High performance oils aid transmission development

A new range of high performance traction oils from Shell lubricants companies is contributing to the success of an evolutionary infinitely variable transmission technology developed by Torotrak.

A new range of high performance traction oils from Shell lubricants companies is contributing to the success of an evolutionary infinitely variable transmission (IVT) technology developed by Torotrak.

The Torotrak IVT is an advanced transmission technology which has a continuous range of ratio and is being increasingly recognised by the general automotive and off-highway vehicle markets as a logical replacement for today's stepped ratio automatic transmission systems.

Unlike with conventional automatic transmission, the ratio range is not provided by a system of gears, but by a full toroidal variator which consists of a set of discs and rollers.

Power transmission is achieved by traction (via an extremely thin, but extremely viscous, elasto-hydrodynamic fluid film) and not through metal-to-metal friction.

The IVT variator could not function without the use of sophisticated traction fluids and it is Shell's work in this field over a number of years as well as its global reputation for the development of new technology, which has proved invaluable to Torotrak's development programme.

Lubricant in the IVT is not only required to transmit torque between the variator's disks and rollers: it also needs all the usual characteristics of an automatic transmission fluid.

In the past, it has been shown that lubricants formulated to give high traction properties tend to exhibit poor low temperature viscosity: overcoming this has been one of Shell's major challenges.

During development of the current IVT, several fluids have been developed by Shell specifically for this application and have been tested for traction performance using small and full-scale rigs.

The resulting final lubricant has a combination of molecular structures so that, as an oil film, it responds rapidly to high pressures, allowing transfer of force across the film, yet has stable characteristics in service.

Significant improvements in hardware durability have been achieved by optimising the fluid composition.

Development work by Shell has also focused on blending fluids to achieve different low temperature viscosities, and it is now feasible to achieve the desired traction performance at high operating temperatures, whilst maintaining the ability to operate below -30C.

Although Torotrak's IVT system is state-of-the-art, the concept of traction drives is not new and Shell has been working with the company on the development of traction fluids for some 20 years.

The programme has been stepped up since the mid-1990s as Torotrak has progressed towards formal commercial agreements with vehicle manufacturers and transmission suppliers.

The Torotrak IVT offers several major functionality benefits, not least a significant improvement in fuel economy.

Its ability to continually change ratio enables the engine to run at optimum performance where required power is delivered with minimum fuel burn.

This means that vehicles fitted with an IVT have improved fuel economy by between 12 and 20% across a range of standard manual cars.

This level may also be improved on in some conventional automatic cars.

A corresponding reduction in carbon dioxide emissions is a natural consequence of IVT's fuel saving capability.

Continuous delivery of power and torque rather than stepped ratios, means that shifts are not felt every time the vehicle changes gear resulting in a smoother driving experience.

James Batchelor, Torotrak's Commercial Director commented: "The importance of high performance traction fluids to the IVT system cannot be overstated and it's essential that we work with companies such as Shell that fully understand our technology and our business".

"We have, over a number of years, established a deep, long-lasting strategic relationship with Shell Lubricants and this has become increasingly important as Torotrak and the industry move towards high volume applications of IVT".

These high volume applications are now set to come not just from the mainstream automotive sector, but also off-highway vehicle sectors such as agriculture and the construction industry.

Vehicles such as tractors, combine harvesters, diggers and fork-lifts, for example, can benefit from features such as low-speed all terrain cruise control, uphill/downhill speed control and forward to reverse shuttling without the use of gears.

Batchelor concludes: "We are now working with a number of vehicle manufacturers and tier one transmission suppliers with the objective of getting them to use IVT technology under licence in volume automotive applications as soon as possible".

"The important development work and support provided by partners such as Shell takes us ever closer to this outcome".

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