Transient vibro-acoustic analysis of squeal events based on the experimental bench FIVE@ECL

Abstract

The proposed study investigates the transient and stationary non-linear vibrations and acoustic phenomena occurring during the squeal phenomenon. Experiments are performed on the test bench Friction-Induced Vibration and noisE at Ecole Centrale de Lyon (FIVE@ECL).

The first major contribution of the study is to demonstrate the ability of this test bench to reproduce transient squeal events for a given operational condition, allowing to conduct a thorough and robust study on the physical understanding of transient vibration and acoustic squeal events. The second main contribution is to discuss the potential links between the emergence of vibrations on the two pads, the disc and the caliper, and the squeal noise in near-field and far-field.

Introduction

The subject of friction-induced vibrations and squeal noise is considered as one of the main issues of industrial brakes design. Understanding the physical phenomena linked to brake squeal is not obvious since it involves and requires a good overview of many scientific fields, such as structural dynamics, acoustics, tribology or thermodynamics. Generally speaking, squeal noise generated by friction induced vibration leads to a loud and annoying noise as well as a feeling of poor quality for the users. Reviews providing an understanding of this phenomena of friction-induced vibration as well as descriptions of potential mechanical mechanisms and physical factors that may be involved in brake squeal can be found in [1], [2], [3], [4], [5].

From an experimental point of view, both industrial and academic test rigs have been developed in order to propose contributions for a better understanding of the phenomena of brake squeal, as well as to investigate which physical phenomena could be the cause of the brake noise. For example some rely on research more focused on friction-induced vibrations [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], while others study the subject via thermal considerations [18], [19] or a tribological point of view [20], [21], [22], [23], [24], [25]. On the other hand, some researchers [23], [26], [27], [28] are also interested in dealing with the problem of brake squeal by considering additionally the problem of acoustic radiated noise due to friction-induced vibration or roughness at the frictional interface. Nevertheless, in most cases, only one microphone is used for squeal noise measurement, except for studies specifically dedicated to acoustic holography on brake squeal in order to measure the disc motion and the associated traveling waves [29], [30]. Thereby a specific study for a better understanding of the link between friction-induced vibrations and squeal noise via acoustic measurements is not deeply conducted. The use of microphone array in far-field to investigate links between friction-induced vibration and squeal noise will be one of the contribution of the proposed study.

The proposed experimental study is carried out from the bench Friction-Induced Vibration and noisE at Ecole Centrale de Lyon (FIVE@ECL). This experimental bench has been developed by the authors since 2015 to characterize brake squeal from the self-excited vibrations of a disc brake assembly and the generated acoustic noise in near- or far-field [31]. A complete analysis of the stationary squeal event has already been proposed in [31] and the reproducibility of both squeal frequency content and radiated acoustic profiles in far field for a given set of operational parameters and for a specific brake system have been demonstrated in the case of stationary squeal events. In the present study the major contribution aims at proposing an extension of these previous results [31] by demonstrating the repeatability of squeal events also from a transient point of view.

The paper is organized as follows: firstly, a brief description of the experimental bench FIVE@ECL, as well as the main characteristic of brake squeal coming form the previous study performed by the authors [31] are given. Secondly, a deep analysis of the repeatability of the squeal time signature from experimental tests performed on the bench FIVE@ECL is discussed. This subject will be treated by investigations on both friction-induced vibration and squeal noise. Finally, the potential links between friction-induced vibrations and squeal noise for transient and stationary squeal events will be highlighted.