Leakage Detection In a Fuel Evaporative System
On-Board Diagnostics (OBD) regulations require that the fuel system in
personal vehicles must be supervised for leakages. Legislative
requirement on the smallest leakage size that has to be detected is
decreasing and at the same time the requirement on number of leakage
checks are increasing. A consequence is that detection must be
performed under more and more diverse operating conditions. This paper
describes a vacuum-decay based approach for evaporative leak
detection. The approach requires no additional hardware such as pumps
or pressure regulators, it only utilizes the pressure sensor that is
mounted in the fuel tank. A detection algorithm is proposed that
detects small leakages under different operating conditions. The
method is based on a first principles physical model of the pressure
in the fuel tank. Careful statistical analysis of the model and
measurement data together with statistical maximum-likelihood
estimation methods, results in a systematic design procedure that is
easily tuned with few and intuitive parameters. The approach has been
successfully evaluated on real data measured in a research laboratory.
Erik Frisk and Mattias Krysander
IFAC World Congress,
2008
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