• 드라이브 ㆍ 컨트롤
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• 제11권4호
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• pp.25-31
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• 2014

This paper details application of a DLC(Diamond Like Carbon)-coating to the swash plate and the ball joint of pistons that make sliding contact with the piston shoes of an axial piston pump. This process, aimed to reduce the frictional and leakage power losses of the hydrostatic piston shoe bearings at the low speed range. At lower speeds than 100rpm, the positive effects of the DLC-coating on the power loss reduction of the hydrostatic piston shoe bearings could be confirmed. These effects resulted in little improvement in volumetric efficiency of the test pump, but the mechanical efficiency could be raised by up to 5% at 100rpm; here, the DLC-coated swash plate played a more dominant role than the DLC-coated ball joint.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.171-176
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• 2008

As one way of design optimization of two-stage two-cylinder rotary compressor used for R410A heat pump application, displacement volume ratio, being defined by the ratio of the second stage cylinder volume to that of the first stage, has been varied and its effect on the compressor performance has been investigated by a computer simulation program. For simplicity, only the cylinder height of the second stage was varied to change the volume ratio. With increasing the volume ratio in the range of VR=$0.55{\sim}0.9$, volumetric efficiency increased monotonically, but adiabatic efficiency showed a maximum at around VR=0.6. Mechanical efficiency was little influenced by the volumetric ratio. As a consequence, maximum improvement of the compressor performance was found at around VR=0.7. Compared to a one-stage two-cylinder rotary compressor with about the same cooling capacity, COP improvement was about 6.96%.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1383-1392
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• 2009

A disadvantage in the design of a hypotrochoidal gear pump as in a gerotor pump is a lack of parts that can be adjusted to compensate for wear in the rotor set, and as a consequence, it causes a sharp reduction of volumetric efficiency. In this paper, an attempt has been made to reduce the wear rate between the rotors of a hypotrochoidal gear pump. Using the knowledge of shape design on the rotors, the contact stresses without hydrodynamic effect between the rotors' teeth are evaluated through the calculation of the Hertzian contact stress. Based on the above result and the sliding velocity between the rotors, a genetic algorithm (GA) is used as an optimization technique for minimizing the wear rate proportional factor (WRPF). The result shows that the wear rate or the WRPF can be reduced considerably, e.g. approximately 12.8% in this paper, throughout the optimization using GA.

• Tribology and Lubricants
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• 제14권1호
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• pp.64-69
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• 1998

A numerical analysis is carried out to study the effect of piston shape on the lubrication characteristics between the cylinder and piston in hydraulic piston pumps. The results showed that the shape of piston affect significantly the pressure distribution in the clearance, the lateral force acting on the piston and leakage flow through the clearance. Partially tapered piston is more effective than any other piston shapes because it reduces the possibility of hydraulic locking and improves the volumetric efficiency of the pump.

• 한국수소및신에너지학회논문집
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• 제34권1호
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• pp.59-68
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• 2023

In this study, the performance of high-pressure fuel pumps was compared to find a high-pressure pump suitable for dimethyl ether (DME) fuel, and to establish a database of basic data on flow rates. The use of DME in compression ignition engines can reduce pollutant emissions. The cetane value of DME is higher than that of diesel fuel. The physical properties of DME are similar to liquefied gasoline gas (LPG), and when pressurized at a pressure of 6 bar or more, it changes from gas to liquid. Two types of high pressure pumps used in this study were independent injection type pump and a wobble plate type pump. Two high-pressure pumps with different injection types were compared. By measuring and comparing the performance changes of the two high-pressure pumps, a pump suitable for DME was selected and performance improvement measures were proposed. The changed experimental conditions to measure the performance change of the high pressure pump were increased in the units of 100 to 1,000 rpm and 100 rpm, and the experiment was performed at common rail pressures 300 and 400 bar. it was confirmed that the DME inside the fuel supply system remained in a liquid state through temperature sensors, pressure sensors, and pressure gauges. As a result of the experiment, it was confirmed that the flow rate discharged from the high-pressure fuel pump increased as the motor rotational speed increased, and the flow rate of the high-pressure fuel pump

• 한국해양공학회지
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• 제24권6호
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• pp.76-80
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• 2010

Oil hydraulic piston pumps are being extensively used around the world, because of their simple design, light weight, effective cost, etc. An oil hydraulic pump is likely to have the serious problems of high leakage, friction, and low energy efficiency after a long period of use. In an oil hydraulic piston pump, the clearance between the valve block and piston plays an important role for volumetric and overall efficiency. In this study, the wear property of the SACM645 material with DLC coating used for a hydraulic piston pump was determined by experimentation with variable heat treatment. To investigate the effect according to the piston surface condition, five different types of specimens were prepared. The maximum tensile strengths of the QT and QT Nitration specimens had similar values of about 800 MPa, but the strains indicated a big difference. In a wear test, the wear characteristic of the DLC coating specimen was shown to be excellent. The QT, QT + IH, QT + Nitration, and matirx specimen showed similar wear characteristics. In the case of a dry condition without oil, the DLC coating specimen had good wear resistance, with no wear shown.

• 설비공학논문집
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• 제11권2호
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• pp.193-204
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• 1999

Performance of a variable-speed, roller-type vane compressor was evaluated at low evaporating temperature. First, an experimental investigation was conducted to examine the performance variation as functions of both outdoor temperature and rotating speed. For this purpose, a typical heat pump was implemented as a test apparatus to measure mass flow rate and power input. Secondly, computational investigations corresponding to the heat pump test conditions were performed to predict compressor performance using ORNL Map-Based compressor model. Results obtained from the heat-pump experiments showed that both mass flow rate and power consumption were sensitively dependent on both evaporating temperature and compressor speed as was predicted from the computational results. From the comparisons of both experimental and computational results, it was well recognized that the ORNL model was subjected to larger error in the accuracy of prediction as outdoor temperature decreased. When the outdoor temperature was above $-5^{\cire}C$, errors of predicted values corresponding to both mass flow rate and power consumption were estimated as $\pm$10% and $\pm$ 15%, respectively. Finally, it is suggested that the ORNL model needs to be re-evaluated if compressor map data tested below $-5^{\cire}C$(in evaporating temperature) are available.

• 대한기계학회논문집A
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• 제35권5호
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• pp.555-559
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• 2011

본 연구는 유압 피스톤 펌프 재료로 사용되고 있는 SACM645소재를 사용하여 모재, QT(quenching & tempering) 시험편 및 QT 질화시험편의 피로특성을 조사하였다. 피로특성 조사결과는 다음과 같다. QT 질화시험편은 피로한도가 인장강도의 80%로 나타나 아주 높은 값을 나타내었다. 이것은 시험편 표면에 단단한 질화처리를 실시하여 피로균열의 발생을 지연시켰고, 피로균열이 발생하더라고 소재가 단단하여 균열진전속도가 늦었다고 판단된다. 파면 관찰결과 피로균열진전 영역에서는 모두 스트라이에이션이 관찰되었고, 피로균열진전 이외의 영역에서 QT 시험편은 벽개파괴의 양상을, 모재와 Qt 질화시험편은 딤플 파괴의 양상을 나타내었다.

• 대한기계학회논문집B
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• 제35권9호
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• pp.875-882
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• 2011

회전차 외경 가공에 따른 축추력 평형 및 체적 효율 변화에 대하여 고찰하였다. 평형장치로 평형피스톤이 장착된 저비속도 다단 원심 펌프를 연구 대상으로 해석을 수행하였다. 수평축 다단 펌프와 2종의 수직축 다단 펌프에 대해 해석 수행을 한 결과, 회전차 외경 가공에 의해 펌프 전방으로 추가적인 축추력이 발생하였다. 이러한 축추력 불균형은 수평축 펌프보다 수직축 펌프에서 크게 발생하였다. 축추력 불균형을 방지하기 위해 평형피스톤의 외경을 증가시키는 방안을 제시하였고, 이를 위해 필요한 평형피스톤의 직경 변화율을 산출하였다. 피스톤의 직경 변화량은 회전차 외경 가공률에 비례하여 증가하였다. 피스톤 직경 변화량이 클수록 틈새 면적 증가로 인해 체적효율이 감소하므로, 피스톤의 길이를 함께 증가시켜 체적 효율의 감소를 방지하는 것이 효과적이다.

• 한국산학기술학회논문지
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• 제16권5호
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• pp.3044-3050
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• 2015

본 연구는 자동변속기용 유량제어 오일펌프의 성능을 해석하는데 목적이 있다. 이를 위하여 유량제어 오일펌프의 해석적 모델을 개발하였으며 회전속도 변화에 따른 토출유량, 구동토크, 캐비테이션 발생량 등의 내부 유동특성을 분석하여 고찰하였다. 해석결과, 회전속도가 높아짐에 따라 캐비테이션 발생율이 증가하였으며 체적효율은 2200 RPM에서 90%이상으로 나타났지만 회전속도가 상승함에 따라 감소하여 5000 RPM에서 81%까지 줄어드는 것으로 나타났다. 또한 흡입부 초기에 챔버 내 캐비테이션 비율이 20%~30%로 매우 높은 비율을 보였는데 압축에 의해 붕괴 이후의 캐비테이션 비율은 13% 이하로 낮게 형성되었다. 하지만 고속인 5000 RPM에서 17%로 빠른 속도로 발생량이 증가하는 현상도 확인되었다.