Oxygen gas sensor sensitive at low and high oxygen partial pressure - consists of high purity cerium-oxide to which noble metal electrodes are attached

摘要

The resistive sensor, which detects the content of oxygen and oxidisable gases in exhaust gas, consists at least partly of pure CeO2. To obtain a change in resistivity of the sensor of pref. at least 1 order of magnitude for a change in p(O2) of about half an order of magnitude in exhaust gas with a lambda of 1 +/- 0.05 CeO2 with a purity of 98% is used at a temp. of at least 1000 deg.C.. In lean air/fuel mixtures with a lambda of up to 1.8 the purity of CeO2 pref. is 99.99% if operated at 700 deg.C., 99.96% if operated at 800 deg.C. and 99.91% if operated at 900 deg.C.. To construct the sensor pref. powdered CeO2 is mixed with an adhesion promoter, e.g. glass-frit, an organic binder and deposited on a substrate, which has been provided with interdigitated electrode contacts, as a thick film and fired. Alternatively the CeO2 (26) can be deposited by HF sputtering, again on a substrate (24) with an electrode structure (20,21). The surface of the sensor layer may be activated catalytically by depositing metal particles on it. The substrate may also carry a temp. sensor (27,28) and be provided with a heater, e.g. on the back. USE/ADVANTAGE - The sensor has improved sensitivity to oxygen over a larger range of partial pressures than conventional sensors, for a lambda range from 1.05-1.8 which can be used in the presence of reducing gases. The use of a thin layer, e.g. 5-10 micron, results in fast reaction times, e.g. in the order of 10-5 msecs.. The sensor gives a good reproducibility and is used for engine management.