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The basic characteristics of the TiO2 sensor were introduced on a previous SAE paper which was submitted by NGK Spark Plug Co., Ltd. and further discussed on several other papers which have also been recently published. This paper will describe the effect of a precious metal catalyst on vehicle emissions. Emphasis is placed on the effect of the distribution of the precious metal catalyst in the titania element which significantly affects the reaction among unburned components in the exhaust gas as well as sensor performance. The relationship between the catalyst distribution in the sensor element, and the closed loop emission results, including test variability, will also be discussed in this paper.

A new low cost, quick responding, and compact NOx sensor using ZrO2 thick film and the meter have been developed. The sensor is amperometric and consists of two cells: the first cell is an oxygen pumping cell; the second cell is also oxygen pumping cell extracting oxygen from NOx by dissociating it into O2 and N2 gas. The oxygen pumping current in the second cell is proportional to the NOx gas concentration in the second cell and the exhaust gas. The meter is small size, light weight and can measure NOx and A/F ratio at the same time. An unique electronic algorithm is also developed to optimize the electrochemical control system effectively.