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This paper presents results of experimental judder investigations on different vehicles. Judder excitation via machined discs or distorted drums will be explained with emphasize on controlling both the total variation value as well as order components. Transfer functions that characterize both the brake excitation (e.g. brake torque variation as an output and crum cylindricity variation as input) as well as transfer functions that characterize vehicle sensitivity will be presented. Transfer functions such as shake sensitivity and nibble sensitivity will be explained and case studies will be presented. The case will be made that using transfer functions for judder analysis can be a valuable tool for NVH engineers in the automotive industry.

This paper presents new analysis methods for brake judder data. First, a distinction is made between Thickness Variation, TV, judder (shudder or roughness) caused by the geometry variation of the brake rotor, and thermal judder caused by thermal caused changes to the friction couple. Spectrograms of vibration signals are used to distinguish between the two types of judder. Instrumentation of vehicles in order to get significant data is also provided. A linear model is used to describe the mechanism of judder generation. Different case studies are provided. Special tools of analysis like spectrograms, power time and spectral densities, and zero crossing frequency estimates are applied to real data.

As part of the development of a new SAE Recommended Practice for brake rotor modal frequencies measurement and control, the SAE Brake NVH Standards Committee developed detailed recommendations for such measurement, data reporting and use in quality control. This paper addresses the need for formalizing measurement techniques of rotor modal frequencies and documenting the proper set up and measurement parameters. Additionally, a rotor mode classification system is proposed so that important rotor modes may be tracked. Statistical control of modal frequencies is presented and practical limits are defined

“Creep groan” is a braking systems noise that is observed when a vehicle is starting to move from a stopped condition with brake pressure applied. Motion takes place when brake pressure is reduced while a motive force, such as an idling engine through an automatic transmission, or gravity due to the vehicle being on a slope, is present. The vibration causing the sound is commonly thought to result from friction force variation in stick-slip mode. Detection and evaluation of “creep groan” noise has been a challenge for NVH test groups. First, this sound typically is not purely tonal like the more common brake squeal, although ultimately it may produce a tonal subjective impression. In this work the authors study different methods that may be applied to “creep groan” detection and evaluation.

This paper presents results of experimental investigation into the creep groan problem of disc brakes when used on rear axles of cars and light trucks. Improvements in test procedures and data analysis leads to clearly defined limit cycles in the motion of brake components. The limit cycles are related to both brake design and axle resonances. Creep groan frequency and signature are shown to depend on the choice of friction material. Simple monotonic friction models are shown to be limited in their capability of describing creep groan motion.

NVH development is an important part of modern brake product development plans. This paper analyzes a typical NVH development process and identifies gaps in available development technologies and processes that when filled can improve the brake NVH development effort. The paper also discusses how the disciplines of simulation, component testing, dynamometer testing, and vehicle testing are currently integrated and proposes more effective processes of development. The paper identifies opportunities for contributions from professional societies and standardization organizations, vendors of test equipment and software, test laboratories, university research centers as well as brake suppliers' engineering centers to improve the engineering toolbox and fill the gaps in brake NVH development.

A general modal instability model that describes the squeal problem for both disc brakes and drum brakes is presented. The model includes different sources of instability. Brake input mobility measurements under conditions of static and dynamic braking are presented and analyzed in light of the general modal instability model. Time frequency analysis is used to differentiate between simple one frequency squeals and complex multiple frequency squeals. Investigation of some of the brake design parameters that affect brake stability is presented.