Fuel Tank Vent Valve

Fuel Tank Vent Valve (TEV)

The tank vent valve provides managed regeneration of carbon canister (AKF) using scavenging air. The scavenging air drawn through the carbon canister is enriched with hydrocarbons (HC) according to the level of charge of the activated carbon (HC) and then fed into the engine for combustion.

The development of hydrocarbons from the fuel tank is highly dependent on:
- the fuel and ambient temperatures
- air pressure
- the fuel level within the tank

The tank vent valve is closed when in a flow-free state. This prevents fuel vapors from the AKF reaching the intake manifold when the engine is not running.

On-board diagnosis II
Regardless of the pollutants created by the combustion within the engine, a vehicle will emit considerable amounts of unburned hydrocarbons. These hydrocarbon emissions can stem from leaks in the fuel and fuel tank breather system, but may also be due to exhaustive storage capacity of the carbon canister (carbon canister becomes permeable).

For this reason, a further OBD II requirement concerns the fuel system and the fuel tank ventilation system. The maximum permissible level of escaping fuel fumes has been determined anew. Moreover, leaks larger than 0.5 mm in the fuel and fuel tank breather system must be recognized by the DME.

To this end, the following measures have been implemented:
- Fuel supply to the injection rail via the fuel filter with integrated pressure regulator.
- The fuel controlled by the fuel pressure regulator is routed in the filter via the return line to the fuel tank.
- A modified injection tube counteracts the formation of vapor bubbles and now no longer features a fuel return line to the fuel tank.
- Realization of a fuel tank leakage diagnosis facility in the engine control module with the aid of a motor-driven pressure pump (vane pump) and a changeover valve with integrated reference leak orifice (0.5 mm) > diagnosis module for fuel tank leakage (DMTL)