Turbomachine Bearing Support Decoupling via Double Centering

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Solution Overview

Problem

Existing decoupling mechanisms for turbomachine bearing supports, such as those using fusible screws, are prone to uncontrolled breakage due to shear forces in addition to tensile forces, leading to unpredictable and potentially damaging vibrations during rotor imbalance.

Innovation Solution

The introduction of a double centering mechanism using circular grooves and ribs, combined with a clearance between the fusible screws and upstream orifices, ensures that the screws are only subjected to tensile forces, eliminating shear forces and providing controlled decoupling of the bearing support.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If fusible screws are used to fix bearing support parts, then the bearing support can be decoupled in case of imbalance, but the screws are subjected to both tensile and shear forces leading to uncontrolled breakage

Engineering Contradiction:

Improvecontrolled decouplingVSAvoiduncontrolled vibrations

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The bearing support is divided into upstream and downstream parts that can be decoupled through fusible screws. The screws are segmented into a retained portion (threaded, engaged with orifices) and a broken portion (smooth, sacrificial), allowing controlled failure mode where only the broken portion shears off while the threaded portion remains to maintain structural integrity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the fusible screw have different geometric properties: the retained portion has threads for engagement and tensile strength, while the broken portion has a reduced smooth section designed to shear. The orifices have different configurations (upstream orifice without centering portion, downstream orifice with centering portion) to create specific stress distributions.

Inventive Principle:

Principle #3Local quality

Solution Approach 3:

The invention adds a geometric dimension by providing different orifice configurations in the upstream and downstream parts. The downstream orifice includes a centering portion that contacts the broken portion, creating a geometric constraint that prevents tangential movement and eliminates shear forces, transforming the failure mode from 2D shear-tension combination to 1D tensile-only failure.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If fusible screws with centering portion are used, then the screws can be retained during assembly, but shear forces appear on the screws due to tangential contact during relative movement

Engineering Contradiction:

Improvescrew retentionVSAvoidshear force on screws

Core Design Contradiction:

Ease of manufactureVSForce

Solution Approach 1:

Instead of using a centering portion on the screw (which creates shear), the invention inverts the approach by placing the centering portion on the orifice itself. The downstream orifice has an enlarged portion that contacts the broken portion, while the upstream orifice has no centering portion, allowing the screw to be retained during assembly without subjecting it to shear forces.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The centering function is extracted from the screw and transferred to the orifice structure. The broken portion of the screw serves only as a sacrificial element that is sheared off, while the centering action is performed by the downstream orifice's enlarged portion contacting the broken portion, eliminating the harmful shear forces on the retained screw.

Inventive Principle:

Principle #2Taking out (Extraction)

3Strength

If the bearing support is rigidly connected, then structural strength is maintained, but damage is transmitted to the stator during rotor imbalance

Engineering Contradiction:

Improvebearing support strengthVSAvoidvibration transmission

Core Design Contradiction:

StrengthVSObject-generated harmful factors

Solution Approach 1:

The bearing support transitions from a static rigid connection to a dynamic decouplable connection. The fusible screws provide a controlled failure mechanism that allows the bearing support to transition from a connected state (maintaining strength during normal operation) to a decoupled state (preventing vibration transmission during imbalance), making the system adaptive to operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The fusible screws act as a pre-designed sacrificial element that fails in a controlled manner to protect the stator. The broken portion is designed to shear off at a predetermined load, providing beforehand protection against the transmission of harmful vibrations and shocks to the stator during rotor imbalance events.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentEP2071138B1Device for uncoupling a bearing support having double centring

Publication Date: 2010.11.17 SN DETUDE & DE CONSTR DE MOTEURS DAVIATION (S N E C M A)

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Figure 10

AI summary

The invention relates to a decoupling device for a bearing support (7) in a turbomachine, said bearing support (7) comprising an upstream portion (1) and a downstream portion (2) respectively comprising a plurality of upstream (10) and downstream (20) orifices through which shear screws (3) pass. It is characterized in that it comprises, between each upstream orifice (10) and the shear screw (3) passing through it, a clearance (4) preventing any contact between the upstream orifice (10) and the shear screw (3), and in that the upstream portion (1) and the downstream portion (2) of the bearing support (7) are in contact with each other by surfaces forming a double centering means (14, 24, 15, 25).