On-Board Refueling Vapor Recovery Function - GF47.10-P-3004KJ

ENGINE 281.910 in MODEL 453.3/4 with CODE 494 (US version) 

Courtesy of MERCEDES-BENZ USA

Schematic diagram 

On-board refueling vapor recovery, general points 

The law requires, that the refueling gases in the vehicle are collected (Onboard Refueling Vapor Recovery). Fuel and refueling vapors must be separated in order to prevent fuel from flowing into the activated charcoal canister (77) due to any inappropriate refueling or a defective nozzle.

Function sequence for on-board refueling vapor recovery 

Owing to its form, the filler neck (45) functions as a suction jet pump. The fuel coming from nozzle thus accelerates in the filler neck (45) and the air around the nozzle is suctioned into the fuel tank (75). As a result of this air intake, the refueling vapor are not able to gather at the filler neck and are able to escape.

The fuel vapors flow through the aeration/vent valves (75/2) and aeration/vent lines and the aeration/vent lines (A) to the activated charcoal canister (77), where they are stored. The fueling, pressure limiting valve, pressure limiting valve and the vent valve (75/1) also prevent any overfilling by closing off the aeration/vent lines (A).

Rollover valves are integrated at the top of the aeration/vent valves (75/2). If fuel gets into aeration/vent valves (75/2), the aeration/vent lines to the activated charcoal canister (77) are closed off, thus preventing fuel from flowing into the activated charcoal canister (77). The aeration/vent valves (75/2) can also close briefly if there is sudden braking or acceleration, or when cornering.

For an opened purging switchover valve the fueling gases are suctioned together with the fuel gases from the activated charcoal canister (77) over the purge line (B) and the dashpot (58) by the engine and burnt.

The ME-SFI [ME] control unit (N3/10) regulates the feed to the engine over the fuel tank bleed valve. The ME-SFI [ME] control unit regulates the pressure in the activated charcoal canister (77) over the activated charcoal canister shutoff valve, for example to check the system for leaktightness. The pressure in the fuel tank (75) is determined over the fuel tank pressure sensor.

Detailed information about the leak test and pressure measurement can be taken from the system description "System purging with leak test function".