Contribution to the definition of the torsional stiffness of the crankshaft of a diesel engine used in heavy-duty vehicles

Abstract

A new approach for determining the torsional stiffness coefficient of an equivalent mechanical system's crankshaft section, which can be used to study torsional vibrations, is presented. In order to describe mathematically the torsional vibration of a reciprocating engine, it is necessary to replace the actual system consisting of the crankshaft, connection rods, and reciprocating elements by an equivalent system, usually modelled as a lumped-parameter system. The present authors, in accordance with their personal experiences, have found the determination of the equivalent system's parameters to be a very important and demanding task, especially in regard to torsional stiffness and damping coefficients. This paper analyses all aspects of determining a crankshaft section's torsional stiffness coefficient, which is the most complex element in a torsional dynamic model of a crankshaft. The method analysing the crank torsional stiffness coefficient determination has been given in the literature. The real boundary conditions of the crankshaft are emphasized as a problem, which makes determination of the torsional stiffness coefficient of the crankshaft section even more difficult. An indirect method for this determination is explained in this paper. By using this method, the real boundary conditions of the crankshaft of the diesel engine used in heavy-duty vehicles are considered, and the results obtained are reliable and confirmed by experiment.