Tolerant Ethanol Estimation in Flex-fuel Vehicles during Maf Sensor Drifts

Flexible fuel vehicles (FFVs) can operate on a blend of ethanol and gasoline in any volumetric concentration of up to 85% ethanol (93% in Brazil). Existing FFVs rely on ethanol sensor installed in the vehicle fueling system, or on the ethanoldependent air-to-fuel ratio (AFR) estimated via an exhaust gas oxygen (EGO) or λ sensor. The EGO-based ethanol detection is desirable from cost and maintenance perspectives but has been shown to be prone to large errors during mass air flow sensor drifts [1, 2]. Ethanol content estimation can be realized by a feedback-based fuel correction of the feedforward-based fuel calculation using an exhaust gas oxygen sensor. When the fuel correction is attributed to the difference in stoichiometric air-tofuel ratio (AFR) between ethanol and gasoline, it can be used for ethanol estimation. When the fuel correction is attributed to a mass air flow (MAF) sensor error, it can be used for sensor drift estimation and correction. Deciding under which condition to blame (and detect) ethanol and when to switch to sensor correction burdens the calibration of FFV engine controllers. Moreover, erroneous decisions can lead to error accumulation in ethanol estimation and in MAF sensor correction. In this paper, we present a cylinder air flow estimation scheme that accounts for MAF sensor drift or bias using an intake manifold absolute pressure (MAP) sensor. The proposed fusion of the MAF, MAP and λ sensor measurements prevents severe mis-estimation of ethanol content in flex fuel vehicles. NOMENCLATURE AFRs Stoichiometric air-to-fuel ratio e Volume fraction of ethanol in ethanol-gasoline blend em Mass fraction of ethanol in ethanol-gasoline blend pm Intake manifold absolute pressure R Gas constant ∗Address all correspondence to [email protected]. Tm Intake manifold temperature Vd Total displaced cylinder volume Vm Intake manifold volume Wcyl Air flow rate into the cylinder Wf b Feedback fuel flow command Wf f Feedforward fuel flow command Wf f1 Feedforward fuel flow command not compensated by the fuel puddle dynamics Wθ Air flow rate through the throttle αtr Triggering signal for switching between ethanol adaptation and others βtr Triggering signal for switching on MAF sensor drift adaptation ηv Volumetric efficiency θ Throttle angle λ Ratio of actual AFR to stoichiometric AFR, measured by an EGO sensor τMAF MAF sensor time constant