Outer Diameter Nut Piloting for Gas Turbine Rotor Balance

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Solution Overview

Problem

Conventional designs for securing rotating components in gas turbine engines face challenges with balance repeatability and vibration due to lack of precise piloting, often requiring close tolerances and interference fits, which are costly and labor-intensive to maintain.

Innovation Solution

The solution involves piloting the nut on its outer diameter, providing radial positioning control without the need for precise inner diameters, using a nut spacer or a pocket in the rotor to maintain perpendicularity and reduce shaft bending, thereby enhancing balance repeatability and reducing the risk of rotor bow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional inner diameter piloting is used to position the nut on the shaft, then radial positioning control is achieved, but the nut loses radial piloting when tightened due to expansion of the locating hole, requiring close tolerances and interference fits that are costly and labor-intensive

Engineering Contradiction:

Improveradial positioning controlVSAvoidcost and labor

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent inverts the conventional piloting approach by moving from inner diameter piloting (through the locating hole) to outer diameter piloting (using the locating knurl on the nut's outer surface). This inversion eliminates the problem of hole expansion during tightening, as the piloting surface is on the exterior where compression does not cause dimensional changes. The locating knurl provides a compressed, dimensionally stable outer diameter that maintains radial positioning control without requiring close tolerances or interference fits.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the physical state of the piloting surface by applying compression to the locating knurl, which reduces its diameter and creates a precise, stable outer dimension. This parameter change (compression-induced diameter reduction) provides a reliable piloting surface that maintains radial positioning without requiring the shaft and nut to be machined to close tolerances, thereby reducing manufacturing cost and labor.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If close tolerances and interference fits are used to maintain nut radial piloting, then balance repeatability is improved, but manufacturing complexity and labor increase significantly

Engineering Contradiction:

Improvebalance repeatabilityVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

By inverting the piloting location from the inner locating hole to the outer diameter with locating knurl, the patent eliminates the need for close tolerances and interference fits. The outer diameter piloting surface is compression-stabilized and does not change dimension during tightening, providing reliable radial positioning and balance repeatability through a simpler manufacturing process without requiring precise shaft-nut fits.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The locating knurl acts as a sacrificial, compression-sensitive element that deforms to provide precise dimensional control. Rather than requiring the entire shaft and nut assembly to be machined to close tolerances, the patent uses this localized, easily manufactured knurl feature to achieve the necessary precision, thereby reducing overall manufacturing complexity while maintaining reliability.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Manufacturing precision

If inner diameter piloting is used, then radial positioning is provided, but excessive deflective pressure is applied to the shaft during tightening, causing rotor bow and reducing balance repeatability

Engineering Contradiction:

Improveradial positioningVSAvoidshaft bending and rotor bow

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent moves the piloting function from the inner locating hole to the outer diameter, eliminating the mechanical constraint that causes excessive deflective pressure on the shaft. The locating knurl on the outer surface provides radial positioning through compression of the knurl itself, not through constraint of the shaft, thereby preventing shaft bending and rotor bow while maintaining radial positioning control.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The locating knurl serves as an intermediary element between the nut and the shaft, providing radial positioning control without directly constraining the shaft. The knurl compresses under load to maintain dimensional stability, absorbing the positioning function and preventing the transmission of excessive deflective pressure to the shaft, thereby eliminating rotor bow.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7470115B2Outer diameter nut piloting for improved rotor balance

Publication Date: 2008.12.30 HONEYWELL INTERNATIONAL INC

AI summary

The present invention provides for outer diameter piloting of a nut that secures stacked components to a tie-shaft or other threaded components used to axially secure one or more rotating components. Unlike conventional inner diameter piloting methods, machining a precise inner diameter of the nut is not needed. The nut face of the present invention has superior perpendicularity with the tie-shaft and the radial pilot is not lost when the nut is loaded. Outer diameter nut piloting may be conducted by using a nut alone or a nut in combination with a nut spacer, a pocket in the rotor, a nut spacer seat, or a nut piloting insert.