CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon provisional U.S. application Serial No. 60/062,616, filed Oct. 22, 1997, upon which priority is claimed. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a fuel delivery system for two-cycle and four-cycle internal combustion engines, and more particularly, for a feedback fuel regulator for use on model aircraft, comprising a microprocessor, an in-line fuel valve, and one or more engine operating condition sensors including an exhaust gas temperature sensor, to regulate the optimum fuel mixture. While the invention is described in detail with respect to its application in model aircraft engines, those skilled in the art will recognized the wider applications of the inventive principles disclosed hereafter. 
     A typical model airplane engine  10  (FIGS. 1A-1C) is a single cylinder engine having a very simple carburetor  12  including a fixed bore single air intake venturi and a non-variable fuel jet orifice at a constant throttle valve position, without a fuel bowl for air and fuel intake. The typical engine  10  additionally includes a very simple single-chamber expansion type of muffler  14  connected to the engine exhaust port  16  for handling and muffling exhaust gasses. The air flow through the air intake venturi produces in the venturi throat a partial vacuum which draws fuel into the intake airstream from the engine fuel tank, through the fuel jet. Fuel pressure conventionally is also supplied from the exhaust back pressure, commonly connected to the fuel tank. The carburetor has a throttle valve  18  which is adjustable to regulate air and fuel flow to the engine, and thereby regulate the speed of the engine  10 . It is well known in the art that the venturi partial vacuum is rather weak, and results in extremely unreliable engine operation due to variations in aircraft attitude in flight causing variations in fuel head pressure and also due to extremely high centrifugal forces imposed on the aircraft during aerobatics maneuvers, routinely exceeding ten times the gravitational force. 
     Accordingly, conventional fuel systems fail to produce optimum fuel regulation for maximum power and fuel efficiency. It is known in the art that a doubling in the rate of air intake into a fixed bore single air intake venturi will cause a four-fold increase in venturi partial vacuum fuel draw. This means that at a constant degree of throttle opening in a model aircraft engine, as the engine increases in revolution per minute (rpm) during acceleration, a disproportionately higher amount of fuel than air will be drawn in to the carburetor, causing a rich mixture and inefficient operation. A rich mixture decreases the available torque and limits the engine&#39;s power potential as it gains speed. The most efficient way to extract power from a model aircraft engine is to have the engine run at full throttle, turning a large size propeller  20  of low to medium pitch, at the rpm of maximum torque while standing still (static rpm) to achieve good acceleration to in-flight speeds. The in-flight rpm should correspondingly increase to approach the maximum power peak. However, as the engine unloads in-flight, its fuel-air mixture becomes richer than necessary for producing peak power, hence torque and power decrease despite an increase in engine rpm. 
     Ideally, to compensate for the increased fuel draw during unloaded in-flight operation, a needle valve  22  in the carburetor  12  is adjusted to decrease the needle-valve opening, and correspondingly the fuel flow, for peak power output every time the engine rpm is allowed to increase by reducing the engine load. However, the carburetor needle valve  22  is normally not manually adjustable in a model aircraft while in flight, and must be set at a fixed setting resulting in less than perfect engine operation prior to each flight. 
     BRIEF SUMMARY OF THE INVENTION 
     Among the several objects and advantages of the present invention are: 
     The provision of a new and improved fuel regulator to optimize the fuel mixture for two-cycle and four-cycle engines; 
     The provision of the aforementioned fuel regulator which eliminates the need to adjust fuel regulating needle valves; 
     The provision of the aforementioned fuel regulator which is configured for installation between a fuel tank and a carburetor; 
     The provision of the aforementioned fuel regulator which includes an exhaust gas temperature sensor to continually regulate fuel mixture; 
     The provision of the aforementioned fuel regulator which is capable of operation under low fuel pressures, in the range of 1-15 pounds; 
     The provision of the aforementioned fuel regulator which may include additional inputs from engine operating condition sensors and an exhaust gas temperature sensor to continually optimize the fuel mixture; and 
     The provision of the aforementioned fuel regulator which is adapted for use in model aircraft engines. 
     Briefly stated, the fuel regulator of the present invention comprises a microprocessor, a thermal sensing device, which, in the preferred embodiment is a thermocouple operatively arranged to sense exhaust gas temperature, and an in-line fuel regulating valve installed between the fuel tank and the carburetor. During operation, the microprocessor receives signals from the exhaust gas temperature sensor and any additional engine operating condition sensors. These signals are compared with stored reference valve to determine the optimum fuel mixture for the current engine operating conditions. If the current engine operating conditions require a variation in the fuel mixture settings, the microprocessor regulates the degree and/or rate of opening of the in-line fuel regulating value, and accordingly regulates the flow of fuel into the carburetor. 
     The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the accompanying drawings which form part of the specification: 
     FIGS. 1A,  1 B, and  1 C are a rear view, a side view, and a top-down view respectively of a typical two-cycle model aircraft engine and muffler combination. FIG. 1C has a part of the engine cut away at line A-A′; 
     FIG. 2 is a diagrammatic illustration of the interconnecting components of the fuel regulator of the present invention; 
     FIG. 3 is an diagrammatic illustration of a parallel fuel flow circuit; 
     FIG. 4 is a diagrammatic illustration of the electronic components interconnected to the fuel regulator microprocessor shown in FIG. 2; 
     FIG. 5 is a flow chart illustrating the steps traversed by the microprocessor employed in the fuel regulator shown in FIG. 2 during a startup sequence; 
     FIG. 6 is a flow chart illustrating the steps in the cyclic fuel regulation operation performed by the microprocessor shown in FIG. 2 during engine operation; and 
     FIG. 7 is a flow chart illustrating the steps in the cyclic fuel regulation operation performed by the microprocessor shown in FIG. 2 during the optimum EGT hunting. 
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description illustrates the invention by way of example and not by way of limitation. The description will clearly enable one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what we presently believe is the best mode of carrying out the invention. 
     Referring now to FIG. 2, the various components of the fuel regulator  24  of the present invention are shown interconnected with the engine  10  and flight control system  26  of a typical model aircraft. The main components of the fuel regulator  24  are a microprocessor  28  and an in-line fuel regulator valve  30 , preferably driven by a pulse width modulated signal controlled by the microprocessor. The microprocessor  28  is powered by an external power source, preferably the same battery power source providing power to the flight control systems  26 , but may be powered independently. Typically the flight control system  26  receives electrical power from an on-board battery  32 , in which case a power lead  34  is connected to the microprocessor  28 . 
     The in-line fuel regulator valve  30  is preferably a solenoid valve, with the degree of opening controlled by a pulse width modulated signal sent from the microprocessor  28 , and is capable of operating under either vacuum or slight pressure conditions. The preferred operating condition for the fuel-regulator value is with a low fuel pressure, i.e., on the order of 1-15 pounds of pressure. Fuel line pressure may be generated by a fuel pump, exhaust gas pressure, or by engine delivered pressure. Other delivers methods, including the traditional venturi vacuum draw, are compatible with the broader aspects of our invention. 
     Those skilled in the art also will recognize that numerous other types of fuel regulator valves, including multiple, variable-orifice, butterfly, ball, and gate valves may be employed, including valves employing control signals other than pulse width modulation. Additionally, to allow for precise fuel flow control, a parallel fuel flow circuit shown in FIG. 3 may be included wherein only a portion of the fuel flowing from the fuel tank  33  into the engine  10  is regulated by the fuel regulator valve  30 , with the remainder continually flowing directly to the engine  10 . For example, if the capacity of fuel regulator valve  30  is capable of accurately controlling 20% of the fuel flow to the engine  10 , 80% of the fuel will be routed to the engine through a parallel fuel line and a fixed valve  35 , and only 20% metered through the fuel regulator valve  30 . 
     To determine the optimum fuel mixture, the microprocessor  28  receives input signals representative of the current operating conditions of the engine  10 . A temperature sensor  36  placed in the exhaust system  38  of the engine  10  provides the microprocessor  28  with an indication of the current exhaust gas temperature (EGT). The temperature sensor  36  is preferably a conventional thermocouple sensor, adapted for operation within the temperature range encountered in exhaust gases, i.e. from room temperature through about 1500° F. As is seen in FIG. 4, appropriate conventional circuitry  37  is included with the thermocouple sensor  36  to compensate for any cold junction temperatures that may be encountered during engine operation. Additionally, a convention clock circuit  39  is provided. 
     Those skilled in the art will recognize that additional engine operating condition sensors, such as an engine tachometer  39  or a throttle position sensor  40  interconnected with the throttle control element  42  of the flight control system  26  may be utilized in conjunction with the temperature sensor  36  to provide the microprocessor  28  with an indication of the current operating conditions of the engine  10 . Signals, such as those corresponding to the engine speed, or high and low throttle positions for the particular engine  10  to which the fuel regulator  28  is connected, are stored in an long-term memory  43 , typically a conventional EEPROM or other non-volatile memory device compatible within the broader aspects of the invention. 
     In the preferred embodiment, the conventional EEPROM  43  additionally stores preprogrammed modes of operation for the microprocessor  28 , corresponding to different engines to which the system is connected, different EGT ranges, and corresponding fuel regulator valve settings. Each operational mode stored in the EEPROM  43  is optimized for the specific characteristics of a brand or model of engine. Those skilled in the art will recognize that alternate embodiments, as shown in FIG. 4, may employ a number of input selecting devices, such as switches, S 1 -S 5 , for selecting a mode of operation. The selection of switches S 1 -S 4  in combination select one of sixteen sets of operating parameters for the fuel regulator  28 . These operating parameters may include the initial fuel regulating valve  30  opening, and the ideal operating temperature range. As will be described below, the selection of switch S 5  places the fuel regulator  28  into a configuration mode wherein parameters may be entered and stored, for example, corresponding to the “low” or “neutral” and “high” or “open” throttle positions. Other embodiments may utilize a fewer or a greater number of selecting devices which may take forms other than the switches illustrated. 
     Referring next to FIG. 5, a flow chart is shown of the steps traversed by the microprocessor  28  employed in the embodiment of FIGS. 2 and 4. Upon initial power-up (Block  100 ), the preferred embodiment retrieves the operating parameters from EEPROM storage  43  and transfers them to the microprocessor  28  (Block  101 ), a signal is provided to the operator (Block  102 ) that the fuel regulator system  24  is operational and is ready to being regulating the fuel mixture flowing to the engine  10 . This signal is preferably provided by flashing a green colored light emitting diode LED controlled by the microprocessor  28 . 
     In alternate embodiments employing input selecting devices, such as switches, S 1 -S 5 , the microprocessor  28  follows the alternative manual startup sequence indicated in FIG.  5 . After powerup (Block  100 ), a signal is provided to the operator, preferably by flashing a red light emitting diode (Block  103 ), indicating that the system is ready to receive operator input. If provided, the system next checks the status of the manual input switch S 5  (Block  104 ). If switch S 5  is in the “on” position, the microprocessor  28  begins a configuration cycle (Block  107 ). In the embodiment shown, the configuration cycle corresponds to the input of throttle position information, wherein a low and a high throttle position readings are taken from the optional throttle position sensor  40  and stored. As described above, the configuration cycle  107  may include steps corresponding to the input of other operating parameters, such as minimum and maximum engine speeds. 
     During the illustrated configuration cycle, the microprocessor signals the operator to place the throttle in the “low” or “neutral” position (Block  108 ). This signal is preferably provided by flashing a colored light emitting diode of a different color than the power-up signal (Block  102 ). The microprocessor  28  then reads a first signal from the throttle position sensor  40  (Block  110 ) and stores the value in an internal register. Next, the microprocessor  28  signals the operator (Block  112 ) to place the throttle in the “high” or “open” position. A second signal reading is taken from the throttle position sensor  40  (Block  114 ) and the value stored in a second internal register. Upon storing both values in internal registers, the microprocessor  28  copies the values to a long-term storage device (Block  116 ) such as EEPROM  43  or other suitable non-volatile device. Finally, upon completion of the storage step (Block  116 ), the microprocessor  28  again signals the operator (Block  118 ), indicating the configuration cycle is complete, and returning to the switch status check (Block  104 ). Those skilled in the art will readily recognize that similar configuration cycles may be employed to input other information into the microprocessor, for example, indicating high and low values for engine revolutions per minute. 
     If switch S 5  is not selected, or is not included in the embodiment, the microprocessor determines which of switches S 1 -S 4  are in an “on” position (Block  120 ) to load the initial operating parameters (Block  122 ) of the in-line fuel regulator valve  30  for startup of the engine  10  and the nominal temperature range for optimum performance. The fuel regulator valve  30  is then opened (Block  124 ) to the appropriate setting, and a signal is provided to the operator (Block  102 ) that the microprocessor  28  is ready to being regulating the fuel mixture flowing to the engine  10 . 
     As shown in FIG. 6, the regulation of the fuel mixture during engine operation is performed as a closed loop procedure which includes a “hunting” cycle to locate the optimum fuel mixture within a predetermined EGT range. The microprocessor  28  receives a signal from the exhaust gas temperature sensor indicative of the current exhaust gas temperature (Block  127 ) and compares it with a predetermined upper value for the lowest operating temperature range stored in memory, for example: 450° F., (Block  128 ). If the exhaust gas temperature is lower than the upper range value, the microprocessor  28  next determines if the temperature is within the temperature range currently in-use (Block  130 ). If the temperature is not within the temperature range currently in use, the microprocessor loads the appropriate temperature range containing the current EGT and the corresponding fuel regulator valve  30  initial control setting from the EEPROM (Block  132 ). Once the appropriate temperature range and fuel regulator control settings are loaded from the EEPROM, or if the temperature range is already loaded, the microprocessor begins hunting for the optimum EGT within the current temperature range (Block  134 ). 
     As shown in FIG. 7, the microprocessor  28  begins hunting (block  134 ) for the optimun EGT by checking the present temperature (Block  138 ) and compares it with the previous temperature, for example, 0° at startup. The microprocessor  28  then decides whether the present temperature is higher, lower, or the same as (Block  140 ) the previous temperature. The microprocessor  28  then checks for the last operational command, for example, decrement at start up (Block  140  A or B). If the temperature is higher (Block  140 B), and the last operation was decrement, the microprocessor  28  will decrement again (Block  142 B). If the temperature was higher (Block  140 B), and the last operation was increment, the processor will increment again (Block  136 B). If the temperature is found to be lower (Block  140 A), and the last operation was decrement, the processor will increment (Block  136 A). If the temperature was lower and the last operation was increment, the processor will decrement (Block  142 A). If the present temperature (Block  138 ) is found to be the same as the previous temperature, the microprocessor  28  neither increments nor decrement. Then the microprocessor  28  stores the present temperature and the result of its decision to increment or decrement as last temperature and operation respectively (Block  139 A). The microprocessor then returns to the main loop FIG. 6, and repeats the cycle. 
     By continually cycling through hunting operation steps outlined above, the microprocessor  28  of the fuel regulator  24  is capable of properly adjusting the fuel mixture to a wide variety of operating conditions for the engine  10  by regulating the opening of the fuel regulator valve  30 . In the alternative, a check of additional engine operating condition sensors, such as the tachometer  39  or throttle position sensor  40  may be incorporated into the fuel regulation cycle, if desired, and may take precedence over the EGT ranges described above. 
     For example, if the throttle position is within the nominal range selected, for example 95-100%, the microprocessor  28  receives a signal from the throttle position sensor indicative of the current throttle position and compares it with a predetermined value stored in memory, for example 95-100%. If the throttle position sensor signal is lower than the upper range value, the microprocessor  28  next determines the last operation, i.e., increment or decrement. The hunting process continues as described above, the object being to drive the throttle position to maximum en-leanment. As indicated, maximum en-leanment is delivered by the method described above, regardless of the condition being monitored. As will be appreciated, while this alternate embodiment operates in a relatively small throttle opening range, other alternate embodiments may operate over a full range of throttle openings or be responsive to engine speed in addition to EGT. 
     Those skilled in the art will see that the low pressure fuel regulator of the present invention provides a significant improvement over the prior art in terms of reaching and maintaining optimum engine performance levels utilizing an exhaust gas temperature sensor. Although described in connection with model airplane engines, it should be noted that the various embodiments and ramifications discussed herein may be applicable to small-sized internal combustion engines of all types, including those employing multiple combustion cylinders. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results are obtained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. In that regard, numerous variations will be apparent to those skilled in the art in view of that description. Merely by way of example, ranges given for microprocessor operation may be varied. Likewise, other input information to the microprocessor may be used. The microprocessor itself may vary or take other forms. The application of the invention to internal combustion engines besides model airplane motors is particularly relevant. These variations are merely illustrative.
A fuel regulator for two-cycle and/or four-cycle internal combustion engines, particularly those found in model airplanes, comprises a microprocessor, a thermocouple exhaust gas temperature sensor, and a fuel regulating valve installed in a low-pressure fuel delivery system between the fuel tank and the carburetor. During operation, the microprocessor continually receives signals from the exhaust gas temperature sensor. These signals are compared with stored temperature ranges to determine the optimum fuel mixture for the current engine operating conditions. If the current engine operating conditions require a variation in the fuel mixture setting, the microprocessor adjusts the degree of opening of the in-line fuel regulating value, and accordingly regulates the flow of fuel into the carburetor.