Wrightbus, which estimates a five-year operator payback for the technology, exhibited a KERS-equipped bus at the Cenex LCV show this month. This is the first customer bus from Arriva to be fitted with the system and will be the first fully mechanical hybrid bus to travel on a public service route in the UK.

By recovering kinetic energy the bus would otherwise lose under braking, and mechanically transferring this energy to spin up a high speed carbon fiber and steel flywheel, the Flybrid KERS can store significant proportions of the available energy. The high-efficiency system then transfers the stored energy back to the driveshafts of the bus, reducing load on the engine under acceleration and thus saving fuel and reducing emissions including CO₂ and particulates.

As part of the project with Wrightbus, Torotrak also developed an accurate route simulation tool which allows operators to calculate the potential savings on various routes using the Flybrid system. This has been validated by testing using the industry standard duty cycles at Millbrook Proving Ground.

The in-vehicle work at Millbrook has confirmed that we can now accurately predict energy flows in and out of the system. Combined with our complex model of real-world operating conditions, we can now provide operators with robust predictions for fuel savings on their different routes.

—Jon Hilton, Torotrak product development director

Operators can also expect further savings from the purely mechanical system, which uses no high voltages and is designed for the full service life of the bus. Torotrak believe resale values for these Flybrid KERS-equipped vehicles will also remain high.