Frustoconical Input Shaft With Bellows for Torque and Misalignment
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Solution Overview
Problem
Propulsive systems with reduction mechanisms face challenges in reconciling stiffness and flexibility levels to manage overloads, mechanical resistance, and optimizing axial size, while also dealing with complex mechanical constraints and assembly complexities.
Innovation Solution
A tree for propulsive systems with a trunconic barrel and symmetrical bellows configuration, where the barrel's angle and bellows' diameters are optimized to decouple static and dynamic constraints, allowing for increased robustness and flexibility, and facilitating manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a rigid shaft is used to transmit torque, then torque transmission capability is improved, but mechanical stresses concentrate at the junction with bellows reducing shaft life
Solution Approach 1:
The shaft transitions from a uniform rigid structure to a non-uniform frustoconical structure with varying local properties. The larger diameter at the bellows junction provides local reinforcement where dynamic stresses concentrate, while the smaller diameter at the turbine interface optimizes torque transmission. This local quality variation redistributes stress concentrations and improves overall shaft reliability while maintaining power transmission capability.
2Strength
If the shaft diameter is increased to reduce static stresses, then mechanical strength is improved, but the flexibility to compensate misalignments deteriorates
Solution Approach 1:
The shaft geometry parameters are changed from a uniform cylindrical shape to a frustoconical shape with specific diameter ratios. The larger diameter portion (D1) provides flexibility and misalignment compensation capability, while the smaller diameter portion (D2) provides structural strength. This parameter change allows the shaft to simultaneously achieve both flexibility and strength requirements that cannot be met with a uniform diameter design.
3Reliability
If a frustoconical shaft geometry is used, then stress distribution is improved, but manufacturing complexity increases
Solution Approach 1:
The shaft employs a frustoconical geometry with smooth curved transitions between different diameter sections. This curved geometry is more favorable for manufacturing using common processes like turning, forging, or casting compared to sharp transitions or complex geometries. The curvature allows for gradual stress distribution while maintaining manufacturability through standard aerospace manufacturing techniques.
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 configuration enhances the mechanical robustness and flexibility of the tree, increasing its lifespan by distributing static and dynamic stresses across different areas, thus improving the overall mechanical performance and assembly efficiency.
Implementation Method 1
The bellows act as a spring and each have a rotational flexibility of the shaft bending type relative to its theoretical axis of rotation
Data Source
Figure 1
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AI summary
The present invention relates to a shaft (15) for a propulsion system (1) configured to rotate a reducing mechanism (12) about a rotational axis (X), the shaft (15) comprising: - a first end (16) configured to engage with an input gear (14) of the reducing mechanism (12), - a first bellows (17) and a second bellows (18), the first bellows (17) and the second bellows (18) being rotationally symmetrical about the rotational axis (X), the first bellows (17) extending between the first end (16) and the second bellows (18), and - a frustoconical body (19) mechanically connecting the first bellows (17) and the second bellows (18).