Effects of filtering the angular motion of the crankshaft on the estimation of the instantaneous engine friction torque

The focus of this study is to investigate the effects of filtering the actu al angular displacement, velocity and acceleration of the crankshaft on the computation of the instantaneous engine friction torque. These effects are isolated from those of measurement errors and/or noise by relying on a det ailed model of the crank-slider mechanism to generate the rigid and flexibl e motions of the piston/connecting-rod/crankshaft mechanism along with the engine friction torque. The (P - omega) method is used herein to estimate t he instantaneous engine friction torque based on the actual and the filtere d angular displacement, velocity and acceleration of the crankshaft. The di gital simulation results have demonstrated that the (P - omega) method cann ot produce an acceptable estimation of the instantaneous engine friction to rque in spite of filtering the actual angular motion of the crankshaft. It should be mentioned that the low-pass filter is commonly implemented to att enuate the measurement noise and the effects of structural deformations on the measured angular velocity of the crankshaft. However, the ineffectivene ss of the low-pass filter stems from the non-linearities of the crank-slide r mechanism that induced superharmonic and combination resonance frequencie s in the angular displacement, velocity and acceleration of the crankshaft. The filter has severely attenuated some of the superharmonic resonance fre quencies, which constitute an important part of the rigid-body behavior of the crankshaft that is needed by the (P - w) method to accurately predict t he engine friction torque. Moreover, the filtered signals would still be co ntaminated by the combination resonance frequencies that may appear in the low-frequency range commonly assumed to be dominated by the frequency compo nents of the rigid-body motion of the crankshaft. (C) 2000 Academic Press.