Planetary Sun Gear with Variable Wall Thickness for Hoop Stress Reduction
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Solution Overview
Problem
Traditional planetary wheel end assemblies experience high hoop stresses due to axle shaft splines and gear teeth bending, requiring larger sun gears that are costly and inefficient to manufacture, and result in insufficient radial wall thickness.
Innovation Solution
A planetary wheel end assembly with a sun gear configuration featuring varying diameters and radial wall thickness along its length, where the sun gear body has a greater outermost diameter and radial wall thickness at the inboard end than at the outboard end, and the axle shaft is supported by a rotational element within the planetary spider to reduce stresses and allow for broached splines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the sun gear size is increased in radial and axial directions to reduce hoop stresses, then the stress resistance is improved, but the weight and manufacturing cost increase and the spline can no longer be broached
Solution Approach 1:
The sun gear is designed with non-uniform thickness distribution, having greater thickness at the inboard end where hoop stresses are highest and tapering toward the outboard end. This local variation in geometry provides stress-resistant properties where needed while maintaining manufacturability through broaching processes
Solution Approach 2:
The solution moves from uniform two-dimensional sun gear geometry to three-dimensional variable thickness geometry, creating an optimized stress distribution profile that maintains broachability while improving strength
2Power
If a larger diameter axle shaft is used to handle increased input torque, then the torque capacity is improved, but the radial wall thickness of the sun gear becomes insufficient
Solution Approach 1:
The sun gear thickness is locally optimized at the inboard end to provide sufficient radial wall thickness for broached splines while accommodating the larger axle shaft diameter needed for high torque applications
3Ease of manufacture
If traditional sun gear configuration is used with uniform dimensions, then the manufacturing process is simple, but the hoop stresses are high and radial wall thickness is insufficient
Solution Approach 1:
The sun gear transitions from uniform thickness to non-uniform thickness distribution, with greater thickness at the inboard end where hoop stresses occur, while maintaining compatibility with broaching manufacturing processes
Data Source
AI summary
A planetary wheel end assembly includes an axle shaft having an inboard end and an outboard end and a planetary gear assembly that receives driving input from the axle shaft. The planetary gear assembly includes a sun gear that is fixed for rotation with the axle shaft, a plurality of planet gears that are in meshing engagement with the sun gear, a non-rotating ring gear that is in meshing engagement with the planet gears, and a planetary spider that supports the plurality of planet gears. The planetary spider provides driving output to rotate a wheel component. The sun gear includes a sun gear body having a plurality of sun gear teeth in meshing engagement with the planet gears and a plurality of splines that are coupled with mating splines on the axle shaft. The plurality of splines are axially inboard of the plurality of sun gear teeth.