Patent ID: 7418856
Filing Date: 2008-09-02
Classification: F02M

Abstract:
1. Method for checking the gastightness of a motor vehicle tank ventilation system, the system comprising: a fuel tank, an adsorption filter, ventilation line connecting the fuel tank to the adsorption filter, a fresh air line which connects the adsorption filter to the atmosphere and in which a controllable check valve is located as the adsorption filter check valve (AAV), a regeneration line which connects the adsorption filter to the intake manifold of the internal combustion engine and in which there is a controllable regeneration valve as the tank ventilation valve (TEV), at least one pressure sensor in the tank ventilation system, and a control/evaluation unit, to check the tank ventilation system with the adsorption filter check valve (AAV) closed by controlled opening of the tank ventilation valve (TEV), a negative pressure being produced in the tank ventilation system with a pressure variation which is evaluated after controlled closing of the tank ventilation valve (TEV) for tank leak diagnosis, the method comprising: during operation of the internal combustion engine the pressure in the tank ventilation system is set to the ambient pressure level (P at a stable operating point of the internal combustion engine the adsorption filter check valve (AAV) is closed and the tank ventilation valve (TEV) is opened, by which a negative pressure builds up, the negative pressure buildup is determined up to a specified negative pressure buildup threshold (P when the negative pressure buildup threshold (P the negative pressure decay is determined up to a specified negative pressure decay threshold (P the negative pressure buildup time (t