Unison ring gear assembly

1. A unison ring assembly, comprising:

a first unison ring and a second unison ring concentrically aligned along a principal axis, the first and second unison rings being rotatable about the principal axis; and

a gear mechanism configured to simultaneously rotate the first and second unison rings about the principal axis,

wherein the gear mechanism includes a planetary gearset, and

wherein a planet gear of the planetary gearset is eccentrically mounted so as to have a rotational axis that is offset by different amounts relative to each of the first and second unison rings.

2. The unison ring assembly as claimed in claim 1 , wherein the first unison ring is a ring gear of the planetary gearset and the second unison ring is a sun gear of the planetary gearset.

3. The unison ring assembly as claimed in claim 2 , wherein the rotational axis of the planet gear is closer to the second unison ring than to the first unison ring.

4. The unison ring assembly as claimed in claim 1 , wherein the gear mechanism is configured to rotate the first and second unison rings at different speeds.

5. The unison ring assembly as claimed in claim 1 ,

wherein the planet gear includes a first segment that engages with a ring gear of the planetary gearset and a second segment that engages with a sun gear of the planetary gearset, and

wherein the gear ratio between the first segment and the ring gear is different than the gear ratio between the second segment and the sun gear.

6. The unison ring assembly as claimed in claim 1 , wherein the first unison ring is radially outwards of the second unison ring with respect to the principal axis.

7. The unison ring assembly as claimed in claim 1 ,

wherein the first and second unison rings include radially facing surfaces that oppose each other,

wherein the planetary gearset comprises a plurality of planet gears distributed around the first and second unison rings so as to be between the radially facing surfaces, and

wherein the planet gears are arranged to concentrically align the unison rings about the principal axis.

8. The unison ring assembly as claimed in claim 1 ,

wherein the first and second unison rings include axially facing surfaces that oppose each other, and

wherein the planet gear is provided between the axially facing surfaces to axially locate sun and ring gears of the planetary gearset relative to the principal axis.

9. The unison ring assembly as claimed in claim 8 , wherein the rotational axis of the planet gear is angularly offset relative to the principal axis such that the planet gear is arranged to axially and radially align the first and second unison rings.

10. The unison ring assembly as claimed in claim 1 , further comprising at least one actuator connected to and configured to directly rotate at least one of a ring gear, the planet gear, and a sun gear of the planetary gearset.

11. The unison ring assembly as claimed in claim 1 , wherein the unison ring assembly is for a gas turbine engine.

12. A gas turbine engine comprising the unison ring assembly as claimed in claim 1 .

13. The gas turbine engine as claimed in claim 12 , wherein the first and second unison rings are connected to variable stator guide vanes.

14. The unison ring assembly as claimed in claim 1 , wherein the planet gear is asymmetric about the rotational axis of the planet gear.

15. The unison assembly as claimed in claim 14 ,

wherein the planet gear includes a first segment and a second segment, and

wherein a radius of the first segment is greater than a radius of the second segment.

16. The unison assembly as claimed in claim 15 , wherein the pitch of teeth of the first segment is greater than the pitch of teeth of the second segment.

17. The unison assembly as claimed in claim 16 , wherein the first and second segments of the planet gear are pie-shaped.

18. The unison assembly as claimed in claim 1 , wherein a range of angular rotation of the first unison ring is different than a range of angular rotation of the second unison ring for a common angle of the planet gear.