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With the current use of bio-renewable fuel, the application of Ethanol in Flex-Fuel vehicles presents a very low CO2 emission alternative when the complete cycle, from plantation, fuel production, till vehicle use, is considered. In Brazil more than 80% of the car production is composed of Flex-Fuel vehicles. Due to the lower heating content of the Ethanol, more aggressive combustion calibrations are used to obtain the same engine power than when burning gasoline. Such Ethanol demands, associated with the continuous increase of engine specific power has lead to thermo-mechanical loads which challenges the tribology of piston rings. The ethanol use brings also some specific tribological differences not very well understood like fuel dilution in the lube oil, especially on cold start, corrosive environment etc. Under specific driving conditions, incipient failures like spalling on nitrided steel top rings have been observed.

The present study looks into different possibilities for tribological optimization of the piston/bore system in heavy duty diesel engines. Both component rig tests and numerical simulations are used to understand the roles of surface specifications, ring pack, and lubricant in the piston/bore tribology. Run-in dynamics, friction, wear and combustion chamber sealing are considered. The performance of cylinder liners produced using a conventional plateau honing technology and a novel mechanochemical surface finishing process - ANS Triboconditioning® - is compared and the importance of in-design “pairing” of low-viscosity motor oils with the ring pack and the cylinder bore characteristics in order to achieve maximum improvement in fuel economy without sacrificing the endurance highlighted. A special emphasis is made on studying morphological changes in the cylinder bore surface during the honing, run-in and Triboconditioning® processes.

Due to several market demands of higher wear and scuffing resistance, Duplex PVD (Physical Vapor Deposition) CrN top ring has been used in Heavy Duty Diesel (HDD) engines. The ring comprises a nitrided high chromium stainless steel with a PVD ceramic CrN coating. For High Speed Diesel (HSD) vehicles with lower demands, MAHLE has developed an alternative PVD coated ring, which balances the cost and performance ratio. This alternative, named High Value PVD (HV-PVD), consists of applying the best resistant coating for wear and scuffing, PVD, onto a less costly ring material, Ductile Cast Iron. The HV-PVD top ring has been tested in HSD engines and shown excellent performance. Additional advantages of the HV-PVD are its lower friction coefficient and better tribological compatibility with the cylinder bore materials when compared to the traditional galvanic chrome based coatings. Such features lead to reduced engine friction and lower cylinder wear.

Low viscosity combined with appropriated additive technology is one of the main paths to reduce friction on Internal Combustion Engines. Japan is on the cutting edge of low viscosity oils, having already available SAE 0W-8 in the market. On the other hands, in emergent countries like Brazil, SAE 15W-40 is still used in some passenger cars while the Japanese origin car brands use SAE 0W-20. Lubricant friction additives type also differs depending on the original equipment manufacturer (OEM) origin, and the Japanese ones usually containing high amounts of the Molybdenum type. In this paper, some of the advantages and challenges of using low viscosity oils are discussed and emphasis is given in the friction reduction obtained with the synergic effects of the right choice of additives components type and the material/coating used in the engine parts. Ring-liner rig and floating liner engine tests comparing different oils will be presented.

The cylinder bore honing quality is an essential factor for a good engine performance and durability. A bad surface finish can result in an excessive lubricant oil consumption, high piston ring wear and scuffing occurrence. In this paper the most important characteristics of bore honing for cast iron cylinders and their influence in the combustion engine performance are described and discussed. Despite its importance, the bore honing is commonly undervalued due to various reasons including the difficulty of a practical but sufficient method of quality qualifying. Some honing commonly misunderstood concepts are detailed and SEM photographs of bore surface from both good and bad finish are presented. At the end of this paper it is also presented a recommendation for a practical evaluation method of honing quality.

The evolution of internal combustion engines has led to friction reduction as well as to gaseous emissions reduction, demanding the use of narrower rings. Nodular cast iron is used satisfactorily for compression piston rings, with wear resistant coatings to improve their durability. However, for more severe applications and rings narrower than 1.2mm, even the nodular cast iron mechanical resistance is not enough. In this way, the use of steel is recommended, which may have its tribological properties improved by the nitriding thermochemical treatment. This paper presents the characteristics of the materials and of the nitriding process of compression and oil control rings as well as bench and dynamometric test results run during the development of these products.