A PROPORTIONAL AIR FUEL RATIO ZIRCONIA OXYGEN SENSOR

A novel time-sharing control circuit is used to convert a linear lean exhaust gas oxygen sensor into a proportional extended range (lean or rich exhaust) sensor. The time-sharing oscillator allows a single electrochemical cell to act as both the voltage sensor and as an oxygen pump, thus reducing the complexity of sensor geometry and fabrication compared to the universal exhaust gas oxygen (UEGO) sensor design. The control circuit has been demonstrated in the laboratory using two forms of commercially available ZrO2 cells: (1) a design with a small chamber that opens to the exhaust by a small hole; (2) a design that provides for a limited diffusion region by use of a porous ceramic layer over the outer electrode. The porous-layer design (or a ceramic coating with one or more holes) appears to be a potential candidate for a linear exhaust gas sensor where interest is primarily in a linear response around stoichiometry.