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Finite element simulations are widely used for simulating disc brake squeal and the aim of this paper is to further increase the understanding of the effect of insulators. An earlier paper has presented an experimental technique for measuring the properties of the viscoelastic materials [1] and it has been shown how these data can be used in simulating brake response [2]. This paper deals with the sensitivity of a FE brake model to frequency dependent shim material properties and it is documented that with the current options for modeling shims in complex eigenvalue analysis it is only possible to accurately simulate response in a narrow frequency range. A procedure to find optimized parameters for a current damping model is discussed. The best α and β values for a Rayleigh damping model is found by obtaining a least square best fit in a frequency range of interest.

Since 1996 a 2nd Generation EBS has been available in Europe as an advanced brake system offering a variety of advantages to the OEM as well as to the truck and fleet owner. EBS enhances vehicle safety and improves the braking performance to a “passenger car like” braking feel, allowing less experienced drivers better vehicle handling. The brake lining wear control and retarder integration allow the reduction of operational costs. The safety enhancements achieved by EBS in conjunction with disc brakes, are rewarded by European truck insurance companies by lower insurance fees. The importance of EBS will still gain significantly through the developments in process. EBS is the platform for ESP and ACC, which will be a major contributer to better integration of trucks in dense traffic flow.

This article, as part III of a series, briefly reviews some of the representative literature on brake squeal testing and evaluation. It discusses the potential influence of variation within brake components and operational conditions on brake squeal dynamometer tests and their correlation to vehicle road tests. Roles and challenges of component/system parameter measurements such as brake pad damping, disc rotor in-plane mode and friction induced vibration characteristics, friction coefficient, moisture absorption and elastic constants of lining material, and contact stiffness are addressed. An application example of a reliability method to assure dynamometer test results are statistically significant is presented. The advantages of using laser metrology are also briefly described, especially the measurement of 3D squeal operational deflection shape. Lastly, general future research directions are outlined.

Since the brake colloquium in 2004 the role of climatic conditions and their relations to noise occurrence, sound pressure level and friction coefficient level is widely discussed in the US and European working groups on brake noise. A systematic study has been started to investigate the influence of relative humidity, absolute humidity and temperature on brake noise and the corresponding friction coefficient level. In this study an enormous effort was taken to keep the influences of the brake parameters, e.g. lining material, Eigenfrequencies and dimensions of the different components as small as possible to investigate the climatic influence only. Strategic humidity and temperature levels were tested according to the Mollier-Entropy-Enthalpy-Diagram which are corresponding to the seasons in the various international regions. A regression analysis evaluates the correlation and the influence of each parameter to noise and friction coefficient level.

This paper applies the existing techniques used in the CAE simulation for calculation of potential high frequency (>10 kHz) squeal from disc brake system. The goal is to investigate the component interaction at the system level. A simulated dynamometer process is developed using stability analysis at different pressures and friction coefficient combinations. From the identified squealing condition, coupled with measured ODS, dynamic characteristics at system level are tracked to the components contribution based on the mode merging phenomenon as the system turns unstable due to friction coupling. The component contribution is based on the strain energy of the component in the system mode and MAC between mode components in free condition and system real modes. Special focus on rotor dynamics is discussed and its effect on system instability at high frequency range.

Disc brake squeal is a very complicated phenomenon, and the influence of insulators in suppressing squeal is not fully understood. The aim of this paper is increase the understanding of the effect of insulators. A previous paper [1] presented an experimental technique for measuring the frequency- and temperature- dependent properties of viscoelastic materials currently used in insulators. The present work continues by considering the coupled vibrations of the brake pad and insulator. A comparison of natural frequencies found from experimental modal analysis and finite element modeling indicates agreement to with 5%. Experimentally determined modal loss factors of the brake pad vary dramatically with frequency, changing by a factor of 2 over the frequency range 2-11 kHz. A method for including this frequency dependence, as well as the frequency dependence of the insulator material, in state-of-the-art finite element software is proposed.

This paper details the use of experimental and test data based analytical techniques to resolve brake squeal. External excitation was applied to the brake system during operation on an inertia dynamometer and FRF measurements were taken. The operating conditions were varied with respect to disc velocity and brake line pressure. An experimental modal analysis under operating (EMA-OC) was performed on a disc brake, with a 2.6 kHz squeal, during squealing and non-squealing operational conditions. Two modes close in frequency to the 2.6 kHz squeal were identified from modal analysis of the brake system in a non-squealing operational condition which were not individually present during squealing conditions. These two modes were assumed to be the modes which couple due to friction and thus produce squeal in operation. A sensitivity analysis was then conducted on the modal model obtained from an EMA-OC non-squealing operational case.

This paper illustrates the importance of road vibration in the study of disc thickness variation generation in disc brake rotors, showing that laboratory conditions must include vibration as well as realistic reproductions of speeds, pressures, and inertia, etc. Such conditions are made possible with the Bosch Road Load Dynamometer (RLD). A related paper, Road Load Dynamometer: Combining Brake Dynamometry with Multi-Axis Road Vibration, SAE 2003-01-1638, showed that the RLD could accurately and repeatedly reproduce field conditions, but did not contain disc thickness variation (DTV) generation data. This paper contrasts rotor wear data for a controlled experiment on the RLD, with and without vibrational input. In the control group, DTV generation data comparable to vehicle test results were recreated. In the experimental group, similar hardware was subjected to the same tests except for the absence of vibration input.