Torotrak : Seamless Power Delivery and Improved Fuel Efficiency in CVT Applications

Latest Toroidal Transmission Technologies Offer Seamless Power Delivery and Improved Fuel Efficiency in CVT Applications

New developments for passenger cars and EVs presented at major drivetrain conference

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24 June, 2016… Torotrak Group, a leading developer and supplier of vehicle emissions reduction and fuel efficiency technologies, recently presented new advances in CVT (Continuously Variable Transmission) technology that promise increased energy efficiency and performance in light automotive applications, including electric vehicles. Providing a wider ratio spread and seamless power delivery, the developments by Torotrak are expected to further stimulate the popularity of CVTs, already predicted to reach global sales of 12m per annum by 2020.

Speaking at the 2016 International VDI Congress 'Drivetrain for Vehicles' in Friedrichshafen, Germany, on 22 June, John Fuller, Director of Concepts & IP for Torotrak Group, delivered a presentation entitled, 'High efficiency 'full-toroidal' traction drive CVT - Technology improvements and application to front wheel drive cars', discussing the latest advances that optimise variator technology for the light vehicle market.

By combining its extensive experience in main drive and auxiliary drive transmissions, Torotrak has designed a variator concept with ratio spread of up to 12, operated by a low cost actuation system. The variator is suitable for both front and rear wheel drive platforms and should be highly scalable, with the traditional hydraulic version having already been demonstrated to power levels in excess of 300kW.

'Market preferences are shifting from conventional automatics to CVTs,' commented Fuller. 'Our solution can accelerate that trend by satisfying the needs of front wheel drive but also potentially rear wheel drive layouts, where the high torque levels and packaging constraints can be more challenging for conventional CVT technology.'

Torotrak Group's experience of auxiliary drives has led to reductions in system cost, in particular through the use of cost effective variator ratio control using the company's PitchSteer technology. This enables a wide transmission ratio range which can improve vehicle efficiency in various ways: firstly, by reducing the amount of energy dissipation when pulling away from stationary and secondly by enabling the engine to run at lower speeds when cruising. Furthermore, the wide variator ratio spread enables simple and efficient transmission designs which maximise the use of 'power splitting', whereby only a fraction of the motive power is transferred by the variator, the remainder being transmitted by a direct mechanical path.

The transmission can also be configured as an IVT (Infinitely Variable Transmission) with a 'geared neutral', that can further improve fuel economy by removing the need for an inefficient vehicle launch device which loses power as it slips. The system may be arranged to suit driver preferences in individual markets, for example to give the familiar driving sensation of a torque converter.

Fuller also explained how electric vehicles (EVs) could benefit from the latest variator developments. 'By increasing the wheel torque at low vehicle speeds, a toroidal CVT can improve gradeability and performance, or be an enabler for a downsized electric powertrain that is lower in cost and weight,' he said. 'With the CVT configured to achieve efficiencies in excess of 95%, there is also potential to increase EV range'.

The Torotrak Group presentation also examined the impact that toroidal CVTs and IVTs could have when used in autonomous vehicles. By providing continuous drive torque through seamless shifting, the technology is able to overcome the unpleasant sensation of torque interruption, to which occupants of such vehicles are highly sensitive.

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