Asymmetric Bellows Boot for CV Joints
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Solution Overview
Problem
Conventional boots for constant-velocity universal joints face challenges in achieving compactness and weight reduction while maintaining durability and assembly workability, often requiring preliminary compression that increases assembly load and reduces longevity due to increased stress on bellows roots.
Innovation Solution
A boot design featuring a truncated cone-shaped bellows with specific root and crest configurations, including a thermoplastic polyester elastomer composition, that eliminates the need for preliminary compression, enhancing bendability and durability by optimizing membrane lengths and reducing contact-surface pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the outside diameter of bellows is diminished to make the boot more compact, then the weight and volume of the boot are reduced, but the membrane length of the crests is shortened requiring greater root depth which causes the roots to be bit between cup and shaft, reducing durability
Solution Approach 1:
The bellows is designed with asymmetric root depths where roots on the minor-diameter fastener side have greater depth than roots on the major-diameter fastener side. This asymmetric configuration allows the bellows to accommodate the different displacement magnitudes on each side while preventing roots from being pinched between the cup and shaft, thus maintaining durability while achieving compactness
Solution Approach 2:
Different regions of the bellows are given different root depths according to their specific functional requirements. The roots on the minor-diameter side are made deeper to handle larger displacement, while roots on the major-diameter side are shallower. This localized optimization allows the boot to be compact overall while maintaining durability in critical areas
2Ease of manufacture
If preliminary compression is applied to assemble the boot, then the boot can be fitted onto the constant-velocity universal joint, but the assembly load increases and stress on bellows roots increases, reducing longevity
Solution Approach 1:
The bellows is designed with pre-calculated root depths and membrane lengths that are optimized before assembly. The asymmetric root depth configuration is established during manufacturing, allowing the boot to be assembled without preliminary compression. This preliminary design optimization eliminates the need for compression during assembly, reducing assembly load and preserving boot longevity
3Adaptability or versatility
If the number of crests and roots is increased to improve bendability, then the boot can follow changing angles better, but the pitches between crests and roots narrow making blow molding difficult
Solution Approach 1:
Instead of uniformly increasing the number of crests and roots throughout the bellows, the invention applies additional crests and roots only in specific regions where bendability is most needed. This partial application maintains adequate pitches for blow molding in other regions while achieving improved bendability in critical areas
Data Source
AI summary
A boot for constant-velocity universal joint includes a major-diameter fastener, a minor-diameter fastener, and a bellows. The bellows includes a first root, a first crest, a second root, a second crest, a third root, a third crest, a fourth root, a fourth crest, a fifth root and a fifth crest. The first crest, the second crest, the third crest, the fourth crest and the fifth crest have a top, respectively, and the tops of the second crest, third crest and fourth crest are disposed on an outer peripheral side with respect to a line L1, which the tops of the first crest and fifth crest make there between, in a cross section involving the central axis of the bellows.