Reliable gearbox for gas turbine engine
An engine for an aircraft has an engine core having a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan having a plurality of fan blades; and a gearbox. The gearbox is arranged to receive an input from a gearbox input shaft portion of the core shaft and to output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft. The gearbox is an epicyclic gearbox and has a sun gear, a plurality of planet gears, a ring gear, and a planet carrier. The planet carrier and the gearbox support each have a torsional stiffness, and a carrier to gearbox support torsional stiffness ratio is greater than or equal to 2.3.
1. A gas turbine engine for an aircraft comprising:
an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor;
a fan located upstream of the engine core, the fan comprising a plurality of fan blades;
a gearbox that receives an input from a gearbox input shaft that is a portion of the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox comprising a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the plurality of planet gears are mounted; and
a gearbox support arranged to support the gearbox in a fixed position within the gas turbine engine and having a torsional stiffness, wherein
a planet carrier to gearbox support torsional stiffness ratio of:
a
torsional
stiffness
of
the
planet
carrier
the
torsional
stiffness
of
the
gearbox
support
is in the range from 2.3 to 300.
2. The gas turbine engine of claim 1 , wherein the planet carrier to gearbox support torsional stiffness ratio is in the range from 2.6 to 50.
3. The gas turbine engine of claim 1 , wherein the torsional stiffness of the planet carrier is in the range from 1.60×10 8 to 1.00×10 11 Nm/rad.
4. The gas turbine engine of claim 1 , wherein a torsional stiffness of the gearbox input shaft is in the range from 1.4×10 6 Nm/radian to 2.5×10 8 Nm/radian.
5. The gas turbine engine of claim 1 , wherein the torsional stiffness of the gearbox support is in the range from 4.2×10 7 Nm/radian 1.0×10 10 Nm/radian.
6. The gas turbine engine of claim 1 , wherein the fan has a fan diameter in the range from 240 to 280 cm, and the planet carrier to gearbox support torsional stiffness ratio is in the range from 2.5 to 5.5.
7. The gas turbine engine of claim 1 , wherein the fan has a fan diameter in the range from 330 to 380 cm, and the planet carrier to gearbox support torsional stiffness ratio is in the range from 3.5 to 15.
8. The gas turbine engine of claim 1 , wherein the torsional stiffness of the planet carrier multiplied by the torsional stiffness of the gearbox support is in the range from 5.0×10 15 N 2 m 2 rad −2 and 1.0×10 19 N 2 m 2 rad −2 .
9. The gas turbine engine of claim 1 , wherein
the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft;
the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and
the second turbine, the second compressor, and the second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.
10. The gas turbine engine of claim 1 , wherein the planet carrier comprises a forward plate and a rearward plate and pins extending between the forward plate and the rearward plate, each of the pins being arranged to have one of the plurality of planet gears mounted thereon.
11. The gas turbine engine of claim 10 , wherein the planet carrier further comprises lugs extending between, the forward plate and the rearward plate, the lugs being arranged to pass between adjacent ones of the plurality of planet gears.
12. The gas turbine engine of claim 1 , wherein the gearbox comprises 3, 5, or 7 planet gears.
13. The gas turbine engine of claim 1 , wherein the fan has a fan diameter greater than 240 cm and less than or equal to 380 cm.
14. The gas turbine engine of claim 1 , wherein the gearbox is a star gearbox, in which the planet carrier does not rotate in use.
15. The gas turbine engine of claim 1 , wherein a pitch circle diameter of pins on which the plurality of planet gears are mounted is in the range from 0.38 to 0.65 m.
16. The gas turbine engine of claim 1 , wherein the core shaft provides a mounting for the sun gear on which the sun gear moves.
17. The gas turbine engine of claim 1 , wherein a gear ratio of the gearbox is in the range from 3.2 to 4.5.
18. A propulsor for an aircraft comprising:
a fan comprising a plurality of fan blades;
a gearbox;
a motor for driving the fan via the gearbox, wherein the gearbox is arranged to receive an input from a gearbox input shaft that is a portion of the core shaft driven by the motor and to output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox comprising a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the plurality of planet gears are mounted; and
a gearbox support arranged to support the gearbox in a fixed position within the propulsor and having a torsional stiffness, wherein
a planet carrier to gearbox support torsional stiffness ratio of:
a
torsional
stiffness
of
the
planet
carrier
the
torsional
stiffness
of
the
gearbox
support
is in the range from 2.3 to 300.
19. The propulsor of claim 18 , wherein the planet carrier to gearbox support torsional stiffness ratio is in the range from 2.6 to 50.
20. The propulsor of claim 18 , wherein a torsional stiffness of the gearbox input shaft is in the range from 1.4×10 6 Nm/radian to 2.5×10 8 Nm/radian.