Investigations on the thermal behavior of plastic crossed helical gears

Abstract Electric drives as compact as possible are in demand for a wide range of applications. In addition to being used as positioning drives in medical technology or robotics, such compact electric drives are increasingly used in transportation applications, such as electric bicycles or scooters, as well as in auxiliary drives and actuators in automotive vehicles. Crossed helical gears offer many advantages for such applications due to their high transmission ratio in one stage, and their flexibly selectable axis crossing angle. Using plastics as gear set material can be advantageous in terms of NVH behavior, efficiency, emergency running properties, and especially production costs. Cost- and space-saving and resource-efficient drives can be developed with these properties. At present, only limited scientific research has been carried out on crossed helical gears using plastic materials, and there are only type-specific methods for load-carrying capacity calculation and testing in the literature. These approaches are mainly based on investigations on the pairing of a steel worm with a plastic wheel, and therefore applicable to plastic/plastic pairings only to a limited extent. In particular, the calculation methods developed for metal crossed helical gears do not consider the complex non-linear and highly temperature-dependent material properties of plastics and are therefore not directly transferable. This paper presents a method for designing and testing plastic crossed helical gears concerning temperature behavior and thermal load limits. An adapted calculation approach is developed based on the established integral temperature method according to Michaelis [1, 2] and takes into account the temperature dependency of the material properties of the plastic used. The applicability of the method is demonstrated by means of a theoretical calculation study and experimental investigations. In this context, an exemplary crossed helical gear in the pairing PEEK/PEEK is examined within a new flexible test rig concept, which was developed and built-up. The comparison of the experimental results with the theoretical values from the calculation study shows good correspondence.