Motor noise of urban rail vehicles: sources, frequency distribution and control
Motor noise comes mainly from three areas: electromagnetic vibration, bearings and the cooling fan, and its frequency spread is wide.
Where the noise comes from
Electromagnetic vibration is the main source: the electromagnetic field inside the motor makes the structure vibrate, and the vibration is then radiated as noise through the air. Bearing wear and imbalance cause vibration and noise, and the motor fan makes noise as it runs.
Frequency distribution
Motor noise runs from the 50–200 Hz low band to the 2–5 kHz high band. Electromagnetic noise is tied mainly to the motor's working frequency, mostly low to mid; bearing noise depends on rotating speed, mostly mid to high; fan noise varies with fan speed, mostly mid to high.
Control approach
Electromagnetic vibration: optimise the motor design, for example better electromagnetic materials and a coil design that lowers field non-uniformity; damping materials such as water-based damping coatings can reduce the transmission of electromagnetic vibration noise. Bearings: maintain and replace regularly, choose high-quality bearings and ensure accurate installation and balance. Fan: use a low-noise fan, optimise blade design and set the speed sensibly.