Patent ID: 12188425

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG.1shows a flowchart of an exemplary method100for determining the size of a leak in a fuel tank system of a vehicle having an internal combustion engine. The internal combustion engine of the vehicle is started at102and one or more parameter values, which are significant for the further method sequence, are calculated at104. These parameter values can be a stoppage time of the vehicle, i.e., how long the vehicle was switched off before starting102, and/or a difference between the fuel temperature in the tank system and the ambient temperature. It is important that an indication of the calmness and stability of the fuel in the tank can be derived from the parameter value(s). Then (using the calculated parameter values) it is checked at106whether at least one of a plurality of diagnostic conditions is fulfilled. A first diagnostic condition of the plurality of diagnostic conditions is fulfilled for example if the stoppage time is longer than a predetermined minimum stoppage time. A second diagnostic condition of the plurality of diagnostic conditions is fulfilled, for example, if the temperature difference is smaller than a predetermined maximum temperature difference. A third diagnostic condition of the plurality of diagnostic conditions is fulfilled, for example, if an idling phase of the internal combustion engine with a predetermined duration is implemented. A fourth diagnostic condition of the plurality of diagnostic conditions is fulfilled, for example, if the internal combustion engine is operated in idling mode and stop-start prevention is realized. If one or more of these diagnostic conditions is fulfilled, it can be assumed that the fuel has been calm for a while and that an LDV analysis can be carried out.

If none of the diagnostic conditions is fulfilled (N=NO at106), the method ends (at least temporarily) at107, where it can of course be restarted at a later time. If at least one of the plurality of diagnostic conditions is fulfilled (J=YES at106), then an LDV method having the steps described below is carried out. The fresh air supply of the fuel tank system is closed at108by closing the electrically actuated shut-off valve. After the fresh air supply has been shut off, there is a wait at110until a predetermined waiting time has elapsed so that the evaporation of fuel can possibly take place. The evaporation rate can be determined by a pressure measurement. The fuel tank system is then evacuated at112in that gases are sucked from the tank system via the tank vent valve TEV by the internal combustion engine or by a scavenging air pump. The suction takes place until the pressure is reduced by a predetermined amount, for example 10 mbar. The time profile of the pressure in the fuel tank system is then recorded at114and the size of a leak in the fuel tank system is determined at116based on the recorded time profile of the pressure, for example, based on a gradient of the time-dependent pressure profile. The greater the gradient, the greater the leak. However, if the gradient corresponds to the previously determined evaporation rate, there is no leak.

The method100just described can be carried out directly by the engine controller with the aid of hardware which is already present (for example pressure sensor, shut-off valve, vent valve and scavenging air pump).

FIG.2shows time profiles of pressure220and a control signal230for a shut-off valve and a control signal240for a scavenging air pump when carrying out the method shown inFIG.1. Up to the time T1, the vehicle travels with an open shut-off valve and active scavenging air pump, where the pressure220in the fuel system varies. At time T1, the vehicle is stopped (or halted and switched to idling mode), i.e., the tank vent valve is closed, the scavenging air pump is deactivated and the shut-off valve is then closed. At time T2, the above-described waiting110begins. During this time, the pressure220increases by an amount222until the end of the waiting at time T3. The above-described evacuation112of the fuel tank system now begins in that the scavenging air pump is reactivated and the tank vent valve is opened. At time T4, the desired negative pressure224, of for example 10 mbar, is achieved and the scavenging air pump and the tank vent valve are stopped again. The pressure220in the still closed system then increases to a greater or lesser extent owing to vaporization and a possible leak. In this case,FIG.2shows three possible pressure profiles226,227,228from time T5, which each correspond to different situations. The flat profile226has an increase or gradient which is comparable with the pressure increase measured between time T2and time T3due to evaporation. In this case, it is concluded that there is no leak. The somewhat steeper profile227exceeds the measured evaporation rate and corresponds for example to a leak size of 0.5 mm. The steepest profile228also exceeds the measured evaporation rate and corresponds for example to a leak size of 1 mm. At time T6, the shut-off valve of the fresh air supply is reopened and the scavenging air pump and the tank vent valve are reactivated.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.