Patent ID: 7854161
Filing Date: 2010-12-21
Classification: F01N,F02D,Y02T

Abstract:
1. A diagnostic method for testing and diagnosing a cause of malfunction of a Selective Catalytic Reduction (SCR) aftertreatment system for reduction of NOx in an exhaust gas passage of an internal combustion engine, the SCR system comprising a dosing system that injects a fluid reducing agent into exhaust upstream from a catalyst reactor and a downstream side NOx sensor for supervising NOx emission in the exhaust downstream from the reactor, the diagnostic method comprising the steps of: setting a torque range and a speed range of the engine to a predetermined interval and adjusting a fluid agent mass flow to a level which is normal for the interval, measuring and registering a mean NOx sensor value for the mass flow, increasing the mass flow to a level which is higher than normal for the interval, measuring and registering another mean NOx sensor value related to the increased mass flow, comparing the two registered NOx sensor values and determining if, on one hand, the NOx sensor value for normal mass flow is higher than the NOx sensor value for increased mass flow, or, on the other hand, the NOx sensor value for normal mass flow is lower than the NOx sensor value for increased mass flow.