Hybrid Gear

John H. Glenn Research Center, Cleveland, Ohio

Reducing stiffness-induced gear noise and making lighter-weight gearing components would be a substantial advantage over the current all-metallic configuration. The use of composites to join metallic hubs to the metallic gear rim would reduce manufacturing costs of large aerospace gears, with weight reductions and modified noise/vibration response. All-metallic gearing components do little to dampen the gear meshing noise induced by the nonlinear tooth stiffness during the meshing process. With a composite web, this metallic path for vibration and noise transfer would be eliminated and alter the resultant transmitted noise/vibration.

(a) An isometric view of the modified hybrid gear and (b) prototype hybrid gear.

A hybrid gear was developed that can transfer the same level of torque as an all-metallic traditional gearing component. In rotorcraft drive systems, lightweight and high load capacity are desirable attributes. The hybrid gear attaches to a metallic shaft and outer gear rim with composite layup between the shaft interface and the gear tooth rim. The composite layup serves two purposes: (1) to lighten the gear member while having similar torque carrying capability, and (2) to alter the impact loading driven noise/vibration that is typical in gear systems.

Three main features of the composite gear are the outside toothed rim, the composite web, and the gear feature that connects to a shaft or serves as the shaft of the gear. Within the composite material, there are outer and inner plies. There is a toothed region, as well as an internal polygon drive where the composite would pass the gear forces and torque. Aerospace gears are fabricated with minimum rim thickness for minimum weight.

The hybrid gear is assembled in a fixture that provides the proper alignment for the gear about its rotational axis. One material/design approach uses an in-plane and quasi-isotropic carbon fiber/epoxy matrix composite material and a compression molding process for fabrication. Alternative embodiments for a planar gear could utilize other fiber types, fiber architectures, and matrix materials. They could also include gears of more complex shapes.

This work was done by Robert F. Handschuh and Gary D. Roberts of Glenn Research Center.

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