Method and arrangement for diagnosing a tank-venting system

A method for checking the tightness of a tank-venting system used with an internal combustion engine having an intake pipe, the tank-venting system including a fuel tank wherein fuel vapor forms, a storage device connected to the fuel tank, the storage device having a vent opening and a device for closing the vent opening, and a tank-venting valve interconnecting the intake pipe and said storage device whereby said fuel vapor is conducted from said tank to said intake pipe via said storage device and said tank-venting valve, the method comprising the steps of:

• (a) during operation of the engine and while said venting opening is closed, carrying out one of the following:
• (a1) opening said tank-venting valve and drawing a predetermined quantity of gaseous substance through said tank-venting valve, or
• (a2) opening said tank-venting valve and drawing a gaseous substance through said tank-venting valve so long until a predetermined underpressure is reached in said tank-venting system,
• so that a pressure fluctuation is produced in said tank-venting system with said pressure fluctuation being characterized by a plurality of characteristic variables;
• (b) evaluating at least one of said characteristic variables to judge the tightness of said tank-venting system;
• closing said tank-venting valve after carrying out said steps (a) and (b) and then again opening said tank-venting valve after a predetermined time has elapsed;
• predetermining the frequency of the repetition of said steps (a) and (b) and the volume of said gaseous substance drawn off each time so that the average volume flow drawn off by suction corresponds to a leakage flow which is just permissible;
• judging said tank-venting system as not being tight when the mean value of said pressure fluctuation determined over several periods does not drop by a predetermined minimum value;
• and,
• generating a periodic pressure fluctuation by directly repeating said method periodically.

A method for checking the tightness of a tank-venting system used with an internal combustion engine having an intake pipe, the tank-venting system including a fuel tank wherein fuel vapor forms, a storage device connected to the fuel tank, the storage device having a vent opening and a cutoff valve for closing the vent opening, and a tank-venting valve interconnecting the intake pipe and said storage device whereby said fuel vapor is conducted from said tank to said intake pipe via said storage device and said tank-venting valve, the method comprising the steps of:

• (a) with said cutoff valve closed, opening said tank-venting valve so long until a predetermined underpressure is provided as a start value for the subsequent pressure fluctuation;
• (b) during operation of the engine and while said venting opening is closed, carrying out one of the following:
• (b1) opening said tank-venting valve and drawing a predetermined quantity of gaseous substance through said tank-venting valve, or
• (b2) opening said tank-venting valve and drawing a gaseous substance through said tank-venting valve so long until a predetermined underpressure is reached in said tank-venting system,
• so that a pressure fluctuation is produced in said tank-venting system with said pressure fluctuation being characterized by a plurality of characteristic variables;
• and,
• (c) evaluating at least one of said characteristic variables to judge the tightness of said tank-venting system.

A method for checking the tightness of a tank-venting system used with an internal combustion engine having an intake pipe, the tank-venting system including a fuel tank wherein fuel vapor forms, a storage device connected to the fuel tank, the storage device having a vent opening and a cutoff valve for closing the vent opening, and a tank-venting valve interconnecting the intake pipe and said storage device whereby said fuel vapor is conducted from said tank to said intake pipe via said storage device and said tank-venting valve, the method comprising the steps of:

• (a) with said cutoff valve closed, opening said tank-venting valve so long until a predetermined underpressure is provided as a start value for the subsequent pressure fluctuation;
• (b) during operation of the engine and while said venting opening is closed, carrying out one of the following:
• (b1) opening said tank-venting valve and drawing a predetermined quantity of gaseous substance through said tank-venting valve, or
• (b2) opening said tank-venting valve and drawing a gaseous substance through said tank-venting valve so long until a predetermined underpressure is reached in said tank-venting system,
• so that a pressure fluctuation is produced in said tank-venting system with said pressure fluctuation being characterized by a plurality of characteristic variables;
• (c) evaluating at least one of said characteristic variables to judge the tightness of said tank-venting system;
• and,
• (d) determining the value of the volumes of said gaseous substances, which are drawn off by suction to adjust the pressure fluctuations periodically, in dependence upon the speed with which the predetermined underpressure as said start value is reached.