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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.

In the last years, sophisticated analyses and control of topography parameters have been introduced to study engine bore cylinders. Such surface characteristics have impact on friction and wear of the engine, with effects on fuel consumption and durability. Among such characteristics, folded metal blocking the honing grooves has received much attention, but its quantification and actual impact on engine performance is still under discussion, both in the academia and in the industry. In this work, a methodology was developed to mathematically quantify the folded metal present in engine bores. The method is compared to others described in the literature and in use by some European automotive manufacturers. The quantification method, based on topography measurements, was also compared with other analyses, such as optical and scanning electron microscopy. The necessary resolution of the topography measurement and some recommendations for the analysis are given.

Five automotive oils, with different viscosity grades, were tested under different loads and speeds in a reciprocating test using piston rings and cylinder liners. Starved and fully-flooded conditions were also considered in order to analyze the influence of lubricant supplier in the lubrication regimes, especially in boundary-mixed transition. The expected Stribeck curve behavior was observed, and more interesting visualization appeared when the viscosity value was extracted from the Stribeck abscissa axis. The higher viscosity oils showed lower friction coefficient at low speed/load ratios. Such behavior is usually neglected and may be significant to understand the triblogical behaviour of engineering components. Computer simulation showed similar results, including the “cross-over” speed/load when the lower viscosity oils start to show lower friction.

The so-called Modified Martempering discussed in this work differs from the standard martempering by that the temperature of the quenching bath is below the Ms point. In spite of the fact the lower temperature increases the severity of quenching, this also usually avoids the bainite formation, and by this reason, it is possible to make a fair comparison between different processes, which result in different microstructures. The present study shows the results in terms of mechanical properties, impact resistance in special of a cold work tool steel class, after being heat treated by the isothermal modified martempering process, as well as a comparison with the conventional quenching and tempering process and the austempering as well.

The tempering effect on as-quenched compressive residual stress of commercial carburized samples is the main objective of this work. The compressive residual stress developed during the quenching process of carburized parts is fairly well known. The study was performed using SAE 4120 RH steel samples with two different diameters of 15 and 38 mm, which resulted in different cooling rates, with a direct effect on the core microstructure. The carburized surface microstructures were considered similar. The smaller diameter core microstructures were predominantly martensitic however bainitic in the larger bars samples. The as-quenched surface compressive residual stress was lower in the smaller diameter samples. The 15 mm diameter samples showed two different types of behavior, i.e., the compressive stress for lower temperatures during tempering process was reduced, whereas the values were increased at higher temperatures.

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.

Metal in general presents two distinct regions in tension by deformation curves, one elastic and other plastic. At the elastic region, there is a direct proportionality between applied load and correspondent deformation. This can be called an elastic linear behavior of the material. Considering graphite content cast iron with lamellar morphology this behavior does not follow the same pattern. Since the beginning of the loading those materials present non-linear behavior with the load applied. In this report will be presented microstructure analysis, micro and macro hardness tests and a precise determination of tension versus deformation curves of perlitic gray cast iron with predominant Type A graphite to get the real tension profile developed when flexion loads are applied.

The Greenwood model has been extensively used for calculation of the asperity pressures under mixed lubrication conditions, but usually assuming that the surfaces are gaussian. In this work, the Greenwood parameters are calculated from actual, non-gaussian, engine surfaces measured by White Light Interferometer. Results from 2D profiles and 3D measurements are compared. An improved way to calculate the Greenwood parameters and to apply them for estimation of the contact area and pressure is described. To illustrate the methodology, some examples of topography characterization and modeling for engine liners are presented. The influence of the asperity summit height average on the predicted contact area calculation is discussed. To explore and validate the proposed method, several WLI measurements from different engine HDD liners were analyzed using a proprietary code.

One of the problems related to the gray cast iron cylinder liner, and others materials, transportation is the possibility of the surface corrosion due to a non-controlled environment. The manufacturer has the responsability to guarantee the product free of corrosion up to the opening at final destination. Aiming to evaluate the liners transportation, regarding the corrosion potential during the transportation cycle, Magneti Marelli Cofap did experiments where the atmospheric conditions inside the pallets were measured. Using a special device it was possible to check the temperature, absolute humidity and relative humidity variations at every step, which were pre-set by using an specific software. The main reason for variations that might happen at the liner surface are related to transportation and storage. The corrosion rate will be determined by physical and chemical atmospheric conditions.

The quality of the nitrocarburized layer has a decisive influence in the service life of components with pistons that work together with polymeric seals, since it interferes in the abrasion and wear mechanisms of the involved materials. Thus it is necessary to select the most adequate process to apply in a given component aiming for a quality improvement and warranty costs reduction. The literature offers a great volume of information about the different nitriding processes, but there are few reports comparing them. In this paper the salt bath and plasma processes are discussed concerning the white layer metallography, roughness and the process effect on corrosion resistance of gas spring rods manufactured with SAE 1040 steel.

The nitriding process improves in some applications the fatigue resistance of mechanical components. There is a lack of information about the nitriding process effect on the toughness of components. It is well known that the austempering heat treatment improves the toughness of the nodular cast iron. Some efforts have been made to find a compromise between the toughness of the bainitic structure of nodular cast iron and the high wear resistance undertaken by the nitriding process. Nitriding causes smaller dimensional problems if compared with other termochemical processes in steel and cast iron, but during exposure to the nitriding temperature the stabilized austenite of the nodular cast iron bainite may decompose, and induce component distortion. It is well known that the stabilized austenite is responsible for high toughness of the nodular cast iron.

This work compares the typical manufacturing process of cast iron piston rings with chromium or molybdenum coating with the more recent nitriding steel process. Environmental impact of the processes is estimated by their material losses, consumption of energy and hazardous waste. Despite all technological development, the nowadays production process of a typical piston ring still implies that the finished part has only 30% of the iron initially cast. A more recent design, nitrided steel piston ring, reduces substantially material losses during the part manufacturing. It also substitutes high polluter processes as chromium plating or metal spray for the lower polluter gas nitriding. Production of Nitrided Steel Rings (NSR) uses 40% less energy, needs 78% less raw material and produces almost 10 times less hazardous waste. NSR has significant lower environmental impact in comparison with the traditional Coated Iron Ring (CIR). NSR also has environmental advantages during use.

Engine developments have led to higher mechanical and thermal loads on the components, at the same time that lower friction losses are also sought. Therefore, the development of better materials and of surface treatments has received great emphasis. This paper presents the results of dynamometric engine tests with a proposed piston ring pack, composed of a gas nitrided steel top ring, a nitrided gray cast iron second ring and a normal production chrome plated oil ring. The proposed pack showed very low wear when applied to a medium duty diesel engine, besides being a cost-effective alternative to the conventional pack with moly coated and chrome plated (respectively in the top and second) rings. The proposed pack also caused very low wear on the cylinder bore, specially near the TDC, where the bore wear is usually maximum.

The automotive industry has been increasing stainless steel consumption daily. Some important parts of a car should keep using carbon steel, however, the exhaust system must use stainless steel tubes since the gas from engine cannot corrode those tubes, avoiding catalytic conversor contamination. Among stainless steel groups, ferritic has been choosing due to costs and strong high temperatures resistance. This report starts studying ferritic stainless steel welded tubes mechanical properties (ABNT 409 stabilized), raw material for exhaust systems. Some welded tubes have been produced with internal bead rollers, to compare, afterwards, with tubes which were produced without bead hardening. The results shows that hardening induced by bead rolling causes material elongation reduction, that could lead problems on the tube forming operation during exhaust system production. Those materials have been analyzed by optical and electronic microscopy, Vickers micro hardness and tensile test.

The components of the piston/ring/liner system must have their wear resistance increased to meet the new engine requirements. The engine operating conditions can be even worse if corrosive wear in the engine is expected to occur. This paper presents a study to improve the wear resistance of piston ring coatings and liner materials by the addition of chromium carbide and carbide forming alloying elements, respectively. The engine tests were run with high sulfur fuel (about 1.0 wt%) and lubricant with low total base number (TBN) with the objective of increasing the corrosive conditions. The results show the improvement of the ring coatings wear resistance with the increase of the chromium carbide content. The cylinder liner materials also presented lower wear rates when they had hard particles, mainly due to the addition of niobium, vanadium and titanium.

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.

The piston rings are responsible for maintaining some engine functioning parameters in an acceptable range, mainly the lubricant oil consumption and the blow-by gases flow from the combustion chamber to the crankcase. The wear resistance of these components is related to their capacity of properly exerting these functions during the whole engine life. In Diesel engines, all the rings have a wear resistant coating applied to their contact face with the cylinder wall. However, the chrome plating of the second groove compression ring is a conservative solution with the possibility of the development of lower cost alternatives. This paper presents the results of engine tests that compare the wear resistance of second groove rings with chrome plating and rings made of nitrited gray cast iron. Test results with similar gray cast iron rings are also analyzed to infer the influence of the nitriding treatment on the wear resistance of this material.

The first groove piston rings are highly loaded due to the combustion chamber nearness. They support high pressure against the cylinder wall, high working temperature and low lubricant level. In critical working condition, it could be used flame sprayed molybdenum coating the rings from 99.9% purity wires. The wire flame spray process limitation is the deposition of only one material. Here it is presented a new concept for getting wear resistant coatings on first groove piston rings, by flame spraying, by applying simultaneously materials with different characteristics from wires. Comparative results between the proposal (Moly + Inox) and the conventional (Moly) coating are presented. The simultaneous application of stainless steel and molybdenum decreases the first groove piston rings wear without loss of scuffing resistance.

The higher load in heavy duty Diesel engines and the use of piston ring coatings with higher wear resistance cause more severe working conditions to the cylinder liners. In some cases, high localized wear occurs at the top dead center (TDC) of the first groove ring, where the loads and lubrication conditions are critical. It was studied the effect of the addition of hard particles on cylinder liner materials. The presence of these particles was obtained through the use of small quantities of strong carbide forming alloying elements: Vanadium, Niobium and Titanium. Cylinder liners with hard particle addition were tested in comparison to regular liners. This test used high sulfur fuel (> 1.0 wt %) and low additivation lubricant oil, maintaining the same ring pack configuration for both liners. The results showed sensible liner wear reduction at the TDC of the first ring without compromising the ring pack performance.

The application of multipiece oil control rings (two segments or rails and one expander) to Otto engines is very efficient and has been used for many years. However, development work to improve their performance, durability and manufacturing costs is desirable. The contoured segment is an alternative to reduce the variation of oil ring unit pressure during engine life. This paper shows the results of engine tests with this component, where nitrided segments with regular stainless steel expanders and nitrided expanders were used. The results showed satisfactory behaviour, with low wear between segments and nitrided expanders as well as between segments and the cylinder wall.