Electrification of automobiles is one promising method for the reduction of CO₂ emission. For further contribution to carbon neutrality, electrical consumption of electrified vehicles should be minimized to extend their range. Electrical consumption can be saved by reducing torque losses in transaxles such as churning loss and friction loss. Since the magnitude of these losses is influenced by properties of lubricants used in transaxles, it is important to properly design lubricant formulation to achieve high transmission efficiency. In this paper, recent technological trends in lubricants for electrified vehicles are explained focusing on viscosity reduction, traction reduction by high performance base oil, and friction reduction by a friction modifier.

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As global warming intensifies, nations worldwide are implementing various measures to mitigate carbon dioxide emissions. Within the automotive sector, low-friction mechanical seals may serve as an important means of enhancing both energy efficiency and fuel economy. In this paper, we present case studies and discuss the technical features of surface-textured mechanical seals designed to achieve low friction. Examples include mechanical seals used in automotive water pumps, shaft water-cooled motors, low-boiling-point refrigerant-cooled motors, and reduction gearboxes. Surface-textured mechanical seals demonstrate significantly lower friction compared with conventional seals across various automotive drive systems. Some drive systems incorporating these seals have already been commercialized, contributing to improved energy consumption and fuel economy.

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This paper reviews low-friction technologies in hub unit bearings. A hub unit bearing is a key component in vehicles and contributes to friction losses that affect fuel efficiency, particularly in battery electric vehicles (BEVs). Various low-friction technologies have been developed for both the bearing and seal components, while maintaining bearing reliability. For the bearing component, improvements in grease reduce friction primarily through lower viscosity and channeling. For the seal component, friction reduction methods include not only grease optimization but also structural enhancements such as modifying seal lip geometry and incorporating labyrinth and gutter designs. These technologies play an important role in supporting the transition to carbon neutrality.

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This paper reviews the recent technological evolution of constant velocity joints (CVJs) in response to the global shift toward carbon neutrality and electrification of vehicles. It highlights the structural principles and historical development of CVJs, analyzes the performance requirements driven by EV trends, and introduces the latest innovations from leading manufacturers. The study also discusses the environmental contributions of high-efficiency CVJs and outlines future prospects for the industry.

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Wet multi-plate clutches are used for various functions in the drivetrain, such as torque engagement/disengagement and gear shifting. Drag torque when the clutches are disengaged, is the most influential factor affecting fuel and energy consumption. This paper explains the main mechanisms of the drag torque phenomenon using experiments and modeling.

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One of the characteristics of disc brakes that contributes to fuel efficiency and electricity consumption is drag torque. In this report, the effects of wind flow on drag torque are quantified by CFD analysis for the purpose of reducing drag torque in urban driving, leading to the elucidation of drag torque phenomena and prediction techniques.

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Lubricants are important factors in reducing energy loss and extending the life of components. Various lubricants are used depending on the application, and solid lubricants have been used as additives to complement the functions. Molybdenum disulfide is a solid lubricant with a distinctive layered structure and has been widely used. In recent years, many cases have been reported in which nanoparticles are used as lubricant additives. This paper reports on the characteristics of nanosized molybdenum disulfide, which has the properties of both nanoparticles and molybdenum disulfide, and its application as an additive to oils, greases, and coatings.

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Recent friction force microscopy (FFM) observations of sliding friction on a cleaved NaCl surface submerged in ethanol have revealed characteristic stick-slip patterns at atomic resolution. To elucidate the relationship between the motion of ethanol molecules and macroscopic friction/lubrication, we employ a computational FFM model that couples interfacial atomic motion with the dynamics of the FFM cantilever. This model enables us to study the fundamental mechanisms of friction and lubrication in a liquid environment across a wide range of scales. Our results identify a layered ethanol tribofilm on the NaCl surface; while a slip plane between these layers leads to stick-slip motion, an ethanol-rich environment transitions the system toward fluid lubrication.

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[in Japanese]

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