Power Loss and Damage Behavior of Gears Operating Under Loss of Lubrication

Geared turbofans need to withstand loss of lubrication due to inevitable off-design conditions. Additionally, the loss of lubrication specifications that have to be fulfilled are getting stricter. For a loss of lubrication event, today's geared turbofans are equipped with secondary oil supply systems. Their omission would reduce space and weight and, consequently, carbon emissions. However, this requires geared transmissions to withstand loss of lubrication events. In order to enable this, knowledge of the power loss and damage behavior of gears under loss of lubrication is required first. In this study, power loss and bulk temperature measurements of test gears under loss of lubrication on an FZG gear efficiency test rig are presented. Hertzian pressures in the pitch point up to 1723 N/mm² and circumferential speeds up to 20 m/s were considered. The experimental results show the characteristics of increasing power loss and bulk temperatures under loss of lubrication depending on load and speed. At moderate operating conditions, no damage occurs within 20 s under loss of lubrication, whereas a load increase results in slight scuffing, and a speed increase results in severe scuffing. Oil centrifugation has a strong effect on the loss of lubrication performance. Additional experiments under reduced quantity lubrication demonstrate the impact of the remaining oil on the survivability of gears facing the loss of lubrication.