Axle assembly having a gear reduction unit and an interaxle differential unit

1. An axle assembly comprising:

a housing assembly that receives a differential assembly;

an input shaft that is at least partially received in the housing assembly and is rotatable about a first axis;

a gear reduction unit that is operatively connected to the input shaft, wherein the gear reduction unit includes a planetary gear set that has a sun gear and a planetary ring gear that are rotatable about the first axis and a planet carrier that rotatably supports a planet pinion that is in meshing engagement with the sun gear and the planetary ring gear, wherein the planetary ring gear is moveable between a first position in which the planetary ring gear is coupled to the housing assembly such that the planetary ring gear does not rotate about the first axis and a second position in which the planetary ring gear is coupled to the planet carrier such that the planet carrier and the planetary ring gear are rotatable together about the first axis; and

an interaxle differential unit that is at least partially received in the planet carrier and that operatively connects the planetary gear set to the differential assembly and an output shaft.

2. The axle assembly of claim 1 wherein the planetary ring gear is moveable along the first axis between the first position, the second position, and a neutral position that is disposed between the first position and the second position, wherein torque is not transmitted from the input shaft to the planet carrier when the planetary ring gear is in the neutral position.

3. The axle assembly of claim 1 wherein the planetary gear set provides gear reduction from the input shaft to the output shaft and the differential assembly when the planetary ring gear is in the first position.

4. The axle assembly of claim 3 wherein the planetary gear set does not provide gear reduction from the input shaft to the output shaft and the differential assembly when the planetary ring gear is in the second position.

5. The axle assembly of claim 1 wherein the planetary ring gear is coupled to the housing assembly and is disengaged from the planet carrier when in the first position. and the planetary ring gear is coupled to the planet carrier and is disengaged from the housing assembly when in the second position.

6. The axle assembly of claim 5 further comprising an actuator that moves the planetary ring gear between the first position and the second position.

7. The axle assembly of claim 6 wherein the actuator includes a clutch pack that actuates the planetary ring gear to the first position and a biasing member that extends from the housing assembly to the planetary ring gear that actuates the planetary ring gear to the second position.

8. The axle assembly of claim 1 further comprising a drive pinion that provides torque to the differential assembly, is rotatable about the first axis, and is operatively connected to the interaxle differential unit, wherein the output shalt is received in the drive pinion and is rotatable about the first axis, and the interaxle differential unit operatively connects the gear reduction unit to the drive pinion and the output shaft.

9. The axle assembly of claim 8 wherein the drive pinion is rotatable with the output shaft when the interaxle differential unit is locked and the drive pinion is rotatable with respect to the output shaft when the interaxle differential unit is unlocked.

10. The axle assembly of claim 1 further comprising a drive gear that is rotatable about the first axis and is operatively connected to the interaxle differential unit, a driven gear that meshes with the drive gear and is rotatable about a third axis, and a drive pinion that is rotatable about the third axis to provides torque to the differential assembly.

11. The axle assembly of claim 1 wherein the planetary ring gear has a first planetary ring gear face gear that engages the housing assembly when the planetary ring gear is in the first position.

12. The axle assembly of claim 11 wherein the first planetary ring gear face gear is disengaged from the housing assembly when the planetary ring gear is in the second position.

13. The axle assembly of claim 1 wherein the planetary ring gear has a first planetary ring gear face gear that mates with a housing face gear of the housing assembly when the planetary ring gear is in the first position.

14. The axle assembly of claim 13 wherein the housing face gear is provided with a differential carrier of the housing assembly.

15. The axle assembly of claim 1 wherein the planetary ring gear has a second planetary ring gear face gear that is selectively engageable with the planet carrier.

16. The axle assembly of claim 15 wherein the second planetary ring gear face gear is disengaged from the planet carrier when the planetary ring gear is in the first position.

17. The axle assembly of claim 15 wherein the second planetary ring gear face gear is disengaged from a planet carrier face gear of the planet carrier when the planetary ring gear is in the first position.

18. The axle assembly of claim 15 wherein the second planetary ring gear face gear engages a planet carrier face gear of the planet carrier when the planetary ring gear is in the second position.

19. The axle assembly of claim 15 wherein the second planetary ring gear face gear is disposed opposite the first planetary ring gear face gear.

20. The axle assembly of claim 1 wherein a biasing member urges the planetary ring gear toward the second position.