HYBRID ALTERNATOR

Abstract: A hybrid alternator comprising a stator (702) and a rotor (710) mounted for rotation within the stator and separated therefrom by an air gap. The rotor has a rotor core defining a plurality of magnetic poles (716) wherein adjacent ones of the magnetic poles have alternating north and south magnetic fields. The plurality of magnetic poles comprises a plurality of permanent magnet poles (716a, 716b) and a plurality of electromagnetic poles (716). Each permanent magnet pole is defined by a permanent magnet (718). The plurality of permanent magnet poles comprises two (2) sets of diametrically positioned permanent magnet poles. The hybrid alternator also includes a temperature monitoring voltage regulator that provides protection against overheating damage while permitting the alternator to significantly exceed its rated output for short periods of time or in colder ambient temperatures.

Description: HYBRID ALTERNATOR Background Of The Invention 1. Field of the Invention This invention relates to alternators of the type that are used in vehicles to provide electrical power for running accessories and charging batteries. More particularly, this invention relates to a high-efficiency hybrid alternator in which the rotating magnetic field is provided by a rotor having permanent magnet poles and wound field poles operating in combination. The invention also relates to a temperature monitoring voltage regulator specially designed to automatically regulate bi-directional current flow in the rotor winding to control the output voltage of hybrid alternators and to permit increased alternator output whenever the alternator temperature is below a predetermined maximum operating temperature. 2. Description of Related Art The automotive industry has been attempting to increase the efficiency of motorized vehicles, both at idle and at running speeds. The alternator design most commonly found in vehicles has been used for approximately twenty-five to thirty years and is inexpensive to produce, but exhibits very low efficiency levels, as low as 40-50%. The problem is particularly acute at low RPMs where high excitation levels in the rotor winding are required to produce the desired voltage, leading to very low efficiency. In conjunction with the desire for higher efficiency is the need to supply alternators that have larger electrical ratings because modern vehicles have many more motors and require much more electrical power. Moreover, fuel efficiency of vehicles is closely related to the weight of the vehicle and it is desirable to decrease the weight of the alternator so as to minimize the total vehicle weight. These objectives are achieved when the efficiency of the alternator is increased. The increased power usage in vehicles has also led to an interest in using components that operate at higher voltages than the standard 12 volts presently used in automobiles. At the same time, it is foreseen that 12 volt power will be required in such vehicles in addition to the higher voltage. It is known to provide dual voltage alternators by providing two windings on the stator. However, when a single winding is used on the rotor, it is difficult to properly regulate the two different voltage outputs as different levels of rotor excitation current may be required for the different circuits. Single and dual voltage alternators of the type represented by the present invention may also be used in various non-engine driven applications, such as wind or water driven applications, for the efficient generation of electrical power. Hybrid alternators significantly inσease their efficiency by using permanent magnets to produce a high level of magnetic flux immediately, while the alternator is operating at low speed. Using the hybrid alternator disclosed herein, the alternator will produce full rated alternator current and voltage output at engine idling speed when installed in an automobile or other vehicle. This can be contrasted with prior art alternators that are incapable of producing their full rated output until they are turning at speeds far above their rotational speed at idle. The full rated output of the hybrid alternator is achieved at low speed by supplementing the magnetic flux produced by the permanent magnets. The supplementing magnetic flux is produced by a rotor winding having a forward rotor winding current induced therein by a forward polarity voltage applied across the winding. This is referred to as the boosting mode or the forward polarity mode in which the wound field induced magnetic field is in the same direction as, and supplements, the permanent magnet induced magnetic field. As the alternator RPM increases, however, the magnetic flux from the permanent magnets produces a greater output and the need for the supplementing flux from the rotor winding deσeases. Ultimately, at a sufficiently high speed, all of the alternator's rated output is available solely from the permanent magnet induced magnetic field, and no additional current is needed in the rotor winding. Generally, this transition occurs at a speed well below the maximum anticipated operating speed of the alternator. As the rotor speed exceeds this transition point, with the engine operating at a high speed, the flux from the permanent magnets is too great and must be reduced to avoid producing damaging overvoltages and overcurrents. This is accomplished by operating the hybrid alternator in the bucking mode or the reverse polarity mode in which a reverse polarity voltage is applied to the rotor winding. The reverse polarity voltage produces a reverse current in the rotor winding. The reverse current generates a magnetic flux which opposes the magnetic flux from the permanent magnets, thereby reducing the output of the alternator to maintain the desired output voltage. The necessity for both forward and reverse rotor winding excitation current imposes certain limitations and requirements on the voltage regulator for the hybrid alternator which are not required in the case of conventional alternators. Although hybrid alternators of a low efficiency claw pole or Lundell type design are known, the existence of these limitations and requirements has not heretofore been recognized by the art even when producing voltage regulators for hybrid alternators. A first problem is related to the inductive effects of switching the highly inductive rotor winding, particularly to transition between the forward and reverse polarity excitation modes. The problem is most acute when the alternator is lightly loaded and a battery is not connected to the alternator. In this condition, a net instantaneous negative current may be introduced onto the main power bus. Current induced in the field winding stores significant energy in the magnetic field of the rotor winding. This energy can cause voltage spikes due to sudden load changes or when switching the voltage to drive the rotor winding. To reduce the output voltage of a hybrid alternator, the prior art has simply indicated that the reverse polarity mode should be applied to reduce or reverse the current in the field winding. However, before the current can be reversed, the previously induced magnetic field must collapse. During this collapse, the forward current originally induced in the forward polarity mode continues back up into the main power bus leading to the battery and all of the automobile accessories. In implementing the prior art system of regulation, a bridge circuit has been used providing two state voltage pulse width modulation. This type of modulation results in negative current steps into the main power bus with the negative step amplitude equal to the magnitude of the field current. If the load current on the main power bus is less than the magnitude of the field current, a net negative current is applied to the bus. This current has no place to go because the alternator diodes prevent negative current flow into the alternator and result in a destructive voltage spike unless suppressed by the battery or a large bus capacitor. If a battery is connected to the alternator as in the normal case, the battery can be relied upon to absorb any net negative current after the battery's other loads. Alternatively, a large capacitor can be used to absorb this energy. However, the first method cannot be relied upon as a battery may not always be present capable of absorbing the reverse current. Using a capacitor is extremely expensive, particularly when capacitors adequate for handling all the energy stored in the rotor winding are used that are temperature rated for use under the hood of an automobile. If the battery were to be removed, without a capacitor there would be no place for the net reverse current on the main power bus to go unless a large filter capacitor is placed across the circuit where the battery connection normally exists. If moderate frequency pulse width modulation techniques are employed, this capacitor can be of reasonable value. However, for lowest costs and small physical size an aluminum electrolytic capacitor would be desirable. Aluminum electrolytic capacitors, however, are not normally designed to tolerate temperatures in excess in 105°C and thus, they could not be easily housed in the hot environment of the alternator in the vicinity of the vehicle engine. Even if they were somewhat isolated from the hot alternator itself so as to avoid temperatures above 105°C the life of capacitors is rapidly reduced with inσeasing temperature. Thus, the under the hood environment would normally not permit the use of aluminum electronics. Higher temperature tantalum capacitors could be used but they are physically larger and much more expensive and are thus less attractive for a cost sensitive high volume automotive application. Also, even if capacitors are used to absorb the switching transients, there is still a potential problem due to the large energy storage and long time constant of the field coil. For example, if the alternator speed or load should abruptly change so as to cause the alternator regulator to change the field voltage polarity from near full voltage (e.g. boost in the forward polarity mode) in one direction to significant voltage in the other direction (e.g. buck in the reverse polarity mode) a large voltage transient would tend to occur if no battery were present and the system was unloaded (except for field coil). In this situation the initial energy in field coil would tend to go into the capacitor and the voltage would be excessive unless the capacitor were extremely large or the bus voltage were clamped. Although only moderate sized capacitors would be required to handle the ripple current from the pulse with modulation, the capacitor would have be physically very large to be able handle the high energy in a field winding without σeating an excessive voltage. Even if voltage clamps were employed to limit the capacitor voltage, the costs would be excessive, there would be continuing concerns over reliability due to the high temperature environment, and the size of the components would σeate a problem in the σamped environment under the hood. A solution allowing the use of pulse width modulation techniques, even if the battery is not present, and one that does not require a large capacitor is needed. A second, more subtle, problem is that precautions must be taken to prevent the voltage regulator that is providing the reverse current in the reverse polarity mode from being inactivated when the vehicle is turned off. At very high engine and alternator speeds, the magnetic flux from the permanent magnet is almost completely canceled by the oppositely directed magnetic flux in the hybrid rotor winding. If the canceling flux were to be immediately turned off, e.g. by turning off an ignition switch with the alternator operating at a high rotational speed, the output voltage of the alternator would rapidly inσease to damaging levels for the electrical components in a typical automobile. The present invention incorporates an automatic interlock which powers the voltage regulator automatically and independently of the ignition system of the vehicle to prevent it from inadvertently being deactivated. The design of the automatic interlock is such that little or no current is drawn from the vehicle battery when the vehicle is off, which might tend to discharge the vehicle battery. The preferred embodiment of the voltage regulator also incorporates transient voltage suppression in a novel way that permits certain switches (preferably FETs) needed for the purpose of switching the rotor winding between forward and reverse polarity modes to perform a second function of suppressing voltage transients that might damage the voltage regulator or other systems on the battery bus. A hybrid alternator constructed according to the description above is preferably designed to produce its full rated output at all engine speeds from idle to the maximum engine speed at redline. Two limitations on the maximum power output of the alternator are the maximum flux that the rotor windings, in combination with the permanent magnets, can produce and the thermal capability of the alternator to dissipate excess heat under continuous full output operation in high ambient temperature conditions. The first limitation usually dominates at low speed operation and the second more often dominates at higher speeds. Improving the alternator operation with respect to either limitation usually results in inσeased cost or undesirably inσeases the physical size of the alternator. To produce greater magnetic flux requires inσeasing current flow through the rotor windings (larger wire diameter and larger windings) or inσeasing the number or strength of the permanent magnets. Both options greatly affect the cost and size of the hybrid alternator. Improved thermal capability requires additional internal or external fans, larger cooling fins on the alternator case, larger airflow passages in the interior of the rotor or special electronic components that can continuously operate at higher temperatures. A hybrid alternator is preferably designed to safely produce its full rated power output over its entire speed range under worst case expected ambient temperatures. As a result, the cooling and magnetic flux limitations are balanced during the alternator design process. This results in an alternator that has just enough magnetic flux capacity to generate the desired full rated output power at engine idling speed and just enough cooling at all other speeds during worst case high ambient temperatures to keep the alternator below a desired maximum operating temperature. However, this type of design results in excess power output capacity for the alternator when the alternator is not operating in worst case conditions. Moreover, even under worst case conditions, the alternator will not instantly reach the maximum operating temperature when producing full output. During the warm up period, while the alternator temperature is below the maximum operating temperature, it also has excess power output capacity that may be usefully exploited. In view of the problems with the prior art, one object of the present invention is to provide an alternator which operates efficiently at low RPMs. Another object of the invention is to provide an alternator which uses a permanent magnet assembly in the rotor to provide a rotating permanent magnetic field in combination with a rotating variable magnetic field generated by a rotor winding. Still another object of the invention is to provide an alternator which weighs less than current alternators at the same output power or which produces a higher output at the same weight. Yet another object of the present invention is to provide an efficient dual voltage alternator, preferably in which both voltages are well regulated under varying loads. Another object of the invention is to provide a voltage regulator for a hybrid alternator that automatically interlocks to prevent the regulator from being deactivated when the alternator is in the reverse polarity mode. Still another object of the invention is to provide a voltage regulator for a hybrid alternator which provides voltage transient suppression. A further object of the invention is to provide a voltage regulator for a hybrid alternator that allows the alternator to operate without a battery attached and without requiring expensive capacitors or voltage clamps. Yet another object of the invention is to provide a hybrid alternator which provides the maximum rated output voltage and current when a vehicle in which the alternator is installed is operating at idle speed. A further object of the invention is to provide an alternator which is maximally cooled through radial cooling slots located in the stator. Still another object of the invention is to provide an alternator which can safely exploit excess power output capacity in operating regimes limited by the alternator's cooling capacity without risk of damaging the alternator from overheating. Summary of the Invention The above, and other objects which will be apparent to those skilled in the art, are accomplished in the present invention in which, in a first aspect, is directed to a hybrid alternator comprising a stator, and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor having a rotor core defining a plurality of magnetic poles, adjacent ones of the magnetic poles having alternating north and south magnetic fields, the plurality of magnetic poles comprising at least one permanent magnetic pole defined by a permanent magnet, and a plurality of electromagnetic poles, each of which is defined by a wound field. In a related aspect, the present invention is directed to a hybrid alternator comprising a stator having a stator winding, a rotor mounted for rotation within the stator and separated therefrom by an air gap, the rotor including a rotor core defining a plurality of rotor field poles, at least one permanent magnet, the magnet being attached to a corresponding rotor field pole to define a permanent magnetic pole, the magnet being attached in a manner such that it forms a portion of the rotor perimeter, and a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, the electromagnetic and permanent magnet poles defining a plurality of magnetic poles, adjacent ones of the magnetic poles having alternating north and south magnetic fields. ln another aspect, the present invention is directed to a hybrid alternator comprising a stator having a stator winding, a rotor mounted for rotation within the stator and separated therefrom by an air gap, the rotor including a rotor core defining a plurality of rotor field poles, at least one permanent magnet, the magnet being positioned within the rotor perimeter and associated with a pair of adjacent rotor field poles to form adjacent permanent magnetic poles, and a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, the electromagnetic and permanent magnetic poles defining a plurality of magnetic poles, adjacent ones of the magnetic poles having alternating north and south magnetic fields. In a related aspect, the present invention is directed to a hybrid alternator comprising a stator having a stator winding, a rotor mounted for rotation within the stator and separated therefrom by an air gap, the rotor including a rotor core defining a plurality of rotor field poles, each of which having a pole shoe, at least one permanent magnet, the magnet being mounted between the rotor core and said pole shoe to form a permanent magnetic pole, and a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, the electromagnetic and permanent magnetic poles defining a plurality of magnetic poles, adjacent ones of the magnetic poles having alternating north and south magnetic fields. In another aspect, the present invention is directed to a hybrid alternator comprising a stator having a stator winding, a rotor core mounted for rotation within the stator and separated therefrom by an air gap, said core defining a plurality of rotor field poles, each of which having a longitudinal axis substantially parallel to the rotor core rotational axis, said rotor field pole including a body portion radially extending from said core to an end surface and having a first longitudinal length, and an end portion attached to said end surface and having a second longitudinal length that is greater than said first longitudinal length. In a further aspect, the present invention is directed to a hybrid alternator comprising a rotor core mounted for rotation within the stator and separated therefrom by a radial air gap, the rotor including a shaft mounted for rotation within the stator, a wound field rotor portion mounted on the shaft for rotation within a first longitudinal region of the stator, the wound field rotor portion having a rotor winding and multiple electromagnet poles wherein each electromagnetic pole includes a rotor field pole having a longitudinal axis substantially parallel to said shaft and including a body portion radially extending from said rotor core to an end surface and having a first longitudinal length and an end portion attached to said end surface and having a second longitudinal length that is greater than said first longitudinal length, and a permanent magnet rotor portion mounted on the shaft in longitudinally spaced relation to the wound field rotor portion for rotation within a second longitudinal region of the stator, the permanent magnet rotor portion having multiple permanent magnetic poles. In one embodiment, the hybrid alternator of the present invention comprises a rotor excitation circuit connected to the rotor winding in the wound field rotor portion for producing a forward excitation current through the rotor winding to inσease output from the alternator in a boosting mode and a reverse excitation current through the rotor winding to deσease output from the alternator in a bucking mode. In another embodiment, the hybrid alternator further includes a voltage regulator for controlling bi-directional current flow through a winding of an alternator to control an output voltage of the alternator, the voltage regulator comprising a voltage monitoring circuit connected to monitor the output voltage of the alternator, the voltage monitoring circuit producing an error signal indicating the output voltage of the alternator should be inσeased or deσeased, a switching circuit connected to the rotor winding and arranged to connect the winding in multiple modes, including a forward polarity mode in which a forward polarity voltage is applied to the rotor winding, a reverse polarity mode in which a reverse polarity voltage is applied to the rotor winding, and a decay mode in which current induced in the rotor winding when connected in the forward or reverse polarity mode is permitted to decay without inducing damaging voltages in the voltage regulator, and a control circuit connected to the switching circuit, responsive to the error signal of the monitoring circuit, the control circuit controlling the switching circuit to enter the forward polarity mode to inσease the output voltage of the alternator, to enter the reverse polarity mode to deσease the output voltage of the alternator and to enter the decay mode whenever switching away from the forward or reverse polarity mode. Another embodiment of the hybrid alternator of the present invention comprises a stator, and a rotor mounted for rotation within the stator and separated therefrom by an air gap. The rotor has a rotor core defining a plurality of magnetic poles wherein adjacent ones of the magnetic poles having alternating north and south magnetic fields. The plurality of magnetic poles comprises a plurality of permanent magnet poles and a plurality of electromagnetic poles. Each permanent magnet pole is defined by a permanent magnet. The plurality of permanent magnet poles comprises two (2) sets of diametrically positioned permanent magnet poles. Each permanent magnet is positioned within the rotor perimeter and associated with a pair of adjacent magnetic poles to form adjacent permanent magnet poles. A further embodiment of the hybrid alternator of the present invention comprises a stator having a stator winding, a rotor mounted for rotation within the stator and separated therefrom by an air gap. The rotor has a rotor core that defines a plurality of rotor field poles and a plurality of permanent magnets. Each magnet is positioned within the rotor perimeter and mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles. The plurality of permanent magnet poles comprises two (2) diametrically positioned sets of permanent magnet poles. A rotor winding is associated with the remaining rotor field poles and defines a plurality of electromagnetic poles. The plurality of electromagnetic poles comprises two (2) diametrically positioned sets of electromagnetic poles. The electromagnetic and permanent magnet poles define a plurality of magnetic poles. Adjacent ones of the magnetic poles have alternating north and south magnetic fields. Another embodiment of the hybrid alternator of the present invention is a stator having a stator winding, and a rotor mounted for rotation within the stator and separated therefrom by an air gap. The rotor includes a rotor core that defines a plurality of rotor field poles asymmetrically positioned about the rotor core. Each rotor field pole comprises a body radially extending from the rotor core to an end surface. The rotor also includes a plurality of permanent magnets, each of which being positioned within the rotor perimeter and mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles. The plurality of permanent magnet poles comprises two (2) diametrically positioned sets of permanent magnet poles wherein each set of permanent magnet poles comprises four (4) adjacent permanent magnet poles. Each permanent magnet is arranged in a manner such that the direction of magnetization is oriented circumferential ly relative to the rotor core rotational axis. A rotor winding is associated with the remaining rotor field poles to define a plurality of electromagnetic poles. The plurality of electromagnetic poles comprises two (2) diametrically positioned sets of electromagnetic poles. Each set of electromagnetic poles comprises two (2) adjacent electromagnetic poles. The electromagnetic and permanent magnet poles define a plurality of magnetic poles wherein adjacent ones of the magnetic poles have alternating north and south magnetic fields. The alternator further includes a plurality of rotor field pole shoes. Each shoe is asymmetrically mounted to the end surface of a corresponding one of the pole bodies such that the rotor field shoes are equidistantly spaced from one another. Another embodiment of the hybrid alternator uses a novel connection arrangement between the rotor winding and the stator winding. By using this arrangement, a simplified voltage regulator may be used that significantly reduces component costs. The voltage regulator alternately connects one end of the rotor winding between the positive end of the battery and ground. The other end of the rotor winding is connected to the neutral point of the stator (which operates at approximately half the battery voltage). The switching circuit in the regulator needs only two switches for alternately connecting the rotor to transition between the forward and reverse polarity modes. The hybrid alternator is designed such that it produces the full rated output voltage and current when the vehicle is operating at idle speed and continues to produce that full rated output over its entire operating range of speeds. Another aspect of the invention includes a temperature monitoring voltage regulator for controlling bi-directional current flow through a winding of a hybrid alternator that adjusts the output voltage of the hybrid alternator according to the temperature of the alternator to limit power output when the alternator temperature approaches a predetermined maximum operating temperature. The temperature monitoring voltage regulator includes a voltage monitoring circuit, a temperature sensor, a switching circuit and a control circuit. The voltage monitoring circuit is connected to monitor the output voltage of the alternator and produces an error signal indicating that the output voltage of the alternator should be inσeased or deσeased. The temperature sensor is adapted to be mechanically mounted in thermal contact with the hybrid alternator, preferably the heatsink of the output diode bridge, to sense the alternator temperature. The temperature sensor is electrically connected to the voltage monitoring circuit and modifies the error signal to reduce the output voltage of the hybrid alternator as the temperature sensor senses an alternator temperature approaching a predetermined maximum alternator temperature. -12- The switching circuit is connected to the rotor winding and can connect the winding in either a forward polarity mode, in which a forward polarity voltage is applied to the winding, or a reverse polarity mode in which a reverse polarity voltage is applied to the rotor winding. The control circuit is responsive to the error signal of the monitoring circuit and directs the switching circuit to enter the forward polarity mode whenever necessary to inσease the output voltage of the alternator, and to enter the reverse polarity mode to deσease the output voltage of the alternator. In the most highly preferred embodiment, the temperature sensor is a thermistor, and the switching circuit also includes the decay mode. Brief Description of the Drawings Fig. 1 is a longitudinal σoss sectional view parallel to and through the shaft of a hybrid alternator according to the present invention. Fig. 2 is a σoss sectional view along the line 2-2 perpendicular to the rotor shaft and through the wound field rotor portion of the alternator. Fig. 3 is a σoss sectional view along the line 3-3 perpendicular to the rotor shaft and through the permanent magnet rotor portion of the alternator. Fig. 4 is an electrical circuit diagram of the alternator of the present invention with a rotor excitation circuit for voltage regulation and a voltage converter circuit for producing a second output voltage. Fig. 5 is a graph of field current versus engine RPM necessary to maintain a constant voltage output in a typical embodiment of the present invention. Fig. 6 is a σoss sectional view taken parallel to the rotor shaft of a first alternative embodiment of the invention employing a solid disk-shaped permanent magnet. Fig. 7 is a side elevational view of a ten pole disk-shaped permanent magnet used in the first alternative embodiment of the invention shown in Fig. 6. Fig. 8 is a front elevational view of a segmented flux channeling element used in the first alternative embodiment of the invention shown in Fig. 6. Fig. 9 is a σoss sectional view of the segmented flux channeling element along the line 9-9 shown in Fig. 8. Fig. 10 is a σoss sectional view of a second alternative embodiment of the invention using embedded permanent magnets. Fig. 11 is a σoss sectional view along the line 1 1-1 1 in Fig. 10 showing the embedded permanent magnet portion of the rotor. Fig. 12 is a block diagram of a voltage regulator for a bridge circuit controlled rotor winding of a hybrid alternator. Fig. 13 is a detailed circuit diagram of a circuit in accordance with the block diagram of Fig. 12. Fig. 13A is a detailed circuit diagram of a temperature monitoring voltage regulator based on the circuit in Fig. 13 in which a temperature sensor is used to adjust the alternator output voltage to permit higher than rated alternator output whenever the alternator temperature is below a predetermined maximum operating temperature. Fig. 14 is a wiring diagram of a novel arrangement for a hybrid alternator in which the rotor winding is connected to the neutral point of the stator winding. Fig. 15 is a wiring diagram of a hysteresis modulator which provides improved regulator dynamic performance, as compared to the corresponding hysteresis inverter elements in Fig. 13. Fig. 16 is a longitudinal σoss-sectional view parallel to and through the shaft of an alternate embodiment of the hybrid alternator of the present invention. Fig. 17 is a σoss-sectional view along line 17-17 perpendicular to the rotor shaft of the alternator of Fig. 16. Fig. 17A is a partial enlarged view of a permanent magnet pole shown in Fig. 17. Fig. 18 is a σoss-sectional view similar to Fig. 17, of an alternate embodiment of the alternator of Fig. 16. Fig. 18A is a partial enlarged view of a permanent magnet pole shown on Fig. 18. Fig. 19 is a σoss-sectional view similar to Fig. 17, of a further embodiment of the hybrid alternator of Fig. 16. Fig. 19A is a σoss-sectional view, similar to Fig. 17, of another embodiment of the hybrid alternator of Fig. 16. Fig. 20 is a front elevational view of a rotor pole configuration that may be utilized by the hybrid alternator of the present invention and the alternate embodiments thereof. Fig. 21 is a top plan view of the rotor pole of Fig. 20 taken along lines 21- 21. Fig. 22 is a perspective view of the rotor pole configuration of Fig. 20. Fig. 23 is a front elevational view of an alternate embodiment of the rotor pole configuration of Fig. 20. Description of the Preferred Embodiments Referring to Fig. 1, the alternator of the invention includes a stator 10 having a first longitudinal stator region 12 and a second longitudinal stator region 14. A three phase stator winding 16, as shown in Fig. 4, extends through slots 18 (shown in Figs. 2 and 3) formed on the interior of the stator 10. A rotor, generally indicated with arrow 20 is mounted for rotation within the stator 10 on a shaft 22. The rotor includes a wound field rotor portion 24 which rotates within the first stator region 12 and a permanent magnet rotor portion 38 which rotates within the second stator region 14. The wound field rotor portion 24 has a rotor winding 28 which can be excited to produce a magnetic field whenever current is applied through slip rings 30, 32 on the shaft 22. Conventional brushes (not shown) would be mounted within region 34 of case 36 to make contact with slip rings 30, 32 and allow excitation current to be supplied to the rotor winding. The permanent magnet rotor portion 38 is mounted on the shaft 22 in longitudinally spaced relation from the wound field rotor portion 24. It includes a plurality of permanent magnets 40 disposed about its perimeter mounted such that the direction of magnetization is radially oriented relative to the rotor shaft. The magnets maintain a multiple pole permanent magnetic field which extends aσoss the air gap between the rotor and stator. Fig. 2 is a σoss section through the first region 12 of the stator within which the wound field rotor spins. The wound field rotor is conventionally formed from multiple thin laminations having the σoss sectional shape seen in Fig. 2 stacked adjacently along the rotor shaft. Alternately, the wound field rotor poles may be constructed using solid cast magnetic material. Each lamination on the rotor includes a plurality of poles 42 around which the rotor windings 28 are arranged with alternate poles being wound in opposite directions to produce alternating north and south magnetic fields. Thus, the first region 12 of the stator and the wound field rotor portion 24 of the rotor act as a salient pole alternator to generate output from the stator windings 16 through output leads 44, 46 and 48 (shown in Figs. 1 and 4) whenever an excitation current is supplied to the rotor windings 28. Hybrid Alternator - Radially Magnetized Permanent Magnets Fig. 3 is a σoss section through the permanent magnet rotor portion of one embodiment of the alternator. The permanent magnet rotor portion includes eight (8) permanent magnets 40 shaped as rectangular slabs and held in the permanent magnet rotor laminations 38. Alternate designs may use more or less than eight magnetic poles, but will always have the same number of poles as the wound field rotor. Shapes other than rectangular slabs may be used, for example the thickness of the slab may be varied to match the curve of the rotor. Each permanent magnet slab is magnetized through its thickness and mounted such that the direction of magnetization extends radially, i.e., in a direction which is perpendicular to the shaft 22 and normal to the large faces of the slab 40. The slabs are held in openings in the laminations 38 around the perimeter of the permanent magnet rotor and alternate, with the north pole of one slab facing outward and the north pole of the next slab facing inward. In this way, the magnetic field generated by the wound rotor adds to the permanent magnetic field when a forward excitation current is applied to the rotor winding 28 and subtracts from the permanent magnetic field when a reverse current is applied. The permanent magnets in the design illustrated are formed of neodymium, however other magnetic materials such as ceramic or samarium-cobalt magnets may also be used and may be preferred in particular applications. In production, the neodymium magnets are nickel plated. In addition to the openings which hold the magnets, the laminations 38 include multiple openings 50 to reduce weight and allow for cooling air flow through the alternator. Those familiar with electric machines in general and alternators in particular will understand that the permanent magnets 40 provide a permanent magnetic field at the rotor which induces a voltage in the stator winding 16 whenever shaft 22 is rotated. Rotation of the shaft is generally accomplished with a belt and pulley drive, however a gear drive or other means may also be applied. In the design shown in Fig. 1, the stator windings 16 extend from the first stator region surrounding the wound field rotor portion continuously through the second stator region surrounding the permanent magnet portion. Thus, as shaft 22 rotates, a voltage is induced in the stator winding 16 which is partially a result of the magnetic field from the permanent magnets and partially a result of the magnetic field generated by excitation current in the windings 28 of the wound field rotor portion. It is also possible to use separate windings on the two stator sections and combine their outputs electrically. In the design shown in Figs. 1, 2 and 3, the stator portion of the alternator is the same in region 14 as in region 12 and includes identical slots 18 and stator windings 16. The slots 18 may, however, be skewed such that there is a twist along its length. The purpose of the twist is to prevent magnetic cogging. In the absence of such a twist, magnetic cogging and unwanted vibration is created due to variable reluctance caused by slot openings in the air gap between the stator and the rotor. The stator is formed as a stack of thin laminations of electrical grade steel. Each member of the stack is rotational ly offset from its adjacent members sufficiently to form the twist of one stator slot pitch along its length. Although it is not shown in Fig. 3, the permanent magnet portion may include a premanufactured cylindrical sleeve of a lightweight but strong material such as a carbon fiber bonded in a resin. The sleeve has a thin wall thickness and a diameter equal to the diameter of the permanent magnet rotor portion. It surrounds the permanent magnet rotor portion and prevent the magnets 40 from being thrown outward and damaging the stator under the centrifugal force generated as a result of high speed operation. In production versions of the invention, the preferred means of retaining the permanent magnets on the rotor is to attach them with counter-sunk sσews, as shown in Fig. 24, to prevent the magnets from becoming dislodged from the rotor pole during the rotation of the rotor. However, other means of retaining the magnet to the rotor field poles may be used. For example, a pair circular endplates mounted on the shaft on both sides of the rotor may be used wherein each endplate has a lip portion projecting substantially parallel to the shaft that extends about halfway aσoss the width of the rotor and above the magnet so as to form a pole shoe. Alternatively, the endplates can be configured such that the lip portions extend over a pole shoe mounted on top of the permanent magnet. Furthermore, epoxy-type adhesives may also be used to secure the permanent magnets to the rotor field poles. Other mechanical means for holding the permanent magnets to the rotor will be apparent to those skilled in the art. -17- As the alternator shaft 22 begins to spin, the magnet portion will induce a voltage in the stator winding 16 which is be rectified to produce a desired output voltage. Referring to Fig. 4, a typical stator winding 16 is composed of three legs connected to a full wave voltage rectifier formed by six power diodes 60. The power diodes 60 rectify the output and provide charging power to charge battery 62 and to supply a vehicle with power for accessories over output 64. At low RPMs the output from the alternator due to the permanent magnets is insufficient to provide the full voltage needed at output 64. Accordingly, a forward excitation polarity is applied to rotor winding 28. This inσeases the current in the rotor, inσeases the strength of the magnetic field generated by the rotor winding, and inσeases the output from the stator windings 16 to boost the output voltage to the desired level. The forward polarity and forward current induced thereby is the current and polarity which causes the magnetic field from the rotor winding to add to the magnetic field from the permanent magnets in a boosting mode. The necessity to boost the output by supplying a forward excitation current to the rotor windings 28 occurs only at low engine RPMs. As the engine speed inσeases, the output from the stator inσeases and a point is reached at which the desired output voltage is produced by the stator solely due to the permanent magnet rotor portion. At this speed, no excitation current needs to be supplied to the rotor winding 28. Above this speed, however, the permanent magnet rotor portion would produce an over voltage in the stator windings. To counteract the excess voltage at high RPMs, the rotor winding 28 is supplied with a reverse excitation current which deσeases output from the alternator in a bucking mode. Fig. 5 provides a graph of wound field current in rotor winding 28 needed to maintain a constant output voltage at output 64 from the stator windings 16 as a function of engine RPM. The graph is provided for illustration of one possible implementation of the invention. Changes in gearing of the alternator to the engine, the number of turns and resistance of windings on the rotor and stator, and the relative strengths of the fields generated by the magnets and rotor winding all will affect the actual curve for any specific application. Referring to Fig. 5, it can be seen that the boost portion of the curve 66 in which a forward excitation current is required occurs from idle at approximately 600 RPM until 1200 RPM is reached. As the RPM inσeases from 600 RPM to 1200 RPM, the amount of forward excitation current needed to maintain the constant output voltage deσeases, reaching zero at point 70. At this point, all of -18- the excitation is derived from the permanent magnet rotor portion. At speeds in excess of 1200 RPM, the buck portion 68 of the curve is entered. In this section of the curve, a reverse excitation, indicated by the negative current values on the vertical axis, is required to prevent the output voltage from exceeding the desired level. The σossing point 70 between the boosting mode and bucking mode will vary with load and may be adjusted by varying the relative proportion of output between the wound field rotor portion and the permanent magnet rotor portion. Referring to Fig. 1 , this can be accomplished by adjusting the strength of the permanent magnets 40 or the field generated by the rotor winding. Alternatively, it may be changed by varying the relative sizes of the permanent rotor portion 14 and the wound field rotor portion 12. In Fig. 1 , these have been illustrated as being of approximately equal size, but the ratios may be varied as desired to adjust the σossing point between the boost and buck regions of operation. Dual Voltage Hybrid Alternator In the simplest form of the invention shown in Fig. 1, the stator winding 16 uses a conventional wiring layout shown in Fig. 4. However, other stator winding arrangements may be employed. For example, it is known to wire the stator with two independent windings so as to produce two different output voltages. The present invention contemplates this method of dual voltage generation where it is desired to have a 12 volt output as well as a higher voltage output, typically 48 volts. A preferred method of dual voltage operation, however, is to use a voltage converter circuit of the type desσibed in connection with Fig. 4. Other variations of the invention are also contemplated. For example, in a single voltage configuration, the stator winding may comprise two independent stator windings, one found only within the first region 12 surrounding the wound field rotor portion and one found within the second region 14 surrounding the permanent magnet rotor portion. The outputs from these separate stator windings are then combined electrically as needed to produce the desired output voltage. Continuing to refer to Fig. 1 , it can be seen that there is a gap 52 between the two regions of the stator. The gap should be made of a relatively low magnetic permeability material to isolate the magnetic regions of the stator 12 and 14. The gap may be a simple air gap, or it may be partially or completely filled with a solid material of low magnetic permeability such as plastic or the like. Where the stator winding 16 extends from one region 12 completely through the gap to the second region 14, the gap may be filled with a material having the same σoss sectional shape perpendicular to the rotor as the stator to provide a continuous slot 18 within which the stator wires forming winding 16 may lie. Hybrid Alternator - Radial Cooling Slots Through Stator In the preferred embodiment, the air gap 52 between stator sections 12 and 14 is not solid, but is open to the outside air. Cooling air is permitted to enter the interior of the alternator through air gap 52 between the stator sections where it is then ducted out of the alternator at the ends. Typically this would be done by fans located at one or both ends of the alternator (not shown). The two section geometry for the stator illustrated in Fig. 1 allows the cooling air flow to be ducted into the center region of the alternator where the cooling is most needed. This construction enhances the dissipation of thermal energy in the unit while at the same time maximizing the power output density. The air gap is preferably provided with an axial spacer having a series of radially oriented openings which open the air gap over approximately 85% of the surface area of the spacer's circumferential section to allow cooling air into the warmest part of the alternator. Arrow 53 indicates the entrance of cooling air into the alternator interior radially flowing through the stator in contrast to the prior art where the air flows only longitudinally in this section. The air entering radially through the stator may flow through the gap between the rotor and the stator. The wound field rotor section may also be provided with air flow openings that are axially aligned and correspond to the air flow passages 50 in the permanent magnet section. Air drawn into the center of the alternator through the stator core flows aσoss σitical sections of the stator coil, sections of wound field coils and diodes as well as through the permanent magnet section. In addition to deσeasing the temperature of the alternator and inσeasing air flow, by providing air flow openings in the stator core spacer and in the rotor sections, the total weight of the alternator is significantly reduced. The air flow openings in the regions referred to are located in sections of the alternator which do not carry significant magnetic flux. Consequently adding these openings and air flow holes does not diminish the electrical output of the alternator or affect its efficiency. In contrast, the current state of the art Lundell or claw pole geometry alternators do not allow anything more than double end ventilation. It is not -20- possible to ventilate through the mid section of the stator core nor is there an opportunity to ventilate through the rotor area because the Lundell and claw pole construction is a relatively solid mass construction with no voids or areas that could be devoted to the air flow. By providing additional parallel air flow paths, cooling fans in the alternator do not need to develop as much of a pressure differential to cause a given volume of air to flow. This reduces overall alternator noise and/or permits fan blade diameter and blade design to be altered to reduce the total size of the alternator. The air flow is particularly valuable in keeping the temperature of the permanent magnets as low as possible under all conditions of operation. This enhances the output of the alternator and minimizes the risk of demagnetization at high temperatures. This allows the alternator to be rated at the highest possible output in the high temperature conditions that exist under the hood of modern automobiles. Voltage Regulation ■ Basic Two State PWM Regulator In order to maintain a desired constant output voltage from the alternator, it is necessary to feed a forward or reverse excitation current into the rotor winding 28 which varies in a manner similar to that shown in Fig. 5. Fig. 4 illustrates a rotor excitation circuit appropriate for achieving this objective. The rectified output 64 from the stator is compared to a reference voltage 80 in a summing circuit 82 which subtracts the reference voltage 80 from the output voltage 64 and provides an error signal on line 84 to function generator 86. The function generator controls modulator 88 which provides a forward excitation current to field winding 28 through the slip rings 30, 32 whenever the output voltage 64 is below the reference voltage 80. Typically, the reference voltage is set to the desired charging voltage for battery 62. The function generator provides a reverse excitation current to field winding 28 whenever the output voltage 64 rises above the reference voltage 80. Function generator 86 acts as an amplifier compensation block to control modulator 88 as needed to supply the desired forward or reverse field current and produce the desired output voltage. The amplification and compensation produced is dependent upon the error signal on line 84 determined as the error between the output voltage at 64 and the reference voltage 80. Function generator 86 and modulator 88 may be arranged to simply provide a steady, i.e., unswitched and unpulsed continuously linearly variable, forward or reverse excitation current in the amount needed to produce the desired output and to thereby linearly reduce the error signal 84 to zero. This produces a linear regulation scheme in which the linear output of the modulator 88 is the same as the average current needed to produce the desired output voltage. However, it is only necessary for the average current to approximate the desired levels, and so a preferred method of regulation is to arrange the function generator 86 and modulator 88 to use pulses to adjust the average current through rotor winding 28. Pulses of a positive polarity cause a forward voltage to be applied to the field winding and pulses of a reverse polarity cause a reverse voltage to be applied. The width of the pulses is varied to vary the average current through the field winding. This provides an electrically efficient circuit design to control the magnitude and direction of the average field current. This constitutes the basic two state pulse width modulation (PWM) voltage regulator circuit that alternately switches directly between the forward and reverse polarity modes. Voltage Regulation - Dual Voltage Alternator The rotor excitation circuit comprising elements 80-88 provides a constant output voltage at 64 to supply electrical circuits and charge battery 62. If the alternator is to be a single voltage alternator, this is sufficient. If the alternator is to be a dual output voltage alternator, then typically one of two alternative designs will be used. In the simplest design, the stator will be provided with a second winding as previously mentioned. The error signal 84 may be based upon the output from only one of the two stator windings, with the second output permitted to seek its own level as the first is regulated. Alternatively, an error signal which is a function of the output voltage from both windings may be used so that neither output is fully regulated, but both are held approximately to the desired level set by the composite error signal. However, Fig. 4 illustrates a preferred alternative design for a dual output voltage alternator according to the invention. In this design, the alternator is principally a single output voltage alternator producing a constant voltage at output 64 for battery 62 which is the higher voltage battery. Instead of producing the second voltage from a second winding, it is provided by a voltage converter circuit 90. In a manner similar to that desσibed for the excitation circuit above, a reference voltage 94 is summed with an output voltage 96 connected to the second battery 92 in a summing circuit 98 to produce an error signal on line 100. A function generator 102 controls a modulator 104. Modulator 104 generates a series of pulses to turn switch 106 on and off in a switching power supply design. The switching power supply is conventional and produces a voltage regulated output which is filtered with capacitor 108 and coil 110. The voltage source for the switching regulator must be higher than its output voltage and may be connected either to output 64 over line 114 or directly to the stator windings 16 over dashed line 116. Generally, one source or the other would be selected and the connection would be made permanently over line 114 or 116 instead of through a switch 118. Hybrid Alternator - Axially Magnetized Permanent Magnet Fig. 6 shows a first alternative embodiment of the alternator generally indicated at 200, employing a pair of solid disk-shaped permanent magnets 210, 212 magnetized with multiple poles. The disk may be made of a bonded permanent magnet material. The stator 214 is essentially similar to the stator 14 desσibed in connection with the previous embodiment, and, accordingly, is shown only in outline form. It generally will include a three phase winding wound into the slots in a laminated or cast stator made of a good grade of electrical steel. Dual windings may be used in dual voltage output designs, if desired. Stator air gaps corresponding to stator air gap 52, described previously, may be introduced on either side of the wound field rotor portion to isolate the permanent magnet portion of the stator from the wound field portion. A single permanent magnet portion may be used similar to the design described in connection with Figs. 1-3 or two permanent magnet portions longitudinally separated on opposite sides of the wound field rotor portion may be used as shown in the embodiment of Fig. 6. The solid disk permanent magnet element is shown separately in Fig. 7. It could be made of separate permanent magnet elements, but is preferably made as a single piece, magnetized through its thickness, in a longitudinal direction, parallel to the shaft when assembled. This is 90° (ninety degrees) to the direction of magnetization of the permanent magnets shown in Figs. 1 and 3 where the magnetization is radially oriented instead of longitudinally. In order to generate electricity, the field lines of the rotor must penetrate the air gap 216 between the rotor and the stator and cut the stator windings. With the magnetic field turned longitudinally, the magnetic flux must be turned and directed up to the air gap. This is accomplished with a flux channeling element generally indicated with reference numeral 218 made up of multiple pole segments 220 as shown in Figs. 8 and 9. Individual pole segments 220 carry the flux from the permanent magnet disk 210 up to the air gap 216 to penetrate the stator windings. A second flux channeling element comprises a flux return plate 222. Two flux return plates are used, located at the end faces of the rotor, one for each magnetic disk. By forming the permanent magnet in a solid disk and rotating the direction of magnetization, improved mechanical strength is achieved and greater magnet size and surface areas results. This provides for an inherently strong design and allows the magnetic flux exiting the large face areas of the disk to be concentrated as it is channeled up to the air gap by the pole segments 220. In the preferred configuration of this embodiment, the pole segment pieces 220 are shaped with openings 224 which wrap around the winding extensions in the wound rotor. This shape give added strength to the windings and allows very high rotational speeds to be achieved without damage to the rotor. The end pieces 222, permanent magnet disks 210, pole segment pieces 220 and the wound rotor section are held together by rivets 226 extending through holes 228 and 230 in the segment pieces and magnetic disk respectively. The rotor components of Fig. 6 are mounted on shaft 22 in a manner identical to that shown in Fig. 1. Shaft 22 will be journaled in a housing and have slip rings contacted by brushes for supplying current to the wound field rotor section. Voltage output and regulation is identical to that desσibed previously. Hybrid Alternator - Circumferentially Magnetized Permanent Magnet Yet another embodiment of the invention is shown in Figs. 10 and 1 1 and generally indicated with reference numeral 300. In this embodiment, permanent magnets 302 are embedded in a retainer 304, formed of a non-magnetic material such as aluminum, which forms a hub around the rotor shaft 22. The retainer isolates the magnets magnetically from the hub and holds them securely. As in each of the previous two designs, the permanent magnets 302 are magnetized through their thickness. However, they are mounted with the direction of magnetization oriented in yet a third direction, in this case circumferentially relative to the shaft. The embedded magnets in Fig. 11 are inserted into the non¬ magnetic retainer with alternate orientations between flux channeling elements 306 located circumferentially adjacent to and between the magnets 302. The flux channeling elements 306 are made of a material that has high magnetic permeability. They direct the magnetic flux, as indicated by arrows 308 from the magnets to the air gap between the rotor and stator. This design like the design desσibed in connection with Figs. 6-9 permits a relatively large amount of permanent magnet material to be used in a small space, with the flux being concentrated at the rotor perimeter. In some applications, this allows the use of less expensive permanent magnets which reduces cost. In other applications using high energy magnets, the design in Figs. 1-3 may be preferred. The stator 310 will be substantially identical to the stator desσibed in connection with Figs. 1-3. A non-magnetic end cap 312 provides support for the wound field rotor extensions in the wound field portion 314. A similar end cap for the rotor windings may be incorporated into the magnet retainer as shown, or may be formed as a separate piece. It should be noted that while this end cap piece is similar in appearance to the magnetic material piece 220, in Fig. 6, it is formed of a non-magnetic material in this design and of a magnetically permeable material in Fig. 6. Voltage Regulator - Three State Design Fig. 12 illustrates a block diagram of a first preferred embodiment of a bridge circuit type of three state voltage regulator. The voltage regulator controls bi-directional current flow through a winding 400 on the rotor of a hybrid alternator of a type previously desσibed. The regulator may also be used with other types of alternators or devices requiring three state control. The rotor winding 400 in combination with the permanent magnet portion of the rotor induces a flux in the stator winding 402, 404, 406 of the hybrid alternator. Bi-directional current flow is achieved through the use of four switches 408, 410, 412 and 414 arranged in a bridge configuration to form a switching circuit. A first upper switch 408 is connected to a first end of the winding 400 and forms with a first lower switch 414 a first pair of switches. When these switches are closed, the first end of the rotor winding 400 is connected to the positive end of the battery 416 over the positive bus 418 and the second end of the rotor winding 400 is connected to the negative end of the battery 416 over the ground 420. When the first pair of switches 408, 414 are closed, the voltage regulator said to be in the forward polarity mode or in the boosting mode, and forward current flows from the first end of the rotor winding 400, connected to switch 408, to the second end of the rotor winding 100, connected to switch 414. A second upper switch 410 forms with a second lower switch 412 a second pair of switches. When the second pair of switches is closed, a second end of the rotor winding 400 is connected to the positive bus 418 and the first end is connected to the ground 420. In this configuration the voltage regulator is said to be in the reverse polarity mode or the bucking mode. Control logic is provided to make these modes mutually exclusive. Winding 400 is wound onto the rotor so that in the forward polarity mode the magnetic flux produced by forward current flow is added to the magnetic flux provided by the permanent magnet section of the rotor. Conversely in the reverse polarity mode, a reverse current flow through the rotor winding 400 will generate magnetic flux of the opposite polarity which is subtractively combined with the magnetic flux from the permanent magnets. In order to regulate the output of the hybrid alternator, the prior art has simply switched the rotor winding 400 between forward and reverse polarity modes as desσibed in the basic PWM regulator above. A voltage regulator which operates in only these two modes may be referred to as a two state PWM voltage regulator. The voltage regulator is switched into the forward polarity mode whenever it desired to inσease the output and is switched into the reverse polarity mode whenever it is desired to deσease the output. As discussed above, however, when a forward current has been induced into the rotor winding 400 through switches 408 and 414, considerable energy is stored in the magnetic field produced by coil 400. If the first pair of switches 408 and 414 are immediately opened and the second pair of switches 410, 412 are immediately closed, the forward current induced in the forward polarity mode will continue to flow as the magnetic field from rotor winding 400 slowly collapses. Under certain conditions, this forward field current will continue to flow as reverse current through the second upper switch 410 and in lower switch 412. It will also appear as a reverse current on the positive bus 418. If the net loads on the bus are low, and provided that battery 416 is connected, this reverse current normally enters the battery and charges it slightly. However, in the absence of a battery or other conditions likely to occur, a large voltage spike will be produced which may damage the vehicle components. These spikes and other spikes produced as a result of changing loads on the electrical system of the vehicle could be handled by placing a capacitor aσoss the terminals of the battery 416 from the positive bus 418 to ground 420. However, a capacitor of sufficient size with a temperature rating suitable for operation under the hood of a vehicle would be expensive. Accordingly, the preferred embodiment of the voltage regulator employs a configuration which may be referred a three state voltage regulator design. In this construction, the voltage regulator employs a normal forward polarity mode for starting the flow of a forward current in winding 400 or for inσeasing an existing forward current flow. The reverse polarity mode is used for starting a reverse current flow or inσeasing the magnitude of the reverse current flow. The third mode, referred to here as a decay mode, is entered after the voltage regulator leaves the forward or reverse polarity mode. In the decay mode (which might also be considered a zero voltage or zero polarity mode), current induced in either of the two other modes is permitted to circulate through the rotor winding and decay towards zero without inducing any damaging voltages in the remainder of the circuit. The decay is entered after either of the other two modes whenever the decay current is present to prevent a direct transition from the forward polarity mode to the reverse polarity mode, or the opposite transition which would result in reverse current being applied to the main power bus. Those familiar with four element bridge circuits, for example full wave, bridge rectifiers and the like, will recognize that in the conventional use of bridge circuits opposite pairs of elements are intended to conduct simultaneously. Thus, the first pair of switches conduct in one state and the second pair of switches conduct in the second state. In this three state design, two elements that are directly opposite to one another (instead of diagonally opposite to one another) are opened simultaneously and current is allowed to flow through the remaining two elements in a circulating decay current pattern. For example, in the forward polarity mode, switches 408 and 414 are closed. In the decay mode, switch 408 is opened while switch 414 remains closed. In some implementations of the invention, switch 412 would be closed at this time to provide a conducting path in the forward direction down through the first lower switch 414 and back up in a reverse direction through second lower switch 412. As discussed more fully below, however, switches 412 and 414 are semiconductor switches, preferably field effect transistors which have the property that they can conduct in the reverse mode through an internal diode without applying a control signal to close the switch. This internal diode generates a voltage drop when reverse current flow is occurring which is used to detect the presence of decay current. The decay mode may also be implemented by allowing the decay current to flow through upper switches 408 and 410. Continuing to refer to Fig. 12, the voltage produced by the combined effect of the magnetic flux from the rotor 400 and the permanent magnets on the rotor is generated by the stator windings 402, 404 and 406 and is rectified in a conventional three phase full wave bridge rectifier composed of six diodes 422, 424, 426, 428, 430 and 432. These six diodes correspond to diodes 60 in Fig. 4. The rectified output is fed to the battery 416 over the positive power bus 418 and also feeds the electrical load of the vehicle over a connection (not shown) to the power bus 418. The output voltage of the alternator is monitored over wire 434 by a voltage monitoring circuit 436. The voltage monitoring circuit compares the output voltage of the alternator to a reference voltage from the voltage reference circuit 438 and produces an error signal on line 440. The error signal 440 is applied to the input of control circuit 442. The control circuit 442 includes a primary circuit 444, a decay current detecting circuit 446 and logic circuit 448. The primary circuit is directly responsive to the error signal of the monitoring circuit over line 440 and produces one or more primary control signals that signal the logic circuit 448 to inσease or deσease the output of the alternator. In the basic two state PWM regulator, the primary control signal would have been used to turn on the first pair of switches when an increased output was desired and to turn on the second pair of switches when a decreased output was desired. In the present invention however, the primary control signals are modified in the logic circuit 448 with information obtained from the decay current detecting circuit 446 before secondary control signals are produced. The secondary control signals control the states of the switches 408, 410, 412 and 414 individually over control lines 450, 452, 454 and 456. The decay current detecting circuit 446 is connected to monitor the decay current in rotor winding 400. In the preferred design this monitoring is conveniently done by connections 458 and 460 between the decay current detecting circuit 446 and the first and seconds ends of the winding 400. The decay -28- circuit detecting circuit 446 produces one or more inhibiting signals which are applied to inputs of the logic circuit 448 over lines 462, and 464. Those familiar with the art will recognize that there are other ways to monitor the decay current in winding 400. Automatic Interlock and Internal Voltage Regulator Power Supply Three additional diodes 466, 468 and 470 provide independent power to an internal power supply 472 producing V cc power. The internal power supply 472 supplies power for operating the voltage regulator circuitry. This voltage is regulated to provide the control voltage power supply for the regulator. Since the hybrid alternator contains both a permanent magnet and wound field, the alternator begins to generate a voltage as soon as it begins turning. As the voltage becomes larger it generates enough voltage to power the electronics so that additional boost field can be generated. All of this occurs even before the vehicle reaches idling speed, so that at idle, the voltage regulator is functioning properly. Operating the system in this manner provides an automatic interlock so that the voltage regulator loop is disconnected and draws almost zero field and control current when the alternator is not turning, but automatically connects the voltage regulator electronics as the alternator speeds up. An automatic interlock is very important in a hybrid alternator because the field current should never be shut down when the system is operating at high speeds as severe overvoltages and overcurrents will occur. This is in distinct contrast to present alternators which allow the ignition switch to turn off the voltage regulator field. It is important that the alternator field current be zero when the vehicle is not operating and the engine is off to avoid battery drain, but this should not be done with the ignition key alone. This is because the ignition could accidentally be turned off when the alternator is operating at high speed. Fig. 13 is a detailed schematic circuit diagram corresponding to the block diagram of Fig. 12. Battery 416 is connected to the six (6) bridge rectifier output diodes 422-432 which are connected in turn to the stator windings 402, 404 and 406 in the manner illustrated in Fig. 12. The stator windings 402, 404 and 406 are not shown in Fig. 13, but their connection is entirely conventional. The internal power supply 472 comprises a zener diode 500 regulating the output voltage V cc of an NPN transistor 502. Three terminal voltage regulating devices and other voltage regulating circuits would also be suitable. The voltage monitoring circuit 436 monitors the battery voltage 416 over wire 434 which produces a voltage drop aσoss the resistor bridge 504, 506 and 508. Resistor 506 is made adjustable to adjust the output voltage of the regulator. The scaled output voltage of the alternator is compared in error amplifier 510 with the reference voltage from the voltage reference circuit 438. The voltage monitoring circuit performs error amplification and loop compensation. The reference voltage from reference voltage source 438 is applied to one input of error amplifier 510 and the other input is connected to a voltage divider from the battery. Integral compensation is provided by the capacitive nature of the feedback network between the inverting input of the error amplifier 510 and the output. The compensating network is generally indicated with reference arrow 512. This network eliminates DC error in the regulator voltage over the complete range of speed and load on the alternator. The output of the error amplifier is an amplified error signal on line 440 which is provided to the primary circuit section 444 of the control circuit 442. The error signal is applied to the input of a simple hysteresis block formed by a hysteresis inverter 516 which acts as a two state modulator. When the alternator output is too high, the error signal 440 will be lower and the output of the hysteresis inverter 516 will switch high. This high signal always causes the net field in the alternator to be deσeasing. Alternately, when 516 is low the net field in the alternator is inσeasing. The primary circuit 444 produces four primary control signals on lines 518, 520, 522 and 524. The primary control signal on line 518 is taken directly from the output of the two state modulator 516 and the primary control signal on line 520 is the inverted opposite of that signal. Primary control signal 520 is produced by the inverter 526. The control signals on lines 518 and 520 could be used to drive the diagonally opposite switch pairs of the switching bridge in a two state basic PWM regulator design. They serve as the starting point for the modified control shown here that results in the secondary control signals that actually perform the desired switching. The hysteresis in the inverter 516 in combination with the gain and dynamics of the error amplifier block 436 controls the voltage error and sets the natural oscillation frequency of the loop. The function of the primary inverter 516 could also be performed by a pulse width modulator with a ramp oscillator and corresponding components, however such a design would be more complex and more expensive than the simple digital circuitry shown in Fig. 13. The hysteresis inverter formed by 516 and the positive feedback resistors as shown in Fig. 13 may be replaced by the improved circuit of Fig. 15 which discloses a hysteresis modulator formed by 516 and the resistor capacitor feedback network surrounding it. In this improved circuit, the comparator/operational amplifier element 516 includes feedback to the positive terminal and a first order filter to the negative feedback side providing a hysteresis modulator. This circuit provides improved regulator dynamic performance, as compared to the corresponding elements in Fig. 13, by allowing the modulator frequency to be set well above the loop σossover frequency. The primary control signals on lines 518 and 520 are accompanied by delayed copies of the primary control signals on lines 522 and 524 which are generated by inverters 528 and 530. The output from hysteresis inverter 516 is delayed in a simple resistor capacitor delay generally indicated with reference arrow 532. Thus, primary control line 522 carries a delayed version of the primary control signal of line 520. Line 524 carries a delayed version of the primary control signal on line 518. The primary control signals on lines 518 and 520 are used to provide inputs to the logic circuit 448 which ultimately produces the secondary control signals for switching the switches directing current through the winding 400. Switching elements 408, 410, 412 and 414 in Fig. 12 correspond to field effect transistors (FETs) 534, 536 and 538 and 540 with their associated drive electronics in Fig. 13. When FET 534, corresponding to the first upper switch, and FET 540, corresponding to the first lower switch, are on, the alternator is said to be in the forward polarity mode. When FETs 536 and 538 are on, the alternator is said to be in the reverse polarity mode. The alternator may be said to be in the decay mode whenever both of the upper FETs are off or both of the lower FETs are off indicating that no voltage is being applied to the winding 400 from the battery or alternator output. Different implementations of the invention may turn off both upper switches to disconnect the winding 400 from the battery or both lower switches may be turned off. With additional components other configurations for applying zero voltage to the winding 400 may be employed. -31- In addition to disconnecting the winding 400 from the battery, the winding must be connected so that the current can decay without inducing damaging voltages in the remaining circuitry of the voltage regulator or elsewhere in the automobile. This is accomplished by allowing the decay current to recirculate through two of the switches connected to opposite ends of winding 400. In the preferred design shown in Fig. 13, the recirculating circuit is carried through the lower two FETs. However, the recirculating current could alternatively be carried in the upper two FETs or through other components. Both FETs 538 and 540 could be turned on to carry the recirculating circuit however the FETs have an internal diode which will permit them to carry a reverse current even when they are not biased on. When left off, the recirculating decay current induces a voltage aσoss the internal diode of the lower FET which is sensed by. the decay current detecting circuit 446 over lines 458 and 460 connected to the first and second ends of the winding 400. Diodes 542 and 544 isolate comparators 546 and 548 from the FETs whenever the drain of the FET is high during the forward or reverse polarity mode. One side of the comparators 546 and 548 has a voltage reference obtained from a voltage divider and the voltage reference source 438 Vref and the other side has a filtered version of a voltage which is one diode drop above the FET drain voltage when it is near ground. Diode 542 and 544 raise the voltage level by one diode voltage drop so that no negative voltages are needed on the inputs of comparators 546 and 548. The logic circuit 448 is implemented in Fig. 13 with logic gates 550, 552, 554, 556, 558, 560 and 562. The logic circuit implemented in these gates accepts the primary control signals and inhibiting signals over lines 462 and 464 from the decay current detecting circuit 446 to produce the secondary control signals on lines 450, 452, 454, 456. When a secondary control signal such as the secondary control signal 454 switches high, its associated FET, e.g. FET 534 turns on. The logic function performed by gates 550, 552 and 554 is identical to the logic function performed by gates 556, 558, 560, and 562. Different logic elements are used to implement the same logic function in order to reduce component count which can be implemented on only two logic chips. Logic gates 550 and 562 control the upper FETs 534 and 536 respectively. -32- Logic gate 550 is a triple input AND gate. Its output is high and the corresponding FET 534 is on only when all three inputs to the triple input AND gate are high. These three inputs are the primary undelayed PWM control signal on line 518, the delayed primary control signal PWM on line 524 and the inhibiting signal on line 464 from the decay current monitoring circuit monitoring reverse current in FET 540. The presence of the inhibiting signal on line 464 indicates the presence of reverse decay current in the winding 400 as a result of a decaying current originally induced in the reverse polarity mode. The inhibiting signal on 464 is holding the second lower FET 538 on and inhibiting FET 534 immediately above it from being switched on at the same time. Once the current induced in the reverse polarity mode decays to a sufficiently small value, the inhibiting signal on 464 switches state allowing the circuit to change modes. Although the voltage exciting the field winding has three modes namely the forward polarity mode, the reverse polarity mode and the decay mode, the FETs actually have four different states. In the forward polarity mode FET 534 and 540 conduct. In the reverse polarity mode FETs 536 and 538 conduct. In the decay mode (two states), both FETs 534 and 536 are off. The decay mode has two different states, a forward decay mode and a reverse decay mode. In the forward decay mode, the current induced in the forward polarity mode is allowed to decay and FET 540 is held on with FET 538 remaining off, but conducting through its internal diode. In the forward decay mode, the decay current continues to flow through the winding 400 in the same direction as its flows when in the forward polarity mode. In the reverse decay mode, FET 538 is on and FET 540 is off, but conducting through its internal diode with reverse current circulating through the winding 400 down through FET 538 and back up through FET 540. The present invention utilizes a bridge circuit arrangement to provide bilateral voltage excitation of the winding 400. The voltage monitoring circuit 436 provides basic error amplification to produce the error signal on line 440. The voltage regulation loop contains a compensation block to shape the loop frequency response to provide for tight control of the average battery voltage. The compensated amplifier output error signal on line 440 drives a pulse width modulator, or other two state modulator, which indirectly drives a full bridge output stage to provide the bi-directional current through winding 400 which is connected aσoss the center taps of the bridge. Logic circuit 448 modifies the output of primary circuit 444 to allow a third state of voltage excitation of near zero voltage applied to the winding 400 whenever the field current magnitude is being deσeased. Primary control signals from primary circuit 444 act to directly turn on the diagonally located pair of bridge switches. However a zero voltage excitation is employed whenever the magnitude of the field current is to deσease. When the field current's instantaneous magnitude is being commanded to inσease by the primary control signals from 444, full bus voltage of appropriate polarity is applied to the field coil by exciting the appropriate diagonal pair of bridge elements. However, when the field current magnitude is being reduced, only the upper switch in the previously conducting diagonal pair of swishes is turned off. By utilizing a delay in the turn off of the lower diagonal switch and turn on delays in the opposite diagonal switches, the inductive field current that was flowing in the upper switch transfers to negative current in the switch element immediately below the one being turned off. Current flow in the lower diagonal switch continues due to the previously desσibed delay in its turn off. Its lower diagonal switch is then commanded to remain on by the presence of reverse current in the other lower switch. When the reverse conducting power switch is an FET, as shown in the preferred embodiment of Fig. 13, and when that switch has a delayed turn on, the reverse current first flows through the FET's intrinsic diode generating a voltage drop of about -0.6 voltages. If the lower reverse conducting FET were turned on, the reverse circulating current would also flow through FET on resistance leading to a lower voltage drop. As desσibed above in the preferred implementation of this invention this FET is kept off during the decaying current in order to allow the voltage across the FET's intrinsic diode to provide a simple indicator of the presence of decaying field current. The nonlinear diode characteristic provides a reasonable voltage level even for small currents. This allows the use of a simple voltage comparator in the form of comparators 546 and 548, to indicate the presence of field current. When the intrinsic diode voltage is more negative than a threshold set by reference voltage source 438 and the resistor divider below that point, the presence of reverse current is indicated. -34- When the comparator indicates the presence of field current in the reverse conducting switch, the drives to the opposite diagonal elements are inhibited by the comparator signal and drive to the lower FET which is conducting the decaying field current is kept on. After the comparator indicates near zero field current, it is safe to excite the opposite diagonal bridge elements as commanded by the primary control signals of the primary circuit 444. Switching the new diagonal pair on at zero field current will not introduce any negative current into the bus and therefore causes no harmful voltage spikes if the battery becomes disconnected when the system is lightly loaded. Control Logic and Method of Three State Regulation The primary control loop contains the voltage monitoring circuit 436 monitoring the output on line 434 and includes an error amplifier operating on the difference between the battery voltage and the reference 438. The amplified error signal drives a pulse width modulator, or other two state modulator, incorporated in primary circuit 444 to produce the primary control signals, which include the PWM signal at the output of the two state modulator, the inverted PWM signal and delayed copies of those two signals. The primary PWM control signal switches between the on state and the off state. During the on state it is set to turn on one diagonal pair and the opposite diagonal pair during the off state and vice versa. Because of the two state basic step up, digital logic is preferred for implementing the control system. The actual switch commands are modified by delays, inhibits and other signals to produce a more complex switching structure and avoid negative bus current as desσibed below. When inσeasing the instantaneous magnitude of field current through the winding 400, the appropriate diagonal bridge pair is fully on. However, to avoid negative current steps into the bus, the bridge operates to let the field current decay naturally in a circulating current loop containing only the lower switches rather than forcing a more rapid decay with reverse excitation from the bus. To set up this natural decay, both the upper bridge elements are off and the decaying field current circulates in the lower bridge elements. One lower bridge element conducts in a forward direction while the other conducts in reverse. This natural decay continues until the two state modulator, corresponding to hysteresis inverter 516, changes state again or the field current goes to zero. In the first case, the originally conducting pair comes on again. In the latter case, when the field current reaches zero, the opposite diagonal pair comes on. The natural decay feature is performed by inhibiting the turn on of the new diagonal pair until the decay current has approximately reached zero. Overall operation in the preferred design is thus multiple state with four states of operation of the output switches taking place or three states of instantaneous voltage aσoss the field winding if the switch device drops are neglected. The three states of instantaneous field winding voltage are plus battery voltage, zero voltage and minus battery voltage. The preferred method of operation of the invention employs the following steps: (1) the on upper device turns off immediately in response to an undelayed PWM off command, (2) the turn off of the lower elements is delayed and all bridge element turn ons are delayed an equal or longer time allowing circulating current in the lower bridge elements to automatically take place when the upper device turns off, (3) threshold comparators on each lower switch indicate the presence of reverse current (decaying field current) in that device and that logic signal is used to perform the following steps: a) The FET drive on the reverse conducting switch is inhibited to avoid interfering with the threshold voltage measurement; b) The turn off drive on the new upper diagonal switch is inhibited because the switch below it will be on for the circulating decay current; c) The drive on the other lower FET will be forced to remain on to carry the decaying circulating current; d) If the primary control signals return to their original state before the field current goes to zero, the original diagonal pair of output devices will come back on and the magnitude of field current begins to inσease again. This is the normal mode of operation when operating at constant speed and fixed loads. The system will operate between driving the field winding with the bus voltage in one state and having the field decay with circulating currents in the lower FETs for the other state. This full drive voltage followed by zero drive voltage operates in the same manner independent of the direction of the average field current. Thus, in normal operation at relatively low alternator speeds, with a fixed load, the alternator will cycle between the forward polarity mode and the decay mode (more specifically, -36- between the forward polarity mode and the forward decay mode). When the alternator is operating at relatively high speeds, the alternator will cycle between the reverse polarity mode and the decay mode (more specifically, between the reverse polarity mode and the reverse decay mode). During these normal cycles between the forward or reverse polarity mode and the decay mode, the primary control signal on line 518 will be alternating between the on and off states. e) Only when the field current goes to zero before the primary signal on line 518 returns to its original state does the opposite bridge pair come on and the current in the rotor winding 400 change direction. This type of operation will occur if the average field current is near zero or if the alternator speed or load changes abruptly. Temperature Monitoring Voltage Regulator Fig. 13A provides a circuit diagram of the preferred embodiment of a temperature monitoring voltage regulator in accordance with the present invention. The circuit illustrated substantially corresponds to the circuit diagram of the three- state voltage regulator shown in Fig. 13, except that the voltage monitoring circuit 436 has been modified to replace resistor 508 with temperature sensor 509. Temperature sensor 509 is mounted in thermal contact with the hybrid alternator so that it can monitor the alternator temperature, and has a variable resistance that is a function of temperature. A preferred location for mounting temperature sensor 509 is on a common heatsink with the output diodes 422-432. Other mounting locations are also suitable. Generally, a mounting location near the most heat sensitive components of the alternator or near the location where the most heat is produced by the alternator is preferred. The function of the temperature sensor 509 is to adjust the error signal at the output of the voltage monitoring circuit (on line 440) whenever the alternator approaches or exceeds a preset alternator temperature. In the embodiment shown in Fig. 13A, the temperature sensor 509 is preferably a thermistor with a positive temperature coefficient (PTC). This type of PTC thermistor sensor has a resistance that is a nonlinear function of temperature. At temperatures below a σitical temperature, the PTC thermistor has a relatively constant resistance. This constant resistance appears in the resistive voltage divider formed by resistors 504, 506 and the sensor 509, and the voltage regulator acts in exactly the manner desσibed in connection with Fig. 13 incorporating resistor 508. This produces a voltage at the input of the error amplifier 510 that is directly proportional to the output voltage of the alternator. If the alternator output voltage rises or falls in response to a changing load, the rise or fall is sensed by the error amplifier relative to the reference voltage from 438 and the alternator output is adjusted, as previously desσibed, to hold the desired output voltage constant. As the alternator heats up and approaches the σitical temperature of the thermistor, however, the thermistor's resistance begins to inσease dramatically. The portion of the output voltage that appears aσoss temperature sensor 509 in the resistive divider inσeases correspondingly. The error amplifier 510 sees this voltage inσease as an apparent inσease in the output voltage of the alternator, and begins to deσease the output voltage in response. As the output voltage drops, the output power of the alternator decreases and the alternator temperature being sensed deσeases. The result is that the alternator can produce significantly more power than its rated output for as long as the thermistor temperature remains below its σitical temperature. With the proper selection of thermistor, having a desired variable resistance as a function of temperature, any desired maximum operating temperature for the hybrid alternator may be set. An appropriately designed hybrid alternator constructed with a temperature monitoring regulator of the type desσibed will be able to continuously provide its full rated power output at any engine speed and at any ambient temperature. It will be able to provide this power from the instant the engine first begins to turn the alternator. At speeds above idling speed, the hybrid alternator will be able to provide significantly more than its full rated power output. Even under worst case high ambient temperatures extra output is available for a short time until the alternator reaches its maximum operating temperature set by the temperature sensor and the design of the voltage regulator. Thereafter it will be limited by the design cooling of the alternator and will be able to continuously produce its full rated output. Under cooler ambient temperatures than the worst case conditions, the alternator will be able to continuously produce greater than its rated output. This assumes that the engine is turning sufficiently fast that the alternator output is not limited by the magnetic flux the rotor windings can produce in combination with the permanent magnets. If the load on the alternator is so great that the alternator's cooling capacity is exceeded, the temperature monitoring voltage regulator will reduce the alternator voltage output. The alternator's power output is reduced just enough to continuously hold the alternator at or near the σitical temperature of the thermistor, i.e. at the maximum safe operating temperature of the alternator. In this way the alternator is protected against damage from overheating when its rated output is exceeded. Those familiar with the art will recognize that a negative temperature coefficient (NTC) resistive device or equivalent circuit could also be used instead of the PTC thermistor 509, by replacing resistor 504 in the upper branch of the resistive divider with the NTC element and by reinserting resistor 508 in the lower branch. Alternatively, the variable resistance of a temperature sensor may be used to modify the reference voltage seen by the error amplifier at the other input to error amplifier 510. This could be accomplished by using a resistive bridge similar to the resistive bridge shown in Fig. 13A, except placing that bridge at the non- inverting input of the error amplifier and applying the reference voltage aσoss the bridge. The variable resistance due to temperature would then vary the reference voltage and thereby modify the error signal to control the output voltage and output power. Other types of temperature sensors, such as thermocouples, temperature sensitive diodes, etc. along with additional circuitry, as needed, may also be used. Further, although the preferred embodiment is based upon the three state voltage regulator design, a two state voltage regulator design as shown in Fig. 4 may also be used. The modification necessary to implement the invention in a two state voltage regulator design corresponds exactly to the modification desσibed above for the three state design. Preferably a resistive bridge is formed with a sensor having a nonlinear variable resistance as a function of temperature, and the bridge is used at one of the inputs to the summing circuit 82 either to modify the sensed alternator output voltage or to modify the reference voltage. In either case the resistive bridge is arranged to deσease the output voltage of the alternator as the maximum desired operating temperature is reached. Transient Suppression The voltage regulator illustrated in Fig. 13 incorporates a unique method of suppressing voltage transients, such as those generated in a classic "load dump" situation well known in the automotive industry. Load dump is a situation where a heavy battery load is suddenly switched off or when the battery itself is disconnected while drawing heavy current. In this situation a suppresser device is required to handle the inductive energy stored in the alternator windings. The present voltage regulator uses a signal level zener diode 580 with directing diodes 582, 584, 586 and 588 that turn on the bridge FET diodes so that the bridge FETs can absorb the transient. FET devices are able to handle large power impulses effectively and thus the bridge arrangement when properly controlled in a transient voltage situation allows these devices to perform a dual function. The remaining transistors and inverters 590 and 592 are drive circuitry which drives the various FETs in the bridge circuit. The upper power FETs 534 and 536 are directly driven with conventional NPN/PNP level translation circuitry. The PNP transistors 594 and 596 nearest the FET gates provide active gate pull down. The FETs are turned on and off relatively slowly with the circuitry shown to minimize interference. The field current modulation can produce current steps in the alternator output ranging between full alternating field current and zero. Since the alternator has a finite output inductance, it cannot change its current instantly. Slower rise and fall times on the power FETs partially alleviate this problem and the voltage clamp arrangement provided by zener diode 580 and its associated diodes 582-588 protects the FETs from reaching their breakdown voltage should be short voltage excursions exceed the clamp voltage. A clamp voltage of about 27 volts is used. Inverters 590 and 592 are arranged as two charge pump oscillators. The oscillators, with the rectifying and related circuitry generally indicated with arrows 591 and 593 provide a voltage higher than the battery voltage on line 595 for driving the upper power FETs to switch the battery voltage. Neutral Point Connected Alternator Fig. 14 illustrates a novel wiring arrangement for a hybrid alternator in which the rotor winding 600 is connected to the neutral point connection of the stator windings 602, 604 and 606. As discussed above, the rotor winding 600 of a hybrid alternator must be supplied with a forward polarity voltage to inσease the alternator output voltage and a reverse polarity voltage to deσease the alternator output. This polarity reversal is achieved in the three state voltage regulator shown in Fig. 12 with a bridge circuit which alternately turns on opposite diagonal pairs of switches in a four element bridge circuit. One pair connects the rotor winding between full battery voltage and ground to produce the forward current, and the diagonally opposite pair connects the rotor winding between full battery voltage and ground with the opposite polarity to induce reverse current flow through the winding. The bridge circuit requires at least four switching elements to accomplish this polarity reversal. In the circuit shown in Fig. 14, however, only two switches are needed. A first end of the rotor winding 600 is connected to the neutral point 608 of the stator winding and the second end is connected to a switching circuit 624 in a voltage regulator 642. The neutral point 608 of the alternator of Fig. 14 is at the center point of the three individual stator windings 602, 604 and 606. Multiphase windings composed of different numbers of individual stator windings connected together at one end to form a star may also be used. The multiphase stator winding is conventionally rectified in a multiphase bridge rectifier composed of diodes 612-622. Because the neutral point of a star configured stator winding operates at approximately one half the output voltage applied to the battery 610, a forward current can be induced in the rotor winding 600 simply by connecting the opposite end of the rotor winding to the positive end of the battery 610. Alternatively, to induce a negative current in the rotor winding, the opposite end can be connected to ground. Although the voltage applied to the rotor winding in this configuration is less than the voltage applied in a bridge configuration, the current may be made comparable by adjusting the number of turns and the impedance of the rotor winding to produce the desired magnetic flux. The switching of the second end of the rotor winding between battery and ground is accomplished with a switching circuit 624 that needs only two switches 626 and 628. The operation of switches 626 and 628 is controlled by a control circuit 630 over primary control lines 632 and 634. Control circuit 630 closes switch 626 and opens switch 628 to apply a forward polarity voltage to the rotor winding 600. Switch 626 is opened and switch 628 is closed to apply a reverse polarity voltage to the rotor winding 600. By driving the switches in complementary fashion and by using a varying duty cycle from 0 to 100 percent, the average voltage aσoss the field coil can be controlled to range between full boost and full buck to account for various speeds and loads. During the forward polarity mode, current flows from the battery, through switch 626, through the rotor winding 600 to the neutral point 608 and from there out the individual stator windings 602-606 and bridge diodes 612-622. The specific amounts of current flowing through the specific stator windings and bridge diodes depends on the phase of the alternator and varies as the alternator rotates. -41- A monitoring circuit 636 monitors the output voltage over line 638 by comparing the output voltage to a reference voltage 640. The voltage regulator 642 is essentially a two state PWM voltage regulator of the basic type previously desσibed. However, instead of using the primary control signals to turn on and off diagonal pairs of switches in a bridge circuit, the primary control signals are used to turn on and off only two individual switches 626 and 628. In applications where the basic two (2) state PWM control scheme for the voltage regulator is suitable, the reduction in voltage regulator cost due to using only two switches when used with a neutral point connected hybrid alternator will be significant. The neutral point connected hybrid alternator has a further advantage that the alternator field current automatically goes to zero at zero speed. Thus, the ajternator drive does not have to be disabled to turn off alternator current when the ignition is turned off. The control electronics may be designed to consume very little power, and thus may be left continuously on without risk of discharging the battery. In this manner, the neutral point connected hybrid alternator achieves the automatic interlock function previously described in which the regulator is automatically powered when the alternator begins to rotate and automatically unpowered when the alternator stops rotating. The control circuit 630 may be a simple two state hysteresis amplifier, a simple inverter with hysteresis, a comparator or operational amplifier with feedback to produce hysteresis, a standard pulse width modulator, etc. The neutral point connected rotor winding may also be driven with a linear drive in which the current is smoothly varied between a forward maximum and a reverse maximum using alternative control systems. Because the rotor winding is rotating and the stator windings are fixed, the field winding to the connection to the neutral point and the switching circuit will be made through slip rings in a conventional way. Hybrid Altemator-With Single Rotor Having Poles Fitted With Permanent Magnets And Field Windings Figs. 16 and 17 show an alternate embodiment of the hybrid alternator of the present invention. Hybrid alternator 700 includes a stator 702 having a longitudinal stator region 704. A three phase stator winding 706 (also the same as winding 706 shown in Fig. 4) extends through slots 708 formed on the interior of stator 700. A rotor 710 is mounted for rotation within stator 702 on shaft 712. -42- Rotor 710 comprises core 714 (indicated by the area within the circular dotted line in Fig. 17) and defines a plurality of magnetic rotor field poles 716. Poles 716 are configured to have alternating north and south magnetic fields. The rotor 710 may be conventionally formed from multiple thin laminations having the σoss-sectional shape seen in Fig. 17 stacked adjacently along rotor shaft 712. Alternately, the rotor field poles may be constructed using solid cast magnetic material. Fig. 17 is a σoss-section through stator region 704 of stator 702 within which rotor 710 rotates. Two (2) of the magnetic poles 716 include permanent magnet 718 mounted on the end thereof to define permanent magnetic poles 716a and 716b. The remaining magnetic poles are wound field rotor poles and have rotor windings 720 wherein alternate poles positioned between poles 716a and 716b are wound in opposite directions to produce alternating north and south magnetic fields. Permanent magnets 718 have a "bread-loaf" shape that matches the curve or perimeter of rotor 710. The rotor field pole bodies that are part of the permanent magnetic poles are preferably tapered as shown in Fig. 17. The pole bodies may also be configured to have a uniform width, or other geometric shapes may be used. Furthermore, although Fig. 17 shows rotor 710 having ten (poles) 716 wherein two (2) poles are permanent magnetic poles diametrically positioned, alternate configurations may also be used. For example, alternate designs may utilize more or less than two (2) permanent magnetic poles. Furthermore, if more than two (2) permanent magnetic poles are used, the position of these poles with respect to one another may be varied. Each magnet 718 is magnetized through its thickness and mounted such that the direction of magnetization extends radially as indicated by arrow 721 , i.e., in a direction which is perpendicular or radial to shaft 712 and normal to the large faces of magnets 718. The magnets are held in openings in rotor laminations 715 around the perimeter of rotor 710. Referring to Fig. 17A, it is preferred that magnets 718 are secured to rotor field pole body 717 via sσew 719 that is counter- sunk to be flush with the top surface of magnet 719. If permanent magnets are to placed adjacent one another, then the north pole of one magnet must face outward and the north pole of the next magnet must face inward or vice-versa, in order to effect alternating north and south magnetic poles throughout the entire rotor perimeter. The permanent magnets 716a, 716b are fabricated from the same materials discussed above for the other embodiments shown in Figs. 1-3. Laminations 715 include multiple openings 722 to reduce weight and allow for cooling air flow through the alternator. Fig. 18 is a view similar to Fig. 17 of a further alternator embodiment. Alternator 750 is similar to alternator 700 and includes stator 702 having a longitudinal stator region and rotor 752. Rotor 752 comprises core 754 (indicated by the area within the dotted line in Fig. 18) and defines a plurality of rotor field poles 756. Poles 756 are configured to have alternating north and south magnetic fields. Rotor 754 may be conventionally formed from multiple, thin laminations having the σoss-sectional shape seen in Fig. 18 stacked adjacently along rotor shaft 712. Alternately, the rotor field poles may be constructed using solid cast magnetic material. The laminations include multiple openings 755 to reduce weight and allow for cooling air flow through the alternator. Magnetic poles 756a and 756b are permanent magnet poles and include permanent magnets 758a and 758b, respectively. Permanent magnet 758a is mounted between body portion 760a and pole shoe 762a. Similarly, permanent magnet 758b is mounted between body portion 760b and pole shoe 762b. The placement of the permanent magnets between the pole body and the pole shoe improves the mechanical integrity of rotor 752 and reduces vibrations during rotation of the rotor. Similar to rotor 710, the remaining magnetic poles of rotor 752 are wound field rotor poles and have rotor windings 764 wherein alternate poles positioned between poles 756a and 756b are wound in opposite directions to produce alternating north and south magnetic fields. Permanent magnets 758a and 758b have a substantially rectangular shape. Pole shoes 762a, 762b have a "bread-loaf shape that matches the curve or perimeter of rotor 710. However, other pole shoe and magnet shapes may be used. Although Fig. 18 shows rotor 752 having ten (10) poles wherein two (2) of the poles are permanent magnetic poles diametrically positioned, alternate configurations may be used. For example, alternate designs may utilize more or less than two (2) permanent magnets. Furthermore, if more than two (2) permanent magnets are used, the position of the magnets with respect to one another may be varied. As desσibed above for permanent magnets 718 of rotor 710, permanent magnet 758a and 758b are magnetized through its thickness and mounted such that the direction of magnetization extends radially as indicated by arrow 721, i.e., in a direction which is perpendicular to shaft 712 and normal to the large faces of the magnets. Referring to Fig. 18A, it is preferred that pole shoe 762a and magnet 758a are secured to rotor pole body 760a via sσew 719 that is counter-sunk to be flush with the top surface of pole 762a. Pole shoe 762b and magnet 758b are secured to pole body 760b in the same manner. Referring to Fig. 19, a further embodiment of the alternator of the present invention is shown. Alternator 800 includes stator 802 which has a longitudinal stator region and a rotor 808 which is mounted for rotation within stator 802 on a shaft. A three phase stator winding 804 extends through slots 806 formed on the interior of stator 802. Rotor field poles 810 radially extend form rotor core 812 which is defined as the area within the dotted line. Poles 810 are magnetic poles wherein adjacent ones of the poles 810 produce alternating north and south magnetic fields. Poles 810a-d are permanent magnet poles and are formed by magnets 814a and 814b. Magnet 814a is contiguous to and mounted between poles 810a and 810b. The permanent magnets 814a and 814b effect a magnetic field that is oriented circumferentially relative to the rotor core rotational axis. The magnetic field is indicated by arrow 815 in Fig. 19. Magnet 814a is mounted between poles 810a and 810b in a manner such that magnet 814a is within the rotor perimeter. Non-magnetic spacer 816a magnetically isolates permanent magnet 814a from rotor core 812. Spacer 816a can be fabricated from non-magnetic material such as aluminum. However, an air gap or space may also be used without any non-magnetic material. Similarly, magnet 814b is contiguous to and mounted between poles 810c and 81 Od. Magnet 814b is mounted between poles 810c and 81 Od in a manner such that magnet 814b is within the rotor perimeter. Non-magnetic spacer 816b isolates permanent magnet 814b from rotor core 812. As stated above, an air gap or space may be used in place of a non-magnetic material. Thus, magnets 814a and 814b effect two (2) pairs of adjacent permanent magnet poles. The remaining rotor poles have rotor windings 818 arranged such that alternate poles are wound in opposite directions to produce alternating north and south magnetic fields. The design configuration of rotor 808 offers significant advantages. One advantage is that since magnets 814a and 814b are directly in series with the near half of the steel rotor poles 810a and 810b, and the far half of poles 810a and 810b may be utilized with the adjacent wound field poles on either side of the permanent magnet pole pair. Thus, the permanent magnet poles 810a and 810b do not magnetically present a high reluctance to the adjacent wound fields. Another advantage is that permanent magnets 814a and 814b may be realized by low cost ferrite magnets. The aforementioned advantages also apply to the permanent magnet pole pair comprised of poles 810c, 81 Od and permanent magnet 814b. Although two (2) diametrically positioned permanent magnet poles are shown, other configurations may also be used. For example, only one (1) permanent magnet pole pair maybe used. Another example is two (2) permanent magnet pole pairs that are not diametrically positioned on rotor 808. Designs utilizing different proportions of permanent magnet poles to electromagnetic poles may be used. Furthermore, although Figs. 17, 18 and 19 show rotors 710, 752 and 808, respectively, using ten (10) rotor field poles, the rotors may be configured to define more or less than ten (10) rotor field poles. The alternator hybrid alternator embodiments of Figs. 17-19 may be operated with a field regulator that can be operated in bucking and boosting modes desσibed above. Furthermore, the alternate hybrid alternator embodiments of Fig. 17-19 may be used with the two (2) and three (3) state voltage regulators desσibed above. Additionally, the hybrid alternators of Fig. 17-19 may be configured as neutral point connected alternators as desσibed above. Referring to Fig. 19a, a further embodiment of the alternator of the present invention is shown. Alternator 900 includes stator 902 which has a longitudinal stator region and a rotor 908 which is mounted for rotation within stator 902 on a shaft. A three phase stator winding 904 extends through slots 906 formed on the interior of stator 902. Twelve (12) rotor field poles 910 radially extend from rotor core 912. It is highly preferred that core 912 be non-magnetic in order to magnetically isolate permanent magnets 914a-f from rotor core 912. Such magnetic isolation prevents flux from flowing from a portion of a magnet having one polarity, through rotor core 912 and to a portion of another magnet having an opposite polarity. For example, non-magnetic core 912 prevents flux from flowing through core 912 and between the S-pole of magnet 914a and the N-pole of magnet 914c. Thus, such magnetic isolation eliminates an unusable flux path at the point of isolation and forces the flux to be focused toward active air gap 913 which is between rotor 908 and stator 902. In a preferred embodiment, core 912 is fabricated from a non-magnetic material such as aluminum, copper, brass, plastic and ceramic. As shown in Fig. 19A, non-magnetic core 912 has a pair of PCI7US96/03914 -46- diametrically positioned substantially dovetail shaped male formations 913 and 915 which are disposed in corresponding substantially dovetail shaped female formations 917 and 919, respectively, formed in rotor 908. Such a configuration prevents core 912 from rotating with respect to the remaining portion of rotor 908. It is highly preferred that the number of slots 906 be equal to 3 times the number of poles. Thus, as shown in Fig. 19A, there are 36 slots 906 formed on the interior of stator 902. Poles 910 are magnetic poles wherein adjacent ones of the magnetic poles 910 produce alternating north and south magnetic fields. Poles 910a-h are permanent magnet poles and are formed by magnets 914a-f. Magnet 914a is contiguous to and mounted between poles 910a and 910b. Magnet 914 b is contiguous to and mounted between poles 910b and 910c and magnet 914c is contiguous to and mounted between poles 910c and 91 Od. Similarly, magnet 914d is contiguous to and mounted between poles 91 Oe and 91 Of. Magnet 914e is contiguous to and mounted between poles 91 Of and 91 Og, and magnet 914f is contiguous to and mounted between poles 91 Og and 91 Oh. Magnets 914a-c effect four (4) adjacent and contiguous permanent magnet poles. Similarly, magnets 914d-f effect four (4) adjacent and contiguous permanent magnet poles that are diametrically position in relation to the permanent magnet poles produced by magnets 914a-c. The remaining four (4) rotor poles comprise electromagnetic poles 910i-l. Poles 91 Oi and 91 Oj are diametrically positioned in relation to poles 9101 and 910k, respectively. Poles 910i-l have rotor windings 918 arranged such that alternate poles are wound in opposite directions to produce alternating north and south magnetic fields. Magnets 914a-f are mounted between the poles in a manner such that magnets 914a-f are within the rotor perimeter. Permanent magnets 914a-f effect a magnetic field that is oriented circumferentially relative to the rotor core rotational axis. Thus, magnets 914a-f are magnetized transversely aσoss the narrow, but variable, dimension thereof (see arrow 915 in Fig. 19a). Such a magnet configuration is referred to herein as the "focused flux configuration." Alternator 900 offers significant advantages. One advantage is that because magnets 914a and 914c are directly in series with the near half of the steel rotor poles 910a and 91 Od, respectively, the far half of poles 910a and 91 Od may be utilized with adjacent wound field poles 910k and 91 Oi, respectively. Furthermore, the permanent magnet poles 910a and 910d do not magnetically present a high reluctance to the adjacent wound fields. Similarly, magnets 914d and 914f are directly in series with the near half of the steel rotor poles 91 Oe and 91 Oh, respectively. Thus, the far half of poles 91 Oe and 91 Oh may be utilized with adjacent wound field poles 9101 and 91 Oj, respectively. Permanent magnet poles 91 Oe and 91 Oh also do not magnetically present a high reluctance to the adjacent wound fields. Another advantage of such a configuration as desσibed above is that magnets 914a-f do not interfere with the wound field flux. A further advantage of alternator 900 is that twelve (12) rotor poles provide an output frequency that can be used to implement a variety of electronic functions associated with the operation of motor vehicles such as an automobile. In a preferred embodiment, permanent magnets 914a-f may be realized by low cost ferrite magnets such as sintered ferrite. However, other types of magnets also may be utilized such as bonded neodymium, bonded ferrite or samarium cobalt. As shown in Fig. 19a, the wound field pole bodies of poles 910i-l are circumferentially positioned on rotor core 912 by a predetermined distance and pole shoes 920a-d are positioned on the wound field pole bodies in a manner such that all twelve (12) pole shoes are equidistantly spaced, relative to one another, around the rotor circumference. Such a configuration provides significantly more field winding space for the two (2) pairs of adjacent wound field poles 91 Oi, 91 Oj and 910k, 9101, thereby inσeasing the available excitation ampere-turns and the power density of the alternator. All twelve (12) pole bodies are asymmetrically spaced so as to inσease the space available for receiving windings and inσease air flow in the areas between adjacent wound field coils (poles 910i, 91 Oj and 910k, 9101) thus reducing the operating temperature of the alternator. In a preferred embodiment, the pole bodies of the rotor field poles positioned between a magnet and a wound field pole, such as poles 910a, 91 Od, 91 Oe and 91 Oh, have a geometric shape (length and width) that corresponds to the resultant summation of flux contributed by the magnet on one side, and the wound field pole on the other side. Thus, poles 910a, 910d, 910e, and 910h are referred to as contribution poles. The geometrical shape of the pole bodies of poles 910a, 91 Od, 91 Oh and 91 Oe are chosen so as to allow the poles to carry a predetermined pole flux. Thus, the geometrical shape of the pole body of poles 910a, 910d, 910e and 91 Oh may be different than the pole bodies of the poles positioned between the magnets or the pole bodies of the wound field poles. For example, as shown in Fig. 19a, the 1 -48- geometrically shape, e.g. width, of poles 910a, 910d, 910e and 910h is different than the pole body width used for the poles positioned between magnets since the body of poles 910a, 901 d, 91 Oe and 91 Oh do not taper as does the pole body of pole 910c. Thus, the single-stack hybrid alternator embodiments shown in Fig. 19a offers the following significant advantages: a) reduced complexity of design. For example, the design configuration of Fig. 19a eliminates stator insulating spacer 52 as shown in Fig. 1; b) overall reduction in size of the alternator; c) improved cooling and ventilation of the alternator thereby reducing the probability of overheating; d) reduced manufacturing costs; e) a power density that is substantially the same as the double-stacked configuration shown in Fig. 1; f) outputs a frequency that can be used to implement electronic functions necessary for the operation of a motor vehicle; g) can utilize low cost ferrite magnets; and h) prevents unusable flux from flowing through the rotor core. Although eight (8) permanent magnet poles (two diametrically positioned sets of four (4) permanent magnet poles) are shown, other configurations may also be used. For example, different proportions of permanent magnet poles to electromagnetic poles may be used. Furthermore, the rotor may be configured to define more or less than twelve (12) rotor field poles. For example, the rotor may b configured to define 8, 10 or 14 rotor field poles. The aforementioned advantages would also be realized with the aforementioned variations. The hybrid alternator embodiment of Fig. 19a may be operated with a field regulator that can be operated in bucking and boosting modes desσibed above. Furthermore, the hybrid alternator Fig. 19a may be used with the two (2) and three (3) state voltage regulators desσibed above. Additionally, the hybrid alternator of Fig. 19a may be configured as a neutral point connected alternator as described above. Indented Rotor Field Poles Referring to Figs. 20-22, rotor field pole 850 comprises body portion 852 and pole shoe portion 854. Body portion 852, radially extends from rotor core 856 to and end surface 858. Body portion 852 has a longitudinal axis substantially parallel to shaft 860, a longitudinal length LI and a width WI . Pole shoe portion 854 is attached to end surface 858, has a longitudinal length L2 that is greater than body portion length LI, and a width W2. Thus, body portion 852 is indented along its entire perimeter from pole shoe portion 854 by a distance A. Dotted line 853 in Figs. 21 and 22 represents the perimeter of body portion 852. Since indenting the pole body 852 would reduce the pole body longitudinal length to LI , the pole body width is inσeased by a proportional amount to width WI so as to maintain the necessary pole body σoss-sectional area. Rotor field pole 850 may be fabricated from a cast, high permeability steel piece wherein the indentations are directly formed by casting or by machining. An alternate indented rotor field pole configuration is shown in Fig. 23. Rotor field pole 862 is comprised of end caps 864a, 864b and central body portion 866. Caps 864a, 864b are rigidly attached to central body portion 866. The center body portion has a longitudinal length L3 and each cap has a longitudinal length of L4. The overall longitudinal length of central body portion 862 is L1 , which is the same as pole 850, and is the sum of L3 + 2xL4. Cap 864a comprises an end portion 865a and a body portion 867a. Body portion 867a and end portion 865a have lengths L4 and L5, respectively. The difference in length between L5 and L4 is represented by the letter A. Thus, body portion 867a is indented from end portion 865a by a distance A. Similarly, cap 864b comprises end portion 865b and a body portion 867b. Body portion 867b and end portion 865b have lengths L4 and L5, respectively. The difference in length between L5 and L4 is represented by the letter A. Thus, body portion 867b is indented from end portion 865b by a distance A for the entire perimeter of body portion 866. The indentation distance A can be varied according to the number of required turns of the rotor field windings and/or whether it is desired to have the windings extend beyond the stator wound field stack section. The indentation on both ends of the rotor field provide a natural winding support on either end of the rotor pole thus making unnecessary the use of round, pole shoe support pins. Furthermore, an inσease in the number of rotor field poles can be realized since the rotor field poles can be wound such that the windings do not extend beyond edges 854a, 854b and 854c of rotor field pole 852, or edges 869a, 869b and 869c of pole 862, thereby allowing the rotor field poles to be spaced closer together. This feature also allows wound field portion 24 to be positioned closer to -50- permanent magnet rotor portion 38 of the alternator of Fig. 1. Since the perimeter of the pole body is reduced, the net mean turn of the rotor windings is reduced. Therefore, less wire is required than conventional pole bodies. A reduction in the amount of wire also effects a deσease in resistance to current flowing through the windings thereby reducing power consumption. Additionally, the reduction in the amount of wire also reduces weight and cost to manufacture the rotor. Furthermore, the reduction in the amount of wire reduces the wound field winding thickness thereby facilitating heat transfer from the winding. This improves heat conduction and reduces the probability of over heating. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above desσiption or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. While the invention has been illustrated and described in what are considered to be the most practical and preferred embodiments, it will be recognized that many variations are possible and come within the scope thereof, the appended claims therefore being entitled to a full range of equivalents. Thus, having desσibed the invention, what is claimed is:

Claims: Claims 1. A hybrid alternator comprising: a stator; and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor having a rotor core defining a plurality of magnetic poles, adjacent ones of the magnetic poles having alternating north and south magnetic fields, the plurality of magnetic poles comprising a plurality of permanent magnet poles and a plurality of electromagnetic poles, each permanent magnet pole being defined by a permanent magnet, said plurality of permanent magnet poles comprising two (2) sets of diametrically positioned permanent magnet poles, each permanent magnet being positioned within the rotor perimeter and associated with a pair of adjacent magnetic poles to form adjacent permanent magnet poles. 2. The hybrid alternator of claim 1 wherein each set of permanent magnet poles includes three (3) magnets. 3. The hybrid alternator of claim 2 wherein each set of permanent magnet poles comprises four (4) permanent magnet poles and said plurality of electromagnetic poles comprises four (4) electromagnetic poles. 4. The hybrid alternator of claim 1 wherein said rotor core defines a plurality of rotor field poles, each of which being associated with a corresponding magnetic pole. 5. The hybrid alternator of claim 1 wherein each of said magnets is formed from a magnetic material chosen from ferrite, neodymium, ceramic and samarium- cobalt. 6. The hybrid alternator of claim 4 wherein each rotor field pole and each magnet has a longitudinal axis substantially parallel to the rotor rotational axis, each rotor field pole and each magnet radially extending from said rotor core, each permanent magnet being mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles. -52- 7. The hybrid alternator of claim 4 wherein each magnet is magnetically isolated from said rotor field core. 8. The hybrid alternator of claim 6 wherein each rotor field pole comprises: a body radially extending from said rotor core to an end surface; and a rotor field pole shoe mounted to said end surface. 9. The hybrid alternator of claim 8 wherein said rotor field pole bodies are asymmetrically spaced on said rotor core. 10. The hybrid alternator of claim 9 wherein each rotor field pole shoe is asymmetrically attached to a corresponding rotor field pole body in a manner such that said pole shoes are equidistantly spaced in relation to one another. 11. The hybrid alternator of claim 8 wherein each rotor field pole body has a predetermined width and length that corresponds to a specific pole flux. 13. The hybrid alternator of claim 1 wherein each permanent magnet is arranged in a manner such that the direction of magnetization is oriented circumferentially relative to the rotor core rotational axis. 14. The hybrid alternator of claim 10 wherein the pole body of each rotor field pole positioned between one of said magnets and one of said electromagnetic poles has a geometrical shape that corresponds to the summation of flux contributed by said magnet and said electromagnetic pole. 15. A hybrid alternator comprising: a stator having a stator winding; and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor including: a rotor core defining a plurality of rotor field poles, a plurality of permanent magnets, each of which being positioned within the rotor perimeter and mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles, said plurality of permanent magnet poles comprising two (2) diametrically positioned sets of -53- permanent magnet poles, the permanent magnets being magnetically isolated from the rotor core; and a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, said plurality of electromagnetic poles comprising two (2) diametrically positioned sets of electromagnetic poles, said electromagnetic and permanent magnet poles defining a plurality of magnetic poles, adjacent ones of said magnetic poles having alternating north and south magnetic fields. 16. The hybrid alternator of claim 15 wherein each set of permanent magnet poles comprises four (4) adjacent permanent magnetic poles and each set of electromagnetic poles comprises two (2) adjacent electromagnetic poles. 17. A hybrid alternator comprising: a stator having a stator winding; and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor including: a rotor core defining a plurality of rotor field poles asymmetrically positioned about the rotor core, each rotor field pole comprising a body radially extending from said rotor core to an end surface, a plurality of permanent magnets, each of which being positioned within the rotor perimeter and mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles, said plurality of permanent magnet poles comprising two (2) diametrically positioned sets of permanent magnet poles, each set of permanent magnet poles comprising four (4) adjacent permanent magnet poles, each permanent magnet being arranged in a manner such that the direction of magnetization is oriented circumferentially relative to the rotor core rotational axis, the permanent magnets being magnetically isolated from said rotor core; a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, said plurality of electromagnetic poles comprising two (2) diametrically positioned sets of electromagnetic poles, each set of electromagnetic poles comprising two (2) adjacent electromagnetic poles, said electromagnetic and permanent magnet -54- poles defining a plurality of magnetic poles, adjacent ones of said magnetic poles having alternating north and south magnetic fields, and a plurality of rotor field pole shoes, each of which being asymmetrically mounted to said end surface of a corresponding one of said pole bodies, said rotor field shoes being equidistantly spaced from one another. 18. The hybrid alternator of claim 17 wherein the rotor field pole body of each rotor field pole positioned between one of said magnets and one of said electromagnetic poles has a geometrical shape that corresponds to the summation of flux contributed by said magnet and said electromagnetic pole. 19. The hybrid alternator of claim 16 wherein each of said magnets is formed from a magnetic material chosen from ferrite, neodymium, ceramic and samarium- cobalt. 20. A temperature monitoring voltage regulator for controlling bi-directional current flow through a winding of a hybrid alternator, the voltage regulator comprising: a voltage monitoring circuit connected to monitor the output voltage of the hybrid alternator, the voltage monitoring circuit producing an error signal indicating that the output voltage of the hybrid alternator should be inσeased or deσeased; a temperature sensor adapted to be mounted in thermal contact with the hybrid alternator, the temperature sensor being electrically connected to the voltage monitoring circuit and modifying the error signal to reduce the output voltage of the hybrid alternator above a predetermined temperature; a switching circuit connected to the winding and arranged to connect the winding in a forward polarity mode in which a forward polarity voltage is applied to the winding and a reverse polarity mode in which a reverse polarity voltage is applied to the winding; a control circuit connected to the switching circuit, responsive to the error signal of the monitoring circuit, the control circuit controlling the switching circuit to enter the forward polarity mode to inσease the output voltage of the alternator, and to enter the reverse polarity mode to deσease the output voltage of the alternator. 21. A temperature monitoring voltage regulator according to claim 20 wherein the temperature sensor comprises a thermistor. 22. A temperature monitoring voltage regulator according to claim 21 wherein the thermistor has a positive temperature coefficient. 23. A temperature monitoring voltage regulator according to claim 20 wherein the temperature sensor has a variable resistance that varies nonlinearly. 24. A temperature monitoring voltage regulator according to claim 20 wherein the switching circuit is arranged to connect the winding in a decay mode in which current induced in the winding when connected in the forward or reverse polarity mode is permitted to decay without inducing damaging voltages in the voltage regulator, and wherein the control circuit controls the switching circuit to enter the decay mode whenever switching away from the forward or reverse polarity mode. 25. A temperature monitoring voltage regulator according to claim 20 wherein the voltage monitoring circuit includes an error amplifier having first and second inputs, the first input being connected to a reference voltage, and the second input being connected to a voltage divider incorporating the temperature sensor. 26. A hybrid alternator in combination with a temperature monitoring voltage regulator, the hybrid alternator comprising: a stator having a stator winding; and a rotor mounted for rotation within the stator, said rotor including a plurality of permanent magnets, and a rotor winding; and the voltage regulator comprising: a voltage monitoring circuit connected to monitor the output voltage of the hybrid alternator, the voltage monitoring circuit producing an error signal indicating that the output voltage of the hybrid alternator should be inσeased or deσeased; a temperature sensor mounted in thermal contact with the hybrid alternator, the temperature sensor being electrically connected to the voltage monitoring circuit and modifying the error signal to reduce the output voltage of the hybrid alternator above a predetermined temperature; a switching circuit connected to the rotor winding and arranged to connect the rotor winding in a forward polarity mode in which a forward polarity voltage is applied to the rotor winding and a reverse polarity mode in which a reverse polarity voltage is applied to the rotor winding; a control circuit connected to the switching circuit, responsive to the error signal of the monitoring circuit, the control circuit controlling the switching circuit to enter the forward polarity mode to inσease the output voltage of the alternator, and to enter the reverse polarity mode to decrease the output voltage of the alternator. 27. The hybrid alternator according to claim 26 wherein the input of the voltage converter circuit is connected directly to the stator winding. 28. The hybrid alternator according to claim 26 wherein the input of the voltage converter circuit is connected to a rectified output voltage from the stator winding. 29. The hybrid alternator of claim 1 wherein the wound fields include a rotor winding, the hybrid alternator further includes a voltage regulator for controlling bidirectional current flow through a winding of an alternator to control an output voltage of the alternator, the voltage regulator comprising: a voltage monitoring circuit connected to monitor the output voltage of the alternator, the voltage monitoring circuit producing an error signal indicating that the output voltage of the alternator should be increased or deσeased; a switching circuit connected to the winding and arranged to connect the winding in multiple modes, including: a forward polarity mode in which a forward polarity voltage is applied to the winding, a reverse polarity mode in which a reverse polarity voltage is applied to the winding, and a decay mode in which current induced in the winding when connected in the forward or reverse polarity mode is permitted to decay without inducing damaging voltages in the voltage regulator; and a control circuit connected to the switching circuit, responsive to the error signal of the monitoring circuit, the control circuit controlling the switching circuit to enter the forward polarity mode to inσease the output voltage of the alternator, to enter the reverse polarity mode to deσease the output voltage of the alternator and to enter the decay mode whenever switching away from the forward or reverse polarity mode. 30. The hybrid alternator of claim 1 wherein said permanent magnetic pole defines a permanent magnetic flux field, said stator includes a stator winding having a neutral point voltage, and said wound field includes a rotor winding having a first end connected to the neutral point on the stator winding and a second end adapted for connection to a switching circuit in a voltage regulator, the wound fields producing a rotor wound magnetic flux field that additively combines with the permanent magnetic flux field when the switching circuit connects the second end to a voltage greater than the neutral point voltage and producing a rotor magnetic flux field that subtractively combines with the permanent magnetic flux field when the switching circuit connects the second end to a voltage less than the neutral point voltage. 31. A hybrid alternator comprising: a stator; and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor having a rotor core defining a plurality of magnetic poles, adjacent ones of the magnetic poles having alternating north and south magnetic fields, the plurality of magnetic poles comprising a plurality of permanent magnet poles and a plurality of electromagnetic poles, each permanent magnet pole being defined by a permanent magnet, said plurality of permanent magnet poles comprising two (2) sets of diametrically positioned permanent magnet poles, each permanent magnet being positioned within the rotor perimeter and associated with a pair of adjacent magnetic poles to form adjacent permanent magnet poles. 32. The hybrid alternator of claim 31 wherein each set of permanent magnet poles includes three (3) magnets. 33. The hybrid alternator of claim 32 wherein each set of permanent magnet poles comprises four (4) permanent magnet poles and said plurality of electromagnetic poles comprises four (4) electromagnetic poles. 34. The hybrid alternator of claim 31 wherein said rotor core defines a plurality of rotor field poles, each of which being associated with a corresponding magnetic pole. 35. The hybrid alternator of claim 31 wherein each of said magnets is formed from a magnetic material chosen from ferrite, neodymium, ceramic and samarium- cobalt. 36. The hybrid alternator of claim 34 wherein each rotor field pole and each magnet has a longitudinal axis substantially parallel to the rotor rotational axis, each rotor field pole and each magnet radially extending from said rotor core, each permanent magnet being mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles. 37. The hybrid alternator of claim 34 wherein each magnet is magnetically isolated from said rotor field core. 38. The hybrid alternator of claim 36 wherein each rotor field pole comprises: a body radially extending from said rotor core to an end surface; and a rotor field pole shoe mounted to said end surface. 39. The hybrid alternator of claim 38 wherein said rotor field pole bodies are asymmetrically spaced on said rotor core. 40. The hybrid alternator of claim 39 wherein each rotor field pole shoe is asymmetrically attached to a corresponding rotor field pole body in a manner such that said pole shoes are equidistantly spaced in relation to one another. 41. The hybrid alternator of claim 38 wherein each rotor field pole body has a predetermined width and length that corresponds to a specific pole flux. 42. The hybrid alternator of claim 31 wherein each permanent magnet is arranged in a manner such that the direction of magnetization is oriented circumferentially relative to the rotor core rotational axis. 43. The hybrid alternator of claim 40 wherein the pole body of each rotor field pole positioned between one of said magnets and one of said electromagnetic poles has a geometrical shape that corresponds to the summation of flux contributed by said magnet and said electromagnetic pole. 44. A hybrid alternator comprising: a stator having a stator winding; and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor including: a rotor core defining a plurality of rotor field poles, a plurality of permanent magnets, each of which being positioned within the rotor perimeter and mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles, said plurality of permanent magnet poles comprising two (2) diametrically positioned sets of permanent magnet poles, the permanent magnets being magnetically isolated from the rotor core; and a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, said plurality of electromagnetic poles comprising two (2) diametrically positioned sets of electromagnetic poles, said electromagnetic and permanent magnet poles defining a plurality of magnetic poles, adjacent ones of said magnetic poles having alternating north and south magnetic fields. 45. The hybrid alternator of claim 44 wherein each set of permanent magnet poles comprises four (4) adjacent permanent magnetic poles and each set of electromagnetic poles comprises two (2) adjacent electromagnetic poles. 46. A hybrid alternator comprising: a stator having a stator winding; and a rotor mounted for rotation within the stator and separated therefrom by an air gap, said rotor including: -60- a rotor core defining a plurality of rotor field poles asymmetrically positioned about the rotor core, each rotor field pole comprising a body radially extending from said rotor core to an end surface, a plurality of permanent magnets, each of which being positioned within the rotor perimeter and mounted between a pair of adjacent rotor field poles to form adjacent permanent magnet poles, said plurality of permanent magnet poles comprising two (2) diametrically positioned sets of permanent magnet poles, each set of permanent magnet poles comprising four (4) adjacent permanent magnet poles, each permanent magnet being arranged in a manner such that the direction of magnetization is oriented circumferentially relative to the rotor core rotational axis, the permanent magnets being magnetically isolated from said rotor core; a rotor winding associated with the remaining rotor field poles to define a plurality of electromagnetic poles, said plurality of electromagnetic poles comprising two (2) diametrically positioned sets of electromagnetic poles, each set of electromagnetic poles comprising two (2) adjacent electromagnetic poles, said electromagnetic and permanent magnet poles defining a plurality of magnetic poles, adjacent ones of said magnetic poles having alternating north and south magnetic fields, and a plurality of rotor field pole shoes, each of which being asymmetrically mounted to said end surface of a corresponding one of said pole bodies, said rotor field shoes being equidistantly spaced from one another. 47. The hybrid alternator of claim 46 wherein the rotor field pole body of each rotor field pole positioned between one of said magnets and one of said electromagnetic poles has a geometrical shape that corresponds to the summation of flux contributed by said magnet and said electromagnetic pole. 48. The hybrid alternator of claim 45 wherein each of said magnets is formed from a magnetic material chosen from ferrite, neodymium, ceramic and samarium- cobalt. 49. A temperature monitoring voltage regulator for controlling bi-directional current flow through a winding of a hybrid alternator, the voltage regulator comprising: a voltage monitoring circuit connected to monitor the output voltage of the hybrid alternator, the voltage monitoring circuit producing an error signal indicating that the output voltage of the hybrid alternator should be inσeased or deσeased; a temperature sensor adapted to be mounted in thermal contact with the hybrid alternator, the temperature sensor being electrically connected to the voltage monitoring circuit and modifying the error signal to reduce the output voltage of the hybrid alternator above a predetermined temperature; a switching circuit connected to the winding and arranged to connect the winding in a forward polarity mode in which a forward polarity voltage is applied to the winding and a reverse polarity mode in which a reverse polarity voltage is applied to the winding; a control circuit connected to the switching circuit, responsive to the error signal of the monitoring circuit, the control circuit controlling the switching circuit to enter the forward polarity mode to increase the output voltage of the alternator, and to enter the reverse polarity mode to decrease the output voltage of the alternator. 50. A temperature monitoring voltage regulator according to claim 49 wherein the temperature sensor comprises a thermistor. 51. A temperature monitoring voltage regulator according to claim 50 wherein the thermistor has a positive temperature coefficient. 52. A temperature monitoring voltage regulator according to claim 49 wherein the temperature sensor has a variable resistance that varies nonlinearly. 53. A temperature monitoring voltage regulator according to claim 49 wherein the switching circuit is arranged to connect the winding in a decay mode in which current induced in the winding when connected in the forward or reverse polarity mode is permitted to decay without inducing damaging voltages in the voltage regulator, and wherein the control circuit controls the switching circuit to enter the decay mode whenever switching away from the forward or reverse polarity mode. 54. A temperature monitoring voltage regulator according to claim 49 wherein the voltage monitoring circuit includes an error amplifier having first and second inputs, the first input being connected to a reference voltage, and the second input being connected to a voltage divider incorporating the temperature sensor. 55. A hybrid alternator in combination with a temperature monitoring voltage regulator, the hybrid alternator comprising: a stator having a stator winding; and a rotor mounted for rotation within the stator, said rotor including a plurality of permanent magnets, and a rotor winding; and the voltage regulator comprising: a voltage monitoring circuit connected to monitor the output voltage of the hybrid alternator, the voltage monitoring circuit producing an error signal indicating that the output voltage of the hybrid alternator should be inσeased or deσeased; a temperature sensor mounted in thermal contact with the hybrid alternator, the temperature sensor being electrically connected to the voltage monitoring circuit and modifying the error signal to reduce the output voltage of the hybrid alternator above a predetermined temperature; a switching circuit connected to the rotor winding and arranged to connect the rotor winding in a forward polarity mode in which a forward polarity voltage is applied to the rotor winding and a reverse polarity mode in which a reverse polarity voltage is applied to the rotor winding; a control circuit connected to the switching circuit, responsive to the error signal of the monitoring circuit, the control circuit controlling the switching circuit to enter the forward polarity mode to increase the output voltage of the alternator, and to enter the reverse polarity mode to deσease the output voltage of the alternator.

Inventors: CURTISS WILLIAM P, FRANCIS WILLARD P, SYVERSON CHARLES D, CURTISS, WILLIAM, P., FRANCIS, WILLARD, P., SYVERSON, CHARLES, D.
Applicants: ECOAIR CORP, ECOAIR CORP.
Application year: 1996
Main classification: H02K21
IPC codes: H02H5, H02H7, H02K1, H02K3, H02K9, H02K11, H02K16, H02K19, H02K21, H02P9