Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
1999-11-10
2001-10-23
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
C701S031000, C073S04050R, C073S049200, C073S049700, C123S520000
Reexamination Certificate
active
06308119
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the diagnosis of an automotive evaporative emission system, and more particularly to a method for diagnosing the existence of air leaks in the system.
BACKGROUND OF THE INVENTION
In automotive evaporative emission systems, fuel vapor generated in the vehicle fuel tank is captured in a charcoal-filled canister and subsequently supplied to the engine air intake through a solenoid purge valve. Since the effectiveness of the system can be significantly impaired by faulty operation of a component or by a leak in one or more of the hoses or components, the engine controller is generally programmed to carry out a number of diagnostic algorithms for detecting such failures. If faulty operation is detected, the result is stored and a “check engine” lamp is activated to alert the driver so that corrective action can be taken.
Experience has shown that small leaks in the evaporative system can be particularly difficult to reliably detect and diagnose due to variability of fuel characteristics, driving schedules, and environmental conditions. While small leaks can theoretically be detected at engine idle by closing off the air vent, drawing the system below atmospheric pressure with engine vacuum, and then monitoring the change in system pressure, it is difficult to obtain reliable test data in a short period of time because of the time required to evacuate and establish vapor generation equilibrium in the system. Accordingly, what is needed is a method of quickly and reliably diagnosing evaporative emission system leaks at engine idle.
SUMMARY OF THE INVENTION
The present invention is directed to an improved method of diagnosing evaporative emission system leaks at engine idle, wherein the system is closed and drawn down to a sub-atmospheric pressure early in a driving cycle prior to the achievement of an idle condition appropriate for leak testing. When the test enabling conditions other than engine idle are met, the system vent is closed, and the purge valve is modulated to regulate the fuel tank pressure at a sub-atmospheric value at or near the leak test pressure to be used at engine idle. When engine idle is achieved, the purge valve is closed, and the leak test is conducted with little or no delay. The time required to conduct the leak test is improved because the system pressure is at or near the test pressure when the engine idle condition is achieved, and at the same time, the reliability of the leak test data is improved because vapor generation equilibrium in the fuel tank is more nearly achieved when the leak test is initiated.
Additionally, the existence of a large leak can be diagnosed even if engine idle operation is not achieved within an allowable period, if the purge valve is unable to draw the system pressure down to the preset target within a predefined interval.
REFERENCES:
patent: 5542397 (1996-08-01), Takahata et al.
Grieve Malcolm James
Majkowski Stephen F.
Simpson Kenneth M.
Steckler Michael J.
Cichosz Vincent A.
Cuchlinski Jr. William A.
Delphi Technologies Inc.
Donnelly Arthur D.
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