Turbine engine gearbox

Abstract

A gas turbine engine comprises a fan, a compressor, a combustor, and a fan drive turbine rotor. The fan drive turbine drives the fan through a gear reduction. The gear reduction includes at least two double helical gears in meshed engagement. Each of the at least two double helical gears are disposed to rotate about respective axes, and each have a first plurality of gear teeth axially spaced from a second plurality of gear teeth by a spacer. Each of the first plurality of gear teeth has a first end facing the spacer and each of the second plurality of gear teeth has a first end facing the spacer. Each first end of the first plurality of gear teeth is circumferentially offset from each first end of the second plurality of gear teeth. A gear ratio of the gear reduction is greater than about 2.3:1. A method is also disclosed.

What is claimed is: 
     
         1 . A gas turbine engine comprising:
 a fan;   a compressor and a combustor;   a fan drive turbine rotor to drive the fan through a gear reduction;   the gear reduction including at least two double helical gears in meshed engagement, each of the at least two double helical gears disposed to rotate about respective axes, and each of the at least two double helical gears having a first plurality of gear teeth axially spaced from a second plurality of gear teeth by a spacer, wherein each of the first plurality of gear teeth has a first end facing the spacer and each of the second plurality of gear teeth has a first end facing the spacer, with each first end of the first plurality of gear teeth being circumferentially offset from each first end of the second plurality of gear teeth; and   a gear ratio of said gear reduction being greater than about 2.3:1.   
     
     
         2 . The gas turbine engine as set forth in  claim 1 , wherein the fan drive turbine for driving a compressor rotor of the compressor, along with the fan through the gear reduction. 
     
     
         3 . The gas turbine engine as set forth in  claim 1 , wherein the gear reduction includes an epicyclic gear system. 
     
     
         4 . The gas turbine engine as set forth in  claim 3 , wherein the gear reduction is an epicyclic gear system that includes a sun gear, a ring gear, and a plurality of intermediate gears that engage the sun gear and ring gear. 
     
     
         5 . The gas turbine engine as set forth in  claim 4 , wherein said at least two helical gears are part of said plurality of intermediate gears. 
     
     
         6 . The gas turbine engine as set forth in  claim 1 , wherein the gear ratio of the gear reduction being greater than or equal to about 2.5:1. 
     
     
         7 . The gas turbine engine as set forth in  claim 1 , wherein there are two additional turbine rotors, with one of the two additional turbine rotors driving a low pressure compressor rotor, and a second of the additional turbine rotors driving a high pressure compressor rotor. 
     
     
         8 . The gas turbine engine as set forth in  claim 7 , wherein the gear reduction includes an epicyclic gear system. 
     
     
         9 . The gas turbine engine as set forth in  claim 8 , wherein the gear reduction is an epicyclic gear system that includes a sun gear, a ring gear, and a plurality of intermediate gears that engage the sun gear and ring gear. 
     
     
         10 . The gas turbine engine as set forth in  claim 9 , wherein said at least two helical gears are part of said plurality of intermediate gears. 
     
     
         11 . A method of designing a gas turbine engine comprising:
 providing a fan, a compressor and a combustor;   providing a fan drive turbine rotor to drive the fan through a gear reduction;   the gear reduction including at least two double helical gears in meshed engagement, each of the at least two double helical gears disposed to rotate about respective axes, and each of the at least two double helical gears having a first plurality of gear teeth axially spaced from a second plurality of gear teeth by a spacer, wherein each of the first plurality of gear teeth has a first end facing the spacer and each of the second plurality of gear teeth has a first end facing the spacer, with each first end of the first plurality of gear teeth being circumferentially offset from each first end of the second plurality of gear teeth; and   a gear ratio of the gear reduction being greater than about 2.3:1.   
     
     
         12 . The method as set forth in  claim 11 , wherein the fan drive turbine for driving a compressor rotor, along with the fan through the gear reduction. 
     
     
         13 . The method as set forth in  claim 12 , wherein the gear reduction is an epicyclic gear system that includes a sun gear, a ring gear, and a plurality of intermediate gears that engage the sun gear and ring gear. 
     
     
         14 . The method as set forth in  claim 13 , wherein said at least two helical gears are part of said plurality of intermediate gears. 
     
     
         15 . The method as set forth in  claim 11 , wherein the gearbox includes an epicyclic gear system. 
     
     
         16 . The method as set forth in  claim 15 , wherein the gear reduction is an epicyclic gear system that includes a sun gear, a ring gear, and a plurality of intermediate gears that engage the sun gear and ring gear. 
     
     
         17 . The method as set forth in  claim 16 , wherein said at least two helical gears are part of said plurality of intermediate gears. 
     
     
         18 . The method as set forth in  claim 17 , wherein the gear ratio of the gear reduction being greater than or equal to about 2.5:1. 
     
     
         19 . The method as set forth in  claim 11 , wherein there are two additional turbine rotors, with one of the two additional turbine rotors driving a low pressure compressor rotor, and a second of the additional turbine rotors driving a high pressure compressor rotor.