• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.143-149
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• 2002

Ball reducer with waved grooves has many advantages over other reducers for the high-reduction ratios, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in the contact geometry. In this study, we have investigated the traces of contact between ball and outer race and the working behaviors with a certain reduction ratio. In order to verify the contact behaviors between ball and outer race, which determines the critical endurance life the contact velocity and load are computed for a cycle. During some period of a cycle, the contact velocity reverses its direction very suddenly, which causes undesirable endurance performance of this machinery. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very common in many contact phenomena.

• Journal of Chest Surgery
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• 제15권2호
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• pp.250-253
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• 1982

A persistent left superior vena cava draining into the left atrium associated with atresia of the coronary sinus-ostium, ASD, and PDA is a rare congenital anomaly. The patient was a 4 year-old female whose complaints were frequent URI and exertional dyspnea. The congenital heart anomaly was suspected at 2 months of her age. Chest films showed cardiomegaly [C-T ratio, 75%]. EKG, Echocardiography, cardiac catheterization and angiocardiography were performed. Open heart surgery was done under impression of LV-RA shunt, bilateral superior vena cavae, and ASD. At the time of operation, huge LA and RA, inferior vena caval defect of a secundum type ASD [1.5 x 3cm in diameter], absence of innominate vein, atresia of the coronary sinus-ostium, and persistent LSVC draining into LA were noted. Direct suture closure of ASD and ligation of LSVC were done. The patient`s postoperative course was somewhat eventful: systolic murmur at apex remained. Four months after the operation, congestive heart failure attacked a few times. PDA that was overlooked at the time of open heart surgery was detected through postoperative cardiac catheterization in.4 months later. Emergent operation for closure of PDA was performed on the day of recatheterization. After that, patient`s heart failure was easily controlled without any notable problem.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1075-1080
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• 2007

In order to reduce energy consumption, secondary controlled system has been applied to many types of equipments. In lifting equipments or press machines using hydraulic cylinder, a hydraulic transformer is used as a control component instead of a valve for motion control and a component for recovering potential energy of load. The transformer is a combination of a variable displacement pump/motor as a secondary controlled element and a fixed displacement pump/motor. In this paper the effect of transformer is studied. Multiple closed loop controllers with displacement feedback of variable pump/motor, speed feedback and position feedback of cylinder are used. The efficiency and energy consumption when cylinder is driven up and down is calculated by simulation. Simulation results show that considerable energy saving is achieved by choosing load ratio, circuit type and supply pressure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.185-190
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• 2007

최근 반도체 및 디스플레이 산업 등에서 초정밀 가공, 측정 등이 필요함에 따라, 외란과 내부 진동을 차단하는 방진 시스템에 대한 연구가 활성화 되고 있다. 기존에 소개된 여러 방진 시스템 중에서 가장 많이 연구되는 공기스프링은 압축 공기를 이용하여 큰 하중을 지지할 수 있으면서 상대적으로 낮은 강성으로 낮은 고유진동수를 유지할 수 있다. 본 연구는 기존의 레벨링 밸브를 이용한 수동 방진 시스템을 분석하여 이를 개선하고 능동 방진 시스템을 설계한다. 공기의 비선형 특성에 기인하는 복잡한 비선형 시스템 제어에 PID 제어기 보다 유리한 퍼지 제어기를 설계하였고, 실험과 해석을 비교하였다.

• Journal of Chest Surgery
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• 제16권1호
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• pp.40-48
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• 1983

Tetralogy of Fallot is characterized by the interventricular septal defect associated with obstruction of the right ventricular outflow. The importance of the latter anatomic malformation was clinically evaluated according to the angiographic measurements of the pulmonary arteries along with the pulmonary valve annulus. Seventy of a total 76 patients operated on during a whole year of 1981 were the patients for clinical evaluation. Fifteen patients died within 1 month after operation with the operative mortality of 21.4%. The young age and the severity of pulmonary arterial hypoplasia were ones among the surgical risk factors at a total corrective surgery of tetralogy. Preoperative angiographic measurements of the pulmonary arteries to speculate the expected postoperative ratio between the left ventricular and the right ventricular pressures were retrospectively calculated according to the formula. The predicted values of P RV/LV greater than 0.5 carried apparenliy higher complication and mortality rates than the group of P RV/LV less then 0.5. The selection of the candidates for either a total correction or the staged operation In tetralogy of Fallot can be evaluated on the preoperative angiographic measurements and the expected Improvements of the clinical results were discussed.

• 오토저널
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• 제14권2호
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• pp.34-43
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• 1992

The purpose of this study is to consider the performance and exhaust characteristics in the practical engine according to the cooling water temperature change of engine and to set up the optimum cooling condition and to obtain the optimum operating condition of thermostat in the cooling system. In order to accomplish the purpose of this study, authors have used the following procedure. 1. This study is to investigate the influence of the cooling water temperature on the engine performance and the exhaust gas, authors regulated the cooling water temperature by using the special closing circuit and measured the concentration of exhaust gas by using the exhaust gas measuring system in the exhaust pipe. 2. This study carried out the experiment by regulating the opening degree of throttle valve and engine speed in the dynamometer and by changing the cooling water temperature, at the same time kept air-fuel ratio constant and made the spark ignition time MBT(Minimum spark advance for Best Torque) 3. This study measured the cooling water temperature by using the K-type thermocouple centring around the easy over-heated parts and by installing a special closing circuit. Therefore, in this study, authors intend to examine the influence of the cooling water temperature on the engine performance, exhaust gas and present the basic materials needed in the engine design including the optimum operating time control system for the cooling water temperature.

• 한국자동차공학회논문집
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• 제18권6호
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• pp.70-75
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• 2010

Compressed air represents an energy source and an force-transmission medium for brake systems on medium-heavy and heavy-duty commercial vehicles. However, one disadvantage is the tendency of air to absorb moisture in the form of water vapor. This water vapor condenses once the air, which is heated during compression, cools back to ambient temperature upon emerging from the air compressor. The resulting condensation assumes the form of moisture in pneumatic lines, air tanks, cylinders and valve assemblies and can have negative consequences for the brake system and vehicle safety. The pneumatic systems on today's vehicles are equipped with air dryers, in which the supplied air is dried according to the adsorption principle. In the systems, the compressed air flows through a granular desiccant with molecular sieves which captures the water molecules.

• 설비공학논문집
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• 제27권6호
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• pp.321-327
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• 2015

This study presents an HFC152a refrigerant air conditioner as an alternative to HFC134a, which is currently used in mobile air conditioning systems. Cool-down performance tests of an HFC152a air conditioning system were conducted and compared to a baseline HFC134a air conditioner. The experimental set-up consisted of a belt-driven compressor, a sub-cooled type condenser, an evaporator, and a block-type thermal expansion valve (TXV). A drop-in test was carried out on the mobile air conditioning system under various vehicle running speeds in a climate-controlled wind tunnel (CWT). Additionally, to optimize the HFC152a air conditioning system, the effects of the TXVs on the performance were studied. The results show that compared to the HFC134a air conditioning system, the refrigerant charge quantity was reduced by approximately 20%, the discharge pressure was reduced by about 350~430 kPa, and the air discharge temperature at vehicle running conditions was $0.5{\sim}1.5^{\circ}C$ lower. In addition, good compressor durability was expected due to the lower compression ratio.

• 한국유체기계학회 논문집
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• 제19권5호
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• pp.28-34
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• 2016

Though a peristaltic pump is a crucial element in miniaturized drug delivery systems, it has some intrinsic disadvantages such as backflow and flow fluctuation. To overcome these limitation, we have developed valve-less peristaltic pump system including orifice and stagnation chamber. we measured flow rate to investigate the performance of rotary peristaltic pump with three rollers and an elastomeric tube pumping a viscous fluid. The flow fluctuations and the backflow happen as a result from the disengagement of the contact interaction between the rollers and the tubes. Stagnation chamber installed in front of orifice plate was composed of rubber tube and gas chamber. By changing orifice hole diameter with stagnation chamber flow rate and pressure in the tube was regulated. The obtained maximum reduction ratio of flow fluctuation is 96.79%.

• 한국수소및신에너지학회논문집
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• 제19권6호
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• pp.474-481
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• 2008

수소 기관에서 역화없이 고성능과 저$NO_x$를 실현시키기 위하여 밸브 타이밍 변화에 따른 흡기관 분사식 수소 기관의 성능을 파악하고 가솔린의 경우와 비교하였다. 그 결과 흡기밸브 타이밍은 역화억제와 성능향상에 큰 영향을 미치는 것을 확인하였다. 흡기밸브타이밍의 진각은 역화를 억제하며 효율과 출력을 동시에 향상된다. 비록 흡기밸브 타이밍 변화에 의해 NOx는 증가하지만, 희박영역인 출 ${\Phi}=0.5$에서 현저히 감소된다. 또한 열효율은 ${\Phi}=0.5$ 토크는 ${\Phi}=1.0$에서 가장 높게 나타난다. 흡기밸브 타이밍을 $ATDC20^{\circ}$에서 TDC로 변화시켰을 때, ${\Phi}=1.0$에서 토크는 약 28% 증가되고, ${\Phi}=0.5$에서 효율은 약 7%향상된다.