Tripod CV Joint Leg Shaft Geometry for Low Vibration at Large Angles
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Solution Overview
Problem
Existing tripod type constant velocity universal joints experience increased vibration and slide resistance when the operating angle exceeds a predetermined limit, particularly under high torque conditions or with prolonged use.
Innovation Solution
The tripod type constant velocity universal joint design includes an outer joint member with track grooves, a tripod member with leg shafts, and inner rings that allow rollers to move axially, featuring an elliptical shape and a hardened layer on the leg shafts to reduce vibration and improve durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the curvature radius r and minor axis/major axis ratio b/a are determined to minimize contact surface pressure, then induced thrust and slide resistance are reduced up to a predetermined operating angle, but when the operating angle exceeds this limit, the roller unit tilts causing increased induced slide and slide resistance
Solution Approach 1:
The patent modifies the geometric parameters of the leg shaft, specifically changing the outer peripheral surface from a straight shape to an inclined shape in the axial direction. This parameter change allows the contact point between the leg shaft and inner ring to move along the inclined surface, preventing roller unit tilt even at large operating angles and maintaining low induced thrust and slide resistance throughout the operating range.
2Ease of operation
If the outer peripheral surface of the leg shaft is formed in a straight shape parallel to the axial line, then the roller unit can swing with respect to the leg shaft, but the roller unit tilts when the operating angle exceeds a predetermined limit
Solution Approach 1:
The patent introduces asymmetry by forming the outer peripheral surface of the leg shaft with an inclination rather than a straight shape parallel to the axial line. This asymmetric inclined surface guides the contact point movement in a specific direction, preventing the roller unit from tilting while maintaining its swing capability, thus resolving the contradiction between ease of operation and force reduction.
3Stress or pressure
If the contact area between the leg shaft and inner ring is minimized, then surface pressure is reduced, but the leg shaft durability decreases under high torque conditions
Solution Approach 1:
The patent applies local quality by forming a hardened layer specifically on the outer peripheral surface of the leg shaft where contact with the inner ring occurs. This localized hardening increases surface durability and resistance to wear under high torque conditions without changing the overall contact area or pressure distribution, thus resolving the contradiction between reduced surface pressure and enhanced durability.
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 reduces vibration and maintains low slide resistance over a larger operating angle range, even with prolonged use and high torque, by minimizing contact area and enhancing the leg shaft's durability through a hardened layer.
Implementation Method 1
a plurality of needle rollers (13) which enable relative rotation between the inner ring (12) and the leg shaft (32)
Implementation Method 2
an effective hardened layer depth, with limit hardness of 600 HV, of the hardened layer (16) is equal to or more than a shear stress depth
Data Source
AI summary
In a state where a joint forms a normal operating angle and an axial line of an inner ring is not tilted with respect to an axial line of a leg shaft, when a curvature radius and a minor axis/major axis ratio at which a contact area between an inner ring inner peripheral surface and a leg shaft outer peripheral surface is minimized are set as respective reference values, the minor axis/major axis ratio is set to the reference value, and the curvature radius is set to be smaller than the reference value. In addition, a carbon content in a core portion of a tripod member is set to 0.23 to 0.44%, and a hardened layer is formed through carburizing and quenching on a surface of each leg shaft.