Effect of disc-pad contact modification on the brake judder source using a simplified elasto-kinematic model

The brake torque variation (BTV) generated due to geometric irregularities in the disc surface is generally accepted as the fundamental source of brake judder; geometric imperfections or waviness in a disc brake caliper system is often quantified as the disc thickness variation (DTV). Prior research has mainly focused on the vibration path(s) and receiver(s), though such approaches grossly simplify the source (frictional contact) dynamics and often ignore caliper dynamics. Reduction of the effective interfacial contact stiffness could theoretically reduce the friction-induced torque given a specific DTV, although this method would severely increase static compliance and fluid volume displacement. An experiment is designed to quantify the effect of disc-pad contact modifications within a floating caliper design on BTV as well as on static compliance. The major objective of this experiment is to determine if changes in the disc-pad contact geometry can also reduce BTV without limiting the static compliance of the caliper system. A conceptual half-caliper model is proposed to explain the observed effects of pad modifications. This simplified elasto-kinematic model uses the elastic center concept on a pad subject to spatially phased periodic displacement inputs (DTV) at the disc-pad interface. It is utilized to determine the effective variation in normal load. The model is finally employed to determine the sensitivity of key physical parameters and to identify trends that might reduce BTV.