GKN has produced for BMW’s i8 hybrid sports car the industry’s first two-speed eAxle.
“GKN’s customers aren’t just looking to make their next car more efficient; they want to create new driving experiences,” said GKN Automotive CEO Andrew Reynolds-Smith. “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.”
GKN explained giving the electric motor an additional gear ratio improves acceleration and pure electric range, benefiting both driving dynamics and CO2 emissions. GKN added its 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,” said GKN. A conventional or hybridized 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. GKN explained no other hybrid architecture offers such a strong combination of efficiency, traction, dynamics and packaging.
Until now electric and axle-split hybrid vehicles have used single-speed transmissions; using a fixed ratio limits electric drives in terms of either acceleration or top speed as they must disconnect at certain speeds to prevent the motor turning too quickly. GKN stated its two-speed eAxle is the first to enable the electric drive to boost the vehicle’s performance across its entire speed range.
Designing the two-speed eAxle for a high-performance sports car application placed tight packaging requirements on GKN’s development team; the eAxle in the BMW i8 weighs just 27 kilograms and measures less than 325 mm by 562 mm by 313 mm.
To make the system narrower, the shift mechanism sits on the input shaft instead of the intermediate shaft in the middle of the transmission. GKN acknowledged precise software control of the eMotor and the synchro-actuation achieves a smooth gearshift in all conditions, even with the input shaft spinning at up to 11,400 rpm.
“Gear shifts are completely transparent to the driver,” said Theodor Gassmann, GKN Driveline’s Vice President Product Technoloy eDrive Systems. “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 percent 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,” said Gassmann. “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.”