Exhaust gas sensor with high water splash resistant layer for lower emission 2020-01-0565
In the future, in order to realize CO2 reduction and clean exhaust gas, it is necessary to reduce emissions at engine start condition. Therefore, quick feedback control and quick response is required for Air-fuel ratio (hereafter, A/F) sensor that control exhaust gas concentration. Conventional sensor does not perform feedback control during engine start condition that generates a large amount of water splash from the exhaust pipe in order to reduce thermal shock. In addition, upper limit of the cover hole diameter is set to protect the sensor element in terms of thermal shock caused by water splash. Therefore, high water splash resistance layered exhaust gas sensor development is necessary in order to achieve quick feedback control and quick response. The water repellent phenomenon due to the Leidenfrost effect was focused as a means to improve water splash resistance. To produce that effect, it was clarified that the water evaporation behavior on the water splash resistance layer and the temperature change tendency of sensor element at the moment the water splash resistance layer was received water. And thermal conductivity is an important parameter for exerting the Leidenfrost effect, it was also found that the thermal conductivity range of the water splash resistance layer that occurs the Leidenfrost effect. In addition, it was found the porosity range of the water splash resistance layer to achieve the thermal conductivity target minimizing the response deterioration during the Leidenfrost effect is expected. As a result, by providing the water splash resistance layer with water repellent function, feedback control right after engine start condition was realized and 27% responsiveness was improved. Through this research, A/F sensor with water repellent function can be commercialized as a mass production sensor, which will be sequentially adopted for sensors after 2019.