The base oil is the main constituent of a lubricating oil. Its physical properties such as viscosity, viscosity index, pour point and flash point will help formulators select the correct base oil for the application. When formulating for electric vehicles, additional criteria such as electrical breakdown voltage, electrical conductivity and copper compatibility must also be taken into account. This paper aims to explore the potential of Group V oils as potential base stocks for electric vehicles.

The first-generation hybrid and electric vehicle powertrains were developed using conventional automatic transmission fluids (ATF), but these are being superseded by a new generation of fluid technology, increasingly termed driveline “e-fluids”using specific additive packages optimised for each application. When lubricants are in direct contact with powered motor windings, or other exposed electrical components, characteristics such as preventing copper corrosion and raised fluid electrical resistivity are of major importance. This is in addition to providing wear performance as required, which is an improvement on the nature of fluid types and increasingly being selected by OEMs (original equipment manufacturers). Additionally, motor efficiency increases with greater cooling and reduced spin loss, both improved through use of new lower viscosity base oils. The types of additive components now being used have changed significantly, and a latest type are now “sulfur-free”of active additive sulfur. Additionally, the selection of suitable base oil characteristic is key to the overall e-fluid performance.

As the electrification of vehicles such as BEV and HEV has been progressed to achieve carbon neutrality, improving the fuel efficiency of engines installed in HEV and PHEV remains an important challenge, and engine oil has also played a major role in reducing CO₂emissions. Fuel economy engine oil technologies such as 0W-16 and 0W-8 are being developed, contributing to the reduction of CO₂emissions in new vehicles. On the other hand, conventional low viscosity engine oils also require engine side adaptations, such as securing oil pressure, since the viscosity at high temperatures is also lowered. To address this issue, flat viscosity oil technology is being investigated, in which the viscosity at high temperatures is the same or higher than that of conventional oil, the viscosity only at medium and low temperatures is lowered. This technology has a good potential to improve fuel economy not only for new vehicles, but also for in-use vehicles, and will be able to make a significant contribution to carbon neutrality.

If it is possible to add new benefits to lubricants that increase the performance of electric power unit, it will greatly contribute to technological innovation. It is not impossible for engineers who know the evolution of lubricants in the past, and we believe that it will help the evolution of hardware. The required performance for lubricating oil can be considered as heat capacity, thermal conductivity, insulation, antifoaming, polar pressure, wetness, foam growth inhibition, and low temperature low viscosity.

In recent years, growing concern about environmental issues has led to the expanding use of electric vehicles, which help reduce carbon dioxide emissions. Cooling the battery and motor is important for electric vehicles in order to improve efficiency and reliability. Oil cooling systems using lubricants can cool the battery and motor directly and are expected to provide high cooling performance. This report describes the recent trends in evaluation methods for the cooling performance of lubricants and the influence of lubricants properties on cooling performance.

This article describes the technologies in grease lubrication for rolling bearings corresponding to electrification of vehicles (HEV/EV). In HEV/EV, grease lubricates bearings in powertrain, as well as hub unit bearings. Powertrain bearings are operated High-temperature, High-speed and voltage conditions, greases are required long life, energy efficiency, noise reduction and anti-electrical pitting. Hub unit bearings are required energy efficiency and long flaking life in water containing conditions, greases are also required low torque and water resistance.

This paper focuses on the ZnDTP-derived tribofilm formation process in the early stage of sliding, mainly on the formation of a sulfide layer and a polyphosphate layer, in studying the formation process on a steel surface with roughness equivalent to that of an actual machine. Unlike the results of ZnDTP single-formulated oil using a regular mirror-finished steel test piece, the sulfur-based tribofilm was preferentially formed at the initial sliding stage on the steel test piece with relatively large roughness equivalent to the actual machine level. It was also found that it took longer to form a phosphorus-based tribofilm that exhibited wear resistance. Thus, the behavior of tribofilm formed on the test pieces with roughness equivalent to the actual machine level differed significantly from that of the mirror-finished test pieces. In particular, it was found that the sulfurization reaction in the early stage of sliding is important through the corrosive wear of the top of roughness, and played an important role in controlling the subsequent tribological behavior.

Improvement study of the prediction methodology which represents the friction properties of rubber blocks on ice has been conducted. The 2-D coupled block model with sipes and the mechanical analysis methodology have been applied towards the intuitive understanding of tribology mechanisms and improvement of grip performances of winter tires on icy road surface. The effects of the ploughing of ice surface by sipe edges and the decrease of actual contact area caused by the block deflection are taken into account in order to evaluate the effects of the sipe density and the block stiffness of tread pattern. It had been derived that the contribution of ploughing resistance of sipe edges to friction coefficient on ice could be negligible and that the main factors of friction improvements by sipe edges were assumed to be "scraping effects" which improved adhesive friction and adhesion ratio in the contact patch by scraping away softened ice layer and water film on the ice surface. The characteristics of predicted friction coefficients regarding the sipe density had been partly validated with experimental results. Predicted friction coefficients were described as the diagram of the sipe density and the block stiffness. The diagram expressed that the compatibility of these two prime factors would be effective in the increase of friction coefficient on ice. This result suggests the potential of sipe structure improvements on the tread pattern of winter tires.