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Wrightbus Flybrid flywheel KERS bus entering service with Arriva

Following a successful validation program, a new Flybrid bus KERS (Kinetic Energy Recovery System), developed by Torotrak PLC will enter service in the UK with operator Arriva, applied in a Wrightbus bus.

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.



Great stuff, hybridisation is a real fuel saver, be it mechanical, electrical or hydraulic.
The trick is to find the cheapest, most reliable system and roll it out into as many vehicles as possible.
Especially stop/start city vehicles like buses, delivery vans and bin trucks (and taxis).


Let's see what's available today:

  1. Hydraulic hybrids (hydraulic pump pressurizing nitrogen-filled accumulator).
  2. Compressed-air hybrid (ambient air).
  3. Mechanical flywheel hybrid.
  4. Electric hybrids:
    • Battery storage.
    • Supercapacitor storage.
    • Flywheel storage.
It seems like there ought to be more of these things out there, given all the available options.

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