Jatco-Nissan CVT adds planetary gear state for greater ratio span
Working together
with its part-owned transmission supplier Jatco, Nissan has developed a next-generation CVT that is
lighter, more compact, more efficient and which has a 20 percent broader ratio span than any other CVT.
The new XTRONIC, aimed at compact cars, achieves its wide 7.3:1 ratio spread through the addition of a two-speed planetary sub-geartrain. This allows it to avoid traditional CVT compromises and to be more effective at both ends of the speed range. The new system is able to both provide a low initial ratio for positive starting off performance and a high ratio - engaged at around 20 km/h - to allow greater maximum speeds, improved fuel economy and lower noise levels thanks to lower engine speeds. The planetary sub-transmission remains in high during deceleration in order to keep engine revolutions low, again saving fuel and hence lowering CO2 emissions.
A further advantage of the two-stage system is that the steel push-belt and pulleys can be smaller, benefiting compactness and weight. This in turn allows the belt to run with less lubricant drag as it is clear of the oil sump. Nissan and Jatco put the overall friction reduction at 30 percent compared with conventional CVT designs. The launch device is still a torque converter, which locks up fully at around 15 km/h.
The companies claim an overall fuel economy improvement of 10 percent over comparable vehicles fitted with the familiar type of CVT. Nissan has not yet disclosed the transmission's torque and power ratings, nor stated which of its models will feature the new XTRONIC system.
One candidate could be the compact urban crossover based on the Qazana concept shown at the 2009 Geneva show and set for commercial launch in 2010.
Story Filed: 11/24/2009
By Tony Lewin, managing editor DCTfacts.com