What now for torotrak kers

With Torotrak, an actor who wants to establish a completely different, purely mechanical principle with a flywheel accumulator is now entering this still open race. At the beginning of 2014, Torotrak, an engineering service provider with a focus on motor vehicles from Great Britain, bought the British company Flybrid, which developed the Flybrid KERS flywheel storage system in 2007, originally for Renault's Formula 1 team.

"Flybrid" is a combination of "Flywheel" (flywheel) and hybrid. Today, a modified form of the flywheel storage system is supposed to make buses more efficient - Torotrak has decided to use cars later. The characteristics of this technology are theoretically better suited to the peculiarities of urban bus operation than the previously used storage of kinetic energy in batteries. In the test vehicle, the storage unit can hold a maximum of 670 kJ and delivers a peak power of 135 kW.

Torotrak is testing flywheel technology in the StreetLite midi, a two-axle city bus from the manufacturer Wrightbus. The low-floor bus with 33 to 45 seats and a maximum of 70 passengers is powered by a 185 hp four-cylinder diesel engine from Cummins.

The flywheel storage device has a lower energy density than a battery, but offers a higher power density, i.e. short-term power output and power consumption. In this respect, it is similar to the concept of the hydropneumatic accumulator, which Bosch in collaboration with PSA Peugeot Citroën has already scaled down from the size of a truck to a car. It is therefore predestined for the short-distance sprints that are typical in city bus traffic and can help a heavy bus to accelerate more efficiently from a standstill than electric hybrid technology, which has to be dimensioned rather heavily for the same performance. On the other hand, it is also clear that longer, emission-free stages will remain a domain of battery-electric concepts.

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