A study of the interface pressure distribution between pad and rotor

A general overall improvement with NVH issues in high volume production cars continues to highlight the problems of brake noise and its affect on vehicle acceptability. There are many theories attributed to brake noise but at the higher frequencies the mechanism is generally related to the friction pair of disc and pad and the associated interface geometry.

This paper shows that the interface geometry can be directly related to the frequency being generated and the resulting variation in frequency with pressure. In addition it is shown that a change in interface geometry may in fact eliminate noise which will return as the geometry re-establishes itself. It is also shown that there is a strong relationship between the interface pressure distribution, the effective centre of pressure and the propensity of the brake to generate noise. It is shown that with a leading centre of pressure the brake is more prone to noise and with a trailing centre of pressure more likely to be stable. The analysis infers that the centre of pressure may vary both along the pad and radially during braking which adds to the complex analysis of instability.

The paper analyse the interfacial pressure distribution, at the disc/pad interfaces under a normal sliding condition. The paper also investigate the propensity of a brake to generate noise over a range of hydraulic pressure under conditions which allow a mechanically induced offset centre of pressure between pad and rotor to be varied.

The work includes both analysis and practical applications of successful noise fixing through the consideration of pressure distribution and centre of pressure.

Further work is continuing using an opposed 12 piston calliper to vary pressure along the length of the pad. This work combined with pressure distribution measurements, wear measurements and thermal imaging will significantly extend the understanding of pad interface geometry.