Toshiharu Kazama

Application of a Mixed Lubrication Model for Hydrostatic Thrust Bearings of Hydraulic Equipment

On mixed and fluid film lubrication the characteristics of hydrostatic bearings for hydraulic equipment are studied numerically. By applying a mixed lubrication model derived in a previous paper to the bearings, we clarify the effects of the surface roughness, eccentric or moment loads, supply pressure and speed of rotation on the friction, flow rate, and power losses. Introducing the concept of a ratio of hydrostatic balance, we show that the minimum power loss is given as the ratio becomes close to unity

Experiment on Mixed Lubrication of Hydrostatic Thrust Bearings for Hydraulic Equipment

Mixed lubrication characteristics of hydrostatic thrust bearings are examined experimentally. The effects of the surface roughness, supply pressure, loads, speed of rotation and size of restrictors on the frictional force, leakage-flow rate and power losses are clarified. Introducing the concept of mean pressure based on load-carrying capacity due to asperities, and the ratios of hydrostatic balance and leakage-flow rate, the experimental data can be normalized. Also good agreement is found between theoretical results based on a mixed lubrication model presented in a previous paper and the experiment.

Optimum design of bearing and seal parts for hydraulic equipment

Abstract Reasonable design criteria for the optimum size of bearing and seal parts of hydraulic equipment are presented. The minimum power loss, minimum size (or maximum load-carrying capacity) and maximum moment stiffness, as well as maximum stiffness, are adopted as the optimum conditions. In this study, we treat circular hydrostatic thrust bearings as the bearing and seal parts. The basic equations considering the effects of cyclic changes in supply pressure and eccentric loads, and elastic deformation of the parts are derived. The design parameters are contracted to three direct parameters, i.e. the radius of the bearing and seal parts, the ratio of a pocket radius, and the aspect ratio of a restrictor. We derive analytically the optimum criteria of hydrostatic thrust bearings with a capillary restrictor under the condition of concentric loads in a steady state. Also we clarify the effects of unsteady state operating conditions, physical properties of fluids, elastic deformation and eccentric loads and evaluate the criteria by means of power losses, stiffness and size.

On the effects of the temperature profile approximation in thermal Newtonian solutions of elastohydrodynamic lubrication line contacts

Abstract The assumptions of a quadratic temperature profile and mean viscosity across the film, which are frequently used in the analysis of thermal elastohydrodynamic lubrication (EHL), are examined and discussed. Two different approaches for solving the thermal EHL problem are compared for line contact conditions, namely (a) a one-dimensional model based upon both the assumption of a quadratic temperature profile and the adoption of the mean physical properties across the film and (b) a two-dimensional model which includes changes in temperature and physical properties of a lubricant across the film and which takes into account the conditions of reverse flow and heat convection across the film occurring at the inlet region. A multi-grid algorithm is implemented to solve these two conditions. The temperature profile and the general solutions in the conjunction obtained in both approaches are compared. For the one-dimensional model, results reveal that temperature peaks just prior to the inlet of the conjunction. This feature is not apparent in the two-dimensional model and results in lower values in film thickness and larger frictional coefficients than in the two-dimensional model. In the high-pressure region, both equations yield almost the same mean temperature.

Optimum design of hydrostatic spherical bearings in fluid film lubrication

The optimum design of hydrostatic spherical bearings in fluid film lubrication is examined theoretically. The analytical solutions are derived for both fitted and clearance types of bearings with capillary and orifice restrictors. The optimal size based on the minimum power loss and the maximum stiffness is presented, and the difference between two types of hearings is discussed.

Effects of approximations regarding stress and temperature profiles on the solution in thermal elastohydrodynamically lubricated line contacts

Abstract The assumptions of both a Couette flow dominance and a quadratic temperature profile across the film are commonly used in the analysis of thermal non-Newtonian elastohydrodynamic lubrication. In such calculations, the conduction across the film and the energy dissipation are assumed to be the main phenomena in the prediction of temperature rise. Consequently the gradients of the physical properties across the film as well as the reverse flow and the heat convection in all directions are assumed to have no or little impact on the general characteristics of the temperature profiles and therefore can be neglected. The objective of this paper is to assess the quality of these approximations. A comparison between both the simplified and the complete non-Newtonian thermal approach is made for the line contact problem. The complete solution is based upon the resolution of a two-dimensional energy equation, which is fully coupled with the non-Newtonian Reynolds equation. The analysis reveals some local discrepancies between both the simplified and the complete solutions. These differences are clearly visible at the inlet of the contact where a bump in the temperature profiles disappears in the simplified approach. The results also show a significant difference in the levels of temperature predicted within the high-pressure region between the simplified and complete approach. In regard to the friction coefficient, the simplified calculation forecasts a lower coefficient than that obtained with the complete formulation.

A comparative Newtonian and thermal EHL analysis using physical lubricant properties

The influence of changes in specific heat and thermal conductivity of lubricants on the thermal EHL solutions of the line contact is examined in detail. Five Newtonian lubricants were considered; representative of mineral oils, polyalphaolefin and polyglycol. To account for the variations of temperature and physical properties across the film, the complete two dimensional energy equation was applied. The overall numerical strategy was integrated into a multigrid algorithm to accelerate the convergence of the solutions. The results reveal that temperature is significantly affected by the changes in thermal conductivity in the high pressure region of the contact. By contrast, the variations in specific heat with temperature and pressure are small and have seldom impact on the lubricated conditions of the contact and thus can be neglected.

Comparison of Cavitation Erosion Test Results between Vibratory and Cavitating Jet Methods

Abstract The relationship between the vibratory and cavitating jet test methods was determined experimentally. Six metallic specimens were made of aluminum alloy, superduralumin, high-strength brass, stainless steel, carbon steel and chromium-molybdenum steel. The specimen surface was eroded as fine and uniform pattern with the vibratory method, but was rough and ring-shaped with the jet method. Striation and plastic deformation were clearly observed in the specimens eroded by jet cavitation. The volume loss was the largest for aluminum alloy, followed by superduralumin, high- strength brass and steel. Both test methods yielded the same descending order for the volume loss. The ratio of volume loss by the vibratory method compared to the cavitating jet method became constant as the time proceeded.

Mixed and Fluid Film Lubrication Characteristics of Worn Journal Bearings

The mixed and fluid film lubrication characteristics of plain journal bearings with shape changed by wear are numerically examined. A mixed lubrication model that employs both of the asperity-contact mechanism proposed by Greenwood and Williamson and the average flow model proposed by Patir and Cheng includes the effects of adsorbed film and elastic deformation is applied. Considering roughness interaction, the effects of the dent depth and operating conditions on the loci of the journal center, the asperity-contact and hydrodynamic fluid pressures, friction, and leakage are discussed. The following conclusions are drawn. In the mixed lubrication regime, the dent of the bearing noticeably influences the contact and fluid pressures. For smaller dents, the contact pressure and frictional coefficient reduce. In mixed and fluid film lubrication regimes, the pressure and coefficient increase for larger dents. Furthermore, as the dent increases and the Sommerfeld number decreases, the flow rate continuously increases.

Experimental Study of Jet Cavitation Erosion Applicable to Oil and Water-Hydraulic Equipment

Hydraulic components, such as valves, pumps, and actuators, include many narrow passages in the form of nozzles, orifices, and gaps. Cavitation can occur when jets flow from high to low pressure through such sections, making it unavoidable for jets containing cavitation bubbles to impinge on the inner walls of hydraulic components. This report summarizes a series of experiments involving erosion tests, flow visualization, and pressure measurements with hydraulic oils and municipal water. For the erosion tests, the ASTM G134, Standard Test Method for Erosion of Solid Materials by a Cavitating Liquid Jet, method of jet cavitation erosion is used to evaluate the eroded mass loss and the specimen’s surface damage. The experimental apparatus consists of a stainless steel cylindrical chamber, a high-pressure hydraulic pump, and auxiliary hydraulic components. The main test parameters are the standoff distance, cavitation number, nozzle outlet geometry, specimen surface shape, and liquid type. The specimen mass is measured, and the eroded surfaces are recorded at specific intervals. For the visualization tests, an acrylic chamber and a digital video camera are used. Video frames are extracted as pictures and are processed by superposition. For the pressure measurements, pressure-sensitive films are used to estimate the pressure distributions on the impinged surfaces. The films are bonded on the specimen surface beforehand, exposed to the cavitating jets for a short period, and then analyzed using an image analysis system. Overall, by comparing the mass loss, surface damage, visualization pictures, and pressure mapping, the effects of the experimental parameters on the erosion characteristics are examined. Moreover, design approaches that are applicable to both oil and water-hydraulic components are proposed in order to reduce erosion by cavitating jets.