Linear lambda control

The introduction of ULEV required additional measures to improve lambda control accuracy plus extended malfunction diagnostics [14, 15]. Furthermore, the development of gasoline direct-injection engines and advanced electronic diesel control needed linear lambda control using the whole lambda range of X = 0.7-air. 

However, the lambda sensors in the potentiometric mode, due to their log dependence on oxygen partial pressure, cannot be used in lean-bum conditions, as deviations of a few mV are sufficient to produce imacceptable errors in the control of air/fuel ratio. This has led to the development of amperometric sensors, in which current is measured which has a linear dependence upon oxygen concentration (Kaneko et al. 1987, Maskell and Steele 1988). 

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