Braking noise of urban rail vehicles: frequency distribution and control
Braking noise comes mainly from contact and friction between wheel and brake when the braking system works, and it is concentrated in the mid-to-high band.
Frequency distribution
Braking noise is concentrated in the mid-to-high band from 500 Hz to 3 kHz and may also extend to lower and higher frequencies.
Where each band comes from
Mid-to-high band: sliding friction between brake pad and wheel rim; the heat of braking can locally melt and bond pad and rim, producing a squeal that can reach several kilohertz. Low band: vibration of the braking system and impact noise when brake and wheelset make contact. High band: fast movement of the brake and sudden stops of the braking system.
Control approach
Mid-to-high band: optimise the braking system design, use high-performance pads and an optimised braking strategy; for systems that may squeal, improve the pad and rim material and reduce the heat generated in braking. Low band: improve the vibration behaviour of the braking system and the contact between brake and wheelset. High band: use advanced braking such as electric braking to reduce sudden stops of the braking system.