Bicycle Bottom Bracket Force Sensor Isolating Parasitic Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bicycle power meters struggle to accurately measure effective pedalling output due to parasitic forces and variations in pedalling style, leading to inaccurate readings and market rejection.
Innovation Solution
A force sensor for the bicycle bottom bracket with a specifically designed deformation behavior, featuring a hollow cylindrical shape with three rings, including an outer ring for radial movement, an inner ring for fixation, and a central ring with strategically placed deformation sensors to measure shear and deflection, eliminating parasitic forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If deformation sensors are placed on conventional components (crank, spider, or axle), then the device complexity is reduced, but the measurement precision deteriorates due to parasitic forces and pedalling style variations
Solution Approach 1:
The patent introduces a bottom bracket as an intermediary component between the crankset and frame. This bottom bracket includes a deformation element with a specific geometry designed to isolate the measurement from parasitic forces. The deformation element acts as a mediator that only responds to torque-induced deformation, filtering out other forces such as bearing loads and pedalling style variations. This allows accurate power measurement without requiring complex sensor arrays on multiple components.
2Measurement precision
If strain gauges are placed on both cranks to measure force from each leg, then the measurement precision improves, but the device complexity and cost increase due to duplication of sensors and electronics
Solution Approach 1:
The patent merges the measurement function into a single bottom bracket unit that captures the combined output of both legs. The deformation element is positioned to measure the total torque generated by both cranks simultaneously. By combining the measurement at the bottom bracket rather than using separate sensors on each crank, the system achieves accurate bilateral leg measurement while eliminating the need for duplicate electronic components and complex calibration procedures.
Solution Approach 2:
The bottom bracket serves multiple functions: it acts as the structural connection between crankset and frame, provides bearing support, and simultaneously functions as the measurement platform. The deformation element within the bottom bracket universally captures the power output from both legs regardless of which leg is applying force, making the system adaptable to all pedalling styles without requiring additional sensors or configuration changes.
3Measurement precision
If pressure sensors are placed between the bearing and bicycle or blocks with strain gauges are used, then the device complexity is reduced, but the measurement precision deteriorates because parasitic forces are not discriminated
Solution Approach 1:
The patent applies local quality by designing the deformation element with a specific geometry optimized for torque measurement. The deformation element has a particular shape and material properties that make it selectively responsive only to torque-induced stresses while being insensitive to other forces. This localized optimization of the measurement component's properties allows it to filter out parasitic forces such as bearing loads and axial forces, providing accurate power measurement without complex signal processing.
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
The sensor provides accurate, real-time measurements of pedalling output, unaffected by parasitic forces, and is capable of detecting pedalling output at various speeds, ensuring precise data transmission for rider feedback or motor assistance.
Implementation Method 1
measuring the deformation of the bottom bracket due to the load applied to the crank axle
Data Source
AI summary
A force sensor is disclosed for the bottom bracket of a bicycle, designed as a hollow cylindrical piece divided into an outer ring with an indentation along the entire perimeter thereof to accommodate a mechanical stop, an inner ring and a central ring with at least four openings disposed around the perimeter and which are positioned such that they form four arms, two identical arms having a larger arc in the vertical axis and two identical arms having a smaller arc in the horizontal axis, with at least one sheer strain gauge placed on each arm having a smaller are and at least one bending strain gauge on each arm having a larger arc. This strain gauge arrangement allows the effective force to be measured by omitting parasitic forces, thereby obtaining precise information regarding the power exerted by a cyclist, which is useful for optimising motors in electric bikes.