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UTILIZING EXPONENTIAL DECAY COOLING CURVES TO PREDICT LIQUID FUEL TEMPERATURE STABILIZATION AFTER KEY OFF

IP.com Disclosure Number: IPCOM000238396D
Publication Date: 2014-Aug-22
Document File: 2 page(s) / 267K

Publishing Venue

The IP.com Prior Art Database

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UTILIZING EXPONENTIAL DECAY COOLING CURVES TO PREDICT LIQUID FUEL TEMPERATURE STABILIZATION AFTER KEY OFF

Vehicles sold in North America are required to perform Evap leak detection as part of OBDII requirements. Green states required to monitor for 0.02" leaks whereas federal states have to perform
0.04" leak tests.Many OEMs prefer to perform the leak diagnostics in a noise free static environment hours after the vehicle shuts down. This allows the fuel temperature to stabilize.Some OEMs wait until enough fuel cooling has occurred and/or natural vacuum has been generated inside fuel tank before commencing with Evap leak detection.Current strategy wakes upthePCM arbitrarily hours after key off to determine if fuel has cooled down.If fuel is still hot, a "snooze" strategy re-wakes the PCM again after few hours. Waking up the PCM hours later in anticipation of fuel cooling or a delta temperature drop is probabilistic as the vehicle could have been keyed off in the morning hours where temperature and sun loading will most likely heat up the fuel. Also, algorithms relying on cooling to generate natural vacuum will find it futile to wake up in the middle of the day.Sometimes strange weather patterns can cause temperature to rise at night and drop during the day.Waking up PCM randomly consumes battery power, cycling Evap valves unnecessarily reduces their expected life and running Evap leak routines at the wrong time of day causes false failures.

Method

The commonly accepted method for engine cooldown is when Engine Coolant Temperature (ECT) reaches near Ambient Air Temperature (AAT). The method centers around utilizing exponential decay to model cooling curves for ECT at various ambie...