Implementing an energy recovery system (ERS) is an effective solution to improve energy efficiency for hydraulic excavators (HEs). A flywheel energy recovery system (FERS) is proposed based on this concept. A hydraulic pump motor (PM) is employed as the energy conversion component and a flywheel is used as the energy storage component. Since the pressure is low because the bucket is usually empty as the boom lowers, a relatively large PM should be used in the FERS. To overcome this drawback, a novel compound energy recovery system integrating flywheel and flow regeneration (FFERS) is proposed in this paper. The working principle of the system is analyzed in detail. The introduction of flow regeneration has two benefits; one is downsizing the displacement of PM and the other one is an extra improvement of energy efficiency. The primary parameters of both are matched based on a 4 t excavator. Compared with the PM used in the FERS, the PM displacement in the FFERS is reduced by 71%. For comparison, a general model that can operate in either the FERS mode or the FFERS mode is developed in AMESim. The modeling results show that the FFERS with a downsized PM contributes a 13% increase in energy recovery and reutilization efficiency (62%) as compared with the FERS.
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