The NuVinci continuously variable planetary (CVP) transmission is a specific type of continuously variable transmission (CVT) developed by Fallbrook for vehicles and machines. A CVP is a type of CVT that also provides functionality of a planetary or epicyclic gear set.
Fallbrook has stated that the word "NuVinci" refers to Leonardo da Vinci who, in 1490, developed a drawing describing how a CVT might work.
The NuVinci CVP was first available in December 2006 for bicycles in The Netherlands . Since then, the NuVinci CVP and bicycles equipped with it have been the recipients of several awards, including a 2007 R&D 100 Award, a 2007 Popular Science Best of What’s New, 2007 Technology of the Year and Bike of the Year in The Netherlands, and an iF Design EUROBIKE Gold 2008 Award.
NuVinci CVPs are also currently under development for other products including residential wind power turbines, light electric vehicles, outdoor power equipment, and automotive front-end accessory drives.
The NuVinci CVP uses a set of rotating and tilting balls positioned between the input and output discs of a transmission. 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.
Two factors allow the NuVinci CVP to provide a continuously variable ratio range in a compact package. The first is the geometric configuration of the drive, which is based on differing contact radii of a sphere. Contacting a rotating sphere at two different locations relative to the sphere’s rotational axis will provide a “gear ratio”, which can range from “underdrive” to “overdrive” depending on the location of the contact points for input and output torque and speed.
The CVP is shifted by tilting the axes of the spheres in a continuous fashion, to provide different contact radii, which in turn drive input and output discs.
The second factor is elastohydrodynamic lubrication, or EHL. Transmissions that use EHL to transfer power are known as “traction drives”. A traction drive transmission operates utilizing a traction fluid that, under normal circumstances and pressure, provides lubrication for the drive. When this traction fluid undergoes high contact pressures under rolling contact between two very hard steel elements, such as at the contact point of a sphere riding on a cone as in the CVP, the fluid undergoes a near-instantaneous phase change to an elastic solid. Within this traction “patch,” molecules of the fluid stack up and link to form a solid, through which shear force and thus torque can be transferred. The rolling elements are actually not in physical contact in this traction patch.
The CVP takes advantage of multiple planets to transfer torque through multiple fluid patches. The spheres are placed in a circular array around a central idler (sun) and contact separate input and output traction rings. This configuration allows input and output to be concentric and compact. The result is the ability to sweep the transmission through the entire ratio range smoothly, while in motion, under load, or stopped. CVP operation is not limited to CVT functionality alone. Configuring the device into different “power paths” as one might do with an epicyclic or planetary gear set can provide additional drive functions.
Comparing the NuVinci CVP to conventional transmissionsEdit
The NuVinci CVP offers a number of advantages over conventional transmission technologies. The CVP itself is less complex and has far fewer parts, so it is less costly to manufacture. Since the CVP keeps the engine (human or motorized) operating in its optimum range, it improves overall system efficiency and performance.
From a vehicle design standpoint, the NuVinci CVP offers the ability to accept multiple inputs while varying speed and ratio, managing torque and providing single or multiple power outlets. By supporting 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.
The NuVinci CVP’s simple design and low part count make it easily scalable, with tooling that can be used across a wide variety of applications.
Comparing the NuVinci CVP to other CVTsEdit
NuVinci technology 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, thus lowering total clamping force required and significantly improving durability, control stability, and torque density.
This arrangement makes the NuVinci CVP 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 high-pressure hydraulics.
The NuVinci CVP reduces energy consumption through its continuous speed changing characteristics, allowing the power input prime mover (such as a gasoline engine or electric motor) to operate in its most efficient speed range. As a result, the NuVinci CVP can potentially replace the planetary gear transmission in most mechanical devices.
The NuVinci CVP creates additional options for vehicle designers. Input and output shafts may be either in-line, offset, or in a U configuration (input and output both coaxial and coplanar), making the transmission simpler, smaller, lighter and easier to package. The CVP delivers a large amount of torque capacity 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. Transmission control is stable, linear and does not require a major control system development effort.
Applications for the NuVinci CVPEdit
The NuVinci CVP is applicable to almost any product using a mechanical power transmission.
Current applications either commercialized or under development include:
Bicycles The NuVinci CVP replaces derailleurs and internally-geared hubs, and provides a similar gear ratio range (about 3.5:1) to that found on most performance bicycles, though bicycles with triple derailleurs or with a Rolhoff 14-speed hub gear have a gear ratio range exceeding 5:1. Because the drivetrain is continuously variable, it is easy for the rider to adjust to the optimal ratio for any speed or terrain, and there are no jolts or power losses associated with changing gears.
By conventional standards, a NuVinci CVP bicycle hub is considered heavy. The second generation model N171B weighs between 3.85 and 3.95 kilograms, including freewheel and mounting hardware. However, in the bicycle markets initially served by the NuVinci CVP (cruiser, comfort, and commuter); rider feedback has generally favored the advantages and ride experience of the NuVinci CVP over its weight.
The efficiency of a NuVinci CVP, while seemingly a straightforward measurement, is difficult to pinpoint because its approach to transferring power from the pedal to the wheels is so different. By conventional laboratory means of measuring efficiency of a single fixed ratio or a series of discrete ratios, no CVT can ever measure up to a derailleur.
Outside the laboratory, however, other factors come into the equation, including the comparative simplicity of finding the optimum cadence for a given terrain with a simple twist of the wrist, compared to shifting among 27 fixed ratios on a derailleur; the ability to seamlessly and precisely optimize cadence during a ride; the ability to shift while stopped; and the elimination of torque interruptions inherent in the movement of the chain from sprocket to sprocket. Rider feedback – particularly from inexperienced riders – suggests that these benefits mitigate any efficiency issues.
Ellsworth Handcrafted Bicycles, a recognized innovator in the bicycle industry, was an early adopter of the NuVinci CVP, designing The Ride™ performance lifestyle bicycle around the CVP. In 2007, The Ride received top honors in Popular Science magazine’s annual Best of What’s New review of significant new products. Batavus, a Netherlands-based division of Accell Group, was the first European manufacturer to adopt the NuVinci CVP.
Electric/Hybrid Vehicles NuVinci CVP technology allows the motor in an electric or hybrid vehicle to operate more efficiently by not overloading it in normal operation. It improves hill climbing ability, acceleration, top-end speed, load carrying and towing capacity, as well as range and battery life.
Wind Energy The NuVinci CVP makes possible a low-cost variable speed wind turbine that increases power and replaces one stage of the speed increaser. According to a technical report produced by the National Renewable Energy Laboratories (NREL) and presented at the 2005 WindPower Conference and Exposition, NuVinci technology can potentially reduce cost of energy (COE) by 5.5% or more.
NuVinci technology also improves a wind turbine’s ability to capture gusts and vary rotor speed to optimize tip speed ratio at all velocities. It is capable of handling wind turbine torque levels and mechanically produces up to a 400% ratio range, with rapid shifting over an infinite number of gear ratios.
Viryd, an independent company and NuVinci technology licensee, has announced plans to market a residential class wind turbine equipped with a NuVinci CVP in late 2009. In October 2009, Viryd was selected to participate in a U.S. Department of Energy-funded wind energy industry research consortium lead by the Illinois Institute of Technology (IIT).
Outdoor Power Equipment This segment includes lawn and garden tractors, industrial utility vehicles, golf carts and neighborhood electric vehicle neighborhood vehicles. Because its design keeps both internal combustion and electric motors operating in their optimum range, the NuVinci CVP improves acceleration, ride quality, speed, fuel economy and range.
Automotive There are three applications of NuVinci technology currently under development for the automotive industry, all relating to front-end accessories. These applications, alternator-mounted, crankshaft-mounted and supercharger, improve engine performance and increase fuel economy by enabling front-end accessories run at their optimal speed – regardless of engine speed. Engine downsizing (or engine size optimization) is one of the major strategies being pursued by automakers in order to meet more stringent government fuel economy standards announced in May 2009.
- ↑ Frank Markus, “The NuVinci Code” Motor Trend, September 2006; see also, http://www.fallbrooktech.com/Nuvinci.asp
- ↑ See generally, http://consumerguideauto.howstuffworks.com/the-cvt-nissans-answer-to-fuel-efficiency-cga.htm; and also NuVinci Demo http://www.fallbrooktech.com/02_Demo.asp
- ↑ 3.0 3.1 3.2 id.
- ↑ B.O. Jacobson, Rheology and Elastohydrodynamic Lubrication, (Burlington, MA: Elsevier, 1991)
- ↑ id., and see NuVinci Demo http://www.fallbrooktech.com/02_Demo.asp
- ↑ See http://auto.howstuffworks.com/cvt3.htm
- ↑ Template:Cite web
- ↑ See Gear Inch Comparison, http://www.fallbrooktech.com/08_bike_specs.asp
- ↑ See “Advantages” at http://en.wikipedia.org/wiki/Continuously_variable_transmission
- ↑ See www.popsci.com/popsci/flat/bown/2007/recreation/item_98.html
- ↑ Loren McDaniel, Jeremy Carter, Christopher Vasiliotis, Use of a Continuously Variable Transmission to Optimize Electric Vehicles (Cedar Park, TX: Fallbrook Technologies Inc., 2008)
- ↑ PCT publication WO 2007/025056 A1
- ↑ J. Cotrel, Assessing the Potential of a Mechanical Continuously Variable Transmission, (Golden, CO: National Renewable Energy Laboratory, 2004)
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Scott McBroom, A Continuously Variable Accessory Drive for Alternators and Other Engine-Driven Accessories (Cedar Park, TX: Fallbrook Technologies Inc., 2009)
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