Epicyclic Gear System Having Two Arrays Of Pinions Mounted On Flexpins With Compensation For Carrier Distortion

Abstract

An epicyclic gear system (A) includes sun and ring gears ( 2, 4 ) and planet pinions ( 6, 8 ) arranged in two side-by-side arrays (a, b) between the sun and ring gears, there also being a carrier ( 10, 50 ) to which planet pinions are coupled through flexpins ( 30 ). The carrier has primary and secondary walls ( 20, 22 ) between which the pinions are located and webs ( 24 ) connecting the walls. The flexpins for one array of pinions are cantilevered from the primary wall and the flexpins for the other array of pinions are cantilevered from the secondary wall. When the gear system operates, the carrier along its primary wall is subjected to an externally applied torque which transfers through the system at the planet pinions of the two arrays. The load path (pa) for the pinions at the primary wall is shorter than the load path (pb) for the pinions at the secondary wall, and this disparity causes the carrier to distort. To compensate for this distortion so that the pinions of the two arrays will mesh more evenly with the sun and ring gears, the flexpins of the first array are offset angularly with respect to the flexpins of the second array, or the teeth of the pinions in the first array are narrower than the teeth of the pinions of the second array, or the primary wall of the carrier has areas ( 40, 44 ) of weakness where the flexpins of the first array are cantilevered from it, or the flexpins of the first array are more flexible than the flexpins of the second array. As a consequence, the pinions of the two arrays mesh better under load with the sun and ring gears and share the transfer of torque more evenly.

1 . An epicyclic gear system comprising:
 a sun gear having an axis;   a ring gear surrounding the sun gear and having an axis that coincides with the axis of the sun gear;   first planet pinions meshing with the sun and ring gears in a first array;   second planet pinions meshing with the sun and ring gears in a second array that is offset axially from the first array; and   a carrier having first flexpins coupled to the first planet pinions and second flexpins coupled to the second planet pinions, the carrier further having a coupling region at which torque is applied to the carrier when the gear system is subjected to a load, with the torque transferring between the coupling region and the first flexpins through first load paths and between the coupling region and the second flexpins through second load paths that are longer than the first load paths, and with the difference in lengths of the load paths causing a distortion in the carrier,   and means for compensating for the distortion to enable the first and second pinions to mesh more evenly with the sun and ring gears when torque is applied to the carrier.   
     
     
         2 . An epicyclic gear system according to  claim 1  wherein the means for compensating comprises an angular offset of the first flexpins from the second flexpins in the absence of torque applied to the carrier. 
     
     
         3 . An epicyclic gear system according to  claim 1  wherein the means for compensating comprises the teeth on the first pinions being narrower than the teeth on the second pinions. 
     
     
         4 . An epicyclic gear system according to  claim 1  wherein the means for compensating enables the first flexpins and the second flexpins to undergo substantially the same deflection when torque is transferred in spite of distortion in the carrier caused by differences in the length of the load paths. 
     
     
         5 . An epicyclic gear system according to  claim 4  wherein the means for compensating comprises areas of weakness in the carrier at the first flexpins. 
     
     
         6 . An epicyclic gear system according to  claim 4  wherein the means for compensating comprises the first flexpins being more flexible than the second flexpins. 
     
     
         7 . An epicyclic gear system according to  claim 1  wherein the carrier has first and second walls and webs connecting the walls; and wherein the first flexpins are cantilevered from the first wall and the second flexpins are cantilevered from the second wall. 
     
     
         8 . An epicyclic gear system according to  claim 7  wherein the means for compensating includes areas of weakness in the first wall where the first flexpins are cantilevered from the first wall. 
     
     
         9 . An epicyclic gear system according to  claim 8  wherein the areas of weakness are formed by slots or grooves in the first wall. 
     
     
         10 . An epicyclic gear system according to  claim 9  wherein the slots or grooves are arcuate and follow the contour of the first flexpins. 
     
     
         11 . An epicyclic gear system according to  claim 9  wherein the slots or grooves lie along a circle that circumscribes the axes of the first flexpins. 
     
     
         12 . An epicyclic gear system comprising:
 a sun gear having an axis;   a ring gear surrounding the sun gear and having an axis that coincides with the axis of the sun gear;   first planet pinions meshing with the sun and ring gears in a first array;   second planet pinions meshing with the sun and ring gears in a second array that is offset axially from the first array; and   a carrier including:   a first wall;   a second wall spaced axially from the first wall;   webs connecting the first and second walls;   first flexpins cantilevered from the first wall and projecting into the first pinions;   sleeves interposed between the first flexpins and the first pinions and being cantilevered from the ends of the first flexpins that are remote from the first wall;   second flexpins cantilevered from the second wall and projecting into the second pinions;   more sleeves interposed between the second flexpins and the second pinions and being cantilevered from the ends of the second flexpins that are remote from the second wall; and   a coupling region at which the carrier is subjected to a torque when a load is transferred through the gear system, with that torque transferring to the first pinions through first load paths that pass through the first flexpins and transferring to the second pinions through second load paths that pass through the second flexpins, the second load paths being longer than the first load paths and causing a greater distortion of the carrier along the second load paths than along the first load paths when a load is transferred through the gear system; and   means for compensating for the greater distortion along the second load paths than along the first load paths to enable the first and second pinions to mesh more evenly with the sun and ring gears in spite of the distortion.   
     
     
         13 . An epicyclic gear system according to  claim 12  wherein the means for compensating comprises an angular offset of the first flexpins from the second flexpins in the absence of torque applied to the carrier. 
     
     
         14 . An epicyclic gear system according to  claim 12  wherein the means for compensating comprises the teeth on the first pinions being narrower than the teeth on the second pinions. 
     
     
         15 . An epicyclic gear system according to  claim 12  wherein the means for compensating includes areas of weakness in the first wall where the first flexpins are cantilevered from the first wall. 
     
     
         16 . An epicyclic gear system according to  claim 15  wherein the areas of weakness are formed by slots or grooves in the first wall adjacent the first flexpins. 
     
     
         17 . An epicyclic gear system according to  claim 16  wherein the slots or grooves are arcuate and follow the contour of the first pins. 
     
     
         18 . An epicyclic gear system according to  claim 16  wherein the slots or grooves lie along a circle that circumscribes the axes of the first flexpins. 
     
     
         19 . An epicyclic gear system according to  claim 12  wherein the means for compensating comprises the first flexpins being more flexible than the second flexpins. 
     
     
         20 . An epicyclic gear system comprising:
 a sun gear having an axis;   a ring gear surrounding the sun gear and having an axis that coincides with the axis of the sun gear;   first planet pinions meshing with the sun and ring gears in a first array;   second planet pinions meshing with the sun and ring gears in a second array that is offset axially from the first array; and   a carrier having first flexpins coupled to the first planet pinions and second flexpins coupled to the second planet pinions, the carrier further having a coupling region at which torque is applied to the carrier when the gear system is subjected to a load, with the torque transferring between the coupling region and the first flexpins through first load paths and between the coupling region and the second flexpins through second load paths, the first load paths being stiffer than the second load paths with the difference in the stiffness of the load paths causing a distortion in the carrier,   and means for compensating for the distortion to enable the first and second pinions to mesh more evenly with the sun and ring gears when torque is applied to the carrier.