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).
Analysis of hypoid gear design, load carrying capacity, wear characteristics, and comparison with spiral bevel gears.
| Identifier | ExFiles\Box 136\5\ scan0132 | |
| Date | 26th January 1926 guessed | |
| angle, the usual profile action of rolling and sliding, and, in addition, the endwise sliding. The endwise sliding is in the nature of the action of a screw, and thus it adds a motion known for quietness to the already smooth action of spiral bevels. As to load carrying capacity, the gear of the pair having a very low spiral angle does not have to carry a thrust component of any great amount. Consequently all tooth strength is available for transmitted load. The pinion is of larger diameter and runs with higher peripheral speed than in the case of spiral bevels. Consequently the tooth load is less for the same transmitted horse power. This added load carrying capacity of both gear and pinion makes it possible to increase the load on a given pair of gears, or what makes more appeal, to reduce the gear diameter for the same load, and lower the floor or increase road clearance. Another factor in lowering the floor is that the pinion offset is more generally below center than above, and the propeller shaft takes a corresponding lowered position at the rear axle end. In considering wear, the only factor of difference between hypoids and spiral bevels is that the hypoids have endwise sliding action. The amount of this is slight as compared with worm drives, for example (being only about 25% as much on the average as for a worm drive of 45° lead angle for the same angular movement of the driven member). This sliding movement is sufficient to spread the oil film and improve the wearing condition rather than otherwise. As a matter of fact, automobile test runs have been made covering many thousand miles of driving, and inspection has shown the gears to be in as good condition as when new. PINION The most important points in the design of hypoid gears are the direction and amount of offset of the pinion axis from the center line of the gear. In rear axles the location of the pinion axis below the gear is highly favored because in this position the hand of spiral of the pinion is left, as is usual in spiral bevel drives, and the axial thrust is away from the gear on forward drive. This lowered position of the propeller shaft also opens up great possibilities of lowered floor boards. Placing the pinion above center necessarily calls for right hand spiral. This may prove to be the best arrangement in some cases, in spite of the inward direction of thrust. -2- Gleason Works - Rochester, N.Y. | ||