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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application derives priority from and otherwise claims the benefit of U.S. provisional application 61 / 028,274, filed 13 Feb. 2008, and U.S. provisional application 61 / 125,715, filed 28 Apr. 2008, both of which are incorporated herein by reference.TECHNICAL FIELD[0002]This invention relates in general to epicyclic gear systems, and more particularly to an epicyclic gear system having its planet pinions arranged in two arrays on flexpins with compensation for carrier distortion.BACKGROUND ART[0003]The typical epicyclic gear system has a sun gear, a ring gear surrounding the sun gear, and planet pinions located between and engaged with the sun and ring gears, and in addition, it has a straddle-type carrier that provides pins about which the planet pinions rotate, with the pins being anchored at both ends in the carrier. A gear system so configured has the capacity to transfer a large amount of power in a relatively compact configuration...

AI Technical Summary

Benefits of technology

[0006]The cantilevers produce high stresses in the flexpins, and to have more moderate stresses, some carriers have two walls with flexpins anchored in each of the walls and, of course, a separate planetary pinion around each flexpin. This doubles the number of flexpins to share the torque transferred through the system and thus reduces the unit load applied to each flexpin. The planet pinions are arranged in two arrays between the walls, there being for each pinion in the one array and corresponding pinion aligned with it in the other array. Spaces exist between pairs of corresponding pinions and webs extend between the two walls in these spaces. The carrier, whether it rotates or not, is subjected to an externally applied torque at one of its walls. The planet pinions transmit torque through the system, but the lengths of the load paths from the flexpins on the two walls differ, the load paths from the flexpins on the primary wall, which is subjected to the external torque, being considerably shorter than the load paths from the flexpins on the other or secondary wall. This renders the array, identified with the shorter load paths stiffer than the array identified with the longer load paths. The carrier undergoes a distortion that causes the flexpins on the secondary wall displace angularly with respect to the flexpins on the primary wall, reference being to the axis of the planetary system. Since the planet pinions of the two arrays mesh with the sun and ring gears, the displacement causes an uneven sharing of the torque transmitted at the teeth where the pinions mesh with the sun and ring gears.

Problems solved by technology

But heavy loads tend to distort the carrier and its pins and skew the axis about which the planet pinions rotate.

Under such conditions, the planet pinions do not mesh properly with the sun and ring gears.

This causes excessive wear in the planet pinions and the sun and ring gears, generates friction and heat, and renders the entire system overly noisy.

Since the planet pinions of the two arrays mesh with the sun and ring gears, the displacement causes an uneven sharing of the torque transmitted at the teeth where the pinions mesh with the sun and ring gears.

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