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GKN Driveline’s successful development of a high-performance electric axle for Porsche’s advanced plug-in hybrid supercar means it will be working more closely with the German carmaker.
Porsche has upgraded GKN to ‘technology partner’ status for its eAxle, which supplements the 918 Spyder’s hybridised 4.6-litre V8 engine, allowing full-electric mode, all-wheel drive, and provides a boost function. The module has maximum power of 95kW and can deliver up to 1,500Nm of torque to the front wheels via a fixed gear ratio.
A specially developed compact differential engages the torque, giving the car optimum power distribution at all times. The differential also disengages the module to minimise drag losses and maximise efficiency. At speeds above 265km/h (164mph), a clutch isolates the electric motor to prevent it from over-spinning.
A key target for the car was achieving the lowest possible centre of gravity and ground clearance. To achieve this, GKN positioned the output overhead, using an innovative lubrication concept to manage the oil flow. The oil reservoir is positioned above, not below, the geartrain. Oil is gravity-fed down onto the bearings and gears until it reaches the high-speed input at the bottom, where it is then circulated back to the oil reservoir at the top.
This design minimises the amount of oil on the input shaft, keeping churning losses low. To ensure the critical areas remain lubricated even in disconnect mode, the motor is driven for brief, intermittent intervals to maintain a constant flow of oil.
The tight packaging on the car also means there was almost no air flow around the transmission and so water cooling was needed to manage the heat generated by the module’s high power density.
Christian Hauck, Porsche’s powertrain manager, said the challenge was to deliver a sports car capable of setting a record lap time on the Nürburgring and of achieving fuel efficiency of three litres per 100km. “This placed huge demands on our engineers and suppliers. GKN’s role in the development programme has earned it Porsche ‘technology partner’ status.”
Peter Moelgg, GKN’s president of engineering, added: “This was the perfect opportunity
for our e-drive team to demonstrate how putting the right technology onboard can improve both fuel efficiency and dynamic performance.”