Noise Characteristics and Dominant-Frequency Migration in a PMSM-Driven High-Speed Axial Piston Pump System over a Wide Operating Range

Axial piston pumps driven by a permanent magnet synchronous motor (PMSM) are important for improving the power density and energy efficiency of electrohydraulic power units. However, operation at high speeds can intensify vibration and noise through multiple coupled excitation sources. To characterize the overall noise behavior and the evolution of dominant frequencies in these systems, this study experimentally investigates a PMSM-driven axial piston pump over rotational speeds from 1000 to 5000 r/min and pressures from 10 to 35 MPa. Synchronous sound pressure measurements at five locations, sound pressure level (SPL) analysis using A-weighting, and frequency versus speed spectral mapping are used to characterize the spatial distribution and spectral evolution of the radiated noise. Overall, A-weighted SPL tends to increase with pressure, although it decreases at some low-pressure operating points, and its dependence on rotational speed is nonmonotonic. High noise regions are concentrated at 4500 to 5000 r/min and 25 to 35 MPa. The noise exhibits strong spatial directivity: the motor side region and the measurement location on the high-pressure outlet side (P1) together account for 94.4% of the maximum SPL occurrences across all 54 operating conditions. The dominant spectral peaks in the noise signals generally occur at the piston passing frequency (PPF) and its harmonics. As speed increases, the dominant order shifts from the 3rd, 4th, and 5th harmonics at low speeds to the 2nd harmonics at medium speeds, and finally to the PPF itself at 4500 to 5000 r/min. This migration is associated with different PPF harmonics successively entering a high response band near 1 kHz. The proposed acoustic characterization framework provides frequency domain targets for subsequent structural optimization, fluid pulsation suppression, and sound quality improvement in high-speed pumps.