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A thick film type oxygen sensor has been developed. It has the unique structure and principle to achieve the fast light off and a compact configuration. The main part of the uniqueness is the self generation of oxygen from exhaust gas, as the reference. In another words, this does not require fresh air from atmosphere as the conventional thimble type oxygen sensor and no output is shifted down by the change of the reference oxygen partial pressure. The other advantage is monolithic nature of the sensing element and the heater, which makes the sensor start working about in 10 seconds with small wattage. The combination of these two key technologies enables the oxygen sensor to be small and free from location issue.

Two distinctive λ sensors have been developed for a compressed natural gas (CNG) vehicle that complies with OBD-II. As the upstream sensor, there is employed an element which obtains an additional catalyst coating layer to enhance combustion of CH4 and H2 that reaches to the surface of the element. Meanwhile, as the downstream sensor, there is employed an element having an electrode that is intentionally inactive with CH4, to eliminate the temperature dependent chemical reaction of CH4 remaining after the catalyst converter, and to avoid false catalyst monitoring. Use of the above two kinds of λ sensors enables construction of an O2 feedback system for a CNG engine that complies with OBD-II.

This paper discusses the recently developed titania sensors which are now under production in the Japanese market. The sensor's submersible design allows for more flexibility of installation, and since the titania thick film sensor is less sensitive to lead poisoning, its use in both the United States, where lead contamination in unleaded gas can still be observed, and in Europe, where leaded gasoline may still be available in certain countries, indicates the need for an inexpensive, mass produced sensor. The titania sensors exhibit the following characteristics: They are compact in size and completely submersible; they show a tolerance towards lead poisoning; they experience less lambda shifting; less deterioration, and acute sensitivity. This paper offers an attractive alternative to the zirconia sensor which many vehicles currently use because of past success in its development.