Micropitting, pitting and wear are typical gear failure modes, which 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 on external gears.
The target of a 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 carried out.