Bottom Bracket Torque Sensor Layout for Compact E-Bike Drives

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Solution Overview

Problem

Existing electric mountain bikes face challenges with large drive unit diameters due to the need for a hollow torsion measuring shaft, leading to increased weight, complexity, and installation space conflicts, which affect handling and safety.

Innovation Solution

A compact electric bicycle drive unit is designed coaxially with the bottom bracket, incorporating a torque sensor in the axial region of the hollow output shaft to measure rider torque independently of motor torque, eliminating the need for a hollow torsion measuring shaft and reducing overall size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a hollow torsion measuring shaft is used to measure rider torque, then torque measurement capability is achieved, but drive unit diameter and weight increase

Engineering Contradiction:

Improvetorque measurement capabilityVSAvoiddrive unit diameter

Core Design Contradiction:

Measurement precisionVSLength of moving object

Solution Approach 1:

The patent combines the torque measurement function with the existing hollow output shaft of the drive unit. Instead of adding a separate hollow torsion measuring shaft, the output shaft itself is utilized for torque measurement, eliminating the need for additional components and reducing overall diameter.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The hollow output shaft serves multiple functions: it transmits motor torque to the drivetrain and simultaneously serves as the torsion measuring shaft for detecting rider torque. This multi-functionality eliminates the need for dedicated measurement components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If a hollow torsion measuring shaft is added to measure rider torque, then torque measurement is enabled, but device complexity and installation space requirements increase

Engineering Contradiction:

Improverider torque measurementVSAvoiddrive unit structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges the torque measurement function into the existing output shaft structure, eliminating the need for separate measurement components and reducing structural complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent extracts the torque measurement function from a potential separate component and integrates it into the existing output shaft, removing the need for additional hollow torsion measuring shafts and associated structures.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If a hollow torsion measuring shaft is used, then rider torque can be measured, but weight and cost increase

Engineering Contradiction:

Improvetorque measurement capabilityVSAvoiddrive unit weight

Core Design Contradiction:

Measurement precisionVSWeight of moving object

Solution Approach 1:

The patent combines the torque measurement function with the existing hollow output shaft, eliminating the need for additional weighty components like separate hollow torsion measuring shafts.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The output shaft performs both torque transmission and torque measurement functions, eliminating the need for dedicated measurement components that would add weight.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 design allows for a more compact, lightweight, and cost-effective drive unit that optimally integrates into the bicycle frame, improving handling and safety by lowering the center of gravity and reducing installation space conflicts.

Implementation Method 1

a torque sensor device ST for measuring a rider total torque TR

Methodology Applied

Scientific EffectStrain gauge measurement: Piezoresistive Effect

Implementation Method 2

The axial region PA is defined by a hollow output shaft portion SOS, through which both the rider total torque TR and the motor torque TM pass during operation of the drive unit DU

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Data Source

PatentUS12576946B2Bicycle torque sensor

Publication Date: 2026.03.17 SRAM

AI summary

An electric bicycle drive unit for arrangement in a bottom bracket region of a bicycle frame, coaxially to the bottom bracket, is provided. The drive unit includes a torque sensor device for measuring a rider total torque. Rider total torque may include left-hand rider torque and a right-hand rider torque. The drive unit may include a bottom bracket shaft, an electric motor device arranged coaxially to the bottom bracket shaft, a hollow output shaft for transmitting a motor torque and the rider total torque to a bicycle drivetrain, and a rider moment coupling device for coupling the rider torque from the bottom bracket shaft to the hollow output shaft, and a motor torque coupling device for coupling the motor torque to the hollow output shaft. A torque measurement device is also provided.