1993-11-01

Practical Evaluation and FEM-Modelling of a Squealing Disc Brake 933071

Earlier works, coped with the problem of brake noise, described the dynamical behaviour of brake system components or excitation mechanisms, as the stick-slip effect. This work describes a pathway to simulate the dynamical behaviour of lumped mass system, excited by different mechanisms. One part of the paper focuses on the mechanical parameters of a lumped mass system, taking into account the geometry of the brake and mechanical properties of the friction material. This gives rise to the correct description of the energy dissipation into the boundary layer and the systems response resulting (e. g. pad end flutter). As a first step a FEM model of the entire brake is developed. By means of this model the sensitivity of systems eigenmodes regarding different mechanisms of excitation can be calculated. The eigenfrequencies with the highest sensibility of excitation are used for the assessment of the mechanical parameters of a simplified lumped mass system. With this model simulations are carried out in order to show the validation of possible excitation mechanisms. The results give evidance of the existence of certain mechanisms under particular driving conditions. Results of validation measurements for these particular conditions are given. Further simulations widen the lumped mass system to more degrees of freedoms, excited parallel by friction mechanism. This model gives the same prinicpal findings, as the simple one.By means of a special testing device the experimental evaluation of the mechanism of friction is possible and is used for the improvement of the models mentioned above. CONTENTS 1 Introduction 2 Measurement and calculation of the eigenmodes of a squealing brake 2.1 Vibration measurements on a noise dynamometer 2.2 FEM modelling of the VWII brake 2.3 Results of the simulation 3 Mechanisms of excitation and system properties 3.1 Fundamentals of the stick-slip effect 3.2 Generalised mechanism of excitation 4 Simulation of the stick-slip effect by lumped mass systems 4.1 Extended lumped mass system 4.2 Simulation with an extended lumped mass system 5 Measurement of excitation at the tribometer

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