Compact hybrid electrohydraulic actuators using smart materials: A review

Abstract

The development of compact hybrid electrohydraulic actuators driven by various smart materials has been widely reported in the literature in recent years. Such solid-state-induced strain actuators have applications in a variety of aerospace and automotive and mechanical engineering fields. These devices are capable of producing high stroke (or displacement) and high force (or pressures) in a compact form factor by utilizing the large bandwidth and energy density of currently available smart materials. The basic operation of these hybrid actuators involves high-frequency bidirectional operation of an active material that is converted to unidirectional motion of a hydraulic fluid by a set of valves. Over the last decade, several prototype hybrid actuators have been designed using piezoelectric (PZT-5H), magnetostrictive (Terfenol-D), and electrostrictive (PMN-PT) materials as the driving elements, with actuation frequencies ranging from 10 Hz to 1 kHz. Power outputs and volumetric flow rates have reached up to 20 W and 40 cm3/s, respectively. Different mathematical models have been developed to evaluate the performance of these hybrid actuators. While early efforts focused on a simple, quasi-static approach to simulate pump operation, more complex dynamic models have been recently developed to capture the complex interaction between the smart material and the transmission fluid at high operating frequencies. The objective of this survey is to review the state-of-the-art in compact hybrid electrohydraulic actuation systems and to summarize design and modeling efforts.