Energy management of a hydraulic hybrid passenger vehicle

Hydraulic Hybrid vehicles offer an opportunity for significant reduction in fuel consumption through the use of energy storage. This vehicle architecture uses a variable displacement pump/motor combination to transfer energy between the mechanical and hydraulic domains and a high pressure accumulator for energy storage. Fluid Power was chosen as the medium for energy storage because the accumulator has a superior power density to electric batters and it can be safely charged and discharged repeatedly over the full range of storage capacity. However, to utilize this additional capability, a supervisory control known as an energy management strategy (EMS) is needed. Model Predictive Control was selected for design the (EMS) because it provides an effective method of regulating the additional degrees of freedom within the powertrain without requiring advance knowledge of the duty cycle. This control technique uses a model of the powertrain to predict its response to a sequence of control decisions over a finite horizon. In this way, the control sequence which minimizes a chosen objective function can be determined. The proposed controller will utilize the energy storage capability of the hydraulic hybrid to optimize the efficiency of the powertrain while satisfying the operator’s demands.