Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-04-16
2001-04-24
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
Reexamination Certificate
active
06220229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to evaporative emission control systems for automotive vehicles and more particularly to an apparatus for determining if a leak is present in an evaporative emission control system for an automotive vehicle.
2. Description of the Related Art
An 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 running. 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 this instance, if a fuel vapor flow passage extending from the fuel tank to the intake pipe has a leak or the fuel vapor flow passage has a connecting portion of which seal is defective, the fuel vapors are released to the atmosphere. To prevent such evaporative fuel emission, a diagnostic system has been proposed to determine if a leak is present in the evaporative emission control system, as disclosed in Japanese provisional patent publication No. 7-139439. A leak of the above described fuel vapor flow passage can be checked by closing the passage so that the passage is in the form of a closed space, i.e., by closing the passage in a way as to prevent fluid communication between the inside and the outside of the passage, and observing a variation of the internal pressure of the fuel vapor flow passage after the passage is pressurized in such a way that the internal pressure of the passage and the atmospheric pressure differ relatively firm each other. The diagnostic system of the above described publication thus includes a vent control valve provided to an atmospheric vent of the canister to selectively open and close the atmospheric vent. The atmospheric vent of the canister is closed by the vent control valve when the above described passage is to be closed so as to be in the form of a closed space. The diagnostic system also includes a pressure sensor provided to the above described fuel vapor flow passage for checking a pressure variation of gas enclosed in the passage. A negative pressure produced in the intake pipe portion downstream of the throttle valve is introduced into the fuel vapor flow passage for negative pressurization thereof, whereby to check if a leak is present in the passage.
SUMMARY OF THE PRESENT INVENTION
However, if the mixture of air and fuel vapors in the above described passage is drawn by intake vacuum into the intake pipe, variations of the air-fuel ratio of the engine will result. To prevent such variations of the air-fuel ratio, it has heretofore been practiced to conduct a leak detection during a feedback control of the air-fuel ratio. A three way catalytic converter will become most effective when the air-fuel mixture has a stoichiometric ratio or a ratio adjacent thereto. For this reason, the feedback control of the air-fuel ratio is performed on the basis of the output of an oxygen sensor disposed upstream of the three way catalytic converter so that the air-fuel ratio is included within a predetermined range having a stoichiometric ratio at its center. By the feedback control of the air-fuel ratio, it is intended to prevent variations of the air-fuel ratio due to introduction of the mixture of air and fuel vapors into the intake manifold from the above described fuel vapor flow passage.
However, the feedback control of the air-fuel ratio has for its main purpose to eliminate a steady-state deviation due to variations of the flow rate characteristics of an injector and an air flow meter resulting from variations in the manufacture thereof. Thus, the responsive speed of the feedback control is not so high, so the three way catalytic converter cannot be most effective until the air-fuel ratio returns to a value adjacent a stoichiometric ratio after a variation of the air-fuel ratio is caused.
Further, the feedback control of the air-fuel ratio requires the oxygen sensor to have been in an activated condition. Thus, it has heretofore been impossible to conduct the diagnosis of leak before the feedback control of the air-fuel ratio starts (e.g., immediately after the engine starts).
It is accordingly an object of the present invention to provide a leak detection apparatus for an evaporative emission control system for an internal combustion engine which is capable of conducting a diagnosis of leak before the feedback control of the air-fuel ratio starts, for example, immediately after the engine starts.
It is a further object of the present invention to provide a leak detection apparatus of the foregoing character which utilizes consumption of fuel in a fuel tank for attaining negative pressurization of a fuel vapor flow passage extending from a fuel tank to a purge control valve.
To achieve the foregoing objects, the present invention is an apparatus for detecting a leak in an evaporative emission control system for an internal combustion engine including a fuel tank, a canister for collecting fuel vapors from the fuel tank, a purge control valve disposed between the canister and the intake pipe for controlling flow of the fuel vapors from the canister to the intake pipe such that a fuel vapor flow passage is provided which extends from the fuel tank to the purge control valve by way of the canister. The apparatus includes a vent control valve for selectively opening and closing an atmospheric vent of the canister, an actuating device for actuating the purge control valve and the vent control valve to fully close immediately after the engine starts and thereby closing the fuel vapor flow passage in such a way as to prevent communication between an inside and outside of the fuel vapor flow passage, a pressure sensor for detecting a pressure in the fuel vapor flow passage, and a diagnostic device for detecting a leak on the basis of the pressure in the fuel vapor flow passage which reduces with increase of consumption of fuel in the fuel tank after the fuel vapor flow passage is closed.
REFERENCES:
patent: 5158054 (1992-10-01), Otsuka
patent: 5261379 (1993-11-01), Lipinski et al.
patent: 5295472 (1994-03-01), Otsuka et al.
patent: 5327873 (1994-07-01), Ohuchi et al.
patent: 5333589 (1994-08-01), Otsuka
patent: 5590634 (1997-01-01), Shinohara
patent: 5857447 (1999-01-01), Shinohara
patent: 6-81728 (1994-03-01), None
patent: 7-139439 (1995-05-01), None
Kawamura Katsuhiko
Kawano Akihiro
Foley & Lardner
Moulis Thomas N.
Nissan Motor Co,. Ltd.
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