U.S. patent number 3,921,612 [Application Number 05/505,540] was granted by the patent office on 1975-11-25 for apparatus for and method of controlling air-fuel mixture in a carburetor of an automotive internal combustion engine.
This patent grant is currently assigned to Nissan Motor Company Limited. Invention is credited to Shigeo Aono.
United States Patent |
3,921,612 |
Aono |
November 25, 1975 |
Apparatus for and method of controlling air-fuel mixture in a
carburetor of an automotive internal combustion engine
Abstract
The richness of an air-fuel mixture produced by a carburetor of
an internal combustion engine of an automotive vehicle, by
increasing the pressure of air behind the fuel in a fuel discharge
circuit for enrichment of the air-fuel mixture if the mixture is
found excessively lean or injecting pressurized air into the fuel
flowing in the fuel discharge circuit for leaning out the mixture
if the mixture is found excessively rich. Increasing the air
pressure behind the fuel in the fuel discharge circuit gives rise
to an increase in the flow rate of the fuel to be discharged and
injection of pressurized air into the fuel flowing in the fuel
discharge circuit is causative of reduction of density of the fuel
to be discharged and accordingly contribute to reduction of the
flow rate of the fuel discharged from the circuit.
Inventors: |
Aono; Shigeo (Seki,
JA) |
Assignee: |
Nissan Motor Company Limited
(Yokohama, JA)
|
Family
ID: |
14414660 |
Appl.
No.: |
05/505,540 |
Filed: |
September 13, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Sep 19, 1973 [JA] |
|
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48-105701 |
|
Current U.S.
Class: |
123/438; 123/699;
261/DIG.67; 261/39.1; 261/121.4; 60/276; 261/DIG.19; 261/19;
261/72.1 |
Current CPC
Class: |
F02M
3/09 (20130101); F02M 7/24 (20130101); F02M
7/11 (20130101); F02D 35/00 (20130101); F02M
7/28 (20130101); Y10S 261/67 (20130101); Y10S
261/19 (20130101) |
Current International
Class: |
F02M
3/09 (20060101); F02D 35/00 (20060101); F02M
7/11 (20060101); F02M 7/28 (20060101); F02M
7/00 (20060101); F02M 3/00 (20060101); F02B
032/00 (); F24F 003/14 (); F02D 011/08 () |
Field of
Search: |
;123/32EA,32AE,119R,13R
;261/72R,121B,19,39R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Cop; Ronald B.
Claims
What is claimed is:
1. An apparatus for controlling the richness of an air-fuel mixture
produced by a carburetor of an internal combustion engine of an
automotive vehicle, comprising first passage means having an outlet
end open into a substantially closed space behind the fuel in a
fuel discharge circuit of the carburetor; second passage means
having an outlet end open into said fuel discharge circuit; a
source of pressurized air; air-flow regulator valve means in
communication with the source of pressurized air and operative to
regulate the flow rate of pressurized air through the valve means
when actuated; air-flow shift valve means having a first operative
condition providing communication between said air-flow regulator
valve means and said first passage means and a second operative
condition providing communication between said air-flow regulator
valve means and said second passage means; and an electric control
unit responsive to predetermined operating conditions of the
vehicle and operative to supply a first control signal to said
air-flow regulator valve means for varying the flow rate of
pressurized air through the regulator valve means in accordance
with said operating conditions of the vehicle and a second control
signal to said air-flow shift valve means for holding the air-flow
shift valve in said first operative condition when the vehicle
operating conditions are representative of an excessively lean
condition of the air-fuel mixture being produced in the carburetor
or in said second operative condition when the vehicle operating
conditions are representative of an excessively rich condition of
the air-fuel mixture.
2. An apparatus as claimed in claim 1, in which said electric
control unit is responsive to the rate of flow of atmospheric air
in said carburetor and is operative to produce said first control
signal which is effective to decrease the rate of flow of
pressurized air through said air-flow regulator valve means when
the rate of flow of atmospheric air in the carburetor increases in
a range lower than a first predetermined level and to increase the
rate of flow of pressurized air through the regular valve means
when the rate of flow of atmospheric air in the carburetor
increases in a range higher than a second predetermined level and
said second control signal which is effective to hold said air-flow
shift valve means in said first operative condition when the rate
of flow of atmospheric air in the carburetor is lower than said
first predetermined level and in said second operative condition
when the rate of flow of atmospheric air in the carburetor is
higher than said first predetermined level.
3. An apparatus as claimed in claim 2, in which said electric
control unit comprises a flow control circuit responsive to the
rate of flow of atmospheric air in the carburetor and operative to
produce a train of pulses having pulsewidths which are decreased as
the rate of flow of atmospheric air in the carburetor increase in
the range lower than said first predetermined level and which are
increased as the rate of flow of atmospheric air in the carburetor
decrease in the range higher than said second predetermined level,
said train of pulses constituting said first control signal.
4. An apparatus as claimed in claim 3, in which said air-flow
regulator valve means comprises electromagnetically operated
actuating means electrically connected to said flow control circuit
for being energized by said train of pulses and actuating the
air-flow regulator valve means into open condition in cycles which
are dictated by said pulses produced by said flow control
circuit.
5. An apparatus as claimed in claim 3, in which said air-flow shift
valve means comprises electromagnetically operated actuating means
electrically connected to said electric control unit for being
energized by said second control signal for actuating the shift
valve means between said first and second operative conditions
thereof.
6. An apparatus as claimed in claim 4, in which said flow control
circuit comprises function generating means operative to produce a
signal voltage having a waveform which gradually declines as the
rate of flow of atmospheric air in the carburetor increases in the
range lower than said first predetermined level and which gradually
increases as the rate of flow of atmospheric air in the carburetor
increases in the range higher than said second predetermined level,
adding means for adding a steady-state saw-tooth voltage to the
signal voltage delivered from said function generating means for
producing a saw-tooth signal voltage, and comparing and pulse
generating means for comparing said saw-tooth signal voltage with a
predetermined reference voltage and producing said train of pulses
when the saw-tooth signal voltage is higher than said reference
voltage.
7. An apparatus as claimed in claim 1, in which said electric
control unit is responsive to variation in engine temperature lower
than a predetermined level and is operative to produce said first
control signal which is effective to decrease the rate of flow of
pressurized air through said air-flow regulator valve means as the
engine temperature rises toward said predetermined level and said
second control signal which is effective to hold said air-flow
shift valve means in said first operative condition thereof in
response to the engine temperature lower than said predetermined
level.
8. An apparatus as claimed in claim 7, in which said electric
circuit comprises a flow control circuit responsive to the
variations in the engine temperature lower than said predetermined
level and operative to produce a train of pulses having pulsewidths
which are decreased as the engine temperature rises toward said
predetermined level, said train of pulses constituting said second
control signal.
9. An apparatus as claimed in claim 8, in which said air-flow
regulator valve means comprise electromagnetically operated
actuating means electrically connected to said flow control circuit
for being energized by said train of pulses and actuating the
air-flow regulator valve means into open condition in cycles which
are dictated by said pulses produced by said flow control circuit
when the engine temperature is lower than said predetermined
level.
10. An apparatus as claimed in claim 8, in which said air-flow
shift valve means comprises electromagnetically operated actuating
means electrically connected to said flow shift control circuit for
being energized by said second control signal for actuating the
shift valve means between said first and second operative
conditions thereof.
11. An apparatus as claimed in claim 9, in which said flow control
circuit comprises function generating means operative to produce a
signal voltage having a waveform which gradually declines as the
engine temperature rises toward said predetermined level, adding
means for adding a steady-state saw-tooth voltage to said signal
voltage for producing a saw-tooth signal voltage, and comparing and
pulse generating means for comparing said saw-tooth signal voltage
with a predetermined reference voltage and producing said train of
pulses when the saw-tooth signal voltage is higher than the
reference voltage.
12. An apparatus as claimed in claim 1, in which said electric
control unit is responsive to variation in the temperature in the
intake manifold of the engine and to idling condition of the engine
and is operative to produce said first control signal which is
effective to increase the rate of flow of pressurized air through
said air-flow regulator valve means as the intake manifold
temperature rises beyond a predetermined level and said second
control signal which is effective to hold said air-flow shift valve
means in said second operative condition thereof during idling of
the engine.
13. An apparatus as claimed in claim 12, in which said electric
control unit comprises a flow control circuit responsive to the
variation in the temperature in the engine intake manifold and
operative to produce a train of pulses having pulsewidths which are
increased as the intake manifold temperature rises beyond said
predetermined level, said train of pulses constituting said first
control signal, and a flow shift control circuit responsive to the
idling condition of the engine and operative to produce a control
current when the engine is in the idling condition, said control
current constituting said second control signal.
14. An apparatus as claimed in claim 13, in which said air-flow
regulator valve means comprise electromagnetically operated
actuating means electrically connected to said flow control circuit
for being energized by said train of pulses and actuating the
air-flow regulator valve means into open condition in cycles which
are dictated by said pulses produced by said flow control circuit
when the intake manifold temperature is higher than said
predetermined level.
15. An apparatus as claimed in claim 13, in which said air-flow
shift valve means comprises electromagnetically operated actuating
means electrically connected to said electric control unit for
being energized by said control current for actuating the shift
valve means between said first and second operative conditions
thereof.
16. An apparatus as claimed in claim 14, in which said flow control
circuit comprises function generating means operative to produce a
signal voltage having a waveform which gradually increases as the
cooling water temperature rises beyond said predetermined level,
adding means for adding a steady-state saw-tooth waveform to said
signal voltage for producing a saw-tooth signal voltage, and
comparing and pulse generating means for comparing said saw-tooth
signal voltage with a predetermined reference voltage and producing
said train of pulses when the saw-tooth signal voltage is higher
than the reference voltage.
17. An apparatus as claimed in claim 1, in which said electric
control unit is responsive to change in the vehicle speed and is
operative to produce said first control signal which is effective
to abruptly increase the rate of flow of pressurized air through
said air-flow regulator valve means during an incipient stage of
change of the vehicle speed and said second control signal which is
effective to hold said air-flow shift valve means in said first
operative condition thereof in response to an increase in the
vehicle speed and in said second operative condition thereof in
response to a decrease in the vehicle speed.
18. An apparatus as claimed in claim 17, in which electric control
unit comprises a flow control circuit responsive to the change in
the vehicle speed and operative to produce a train of pulses having
pulse-widths which are abruptly increased at said incipient stage
of the change of the vehicle speed, said train of pulses
constituting said first control signal, and a flow shift control
circuit responsive to an increase and a decrease in the vehicle
speed and operative to produce a control current when the vehicle
speed is increased or decreased, said control current constituting
said second control signal.
19. An apparatus as claimed in claim 18, in which said air-flow
regulator valve means comprise electromagnetically operated
actuating means electrically connected to said flow control circuit
for being energized by said train of pulses and actuating the
regulator valve means into open condition in cycles which are
dictated by said pulses produced by said flow control circuit
during the incipient stage of the change of the vehicle speed.
20. An apparatus as claimed in claim 18, in which said air-flow
shift valve comprise electromagnetically operated actuating means
electrically connected to said flow shift control circuit for being
energized by said control current and actuating said air-flow shift
valve between said first and second operative conditions
thereof.
21. An apparatus as claimed in claim 19, in which said flow control
circuit comprises function generating means operative to produce a
signal voltage having a waveform with a relatively short risetime
in response to a change in the vehicle speed, adding means for
adding a steady-state saw-tooth voltage to said signal voltage for
producing a saw-tooth signal voltage, and comparing and pulse
generating means for comparing said saw-tooth voltage with a
predetermined reference voltage for producing said train of pulses
when the saw-tooth signal voltage is higher than said reference
voltage.
22. An apparatus as claimed in claim 1, in which said air-flow
regulator valve means comprise an air-inlet port in communication
with said source of pressurized fluid, an air-outlet port in
communication with said air-flow shift valve means, a valve member
which is movable between a first position providing communication
between the air-inlet port and the air-outlet port and a second
position interrupting the communication between the ports, and
electromagnetically operated actuating means responsive to said
first control signal for actuating said valve member between said
first and second positions when energized and de-energized by the
first control signal.
23. An apparatus as claimed in claim 22, in which said electric
control unit comprises a flow control circuit responsive to said
operating conditions of the vehicle and operative to produce a
train of pulses having pulsewidths dictated by the vehicle
operating conditions whereby said actuating means is energized in
cycles by said pulses produced from the flow control circuit, said
train of pulses constituting said first control signal.
24. An apparatus as claimed in claim 1, in which said air-flow
shift valve means comprises an air-inlet port in communication with
said air-flow regulator valve means, a first air-outlet port in
communication with said first passage means, a second air-outlet
port in communication with said second passage means, a valve
member which is movable between a first porition providing
communication between said air-inlet port and said first air-outlet
port and a second position providing communication between said
air-inlet port and said second air-outlet port, and
electromagnetically operated actuating means responsive to said
second control signal for actuating said air-flow shift valve
between said first and second operative conditions when energized
and de-energized by said second control signal.
25. An apparatus as claimed in claim 24, in which said electric
control unit comprises a flow shift control circuit responsive to
said operating conditions of the vehicle and operative to produce a
control current responsive to an excessively rich or lean condition
of the air-fuel mixture produced in the carburetor whereby said
actuating means is energized or de-energized in accordance with the
excessively rich or lean condition of the air-fuel mixture.
26. A method of controlling the richness of an air-fuel mixture
produced by a carburetor of an internal combustion engine of an
automotive vehicle, comprising producing a first control signal
responsive to predetermined operating conditions of the vehicle, a
second control signal responsive to an excessively rich or lean
condition of the air-fuel mixture being produced in the carburetor,
producing a flow of pressurized air, varying the rate of flow of
pressurized air by said first control signal, and injecting the
pressurized air into a substantially closed space behind the fuel
in a fuel discharge circuit of the carburetor in response to the
excessively lean condition of the air-fuel mixture or into the fuel
flowing in the fuel discharge circuit in response to the
excessively rich condition of the air-fuel mixture in accordance
with said second control signal.
27. A method as claimed in claim 26, in which said operating
conditions of the vehicle include the rate of flow of atmospheric
air in the carburetor.
28. A method as claimed in claim 27, in which said first control
signal is effective to decrease the rate of injection of said
pressurized air as the rate of flow of atmospheric air in the
carburetor increases in a range lower than a first predetermined
level and to increase the rate of injection of the pressurized air
as the rate of flow of atmospheric air increases in a range higher
than a second predetermined level and in which said second control
signal is effective to direct the flow of pressurized air into said
space responsive to the unduly lean condition of the air-fuel
mixture and into the fuel flowing in the fuel discharge circuit in
response to the unduly rich condition of the air-fuel mixture.
29. A method as claimed in claim 28, in which said first control
signal is produced by producing a signal voltage having a waveform
which gradually decreases as the rate of flow of atmospheric air in
the carburetor increases in the range lower than said first
predetermined level and which gradually increases as the rate of
flow of atmospheric air increases in the range higher than said
second predetermined level, adding a steady-state saw-tooth voltage
to said signal voltage for producing a saw-tooth signal voltage,
comparing said saw-tooth signal voltage with a predetermined
reference voltage and producing a train of pulses as said first
control signal when the saw-tooth signal voltage is higher than
said reference voltage, said train of pulses constituting said
first control signal.
30. A method as claimed in claim 26, in which said operating
conditions of the vehicle include the temperature of the cooling
water the engine and idling condition of the engine.
31. A method as claimed in claim 30, in which said first control
signal is effective to increase the rate of injection of said
pressurized air as the cooling water temperature increases beyond a
predetermined level and in which said second control signal is
effective to direct the flow of the pressurized air into the fuel
flowing in said fuel discharge circuit in response to the idling
condition of the engine.
32. A method as claimed in claim 31, in which said first control
signal is produced by producing a signal voltage having a waveform
which gradually increases as the cooling water temperature rises
beyond said predetermined level, adding a steady-state saw-tooth
voltage to said signal voltage for producing a saw-tooth signal
voltage, comparing the saw-tooth signal voltage be added to the
signal voltage with a predetermined reference voltage and producing
a train of pulses as said first control signal when the saw-tooth
signal voltage is higher than said reference voltage.
33. A method as claimed in claim 26, in which said operating
conditions of the vehicle include the engine temperature.
34. A method as claimed in claim 33, in which said first control
signal is effective to decrease the rate of injection of said
pressurized air as the engine temperature increases in a range
lower than a predetermined level and in which said second control
signal is effective to direct the flow of said pressurized air into
said space behind the fuel in the fuel discharge circuit in
response to the engine temperature lower than said predetermined
level.
35. A method as claimed in claim 34, in which said first control
signal is produced by producing a signal voltage having a waveform
which gradually decreases as the engine temperature rises toward
said predetermined level, adding a steady-state saw-tooth voltage
to said signal voltage for producing a saw-tooth signal voltage,
comparing the saw-tooth signal voltage with a predetermined
reference voltage and producing a train of pulses as said first
control signal when the saw-tooth signal voltage is higher than the
reference voltage.
36. A method as claimed in claim 26, in which said operating
conditions of the vehicle include change in the vehicle speed.
37. A method as claimed in claim 36, in which said first control
signal is effective to abruptly increase the rate of injection of
said pressurized air during an incipient stage of change of the
vehicle speed and said second control signal is effective to direct
the flow of said presssurized air into said space behind the fuel
in the fuel discharge circuit in response to an increase in the
vehicle speed and into the fuel flowing in the fuel discharge
circuit in response to a decrease in the vehicle speed.
38. A method as claimed in claim 37, in which said first control
signal is produced by producing a signal voltage having a waveform
which has a relatively short resetime responsive to the change in
the vehicle speed, adding a steady-stage saw-tooth voltage to said
signal voltage for producing a saw-tooth signal voltage, comparing
the saw-tooth signal voltage with a predetermined reference
voltage, and producing a train of pulses as said first control
signal when the saw-tooth signal voltage is higher than the
reference voltage.
Description
The present invention relates generally to internal combustion
engines of automotive vehicles and, particularly, to mixture
induction systems such as carburetors of the automotive internal
combustion engines. More specifically, the present invention is
concerned with an apparatus for and a method of controlling the
richness, or an air-to-fuel ratio, of an air-fuel mixture to be
supplied from the carburetor to the combustion chambers of the
engine.
It is well known in the art of the carburetors of the automotive
internal combustion engines that the flow rate of fuel into the
carburetor varies with the rate of flow of air through the
carburetor and is causative of formation of an excessively lean or
excessively rich air-fuel mixture responsive to a relatively high
or low flow rate of air through the carburetor. Various attempts
have thus far been made to compensate for the excessive richness or
leanness of the air-fuel mixture but none of such attempts have
proved completely successful.
An object of the present invention is to provide an apparatus for
and a method of controlling the air-to-fuel ratio of an air-fuel
mixture produced in a carburetor of an automotive internal
combustion engine so that the air-fuel mixture supplied to the
engine is proportioned to an optimum richness throughout the
varying operating conditions of the vehicle.
In accordance with one important aspect of the present invention,
such an object will be accomplished basically in an apparatus which
comprises first passage means having an outlet end open into a
substantially closed space behind the fuel in a fuel discharge
circuit of the carburetor where the pressure difference between the
fuel outlet and the float chamber become larger; second passage
means having an outlet end open into the fuel discharge circuit; a
source of pressurized air; air-flow regulator valve means in
communication with the source of pressurized air and operative to
regulate the flow rate of pressurized air through the valve means
when actuated; air-flow shift valve means having a first operative
condition providing communication between the air-flow regulator
valve means and the first passage means and a second operative
condition providing communication between the air-flow regulator
valve means and the second passage means; and an electric control
unit responsive to predetermined operating conditions of the
vehicle and operative to supply a first control signal to the
air-flow regulator valve means for varying the flow rate of
pressurized air through the regulator valve means in accordance
with the operating conditions of the vehicle and a second control
signal to the air-flow shift valve means for holding the air-flow
shift valve in the first operative condition when the vehicle
operating conditions are representative of an excessively lean
condition of the air-fuel mixture being produced in the carburetor
or in the second operative condition when the vehicle operating
conditions are representative of an excessively rich condition of
the air-fuel mixture. The electric control unit may be responsive
to the rate of flow of atmospheric air in the carburetor and
operative to produce the first control signal which is effective to
decrease the rate of flow of pressurized air through the air-flow
regulator valve means when the rate of flow of atmospheric air in
the carburetor increases in a range lower than a first
predetermined level and to increase the rate of flow of pressurized
air through the regulator valve means when the rate of flow of
atmospheric air in the carburetor increases in a range higher than
a second predetermined level and the second control signal which is
effective to hold the air-flow shift valve means in the first
operative condition when the rate of flow of atmospheric air in the
carburetor is lower than the first predetermined level and in the
second operative condition when the rate of flow of atmospheric air
in the carburetor is higher than the first predetermined level. Or
otherwise, the electric control unit may be so arranged as to be
responsive to variation in engine temperature lower than a
predetermined level and operative to produce the first control
signal which is effective to decrease the rate of flow of
pressurized air through the air-flow regulator valve means as the
engine temperature rises toward the predetermined level and the
second control signal which is effective to hold the air-flow shift
valve means in the first operative condition thereof in response to
the engine temperature lower than the predetermined level. Where
desired, the electric control unit may be so arranged as to be
responsive to variation of the temperature in the intake manifold
of the engine and to idling condition of the engine and operative
to produce the first control signal which, in this instance, is
effective to increase the rate of flow of pressurized air through
the air-flow regulator valve means as the temperature of the intake
manifold increases beyond a predetermined level and the second
control signal which is effective to hold the air-flow shift valve
means in the second operative condition thereof during idling of
the engine. Or still otherwise, the electric control unit forming
part of the apparatus according to the present invention may be so
arranged as to be responsive to change in the vehicle speed and
operative to produce the first control signal which is effective to
abruptly increase the rate of flow of pressurized air through the
air-flow regulator valve means during an incipient stage of change
of the vehicle speed and the second control signal which is
effective to hold the air-flow shift valve in the first operative
condition thereof in response to an increase in the vehicle speed
and in the second operative condition in response to a decrease in
the vehicle speed. The air-flow regulator valve means may comprise
an air-inlet port in communication with the source of the
pressurized air, an air-outlet port in communication with the
air-flow shift valve, a valve member which is movable between a
first position providing communication between the air-inlet port
and the air-outlet port and a second position interrupting the
communication between the air-inlet port and the air-outlet port,
and electromagnetically operated actuating means responsive to the
previously mentioned first control signal for actuating the valve
member between the first and second positions thereof when
energized and de-energized by the first control signal. Likewise,
the air-flow shift valve means may comprise an air-inlet port in
communication with the air-outlet port of the air-flow regulator
valve means, a first air-outlet port in communication with the
previously mentioned first passage means, a second air-outlet port
in communication with the previously mentioned second passage
means, a valve member movable between a first position providing
communication between the air-inlet port and the first air-outlet
port and a second position providing communication between the
air-inlet port and the second air-outlet port, and
electromagnetically operated actuating means responsive to the
second control signal for actuating the valve member into the first
or second position thereof when the actuating means is energized or
de-energized.
In accordance with another important aspect of the present
invention, there will be provided a method of controlling the
richness of an air-fuel mixture in a carburetor of an internal
combustion engine, comprising producing a first control signal
which is responsive to predetermined operating conditions of the
vehicle, a second control signal responsive to an unduly rich or
lean condition of the air-fuel mixture being produced in the
carburetor, producing a flow of pressurized air, varying the rate
of flow of the pressurized air by the first control signal, and
injecting the pressurized air into a substantially closed space
behind the fuel in a fuel discharge circuit of the carburetor in
response to the excessively lean condition of the air-fuel mixture
or into the fuel flowing in the fuel discharge circuit in response
to the excessively rich condition of the air-fuel mixture in
accordance with the second control signal.
While it has been stated in the above description that the richness
of the air-fuel mixture to be produced in the carburetor is
controlled in accordance with the rate of flow of atmospheric air
through the carburetor, the temperature in the engine, the
temperature of the cooling water of the engine under idling
condition, or the change in the vehicle speed (viz., the
accelerating or decelerating condition of the vehicle, the richness
of the mixture may be varied in accordance with other operating
variables of the vehicle such as the altitude of a road on which
the vehicle is running, the temperature in the exhaust system,
and/or the concentration or concentrations of one or more specific
compounds contained in the exhaust gases.
The features of the apparatus and method according to the present
invention will become more apparent from the following description
taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic sectional view which shows a representative
example of an arrangement including a carburetor and a fuel
discharge circuit of an ordinary automotive internal combustion
engine;
FIG. 2 is a graph indicating a general tendency of air-flow
characteristics of a usual carburetor such as the carburetor
illustrated in FIG. 1;
FIG. 3 is a schematic sectional view, partly in a block diagram, of
a preferred embodiment of the apparatus according to the present
invention;
FIG. 4 is a fragmentary sectional view showing part of a fuel
discharge circuit of a variable-area venturi of a constant-vacuum
carburetor having incorporated therein a modification of the
embodiment illustrated in FIG. 3;
FIGS. 5a to 5g are graphs which indicate various waveforms of
signals produced in an electrical arrangement forming part of the
embodiment illustrated in FIG. 3;
FIGS. 6a to 6c are graphs which indicate waveforms of signals which
may be produced in the electrical arrangement of the embodiment
illustrated in FIG. 3 where it is desired that the device embodying
the present invention is so arranged as to be responsive to engine
temperature;
FIGS. 7a to 7c are graphs which are similar to those of FIGS. 6a to
6c, respectively, but which show waveforms of signals which may be
further produced in the electrical arrangement of the embodiment
illustrated in FIG. 1 where it is desired that the device embodying
the present invention is so arranged as to be responsive to the
temperature in the intake manifold of the engine; and d
FIGS. 8a and 8c are also similar to FIGS. 6a to 6c, respectively
but now show waveforms of signals which may be produced where it is
desired that the device embodying the present invention is so
arranged as to be responsive to accelerating and decelerating
conditions of the vehicle.
Referring to the drawings, first to FIG. 1, a carburetor 10 is
shown to have a fixed-area venturi 12 which is located downstream
of an air horn 14 and upstream of a carburetor throttle valve 16
which is rotatable on a shaft 18 between a closed-throttle position
illustrated and a full-throttle position. A float chamber or fuel
reservoir 20 has positioned therein a float 22 which is pivotally
cantilevered as at 24 to the side wall of the float chamber 20. The
float 22 carries thereon a needle valve 26 which is movable into or
out of a fuel inlet port 28 formed in, for example, the top wall of
the float chamber 20 as shown. The fuel inlet port 28 of the float
chamber 20 is in constant communication with an outlet port of a
fuel pump (not shown) that delivers fuel to the float bowl 20 when
the needle valve 26 is withdrawn from the fluid inlet port 28 of
the bowl 22 as shown. From the bottom portion of the float bowl 20
do extend a main fuel discharge circuit 30 and an idle and
low-speed fuel discharge circuit 32 through a main fuel metering
jet 34 and an idle and low-speed fuel metering jet 36,
respectively. The main fuel discharge circuit 30 terminates in a
fuel discharge nozzle 38 which is open in the venturi 12 while the
idle and slow-speed fuel discharge circuit 32 terminates in an idle
port 40 and slow-speed ports 42 and 42' bypass the venturi 12 and
the throttle valve 16. The carburetor 10 herein shown is assumed to
be of the "balanced" type and, thus, the float chamber 20 is vented
to the atmosphere through a venting passageway 44 which opens into
the air horn 14 located upstream of the venturi 12. The
construction of the carburetor per se is well known in the art and,
therefore, further detailed description thereof will not be herein
incorporated.
In the carburetor thus constructed and arranged, the fuel in the
float chamber 20 is injected from the fuel discharge nozzle 38 into
the venturi 12 by a motivating force which results from a
differential pressure which is developed across the venturi 12 due
to a vacuum created in the intake manifold of the engine when the
engine is in operation. The flow rate per unit time of the liquid
fuel to be injected from the discharge nozzle 38 into the venturi
12 is, as is well known, given by a formula:
where C.sub.f is a constant herein called the "coefficient of
discharge" of liquid fuel, S is the cross sectional area of the
fuel discharge nozzle 38, g is the acceleration due to gravity, d
is the density of the liquid fuel, P.sub.1 is the absolute pressure
prevailing in the air horn 14 or upstream of the venturi 12 of the
carburetor 10, and P.sub.2 is the pressure developed immediately
downstream of the venturi 12. In the shown carburetor 10 in which
the float chamber 20 is vented to the air horn 14 through the
venting passageway 44, the pressure P.sub.1 is equal to the
pressure which is developed atop the liquid fuel in the float
chamber 20 and is, thus, representative of the air pressure obtains
behind the liquid fuel to be injected into the venturi 12 through
the main fuel discharge circuit 30.
FIG. 2 illustrates the variation of the above mentioned coefficient
of discharge C.sub.f in terms of the rate of flow of air Q across
the venturi 12 in the carburetor 10 illustrated in FIG. 1. As will
be evident from FIG. 2, the coefficient of discharge C.sub.f
increases with a generally exponential curve A to B as the air-flow
rate Q increases from Q.sub.a to Q.sub.b through a range of
relatively low level and with a curve C to D as the air-flow rate Q
increases from Q.sub.c to Q.sub.d through a range of relatively
high level, although the coefficient of discharge C.sub.f remains
substantially constant throughout the range indicated by a curve B
to C. From the curves illustrated in FIG. 2 and from the previously
shown mathematic relation between the coefficient of discharge
C.sub.f and the mass flow of the fuel, it will be apparent that the
mass flow of the fuel to be injected into the venturi 12 of the
carburetor 12 varies in a non-linear relation which follows the
curve A to B and the curve C to D as the air-flow rate Q across the
venturi 12 varies in the range between Q.sub.a amd Q.sub.b or the
range between Q.sub.c and Q.sub.d. As a result of such a non-linear
variation of the flow rate of the fuel to be injected into the
venturi 12 of the carburetor, the air-fuel mixture produced in the
carburetor will be excessively leaned out if the air-flow rate Q
falls within the range between Q.sub.a and Q.sub.b and excessively
enriched if the air-flow rate Q falls within the range between
Q.sub.c and Q.sub.d.
To compensate for the excessive leanness or richness of the
air-fuel mixture, a variety of attempts have thus far been made.
Provision of the bypass ports including the idle port 40 and the
slow-speed ports 42 and 42' in the carburetor 10 as shown in FIG. 1
is one of such attempts. Another attempt is to provide two or more
venturi tubes as in double or tripple venturi carburetors so that
the flow characteristics resulting from the non-linear variation of
the mass flows of the fuel into the individual venturi tubes are
cancelled or moderated by each other. None of the attempts thus far
made has, however, succeeded in providing linearly varying fuel
flow characteristics of the carburetor and, for this reason, only
practical compromise has been to design and engineer a carburetor
that will exclusively match the inherent performance
characteristics of an engine of a particular make. Such a
compromise will apparently give rise to reduction in the production
efficiency and an increase in the production cost of the
carburetor.
The present invention proposes to control the flow rate of the
liquid fuel to be injected into the carburetor by varying the air
pressure P.sub.1 behind the liquid fuel or the density d of the
liquid fuel in accordance with various operational variables of the
automotive vehicle such as the air-flow rate in the carburetor, the
vacuum developed in the intake manifold of the engine, the
revolution speed of the engine, the engine temperature, the
combination of the temperature in the engine intake manifold and
the carburetor throttle opening, the accelerating or decelerating
conditions of the vehicle, the altitude of a road on which the
vehicle is running, the temperature of exhaust gases from the
engine, and/or the concentration or concentrations of a specific
compound or compound in the exhaust gases.
Reference will now be made to FIG. 3 which illustrates the
preferred embodiment of the air-fuel mixture control apparatus
according to the present invention, wherein the parts and units
which have their counterparts in the carburetor shown in FIG. 1 are
designated by like reference numerals. The apparatus embodying the
present invention as shown in FIG. 3 largely consists of a source
46 of pressurized air, a solenoid-operated air-flow regulator valve
unit 48, a solenoid-operated air-flow shift valve unit 50 and an
electric control unit which is designated in its entirety by
reference numeral 52.
The source 46 of pressurized air may be constructed and arranged in
any desired manners but is herein shown, by way of example, as
consisting of an air-feed pump 54 which is operative to pump out
pressurized air from its discharge port and a pressure governor 56
which has an inlet port in communication with the discharge port of
the air-feed pump 54 and which is adapted to deliver a
substantially constant air pressure from its outlet port. The
air-feed pump 54 is usually driven by the power output of the
engine (not shown).
The solenoid-operated air-flow regulator valve unit 48 comprises an
elongate valve housing 58 and a spool valve member 60 which is
axially movable in the valve housing 58. The valve housing 58 is
formed with an air-inlet port 62, an air-outlet port 64 and a vent
66 which is open to the atmospheric air. The air-inlet port 62 of
the valve housing 58 is in communication with the outlet port of
the pressure governor 56. On the other hand, the spool valve member
60 is formed with axially spaced first and second lands 68 and 70
and a circumferential groove 72 which is located between the lands
68 and 70. The spool valve member 60 is movable between a first
axial position having the first land 68 located to uncover the
air-inlet port 62 and the second land 70 located to cover the vent
66 and a second axial position having the first land 68 located to
cover the air-inlet port 62 and the second land 70 located to
uncover the vent 66 as seen in FIG. 3. The circumferential groove
72 of the spool valve member 60 is in constant communication with
the air-outlet port 64 irrespective of the axial position of the
spool valve member 60 relative to the valve housing 58 so that the
air-outlet port communicates through the circumferential groove 72
with the air-inlet port 62 when the spool valve member 60 is in the
first axial position thereof and with the vent 66 when the spool
valve member 60 is in the second axial position thereof. The spool
valve member 60 is biased toward the second axial position thereof
by means of a preload spring 74 which is shown to be seated at one
end on an outer end face of the first land 68 of the valve member
60 and at the other end on an annular spring seat member 76 which
is secured to or integral with the inner peripheral surface of the
valve housing 58. The spool valve member 60 further has an axial
extension 78 projecting from the outer end face of the first land
68 thereof and has carried at the leading end of the axial
extension 78 an armature core 80 which is coaxially surrounded by
an exciting coil 82. The armature core 80 and the exciting coil 82
constitute, in combunation, a solenoid to actuate the spool valve
member 60 when the exciting coil 82 is energized. When, thus, the
exciting coil 82 of the solenoid is energized from an external
source as will be discussed in more detail, then the armature core
80 is driven to axially move from its initial position illustrated
and, in turn, drives the spool valve member 60 from the second
axial position illustrated in FIG. 3 to the first axial position.
Thus, the solenoid-operated air-flow regulator valve unit 48 has a
first condition providing communication between the air-inlet port
62 and the air-outlet port 64 thereof with the exciting coil 82 of
the solenoid energized and a second condition interrupting the
communication between the ports 62 and 64 and providing
communication between the air-outlet port 64 and the vent 66 with
the exciting coil 82 of the solenoid de-energized.
The solenoid-operated air-flow shift valve unit 50 is constructed
largely similarly to the above described air-flow regulator valve
unit 48 and comprises an elongate valve housing 84 and a spool
valve member 86 which is axially movable in the valve housing 84.
The valve housing 84 is formed with an air-inlet port 88, a first
air-outlet port 90 and a second air-outlet port 92. The air-inlet
port 88 is in communication with the air-outlet port 64 of the
air-flow regulator valve unit 48. On the other hand, the spool
valve member 86 is formed with axially spaced lands 94 and 96 and a
circumferential groove 98 which is located between the lands 94 and
96. The spool valve member 86 thus constructed is movable between a
first axial position having the first land 94 located to uncover
the first air-outlet port 90 and the second land 96 located to
cover the second air-outlet port 92 as illustrated in FIG. 3 and a
second axial position having the first land 94 located to cover the
first air-outlet port 90 and the second land 96 located to uncover
the second air-inlet port 92. The air-inlet port 88 is in constant
communication with the circumferential groove 98 in the spool valve
member 86 so that the air-inlet port 88 communicates through the
circumferential groove 98 with the first air-inlet port 90 when the
spool valve member 86 is, as shown, in the first axial position
thereof and with the second air-outlet port 92 when the spool valve
member 86 is in the second axial position thereof. The spool valve
member 86 is biased toward the first axial position by means of a
preload spring 100 which is shown to be seated at one end on an
outer end face of the second land 96 of the valve member 86 and at
the other end on an end wall of the valve housing 94. The spool
valve member 86 has an axial extension 102 projecting from an outer
end face of the first land 94 of the valve member 86 and has
carried at leading end of the axial extension 102 an armature core
104 which is coaxially surrounded by an exciting coil 106. The
armature core 104 and the exciting coil 106 constitute in
combination a solenoid to actuate the spool valve member 86 when
the coil 106 is energized. When the exciting coil 106 is thus
energized from an external power source, then the armature core 104
is driven to axiallly move from its initial position illustrated
and, in turn, drives the spool valve member 86 from the first axial
position to the second axial position. The air-flow shift valve
unit 50 has a first operative condition providing communication
between the air-inlet port 88 and the first air-outlet port 90 with
the exciting coil 106 de-energized and a second operative condition
providing communication between the air-inlet port 88 and the
second air-outlet port 92 with the exciting coil 106 energized.
The first air-outlet port 90 of the air-flow shift valve unit 50
communicates through a restriction or orifice 108 with an air-inlet
port 110 which is formed in the top wall of the float bowl 20. On
the other hand, the second air-outlet port 92 of the shift valve
unit 50 is branched into main and auxiliary air passageways 112 and
114, respectively. The main air passageway 112 is led through a
restriction or orifice 116 to a main air bleed 118 which is open
into the previously mentioned main fuel discharge circuit 30
terminating at the fuel discharge nozzle 38. Likewise, the
auxiliary air passageway 114 is led through a restriction or
orifice 120 to an auxiliary air bleed 122 which is open into the
idle and low-speed fuel discharge circuit 32. The idle and
low-speed fuel discharge circuit 32 is herein shown as terminating
in the idle port 40 and only one low-speed port 42. Designated by
40a is an idle adjustment screw for adjusting the rate of discharge
of the fuel from the idle port 40.
The carburetor has been assumed to be of the constant-choke type
having a fixed venturi area. If desired, however, the apparatus
embodying the present invention may be incorporated into a
carburetor of the constant-vacuum type having a variable-area
venturi which comprises, as shown in FIG. 4, a piston 124 movable
in a direction perpendicular to the path of carburetor air and a
needle valve 126 projecting from the leading end of the piston 124
and movable back and forth in a fuel jet 128 leading from a main
fuel discharge circuit of the carburetor. With the variable-area
venturi thus constructed, the main air passageway 112 leading from
the second air-outlet port 92 of the air-flow shift valve unit 50
of the apparatus shown in FIG. 3 may open into the fuel jet
128.
The two valve units 48 and 50 above described are controlled by the
electric control unit 52. The control unit 52 consists of a flow
control circuit 130 to control the rate of flow of air through the
air-flow regulator valve unit 48 and a flow-shift control circuit
132 to control the direction of flow of air through the air-flow
shift valve unit 50. The flow control circuit 130 comprises a
function generator 134 having a plurality of input terminals which
are respectively connected to sensors (not shown) to detect various
operating conditions of the vehicle such as the air-flow rate
through the carburetor, the vacuum developed in the intake manifold
of the engine, the revolution speed of the engine, the temperature
in the engine intake manifold, the carburetor throttle opening, the
vehicle speed, the altitude of a road on which the vehicle is
running, the temperature of the exhaust gases from the engine, and
the concentration or concentrations of a compound or compounds
contained in the exhaust gases. The function generator 134 is
operative to produce at its output terminal a signal voltage V
which is representative of a certain function which is determined
from any combination of these operating conditions of the vehicle,
examples of the waveforms of the signal voltage V being indicated
in FIGS. 5a and 5b. The signal voltage V is fed to an adding
circuit 136 which is constantly biased with a voltage V.sub.t
having a steady-state saw-tooth waveform as indicated in FIG. 5c.
The signal voltage V is thus added with the saw-tooth voltage
V.sub.t in the adding circuit 136 which therefore produces at its
output terminal a saw-tooth signal voltage V.sub.s which is higher
than the saw-tooth voltage V.sub.t a value corresponding to the
signal voltage V, as will be seen in FIG. 5d or 5f. The output
terminal of the adding circuit 136 is connected to a combination
comparator and pulse-generator 138 on which a fixed reference
voltage V.sub.r is constantly impressed. The combination comparator
and pulse-generator 138 is thus operative to compare the saw-tooth
signal voltage V.sub.s supplied from the adding circuit 136 with
the reference voltage V.sub.r and to produce a pulsating current
I.sub.p when the former is higher than the latter as will be seen
in FIG. 5e or 5g. The combination comparator and pulse generator
138 has an output terminal connected through a line 140 to the
exciting coil 82 of the solenoid of the air-flow regulator valve
unit 48 so that the coil 82 is energized cyclically by the
pulsating current I.sub.p delivered from the combination comparator
and pulse generator 138.
On the other hand, the flow-shift control circuit 130 comprises a
discriminator 142 which has a plurality of input terminals which
are common to those of the function generator 134 and are thus
supplied with signals representative of the previously mentioned
various operating conditions of the vehicle. The discriminator 142
is operative to detect from these signals a condition in which the
air-fuel mixture being produced in the carburetor is unduly rich or
lean for the sensed operating conditions of the vehicle, producing
a control signal when such a condition is detected. In the present
context, the discriminator 142 is assumed, by way of example, to be
so arranged as to produce a control current I.sub.c responsive to
an unduly rich air-fuel mixture condition and to produce no output
voltage responsive to an unduly lean air-flow mixture condition.
The discriminator 142 has an output terminal which is connected
through a line 144 to the exciting coil 106 of the solenoid of the
air-flow shift valve unit 50. The air flow shift valve 50 is, thus,
held in the first operative condition providing the communication
between the air-inlet port 88 and the first air-outlet port 90
thereof in the absence of the control current I.sub.c at the output
terminal of the discriminator 142 and is actuated into the second
operative condition providing the communication between the
air-inlet port 88 and the second air-outlet port 92 thereof in the
presence of the control current I.sub.c at the output terminal of
the discriminator 142. Designated by reference numeral 146 is a
capacitor which may be connected between the output terminal of the
discriminator 142 and the exciting coil 106 of the air-flow shift
valve unit 50 for the reason to be explained later.
Operation of the mixture control apparatus thus constructed and
arranged will now be described with reference to FIG. 3 and
concurrently to FIGS. 5a to 5g.
As the signals to be fed to the control unit 52, various kinds of
variables may be used which are representative of the previously
mentioned operating conditions of the vehicle. For the simplicity
of description, however, it will be pro tempore assumed that the
control unit 52 is arranged to be responsive to the rate of air
flow Q through the carburetor. Description will be thereafter made
as to the cases in which other variables representative of, for
example, the engine temperature, the temperature in the engine
intake manifold, the carburetor throttle opening, the vehicle speed
or the like.
The air-flow rate Q in the carburetor may be directly measured by a
flow meter positioned anywhere in the carburetor. In the embodiment
illustrated in FIG. 3, however, the air-flow rate Q is assumed to
be approximated from a signal S.sub.n representative of the
revolution speed of the crankshaft of the engine and a signal
S.sub.v representative of the vacuum which is developed in the
intake manifold of the engine.
When, now, the signals S.sub.n and S.sub.v are fed to the function
generator 134 of the control unit 52, the function generator 134 of
the control unit 52, the function generator 134 produce a signal
voltage V which has a waveform V.sub.ab shown in FIG. 5a if the
air-flow rate Q approximated by the function generator 134 from
input signals S.sub.n and S.sub.v falls within the range between
Q.sub.a and Q.sub.b indicated in FIG. 2 or which has a waveform
V.sub.cd shown in FIG. 5b if the approximated air-flow rate Q falls
within the range between Q.sub.c and Q.sub.d. As seen in FIG. 5a,
the signal voltage V.sub.ab droops as the air-flow rate Q increases
from Q.sub.a to Q.sub.b whereas, as seen in FIG. 5b the signal
voltage V.sub.cd gradually rises as the air-flow rate Q increases
from Q.sub.c to Q.sub.d.
when, thus, the signal voltage V of the waveform V.sub.ab is
delivered from the function generator 134 and if the air-flow rate
Q is at a level Q.sub.1 (which is assumed to be on a lower side of
the range Q.sub.a -Q.sub.b as seen in FIG. 5a), the voltage V will
be at a level indicated by V.sub.1 in FIG. 50a so that the adding
circuit 136 supplied with the steady-state saw-tooth voltage
V.sub.t shown in FIG. 5c produces a signal voltage V.sub.s which
has a saw-tooth waveform V.sub.s1 indicated in FIG. 5d. The signal
voltage V.sub.s thus produced from the adding circuit 136 is
similar in waveform to the initially supplied saw-tooth voltage
V.sub.t and is higher then the saw-tooth voltage V.sub.t by a value
equal to the level V.sub.1 of the output voltage V from the
function generator 134. The saw-tooth signal voltage V.sub.s
delivered from the adding circuit 136 is supplied to the
combination comparator and pulse generator 138 and is compared with
the fixed reference voltage V.sub.r (FIG. 5d). The combination
comparator and pulse generator 138 produces a pulsating current
I.sub.p having pulsewidths t.sub.1 (FIG. 5e) which correspond to
the intervals in which the saw-tooth signal voltage V.sub.s is
higher than the reference voltage V.sub.r as will be seen from
FIGS. 5d and 5e. The pulsating current thus delivered from the flow
control circuit 130 is fed through the line 140 to the exciting
coil 82 of the solenoid of the air-flow regulator valve unit 48.
The exciting coil 82 is consequently energized in cycles that
correspond to the repetition frequency of the pulses P and
cyclically actuates the spool valve member 60 into the first axial
position thereof, providing communication between the air-inlet
port 62 and the air-outlet port 64 at a frequency substantially
equal to the pulsating cycles of the current supplied to the coil
106. Pressurized supplied from the air-feed pump 54 through the
pressure governor 56 is in this manner passed through the air-flow
regulator valve unit 48 to the air-flow shift valve 50 at a
frequency and at time intervals which are dictated by the train of
pulses P indicated in FIG. 5e. Simultaneously as the pulsating
current I.sub.p is thus produced from the flow control circuit 130,
the discriminator 142 of the flow shift control circuit 132 forming
part of the electric control unit 52 is operative to detect the
richness of the air-fuel mixture being produced in the carburetor
and delivers the control current I.sub.c provided the air-fuel
mixture is found to be unduly rich. Under the condition in whch the
air-flow rate Q is in the range of between Q.sub.a and Q.sub.b,
however, the air-fuel mixture produced in the carburetor is unduly
lean and, as a consequence, the discriminator 142 remains
inoperative to proudce the control current I.sub.c. The exciting
coil 106 of the air-flow shift valve unit 50 is therefore kept
de-energized so that the spool valve member 86 of the valve unit 50
is maintained in the first axial position illustrated in FIG. 3,
providing communication between the air-inlet port 88 and the first
air-outlet port 90. Pressurized air which has been passed through
the air-flow regulator valve unit 48 is now passed through the
air-flow shift valve unit 50 to the air-inlet port 110 of the float
bowl 20 and is admitted into the top of the liquid fuel stored in
the bowl 20, thereby giving rise to an increase in the air pressure
P.sub.1 behind the liquid fuel to be discharged. As will be
understood from the previously shown mathematic relation, the
increase in the pressure P.sub.1 behind the fuel to be discharged
results in an increase in the mass flow of the fuel injected from
the main fuel discharge nozzle 38 into the venturi 12 (or the
variable-area venturi shown in FIG. 4) and is thus effective to
enrich the air-fuel mixture produced in the carburetor. The rate of
increase in the mass flow of the fuel discharged from the fuel
discharge nozzle 38 is largely proportional to the square root of
the rate of increase in the pressure of air in the float bowl 20
and the increasing rate of the air pressure P.sub.1 is, in turn,
dictated by the pulsewidths and the pulse repetition frequency of
the pulsating current I.sub.p produced from the flow control
circuit 130 and accordingly by the waveform V.sub.ab (FIG. 5a) of
the signal voltage V produced by the function generator 134. If,
thus, the approximated rate of air flow Q through the carburetor is
at a level Q.sub.2 which is on a higher side of the range of
between Q.sub.a and Q.sub.b so that the signal voltage V delivered
from the function generator 134 is at a level V.sub.2 which is
lower than the previously mentioned level V.sub.1 as seen in FIG.
5a, the adding circuit 136 will produce a signal voltage V.sub.s
having a saw-tooth waveform indicated by V.sub.s2 in FIG. 5f and as
a consequence the pulsating current I.sub.p produced from the
combination comparator and pulse generator 138 will be such that is
shown in FIG. 5g, having pulsewidths t.sub.2 which are smaller than
the pulsewidths t.sub.1 of the pulsating current C.sub.p produced
when the air-flow rate Q is lower than Q.sub.2. From this, it will
be apparent that, when the air-flow rate Q is at a relatively high
level in the range of between Q.sub.a and Q.sub.b, the pressure
P.sub.1 of air behind the liquid fuel to be discharged into the
venturi of the carburetor stepped up at a relatively low rate and
accordingly the air-fuel mixture produced in the carburetor is
enriched at a moderate rate.
When, on the other hand, the flow rate Q of air through the
carburetor is within the range of between Q.sub.c and Q.sub.d
indicated in FIG. 2, then the function generator 134 delivers a
signal voltage V which now has a waveform V.sub.cd which increases
as the air-flow rate Q increases from Q.sub.c to Q.sub.d indicated
in FIG. 5d. If, in this instance, the air-flow rate Q is at a level
Q.sub.3 which is on a lower side of the range between Q.sub.c and
Q.sub.d, the signal voltage V will be at a level indicated by
V.sub.3 in FIG. 5b so that the signal voltage V.sub.s produced from
the adding circuit 136 has a saw-tooth waveform which is similar to
the waveform V.sub.s2 shown in FIG. 5f. The saw-tooth signal
voltage V.sub.s thus produced from the adding circuit 136 is
compared with the reference voltage V.sub.r in the combination
comparator and pulse generator 138, which produces a pulsating
current I.sub.p composed of a train of pulses which are similar to
those shown in FIG. 5g. The air-flow regulator valve unit 48 is
consequently actuated into the previously mentioned first condition
repeatedly in cycles and at time intervals which are dictated by
the pulse repetition frequency and the pulsewidths of the pulses
constituting the pulsating current I.sub.p. Simultaneously as the
pulsating current I.sub.p is in this manner supplied from the flow
control circuit 130, the discriminator 142 of the flow shift
control circuit 132 of the electric control unit 52 is operative to
detect the air-to-fuel ratio of the air-fuel mixture being produced
in the carburetor. When the air-flow rate Q in the carburetor falls
within the range of between Q.sub.c and Q.sub.d, the air-fuel
mixture produced in the carburetor is unduly rich for the operating
conditions of the vehicle as previously mentioned and, for this
reason, the discriminator 142 delivers the control current I.sub.c
so that the exciting coil 106 of the solenoid of the air-flow shift
valve unit 50. The armature core 104 is consequently driven to
axially move from its initial position illustrated and, in turn,
drives the spool valve member 86 to move from the first axial
position to the second axial position thereof against the opposing
force of the preload spring 100. The communication which has been
established between the air-inlet port 88 and the first air-outlet
port 90 of the valve unit 50 with the second air-outlet port 90
closed by the first land 94 of the spool valve member 86 and,
instead, communication is provided between the air-inlet port 88
and the second air-outlet port 92 of the valve unit 50 through the
circumferential groove 98 in the valve member 86 with the second
land 96 of the spool valve member 86 moved off the second
air-outlet port 92. Pressurized air cyclically passed through the
air-flow regulator valve unit 48 is now directed through the
air-flow shift valve 50 to the previously mentioned first and
second air passageways 112 and 114. Air under pressure is
consequently injected through the main and auxiliary air bleeds 118
and 122 leading, in the embodiment shown in FIG. 3, from the first
and second air passageways 112 and 114, respectively, into the main
fuel discharge circuit 30 and the idle and low-speed fuel discharge
circuit 32. The liquid fuel in the main fuel discharge circuit 30
or the idle and low-speed fuel discharge circuit 32 is thus mixed
with air under pressure on its way to the main fuel discharge
nozzle 38 or the idle port 40 and the low-speed port 42. The fuel
to be ejected from the main fuel discharge nozzle 38 or the idle
port 40 and the low-speed port 42 is in an emulsified state with
pressurized air injected thereinto and as a consequence reduces its
viscosity and accordingly the density thereof. As will be
understood from the previously shown mathematical relation, the
reduction in the density of the fuel results in a decrease in the
mass flow of the fuel injected into the carburetor and gives rise
to an increase in the art-to-fuel mixture produced in the
carburetor. The air-fuel mixture is in this manner leaned out to an
optimum richness when the air-flow rate Q through the carburetor is
at the level Q.sub.3 in the range of between Q.sub.c and Q.sub.d.
The rate of decrease in the mass flow of the fuel discharged from
the main fuel discharge nozzle 38 is largely proportional to the
square root of the rate of decrease of the density d of the fuel
and, in turn, the decreasing rate of density d of the fuel is
dictated by the pulsewidths and the pulse repetition frequency of
the pulsating current I.sub.p supplied to the solenoid of the
air-flow regulator valve unit 48. If, thus, the approximated rate
of air flow Q computed by the function generator 134 is at a level
Q.sub.4 which is on a higher side of the range between Q.sub.c and
Q.sub.d so that the signal voltage V delivered from the function
generator 134 is at a level V.sub.4 which is higher than the
previously mentioned voltage level V.sub.3 as seen in FIG. 5b, the
saw-tooth voltage V.sub.t produced by the adding circuit 136 will
have a waveform which is similar to that indicated in FIG. 5d with
the result that the pulsating current I.sub.p delivered from the
combination comparator and pulse generator 138 will be such that is
illustrated in FIG. 5e. From this it will be understood that the
air-fuel mixture produced in the carburetor when the air-flow rate
Q in the carburetor is in the range of between Q.sub.c and Q.sub.d
is leaned out at a rate which decreases as the air-flow rate Q
increases from the level Q.sub.c to the level Q.sub.d in accordance
with the waveform V.sub.cd of the signal voltage V delivered from
the function generator 134. The waveforms of the signal voltage V
produced by the function generator 134 may be selected and varied
in a manner to match the specific performance characteristics of
the engine, particularly, the carburetor therefor so that the
air-to-fuel mixture supplied to the engine is at all times
maintained optimum for the varying operating conditions of the
vehicle. Major considerations that should be taken into account in
determining the waveforms to be produced by the function generator
134 may include the relative positions of the main fuel discharge
nozzle 38, the idle port 40 and the low-speed port 42 and the ratio
between the discharge rates of the nozzle 38 and the idle and
low-speed ports 40 and 42 so that the fuel discharged from the
discharge nozzle 38 is prevented from sticking to the throttle
valve 16 and failing to be sufficiently atomized in the carburetor
especially when the throttle valve 16 is in a closed-throttle or
part-throttle position.
The engine may malfunction transiently when the flow of pressurized
air is shifted in the air-flow shift valve unit 50 by the switching
action of the flow shift control circuit 48. Such a temporary
malfunction of the engine can be prevented if the capacitor 146 is
connected between the output terminal of the discriminator 142 of
the flow shift control circuit 132 and the exciting coil 106 of the
air-flow shift valve unit 48 as indicated by phantom lines in FIG.
3 so that the control current I.sub.c is gradually increased or
decreased when the control current is initially delivered from the
discriminator 142 or the supply of the current therefrom is
interrupted.
Although, moreover, the air-flow regulator valve unit 48 has been
described as being electrically energized by a train of pulses,
such is merely by way of example and, therefore, the regulator
valve unit 48 may be energized by a current having any other
waveform insofar as the valve unit 48 is operable to pass the flow
of pressurized air at a rate which is dictated by the waveform
produced by the function generator 134. The cyclic operation of the
air-flow regulator valve unit 48 by the pulsating current I.sub.p
is, however, conductive to reducing the static friction between the
inner peripheral surface of the valve housing 58 and the lands 68
and 70 of the spool valve member 60 and will thus guarantee the
sensitive and accurate response of the valve unit 48 to the signal
produced by the function generator 134. The dithering motions of
the spool valve member 60 of the air-flow regulator valve unit 48
may create pulsations of the pressure of air directed to the float
bowl 20 or the fuel discharge circuits 30 and 32. Where this is an
important consideration, the frequency of the saw-tooth voltage
V.sub.t impressed on the adding circuit 136 may be raised to an
appropriate level and/or the orifices 108, 112 and 114 and/or the
air passageways leading from these orifices may be calibrated to
have appropriate cross sectional areas with a view to cancelling
the pulsations of the air pressure.
While the embodiment illustrated in FIG. 3 has been described as
being operative in responsive to the air-flow rate Q in the
carburetor or, more specifically, the revolution speed of the
engine crankshaft and the vacuum developed in the intake manifold
of the engine, this is solely for the pupose of illustration of the
apparatus and the method according to the present invention and,
thus, the electric control unit 52 may be supplied, in addition to
the signals S.sub.n and S.sub.v representative of the engine
crankshaft revolution and the intake manifold vacuum, with any
other signals which are commonly designated by S.sub.d in FIG.
3.
As one of the additional input signals S.sub.d which may be
impressed on the function generator 134 and the discriminator 132,
a variable representing the temperature of the engine may be used
so as to cope with the cold starting of the engine. In this
instance, the function generator 134 may be so arranged as to
produce a signal voltage V.sub.e which gradually decreases as the
engine temperature T.sub.e rises in a relatively low range as
indicated in FIG. 6a. The drooping signal voltage V.sub.e is added
with the previously mentioned steady-state saw-tooth voltage
V.sub.t (FIG. 5c) and is formed into a saw-tooth signal voltage
V.sub.se indicated in FIG. 6b. The saw-tooth signal voltage
V.sub.se delivered from the adding circuit 136 is compared with the
predetermined reference voltage V.sub.r by the combination
comparator and pulse generator 138, which thus produces a pulsating
current I.sub.pe composed of a train of pulses indicated in FIG. 6c
when the input voltage V.sub.se is higher than the reference
voltage V.sub.r. On the other hand, the signal representative of
the temperature of the engine being started from cold disables the
discriminator 142 from producing the control current I.sub.c. The
exciting coil 106 of the solenoid-operated air-flow shift valve
unit 50 is consequently held in the first operative condition
thereof providing communication between the air-inlet port 88 and
the first air-outlet port 90 as shown. Pressurized air delivered
from the air-feed pump 54 is thus directed through the valve units
48 and 50 into the float bowl 20 at rate which is dictated by the
pulse repetition frequency and the pulsewidths of the pulsating
current I.sub.pe fed to the exciting coil 82 of the air-flow
regulator valve unit 48. The air-fuel mixture produced in the
carburetor is enriched by reason of the increased air pressure
P.sub.1 behind the fuel to be discharged from the main fuel
discharge circuit 30 and the idle and low-speed fuel discharge
circuit 32 during cold starting of the engine. The rae of injection
of pressurized air into the float bowl 20 is diminished and
accordingly the air-to-fuel ratio of the mixture is reduced (viz,
the air-fuel mixture is made leaner) as the engine temperature
T.sub.e increases toward an ordinary operating level as will be
understood from the pulse train shown in FIG. 6c.
It is well known that the engine fails to operate properly if the
air-fuel mixture supplied thereto is unduly enriched when the
temperature in the intake manifold of the engine is increased to
cause reduction in the density of the mixture flowing into the
combustion chambers of the engine, especially during idling of the
engine. For the purpose of preventing this condition from being
invited in the engine, the additional signals S.sub.d to be
supplied to the function generator 132 and the discriminator 142 of
the electric control circuit 52 may include a signal representative
of the temperature in the intake manifold of the engine and a
signal representative of the idling condition of the engine. In
this instance, the function generator 132 is responsive to the
signal representative of the temperature T.sub.m of the engine
intake manifold and is thus operative to produce a signal voltage
V.sub.m which has a waveform gradually increasing as the
temperature T.sub.m of the engine intake manifold increases as
indicated in FIG. 7a. As will be understood from the previous
discussion, the signal voltage V.sub.m thus delivered from the
function generator 132 is added with the saw-tooth voltage V.sub.t
in the adding circuit 134 and is formed into a saw-tooth signal
voltage V.sub.sm shown in FIG. 7b. The saw-tooth signal voltage
V.sub.sm is then compared with the predetermined reference voltage
V.sub.r in the combination comparator and pulse generator 138 so
that, when the former is higher than the latter, a pulsating
current I.sub.pm is produced which is composed of a train of pulses
indicated in FIG. 7c. On the other hand, the discriminator 142 is
responsive to the signal representative of the idling condition of
the engine and is operative to produce the control current I.sub.c.
The exciting coil 106 of the solenoid-operated air-flow shift valve
unit 50 is energized by the control current I.sub.c so that the
shift valve unit 50 is actuated from the first operative condition
into the second operative condition thereof, providing
communication between the air-inlet port 88 and the second
air-inlet port 92 of the valve unit 50. Pressurized air is now
injected into the main fuel discharge circuit 30 and the idle and
low-speed fuel discharge circuit 32 through the main and auxiliary
air bleeds 118 and 122, respectively. Under the idling condition of
the engine, only the idle and low-speed fuel discharge circuit 32
is operative to discharge the fuel from the idle port 40 with the
main fuel discharge nozzle 38 and the low-speed port 42 kept
inoperative. The fuel on its way to the idle port 40 is thus mixed
with pressurized air injected through the auxiliary air bleed 122
into the low-speed fuel discharge circuit 32. The density of the
fuel discharged from the idle port 40 is thus reduced and
accordingly the air-fuel mixture resulting from the fuel is leaned
out to an air-to-fuel ratio which is optimum for the idling
operating of the engine with the intake manifold of the engine at
an elevated temperature. As will be understood from the variation
of the pulsewidths of the pulsating current I.sub.pm indicated in
FIG. 7, the air-fuel mixture produced in the carburetor is leaned
out at a rate that increases as the temperature T.sub.m in the
engine intake manifold rises during the idling condition of the
engine.
The richness of the air-fuel mixture to be supplied to the engine
may be increased or descreased when the vehicle is accelerated or
decelerated, respectively. To achieve this end, a change of vehicle
speed may be used as one of the additional signals S.sub.d to be
supplied to the function generator 132 and the discriminator 142.
In this instance, the function generator 132 may be so arranged as
to produce a signal voltage V.sub.v having an upwardly convex
waveform having a relatively steep tail ramp or, in other words, a
relatively short rise-time and a gradually disclining leading ramp
or a relatively long fall-time as indicated in FIG. 8a. A saw-tooth
signal voltage V.sub.sv shown in FIG. 8b is obtained in the adding
circuit 134 from this signal voltage V.sub.v so that, upon
comparision with the predetermined reference voltage V.sub.r in the
combination comparator and pulse generator 138, a pulsating current
I.sub.pv composed of a train of pulses formed as indicated in FIG.
8c is produced and applied to the exciting coil 82 of the
solenoid-operated air-flow regulator valve unit 48. On the other
hand, the discriminator 142 of the flow shift control circuit 132
is responsive to the signal representative of the change in the
vehicle speed and produces the control current I.sub.c is the
signal is indicative of a decrease in the vehicle speed, viz., a
decelerating condition of the vehicle. When, thus, the vehicle is
decelerated during normal cruising, the solenoid-operated air-flow
shift valve unit 50 is energized by the control current I.sub.c
from the discriminator 142 and is actuated from the first operative
condition into the second operative condition thereof. Pressurized
air is in this manner injected into the fuel being directed toward
the main fuel discharge nozzle 38 and the idle and low-speed ports
40 and 42 with a consequent decrease in the richness of the
air-fuel mixture produced in the carburetor at an incipient stage
of the decelerating condition of the vehicle. The signal voltage
V.sub.v produced by the function generator 132 steeply rises in
response to the initial decrease of the vehicle speed as will be
seen in FIG. 8a so that the air-fuel mixture produced in the
carburetor is leaned out for a short while during the initial stage
of the deceleration. When, however, the vehicle is accelerated
during normal cruising, the air-flow shift valve unit 50 remains
de-energized in the absence of the control current I.sub.c from the
discriminator 142 and is maintained in the first operative
condition. Pressurized air is therefore directed into the float
bowl 20 and enriches the air-fuel mixture produced in the
carburetor during an incipient stage of the acceleration of the
vehicle.
Besides the additional signals S.sub.d above described, signals
representative of the altitude of a road on which the vehicle is
running, the temperature of the exhaust gases and/or the
concentration or concentrations of one or more specific compounds
contained in the exhaust gases may be impressed on the electric
control unit 52 of the embodiment illustrated in FIG. 3.
While a few embodiments of the apparatus according to the present
invention have been herein described and shown, there are simply
illustrative of the gist of the present invention and, as such,
such embodiments may be changed or modified in numerous manners and
applied to carburetors of any types other than those which have
been described and shown herein.
* * * * *