Harmonic Drive Reducer for Variable Pitch Propeller Rotor
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Solution Overview
Problem
Existing variable pitch propeller rotor systems face challenges with complex and heavy pitch control mechanisms, high backlash, and reduced reliability due to epicyclic gearboxes, especially when the propeller is located at the rear of a gas turbine engine, which complicates maintenance and compromises aerodynamic efficiency.
Innovation Solution
A harmonic drive reduction gear system is used, where a flex spline is driven by a wave generator to reduce speed, allowing for a compact and lightweight design with minimal backlash and high torsional stiffness, enabling precise blade pitch control and reduced obstruction in the gas flow path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If epicyclic gearboxes are used for pitch control, then speed reduction is achieved, but backlash increases and control precision deteriorates
Solution Approach 1:
The patent replaces the traditional epicyclic mechanical gearbox with a harmonic drive system that uses elastic deformation of a flexspline and wave generator mechanics. This substitution eliminates tooth clearance and backlash inherent in conventional gear systems, achieving precise blade pitch control while maintaining speed reduction functionality.
Solution Approach 2:
The patent employs a flexspline - a thin-walled elastic shell component that can be deformed by the wave generator. This flexible component enables the harmonic drive mechanism to achieve continuous tooth engagement without backlash, resolving the contradiction between speed reduction and control precision.
2Speed
If epicyclic gearboxes are used for pitch control, then speed reduction is achieved, but system weight increases
Solution Approach 1:
The patent replaces the heavy epicyclic gearbox with a more compact harmonic drive system. The harmonic drive achieves the same speed reduction ratio with significantly fewer and lighter components, reducing the overall weight of the pitch control mechanism while maintaining functional performance.
3Speed
If epicyclic gearboxes are used for pitch control, then speed reduction is achieved, but system complexity increases
Solution Approach 1:
The patent replaces the complex multi-component epicyclic gearbox with a simpler harmonic drive system consisting of primarily three components: the wave generator, flexspline, and circular spline. This substitution reduces the number of parts, simplifies assembly, and improves reliability while achieving the required speed reduction.
4Force
If large diameter pitch input shafts are used to transmit torque across exhaust annulus, then torque transmission is sufficient, but aerodynamic efficiency deteriorates
Solution Approach 1:
The patent replaces the large-diameter shaft system with a harmonic drive mechanism that provides high torque multiplication through its reduction ratio. This allows the use of a smaller pitch input shaft that extends across the exhaust annulus with minimal aerodynamic interference, thereby maintaining torque transmission capability while improving aerodynamic efficiency.
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
The harmonic drive reduction gear system provides accurate and reliable blade pitch control with reduced weight and improved aerodynamic efficiency by allowing a smaller diameter pitch input shaft, enhancing the overall performance and maintainability of the variable pitch bladed rotor.
Implementation Method 1
The flex spline is radially flexible, and is deformed by the wave generator into a lobed configuration, which is typically two-lobed and so is of generally elliptical form.
Implementation Method 2
Teeth at the lobes of the flex spline mesh with teeth of the circular spline, while regions of the flex spline away from the lobes are out of mesh with the circular spline.
Data Source
AI summary
A bladed rotor comprises a rotor body 2 carrying blades 6, whose pitch can be varied by means of a pitch input shaft 10. The pitch input shaft 10 drives the respective blade 6 about a spanwise axis X of the blade through a harmonic drive reduction gear 14. The harmonic drive reduction gear 14 comprises a wave generator 16 which is fixed for rotation on the pitch input shaft 10 and a flex spline which meshes with a circular spline 20 and is secured to the blade 6.