Effects of structural deformations of the crank-slider mechanism on the estimation of the instantaneous engine friction torque

The focus on the current study is to assess the effects of structural defor mations of the crankshaft/connecting-rod/piston mechanism on the computatio n of the instantaneous engine friction torque. This study is performed in a fully controlled environment in order to isolate the effects of structural deformations from those of measurement errors or noise interference. There fore, a detailed model, accounting for the rigid and flexible motions of th e crank-slider mechanism and including engine component friction formulatio ns, is considered in this study. The model is used as a test bed to generat e the engine friction torque, T-fa, and to predict the rigid and flexible m otions of the system in response to the cylinder gas pressure. The torsiona l vibrations and the rigid body angular velocity of the crankshaft, as pred icted by the detailed model of the crank-slider mechanism, are used along w ith the engine load torque and the cylinder gas pressure in the (P - omega) method to estimate the engine friction torque, T-fe. This method is well s uited for the purpose of this study because its formulation is based on the rigid body model of the crank-slider mechanism. The digital simulation res ults demonstrate that the exclusion of the structural deformations of the c rank-slider mechanism from the formulation of the (P - omega) method leads to an overestimation of the engine friction torque near the top-dead-center (TDC) position of the piston under firing conditions. Moreover, for the re mainder of the engine cycle, the estimated friction torque exhibits large o scillations and takes on positive numerical values as if it is inducing ene rgy into the system. Thus, the adverse effects of structural deformations o f the crank-slider mechanism on the estimation of the engine friction torqu e greatly differ in their nature from one phase of the engine cycle to anot her. (C) 1999 Academic Press.