Piston ring with Thick @ Tips feature for highly demanded HDD Applications

摘要

CrN PVD (Physical Vapor Deposition) coating has been used as the main protection in the top rings contact face mainly in Medium and Heavy Duty Diesel (MHD) engines. Compared to conventional galvanic coatings, PVDs have offered an excellent wear and scuffing resistance for most of the applications. However, for high severity Heavy Duty Diesel (HDD) applications due to more demanding boundary conditions in new engine generations (high PCPs, low viscosity oils, etc.), the use of conventional thicknesses of PVD coatings can compromise the durability with an worn out coating in the highly loaded tip regions, exposing the base material. An increase of the overall coating thickness of the PVD can significantly impact the cost of the ring. In order to prevent a base material exposure and ensure the highest durability and robustness during the whole engine lifecycle, MAHLE has patented a cost efficient solution where the PVD coating thickness is gradually increased from circumferential position 90/270° until the ring tips. In this area of the tips, the coating thickness is up to 3 times higher than the usual minimum value of 20μm, which more than enough to withstand the most aggressive working environments. Preserving an adequate thickness sufficient to avoid the base material exposure, which may avoid over engineering by increasing the thickness, in the rest of the ring, where it is not needed. This article presents how this concept was developed and engine test results showing the benefits of this new technology.