Hirth Tooth Coupling Assembly for Torque Tube Alignment
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Solution Overview
Problem
Misalignment of the torque tube during assembly in gas turbine engines leads to damage and incorrect operation of the variable inlet guide vanes, as existing alignment features are misleading and can be sheared without proper engagement.
Innovation Solution
A hirth tooth coupling with skipped teeth and cutouts on the torque tube and bell crank sides, allowing for intuitive alignment by preventing engagement until proper alignment is achieved, ensuring correct meshing and reducing the risk of damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a flat alignment feature is used on the bolt connecting the torque tube, then assembly is simplified, but misalignment up to one tooth off occurs causing vanes schedule to be off by more than 10 degrees and damage to the torque tube
Solution Approach 1:
The patent applies asymmetry by using a skipped tooth feature on the torque tube side and a corresponding cutout on the bell crank side. This asymmetric design ensures that only one specific alignment position is possible, preventing misalignment while maintaining ease of assembly through intuitive engagement.
Solution Approach 2:
The hirth tooth coupling with skipped tooth and cutout features enables self-alignment during assembly. The mechanic can easily identify the correct position by the unique fit between the skipped tooth and cutout, allowing the assembly to self-correct and self-verify alignment without requiring complex alignment procedures or tools.
2Ease of operation
If the original alignment feature is used, then assembly appears simple, but the feature gives false engagement feedback tricking the mechanic into believing the torque tube is correctly positioned when it is not
Solution Approach 1:
The skipped tooth and cutout design provides unambiguous feedback during assembly. The unique geometric relationship between these features creates a single correct engagement position that is easily verifiable by the mechanic, eliminating false feedback and ensuring reliable alignment verification through tactile and visual confirmation.
3Device complexity
If the original alignment feature is used, then assembly proceeds without additional features, but the alignment feature is sheared through during torquing without the mechanic noticing
Solution Approach 1:
The asymmetric skipped tooth and cutout features create a unique engagement geometry that prevents misalignment. This design ensures correct positioning before torquing, preventing the shearing issue while maintaining relatively simple assembly features that are easy to manufacture and inspect.
Data Source
AI summary
A torque tube with a hirth tooth coupling including a torque tube side attached to a case side of the torque tube, a skipped tooth formed in a torque tube side end face, multiple torque tube side teeth formed in the torque tube side end face; a bell crank side in operative communication with the torque tube side opposite the case side of the torque tube, the bell crank side comprising a bell crank side end face, a cutout formed in the bell crank side end face, multiple bell crank side teeth formed in the bell crank side end face, wherein the skipped tooth is configured to operatively couple with the cutout to engage the torque tube side and the bell crank side of the hirth tooth coupling, wherein the multiple torque tube side teeth are configured to engage with the multiple bell crank side teeth.