Adjuster rings are used in commercial vehicle axle assembly to preload differential bearings and provide support in the axial direction. Adjuster along with the carrier and bearing cap combined to form a threaded joint. Adjuster with external threads engages with internal threads formed in carrier and bearing cap.
Preload in differential assembly maintains the system rigidity and helps to maintain an optimized hypoid gear engagement. An adequate preload is important to achieve a desirable bearing life. Reduction in thread engagement at adjuster joint fully or partially will cause a reduction in preload and can lead to gear misalignment. This can cause severe durability concerns.
In some cases, it is observed that under vehicle operating loads adjuster ring is backed off from its assembled condition by bending the split pin (split pin is, positive lock, used to maintain adjuster position) and adjuster threads were stripped off. Adjuster ring threads are designed using standard theoretical formulas. Typically, these formulas consider full thread engagement length for calculating thread strength and results in overestimation of thread capacity. It is essential to take into account reduction in thread engagement area due to thread misalignment and component deformations under actual operating load condition.
This paper proposes an innovative way of combining finite element simulation and theoretical formulas to accurately predict thread strength. Finite element simulation enables accurate prediction of thread engagement length and pinpoint stripping location. Thread engagement length from FEA is then used as an input to analytical calculations. Analytical calculations were first correlated with controlled test environment. A correlation map was developed using the test scatter and analytical calculations to predict threaded joint ultimate strength.
The proposed method and undelaying hypothesis are able to predict thread stripping under normal load conditions and abusive load conditions.