Torque based combustion phasing control

Doctoral thesis, 2005

Due to environmental aspects and emission legislations the automotive industry is striving towards more efficient combustion engines. Many engine control systems in production today are based on look-up tables which are calibrated for different operating conditions. Improvements can be done by constructing better control systems to make the engine run in optimal operating conditions more often than conventional control systems are able to do today. One such improvement could be to replace some look-up tables with feedback control of wisely chosen properties of the combustion process. However, even if a promising property is found and quantified it must be measurable either directly or indirectly. Also, the property must be controllable using a suitable actuator. This thesis concentrates on estimating individual cylinder combustion phasing using a torque sensor mounted on a crankshaft. The combustion phasing is quantified using a measure called 50% torque ratio and it is controllable by modifying the spark advance for each cylinder. A control system has been implemented in an engine test bench to be able to test the ideas. Several test cases have been designed to demonstrate the capability of the system to control the combustion phasing individually for each cylinder and to compensate for simulated external disturbances in steady-state conditions. The control system is also equipped with self-optimising functionality by using an extremum seeking controller to detect for which value of the torque ratio that maximises generated work from each cylinder. The resulting implemented control system is capable of maintaining a desired set-point for the torque ratio in steady-state conditions. Transient conditions have not been evaluated. The extremum seeking controller is demonstrated to be able to find a torque ratio for each cylinder which maximises the generated work.