Note: Descriptions are shown in the official language in which they were submitted.
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.
2 ~
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 .
,.... .... .
' 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.
~
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.
...,..~.. : ...
7 :
. ...
. .
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.
. .
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
:" ~ ' .
12 ~
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 ~;
. ,' ', ' '
13
. . ~ . .
''`'"'.
.
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.
~,' "
16
-: .
- - .. ..... : .: .. . ~. .
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 -,~
. ' ~ .
17 '
.. . . . , :
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
18
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,
1 9
. .
~ 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
21
- . . , :.
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
22
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
23
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
.
24
:
\
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
26
., . :
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
. ' ,:',
28
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.
29
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
-:
33
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
'
34
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~
..... ~
