In recent years, the viscosity of engine oils gets lower and cylinder pressure gets higher to improve thermal efficiency of internal combustion engines. Therefore, engine bearings are increasingly used in the boundary lubrication region with the decrease in oil film thickness, and it is necessary to improve seizure resistance and fatigue resistance. On the other hand, MoDTC and ZnDTP are widely used in engine oils to reduce friction and prevent seizure in the boundary lubrication region. It is well known that their effects are different depending on conditions such as sliding materials. However, there are few studies on copper alloys used in engine bearings. So, it is required to understand the effects of copper alloys on friction in engine oils. In this study, effect of chemical composition in copper alloy on tribofilm formation are investigated by using a ball-on-disk type sliding tester in lubricating oils with ZnDTP and MoDTC. As a result, solid solution strengthening components of copper such as Sn, Ni affected tribofilm formation and running-in. In particular, Ni is highly reactive and promoted tribofilm formation. In addition, Bi contained copper alloy can obtain low friction after running-in due to the oriented MoS₂on the top surface.

High-speed deep-groove ball bearings for the eAxle of electric vehicles must adapt to higher rotational speed conditions, because eAxle motor speed increases to downsize the unit. Therefore, it is necessary to clarify the lubrication process of ball bearings at the high rotational speeds to prevent seizure and wear. The oil-film thickness between outer-ring and ball, and the oil distribution around balls in 6008 deep-groove ball bearings incorporating experimental quartz outer rings were measured under high-speed conditions, with speeds exceeding 20,000 min^-¹. These measurements were carried out by employing the three-wavelength flash-light optical interferometry method and the UV-LED light-induced fluorescence method. It was found that the oil-film thickness did not increase even when the rolling speeds increased, which is in contrast to the EHL theory under sufficient lubrication condition. Contrary to the EHL theory, these phenomena can be attributed to the oil starvation and lowering effective viscosity of oil containing bubbles resulting from aeration under high-speed conditions.