Patent ID: 8751174

Claim:
A method for determining the cross sectional area of a leak in the liquid-containing tank device of a vehicle, in particular of a motor vehicle, the liquid influencing the pressure in the tank device by evaporation, with the following steps: generating a first pressure as a reference pressure in the tank device at a first instant (t 1 ), detecting a first pressure characteristic up to a second instant (t 2 ), generating a second pressure at a third instant (t 4 ), the first pressure and the second pressure being chosen to be different, detecting a second pressure characteristic up to the fourth instant (t 5 ), determining the pressure gradient of the first pressure characteristic at the second instant (t 2 ) and of the pressure gradient of the second pressure characteristic at the third instant (t 4 ), determining the first pressure difference of the pressure at the second instant (t 2 ) from the reference pressure, determining the second pressure difference of the pressure at the third instant (t 4 ) from the reference pressure, computing the cross sectional area of the leak depending on the determined pressure gradient and the pressure differences, based on an equation: A = ⁢ ( V p ⋆ α ⋆ ρ 2 ⋆ R ⋆ T ) ⋆ 1 Δ ⁢ ⁢ p 4 ⋆ { { ( dp / dt ) 4 - ( dp / dt ) 2 } ( 1 + Δ ⁢ ⁢ p 2 Δ ⁢ ⁢ p 4 ) } , wherein A is the cross sectional area of the leak, V is the volume of the tank device, p is the density of a gas flowing through the leak, α is a flow characteristic that designates the leak as an orifice plate, R is the universal gas constant, T is the temperature of the gas flowing through the leak, Δp 2 is the first pressure difference, Δp 4 is the second pressure difference, (dp/dt) 2 is pressure gradient of the first pressure characteristic at the second instant, and (dp/dt) 4 is the pressure gradient of the second pressure characteristic at the third instant, assuming that the evaporation rate is constant in the tank device, and that a leak rate is established which is proportional to the square root of the respective pressure difference.