• Journal of Mechanical Science and Technology
• /
• 제17권2호
• /
• pp.246-253
• /
• 2003

The tribological mechanism between the valve plate and the cylinder block in oil hydraulic axial piston pumps plays an important role on high power density. In this study, the fluid film thickness between the valve plate and the cylinder block was measured with discharge pressure and rotational speed by use of a gap sensor, and a slip ring system in the operating period. To investigate the effect of the valve plate shapes, we designed two valve plates with different shapes . the first valve plate was without a bearing pad, while the second valve plate had a bearing pad. It was found that both valve plates behaved differently with respect to the fluid film thickness characteristics. The leakage flow rates and the shaft torque were also experimented in order to clarify the performance difference between the valve plate without a bearing pad and the valve plate with a bearing pad. From the results of this study, we found out that in the oil hydraulic axial piston pumps, the valve plate with a bearing pad showed better film thickness contours than the valve plate without a bearing pad.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
• /
• pp.228-234
• /
• 2000

The vibration characteristics of the pad fluttering in a fluid film tilting pad journal bearing(4-pad LBP) have been investigated experimentally under the different values of oil supply flow rate, bearing load and shaft speed. The vibration characteristics of the pad fluttering are estimated by measuring the time signal of circumferential distribution of the film thickness and the cascade plot of the response of the relative displacement between the bearing and the shaft. It is shown that the vibration frequency of the pad fluttering has a sub-synchronous frequency and 31mos1 does not change by the increase of shaft speed. However the vibration amplitude is increased by the increase of shaft speed. From those experimental results, pad fluttering can be thought of as a self-excited vibration. The incipient pad fluttering velocity is increased by the increase of oil supply rate and by the decrease of bearing load. It is observed that the vibration amplitude of the pad fluttering can be decreased by the control of supply oil flow rate effectively. And also It is known that the outbreak of pad fluttering does not concern with the shaft vibration.

• 대한기계학회논문집B
• /
• 제25권1호
• /
• pp.71-77
• /
• 2001

A flow visualization study using the oil film method and the smoke-laser light sheet arrangement is carried out to investigate the three-dimensional flow pattern around the free end surface region of a finite circular cylinder (aspect ratios of 1.25 and 4.25) mounted on a flat plate. The experiment is performed for the cases of two Reynolds numbers: 5.92${\times}$10$^3$and 1.48${\times}$10(sup)5. Various kinds of singular points on the free-end surface are disclosed from the oil surface flow visualization. The smoke-laser light sheet visualization, to aid in understanding the oil streak-line patterns, clearly demonstrates that a pair of tornado-like vortices marched along the downstream together with a pair of side tip vortices. A topological sketch to characterize the surface flow and the four vortices emanating from the top surface is included.

• Journal of Mechanical Science and Technology
• /
• 제14권9호
• /
• pp.928-934
• /
• 2000

This paper describes a method developed for the simulation of ring pack lubrication characteristic in an internal combustion engine. In general, the quantity of oil supply for piston ring lubrication may be insufficient in filling the entire volume formed at the interference between the piston ring and the cylinder liner. Thus the oil starvation condition should be considered in analyzing piston ring lubrication. In order to reasonably estimate the amount of oil left over on the cylinder liner, the flow rate at the posterior portion of the interface should be calculated with an adequate boundary condition that confirms flow continuity condition. In this analysis, oil starvation and open-end boundary conditions are considered at the inlet and outlet of the piston rings. The lubrication characteristic of each piston ring is obtained by an iterative method with sequential steps. It is revealed that piston rings are operated under oil starvation in most operating cycles and the result under these conditions are quite different from that with the fully-flooded assumption.

• Tribology and Lubricants
• /
• 제33권1호
• /
• pp.23-30
• /
• 2017

The electric controlled marine diesel engine has fuel pump generating the high pressurized fuel for fuel injection to combustion chamber via a common rail. Fuel pump consists of a cam-roller system. Journal bearing installed between a roller and a cam-roller pin is subjected to fluctuating heavy and instant loads by cam lift. First, Kinematic analysis is carried out to predict bearing loads during one cycle acting on the journal bearing. Second, flexible multi-body dynamic analysis and transient elasto-hydrodynamic(EHD) lubrication analysis for journal bearing considering elastic deformation of cam-roller pin, roller and bearing are conducted using AVL EXCITE/PU software to predict lubrication performance. The clearance ratio and journal groove shape providing lubrication oil are important parameter in bearing design having good performance and can be changed easier than other design parameters such as diameter, width, oil supply pressure and bearing material grade. Generally, journal bearing performance is represented by the minimum oil film thickness(MOFT) and peak oil film pressure(POFP). As well as the traditional design parameters(MOFT, POFP), in this study, temperature rise of lubrication oil is also evaluated through the side leakage flow of supplied oil. By the evaluating MOFT, POFP and temperature rise, the optimum bearing clearance ratio is decided.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
• /
• pp.381-382
• /
• 2002

The Fluid film between the valve plate and the cylinder block was measured by use of a gap sensor and the mercury-cell slip ring unit under real working conditions. During the operating periods, experiments with discharge pressure, revolution speed, and valve geometry was carried out for the fluid film on the valve plate. To investigate the effect of the valve shape, we designed two valve plates each having a different shape; the first valve plate was a plane valve plate. while the second valve plate was a spherical valve plate. It was noted that these two valve plates observed different aspects of the fluid film characteristics between the cylinder block and the valve plate. The leakage flow rate and the shan torque were also investigated in order to clarify the difference between these two types of valve plates. From the results of this study. we found that the spherical valve plate estimated good fluid film patterns and performance more than the other valve plate in oil hydraulic axial piston pumps.

• Tribology and Lubricants
• /
• 제2권2호
• /
• pp.12-19
• /
• 1986

냉각성, 난연성, 그리고 경제성의 면에서 우수한 윤활특성을 갖고 있는 이멀션윤활제를 사용하여 로울러와 프레이트간의 선접촉 및 광간섭계의 실험장치를 통하여 탄성유체윤활 영역에서의 윤활기구 및 분산립자의 거동기구를 명확히 하여 다음과 같은 결론을 얻었다. 1. 스퀴즈 유막내의 유동은 윤활간극이 비교적 넓은 경우와 좁은 경우로 대별하여 전자의 경우에는, 입자분포 및 속도분포의 영향이 크게 나타나며, 후자의 경우는 이멀션입자가 간극내에 정지하여 유막두께의 감소와 더불어 변형되어 간다. 2. 스퀴즈 유막내의 O/W, W/O 각 이멀션의 유동은 간극이 클 경우, 입경에 의한 속도차가 역으로 나타나고, 작은 경우에는 잔류액적의 분포가 서로 다르며 그밖에 O/W 형은 W/O 형에 비하여 분산입자가 쉽게 변형하는 것을 알 수 있다. 3. EHL영역입구부에서는 입자의 유동속도가 극히 적은 정체영역이 존재하며, 그 부근에서의 입자의 거동은 입경에 따라서 다르다. 4. 2색광에 의한 광간섭선의 관찰에 의하여 탄성유체윤활 영역내를 통과하는 이멀션유를 확인함과 동시에 EHL영역입구부에서의 분열거동이 관찰되었다.

• 드라이브 ㆍ 컨트롤
• /
• 제18권4호
• /
• pp.84-90
• /
• 2021

Viscosity of hydraulic oils decreases due to loss reduction and efficiency increase of fluid power systems. However, low viscosity is not always appropriate due to the induction of large leakage and small lubricity. Therefore, a detailed study on the optimum viscosity of hydraulic oils is necessary. In this study, based on the thermohydrodynamic lubrication theory, numerical simulation was conducted using the slipper model of swashplate-type axial piston pumps and motors. The viscosity grades' (VG) effects of oils on power losses are mainly discussed numerically in fluid film lubrication, including changes in temperature and viscosity. The simulation results reveal that the flow rate increases and the friction torque decreases as VG decreases. The film temperature and power loss were minimised for a specific oil with a VG. The minimum conditions regarding the temperature and loss were different and closed. Under various operating conditions, the film temperature and power loss were minimised, suggesting that an optimum hydraulic oil with a specific VG could be selected for given operating conditions of pressure and speed. Otherwise, a preferable operating condition must be established to determine a specific VG oil.

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

• Tribology and Lubricants
• /
• 제10권1호
• /
• pp.69-77
• /
• 1994

Oil flow pass of hermetic scroll compressor with back pressure chamber was described. Dynamic analysis was preceded in order to obtain the loads on the lubricating contacts. The mobility method of dynamically loaded journal bearings was applied to the crank jornal bearing and lower main bearing, and they could be designed to operate under fluid film lubrication. From the consideration of their film thicknesses and oil flow rates, optimal bearing clearances or other bearing dimensions could be assessed. The major friction loss was calculated to be from the axial force between the two scrolls. Therefore, it was suggested that the designers should be careful to reduce the over-turning moment on the orbiting scroll.