Increasing hydraulic energy storage capacity: Flywheel-accumulator

The energy storage density of hydraulic accumulators is significantly lower than energy storage devices in other energy domains. As a novel solution to improve the energy density of hydraulic systems, a flywheel-accumulator is presented. Energy is stored in the flywheel-accumulator by compressing a gas, increasing the moment of inertia of the flywheel by adding hydraulic fluid, and by increasing the angular velocity of the flywheel. Through a numerical model of the energy flows in the system, the energy storage of the flywheel-accumulator was demonstrated to be approximately 10 times greater than a conventional accumulator. Furthermore, the flywheel-accumulator allows the hydraulic system pressure to be independent of the quantity of energy stored. The integral flywheel-accumulator presents numerous future research challenges, yet offers the potential to transform and enable numerous applications including plug-in hydraulic hybrid vehicles.