Comprehensive Theory of Viscous Coupling Operation

Viscous couplings continue to be an important part of modern automobile drive systems and provide a cost effective and reliable traction control system. Several million units are built into vehicles each year. While the operation of the viscous coupling under simple shear torque mode was reasonably well understood, its operation under ‘humping’ or torque amplified mode was not fully understood. Current explanations do not fully account for all observed phenomena and certainly cannot provide a simulation and design optimization tool.

This paper describes a comprehensive theory that utilizes thermodynamic, fluid mechanic, structural and mechanical analysis and verifies the mathematical model with a visual simulation tool and correlates the results to experimental observations. The proposed theory identifies, defines and explains the conditions necessary for initiating and sustaining the self-induced torque amplification that is the essential part of the ‘humping’ phenomena. The hypotheses are validated by the reasonable agreement of the model with test results.