Bicycle Sprocket Assembly Non-Threaded Fastener Weight Reduction
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Solution Overview
Problem
Conventional bicycle front sprocket assemblies attached with threaded fasteners result in a heavier design due to the bulkiness of fixing nuts and bolts, which increases the overall weight and complexity of the crank assembly.
Innovation Solution
A bicycle front sprocket assembly design that attaches at least one sprocket to the crank arm using non-threaded fasteners, such as pins or rivets, and incorporates a sprocket carrier with a torque transmitting profile and axial protuberances to secure the sprockets, reducing weight and simplifying manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If threaded fasteners (fixing nuts and bolts) are used to attach sprockets to the crank arm, then the attachment strength and reliability are improved, but the weight and device complexity increase due to the bulkiness of the fasteners
Solution Approach 1:
The patent removes the threaded fasteners (nuts and bolts) from the crank assembly by integrating the sprocket attachment function directly into the crank arm structure. The sprocket is secured through interference fit and deformation of the crank arm's protrusions, eliminating the need for separate fastening components and thereby reducing weight while maintaining attachment strength.
Solution Approach 2:
The patent combines the sprocket mounting function with the crank arm structure itself. The crank arm includes integrated protrusions that engage with corresponding recesses in the sprocket, merging the fastening function into the structural component. This integration eliminates separate fasteners and reduces overall assembly complexity and weight.
2Reliability
If threaded fasteners (fixing nuts and bolts) are used to attach sprockets to the crank arm, then the attachment reliability is improved, but the device complexity increases due to multiple fastening components
Solution Approach 1:
The patent combines the sprocket mounting function with the crank arm structure itself. The crank arm includes integrated protrusions that engage with corresponding recesses in the sprocket, merging the fastening function into the structural component. This integration eliminates separate fasteners and reduces overall assembly complexity and weight.
Solution Approach 2:
The patent removes the threaded fasteners (nuts and bolts) from the crank assembly by integrating the sprocket attachment function directly into the crank arm structure. The sprocket is secured through interference fit and deformation of the crank arm's protrusions, eliminating the need for separate fastening components and thereby reducing weight while maintaining attachment strength.
3Reliability
If threaded fasteners are used to attach sprockets, then the attachment security is improved, but the manufacturing complexity and time increase
Solution Approach 1:
The crank arm protrusions are pre-formed with the appropriate geometry for interference fit engagement during the crank arm manufacturing process. This preliminary preparation allows for quick assembly of the sprocket without requiring separate fastening operations, thereby simplifying manufacturing while ensuring secure attachment through the interference fit mechanism.
Data Source
AI summary
A bicycle front sprocket assembly is basically provided with a first sprocket, a second sprocket, a sprocket carrier and a chain guiding portion. The first sprocket includes a first sprocket body and a plurality of first sprocket teeth disposed on a first outer periphery of the first sprocket body, The second sprocket includes a second sprocket body and a plurality of second sprocket teeth. The second sprocket teeth are disposed on a second outer periphery of the second sprocket body. The sprocket carrier includes a torque transmitting profile and a sprocket mounting portion. The chain guiding portion is positioned between the first and second sprockets in an axial direction parallel to a rotational center axis of the bicycle front sprocket assembly. At least one of the first and second sprockets is mounted to the sprocket mounting portion of the sprocket carrier by a non-threaded fastener.