Investigation Of Brake Pad Vibration Under Dynamic Squeal Conditions

Brake squeal is a highly complex noise mechanism resulting from friction induced vibration which excites many separate but mechanically connected components within the brake system. Often this can be broken down into the whole corner assembly, including suspension, at low frequencies while at the higher frequencies only the friction couple of disc and pads are of interest. The brake disc plays the role of the noise emitter and therefore must be excited through the friction pair interface in order to generate noise. It is therefore of interest to identify how the brake pad vibrates in relation to the disc mode of vibration. This paper presents measurements of pad vibration under dynamic squeal conditions on a laboratory dynamometer. Measurements are made using piezo-electric beams mounted about the inboard and outboard brake pad. Various squeal frequencies are investigated including a phenomenon where a pair of squeal frequencies, close in value, are seen to emanate at different brake pressure applications. This phenomenon is of particular interest as the noisy regions are separated by quiet zones within the brake application. This “switching” between the two frequencies can be related to the pad mode of vibration (torsion or bending) which in turn may be related to the disc mode “fixing” about the pads. Finite element analysis is used to investigate the free-free pad modes of vibration with experimental “shaker” testing used to correlate and confirm the results