Assignment

Already with the introduction of the Lambda-control with catalytic converters, all the vehicle emissions were regulated by law. This also included the paint and the fuel-vapour evaporating from the tank. Should high pressure in the tank exist, only air may escape to the outside.

Function

The tank may not be hermatically sealed. Indeed, the active carbon filter should trap the fuel portion in the escaping vapours. They have to pass through a carbon granulate (see picture 2), which stores the fuel in a liquid form. The active carbon filter is cleaned again when the filter-purge-valve (component 'A' in figure 3) opens and fresh air is sucked into the engine through the active carbon filter.

In this case the Lambda control circuit may not be lastingly disturbed. If. e.g., when idling, more fuel than required is offered for a mixture, the control device must engage and close the connection between the inlet manifold and the active carbon filter or limit it through pulse width modulation. The Lambda value may, under no circumstances, fall below the allowed level. The injector-valves are automatically adjusted to accordingly shorter opening times by the Lambda control.

By the way, the ability of the control device to flush the active carbon filter is regularly checked in the OBD-system. The control device opens the purge-valve and checks the measurable enrichment or possibly also the leaning in the exhaust gas system. This process is often repeated, possibly because, depending on the state of the active carbon filter, a varying result is not always achieved.

Should possible structural alterations take place, it must be ensured that the standard lay-out of the bleed-off pipe is not changed because it is thus laid out, that even if the vehicle is lying on its side or on ist roof, the tank cannot empty itself. 05/10