Note: Descriptions are shown in the official language in which they were submitted.
~ 835~ ~
This invcn-ti.on rel.ates to a spark-ignition internal
combustion engine of the type wherein two spark plugs
are disposed within a combustion chamber of the engine
to reliably igni.te an air-fuel mixture mixed with inert
gases.
In connection with purification of the exhaust
gases discharged from the combustion chambers of spark-
ignition internal combustion engine, it has been already ::~
proposed that an air-fuel mixture is combusted in the
combustion chamber in the presence of inert gases such .~
as exhaust gases recirculated into the combustion - :
chamber and combusted gases remaining in the combustion
chamber, by ignition with two spark plugs disposed within .
the combustion chamber (dual spark-ignition system),
::
~5 thereby achieving a considerable decrease in the emis- `~
: ~ .
sion level of nitrogen oxides (NOx) without deterioration :~ -
-~ . ,.
of stable engine operation.
This NOx decreasing effect results from the fact .
that, according to the dual spark-ignition system, the
combustion volume alotted to each spark plug is con-
siderably decreased compared with prior art spark ::
ignition system whsre only one spark plug is disposed ~
within a combustion chamber. Accordingly, combustion ~ ~:
of the air-fuel mixture is accomplished within an
extremely short period of time and therefore stable -
- 2 -
:
8355 `:
combustion of the air-fuel mixture is carried out in
the combustion chamber even if a relatively large
amount Or the inert gas is present with the air-fuel
mixture in the combustion chamber. The combustion
carried out in the presence of the large amount of the
inert gases lowers the maximum temperature of combustion
and consequently suppresses NOx generation durlng same.
However, it is now required to further improve the
NOx generation suppressing effect and to increase the
post combustion NOx reduction of same in order to
further decrease the overall NOx emission level of ths
engine. Additionally, it is also required to decrease
the emission levels of carbon monoxide (C0) and hydro~
carbons (HC) which are generated by incomplete combustion
~5 of fuel.
It is, therefore, a general object of the present -
invention is to provide a spark-ignition internal
combustion engine capable of producing very low concen-
:.
trations of NOx, C0, and HC.
Another object of the prcsent invention is to
provide a spark-ignition internal combustion engine in
which the NOx emission level is decreased firstly by
combusting the air-fuel mixture in the presence of
inert gases and thereafter reducing NOx in the three-
way catalytic converter, whereas C0 and HC emission
~ 3 ~
:
~4B3~5
:
levels are decreased firstly by comb~lsting an approxi-
mately stoichiometric air-fue~ mixture and thereafter
by oxicli~ing them in the three-way catalytic converter.
A further object of the present invention is
provide a spark-ignition internal combustion engine of
the type where an air-fuel mixture mi~sd with inert
gases is ignited with a dual spark-ignition system,
which is further equipped with a three-way catalytic
- converter for reducing NOx and oxidi~ing CO and HC,
and with an air-fuel ratio control device for controlling
the air-fuel ratio of the mixture supplied to the com- ;
bustion chamber so as to feed the three-way catalytic
converter with exhaust gases most suited for achieving
the highest mutual conversion efficiencies in thc three- ;~
way converter.
:, :
Other objects, features, and advantages of the
,. ~
- spark-ignition internal combustion engine in accordance
.
~ with *he present invention will become more apparent
- as the following description of preferred embodiments
,~ ,
thereof progresses, taken in conjunction with the ac- ;
companying drawings, in which~
Fig. 1 is a schematic plan yiew of a preferred ~,
embodiment of a spark-ignition internal combustlon -
engine in accordance with the present invention;
Fig. 2 is a vertical section view of a carburetor
, ~
- 4 ~ ~
'~
~,
~.
.
.
355
employed in the engine oI` ~ig. 1;
~ig. 3 is a v~rtical section view of a cylinder
portion Or the engine of Fig. 1;
Fig. Il is a plan view of a cylinder head portion
defined by the cylinder of Fig. 3;
Fig. 5 is a graph showing the characteristics of
a three-way catalytic converter employed in the engine
of Fig. 1, in terms of conversion efficiency and air-
fuel ratio of the mixture supplied to the combustion
chamber of the engine of Fig. 1; and
Fig. 6 is a schematic plan view of another pre-
ferred embodiment of the spark~ignition internal
combustion engine in accordance with the present
invention
Y5 Referring now to Fig. 1, 2, 3 and 4 of the drawings,
a preferred embodiment of a spark~ignition internal com-
bustion engine in accordance with the present invention
is shown, in which the engine is generally designated by
,~
the reference numeral 10. The engine of this instance -~
is an in-line, four cylinder type and therefore the
engine proper 11 has four aligned combustion chambers
C1 to C4 therein. As clearly shown in Fig. 3, each com-
bustion ~hamber is defined by the cylindrical inner wall
of a cylinder 12 formed in a cylinder block 13, the inner
wall of a cylinder head 14 closing the one (upper) end of ~;
- 5 -
~ : ~ . :
:: ~ , ,- . : . .
.
~0~335~i
the cylinder 12 and the crown of a piston 16. Each
combustion chamber is commllnicabLe through each intake
port 18 with an intake mani~old 20 of the intake system
(no n~mleral) which manifold communicates with a carbu-
retor 22 formirlg part of air-fuel mixture supply means
24. Reference numeral 25 indicates intake valves.
Furthermore, each combustion chamber communicates
through each exhaust port 26 with an exhaust manifold
28 which connects to a connecting pipe 30 forming part
of an exhaust passage 31 of the exhaust system (no
numeral). The reference numeral 27 indicates exhaust
valves. The connecting pipe 30 is connected to a so-
called three-way catalytic converter 32 capable of
reducing nitrogen oxides (NOx) and oxidizing carbon
~5 monoxide (CO) and hydrocarbons (HC). The three-
way catalytic converter 32, in turn, communicates with
the atmosphere to discharge the exhaust gases purified ;
in the converter 32 into the atmosphere.
As best seen in Fig. 2, the carburetor 22 has a
throttle valve 34 rotatably disposed within the air-
fuel mixture induction passage 36 thereof. A main
venturi portion 38 is located upstream of the throttle
valve 34, and a secondary venturi portion 40 is located
adjacent the main venturi portion 38. Opened to the
secondary venturi portion 40 is a main discharge nozzle
- 6 _ ;
' ,; ' , , "' . ,". ' ' . . ' ~ ' ' ' "' '~ ', . ', ' ' ' ' ' ' ' ; '
... .: :
~L~4~5~i
l~2 of a main circuit (no numeral) which nozzle 42 is
communicated with a main well 44 which is in turn
commllnica-ted w:ith a float bowl 46 through a main fuel
passage 48 having therein a main jet 50. The main
well 41l has a main air bleed 52 and a firs-t auxiliary ~:
air bleed 51l. The main well 44 is further communicated
through a jet or a restrictor 56 with a fuel passage 58
of a low-speed circuit (no numeral) which passage 58 is
communicated with a slow port 60 opened to the air-fuel
mixture induction passage 36 downstream of the main
venturi portion 38. The fuel passage 58 has a low-
speed circuit air bleed 62 and a second auxiliary air
bleed 64.
A first solenoid valve 66 or first air flow amount
control means is disposed for opening or closing the
first auxiliary air bleed 54 and arranged to take a
; first state wherein the actuating rod or member 66a
thereof is moved with respect to the first auxiliary
air bleed 54 to increase the flow amount of air inducted `
through the first auxiliary air bleed 54 into the main
well 44 above a predetermined level, and take a second
state wherein the actuating rod 66a thereof is moved . ~.
with respect to the first auxiliary air bleed 54 to
decrease the flow amount of the air inducted through
the auxiliary air bleed 54 into the main well 44 below ~ :
,:
.
~, ':, ' , . : '
~a34133S~
the predetermined level. A second sol0noid valve 68
or second air flow contro]. means is electrically con-
nectecl in parallel with the first solenoid valve 66
and arrangec~ to be operated similarly to the first
solenoid valve 66. The first and second solenoid -;
valves 66 and 68 form part of air-fuel ratio control ~ .
means 70 and electrically connected to a control circuit
72. ~ :
The control circuit 72 is arranged to generate a ~ ~
10 first command signal for placing the first and second :
solenoid valves 66 and 68 into the first state and a ; :
second command signal for placing the first and second
solenoid valves 66 and 68 into the second state. The
control circuit 72 is electrically connected to an
15 exhaust gas sensor 74 which is disposed within the
connecting pipe 30 upstream of the catalytic converter
32. The exhaust gas sensor 74 is arranged to generate :~
a first information signal (which may be a voltage
signal) for causing the control circuit 72 to generate ~ :
20 the first command signal when the exhaust gases passing .~
through the connecting pipe 30 have a first composition ~.
indicating that the combustion chambers are fed with an ~:
air-fuel mixture richer than that having the stoichio~
metric air-fuel ratio (14.8:1), and a second information ~;
25 signal for causing the control circuit 72 to generate
- 8 -
' . '
:' ~
:, ., ~ . ~: . .
the second conun~nd signal when the exhaust gases passing
through the connect.ing p:ipe 30 have a second composition
indicating that the combustion chambers 18 are fed with
an air-fuel mixture leaner than that having the stoichi-
ometric ratio. The exhaust gas sensor 74 lllay be oxygen
(2) sensor, a nitrogen oxides ~NOx) sensor, a carbon
monoxide (C0) sensor, a carbon dioxide (C02) sensor or
a hydrocarbon (HC) sensor which respectively detect the ; ~:~
concentrations of 2~ NOx, C0, C02 or ~IC contained in
the exhaust gases discharged from the combustion chambers.
In order to operate the first and second air flow amount
control means 66 and 68 in the above discussed manner,
the control circuit 72 may be arranged to set, as a
reference voltage, a specified voltage signal generated ~-
by the exhaust gas sensor 74 when the air-fuel mixture
having stoichiometric air-fuel ratio is supplied into :~
the combustion chambers, and to generate the first com- :~
mand signal when the level of the voltage signal from - :
the sensor 74 is lower than that of the specified
voltage signal., indicating that the combustion chambers ~ :
are fed with the air-fuel mixture leaner than the stoi-
chiometric mixture and the second command signal when ~:
the level of the voltage signal from the sensor 74 is
~ higher than that of the specified voltage signal, indi- : :
: 25 cating that the combustion chambers are fed with the :
_ g _ ' ' ~.' `'' ',
~.
, .
,
.
air-fuel mi~ture r:icher than the stoichiometric
mix-ture.
Connected to the exhaust manifold 28 and the
intake manifold 20 is a conduit 76 or conduit means
for recirculating or suppJ,ying a portion of the exhaust
gases passing through the exhaust manifold 28 into the
combustion chambers C1 to C~ through the intake manifold
20. The concluit 76 forms part of exhaust gas recirculat- `-' : '
ing means 78 or an exhaust gas recirculation system. A :
control valve 80 is disposed in the conduit 76 and is '
arranged to control the amount of the recirculated
exhaust gases with respect to the amount of the intake ',~
air induced through the intake system in response, for
,
example, to the venturi vacuum which is a function of , : :
the amount of the intake air. The venturi vacuum is ~' ~
generated at the venturi portion of the carburetor 22. ~,' ~ . .
The exhaust gas recirculating means 78 functions to ~:
- add substantially inert gaS to the air-fuel mixture in
the combustion chamber by only itself or in combination
with other measures such as, for example, controlling . ~ '
so-called valve overlap of the intake and exhaust valves :,~
25 and 27. It will be appreciated that addition of a ' ,,'`
`: relatively large amount of the substantially inert gas ','
. to the air-fuel mixture in the combustion chamber ,~
results in lowering the maximum temperature of the
':~' "
- 10 _ ,
..
,.
.. . .
835~i
combustion carried out in the combustion chamber, causing
a recluction of the NOx emission level. The substantially
inert gas consists of mixed gases which substantially clo
not par-ticipate or remain substantially iner-t in the com-
bustion in the combustion chamber and therefore include
residual gas or combustion gas which is not discharged
from the combustion chamber during the exhaust stroke and
remains in the combustion chamber, recirculated exhaust
gas which is recirculated or supplied into the combustion
chamber by exhaust gas recirculation system 78, nitrogen
gas (N2) contained in the intake air. It will be under-
stood thai the residual gas and the recirculated exhaust
gas contain amongst other things carbon dioxide (C02),
water vapour (1~20) and nitrogen gas. With respect to
the residual gas, when the valve overlap of the intake
and exhaust valves 25 and 27 is set, for instance, at
about 35 to 60 degrees of crank angle of the engine, 20 ~-
to 30% of the residual gas remains in the combustion
chamber during low engine speed operating range. Accord~
ing to the present invention, the weight ratio of the
fuel substantially combusted in the combustion chamber ~ ~;
or the fuel in the air-fuel mixture in the combustion
chamber and the substantially inert gas added to the
air-fuel mixture supplied to the combustion chamber,
is selected to be within the range from 1:13.5 to
- 11 - : '
'~
' '
: , . . . : -: : . :
, . . . . . .
~.~4~; ~S~
1:22.5 (this weight ratio will be referred to as
"fuel-inert gas ratio" hereinafter) during normal
engine operation.
i In order to reliably ignite the air-fuel mixture
mixed with such a larse amount of the substantially
inert gas, two spark plugs 82a and 82b, as best seen
in Figs. 3 and 41 are disposed in each combustion
chamber in such a manner that the two spark plugs 82a
and 82b are installed through the cylinder head 14 and ~ ~-
their electrodes are projected into each combustion ~ ~
chamber. The two spark plugs 82a and 82b are located ~ ;
, ~.
spaced oppositely from the center axis Xc of the cyl~
inder 12 and near the periphery of the combustion -
. .
chamber. The locations of the two spark plugs 82a
and 82b are preferably such that an intermediate point
; of the spark gap or the distance between the two elec- ` ;;-
trodes of the spark plug 82a and an intermediate point
of the spark gap of the spark plug 82b constitute an
.~
angle ranging from 110 to 180 degrees with respect to
the center axis Xc of the cylinder 12, and the shortest
distance L between the intermediate point of the spark
gap of each spark plug and the center axis Xc is 0.15
to 0.45 times of the diameter D of the cylinder bore.
With this location of the two spark plugs 82a and
82b, the combustion volume alotted to each spark plug ;~
.
,~ , `
: ~ . :
- 12 _
;` ' ''~ '' '.
.. . .
:.:. : ,:... .. . ...
.:-:: : - :
:::: -
is approximate:ly one half Or the combustion chamber
volume causins shortening of flame propasation distance
per spark plug and therefore the combustion time. In
general, shortened combus-tion time results in an im-
provement in the efficiency of converting combustion
energy or pressure into mechanical work, thereby achiev-
ing improvement in fuel consumption characteristics and
engine power output performance. Additionally, even
when the above-mentioned fuel-inert gas ratio is as
high as 1:13.5 to 1:22.5, reliable ignition and stable ;~
combustion of the air-fuel mixture in the combustion
chamber achieved. If the locations of the two spark
plugs 82a and ~2b are excessively close to each other,
the ignition effect -thereof is similar to that in the
,15 combustion chamber with only one spark plug. It will
be appreciated from the foregoing that the above-men-
tioned locations of the two spark plugs contribute to
reliable ignition and stable combustion of the air-fuel ~-
mixture in the combustion chamber.
With respect to the selected fuel-inert gas ratio
range: if the ratio of the inert gas is lower than its
lower limit 1:13.5, the NOx decreasing effect is reduced~
whereas if it is higher than its upper limit 1:22.5,
stable combustion in the combustion charnber is not
possible even with the most effective ignition with ~ -
~' . .
~` .
- 13 -
: :.
~4i~
the two spark plugs 82a and 82b. Additionally, the
NOx clecrcasin$ effect is not improved to any extent
by doing same. Unstable combustion in the combustion
chamber inevitably causes noticeable deterioration of
the fuel economy characteristics and the engine outpu-t
power performance.
In this connection, the fuel-inert gas ratio is
calculated as follows: since the weight ratio of the
; fuel (gasoline or petrol) and the atmospheric air in
the stoichiometric air-fuel mixture is 1:14.7 and the
volume ratio of oxygen gas (2) and nitrogen gas (N2)
is 21:79, the weight ratio of the fuel and nitrogen
gas is obtained to be 1:11.3. Given the above facts, ~ -
assuming that the exhaust gases containing the residual
i5 gases occupy X% by volume of the amount of intake air,
the weight ratio of the fuel and total inert gas in the
combustion chamber is represented as 1-(11.3+14.7x1oo)
since the weight ratio of the air and the exhaust gases
or the residual gases is about 1:1~ Accordingly when
the amount of the exhaust gas recirculated into the
combustion chamber is 10% with respect to the amount
of intake air and the residual gases occupy 20% of the
volume of the intake air, the fuel-inert gas ratio is
1:(11.3+14.7xloo)=1:15.7. ~ ~;
Fig. 5 shows the characteristics of the three-way ~ ~
,, ;" : ~ "
- 14 -
::
.. . . ... ..
.~ ,
: ~ : , , -
3S5
catalytic converter 32, in which ~he conversioT1 effi-
ciencies of NOx, CO and 11C are respectively represented
by lines a, b and c, in term of air-fuel ratio of the
air-fuel mixture supplied to the combustion chamber of`
the engine. As is apparent from this figure, it is
necessary for obtaining the highest mutual conversion
efficiencies of NOx, C0 and 11C to supply the combustion
chamber of the engine with the air-fuel mixture having
a narrow air-fuel ratio range including the stoichio-
metric air-fuel ratio. Accordingly, if an air-fuel
mixture leaner or richer than the stoichiometric air-
fuel mixture is supplied to the combustion chamber, the
efficiency of at least one of NOx, C0 and HC abruptly
drops. It will be understood from the foregoing that
the air-fuel ratio of the air-fuel mixture supplied to ~ -
the combustion chamber must be strictly controlled at
approximately stoichiometric or within the narrow air-
fuel ratio range, in order to produce the highest
mutual conversion efficiencies in the three-way catalytic ;~
converter 32. -
With the arrangement hereinbefore described, during
operation of the engine lO, a considerably large amount
Or the inert gas containing the recirculated exhaust
gases through the exhaust gas recirculating means 78
and the residual gas remaining in the combustion chamber
:
:,
- 15 ~ ~
~ .,
.: .: : , :, :
~48355 ~:~
is mixed with the air-fuel mixture inducted into the
combustion chambers. The air-fuel mixture mixed with
the inert gas is ignited and effectively burned by the
two spark plugs ~2a and 82b disposed within each the
combustion chamber. With these spark plugs arrangement,
when the air~fuel mixture in the combustion chamber is ;
ignited, two flame fronts are produced adjacent the
inner wa]l surface of the combustion chamber, or quench
area. These flame fronts move toward the centre of the ~;
combustion chamber, heating it to a high temperature.
Therefore, the distance of flame propagation is shortened
compared with a conventional engine using only one spark ~ ;
plug. Thus combustion, as a result of the plurality of
spark plugs, is faster and completed at the central
portion of the combustion chamber thereby accomplishing
stable and smooth combustion even though such a large
amount of the inert gas is mixed with the air-fuel mixture
to be combusted in the combustion chamber. Due to the
effect of the inert gas, the maximum temperature within
the combustion chambers is lowered and accordingly the
- emission level of NOx is reduced as compared with the
engine without the exhaust gas recirculating means.
Now, when the combustion chambers are fed with the
air fuel mixture richer than that having stoichiometric
air-fuel ratio, the first and second solenoid valves 66
- .
- 16 -
~ ~ "' '' ' '' ' , ..
.,: . . .
3~
and 68 are operated to increase the amounts of air
inducted respectively -through the first and second
auxiLiary air bleeds 54 and 61 into the main well 41
and the ruel passage 58 of the low-speed circuit.
Thus, the amount of fuel flowing through the main
nozzle 42 and the slow port 60 is decreased and
accordingly the air-fuel mixture fed into the com-
bustion chambers is made leaner. On the con-trary,
when -the combustion chambers are fed with the air-
fuel mixture leaner than that having stoichiometricair-fuel ratio, the first and second solenoid valves
66 and 68 are operated to decrease the amount of air
inducted respectively through the first and second
auxiliary air bleeds 511 and 64 into the main well 44
~5 and the fuel passage 58 of the low-speed circuit.
Thus, the amount of fuel through the main nozzle 42
` and the slow port 6~ is increased and accordingly,
the air-fuel mixture fed into the combustion chambers
is enriched. As discussed above, the air-fuel ratio
of the mixture supplied into the combustion chambers
~- can be always maintained accurately at the stoichio-
metric air-fuel ratio or near same. ~ ;
Now~ in addition to less generation of CO and
HC because of combustion of stoichiometric air-fuel
mixture, the generated CO and ~IC are further oxidized
- l7 - ;`
' ' ' ~ . :
:- ' : :. ' : .
:.:
s~ :~
in the three-way catalyt.ic converter 32 to even
further reduce the emission levels of C0 and HC. The
relative].y small amount of NOx contained in the exhaust
gases discharged from the combustion chambers is also
further reduced in the three-way catalytic converter
32 to more reduce the emissibn level thereof~ .
It will be understood that since the ai.r-fuel ratio
of the air-fuel mixture supplied to the combustion
chamber is always accurately controlled at approximately
stoichiometric, variation or change in the emission level
of NOx, C0 and HC is minimized providing more accurate :~
and improved control of noxious constituents contained .~ :~
~ in the exhaust gases. ;~
: While the solenoid valves 66 and 68 have been shown ,: '~
~5 and described to control the air amount inducted from ; ~ ;
the auxiliary air bleeds 54 and 64, it will be understood ~ ~ -
that similar solenoid valves may be alternately or addi-
tionally disposed in the main fuel passage 48 and the ., ;
low-speed circuit fuel passage 58 in order to directly
control the amount of fuel supplied from the main dis-
charge noz,zle 42 and the slow port 60. '~
Fig. 6 illustrates another preferred embodiment of .~ ~;
the spark-ignition internal combustion engine 10' in
accordance with the present invention, in which descrip- ~.
tion of similar parts to that of the embodiment in Fig. 1
.
....
. . .
' ' ' " . ' , ' ,. ;~': ' '
~ ; .: . , ,
3~i5
will be omitted for the purpose of sil~plicity of
explanat:ion by deslgnating Iike parts at like refer-
ence numeraIs. This engine 10' is similar to that of
I~`ig. 1 except for an electrically controlled fuel
injection system emp1oyed in place of carburetor 22 of
Fig. 1.
As shown, the engine 10' is equipped with intake
passage means 84 fluidly communicating with a conduit
85 which defines therein a throttle chamber 85a in which
a throttle valve 86 is movably disposed. The intake
passage means 84 is formed with four branch passages
(no numerals)which are respectively communicable with
the four combustion chambers C1 to C4. Disposed respec-
tively at the four branch passages are fuel injectors
90a, 90b, 90c and 90d forming part of an electronically
controlled fuel injection system. The injectors extend ~ -
,
into the branch passages of the intake passage means B~ ~ .
to inject a fuel mist into the air stream passing through
the branch passages. Accordingly, the fuel mist from the
injectors is inducted into the combustion chambers with
air and recirculated exhaust gas to form the air-fuel
mixture within the combustion chambers.
~ ach fuel injector is arranged to take the first
state wherein the injection time for injecting the fuel
is decreased below a predetermined level to decrease the
_ I9 _
~'
,, , . -. - , . , : .
' ,,:, . . , .. '' , ::
~4~3355 :
:.
amount of fuel inje~-tecl by one in;jection and a second ~,
j~ state wherein the i,njectioJl time is increased above the
precletermined level to increase the amount of fuel ~'- .
injected by one injection. The each fuel injector is ;~
electrically connected to the control circuit 72'
forming part of the air-fuel ratio control means (no -
' numeral ) . The circuit is arranged to generate a first ';
command signal to place each fuel injector into the `
~; first state and a second command signal to place each
fuel injector into the second state. The control circuit ~ ~ ,
72' is, in turn, electrically connected to the exhaust ~ - -
gas sensor 74 located within an exhaust manifold 92 '' ~ -
serving as a thermal reactor or reactor means forming
, part of the exhaust passage 31. The exhaust manifold '~
~ 15 92 is communicable with the four combustion chambers C~
', to C4 through so-called siamesed exhaust ports 94 each
~ .
- of which is formed in the cylinder head 14 such that the
outlets of the exhaust ports of two adjacent combustion ,~ ', '
chambers are combined to form an only one outlet. Refer- "
ence numeral 96 indicates port liners which cover the
,, inner surface of the siamesed exhaust ports 94. The
.,
exhaust manifold 92 'communicates through the connecting
pipe 30 with the,three-way catalytic converter 32. '~
;; ' The, control circuit 72' is designed to supply the '; '`
'`25 fuel injectors 90a to 90d with command sigDals for
- 20- ,
' . :
~483~iS ``: ~ ~
causing the fuel injectors to inject -the optimum amounts
of fucl at the optirnum timings in response no-t only to
the inforn~ation signals from the exhaust gas serlsor 74
but also to the infortl~ation signals from an intake air
temperature sensor, a throttle position (opening degree)
sensor, an air flow amount sensor, and an engine coolant
temperature sensor.
It is to be noted that since the temperature of the
exhaust gases discharged from the combustion chambers,
~0 in this instance, is maintained relatively high because
of the siamesed exhaust ports and the port liners 96,
HC and C0 contained in the exhaust gases discharged from
the combustion chambers are effectively burned within
the exhaust manifold 92 serving as a thermal reactor,
making it possible to decrease the capacity or volume of
the three-way catalytic converter 32. Additionally, if
the outer surface of the exhaust passage 31 is heat- ~ ;
insulated, the noxious gas decreasing effect of the
three-way catalytic converter 32 may be furthermore
improved.
With the engine 10' of this instance, the fuel ;
injection from the fuel injectors provides improved
fuel distribution to respective combustion chambers.
Improved volumetric efficiency is also realized and
therefore more stable operation of the engine and
- 21 - '~
-:
: ~
- :. . , , . , , :
.~ : ' ' ,. .. .
~4~3355
improved engine power output performance are obtained.
I~Thile on1y rour cy]inder eng:ines have been shown
ancl described here:inbefore, it will be understood that
the principle of the present invention may be applied
to engines having any other number of cylinders.
It will be appreciated that the stoichiometric
air-fuel ratio of the mixture supplied to the combustion
chamber may be somewhat modified during engine warm-up
period or high engine speed and load operation in order
to obtain more stable engine operation and high engine
output power.
As is apparent from the foregoing discussion that,
according to the present invention, NOx emission is
effectively prevented firstly by suppressing NOx
generation in the combustion chamber and thereafter
:-
by reducing the relatively small amount of NOx in the
three-way catalytic converter. While, C0 aDd HC emis-
sions are also effectively prevented firstly by supplying
the combustion chamber with stoichiometric air-fuel
mixture and thereafter by oxidi7ing the C0 and HC in
the three-way catalytic converter. Therefore~ the
noxious constituents in the exhaust gases discharged
from the combustion chamber are almost completely
removed to discharge the harmless exhaust gases into
the atmosphere. Additionally, since the air-fuel ratio
- 2? _
: .
' -', ' ' . : ~
~.: - ' ' , ' '
S5
of the air-fuel mixture sul)plied to the combustion
chambers of the engine is controlled with a high
degree of accuracy a-t approximately stoichiometric,
the fuel consumption of the engine is improved, con-
tributing to ruel economy.
, ~, .
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.
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