to reduce the engine out nox as much as possible this may often be done by a massive exhaust gas recirculation which is not necessarily optimal for soot emissions and fuel efficiency it may often be thought from an overall optimality point of view that the engine control system rely on the aftertreatment mechanism to reduce nox emissions instead the engine control system should control the aftertreatment temperature to maximize its efficiency this may be achieved virtually only by coordinated control the present approach may utilize modeling and control technology first models of the engine and after treatment subsystems may be created the models of the engine and exhaust after treatment subsystems may track actual engine and exhaust after treatment subsystems from these models one or more multivariable controllers may be synthesized a multi variable controller may address the inherent interactions of an overall coordinated engine scr control system the present description may treat the models of the engine and exhaust after treatment subsystems as actual subsystems a series of fig1 4 indicate some basic elements of an engine and emission control approaches which lead up to fig5 and 6 which show examples of the present system fig1 is a diagram of a basic engine plant model system 10 input 12 w eng may incorporate detected engine speed fueling rate ambient conditions such as temperature and air pressure and so on input 13 u eng may incorporate signals to actuators on the engine e g variable geometry turbine vgt exhaust gas recirculation egr throttles fuel injection specifications variable valve actuation vva and so on u201c u.