Part-funded by the UK’s Technology Strategy Board as part of its Low Carbon Vehicles initiative, the Flybus consortium has brought together engineers from bus maker Optare, engineering consultancy Ricardo and traction drive technology specialist Torotrak. Automatic transmission supplier Allison Transmission Inc is also participating in the project on a self-funded basis.
The Flybus system, which has the potential to cost significantly less than current electric hybrids, uses a Ricardo Kinergy flywheel as the energy storage medium and a Torotrak continuously variable transmission (CVT) as the means of transferring energy between the wheels and the flywheel. The entire installation is mounted on the existing Allison 2000 series transmission’s Power Take Off facility.
The Flybus system, just like electric hybrids, recycles the kinetic energy that would otherwise be wasted when the vehicle brakes. As the bus decelerates, the CVT transfers energy from the vehicle wheels to the flywheel, spinning it up to speeds of around 60,000rpm. As the vehicle pulls away from rest, the CVT returns energy from the flywheel to the wheels, reducing the engine power requirement and hence lowering fuel consumption.
A key enabler of this technology is the Torotrak CVT, which can transfer in excess of 60kW of power in a package weighing less than 10Kg. High levels of efficiency, together with ‘torque control’ – in which torque rather than ratio is controlled – make the technology an ideal fit for a flywheel drive. The second key enabler is Ricardo’s Kinergy
flywheel, which uses a compact and low cost magnetic coupling to transmit torque to the
flywheel whilst providing the required step-up gearing. Furthermore, use of a magnetic
drive facilitates flywheel operation within a sealed vacuum, whilst eliminating the need
for inefficient mechanical gearing and rotating seals. The result is a system which
exhibits very low levels of power loss.
The unit installation is now complete and initial test work underway. Further driveability
work will take place before starting evaluation of the fuel economy benefits on the
vehicle.
Fuel economy measurements will be carried out over the Millbrook London Transport
Bus (MLTB). The Consortium is expecting the results to be available in Spring 2012.