Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates in general to internal
combustion engines of automotive vehicles and, particularly, to a
method of and a system for controlling the air-to-fuel ratio in an
automotive internal combustion engine of the type using a catalytic
converter provided in the exhaust system for exhaust cleaning
purposes.
Some modernized automotive vehicles are now equipped
with catalytic converters in the exhaust systems of the engines for
the purpose of converting toxic air contaminative contents of the
engine exhaust gases into harmless composition before the exhaust
gases are discharged into the open air. A typical example of such
catalytic converters is the one that uses an oxidative catalyst
effective to re-oxidize unburned combustible residues of, for
example, hydrocarbons (HC) and carbon monoxide (CO) in the exhaust
gases emitted from the engine cylinders into harmless compounds
such as carbon dioxide and water. Experiments conducted with an
oxidative catalyst of this nature have revealed that the catalyst
is not only reactive to these combustible compounds but is operable
j to reduce nitric oxides (NOX) in the exhaust gases provided the
exhaust gases to be processed by the catalyst are conditioned to
contain exhaust compounds in proportions within a certain range
which is dictated by the air-to-fuel ratio of the mixture combusted
in the engine cylinders. The catalytic converter using an oxidative
catalyst thus exhibits triple effects to the exhaust gases of an
internal combustion engine and is capable of reducing the different
types of air contaminative compounds in a single unit when the
combustible mixture supplied to the engine cylinders is proportioned
to an air-to-fuel ratio within a certain range. The experiments
have further revealed that it is the stoichiometric ratio of about
14.8:1 that enables the triple-effect or "three-way" catalytic con-
verter to produce its maximum conversion efficiency against the
three kinds of air contaminative compounds in the exhaust gases.
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It is, for this reason, desirable to have an internal combustion
engine of the type using a triple-effect catalytic converter pro-
vided with a mixture ratio control system adapted to regulate the
air-to-fuel ratio of the mixture to be produced in the mixture
supply system of the engine toward the stoichiometric level.
The mixture ratio control system used in combination with
a triple-effect catalytic converter comprises an exhaust sensor
operative to detect the concentration of a prescribed type of che-
mical component contained in the exhaust gases and to produce an
analog signal indicative of the detected concentration of the par-
ticular component of the exhaust gases. The chemical composition
of the exhaust gases is a fairly faithful representation of the
air-to-fuel ratio of the mixture produced in the mixture supply
system of an engine and, therefore, the mixture ratio control
system operating on the basis of the signal thus delivered from the
exhaust sensor is capable of accurately and reliably controlling
the air-to-fuel ratio of the mixture to be produced in the mixture
supply system toward a predetermined value such as the stoichiome-
tric ratio.
The chemical component to be detected by the exhaust sen-
sor may be oxygen, carbon monoxide or dioxide, hydrocarbons or ni-
tric oxides although oxygen in particular is preferred for ease of
detection.
The analog signal produced by the exhaust sensor is fed
to an electric control circuit connected to a solenoid-operated
valve unit which is arranged to vary the flow of air or fuel to be
delivered into the mixture supply system of the engine in accordance -
with the output signal produced by the control circuit on the basis
of the analog signal supplied from the exhaust sensor. The output
signal from the control circuit is usually in the form of a train
of pulses which are varied in pulsewidth and frequency in such a
manner as to eliminate or reduce a difference, if any, between the
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~alogsignal produced by the exhaust sensor and a reference signal
representative of a predetermined air-to-~uel ratio such as the
stoichiometric ratio. The valve unit is thus operated to alterna-
tely open and close at a frequency and for durations dictated by
the frequency and pulsewidths of the pulses supplied to the unit
and controls the flow of air or fuel to be delivered into the m~x-
ture supply system in such a manner that the air-to-fuel ratio of
the mixture approaches the value represented by the reference slgnal
impressed on the control circuit.
By virtue of the signal delivered from the exhaust sènsor,
the control circuit is capable of accurately monitoring the air-to-
fuel ratio of the mixture combusted in the engine cylinders so that
the air-to-fuel ratio of the mixture produced in the mixture supply
system of the engine is constantly regulated toward a predetermined
value such as the stoichiometric ratio enabling the catalytic con-
verter to exhibit its maximum conversion efficiency against the dif-
ferent types of air contaminative compounds. As will be readily
understood by those skilled in the art, however, it is extremely
difficult and practically even impossible to have the air-to-fuel
ratio of the mixture regulated strictly and maintained at a prede-
termined value throughout the varying operating conditions of the
engine especially when the engine is of the type using a carburetor
as the mixture supply system. This is because of the changes and
fluctuations in the operating and ambient conditions of the engine,
external disturbances such as the shocks and vibrations transferred
to the mechanical components of the mixture control system and,
particularly, the delay involved in feeding back the information
from the exhaust system to the mixture control system and in moni-
toring the air-to-fuel ratio of the mixture from the exhaust gases
resulting from the mixture produced in the mixture supply system.
One of the most important considerations to be paid for
exploiting the potential advantages of a mixture control system of
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the described character is, therefore, to reduce the delay in the
response of the control system to the air-fuel mixture produced in
the mixture supply s~stem. A most expedient approa~h to realizing
such a scheme is to reduce the period of time from which the air-
fuel mixture produced in the mixture supply system is admitted
into the engine cylinders and the period of time for which the
exhaust gases produced in the cylinders are passed to the exhaust
sensor located in the exhaust system. The velocities of the streams
of the air-fuel mixture flowing toward and into the engine cylinders
and the velocities of the streams of the exhaust gases discharged
from the cylinders are basically dictated by the output speed of
the engine and, thus, reducing such velocities is subject to limi-
tation because of the limitations imposed on the performance of the
engine.
In an internal combustion engine using a carburetor as
the mixture supply system, the air-fuel mixture produced in the
carburetor is passed through the intake manifold partly in a vapo-
rized gaseous state and partly in a liquid state flowing or creeping
on the inner peripheral surface of the intake manifold, as is well
known in the art. Experiments have revealed that the mixture in the
gaseous state accounts for approximately 40 per cent of the total
flow of the mixture at high engine speeds and approximately 60 per
cent at low engine speeds. Further analyses have shown that the
velocity of the stream of the mixture in a perfectly atomized state
substantially equals the velocity of a stream of air through the
intake manifold and reaches-to approximately a hundred times the
velocity of the mixture in a liquid state flowing on the inner sur-
face of the intake manifold. The air-fuel mixture produced in the
carburetor will thus be enabled to reach the engine cylinders in
a shortened period of time if the mixture is perfectlyatomized in
its entirety when being passed through the intake manifold.
The existence of the air-fuel mixture of liquid state in
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the intake manifold is objectionable not only from the above-des-
cribed point of view but because such a mixture tends to be irre-
gularly distributed to the runners leading to the different engine
cylinders or may be sucked in bulk into the engine cylinders and
produce undue enrichment of the mixture in the cylinders during
deceleration of the engine, causing deterioration of the performance
efficiency of the engine and resulting in emission of increased
quantities of air contaminative compounds.
The present invention aims at resolution of these problems
by preheating the air-fuel mixture in the intake manifold of the
engine to a temperature within a prescribed range for forcibly
causing the mixture to be substantially perfectly evaporated when
being passed through the intake manifold, so as to minimize the
delay in the response of the mixture control system of the described
nature to the variation in the air-to-fuel ratio of the air-fuel
; mixture produced in the carburetor and to assure the engine to
operate at all times in proper condition.
In accordance with one important aspect of the present
invention, there is provided in an internal combustion engine
including a carburetor connected to the cylinders of the engine
through an intake manifold including a riser portion, and an
exhaust system having incorporated therein a catalytic converter
which is reactive to at least one type of air contaminative com-
; pound contained in the exhaust gases discharged from the engine
cylinders and passed through the converter and which is operative
to produce a maximum conversion efficiency when the air-fuel mix-
ture produced in the carburetor is proportioned to a predetermined
air-to-fuel ratio, the air-to-fuel ratio of the mixture produced
in the carburetor from the exhaust gases passed through the exhaust
system, regulating the air-to-fuel ratio of the mixture to be pro-
duced in the carburetor toward the above-mentioned predetermined
ratio, a method of controlling the air-to-fuel ratio to be produced
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in the carburetor, comprising monitoring the air-to-fuel ratio of
the mixture produced in the carburetor from the exhaust gases flowing
in the exhaust system, regulating the air-to-fuel ratio of the mix-
ture to be produced in the carburetor toward the above-mentioned
predetermined ratio, directing the hot exhaust gases through a
passageway in heat conductive contact with the riser portion of the
intake manifold for transferring heat from the exhaust gases to the
air-fuel mixture in the intake manifold, detecting the temperature
` of the exhaust gases passed through the passageway and regulating
theflow of the exhaust gases through the passageway for maintaining
substantially constant the quantity of heat in the exhaust gases
passed through the above-mentioned passageway.
In accordance with another important aspect of the present
invention, there is provided an internal combustion which comprises
-~ a carburetor connected to the cylinders of-the engine through an
intake manifold including a riser portion; an exhaust system having
incorporated therein a catalytic converter which is reactive to at
: least one type of air contaminative compound contained in the
exhaust system discharged from the engine cylinders and passed
through the converter and which is operative to produce a maximum
: conversion efficiency when the air-fuel mixture produced in the
carburetor is proportioned to a predetermined air-to-fuel ratio,
- the exhaust system having a wall portion constituted by the riser
: portion of the intake manifold; a mixture control system adapted to
. monitor the air-to-fuel ratio of the mixture produced in the carbu-
retor from the exhaust gases flowing through the exhaust system and
to control the air-to-fuel ratio of the mixture to be produced in
the carburetor toward the above-mentioned predetermined ratio; and
a device for forcibly evaporating the air-fuel mixture in the intake
manifold, the device comprising a flow control valve located within -:~
the exhaust system in the neighbourho~d of the aforesaid wall portion
of the exhaust system for providing a passageway of exhaust gases
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in heat conductive contact with the riser portion of the intake~
manifold, and heat-sensitive valve control means including a ~
helical bimetallic spring which is anchored at one end to the fl-ow
control valve and at the other end to a wall portion of the exhaust
system for varying the flow rate of the exhaust gases through the
passageway substantially in inverse proportion to the temperature
of the exhaust gases passed through the passageway.
The features and advantages of the improvements according
to the present invention will be more clearly understood from the
following description taken in conjunction with the accompanying
; drawings, in which: -
Fig. 1 is a schematic partially cut-away view showing
part of an internal combustion engine embodying the present inven-
tion;
Fig. 2 is a block diagram showing a preferred example of
an electric control circuit forming part of a mixture control system
incorporated into the internal combustion engine illustrated in
Fig. l;
Fig. 3 is a graph which shows a representative example of
; 20 the relationship between the percentage of evaporation of the air-
; fuel mixture in the intake manifold of an engine and the velocity
of the stream of the mixture through the intake manifold in texms
; of an index number which is assumed to be 100 when the velocity-~of
the mixture stream is equal to the velocity of the stream of air
through the intake manifold; and
Fig. 4 is a graph in which curve a (in broken lines) and
; curve b ~in dot-and-dash lines) demonstrate the concentrations of
, carbon monoxide (CO) in the exhaust gases discharged into the at-
mosphere when a vehicle is driven at a speed varying as shown by
curve c (in full lines), wherein the characteristics indicated'by
the curve a are observed in an internal combustion engine provided
with mixture preheating means in accordance with the present inven-
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tion and the characteristics indicated by the curve b are observed
in an ordinary internal combustion engine which is void of such
means.
Referring to the drawings, first to Fig. 1, an internal
combustion engine includes a carburetor 10 which is assumed, by way
of example, to be of a down-draft type having a mixture delivery
pipe 12 connected at its upper end to an air cleaner 14 through an
air horn 16 and at its lower end to an intake manifold 18 leading
to the engine cylinders in a cylinder block 20. The mixture delive-
10 ry pipe 12 has provided therein a venturi 22 located below the air
. h~rn 16 and a throttle valve 24 located below the venturi 22.
Though not shown, the venturi 22 is in communication with a main
fuel delivery circuit of the engine through a main fuel discharge
- nozzle projecting into the venturi 22 for being supplied with fuel
in an emulsified state when the throttle valve 24 is open, while the
throttle valve 24 is mechanically connected to an accelerator pedal
.~ for being moved between fully open and fully closed positions through
a part throttle position depending upon the depth to which the ac-
celerator pedal is depressed, as is well known. The intake mani-
i
:: 20 fold 18 has a riser portion 26 which is located below the mixture
delivery pipe 12 and which merges into a plurality of runner por-
- tions (not shown) respectively leading to the intake ports of the
~ individual engine cylinders in the cylinder block 20.
The internal combustion engine further comprises an :~
exhaust system which.includes an exhaust manifold 28 and an exhaust
pipe 30 leading downstream from the exhaust manifold 28. Though
not shown, the exhaust manifold 28 consists of a plurality of branch
tube portions respectively leading from the exhaust ports of the
individual engine cylinders in the cylinder block 20 and a single
. 30 "plenum" tube portion merging downstream out of the branch tube
portions and connected at its leading end to the exhaust pipe 30,
as is well known. The exhaust pipe 30 is connected through a muffler
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or mufflers to a tail pipe which is open to the atmosphere at its
terminal end, though not shown.
The exhaust system is arranged with a catalytic converter
32. The catalytic converter 32 is shown to be mounted in the ex-
haust pipe 30 but, if desired, the same may be mounted on the above-
mentioned plenum tube portion of the exhaust manifold 28. The cata-
lytic converter 32 is herein assumed, by way of example, to be of
the previously described triple-effect type which is effective to
process the three different kinds of air contaminative compounds
of hydrocarbons, carbon monoxide and nitrogen oxides contained in
the exhaust gases discharged from the engine cylinders. The cata-
lytic converter 32 is, thus,permitted to produce its maximum con-
version efficiency when supplied with exhaust gases which have
resulted from an air-fuel mixture proportioned to the stoichiometric
ratio of approximately 14.8:1 when the engine is of the type which
is gasoline powered. To produce an air-fuel ratio proportioned to
such a ratio in the mixture delivery pipe 12, the carburetor 10 is
provided with a mixture control system which is adapted to regulate
the air-to-fuel ratio of the mixture to be produced in the mixture
delivery pipe 12 toward the stoichiometric ratio throughout the va-
rious modes of operation or during predetermined modes of operation
- of the engine. The mixture ratio control system comprises an
exhaust sensor 34 provided in the exhaust system to detect the con-
centration of a prescribed type of chemical component of the exhaust -
gases discharged from the engine cylinders. For the purpose of des-
cription, the exhaust sensor 34 is herein assumed, by way of
; example, to be of the type which is sensitive to oxygen contained
in the exhaust gases passed therethrough. If desired, however! the
exhaust sensor 34 of this nature may be replaced with an exhaust
sensor of the type which is sensitive to, for example, hydrocarbons,
carbon monoxide or dioxide or nitric oxides in the exhaust gases.
The exhaust sensor 34 is, furthermore, shown to be located in the
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exhaust manifold 28 with the catalytic converter 32 mounted in the
exhaust pipe 30 but, if desired, the same may be located in the
exhaust pipe 30 preferably upstream of the catalytic converter 32.
If the catalytic converter 32 is mounted in the plenum tube portion
of the exhaust manifold 28 as previously mentioned, then it is pre-
ferable to have the exhaust sensor 34 mounted on the particular por-
tion of the exhaust manifold 28 upstream of the catalytic converter
32 thus arranged.
The exhaust sensor 34 produces an analog output signal S_
closely related to the detected concentration of the oxygen in the
exhaust gases passed therethrough and supplies the signal S_ to an
electric control circuit 36. The control circuit 36 is arranged to
produce an output signal S_ that varies with the analog input signal
S_ impressed thereon. The output signal S_ is fed to a suitable
solenoid-operated valve unit 38 associated with the air delivery
means and/or fuel delivery means (not shown) of the carburetor 10
and controis the rate of flow of air or fuel or the rates of flows
of both air and fuel to be delivered into the mixture delivery pipe
12 in such a manner that the air-to-fuel ratio of the mixture pro-
20 duced in the mixture supply system is regulated toward a stoichio-
metric value. The solenoid-operated valve unit 38 may be of a two-
position type having open and closed conditions or of the type which
is continuously operable between open and closed conditions. If
the valve unit 38 is of the two-position type, the control circuit
36 should be arranged to deliver, as the above-mentioned output si-
gnal Sc, a train of pulses having a frequency and pulsewidths that
vary with the analog input signal S_ impressed on the circuit 36.
Fig. 2 shows a preferred example of the control circuit 36 arranged
to achieve such a function.
Referring to Fig. 2, the control circuit 36 is shown to
comprise a comparator 40, a proportional amplifying integrator 42,
a saw-tooth or triangular pulse generator 44 and a pulsewidth modu-
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lator 46. The comparator 40 has a first input terminal connected
to the output terminal of the above-mentioned exhaust sensor 34 and
a second input terminal on which a reference signal Sr is constantly
impressed. The reference signal S_ is representative of the con-
centration of oxygen in the exhaust gases resulting from a stoichio-
metric air-fuel mixture.
The comparator 40 is operative to compare the output~'
signal So with the reference signal S_ and produces a binary output
signal Sl which assumes a logic "0" value when the voltage of the
signal S_ is greater in magnitude than the reference signal Sr (viz.,
when the air-fuel mixture supplied to the engine cylinders is richer
than a stoichiometric mixture) and a logic "1" value when the former
is smaller in magnitude than the latter (viz., when the mixture
supplied to the cylinders is leaner than a stoichiometric mixture).
The binary signal Sl produced by the comparator 40 is fed to the
proportional amplifying integrator 42 which is arranged to produce
a linear ramp signal S2 which increases or decreases in response
to the input signal Sl of the logic "0" or "1" value, respectively.
On the other hand, the saw-tooth or triangular pulse generator 44
is operative to produce a train of saw-tooth or triangular pulses
S3 having equal pulsewidths and a predetermined constant frequency.
The ramp signal S2 from the proportional amplifying integrator 42
and the train of saw-tooth or triangular pulses S3 from the pulse
generator 44 are fed to the pulsewidth modulator 46. The pulsewidth
modulator 46 is, in effect, a comparator and is thus operative to
compare the ramp signal S2 with the saw-tooth or triangular pulses
S3, thereby producing a train of square-shaped pulses having posi-
tive durations when the signal S2 is lower in magnitude than the
saw-tooth or triangular pulses S3. The train of square-shaped pul-
ses produced in this fashion by the pulsewidth modulator 46 provides ~ -
the previously mentioned control signal Sc and is delivered from the -
control circuit 36 to the soneoid-operated valve unit 38. The
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valve unit 38 is consequently controlled to open and close at in-
tervals dictated by the pulses Sc which are fed in succession to
the valve unit. --
The mixture control system thus arranged depends for~its
performance upon the reliability of the signal delivered by the(~
exhaust sensor 34. Because, however, there is an appreciable diffe-
rence between the time at which an air-fuel mixture is produced in
the mixture delivery pipe 12 of the carburetor 10 and the time ~t
which the exhaust gases resulting from the mixture reaches the e~haust
10 sensor 34 and because of the fact that the air-to-fuel ratio of~the
mixture produced in the carburetor 10 is subject to fluctuation which
is practically beyond the control of the mixture control and the
carburetor per se, the signal produced by the exhaust sensor 34 is
not faithfully representative of the air-to-fuel ratio of the mix-
ture produced at the very instant at which the signal is delivered
t~ ~ from the sensor 34. The intent of the present invention is to`re-
duce such a time difference to a minimum by promoting the evapora-
; tion of the air-fuel mixture being passed through the intake mani-
fold. The degree of evaporation of the air-fuel mixture in the;
intake manifold is closely related to the velocity of the stream
of the mixture through the intake manifold and the mixture flow~
~ ` through the intake manifold at a velocity which is approximately
Z equal to the velocity of the stream of air t~rethrough when the-
mixture is evaporated substantially perfectly, as will be seen ;:
from the curve of Fig. 3. ~-
To achieve such an intent of the present invention, the
exhaust manifold 28 of the engine illustrated in Fig. 1 has a wall
portion constituted by the riser portion 26 of the intake manifold
' ~ 18 and a flow control valve 48 is provided within the exhaust mani-30 fold 28 in the neigh~ourhood of the particular wall portion. The
flow control valve 48 is rotatable with a shaft 50 journalled to
the exhaust manifold and provides a passageway 52 through which the
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exhaust gases entering the exhaust manifold 28 are brought into heat
conductive contact with the riser portion 26 of the intake manifold
28. The valve 48 is rotatable about the axis of the shaft 50 bet-
ween an angular position indicated by full lines for providing a
maximum flow rate through the passageway 52 and an angular position
indicated by phantom lines for providing a minimum flow rate through
the passageway 52. The valve 48 is moved between these two angular
positibns by means of a helical bimetallic spring 54 which is
;- anchored at one end to the shaft 52 and at the other end to an
internal wall portion of the exhaust manifold 28 as indicated at 56.
The bimetallic spring 54 is arranged to move the valve 48 between
the above-mentioned two positions in such a manner as to vary the
flow rate of the exhaust gases through the passageway 52 substantial-
ly in inverse proportion to the temperature of the hot exhaust gases
as detected by the bimetallic spring 54 so that the quantity of heat
in the exhaust gases passed through the passageway 52 and according-
ly the quantity of heat transferred through the riser portion 26 of
the intake manifold 18 to the air-fuel mixture flowing through the
intake manifold 18 are maintained substantially constant. The bi-
metallic spring 54 is preferably selected and arranged to maintainthe temperature of the riser portion 26 of the intake manifold 18
within the range of between about 100 C and about 250 C.
To provide an increased heat exchange efficiency through
the riser portion 26 of the intake manifold 18, the riser portion `
26 may be corrugated or ridged as shown.
Fig. 4 illustrates by curve _ the concentration of an air
contaminative compound (exemplified by carbon monoxide) contained
in the exhaust gases discharged into the atmosphere when the flow
control valve 48 of the arrangement shown in Fig. 1 is operated by
the bimetallic spring 54 in such a manner as to maintain the tempe-
rature of the riser portion 26 of the intake manifold 18 at appro-
ximately 180C. From comparison between this curve _ and the
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106'~103
curve b which is indicative of the concentration of carbon monoxide
in the exhaust gases dischar~ed from an ordinary internal combus-
tion engine provided with a catalytic converter and a mixture con-
trol system of the described nature but void of the mixture eva~o-
rative means, the advantages achieved by the present invention will
be self-explanatory. -
~
The lower and upper limits 100C and 250C of the above-
mentioned temperature range have been specified with a view to
enabling the air-fuel mixture to be sufficiently atomized and pro-
l.0 vlding acceptable mixture induction efficiency. ~
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