TRANSMISSIONS: THE NEXT (STEPLESS) STEP?

Several developments in the car industry indicate that cars in the 21st century will mainly use gearless and stepless transmission systems. This article explains some of the possibilities. Since the introduction of automatic transmission in the 1920s, there has until recently been little real change in the transmission industry. Peak power of usually about 6500rpm is needed for best acceleration and top speed, and peak torque near about 3500-4000rpm is needed for optimal fuel consumption. To maintain these states for any road speed, it is necessary to decouple the fixed links between engine and wheels required by conventional mechanical gearboxes. Perhaps the best-known continuously variable transmission (CVT) is the Van Doorne Transmission (VDT) system of variable-diameter pulleys, already supplied to over 250,000 cars, and expected to exceed a million by 2000. It typically has 13% better fuel economy, and 7-8% faster acceleration than a mass-produced four-speed automatic gearbox. The Torotrak infinitely variable transmission (IVT), using a double-toroid concept, is claimed to have 15% less fuel consumption and 30% less emissions than the gearbox. Other possibilities include: (1) 'intelligent' automatic mechanical gearboxes; (2) the Lotus hydromechanical transmission; and (3) electric drive systems.