Power Transmission of Half-Toroidal Traction Drive Continuously Variable Transmission (Four-Wheel-Drive CVT Design and Its Performance)

Four-wheel drive offers cruising stability and high road gripping force at the expence of the power weight ratio due to implementation of an additional mechanism of a center differential gear box with a torque split clutch. We developed a dual-cavity half-toroidal traction-drive continuously variable power transmission (CVT) for 3 L passenger cars in 1990, which can be easily remodelled into a CVT with two output shafts since it has two independent CVT units. Since the CVT has a hydraulic-control equal-force-transmitting mechanism for speed ratio control, it is easy to synchronize the force transmission of front and rear axles without using a center differential gear box. In this paper we describe the mechanism, efficiency and control principle for the equivalent function of a center differential gear box of the four-wheel-drive CVT with nominal input torque capacity of 250 N•m, rotational speed of 5500 rpm and maximum speed ratio range of 1: 8.7.