Optimizing Energy Efficiency in Closed-Circuit Hydrostatic Transmissions: Advancing Charge Pump System Control

Abstract

While closed-circuit hydrostatic transmissions (HTs) achieve remarkable efficiencies (≤98%) in their main pump-motor units, auxiliary charge pump systems remain a significant source of avoidable energy loss. This review synthesizes current research to demonstrate that conventional fixed-operation charge pumps-operating continuously at ~25 bar pressure and 10-20% of main pump flow-waste substantial energy due to misalignment with actual system demands. Charge pumps perform critical functions: compensating for internal leakage, providing filtration/cooling, supplying servo-control pressure, preventing cavitation, and ensuring lubrication. However, their static operation causes continuous throttling losses and heat generation. Recent advances in variable-displacement pumps and adaptive control strategies (e.g., pressure compensation, servo-proportional control) enable dynamic adjustment of charge pressure and flow, unlocking 20-45% energy savings without compromising functionality. We identify charge system optimization as the next frontier for HT sustainability and prioritize research directions: robust adaptive algorithms, digital hydraulic integration, and standardized validation frameworks.