|FHSPV flywheel CVT system layout. Click to enlarge.
A research vehicle fitted with a flywheel hybrid system including stop-start has demonstrated improvements in fuel economy of up to 22.4% in the new European ARTEMIS test cycles. Developed by a consortium of British companies as part of the Government-supported Flywheel Hybrid System for Premium Vehicles (FHSPV) program, the mechanically-driven flywheel system delivers up to 80 bhp (82 PS, 60 kW) of recovered energy from a self-contained hybrid module. (Earlier post.)
The new Common ARTEMIS Driving Cycles (CADC), developed within the European research project ARTEMIS (Assessment and reliability of transport emission models and inventory systems), include three real-world driving cycles (urban, rural road and motorway) designed to be representative of the actual conditions of vehicle usage and driving and to reproduce the diversity of the observed driving conditions. In the industry-standard NEDC cycle, the flywheel hybrid including stop-start achieved an 11.9% improvement.
|FHSPV flywheel CVT component details. Click to enlarge.
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 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 60,000 rpm. The CVT, which manages the flywheel’s speed and the flow of energy in each direction, has been built by 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 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. 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.—Torotrak CEO Dick Elsy
Volvo Car Corporation will begin testing of a flywheel drive on public roads later this year. (Earlier post.)