Current-Mode Motor Control for E-Bike Crankset Torque
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Solution Overview
Problem
Existing methods for current-mode control of pedaling assistance motors on electric power-assisted bicycles require additional sensors, are not universal, and complicate the assembly process.
Innovation Solution
An automatic method for current-mode control that uses a single force sensor to measure the torque resultant on the crankset, calculating the assistance torque and cyclist torque without needing specific configuration for each crankset/derailleur assembly, by injecting a continuous control current and applying proportionality coefficients based on the chainring teeth number.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two sensors are placed on the crankset (one on the axis to measure total force and one on the front derailleur to determine chainring), then the torque measurement and chainring identification are achieved, but the assembly is complicated and the device complexity increases
Solution Approach 1:
The patent extracts the chainring identification function from a separate sensor on the derailleur and integrates it into the existing force sensor measurements. By analyzing the force measurements already taken by the single force sensor on the crankset axis, the system determines chainring engagement without requiring an additional dedicated sensor, thus eliminating the need for the second sensor while maintaining measurement capability
Solution Approach 2:
The single force sensor on the crankset axis is made multi-functional: it simultaneously measures the total force for torque calculation and provides data for chainring identification. This universal sensor replaces the need for two separate sensors, simplifying the assembly while maintaining both measurement functions
2Adaptability or versatility
If a sensor is placed on the front derailleur to determine the chainring, then the chainring identification is achieved, but the solution is not universal as different derailleurs have different technologies
Solution Approach 1:
The patent segments the chainring identification problem from the derailleur-specific hardware and relocates it to the crankset-based force measurement system. By analyzing force patterns from the single force sensor on the crankset, the system identifies chainring engagement independently of derailleur technology, making the solution universal across different bicycle configurations
Solution Approach 2:
The force sensor on the crankset axis serves as an intermediary that indirectly determines chainring engagement through force measurement analysis rather than directly detecting chainring position. This intermediary approach bypasses the need for derailleur-specific sensors and works universally with different derailleur technologies
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 method simplifies the implementation, eliminates the need for additional sensors, and provides a universal solution, making it more economical, reliable, and easier to assemble compared to prior art.
Implementation Method 1
a sensor (16) measuring a value of a longitudinal resultant, on a predetermined axis, of a total torque (CTotal) exerted on a shaft (6) of the crankset (1) and resulting from a torque (CCyclist) exerted by the cyclist and from an assistance torque (Cmot) generated in the motor (12)
Implementation Method 2
a pedaling assistance motor (12) mounted on this frame (2)... injecting, at a given instant, a continuous control current, of known value, into the motor (12) to generate, in the motor (12), an assistance torque proportional to the injected current
Data Source
AI summary
An automatic method for controlling in current-mode a motor for assisting with pedaling on an electrically assisted pedal cycle equipped with a sensor that measures a resultant force on its pedal and gear mechanism is provided, including injecting a control current into the motor to generate an assistance torque and computing the value of the assistance torque; computing a value of the longitudinal resultant of the assistance torque by applying a second coefficient of proportionality to the torque value computed in the preceding step; measuring a value of the longitudinal resultant of the total torque; computing a value of the longitudinal resultant of the torque exerted by the cyclist; computing an average value of the torque exerted by the cyclist over a fraction of a crank rotation; computing the value of the assistance torque to be generated in the motor; and deducing the value of the current to be injected.