A. Yamaguchi

Bio: A. Yamaguchi is an academic researcher from Yokohama National University. The author has contributed to research in topics: Bearing (mechanical) & Hydraulic motor. The author has an hindex of 2, co-authored 2 publications receiving 85 citations.

Effect of bias voltage on microstructure and properties of Ti-doped graphite-like carbon films synthesized by magnetron sputtering

Abstract: Ti-doped graphite-like carbon (GLC) films with different microstructures and compositions were fabricated using magnetron sputtering technique. The influence of bias voltages on microstructure, hardness, internal stress, adhesion strength and tribological properties of the as-deposited GLC films were systemically investigated. The results showed that with increasing bias voltage, the graphite-like structure component (sp2 bond) in the GLC films increased, and the films gradually became much smoother and denser. The nanohardness and compressive internal stress increased significantly with the increase of bias voltage up to ?300 V and were constant after ?400 V. GLC films deposited with bias voltages in the range of -300–-400 V exhibited optimum adhesion strength with the substrates. Both the friction coefficients and the wear rates of GLC films in ambient air and water decreased with increasing voltages in the lower bias range (0–-300 V), however, they were constant for higher bias values (beyond ?300 V). In addition, the wear rate of GLC films under water-lubricated condition was significantly higher for voltages below ?300 V but lower at high voltage than that under dry friction condition. The excellent tribological performance of Ti-doped GLC films prepared at higher bias voltages of ?300–-400 V are attributed to their high hardness, tribo-induced lubricating top-layers and planar (2D) graphite-like structure.

Modelling a Variable Displacement Axial Piston Pump in a Multibody Simulation Environment

Abstract: Analysis of a variable displacement axial piston pump, as in other complex fluid power and mechanical systems, requires appropriate insight into three multidisciplinary domains, i.e., hydraulics, mechanics and tribology. In recent years, at FPRL, modelling of axial piston pumps has evolved in AMESim (one-dimensional code) where a threedimensional mechanical approach has required generation of proprietary libraries leading to the evaluation of internal forces/reactions in all pump subsystems. Tribologic aspects in axial piston pumps modelling are also being investigated but AMESim, in this respect, does not appear as the appropriate computational environment. Consequently, a new approach has been initiated grounded on MSC.ADAMS. In this perspective, the paper details how the model has been developed through proprietary macros that automatically originate all pump subsystems parametrically and further apply required constraints and forces (springs, contacts, and pressure forces). The ADAMS environment has also been selected due to co-simulation capabilities with AMESim. Accordingly, the paper elucidates how the entire modelling has been construed where hydraulics is managed in AMESim while ADAMS takes care of mechanics. A comparison between simulated and experimental steady-state characteristics of the axial pump is also presented. As such this paper indicates an innovative methodology for the analysis of complex fluid power systems in the hope that, eventually, tribology will also fit into the scene

Seals Based on Magnetic Fluids for High Precision Spindles of Machine Tools

Abstract: The research work reported in this paper is focused on the use of magnetic fluids as active elements in seals for improving sealing capacity and minimizing friction torque, with application to the spindles of high precision machine tools. The prototype design was optimized following numerical computation of the magnetic field in the rings of the seal. Two magnetic fluids were analyzed for their use in the seals: a ferrofluid and magnetorheological fluid. The sealing capacity of the MRF based seals was higher than 45 kPa per ring, but the friction of the seal in the bearing was 8 N·m, too large for the use in precision spindles of machine tools because of the energy consumption and heat generation. The ferrofluid seal achieved sealing capacity around 9 kPa per ring, good enough to be used in the spindles of machine tools, with a friction 0.25 N·m and low energy consumption. The feasibility of using ferrofluids for developing high performance seals for high precision spindles and the validity of the simulation models has been demonstrated experimentally.

Effect of surface non-flatness on the lubrication characteristics in the valve part of a swash-plate type axial piston pump

Abstract: The objective of this application study was to investigate the effect of surface non-flatness on the lubrication characteristic of the bearing/sealing part between cylinder barrel and valve plate in a hydrostatic axial piston pump. A developed numerical algorithm facilitated the simultaneous calculation of time-varying cylinder pressure, rotating body motion, and fluid film pressure to observe fluid film geometry and power loss. It was shown that an ideally flat surface might not form full fluid lubrication film properly, and that small-scale machining error, surface waviness, may increase the film thickness to some degree. The shape model of surface waviness considered waviness unit shape as well as its surface lay. However the results demonstrated that surface non-flatness of such small scale did not form the desirable fluid film geometry which minimized the power loss yet. Providing some surface design tips, two particular curved surfaces whose pressure-generating mechanisms differ were selected and analyzed in variation with their shapes and operating conditions. This study asserted that a circumferentially wavy surface would make better performance of motion stability and power efficiency than a radially wedged land surface, and finally that the non-flatness design strategy should be applied with re-considering the clamping ability.