Rotor cooling in rotary electric machines

A rotary electric machine including a stator in which a rotor is journalled. Coolant passages for a rotor winding are defined by the interstices between precision wound turns and winding layers to assure uniform distribution of coolant during operation to avoid mechanical balance problems and uniform cooling of components to assure long life.

FIELD OF THE INVENTION 
This invention relates to rotary electric machines, and more particularly, 
to the cooling of rotor windings in such machines to achieve high 
operational efficiencies. 
BACKGROUND ART 
Prior art of possible relevance includes the following U.S. Pat. Nos.: Cain 
3,049,633; Smith 3,743,867; Kullmann 4,037,124; Deis 4,037,312; and Hunt 
4,139,789. 
It has long been known that the efficiency of rotary electric machines can 
be increased by cooling the windings thereof. Generally, efforts at 
cooling have involved either the use of hollow electrical conductors which 
in turn serve as the conduits for the coolant or confining the windings in 
a passage and flowing the coolant through such passage such that it 
contacts the conductors in heat exchange relation. 
The former approach, while quite effective, is quite complex mechanically 
and hydraulically with the result that it is quite expensive and does not 
lend itself well to small, lightweight application such as generators 
utilized in aircraft. 
The latter approach also works well but as typically implemented, requires 
the use of mechanical spacers in the windings thereby complicating the 
construction and/or results in unequally sized fluid flow paths which 
encourage non-uniform heat transfer and create balance problems during 
operation of the machine where employed to cool rotor windings, 
particularly in high speed machines. 
The present invention is directed to overcoming one or more of the above 
problems. 
SUMMARY OF THE INVENTION 
It is the principal object of the invention to provide a new and improved 
means for cooling rotor windings in a rotary electric machine. More 
specifically, it is an object of the invention to provide a rotor winding 
cooling system that is simple in construction, provides for uniform heat 
transfer, and assures a balanced coolant distribution to avoid mechanical 
balance problems thereby suiting the rotor for use in a high speed rotary 
electric machine. 
An exemplary embodiment of the invention achieves the foregoing objects in 
a rotary electric machine including a stator having a rotor receiving 
opening. A rotor is journalled within the opening and includes a body of 
magnetizable material having at least two opposed axially extending slots. 
End turn supports are disposed on each end of the body and each has a 
radially extending, axially opening slot aligned with the slots in the 
body to define a continuous passage for the receipt of windings. At least 
one winding is disposed in the passage and is composed of a plurality of 
turns of an electrical conductor having a generally circular cross 
section. The turns of the winding are precision wound in a plurality of 
layers such that the interstices between the turns define uniformly sized 
axially extending coolant passages. Spacers are disposed in each of the 
slots in the end turn supports and spaced that turns of adjacent layers a 
sufficient distance to allow a coolant to enter into or exit from the 
coolant passages and means are provided for circulating a liquid coolant 
through the passages and the slots in the end turns supports for cooling 
purposes. 
Preferably, the turns are precision wound in a plurality of layers such 
that each successive turn in a given layer is parallel to and in 
substantial abutment with the preceding turn and the turns in each 
successive layer are generally parallel and generally in abutment with at 
least one turn in each of the preceding and succeeding layers within the 
body slots. 
In a highly preferred embodiment, the turns, when viewed in cross section 
define a honeycomb-like matrix. 
Coolant galleries are disposed in each end of the rotor adjacent the end 
turn supports and are in fluid communication with the associated slot in 
the corresponding end turn support. The circulating means interconnects 
the coolant galleries for circulating the coolant. 
Other objects and advantages will become apparent from the following 
specification taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An exemplary embodiment of a rotary electric machine is shown in the 
drawings and with reference to FIG. 1 is seen to be in the form of a 
so-called brushless generator. However, it is to be understood that the 
invention is not so limited, but could be applied to any rotary electric 
machine requiring rotor cooling. 
In the preferred embodiment, the generator is intended to operate at 24,000 
RPM and includes a two pole rotor as will become more fully apparent 
hereinafter. 
The generator includes a stator, generally designated 10 including a stator 
core 12 and stator windings, only the end turns 14 of which are shown. The 
core 12 includes a central opening 16 for receipt of a rotor, generally 
designated 18. The rotor 18 is journalled within the opening 16 by 
suitable bearings at opposite ends of the rotor, one such set of bearings 
being illustrated at 21. 
The rotor 18 includes a central body 20 formed of magnetic material. The 
body 20 is in turn flanked by end turn supports 22. The end turn supports 
22 are secured to respective end shafts 24 and 26 which axially journal 
the rotor 18 within the opening 16. An exterior can or cylindrical sleeve 
28 surrounds the body 20 and the end turn supports 22 as well as radially 
outer portions of the end shafts 24 and 26. 
As seen in FIGS. 1 and 2, the body 20 includes opposed, axially extending, 
radially outwardly opening slots having opposite edges shown at 30 and 32. 
Thus, that portion of the body 20 between the slot edges 30 and shown at 
34 in FIG. 2 forms one pole of the rotor while the opposite portion shown 
at 36 in FIG. 2 forms the remaining pole. 
Each of the end turn supports 22 includes a radially extending, axially 
opening slot 38 (FIGS. 1 and 2) and it will be appreciated from a 
consideration of FIGS. 1 and 2 that the slots 38 in the end turn supports 
22 along with the slot defined by the edges 30 and 32 define a continuous, 
closed loop passage for receipt of the rotor winding, generally designated 
40. 
As seen in FIGS. 3 and 4, the winding 40 is made up of a plurality of 
layers 42, 44, 46, 48, 50, 52 and 54. And as can be seen in FIG. 4, each 
of the layers 42-54 is made up of several turns. With relation to the 
layer 42, the turns are shown at 56, 58, 60, 62, 64, 66, 68, 70 and 72. 
The layers 44-54 have a similar number of turns. 
The entire winding 40 is made of any suitable electrical conductor having a 
generally circular cross-section provided, of course, with suitable 
insulation (not shown). The turns and the layers are precision wound in 
the passage. The term precision wound is intended in its usual sense and 
is opposed to random winding wherein no particular effort is made to 
assure that each successive turn be wound in a particular location. 
In the usual case, precision winding will dictate that each successive turn 
in a given layer is parallel to and in substantial abutment with the 
preceding turn and that the turns in each successive layer are parallel to 
and in abutment with at least one turn in the preceding layer. Generally 
speaking, in order to maximize the number of turns that may be received in 
a slot of given cross section, it is desirable that the turns of each 
successive layer additionally are in abutment with two turns in both the 
preceding and the succeeding layer to define a honeycomb-like matrix of 
conductors as is illustrated somewhat fragmentarily in FIG. 5. 
As can be seen in that Figure, the precision winding results in a plurality 
of interstices 74 between each triangular array of three conductors whrch 
are uniform in size. Such interstices 74 define coolant passages for a 
cooling fluid to cool the winding 40. In other words, precision winding 
results in interstices between the various turns defining uniformly sized 
coolant passages. 
As can be appreciated from a consideration of FIGS. 1 and 5, the coolant 
passages defined by the interstices 74 extend axially of the rotor body 
20. It will also be appreciated that due to the contact between adjacent 
conductors or turns, means must be provided whereby coolant can achieve 
access to or egress from the interstices 74. 
Referring now to FIGS. 3 and 4, this is achieved through the use of spacers 
76 disposed between each of the layers 42-54 at the end turns of the 
winding, namely, those portions of the winding that extend radially within 
the slot 38 in each of the end turn supports 22. The spacers 76 are shown 
in somewhat exaggerated form in the drawings but their size only need be 
sufficient to space the turns of adjacent ones of the layers a sufficient 
distance to allow coolant to enter into or exit from the interstices 74 of 
the axially extending portion of the winding. 
Returning to FIG. 1, the end shaft 26 adjacent the left-most end turn 
support 22 includes an interior gallery 80 which is in fluid communication 
with the radially inner portion of the associated slot 38 between upper 
and lower sets 82 and 84 of the winding 40. Reliefs such as shown at 86 in 
FIG. 2 extending axially inwardly from the layer 42 to the layer 54 assure 
that fluid communication from the interstices 74 through the spaced end 
turns of the winding to the gallery 80 is provided. 
A similar gallery, generally designated 90 is provided adjacent the 
right-hand end turn supports 22 and by similar means is in fluid 
communication with the interstices 74 at that axial end of the winding. 
The gallery 90 may include other components including, for example, a 
centrifugal filter 92 and various means including an air vent passage 94 
which forms no part of the present invention. 
A pump 96 is connected by a conduit 98 to a transfer tube 100 to the 
gallery 90. A conduit 102 suitably connected to the interior of the end 
shaft 26 and thus in fluid communication with the gallery 80 via a bore 
104 is connected to an air/oil separator 104 which in turn is connected to 
the pump 96. Thus, the pump 96 is operative to circulate a coolant, 
typically oil, to the gallery 90, through the slots 38 in the rightmost 
end turn support 22 to the interstices 74. The coolant, after cooling the 
winding, will emerge from the interstices 74 within the leftmost end turn 
support 22 to flow to the gallery 80 where it will be returned to the pump 
96. Typically, a suitable heat exchanger (not shown) will be included in 
the circuit. 
The winding 40 is maintained in the slots defined by the edges 30 and 32 in 
the body 20 by conventional wedges 106 and the entire interior of the 
rotor, specifically, the rotor body 20 is sealed by the can 28 to prevent 
leakage of oil to the air gap between the rotor 18 and the stator 10. 
From the foregoing, it will be appreciated that a rotor construction made 
according to the invention is ideally suited for lightweight high speed 
applications such as aircraft generators. The system is simple in 
construction, avoiding the need for hollow conductors serving as coolant 
conduits. Importantly, the use of a precision wound winding assures that 
the interstices 74 forming the coolant passages are uniformly sized in 
cross section to provide two distinct advantages. The first advantage is 
that of assurance of uniform distribution of the coolant throughout the 
rotor to avoid mechanical balance problems particularly when the machine 
is operating at high speed. The second advantage is that uniform cooling 
is achieved since the flow rate through each of the interstices 74 will be 
substantially equal, thereby preventing undesirable hot spots from 
developing.