A Control-Oriented and Physics-Based Model of the Engine Crank Mechanism Friction for the Base Calibration: Parametric Analysis

Over the last decades, internal combustion engines have undergone a continuous evolution to achieve better performance, lower pollutant emissions and reduced fuel consumption. This evolution involved changes in the engine architecture needed to perform advanced management strategies. Therefore, Variable Valve Actuation, Exhaust Gas Recirculation, Gasoline Direct Injection, turbocharging and powertrain hybridization have widely equipped modern internal combustion engines. However, the effective management of a such complex system is due to the contemporaneous development of the on-board Engine Electronic Control Unit (ECU). In fact, the additional degrees of freedom available for the engine regulation highly increased the complexity of engine. In the design phase of the engine architecture and in the subsequent base calibration process, it is of fundamental importance to analyse the energy flows of the individual mechanical components, or to predict the friction in the eventuality of possible component modifications. The use of the 1D models allows the thermo-fluid dynamics simulation of the adopted solutions and the evaluation of the corresponding energy effects. Currently, the Friction Mean Effective Pressure (FMEP) analysis is entrusted to empirical relationships whose use is bound to the need to calibrate the relationship itself by means of experimental data of the engine. These models do not allow to predict the effect of any architectural changes in terms of FMEP. In order to overcome this criticality, the authors propose the possibility of using specific numerical Physics-Based models based on a multi body approach. A parametric approach to analyse the sensitivity of the model has been conducted. From these analyses, it is possible to take advantage of the parameters identified for its calibration. To determine the quality of the model used in reproducing physical phenomena, 14 experimental FMEP measurements were used: from the first results obtained, we note that the modelling approach used respects, for at least two orders of magnitude, the experimental mechanical losses. In particular, the average deviation estimated between the simulated and experimental FMEP values in the 14 operating points is about 12%.