AGMA 04FTM12 PDF

Involute splines in torque transmitting joints are prone to non-uniform contact loading along their length especially in lightweight, relatively flexible applications such as a helicopter main rotor shaft-to-rotor hub joint. The structural stiffness and internal load paths of the two members in the joint affect spline tooth contact pressure distribution. In such applications, in the absence of lead corrections, the torque is transferred non-uniformly along the length of the spline resulting in a concentration or peaking of the tooth contact load at one end of the spline.

A significantly improved tooth load distributionwas achieved for splines for the Low Maintenance Rotor (LMR) version of the CH-47 Chinook helicopter main rotor shaft-to-rotor hub joint by applying, to the internally splined member, complex lead corrections which varied continuously along the length of the spline. The required lead corrections were determined analytically using finite element methods (FEM). Rotor hub splines with the analytically determined lead corrections were manufactured and tested under design load conditions. A standard CH-47 rotor shaft-to-hub joint, which uses a step lead correction between splines, was previously tested. Strain gages were used to infer contact load distribution along the length of the splines.

Test data indicated that the complex lead corrections resulted in a nearly uniform contact load distribution along the length of the spline at the design torque load. The data also showed that the load distribution for the splines with the complex lead corrections was significantly improved relative to the contact load distribution of the baseline splines. This work was performed under the U.S. Army Aviation and Missile Command (AMCOM) Low Maintenance Rotor (LMR) hub development contract DAAH01-99-3-R001.