Low carbon vehicle specialist Torotrak Group is presenting its solution to the conflicting demands of increased urban transport capacity and improved inner-city air quality at a conference in Berlin between December 7-10.
The company has developed a mechanical KERS (Kinetic Energy Recovery System) to hybridise a bus and says it dramatically reduces cost in comparison to a conventional battery hybrid system.
'Increasing population density in the established markets and growing urban transport needs in developing countries are creating acute pressures for a cost-effective but environmentally aware solution,' said Tobias Knichel, Torotrak's business development director.
'Our Flybrid mechanical flywheel system is around a quarter of the cost of traditional battery hybrid technology and is ideally suited to the start-stop urban cycles experienced by public transport vehicles.'
In a paper titled Developing a cost efficient flywheel hybrid system for city buses, Knichel will share Torotrak's experiences of the systematic development and validation of its bus KERS and detail the route from prototype to volume manufacture.
The presentation ' which is scheduled for Session O of the symposium on the Wednesday afternoon ' will focus on the application of the technology to a Wrightbus StreetLite Midi bus which has been running in public service since Q1 2015.
'One of the greatest challenges was to prove the safety of the system,' said Knichel.
'As the safety margins of our flywheel technology are very high, it is very difficult to trigger a failure in either the cyclic fatigue or the single overload cases.
'The Flybrid KERS for buses has a design life of 1,000,000km and 8,000,000 charge/discharge cycles ' which is equivalent to the working life of the vehicle to which it is fitted.'
The Flybrid KERS uses a high-speed flywheel to capture energy that would otherwise be lost as heat in the brakes when the bus is decelerating. This stored energy is then transferred mechanically back to the wheels and used to accelerate the vehicle, offering significant savings in fuel consumption, CO2 and other harmful emissions by reducing the engine power required to propel the vehicle.
'Being a purely mechanical system, it avoids the inevitable losses that occur when battery-based systems change energy from one form to another, for example mechanical to AC, to DC, to chemical, and back again,' said Knichel.
'Additionally, it overcomes environmental issues regarding end-of-life disposal of batteries containing rare earth metals or acids.'
He said the cost of the system is also much lower than a full battery electric hybrid, meaning that operators should achieve faster payback - within five years.
The Flybrid bus technology has already won the SMMT Award for Automotive Innovation in 2014, being cited as a potential game-changer for the UK vehicle industry due to its affordability and low carbon credentials.
