Bicycle Crank Arm Assembly Sprocket Twisting Prevention
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Solution Overview
Problem
Conventional bicycle crank arm assemblies experience significant twisting deformations in the front sprocket due to pedaling stresses, leading to reduced motion transmission efficiency, especially in light material sprockets.
Innovation Solution
The design incorporates additional crank arm elements that contact the front sprocket on both sides, extending along non-radial and circumferential directions, to effectively block twisting deformations and provide stable contact, allowing for different sprocket diameters and easier maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the coupling arms and coupling elements are made with very low thickness to reduce overall weight, then the weight of the assembly is reduced, but the front sprocket experiences increased twisting deformation
Solution Approach 1:
The patent introduces a new spatial dimension for contact by extending crank arm elements in the circumferential direction around the rotation axis. This creates contact surfaces that wrap around the front sprocket, blocking twisting deformation through a dimensional approach rather than simply increasing thickness in the radial direction.
Solution Approach 2:
The patent employs composite materials, specifically carbon fibre reinforced plastic (CFRP), to manufacture the crank arm. This allows the coupling arms to maintain very low thickness for weight reduction while the composite material provides sufficient structural strength and rigidity to prevent excessive sprocket deformation.
2Weight of moving object
If light material front sprockets are used to reduce weight, then the weight of the assembly is reduced, but the twisting deformation is accentuated
Solution Approach 1:
The patent implements preliminary anti-action by positioning crank arm elements that extend in non-radial directions to preemptively block twisting deformation before it can occur during pedalling. The contact surfaces are strategically placed to counteract the twisting forces that light material sprockets are prone to experience.
3Stability of the object's composition
If the crank arm elements extend along non-radial directions to block twisting deformation, then the stability of the front sprocket is improved, but the device complexity increases
Solution Approach 1:
The patent merges multiple functions into the crank arm elements: they provide both the primary coupling function and the twisting prevention function through their circumferential extension. This integration avoids adding separate components, thereby reducing overall device complexity while achieving enhanced stability.
4Adaptability or versatility
If multiple crank arm designs are created for different sprocket diameters, then the adaptability to different sprocket sizes is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent achieves universality by designing a single crank arm configuration with circumferentially extending elements that can accommodate front sprockets of various diameters. The contact surfaces adapt to different sprocket sizes without requiring different crank arm designs, simplifying manufacturing and inventory management.
Data Source
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AI summary
A right crank arm assembly (1) for a bicycle, comprises a right crank arm (5) and at least one front sprocket (10) coupled with the crank arm at at least one coupling portion (44) of the crank arm. The front sprocket (10) has an inner side adapted, in use, to face towards the frame of the bicycle and an outer side opposite the inner side. The assembly (1) comprises at least one first crank arm element (30) which acts in contact with the front sprocket (10) on one of said sides and at least one second crank arm element (35) which acts in contact with the front sprocket (10) on the other of said sides. The contact action of the crank arm elements on the two opposite sides of the front sprocket prevents the twisting deformation of the front sprocket during pedalling. Such a deformation would cause a reduction in the transmission efficiency of the right crank arm assembly.