Spline Centering, Piloting, and Toggle: Torsional Stiffness, Shaft Bending, and Centering of Moment Loads
Common practice for a splined joint is to assume that the load is theoretically transmitted along the entire length of the tooth face, but several factors, including axial spline length and the ratio of hub to shaft torsional stiffness, can impact how the load is distributed along the tooth face. Previous papers have considered the effect of pure torque and combined torque plus radial load, but few have described the impact of splines loaded with torque plus both moment and radial load.
A spline with short axial length, if sufficient torque is applied, can center a hub that is subjected to a radial load. A sufficiently long spline may be able to center a hub that has both radial and moment loads acting upon it – but if the hub torsional stiffness is much higher than the shaft stiffness there may not be sufficient torque transfer at the far end of the spline to center the hub against its moment load.
This paper describes the behavior of spline interfaces in piloted (radially offset), full toggle, half toggle, and centered alignment states. These alignment states are created by a combination of part geometry and load conditions. Part geometry includes the influence of torsional stiffness of the hub relative to the shaft stiffness, and spline length to diameter ratio. Load conditions considered include combinations of torque, radial load, and moment load. Splines with a large length-to-diameter ratio are modeled as a set of two short splines to describe their alignment state. The amount of misalignment allowed in piloted, full toggle, and half toggle is calculated, and a chart of misalignment load factor vs. torque and stiffness ratio (hub to shaft) is provided.
Authors: Stephen McKenny and Dustin Eseltine
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