The obnoxious brake squeal: New ideas about an old problem
Prof. Peter Hagedorn, TU Darmstadt
Date: Thursday, November 15, 2012
Place: EA 409
The obnoxious brake squeal is a nuisance to the general public and a considerable cost factor to the automotive industry trying to produce squeal-free brakes. Fortunately it does not interfere with the function of the brake and is a comfort problem ‘only’. It is a very old problem and has basically been around as long as there are brakes. In the last decades, considerable effort has been devoted to the study of brake squeal with view to reducing the noise generated over a broad range of frequencies (1-12kHz). To this end, a large variety of mathematical-mechanical models has been developed, studying various instability phenomena. A large empirical effort is spent in industry even today to eliminate or reduce brake squeal. This clearly shows that the problem is yet not completely understood and needs further attention.
The squealing noise is usually reduced by such passive means as modification of brake material, introduction of damping elements in the pad, etc. Some possibilities of controlling the noise by active means in addition to the passive damping are also being studied in Darmstadt in close cooperation with industry. In the dynamics group in Darmstadt different mathematical brake models have been developed and checked against experiments with a floating calliper disc-brake on a specially constructed test rig. We believe that our models capture most of the essential features of the dynamic behaviour of the brake squeal within a frequency range of 1-5 kHz.
Good mathematical and mechanical models for the excitation mechanisms leading to brake squeal will be helpful for developing squeal-free brakes without lengthy tests in the laboratory. Often brake squeal is associated with a negative slope of the friction coefficient with respect to the relative contact velocity. In this presentation it is shown that even for constant coefficients of friction, the contact forces lead to self-excitation if the contact kinematics is carefully modelled. This will be illustrated using extremely simple mechanical models. Very large finite element models used by the car and brake manufacturers to model the brake dynamics, have so far not contributed to a better understanding of the problem.
About the Speaker:
Peter Hagedorn was born in 1941 in Berlin, Germany. He grew up in Brazil, where he graduated (Engineer’s degree) in mechanical engineering in 1964 at EPUSP and in 1966 earned his doctoral degree at the same University. He then worked as a research assistant and later as ‘dozent’ (similar to lecturer) at the University of Karlsruhe, Germany. In 1971 he got his ‘habilitation’ (similar to Dr. Sc.) at Karlsruhe. From 1973 to 1974 he was a visiting Research Fellow at the Department of Aeronautics and Astronautics, Stanford University. Since October 1974 he is full professor of mechanics at the Technische Universität Darmstadt and head of the Dynamics and Vibrations group. He also has served as visiting professor at Rio de Janeiro (Brazil), Berkeley, Paris, Irbid (Jordan) and Christchurch (New Zealand), where he also holds an Adjunct Professorship at UCC. He has served as Head of Department and Vice-President to his home University in Darmstadt and he is serving in a number of professional and editorial committees. He is author of over 250 papers and nine books on a variety of topics in the general field of dynamics and vibrations and analytical mechanics. He is currently head of the Dynamics and Vibrations Group at the Chair of Numerical Methods in Mech. Engineering (fnb, Professor Schäfer) at TU Darmstadt, Associated to the Graduate School of Computational Engineering.