A method and apparatus for controlling the operation of a “lean-burn” internal combustion engine in cooperation with an exhaust gas purification system having an emissions control device capable of alternatively storing and releasing NOx when exposed to exhaust gases that are lean and rich of stoichiometry,...http://www.google.co.uk/patents/US6843051?utm_source=gb-gplus-sharePatent US6843051 - Method and apparatus for controlling lean-burn engine to purge trap of stored NOx 
