Hollow Shrink-Fit Rotor Shaft Assembly for High-Speed Coupling
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Solution Overview
Problem
The existing shrink-fit coupling method for rotor assembly in turbomachines is complicated due to increased centrifugal forces at high rotation speeds, leading to reduced coupling efficiency and potential shaft damage, especially when assembling multiple parts, which requires significant force and can result in axial force imbalances.
Innovation Solution
Incorporating an internal cavity in the shaft with an internal diameter greater than or equal to 50% of the external diameter of the axial shrink-fit portion, allowing radial deformation during rotation to maintain coupling, reducing the initial shrink-fit difference between the shaft and parts, and utilizing additive manufacturing for precise cavity creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the internal diameter of the part is dimensioned as a function of its maximum deformation to maintain coupling at maximum rotation speed, then the coupling by shrinking is maintained at high speed, but the assembly of parts on the shaft becomes relatively complicated and requires significant force
Solution Approach 1:
The shaft is designed with a hollow internal cavity that allows the shaft wall to deform dynamically during rotation. The shaft transitions from a rigid structure to a flexible one that can adapt its shape under centrifugal forces, enabling the shaft to accompany the radial deformation of the coupled part and maintain shrink-fit coupling at high speeds without requiring excessive assembly force
Solution Approach 2:
The invention changes the physical parameter of the shaft from solid to hollow, creating a compliant structure. The hollow cavity allows the shaft wall thickness to be optimized so that the shaft can radially expand during rotation, matching the deformation of the coupled part and maintaining the shrink-fit interface pressure even at maximum rotation speed
2Quantity of substance
If multiple parts are assembled on the same shaft, then more parts can be coupled, but the part must travel farther on the shaft and there is a risk of shaft damage
Solution Approach 1:
The hollow shaft design provides dynamic compliance that reduces impact forces during assembly. When multiple parts are being assembled, the shaft can deform radially to accommodate the insertion forces, preventing stress concentration and potential damage that would occur with a rigid solid shaft
Solution Approach 2:
The hollow cavity in the shaft acts as a built-in cushion that absorbs assembly forces before they reach critical levels. The cavity allows the shaft wall to deform and absorb impact energy during the assembly process, protecting the shaft from damage when multiple parts are being installed in sequence
3Reliability
If the shrink-fit coupling is increased at rest to ensure maintenance at maximum speed, then the coupling is maintained at high speed, but the force required for assembly increases significantly
Solution Approach 1:
The hollow shaft design transforms the coupling system from a static high-force requirement to a dynamic adaptive system. At rest, the shaft maintains sufficient but not excessive shrink-fit coupling. During rotation, the shaft wall deforms radially to maintain the coupling interface pressure, eliminating the need for extremely high initial assembly forces while ensuring reliable coupling at maximum speed
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 design reduces the force required for assembly, allows for more parts to be coupled on a single shaft, minimizes axial clamping forces, and decreases the rotor's mass while maintaining torque transmission at high speeds, up to 100,000 rpm.
Implementation Method 1
during the rotation of the rotor, that is to say of the shaft and of the shrink-wrapped parts, the centrifugal force deforms the parts outwards in a radial direction
Implementation Method 2
the wall of the shaft, defined between the inside diameter of the internal cavity and the outside diameter of the axial shrink-fit portion of the shaft, can deform outwards in a radial direction and accompany the deformation outwards in the radial direction of the element
Implementation Method 3
the shrink-fit coupling between the shaft and the part is higher at rest than during the rotation of the rotor
Data Source
Figure 1~3
Figure 4~8
Figure 7
AI summary
The invention concerns an assembly comprising a shaft (12) and an element (16) configured to be coupled on the shaft (12) by shrink-fitting, the shaft (12) comprising an inner cavity (20) in an axial shrink-fitting portion (P12), an internal diameter (Di20) of the inner cavity (20) being greater than or equal to 50% of an external diameter of the axial shrink-fitting portion (P12) and a difference (H) between the external diameter of the axial shrink-fitting portion (P12) and an internal diameter of the axial shrink-fitting portion (P16) of the element (16) being less than or equal to 50 μm when the element (16) is not coupled to the shaft (12), the external diameter of the axial shrink-fitting portion (P12) of the shaft (12) being greater than the internal diameter of the axial shrink-fitting portion (P16) of the element (16). The invention also concerns a method for manufacturing such an assembly.