Allison Transmission has signed a global licensing agreement with U.K.-based Torotrak. Under the terms of the deal, Allison will acquire around 10% of the Torotrak equity, worth around £7.1 million with initial license payments.
The U.S.-based transmission manufacturer has gained license rights to Torotrak’s infinitely variable transmission (IVT) and options over global manufacturing and sales exclusive rights in the light- to medium-duty truck and bus sectors. This applies to vehicles up to 14-t (15.5-ton) gross vehicle weight (GVW). The company will gain similar options relating to heavier trucks and buses at a later date.
As a result, development work will begin immediately on a new medium-duty truck transmission. Torotrak will help build the first prototype.
Torotrak has already signed agreements with Tata Motors of India and a major un-named European truck manufacturer. Of the major European truck manufacturers, only Daimler, Scania, and Volvo produce their own transmissions.
“Allison may take disc and roller technology from an assured source that we have currently,” Torotrak CEO Dick Elsy told AEI. “We’re working with people like Jtekt in Japan, but there’s also a number of other bearing manufacturers we’re now working with, but that’s an open question at the moment.
“In terms of the next few years with Allison, it’s all about helping them design, configure, and optimize the technology for their own use," Elsy said. "Already, even while we’re working on this, we’re finding new ways of constantly improving it. We’re taking cost out, fewer parts count. So we’re on this journey of continuous improvement.”
Torotrak claims 94% efficiency for the transmission, whose design origins date back over 20 years. The IVT system transfers power from the engine via a full “toroidal variator,” which packages three rollers between an input and output disc. The gear ratio can be varied infinitely by altering the angle the rollers describe between the input (from the engine) and output discs. The contact between the rollers and input and output discs is made through a traction fluid, which is 1 µm (39 µin) thick. The fluid has been developed by a number of partners, principally Shell.
As an automotive transmission, output from the engine and IVT is fed through an epicyclic gear set, which can increase the overall spread of ratios available from the system to provide very low overdrive gearing and a range of additional features. These include a geared neutral, cruise control with retardant effect and reversing sensors, which can bring the vehicle to a halt.
“One of the benefits is that you can begin to get higher levels of efficiency,” said Elsy. “Depending on how you configure it, you can put the larger proportion of the power through the gear sets, with a smaller proportion of the power going through the variator, so you can begin to climb your efficiency above that of the variator.”
Elsy joined Torotrak as CEO from Jaguar in 2003. “When I arrived, the technology was too big, too heavy, and too expensive, so we set about making it smaller, lighter, and cheaper," he explained. "The way we have achieved that is by working on the geometry and surface finish of the discs and rollers. Just down to the crown radius of the roller and how that matches the disc is a really important piece of IP. What we have done is not only the mathematical modeling and design work, but also prove the traction performance of certain radii on the rollers and the clamp force together and the fluid and the surface finish and the materials. We’ve worked our way through this mix of variables and spent £60 million. In the truck world, in particular, it has to be nigh-on bulletproof.”
The traction fluid has also been a focus for development. “We’ve been exploring and have developed with Shell, in particular, enhanced levels of fluid which give greater traction performance in the contact patch, and we’ve been managing an interesting trade-off,” Elsy said. “The more 'bite' you get, the more viscous the fluid is at low temperatures. So we’ve been developing the fluids to have the same characteristics down to -30ºC now. The limiting factor there is your ability to pump it through the hydraulics. We’ve stretched the life of the variator for a given size. It follows the same fatigue-life laws as a roller bearing, basically.
“Since 2003, we’ve increased the life of the variator by about nine times. That then opened the doors to great longevity of the unit, then with that much spare capacity, so we’ve been able to reduce the size of the parts. For a given power output, the size of variators has come down dramatically.
“The other limiting factor is heat," Elsy continued. "The performance of the unit is crucial to how quickly you get heat away from the contact patches. If you don’t get it away quickly, traction performance tails off, so therefore you have to make the variator bigger. We’ve done a lot of development work on variator cooling, and those breakthroughs have enabled us to run higher powers in smaller variators.”
Torotrak has developed kinetic energy recovery systems (KERS) for Formula One this season, working with partners Xtrac and Flybrid Systems. A road-car system is under development with Jaguar Cars. “This is an area of real interest for us, as a next step in the commercial-vehicle sector,” Elsy said. “If you’ve got a vehicle that’s stopping and starting a lot, it’s amazing how much energy you can harvest.”
Torotrak claims that compared with an electrical hybrid system, a mechanical flywheel-based system would be half the weight, half the volume, and around half the cost. At the same time, the system offers twice the efficiency of an electrical hybrid system able to return around 70% of the recovered energy to the drivetrain.
Testing with an Optare light bus equipped with a Torotrak IVT from a large SUV with fairly basic modifications in place of a torque converter automatic has yielded fuel consumption savings of almost 20%. A similar bus equipped with a flywheel hybrid system with a Torotrak variator transferring energy from engine to flywheel and back again could potentially yield substantial savings in fuel consumption and emissions.