Activation and setpoint values

When the engine is started after it has been switched off for a certain period of time, the tank vent valve remains closed as long as the engine temperature is still below 40°C. However, the fuel tank is still ventilated to the ambient air via the carbon canister. The fuel vapours that escape here are collected by the carbon canister. In the 1st adaptation phase, the fuel tank ventilation valve is closed. For the 3 load ranges (idle speed, lower load range and medium load range), a fuel mixture adaptation as deviation to Lambda value = 1 is made at certain engine speeds and load ranges. In the 2nd tank ventilation phase, the tank vent valve may be opened for the entire phase (270 seconds), provided no other requests are pending (for example, overrun fuel cutoff or diagnosis). In the 2nd adaptation phase, the fuel tank ventilation valve is closed again. For the 3 load ranges (idle speed, lower load range and medium load range), a fuel mixture adaptation as deviation to Lambda value = 1 is made at certain situations for load and engine speed. All other adaptations run in exactly the same way.

Fig 1: Tank-Ventilation Valve Signal Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Observe the following setpoint values for the tank vent valve: