Infinitely variable transmission for next century’s vehicles

Simplifying transmissions making them easier to make, and smaller and lighter than conventional gearboxes

Under development by Torotrak is a Series III version of its infinitely variable transmission (IVT) for fitment to a fleet of test vehicles from early 2000. It will be the first version with full integration of the gearbox and engine control systems, and working as a partner for a critical part of the programme is Zytek Automotive.

An earlier phase demonstrated fuel economy improvements of more than 17% compared with a manual transmission. For the Series III, Zytek will fit its own flexible engine management system (EMS), allowing further optimisation of the control strategy, and full control integration with the gearbox.

The Torotrak IVT is able to provide a smooth, stepless transition from full reverse through to high overdrive – a truly infinitely variable transmission. It is suitable for all sizes of vehicle, including large commercials, as well as non-automotive applications, such as jump-jet auxiliary drives and windmills.

At the heart of the system is a `variator’ in which metal rollers transfer power from input discs to output discs via a specially developed traction fluid. The drive ratio reflects the angle of the rollers located in the toroidal cavity formed by the discs. The need for a clutch is eliminated by taking the output through an epicyclic gearset and the software can be calibrated to provide the drive feel required by the vehicle manufacturer, including the option of step changes to provide `manual’ operation.

The system has few components, making it simpler to make, smaller and lighter than a conventional gearbox. Zytek will replace the engine management systems of the development vehicles with its own EMS V, which uses a highly flexible twin processor architecture similar to the company’s Formula 1 EMS. The new system will be mapped and calibrated at Zytek’s Repton Powertrain Centre. The first development vehicle will be a 5.4l Ford Expedition.

In the completed installation, commands from the throttle pedal sensor will be received by the transmission controller where the required engine power and torque will be calculated based on vehicle speed and fuel economy maps. This is then translated into an engine speed requirement and a gearbox hydraulic pressure requirement to maintain the required torque level. The electronic throttle is opened the appropriate amount and a position signal from the throttle potentiometer is sent to the EMS.

Zytek Automotive Tel: 0121 323 2323