• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.99-107
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• 2004

Lubrication characteristics between a cylinder block and a valve plate for high speed bent-axis type hydraulic pump play an important role in volumetric efficiency and durability of pump. In this paper, a finite element method is presented for the computation of the pressure distribution between a cylinder block and a valve plate for high speed bent-axis type hydraulic pump. Also, a Runge-Kutta method is applied to simulate the cylinder block dynamics of three-degrees of freedom motion. From the results of computation, we can draw two major conclusions. One is related to the fluid film characteristics between a cylinder block and a valve plate and the other is related to the average leakage that is determined by the pressure gradient and the clearance near the discharge port. The numerical results of cylinder block dynamics were compared with the experimental results using eddy-current type gap sensors those are fixed at a pump housing.

• Journal of Mechanical Science and Technology
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• 제19권2호
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• pp.655-663
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• 2005

Tribological characteristics in the sliding parts of oil hydraulic piston pumps are very important in increasing overall efficiency. In this study, the fluid film between the valve plate and the cylinder block was measured by using a gap sensor and the mercury-cell slip ring unit under real working conditions. To investigate the effect of the valve shape, we designed three valve plates each having a different shape. One of the valve plates was without bearing pad, another valve plate had bearing pad and the last valve plate was a spherical valve plate. It was noted that these three valve plates observed different aspects of the fluid film characteristics between the cylinder block and the valve plate. The leakage flow rates and the shaft torque were also investigated in order to clarify the performance difference between these three types of valve plates. From the results of this study, we found that the spherical valve plate estimated good fluid film patterns and good performance more than the other valve plates in oil hydraulic axial piston pumps.

• 한국정밀공학회지
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• 제30권11호
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• pp.1153-1160
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• 2013

SMISMO valve configuration is now starting to draw attention of the researchers of the construction equipment industry to increase the fuel efficiency of their equipment like excavators and wheel-loaders. An open-loop control strategy for grading operation of hydraulic excavator systems using SMISMO valve configuration is investigated in this paper. Tabor's algorithm for 1 d.o.f. SMISMO system under the assumption of quasi-static operation is revealed as not adequate for multi d.o.f. system with large moment of inertia even though the motion of the system is slow. New parameters are proposed in this paper. It modifies Tabor's open-loop control strategy for the grading operation of hydraulic excavators using SMISMO valve configuration. A simulation-based parameter tuning method is also proposed. It uses GA (Genetic Algorithm) to find the best parameter values. Simulation study for a practical hydraulic excavator shows the validity of the proposed open-loop control strategy.

• 드라이브 ㆍ 컨트롤
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• 제9권1호
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• pp.1-9
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• 2012

Nowadays, various researches about eco-friendly vehicles such as hybrid electric vehicle, fuel cell vehicle and electric vehicle have been actively carried out. Since most of these green cars have electric motors, the regenerative energy technology can be used to improve the fuel economy and the energy efficiency of vehicles. The regenerative brake is an energy recovery mechanism which slows a vehicle by converting its kinetic energy into electric energy, which can be either used immediately or stored until needed. This technology plays a significant role in achieving the high energy usage. However, there are some technical problems for controlling the regenerative braking and the electro-hydraulic brake during switching at transient region. In this paper, the performance simulator for fuel-cell vehicle is developed and transient response characteristics of the regenerative braking system are analyzed in the various driving situations. And the hardware-in-the-loop simulation of electro-hydraulic brake is performed to validate the transient characteristics of the regenerative braking system for fuel-cell electric vehicle.

• 유공압시스템학회논문집
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• 제4권3호
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• pp.1-6
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• 2007

The leakage generated from the clearance between the cylinder bore and the piston is one of the most serious problems in the hydraulic piston pump, and it even results in terrible decrease of the volume efficiency at a great velocity and high pressure. In this paper, the lubrication characteristic of the hydrostatic slipper bearing equipped in the hydraulic piston pump has been worked out by experimentation with three model bearings of different shape. Preparatory to this, not only the three models of piston-slipper were designed, but the corresponding experimental apparatus were also manufactured. As a result, it was verified that, according to the supply pressure, the hydrostatic bearing part of the slipper is severely affected by the pocket pressure, land pressure, oil film thickness, and leakage flow.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.891-895
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• 1996

Performance and efficiency of hybrid (hydraulic-mechanical) pick-up device of deep sea manganese nodules collector are very sensitive to altitude and altitude of pick-up head relative to undulating seafloor. For this reason, motion control of pick-up head relative to the changing deep sea topography and other disturbances is of particular importance in design of pick-up device. The concept of design axiom is applied to a pick-up device of hybrid type. Kinematic analysis conducted in absolute Cartesian coordinates gives position, velocity, and acceleration of the hydraulic cylinders which enable the pick-up head to keep the preset optimal distance from seafloor. Inverse dynamic analysis provides the driving forces of hydraulic cylinders and the reaction forces at each joint. Design sensitivity analysis is performed in order to investigate the effects of possible design variables on the change of the maximum strokes of hydraulic cylinders. The direct differentiation method is used to obtain the design sensitivity coefficients.

• 한국물환경학회지
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• 제22권1호
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• pp.91-96
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• 2006

Many small scale Sewage Treatment Plants (STPs) are currently being constructed at many rural areas. The STPs in rural area suffer from low concentration and large inflow quantity fluctuation during wet weather mainly due to illicit combined sewer system. Sequencing Batch Reactor (SBR) is a process effectively coping with these obstacles. The main objective of this study was to evaluate SBR with high hydraulic loading and low inflow concentration. The operating conditions tested were: organic loading rate = $0.17-0.42KgBOD/m^3/d$, hydraulic loadings = $12.1-61.5m^3/m^2/d$, average MLSS concentration = 2500 mg/L, F/M ratio = 0.026-0.17 KgBOD/Kg MLSS, HRT = 9-12 hr HRT, and SRT = 5.6-33.6 days. Organic loading rate on SBR did not impact significantly on BOD and SS removal efficiencies. To increase treatment efficiencies, low hydraulic loading rate with low concentration was required. The results suggested that low influent concentration with high inflow rates during wet weather requires extended time for settling.

• 로봇학회논문지
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• 제16권2호
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• pp.86-93
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• 2021

This paper proposes a controller to regulate the supply pressure of the hydraulic power unit (HPU) for driving a bipedal robot. We establish flow rate models for charging accumulator, actuating joints and leaking from actuators and spool valves. This determines the pump driving motor speed to satisfy the demanded flow rate for operating the bipedal robot without the energy loss caused by the bypass through a pressure regulating valve. We apply proposed controller to an onboard HPU mounted on top of bipedal robot platform with twelve degrees of freedom. We implement air-walking motion and squat motion which require variable flow rate to the bipedal robot. Through this experiment, the energy efficiency of proposed controller was verified by comparing the electric energy consumed when the controller was applied and when the pump operated at constant speed. We also shows the capability of the HPU's control performance to regulate supply pressure.

• 드라이브 ㆍ 컨트롤
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• 제15권4호
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• pp.17-22
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• 2018

Mobile hydraulics require higher energy efficiency, and a simpler as well as robust design, than general industrial hydraulics. The 6/3-way directional control valve is widely used as a mobile hydraulic control valve. However, since the 6/3-way directional control valve is a spool type valve, it is difficult to maintain the load. A counterbalance valve is typically used, to maintain the load, and lift down. However, in an industrial field using a mobile hydraulics device, a pilot controlled check valve may be used to implement holding and lifting operation of the self-weight load, and a relief valve may be used simply to exert back pressure. But no comparative analysis of advantages and disadvantages of each method was revealed. In this study, various methods of holding and unloading load with self-weight in mobile hydraulics are investigated, and compared through simulation using AMESim software. This is experimentally verified by using Festo's mobile hydraulic test rig TP800.

• 한국해안·해양공학회논문집
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• 제28권2호
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• pp.73-80
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• 2016

파의 왕복운동을 지속적인 일방향 회전운동으로 유도하여 발전기의 가동에 있어 기계적인 손실 에너지를 감소시켜 발전효율을 극대화시킬 수 있는 파의 수평왕복운동을 직접 이용하는 가동물체형 파력발전장치가 개발되었다. 그리고 실제 전력생산에 관한 수리실험이 수행되었고 그 결과가 토의되었다. 수리실험에서 부력 탱크의 형상에 따른 발전장치의 발전효율은 파력판의 무게를 충분히 지탱하는 직경 9 cm의 고정식 부력 탱크가 평균발전효율 14.6%로 좋은 결과를 보였으며 효율이 좋을 것으로 기대되었던 부력 탱크가 자유로이 승강하는 경우는 발전효율이 8.5%로 좋지 못한 결과를 보였다. 그리고 여러 파랑조건에 따른 직경 9 cm의 고정식 부력 탱크형 발전모형의 평균발전 효율이 수심 90 cm에서 기어비 2단 3.9%, 3단 4.9%, 4단 4.9%, 5단 12%, 6단 10.0%, 7단 3.1%, 그리고 8단 3.0%를 나타냈으며, 수심 80 cm의 기어비 5단에서 15%의 발전효율이 계측되었다. 따라서 이 파력발전장치는 수심 80~90 cm의 기어비 5단에서 비교적 높은 13.5%의 평균발전효율을 얻을 수 있었다.