Torotrak outlines advances in its full-toroidal traction-drive CVT using PitchSteer; EV applications as well
At the 2016 International VDI Congress “Drivetrain for Vehicles” in Friedrichshafen, Germany, John Fuller, Director of Concepts & IP for Torotrak Group, presented and discussed the company’s latest advances to optimize its full-toroidal variator technology for the light vehicle market as applied in continuously variable transmissions (CVTs).
Torotrak’s main drive CVTs combine its full toroidal traction drive variator with other conventional transmission components. 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.
Torotrak expects that the developments, which provide a wider ratio spread and seamless power delivery, will further stimulate the popularity of CVTs, already predicted to reach global sales of 12 million per year by 2020.
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. 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.—John Fuller
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.
Torotrak introduced PitchSteer in November 2105 (earlier post) as a low-cost method of control that reduces the actuation power requirement of the Torotrak variable drive for devices such as superchargers—e.g., the Torotrak V-Charge.
At that time, the company said that it believed that PitchSteer, as well as DriveDisconnect—which provides a zero output speed capability within the variator itself to provide the functionality of a disconnect clutch without the cost or weight penalty—could also be used in other applications such as main drive CVTs and IVTs.
In the CVT, using PitchSteer enables a wide transmission ratio range which can improve vehicle efficiency in various ways: first, 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 maximize 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 said that electric vehicles could also 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. With the CVT configured to achieve efficiencies in excess of 95%, there is also potential to increase EV range.—John Fuller
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.