Analysis of tight corner braking phenomenon in full-time 4WD vehicles

Viscous coupling units (VCUs) are widely used in full-time four-wheel drive vehicles (full-time 4WDs) as a differential limiting device. A VCU must provide optimized torque transfer characteristics both for maximum traction and for maneuverability during tight cornering. We analyzed the effect of VCU torque transfer characteristics on the development of a “tight corner braking phenomenon”. The results of this analysis were verified to have a high correlation with experimental data, and have enabled us to determine the optimum torque transfer characteristics which allow for minimization of the tight corner braking phenomenon for any given VCU design.