Most of the efforts to produce more environmentally-friendly cars in recent years have focused on alternative fuels and more efficient engines. UK-based engineering company, Torotrak, has instead decided to turn its expertise to another vehicle component with the development of a new generation transmission that it claims can not only slash CO2 emissions and improve fuel efficiency, but also boost performance.
Instead of the conventional toothed gears found in traditional transmissions, the company’s Continuously Variable Transmissions (CVTs) and Infinitely Variable Transmissions (IVTs) use innovative steel discs and rollers. When used in place of a conventional gearbox the new transmission offers seamless acceleration from standstill to cruising speed and back again, thereby reducing harmful exhaust gases by eliminating 'emission spikes' caused by gear changes.
Fuel efficiency is also increased because, even at high speeds, the transmission ensures that the engine operates at low speed and at optimum efficiency, generating around half the normal fuel-burning revs.
The core of both the CVT and IVT technology is a traction drive ‘toroidal variator’, which incorporates smooth, saucer-shaped discs and circular rollers. This variator allows the transmission to deliver a stepless range of ratios to meet all driving conditions.
A CVT is the simplest form of transmission to use a toroidal variator. It offers a ratio spread of around seven and requires a starting device such as a clutch or torque converter to launch the vehicle from rest.
An IVT is more sophisticated employing an epicyclic gear set in conjunction with the variator to provide a ‘geared neutral’ function with a seamless transition from reverse to forwards motion. Torotrak’s typical IVT is configured to provide a ratio spread in excess of seven and provides high levels of overdrive gearing. With an IVT, no starting device is required.
Torotrak says a specially-developed oil-like fluid, with unusual lubricating and traction properties, ensures grip between the rotating rollers and discs to transfer torque through the transmission from the engine to the driven wheels. The result is smooth power delivery, faster acceleration, improved fuel economy and reduced emissions.
The company says its variable drive technology also has applications beyond transmissions. By fitting small, low-cost variable drive units to components such as superchargers, turbochargers and alternators, as well as engine cooling and air conditioning systems, Torotrak says they can be made to operate more efficiently.
Torotrak technology was already being used to develop new kinetic energy recovery systems (KERS) proposed for F1, and now Torotrak’s new generation transmission technology has attracted interest from gearbox manufacturers, mainstream car manufacturers and their component suppliers faced with meeting ever tighter emissions legislation and volatile fuel costs.