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This study aims at analyzing the causes of noise in a heavy vehicle brake system (6x2 tractor) and proposing solutions to improve comfort during braking as it is known that, during the activation of the automotive brakes, noise can be generated in different frequency bands that can cause discomfort to the user and the study of how to reduce it is considerably important to bring more comfort in its use. As a working methodology, firstly, comparative analysis of dimension and material were performed between the axle assembly that presented noise and another axle assembly of a vehicle with no noise adopted as reference. This information was used as the basis for the frequency and acceleration virtual analysis that were validated with vehicle instrumentation and data acquisition. In parallel, vehicle tests with different brake friction materials were conducted.

The need to predict the durability of the friction material is a constant pursuit of the application engineer. In fact, the difficulty in reproducing by means of laboratory tests the actual conditions of application of the friction materials makes it essential to understand the influence of the test parameters on the wear of the friction material. Currently, durability data is extracted from dynamometer tests, where the parameters of speed, pressure, and decelerations are applied and divided into blocks of temperature, which do not represent exactly the actual driving condition of the vehicle. Thus, the objective of this study is to compare the pad wear when subjected to two wear test models: The first one is based on the wear test procedures traditionally found in the light and heavy vehicle (repetitive matrix) and the second an alternating wear matrix, which results in friction material disturbs, more similar to the field condition.

Analytical models used to design most of drum brake systems assume rigid body behavior of shoes and drum, resulting in sinusoidal pressure distribution in the friction interface. This approach leads to various limitations and sometimes incoherent results at typical applications since brake components are highly deformable and the contact pressure distribution plays an important role on the brake system efficiency. This study addresses a numerical analysis of drum brake pressure distribution, using Finite Element Method and considering shoes and drum as flexible bodies. The model validation from experimental procedure, where brake components were instrumented in an inertial dynamometer test. Once the pressure distribution can not be accurately measured, this research uses strain field measurements to calibrate the numerical model. This model is nonlinear, implying in convergence difficulties.

The present work presents evaluation of the sliding surface morphology of brake pads during stick-slip. A low-metallic (LM) and a Non Asbestos Organic (NAO) brake friction materials were subjected to slide against a brake disc under conditions favorable to produce stick-slip phenomenon. The experiments were conducted in a laboratory-scale tribometer, which was especially designed to test brake pads used in vehicle. Delta torque divided by slip time (dT/dtslip) was the parameter used to quantify stick-slip propensity. In addition, optical microscope images of the material's surface were obtained at different stages of the braking test. These images were post-processed in appropriate computational software and by means of the segmentation technique, the real contact area, size and amount of contact plateaus related to the brake pad surface were estimated. This technique was effective to quantify the differences in the sliding surface morphology during low speed braking test.

The present paper addresses an investigation about the definition of a parameter for quantifying the creep-groan propensity in brake pads. Creep-groan is a self-excited vibration caused by stick-slip phenomenon [1, 2, 3]. For the definition of the creep-groan propensity parameter, extensive experimental work was performed on a laboratory-scale tribometer. The experiments are divided in two main parts: (i) study of correlation between accelerometer signal with physical and operating parameters. (ii) validation of the chosen parameter, which was based on stick-slip tests performed with three different materials, one low-metallic (low-met) and two non-asbestos organic (NAO 1 and 2). From the first study, it was found that both the slip power and mean torque multiplied by torque variation showed a slightly higher correlation with the acceleration signal.

Creep groan is a low-frequency (20-300Hz) self-excited brake vibration caused by stick-slip phenomena at the friction interface observed at very low vehicle speed. The creep groan propensity of friction materials is closely related with the difference (Δμ) between the static (μs) and the kinetic (μk) coefficients of friction. In this study, a NAO brake pad material was used as a base formulation and the abrasives tested were commercial grade of black iron oxide, chromite, zirconium oxide, magnesium oxide and aluminum oxide. Experimental results were obtained by testing seven different friction material formulations, in which the type of abrasives or its hardness or its particle size was changed in order to explore the impact of these variables on the stick-slip occurrence. A laboratory-scale tribometer was used to investigate the influence of different types of abrasives and their physical properties in the stick-slip.