Hybrid duplex ball bearing assembly

1. A hybrid duplex ball bearing assembly, the bearing assembly comprising:

a forward bearing;

an aft bearing; and

a preload spring, the preload spring disposed adjacent the aft bearing and configured to apply an axial force to push the aft bearing toward the forward bearing, wherein the forward bearing and aft bearing share an inner race, wherein the aft bearing is not radially loaded.

2. The bearing assembly of claim 1 , wherein the axial force applied by the preload spring is about 100 pounds-force.

3. The bearing assembly of claim 1 , wherein the forward bearing and the aft bearing are angular contact bearings each including a contact angle, and wherein the contact angles of the forward bearing and the aft bearing converge at a point within the bearing assembly.

4. A hybrid duplex ball bearing assembly, the bearing assembly comprising:

a forward bearing;

an aft bearing; and

a preload spring, the preload spring disposed adjacent the aft bearing and configured to apply an axial force to push the aft bearing toward the forward bearing, wherein the forward bearing and aft bearing share an inner race, wherein the forward bearing forms a radial clearance fit with the aft bearing such that the aft bearing carries no radial load.

5. The bearing assembly of claim 4 , wherein the aft bearing carries only the axial force of the preload spring.

6. The bearing assembly of claim 4 , wherein the preload spring applies an axial force to push the aft outer race and the forward outer race toward one another.

7. A hybrid duplex ball bearing assembly, the bearing assembly comprising:

an inner race including a forward portion and an aft portion;

a forward outer race disposed around the forward portion of the inner race;

a forward bearing cage;

a plurality of forward ball bearings disposed between the forward portion of the inner race and the forward outer race and spaced apart from one another by the forward bearing cage;

an aft outer race disposed around the aft portion of the inner race;

an aft bearing cage;

a plurality of aft ball bearings disposed between the aft portion of the inner race and the aft outer race and spaced apart from one another by the aft bearing cage; and

a preload spring disposed adjacent the aft outer race, the preload spring configured to apply an axial force to the aft outer race in the direction of a forward thrust load along the shaft, wherein the aft outer race and the plurality of aft ball bearings are not radially loaded.

8. The bearing assembly of claim 7 , wherein the preload spring applies an axial force to push the aft outer race and the forward outer race toward one another.

9. The bearing assembly of claim 8 , wherein the axial force applied by the preload spring is about 100 pounds-force.

10. The bearing assembly of claim 7 , wherein:

the forward outer race, the plurality of forward ball bearings, and the forward portion of the inner race form a forward contact angle, and

the aft outer race, the plurality of aft ball bearings, and the aft portion of the inner race form an aft contact angle, and

wherein the forward contact angle and the aft contact angle converge at a point within the bearing assembly.

11. The bearing assembly of claim 10 , wherein the preload spring applies an axial force to push the aft outer race and the forward outer race toward one another.

12. A hybrid duplex ball bearing assembly, the bearing assembly comprising:

an inner race including a forward portion and an aft portion;

a forward outer race disposed around the forward portion of the inner race;

a forward bearing cage;

a plurality of forward ball bearings disposed between the forward portion of the inner race and the forward outer race and spaced apart from one another by the forward bearing cage;

an aft outer race disposed around the aft portion of the inner race;

an aft bearing cage;

a plurality of aft ball bearings disposed between the aft portion of the inner race and the aft outer race and spaced apart from one another by the aft bearing cage; and

a preload spring disposed adjacent the aft outer race, the preload spring configured to apply an axial force to the aft outer race in the direction of a forward thrust load along the shaft, wherein at least a portion of the aft outer race is disposed within the forward outer race.

13. The bearing assembly of claim 12 , wherein the preload spring applies an axial force to push the aft outer race and the forward outer race toward one another.

14. A hybrid duplex ball bearing assembly, the bearing assembly comprising:

an inner race including a forward portion and an aft portion;

a forward outer race disposed around the forward portion of the inner race;

a forward bearing cage;

a plurality of forward ball bearings disposed between the forward portion of the inner race and the forward outer race and spaced apart from one another by the forward bearing cage;

an aft outer race disposed around the aft portion of the inner race;

an aft bearing cage;

a plurality of aft ball bearings disposed between the aft portion of the inner race and the aft outer race and spaced apart from one another by the aft bearing cage; and

a preload spring disposed adjacent the aft outer race, the preload spring configured to apply an axial force to the aft outer race in the direction of a forward thrust load along the shaft, wherein the forward outer race forms a clearance fit with the aft outer race such that the aft outer race carries no radial load.

15. The bearing assembly of claim 14 , wherein the aft outer race carries only the axial force of the preload spring.

16. A hybrid duplex ball bearing assembly, the bearing assembly comprising:

an inner race including a forward portion and an aft portion;

a forward outer race disposed around the forward portion of the inner race;

a forward bearing cage;

a plurality of forward ball bearings disposed between the forward portion of the inner race and the forward outer race and spaced apart from one another by the forward bearing cage;

an aft outer race disposed around the aft portion of the inner race;

an aft bearing cage;

a plurality of aft ball bearings disposed between the aft portion of the inner race and the aft outer race and spaced apart from one another by the aft bearing cage; and

a preload spring disposed adjacent the aft outer race, the preload spring configured to apply an axial force to the aft outer race in the direction of a forward thrust load along the shaft, wherein the inner race further comprises:

an inner surface and an opposing outer surface; and

a plurality of holes formed through the inner race fluidly communicating the inner surface and the outer surface,

wherein the forward outer race and the aft outer race form a lubricant drain therebetween in fluid communication with the plurality of holes.

17. The bearing assembly of claim 16 , wherein the preload spring applies an axial force to push the aft outer race and the forward outer race toward one another.

18. A turbine engine, the turbine engine comprising:

a main shaft;

a bearing housing; and

a duplex bearing assembly connected to the main shaft and disposed within and connected to the bearing housing, the bearing assembly comprising:

a forward angular contact bearing;

an aft angular contact bearing; and

a preload spring, the preload spring disposed adjacent the aft bearing and configured to apply an axial force to push the aft bearing toward the forward bearing, wherein the forward bearing and the aft bearing share an inner race, wherein the aft bearing is not radially loaded.

19. The turbine engine of claim 18 , wherein the axial force applied by the preload spring is about 100 pounds-force.

20. The turbine engine of claim 18 , wherein the forward bearing and the aft bearing are angular contact bearings each including a contact angle, and wherein the contact angles of the forward bearing and the aft bearing converge at a point within the bearing assembly.