In swash plate type axial piston pumps, slipper/swash plate sliding surfaces is subject to high fluctuating load. Therefore, the slippers are required to provide stable operation and reduce losses due to sliding. The behavior of the slipper fluctuates in a complex manner due to changes in the hydraulic pressure in the cylinder and inertial forces caused by the reciprocating motion of the piston. However, the time variation of the oil film thickness distribution of the slipper has not been measured. Furthermore, there are no measurements of the movement of the spherical joint connecting the slipper and piston, which affects the slipper behavior. In this study, the visualized sliding test rig with a sapphire glass swash plate was developed. The oil film thickness distribution of the slipper and the rotation of the slipper and the piston were measured continuously during one rotation of the pump.

This paper formulated a modified Reynolds equation that can calculate the lubrication characteristics of bearings with high-viscosity surface layers on both bearing surfaces expressed by arbitrary viscosity function. From comparison with the measured effective viscosity of engine oil with metallic detergent, the saturated viscosity function was determined, where the effective viscosity saturates to 500 times the bulk viscosity when the gap decreases to the saturated viscosity film thickness 2z_c of 100 nm. Then, the lubrication characteristics of micro-tapered pad bearing of 250 µm in length were analyzed. The load capacity was ~70 times the bulk viscosity case when the trailing gap h_T decreased to 2z_c. Next, the effective viscosity of engine oil with only a viscosity modifier additive can be obtained by using another viscosity function in which the increasing rate in viscosity is maximum on the bearing surface and 2z_c is ~60 nm. Using this viscosity function, the bearing characteristics of tapered pad bearing were analyzed. The load capacity was ~13 times the bulk viscosity case when h_T was z_c. For both the viscosity functions, the load capacity was almost the same if the film thickness of the one-side model is twice as large as that of the two-side model.

High-pressure viscosity of lubricant is important for elucidating the lubrication state of metalworking, bearing and gear in the elastohydrodynamic lubrication (EHL) region. The van der Waals type viscosity equation was derived in a previous report and it was applied to the estimation of high-pressure viscosity. Furthermore, I accumulated the data of various lubricants for three material-specific constants included in this equation, namely absolute zero viscosity µ_t=0 [mPa･s], viscosity coefficient S [GPa/K²], and pressure constant P_V [GPa]. In this study, a multiple regression equation was derived by conducting the multiple regression analysis on the three material-specific constants as target variables, while the physical properties and the chemical structure of the lubricant were explanatory variables. As a result, it was revealed that the three material-specific constants (η_{t=0 mr-eq}, S _mr-eq, P_{V mr-eq}) in the van der Waals type viscosity equation and the high-pressure viscosity η_mr-eq [mPa･s] could be estimated from this multiple regression equation for unknown lubricants only by analyzing their physical properties and chemical structures, without experimentally measuring viscosity using high-pressure viscosity test apparatus.