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This paper discusses the properties of EGO sensors based on thick TiO2 films. These devices are fabricated by depositing a TiO2 film on an insulating or conducting substrate. In addition to being inherently inexpensive, planar techniques provide flexibility in the fabrication of multicomponent structures incorporating temperature compensation and heating elements. Furthermore, TiO2 film sensors are found to possess faster transient response than available ZrO2 and ceramic TiO2 sensors. Results of engine studies of the properties of these new TiO2sensors will be presented and discussed.

An engine-dynamometer study was performed to quantify the air-fuel ratio (A/F) offset between the window of a three-way catalyst (TWC) and the closed-loop control point of an exhaust gas oxygen (EGO) sensor. In this study, the effects of rpm, torque, EGR, and A/F modulation were explored along with the age of the TWC and EGO sensor. In general, it was determined that the closed-loop EGO sensor control point shifts lean as a function of increasing feedgas NOx concentration, thus causing the engine A/F to move away from the high NOx conversion efficiency regime of the TWC.