Torsional Vibration Analysis of a Test Rig Driveline Equipped with a Flexible Coupling

The paper deals with a case study from the automotive industry and relative to a test rig of internal combustion engines: the output shaft of the engine transmission is connected with an electromechanical brake by means of a transmission shaft which hosts a torsional coupling with rubber elements. The engine test cell was developed several years ago; over years, the engine operations and performance have been changed, in terms of output power and torque, entailing more severe dynamic loads affecting the driveline members. In this scenario, early failures of the rubber elements of the flexible coupling have occurred. The goal is to solve the problem by bringing the fewest possible modifications to the cell layout. An experimental campaign was thus carried out, with the aim of characterizing the current system dynamic behavior and finding possible modifications able to solve the problem. In particular, torsional vibration measurements have been achieved by a coder-based technique using high-quality optical sensors and equidistantly spaced markers (zebra tape) on the rotating components. The measured data were analyzed in the Time, Frequency, Time-Frequency, and Order domains. The paper presents the experimental setup, the data processing and the results obtained from tests performed on the original system and on a modified version of the transmission driveline, after changing the elastodynamic properties of the coupling. Key-Words: Torsional Vibration; Instantaneous Angular Speed; Flexible Coupling; Experimental Test; TimeFrequency Analysis; Order Analysis