Abstract:
An engine control system for maintaining the operator-commanded speed setting of an internal combustion engine over a range of engine loads and for easy starting and improved efficiency over a range of ambient and engine operating temperatures. The engine control system includes a governor assembly driven by the engine, the governor assembly supplying an output to a sensor assembly through a mechanical coupling member operator. The sensor assembly provides an engine speed control signal which corresponds to operator commanded engine speed and actual engine speed. The engine speed control signal is provided to a throttle actuator to control actual engine speed is controlled to correspond with the operator-commanded engine speed regardless of loads imposed on the engine.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/416,859 filed Oct. 8, 2002 and claims the benefit of U.S. Provisional Application No. 60/448,263 filed Feb. 17, 2003. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to engine control for internal combustion engines and, more particularly, for small internal combustion engines of the type which are used in a variety of applications, such as walk-behind lawnmowers, lawn and garden implements, generators, or in small utility vehicles such as riding lawnmowers, lawn tractors, and the like. 
   2. Description of the Related Art 
   Small internal combustion engines generally include an operator-selected command speed setting, for example, a throttle control for utility vehicles or a normal/idle switch for generators. However, driving a variable load may reduce or increase the engine speed from the commanded setting. For example, in a lawnmower powered by an internal combustion engine, it is desired that the commanded speed of the engine remain relatively constant under a variety of loading conditions. Thus, it is desired that whether the lawnmower encounters tall grass or short grass, the engine speed which has been selected by the operator should remain constant. Likewise, in the case of a generator, it is desired that the alternator output frequency, i.e., the engine drive speed, remain constant despite changes in the electrical loads connected to the alternator output. 
   To regulate engine speed, small internal combustion engines generally include a mechanical speed-regulating governor, such as an air vane mechanism or a centrifugal flyweight mechanism sensitive to engine speed. For engines having a carburetor, the throttle valve is generally mechanically linked to both the governor and the operator throttle control. Therefore, the throttle valve is acted upon by a first force related to the commanded speed setting and a second force corresponding to the governor and related to the actual engine speed. 
   A disadvantage of known engine control systems for small internal combustion engines is the potential unreliability of cables, springs, and linkages that are used to transmit and combine the inputs from the operator-commanded engine speed and the actual engine speed. Such components might bind, require lubrication, or may fail from mechanical vibrations or loading. 
   Another disadvantage of known engine control systems for small internal combustion engines is the difficulty of mechanically adjusting the amount of movement of the throttle valve as it relates to the commanded engine speed setting or the actual engine speed and the difficulty of providing dampening of transients due to engine speed changes. 
   Yet another disadvantage of known speed control mechanisms for small internal combustion engines is that ambient temperature and engine operating conditions are not taken into account to adjust the fuel-to-air ratio for easy starting and optimum efficiency for a range of ambient engine conditions. 
   What is needed is an engine control system for internal combustion engines that reliably accounts for the commanded engine speed setting and the actual engine speed to drive the throttle and fuel controls, and that accounts for the ambient and engine operating temperatures to provide an efficient fuel-to-air ratio. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to an engine control system for an internal combustion engine. The engine control system may include a governor assembly, engine speed sensor, control circuit, and fuel system. The governor assembly and sensor are coupled by a coupling member. The coupling member is displaced relative to the governor assembly according to the engine speed. The sensor detects the displacement of the coupling member and outputs an electrical speed signal related to the actual engine speed. 
   A first and second exemplary engine control system includes a control circuit that provides a speed command signal to control the intake system of the engine, including air flow, fuel flow, and/or air-to-fuel ratio, to correlate the actual engine speed to the operator-commanded speed setting. The speed command signal is a function of both commanded speed and the actual engine speed, which may be detected by the governor assembly and sensor. 
   A third exemplary engine control system includes a control circuit and may also include a combination of an exhaust temperature sensor cylinder head temperature, an intake temperature sensor, and/or mass air flow for detecting ambient and engine operating conditions. The output of the sensors is used to control one or both of a throttle signal and a fuel flow signal for adjusting the fuel-to-air ratio for a more efficient engine start and efficiency over a range of operating conditions. 
   The control systems may also include elements of a fuel system. For a first exemplary fuel system, a fuel signal is supplied to control the speed of a fuel pump motor, thereby controlling the fuel flow through a fuel injector. A second exemplary fuel system provides the fuel flow signal to a solenoid which controls the fuel flow through a regulator valve, thereby controlling the fuel flow through the fuel injector. 
   Small internal combustion engines used in a variety of applications generally include an operator-controlled commanded speed setting. However, as the engine drives a variable load, the engine may slow from the commanded speed when the load is increased, or overshoot the commanded speed when the load is decreased. The invention provides an engine control system that provides constant engine speed under varying loads by determining engine control inputs from both the operator-commanded speed and the actual engine speed. 
   Advantageously, the present engine control system for internal combustion engines provides operator setting, detection, and adjustment of engine speeds using electrical components and electrical signals in the place of certain mechanical components which had typically been used in known systems. The electrical and other components of the present engine control system reliably transmit engine control signals and provide for simple adjustment of engine control and dampening of the response of the engine control system to changes in the engine speed. 
   Additionally, the second exemplary speed control system may provide a combination of intake air temperature sensing, intake mass airflow sensing, exhaust gas temperature sensing, and cylinder head temperature sensing to adjust the fuel flow for optimal cold start, hot start, and performance over a range of operating temperatures and other conditions. 
   In one form thereof, the present invention provides an engine control system for an internal combustion engine, including a governor assembly mounted to and driven by the engine and responsive to engine speed; a coupling member associated with the governor assembly, the coupling member displaceable by the governor assembly according to engine speed; and a position sensor controlled by the coupling member, the position sensor detecting the displacement of the coupling member and outputting an electrical speed signal corresponding to the displacement and to engine speed. 
   In another form thereof, the present invention provides an internal combustion engine, including an engine housing; an engine control device connected to the housing; a governor assembly connected to the housing and responsive to engine speed; a coupling member coupled with the governor assembly and movably displaced by the governor assembly in response to engine speed; and a position sensor mounted to the housing and detecting the position of the coupling member, the position sensor outputting an electrical speed signal, the speed signal acting upon the engine control device to adjust the engine speed. 
   In a further form thereof, the present invention provides an engine control system for an internal combustion engine, including a governor assembly driven by the engine, the governor assembly having a spool capable of translating axially in response to the engine speed; a rotary shaft associated with the spool such that the rotary shaft is rotationally displaced upon translation of the spool; a spring coupled between the engine and the rotary shaft, the spring resisting rotational displacement of the rotary shaft; and a rotary position sensor capable of detecting the rotational position of the rotary shaft and outputting an electrical speed signal corresponding to the position. 
   In another form thereof, the present invention provides a method of controlling the speed of an internal combustion engine having a mechanical governor and at least one of an intake throttle and a fuel injector, including the steps of driving the governor to produce an output proportional to engine speed; sensing the governor output; determining an actual engine speed from the governor output; supplying a commanded engine speed signal; and controlling at least one of the intake throttle and fuel injector based on the actual engine speed signal and the commanded engine speed signal. 
   In yet a further form thereof, the present invention provides an engine control system for a small internal combustion engine, the system including at least one of a voltage supply and a current supply, a governor sensor having an input and an output, the governor input coupled to the at least one of a voltage supply and current supply, an operator control sensor having an input and an output, the operator control sensor input coupled to the governor sensor output, and at least one of an intake throttle actuator and a fuel flow controller coupled to the operator control sensor output. 
   In a further form, the present invention provides an engine control system for a small internal combustion engine, the system including at least one of a voltage supply and a current supply; an operator control sensor having an input and an output, the operator control sensor input coupled with the at least one of a voltage supply and a current supply; a governor sensor having an input and an output, the governor sensor input coupled to the operator control sensor output; and at least one of an intake throttle actuator and a fuel flow controller coupled to the governor sensor output. 
   In yet another form, the present invention provides an engine control system for a small internal combustion engine, the system including an operator control sensor providing a command signal; an engine speed sensor providing a speed signal; a control circuit receiving the command signal and the speed signal and providing a fuel control signal; and a fuel flow device having an actuator adapted for adjusting the fuel flow through the fuel flow device, the actuator receiving the fuel control signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1A  is a cutaway perspective view of a small internal combustion engine having an engine speed sensor in accordance with the present invention; 
       FIG. 1B  is a top view of the small internal combustion engine shown in  FIG. 1A ; 
       FIG. 2  is a sectional view of a portion of the engine speed sensor of  FIG. 1A , taken along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  is a schematic diagram of a portion of a first exemplary engine control system, according to the present invention; 
       FIG. 4  is a graph illustrating the magnitude of the engine command signal in relation to adjustment of the operator control of the engine control system of  FIG. 3 ; 
       FIG. 5  is a graph illustrating the magnitude of the speed signal in relation to the engine speed sensed by the speed sensor of the engine control system of  FIG. 3 ; 
       FIG. 6A  is a block diagram schematically illustrating the first exemplary engine control system, a portion of which is shown in  FIG. 3 ; 
       FIG. 6B  is a block diagram schematically illustrating a second exemplary engine control system according to the present invention; 
       FIG. 7  is a block diagram schematically illustrating a third exemplary engine control system according to the present invention; 
       FIGS. 8A through 8E  are graphs illustrating the relationship between various components and signals of the third exemplary engine control system shown in  FIG. 7 ; 
       FIG. 9  is a schematic diagram of the third exemplary engine control system of  FIG. 7 ; 
       FIG. 10  is a sectional view of the throttle portion of the engine control system taken along lines  10 — 10  of  FIG. 1A ; 
       FIG. 11  is a schematic diagram of an exemplary fuel controller of the engine control system; 
       FIG. 12  is a first exemplary fuel system of the engine control system; and 
       FIG. 13  is a second exemplary fuel system of the engine control system. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION 
   Referring to  FIG. 1A , small internal combustion engine  20  is shown, including engine housing  22  with crankcase  24 , crankshaft  26  located internal to and supported by housing  22 , and flywheel  28  mounted to an end of crankshaft  26  extending outside of housing  22 . Crankshaft  26  is coupled to a piston (not shown) via a connecting rod (not shown), and further drives a valve train for actuating intake and exhaust valves within engine housing  22 . The drive train of engine  20  may be of the overhead valve (OHV), overhead cam (OHC) L-head/side valve type, or another drive train type known in the art. Crankshaft gear  30 , or another suitable drive mechanism, is mounted on crankshaft  26  for driving governor gear  32  of flyweight governor assembly  34 . Flyweight governor assembly  34  may be located inside crankcase  24 , and may be supported by housing  22 . Referring to  FIG. 1B , cylinder head  36  is supported by housing  22  and is connected to intake  38  and exhaust  40 . 
   Referring again to  FIG. 1A , engine speed sensor  42  may be supported by engine housing  22 , and generally includes flyweight governor assembly  34  and sensor assembly  44 . Engine speed sensor  42  may be coupled to operator throttle control  46  and provide speed control signal  48 , as shown in the schematic diagram of a portion of first exemplary engine control system  50  in FIG.  3 . 
   Referring to  FIG. 2 , flyweight governor assembly  34  is rotatably supported on housing  22  by governor support  52 , which may be a stub shaft, for example, and includes governor gear  32 , flyweights  54 , spool  56 , and spindle  58 . Governor gear  32  is engaged by crankshaft gear  30  ( FIG. 1A ) such that flyweight governor  34  rotates proportionally to the speed of crankshaft  24  when engine  20  is running. Weights  54  are pivotably mounted to governor gear  32 . Spool  56  is slidably mounted on spindle  58  and is supported by lever portions  60  of weights  54  such that spool  56  is moveable axially on spindle  58 . When governor gear  32  is driven by crankshaft gear  30  above a predetermined speed, weights  54  swing outwardly under centrifugal force, rotating weight levers  60  and pushing spool  56  axially away from governor gear  32 . As the engine speed slows, weights  54  return inwardly, allowing spool  56  to axially translate toward governor gear  32 . 
   Sensor assembly  44  generally includes rotary shaft  62 , coil spring  64 , spring housing  66 , and rotary sensor  68 . Rotary shaft  62  transmits the engine speed from flyweight governor  34  to sensor  68 , and includes first end  70  having radially extending rotary lever  72 , and second end  74  which extends through engine housing  22  to rotary sensor  68 . Rotary shaft  62  is rotationally supported by bushing  76  within housing  22 . Lever  72  is positioned in contact with spool  56  so that axial translation of spool  56  displaces lever  72  to rotate rotary shaft  62 . Thus, as governor assembly  34  is driven above a predetermined speed, rotary shaft  62  and sensor  68  are rotated proportionally to the speed of engine  20 . 
   Coil spring  64  is coupled between rotary shaft  62  and engine housing  22  and provides resistance to rotation of rotary shaft  62 . Thus, as the engine speed slows and weights  54  of flyweight governor  34  pivot inwardly, allowing spool  56  to translate toward governor gear  32 , coil spring  64  rotates rotary shaft  62  such that rotary lever  72  remains in operational contact with spool  56 , thereby returning rotary shaft  62  to its undisplaced, low speed rotational position. 
   Although located external to engine housing  22  in the exemplary embodiment, coil spring  64 , spring housing  66 , and/or sensor  68  may alternatively be positioned within the interior of engine housing  22 , and flyweight governor assembly  44  may be alternatively positioned exteriorly of engine housing  22 . Additionally, although the exemplary embodiment includes rotary shaft  62  which is rotationally displaced by flyweight governor  34 , other means of sensing engine speed and providing an input to sensor  68  may be used, for example, flyweight governor  20  may actuate a linear member, the position of which is sensed by a position sensor. 
   Referring to  FIGS. 1A and 2 , coil spring  64  includes interior end  78  coupled to rotary shaft  62  and exterior end  80  coupled to spring housing  66 . Spring housing  66  defines bore  82  for passage of rotary shaft  62  therethrough, and recess  84  for receiving coil spring  64  between coil spring housing  66  and engine housing  22 . Spring housing  66  is mounted to engine housing  22  by fasteners  86  which pass through spring housing slots  88 . As shown in  FIG. 1 , spring housing slots  88  are arcuately shaped. 
   For adjustment of the rotational tension applied on rotary shaft  62  by coil spring  64 , spring housing  66  may be coarsely rotationally adjusted by aligning selected slots  88  with selected mounting holes  90  defined in engine housing  22 , and then inserting fasteners  86  through slots  88  into mounting holes  90 . The tension of coil spring  64  may then be finely adjusted by further rotating spring housing  66  with fasteners  86  extending through arcuate slots  88 , followed by tightening fasteners  86  to secure spring housing  66  relative to engine housing  22 . Similarly, the tension of coil spring  64  may be adjusted after initial assembly of sensor assembly  44  by loosening fasteners  86 , rotating spring housing  66  to a selected position, and re-tightening fasteners  86 . 
   In the embodiment shown in  FIGS. 1A and 2 , rotary sensor  68  is a potentiometer. Rotary sensor  68  includes a cup-shaped sensor housing  92  having pocket  94  and mounting flange  98  extending around the periphery of sensor housing  92 . Pocket  94  receives potentiometer disk  96  having arcuate resistor contact area  100  for producing actual speed signal  48  (FIG.  3 ). 
   Mechanical calibration adjustment of speed signal  48  may be provided by rotating sensor housing  92  relative to engine housing  22 . Specifically, as shown in  FIG. 1A , flange  96  of sensor housing  92  includes arcuate slots  102  which allow fine rotational adjustment of sensor housing  92  with respect to spring housing  66 . After such adjustment, fasteners  104  are tightened to fix the position of sensor housing  92  with respect to spring housing  66  and therefore, in turn, to fix the position of sensor housing  92  with respect to engine housing  22 . 
   Cable  106  supplies an electric signal or voltage to one end of resistor  100  and a ground connection to another end of resistor  100 . In the exemplary embodiment, the supplied signal is command signal  108  provided by operator control  46 , as shown in FIG.  3 . Wiper  110  is mounted on rotary shaft  62  at second end  74  thereof. Wiper  110  contacts resistor  100  and rotates relative to potentiometer disk  96  as rotary shaft  62  is rotated. Thus, resistor  100  and wiper  110  act as a variable voltage divider, with wiper  110  providing speed control signal  48  as a variable potential having a value between operator command signal  108  and ground, which varies according to the displacement of rotary shaft  62  and thus according to the speed of engine  20 . Rotary sensor  68  receives second end  74  of rotary shaft  62  and detects the rotational displacement of rotary shaft  62 . Based on the rotational displacement of rotary shaft  62 , rotary sensor  68  outputs engine control signal  48  ( FIG. 3 ) via cable  106 . 
   Referring to  FIG. 3 , a partial schematic diagram for an exemplary control circuit for first exemplary engine control system  50  includes operator control  46  and rotary sensor  68 . Both operator control  46  and rotary sensor  68  are implemented as potentiometers operating as linear voltage dividers. To provide engine speed command signal  108 , operator control  46  is supplied with a voltage, such as a positive battery supply. Command signal  108  varies from a lower voltage for an idle or slow engine speed setting to a higher voltage for full throttle or a high speed engine setting, as shown graphically in FIG.  4 . 
   Speed command signal  108  is provided to potentiometer  98  of rotary sensor  68 . Rotary sensor  68  is driven by mechanical governor  34  such that speed control signal  48  output at wiper  110  is proportionally equal to or relatively close to command signal  108  for a low speed or under speed condition, and proportionally less than command signal  108  for a high or over speed engine condition, as shown graphically in FIG.  5 . This arrangement provides for control of the engine speed under variable engine load conditions as the engine speed may tend to decrease or increase from the commanded speed with changing engine loading. Although command signal  108  is provided for controlling engine speed, modification of command signal  108  is modified by rotary sensor  68  to produce speed control signal  48 ; therefore, control signal  48  is a function of both commanded and actual engine speed. Alternatively, the output of rotary sensor  48  may supply operator control  46  and the output of operator control  46  providing control signal  48 , also a function of both commanded and actual engine speed. 
   Referring to  FIG. 6A , in first exemplary engine control system  50 , speed control signal  48  is provided by voltage dividing command signal  108  according to the actual engine speed sensed by sensor  68 . More particularly, engine crankshaft  26  drives flyweight governor  34  in accordance with the engine speed, as described above. Rotary governor shaft  62  couples flyweight governor  34  to sensor  68 , and tension spring  64  is coupled with rotary shaft  62  so that displacement of rotary shaft  62  is normally biased to a lower resistance for sensor  68  for a lower engine speed, therefore minimizing the voltage adjustment to command signal  108  (FIG.  5 ). Sensor  68  detects the displacement of rotary shaft  62  and reduces command signal  108  as the engine speed increases, thereby providing speed control signal  48 . Although sensor  68  in the exemplary embodiment is a potentiometer ( FIG. 3 ) or other linear voltage device supplied by a command signal  108  and ground, other sensor devices, such as, for example, a rotary encoder or a linear variable resistor, may also be used in a similar or related control scheme. 
   As shown in  FIG. 6A , control signal  48  may be provided directly to throttle actuator  112  for controlling throttle  114  (FIGS.  1 A and  6 A). Throttle  114  may control both the fuel and air supplied to engine  20 , and therefore the engine speed. Throttle actuator  112  moves throttle  114  by using a solenoid, transducer, or other electromechanical device, as shown in FIG.  10 . 
   Engine control system  50  may also control an engine having fuel injector  116 . Referring still to  FIG. 6A , control signal  48  may be provided to fuel control device  118 , which controls fuel flow to injector  116 , in the same manner in which control signal  48  is provided to throttle actuator  112  as described above. 
   Second exemplary engine control system  120 , shown in  FIG. 6B , may include the same elements as first exemplary engine control system  50  shown in FIG.  6 A. However, speed sensor  68  and operator control  46  are differently arranged in second exemplary engine control system  120 . Specifically, speed sensor  68  receives a fixed voltage supply, for example, from a battery, and produces measured speed signal  122 . Measured speed signal  122  is supplied to operator control  46 . Operator control  46  provides speed control signal  48  to throttle actuator  112  and/or fuel control device  118 . 
   Third exemplary engine control system  130 , shown in  FIG. 7 , may alternatively provide speed control signal  48  and command speed signal  108  separately to an engine control module (ECM)  124 . ECM  124  may sum, compare, filter, or otherwise operate on the signals to provide throttle signal  126  to throttle actuator  112  and fuel control signal  128  to fuel control device  118 . 
   Advantageously, flyweight governor  34  and sensor  68  of engine control systems  50 ,  120 ,  130  provide control signal  48  which may be related to actual and commanded engine speed, which may be used to control the intake system of an engine, and which may be easily electrically or electronically filtered, buffered, amplified, limited, or attenuated to better control the magnitude and oscillation of transient speed adjustments generally associated with known engine control systems which only include mechanical components. It is also advantageous in many applications related to small internal combustion engines to provide electrically transmitted signals, rather than signals transmitted by cables or other mechanical conduits. 
   Other linear operations adjusting the actual engine speed to the commanded engine speed, including increasing or decreasing the engine speed, filtering engine speed transients, and other control operations known in the art, may also be incorporated into engine control system  50 ,  120 , and  130 . For example, the outputs of operator control  46  and governor sensor  68  to adjust throttle signal  126  and fuel control signal  128 , based on a fixed proportion determined by discrete analog circuit elements, or based on a stored schedule or function. 
   Third exemplary engine control system  130  may also include other sensors in order to provide for easy starting and optimum efficiency over a range of ambient and engine operating temperatures and conditions. Throttle control signal  126  is provided by adjusting the output of operator control  46  according to the actual engine speed sensed by governor sensor  68 . Engine crankshaft  26  drives flyweight governor  34  in accordance with the engine speed, as described above for the first exemplary embodiment. Rotary governor shaft  62  couples flyweight governor  34  to sensor  68 , and tension spring  64  is coupled with rotary shaft  62  so that displacement of rotary shaft  62  is normally biased to provide a higher signal output TO 1  from sensor  68  for a lower engine speed, as shown in FIG.  8 A. 
   Operator control  46  provides an operator-commanded speed signal having a higher signal output TO 2  from operator control  46  for a higher commanded speed, as shown in FIG.  8 B. Throttle signal  126  is determined by ECM  124  as a function of TO 1  and TO 2 . Zero calibration  132  ( FIG. 7 ) is provided for adjusting the minimum voltage or current of throttle control signal  126  and/or fuel control signal  128  at the lowest operator command speed setting. Output calibration  134  is provided for adjusting the voltage or current span of throttle control signal  126  and/or fuel control signal  128 . 
   As shown in  FIG. 7 , governor sensor  68 , operator control  46 , output calibration  134 , and zero calibration  132  may all be used to determine throttle control signal  126  for controlling throttle actuator  112 , which in turn mechanically drives throttle  114 , and to determine fuel control signal  128  for controlling fuel control device  118 , which in turn determines the fuel flow through fuel injector  116 . For example, if governor sensor  68  senses an over-speed condition, throttle control signal  126  will be reduced by governor sensor  126  proportional to the over-speed, thus reducing throttle control signal  126  and adjusting throttle  114  to slow the engine speed. Such an over-speed condition may be more likely when the operator-commanded speed is high and the engine is exposed to a low or reduced load. In the case of a heavily loaded engine  20 , it is likely that the engine speed will be limited by the load and that governor sensor  68  will not act to reduce throttle control signal  126  to close throttle  114 . 
   Third exemplary engine control system  130  also provides engine control in response to ambient and engine operating conditions. Specifically, exhaust temperature sensor  136 , shown mounted in exhaust passage  40 , which is coupled to muffler  138  in  FIG. 1B , senses the engine gas exhaust temperatures flowing from engine  20 . Intake temperature sensor  140 , shown mounted in intake passage  38  in  FIG. 1B , provides sensing of ambient air drawn into engine  20  and also of engine cylinder head  36  operating temperature. Thus, as shown in  FIG. 7 , exhaust gas temperature sensed by sensor  136  and intake and cylinder head temperature sensed by intake sensor  140  may be used to determine fuel control signal  128  for controlling fuel control device  118 . Output calibration  134  or a separate output calibration for fuel control may also provide voltage and current scaling to set the maximum fuel control signal  128 . Similarly, zero calibration  132  or a separate zero calibration device may provide the minimum setting for fuel control signal  128 . 
   Additional sensors used to determine throttle control signal  126  and/or fuel control signal  128  may also be included and coupled to ECM  124 , for example, mass air sensor  144  and cylinder head temperature sensor  142 . 
   In the case of starting a cold engine in cold conditions, it is desirable to provide a rich fuel-to-air mixture, and thus a higher fuel control signal  128  for increased fuel flow. Therefore, as shown in  FIG. 8C , at a low intake temperature a high signal IO 1 , is provided for fuel control signal  128 . 
   As exhaust gas temperatures are directly related to a rich or lean mixture, as shown in  FIG. 8D , as the exhaust temperature increases signal IO 2  is provided to increase fuel control signal  128 , thus enriching the mixture and reducing the engine operating temperature for cooler engine operation. Fuel control signal  128  may be a function of signals IO 1  and IO 2 . 
   Depending on the implementing circuit configuration, the output of intake temperature sensor  140  may inversely relate to intake temperature, and the output of exhaust temperature sensor  136  may proportionally relate to exhaust temperature, as shown in  FIGS. 8C and 8D . 
   In order to limit the leaning effect that exhaust temperature sensor  136  would have during a cold-start operating condition, exhaust temperature sensor  136  may be disabled under cold-start conditions, such as by intake temperature sensor  140  sensing a temperature below a preset level. 
   Intake mass airflow sensor  144  may be implemented, for example, as shown in FIG.  10 . Throttle  114  includes intake opening  146 , narrowing venturi  148 , and intake pipe connection  150 . As throttle actuator  112  adjusts throttle plate  152 , thereby restricting the airflow through throttle  114 , the pressure differential generated at narrowing venturi  148  varies proportionally with the mass airflow into engine  20 . Throttle actuator  112  may be biased by an internal spring to a position that closes throttle plate  152 , thereby restricting airflow into the cylinder of engine  20 . Venturi tube  154  conducts vacuum to cylinder  156 , in which piston  158  translates against spring  160  in accordance with a differential between ambient air pressure  162  and the lower pressure present in venturi tube  89 . As piston  158  translates, connecting member  164  actuates intake mass airflow sensor  144  and fuel pump cutoff switch  166 , which supplies power to fuel pump  168  (FIG.  9 ). 
   Intake mass airflow sensor  144  may be a variable resistor, such as a potentiometer, that is mechanically driven by connecting member  164 . Alternatively, intake mass airflow sensor  144  may be another sensor type capable of measuring pressure or the displacement of connecting member  164 . Thus, intake mass airflow sensor  144  provides a variable voltage or current signal proportional to the mass airflow through throttle  114 . Additionally, fuel pump cutoff switch  166  provides a safety shutoff for fuel pump  168  when insufficient airflow is present through throttle  114 , i.e., engine  20  is not running or drawing air through throttle  114 . 
   Referring to  FIG. 8E , as the intake mass airflow increases, requiring additional fuel to maintain an optimum fuel-to-air mixtures, signal  102  increases, thus increasing fuel control output signal  128  to fuel injector  282 . 
   Referring to  FIG. 9 , an exemplary circuit implementing third exemplary engine control system  130  is shown. Engine control system  130  may also be implemented by other circuit configurations, including analog, digital, and microprocessor based circuits. Power to engine control system  130  may be provided by a 12 volt D.C. power source, such as battery B 1 . Output calibration  134  may be provided by variable resistor R 1  that operates with voltage dividing resistor R 2  to adjust the voltage supplied to sensor bridge network  170 . Output voltage calibration  134  is provided to adjust the maximum voltage output to throttle actuator  112  and fuel control device  118  at the highest operator command speed setting. Variable resistor R 2  is coupled between the output of variable resistor R 1  and ground and, along with fixed resistor R 3 , provides zero adjust circuit  132  for adjusting the minimum voltage provided to throttle actuator  112  and fuel control device  118  at a minimum operator control speed setting. 
   The output signal of variable resistor R 1  is provided to variable resistor R 4 , which is coupled in series with variable resistor R 5  and throttle actuator  112 . Rotary governor sensor  68  comprises variable resistor R 4  and, as shown in  FIG. 8A , has an increased resistance with increased governor speed, therefore reducing throttle control signal TO 1 , provided to variable resistor R 5 . Operator control sensor  46  comprises variable resistor R 5  and, as shown in  FIG. 8B , has a lower resistance value at increased operator-commanded speeds, thereby providing an increased throttle control output signal TO 2  at higher-commanded speeds. 
   Exhaust temperature sensor  136  comprises thermistor R 6 , or a similar temperature-sensing device, such as a resistance temperature detector (RTD). Intake mass airflow sensor  144  comprises variable resistor R 8 . Third exemplary engine control system  130  includes only one of exhaust temperature sensor  136  and intake mass airflow sensor  144 . Intake temperature sensor  140  comprises thermistor R 7 , or a similar temperature-sensing device such as an RTD. 
   Either exhaust temperature sensing device  136  or intake mass airflow sensor  144  and intake temperature sensor  140  are coupled in series between variable resistor R 1  and battery B 1  ground. Fuel control device  118  is coupled to the node between the two sensors. The signal reference IO ref  for fuel control device  118  may be coupled to resistor R 3  of zero adjust circuit  132 , or to another node in engine control system  130 , for example, battery B 1  ground. 
   As shown in  FIG. 8C , as intake temperature increases, the resistance value of thermistor R 7  decreases, thus reducing signal IO 1  and fuel control signal  128  as intake temperature increases. As shown in  FIG. 8D , the resistance value of thermistor R 6  decreases as exhaust temperature increases, thus increasing signal IO 2  and fuel control signal  128  as exhaust temperature increases. Alternatively, if engine control system  130  includes variable resistor R 8  of intake mass airflow sensor  144 , as the intake mass airflow increases, the resistance of variable resistor R 8  decreases, thus increasing signal IO 2  and fuel control signal  128  as intake mass airflow increases. 
   Referring to  FIG. 11 , exemplary fuel controller voltage to current amplifier  172  is shown. Amplifier  172 , or another such exemplary power amplifying circuit known in the art provides linear driving of DC motors, solenoids, and the like. For third exemplary embodiment control system  130 , amplifiers  172  may be used for linear driving of throttle actuator  112  and fuel control device  118 . Specifically, throttle control signal  112  and fuel control signal  128  may be provided at the resistor R 9  input to each of two amplifiers  172 . The arrangement of circuit elements in amplifier  172 , exemplary values of which are listed in Table 1, provide linear voltage to current transfer to drive throttle actuator  112  or fuel control device  118 . Specifically, resistor R 12  senses the current output of amplifier  172  so that the output current is linear to the input voltage at resistor R 9 . 
     FIG. 12  shows first exemplary fuel system  174  which provides fuel flow control and may be included with any of engine control systems  50 ,  120 , and  130 . Fuel system  174  includes fuel pump  176  for pumping fuel from fuel tank  178  through fuel injector  116  and into intake port opening  146  of engine  20 . Fuel pump  176  draws fuel from fuel tank  178  through vapor separator tank  180 . Vapor separator tank  180  provides a trap to remove fuel vapors that may be generated in fuel system  174  under elevated operating temperatures. Return fuel line  182  includes restricting orifice  184  and provides a fuel flow path between the junction of the output of pump  176  and fuel injector  116  and the junction of fuel tank  178  and vapor separator  180 . Check valve  186  is coupled between the output of pump  176  and fuel injector  116 . When pump  176  is stopped, check valve  186  prevents fuel from entering intake port  146  and prevents air from intake port  176  from entering fuel system  174 . 
   The fuel pressure, and therefore the fuel flow, at fuel injector  116  is controlled by a combination of the flow restriction provided by restricting orifice  182  and the fuel pressure created by fuel pump  176 . To control the resulting fuel flow through fuel injector  116 , fuel pump  176  is driven by variable speed motor  118   a , which serves as the fuel control device discussed above. Thus, variable speed motor  118   a  may be driven by fuel control signal  128  in order to provide a desired fuel flow to engine  20 . By adjusting the range of fuel control signal  128 , for example, by adjusting output calibration  134  and zero calibration  132  in third exemplary engine control system  130 , the fuel pressure can be controlled between 0 psi and a value approaching the deadhead pressure of pump  176 . 
     FIG. 13  shows second exemplary fuel system  188  which controls fuel flow through fuel injector  116  into intake port  146  of engine  20  and may be used with any of exemplary engine control systems  50 ,  120 , and  130 . Fuel system  188  includes fuel pump  176  which is driven by single speed electric motor  190  and pumps fuel from fuel tank  178  through fuel injector  116 . Similar to first exemplary fuel system  174 , second exemplary fuel system  188  also includes fuel separator  180  between fuel tank  178  and pump  176  and check valve  186  prevents return of fuel through return fuel line  182  and fuel injector  116  when fuel pump  176  is stopped. 
   The fuel pressure for second exemplary fuel system  188  and therefore the fuel flow through fuel injector  116  is determined by the constant speed of and therefore fuel flow through fuel pump  176  and the variable fuel flow through return line  182 , which is controlled by fuel bypass regulator  192 . To achieve a constant fuel flow at pump  176 , motor  190  is driven by a fixed power source, such as battery B 1 . To control the return line  182  flow and therefore the fuel flow through fuel injector  116 , fuel bypass regulator  192  is actuated by solenoid  118   b . Solenoid  118   b  may be driven by fuel control signal  128 . Solenoid  118   b  and fuel bypass regulator  192  provide the fuel control device discussed above and provide linear fuel flow control of fuel system  188 . 
   Fuel bypass regulator  192 , which may be, for example, a device such as the one disclosed by U.S. patent application Ser. No. 10/641,556, entitled “Bypass Pressure Regulator,” by Rado, filed Aug. 15, 2003, the assignee of which is the assignee of the present application, the disclosure of which is hereby incorporated herein. While the referenced disclosed bypass regulator includes a valve and spring to provide fuel flow when the fuel pressure exceeds a certain preset level, fuel bypass regulator  192  provides a variable fuel flow and therefore a variable fuel pressure by adding linear solenoid  118   b  which adjusts the pressure that spring  194  applies to valve shuttle  196  of regulator  192 . The inventive arrangement of fuel bypass regulator  192  and solenoid  118   b  allows fuel control signal  128  to regulate the fuel flow through fuel return line  182 , thereby providing for linear control of fuel flow through fuel injector  116 . 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Component Label 
               Value 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               R9 
               4900 
             
             
                 
               R10 
               100 
             
             
                 
               R11 
               500 
             
             
                 
               R12 
               0.1 
             
             
                 
               U1 
               LF358NS 
             
             
                 
               Q1 
               BD135/PLP 
             
             
                 
                 
             
           
        
       
     
   
   While this invention has been described as having exemplary embodiments, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.