Dynamic Modeling of Magnetostrictive Hydraulic Pump

Recently, there has been substantial research on the development of a hybrid hydraulic pump driven by various smart materials. Piezo-hydraulic actuators have already been developed for potential use in smart rotor applications. However, at high actuation frequencies, piezo-stacks generate significant heat mainly due to the hysteresis losses that can deteriorate their performance and permanently damage the piezo material. In contrast, magnetostrictive materials are more robust than piezostacks, especially at high temperatures, while offering almost the same bandwidth and higher maximum induced strain when compared with piezoelectric stacks. Also, the magnetostrictive material usually has a particular frequency range where the hysteretic losses taking place are minimum and consequently the operation results in least heat generation. As a result, to operate the pump with higher flow rate with minimum heat generation and maximum efficiency, we need to know the system resonance. Moreover, the hybrid pump with smart material is mechanically more complex than a single rod actuator; consequently, it can have more than one resonant frequency depending on the number of degrees of freedom of the system. A hybrid pump using the magnetostrictive material Terfenol-D has been developed in our laboratory with hydraulic oil as the working fluid. Several key design parameters, which include output cylinder size, diaphragm thickness, reed valve thickness and tubing diameter, along with operational conditions, like input current and bias pressure within the fluid, have been varied to identify a set of optimum driving conditions. Tests at no-load have been carried out for unidirectional motion of the output piston. In this paper, we develop a dynamic model of the hydraulic hybrid actuator to show the basic operational principle and compare the simulated data with test results. The final target of this study is to find optimal operational frequency to get highest performance and also to predict the pump sizing for a desired output velocity and load lifting capability.