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A boost to fuel efficiency and driver comfort down on the farm

05 January 2010

The Italian agricultural transmissions specialist, Carraro Drive Tech has developed a new and highly efficient transaxle assembly concept based on Torotrak’s innovative toroidal infinitely variable transmission technology

Back in November, at the Agritechnica Exhibition in Hanover, Carraro DriveTech previewed a new transaxle concept incorporating Torotrak’s toroidal infinitely variable transmission (IVT) technology, which is claimed to be the most efficient of its type on the market. The VaryT transaxle assembly delivers significant improvements in fuel economy and emissions, together with better productivity and control for agricultural and off-highway applications.

Carraro DriveTech, an Italian company and a licensee of Torotrak, is an industry leader in the development and production of agricultural and materials handling transmissions. The company believes the VaryT concept will provide important reductions in fuel consumption and CO2 emissions whilst also increasing productivity and driver comfort.

The VaryT range of transaxles (combining a step-less transmission plus vehicle axle all in one unit) uses Torotrak’s full-toroidal traction drive to deliver significant benefits, including a continuously variable transmission ratio that is independent of engine speed. Crucially, it also allows full traction capability even at zero ground speed.

End users will also benefit from the flexible nature of the technology; control of the vehicle is simple and intuitive with seamless transition from forwards, through neutral to reverse. Lower noise levels, the elimination of launch or reversing clutches and the inclusion of features such as accurate cruise control, even at working speeds irrespective of external load conditions, reduce driver fatigue to allow longer continuous working time with improved levels of safety and productivity.

Unveiling the concept at the Hanover event, Carraro confirmed its intention to develop a family of VaryT transaxles over the next five years for use in a wide range of agricultural tractors and specialised vehicles. The company hopes to transfer the benefits of toroidal transmission technology across a range of applications from 40hp to more than 160hp, from lightweight tractors to more complex and specialised off-highway vehicles.

How does IVT work?
Torotrak’s infinitely variable transmission (IVT) avoids the constraints of stepped ratio automatic transmissions and, unlike continuously variable transmissions, there is no torque limitation. The ratio range is provided not by a system of gears, as is the case with conventional automatic transmissions, but by a ‘variator’.

Inside the variator are two pairs of discs. The space between each pair of discs forms a hollow doughnut shape or 'toroid'. Within each toroidal space there are three rollers. These rollers transmit drive from the outer, engine driven discs to the output discs located in the centre. The rollers transfer power between the input discs and the output discs via a traction fluid. Each roller is attached to a hydraulic piston. The pressure in the pistons can be increased or decreased to create a range of reaction torque within the variator. The Torotrak variator shown here is an inline piston design.

IVT is torque controlled rather than ratio controlled. Software determines the torque required at the road wheels and then ‘requests’ torque from the transmission rather than setting a specific ratio. The engine can then be used to deliver power at its most efficient operating point.

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