Rolling transmission offers a smooth ride

Click here to watch “Continuously Variable Planetary“ to learn more about Fallbrook Technologies’ NuVinci Series scalable transmission.

It is not uncommon for a technology to be versatile. It is perhaps one of the greatest strengths of a component to be functional across a variety of system applications and vehicle platforms. The NuVinci patented continuously variable planetary (CVP) transmission from Fallbrook Technologies Inc., San Diego, CA, hits markets ranging from commercial trucks to bicycles to wind turbines.

The NuVinci technology is a scalable and adaptable CVP technology that controls the relationships of speed and torque through a system of rotating and tilting balls (made of basic bearing steel) between the input and output components of a transmission. The tilting of the balls changes the contact diameters and varies the speed ratio resulting in a seamless and continuous transition to any ratio within its range.

The NuVinci system, compared to other continuously variable transmissions, features fewer components and costs less to manufacture, while still improving overall vehicle performance.

Drawbacks to CVT technology

Often described as the ‘Holy Grail’ of mechanical engineering, continuously variable transmissions (CVTs) allow for an infinite number of gear ratios versus mechanical transmissions with a fixed number of gear ratios. The NuVinci CVP enables vehicle accessory systems, such as air conditioning compressors, to run more efficiently regardless of the speed at which the engine is running by continuously optimizing the compressor speed.

Rob Smithson, VP of product development at Fallbrook has been with the company since 2002. His previous 20 years of work as an engineer in the automotive and aerospace industries, as well as working with Southwest Research Institute in San Antonio, TX, introduced him to “every existing CVT technology out there.”

“The problem with CVTs,” Smithson explains, “is they are all some combination of heavy, delicate and expensive. Fallbrook’s was the first CVT I saw that was light enough, compact enough, efficient enough and rugged enough to put on an application that is a real problem for any other CVT, and that’s the bicycle.”

Those same traits have been in demand by engineers for years for units such as accessory drives, auxiliary power units (APUs) and power take-offs (PTOs) where it is ideal that the device operate at a constant speed. Unfortunately, it is often tied to engine speed, causing a less than optimal design choice.

In certain industries such as transit buses and military applications, there is a lot of idle time. A CVT allows the alternator to be sped up at idle, then slowed down when the vehicle is in motion without over speeding it, but “inevitably you run into problems with controls and control stability with conventional CVT technologies,” says Smithson.

The NuVinci technology solution

The unique mechanical geometry of the NuVinci device—an array of spheres around a central idler with two rings to transfer the power in and out—is what Smithson claims allows Fallbrook’s CVP to solve the common shortcomings of present day CVTs. The Delta Series accessory drives and drivetrain technology decouple accessories from engine RPM, allowing the accessory to run at the optimum speed regardless of engine speed. Their flexible packaging (in-line or concentric input/output shafts) enable use of existing beltlines.

Traction devices transfer torque across a thin layer of fluid between two metal rolling elements. The systems tend to use expensive, non-standard parts that can be difficult to manufacture.

Fallbrook’s NuVinci CVP is a traction drive, but uses a common part shape: the ball-bearing. “People know how to make the parts that make up our device,” says Smithson. The spheres are made of standard bearing steel. “We’re not using any exotic materials or material processes.” This results in a simplified manufacturing process, lowering part production costs and allowing for easier part replacement.