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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.


Readers' comments (4)

  • Given that a motor can produce full torque from zero speed right up to maximum speed, it is not at all clear what benefits a gearbox would bring for all its extra weight and complexity. Could someone please explain?

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  • The electric motor does not produce max torque all the time, and as a consequence the current demand by the motor varies with load. The more current drawn causes more losses principally in the form of heat. to preserve the load on the battery pack, changing gears will allow a higher voltage motor running at higher speeds with lower current demand and therfore less heat is generated, and the battey will last longer, wehter this is enough of a reason, i have not looked at the maths yet, but it is interesting

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  • The electric motor has (as did the internal combustion engine) operating points with good and poor efficiency. E.g. at a standstill, at startup, with high (or full) of torque, the efficiency is 0% (zero), because there is no movement ...
    Only with the onset of movement increases the efficiency from 0% to ca. 70% at ca. quarter of speed, and to maximum effiziency at about half speed.
    Electric motor also do not like the start-stop operation.
    By a gear, the start phase is shortened significantly and the best operating point is moved in the "broad"

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  • With a gearbox you can tailor the maximum efficiency range of the motor to the vehicles speed, load, etc. This also allows the modern vehicle electronics with speed, load sensing, throttle position, etc to be tailored to suit an electric motor.

    Anything which improves the efficiency of an electric motor and lowers its battery consumption is a step forwards, and this development is potentially a massive step.

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