Concentric Planetary Gear Train Torque Distribution

Solution Overview

Problem

Gas turbine engines face challenges with large diameter gear trains that experience wear and failure due to high centrifugal forces, leading to design compromises such as restricted main gas path and increased weight.

Innovation Solution

A gear train design with multiple sun gears, planet gears, ring gears, and planet carriers, where an output member extends between planet carriers to distribute torque and includes hydraulic cylinders and sensors to control torque distribution, reducing the diameter and weight of the gear train.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the gear train diameter is increased to withstand high torque, then the torque capacity is improved, but the centrifugal forces increase causing wear and failure

Engineering Contradiction:

Improvetorque capacityVSAvoidgear train durability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The gear train is divided into multiple independent planetary gear sets (first and second planetary gear sets) that share the torque load. Each planetary gear set operates at a smaller diameter, reducing centrifugal forces while collectively handling the required torque through parallel torque paths from multiple sun gears to the output member.

Inventive Principle:

Principle #1Segmentation

2Strength

If the gear train diameter is increased to withstand high torque, then the torque capacity is improved, but the weight increases

Engineering Contradiction:

Improvetorque capacityVSAvoidgear train weight

Core Design Contradiction:

StrengthVSWeight of moving object

Solution Approach 1:

The gear train is divided into multiple independent planetary gear sets (first and second planetary gear sets) that share the torque load. Each planetary gear set operates at a smaller diameter, reducing centrifugal forces while collectively handling the required torque through parallel torque paths from multiple sun gears to the output member.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first and second planetary gear sets are arranged concentrically around the input shaft, with gear components nested within the overall structure. The output member extends through the center of both planetary gear sets, allowing compact arrangement that reduces overall diameter and weight while maintaining torque capacity.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Strength

If the gear train diameter is increased to withstand high torque, then the torque capacity is improved, but the main gas path is restricted

Engineering Contradiction:

Improvetorque capacityVSAvoidmain gas path area

Core Design Contradiction:

StrengthVSArea of stationary object

Solution Approach 1:

The first and second planetary gear sets are arranged concentrically around the input shaft, with gear components nested within the overall structure. The output member extends through the center of both planetary gear sets, allowing compact arrangement that reduces overall diameter and weight while maintaining torque capacity.

Inventive Principle:

Principle #7Nested doll (Nesting)

Data Source

PatentUS10203023B2Gear trains

Publication Date: 2019.02.12 ROLLS ROYCE PLC

AI summary

A gear train comprising: an input shaft; a first sun gear coupled to the input shaft; a plurality of first planet gears engaging the first sun gear; a first ring gear engaging the plurality of first planet gears; and a first planet carrier coupled to the plurality of first planet gears; a second sun gear coupled to the input shaft; a plurality of second planet gears engaging the second sun gear; a second ring gear engaging the plurality of second planet gears; and a second planet carrier coupled to the plurality of second planet gears; and an output member coupled to the first planet carrier at a first torque transfer location and coupled to the second planet carrier at a second torque transfer location, different to the first torque transfer location.