RELIABILITY OF POWERTRAIN COMPONENTS EXPOSED TO EXTREME TRIBOLOGICAL ENVIRONMENTS

Results are presented from tests on a formulated 15W-40 mil-spec engine/transmission fluid to examine the impact of additives on improving its reliability and durability under extreme tribological conditions. A block-on-ring (BOR) configuration was used to measure the effect of five additives (an emulsion-based boric acid, tricresyl phosphate, particulate-based boron nitride, particulate-based MoS₂, and particulate-based graphite) on the critical scuffing load as a function of additive concentration and time to scuff during oil-off tests (starved lubrication). A four-ball configuration was used to evaluate the impact of simulated engine grit/sand on the abrasive wear of steel as a function of grit size and loading.

The results demonstrated that the additives increased the load for scuffing by 50 to 100% for the formulated oil and by 50 to 150% for the unformulated base fluid used in the formulated oil. Two of the additives (emulsion-based boric acid and tricresyl phosphate) doubled the time to scuffing for the formulated fluid. The use of boric acid and tricresyl phosphate in the base fluid increased the time to scuff significantly more. In both fluids, a low-friction regime was frequently observed during the tests and, when present, resulted in greatly increased survival times.

Oil-off tests were performed to simulate a loss-of-lubricant condition. The results revealed a novel trend – the formation of a low-friction regime under the starved (drained-oil) lubrication condition. When a low-friction regime occurred (after the oil was drained from the test cup), the time to scuffing increased dramatically.