Electric air-to-fuel ratio control system

A function signal having a desired characteristic curve is generated through the logical operation on a vehicle speed signal indicative of the speed of a vehicle, a ratio signal indicative of the air-to-fuel of the mixture supplied to the engine mounted on the vehicle, and a pressure signal indicative of the pressure in the intake manifold of the engine. The position of an electromagnetic valve for adjusting the amount of fuel supplied to the engine is controlled in response to the function signal, thereby controlling the air-to-fuel of mixtures in accordance with the various driving conditions of the vehicle including the vehicle speed.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
The present invention relates to air-to-fuel ratio control systems, and 
more particularly the invention relates to a control system for 
electrically controlling the air-to-fuel ratio of the mixture produced in 
the carburetor of an internal combustion engine for automobiles. 
2. DESCRIPTION OF THE PRIOR ART 
Conventional internal combustion engines for automobiles have been so 
constructed that the weight ratio between the amount of intake air and the 
amount of fuel to be mixed, i.e. the air-to-fuel ratio of the mixture 
produced in the carburetor is controlled in accordance with a few engine 
operating conditions such as the throttle opening and the amount of intake 
air. However, with a recent tendency toward cleaner exhaust emissions, the 
demand for reduction in fuel consumption necessitated by a recent steep 
rise in the price of gasoline, etc., increasingly complicated air-to-fuel 
ratio controlling characteristics are required for the carburetors, and 
moreover there also exists a need for highly accurate air-to-fuel ratio 
control. 
On the other hand, the driver of an automobile carrying an internal 
combustion engine requires, as the essential requisites for the driving of 
his vehicle, that the driver can drive his vehicle at any desired speed, 
and that improved driveability in terms of acceleration performance, etc., 
is ensured. In view of the fact that the vehicle speed has an important 
bearing on the needs of the society, i.e., cleaner exhaust emissions and 
reduced fuel consumption, it should be appreciated that the speed of the 
automotive vehicle among vehicle driving conditions is an important 
control parameter for the internal combustion engine mounted on the 
vehicle. However, none of prior art systems have regarded it as important. 
SUMMARY OF THE INVENTION 
With a view to meeting these requirements, it is the object of this 
invention to provide an electric air-to-fuel ratio control system which is 
capable of controlling, in accordance with the driving conditions of an 
automotive vehicle including its speed, the air-to-fuel ratio of the 
mixture produced in the carburetor of the internal combustion engine 
mounted on the vehicle. 
In a preferred embodiment shown herein, the system of this invention 
comprises driving condition detecting means including a vehicle speed 
detector, and a function voltage generator which determines a desired 
air-to-fuel ratio to be controlled by utilizing the detected driving 
conditions as control parameters. The air-to-fuel ratio of the mixture 
supplied to the engine is controlled in accordance with the function 
voltage, thereby controlling the air-to-fuel ratio of the mixture produced 
in the carburetor in accordance with the driving conditions including the 
vehicle speed and a driving condition as detected by detecting means. In 
accordance with this invention, the air-to-fuel ratio of the mixture 
supplied to a vehicle mounted internal combustion engine for automobiles 
is controlled at a value suitable for exhaust emission control purposes in 
the low speed range of the vehicle, while in the intermediate and high 
speed ranges of the vehicle where there is no particular need to control 
exhaust emissions, either fuel economy operation or high power output 
operation of the engine is accomplished in accordance with the driving 
conditions of the vehicle, thus realizing an air-to-fuel ratio control 
which is capable of meeting the requirements of the engine under various 
driving conditions of the vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described in greater detail with 
reference to the accompanying drawings. 
Referring first to FIG. 1, there is illustrated a block diagram of an 
embodiment of this invention. In the FIG. 1, numeral 101 designates a 
vehicle speed detector which is capable of detecting the speed of a 
vehicle by detecting the rotational speed of the driving shaft leading 
from the transmission output shaft to the axles, the speedometer cable or 
the like. Numeral 102 designates a detector for detecting a driving 
condition other than the vehicle speed, e.g., a detector for detecting an 
engine operating condition such as the pressure in the intake manifold. 
Numeral 26 designates an electric control circuit comprising a function 
voltage generator 103 and a drive circuit 104. The function voltage 
generator 103 utilizes the detection signals generated from the driving 
condition detectors 101 and 102 as control parameters for generating a 
function voltage to determine a target value for the carburetor 
air-to-fuel ratio control. Numeral 105 designates an electromagnetic valve 
constituting adjusting means, and the drive circuit 104 converts the 
function voltage into a drive voltage which is suitable for the control 
method of the electromagnetic valve 105. The electromagnetic valve 105 is 
a flow control actuator for varying the passage area of a fuel measuring 
system 106 such as the fuel passage, air bleed or the like of the 
carburetor in response to the drive voltage, thereby controlling the 
air-to-fuel ratio of the mixtures sucked into the engine. 
An embodiment of the invention will be described hereinbelow. Referring to 
FIG. 2 schematically showing the construction of the principal parts of 
the embodiment shown in FIG. 1, the basic construction of a carburetor 20 
comprises, as known well, a float 1, a float chamber 2, a main jet 3, a 
fuel passage 4, an air bleeder pipe 6, an air nozzle 7, an air jet 8, a 
main nozzle 9, venturies 10 and 11, a throttle valve 12, a bypass hole 18, 
a low-speed hole 19, an adjusting screw 16, a low-speed jet 15, and a 
low-speed air bleeder 17. In this embodiment, an electromagnetic valve 27 
is connected to the main jet 3 in the fuel measuring system of the 
carburetor 20 so that the effective area of the main jet 3 is controlled 
in response to the drive voltage generated from the electric control 
circuit 26. Numeral 24 designates a vehicle speed detector for detecting 
the running speed of the vehicle, and the vehicle speed detector 24 is 
attached to the speedometer cable take-off shaft of a transmission 25 of 
an engine 21. In this embodiment, other driving condition detectors than 
the vehicle speed detector 24 include an intake pressure detector 28 
disposed in an intake manifold 22 to detect the pressure in the intake 
manifold, and an oxygen content detector 29 disposed in an exhaust 
manifold 23 to detect the oxygen content of exhaust gases, whereby the 
air-to-fuel ratio of the mixtures produced in the carburetor 20 is 
controlled by utilizing the vehicle speed, intake manifold pressure and 
exhaust gas oxygen content as control parameters. Numeral 30 designates a 
three-way catalytic converter. 
FIG. 3 illustrates a wiring diagram showing one form of the electric 
control circuit 26. In the Figure, numeral 103 designates the function 
voltage generator whose construction will be described hereinafter. 
Numeral 24 designates the vehicle speed detector comprising a rotary 
magnetic operatively associated with the speedometer cable take-off shaft 
of the vehicle transmission and a reed switch actuated by the rotary 
magnet, whereby a vehicle speed pulse signal having a frequency 
proportional to the vehicle speed is generated and it is then converted to 
a voltage by a known type of frequency-to-voltage converter 37 comprising 
transistors 48 and 49, etc., thereby generating at a point B a voltage or 
vehicle speed voltage proportional to the vehicle speed. This vehicle 
speed voltage characteristic is shown in FIG. 4, in which the abscissa 
represents the vehicle speed S km/h) and the ordinate represents the 
vehicle speed voltage V.sub.S at the point B. The vehicle speed voltage 
V.sub.S generated at the point B is applied as an input signal to two 
vehicle speed function voltage generators 38 and 39 respectively, 
including differential-type operational amplifiers 50 and 51. 
Consequently, the resulting function voltages generates at output points D 
and F of the vehicle speed function voltage generators 38 and 39 have the 
characteristics shown in FIGS. 5 and 6, in which the abscissal represent 
the vehicle speed voltage V.sub.S and the ordinates reperesents the 
function voltages V.sub.D and V.sub.F generated at the points D and F, 
respectively. 
Numeral 28 designates the intake pressure detector disposed in the intake 
manifold 22 and comprising a pressure switch designed so that its contacts 
are closed when the intake manifold pressure P is equal to or lower than a 
preset value P.sub.1, i.e., when P.ltoreq. P.sub.1, whereas the contacts 
are opened when the pressure P exceeds the preset value P.sub.1, i.e., 
when P &gt; P.sub.1, and the detector 28 is connected to a resistor 64 at a 
point P to produce the pressure function voltage V.sub.P shown in FIG. 7. 
In the Figure, the abscissa represents the intake manifold absolute 
pressure P (mmHg) and the ordinate represents the pressure function 
voltage V.sub.P at the point P. 
Numeral 29 desigantes the oxygen content detector, disposed in the exhaust 
manifold 23 which is constructed as shown in FIG. 8 by way of example. 
Namely, it comprises a sintered zirconia tube 291 having its inner and 
outer surfaces subjected to platinum surface treatment to produce 
catalytic action, and electrodes 292 and 293 between which is produced an 
electromotive force U.sub.S corresponding to the oxygen content in the 
exhaust gases. The electromotive force characteristic of the oxygen 
content detector 29 is shown in FIG. 9. In the Figure, the absicca 
represents the excess air ratio .lambda., namely, where the fuel used is 
gasoline the air-to-fuel ratio of 14.5 : 1 corresponds to .lambda.=1, and 
the ordinate represents the electromotive force U.sub.S produced between 
the electrodes 292 and 293. The oxygen content detection signal U.sub.S is 
applied as an input to an oxygen content function voltage generator 36 
comprising a differential-type operational amplifier 47 which in turn 
produces at its output point A the oxygen content function voltage V.sub.A 
shown in FIG. 10. These function voltages are selectively passed through a 
selection circuit which generates a target function voltage V.sub.J for 
determining the air-to-fuel ratio. Diodes 56 and 57 and a resistor 62 
constitute an upper limit selection circuit, whereby a greater one of the 
function voltages V.sub.D and V.sub.P is selected to produce a value 
V.sub.G at a point G. Diodes 52 and 53 and a resistor 60 constitute a 
lower limit selection circuit, whereby a smaller one of the function 
voltages V.sub.A and V.sub.G is selected to produce a value V.sub.H at a 
point H. Diodes 58 and 59 and a resistor 63 constitute another lower limit 
selection circuit, whereby a smaller one of the function voltages V.sub.F 
and V.sub.P is selected to produce a value V.sub.I at a point I. Diodes 54 
and 55 and a resistor 61 constitute another upper limit selection circuit, 
whereby a greater one of the function voltages V.sub.H and V.sub.I is 
selected to produce a value V.sub.J at a point J. Thus, the resulting 
target function voltage V.sub.J produced at the point J has a pattern as 
shown in FIG. 11 in which the abscissa represents the vehicle speed S. In 
the Figure, the solid line indicates the pattern of the target function 
voltage V.sub.J obtained when the intake manifold vacuum P is lower than 
the preset value P.sub.1 of the vacuum switch 28, and the dotted line 
indicates the similar pattern obtained when P &gt; P.sub.1. Numeral 104 
designates the drive circuit which in this embodiment generates a timing 
pulse voltage at a predetermined repetition period which is independent of 
the engine rotational speed, and the time duration of this timing pulse is 
subjected to pulse-duration modulation in accordance with the target 
function voltage V.sub.J generated from the function voltage generator 
103, thereby generating a drive voltage to actuate the electromagnetic 
valve 27. Numeral 33 designates a sawtooth wave generator comprising 
differential-type operational amplifiers 41 and 42, a capacitor 43 and a 
resistor 44. The sawtooth wave generator 33 includes a Schmitt 
configuration and an integrator configuration which are connected to each 
other to constitute a closed loop circuit, thus generating at a point K a 
sawtooth wave voltage of a predetermined frequency. Numeral 34 designates 
a comparator comprising a differential-type operational amplifier 45 which 
receives as its inverting input signal the sawtooth wave voltage generated 
at the point K and as its non-inverting input signal the target function 
voltage V.sub.J generated at the point J to generate at an output point L 
a timing pulse voltage having a frequency equal to the frequency of the 
sawtooth wave voltage at the point K and a pulse duration proportional to 
the target function voltage V.sub.J at the point J. Namely, the sawtooth 
wave generator 33 and the comparator 34 constitute a pulse duration 
modulator whose characteristic is shown in FIG. 12. In the Figure, the 
abscissa represents the modulating voltage, in this case, the target 
function voltage V.sub.J is used, and the ordinate represents the time 
duration .tau. of the timing pulse generated at the point L. Thus, since 
the repetition frequency of the sawtooth wave voltage at the point K is 
constant, the repetition frequency of the timing pulse at the point L is 
maintained at a predetermined value irrespective of the engine rotational 
speed. As a result, the ratio between the time duration and the repetition 
period of the timing pulse or duty cycle d versus modulating voltage 
V.sub.J characteristic becomes as shown in FIG. 12. In the Figure, the 
ordinate represents the duty cycle d and the abscissa represents the 
modulating voltage V.sub.J. Consequently, the timing pulse at the point L 
is amplified by an amplifier 35 comprising a transistor 46, thereby 
producing a drive voltage for the electromagnetic valve 27. FIG. 2 shows 
one form of the electromagnetic valve 27 adapted for operation with the 
drive circuit shown in FIG. 3, in which when no timing pulse is applied to 
an exciting coil 271 of the electromagnetic valve 27, a moving core 272 is 
returned by a spring 273 and held in place by a stopper, with the result 
that the effective area of the main nozzle 3 in the carburetor 20 is 
decreased by a needle 274 coupled to the moving core 272, and the 
air-to-fuel ratio of the mixture produced in the carburetor 20 is 
increased, that is, the mixture is leaned out. On the other hand, when a 
timing pulse is applied to the exciting coil 271, the resulting 
electromagnetic attraction causes the moving core 272 and the needle 274 
to move to the right, with the result that the effective area of the main 
nozzle 3 is increased, and the air-to-fuel ratio of the mixture produced 
in the carburetor 20 is decreased, that is, the mixture is enriched. Thus, 
since the repetition frequency of the timing pulse is selected so that the 
delay in the opening and closing operation of the electromagnetic valve 27 
is negligible, the duration of opening of the electromagnetic valve 27 for 
every operating cycle thereof (the sum of the opening time and the closing 
time of the vavle) becomes equal to the ratio between the repetition 
period T and the time duration .tau. of the timing pulse or the duty cycle 
d = .tau./T (in this case, the repetition frequency of the timing pulse 
must be determined by taking into consideration the response of the 
carburetor fuel supply system and the engine), and the air-to-fuel ratio M 
of the mixtures produced in the carburetor 20 decreases with increase in 
the duty cycle of the timing pulse. This relation is graphically 
represented in FIG. 13, in which the abscissa represents the pulse 
duration .tau. and the duty cycle d of the timing pulse and the ordinate 
represents the air-to-fuel ratio M. 
With the construction described above, the operation of this embodiment is 
as follows. When the vehicle speed is S &lt; S.sub.1, e.g., when the vehicle 
is running at relatively low speeds lower than about 50 km/h, the vehicle 
is in an exhaust gas purifying driving range or a range where the emission 
of harmful gases must be reduced as far as possible, and cleaner exhaust 
emission driving conditions are required. In this case, the lower limit 
voltage V.sub.2 is selected as the function voltage V.sub.I while the 
function voltage V.sub.A is selected as the function voltage V.sub.H. As a 
result, the function voltage V.sub.A is selected as the target function 
voltage V.sub.J irrespective of the intake manifold pressure P, since the 
greater one of the function voltages V.sub.H and V.sub.I is selected to 
produce the value V.sub.J at the point J. It should be noted here that in 
the present system the air-fuel mixture is controlled to have the 
stoichiometric air-to-fuel ratio, if the amount of fuel to be supplied to 
the engine is controlled only by the function voltage V.sub.A. The reason 
for this is as follows. If the oxygen content detector 29 detects that the 
excess air ratio .lambda. of the mixture is larger than one, the function 
voltage V.sub.A become larger than the intermediate voltage V.sub.1 and in 
turn the duty cycle d is increased. When the duty cycle d is increased, 
the amount of fuel to be supplied to the engine is increased, whereby the 
excess air ratio .lambda. is decreased. Thus, the function voltage V.sub.A 
is reduced to approach the voltage V.sub.1. In a similar manner, when the 
function voltage V.sub.A is smaller than the voltage V.sub.1, the duty 
cycle d is decreased, whereby the excess air ratio .lambda. is increased. 
Thus, the function voltage V.sub.A is increased to approach the voltage 
V.sub.1. 
Accordingly, the function voltage V.sub.J remains at the voltage V.sub.1 
when the function voltage V.sub.A is selected as the target function 
voltage V.sub.J. Thus, the target function voltage V.sub.J is controlled 
at V.sub.J = V.sub.1 according to FIG. 11 and the timing pulse duty cycle 
d is controlled at d = d.sub.1 according to FIG. 12, thereby controlling 
the air-to-fuel ratio of the mixture with the carburetor air-to-fuel ratio 
M = 14.5 : 1 (air excess ratio .lambda. = 1) as the desired value 
according to FIG. 13. This permits the three-way catalytic converter 30 to 
purify the harmful constituents, i.e., CO, HC and NO.sub.x in the exhaust 
gases with the maximum efficiency. With the vehicle speed S &gt; S.sub.1 and 
the intake manifold pressure P .ltoreq. P.sub.1, the vehicle is in the 
intermediate and high speed normal running range where the vehicle is 
driven at intermediate and high speeds requiring no large acceleration 
performance, and in this range reduction in the fuel consumption is 
required, thus making it desirable to drive the vehicle under economical 
fuel consumption driving conditions where the air-to-fuel ratio is 
increased. In this case, both the function voltages V.sub.G and V.sub.I 
have the voltage V.sub.2. Thus, the smaller one of the function voltages 
V.sub.A and V.sub.G, i.e., the voltage V.sub.2 is selected as the function 
voltage V.sub.H. Accordingly, the target function voltage V.sub.J has the 
voltage V.sub.2 since both the function voltages V.sub.H and V.sub.I are 
the voltage V.sub.2. Thus, V.sub.J = V.sub.2 is determined accordingly to 
FIG. 11, d = 0 according to FIG. 12 and M = 16 : 1 according to FIG. 13. 
Similarly, with the vehicle speed S.sub.1 &lt; S &lt; S.sub.2 and the intake 
manifold pressure P &lt; P.sub.1, the vehicle is in the intermediate speed 
and high power output driving range where both the moderate acceleration 
performance and fuel consumption economy are required and planned. In this 
case, both the functional voltages V.sub.G and V.sub.I have the voltage 
V.sub.1. Accordingly the voltage V.sub.1 is selected as the target 
function voltage V.sub.J. Thus, V.sub. J = V.sub.1 is determined according 
to FIG. 11 and d = d.sub.1 according to FIG. 12 and hence controlling the 
air-to-fuel ratio with M = 14.5 : 1 as a target ratio according to FIG. 
13. The vehicle speed S.sub.2 is determined at about 100 km/h. With the 
vehicle speed S &gt; S.sub.2 and the intake manifold pressure P &gt; P.sub.1, 
the vehicle is in the high speed and power output driving range where both 
the high speed and high acceleration performance are required, thus 
planning high power output driving conditions where the air-to-fuel ratio 
is decreased. In this case, the target function voltage has the upper 
limit voltage V.sub.3 since the voltage V.sub.3 is selected as the 
function voltage V.sub.I. Thus, V.sub.J = V.sub.3 is determined according 
to FIG. 11, d = 1.0 according to FIG. 12 and hence M = 13 : 1 according to 
FIG. 13. Thus, FIG. 14 shows the resulting control pattern of the 
air-to-fuel ratio M (ordinate) which is provided by the carburetor 20, 
with the vehicle speed S (absicssa) and the intake manifold pressure P 
(parameter). Thus, the required characteristic for the engine is ensured 
to suit all the different driving conditions of the vehicle. 
While, in the embodiment shown by the wiring diagram of FIG. 3, three 
different detectors are used as the required driving condition detectors, 
it is possible to use various detectors for detecting the amount of air 
drawn into the engine, engine rotational speed, engine temperature, 
pressure, etc., and using the resulting outputs as the additional control 
parameters to produce the target function voltage and thereby control the 
air-to-fuel ratio. 
Further, while, the intake pressure detector 28 shown in FIG. 3 comprises a 
pressure switch whose output changes in a stepwise manner at the preset 
pressure P.sub.1, it is possible to use for example a semiconductor 
pressure transducer to detect continuously the pressure in the intake 
manifold. FIG. 15 illustrates a wiring diagram showing one form of such 
pressure transducer, in which numeral 28 designates a semiconductor 
pressure transducer, 71 a differential-type operational amplifier for 
amplifying the transducer output signal to produce a pressure function 
voltage V.sub.P. The resulting intake pressure function voltage 
characteristic is shown in FIG. 16, in which the ordinate represents the 
intake pressure function voltage V.sub.P and the abscissa represents the 
intake manifold pressure P. FIG. 17 shows the air-to-fuel ratio control 
characteristic obtained by using this pressure function voltage generating 
circuit in place of the intake pressure detector 28 of FIG. 3 comprising a 
pressure switch, and consequently the intake manifold pressure changes 
continuously from small to large values, thus making it possible to 
continuously control the air-to-fuel ratio throughout the range of the two 
solid lines and the hatched line defined by the former and thereby 
accomplishing finer control of the air-to-fuel ratio. 
Referring now to FIG. 18, there are shown another embodiment of the 
electromagnetic valve 27 and the amplifier circuit 35 of the drive circuit 
adapted for use with this electromagnetic valve. The electromagnetic valve 
comprises a moving core 272' centrally disposed between a pair of exciting 
coils 271' and 271", and a needle 274' coupled to the moving core 272' to 
vary the effective area of the carburetor main jet 3, whereby the exciting 
currents for the pair of exciting coils 271' and 271" are supplied by the 
collector currents of transistors 46' and 46". The base of the transistor 
46" is connected through the inverter 279 to the terminal L of the pulse 
modulator of FIG. 3, and the base of the transistor 46' is connected to 
the point L. Consequently, the "on" time of the transistor 46' is equal to 
the timing pulse duration .tau., and the "on" time of the transistor 46" 
is equal to the "off" period of the timing pulse, with the result that the 
average current in the exciting coil 271' is proportional to the timing 
pulse duty cycle d, and the average current in the exciting coil 271" is 
proportional to (1-d). If the characteristics of the exciting coils 271' 
and 271" are symmetrical, a magnetic attraction is produced whose 
magnitude is represented by the effective core position in the exciting 
coils and the average value of the exciting currents. Thus, if the moving 
core position is shown in terms of its distance X from a stopper means 
275', then the moving core position or the distance X is determined in 
accordance with the duty cycle of the timing pulse as shown in FIG. 19. As 
a result, when d = 0, then X = 0 and the effective area of the main jet 3 
is reduced to a minimum, while when d = 1.0, then X = X.sub.m and the 
effective area of the main jet 3 is increased to a maximum. FIG. 20 shows 
the resulting control characteristic of the air-to-fuel ratio M in the 
carburetor 20 in relation to the position X. Thus, by replacing the 
amplifier circuit 35 in the wiring diagram of FIG. 3 by the circuit shown 
in FIG. 18, it is possible to control the air-to-fuel ratio in the 
carburetor in the previously mentioned manner with the electromagnetic 
valve shown in FIG. 18. 
FIG. 21 shows still another embodiment of the electromagnetic valve 27. In 
the Figure showing an example of moving coil type electromagnetic valve, a 
moving coil 372 is disposed in the gap of a magnetic path formed by a 
permanent magnet 371 and yokes 374 and 375, and a needle 373 is coupled to 
the moving coil 372 to vary the effective area of the carburetor main 
nozzle 3. In the Figure, numeral 377 designates a stopper, 378 an 
amplifying transistor constituting an emitter follower circuit, 379 a 
spring. FIG. 22 shows variation of the position X of the moving coil 372 
in relation to the voltage V.sub.J applied to a signal input terminal J' 
of the amplifying transistor 378. Also, the resulting control 
characteristic of the air-to-fuel ratio M in the carburetor 20 in relation 
to the position X is the same as shown in FIG. 20. Thus, by connecting the 
terminal J' to the function voltage generating terminal J of the function 
voltage generator 103 of FIG. 3, it is possible to cause the exciting 
current to flow in the moving coil 372 in proportion to the function 
voltage V.sub.J, thus making it possible to control the effective area of 
the main jet and thereby control the air-to-fuel ratio in the similar 
manner as mentioned previously. 
While, in the above-described embodiment, the electromagnetic valve is 
mounted on the carburetor in a manner that it acts on the main jet of the 
carburetor, it is possible to cause the electromagnetic valve to act on 
any component part of the fuel measuring system of the carburetor. For 
example, it is possible to cause the electromagnetic valve to act on any 
of the fuel passage 4, the air bleeder pipe 6, the air nozzle 7, the air 
jet 8 and the main nozzle 9, or alternately a separate fuel measuring 
system for the electromagnetic valve may be disposed in the conventional 
fuel measuring system of the carburetor. 
Further, while the carburetor shown in FIG. 2 is of the single barrel type, 
the air-to-fuel ratio may be controlled similarly by mounting an 
electromagnetic valve in either one or both of the primary fuel measuring 
system and the secondary fuel measuring system of a two-barrel carburetor 
in the similar manner as mentioned previously. 
Furthermore, while, in the above-described embodiment, the effective area 
of the main jet in the fuel measuring system of the carburetor is 
controlled by the electromagnetic valve 27 in response to the function 
voltage V.sub.J from the function voltage generator 103, the air-to-fuel 
ratio of the mixtures supplied to a vehicle mounted internal combustion 
engine may be controlled by such means which for example controls the 
pressure in the carburetor float chamber or the amount of air supplied 
into the carburetor.