Stack-type piezoelectric actuators, which usually consist of several ceramic layers connected in series, are widely used in piezoelectric direct-drive servo valves (PDDSV). However, poor pulling force capacity of this kind of actuators affects the performances of the direct-drive servo valves. This article presents a new type of PDDSV, whose spool-driving mechanism is composed of a set of independent parts that are not fixed together but are in contact with each other. This multi-body contacting spool-driving mechanism provides bidirectional movement of the spool by a preloaded stack-type piezoelectric actuator and a driving disc spring. This prevents the stack-type piezoelectric actuator from bearing the pulling force due to the inertia and friction of the spool. Design of the proposed servo valve is illustrated in detail and its characteristics are also predicted. Based on a nonlinear dynamic model of the multi-body contacting spool-driving mechanism, a comprehensive dynamic simulation model of the proposed PDDSV is established. Static and dynamic characteristics of the proposed PDDSV have been studied experimentally and good agreements between experimental and simulation results are observed. The dynamic performances of the proposed PDDSV are compared with the existing piezoelectric servo valves, which demonstrate that the proposed PDDSV has satisfactory dynamic characteristics for high-frequency applications.
The reduction of fluid ripple in pipes is extremely important for the reliability and safety of aircrafts and ships. Currently, most researches only pay attention to the discharge port and ignore the suction port and the inherent characteristic of the axial pump between both ports, which may cause significant underestimation of fluid ripple especially in the closed-loop hydraulic system. Therefore, the aim of this study is to propose a novel passive fluid ripple attenuator, which can simultaneously reduce discharge and suction pulsation of the axial-piston pump, and adapt to the condition of frequent change of load reversing in closed hydraulic system. First, the phase matching rule is discovered between discharge and suction ripple, and then based on that, the proposed discharge and suction self-oscillation principle is verified through simulation on the phase relationship of the pump internal pistons, instead of considering the two separately as before. The attenuator designed with the concept of the discharge and suction self-oscillation principle is presented, and models of how ripple generates and the attenuator works are represented analytically. The corresponding simulation model is established, and the result indicates that the ripple of both ports of the piston pump is weakened significantly. Moreover, one testing platform is developed, and the experimental study is conducted on the discharge and suction ripple. It proves that the proposed attenuator based on discharge and suction self-oscillation principle can reduce the fluid ripple effectively.
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