NON-UNISON DYNAMICS OF MULTIPLE CENTRIFUGAL PENDULUM VIBRATION ABSORBERS

Centrifugal pendulum vibration absorber (CPVA) systems are used to dec rease steady state torsional vibration levels and extend operating ran ges for rotating and reciprocating machinery. They are typically sized and designed for a given harmonic using the assumption that a set of identical absorbers move in exact unison. Herein an investigation is c arried out to determine the consequences, in terms of system performan ce, of a recently uncovered dynamic instability of this unison motion. The system considered consists of a rigid rotor and N CPVA's riding o n epicycloidal paths tuned to order n, the same as the dominant order of the applied torque. Using two co-ordinate transformations and the m ethod of averaging, the system dynamics can be modelled by a set of 2N first order, internally resonant, autonomous differential equations. A bifurcation analysis of these equations shows that the post-bifurcat ion dynamics, in which a single absorber moves out of step with its pa rtners, is dynamically stable and leads to the worst-case (that is, th e smallest) operating torque range. Furthermore, it is found that the rotor acceleration undergoes a mild saturation, leading to slightly im proved performance beyond the instability. Analytical estimates of the torque range and the rotor acceleration are derived based on a trunca ted version of the equations, and more accurate estimates are obtained from a numerical solution of the non-truncated equations. The results are compared with numerical simulations. (C) 1997 Academic Press Limi ted.