Apparatus for controlling the proportion of air and fuel in an air-fuel mixture of the internal combustion engine

An apparatus for controlling the proportion of air and fuel in the air-fuel mixture of the internal combustion engine includes a carburetor having a main system fuel tube, a main system air-bleeding passage, a slow system fuel tube and a slow system air-bleeding passage, and a proportional control solenoid valve including an air-inlet port, a first outlet port communicating with the main system air-bleeding passage, a second outlet port communicating with the slow system air-bleeding passage and a moving-coil linear motor incorporated therein, wherein the proportional control solenoid valve is adapted to supply air to the main system air-bleeding passage and the slow system air-bleeding passage at a flow rate proportional to the level of the intensity of an electric current supplied to the moving-coil linear motor when the intensity of the electric current lies within a range between two predetermined values Imin and Imax.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus to control the ratio of air 
to fuel of the air-fuel mixture which is supplied to an internal 
combustion engine, and more particularly to an apparatus provided for 
controlling the amount of air supplied to the main system fuel passage and 
the slow system fuel passage of a carburetor for supplying an air-fuel 
mixture to an internal combustion engine by means of a single proportional 
control solenoid valve. 
2. Description of the Prior Art 
It is known to incorporate a catalytic converter have ternary catalytically 
active substances into the exhaust system of the internal combustion 
engine of an automobile in order to simultaneously reduce the injurious 
components of the exhaust gas, such as hydrocarbons (HC), carbon monoxide 
(CO) and nitrogen oxides (NOx). It is required to supply an air-fuel 
mixture of an air-fuel ratio corresponding to the stoichiometric air-fuel 
ratio into the cylinders of an internal combustion engine, since the 
maximum cleaning efficiency of the ternary catalytically active substances 
is attained when the exhaust gas is produced by the combustion of an 
air-fuel mixture of the stoichiometric air-fuel ratio. An air-fuel ratio 
controller to meet such a requirement is proposed, which includes a main 
system air-bleeding passage connected to the main system fuel passage 
connecting to the main jet of a carburetor, a slow system air-bleeding 
passage connected to the slow system fuel passage connecting to the slow 
system fuel supply port of the carburetor, and a main system proportional 
control solenoid valve for controlling the main air bleeder and a slow 
system proportional control solenoid valve for controlling the slow air 
bleeder, which are disposed within the main system air-bleeding passage 
and the slow system air-bleeding passage, respectively, and are adapted to 
be controlled by a control signal provided by converting the output signal 
of an oxygen sensor disposed within the exhaust passage of the engine by 
means of an electronic control unit. It is proposed to control the rate of 
air to be supplied to the main system fuel passage and to the slow system 
fuel passage through the main system air-bleeding passage and through the 
slow system air-bleeding passage, respectively, with an air-fuel ratio 
controller as described above, so that the air-fuel ratio of the air-fuel 
mixture which is supplied into the cylinders of an engine is controlled so 
as to be close to the stoichiometric air-fuel ratio. 
However, heretofore known air-fuel ratio controllers of this type for 
carburetor are provided with individual proportional control solenoid 
valves in the main system air-bleeding passage and the slow system 
air-bleeding passage, respectively, and are adapted to control both 
proportional control solenoid valves simultaneously with the control 
signal of a single system provided by the control signal producing circuit 
of an electronic control unit. Accordingly, the electronic control unit is 
required to supply an electric current simultaneously to the main system 
and the slow system proportional control solenoid valves. Therefore, the 
electronic control unit is necessary to be capable of supplying an 
electric current twice as much as that to be supplied to a single 
solenoid. Thus such conventional air-fuel ratio controllers have a 
disadvantage that the control signal producing circuit of the electronic 
control unit must consist of elements which have superior current 
capacities. 
SUMMARY OF THE INVENTION 
The primary object of the present invention is to provide an apparatus 
capable of controlling the amount of air which is supplied to the main 
system fuel passage and the slow system fuel passage of a carburetor for 
supplying an air-fuel mixture to an internal combustion engine with a 
single proportional control solenoid valve. 
According to the present invention, there is provided an apparatus for 
controlling the proportion of air and fuel in the air-fuel mixture of the 
internal combustion engines, including in combination: a carburetor, a 
proportional control solenoid valve and control means for controlling the 
solenoid valve. The carburetor includes an air horn tube having a venturi 
tube and a throttle valve and being connected to the intake manifold of an 
internal combustion engine, a main system fuel tube opening into the main 
nozzle of the venturi tube at one end thereof and communicating with a 
main system fuel passage through the other end thereof, a slow system fuel 
tube opening into a slow system fuel supply port which is adjacent to the 
throttle valve of the air horn tube at one end thereof and communicating 
with a slow system fuel passage through the other end thereof. The 
proportional control solenoid valve includes a box-shaped housing formed 
of a magnetic material and provided with an air-inlet port, a first outlet 
port connected to the main system air-bleeding passage and a second outlet 
port connected to the slow system air-bleeding passage, a single iron core 
having a tubular periphery, supported by the housing at opposite ends 
thereof and provided with separately formed first and second passages 
communicating with the first outlet port and the second outlet port, 
respectively, at the opposite end thereof, first valve openings formed in 
the shape of an oblong circle extending axially of the iron core in the 
portion of the iron core provided with the first passage and adapted to 
allow communication of the first passage with the air-inlet port, and 
second valve openings formed in the shape of an oblong circle extending 
axially of the iron core in the portion of the iron core provided with the 
second passage and adapted to allow communication of the second outlet 
port with the air-inlet port, single bobbin axially slidably mounted on 
the periphery of the iron core, provided with a solenoid wound around the 
periphery in an axial portion thereof and having a first valve element and 
a second valve element for opening and closing the first valve openings 
and the second valve openings, spring means urging the bobbin in one axial 
direction of the iron core and at least one pair of permanent magnets 
fixed to the housing at a position corresponding to the solenoid and so 
disposed that the flux of the magnetic force thereof is passing 
perpendicular to the solenoid. The control means is provided for supplying 
analog electric signals to the solenoid of the proportional control 
solenoid valve, whereby the bobbin of the proportional control solenoid 
valve moves axially along the iron core by a distance proportional to the 
level of the analog electric signal applied to the solenoid by the control 
means and the first valve element and the second valve element each formed 
in the bobbin open the first valve openings and the second valve openings, 
respectively, by the respective areas corresponding to the level of the 
analog electric signals applied to the solenoid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the accompanying drawings, and first to FIG. 1, indicated by 
reference numeral 1 is an internal combustion engine and by reference 2 is 
a carburetor. The carburetor 2 is mounted on the intake manifold 9 of the 
engine 1 by joining the air horn tube 11 thereof to the intake manifold 9. 
A catalytic converter 16a having ternary catalytic active substances is 
attached to the exhaust manifold 16. 
The carburetor is provided, within the air horn tube 11, with a venturi 
tube 12 and a throttle valve 13 and is connected to the intake manifold 20 
of the engine at the downstream end of the air horn tube 11 and receives 
an air cleaner on the upstream end of the air horn tube 11. 
A main nozzle 12b formed at one end of a main system fuel tube 12a is 
opening into the venturi tube 12. The main system fuel tube 12a is 
connected to a float chamber 28 through a main system fuel passage 29a and 
a main system adjusting jet 28a. An air-bleeding tube 18a is disposed 
within the main system fuel passage 29a and is opened into the atmosphere 
through a fixed jet 18b. The main system fuel tube 12a is connected to the 
first outlet port 10b of a proportional control solenoid valve 10 through 
a main air-bleeding passage 18. A slow system fuel passage 29b is branched 
from the main system fuel passage 29a. The slow system fuel passage 29b is 
connected, through a slow system fuel tube 19a, to a slow system fuel 
supply port including an idling fuel jet 14 and a slow fuel port 15 which 
are opened into the air horn tube 11 in the vicinity of the throttle valve 
13. Further, the slow system fuel passage 29b is opened into the 
atmosphere through a fixed jet 19b and is connected to the air-inlet port 
10a of the proportional control solenoid valve 10 through the slow system 
air-bleeding passage 19. 
An oxygen sensor 17 is attached to the exhaust manifold 16 of the internal 
combustion engine 1 and the output signal 17a of the oxygen sensor 17 is 
applied to an electronic control unit 20. The proportional control 
solenoid valve 10 is controlled by control signals provided by the 
electronic control unit 20. 
The description of the proportional control solenoid valve 10 will be 
provided hereinafter with reference to FIG. 2. The proportional control 
solenoid valve 10 comprises a box-shaped housing formed by coaxially, 
sequentially, hermetically and fixedly joining a stepped cylindrical end 
portion 21 formed of a magnetic material and having the first outlet port 
10b communicating with the main system air-bleeding passage 18, a stepped 
cylindrical yoke 25 formed of a magnetic material and having a plurality 
of through holes 25a and 25b which are formed in the peripheral wall 
thereof and a disc-shaped end cover 23 having the second outlet port 10c 
communicating with the slow system air-bleeding passage 19, and a 
moving-coil linear motor 30 disposed within the yoke 25 of the housing. 
A filter cover 22 forming an annular air-inlet port 10a along the outer 
surface thereof and holding a filter 24 therein is hermetically fixed to 
the yoke 25 so as to allow communication of the inside space of the 
housing with the air-inlet port 10a through the through holes 25a and 25b 
formed in the yoke 25 and through the filter 24. 
The moving-coil linear motor 30 comprises an iron core 31 which is 
hermetically held between the end portion 21 and the end cover 23 and is 
provided with a first passage P.sub.1 communicating with the first outlet 
port 10b at the left end and a second passage P.sub.2 communicating with 
the second outlet port 10c at the right end as shown in FIG. 2, which are 
formed separately, a bobbin 32 axially slidably mounted on the iron core 
31 in the left portion thereof, a solenoid 33 wound on the bobbin 32, a 
spring holder 34 fitted on the iron core 31 in the right portion thereof 
and adapted for positional adjustment, a pair of conductive compression 
springs 36 and 37 interposed between the spring holder 34 and a 
nonconductive spring holder 35 fitted on the right-hand extension of the 
bobbin 32, and a pair of permanent magnets 38 and 39 fixed to the yoke 25 
so provided that the flux of the magnetic force thereof is passing 
substantially perpendicular with respect to the winding of the solenoid 
33. The respective left ends of the compression coil springs 36 and 37 are 
connected to the corresponding terminals of the winding of the solenoid 
33, while the respective right ends are connected to lead wires 50a and 
50b, respectively. The compression coil springs 36 and 37 are electrically 
insulated from the spring holder 34. Thus the axial sliding movement of 
the bobbin 32 of the linear motor 30 is controlled proportionally to the 
intensity of the current which is supplied to the solenoid 33 through the 
lead wires 50a and 50b and the compression coil springs 36 and 37. 
A plurality of first valve openings 31a formed in an oblong circle 
extending axially of the iron core 31 are formed at equal circumferential 
intervals in the iron core 31 in the portion thereof provided with the 
first passage P.sub.1. A first valve element 32a is formed on the inner 
circumference of the left end portion of the bobbin 32. A first control 
valve V.sub.1 including the first valve openings 31a and the first valve 
element 32a is formed between the iron core 31 and the bobbin 32. While no 
electric current is supplied to the solenoid 33, the first control valve 
V.sub.1 closes the first valve openings 31a and the first valve element 
32a is positioned a distance l to the left from the left end of the first 
valve openings 31a. A plurality of second valve openings 31b each of the 
shape of an oblong circle extending axially of the iron core 31 are formed 
at equal circumferential intervals in the right-hand portion of the iron 
core 31 provided with the second passage P.sub.2. An annular recess 32c 
communicating with through holes 32d formed at appropriate intervals are 
formed in the inner circumference of the right-hand portion of the bobbin 
32. A stepped second valve element 32b is formed at the right end of the 
annular recess 32c. A second control valve V.sub.2 including the second 
valve openings 31b and the second valve element 32b is formed between the 
iron core 31 and the bobbin 32. While no electric current is supplied to 
the solenoid 33, the second control valve V.sub.2 closes the second valve 
openings 31b and the second valve element 32b is positioned a distance l 
to the left from the left end of the second valve openings 31b. When an 
electric current is supplied to the solenoid 33 of the linear motor 30, 
the bobbin 32 is caused to move rightward against the resilient force of 
the compression coil springs 36 and 37. When the bobbin 32 is moved from 
the left extreme position by a distance l, the first valve element 32a and 
the second valve element 32b of the first control valve V.sub.1 and the 
second control valve V.sub.2 start opening the first valve openings 31a 
and the second valve openings 31b, respectively (the distance l will be 
designated as "an idle stroke" hereinafter). After the first control valve 
V.sub.1 has opened the first valve openings 31a, air is supplied to the 
main system air-bleeding passage 18 through the air-inlet port 10a, filter 
24, through holes 25a and 25b of the yoke 25, first valve openings 31a, 
first passage P.sub.1 and first outlet port 10b. After the second control 
valve V.sub.2 has opened the second valve openings 31b, air is supplied to 
the slow system air-bleeding passage 19 through the air-inlet port 10a, 
filter 24 through holes 25a and 25b of the yoke 25, a through hole 35b 
formed through the spring holder 35, second valve openings 31b and second 
outlet port 10c. The respective quantities of air which is supplied into 
the main system air-bleeding passage 18 and the slow system air-bleeding 
passage 19 are controlled corresponding to the respective opening areas of 
the first valve openings 31a and the second valve openings 31b, and hence 
corresponding to the intensity of the electric current which is supplied 
to the solenoid 33 of the linear motor 30. 
The oxygen sensor, as generally known, is sensitive to the oxygen partial 
pressure in the exhaust gas. Such an oxygen sensor having a solid 
electrolyte, preferably made of zirconium oxide, has previously been 
proposed. It is known that the output of an oxygen sensor of this type 
changes suddenly in a very short response time when the air-fuel ratio of 
the air-fuel mixture supplied to an internal combustion engine is 
equivalent to a fixed value around the stoichiometric air-fuel ratio. 
Generally, the oxygen sensor does not provide any output signal while the 
air-fuel ratio of the air-fuel mixture being supplied to the engine is 
smaller than the fixed value (lean air mixture), whereas the oxygen sensor 
provides an output signal when the air-fuel ratio exceeds the fixed value. 
The electronic control unit 20 shown in FIG. 1 is adapted to increase the 
electric current of the output signal 20a gradually with the lapse of time 
whie the output signal 17a of the oxygen sensor 17 is applied to the 
electronic control unit 20 and to reduce the electric current of the 
output signal 20a gradually with the lapse of time while no output signal 
17a of the oxygen sensor 17 is applied to the electronic control unit 20. 
Accordingly, when the output signal 17a of the oxygen sensor 17 is applied 
to the electronic control unit 20, the electronic control unit 20 applies 
an analog electric signal 20a, which increases with the lapse of time, to 
the solenoid 33 so that the bobbin 32 is caused to move by a distance 
proportional to the value of the signal. The movement of the bobbin 32, as 
described hereinbefore, results in an air supply to the main system 
air-bleeding passage 18 and the slow system air-bleeding passage 19. 
The features of the apparatus for controlling the proportion of air and 
fuel in the air-fuel mixture of the internal combustion engine thus 
constituted in accordance with the present invention will be described 
hereinafter with reference to the aforementioned embodiment. The distance 
of the movement of the bobbin 32 is proportional to the intensity of 
electric current supplied to the solenoid 33 of the linear motor 30. The 
idle stroke of the bobbin 32 of the linear motor 30 from the closing 
position to the start of opening is l, which is common to the first 
control valve V.sub.1 and the second control valve V.sub.2. Accordingly, 
the control valves V.sub.1 and V.sub.2 start opening at a current 
intensity of Imin, then the air flow rate increases in proportion to the 
current intensity with the increase in the electric current and finally, 
an utmost flow rate Qmax is attained at a current intensity of Imax in 
which the valve openings 31a and 32a are fully opened. Therefore, the air 
supply control for the main system air-bleeding passage as well as for the 
slow system air-bleeding passage, hence the air-fuel ratio control of the 
carburetor, can be attained through the supply of an electric current 
corresponding to the opening degree of the first or the second control 
valve V.sub.1 or V.sub.2 capable of providing a required air-bleeding rate 
from the electronic control unit 20 to the solenoid 33 of the proportional 
control solenoid valve 10. 
It will be well understood from what has been described hereinbefore that 
the apparatus for controlling the proportion of air and fuel in the 
air-fuel mixture in accordance with the present invention is capable of 
actuating two control valves with a control signal current for controlling 
a single proportional control solenoid valve of an intensity which is 
substantially the same with that of a current which is necessary for 
controlling a conventional proportional control solenoid valve having a 
single control valve, thus attaining the object of the present invention. 
Furthermore, the present invention provides also an advantage that the 
load on the power source for driving the electronic control unit can be 
reduced, since a reduced electric current is necessary. Still further, the 
use of a single proportional control solenoid valve integrally including 
two control valves simplifies the constitution of the apparatus for 
controlling the proportion of air and fuel in the air-fuel mixture. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.