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Brake squeal signatures (2 kHz to 18 kHz) have tonal content highly dependent on the specific brake system structural architecture. The challenge in minimizing squeal involves correctly identifying the conditions (temperature, apply pressure, rotor speed as some basic parameters) of occurrence, defining the underlying structural dynamics of the system and applying appropriate suppression solutions. The quantitative metric of improvement is the cumulative event percentage of occurrence. Design variables of the brake system and performance attribute targets extend the challenge beyond the level of just reducing noise. Consideration of material costs, manufacturing/assembly factors, durability, thermal management as well as other factors narrow the solution space significantly. Compressed late stage development is not uncommon in reaching acceptable levels of performance and is a primary reason for following a well defined process flow with provision for alternative solutions.

The disc brake corner assembly is comprised of several subsystems (brake pad, caliper, rotor etc.) which have interfaces between two or more of these structures. The brake pad assembly as the subsystem connecting the rotor to the caliper has specific areas of contact which influence the onset and potential to control brake squeal. The primary excitation interface occurs between the friction pad and rotor surface. The contact is initiated by the piston apply force on the brake pad insulator. Contact interface reaction forces, displacements and deformations are generated and form the natural and geometric boundary conditions of the overall system. Brake squeal characteristics are strongly affected by these conditions. The study focuses on brake system dynamic response to interface contact conditions. The brake insulator and pad assembly interacting with the brake piston as well as caliper are evaluated.

The environmental effect on brake system noise characteristics has introduced increased expectations in overall performance as well as associated challenges in the design of brake insulators that can provide optimal noise control within specific temperature extremes. The condition of cold noise brake squeal which is classically defined between 0 to 50C (pad lining temperature) and environmental conditions as low as -50C depending on regional applications has become a major part of customer requirements. This is evident by the proliferation of vehicle and dynamometer test validation protocols (e.g. Minneapolis City Traffic (MCT), GMW 14591, Ford Cold Noise Procedure (CTEP 420), J2521, Federal Mogul (FM204B)) which devote a significant part of the cumulative brake squeal occurrences within the cold noise regime.

Meeting specific bonded insulator attachment specifications depend on the type of bonding polymer selected as well as application conditions. These conditions include initial apply parameters (time, temperature and pressure), backing plate surface characteristics (surface material, flatness, finish) and strength properties that avoid cohesive, adhesive or mixed mode failures during operating life of the braking pad assembly. “T-pull” and “Lap Sheaf testing provide an overall quantitative method to determine tensile and shear load/deflection properties. They do not assess the three dimensional dynamic stress state of the bond during braking conditions which involve the influence of temperature, apply pressure, rotational inertial forces and cyclic frequency/strain rate effect. The operational factors which change the state of bond have an effect on damping performance and ability to control overall system noise.