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Future Electric Vehicle Transmissions May Have Multi-Speed Gearboxes


Audi A3 e-tron transmissionFor the most part, electric vehicle manufacturers have eschewed the multi-speed transmission in favor of a simpler and lighter single speed transmission.

The reason for this is that electric vehicles do not really need a transmission, at least that is what electric-vehicle manufacturers thought. Because an electric motor is more easily balanced than a standard internal combustion engine (ICE), it does not really need multiple gears to keep it from going over safe maximum speed. In a conventional vehicle, the ICE needs a multi-speed gearbox to keep it in its most effective range, considering power, torque, and efficiency.

In an electric vehicle, however, the electric motor can safely be used up to 10,000 RPM or more without losing its power effectiveness, nor its efficiency. In fact, Tesla Motors considered multi-speed transmissions for the Tesla Roadster, but rejected them in the end. No one doubts the effectiveness of the single-speed transmission for power and efficiency, and especially range, in the case of the Tesla Roadster and the Tesla Model S, the leading electric vehicles on the market, today.

Now, with the introduction of powerful plug-in hybrid electric vehicles (PHEV), such as the Audi E-Tron PHEV and the Porsche Panamera S E-Hybrid, multi-speed transmissions are again up for debate. The Audi E-Tron PHEV, for example, using a multi-speed transmission, can reach a top speed of 80 MPH on battery power alone, and has a range of up to 31 miles. It can do this only because of its multi-speed transmission which, in spite of its weight and complexity, actually makes the electric-vehicle (EV) portion more efficient.

Most of the hybrid electric vehicles (HEV) and PHEVs on the market make use of single-speed transmissions or constant-velocity transmissions (CVT), or even no transmission, such as the direct-drive in the Volkwagen e-Bora. Could the foray of big companies like Audi into PHEV multi-speed transmissions encourage other automakers to consider them for their EVs and PHEVs?

Images © Audi

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