Adjustable Tie Rod Turbine Case for Bearing Centerline Offset
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Solution Overview
Problem
Existing methods for adjusting the center line of a bearing mount relative to a turbine casing in gas turbine engines are non-adjustable and require lengthy manufacturing coordination, making it difficult to optimize blade tip clearances and account for structural changes due to weight sag, deflection, and case distortion.
Innovation Solution
The use of adjustable tie rods allows for the offset adjustment of the bearing center line by varying the length of tie rods and tightening nuts, enabling easy reconfiguration to balance blade tip and seal clearances without the need for extensive machining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the bearing is offset by machining the inner case bearing flanges to be nonconcentric with the outer case flanges, then the center line offset is achieved, but the manufacturing complexity and lead time increase significantly
Solution Approach 1:
The offset adjustment function is segmented from the bearing flange machining and assigned to the tie rod assembly. Instead of machining the inner case bearing flanges to be nonconcentric, the tie rods are made adjustable in length, allowing the outer case to be offset relative to the inner case through modular length adjustment of individual tie rods.
Solution Approach 2:
The tie rod length is made dynamically adjustable through threaded sections and lock nuts, replacing the static fixed offset achieved by precision machining. This allows the bearing center line offset to be adjusted and readjusted as needed, transforming a complex one-time machining operation into a simple adjustable mechanism.
2Manufacturing precision
If the bearing is offset by machining the inner case bearing flanges to be nonconcentric with the outer case flanges, then the center line offset is achieved, but the adjustment capability is lost after machining
Solution Approach 1:
The tie rod incorporates a threaded section with a lock nut that enables dynamic adjustment of the tie rod length. This allows the bearing center line offset to be adjusted during assembly or maintenance, providing adaptability that was lost in the conventional machined flange approach.
Solution Approach 2:
The tie rod length parameter is made variable through the threaded adjustment mechanism. By changing the effective length of the tie rod (through rotation of the lock nut on the threaded section), the bearing position offset can be modified to accommodate different operational requirements or wear conditions.
3Ease of manufacture
If conventional tie rods are used with fixed lengths, then the manufacturing process is simple, but the blade tip clearances cannot be optimized
Solution Approach 1:
The tie rod includes a threaded section that allows for length adjustment, enabling optimization of blade tip clearances by varying the tie rod effective length. This maintains manufacturing simplicity while adding the capability for precision clearance adjustment that was previously impossible with fixed-length tie rods.
Solution Approach 2:
The tie rod length parameter can be varied to optimize blade tip clearances. The threaded adjustment mechanism allows the effective length to be changed within a range, providing the ability to fine-tune the bearing position and consequently the blade tip clearances without complicating the basic manufacturing process.
4Stability of the object's composition
If the bearing position is fixed by machining, then the structural changes due to weight sag and case distortion cannot be compensated
Solution Approach 1:
The adjustable tie rod mechanism provides a means to compensate for structural changes such as weight sag and case distortion that occur during operation. While the bearing position remains stable during operation, the ability to readjust the tie rod length allows compensation for cumulative distortions, maintaining clearance balance and reliability over the engine lifecycle.
Data Source
Figure 1
Figure 2~3
AI summary
A turbine housing section includes a radially inner case centered on a first axis, and a radially outer case spaced radially outwardly of the inner case, and centered on a second axis. The first and second axes are offset relative to each other. A plurality of tie rods include a threaded nut received on a tie rod, with the plurality of tie rods connecting the inner and outer cases. The plurality of tie rods are spaced circumferentially about both of the first and second axes, and extend for distinct lengths between the inner and outer cases such that the inner and outer cases are held at a position wherein the first and second axes are offset