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Governmental legislation with regards to emissions is an important driver for Heavy Duty Diesel (HDD) engine developments. To reach the targets, in most of cases it is necessary to increase the thermal-mechanical loads, increasing the level of technical demand for the engine components. Besides that, other important aspects drive the engine development, as the cost of ownership, demanding for instance an extended oil draining interval, which leads to harsher environment for the engine components. In order to cope with the modern engine demands, this article presents a piston and piston rings specially designed to meet these targets in a robust way. Starting with the ring pack, CrN based coatings applied by PVD (Physical Vapor Deposition) are commonly applied to top ring face to reach durability targets.

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.

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.