Offset Bicycle Sprocket Structure for Chain Skew Stability

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Solution Overview

Problem

Bicycle chain drives face challenges with increased chain skew due to multiple pinion arrangements, leading to sprocket instability and potential buckling under high chain tensile forces, especially with increased numbers of pinions and varying sprocket sizes.

Innovation Solution

A single sprocket design with an offset tooth center plane and a connecting region formed by arms that extend radially between the hub and tooth regions, providing increased rigidity and stability while maintaining a lightweight structure, and featuring alternating thick and thin teeth for improved chain guidance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple pinion arrangements are used to spread available gears, then gear range is improved, but chain skew increases leading to sprocket instability and buckling risk

Engineering Contradiction:

Improvegear rangeVSAvoidsprocket stability

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The patent introduces axial offset between the tooth center plane and hub center plane, adding a dimensional parameter to the sprocket design. This axial displacement allows the chain line to be adjusted independently from the hub mounting position, compensating for chain skew caused by multiple pinion arrangements while maintaining sprocket stability

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The connecting region is designed with non-uniform cross-sectional properties, being thicker in the axial direction at critical locations. This local reinforcement provides additional rigidity where chain tensile forces and skew create maximum stress, preventing buckling while keeping other areas lightweight

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If large pinions are arranged axially inwards to increase gear spread, then gear range is improved, but chain skew and chain tensile forces increase causing sprocket buckling

Engineering Contradiction:

Improvegear spreadVSAvoidsprocket resistance to buckling

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

By introducing axial offset between tooth and hub center planes, the patent creates an additional degree of freedom in positioning the chain line. This allows compensation for the chain skew generated by inwards-arranged large pinions, reducing the lateral component of chain tensile forces that cause buckling

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The connecting region features localized axial thickening that provides targeted reinforcement against buckling forces. This local quality enhancement strengthens the sprocket precisely where the combination of chain skew and high tensile forces from inwards-arranged pinions creates maximum stress concentration

Inventive Principle:

Principle #3Local quality

3Stability of the object's composition

If small front sprockets are used to improve stability, then sprocket stability is improved, but chain tensile forces increase due to changed transmission ratio

Engineering Contradiction:

Improvesprocket stabilityVSAvoidchain tensile forces

Core Design Contradiction:

Stability of the object's compositionVSForce

Solution Approach 1:

The connecting region is designed with increased axial thickness at critical stress points, providing local reinforcement that enables the use of smaller sprocket diameters without compromising stability. This local strengthening allows the reduced moment arm to be compensated by enhanced structural rigidity where forces are transmitted

Inventive Principle:

Principle #3Local quality

4Stability of the object's composition

If connecting region is reinforced axially to increase rigidity, then sprocket stability is improved, but weight increases

Engineering Contradiction:

Improvesprocket rigidityVSAvoidsprocket weight

Core Design Contradiction:

Stability of the object's compositionVSWeight of moving object

Solution Approach 1:

Instead of uniform reinforcement, the connecting region features localized axial thickening only where structurally necessary to resist chain-induced stresses. This selective reinforcement provides the required rigidity and buckling resistance while minimizing material usage and overall weight

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The connecting region is segmented into zones of different thickness, with reinforcement concentrated in areas experiencing highest stress from chain skew and tensile forces. This segmentation allows optimal distribution of material, providing rigidity where needed while keeping weight low in less critical areas

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11378171B2Single sprocket

Publication Date: 2022.07.05 SRAM

AI summary

A single sprocket for mounting on a pedal crank of a bicycle is provided. The sprocket h is mounted rotatably about an axis of rotation of a bicycle, and for engaging in a bicycle chain with chain inner link plate pairs and chain outer link plate pairs. The sprocket includes an axial outer side, an axial inner side, a hub region, a tooth region and a connecting region. A tooth center plane of the sprocket is offset inwards in the axial direction with respect to a hub center plane.