Patent ID: 6968680

Claim:
A method for controlling an emission system, the system having an engine and an exhaust through which exhaust gasses flow, said exhaust having at least a first and second catalyst arranged in parallel adapted for reducing NOx emissions with incoming reductants, and said exhaust also having at least one reductant delivery device, said reductant delivery device located downstream of the engine, the method comprising: when requested based on a first operating condition, diverting at least a portion of exhaust gas flow from said second catalyst to a first path to said first catalyst and providing reductant from the reductant delivery device into a second path to said second catalyst in the exhaust system that reaches said second catalyst to reduce NOx in said second catalyst; and when requested based on a second operating condition, diverting at least a portion of exhaust gas flow from said first catalyst to said second path and providing reductant from the reductant delivery device into said first path in the exhaust system that reaches said first catalyst to reduce NOx in said first catalyst, wherein the reductant delivery device is in the engine exhaust.