Purging Function - GF47.30-P-3015MNB
Engine 178.9 In Model 190
Schematic diagram of fuel tank aeration and ventilation
Purging function requirements, general points
- Circuit 87M (Engine management ON)
- Engine started for at least 60 to 80 s
- Coolant temperature > 40°C
- Engine not in deceleration mode
- Engine not in the lambda adaptation phase
Purging, general points
When the fuel tank is being ventilated, no fuel vapors should escape into the outside air.
The fuel vapors are stored in the activated charcoal canister and burnt later in the Engine.
In order to enable the purging, the ME-SFI [ME] control unit (N3/10) reads in the following signals:
- Coolant temperature sensor (B11/4), coolant temperature
- Left and right charge air temperature sensors (B17/14, B17/15), charge air temperature
- Pressure sensor downstream of left and right throttle valve (B28/22, B28/23), boost pressure
- Crankshaft Hall sensor (B70), Engine RPM
- LH and RH oxygen sensor sensor elements upstream of catalytic converter (G3/3b1, G3/4b1), oxygen and nitrogen contents
Function sequence for purging
Ventilation of the fuel tank (operational ventilation) takes place over the aeration/vent valves, the aeration/vent lines and the activated charcoal canister.
The fuel vapors here flow to the activated charcoal canister, where they are stored and from where they are extracted into the charge air distributor when purging is enabled.
When the Engine is running, the fuel vapors stored in the activated charcoal canister are drawn off through the left and right purging switchover valves and combusted in the Engine.
The left and right purging switchover valves are actuated by the ME-SFI [ME] control unit at the ground end to regulate the purging quantity by means of an electric signal between 0 and 500 mA.
The purging quantity is determined through regulation of the opening cross-section of the left and right purging switchover valves.
The idle speed control prevents the purging from causing a change in RPM when the Engine is at idle. The fuel/air mixture is leaned out depending on the level of fuel vapors load in the activated charcoal canister.
Function sequence for purging
- Function sequence for neutral purging
- Function sequence for wide open throttle purging
Function sequence for partial load purging
In idling, the fuel vapors stored in the activated charcoal canister are suctioned off by the existing vacuum via the left and right purging switchover valves, the partial load operation check valves and the partial load purge lines behind the throttle valves and burned in the Engine.
Function sequence for wide open throttle purging
In wide open throttle operation the fuel vapors are suctioned off through the wide open throttle operation check valve and the wide open throttle purge line.
The vacuum required for this is generated by a Venturi nozzle. The fuel vapors are then routed over the wide open throttle purge lines, ATLs and the charge air coolers to the charge air distributors.
To check whether wide open throttle purging can be enabled, the left and right purging switchover valves are opened suddenly three times in succession. Pressure peaks of > 120 mbar must be registered here. The purging pressure sensor (B4/4) detects the given pressure conditions in the wide open throttle purge line, and forwards a signal to the ME-SFI [ME] control unit.
Schematic representation of purging
| Electrical function schematic for purge control | PE47.30-P-2052-97HBA | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNB |