Automotive disc brake squeal

Thermal and thermomechanical effects in dry sliding

Hot spotting in automotive friction systems

Thermoelastic instability in automotive drum brake systems is investigated using a finite layer model with one-sided frictional heating. With realistic material properties of automotive brakes, the stability behavior of the one-sided heating mode is similar to that of the antisymmetric mode of two-sided heating but the critical speed of the former is higher than that of the latter. The effects of the friction coefficient and brake material properties on the critical speeds are examined and the most influential properties are found to be the coefficient of friction and the thermal expansion coefficient of drum materials. Vehicle tests were performed to observe the critical speeds of the drum brake systems with aluminum drum materials. Direct comparisons are made between the calculation and measurement for the critical speed and hot spot spacing. Good agreement is achieved when the critical speeds are calculated using the temperature-dependent friction material properties and the reduced coefficient of friction to account for the effect of intermittent contact.

Frictionally Excited Thermoelastic Instability in Automotive Drum Brakes

Summary High-frequency train-track interaction and mechanisms of wheel/rail wear that is non-uniform in magnitude around/along the running surface are surveyed. Causes, consequences and suggested remedies to relieve the problems are discussed for three types of irregular wheel/rail wear: (1) short-pitch rail corrugation on tangent tracks and large radius curves, (2) wheel corrugation as caused by tread braking, and (3) wheel polygonalisation. The state-of-the-art in modelling of dynamic train-track interaction in conjunction with prediction of irregular wear is reviewed.

Train-Track Interaction and Mechanisms of Irregular Wear on Wheel and Rail Surfaces

Thermal distortion in brakes due to frictional heating causes localized contact and high temperatures (hot spots) with consequent thermal damage to the sliding components. This paper examines the effect of brake design and operating parameters on the maximum temperature reached. Previous solutions for steadystate sliding are reviewed and the effects of hot spots being in intermittent contact due to the geometric design of the brake are discussed. Approximate solutions for transient thermoelastic contact are extended to the case of uniform deceleration to determine the duration of the stop for which thermoelastic effects will be significant. If the stop is sufficiently slow for hot spots to develop, the temperatures will generally be high. However, high temperatures are also reached in sufficiently rapid stops due to the high rate of energy dissipation. An optimum is found between these extremes.

J. R. Waring

Papers

Implications of Thermoelastic Instability for the Design of Brakes