Clutch Between Starter-Generator and Accessory Gear Box

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Solution Overview

Problem

The implementation of high power electric starter/generator (ESG) units on aircraft engines poses a challenge as they can impose torque spikes to the accessory gear box (AGB), risking damage, and existing solutions require complex and costly shear sections to mitigate this issue.

Innovation Solution

Incorporating a clutch, such as a cone clutch, between the ESG and the AGB that can slip in response to a predetermined torque level, eliminating the need for a shear section and preventing metal-to-metal contact in case of ESG failure, thereby smoothing out torque spikes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a high power electric starter/generator is implemented on aircraft engines, then electrical power output is improved, but torque spikes damage the accessory gear box

Engineering Contradiction:

Improveelectrical power outputVSAvoidaccessory gear box durability

Core Design Contradiction:

PowerVSStrength

Solution Approach 1:

A clutch mechanism is introduced as an intermediary component between the electric starter/generator and the accessory gear box. This clutch engages and disengages based on torque conditions, mediating the torque transmission to protect the gear box from damage while allowing the high power ESG to operate.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The clutch is designed to slip or disengage before excessive torque can reach the accessory gear box, providing beforehand protection against torque spikes. This preventive mechanism cushions the system against potential damage before it occurs.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Strength

If a shear section is incorporated in the shaft to prevent damage, then accessory gear box protection is improved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improveaccessory gear box protectionVSAvoidshaft structure complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The clutch serves as an intermediary protective mechanism that replaces the need for a complex shear section in the shaft. By placing the protection function in the clutch, the shaft structure can remain simpler while achieving the same protective goal.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention replaces the mechanical shear section concept with a clutch-based torque limitation system. This substitution allows for easier manufacturing and maintenance while achieving comparable protection against torque spikes.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Strength

If oversized gears and bearings are used to accommodate torque spikes, then accessory gear box strength is improved, but manufacturing complexity and maintenance difficulty increase

Engineering Contradiction:

Improveaccessory gear box strengthVSAvoidmanufacturing simplicity

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The clutch acts as an intermediary that limits torque transmission to normal operating levels, allowing the use of standard-sized gears and bearings rather than oversized components. This maintains adequate strength while simplifying manufacturing.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The clutch changes the torque parameter transmitted to the accessory gear box by engaging and disengaging based on torque conditions. This dynamic parameter control allows standard components to handle variable torque loads without requiring oversized design margins.

Inventive Principle:

Principle #35Parameter changes

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 prevents damage to the AGB and reduces the need for oversized gears and bearings, simplifying manufacturing and maintenance while ensuring protection against torque spikes during ESG failures.

Implementation Method 1

a clutch operably disposed between the accessory gear box and the starter generator. The clutch is operable to slip in and out of full engagement in response to a first predetermined level of torque between the starter/generator and the accessory gear box

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentEP2415991B1Clutch between auxiliary gear box and starter-generator of a turbofan engine

Publication Date: 2016.10.05 ROLLS ROYCE CORP

Figure 1
Figure 2~3

AI summary

A turbine engine (10) is disclosed herein. The turbine engine includes a starter/generator (54) operable to deliver rotational power in a first mode of operation and to generate electrical power in a second mode of operation. The turbine engine also includes an accessory gear box (56) mechanically coupled to the starter/generator. The turbine engine also includes a shaft (46) mechanically coupled to the accessory gear box such that the accessory gear box is operably disposed between the shaft and the starter/generator. The turbine engine also includes a clutch (60) operably disposed between the accessory gear box and the starter generator. The clutch is operable to slip in and out of full engagement in response to a first predetermined level of torque between the starter/generator and the accessory gearbox.