Thermal properties of S-gears in comparison with involute gears

Abstract

The tests with small plastic gears, which were conducted to assess Wöhler curves for S- and E-gears indicated improved behaviour of S-gears, which is due to their geometry. However, the thermal load of the gears in contact is of a crucial importance. Therefore, the paper focusses on the differences in thermal load of cylindrical, spur, plastic involute and S-gears. Whereas there are thermal (temperature) models at disposal for the involute gears, no models are available for the S-gears. Such a model should reflect actual flank shape and difference in actual thermal behaviour deriving from there. So, frictional power along the path of contact, work of friction and deriving flash temperatures along the path of contact were calculated for both gear types, which disclosed lower thermal load of S-gears. Small E- and S-gears made of polyacetal and nylon were manufactured by milling. So, gears were of higher quality and reflected actual tooth flank geometry. The later long-term experiments were planned with smaller loads to run up to 10 or 20 million cycles; in this context they were focused on measurements of a steady state bulk temperature which helped in assessment of actual contact circumstances and contact temperatures.