New epicyclic drive technology from Infinitrak joint venture eliminates gears to enhance refinement, durability, cost, weight and packaging

First application will be in a forthcoming compact and cost-effective Infinitely Variable Transmission developed by Infinitrak for the Outdoor Power Equipment (OPE) market

Infinitrak, the US based joint venture company owned by transmission innovation specialist Torotrak and OPE market leader MTD, has developed a new type of epicyclic drive that replaces gears with traction spheres, combining the functionality of a thrust bearing and an epicyclic drive stage. The first application of the traction drive epicyclic will be in a compact and affordable Infinitely Variable Transmission, developed by Infinitrak for the outdoor power equipment (OPE) market.

“One of the most challenging issues in any transmission is minimising noise levels, and this is particularly the case in low-cost OPE drive units since the precision and geometries required for refined operation with conventional gear sets can add significantly to product complexity and cost,” explains Infintrak’s Chief Operating Officer, Rob Oliver.

To address this issue, the new epicyclic replaces conventional gears with spherical traction drive elements that transfer torque through traction fluid using the same mechanism proven by Torotrak for its full-toroidal variator technologies. Eliminating meshing teeth ensures very low noise, while the use of fewer moving parts combined with materials and manufacturing technologies already proven in established ball bearing applications reduces cost and weight as well as providing increased durability compared with conventional epicyclic systems.

Epicyclic drives play a fundamental role in Infinitely Variable Transmissions (IVTs). Without an epicyclic drive, a full-toroidal variator based on Torotrak’s traction drive technology works as a continuously variable transmission (CVT) that can change speed steplessly over a wide range of ratios. To allow the direction of drive to be changed within the transmission, giving it an in-built ‘forwards-through-neutral-to-reverse’ capability, an epicyclic arrangement is added to manage the input to and output from the variator, transforming the CVT into an IVT.

A conventional epicyclic gear train consists of a central gear (the sun gear) around which several planet gears are mounted on a rotating carrier. These gears also mesh with an outer, internally toothed ring (the annulus). By connecting the variator input to the sun and the variator output to the annulus, the planet carrier rotates at the speed difference between the two which can be positive, negative or zero. The planet carrier, effectively the output from the transmission, is connected to the vehicle’s axle allowing the machine to move seamlessly from forward, through geared neutral (a condition where the engine and elements of the transmission are turning but the wheels are not), to reverse.

In the new traction drive epicyclic, the planet gears are replaced with steel spheres running in prescribed tracks in the rear face of the variator output disc and the end plate, which replaces the conventional annulus.

Engineers at OPE transmission specialist Infinitrak have also been successful in integrating the thrust bearing function (which is required to provide a reaction for the clamping forces within a single cavity variator transmission) within the epicyclic arrangement. This significantly reduces the number of moving parts, cutting weight, reducing packaging requirements and providing increased power density.

The first production application of Infinitrak’s new traction epicyclic technology will be in a new transmission being finalised for launch in the outdoor power equipment (OPE) market  “There is nothing on the market like this,” concludes Rob Oliver.  “We expect that the ease of control, refined operation, low noise and enhanced durability offered by the new transmission will make it highly competitive in this significant market sector.”

About Torotrak

Torotrak is the world’s foremost developer of full-toroidal traction drive technology. The company designs highly efficient continuously variable transmissions (CVT) and infinitely variable transmissions (IVT) to reduce energy consumption and harmful emissions. Its transmissions also deliver outstanding levels of functionality, performance and driving refinement. Torotrak develops main drive transmissions as well as variable ratio drive units for application in flywheel-based mechanical hybrid systems and for use as auxiliary drives.

Torotrak operates in the automotive, truck, bus, off-highway and agricultural markets, in motor sport and in the outdoor power equipment (OPE) market through its joint venture business, Infinitrak.  Torotrak’s customers are widely spread across Europe, North America, India and Japan, and include major vehicle makers and tier-one transmission manufacturers.

Torotrak plc is fully listed on the London Stock Exchange.

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About Infinitrak

Infintrak LLC was established in 2005 to develop, manufacture and commercialise full-toroidal traction drive transmission technology in the Outdoor Power Equipment (OPE) and related markets. Infinitrak combines the world leading expertise of its two founding parent companies, Torotrak plc in the UK and MTD Holdings Inc in the USA. Torotrak brings its expertise and patented know-how in the field of full-toroidal traction drive transmission technology, whilst MTD is contributing world-class manufacturing skills alongside its leading position in the OPE market place.

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About epicyclic traction drive technology

The concept of the epicyclic traction drive is simple and is analogous to a large angular contact ball bearing; the traction spheres correspond to the balls in a conventional race and act as planet gears, whilst the carrier plate corresponds to the cage in a ball bearing and replaces the conventional epicyclic’s planet carrier. The annulus corresponds to the outer race of the bearing and is connected to the variator input shaft, while the inner race is formed as a track on the rear of the variator output disc and acts as the sun gear. Instead of using meshing teeth to transfer power, shearing traction fluid provides a silent and efficient drive from the two inputs (sun and annulus) though the spheres to the output – the carrier plate.