Turbine Rotor Tie Bolt With Variable Stiffness Spring Segment

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Solution Overview

Problem

In gas turbine engines, the differing coefficients of thermal expansion between rotating wheel assemblies and tie bolts lead to a loss of clamp load due to uneven thermal growth, requiring high pre-stretch loads during assembly to maintain connection, which can be inefficient and difficult to manage.

Innovation Solution

A tie bolt design incorporating a cylindrical segment and a spring segment with a varying outer diameter to form a bellows feature, providing a lower stiffness than the cylindrical segment, allowing for thermal expansion and contraction while maintaining axial compressive force on bladed wheels, thereby reducing the need for large assembly loads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high pre-stretch loads are applied during assembly to accommodate thermal expansion differences, then the tie bolt can maintain connection between rotating wheel assemblies, but the assembly process becomes complex and requires specialized tools

Engineering Contradiction:

Improveconnection maintenanceVSAvoidassembly process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The tie bolt is designed with varying stiffness parameters along its length, transitioning from a rigid cylindrical segment to a flexible spring segment. This parameter change allows the tie bolt to naturally accommodate thermal expansion differences without requiring high pre-stretch loads or specialized assembly tools, thereby maintaining connection reliability while simplifying the assembly process

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The spring segment provides dynamic compliance to the tie bolt, allowing it to flex and adapt to thermal growth variations during engine operation. This dynamic capability eliminates the need for rigid, high-stress assembly procedures and specialized tools, while still maintaining reliable connection between rotating wheel assemblies

Inventive Principle:

Principle #15Dynamics

2Device complexity

If a rigid tie bolt is used to maintain axial connection, then assembly is simpler, but thermal expansion differences cause loss of clamp load

Engineering Contradiction:

Improveassembly processVSAvoidclamp load maintenance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The tie bolt is segmented into two distinct portions: a cylindrical segment with high stiffness for structural integrity and a spring segment with low stiffness for thermal compliance. This segmentation allows each portion to perform its specific function, maintaining clamp load reliability while keeping assembly simple

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the tie bolt have different mechanical properties tailored to their specific functions. The cylindrical segment provides rigidity where needed for connection stability, while the spring segment provides flexibility where needed for thermal accommodation, ensuring reliable clamp load maintenance without complicating assembly

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If the tie bolt stiffness is reduced to accommodate thermal growth, then thermal expansion is better accommodated, but the axial compressive force may drop below predetermined values

Engineering Contradiction:

Improvethermal expansion accommodationVSAvoidaxial compressive force

Core Design Contradiction:

Adaptability or versatilityVSForce

Solution Approach 1:

The tie bolt is divided into a cylindrical segment that maintains high stiffness and a spring segment that provides flexibility. This segmentation ensures that the overall tie bolt structure maintains sufficient axial compressive force while the spring segment accommodates thermal expansion, preventing force drop below predetermined values

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The tie bolt combines materials or structural elements with different stiffness characteristics in a single component. The cylindrical segment uses high-stiffness material for force transmission, while the spring segment uses low-stiffness material for thermal compliance, achieving both thermal accommodation and force maintenance simultaneously

Inventive Principle:

Principle #40Composite materials

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 ensures that the axial compressive force on bladed wheels is maintained above a predetermined value throughout the engine cycle, accommodating thermal growth differences and reducing assembly complexities, allowing for smaller axial loads and potentially eliminating the need for specialized tools.

Implementation Method 1

The spring segment may deform elastically to accommodate thermal growth of the rotor

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

thermal growth caused during use of the gas turbine engine assembly

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS11519271B2Turbine engine rotor with flexibly coupled tie bolt

Publication Date: 2022.12.06 ROLLS ROYCE NORTH AMERICAN TECHNOLOGIES INC

AI summary

A rotor assembly includes a plurality of wheels and a tie bolt that extends through the plurality of wheels and applies a compressive force to the plurality of wheels. The tie bolt includes a first segment with a first stiffness and a second segment with a second stiffness to allow for thermal growth of the plurality of wheels.