Abstract:
A load control system, in certain aspects, may be configured to decrease the amount of noise pollution of a prime mover (e.g., engine) of a service pack in that it may not require the prime mover to operate at higher discrete operating speeds to deliver small amounts of air from the air compressor. The load control system may also only increase the speed of the prime mover to a minimum discrete speed required, keeping noise at a minimum. The load control system may also maximize fuel efficiency by not operating the prime mover at the highest discrete speed at all times. More specifically, the lower operating speeds may lead to less fuel consumption.

Description:
BACKGROUND 
     The invention relates generally to a system for controlling the speed of a prime mover (e.g., an engine). More specifically, the invention relates to the control of a prime mover of a work vehicle service pack based on loads of an air compressor of the work vehicle service pack. 
     The prime mover of the work vehicle service pack generally drives various loads, such as the air compressor, an electrical generator, and a hydraulic pump. These various loads can potentially overload the prime mover, reduce fuel efficiency, increase pollutant emissions, and so forth. In addition, the prime mover may become extremely noisy when driving the loads of the air compressor. More specifically, the prime mover may only operate at a limited number of discrete operating speeds. As such, in order to meet the pneumatic loads, the prime mover may frequently operate at one of the higher discrete operating speeds, increasing the fuel usage of the prime mover. 
     BRIEF DESCRIPTION 
     Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
     A load control system, in certain aspects, may be configured to decrease the amount of noise pollution of the prime mover (e.g., engine) of a work vehicle service pack. In particular, the load control system may not require the prime mover to operate at higher discrete operating speeds to deliver small amounts of air from the air compressor. The load control system may also only increase the speed of the prime mover to a lower discrete operating speed, keeping noise at a minimum. The load control system may also maximize fuel efficiency by not operating the prime mover at the highest discrete operating speed at all times. More specifically, operating the prime mover at lower operating speeds may lead to less fuel consumption. 
    
    
     
       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 diagram of an embodiment of a work vehicle having a service pack with a load control system; 
         FIG. 2  is a diagram of an embodiment of power systems in the work vehicle of  FIG. 1 , illustrating support systems of the service pack completely separate and independent from support systems of a work vehicle engine; 
         FIG. 3  is a diagram of an embodiment of power systems in the work vehicle of  FIG. 1 , illustrating support systems of the service pack highly integrated with support systems of the work vehicle engine; 
         FIGS. 4A-4C  are diagrams of the service pack with different arrangements of an electrical generator, a hydraulic pump, and an air compressor driven by a service pack engine; 
         FIG. 5  is a block diagram illustrating an embodiment of the load control system for the service pack of  FIGS. 1-4 ; 
         FIG. 6  is another block diagram of an embodiment of the load control system for the service pack, further illustrating how the service engine may be configured to drive the air compressor; and 
         FIG. 7  is a flowchart illustrating an exemplary method for controlling the operating speed of the service engine based on sensed loads on the air compressor. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     In certain embodiments, a load control system may be configured to control an air compressor, which may be a part of a service pack mounted on a work vehicle or other mobile application. The load control system may ensure that the air compressor delivers an adequate amount of air pressure based on a load applied to the air compressor. The load control system may turn the compressor on and off, identify a maximum air pressure that a regulator of the air compressor is set to, and allow for electronically setting a minimum pressure setting that an operator of the air compressor may use. In order to get the maximum amount of air flow from the air compressor, the operating speed of the air compressor may be increased. The load control system may monitor a pressure associated with the air compressor (e.g., the pressure in an air reservoir associated with the air compressor), and may determine whether a load is applied to the air compressor. Based at least in part on this determination, the load control system may decide whether or not to increase the speed of the engine driving the air compressor. The type of load applied to the air compressor may be determined by monitoring the rate of change in tank pressure, the total change from the maximum pressure, whether the pressure has dropped below the minimum pressure setting, and so forth. 
     At low air compressor loading levels, the load control system may ensure that the engine stays at as low a speed as possible, thereby providing the best fuel economy and lowest noise level. At increased air compressor loading levels, the load control system may increase the engine speed according to the load applied. If the load control system detects that the pressure is falling below the minimum pressure setting, it may increase the engine speed even further. The load control system may, in certain embodiments, have a limited number of discrete operating speeds (e.g., 1800 revolutions per minute (rpm), 2600 rpm, 3200 rpm, and 3600 rpm) but may also operate at a continuously variable speed. 
     In certain embodiments, the disclosed load control techniques may be used with various service packs to prevent an overload condition of a diesel engine power source that is directly coupled to multiple loads, specifically an air compressor, hydraulic pump, and electrical generators, where the individual and/or combination of these loads have the potential to overload the diesel engine power source. For example, the disclosed embodiments may be used in combination with any and all of the embodiments set forth in U.S. application Ser. No. 11/742,399, filed on Apr. 30, 2007, and entitled “ENGINE-DRIVEN AIR COMPRESSOR/GENERATOR LOAD PRIORITY CONTROL SYSTEM AND METHOD,” which is hereby incorporated by reference in its entirety. By further example, the disclosed embodiments may be used in combination with any and all of the embodiments set forth in U.S. application Ser. No. 11/943,564, filed on Nov. 20, 2007, and entitled “AUXILIARY SERVICE PACK FOR A WORK VEHICLE,” which is hereby incorporated by reference in its entirety. 
       FIG. 1  illustrates a work vehicle  10  in accordance with the present invention. The work vehicle  10  is illustrated as a work truck, although any suitable configuration for the work vehicle  10  may be utilized. In the illustrated embodiment, the work vehicle  10  includes a service pack  12  for supplying electrical power, compressed air, and hydraulic power to a range of applications, designated generally by reference numeral  14 . The work vehicle  10  has a main vehicle power plant  16  based around a work vehicle engine  18 . Although the invention is not limited to any particular configuration or equipment, work vehicle engines of this type will typically be diesel engines, although gasoline engines may be used in some vehicles. 
     The vehicle power plant  16  may include a number of conventional support systems. For example, the work vehicle engine  18  may consume fuel from a fuel reservoir  20 , typically one or more liquid fuel tanks. An air intake or air cleaning system  22  may supply air to the work vehicle engine  18 , which may, in certain applications, be turbo-charged or super-charged. A cooling system  24 , which may typically include a radiator, a circulation pump, a thermostat-controlled valve, and a fan, may provide for cooling the work vehicle engine  18 . An electrical system  26  may include an alternator or generator, along with one or more system batteries, cabling for these systems, cable assemblies routing power to a fuse box or other distribution system, and so forth. A lube oil system  28  may typically be included for many engine types, such as for diesel engines. Such lube oil systems  28  typically draw oil from the diesel engine crankcase and circulate the oil through a filter and cooler, if present, to maintain the oil in good working condition. Finally, the power plant  16  may be served by an exhaust system  30 , which may include catalytic converters, mufflers, and associated conduits. 
     The service pack  12  may include one or more service systems driven by a service engine  32 . In a present embodiment, the service pack  12  may provide electrical power, hydraulic power, and compressed air for the various applications  14 . In the diagrammatical representation of  FIG. 1 , for example, the service engine  32  may drive a generator  34 , a hydraulic pump  36 , and an air compressor  38 . The service engine  32  may be of any desired type, such as a diesel engine. However, certain embodiments may use gasoline engines or other types of engines. The generator  34  may be directly driven by the service engine  32 , such as by close coupling the generator  34  to the service engine  32 , or may be belt-driven or chain-driven. The generator  34  may include three-phase brushless types, capable of producing power for a range of applications. However, other types of generators  34  may be employed, including single-phase generators and generators capable of producing multiple power outputs. The hydraulic pump  36  may be based on any conventional technology, such as piston pumps, gear pumps, vane pumps, and so forth and may be used with or without closed-loop control of pressure and/or flow. The air compressor  38  may also be of any suitable type, such as a rotary screw air compressor. Other suitable air compressors  38  may include reciprocating compressors, typically based upon one or more reciprocating pistons. 
     The systems of the service pack  12  may include appropriate conduits, wiring, tubing, and so forth for conveying the service generated by these components to an access point  40 . Convenient access points  40  may be located around the periphery of the work vehicle  10 . In a presently contemplated embodiment, all of the services may be routed to a common access point  40 , although multiple access points  40  may certainly be utilized. The diagrammatical representation of  FIG. 1  illustrates the generator  34  as being coupled to electrical cabling  42  (for AC power supply) and  44  (for 12-volt DC power supply), whereas the hydraulic pump  36  is coupled to a hydraulic circuit  46 , and the air compressor  38  is coupled to an air circuit  48 . The wiring and circuitry for all three systems will typically include protective circuits for the electrical power (e.g., fuses, circuit breakers, and so forth) as well as valving for the hydraulic and air service. For the supply of electrical power, certain types of power may be conditioned (e.g., smoothed, filtered, and so forth), and 12-volt power output may be provided by rectification, filtering, and regulating of the AC output. Valving for hydraulic power output may include, by way example, pressure relief valves, check valves, shut-off valves, as well as directional control valving. 
     In certain embodiments, the generator  34  may be coupled to the work vehicle electrical system  26 , and particularly to the work vehicle battery  50 . Thus, as described below, not only may the service pack  12  allow for 12-volt loads to be powered without operation of the main work vehicle engine  18 , but the work vehicle battery  50  may serve as a shared battery, and may be maintained in a good state of charge by the service pack generator output. 
     The cabling, circuits, and conduits  42 ,  44 ,  46 , and  48  may route service for all of these systems directly from connections on the service pack  12 . For example, connections may be provided at or near the access point  40  of the service pack  12 , such that connections can easily be made without the need to open an enclosure of the access point  40 . Moreover, certain control functions may be available from a control and service panel  52 . The control and service panel  52  may be located on any surface of the work vehicle  10  or at multiple locations on the work vehicle  10 , and may be covered by doors or other protective structures. The control and service panel  52  need not be located at the same location, or even near the locations of the access point  40  to the electrical, hydraulic, and compressed air output points of the service pack  12 . For example, the control and service panel  52  may be provided in a rear compartment covered by an access door. The control and service panel  52  may permit, for example, starting and stopping of the service engine  32  by a keyed ignition or starter button. Other controls for the service engine  32  may also be provided on the control and service panel  52 . The control and service panel  52  may also provide operator interfaces for monitoring the service engine  32 , such as fuel level gages, pressure gages, as well as various lights and indicators for parameters such as pressure, speed, and so forth. The control and service panel  52  may also include a stop, disconnect, or disable switch that allows the operator to prevent starting of the service engine  32 , such as during transport. 
     As also illustrated in  FIG. 1 , a remote control panel or device  54  may also be provided that may communicate with the control and service panel  52  or directly with the service pack  12  wirelessly. The operator may start and stop the service pack engine  32 , and control certain functions of the service pack  12  (e.g., engagement or disengagement of a clutched component, such as the air compressor  38 ) without directly accessing either the components within the service pack  12  or the control and service panel  52 . 
     As noted above, any desired location may be selected as a convenient access point  40  for one or more of the systems of the service pack  12 . In the illustrated embodiment, for example, one or more alternating current electrical outputs, which may take the form of electrical receptacles  56  (for AC power) and  58  (for 12-volt DC power) may be provided. Similarly, one or more pneumatic connections  60 , typically in the form of a quick disconnect fitting, may be provided. Similarly, hydraulic power and return connections  62  may be provided, which may also take the form of quick disconnect fittings. 
     In the embodiment illustrated in  FIG. 1 , the applications  14  may be coupled to the service pack  12  by interfacing with the outputs provided by the AC electrical receptacle  56 . For example, a portable welder  64  may be coupled to the AC electrical receptacle  56 , and may provide power suitable for a welding application  66 . More specifically, the portable welder  64  may receive power from the electrical output of the generator  34 , and may contain circuitry designed to provide for appropriate regulation of the output power provided to cables suitable for the welding application  66 . The presently contemplated embodiments include welders, plasma cutters, and so forth, which may operate in accordance with any one of many conventional welding techniques, such as stick welding, tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, and so forth. Although not illustrated in  FIG. 1 , certain of these welding techniques may call for or conveniently use wire feeders to supply a continuously fed wire electrode, as well as shielding gases and other shielding supplies. Such wire feeders may be coupled to the service pack  12  and be powered by the service pack  12 . 
     Similarly, DC loads may be coupled to the DC receptacle  58 . Such loads may include lights  68 , or any other loads that would otherwise be powered by operation of the main work vehicle engine  18 . The 12-volt DC output of the service pack  12  may also serve to maintain the work vehicle battery charge, and to power any ancillary loads that the operator may need during work (e.g., cab lights, hydraulic system controls, and so forth). 
     The pneumatic and hydraulic applications may similarly be coupled to the service pack  12  as illustrated in  FIG. 1 . For example, a hose  70  or other conduit may be routed from the compressed air source at the outlet  60  to a pneumatic load  72 , such as an impact wrench. However, many other types of pneumatic loads  72  may be utilized. Similarly, a hydraulic load  74 , such as a reciprocating hydraulic cylinder may be coupled to the hydraulic service  62  by means of appropriate hoses or conduits  76 . As noted above, certain of these applications, particularly the hydraulic applications, may call for the use of additional valving. Such valving may be incorporated into the work vehicle  10  or may be provided separately either in the application itself or intermediately between the service pack  12  and the hydraulic actuators. It should also be noted that certain of the applications  14  illustrated in  FIG. 1  may be incorporated into the work vehicle  10 . For example, the work vehicle  10  may be designed to include a man lift, scissor lift, hydraulic tail gate, or any other driven systems which may be coupled to the service pack  12  and driven separately from the main work vehicle engine  18 . 
     The service pack  12  may be physically positioned at any suitable location in the work vehicle  10 . For example, the service engine  32  may be mounted on, beneath or beside the vehicle bed or work platform rear of the vehicle cab. In many such work vehicles  10 , for example, the work vehicle chassis may provide convenient mechanical support for the service engine  32  and certain of the other components of the service pack  12 . For example, steel tubing, rails, or other support structures extending between front and rear axles of the work vehicle  10  may serve as a support for the service engine  32 . Depending upon the system components selected and the placement of the service pack  12 , reservoirs may also be provided for storing hydraulic fluid and pressurized air, such as hydraulic reservoir  78  and air reservoir  80 . However, the hydraulic reservoir  78  may be placed at various locations or even integrated into an enclosure of the service pack  12 . Likewise, depending upon the air compressor  38  selected, no air reservoir  80  may be used for compressed air. 
     The service pack  12  may provide power for on-site applications completely separately from the work vehicle engine  18 . That is, the service engine  32  may generally not be powered during transit of the work vehicle  10  from one service location to another, or from a service garage or facility to a service site. Once located at the service site, the work vehicle  10  may be parked at a convenient location, and the main work vehicle engine  18  may be shut down. The service engine  32  may then be powered to provide service from one or more of the service systems described above. In certain embodiments, clutches or other mechanical engagement devices may be provided for engagement and disengagement of one or more of the generator  34 , the hydraulic pump  36 , and the air compressor  38 . Moreover, where stabilization of the work vehicle  10  or any of the systems is beneficial, the work vehicle  10  may include outriggers, stabilizers, and so forth, which may be deployed after parking the work vehicle  10  and prior to operation of the service pack  12 . 
     Several different scenarios may be implemented for driving the components of the service pack  12 , and for integrating or separating the support systems of the service pack  12  from those of the work vehicle power plant  16 . One such approach is illustrated in  FIG. 2 , in which the service pack  12  is entirely independent and operates completely separately from the work vehicle power plant  16 . In the embodiment illustrated in  FIG. 2 , the support systems for the work vehicle power plant  16  are coupled to the work vehicle engine  18  in the manner set forth above. In this embodiment, the service pack  12  may reproduce some or all of these support systems for operation of the service engine  32 . For example, these support systems may include a separate fuel reservoir  82 , a separate air intake or air cleaning system  84 , a separate cooling system  86 , a separate electrical protection and distribution system  88 , a separate lube oil system  90 , and a separate exhaust system  92 . 
     Many or all of these support systems may be provided local to the service engine  32 , in other words, at the location where the service engine  32  is supported on the work vehicle  10 . On larger work vehicles  10 , access to the location of the service engine  32 , and the service pack  12  in general, may be facilitated by the relatively elevated clearance of the work vehicle  10  over the ground. Accordingly, components such as the fuel reservoir  82 , air intake or air cleaning system  84 , cooling system  86 , electrical protection and distribution system  88 , and so forth, may be conveniently positioned so that these components can be readily serviced. Also, the hydraulic pump  36  and air compressor  38  may be driven by a shaft extending from the generator  34 , such as by one or belts or chains  94 . As noted above, one or both of these components, or the generator  34  itself, may be provided with a clutch or other mechanical disconnect to allow them to idle while other systems of the service pack  12  are operative. 
       FIG. 3  represents an alternative configuration in which the service pack  12  support systems are highly integrated with those of the main work vehicle power plant  16 . In the illustrated embodiment of  FIG. 3 , for example, all of the systems described above may be at least partially integrated with those of the work vehicle power plant  16 . Thus, coolant lines  96  may be routed to and from the work vehicle cooling system  24  of the work vehicle  10 , while an air supply conduit  98  may be routed from the air intake and cleaning system  22  of the work vehicle  10 . Similarly, an exhaust conduit  100  may route exhaust from the service engine  32  to the exhaust system  30  of the work vehicle  10 . The embodiment of  FIG. 3  also illustrates integration of the electrical systems of the work vehicle  10  and the service pack  12 , as indicated generally by electrical cabling  102 , which may route electrical power to and from the distribution system  26  of the work vehicle  10 . The systems may also integrate lube oil functions, such that lubricating oil may be extracted from both crank cases in common, to be cleaned and cooled, as indicated by conduit  104 . Finally, a fuel conduit  106  may draw fuel from the main fuel reservoir  20  of the work vehicle  10 , or from multiple reservoirs where such multiple reservoirs are present on the work vehicle  10 . 
     In presently contemplated embodiments, integrated systems of particular interest include electrical and fuel systems. For example, while the generator  34  of the service pack  12  may provide 110-volt AC power for certain applications, its ability to provide 12-volt DC output may be particularly attractive to supplement the charge on the work vehicle battery  50 , for charging other batteries, and so forth. The provision of both power types, however, makes the system even more versatile, enabling 110-volt AC loads to be powered (e.g., for tools, welders, and so forth) as well as 12-volt DC loads (e.g., external battery chargers, portable or cab-mounted heaters or air conditioners, and so forth). 
     Integrated solutions between those of  FIG. 2  and  FIG. 3  may also be utilized. For example, some of the support systems may be separated in the work vehicle  10  both for functional and mechanical reasons. Embodiments of the present invention thus contemplate various solutions between those shown in  FIG. 2  and  FIG. 3 , as well as some degree of elimination of redundancy between these systems. For instance, at least some of the support systems for the main work vehicle engine  18  may be used to support the service pack  12 . For example, at least the fuel supply and electrical systems may be at least partially integrated to reduce the redundancy of these systems. The electrical system may thus serve certain support functions when the work vehicle engine  18  is turned off, removing dependency from the electrical system, or charging the vehicle battery  50 . Similarly, heating, ventilating, and air conditioning systems may be supported by the service pack engine  32 , such as to provide heating of the work vehicle  10  when the main work vehicle engine  18  is turned off. Thus, more or less integration and removal of redundancy may be possible. 
     The foregoing service pack systems may also be integrated in any suitable manner for driving the service components, particularly the generator  34 , hydraulic pump  36 , and air compressor  38 , and particularly for powering the on-board electrical system.  FIGS. 4A-4C  illustrate simplified diagrams of certain manners for driving these components from the service engine  32 . In the embodiment illustrated in  FIG. 4A , the generator  34  may be close-coupled to the output of the engine  32 , such as directly to the engine flywheel or to a shaft extending from the engine  32 . This coupling may be disposed in a support housing used to support the generator  34  on the engine block or other engine support structures. A sheave  108  may be mounted to an output shaft extending from the generator, and similar sheaves  110  and  112  may be coupled to the hydraulic pump  36  and air compressor  38 . One or more belts and/or clutches may be drivingly coupled between these components, and an idler  114  may be provided for maintaining tension on the belt. Such an arrangement is shown in  FIG. 4B , in which the hydraulic pump  36  is driven through a clutch  116 , such as an electric clutch. Although not shown specifically, any one of the components may be similarly clutched to allow for separate control of the components. Such control may be useful for controlling the power draw on the service engine  32 , particularly when no load is drawn from the particular component, and when the component is not needed for support of the main vehicle engine systems (e.g., maintaining a charge on the vehicle batteries). 
     These components may be supported in any suitable manner, and may typically include some sort of rotating or adjustable mount such that the components may be swung into and out of tight engagement with the belt to maintain the proper torque-carrying tension on the belt and avoid slippage. More than one belt may be provided on appropriate multi-belt sheaves, where the torque required for turning the components is greater than that available from a single belt. Other arrangements, such as chain drives, may also be used. Moreover, as described above, the generator  34  may also be belt or chain driven, or more than one component may be driven directly by the service engine  32 , such as in an in-line configuration. In a further alternative arrangement, one or more of the components may be gear driven, with gearing providing any required increase or decrease in rotational speed from the output speed of the service engine  32 . An exemplary arrangement of this type is shown diagrammatically in  FIG. 4C . In the illustrated arrangement, a support adapter  118  mounts the generator  34  on the service engine  32 , and the hydraulic pump  36  and air compressor  38  are driven by a gear reducer  120 . In such arrangements, one or more clutches may still be provided upstream or downstream of the gear reducer  120  for selective control of the components. 
     The particular component or components that are directly and/or indirectly driven by the service engine  32  may be selected based upon the component and engine specifications. For example, it may be desirable to directly drive the hydraulic pump  36 , and to drive the generator  34  via a belt or gear arrangement, permitting the service engine  32  to operate at a higher speed (e.g., 3200 rpm) while allowing a reduced speed to drive the generator  34  (e.g., 1800 rpm for near 60 Hz AC output of a 4 pole generator). 
       FIG. 5  is a block diagram illustrating an embodiment of a load control system  122  for the service pack  12  of  FIGS. 1-4 . As described in greater detail below, the load control system  122  may be configured to adjust the operating speed of the service engine  32  based at least in part on loads sensed on the air compressor  38 . As illustrated, the load control system  122  interfaces with the service engine  32 , the air compressor  38  as Load A, the hydraulic pump  36  as Load B, and the generator  34  as Load C. The service engine  32  may be configured to selectively drive one or more of the Loads A, B, and C (e.g., compressor  38 , pump  36 , and generator  34 ) based on load sense feedback to a controller  124 . In particular, the controller  124  may receive a load sense  126  and/or RPM feedback  128  from the service engine  32 . The controller  124  also may receive output load sense  130  from one or more of the Loads A, B, and C (e.g., compressor  38 , pump  36 , and generator  34 ). In addition, the controller  124  may receive operator input  132  regarding desired services, priority of the Loads A, B, and C, and so forth. In response to the load sense  126 , the RPM feedback  128 , and/or the output load sense  130 , the controller  124  may provide an RPM set-point  134  to the service engine  32  and/or load control  136  to the various Loads A, B, and C (e.g., compressor  38 , pump  36 , and generator  34 ). 
     In the illustrated embodiment, the controller  124  is configured to manage or control all or part of the major power or load functions of the unit. For example, the controller  124  may utilize the engine load sense  126  signal from the service engine  32  to determine how much additional load can be applied to the engine  32  without overloading the engine  32 . For example, the load sense  126  may include a measurement of horsepower, torque, exhaust temperature, throttle/actuator position, or another suitable measurement directly associated with the service engine  32 . By further example, the load sense  126  may use throttle/actuator position of a carburetor or fuel injection system as a measurement of fuel quantity being injected into the service engine  32 , which in turn provides an indication of load on the service engine  32 . Thus, an increase in fuel injection may indicate an increase in load on the service engine  32 , whereas a decrease in fuel injection may indicate a decrease in load on the service engine  32 . If the load sense  126  indicates or predicts an overload condition on the service engine  32 , then the controller  124  can adjust or turn on/off the output to the various Loads A, B, and C (e.g., compressor  38 , pump  36 , and generator  34 ) via the load control  136 , thereby reducing or preventing the possibility of overloading the service engine  32 . 
     In certain embodiments, the controller  124  utilizes both the engine load sense  126  signal along with the engine RPM feedback  128  signal to accurately determine and manage the load on the service engine  32 . The controller  124  can then determine the current load, remaining available load that can be applied to the service engine  32  for a given RPM, and any potential overload condition based on the load sense  126  signal, RPM feedback  128  signal, and RPM set-point  134 . 
     In certain embodiments, the controller  124  may utilize the output load sense  130  signal alone or in combination with the load sense  126  signal and/or RPM feedback  128  signal to accurately determine and manage the load on the service engine  32 . For example, the output load sense  130  signal may relate to a pneumatic load  138  associated with pneumatic power  140  generated by the air compressor  38 . The pneumatic load  138  may relate to air pressure, air flow rate, or some other suitable load measurement. The output load sense  130  signal may also relate to a hydraulic load  142  associated with hydraulic power  144  generated by the hydraulic pump  36 . The hydraulic load  142  may relate to hydraulic pressure, hydraulic flow rate, or some other suitable load measurement. The output load sense  130  signal may also relate to an electrical load  146  associated with AC/DC electrical power  148  generated by the generator  34 . Likewise, the output load sense  130  signal may relate to an electrical load  150  associated with AC electrical power (fixed frequency)  152  generated by a synthetic power converter  154  coupled to the generator  34 . The electrical loads  146  and  150  may relate to current, voltage, or some other suitable load measurement. Each of these load signals  138 ,  142 ,  146 , and  150  of the output load sense  130  may be used alone or in combination with the engine load sense  126  and/or RPM feedback  128  to make load adjustments and/or engine adjustments to power match the service engine  32  with the various Loads A, B, and C (e.g., compressor  38 , pump  36 , and generator  34 ). 
     The controller  124  may be configured to generate and transmit load control signals  156 ,  158 ,  160 , and  162  via the load control  136  to the compressor  38 , the hydraulic pump  36 , the generator  34 , and the synthetic power converter  154  based on load sense  126 , the RPM feedback  128 , and/or the output load sense  130 . For example, the controller  124  may be configured to selectively engage or disengage one or more of the loads (e.g., compressor  38 , pump  36 , generator  34 , and converter  154 ), individually adjust output levels of the loads, or a combination thereof. For example, the controller  124  may provide load control  136  (via signals  156 ,  158 ,  160 , and  162 ) that prioritizes the various loads, and then shuts off and/or reduces output of the less important loads if the service engine  32  cannot meet the demands. For example, the operator input  132  may prioritize the loads as: (1) electrical power  148 , (2) pneumatic power  140 , (3) electrical power  152 , and (4) hydraulic power  144 . 
     However, any other prioritization of the loads may be selected by the user or set as a default for the controller  124 . If the controller  124  then receives load sense  126 , RPM feedback  128 , and output load sense  130  indicative of a possible overload condition on the engine  32 , then the controller  124  may provide load control  136  that increases the RPM set-point  134  and/or reduces or shuts off the lowest priority load (e.g., hydraulic power  144 ). If this is sufficient to prevent an overload condition, then the controller  124  may not make any further changes until the controller  124  identifies another potential overload condition. If this is not sufficient to prevent the overload condition, then the controller  124  may take further measures. For example, the controller  124  may provide load control  136  that further increases the RPM set-point  134  and/or reduces or shuts off the next lowest priority load (e.g., electrical power  152 ). If this is sufficient to prevent an overload condition, then the controller  124  may not make any further changes until the controller  124  identifies another potential overload condition. However, again, if this is not sufficient to prevent the overload condition, then the controller  124  may take further measures continuing with the next lowest priority loads. In each step, the controller  124  may reduce output and/or disconnect devices coupled to the various loads (e.g., compressor  38 , pump  36 , generator  34 , and converter  154 ). 
     Likewise, the controller  124  may provide load control  136  that prioritizes the various loads (e.g., compressor  38 , pump  36 , generator  34 , and converter  154 ), and then turns on and/or increases power output of the loads in order of priority if the service engine  32  exceeds the demands. In other words, the controller  124  can make adjustments for both overload and underload conditions to better power match the capabilities of the service engine  32  with the loads (e.g., compressor  38 , pump  36 , generator  34 , and converter  154 ). For example, in the case of an underload condition (e.g., wasted power), the controller  124  may simply reduce the RPM set-point  134  if additional output power is not needed from the compressor  38 , pump  36 , generator  34 , or converter  154 . Otherwise, if there is an underload condition and a need for additional output power, then the controller  124  may increase pneumatic power  140 , hydraulic power  144 , electrical power  148 , and/or electrical power  152 . Again, the controller  124  may increase power based on the priority of loads (e.g., compressor  38 , pump  36 , generator  34 , and converter  154 ). Thus, if the highest priority is pneumatic power  140 , then the controller  124  may increase pneumatic power  140  prior to increasing hydraulic power  144 . However, any suitable priority of loads is within the scope of the disclosed embodiments. 
     In certain embodiments, the service pack  12  may include a direct coupling, belt and pulley system, gear and chain system, clutch system, or a combination thereof, between the service engine  32  and the Loads A, B, and C (e.g., compressor  38 , pump  36 , and generator  34 ). As illustrated, the service engine  32  includes a clutch  164  configured to selectively engage and disengage the air compressor  38 . Likewise, a clutch may be used between the service engine  32  and the hydraulic pump  36  and/or the generator  34 . The clutch  164  may be used to remove or add a load (e.g., compressor  38 ) to the service engine  32  based on the load control  136 . In some embodiments, the system  122  may include a switch, valve, or other actuator configured to engage and disengage each load, either individually or collectively with the other loads. Indeed, instead of using the clutch  164  to remove or add a load to the service engine  32 , in certain embodiments, the clutch  164  may not be used at all. Rather, the service engine  32  may be directly driven and a valve may be turned off and on to activate or deactivate a load (e.g., compressor  38 ). In any event, the controller  124  can more closely power match the service engine  32  with the various loads (e.g., compressor  38 , pump  36 , generator  34 , and converter  154 ). 
     As illustrated, the air reservoir  80  may be associated with a valve  166  for controlling the flow of air from the air compressor  38  to the air reservoir  80 . Likewise, the hydraulic reservoir  78  may similarly be associated with a valve  168  for controlling the flow of hydraulic fluid from the hydraulic pump  36  to the hydraulic reservoir  78 . In particular, in certain embodiments, the flow of air into the air reservoir  80  may be controlled by selectively engaging or disengaging the clutch  164  while simultaneously disengaging or engaging the valve  166 . Further, in other embodiments, the clutch  164  may not be used at all. Rather, in these embodiments, the service engine  32  may be directly driven and the valve  166  alone may be used to control the flow of air into the air reservoir  80 . Likewise, the flow of hydraulic fluid into the hydraulic reservoir  78  may be similarly controlled. In addition, the air compressor  38 , valve  166 , and air reservoir  80  may be associated with sensors  170  for use in the control of the air compressor  38 , valve  166 , and air reservoir  80 . Likewise, the hydraulic pump  36 , valve  168 , and hydraulic reservoir  78  may be similarly associated with sensors  172  for use in the control of the hydraulic pump  36 , valve  168 , and hydraulic reservoir  78 . More specifically, the sensors  170 ,  172  may generate signals corresponding to pressure, temperature, flow rate, tank level, vibration, and so forth. These signals may be sent to the controller  124  where they may be utilized for load control  136 . 
     In particular, in the disclosed embodiments, the sensors  170  may enable loads on the air compressor  38  to be sensed. More specifically, in certain embodiments, the sensors  170  may include pressure sensors for sensing changes in pressure within the air reservoir  80 . Further, in other embodiments, the sensors  170  may include flow meters for sensing the flow of air to and/or from the air reservoir  80 . The control signals relating to the sensed loads on the air compressor  38  may be sent to the controller  124 , which may adjust an operating parameter of the service engine  32  based at least in part on the control signals relating to the sensed loads. 
       FIG. 6  is another block diagram of an embodiment of the load control system  122  for the service pack  12 , further illustrating how the service engine  32  may be configured to drive the air compressor  38 . The operating speed of the service engine  32  may be regulated at least in part by the service engine  32 , the air compressor  38 , and associated equipment. In particular, this section of the load control system  122  may include the service engine  32 , the air compressor  38 , the air reservoir  80 , a governor  174 , the clutch  164 , the valve  166 , the controller  124 , and a user interface  176 . In this configuration, the speed of the service engine  32  may be regulated at least partially by the governor  174 , and the transfer of torque from the service engine  32  to the air compressor  38  may be regulated by the clutch  164 . As will be discussed in detail below, the controller  124  may implement a control algorithm to coordinate the operation of the governor  174 , the clutch  164 , and the valve  166  based on various inputs and parameters, such as pressure drops associated with the air reservoir  80 . 
     The governor  174  may generally be configured to regulate the speed of the service engine  32  based on a desired speed level. In certain embodiments, the service engine  32  may be configured operate at discrete operating speeds (e.g., 1800 rpm, 2600 rpm, 3200 rpm, and 3600 rpm). However, in other embodiments, the service engine  32  may be configured to operate at continuously variable operating speeds. The governor  174  may include an electronic governor configured to control the service engine  32  based on the input control signals and monitored parameters of the service engine  32  and/or the air compressor  38 . For example, the governor  174  may receive a speed control signal  190  commanding a given speed and the governor  174  may then generate an output signal to control a throttle of the service engine  32 . The output may include an electrical control of the service engine  32  or may include mechanical actuation of the throttle of the service engine  32 . 
     The speed control signal  190  may be generated by the controller  124 . In such an embodiment, the speed control signal  190  may be produced based on a control algorithm embedded on memory within the controller  124 . For example, the controller  124  may monitor the operating speed and command the governor  174  to increase or decrease the speed of the service engine  32  accordingly. In other embodiments, the governor  174  may include an onboard control loop (such as a proportional-integral-derivative (PID) controller) that regulates the output to the service engine  32 . Thus, the governor  174  may independently regulate the service engine  32  to meet the parameters requested by the speed control signal  190  output by the controller  124 . In other words, the governor  174  may receive a signal requesting a given speed and implement its own routine to regulate the service engine  32  to the desired speed. The governor  174  may include any mechanism configured to receive the speed control signal  190  and regulate the service engine  32  based on the speed control signal  190 . 
     The governor  174  may be mounted to the service engine  32  in various configurations that enable the governor  174  to regulate the service engine  32 . In an embodiment, the governor  174  may be mechanically coupled to the service engine  32 . Mechanically coupling the governor  174  to the service engine  32  enables the governor  174  to manipulate components of the service engine  32 , including a carburetor throttle shaft, and the like. Mechanically coupling the governor  174  may include providing the service engine  32  with the governor  174  built into the service engine  32 , directly attaching the governor  174  to the body of the service engine  32 , or providing the governor  174  as a separate component with a linkage to the service engine  32 . Other embodiments may include electrically coupling the governor  174  to control circuitry located within the service engine  32 . 
     The clutch  164  is configured to control the transfer of power from the service engine  32  to the air compressor  38 . The power transferred may include mechanical power in the form of torque. The service engine  32  may include a drive shaft  178  and a stub shaft  180 , which may both be rotated by the service engine  32 . For simplicity, the remainder of the discussion refers to the transfer of power via the stub shaft  180 , although similar systems may also make use of the drive shaft  178 . The stub shaft  180  may be coupled to the compressor drive shaft  182  via a drive belt  184 , a pulley  186 , and a compressor pulley  188 . Accordingly, the power from the service engine  32  may be received by the air compressor  38  as torque. In the illustrated embodiment, the clutch  164  is positioned between the service engine  32  and the air compressor  38  and may be configured to control the transfer of torque between the service engine  32  and the air compressor  38 . Configuring the clutch  164  to transfer the torque is generally referred to as engaging the clutch  164 . The power required to operate the air compressor  38  may increase the demand for power from the service engine  32 . Accordingly, engaging the clutch  164  increases the overall load on the service engine  32 , while disengaging the clutch  164  decreases the load of the air compressor  38  on the service engine  32 . However, as described above, in certain embodiments, the clutch  164  may not be used at all. Rather, in these embodiments, the service engine  32  may be directly driven and the valve  166  alone may be used to activate or deactivate the air compressor  38 . 
     The clutch  164  may include any device configured to regulate the amount of torque transferred between the service engine  32  and the air compressor  38 . For example, an embodiment includes an electric clutch that has two electromagnetic plates complementary to one another. In such an embodiment, the clutch  164  may enable or disable in response to a control signal. For example, if the clutch  164  receives a signal to engage, the electromagnetic plates may be energized to draw the two plates together and create friction. Energizing the plates may include a digital input configured to fully engage or disengage the clutch  164  or an analog input configured to provide proportional friction and, thus proportional transfer of torque. For example, a digital signal may cause the two plates to energize fully and provide full friction. An analog signal may enable the plates to partially energize and, thus, vary the amount of friction generated in the clutch  164 . In an embodiment, the clutch control signal  192  configured to operate the clutch  164  may be generated by the controller  124 . The clutch  164  may also include any other mechanisms configured to vary the amount of torque transferred between the service engine  32  and the air compressor  38 . 
     The location of the clutch  164  may be varied to accommodate any number of applications. As illustrated in  FIG. 6 , the clutch  164  is located in-line with the compressor drive shaft  182 . Similarly, the clutch  164  may be located in-line with the stub shaft  180  and may be configured to enable or disable the transfer of torque to the pulley  186  and, thus, the torque provided to the air compressor  38 . Further, an embodiment may include the clutch  164  built into a pulley. For example, the pulley  186  or the compressor pulley  188  may include a clutch pulley configured to transfer torque via engagement in response to a clutch control signal  192 . Further, the load control system  122  may include a belt tensioning mechanism configured to increase or decrease the tension of the drive belt  184  based on the clutch control signal  192 . Accordingly, the clutch control signal  192  may be configured to generate a response to tension the drive belt  184  (i.e., enable the clutch). 
     As described above, the controller  124  is configured to coordinate operation of the load control system  122 . More specifically, the controller  124  monitors any number of inputs (e.g., from the service engine  32 , the air compressor  38 , and so forth), and also outputs various commands to control the operating speed of the service engine  32  via the governor  174  and the power (i.e., torque) transferred to the air compressor  38  via the clutch  164 . As illustrated in  FIG. 6 , the controller  124  is electrically coupled to the governor  174 , the clutch  164 , and the valve  166 . The controller  124  may be configured to transmit various parameters to the governor  174 , including the speed control signal  190  indicative of a desired engine operating speed. For example, the speed control signal  190  may include a set level or value representative of the desired engine speed. In response to the speed control signal  190 , the governor  174  may regulate the speed of the service engine  32 , as described previously. 
     The controller  124  may also be electrically coupled to the clutch  164  and the valve  166  and may be configured to control engagement of the clutch  164  via the clutch control signal  192  and to control a valve position of the valve  166  via a valve control signal  194 . In an embodiment where the clutch  164  is configured to provide a digital clutch control signal  192 , the controller  124  may output the clutch control signal  192  above or below a threshold value to enable or disable the clutch  164 . For example, based on the determination to engage or disengage the clutch  164 , the controller  124  may output a digital high or digital low clutch control signal  192 . Similarly, in an embodiment of the clutch  164  that has the ability to incrementally vary the amount of torque transmitted, the controller  124  may output an analog signal proportional to the desired torque transfer. In such a configuration, the clutch control signal  192  may be configured to ramp up transferred torque to reduce the shock to the load control system  122  and the service engine  32  as the air compressor  38  begins to draw power from the load control system  122 . 
     Further, the controller  124  may receive and process various inputs. In an embodiment, inputs to the controller  124  may include any number of engine parameters and system parameters. For example, the controller  124  may receive signals indicative of actual engine speed, a signal relating to engine coolant temperature, engine oil temperature, system temperature, or other parameters related to assessing the performance of the service engine  32 . In particular, the controller  124  may receive signals indicative of loads on the air compressor  38  which, in certain embodiments, may be generated by pressure drops within the air reservoir  80 . However, in other embodiments, the signals may be indicative of air flow rates, air temperature, load and/or power of the air-driven device, and so forth. As such, the signals may be provided directly from the service engine  32 , the governor  174 , the clutch  164 , the air compressor  38 , the valve  166 , the air reservoir  80 , or any other components of the load control system  122 . 
     The load control system  122  may also incorporate user input via the user interface  176  in communication with the controller  124 . In certain embodiments, the user interface may be a part of either the control and service panel  52  or the remote control panel or device  54  of  FIG. 1 . However, the user interface  176  need not be limited to these two panel components. In an embodiment, the user interface  176  may include a switch or a plurality of switches configured to turn the air compressor  38  off and on. For example, the user interface  176  may include a mechanical or digital switch that the user turns on to start the air compressor  38 . Further, the user interface  176  may also include any number of inputs to increase the flexibility of the system. For example, the user interface  176  may enable an operator to enter parameters relevant to a control algorithm implemented by the controller  124 . 
       FIG. 7  is a flowchart illustrating an exemplary method  196  for controlling the operating speed of the service engine  32  based on sensed loads on the air compressor  38 . The method may begin at block  198 , which may include an operator turning on power to the service engine  32 . For example, the operator may flip a switch, such as on the user interface  176  of  FIG. 6 , to start the service engine  32 . In one embodiment, the clutch  164  may be disengaged at startup to ensure that the service engine  32  is started without the additional loading of the air compressor  38 . For instance, the controller  124  may maintain the clutch  164  in a disabled state until the controller  124  determines that the service engine  32  is properly configured to support the startup load of the air compressor  38 . Embodiments may also include starting the service engine  32  with the clutch  164  in the same state that it was in when the service engine  32  was previously shut down. 
     Once the air compressor  38  is turned on, the controller  124  may monitor the pressure in the air reservoir  80 . This may be done using a micro-processor with an analog-to-digital (ADC) converter coupled to a pressure sensor. As the pressure in the air reservoir  80  increases, the controller  124  may determine a pressure rating set point associated with the air compressor  38 . More specifically, the controller  124  may determine the maximum pressure and corresponding ADC value. Conversely, the minimum pressure setting is the pressure at which the operator wants the pressure to stay at or above. This may be set remotely by using the user interface  176 . Once the pressure in the air reservoir  80  has stabilized at the maximum pressure setting, the controller  124  may use this maximum pressure setting, along with any change in pressure, to determine loads on the air compressor  38  as well as appropriate responses. 
     A rate of change in air pressure in the air reservoir  80  may, in certain embodiments, be found by sampling the air pressure at a suitable time increment (e.g., every one second). This value may then be subtracted from the previous sample to find the change. Eventually, a pressure drop will be detected, as illustrated in block  200 . If, while at the maximum pressure setting, the change in pressure is less than a pre-determined amount (e.g., less than 0.1%), then the controller  124  may gradually allow the service engine  32  to return to its lowest operating speed. For instance, for illustration purposes, it may be assumed that the service engine  32  has four discrete operating speeds, e.g., 1800 rpm, 2600 rpm, 3200 rpm, and 3600 rpm. Therefore, if the change in pressure is less than the pre-determined amount, the speed of the service engine  32  may gradually be decreased to 1800 rpm. For example, if the original speed of the service engine  32  was 3600 rpm, the controller  124  would step down to 3200 rpm, then 2600 rpm, and finally 1800 rpm. This stepping down of operating speeds may, in certain embodiments, be completed within a few seconds. 
     For instance, at block  202 , the controller  124  may determine whether the change in pressure is below the pre-determined value. If the pressure drop is under the pre-determined value, the method  196  may continue to block  204 , where the operating speed of the service engine  32  is decreased. Once the operating speed of the service engine  32  has been decreased, the method  196  may continue to block  206 , where it is determined whether the service engine  32  is currently at its lowest operating speed (e.g., 1800 rpm). If the service engine  32  is not currently at its lowest operating speed, the method  196  may continue back to block  202 , where the controller  124  may again determine whether the change in pressure is below the pre-determined value. 
     If, at block  206 , it is determined that the service engine  32  is at its lowest operating speed, the method  196  may continue to block  208 , where the controller  124  may cause the valve  166  to be disengaged (e.g., closed). The disengagement of the valve  166  may cause the air compressor  38  to cease pushing air into the air reservoir  80  and, therefore, may lower the amount of horsepower (hp) needed from the service engine  32 . In certain embodiments, air from the air compressor  38  may also be vented to the atmosphere while sealing off the air reservoir  80 . After the valve  166  has been disengaged, the method  196  may continue to block  210 , where it is determined whether there has been any further pressure drop in the air reservoir  80 . For instance, if there is no additional load for five minutes, the clutch  164  may also be disengaged (block  212 ), further decreasing the load on the service engine  32 . This may allow for more power being available from the service engine  32  for other functions and, additionally, may decrease fuel usage. However, if there has been further pressure drop in the air reservoir  80 , the method  196  may continue to block  202 , where the controller may again determine whether the change in pressure is below the pre-determined value. Once the service engine  32  is at its lowest operating speed and the valve  166  and clutch  164  have been disengaged, the method  196  may continue to block  200 , where the controller  124  may resume monitoring for further pressure drops in the air reservoir  80 . 
     If, at block  202 , the controller  124  determines that the pressure drop in the air reservoir  80  is above the pre-determined value, the method  196  may continue to blocks  214  and  216 , where the valve  166  and/or clutch  164  may be engaged and the operating speed of the service engine  32  may gradually be increased. In certain embodiments, for changes in pressure within the air reservoir  80  greater than a certain amount (e.g., 1%, 2%, 3%, 4%, 5%, and so forth), a “high load flag” may be set, and the controller  124  may cause the speed of the service engine  32  to be increased. For a “high load flag,” the operating speed of the service engine  32  may increase to 3200 rpm and even 3600 rpm, if necessary. 
     If the change in pressure does not cause a “high load flag,” the controller  124  may compare the difference in pressure from the maximum pressure. If the pressure is below a first pressure level (e.g., 20-40% of the difference between the maximum and minimum pressure settings), the valve  166  may be opened and the air compressor  38  may begin pushing air into the air reservoir  80 . If the load continues to cause the pressure to drop and the pressure falls below a second pressure level (e.g., 40-60% of the difference between the maximum and minimum pressure settings), the operating speed of the service engine  32  may be increased such that the pressure is prevented from dropping further. If the load is so high that the pressure drops below the minimum pressure setting, the controller  124  may increase the operating speed of the service engine  32  to a maximum operating speed (e.g., 3600 rpm). In other embodiments, the operating speed of the service engine  32  may be continuously variable proportional to the pressure drop, as opposed to be increased at incremental steps. 
     Therefore, the controller  124  may ensure that, under certain operating conditions, the pressure drop in the air reservoir  80  does not have to reach the minimum pressure setting before the air compressor  38  begins pushing air into the air reservoir  80 . As such, the pressure in the air reservoir  80  may be maintained closer to the maximum pressure setting for greater periods of time while still ensuring that the service engine  32  runs at a relatively low operating speed. Under certain conditions, this may lead to a substantial increase (e.g., 20%, 25%, 30%, 35%, and so forth) in usable time for the air compressor  38 . In other words, periods of time where an operator of the air compressor  38  will be kept waiting while the service engine  32  powers back up to fill the air reservoir  80  with air may be substantially reduced. 
     Other embodiments of the load control system  122  described above may be utilized. For instance, instead of detecting loads on the air compressor  38  by monitoring pressure changes in the air reservoir  80 , in certain embodiments, a flow meter (e.g., a positive displacement flow meter) may be used to measure the flow rate of air from the air reservoir  80 . By measuring the flow of air from the air reservoir  80 , loads on the air compressor  38  may be estimated by the controller  124 . In addition, instead of using a service engine  32  with discrete operating speeds, a variable speed service engine  32  may be used. In fact, the ability to vary the speed of the service engine  32  across a broader range of operating points may lead to more precise control of the pressure within the air reservoir  80 . Also, in certain embodiments, the controller  124  may simply turn the air compressor  38  on when the pressure within the air reservoir  80  decreases to the minimum pressure setting and turn the air compressor  38  off when the pressure within the air reservoir  80  increases to the maximum pressure setting. In other embodiments, the operating speed of the service engine  32  may be adjusted based on other operating parameters indicative of the load on the air compressor  38 . For instance, the operating speed of the service engine  32  may be adjusted based on temperature of the compressed air, stress/strain on the air reservoir  80 , power and/or output of the equipment driven by the compressed air, an on/off state of the equipment driven by the compressed air, ratings/demand of the equipment driven by the compressed air, and so forth. 
     The disclosed embodiments provide several advantages. For example, the load control system  122  may reduce the overall noise generated by the service engine  32  and air compressor  38  by running the service engine  32  only as fast as needed to satisfy the load requirements on the air compressor  38 . In addition, the load control system  122  may increase the fuel economy of the service engine  32  since the lower operating speeds may generally lead to lower fuel consumption by the service engine  32 . Also, the load control system  122  may allow an operator to set the minimum and maximum pressure settings. This may help by increasing the output of the air compressor  38  before the tools used by the operator run out of air. For example, tools often have certain pressure ratings and, if the tool being used requires 130 pounds per square inch (psi) of pressure from the air reservoir  80  and the minimum pressure setting is 100 psi, the tool will operate at reduced efficiency when the pressure drops below 130 psi. The air compressor  38  will not turn back on until it reaches 100 psi, the minimum pressure setting. However, if the minimum pressure setting is changed to 130 psi, the next time the pressure drops from the maximum pressure to 130 psi, the air compressor  38  will turn on and keep the 130 psi of pressure supplied to the tool. This option allows the operator to set the air compressor  38  to whatever settings satisfy the operator&#39;s particular requirements. In other words, the air compressor  38  is user-adjustable to ratings of the equipment used and/or loads applied to the equipment, rather than just having a standard minimum pressure setting. In addition, another advantage is that the load control system  122  does not require an expensive flow meter, although one may be used. Rather, the load control system  122  utilizes pressure sensors and monitors changes in pressure over time. 
     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.