Abstract:
A hybrid electrical machine having a permanent magnetic rotor field in addition to an electrically excited rotor field is disclosed. The generator rotor ( 220 ) has two opposing claw segments ( 226, 228 ) mounted at opposite ends of a rotor shaft ( 222 ). A third, center claw segment ( 232 ) is mounted on the rotor shaft between the first and second claw segments. A first wound field coil ( 224 ) is mounted on the rotor shaft between the first and third claw segments, and a second wound field coil ( 234 ) is mounted between the second and third claw segments. One or more permanent magnets ( 230, 231 ) may be provided about the periphery of the first, second, and/or third claw segments.

Description:
BACKGROUND OF THE INVENTION 
     1. The Technical Field 
     The invention relates generally to electrical machines, such as motors and generators, and, more particularly, to electrical machines having hybrid rotors, i.e., both electric and permanent magnet excitation. 
     2. The Prior Art 
     Lundell-type electrical machines are well-known in the art. For example, Lundell-type electrical generators have long been used in the automotive industry to provide electrical power for automobiles and trucks. Due to consumer demand for power consuming convenience and luxury items, such as high-powered sound systems, power windows, and the like, as well as the need for the complicated control systems required to meet government emission and safety standards, electrical demands on modern automobiles have increased substantially over the years. Although the output of a conventional Lundell-type generator can be increased to meet the increased electrical demand, the additional electrical output comes at the expense of additional size and weight. Since underhood space on modern automobiles is limited, the use of a physically larger generator to meet a vehicle&#39;s increased electrical demands might not be an acceptable design solution in some cases. Further, as vehicle weight increases, fuel economy and performance decrease. 
     An electrical generator&#39;s output can be increased without a proportional increase in size and weight by using a permanent magnetic field to supplement the conventional electrically-generated rotor field. U.S. Pat. Nos. 4,959,577 and 5,483,116 disclose hybrid Lundell-type generators having a plurality of discrete permanent magnet segments located between the interleaved fingers of the rotor claw segments. However, the designs disclosed by the foregoing references involve complicated arrangements of magnets and magnet holders, thus making the generator difficult to assemble. 
     It would be desirable to provide an electrical generator which provides high specific output, using proven design principles, in a relatively lightweight, compact, easy-to-assemble package. 
     SUMMARY OF THE INVENTION 
     The invention is a hybrid Lundell-type electrical machine characterized by a rotor whose magnetic field is established using one or more conventional field coils and one or more permanent magnets. 
     A conventional Lundell-type generator rotor includes a bobbin-wound field coil mounted on a rotor shaft to generate a magnetic field. The magnetic field flux is transferred through two claw-type rotor segments forming the north and south poles, respectively, of the magnet thus-created. The magnetized rotor assembly spins inside a stator having a number of windings which are “cut” by the magnetized rotor&#39;s flux lines so as to induce an electrical current in the stator windings. 
     The output of a Lundell-type generator is a function of the rotor magnetization, among other parameters. Rotor magnetization is a function of the magnetic field strength in the rotor, which, in turn, is a function of the field coil excitation current. That is, by increasing the field coil excitation current, and thereby increasing the induced magnetic field strength in the claw segments, the rotor magnetization can be increased. However, the magnetization of the claw segments can be increased only up to a certain level, based on the size and material composition of the claw segments, beyond which the claw segments become magnetically saturated. Once the claw segments become saturated, their magnetization does not continue to increase with increased magnetic field strength. Therefore, as a practical matter, the maximum rotor magnetization in a conventional Lundell-type generator is a function of the rotor&#39;s size and, more particularly, the claw segments&#39; size. 
     Permanent magnets can be used in lieu of a field coil to magnetize a generator rotor, and they can provide greater rotor magnetization than a field coil of comparable size. However, the output voltage of a generator using only a permanent magnet to establish rotor magnetization is not easily controlled. 
     The present invention is directed to a hybrid electrical machine whose rotor magnetization is established using a combination of one or more electrically excitable field coils and one or more permanent magnets; the remainder of the machine may be conventional. The permanent magnet provides a base level of rotor magnetization. The rotor&#39;s magnetization can be increased above the base level of magnetization provided by the permanent magnet, subject to the limitations discussed above, by electrically exciting the field coil. Since a permanent magnet of a given size can effect a greater level of rotor magnetization than a field coil/claw segment assembly of the same size, a hybrid rotor according to the present invention can achieve a higher level of magnetization than a conventional rotor of the same size. Alternatively, a hybrid rotor according to the present invention having a predetermined level of magnetization can be smaller and lighter than a conventional Lundell-type generator rotor having the same level of magnetization. 
     A first embodiment of a hybrid rotor according to the present invention comprises an otherwise conventional Lundell-type generator rotor (i.e., a rotor shaft having a field coil and two claw segments, each claw segment having a plurality of axially-extending fingers) having one or more radially-magnetized permanent magnets located about the periphery of each of the claw segments. In a preferred embodiment, a ring magnet is provided for each claw segment (i.e. each hybrid rotor includes two ring magnets). In an alternate first embodiment, a plurality of discrete magnets may be used in place of one or both of such ring magnets. In any case, the magnet or magnets associated with each claw segment have a number of magnetic poles equal to twice the number of fingers associated with the respective claw segment. 
     In a second embodiment of the invention, the hybrid rotor includes first and second claw segments mounted on a shaft, as would a conventional Lundell-type generator rotor. The rotor further includes a third claw segment located between the first and second claw segments. The third claw segment has fingers extending axially in both directions, towards both the first and second claw segments, such that the fingers of the third claw segment are interleaved with the fingers of the first and second claw segments. A first field coil is located between the first and third claw segments and a second field coil is located between the second and third claw segments. One or more permanents magnets are located about the periphery of the first and second claw segments, in the same manner as discussed above for the first embodiment. In an alternate second embodiment, one or more permanent magnets are located about the periphery of the third claw segment, but not the first and second claw segments. In another alternate second embodiment, one or more permanent magnets are located about the periphery of the first, second, and third claw segments. 
     In a third embodiment of the invention, the hybrid rotor includes first and second claw segments mounted on a non-magnetic shaft. The rotor further includes a third claw segment located between the first and second claw segments. The third claw segment has fingers extending axially in both directions, towards both the first and second claw segments, such that the fingers of the third claw segment are interleaved with the fingers of the first and second claw segments. A first field coil is located between the first and third claw segments, and an axially-magnetized permanent magnet comprising a ring magnet or a plurality of discrete magnets is located between the second and third claw segments. In an alternate third embodiment, one or more radially-magnetized permanent magnets also may be located about the periphery of the first, second, and/or third claw segments. 
     This application is being filed contemporaneously with related U.S. patent application Ser. No. 09/650,334 entitled “Hybrid Electrical Machine with Axial Flux Magnet,” and related U.S. patent application Ser. No. 09/649,306 entitled “Hybrid Electrical Machine with Axially Extending Magnets,” both of which are owned by common assignee Delphi Technologies, Inc. 
     Additional advantages and features of the present invention will become apparent from the reading of the attached description and the following set of drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a conventional prior art Lundell-type generator rotor; 
     FIG. 2 is a perspective view of a first embodiment of a hybrid generator rotor according to the present invention; 
     FIG. 3 is a perspective view of a second embodiment of a hybrid generator rotor according to the present invention; 
     FIG. 3 a  is a perspective view of a variation of the second embodiment of a hybrid generator rotor according to the present invention; 
     FIG. 4 is a perspective view of a variation of a second embodiment of a hybrid generator rotor according to the present invention; 
     FIG. 5 is a perspective view of another variation of a second embodiment of a hybrid generator rotor according to the present invention; 
     FIG. 6 is a perspective view of a further variation of a second embodiment of a hybrid generator rotor according to the present invention; 
     FIG. 7 is a perspective view of a third embodiment of a hybrid generator rotor according to the present invention; and 
     FIG. 7 a  is a perspective view of a variation of the third embodiment of a hybrid generator rotor according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a conventional Lundell-type generator rotor  20 . Rotor  20  comprises a shaft  22 , a field coil  24 , a first claw segment  26 , and a second claw segment  28 . Field coil  24  is mounted on shaft  22  between first and second claw segments  26  and  28 , respectively. 
     FIG. 2 illustrates a first preferred embodiment of a hybrid generator rotor according to the present invention. Hybrid rotor  120  comprises a shaft  122 , a field coil  124 , a first claw segment  126  and a second claw segment  128 . Field coil  124  is located on shaft  122  between first and second claw segments  126  and  128 . Each of first and second claw segments  126  and  128  includes a plurality of axially extending fingers  126 ′ and  128 ′. Fingers  126 ′ of first claw segment  126  are interleaved with fingers  128 ′ of second claw segment  128 , so as to substantially encapsulate field coil  124 . Each of first and second claw segments  126  and  128  also includes an axially-extending shelf  127  and  129 , respectively, which acts as a support and magnetic backiron for one or more permanent magnets. In a preferred embodiment, a radially-magnetized ring magnet having a number of poles equal to twice the number of claw fingers  126 ′ or  128 ′ on claw segments  126  and  128 , respectively, is mounted on each shelf  127  and  129 . In other embodiments, either or each of ring magnets  130  may be replaced with a plurality of radially-magnetized discrete magnets, such as a plurality of bar magnets (see FIG.  3 A). In any case, the ring magnet  130  or the plurality of bar magnets (see FIG. 3A) associated with each claw segment  126 ,  128  has a number of magnetic poles equal to twice the number of fingers associated with the respective claw segment  126 ,  128 . 
     FIG. 3 illustrates a second embodiment of a hybrid generator rotor according to the present invention. Hybrid rotor  220  comprises a shaft  222 , a first claw segment  226 , and a second claw segment  228 . Hybrid rotor  220  further includes a third claw segment  232  which is located between first and second claw segments  226  and  228 . First claw segment  226  has a plurality of axially-extending fingers  226 ′ and second claw segment  228  also has a plurality of axially-extending fingers  228 ′. Third claw pole segment  232  has a first plurality of axially-extending fingers  232 ′ and a second plurality of axially-extending fingers  232 ″. A first field coil  224  is located between first claw pole segment  226  and third claw pole segment  232 , such that first field coil  224  is substantially encapsulated by claw fingers  226 ′ and  232 ′. A second field coil  234  is located between second and third claw pole segments  228  and  232 , such that second field coil  234  is substantially encapsulated by claw fingers  228 ′ 0  and  232 ″. 
     Each of first and second claw segments  226  and  228  also includes an axially-extending shelf  227  and  229 , respectively, which acts as a support and magnetic backiron for one or more permanent magnets. In a preferred embodiment, a ring magnet  230  is mounted on each shelf  227  and  229 . In other embodiments, either or each of ring magnets  230  may be replaced with a plurality of discrete magnets, such as a plurality of bar magnets, mounted on axially-extending shelves  227  and  229 . In any case, the ring magnet  230  or the plurality of bar magnets  225  shown in FIG. 3A associated with each claw segment  226 ,  228  has a number of magnetic poles equal to twice the number of fingers associated with the respective claw segment  226 ,  228 . 
     FIG. 4 illustrates a variation of the foregoing second embodiment wherein rotor  220  comprises third claw segment  232  is provided with a circumferential channel  233  about its periphery. In a preferred embodiment, a ring magnet  231  is mounted within channel  233 . In an alternate embodiment, ring magnet  231  may be replaced with a plurality of discrete magnets, such as a plurality of bar magnets (not shown), mounted within channel  233  about the periphery of claw segment  232 . In another alternate embodiment, third claw segment  232  may be split axially into two sections  232 A and  232 B, each having an axially-extending shelf  233 A and  233 B, respectively, wherein ring magnet  231  is mounted on axially-extending shelves  233 A and  233 B. See FIG.  5 . 
     FIG. 6 illustrates another variation of the foregoing second embodiment wherein third claw segment  232  is provided with a circumferential channel  233  about its periphery and wherein one or more permanent magnets, such as ring magnet  231 , are mounted within channel  233 , but wherein first and second claw segments  226  and  228  do not have any permanent magnets associated therewith. Accordingly, in this embodiment, first and second claw segments  226  and  228  preferably lack the axially-extending shelves  227  and  229  provided in those embodiments wherein permanent magnets are associated with first and second claw segments  226  and  228 , as shown in, for example, FIGS. 3 and 4. 
     FIG. 7 illustrates a third embodiment of a hybrid generator rotor according to the present invention. Hybrid rotor  320  comprises a non-magnetic shaft  322 , a first claw segment  326 , and a second claw segment  328 . Hybrid rotor  320  further includes a third claw segment  332  which is located between first and second claw segments  326  and  328 . First claw segment  326  has a plurality of axially-extending fingers  326 ′ and second claw segment  328  also has a plurality of axially-extending fingers  328 ′. Third claw pole segment  332  has a first plurality of axially-extending fingers  332 ′ and a second plurality of axially-extending fingers  332 ″. A first field coil  324  is located between first claw pole segment  326  and third claw pole segment  332 , such that first field coil  324  is substantially encapsulated by claw fingers  326 ′ and  332 ′. In a preferred embodiment, an axially-magnetized ring magnet  336  is located between second and third claw segments  328  and  332 , such that ring magnet  336  is substantially encapsulated by claw fingers  328 ′ and  332 ″. There may also be a combination of a ring magnet and a soft magnetic material axial spacer in the same space occupied by the ring magnet alone in FIG. 7, as is shown in FIG. 7 a , which has spacer  329  below ring magnet  336 . In other embodiments, a plurality of axially-magnetized discrete magnets, such as a plurality of bar magnets  225 , as seen in FIG. 3 a , may replace ring magnet  336 . In variations of the third embodiment (not illustrated), one or more permanent magnets also may be located about the first, second, and/or third claw segments  326 ,  328 , and  332 , in the manner shown in FIGS. 3,  4 , and  5 . 
     The foregoing disclosure is intended merely to illustrate certain preferred embodiments of the invention. It is contemplated that those skilled in the art may find numerous ways to modify these embodiments without departing from the scope and spirit of the invention. As such, the scope of the invention is defined by the appended claims and not by the details of the specification.