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[구조강도부문] 디스크 브레이크의 패드 수명 예측에 관한 연구
여태인(Taein Yeo) 한국자동차공학회 2001 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2001 No.11_2
This paper presents a numerical technique to analyze the wear life of automotive disk brake pad, where FFT-FEM method is adopted to determine the transient temperature distribution of the disk surface. A specimen of frictional material is tested on a small scale brake dynamometer to find the dependency of the wear rate on temperature change, from which and the temperature analysis results, given the wear life test mode, the wear behavior of the pad material for the vehicle can be predicted.<br/> Numerical example show the predicted wear life of the vehicle coincides with the recommended time interval for replacing the pads.<br/>
등가 물성치를 이용한 브레이크 디스크의 축대칭 유한 요소 해석에 관한 연구
여태인(Taein Yeo) 한국자동차공학회 2002 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2002 No.5_3
In automotive brake systems, the frictional heat generated can cause high temperature at the intetface of rotor and pad which may deteriorate the material properties of the sliding parts and can result in brake fude. Normally, a pieshaped 3-dimentional model is adopted to calculate temperature of ventilated disk using finite element method. To overcome the difficulties in preparing 3D finite element model and reduce the computational time requiIcd, the ventilated rotor is to be represented, in tins study, as an axisynuretric finite element model for which, taking into consideration the effects of the cooling passages, a homogenization technique is used to obtain tile equivalent thermal properties and boundary conditions for thee elements placed at the vent holes. Numerical tests using tile proposed method are found to be satisfactory compared with those of three dimensional analysis.
마찰 접촉시 열탄성적 불안정성의 유한요소법에 의한 해석
여태인(Taein Yeo) 한국자동차공학회 1997 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1997 No.11_2
A finite element analysis technique was developed to investigate the frictionally-excited thermoelastic instability(TEI) in an automotive disk brake system which causes a radially uneven surface of disk known in the brake industry as banding. A small perturbation in temperature is introduced into the system otherwise in thermal equilibrium. The finite element equations for the heat conduction problem and the elasticity problem are coupled through the frictional heat at the interface and solved to give a transient response of the perturbation. Instability is indicated when the brake system is operated above the critical speed and the perturbation grows in time. A numerical example shows that the banding is likely to occur for a new and thick pad with low thermal conductivity and high thermal expansion coefficient.
정찬명(Chanmyeong Jung),여태인(Taein Yeo) 한국자동차공학회 2002 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2002 No.5_3
Frequency analysis of brake parts in the design stage are useful to predict the occurrence of squeal noise in the brake system. To analyze the required high frequency vibrations of the brake system needs informations of contacting boundaIy conditions for the interacting parts. I this study, the effects of boundary conditions on the calculated natural frequency for the brake systems composed of disk and pad are investigated using finite element method.<br/> It is concluded that the B.C.'s for the pad backplate have considerable effects on the resulting vibration modes and, therefore, the effects of caliper piston and finger should be considered carefully in the course of modeling, whereas the frictional coefficient at the sliding surface have minor effects on the results and the frictionless sliding could be assumed for it.
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.
공창섭,여태인 울산대학교 1998 공학연구논문집 Vol.29 No.2
자동차의 디스크 브레이크에서 발생하는 페이드 현상은 디스크 면의 온도 증가에 따른 패드의 마찰계수의 감소에 따라 일어난다. 본 연구에서는 디스크 브레이크의 페이드 해석을 위하여 수치 해석적인 방법을 사용하였다. FFT-FEM(Finite Fourier Transform - Finite Element Method) 법으로 디스크의 제동 시간에 따른 과도기적 표면 온도를 해석하였으며, 온도에 따라 변화하는 마찰 계수식을 이용하여 반복 제동시의 페이드 율을 계산하였다. 수치해석 결과 벤티레이티드 디스크는 솔리드 디스크에 비하여 약 15-20% 정도 페이드 감소 효과가 있다는 것을 보여준다. This paper presents a numerical technique to predict fade phenomenum of an automotive disk brake caused by decrease of frictional coefficient as the temperature of the frictional surface is increased. FFT-FEM method(Finite Fourier Transform - Finite Element Method) is adopted to determine transient temperature distribution of the disk with convenctive cooling, which, combined with temperature-dependent frictional coefficient, is successfully used to compute the fade ratios during repeated brake applications. Numerical examples show that the ventilated disk is about 15-20% more effective in fade prevention than the solid disk for the vehicle data used in the simulation.
유한한 접촉면적이 서로 미끄럼운동을 하고 있는 두 물체의 TEI에 미치는 영향
여태인 울산대학교 1995 공학연구논문집 Vol.26 No.1
반무한 강체위에서 미끄러지고 있는 반무한 스트립의 열탄성적 불안정성을 선형 섭동법을 사용하여 조사하였다. 마찰열 및 물체내에서의 열전달, 그 결과 생기는 접촉 압력의 변화등을 고려하였다. 스트립에 관한 Papkovitch-Fadle의 고유함수 및 열응력에 대한 특별해 등을 사용하여 섭동을 급수해의 형태로 표현하였다. 시간에 따라 지수적으로 증가하는 섭동형태를 가정하여 얻어지는 등차연립방정식에서 시스템이 불안정하게 되는 임계미끄럼 속도를 구할 수 있었다. 수치적 결과를 두 반무한 평판 모델의 경우와 비교하였으며 유한한 접촉면적은 임계속도의 크기에 상당한 영향을 미친다는 것을 보였다. The instability of a semi-infinite strip in sliding contact with a rigid half-plane is investigated using linear perturbation methods. Frictional heating and transient heat transfer in the bodies are treated along with the pressure produced on the contact area by these. Possible perturbations are expressed in the form of an eigenfunction series, using the Papkovitch-Fadle eigenfunctions for the strip and related eigenfunctions for the thermoelastic particular solution. Selection of perturbations that can grow exponentially in time lead to a simultaneous homogeneous system of equations for the coefficient of the series with the sliding velocity involved. Numerical results are compared with those from the two half-planes model to demonstrate that the finite contact area has comparatively large effects on the critical sliding speed.