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What is claimed is:
1. An air-to-fuel ratio control system for internal combustion engines
comprising:
a carburetor, provided in the intake passage of an engine of a vehicle, for
supplying said engine with air-fuel mixture, said carburetor including a
float chamber in which fuel is stored, a venturi at which said fuel is
mixed with air, and a fuel passage which communicates said float chamber
with said venturi;
a speed detector for generating a first signal indicative of the vehicle
speed;
an air-to-fuel ratio detector, provided in the exhaust passage of said
engine, for generating a second signal related to the air-to-fuel ratio of
said mixture supplied to said engine;
a pressure detector, provided in said intake passage, for generating a
third signal indicative of the pressure in said intake passage;
a frequency-to-voltage converter circuit connected to said speed detector,
for generating a fifth voltage signal whose voltage corresponds to the
frequency of said first signal;
a first vehicle-speed function voltage generator connected to said
frequency-to-voltage converter circuit, for generating a sixth voltage
signal related to the comparison of said fifth voltage signal to a first
predetermined level;
a second vehicle-speed function voltage generator connected to said
frequency-to-voltage converter circuit, for generating a seventh voltage
signal related to the comparison of said fifth voltage signal to a second
predetermined level;
a first logical circuit connected to said first vehicle-speed function
voltage generator and said pressure detector, for generating a first
logical output signal from said second sixth signal and said third signal;
a second logical circuit connected to said second vehicle-speed function
voltage generator and said pressure detector, for generating a second
logical output signal from said seventh voltage signal and said third
signal;
a third logical circuit connected to said first logical circuit and said
air-to-fuel ratio detector, for generating a third logical output signal
from said first logical output signal and said second signal; and
a fourth logical circuit connected to said second and third logical
circuits, for generating a fourth signal by logical operation on said
second and third logical output signals so that said fourth signal
corresponds to said second signal when the speed of said vehicle is less
than a first predetermined value, to one of said second and third signals
when the speed of said vehicle is between said first value and a second
predetermined value greater than said first value and to said third signal
when the speed of said vehicle is greater than said second value; and
electromagnetic valve means, connected to said function signal generator
and provided in said fuel passage, for controlling the amount of fuel
flowing therethrough in response to said fourth signal, whereby the
air-to-fuel ratio of said mixture is switched in response to said speed of
said vehicle.
2. An air-to-fuel ratio control system as set forth in claim 1, wherein
each of said first, second, third and fourth logical circuits includes at
least two diodes.
3. An air-to-fuel ratio control system as set forth in claim 1 wherein:
said electromagnetic valve means includes:
a moving core having a needle valve portion which moves to control the
amount of fuel flowing through said fuel passage, and
first and second exciting coils electromagnetically coupled to said moving
core, the needle valve portion of said moving core being moved in one
direction to increase the amount of fuel upon the energization of said
first exciting coil, and being moved in the other direction to decrease
the amount of fuel upon the energization of said second exciting coil; and
said system further comprises:
a pulse generator, connected between said electromagnetic valve means and
said function signal generator, for generating a pulse signal having a
fixed frequency and a time duration which varies in response to said
function signal, said pulse signal controlling said electromagnetic valve
means, said pulse generator including first and second energizing circuits
connected to said first and second exciting coils, respectively, for
alternately energizing said first and second exciting coils in response to
said pulse signal, whereby the position of said moving core being varied
in accordance with the duty cycle of one of said energizing means.
4. An air-to-fuel ratio control system as set forth in claim 1, wherein
said pressure detector includes mechanical switch means which is actuated
at a predetermined level of pressure.
5. An air-to-fuel ratio control system as set forth in claim 1, wherein
said pressure detector includes a pressure sensitive semiconductor for
generating an output signal, in analog form, corresponding to the pressure
in said intake passage.
6. An air-to-fuel ratio control system for internal combustion engines
comprising:
a carburetor, provided in the intake passage of an engine of a vehicle, for
supplying said engine with air-fuel mixture, said carburetor including a
float chamber in which fuel is stored, a venturi at which said fuel is
mixed with air, and a fuel passage which communicates said float chamber
with said venturi;
a speed detector for generating a first signal indicative of the vehicle
speed;
an air-to-fuel ratio detector, provided in the exhaust passage of said
engine, for generating a second signal related to the air-to-fuel ratio of
said mixture supplied to said engine;
a pressure detector, provided in said intake passage, for generating a
third signal indicative of the pressure in said intake passage;
a function signal generator, connected to said detectors, for generating a
fourth signal related to said second signal when the speed of said vehicle
is less than a first predetermined value, to one of said second and third
signals when the speed of said vehicle is between said first value and a
second predetermined value, greater than said first value and to said
third signal when the speed of said vehicle is greater than said second
value;
magnetic path forming means having a permanent magnet;
a moving core having a needle valve portion which moves to control the
amount of fuel flowing through said fuel passage, said moving core
mounting an exciting coil thereon;
spring means connected to said magnetic path forming means and said moving
core, for biasing said moving core; and
current control means connected between said function signal generator and
the exciting coil mounted on said moving core, for controlling a current
to said exciting coil in proportion to the voltage of said fourth signal.
7. In an automotive vehicle driven by an internal combustion engine having
a carburetor for supplying air-fuel mixture, an air-to-fuel ratio control
system comprising:
a plurality of condition detectors for detecting the operating conditions
of said engine, respectively;
a speed detector for detecting the travelling speed of said vehicle;
a function generator connected to said condition detectors and said speed
detector for generating an output according to first and second functions
when said travelling speed of said vehicle is lower and higher than a
predetermined speed, respectively, said first function related to at least
one of said operating conditions of said engine and said second function
related to at least one of said operating conditions of said engine
different from said at least one of said operating conditions related to
said first function;
a pulse generator connected to said function generator for generating a
train of pulse signals at a fixed frequency, each of said pulse signals
having respective time intervals proportional to said function output;
a needle valve positioned in said carburetor for controlling the
air-to-fuel ratio of air-fuel mixture supplied to said engine in
proportion to the position thereof; and
electromagnetic means having a movable core secured to said needle valve
and a first and second exciting coils arranged longitudinally such that
said movable core is moved therethrough, longitudinally such that said
movable core is moved therethrough, said first and second coils being
connected to said pulse generator to be energized in response to the
presence and the absence of said pulse signals, respectively for
controlling the position of said movable core in proportion to said time
intervals of said pulse signals.
8. An air-to-fuel ratio control system according to claim 7, wherein said
carburetor includes a float chamber in which fuel is stored, a venturi at
which said fuel is mixed with air and a fuel passage which communicates
said float chamber with said venturi, and wherein said needle valve is
positioned in said fuel passage to control the amount of fuel flowing from
said float chamber to said venturi.
9. An air-to-fuel ratio control system according to claim 8, wherein said
condition detectors includes an air-to-fuel ratio detector for detecting
the air-to-fuel ratio of air-fuel mixture supplied to said engine in
response to the oxygen concentration in the exhaust gases and a pressure
detector for detecting the pressure in the intake manifold of said engine,
and wherein said first function is related to said air-to-fuel ratio
detected by said air-to-fuel ratio detector and said second function is
related to said pressure detected by said pressure detector. |
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Claims |
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Description |
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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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the construction of an electric
air-to-fuel ratio control system according to an embodiment of the
invention.
FIG. 2 is a partial sectional schematic diagram showing the principal
mechanical parts of the system according to the invention.
FIG. 3 is a wiring diagram showing a detailed construction of the electric
circuit section of the system according to the invention.
FIG. 4 is a vehicle speed voltage characteristic diagram.
FIGS. 5 and 6 are vehicle speed function voltage characteristic diagrams.
FIG. 7 is an intake manifold pressure function voltage characteristic
diagram.
FIG. 8 is a sectional view showing the principal parts of an oxygen content
detector.
FIG. 9 is an output signal characteristic diagram of the oxygen content
detector of FIG. 8.
FIG. 10 is an oxygen content function voltage characteristic diagram.
FIG. 11 is a target function voltage characteristic diagram.
FIG. 12 is a pulse duration modulation characteristic diagram.
FIG. 13 is an air-to-fuel ratio variation characteristic diagram.
FIG. 14 is an air-to-fuel ratio control characteristic diagram.
FIG. 15 is a wiring diagram showing another construction of the intake
manifold pressure function voltage generator.
FIG. 16 is an intake manifold pressure function voltage characteristic
diagram.
FIG. 17 is an air-to-fuel ratio control characteristic diagram.
FIG. 18 is a schematic diagram showing another detailed construction of the
electromagnetic valve.
FIG. 19 is a characteristic diagram of the electromagnetic valve shown in
FIG. 18.
FIG. 20 is a position X versus air-to-fuel ratio M characteristic diagram.
FIG. 21 is a schematic diagram showing still another construction of the
electromagnetic valve.
FIG. 22 is a characteristic diagram of the electromagnetic valve shown in
FIG. 21.
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 > 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 > 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 < 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 > 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 < S < S.sub.2 and the intake
manifold pressure P < 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 > S.sub.2 and the intake manifold pressure P > 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.
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