Examination of high-speed helical gear mesh efficiency and influences

The economic pressures of rising fuel prices and increased power requirements for automotive transmissions have pushed for innovations and improved efficiency in transmission design. Gear scuffing and failure is a complex process involving many factors, particularly gear speed. This thesis investigates the benefits of synthetic lubricants over mineral lubricants for transmission applications, as well as the feasibility of automotive high speed gear meshes that reduce scuffing. Several key areas of an automotive gear mesh application were investigated, including EHD contact, gear manufacturing, power loss, as well as both lubricant and lubrication influences.; The method involved a four-square test bench with a high speed helical gear mesh, which tested the real gear mesh of a production transmission with various torques and surface pressures. Tests were also run on a mini-traction machine (MTM) and the test bench results were compared with MTM traction curves. Three transmission lubricants were run in the four-square test bench gear mesh as well as on the MTM, at various temperatures. Post-test SEM failure analysis was conducted using a Wyko machine, which measured non-contacting surface replicas of scuffed and non-scuffed gear teeth. Other areas investigated were power loss and heat removal to improve mechanical efficiency.; The results demonstrated unmistakable power loss for the gear mesh, allowing further analysis regarding oil performance. Comparisons were made between the base oil composition, molecular structure, additives, and VII of the three lubricants and their test performance. A key finding of this research is that the EHD contact velocity is three times higher than was previously assumed with other oil film thickness gear calculations used by scientists and engineers.; Additional results of this research clearly show that MTM results and four-square test bench results cannot be compared, even for trend analysis. Also, power loss found in transmission tests is significant, and should be addressed more aggressively. Lower drag torques are possible with certain base oil compositions, as kinematic viscosity losses are addressed, and energy is conserved.