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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 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.

A damper and a gas spring being a thermo engine which vibrational energy absorption occurs over heat transformation, requires very specific properties of thermo chemical stability from the hydraulic fluid as well as shear strength by heat and pressure effect. It competes to the hydraulic fluid the task of this transformation vehicle. The absorption performance of a damper depends on variation of physical-chemical properties of the hydraulic fluid under heat effect and the maintenance of this performance depends on conservation of those properties during time. The traditional hydraulic fluids for this application, despite its thermo-chemical stability, suffer a deterioration process of those properties under severe operating conditions and consequently reflect in the damper component lifetime.

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.

The fuel economy and gaseous emissions features have led the engine developments for the last few years. Various actions taken to meet these objectives imposed the necessity of components, in this case oil control rings, with higher mechanical resistance, durability and efficiency during the engine life. A new nodular cast iron alloyed with Niobium was developed. The presence of Niobium carbides raises significantly the wear resistance of this material. New configurations of oil control rings with taper faces or barrel faces showed a better performance if compared with two-piece conventional rings. The contact surface height variation during the engine life (and also the mean specific contact pressure variation in the ring land and cylinder wall contact) brings benefits in the oil consumption reduction without compromising the durability of rings and cylinders.

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 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 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.