3 formed of a superconductive material are mounted on the 
outer side surface of the coil-carrying shaft 2. Each field coil 3 has 
substantially the form of a rectangular loop which has two straight sides 
running in the axial direction of the coil-carrying shaft 2, and the two 
circularly curved portions running in the circumferential direction 
thereof, the cross-sections of the curved portions of field coil 3 being 
schematically shown in FIG. 1. A pair of slip rings 11 is fitted around 
the non-driving end shaft 9 for the purpose of receiving field current 
supplied to the field coils 3. 
A central liquid helium container 15 is defined by the inner surface of the 
coil-carrying shaft 2 and a pair of end plates 7 having the form of disks, 
liquid phase helium being supplied thereto through the helium supply pipe 
schematically shown at P1 extending through the central bore 9B of the 
non-driving side end shaft 9. A peripheral liquid helium container 15A is 
defined by the outer surface of the coil-carrying shaft 2 and a 
cylindrical outer wall 6, liquid helium being supplied thereto through 
communication ports (not shown) extending through the coil-carrying shaft 
2 in the radial direction thereof. Thus, the field coils 3 are cooled by 
the liquid helium contained in the central and peripheral helium 
containers 15 and 15A. A low temperature damper 5 having the form of a 
hollow cylinder is disposed between the outer wall 6 of the peripheral 
helium container 15A and the normal temperature damper 4, and is fixedly 
mounted on the outer surface of the torque tubes 1. The cylindrical spaces 
between the normal temperature damper 4 and the low temperature damper 5, 
and between the low temperature damper 5 and the outer wall 6 of the 
peripheral helium container 15A, are kept at a high vacuum, thereby 
preventing the heat from outside from entering into the low temperature 
portion adjacent to the helium containers 15 and 15A. The spaces 14A 
within the torque tubes 1 are also kept at a vacuum, and radiation shields 
13 having the form of annular plates are fixedly mounted on the inner 
surface of the torque tubes 1 for the purpose of preventing radiation heat 
from entering into the low temperature portion. Each torque tube 1 has 
formed on the outer side surface thereof a stepped out portion 1A in which 
a heat exchanger is formed, which comprises a helical groove defined on 
the circumferential surface of the stepped out portion 1A, and a lid 12A 
having the form of a hollow cylinder which covers the groove 12B. The 
helium contained in the central container 15 is supplied to one end of 
each groove 12B through the pipe schematically shown at P2, and exhausted 
from the other end of each groove 12B through the pipe schematically shown 
at P3 which leads the helium out through the central bore 9B of the 
non-driving side end shaft 9. Thus, the torque tubes 1 having a small 
thickness are cooled by the heat exchanger 12 and the conduction heat 
entering into the low temperature portion through the torque tubes 1 is 
minimized. 
FIG. 2 shows the cross-section of the coil-carrying shaft 2 taken along the 
line II--II of FIG. 1. The portions of the field coils 3 running in the 
axial direction of the coil-carrying shaft 2 are fitted into the grooves 
17 formed on the surface of the coil-carrying shaft 2 corresponding 
thereto, electrically insulating layers 18 being interposed therebetween. 
The outer surfaces of the field coils 3 are covered by electrically 
insulating covers 20, and a plurality of wedges 19 are fitted into the 
recesses formed on the side surfaces of the grooves 17 above the portions 
thereof accommodating the field coils 3. Thus, the portions of the field 
coils 3 running in the axial direction of the coil-carrying shaft 2 are 
securely fitted into the grooves 17 and held in the proper positions 
thereof by the wedges 19. As the superconductive field coils 3 are wound 
around the line C--C of FIG. 2, a large magnetic field is established 
which has a polar axis corresponding to the line C--C. 
FIGS. 3 and 4 show a cross-section and a perspective view of an end portion 
of the coil-carrying shaft 2 respectively. The end portions of the field 
coils 3, i.e., the portions thereof running in the circumferential 
direction of the coil-carrying shaft 2, are disposed in the pair of 
annular indentations 17A which are formed at the end portions of the 
coil-carrying shaft 2 in the circumferential direction thereof. The 
electrically insulating layers 21 are interposed between the bottom 
surfaces of the indentations 17A and the end portions of the field coils 
3, and the spaces left by the field coils 3 in the indentations 17A are 
filled by the electrically insulating fillers 23 which are tightly fitted 
thereinto. The outer surfaces of the field coils 3 and the fillers 23 are 
covered by electrically insulating covers 22, and a coil-end keeper sleeve 
16 having the form of a hollow cylinder is fitted by a shrinkage fit 
method around the coil-carrying shaft 2 over each of the indentations 17A 
formed at the two end portions of the coil-carrying shaft 2. Thus, the end 
portions of the field coils 3 are also securely and reliably held in the 
proper positions thereof by the fillers 23 and sleeves 16. 
Referring now to FIG. 5 of the drawings, another mounting structure of the 
end portions of the field coils 3 is described. 
A pair of coil-end keeper sleeves 16 are shrinkage-fitted onto the 
coil-carrying shaft 2 of FIG. 5 at only one end thereof, i.e., the one end 
situated near the central portion of the coil-carrying shaft 2, and an 
annular inter-engagement ring 24 for preventing the slippage of each of 
the sleeves 16 with respect to the coil-carrying shaft 2 is fitted into an 
annular groove corresponding thereto in the outer and inner surfaces of 
the coil-carrying shaft 2 and each of the coil-end keeper sleeves 16 
respectively. The other end of each of the sleeves 16 situated near the 
torque tubes 1 is not shrinkage-fitted, beacause when both ends of the 
coil-end keeper sleeves 16 are shrinkage-fitted to the coil-carrying shaft 
2, the surfaces of the sleeve 16 at both ends thereof which are 
shrinkage-fitted are subjected to friction due to the vibrations of the 
coil-carrying shaft 2, and the heat generated by the friction causes 
fretting abrasion on the shrinkage-fitted surfaces. 
In the case of the mounting structure of the end portions of the field 
coils 3 of FIG. 5, electrical insulation is necessary between the 
superconductive field coils 3 and the inter-engagement rings 24 which are 
fitted around the coil-carrying shaft 2 over the whole circumference 
thereof. Thus, if the inter-engagement rings 24 for preventing the 
slippage of the sleeves 16 are disposed at the ends of the sleeves 16 
which are situated near the central portion of the coil-carrying shaft 2, 
then the inner diameter of the rings 24 cannot be made smaller than the 
diameter of the outer surfaces of the insulating covers 20 which are 
disposed on the axially running portions of the field coils 3 under the 
inter-engagement rings 24. The position of the rings 24, therefore, 
determines the thicknesses of the electrically insulating covers 22 and 
20, which should be made greater than are necessary for electrical 
insulation except for the portions thereof situated under the rings 24. 
Thus, the spaces occupied by the field coils 3 become smaller as compared 
to the dimension of the rotor, which results in larger dimensions of the 
superconductive rotary electric machines. 
FIG. 6 shows a portion of an end portion of another rotor according to the 
present invention. Each of the pair of sleeves 16 is shrinkage-fitted to 
the coil-carrying shaft 2 only at one end thereof which is situated near 
the torque tubes 1, an annular inter-engagement ring 24 being fitted into 
the annular groove corresponding thereto formed on the outer and inner 
surfaces of the coil-carrying shaft 2 and each of the sleeves 16, for the 
purpose of preventing slippage of the sleeves 16 with respect to the 
coil-carrying shaft 2. Other portions of the rotor of FIG. 6 are 
constructed similarly to that of FIG. 5, which in turn is constructed in 
the same way as that of FIGS. 1 through 4 except for the portions 
specifically described above. In the case of the mounting structure of 
FIG. 6, the rings 24 are situated outside the surface portion of the 
coil-carrying shaft on which the field coils 3 are disposed, so that the 
electrically insulating covers 20 and 22 can be made to have smaller 
thicknesses which is enough for electrical insulation.