Details On BMW i8's GKN 2-Speed eAxle

BMW i8 has been on the market for some time now, collecting positive reviews from all over the world. And just now GKN is boasting that it contributed to that success.

In 24 months, GKN developed a two-speed eAxle for the front wheels of the i8, powered by an electric motor.

The motor power stands at 96 kW, while torque reaches 250 Nm (184 lb-ft). Input motor speed can reach 11,400 rpm.

The rear wheels are powered by a  three-cylinder combustion engine.

Instead of a single-speed reduction gearbox, BMW and GKN opted for 2-speed to not sacrifice top speed or acceleration. The eAxle weighs just 27 kg, so probably not much more than a single-speed, and can work with up to 97% efficiency.

"Giving the electric motor an additional gear ratio improves acceleration and pure electric range, benefiting both driving dynamics and CO2 emissions. GKN’s two-speed eAxle also enables the motor and all its associated systems to be downsized, reducing mass and further increasing efficiency.

eAxle technology enables automakers to produce “axle-split hybrids”. A conventional or hybridised engine provides the primary power to either the front or rear wheels, with the other axle driven by an eAxle module. The technology responds intelligently to deliver an instant high-torque all-wheel drive experience, a useful pure electric range or a refined, efficient parallel hybrid mode. No other hybrid architecture offers such a strong combination of efficiency, traction, dynamics and packaging.

To make the system narrower, the shift mechanism sits on the input shaft instead of the intermediate shaft in the middle of the transmission. Even with the input shaft spinning at up to 11,400rpm, GKN’s precise software control of the eMotor and the synchro-actuation achieves a smooth gearshift in all conditions."

GKN Automotive CEO Andrew Reynolds-Smith stated:

“GKN’s customers aren’t just looking to make their next car more efficient; 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.”

Theodor Gassmann, GKN Driveline’s Vice President Product Technology eDrive Systems, commented:

“Being the first Tier One to deliver a two-speed eAxle demonstrates GKN’s leadership in electric drive technologies and hybrid driveline systems. Two-speed eAxles will help manufacturers enhance hybrid and electric drivetrains and support the trend to downsize eMotors to reduce weight and cost. With the technology proven in a high-performance vehicle with high levels of refinement, significant savings in CO2 are possible.”

“Gear shifts are completely transparent to the driver. The smooth electromechanically actuated shift between the synchronised ratios has enabled our eAxle to set new benchmarks for comfort and NVH. The eAxle combines superior efficiency of 97% with high gear shift comfort and low gear noise. And yet the shift mechanism is a proven technology with components already in series production, providing a robust and cost-effective solution.”

“By drawing on all the expertise and knowledge within GKN’s global engineering network, we were able to take the eAxle from concept to production in just 24 months. Going forward, pairing electric powertrains with multi-speed transmissions is enabling GKN to supply downsized eDrive modules for future hybrid and electric vehicles. The technology also enables more radical future eMotor downsizing strategies.”

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