Variable Vane Face Gear Actuation With Adjustable Backlash
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Solution Overview
Problem
Existing gas turbine engine actuating systems for variable vanes face challenges with high backlash and limited adjustment of angular accuracy, primarily due to manufacturing tolerances, which affect the positional accuracy and performance of the vanes.
Innovation Solution
The implementation of a face gear and pinion actuating system with a bearing assembly having zero radial clearance and the use of shims to adjust the backlash between the face gear and pinions, allowing for precise control of the angular position of the vanes by setting a predetermined backlash value, minimizing errors in motion and optimizing positional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional spur ring gear meshed with spur pinions is used to actuate variable vanes, then the system structure is simple, but the backlash is relatively high and angular accuracy is limited due to manufacturing tolerances
Solution Approach 1:
The patent changes the fundamental gear geometry parameters by transitioning from spur gears to face gears with radial teeth. This parameter change fundamentally alters the meshing characteristics, enabling reduced backlash while maintaining reasonable manufacturing tolerances. The face gear configuration with teeth extending radially from the pitch circle creates a different engagement pattern that inherently reduces angular play.
Solution Approach 2:
The patent introduces a specialized bearing assembly as an intermediary element between the face gear and the stationary structure. This bearing assembly with zero radial clearance acts as a mediator that eliminates radial play, thereby reducing overall system backlash. The bearing serves as a precision intermediary that compensates for and controls the clearance between moving and stationary components.
2Manufacturing precision
If manufacturing tolerances are tightened to reduce backlash, then angular accuracy improves, but manufacturing cost and complexity increase
Solution Approach 1:
By changing the gear type from spur to face gear with radial teeth, the patent alters the critical dimensions that affect backlash. This parameter change shifts the sensitivity of backlash to manufacturing tolerances, making the system less sensitive to typical machining variations while achieving better angular accuracy without proportionally increasing manufacturing difficulty.
Solution Approach 2:
The patent replaces the traditional spur gear mechanical system with a face gear system combined with a zero-clearance bearing assembly. This substitution creates a new mechanical architecture where backlash is controlled through the bearing's zero radial clearance rather than relying solely on tight gear tooth tolerances, thereby easing manufacturing requirements while maintaining precision.
3Measurement precision
If zero radial clearance bearing assembly is used in the face gear actuating system, then angular position accuracy is improved, but device complexity increases
Solution Approach 1:
The bearing assembly performs multiple functions simultaneously: it supports the face gear rotation, eliminates radial clearance, positions the gear accurately, and maintains zero radial clearance under varying loads. By consolidating these multiple functions into a single bearing assembly component, the patent achieves high angular position accuracy without proportionally increasing overall device complexity.
Solution Approach 2:
The patent merges the functions of radial support, clearance elimination, and positional accuracy control into a single integrated bearing assembly. This merging of functions reduces the number of separate components needed and simplifies the overall structure while achieving the desired angular position accuracy through the zero radial clearance design.
Data Source
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AI summary
A variable vane assembly for a gas turbine engine has an actuating system including a rotatable face gear (40) and a respective pinion (42) engaged to and extending transversely from the end of each of the moveable vanes (32). The teeth (50) of each pinion (42) define land surfaces (50b, 50t) angled with respect to adjacent ones of the land surfaces (48b, 48t) of the teeth (48) of the face gear (40) meshed therewith. A smallest axial distance between the adjacent land surfaces of the meshed pinion (42) and face gear teeth (48) define a backlash (b) of the actuating system. At least one shim (60, 62) has a thickness adjusting an axial distance between the pinion (42) and the face gear (40) to set the backlash to a predetermined value.