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Curvic coupling fatigue life enhancement through unique compound root fillet design

Imported: 24 Feb '17 | Published: 06 Jan '04

Sandeep Muju, Robert S. Sandoval

USPTO - Utility Patents

Abstract

A lower stress and higher service life curvic coupling design is disclosed for use on coupling mechanisms for assembly of components that comprise rotating elements, such as impellers, turbine wheels and couplings for gas turbine engines and other types of engines having highly stressed components. The curvic coupling design includes a compound fillet radius, comprised of a large and a small radius, located between the root and the pressure surface of all splined teeth on the torque transmitting coupling halves. The larger radius, with its lower stress concentration, is positioned in the root area where the background hoop stresses act, thereby resulting in a lower fillet peak stress value. The smaller radius smoothly connects the larger radius with the pressure surface, minimizing the penetration of the fillet surface towards the mating tooth, thereby allowing proper clearances to be maintained. The smaller radius is in a region where the background stresses are low, and therefore its higher stress concentration is not detrimental to the overall design. The inventive curvic coupling design ultimately resulted in a three-fold increase in service life.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the rotating elements of a typical gas turbine engine showing curvic coupling applications in accordance with the present invention;

FIG. 2 is a cross sectional view showing attachment of gas turbine engine wheels by means of curvic couplings in accordance with the present invention;

FIG. 3 is a perspective view showing details of matching male and female curvic coupling teeth in accordance with the present invention;

FIG. 4 is a side view of a singular prior art curvic coupling tooth;

FIG. 5 is an enlarged, detailed view of a curvic coupling tooth taken along view A of FIG.

4 and showing the inventive compound fillet radius when matching male and female curvic coupling teeth are in a mated state in accordance with the present invention;

FIGS. 6A and 6B are a comparison of stress contours for a prior art (FIG. 6A) single 0.040 inch fillet and a compound (FIG. 6B) 0.120/0.050 inch fillet in accordance with the present invention; and

FIG. 7 is a graph that shows the sensitivity of fillet stress concentration factor to the size of the fillet, based on two dimensional finite element methods.

Claims

1. A toothed coupling mechanism for transmitting torque between rotating elements, said toothed coupling mechanism comprising:

2. The toothed coupling mechanism of claim 1, wherein said minor fillet connects said major fillet with said second pressure surface, thereby minimizing the penetration of a surface of said compound fillet toward a matching tooth.

3. The toothed coupling mechanism of claim 1, wherein said major radius is about 0.120 inches, and said minor radius is about 0.050 inches.

4. The toothed coupling mechanism of claim 1, wherein said at least one male curvic coupling have a concave tooth profile and said female curvic coupling teeth have a convex tooth profile.

5. A toothed coupling mechanism for maintaining assembly of rotating elements to a shaft in engines having hoop stressed components, said toothed coupling mechanism comprising:

6. The toothed coupling mechanism of claim 5, wherein torque is transmitted between the rotating elements via said at least one male curvic coupling tooth and said at least one female curvic coupling tooth, and wherein a ratio of said larger radius to said smaller radius is greater than 1.0.

7. The toothed coupling mechanism of claim 5, wherein said first pressure surface has a concave tooth profile and said second pressure surface has a convex tooth profile, whereby a centering action is provided for maintaining assembly of the rotating elements to the shaft.

8. A gas turbine engine comprising a toothed coupling mechanism for maintaining assembly of a plurality of rotating elements to a shaft and transmitting torque between at least two rotating elements of said plurality of rotating elements in said gas turbine engine, wherein said toothed coupling mechanism comprises:

9. The toothed coupling mechanism of claim 8, wherein said larger radius is about 0.120 inches, and said smaller radius is about 0.050 inches.

10. A coupling mechanism, comprising:

11. The coupling mechanism according to claim 10, wherein: