• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.21-30
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• 2017

Of the marine engine components, the piston crown and exhaust valve are repaired most frequently. These works are conducted through conventional welding processes such as GTAW or SAW, domestically in marine engine repair factories. New high-efficiency welding or overlay processes such as tandem SAW, tandem MAG, hybrid TIG-MIG welding, pulsed-GMAW, CMT welding, and super TIG welding have been developed recently. Moreover, the plasma transfered arc (PTA) process is an efficient spray method for overlaying on the exhaust valve. In this review paper, the new high-efficiency repair welding methods are introduced for marine engine components. The problems due to repair welding for marine engine components are also presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.291-298
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• 2013

In this paper a new hybrid-type control system is proposed which reduces the pump speed of an electro-hydraulic actuator consisting of a pressure-compensated variable displacement piston pump and a valve-controlled hydraulic cylinder, whenever the flow rate demand is low. In order to avoid interfering with the pressure regulator which also has an effect on swash plate angle, the pump speed is changed in proportion to the mean value of the speed component of position commands. Additionally a pressure switch is employed to prevent the system pressure from getting lower than a reference value. Based on computer simulation & experimental results, it is shown that the hybrid control can save the idling power up to 44% at a stand-by mode by reducing the pump speed from 1,800 rpm to 600 rpm without affecting the dynamic response of the electro-hydraulic actuator.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.744-745
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• 2008

IT기기, 통신시기, 반도체 기기 등은 점점 더 고성능화되면서 속도도 빨라지고 기능도 추가되는 추세이다. 이러한 IT기기들은 속도와 더불어 열문제는 더욱더 크게 강조되고 있는 실정이며 개인용으로 많이 사용하고 있는 PC의 경우 더 이상 속도를 높이지 못하고 있는 실정이다. 이러한 열문제는 100W까지는 Heat pipe 등으로 냉각이 가능하였으나 거의 한계수준에 도달한 상황이다. 이러한 상황에서 일부 메니아들은 빠른 속도의 통신이나 작업을 위해서 수냉식 전용 냉각기를 설치하여 현재의 기능보다 더 좋은 환경에서 사용하고자 하고 있다. 본 연구에서는 수냉식 냉각기보다 더 큰 열용량을 가진 CPU의 냉각을 위해서 냉매 압축기를 적용하고자 하였으며 냉매 압축기에 사용하기 위한 선형압축기를 개발하고자 하였다. 즉 선형압축기에 의해서 압축된 냉매를 사용하여 CPU를 냉각하기 위해서 본 연구를 시작하였다. 본 연구에서는 선형전동기를 공진구동형 스프링을 장착하여 50-100Hz로 공진구동하는 액추에이터를 제작하여 그 특성을 알아보았다. 먼저 제자과정과 제작후 추력과 공진구동 설계 및 공진구동시 전기적, 기계적 특성변화를 확인하였으며 피스톤과 실린더 및 흡입밸브와 배기밸브 등을 장착하여 선형압축기로서 시운전까지 수행하였다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.195-199
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• 2005

As vehicles are recently becoming more important in our life, the study for engine capacity has been conducted for many years. Specially, the study on lubrication in the engine is needed to develop engine capacity. The role of lubrication is to reduce fraction, manage the temperature and protect from corrosion etc. At the view point of the engine, lubrication and cooling of the engine have an effect on the life and efficiency, so we have to study this problem. Ball check valve is located in the inlet of the Oil Jet. Ball check valve is used to control the flow rate of the engine oil, which cools and lubricates the engine. Flow rate at the oil jet is very important, so the study for this problem is needed to conduct researches. The point of this study is to compute the flow rate and the flow in oil jet. The results of this study is that the mass flow rate is satisfied with the research which is obtained at the experiment.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.181-187
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• 2006

The present study deals with the experimental facility for PSD (POGO Suppression Device) performance test systems. Basically there are two methods to pulsate the system; whole-feeding-system pulsation and working-fluid pulsation. The latter method adopts either a piston-type pulsator or a restrict-type pulsator. The working-fluid pulsation using a restrict-type pulsator was considered to be the most appropriate experimental system to study the effects of the primary parameters, and a practical design of the system was proposed. Also, the experimental facility adopts the ball valve type pulsator considering the leak problem of the plate type pulsator.

• Journal of Drive and Control
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• v.15 no.4
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• pp.11-16
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• 2018

Pilot operated control valve for $CO_2$ refrigerant is a valve that can perform various functions according to the user's intention by replacing pilot units, widely used for flow rate, pressure, and temperature control of refrigeration and air conditioning systems. In addition, $CO_2$ refrigerant, that requires high pressure and low critical temperature, can be installed and used in all positions of the refrigeration system, regardless of high or low pressure. In this paper, response characteristics are modeled and analyzed based on behavior of the main piston of the pilot-operated control valve. Although various factors influence operation of the main piston, this paper analyzes the effect of equilibrium pressure depending on valve installation position and application, and inlet and outlet orifice size of the load pressure feedback chamber to determine feedback characteristics of the main piston. As a result, it was possible to quantitatively analyze the effect of change in equilibrium and load pressure feedback chamber flow path size on the change in main piston dynamic and static characteristics.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.953-960
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• 2019

The Miller cycle is a diesel engine that has been developed in recent years that it can reduce NOx and improve fuel consumption by reducing the compression ratio through intake valve closing (IVC) time control. The Miller cycle can be divided into the early Miller method of closing the intake valve before the bottom dead center (BDC) and the late Miller method of closing the intake valve after the BDC. At low speeds, the late Miller method is advantageous as it can increase the volumetric efficiency; while at medium and high speeds, the early Miller method is advantageous because of the high internal temperature reduction effect due to the expansion of the intake air during the piston lowering from IVC to BDC. Therefore, in consideration of the ef ects of the early and late Miller methods, it is necessary to adopt the most suitable Miller method for the operating conditions. In this study, a two-stage turbo charge system was applied to four-stroke engines and the process of enhancing the Miller effect through a reduction of the intake and exhaust valve overlap as well as the valve change adjustment mechanism were considered. As a result, the ef ects of fuel consumption and Tmax reduction were confirmed by adopting the Miller cycle with a two-stage supercharge, a reduction of valve overlap, and an increase of suction valve lift.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1335-1340
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• 2004

Due to the distinct advantages of comfort, drive ability and fuel economy standard, the variable displacement swash plate type compressor which can control the compressor displacement by increasing or reducing the swash plate angle has been developed for automotive air-conditioning system. That can be obtained constant temperature of car room on the variation cooling capacities or engine speeds. This paper was carried out the analysis of swash plate behavior to obtain the forces and moments applied to the swash plate and to get the variable controlability on the variation of compressor speeds and swash plate chamber pressures. The results of simuation agree very well with the experimental data.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.4
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• pp.188-194
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• 2013

Hydrostatic pumps and motors occupy an important position in hydraulic system. There are a lot of researches on characteristics of hydraulic pumps, but not hydraulic motors. So in order to know the characteristics of hydraulic motors we had this research. The purpose of this study is to derive and analyze the theoretical calculation of hydraulic axial piston motor torque and torque ripples. Then, analyzed the differences between torque ripples with dead place and without dead place on the valve plate, and modeling a hydraulic motor with AMESim software. Finally, theoretical calculation of hydraulic motor torque ripples was verified from the viewpoint of simulation.

• Tribology and Lubricants
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• v.14 no.4
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• pp.23-28
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• 1998

To increase the efficiency of the hydraulic axial piston pumps, it is need to know the various characteristics in the sliding contact parts of them. Especially, friction characteristics between the cylinder block and the valve plate in the hydraulic axial piston pumps plays an important role to high power density. In this paper, we tried to clarify friction characteristics between the cylinder block and the spherical valve plate in bent-axis-type axial piston pump in experimentally. Results are arranged as follow; (1) friction torque between the cylinder block and the spherical valve plate has a proportional relation to weight or rotational speed, and is strongly affected by temperature. (2) Friction torque strongly depends on force balance ratio in valve plate. (3) In this experiment, lubrication condition between the cylinder block and the spherical valve plate is under hydrodynamic lubrication.