Development of the Next-Generation Half-Toroidal CVT with Geared Neutral and Power-Split Systems for 450 N-m Engines

The world’s first vehicle with a half-toroidal CVT POWERTOROS Unit has been manufactured since November 1999. This continuously variable transmission (CVT) has a torque capacity of 390 N-m and ratio coverage of 4.33. In recent years, demand for a next-generation half-toroidal CVT that provides better fuel economy and ease of assembly and mounting has been growing in response to global environmental issues. The authors developed a new halftoroidal CVT that offers a wider ratio range, a more compact size, higher torque capacity, and higher efficiency. Major features of this new half-toroidal CVT include a gearedneutral system and a power-split system. We successfully downscaled the current CVT by eliminating conventional launching devices, such as the torque converter, friction clutch, etc., and focused our energies on a geared-neutral system. In concert with such steps, we achieved higher efficiency in the mid- to high-speed ranges by using a power-split system. Whether operating in low-speed or high-speed mode, the geared-neutral system combined with the power-split system, provides a wider ratio coverage and better fuel economy. Major challenges of this CVT included control optimization vehicle acceleration from a stop using the geared-neutral system, and mode changing between the geared-neutral and power-split systems. We mounted both systems to a test vehicle, the Lexus LS430 (430 N-m), and demonstrated the effectiveness of our unique control concept for accelerating the vehicle from a stop, and mode changing between low- and high-speed driving. Bench test results and an evaluation of the driver’s operation and performance feel of the vehicle are also reported.