Development of a New Test Method to Investigate the Scuffing Load Carrying Capacity of Hypoid Gear Oils

Highly loaded hypoid gears, which are preferably used in vehicle axle drives, exhibit an unfavorable combination of high sliding velocities and high contact stresses in tooth contact with regard to the failure mode scuffing. For this reason, the scuffing load carrying capacity is a decisive design criterion in the development of hypoid gears. In addition to the gear geometry, the entire tribological system of the gearbox must also be taken into account. Beyond the loads and speeds that occur during gear operation, the lubricant used and its additives have a significant influence on scuffing load capacity. Since it is generally impossible to determine the influence of the lubricant on the load carrying capacity of gears on the basis of physical or chemical oil data alone, experimental test methods are necessary. In order to be able to investigate and classify the scuffing resistance of hypoid oils, an experimental test method was developed based on theoretical investigations. To determine the test procedure and the corresponding load stages in the newly developed test, the flash temperature according to ISO/TS 10300-20:2021 was used as the relevant variable. In order to achieve a reproducible test procedure, a running-in procedure was specified based on the results of experimental investigations on the FZG hypoid back-to-back test rig. This paper presents the development and detailed description of a new test method for classifying and investigating the scuffing resistance of highly loaded hypoid oils, as well as initial experimental results.