Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-08-30
2001-04-24
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
Reexamination Certificate
active
06220230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to evaporative emission control systems for internal combustion engines, and more particularly to an evaporative emission control system of the type which is capable of making a leak diagnosis, i.e., capable of detecting if a leak is present in the evaporative control system.
2. Description of the Related Art
An internal combustion engine for current automotive vehicles includes an evaporative emission control system. The evaporative emission control system includes a canister containing activated charcoal to collect and store volatile fuel vapors from a fuel tank during the time the engine is not inning. The evaporative emission control system also includes a purge line or conduit connecting between an intake pipe portion downstream of a throttle valve and the canister. The purge line opens under a predetermined condition after start of the engine to draw fresh air into the canister and purge the canister. The collected volatile fuel vapors are thus drawn from the canister into the intake pipe, for combustion within a combustion chamber of the engine.
In such an evaporative emission control system, if a conduit between the fuel tank and the intake pipe has a leak or the conduit has a connecting portion of which seal is defective, the fuel vapors are released to the atmosphere. To prevent such evaporative fuel emission, there has been proposed an evaporative emission control system which is adapted to make a leak diagnosis, i.e., which is capable of determining if a leak is present in the evaporative emission control system.
A leak diagnosis can be made by closing the above described conduit in a way as to prevent communication between the inside and outside of the conduit, putting the inside of the thus closed conduit into a condition wherein there is a difference in pressure between the inside and outside of the conduit, and observing a variation of the pressure in the conduit. For example, an evaporative emission control system disclosed in Japanese Patent Provisional Publication No. 5-79408, is adapted to make a leak diagnosis by reducing the pressure in the above described conduit by using an intake vacuum prevailing in an intake pipe portion downstream of a throttle valve during operation of an engine.
SUMMARY OF THE INVENTION
However, the above described prior art evaporative emission control system is constructed so as to communicate the intake pipe directly with the fuel tank at the time of reducing the pressure in the above described conduit, so the fuel vapors in the fuel tank may possibly be drawn into the engine during the time of reducing the pressure in the conduit to cause a variation of the air/fuel ratio and therefore an unstable operation of the engine.
Further, the higher the vehicle speed the more the intake vacuum developed in the intake pipe, so a higher vehicle speed is desirable for reducing the pressure in the conduit. However, a high vehicle speed will increase the pressure in the conduit due to sloshing (i.e., splash of the fuel in the fuel tank causing variations of the fuel surface), thus increasing the possibility of erroneous diagnosis. So, a lower vehicle speed is desirable for making a leak diagnosis. The prior art system is adapted to reduce the pressure in the conduit and make a leak diagnosis irrespective of the vehicle speed, and therefore cannot meet the above two requirements at the same time.
The present invention has been made in view of the above problems inherent in the prior art system and has for its object to provide an evaporative emission control system for an internal combustion engine which is free from a problem that the fuel vapors in the fuel tank are drawn into the engine during reduction of the pressure in the conduit to cause an unstable operation of the engine, and can attain efficient reduction of the pressure in the conduit and a highly reliable leak diagnosis at the same time.
To achieve the foregoing object, the present invention provides an evaporative emission control system for an internal combustion engine including a canister having an atmospheric vent, a first conduit providing communication between a fuel tank and the canister, a second conduit providing communication between the canister and an intake pipe portion downstream of a throttle valve of the engine, a bypass valve disposed between the fuel tank and the canister and mounted on the first conduit for selectively allow and prevent communication between the fuel tank and the canister, a purge control valve disposed between the canister and the intake pipe portion and mounted on the second conduit for selectively allow and prevent communication between the canister and the intake pipe portion, and a vent control valve for selectively opening and closing the atmospheric vent of the canister. The evaporative emission control system includes a pressure reducing device for closing the vent control valve and the bypass valve wile opening the purge control valve for thereby introducing a vacuum prevailing in the intake pipe portion into a portion of the first and second conduits extending between the bypass valve and the intake pipe portion and thereby reducing a pressure in the portion of the first and second conduits to a predetermined value and thereafter closing the purge control valve, a pressure measuring device for opening the bypass valve after reduction of the pressure in the portion of the first and second conduits to the predetermined value and measuring a pressure variation in a portion of the first and second conduits extending between the fuel tank and the purge control valve after lapse of a predetermined time from the opening of the bypass valve, and a diagnostic device for making a leak diagnosis on the basis of the pressure variation measured by the pressure measuring device.
REFERENCES:
patent: 5495842 (1996-03-01), Yamanaka et al.
patent: 5592923 (1997-01-01), Machida
patent: 5617832 (1997-04-01), Yamazaki et al.
patent: 5647332 (1997-07-01), Hyodo et al.
patent: 5857447 (1999-01-01), Shinohara
patent: 5-79408 (1993-03-01), None
Kawamura Katsuhiko
Kawano Akihiro
Foley & Lardner
Moulis Thomas N.
Nissan Motor Co,. Ltd.
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