Double-Roller Tripod CV Joint Geometry for Root 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 torque loads.
Innovation Solution
A tripod type constant velocity universal joint with a carbon content of 0.23% to 0.44% in the tripod member, featuring a hardened layer formed by carburizing, hardening, and tempering, and specific geometric configurations such as R/PCD≥0.0850 and t/PCD≥0.145, which enhance the strength and durability of the root portion of the leg shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the carbon content of the tripod member is increased to improve contact portion durability, then the surface hardness and wear resistance improve, but the toughness and fatigue strength of the root portion deteriorate
Solution Approach 1:
The patent applies different carbon contents to different regions of the tripod member. The contact portion (outer peripheral surface of leg shaft) has a carbon content of 0.23% to 0.44% to achieve high surface hardness and wear resistance, while the root portion maintains lower carbon content to preserve toughness and fatigue strength. This spatial 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 pressure resistance, then the contact portion durability improves, but the torsion strength of the root portion decreases
Solution Approach 1:
The hardened layer is formed only on the outer peripheral surface of the leg shaft where contact with the inner ring occurs, not on the root portion. This localized hardening provides wear resistance at the contact surface while leaving the root portion with adequate toughness to withstand torsional loads.
3Strength
If the radius of curvature at the intermediate portion is increased to improve root portion strength, then the torsion strength improves, but the compactness of the design decreases
Solution Approach 1:
The patent specifies a radius of curvature R at the intermediate portion satisfying R/PCD ≥ 0.0850, where PCD is the pitch circle diameter of roller guide surfaces. This parameter optimization achieves adequate root portion strength while maintaining reasonable design compactness.
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 solution improves the durability and torsion strength of the leg shaft, particularly at the root portion, while maintaining adequate toughness and allowing for design flexibility.
Implementation Method 1
a hardened layer is formed by carburizing, hardening, and tempering
Implementation Method 2
a hardened layer is formed by carburizing, hardening, and tempering
Implementation Method 3
a hardened layer is formed by carburizing, hardening, and tempering
Data Source
AI summary
In a tripod type constant velocity universal joint 1 of a double roller type, R/PCD≥0.0850 and t/PCD≥0.145, where PCD is a pitch circle diameter of a roller guide surface 6 of an outer joint member 2. R is a radius of curvature at an intermediate portion between a body portion 31 and a leg shaft 32 of a tripod member 3, and t is a minimum distance from a large-diameter portion 34a of a spline 34 of the tripod member 3 to an intermediate portion 33.