Differential Ring Gear Weld Geometry for Fatigue Crack Resistance
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Solution Overview
Problem
Existing welded connections between differential crowns and housings in motor vehicle transmission differentials are prone to fatigue failure and cracking due to stress concentrations and notch effects at the weld bead, especially under axial forces generated by helical ring gear teeth.
Innovation Solution
The design features cutouts in the mass of the case and crown with an angle greater than 90° between the connecting surface and the tangent plane at the entrance, and a significant radius of curvature at the bottom of the cutouts to reduce stress concentrations and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional circular degassing cutouts are used in the case and crown, then gas evacuation during welding is improved, but stress concentrations and notch effects occur at the weld bead ends causing fatigue failure and cracking
Solution Approach 1:
The patent applies curvature by replacing the traditional circular cutout shape with an oval-shaped degassing form. This oval geometry features rounded entrances and a curved bottom with large radius of curvature, eliminating sharp angles and stress concentration points. The curved surfaces distribute stresses more uniformly throughout the structure, preventing fatigue failure and cracking while maintaining effective gas evacuation during the welding process.
2Reliability
If the degassing form angle is reduced to approximately 60° to improve gas evacuation, then welding quality improves, but crack risk increases due to sharp angles at the weld bead ends
Solution Approach 1:
The oval-shaped degassing form replaces sharp angular features with continuously curved surfaces. The rounded entrances and curved bottom eliminate the sharp 60° angles that cause stress concentration and crack initiation. The large radius of curvature at the bottom and smooth transitions throughout the oval geometry distribute stresses uniformly, preventing crack formation while maintaining the opening angle necessary for effective gas evacuation during welding.
3Strength
If the degassing form angle is increased to improve fatigue resistance, then stress concentration is reduced, but gas evacuation capability during welding is compromised
Solution Approach 1:
The oval geometry achieves an optimal balance between fatigue resistance and gas evacuation. The elongated oval shape provides sufficient opening angle and volume for effective gas escape during welding, while the continuously curved surfaces with large radius of curvature eliminate stress concentration points. This curved geometry distributes welding-induced stresses uniformly, maintaining high fatigue resistance without compromising weld quality.
4Ease of manufacture
If conventional cutout shapes are used for degassing, then manufacturing is simplified, but the connection is prone to fatigue failure under axial forces from helical ring gear teeth
Solution Approach 1:
The oval-shaped degassing form with its continuously curved surfaces and large radius of curvature at the bottom eliminates sharp angles that cause stress concentration and fatigue failure. While slightly more complex than simple circular cutouts, the oval geometry can be manufactured using standard machining or forming processes. The curved surfaces distribute axial forces from the helical ring gear teeth uniformly throughout the connection, significantly improving fatigue resistance and overall connection strength.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A welded connection between a differential ring gear (5) and the casing (4) of same, having a substantially cylindrical connecting surface (6) between an outer face of the casing and an inner face of the ring gear, in which there is provided a hollow degassing form (7) consisting of two opposing cutouts (7a) in the mass of the casing and that of the ring gear on either side of the connecting surface of same, characterised in that the cutouts (7a) have an angle (α) greater than 90° between the connecting surface (6) and the tangent plane at the entrance (7b) of the cutout, and a radius of curvature that is greater at the bottom of the cutout (7c) than in the transition areas between same and the entrance of the cutout.