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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.

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.

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.

This two-part paper provides a systematic approach for identifying the fundamental causes of both low and high frequency brake squeal using advanced analytical and experimental methods. Also shown are methods to develop solutions to reduce or eliminate squeal by investigating effective structural countermeasures. Part I presented here is focused on low frequency squeal (2.2 & 5.5 kHz). In order to better understand the mechanism of squeal generation, this study started with the component modal alignment analysis around problem frequencies based on the component EMA (Experimental Modal Analysis) data in free-free condition. Then, the brake system EMA was conducted to gain insight into the potential system modes which caused the squeal. The last step of the brake squeal diagnosis utilized the ODS (Operational Deflection Shape) result to identify the key components involved in the squeal event.

The modal characteristics of a brake pad are important factors affecting brake squeal. The most frequently used counter-measures for eliminating or reducing squeal, especially at high frequency, are the modification of: the modal frequencies, damping, contact modal shapes or patterns of a pad by making a chamfer or slot, or selecting a different under-layer, lining material or insulator. This paper describes the development of the methods for the measurement of pad modal characteristics such as modal damping, frequency and contact mode shape. It provides comparison among three methods: accelerometer-hammer, laser-hammer, and laser/non-contact shaker with test data and CAE simulation. Subsequently, laser/non-contact shaker was used to evaluate the process capability of pad manufacturing in terms of modal damping and natural frequency. This method was also employed to investigate the effect of pad chamfer, under-layer and the insulator on pad modal characteristics.

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.