Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
ENGINE INTAKE A/F RATIO CONTROL SYSTEM IN OUTBOARD ENGINE SYSTEM
This is a divisional of Canadian patent
application 2,339,260 in which PCT national phase was
entered on February 1, 2001.
FIELD OF THE INVENTION
The present invention relates to an engine intake A/F
(air-fuel) ratio control system in an outboard engine system
which includes an engine disposed in an engine room defined by
an engine support connected ~to an upper portion of an extension
case and by an engine cover covering the engine support, and
a catalytic converter incorporated in an exhaust system for the
engine, so that an exhaust gas exiting from the exhaust system
is discharged under the external water surface via an inside
of the extension case, the intake A/F ratio control system being
operable to control the air-fuel ratio of an air-fuel mixture
to be supplied from a carburetor to the engine.
BACKGROUND ART
There is a conventionally known outboard engine system
including a catalytic converter incorporated in an exhaust
system for an engine, for purifying an exhaust gas (for example,
see Japanese Utility Model Publication No.59-18092).
It should be noted here that the catalytic converter
exhibits the highest purifying function in an extremely narrow
range A of A/F ratio of an exhaust gas around a theoretic A/F
ratio ( 14 . 6 ) , as shown in Fig. l7 . Therefore, when a ~catalyt~ic
converter is used for purifying an exhaust gas from an engine,
it' is a conventional common practice to detect an A/F ratio of
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an exhaust gas by an 02 sensor varying an output largely at about
a theoretic A/F ratio, and to control the A/F ratio of an air-fuel
mixture drawn into the engine, so that the 02 sensor produces
an output corresponding to the theoretic A/F ratio, whereby the
exhaust gas is always purified with a good efficiency by the
catalytic converter.
The OZ sensor varies the output largely relative to a
variation in A/F ratio in the range A, but a variation in output
relative to a variation in A/F ratio is little produced in a
range other than the range A. Therefore, the use of the Oz sensor
is advantageous for controlling the A/F ratio of the exhaust
gas to the theoretic A/F ratio with a good efficiency, but when
the tolerance of. the purifying rate of th~. catalytic converter
is set relatively widely with the engine output taken into
consideration to a certain extent, it is extremely difficult
to carry out the control of the A/F ratio with the 02 sensor.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished with such
circumstances in view, and it is an object of the present
invention to provide an engine intake A/F ratio control system
in an outboard engine system of the above-described type,
wherein, in any of a case when. the tolerance of the purifying
rate of a catalytic converter is set relatively widely with an
engine output taken into consideration to a certain extent,
irrespective of a narrow range including a theoretic /F ratio,
and a case when the set range is shifted to a rich side of the
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A/F ratio with the engine output taken into serious
consideration, the A/F ratio of an exhaust gas can be controlled
properly to a desired target value.
To achieve the above object, according to a first aspect
and feature of the present invention, there is provided an
engine intake A/F ratio control system in an outboard engine
system which includes an engine disposed in an engine room
defined by an engine support connected to an upper portion of
an extension case and by an engine cover covering the engine
support, and a catalytic converter incorporated in an exhaust
system for the engine, wherein an exhaust gas exiting from the
exhaust system is discharged under external water surface via
an inside of the extension case, characterized in that the
engine intake A/F ratio control system comprises a secondary
air passage connected to a carburetor provided in an intake
system for the engine for supplying secondary air for regulating
the A/F ratio of an air-fuel mixture produced in the carburetor;
a duty control unit connected to a duty control valve connected
to the secondary air passage for controlling the duty ratio of
a pulse applied to a coil of the duty control valve; and an LAF
sensor (LINEAR AIR-FUEL RATIO SENSOR) mounted to the. exhaust
system for detecting an A/F ratio of an exhaust gas flowing
through the exhaust system, thereby outputting a detection
signal proportional to the A/F ratio to the duty control unit .
With the first feature, the A/F ratio of the air-fuel
mixture in the carburetor, to be supplied to the engine can be
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controlled in a wide operating range of the engine extending
from a low load to a high load by regulating the duty ratio of
the pulse applied to the duty control valve by the duty control
unit, based on the detection signal of the LAF sensor
proportional to tile A/F ratio of the exhaust gas, thereby
improving the properties of the exhaust gas and enhancing the
engine output.
Namely, the output from the LAF sensor is proportional
to the A/F ratio of the exhaust gas. Therefore, the A/F ratio
of the exhaust gas can be controlled to a narrow range including
a theoretic A/F ratio, and also in any of a case when the
tolerance of the purifying rate of the catalytic converter is
set relatively. widely with an engine output taken into
consideration to a certain extent , and a case when the set range
is shifted to a rich side with the engine output taken into
serious consideration, the A/F ratio of t,~e exhaust gas can be
controlled properly to a desired target value. Therefore, it
is possible to carry out the control operation depending on the
operating conditions of the engine such as a mode with the
purification taken into serious consideration, a mode with the
purification and output taken in consideration and a mode with
the output taken into serious consideration. An increase in
engine output enables the size of the engine to be reduced and
hence, it is easy to place the engine in a narrow engine room
in the outboard engine system..
According to a second aspect and feature of the present
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invention, in addition to the above first feature, a mounting
wall is formed in a side wall of an exhaust line integrally
connected to the engine to form a portion of the exhaust system,
the side wall facing sideways of the outboard engine system,
the mounting wall being inclined inwards of the exhaust line
toward a ~ lower portion thereof ; and the LAF sensor is mounted
substantially vertically to the mounting wall.
With the second feature., the mounting wall of the exhaust
line is inclined inwards of the exhaust line toward it's lower
portion. Therefore, the length of protrusion of the LAF sensor
mounted substantially vertically to the mounting wall in an
outward direction of the outboard engine system can be
suppressed to a value as small as possible, whereby the contact
of the sensor with another portion or component can be avoided
to the utmost , and the detection of the A/F ratio of the exhaust
gas can be carried out reliably. Moreover, the LAF sensor is
directed outwards of the outboard engine spstem and hence, it
is possible tv easily attach and detach the LAF sensor to and
from the mounting wall.
According to a third aspect and feature of the present
invention, in addition to the second feature, the exhaust line
and the mounting wall are formed on the engine support covered
with a detachable undercover, and the LAF sensor mounted to the
mounting wall is covered with the undercover.
With the third feature, the undercover serves as a
protective wall for the LAF sensor, thereby enabling the contact
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of another portion or component with the sensor to be prevented.
In addition, the attachment and detachment of the LAF sensor
can be carried out easily in a state in Which the undercover
has been removed.
According to a fourth aspect and feature of the present
invention , there is provided an engine intake A/F ratio control
system in an outboard engine system comprising a multi-cylinder
engine including a plurality of carburetors for individually
supplying an air-fuel mixture into a plurality of cylinders,
characterized in that the engine intake A/F ratio control system
comprises a single common duty control valve connected to air
bleeding chambers in the plurality of carburetors through a
dispensing tube, sand a duty control unit connected to the duty
control valve for controlling the duty ratio of a pulse applied
to a coil of the duty control valve.
With the fourth feature, the amount of air mixed into a
fuel passed through each of main nozzles df the plurality of
carburetors can be controlled by duty-controlling of the pulse
applied to the single duty control valve, thereby equally
controlling the A/F ratios of the air-fuel mixtures supplied
to the plurdlity of cylinders in the engine, while~promoting
the atomization of the fuel in the air-fuel mixture.
According tc a fifth aspect and feature of the present
invention, in addition to the fourth feature, the number of the
carburetors is three; three outlet tubes of the dispensing tube
made of a hard material are connected to the air-bleeding
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chambers in the three carburetors; and an air outlet of the duty
control valve is connected to a single inlet tube of the
dispensing tube, the single inlet tube and the three outlet
tubes being disposed so that all of angles formed by the outlet
tubes with respect to the inlet tube at connections of these
tubes are substantially equal to one another.
With the fifth feature, the resistances in flow paths
extending from the single duty control valve to the plurality
of carburetors can be equalized, thereby reliably and equally
controlling the intake A/F ratios for the plurality of cylinders
of the engine .
According to a sixth aspect and feature of the present
invention, in addition to the fourth feature, further including
an LAF sensor provided in an exhaust passage in the engine for
detecting an A/F ratio of an exhaust gas flowing through the
exhaust passage to output a detection signal proportional to
the AjF ratio, an output portion of the' LAF sensor being
connected to an input portion of the duty control unit.
With the sixth feature, the intake A/F ratio for each of
the cylinders can be controlled in accordance with the A/F ratio
of the exhaust gas in a wide operating range of the engine
extending from a low load to a high load, thereby improving the
properties of the exhaust gas from the engine at all times.
According to a seventh aspect and feature of the present
invention, in addition to the fourth feature, the duty control
valve includes a valve member accommodated therein and operated
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to open the duty control valve upon excitation of the coil, ,the
duty control valve being provided with a valve case having an
air outlet opened and closed by the valve member, and an outer
case surrounding the valve case to define a cylindrical air
chamber around the valve case, the valve case being provided
with a through-bore which permits an upper portion of the air
chamber to communicate with the inside of the valve case, and
the outer case being provided with an air inlet which opens a
lower portion of the air outlet to the atmosphere. .
With the seventh feature, water is sprinkled over the duty
control valve from the outside, and even if such water enters
the air inlet of the valve, the vigor of the water can be
attenuated in the air chamber, whereby the entering of the water
into the overlying through-bore and thus into the valve case
can be prevented.
According to an eighth aspect and feature of the present
invention, in addition to the sixth feature, a catalytic
converter is incorporated in the exhaust passage.
With the eighth feature, the properties of the exhaust
gas can be improved by the purifying effect of the catalytic
converter.
According to a ninth aspect and feature of the present
invention, in addition to the .sixth feature, a first catalytic
converter is mounted in an exhaust collecting chamber
communicating with a plurality of exhaust~ports in the engine;
a second catalytic converter is incorporated in an exhaust
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passage downstream of the exhaust collecting chamber; and the
LAF sensor is provided in an exhaust passage between both of
the catalytic converters.
With the ninth feature, the properties of the exhaust gas
can be improved at all times in a wide operating range of the
engine extending from a low temperature to 'a high temperature
by the purifying effects of the first and second catalytic
converters . Moreover, the LAF sensor can be placed easily in
the exhaust passage between both of the catalytic converters.
According to a tenth aspect and feature of the present
invention, in addition to the fourth feature, an accelerating
pump is connected to a flow path connecting each of the
air-bleeding chambers in the plurality of carburetors with the
single common duty control valve, the accelerating pump
pressurizing the flow path'in operative association with. a rapid
opening of a throttle valve in each of the carburetors.
With the tenth feature, the flow path connecting each of
the air-bleeding chambers in the plurality of carburetors with
the single common duty control valve is utilized for both of
control of the amount of air bled and control of the acceleration ,
and both of the controls can be satisfied by a simple structure.
According to an eleventh aspect and feature of the present
invention, there is provided an engine intake A/F ratio control
system in an outboard engine system, comprising a secondary air
passage connected to a carburetor mounted in an intake system
in an engine for supplying secondary air for regulating the A/F
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ratio of an air-fuel mixture produced in the carburetor, and
a duty control valve connected to the secondary air passage to
control the amount of secondary air supplied to the carburetor
by controlling the duty ratio of a pulse applied to a coil of
the duty control valve, characterized in that a surge tank and
an orifice..,are incorporated in series in the secpndary air
passage.
With the eleventh feature, even if a pressure pulsation
is produced~in the secondary air passage with the turning~on
and off of the'pulse applied to the coil of the duty control
valve, the pressure pulsation can be attenuated effectively by
a damping effect of the surge tank and a constricting resistance
of the orifice..
According to a twelfth aspect and feature of the present
invention, in addition to the eleventh feature, the secondary
air passage is connected to an air-bleeding chamber defined
around a main nozzle of the carburetor.
With the twelfth feature; the secondary air supplied from
the secondary air passage to the air-bleeding chamber is mixed
with a fuel passed through the main nozzle and hence, the
regulation of the A/F ratio of an air-fuel mixture-and the
promotion of the atomization of the fuel can be provided
simultaneously.
According to a thirteenth aspect and feature of the
present invention, there is provided an engine intake A/F ratio
control system in an outboard engine system comprising a
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multi-cylinder engine disposed in an engine room defined by an
engine support connected to an upper portion of an extension
case and by an engine cover covering the engine support , with
a crankshaft of the engine being turned vertically and a
cylinder head of the engine being turned rearwards of a hull,
and a plurality of carburetors mounted in a vertical arrangement
in the engine for individually. supplying an air-fuel mixture
to a plurality of cylinders, characterized in that the engine
intake A/F ratio control system comprises a .single common duty
control valve connected to air-bleeding~chambers in the
plurality of carburetors through a dispensing tube, a duty
control unit connected to the duty control valve for controlling
the duty ratio of~ a pulse applied to a coil of the duty control
valve, and a surge tank incorporated in a flow path connecting
the dispensing tube and the duty control valve to each other .
With the thirteenth feature, the amount.of air bled, which
is to be mixed with a fuel passed through eachCof the main nozzles
of the plurality of carburetors, can be controlled by duty- .
controlling the pulse applied to the single duty control valve,
thereby equally controlling the intake A/F ratios for the
plurality of cylinders in the engine, while improving the
atomization of the fuel infected from the main nozzle.
Therefore, the only one duty control valve suffices for use,
thereby providing a simplification in arrangement, and enabling
the engine to be placed easily in the narrow engine room in the
outboard engine system, while avoiding the interference with
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another part or component. Moreover, if a pressure pulsation
is produced in a flow path extending from the duty control valve
to each of the air-bleeding chambers With the turning-on and
off of the pulse applied to the duty control valve, the pressure
pulsation can be attenuated effectively by the damping effect
of the surge tank.
According to a fourteen aspect and feature of the present
invention, in addition to the thirteenth feature, an LAF sensor
is provided~in an exhaust~passage in the engine for.detecting
an A/F ratio of an exhaust gas flowing~through the exhaust
passage to output a detection signal proportional to the A/F
ratio of the exhaust gas , an output portion of the LAF sensor
being connected .to an input portion of the duty control unit .
With the fourteenth feature, the intake A/F ratio for each
of the cylinders can be controlled in accordance with the A/F
ratio of the exhaust gas in a wide operating range of the engine
extending from a low load to a high load. Thus , it is possible
to improve the properties of the exhaust gas from the engine
at all times.
According to a fifteenth aspect and feature of the present
invention, in addition to the first feature, the plurality of
carburetors are disposed on one of left and right sides of a
cylinder block; the surge tank is disposed in one of a first
space defined at the rear of the carburetors by a side of the
cylinder head and an inner surface of the engine cover and a
second space defined by a rear surface of the cylinder head and
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the inner surface of the engine cover, and a fuel pump is disposed
in the other of the first and second spaces and is driven by
a valve-operating cam shaft carried in the cylinder head~to
supply a fuel to each of the carburetors.
With the fifteenth feature, it is possible to carry out
the disposition of the fuel pump and the surge tank by
effectively utilizing the first space at the rear of the
carburetors and the second space at the rear of the cylinder
head to contribute to the compactness of the engine room.
According to a sixteenth aspect and feature of the present
invention, in addition to the first, eighth or ninth feature,
the exhaust system is provided with an exhaust box, an inlet
case which is connected to the exhaust system at a location
upstream of the exhaust box and opens at a lower~end thereof
into the exhaust box, and an outlet case which opens at an upper
end thereof into the exhaust box above a. lower end of the inlet
case and also opens at a lower end thereof below the exhaust
box; the catalytic converter is mounted in the inlet case; and
a drainage pipe bent into an inverted U-shape is mounted to the
exhaust box, with one of lower,ends of the drainage pipe opening
in the proximity to an internal bottom surface of the exhaust
box , and the other lower end opening below the exhaust box.
With the sixteenth feature, during operation of the
engine, an exhaust pressure of the engine is agplied to the
inside of the exhaust box to produce a difference in pressure
between the inside of the exhaust box and the inside of the
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extension case. Therefore, when water has been accumulated in
the bottom of the exhaust box by any reason, such water is
discharged through the drainage pipe into the extension case
under the action of the difference in pressure. The bent
portion of the drainage pipe is located above both of its lower
ends and hence, unless the water level within the. extension case
is raised, so that the bent portion of the drainage pipe is
submerged under the water, the entrance of the water from the
drainage pipe into the exhaust box 115 can be prevented.
Therefore, it is .possible to prevent the entrance of the water
into the catalytic converter within the inlet case, thereby
prolonging the life of the catalytic converter.
According.to a seventeenth aspect and feature of the
present invention, in addition to the sixteenth feature, a
central bent portion of the drainage pipe is disposed at
substantially the same level as of an upper end of the outlet
case.
With the seventeenth feature, water-entrance preventing
limit water levels in the outlet case and the drainage pipe can
be set substantially equivalently, thereby enhancing the
function of preventing the entrance of water into the exhaust
box.
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Thus, in a broad aspect the present invention is
an engine intake A/F ratio control system in an outboard
engine system comprising a plurality of carburetors for
individually supplying an air-fuel mixture into a plurality
of cylinders, wherein said intake A/F ratio control system
comprises a single common duty control valve connected to
air bleeding chambers in the plurality of carburetors
through a dispensing tube, and a duty control unit connected
to said duty control valve for controlling the duty ratio of
a pulse applied to a coil of said duty control valve.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
system, comprising a plurality of carburetors for
individually supplying an air-fuel mixture into a plurality
of cylinders, wherein said intake A/F ratio control system
comprises a single common duty control valve connected to
air bleeding chambers in the plurality of carburetors
through a dispensing tube, and a duty control unit connected
to said duty control valve for controlling the duty ratio of
a pulse applied to a coil of said duty control valve, and
wherein a plurality of outlet tubes of said dispensing tube
made of a hard material are connected to said air-bleeding
chamber in said respective carburetors; and an air outlet of
said duty control valve is connected to a single inlet tube
of said dispensing tube, said single inlet tube and said
outlet tubes being disposed so that all of angles formed by
said outlet tubes with respect to said inlet tube at
connections of these tubes are substantially equal to one
another.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
system, comprising a plurality of carburetors for
individually supplying an air-fuel mixture into a plurality
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of cylinders, wherein said intake A/F ratio control system
comprises a single common duty control valve connected to
air bleeding chambers in the plurality of carburetors
through a dispensing tube, and a duty control unit connected
to said duty control valve for controlling the duty ratio of
a pulse applied to a coil of said duty control valve, and
wherein said duty control valve includes a valve member
accommodated therein and operated to open said duty control
valve upon excitation of the coil, said duty control valve
being provided with a valve case having an air outlet opened
and closed by said valve member, and an outer case
surrounding said valve case to define a cylindrical air
chamber around said valve case, said valve case being
provided with a through-bore which permits an upper portion
of said air chamber to communicate with the inside of said
valve case, and said outer case being provided with an air
inlet which opens a lower portion of said air outlet to the
atmosphere.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
system, comprising a plurality of carburetors for
individually supplying an air-fuel mixture into a plurality
of cylinders, wherein said intake A/F ratio control system
comprises a single common duty control valve connected to
air bleeding chambers in the plurality of carburetors
through a dispensing tube, and a duty control unit connected
to said duty control valve for controlling the duty ratio of
a pulse applied to a coil of said duty control valve, and
further including a sensor and a catalytic converter
incorporated in said exhaust passage at a location upstream
of the sensor.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
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system, comprising a plurality of carburetors for
individually supplying an air-fuel mixture into a plurality
of cylinders, wherein said intake A/F ratio control system
comprises a single common duty control valve connected to
air bleeding chambers in the plurality of carburetors
through a dispensing tube, and a duty control unit connected
to said duty control valve for controlling the duty ratio of
a pulse applied to a coil of said duty control valve, and
further including a sensor and a first catalytic converter
mounted in a single common exhaust collecting chamber
communicating with a plurality of exhaust ports in the
engine (E), and a second catalytic converter incorporated in
an exhaust passage downstream of said exhaust collecting
chamber, said sensor being provided in an exhaust passage
between both of said catalytic converters.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
system, comprising a plurality of carburetors for
individually supplying an air-fuel mixture into a plurality
of cylinders, wherein said intake A/F ratio control system
comprises a single common duty control valve connected to
air bleeding chambers in the plurality of carburetors
through a dispensing tube, and a duty control unit connected
to said duty control valve for controlling the duty ratio of
a pulse applied to a coil of said duty control valve,
further including an accelerating pump connected in a flow
path connecting each of the air-bleeding chambers in the
plurality of carburetors with said single common duty
control valve, said accelerating pump pressurizing said flow
path in operative association with a rapid opening of a
throttle valve in each of said carburetors.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
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system comprising a mufti-cylinder engine disposed in an
engine room defined by an engine support connected to an
upper portion of an extension case and by an engine cover
covering said engine support, with a crankshaft of the
engine being turned vertically and a cylinder head of the
engine being turned rearwards of a hull, and a plurality of
carburetors mounted in a vertical arrangement in said engine
for individually supplying an air-fuel mixture to a
plurality of cylinders, wherein said engine intake A/F ratio
control system comprises a single common duty control valve
connected to air-bleeding chambers in the plurality of
carburetors through a dispensing tube, a duty control unit
connected to said duty control valve for controlling the
duty ratio of a pulse applied to a coil of said duty control
valve, and a surge tank incorporated in a flow path
connecting said dispensing tube and said duty control valve
to each other.
In another aspect, the invention contemplates an
engine intake A/F ratio control system in an outboard engine
system, comprising a mufti-cylinder engine disposed in an
engine room defined by an engine support connected to an
upper portion of an extension case and by an engine cover
covering said engine support, with a crankshaft of the
engine being turned vertically and a cylinder head of the
engine being turned rearwards of a hull, and a plurality of
carburetors mounted in a vertical arrangement in said engine
for individually supplying an air-fuel mixture to a
plurality of cylinders, wherein said engine intake A/F ratio
control system comprises a single common duty control valve
connected to air-bleeding chambers in the plurality of
carburetors through a dispensing tube, a duty control unit
connected to said duty control valve for controlling the
duty ratio of a pulse applied to a coil of said duty control
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valve, and a surge tank incorporated in a flow path
connecting said dispensing tube and said duty control valve
to each other, and wherein the plurality of carburetors are
disposed on one of left and right sides of a cylinder block;
said surge tank is disposed in one of the first space
defined at the rear of said carburetors by a side of the
cylinder head and an inner surface of said engine cover and
a second space defined by a rear surface of the cylinder
head and the inner surface of said engine cover, and a fuel
pump is disposed in the other of said first and second
spaces and is driven by a valve-operating cam shaft carried
in the cylinder head to supply a fuel to each of said
carburetors.
In another aspect, the invention contemplates an
outboard engine system comprising an exhaust system which is
provided with an exhaust box, a catalytic converter; and a
drainage pipe bent into an inverted U-shape is mounted to
said exhaust box, with one of lower ends of said drainage
pipe opening in the proximity to an internal bottom surface
of said exhaust box and the other lower end opening below
said exhaust box.
In another aspect, the invention contemplates an
outboard engine system comprising an exhaust system which is
provided with an exhaust box, an inlet case which is
provided at a location upstream of said exhaust box and
opens at a lower end thereof into said exhaust box, and an
outlet case which opens at an upper end thereof into said
exhaust box above a lower end of said inlet case and also
opens at a lower end thereof below said exhaust box; and a
water discharge device which is associated with an inside of
the exhaust box and operates to discharge water inside the
exhaust box depending on a pressure within the exhaust box.
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The above and other objects, features and
advantages of the invention will become apparent from the
following description of the preferred embodiment taken in
conjunction with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig.l is a side view of the entire arrangement of an
outboard engine system; .
Fig . 2 is an enlarged side view of an engine section shown
. in Fig. l;
Fig.3 is~an enlarged side view of an essential portion
shown in Fig.2;
Fig. 4 is a sectional view taken along a line 4-4 in Fig.2;
Fig.5 is a partially broken-away front view of the
outboard engine system;
Fig. 6 is a sectional view taken along a line 6-6 in Fig.3;
Fig.7 is an illustration of the entire arrangement of a
control system for carburetors in Fig.3;
Fig . 8 is a vertically sectional side view of a duty control
valve in Fig.7;
Fig.9 is an enlarged view of a portion indicated by 9 in
Fig. 7;
Fig.lO is a sectional view taken~along a line 10-10 in
Fig.9;
Fig. 11 is a partially vertical sectional plan view of a
surge tank in Fig.7;
Fig .12 is a view of an upper half in~ section taken along
a line 12-1~ in Fig.4;
Fig .13 is a view of a lower half in~ section taken along
the line 13-13 in Fig.4;
Fig.l4 is a sectional view taken along a line I4-14 in
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Fig. l2;
Fig.l5 is a sectional view taken along a line 15-15 in
Fig. l3;
Fig.l6 is a view taken in the direction of an arrow 16
in Fig.lS;
Fig .17 is a diagram showing the relationshig between the
purifying rate of three-dimensional catalytic converters and
the A/F ratio of an exhaust gas and the relationship between
outputs from an OZ sensor and an LAF sensor and the A/F ratio
of the exhaust gas.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to Figs.l and 2, an outboard engine system O
includes an extension case 1, and a mount case 2 (an engine
support ) coupled to an upper portion of the extension case 1.
A water-cooled in-line type 3-cylinder and 4-cycle engine E is
mounted and supported on an upper surface of the amount case
2 with its crankshaft 14 disposed vertically. The mount case
2 includes a flange portion 2a around its outer periphery, and
an extension case 3 , which opens upwards , is bolted to an upper
surface of the flange portion 2a. An engine cover 4 is
detachably mounted at an upper portion of the extension case
3. An engine room 29 accommodating the engine E is defined by
the engine cover 4, the mount case 2 and the extension case 3.
Referring to Figs.2 and 5, an annular undercover 5 is
mounted between the extension case 3 and the extension case 1
to cover an outer peripheral surface of the mount case 2. The
CA 02505799 1999-08-03
.- . ,.
17
undercover 5 is made of a synthetic resin having an elasticity,
and has a single abutment 5a formed at a front portion adjacent
a hull. In mounting the undercover 5,.first, an abutment 5a
of the extension case 3 is opened largely, and the undercover
is disposed to surround the mount case 2. At the same time,
an end edge of a lower portion of the undercover 5 is engaged
with an annular step la formed around an outer periphery of an
upper portion of the extension case 1. On the one hand, .an upper
end of the undercover 5 is coupled to the extension case 3 by
a tapping screw (not shown), and ends of the abutment are
fastened to each other by bolts 32 , so that the abutment 5a 'of
the undercover 5 is closed. In this manner, the undercover 5
forms a continuous surface which permits the outer peripheral
surfaces of the extension case 3 and the extension case 1 to
be continuous to each other, while covering the mount case 2.
Referring to Figs .1 to 4 , 6 and 12 , the engine E includes
a cylinder block 6, a crankcase 7, a cylinder head 8, a head
cover 9 and a belt cover 10. The cylinder block 6 and the
crankcase 7 are mounted on the upper surface of the mount case
2 with the cylinder head 8 turned rearwards of the hull. A
piston 12 is slidably received in each of three cylinders 11
defined in the cylinder block 6, and the crankshaft 14 connected
to the pistons 12 through a connecting rod 14 is carried' between
the cylinder block 6 and the crankcase 7 to face vertically.
A valve-ogerating camshaft 15 .is carried in the cylinder head
8 in parallel to the crankshaft 14 and driven by the crankshaft
CA 02505799 1999-08-03
I8
14 through a timing belt device 16 covered with the head cover
10.
A driving shaft 17 is connected to a lower end of the
crankshaft 14 through a transmitting gear to extend downwards
within the extension case 1, and is connected at its lower end
to a propeller shaft 21 having a propeller 20 at its rear and
through a bevel gear mechanism 19 provided within the gear case
18. A shift rod 22 is connected at its lower end to a front
portion of the bevel gear mechanism 19 in order to switch over
the direction of rotation of the propeller shaft 21 to a normal
direction yr a reverse direction.
A swivel shaft 25 is fixed between a pair of left and right
upper arms 23 suQporting the-mount case 2 and a pair of left
and right lower arms 24 supporting the extension case 1. A
swivel case 26 rotatably supporting the swivel shaft 25 is
vertically swingably supported through a tilting shaft 28 an
a stern bracket 27 mounted on a transom T'of the hull.
As shown in Figs.3, 4 end 6, three intake ports 30
corresponding to the three cylinders 11 are opened in one side
of the cylinder head 8 , and three intake pipes 31 are secured
to the one side of the cylinder head 8 to communicate with the
intake ports 30 individually. Three carburetors 33 are
connected individually to upstream ends of the intake pipes 31.
The intake pipes 31 are bent forwards ( toward the hull ) in order
to ensure that the carburetors 33 are disposed compactly on one
side of the cylinder block 6. Moreover, the intake pipes 31
CA 02505799 1999-08-03
19
are inclined with their upstream ends turned upwards, in order
to allow a liquid fuel adhered to inner walls of the intake pipes
31 to flow down naturally toward the intake ports 30.
Pivotally supported on a body 34 of each of the carburetors
33 are a butterfly-type throttle valve 35 for opening and
closing an intake path 34a in the carburetor body 34 , and a choke
valve 36 positioned upstream of the throttle valve 35. A common
intake chamber 37 is connected to upstream ends of the intake
paths 34a in all 'the carburetors 33. The~~intake chamber 37 has
a front end extending to ahead of the crankcase 7 , and an intake
bore 37a is provided at one side of the~intake chamber 37 to
open into the engine room 29. Therefore, air flowing from an
air introducing bore 4a in an upper portion of the engine cover
4 fnto the engine room 29 is introduced through the intake bore
37a into the intake chamber 37, where the air is dispensed into
the intake paths 34a in the three carburetors 33. An intake
sound generated in each of the intake path's 34a is attenuated
in the intake chamber 37.
Referring to Fig.6, an intake valve 39 and an exhaust valve
40 for opening and closing the intake port 30 and the exhaust
port 38 corresponding to each of the cylinders 11 respectively
are mounted in the cylinders 8; and opened and closed by the
cam shafts 15 through an intake rocker arm,41 and an exhaust
rocker arm 42. A pump driving cam 15a is provided on the
camshaft 15. A reciprocating fuel pump 44 is mounted on one
side of the cylinder head 8 adjacent the intake port 30, and
CA 02505799 1999-08-03
,.
has a push rod 44a which is slidably carried on a support wall
8a within the cylinder head 8 and engaged at its tip end with
the pump driving cam 15a.
As shown in Fig.3, the fuel pump 44 includes a single inlet
pipe 441 and two outlet pipes 440. A fuel inlet tube 451
connected to a fuel tank (not shown) within the hull is connected
to the inlet pipe 441, and a fuel outlet tube 45o connected to
float chambers in two upper carburetors 33 is connected to one
of the outlet pipes 440, while a fuel outlet tube 45o connected
to a float chamber in the lowermost carburetor 33 is connected
to the other outlet pipe 450. Therefore, during rotation of
the camshaft 15 , the pump driving cam 15a drives the fuel pump
44 and hence, the pump 44 can pump fuel out of the fuel tank
(not shown) to supply the fuel into the float chamber in each
of the carburetors 33.
The three carburetors 33 are disposed vertically with the
intake paths 34a disposed horizontally-along the side of the
cylinder block 6. The throttle valve 35 of each carburetor 33
has a valve stem 35a disposed. to extend horizontally through
the intake path 34a, and a throttle-operating lever 47 is
secured to an outer end of the valve stem 35a. The three
throttle operating levers 47 are connected to one another
through an interlocking link 48. The choke valve 36 of each
carburetor 33 has a valve stem 36a which is also disposed to
extend horizontally through the intake path 34a, and a choke
operating lever 49 is secured to an outer end of the valve stem
CA 02505799 1999-08-03
<.....
21
36a. The three choke operating levers 49 are connected to one
another through an interlocking link 50. In this manner, a
multi-carburetor structure C is formed by the three carburetors
33. '
Referring to Figs.3, 4 and 12, three ribs 51 are formed
in a vertical arrangement on a side of the cylinder block 6 of
the engine E adjacent the carburetors 33 to extend axially of
the cylinder 11, so that they are passed through the
intermediate and lowermost carburetors 33. A breather passage
52 is defined in each of the ribs 51 permit the communication
between the crank chamber in the crankcase ? and a valve-
operating chamber in the cylinder head 8. To form the outboard
engine system O compactly, 'the three carburetors 33 are disposed
in proximity to the side of the cylinder 'block 6 , , but in this
case, a dead space is created above the uppermost rib 51. A
throttle sensor 53 is mounted at an inner end of the valve stem
35a of the throttle valve 35 of the uppermost carburetor 33 by
utilizing the dead space. Therefore, the throttle sensor 53
can be attached to the valve stem 35a from above the engine E
and detached from the valve stem 35a without being obstructed
in any way by the rib 51. This leads to a good maintenance,
and also the throttle sensor 53 is surrounded and protected by
the cylinder block 6 and the carburetor 33 , and can be prevented
from being damaged due to the contact with other parts. The
throttle sensor 53 detects an opening degree of the throttle
valve 35 as an amount of air drawn in the engine E, in other
CA 02505799 1999-08-03
G . 22
words, as a load. The single throttle sensor 53 suffices,
because the throttle valves 35 of the three carburetors 33 are
operatively associated with one another, as described above.
A follower arm 55 having a roller 55a pivotally supported
at its tip end is connected to any one of the three throttle
operating levers 47 ( the lowermost throttle operating lever in
the illustrated embodiment ) , while a driving arm 56 is pivotally
supported on a bracket (not shown) mounted on the lowermost
carburetor 33 . The roller 55a of the follower arm 55 is provided
to engage a cam groove 56a provided in the driving arm 56. A
throttle drum 57 is fixedly mounted on a boss of the driving
arm 56 , and an operating wire 58 connected to a control lever
( not shown ) mounted in a cabin in the hull is connected to the
throttle drum 57.
When the operating wire 58 is operated in an accelerating
direction to turn the throttle drum 57~in the direction
indicated by an arrow A in Fig.3, the roller 55a is moved
following the cam groove 56a in the driving arm 56 rotated along
with the throttle drum 57 . Thus , the follower arm 55 can turn
all of the throttle operating levers 47' in a direction to open
the throttle valve 35. When the operating wire 58 is operated
in a decelerating direction to turn the throttle drum 57 in the
direction opposite from the arrow A, all of the throttle
operating levers 47 can be of course turned in a direction to
close the throttle valve'35.
Referring to Fig.7, each of the carburetors 33 includes
CA 02505799 1999-08-03
23
a main nozzle 60, which opens into a Venturi portion of the intake
path 34a. The main nozzle 60 communicates with an area under
the liquid level of the fuel in a float chamber 62 through a
main jet 61. A large number of air-bleeding bores 63 are made
in a peripheral wall of the main nozzle 60, and a cylindrical
air-bleeding chamber 64 is provided in communication with the
air-bleeding bores 63 to surround the main nozzle 60. A tube
joint 65 is projectingly provided on an outer side of the
carburetor 33 to communicate with an upper portion of the
air-bleeding chamber 64.
A single common duty control valve 68 is connected to the
tube joints 65 of the three carburetors 33 through a dispensing
tube 66 and a surge tank 67.
As shown in Figs.7, 9 and 10, the dispensing tube 66 is
_. made of a metal or a hard synthetic resin and comprised of a
single inlet tube 661 integrally connected with three outlet
tubes 66Z, 663 and 66d through a connecting member 69. In this
case, the single inlet tube 661 and the three outlet tubes 662,
663 and 664 are disposed, so that all of angles formed by the
outlet tubes 6f2, 663 and 66~ with respect to the inlet tube 661
at their connections are substantially equal to one another.
In the illustrated embodiment, such angles are substatntially
90° .
The three outlet tubes 662, 663 and 664 may be gently curved
toward the corresponding carburetors 33, as required, and
CA 02505799 1999-08-03
24
connected to the tube joints 65 of the three carburetors 33
through flexible tubes 70, respectively.
On the other hand, the surge tank 67 is made of a synthetic
resin and includes a pair of tube joints 67a and 67b isolated
from each other, as shown in Fig.ll. One of the tube joints
67a is connected. to the inlet tube 651 through a flexible joint
T1, and .the other tube joint 67b is connected to a tuba joint
68a of the duty control valve 68 through a flexible tube 72.
An orifice 73 is defined in that tube joint 67a of the surge
tank 67, which is connected to the inlet tube 651.
The dispensing tube 66 and the flexible tubes 70, 71 and
72 form a secondary air passage P for supplying secondary air
for regulating .a air-fuel mixture A/F to the air-bleeding
chamber 64, and thus the surge tank 67 and the orifice 73 are
incorporated in series in the~secondary air passage P.
As shown in Fig.B, the duty control valve 68 includes a
stationary core 75, a coil 76 surrounding the stationary core
75, and a coil housing 77 in which the stationary core 75 and
the coil 76 are accommodated. A. valve case 7.8 and an outer case
79 covering the valve case 78 are secured to one end of the coil
housing 77. A valve seat 80 and an air outlet 81 connected to
the valve seat 80 are formed at one end of the valve case 78.
A valve member 82 cooperating with the valve seat 80 is
accommodated within the valve case 78, and a movable core 83
integrally formed on the valve member 82 is opposed to the
stationary core 75. A valve spring 84 is mounted under
CA 02505799 1999-08-03
w
compression~between both the cores 75 and 83 for biasing the
valve member 82 in a closing direction, i.e., in a direction
to seat the valve member 82 on the valve seat 80.
The outer case 79 is provided at an end opposite from the
coil 76 with a joint mounting bore 85 into which the tube joint
68a is press-fitted, and one end of the valve case 78 is fitted
air-tightly into an inner end of the tuba mounting bore 85 with
a seal member 86 interposed therebetween. A cylindrical air
chamber 87 is defined between the valve case 78 and the outer
case 79, excluding such fitted portion of the valve case 78.
The outer case 79 is provided with an air inlet 88 for opening
the air chamber 87 into the atmosphere on the side of the coil
?6, and the valve case T8 is provided with a through-bore 89
which permits the air chamber 87 into communication with the
inside of the valve seat 80 on the side opposite from the air
inlet 88.
The duty control valve 68 formed in the above manner is
supported on a bracket 90 secured in place in the engine E at
an attitude.~with the tube~joint 68a being above the coil 76,
i.e., at an attitude with the air inlet 88 located below the
air outlet 81. Such attitude of the duty control valve 68
ensures that if splashes of seawater or the like entering the
engine room 29~should enter the air inlet 88 powerfully, the
vigor of the splashes is attenuated immediately in the
cylindrical air chamber 87 and hence, the splashes do not reach
the through-bore 89 located on the upper side and flow to the
CA 02505799 1999-08-03
zs
outside through the air outlet 81. Thus, it is possible to avoid
the entering of the splashes into the valve case 78.
When the coil 76 is excited in the duty control valve 68
during operation of the engine E, the movable core 83 is
attracted to the stationary core 75 against a load of the valve
spring 84 , whereby the valve member 82 is moved away from the
valve seat 80 to open the air butlet 81. As a result, the air
entering the air chamber 87 through the air inlet 88 is passed
through the through-bore 89 and the air outlet 81 and dispensed
into the air-bleeding chambers 64 in the three carburetors 33
via the surge tank 67 by the dispensing tube 66.
In the intake path 34a in each of the carburetors 33, an
amount of intake. air corresponding to the opening degree of the
throttle valve, 35 flows toward the intake port 30 in the engine
E , and a negative pressure generated at an upper end of the main
nozzle 60 with such flowing of the air causes the fuel metered
by the main jet 61 to be ejected through the main nozzle 60 and
drawn into the corresponding cylinder 11, while producing an
air-fuel mixture together with the intake air flowing through
the intake path 34a.
At this time, the air dispensed into each of the air-
bleeding chambers 64 is passed through tY~e large number of
air-bleeding bores 63 in the main nozzle 60 and mixed with the
fuel flowing upwards within the main nozzle 60 and hence, the
atomization of the fuel can be promoted. If the amount of fuel
mixed, i. e. , the amount of air bled; is increased, the A/F ratio
CA 02505799 1999-08-03
"~,
27
of the air-fuel mixture produced in the intake path 34a can be
decreased. On the other hand, if the amount of fuel mixed, i . a . ,
the amount of air bled, is decreased, the A/F ratio of the
air-fuel mixture can be increased.
In order to control such amount of air bled, a duty control
unit 92 is connected to the coil ?6 of the duty control valve
68. Connected to an input portion of the duty control unit 92
are an engine rotational speed sensor 93 for detecting a
rotational speed of the engine E, the throttle sensor 53, and
an output portion of an LAF sensor 94 ( see Fig.13 ) for detecting
the AjF ratio of an exhaust gas to output a detection signal
proportional to the A/F ratio.
Therefore,' the duty control unit 92 is capable of
determining a magnitude of an engine load based on detection
signals from the engine rotational speed sensor 93 and the
throttle sensor 53, determining the AjF ratio of the exhaust
gas based on a detection signal from the LAF sensor 94,
determining a duty ratio of a pulse applied to the coil ?6 based
on the magnitude of the engine load and the AJF ratio of the
exhaust gas, and controlling the total time of opening operation
of the valve member 82 to regulate the amount of air bled into
each of the carburetors 33. Thus, it is possible to regulate
the A/F ratio of the air-fuel mixture to a desired value
corresponding to the engine load and the AjF ratio of the exhaust
gas , while improving the atomization of the fuel in the air-fuel
mixture supplied from each of the carburetors 33 into the
CA 02505799 1999-08-03
28
corresponding cylinder 11, thereby enhancing the output
performance of the engine E and the properties of the exhaust
gas.
Moreover, the amount of air bled into the plurality of
carburetors 33 can be controlled by the single common duty
control valve 68 and hence, the arrangement can be simplified
to contribute to a reduction in cost, and the placement of the
engine in the narrow engine room 29 in the outboard engine system
O can be carried out easily without being interfered with
another part.
In dispensing the air metered by the single common duty
control valve 68 into the three carburetors 33 by the dispensing
tube 66 , ,when the air exiting from the inlet tube 661 is diverted
into the three outlet tubes 662, 663 and 66~, the .courses are
obliged to be bent at substantially the same angle, because the
single inlet tube 661 and the three outlet tubes constituting
the dispensing tube 66 are disposed, so that all of the angles
formed by the outlet tubes 662, 663 and 664 with respect to the
inlet tube 661 at the fitted portions thereof are substantially
equal to one another, as described above . Thus , the resistances
in the flow paths can be equalized, thereby equally dispensing
the air into the outlet tubes 662, 663 and 664. Moreover, since
each of the outlet tubes 662, 663 and 664 is bent gently toward
the corresponding carburetor 33, as required, it is possible
to prevent a difference from being produced between the
resistances in the flow paths extending from the three outlet
CA 02505799 1999-08-03
29
tubes 66a, 663 and 66,, to the corresponding carburetors 33, to
the utmost . In this way, the amount of air bled into the three
carburetors 33 can be controlled equally.
A,pressure pulsation is produced in the flow path
extending from the duty control valve 68 to the air-bleeding
chamber 64 with the turning-on and oft of the application of
the pulse to the coil 76. However, because the surge tank 67
and the orifice 73 are incorporated in series in the common flow
path connecting the dispensing tube 66 and the duty control
valve 68 to each other, the pressure pulsation can be attenuated
effectively by the damping effect of the surge tank 67 and a
constricting resistance of the orifice 73. Therefore, it is
possible to prevent the generation of a vibration and a noise
due to such pressure pulsation, and it is also possible to
provide the compactness of the surge tank 67 by use of the orifice
73 in combination with the surge tank 67..
Referring to Fig.4, the fuel pump 4~ is mounted to one
side of the cylinder head 8, so that it is located in the rear
of the carburetors 33 disposed on one side of the cylinder block
6 , and a mounting piece 95 for the surge tank 67 is secured to
a rear surface of the head cover 9 by a bolt 96. so that the
surge tank 67 is located at the rearmost portion of the engine
E. With such arrangement, a first space S1 defined at the rear
of the carburetor 33 by one side of the cylinder head 8 and an
inner surface of the engine cover 4 is utilized effectively for
placement of the fuel pump 44, and a second space S2 defined
CA 02505799 1999-08-03
_.
by a rear surface of the head cover 9 and the inner surface of
the engine cover 4 is utilized effectively for placement of the
surge tank 67. This can contributes to the compactness of the
outboard engine system O.
Referring again to Figs.3 and 7, an accelerating pump 100
is connected to the driving arm 56 through a pushrod 101 and
is operated when the driving arm 55 is turned in an accelerating
direct ion , i . a . , in the direction indicated by an arrow R . The
accelerating pump 100 includes a diaphragm housing 102 secured
in place to the engine E, and a diaphragm 105 which divides the
interior of the diaphragm housing 102 into an atmospheric
chamber 103 and an operating chamber 104. The driving arm 56
is connected to the diaphragm 105 through the pushrod 101, and
the operating chamber 104 is connected in place to the
dispensing tube 66 through a one-way throttle valve 106. The
one-way throttle valve 106 is designed so that when the air flows
from the operating chamber 104 toward the Q3.spensing tube 66,
the one-way throttle valve 106 is opened and provides a
throttling resistance to the flow of the air in an opposite
direction.
Thus, when the driving arm 56 is turned in the accelerating
direction A, the pushrod 101 operates the diaphragm 105 so as
to pressurize the operating chamber 104. When the operating
chamber 104 is pressurized, the.air within the operating chamber
104 is pumped through the dispensing tube 66 into the air-
bleeding chamber 64 in each of the carburetors 33 , while opening
CA 02505799 1999-08-03
31
the one-way throttle valve 106: Therefore, such air urges the
liquid level of the fuel within the air-bleeding chamber 64 to
force the fuel into the main nozzle 60 through the large number
of air-bleeding bores 63, thereby promoting the a jection of the
fuel from the nozzle 60. Therefore, in an accelerating
operation for rapidly opening the throttle valve 35, the
retarding of the increasing of the amount of fuel ejected can
be eliminated despite a sudden increase in aitiount of air drawn,
thereby providing a good accelerating property to the engine
E.
On the other hand, in a decelerating operation for rapidly
closing the throttle valve 35, to the contrary, the pushrod 101
operates the diaphragm 105 so as to depressurize the operating
chamber 104. Therefore, a negative pressure generated in the
operating chamber 104 is transmitted to the air-bleeding
chamber 64 in each of the carburetors 33, while being limited
in transmission speed by the one-way throttre valve 106 . Thus ,
the ejection of the fuel from the main nozzle 60 can be suppressed
moderately to contribute to a reduction in amount of fuel
consumed.
In this way, the dispensing tube 66 is used for both of
an air passage for controlling the amount of air bled to each
of the carburetors 33 and an air passage for controlling the
acceleration and deceleration of each of the carburetors 33.
Thus, it is possible to simplify a piping to a large extent.
Referring to Figs . 12 to 16 , the exhaust port 38 defined
CA 02505799 1999-08-03
,.
32
in the cylinder head 8 in correspondence to each of the cylinders
11 and a vertically long exhaust-collecting chamber 110 defined
in a side of the cylinder black 6 opposite from the carburetors
33 are in communication with each other at a joint between the
cylinder block 6 and the cylinder head 8. A first three-
dimensional catalytic converter 111 is mounted in the
exhaust-collecting chamber 110.
A continuous exhaust line 114 is integrally formed on one
side of the mount case 2 to which the lower surface of the
cylinder block 6 is bonded, and on one side.of an oil tank 113
bonded to the lower surface of the mount case 2. The exhaust
line 114 is connected to a lower portion of the exhaust-
collecting chamber 110. A connecting flange connected to an
upper portion of an exhaust box 115 is -secured to a lower end
of the exhaust line 114 by a bolt 117, and a support piece 118
welded to an outer side of a lower portion of the exhaust box
115 is secured to a bottom of an oil tank'l13 by a bolt 119.
The oil tank 113 stores a lubricating oil for the engine E.
The exhaust box 115 includes a large-diameter inlet case
120 coupled to a ceiling plate 115a of the exhaust box 115 to
permit the exhaust line 114 to communicate with the exhaust
collecting chamber 110, and a small-diameter outlet case 121
which is coupled to a bottom plate llb in line with the inlet
case 120, and which opens at its upper end into an upper portion
of the exhaust box 115 and at its lower end into the extension
case 1. A second three-dimensional catalytic converter 112 is
CA 02505799 1999-08-03 "'
~.~.,
", 33 ,
mounted in the inlet case 120.
Thus, exhaust gases discharged from the cylinders 11 into
the exhaust ports 38 meet one another in the exhaust collecting
chamber 110, and the resulting exhaust gas flows via the exhaust
line 114 toward the exhaust box 115; passes sequentially through
the inlet case 120 and the outlet case 121; and is discharged
into the extension case 1. Than, the exhaust gas is discharged
into external water through the inside of the propeller 20 along
with cooling water which has cooled the engine E.
The first three-dimensional catalytic converter 111 is
mounted in the exhaust collecting chamber 110, and the second
three-dimensional catalytic converter 112~is mounted in the
inlet case 120 .of the exhaust box 115 , as described above .
Therefore, The exhaust gas passed through these converters 111
and 112 can be purified effectively in a wide operating range
of the engine E extending from a cool state to a warmed-up state .
In other words. HC, C02 and NOR can be removed from the exhaust
gas. Particularly, the AJF ratio of the air-fuel mixture in
the carburetor 33 to be supplied to the engine E can be controlled
in a wide operating range of the engine E extending 'from a low
load to a high load by regulating the duty ratio of the pulse
applied to the duty control valve 68 by the duty control unit
92, based on the detection signal from the LAF sensor 94 as
described above, thereby improving the properties of the
exhaust gas and enhancing the engine output.
Namely, the output from the LAF sensor 94 is proportional
CA 02505799 1999-08-03
34
to the A/F ratio of the exhaust gas, as shown in Fig.l7, and
hence, the A/F ratio of the exhaust gas can be controlled to
a narrow range A including a theoretic A/F ratio, and moreover,
in any of a case A' when the tolerance of the purifying rate
of the catalytic converters 111 and 112 has been set relatively
widely with the engine output taken into consideration to a
certain extent, and a case B when the set range is shifted to
a rich side with the engine output taken into serious
consideration, the A/F ratio of the exhaust gas can, be
controlled properly to a desired target value. Therefore, it
is possible. to carry out the control operation depending on the
operating conditions of the engine such as a mode with the
purification taken into serious consideration, a mode with the
purification and output taken in consideration and a mode with
the output taken into serious consideration. An increase in
engine output enables the size of the engine to be reduced and
hence, it is easy to place the engine in the narrow engine room
in the outboard engine system.
The exhaust collecting chamber 110 is opened by
separating the cylinder head 8 from the cylinder block 6 and
hence, the attachment and detachment of the first catalytic
converter 111 can be carried out easily by such opening.
On the other hand, in the exhaust box 115 , an upper end
of the outlet case 121 is disposed above a lower end of the inlet
case 120. Therefore, even if the water level within the
extension case 1 is raised, the entrance of water into the inlet
CA 02505799 1999-08-03
case 120 and thus into the second catalytic converter 112 can
be avoided, unless the outlet case 121 is submerged under water .
In the above-described dispositions of the inlet case 120
and the outlet case 121, however, water drops produced with the
purifying action provided for the exhaust gas by the first and
second catalytic converters 111 and 112 are accumulated in the
bottom of the exhaust box 115. To discharge the accumulated
water, a drainage pipe 122 is mounted to the exhaust fox 115.
The drainage pipe 122 is formed by bending a pipe having a
diameter far smaller than that of the outlet case 121 into an
inverted U-shape, and has one lower end 122a which is disposed
to open in proximity to an upper surface of the bottom plate
llb of the exhaust box 115, and the other lower end 122b which
is disposed to open below the bottom plate llb outside the
exhaust box 115.
During operation of the engine E , an exhaust pressure is
always applied to the inside of the exhausf box 115 and hence,
a difference in pressure is produced between the inside of the
exhaust box 115 and the inside of the extension case 1.
Therefore, when the water has been accumulated on the bottom
plate llb of the exhaust box 115 with the purification of .the
exhaust gas provided by the first and second catalytic
converters 111 and 112, the water is discharged through the
drainage pipe 122 into the extension case 1 by the pressure
difference. Thus, the water can be prevented from entering the
second catalytic converter 112. In addition, the bent portion
CA 02505799 1999-08-03
. ~ a...,
of the drainage pipe 122 is located above the opposite lower
ends of the drainage pipe 122 and hence, even if the water level
within the extension case 1 is raised, the water can be also
prevented from being entering the exhaust box 115 from the
drainage pipe 122, unless the bent portion of the drainage pipe
122 is submerged under the water.
As shown in Fig.l3, the LAF sensor 94 is mounted to the
exhaust line 114 integrally formed on the mount case 2 in the
following manner: A mounting wall 114a is formed on a side of
the exhaust line 114 facing outwards of the outboard engine
system O, so that it is inclined inwards of the exhaust line
114 toward its lower portion. The LAF sensor 94 is screwed to
the mounting wall 114a at a substantially vertical attitude,
and provided at its tip' end with a detecting portion 94a
protruding to a center portion within the exhaust line 114.
The LAF sensor 94 is disposed in an annular space 124
defined by the mount case 2 and the under Gover 5 surrounding
the mount case' 2 . If the LAF sensor 94 is as long as it is not
accommodated fully in the annular space 124, as in the
illustrated embodiment, an outward bulging portion. 5b for
receiving an outer end of the LAF sensor 94 is formed at a portion
of the undercover 5.
Since the mounting wall 114a of the exhaust line 114 is
inclined inwards of the exhaust line 114 toward its lower
portion, as described above, the length of protrusion of the
LAF sensor mounted at the vertical attitude ~o the mounting wall
CA 02505799 1999-08-03
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3?
114a in an outward direction of the outboard engine system O
can be suppressed to a value as small as possible, whereby the
contact of the sensor 94 with another portion or component can
be avoided to the utmost, and the detection of the A/F ratio
of the exhaust gas can be carried out reliably. Moreover, it
is possible to easily attach and detach~the LAF sensor 94 to
and from the mounting wall 114a, because the LAF sensor 94 is
directed outwards of the outboard engine system O. .
Furthermore, since the LAF sensor 94 is disposed in the
annular space 124 inside the undercover 5, the undercover 5
serves as a protective wall for the LAF sensor 94 to. prevent
the contact of another portion or component with the LAF sensor
94. Additionally, the undercover 5 is capable of being removed
in the above-described manner and hence, in a state in which
the undercover 5 has been removed, the attachment and detachment
of the LAF sensor 94 can be carried out easily.
In Figs.l2 and 14, reference character 125 denotes a
cooling water packet for the engine E.
Although the embodiment of the present invention has been
described in detail, it will be understood that the. present
invention is not limited to the above-described embodiment , and
various modifications in design may be made without departing
from the spirit and scope of the invention defined in claims .
For example, the engine E may be a multi-cylinder engine other
than the three-cylinder engine. Any one of the first and second
converters 111 and 112 can be omitted.
