EVAP SYSTEM RECIRCULATION TUBE DIAGNOSTIC
Publication Date: 2017-Jan-19
The IP.com Prior Art Database
EVAP SYSTEM RECIRCULATION TUBE DIAGNOSTIC Evap systems in North America have a recirculation tube that connects the fuel filler “cup” to the rest of the Evap system. The purpose of the recirculation tube is two-fold: 1) It recirculates fuel vapors during refueling. This reduces air entrainment hence reducing vaporization inside the tank. By doing so, the size of the carbon canister is decreased which results in cost savings as activated carbon pellets are expensive. This is critical because it effects the canister sizing and emission certification. 2) It provides a path to the filler neck for Evap leak detection at the cap area. With bottom feeding tanks, at certain high fuel levels the vapor “communication” to the filler neck becomes blocked by the fuel at the spud valve. Hence any leaks in the cap area will go undetected without the recirculation line. Recirc tube typically has orifices in it on the order of 2mm to 3.5mm. If blockages occur in the recirculation line orifice, the Evap leak detection monitor false passes a leak at the cap area. This is especially true in bottom feeder fuel tanks where fuel can submerge the filler neck/spud valve. Prior art methods have evacuated a fuel tank to -20InH2O at high fuel levels to crack open the capless to validate the recirc line path for blockages. Most fuel tanks are plastic and unable to withstand large vacuum levels. Method
Not all filler necks have spring actuated capless flaps. OEMs continue to use cap designs and plastic vented fuel tanks.
This method opportunistically diagnoses the recirc line during a refueling event when residual liquid fuel level is such
that the filler neck spud valve is submerged in liquid fuel. This creates a liquid seal that isolates the filler neck area from
the fuel tank. With the spud valve covered by liquid, the o...