Abstract:
A system and method are provided for controlling an internal combustion engine driving a generator/welder or a stand-alone generator. Controlling the engine may include altering the engine speed based upon a detected demand on the generator and/or operating parameters of a welder. For example, the engine speed may be increased based on a detected draw on the generator and/or the operating parameters of the welder. In addition, the engine speed may be automatically decreased to a non-standard idle speed or the engine may be automatically turned off if no demand is detected for a period of time. Additionally, the engine speed may be increased if only frequency-insensitive demands are detected on the generator. Combinations of these and further methods may be executed. Various devices are provided for implementing the above methods.

Description:
BACKGROUND 
     The invention relates generally to a system and method for controlling an engine driving a generator based on engine conditions and generator load. 
     Engine-driven generators are commonly used to provide electrical power in locations where conventional electrical power is not readily available. Both gasoline and diesel engines are used to drive such generators, and the power produced is typically either 120 VAC or 240 VAC. An engine-driven generator may be used to supply power to a welding gun (e.g., torch, arc, or the like) for applications such as, for example, stick electrode welding, MIG welding, TIG welding, etc. These welding systems include a control system to regulate the power produced by the generator, thereby making it suitable for arc welding, plasma cutting, and similar operations. 
     Typical welding systems offer the user little customizable control over the engine settings. For example, the engine may employ an engine governor to control the engine speed. When the welding gun or an auxiliary device is connected to the system and turned on, the engine speed may increase to the speed required to power the load. This speed increase may be determined by a generic governor curve which slowly increases the engine speed to substantially prevent overshooting the required speed. No distinction is made between the weld load and the auxiliary load, such as a light, which may require significantly less power to operate than the welder. 
     In addition, during periods of non-use of the typical welding system, the engine speed may be reduced to an idle speed. However, this idle speed may still consume a great deal of energy and produce substantial noise levels. A user may have no choice but to endure these inconveniences or to manually turn the engine off when it will not be used for some time. The engine must then be manually restarted before the welding gun may be used again. 
     BRIEF DESCRIPTION 
     In accordance with certain aspects of the invention, a method for controlling an engine-driven generator/welder includes monitoring for a voltage and/or current draw on welding and auxiliary outputs of the generator, and controlling the speed of the internal combustion engine based upon the detected draw. 
     There is further provided a method for controlling an engine-driven generator/welder, including monitoring for a demand on a welding output of the generator, increasing the speed of the internal combustion engine using a custom control regime based on preset operating parameters when the demand is detected, and transitioning to an engine speed control regime based upon the engine speed. 
     The invention also provides an engine-driven generator/welder system, including an internal combustion engine, a generator driven by the internal combustion engine, and a controller configured to detect a weld demand on the welding power generator and to control the internal combustion engine at least in part based upon the detected weld demand and/or preset operating parameters. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a diagrammatical overview of an integrated engine and generator control scheme in accordance with certain aspects of the invention, permitting improved control of engine and generator functions; 
         FIG. 2  is a block diagram of an engine-driven generator/welder system according to an embodiment of the present invention; 
         FIG. 3  is an engine speed graph according to an embodiment of the present invention; 
         FIG. 4  is a flow chart illustrating an engine control process for producing a series illustrated in the engine speed graph of  FIG. 3  according to an embodiment of the present invention; 
         FIG. 5  is a flow chart illustrating a further engine control process for producing another series illustrated in the engine speed graph of  FIG. 3  according to an embodiment of the present invention; 
         FIG. 6  is another engine speed graph according to an embodiment of the present invention; 
         FIG. 7  is a flow chart illustrating another engine control process for producing a series illustrated in the engine speed graph of  FIG. 6  according to an embodiment of the present invention; 
         FIG. 8  is a flow chart illustrating still another engine control process for producing yet another series illustrated in the engine speed graph of  FIG. 6  according to an embodiment of the present invention; 
         FIG. 9  is a further engine speed graph according to an embodiment of the present invention; 
         FIG. 10  is a flow chart illustrating yet another engine control process for producing a series illustrated in the engine speed graph of  FIG. 9  according to an embodiment of the present invention; and 
         FIG. 11  is an engine speed graph produced via a combination of the engine control processes illustrated in  FIGS. 4 ,  5 ,  7 , and  9  according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to control of an engine driving an electrical generator. An engine powering a generator/welder may include controls which affect the engine speed, ignition, fuel injection, spark timing, and any other controllable parameter of the engine based on various inputs. Such inputs may include, for example, currents or voltages supplied to loads, such as a welding gun and/or an auxiliary device, preset welding parameters, and time. 
       FIG. 1  is a diagrammatical overview of an exemplary integrated engine and generator control scheme in accordance with aspects of the present invention. As described in greater detail below, the system can be applied to a range of engines, such as gasoline engines and diesel engines. Moreover, the engine may include a wide range of measurable, observable and controllable parameters, such as, by way of example only, fuel flow, throttle position, speed, torque, power, spark advance (e.g., for gasoline engines), and so forth. Certain of these controls may be implemented mechanically, electromechanically or electronically, such as through the use of an electronic governor. In general, the engine will be started and will operate at speeds as determined by an integrated controller illustrated in  FIG. 1 . The integrated controller can cause the engine to operate at particular speeds depending upon optimal operating conditions, draw by particular loads, as summarized in greater detail below, and so forth. 
     In the embodiment illustrated in  FIG. 1 , the engine will drive a generator. Indeed, while the generator represents a load for the engine, the generator is, itself, a power source for electrical loads. In the diagrammatical illustration of  FIG. 1 , other electrical power sources may also be included in the system, such as batteries, grid converters configured to draw power from an electrical grid and to provide it to electrical loads. In certain presently contemplated systems, the generator will operate in parallel with other electrical power sources such as batteries and grid converters. In terms of the engine operation, the loads are drawing electrical power from the generator, and/or other electrical power sources, can influence the control of the engine by the intermediary of the integrated controller. Thus, electrical parameters may be sensed for the generator, batteries, grid converters, and other electrical power sources and the integrated controller may use these sensed parameters to control the operation and performance of the engine. It should also be noted that the integrated controller may also regulate certain functions of the electrical power sources. For example, the controller may regulate a field of the generator so as to control power production by the generator in accordance with needs of electrical loads and coordinated with speed and torque control of the engine. In presently contemplated applications, the electrical power sources will generate controlled electrical power which is available for a variety of loads. The electrical power may be a function of the speed at which the engine turns the generator and the number of poles included in the generator, or this power may further processed as described below. 
       FIG. 1  also illustrates a number of exemplary loads that may draw electrical power from the electrical power sources, including the engine-generator set. In the presently contemplated embodiments, these include a welder and certain auxiliary loads. As will be appreciated by those skilled in the art, the welder requires significant power for creation of electrical arcs used to fuse metals in welding operations. The welder illustrated in  FIG. 1  may convert power from the generator to power appropriate for the particular welding operation to be performed. As also described below, such welding operations may require constant voltage output regimes, constant current regimes, or various pulsed regimes, depending upon the nature of the welding operation. Auxiliary loads may include both alternating current and direct current loads, with output from the power sources being converted as necessary for the particular loads. In certain embodiments, the integrated controller may operate the engine at appropriate speeds and power levels to accommodate both welding loads and auxiliary loads. For example, tools, lights, and other loads designed to operate on alternating current at frequencies of a power grid (e.g., 60 Hz in North America) may require the engine to operate at specific speeds, depending upon the number of pulls of the generator. The integrated controller may sense output of the generator and output of the loads, or draw by the loads to regulate engine speed accordingly. 
     Other loads that may be powered by the system illustrated in  FIG. 1  may include a battery charger. In many mobile applications, for example, it may be useful to drive the engine as an auxiliary power source to charge a vehicle battery. Several other loads are also illustrated in  FIG. 1 , by way of a non-exhaustive list. Such other loads may include plasma cutters, wire feeders, alternating current sources used for specific operations, such as tungsten inert gas (TIG) welding, various welding accessories, power converters, such as inverters and choppers, and so forth. As with the welder and the auxiliary loads discussed above, the integrated controller may coordinate operation of the engine and/or generator to accommodate such loads based, for example, upon detection of connections, power draw, signatures of particular tools, and so forth. 
     The integrated controller may also take into account for control of the engine and/or generator, inputs from a variety of sources, several of which are listed in the diagram of  FIG. 1 . Presently contemplated sources for control include various operator inputs. Such operator inputs may be included in a control panel or human interface on the welders/generator cabinet. By way of example, operator inputs may set weld parameters as discussed below. However, operator inputs may also include manual override of speeds, manual input of desired noise or fuel usage, and so forth. Inputs may also be networked as illustrated in  FIG. 1 . Such networked inputs may include, for example, inputs received via a dedicated network connection, a LAN connection, a WAN connection, wirelessly, and so forth. Indeed, any of the inputs or even controlled parameters are regulated by the integrated controller may be input by an operator or by a network. Other input sources may include commands or requests for specific power or electrical parameters from any one of the loads coupled to the electrical power sources. Such inputs may further include devices coupled directly or indirectly to the engine and not through the electrical power sources. For example, in certain applications the engine may drive other devices (not shown in  FIG. 1 ) such as air compressors, hydraulic pumps, and so forth, and the integrated controller may receive inputs indicating that such devices are active and join power from the engine, and alter the engine speed, fuel flow rate, output torque or power, and so forth based upon such inputs. 
     The integrated controller itself may take any suitable form, and will typically include one or more power supplies and one or more processors with associated memory for storing sensed parameter values, control programs, and so forth. Because the system, in many applications, will be mobile, the integrated controller will typically be packaged in a robust manner capable of operation in difficult environmental conditions along with the engine, generator, and other components of the system. The processor may include any suitable digital processor, such as microprocessors, field programmable gate arrays, and so forth. Memory devices may be provided as part of the processor package, such as in the case of a field programmable gate array, an additional memory may include flash memory, random access memory, read only memory, programmable read only memory, and so forth. The control routines for regulating operation of the engine and the generator may be written in any suitable computer language, and such code is considered to well within the ambit of those skilled in the art based upon the various control regimes discussed below. 
     The degree of integration of control implemented by the integrated controller may vary depending upon the sophistication of the control regimes envisaged. For example, as described in greater detail below, the integrated controller may sense certain electrical parameters of the power sources, and particularly those of the generator, and perform relatively simple operations, such as speed control based on throttle positions, fuel flow rate, and so forth for the engine. Much more sophisticated control regimes may, however, be implemented in which the controller regulates both parameters of the engine and parameters of the generator to accommodate particular loads and power needs. 
     As discussed above, depending upon the engine design, the generator design, and the anticipated loads, the integrated controller may perform various functions specifically adapted for those machines. In certain presently contemplated applications, for example, many functions of the engine may be controlled mechanically, and the engine may be based upon carborated fuel mixing. In other applications, the engines will include fuel injected versions. Mechanical or electronic governors may be accommodated, with carborated fuel mixing or fuel injection. As will be appreciated by those skilled in the art, for mechanical governors, the controller generally will not control the throttle position. Similarly, engines in the system may be single cylinder, twin cylinder, three cylinder or more, and may be liquid or air cooled. 
     As also mentioned above, control may be based upon the particular design of the generator and any other electrical power sources in the system. For example, in certain presently contemplated designs, the generator may employ an electrical rheostat for field control. Such field control may be regulated by the integrated controller. In such applications, the integrated controller may also control injectors for the engine, and all of such control may be based upon inputs from a welder, auxiliary loads of various types, and so forth. 
       FIG. 2  illustrates an engine driven welding and power generating system  10  in accordance with an embodiment of the present invention. The system  10  generally includes an engine  12 , a weld generator  14 , and a generator  16  for providing auxiliary power output. An integrated control system includes an engine controller  18  and a welder controller  20 , which can be fully or partially integrated to receive inputs for control from the engine, the weld generator and the auxiliary generator, and produce outputs for control of the engine, the generator, or both. The weld generator provides power for a welder  22 , which may be controlled by the weld controller  20 . The welder will typically include a welding gun (e.g., a MIG or TIG torch, stick handle, etc.). Various auxiliary loads or devices  24  (e.g., lights, power tools, radios, etc.) may be powered by power from the auxiliary generator  16 . The engine  12  may be a gasoline or diesel engine which drives the generators. 
     As illustrated in  FIG. 2 , the controller  18  may receive inputs from the engine  12 , a user interface  52 , and/or power outputs from the generators. For example, sensors disposed within or coupled to the engine  12  may provide engine information to the controller  18  relating to engine operating conditions, settings, transient conditions, and so forth. Exemplary sensors may include a temperature sensor  26 , an oxygen sensor  28 , a manifold pressure sensor  30 , an RPM sensor  32 , a crank position sensor  34 . Further engine sensors may detect information regarding the throttle position, the fuel injection rate, the spark timing, mass air flow rate, and so forth. In addition, sensors coupled to the one or more power outputs of the generators  14  and  16  may provide information about loads drawing power from the generators (e.g., the welder  22  and/or the auxiliary loads  24 ). For example, a voltage sensor  36  and/or a current sensor  38  may be coupled to power output lines of the generator  14  to enable the controller to determine whether a load (e.g., welder  22 ) is drawing power from the generator, and the level of power draw. Similarly, a voltage sensor  40  and/or a current sensor  42  may be coupled to power output lines of generator  16  to detect draws from that generator. User inputs (e.g., preset operating parameters) may also be supplied to the controller via the user interface  52 . Exemplary preset operating parameters may include current and voltage requirements, process type (e.g., constant current, constant voltage, MIG, TIG, stick), wire electrode or stick size, and so forth. The user interface  24  may be integral with the system or may be an independent device, such as, for example, an input panel, a remote control system, and so forth. The user interface  24  may include, for example, a user input device such as a keypad, a keyboard, a mouse, a touch-screen, dials, switches, potentiometers, LEDs, lights, etc., and a display, such as a monitor, a CRT display, an LCD screen, etc. 
     In addition to receiving engine, process, and load information from inputs, the controller may send control signals to various engine systems. As described in more detail below, the controller may process some or all of the information gathered from the sensors  38 - 42  and/or input via the user interface  52  to alter engine operation settings. For example, the controller may manage an engine governor  44  (e.g., via a throttle plate), the ignition or crank timing  46 , a fuel injector  48  and its timing, a spark timer  50 , or any other engine component which may be controlled. To process all of the signals input to and output from the controller, the controller may, for example, include discrete analog and/or digital circuits, a logic device, a microprocessor, a microcontroller, a programmable logic controller, a field-programmable gate array, a complex programmable logic device, etc. 
       FIG. 3  is a graph  54  of generator speed  56  (e.g., revolutions per minute) versus time  58  in accordance with embodiments of the present invention. Referring generally to  FIG. 2  for the components of system  10  and to  FIG. 3  for the graph  54 , an idle speed  60  may be around 1800-2400 rpm for an internal combustion engine such as a two-cylinder gas engine. In another embodiment, a diesel engine may operate with an idle speed around 600-1200 rpm. The engine  18  powering the weld generator  14  and the auxiliary generator  16  may operate at an operating speed  62 . Generally, the normal operating speed  62  is the engine speed at which a synchronous power output frequency is produced. American devices typically utilize a 60 Hz frequency, and other devices utilize a 50 Hz frequency. The normal operating speed  62  of an exemplary two-cylinder gas engine may be about 3600 rpm, producing an alternating current with a frequency of about 60 Hz. An engine-driven four-pole generator may produce a 60 Hz frequency at about 1800 rpm. The engine operating speed  62  may be approximately based on the following equation: 
     
       
         
           
             
               
                 
                   
                     s 
                     = 
                     
                       
                         120 
                         ⁢ 
                         f 
                       
                       P 
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where s is the speed of the engine (rpm), f is the target frequency (Hz), and P is the number of poles in the generator. Other idle and operating speeds  60  and  62  may be used depending, for example, on the engine type (e.g., gasoline or diesel) and the engine design (e.g., number of cylinders, number of poles, etc.). 
     A trace  64  illustrates ramp-up of the engine speed  56  from the idle speed  60  to the operating speed  62  as observed in traditional engine control systems. For example, the welder  22  and/or the auxiliary load  24  may be turned on at a time  66 . Due to the increase in required torque when the engine load is increased, the speed  56  of the engine  12  initially decreases. After some time, the engine governor  44  detects the change in the engine speed  56  and increases the fuel flow rate to increase the engine speed  56  to compensate for the increased load. The engine speed  56  then increases to the operating speed  62  based on a governor curve. A traditional rpm-based control regime may utilize a generic governor curve to ramp up the engine speed  56  to the required speed for a given load (and to maintain the speed in an rpm-closed loop). That is, the engine speed  56  is ramped up relatively slowly so that the required speed for a given load is not greatly surpassed (i.e., to limit “overshoot”). To reach and maintain the operating speed  62 , the controller may employ various control techniques, such as, for example, closed-loop control, open-loop control, PID control, direct pole placement, optimal control, adaptive control, intelligent control, non-linear control, etc. After a time  68 , the engine speed  56  is generally constant at the operating speed  62 . As can be seen in the graph  54 , the trace  64  exhibits a significant droop after the load is introduced before the governor  44  begins to ramp up the engine speed  56 . 
     In contrast, a trace  70  illustrates an improved technique for ramping up the engine speed  56  when the welder  22  draws power from generator  14 . A user may input settings, such as the required current and voltage for the welder  22 , via the user interface  52 . The controller may then sense when the welder  22  is operative by monitoring the drawn voltage and current via the sensors  36  and  38  on the welding power output. Upon detection of a draw on the generator  14 , the controller may send a signal to the engine governor  44  to immediately begin ramping up the engine speed  56  based on a modified governor curve. For example, the user-input settings may be utilized in a lookup table, an algorithm, etc. to determine the governor curve which most efficiently increases the engine speed  56  to the desired operating speed  62 . The controller  22  may store information on any number of input-specific governor curves in addition to the generic governor curve. When the welder  22  begins to draw power at the time  66 , the engine speed  56  may decrease briefly under the load. However, because a signal is sent to the engine governor  44  as soon as the draw is detected, the governor  44  begins ramping up the engine speed  56  much faster than in the traditional engine control system illustrated by the trace  64 . Therefore, the engine speed  56  may be generally constant at the operating speed  62  after a time  72 . The delay from the onset of engine loading to the time  72  may be significantly less than that to the time  68  (traditional control) at which the trace  64  maintains the operating speed  62 . 
     Furthermore, the controller may employ different control regimes at different times in the ramp-up and speed maintaining process. For example, trace  70  illustrates a preset-based control regime further illustrated in  FIG. 4 . In contrast, trace  64  illustrates a traditional rpm-based control regime. As can be seen in the graph  54 , the preset-based control regime (trace  70 ) could overshoot the operating speed  62  to a greater extent than the rpm-based control regime (trace  64 ). This phenomenon may be attributed to the techniques employed by the respective control regimes in increasing the engine speed  56 . To combine the increased speed ramp-up in the preset-based control regime with the stabilization of the rpm-based control regime, the controller may switch from one control regime to the other, such as depending on the engine speed  56 . For example, at a time  74 , as the engine speed  56  approaches the target operating speed  62  using the preset-based control regime (trace  70 ), the controller may switch to the rpm-based control regime (trace  64 ). By changing control regimes, the benefits of each type of control may be optimized. 
       FIG. 4  illustrates a process  76  by which the trace  70  ( FIG. 3 ) may be generated. Referring to  FIG. 2  for the components of system  10 , to  FIG. 3  for the graph  54 , and to  FIG. 4  for the process  76 , preset operating parameters may be input (block  78 ), such as via the user interface  52 . The preset operating parameters may include, for example the current and voltage required by the welder  22 , a welding regime, details of the regime, etc. The engine load may then be determined based on the input settings for the welder  22  (block  80 ). That is, the idle speed  60 , the operating speed  62 , and/or the anticipated load to achieve the requisite current and voltage outputs for the welder  22  may be determined. For example, a lookup table, an algorithm, etc. may be utilized to determine the engine load, the idle speed  60 , and/or the operating speed  62  required for the load. These may be determined empirically, a priori, by testing of the engine under anticipated load conditions. After the operating parameters are input, the engine  12  may idle for a period of time (block  82 ), for example, while the user prepares the welder  22 . When the welder  22  becomes operative (e.g., an arc is struck), the controller senses a draw on the generator  14  (block  84 ). The controller may then send a signal to the engine governor  44 , ignition/crank input  46 , the fuel injector  48 , the spark timer  50 , etc., to begin ramping up the engine speed  56  from the idle speed  60  to the operating speed  62  (block  88 ). The ramp-up process may utilize an engine governor curve based on the user input settings and the anticipated operating speed  62 . For example, if the welder  22  requires output power that is generated when the generator operates at a speed  62  of 3600 rpm, the controller may adjust the engine operating settings to open the engine throttle to the requisite position for operating the engine at 3600 rpm. The engine then quickly ramps up to the operating speed  62 . 
       FIG. 5  illustrates a process  90  by which the engine control regime may be changed. Referring to  FIG. 3  for the graph  54  and to  FIG. 4  for the process  90 , the engine speed  56  may ramp up using the preset-based control regime (block  92 ). The engine speed  56  may then be monitored (block  94 ) and compared to the target operating speed  62  (block  96 ). If the engine speed  56  is not near the operating speed  62 , the ramp up continues using the preset-based control regime (block  92 ). However, if the engine speed  56  is near the operating speed  62 , the rpm-based control regime may be implemented (block  98 ). The threshold after which the engine speed  56  may be considered “near” the operating speed  62  may be a preset value, a user-input value, a percentage of the operating speed  62 , or another appropriate level. 
       FIG. 6  is a graph  100  of the engine speed  56  versus the time  58  in accordance with embodiments of the present invention. Referring generally to  FIG. 2  for the system  10  components and to  FIG. 6  for the graph  100 , in addition to the idle speed  60  and the rated speed  62 , a low idle speed  102  and an engine off speed  104  (i.e., stopped) are illustrated. For example, an engine with an idle speed  60  of 1800 rpm may have a low idle speed  102  of around 1600 rpm, although other low idle speeds  102  may be implemented. Reducing the engine speed  56  or turning the engine off during non-use serves to cool the engine and to reduce noise and fuel consumption when not servicing a load. In another embodiment, a high idle speed  105  may be implemented to anticipate demand of the welder  22  based on preset operating parameters. For example, if the engine has an idle speed  60  of 1800 rpm and a preset operating speed  62  of 3600 rpm, the high idle speed  105  may be approximately 3000 rpm. The high idle speed  105 , for example, may enable a faster increase to the operating speed  62  when the engine idles intermittently. 
     Traces  106 ,  108 , and  114  illustrate possible energy-saving techniques which may be implemented in the system  10 . For example, if there is no draw on the generators after a time  110 , the engine speed  56  may decrease from the idle speed  60  to the low idle speed  102  (trace  106 ), or operation of the engine may be temporally interrupted (trace  108 ), reducing the engine speed  56  to the engine off speed  104 . Upon detection of a draw on the engine at a time  112 , the engine speed  56  may ramp up to the operating speed  62  using any of the control techniques discussed above. Furthermore, a combination of the low idle speed  102  and the engine off speed  104  may be employed, as illustrated by a trace  114 . For example, the engine speed  56  may decrease to the low idle speed  102  after the time  110  and may then decrease to the engine off speed  104  after a time  116 . 
     In another embodiment, the engine speed  56  may initially decrease from the operating speed  62  to the high idle speed  105 . Upon detection of a draw on the generators, the engine speed  56  may return to the operating speed  62 . However, if there is no draw detected after the time  110 , the engine speed  56  may decrease from the high idle speed  105  to a lower speed (e.g., the idle speed  60 , as illustrated by the trace  109 ; the low idle speed  102 ; the engine off speed  104 ; or another engine speed  56 ). It should be noted that the times  110 ,  112 , and  116  may be different for different idle regimes. For example, it may be desirable to maintain the engine at the high idle speed  105  for a shorter period of time than for the idle speed  60  before transitioning to a lower engine speed  56 . 
     Turning to  FIG. 7 , a process  118  by which the traces  106 ,  108 , and  114  ( FIG. 6 ) may be generated is illustrated. Referring to  FIG. 2  for the system  10  components, to  FIG. 6  for the graph  100 , and to  FIG. 7  for the process  118  steps, the engine  18  may operate at the high idle speed  105  or the idle speed  60  (block  120 ). The controller may monitor the current and voltage draws on the power outputs to determine if a load is drawing on the generators (block  122 ). If there is no draw, the engine speed  56  may be decreased to the idle speed  60  (e.g., from the high idle speed  105 ), to the low idle speed  102  (e.g., from the idle speed  60  or the high idle speed  105 ), or to the engine off speed  104  (e.g., from the idle speed  60 , the low idle speed  102 , or the high idle speed  105 ) (block  124 ). After the engine speed  56  decreases, the controller may continue to monitor the current and/or voltage from the generators via the sensors  36 - 42  (block  126 ). If either the welder  22  or the auxiliary load  24  draws a current and/or voltage, the engine may restart and/or the engine speed  56  may be ramped up to the operating speed  62  (block  128 ). In addition, a switch may be used to restart the engine after shutdown. For example, the welder  22  may include a switch so that the engine can be started remotely. If there is no draw on the generators, the engine speed  56  may remain at the idle speed  60  or the low idle speed  102 , or the engine may remain off (block  124 ). It should be noted that while four idle/off speeds are illustrated in the graph  100  ( FIG. 6 ) and the process  118  ( FIG. 7 ), any number and/or combination of idle/off speeds may be implemented in accordance with the present disclosure. 
       FIG. 8  illustrates a process  130  which incorporates multiple reductions in the engine speed  56 , as illustrated by the trace  114  ( FIG. 6 ). Referring to  FIG. 2  for the system  10  components, to  FIG. 6  for the graph  100 , and to  FIG. 8  for the process  130  steps, the engine may idle at the idle speed  60  (block  132 ). The controller may monitor the engine speed  56  and/or the current and voltage draws on the generators to determine how long the engine has been at idle (block  134 ). If the engine  18  has not been at idle for the predetermined time, the engine speed  56  may remain at the idle speed  60  (block  132 ). However, if the engine has been at idle for a predetermined time, the engine speed  56  may decrease to the low idle speed  102  (block  136 ). The controller may then continue to monitor the engine speed  56  to determine how long the engine has been at the low idle speed  102  (block  138 ). If the engine has not been at the low idle speed  102  for the predetermined time, the engine speed  56  may remain at the low idle speed  102  (block  136 ). If the engine has been at the low idle speed  102  for a predetermined time, the engine may be temporally shut off, decreasing the engine speed  56  to the engine off speed  104  (block  140 ). After the engine shuts down, the controller may continue to monitor the sensors  36 - 42  for a load (block  142 ). If either the welder  22  or the auxiliary load  24  is turned on (i.e., begin to draw power, or demand power), the engine  18  may restart and the engine speed  56  may be ramped up to the rated speed  62  (block  144 ). In addition, a switch may be used to restart the engine after shutdown. For example, the torch  20  may include a switch so that the engine can be started remotely. If no load is detected, the engine may remain off (block  140 ). It should be understood that different combinations of idle speeds may be implemented in the process  130 , and any number of speeds may be employed to implement a gradual reduction in the engine speed  56 . 
     Turning to  FIG. 9 , a graph  146  of the engine speed  56  versus the time  58  is illustrated in accordance with embodiments of the present invention.  FIG. 2  is generally referred to for the system  10  components, and  FIG. 9  is referred to for the graph  146 . In this aspect of the present invention, an “intelligent overspeed”  148  may be implemented to improve power output for welding, particularly when an auxiliary load  24  is not drawing power from generator  16  or is not sensitive to the frequency supplied by the generator  16 . It may be desirable to increase the speed  56  of the engine, and therefore the output of the generator  14 , when performing high-amperage processes, such as, for example, gouging, wire welding with a large wire, stick welding with a large stick, or processes involving multiple inverters. A trace  150  illustrates the use of the intelligent overspeed  148 . At a time  152 , the engine speed  56  may be increased from the normal operating speed  62  to a higher speed  148 . The higher speed  148  may be an engine speed  56  at which the welder  22  operates more efficiently (e.g., 3700-3800 rpm for a 2-pole gasoline engine, or 2400-3000 rpm for a 4-pole diesel engine). Other speeds  148  may be implemented depending on the operating parameters of the system and the welder  22 . In addition, the speed  148  may be a preset value, a user-input value, a value determined based on the weld settings, or any approximate speed. 
     In order to generate power at a higher frequency without damaging frequency-dependent auxiliary loads  24 , it may be desirable to provide a control scheme that prevents the engine speed from increasing when a frequency-dependent auxiliary load  24  is being utilized. For example, the system may be equipped with a proprietary auxiliary power socket in addition to or in place of a standard auxiliary socket. A frequency-independent auxiliary load may have a corresponding proprietary plug such that only frequency-independent auxiliary loads may be plugged into the auxiliary power socket. In the corresponding control regime, then, the engine speed  56  may not be increased if power is being drawn from the standard power socket but may be increased if power is being drawn from the proprietary power socket. In another embodiment, the controller may determine whether an attached auxiliary load is frequency-dependent. The engine speed may be increased only if there is no frequency-dependent auxiliary load drawing power from the system. Furthermore, in another embodiment, the system may include power management technology which regulates output voltage independent of input voltage, frequency, phase, etc. For example, Auto-Line™ technology, available from Miller Electric, may provide such power stability. The auxiliary sockets may therefore have regulated power output, while the weld power output may be variable-frequency. 
       FIG. 10  illustrates a process  154  by which the trace  150  ( FIG. 9 ) may be generated. Referring to  FIG. 2  for the system components, to  FIG. 9  for the graph  146 , and to  FIG. 10  for the process  154 , the engine may operate at the operating speed  62  (block  156 ). That is, the welder and/or the auxiliary load may draw power from the generator. Using the sensors  36 - 42 , the controller may determine whether power is being drawn from the weld power output and/or the auxiliary power output of the generators (blocks  158  and  162 ). If welding power is not being drawn (i.e., the welder is not being operated), and if a frequency-dependent auxiliary load is drawing power (i.e., a frequency-dependent device is being utilized), the engine speed  56  may be maintained at the normal operating speed  62  (block  160 ). However, if welding power is being drawn (i.e., the welder is in use) and there is no frequency-dependent auxiliary load drawing power (i.e., no auxiliary device is in use, or only a frequency-independent auxiliary device is in use), the controller may increase the engine speed  56  to the higher speed  148  (block  164 ). By increasing the engine speed  56 , the generators are able to output power at a higher frequency. The welding gun  14  may operate more efficiently using the higher frequency power. 
     Finally,  FIG. 11  illustrates a graph  166  of the engine speed  56  versus the time  58  illustrated in accordance with embodiments of the present invention. Referring to  FIG. 2  for the system  10  components and to  FIG. 11  for the graph  166 , a trace illustrates the combination of multiple aspects of the present invention. For example, the engine may start at the idle speed  60 . At a time  170 , the controller may detect a draw on the generator by the welder. Based on preset operating parameters input at the user interface, the engine speed  56  may ramp up quickly using the preset-based control regime. At a time  172 , as the engine speed  56  approaches the target operating speed  62 , the controller may switch to the rpm-based control regime. The engine speed  56  may then stabilize at the operating speed  62 . After a time  174 , the controller may determine that neither the welder nor an auxiliary load is not in use and reduce the engine speed  56  to the idle speed  60 . After no detected power draw for a further time  176 , the controller may reduce the engine speed  56  to the low idle speed  102 . Likewise, if no draw is detected after a time  178 , the controller may shut down the engine, effectively reducing the engine speed to the engine off speed  104 . When a load is detected at a time  180 , the controller may turn the engine on and ramp up the engine speed  56  to the operating speed  62 . Once again, the controller may transition from the preset-based control regime to the rpm-based control regime at a time  182 . At a time  184 , if the controller determines that there is not a frequency-dependent load on the engine (e.g., only the welder is in operation, or the welder and a non-frequency dependent device are in operation), the engine speed  56  may be further ramped up to the higher speed  148 . 
     It should be appreciated that any or all of the embodiments disclosed herein may be implemented in a single system, generator/welder, or generator. While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.