Abstract:
A generator system includes a prime mover having a drive shaft and a throttle, a driven member having a rotor disposed on a rotor shaft, and a continuously variable transmission pulley system. The transmission pulley system includes a drive pulley coupled to the drive shaft and having a variable drive pulley effective diameter. A driven pulley coupled to the rotor shaft has a variable driven pulley effective diameter responsive to varying torque on the rotor shaft. A belt configured to engage the drive pulley and the driven pulley has a belt tension, wherein the drive pulley effective diameter varies in response to the belt tension.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/404,808, filed Mar. 16, 2009, now U.S. Pat. No. 8,267,835, which claims priority to U.S. Provisional Patent Application No. 61/037,388, filed Mar. 18, 2008, the entire contents of all of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a transmission and governor for a portable, residential, or small business generator system. 
         [0003]    Typical generator systems employ direct drive transmissions to couple an engine to an alternator. Direct drive systems typically fix the engine speed at 3,000 rpm (50 Hz) or 3,600 rpm (60 Hz), depending upon the required output current frequency. Due to the nature of direct drive transmission, such systems are inefficient and excessively noisy during low load operation. Some generator systems employ an inverter to allow the engine to operate at speeds that are proportionate to the power demand. A generator is rotated at a variable speed and its output is converted into direct current. Then, the inverter creates a sinusoidal output from the direct current at the desired output voltage and frequency (e.g., 120 VAC, 60 Hz). However, inverters are complex and expensive. 
       SUMMARY 
       [0004]    In one embodiment, the invention provides a generator system for a portable, residential or small business generator including an engine, an alternator, a continuously variable transmission pulley system and a governor. The engine includes a drive shaft and a throttle. The alternator includes a rotor disposed on a rotor shaft. The continuously variable transmission pulley system includes a drive pulley coupled to the drive shaft, a driven pulley coupled to the rotor shaft, and a belt configured to engage the drive pulley and the driven pulley. The governor adjusts the engine throttle to control the speed of the engine in response to a speed of the rotor shaft. 
         [0005]    In another embodiment the invention provides a continuously variable transmission pulley system for a generator, including a drive pulley having a first sheave and a second sheave, a driven pulley having a third sheave and a fourth sheave, and a belt that engages the drive pulley and the driven pulley. The belt is disposed between the first sheave and the second sheave, and between the third sheave and the fourth sheave. The driven pulley is configured to open and close to change a diameter of the belt disposed between the third sheave and the fourth sheave in response to a load on the generator. 
         [0006]    In another embodiment, the invention provides a method of controlling a generator having an engine, an engine throttle, and an alternator, the alternator having a rotor and a rotor shaft and the engine having a drive shaft. The method includes coupling the drive shaft of the engine to the rotor shaft of the alternator such that a rotational speed of the rotor shaft is capable of being different than a rotational speed of the drive shaft, adjusting a ratio of rotor shaft speed to drive shaft speed in response to a torque on the rotor shaft, and maintaining a substantially constant rotor shaft speed. 
         [0007]    In another embodiment, the invention provides a generator system including a prime mover having a drive shaft and a throttle, a driven member having a rotor disposed on a rotor shaft, and a continuously variable transmission pulley system. The transmission pulley system includes a drive pulley coupled to the drive shaft and having a variable drive pulley effective diameter. A driven pulley coupled to the rotor shaft has a variable driven pulley effective diameter responsive to varying torque on the rotor shaft. A belt configured to engage the drive pulley and the driven pulley has a belt tension, wherein the drive pulley effective diameter varies in response to the belt tension. 
         [0008]    In another embodiment, the invention provides a generator system including a prime mover having a drive shaft and a throttle, a driven member having a rotor disposed on a rotor shaft, and a continuously variable transmission pulley system. The transmission pulley system includes a drive pulley coupled to the drive shaft and having a variable drive pulley effective diameter. A driven pulley coupled to the rotor shaft has a variable driven pulley effective diameter responsive to varying torque on the rotor shaft. A belt is configured to engage the drive pulley and the driven pulley. A governor is configured to adjust the throttle to control the speed of the engine in response to a speed of the rotor shaft. 
         [0009]    In another embodiment, the invention provides a method of controlling the operation of a generator having a driven shaft. The method includes coupling a driven pulley to the driven shaft, the driven pulley having a variable effective diameter. The method further includes providing a prime mover having a drive shaft and coupling a drive pulley to the drive shaft, the drive pulley having a variable effective diameter. The method also includes engaging a belt with the drive pulley and the driven pulley such that the driven shaft rotates in response to rotation of the drive shaft, the belt having a belt tension. The method additionally includes adjusting the effective diameter of the driven pulley in response to varying torque on the driven shaft and adjusting the effective diameter of the drive pulley in response to variations in the belt tension. 
         [0010]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a generator system according to the invention having one construction of a driven pulley in a continuously variable transmission (CVT) pulley system. 
           [0012]      FIG. 2  is a schematic view of the generator system of  FIG. 1  having another construction of a driven pulley in the CVT pulley system. 
           [0013]      FIG. 2A  is a detailed view of a portion of the driven pulley of  FIG. 2 . 
           [0014]      FIG. 3  is another schematic view of the generator system of  FIG. 1  showing the continuously variable transmission (CVT) pulley system in greater detail. 
           [0015]      FIG. 4  is a schematic view of the CVT pulley system according to the invention. 
           [0016]      FIG. 5  is an exploded view of the driven pulley of  FIGS. 1 and 3 . 
           [0017]      FIG. 6  is a schematic view of a pulley system according to a second embodiment of the invention. 
           [0018]      FIG. 7  is a plot of test data corresponding to a prototype of the first embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0020]      FIGS. 1-2  illustrate a portable generator  10  having an engine  12 , an alternator  14 , a continuously variable transmission (CVT) pulley system  16  and a governor  19 . The generator  10  converts engine rotation into electrical power to supply power-consuming devices or loads (not shown) electrically connected to the generator&#39;s output. The connected loads require electrical power within narrow voltage and frequency ranges, such as plus-or-minus five percent. The magnitude of the total electrical load depends on the type and number of power-consuming devices drawing power from the generator  10 . In the illustrated construction, the engine  12  and alternator  14  are positioned side-by-side. In another construction, the engine  12  and alternator  14  may be positioned one on top of the other, facing each other, or the like. The generator  10 , as described herein, could also be configured for use as a residential or small business generator and is not limited to portable generators. 
         [0021]    In the illustrated construction, the engine  12  is an air-cooled internal combustion gasoline engine having a drive shaft  18  preferably delivering an output of between  2  and  45  horsepower (hp) and preferably operating at a speed range of between 200 rpm and 4000 rpm, with speeds of between about 1,500 rpm and 3,800 rpm being preferred for spark-ignition internal combustion engines. The speed of the engine  12  is controlled by a throttle  20 . The drive shaft  18  has a central axis A. In other constructions, the engine  12  may deliver an output more than 45 hp. Other constructions may also employ fuels such as diesel, propane, natural gas, and the like. Such engines may run at speeds as low as 200 rpm. 
         [0022]    In the illustrated construction, with reference particularly to  FIG. 2 , the alternator  14  is a conventional single-phase alternating current (AC) generator having a stator  21 , a rotor  23  and a rotor shaft  22 , as is well known in the art. The total electrical load on the generator  10  is felt by the alternator  14  as a torque on the rotor shaft  22 . The rotor shaft  22  has a central axis B. In order to provide steady alternating current having a substantially constant frequency, the alternator  14  must substantially maintain a target rotor speed. In the preferred construction, the target rotor speed is approximately 3600 rpm. A tolerance of approximately plus or minus five percent is preferred, but larger tolerances are possible. In other constructions, the alternator  14  may have a target rotor speed of about 3000 rpm to generate 220 volts, 50 Hz alternating current to power loads in Europe, for example. 
         [0023]    As shown in  FIGS. 1-5 , the CVT pulley system  16  includes a drive pulley  24 , a driven pulley  26 , and a belt  28  disposed between and engaging the drive pulley  24  and the driven pulley  26 . (An alternative construction of the driven pulley  26  is shown as  26   a  in  FIGS. 1 ,  3  and  5  and will be explained in greater detail below. All description of the driven pulley  26  can be applied to the construction of  26   a,  except as explained below.) In the illustrated constructions of  FIGS. 1-5 , the drive pulley  24  and the driven pulley  26 ,  26   a  are variable diameter pulleys and the belt  28  is a conventional V-belt having a tapered width to adjust to varying diameters of the drive and driven pulleys  24 ,  26 ,  26   a.  The drive pulley  24  has a spring-loaded variable diameter and the driven pulley  26 ,  26   a  has a torque-sensitive variable diameter, as will be explained in greater detail below. The effective diameter of a pulley at any given point in time is equal to two times the pitch radius of the belt  28  that engages the pulley. The belt pitch radius is the radial distance from the pulley axis of rotation to embedded tensile cords within the belt construction. Each pulley has a minimum and a maximum possible effective diameter, which depends upon the geometry of the pulley, and the effective diameter may have a value anywhere between the minimum and the maximum possible effective diameter. The geometry of the pulleys will be described in greater detail below. 
         [0024]    With reference to  FIG. 2 , the drive pulley  24  is coupled to the drive shaft  18  of the engine  12 . The driven pulley  26  is coupled to the rotor shaft  22  of the alternator  14 . The CVT pulley system  16  connects the drive shaft  18  to the rotor shaft  22 , so the alternator  14  is effectively driven by, or in response to, the engine  12 . In the illustrated construction of  FIG. 3 , the axes A and B are spaced apart by a first distance E, preferably about 12 inches. The outermost length between the outer circumference of the drive pulley 24 is a second distance F, preferably about 21.5 inches. The depth of the drive pulley  24  is a third distance G, preferably about 5.9 inches. The offset between portions of the drive and driven pulleys  24 ,  26 ,  26   a  closest to the engine  12  and alternator  14 , respectively, is a fourth distance H, preferably about 0.8 inches. In other constructions, these distances will vary depending on the pulleys used, the size of the generator, etc. It is to be understood that these dimensions are not meant to limit the scope of the invention, and other suitable dimensions are possible. 
         [0025]    With reference to  FIG. 2 , the drive pulley  24  includes a first sheave  30 , a second sheave  32 , and an axial spring  34 . The first sheave  30  has a first inclined, or curved, surface  36  on which a portion of the belt  28  rides. The first sheave  30  is coupled to the drive shaft  18  of the engine  12  and rotates with the drive shaft  18 . The first sheave  30  is axially fixed to the drive shaft  18  at a first location  38  along the axis A. The second sheave  32  has a second inclined, or curved, surface  40  on which another portion of the belt  28  rides. The second surface  40  faces the first surface  36 , and the belt  28  is disposed between the first surface  36  and the second surface  40 . The second sheave  32  is coupled to the drive shaft  18  and rotates with the drive shaft  18 . A fixed portion  42  of the second sheave is axially fixed to the drive shaft  18  at a second location  44  along the axis A. A moveable portion  46  of the second sheave includes the second surface  40  and is moveable along the axis A between the first location  38  and the second location  44 . The moveable portion  46  translates axially and rotates with the drive shaft  18 . The axial spring  34  is a compression spring coupled to the moveable portion  46  of the second sheave at one end and coupled to the fixed portion  42  of the second sheave at another end. The axial spring  34  biases the moveable portion  46  of the second sheave toward the first sheave  30 . Therefore, the second surface  40  is biased toward the first surface  36 . It should be noted that the second sheave  32  remains axially and radially aligned with the first sheave  30  as the second sheave  32  moves with respect to the first sheave  30 . The maximum effective diameter of the drive pulley occurs when the first and second surfaces are as close together as possible. In this condition, the belt  28  rides high on the drive pulley  24  and has a large diameter where the belt  28  engages the drive pulley  24 . In the illustrated construction, the first sheave  30  is disposed between the second sheave  32  and the engine  12 . It is to be understood that in another construction, the second sheave  32  may be disposed between the first sheave  30  and the engine  12 . 
         [0026]    As shown in the construction of  FIG. 2 , the driven pulley  26  includes a third sheave  48 , a fourth sheave  50 , a first cam surface  52 , a second cam surface  54 , and a torsional spring  56 . The first and second cam surfaces  52 ,  54  are shown in detail in  FIG. 2A . The third sheave  48  has a third inclined, or curved, surface  58  on which a portion of the belt  28  rides. The third sheave  48  is coupled to the rotor shaft  22  of the alternator  14  and rotates with the rotor shaft  22 . The third sheave  48  is axially fixed to the rotor shaft at a first location  60  along the axis B. The fourth sheave  50  has a fourth inclined, or curved, surface  62  on which a portion of the belt  28  rides. The fourth surface  62  faces the third surface  58 , and the belt  28  is disposed between the fourth surface  62  and the third surface  58 . The fourth sheave  50  is coupled to the rotor shaft  22  of the alternator  14  and rotates with the rotor shaft  22 . A fixed portion  64  of the fourth sheave is axially fixed to the rotor shaft  22  at a second axial location  66  along the axis B. 
         [0027]    With further reference to  FIG. 2 , the fixed portion  64  of the fourth sheave includes the first cam surface  52 , or first ramp, and a moveable portion  68  of the fourth sheave includes the second cam surface  54 , or second ramp, that is in opposition to and in contact with the first cam surface  52 . The second cam surface  54  is configured to follow the first cam surface  52  as the second cam surface  54  rotates with respect to the first cam surface  52 . The first cam surface  52  acts as a wedge, so the moveable portion  68  of the fourth sheave moves axially away from the fixed portion  64  of the fourth sheave when the moveable portion  68  rotates in a first direction relative to the fixed portion  64 . Accordingly, the moveable portion  68  moves axially towards the fixed portion  64  when the moveable portion  68  rotates in a second direction relative to the fixed portion  64 . It is to be understood that the first cam surface  52  and the second cam surface  54  may have many different geometries to achieve various desired effects as the second cam surface rotates with respect to the first cam surface, and may include roller-type followers and the like to reduce the coefficient of friction between the first and second cam surfaces  52 ,  54 . Generally, the first cam surface  52  and the second cam surface  54  form a helical cam, as is understood by those skilled in the art. One suitable drive pulley assembly is a model  340  torque converter made by Hoffco. 
         [0028]    With reference to  FIG. 2 , the fixed portion  64  of the fourth sheave is coupled to the moveable portion  68  of the fourth sheave by way of the torsional spring  56 . The torsional spring  56  biases the moveable portion  68  of the fourth sheave toward the third sheave  48 . Therefore, with the belt  28  removed, the fourth surface  62  is biased toward the third surface  58 . It should be noted that the third sheave  48  and the fourth sheave  50  remain axially aligned as the fourth sheave  50  moves with respect to the third sheave  48 . However, the third sheave  48  and fourth sheave  50  change their radial alignment relative to one another as the fourth sheave  50  moves axially with respect to the third sheave  48 . In the illustrated construction, the fourth sheave  50  is disposed between the third sheave  48  and the alternator  14 . It is to be understood that in another construction, the third sheave  48  may be disposed between the fourth sheave  50  and the alternator  14 . 
         [0029]    In another construction of the driven pulley, referred to with the numeral  26   a  and shown in  FIG. 5 , the torsional spring  56  can be replaced with an axial spring  72  that biases the third and fourth sheaves  48 ,  50  closed. In this construction, the driven pulley  26   a  includes a fifth sheave  48   a,  a sixth sheave  50   a,  a helical groove  52   a,  a pair of rollers  53   a,  and the axial spring  72 . The fifth sheave  48   a  has a fifth inclined, or curved, surface  58   a  on which a portion of the belt  28  rides. The fifth sheave  48   a  is coupled to the rotor shaft  22  of the alternator  14  and rotates with the rotor shaft  22 . The fifth sheave  48   a  is axially fixed to the rotor shaft  22  at a location along the axis B. The sixth sheave  50   a  has a sixth inclined, or curved, surface  62   a  on which a portion of the belt  28  rides. The sixth surface  62   a  faces the fifth surface  58   a,  and the belt  28  is disposed between the sixth surface  62   a  and the fifth surface  58   a.  The sixth sheave  50   a  includes a pair of rollers  53   a  coupled thereto, such as by way of apertures  55   a.  The rollers  53   a  are sized to fit within the helical groove  52   a  and engage the helical groove  52   a.  Rolling of the rollers  53   a  within the helical groove  52   a  results in axial and radial translation of the sixth sheave  50   a  with respect to the fifth sheave  48   a.  This construction of the driven pulley  26   a  behaves substantially the same way as the first construction of the driven pulley  26  in response to torque on the rotor shaft  22 , except that the structure is slightly different. It is, therefore, to be understood that there are other possible constructions of the CVT pulley system  16  that carry out substantially the same function while being configured differently. 
         [0030]    With reference to  FIG. 2 , the governor  19  mechanically or electrically couples the rotor shaft  22  to the engine throttle  20 . In a preferred construction, the governor  19  is an electronic governor to achieve a faster response time than a typical mechanical governor. The governor, denoted generally as  19 , is preferably electronic and includes an rpm sensor  70  on the alternator rotor shaft  22 , a throttle actuator  74 , and an electronic control unit (ECU)  76 . One suitable ECU is a Woodward APECS 500 single speed electronic engine controller. The rpm sensor  70  is electrically connected to an input of the ECU  76  to transmit a signal at least once per rotor revolution. In a preferred construction, the rpm sensor  70  includes a stationary permanent magnet and generates a signal with the passing of each tooth on a toothed wheel coupled to the rotor shaft  22 . In another construction, the rpm sensor  70  includes a toothed wheel, or other rotatable magnet carrier, coupled to the rotor shaft  22 , the toothed wheel having one or more permanent magnets coupled thereto. A permanent magnet sensor is disposed radially from the rotor shaft  22  and generates a pulse each time the one or more permanent magnets on the toothed wheel pass a fixed coil that is part of the magnet sensor. This construction, however, does not generate as high a resolution as the aforementioned construction of the rpm sensor. The ECU  76  is electrically connected to the throttle actuator  74  to provide control signals to the throttle actuator  74 . The throttle actuator  74  is preferably a pulse width modulated spring-biased rotary actuator, but a stepper motor could be used. The actuator  74  controls the position of the throttle  20 , and therefore the speed of the engine  12 . The ECU  76  is programmed to maintain the target rotor speed, as described above. When the rotor speed drops significantly below the target rotor speed, as sensed by the rpm sensor  70 , the ECU  76  commands the throttle actuator  74  to increase the speed of the engine  12  by moving the throttle valve toward the wide open position. Conversely, when the rotor speed increases above the target rotor speed, as sensed by the rpm sensor  70 , the ECU  76  commands the throttle actuator  74  to decrease the speed of the engine  12  by moving the engine throttle valve toward the closed position. In other constructions, a different type of rpm sensor may be employed. Furthermore, a different type of governor that achieves the desired control may be employed. 
         [0031]    For example, in another construction, the governor  19  may be mechanical. In this construction (not shown), the engine  12  preferably also has a carburetor and a carburetor throttle valve to control the air/fuel mixture and therefore the speed of the engine  12 . A mechanical governor uses a control linkage from the rotor shaft or the driven pulley to the throttle valve to increase the engine speed when the rotor speed significantly drops below the target rotor speed, or to decrease the engine speed when the rotor speed is significantly above the target rotor speed. 
         [0032]    Referring again to  FIG. 2 , an engine rpm limiter, or shutdown switch,  82  may be mechanically or electrically coupled to the engine ignition (not shown) and includes an engine speed sensor. The shutdown switch  82  may be disposed within an engine ignition coil. In the event of a broken or malfunctioning belt  28 , the rotor shaft speed may decrease, causing the ECU  76  to increase the speed of the engine  12 . If the belt  28  fails to transmit rotation of the drive shaft  18  into rotation of the rotor shaft  22 , the governor  19  could continue to increase the engine speed without causing a subsequent rotor speed increase. In this situation, the rpm limiter or shutdown switch  82  grounds the ignition pulses when an excessive engine speed is detected, preventing the engine  12  from reaching an excessive speed in the event of a malfunction. 
         [0033]    In operation, the driven pulley  26  is a torque-sensitive pulley that increases in effective diameter as torque on the rotor shaft  22  increases. While the belt  28  is removed (and the driven pulley  26  is not in operation) the third sheave  48  and the fourth sheave  50  (or the fifth sheave  48   a  and sixth sheave  50   a  in the construction of  FIG. 5 ) are as close to each other as possible because of the biasing force of the torsional spring  56  (or the axial spring  72  in the construction of  FIG. 5 ). During operation with the belt  28  in place, however, the moveable portion  68  of the fourth sheave (or the sixth sheave  50   a ) is forced away from the third sheave  48  against the biasing force of the torsional spring  56  (or axial spring  72 ) by belt tension. Increases in torque, or load, on the rotor shaft  22  act with the force of the torsional spring  56  (or axial spring  72 ) to force the inclined surfaces  58  (or  58   a ),  62  (or  62   a ) together to increase the effective diameter of the driven pulley  26  (or  26   a ). As the moveable portion  68  of the fourth sheave (or the sixth sheave  50   a ) rotates relative to the fixed portion  64  of the fourth sheave (or the fifth sheave  48   a ), the second cam surface  54  rides up on the first cam surface  52  as described above (or the rollers  53   a  ride in the helical groove  52   a ), thus closing the gap between moveable portion  68  of the fourth sheave (or the sixth sheave  50   a ) and the third sheave  48  (or the fifth sheave  48   a ), which increases the effective diameter of the driven pulley  26  (or  26   a ). The driven pulley  26  (or  26   a ) “demands” more belt from the drive pulley  24 . The rate of effective diameter increase of the driven pulley  26  (or  26   a ) with respect to torque depends upon the geometry of the first cam surface  52  and the second cam surface  54  (or the helical groove  52   a ), as described above. 
         [0034]    The drive pulley  24  acts as a belt-tensioner. In response to changes in effective diameter of the driven pulley  26 ,  26   a  and therefore changes in belt tension, the drive pulley  24  changes effective diameter to take up slack or to provide slack in order to maintain an acceptable level of tension in the belt  28 . If there is not enough tension in the belt  28 , the belt  28  may slip or fail to engage one or both of the pulleys  24 ,  26 ,  26   a  thereby decreasing the efficiency of the system  10 . If there is too much tension in the belt  28 , the belt  28  may wear more quickly and be prone to failure. For example, when the load on the alternator  14  increases, the torque on the rotor shaft  22  increases, and therefore the effective diameter of the driven pulley  26 ,  26   a  increases and the tension in the belt  28  increases. The extra tension in the belt  28  acts against the axial spring  34  in the drive pulley  24 , pushing the first and second sheaves  30 ,  32  apart, so the effective diameter of the drive pulley  24  decreases to lower the tension in the belt  28  to an acceptable level. Conversely, when the load on the alternator  14  decreases, the torque on the rotor shaft  22  decreases, and therefore the effective diameter of the driven pulley  26 ,  26   a  decreases creating slack in the belt  28 . The force of the axial spring  34  is now dominant and biases the first and second sheaves  30 ,  32  closer together to increase the effective diameter of the drive pulley  24  and take up slack in the belt  28 . 
         [0035]    In another construction, a fixed-diameter drive pulley  84  may be employed, as shown in  FIG. 6 , instead of the variable-diameter drive pulley  24 . In this construction, a belt tensioner  86  is employed to compensate for changes in belt tension. Belt tensioner  86  is preferably a pivoting swing arm type tensioner, as shown. As described above, an electrical or mechanical governor may be employed. In this construction, however, a mechanical governor may additionally employ a control linkage from the belt tensioner  86  to the throttle valve to control the engine speed based on rotor shaft torque. 
         [0036]    The effect that the relationship between the drive and the driven pulleys  24 ,  26 ,  26   a  of the illustrated constructions has on transmission ratio should also be noted. In the illustrated construction, the drive pulley  24  is generally larger in effective diameter than the driven pulley  26 ,  26   a  as shown by an instantaneous effective diameter C of the drive pulley and an instantaneous effective diameter D of the driven pulley in  FIG. 4 . In a preferred construction, the CVT pulley system  16  has a step-up ratio of 1.5 when the load is minimal. Therefore, for each revolution of the drive shaft  18 , there are 1.5 revolutions of the rotor shaft  22 . When the torque (i.e., load) on the alternator  14  increases, the effective diameter of the driven pulley  26 ,  26   a  increases and the effective diameter of the drive pulley  24  decreases to maintain proper belt tension. In the preferred construction, the CVT pulley system  16  will shift progressively to a 1.111 speed reduction ratio as the load increases. Therefore, for each revolution of the drive shaft  18  at increased torque, there are fewer revolutions of the rotor shaft  22  than at a lower torque. The increase of torque therefore results in a decrease of rotor speed. The governor  19  then signals for an increase in engine speed in order to return the rotor shaft  22  to the target rotor speed. Conversely, when the torque on the alternator  14  decreases, the effective diameter of the driven pulley  26 ,  26   a  decreases and the effective diameter of the drive pulley  24  increases to maintain proper belt tension. Therefore, for each revolution of the drive shaft  18  at decreased torque, there are more revolutions of the rotor shaft  22  than at a higher torque. The decrease of torque therefore results in an increase of rotor speed. The governor  19  then signals for a decrease in engine speed in order to return the rotor shaft  22  to the target rotor speed. Thus, the generator  10  operates to maintain a substantially constant rotor speed, which provides a steady supply of alternating current for power-consuming devices. In other constructions, other transmission ratios may be employed to achieve other desired results. 
         [0037]    The relationship between load (i.e., torque on the rotor shaft  22 ) and engine speed, as described above, is confirmed by the test data. That is, engine speed decreases with decreasing loads and increases with increasing loads.  FIG. 7  is a plot test data from a prototype of the generator  10  showing engine speed vs. load. The engine runs at a speed of approximately 3900 rpm for an electrical load of approximately 2300 watts, at a speed of approximately 3400 rpm for an electrical load of approximately 1700 watts, at a speed of approximately 2700 rpm for an electrical load of approximately 1000 watts, and at idle speed (approximately 1900 rpm) for substantially no electrical load. As shown, the engine speed is significantly less than 3600 rpm for lower electrical loads, which saves fuel and is more efficient than a direct drive system. 
         [0038]    The generator  10  also provides quieter operation, lower exhaust emissions, reduced engine wear, and improved fuel economy over typical direct drive generators because the engine speed decreases at lower electrical loads. 
         [0039]    Thus, the invention provides, among other things, a portable, residential, or small business generator employing a CVT pulley system.