Nissan's Xtronic CVT Technology Delivers
Nissan Motor Co., Ltd. introduced its first version of the Continuously Variable Transmission (CVT) to the Japanese market in the 1992 March compact. Since then, Nissan has made a number of industry-leading advances in CVT technology that have allowed it to expand the application of the advanced transmission for use with higher-torque engines.
This extensive work continues to pay off for model year 2007, with the expanded availability of the advanced Xtronic CVTÔ on a variety of Nissan vehicles in North America, including Altima (non-Hybrid models), Maxima, Murano, Sentra and Nissan’s all-new, entry-level model, the Nissan Versa hatchback and sedan. The Xtronic CVT is standard on both Maxima and Murano.
The Xtronic CVT differs from conventional automatic transmissions by featuring an infinitely variable gear ratio between its lowest and highest gears. Whereas a traditional automatic transmission typically makes large ratio jumps from one static gear to the next, the Xtronic CVT flows smoothly by transitioning through gear ratios with the feel of one perfectly calibrated gear.
The latest, third-generation Xtronic CVT retunes a number of features to improve performance, including the use of a smaller, more efficient oil pump; the adoption of a compact chain drive for 2.0-liter engine applications (which reduces the transmission size as a whole); and improvement of the precision of the pulley diameter control, allowing for more efficient belt pressure, more reliable torque transfer and improved fuel economy.
“Across the industry, manufacturers are sacrificing performance for efficiency and economy,” said Bill Bosley, vice president and general manager, Nissan Division. “But we refuse to detract from the Nissan driving experience. The expanded use of our advanced Xtronic CVT is the ideal way to offer sporty performance and fuel efficiency in one package.”
How Xtronic CVT Works While automatic and manual transmissions use multiple gear sets with an integral clutch and bands to achieve separate gear ratios, Xtronic CVT uses an infinitely adjustable ratio design. For example, instead of jumping from a 2nd gear ratio of 1.950 to a 3rd gear ratio of 1.392, Xtronic CVT can rapidly progress through 1.950, 1.949, 1.948 - stepping seamlessly through 1.392 as the diameter of its pulleys gradually adjust. Because of this progression, the Xtronic CVT “changes” ratios with no perceptible pauses, jerks or lurches, virtually eliminating traditional shift shock.
Each pulley is composed of two stout cones, each point facing the other, similar to a yo-yo. A steel belt with a V-shaped cross section connects the cones. As the engine speed increases, the cones of the drive pulley slowly come together, gradually pushing the belt further from the pulley’s axis. Simultaneously, the driven pulley’s cones are moving farther apart, easing the belt closer to the axis of the driven pulley.
The pulleys are controlled to proportionately expand and contract so the ratio of the drive diameters between the two pulleys can be varied over a wide range. The Xtronic CVT offers a spread of “gear” ratios between its lowest and highest range (2.371:1 to 0.439:1 for the 3.5-liter V6 engine; 2.349:1 to 0.394:1 for the 2.5-liter 4-cylinder engine; 2.349:1 to 0.394:1 for the 2.0-liter 4-cylinder engine and 2.561:1 to 0.427:1 for the 1.5-liter through 1.8-liter 4-cylinder engines).
At the heart of the Xtronic CVT is a high-strength, flexible steel belt. The strength of this belt enables the transmission to handle a high amount of torque input, fitting for multiple sizes, displacements and power levels of different Nissan engines.
Xtronic CVT Benefits Xtronic CVT offers a number of benefits over traditional automatic or manual transmissions. The most obvious benefit is the smooth ratio changes, versus the “clunk” of a shifting transmission that is familiar to most drivers. In eliminating these “steps,” the Xtronic CVT allows the engine to run closer to its optimal rpm, rather than dipping below or working above it like an automatic or manual transmission. By maintaining ideal engine speed and avoiding unnecessary engine rpm, the Xtronic CVT optimizes fuel economy and emissions performance.
For additional fuel economy, Xtronic CVT offers an expanded torque converter lockup range. While a conventional automatic transmission locks up in the mid-to-high speed range, a traditional CVT transmission only benefits from the torque converter at startup. Recognizing this, Nissan engineered the Xtronic CVT torque converter with a lockup range that extends further into lower speeds, allowing for a better range of manual-transmission-like direct transfer of efficient engine power.
Additionally, Xtronic CVT has numerous other advantages over conventional CVT transmissions. Xtronic CVT boasts a wider gear ratio, which allows for improvements in both performance and economy. And, thanks to smaller minimum drive pulley radius, Xtronic CVT delivers better acceleration performance than traditional CVTs, and its smaller minimum driven pulley radius allows for better fuel economy.
“Nissan Motor Co., Ltd. has been a leader in CVT research since the 1970s and currently offers CVTs in Asia and Europe in addition to the North American market, where our advanced Murano SUV paved the way for Nissan’s expansion of Xtronic CVT technology in the United States,” said Bosley. “We’re pleased that Nissan is now able to offer a great balance of what drivers need – as well as what they want – in a broad range of vehicles, from our flagship Maxima to our entry-level Versa.”