Abstract:
An electric generator is disclosed having a high efficiency over wide ranges in rotor speed and power output requirements. Output voltage control is achieved by providing the power output windings with variable adjustment. This variable adjustment determines the number of turns that are used for the power output on the power output windings themselves. When excess voltage is generated, turns used on the power output windings are reduced thereby reducing output voltage and increasing efficiency by lowering the power output winding resistance. When the voltage generated is low, more turns on the power output windings are activated thereby increasing the voltage of the generator itself. This voltage control occurs prior to any voltage modification outside of the generator. A sensor and feedback mechanism is used to automatically adjust the power output windings thereby attaining maximum efficiency at the desired voltage and power level.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to electric generators and more particularly relates to generators and alternators operating at high efficiency which are suitable for use under a variety of changing conditions. 
   2. Description of Related Art 
   There are numerous generators used throughout the world for generating electric power. Such generators use the basic principal of electromagnetic induction to convert the energy of motion into electricity. If an electrical conductor such as a wire is moved through a magnetic field, or conversely if a magnetic field is made to change in the presence of such a conductor, an EMF or voltage will be induced in the conductor. The voltage induced in the conductor is determined by the following factors:
         (1) If the conductor is a wire in the form of a coil the greater the number of turns in the coil, the greater will be the induced EMF.   (2) The faster the conductor moves through the magnetic field the greater will be the induced EMF.   (3) The stronger the interacting magnetic field is the greater will be the induced EMF. If the conductor is stationary but the magnetic field changes (such as the case with permanent magnet alternators) the faster the rate of change the greater will be the induced EMF.       

   When power is required such as for lighting applications, a connection is made between the producing conductor of the generator and to the device. This causes a current to flow from the generator to the device. Whenever a generator delivers power to some device an associated mechanical drag on the moving parts of the generator results. The more power that is pulled from a generator, the greater will be the mechanical requirements needed to keep the generator producing power. Many generators such as the ones powered by gasoline engines used in portable applications are designed to run at a fixed speed under the conditions of a given load. Such generators work well because the source of mechanical power (the gasoline engine) can be controlled and soon reaches a steady state for any given load. In many cases, this is quite suitable. 
   There are many generators that are designed to produce power under varying conditions of speed and required power output. A good example of this type of generator is the alternator used to power the electrical systems in automobiles. The power output of such alternators must be carefully controlled to maintain proper battery life. If not enough power is supplied to the battery and the associated electrical needs of the car, the battery will run down. If too much power is delivered to the battery, the battery will overcharge resulting in reduced battery life, and possibly over voltages which can damage certain electrical components in the electrical system of the automobile. In addition to the changing needs of the automobiles electrical system, the speed of the engine is always changing. Sometimes the engine is slowly idling at a few hundred RPM. Other times, the engine is running at several thousand RPM. Because of this, alternators used for the generation of power in automobiles have electrical circuitry which regulates the output power of the alternator to the needs of the electrical system. This is accomplished by employing two sets of electromagnets. One set is located into the rotary portion of the alternator or rotor, and the other set of electromagnets is located in the stationary portion of the alternator or stator. The rotor electromagnets require electrical power to produce the initial magnetic field. This power comes from a set of brushes that supply electricity to the commutator of the rotor to deliver power to their windings while at the same time allowing the rotor to rotate. The rotor electromagnet consists of many turns of a light gauge wire such as # 21 . Because of this, not much current will flow into this electromagnet. This results in a low power demand on the brushes. The stator electromagnet consists of a few turns of heavy gauge wire such as # 14 . The stator windings produce a substantial amount of AC current due to the changing magnetic field caused by the rotating rotor electromagnet. This AC current is then rectified to DC using diodes. Voltage regulation circuitry is used to control power going into the rotor electromagnet. In this way, a small amount of control current in the rotor results in a very large change in output current and voltage from the stator windings. This configuration works well for electric generators and alternators employing rotating electromagnet windings because a fine control in voltage output is easily attained under constant or variable speed conditions. 
   Numerous alternators have been built employing permanent magnets in the rotor, and electromagnets in the stator. These alternators can be used to generate AC power, or alternatively can have their power rectified with diodes to produce DC power. Such alternators are inherently more reliable because of their brushless design. They also have fewer moving parts to wear out and do not require input power to provide output power. These brushless permanent magnet alternators also produce less heat owing to the fact that there are no rotor windings. Such alternators have been employed in motorcycles and other lightweight vehicles. For example, The Ducati SL500 Pantah alternator is used in many Ducati motorcycles. This particular alternator is a permanent magnet alternator employing a rotor having permanent magnets surrounded by a stator electromagnet assembly. This permanent magnet alternator is designed to be used with a specific regulator, the SL500 Pantah regulator which rectifies the AC power from the alternator as well as regulating the output power. Many motorcycles utilize an external rotor which doubles as the flywheel. As usual, voltage regulation is carried out using electrical circuitry which is placed between the output from the alternator and the battery. Such an approach while being rather simple, cost effective, and straightforward has its drawbacks. The alternator output voltage to the regulating circuitry is dependent on rotor speed. Because of this the power output from such alternators is rarely occurring under optimum conditions of efficiency. When operating at low RPM values such permanent magnet alternators must have enough windings to provide sufficient voltage for the electrical system. Such windings often have relatively high electrical resistance owing to the need to use small gauge wire to fit many turns of wire on the stator electromagnet. Conversely, in order to deliver substantial current at high RPM conditions without excessive voltage, the wire diameter needs to be of a relatively large gauge with only few turns needed. In practice a compromise in performance on either end of the RPM scale is reached by choosing an intermediate gauge wire diameter having a substantial number of turns. Such systems have a difficult time delivering the needed power under the wide ranges of RPM values normally experienced during use. Despite these drawbacks existing electrical systems employing permanent magnet alternators have a proven record of reliability for use in motorcycles and other lightweight vehicles. Further improvements in efficiency and reliability of systems employing these permanent magnet alternators can be expected by the use of improved power control circuitry. 
   In addition to alternators for vehicle use permanent magnet alternators are being increasingly employed in generators used in standby power applications as well as generators used in alternative energy systems utilizing forms of power such as wind and hydroelectric. One example of such a system is outlined in U.S. Pat. No. 4,720,640. In this patent, a turbine is driven by a fluid such as moving air or moving water. On the periphery of this turbine are located permanent magnets. A stator consisting of multiple electromagnets is located around the outside periphery of the rotor permanent magnets with the electromagnet pole faces located in close coupling proximity to the pole faces of the rotor permanent magnets. A similar system is outlined in U.S. Pat. No. 5,696,419 to Rakestraw. As in U.S. Pat. No. 4,720,640, a fluid driven impeller having a periphery of permanent magnets is employed as the rotor. The stator electromagnets are C-Shaped and straddle the permanent magnet pole faces in the rotor. One advantage this system offers for some applications is a power curve that tends to be self-limiting under the conditions of high RPM. Despite these and other numerous advances in generators and alternators there is a need for an alternator or a generator having variable power output windings employing electrical circuitry which will automatically vary the number of these windings based on running RPM and needed power demands. In this way the power output of the generator itself can compensate for changes in RPM and load requirements with minimal or no voltage regulation circuitry required. 
   Power generating windmills are a prime example. Wind speeds are always changing, however, the output voltage during power delivery needs to be relatively constant. In low wind conditions the ideal power generating electromagnet windings are preferably large in number to generate the needed voltage to power these energy systems. In addition the generator rotor drag caused by the output power has to be somewhat limited to prevent the stalling of the generator. Because of this many turns of a relatively small gauge electromagnet wire would be desired. During high wind conditions a few turns of a relatively heavy gauge wire would be the desire. In this way enough current at a suitable voltage can be delivered to make use of the power available under high wind conditions, not overheat from too high a winding resistance, and be able to create enough mechanical drag to keep the windmill impeller from spinning too fast and flying apart. 
   Other examples include alternators for use in vehicles such as automobiles, motorcycles, trucks, and the generation of electric power from variable speed sources and/or for variable power requirements. 
   In view of the foregoing, it is an object of this invention to provide an electric generator or alternator which eliminates the need for armature brushes. 
   It is a further object of this invention to provide a generator or alternator having a high efficiency under the conditions of changing rotor speed. 
   It is a further object of this invention to provide a generator or alternator having variable output voltage characteristics. 
   Finally, it is an object of this invention to reduce the requirements of power control circuitry normally used to modify generator output voltage into a useable form. 
   SUMMARY OF THE INVENTION 
   This invention therefore proposes a permanent magnet generator or alternator having one or more variable power output windings along with electrical circuitry for automatically and continuously varying the number of activated turns on power output windings based on power demands, rotor speed, or both. Variable turn windings are employed in the output power stator electromagnet assembly. Multiple triacs or other switching circuitry may be used to activate individual turns on the power output windings. Finally, a sensor is used to determine the appropriate time to activate windings. If RPM sensing is important and a permanent magnet alternator is the desired generator the output voltage of the generator itself can be used as a signal source for changeover. Alternatively a small coil can be placed in the proximity of the rotor magnets to provide a voltage signal which is proportional to RPM as well. If the signal has substantial power such as would be the case of using the generator output voltage itself as the signal a relay may be wired directly to the signal source. If the signal is low in power then semi-conductor amplification circuitry may be used. In either case some circuitry is needed for signal generation and/or variable power output winding activation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the rotary portion of a traditional permanent magnet alternator employed in Ducati motorcycles, which is also suitable for use in this invention. 
       FIG. 2  shows the electromagnet stator portion of a traditional permanent magnet alternator employed in Ducati motorcycles. 
       FIG. 3  shows a core cross section of the sliding brush portion of a variac (variable autotransformer) used to vary the output voltage. 
       FIG. 4  shows variable output electromagnet contacts utilizing a sliding brush assembly which employs a small electric motor for automatic output voltage adjustment. 
       FIG. 5  shows circuitry for sensing output voltage from a generator utilizing two relays. 
       FIG. 6  shows a permanent magnet alternator having a rotor of permanent magnets and electromagnets having multiple contactors. 
       FIG. 7  shows a permanent magnet alternator having an outer rotor of permanent magnets and an inner stator electromagnet portion having multiple contactors suitable for the variable output aspects of this invention. 
       FIG. 8  shows a permanent magnet alternator having a disc rotor with permanent magnets and a stator having an electromagnet portion having multiple contactors equipped for controlling uniform output voltage. 
   

   DESCRIPTION OF THE INVENTION 
     FIG. 1  shows the rotary portion of a traditional permanent magnet alternator employed in Ducati motorcycles. This type of rotor having permanent magnets attached is typical of the permanent magnet alternators employed in motorcycles. 
   Rotary portion  2  consists of steel drum portion  6  having permanent magnets  4  mounted along outside edge portion  5 . Front face portion  6  has mounting means consisting of central hole  8  along with a notch  10  for a keyway. Fastening holes  12  are used to properly secure rotary portion  2  to rotating parts on the motorcycle. Also shown are pole faces  14 , and  16  of permanent magnets  4  which alternate with each permanent magnet around outside edge portion  5  of rotary portion  2 . 
   This rotary portion creates a changing magnetic field when rotated within the stationary electromagnet portion of FIG.  2 . It should be noted that the faster rotary portion  2  of  FIG. 1  spins, the greater will be both the output voltage and output frequency of AC power produced in the stationary electromagnet portion of FIG.  2 . 
     FIG. 2  shows the electromagnet stator portion  18  of the traditional permanent magnet alternator utilizing rotary portion  2  of  FIG. 1  (not shown). Electromagnet core  20  is formed of ferromagnetic material in the traditional fashion. Electromagnet windings  22  are comprised of electromagnet wire  28  wrapped around electromagnet core pole faces End portions  24 , and  26  of electromagnet windings  22  provide power output. 
     FIG. 3  Shows a core cross section along with the sliding brush portion of a variac (variable autotransformer) used to vary output voltage from an AC source. Electromagnet core  32  is in the shape of an iron ring. Electromagnet windings  34  are tightly wrapped around electromagnet core  32  forming a toroid. Upper surface portion  36  of electromagnet windings  34  are free from electrical insulation and therefore are suitable for making electrical contact. Sliding brush  38  is made to contact upper surface portion  36  of electromagnet windings  34  by way of downward force exerted from brush holder  40 . Also shown is pigtail  42  which provides electrical output from sliding brush  38 . 
   A variac (variable output autotransformer) provides variable voltage output by changing the number of turns that are activated on the output side. This is accomplished by way of the sliding brush contact arrangement to the individual windings themselves. The result is a fairly concise adjustable voltage output which is substantially continuous. It should be noted however that the voltage output is not completely continuous owing to the fact that as each individual winding is activated there is a discrete voltage jump of a fraction of a volt. The number of windings is such that for all intensive purposes the output is substantially continuously variable in nature. 
     FIG. 4  shows variable output electromagnet contacts utilizing a sliding brush assembly which employs a small electric motor for automatic output voltage adjustment. Base plate  44  is used to mount small electric motor  46  into place using motor mount  48 . Small electric motor  46  is reversible thus allowing the shaft to spin clockwise or counter clockwise. Permanent magnet DC electric motors are suitable for this purpose and are available in a variety of sizes. Helical threaded portion  50  is attached to motor shaft  52  using shaft coupler  54 . Also shown is bearing mount  56  which secures bearing  58  to base plate  44 . Bearing  58  provides support for helical threaded portion  50  while at the same time allowing rotation in either direction. Also shown is brush  60  which is fastened to helical threaded portion  50  by way of threaded nut  62  such that when threaded portion  50  rotates, brush  60  moves in a straight line along threaded portion  50 . Contact plate  64  consists of insulated plate  66  along with wire contacts  68 . Wire contacts  68  represent the individual ends of electromagnet windings from the electromagnet portion of a permanent magnet alternator (not shown). Wire bundle  70  carries wires to the individual electromagnet windings of the variable output generator or alternator of this invention. Also shown are input motor leads  72 , and  74  which supply power when needed to small electric motor  46 . Attached to motor leads  72 , and  74  is relay switching box  76  which activates small electric motor  46  when needed. DC power is supplied to relay box  76  by way of power input leads  78 ,  80 , and  82 . Also shown are generator output voltage sensor leads  84 , and  86  which sense the output voltage of the generator (not shown). 
   When the output voltage of the generator (not shown) falls below the desired voltage, one of the voltage sensing relays in box  76  is activated, power is applied to small electric motor  46  causing threaded shaft portion to rotate. Brush  60  then slides along wire contacts  68  thereby increasing the number of turns activated in the output of the electromagnet portion of the generator or alternator of this invention thereby maintaining the desired output voltage. Conversely, when the output voltage of the generator or alternator of this invention is in excess, one of the voltage sensing relays in box  76  is activated, power is applied to small electric motor  46  causing threaded shaft portion to rotate. Brush  60  then slides along wire contacts  68  thereby decreasing the number of turns activated in the output of the electromagnet portion of the generator or alternator of this invention thereby maintaining the desired output voltage. 
   There are several advantages to be realized from modifying the number of turns in the output electromagnet windings of a permanent magnet alternator or generator. When the rate of rotation increases in the rotating portions of these devices the voltage output increases. Reducing the output voltage by limiting the number of turns that are activated on the electromagnet windings themselves provides voltage control along with the added bonus of reduced electromagnet winding resistance. This aspect is advantageous owing to the fact that winding resistance in generators is source of efficiency losses. Reducing this winding resistance therefore results in a direct increase in the overall efficiency of the operating device. 
   In addition, inductive reactance effects will start to limit output power as the power output frequency increases with rotation speed. The effects of inductive reactance are based on frequency and inductance. The greater the frequency, the greater will be the inductive reactance to any given coil such as the electromagnet portion of a permanent magnet alternator. The greater the number of turns on an inductor, the greater will be the inductive reactance on any given inductor. Added benefits may be realized by modifying the number of turns used in the electromagnet portion of a permanent magnet alternator. 
     FIG. 5  shows circuitry located in relay box  76  of  FIG. 4  which is used for sensing output voltage from a generator utilizing two relays. Leads  84 , and  86  come in from the generator or alternator and are converted to DC voltage by full wave bridge rectifier Capacitor  90  smoothes out the voltage making it suitable for activation of relays  92 , and  94 . Variable resistors  96 , and  98  are adjustable and thus controls the activation point for relay  92 . Likewise, variable resistors  100 , and  102  control the activation point for relay  94 . DC voltage power supplies  104 , and  106  are activated by relays  92 , and  94  in such a way as to have the voltage output of the power supplies reversible with respect to output leads  108 , and  110 . Relay  94  is activated when the incoming voltage supplied by leads  84 , and  86  falls below the desired value. Contactor  112  of relay  94  connects lead  114  of power supply  106  thereby providing positive voltage to output lead  108 , and negative voltage to output lead  110 . Relay  92  is activated when the incoming voltage supplied by leads  84 , and  86  rises above the desired value. Contactor  116  of relay  92  connects lead  118  of power supply  104  thereby providing negative voltage to output lead  108 , and positive voltage to output lead  110 . 
     FIG. 6  shows a permanent magnet alternator having a rotor of permanent magnets and electromagnets having multiple contactors suitable for the variable output aspects of this invention. Variable output permanent magnet alternator  120  is shown having outer generator casing  122  enclosing electromagnets  124 , and  126 . Also shown are permanent magnets  128 , and  130  having pole faces  132 , and  134  facing outward in a radial direction. These pole faces are of alternate polarity Pole face  132  is a north pole, and pole face  134  is a south pole. When more permanent magnet pole faces are employed it is to be understood that they alternate with each successive pole face all of the way around. Permanent magnets  128 , and  130  are attached to generator shaft  136 . Electromagnet windings  138  provide power output from brushless permanent magnet alternator  120 . Lead  140  is the common lead and is shown directly connected to full wave bridge rectifier  142 . Full wave bridge rectifier  142  consists of four diodes arranged together in the bridge as shown. Multiple output leads from individual windings  138  are shown as wire bundle  144 . Common output lead  140  and multiple output wire bundle  144  are wired to variable output electromagnet circuitry  214  shown in detail in FIG.  4 . Also shown is endcap  146  which provides support for permanent magnet brushless shaft Small electric generator  148  is also shown. Small generator  148  is suitable for sensing alternator RPM and may be employed in controlling the activation of variable electromagnet windings  138 . 
     FIG. 7  shows a permanent magnet alternator having an outer rotor of permanent magnets and an inner stator electromagnet portion having multiple contactors suitable for the variable output aspects of this invention. Variable output permanent magnet alternator  150  is shown having outer alternator casing  152  enclosing permanent magnets  154 , and  156 . Permanent magnets  154  and  156  are attached to inside surface portion  158  of outer alternator casing  152 . Furthermore pole faces  160  and  162  of permanent magnets  154  and  156  face radially inward and alternate with each successive permanent magnet all of the way around. Electromagnets  166  are attached to generator shaft  164 . Electromagnet windings  168  provide power output from brushless permanent magnet alternator  150 . Lead  170  is the common lead and is shown directly connected to full wave bridge rectifier  172 . Full wave bridge rectifier  172  consists of four diodes arranged together in the bridge as shown. Multiple output leads from individual electromagnet windings are shown as wire bundle  174 . Common output lead  170  and multiple output wire bundle  174  are wired to variable output electromagnet circuitry  214  shown in detail in FIG.  4 . Also shown is end cap  176  which provides support for permanent magnet brushless alternator shaft  164 . Small electric generator  178  is suitable for sensing the RPM of the alternator and may be employed in controlling the activation of variable electromagnet windings  168 . 
     FIG. 8  shows a permanent magnet alternator having a disc rotor with permanent magnets and a stator having an electromagnet portion having multiple contactors equipped for controlling uniform output voltage. Variable output permanent magnet alternator  180  is shown having outer alternator casing  182  enclosing electromagnets  184 , and  186 . Also shown are permanent magnets  188 , and  190  having pole faces  192  and  194  on top and bottom surfaces so that the direction of magnetization is transverse through rotary disc portion  196 . When more permanent magnet pole faces are employed it is to be understood that they alternate with each successive pole face all of the way around the disc. Rotary disc portion  196  is attached to shaft  198 . Front shaft bearing  200  rotatably attaches shaft  198  to front end portion  202  of alternator casing  182 . Electromagnet windings  204  are also shown. Electromagnet windings  204  provide power output from brushless permanent magnet alternator  180 . Also shown is small electric generator  206 . Small electric generator  206  is capable of producing a voltage output signal that is proportional to speed and therefore may be employed in controlling the activation of variable electromagnet windings  204 . Generator  206  is securely fastened to back end portion  208  of outer alternator casing  182 . Variable electromagnet windings  204  have a common output lead  210  and a multiple output wire bundle  212 . Common output lead  210  and multiple output wire bundle  212  are wired to variable output electromagnet circuitry  214  shown in detail in FIG.  4 . Also shown is full wave bridge rectifier  216  which rectifies the output current from permanent magnet alternator  180 . Full wave bridge rectifier  216  consists of four diodes arranged together in the bridge as shown. 
   Those skilled in the art will understand that the embodiments of the present invention described above exemplify the present invention and do not limit the scope of the invention to these specifically illustrated and described embodiments. The scope of the invention is determined by the terms of the appended claims and their legal equivalents, rather than the described examples. In addition, the exemplary embodiments provide a foundation from which numerous alternatives and modifications may be made, which alternatives and modifications are also within the scope of the present invention defined by the appended claims.