Patent ID: 8225648

Claim:
A particulate matter sensor for sensing particulate matter present in exhaust gasses flowing from an upstream end to a downstream end of an exhaust conduit for an internal combustion engine, said particulate matter sensor comprising: a sensing element with a sensing face, said sensing face configured to extend into said exhaust conduit, and further configured to provide a signal indicative of an amount of particulate matter detected in said exhaust conduit; an inner shield surrounding said sensing face and having an inner shield inlet passage for admitting exhaust gases into said inner shield to be sensed by said sensing face, said inner shield also having an exit passage to allow exhaust gases to exit said inner shield; and an outer shield surrounding a portion of said inner shield to define an outer shield chamber extending axially beyond said inner shield, said outer shield having an outer shield inlet passage configured for communicating exhaust gases into said outer shield chamber from said upstream end of said exhaust conduit, wherein exhaust gases enter said inner shield from said outer shield chamber.