Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-05-10
2001-02-20
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S519000
Reexamination Certificate
active
06189515
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a system for resetting a vapor purge flow rate to prevent rich air/fuel conditions in an engine. More particularly, the present invention relates to a vapor purge flow rate reset system based on fuel tank vacuum level conditions.
BACKGROUND OF THE INVENTION
Government regulations concerning the release into the atmosphere of various exhaust emission constituents from automotive vehicles are becoming increasingly more stringent. As the regulations relating to emissions of oxides of nitrogen, carbon monoxide, and unburned hydrocarbons become more stringent, it is necessary to control the engine combustion process to avoid unnecessary instabilities and thus prevent formation of undesirable exhaust emissions.
Evaporative emission control is an important consideration in automotive design and necessitates that fuel vapor arising from the engine fuel system be drawn into the engine and burned. Because the fuel vapor can be combusted by the engine, an excessive flow of vapor may cause combustion instability, or perhaps even engine roughness or stalling.
U.S. Pat. No. 5,460,143 discloses an evaporative emissions control system in which a pressure transducer prevents purging of a carbon canister in the event that the fuel tank pressure falls to a negative value. U.S. Pat. No. 5,816,223 discloses a system in which purging is controlled not only when the tank pressure becomes negative, but in response to rapid fluctuations in the tank pressure whether at a positive or negative pressure. Rapid fluctuations may cause the air and fuel vapor entering the engine from the purge line of a carbon evaporative emission control canister to alter the combustion process.
Some fuel system vapor storage purge strategies rely on purge control valves that regulate a constant purge air/vapor mixture flow rate entering the engine for combustion. Constant flow regulation is attempted for vacuum levels ranging from very high to only a few inches of mercury below which the valve flow rate drops off. Under equilibrium conditions, fuel tank vacuum is equal to vapor storage canister system flow restriction. Vapor storage canister system flow restriction is a function of purge air flow through the system.
When the manifold vacuum falls below the constant purge flow vacuum levels, such as when the throttle is depressed for more engine power, significant purge flow can be lost. This loss in purge flow results in vapor storage canister flow restriction levels decreasing which, in turn, decreases the fuel tank vacuum levels. The tank vacuum levels decrease by drawing air into, or generating vapor within, the fuel tank vapor space to equalize system vacuums.
When the manifold vacuum increases, purge flow increases which creates higher vapor storage canister system flow restrictions. Fuel vapor mass must be drawn from the fuel tank vapor space in order to equalize the system vacuum levels. If a sufficiently large enough vapor mass is drawn from the fuel tank, undesirable rich engine air/fuel ratio conditions are created.
SUMMARY OF THE INVENTION
The present invention presents a system for preventing a rich engine air/fuel ratio condition from occurring when there is a change in the purge flow restriction based on engine conditions, i.e. when the throttle is depressed for more engine power.
The invention is advantageous in that it causes a change in the purge flow restriction based on engine operating conditions. According to the present invention, the foregoing and other objects and advantages are obtained by introducing a method for comparing the current system pressure against calibrated target levels. The method compares values for a predetermined period of time to determine whether or not the purge duty cycle needs to be reset and adjusted in order to prevent rich engine fuel/air conditions.
One object of the present invention is to identify a condition of high possibility of rich engine air/fuel ratio. Another object is to monitor engine air mass and determine if purge flow needs to be reset in order to avoid a rich engine air/fuel ratio condition.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.
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Jamrog James Richard
Stukenborg Douglas Alan
Drouillard Jerome
Ford Global Technologies Inc.
Moulis Thomas N.
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