브레이크 마찰재의 stick-slip 현상에 관한 연구

박지상(Jisang Park),김경웅(Kyungwoong Kim) 한국트라이볼로지학회 2006 한국트라이볼로지학회 학술대회 Vol.2006 No.11

Recently, the creep groan noise occurring from the brake system causes severe problems and stick-slip phnomena are known as the main source of the creep groan noise. In this paper, the friction characteristics of stick-slip phenomena between a brake disc and brake friction materials are examined with the experiments using 9 different brake friction materials in 11 environmental conditions (3 different relative humidity and 4 different disc temperature). The priority of brake friction materials for the creep groan noise can be determined by experimental results. Moreover, numerical analysis which simulates the experiments is conducted. Finally, by matching numerical results to the experimental results, the behavior of friction coefficient according to the relative velocity between a brake disc and brake friction materials can be deduced.

휠 센서를 이용한 타이어와 지면간 마찰계수 추정 및 측정오차에 관한 연구

박승욱(Seunguk Park),김경웅(Kyungwoong Kim),나병철(Byungchul Na) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_2

If the real-time maximum traction force between the tire and the road can be precisely estimated. it would be easier to control the vehicle behavior. Usually, estimation of friction coefficient requires tire tread stiffness and tire contact length on road surface. But in this research, tire tread stiffness property and contact length are obtained from traction force and self-aligning moment. Using the estimation method introduced in this paper, only required parameters are lateral, longitudinal, vertical force, self-aligning moment and rotational speeds of all wheel. Isotropic tire brush model is used to obtain the equations of traction force and self-aligning moment. Validation of developed algorithm is performed based on real tire data, and the possibility of friction coefficient estimation is confirmed. Error analysis of wheel sensor error was also concerned.

마찰을 고려한 포일 저널베어링의 성능해석

이동현(Donghyun Lee),김영철(Youngchul Kim),김경웅(Kyungwoong Kim) 한국트라이볼로지학회 2006 한국트라이볼로지학회 학술대회 Vol.2006 No.6

In foil bearings, the friction between bumps and their mating surfaces is the major factor which exerts great influence on the performance. Especially, the Coulomb damping which is generated by friction increases the stability of bearing. Therefore, the need for developing analytical tool for friction in a foil bearing performance analysis has been well-recognized. In this paper, a method of considering friction in a foil bearing performance analysis is proposed. To simulate bump motion with friction the algorithm to consider stick-slip phenomenon occurred at a frictional interface is developed using finite element method. By using the proposed method, a nonlinear transient analysis is performed. The results of the analysis show that the relative motion between bumps and their mating surface provide Coulomb damping which is represented by hysteresis loop between applied load and vertical deflection of the bump. An increase in movability of bumps is an effective method of achieving Coulomb damping to enhance stability level of foil bearing. In addition, various static equilibrium positions are available by considering the friction.

마찰을 고려한 포일저널베어링의 동특성해석 : 회전불균형 응답

이동현(Donghyun Lee),김영철(Youngcheol Kim),김경웅(Kyungwoong Kim) 한국트라이볼로지학회 2007 한국트라이볼로지학회 학술대회 Vol.2007 No.6

The dynamic performance of air foil bearings relies on a coupling between a thin air film and an elastic foil structure. A number of successful analytical techniques to predict dynamic performance have been developed. However, the evaluation of its dynamic characteristic is still not enough because of the mechanical complexity of the foil structure and strong nonlinear behavior of friction force. This work presents a nonlinear transient analysis method to predict dynamic performance of foil bearings. In this method, time dependent Reynolds equation is used to calculate pressure distribution and a finite element method is used to model the bump foil structure. The analysis is treated with a direct implicit integration technique that can handle nonlinear problems and the stick-slip algorithm is used to consider friction force. Using this method the response to the mass unbalance excitation is investigated for various design parameters and operating conditions. The results of analysis show that foil bearing is very effective on the restriction of vibration at the resonance frequency compared to the rigid surface bearings and the effectiveness depends on the operating conditions, static load and a amount of mass unbalance. In addition, there exist optimum values of friction coefficient, bump foil sti예less and number of circumferential slit with regards to minimizing dynamic response at the resonance frequency. These optimum values are system dependent.

범프포일의 3차원 형상을 고려한 공기 포일저널베어링의 정특성 해석

이동현(Donghyun Lee),김영철(Youngchul Kim),김경웅(Kyungwoong Kim) 한국트라이볼로지학회 2005 한국윤활학회지(윤활학회지) Vol.21 No.6

The calculation of bump foil deflection is very important to predict the performance of foil bearings more accurately, because the foil bearings consist of top foil and its elastic foundation usually called bump foil. For the purpose of this, a finite element model considering 3-dimensional structure of the bump foil is developed to calculate the deflection of inter-connected bump. The results obtained from the suggested model are compared and analyzed with those from the previous proposed deflection models. In addition, load capacity of the foil bearings is analyzed by using this model.

범프포일의 3차원 형상을 고려한 공기 포일저널베어링의 정특성 해석

이동현(Donghyun Lee),김영철(Youngchul Kim),김경웅(Kyungwoong Kim) 한국트라이볼로지학회 2005 한국트라이볼로지학회 학술대회 Vol.2005 No.6

The calculation of bump foil deflection is very important to predict the performance of foil bearings more accurately, because the foil bearings consist of top foil and its elastic foundation usually called bump foil. For the purpose of this, a finite element model considering 3-dimensional structure of the bump foil is developed to calculate the deflection of inter-connected bump. The results obtained from the suggested model are compared and analyzed with those from the previous proposed deflection models. In addition, load capacity of the foil bearings is analyzed by using this model.

마찰을 고려한 포일 저널베어링의 안정성 해석

이동현(Donghyun Lee),김영철(Young-Cheol Kim),김경웅(Kyungwoong Kim) 한국트라이볼로지학회 2008 한국트라이볼로지학회 학술대회 Vol.2008 No.11

One of the main interests of air foil bearings lies in their superior rotordynamic characteristics. The dynamic performance of air foil bearings relies on a coupling between a thin air film and an elastic foil structure. A number of successful analytical techniques to predict dynamic performance have been developed. However, the evaluation of its dynamic characteristic is still not enough because of the mechanical complexity of the foil structure and strong nonlinear behavior of friction force. This work presents a nonlinear transient analysis method to predict dynamic performance of foil bearings. In this method, time dependent Reynolds equation is used to calculate pressure distribution and a finite element method is used to model the bump foil structure. The analysis is treated with a direct implicit integration technique that can handle nonlinear problems and the stick-slip algorithm is used to consider friction force. Using this method the sub-synchronous motion of foil journal bearing indued from instability is investigated for various design parameters and operating conditions. The results of analysis show that foil bearing is very effective on the restriction of sub-synchronous vibration compared to the rigid surface bearings. In addition, there exist optimum values of friction coefficient and number of circumferential slit with regards to minimizing sub-synchronous vibration of foil bearing.

강한 측력이 작용하는 피스톤 펌프의 왕복동 피스톤 기구 부에서의 윤활모형에 관한 연구

신정훈(JungHun Shin),정동수(DongSoo Jung),김경웅(KyungWoong Kim) 한국트라이볼로지학회 2014 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.30 No.2

The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.