Refueling Intention Detection, Basic Function - GF47.00-P-1002A

Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 

Engine 177, 256 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 

General 

Vehicle with conventional drive 

Because of external influences, e. g. in the event of fluctuations in temperature, pressure in the fuel tank can increase by up to 0.35 bar. When opening the fuel filler cap, pressure compensation occurs with the surrounding area, meaning fuel vapors enter the environment. The refueling intention detection has the function of holding back the escaping fuel vapors during the refilling process.

Vehicle with hybrid drive system 

Evaporative emissions form in the fuel tank. These evaporative emissions are normally stored in an activated charcoal canister and then fed to the engine for combustion. To prevent the evaporative emissions from being released into the atmosphere during electric-only mode (i.e. without the combustion engine) and given the finite storage capacity of the activated charcoal filter, a pressure tank system can be used to isolate the fuel tank against the atmosphere by means of a shutoff valve. When the shutoff valve is closed, the evaporation causes the pressure in the tank system to increase.

Function requirements 

• Vehicle speed < 2 km/h
• Vehicle not locked from outside

Function 

If the driver activates the refueling intention detection switch, the "request for fuel tank ventilation" signal is transmitted to the combustion engine control unit. The LED in the refueling intention detection switch flashes. The message that the fuel tank is being bled appears in the instrument cluster.

The combustion engine control unit checks the actual pressure in the fuel tank and starts the ventilation by actuating the fuel tank shutoff valve. The pressure in the fuel tank is then reduced via the activated charcoal canister, and the fuel vapors are collected in the activated charcoal filter.

The combustion engine control unit monitors the pressure in the fuel tank via the fuel tank pressure sensors. When the fuel tank has been bled, the "fuel tank bled" signal is transmitted to the left front door control unit.

At the same time, the "Release fuel filler flap" signal is sent to the body/drivetrain signal acquisition and actuation module.

The body/drivetrain signal acquisition and actuation module operates an actuator to open the fuel filler flap.

In the IC a message indicates to the driver that the tank readiness was created. The LED in the refueling intention detection switch lights up permanently.

The ventilation of the fuel tank generally lasts less than a minute. Under certain conditions, ventilation can last up to ten minutes.

The following causes for this are possible:

• Initial status of the fuel
• Fuel temperature
• Fuel tank fill level
• Ambient temperature

To protect the vehicle from being over-filled, the fuel vapor shutoff valve is actuated at the same time that the central locking system fuel filler cap actuator is operated. As a result, the operational ventilation of the fuel tank is inhibited and the refueling volume is limited. Once refueling has been completed and the fuel filler flap has been closed, actuation of the fuel vapor shutoff valve stops. The operational ventilation is enabled again.