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The propensity of brake squeal depends significantly on the vibrational characteristics of disc rotors. In this study, we focused on the differential effects of disc dimensions on the natural frequencies of various vibration modes. We analyzed the results of the CAE factorial experiments presented in our previous paper, which were conducted on four disc rotors with different designs such as front-and back-vented and solid discs. As a result, the effects of disc dimensions on natural frequencies were confirmed to depend on vibration modes, their orders (or the number of nodal diameters), and the basic design of disc rotors. The dimensions that change the stiffness of the friction ring such as ventilation-path width and fin thickness had larger effects on the out-of-plane circumferential modes of high orders than those of low orders. The dimensions around the necking, on the other hand, had a large effect on the low-order modes.

Reducing vehicle weight for promoting a sustainable global environment is one of the most significant challenges in the automotive industry. It is difficult to replace cast iron with lighter brake-disc material for ordinary vehicles. Material homogeneity also affects the thermal strength of brake discs. In our previous study, we established an integrated system for developing and manufacturing homogeneous brake discs to reduce judder. With our system, we maintained the thermal strength of a lightweight brake disc by improving its material homogeneity. As a result, we can optimize the brake disc design for reducing a disc's weight and contribute toward sustaining our global future.

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 studied the relationship between disc thickness variation (DTV) and casting material properties and clarified that the circumferential homogeneity of brake discs has significant effects on brake judder. As a solution, we established an integrated system for developing and manufacturing homogeneous brake discs to reduce judder by making the most of our integrated business process from R&D through manufacturing, including our in-house foundries. The system we developed consists of the following elements: foundry engineering to obtain homogeneous discs, an original flake graphite structure index (K-FGI) to measure the homogeneity of our products, and accelerated wear tests on a brake dynamometer to estimate the potential on-brake DTV growth.

A disc rotor is one of the friction pair in a brake system, but its behavior as friction material is seldom studied. The authors had found that some used discs in the field with large DTV wore locally at the same angular position on both the in-board and out-board friction surfaces. This phenomenon suggests that these discs have non-uniformity in the casting material properties such as the graphite structure and/or matrix. To identify the relationship between local wear and casting material properties, a design of experiment (DOE) is performed. Surrogate discs with non-uniform material properties are intentionally cast and tested on a chip-on-disc type friction tester. Local wear is reproduced and it is found that circumferential non-uniformity in the casting material has some correlation with disc local wear. The local wear depth also depends on the friction materials and gray cast iron grades.