Modeling of a Hydraulic Energy Regeneration System: Part I—Analytical Treatment

Hydraulic regeneration systems have been considered by the automotive industry for implementation in hybrid vehicles for a number of years. The combination of an internal combustion engine and an energy storage device has great potential for improving vehicle performance and fuel economy as well as reducing brake wear. This study describes an analytical model of a hydraulic regeneration system consisting of an accumulator, an oil reservoir, a variable-displacement pump/motor, connecting lines and a flywheel which is used to simulate vehicle inertia. An integration algorithm is used to simultaneously solve the governing equations and predict the system performance. Variables including accumulator pressure and temperature, pump/motor torque and efficiencies, pressure losses, and flywheel speed as functions of time are predicted. Power losses and round-trip efficiencies can be readily determined once the system performance variables have been calculated.