• Tribology and Lubricants
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• v.14 no.1
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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.

• Tribology and Lubricants
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• v.10 no.3
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• pp.47-53
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• 1994

Thin film flow in the clearance between cylinder bore and axially moving compositeshape piston is analyzed to study the effect of piston shape on the lubrication characteristics of hydraulic piston pump and motor. It is shown that the piston shape significantly affect the distribution of fluid film pressure, lateral force acting on the piston and leakage flow rate in the clearance. And it is also shown that the composite-shape piston is more effective than the cylindrical piston under tilted condition to reduce the possibility of hydraulic locking. Therefore, the results of present study can be used usefully in the design-and manufacturing of hydraulic piston pump and motor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.11
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• pp.904-913
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• 2002

In this study, a dynamic analysis of the reciprocating compression mechanism considering viscous friction force of a piston used in small refrigeration compressors is performed. The length of cylinder in this class of compressors is shortening to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder liner is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the compression mechanism dynamics, the change in bearing length of the piston and all corresponding viscous forces and moments are considered in order to determine the trajectories of piston and crankshaft. The piston orbits for viscous friction model and Coulomb friction model were used to compare the effect of the friction forces of piston on the dynamic trajectories of piston. To investigate the effect of friction force acting on the piston for the dynamic characteristics of crankshaft, comparison of the crankshaft loci is given in both viscous model and Coulomb model. Results show that the viscous friction force of piston must be considered in calculating for the accurate dynamic characteristics of the reciprocating compression mechanism.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.6
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• pp.506-513
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• 2011

This paper is concerned with a study on the control effect of the MR damper using the cutout piston. The MR damper has passive damping force by the oil pressure and controllable damping force by the magnetic effect. As the velocity of the MR damper's piston increases the passive damping force increases and the ratio of the controllable damping force to the total damping force is decreased. Consequently, the control performance of the MR damper is reduced according to the increase of the velocity. In this paper, the cutout piston concept is applied to the MR damper to improve MR damper's control performance by reducing the passive damping effect. The MR damper with the cutout piston has been designed and manufactured and its hydraulic and electromagnetic analysis has been performed to predict its performance. The control performances of the MR damper with the cutout piston are verified through the comparison of experiment results and simulation results.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.3
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• pp.22-33
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• 1993

A theoretical analysis of predicting the detailed motion of a piston-crank mechanism within piston-guide clearance is presented, and the analysis is applied to the piston motion in a gasoline engine. A piston movement program is developed to calculate the piston attitude relative to the bore, the piston to bore impact velocity and kinetic energy loss and the net transverse force acting on the piston. This paper presents the formulation of a set of differential equations governing the transverse and rotational motion of a piston. These equations of motion were solved by well established Runge-Kutta method. As a result of this study, it is possible to predict the effects of piston geometry and piston pin offset on a piston motion and kinetic energy loss.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.385-396
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• 2000

The secondary motion of piston occurs due to the transient forces and moments in the clearances between piston skirt and cylinder liner The motions are very related to the skirt profile and the magnitude of piston-pin offset. Above all, the elastic deformation is another major effect on the piston secondary motion that has not been considered in the previous researches. In this work, the effects of elastic deformation of the piston skirt on the secondary piston motion are studied for the frictional power loss by using commercial softares, PISDYN and ANSYS.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.3
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• pp.240-246
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• 2014

In order to develop a universal cryogenic piston pump of small size for increasing utilization of liquid hydrogen, dynamic compression performance of piston pump were evaluated and improvements were also discussed for piston rod and piston tip. The cryogenic piston pump has crosshead structure and inclined cup shape piston tip. As the results, it was found that i) insulation of heat flow from piston-rod part is required for stable operation ii) improving the self-clearance adjustment effect of piston tip and reducing piston eccentricity were desirable to promote pumping pressure and operating range.

• Tribology and Lubricants
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• v.17 no.6
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• pp.435-440
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• 2001

A numerical analysis between the piston and cylinder in hydraulic piston pumps under reciprocating motion is presented. A finite difference method and the Newton-Raphson method are used simultaneously to solve the Reynolds equation in the clearance and the equation of motion for the piston. The tapered piston showed stable behaviors regardless of their initial eccentric positions in the clearance, and the reciprocating speed affect highly on the piston end trajectories. Therefore, the numerical methods and results of present study can be used in the lubrication study of other piston-cylinder type fluid machineries.

• KSTLE International Journal
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• v.2 no.1
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• pp.17-21
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• 2001

Surface treatment technologies are frequently used to improve mechanical properties of surface layers of machinery components in many practical situations. Surface hardness of piston in the oil hydraulic piston pumps is very important about wear resistance. To improve hardness, wear resistance of the oil hydraulic axial piston pump, it is needed to know the surface layer characteristics in the sliding contact parts. This paper reports an experimental study on surface treatment characteristics in the piston of the oil hydraulic axial piston pump. We investigated the surface wear of a piston between untreated and nitriding-treated surfaces. We obviously observed that the surface hardness of piston in the oil hydraulic axial piston pump plays an important role to have wear resistance and remain a longer life.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.142-150
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• 1997

A numerical analysis is carried out to study the effect of piston shape on the lubricaton characteristics between the cylinder and piston in hydraulic piston pump. The shapes of piston affect significantly the pressure distributions, the lateral force and leakage flowrate. Composite shaped piston is more effective than other shapes which not only reduces the possibility of hydraulic locking but improves the volumetric efficiency of the piston pump.