Shear Section in Geared Turbine Drive for Overspeed Protection
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Solution Overview
Problem
In geared turbofan engines, the failure of the shaft from the fan drive turbine poses a risk as it leads to uncontrolled speed of the fan drive turbine without a compressor to slow it down, potentially causing overspeed and damage.
Innovation Solution
A shear section in the drive connection between the fan drive turbine and the gear reduction is designed to be weaker than other sections, located aft of the thrust bearing, to facilitate controlled failure and prevent damage by fracturing before other parts, thus ensuring safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a gear reduction is incorporated between the fan drive turbine and the low pressure compressor, then the fan and low pressure compressor can rotate at a common speed, but the shaft from the fan drive turbine may fail leading to uncontrolled overspeed of the turbine
Solution Approach 1:
A shear section is intentionally designed into the drive connection between the fan drive turbine and the gear reduction. This shear section is positioned aft of the thrust bearing and is designed to fail at a predetermined load, thereby preventing excessive overspeed of the fan drive turbine while allowing the fan and low pressure compressor to rotate at a common speed through the gear reduction.
2Reliability
If the shear section is positioned forward of the thrust bearing, then it can provide overspeed protection, but the turbine rotor may move forward causing damage to other components
Solution Approach 1:
The shear section is strategically positioned aft of the thrust bearing to ensure that when it fails under excessive load, the fan drive turbine rotor moves rearward away from the combustor and other forward components. This positioning prevents the rotor from moving forward and causing damage to the combustor, bearings, or other components located forward of the thrust bearing.
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 solution effectively addresses the risk of overspeed by ensuring the turbine rotor moves rearward and blades contact vanes, resisting or preventing further rotation, thereby preventing damage and ensuring safety in case of excessive load or failure.
Implementation Method 1
A shear section in a drive connection connecting the fan drive turbine to the gear reduction is weaker than other portions of the drive connection
Implementation Method 2
The shear section is designed to be weaker than other sections, located aft of the thrust bearing, to facilitate controlled failure and prevent damage by fracturing before other parts
Implementation Method 3
a thrust bearing mount the fan drive turbine, the thrust bearing being aft of a location of the combustor
Implementation Method 4
A fan drive turbine drives a gear reduction to, in turn, drive the low pressure compressor and the fan at a speed which is slower than a speed of the fan drive turbine
Data Source
AI summary
A turbine engine has a fan and a low pressure compressor that rotate at a common speed and in a common direction. A fan drive turbine drives a gear reduction to, in turn, drive the low pressure compressor and the fan at a speed which is slower than a speed of the fan drive turbine. A combustor intermediate the low pressure compressor and the fan drive turbine and a thrust bearing mount the fan drive turbine, the thrust bearing being aft of a location of the combustor. A shear section in a drive connection connecting the fan drive turbine to the gear reduction is weaker than other portions of the drive connection. The shear section is aft of the thrust bearing.