Three-speed gearbox could improve efficiency of EVs

Automotive firm Antonov has unveiled a three-speed gearbox that could improve the efficiency of electric vehicles (EVs) and give a smoother gear change.

The Warwick-based transmission manufacturer says its design for an automatic, scalable, twin-clutch gearbox could be used in a variety of vehicles, replacing the one-speed transmissions typically used at the moment.

The gearbox, a model of which was revealed at last week’s Low Carbon Vehicle show (LCV2010), was developed under the Technology Strategy Board (TSB) programme that produced Jaguar’s Limo Green prototype extended-range electric car.

The current Limo Green model features a two-speed version of Antonov’s gearbox and the three-speed transmission is scheduled for evaluation by Jaguar early next year. Antonov says there is also the potential for a four-speed system.

Most EV manufacturers have previously avoided multiple-speed transmissions ‘partly because they thought they didn’t need them, partly because they couldn’t package them and partly because they weren’t very efficient’, Antonov’s business development manager David Paul told The Engineer.

‘As EVs have become more popular, particularly high-performance ones, manufacturers are beginning to realise that there’s a limit to the performance of the vehicles,’ he said.

Antonov 3-speed powershift transmission for electric vehicles
Antonov’s three-speed powershift transmission for electric vehicles

Multiple gears allow the engine to use energy more efficiently and Antonov says its transmission has an efficiency of around 96 per cent, approaching that of manual gearboxes, while an adapted conventional transmission would produce a rating of under 90 per cent.

Antonov’s system also has a twin-clutch system that allows it to pre-select a gear while another is still in use, ensuring a smoother transition. The vehicle can also change gear while the motor is stationary. ‘There is no three-speed [electric] transmission on the market with single-shift quality like this,’ said Paul.

Because of its scalable design, the gearbox can be adapted for different purposes and vehicles. ‘This transmission has its own controller, so we can manage the complete energy of the vehicle such that it will select a gear based on its best range, for example, or best performance or best comfort,’ said Paul.

‘We’ve had enquiries, for example, from electric buses. It would improve comfort for standing passengers because you’d get no movement at all from the gear changes – it’s completely seamless.’

While the transmission is particularly suited to more powerful vehicles, Paul said there would also be an advantage in having multiple gears in small electric city cars if the transmission could be made small enough and produced for a mass market.

Car manufacturers are starting to capitalise on the design freedom offered by low-carbon electric vehicles. Click here to read more.