Development of Fast Response Time PM Sensor 2020-01-0390
Automotive manufacturers are working towards protecting the global environment by using filters to reduce particulate matter (PM) emissions from their vehicles. There is a growing demand for sensors that detect the small amounts of PM leaking through these filters, as they can aid in performing on-board diagnostics (OBD) and monitoring the function of these filters. Currently, vehicles predominantly use an electric resistance type PM sensor, which applies a voltage between electrodes, collects PM, and senses the generation of PM path. However, in response to tightening regulations on PM-OBD, the response time of the sensor needs to be optimized. Furthermore, the fast response time must not degrade the poisoning resistance in order to ensure durability. To shorten sensor response time, we have developed a 20 μm-gap electrode structure using a cross-section of laminated alumina sheets with printed electrodes, which can form PM paths at small PM amounts. The new structure has an improved electrode layout, designed with the assistance of electric field simulation. The improved layout reduces electrical interference between the pairs of electrodes, and attracts more PM. This structure has a shortened response time which enables multiple PM measurements in a single drive cycle. Temperature control methods have been developed to increase the sensor’s resistance to poisoning. This prevents the contamination of the electrode when the sensor is not actively detecting PM. By utilizing the Leidenfrost effect for liquid phase poisoning substances, and the thermophoresis effect for solid phase poisoning substances, the electrodes can be sufficiently protected from poisoning. The new temperature control method has demonstrated its durability without changes in response time, even under severe conditions in exhaust gases.