Concentric Motor Driveshafts With Shear Sections for Jam Tolerance

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Solution Overview

Problem

Existing electric motor systems in rotorcraft face challenges in accommodating component failures such as jams or bearing degradation without increasing cost, weight, and space, as traditional clutch mechanisms like sprag clutches are costly and inefficient.

Innovation Solution

The implementation of a concentric electric-motor driveshaft arrangement with shear sections in the driveshafts allows for independent operation of stacked electric motors, enabling one motor to freewheel and continue transmitting torque to the gearbox while the other motor can still operate, thus avoiding the need for costly clutch systems.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional clutch mechanisms like sprag clutches are integrated into each motor to accommodate component failures, then the motor system can continue to operate during failures, but the cost, weight, and space requirements increase significantly

Engineering Contradiction:

Improvemotor system operation during component failureVSAvoidmotor system weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The invention extracts the clutch mechanism from the motor assembly and replaces it with a driveshaft shear section. The shear section is a simple structural element integrated into the driveshaft that shears under excessive load, allowing the failed motor to disconnect automatically without requiring complex clutch mechanisms in each motor.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The driveshaft shear section acts as a disposable, low-cost safety element. When a motor fails and creates excessive load, the shear section is designed to fail first, sacrificing itself to protect the more expensive and critical motor and clutch components. This allows the system to continue operating with one motor while avoiding the need for expensive clutch mechanisms.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If traditional clutch mechanisms like sprag clutches are integrated into each motor to accommodate component failures, then the motor system can continue to operate during failures, but the device complexity and space requirements increase significantly

Engineering Contradiction:

Improvemotor system operation during component failureVSAvoidmotor system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention merges the failure protection function into the driveshaft structure itself through the shear section. Instead of adding a separate clutch mechanism to each motor, the driveshaft is designed with a weakened section that automatically fails to protect the system, combining multiple functions into a single structural element.

Inventive Principle:

Principle #5Merging (Combining)

3Weight of moving object

If concentric driveshafts with shear sections are used instead of clutch mechanisms, then weight and cost are reduced, but the system must rely on shear section failure to protect against motor jams

Engineering Contradiction:

Improvemotor system weightVSAvoidprotection against motor jams

Core Design Contradiction:

Weight of moving objectVSReliability

Solution Approach 1:

The driveshaft shear section is designed beforehand to fail at a specific load threshold. This pre-engineered weakness acts as a safety valve that activates before the motor or other critical components can be damaged by excessive load from a jam or binding condition.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The invention converts the potentially harmful effect of motor jamming into a beneficial protective mechanism. When a motor jams, the excessive load causes the shear section to fail, which automatically disconnects the jammed motor from the drivetrain, preventing further damage and allowing the system to continue operating with the remaining motors.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 allows for failure-resistant electric-motor systems that reduce weight, cost, and space constraints while ensuring continued operation of the rotorcraft, even in the event of a motor jam or binding, by using concentric driveshafts with shear sections to disconnect the faulty motor and maintain torque transmission.

Implementation Method 1

a forward electric-motor driveshaft splined to the forward electric-motor assembly and comprising a forward electric-motor drive-shaft shear section, and a rear electric-motor driveshaft splined to the rear electric-motor assembly and comprising a rear electric-motor drive-shaft shear section

Methodology Applied

Scientific EffectShear stress: Shear Stress

Data Source

PatentUS11994200B1Concentric electric-motor driveshaft system and method

Publication Date: 2024.05.28 TEXTRON INNOVATIONS INC

AI summary

An electric-motor system includes a forward electric-motor assembly, a rear electric-motor assembly arranged in series relative to the forward electric-motor assembly, a forward electric-motor driveshaft splined to the forward electric-motor assembly and comprising a forward electric-motor drive-shaft shear section, and a rear electric-motor driveshaft splined to the rear electric-motor assembly and comprising a rear electric-motor drive-shaft shear section, at least a portion of the rear electric-motor driveshaft arranged concentrically within the forward electric-motor driveshaft. The forward electric-motor driveshaft and the rear electric-motor driveshaft rotate about a common axis.