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Are multispeed transmissions the future of EVs?


One of the many ways in which current EVs differ from legacy vehicles is that they don’t shift gears. While modern ICE vehicles sport 8- and 9-speed automatics, 7-speed manuals and continuously variable transmissions, which help to improve fuel efficiency, most EVs get by with a simple single-speed gearbox.

Conventional wisdom is that, because electric motors deliver high torque through a much wider range of RPMs, there’s no need for a multispeed transmission. Tesla originally designed the Roadster with a 2-speed transmission, but shelved it because it wasn’t durable enough.

James Potter, Controls Manager for ZF Powertrain Technology, thinks this will change with the next generation of EVs. “For passenger cars, I would say we will probably eventually rise up to 3- or 4-speeds,” Potter told WardsAuto. “Two-speeds are coming out, and that will be the next generation.” He sees no need for an EV to have more than four gears.

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A 3- or 4-speed transmission could yield a range improvement of up to 20%, says Potter, “if you optimized everything, reduced the motor and optimized the gear ratios.” A multi-gear transmission would deliver greater efficiency on the highway, although a 1- or 2-speed transmission is fine for city driving.

Potter also foresees a hybrid transmission with integrated electric motors, similar to the 2-Mode transmission that GM developed with BMW and Daimler a few years ago. ZF currently produces a hybrid transmission, which replaces the torque converter with an electric motor, for ActiveHybrid versions of the BMW 3-, 5- and 7-Series.


Source: WardsAuto


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