Abstract: A system and a method to control air flow during a transition in an internal combustion engine, in which intake valves are operated by more than one type of actuation device, is disclosed. Based on demanded engine torque, engine speed and transition type, throttle position and closing time of a randomly operable intake valve are determined such that a smooth transition can be accomplished.

Abstract: A method and apparatus for operating a lean-burn internal combustion engine in cooperation with an exhaust gas purification system having a three-way catalyst and a NOx trap located downstream of the three-way catalyst includes a controller which calculates current levels of tailpipe NOx during lean engine operating conditions based upon the difference between a determined instantaneous feedgas NOx concentration and a determined instantaneous trap efficiency. The controller discontinues lean engine operation when the tailpipe NOx, expressed in terms of either grams-per-mile or grams-per-hour, exceeds a predetermined threshold level, either instantaneously or as averaged over the course of a trap purge-fill cycle.