• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.237-242
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• 2000

In this paper, an experiment was carried out to measure the hydrodynamic oil pressure distribution in the clearance gap between a piston and cylinder. The results showed that the pressure distributions are highly affected by the eccentricity of the piston. Therefore present experimental method can be used to enhance the performance of hydraulic piston pumps. Further experimental studies for various operating conditions and improvement in data acquisition methods are required to obtain more accurate results.

• Journal of Aerospace System Engineering
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• v.11 no.3
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• pp.8-15
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• 2017

In this paper, an equivalent brake hydraulic circuit with a piezoelectric hydraulic pump was constructed, and load pressure control for better pressurization/depressurization characteristics was conducted. To understand pressurization/depressurization characteristics of the equivalent hydraulic circuit, the relation between the load pressure and the input voltage was revealed experimentally. Experiments were also conducted to observe effect of the solenoid valve on depressurization characteristics. In the pressurization experiment, it was validated that transient response time required to achieve desired load pressure may be reduced through voltage control to change pressurization gradient. By applying the valve on/off time control and voltage control, it was also possible to reduce response time in the depressurization process. Therefore, transient response time may be improved within 10ms for pressurization and within 30 ms for depressurization using the control technique suggested in this study. The load pressure control method proposed in this study is useful for controlling load pressure of a hydraulic brake system with the piezoelectric hydraulic pump.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.335-340
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• 1992

유압 시스템(System)은 원동기의 기계적 에너지를 유압펌프가 작동유를 압력 에너지의 형태로변환 시켜 이것을 유합 실린더(Cylinder)등의 엑츄에이터(Actuator)가 다시 기계적 에너지로 변환시켜 부하 를 구동하게한다. 상용차(NT-1, KH 등)용 파워스티어링(Power Steering)에 장착되는 Vane Type Oil Pump (이하 VOP)가 바로 이와같은 역할을 담당하고 있다. 본 연구에서는 VOP의 성능과 관련되어지는 주요 제원(Parameter)인 미끄럼부에서의 틈새, 작동유점도, 압력변화, 회전수 등을 다양하게 변화시키는 모의실험(Simulation)을 통하여각각의 조건하에서얻어지는 누설 유량과 체적효율을 수치적 으로 예측하고 이것을 주요제원을 고려하여 해석해서 정량적인 값을 얻는 것을 목적으로한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.677-687
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• 2017

Aircraft can often be exposed to a variety of environments and vibrations such as engine, hydraulic pump, aerodynamic force. These may cause cracking and destruction of the mechanical structure and sub-components by high-cycle fatigue. The axial piston type pump which is usually applied to the aircraft hydraulic pump can be necessarily accompanied by the fluid pulsation by continuous rotation of the axial piston. The fatigue crack was identified at the dampener fitting welding zone to prevent vibration damping during the running of aircraft equipped with this type of pulsation hydraulic pump. In order to understand the root cause of this matter, fracture and component analyses were carried out and also integral type dampener fitting was applied to prevent recurrence of the crack as a subject of design improvements. Structural integrity stress analysis, fatigue analysis, qualification test and aircraft system equipped test was conducted to verify the design validity in application to integral type dampener fitting. The test results were sufficiently satisfactory with the demand lifetime of the material from the various types of test as conducted and the subject of design improvement in this study could be objectively evaluated that shall be applied to the operational aircraft.

• Transactions of The Korea Fluid Power Systems Society
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• v.2 no.4
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• pp.14-22
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• 2005

The safety factor of hydraulic piston pumps & motors due to high pressurization, high speedization and low weight/volume realization to enhance the output density shows a tendency to decrease. Therefore more effective test methods are necessary to predict the exact life. The failure of hydraulic pumps & motors operating in high pressure and high speed mainly occurs in piston-shoe assemblies, and the major failure mode is wearout of the shoe surface. The sensitive parameters in the endurance life test are speed, pressure and temperature, and the failure production increases in proportion to the operating time. In this research, the authors propose the combined accelerated life test model using the analysis method of the combined accelerated life test results of piston-shoe assemblies by applying simultaneously high speed, high pressure and high temperature in accordance with variation of speed, pressure and temperature to reduce the life test time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.3
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• pp.1008-1013
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• 2012

Electro-hydraulic power steering (EHPS) system is the power-assisted steering which operates the hydraulic pump by BLDC motors for assisting the steering force. EHPS consists of BLDC motor, gear pump, oil-hydraulic circuit and steering system. Since EHPS is a convergence system consisting of electricity and electronic, hydraulic and mechanical system, it is difficult to establish the simulation model. In this paper, the mathematical model of EHPS system components were presented, and the simulations of the multi-domain system were performed by using AMESim. The trial and error of development would be reduced by using this simulation results, and it would be helpful for developing high-quality EHPS.

• 기계와재료
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• v.25 no.3
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• pp.6-15
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• 2013

유압프레스의 단점을 극복하기 위해서 서보모트를 장착하여 성형속도를 높인 서보 유압프레스를 개발하게 되었으며, 특히나 서보모터를 국내산으로 적용하여 듀얼형으로 유압시스템의 효율성을 높여 최종적으로 개발함으로써 서보 유압프레스를 완전 국산화하였다. 또한 하사점 위치 제어의 용이성을 확보하기 위해 프레스 램용 메인 실린더에 톱니나사부를 만들어 임의의 위치에 정지할 수 있는 정지정도 및 하사점 위치 제어정밀도를 향상시켰으며, 유량의 미세 제어를 통해 프레스 램의 동작성을 개선코자 하였다. 다이쿠션은 메인 실린더와의 연계 제어를 통해 제품의 손상 방지 및 제품 추출의 용이성을 확보하였으며, 소재의 종류나 제품의 형상 특성에 따라 프리모션 제어가 가능한 지식기반형 자율제어 시스템을 적용하였다. 듀얼 서보시스템과 유압펌프가 연계구동함에 따라 기존 유압프레스 보다 약 40%이상의 에너지절감을 달성할 수 있을 것으로 예측되며, 현재 에코머신 인증제도에 대한 논의가 활발한 시점에서 매우 적합하고 필요한 하이브리드형 서보 유압프레스의 국산화 개발 사례라고 하겠다.

• 기계와재료
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• v.11 no.2 s.40
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• pp.37-43
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• 1999

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.7-14
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• 2018

In this study, a new check valve was studied to improve the load pressure of a brake system with a small piezoelectric-hydraulic pump. During the pressurization process, the steady-state pressure at the load is affected by the ratio of the cross-sectional area of the check valve the chamber pressure and load pressure. Since the flow path cover of the check valve is made wider than the cross-sectional area of the output flow to prevent backflow, a method of reducing the area ratio is proposed for a higher load pressure by mounting an additional mass to a thin plate spring type check valve. To identify the effect of mounting an additional mass to the existing check valve on the load pressure, a simple brake system with a small piezoelectric-hydraulic pump was modeled using a commercial code AMESim. The AMESim modeling was verified by comparing the simulation results with the experimental results of the pump the existing check valve. The additional mass was added to the verified AMESim modeling and higher load pressure was able to be obtained through simulation. The 35% performance improvement in load pressure identified by carrying out pressurization test of the brake system after adopting the new check valve the small piezoelectric-hydraulic pump.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.218-223
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• 1997

유압장치의 핵심부품인 유압 제어밸브(hydraulic control valve)는 유압펌프 등에 의하여 가압된 유압유의 압력과 유량을 제어하고 유동방향을 변화시키는 주요기능을 수행한다. 특히, 대부분의 제어밸브는 스푸울(spool)과 슬리브(sleeve)를 기본구조로 채용하고 있다. 피스톤 형상인 스푸울이 슬리브내를 왕복운동하면 스푸울과 슬리브 사이의 간극(clearance)에서는 점성유체인 유압유의 윤활작용에 의하여 원주방향으로 비대칭인 유체압력이 발생한다. 이 결과로 스푸울에 측력(lateral force)이 작용하며, 조건에 따라서는 스푸울에 작용하며, 조건에 따라서는 스푸울에 작용하는 마찰력이 증대할 뿐만 아니라 스푸울과 슬리브의 내벽에 과도한 마멸(wear)을 유방시키기도 하여 제어밸브의 성능을 크게 저하시키기도 한다. 유압공학분야서는 이를 유체고착(hydraulic locking) 현상이라고 부른다. 본 논문에서는 항공기 Flap actuator의 Selector manifold에서 사용되는 스푸울 밸브의 성능에 큰 영향을 미칠 것으로 예상되는 스프울과 슬리브 사이 간극에서의 윤활특성을 이론적으로 조사하고자 한다.