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김기정(KiJung Kim),이종민(JongMin Lee),김창현(ChangHyun Kim),한형석(HyungSuk Han) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
The dynamic interaction between switch and Maglev(Magnetic levitation) vehicle must be investigated to ensure the running stability of the vehicle. The Maglev switch usually has higher natural frequencies because it is made of mainly steel structures. Due to the vibration characteristics, resonance between electromagnetic suspension and switch could be occurred, which causes instability. The objective of the paper is to study the dynamic interaction considering the flexibility of switch. The 3-d flexible multibody dynamic model including magnetic levitation control system is proposed. With the coupled, the dynamic interaction of the vehicle with the flexible switch is numerically analyzed. The results from the numerical simulations could be applied to optimum structural design of the switch ensuring stability.
김기정(KiJung Kim),황희정(Heejeong Hwang),장호(Ho Jang),김성진(SeongJin Kim),박흥식(HongSik Park) 한국트라이볼로지학회 2008 한국윤활학회지(윤활학회지) Vol.24 No.4
Tribological properties of ceramic brake discs were investigated using a commercial friction material. The discs were manufactured by liquid silicon infiltration (LSI) into a C-C preform. The disc surface was modified by two different methods, producing sliding surfaces with chopped carbon fibers and carbon felt. In addition, the composition of the surface was also changed. Friction characteristics of the discs were examined using a 1/5 scale dynamometer. Results showed that the type and composition of the disc surface significantly affected the level of braking effectiveness and high temperature brake performance. The discs with felt surfaces showed higher friction levels than those with chopped fiber surfaces and SiC tended to increase the friction level while C lowered the friction coefficient. The ceramic disc was more sensitive to the deceleration rate than gray iron, showing high speed sensitivity.
김기정(Kijung Kim),김기범(Kibum Kim),김성진(Seong Jin Kim),박현달(Hyundal Park) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
The novel PM (powder metallurgy) steel for automotive power-train gear components were developed to reduce manufacturing cost, while meeting the requirements. The high-density PM steel was manufactured by mixing using special Cr-Mo atomized iron powders, high-pressure compaction, and sintering. Tensile strength, charpy impact, bending fatigue, and contact fatigue tests for the PM steel were carried out comparing to the conventional forged steel. The pinion gears for 6-speed auto-transmission were also manufactured by helical pressing, sintering, and external rolling process (selective surface densification). In order to evaluate the durability of the PM parts, the auto-transmission durability tests were performed using dynamometer tests. Results showed that the PM steel fulfilled the requirements for pinion gears indicating suitable bending and contact fatigue strengths. The PM gears also showed improved gear tooth profile and better performance during the transmission durability tests. In particular, the PM gears manufactured by helical pressing and selective surface densification showed a significant advantage in reducing the manufacturing cost of about 30% as compared to the conventional forged steel gear manufactured by tooth machining (hobbing, shaving, and grinding) process.
한종부(Jongboo Han),김기정(Kijung Kim),김창현(Changhyun Kim),한형석(Hyungsuk Han) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
EMS-type urban Maglev vehicles should maintain the levitation within an allowable range of air gap in order to run without touching the guideway. Generally, irregularities in a guideway are generated by manufacture and construction tolerance, as well as by thermal deformation. Though such irregularities of a guideway might influence the curving negotiation and ride quality of Maglev vehicles, there has been a lack of research considering the irregularities of guideway curve. Therefore, an analysis of the dynamic behavior of Maglev vehicles running over a curved guideway that consider irregularities is needed. The goal of this study is to propose a dynamic model considering the irregularities of a curved guideway, and to predict curving negotiation. Since the proposed model is based on 3-dimensional multibody dynamics, it enables more realistic simulation.