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Compressibility is a common quality metric for friction materials. In addition, it is typically used as an engineering parameter for brake system design and performance. Compressibility (or elastic properties) of the friction material can effect brake roughness, pedal feel, and noise performance. A characterization technique is presented to determine the cyclic compressibility (over ± 1 kN) as a function of preload, temperature, frequency and time. The initial motivation was related to modeling of brake roughness, but applications to pedal feel and brake noise are also explored. For a given semi-metallic material, changing the temperature from 20 to 300°C or the preload from 8 to 4 kN both halve the cyclic compressibility. Less significantly, a change in frequency from 20 to 1 Hz reduces the cyclic compressibility by 10%. Differences between linings are also considered.

Pedal feel is one of the first customer touch points during a driving experience, and as such can be an important contributor to quality perception and customer appeal. Many brake system design characteristics contribute to pedal feel, and although not the largest contributors, the brake linings play a role. Friction material properties that influence pedal feel include: friction level, in-stop friction rise, ambient compressibility and hot compressibility. These properties have been measured on a series of commercial friction materials intended for passenger cars and light trucks. Vehicle tests have also been performed to compare objective and subjective evaluations of pedal feel for the different linings on the same vehicle brake system. The testing was designed to identify the contribution of the linings to the brake system's responsiveness and feel. This paper will discuss the correlation between friction material properties and vehicle tests for pedal feel.

In order to enhance the ability of engineers to quickly and easily evaluate new heat shield materials and construction methods for the underhood and underbody regions of the vehicle, a standardized rig test is being developed. The issues involved in the development of this test method are discussed as well as the important parameters. Test results for different heat shield materials are also presented.