We Claim:
1. A planet gearbox for connection to a carrier of an epicyclic gearing arrangement that has only a single input and a single output and that includes a sun gear and a ring gear surrounding the planet gearbox and the sun gear, the planet gearbox comprising:
a support pin configured to be fixed to the carrier and defining a cylindrical outer surface that is radially equidistant from a central axis that extends in an axial direction;
an inner race defining a cylindrical inner surface that is non-rotatably connected to the cylindrical outer surface of the support pin, the inner race defining an outer surface that defines at least one track, each track defined in the outer surface being configured to receive and rotatably guide therein a respective plurality of cylindrical rollers;
a respective plurality of cylindrical rollers rotatably disposed within each respective track of the inner race;
wherein each roller defines a cylindrical outer surface that is disposed with an axis of rotation that extends in a direction parallel to the axial direction, and the cylindrical outer surface of each roller is defined by a diameter that extends through the axis of rotation along a direction that is normal to the axis of rotation, wherein the outer cylindrical surface of each roller defines a length in the direction parallel to the axis of rotation of the roller, and the ratio of each roller’s length to each roller’s diameter is greater than one;
for each respective track, a respective roller cage disposed between the inner race and the outer race, wherein there is a small clearance between each roller cage and the inner race, each respective roller cage being configured to maintain in each respective track a respective separation between each respective roller in each pair of adjacent rollers in that respective track, each roller cage defining a first plurality of generally cylindrical openings, each generally cylindrical opening defining a major axis in the axial direction and a minor axis in the circumferential direction, each of the openings being spaced equidistantly apart circumferentially around the respective roller cage by a plurality of
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equidistantly spaced apart webs, each web extending in the axial direction and defining a cross-web thickness in the circumferential direction; and
an outer race defining an inner cylindrical surface contacting each respective plurality of cylindrical rollers, the outer race defining an outer cylindrical surface that defines a gearing surface that is configured to mesh with both the sun gear and the ring gear;
wherein each web of each roller cage has a cross-web thickness that measures 15% to 25% of the diameter of one of the rollers.
2. The planet gearbox as claimed in claim 1, wherein each web of each roller cage has a cross-web thickness that measures 15% to 20% of the diameter of one of the rollers.
3. The planet gearbox as claimed in claim 1, wherein the small clearance between the roller cage and each inner race is on the order of 0.005 to 0.050 inches inclusive.
4. The planet gearbox as claimed in claim 3, wherein each track defines a pair of guiderails, which extend continuously in the circumferential direction around the outer surface of the inner race and radially outwardly from an annular raceway defined in the outer surface of the inner race, each track defines a pair of sidewalls that together define the two extreme edges of the raceway and extend radially between the raceway and the respective guiderails, wherein the small clearance between each roller cage and the inner race is defined between the respective roller cage and the respective guiderails of the respective track of the inner race.
5. The planet gearbox as claimed in claim 1, wherein the generally cylindrical openings in each respective roller cage are aligned in a circumferential row disposed above a respective track of the inner race, each generally cylindrical opening of the respective roller cage is bounded in the circumferential direction
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by a pair of opposing and spaced apart shoulder elements, wherein each respective roller is disposed with its cylindrical outer surface extending through a respective opening defined by the respective roller cage, wherein the small clearance between each respective roller cage and the respective track of the inner race is defined between the respective shoulder elements of the respective roller cage and the respective guiderails of the respective track of the inner race.
6. The planet gearbox as claimed in claim 1, wherein at least one of the webs of at least one roller cage is a split web.
7. The planet gearbox as claimed in claim 1, wherein the gearing surface of each cylindrical outer race is a double helical gearing surface with the bias of each one of the two double helical gearing surfaces of the outer race being disposed nonparallel with the other one of the two double helical gearing surfaces of the outer race.
8. The planet gearbox as claimed in claim 1, wherein each track extends circumferentially around the outer surface of the inner race, each track defining a raceway surface extending circumferentially and concentrically with respect to the inner cylindrical surface of the inner race and contacting a portion of each of the cylindrical outer surfaces of the rollers disposed in the respective track, each track defining a pair of radially extending sidewalls that are spaced apart in the axial direction from each other.
9. The planet gearbox as claimed in claim 1, wherein the inner cylindrical surface of the inner race is press-fitted to the cylindrical outer surface of the support pin.
10. The planet gearbox as claimed in claim 1, wherein each of the rollers is formed of ceramic material.
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11. A gas turbine engine comprising:
a fan including a plurality of blades extending radially from a hub and rotatable about a first axis of rotation defined centrally through the hub; a compressor disposed downstream from the fan; a turbine disposed downstream of the compressor; a rotatable input shaft mechanically coupling the compressor to rotate in unison with the turbine;
an epicyclic gearing arrangement that has only a single input and that includes a carrier, a sun gear rotatable about a second axis of rotation that is parallel to the first axis of rotation, a ring gear disposed circumferentially around the sun gear, at least one planet gearbox that is carried by the carrier and houses a planet gear rotatable with respect to the carrier about a third axis of rotation that is parallel to the second axis of rotation, wherein the at least one planet gear meshes with both the sun gear and the ring gear; and
an engine envelope surrounding the fan, the compressor, the turbine and the epicyclic gearing arrangement, wherein one of the ring gear and the carrier is non-rotatably coupled to the engine envelope; and the planet gearbox further including:
a support pin fixed to the carrier and defining a cylindrical outer surface that is equidistant from a central axis that extends in an axial direction,
an inner race defining an inner cylindrical surface that is non-rotatably connected to the cylindrical outer surface of the support pin, the inner race defining an outer surface that defines at least one track, each track being configured to receive and rotatably guide therein a respective plurality of cylindrical rollers,
an outer race defining an outer cylindrical surface that defines a gearing surface of the planet gear and that is configured to mesh with both the sun gear and the ring gear, the outer race defining an inner cylindrical surface that is opposed to the outer cylindrical surface of the outer race,
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a plurality of rollers disposed in each track of the inner race, each roller being free to rotate about a fourth axis of rotation that is parallel to the third axis of rotation, each roller defining a cylindrical outer surface contacting both the inner race and the inner cylindrical surface of the outer race, each roller defining a length in the direction parallel to the fourth axis of rotation and wherein the ratio of each roller’s length to each roller’s diameter is greater than one, and
for each respective track, a respective roller cage disposed between the inner race and the outer race, wherein there is a small clearance between each roller cage and the inner race, each respective roller cage being configured to maintain in each respective track, a respective separation between each respective roller in each pair of adjacent rollers in that respective track, each roller cage defining a first plurality of generally cylindrical openings, each generally cylindrical opening defining a major axis in the axial direction and a minor axis in the circumferential direction, each of the openings being spaced equidistantly apart circumferentially around the respective roller cage by a plurality of equidistantly spaced apart webs, each web extending in the axial direction and defining a cross-web thickness in the circumferential direction,
wherein each web of each roller cage has a cross-web thickness that measures 15% to 25% of the diameter of one of the rollers.
12. The planet gearbox as claimed in claim 11, wherein each web of each roller cage has a cross-web thickness that measures 15% to 20% of the diameter of one of the rollers.
13. The planet gearbox as claimed in claim 11, wherein the small clearance between the roller cage and each inner race is on the order of 0.005 to 0.050 inches inclusive.
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14. The planet gearbox as claimed in claim 13, wherein each track defines a pair of guiderails, which extend continuously in the circumferential direction around the outer surface of the inner race and radially outwardly from an annular raceway defined in the outer surface of the inner race, each of the tracks defines a pair of sidewalls that together define the two extreme edges of the raceway and extend radially between the raceway and the respective guiderails, wherein the small clearance between each roller cage and the inner race is defined between the roller cage and the guiderails of the inner race.
15. The planet gearbox as claimed in claim 11, wherein each roller cage defines a circumferential row disposed above a respective track of the inner race, each circumferential row defining a plurality of generally cylindrical openings, each generally cylindrical opening defining a major axis in the axial direction and a minor axis in the circumferential direction, the openings in each row being spaced equidistantly apart circumferentially around the respective cage with the number of openings in each row being equal to the number of rollers disposed in the respective track disposed beneath the respective row of the respective roller cage, wherein each respective roller is disposed with its cylindrical surface extending through a respective opening defined by the respective roller cage.
16. The gas turbine engine as claimed in claim 11, wherein the compressor is a low pressure compressor, wherein the turbine is a low pressure turbine, and wherein the shaft is a low pressure shaft mechanically coupling the low pressure compressor to the low pressure turbine.
17. The planet gearbox as claimed in claim 11, wherein the ratio of each roller’s length to each roller’s diameter is greater than 1.3.
18. The planet gearbox as claimed in claim 11, wherein each roller has a length-to-diameter ratio that falls within the range from 1.3 to 1.8, inclusive.
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19. The planet gearbox as claimed in claim 11, wherein the gearing surface of each cylindrical outer race is a double helical gearing surface with the bias of each one of the two double helical gearing surfaces of the outer race being disposed nonparallel with the other one of the two double helical gearing surfaces of the outer race.
20. The planet gearbox as claimed in claim 11, wherein the inner cylindrical surface of the inner race is press-fitted to the cylindrical outer surface of the support pin.
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