Application of DLC Coating in Cylinder Liners for Friction Reduction

In the past decades, continuous improvement to the finishing process (honing) of cylinder liner has led to a considerable reduction in engine friction, wear and oil consumption via optimization of the running surface topography. However, in order to meet the constantly restrictive environmental regulations, the automotive industry has invested in reducing fuel consumption and exhaust emission to expressive low levels mainly by minimizing friction losses. The properties of Diamond-like carbon (DLC) coatings are known to offer superior wear resistance and low friction making it suitable for many different tribological applications. This paper discusses the application of DLC in Heavy Duty Diesel (HDD) cylinder liners as an alternative to reduce friction on the power cell as well as its tribological performance when submitted against coated top piston rings with CrN. Reciprocating rig and fired engine tests are presented. Evaluation criteria for rig test included friction under lubricated condition at constant oil temperature of 120°C. Test results show that DLC coating improved tribological system decreasing friction losses by 19%. Finally, results from a short durability test on HDD engine platform have confirmed a significant reduction of 2.5% on specific fuel consumption as well as superior wear resistance of DLC coated cylinder liners when compared with base uncoated ones. INTRODUCTION Approximately 40% of the energy consumed by Heavy Duty Diesel (HDD) engine is converted to useful work and up to 15% of the total energy is related to friction [1, 2]. A well accepted approach to increase the effective work on the Internal Combustion Engines (ICE) is to reduce the energy losses [1]. Although the specific friction share among the components depends on several factors, for instance, engine design and operation condition, it is accepted that the pistoncylinder systems is a large contributor to friction, consequently those components are naturally selected for design optimization due to good potentials of friction reduction [2,3]. Piston and piston ring-pack are the two largest contributors to engine mechanical losses as detailed in the Figure 1. It is also known that changes in the cylinder bore topography are considered to be one of the variants to reduce friction losses [4,5]. Design optimization of the power cell components was and is still widely explored for reduction of mechanical losses on modern ICE. Another feasible approach for losses reduction is the application of low friction protective films on the components. A lot of effort has been made to develop antifriction coatings for piston rings and piston skirts. However Application of DLC Coating in Cylinder Liners for Friction Reduction 2012-01-1329 Published 04/16/2012 Edney Deschauer Rejowski Mahle Metal Leve S A Paulo Mordente Sr Mahle Metal Leve SA Marina Fuser Pillis Nuclear and Energ. Research InstIPEN Tom Casserly Sub-One Technology, Inc. Copyright © 2012 SAE International doi:10.4271/2012-01-1329 Gratis copy for Edney Rejowski Copyright 2012 SAE International E-mailing, copying and internet posting are prohibited Downloaded Thursday, March 15, 2012 12:15:11 PM