Theoretical and experimental analysis of the effect of misaligned ring gear on performance of internal gear motors/pumps

Misalignment is an undesired phenomenon for all types of rotating machines because it decreases their performance and the lifespan. For the internal gear motor/pump, there are many elements that can cause misalignment; e.g. manufacturing or assembly errors, asymmetric load. Consequences of the misaligned ring gear leads to the metal-to-metal contact between the ring gear and the housing. An analytical and experimental study concerning the effect of misalignment on the performance of the internal motor/pump are presented in this paper. A new mathematical model has been governed to determine the eccentricity, the position angle, the minimum oil film as well as the misalignment angle around x- and y-axes. A test rig has been designed to evaluate experimentally the effects of operating parameters on the misaligned angle. The experimental results point out that the minimum oil film thickness can be reduced up to 18 % due to misalignment. This leads to the solid contact at one of two ring gear sides whereas at the mid-plane the minimum film thickness is not fallen below the permissible film thickness. Hence, for more accurate prediction of the performance and the lifespan of internal gear motor/pump, the effect of misalignment must be considered in calculation at the early design stage. After experiments, the inspection of the test motor was performed to prove the accuracy of the calculation.