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Ultra Low Emission Vehicle (ULEV) and proposed Super Low Emission Vehicle (SULEV) requirements along with Lean Burn Systems will require improved Engine Management Systems and new catalyst technologies. High performance, reliable exhaust gas/catalyst temperature sensors are one of the key enabling technologies needed for these next generation engine management systems and catalysts. The demand for accurate, high temperature Exhaust Gas Temperature Sensors (EGTS) is growing quickly. Gasoline direct injection engine lean NOx catalyst traps, On Board Diagnostic catalyst monitoring systems, Diesel engine active lean NOx catalyst systems and large Diesel engine diagnostics and protection functions all require accurate measurement of exhaust gas temperature over a wide range. Added to these requirements are the need for short response times, low production costs, and a high sensitivity linear signal for direct input into engine management controllers.

There are three primary parameters that must be controlled in an engine for optimum performance; air, fuel (A/F ratio), and ignition (spark). Similarly, there are three primary parameters that must be controlled in a three-way catalyst for optimum performance; air, fuel (A/F ratio), and energy (temperature). Currently, most engine management systems provide closed loop control on the A/F ratio via oxygen sensor feedback, but temperature control is left to open loop methods with models and calculations. This paper will describe the benefits of closed loop catalyst temperature control (directly measured) for reducing emissions and providing a more robust catalyst monitor function. This catalyst monitor function will include measurement of catalyst lightoff performance which is the dominant effect causing HC tailpipe emissions to exceed OBD threshold levels. The lightoff measurement is not effected by driving cycle.