Torque Sensor Deformable Structure for Compact E-Bike Transmissions
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Solution Overview
Problem
In applications like electrically-assisted bicycle transmissions, the limited space constrains the design of test bodies used to determine torque between rotating members, requiring a compact and mechanically resistant system that accurately measures angular deflection while resisting high torques, such as 250 Nm, without excessive deformation.
Innovation Solution
A compact torque determination system featuring a test body with an inner and outer bushing connected by a deformable structure comprising angularly distributed branches with specific geometric sections that allow for angular deflection, enabling accurate torque measurement while maintaining mechanical strength and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the test body is made compact to fit limited space in bicycle transmissions, then the radial dimensions are reduced, but the deformable structure becomes more constrained and difficult to design
Solution Approach 1:
The deformable structure is segmented into multiple branches (typically 3-6 branches) angularly distributed around the axis of rotation. Each branch is a separate elastic element that can deform independently, allowing the structure to achieve the required angular deflection while maintaining compact radial dimensions. This segmentation enables the test body to fit within limited space while preserving mechanical functionality.
Solution Approach 2:
The branches are designed with an inclined orientation relative to the radial direction, forming an angle between 10° and 45° with the radial line. This angular inclination allows the branches to extend further in the axial direction rather than radially, effectively utilizing the third dimension (axial space) to achieve the required deflection length without increasing radial footprint. This dimensional transition enables compact radial dimensions while maintaining sufficient branch length for reliable torque transmission and measurable angular deflection.
2Measurement precision
If the deformable structure is made more flexible to increase angular deflection for accurate measurement, then measurement precision improves, but mechanical strength decreases and reliability suffers
Solution Approach 1:
The deformable structure consists of multiple discrete branches distributed angularly around the axis. This segmentation allows the total flexibility requirement to be distributed across multiple elements, where each branch provides a portion of the total angular deflection. The combined effect of multiple branches achieves the required measurement precision while each individual branch maintains sufficient mechanical strength.
Solution Approach 2:
The branches exhibit non-uniform cross-sectional properties along their length, with the cross-section varying to optimize the balance between flexibility and strength. The branches are designed with specific geometric characteristics including inclined orientation and varying thickness, creating local quality variations that maximize angular deflection in the measurement region while maintaining structural integrity in load-bearing regions.
3Measurement precision
If the branch length is increased to reduce stiffness and maximize angular deflection, then measurement sensitivity improves, but the radial space requirement increases
Solution Approach 1:
The branches are oriented at an angle between 10° and 45° relative to the radial direction, causing them to extend primarily in the axial dimension rather than radially. This angular orientation allows the branches to achieve the necessary length for reduced stiffness and increased angular deflection while confining their radial footprint to a minimum. The effective lever arm for torque transmission is increased through axial extension rather than radial expansion.
Solution Approach 2:
Multiple branches are distributed angularly around the axis, allowing the system to achieve the required total flexibility through the combined effect of several shorter elements rather than relying on a single long radial element. This segmentation enables the use of shorter individual branches that fit within radial constraints while the collective arrangement provides sufficient total deflection for sensitive torque measurement.
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 system effectively determines torque applied between rotating members in a compact and reliable manner, ensuring minimal deformation and mechanical strength, even under high torque conditions, by utilizing an S-shaped deformable structure with inclined branches that maximize length and reduce stiffness, thus accommodating the spatial constraints of bicycle transmissions.
Implementation Method 1
a ring (13, 14) carried by each of the bushings (5, 6) and comprising respectively an inner magnetic track (13a) and an outer magnetic track (14a) able to emit a periodic magnetic signal representative of the rotational displacement of the corresponding ring (13, 14)
Implementation Method 2
a sensor comprising a first (15) - respectively a second (16) - pattern of sensing elements arranged at a reading distance from the inner track (13a) - respectively the outer track (14a) - to form a signal representative of the angular position of the corresponding ring (13, 14)
Implementation Method 3
said bushings being connected concentrically around the axis by a deformable structure which is arranged to transmit the torque between the members while allowing an angular deflection between said bushings as a function of the torque applied between the members
Data Source
AI summary
A system for determining a torque applied between two rotating members, including a test body having an inner bushing and an outer bushing concentrically connected by a deformable structure, and a device for determining an angle between the bushings which is a function of the applied torque, the deformable structure comprising a set of branches angularly distributed between the bushings, each of said branches extending in a direction between an inner end and an outer end, said direction forming an angle with the diametral direction passing through said inner end, each of the branches having a foot section extending from the inner end to said direction and a head section extending from the direction to the outer end, the sections forming a convex bend for the foot section and a concave bend for the head section.