Abstract:
A computer-assisted method for controlling the delivery of fuel to an engine. The method includes receiving an input signal indicative of a sensed speed of the engine, validating that the engine is in a cruise power mode based on the input signal, and providing an output signal based on a sensed engine operating condition for adaptively controlling the fuel delivery to the engine when the engine is operating in the cruise power mode. Also, a fuel control module. The fuel control module includes a first portion configured for receiving an input signal indicative of a sensed speed of an engine, a second portion configured for validating that the engine is operating in a cruise power mode based on the input signal, and a third portion configured for providing an output signal based on a sensed engine operating condition for controlling fuel delivery to the engine when the engine is operating in the cruise power mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     (Not Applicable) 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     (Not Applicable) 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to a method and system for controlling the fuel delivery to an engine and, more particularly, to a method and system for controlling the fuel delivery to an engine using adaptive techniques. 
     2. Description of the Background 
     In certain applications of internal combustion piston engines, it is desirable to supply an over-rich fuel to air mixture under certain operating conditions. For example, during take-off and climb of an aircraft, the aircraft engine must typically be supplied an over-rich fuel to air mixture. The pilot of the aircraft must manually weaken the mixture when the aircraft reaches low power cruising conditions. The pilot must monitor relevant engine operating parameters via the cockpit instrumentation to periodically adjust the fuel mixture. The fuel mixture must be precisely determined because of the need to ensure adequate fuel supply and to limit engine temperature during the high power, flight safety critical, portions of the aircraft&#39;s flight. Thus, the pilot has to devote considerable and constant attention to the instruments to ensure that the fuel flow is reduced during cruise conditions. Typically, the pilot monitors the engine temperature and power reading instruments to set the fuel mixture within pre-defined parameters at which it is assumed that the ideal engine operating point will be attained. The pilot must also monitor the aircraft speed and altitude and ambient temperature and pressure variations, which can affect the required fuel mixture. 
     When a pilot must devote attention to the aircraft flight path, other aircraft in the vicinity, etc., the pilot may fail to properly weaken the fuel mixture. This results in high levels of exhaust pollutant emissions, carbon buildup on cylinder head components, and, possibly, such high fuel consumption that the planned flight duration of the aircraft may not be achievable. Also, an overly weak fuel mixture can result in reduced engine life due to the overheating of cylinder head components and can also result in a failure of the engine to adequately respond if it were suddenly necessary for the pilot to increase engine power for some flight situation purpose. 
     In addition to engines which rely on manual pilot intervention to set the fuel mixture, some aircraft engines have electronic engine controls which measure the relevant engine and aircraft operating parameters, digitally process the information, and activate effectors which automatically set the fuel mixture (and other engine functions such as ignition timing) according to preset scheduled values. These systems have the disadvantage in that they rely on predetermined engine characteristic schedules, typically for an average or minimum rated power engine. Thus, they do not take into account engine to engine variations or changes in the desired schedule characteristics with performance changes over the service life of the engine. Thus, under certain conditions, an engine could operate at a fuel mixture as much as five percent away from its ideal stoichiometric fuel mixture. 
     Thus, there is a need for a system and method for controlling the fuel delivery to an engine which requires no pilot intervention. There is also a need for a system and method for controlling the fuel delivery to an engine which does not rely on predetermined engine characteristic schedules to determine the amount of fuel to deliver to the engine. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a computer-assisted method for controlling the delivery of fuel to an engine. The method includes validating that the engine is in a cruise power mode and adaptively controlling the fuel delivery to the engine based on sensed engine operating conditions. 
     The present invention represents a substantial advance over prior systems and methods for controlling the fuel delivery to an engine. The present invention has the advantage that it provides for a system and method for controlling the fuel delivery to an engine which requires no pilot intervention. The present invention also has the advantage that it provides for a system and method for controlling the fuel delivery to an engine which does not rely on predetermined engine characteristic schedules to determine the amount of fuel to deliver to the engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein: 
     FIG. 1 is a diagram illustrating an aircraft propulsion and control system in which the present invention may be used; 
     FIG. 2 is a diagram illustrating a process flow through the fuel control module illustrated in FIG. 1 during the validation process; 
     FIG. 3 is a diagram illustrating a process flow through the fuel control module illustrated in FIG. 1 during the calibration process; and 
     FIG. 4 is a diagram illustrating another process flow through the fuel control module illustrated in FIG. 1 during the calibration process. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements found in a typical aircraft propulsion and control system. For example, specific operating system details and modules contained in the electronic engine controller are not shown. Also, the power supply, specific ignition timing system components, and certain fuel system components are not shown. Those of ordinary skill in the art will recognize that other elements may be desirable to produce an operational system incorporating the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
     FIG. 1 is a diagram illustrating an aircraft propulsion and control system  10  in which the present invention may be used. The system  10  is described herein as implemented in an aircraft, although it may be implemented in any combustion engine. The system  10  can be used in an engine with any number of cylinders such as, for example, a four, six, or eight cylinder engine. In addition, the system  10  can be implemented in a naturally or supercharged aspirated, air cooled, horizontally opposed, reciprocating direct drive engine. 
     An electronic engine controller  12  accepts various engine parameters as inputs and outputs various control signals to control portions of the system  10 . The controller  12  includes a spark control module  14 , which generates signals directing the charging and discharging of spark plug ignition coils (not shown) to control ignition timing and energy level. The operation of the module  14  is detailed in the patent application “System and Method for Ignition Spark Energy Optimization”, which was filed concurrently herewith by the assignee of the instant application, and which is incorporated herein by reference. A fuel control module  16  generates signals which control the amount of fuel that is delivered by fuel injectors  18 . It is desirable to have one fuel injector per cylinder of an engine  20 . The fuel injectors  18  can be, for example, electromagnetically operated valves which have coils that can be energized and de-energized to open and close the valves. An appropriate fuel injector is detailed in the patent application “Fuel Injector Assembly ”, which was filed concurrently herewith by the assignee of the instant application, and which is incorporated herein by reference. A knock accommodation module  22  generates signals which control engine detonation, or knock, by retarding ignition timing and enriching the fuel mixture at the fuel injectors  18 . An engine speed control module  24  generates signals which determine how much current should be applied to a coil (not shown) in a governor  30  to change the angle of a propeller  28 . 
     A fuel pump control module  32  generates signals which control the delivery of fuel by an electric fuel pump  34  from a fuel tank  36  to the fuel injectors  18 . An annunciator control module  38  generates signals which determine which of annunciators  40 , if any, are illuminated such as during a component failure or when conditions such as low engine oil pressure or high engine oil temperature are present. A fault detection module  42  detects faults in the controller  12  and, upon confirming the presence of a fault, annunciates the fault via the annunciators  40 . 
     An input/output module  44  receives input signals from the an input interface  46  and outputs signals via an output interface  48 . The input interface  46  receives various input signals from sensors throughout the system  10 . The interface  46  receives a manifold pressure signal Pm from a manifold pressure sensor (not shown) which can be located on, for example, the body of a throttle  50  or on the induction plenum (not shown) or induction splitter (not shown) of the engine  20 . The throttle  50  controls the amount of air that is introduced into the cylinders (not shown) of the engine  20 . The interface  46  receives a fuel pressure signal Pf from a fuel pressure sensor (not shown) which can be mounted on, for example, the fuel distribution block (not shown) of the engine  20 . The manifold pressure and fuel pressure sensors can be, for example, resistance strain gauges. The interface  46  receives a manifold temperature signal Tm from a manifold temperature sensor (not shown) which can be located on, for example, the body of the throttle  50  or on the induction plenum (not shown) or induction splitter (not shown) of the engine  20 . The manifold temperature sensor can be, for example, a thermistor. The interface  46  receives a throttle position sensor signal TPS from a throttle position sensor (not shown) located on the body of the throttle  50 . The throttle position sensor can be, for example, a potentiometer. The interface  46  receives a turbine inlet temperature sensor signal Tt from a turbine inlet sensor of the engine  20 . The interface  46  receives a cylinder head temperature signal Tc from a cylinder head temperature sensor located on, for example, the thermowells of each cylinder (not shown) of the engine  20 . The turbine inlet temperature and the cylinder head temperature sensors can be, for example, thermistors. The interface  46  receives an exhaust gas temperature signal Te from an exhaust gas temperature sensor  52  which are located in each exhaust pipe  54  at, for example, a location approximately  2  inches from the exhaust pipe to cylinder mating flange (not shown). The exhaust gas temperature sensor can be, for example, a thermocouple. The interface  46  receives a crankshaft speed sensor signal Ne and a camshaft speed sensor signal Nc from a speed sensor assembly (not shown) which is mounted on the engine  20 . The crankshaft speed and camshaft speed sensors can be, for example, Hall effect, magnetically biased, magnetic pickups. The interface  46  receives a knock sensor signal K from a knock sensor (not shown) which is located on, for example, the cylinder heads of air cooled engines and the engine case for unitized block liquid cooled engines. The knock sensor can be, for example, a piezoelectric accelerometer. 
     The output interface  48  outputs a spark signal SP, which is generated by the spark control module  14  and the knock accommodation module  22 , to control the spark coil current and timing of pulses to interrupt the spark coil primary winding current and generate a spark at each spark plug (not shown) located in the engine  20 . The interface  48  outputs a fuel injection signal FI, which is generated by the fuel control module  16  and the knock accommodation module  22 , to control the opening and closing of the valves (not shown) in the fuel injectors  18 . The interface  48  outputs a speed control signal SC, which is generated by the engine speed control module  24 , to the governor  30 . The signal SC can be, for example, a pulse width modulated signal that causes the governor  30  to change the pitch of the propeller  28  as appropriate. The interface  48  outputs a fuel pump control signal FP, which is generated by the fuel pump control module  32 , to control the operation of the fuel pump  34 . The output interface  48  outputs an annunciator signal A, which is generated by the annunciator control module  38 , to the annunciators  40 . 
     The interfaces  46  and  48  can be implemented using, for example, one or a plurality of RS-485 serial data buses. 
     The controller  12  can be implemented as, for example, a microprocessor such as, for example, an N87C196KT microprocessor, sold by Intel Corporation of Santa Clara, California, with or without internal memory or an application specific integrated circuit (ASIC). The modules  14 ,  16 ,  22 ,  24 ,  32 ,  38 ,  42  and  44  can be implemented using any type of computer instruction types such as, for example, microcode, and can be stored in, for example, an electrically erasable programmable read only memory (EEPROM) or can be configured into the logic of the controller  12 . The controller  12  can be mounted on, for example, the mount frame (not shown) of the engine  20  or on either side of the firewall (not shown) of the engine  20 . 
     The module  16  utilizes a closed loop “hill climbing” adaptive technique when the engine  20  is in a cruise power mode. The module  16  first validates that the engine  20  is in cruise power mode and then calibrates the delivery of fuel to the engine  20  to maintain a stoichiometric mixture. 
     FIG. 2 is a diagram illustrating a process flow through the fuel control module  16  illustrated in FIG. 1 during a validation process. The validation process ensures that the aircraft is operating in an appropriate cruise power mode so that a calibration process may be entered to control the fuel delivery to the engine  30  such that a stoichiometric fuel/air mixture is found. The flow through the module  16  enters at block  70 , where the controller  12  determines if the aircraft is being operated in a cruise power mode by determining, based on the speed sensor signals Nc and Ne, whether the speed of the engine  20  is below a maximum power speed such as, for example, 75% of the maximum speed of the engine  20 . This check is necessary to prevent the calibration process of the module  16  from being inhibited by excessively high engine temperatures that could occur at high engine speeds. Alternatively, a pilot-activated switch could be used at block  70 . If the speed is not less than the maximum power speed, the flow remains at block  70 . If the speed is less than the maximum power speed, the flow advances to block  74 . 
     At block  74 , the module  16  determines, based on the fault status generated by the fault detection module  42 , whether each cylinder of the engine  20  is under control of nominated control logic in the controller  12  rather than backup logic in the controller  12 . The backup logic would control a cylinder if a control fault had been previously detected by the controller  12 . If the logic is not under the control of the nominated control logic, the flow moves to block  70 . If the logic is under the control of the nominated control logic, the flow moves to block  76 . At block  76 , the module  16  determines if the calibration process, as discussed hereinbelow in conjunction with FIG. 3, is complete (i.e. a stoichiometric fuel mixture has been found). If the calibration process is not complete, the module  16  determines at block  78  whether the engine  20  has attained a minimum operating temperature as measured by the cylinder head temperature signal Tc. The minimum temperature can be, for example, 380° F. If the calibration is complete, the flow ends at block  77 . 
     The module  16  determines, at blocks  80 ,  82 , and  84 , whether the engine  20  is running steadily without significant transient perturbations. At block  80 , the module  16  determines if the engine  20  has a steady inlet manifold pressure as measured by the manifold pressure signal Pm. At block  82 , the module  16  determines if the engine  20  is operating at a steady speed as measured by the crankshaft and camshaft speed sensor signals Ne and Nc. If the inlet pressure or the engine speed are not steady, the flow moves to block  70 . If the inlet pressure and the engine  20  speed are steady, the module  16  determines at block  84  whether the inlet pressure and the engine  20  speed have been steady for a predetermined cycle count. Such a cycle count could be, for example, 1500 engine cycles. If the inlet manifold pressure and the engine  20  speed were not steady for the cycle count, flow returns to blocks  80  and  82 . If the inlet manifold pressure and the engine  20  speed were steady for the cycle count, flow moves to the calibration process, which is discussed hereinbelow in conjunction with FIG.  3 . 
     FIG. 3 is a diagram illustrating a process flow through the fuel control module  16  illustrated in FIG. 1 during the calibration process. The flow starts at block  86 , where a short time delay is introduced to reset the logic decision blocks in the controller  12  as necessary. The time delay can be, for example, 50 engine cycles. The flow then moves to block  88 , where the module  16  commands the appropriate injector of the fuel injectors  18 , via the FI output signal, to decrease the amount of fuel metered by the that injector, thus weakening the fuel to air mixture introduced to the cylinder of the engine  20  that is about to fire. The fuel can be decremented by, for example, 0.001 fuel/air ratio per every 50 engine cycles. The flow then moves to block  90 , where the module  16  determines, based on the exhaust gas temperature signal Te, if the exhaust gas temperature has increased or decreased in response to the fuel flow decrement of block  88 . If the exhaust gas temperature is increasing, a rich flag is set at block  92 , which indicates that the fuel to air ratio is too rich. After the rich flag is set at block  92 , the module  16  checks, at block  94 , whether the maximum permitted fuel flow reduction (Δ) has been reached. The maximum permitted reduction is a preset limit used to prevent unsafe operation of the engine  20  if it has significantly diverged from its design point due to, for example, engine wear or an undetected fault condition. The maximum permitted reduction can be, for example, to a full lean mixture. If the maximum reduction has been reached, the flow proceeds to block  76  of FIG. 2 to indicate that calibration is complete. If the maximum reduction has not been reached, the flow moves to block  88 , where the fuel flow is further decremented. 
     If the exhaust gas temperature is not increasing as determined at block  90 , the fuel to air mixture is weak, i.e. the mixture is on the “lean” side of the stoichiometric operating point of the engine  20 . The flow thus advances to block  96 , where the fuel flow is incremented. The flow then advances to block  98 , where the module  16  determines, via the exhaust gas temperature signal Te, if the exhaust gas temperature is increasing. If the exhaust gas temperature is increasing, the flow moves to block  100 , where a weak flag is set indicating that the fuel to air mixture is weak. The flow then advances to block  102 , where the module  16  determines whether the maximum permitted fuel flow increase (Δ) has been reached. The maximum permitted increase is a preset limit used to prevent unsafe operation of the engine  20  if it has significantly diverged from its design point due to, for example, engine wear or an undetected fault condition. The maximum permitted increase can be, for example, to a full rich mixture. If the maximum increase has been reached, the flow proceeds to block  76  of FIG. 2 to indicate that calibration is complete. If the maximum permitted increase is not present as determined at block  102 , the flow moves to block  96 , where the fuel flow is further incremented. The fuel flow can be incremented by, for example,  0 . 001  fuel/air ratio per every  150  engine cycles. 
     If the exhaust gas temperature is not increasing as determined at step  98 , the flow advances to step  88 , where the fuel flow is decremented. 
     The calibration process described in conjunction with FIG. 3 thus locates the stoichiometric operating point of the engine  20 . The engine  20  thus continues to operate around the stoichiometric point and the fuel flow alternately moves between slightly rich and slightly lean. This ensures that the stoichiometric operating point is maintained even if slight changes in ambient temperature and pressure, or small changes in the aircraft flight path, affect the engine  20  operating point. 
     FIG. 4 is a diagram illustrating another embodiment of a process flow through the fuel control module  16  illustrated in FIG. 1 during the calibration process. The operation of the flow illustrated in FIG. 4 is similar to that of the operation of the flow illustrated in FIG.  3 . However, when the rich flag is set at block  92  or the weak flag is set at block  100 , block  104  performs a check to determine if a rich flag was immediately set after a weak flag was set or a weak flag was immediately set after a rich flag was set. If one of these conditions exists, the flow advances to block  76  of FIG. 2 to indicate that the calibration process has ended. The engine  20  thus continues to operate without perturbation in fuel flow using the operating point determined using the process of FIG.  4 . If the flag check at block  104  determines that a rich flag was not immediately set after a weak flag was set or a weak flag was not immediately set after a rich flag was set, the flow advances to either block  94  or  102 , depending on whether block  104  was entered from block  92  or block  100 . 
     Although the calibration processes illustrated in conjunction with FIGS. 3 and 4 use the exhaust gas temperature signal Te to monitor the fuel to air mixture, other parameters may be used. For example, the engine  20  cylinder head temperature signal Tc could be used in place of or in combination with the signal Te. 
     While the present invention has been described in conjunction with preferred embodiments thereof, many modifications and variations will be apparent to those of ordinary skill in the art. The foregoing description and the following claims are intended to cover all such modifiction and variations.