Tripod CV Joint Leg Shaft Geometry for Root Strength and Durability
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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 due to increased hardness and decreased toughness.
Innovation Solution
A tripod type constant velocity universal joint with a steel material having a carbon content of 0.23 to 0.44% and a hardened layer on the leg shafts, featuring regions with different radii of curvature to reduce stress concentration and enhance torsion strength at the root portion, along with optimized heat treatment processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the carbon content of steel material is increased to improve contact portion durability, then the durability at the contact portion is improved, but the fatigue strength and torsion strength at the root portion decrease
Solution Approach 1:
The invention 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 0.30-0.44% to ensure high durability under high surface pressure, while the root portion (intermediate portion) has a carbon content of 0.23-0.35% to maintain adequate fatigue and torsion strength. This spatial differentiation of material properties resolves the contradiction between contact durability and root strength.
Solution Approach 2:
The invention changes the carbon content parameter across different regions of the steel material. By controlling the carbon content to vary from 0.23-0.35% at the root portion to 0.30-0.44% at the contact portion, the material properties are optimized for each specific functional requirement, simultaneously achieving both contact durability and root strength.
2Reliability
If carburizing and quenching are performed to increase hardness, then the durability at the contact portion is improved, but the toughness decreases
Solution Approach 1:
The heat treatment process is applied locally to different regions. The contact portion undergoes carburizing and quenching to achieve high hardness and durability, while the root portion maintains lower carbon content and avoids aggressive heat treatment to preserve toughness. This localized application of heat treatment resolves the contradiction between durability and toughness.
Solution Approach 2:
The invention changes the physical parameters of the steel material through controlled heat treatment. The contact portion is subjected to carburizing and quenching to achieve high hardness, while the root portion is kept with lower carbon content and different heat treatment conditions to maintain toughness, thus resolving the contradiction between durability and toughness.
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, by reducing stress concentration and maintaining toughness, even under high torque loads.
Implementation Method 1
the tripod member is made of a steel material having a carbon content of 0.23 to 0.44%, and an effective hardened layer having a limit hardness of 600 Hv is provided
Implementation Method 2
the tripod type constant velocity universal joint of the double roller type is obtained, for example, by carburizing and quenching chromium-molybdenum steel having the amount of carbon of 0.34% and then performing high-temperature tempering
Implementation Method 3
carburizing and quenching chromium-molybdenum steel having the amount of carbon of 0.34% and then performing high-temperature tempering
Data Source
Figure 1~2
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Figure 5~6
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.