Method and arrangement for checking the operability of a tank-venting system

An arrangement for testing the operability of a tank-venting apparatus of a motor vehicle having an internal combustion engine, the tank-venting apparatus including a tank having a tank pressure sensor, an adsorption filter, said absorption filter being connected to the tank via a tank supply line, and a venting line closable by a shutoff valve (AV) and a tank-venting valve (TEV) which is connected to the adsorption filter via a valve line, the arrangement comprising:

• a valve control unit for opening and closing the shutoff valve (AV) and the tank-venting valve (TEV);
• a sequence control for driving the valve control unit;
• an operating-condition determination unit for determining the values of operating variables of the motor vehicle having an engine and a tank-venting apparatus;
• an evaluation unit for evaluating the operability of the tank-venting apparatus based on the underpressure building up in the tank after the sequence control has closed the shutoff valve via the valve control unit and has opened the tank-venting valve;
• the determination unit is configured as a pressure-gradient test unit and
• the sequence control and the pressure-gradient test unit are so configured that:
• the sequence control checks operating variables of the motor vehicle including engine and tank-venting apparatus, said operating variables being measurable only during the test method, and interrupts the underpressure buildup test when the operating variable values indicate that the measured tank-pressure values permit no reliable statement as to the operability of the apparatus;
• the test unit determines the apparatus as being not operable at that time and terminates the method when the underpressure buildup gradient lies below a threshold;
• the sequence control closes the tank-venting valve;
• the test unit measures the underpressure decaying in the tank and checks operating variables of the motor vehicle including the engine and tank-venting apparatus, the operating variables being measured only during the test method, and the underpressure decay test is interrupted when the operating variable values indicate that the measured tank-pressure values permit no reliable statement as to the operability of the apparatus and when the test unit determines the apparatus as being not operable at that time when the underpressure decay gradient lies above a threshold and otherwise determining the apparatus to be operable at that time;
• and,
• the sequence control opens the shutoff valve and terminates the method.