Role of the Crank-Slider Structural Deformations in the Prediction of the Instantaneous Engine Friction Torque

Abstract

Abstract The focus of the current study is to assess the effects of structural deformations of the crankshaft/connecting-rod/piston mechanism on the computation of the instantaneous engine friction torque. This study has to be performed in a fully controlled environment in order to isolate the effects of structural deformations from those of measurement errors or noise interference. Therefore, a detailed model, accounting for the rigid and flexible motions of the crank-slider mechanism and including Rezeka and Henein’s (1984) engine component friction formulations, is considered in this study. The model is used as a test bed to generate the engine friction torque, Tfa, and to predict the rigid and flexible motions of the system in response to the cylinder gas pressure. The torsional vibrations and the angular velocity of the crankshaft, as predicted by the detailed model of the crank-slider mechanism, are used along with the cylinder gas pressure in the (P-ω) method to estimate the engine friction torque, Tfe. This method is well suited for the purpose of this study because its formulation is based on the rigid body model of the crank-slider mechanism. The digital simulation results demonstrate that the exclusion of the structural deformations from the formulation of the (P-ω) method leads to an overestimation of the friction torque near the top-dead-center (TDC) position of the piston under firing conditions. Moreover, for the remainder of the engine cycle, the estimated friction torque exhibits large oscillations and takes on positive numerical values as if it is inducing energy into the system.