Assessment of Flywheel-System Benefits in Selected-Vehicle Applications

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Assessment of Flywheel-System Benefits in Selected-Vehicle Applications

L. Forrest / L. H. Kubo

A study was made of the performance characteristics of vehicle systems incorporating energy storage flywheels. The study focused on two specific automotive applications in which the capabilities of flywheel-equipped vehicles were compared to their non-flywheel counterparts: (1) an intermediate-class passenger car/urban taxi with conventional internal combustion engine (ICE) drive (fuel conservation application of the flywheel system), and (2) a subcompact-class commuter car with electric drive (range extension application of the flywheel system). The intermediate-class vehicle was examined in both series and parallel drivetrain configurations. In the series configuration drivetrain, the flywheel effectively drives the vehicle while the engine operates in an on-off mode to maintain flywheel speed. In the parallel configuration drive-train, the engine drives the vehicle in a conventional manner, while the flywheel operates to augment the engine power output as needed to meet road load. The drivetrain examined for the subcompact vehicle incorporates a battery-powered dc traction motor and a hermetically sealed flywheel-motor/generator unit that outputs electrical energy to augment the battery source. The performance characteristics of these flywheel vehicle systems were analyzed using a computer-based vehicle simulation program (HYFLY). The performance figure-of-merit employed in the analysis of the heat engine/flywheel vehicles was fuel economy benefit (percent fuel economy improvement over baseline vehicle), and that for the battery/flywheel vehicle was range extension benefit (percent range improvement over baseline vehicle). The fuel economy parameter was evaluated for taxi, urban, highway, and composite driving conditions, and the range parameter was evaluated principally for the J227a(D) driving schedule. (ERA citation 08:055947)