Composite Bicycle Crank Arm Reducing Weight While Maintaining Strength
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Solution Overview
Problem
Bicycle crank arms require a balance between high strength, rigidity, and lightweight materials to prevent damage and deformation while minimizing weight, which existing solid metal and composite materials have not adequately addressed.
Innovation Solution
A composite bicycle crank assembly featuring a hollow pipe-shaped crank axle made of chrome-molybdenum steel and crank arms constructed from stamped or pressed metal sheets with integrated fiber-reinforced resin materials, combined with adhesive and spline connections for enhanced strength and rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid metal crank arms are used, then strength and rigidity are improved, but weight increases
Solution Approach 1:
The crank arm is constructed as a composite structure combining a metal substrate (providing strength and rigidity) with a plastic material layer (reducing weight). This composite approach allows the crank arm to maintain the necessary mechanical properties while significantly reducing overall weight compared to solid metal construction.
Solution Approach 2:
The plastic material is selectively applied to specific regions of the crank arm where full metal construction is not necessary. This localized application optimizes the weight-strength ratio by providing metal reinforcement only where structural demands require it, while using lighter plastic material in less critical areas.
2Weight of moving object
If hollow crank arms with recesses are used, then weight is reduced, but strength and rigidity may be compromised
Solution Approach 1:
The hollow crank arm structure is reinforced with a plastic material layer applied to the internal surfaces of the hollow sections. This composite reinforcement compensates for the potential strength loss from hollow construction while maintaining the weight reduction benefits, creating a optimized weight-strength balance.
3Weight of moving object
If fiber reinforced resin material is used, then weight is reduced, but manufacturing complexity increases
Solution Approach 1:
The plastic material layer is applied in a molten or semi-molten state and then cooled to solidify, forming an integrated composite structure. This parameter change from liquid to solid state allows the material to conform to complex crank arm geometries and hollow sections, achieving weight reduction without proportionally increasing manufacturing complexity.
Data Source
AI summary
A bicycle crank assembly is provided that basically provided with a crank arm that includes a first outer shell, a second outer shell, a first axle supporting member and a second axle supporting member. The first outer shell has a first elongated portion with a first axle attachment end. The second outer shell has a second elongated portion with a second axle attachment end. The first and second outer shells are adhesively attached together to form an interior cavity therebetween. The first axle supporting member is disposed at the first axle attachment end of the first outer shell. The first axle supporting member has a first bore with a first splined inner surface that is at least partially disposed in the interior cavity between the first and second outer shells. The second axle supporting member is disposed at the second axle attachment end of the second outer shell. The second axle supporting member has a second bore with a second splined inner surface that aligns with the first splined inner surface of the first bore and that is at least partially disposed in the interior cavity between the first and second outer shells.