From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical document detailing the characteristics, advantages, and production of hypoid gears and pinions.
| Identifier | ExFiles\Box 136\5\ scan0133 | |
| Date | 26th January 1926 guessed | |
| It is well known that a pinion whose thrust during forward drive is toward the gear must be held in position even more rigidly than one having thrust in the opposite direction, because movement toward the gear takes up the backlash and allows the pinion teeth to wedge into the gear teeth. While this arrangement has been unpopular in the past for the reason stated, a sufficiently rigid design can be worked out so as to make right hand spiral available for use. The amounts of offset of the pinion already in use are 1½", 2", 2½" and 3", and these, with the possible addition of 3½", seem to cover the requirements of rear axle gears. The variation is to accommodate gears of varying diameters and ratios. Practical considerations will sometimes alter the theoretical amount a half inch either way. To give an idea of some of the characteristics of hypoid gears an average has been made of the results, obtained in four different combinations between 4½ and 5 to 1 ratio. This is a comparison between spiral bevel gears and hypoid gears. In each case the number of teeth in gear and pinion and the diameter of the gear were the same for bevels and hypoids. The load figures are based on the same power delivered to the rear axle. The hypoids show as follows: 20% increase in pinion diameter. 12% less normal tooth load. 16% less tangential tooth load. 9% forward) less endwise thrust 16% reverse) load. 5% forward) more separating pressure 13% reverse) (on account of 20° pressure angle) 26% as much endwise sliding motion as for a worm drive of 45° angle. Greater diameter increase of the pinion may be obtained when desired, as for instance in higher ratios. This, however, requires a higher spiral angle with a slight increase in axial thrust. In many cases advantage can be taken of the reduced loads by cutting down gear diameter about 10% without increasing unit stress in the material. PRODUCTION. The production operations for hypoid gears and pinions are in general the same as for spiral bevels. Preparation of the blanks varies only in diameter and angles of the blanks. Operations following the cutting do not change, except that for testing, burnishing and lapping, machines must be used -3- Gleason Works - Rochester, N.Y. | ||