Method for diagnosis of tank leakage

Abstract

In a prior art method proposed for determining the outgassing of fuel, the outgassing at the ambient pressure is determined, and it is not taken into consideration that with the tank leakage diagnosis, a negative pressure exists inthe fuel tank. Since with negative pressure, more fuel gases out than with ambient pressure, too small of an outgassing is determined. With the tank leakage diagnosis, the fuel tank is evacuated at a diagnostic pressure and subsequently, a pressure increase is measured. From the trend of the pressure increase over the time, a leak is closed. Since the outgassing also affects a pressure increase, the measured total pressure increase must be corrected to the outgassing pressure increase. Since with the proposed method, the outgassing pressure increase is determined to be too small, frequently false reports can occur. The method of the present invention proposes to determine the outgassing at the same pressure that prevails with the tank leakage diagnosis in the fuel tank (1). A check valve (10) is regulated in a ventilation line, such that, in this manner a predetermined pressure corresponding to the diagnostic pressure in the fuel tank (1) is adjusted.

Dependencies are inferred from the claim text.