Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2000-02-17
2002-10-08
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S289000, C060S292000, C060S302000, C123S059500, C123S580000, C123S585000, C123S699000, C440S076000, C440S012610
Reexamination Certificate
active
06460330
ABSTRACT:
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.
17
. Therefore, when a catalytic converter is used for purifying an exhaust gas from an engine, it is a conventional common practice to detect an A/F ratio of an exhaust gas by an O
2
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 O
2
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 O
2
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 O
2
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 the 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 O
2
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 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 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 the 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 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 a narrow engine room in the outboard engine system.
According to a second aspect and feature of the present 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 its 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 system and hence, it is possible to 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 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 d
Fukuda Yoshihiko
Kawasaki Toyokazu
Yoshida Hiroyuki
Arent Fox Kintner Plotkin & Kahn
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
Tran Binh
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