Design optimization of a hydraulic flywheel accumulator for a hydraulic hybrid vehicle

Abstract

The hydraulic flywheel accumulator is a novel energy storage device that has the potential to overcome major drawbacks of conventional energy storage methods for mobile hydraulic systems. By employing a rotating pressure vessel, the hydraulic flywheel accumulator stores energy in both the hydro-pneumatic domain and the rotating kinetic domain. This allows for energy storage densities many times higher than conventional hydraulic accumulators and adds a degree of freedom that decouples state of charge from the hydraulic system pressure. This paper summarizes various mechanical stress and energy models developed to describe the behavior of the hydraulic flywheel accumulator. The models are used in an example design optimization to illustrate the utility of the hydraulic flywheel accumulator. The resulting design solution delivers an energy storage density at least six times greater than traditional composite hydraulic accumulators while exhibiting efficiencies above 75%.