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최혁(Hyock Choi),여태인(Taein Yeo) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The frictional heat generated at the interface of the rotor and pad of an automotive disk brake can result in thermal distortion of the frictional surface. Known as coning, this effect is found to be the main cause of RTV (rotor thickness variation) and judder. It is, therefore, important to predict the temperature rise and thermal deflection in the early design stage. For these purposes, a pie-shaped model is usually used for a ventilated disk that is evidently three dimensional in shape due to its vent holes. In this paper a new analysis technique is adopted for a ventilated disk in which the rotor is represented using an axisymmetric finite element model. To take into consideration the effects due to the cooling passages, a homogenization technique is used to give the equivalent diffusivity and elastic modulus for elements located at the vent holes. The convective heat transfer coefficients on the disk surface were obtained by CFD analysis and compared to the experimental results in terms of the outlet air speed at the vent holes. Temperature and the resulting runout of the disk were also determined by FEM analysis and compared to the ones from brake dynamometer tests. It is concluded that the assumption of a rotating disk in an infinite field in CFD analysis overestimate the cooling at the disk surface while predicting accurate values at the vent holes. The large undercut is proved to be effective in diminishing the amount of coning. The proposed axisymmetric FEM procedure can be successfully applied in practice, replacing 3-dimensional finite element analysis for optimal shape design to reduce judder in a ventilated disk.