E-Bike Motor Unit Force Sensing for Precise Torque Calculation
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Solution Overview
Problem
Existing external force measurement systems for bicycles lack precision and durability, particularly in measuring forces applied to spindles, and are prone to environmental influences and drift over time.
Innovation Solution
An external force measurement unit comprising a load cell with radial flaps and strain gauges, an evaluation unit for resistance measurement, and additional features like a freewheel and angular encoder, which improves force calculation and position recognition, and includes a motor housing for protection and integration with the bicycle frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauges are arranged on flaps to measure external force, then measurement precision is improved, but device complexity increases due to multiple components (load cell, support ring, flaps, strain gauges, evaluation unit)
Solution Approach 1:
The measurement unit is segmented into distinct functional components: load cell with support ring, flaps with strain gauges, and evaluation unit. This segmentation allows each component to perform its specific function optimally while enabling independent calibration and replacement, resolving the contradiction between precision and complexity.
Solution Approach 2:
The flaps act as intermediary elements that transmit external force from the spindle to the strain gauges. This intermediary mechanism enables precise force measurement while isolating the strain gauges from direct contact with the spindle, reducing complexity in force transmission.
2Measurement precision
If offset determination for spindle weight is implemented, then measurement precision is improved, but loss of time increases due to additional calibration steps
Solution Approach 1:
The offset caused by spindle weight is determined during preliminary calibration before actual measurements. This preliminary action establishes a baseline that eliminates the need for continuous compensation during operation, improving measurement precision while minimizing time loss to a single calibration event.
Solution Approach 2:
The evaluation unit automatically performs offset determination and compensation without requiring manual intervention. The system self-calibrates by measuring the offset when no external force is applied and automatically compensates for it during subsequent measurements, improving precision without adding operational time.
3Measurement precision
If lever arm position determination is included, then measurement precision is improved, but device complexity increases due to additional sensors and calculations
Solution Approach 1:
The evaluation unit performs multiple functions: it processes strain gauge signals, determines offset compensation, calculates lever arm position, and computes external force. This multi-functionality consolidates what could be separate complex subsystems into a single integrated unit, improving precision without proportionally increasing overall system complexity.
Solution Approach 2:
The system replaces mechanical lever arm position sensors with computational geometry methods. The evaluation unit calculates lever arm position based on coordinates of the pedal crank and spindle, eliminating the need for additional mechanical position sensors and reducing device complexity while maintaining measurement precision.
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 solution provides a precise, durable, and cost-effective method for measuring external forces on bicycles, enhancing the accuracy of torque calculation and reducing environmental impact, while improving the overall quality and reliability of the measurement system.
Implementation Method 1
a first strain gauge which is arranged on the first flap and a second strain gauge, which is arranged on the second flap, wherein depending on a change of length of the first flap or the second flap due to a material expand the first strain gauges and/or the second strain gauge is adapted to change their respective resistance
Data Source
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AI summary
The invention relates to a motor unit for an electrically assisted bicycle, the motor unit having only one freewheeling device, and to an electrically assisted bicycle.