Carraro launches concept variable transmission transaxle

  • 03-Dec-2009 01:58 EST
The Torotrak toroidal variator replaces a mechanical/hydrostatic transmission in Carraro's VaryT transaxle.

Carraro DriveTech, the Italian-based manufacturer of axles, transmissions, and epicycloidal drives displayed a concept transaxle designed for agricultural and other off-highway applications at the recent Agritechnica. The transaxle, named VaryT, introduces a Torotrak toroidal transmission in place of a hydrostatic/shunted hydrostatic drive in a transaxle casing.

“At the heart of any variable-speed transmission is the variator, and in the Carraro VaryT it’s a very high efficiency mechanical unit across a wide speed range, which is unlike some of the hydrostatic options. It’s a very power-dense solution, which means we can have a compact overall transmission, ideal for small tractors," Roger Weyman, the Agricultural Director of Torotrak, told SOHE.

"It’s also a mechanical solution that is in Carraro’s sphere of expertise, in terms of design, development, and manufacturing," he said. "So that leads them to have control over the cost of design and manufacturing. Carraro can manufacture the whole of that variator unit, which they could not do with a hydrostatic unit. That would have to be a bought-in component, which means the cost cannot be controlled as well.”

One aspect of the Torotrak transmission is its “geared neutral” design: torque can be applied to both ends of the variator, and neutral is derived by balancing torque input and output to it. “That’s very important as a safety element,” said Weyman. “You can imagine a vineyard tractor on a very steep hillside. Switch into geared neutral and the tractor is completely safe. Stopping, reversing, all from geared neutral is very intuitive and very safe.”

Carraro claims improved fuel consumption and reduced carbon dioxide emissions because the variator will select the most appropriate gearing for the operation. It is difficult to quantify the efficiency gains because tractor operations vary greatly, but Weyman told SOHE that for applications such as forklifts, a 20% reduction in fuel consumption is typical.

Carraro has adopted an electronic control system with a joystick control; a hydro-mechanical control system could also be used. The system is said to provide a seamless transition between forward, neutral, and reverse. Lower noise levels are claimed for the transmission compared with a conventional transaxle. Launch or reversing clutches can also be eliminated, and accurate cruise control is possible even at working speeds regardless of external load conditions.

The company has said that it will develop a family of VaryT transaxles over the next five years for use in a wide range of agricultural tractors and specialized vehicles. The concept module, known as VaryT 5, can handle up to around 75 hp (56 kW). The company also plans to develop the VaryT 10 and VaryT 15, which will be capable of handling power ratings up to around 160 hp (199 kW). VaryT has been designed as a zero-maintenance system.

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