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Technical Paper

Piston Ring Pack and Cylinder Wear Modelling

Wear of piston ring and cylinder was modelled through a computer code that calculates the hydrodynamic and roughness contact pressures acting on the contact surfaces. Both pressures are fully and coupled solved through, respectively, Reynolds equation and Greenwood-Williamson model. Piston secondary motion and piston groove thermal deformations are considered. The latter was discovered to be fundamental in defining the top ring worn profile. Due to the rough contact pressures, the model predicts material removal from both piston ring and cylinder surfaces and recalculates the system, hence simulating the evolution of the worn sliding surface of both parts. The predicted wear of the piston ring pack and the cylinder wall are compared with a medium duty diesel engine tested for 750 hours in dynamometer.
Technical Paper

Nitrided Piston Ring Pack for Diesel Engines

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.
Technical Paper

Liner Honing Quality Main Characteristics

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.
Technical Paper

High Value PVD Top Ring for High Speed Diesel Engines

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.
Technical Paper

Folded Metal Effect on Lubricant Film Thickness and Friction Using a Mixed Lubrication Deterministic Model

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.
Technical Paper

Effect of Lubricant Viscosity and Friction Modifier on Reciprocating Tests

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.
Technical Paper

Comparison of the Potential to Reduce Fuel Consumption by Engine Energy Losses Mapping

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.
Technical Paper

A new tribology test procedure to investigate ethanol dilution on engine oils

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.