Annular Combustion Chamber Alternating Fasteners Tolerance Stacking
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Solution Overview
Problem
The assembly of annular combustion chambers for turbomachines with one-piece fairings faces issues due to significant manufacturing tolerances, leading to poor docking and increased risk of cracks under vibratory stresses, necessitating additional tightening torque and potentially causing damage.
Innovation Solution
The combustion chamber design alternates the placement of fasteners between longitudinal walls and the chamber bottom and fairing, reducing manufacturing tolerances by one-third, enhancing flexibility and reducing rigidity, while maintaining effective tightening through a specific arrangement of first and second fasteners and incorporating notches on flanges for easier assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same fasteners are used to join longitudinal walls to both the chamber bottom and the fairing, then the assembly structure is simple, but manufacturing tolerances stack up causing poor docking and increased crack risk
Solution Approach 1:
The patent divides the fastening system into two distinct groups: first fasteners joining the longitudinal walls to the chamber bottom, and second fasteners joining the longitudinal walls to the fairing. This segmentation breaks the continuous tolerance stacking path, reducing cumulative tolerance errors and improving docking precision between components.
2Manufacturing precision
If additional tightening torque is applied to compensate for clearances from manufacturing tolerances, then the docking precision improves, but the risk of forming cracks at the bolts increases
Solution Approach 1:
By segmenting the fastening system into two independent groups (first fasteners for bottom connection, second fasteners for fairing connection), the patent reduces cumulative tolerance stacking. This allows adequate tightening torque to be applied without excessive force, maintaining reliability by preventing bolt cracks while achieving sufficient docking precision.
3Manufacturing precision
If the manufacturing tolerances of combustion chamber elements are reduced, then the docking precision improves, but the manufacturing cost increases significantly
Solution Approach 1:
Instead of reducing manufacturing tolerances across all components (which would increase cost), the patent segments the fastening system to reduce tolerance stacking effects. This allows standard manufacturing tolerances to be maintained while achieving better docking precision, avoiding significant cost increases.
Solution Approach 2:
The patent addresses the tolerance problem not by tightening dimensional constraints in the manufacturing domain, but by changing the structural arrangement in the assembly domain. The alternating fastener pattern creates a more flexible assembly structure that accommodates tolerances without requiring tighter manufacturing controls.
4Force
If the assembly is made more rigid to maintain tightening force, then the tightening efficiency improves, but the docking between elements worsens due to tolerance stacking
Solution Approach 1:
The segmented fastening system allows the assembly to maintain sufficient tightening force through two separate fastening groups rather than one rigid continuous path. This segmentation provides flexibility to accommodate tolerance variations while maintaining adequate clamping force for effective tightening.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The chamber (4) has a single-piece cowling (12) covering a chamber bottom (10), and inner and outer longitudinal walls (6, 8) fixed on the bottom and the cowling. Fixing systems between the inner longitudinal wall and the chamber bottom are situated opposite to other fixing systems between the outer longitudinal wall and the cowling. The latter fixing systems are situated opposite to the former fixing systems between the outer longitudinal wall and the chamber bottom. Flanges of the cowling have notches between the longitudinal walls and the chamber bottom.