Dana Opens New Chapter on CVTs

A dedicated development center is hustling the unique VariGlide “spherical traction drive” toward 2020 production.

January 1, 2018

Lindsay Brooke

Any emerging technology that warrants its own dedicated development center — 40,000 ft2, staffed by 40 engineers and loaded with state-of-art design engineering, analysis, metallurgy, machining, prototyping and test cells with four dynamometers — must be considered a competitive threat. That’s the buzz within the powertrain community about Dana’s Cedar Park, TX, tech center, and the highly anticipated VariGlide continuously-variable planetary transmission under development there since 2014.

The VariGlide variator unit showing the torque-input ring (on right, purple) and output ring (at left). The planetary spheres rotate on small axles. (Credit: DANA)

VariGlide is slated to enter production at one or more light vehicle OEMs in 2020. Dana engineers claim it will offer up to 10% greater fuel efficiency than incumbent CVTs, with improved drivability and NVH characteristics. It is “highly scalable” according to company engineers and its compact design enables it to effectively slot into existing transmission housings without significant modification.

“We think Dana’s going to be a serious player in more efficient, next-generation transmissions,” said an engineering director at a European OEM, who spoke with Automotive Engineering at the 2017 Frankfurt Motor Show. “From what we know already about VariGlide, it may open a new chapter for the CVT.”

Tilting the spherical planets changes the relative contact diameters. A variable ratio sweep is possible in 0.2 s. (Credit: DANA)

Heart of the Cedar Park facility is a formidable engineering and manufacturing team of industry veterans hailing from global automakers, equipment makers such as JCB, and tech suppliers including Bosch, Ricardo and Tremec. They’re doing manufacturing process development in parallel with component and systems engineering. Working on the critical path has resulted in a 97% reduction in cycle time on some of the key internal hardware, noted Ed Greif, Dana’s Senior Director-Powertrain Innovations.

As AE readers know, the basic technology has been brewing for a decade and a half. Fallbrook Technologies, originally based in San Diego, initiated its development in 2004 (see SAE Technical Paper, Configuration Analysis of a Spherical Traction Drive CVT/IVT; http://papers.sae.org/2004-40-0009 .) Seeing potential commercial markets in various industry sectors, Dana in 2012 took out an exclusive technology license for light duty (less than 10,000 lb GVW) on-highway applications. Three other primary licensees include Allison (10,000-lb GVW), TEAM Industries (ATVs) and Continental (e-bikes).

Schematic of VariGlide 2-mode that offers up to 8:1 ratio spread. The power flow direction changes with each forward motion change. (Credit: DANA)

“Importantly, none of us compete directly,” explained Greif. “We meet monthly to exchange data and information; it works out really well. Each company has specializations and feed info back into ‘the pool.”

Fallbrook “lacked the commercialization capability that Dana has,” said Bob Pyle, President of Dana Light Vehicle Driveline Technologies. “It was our job to figure out how to apply the technology to automotive applications, and we’ve taken it to a higher level. When Fallbrook passed the design to us [then known generally as CVP, for Continuously Variable Planetary, and still called NuVinci for e-bike use], it was at an efficiency level of about 89%. We’ve taken that to north of 95% efficiency.”

4-mode capability

VariGlide doesn’t use a hydraulic pump, enabling high internal efficiiencies, said Engineering Director Patrick Sexton. (Credit: LINDSAY BROOKE)

Close cooperation among Dana design and manufacturing engineers is paying off in reduced component processing time at Cedar Park, according to Ed Greif, Senior Director-Powertrain Innovations. (Credit: LINDSAY BROOKE)

Operationally, VariGlide offers the best of both worlds: the utility of a conventional planetary automatic with the smooth continuous ratio change of a CVT — but without the former’s gear and clutch mechanisms, and without the latter’s belt or chain and two pulleys (known in CVT-speak as the ‘variator’). During our visit to Cedar Park, we briefly tested a Cadillac ATS demonstrator fitted with the latest prototype VariGlide and found it to be as buttery-smooth as the stock GM 8L45 8-speed automatic (which is benchmark), but with quieter, quicker ratio changes — at least the ones that were perceivable. It has electric-motor-like operating characteristics.

Inside the VariGlide’s compact case, a set of hardened steel “planet” spheres rotating on dedicated axles is arrayed around a central “sun” that transfers torque between two carrier rings. One ring serves as the torque-input side; the other output ring transfers that torque to the driveline. Tilting the spheres on one carrier ring by up to 7°, while the other ring remains stationary, changes their contact diameters on the rings. This permits an infinite range of speed ratios.

“Kinematically it works like a planetary gear set, when you think about the ratios between two points,” said Gordon McIndoe, a Dana transmission expert. “It provides only a 4:1 native ratio spread so it is application dependent. We can deliver stable ratio control, electrically or hydraulically, in 2-mode or 4-mode operation. Our ratio control is independent of load. The continuous transition to any ratio within its range maximizes overall powertrain efficiency and accessory performance, on demand.”

He said VariGlide is capable of supporting more than 300 power-path configurations and can sweep through all ratios in 0.2 s, compared with the two seconds it takes typical CVTs to do so.

A key to the unit’s internal efficiency is a proprietary lubricant developed for the unique transmission. The fluid temporarily transitions to a solid under high pressure. Its fluid properties provide internal ‘grip’ which helps torque transfer within the mechanism, Sexton explained, proven in nearly 90,000 hours of durability testing racked up on the core technology as of fall 2017.

McIndoe and Patrick Sexton, Engineering Director-Light Vehicle Driveline technologies, claim VariGlide is capable of higher torque density than other CVT types and lower NVH compared with gear-and-clutch devices. The unit also is capable of splitting torque, as in a conventional fixed planetary automatic. The co-axially-mounted system also affords more flexible drive inputs and outputs that helps optimize packaging in the vehicle, they said.

The design reduces driveline and vehicle energy consumption by continuously optimizing ratio between the driving and driven devices, allowing them to operate in their most efficient speed range. Without the belt-and-pulley variators of traditional CVTs, there is no need for the high (up to 900 psi/6205 kPa) hydraulic pressures required for belt-clamping control. “This means VariGlide doesn’t use a hydraulic pump, so we’ve eliminated the parasitic losses associated with that,” explained Sexton.

Overall, the VariGlide’s mechanical characteristics lend themselves to lower cost manufacturing than those of traditional CVTs, the Dana experts claim, with simple part geometries. According to Greif, Dana will manufacture the variator and supply it to OEMs and to transmission Tier 1s. Dana has over 1000 U.S. and international patents issued or pending, some generated from Cedar Park and including a potentially more efficient 4-mode VariGlide under development.

Powersplit for forklifts

Four-mode Variglide begins testing in 2019. Neat packaging. (Credit: DANA)

To vehicle OEMs, each tenth of a percent of a fuel efficiency improvement will be worth pursuing in the next decade, as global emissions regulations tighten. All seek to avoid compromising performance in the quest for reduced CO₂. Decoupling engine accessories from crankshaft speed is another potential benefit of the VariGlide transmission, the Dana team notes. It creates a ‘cascade’ effect that enables use of a smaller accessory package without hindering performance.

That ability to decouple engine speed from a vehicle’s travel speed convinced Dana leadership to pursue VariGlide development for the global materials-handling industry.

The transmission’s performance characteristics align with the rapid and abrupt acceleration, deceleration, and pinpoint positioning required for forklift-truck duty, without the need for forward and reverse clutches (see 2015 SAE Technical paper http://papers.sae.org/2015-01-1104/ .)

During our Cedar Park visit, we observed a VariGlide-equipped 2.4-ton Hyster “high-low” practicing pick-and-place work in the facility’s loading dock area. According to engineers, Dana projects fuel savings of up to 20% for a standard-size forklift operating in a typical duty cycle. The technology can be scaled for use in forklifts up to 3.5 tons ratings.

Dana is expected to implement VariGlide technology in select Spicer powershift transmissions. It will also offer the technology to forklift OEMs as a module offering a standard powersplit configuration.

VariGlide’s 2020 market entrance underscores not only Dana’s faith in the fundamental Fallbrook technology, but also the fact that the next decade will see many exciting new driveline solutions emerge beyond the battery-electric “revolution” that is taking longer to arrive than some expected.