It is our great honor to publish this special issue in Tribology Online. This special issue includes the papers accepted after a rigorous peer review process.

The Joint International Conference on Micromechatronics for Information and Precision Equipment (MIPE2022) was held at Nagoya University (Nagoya, Japan) from August 28 to 31, 2022, with the aim of promoting innovation in mechatronics technology including tribology and the advancement of mechatronic systems through integration with information technology. This conference was held in a hybrid way of on-site and online, and the number of participants was 248 from Japan and 66 from overseas, totaling 314 participants.

This conference was co-hosted by the Information, Intelligence and Precision Equipment (IIP) Division of the Japan Society of Mechanical Engineers (JSME) and the Information Storage and Processing Systems (ISPS) Division of the American Society of Mechanical Engineers (ASME). For intensive international discussions, the two divisions jointly hold this conference every three years since 2003, alternating between Japan and the U.S. This year's conference is the seventh. Japanese Society of Tribologists was a co-sponsor of this conference.

Finally, we would like to thank all those involved in the editorial work of this issues. We would also like to thank the contributors to this issue.

The electrical failure of bearings has become a critical issue that restricts the lifetime of all-electric motor-based power systems in electric vehicles (EVs). This study aims to explain the electrically induced frictional behavior of lubricants. The effect of external electric current applied between the friction pairs on tribological properties was examined using a disk-on-ring friction tester. The surface potential analysis demonstrated that applying a positive electric current by connecting the friction surface to the cathode decreased surface activity, whereas a negative electric current increased it. The direction of the electric current influenced the friction coefficient, with a rapid increase observed when a positive current was applied. The lower ring’s friction surface exhibited reduced lubricant adsorption. Consequently, fewer lubricant molecules were transferred to the friction interface, producing a high friction coefficient. Moreover, the wear surface experienced pitting after applying an external electric current, suggesting that pitting contributed to accelerated wear. These findings provide insights into the influence of electric current on the tribological properties of lubricants and have implications for the design of tribological systems in EVs.

Reducing the viscosity of the lubricant is an effective way to improve the energy efficiency of automobiles. However, designing a lubricant with the desired properties requires elucidating the relationship between viscosity and molecular structure. In this study, we measured the temperature dependence of the dielectric relaxation of model lubricants with different molecular structures. Dielectric relaxation measurements were used to evaluate the influence of ambient viscosity on the motility of single molecules. In addition, we measured the temperature dependence of the lubricant viscosity using a rotational viscometer. By comparing the flow viscosity and dielectric relaxation measurement results, we showed that the activation volume and energy of the luburicant, which determine viscosity, can be resolved. As a result, we succeeded in quantitatively evaluating the contribution of molecular structure to changes in the activation energy, and elucidated the effect of the density of polar groups per molecule on changes in the activation volume.

The surface interaction stress distributions (pressure and shear stress) and forces (normal and shear force) between a sphere and a half-space with a one-dimensional periodic material distribution are calculated numerically. The interaction is based on the Lennard-Jones (LJ) potential and the periodic material distribution is expressed as a Fourier series. With a minimum surface distance of 0.2 nm, size effects of the spherical radius on the interaction stresses and forces are quantitively calculated and discussed. The stress distributions show strong correlations with spherical radius and material distribution of the half-space. The interaction forces were calculated by integrating the interaction stresses acting on the spherical surface. They were calculated at every position in the half-space with the one-dimensional periodic material distribution. We reveal the dependence of the spherical radius on the interaction forces. Under the conditions of this study, the normal force increases linearly, whereas the shear force exhibits a local minimum and increases with spherical radius.