Performance modeling of a piezohydraulic actuation system with active valves

Piezohydraulic actuation is the use of hydraulic fluid to rectify the high frequency, small stroke oscillation movement of the piezoceramic stack into a unidirectional movement at a specific combination of stroke and force. In recent years, piezohydraulic pumps have been studied and developed by several groups. This paper presents two steady flow models based on different approximations of the hydraulic fluid. In the first model we assume a fully developed incompressible viscous flow, and in the second model we incorporate the compressibility of hydraulic fluid into our model. These two models are derived based on the energy equations for hydraulic flow in a circular pipe. Major and minor losses are identified and incorporated into the models. Assumptions and approximations were made to minimize computation effort while achieving good accuracy. A piezohydraulic actuation system with active valves is then built and tested. Comparison with test results shows that the simulations accurately predict system performance under loads at which value leakage is not present. The results reveal that friction losses due to viscosity are a major limitation of performance for the current test setup when operating at higher frequencies. Timing studies of the active vales show the valve timing is important to the performance of the system.