Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1999-08-25
2001-11-06
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S049200, C073S118040
Reexamination Certificate
active
06311548
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to fuel tanks for vehicles and, more particularly, to a method of validating a diagnostic leak detection test for a fuel tank in a vehicle.
BACKGROUND OF THE INVENTION
Increasing awareness of the effects of vehicle evaporative and exhaust emissions has resulted in regulations at both state and federal levels to control these emissions. In particular, on-board diagnostic regulations require that certain emission related systems on the vehicle be monitored, and that a vehicle operator be notified if the system is not functioning in a predetermined manner.
One example of an emission related system is a fuel system, which includes a fuel tank for storing a fuel. Vapors from the fuel collect within the fuel tank. Occasionally, the fuel tank may develop a leak due to a hole, such as from a sharp object puncturing the fuel tank. Therefore, vapors present within the tank may inadvertently escape from the fuel tank and into the atmosphere. A primary component of the fuel vapor is hydrocarbon, which is known to have a detrimental effect on air quality. Currently, on-board diagnostic regulations require that a diagnostic small leak test and a very small leak test be performed periodically while the vehicle is operational, to detect a leak in the fuel tank. If a leak is detected by the diagnostic test, the vehicle operator is notified.
Various test procedures are used to detect a small leak or very small leak in the fuel tank. In one example, an overall slope of a vacuum decay rate is determined by measuring an induced vacuum within the fuel tank at a beginning of a test and the vacuum at the end of the test. If the overall slope does not meet a predetermined criteria, there may be a leak in the fuel tank. One example of a predetermined criteria is a maximum slope threshold. However, a shortfall of the overall slope test procedure is that it does not account for conditions when the vacuum decay rate is not decreasing in a predictable manner, due to a typical operating condition of the vehicle. For example, fuel slosh, or turbulence of the fuel within the fuel tank occurs when the vehicle undergoes a series of sudden movements. Fuel slosh may affect the actual vacuum decay rate positively or negatively. Consequently, a driver occupant of the vehicle could either be erroneously notified of a malfunction, or fail to be notified, depending on the circumstance. Thus, there is a need in the art for a reliable method of validating a diagnostic leak detection test that is not sensitive to fluctuations in vehicle operating conditions.
SUMMARY OF INVENTION
It is, therefore, one object of the present invention to provide a method of validating a diagnostic leak detection test for a fuel tank on a vehicle.
It is another object of the present invention to provide a method of validating a diagnostic leak detection test for a fuel tank on a vehicle, that evaluates a rate of vacuum decay within discrete segments of time, to confirm the results of the diagnostic leak test.
To achieve the foregoing objects, the present invention is a method of validating a diagnostic leak test for a fuel tank on a vehicle. The method includes the steps of determining a vacuum decay rate of a fuel vapor in the fuel tank and dividing the vacuum decay rate into segments. The method also includes the steps of determining a slope of the segments, determining if a difference between two consecutive slopes of the segments meet a predetermined criteria, and validating the leak detection test if the difference meets the predetermined criteria.
One advantage of the present invention is that an improved test for detecting a leak in a fuel tank of a vehicle is provided. Another advantage of the present invention is that a method of validating a diagnostic leak detection test for the fuel tank compares a rate of vacuum decay for one segment with another segment, to confirm the results of the diagnostic leak detection test. Still another advantage of the present invention is that the method of validating a diagnostic leak detection test for the fuel tank is not affected by vehicle operating conditions. Yet another advantage of the present invention is that the method of validating a diagnostic leak detection test for the fuel tank compares consecutive slope segments of a vacuum decay rate, to determine if the overall curvature is convex.
Other objects, features and advantages of the present invention will be readily appreciated, as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.
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Breidenbach Hallett D.
Majkowski Stephen F.
Simpson Kenneth M.
Cichosz Vincent A.
Delphi Technologies Inc.
Wiggins David J.
Williams Hezron
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