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Brake judder is one of the most serious problems in automotive-brake systems. It is basically a forced vibration caused by the friction-surface geometry of a brake disc, and therefore, disc rotors play a significant role in judder. There are two types of judder: cold and hot. Hot judder is caused by the thermo-mechanical deformation of a brake disc due to high-speed braking. There are several shapes of deformation, e.g., coning and circumferential waviness. Circumferential waviness is caused by thermo-mechanical buckling and typically found as a butterfly shape in a 2nd rotational-order and hot-spotting. In a previous paper, two groups of disc castings with different material homogeneity were machined intentionally to have two kinds of dimensional variations.

Brake squeal is a critical issue for automotive brake systems and its propensity significantly depends on the natural frequencies of brake discs. The variation in natural frequencies is caused by various factors in the disc manufacturing process, from foundry through machining. To reduce this variation, we analyzed the factorial effects of material and dimensional properties on natural frequencies of brake discs with various configurations by conducting intensive computer-aided engineering experiments. These experiments were performed accurately and quickly with the help of our original brake disc design system. As a result, we determined the critical factors affecting the natural frequencies of brake discs and their contribution.

We describe our practical procedure of designing thermally robust brake discs using conventional CAE. First, we review the literature describing brake judder, measurement technologies, and CAE focusing on brake discs. Second, we present some experimental results confirming what effect the basic configurations of brake discs have on thermal behaviors and the correlation between CAE simulation and physical test results. Finally, we propose a design strategy for developing thermally stable brake discs with an outer-hat configuration. We carried out a series of CAE experiments based on the Taguchi Method and determined the critical parameters for reducing the amount of coning. We also present some simplified models using classical theory regarding the strength of materials to discuss what effect the dimensional parameters have on the discs' thermal deformation.

We have constructed an original brake disc design system by standardizing, automating, and speeding up each design process. This system consists of two steps. In the first step, a designer, without professional knowledge or skills regarding CAE, can easily carry out FEA by manipulating pull-down menus, parametric design, and automated modeling and meshing. Further, our new computer program automatically identifies each eigenmode. It takes less than two hours for a complete FEA of a new design. In the second step, the developed postprocessor makes it easier and faster to compare the simulated results of many design alternatives and determine the optimum solution. Through the accumulation of vast numbers of FEA cases and tests for validation, we have obtained the knowledge of the effects of disc configurations, dimensions, and material properties on resonant frequencies and thermal deflections.

The necessity of a high-precision disc to reduce brake judder was reconfirmed from the three viewpoints: a literature review, experiments, and bench marking. Geometric accuracy is the critical issue that brake disc suppliers must address to improve the NVH performance of automobiles. We have achieved disc lateral runout of less than 20 micrometers after rough and semi-finish turning operations by increasing the rigidity of lathe components and tool holders, improving work-holding devices, selecting appropriate cutting insert material and geometries, and optimizing cutting conditions. With an additional grinding process, by selecting the most suitable abrasive wheels, optimizing grinding conditions, and keeping the alignment of the work-piece and grinding-wheel spindles accurate through productive maintenance based on the in-line measurement data, we can correct the geometric dimensions of the disc friction plates to obtain higher accuracy.