Flywheel hybrid vehicle delivers 22.4 per cent better fuel economy 07 September 2011

Improvements in fuel economy of up to 22.4% are being claimed for a research vehicle on stop-start duty, fitted with a new flywheel hybrid system.

Developed by a consortium of British companies as part of the UK government-supported Flywheel Hybrid System for Premium Vehicles (FHSPV) programme, the mechanically-driven flywheel system delivers up to 80bhp (82ps, 60kW) of recovered energy.

The figure of 22.4% was achieved using the new ARTEMIS test cycle, which represents typical real-world usage. Under the NEDC cycle, the flywheel hybrid, including stop-start, achieved 11.9% better fuel economy.

"The research shows the potential of mechanical hybrids as an affordable alternative to battery hybrids," states Prodrive head of vehicle engineering David Hemming. "Both the fuel economy results and the driveability are impressive, even with early-stage calibrations and no other design optimisation."

The FHSPV vehicle recovers energy via the rear differential, through a CVT (continuously variable transmission) into a high-speed flywheel. When the driver reapplies the accelerator, the CVT transfers energy back to the wheels.

The flywheel and its drive system are installed adjacent to the rear axle, in the space normally occupied by the spare wheel, and the whole system weighs 80kg. Hemming says minimal body and packaging changes were required to integrate the system, and adds that there is no change to the driveline configuration.

Designed by Flybrid Systems, the flywheel is constructed from carbon composite and operates in a partial vacuum, allowing it to spin at up to 60,000rpm. The CVT, which manages the flywheel's speed and the flow of energy in each direction, has been built by precision-engineering firm Xtrac, using Torotrak's traction drive technology.

"There is growing support for flywheel hybrid systems across the industry, fundamentally driven by affordability," comments Torotrak CEO Dick Elsy.

"From Torotrak's work in this market, the directional costs of the system look to be less than half of the cost of equivalent battery/electric hybrids. A mechanical hybrid with stop/start, at a transaction price that makes sense, has significant potential for widespread application in the drive to reduce CO2," he states.

Author
Brian Tinham

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