Abstract
Half-toroidal CVTs have been developing for next-stage power transmissions for automobiles since 1980 in Japan. Refined synthetic-traction fluid and heat-treated steels extend the transmitting capacity over 250kW at a maximum Hertzian pressure of 3GPa and a traction coefficient of 0.05at 75 ? . The traction drive inheres scientific themes of traction-fluid rheology, spin in EHL contact, heat-transfer of rolling elements, life prediction and stability of a speed-ratio servomechanism. This paper focuses the influence of spin in the traction contact on the efficiency and heat generation, and shows a recently developed dual-cavity 4WD-CVT for distributing torque to front and rear axles without a center differential gear unit by controlling front and rear speed-ratios independently. It transmits nominal input-torque of 270Nm and rotational speed of 5600rpm in a variable speed-ratio range of 1:8.7.