Editorial: Special Issue “Automotive Tribology”

The automotive industry faces new challenges and fast technological changes. The continuous increase in the severity of government regulations outlines new targets about fuel consumption, pollution, and mechanical efficiency; hence, hybrid vehicles (HEVs) and plug-in hybrid vehicles (PHEVs) are likely to become mainstream in the future. Nevertheless, according to recent report the annual sales of non-electrified vehicles, HEVs/PHEVs, and battery electric vehicle/fuel cell vehicles will be 4.5 million, 4.5 million (“only” 1.4 million units in 2016), and 1.0 million units, respectively, by 2030 [1]. In other words, although the automobile market is shifting to electrification, in 2030, vehicles equipped with internal combustion engines will still account for approximately 90% of the annual sales volume of passenger vehicles, and further fuel saving of internal combustion engines will be required. On the other side, despite the incessant increase in investments related to the electric vehicles sector, most of the scientific research has been focused on the energy efficiency and performance of batteries and electric powertrains, whereas topics related to new and unconventional architectures for brakes, bearings, transmissions, tailored lubrication systems in hybrid or full electric vehicles have been researched so far from tribological point of view in few papers [2–7]. This Special Issue of Lubricants observes the latest developments concerning frictional and wear behavior of complex mechanical systems, by pointing out the remarkable effort from academic and industrial researchers linked to tribological innovations in vehicular field. According to the substantial changes in operating conditions of near future automotive technology, this issue would provide useful support to engineers responsible for developing the most efficient and dependable systems with focus on reduced viscosity lubricant, valvetrain friction and lubrication, vegetable oil–diesel fuel mixtures, friction losses in gasoline and diesel engines of passenger car. In Reference [8], the effect of reducing CO2 emissions and cost analysis of ultra-low viscosity (ULV) engine oils for passenger vehicles are considered. More specifically, the authors analyzed the effect of reducing life cycle CO2 emissions by reducing engine oil viscosity and extending the oil drain interval estimated by taking into account both mineral engine oil and synthetic engine oil. In the research, CO2 emissions during vehicle operation were based on small gasoline engines in NEDC or New European Driving Cycle mode. In the framework of complex coupling between engine dynamics and the lubrication regime of bearings, piston assembly, and valvetrain—an experimental apparatus for film thickness and shape estimation in a cam-follower line contact using optical interferometry—is presented with the paper [9]. The basic principles of the interferometric techniques and the color spaces used to describe the color components of the fringes of the interference images are reported by the authors. The encouraging results evidence the clear capabilities of the proposed technique as well as some practical problems intrinsically related to the cam-follower contacts, such as: the quick motion of the contact point, the geometrical errors, the surface defects, and the non-perfect parallelism of the contacting bodies. However, the developed methodology seems to be able to perform the analysis of different images by catching the values of the film thickness during the camshaft rotation. In the same area of investigation,