System inversion approach on a crankshaft of an internal combustion engine

This paper presents a method for inversion of a five-input-one-output mechanical system, a crankshaft of an internal combustion engine. The inputs are the individual torque contributions from each cylinder combustion and the output is the total momentary torque output of the engine. The system inversion problem appears when individual combustion classification of a multi-cylinder engine is desired based on a measurement of the output signal only. The crankshaft can be represented as a linear system with modifications to the input signals. The system inversion method requires that only one input signal at a time is estimated, and the others are regarded as known. The linear part of the crankshaft model was found front two sources; physical modeling and identification of a black-box model. The cylinder individual estimated input torque is used for an estimation of a combustion phasing measure for comparison. The combustion phasing measure used is the 50% Torque Ratio and was calculated for both the measured and the estimated input torque. The physical model shows good correlation for low engine speeds but with an offset. The identified black-box model shows good performance at both 1000 and 3000 rpm without any offset.