Dry and Wet Modal Comparison of an Electro-Hydraulic Pump and Its Electromagnetic Vibration Analysis

The electro-hydraulic pump (EHP), as the primary power component of the electro-hydrostatic actuator, typically operates in a wet environment filled with hydraulic oil, thereby experiencing vibration response alterations due to the added mass of the fluid. Accurate identification of the wet modal characteristics is essential for improving the fidelity of electromagnetic vibration prediction in EHPs. In this work, an integrated EHP is investigated. A finite-element model is established to perform dry and wet modal analyses, from which the first nine natural frequencies and associated mode shapes are extracted. Dry and wet experimental modal tests are then conducted using an impact-hammer setup to validate the numerical model. The results indicate a systematic reduction in natural frequencies under oil-filled conditions, with more pronounced shifts in the lower-order modes; a maximum decrease of 10.92% is observed. On this basis, the stator tooth electromagnetic forces are obtained from two-dimensional electromagnetic finite-element simulations, and vibration responses are predicted via modal superposition using either dry or wet modal parameters. Finally, vibration measurements are performed under oil-filled operating conditions. The measured spectra exhibit pronounced tonal components at the electrical fundamental frequency and its even harmonics, and wet modal-based electromagnetic vibration prediction improves the accuracy by 78.90% relative to the dry modal-based prediction. These findings provide both theoretical support and practical guidance for low-vibration and low-noise design of EHPs.