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The largest portion of hydrocarbon and/or carbon monoxide emissions is released during engine cold-transient operation. To achieve closed loop control as quickly as possible, a fast light off (FLO) oxygen sensor is required. The heater, element and structure of the thimble-type oxygen sensor that has been used in the market for some time has been improved to achieve closed loop control within 15 seconds. The heater is improved by concentrating the heating area and by lowering its resistance. The heater life is similar to that of the current type by using new materials and adopting new heater temperature control strategies. In addition to the efficiency of heat transfer, the low temperature characteristics of the element have also been improved. The fast light off thimble-type oxygen sensors can now be put to practical use to achieve emission reductions.

The oxygen sensor for automobiles is widely used for the exhaust gas control system by using a three way catalyst and constitutes a very important function part of combustion control system in the internal combustion engine. The air-fuel ratio is controlled at the stoichiometric point, where the best purification efficiency is obtained. Recently a wide range air-fuel ratio control system has been developed for the areas of lean burn combustion for fuel economy, low emissions at low temperature starts, and full power control at W.O.T. with rich burning. The UEGO (Universal Air-Fuel Ratio Heated Exhaust Gas Oxygen) sensor has been developed to meet the wide range of air-fuel ratio control. This UEGO sensor indicates output proportionally for all ranges of air-fuel ratio, unlike the conventional oxygen sensor which detects only the stoichiometric point.