Control of gas turbine engine

Systems, devices, and methods for controlling a fuel supply for a turbine or other engine using direct and/or indirect indications of power output and optionally one or more secondary control parameters.

TECHNICAL FIELD

The application relates to the operation of turbine engines and, more specifically, to methods and apparatus for control of the supply of fuel provided to gas turbine engines using electronic engine control systems.

BACKGROUND

Many new aircraft engines, including both engines currently in development and engines recently certified for flight use, employ electronic engine control systems. As well, older aircraft, designed before electronic control systems were common, are sometimes retrofitted with such systems. Among other advantages, electronic engine control systems can help to reduce pilot workload, provide simpler and more efficient interfaces with modern cockpit control systems, provide improved protection for engines against extreme operating conditions, and enhance prognostic and diagnostic capabilities.

An important parameter to be controlled by an electronic engine controller in a turboprop or turboshaft engine is engine output power (or output torque). Such power is most often controlled through control of the rate of fuel flow provided to the engine.

For measuring and reporting current engine power output, prior art engine controllers have typically employed mechanical transducers, such as phase-shift torque meters. Such mechanical transducers, however, require space and add weight to an engine; the addition of either volume or weight to engines is typically undesirable, particularly in aerospace applications. In a turboprop or turboshaft engine, for example, the use of such transducers can require modification of the reduction gearbox (RGB) and associated components.

SUMMARY

The disclosure provides, in various aspects, methods, systems, and devices for controlling the supply of fuel to engines, including particularly aircraft-mounted turbine engines such as turboshafts or turboprops.

In various aspects, for example, the disclosure provides methods of controlling such fuel supplies, the methods comprising steps of monitoring a differential oil pressure, such as the differential pressure measured across the reduction gear box (RGB), associated with an operating engine, the differential engine oil pressure determined using signals representing at least two measured operating engine oil pressures, to determine whether a change in the monitored differential engine oil pressure has occurred; upon determining that a change in the monitored differential engine oil pressure has occurred, using signals representing at least one other aircraft or engine operating parameter to determine whether the change in differential engine oil pressure corresponds to a desired change in an output power level for the engine; and if it is determined that the change in differential engine oil pressure does not correspond to a desired change in an output power level for the engine, calculating a desired fuel flow rate for the engine and either providing a corresponding command signal to an engine fuel supply controller or causing a current fuel flow rate to be continued for a determined time interval.

In further aspects, the disclosure provides methods of controlling such fuel supplies, in which the methods comprise monitoring a differential oil pressure associated with an operating engine, the differential engine oil pressure determined using signals representing at least two measured operating engine oil pressures, to determine a corresponding indicated engine output power level; monitoring at least one other aircraft or engine operating parameter to determine whether the indicated engine output level corresponds to a desired output power level for the engine; and if the indicated engine output level does not correspond to the desired output power level for the engine, calculating a desired fuel flow rate for the engine and either providing a corresponding command signal to an engine fuel supply controller or causing a current fuel flow rate to be continued for a determined time interval.

In further aspects the disclosure provides systems and devices, including controllers, for controlling the supply of fuel to such engines according, for example, to such methods.

Further details of these and other aspects of the subject matter of this application will be apparent from the detailed description and drawings included below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various aspects of embodiments of systems, devices, and methods in accordance with the disclosure are described through reference to the drawings.

FIG. 1is a schematic diagram of a system100for controlling a fuel supply for an engine200in accordance with the disclosure.

In the example shown, turbine engine200is a turboprop engine suitable for use in providing primary flight power for an aircraft. In the example, engine200comprises a gas generator section202and a power module212. Gas generator section202includes an accessory gearbox (not shown), a multi-stage compressor206, a reverse-flow combustor208, and a high pressure compressor turbine210. In the example shown, power module212comprises power turbine214(which may be multi-stage) and reduction gearbox (RGB)216for stepping down the rotational speed of turbine shaft220to a speed appropriate for a driving propeller shaft.

The operation and interactions of components202-220of engine200and other engines suitable for use in implementing systems, devices, and methods according to the disclosure will be well understood by those skilled in the relevant arts. As will be further understood by those skilled in such arts, the systems and methods disclosed herein are suitable for use in controlling fuel supplies for a wide variety of both turbine and non-turbine engines in addition to those described herein.

In a gas turbine engine such as a turboprop engine200or a turboshaft engine, engine output power is generally dependent, among other factors, on the rotational speed of gas generator shaft220. Control of the speed of a gas generator such as that of gas generator section202, and therefore gas generator shaft220, ofFIG. 1can be accomplished by regulating the amount of fuel supplied to the combustion chamber (e.g., combustor208ofFIG. 1) in view of other factors such as altitude, inlet pressure, and inlet temperature.

In systems and methods according to the disclosure, the amount of fuel provided to a combustor (or other fuel injection system), and thereby the engine output power, can be regulated by an electronic engine control system (EEC110) such as a Full-Authority Digital Electronic Control (FADEC) system. Such EECs110can use any one or more of a number of parameters as input in determining the amount of fuel to be supplied to the combustor in order to achieve or maintain a desired engine power output. Examples of such parameters can include current output power, altitude, inlet and outlet air pressures, and inlet and outlet air temperatures.

As shaft output power can be expressed as:
Shaft output power=(Shaft torque)×(propeller speed),
primary desirable factors in controlling fuel supply can include propeller speed (Np) and parameters which are directly proportional to shaft torque, such as differential engine oil pressure measured across the RGB in a turboprop and/or stress and/or strain in the shaft. Thus primary input sources for use by EEC110in determining current or desired output power, and thereby desired fuel flow, can include, for example, phase-shift torque meters and/or differential oil pressures transducers placed at, for example, the oil inlet and outlet of the RGB in a turboprop.

Thus, as described below, system100for controlling the fuel supply to engine200, can comprise, among other components, one or more automatic data processors (e.g. EECs)110and one or more sensors or other input devices102,104for assessing and/or confirming engine output power levels, for calculating desired fuel flow rates for the engine200, and for issuing command signals to fuel pumps and/or other fuel control components114to cause such calculated desired fuel flow rates to be provided to the engine.

Primary input sensor(s)102may be provided for acquiring signals representing engine output power or parameters useful in determining engine output power. Such signals may represent direct measures of output power (as for example in the case of phase-shift torque controllers, differential oil pressures, and or propeller speed indicators), or indirect measures, through measurement of parameters which may be used to deduce output power.

Input sensor(s)104can be provided to acquire data signals representing parameters relevant to engine operation or otherwise useful in confirming the current output power; which, for example may be indirectly associated with engine performance, and/or used to confirm conditions in which an engine200is operating, and thereby to confirm the meaning of output readings of one or more transducers102, and thereby confirm current and desired engine output and fuel supply settings. Examples of parameters readable by sensors104that can be used to confirm a primary engine power output indication can include vertical or other accelerations at the engine location, main oil pressure, which can for example be affected by aircraft accelerations, and/or the rotational speed Ng of the gas generator, e.g., section202inFIG. 1. While main oil pressure and accelerometer readings can be used to acquire information regarding movement of the aircraft or other vehicle in which an engine is mounted, factors such as Ng can be use to confirm whether in fact a significant change in engine operation has occurred.

In the example shown inFIG. 1, system100for controlling the fuel supply of engine200comprises an engine output power transducer102in the form of a differential oil pressure transducer300such as, for example, that shown schematically inFIG. 2. As will be understood by those skilled in the relevant arts, the differential oil pressures provided by transducer102,300can be interpreted as providing a direct measure of the output torque of engine200, and therefore is directly proportional to engine output power.

Operation of an embodiment of a fuel control system100in accordance with the disclosure may be described in conjunction with such a transducer102,300. Those skilled in the relevant arts, however, will understand that phase-shift torque meters and other direct measures of engine torque can be used as input sources102.

In the embodiment shown inFIGS. 1 and 2, differential oil pressure transducer102,300can be disposed proximate a first stage reduction gear224of RGB216, and can comprise a ring gear302, cylinder304, piston306connected to valve310, and spring312. Rotation of ring gear302can be resisted by helical splines, which can impart an axial movement of the ring gear and to piston306. Movement of piston306can cause valve310to move against spring312, opening a valve orifice and allowing flow of pressurized oil into torque pressure chamber314. Movement of piston306can continue until the pressure of oil in chamber314is proportional to the torque being transmitted to ring gear302. Because external pressure can vary and can affect the total pressure applied to piston306, the internal RGB static pressure applied at chamber316can be applied to the reverse side of piston306, resulting in measurement of differential oil pressure in the RGB216. This RGB differential pressure can be interpreted as a measure of torque applied to output shaft218by the RGB216, and therefore can be used as a control parameter in determining and controlling the amount of fuel supplied to engine200.

As will be understood by those skilled in the relevant arts, transducers102, including any transducers300, can be of any suitable form for accomplishing the purposes described herein; the arrangement shown inFIG. 2is merely an exemplary embodiment of a single type of transducer that can be used in implementing the methods, systems, and devices disclosed herein.

FIG. 3is a schematic diagram of a system100for controlling a fuel supply for an aircraft-mounted turbine engine in accordance with the disclosure. System100is suitable for use, for example, in controlling a fuel supply for an engine such as that shown at200inFIG. 1. System100comprises one or more sensors102for reading and transducing engine operating parameters such as, for example, differential oil pressure (see, for example, sensor300ofFIGS. 1 and 2), propeller speed Np, and shaft torque (not shown). System100can further comprise one or more sensors104for reading and transducing other parameters associated with operation of the engine200, such as, for example, inter-turbine temperature ITT, engine inlet temperature T1, main oil pressure MOP, and main oil temperature MOT; and other parameters such as power supply output386, relay status388, A/C discretes390, cockpit power control lever (e.g., power control lever rotating variable differential transformer PCL RVDT392), and other avionics devices394. One or more communications channels106,108, such as digital buses, electronic engine controls (EECs)110,110′ and fuel control units (FCUs)114are also provided. In the embodiment shown, redundant EECs110,110′ are provided.

As will be understood by those skilled in the relevant arts, the various components of system100may be implemented, separately or jointly, in any form or forms suitable for use in implementing the systems, devices, and methods disclosed herein. For example, sensors102,104for reading and transducing engine operating parameters such as differential oil pressure, shaft stress and/or strain, compressor inlet pressure, propeller speed Np, inter turbine temperature ITT, compressor inlet temperature T1or outlet temperature, main oil pressure MOP, and/or main oil temperature MOT may be of any mechanical, hydraulic, electrical, magnetic, analog and/or digital compatible form(s) suitable for use in implementing desired embodiments of the systems, devices, and methods disclosed. For example, as suggested byFIG. 2, a pressure transducer such as differential oil pressure transducer300may provide mechanical/visual output for full or partial manual control of a turbine engine; in other embodiments, temperature, pressure, or other sensors providing digital and/or analog electromagnetic and/or mechanical signals representing the measured parameters may be used. Many suitable types of transducers are now known; doubtless others will be developed hereafter.

Selection of suitable sensors, transducers, and/or other devices for monitoring values of parameters104will depend, among other factors such as cost, weight, etc., on the nature of the parameters to be monitored; such selection will be well within the scope of those having ordinary skill in the art, once they have been made familiar with this disclosure.

Communications channels106,108, such as those between sensors102,104and EEC/processor110can comprise any single or redundant communications devices or systems, including for example dedicated, direct-wire connections, serial or parallel buses, and/or wireless data communications components, suitable for accomplishing the purposes described herein. As will be understood by those skilled in the relevant arts, it can be desirable in some applications, particularly aerospace applications, to provide sensors102,104, communications channels106,108, processors110, and fuel control units (FCUs)114in redundant sets, particularly with respect to devices which generate, transmit, or process electrical signals. It can further be desirable to provide insulators, firewalls, and other protective devices between components of systems100, and particularly redundant components, so as to preclude multiple failures. Even where a single housing is provided, as in the case for a housing for a differential oil pressure transducer300, multiple redundant sensors may be provided.

FCU114can comprise any relays, switches, and controls, and/or other components, such as pump and/or valve controls, required to control fuel supply at the command of EEC(s)110, as for example by receiving and appropriately responding to command signals provided by EEC and configured to provide a desired fuel flow to engine200. Such components and the use of them in implementing the systems and methods disclosed herein will not trouble those of ordinary skill in the art, once they have been made familiar with this disclosure.

EECs110may comprise any single, multiple, combination, and/or redundant general or special purpose data processors, such as printed integrated circuit boards and associated or auxiliary components such as volatile and/or persistent data storage devices111, relays, and input/output devices, suitable for accomplishing the purposes described herein. Such components may comprise any hardware and/or soft- or firmware and data sets, suitable for use in implementing the systems, devices, and methods disclosed herein.

As one example, EEC software contained in the EEC110and executed in processors associated therewith may include filters to condition the differential oil pressure signal as required. Noise may be present in the signal due to various phenomena that may appear in the signal at various frequencies. For example, since the differential pressure oil transducer300is located above the RGB216in close proximity to the propeller, the oil pressure transducer300may respond to the frequency with which propeller blades pass the transducer. Pulses within the signal related to such phenomena could easily be filtered via software to ensure the EEC is processing a true output power or torque signal.

A wide variety of suitable transducers, communications units, data processors, memories, relays, communications devices, fuel control devices, and other components are now available, and doubtless others will hereafter be developed. Those skilled in the relevant arts will not be troubled by the selection of suitable components, once they have been made familiar with the contents of this disclosure.

FIGS. 4 and 5are schematic flow diagrams of exemplary processes400,500for controlling a fuel supply for an aircraft-mounted turbine engine in accordance with the disclosure. Processes400,500are suitable for use, in conjunction with systems100, in implementing controls for fuel supplies for engines such as that shown at200inFIG. 1.

Process400depicts a process for controlling a fuel supply for a turbine or other engine using direct and/or indirect, or primary, indications of power output and optionally one or more secondary, or confirmatory, control parameters according to embodiments of the disclosure. At402, a current value or level of power output of the engine200is determined. For example, a direct reading of power output of shaft218can be determined using, for example, a mechanical means such as a phase shift torque probe. Alternatively, a proportional measure of power output, such as differential RGB oil pressure, may be employed as a control parameter, in either case using one or more of sensors102to provide signals representing any one or more of such parameters to EEC(s)110(and110′). For example, as shown at402a differential oil pressure across an RGB may be obtained, using a transducer such as differential oil pressure transducer102,300ofFIG. 2to provide for processing by EEC(s)110and/or110′, and optionally for long- or short term storage in one or more memories111, a signal representative of or otherwise useful in determining current power output of the engine200. EEC110may process such signals into any form suitable for further processing in calculating a desired fuel flow rate and preparing any desired control command signals.

At404a determination may be made as to whether the power reading obtained or determined at402indicates that a change in power has occurred. For example, a primary reading of power output of shaft218made at402can be compared with data representing a previous output reading previously stored in persistent or volatile digital memory111by EEC110. From such comparison it can be determined, visually or automatically, that power output is indicated to have increased or decreased, or to be desired. A visual determination may be made, for example, by providing suitable output signals EEC110to a cockpit display for review by a pilot, who can, by repeatedly checking the display, determine that a change in engine output power is indicated. For further example, a signal representing a second or subsequent differential engine oil pressure can be obtained, using a suitably-configured transducer, such as differential oil pressure transducer300ofFIG. 2, data processor110, and volatile and/or persistent data storage111, and compared to one or more previously-acquired signals, using suitably-programmed mathematical algorithms, to determine whether a change in the monitored differential engine oil pressure is indicated to have occurred. Such information may or may not be communicated to a pilot of the aircraft by EEC110,110′.

If at404it is determined that no change in engine power output is indicated, at405, the process can return to402. For example, in an embodiment using an automatic data processor control in an EEC, process control can be returned to logic block402for one or more subsequent readings of engine power output indicators, so that continual monitoring of engine power output can be maintained; at any pass through logical blocks402,404, where a change in engine output power is indicated, control can proceed to block406.

If at404it is indicated that a change in engine power output has occurred relative to one or more previous power readings, or if it desired to confirm that in fact no change has occurred, at406data representing a secondary, or confirmatory, power and/or fuel control parameter may be acquired, for use in confirming that a change in power has actually occurred. Such secondary parameter reading(s) can be used to affirm or contradict the change in power output indicated at404.

For example, it is possible, under some circumstances, particularly where an indirect measure of power output is used, that an erroneous change in power output may have been indicated at404. For example, during certain maneuvers of an aircraft or other vehicle, such as a zero-g or a negative-g aircraft operation (which may be encountered for example during turbulence or in sudden descents), acceleration of oil within the oil tank may cause an incorrect oil pressure reading, which, if differential oil pressure is being used as an indicator of engine power output, can result in an incorrect indication of a power change—either, for example, by indicating that a change has occurred when in fact none has, or by exaggerating or minimizing the indication of a true power change. For example, in such circumstances oil may be accelerated away from the bottom of the tank where the oil pump is located, causing the oil pump to cavitate, with a consequent drop in MOP. Such a drop in MOP can in turn result in a loss of differential oil pressure which is not necessarily connected with a change in engine power output. This is illustrated, for example, inFIG. 6, which represents a plot of oil pressure and vertical acceleration versus time during a negative-g maneuver by an aircraft or other vehicle.

FIG. 6illustrates the effect of vertical accelerations on a number of parameters that can be used to confirm whether an indicated change in engine power output has in fact occurred. As may be seen in the Figure, factors such as main oil pressure (MOP) can be significantly correlated with vertical acceleration (NZ), and therefore can be useful as in confirming whether an indicated power change might be erroneous, and in fact indicate a change in vertical accelerations. Other factors, such as gas generator speed Ng (NG) are less strongly correlated to vertical acceleration, and therefore can be useful in confirming that in fact no change in output power is likely to have taken place, despite an indication to the contrary. Those skilled in the relevant arts will understand that the utility of various operating parameters in verifying engine performance will depend upon the construction of a particular vehicle, the operating conditions, and other factors. The identification and use of many such factors should not present significant difficulties, once such persons have been made familiar with this disclosure.

Thus where at404it is indicated that a change in engine power output has occurred relative to one or more previous power readings, at406, a secondary power and/or fuel control parameter may be acquired, for use in confirming that a change in engine output power has actually occurred, or has occurred at a desired level. This can be useful, for example, when no change in power setting is desired, as for example where a FADEC or other system is configured to provide a desired constant power output: to change power when, for example, in fact no change is desired, or appropriate, and none has in fact taken place, could cause inconvenient and even dangerous changes in actual engine power settings. It can also be useful where, for example, a desired change in engine power has been requested, but subsequent changes in aircraft operating conditions cause an apparent change in engine power output that is not accurate.

As an example of the use of a secondary or confirmatory parameter to confirm whether a change in engine power output has occurred, or has occurred within a desired limit, one or more signals382representing acceleration of one or more parts of the aircraft can be acquired and interpreted, to determine whether the apparent power change determined at404, or any part of such apparent power change, is accurate. For example, signals representing acceleration of the aircraft at, for example, the location of the engine may be obtained, or determined using acceleration at one or more other points, transposed mathematically to the location of the engine to determine whether the engine or any part of it is subject to acceleration that might cause an erroneous power indication.

For example, one or more locations on the aircraft or other vehicle may be equipped with one or more accelerometers104,382(FIGS. 1,2), which would provide various components of aircraft vertical, horizontal, and rotational acceleration to EEC110or other flight control computer. Such parameter(s) (possibly along with other air data parameters such as air speed and altitude) may in turn be communicated to the engine EEC via a data bus or other digital or analog communications means106,108. Again, such secondary parameter(s) may be used to determine whether a change in differential oil pressure detected at404is due to aircraft operations rather than a change in output power.

In other embodiments, secondary parameter(s) obtained at406may include inputs from other sensors104, such as gas generator speed or inter turbine temperature ITT. Engine power output may be calculated based on these inputs using, for example, a digitized engine performance module within software stored in or otherwise executed by the EEC110. This may then be compared to the power output determined at402and/or to previous power output readings in order to determine whether a change in power has occurred or is correctly indicated at402.

It is also possible to use pilot-initiated control inputs as primary or secondary indicators of desired power settings. For example, control input from PCL RVDT104,392can be used to indicate a desired output setting.

At408it is determined whether or not actual engine power output needs to be modified to meet current intended flight commands, and if so, to what extent. For example, data signals representing actual power output may be compared to data signals representing desired power output, using known computer algorithms. It having been determined whether the power setting indicated at402is correct or needs correction, control of the process400can be transferred to logic block412.

As mentioned above, where it is determined at408that actual power output requires correction, the power output can be modified by increasing or decreasing the fuel flow f. At412, the fuel flow f required to compensate for any difference in indicated and desired or otherwise commanded power settings is calculated. As will be understood by those skilled in the relevant arts, calculation of the desired f will depend upon a number of factors, including the type and model of engine used, the type and model of aircraft or other vehicle in which it is installed, the operating conditions of the engine and vehicle, the type of fuel used and its condition, and optionally others.

At414, signals representing the calculated desired or required fuel flow f is output by the EEC system, for use, for example, in providing output command signals for a fuel pump or other device, and control of process400can return to402.

If it is determined at408that a change in power is not desired, then control of the process400passes to logic block410, at which the current fuel flow f may be held constant for a fixed or other determined time interval (for example, ten seconds) and control of the process400can returns to control block402.

Where an erroneous change in power output had been detected at404, the time interval applied at410is preferably long enough to allow the situation which caused the erroneous output power detection to pass, but in any case is preferably short enough to prevent the development of other possibly detrimental changes in flight or other vehicle conditions. For example, in the event that a momentary loss or reduction of MOP is experienced, as mentioned above and shown inFIG. 6, and a corresponding loss of differential oil pressure also occurs, at410the engine fuel flow may be held for a predetermined period long enough to give both the MOP and the differential oil pressure a chance stabilize, so long as no danger to flight safety has a chance to arise. After the designated time interval has passed, if the MOP and differential oil pressure have not recovered (i.e. signaling some other issue such as sensor failure), the engine power may be reduced, engine control may be governed using another input parameter, such as gas generator speed or inter turbine temperature (ITT) and/or the aircraft may fly in a degraded mode. Alternatively, in addition to or in lieu of using predetermined intervals of fixed length, various parameters102,104can be monitored to determine when a condition giving rise to erroneous power readings has abated, so that control can be resumed based on primary power indication factors.

Suitable methods and algorithms for determining fixed or variable time intervals for application at block410in holding current fuel flow f constant are known, and their use will be within the scope of those skilled in the relevant arts, once they have been made familiar with this disclosure.

FIG. 5provides a schematic diagram of another embodiment,500, of a process for controlling a fuel supply to a turbine or other engine according to the disclosure, suitable for implementation using systems and devices disclosed herein, including for example engine200ofFIG. 1and system100as described. Many of the individual process steps502,504, etc., are similar in form and alternative to various steps of process400, and form, to some degree, corresponding parts of process500. Thus in many cases the description below details only those portions of process500which differ significantly from their counterparts in process400.

At502, a current value or level of power output of the engine200is determined. For example, a direct reading of power output of shaft218can be determined using, for example, a mechanical means such as a phase shift torque probe. Alternatively, an indirect or proportional measure of power output may be employed as a surrogate control parameter using, for example, one or more of sensors102providing signals representing any one or more of a number of parameters (as, for example, disclosed herein). For example, as shown at402a differential oil pressure across an RGB may be obtained, using a transducer such as differential oil pressure transducer102,300ofFIG. 2to provide for processing by EEC(s)110,110′ and optionally for long- or short term storage in one or more memories111, a signal representative of or otherwise useful in determining current power output of the engine200. EEC(s)110,110′ may process such signals into any form suitable for further processing in calculating a desired fuel flow rate and preparing any desired control command signals.

At504an output signal representing a parameter useful in confirming the accuracy of the power output indication determined at502is obtained. For example, signals representing one or more additional flight and/or engine operating conditions, including for example acceleration, altitude, temperature, or other parameters (as for example described herein), may be obtained, using for example one or more transducers104, and provided to EEC(s)110,110′.

At506, using data acquired at502,504, EEC(s)110,110′ can determine whether the current fuel flow rate f is correct, in view of current power command settings obtained from, for example, power settings set by a pilot using a control input such as PCL RVDT104,390or by an automatic flight control system. For example, as described herein data representing a differential oil pressure obtained at502is used by EEC(s)110,110′ executing suitably-configured power setting software, to determine a corresponding apparent engine power out put; and the secondary data acquired at504is used, as described herein, to confirm whether the power setting determined using the value acquired at502is correct.

Once the actual power output determined by comparing the values acquired at502,504is determined, at508EEC110can compare the actual power setting to command power settings indicated by cockpit controls or other sources, and as described herein a corresponding suitable fuel flow rate f may be determined and at510used to provide corresponding command signals to a fuel control unit114(FIG. 1) or other device.

If either at506the current fuel flow rate f is determined to be correct or suitable output command signals have been provided at510, control can return to502so that continuous or continual monitoring of engine operating conditions may be maintained.

The above descriptions are meant to be exemplary only, and those skilled in the relevant arts will recognize that changes may be made to the embodiments described without departing from the scope of the subject matter disclosed. Still other modifications which fall within the scope of the described subject matter will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

Unless specified herein, or inherently required by the processes themselves, the order of steps shown in processes disclosed is not significant, and such order may be changed without departing from the meaning or scope of the disclosure.