SE1750505A1 - Engine control strategy - Google Patents

Abstract

A method and apparatus controlling the fuel-to-air ratio of a fuel and air mixture supplied to an operating engine includes the steps of determining a first engine speed before enleanment of the mixture, determining a second engine speed near or at the end of a period of enleanment of the mixture, and after ending the enleanment, determining whether the engine speed recovers within a predetermined range of the first engine speed and if so determining a delta speed difference between the first and second speeds and using this delta speed difference as a factor in determining a change in the fuel-to-air ratio of the fuel mixture supplied to the engine.

Description

2630.3388.003 [1148] ENGINE CONTROL STRATEGY Reference to Related Applications This application is a continuation-in-part of PCT lntemational ApplicationSerial Number PCT/US15/59376 filed November 6, 2015 Which claims the benefit ofU.S. Provisional Patent Application Serial No. 62/075,945 filed November 6, 2014.The disclosure of each of these applications is incorporated herein by reference in its entirety.

Technical Field The present disclosure relates generally to an engine control strategy.

Background Combustion engines are provided With a fuel mixture that typically includesliquid fuel and air. The air/fuel ratio of the fuel mixture may be calibrated for aparticular engine, but different operating characteristics such as loads, acceleration,deceleration, type of fuel, altitude, condition of filters or other engine components,and differences among engines and other components in a production run may affect engine operation.

Summaryln at least some implementations, a method of controlling a fuel-to-air ratio of a fuel and air miXture supplied to an operating intemal combustion engine includesthe steps of determining a first engine speed before changing and preferably enleaningthe fuel-to-air miXture supplied to an operating engine, enleaning the fuel-to-air ratio,determining a second engine speed near or at the end of the enleanment, after endingthe enleanment (retuming to the fuel-to-air ratio just before enleanment) determiningWhether the engine speed recovers Within a predetermined range of the first enginespeed and if so determining a delta speed difference between the first engine speedand the second engine speed and if the delta speed difference is a positive valueenriching the fuel-to-air ratio of the miXture supplied to the engine or if the deltaspeed difference is a negative value enleaning the fuel-to-air ratio of the miXturesupplied to the engine. ln some implementations, the first engine speed may bedeterrnined for a first number of engine revolutions and the enleaning of thefuel-to-air ratio may occur for a second number of engine revolutions greater than the first number of engine revolutions. ln some implementations, a plurality of delta speed differences between the first and second engine speeds may be determined andif more than half of this plurality of the delta speed differences are positive values,enriching the fuel-to-air ratio supplied to the engine or if more than half of thisplurality are negative values, enleaning the fuel-to-air ratio of the mixture supplied tothe engine.

In at least some implementations, a method of controlling engine idle speedincludes: comparing engine speed to a speed threshold where the speed threshold mayinclude a range of speeds; if the engine speed is outside of the speed threshold, adjusting the timing of anignition spark up to a threshold amount of ignition timing adjustment; and if the engine speed is not within said speed threshold after adjustment up to thethreshold amount of ignition timing adjustment then adjusting the air/fuel mixtureprovided to the engine to bring the engine speed within said speed threshold.

In at least one example, the air/fuel mixture adjustment may be provided in anamount sufficient to reduce the magnitude of a previously made ignition timingadjustment. In at least one example, when the ignition timing adjustment reaches thehigh side of the threshold amount of ignition timing adjustment the fuel mixture isleaned out to increase the engine speed. The high side of the threshold amount ofignition timing adjustment may be the maximum increase in spark advance within thethreshold for ignition timing adjustment. And in at least one example, when theignition timing adjustment reaches the low side of the threshold amount of ignitiontiming adjustment the fuel mixture is enriched to decrease the engine speed. The lowside of the threshold amount of ignition timing adjustment may be the maximumdecrease in spark advance within the threshold for ignition timing adjustment.

In at least some implementations, a method of detecting engine cyclesincludes: deterrnining the time for consecutive engine revolutions; comparing the time of a revolution to a consecutive revolution; repeating the comparison for a first threshold number of revolutions; and deterrnining if every other revolution is either faster or slower than theintervening revolutions for a second threshold number of revolutions.

In at least one example, when the second threshold is satisfied an ignitionspark is skipped based upon the engine revolution timing.

In at least one example, if the second threshold is not satisfied within the firstthreshold number of engine revolutions, then an ignition spark is skipped every other engine revolution and then the engine speed is deterrnined. If the deterrnined engine speed indicates that the engine speed has not decreased below a threshold amount, theignition event skipping may be continued. And in addition to continuing the ignitionevent skipping, the fuel supply to the engine may be adjusted to correspond to theengine intake cycle. If the deterrnined engine speed indicates that the engine speedhas decreased below a threshold amount, the ignition event skipping may be changedto the opposite engine revolutions. After the ignition event skipping is changed, thefuel supply to the engine may be adjusted to correspond to the engine intake cycle.

In at least some implementations, a method of controlling engine accelerationor deceleration, includes: determining occurrence of an engine acceleration or deceleration;adjusting ignition timing within preselected threshold limits duringacceleration or deceleration of the engine; and adjusting an air-fuel mixture delivered to the engine during acceleration anddeceleration of the engine.

In at least one example, the ignition timing may be adjusted up to a thresholdamount of adjustment either before or while the air-fuel miXture adjustment occurs.When an engine acceleration is determined the ignition timing may be advanced andthe air-fuel mixture may be enriched. When an engine deceleration is deterrnined theignition timing may be retarded and the air-fuel miXture may be enriched. In at leastsome engine systems, the air-fuel miXture is controlled by controlling a valve thatreduces fuel flow to the engine and the air-fuel miXture may be controlled by reducingthe period of time that the valve reduces fuel flow to the engine to enrich the miXtureor by increasing the time that the valve reduces fuel flow to the engine to enlean the miXture.

Brief Description of the Drawings The following detailed description of preferred implementations and bestmode will be set forth with regard to the accompanying drawings, in which: FIG. l is a schematic view of an engine and a carburetor including a fuelmiXture control device; FIG. 2 is a fragmentary view of a flywheel and ignition components of theengine; FIG. 3 is a schematic diagram of an ignition circuit; FIG. 4 is a flowchart for an engine control process; FIG. 5 is a graph of a representative engine power curve; FIGS. 6-8 are graphs showing several variables that may be tracked during an engine speed test; FIG. 9 is a flow chart of an example of an engine idle operation controlprocess; and FIG. 10 is a flow chart of an example of an engine ignition and/or fuel controlprocess.

FIG. 11 is a graph of curves of lambda versus engine speed for a four-strokesingle cylinder small displacement engine; FIG. 12A is an initial part of a flow chart for an engine fuel control process; FIG. 12B is the rest of the flow chart of FIG. 12A for the engine fuel controlprocess; and FIG. 13 is a graph showing various variables of the engine fuel control processof FIGS. 12A and 12B of a four-stroke single cylinder engine.

Detailed Description Referring in more detail to the drawings, FIG. 1 illustrates an engine 2 and acharge forming device 4 that delivers a fuel and air mixture to the engine 2 to supportengine operation. In at least one implementation, the charge forrning device 4includes a carburetor, and the carburetor may be of any suitable type including, forexample, diaphragm and float bowl carburetors. A diaphragm-type carburetor 4 isshown in FIG. 1. mixture control device 8 capable of altering the air/fuel ratio of the mixture delivered The carburetor 4 takes in fuel from a fuel tank 6 and includes a from the carburetor. To determine a desired instantaneous air/fuel ratio, a comparisonis made of the engine speed before and after the air/fuel ratio is altered. Based uponthat comparison, the mixture control device 8 or some other component may be usedto alter the fuel and air mixture to provide a desired air/fuel ratio.

The engine speed may be determined in a number of ways, one of which usessignals within an ignition system 10 such as may be generated by a magnet on arotating flywheel 12. FIGS. 2 and 3 illustrates an exemplary signal generation orignition system 10 for use with an internal combustion engine 2, such as (but notlimited to) the type typically employed by hand-held and ground-supported lawn andgarden equipment. Such equipment includes chainsaws, trimmers, lawn mowers, andthe like. The ignition system 10 could be constructed according to one of numerousdesigns, including magneto or capacitive discharge designs, such that it interacts withan engine flywheel 12 and generally includes a control system 14, and an ignitionboot 16 for connection to a spark plug (not shown).

The flywheel 12 rotates about an axis 20 under the power of the engine 2 and includes magnets or magnetic sections 22. As the flywheel 12 rotates, the magnetic sections 22 spin past and electromagnetically interact With components of the controlsystem 14 for sensing engine speed among other things.

The control system 14 includes a ferromagnetic stator core or lamstack 30having wound thereabout a charge winding 32, a primary ignition winding 34, and asecondary ignition winding 36. The primary and secondary windings 34, 36 basicallydefine a step-up transformer or ignition coil used to fire a spark plug. The controlsystem also includes a circuit 38 (shown in FIG. 3), and a housing 40, wherein thecircuit 38 may be located remotely from the lamstack 30 and the various windings. Asthe magnetic sections 22 are rotated past the lamstack 30, a magnetic field isintroduced into the lamstack 30 that, in tum, induces a voltage in the variouswindings. For example, the rotating magnetic sections 22 induce a voltage signal inthe charge winding 32 that is indicative of the number of revolutions of the engine 2in the control system. The signal can be used to determine the rotational speed of theflywheel 12 and crankshaft 19 and, hence, the engine 2. Finally, the voltage inducedin the charge winding 32 is also used to power the circuit 38 and charge an ignitiondischarge capacitor 62 in known manner. Upon receipt of a trigger signal, thecapacitor 62 discharges through the primary winding 34 of the ignition coil to inducea stepped-up high voltage in the secondary winding 36 of the ignition coil that issufficient to cause a spark across a spark gap of a spark plug 47 to ignite a fuel and airmiXture within a combustion chamber of the engine.

In normal engine operation, downward movement of an engine piston during apower stroke drives a connecting rod (not shown) that, in tum, rotates the crankshaft19, which rotates the flywheel 12. As the magnetic sections 22 rotate past thelamstack 30, a magnetic field is created which induces a voltage in the nearby chargewinding 32 which is used for several purposes. First, the voltage may be used toprovide power to the control system 14, including components of the circuit 38.Second, the induced voltage is used to charge the main discharge capacitor 62 thatstores the energy until it is instructed to discharge, at which time the capacitor 62discharges its stored energy across primary ignition winding 34. Lastly, the voltageinduced in the charge winding 32 is used to produce an engine speed input signal,which is supplied to a microcontroller 60 of the circuit 38. This engine speed inputsignal can play a role in the operation of the ignition timing, as well as controlling anair/fuel ratio of a fuel miXture delivered to the engine, as set forth below.

Referring now primarily to FIG. 3, the control system 14 includes the circuit38 as an example of the type of circuit that may be used to implement the ignitiontiming control system 14. However, many variations of this circuit 38 may altematively be used without departing from the scope of the invention. The circuit 38 interacts With the charge winding 32, primary ignition winding 34, and preferably akill switch, and generally comprises the microcontroller 60, an ignition dischargecapacitor 62, and an ignition thyristor 64.

The microcontroller 60 as shown in FIG. 3 may be an 8-pin processor, whichutilizes internal memory or can access other memory to store code as well as forvariables and/or system operating instructions. Any other desired controllers,microcontrollers, or microprocessors may be used, however. Pin l of themicrocontroller 60 is coupled to the charge winding 32 via a resistor and diode, suchthat an induced voltage in the charge winding 32 is rectified and supplies themicrocontroller with power. Also, when a voltage is induced in the charge winding32, as previously described, current passes through a diode 70 and charges theignition discharge capacitor 62, assuming the ignition thyristor 64 is in a non-conductive state. The ignition discharge capacitor 62 holds the charge until themicrocontroller 60 changes the state of the thyristor 64. Microcontroller pin 5 iscoupled to the charge winding 32 and receives an electronic signal representative ofthe engine speed. The microcontroller uses this engine speed signal to select aparticular operating sequence, the selection of which affects the desired spark timing.Pin 7 is coupled to the gate of the thyristor 64 via a resistor 72 and transmits from themicrocontroller 60 an ignition signal which controls the state of the thyristor 64.When the ignition signal on pin 7 is low, the thyristor 64 is nonconductive and thecapacitor 62 is allowed to charge. When the ignition signal is high, the thyristor 64 isconductive and the capacitor 62 discharges through the primary winding 34, thuscausing an ignition pulse to be induced in the secondary winding 36 and sent on to thespark plug 47. Thus, the microcontroller 60 governs the discharge of the capacitor 62by controlling the conductive state of the thyristor 64. Lastly, pin 8 provides themicrocontroller 60 with a ground reference.

To summarize the operation of the circuit, the charge winding 32 experiencesan induced voltage that charges ignition discharge capacitor 62, and provides themicrocontroller 60 with power and an engine speed signal. The microcontroller 60outputs an ignition signal on pin 7, according to the calculated ignition timing, whichtums on the thyristor 64. Once the thyristor 64 is conductive, a current path throughthe thyristor 64 and the primary winding 34 is formed for the charge stored in thecapacitor 62. The current discharged through the primary winding 34 induces a highvoltage ignition pulse in the secondary winding 36. This high voltage pulse is thendelivered to the spark plug 47 where it arcs across the spark gap thereof, thus igniting an air/fuel charge in the combustion chamber to initiate the combustion process.

As noted above, the microcontroller 60, or another controller, may play a rolein altering an air/fuel ratio of a fuel mixture delivered by a carburetor 4 (for example)to the engine 2. In the embodiment of FIG. l, the carburetor 4 is a diaphragm typecarburetor with a diaphragm fuel pump assembly 74, a diaphragm fuel meteringassembly 76, and a purge/prime assembly 78, the general construction and function ofeach of which is well-known. The carburetor 4 includes a fuel and air mixing passage80 that receives air at an inlet end and fuel through a fuel circuit 82 supplied with fuelfrom the fuel metering assembly 76. The fuel circuit 82 includes one or morepassages, port and/or chambers formed in a carburetor main body. One example of acarburetor of this type is disclosed in U.S. Patent No. 7,467,785, the disclosure ofwhich is incorporated herein by reference in its entirety. The mixture control device 8is operable to alter the flow of fuel in at least part of the fuel circuit to alter the air/fuelratio of a fuel mixture delivered from the carburetor 4 to the engine to support engineoperation as commanded by a throttle.

For a given throttle position, the power output for an engine will vary as afunction of the air/fuel ratio. A representative engine power curve 94 is shown inFIG. 5 as a function of air/fuel ratio, where the air/fuel ratio becomes leaner from left-to-right on the graph. This curve 94 shows that the slope of the curve on the rich sideis notably less than the slope of the curve on the lean side. Hence, when a richer fuelmixture is enleaned the engine speed will generally increase by a lesser amount thanwhen a leaner fuel mixture is enleaned by the same amount. This is shown in FIG. 5,where the amount of enleanment between points 96 and 98 is the same as betweenpoints l00 and l02, yet the engine speed difference is greater between points l00 andl02 than it is between points 96 and 98. In this example, points 96 and 98 are richerthan a fuel mixture that corresponds to engine peak power output, while point l00corresponds to a fuel mixture that provides engine peak power output and point l02 isleaner than all of the other points.

The characteristics of the engine power curve 94 may be used in an enginecontrol process 84 that determines a desired air/fuel ratio for a fuel mixture deliveredto the engine. One example of an engine control process 84 is shown in FIG. 4 andincludes an engine speed test wherein engine speed is determined as a function of achange in the air/fuel ratio of the fuel mixture, and an analysis portion where datafrom the engine speed test is used to determine or confirm a desired air/fuel ratio ofthe fuel mixture.

The engine control process 84 begins at 86 and includes one or more enginespeed tests. Each engine speed test may essentially include three steps. The steps include measuring engine speed at 87, changing the air/fuel ratio of the fuel mixture provided to the engine at 88, and then measuring the engine speed again at 92 after atleast a portion of the air/fuel ratio change has occurred.

The first step is to measure the current engine speed before the fuel miXture isenleaned. Engine speed may be determined by the microcontroller 60 as noted above,or in any other suitable way. This is accomplished, in one implementation, bymeasuring three engine speed parameters with the first being the cyclic engine speed.This is the time difference for one revolution of the engine. In most engines, there isa large amount of repeatable cyclic engine speed variation along with a significantamount of non-repeatable cyclic engine speed variation. This can be seen in FIG. 6,where the cyclic engine speed is shown at 104. Because this cyclic variability isdifficult to use in further determinations, a rolling average (called Fl-XX) is created,where XX is the number of revolutions being averaged, and generally Fl is a lowaveraging value such as 4 or 6. This greatly eliminates the large repeatable cyclicengine speed variation but does not dampen out too much the non-repeatable cyclicengine speed variation. The third engine speed value is F2-XX, and P2 is a greateraveraging value, such as 80 revolutions. This amount of averaging greatly dampensout any variations of speed change and the intent is to dampen out the effect of theenleanment engine speed change. Now that there are two usable rpm values, F1-6 andF2-80 in this example, the difference of these values can be used to represent theengine speed change caused by the enleanment of the fuel miXture during an enginespeed test.

In addition to measuring engine speed, the engine speed test includes changingthe air/fuel ratio of the fuel miXture delivered to the engine. This may beaccomplished with the miXture control device, e. g. solenoid valve 8 may be actuatedthereby changing an air/fuel ratio of a miXture delivered to the engine 2 from thecarburetor 4. In at least some implementations, the solenoid valve 8 may be actuatedto its closed position to reduce fuel flow to a main fuel port or jet 90, therebyenleaning the fuel and air miXture. The valve 8 may be closed for a specific timeperiod, or a duration dependent upon an operational parameter, such as engine speed.In one form, the valve 8 is closed (or nearly closed) for a certain number or range ofengine revolutions, such as 1 to 150 revolutions. This defines an enleanment periodwherein the leaner fuel and air mixture is delivered to the engine 2. Near, at or justafter the end of the enleanment period, the engine speed is again determined at 92 asnoted above.

FIGS. 6-8 show engine speed (in rpm) versus number of engine revolutions during one or more engine speed tests. F1-6 is shown by line 106, F2-80 is shown by line 108, the solenoid actuation signal is shown by line 110, and a fuel/air ratio(Lambda) is shown by line 112.

FIG. 6 shows the initial air/fuel ratio to be rich at Lambda=0.81. The amountof enleanment in the example test was 50 degrees for 20 revolutions. This means thatthe solenoid valve was actuated 50 degrees earlier in the engine stroke than it wouldhave been for normal engine operation (e. g. operation other than during the test). Theincreased duration of solenoid actuation leads to an enleaned fuel mixture. From thisenleanment, the average rpm difference of F1-6 and F2-80 is 30 rpm. Because theenleanment is so large, 50 degrees, a decrease of 30 rpm is observed even though theinitial air/fuel ratio is still 6% richer than a fuel mixture ratio that would yield peakengine power.

FIG. 7 shows the same 50 degree enleanment test for 20 revolutions but thestarting air/fuel ratio is at Lambda = 0.876 which approximately corresponds to peakengine power. The average engine speed difference between F1-6 and F2-80 in thisexample is 148 rpm, approximately five times greater than the speed difference from astarting air/fuel ration of Lambda=0.81.

Because the process as described involves enleaning a fuel mixture, the initialor calibrated air/fuel ratio should be richer than desired. This ensures that at leastsome enleanment will lead to a desired air/fuel ratio. In at least someimplementations, the initial air/fuel ratio may be up to about 30% richer than the fuelmixture corresponding to peak engine power. Instead of or in addition to enleaning,enriching the fuel mixture may be possible in a given carburetor construction, and inthat case the engine speed test could include an enriching step if an unduly leanair/fuel ratio where deterrnined to exist. Enriching may be done, for example, bycausing additional fuel to be supplied to the engine, or by reducing air flow. Theprocess may be simpler by starting with a richer fuel mixture and enleaning it, asnoted herein.

Referring again to the engine control process shown in FIG. 4, the two enginespeed measurements obtained at 87 and 92 are compared at 93. To improve theaccuracy of the engine control process, several engine speed tests may be performed,with a counter incremented at 97 after each engine speed test, and the countercompared to a threshold at 99 to determine if a desired number of engine speed testshave been performed. If a desired number of tests have been performed, the process84 then analyzes the data from the engine speed test(s).

To determine whether the fuel mixture delivered to the engine before theengine speed tests were performed was within a desired range of air/fuel ratios, the engine speed differences determined at 93 are compared against one or more thresholds at 95. Minimum and maximum threshold values may be used for theengine speed difference that occurs as a result of enleaning the fuel mixture providedto the engine. An engine speed difference that is below the minimum threshold(which could be a certain number of rpm's) likely indicates that the air/fuel ratiobefore that enleanment was richer than a mixture corresponding to peak enginepower. Conversely, an engine speed difference that is above the maximum threshold(which could be a certain number of rpm's) indicates that the air/fuel ratio became toolean (indicating the fuel mixture started leaner than a peak power fuel mixture, asnoted above). In at least some implementations, the minimum threshold is l5rpm,and the maximum threshold is 500rpm or higher. These values are intended to beillustrative and not limiting - different engines and conditions may permit use ofdifferent thresholds.

In the process 84 shown in FIG. 4, the engine speed test is performed multipletimes in a single iteration of the process 84. ln one iteration of the process 84, it isdeterrnined at 95 if the engine speed difference of any one or more of the enginespeed tests is within the threshold values, and if so, the process may end at lOl. Thatis, if a threshold number (one or more) of the determined engine speed differencesfrom 93 are within the thresholds, the process may end because the starting air/fuelratio (e.g. the air/fuel ratio of the mixture prior to the first engine speed test of thatprocess iteration) is at or within an acceptable range of a desired air/fuel ratio. In oneimplementation, five engine speed tests may be performed, and an engine speeddifference within the thresholds may be required from at least three of the five enginespeed tests. Of course, any number of engine speed tests may be performed(including only one) and any number of results within the thresholds may be required(including only one and up to the number of engine speed tests performed).

If a threshold number of engine speed differences (deterrnined at 93) are notwithin the thresholds, the air/fuel ratio of the mixture may be altered at l03 to a newair/fuel ratio and the engine speed tests repeated using the new air/fuel ratio. At 95, ifan undesired number of engine speed differences were less than the minimumthreshold, the air/fuel ratio of the fuel mixture may be enleaned at l03 before theengine speed tests are repeated. This is because an engine speed difference less thanthe minimum threshold indicates the fuel mixture at 87 was too rich. Hence, the newair fuel ratio from l03 is leaner than when the prior engine speed tests wereperformed. This can be repeated until a threshold number of engine speed differencesare within the thresholds, which indicates that the fuel mixture provided to the enginebefore the engine speed tests were conducted (e.g. at 87) is a desired air/fuel ratio.

Likewise, at 95, if an undesired number of engine speed differences were greater than the maximum threshold, the air/fuel ratio of the fuel mixture may be enleaned less, oreven enriched, at 103 before the engine speed tests are repeated. This is because anengine speed difference greater than the maximum threshold indicates the fuelmixture at 87 was too lean. Hence, the new air fuel ratio from 103, in this instance, isricher than when the prior engine speed tests were performed. This also can berepeated until a threshold number of engine speed differences are within thethresholds, with a different starting air/fuel ratio for each iteration of the process.

When a desired number of satisfactory engine speed differences (i.e. betweenthe thresholds) occur at a given air/fuel ratio, that air/fuel ratio may be maintained forfurther operation of the engine. That is, the solenoid valve 8 may be actuated duringnormal engine operation generally in the same manner it was for the engine speedtests that provided the satisfactory results.

FIG. 8 shows a fuel mixture adjustment test series starting from a rich air/fuelratio of about Lambda=0.7, and ending with an air/fuel ratio of about Lambda=0.855.In this series, the enleanment step was repeated several times until a desired numberof engine speed differences within the thresholds occurred. That resulted in a chosenair/fuel ratio of about Lambda=0.855, and the engine may thereafter be operated witha fuel mixture at or nearly at that value for improved engine performance by controlof the solenoid valve 8 or other mixture control device(s).

As noted above, instead of trying to find an engine speed difference (afterchanging the air/fuel ratio) that is as small as possible to indicate the engine peakpower fuel mixture, the process may look for a relatively large engine speeddifference, which may be greater than a minimum threshold. This may be beneficialbecause it can sometimes be difficult to determine a small engine speed differenceduring real world engine usage, when the engine is under load and the load may varyduring the air/fuel ratio testing process. For example, the engine may be used with atool used to cut grass (e.g. weed trimmer) or wood (e.g. chainsaw). Of course, theengine could be used in a wide range of applications. By using a larger speeddifference in the process, the “noise” of the real world engine load conditions haveless of an impact on the results. ln addition, as noted above, there can be significantvariances in cyclic speed during normal operation of at least some small enginesmaking deterrnination of smaller engine speed differences very difficult.

As noted above, the engine load may change as a tool or device powered bythe engine is in use. Such engine operating changes may occur while the enginespeed test is being conducted. To facilitate deterrnining if an engine operatingcondition (e.g. load) has changed during the engine speed test, the engine speed may be measured a third time, a sufficient period of time after the air/fuel ratio is changed 11 during an engine speed test to allow the engine to recover after the air/fuel ratiochange. If the first engine speed (taken before the fuel miXture change) and the thirdengine speed (taken after the fuel miXture change and after a recovery period) aresignificantly different, this may indicate a change in engine load occurred during thetest cycle. In that situation, the engine speed change may not have been solely due tothe fuel miXture change (enleanment) during the engine speed test. That test data mayeither be ignored (i.e. not used in further calculation) or a correction factor may beapplied to account for the changed engine condition and ensure a more accurateair/fuel ratio deterrnination.

In one form, and as noted above, the miXture control device that is used tochange the air/fuel ratio as noted above includes a valve 8 that interrupts or inhibits afluid flow within the carburetor 4. In at least one implementation, the valve 8 affectsa liquid fuel flow to reduce the fuel flow rate from the carburetor 4 and thereby enleanthe fuel and air miXture delivered from the carburetor to the engine. The valve maybe electrically controlled and actuated. An example of such a valve is a solenoidvalve. The valve 8 may be reciprocated between open and closed positions when thesolenoid is actuated. In one form, the valve prevents or at least inhibits fuel flowthrough a passage 120 (FIG. 1) when the valve is closed, and permits fuel flowthrough the passage when the valve is opened. As shown, the valve 8 is located tocontrol flow through a portion of the fuel circuit that is downstream of the fuelmetering assembly and upstream of a main fuel jet that leads into the fuel and airmiXing passage. Of course, the valve 8 may be associated with a different portion ofthe fuel circuit, if desired. By opening or closing the valve 8, the flow rate of fuel tothe main fuel jet is altered (i.e. reduced when the valve is closed) as is the air/fuelratio of a fuel miXture delivered from the carburetor. A rotary throttle valvecarburetor, while not required, may be easily employed because all fuel may beprovided to the fuel and air miXing passage from a single fuel circuit, although othercarburetors may be used.

In some engine systems, an ignition circuit 38 may provide the powernecessary to actuate the solenoid valve 8. A controller 60 associated with or part ofthe ignition circuit 38 may also be used to actuate the solenoid valve 8, although aseparate controller may be used. As shown in FIG. 3, the ignition circuit 38 mayinclude a solenoid driver subcircuit 130 communicated with pin 3 of the controller 60and with the solenoid at a node or connector 132. The controller may be aprogrammable device and may have various tables, charts or other instructionsaccessible to it (e.g. stored in memory accessible by the controller) upon which certain functions of the controller are based. 12 The timing of the solenoid valve, when it is energized during the portion of thetime when fuel is flowing into the fuel and air miXing passage, may be controlled as acalibrated state in order to determine the normal air/fuel ratio curve. To reduce powerconsumption by the solenoid, the fuel miXture control process may be implemented(that is, the solenoid may be actuated) during the later portion of the time when fuelflows to the fuel and air miXing passage (and fuel generally flows to the fuel meteringchamber during the engine intake stroke). This reduces the duration that the solenoidmust be energized to achieve a desired enleanment. Within a given window,energizing the solenoid earlier within the fuel flow time results in greater enleanmentand energizing the solenoid later results in less enleanment. In one example of anenleanment test, the solenoid may be energized during a brief number of revolutions,such as 30. The resultant engine speed would be measured around the end of this 30revolution enleanment period, and thereafter compared with the engine speed beforethe enleanment period.

With a 4-stroke engine, the solenoid actuated enleanment may occur everyother engine revolution or only during the intake stroke. This same concept ofoperating the solenoid every other revolution could work on a 2-stroke engine withthe main difference being the solenoid energized time would increase slightly. Atslower engine speeds on a 2-stroke engine the solenoid control could then switch toevery revolution which may improve both engine performance and system accuracy.

FIG. 11 illustrates lambda versus RPM curves for a spark ignited gasolinepowered four-stroke engine with a displacement of 25 cubic centimeters (cm3). Thisis a single cylinder engine with a diaphragm carburetor 4 of the type shown in FIG. 1which includes a miXture control device 8, such as a norrnally open solenoid valve, anignition system 10, control system 14, and a control circuit such as the control circuit38 with a microcontroller 60. This engine was designed to be used on a lawn trimmerwhich may have a working head such as a string trimmer or a rotary blade trimmer.This engine may have a peak power output in the range of about 6,000 rpm to 11,000rpm with a lambda air-to-fuel ratio of substantially 0.85.

FIGS. 12A and 12B combined, provide a flow chart of at least some of thesteps of a fuel control process which may be used to determine and control theair-to-fuel ratio of a small displacement engine which may have a single cylinder witha displacement in the range of about 15-60 cubic centimeters (cm3) including such anengine norrnally operating in the range of about 3,000 - 11,000 rpm such as, forexample, the spark ignited gasoline powered single cylinder engine with a 25 cm3 displacement with the lambda curves of FIG. 11. FIG. 13 illustrates a graph of engine 13 speed and lambda data of this engine having the lambda versus RPM curves ofFIG. 11 during a portion of the process of the flow chart of FIG. 12A and 12B.

As shown in PIGS. 12A and 12B an engine control process 450 begins at 452typically on or shortly after engine start up and proceeds to step 454 to deterrnine ifthe engine is operating at a speed R1 significantly greater than its idling speed, such asin the range of 6,500 - 10,000 rpm. If not, it retums to the start and repeats step 454until it has determined that the engine is operating in the speed range R1 and if so,proceeds to both the steps 456 and 458. ln step 456, the microcontroller accumulatesand stores the engine speed for 80 consecutive revolutions (PRPM - 80) on a first in,first out (PIPO) basis for use in a downstream step.

In step 458, it is determined whether or not the engine is operating at arelatively constant or stable speed by determining whether the engine speed varied byless than 250 rpm over a period of 50 consecutive revolutions. lf not, the processreturns to step 454. If so, the process advances to steps 460 and 462. ln step 460,microcontroller counts a number of consecutive engine revolutions, such as 200revolutions, and when it reaches 200 revolutions returns the process to step 454 andbegins counting the next 200 engine revolutions. Thus, all of the remaining steps areaccomplished within 200 engine revolutions or aborted and retumed to step 454.

In step 462, either a total or average engine speed for 6 revolutions(P1 rpm - 6) is determined and held in a buffer immediately before starting a fuelmixture enleanment step 464. ln step 464, the air-to-fuel ratio supplied by thecarburetor to the operating engine is enleaned for a fixed number of enginerevolutions significantly greater than P1 rpm - 6 such as, for example, 50 revolutions.In step 466, the engine speed is determined for a small number of revolutions near orat the end of the enleanment of step 464, such as the last six revolutions of theenleanment (P2 rpm - 6) and stored for potential use in some subsequent steps.

After ending of the enleanment, the process may advance to step 468 todetermine whether the engine has recovered from the enleanment after the air-to-fuelratio retums to that used before the start of the enleanment. In step 468, a comparisonis made between the engine speed P1 rpm - 6 (just before enleanment) to determinewhether within 75 consecutive engine revolutions it becomes approximately equal toPRPM - 80 determined in step 456. If not, the remainder of the process is aborted andit retums to the beginning of step 454. If step 468 deterrnines the engine speed hasrecovered within 75 revolutions, the process may then proceed to step 470 whichdeterrnines and stores the difference (Arpm) between the engine speed near or at theend of the enleanment (P2 rpm - 6) and the engine speed just before starting the enleanment (P1 rpm - 6). Desirably, but not necessarily, this Arpm is stored for at 14 least a few repetitions of the steps of 454 through 468, to provide several Arpm values(Arpm l-n) such as, for example, 1-5 values. The Arpm l-n values may be allsubstantially the same, or some positive and some negative. After obtaining andstoring l-n Arpm values, the process may advance to step 472 Which deterrninesWhether there is any significant change in any of the n values of Arpm such as in 5values. If all 5 values fall Within a predetermined range of speed change, such a -85rpm to +100 rpm, step 472 considers this to be no substantial change and advances tostep 474 Which actuates the solenoid 8 to make a relatively small enleanment changein the air/fuel ratio such as not more than 1% and desirably 0.25% or a quarter of onepercent and at step 476 the microcontroller changes the solenoid open time to do so.

If step 472 determines that any of the Arpm l-n values Were a substantialchange in engine speed (outside of the -85 to +100 rpm threshold), the processadvances to step 478 Which deterrnines Whether some fraction or portion of the speedchanges such as three out of five Were either positive Arpm or negative Arpm Within25 engine revolutions and if so, advances to step 480 Which deterrnines a relativelylarge change of the air/fuel ratio such as 5% should be made for the next series of nArpm values and advances to step 476 to control the solenoid to affect this relativelylarge change of the air/fuel ratio. If step 478 deterrnines that 3 of the 5 Arpm valuesWere neither positive nor negative Within 25 engine revolutions, the process mayproceed to step 482, Which deterrnines Whether at least 3 of these 5 Arpm values Wereeither positive or negative Within 50 engine revolutions, and if so, proceeds to step484, Which determines the solenoid open time for a medium change of the air/fuelratio such as 21/z% and then advances to step 476 to control the solenoid to affect thismedium change of the air/fuel ratio. In each of steps 480 and 482 if at least 3 of the 5Arpm changes (P2 - P1) are positive, an enrichment of the air-to-fuel ratio of 5% or21/z% respectively, is determined and made, or if at least 3 of the 5 Arpm changes arenegative, an enleanment of the air-to-fuel ratio of 5% or 21/z% respectively, isdeterrnined and made. In step 482, if 3 of the 5 Arpm speed changes are neitherpositive nor negative, then no change is made in the air-to-fuel ratio and the processreturns to the beginning of step 454.

In step 476, after each change of the solenoid closed or open time, the processreturns to the beginning of step 454 to develop an updated set of Arpm l-n values.Since the enleanment step 464 and recovery step 468 together are carried out in 125engine revolutions, and in step 460 the counter aborts the process after each 200engine revolutions, the engine typically Will reach a stable operating condition before the beginning of the next set of Arpm l-n values is deterrnined and saved in step 470.

As illustrated in FIG. 13, if the engine is operating at an A/F ratio of lambda0.835 at an P1 rpm - 6 speed of about 9,380 rpm just before its A/F ratio at 490 Wasenleaned 5% or to a lambda of about 0.877 for 50 revolutions, this resulted in anaverage engine speed for the last 6 revolutions of enleanment (P2 rpm - 6) of about9,305 rpm, and after this enleanment the FRPM - 6 engine speed recovered at 492 asdeterrnined in step 468 in about 30 revolutions, and as deterrnined in step 458 over250 revolutions the engine speed varied by less than 200 rpm. Thus, the Arpm[FÅFRPM - 6 last) - F1(FRPM - 6 before start)] of -75 rpm is a valid Arpm, asdeterrnined and saved in step 470. The next enleanment at 494, Which due to thecounter of step 460, starts 200 revolutions after the first enleanment at 490, of the A/Fratio by 5% to a lambda of about 0.835 for 50 revolutions resulted in an averageengine speed F; of the last 6 revolutions of this enleanment of 9,265 rpm. Theaverage engine speed P1 for the 6 revolutions just before the start of this nextenleanment is 9,370 rpm. After this second enleanment the engine speed recovered at496 Within 75 revolutions as determined in step 468 and as deterrnined in step 458 theAR1 for this second enleanment Was about 220 rpm. Thus the second enleanmentproduced a valid Arpmg engine speed change of -105 rpm as deterrnined and stored instep 470.

The process 450 may be repeated many times per minute of engine operationand therefore can provide extremely good control of the desired air/fuel ratio of theoperating engine over a Wide range of operating speeds. For example, if the engineWas running for one full minute at a speed in the range of 9,000-9,200 rpm the processcould obtain as many as about 45 sets of valid values for Arpm 1-5 on Which to makeany needed adjustments in the A/F ratio of the fuel mixture supplied by the carburetorto the running engine and With the engine operating for one minute at an essentiallyconstant speed in the range of 7,000-7,200 rpm the process could obtain about 35 setsof valid Arpm 1-5 values on Which to make any needed adjustments in the A/F ratio.

The number (x) of engine revolutions in each of steps 456 and 468 issignificantly greater than the number of engine revolutions in each of steps 462 and466, for example, may be at least 6 times greater, and desirably at least 9 timesgreater. The period of enleanment of step 464 needs to be long enough to potentiallyprovide a significant change in engine speed, and short enough that it does notsignificantly adversely affect engine performance. For example, in step 464 theperiod of enleanment may be at least 3 times, and desirably 7 times greater than thenumber of engine revolutions of step 462 or 466. The recovery period of step 468may be sufficient for the engine to return to a speed at least substantially equal to its speed just before beginning the enleanment of step 464, for example, at least for the 16 same number of engine revolutions as the period of enleanment, and desirably at least1.25 times such engine revolutions of enleanment.

For a gasoline powered spark ignited single cylinder 4-stroke engine with adisplacement of 15-60 cm3, the step 454 engine speed R1 may be at least 4,500 rpmand desirably at least 5,000 rpm, AR1 of step 458 may be at least 100 rpm for at least20 revolutions, P1 of step 462 and F; of step 466 may be for at least 3 revolutions, theenleanment of step 464 may be for at least 10 revolutions, and FRPM of step 456 andthe recovery of step 468 may be for at least 20 revolutions.

For a gasoline powered spark ignited single cylinder 2-stroke engine with adisplacement of 15-60 cm3, the step 454 engine speed R1 may be at least 4,000 rpmand desirably at least 7,000 rpm, AR1 of step 458 may be at least 100 rpm for at least20 revolutions, P1 of step 462 and F; of step 466 may be for at least 3 revolutions, theenleanment of step 464 may be for at least 20 revolutions, and FRPM of step 456 andthe recovery of step 468 may be for at least 40 revolutions.

Since the only sensor required for implementation of the process 450 is thespeed of the running engine, and this speed is already sensed and deterrnined by thecontrol circuitry 38 to select and provide the desired ignition timing of the operatingengine, this process may be implemented without any additional sensors of otherengine operating parameters and by the use of processes such as the process 450implemented by appropriate software eXecuted by the microcontroller and othercomponents of the control circuit 38 to determine and change as needed the A/F ratiofor efficient operation of the engine by controlling the open time or the closed time ofa solenoid actuated valve controlling the quantity of fuel in the air/fuel miXturesupplied by the carburetor to the running engine.

It is also believed possible to utilize the system to provide a richer air/fuelmiXture to support engine acceleration. This may be accomplished by altering theignition timing (e.g. advancing ignition timing) and/or by reducing the duration thatthe solenoid is energized so that less enleanment, and hence a richer fuel mixture, isprovided. When the initial carburetor calibration is rich (e. g. approximately 20-25%rich), no solenoid actuation or less solenoid actuation will result in a richer fuelmiXture being delivered to the engine. Further, if the amount of acceleration oracceleration rate can be sensed or determined, a desired enrichment amount could bemapped or deterrnined based on the acceleration rate. Combining both the ignitiontiming advance and the fuel enrichment during transient conditions, both accelerationand deceleration can be controlled for improved engine performance. lgnition timingmay be controlled, in at least some implementations, as disclosed in U.S. Patent No. 7,000,595, the disclosure of which is incorporated by reference herein, in its entirety. 17 Idle engine speed can be controlled using ignition spark timing. While notWishing to be held to any particular theory, it is currently believed that using a similarconcept, fuel control could be used to improve the idle engine speed control andstability. conditions such as come-down. The combination of ignition and fuel control during This could be particularly useful during the end of transient engine idle could improve engine performance. lgnition timing control is considered a fast response control method in that theengine speed or other engine parameter may change quickly When the ignition timingis changed. HoWever, the controllable engine speed range is constrained by themaximum and minimum amount of ignition timing advance the engine can tolerate.Air/fuel mixture changes are considered a someWhat sloWer response control methodin that the engine operating changes may be sloWer than With an ignition timingchange. Combining the sloWer response air fuel mixture control With the fasterresponse ignition control can greatly expand the engine speed control range, and thismay be particularly useful, in at least some engines and applications, at engine idle ornear idle operating speeds and conditions. Of course, the innovations disclosed hereinare not limited to idle and near-idle engine operation.

As noted above, the range of engine speed control that may be achieved byignition timing control (e. g. advancing or retarding ignition events) is confined to thecombustible range of ignition advance. Practical limitations could be even narroWerin any given engine application, around 20-30 degrees of ignition advance, to ensureproper engine performance such as acceptable acceleration, roll-out, come-down, etc.While most engines can experience performance benefits from ignition timing basedidle engine speed control, it is possible to exceed the ignition control range Which cannegatively affect engine performance in at least some instances, such as Whendifferent fuel is used or the air density changes from altitude and temperature changes.Some of these changes or combinations of changes can effectively exceed the ignitiontiming idle speed control range resulting in the idle speed exceeding its specified set-point. To expand the effective idle engine speed control Window the addition of fueland air mixture control (i.e. changing the air/fuel ratio of the mixture delivered to theengine) can be combined With ignition timing.

In a combined control system, a desired threshold of ignition timing changemay be established, and a desired engine idle speed threshold, likely set as a range ofspeed, may also be established. Idle engine speed outside of the engine idle speedthreshold may first result in a change of the engine ignition timing. The ignitiontiming may be altered up to the ignition timing change threshold, and if the engine speed ends up Within the engine idle speed threshold by only the change in ignition 18 timing, nothing more needs to be done. Subsequent engine speed changes may behandled in the same manner. lf, however, the ignition timing is altered up to thethreshold ignition timing change and the engine speed is still outside of the enginespeed threshold, then the fuel and air mixture ratio may be altered until the enginespeed is within the threshold. This combination of ignition timing control and air/fuelmixture control can greatly expand the ability to control engine idle speed for allenvironmental conditions. Further, utilizing the faster response ignition timingcontrol as the first measure to control engine idle speed enables more rapid enginespeed control in many instances, and only when that is insufficient is the slowerresponse fuel/air adjustment control implemented. This enables more rapid andresponsive engine speed control. lncreases in spark advance (where the spark is the start of an ignition event)generally result in increases in engine speed and decreases in spark advance generallyresult in engine speed decreasing. Likewise since most small engine carburetors areinitially set with a slightly rich air/fuel mixture (and slightly open throttle valvesetting), increasing the air/fuel mixture ratio (which makes the air/fuel mixture leaner,for example from 9:1 to 11:1) will result in an engine idle speed increase anddecreasing the air/fuel mixture (which makes the air/fuel mixture richer, for examplefrom 13:1 to 10: 1) will generally result in an engine speed decrease.

In a representative system, the ignition timing control threshold may be set atplus or minus four (4) degrees of the normal ignition timing, where the degreesindicate the angular engine position relative to TDC or some other reference positionat which the ignition spark is provided. Once the ignition control threshold isexceeded on the high side (e.g. at +4°) the fuel mixture can then be leaned out toincrease the engine speed while maintaining the ignition timing within the threshold,or even allowing a reduction in the magnitude of the ignition timing change from thenominal/norrnal ignition timing. Likewise, if the ignition timing advance is reducedbelow the low threshold (e.g. -4°) the air/fuel mixture can be richened to reduce theengine speed while maintaining the ignition timing within the threshold, or evenallowing a reduction in the magnitude of the ignition timing change from the normalignition timing.

One representative control process 200 is generally shown in FIG. 9. Theprocess starts at 201, the engine speed is checked at 202 and a deterrnination is madeat 204 as to whether the engine is idling or near enough to idle for the process. In thisexample, the process is used only for engine idle and near idle operation and otherstrategies may be used when the engine is not at or near idle, if desired. If the engine operation does not satisfy the first condition then the process may end at 205. If the 19 engine operation satisfies the first condition, then it is determined in 206 whether theengine speed is within a desired range for idle or near idle operation. If the enginespeed is within the threshold, then the process may be started over, to again checkengine idle operation as desired. This check may be run at any desired periodictiming.

If the engine speed is outside of the threshold, then it is deterrnined at 208whether the maximum ignition timing adjustment has already been made (i.e. if theignition timing is within a threshold range). If the ignition timing is within itsthreshold, then the ignition timing may be adjusted at 210 up to its threshold in one ormore iterative steps or otherwise, as desired. If additional ignition timing is notavailable within that threshold, then the process continues to 212 where the air/fuelmixture may be adjusted to provide a desired engine speed change. The process maycontinue to check engine speed periodically (such as every revolution or at longerintervals) or the process may end. The process may be run again, as desired, tomonitor and change as needed the engine idle speed operation.

Additional control calibration techniques can be applied to further refine theidle speed stability and accuracy. Things like looking statistically at the number ofrevolutions or time the ignition timing has exceeded the threshold or the standarddeviation of the ignition timing value exceeding the threshold value can further refinethe strategy. Among other things, the normal ignition timing may be altered, and orthe ignition timing control threshold adjusted, depending upon actual engine operatingdata.

By knowing which phase the engine is operating on the total electrical powerconsumption used by the engine can be greatly reduced when only consumingelectrical power every other revolution. This is particularly beneficial at low enginespeeds when the power generation capacity of the ignition module is often less thanthe required power to control the engine every revolution (ignition timing andsecondary electrical loads such as an electronic carburetor).

Four stroke engines have four distinct cycles; intake, compression, power andexhaust. These four cycles take place over two engine revolutions. Beginning at TDCthe intake cycle begins and at the subsequent BDC the intake cycle ends and thecompression stroke begins. At the next TDC the compression cycle is completed andthe power stroke begins. At the next BDC, the power cycle is completed and theexhaust stroke begins. Hence, the intake and compression cycles occur in one enginerevolution and the power and exhaust cycles occur in the next engine revolution. Thetime for the engine revolution including the intake and compression cycles is greater (slower engine speed) than the time for the engine revolution power and exhaust cycles (faster engine speed). This is largely due to losses from intake pumping andcompression resulting in the engine speed decreasing during the intake andcompression engine revolution. Conversely during the power or combustion cycle theengine speeds up due to the increase in pressure developed during a combustionevent.

The difference in speed is detectable with the use of a microprocessor clocksuch as is found in digital ignition modules. Measuring the time for an enginerevolution may be performed on small engines that have a single magnet groupmounted on/in the flywheel. As the flywheel magnet rotates past the ignition modulean electrical signal is produced that can be used as a crankshaft angle measurement.Every engine revolution produces one electrical signal therefore the time betweenthese signals represents the average engine speed for a single revolution. Furtherrefinement of this concept can be done with multiple magnet groups thereby allowingdetection of the individual engine cycles rather than the just the engine revolution thatproduces power. This also will result in greater crankshaft angular resolution (abilityto determine crankshaft position) within a single engine revolution.

Since there can be a large amount of cyclic variation from revolution torevolution, it sometimes can be difficult to guarantee the deterrnination of the enginerevolutions (e. g. the revolution that corresponds to the intake and compression cycles,or the revolution that corresponds to the power and exhaust cycles).

To improve the accuracy of phase detection, a process that deterrnines enginespeed for a number of engine revolutions may be used. An example of such a processis described below. At engine startup, an ignition spark is provided every enginerevolution, as is common, and a threshold number of engine revolution speeds or timeis recorded. ln one example, the time for each of 20 engine revolutions is recorded,and this data may be recorded in any suitable manner on any suitable device, such asbut not limited to a First-ln-First-Out (FIFO) buffer. In this way, the last or mostrecent 20 engine revolution times/speeds are stored. Of course, the data for more orfewer engine revolutions may be used and 20 is just one example.

After a threshold number of engine revolutions, for example chosen to permitthe engine speed to stabilize, the recorded engine revolution data is checked to see ifan altemating pattem has occurred, for example where every other revolution islonger than the intervening revolutions. The second threshold may be any desirednumber of engine revolutions, or it may simply be a time from engine start or otherengine event. In one example, the second threshold is l2 revolutions although other numbers of revolutions can be utilized as desired. 2l The process may look at any number of engine revolution times/speeds todetermine if a desired pattern has occurred. For example, the process may look at all20 recorded engine revolution times to determine if the desired timing pattern hasoccurred. And the process may continue until 20 consecutive engine revolutionsshow a desired timing pattern, e. g. every other revolution being shorter or longer thanthe intervening revolutions. This analysis may be conducted for a given number ofengine revolutions after engine starting, or some other chosen engine event. Forexample, in one form, this analysis of the last 20 revolutions occurs for only the first50 engine revolutions after engine starting. This relatively short window may bechosen to reduce the likelihood that the engine operation will change (for example,due to throttle valve actuation) which would cause an engine speed change not due tothe various engine cycle effects.

A general description of the process 300 is shown in FIG. l0. At 306 it isdeterrnined if the desired number of consecutive (or perhaps a threshold percentageof) engine cycles indicates a desired pattern of engine speed changes within a desiredwindow of engine revolutions, then the process may continue to 308 wherein anignition event is skipped every other revolution. In one form, the ignition event isprovided only during the engine revolution including the power cycle and an ignitionspark is not provided during the engine revolution including the intake andcompression cycles. This avoids wasting an ignition spark and the energy associatedtherewith. Also, fuel may be provided from the carburetor or other fuel supplyingdevice only during the correct engine revolution or cycle, e.g. the engine revolutionincluding the intake and compression cycles, which is noted at 3l0. In this way, moreefficient engine operation can be achieved to conserve electrical energy, conserve fueland reduce engine emissions.

When ignition events are skipped, a check of the engine speed can beperformed at 3l2 to ensure that the engine speed is not adversely affected, whichcould mean that the incorrect spark is being skipped. For example, if after a couple ofskipped ignition events the engine speed decreases beyond a threshold, this couldmean that the ignition spark needed for combustion was skipped. If an engine speeddecrease is detected, the ignition spark may be provided every engine revolution at3l4, or the skipped spark may be changed to the other engine revolution and a checkof the engine speed performed to see if the ignition spark is being provided during thecorrect engine revolution.

The engine speed check may occur as the revolutions are recorded, or thecheck may look to previously recorded data for engine revolutions. In the example below, the most recent engine revolution recorded is rpm[0], the previous revolution 22 is rpm[-l], the revolution before that is rpm[-2], etc. For the engine cycle/revolutiondetection to be considered successful , then the recorded revolution data needs tosatisfy: ( rpm[0] > rpm[-1] ) AND ( rpm[-1] < rpm[-2] ). lf satisfied, then the reviewcontinues to ( rpm[-2] > rpm[-3] ) AND ( rpm[-3] < rpm[-4] ). And so on until athreshold number of revolutions satisfy the pattern, where the threshold number ofrevolutions needed can be any number up to and including all of the revolutionsstored on the buffer. When the threshold number of revolutions satisfies the pattern,the system moves to the next phase which is to skip ignition events and provide fuelin accordance with the determined engine revolutions and the engine cycles occurringduring these revolutions.

If the desired number of consecutive engine revolutions does not indicate adesired pattern of engine speed changes within a desired window of enginerevolutions (a "no" response at 306), then the ignition event may be terminated or notprovided every other engine revolution for a determined number of enginerevolutions. While in FIG. 10 the "skip ignition" step is shown as 308 in eitherdetermination from 306, where the threshold revolution criteria is satisfied at 306, the"skip ignition" occurs based on this data, and when the criteria is not satisfied, theskip ignition occurs based on something else. When to skip the spark may be chosenbased upon an analysis of the recorded revolutions (e. g. if more revolutions are slowerthan the others, on an every other revolution basis, then this information may be usedfor the initial spark skip even though the full threshold of revolutions did not satisfythe set rule) or the next scheduled or any subsequent spark may be skipped withoutregard to the recorded data. In one example, an ignition event is skipped every otherengine revolution for four engine revolutions. If the engine speed does not decreasebeyond a threshold after the skipped ignition events (as determined at 312), then thesystem considers that the ignition events were skipped during the correct enginerevolutions. Subsequent ignition events may also be skipped during correspondingengine revolutions, and the fuel supply may also be controlled based on this timing.If, however, the engine speed does decrease beyond a threshold after the skippedignition events, then the ignition events were skipped during the incorrect enginerevolutions. Subsequent skipped ignition events can then be set to the other enginerevolutions and the fuel supply to the engine may also be controlled based on thistiming. Subsequent checking of engine speed may also be used to ensure the skippedignition events are not adversely affecting engine speed.

Additionally statistical analysis of the altemating pattem can be performed to provide an accurate determination of engine cycle/phase when there are larger 23 amounts of cyclic variation or small differences in cyclic engine speed. This type ofanalysis can be done to effectively reduce the deterrnination time required.

In general, most small engines idle run quality is best when the ignition timingis slightly retarded and the air/fuel mixture is near optimum. But during theseconditions most small engines will also experience performance problems during fasttransient accelerations and decelerations. To help alleviate this issue, both rapidlyadvancing the ignition timing and enriching the fuel mixture for several revolutionscan improve engine performance. The difficulty in doing so on small low costengines stems from not having sensors to indicate that a rapid load change is startingto occur, such as a throttle position sensor or a manifold pressure sensor.

This disclosure describes how using the raw ignition signal along withcontrolling ignition timing and fuel mixture on a cyclic basis can improve engineperformance during these fast transient conditions. Controlling ignition timing basedon transient changes in the ignition signal has been described in U.S. Patent7,l98,028. Use of these detection methods can now be applied to rapidly change theignition timing and also rapidly change the fuel mixture via an electronic fuel controlactuator in the carburetor, thereby improving the acceleration and decelerationqualities of the engine.

One example of a fuel control actuator includes a solenoid that blocks at leasta portion of the fuel flow during the engine intake cycle. As an example, if theblocking action norrnally occurs at the end of the intake cycle, the fuel mixture canbe leaned-out by activating a norrnally open solenoid at an earlier crank angleposition, in other words by blocking at least some fuel flow for a longer duration ofthe intake cycle. Many possible calibration configurations exist but an example mightbe activating the solenoid at 200° ATDC results in a Lambda value of 0.78 (rich) anda solenoid activation angle of l45°ATDC results in a Lambda value of 0.87 (9%leaner). Therefore, changing the solenoid activation angle to a richer Lambda setting(less fuel flow blocking) during transient accelerations can improve the engineresponse and performance. This enriching of the mixture during acceleration can betailored up to a full rich setting (no solenoid activation, so no fuel flow blocking) andalso controlled for any number of engine revolutions after the detection of a transientchange has occurred. Additionally, the fuel flow control can be optimized in anynumber of ways, for example, running full rich (no fuel flow blocking) for a certainnumber of revolutions and decreasing the richness of the fuel mixture (i.e. increasingthe fuel flow blocking) at a set rate for a certain number of additional revolutions. Injust one of nearly limitless examples, no fuel flow blocking may be provided for 3 revolutions and the richness may be decreased (i.e. increased fuel flow blocking) for 24 revolutions. Many additional options for the actual control calibration exist.Likewise control of the deceleration performance can be improved through similarcontrol techniques, and in at least some implementations, the richness of the fuelmiXture can be increased (i.e. decreasing the fuel blocking) during the decelerationevent. During acceleration, the ignition timing may also be advanced up to itsmaximum advancement, Which may be a predeterrnined and/or calibrated valuerelative to a nominal or normal ignition timing for a given engine operating condition.During deceleration or come-down periods, the ignition timing may be retarded for adesired time (such as, but not limited to, a certain number of revolutions). When toalter/retard/advance the ignition timing and by how much to alter the timing may bepredeterrnined or calibrated values. In this Way, the ignition timing and fuel controlmay be adjusted together or in series during acceleration and deceleration of theengine.

While the forms of the invention herein disclosed constitute presentlypreferred embodiments, many others are possible. It is not intended herein to mentionall the possible equivalent forms or ramifications of the invention. It is understoodthat the terms used herein are merely descriptive, rather than limiting, and that various changes may be made Without departing from the spirit or scope of the invention.

Claims (22)

1. Claims:1. A method of contro11ing a fue1-to-air ratio of a fue1 and air miXture supplied to an operating engine, comprising the steps of: (a) deterrnining a first engine speed before en1eaning the fue1 and air miXture supplied to the engine for a first number of engine revo1utions; (b) en1eaning the fue1-to-air ratio of the miXture for a second number of engine revo1utions greater than the first number of engine revo1utions; (c) deterrnining a second engine speed for a third number of enginerevo1utions near or at the end of the second number of engine revo1utions; (d) after ending the en1eaning, determining Whether the engine speedrecovers Within a predeterrnined recovery range of the first enginespeed Within a predetermined fourth number of engine revo1utionsgreater than the third number of engine revo1utions and, if so,deterrnining a de1ta speed difference between the first engine speed and the second engine speed; and (e) if the de1ta speed difference is a positive va1ue enriching the fue1-to-airratio of the miXture supp1ied to the engine or if the de1ta speeddifference is a negative va1ue en1eaning the fue1-to-air ratio of the miXture supp1ied to the engine.
2. 2. The method of c1aim 1, further comprising repeating steps (a) through (d) toobtain a p1ura1ity of de1ta speed differences and if at 1east one ha1f of the p1ura1ity ofde1ta speed differences are a positive va1ue enriching the fue1-to-air ratio supp1ied tothe engine or if a negative va1ue en1eaning the fue1-to-air ratio of the miXture supp1ied to the engine.
3. 3. The method of c1aim 2, Wherein the p1ura1ity of de1ta speed differences is at 1east five speed differences.
4. 4. The process of c1aim 1, Which a1so comprises determining Whether theengine is operating at a speed of at 1east 4,000 rpm during each of steps (a) through(d) and if not, not using the de1ta speed difference in step (e), or Which process a1so comprises deterrnining Whether the engine is operating ata speed of at 1east 5,000 rpm during each of steps (a) through (d) and if not, not usingthe de1ta speed difference in step (e). 26
5. 5. The process of c1aim 1, Which also comprises before step (a), determiningWhether any change in engine speed over at 1east 20 revo1utions is 1ess than 250 rpmand on1y if so, proceeding to step (a) of determining a first engine speed, or Which process a1so comprises before step (a), deterrnining Whether any changein engine speed over at 1east 20 revo1utions is 1ess than 100 rpm and on1y if so, proceeding to step (a) of deterrnining a first engine speed.
6. 6. The method of c1aim 1, Wherein the first number of engine revo1utions is at1east 3 revo1utions, or Wherein the first number of engine revo1utions is at 1east 6 reVo1utions.
7. 7. The method of c1aim 1, Wherein the third number of engine revo1utions is at1east 3 revo1utions, Wherein the third number of engine revo1utions is at 1east 6revo1utions, or Wherein the first number of engine revo1utions is the same as the third number of engine reVo1utions.
8. 8. The method of c1aim 1, Wherein the second number of engine revo1utions isat 1east 10 revo1utions, Wherein the second number of engine revo1utions is at 1east 20revo1utions, or Wherein the second number of engine revo1utions is at 1east 50 reVo1utions.
9. 9. The method of c1aim 1, Wherein the fourth number of engine revo1utions isat 1east 20 revo1utions, Wherein the fourth number of engine revo1utions is at 1east 40revo1utions or Wherein the fourth number of engine revo1utions is at 1east 75 reVo1utions.
10. 10. The method of c1aim 1, Which a1so comprises determining Whether steps(a) through (d) of c1aim 1 have been comp1eted Within a predeterrnined fifth numberof engine revo1utions and if not, not using in step (e) any de1ta speed difference not deterrnined Within such fifth predeterrnined number of engine revo1utions.
11. 11. The method of c1aim 10, Wherein the fifth number of engine revo1utions is at 1east 200 engine revo1utions.
12. 12. The process of c1aim 1, further comprising repeating steps (a) through (d)to obtain a p1ura1ity of de1ta speed differences and if a11 of such p1ura1ity of de1ta 27 speed differences are Within a predetermined range then enleaning the fuel-to-air ratioof the fuel miXture supplied to the engine a small amount of not more than 1% of the fuel-to-air ratio of step (a) before the enleaning of the fuel-to-air ratio.
13. 13. The method of claim 12, Wherein the predeterrnined range of such plurality of delta speed differences is in the range of -85 rpm to +100 rpm.
14. 14. The method of claim 1, further comprising repeating steps (a) through (d)to obtain a plurality of delta speed differences and Within 25 engine revolutions ifmore than half of such plurality of delta speed differences are outside of apredetern1ined speed range and positive values, enriching the fuel-to-air ratio suppliedto the engine or if negative values enleaning the fuel-to-air ratio of the miXturesupplied to the engine, and by a relatively large change of not more than 5% of thefuel-to-air ratio of the miXture supplied to the engine before enleaning the fuel-to-air ratio of the miXture supplied to the engine.
15. 15. The method of claim 14, Wherein for such plurality of delta speed differences such predetern1ined speed range is -85 rpm to +100 rpm.
16. 16. The method of claim 1, further comprising repeating steps (a) through (d)to obtain a plurality of delta speed differences Within 50 engine revolutions and morethan 25 engine revolutions and if more than half of such plurality of delta speeddifferences are outside a predeterrnined speed range and positive values or negativevalues, a relatively medium change of the fuel-to-air ratio of the fuel miXture suppliedto the engine is made of not more than 21/2% of the fuel-to-air ratio of the fuel miXturesupplied to the engine before enleaning the fuel-to-air ratio of the miXture supplied to the engine.
17. 17. The method of claim 16, Wherein the predeterrnined range for such plurality of delta speed differences is -85 rpm to +100 rpm.
18. 18. The method of claim 17, Wherein if more than half of such plurality ofdelta speed differences are positive values the fuel-to-air ratio of the miXture suppliedto the engine is enriched or is more than half of such plurality of delta speeddifferences are negative values the fuel-to-air ratio of the miXture supplied to the engine is enleaned. 28
19. 19. The method of claim 1, Wherein the fourth number of engine revolutions isat least six times greater than the third number of engine revolutions, or Wherein thefourth number of engine revolutions is at least equal to the second number of engine revolutions.
20. 20. The method of claim 1, Wherein the second number of engine revolutions is at least three times greater than the first number of engine revolutions.
21. 21. The process of claim 1 implemented by a microcontroller having an inputof the speed of the engine and an output controlling a Valve capable of changing the fuel-to-air ratio of the fuel and air miXture supplied to an operating engine.
22. 22. The process of claim 19 Wherein the engine is a single cylinder engine having a displacement of not more than 60 cubic centimeters. 29