Strength of a pinion-motor shaft connection: computational and experimental assessment

摘要

Load capacity of keyway couplings is usually calculated according to standards (e.g. DIN6892, DIN743) based on nominal stress and simplifying assumptions dating back to several decades. Detailed modeling of keyway couplings is still a research topic, because of the complex mechanical behaviour involved. Moreover, the current standards apply only to usual geometries the designer sometimes needs to depart from, especially for the sake of compacity. This is the case in gearmotors, where the input pinion is directly fixed on the electric motor shaft. This requires, for small diameter pinions, that the pinion shaft be inserted in the hollow motor shaft end. In the design investigated hereunder, a special key is built in an opening in the hollow shaft wall. This design is substantially different from usual shaft-hub connections; it combines a geometrical notch with an interference fit, and is submitted to a peculiar stress distribution. This article explains the detailed investigations made on such a connection. After summarizing the different possible failure modes on classical keyway connections, it explains how a simple interference fit behaves under an external load. Despite its inherent limitations, a FE model gives valuable insight into the connection behaviour: especially the influence of the interference fit, the load combination and the progressive stress stabilization after a few revolutions, due to the combination of friction and relative deformations. Static test results are then presented, and the challenges of a realistic fatigue tests are analyzed. A simplified dimensioning strategy is finally set out, which is more suited to practical application in the design office.