Gear Production
Issue link: http://gear.epubxp.com/i/155418
Figure 3. This gear box used in testing has the composite hybrid driving gear on the left, while the gear on the right is driven. • Hybrid gear left side, all-steel gear right side • All-steel gear left side, hybrid gear right side • Hybrid gear both sides. The four confgurations employed were 2,500, 5,000, 7,500 and 10,000 rpm at 50, 100, 200 and 300 psi load pressure. Vibration was measured using an accelerometer on the driven gear and expressed in Gs. The noise level was recorded using a handheld sound level meter at a distance of 1 inch (25.4 mm) from the test gearbox cover. Test data showed that among the four confgurations tested, vibration was greatest (15.933 Gs) in the steel-on-steel combination at 10,000 rpm and 300 psi load. The maximum vibration in the other three confgurations at 10,000 rpm/300 psi was: composite (driver)on-steel combination = 13.016 Gs; steel (driver)-on-composite = 7.025 Gs; composite-on-composite = 12.766 Gs. In sound testing, the steel-on-steel combination produced the "loudest" measurement of 103 db at 10,000 rpm, but the composite-on-composite combination wasn't far behind at 100 db, also at 10,000 rpm. In general, the data were mixed as to how consistently the composite material might be able to attenuate vibration and noise. The paper's authors attribute this to manufacturing imperfections in the composite that might be corrected in a more robust fabrication process. For example, no grinding of the gear teeth was performed post-attachment of the composite. In addition, the composite curing actually reduced the backlash of the components due to stretching of the metal outside rim; the backlash also was not consistent around the gear. NASA Glenn also conducted long-term testing of the hybrid gear to assess performance over an extended period of time. The hybrid gears were run for more than 300 x 106 revolutions at 10,000 rpm and 250 psi torque load with an oil inlet temperature of 120°F/49°C. The hybrid gears, the authors report, operated without any problem during this extended period. NASA Glenn ultimately concluded that hybrid gears show promise given their ability to operate over a long period of time. Further, powerto-weight ratios aboard a rotorcraft could be possible with the replacement of steel webs with composites. Finally, reduced noise and vibration would be expected using a hybrid gear if manufacturing processes are refned to produce aerospace-quality gears. September 2013—25