Research on the energy transfer and efficiency performance of an electro-hydrostatic actuator for wheel-legged robot joint

Intelligence and electrification stimulate the development of wheel-legged robots (WLRs), providing excellent environmental adaptability and mobility. This paper investigates a novel electro-hydrostatic actuator (EHA) with a four-quadrant working principle, two models of electro-hydraulic drive and energy recovery integrated into WLR joints. The range and stability of WLRs will be dramatically improved by utilizing highly efficient EHAs with a high force-to-weight ratio. Mathematical models depending on the force and velocity characteristics are developed and analyzed to explore the energy conversion mechanism. Furthermore, experiments and parameter identification are performed to verify the feasibility and obtain unknown parameters, including torque, leakage, and damping coefficients. The analysis results indicate that the presented EHA is highly efficient, achieving a drive efficiency of up to 87 % and an energy recovery efficiency of up to 88 %. The primary concentration of loss is pressure reduction within the hydraulic circuit. Practical solutions to promote the work and the average efficiency are given in the last. The research will provide theoretical guidance, aiding further structural optimization and control strategies.