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Enhancement of the Accuracy of the Modified (P–ω) Method Through the Implementation of a Nonlinear Robust Observer

[+] Author Affiliations
G. A. Kfoury, N. G. Chalhoub, N. A. Henein

Wayne State University

W. Bryzik

U.S. Army Tank-Automotive RDE Center

Paper No. IMECE2005-80115, pp. 1087-1096; 10 pages
doi:10.1115/IMECE2005-80115
From:
  • ASME 2005 International Mechanical Engineering Congress and Exposition
  • Dynamic Systems and Control, Parts A and B
  • Orlando, Florida, USA, November 5 – 11, 2005
  • Conference Sponsors: Dynamic Systems and Control Division
  • ISBN: 0-7918-4216-9 | eISBN: 0-7918-3769-6
  • Copyright © 2005 by ASME

abstract

The original version of the (P–ω) method is a model-based approach developed for determining the instantaneous friction torque in internal combustion engines. This scheme requires measurements of the cylinder gas pressure, the engine load torque, the crankshaft angular displacement and its time derivatives. The effects of the higher order dynamics of the crank-slider mechanism on the measured angular motion of the crankshaft have caused the (P–ω) method to yield erroneous results, especially, at high engine speeds. To alleviate this problem, a nonlinear sliding mode observer has been developed herein to accurately estimate the rigid and flexible motions of the piston-assembly/connecting-rod/crankshaft mechanism of a single cylinder engine. The observer has been designed to yield a robust performance in the presence of disturbances and modeling imprecision. The digital simulation results, generated under transient conditions that represent a decrease in the engine speed, have illustrated the rapid convergence of the estimated state variables to the actual ones in the presence of both structured and unstructured uncertainties. Moreover, this study has proven that the use of the estimated rather than the measured angular displacement of the crankshaft and its time derivatives can significantly improve the accuracy of the (P–ω) method in determining the instantaneous engine friction torque. However, the effects of structural deformations of the crank-slider mechanism have rendered the original version of the (P–ω) method to be inapplicable at high engine speeds. This problem has been addressed herein by modifying the formulation of the (P–ω) method in order to account for the first two elastic modes of the crankshaft torsional vibration. The simulation results confirm the good performance of the modified (P–ω) method in determining the instantaneous friction torque at high engine speeds.

Copyright © 2005 by ASME

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