A research vehicle equipped with a flywheel hybrid system including stop-start has revealed fuel economy improvements of up to 22.4 percent based on the latest ARTEMIS test cycle, which represents today’s usual real-world usage.
The mechanically driven flywheel system is developed a group of British companies as part of the government-supported Flywheel Hybrid System for Premium Vehicles (FHSPV) program.
This system provides a maximum of 80bhp (82PS, 60kW) of recovered energy from a self-contained hybrid module. In the industry-standard NEDC cycle, the flywheel hybrid with stop-start achieved an improvement of 11.9 percent.
The group believes that mechanical hybrids provide solutions to the many challenges that relates to the electric hybrids. There is no inefficient conversion of energy from kinetic to electrical to chemical and vice versa. Moreover, the packaging, weight, recycling and cost issues related to the batteries are eliminated.
David Hemming, Prodrive’s head of vehicle engineering, has confirmed that the research reveals the potential of mechanical hybrids as a cheap alternative to battery hybrids. He further stated that both the driveability and the fuel economy results are impressive, even with early-stage calibrations and no other design optimization.
The research vehicle recovers energy through the rear differential with a continuously variable transmission (CVT) into a high-speed flywheel. When the driver applies the accelerator again, the CVT smoothly brings the energy back to the wheels.
The flywheel and its drive system are fitted near the rear axle, in an area where the spare wheel normally is found. The entire system weighs 80 kg. Minimal packaging and body changes were needed to incorporate the system.
The driveline configuration was not changed. The flywheel, designed by Flybrid Systems, is built from carbon composite. It operates in a partial vacuum, letting it spin at a maximum of 60,000rpm. Controlling the speed of the flywheel as well as the flow of energy in each direction, the CVT has been developed by precision-engineering firm Xtrac utilizing proven traction drive technology from Torotrak.