Patent Publication Number: US-2012038234-A1

Title: Compact high power alternator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of and claims priority to U.S. patent application Ser. No. 12/368,212, filed Feb. 9, 2009 which claims priority to U.S. Provisional Application No. 61/026,954, filed Feb. 7, 2008, the contents of which are incorporated herein in their entirety. 
    
    
     DESCRIPTION OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to machines for converting between mechanical and electrical energy, and in particular to compact high power alternators using permanent magnets. 
     2. Background of the Invention 
     An alternator typically comprises a rotor mounted on a rotating shaft and disposed concentrically and interior relative to a stationary stator. Alternatively, a stator may be positioned concentrically within a rotor. An external energy source, such as a motor or turbine, commonly drives the rotating element, directly or through an intermediate system such as a pulley belt. Both the stator and the rotor have a series of poles. Either the rotor or the stator generates a magnetic field, which interacts with windings on the poles of the other structure. As the magnetic field intercepts the windings, an electrical current is generated, which is provided to a suitable load. The induced current is typically applied to a bridge rectifier, sometimes regulated, and provided as an output. In some instances, the regulated output signal is applied to an inverter to provide an AC output. 
     Conversely, the device can act as a motor if an appropriate electrical signal is applied to the windings. 
     In general, permanent magnet alternators are well-known. Such alternators use permanent magnets to generate the requisite magnetic field. Permanent magnet generators tend to be much lighter and smaller than traditional wound field generators. Examples of permanent magnet alternators are described in U.S. Pat. No. 5,625,276 issued to Scott et al. on Apr. 29, 1997; U.S. Pat. No. 5,705,917 issued to Scott et al. on Jan. 6, 1998; U.S. Pat. No. 5,886,504 issued to Scott et al. on Mar. 23, 1999; U.S. Pat. No. 5,929,611 issued to Scott et al. on Jul. 27 1999; U.S. Pat. No. 6,034,511 issued to Scott et al. on Mar. 7, 2000; and U.S. Pat. No. 6,441,222 issued to Scott on Aug. 27, 2002, and U.S. application Ser. No. 10/889,980 entitled “Compact High Power Alternator” filed on Jul. 12, 2004 by Lafontaine, et al. (hereinafter referred to as the “Lafontaine et al. application”). To the extent not inconsistent with disclosures of embodiments of the present invention herein, the abovementioned references are fully incorporated by reference herein for all purposes. 
     The power supplied by a permanent magnet generator varies significantly according to the speed of the rotor. In many applications, changes in the rotor speed are common due to, for example, engine speed variations in an automobile, or changes in load characteristics. Accordingly, an electronic control system is typically employed. An example of a permanent magnet alternator and control systems therefore is described in the aforementioned U.S. Pat. No. 5,625,276 issued to Scott et al. on Apr. 29, 1997. Examples of other control systems are described in U.S. Pat. No. 6,018,200 issued to Anderson, et al. on Jan. 25, 2000. To the extent not inconsistent with disclosures of embodiments of the present invention herein, the abovementioned references are fully incorporated by reference herein for all purposes. 
     In such permanent magnet alternators, the efficiency is inversely proportional to the “air gap” separating the magnets from the stator. Such air gaps are often in the range of 20 to 40 thousands of an inch. The output produced by a stator is proportional to the square of the air gap diameter (additionally defined in relation to  FIG. 1F , below), therefore it is particularly advantageous to maximize the air gap diameter as is allowed by the particular application. 
     Typically alternators in automotive applications are equipped with mounting appendages, more commonly known as mounting lugs that are used to both fasten the alternator to the engine block by means of an intermediate bracket and to allow the alternator to function properly without belt slippage by a means that will be described later. A common arrangement known as a J180 or hinge type mount, (also known as a three-point mount) includes three mounting lugs for that purpose. Two of the mounting lugs are located at the front and rear of the alternator and are in alignment axially. The two aligned lugs are fasten to a corresponding structure on the engine by use of a bolt passing through the two lugs and mounting bracket to in effect act as a hinge. A third mounting lug, commonly known as the upper adjusting lug, is typically positioned on the front portion of the alternator and is in opposition radially from the first two lugs. The upper adjusting lug is mounted to a device equipped with a jackscrew to both rotate the alternator about the hinge formed by the first two lugs and to lock the alternator in place once proper belt tension is achieved. Jackscrews may not always be present in all brackets of this type in which case the alternator is rotated about the hinge by use of a lever, typically a wooden stick, and is then fastened by means of a simple bracket and locking fastener designed for that function. In either case the alternator functions as both the power producing component of the electrical system and the tensioner for the automotive belt that passes over the alternator pulley to the corresponding drive pulley, typically the engine crankshaft pulley. In certain engines, typically large diesels, an internally coupled auxiliary drive shaft is equipped with a pulley that used to drive the alternator instead of the crankshaft pulley. 
     Although effective as a means of mounting the alternator and applying tension to the drive belt, the J180 standard, having only three mounting points, leaves a large portion of the alternator cantilevered. With only three mounting lugs, the alternator is subjected to ‘whipping’ about the cantilevered portion which in turn magnifies the effects of acceleration. Typically these destructive forces are found in both gasoline and diesel engine applications but are most severe during startup of a diesel engine. Violent accelerations are also encountered when the vehicle is subjected to sudden changes in direction, for example, when hitting a pothole or other similar road hazard. The effect of these forces is to greatly reduce the life expectancy of an alternator. 
     Recent advances in automotive belt engineering has led to the development of the automatic belt tensioner assemblies, that through the use of an integral torsion spring, apply the required tension to the belt thereby eliminating the need for the alternator to function as the belt tensioner. In this arrangement the alternator lugs are hard mounted to a fixed bracket eliminating the need for a hinge and jack screw. Utilizing automatic belt tensioners has been beneficial in that correct belt tension is always correctly applied but destructive g forces are still observed in alternators using the J-180 hinge mount and the variations utilizing three point mounting lugs since the portion of the alternator without a mounting lug is still subjected to whipping. 
     In an attempt to further reduce observed destructive forces, the Society of Automotive Engineers (SAE) issued the Pad Mount Alternator Specification Proposal as a method to fastened alternators to engines (SAE document 2002-01-1282). The Pad Mount Alternator Specification Proposal includes four specification versions, 2-1 through 2-4. 2-1 and 2-4 have yet to gain wide acceptance and are intended for future use, whereas 2-2 and 2-3 have gained general acceptance by heavy-duty engine manufacturers with alternators now being built to the proposed standards. As will be described later, the Pad Mount alternator utilizes four mounting lugs that hard mount the alternator to the engine block. A variation of the J180 mount that includes a fourth mounting lug has also been developed in an attempt to reduce destructive forces. In either case the alternator is hard mounted to the engine at four points. The SAE Pad Mount standard as well as the J180 four point variant physically limits overall alternator diameter due to the fixed distances between mounting lugs used to fasten the alternator. Presently with overall diameter being limited, the only effective means of increasing alternator output in a Pad Mount alternator is to increase the overall axial length. This approach limits output to proportional increases with axial length. It is very desirable then to develop methods of increasing alternator output while conforming to the predefined geometry imposed by the SAE Pad Mount standard or for that matter, any four point mount alternator. 
     The rotating portion of a permanent magnet alternator comprises a rotor with permanent magnets affixed thereto. In a given application in which the overall diameter of the alternator is limited, one means to significantly increase output is to increase the overall length of the stator. As discussed in the Lafontaine et al. application, as the rotor in this type of alternator is open-ended, it is in effect cantilevered and subject to deflection when exposed to severe radial loads. Therefore the effective length for this type of alternator is limited by the amount of radial load the rotor can resist to prevent the permanent magnets from clashing with the stator. While a permanent magnet rotor can be designed to resist most loads, practical limits in terms of size and overall weight tend to make this approach impractical beyond certain lengths. It is desirable, therefore, to design a permanent magnet machine in which the output is substantially increased but not limited by rotor length. 
     There has been over time a steady increase in demand to power electrical tools remotely from the power grid. This need is acutely felt by field service personnel tasked with repairing equipment in areas where access to line-level voltages such as 110 VAC is impractical or completely unavailable. One method utilized to solve this problem is through the use of a generator set or, ‘gen-set’ to produce the AC power required by hand drill, radial saws and diagnostic equipment etc. A drawback to this method lies in the intense maintenance required by gen-sets as well as the inconvenience of carrying a large heavy piece of equipment not directly connected to the work done by field service personnel. On the other hand, if an under-hood alternator were capable of delivering both the vehicle system DC power and AC power for external uses, it would eliminate the cost and burden of having a generator set. When considering a single alternator to produce, for example, 12 VDC vehicle power and 110 VAC power, inefficiencies inherent in either boosting the voltage to 110 if the alternator is optimized to produce 12 VDC or conversely to step down to 12 V DC if the alternator is optimized to produce 110 VAC become problematic. Therefore it would be a particular advantage to produce an alternator capable of multiple electrical outputs for independent output voltages or current configurations optimized for a particular task. Specifically what output voltage range optimized for the 12 VDC and a second independent voltage range optimized for the 110 VAC. 
     The effects of magnetic fringing are well known and can be utilized to increase power of a permanent magnet machine. In a permanent magnet alternator, constraining the total available axial length for a given application imparts constraints to the alternator&#39;s axial stator length. This is because in addition to the stator fitting within the alternator, the front and rear end plates, the rotor, and necessary clearances for all turns must all also share the same limited axial length. In permanent magnet machines, an opportunity to extend the length of the magnet beyond both stator faces is possible without impacting the overall length of the alternator. The magnetic fringing fields created in this approach would extend beyond the stator and intercept the winding end turns that also extend beyond the stator. The result is flux interacting with the windings that extend beyond the stator face which in turn produces more power for a given length of stator. It would be desirable then to design an alternator that utilizes magnetic fringing as a means to increase power for a fixed length of stator. 
     Permanent magnet machines tend to demonstrate an undesirable cogging effect. The cogging effect is a direct result of a permanent magnet alternators&#39; geometry in which magnets are radially disposed equally about the rotor, alternating both north and south poles and creating a gap between each magnet. The stator comprises teeth and slots are matched to the geometry of the magnets. At rest, the magnetic field produced by the permanent magnets results in a force that predisposes the magnets to align directly over corresponding teeth on the stator. As the rotor begins to spin, the magnetic field produced by the permanent magnets creates a resistance to rotation as the potential energy of the assembly is increased. As rotation continues potential energy reaches its maximum when the permanent magnets are aligned midway in the gap between adjacent stator teeth. From the midway point, further rotation produces an acceleration that ends when the magnets are again aligned directly over the adjacent teeth on the stator. This deceleration and subsequent acceleration produces the cogging effect observed in permanent magnet alternators. It is important to note that the net effect of that cycle is a zero net effect on energy used to rotate the alternator. The cogging of permanent magnet alternators produces several undesirable characteristics. Two of these effects are merely aesthetic: the first, a high-pitched sound not unlike a siren is produced; the second is the inability to freely spin the alternator due to resistance produced by the magnetic field of the permanent magnets. Since conventional Lundell alternators spin freely in the absence of an excitation field, it is perceived that the permanent magnet alternator is not functioning properly. The third and more deleterious effect is found in larger permanent magnet alternators in which the acceleration and deceleration of cogging produces vibrations that over time can prematurely wear down alternator components. That same acceleration and deceleration also produces undesirable forces on the drive belt spinning the alternator, shortening its useful life. The Lafontaine et al. application describes reducing cogging through the use of a skewed stator. As noted in the Lafontaine et al. application one possible means of fastening a skewed stator is through the use of a hold down ring. 
     Due to the nature of its geometry, a hold down ring and its fasteners protrude into the central core, possibly negatively impacting airflow. To maintain adequate cooling fluid flow, it would be beneficial to reduce obstructions that would impede that flow. It would therefore be beneficial to produce a means of fastening a skewed stator without negatively impacting airflow. 
     SUMMARY OF THE INVENTION 
     The present invention provides a particularly advantageous machine for converting between mechanical and electrical energy. Certain embodiments provide for improved alternators that operate within the limitations imposed by the SAE Pad Mount standard. 
     Various aspects of the invention provide a means of significantly increasing the output of permanent magnet alternators while addressing the issues of radial loading applied to a permanent magnet alternator rotor. 
     Another aspect of the invention allows for the production of power in two discrete voltages, and in an alternative embodiment, at least one output of the alternator is direct current and another output is alternating current. 
     In applications where diameter and overall axial length are limited, an aspect of this invention allows for a marked increase in output capability without increasing axial length through the use of magnetic fringing. 
     One aspect of the invention offers an effective means of mounting a skewed stack that eliminates or reduces cogging that is present in a permanent magnet machine without negatively impacting airflow. 
     One aspect of the invention reduces cogging by radially offsetting opposing magnets of a dual rotor permanent magnet machine. 
     One aspect of the invention includes a power conversion apparatus comprising: a shaft, a first stator, a second stator, a first rotor and a diametrically opposed second rotor. The shaft, stators, and rotor casings may be coaxially disposed with the rotor casings mounted on the shaft. The first and second stators respectively include at least one winding. The first rotor further comprises a first plurality of permanent magnets coupled to the first rotor and disposed proximate to the first stator, separated from the first stator by a first predetermined gap distance, such that relative motion of the first stator and first rotor causes magnetic flux from the magnets to magnetically interact with the first stator winding. Also, the second rotor further comprises a second plurality of permanent magnets coupled to the second rotor and disposed proximate to the second stator, separated from the second stator by a second predetermined gap distance, such that relative motion of the second stator and second rotor causes magnetic flux from the magnets to magnetically interact with the second stator winding. The respective first and second plurality of permanent magnets have a respective predetermined length beyond a respective predetermined first and second stator face lengths. 
     Another aspect of the present invention comprises a cooling system for directing coolant flow into thermal contact with at least one of the winding and magnets. The cooling system generates sufficient coolant flow through&#39;a predetermined flow path at and above a predetermined speed to dissipate heat generated and maintains a temperature of the magnets below a predetermined destructive level. The disposition of at least one of a first and second stator slots and respective permanent magnets is skewed by a predetermined amount relative to the axis of the first and second stator. Also, the radial position of the slots at the first core side face is offset from the radial position of the slots at the second core side face. In one embodiment, the shaft has a predetermined diameter and includes shaft tapered portions disposed between the ends of the shaft at predetermined positions relative to the first and second stators. The diameter of the shaft tapered portions vary in accordance with a predetermined taper from a minimum diameter to a predetermined maximum diameter greater than the shaft predetermined diameter. The first and second rotors include a hub and a central through-bore having the predetermined taper corresponding to a taper of at least one shaft tapered portion of the shaft. The diameter of the tapered through-bore varies in accordance with the predetermined taper from a minimum through-bore diameter greater than the shaft predetermined diameter to a predetermined maximum through-bore diameter. The first and second rotors hub are disposed with the shaft journaled and extending through the hub through-bore, with the shaft tapered portion received in the through-bore with interior surface of the through bore and exterior surface of the shaft tapered portion in mating contact, wherein cooperation of the tapered first and second rotor bore is in surface contact with the&#39;shaft tapered portion positions the first and second rotors both axially and radially with respect to the shaft and first and second stators, coupling the first and second rotors to the shaft for rotation therewith. In one embodiment, the first and second rotors and shaft may comprise an integral unit. The first rotor may be mounted on the first endplate; and the first stator is mounted for rotation relative to the first endplate. 
     In another embodiment, the shaft is rotatably coupled to the first endplate. The first and second rotors comprise endcaps coupling a cylindrical casing to the shaft; the casing and endcaps comprising an integral unit. 
     In one aspect of the present invention the cooling system further comprises at least a first passageway through the first end plate in fluid communication with the predetermined flow path. The cooling system coolant may be air, and the cooling system further includes a forced air supply disposed to move air through the first endplate passageway, and the predetermined flow path. The forced air supply comprises a fan asynchronous with respect to rotation of the first stator. In another embodiment, the cooling system further comprises at least a passageway through a first stator core and a first passageway through the first rotor in fluid communication with the first stator core passageway. 
     In one embodiment, the cooling system further comprises a fan mounted for rotation with the first rotor disposed to move coolant through the first stator core passageway. The stator winding includes end turns bent into the path of coolant flow through the first stator core passageway. Additionally, the cooling system further comprises a deflector surface disposed between the first stator and first rotor to direct coolant flow from the first stator passageway into thermal contact with winding end turns. Another embodiment includes a second end plate, wherein: the second rotor is mounted on the second endplate; and the second stator is mounted for rotation relative to the second endplate. The shaft may be rotatably coupled to the second endplate. 
     The cooling system may further comprise at least a second passageway through the second end plate in fluid communication with the predetermined flow path. 
     In another embodiment, the cooling system coolant is air, and the cooling system further includes a forced air supply disposed to move air through the second endplate passageway, and the predetermined flow path. The forced air supply may comprise a fan asynchronous with respect to rotation of the second stator. The cooling system may further comprise at least a passageway through a second stator core and a passageway through the second rotor in fluid communication with the second stator core passageway. Also, the cooling system may further comprise a fan mounted for rotation with the second rotor disposed to move coolant through the second stator core passageway. The second stator winding includes end turns bent into the path of coolant flow through the second stator core passageway. Additionally, the cooling system further comprises a deflector surface disposed between the second stator and second rotor to direct coolant flow from the second stator passageway into thermal contact with winding end turns. In an alternative embodiment, the cooling system further comprises a rotor deflector disposed between the first and second rotors. An additional embodiment may include a second endplate, and an outer casing, wherein: the first and second rotor casings, first and second stator cores, and outer casing are concentric with the shaft; the shaft is rotatably coupled to the first and second endplates; the second rotor is mounted on the second end plate; and the first and second stator is coupled to the shaft for rotation therewith between the first and second endplates and within the outer casing. 
     The cooling system may comprise a passageway through the first and second stator core and a passageway through the first and second rotor in fluid communication with the first and second stator core passageway. The first and second rotor passageway may be disposed such that coolant flow is directed through a first end plate passageway, into thermal contact with the first stator first winding end turns, through the first stator core passageway, into thermal contact with the first stator second winding end turns, into thermal contact with the second stator first winding end turns, through the second stator core passageway, into thermal contact with the second stator second winding end turns, through a second end plate passageway; and into thermal contact with the first and second magnets. Another embodiment includes respective tie rods cooperating with the first and second end plates, compressing the first and second end plates against the outer casing; the first and second endplates, outer casing, and tie rods cooperating to maintain alignment of the shaft, first and second rotors and first and second stators. The coolant is air and the cooling system may include at least one forced air supply disposed to move air through the first and second endplate passageway, and the first and second stator core passageways. The forced air supply may comprise at least one electric fan. The electric fans may be mounted on the first and second endplates. In an alternative embodiment, the forced air supply comprises at least one fan disposed to rotate with the shaft. 
     Additionally, the first rotor and first stator pairing and second rotor and second stator pairings may comprise independent electrical outputs. The independent outputs may be configured to respectively provide a direct current and an alternating current. For instance, the first rotor and stator pairing and second rotor and stator pairing are configured to provide an output voltage range optimized for 12 VDC and a second independent voltage range optimized for 110 VAC. 
     In an alternative embodiment, the face length of the magnets are configured to produce magnetic fringing stators. Also, the opposing magnets may be configured radially offset to reduce cogging. The laminations of the first and second stators may be configured to be skewed to reduce cogging. 
     In an alternative embodiment the first and second stators include a plurality of windings, the end turns of such windings extending outwardly beyond the core by varying distances to present a lattice-like structure in the coolant flow path. The end turns extend outwardly beyond the core peripheral portion side faces to provide spaces between the end turns and core peripheral portion side faces, whereby dissipation of heat generated in the winding is facilitated. In one embodiment the first and second rotors, first and second stators, cooperate as a compact high power alternator for a vehicle. Alternatively, the first and second rotors and first and second stators, cooperate as a compact high power alternator to retrofit existing vehicles. 
     Also, the design of the first rotor and diametrically opposed second rotor aids in resisting apparatus deformation due to acceleration. The design of the first rotor and diametrically opposed second rotor reduces the length of the moment arm of the apparatus wherein deformation of the plurality of rotors is decreased. 
     An alternative embodiment of the present invention includes a power conversion apparatus comprising: a shaft, a first stator, a second stator, a first rotor and a diametrically opposed second rotor. The shaft, stators, and rotor casings are coaxially disposed with the rotor casings mounted on the shaft. The first and second stators include at least one winding. The first rotor includes a first plurality of permanent magnets disposed proximate to the first stator, separated from the first stator by a predetermined gap distance, such that relative motion of the first stator and first rotor causes magnetic flux from the magnets to magnetically interact with the first stator winding. Also, the second rotor includes a second plurality of permanent magnets disposed proximate to the second stator, separated from the second stator by a predetermined gap distance, such that relative motion of the second rotor and second stator causes magnetic flux from the magnets to magnetically interact with the second stator winding. The respective permanent first and second plurality of magnets have a predetermined length beyond a predetermined first and second stators individual face lengths. Additionally, there may be four lugs that couple the apparatus to a surface. The disposition of at least one of the first and second stator slots and respective permanent magnets is skewed by a predetermined amount relative to the axis of the first and second stator; and wherein the first rotor and stator pairing and second rotor and stator pairing comprise independent output voltages. These independent output voltages may comprise a direct current and an alternating current. For instance, the first rotor and first stator pairing and second rotor and second stator pairings are configured to provide an output voltage range optimized for 12 VDC and a second independent voltage range optimized for 110 VAC. 
     It is to be understood that the descriptions of this invention herein are exemplary and explanatory only and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the figures of the appended drawings, wherein like designations denote like elements. 
         FIG. 1A  is a front view of an existing embodiment of a Pad Mount alternator as reference for the present invention.  FIG. 1A  includes a cut-away view along line B-B. 
         FIG. 1B  is a top view of the Pad Mount alternator of  FIG. 1A . 
         FIG. 1C  is a rear view of the Pad Mount alternator of  FIG. 1A . (View C-C in  FIG. 1B ). 
         FIG. 1D  is a schematic sectional view (taken along line DD in  FIG. 1B ) of the Pad Mount alternator of  FIGS. 1A and 1B . 
         FIG. 1E  is a schematic sectional view (taken along line EE in  FIG. 1B ) of the Pad Mount alternator of  FIGS. 1A and 1B . 
         FIG. 1F  is a detail view (taken along circle FF in  FIG. 1E ) of the Pad Mount alternator of  FIGS. 1A and 1B . 
         FIG. 1G  is a schematic sectional view (taken along line AA in  FIG. 1A ) of the Pad Mount alternator of  FIGS. 1A and 1B . 
         FIG. 1H  is a schematic sectional view (taken along line AA in  FIG. 1A ) of the Pad Mount alternator of  FIGS. 1A and 1B  illustrating a larger diameter rotor. 
         FIG. 1I  is a schematic sectional view (taken along line AA in  FIG. 1A ) of the Pad Mount alternator of  FIGS. 1A and 1B  illustrating an axially longer rotor. 
         FIG. 2A  is a front view of the first embodiment of a Pad Mount alternator in accordance with the present invention illustrating a method of increasing output utilizing two diametrically opposed but unified rotors. ( FIG. 2A  includes a cut-away view along line G-G). 
         FIG. 2B  is a top view of the Pad Mount alternator of  FIG. 2A . 
         FIG. 2C  is a rear view of the alternator of  FIG. 2A  (View I-I in  FIG. 4B ). 
         FIG. 2D  is a section view of the alternator of  FIG. 2B  (taken along line J-J). 
         FIG. 2E  is a schematic sectional view (taken along line H-H in  FIG. 2A ) of the Pad Mount alternator of  FIGS. 2A and 2B . 
         FIG. 3A  is a front view of a second embodiment of an alternator in accordance with the present invention that maximizes output utilizing two diametrically opposed but unified rotors of equal diameters and lengths.  FIG. 3A  includes a cut-away view taken along-line K-K. 
         FIG. 3B  is a top view of the alternator of  FIG. 3A . 
         FIG. 3C  is a rear view of the alternator of  FIG. 3A  (View M-M of  FIG. 3B ). 
         FIG. 3D  is a schematic sectional view (taken along line N-N in  FIG. 3A ) of the alternator of  FIGS. 3A and 3B . 
         FIG. 3E  is a schematic sectional view (taken along line L-L in  FIG. 3A ) of the alternator of  FIGS. 3A and 3B . 
         FIG. 3F  is a schematic sectional view (taken along line L-L in  FIG. 3A ) of the alternator of  FIGS. 3A and 3B  that maximizes output utilizing two diametrically opposed but unified rotors of equal diameters and unequal lengths, illustrating stator and rotor groups of unequal length. 
         FIGS. 4A-4C  is simplified schematics illustrating the effects of radial loading on alternator rotors (Alternators in  FIG. 1A-1I ). 
         FIGS. 4D-4F  are simplified schematics illustrating the effects of radial loading on diametrically opposed but unified rotor of equal diameter and length (Alternator in  FIG. 3A-3D ). 
         FIGS. 4G-4H  are simplified schematics illustrating the effects of radial loading on diametrically opposed but unified rotors of unequal diameters (Alternator in  FIG. 2A-2E ). 
         FIGS. 4I-4J  are simplified schematics illustrating the effects of radial loading on diametrically opposed but unified rotors of equal diameters but unequal lengths (Alternator in  FIG. 3F ). 
         FIG. 5A  is a front view of a fifth embodiment of an alternator in accordance with the present invention that maximizes output for a given diameter utilizing two discrete rotors  FIG. 5A  includes a cut-away view taken along line  0 - 0 . 
         FIG. 5B  is a top view of the alternator of  FIG. 5A . 
         FIG. 5C  is a rear view of the alternator of  FIG. 5A  taken along line Q-Q ( FIG. 5C  includes a cutaway view taken along line T-T). 
         FIG. 5D  is a section view of the alternator of  FIG. 5B  taken along line R-R ( FIG. 5D  includes a cut-away view taken along line U-U). 
         FIG. 5E  is a partial section view of the alternator of  FIG. 5B  taken along line S-S ( FIG. 5E  includes a cut-away view taken along line V-V. 
         FIG. 5F  is a schematic sectional view (taken along line P-P in  FIG. 5A ) alternator of  FIGS. 5A and 5B . 
         FIG. 5G  is a schematic sectional view (taken along line P-P in  FIG. 5A ) of the Pad Mount alternator of  FIGS. 5A and 5B  with the option of two closely spaced discrete rotors. 
         FIG. 6A  is a front view of a sixth embodiment of a Pad Mount alternator in accordance with the present invention that maximizes output utilizing magnetic fringing. 
         FIG. 6B  is a schematic sectional view (taken a long line, X-X in  FIG. 6A ) illustrating magnet overhang. 
         FIG. 7A-7G  are detailed views detailing a method to fasten skewed permanent magnet alternator stators. 
         FIG. 8A  is a detailed view of a dual rotor with offset magnets. 
         FIG. 8B  is a detailed cut away view of the dual rotor in  FIG. 8A  take along line Y-Y. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring now to  FIGS. 1A-1G , as described by Lafontaine et al., to maximize power output in a permanent magnet machine, it is desirable to maximize certain dimensions such as the diameter of a stator and rotor. Put another way, it would be desirable to maximize the diameter of a circle described about the outer radius of the teeth  158  of the core  156  given size, housing, and mounting constraints. This diameter is referred to herein as the air gap diameter Dag (see  FIG. 1F ). As discussed above, the Society of Automotive Engineers, (SAE) has proposed four mounting standards, versions  2 - 1  through  2 - 4 , suitable for vehicle applications. The mounting hole pattern shown in  FIG. 1B  with its radial spread between bolts  103  and  107  and between bolts  105  and  109 , set at 190.0 mm, and axial spread between bolts  103  and  105  and between bolts  107  and  109 , set at 126.3 mm conforms to SAE Pad Mount version 2-3 and is commonly found in truck applications.  FIG. 1A  shows mounting surface  111  of alternator  100  contacting mounting bracket  101  which maintains radial clearance required for the alternator, as proposed by SAE as a minimum of 70.0 mm but typically 102 mm is utilized. Unless otherwise indicated herein, all dimensions are provided in inches. 
     When considering mounting bolts  103 ,  105 ,  107  and  109  in Pad Mount applications there are two current methods of increasing power. The first is to increase the diameter of the rotor such that its overall length fits between the axial spread of the mounting bolts to avoid interference as best seen in  FIG. 1H . The second method is to increase the overall length of the rotor by selecting a rotor diameter that avoids interference with the radial spread of the mounting bolts as best seen in  FIG. 1I . Of the two methods, increasing diameter is more desirable since the increase in power is proportional to the square of the diameter whereas increasing rotor length only yields an increase in power proportional to length. 
     Conventional alternator manufacturers have chosen to design alternators with the overall stator and armature diameters within the radial spread as proposed by the SAE. This is in part due to the increase the armature of a conventional alternator adds to the overall diameter, i.e. a modest increase in power for a conventional alternator translates to an unacceptable increase in diameter. As a result the approach has been to increase the axial length rather than diameter.  FIG. 1G  shows witness line  113  illustrating the maximum air gap diameter from the central axis of the alternator that could be attained in an alternator when restricted by the radial spread of the mounting bolts. In reality the maximum attainable radius for the rotor is further reduced due to material of endplate  126  surrounding each mounting bolt. Although the preferred method of increasing output is to increase the overall air gap diameter, the possible overall axial length is limited thereby limiting potential output. Conversely, increasing the axial length of the rotor to improve output is limited due to the diminished air gap diameter. It would be desirable therefore to incorporate both increased diameter and increased axial length in a single Pad Mount alternator to maximize potential output. 
     Referring now to  FIGS. 1A-1G  an apparatus for converting between mechanical and electrical energy, e.g., alternator  100 , which conforms to SAE proposed pad mount standard version  2 - 3 , comprises: a shaft  110 , preferably including a tapered projecting portion  112  and a threaded portion  114  (best seen in  FIG. 1G ); a rotor  116 ; a stator  118 ; a front endplate  120 ; a front bearing  122 ; a rear endplate  126 ; a rear shaft retaining rings  128 ; a rear bearing  130 ; an outer casing  132  and respective tie rods  134 . Rotor  116  is mounted on shaft  110  for rotation with the shaft. Stator  118  is closely received within rotor  116 , separated from rotor  116  by a small air gap AG. Front endplate  120 , front bearing  122 , rear bearing  130 , rear endplate  126 , outer casing  132  and tie rods  134  cooperate as a support assembly to maintain alignment of shaft  110 , rotor  116 , and stator  118 . Shaft  110  is maintained by bearings  122  and  130 , which are mounted on front endplate  120  and rear endplate  126 , respectively, and rotatably maintain and align shaft  110  concentric and perpendicular with the endplates. Rotor  116  is mounted for rotation on shaft  110  and fixed axially by jam nut  124 , positively positioned by cooperation with tapered shaft portion  112 . Rear endplate  126  mounts and locates stator  118  so that it is disposed within rotor  116  properly aligned with shaft  110  and rotor  116 . Outer casing  132  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  120  and rear endplate  126 . Tie rods  134 ; compress endplates  120  and  126  against outer casing  132 , keeping the components squared and in alignment. 
     In a typical automotive alternator application, pulley  136 , fan  138  and nut  140  are mounted on the end of shaft  110 . Power from an engine (not shown) is transmitted through an appropriate belt drive (not shown) to pulley  136 , and hence shaft  110 . Torque so applied to the shaft  110  in turn causes rotor  116  to rotate about stator  118 . Rotor  116  generates a magnetic field, which interacts with windings on stator  118 . As the magnetic field intercepts the windings, an electrical current is generated, which is provided to a suitable load. The induced current is typically applied to a bridge rectifier, sometimes regulated, and provided as an output. In some instances, the regulated output signal is applied to an inverter to provide an AC output. 
     As best seen in  FIG. 1G , rotor  116  preferably comprises an endcap  142 , a cylindrical casing  144  and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  146  disposed in the interior side wall of casing  144 . 
     As best seen in  FIG. 1D , rotor endcap  142  is suitably substantially open, including a peripheral portion  131 , respective cross-arms  148  and a central rotor hub  150  to provide for connection to shaft  110 . Respective air passageways  152  are provided through endcap  142 , bounded by peripheral portion  131 , adjacent cross arms  148 , and central hub  150 . Central rotor hub  150  includes a through-bore  154  having a predetermined taper (e.g. 1 in. per foot) corresponding to that of shaft portion  112 . In assembly, shaft  110  is journaled through bore  154 , such that shaft tapered portion  112  is received in bore  154  just forward of threaded shaft portion  114 . Threaded shaft portion  114  cooperates with jam nut  124  to positively locate rotor  116  on shaft  110 . In general, the thickness of crossarms  148  is suitably chosen to be as thin as possible (to minimize weight and material cost) while still capable of withstanding expected loads, suitably in the range of ⅜ in. to ⅝ inch at its thinnest point. Since rotor casing  144  is, in effect, cantilevered from endcap  142 , the necessary thickness is proportional to the length of casing  144 . Rotor hub  150 , in the vicinity of bore  154 , is suitably thick enough to provide adequate surface contact with tapered shaft portion  112 , suitably on the order of 1½ inch. 
     Stator  118  suitably comprises a core  156  and conductive windings  170 . Core  156  suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). As best seen in  FIGS. 1E and 11F , core  156  is generally-cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth  158  and slots  160 . The tooth alignment is typically axial but under certain control systems requiring the acquisition of waveform timing and/or to eliminate the cogging effect found in axially aligned laminations, the laminations can be progressively skewed of a prescribed tooth offset from end to end (preferably but not limited to an offset of one tooth) as will be explained later, a method of securing a skewed stator without negatively impacting air flow will be explained. Core  156  is preferably substantially open, with a central aperture  162 , and suitably includes crossarms  164  and axial through-bores  166  to facilitate mounting to rear endplate  126  using mounting bolts  168 . As will be described later radial slots can be utilized to mount the lamination stack to optimize air flow through central aperture  162   
     Windings  170 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on core  156 , wound through a respective slot  160 , outwardly along the side face of core  156  around a predetermined number of teeth  158 , then back through another slot  160 . 
     In assembly, stator  118  is disposed coaxially with rotor  116 , and is closely received within interior cavity of rotor  116 . As will be explained, rear endplate  126  mounts and locates stator  118  so that it is properly aligned within internal chamber of rotor  116 . The peripheral surface of stator core  156  is separated from the interior surface of magnets  146  by a small predetermined air gap AG (best seen in  FIG. 1F ). Air gap AG is suitably in the range of 20 to 40 thousands of an inch, and in the embodiments of  FIGS. 1A-1I  on the order of 30 thousands of an inch, e.g., 31 thousands of an inch. Accordingly, the inner diameter of casing  144 , magnets  146 , and outer diameter of stator core  156  are preferably held to close tolerances to maintain alignment. It is important that rotor  116  and stator  118  be carefully aligned, and displacement of the elements from their normal positions due to external forces on the alternator held below a threshold value. 
     As noted above, alignment of shaft  110 , rotor  116 , and stator  118  achieved by a bearing structure comprising front endplate  120 , front bearing  122 , rear bearing  130 , rear endplate  126 , outer casing  132  and tie rods  134 . Bearings  122  and  130 , in effect, provide respective points of rotatable connection between shaft  110  and the bearing structure. Bearings  122  and  130 , and hence shaft  110 , are disposed concentric and perpendicular with endplates  120  and  126 , respectively. Rotor  116  is preferably positively positioned with respect to shaft  110  through cooperation of tapered rotor hub through bore  154  and tapered shaft portion  112 . Stator  118  is located relative to and aligned with shaft  110 , and hence rotor  116 , by rear endplate  126 . The alignment of endplates  120  and  126  is maintained by outer casing  132  and tie rods  134 . 
     Front endplate  120  is suitably generally cylindrical, including: a centrally disposed hub  174 , including a coaxial aperture  176  with a peripheral portion  178  including respective (e.g. 4) counter bored holes  180  disposed at predetermined radial distances from the center of aperture  176 , distributed at equal angular distances, to receive tie rods  134 ; and respective (e.g., 4) crossarms  182  connecting peripheral portion  178  to hub  174 , and defining respective air passages  184 . Front endplate  120  is dimensioned and machined to high tolerance (e.g. plus or minus 0.0008 TYP for aperture  176 , 0.005 TYP for other features, such as tie rod hole  180  patterns, outer case shoulder, mounting hole patterns), suitably formed of metal e.g. cast aluminum, and should be sufficiently strong to withstand the rotational loads created by the turning of shaft  110  and rotor  116 , as well as side loading that occurs as a result of the belt pulling on pulley  136 . Front bearing  122  is closely received in bearing sleeve  186 . Front endplate  120  and bearing sleeve  186  which is used to distribute the stresses produced by the loads transferred from shaft  110  to bearing  122 . Bearing sleeve  186  locates front bearing  122  and shaft  110 . 
     Rear endplate  126  carries and locates rear bearing  130 , mounts and locates stator  118 . Rear endplate  126  suitably includes a stepped central hub  188  having a forward reduced diameter portion  190  and central aperture  192  there through, and a generally cylindrical rearward going outer peripheral portion  194 , preferably having the same outer profile as front endplate  120 , connected to hub  188  by respective crossarms  145 . Respective tapped holes  196  are provided cylindrical outer peripheral portion  194 , at the same radial distance from center and angular dispositions as counter bored holes  180  in front endplate  120 . A predetermined number of tapped holes  196  (e.g. 4) corresponding to stator crossarm bores  166  are provided in the stepped surface of projection  188 . The outer diameter of reduced diameter portion  190  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  198  on crossarms  164 , so that rear endplate portion  190  may be closely received within the concentric radial locating features  198  on crossarms  164  of stator  118 . Rear endplate  126  is dimensioned and machined to high tolerance (e.g. plus or minus 0.0008 TYP for central aperture  192 , 0.005 TYP for other features, such as tapped holes  196  patterns, outer case shoulder, mounting hole patterns), suitably formed of metal e.g. cast aluminum. Rear bearing  130  is closely received within aperture  192  of rear endplate hub  188  and thus centers shaft  110 . Stator  118  is mounted on hub  188 , with reduced diameter hub portion  190  received within the concentric radial locating features  198  on crossarms  164  of stator  118  and the stator rear sidewall against the hub step. Respective bolts  168  journaled through bores  166  and secured in tapped holes  196 , secure stator  118  to rear endplate  126 . Stator  118  is thus positively located and aligned relative to shaft  110 . Since endplates  120  and  126  are held in alignment with each other by outer casing  132  and tie rods  134 , shaft  110  (and tapered portion  112 ) is held in alignment with endplates  120  and  126  by bearings  122  and  130 , and stator  118  is positively positioned and aligned with shaft  110  by endplate  126 , the positive positioning and a centering of rotor  116  on shaft  110  also provides relative positioning and alignment between rotor  116  and stator  118 . 
     For a given stator length, increasing the diameter of a stator and rotor of a permanent magnet machine, more specifically, increasing the air gap diameter Dag produces a significant increase in output (output increases by the square of the diameter). 
     Referring now to  FIG. 1H , increasing the air gap diameter significantly increases output of alternator  100  without changing any components other than increasing the diameter of the rotor and stator. Alternator  147 , which also conforms to SAE proposed pad mount standard version 2-3, comprises: a shaft  110 , preferably including a tapered projecting portion  112  and a threaded portion  114  (best seen in  FIG. 1H ); a rotor  115 ; a stator  123 ; a front endplate  120 ; a front bearing  122 ; a rear endplate  126 ; a rear shaft retaining rings  128 ; a rear bearing  130 ; an outer casing  132  and respective tie rods  134 . 
     Rotor  115  is mounted on shaft  110  for rotation with the shaft  110 . Rotor  115  has a larger diameter then that of rotor  116  and extends beyond witness line  113 . Like rotor  116 , rotor  115  is comprised of an endcap  117 , a cylindrical casing  119  and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  121  disposed in the interior side wall of casing  119 . Rotor endcap  117  is suitably substantially open, including a peripheral portion  137 , respective cross-arms (not shown) and a central rotor hub  139  to provide for connection to shaft  110 . Respective air passageways  152  are provided through endcap  117 , bounded by peripheral portion  137 , adjacent cross arms (not shown), and central hub  139 . Central rotor hub  139  includes a through-bore  141  having a predetermined taper (e.g. 1 in. per foot) corresponding to that of shaft portion  112 . In assembly, shaft  110  is journaled through bore  141 , such that shaft tapered portion  112  is received in bore  141  just forward of threaded shaft portion  114 . Threaded shaft portion  114  cooperates with jam nut  124  to positively locate rotor  115  on shaft  110 . In general, the thickness of the crossarms (not shown) is suitably chosen to be as thin as possible (to minimize weight and material cost) while still capable of withstanding expected loads, suitably in the range of ⅜ in. to ⅝ inch at its thinnest point. Since rotor casing  119  is, in effect, cantilevered from endcap  117 , the necessary thickness is roughly proportional to the length of casing  119 . Rotor hub  139 , in the vicinity of bore  141 , is suitably thick enough to provide adequate surface contact with tapered shaft portion  112 , suitably on the order of 1½ inch. In all physical and functional respects, rotor  115  is similar to rotor  116  of alternator  100   
     There is a corresponding increase in the diameter of stator  123  to match that of rotor  115  which increases the air gap diameter Dag. Stator  123  suitably comprises a core (not shown) and conductive windings  170 . The stator core suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). The core is generally cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth and slots (reference  FIG. 1E ) and is preferably substantially open, with a central aperture  127 , and suitably includes crossarms (not shown) and axial through-bores  129  to facilitate mounting to rear endplate  126  using mounting bolts  168 . Windings  170 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on the core (not shown), wound through a respective slot (not shown), outwardly along the side face of core (not shown) around a predetermined number of teeth (not shown), then back through another slot (not shown). 
     In assembly, stator  123  is disposed coaxially with rotor  115 , and is closely received within interior cavity of rotor  115 . The peripheral surface of stator core (not shown) is separated from the interior surface of magnets  121  by a small predetermined air gap AG (see, e.g.,  FIG. 1F ). Air gap AG is suitably in the range of 20 to 40 thousands of an inch, and in the embodiments of  FIGS. 1A-1I  on the order of 30 thousands of an inch, e.g., 31 thousands of an inch. Accordingly, the inner diameter of casing  119 , magnets  121 , and outer diameter of stator  123  are preferably held to close tolerances to maintain alignment. It is important that rotor  116  and stator  118  be carefully aligned, and displacement of the elements from their normal positions due to external forces on the alternator held below a threshold value. 
     Stator  123  is mounted on hub  188 , with reduced diameter hub portion  190  received within the concentric radial locating features  198  on crossarms (not shown) of stator  118  and the stator rear sidewall against the hub step. Respective bolts  168  journaled through bores  129  and secured in tapped holes  196 , secure stator  123  to rear endplate  126 . Stator  123  is thus positively located and aligned relative to shaft  110 . Since endplates  120  and  126  are held in alignment with each other by outer casing  132  and tie rods  134 , shaft  110  (and tapered portion  112 ) is held in alignment with endplates  120  and  126  by bearings  122  and  130 , and stator  123  is positively positioned and aligned with shaft  110  by endplate  126 , the positive positioning and a centering of rotor  115  on shaft  110  also provides relative positioning and alignment between rotor  116  and stator  118 . In all respects, physical and functional, stator  123  is similar to stator  118  of alternator  100 . 
     The second method of improving output in a permanent magnet machine is achieved by increasing the axial length of both the rotor and stator. Lengthening the rotor and stator is a less desirable method since the increase in output varies linearly in relationship to increases in length. However, in certain applications increasing length of the rotor and stator may be the only viable method of increasing output. Among other drawbacks to increasing length, as described by Lafontaine et al., the length of the rotor in applications such as engine mounting is practically limited by the forces exerted on the alternator from a cantilevered installation. 
     Referring now to  FIG. 1I ; Alternator  133 , which also conforms to SAE proposed pad mount standard version 2-3, comprises: a shaft  167 , preferably including a tapered projecting portion  112  and a threaded portion  114  (best seen in  FIG. 1H ); a rotor  135 ; a stator  137 ; a front endplate  120 ; a front bearing  122 ; a rear endplate  149 ; a rear shaft retaining rings  128 ; a rear bearing  130 ; an outer casing  132  and respective tie rods  134 . 
     The outer diameter of rotor  135  is designed such that clearance is maintained between rotor casing  175  and rear endplate  149 . Rotor  135  is mounted on shaft  167  for rotation with the shaft  110 . Rotor  135  is comprised of an endcap  177 , a cylindrical casing  175  and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  173  disposed in the interior side wall of casing  175 . Rotor endcap  177  is suitably substantially open, including a peripheral portion  179 , respective crossarms (not shown) and a central rotor hub  181  to provide for connection to shaft  167 . Respective air passageways  183  are provided through endcap  177 , bounded by peripheral portion  179 , adjacent cross arms (not shown), and central hub  181 . Central rotor hub  181  includes a through-bore  183  having a predetermined taper (e.g. 1 in. per foot) corresponding to that of shaft portion  112 . In assembly, shaft  167  is journaled through bore  183 , such that shaft tapered portion  112  is received in bore  183  just forward of threaded shaft portion  114 . Threaded shaft portion  114  cooperates with jam nut  124  to positively locate rotor  135  on shaft  167 . In general, the thickness of the crossarms (not shown) is suitably chosen to be as thin as possible (to minimize weight and material cost) while still capable of withstanding expected loads, suitably in the range of ⅝ in. to 53/4 inch at its thinnest point due to the increased length. Since rotor casing  175  is, in effect, cantilevered from endcap  177 , the necessary thickness is roughly proportional to the length of casing  177 . Rotor hub  181 , in the vicinity of bore  183 , is suitably thick enough to provide adequate surface contact with tapered shaft portion  112 , suitably on the order of 1½ inch. In all physical and functional respects, rotor  135  is similar to rotor  116  of alternator  100 . 
     Rear endplate  149  carries and locates rear bearing  130 , mounts and locates stator  137 . Rear endplate  149  includes a rearward extension  151  to accept the increased length of stator  137  and suitably includes a stepped central hub  153  having a forward reduced diameter portion  155  and central aperture  157  there through, and a generally cylindrical rearward going outer peripheral portion  159 , preferably having the same outer profile as front endplate  120 . Respective tapped holes  161  are provided cylindrical outer peripheral portion  159 , at the same radial distance from center and angular dispositions as counter bored holes  180  in front endplate  120 . A predetermined number of tapped holes  163  (e.g. 4) corresponding to stator  137  crossarm bores  165  are provided in the stepped surface of projection  153 . The outer diameter of reduced diameter portion  155  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features (not shown) on crossarms (not shown), so that rear endplate portion  155  may be closely received within the concentric radial locating features (not shown) on crossarms (not shown) of stator  137 . Rear endplate  149  is dimensioned and machined to high tolerance (e.g. plus or minus 0.0008 TYP for central aperture  157 , 0.005 TYP for other features, such as tapped holes  163  patterns, outer case shoulder, mounting hole patterns), suitably formed of metal e.g. cast aluminum. Rear bearing  130  is closely received within aperture  157  of rear endplate hub  153  and thus centers shaft  167 . Stator  137  is mounted on hub  153 , with reduced diameter hub portion  155  received within the concentric radial locating features (not shown) on crossarms (not shown) of stator  137  and the stator rear sidewall against the hub step. Respective bolts  169  journaled through bores  165  and secured in tapped holes  163 , secure stator  137  to rear endplate  149 . Stator  137  is thus positively located and aligned relative to shaft  167 . Since endplates  120  and  149  are held in alignment with each other by outer casing  132  and tie rods  134 , shaft  167  (and tapered portion  112 ) is held in alignment with endplates  120  and  149  by bearings  122  and  130 , and stator  137  is positively positioned and aligned with shaft  167  by endplate  149 , the positive positioning and a centering of rotor  135  on shaft  167  also provides relative positioning and alignment between rotor  135  and stator  137 . 
     Stator  137 , with its corresponding increase in the length to match that of rotor  135 , suitably comprises a core (not shown) and conductive windings  170 . The stator core suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). The core is generally cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth and slots (reference  FIG. 1E ) and is preferably substantially open, with a central aperture  171 , and suitably includes crossarms (not shown) and axial through-bores  165  to facilitate mounting to rear endplate  149  using mounting bolts  169 . Windings  170 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on the core (not shown), wound through a respective slot (not shown), outwardly along the side face of core (not shown) around a predetermined number of teeth (not shown), then back through another slot (not shown). 
     In assembly, stator  137  is disposed coaxially with rotor  135 , and is closely received within interior cavity of rotor  135 . The peripheral surface of stator core (not shown) is separated from the interior surface of magnets  173  by a small predetermined air gap AG (reference  FIG. 1F ). The air gap AG is suitably in the range of 20 to 40 thousands of an inch, and in the embodiments of  FIGS. 1I  on the order of 30 thousands of an inch, e.g., 31 thousands of an inch. Accordingly, the inner diameter of rotor casing  175 , magnets  173 , and outer diameter of stator  137  are preferably held to close tolerances to maintain alignment. It is important that rotor  135  and stator  137  be carefully aligned, and displacement of the elements from their normal positions due to external forces on the alternator held below a threshold value. 
     As described above, alternators conforming to the proposed SAE Pad Mount standard are limited by the mounting bolt hole pattern. Manufacturers can either increase the air gap diameter Dag, fitting the rotor and stator between the axial mounting bolts or utilize a significantly smaller diameter rotor and stator and staying between the radial spread of the mounting bolts. Referring now to  FIGS. 2A-2E  that illustrate a method of dramatically increasing alternator output by combining diametrically opposed rotor casings while still maintaining compatibility with the SAE proposed Pad Mount Standard. 
     Alternator  200  has many similar features found in alternator  100 ; a shaft  202 , preferably including a tapered projecting portion  112  and a threaded portion  114 ; a jam nut  124 ; front end plate  204 ; a front bearing  122 ; a bearing sleeve  176 ; a rear bearing  130 ; a rear shaft retaining ring  128 ; an outer casing  132  and respective tie rods  134 . Rear end plate  206  has been extended to except rear stator  217  and rotor portion  209 . 
     Rotor  201 , like rotor  116 , has support plate  203 , analogous to rotor endplate  134 ; but is centrally located with two diametrically opposed rotor casing portions  207 ; and  209 ; of unequal diameters. Rotor casing portion  209  is of a reduced diameter sufficient to clear mounting bolts  105  and  109 . Front endplate  206 , unlike front endplate  120 , mounts and locates front stator  215  as well as carrying and locating front bearing  122 . 
     Stators  215  and  217  suitably comprise cores  288  and  290  respectively and conductive windings  272  and  254  respectively. Cores  288  and  290  suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). As best seen in  FIG. 2D , cores  288  and  290  are generally cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth  158  and slots  160 . Both stator  215  and  217  are preferably substantially open, with stator  215  having a central aperture  266  and suitably includes crossarms  224 , radial locating feature  222  and axial through-bores  220  to facilitate mounting to front endplate  204  using mounting bolts  246  and stator  217  having a central aperture  262  and suitably includes crossarms  286 , radial locating feature  284  and axial through-bores  240  to facilitate mounting to rear endplate  248  using mounting bolts  246 . As will be described later radial slots can be utilized to mount the lamination stack to optimize air flow through the central apertures  262  and  266   
     Windings  254  and  272 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on cores  288  and  290 , wound through a respective slot  160 , outwardly along the side face of cores  288  and  290  around a predetermined number of teeth  158 , then back through another slot  160 . 
     In assembly, stators  215  and  217  are disposed coaxially with rotor  201 , and are closely received within interior cavities of rotor  201 . As will be explained, rear endplate  206  mounts and locates rear stator  217  and front endplate  204  mounts and locates front stator  215  so that it is properly aligned within internal chambers of rotor  201 . The peripheral surface of stator cores  288  and  290  are separated from the interior surface of magnets  211  and  213  by a small predetermined air gap diameter Dag (best seen in  FIG. 1F ). 
     Front endplate  204  suitably includes a stepped central hub  208  having a forward reduced diameter portion  210  and central aperture  212  there through, and a generally cylindrical outer peripheral portion  214  connected to hub  208  by respective crossarms  252 . Respective counter bored holes  216  are provided cylindrical outer peripheral portion  214 . A predetermined number of tapped holes  218  (e.g. 4) corresponding to stator crossarm bores  220  are provided in the stepped surface of projection  208 . The outer diameter of reduced diameter portion  210  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  222  on crossarms  224 , so that front endplate portion  210  may be closely received within the concentric radial locating features  222  on crossarms  224  of stator  215 . Front bearing sleeve  176  is closely received within counter bore  226  of front endplate hub  208  and thus centers shaft  202 . Stator  215  is mounted on hub  208 , with reduced diameter hub portion  210  received within the concentric radial locating features  222  on crossarms  224  of stator  215  and the stator front sidewall against the hub step. Respective bolts  293  journaled through bores  220  and secured in tapped holes  218 , secure stator  215  to front endplate  204 . Stator  215  is thus positively located and aligned relative to shaft  202 . 
     Rear endplate  206 , to accommodate the increase in axial length as a result of the addition of rear rotor portion  209  and stator  217 , has cylindrical extension  248  that carries and locates rear bearing  130 , mounts and locates stator  217 . Cylindrical extension  248  must be of adequate strength to support the increased stress as a result of mounting stator  217 . Rear endplate  206 , has a generally cylindrical rearward going outer peripheral portion  234 , preferably having the same outer profile as front endplate  204 , cylindrical extension  248  suitably includes a stepped central hub  208  connected by respective crossarms  244  having a forward reduced diameter portion  230  and central aperture  232  there through. Respective tapped holes  236  are provided cylindrical outer peripheral portion  234 , at the same radial distance from center and angular dispositions as counter bored holes  216  in front endplate  204 . A predetermined number of tapped holes  238  (e.g. 4) corresponding to stator crossarm bores  240  are provided in the stepped surface of projection  228 . The outer diameter of reduced diameter portion  230  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  284  on crossarms  286 , so that rear endplate reduced portion  230  may be closely received within the concentric radial locating features  284  on crossarms  286  of stator  217 . Rear bearing  130  is closely received within aperture  232  of rear endplate hub  228  and thus centers shaft  202 . Stator  217  is mounted on hub  228 , with reduced diameter hub portion  230  received within the concentric radial locating features  284  on crossarms  286  of stator  217  and the stator rear sidewall against the hub step. Respective bolts  246  journaled through bores  240  and secured in tapped holes  238 , secure stator  217  to rear endplate  206 . Stator  217  is thus positively located and aligned relative to shaft  202 . 
     Rotor  201  is mounted on shaft  202  for rotation with the shaft. Stators  215 ; and  217  are closely received within rotor  201 , separated from rotor  201  by a respective air gaps AG. Front endplate  204 , bearing sleeve  186 , front bearing  122 , rear bearing  130 , rear endplate  206 , outer casing  132  and tie rods  134  cooperate as a support assembly to maintain alignment of shaft  202 , rotor  201 , and stators  215  and  217 . Shaft  202  is maintained by bearings  122  and  130 , which are mounted on front endplate  204  and rear endplate  206 , respectively, and rotatably maintain and align shaft  202  concentric and perpendicular with the endplates. Rotor  201  is mounted for rotation on shaft  202 , positively positioned by cooperation with tapered shaft portion  112 . Front endplate  204  mounts and locates stator  215  that it is disposed within rotor  201  properly aligned with shaft  202  and rotor  201 . Rear endplate  206  mounts and locates stator  217  so that it is disposed within rotor  201  properly aligned with shaft  202  and rotor  201 . Outer casing  132  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  204  and rear endplate  206 . Tie rods  134 ; compress endplates  204  and  206  against outer casing  132 , keeping the components squared and in alignment. 
     Referring to  FIG. 2E , a cooling airflow  278  entering alternator  200  is directed over stator windings  254  (preferably through loosely wrapped front-side and rear-side end turns  256  and  258  respectively) by employing a cooling system comprising air passageways  260  in rear end plate  206  (bounded by adjacent rear end plate crossarms  244 , outer portion  248 , and hub  228 ), stator  217  central aperture  262 , rotor air passages  264 , over stator windings  272  (preferably through loosely wrapped front-side and rear-side end turns  274  and  276  respectively) stator  215  central aperture  266  and front end plate air passages  268 . Air flow  278  entering rear end plate air passage way  260  is directed to impinge on windings  254  (rear-side end turns  258 ), Air exiting stator central aperture  262  is directed to impinge on windings  254  (front-side end turns  256 ), by virtue of suitable relative disposition or contouring, or, as in the embodiment of  FIG. 2E , cooperation with a shaft mounted rear deflector  270 . Air exiting rotor air passages  264  is directed to impinge on windings  272  of stator  215  through rear-side end turns  276 . After passing over rear-side end turns  276  is then directed to stator  215  central aperture  266  by use of rotor deflector  282  then over front-side end turns  274  then through front endplate  204  air passageway  268 . An asynchronous forced air supply, e.g., electric fan as outlined by Lafontaine et al., may be mounted to the rear of end plate  206  to enhance air flow. In the preferred embodiment, centrifugal fan  138  is mounted for rotation with shaft  202  between pulley  136  and front end plate  204 . The cross sections, contours (turns and edges) and relative dispositions of the various air passageways are preferably chosen to minimize decreases in air velocity, and maximize airflow over end turns  258 ,  256  of stator  217  and end turns  274 ,  276  of stator  215 . 
     More specifically, cooling air, generally indicated by arrows  278  is introduced into alternator  200  through end plate air passageways  260 . Airflow  278  impinges upon rear end turn  258 . Airflow  278  then splits into respective streams  280  and  282 . After exiting the end turns  258 , air stream  280  flows through stator  217  central aperture  262 , impinges upon rear shaft deflector  270 , is then directed through the front-side loosely wrapped end turns  256 , air flow  280  then enters rotor passageways  264 , impinges on end turns  276  of stator  215  then with the cooperation of rotor deflector  282 , is directed into stator  215  central aperture  266  and then exits alternator  200  through air passageways  268  in front end plate  204 . Air stream  282 , after exiting rear-side end turns  258 , flows between the outside of rotor casing portion  209  and then between rotor portion  207  and the inside of cylindrical portion  248  and outer case  132  then impinges on front side end turns  274  of stator  215  then exits alternator  200  through air passageways  268  in front end plate  204 . Air stream  282  provides cooling of magnets  213 ,  211  and front side end turns  274 . Air stream  280  provides cooling for end turns  258 ,  256  and  276 . 
     As described above, the use of diametrically opposed rotor casings offers an opportunity to significantly increase alternator output without subjecting the rotor to excessive deformation if the entire length of the rotor casing were otherwise cantilevered. In the case of an SAE pad mount alternator, the use of a reduced rotor diameter at one end of a diametrically opposed rotor casing to adequately clear mounting bolts is of particular advantage. In applications in which the diameter of the rotor can be maximized for the entire length of the rotor, maximum output is achieved for that application. Alternator  300 , due to the increased length and singular axial diameter, could not be used in an application conforming to the proposed SAE Pad Mount standard but would also be well suited in a variety of other mounting applications such as the J180 SAE standard or other similar mounting pattern. 
     Referring now to  FIGS. 3A-3E , Alternator  300  has many similar features found in alternator  200  but most notably the diametrically opposed rotors are of equal diameters. Alternator  300  has a shaft  302 , preferably including a tapered projecting portion  112  and a threaded portion  114 ; a jam nut  124 ; front end plate  304 ; a front bearing  122 ; rear endplate  306 ; a rear bearing  130 ; a rear shaft retaining ring  128 ; an outer casing  308  and respective tie rods  310 . Rotor  326  has support plate  328  that is centrally located in rotor casing  330  with two diametrically opposed rotor casing portions  332 ; and  334  that are of equal diameters. 
     Stators  340  and  342  suitably comprise cores  312  and  314  respectively and conductive windings  316  and  318  respectively. Cores  312  and  314  suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). As best seen in  FIG. 3D , cores  312  and  314  are generally cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth  158  and slots  160 . Both stator  340  and  342  are preferably substantially open, with stator  340  having a central aperture  320  and suitably includes crossarms  349 , radial locating feature  351  and axial through-bores  322  to facilitate mounting to front endplate  304  using mounting bolts  359  and stator  342  having a central aperture  324  and suitably includes crossarms  353 , radial locating feature  355  and axial through-bores  393  to facilitate mounting to rear endplate  306  using mounting bolts  313 . 
     Windings  316  and  318 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on cores  312  and  314 , wound through a respective slot  160 , outwardly along the side face of cores  312  and  314  around a predetermined number of teeth  158 , then back through another slot  160 . 
     In assembly, stators  340  and  342  are disposed coaxially with rotor  326 , and are closely received within interior cavity of rotor  326 . As will be explained, rear endplate  306  mounts and locates rear stator  342  and front endplate  304  mounts and locates front stator  340  so that it is properly aligned within internal chambers of rotor  326 . The peripheral surface of stator  340  and  342  are separated from the interior surface of magnets  336  and  338  by a small predetermined air gap AG (see, e.g.,  FIG. 1F ). 
     Front endplate  304  suitably includes a stepped central hub  397  having a forward reduced diameter portion  317  and central aperture  395  there through, and a generally cylindrical outer peripheral portion  321  connected to hub  323  by respective crossarms  325 . Front endplate air passageways  331  are bounded by outer peripheral portion  321 , hub  323  and crossarms  325 . Respective counter bored holes  327  are provided cylindrical outer peripheral portion  321 . A predetermined number of tapped holes  344  (e.g. 4) corresponding to stator crossarm bores  322  are provided in the stepped surface of projection  397 . The outer diameter of reduced diameter portion  317  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  351  on crossarms  349 , so that reduced diameter portion  317  may be closely received within the concentric radial locating features  351  on crossarms  349  of stator  340 . Front bearing sleeve  186  is closely received within counter bore  346  of front endplate hub  397  and thus centers shaft  302 . Stator  340  is mounted on hub  397 ; with reduced diameter hub portion  317  received within the concentric radial locating features  351  on crossarms  349  of stator  340  and the stator front sidewall against the hub step. Respective bolts  359  journaled through bores  322  and secured in tapped holes  344 , secure stator  340  to front endplate  304 . Stator  340  is thus positively located and aligned relative to shaft  302 . 
     Rear endplate  306  carries and locates rear bearing  130 , mounts and locates stator  342 . Rear endplate  306  suitably includes a stepped central hub  348  having a forward reduced diameter portion  350  and central aperture  352  there through, and a generally cylindrical outer peripheral portion  354 , preferably having the same outer profile as front endplate  304 , connected to hub  348  by respective crossarms  356 . Outer peripheral portion  354 , crossarms  356  and hub  348  form rear endplate  306  air passageways  358 . Respective tapped holes  360  are provided in cylindrical outer peripheral portion  354 , at the same radial distance from center and angular dispositions as counter bored holes  327  in front endplate  304 . A predetermined number of tapped holes  362  (e.g. 4) corresponding to stator crossarm bores  393  are provided in the stepped surface projection of hub  348 . The outer diameter of reduced diameter portion  350  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  355  on cross arms  353  of stator  342 , so that reduced diameter portion  350  may be closely received within the concentric radial locating features  355  on cross arms  353  of stator  342 . Rear bearing  130  is closely received within aperture  352  of rear endplate hub  348  and thus centers shaft  302 . Stator  342  is mounted on hub  348 , with reduced diameter hub portion  350  received within the concentric radial locating features  355  on crossarms  353  of stator  342  and the stator rear sidewall against the hub step. Respective bolts  313  journaled through bores  393  and secured in tapped holes  362 , secure stator  342  to rear endplate  306 . Stator  342  is thus positively located and aligned relative to shaft  302 . 
     Rotor  326  is mounted on shaft  302  for rotation with the shaft. Stators  340  and  342  are closely received within rotor  326 , separated from rotor  326  by a small air gap AG (see, e.g.,  FIG. 1F ). Front endplate  304 , bearing sleeve  186 , front bearing  122 , rear bearing  130 , rear endplate  306 , outer casing  308  and tie rods  310  cooperate as a support assembly to maintain alignment of shaft  302 , rotor  326 , and stators  340  and  342 . Shaft  302  is maintained by bearing sleeve  186 , bearings  122  and  130 , which are mounted on front endplate  304  and rear endplate  306 , respectively, and rotatably maintain and align shaft  302  concentric and perpendicular with the endplates  304  and  306 . Rotor  326  is mounted for rotation on shaft  302 , positively positioned by cooperation with tapered shaft portion  112 . Front endplate  304  mounts and locates stator  340  so that it is disposed within rotor portion  332  properly aligned with shaft  302  and rotor  326 . Rear endplate  306  mounts and locates stator  342  so that it is disposed within rotor portion  334  properly aligned with shaft  302  and rotor  326 . Outer casing  308  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  304  and rear endplate  306 . Tie rods  310 ; compress endplates  304  and  306  against outer casing  308 , keeping the components squared and in alignment. 
     Referring again to  FIG. 3E , a cooling airflow is directed over stator windings  318  of stator  342  (preferably through loosely wrapped rear-side and front-side end turns  364  and  366  respectively) by employing a cooling system comprising air passageways  358  in rear end plate  306 , stator  342  central aperture  324 , rotor air passages  329 , stator  340  central aperture  320  and front end plate air passages  331 . Air entering rear end plate air passage way  358  is directed to impinge on rear-side end turns  364  of windings  318 , Air exiting stator central aperture  324  is directed to impinge on windings  318  (front-side end turns  366 ), by virtue of suitable relative disposition or contouring, or, as in the embodiment of  FIG. 3E , cooperation with a shaft mounted rear deflector  333 . Air exiting rotor air passages  329  is directed to impinge on windings  316  of stator  340  (preferably through loosely wrapped rear-side and front-side end turns  335  and  337  respectively). After passing over rear-side end turns  335  is then directed to stator  340  central aperture  320  by use of rotor deflector  339  then over front-side end turns  337  then through front endplate  304  air passageway  331 . An asynchronous forced air supply, e.g., electric fan as outline by Lafontaine et al., may be mounted on the back of rear end plate  306  to enhance air flow. In the preferred embodiment, centrifugal fan  138  is mounted for rotation with shaft  302  between pulley  136  and front end plate  304 . The cross sections, contours (turns and edges) and relative dispositions of the various air passageways are preferably chosen to minimize decreases in air velocity, and maximize airflow over end turns  364 ,  366  of stator  342  and end turns  335 ,  337  of stator  342 . 
     More specifically, cooling air, generally indicated by arrows  341  is introduced into alternator  300  through rear end plate air passageways  358 . Airflow  341  impinges upon rear end turn  364 . Airflow  341  then splits into respective streams  343  and  345 . After exiting the end turns  364 , air stream  343  flows through stator  342  central aperture  324 , impinges upon rear shaft deflector  333 , is directed through the front-side loosely wrapped end turns  366 , rotor passageways  329 , impinges on end turns  335  of stator  340  is, with cooperation of rotor deflector  339 , directed into stator  340  central aperture  320  then partial impinges on end turns  337  and then exits alternator  300  through air passageways  331  in front end plate  304 . Air stream  345 , after exiting rear-side end turns  364 , flows between the outside of rotor casing  303  and the inside of outer casing  308  then impinges on front side end turns  337  of stator  340  then exits alternator  300  through air passageways  331  in front end plate  304 . Air stream  345  provides cooling for magnets  336 ,  338  and end turns  364  and  337 . Air stream  343  provides cooling for end turns  364 ,  366 ,  335  and  337 . 
     The demand is high for a single device to provide multiple electrical outputs for use with possible multiple output voltages and/or current configurations, for example a single apparatus configured to provide 12 VDC to power vehicle systems and  110  VAC to power equipment such as saws and drills for use in remote locations. The alternator stators described in  FIGS. 3A-3E  can be wound independently to produce voltage ranges more closely matching the desired application. For example stator  342  can be optimized to closely match the 12 V DC vehicle system power with stator  340  optimized to more closely match the 110V AC power requirements. The disadvantage in taking this approach with two equally sized stators is for example, the excess capability stator  340  has in powering the 12 VDC vehicle system. Modern trucks typically require 80 amps or less to power vehicle systems. With stators  340  and  342  equally sized, it would not be unexpected to have stator  340  capable of producing 250 to 350 amps of power. In that particular configuration, 170 to 270 amps of power would, in essence, go to ‘waste’. Therefore it would be beneficial in certain applications to have different stator lengths in order to optimize output. Specifically stator  342  could be shortened to more closely match the 80 amp vehicle requirement and stators  340  could be lengthened to deliver the maximum amperage possible for the 110 V AC system. 
     Referring now to  FIG. 3F , Alternator  357  has a shaft  309 , preferably including a tapered projecting portion  112  and a threaded portion  114 ; a jam nut  124 ; front end plate  304 ; a front bearing  122 ; rear endplate  306 ; a rear bearing  130 ; a rear shaft retaining ring  128 ; an outer casing  308  and respective tie rods  310 . Rotor  368  has support plate  370  that is located offset from center in rotor casing  372  with two diametrically opposed rotor casing portions  374  and  376  having equal diameters. Rotor portion  374  and stator  382  are longer than rotor portion  376  and stator  384 . 
     Stators  382  and  384  suitably comprise cores and conductive windings  392  and  394  respectively. Stators  382  and  384  cores suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). Stators  382  and  384  cores are generally, cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth and slots (not shown, reference  FIG. 3D ). Both stator  382  and  384  are preferably substantially open, with stator  382  having a central aperture  396  and suitably includes crossarms (not shown, reference  FIG. 3D ), radial locating feature (not shown, reference  FIG. 3D ) and axial through-bores  398  to facilitate mounting to front endplate  304  using mounting bolts  301  and stator  384  having a central aperture  303  and suitably includes crossarms (not shown, reference  FIG. 3D ), radial locating feature (not shown, reference  FIG. 3D ) and axial through-bores  305  to facilitate mounting to rear endplate  306  using mounting bolts  307 . 
     Windings  392  and  394 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on cores of stator  382  and  384  respectively, wound through respective slots, outwardly along the side face of cores around a predetermined number of teeth, then back through another slot. 
     In assembly, stators  382  and  384  are disposed coaxially with rotor  368 ; and are closely received within interior cavity of rotor  368 . As will be explained, rear endplate  306  mounts and locates rear stator  384  and front endplate  304  mounts and locates front stator  382  so that it is properly aligned within internal chambers of rotor  368 . The peripheral surface of stator cores  382  and  384  are separated from the interior surface of magnets  378  and  380  by a small predetermined air gap AG (see, e.g.,  FIG. 1F ). 
     Front endplate  304 , as previously described, suitably includes a stepped central hub  397  having a forward reduced diameter portion  317 . A predetermined number of tapped holes  344  (e.g. 4) corresponding to stator crossarm bores  398  are provided in the stepped surface of projection  397 . Reduced diameter portion  317  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features (not shown, reference  FIG. 3D ) on crossarms (not shown, reference  FIG. 3D ), so that front endplate portion  304  may be closely received within the concentric radial locating features (not shown, reference  FIG. 3D ) on crossarms (not shown, reference  FIG. 3D ) of stator  382 . Front bearing sleeve  186  is closely received within counter bore  346  of front endplate hub  397  and thus centers shaft  309 . Stator  382  is mounted on hub  397 , with reduced diameter hub portion  317  received within the concentric radial locating features (not shown, reference  FIG. 3D ) on crossarms (not shown, reference  FIG. 3D ) of stator  382  and the stator front sidewall against the hub step. Respective bolts  301  journaled through bores  398  and secured in tapped holes  344 , secure stator  382  to front endplate  304 . Stator  382  is thus positively located and aligned relative to shaft  309 . 
     Rear endplate  306  mounts and locates stator  384 . Rear endplate  306  suitably includes a stepped central hub  348  having a forward reduced diameter portion  350 . A predetermined number of tapped holes  362  (e.g. 4) corresponding to stator crossarm bores  305  are provided in the stepped surface projection of hub  348 . The outer diameter of reduced diameter portion  350  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features (not shown, reference  FIG. 3D ) on cross arms (not shown, reference  FIG. 3D ) of stator  382 , so that reduced diameter portion  350  of rear endplate  306  may be closely received within the concentric radial locating features (not shown, reference  FIG. 3D ) on the cross arms (not shown, reference  FIG. 3D ) of stator  382 . Rear bearing  130  is closely received within aperture  352  of rear endplate hub  348  and thus centers shaft  309 . Stator  384  is mounted on hub  348 , with reduced diameter hub portion  350  received within the concentric radial locating features (not shown, reference  FIG. 3D ) on crossarms (not shown, reference  FIG. 3D ) of stator  384  and the stator rear sidewall against the hub step. Respective bolts  307  journaled through bores  305  and secured in tapped holes  362 , secure stator  382  to rear endplate  306 . Stator  382  is thus positively located and aligned relative to shaft  309 . 
     Rotor  326  is mounted on shaft  309  for rotation with the shaft. Stators  382  and  384  are closely received within rotor  368 , separated from rotor  368  by a small air gap AG (see, e.g.,  FIG. 1F ). Front endplate  304 , bearing sleeve  186 , front bearing  122 , rear bearing  130 , rear endplate  306 , outer casing  308  and tie rods  310  cooperate as a support assembly to maintain alignment of shaft  309 , rotor  368 , and stators  382  and  384 . Shaft  309  is maintained by bearings  122  and  130 , which are mounted on front endplate  302  and rear endplate  306 , respectively, and rotatably maintain and align shaft  309  concentric and perpendicular with the endplates  304  and  306 . Rotor  368  is mounted for rotation on shaft  309 , positively positioned by cooperation with tapered shaft portion  112 . Front endplate  304  mounts and locates stator  384  so that it is disposed within rotor portion  374  properly aligned with shaft  309  and rotor  368 . Rear endplate  306  mounts and locates stator  384  so that it is disposed within rotor portion  376  properly aligned with shaft  309  and rotor  368 . Outer casing  308  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  304  and rear endplate  306 . Tie rods  310 ; compress endplates  304  and  306  against outer casing  308 , keeping the components squared and in alignment. 
     Referring again to  FIG. 3F , a cooling airflow is directed over stator windings  394  of stator  384  (preferably through loosely wrapped rear-side and front-side end turns  311  and  313  respectively) by employing a cooling system comprising air passageways  358  in rear end plate  306 , stator  384  central aperture  303 , rotor air passages  315 , stator  382  central aperture  396  and front end plate air passages  331 . Air entering rear end plate air passage way  358  is directed to impinge on rear-side end turns  311  of windings  394 , Air exiting stator central aperture  303  is directed to impinge on windings  394  (front-side end turns  313 ), by virtue of suitable relative disposition or contouring, or, as in the embodiment of  FIG. 3F , cooperation with a shaft mounted rear deflector  317 . Air exiting rotor air passages  315  is directed to impinge on windings  392  of stator  382  (preferably through loosely wrapped rear-side and front-side end turns  319  and  321  respectively). After passing over rear-side end turns  319  is then directed to stator  382  central aperture  396  by use of rotor deflector  347  then over front-side end turns  321  then through front endplate  304  air passageway  331 . An asynchronous forced air supply, e.g., electric fan as outline by Lafontaine et al., may be mounted on the back of rear end plate  306  to enhance air flow. In the preferred embodiment, centrifugal fan  138  is mounted for rotation with shaft  309  between pulley  136  and front end plate  304 . The cross sections, contours (turns and edges) and relative dispositions of the various air passageways are preferably chosen to minimize decreases in air velocity, and maximize airflow over end turns  311 ,  313  of stator  384  and end turns  319 ,  321  of stator  382 . 
     More specifically, cooling air, generally indicated by arrows  341  is introduced into alternator  357  through rear end plate air passageways  358 . Airflow  341  impinges upon rear end turn  311 . Airflow  341  then splits into respective streams  343  and  345 . After exiting the end turns  311 , air stream  343  flows through stator  384  central aperture  303 , impinges upon rear shaft deflector  317 , is directed through the front-side loosely wrapped end turns  313 , rotor passageways  315 , impinges on end turns  319  of stator  382  then with cooperation with rotor deflector  347 , is directed into stator  382  central aperture  396  then partial impinges on end turns  321  and then exits alternator  357  through air passageways  331  in front end plate  304 . Air stream  345 , after exiting rear-side end turns  311 , flows between the outside of rotor casing  372  and the inside of outer casing  308  then impinges on front side end turns  321  of stator  382  then exits alternator  357  through air passageways  331  in front end plate  304 . Air stream  345  provides cooling of magnets  378 ,  380  and end turns  311  and  321 . Air stream  343  provides cooling for end turns  311 ,  313 ,  319  and  321 . 
     The embodiments of the invention described in  FIGS. 2 and 3  carry with it an ancillary benefit in that deformation of the rotor is greatly reduced during accelerations due to the nature of the physical configuration of the rotor casing and rotor endplate. As described by Lafontaine et al., the maximum length of a rotor is limited by the amount of load the rotor endplate can effectively resist to prevent critical deformation resulting in destructive clashing between magnets and rotor. 
     Referring to  FIGS. 4A-4C  (which have been greatly simplified to improve clarity), In the absence of external forces, rotor  116  of alternator  100  is concentric and perpendicular with shaft  110 ; rotor casing  144  is in a nominal normal position (designated by lines  402  and  404 ) coaxial with shaft  110  and the forward (closest to forward endplate) edge of rotor endcap  142  is in a nominal normal position (designated by line  406 ) perpendicular to the axis of shaft  110 . Components of external forces typically encountered parallel to the axis of shaft  110  tend to have little effect on the disposition of rotor  116 ; rotor endcap  142  and cooperation of rotor hub (not shown), tapered shaft portion  112 , and jam nut (not shown) are sufficiently strong to resist axial movement or distortion of rotor  116 , and, in any event, there is greater tolerance to axial distortions. However, external forces encountered perpendicular to the axis of shaft  110  of sufficient strength will distort rotor  116  if not properly account for. 
     More specifically, rotor  116  has a centroid (center of gravity)  403  that extends out beyond the conjunction of rotor endcap  142  and shaft  110  (indicated a schematically as pivot (cantilever) point  408  creating a moment arm when subjected to accelerations that are perpendicular to shaft  110 . This is true as well for those accelerations that are not completely perpendicular but which present a perpendicular component of the resultant acceleration to shaft  110 . When subjected to accelerations perpendicular to the axis of shaft  110 , rotor casing  144  tends to resist deformation due to its cylindrical shape, however the distortion can manifested itself in rotor endcap  142 . In effect, rotor  116  is cantilevered and in response to perpendicular accelerations, rotor  116 , in effect, pivots about pivot point  408 . Maximum deflection from the nominal normal position is experienced at the portions of rotor  116  farthest from pivot point  408 , i.e. the distal (rear) end of casing  144 , and the outer periphery of endcap  142  (where endcap  142  joins casing  144 ). If the deflection in the vicinity of magnets  146  exceeds air gap AG, e.g. 31 thousands of an inch, magnets  146  will clash with stator  118 , causing possibly destructive interference. 
     For example, as shown in  FIG. 4B , in response to an upward acceleration, rotor  116  will in effect pivot downwardly (as shown but exaggerated for clarity, in a clockwise direction). The upward side of rotor casing  144  will effectively pivot inwardly towards shaft  110 , with the distal end deflected inwardly from the nominal normal position  402  by an amount generally indicated as  410 . The upward periphery of endcap  142  similarly moves to the rear of its nominal normal position  406  by an amount generally indicated as  412 . Conversely, the distal end of downward side of rotor casing  144  will be deflected outwardly from the nominal normal position  402  by an amount generally indicated as  414  and the downward periphery of endcap  142  similarly moves forward of its nominal normal position  406  by an amount generally indicated as  416 . Since cylindrical rotor casing  144  tends to maintain its shape, the amount of deflection of the corresponding upper and lower portions are substantially proportional i.e. deflections  410  and  412  are substantially proportional to deflections  414  and  416 , respectively. 
     Forces from opposite directions will cause mirror image deflections. For example, as shown in  FIG. 4C , in response to a downward acceleration, rotor  116  will in effect pivot upwardly (as shown, in a counterclockwise direction). The downward side of rotor casing  144  will effectively pivot inwardly towards shaft  110 , with the distal end deflected inwardly from the nominal normal position  404  by an amount generally indicated as  418 . The downward periphery of endcap  142  similarly moves to the rear of its nominal normal position  406  by an amount generally indicated as  420 . Conversely, the distal end of upward side of rotor casing  144  will be deflected upwardly from the nominal normal position  402  by an amount generally indicated as  422  and the upward periphery of endcap  142  similarly moves forward of its nominal normal position  406  by an amount generally indicated as  424 . Again, since cylindrical rotor casing  144  maintains its shape, the amount of deflection of the corresponding upper and lower portions are substantially proportional i.e. deflections  418  and  420  are substantially proportional essays to deflections  422  and  424 , respectively. 
     As described above, accelerations perpendicular to shaft  110  tend to deflect rotor  116  such that magnets  146  could clash with stator  118  if the acceleration is severe enough. The problem of rotor deflection increases as the axial length increases, more specifically as the length of the moment arm increases. As with any mechanical system, the rotor can be designed to resist destructive deflections, no matter how severe the acceleration, but in practical terms this would require a rotor with very thick rotor end plates and casings to resist deflection, very undesirable in automotive and other applications in which weight is an important consideration. As was described in  FIGS. 3 , it is possible to dramatically increase the output utilizing diametrically opposed rotors without subjecting the rotor to deformation resulting in a clash between magnets and stator. 
     Referring now to  FIGS. 4D-4F  (which have been simplified to improve clarity), rotor  326  of alternator  300  is comprised of support plate  328  coaxially disposed at the axial center of a single cylindrical rotor casing  330 , forming two diametrically opposed cylindrical casing portions  332  and  334 . Cylindrical casing portion  332  has a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  336  disposed in the interior wall of casing portion  332 . Cylindrical casing portion  334  as well has a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  338  disposed in the interior wall of casing portion  334 . Because rotor support plate  328  of rotor  326  is centrally located within casing  330  the centroid  403  of rotor  326  is located at pivot point  408 . As the alternator is subjected to accelerations, rotor casing portion  332  of rotor  326  will tend to deflect counter clockwise (direction  426 ) about pivot point  408 . Rotor casing portion  334  of rotor  326  will tend to deflect clockwise (direction  428 ) about pivot point  408 . Rotor casing  330  due to its cylindrical shape is very well suited to resist deformation and since centroid  403  of rotor  326  is at pivot point  408 , loads will tend to be transferred along path  430  down through the body of support plate  328  to shaft  110 . Since the forces being transferred through support plate  328  do not extend beyond the body of support plate  328 , there is no moment arm therefore no significant deformation to rotor  326  occurs. 
     As was described in regards to  FIGS. 2A-2E , a method of dramatically increasing output while conforming to the proposed SAE pad mount standard was detailed. This rotor configuration also benefits in its ability to resist deformation due to severe acceleration. 
     Referring now to  FIGS. 4G and 4H  (which have been simplified to improve clarity), rotor  201  of alternator  200  is comprised of two diametrically opposed rotors of unequal diameters. Rotor  201  is comprised of support plate  203  coaxially disposed at the axial center of a dual cylindrical rotor casing  205  forming two diametrically opposed cylindrical casing portions  207  and  209  which is of a lesser diameter. Cylindrical casing portion  207  has a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  211  disposed in the interior wall of casing portion  207 . Cylindrical casing portion  209  as well has a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  213  disposed in the interior wall of casing portion  209 . Rotor support plate  203  of rotor  201  is centrally located within casing  205  but because rotor portion  207  is of a larger diameter than that of rotor portion  209  it has a slightly larger mass which locates centroid  403  of rotor  201  slightly to the left of pivot point  408 . It&#39;s important to note the difference in mass between rotor portions  207  and  209  is relatively small creating a small moment arm during acceleration, much smaller than that of alternator  100  and as would be expected, a smaller amount of distortion. As alternator  200  is subjected to accelerations, rotor casing portion  207  of rotor  201  will tend to deflect counter clockwise (direction  426 ) about pivot point  408 . Rotor casing portion  209  of rotor  201  will tend to deflect clockwise (direction  428 ) about pivot point  408 . Rotor casing  201  due to its cylindrical shape is very well suited to resist deformation and since centroid  403  of rotor  201  is just slightly left of pivot point  408 , loads will tend to be transferred to shaft  110  with only slight deformation to rotor support plate  203  due to the small moment arm presented. 
     Optimizing an alternator by utilizing discrete output is beneficial in applications requiring dual voltage outputs. By producing an alternator with stators of different lengths to produce amperage output at different voltages, an optimization is realized. In such applications the rotor support plate can be engineered to sufficiently resist the deformation caused by the increased centroid length presented during acceleration. 
     Referring now to  FIGS. 4I and 4J , (which have been greatly simplified to improve clarity), In the absence of external forces, rotor  368  of alternator  309  is concentric and perpendicular with shaft  309 ; rotor casing  372  is in a nominal normal position (designated by lines  432  and  436 ) coaxial with shaft  309  and the forward (closest to front endplate  304 ) edge of rotor casing  372  is in a nominal normal position (designated by line  438 ) perpendicular to the axis of shaft  309  and the rearward (closest to rear endplate  306 ) edge of rotor casing  372  is in a nominal normal position (designated by line  440 ) is also perpendicular to the axis of shaft  309 . Components of external forces typically encountered parallel to the axis of shaft  309  tend to have little effect on the disposition of rotor  368 ; rotor support plate  370  and cooperation of rotor hub (not shown), tapered shaft portion  112 , and jam nut (not shown) are sufficiently strong to resist axial movement or distortion of rotor  368 , and, in any event, there is greater tolerance to axial distortions. However, external forces encountered perpendicular to the axis of shaft  309  can be of sufficient strength to distort rotor  368  if not properly account for. 
     More specifically, rotor  368  has a centroid (center of gravity)  403  that extends out beyond the conjunction of rotor support plate  370  and shaft  309  (indicated a schematically as pivot point  408 ) creating a moment arm (cantilever) due to the unequal lengths, when subjected to accelerations that are perpendicular to shaft  309 . This is true as well for those accelerations that are not completely perpendicular but which present a perpendicular component of the resultant acceleration to shaft  309 . When subjected to accelerations perpendicular to the axis of shaft  309 , rotor casing  372  tends to resist deformation due to its cylindrical shape, however the distortion can manifested itself in rotor support plate  370 . In effect, rotor  368  is cantilevered and in response to perpendicular accelerations, rotor  368  pivots about pivot point  408 . Maximum deflection from the nominal normal position is experienced at the portions of rotor  368  farthest from pivot point  408 , i.e. the distal (rotor portion  374 ) end of rotor casing  372 . If the deflection in the vicinity of magnets  378  exceeds air gap AG, e.g. 31 thousands of an inch, magnets  378  will clash with stator  382 , causing possibly destructive interference. For example, as shown in  FIG. 4J , in response to an upward acceleration, rotor  368  will in effect pivot downwardly (as shown but exaggerated for clarity, in a counter clockwise direction). The upward side of rotor portion  374  will effectively pivot downwardly from the nominal normal position  432  by an amount generally indicated as  442 . The downward side of rotor portion  374  will effectively pivot downwardly from the nominal normal position  434  by an amount generally indicated as  444 . Conversely, the upward side of rotor portion  376  will be deflected upwardly from the nominal normal position  432  by an amount generally indicated as  446 , the downward side of rotor portion  376  will be deflected upwardly from the nominal normal position  432  by an amount generally indicated as  448 . Since rotor portion  374  is farthest away from pivot point  408 , it will see the greatest amount of deflection for a given amount of rotation by rotor  368 . Rotor support plate  370  must therefore be of sufficient strength to resist deformation causing destructive clashing between magnets  378  and stator  382 . 
     The alternators described in  FIGS. 2 and 3 , utilizing diametrically opposed rotor casings with a single rotor support plate is of particular advantage in terms of both increased output and ability to resist deformation. Although certainly not as capable in resisting deformation when subjected to substantial acceleration, two independent rotors each consisting of discrete endplates and rotor casings positioned in diametric opposition on a single shaft can attain similar increases in output to that of alternator  300 . Since each rotor casing is in essence cantilevered care must be taken to properly engineer and select materials for the rotor and plates that will resist destructive deformation resulting in rotor magnets clashing with each stator. 
     Referring now to  FIG. 5A-5F , Alternator  500  suitably includes a shaft  502  with two tapered projecting portions,  504  and  506  and two threaded portions  508  and  510 ; two jam nuts  512  and  514 ; front end plate  516 ; a front bearing  122 ; bearing sleeve  186 ; rear endplate  518 , rear shaft retaining rings  128 ; a rear bearing  130 ; twin rotors  530  and  532 ; stators  568  and  570 ; an outer case  520  contain air flow intake vents  522  and respective tie rods  524 . Fans  537  and  539 , in cooperation with vents  522 , cool the heat producing components of alternator  500 . Twin rotors  530  and  532 , as best seen in  FIG. 5F , both preferably comprise an endcap  534  and  536 , a cylindrical casing  538  and  540  respectfully and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  542  disposed in the interior side wall of casing  538  and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  544  disposed in the interior side wall of casing  540 . 
     As best seen in  FIGS. 5D and 5E , rotors  530  and  532  are suitably substantially open, including peripheral portions  546  and  548  respectfully, and respective cross-arms  550  and  552  and a central rotor hubs  554  and  556  respectfully to provide for connection to shaft  502 . Respective air passageways  558  are provided through endcap  534  of rotor  530 , bounded by peripheral portion  546 , adjacent cross arms  550 , and central hub  554 . Respective air passageways  560  are provided through endcap  536  of rotor  532 , bounded by peripheral portion  548 , adjacent cross arms  552 , and central hub  556 . Central rotor hubs  554  and  556  include through-bores  562  and  564  respectively having a predetermined taper (e.g. 1 in. per foot) corresponding to that of shaft portion  504  and  506 . In assembly, shaft  502  is journaled through both bores  562  and  564 , such that shaft tapered portions  504  and  506  are received in bores  562  and  564  just forward of threaded shaft portions  508  and  510 . Threaded shaft portions  508  and  510  cooperate with jam nuts  514  and  516  to positively locate rotors  530  and  532  on shaft  502 . As was previously described, the thickness of crossarms  550  and  552  are suitably chosen to be as thin as possible (to minimize weight and material cost) while still capable of withstanding expected loads. 
     Stators  568  and  570  suitably comprise cores  583  and  585  and conductive windings  572  and  574  respectively. Stators  568  and  570  cores suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). Stators  568  and  570  cores are generally cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth  158  and slots  160 . Both stator  568  and  570  are preferably substantially open, with stator  568  having a central aperture  576  and suitably includes crossarms  575 , radial locating feature  577  and axial through-bores  578  to facilitate mounting to front endplate  516  using mounting bolts  580  and stator  570  having a central aperture  582  and suitably includes crossarms  579 , radial locating feature  581  and axial through-bores  584  to facilitate mounting to rear endplate  518  using mounting bolts  586 . 
     Windings  572  and  574 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on cores  583  and  585  of stator  568  and  570  respectively, wound through respective slots  160 , outwardly along the side face of cores around a predetermined number of teeth  158 , then back through another slot. 
     In assembly, stator  568  is disposed coaxially with rotor  530  and is closely received within interior cavity of rotor  530 . As will be explained, front endplate  516  mounts and locates front stator  568  so that it is properly aligned within internal chambers of rotor  530  and stator  570  is disposed coaxially with rotor  532  and is closely received within interior cavity of rotor  532 . As will be explained, rear endplate  518  mounts and locates rear stator  570  so that it is properly aligned within internal chambers of rotor  532 . The peripheral surface of stators  568  and  570  are separated from the interior surface of magnets  542  and  544  respectively by a small predetermined air gap AG (see, e.g.,  FIG. 1F ). 
     Front endplate  516  suitably includes a stepped central hub  592  having a forward reduced diameter portion  594  and central aperture  596  there through, and a generally cylindrical outer peripheral portion  598 , preferably having the same outer profile as rear endplate  518 , connected to hub  592  by respective crossarms  501 . Respective counter bored holes  503  are provided cylindrical outer peripheral portion. 598 . A predetermined number of tapped holes  553  (e.g. 4) corresponding to stator crossarm bores  578  are provided in the stepped surface of hub  592 . Reduced diameter portion  594  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  577  on crossarms  575  of stator  568 , so that front endplate portion  594  may be closely received within the concentric radial locating features  577  on crossarms  575  of stator  568 . Front bearing sleeve  186  is closely received within counter bore  505  of front endplate hub  592  and thus centers bearing  122  and shaft  502 . Stator  568  is mounted on hub  592 , with reduced diameter hub portion  594  received within the concentric radial locating features  577  on crossarms  575  of stator  568  and the stator front sidewall against the hub step. Respective bolts  580  journaled through bores  578  and secured in tapped holes  553 , secure stator  568  to front endplate  516 . Stator  516  is thus positively located and aligned relative to shaft  502 . 
     Rear endplate  518  carries and locates rear bearing  130 , mounts and locates stator  570 . Rear endplate  518  suitably includes a stepped central hub  509  having a forward reduced diameter portion  511  and central aperture  513  there through, and a generally cylindrical outer peripheral portion  515 , preferably having the same outer profile as front endplate  516 , connected to hub  509  by respective crossarms  517 . Respective tapped holes  519  are provided cylindrical outer peripheral portion  515 , at the same radial distance from center and angular dispositions as counter bored holes  503  in front endplate  516 . A predetermined number of tapped holes  591  (e.g. 4) corresponding to stator crossarm bores  584  are provided in the stepped surface of hub  509 . The outer diameter of reduced diameter portion  511  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  581  on crossarms  579 , so that rear endplate portion  511  may be closely received within the concentric radial locating features  581  on crossarms  579  of stator  570 . Rear bearing  130  is closely received within aperture  513  of rear endplate hub  509  and thus centers shaft  502 . Stator  570  is mounted on hub  509 , with reduced diameter hub portion  511  received within the concentric radial locating features  581  on crossarms  579  of stator  570  and the stator rear sidewall against the hub step. Respective bolts  586  journaled through bores  584  and secured in tapped holes  591 , secure stator  570  to rear endplate  518 . Stator  570  is thus positively located and aligned relative to shaft  502 . 
     Rotors  530  and  532  are mounted on shaft  502  for rotation with the shaft. Stators  568 ; and  570  are closely received within rotors  530  and  532 , separated from rotors  530  and  532  by a small air gap AG. (see, e.g.,  FIG. 1F ) Front endplate  516 , bearing sleeve  186 , front bearing  122 , rear bearing  130 , rear endplate  518 , outer casing  520  and tie rods  524  cooperate as a support assembly to maintain alignment of shaft  502 , rotors  530  and  532 , and stators  568  and  570 . Shaft  502  is maintained by bearing sleeve  186 , bearings  122  and  130 , which are mounted on front endplate  516  and rear endplate  518 , respectively, and rotatably maintain and align shaft  502  concentric and perpendicular with the endplates. Rotors  530  and  532  are mounted for rotation on shaft  502 , positively positioned by cooperation with tapered shaft portions  504  and  506 . Front endplate  516  mounts and locates stator  568  so that it is disposed within rotor  530  properly aligned with shaft  502  and rotor  530 . Rear endplate  518  mounts and locates stator  570  so that it is disposed within rotor  532  properly aligned with shaft  502  and rotor  532 . Outer casing  520  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  516  and rear endplate  518 . Tie rods  524 ; compress endplates  516  and  518  against outer casing  520 , keeping the components squared and in alignment. 
     Referring again to  FIG. 5F , a cooling airflow is directed over stator windings  572  of stator  568  (preferably through loosely wrapped rear-side and front-side end turns  523  and  525  respectively) and over stator windings  574  of stator  570  (preferably through loosely wrapped rear-side and front-side end turns  527  and  529  respectively) by employing a cooling system comprising air intake vents  522 , inter-rotor spatial gap  531 , rotor air passages  560  and  558 , stator central apertures  580  and  582  rear endplate  518  air passageways  533  bounded by adjacent rear end plate crossarms  517 , outer portion  515 , and hub  509  and front end plate  516  air passages  535  bounded by adjacent rear end plate crossarms  501 , outer portion  598 , and hub  592  and fans  537  and  539 . Air entering inter-rotor spatial gap  531  between rotors  530  and  532  through air intake vents  522  of outer case  520  splits with half the airflow entering rotor air passages  560  and the other half entering rotor air passages  558 . Air flow leaving rotor air passage  560  is directed over front-side end turns  529  of stator winding  574 . After leaving front end turns  529 , airflow enters stator  570  central aperture  582  with cooperation of rotor deflector  590  and is then directed over loosely wrapped rear end turns  527  of stator windings  574  by virtue of suitable relative disposition or contouring, or, as in the embodiment of  FIG. 5D , cooperation with a rear deflector  535 . Air flow then enters passageways  533  bounded by adjacent rear end plate crossarms  517 , outer portion  515 , and hub  509  in rear end plate  518  and is driven by fan  539  which is mounted to shaft  502  by nut  589 . Airflow leaving rotor air passage  558  is directed over rear-side end turns  523  of stator winding  572 . After leaving rear end turns  523 , airflow enters stator  568  central aperture  580  with cooperation of deflector  541  and is then directed over loosely wrapped front end turns  525  of stator windings  574  by virtue of suitable relative disposition or contouring, or, as in the embodiment of  FIG. 5D , cooperation with a front deflector  587 . Airflow then enters passageways  535  bounded by adjacent front end plate outer portion  598 , crossarms  501 , and hub  592  in front end plate  516  and is driven by fan  537 . In the preferred embodiment, centrifugal fan  537  is mounted for rotation with shaft  502  between pulley  136  and front end plate  516  and centrifugal fan  539  is mounted for rotation with shaft  502  between nut  589  and rear end plate  518  The cross sections, contours (turns and edges) and relative dispositions of the various air passageways are preferably chosen to minimize decreases in air velocity, and maximize airflow over end turns  523  and  525  of stator  568  and end turns  527  and  529  of stator  570 . 
     More specifically, cooling air, generally indicated by arrows  541  is introduced into alternator  500  through air intake vents  522  and enters inter-rotor spatial gap  531 . Airflow  543  splits into four distinct airflow paths,  545 ,  547 ,  549  and  551 . Airflow  545  enters rotor passageway  558  and impinges on stator end turns  523 . After leaving end turns  523  airflow  545  is re-directed by rotor air deflector  541  and enters aperture  576  of stator  568 . Airflow  545  is then re-directed over end turns  525  by use of front endplate air deflector  587  then leaves stator  500  through air passages  535  driven by fan  537 . Airflow  547  moves between rotor casing  538  and outer case  520  thereby cooling magnets  542  that are attached to rotor casing  538 . Airflow  547  then impinges on end turns  525  after which it enters air passageway  535  leaving alternator  500  driven by fan  537 . Airflow  549  enters rotor passageway  560  and impinges on stator end turns  529 . After leaving end turns  529 , airflow  549  is re-directed by rotor air deflector  590  and enters aperture  582  of stator  570 . Airflow  549  is then re-directed over end turns  527  by use of rear endplate air deflector  535  then leaves stator  500  through air passages  533  driven by fan  539 . Airflow  551  moves between rotor casing  540  and outer case  520  thereby cooling magnets  544  that are attached to rotor casing  540 . Airflow  551  then impinges on end turns  527  after which it enters air passageway  533  leaving alternator  500  driven by fan  539 . Airflows  545  and  547  cool front components, specifically end turns  523  and  525  as well as magnets  542  and airflows  549  and  551  cool rear components, specifically end turns  529  and  527  as well as magnets  544 . 
     Although effective in cooling components of alternator  500 , air intakes  522  may not always be possible for all applications, in which case, an air flow path similar to that of alternator  300  must be utilized. 
     Referring now to  FIG. 5G , Alternator  555  suitably includes a shaft  557  including two tapered projecting portions,  559  and  561  and two threaded portions  561  and  593 ; two jam nuts  512  and  514 ; front end plate  516 ; a front bearing  122 ; bearing sleeve  186 ; rear endplate  518 , rear shaft retaining rings  128 ; a rear bearing  130 ; twin rotors  526  and  528 ; stators  568  and  570 ; an outer case  573  and respective tie rods  595 . Twin rotors  530  and  532 , as best seen in  FIG. 5G , both preferably comprise an endcap  534  and  536 , a cylindrical casing  538  and  540  respectfully and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  542  disposed in the interior side wall of casing  538  and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  544  disposed in the interior side wall of casing  540 . 
     Rotors  530  and  532  are suitably substantially open, including peripheral portions  546  and  548  respectfully, and respective cross-arms  550  and  552  and a central rotor hubs  554  and  556  respectfully to provide for connection to shaft  502 . Respective air passageways  558  are provided through endcap  534 , bounded by peripheral portion  546 , adjacent cross arms  550 , and central hub  554 . Respective air passageways  560  are provided through endcap  536 , bounded by peripheral portion  548 , adjacent cross arms  552 , and central hub  556 . Central rotor hubs  554  and  556  include through-bores  562  and  564  respectively having a predetermined taper (e.g. 1 in. per foot) corresponding to that of shaft portion  559  and  561 . In assembly, shaft  502  is journaled through both bores  562  and  564 , such that shaft tapered portions  559  and  561  are received in bores  562  and  564  just forward of threaded shaft portions  561  and  563 . Threaded shaft portions  561  and  563  cooperate with jam nuts  514  and  516  to positively locate rotors  530  and  532  on shaft  502 . As was previously described, the thickness of crossarms  550  and  552  are suitably chosen to be as thin as possible (to minimize weight and material cost) while still capable of withstanding expected loads. Rotors  530  and  532  are mounted in close proximity axially on shaft  557  such that when rotor  530  is seated on tapered portion  559  and rotor  532  is seated on tapered portion  561  a small gap  565  remains after assembly. This assures the rotors will have proper clearance to fully seat when torque is applied to bolts  512  and  514  respectively. Rotor air passages  558  and  560  are aligned during assembly to create an uninterrupted cooling fluid passageway. 
     Stators  568  and  570  suitably comprise cores  583  and  585  and conductive windings  572  and  574  respectively. Stators  568  and  570  cores suitably comprises laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, that are cut or punched to the desired shape, aligned and joined (e.g. welded or epoxied together in a precision jig to maintain the separate laminations in alignment). Stators  568  and  570  cores are generally cylindrical, with an axially crenellated outer peripheral surface, i.e., includes a predetermined number of teeth  158  and slots  160 . Both stator  568  and  570  are preferably substantially open, with stator  568  having a central aperture  576  and suitably includes crossarms  575 , radial locating feature  577  and axial through-bores  578  to facilitate mounting to front endplate  516  using mounting bolts  580  and stator  570  having a central aperture  582  and suitably includes crossarms  575 , radial locating feature  581  and axial through-bores  584  to facilitate mounting to rear endplate  518  using mounting bolts  586 . 
     Windings  572  and  574 , formed of a suitably insulated electrical conductor, preferably varnished copper motor wire, are provided on cores  583  and  585  of stator  568  and  570  respectively, wound through respective slots  160 , outwardly along the side face of cores around a predetermined number of teeth  158 , then back through another slot. 
     In assembly, stator  568  is disposed coaxially with rotor  530  and is closely received within interior cavity of rotor  530 . As will be explained, front endplate  516  mounts and locates front stator  568  so that it is properly aligned within internal chambers of rotor  530  and stator  570  is disposed coaxially with rotor  532  and is closely received within interior cavity of rotor  532 . As will be explained, rear endplate  518  mounts and locates rear stator  570  so that it is properly aligned within internal chambers of rotor  532 . The peripheral surface of stators  568  and  570  are separated from the interior surface of magnets  542  and  544  respectively by a small predetermined air gap AG (see, e.g.,  FIG. 1F ): 
     Front endplate  516  suitably includes a stepped central hub  592  having a forward reduced diameter portion  594  and central aperture  596  there through, and a generally cylindrical outer peripheral portion  598 , preferably having the same outer profile as rear endplate  518 , connected to hub  592  by respective crossarms  501 . Respective counter bored holes  503  are provided cylindrical outer peripheral portion  598 . A predetermined number of tapped holes  553  (e.g. 4) corresponding to stator crossarm bores  578  are provided in the stepped surface of hub  592 . Reduced diameter portion  594  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  577  on crossarms  575  of stator  568 , so that front endplate portion  594  may be closely received within the concentric radial locating features  577  on crossarms  575  of stator  568 . Front bearing sleeve  186  is closely received within counter bore  505  of front endplate hub  592  and thus centers bearing  122  and shaft  502 . Stator  568  is mounted on hub  592 , with reduced diameter hub portion  594  received within the concentric radial locating features  577  on crossarms  575  of stator  568  and the stator front sidewall against the hub step. Respective bolts  580  journaled through bores  578  and secured in tapped holes  553 , secure stator  568  to front endplate  516 . Stator  516  is thus positively located and aligned relative to shaft  502 . 
     Rear endplate  518  carries and locates rear bearing  130 , mounts and locates stator  570 . Rear endplate  518  suitably includes a stepped central hub  509  having a forward reduced diameter portion  511  and central aperture  513  there through, and a generally cylindrical outer peripheral portion  515 , preferably having the same outer profile as front endplate  516 , connected to hub  509  by respective crossarms  517 . Respective tapped holes  519  are provided cylindrical outer peripheral portion  515 , at the same radial distance from center and angular dispositions as counter bored holes  503  in front endplate  516 . A predetermined number of tapped holes  591  (e.g. 4) corresponding to stator crossarm bores  584  are provided in the stepped surface of hub  509 . The outer diameter of reduced diameter portion  511  is substantially equal to (but slightly less than) the diameter of the concentric radial locating features  581  on crossarms  579 , so that rear endplate portion  511  may be closely received within the concentric radial locating features  581  on crossarms  579  of stator  570 . Rear bearing  130  is closely received within aperture  513  of rear endplate hub  509  and thus centers shaft  502 . Stator  570  is mounted on hub  509 , with reduced diameter hub portion  511  received within the concentric radial locating features  581  on crossarms  579  of stator  570  and the stator rear sidewall against the hub step. Respective bolts  586  journaled through bores  584  and secured in tapped holes  519 , secure stator  570  to rear endplate  518 . Stator  570  is thus positively located and aligned relative to shaft  502 . 
     Rotors  530  and  532  are mounted on shaft  502  for rotation with the shaft. Stators  568 ; and  570  are closely received within rotors  530  and  532 , separated from rotors  530  and  532  by a small air gap AG. (see, e.g.,  FIG. 1F ) Front endplate  516 , bearing sleeve  186 , front bearing  122 , rear bearing  130 , rear endplate  518 , outer casing  520  and tie rods  524  cooperate as a support assembly to maintain alignment of shaft  502 , rotors  530  and  532 , and stators  568  and  570 . Shaft  502  is maintained by bearing sleeve  186 , bearings  122  and  130 , which are mounted on front endplate  516  and rear endplate  518 , respectively, and rotatably maintain and align shaft  502  concentric and perpendicular with the endplates. Rotors  530  and  532  are mounted for rotation on shaft  502 , positively positioned by cooperation with tapered shaft portions  557  and  559 . Front endplate  516  mounts and locates stator  568  so that it is disposed within rotor  530  properly aligned with shaft  502  and rotor  530 . Rear endplate  518  mounts and locates stator  570  so that it is disposed within rotor  532  properly aligned with shaft  502  and rotor  532 . Outer casing  520  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  516  and rear endplate  518 . Tie rods  597 ; compress endplates  516  and  518  against outer casing  573 , keeping the components squared and in alignment. 
     Referring again to  FIG. 5G , a cooling airflow is directed over stator windings  574  of stator  570  (preferably through loosely wrapped rear-side and front-side end turns  527  and  529  respectively) by employing a cooling system comprising air passageways  533  in rear end plate  518 , stator  570  central aperture  582 , rotor air passages  558  and  560 , stator  568  central aperture  576  and front end plate air passages  535 . Air entering rear end plate air passage way  533  is directed to impinge on rear-side end turns  527  of windings  518 , Air exiting stator central aperture  582  is directed to impinge on windings  574  (front-side end turns  529 ), by virtue of suitable relative disposition or contouring, or, as in the embodiment of  FIG. 5G , cooperation with rotor deflector  590 . Air exiting rotor air passages  558  and  560  is directed to impinge on windings  572  of stator  568  (preferably through loosely wrapped rear-side and front-side end turns  523  and  525  respectively). After passing over rear-side end turns  523  is then directed to stator  568  central aperture  576  by use of rotor deflector  541  then over front-side end turns  525  then through front endplate  516  air passageway  535 . An asynchronous forced air supply, e.g., electric fan as outline by Lafontaine et al., may be mounted on the back of rear end plate  518  to enhance air flow. In the preferred embodiment, centrifugal fan  138  is mounted for rotation with shaft  557  between pulley  136  and front end plate  516 . The cross sections, contours (turns and edges) and relative dispositions of the various air passageways are preferably chosen to minimize decreases in air velocity, and maximize airflow over end turns  527 ,  529  of stator  570  and end turns  523 ,  525  of stator  570 . 
     More specifically, cooling air, generally indicated by arrows  567  is introduced into alternator  555  through rear end plate air passageways  533 . Airflow  567  impinges upon rear end turn  527 . Airflow  567  then splits into respective streams  571  and  569 . After exiting the end turns  527 , air stream  571  flows through stator  570  central aperture  582 , impinges upon rotor deflector  590 , is directed through the front-side loosely wrapped end turns  529 , rotor passageways  558  and  560 , then with cooperation of rotor deflector  541 , impinges on end turns  523  of stator  568  is directed into stator  568  central aperture  576  then partial impinges on end turns  525  and then exits alternator  555  through air passageways  535  in front end plate  516 . Air stream  569 , after exiting rear-side end turns  527 , flows between the outside of rotor casings  538  and  540  and the inside of outer case  573  then impinges on front side end turns  525  of stator  568  then exits alternator  555  through air passageways  535  in front end plate  516 . Air stream  569  provides cooling of magnets  544 ,  542  and end turns  574 ,  525 . Air stream  571  provides cooling for end turns  527 ,  529 ,  523  and  525 . 
     The effects of magnetic fringing are well known and can be utilized to increase power of a permanent magnet machine. In conventional permanent magnet machines the length of magnets are generally equal to the stator length. If given the opportunity to extend the length of the magnet beyond both stator faces, the magnetic fringing fields created would extend beyond the stator and intercept the winding end turns which also extend beyond the stator. Therefore, in an embodiment, permanent magnets have predetermined lengths that exceeds predetermined stator face lengths, and in an embodiment with a plurality of stators, the predetermined length of multiple pluralities of magnets may exceed face lengths of respective stator face lengths. The result is an overall increase in flux interacting with the windings that in turn produces more power for a given length of stator. 
     Referring now to  FIGS. 6A and 6B , Alternator  600 , which is very similar to alternator  100  in all regards except that of rotor  602 , conforms to SAE proposed pad mount standard version  2 - 3 , and in accordance with various aspects of the present invention comprises: a shaft  110 , preferably including a tapered projecting portion  112  and a threaded portion  114  (best seen in  FIG. 1E ); a stator  118 ; a front endplate  120 ; a front bearing  122 ; a jam nut  124 ; a rear endplate  126 ; a rear shaft retaining rings  128 ; a rear bearing  130 ; an outer casing  132  and respective tie rods (not shown). Rotor  602  is mounted on shaft  110  for rotation with the shaft  110 . Stator  118  is closely received within rotor  602 , separated from rotor  602  by a small air gap AG (see, e.g.,  FIG. 1F ). Front endplate  120 , bearing sleeve  186 , front bearing  122 , rear bearing  130 , rear endplate  126 , outer casing  132  and tie rods (not shown) cooperate as a support assembly to maintain alignment of shaft  110 , rotor  602 , and stator  118 . Shaft  110  is maintained by bearings  122  and  130 , which are mounted on front endplate  120  and rear endplate  126 , respectively, and rotatably maintain and align shaft  110  concentric and perpendicular with the endplates. Rotor  602  is mounted for rotation on shaft  110 , positively positioned by cooperation with tapered shaft portion  112 . Rear endplate  126  mounts and locates stator  118  so that it is disposed within rotor  116  properly aligned with shaft  110  and rotor  602 . Outer casing  132  has end faces perpendicular to its axis (is preferably cylindrical) and is disposed between front endplate  120  and rear endplate  126 . Tie rods (not shown); compress endplates  120  and  126  against outer casing  132 , keeping the components squared and in alignment. 
     As best seen in  FIG. 6B , rotor  602  preferably comprises an endcap  604 , a cylindrical casing  606  and a predetermined number (e.g. 8 pairs) of alternatively poled permanent magnets  608  disposed in the interior wall of casing  606 . 
     Magnets  608  extend past stator face  610  and  612  of stator  118 . Ideally the extension past the stator face  604  and  606  should be of equal length on both sides and in the range of 3/16 to 5/16 of an inch. Increases beyond that are of little benefit magnetically and only add to the overall cost of an alternator. Since rare earth magnets are one of the most expensive components of a permanent magnet alternator, it is beneficial to only use the minimum amount of magnet material needed to produce the desired output. 
     As described by Lafontaine et al., cogging can present undesirable effects during operation of a permanent magnet machine. When considering dual rotor alternators the effects of cogging are greatly magnified due to the increased overall length of stator, rotor and magnets. Skewing the laminations eliminates the majority of these effects. Due to the nature of rare earth magnets i.e. the magnets must be kept below a certain temperature (curie temperature) to prevent permanent demagnetization, it would be beneficial to develop a method that both allows the skewed stator to be mounted to the rear endplate while minimizing the impact to cooling fluids. 
     Referring now to  FIGS. 7A-7F , stator  700  is suitably comprised of a laminated stack of thin sheets of soft magnetic material, e.g. non-oriented, low loss (lead free) steel, with a core  702  and conductive windings (not shown). Stator  700  is preferably substantially open with a central aperture  704  defined by the cylindrical interior surface  706  of core  704  with suitable crossarms  708  and radial locating features  710  including cylindrical through bores  718  to fasten stator  700  to endplate  720 . The lamination sheets are generally cylindrical, with an axially crenellated outer peripheral surface, i.e., including a predetermined number of teeth  714  and slots  716  that are cut or punched to the desired shape, aligned and joined (e.g., welded or epoxied together in a precision jig to maintain the separate laminations in predetermined alignment). 
     As best seen in  FIG. 7B , the use of cylindrical through bores  718  for mounting a skewed stator is ineffective since the overall axial cross-sectional area of the through bore is reduced due to the progressive skewing of adjacent sheets. This progressive reduction in cross-sectional area makes it impossible for mounting bolts  722  to be journaled through bores  718  to endplate  720  and still maintain perpendicularity due to the interference at point  724 . The use of a clamping ring as described by Lafontaine et al. to hold stator  700  is also less than optimal in that it reduces the effective diameter of the central aperture of stator central aperture  706  to cooling fluids. As best seen in  FIG. 7C , clamp ring  732  is used to hold down stator  700  with cooperation of bolts  722 . The result is reduced diameter portion  734  of clamp  732 . 
     To overcome the progressive reduction in cross-sectional area of cylindrical through bores in a skewed stator and maximize air flow, crossarms  710  should suitably include radially slotted holes  726  to facilitate mounting core  700  to endplate  720 . Optimally, as described by Lafontaine et al., the total angular skew from stator face  728  to stator face  730  is the angle created between adjacent teeth of a stator lamination (See  FIG. 7A ). Therefore to calculate angular skew, .divide the total number of stator teeth by 360°. In the case of a 48 tooth stator, it is 360/48 or 7.50° of skew. To assure adequate clearance for bolts  722  in through bores  732 , the arc circumscribing radial slot  726  must be equal to or slightly greater that the angle created by the desired skew (7.50° in a 48 tooth stator) to assure proper clearance (see  FIGS. 7E and 7F ). As best seen in  FIG. 7G , the radially slotted through-bores  732  allow mounting bolts  722  to thread into holes  738  and remain perpendicular to endplate  720  mounting surface  734 . It would be beneficial to include washer  736  to distribute the clamping forces applied to stator  700  since radial slots eliminates some of the clamping surface that would otherwise be available in a cylindrical through bore. This method of mounting stator  700  allows for the greatest possible cross-sectional area of cooling fluid to pass through the central aperture of stator  700 . 
     As described above, skewing the stator laminations one full tooth eliminates cogging. A stator that has been skewed to that degree will experience a loss in flux density due to the interaction of both magnets and skewed coils as the rotor rotates. A unique opportunity to reduce cogging without adversely affecting flux density can be attained in a dual rotor configuration. 
     Referring now to  FIGS. 8A and 8B , rotor  800  comprises a cylindrical rotor case  802 ; central support plate  804  and magnets  806  and  808 . Magnets  806  are evenly disposed radially within cylindrical rotor case  802 . Magnets  808  are also evenly disposed radially within cylindrical rotor case  802 . The axial edge of magnets  808  is positioned within rotor case  802  such that witness line  810  created by the edge of magnet  808  bisects the central axis of magnet  806 . 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.