Variable-speed epicyclic gearbox for an aircraft propulsion system

1 . An aircraft propulsion system, comprising:

a thermal engine;

a gearbox including an input shaft, an output shaft, an epicyclic gear arrangement, a drive gear, a first layshaft assembly, and a ring gear rotational control device, the input shaft driven by the thermal engine,

the epicyclic gear arrangement including a sun gear, a plurality of planet gears, a ring gear, and a carrier, the sun gear connected to the drive gear, the plurality of planet gears engaged with the sun gear and the ring gear, the carrier mounted on the plurality of planet gears, the carrier connected to the output shaft,

the first layshaft assembly extending along a first layshaft rotational axis and including a first layshaft and a first layshaft input gear, the first layshaft input gear engaged with the drive gear and the input shaft, and

the ring gear rotational control device including a first variable drive assembly coupled with the first layshaft, the first variable drive assembly including a first ring gear drive engaged with the ring gear, the first ring gear drive rotatable about the first layshaft rotational axis, the first variable drive assembly configured to drive rotation of the ring gear with the first ring gear drive; and

a propulsion unit driven by the output shaft.

2 . The aircraft propulsion system of claim 1 , wherein the first variable drive assembly is configured to operate in a selected gear ratio of a continuous range of gear ratios between a maximum gear ratio of the first variable drive assembly and a minimum gear ratio of the first variable drive assembly, and the continuous range of gear ratios is defined between the first layshaft and the first ring gear drive.

3 . The aircraft propulsion system of claim 2 , wherein the maximum gear ratio is greater than 2:1 and the minimum gear ratio is less than 2:1.

4 . The aircraft propulsion system of claim 1 , wherein the first ring gear drive circumscribes and is radially spaced from the first layshaft.

5 . The aircraft propulsion system of claim 1 , wherein the first variable drive assembly further includes a plurality of inner disks and a pivoting arm assembly, the plurality of inner disks is disposed on the first layshaft, the pivoting arm assembly includes a radially fixed gear assembly and a radially variable gear assembly, the radially fixed gear assembly is rotatable about a first axis radially fixed relative to the first layshaft rotational axis, the radially fixed gear assembly includes a first gear engaged with the first ring gear drive, the radially variable gear assembly is rotatable about a second axis radially moveable relative to the first layshaft rotational axis, the radially variable gear assembly includes a plurality of outer disks and a second gear, the plurality of outer disks are engaged with the plurality of inner disks, and the second gear is engaged with the first gear.

6 . The aircraft propulsion system of claim 5 , wherein the first layshaft rotational axis, the first axis, and the second axis are parallel.

7 . The aircraft propulsion system of claim 5 , wherein the first variable drive assembly further includes a pivoting arm member, the radially fixed gear assembly and the radially variable gear assembly are mounted on the pivoting arm member, and the pivoting arm member is pivotable about the first axis.

8 . The aircraft propulsion system of claim 7 , wherein the ring gear rotational control device further includes an actuator coupled with the pivoting arm member, and the actuator is configured to pivot the arm member about the first axis.

9 . The aircraft propulsion system of claim 5 , wherein the radially variable gear assembly is pivotable about the first axis between a first radial position and a second radial position, the first variable drive assembly has a first gear ratio with the radially variable gear assembly in the first radial position, and the first variable drive assembly has a second gear ratio with the radially variable gear assembly in the second radial position.

10 . The aircraft propulsion system of claim 1 , wherein the gearbox further includes a second layshaft assembly, the second layshaft assembly extends along a second layshaft rotational axis and includes a second layshaft and a second layshaft input gear, the second layshaft input gear is engaged with the drive gear and the input shaft.

11 . The aircraft propulsion system of claim 10 , wherein the ring gear rotational control device further includes a second variable drive assembly coupled with the second layshaft, the second variable drive assembly includes a second ring gear drive engaged with the ring gear, the second ring gear drive is rotatable about the second layshaft rotational axis, and the second variable drive assembly is configured to drive rotation of the ring gear with the second ring gear drive.

12 . The aircraft propulsion system of claim 1 , wherein the ring gear includes an inner diameter surface and an outer diameter surface, the plurality of planet gears are engaged with the inner diameter surface, and the first ring gear drive is engaged with the outer diameter surface.

13 . The aircraft propulsion system of claim 1 , wherein the thermal engine is a gas turbine engine including a power turbine shaft, and the power turbine shaft is coupled with the input shaft.

14 . An aircraft propulsion system, comprising:

a thermal engine;

a gearbox that includes an input shaft, an output shaft, a drive gear, a ring gear, a first layshaft assembly, and a ring gear rotational control device, the input shaft driven by the thermal engine, the drive gear and the ring gear coupled with the output shaft, the drive gear, the ring gear, and the output shaft rotatable about an output shaft rotational axis,

the first layshaft assembly extending along a first layshaft rotational axis and including a first layshaft and a first layshaft input gear, the first layshaft input gear engaged with the drive gear and the input shaft, and

the ring gear rotational control device including a first variable drive assembly coupled with the first layshaft, the first variable drive assembly including a first ring gear drive engaged with the ring gear, the first ring gear drive rotatable about the first layshaft rotational axis, the first variable drive assembly configured to drive rotation of the first ring gear drive with the first layshaft and drive rotation of the ring gear with the first ring gear drive; and

a propulsion unit driven by the output shaft.

15 . The aircraft propulsion system of claim 14 , wherein the first variable drive assembly is configured to operate in a selected gear ratio of a continuous range of gear ratios between a maximum gear ratio of the first variable drive assembly and a minimum gear ratio of the first variable drive assembly, and the continuous range of gear ratios is defined between the first layshaft and the first ring gear drive.

16 . The aircraft propulsion system of claim 14 , wherein the first ring gear drive circumscribes and is radially spaced from the first layshaft.

17 . The aircraft propulsion system of claim 14 , wherein the first variable drive assembly further includes a plurality of inner disks and a pivoting arm assembly, the plurality of inner disks is disposed on the first layshaft, the pivoting arm assembly includes a radially fixed gear assembly and a radially variable gear assembly, the radially fixed gear assembly is rotatable about a first axis radially fixed relative to the first layshaft rotational axis, the radially fixed gear assembly includes a first gear engaged with the first ring gear drive, the radially variable gear assembly is rotatable about a second axis radially moveable relative to the first layshaft rotational axis, the radially variable gear assembly includes a plurality of outer disks and a second gear, the plurality of outer disks are engaged with the plurality of inner disks, and the second gear is engaged with the first gear.

18 . The aircraft propulsion system of claim 17 , wherein the radially variable gear assembly is pivotable about the first axis between a first radial position and a second radial position, the first variable drive assembly has a first gear ratio with the radially variable gear assembly in the first radial position, and the first variable drive assembly has a second gear ratio with the radially variable gear assembly in the second radial position.

19 . The aircraft propulsion system of claim 14 , wherein the gearbox further includes a second layshaft assembly, the second layshaft assembly extends along a second layshaft rotational axis and includes a second layshaft and a second layshaft input gear, the second layshaft input gear is engaged with the drive gear and the input shaft.

20 . A method for driving a propulsion unit of an aircraft propulsion system, the method comprising:

driving an input shaft with a thermal engine;

driving an output shaft about an output shaft rotational axis with an epicyclic gear arrangement coupled with the input shaft by a first layshaft assembly, the epicyclic gear arrangement including a sun gear, a plurality of planet gears, a ring gear, and a carrier, the sun gear coupled with the first layshaft assembly, the plurality of planet gears engaged with the sun gear and the ring gear, the carrier mounted on the plurality of planet gears, the carrier connected to the output shaft;

further driving the output shaft by driving the ring gear to rotate about the output shaft rotational axis with a ring gear rotational control device including a first variable drive assembly coupled between the first layshaft assembly and the ring gear, the first variable drive assembly including a first ring gear drive engaged with the ring gear and rotatable about the first layshaft assembly; and

driving the propulsion unit with the output shaft.