Flywheel Hybrid Vehicle Delivers Up To 22.4% Fuel Economy Improvement

In the industry-standard NEDC cycle, the flywheel hybrid including stop-start achieved an 11.9 percent improvement.

The consortium believes that mechanical hybrids solve many of the challenges associated with electric hybrids. There is no inefficient conversion of energy from kinetic to electrical to chemical and back. And the cost, weight, packaging and recycling issues associated with batteries are also eliminated.

“The research shows the potential of mechanical hybrids as an affordable alternative to battery hybrids,” confirms Prodrive’s 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 engineering development vehicle recovers energy via the rear differential through a continuously variable transmission (CVT) into a high-speed flywheel. When the driver reapplies the accelerator, the CVT smoothly transfers the 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 80 kg. Minimal body and packaging changes were required to integrate the system. 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 proven traction drive technology from Torotrak.

Automotive technology specialist Prodrive is responsible for the system’s configuration and integration into the vehicle. Prodrive also developed the system’s complex control strategy and software including preliminary calibrations. Ricardo and Ford provided specialist expertise around alternative technologies and applications.

“There is growing support for flywheel hybrid systems across the industry, fundamentally driven by affordability,” said 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.”