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This paper as part IV of a series articles first very briefly reviews squeal generation process in terms of energy transfer. A squeal reduction and prevention cascade chart including various contribute elements is formed. Subsequently, variation ranges of some key parameters of brake components and system due to manufacturing processes and operational/usage condition changes are given. Design concept of a broad stable and less vibration brake system is proposed and addressed in light of these variations. Robust design criteria and strategies are discussed. Design tools and methods are summarized. At last, some application examples are provided.

Experimental verification is an important approach for understanding the mechanisms of disc brake squeal. One mechanism of disc brake squeal, i.e., coupling of in-plane and out-of-plane vibration modes of disc brake rotor, was found by experiments. Despite the vast amount of experimental data available, little effort has been dedicated to exploring what the time series information can reveal in relevance to squeal. In this paper, a new signal processing tool employing the Empirical Mode Decomposition Method (EMD) and its application to the identification of the characteristics of disc brake squeal will be discussed. The EMD was originally developed for ocean wave mechanics [1] and is particularly useful for the type of non-stationary data found in disc brake squeal. EMD is a time series analysis method that extracts a set of basis functions describing the fundamental characteristics of the response of a system.

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.

Disc brake squeal is a manifestation of the friction-induced self-excited instability of the brake system. One of known techniques in suppressing dynamic instabilities in nonlinear systems is by applying dither. The focus of this paper is to examine, through numerical examples, the feasibility and effects of dither on nonlinear systems as a means of quenching large-amplitude limit cycles. In particular, various ways of introducing the dither, either via modifications of the system characteristics or as external excitation, are explored. The investigation is extended to a disc brake system using finite elements simulations. Numerical results show that large-amplitude vibrations can be suppressed by dither and careful tuning of the amplitude and frequency of the dither can result in an effective quenching. The potential application of this technique to disc brake squeal control is also discussed.

This paper provides a systematic approach to identify the root cause of the squeal noise of a disc brake by using advanced experimental tools. Modal analysis was used to identify the modal participation factors when the brake was squealing according to the reproduced squeal phenomenon and acquired operational displacement shape (ODS) using pulsed electronic speckle pattern interferometry. Modal coupling between the disc and pad/caliper assembly is found to be the key to produce squeal. It has been demonstrated that using mass loading/damping can de-couple the modes between the disc and pad/caliper assembly and reduce the assembly vibration from which the squeal is eliminated.

This paper first gives a brief review on brake squeal mechanisms and then studies in-plane modes/friction process and their contribution to disc brake squeal. Pulsed laser electronic speckle pattern interferometry was used to acquire the operational deflection shape (ODS) of a disc brake when it was squealing. Laser vibrometry was used to obtain mode shapes of brake discs/rotors including both the out-of-plane (transverse) modes and in-plane (radial or tangential) modes. The rubbing friction process with a non-rotation rotor under a free-free boundary condition was used to simulate friction-induced vibration. The coupling between in-plane modes and out-of-plane modes/vibration is believed to be the key to produce squeal. The in-plane modes tend to control the squeal frequency, and the out-of-plane modes/vibration are efficient to generate noise. Many case studies have shown that high frequency disc brake squeal occurs at one or some of its rotor in-plane resonant frequencies.

Chapters written by professional and academic experts in the field cover: analytical modeling and analysis, CEA modeling and numerical methods, techniques for dynamometer and road test evaluation, critical parameters that contribute to brake squeal, robust design processes to reduce/prevent brake squeal via up-front design, and more.