Jae-Youn Jung

Measurment of Fluid Film Thickness on The Valve Plate in Oil Hydraulic Axial Piston Pumps (Part II : Spherical Design Effects)

Tribologtcal 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

Measurement of fluid film thickness on the valve plate in oil hydraulic axial piston pumps (I)-bearing pad effects-

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.

Relation between Pressure Variations and Noise in Axial Type Oil Piston Pumps

Pressure variation is one of the major sources on noise emission in the axial type oil piston pumps. Therefore, it is necessary that the pressure variation characteristics of the oil hydraulic piston pumps be clarified to reduce the pump noise. Pressure variations in a cylinder at the discharge region and the pump noise were simultaneously measured with discharge pressures and rotational speeds during the pump working. To investigate the effects of the pre-compres-sion and the V-notch in the valve plate, we used the three types of valve plates. In this research, it is clear that the pressure variation characteristics of axial type oil piston pumps is deeply related to the pre-compression and to the V-notch design in valve plate. Therefore, we could reduce the pump noise by using the appropriate pre-compression angle and the notch design that are between the suction port and the discharge port in valve plate.

The Lubrication Characteristics of the Vane Tip Under Pressure Boundary Condition of Oil Hydraulic Vane Pump

The Lubrication Mode of line contacts between the vane and the camring in an oil hydraulic vane pump has been investigated. First, the variations of the radial force of a vane were calculated from previous measurements of dynamic internal pressure in four chambers surrounding a vane. Next, the lubrication modes were distinguished with Hooke’s chart, which is an improvement over Johnson’s chart. Finally, the influence of the boundary conditions in the lubrication region on the fluid film lubrication was examined by calculating the film pressure distributions. The results showed that the lubrication mode of the vane tip exists in the rigidvariable-viscosity region, and that discharge pressure higher than 7 MPa greatly affects the oil film pressure in the small and the large arc section because of the Piezo-viscous effect.

Driving mechanism of tapered pistons in bent-axis design axial piston pumps

In order to assure the quality of the bent axis design axial piston pumps driven by tapered pistons, it is necessary to know the characteristics of force applied to tapered pistons and the mechanism for driving the tapered pistons. Since they are able to perform both reciprocating and spinning motions in cylinder block, it is difficult to understand the driving mechanismand-tomeasure the forces applied to tapered pistons experimentally. In the presem study, the theoretical mechanism for driving the tapered pistons is studied by use of the geometric method. The driving area of tile tapered pistons is measured by measuring the strain of a cylinder forced against a tapered piston using an electric strain gauge and a slip ring. The forces applied to tapered pistons is also investigated with the change of discharge wessure and the rotational speed As a results of this investigation, it is concluded that the cylinder block is driven by one tapered piston in a limited area and flue driving area is changed due to space angle of the tapered pistons and the swivel angle of the cylinder block. It is also observed that the force applied to tapered pistons increases as the discharge pressure and the rotational speed increase.

The lubrication characteristics of the vane tip under inlet pressure boundary conditions for an oil hydraulic vane pump

The lubrication modes of line contact between the vane and the camring in an oil hydraulic vane pump have been investigated. First, variations of the radial acting force of a vane were calculated from previously measured results of the dynamic internal pressure in four chambers surrounding a vane. Next, distinctions of the lubrication modes were made using Hooke’s chart, which represents an improvement over Johnson’s chart. Finally, the influence of boundary conditions in the lubrication region on fluid film lubrication was examined by calculating film pressure distributions. The results show that the lubrication modes of the vane tip are a rigidvariable viscosity region. This region discharges pressure higher than 7 MPa, and exerts a great influence on oil film pressure in the large arc section due to the Piezo-viscous effect.

Effect of residual stress on the bending strength of ground Al2O3/TiCN ceramics

Abstract The residual stresses on the surface of the differently ground and polished Al2O3/TiCN ceramics are measured using X-ray diffraction method. The effect of the residual stress on the bending strength is investigated. The residual stresses introduced by surface grinder are tensile, while the residual stresses introduced by universal tooling grinder are compressive. Polishing can smooth the residual stress. Residual stresses induced by grinding process have a significant effect on bending strength.

A Study on Lubrication Characteristics between Piston Ring and Cylinder Bore of Bent-Axis Type Piston Pump

The bent-axis type piston pump which is driven by the piston rod works on the way that the piston rod drives the cylinder block, so the taper angle of the piston rod and the swivel angle between the cylinder block and the shaft are very important design factors. If the above factors can not satisfy the conditions for optimum design, the friction loss between the cylinder bore and the piston increases, and the pump could fail to work under conditions of severe friction and wear. Since the piston reciprocates in the cylinder bore with high velocity, and at the same time it rotates on its own axis and revolves on the center of the cylinder block, there is a decrease of the volume efficiency generated on account of the leakage between the cylinder bore and the piston. Therefore, to prevent this case, the piston ring is designed at the end of the piston, and the friction characteristics between the piston ring and the cylinder bore are in need of research due to its great influence on the performance of piston pump. Thus, in this paper, the elastohydrodynamic lubrication(EHL) analysis of the film thickness, the pressure distribution and the friction force, have been studied between the piston ring and the cylinder bore in the bent-axis type piston pump. The analyzed results show that friction force is influenced by rotating speed and discharge pressure.

Application of superresolution technology in non-contact measurement on edge detection of precise parts

The precision of traditional methods of edge detection of precise Parts with linear CCD only reach &mgr;m because of the size of CCD cells. A sup-pixel edge detection method of CCD based on least square method and derivative operator method is proposed to improve the measurement precision. The Image Gradient obtained using derivative operator method. Point A with the max Gradient is then regarded as the point of the edge, and then the pixels nearby edge are interpolated linearly. For example, a high-speed data acquisition system is designed using high accuracy linear CCD TCD1501D and high speed A/D converter TLC5510. Experimental results show that the resolution &mgr; of the system design is 0.02pixel and the measurement precision is improved by one order of magnitude over traditional methods of edge detection.

The Influence of the vane on the lubrication characteristics between the vane and the rolling piston of a rotary compressor

The rolling piston type rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. The present analysis is part of a research program directed toward maximizing the advantages of refrigerant compressors. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressors. Therefore, theoretical investigation of the lubrication characteristics of a rotary compressor being used for refrigeration and air-conditioning systems was investigated. The Newton-Raphson method was used for a partial elastohydrodynamic lubrication analysis between the vane and the rolling piston of a rotary compressor. The results demonstrated that the vane thickness and the center line position of the vane significantly influenced the friction force and the energy loss between the vane and the rolling piston.