Combustion control using a Model-based MFB50 estimation methodology

The increasing request to reduce pollutant emissions and to improve efficiency required the development of complex engine control strategies implemented in the ECU, with algorithms’ complexity and number of quantities that need to be estimated on-board increasing very fast. MFB50 is a very interesting parameter to be estimated onboard, because an accurate knowledge of its value provides important information about combustion; for example it could be used to determine the angular range in which an HCCI combustion takes place or a setpoint position can be chosen to perform optimal torque combustion control. As previously mentioned, MFB50 could be directly calculated using in-cylinder pressure sensors, but they require additional costs. Furthermore, pressure measurements’ long-term reliability still has to be improved. The methodology described in this paper is based on the analysis of the instantaneous engine speed measurement, that can be performed using the same 60-2 toothed wheel already mounted on-board the vehicle. All the quantities involved in the procedure are already available on-board for other management purposes, that’s why this approach does not require any additional cost. The main steps of the MFB50 estimation algorithm are: a torsional behavior model is first needed in order to estimate the torque harmonic component acting on the crankshaft, and then the relationship between the phase of the torque harmonic component and MFB50 is used to obtain the MFB50 estimation.