06FTM10-2006 pdf free.Fabrication, Assembly and Test of a High Ratio, Ultra Safe, High Contact Ratio, Double Helical Planetary Transmission for Helicopter Applications.
To transcend the limitations of current planetary designs 111, and to investigate improved gear arrangements for helicopter main rotor drives, a high ratio. Ultra-Safe, high contact ratio, staggered and inter- meshed planet, double-helical compound epicyclic gear system concept was developed. The improved transmission is configured as a single stage compound planetary with an axially staggered, interrneshed, spur gear input mesh arid double helical output mesh with an overall ratio of 1 7.5-to- 1. This ratio is approximately equivalent to the existing baseline transmission, wt’iich has a two-stage simple planetary system described above. The DHP gears were sized for the same power and speed operating conditions as the baseline design, 4500 HP at 225 RPM (output). The core DHP transmission configuration is shown in Figure 1.
The unique features of this planetary system are the use of double helical gears for the final mesh and the axially staggered, intermeshed spur gear configuration, which permits the use of six planets rather than three, for greater power density. The overall spatial arrangement is slightly larger than the baseline two-stage planetary system: however the weight of the system is less.
A capacity limiting factor of the simple planetary arrangement is the number of planets that can be accommodated within the internal ring gear diameter. Note that the sun-planet mesh in a compound planetary is not restricted to fit within the internal ring gear diameter. This means that the sun-planet envelope may be radially larger than in a simple planetary design. With the compound planetary, staggering” the planets can circumvent another limitation and substantially increase capacity. In staggered arrangement, the sun gear is lengthened to allow it to mesh with staggered planetary gears. This nearly doubles the number of planet gears which can fit within the compound planetary. resulting in significantly higher capacity and power density for a given gearbox envelope. A fully floating sun gear design was used to aid in uniform load-sharing among the planet gears.
The use of double helical gears in a compound planetary arrangement is another unique feature of this drive. Double helical gears are used extensively in heavy industry — like mill drives. One benefit of the double helical arrangement is increased total contact ratio due to the action of the helix angles in the double helical gears. The increased contact ratio results in higher mesh load capacity and reduces mesh-generated noise. Since the thrust loads developed on each helix within the double helical gear are oriented in opposing directions, the net axial load from a double helical mesh is zero. This permits a simpler support bearing arrangement where large axial load capacity is not required.06FTM10 pdf free download.