Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~5S336
*he pre~ent invcrItic)rl re.late~ genernl:Ly to an
a~Itomotive en~ine carhu.retor, and mor.e p~rticular.ly
to atl improvement in such a carburetor which control~ ~;
the air-fuel mixture ratio in response to an electrical
~:ignal appLied thereto~
Variou~ ~ystems have been propo~ed to optimally
control the air-fuel ratio of` an air-fuel mixture to
an .internal combu~tion engine in dependence of mode~
of eslgine operation in order to effectively reduce
nox.iou~ components (such as nitrogen oxides (NOx),
cnr~)orI monoxide (CO), and hydrocarbons (}IC)) contained
in exhaIlst gases, one of which syJtems is to utilize
the concept of electronic closed loop ~y~tem based on
a sen~ed concentration of a component in exhau~t ga~e~
of the engine. Each of the~e clo~ed loop ~ystems, -
e~pecial:Ly when a ~o-called three-way catalytic con ~:
verter i~ employed for the reduction of the nox~ou~
component~ required to finely control the air- .;
.hIe.L mixture ratio to a considerable extent. This
~0 I~ because the erfect of the three-way catalytic
converter i8 maximized when the air-fuel ratio is
maintained in the vicinity of ~toichiometric air-fuel ..
ratlo. Therefore, a carburetor for u~e with the -
~I.ectronic cLosed loop control Yy~tem is u~ually
e(~ ipped with an electrical unit for the purpose of
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fine control of the air-fuel ratio of the air-fuel mixture.
A three-way catalytic converter, as is well known, has a
characteristic of deoxidizing NOX and oxidizing both CO and HC
at the same timeO
However, none of the conventional mass produced
carburetors has a compensating or auxiliary element which serves
to readily and finely adjust the air-fuel ratio to adequate set
points in a manufacturing process. Furthermore, ready adjust-
ments to compensate for changes of the set points with the
passage of time are not possible. As a result, the conventional
carburetors each, because of the absence of the compensating
element, has not been suitable for mass-production and locked in
reliability of proper operations in effective reduction of the
noxious components due to the undesirable change of the set
points with the passage of time.
It is therefore an object of the present invention to
provide a conventional automotive carburetor with a compensating
or auxiliary element for fine adjustment of an air-fuel mixture
ratio.
More specifically, it is an object of the invention to
provide an internal combustion engine carburetor for use with an
electronic closed loop air-fuel ratio control system to supply
desired air-fuel mixture to the engine for effectively reducing
noxious components in exhaust gases from the engine by a three-
way catalytic converter. It comprises: an intake passage pro- ^~
vided with a venturi; a fuel-containing float bowl; a fuel pas-
sage extending between the venturi and the bowl; a main air
bleed passage connected to deliver air to the fuel passage; an
auxiliary air bleed passage connected to the ~uel passage; an
on/off type electromagnetic valve assembly serving as an
actuator having a plunger arranged to move reciprocally in the -
auxiliary air bleed passage for controlling the rate o~ air
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flow in response to an electrical pulsating signal applied
thereto from the electronic closed loop air-fuel ratio control
system to supply a desired air-fuel mixture to the internal com-
bustion engine; and manually adjustable means disposed in or
adjacent to the auxiliary air bleed for calibrating the maximum
rate of air flowing therethrough by varying the cross-sectional
area of the auxiliary air bleed or by defining the maximum stroke
of the plunger of the elec-tromagnetic valve. ~ -
Embodiments of the invention will now be described
with reference to the appended drawings, wherein:
Fig. l illustrates an example of a conventional auto-
motive carburetor;
Fig. 2 illustrates an example of a conventional electro-
nic ~losed loop control system for use with the Fig. 1 carburetor
and several preferred embodiments of the present invention;
Fig. 3 shows various waveforms whlch demonstrate the
basic control concept of the Fig. 2 system;
Fig. 4 shows a~first preferred embodiment of the
present invention;
Fig. S shows a second preferred embodiment of the
present invention;
Fig. 6a shows a third preferred embodiment of the
present invention; and
Fig. 6b is an enlarged fragmentary view of a part of ;
Fig. 6a. ;
Reference is no~ made to drawings, first to Fig. 1, ~ `
wherein there is schematically illustrated, in a cross-sectional ~ ;~
view, a conventional carburetor for use with an electronic
closed loop air-fuel ratio control system. ~n electro- ;~
magnetic valve assembly lO is provided to control the rate of
air delivered to a fuel passage 14 through an air passaye 12 in
a manner to reciprocally __ _ _ _
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move a plun$er 11 thereof in response to an electrical
E~lllsati~lg si~nal applied theretoO In other wordY~ the
electromngnetic vaLve assembly 10 controls the air-f~el
ratio of an alr-fuel mixture sucked into an intake
~)as~a$e 13 by moving the plunger 11 to R pO9itiQn which
allow~ the air flow to pa~s therethrough or vice versa.
'I`he electrical signal is generated by a pu]L~e generator
10~ which forms part of the control sy~tem to be de-
~cribed l~ter in detail in conjunction with ~igs. 2
and 3. The air passage 12 is opened at its one end
to communicate with the intake passage 13 and connected
at th0 other end to the fuel pa~age 14. The fuel
sAge 1/~ is terminated at a dischar~ing nozzle 16
an(l extends between a f}oat bowl 18 and a ventnri 20.
~5 ~n air bleed hole 22 is located in the upper sectinn
of an air bleed asYembly 24 for introduction of air to
the fuel passage therethrough. ~ '
In the above-mentioned conventional carburetor, ;
when the aforementioned th~ee-wAy catalytic converter
iq employed in order to effectively reduce noxious
com~onent~ in exhaust gase~, the air-fue~ ratio of an
ail-fuel mixture should be finely adjusted. Thi~ i8
becinllse, a~ is described at the outset of this specifi-
Catiotl, the effect of the three-way catalytic converter
'-~5 is maximized in reduction of the noxiou~ components
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wh~n the air-fuel ratio i~ maintain~d in tlle vicinity
of` Ytoichiometry. Therefore, as the air-fuel ratio
is mfilrlly determined by the ratio of open to close
dl~r.ltiorl of the electromMgnetic valve as~embly 10, the
ratio ~hould be finely adju~ted in order to maiJItAin ;~
a richer and a leaner air-fuel mixture a little below
and a little above stoichiometry, re~pectively. In
the above, in order to ~ecure stable engine operation,
the leaner air-fuel mixture i~, in ~enerAl, ~et at an
air exce~ive ratio (viz., aetual air-fuel ratio:
Ytoichiometric air-fuel ratio~ nbout 1~05-l~lOo
llow~ver, it i~ very dlrficult or impossible that
alJ of the curburetors are flnely adjusted, with
re~pect to de~ired ~et points of air-fuel ratio, to a
considerably extent during ma~-production proce~s, ;~ ~;
ancl furthermore, even if finely adjusted~ there i# a
possibility that the de~irable set point~ are liable ;
to change with the pa~sage of time. In the conventional
carburetor for use with an electronic closa Joop alr~
~0 fuel control sy~tem, the above-described attention ha~
not been paid hitherto. ~-
The present invention includes, therefore, an
improved mean~ which is provided in the air passage 12
to readily and finely ad~ju~t the amount of air flowing
'5 t~ere;hrollgh~ and thereby performing the aforementioned
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rl,oYe of the e~fect.ive reduction of the noxiou8
c.om~)onent~ especially when a three-w~ly catalytic
converter :is emp.loyedO
.Ln the following, prior to de~cribing the embodi-
ments of the present invention, exemplified i~ a
corlventiorlal electronic closed loop contro.L ~y~tem
l`or use with both the ~ig. 1 conventional carburetor
alld als0 the embodiments of the present invention. .
~eference i~ now made to ~ig~. 2 and 3q wherein
~chematically illustrated are an example of a conven-
tion.l.l electrical cl.osed loop air fuel control ~y~tem
f`or IJ~e with an internal combu~tion engine 100 having
the cnrburetor shown in Fig. 1 and several waveform~
deveLoped at or derived from different elements of the
Fig. 2 system (Fig. 3). The purpo~e of the syste~ i~
to (?l ectrically control the air-fuel ratio of an air-
f'ueL mixture ~upplied to the engine 100. A sen~or lOZ,
~UCil as an oxygcJI anAly~er, for ~en~ing the concen- ; `
tr(~tion Or oxygen in exhau~t gases i~ dispo~ed in an
exhau.st pipe 101 in ~uch a manner as to be exposed
to -the exhau~t gases. An electrical signal derived ; ~:
.from the sensor 102 i~ fed to a differential ~ignal
generator 104 which generates an electrical signal .
.rep.re~entative of a difference value between the magni~
tlldes of the signal from the ~en~or 102 and a reference :~
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sixrlal. A portion of the wave~orm of the signal from
th~ ~enqor 102 is depicted by reference character A
in l`ig. 3. The reference ~ignal magnitude, which i~
illu~trated by reference charncter ~ in Fig. 3, is
previollsly determined in due con~iderution of optimum
air-f`llel ratio of the air-fuel mixture supplied to the
erlgine 100 for maximi~ing the efficiency of the three-
way catalytlc converter (not shown) provided in the
exhaust pipe 101 downstream of the senAor 102, etc. ~ -
tO rhe ~ignal represerltative of the difference value from
the dii`ferential ~igtlal generator 104 is then fed to
contl~ol rnean~ ~o6 which u~ually include~ a conventional
p~ )roportional-integral) controller. The provi~ion
of the p-i controller, a~ is well known in the art, iY i~
to improYe the efficie~cy of the el~ctronic clo~ed loop
control ~ystem, in other words, to ~acilitate a rapid
tran~ient respon~e of the system. The output signal
from the control means 106, which is depicted by refer-
ence charncter C in Fig. 3, is fed to the next sta~e,
~0 viz., a pulse generator 108 which also receive~ a
di-ther signal ~D in Fig. 3) from a dither signal
generator 110 to generate a signal E consisting of a
train of pulseY as shown in Fig. 3. Each pulse of the
qignal E ha~ A width which corresponds to the duration
wherl the signal D i9 larger than the signal C as
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~chematicnlly ~hown il~ Fig. 3. The train ot plllses
of` the ~ignnl E 1Y then fed to the electromaglletic
valve 10 in order to reg-llate the air-fuel mixture
ratio as de~cribed in connection with Fig. 1.
~ef'ererlCe i9 now made to ~ig. 4, which schemat-
icaLIy illu~tr~te~ a fir~t embodiment of the pre~ent
invention. The first embodiment is analogou~ to the ,~
conventional one aY ~hown in Fig. 1 except that the
~ormer is equipped with a detachable membsr 150 with
a .~llitable orifice (no numeral). The member 150 is
~nllgly fitted in the upper portion of the air paY~age
12 by, ~or example, being ~crewed into a portion
~rovided therein. Therefore, the fine adJu~tment of
the air flow rate i~ readily carried out by replacing
i5 the member 150 by the other one with a more appropriate
orifice.
In Fig. 5, there i~ illustrated a second preferred
embodiment of the present invention wherein a member
152 :i~ added to the conventional carburetor of Fig. 1.
The member 152 i~ preferAbly an reguLating ~crew which
adjll~tably protrude~ into the air p~sage 12 to con-
tinuou~ly vary the cros~-~ectional area of part of the
air pa~ge 12 for changing the amount of air flowing
therethrough, and thereby performing the fine adju~tment
of` the air-fuel ratiu. In Fig. 5, the member 152 i~
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,)rov.i~ed up~tream of the plunger 11, b~lt, alterrlAtively,
i ~ cn~l t)e arranged down~tream thereof'. Furthermore,
the member 152 îs not re~tr.icted to a needle typel but
ally other type may be available on condition th~t the -
at)ove-de~cribed continuous change of the cro~-sectional
area can be obtained.
Finally, reference i8 now made to Figs- 6a and '.
~t:-, wherein a third preferred embodiment of the present ,-~ ~.
invention i~ schematica11y illu~trated. 1`he -third - '~
tO embodiment is equipped with an additional member 154
a~ compared with the conventional carburekor of Fig. 1. '
'I`he member 154 i~ M regulating Ycrew which Yerve~ to
chatlge the Ytroke of the plun~er 11 by means of a
protruding member 156 a~ be~t Yeen in Fig. 6b, and
t,hereby changing the opening at the open position of
the plunger 11. ConYequently, the provi~ion of the ~ ,
e.lement 154 make~ po~sible the aforementioned fine ~'.'
adju~tment of the air-fuel mixture ratio by changing
the amount of the air flowing through the air pa~age
20' 12. ' ` '
In the last mentioned embodiment, another fine
adju~tment of the air-fuel.~ixture ratio can be
achieved by replacing the ~pring 158 by the other one
~ith a more appropriate ~pring constant ~o aQ to .'
regulate the maximum ~troke of the plunger 11, in the - ,
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cn~e of which the member 156 t~ omitted.
From the above, it i~ under~tood that, in ~ccor-
(klllce with the preferred embodiments of the pre~*nt
i nvention, the fine ad justment of the air-fuel mi~cture
rat.. io of a carburetor, which i9 used with an electronic
c.lo~ed loop control Yystem, can be readily performed
in a ~imple man.ner, 80 that the above-deYcribed ~ .
advAntage~ are obtainable with ea~e.
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