DESIGN, MANUFACTURING PROCESSES AND LOAD CAPACITY OF CYLINDRICAL GEAR PAIRS WITH 2 TO 4 PINION TEETH F0R HIGH GEAR RATIO : 1st Report, Design, Manufacture and Surface Durability of the Gear Pairs with 2 to 3 Pinion Teeth

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Practical design methods of cylindrical gear pairs with 2 to 4 pinion teeth for higher gear ratios were investigated to obtain higher load carrying capacities. Using a conventional hob with a pressure angle of 20°and a conventional hobbing machine with special made attachments, the authors designed and made test gear pairs with gear ratios of Z₂/Z₁=41/2 and 38/3. These gear pairs were tested beyond 10×10⁶ pinion rotations using the power circulating gear-load-testing-machines made by the authors. The tooth surfaces of large gears were very likely to pit although the load cycles were appreciably smaller than those on the pinion teeth. It was clearly indicated that a gear with higher hardness than that of the mating pinion had a greater load carrying capacity. The test gear pairs produced much higher sliding due to greater profile shifting than that of gear pairs with numbers of pinion teeth of greater than six, but they showed a comparatively good efficiency of about 93% in the case when the test gear pairs with 3 pinion teeth were used under normal running conditions.