Bicycle Crank Arm Torque Transmission Design
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Solution Overview
Problem
Existing crank arm and chainring carrier assemblies face challenges in providing a quick, simple, and reliable connection that effectively transmits torque for accurate power measurement, especially when integrated with power meter elements.
Innovation Solution
A crank arm and chainring carrier assembly featuring a torque-transmitting coupling with a clearance between pairing features, utilizing a planar seat on the crank arm and angled sections on the chainring carrier holes to align and connect fasteners, ensuring uniform load distribution and preventing redundant torque transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a press fit connection with splined interface is used to attach the chainring carrier to the crank arm, then the connection provides torque transmission capability, but the installation becomes complex and torque measurement accuracy is compromised due to redundant load transfer paths
Solution Approach 1:
The connection interface is segmented into two distinct functional zones: pairing features for positioning and clearance features for torque transmission. This segmentation allows each feature to perform its specific function optimally without interference from the other, simplifying the overall connection design while maintaining torque transmission reliability.
Solution Approach 2:
The torque transmission function is extracted from the pairing features and assigned to a dedicated clearance-based coupling mechanism. This extraction eliminates redundant load transfer paths through the pairing features, ensuring that torque is transmitted only through the intended clearance coupling, thereby improving measurement accuracy while maintaining connection reliability.
2Manufacturing precision
If pairing features are designed to provide precise positioning, then the chainring carrier alignment is improved, but torque transfer through these features creates redundant load paths that affect power measurement accuracy
Solution Approach 1:
The torque transmission function is extracted from the pairing features and assigned to a dedicated clearance-based coupling mechanism. This extraction eliminates redundant load transfer paths through the pairing features, ensuring that torque is transmitted only through the intended clearance coupling, thereby improving measurement accuracy while maintaining connection reliability.
Solution Approach 2:
The clearance between pairing features acts as an intermediary element that allows the chainring carrier to be positioned precisely while preventing torque transfer through the pairing features themselves. This intermediary clearance ensures that torque measurement is not affected by redundant load paths, maintaining measurement precision.
3Reliability
If the chainring carrier is securely attached to the crank arm, then the connection reliability is improved, but the torque transmission path becomes complex and power meter accuracy is compromised
Solution Approach 1:
The connection interface is segmented into two distinct functional zones: pairing features for positioning and clearance features for torque transmission. This segmentation allows each feature to perform its specific function optimally without interference from the other, simplifying the overall connection design while maintaining torque transmission reliability.
Solution Approach 2:
The torque transmission function is extracted from the pairing features and assigned to a dedicated clearance-based coupling mechanism. This extraction eliminates redundant load transfer paths through the pairing features, ensuring that torque is transmitted only through the intended clearance coupling, thereby improving measurement accuracy while maintaining connection reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enables a reliable and accurate torque transmission, maintaining clearance between pairing features to prevent 'clocking' and ensure precise power measurement, while allowing for various chainring patterns and power meter integration without stringent dimensional tolerances.
Implementation Method 1
The torque-transmitting coupling may provide a substantially uniform load introduction between the chainring carrier and the crank arm
Implementation Method 2
A clearance is defined between the first and second pairing features when the first and second pairing features are paired. The clearance may substantially inhibit torque transfer between the first and second pairing features
Implementation Method 3
at least two of the plurality of fasteners having an alignment feature formed thereon to cooperate with the corresponding angled section of the chainring carrier holes to align and connect the chainring carrier on the crank arm
Implementation Method 4
The assembly may include a planar seat on the crank arm. The chainring carrier may be shaped and sized to abut the seat
Data Source
AI summary
A bicycle crank arm and chainring carrier assembly. The assembly includes a crank arm. A chainring carrier is sized and shaped to connect to the crank arm. A first pairing feature is formed on one of the crank arm and the chainring carrier and a second pairing feature is formed on the other of the crank arm and the chainring carrier to position the chainring carrier on the crank arm. A clearance is defined between the first and second pairing features when the first and second pairing features are paired. A torque-transmitting coupling between the crank arm and the chainring carrier is configured to transmit substantially all of the torque applied to the chainring carrier from the crank arm.