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ALTITUDE CHANGE INFERENCE IN VENTED FUEL TANKS

IP.com Disclosure Number: IPCOM000243486D
Publication Date: 2015-Sep-24
Document File: 1 page(s) / 235K

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The IP.com Prior Art Database

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ALTITUDE CHANGE INFERENCE IN VENTED FUEL TANKS

Certain OBD monitors, such as the Evap leak monitor, rely on driving on flat surfaces for robustness. Some powertrain control modules (PCMs) have built in barometric pressure (BP) sensors. Other PCMs infer BP from ETC throttle opening. The Evap leak detection monitor thresholds are typically adjusted for altitude, so BP data is needed at all times. For instance, the bleedup portion of the Evap leak diagnostic can false fail when climbing a hill. Conversely, the leak diagnostic can false pass when descending a hill. Inferred BP is typically obtained when the engine is running and throttle position is in part throttle (cruising or going uphill). During downhill driving or high load driving (closed throttle or Wide Open Throttle, WOT), inferred BP cannot update. BP is inferred from manifold pressure (MAP), BP = MAP + deltaP, where deltaP is the pressure drop across the throttle plate, which is a function of flow and throttle angle. At WOT there is negligible pressure drop, so BP ~= MAP, asat part to closed throttle, flow can be choked (sonic flow). At sonic flow, the flow remains the same no matter what the pressures are on both sides of the throttle. At closed throttle, this flow would be very small.Hence during a hill climb/descent, BP inference is not available. This may be critical for certain onboard diagnostic (OBD) monitors that rely on BP reading. Lack of altitude detection can result in monitor alpha/beta er...