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Fallbrook Targeting Continuously Variable Planetary Transmission at Larger Applications Than Bikes

10 December 2007

New_cvt_diag
Design of the basic NuVinci CVP. Click to enlarge.

Fallbrook Technologies is targeting its NuVinci continuously variable planetary (CVP) transmission at machines larger than the bicycles and other two-wheeled vehicles it currently serves.

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.

Hub_diagram_v7fb_050207_500px
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:

  • Bicycles
  • Light electric vehicles (LEVs)
  • Automobiles
  • All-terrain vehicles (ATVs)
  • Low speed vehicles (lawn tractors and golf carts)
  • Agricultural equipment
  • Wind energy

December 10, 2007 in Fuel Efficiency, Hybrids, Transmissions | Permalink | Comments (12) | TrackBack (0)

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Comments

And explain to me why a bicycle needs a CVT? The regular manual shifter works just great. Easy to maintain. Easy to find replacement parts.

An ordinary bike doesn't really need a CVT. In contrast a Toyota HSD-style transmission would allow a more compact and lighter electric-assist bike.

Personally I would like a bike with a drive shaft and not exposed sprockets and chain to get dirty or caught on.

@Eric -

a bicycle no more *needs* a CVT than a car does, especially since bikes with as many as 24 speeds are available. However, the CVT allows you to change your transmission ratio even when you are stationary, which can be handy. You also avoid all chain-related technical issues.

If the bicycle also feature an electric assist motor, the transmission ratio can be adjusted to keep pedaling speed and forces near optimal values. In theory, this could even be done automatically, but I haven't seen any integrated systems on the market yet. The objective would be to entice car owners to switch to pedalectric transportation for short trips and in highly congested areas when the weather is nice, even in hilly terrain. It also represents a mode of light exercise and is by far the most affordable way to begin the shift away from dino-juice and onto grid electricity. Needless to say, the concept will be more successful wherever dedicated lanes or paths offer cyclists enhanced safety.

Toxic emissions from an ICE are very high immediately after a cold start, until the catalytic converter gets up to temperature. Moreover, the engine will consume additional fuel while the block and oil are warming up. Some fuel ends up in the oil, which therefore has to be changed sooner - discouraging the use of low-friction synthetic oils. Frequent cold starts also reduce the life expectancy of conventional SLI lead-acid batteries.

i'd like a bike with a cvt.

i'd probably be willing to pay about $100 extra for it, if it responded quickly and smoothly over the normal ratio range and would last for 10 years with no maintenance other than a bit of oil every once in a while.

transmission on EVs, however, are a bit tougher sell. you get minimal benefit from them and they have to be designed quite ruggedly to handle so much torque. so, they are expensive, but don't add much value.

This combined with a hub motor might be good. Electric bikes require a lot a power to start from a stop, accelerate and climb. This might extend the range and improve performance.

Luv it,- genius ****

Speaking of the E-bikes, I understand that they are becoming quite popular, especially in Asia. Wouldn't this transmission be useful for enabling energy recovery, thereby extending the range and perhaps removing the other breaking components?

I'd love to see the NuVinci transmission scaled up to automotive applications. Because the NuVinci design can be very compact even on higher-torque applications, it would certainly be useful on vehicles such as B-segment automobiles like the Honda Fit/Jazz and Toyota Yaris. And its scalability means we could see the NuVinci CVP even on high-torque applications like turbodiesel engines.

This appears to be a very elegant design. Scalability claims remain to be proven, but it looks promising. Auto companies suffer from endemic NIH syndrome, so breaking into that market may be tough.

Bicycles are way more efficient than this contraption. Look it up bicycle drive trains are amazingly efficient. Cover the chain up and use an internal hub in back for low maintenance.

Automotive companies do not suffer from NIH syndrome. They suffer from an unwillingness to pay anything above dirt-cheap commodity pricing for parts that don't add market value (visible bling or performance).

The car of today is a technological wonder of 20 years ago because 20 year old technology is cheap enough for their vehicles.

It is ALL about the money.

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