Nowadays, Bismuth (Bi) is being applied as an overlay material for engine bearings instead of Lead (Pb) which is an environmentally harmful material. Bi overlay has already been a solid performer in some automotive engine sectors due to its superior load carrying capacity and good robustness characteristic which are necessary to maintain its longevity during the lifetime of engines. The replacement is also seen on relatively larger size engines, such as Trucks and Off-highway heavy duty applications. Basically, these applications require higher power output than passenger cars, and the expected component lifecycle becomes longer. Though Bi has similar material characteristic to traditional Pb, it becomes challenging for the material alone to satisfy these requirements. Polymer overlay is known for its superior anti-wear performance and longer lifetime due to less adhesion against a steel counterpart than metallic materials (included Bi). However, for heavy duty applications where clean operation condition is difficult to maintain, foreign particle can affect the polymer overlay performance.
In this study it has been found longer bearing lifetime under stringent bearing operation condition is achievable by making an optimal combination of Bi and polymer overlays. In general, thicker overlay has simply more margin for material wearing-off and it contributes to longer bearing lifetime. On the other hand, thicker overlay tends to lose anti-fatigue performance at the same time. On Bi and polymer overlay combination, it showed better fatigue resistance than normal thick single Bi overlay. Furthermore, each rig test confirmed that the combination overcomes polymer overlay robustness issue.