Double Roller Tripod CV Joint Root Geometry for Torsion Strength
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Solution Overview
Problem
The tripod type constant velocity universal joint of the double roller type faces durability issues at the contact portion due to high surface pressure, and the root portion of the leg shaft experiences reduced fatigue strength and torsion strength under repeated tensile loads.
Innovation Solution
A tripod type constant velocity universal joint design featuring a steel tripod member with a carbon content of 0.23 to 0.44%, a hardened layer on the leg shafts, and a unique curvature in the intermediate portion to reduce stress concentration, along with specific radius of curvature ratios and connection regions to enhance torsion strength and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the carbon content of the steel material is increased to improve contact portion durability, then the durability at the contact portion is improved, but the torsion strength at the root portion decreases
Solution Approach 1:
The invention applies different carbon content specifications to different regions of the tripod member. The leg shaft portion (contact portion) requires higher carbon content (0.23-0.44%) for durability, while the root portion maintains lower carbon content to preserve torsion strength and fatigue resistance. This regional differentiation of material properties resolves the contradiction between contact durability and root strength.
2Reliability
If a hardened layer is formed on the leg shaft to increase surface hardness, then the durability under high surface pressure is improved, but the fatigue strength at the root portion is reduced
Solution Approach 1:
The hardened layer is applied selectively only to the leg shaft outer peripheral surface where contact pressure occurs, with a controlled thickness of 0.1-0.5mm. The root portion remains unhardened to maintain its toughness and fatigue strength. This localized hardening approach resolves the contradiction between surface durability and root fatigue resistance.
3Strength
If the radius of curvature in the intermediate portion is increased to reduce stress concentration, then the torsion strength is improved, but the manufacturing complexity increases
Solution Approach 1:
The invention specifies a minimum radius of curvature R1 of 0.5mm in the intermediate portion between the leg shaft and body. This curved transition eliminates stress concentration points that would occur with sharp corners, thereby improving torsion strength. The curvature requirement is integrated into the basic geometric design rather than adding complex manufacturing steps, thus improving strength without proportionally increasing manufacturing complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design improves the durability and torsion strength of the root portion of the leg shaft, maintaining durability even with increased internal hardness and hardened layer depth, while reducing stress concentration and fatigue strength concerns.
Implementation Method 1
each of the leg shafts being provided with a hardened layer of a carburized layer on the surface of each of the leg shafts
Implementation Method 2
the amount of carbon in the steel material can be increased as compared with the related art, and thus, the durability of the leg shaft at the contact portion can be improved
Data Source
AI summary
In a tripod type constant velocity universal joint 1 of a double roller type, a carbon content in a core portion of a tripod member 3 is set to 0.23 to 0.44%, and a hardened layer 16 of a carburized layer is provided on the surface of a leg shaft 32. A first region P having a radius of curvature Ra in a cross section in a direction orthogonal to a joint axial direction including an axial line of the leg shaft 32 and a second region Q having a radius of curvature Rb in a cross section in the joint axial direction including the axial line of the leg shaft 32 are provided in an intermediate portion 33 provided between a body portion 31 of the tripod member 3 and the leg shaft 32. Ra>Rb is set.