Flywheel hybrid technology for buses is not a new idea. By harvesting the energy that is normally lost as heat when braking, and turning it into additional power, fuel savings and emissions reductions of more than 20% are possible. The challenge has always been to produce a system that can stand up to the duty cycle of a typical city bus. High energy transfer rates, frequent stops and starts, and the typical 15 year service life of a bus make this a demanding application requiring highly reliable technology.
Drivetrain system leader and Tier 1 supplier GKN could have the solution. Having acquired a technology first developed for use in Formula One by Williams, the company is developing a version for buses – and plans eventually to offer flywheel hybrids for a range of heavy duty and transport applications.
Although the flywheel was originally developed and tested for Formula One, rule changes led teams to adopt a battery-based kinetic energy recovery system (KERS). Instead, Porsche took an interest and a system was developed and raced in the 2010 911 GT3 R Hybrid race winning car. The early potential was obvious, says Gordon Day, GKN Hybrid Power’s general manager.
Audi Motorsport, looking for a hybrid technology for its Le Mans programme, got in touch and a winning partnership was founded. This year, Audi and GKN celebrated a third victory for the technology in the 24 hour endurance race, despite fierce competition from other manufacturer teams also running hybrid race cars.
“The three years at Le Mans have been a catalyst and a steep learning curve for the technology,” says Day. “Audi’s commitment to winning at Le Mans is total. The stringent performance and conformity of production requirements were a significant step up that helped mature the technology quickly. Dozens of flywheels are put through their paces in race cars, on engine dynos and test rigs and the performance for all of them has to be identical.”
Safety has been a big focus of the development. GKN Hybrid Power’s flywheel designs are supported by a stringent safety case and considerable behind-the-scenes physical testing. “Racing is where the technology has met the pavement,” says Day, “and over three seasons with Audi there have been no surprises. Even in Loic Duval’s car-destroying accident during practice for this year’s Le Mans, the flywheel remained safe and intact.”
With the performance requirements advancing year on year as well, the system has now already undergone seven progressively more challenging iterations. For 2014, not a single component from the previous year was carried over. “The advances in the cooling concepts and the system’s thermal efficiency translate directly into economic benefit in other applications,” says Day. “The drive to develop continuously, to keep winning is also transfering to our other applications.”
Audi tends to use motorsport to demonstrate the technologies it wants to promote in its road cars, but for GKN Hybrid Power, the next commercial application will be a London bus, not a German sports car. Last year, the technology completed a bus demonstration trial in the UK capital, delivering fuel savings of more than 20% on a typical city route. Substantial improvements in exhaust air quality and solid reliability also help make it attractive to city authorities and bus operators.
Having since earned Green Bus Certification, GKN Hybrid Power is focusing on the UK’s 30,000-strong bus fleet. Working with manufacturers, including Alexander Dennis, and some of the main operators such as Go-Ahead Group, the idea is to integrate the flywheel into new vehicles as well as retro fitting, where GKN Hybrid Power’s objective is to upgrade a range of makes of buses currently in service.
As confidence and volumes build, the company plans to offer the technology to international bus markets. Further applications in other heavy-duty vehicles with similar stop-start duty cycles will also follow. Refuse trucks and delivery vehicles are the most likely entry point for the technology into trucks.
Williams’ sale of the technology recognised that for broad market commercialisation and to realise the full potential of the technology, flywheel hybrid technology needs a different level of expertise and resources behind it. For GKN, the system adds to a product portfolio that has evolved out of its delivery of key driveline components to include complete all-wheel drive systems, electric axle modules and pure electric power units.
Flywheel hybrid technology has always sounded like a great idea in theory. Having found the right development environment early on – and a Tier 1 leader now intent on industrialisation – the technology is about to start delivering on its potential.