CA1079591A - Apparatus for controlling the air-fuel ratio in an internal combustion engine - Google Patents

Abstract

APPARATUS FOR CONTROLLING THE AIR-FUEL RATIO
IN AN INTERNAL COMBUSTION ENGINE
Abstract of the Disclosure Apparatus for controlling the air fuel ratio in an in-ternal combustion engine to substantially maintain the ratio at a predetermined value while the engine is operating under various load conditions. The engine has a carburetor with an air passage-way through which air is drawn into the engine. Fuel is supplied to the carburetor through a fuel system and mixed with air passing through the carburetor. The carburetor has a conduit through which air is introduced into the fuel system and the engine further has a chamber for combustion of the resulting air-fuel mixture and combustion products are exhausted. The apparatus comprises an air metering unit fox metering the quantity of air introduced into the fuel system through the conduit to control the air-fuel ratio of the mixture. The presence of oxygen in the combustion products, which is a function of the air-fuel ratio of the mixture, is sensed and a first electrical signal representative of the oxygen content is supplied. The first electrical signal is compared with a prede-termined reference level which is a function of the predetermined value to produce a second electrical signal having first and second signal elements, a first signal element being produced when the air-fuel ratio of the mixture is greater than the predetermined level and a second signal element being produced when the ratio is less than the level. A control responsive to the second electrical signal supplies to the air metering unit a control signal by which the quantity of air introduced into the conduit is controlled. A
change in the control signal is produced whenever the second elec-trical signal has a transition from one signal element to the other thereby for the air metering unit to change the quantity of air introduced into the conduit by an amount necessary to substan-tially maintain the air-fuel ratio at the predetermined value,

Description

Background of the Invention This invention reIates to apparatus for controlling the operation of internal combustion engines and more'particularly to apparatus for controlling the ratio of air to fuel in a mix-ture to be combusted in such an engine.
The control of emissions from internal combustion en-gines and particularly automobile engines has become a major en-vironmental concern. Various federal and state regulatory agen-cies have promulgated emission standards for certain substances found in the combustion products entering the atmosphere through an engine's exhaus~, the most important of these substances being hydrocarbons, carbon monoxide and oxides of nitrogen. To meet emission control standards, various pollution control devices such as catalytic converters and thermal reactors have been de-veloped for use with'automobile engines to reduce the quantities , of unwanted substances emitted into the atmosphere to within pre-scribed limits. , It has been found that mos~ efficient removal of un-wanted substances by pollution control devices is achieved when an engine is operated within a narrow range of air-fuel ratio values for an air-fueI mixture combusted in an engine. Conse-quently, numerous systems have been developed which attempt to '~
maintain the air-fuel ratio of a mixture to be combusted in an ;~-engine within this value range. Examples of systems of this type are disclosed in United States patents 3,939,654, 3,946,198, 3,949,551 and 3,963,009. While the systems disclosed in these patents do tend to keep the air-fueI ratio for a mixture to be ' combusted within the value range where maximum efficiency in re- ~ ' moval is obtained, this is usually accomplished only by constantly '-' adjusting the air-fuel ratio. Further, overadjustments frequently occur whi'ch then require additionaI corrections and the systems respond to ~ransi~ory changes in an engine's operating character-istic to make adjustments when none are'actually needed.

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Summary of the Invention .
Among the several objects of the present invention may be noted the provision of apparatus for controlling the air-fuel ratio in an internal combustion engine; the pro~ision of such ap-paratus for more precisely maintaining the air-fuel ratio at a predetermined value while the engine'is operating under various load conditionsj the provision of such`apparatus for determining when an adjustment in the air-fuel' rat.io of a mixture to be com-busted in the engine should be made to maintain the air-fuel ratio at the predetermined value; che provision of such apparatus for taking a "second look" at a present air-fueL ratio value be-- fore making any ad~ustment thereby to avoid constant adjustment of the air-fuel ratio and response to transient operating condi-tions; the provision of such'apparatus which varies its response time as a function of whether the'engine is operating under steady state or non-steady state conditions; the provision of such appa-ratus which adjus~s the air-fuel' ratio to a preset value when, for example, power is first supplied to the apparatus after its in-stallation or after a power disruption; the provision of such .' apparatus in which the air-fuel ratio is maintained at its last adjusted value between the time the engine is shut down and the '.
next time it is started; the provision of such'apparatus which ~. .
prevents an adjustment in the air-fuel ratio during an engine cold start and when the engine is operated in a certain manner, for ' - example, at wide open throttle; and the provision of such apparatus which is compact in size and convenient to install and operates :;'':
reliablyO .
Briefly, apparatus of the present invention controls the air-fuel ratio in an internal combustion engine to substantially 30 maintain the 'ratio at a predetermined value while the engine is .
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' operating under various load condi~ions. The engine has a carbu- ' retor with at least one air passageway therein through which air is drawn into the engine and fuel from a source thereof is sup-plied to the carburetor through at least one uel system and mixed with the air as it passes ~hrough the carburetor. The carburetor has a conduit through which air is introduced into the system and the engine further has a chamber ~or combustion of the result-ing air-fuel mixture and means ~or exhausting the product~ of said combustion~ The apparatus comprises means ~or met~ring th~ quan-tity of air introduced into the fuel system through the conduit thereby to control the air-fuel ratio of the mixture. The pre-sence of oxygen in the products of combustion is ~ensed and a first electrical signal representative of the oxygen content there-in is supplied, the oxygen content being a Eunction of the air-fuel ratio of the mixture. Th~ first electrical signal is com-pared with a predetermined reference level which i~ a function of the predetermined value to produce a second electrical signal having first and second signal elements, a first signal element being produced when the air-fuel ratio of the mixture is greatex than the predetermined level and a second signal element being pxoduced when the ratio is less than the level. A controller responsive to the second electrical signal suppl ie5 to the meter-ing means a control signal by which the quantity of air intro-duced into the conduit is controlled and produces a change in the control signal whenever the second electrical signal has a transition from one signal element to the other thereby for the metering means to change the quanti~y of air introduced into the - ~
conduit by an amount necessary to substantially maintain the air- ;
fuel ratio at the predetermined value. Other objects and eatures will be in part apparent and in part pointed out hereinafter.
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Fig. 1 is a block diagram of apparatus of the present invention for controlling the air-fuel ratio in an internal com-bustion engine;
Fig. ~A is a sectional view of a carburetor illustratingthe low and high speed circuits of the carburetor and a s~ctional view of a first embodimen~ of an air metering unit o the appara tus of the ,present invention;
Fig. 2B i~ a sectional view of a second embodiment o an air metering unit o the apparatus of the present invention;
Fig. 3 is a schematic circuit diagram of a portion of the apparatus employed with either embodiment of the air metering unit;
Fig. 4 is a sche~atic circuit diagram of controller cir-cuitry of the apparatus for use with the ~irst embodiment of the air metering unit; and Fig. 5 is a ~chematic circuit diagram of controller cir- ~' cuitry of the apparatus for use with the second embodiment of the air metering unit. ', Corresponding reference characters indicate correspond~
ing parts throughout the several views o~ the drawings. ~' -' '.'': ' Referring no~ to the drawings, apparatus of the present ~'~
invention ~or controlling ~he air-fuel ratio in an interna}-com-bustion engine E to substantially maintain the ratio at a prede-termined value while the engine is operating under various load conditions is indicated generally at 1. Engine E has a carburetor ~';

3 with an air passageway 5 through which air is drawn into the ,;,,'- ,'~
engine and fuel F from a source 7 i5 supplied to the carburetor through a~ least one fuel system g and mixed with air passing through the carburetor. The carburetor also has a throttle valve 1, TV to control the flow rate of air through the carburetor and a ~ ' venturi 10 by which a pressure dif~erential is created so thak ~, fuel F is drawn through fuel system g and mixed with air to pro~
duce an air-fuel mixture~ all as is well known in the art~ Car~

'~' ' ~uretor 3 further has a conduit 11 throuyh which air is introduced into fuel systern 9 as will be discussed. ~ngine E further has a chamber 13 for comhustion of the resulting air-fuel mixture and an exhaust system 15 for exhausting the products o~ combustion.
An air metering uni~ generally indicated 17 meters the quantity of air introduced into fuel system 9 through conduit 11 to control the air-uel ratio of the mixture. The unit has an air inlet 19 and an air outlet 21 which communicates with conduit 11. A portion of the air entexing carburetor 3 through passage-way 5 enters a conduit 23 via an opening 25 in the side of the passageway and enters air metering unit 17 through inlet 19. This air enters a cham~er 27 in the metering unit and exits the chamber through outlet 21. Disposed in outlet 21 is a metering pin 29 ~
which is a tapered meterin~ pin and which is insertable into and withdrawable from the outlet to;aon~rol the quantity of air ad-mitted into conduit 11~ The position o metering pin 2~ irl outlet 21 i5 controlled ~y a positioner 31. Withdrawal of metering pin 29 from outlet 21 by the positioner admi~s more air in~o conduit 11 while insertion of the metering pin into the outlet admit~ less air into the conduit. With more air flowing through conduit 11 and entering uel system 9 there is a decrease in the flow rate o~
fuel through the system so that less fuel is mixed with air and the air-fuel ratio of the resulting mixture increases (i.e., the mixture becomes leaner). When less air enters uel system 9 through conduit 11 the flow rate of uel increases, more ~uel is mixed with the air and the air-fuel ratio decreases k.e., the mixture becomes richer). It will be understood that air rnetering unit 17 may be formed as part o~ carburetor 3 or may be a separate unit installed at a conveni~nt location with respect to engine E
and the carburetor.
Among the products of combustion exhausted through sys-tem 21 is free oxygen and the amount of this oxygen is a function of the air~fuel ratio of the mixture combusted in chamber 13, :~

i.e., the richer the mixture the less free oxygen is in the com bustion products and the leaner the mixtura the more free oxygen is present. The presence of oxygen in the products of combustion is sensed by an oxygen sensor 33 from which is supplied a ~irst electrical signal S1 representative of the oxygen content. The dashed line ~EF shown in Fig. 1 represents the oxygen content in the products of con~ustion at the predetermined air-~uel ratio value. Sensor 33 includes a detector 35 positioned in the exhaust system and responsive to ~he oxygen content to generate a voltage whose amplitude is a function of the oxygen content and inversely related thereto, i.e.,the more oxygen present in the exhaust sys-tem ~the leaner the mi*ture) the lower is the amplitude of the generated voltage and vice versa. The detector may be a zirconia type detector or any other suitable oxygen detector. The voltage generated by detector 35 i5 amplified by an amplifier 37 to pro-duce ~irst electrical signal Sl which is an analog signal.
A comparator 39, which is a voltage comparator, compares first electrical signal Sl (the amplitude of the signal) with a predetermined reference level V ref~ (a voltage le~el~ which is a function of the predetermined air-fuel ratio value at which engine E is to operate to produce a second electrical signal S2 having first and second signal elements. A first signal elemenk of the second electrical signal (a logic high) is produced when the air~
fuel ratio of the mixture is greater than the predetermined le~el (the amplitude of signal Sl is less than the re~erence voltage ~
level) and a second signal element (a logic low) is produced when ~ -the ratio is less than the value (the amplitude of signal Sl is greater than the reference voltage level). A transi~ion T from ~;
one signal element to the other occurs whenever the amplitude of signal Sl changes from greater to less than the reference volkage amplitude and vice versa.

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A controller 41 is responsive to second electrical signal S2 to supply to air metering unit 17, and specifically positioner 31 of the air metering unit, a control signal Sc by which the quan-tity of air introduced into conduit 11 is controlled. The control-ler includes a reversible'accumulating control counter 43 and a counter control 4~. The 'counter control is res'ponsive to first and second signal elements of the second electrical signal to increment and decrement the contents of the control counter. ~he contents of the control counter are'incremented when less air is to be intro-duced into conduit 11 and the air-fuel mixture made richer and decremented when more'air is to be introduced into the conduit and the mi~ture made leaner. A timing unit 47 generates a timing signal St having a plurality of signal elements whi'ch are supplied to a count input of control counter 43~ through counter control 45, to increment and decrement its contents. The contents of the control counter are incremented by elements of the timing signal when a first signal eLement of the'second electrical signal is ' supplied to counter control 45 and decremented by timing signal elements when a second signal element of the second elec~rical 2~ signal is supplied to the counter control. Controller 41 further includes an interface circuit 49 to which control counter 43 sup-plies a digital signal representative of the value of its contents. ',,' Interface 4g is responsive to the digital signal to produce the '~ -' control signal supplied to air metering unit 17. Controller 41 is responsive to the second electrical signal to produce a change in the control signal whenever the second electrical signal has a transition T from one'signal element to the other, i.e., the contents of control counter 43 are incremented instead of decrement-ed or vice versa. This res'ults in a change in ~he digital signal supplied to interface 49 and in the'control signal produced by the interface portion of the controller. A change'in the control sig- ' nal supplied to air metering unit 17 res'ults in the air metering ~-unit changing the quanti-ty of air introduced into conduit 11 by an amount necessary to substantiall~ maintain the air-~uel ratio at the predetermined value. Thus, a change in the control signal from controller 41 to positioner 31 of metering unit 17 produce~
a change in the position of metering pin ~9 in outlet 21 and modu-latee the quantity of air introduced into fuel system 9. The air-fuel ratio o~ the mixkure combusted in chamber 13 is thus varied and is driven toward the desired value.
Besides being supplied to controller 41, the second electrical signal is sampled b~ a samipler 51. This sampling occurs over a predet~rmined time in~erval starting when a signal element of the second electrical signal is producecl and its purpose i5 to determine whether a transition between signal elements occurs with-in the time interval. Elements of timing si~nal St are supplied to sampler 51 which includes a time delay counter 53 responsive to the timing signal elements for counting from zero to a preselected value which may, for example, be two and ~or inhibiting counter control 45 from incrementing or decrementing the contents of con-txol counter 43 until the preselected value is xeached. Delay counter 53 supplies first and second signal elements of a delay signal Sd to counter control 45~ A first signal element of the delay signal is supplied to counter control 45 whenever the value o the contents of delay counter 53 is less than the preselecte~i value and a second signal eleMent of the delay signal is supplied to the counter control when the preselected count value is reached.
When a irst signal element is supplied to counter control 45, the counter control is inhibited for passing timing signal elements to control counter 43, as will be discussed, and the contents of the counter are unchanged. Only when a second signal element of ~``
the delay signal is supplied to co~mter control 45 is the contents of counter 43 incremented or decremented. Further, sampler 51 includes a delay counter reset circuit 55 responsive to each tran-sition between signal elements of the seconcl electrical signalto reset tlle value of the clelay counter contents to zero. Con-sequently, if a txansition between signal elements of the second ..
electrical signal occurs within the predete.rmined time interval, i.e., before the count value o counter 53 reaches two, counter control 45 remains inhihited hecause it is still supplied with a first signal element of the delay signal and no change is pro-duced in the contents of control counter 43 or in the control si~nal supplied to air metering unit 17. Thusl controller 41 is responsiv~ to sampler 51 to produce a change in the eontrol signal only i~ no transition between signal elements occurs within the predetermined time interval. If a transition does occux within ..
: the interval, no change in the control signal is produced and the quantity of air introduced into conduit ll remains the same.
-~ The importance of this sampling feature is that it pre- .;
vents continuous adjus-tment of the air-fu~!~.ratio of the combusted : mixture. Thus, for example, momen ary or transient changes which .
occur do not result in an adjustment, when none is ac-~ually needed~
and eliminates the need for a second adjustment which would other-wise result when the transient change is overO By providing for ::
; a "second look'l at the air-fuel ratio relative to the predeter-mined value before making an adjustment, the apparatus responds only to Long term changes and makes an adjustment to the air-fuel ratio only when one is actually needed to rekurn the ratio value to the point where the most efficient removal of substances from ....-.
the exhaust products is accomplished as, for example~ by a cata-lytic converter 56 in the engine's exhaus~ system.
Referring to Fig. 3, the voltage developed by detec~or .. .
35 is supplied through a fil~er network comprised of a resistor Rl and a capacitor Cl and applied to one input (the non-inverting input) of amplifier 37 which is an operational amplifier and in cludes a capacitor CAo Preferably, the amplifier has a field-effect transistor (FET) input circuit which imposes a substantially zero current load on the detector. The amplifier gain-is determined by a pair of resistors R2 and R3 and a feedback capacitor C2 and is, for example, five. From the output of amplifier 37 is sup-plied first electrical signal Sl which is applied to one input of comparator 39, the inverting input of an operational amplifier, through a filter network comprised of a resistor R4 and a capac-itor C3. The comparator has a second input to which is applied the reference level V ref. This level is a voltage developed across a divider network comprised of a pair of resistors R5 and R6 and may, ~or example, represent the air-fuel ratio of the mix-ture at the stoichiometric point. The comparator circuitry fur-ther includes a feedback resistor R7 and a pull-up resistor R~.
First and second signal elements of the second electrical signal are supplied from the output of comparator 39. Because the first ; electrical signal is supplied to the inverting input of the com-parator, a first signal element of the second electrical signal, a logic high, is produced when the amplitude of the first electri-cal signal is less than the reference voltage amplitude and a sec-ond signal element, a logic low, is prod~lced when the amplitude of the first electrical signal exceeds the reference voltage ampli-tude.

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Sampler 51, as noted, includes delay counter 53 and coun-ter reset circuitry 55. Counter 53 is a two-stage binary counter comprised of a pair of ~lip-flops FFl and FF2 respectively. The data input to flip-flop FFl is grounded, while the data input of flip-flop FF2 is connected to the Q output o~ flip-flop FFl. Ele ments of delay signal Sd are supplied to counter control ~5 from the ~ output of flip-flop FF2. Counter reset circuitry 55 includes a pair of diodes Dl and D2 and a pair of R~C networks respectively comprised of a resistor ~9 and a capacitor C4 and a resistor RlQ

- and a capacitor C5. One side of capacitor C4 is connected to the ;- , 1 1 ' .~ , . . .

output of comparator 39, while one side of capacitor C5 is con-nected to the output of a NOR gate Gl which serves to invert the second electrical signal supplied by comparator 39. The cathodes of diodes Dl and D2 are commonly connected and are tied to the ~set input of flip-flop FFl and the reset input of flip-flop FF2.
Further, the cathodes are connected through a resistor Rll to the output of a NOR gate G2, the function of which will be discussed.
The resistance values of resistors R9 and R10 are each approxi-mately one hundred times larger than that of resistor Rll.
lQ With the logic output of gate G2 low, each transition between signal elements of the second electrical signal results in a positive pulse being applied to the set input of flip-flop FFl and the reset input of flip-flop FF2. An element of timing sig-nal St supplied to the clock input of each flip-flop at this time results in the Q output of flip-flop FFl going low and the Q output of flip-flop FF2 going high. This is the reset state of counter 53. When the next element of the timing signal is supplied to the clock inputs of the flip-flops, the ~ output of flip-flop FFl goes from low to high because the data input to the flip-flop is low.
The Q output of flip-flop FF2 however remains high. When the next or second signal element of the timing signal is supplied to the clock inputs of the flip-flops, the Q output of flip-flop E~F2 goes low because the data input to the 1ip-flop is now high. The ~
output of flip-flop FFl however remains high. Subsequent signal elem~nts of the timing signal supplied to the clock input of the flip-flops do not effect a change in the ~ output of either flip-flop unless the flip-flops are reset, in which instance the pre-ceding sequence of events is repeated. ~ first signai element of the delay signal corresponds to the logic high at the Q output 3~ of flip-flop FF2 prior to a second timing signal element being supplied to the clock input of the flip-flops after delay counter ~ ~
53 is reset. A second signal element of the delay signal corres- -~;
ponds to the logic low present at the Q output of flip-flop FF2 :" ~ ' .
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from the time the second timing signal element is supplied to the flip-flops, after the counter is reset, until the counter is again reset.
Elements of the timing signal generated by timing unit 47 and supplied to sampler 51 are developed at a junction point 57 within the timing unit. The timing unit includes a timing capa- ~;
citor C6 and if this capacitor is assumed to be discharged, a volt- -age corresponding to a logic high is present at the junction and is supplied through a resistor Rj. Capacitor C6 is negatively charged through a resistor Rc and the charge level of the capaci-tor is applied to one input of a comparator 58 which is the non-inverting input of an operational amplifier. A reference voltage .... . ..
corresponding to a predetermined charge level of capacitor C6 is applied to a second input of the comparator (the inverting input of the amplifier), this voltage being developed across a divider network comprised of a pair of resistors R12 and R13 respectively when an NPN transistor Ql is conducting and the logic output of a NOR gate G3is high. Base voltage for transistor Ql is supplied through a pair of resistors R14 and R15 respectively and with ca-pacitor C6 discharged, the transistor conducts. Connected between -~capacitor C6 and electrical ground is a PNP transistor Q2 which is biased off when a logic high is present at junction 57. The output of comparator 58 is connected to the base of transistor Q2 through a resistor R16~
With capacitor C6 discharged, a logic high is supplied from the output of comparator 58 because the voltage level at the non-inverting input to the comparator, which corresponds to the capacitor charge level, exceeds the reference voltage. As capa- ;
citor C6 charges, this voltage level decreases and eventually falls below the reference level. When this occurs, the logic out-put of comparator 58 goes low driving junction 57 low. Transistor Ql turns off because of coupling through a capacitor C7 to the low ~;

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comparator output while transistor Q2 is biased into conduction.
Wlth transistor ~2 on, capacitor C6 discharges through a resistor R17. Positive feedback to the non-inverting input of comparator 58 through a capacitor C8 and capacitor C7, forces a complete high to low transition in the comparator output signal. This logic low is maintained while capacitor C7 charges and transis~or Ql is switched back into conduction. Capacitor C6 fully discharges dur-ing this period and when transistor Ql agaln conducts the refer-ence level is again applied to the inverting input of comparator 58 causing a transition at the comparator output from a logic low to high. This takes transistor Q2 out of conduction and capacitor C6 starts charging again. At junction 57, a negative going pulse or signal element of the timing signal has been produced and sup-plied to the clock inputs of flip-flops FFl and FF2. ~;
Referring now to Figs. 2~ and 4, a irst embodiment of air metering unit 17 is shown (Fig. 2A) together with the controller 41 circuitry (Fig. 4) used with the unit. As shown in Fig. 2A, carburetor 3 contains ~wo fuel supply systems, a high-speed (main) system 9A and a low-speed (idle) system 9B. In high-speed system 9A, fuel flows from a bowl B through a metering jet 59 and the flow rate of fuel is controlled by a tapered metering rod 61 posi-tioned in the jet by throttle TV. Fuel metered through jet 59 enters a well 63 from which it is drawn into passageway 5 through a nozzle 65. In low-speed system 9B, fuel leaving jet 59 enters the system through a low-speed jet 67. The fuel is then mixed with air entering the system at an air bleed 69 and the mixture is accelerated through a restriction 71 and mixed with more bleed air entering the system through an air bleed 73. The resultant mixture is discharged into passageway 5 through idle ports 75 which are located downstream from closed throttle Tv For a carburetor 3 as shown in Fig. 2a, air metering unit 17 has two air outlets, 21A and 21B respectively, one for each fuel system and a metering pin ~9A and 29B is disposed in the respective outlets. Outlet 21A communicates with a conduit `
1~

11~ by which air is introduced into fuel system 9A and outlet 21B
communicates with a conduit llB by which air is introduced into fuel system 9B. Air flowing through conduit llA enters fuel sys-tem 9A at a point above the fuel level in well 63. The effect of varying the quantity of air entering system 9A through the conduit is to modulate, in effect, the vacuum pressure on the fuel and thus vary the quantity of fuel delivered through nozzle 65. Air flow-ing through conduit llB enters fuel system 9B between restriction 71 and idle ports 75~ Varying the quantity of air entering system 9B through conduit llB modulates the vacuum pressure at low-speed ~
jet 67 and this controls the quantity of fuel mixed with bleed air. -Metering pins 29A and 29s are both tapered and each is insertable into and withdrawable from its respective air outlet. Positioner 31 of metering unit 17 simultaneously positions both metering pins :
in their respective air outlets in response to the control signal supplied to the positioner from controller 41. It will be under-stood that while the same quantity of air may be in~roduced into fuel systems 9A and 9B through conduits llA and llB, the flow rate of air through the respective conduits is dependent upon which carburetor circuit is in use at any one time.
The positioner 31 shown in Fig. 2A includes a variable position solenoid 77 havin~ at least one and preferably two wind-ings, Wl and W2 respectively, to which the control signal is sup-plied. The solenoid further has an armature 79 movable in either of two directions between a first position Pl representative of a first value of the contents of control counter 43 and a second position P2 representative of a second value of the control counter contents. Position Pl corresponds to the dashed line position shown in Fig. 2A in which the upper end of armature 79 contacts a stop 81 formed on the inner surface of a pole piece 83, while posi-tion P2 corresponds to the dashed line position in Fig. 2A in which the lower end of armature 79 contacts a stop 85 formed on the inner ~.

surface o a pole piece S7. ~rmature 79 has a longitudinal cen-tral bore 59 in whic]l is inserted a shaft ~1 threaded at each end.
A plate 93 has a central threaded bore 95 and is mount~d on one end 97 of shaft 91. Thus, pla~.e 93 is movable with armature 79 as the armature moves het~en first and second positions Pl and P2. ~ pair of sockets 99 are formed in the upper ace of plate 93 and each metering pin has a stem 101 ~hose free end fits into one of these sockets. A spring 103 is positioned between each metering pin and a wall 105 of metering unit 17 to bias the pins toward a posi~ion to close the outlet in which each is disposecl.
Outwardly of each pole piece 83 and 87 is a ~croll spring 107 having a central bore 1~9 in which sha~t ~1 is disposed. The scroll springs are ma~e of a thin, resilient disk shaped mate-rial which is flexible in either direction depen~ing upon the position of armature 79 and shaft 91. Each spring has a portion cut away during its manufacture and the cuts are made in a pre-determined pattern so as armature 79 and shaft 91 move in one direction or the other hetween positions Pl and P2, when a change in the control signal supplied to windings Wl and W2 occurs, the moyement is linear and each movement is for an in-cremental distance between the two positions.
Referring to Fig~ 4, counter control 45 of controller 41 includes a pair of NO~ gates G4 and G5 and a N~ND gate G6.
The delay signal supplied by delay counter 53 is provided to one input of gates G4 and G5 on a line 107. The first and second sig- -nal elements of second electrical signal S2 are supplied to a sec- -ond input of gate G4 on a line 109, while elements of timing sig- ~ ;
nal St are supplied on a line 111 to a second input o~ gate G5 through a NOR gate G7 ~see FigO 3) which acts as an inverter.
The output of ga~e G5 is connected to one input o~ gate G6 and the output of gate G6 is connected to the count input of counter 43.

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Control counter 43 is a ~ive~stage binary counter whose contents may vary between a value of zero and thirty-one and armature 79 is thus movable to any of thirty-two discrete positions depending upon the value of the control counter contents. The position Pl which armature 79 of variable position solenoid 77 may attain corresponds to the zero ~alue while the position P2 corresponds to the value thirty~one. The logic output from gate G4 is supplied to an up/down input of the counter through an in~erter 112 and the logic level supplied to this input determines whether the counter ''~ ' contents are incremented or decremented, the contents being incre~
mented when a logic high is supplied to the input and decremented ' ' when a logic low is supplied to the input. Counter 43 has an in~ ', hibit output which is connected to a second input of gate G6 ~or , ' reasons to be discussed.
As previously indicated, a first si~nal element of delay signal Sd is supplied by delay counter 53 to counter control 45 ~
so long as the value o~ its contents is less than two. When this ', ' signal element (a logic high) is supplied to gate G5, the logic output of the gate is held low and passage o~ timing signal ele- , ments to'counter 43 is inhibited. When a second signal element o~ the delay signal (a logic low] is supplied to gate G5, elements of the timing signal are passed to gate G6. If the value of the contents o~ control counter 43 is less than thirty-one, when the counter is heing incremented, or more than zero when the counter is being decremented, the input signal to gate G6 ~rom the inhibit output of ~ounter 43 is a logic high and timing signal elements are passed to the count input of the counter. ~s the contents of counter 43 change, the digital signal output o~ the counter changes. This signal is supplied on lines 113~ through 113E to ~' inter~ace circuitry 49 and ~ore specifically, to a digital-to-ana- , log converter 115. The digital-to-analog converter is comprised o~ resistors R18, Rl9, R20, R21 and R22 and produces an analog signal Sa at a summing point 117. The amplitude o~ the analog -,~
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signal is a function of the value of the contents of counter 43 and is increased a predetermined amount each time the contents of counter 43 are incremented, decreased by the same predetermined amount each time the counter contents are decremented and remains the same so long as sampler 51 inhibits the supply of timing sig-nal elements to counter control 45.
The analog signal produced at summing point 117 is sup-plied through a current limiting resistor R23 and a resistor R24 to one input of a comparator 119, the non-inverting input of an operational amplifier. The analog signal is fllrther supplied to a unity gain inverting amplifier 121 which includes an operational amplifier 123, an input resistor R24, a pair of resistors R26 and R27 which form a voltage divider and a feedback resistor R28. The inverted analog signal supplied at the output of amplifier 121 is applied through a resistor R29 to one input of a comparator 125, also the non-inverting input of an operational amplifier.
Comparators 119 and 125 compare the amplitude of the analog signal supplied thereto with the amplitude of a reference signal Sr to produce first and second signal elements of the con-trol signal which are supplied to windings Wl and W2 of solenoid77. A fixed-frequency square-wave generator 127 produces a square-wave signal. The generator is comprised of a pair o NAND gates &8 and G9, a pair of resistors R30 and R31 and a capacitor C9 and operates, as is well known in the art, to produce a square wave at a frequency which is, for example lKHz. The square-wave output of generator 127 is supplied through a resistor R32 and a resistor R33 to a pair of integrating circuits generally indicated 129 and ~-131 respectively. Integrating circuit 129 consists of a resis~
tor R34 and a capacitor C10 while integrating circuit 131 consists of a resistor R35 and a capacitor Cll. The output of each cir~
cuit is reference signal Sr, which has a triangular waveform, and this slgnal is supplied to the inverting lnput of comparators 119 and 1~5. Further, the reference signal supplied to each compara-tor is superimposed on a bias voltage level produced by a potenti-ometer 133 and applied to the respective reference signal input paths via a resistor R36 and a resistor R37. The setting of po-tentiometer 133 is such that the bias voltage level on which the reference signal is superimposed is approximately one-half the voltage corresponding to the difference between a logic high and a logic low.
Elements of the control si~nal supplied at the output of comparator 119 are supplied to a driver circuit 135 through a resistor R38. Driver circuit 135 includes a pair of PNP transis-tors ~3 and ~4 and a bias resistor R39 and the output of the driver circuit is connected to winding Wl of solenoid 77 through a radio-fre~uency choke RFCl. ~ pair of resistors R40 and R41 and a capa-citor C12 form a negative feedback circuit by which the amount of current flowing in winding Wl is sensed and a signal indicative thereof provided to a summing point 137. ~lements of the control signal from comparator 125 are supplied to a driver circuit 139 through a resistor R42. Driver circuit 139 comprises a pair of PNP transistors Q5 and Q6 and a bias resistor R43. The output of the driver circuit is connected to winding W2 through a radio-frequency choke RF~ 2 and a pair of resistors R44 and R45 and a capacitor C13 form a negative feedback circuit by which the current flowing in ~inding W2 is sensed and a signal indicative thereof supplied to a summing point 141. Each driver circuit has a diode, D3 and D4 respectively, connected between its output and electri-cal ground. These diodes shunt voltage spikes induced in windings W1 or W2 when a second signal element of the control signal, a low voltage level, is supplied to a winding and a magnetic field pre- ~: :
viously induced in the winding collapses.
Operation of the apparatus is as follows:
Assume that the amount of oxygen in exhaust system 15 is increas- .
ing, indicating that the air-fuel ratio of the mixture is increas- :~

: ing or that the mixture i5 getting leaner. For this condition, . .

~ he amplitude of fixst electrical signal Sl is decrea~ing and this amplitude is comparec1 with reference level Vref b~ comparator 39.
If the amplitude of signal Sl is initially greater than the ref erence level amplitude, it eventually falls helow that level as the mixture keeps getting leaner. When the reference level ampli-tude is passed, a transition T in second electrical signal S2 occurs and the comparator 39 output goes from low to high and a first rather than a second signal element of second electrical signal S2 is produced. This logic high is supplied on line 109 to gate G4 of counter control 45 and to delay counter reset cir-cuitry 55.
~ he logic high i~rom comparator 39 is inverted to a low by gate Gl and is also supplie~l through a current limiting resis-tor R46 and a R-C network compri~ed of a resistor R47 and a capa-citor C14 to one input of gate G3~ The other input to gate G3 is the inverted output of compara~or 39 which is supplied to the gate through a resistor R48 and a R-C network including a resistor R49 and a capacitor C15. A logic high ko either input of gate G3 momentarily forces the gate output low and, as previously discussed, the logic output from gate G3 is supplied to the inverting input of comparator 58. By forcing the logic output of gate G3 momen-tarily low, comparator 58 is forced to supply a logic high at its output regardless of the level to which capacitor C6 is charged, and this prevents capacitor C6 from discharging since transistor Q2 is kept in its non-conducting state. Thus, ~he generation of timing signal elements is momentarily inhibited. Aftex a prede-termined period established by the time-constant of the R-C net~orks, the logic output of gate G3 goes high and timing signal elements are again generated. Gate G3 therefore synchroni~es ~he supply of timiny signal elements to sampling network 51 and controller 41 with the random occurrence of ~ransi~ions bstween signal elements of th~ second slectrical signal.
' . ' ' "

:..'. . ~ ,"
~

Delay counter 53 is reset via reset circuitry 55 upon occurrence of the transition, as previously discussed, and a first signal element (a logic high) of delay signal Sd is supplied on line 107 to gates G4 and G5. This high inhibits gate G5 from pass-ing timing signal elements supplied to it on line 111. If the amplitude of signal S1 does not rise above that of reference level Vref prior to two consecutive timing signal elements being sup-plied to delay counter 53 after it is reset, the counter output changes from a first to a second signal element of the delay sig-nal. Gate G4 now has a logic high and a logic low applied to itsinputs and a logic high is supplied to the up/down input of con-trol counter 53 from inverter 112 signifying that the contents of the counter are to be incremented. Gate G5 is now supplied a logic low on line 107 and passes each timing signal element supplied to it. If the value of the contents of counter 43 is less than thirty-one, the input to gate G6 from the count inhibit output of the counter is high and gate G6 passes the timing signal elements to ... ~ .
the count input of the counter.
Each timing signal element received by counter 43 at its count input results in the contents of the counter being increased by one. If a logic 15w were being supplied to the up/down input of the counter, its contents would be decreased by one for each timing signal element received. Each time the contents of counter 43 are incremented, the composition of the digital signal supplied to interface 49 changes and each change results in a step increase in the amplitude of analog signal Sa produced at summing point 117 and supplied to comparators 119 and 125.
The signal applied to the non-inverting inpuc of compara-tors 119 and 125 is a function of the analog signal amplitude and 3Q the current presently flowing in windings Wl and W2 of solenoid 77. This input signal is developed a~ the respective summing points 137 and 141. The current flowing in the solenoid windings is determined by the amount o~ time a first signal element of the control signal is supplied to each winding as compared to a second - . . , :.

signal element o~ the control signal and this, in turn, is a func~
tion of the amount of time within each cycle of the reference sig-nal that the analog signal amplitude exceeds the reference signal amplitude. ~ith the contents of counter 43 at one value, the ana-log signal amplitude is a level which exceeds the reference signal amplitude for a certain portion of each reference signal cycle.
This results in driver circuits 135 and 139 each being ~n f~r a ~-~r-tion of each cycle and a current flows through each winding and in-duces a magnetic field whose force holds armature 79 at a position between positions Pl and P2O As previously discussed, the posi-tion o~ metering pins 29A and 29B in their respective outlets is determined by the armature position as is the quantity of air ad-mitted into conduits llA and llB.
With an increase in the analog signal amplitude, there is an increase in the voltage level at the non~inverting input to comparator 119 and a decrease in the voltage level at the non-inverting input to comparator 125. This latter is because of the si~nal inversion by amplifier 121. The potentiometer 133 settiny and the values of resistors R36 and R37 are such that when the value of the contents of counter ~3 are at their mid-range value, the input level to both comparators i5 equal. For this condition each comparator supplies a control signal to respective windings Wl and W2 in which the lenyth of time a first signal element is supplied to the winding during a reference signal cycle is equal to the length of time a second si~nal element is supplied to the -~
win~ing.
~ ith the increase at the non-inverting input to compa-rator 119! the input amplitud~ momentarily exceeds the reference signal amplitude throughout the reference si~nal cycle and a first element o~ the control si~nal is continuously supplied to winding ~1, This results in an increase in the average current flowing through the winding and this increase is re~lected at junction 137 through the comparator ll9 feedback circuit. ~n increase in the average current flow results in a decrease in the voltage level input -to the comparator so tha~ the analog signal amplitude begins to fall and again exceeds the reference signal amplitude ~or only a portion of each reference signal cycle. Finally, a steady state condition is reached in which a first signal element of the con-trol signal is supplied to winding Wl for a greater portioil of each reference siynal cycle than before the increase in the analog sigllal amplitude. This portion continue~ to increase as lony as the contents of control counter 43 are incremented.
The opposite occurs at comparator 125 in which the in-crease in analog signal amplitude results in the xeference signal amplitude exceeding the analog signal amplitude throughout a ref-erence signal cycle. ~s a consequence, no current is supplied to winding W2 and the average winding current decreases. This is xeflect~d at junction point 141 as an increase in the voltage level input to comparator 125 and the analog signal amplitude again exceeding the reference signal amplitude for part of each cycle~
Finally, a steady state condition is reached in which ~irst and second signal elements of ~he control signal are supplied to wind-ing W2 in a new ratio with the second signal element being sup-plied for a longer portion of each reference signal cycle than was the case prior to the analog signal amplitude increase. The net result of these changes is khe movement of armature 77 one step closer to position P2 and insertion of the metering pins into their ; -~
respective outlets and enrichment of the air-fuel mixture.
It will be understood that if the contents of counter 43 are decremented, khe re~erse of the situation above described would occur. That is, a step decrease in the analog signal amp-litude results in signal elements o~ the control signal being sup-plied to winding Wl with the porkion o~ time a firs signal elementis supplied to the winding compa~ed to a second signal element be ing less than before the decrease, while ~or the control signal supplied ko windin~ W2 the por~ion increases. Armature 79 thus mo~es one step closer to position Pl and the metering pins are withdrawn from their outlets and the air-fuel mixture is leaned.
The supply of timing signal elements to controller 41 and the resultant change in position of armature 79 and metering pins 29A and 29B continues until the amplitude o~ first electri cal signal Sl crosses reference Ref. This, as described, produces a transition between signal elements of second electrical signal S2 and delay counter reset circuitry 55 responds to the transition ;
to reset delay counter 53 and terminate the supply of a second signal element o~ the delay signal to counter control 45 and sup- -plies a first signal element instead. This inhibits counter con- ~ ;
trol 45 from supplying any further timing signal Plements to con-trol counter 43.
It is important for proper operation of the apparatus ;
that the value of the contents of counter 43 not exceed a maxi-mum value when the counter is being incremented or a minimum value when the counter is being decremented If, for example, the value of the counter contents i5 thirty-one and the counter is being in-cremented, the next timing signal element supplied to the counter results in the capacity of the counter being e~ceeded and the di- -gital signal on lines 113A to 113E representing a zero. Were the capacity to be exceeded, armature ~9, which is at posit70n P2 for a count value of thirty-one would be driven to position Pl. More air would be introduced into conduits llA and llB and the air-fuel mixture would be leaned. This, however, i5 the condition trying to be re~edied and as a result is only made worse. The reverse is true when the counter is being decremented and the value of its contents reaches zero. To prevent this from happen-ing, counter ~3 supplies a logic low to gate G6 whenever one of the two conditions occurs and this inhibits gate G6 from passing `~
timing signal ele~ents to the count input of the counter. This logic low remains until the direction of counting of the counter's .

:

\

contents changes or until an adjustment in the carburetion is made and the value of the counter contents is set to a preset value.
The contents of counter 43 are forcea to a preset value whenever power is first applied to the counter. This occurs, for ' example, when power is first supplied to the apparatus after its '' installation or when power is first applied to the apparatus af-ter power disruption. An ~-C circuit comprised of a capacitor Cp and a resistor Rp pro~l~ a momentary logic high at the preset '' input of the counter and this sets the value of the counter con-tents to a mid range value. Setting the contents of counter 43 to the preset value res'ults in the'air-fuel ratio being adjusted to a mid-range value. Additionally, voltage from a power source, for ' example, an automobile battery B, is continuously supplied to the counter when the engine'is shut down to maintain the value of the counter contents at the 'last value attained prior to engine ' shutdown. This is accomplished, for example,' by regulating the ''' '-battery voltage by a regulator 143 and supplying the regulated voltage output to counter 43 through a clock-fuse circuit gen- ~ ' erally indicated at 145 which is closed even when engine E is shut down. By maintaining the value of the counter contents at ; ' their last attained value,' the air-fuel' ratio of the mixture has approximately the same value'it previously ha'd when the engine is restarted. This helps improve pollution control when the engine is restarted especially when an automobile'in which en-gine E is placed is driven from one part of the country to an- -other where altitude and other atmospheric conditions have a different effect on the air-fuel ratio than the conditions at the previous location.
Referring~now to Figs. 2B and S, a second embodiment of '~
the air metering unit, designated 17', is shown ~Fig. 2B~ as is a controller 41' ~Fig. 5~ for this second embodiment. Air metering unit 17` has two air outlets 21A' and 21B' with metering pins 29A' and 29B' respectively positioned in the outlets. The air metering unit further has a positioner 31' for inserting the metering pins into or withdrawing them from their respective air outlets. Positioner 31' comprises a stepper motor 145 having a stator 147 comprised of a plurality o~ phase displaced windings, for example the four sets W3, W4, W5 and W6 of windings repre-sented in Fig. 5. The stepper motor also has a rotor 149 ro-tatable in either of two directions and the rotor has a longi-tudinal threaded bore 151 through its center. A threaded shaft 153 is received in bore 151 for longitudinal movement in one of two directions depending upon the direction of rotor rotation.
A plate 93' is affixed to end 155 of shaft 153 and metering pins 29A' and 29B' are attached to the plate. A pair of sockets 99' are formed in the upper face of plate 93' and each metering pin has a stem 101' whose free end fits into one of these sockets.
A spring 103' is positioned between each metering pin and a wall 105' of the air metering unit to bias the metering pins to close their associated outlets.
Controller 41l in~ludes a pair of NOR gates G4' and G5' and a NOR gate G10. One input of each gate is supplied with sig-nal elements of the delay signal on line 107 and gate G4' has a second input supplied with signal elements of second electrical ,~... .... .
signal S2 on line 109. Gate G5' has a second input supplied with timing signal elements on line 111 and gate G10 has a second in-put supplied with the output signal from inverter Gl on a line 155, the signal being the inverse of the second electrical signal.
Controller 41' has a control counter 43', which is a two-stage binary counter comprised of a pair of flip~flops FF3 and FF~, -respectively and three NOR gates Gll, G12 and G13. The output ., . :

of G~t~ G5' is connected to the clock input of flip-flop FF3 while -t~e output of gate G4' is collnected to one input of gate Gll through an R-C network consisting of a resistor R50 and a capacitor C16. The outpu-t of gate G10 is connected to one input of gate G12 through an R-C networ]~ comprised of a resistor ~51 and a capacitor C17. The Q output of flip-flop FF3 is connected to a second input of gate Gllt to the data input of th~ flip-flop and to one input of a NOR gate G14 in interface circuit 49'. The Q output of the flip-flop is connected to a second input of gate G12 and to one input o~ a NOR gate G15 in the interface circuit. The outputs of gates Gll and G12 are connected to inputs of gate G13 ~ld the out-put of the gate is connected to the clock`input of flip-flop FF4.
The Q output of flip-flop FF4 is connected to its data input, to a second input of gate G14, and through a resistor R52 to a driver circuit 157 which is comprise-l o:E a pair of NPN transistors Q7 and Q8. The Q output of the flip-flop is connected to a second input of gate G15 and through a resistor R53 to a driver circuit 159 comprised of a pair of NPN transistors Q9 and Q10~ The outputs of gates G14 and G15 are connected to inputs of a NOR gate G16 and the output of gate G16 is connected to both inputs of a NOR
gate G17 and through a resistor R54 to a driver circuit 161 con-sisting o~ a pair of NPN transistors Qll and Q12. The output of gate G17 is connected through a resistor RSS to a driver circuit 163 comprised of a pair of NPN transistors Q13 and Q14.
The circuitry of interface 49~ supplies the control signal to the windings of stator 147 in a first sequence when the contents of control counter 43' are incremented to produce a positive phase ro~ation of stepper motor 145 and movement of shaft 153 in the direction to insert metering pins 2~A' and 29B' -:
into their respective air outleta. Less air i5 then introduced into conduits llA and lln and the air-fuel mixture is enriched.

Interface 49' supplie.s the control signal to the windings in a ~ :
,, ., ".''' - ' 27 :~

second sequence when the counter contents are decremented to pro-duce a negative Phase rotation of the stepper motor and movement of shaft 153 in the direction to withdraw the mete-ring pins from their respective air outlets. More`air is then introduced into the conduits and the air-fueI mixture is leaned. The our sets of stator windings are phase-displaced ninety electrical degrees apart and the sequencing logic of interface 49' supplies the con-trol signal to two of the four sets of windings at any one time, ~ ~`
the two sets to which the control signal is supplied being de-termined by the value of the contents of control counter 43'and changing as the contents are incremented or decremented.
The windings W3 - W6 are arranged such that winding W3 repre-sents a first phase corresponding to 90, winding W4 a second phase corresponding to 270, winding W5 a third phase correspond-ing to 180, and winding W6 a fourth phase corresponding to 0.
Further, stepper motor 145 may, for example, have twelve pole pairs. As a consequence, the supply of the control signal to two of the windings produces a resultant magnetic field which moves rotor 149 in 15 steps, the`direction of movement depending upon whether the contents of counter 43l are incremented or decremented.
Consider, as in the previous example, the situation where the air-fuel mixture is too lean and is to be enriched.
For this condition, a first signal element (a logic high) of the second electrical signal is supplied to gate G4' on line 109 and the inverse of the signal eLement ~a logic low) to gate G10 on line 155. When a second signal element (a logic low) of the delay signal is supplied on line 111 from delay counter 53 r the logic output of gate G4' is low and that of gate G10 high.
If the value of th~e contents of control counter 43' is :
pres`umed to be zero, flip-flops FF3 and FF4 each supply a logic . ' ,:', high at their ~ outputs and a logic low at their Q outputs. Gates Gll and Gl2 each have a hi'gh and low input and supply a logic low to gate Gl3 which, in turn, supplies a logic hi`gh to the clock in-put of flip-flop FF4. When the next timing signal element is sup-plied to gate G5', it is passed by the'gate'to the clock input of flip-flop FF3 triggering the flip-flop. The Q output of the flip~
flop goes high and its ~ outpu-t low. Gate ll now has both inputs low and supplies a logic hi'gh to gate Gl3, and gate Gl2 has both inputs high and supplies' a logic low to gate Gl3. The output sup-plied by gate Gl3 goes low but thi's transition does not trigger flip-flop FF4 whose logic output remains Q high, ~ low.
At interface 49', gate'Gl4 has a high and a low input and gate G15 has both inputs hi'gh; and the gates both supply a logic low to gate Gl6. The'logic output of gate Gl6 is high and '~
turns on driver circuit 161 so that the control signal is supplied to winding W3. At the'same'time, driver circuit 157 is turned on by the logic high at the ~ output of flip-flop FF4 and the contro~
signal is supplied to winding W6. The supply of the control sig-nal to windings W3 and W6 produces a magnetic field by which rotor 149 is,for example, rotated from a 0 position to a 15 position.
When the next timing signal element is passed by gate G5' to flip-flop FF3, the Q output of the flip-flop goes low and its Q output high. Gates' Gll and G12 again each have'a high and a low input and supply a logic low to gate Gl3 whose output now ;' goes high, triggering flip-flop FF4. The Q output of flip-flop FF4 ~
goes high and its Q output low. The value of the 'contents of ~ ' counter 43' now repres'ents two. With the logic outputs of flip flops FF3 and FF4 as indicated, driver circuit 161 is on and the control signal is suppliea to winding W3 and driver circuit 159 ''' is on and the control signal is supplied to winding W5. The re-sultan~ fieId producea in stepper motor 145 moves rotor 149 from its 15 position to a 30 position.

If timing signal elements continue to be supplied to counter 43', i.e., delay counter 53 is not reset, the value of the contents of counter 43'` goes to three and then back to zero.
For a value of three, driver circuits 163 and 159 are on and the control signal is supplied to windings W4 and W5. For a value of zero, driver circuits 163 and 157 are on and the control sig-nal is supplied to windings W4 and W6. In each instance, a mag-netic vector is produced in stepper motor 145 which produces an-other 15 of rotor 149 rotation.
The value of the contents of counter 43' continues the cycle of 0, 1, 2, 3, 0, etc. as the counter is incremented. This .... ..... .
is unlike the operation of control counter 43 discussed previously in which the contents of the counter cannot exceed a maximum or a minimum value. I~ counter 43' were decremented, the value of the contents cycles 0, 3, 2, 1, 0 etc., so that the contents o counter 43' cycle in a first sequence of count values when the counter is incremented and in a s~cond and opposite sequence of count values when the counter is decremented.
It will be understood that the rotation of rotor 149 when counter 43' is decremented is opposite to that produced when the counter is incremented, because the control signals are sup-plied to two of the four windings of stator 147 in a reverse se-quence to that in which they are supplied when the counter is incremented. In either instance, energy induced in the windings when the control signal is supplied to them is given off when the .. . .
control signal is removed. To prevent damage which might occur because of the resultant voltage surge, clamping diodes D5r D6, ~7 and D8 are connected across the respective windings W3 - W6. Also, as with control counter 43, voltage is continuously supplied to -~
control counter 431 even when engine E is shut down, thus for the :, .: .:

counter contents to be at khe last value attained prior to engine shutdown when the engine is restarted.

. - .' . ':
~

Timing unit 47 generates timing signal elements at a first repetition rate when engine E is operating under steady state conditions and at a second and faster repetition rate when a non-steady state condition is created such as when the engine acceler-ates or decelerates. The'operation of timing unit 47 to generate timing signal elements at the first repetition rate which is, for example, 1.5 H~, has been previously described, and involves charg-ing timing capacitor C6 and comparing the charge level of the capacitor with a re~erence voltage level by comparator 58 and dis-charging the capacitor when the reference level is reached. Whensteady state operation of the engine'changes, it is reflected, for example, by a change in engine'manifold pressure. A switch 165 is positioned in the manifold and is responsive ~o pressure changes which occur when a non-steady state'conditi.on is created to close and remain closed until a new steady state condition is reached.
When a steady state condition exists, a capacitor C18 is charged through a resistor R56. As timing capacitor C6 charges, '~
current flows through a pair of res'istors R57 and R58, which form a divider network, and resistor Rc to ground. Current flow through this path'has the effect of reducing the charge rate of capacitor ;~
C5 by decreasing the capacitor charge current. When a non-steady state condition is created, a resistor R59 is connected to ground ... .
through closed switch'165. The flow of current through the di-vider network is reversed and this effectively increases the charge current of capacitor C6, so that the capacitor charges at the sec-ond and faster rate, which'rate is, for example/' approximately ~ ' three times the first rate. This second charge rate continues un- ' ' til switch'165 opens at which time the rate exponentially decays back to the first rate.' The decay rate is determined by the val- '' ues of resistor R56 and capacitor C18. Because discharge of ca .

pacitor C~ is controlled by comparator 58, as described, the pulse . .
width o~ the timing signal el'ements produced at junction 57 is '; '' ' 31 ~' .. . . .. . . . . .. .. . . .. .... .

~7~

maintained substantially c~nstant regardless of the charge rate of capacitor C6 or the repetition rate at whi:ch the timing signal elements are produced.
The rate at which timing signal elements are generated may also be a function of the state of detector 35 or which sig-nal element of second el'ectrical signal S~ is supplied by compar- .
ator 39. Thus, for example, a resistor R60 and a potentiometer 167 may be optionally connected between the input to gate Gl and the non-inverting input of comparator 58. Thus, when the air-fuel mixture is lean, as sensea by detector 35, and a first signal ele-ment of the second electrical signal is supplied at the output of comparator 39, current flows through resistor R60 and potentiometer 167 from the comparator and lowexs the capacitor C6 charging cur- ':
rent and the rate at which timing signal elements are produced.
When detector 35 senses a rich mixture and a second signal element of the second el'ectrical signal is supplied at the output of com-parator 39, the current flow through'resistor R60 and the poten- ' -tiometer is reversed and the rate at which capacitor C6 is charged ', increases. Consequently, a bias toward a leaner air-fuel mixture . .:
20 is created since'the response of the apparatus is slower when a lean . .
mixture is sensed. By connecting a resistor R60A between the out- -put of inverter gate Gl and potentiometer 167 instead of connect~
ing resistor R60 at the gate input, the opposite result is produced , with the bias now toward a richer mixture. . ~.
When engine E is not started for some period Of! ~time ' :
after it is shut down, a cold start condition exists in which the - ' operating temperature of detector 35 is initially less than some .:.' preselected value, for example 400C (752F). In such a situationl ;
it is desirable not to chan~e the control signal supplied to air metering unit 17 until the detector temperature rises abo~e the -.

preselected value.' Since :detector 35 has a temperature-dependent ~' internal impedancer circuitry for preventing a change in the ':
'~ ','.

: 32 control signal comprises a bridge network 169 with the detector impedance included in one leg of the bridge and with another leg of the bridge including an impedance whose value is a function of the detector impedance at the preselected value. One-half of bridge 169 includes the impedance of detector 35, resistor Rl and capacitor Cl and a resistor R61 and a pair of capacitors Cl9 and C20 respectively. The other half of the bridge comprises a pair of resistors R62 and R63 and the bridge is substantially balanced when the detector temperature i5 at the preselected value. The bridge output is connected to a comparator 171 (an operational am-plifier) which includes a pull-up resistor R64. Comparator 171 supplies first and second signal elements of a bridge output sig-nal to one input of gate G2. A first signal element of the bridge output signal (a logic high) is supplied by comparator 171 when the detector temperature is above the preselected value and a sec-ond signal element (a logic low) is supplied when the detector temperature is below the preselected value. When a timing signal element is generated, a pulse is produced by bridge 169 and provid-ed to the non-inverting input of comparator 171. This pulse is a ne~ative going pulse whose amplitude is determined ~y the internal impedance of detector 35 and compared with the reference voltage at the inverting input to the comparator.
The other input to gate G2 is supplied with elements of an enabling signal. An enabling signal element is produced each time a timing signal element is generated. The circuitry for pro-ducing an enabling signal element includes a pair of resistors R65 and R66 respec*ively, a diode D9 and a capacitor C21. One side of capacitor C21 is connected to the output of inverter G7 which, as previously noted, inverts the timing signal produced at junction 57. Thus, the logic output of gate G7 is normally low but goes high during the period an element of the timing signal is produced. As a consequence, an element of the enabliny signal is produced at the trailing edge of a timing signal element and is -:

4~

a momentary high-to-low transition at the input to gate G2 If a first signal element of the bridge output signal is present at the input to gate G2 when an enabling signal element is supplied to the gate, the logic output of the gate is low. As previously described, the output of gate G2 is connected to delay counter 53 and specifically to the set input of flip-:Elop FFl and the reset input of flip-flop FF2. A logic low supplied by gate G2 to counter 53 has no effect on the counter. If, however, a sec~
ond signal element of the bridge output signal is supplied to gate G2 when an enabling signal element is supplied, it indicates that the temperature of detector 35 is below the threshold level and a logic high is supplied by the gate to counter 53 and the ~:
counter is reset. Thus, until the detector temperature exceeds the predetermined value, counter 53 is reset each t.ime a timing signal element, wh.ich normally increments counter 53, is gener-at~d~ Therefore, the contents o~ counter 53 cannot reach the value of two which is necessary in order for controller 41 to ac~
cept timing signal elements and produce a change in the control ...
signal supplied to air metering unit 17. ..
Besides not wanting to change the control signal sup-plied to air metering unit 17 during a cold start, it is also de- ;.
sirable to hold o~f or prevent a change in the control signal at ;~
other times, as for example, during heavy accelerations (wide-open throttle~ For this purpose, a hold off switch 173 is closed ~ :
wh.enever a particular engine operating condition is created during ~:
which no change in the control signal is to be produced~ When switch 173 is closed, the non-inverting input of comparator 171 is effectiyely grounded through a circuit which: includes resistors ~. . .
R67, R68 and ~6~ and a capacitor C22~ With the~non-inverting input of the comparator grounded, a second signal element of the bridge .:
output signal is supplied to gate G2 and results in the gate sup~

plying a logic high to delay counter 53 whenever an enablin~ sig- :
nal element is supplied to the gate. Counter 53 is reset by the ' logic high from gate G2 and continues to be so until switch 173 opens.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous re-sults attained.

As various changes could be made in the above construc-tions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shalI be interpreted as illus-trative and not in a limiting sense~

..... ~

Claims

We Claim:
1. Apparatus for controlling the air-fuel ratio in an internal combustion engine to substantially maintain the ratio at a predetermined value while the engine is operating under various load conditions, the engine having a carburetor with at least one air passageway therein through which air is drain into the engine, fuel from a source thereof being supplied to the carburetor through at least one fuel system and mixed with the air as it passes through said carburetor, said carburetor having a conduit through which air is intro-duced into said system, and the engine further having a chamber for combustion of the resulting air-fuel mixture and means for exhausting the products of said combustion, the apparatus comprising:
means for metering the quantity of air introduced into the fuel system through said conduit thereby to control the air-fuel ratio of the mixture;
means for sensing the presence of oxygen in the products of combustion and for supplying a first electrical signal representative of the oxygen content therein, said oxygen content being a function of the air-fuel ratio of the mixture;
means for comparing the first electrical signal with a predetermined reference level which is a function of said predetermined value to produce a second electrical signal having first and second signal elements, a first signal element being produced when the air-fuel ratio of the mixture is greater than the predetermined level and a second signal element being produced when the ratio is less than the level;
control means responsive to the second electrical signal for supplying to the metering means a control signal by which the quantity of air introduced into the conduit is controlled and for producing a change in the control signal whenever the second electrical signal has a transition from one signal element to the other thereby for the metering means to change the quantity of air introduced into the conduit by an amount necessary to substantially maintain the air-fuel ratio at the predetermined value; and means for sampling the second electrical signal over a predetermined time interval starting when a signal element of the second electrical signal is produced to determine whether a transition between signal elements occurs within said time interval, the control means being responsive to the sampling means to produce a change in the control signal if no transition occurs within said time interval thereby the quantity of air introduced into the conduit is changed but to produce no change in the control signal if a transi-tion does occur within the predetermined time interval whereby the quantity of air introduced into the conduit remains unchanged.
2. Apparatus as set forth in claim 1 wherein the oxygen sensing means includes a detector positioned in the exhaust system and responsive to said oxygen content to generate a voltage whose amplitude is a function thereof.
3. Apparatus as set forth in claim 2 wherein the ampli-tude of the voltage generated is inversely related to said oxygen content and the oxygen sensing means further includes means for amplifying the voltage generated by the detector to produce said first electrical signal.
4. Apparatus as set forth in claim 1 wherein the prede-termined value corresponds to the stoichiometric point for the air-fuel ratio of the mixture and the comparing means comprises a voltage comparator having one input to which is applied the first electrical signal, a second input to which is applied a reference voltage whose amplitude is a function of the oxygen content in the products of combustion at the stoichiometric point and an output from which is supplied the first and second signal elements of the second electrical signal, a first signal element being supplied by the comparator when the first electrical signal amplitude is less than the reference voltage amplitude, a second signal element being supplied when the first electrical signal amplitude exceeds the reference voltage amplitude and a transition from one signal element to the other occurring whenever the first electrical signal amplitude changes from greater to less than the reference voltage amplitude and vice versa.

5. Apparatus as set forth in claim 4 wherein the control means includes a reversible accumulating control counter and counter control means responsive to the first and second signal elements of the second electrical signal for incrementing and de-crementing the contents of the control counter, said contents being incremented when less air is to be introduced into the conduit and the mixture made richer and decremented when more air is to be introduced into the conduit and the mixture made leaner.

6. Apparatus as set forth in claim 5 further including timing means for generating a timing signal having a plurality of signal elements which are supplied to a count input of the control counter for incrementing and decrementing its contents, the con-tents of said control counter being incremented by signal elements of the timing signal when a first signal element of the second electrical signal is supplied to the counter control means and decremented by signal elements of the timing signal when a second signal element of the second electrical signal is supplied to the counter control means.

7. Apparatus as set forth in claim 6 wherein signal elements of the timing signal are also supplied to the sampling means and the sampling means includes time-delay means responsive to the timing signal elements for counting from zero to a pre-selected value and for inhibiting the counter control means from incrementing or decrementing the contents of the control counter until the preselected value is reached.
8. Apparatus as set forth in claim 7 wherein the time-delay means includes a delay counter the contents of which are incremented by signal elements of the timing signal and which sup-plies first and second signal elements of a delay signal to the counter control means, a first signal element of the delay signal being supplied to the counter control means whenever the value of the contents of the delay counter is less than the predetermined value and a second signal element of the delay signal being sup-plied to the counter control means when the preselected count value is reached.

9. Apparatus as set forth in claim 8 wherein the counter control means includes a logic gate having one input to which is applied signal elements of the timing signal, a second input to which is applied the first and second signal elements of the delay signal and an output which is connected to the count input of the control counter, the logic gate inhibiting the supply of timing signal elements to said count input when a first signal element of the delay signal is supplied to the logic gate and the logic gate passing timing signal elements to the count input when a second signal element of the delay signal is supplied to the logic gate.
10. Apparatus as set forth in claim 9 wherein a second signal element of the delay signal is supplied to the logic gate whenever the value of the contents of the delay counter reaches two and wherein the sampling means further includes means respon-sive to each transition between signal elements of the second electrical signal for resetting the value of said contents to zero whereby no second signal element of the delay signal is supplied to the logic gate as long as the contents of the delay counter are reset to zero prior to their value reaching two.

11. Apparatus as set forth in claim 10 wherein the con-trol means further includes interface means responsive to a digital signal supplied by the control counter for producing the control signal supplied to the air metering means and for producing a change in the control signal when the value of the contents of the control counter, as represented by the digital signal, change.

12. Apparatus as set forth in claim 11 wherein the metering means includes an air metering unit having an air inlet, an air outlet communicating with said conduit, a metering pin in-sertable into and withdrawable from the air outlet to control the quantity of air admitted into the conduit and means responsive to the control signal for positioning the metering pin in the air out-let.
13. Apparatus as set forth in claim 12 wherein the car-buretor includes a second fuel system and a second conduit through which air is introduced into said second fuel system and the air metering unit includes a second air outlet communicating with said second conduit and a second metering pin insertable into and with-drawable from said second air outlet to vary the quantity of air admitted into the second conduit through the second opening, the positioning means simultaneously positioning the first and second metering pins in their respective air outlets in response to the control signal.

14. Apparatus as set forth in claim 12 wherein the po-sitioning means includes a variable position solenoid having at least one winding to which the control signal is supplied, an armature movable in either of two directions between a first po-sition representative of a first value of the control counter con-tents and a second position representative of a second value of the control counter contents and a plate movable with the armature to which the metering pin is attached, a change in the control signal supplied to the winding when the counter contents are being incremented producing movement of the armature in one direction whereby the metering pin is inserted into the outlet and less air is introduced into the conduit and a change in the control signal supplied to the winding when the control counter contents are being decremented producing movement of the armature in the oppo-site direction whereby the metering pin is withdrawn from the out-let and more air is introduced into the conduit.

15. Apparatus as set forth in claim 14 wherein the inter-face means includes a digital-to-analog converter for converting the digital signal to an analog signal the amplitude of which is a function of the value of the control counter contents and is increased a predetermined amount each time the contents of the con-trol counter are incremented by one, decreased by the predetermined .
amount each time said contents are decremented by one and remains :
the same so long as the time delay means inhibits the supply of timing signal elements to the control counter, each change in the analog signal amplitude by the predetermined amount resulting in movement of the armature a predetermined distance between the first and second positions.

.' 16. Apparatus as set forth in claim 15 wherein the interface means further includes a second comparing means for comparing the analog signal with a reference signal to produce the control signal supplied to the solenoid windings.

17. Apparatus as set forth in claim 16 wherein the variable position solenoid includes a second winding and the second comparing means includes a pair of comparators each of which has one input to which is applied the analog signal, a second input to which is applied the reference signal and the outputs of each of which are first and second signal elements of the control signal which are supplied to one of the two solenoid windings t a first signal element of the control signal being supplied when the analog signal amplitude is greater than the reference signal amplitude and a second signal element being sup-plied when the analog signal amplitude is less than the reference signal amplitude.

18. Apparatus as set forth in claim 17 wherein the interface means includes a fixed frequency square-wave generator and means for integrating the square-wave signal from the genera-tor to produce the reference signal supplied to the one input of each of the comparators in the second comparing means whereby the reference signal amplitude varies cyclically and the amount of time a first signal element of the control signal is supplied to the solenoid windings as compared to a second signal element there-of is a function of the amount of time within each cycle the ana-log signal amplitude exceeds the reference signal amplitude.

19. Apparatus as set forth in claim 18 wherein the counter control means further includes logic means responsive to the control counter for terminating the supply of timing signal elements to the count input of the control counter whenever the value of the control counter contents reach a maximum value when the control counter is being incremented and a minimum value when the control counter is being decremented thereby to establish a range of values within which the contents of the control counter may vary, the first and second positions between which the solenoid armature is movable respectively representing the maximum and minimum values.

20. Apparatus as set forth in claim 19 wherein the control means includes means responsive to an initial application of power to the control system to set the control counter contents to a mid-range value thereby for the armature to be initially po-sitioned midway between said first and second positions.

21. Apparatus as set forth in claim 20 wherein the con-trol counter is a five-stage binary counter and the armature is movable to any of thirty-two discrete positions depending upon the value of the control counter contents.

22. Apparatus as set forth in claim 12 wherein the po-sitioning means includes a stepper motor having a stator comprised of a plurality of phase displaced windings, a rotor rotatable in either of two directions and having a longitudinal threaded bore therethrough, a threaded shaft received in the bore for longitudinal movement in one of two directions depending upon the direction of rotor rotation and a plate affixed to one end of the shaft to which the metering pin is attached.

23. Apparatus as set forth in claim 22 wherein the interface means includes means for supplying the control signal to the stator windings in a first sequence when the control counter contents are being incremented to produce a positive phase rotation of the stepper motor and movement of the shaft in a direction to insert the metering pin into said outlet and introduce less air into the conduit and in a second sequence when the control counter contents are being decremented to produce a negative phase rotation of the stepper motor and movement of the shaft in a direction to withdraw the metering pin from said outlet and introduce more air into the conduit.

J
24. Apparatus as set forth in claim 23 wherein the stator has four sets of windings phase displaced ninety electrical degrees apart and the sequencing means includes logic means re-sponsive to the digital signal for selectively supplying the con-trol signal to two of the four sets of windings at any one time, the two sets of windings to which the control signal are supplied being determined by the value of the control counter contents and changing as the contents are incremented to produce the posi-tive phase rotation of the stepper motor and as said contents are decremented to produce the negative phase rotation of the stepper motor.

25. Apparatus as set forth in claim 24 wherein the con-trol counter is a two-stage binary counter the contents of which cycle in a first sequence of count values as the control counter is incremented and in a second and opposite sequence of count value as the control counter is decremented.

26. Apparatus as set forth in claim 11 further includ-ing means for continuously supplying power from a power source to the control means when the engine is shut down to maintain the value of the control counter contents at the last value attained prior to engine shutdown thereby for the air-fuel ratio of the mixture to have approximately the same value when the engine is restarted.
27. Apparatus as set forth in claim 11 wherein the timing means includes means for generating elements of the timing signal at a first repetition rate when the engine is operating under steady state conditions and at a second and faster repetition rate when a non-steady state condition is created such as when engine acceleration or deceleration occurs thereby to increase response time of the apparatus during a non-steady state operating condition.

28. Apparatus as set forth in claim 27 wherein the timing means includes a timing capacitor, means for charging said capacitor at a first rate when steady state conditions exist and at a second and faster rate when non-steady state conditions occur, the repetition rate of the timing signal elements generated being a function of the capacitor charging rate, means for discharging the capacitor at a predetermined rate, the pulse width of each timing signal element generated being a function of the capacitor discharge rate, and means responsive to the charge level of the timing capacitor reaching a predetermined level to actuate the discharging means thereby to produce a timing signal element the pulse width of which is maintained substantially constant regard-less of the repetition rate at which it is generated.

29. Apparatus as set forth in claim 28 wherein the dis-charging means includes a transistor connected between the timing capacitor and electrical ground and the actuation means includes an additional comparator having one input to which is applied the charge level of the capacitor, a second input to which is applied a reference level corresponding to the predetermined charge level and an output which is connected to the base of the transistor, an output signal from the comparator maintaining the transistor in a non-conducting state until the capacitor charge level reaches the predetermined value and then switching the transistor into conduction for discharge of the capacitor.

30. Apparatus as set forth in claim 29 wherein the time delay means includes means responsive to each transition between signal elements of the second electrical signal for synchronizing the supply of timing signal elements to the control means and the time delay means with the random occurrence of said transitions.

31. Apparatus as set forth in claim 30 wherein the syn-chronizing means includes means for inhibiting the timing means from generating timing signal elements for a predetermined period after each transition between signal elements of the second elec-trical signal occurs.

32. Apparatus as set forth in claim 31 wherein said inhibiting means comprises a logic gate having an input to which are applied signals derived from the first and second signal elements of the second electrical signal and an output from which is supplied a predetermined iogic level to the second input of the additional comparator for said predetermined period after a transition between said signal elements occurs, the output signal from the additional comparator when said predetermined level is supplied to its second input maintaining the transistor in the discharging means in its non-conducting state whereby the timing capacitor cannot discharge.

33. Apparatus as set forth in claim 11 further includ-ing means responsive to the temperature of the oxygen detector to prevent a change in the control signal supplied to the metering means whenever the detector temperature is less than a preselected value.

34. Apparatus as set forth in claim 33 wherein the oxygen detector has a temperature dependent internal impedance and the change prevention means comprises a bridge network one leg of which includes the detector internal impedance and another leg of which includes an impedance whose value is a function of the detector internal impedance at the preselected temperature value whereby the bridge is substantially balanced when the temperature of the detector is at the preselected value.

35. Apparatus as set forth in claim 34 wherein the change prevention means further includes means for comparing a signal developed across said legs of the bridge to determine if the detector temperature is above or below the preselected value and for supplying first and second signal elements of a bridge output signal, a first signal element of the bridge output signal being supplied when the detector temperature is above the prese-lected value and a second signal element being supplied when the detector temperature is below the preselected value.

33. Apparatus as set forth in claim 35 wherein the change prevention means further comprises means responsive to the bridge output signal for preventing the value of the delay counter contents from reaching two when the detector temperature is below the preselected value.

37. Apparatus as set forth in claim 36 wherein the change prevention means further comprises a reset logic gate having one input to which is applied the first and second signal elements of the bridge output signal, a second input to which is applied an element of an enabling signal which is produced when an element of the timing signal is generated and an output from which a signal is supplied to the reset input of the delay counter to reset the contents of said delay counter to zero if a second signal element of the bridge output signal is supplied to the one input of the reset logic gate when an element of the enabling signal is supplied to its second input.

38. Apparatus as set forth in claim 37 further including hold off means for preventing a change in the control signal.

39. Apparatus as set forth in claim 38 wherein the hold off means includes means for grounding one input to the com-paring means of the change prevention means whereby a second sig-nal element of bridge output signal is continuously supplied to the one input of the reset logic gate and the delay counter is contin-uously reset.

40. Apparatus as set forth in claim 29 further includ-ing means responsive to the second electrical signal for changing the repetition rate at which timing signal elements are produced.

41. Apparatus as set forth in claim 40 wherein said rate changing means includes means for decreasing the timing ca-pacitor charge current when a first signal element of the second electrical signal is produced by said voltage comparator and for increasing the timing capacitor charge current when a second sig-nal element of the second electrical signal is produced by the voltage comparator, the repetition rate at which timing signal elements are produced being lowered when the current flow is de-creased and raised when the current flow is increased.

42. Apparatus as set forth in claim 41 wherein the sampling means includes an inverter for inverting the second electrical signal produced by said voltage comparator and the rate changing means is responsive to said signal produced by said inverter whereby current flowing through the timing capacitor is increased when a first signal element of the second electrical sig-nal is produced and decreased when a second signal element of the second electrical signal is produced.