FZG Rig-Based Testing of Flank Load-Carrying Capacity Internal Gears

摘要

Micropitting, pitting and wear are typical gear failure modes that can occur on the flanks of slowly operated and highly stressed internal gears. However, the calculation methods for the flank load-carrying capacity have mainly been established on the basis of experimental investigations of external gears. The target of the research project was to verify the application of these calculation models to internal gears. Therefore two identical back-to-back test rigs for internal gears have been designed, constructed and successfully used for gear running tests. These gear test rigs are especially designed for low and medium circumferential speeds and allow the testing of the flank load-carrying capacity of spur and helical internal gears for different pairings of materials at realistic stresses. The three planet gears of the test rig are arranged uniformly across the circumference. Experimental and theoretical investigations regarding the load distribution across the face width, the contact pattern and the load-sharing between the three planet gears have been conducted. Furthermore, substantial theoretical investigations of the characteristics of internal gears were performed. Therefore, internal and external spur gears were compared regarding their geometrical and kinematical differences, as well as their impact on the flank load. Based on the results of these theoretical investigations, an extensive test program of load stage tests and speed stage tests of internal gears of different material, different finishing of the flanks and different operating conditions has been performed. The main focus of this test program was on the fatigue failures - micro pitting and wear - at low circumferential speeds. This paper describes the design and functionality of the newly developed test rigs for internal gears and shows basic results of the theoretical studies. It furthermore presents basic examples of experimental test results.