British Busmaker Signs Deal to Install 250 GKN Flywheel Drives

Alexander Dennis Ltd., the U.K.'s largest busmaker, plans to equip 250 of its city buses with electric flywheel hybrid drives developed by GKN plc.

The so-called Gyrodrive flywheels will be supplied by GKN Hybrid Power Ltd., the former Williams Hybrid Power unit GKN acquired in April from Williams Grand Prix Engineering.

The system was inspired by the kinetic energy recovery system Williams developed for its Formula One race car. The device uses a 60-kg (132-lb) carbon-fiber flywheel rotating at 36,000 rpm to capture energy when the bus slows to a stop.

The system then taps the stored energy to drive a GKN electric motor that helps accelerate the bus from rest. The GKN flywheel can store 1.2 megajoules of energy and has peak power of 120 kW.

GKN says the technology can cut bus fuel consumption about 25% and costs significantly less than more conventional battery hybrid systems. Flywheels can't store energy for long periods, so the energy they capture must quickly be used. That makes them well suited for the stop-and-go duty cycle of buses, according to the company.

GKN Hybrid Power will deliver complete Gyrodrive systems, which include the flywheel, axial flux electric motor, a GKN-developed gearbox and installation. The company says its system is designed to last the life of the bus.