Powertrain Torsional Model Development for On-Board Indicated Torque Estimation

Effective and precise torque estimation is a great opportunity to improve actual torque-based engine management strategies. Modern ECU often already implement algorithms to estimate on-board the torque that is being produced by the engine, even if very often these estimation algorithms are based on look-up tables and maps and cannot be employed for example for diagnostic purposes. The indicated torque estimation procedure presented in this paper is based on the measurement of the engine speed fluctuations, and is mainly based on two separated steps. As a first step a torsional behavior model of the powertrain configuration is developed. The enginedriveline torsional model enables to estimate the indicated torque frequency component amplitude from the corresponding component of the instantaneous engine speed fluctuation. This estimation can be performed cycle by cycle and cylinder by cylinder. As a second step the analysis of the relationship between the indicated torque mean value over an engine cycle and the amplitude of its frequency components, allowed defining the final estimation algorithm that reconstructs the indicated torque mean value starting from the instantaneous engine speed fluctuation analysis. The developed approach has been applied with success to a diesel engine mounted on-board a vehicle. The obtained precision is compatible with on-board application like for example torque-based engine management strategies.