E-Bike Pedal Force Sensing With Axial Strain and Nested Torque Transfer

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Solution Overview

Problem

Existing pedal force detection mechanisms in electric-assisted bicycles fail to accurately and efficiently respond to variations in pedal force, leading to inconsistent supply of auxiliary power.

Innovation Solution

A pedal force detection mechanism comprising a torque-transmitting member, main thrust bearing, strain sensing assembly, and main drive gear, which includes a resilient ring-shaped base and strain gauge, allowing for precise detection and diversion of pedal force along the crankshaft's axial direction, with synchronized rotation and axial movement gaps to enhance sensitivity and range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a torque sensing assembly is disposed outside the bushing of the bearing to sense variations in torque, then the device complexity is reduced and ease of manufacture is improved, but the measurement precision and sensing range are insufficient leading to inaccurate pedal force detection

Engineering Contradiction:

Improvepedal force detection accuracyVSAvoiddetection mechanism structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The strain sensing assembly is nested within the torque-transmitting member, with the strain gauge embedded in the torque-transmitting member's wall. This nested configuration allows the detection mechanism to be integrated within the existing crankshaft assembly without adding external components, thereby improving measurement precision while avoiding increased device complexity

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The strain sensing assembly is merged with the torque-transmitting member by embedding the strain gauge directly into the torque-transmitting member's structure. This merging allows the detection function to be combined with the torque transmission function, improving pedal force detection accuracy without requiring separate detection components that would increase device complexity

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If the strain gauge is embedded in the torque-transmitting member with synchronized rotation, then the measurement precision and sensing range are improved, but the device complexity increases due to additional components and assembly requirements

Engineering Contradiction:

Improveauxiliary power supply consistencyVSAvoiddetection mechanism structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The torque-transmitting member serves multiple functions: it transmits torque from the pedal to the crankshaft and simultaneously houses the strain gauge for force detection. The bushing also serves dual purposes as both a bearing support and a mounting structure for the strain sensing assembly. This multi-functionality improves reliability by ensuring consistent auxiliary power supply while avoiding the need for additional dedicated detection components

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If axial-movement gaps and axial-strain gaps are introduced to enhance sensitivity, then the measurement precision is improved, but the device complexity increases due to precise positioning requirements

Engineering Contradiction:

Improvepedal force variation detectionVSAvoidgap dimension control

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

Axial-movement gaps and axial-strain gaps are intentionally designed into the assembly to provide predetermined clearance that accommodates thermal expansion, manufacturing tolerances, and assembly variations. These pre-built gaps ensure that the strain gauge maintains proper contact and alignment with the torque-transmitting member under varying operating conditions, thereby improving measurement precision without requiring extremely tight manufacturing tolerances

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 mechanism provides precise pedal force detection, enabling efficient and accurate supply of auxiliary power based on pedal force variations, with enhanced sensitivity and a larger sensing range compared to conventional systems.

Implementation Method 1

a strain sensing assembly having a strain gauge, a resilient ring-shaped base and a supporting annular base

Methodology Applied

Scientific EffectStrain gauge measurement: Deformation

Data Source

PatentUS12479533B2Pedal force detection mechanism for electric-assisted bicycle

Publication Date: 2025.11.25 MOTIVE POWER IND CO LTD

AI summary

A pedal force detection mechanism for an electric-assisted bicycle includes a torque-transmitting member, a main thrust bearing, a strain sensing assembly, and a main drive gear. The torque-transmitting member transmits and diverts a torque along a crankshaft's axial direction. The main thrust bearing abuts against the torque-transmitting member to transmit the diverted torque. The strain sensing assembly has a strain gauge, resilient ring-shaped base, and supporting annular base. The supporting annular base abuts against a shaft housing. An axial-strain gap is defined between the supporting annular base and the main thrust bearing. The resilient ring-shaped base is fitted between the main thrust bearing and the supporting annular base. A main gear and an internally-connected ring body of the main drive gear are integrally formed with each other. An axial-movement gap is defined between the torque-transmitting member and the internally-connected ring body.