Rotational Shaft Interference Fit Positioning for Impeller Alignment
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Solution Overview
Problem
Existing rotational bodies with interference fits between shafts and impellers often experience misalignment due to centrifugal forces during high-speed rotation, leading to potential breakage, abnormal noise, and alignment issues that cannot be fully corrected by balance adjustments.
Innovation Solution
A rotational body design where the interference fit between the rotational shaft and impeller is located in a region not including the largest outside diameter portion, with a nut screwed onto the shaft to fasten them together, ensuring the interference fit is away from the area of maximum centrifugal force, and employing press-fitting or other assembly methods to maintain alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If interference fit is used between rotational shaft and impeller, then assembly strength is improved, but misalignment occurs during high-speed rotation due to centrifugal forces
Solution Approach 1:
The rotational shaft is divided into multiple sections with different diameters along its axial length. The interference fit portion is specifically located in a region with a smaller diameter, separating it from the largest outside diameter portion of the impeller. This segmentation allows the interference fit to occur in a controlled region that does not experience the maximum centrifugal forces, thereby maintaining both assembly strength and alignment precision.
2Ease of manufacture
If clearance fit is used for assembly, then ease of assembly is improved, but misalignment between center positions occurs leading to eccentric loads
Solution Approach 1:
Instead of using a uniform clearance fit throughout the entire shaft-impeller interface, the invention applies a localized interference fit in a specific region (the smaller-diameter portion of the shaft). This local quality change provides precise center position alignment where needed, while other regions can accommodate easier assembly requirements. The interference fit portion is strategically positioned to ensure accurate centering without requiring excessive assembly force throughout the entire structure.
3Strength
If interference fit portion is placed at largest outside diameter region, then assembly strength is maximized, but gap formation occurs during rotation due to centrifugal forces
Solution Approach 1:
Conventional wisdom suggests placing the interference fit at the largest diameter region to maximize assembly strength. The invention inverts this approach by deliberately positioning the interference fit in a smaller-diameter region away from the largest outside diameter portion. This inversion prevents gap formation during rotation, as the smaller-diameter region experiences lower centrifugal forces, thereby maintaining fit stability while still providing sufficient assembly strength through the interference fit mechanism.
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 prevents misalignment and gap formation between the shaft and impeller during high-speed rotation, ensuring proper alignment and reducing the risk of damage and noise, while allowing for easier assembly and maintaining processing accuracy.
Implementation Method 1
an interference fit portion for fit between the impeller and the rotational shaft where an outside diameter of the rotational shaft is larger than an inside diameter of the insert hole of the hub portion
Data Source
AI summary
A rotational body 1 includes a rotational shaft 2, an impeller 3, and a nut 6. The impeller includes a hub portion 4 having a peripheral surface 4s inclined to the axial direction of the rotational shaft and having an insert hole 4h in which the rotational shaft is inserted, and a blade portion 5. At least one of the rotational shaft or the insert hole of the hub portion has an interference fit portion 10 for fit between the rotational shaft and the impeller, where the outside diameter of the rotational shaft is larger than the inside diameter of the insert hole of the hub portion. The interference fit portion is formed in a region which does not include the largest outside diameter portion 4B where the hub portion has a largest outside diameter, with the rotational shaft and the impeller mating with each other.