Function of Drum Brake

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2003-01-3348

Drum Brake Contact Analysis and its Influence on Squeal Noise Prediction P. Ioannidis, P.C Brooks, D.C Barton
University of Leeds
Copyright © 2003 SAE International

ABSTRACT
A non-linear contact analysis of a leading-trailing shoe drum brake, using the finite element method, is presented. The FE model accurately captures both the static and pseudo-dynamic behaviour at the friction interface. Flexible–to-flexible contact surfaces with elastic friction capabilities are used to determine the pressure distribution. Static contact conditions are established by initially pressing the shoes against the drum. This first load step is followed by a gradual increase of applied rotation to the drum in order to define the maximum reacted braking torque and pseudodynamic pressure distribution at the transition point between sticking and sliding motion. The method clearly illustrates the changes in contact force that take place as a function of the applied pressure, coefficient of friction and initial gap between lining and rotor. These changes in contact area are shown to influence the overall stability and therefore squeal propensity of the brake assembly. Dynamometer tests and experimental modal analysis on individual brake components are used to validate the analytical results.

parameters cause changes to the pressure distribution either directly such as changing the applied pressure or indirectly such as the thermal loading. A drum brake operating temperature of 400ºC for example can cause a typical passenger drum brake diameter to increase by 1 to 1.5 mm [2]. This non uniform thermal expansion of the brake components can lead to alternative contact configurations which will result in variation of the brake factor and may also contribute to squeal generation. Hence, the characterisation of the nature of squeal noise as “fugitive” as documented by many researchers is well justified. The parametric studies reported in this paper concentrate on the effect that the friction coefficient, actuation load and initial installation gap have on both static and pseudo-dynamic pressure distributions of a drum brake. This installation gap is defined as the difference in radius of the drum’s inner surface and the outer surface of each lining when the mechanism is unloaded. To predict the onset of squeal a non-linear static contact analysis is executed and then integrated with the well established complex eigenvalue method to accurately detect possible noise emissions [3]. All possible contact configurations that each brake lining undergoes during its working life need to be incorporated in the analysis in order to be able to predict the system’s potential to squeal. The FE model described below does not account for material wear, and it is therefore not possible to determine the exact contact configuration. For example, crown contact usually takes place during the unburnished stage of a brake’s life. On the other hand when run-in conditions have been achieved, with almost perfect initial conditions, then the pressure distribution will be concentrated on the toe and heel areas of the shoe [4]. Hence, several types of contact have been taken into account in the present analysis and their effect on noise generation has been compared with experimental results. These, preliminary results illustrate the effect that the commonly made assumption of perfect initial conditions has on brake noise, which reinforces the need for an integrated analysis of this type.

INTRODUCTION
Brake squeal is defined as a self-excited, frictioninduced vibration. The high sensitivity of a brake system’s noise propensity to changes in pressure distribution has been apparent for years due to the extensive research undertaken by automotive manufacturers on the vibration behavior of both disc and drum brakes. For the latter type, it is known that the likelihood of squeal increases with an increase in friction coefficient and actuating pressure. Also,...
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