GF47.30-P-3013AMG Fuel Evaporation Control System, Function

GF47.30-P-3013AMG Fuel Evaporation Control System, Function







The fuel evaporation control system prevents fuel vapors escaping to atmosphere.

This is done by temporarily storing fuel vapors from the fuel tank in the activated charcoal canister

When the engine is running, the fuel vapors stored in the activated charcoal canister are drawn off due to the intake manifold vacuum and burned in the engine.

The purge control valve takes on the role of metering fuel vapors out of the activated charcoal canister and is actuated for this (pulsed) by the ME-SFI [ME] control unit by means of a PWM signal (pulse width modulated signal), if:
- Coolant temperature >40 °C
- Engine start before >45 s
- Engine not in the overrun mode
- Engine not in the lambda adaptation phase

The frequency of the PWM signal is selected from a speed dependent characteristic in such a way, that all cylinders are uniformly supplied with fuel vapors.

The purge quantity is determined by constantly opening and closing the purge control valve with on periods of varying lengths.

The idle speed control prevents changes in engine speed resulting from purging. A richer or leaner fuel-air mixture is produced in line with the charge of the activated charcoal canister with fuel vapors.

To prevent pulse noise caused by pulsing of the purge switchover valve there is a fluid reservoir located upstream of the purge control valve.

(USA)
During refueling fuel vapors are also collected from the fuel tank and passed on to the activated charcoal filter (ORVR = Onboard Refueling Vapor Recovery).