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; In other cases the obtained precision is not very high.
This work presents the development of a torque estimation procedure based on the instantaneous engine speed measurement. The steps that allowed defining this procedure are briefly explained in the following.
The definition of a model that describes the torsional behavior of the engine-load system made first possible to analyze the relationship between the corresponding frequency components of the instantaneous engine speed fluctuations and the indicated torque developed by the cylinders. This enabled the development of an indicated torque frequency component estimation algorithm based on the analysis of the instantaneous engine speed fluctuation.
Studying the nature of the relationship of 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 an L4 engine mounted on a test bench. The algorithm can be applied without limitations also to an engine mounted on the vehicle and to other engine configurations as it will be discussed in detail in the paper. The obtained precision is compatible with onboard application, like for example torque-based engine management strategies.