Method for the activation of a tank venting valve of a motor vehicle during a leak test

1. A method of regulating a fuel tank venting valve of a motor vehicle during leak testing of a fuel tank venting system where the fuel tank venting valve is arranged in a recovery line that connects a retention vessel to catch fuel vapors from a fuel tank to an inlet manifold of an operating internal combustion engine, comprising:

sealing the tank venting system from the atmosphere outside the motor vehicle;

opening the fuel tank venting valve to expose the fuel tank and the tank venting system to a relative negative pressure present in the inlet manifold of the operating internal combustion engine; and

regulating the degree of opening of the tank venting valve at least in part as a function of a calculated gas mass flow, {dot over (m)} soll , through the valve, wherein the gas mass flow, {dot over (m)} soll , is calculated based at least in part upon a nominal gas mass flow, {dot over (m)} norm , and a reference pressure, p norm , and then corrected as a function of the external ambient pressure, p A , and;

monitoring a duration of time required to reach a pre-determined vacuum threshold in the fuel tank venting system.

2. The method of regulating a fuel tank venting valve as claimed in claim 1 , further comprising closing the fuel tank venting valve when a predetermined relative negative pressure has been achieved.

3. The method of regulating a fuel tank venting valve as claimed in claim 1 , further comprising partially opening the fuel tank venting valve prior to regulating the degree of opening.

4. The method of regulating a fuel tank venting valve as claimed in claim 1 , wherein a correction factor, K, representative of the degree of opening of the nominal gas mass flow, {dot over (m)} norm , is determined from the external pressure, p A .

5. The method of regulating a fuel tank venting valve as claimed in claim 4 , wherein external temperature, T A , is additionally incorporated into the correction factor, K.

6. The method of regulating a fuel tank venting valve as claimed in claim 5 , wherein the correction factor, K, is determined as the product of a nominal temperature, T norm , and the external pressure, P A , divided by the product of the external temperature, T A , and a nominal pressure, P norm ,

K

=

T

A

*

P

A

T

A

*

P

norm

.

7. A method of regulating a fuel tank venting valve of a motor vehicle during leak testing of a fuel tank venting system where the fuel tank venting valve is arranged in a recovery line that connects a retention vessel to catch fuel vapors from a fuel tank to an inlet manifold of an operating internal combustion engine, comprising:

sealing the tank venting system from the atmosphere outside the motor vehicle;

opening the fuel tank venting valve to expose the fuel tank and the tank venting system to a relative negative pressure present in the inlet manifold of the operating internal combustion engine; and

regulating the degree of opening of the tank venting valve based upon a function depending at least in part on the external ambient pressure outside of the motor vehicle, p A , and a gas mass flow, {dot over (m)} soll , through the valve, wherein an offset value, Δ{dot over (m)}, for regulating the fuel tank vent valve or for the correction of the nominal gas mass flow, {dot over (m)} norm , is determined from a characteristic map which uses the external ambient pressure (p A ) as an input, and

wherein the regulation of the fuel tank venting valve improves the fuel system leak test accuracy.

8. The method of regulating a fuel tank venting valve as claimed in claim 7 , wherein the external pressure, p A , is measured by a differential or absolute pressure sensor.

9. The method of regulating a fuel tank venting valve as claimed in claim 7 , wherein the external pressure, p A , is calculated by a mathematical model that is formed from a plurality of measured variables of the motor vehicle.