Ceramic element sensor

Abstract

An improved sensor having a ceramic element that undergoes a change in an electrical characteristic in response to a change in the partial pressure of oxygen in a mixture of gases to which the ceramic element is exposed. Sensors of this type are used to detect the air-fuel ratio of mixtures supplied to internal combustion engines. Prior art titania and zirconia sensors are characterized by little change in their respective electrical characteristics at operating temperatures below about 350.degree. C. A charge transfer material, platinum, has been applied to the ceramic element to facilitate or make possible the electron transfers required for sensor operation. Loss of the platinum charge transfer material by vaporization, as the result of operation at normal elevated temperatures, has been discovered to be the cause of a loss of sensor response at low sensor operating temperatures. The improved sensor has a charge transfer material comprised of an alloy of platinum and rhodium. This alloy, which preferably is 90% platinum and 10% rhodium, reduces the minimum temperature of operation for the sensor and substantially eliminates the aforementioned vaporization loss of the charge transfer material.

Dependencies are inferred from the claim text.