Main tribological problems in high speed gears are the decrease in power loss and the prevention of tooth surface damages. The tooth mesh friction loss and spin lose (mesh pumping loss, windage loss, lubricant acceleration loss) based on the author’s method for power loss reduction are explained. And how to prevent tooth surface damages depends on lubrication condition under high speed operation is explained.

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The electric transaxle (e-Axle) is a driving unit for electric vehicles that integrates the motor and reduction gear. Oil-cooling type e-Axles, in which the motor is directly cooled by lubricating oil, are rapidly expanding for the thermal management of the motor and the overall efficiency improvement of the unit. In this study, the effects of differences in physical properties, such as kinematic viscosity and traction coefficient of lubricants, on the efficiency of the e-Axle were investigated using an actual e-Axle unit.

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D value is used as an evaluation value for gear design to prevent surface failures such as wear and surface-initiated rolling contact fatigue. The value is defined as the ratio of the sum of maximum height R_z on mating gear tooth surfaces to minimum oil film thickness hmin formed between the mating tooth surfaces. The minimum oil film thickness can be obtained by numerical analysis based on elastohydrodynamic lubrication (EHL) theory or by using regression formulae derived from numerical calculation results under various conditions. In the EHL theory, it is assumed that shear behavior of the oil films is subjected to Newton's law of viscosity. However, the thin oil films less than micrometer order are exposed to remarkable shear rate. Therefore, shear heating of the oil films and a decrease in oil film viscosity depending on the shear rate, that is, shear-thinning occur. The shear-thinning affects not only worm gears, hypoid gears and spiral gears with significant sliding between mating tooth surfaces, but also spur gears where the speed between mating tooth surfaces varies. In the present review paper, main rheological models applied to thermal EHL analysis taking account of the shear-thinning properties of the oil films and their numerical analysis methods are outlined. In addition, calculation formulae of EHL oil film thickness for lubricating oils indicating the shear-thinning properties and some analytical cases applying the numerical analysis or the calculation formula of oil the film thickness to some types of gears are introduced.

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The oil seals used in high-speed gear transmissions are required to maintain low loss torque and high sealing performance, especially with the increasing prevalence of electric vehicles (EVs). The EV market is expanding, particularly in China, with the integrated “e-Axle” system that combines motors, inverters, and reduction gears. This system enables miniaturization and weight reduction, improving power consumption rates, but the increase in rotational speed affects the sealing and lubrication performance of oil seals. Oil seals are composed of synthetic rubber and a metal ring, with the lip section making contact with the shaft surface to create a seal. A metal spring is attached to the lip’s edge, providing elastic and pressing forces to ensure sealing. However, high-speed rotation can lead to insufficient lubrication, increasing friction and heat generation. A significant issue is the poor lubrication of the lip’s sliding surface, which reduces oil film thickness, leading to rubber degradation and wear, ultimately compromising sealing performance. Factors contributing to poor lubrication include the trend toward low-viscosity oils and insufficient oil supply due to the e-Axle’s design. Increased oil temperature lowers viscosity, thinning the oil film and raising the friction coefficient. Additionally, wear debris and sludge from oil degradation can further deteriorate sealing performance. Addressing these challenges requires improving spring load ratios, developing new rubber materials, and enhancing lubrication conditions through design modifications and low-friction coatings. Understanding and resolving these technical issues is crucial for advancing EV technology.

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In order to miniaturize the drive unit which consists of a motor and a reduction gear, it is effective to combine a small and large speed reduction gear with a high speed motor. This paper explains the planetary gear mechanism which can be used as a large speed reduction gear and explains the test results. It also introduces the method for improving the efficiency of high speed gear including this mechanism.

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Electric vehicles are one of the measures to combat global warming, and their widespread use is expected. Drive motors must be small and lightweight, and attempts are being made to increase the motor's speed. However, to provide sufficient driving force from a high-speed motor, it is necessary to combine it with a transmission element, and gears and traction drives are candidates for this. Gears can cause problems with vibration and noise when rotating at high speeds. On the other hand, traction drives are characterized by little meshing vibration, resulting in low vibration and low noise. This paper explains the tribological issues of high-speed traction drives and their various countermeasures.

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Inthisstudy,wecharacterizedtheadsorptionofafewphosphorus-typeanti-wearagentsonanironoxidesurfaceinanester-based stock (diethyl sebacate, DES). In addition, the adsorption properties were compared with those in a non-polar base stock. The phosphorus-type anti-wear agents employed in this study were tricresylphosphate (TCP), tributyl phosphate (TBP), and diphenyl phosphite (DPPhi). Molecular simulation revealed that the absolute adsorption energy increased as TBP, TCP ＜ DES ＜ DPPhi. The combination of experimental results based on frequency modulation atomic force microscopy and quartz crystal microbalance with dissipation monitoring technique suggested that competitive adsorption of DES and the anti-wear agents occurred on the iron oxide surface. DES molecules formed a layered structure on the iron oxide, and the upper layers (except the first layer adsorbed directly on the iron oxide surface) were suggested to be replaced by the anti-wear agents. The competitive adsorption also affected the coefficient of friction.

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一般社団法人日本トライボロジー学会 第69期定時社員総会 議事録議事概要
一般社団法人日本トライボロジー学会 維持会員名簿
本会記事，次号予告，特集号企画主旨，コーヒーブレイク

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