|Design of the basic NuVinci CVP. Click to enlarge.|
The NuVinci transmission 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 NuVinci technology thereby combines the advantages of a toroidal traction CVT with the versatility of the planetary gear arrangement. It uses rolling traction to transfer torque, just as do toroidal transmissions. However, unlike toroidal CVTs, it distributes the transmitted torque over several spheres in an inherently stable configuration, thus lowering total clamping force required and significantly improving durability, control stability, and torque density.
Compared to other continuously variable transmission (CVT) technologies—toroidal, push belt, hydromechanical and chain—the NuVinci CVP is less complex, has fewer parts, offers more stable control and scalability across product lines, and is less expensive to manufacture and assemble, according to Fallbrook.
The NuVinci is based on two primary technology concepts. The first is the geometric configuration of the drive, which is based on differing contact radii of a sphere. The configuration of the components of the device is analagous to a planetary gear set, except that the “planets” are actually spheres.
|Click to enlarge.|
The second is the use of a traction fluid (Invaritorc), developed in partnership with Valvoline. Under normal circumstance and pressures, the traction fluid provides lubrication for the transmission. When the traction fluid undergoes high contact pressures under rolling contact—i.e., the contact point of a sphere on a cylinder as in the NuVinci—the fluid undergoes a near-instantaneous phase change to an elastic solid through which shear force, and thus torque, can be transferred.
WIth multiple spheres in the CVP (from 3 to 12), the transmission thus transfers torque through multiple fluid patches. This configuration allows input and output to be concentric and compact, with distributed torque transfer among the spheres. The result, according to Fallbrook, is the ability to sweep the transmission through the entire ratio range smoothly, while in motion, under load, or stopped.
The unique configuration of the CVP transmission allows for multiple power path configurations in which the device can be incorporated into a drivetrain. Some of these configurations can operate as a CVT, where input(s) and output(s) turn the same direction across the entire speed ratio. Others can operate as an IVT (infinitely variable transmission, where output speed can be reduced down to a powered zero state, and the output can even reverse direction.
Fallbrook points out that a beneficial parallel hybrid application would be to use the device to sum the torque inputs from both power sources and decouple the summed input from the road speed of the vehicle. This would allow each power source to operate in its best respective efficiency range, with the sum then continuously varied to a desired output speed.
Fallbrook has initially identified six major industries for licensing of NuVinci technology:
- Light electric vehicles (LEVs)
- All-terrain vehicles (ATVs)
- Low speed vehicles (lawn tractors and golf carts)
- Agricultural equipment
- Wind energy