Vapor purge estimation using a dual-mode observer

Fuel-tank vapor purge has long been a standard feature on vehicles to meet federally regulated evaporative emissions requirements. The following proposes improvements to the means of estimating purged fuel vapor contribution to the engine without the use of a vapor sensor. An accurate estimate of purged fuel vapor can reduce the burden on the A/F (air to fuel ratio) controller and allow for lower emissions and/or larger purge quantity. Reducing this tradeoff between emissions and purge quantity permits more frequent open-loop A/F control events such as deceleration fuel shutoff (DFSO) which can positively affect vehicle fuel economy.