Phase Detection Relevance in Engine Torque Determined by Instantaneous Engine Speed

Accurate flywheel torque estimation in combustion engines can be used for monitoring engine performance, creating the potential for lowering emissions and fuel costs. Recently a method was proposed to determine the mean flywheel torque from instantaneous engine speed using the n-th order Fourier series, where n is the number of cylinders firing per crank revolution. However, instantaneous engine speed is affected by two separate torque contributions. The torque resulting from reciprocating masses in the engine, i.e., reciprocating torque, and the torque produced by combustion pressure, i.e., gas torque. Gas torque and reciprocating torque signals have the same frequency but are in opposite phases. Since the resultant torque at the flywheel is the sum of gas and reciprocating torques, there is a need to remove reciprocating torque from the total torque at the flywheel. This requires knowing whether gas or reciprocating torque has a larger amplitude. Here, a method is proposed to determine whether gas or reciprocating torque has a larger amplitude via the phase of engine speed; this method is a step towards a practically implementable virtual torque sensor. This methodology of torque estimation is evaluated through on-road testing on a truck powered by a Cummins ISX12G compressed natural gas engine at engine speeds of 1000-2100 RPM and at different transmission gear ratios and throttle conditions. The proposed algorithm demonstrated a mean absolute percentage error of 13.2%.