Variable-Pitch Vane Rod Orifice Clearance Control
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Solution Overview
Problem
In turbomachines, the assembly of variable-pitch vanes with inclined pin axes and radial rod fingers results in significant clearance issues during assembly, leading to imprecision in angular positioning due to the mismatch between the drive square and the rod orifice, causing variability in vane orientation.
Innovation Solution
A control ring system with rods having a radial finger for assembly and an orifice that provides varying clearance in the longitudinal direction, allowing for precise angular positioning by adjusting the orifice dimensions to minimize clearance once the rod is in place, using either a triangular or oblique surface configuration to ensure accurate alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the rod is assembled by radial translation to engage the finger in the control ring, then the finger mounts without clearance in the control ring, but clearance is required at the other end of the rod to engage the orifice on the drive square
Solution Approach 1:
The orifice in the rod is given a dimension in the longitudinal direction of the rod that is greater than the corresponding dimension of the drive square, creating clearance in the longitudinal dimension to facilitate radial assembly while maintaining precision in the radial dimension through the finger-orifice engagement in the control ring
2Ease of manufacture
If clearance is provided in the longitudinal direction of the rod to allow assembly by radial translation, then the rod can be engaged on the drive square, but this leads to significant lack of precision in the angular positioning of the vane
Solution Approach 1:
The orifice is designed with different dimensional characteristics in different directions: it has a larger dimension in the longitudinal direction of the rod to allow assembly clearance, while maintaining precise engagement in the radial direction through the finger-orifice interface in the control ring, thus achieving both assembly ease and positioning precision in their respective dimensions
Data Source
AI summary
A device for controlling variable-pitch vanes in a turbomachine has rods each having at one end a finger for mounting in a control ring and at its other end an assembly orifice for mounting on a drive square of a vane, the axis of the vane being inclined relative to the axis of the finger of the rod, and the assembly orifice in the rod presenting a dimension in the longitudinal direction of the rod that is greater than that of the drive square, and co-operating therewith to define clearance that varies over the height of the drive square and of the orifice.