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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.

With the worldwide trend towards CO2 emission reduction, renewable fuels such as ethanol are gaining further importance. However, the use of ethanol as a fuel can bring some tribological impacts. Friction and wear of engine parts when lubricants are contaminated with ethanol are not very well understood. Within this scenario, the present paper introduces a new procedure to investigate the ethanol dilution on the performance of engine oils. Friction and wear of actual piston ring and liner were evaluated in a reciprocating test designed to emulate real thermomechanical conditions of both urban and highway car use. In addition to fresh oil, lubricant/ethanol emulsions were prepared carefully following two different procedures - unheated and heated mixing. The former to emulate cold start and “bakery” driving use, the latter to reproduce what happens after the engine heats in normal conditions.

With the increase of thermal and mechanical loads, some spark ignition (SI) engines may present excessive wear on the piston top groove. The problem was studied first by numerical simulation. Several parameters were found to influence the groove wear. E.g., ring side face roughness and hardness. But the main influence found was the relative attitude between groove flank and ring side face. As the instantaneous attitude varies during the engine cycle, the problem was studied with a commercial ring dynamics computer program and considering thermal and mechanical deformations that occur in the piston during engine operation. The expected groove wear was estimated by the accumulated “wear load” during critical engine operation regimes. Experimental results of engines with groove wear solved by design optimization are shown.

Piston ring radial pressure effects both the manufacturability of the ring as well as its performance in the engine. While lack of radial contact can cause increased blow-by and lubricant oil consumption, high local contact pressure can cause excessive wear and even scuffing. Current methods to evaluate ring radial pressure fail to identify subtle, local pressure changes. To overcome such limitation, a new method to evaluate ring radial pressure at each peripheral angle was developed. In this experimental procedure, the ring free shape is recorded by an optical device and then this free shape is used as input to code that calculates its radial pressure distribution. In order to validate this method, six different sample variants of ring pressure distribution, (i.e. free shape), have their radial pressure evaluated by two different methods: 1,) the new procedure and 2,) a mechanical jig with 11 circumferentially spaced radial load sensors.

Motivated by the demand for the reduction of fuel consumption, in particular to meet the engine energy efficiency goals of the Brazilian incentives legislation (INOVAR AUTO), this paper proposes a method to identify potential for energy efficiency and exemplifies it through three engines of the Brazilian market. The proposed method consists in identify the engine losses in different operating points (speed x load) through combustion mapping and the basic formulations which describe the energy/losses share. These data are grouped into 12 map sections, allowing the identification of the ones with more improvement potential. The baseline engine is 1.6 l naturally aspirated, port injection and was tested with E100 fuel (100% Ethanol). Engine #2 is similar to the baseline but with 4 valves per cylinder and a lower viscosity oil. The engine #3 is a more advanced engine: turbo charged, direct fuel injection, variable valve train and piloted pumps.

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 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.

In lubricating and specialty oil industries, blending is routinely used to convert a finite number of distillation cuts produced by a refinery into a large number of final products matching given specifications regarding viscosity, flash point, pour point or other properties of interest. To find the right component ratio for a blend, empirical or semi-empirical equations linking blend characteristics to those of the individual components are used. Mathematically, the problem of finding the right blend composition boils down to solving a system of equations, often non-linear ones, linking the desired properties of the blend with the properties and percentage of the blend components. This approach can easily be extended to crankcase lubricants, in which case major blend constituents are base oils, additive packages, and viscosity index improvers. Artificial intelligence (AI) tools allow accurate predictions of the basic physicochemical properties of such blends.

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.

Despite the influence of folded metal material on the lubrication performance of engine cylinder liners has been largely investigated, its effect has not been isolated yet in terms of other surface parameters as Sa, Sq, Vo, Rpk etc. In the present contribution, the isolated effect of folded metal on the performance of engine cylinder liners was investigated by comparing the hydrodynamic and asperity contact pressures through a deterministic mixed lubrication model. From that, the friction coefficients and the engine friction losses were also estimated. The topography of a production car engine block was characterized employing a Non-Contact Surface Profiler System. Folded metal was quantified using in-house algorithms, and so its occurrences were digitally removed. Afterwards, the surfaces with and without folded metal were studied with the deterministic model.

Recently, Gasoline Direct Injection (GDI) engine has reached mass production. Fuel economy up to 35% is claimed, at urban driving conditions, by using stratified charge combustion. It also reduces HC emissions at cold start. Most of the car manufactures are researching GDI or even intend to produce it in the near future. If the promised goals are actually achieved, a great change in the development focus for automotive engines will occur. In GDI engines, ultra lean burn, stratified charge combustion is achieved by injecting fuel directly into the chamber during compression stroke (“late Injection”). In contrast, at higher power conditions, the GDI operates in homogeneous charge and fuel is injected during intake stroke (“early injection”). This paper intends to summarize some information about Gasoline Direct Injection engines and possible effects on Piston rings. First, some basic concepts about combustion, judged to be necessary to understand GDI engines, are introduced.

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.

Many countries are introducing fuel economy regulations in order to reduce the average emissions of light duty vehicles, since fuel consumption of vehicles is an important factor in air pollution. The lubricant has a significant role in reducing friction losses hence the fuel consumption, but the impact depends on the engine operation regime and the manner in which the lubricant components work together to change frictional properties. Different driving cycles are used by different countries and organizations to measure fuel consumption. The most common driving cycles are the European NEDC and the North American FTP-75 vehicle transient cycles. Fuel economy at full load and BSFC (Brake Specific Fuel consumption) are also common methods of measuring engine fuel economy.

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 gas that flows from the combustion chamber to crankcase of internal combustion engines (“Blow-By”) and the reverse flow (“Blow-Back”) have detrimental effects in the engine power, pollutant emissions and lubricant degradation. A main factor to control this flow is the first piston ring gap. The influence of the area defined by the gap, specially of the chamfer at end gap, is analyzed by computer simulation and dynamometer tests. An unusual type of piston ring contact face coating at end gap, allows a reduction of up to 50% in the ring gap area and engine Blow-By.

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 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.

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 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.