Inductance Coil Torque Sensing for Electric Bicycles
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Solution Overview
Problem
There is a need for a simple, inexpensive, and robust method to measure torque and power input to the drive system of an electric-assist bicycle to effectively control the power output of the electric-assist motor.
Innovation Solution
A unitary system that includes non-rotating inductance coils and a conductive or magnetically permeable member, which generates electrical signals indicative of torque and rotational speed, combined by a circuit to produce a power input signal, allowing for precise control of the motor's power output based on rider input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional torque sensing methods are used, then torque measurement is achieved, but the system becomes complex, expensive, and less robust
Solution Approach 1:
The patent replaces traditional mechanical torque sensing mechanisms with a magnetic field-based inductance sensing system. The inductance coils detect changes in magnetic flux caused by the conductive member's position, eliminating the need for mechanical contacts or complex mechanical sensing elements while achieving accurate torque measurement through electrical signal detection.
Solution Approach 2:
The patent introduces a conductive or magnetically permeable member as an intermediary between the rider's torque input and the sensing system. This intermediary modulates the magnetic field from the inductance coils, translating mechanical torque into detectable electrical signals without requiring direct mechanical coupling between the torque source and sensor.
2Device complexity
If simple sensing methods are used, then device complexity is reduced, but measurement precision of torque and power deteriorates
Solution Approach 1:
The patent designs the inductance sensing system to perform multiple measurement functions simultaneously. The same inductance coils and conductive member configuration used for torque detection also enable measurement of rotational speed and direction, providing comprehensive power input data through a single integrated sensing mechanism rather than requiring separate systems for each parameter.
Solution Approach 2:
The patent employs a conductive or magnetically permeable member that interacts with the inductance coils to create a composite sensing system. The combination of the conductive member's magnetic properties and the inductance coils' electromagnetic field generates a synergistic effect that enhances measurement precision while maintaining system simplicity.
3Reliability
If mechanical torque sensors are used, then torque measurement is achieved, but the system becomes less robust and more expensive
Solution Approach 1:
The patent replaces mechanical torque sensors with an electromagnetic inductance-based sensing system that has no moving parts or mechanical contacts. This substitution eliminates wear, friction, and mechanical failure modes while reducing manufacturing complexity and cost, as the system uses standard electromagnetic components rather than precision mechanical assemblies.
Solution Approach 2:
The conductive member in the patent serves dual purposes: it is both a functional component of the drive system and the sensing element itself. The member's inherent magnetic properties enable it to interact with the inductance coils for torque detection without requiring separate sensing components, thereby simplifying manufacturing and improving 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 solution enables accurate and efficient control of the electric-assist motor's power output, enhancing the performance and efficiency of electric-assist bicycles by directly measuring rider input torque and speed.
Implementation Method 1
inductance coils are configured to generate a first electrical signal indicative of said amount of torque based on lateral distance between the rotatable member and the first inductance coils
Implementation Method 2
The conductive member is configured to move eccentrically relative to the inductance coils when the rotatable member rotates and to change the inductance of at least two of the inductance coils as the conductive member moves eccentrically relative to the inductance coils
Data Source
AI summary
A unitary system for an electric-assist bicycle generates signals indicative of power input to a drive system of the bicycle when a rider pedals the bicycle, considering torque applied by the rider, as well as the cadence or speed of the rider's pedaling. Direction of pedaling is also measured using the system. The system utilizes fixed, hard-wired, contactless electronics, namely first and second inductance coils that are non-equally-spaced circumferentially around a first axis, and which generate a first electrical signal indicative of torque based on lateral movement of a conductive or otherwise magnetically permeable rotatable member relative to the coils, and which generate second and third electrical signals indicative of pedaling cadence and direction based on eccentric relative rotational movement of the conductive or otherwise magnetically permeable rotatable member relative to the first and second inductance coils.