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GKN to supply 500 electric flywheel hybrid drive systems to Go-Ahead Group for buses

UK transport operator Go-Ahead Group has ordered 500 electric flywheel Gyrodrive systems from GKN Hybrid Power for use in buses. The Gyrodrive Kinetic Energy Recovery System (KERS) system (featured in Audi’s LeMans-winning R18 e-tron quattro) harvests braking energy normally lost as heat.

When the driver brakes, a traction motor on one of the axles slows the vehicle, generating electricity at the same time. This electricity is used to charge the flywheel, spinning it at up to 36,000 rpm. 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, which helps accelerate the bus back up to speed, generating fuel savings of more than 20% at a significantly lower cost and weight (60 kg, 132 lbs) than battery hybrid alternatives. Useable stored energy is 1.2MJ, with peak power of 120kW.

The GKN Hybrid Power Mk4 eFES is an electrically driven flywheel energy storage system. The motor is a three-phase permanent magnet motor. The magnets are provided by GKN Hybrid Power’s MLC (Magnetically Loaded Composite) material which has the advantage of being both very low on eddy current losses and safe as there are no discrete magnets rotating at the very high rotor speeds of the flywheel to contain in the event of a failure.

The Mk4 eFES has a separate inverter so that the flywheel and inverter combination connect directly to the vehicle’s DC bus. Due to the high speed of the rotor a vacuum is required to reduce friction losses and this is provided by a flywheel mounted vacuum system. An oil cooling system provides direct cooling to the stator coils and the inverter to increase power density.

Key benefits of low mass, compact packaging, electric only coupling to vehicle drive, and low cost point make the Mk4 eFES system a turn-key retro-fit solution. The retro-fit and OE systems are branded as Gyrodrive. The Mk4 eFES also benefits from internal contactors on the DC bus to disconnect from the rest of the hybrid system and real time insulation monitoring of the HV circuit.

The new agreement covers the supply of the complete Gyrodrive system, including the GKN Hybrid Power flywheel as well as GKN’s advanced EVO axial flux electric motor (earlier post), a GKN-designed and manufactured gearbox, and installation. The system is designed to last for the life of the bus, eliminating the need for any battery changes.

Development of the Gyrodrive system was earlier supported by a £2,184,500 (US$3.7-million) grant from the UK Technology Strategy Board (TSB), awarded in 2012. The system was developed by Williams Hybrid Power, GKN, and GKN-Evo, with Go Ahead group performing a fleet trial on a number of different bus types to validate the system performance.

Earlier this year GKN announced the acquisition of Williams Hybrid Power from Williams Grand Prix Engineering Limited to form GKN Hybrid Power, which is focused on delivering complete hybrid solutions across multiple vehicle, power and industrial markets. (Earlier post.)

In April, GKN and its partners received a £7.6-million (US$13-million) grant as part of a £15.6-million (US$26-million) project to apply the Formula One KERS technology for use in public transport, initially city buses. Other consortium members include bus manufacturer Alexander Dennis Limited, technology experts at Coventry University and S&S Windings, a leading niche technology SME. (Earlier post.)

Following successful trials on buses in London, Go-Ahead intends to utilize the technology in cities it serves across the UK, initially in London and Oxford.

This is an important milestone for GKN Hybrid Power. We’ve worked in close partnership with Go-Ahead throughout the development of this innovative technology and it’s very exciting to move into the production phase. The fact that we are using the same groundbreaking technology that helped Audi win at Le Mans for the past three years to improve fuel efficiency in the public transport sector also shows what great innovation there is in the UK’s engineering sector.

—Philip Swash, CEO GKN Land Systems

GKN Hybrid Power is based in Oxfordshire, with final assembly taking place in a new facility at GKN’s site in Telford. The Gyrodrive technology is being further developed for other mass transit markets including trams, construction and agricultural equipment.


Jim McLaughlin

1.2 MJ is about a third of a kWh, less than a standard Prius battery's energy but much higher power.

Full power for ten seconds by my calculations, and 120 kW is 161 horsepower.

5.5 wH/kg is more than an order of magnitude below battery standards, but this is a power solution, not an energy solution. Still compares poorly to super capacitors.

2 kW per kg is nearly an order of magnitude better than batteries, but still not good compared to super capacitors.

Durability might be an interesting comparison. So far I don't see the value proposition.

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