Abstract:
A new improved system and method for end turn retention for wires on a generator rotor for use in high speed applications such as in aircraft applications. The rotor includes a shaft, spokes, supports, and wire winding coils, and at least one cap device. The spokes extend radially outwardly from the shaft, and each support is positioned on an associated spoke. Each coil wraps around an associated support and spoke. Each cap device is coupled to an end of its associated spoke to prevent the windings from moving radially outwardly while the rotor spins. Each support is coupled to an associated cap device, and includes at its radially inward edge a flange protruding away from the respective spoke. Because of the flange and the cap device, slack of the wire coil between the flange and the associated cap is taken up.

Description:
FIELD OF THE INVENTION 
     The present invention relates to high speed generators and, more particularly, to systems and methods for fastening wire coils to the rotors of such generators. 
     BACKGROUND OF THE INVENTION 
     Generator systems that are installed in aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, electrical aircraft systems. 
     Because the generators installed in aircraft will often be variable frequency generators that rotate in the speed range of 12,000 rpm to 24,000 rpm, large centrifugal forces are imposed upon the rotors of the generators. Given these stressful operating conditions, the rotors of the generators should be carefully designed and manufactured, both so that the rotors are reliable and also so that the rotors are precisely balanced. Improper balancing in particular can result not only in inefficiencies in the operation of the generators, but also in a risk of failure of the generators. 
     Among the important components in rotors that should be carefully designed and manufactured in order to guarantee robustness and proper balancing of the rotors are the wire coils of the rotors. The centrifugal forces experienced by the rotors are sufficiently strong as to cause bending of the wires of these coils, which over time can result in mechanical breakdown of the wires. Additionally, because the coils are assemblies of individual wires that can move to some extent with respect to one another and with respect to the remaining portions of the rotors, the coils constitute one of the significant potential sources of imbalance within the rotors. The stresses and movement experienced by the wire coils are particularly problematic at the end turns of the coils, at which wires loop from first directions to second directions on the poles supporting the wires. 
     In order to guarantee robust wire coils and to minimize the amount of imbalance in the rotors that occurs due to the wire coils, the process of initially wrapping the wires of the coils onto the rotors is typically a time-intensive, expensive task. To keep the wrapped coils to within specified tolerances, complicated tooling equipment and an involved process of utilizing shims to guarantee sufficient internal pressure among the wires of the coil are required. Often, the wrapping process involves a significant amount of trial and error before all of the multiple coils on a multi-pole generator are properly configured to have the desired balancing and other characteristics. The difficulty of the wrapping process is greatest at the end turns of the coil wires. 
     Hence, there is a need for a new system and method for supporting and retaining the wire coils in rotors, particularly at the end turns of the coils. There further is a need for a system and method for end turn retention in which the coil wires at the end turns are positioned accurately and held reliably in position. There additionally is a need for such a system and method whereby the wrapping process is made simpler, more accurate and repetitive, and more cost-effective. 
     SUMMARY OF THE INVENTION 
     The present inventors have recognized that end turn supports employed on rotors can be designed to include flanges that provide support to the end turns to limit movement of the wires radially inward. By coupling these supports to end cap hats that limit movement of the wires radially outward, pressure is generated upon the wires in between the flanges and the end cap hats causing the wires to become packed and thereby more robust. At the same time, the coupling of the supports to the end cap hats forces the wires into precise desired locations, thereby improving rotor balance and robustness and simplifying the wrapping process. 
     In particular, the present invention relates to a rotor for use in a high speed generator, where the rotor includes a shaft extending axially through the rotor, a plurality of spokes extending radially from a location along the shaft and a plurality of supports, where each one of the supports is positioned proximate a respective one of the spokes. The rotor further includes a plurality of coils of wire windings, each wrapped around a respective one of the supports and a respective one of the spokes, and at least one cap device coupled to ends of the spokes away from the shaft. The at least one cap device prevents the wire windings of the coils from moving outward away from the shaft beyond outer radial limits. Each support is coupled to the at least one cap device, and each support extends radially inward along its respective spoke from the at least one cap device to at least a respective inner limit. Each support includes at its respective inner limit a respective flange protruding away from the respective spoke, and each flange prevents the wire windings of the respective coil from moving beyond the respective inner limit towards the shaft. 
     The present invention further relates to a support for implementation on a spoke extending outward radially from a shaft of a rotor. The support includes a U-shaped main portion having an outer face and an inner face, where the support is configured so that the inner face of the support is in physical contact with the spoke when the support is supported thereby, and where the support is further configured to support a wire coil that is wrapped around the support along the outer face. The support further includes first and second sides of the U-shaped main portion that are substantially transverse with respect to the outer and inner faces and also with respect to a channel along the inner face through the U-shaped main portion, the channel being configured to receive the spoke. The support additionally includes a flange proximate the first side of the U-shaped main portion and extending outward away from the channel beyond the outer face. The support is configured to be positioned on the spoke so that the first side is closer to the shaft than the second side, and is additionally configured to allow for coupling of the support to a cap hat. 
     The present invention additionally relates to a generator including a stator and a rotor that is rotatably coupled within the stator. The rotor includes a shaft extending axially through the rotor, a plurality of appendages extending radially outward from the shaft, and a plurality of wire coils that are supported away from the shaft by the plurality of appendages. The rotor further includes a first means for preventing outward radial movement of wires of the wire coils beyond respective outer limits, and a second means for preventing inward radial movement of wires of the wire coils beyond respective inner limits. At least one of the first means and second means is secured to the plurality of appendages and, when only one of the first means and second means is secured to the plurality of appendages, the remaining other means is further secured to that one of the first and second means that is secured to the appendages. 
     The present invention further relates to an end cap device for implementation in a rotor including an appendage extending outward radially from a shaft of the rotor and further including a support positioned on the appendage, wherein the support is capable of supporting end turns of a wire coil of the rotor and includes a flange at an inner radial position that limits movement of the end turns radially inward toward the shaft. The end cap device includes a physical barrier, a first fastening element by which the end cap device is coupled to the appendage, and a second fastening element by which the end cap device is coupled to the support. 
     The present invention additionally relates to a method of retaining wires of a coil within a desired radial region relative to a shaft of a rotor. The method includes positioning at least one of a support and an additional element on a first appendage extending radially from the shaft, where the at least one support and additional element includes a flange. The method additionally includes wrapping the wires of the coil onto the support, and providing a cap hat proximate an outer end of the first appendage away from the shaft. The method further includes attaching at least one of the cap hat and the support to the first appendage and, if only one of the cap hat and the support is attached to the first appendage, further attaching the cap hat and the support to one another. The flange extends away from the first appendage and prevents movement of the wires of the coil toward the shaft beyond an inner limit, and the cap hat prevents movement of the wires away from the shaft beyond an outer limit. 
    
    
     Other features and advantages of the high speed generator will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of several components of an exemplary rotor, on which can be employed the present invention; 
     FIG. 2 is a perspective view of the rotor of FIG. 1 on which have been placed additional components, including supports for end turns of wires of coils of the rotor in accordance with one embodiment of the present invention; 
     FIG. 3 is a perspective view of an end portion the rotor of FIGS. 1 and 2, in which still additional components have been added; 
     FIG. 4 is a perspective view of one of the supports employed in the rotor shown in FIGS. 2 and 3; 
     FIG. 5 is an elevation view, shown in cut-away, of a shaft and a spoke of the rotor of FIGS. 1-3, along with one of the supports shown in FIGS. 2-4 and an end cap hat; 
     FIGS. 6 and 7 are elevation views, shown in cut-away, of various embodiments of shafts and spokes of the rotor of FIGS. 1-3, in combination with alternate embodiments of supports and other structures employed to support and retain end turns of wire coil windings; 
     FIG. 8 is a perspective view of the rotor of FIGS. 1-3 in its completely-assembled form; and 
     FIG. 9 is a perspective view of a generator in which the embodiments of the rotor and rotor components shown in FIGS. 1-8 can be employed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, components of an exemplary rotor  100  on which the present invention can be employed include a shaft  110  extending axially through the rotor, four poles  120   a-d  that extend radially away from the shaft  110 , and four spokes  130   a-d  that extend radially away from the shaft  110  at a hub location  140 . The spokes  130   a-d  are radially aligned with, and coupled to, end faces  125   a-d  of the poles  120   a-d,  respectively. As discussed further below, each of the spokes  130   a-d  respectively includes one or more threaded holes  135   a-d  (only holes  135   a  are shown in FIG.  1 ). The rotor  100  presently shown is designed for implementation in high speed generators such as those commonly employed in aircraft. Consequently, the components of the rotor  100  are typically manufactured from high-strength materials. For example, the poles  120   a-d  can be formed from steel, while the shaft  110  and the spokes  130   a-d  can be formed from steel, titanium or high-strength aluminum. It will be appreciated, however, that these materials are only exemplary of a preferred embodiment and that other suitable materials can be employed. 
     Turning to FIG. 2, the rotor  100  of FIG. 1 is shown with additional components. In particular, the rotor  100  further includes wire coils  150   a-c  that are wrapped around respective poles  120   a-c.  The wire coils  150   a-c  typically are made up of hundreds of individual wire loopings around the respective poles  120   a-c.  As shown, the wire coils  150   a-c  loop around the respective spokes  130   a-c  as they loop around the poles  120   a-c.  The portions of the wire coils  150   a-c  that loop around the spokes  130   a-c  are referred to as the end turns  160   a-c  of the wire coils. A fourth wire coil  150   d  having end turns  160   d  is not shown in FIG. 2, although such a coil would be wrapped around the pole  120   d  in a completely-assembled rotor. 
     In order to provide proper support, alignment and retention of the end turns  160   a-d  as they curve around the spokes  130   a-d,  supports  170   a-d  are provided that overlay the respective spokes  130   a-d  and provide support for the end turns  160   a-d.  The end turns  160   d  are not shown in FIG. 2 in order to provide a clearer view of the support  170   d.  As shown, the support  170   d  surrounds the corresponding spoke  130   d  on three of its sides. The support  170   d  has an outer edge  180  that forms a contiguous extension of one of the sides of the pole  120   d  and curves around the spoke  130   d  until it reaches and contiguously joins the opposite side of the pole. Similar to the spokes  130   a-d,  each of the supports  170   a-d  includes one or more threaded holes  175   a-d  (only holes  175   a  are shown), which are discussed further below. 
     Referring to FIG. 3, an end portion of the rotor  100  of FIGS. 1 and 2 is shown with several additional components included. In particular, end turns  160   d  of a fourth wire coil  150   d  are now shown to be wrapped around the support  170   d,  which is positioned about the fourth spoke  130   d.  Thus, each of the poles  120   a-d  now includes its respective wire coil  150   a-d  and in particular includes its respective end turns  160   a-d  wrapped around its respective support  170   a-d  and thus around its respective spoke  130   a-d.    
     In addition, the rotor  100  of FIG. 3 includes an end cap hat  190   a  associated with the pole  120   a.  As shown, the end cap hat  190   a  is a flange or wall having a trapezoidal cross section, and can be made of the same high-strength material as the spokes  130   a-d  (e.g., high-strength aluminum). It is termed an end cap hat because it also interfaces with an end cap (not shown), which is placed over the entire end of the rotor  100  upon completion of its assembly. In alternate embodiments, the end cap hat need not directly interface with an end cap, and can be a flange or wall of any one of a variety of shapes. As shown, the end cap hat  190   a  includes a first set of bolt holes  210   a,b  and a second set of bolt holes  220   a,b.  The first set of bolt holes  210   a,b  are configured to receive bolts (see FIG. 5) to secure the end cap hat  190   a  to the spoke  130   a  (see FIG.  2 ). The second set of bolt holes  220   a,b  are configured to receive bolts (see FIG. 4) that secure the support  170   a  and the end cap hat  190   a  together. As noted above, both the spoke  130   a  and the support  170   a  have corresponding threaded holes  135   a  and  175   a,  respectively. These corresponding holes  135   a  and  175   a  are configured to receive the first set of bolts  210   a,b  and the second set of bolts  220   a,b,  respectively. As a result, the end cap hat  190  is coupled both to the spoke  130   a  and the support  170   a.  Correspondingly, each of the other spokes  130   b-d  and supports  170   b-d  can be coupled in similar fashion to corresponding end cap hats (not shown). 
     The end cap hat  190   a  and other end cap hats corresponding to the other poles  120   b-d  serve the purpose of preventing movement of the wires of the coils  150   a-d  during rotation of the rotor  100 . This in turn helps to protect the rotor coil wires from damage due to bending and mechanical stress during high speed operation of the rotor  100 , maximizes the bending critical speed of the rotor, and helps to maintain the overall balance of the motor. As shown, once the coils  150   a-d  are wrapped onto the poles  120   a-d,  filler elements or wedges  230   a-d  (wedge  230   c  not being shown due to the presence of the shaft  110 ) are added in order to provide additional support to the windings of the coils  150   a-d  and for other purposes (e.g., to reduce the effects of air resistance upon the rotation of the rotor  100  during operation). 
     Referring to FIG. 4, a perspective view of the support  170   a  of FIGS. 2 and 3 is provided to show additional detail of the support. In accordance with a preferred embodiment of the invention, the support  170   a  is an approximately u-shaped component (actually u-shaped when viewed upside down) with first and second ends  240   a,    240   b  that are configured to rest upon the pole  120   a  of the rotor  100  when the support is installed. The ends  240   a,    240   b  are on opposite sides of a channel  250 , through which is positioned the spoke  130   a  when the support  170   a  is installed onto the rotor  100 . 
     Further as shown, the support  170   a  has an outer perimeter or face  260  and an inner perimeter or face  270 . The outer face  260  is, at the ends  240   a  and  240   b,  contiguous with the pole  120   a  when the support  170   a  is installed. The outer face  260 , in between the ends  240   a  and  240   b,  is a generally u-shaped, smoothly-transitioning surface around the outside of the support  170   a  across which the wires of the coil  150   a  can be wrapped. The inner face  270  also is a generally u-shaped surface that proceeds from end  240   a  to end  240   b.  In general, the inner face  270  is configured to physically contact the spoke  130   a  when the support  170   a  is installed on the rotor  100 . In alternate embodiments, neither the spoke  130   a  nor the inner face  270  need have a general u-shape, and also the amount of physical contact between the support and the spoke when the support is installed can vary. Generally, however, the channel  250  of the support  170   a  is designed to be in contact with the spoke  130   a  so that the spoke limits movement of the support, at least with respect to directions that are transverse both to the spoke and the shaft  110 . 
     In accordance with the preferred embodiment of the invention, the support  170   a  includes a lip or flange  280  at or proximate to a first side  290  that is opposite a second side  310 . The second side  310  abuts the end cap hat  190   a  when the support  170   a  and the end cap hat  190   a  are installed on the rotor  100  (see FIG.  5 ). The flange  280  extends beyond the outer face  260  by a distance  320 , which typically will be a distance equaling or greater than the thickness of the coil  150   a  when it is wrapped around the support  170   a.  In the present embodiment, the flange  280  extends beyond the outer face  260  in all directions around the outer face. That is, an outer edge  330  of the flange  280  also takes on a general u-shape. Thus, when the support  170   a  is installed on the rotor  100  over the spoke  130   a,  the flange  280  can be said to extend outward away from the spoke. In alternate embodiments, the flange  280  need not extend beyond the outer face  260  continuously in all directions, but need only extend beyond the outer face  260  at one or more distinct regions (that is, the outer edge  330  need not have a continuous u-shape). 
     Turning to FIG. 5, an elevation view is provided (shown in cut away) of the shaft (including the hub  140 ), the spoke  130   a,  the support  170   a,  and the end cap hat  190   a  when the support  170   a  and the end cap hat  190   a  are installed onto the spoke  130   a.  Both the flange  280  and an outward protrusion portion  355  of the end cap hat  190   a  extend outward away from the spoke  130   a  beyond the outer face  260  of the support  170   a.  Consequently, a trench  340  is created in between the flange  280  and the end cap hat  190   a.  It is within the trench  340  that the end turns  160   a  of the coil  150   a  can be wrapped, and it is due to the outward protrusion  355  of the end cap hat  190   a  and the outer face  260  and the flange  280  of the support  170   a  that the end turns are prevented from moving during rotation of the rotor  100 . 
     It is particularly due to the structure of the support  170   a,  including the flange  280 , that the end turns  160   a  are retained strongly within the trench  340 . As shown, inner bolts  350  fit within bolt holes  210   a,b  of the end cap hat  190   a  and corresponding holes  135   a  of the spoke  130   a  (see FIG.  3 ), and are used to affix the end cap hat  190   a  to the spoke  130   a.  Further, outer bolts  360  fit within bolt holes  220   a,b  (see FIG. 3) and corresponding bolt holes  175   a  (see FIG.  4 ), and are employed to affix the support  170   a  to the end cap hat  190   a,  thereby locking the support  170   a  also with respect to the spoke  130   a.    
     Given that the support  170   a  includes the flange  280 , this configuration allows for pressure to be applied in a predictable manner to the windings of the coil  150   a  and for more precise positioning of the wire windings. Typically, the process for assembling a coil (such as the coil  150   a ) on the rotor  100  includes (a) positioning the support  170   a  onto the spoke  130   a,  (b) wrapping the wire windings of the coil  150   a  onto the pole  120   a,  including the support, (c) affixing the end cap hat  190   a  to the spoke  130   a  using the inner bolts  350 , and then (d) affixing the support  170   a  to the end cap hat  190   a  by tightening the outer bolts  360 . Thus, after the wires are wrapped onto the pole  120   a,  they are forced into a precisely determined position between inner and outer limits  362  and  364 , respectively, through the tightening of the support  170   a  against the end cap hat  190   a,  and pressure is also created among the wires within the trench  340  between the flange  280  and the outward protrusion  355  of the end cap hat  190   a.  In particular, sufficient pressure is created to take all (or almost all) slack out of the coil  150   a.  In certain embodiments, the appropriate amount of tightening of the support  170   a  against the end cap hat  190   a  (sufficient to take the slack out of the coil  150   a ) can be provided by tightening up the bolts  360  to their design torque. 
     Referring to FIGS. 6 and 7, a variety of alternate embodiments of structures for supporting and retaining the end turns of the coils can also be employed on the rotor  100 . For example, in FIG. 6, two alternate embodiments are shown in which a support  170   e  is directly coupled to a spoke  130   e  by way of bolts  380 . The support  170   e  otherwise has the same features as the support  170   a,  including the flange  280 . In order to properly position and affix an end cap hat  190   e  with respect to the spoke  130   e  and the support  170   e,  either bolts  390  can be used to affix the end cap hat directly to the support, or bolts  410  can be employed to affix the end cap hat directly to the spoke. In the latter embodiment, the spoke  130   e  should be extended to fit through a channel  420  through the end cap hat  190   e  so that the bolts  410  can be attached to the spoke. This latter embodiment in which both the support  170   e  and the end cap hat  190   e  are both affixed directly to the spoke  130   e  is less desirable than the other embodiment insofar as no pressure is directly created between the support and the end cap hat. 
     With respect to FIG. 7, another embodiment is provided in which a support  170   f  no longer includes the flange  280 . Instead, when the support  170   f  is installed on a spoke  130   f  by way of a bolt  430 , an end cap hat  190   f  is affixed to the spoke and further a L-type bracket  440  is then affixed to the end cap hat so that the bracket  440  passes above the support and then curves downward to be secured relative to the spoke. The bracket  440  can be attached to the end cap hat  190   f  by way of a bolt  450 . Depending upon the embodiment, the bracket  440  can be secured relative to the spoke  130   f  in any of a number of ways, including by way of bolts or, as shown, by including a toe  460  that fits inside a corresponding recess within the support  170   f.  Using the embodiment of FIG. 7, the wire windings of the coil supported by the support  170   f  pass within a region  470  between the bracket  440  and the support  170   f.  Due to the force applied by the bolt  450  coupling the bracket  440  to the end cap hat  190   f,  pressure again is created among the windings of the coil and the end turns of the coil further are restrained from movement towards or away from the shaft  110  beyond inner and outer limits  480 ,  490  created by the bracket  440  and the end cap hat  190   f.  Because the bracket  440  surrounds the coil and the opposite side of the support  170   f,  in this embodiment, the bracket  440  should be capable of easily conducting (or removing) heat being dissipated by the wire windings. 
     Referring to FIG. 8, the rotor  100  is shown in a completely-assembled form. In particular, the rotor  100  includes, in addition to the poles  120   a-c  (pole  120   d  being hidden from view) and the shaft  110 , end caps  495  at either end of the rotor. Lips  498  of the end caps  495  extend over and around the end cap hats  190   a-d  discussed above. 
     Further referring to FIG. 9, the rotor  100  (including the shaft  110 ) is shown incorporated within a complete generator  500  that also includes a stator  510  surrounding the rotor  100 . The rotor  100  employed within the generator  500  can employ any of the structures discussed above for supporting and retaining the wires of the coils of the rotor, as well as other embodiments of such structures. In addition, rotors similar to rotor  100  with structures similar to those discussed above for supporting and retaining coils can be employed within the generator  500 , including rotors having fewer or more poles than the four poles  120   a-d  shown in FIGS. 1-3 (e.g., six poles). Additionally, while the generator  500  shown in FIG. 8 is the main generator of a generator set (typically used on airplanes) that includes additionally an exciter and a permanent magnet generator (PMG), the generator can in alternate embodiments be an exciter or a PMG. 
     In the case where the generator  500  is the main generator, the coils of the rotor  100  are provided with direct current, while coils (not shown) of the stator  510  conduct alternating current during operation of the generator. However, rotors with structures for supporting and retaining coils that are similar to those discussed above can be employed in other types of machines, on which a variety of different alternating currents and direct currents are employed on the rotor. In particular, such machines can include other types of synchronous, induction-type and DC-type generators and motors. 
     Also, in alternate embodiments, the spokes and poles emanating radially away from the shaft of the rotor can take a variety of different forms such that the manner in which the supports and/or end cap hats are secured at specific radial positions away from the central shaft can vary. For example, appendages coupling the supports and end cap hats to the shaft can take a form other than the spokes  130 . Further, the manner in which the supports and end cap hats are coupled to one another and to the spokes or appendages can vary from the use of bolts as shown. For example, in alternate embodiments, other fastening devices known in the art including glue or welding can be employed. Additionally, the supports and end cap hats can take a variety of different shapes, only some of which are described herein. For example, the individual end cap hats  190   a-d  used with respect to spokes  130   a-d,  respectively, can be replaced with a simple end cap hat ring that extends around the entire circumference of the rotor and caps the ends of all of the spokes of the rotor. Further, end cap hats that cap the ends of more than one spoke but not all of the spokes (e.g., two spokes) can also be employed. 
     Thus, while the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt the teachings of the invention to a particular situation without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.