Effects of Gear Oil Properties on Pitting Life in Rolling Four-Ball Test Configuration

Abstract

There is a connection between the efficiency of oils and their wear and/or surface damage protective properties, an area not so well described in the literature. One such damage mode is macroscale contact fatigue on gear tooth flank surfaces, also called pitting. The present study is aimed at investigating the correlation between gear oils' physical properties, important in terms of gear transmission losses, and pitting life. Eight gear oils were formulated giving different combinations of base oil, viscosity, and concentration of friction modifiers. All eight oils also contained an additive package designed to meet GL-5 specifications. This study consists of three parts. In the first, the oils' physical properties were measured using a set of bench tests. In the second, the pitting lives of the oils were evaluated using rolling four-ball tests. The third part deals with the correlation between the measured physical properties of the oils and their pitting lives. This is achieved through multiple linear regression, with a view to finding the salient properties that have a significant influence on pitting life. The results show that gear oils' physical properties do have a large influence on the pitting lives. Oil properties that lower interfacial tangential stresses are beneficial in enhancing pitting life.

Micro-Pitting and Wear Assessment of PAO vs Mineral-Based Engine Oil Operating under Mixed Lubrication Conditions: Effects of Lambda, Roughness Lay and Sliding Direction

“…Where, Figure 8 presents light optical images of micro-pitted surface (over-rolling direction from right to left) and Figure 9 shows the same surface (rotated for 90 • counter-clockwise) captured with the optical 3D profilometer with local micro-pitting damage assessment. lower EHL friction [25]. This, in turn, reduces the tendency towards micro-pitting by reducing the stresses close to the surface.…”

“…Generally, PAO base oils tend to have lower pressure-viscosity coefficient (a ≈ 20 GPa ), compared to the mineral base oils (a ≈ 30 GPa ). Typically, an oil having a lower pressure-viscosity coefficient will result in lower EHL friction coefficient [25]. Table 1.…”

“…Based on the observations, a higher blend of PAO oil (oil B) increases the severity of the local micro-pitting tendency, compared to a higher blend of mineral oil (oil A), due to having lower wear. However, at a higher lambda ratio, the tendency towards local micro-pitting is completely eliminated for oil B. PAO base oil is known to have a lower pressure-viscosity coefficient [23] and lower EHL friction [25]. This, in turn, reduces the tendency towards micro-pitting by reducing the stresses close to the surface.…”

Impact of oil ageing on gear scuffing in hybrid dual-clutch transmissions

“…Dependent on the additive technology, the base oil and the viscosity, pitting and micropitting can be improved by selection of a suitable oil formulation and is impacted by aged oil. 1,2,3,4,5 In contrast to the previously mentioned failure modes, scuffing is not a durability but a spontaneous damage in automotive transmissions. If a critical scuffing temperature is exceeded, either by a high sump oil temperature or by an elevated gear mass temperature caused by insufficient cooling, the damage occurs immediately.…”

“…Dependent on the additive technology, the base oil and the viscosity, pitting and micropitting can be improved by selection of a suitable oil formulation and is impacted by aged oil. 1,2,3,4,5…”