TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Component: The engine controller determines a desired engine operating condition that satisfies the engine dependent auxiliary device.It commands the engine to attain the desired engine operating condition when the current engine operating condition is not within the acceptable engine operating range.The engine dependent auxiliary device is a catalyst coupled to the engine, a particulate filter coupled to the engine, an air conditioning system coupled to the engine, a cabin heating system provided in the vehicle, a fuel vapor purge system coupled to the engine, or a lean nitrogen oxides (NOX) trap coupled to the engine.It is coupled to the engine by a gear, belt or chain drive.The system further comprises an injector (52) for supplying a reductant into an exhaust stream of the engine upstream of the catalyst; and an energy reservoir coupled to the secondary machine.The secondary machine is one of the machines other than the internal combustion engine.It may generate energy, which may be stored in the energy reservoir, or may remove energy stored in the energy reservoir.The engine controller is coupled to the injector.It commands the injector to supply the reductant in the event that the current operating condition is within the acceptable operating range or at the desired operating condition. The energy reservoir may comprise a battery, a flywheel, a hydraulic fluid reservoir, a thermal reservoir, a spring, or a capacitor.The internal combustion engine includes an intake manifold (12).The catalyst comprises a lean NOx catalyst for reducing NOx when the engine air/fuel ratio is lean of stoichiometry.The acceptable engine operating range provides NOx concentration in an exhaust gas stream discharged from the engine less than a predetermined NOx concentration.It provides a temperature of the catalyst greater than a predetermined temperature. The predetermined NOx concentration is 25 ppm.The predetermined temperature is 300degrees C.The acceptable operating condition range provides a temperature in the particulate filter to exceed an ignition temperature of particulate matter filtered in the particulate filter. It is an operating condition providing a high thermal efficiency of the engine, or an operating condition range providing a manifold vacuum greater than 5 kPa.Preferred Method: The method further comprises determining a desired power at the driving wheels desired by an operator of the vehicle; determining an engine provided power at the driving wheels based on the engine desired operating condition; causing the secondary machine to absorb a difference between the engine provided power and the desired power when the engine provided power is greater than the desired power; and causing the secondary machine to supply a difference between the desired power and the engine provided power when the engine provided power is less than the desired power.A maximum power is determined at the driving wheels that the secondary machine may provide.The commanding step is postponed when a sum of the maximum power and the engine provided power is less than the desired power.A maximum absorption power is determined that the secondary machine may absorb.The commanding step is postponed when a difference of the engine provided power and the desired power exceeds the maximum absorption power.