• 대한기계학회논문집B
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• 제28권11호
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• pp.1322-1331
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• 2004

This paper presents studies on the design of water hydraulic system and components to replace oil with tap-water as the pressure transmission medium in hydraulic systems. In order to improve the performance of water hydraulic system, the thermal and hydraulic properties of tap-water are first investigated. Based on these characteristics, the design parameters, such as the clearances of the moving parts, the cross-sectional area of pipes and relative roughness, are proposed so that the performance of water hydraulic system is the same as that of oil. In addition, the operating ranges, which show the possibility of using water hydraulic system, are examined.

• 한국기계가공학회지
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• 제19권8호
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• pp.110-116
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• 2020

Aircraft hydraulic oil reservoirs made with aluminum 7075 have an anodized coating to enable airtightness and corrosion resistance. To maintain a stable oil pressure, the internal surface roughness of the reservoir should be less than approximately 0.2 ㎛. To this end, precision polishing must be performed. However, ensuring the processing quality is challenging, as most polishing operations are performed manually, owing to which, the inner surface roughness is not uniform, and the product quality is irregular. Therefore, we developed a special superfinishing machine to realize the efficient inner polishing of an aircraft hydraulic oil reservoir, by using an abrasive film to improve the process throughput and uniformity. In the experiment involving the superfinishing of an anodized aluminum 7075 cylinder specimen by using the proposed machine, a higher surface roughness than that achieved in the repetitive manual polishing process could be realized.

• 항공우주시스템공학회지
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• 제4권2호
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• pp.16-20
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• 2010

In General, the hydraulic system of T-50 Advanced Trainer is applied to flight control system, wheel & Brake system and fuel system for aircraft operation. The hydraulic system is operation with pressure of 3000psi. and many mechanical parts which is operated by hydraulic system has been stressed in incomplete environment same as heat and friction. for example, Oil leakage had occurred in the shutoff valve of FFP used in a certain period of time. After study, The crack progressed by fatigue due to the irregular hydraulic pressure and vibration has been identified as the reason of oil leakage. This paper presents life cycle extension plans of FFP shutoff valve by configuration improvements of shutoff valve and FFP hydraulic motor.

• 드라이브 ㆍ 컨트롤
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• 제11권4호
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• pp.39-45
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• 2014

With recent oil price increases, the fuel efficiency of hydraulic excavators has become a serious issue. Researchers have considered weight lightening by high pressurization in order to improve the efficiency of the excavator and pump controlled actuation (PCA) and to reduce pressure loss of hybrid and valves using mechanical inertia. However, high pressurization is not very effective because the excavator operates at a low speed; a hybrid is inefficient because little accumulated inertial energy is accumulated; and PCA is ineffective because control precision and responsibility are low. In this study, a method to minimize air and gas in hydraulic oil has been presented as a simple and new way to increase hydraulic efficiency.

• 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.

• Geomechanics and Engineering
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• 제7권4호
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• pp.403-430
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• 2014

Shale gas formations exhibit strong mechanical and strength anisotropies. Thus, it is necessary to study the effect of anisotropy on the hydraulic fracture initiation pressure. The calculation model for the in-situ stress of the bedding formation is improved according to the effective stress theory. An analytical model of the stresses around wellbore in shale gas reservoirs, in consideration of stratum dip direction, dip angle, and in-situ stress azimuth, has been built. Besides, this work established a calculation model for the stress around the perforation holes. In combination with the tensile failure criterion, a prediction model for the hydraulic fracture initiation pressure in the shale gas reservoirs is put forward. The error between the prediction result and the measured value for the shale gas reservoir in the southern Sichuan Province is only 3.5%. Specifically, effects of factors including elasticity modulus, Poisson's ratio, in-situ stress ratio, tensile strength, perforation angle (the angle between perforation direction and the maximum principal stress) of anisotropic formations on hydraulic fracture initiation pressure have been investigated. The perforation angle has the largest effect on the fracture initiation pressure, followed by the in-situ stress ratio, ratio of tensile strength to pore pressure, and the anisotropy ratio of elasticity moduli as the last. The effect of the anisotropy ratio of the Poisson's ratio on the fracture initiation pressure can be ignored. This study provides a reference for the hydraulic fracturing design in shale gas wells.

• 한국공작기계학회논문집
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• 제11권2호
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• pp.71-79
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• 2002

In this paper, an oil hydraulic pipeline is terminated by both rotary sinusoidal flow generator at upstream oriffice at down stream. The pulsating pressure wave from generated by the rotary sinusoidal flow generator, is measured by using sensor. In the analysis of this paper, a component of the fundamental frequency is obtained by using Laplace transformation.. The experimental and analytical results make clear that (1) viscosity is significant role in hydraulic pipe. (2) When pulsating frequency is matched with the natural frequency, resonance frequency occured periodically. According to the study proposed here, dynamic pressure in a circular oil pipe is expressed in propagation of pressure wave with respect to frequency and Bessel function. The resonance at oil temperature $20^{\circ}$$0^{\circ}C$ in this study. The abrupt change of gain value is due to effect of resonance frequency. The results of experiment are compared with the calculated results, and agreement of both results is fairly good.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.267-272
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• 1995

The paper describes an approach for measuring flow ripple generated by oil hydraulic axial piston pumps. Flow ripple has periodic waveforms due to the cyclic nature of a pump's operation, and interacts with the connected hydraulic systems such as pipes and components to produce a pressure ripple, also known as fluid-borne noise. It is indispensable to measure a flow ripple because increasing of vibration and noise caused by a flow ripple has become a point to be considered and has need of solving these problems. The measurement of flow ripple with high frequencies from oil hydraulic axial piston pumps is msde by using the remote instantaneous flow rate measurement method. As a result, the reverse flow through the relief groove in valve plate has an important effect upon a flow ripple generated by a pumps.

• Tribology and Lubricants
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• 제26권2호
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• pp.136-141
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• 2010

In an oil hydraulic vane pump for an automobile, it is very important that the vane doesn't separate from the camring inner race during the operation of the vane pump. The vane generally has not only the oil hydraulic force acting on the bottom face to contact to camring inner race but there is also an inertial force and viscous force. Because the oil hydraulic force is much larger than the other forces, the contact state between the vane tip and the camring inner race is sufficient. However, the contact state between the vane tip and the camring inner race is only affected by the inertial and viscous forces during the delivery of the vane pump, because the oil hydraulic force acting on the vane is in equilibrium. If the inertial force is larger than the viscous force, which happens when the vane is separated from the camring inner race, the delivery of the vane pump can become unstable or the volume efficiency can become decrease rapidly. Therefore, in this paper, the state of the contact between the vane and the camring is considered. The results show that the rotating speed of the shaft, the operating temperature of the oil, the clearance between the vane and the rotor, and the mass of the vane exert a great influence on the state of the contact between the vane and the camring.

• 대한기계학회논문집
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• 제16권2호
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• pp.191-199
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• 1992

This paper presents in experimental study of the dynamic internal pressure within an oil hydraulic vane pump. The measurements of the dynamic internal pressures near the vane of a pressure balance type of an oil hydraulic vane pump with intravanes has been made to provide the essential information for the study of the pump dynamics and control, the pump design and the analysis of tribological problems in the sliding components. The influences of the discharge pressure and rotating speed of the vane on the dynamic pressure in four chambers surrounding a vane have been investigated. The results indicate that the surge pressures of the chambers at the instant moment of discharge and closure are affected by the rotating speed. The pressure in the intravane chamber maintains almost constant values, which remarkably effects the pulsating discharge pressure.