Continuously Variable Planetary:
The next frontier in IUV drivetrain design

By William Klehm III
CEO, Fallbrook Technologies

Right now, if you’re an IUV designer or OEM, you have two basic choices for drivetrains – a conventional multi-speed gear transmission or a hydrostatic infinitely variable transmission. Although these are fine for certain applications, they don’t really work that well for a lot of IUV’s,

The continuously variable transmission (CVT) has been around for awhile, and has always been considered a great idea in principle for IUV’s, but there has never been a CVT that really brought together the three drivetrain “must-haves”: performance, price and package.

Now there is one. The NuVinci™ continuously variable planetary (CVP) transmission from Fallbrook Technologies Inc. of San Diego, California. The NuVinci CVP eliminates fixed gear ratios, provides excellent torque efficiency for both gas and electric IUV’s, can extend battery life and range, provides a smoother, more enjoyable riding experience, and is both compact and scalable enough to work across a wide range of product lines. The NuVinci CVP is available in both standard continuously variable and infinitely variable (i.e., capable of powered zero) configurations.

What this means is that IUV designers and OEMs now have at their disposal a drivetrain that provides benefits never before possible – a new technology canvas that will enable designers and OEMs to create vehicles that will do their jobs better and provide opportunities to expand the market for IUV’s.

How the NuVinci CVP works

The NuVinci CVP, in its standard continuously variable embodiment, uses a set of rotating and tilting balls positioned between the input and output components of a transmission that tilt to vary the speed of the transmission. Tilting the balls changes their contact diameters and varies the speed ratio. The same basic parts can be used to create an IVT simply by changing the power path within the variator. No external coupling or summing devices are needed.

As a result, the NuVinci CVP offers seamless and continuous transition to any ratio within its range, thus maximizing overall powertrain efficiency, with no jarring or shocks from the shifting process, and improving acceleration, performance and overall vehicle efficiency over conventional IUV transmission options.

Compared to traditional CVTs, the NuVinci CVP is less complex, has considerably fewer parts, offers more stable control and scalability across product lines, is better packaged, and is less expensive to manufacture and assemble.

NuVinci technology combines the advantages of a toroidal traction CVT with the time-proven versatility of the planetary gear arrangement. It uses rolling traction to transfer torque, just like toroidal transmissions. But unlike toroidal CVTs, it distributes the transmitted torque over several spheres in an inherently stable configuration, thus lowering the total clamping force required and significantly improving durability, control stability, and torque density. Torque inputs can be summed or divided, just as in a conventional planetary. Ratio control is stable, and can be actuated down the center line of the transmission, which again is similar to the proven planetary transmission.

Torque is transferred using a special traction fluid that fills the inside of the hub. There is a microscopic space between the rotating ball elements and both the input and output components. When the fluid passes through this microscopic space, the very high pressure of the rolling contact causes it to solidify momentarily. For that moment, the fluid has a rigid structure. This allows torque to be transferred between the ball and the input/output elements, and eliminates the need for any metal-to-metal contact. The fluid is manufactured by Valvoline and is marketed under the brand name Invaritorc™ 638.

The only recommended maintenance for the NuVinci CVP is that the fluid be changed periodically. The change interval will be determined by the manufacturer and type of use, with many applications being fill-for-life.

Benefits for IUV designers and OEMs

Until now, IUV designers had two basic drivetrain choices: a geared transmission or a hydrostatic. Both these choices have significant limitations. The geared transmission can’t be an IVT, and requires torque disruptions to shift. The hydrostatic transmission almost always is an IVT, but is noisy, inefficient, and it struggles with low speed maneuvers under load because its losses are so high.

The NuVinci CVP offers IUV designers and OEMs an entirely new way to approach the drivetrain issue. It is durable, reliable, and much quieter than either a hydrostatic drive or a geared transmission. It also can efficiently handle both high- and low-speed inputs, just like a geared transmission can.

The NuVinci CVP delivers excellent torque efficiency and reduced load sensitivity, which results in a smoother more steady ride under changing loads. It offers a true powered zero state, so the vehicle will not move if it is left running on an incline – something most hydrostatic drivetrains can’t accomplish.  

Applications for IUV’s/ Mobile Equipment

The NuVinci CVP can be designed into just about any type of IUV. Its unique geometry is particularly suited to electric vehicles, because it can be tightly integrated with an electric motor, thus saving cost, weight and package space. It also delivers significant benefits in gas-powered vehicles as well, including more responsive shifting, high torque capacity, and greater durability.

The NuVinci CVP allows both gas and electric motors to operate more efficiently by not overloading them in normal operation. Vehicle performance and rider experience is enhanced with improved hill climbing ability, smoother/quicker acceleration, higher top-end speed, increased load carrying and towing capacity, better accommodation of larger adult riders, and extended range and battery life.

The NuVinci CVP is shifted using an intelligent CVP controller integrated into the vehicle, allowing fully automatic control for both performance and economy operation, or a manual shifting mode for a fun and different rider experience. Under normal operation, shifting will be completely seamless and silent, with no disruption to torque, jerks, clunks or other undesirable characteristics.

The result for any vehicle is improved vehicle performance and efficiency, especially on hills, during low speed maneuvering or repetitive stopping and starting.

For More Information:

NuVinci CVPs are manufactured by ATC, North America’s largest remanufacturer of drivetrain products. For more information, call (866) 904-3630, or visit www.atcnuvinci.com or www.fallbrooktech.com.

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