When the driver accelerates, the system works in reverse. The energy is drawn from the flywheel and converted back into electricity to power the traction motor. This reduces the work done by the internal combustion engine, improving fuel economy by up to 25%, depending on the application.

The Gyrodrive system is a lower cost alternative to conventional battery hybrids. The upfront investment is a fraction of the cost of existing hybrids. With real-world fuel savings of up to 25%, the payback period for bus operators is three to four years. The system is smaller than conventional battery or super-capacitor hybrid units, which means it does not compromise seating or passenger capacity and can be retro-fitted to existing fleets.

The electric flywheel started life in motorsport. In June, GKN’s Gyrodrive system helped power Audi Motorsport’s hybrid race car to a third consecutive victory in the Le Mans 24 Hour endurance race.

Gyrodrive can also help improve the efficiency of other commercial vehicles used in cities. Refuse and delivery truck applications are planned, so are agriculture and construction vehicles. Heavy vehicles with stop-and-go or back-and-forth duty cycles consume a lot of energy that Gyrodrive can recover and regenerate. In the longer term, as volumes increase and costs reduce, GKN expects Gyrodrive to be a viable option for mass-production vehicles.