Constant Velocity Universal Joint Shaft Surface Roughness Control
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Solution Overview
Problem
Existing constant velocity universal joints face challenges in simultaneously achieving compactification and sufficient abrasion suppression on the boot's inner surfaces, with existing solutions either inadequately addressing abrasion or compromising durability and sealing properties.
Innovation Solution
The implementation of a surface roughness control part on the shaft with specific roughness parameters (Rsk < 0, Rpk < 2 µm, and Ra < 4 µm) that contacts the boot's inner surfaces, enhancing durability and compactification by reducing abrasion, and optionally using a thermoplastic polyester elastomer boot with a bellows-like design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the diameter of the boot is increased to suppress abrasion on the inner surfaces, then abrasion resistance is improved, but the boot size increases and compactification is compromised
Solution Approach 1:
The invention applies local quality by creating a specific roughness profile only in the contact region between the shaft and boot inner surface. The surface roughness control part is localized to where the boot contacts the shaft during angular displacement, providing abrasion suppression precisely where needed without requiring the entire boot to be larger. This localized treatment allows the boot to maintain compact dimensions while achieving sufficient abrasion resistance at the critical contact interface.
2Volume of moving object
If the boot is compactified to reduce size, then volume is reduced, but abrasion suppression on inner surfaces becomes insufficient
Solution Approach 1:
The invention applies parameter changes by modifying the surface roughness parameters (Rsk, Rpk, Ra) of the shaft's outer peripheral surface. By controlling these specific roughness parameters within defined ranges, the invention creates optimal contact conditions between the shaft and boot inner surface. This parameter optimization provides sufficient abrasion suppression while allowing the boot to maintain a compact design, as the enhanced surface interaction compensates for the reduced boot dimensions.
3Reliability
If ingredients for suppressing abrasion are added to the boot material, then abrasion resistance is improved to some extent, but fatigue resistance and aging resistance decrease
Solution Approach 1:
The invention applies the intermediary principle by introducing a surface roughness control part on the shaft that acts as a mediator between the shaft and boot. Instead of modifying the boot material itself (which would compromise fatigue and aging resistance), the roughness control on the shaft surface provides abrasion suppression through optimized contact characteristics. This intermediary approach protects the boot material's inherent strength properties while still achieving abrasion resistance through controlled surface interaction.
4Reliability
If a discontinuous coating film is formed on the boot surfaces, then some abrasion suppression is achieved, but sufficient abrasion suppression and durability enhancement cannot be attained
Solution Approach 1:
The invention applies inversion by reversing the conventional approach: instead of coating the boot to suppress abrasion, the invention controls the surface roughness of the shaft. By inverting the treatment location from the boot (flexible component) to the shaft (rigid component), the invention achieves more effective and durable abrasion suppression. The roughness control on the shaft provides consistent contact characteristics that reliably protect the boot inner surface, offering superior abrasion resistance compared to discontinuous coating films on the boot itself.
Data Source
Figure 1
Figure 2~3
AI summary
Provided is a constant velocity universal joint in which a boot can be enhanced in durability and compactified, which are achieved by suppressing abrasion of the boot. In the constant velocity universal joint including: an outer joint member (1); an inner joint member (2); a torque transmitting member (3); a shaft (5); and a boot (6), surface roughness of an outer peripheral surface (5a) of the shaft (5) satisfies Rsk < 0, Rpk < 2 µm, and Ra < 4 µm.