Turbine Control Ring Bushing for Vane Pitch Precision
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Solution Overview
Problem
The control ring in variable-pitch vane stages of turbine engines experiences off-centring due to cold radial clearances, leading to precision issues and wear in the threaded connections, which affects the pitch angle and engine operation.
Innovation Solution
A bushing with an axial bore, through-slot, and outer thread is used to fix the bearing member to the ring body, allowing radial deformation from a loose to a constrained position, thereby immobilizing the member and reducing torque transmission and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cold radial clearances are provided between pads and tracks to allow thermal expansion, then thermal expansion is accommodated, but off-centring of the control ring occurs leading to precision loss
Solution Approach 1:
The bushing acts as an intermediary element between the pad and the control ring. It provides a precise mounting interface that eliminates play in the threaded connection, thereby preventing off-centring of the control ring while still allowing the pad to accommodate thermal expansion of the casing.
Solution Approach 2:
The invention extracts and eliminates the harmful clearance from the threaded connection by introducing the bushing with a through-slot. This removes the source of off-centring while preserving the necessary thermal expansion capability through the pad-bushing-interface.
2Ease of operation
If threaded connections are used to fix pads to the ring, then pads can be mounted and adjusted, but wear and destruction of threaded connections occur due to vibrations
Solution Approach 1:
The bushing serves as a mediator that absorbs and isolates the vibrational stresses from the threaded connection. The through-slot in the bushing allows it to deform radially, accommodating vibrations and preventing stress transmission to the threads, thereby eliminating wear and destruction of the threaded connection.
Solution Approach 2:
The bushing changes its radial parameter (dimension) in response to vibrations, allowing it to flex and absorb vibrational energy. This dynamic parameter change protects the threaded connection from vibrational damage while maintaining secure pad mounting.
3Manufacturing precision
If pads are fixed with adjustment screws and nuts, then fine adjustment of clearance is possible, but clearance causes relative displacement under vibrations leading to connection destruction
Solution Approach 1:
The bushing acts as an intermediary that maintains the precisely adjusted clearance while protecting the threaded connection from vibrational damage. The through-slot allows the bushing to deform and absorb vibrations, preventing relative displacement between the pad and adjustment screw.
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 stabilizes the control ring, preventing wear and ensuring precise positioning, which maintains the correct pitch angle and enhances engine operation by eliminating the risk of thread damage and surging.
Implementation Method 1
a through-slot opening into said bore and designed to allow a substantially radial deformation of the bushing; said bushing being designed so that when it is screwed in it cooperates with said body so as to substantially radially deform from a first position, in which said member or support can be mounted and moved inside said bore, to a second position, in which said bushing is radially constrained and tightly mounted on said member or support
Data Source
AI summary
A control ring for a stage of variable-pitch vanes for a turbine engine includes at least one member for bearing on a casing and means for fixing the member. The member includes a bushing with an axial bore for the passage of the member or an element for supporting the member. A through-slot opens into the bore and allows for substantial radial deformation of the bushing. The member further includes an outer thread for screwing the bushing into a complementary thread of a hole in the body, thereby deforming the bushing. The member or support can be mounted and moved inside the bore, to a second position, in which the bushing is radially constrained and is tightly mounted on the member or support, which is thus immobilized in relation to the bushing.