Convex Spoke Bed Rim Reduces Contact Stress
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Solution Overview
Problem
The geometry of the spoke bed in existing spoked wheels, with a flat or concave surface, leads to high contact stress and bending moments due to the angle of inclination of the spoke, resulting in galling, abrasion, reduced fatigue life, and decreased stiffness, making the wheel more prone to failure and a less responsive ride.
Innovation Solution
A convex outboard surface on the spoke bed with raised and relieved portions provides multiple contact points for the spoke nipple, reducing contact stress and bending moments, allowing for thinner spokes and a stronger rim while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat or concave spoke bed surface is used, then the manufacturing is simple, but the contact stress between spoke nipple and rim becomes excessively high
Solution Approach 1:
The patent applies curvature by transitioning from flat or concave spoke bed surfaces to a convex curved surface. This convex geometry creates a distributed contact area between the spoke nipple and rim, replacing the singular contact point of flat surfaces and the concentrated contact of concave surfaces. The curved surface profile is specifically designed to match the nipple geometry, spreading the load across multiple contact points and significantly reducing contact stress.
Solution Approach 2:
The patent implements local quality by creating a spoke bed with varying curvature - a convex portion at the contact region and a transition to a flatter or concave region elsewhere. This localized convex geometry is precisely where the nipple contacts the rim, providing high contact area exactly where needed, while other regions of the spoke bed maintain their traditional geometry for structural integrity and manufacturing compatibility.
2Device complexity
If the spoke bed has a flat or concave surface, then the structure is simple, but galling and abrasion occur between nipple and rim
Solution Approach 1:
The convex curved surface geometry fundamentally changes the interaction between nipple and rim by distributing contact across a curved interface rather than a flat or point contact. This curved contact geometry reduces relative sliding and micro-movement during nipple adjustment, thereby minimizing galling and abrasion. The smooth convex profile allows for more uniform load distribution and reduced friction during rotational adjustment.
3Device complexity
If the spoke contact point is offset from the spoke centerline, then the spoke bed geometry is simple, but bending moments are introduced reducing fatigue life
Solution Approach 1:
The patent employs asymmetric convex geometry on the spoke bed surface, where the curvature profile is specifically shaped to accommodate the angled spoke insertion while maintaining contact point alignment with the spoke centerline. The asymmetric convex portion creates a natural alignment feature that guides the nipple into proper positioning, ensuring the load path passes through the spoke centerline and eliminating bending moments that would otherwise occur with symmetric flat or concave surfaces.
4Reliability
If the spoke nipple is constricted to maintain radial alignment, then bending moments are reduced, but the spoke bends in a new region causing flex and fatigue
Solution Approach 1:
The convex spoke bed geometry provides self-aligning features that guide the spoke nipple into the correct radial position without requiring external constriction or complex positioning mechanisms. The curved surface profile naturally directs the nipple during installation and adjustment, ensuring proper alignment is achieved through the geometry itself rather than through mechanical constraints that would create bending in other spoke regions.
Data Source
AI summary
An improved vehicle wheel, including an outer rim, a central hub with a central axle and an outer flange and a plurality of spokes extending between the rim and hub. The spokes have a first portion connected to the rim and a second portion opposed to the first portion and connected to said hub. The outer rim includes a spoke bed wall with a spoke hole therethrough for connection with the first end of the spoke. The spoke bed wall has a radially outboard surface, which is a convex outboard surface including a radially outboard apex and a radially inboard portion relative to the apex and adjacent the apex.