TOKYO. - The hot acronym here - and all over the world - is CVT. Automakers suddenly have jumped feet-first into continuously variable transmission development, and now the race is on to see who can make the most of this fascinating, though hardly new, technology.
Nissan is the world's first automaker to bring the unique, "toroidal" CVT to production, although other automakers appear to have imminent production plans for similar toroidal CVT technology. Mazda Motor Corp., for one, also unveiled a toroidal-type CVT here. Nissan's new CVT can handle big engines with big power, formerly a CVT no-no.
Nissan calls its unit Extroid CVT; it is fitted as optional equipment in the company's rear-drive Cedric. That car is equipped with a turbocharged version of the 3L DOHC "VQ" V-6, which produces 276 hp and 286 lb.-ft. (388 Nm) of torque.
The new Extroid CVT uses two sets of "power rollers" to transmit drive torque between an input "disc" connected to the crankshaft side and an output disc connected to the driveshaft side of the CVT transmission. The electro-hydraulically controlled power rollers - four in all - shift their angle of attack in relation to the input and output discs, varying the effective drive ratio.
The ratio of the sizes of the "circles" created by the rotating power rollers and input/output discs corresponds to each element's rotational speed, which also is equal to the effective gear ratio. The overall ratio range is 4.4:1 (see graphic).
Drive, however, does not come from metal-to-metal contact: instead, a special "traction oil" serves to simultaneously lubricate, cool and provide the friction "surface" between the elements.
The application of the Extroid CVT's high surface pressures between elements causes Nissan's traction oil to interlock molecules in such a way as to align them - the oil then bears all of the shear force between the elements. It is an elegant and amazing technology, jointly developed with Japanese oil company Idemitsu.
The only problem, at present, appears to be price. Questioning of engineers and marketing personnel arrives at what seems to be a price premium of approximately $2,500 over a standard 4-speed automatic transmission. Engineers believe this price can be greatly reduced, however, with volume. Currently, Nissan is producing just 300 Extroid CVTs per month.
