The familiar continuously variable steel belt transmissions being introduced for automotive use are “straight” CVT's, where total speed ratio span is limited to capability of the variable speed belt and pulley system. Meeting start-up performance and gradeability requirements penalizes the final drive or axle ratio resulting in the transmission reaching the maximum overdrive ratio prematurely.
The Ford Research front wheel drive Dual Mode CVT employs a torque converter for start-up in addition to a full range of CVT operation as a means of improving both smoothness and fuel economy.
The torque converter and a separate chain drive power path from the engine to the variable speed unit are arranged in parallel. This combination provides an approximate 30% effective increase in ratio coverage to 7:1. Vehicle fuel economy is thus improved an estimated 5-9% during highway driving because the final drive ratio can be reduced 30%. Vehicle start-up through the torque converter is inherently smooth.
A 4 × 4 system is also derived from the base FWD, having a bevel gear power take-off near the vehicle center.