Wednesday, August 5, 2009

NuVinci Continous Transmission

I like what I see here. This problem has been around forever and has been of the mind of every boy who ever picked up a wrench. Most attempts usually foundered on complexity and the contributions of Rube Goldberg.
This looks like it has a good chance. It works by simply changing the rotational angle of the roller balls. Put in enough balls and you should have ample traction and retain excellent balance.

My only obvious concern is that the range wanted may be difficult to attain but possibly not.

This may be a nifty device for a bicycle hub system. The lack of moving parts looks promising although that usually changes pretty quickly on manufacture.

The key point is that a ratio change is effected smoothly by the operator, something never properly achieved to date, and done it appears without a lot of parasitic energy losses.

It also looks to be suitable for robust systems although I am sure we will find weaknesses before it is finished.

NuVinci® Overview

The patented NuVinci technology developed by Fallbrook Technologies Inc. (Fallbrook) is the most practical, economical and universally adaptable continuously variable planetary (CVP) transmission for human-powered and motor-powered vehicles and machines. The NuVinci CVP is ideally suited for applications in many major industries including bicycles, light electric vehicles, tractors, automobiles, trucks, and utility class wind turbines among others.

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.

Click here for links to a demonstration video

Tilting the balls changes their contact diameters and varies the speed ratio. 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 transmissions.

When compared to traditional continuously variable transmissions (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

Distinguishing the NuVinci CVP from Traditional CVTs.

There is a clear distinction between Fallbrook's NuVinci continuously variable planetary (CVP) drive and more traditional continuously variable transmission (CVT) technologies. A CVT is a transmission that is infinitely variable between its high and low range as opposed to a conventional geared transmission where the number of speed ratios between high and low is limited by the number of gears.

The CVT has been called the "holy grail" of transmissions because it eliminates the multiple gears, shifting clutch and many other parts found in conventional transmissions. In place of gears, most CVTs use one or more cones, discs, balls, belts, toroids or other shaped devices for gradually changing ratios. These geometric shapes allow the input or output contact points on any particular device to vary in diameter, thus changing the input to output speed.

The use of CVTs has not become widespread due to multiple problems inherent in traditional designs. These problems include shifting control difficulties, poor efficiency, scalability challenges, questionable reliability and durability, high cost, and other factors.

The NuVinci CVP represents a quantum leap forward over other CVTs as well as conventional mechanical transmissions. These advantages include:

Higher torque density
Smaller size/weight
Easily scalable
More adaptable and versatile
Improved overall performance
Easy to package (less space required)
Lower manufacturing and maintenance costs

How the NuVinci Transmission Works

The NuVinci CVP is continuously variable and infinitely applicable to almost any product using mechanical power transmission. 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 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.

This arrangement makes the NuVinci transmission the only practical CVT to combine the smooth, continuous power transfer of a CVT with the utility of a conventional planetary gear drive. 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. Part shapes are simple and relatively easy to manufacture, and in most applications, there is no need for power-robbing, high-pressure hydraulics.

The NuVinci CVP reduces energy consumption, such as fuel, through its seamless speed changing characteristics, allowing the power input such as a gasoline engine to operate in its most efficient speed range. Overall, the NuVinci CVP’s mechanical and manufacturing characteristics improve performance and reliability while reducing costs over traditional CVTs and stepped transmissions.

As a result, the NuVinci CVP can potentially replace the planetary gear automatic transmission in most mechanical devices.

Key advantages of the NuVinci CVP

Compared to conventional transmission technologies, the NuVinci CVP provides:

Less complexity. There are significantly fewer parts than conventional transmissions and it is potentially much less costly to manufacture.

Overall improved system efficiency. With the NuVinci CVP, it is easy to keep an engine running at its most efficient speed.

Greater acceleration and optimum performance. Acceleration is faster and smoother – right up to the vehicle’s acceleration limits – because it keeps the engine running at peak performance.

Easier shifting. There is no jarring associated with shifting gears.

Ability to accept multiple inputs while varying speed and ratio, managing torque and providing single or multiple power outlets. A NuVinci transmission is the most practical CVT technology to perform all of these tasks simultaneously.

Support for a torque demand rather than a speed demand control solution. The NuVinci CVP solves the low-speed acceleration problem inherent in some torque-demand vehicles.

Scalability and potential to reuse tooling. The technology is highly scalable. The design and implementation of a low-torque application utilizing four balls may involve the same basic parts as a higher torque application with eight or sixteen balls. Also, tooling can be used across a wide variety of applications.

Improved hill-climbing. The NuVinci CVP allows a driver to drive up a hill at the desired speed and in the proper transmission ratio without having to choose, as with traditional geared transmissions, between a gear that is too high and bogs the engine down resulting in a lower speed or a gear that is too low and results in an over revving engine speed.

Compared to CVT alternatives, the NuVinci CVP offers:

Coaxial input and output. The input and output shafts are in-line, making the transmission simpler, smaller, easier to package, and lighter.

Better torque density. A NuVinci CVP delivers a large amount of torque in a relatively small space. It is smaller and easier to package than other CVTs because it does not require an offset shaft and because it can spread torque across any number of traction contacts by using many balls..

Lower manufacturing cost. The transmission uses simple geometry and very simple parts which results in a lower cost. The NuVinci CVP can also be scaled across a wide variety of vehicles in many cases without retooling.

Lower control cost. Transmission control is stable, linear and does not require a major control system development effort.

Power path variability. The technology is easily integrated into a wide range of applications with varying power path requirements or options.

Scalability. The NuVinci CVP’s simple design and low part count make it easily scalable.

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