Self-lubricating gears with oil-impregnated sintered materials

This study shows the first results on the operating behavior of self-lubricating gears based on oil-impregnated sintered material. The term self-lubrication is referred to as oil that bleeds from the open-pored sintered gear and providing lubrication to the gear contact. Experiments were carried out at the FZG efficiency gear test rig. Thereby, the pinion was made of open-pored, case-hardened sintered steel and impregnated with oil, and the wheel was made of conventional case-hardened steel. The total loss in torque and the bulk temperatures of the pinion and wheel were measured for various operating conditions defined by load and circumferential speed. The mean coefficient of friction in the gear contact was derived from the torque loss measurements. Results confirm that self-lubricating tribological systems with oil-impregnated sintered materials can be transferred from model test rigs to gears. The mean coefficient of friction shows the order of magnitude of externally lubricated gears. The tooth flanks after test runs show partially noticeable wear. As the heat dissipation of self-lubrication is limited, bulk temperatures and thermal load limits influence operating behavior significantly. Further work will focus on understanding the mechanisms of the lubricant film formation of self-lubricated, highly-loaded EHL contacts and on extending the thermal load limits.