Search Results

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.

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.

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.

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.

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.