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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.

Vehicle noise and vibration (NVH) is among the important attributes of the vehicle. This attribute has to be designed for in the product development process. This produces challenges that are usually overlooked by researchers in the field. These challenges are assessed in this manuscript. The emphasis here is on the NVH phenomenon at the vehicle level. Little work is being done to study the vehicle noise and vibration from a system or customer perspective. This manuscript brings to the attention of researchers and the NVH community at large the various NVH challenges that constitute complexities to the development engineer and may deserve closer attention.

“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 will survey different noise matrices used in the brake industry to evaluate brake noise performance on dynamometers. Results that show temperature dependence, temperature history, braking power as well as brake pressure and initial velocity will be presented. Statistical analysis of both dynamometer and road test cycles will be presented. The results will emphasize how different cycles cover the space of pressure, initial temperature, initial speed, and stop brake power. Recommendations for controlling the different parameters will be given.

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.

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.