Reversed-Thread Tensioner Nut for Gas Turbine Shaft Assembly
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Solution Overview
Problem
The assembly and disassembly of gas turbine engine components, particularly the high-pressure compressor shaft, are complex and costly due to the intricate arrangement and small clearances, making access to the support bearing difficult, especially in twin-spool forward turbofan engines like the CFM56, where the entire front part needs to be dismantled for maintenance.
Innovation Solution
A tensioner nut system allows for the mounting and dismounting of the high-pressure compressor shaft from the rear of the engine, using a cylindrical nut with reversed threads and a bevel wheel with integral splines, enabling assembly without heating the nut and minimizing interference with air circulation, thus reducing maintenance costs and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the bearing is heated to expand it for assembly, then the shrinking forces are minimized, but the nut is heated and friction in the thread increases
Solution Approach 1:
The patent introduces a thermal protection element that physically segments and isolates the nut from the heated bearing, allowing the bearing to be heated for expansion and assembly while preventing heat transfer to the nut, thus avoiding increased thread friction and protecting the nut from thermal damage
Solution Approach 2:
The thermal protection element acts as an intermediary between the heated bearing and the nut, blocking heat transfer while allowing the assembly process to proceed. This intermediary component enables the bearing to be heated for proper fit without adversely affecting the nut
2Ease of operation
If the nut is retained upstream by a segment in the pinion, then the compressor can be docked, but the entire front part of the engine must be dismantled for access
Solution Approach 1:
The patent inverts the traditional assembly approach by providing access to the nut from the rear of the engine rather than from the front. The tool engages the nut through the rear access, allowing the compressor to be assembled or disassembled by working from the rear, eliminating the need to dismantle the entire front part of the engine
Solution Approach 2:
The patent extracts the nut retention function from the upstream pinion area and relocates it to the rear of the engine. By providing a rear access tool that can engage and manipulate the nut from the rear, the system eliminates the need for front access and the associated complex dismantling procedures
3Temperature
If a thermal protection is placed around the nut, then heating effects are minimized, but the protection is difficult to implement and cannot be installed effectively
Solution Approach 1:
The patent transitions from a three-dimensional thermal protection element surrounding the nut to a two-dimensional thermal protection coating applied to the nut surface. This dimensional change simplifies the implementation while maintaining the thermal protection function
Solution Approach 2:
The patent changes the physical state or form of the thermal protection from a separate mechanical component to a coating layer. This parameter change allows for easier application and installation while achieving the same thermal isolation objective
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 simplifies the maintenance process by allowing single-access rear tooling, reducing costs, and ensuring compact integration without interfering with air circulation, while maintaining effective support and lubrication of the shaft.
Implementation Method 1
To prepare the assembly of the shaft 4, it is necessary to heat the bearing 3 at C in order to expand it and minimize the shrinking forces.
Data Source
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AI summary
The invention relates to a system for securing the end of a shaft (14) of a gas turbine engine engaged inside a sleeve (15) supported by a bearing (3). The system, comprising a nut (16), is characterized in that the nut (16) has a first thread (16f1) through which it is screwed into the shaft (14) and a second thread (16f2) through which it is screwed into the sleeve (15). Advantageously, the thread pitches of the two threads (16f1, 16f2) of the nut (16) are reversed relative to each other so as to form a tensioning nut.