Function of Fuel Evaporation Control System - RA4700HFM0040X(47-0040)

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Function

A fuel evaporation control system is installed to limit the fuel vapors which pass to atmosphere. The fuel vapors stored in the activated charcoal filter are drawn off through the purging switchover valve (Y58/1) at coolant temperatures >80°C and combusted in the engine (not in deceleration mode).

The HFM control unit processes the following information for this purpose:

Engine speed
Air mass
Coolant temperature
Intake air temperature

Fig 1: Identifying Purging Switchover Valve
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The purging switchover valve (Y58/1) is actuated (pulsed) by the HFM control unit with a frequency of 5, 10 or 20 Hz from an rpm dependent map in order to control the purging quantity. As a result, a uniform supply of fuel vapors is assured to all the cylinders. The purging quantity is determined by constantly opening and closing the switchover valve for on and off periods of various lengths.

Purging switchover valve (Y58/1)

It is located below the control unit (N3/6) and is actuated by the control unit if the following conditions exist:

Operating :

Coolant temperature >70°C
Lambda control active (KAT), at the earliest 40 s after start
At the earliest 40 s after start (without KAT)
Engine speed once >1000 rpm (end start recognized)

Not operating :

Coolant temperature <30°C
Lambda control not active (KAT)
Deceleration >4000 rpm
Engine not running

Fig 2: Identifying Purging Switchover Valve
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.