Nissan Expands On Revolutionary CVT
Japanese automaker Nissan has supplied further technical details of the power train incorporating its innovative XTRONIC CVT transmission, which we reported on last year. The three-cylinder engine forms part of Nissan’s ambitious 2010 Green Paper medium term strategy to reduce the company’s vehicle and corporate CO2 emissions. Two main thrusts – Pure Drive, for conventional combustion vehicles and Zero Emissions, for electric models – make up the engineering side of the campaign.
Impressive claims are made for the new XTRONIC CVT transmission, which has the unique feature of a supplementary, two-speed planetary sub-transmission operating in series with the push belt CVT variator. The use of this system has many important benefits, the most obvious being a dramatic stretching of the unit’s overall gear ratio spread from the typical 6.0 of a normal CVT to 7.3. This enables taller overall gearing and lower rpm at cruising speed for lower noise and fuel consumption levels, but without any loss in low-speed drivability or acceleration response.
Far from adding to the bulk of the design, the planetary sub-transmission arrangement enables a more compact (by 10 percent) and lighter (by 13 percent) overall package compared with a conventional unit of similar torque handling capacity.
Efficiency is also enhanced by a significant 30 percent reduction in internal friction, leading Nissan and its transmission partner Jatco to claim a 10 percent drop in fuel consumption compared with a standard CVT.
Though detailed data has not yet been released, the overall benefit is likely to be greater still when the new-generation Nissan engines are taken into account. The three cylinder HR12DE of 1.2 liters achieves a friction reduction of 20 percent through the application of bore circularity machining to the cylinder block, as well as through having fewer moving parts. Nissan claims equal NVH performance to a four cylinder unit through use of a balancer shaft. Preliminary specifications issued at the Geneva motor show in March give an output of 80 hp for the standard version and 99 hp for the supercharged model, which also allows an improvement in CO2 emissions from 115 to 95 g/km. Both versions incorporate an idle-stop system, which accurately positions the crankshaft when the engine is cut. This, claims Nissan, results in an idling stop function that works so smoothly in everyday driving that the driver will “. . . hardly be aware of it.” Part of the idling stop system is an internal lock mechanism on the CVT unit’s sub-planetary gear. This allows the engine to restart on a sloping road without the vehicle rolling backwards.
The engine and transmission combination offer fuel economy of 26 km per liter (less than 4 liters per 100 km) on the Japanese test cycle, prompting Nissan to claim best-in-class performance.
The engine and transmission was first seen on the new Nissan March (Micra in Europe) that launched in Japan in summer 2010. A larger 1.5 liter, four cylinder version of the engine with the novel feature of dual injectors per cylinder was announced at the same time. Set to appear in the new Juke urban crossover, the engine claims a 4 percent saving in fuel consumption and CO2 emissions.
Other measures announced as part of Nissan’s Pure Drive program include an automatic transmission version of the diesel X-TRAIL SUV for the Japanese market, fitted with a new type of NOx trap that uses fewer noble metals but which complies with Japan’s new Long Term Emissions Regulations, the strictest in the world.
Story Filed: 10/02/2010
By Tony Lewin, managing editor DCTfacts.com