A comprehensive study of self-induced torque amplification in rotary viscous couplings

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical and Aerospace Engineering


Bandaru Ramarao

Second Advisor

John LaGraff


Torque, Amplification, Rotary, Viscous couplings, Flow-structure interaction, automotive materials

Subject Categories

Mechanical Engineering


Rotary viscous couplings are important elements of traction control systems in automotive drive trains. The nature of self-induced torque amplification (STA) in rotary viscous couplings is examined in this dissertation.

Investigators have proposed that the increased torque is caused partially by Coulomb friction, but are unable to fully explain the forces necessary to initiate and sustain the friction torque. Current hypotheses, while identifying possible contributory factors, do not provide a coherent explanation consistent with test results and theoretical analysis. Onset of STA correlates strongly with rise in internal pressure within the viscous coupling above a critical threshold, yet no explanation exists for this correlation.

The major contribution of this work is in the development of a coherent theory that identifies, defines and explains the conditions necessary for initiating and sustaining STA in rotary viscous couplings. This work establishes and verifies the processes that produce STA by proposing a sequence of events which are qualitatively viable and consistent with one another, with respect to a chain of causality. The various thermodynamic, hydrodynamic, structural and mechanical processes are delineated and tested using a triangulation methodology consisting of theoretical analysis, computational dynamic simulation and experimental observations.

This investigation differs from others by studying the interaction between fluid mechanics and structural mechanics within the coupling. The reciprocal influences of the structural response of the inner plate tabs upon the fluid dynamics in the gaps between the inner and outer plates is identified as the main cause of the sequence of events that results in STA.

The abruptness of the STA mode is decisively linked to a sudden change of the flow field from a mixture of air and silicone, into a single phase flow of silicone due to internal pressure rise and dissolving of air into the silicone.

The simulation of the dynamics of the STA phenomenon, utilizing mathematical relationships, resulted in a good correlation between the predicted dynamics of torque development and test results.

The hypotheses proposed in this dissertation to explain the complex sequence of events that result in self-induced torque amplification (STA) in rotary viscous couplings, are validated by mathematical and dynamic simulation models and experimental tests.


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