Axial load distribution in a jet engine spline coupling
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Axial Load Distribution in a Jet Engine Spline Coupling. Justin McGrath. Master of Engineering Project Rensselaer Polytechnic Institute Hartford, CT. Spline Coupling Background. Elongated gear teeth Used in high torque applications

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Axial Load Distribution in a Jet Engine Spline Coupling

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Axial load distribution in a jet engine spline coupling

Axial Load Distribution in a Jet Engine Spline Coupling

Justin McGrath

Master of Engineering Project

Rensselaer Polytechnic Institute

Hartford, CT


Spline coupling background

Spline Coupling Background

  • Elongated gear teeth

  • Used in high torque applications

  • Used in jet engines to transfer torque from disks to shafts

  • The pressure faces of the teeth distribute the load


Spline coupling schematic

Spline Coupling Schematic

  • Spline Couplings used in several Pratt & Whitney Engines:

  • F-119

  • F-135

  • PW4000

  • PW2000

  • PW6000


Challenges in spline design

Challenges in Spline Design

  • Even distribution of the torque load on the pressure face of the spline teeth

  • Uneven loading causes premature wear and reduces the life of the coupling system

  • Designers must understand the load behavior of the coupling system to make changes that will even the load

  • This project looks into analyzing axial load distribution in a representative spline coupling


Theoretical methodology

Theoretical Methodology

  • Derived equation of axial load distribution using Tatur’s method:

p(x) – axial load at the root fillet radius

L – Contact length of the coupling system

c – effective tooth height

R – pitch radius

N – Number of teeth

T – tau, the applied torque

α – constant of integration


Finite element methodology

Finite Element Methodology

  • Create 3D model of the coupling system:

  • Import Geometry into ANSYS & apply loads:


Finite element methodology1

Finite Element Methodology

  • Load data is extracted from the finite element model and compared to the theoretical equation:


Results

Results

Both methods show the load peaking at either end of the contact length

The theoretical solution predicts a higher maximum load


Discussion

Discussion

  • The theoretical solution predicts higher loads because:

    • Tatur’s Method assumes 100 % transfer of load with no deflection

    • FE model shows only about 75% of the load is transferred

    • The other 25% is used in bending the teeth, and torsionally deflecting the coupling system


Discussion1

Discussion

  • Both methods converge when looking at a normalized plot

This confirms that the boundary conditions used in the FE model agree with the theoretical boundary conditions


Conclusion

Conclusion

  • The theoretical equation is the more conservative method in analyzing axial load distribution in a spline coupling system as it predicts higher maximum & average loads

  • The theoretical equation is also a much faster method

  • The Finite Element solution more accurately predicts the load that will be seen during engine operation, but it is a time consuming apporach

  • The Finite Element model shows that all else being equal there is more capability in the coupling system when compared to the theorecitcal approach


Back up slides

Back Up Slides

Analytical Calculations

Finite Element Calculations


Back up slides1

Back Up Slides

Table 1 – Material Properties of 3D Spline Coupling Model


Back up slides2

Back Up Slides

Table 2 – Geometric Properties of 3D Spline Coupling Model


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