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Multi-speed transaxles coming for EVs

Two for joy: BMW's plug-in i8 is the first to use a multi-speed gearbox in conjunction with an electric motor, but it could be joined by others.

World-first GKN two-speed eAxle paves the way for electric vehicle gearboxes

13 Nov 2014

SINGLE-SPEED electric vehicles and hybrids could become a thing of the past with the introduction of what is claimed to be the world's first two-speed gearbox for EVs.

Designed by automotive technology giant GKN, the two-speed eAxle has made its debut on BMW's i8 plug-in hybrid supercar.

The axle's British maker says the benefits of EV gears are numerous, paving the way for smaller and lighter motors to reduce weight, increase range, improve vehicle dynamics and driver enjoyment, as well as cut emissions of petrol or diesel hybrids.

Other manufacturers such as Toyota use continuously variable transmissions in their hybrid drives, but GKN claims its solution is the first two-speeder for electric final drive.

Just as a gearbox in a petrol-powered vehicle multiplies the engine's operational range, so too can an EV gearbox, dramatically improving acceleration and top speed.

Existing hybrid vehicles such as Toyota’s Prius that drive the wheels directly from the engine use transmissions, but the new GKN solution is the first geared system for a pure electric drive systems.

GKN's solution weighs 27kg and houses the gearing on the driven axle, much like transaxles that combine a conventional gearbox with the final drive, remotely from the engine.

On top of efficiency gains, eAxle advantages include better weight distribution, more compact transmissions and a lower centre of gravity, says GKN.

The gearbox is compatible with “axle-split” four-wheel-drive vehicles such as the BMW i8, sending primary power to one axle while the other pair of wheels receives drive via a secondary electrical source.

Control of the gears is handled by the driveline management software – not the driver – with gearshifts “completely transparent” to the driver.

GKN Automotive CEO Andrew Reynolds said the future of hybrid and electric vehicles was not just about economy but also driving enjoyment.

“GKN’s customers aren’t just looking to make their next car more efficient,” he said. “They want to create new driving experiences.

“Our expertise in driveline efficiency, torque vectoring and electric drive systems is enabling automakers to connect drivers to the road in new ways.

“We are developing the systems that are helping bring a new generation of electric drive vehicles to life.”

While the first eAxle has only two speeds, transmission speeds could multiply as they have in conventional automatic and manual transmissions.

The first automotive automatic transmissions also had two speeds. This week, Volkswagen detailed its upcoming 10-speed transmission.

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