Bruno, R., Dezotti, R., and Mordente, P., "Power Cell Unit (PCU) for Modern HDD Engines," SAE Technical Paper 2017-36-0301, 2017.
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. The novelty of the top ring described on this paper is that the coating has a differentiated thickness along the ring circumference, being thicker near the ring tips, which are the most critical demanded ring regions in terms of wear. The feature disclosed on this article deliveries extended durability to the product.The ceramic PVD coating copes with the low friction demands, since it presents reduced friction coefficient in comparison to other top ring coatings available on the market (e.g: Ceramic Cr with embedded hard particles). However, the most important friction saving contribution within the ring pack comes through the improvement of the oil control ring design, assuring a suitable oil scraping action with reduced tangential load.Piston design and material have to be also modified to cope with such modern demands. Increased thermal-mechanical loads take conventional aluminum pistons beyond their application limits due to more challenging working conditions. This article describes some design features to reach extended life for these pistons. For more aggressive cases, the use of steel material with special design might be the best solution.