Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-11-15
2001-02-06
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S519000
Reexamination Certificate
active
06182642
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. The present invention further relates to a method of detecting such a leak.
2. Description of the Related Art
A prior art evaporative emission control system for an automotive vehicle prevents emission of evaporative fuel to the open air by introducing the fuel vapors produced in a fuel tank to a canister so that the fuel vapors are temporarily absorbed by the canister, and supplying the collected fuel vapors to an intake system of an engine together with fresh air drawn into the canister through its atmospheric vent, as disclosed in Japanese Patent Provisional Publication No. 5-215020.
In the meantime, if there should occur, in the above described evaporative emission control system, a crack and the like in a fuel vapor flow passage extending from the fuel tank through the canister to a purge valve, the fuel vapors leak, resulting in that the evaporative emission control system is no more operative to produce an expected effect of preventing evaporative emission sufficiently.
Thus, it has been proposed such a leak detection method for detecting if a leak is present in the fuel vapor flow passage or not.
By the method, a current through a motor driven air pump (hereinafter also referred to as pump operating current) when air is forced to pass a reference orifice of a reference bore size by the air pump is detected and determined as a criterion or judgment level. On the other hand, a pump operating current at the time air is forcedly transmitted to the fuel vapor flow passage of the evaporative emission control system by the air pump while bypassing the reference orifice is measured and determined as a leak level. By comparing the leak level with the judgement level, it is determined that a leak is present in the evaporative emission control system when the leak level is smaller than the judgement level.
This method enables to detect a leak accurately and assuredly even when the leak results from a small hole in the fuel vapor flow passage, i.e., even when the leak is small.
However, the above described method has a problem that the pressure of evaporative fuel in the fuel tank is high when the temperature of fuel in the fuel tank is high, so the pump operating current is increased by the influence of increase of pressure in the fuel tank even when the fuel vapor flow passage has such a hole or the like that will cause a detectable leak, resulting in the possibility that a leak that is actually present is erroneously judged as no leak. Further, in case the residual quantity of fuel in the fuel tank (hereinafter also referred to as tank residual) is large, such a possibility is enhanced.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a leak detection apparatus for an evaporative emission control system which can solve the above noted problem inherent in the prior art apparatus.
It is a further object of the present invention to provide a leak detection apparatus of the foregoing character which can exclude the influence of fuel temperature and tank residual on leak detection or diagnosis assuredly and can improve the detection or diagnosis accuracy.
It is a still further object of the present invention to provide a leak detecting method which is free from the above noted problems inherent in the prior art method.
To achieve the foregoing objects, the present invention provides an apparatus for detecting a leak in an evaporative emission control system for an internal carbustion engine including a fuel tank, a canister for collecting fuel vapors from the fuel tank and having a fresh air inlet, and a purge control valve disposed between the canister and an intake pipe for controlling flow of the fuel vapors from the canister to the intake pipe together with fresh air drawn into the canister through the fresh air inlet 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 comprises means for defining an atmospheric vent in communication with the open air, a motor driven air pump having an outlet, a directional control valve capable of connecting the fresh air vent selectively to one of the atmospheric vent and the outlet of the air pump, a bypass conduit providing communication between the fresh air inlet and the outlet of the air pump while bypassing the directional control valve, the bypass conduit having a reference orifice, judgment level determining means for detecting, when the air pump is ON and the directional control valve connects the fresh air inlet to the atmospheric vent, for thereby allowing air from the air pump to pass through the reference orifice of the bypass conduit and thereafter be released to the open air through the directional control valve, a first current through the air pump and determining the first current as a judgment level, leak level measuring means for measuring, at a measurement timing after lapse of a predetermined time from establishment of a condition in which the air pump is ON and the directional control valve connects the fresh air inlet to the outlet of the air pump so that air from the air pump passes through the directional control valve and the fresh air inlet of the canister and is supplied to the fuel vapor flow passage, a second current through the air pump and determining the second current as a leak level, leak judging means for comparing the leak level with the judgment level and judging if a leak is present in the fuel vapor flow passage, fuel temperature detecting means for detecting a temperature of fuel in the fuel tank, and measurement timing variable determining means for determining the measurement timing variably on the basis of the temperature of fuel.
REFERENCES:
patent: 5146902 (1992-09-01), Cook et al.
patent: 5273020 (1993-12-01), Hayami
patent: 5349935 (1994-09-01), Mezger et al.
patent: 5411004 (1995-05-01), Busato et al.
patent: 5575265 (1996-11-01), Kurihara et al.
patent: 5890474 (1999-04-01), Schnaibel et al.
patent: 5975062 (1999-11-01), Bonse et al.
patent: 5-215020 (1993-08-01), None
Foley & Lardner
Moulis Thomas N.
Unisia Jecs Corporation
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