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).
Page discussing gear mounting, tooth load distribution, and displacement in hypoid pinion systems.
| Identifier | ExFiles\Box 114\1\ scan0080 | |
| Date | 11th January 1937 guessed | |
| in order to obtain the minimum maximum pressure. Also, because of the inherently stronger teeth of the hypoid pinion finer pitches may be used yet staying within the requirements of tooth strength against rupture or tooth breakage, but with too fine pitches the tooth deformation may become so great as to offset the advantage of having a larger number of pairs of teeth in contact. The tooth load distribution, however, is considerably altered by the deformation of the carrier or mounting for the bearings, deformation of bearings themselves, and deformation in the pinion shaft and in the differential case on which the gear is mounted. GEAR MOUNTING The rigidity of the gear mountings not only affects the pressures occurring at the contacting zones but also is a determining factor in the quietness of operation of the gears. Referring to Figure 10, the full lines indicate the normal relationship of gear and pinion for a straddle mounted pinion design. The dotted outline indicates much exaggerated, the displaced position of the pinion when subjected to forward driving torque. The pinion is displaced upward through the angle "O" and actually away from the gear by the distance "X". In Figure 11 is shown the relative displacement in an overhung mounting and in Figure 12, full lines again show the normal position of gear and pinion and the dotted lines show that the displacement of the gear and pinion is away from each other. In reverse drive similar deflections occur excepting that the vertical displacements are reversed as are also the axial thrust displacements of the pinion. Displacements, that is the important ones, are usually classified as follows: (1) Pinion lift. (2) Pinion side movement. (3) Pinion axial movement. (4) Gear lift. (5) Gear side movement. These displacements are actually determined by operating the axle unit in a test machine adapted to apply all load variations from no load to the maximum load to which the unit is expected to operate at the full motor torque in low and reverse gears in the car. Micrometer dial indicators are mounted at vital points and the displacements determined by loading the unit with the gears running very slowly, at the same time the gear teeth are painted with red lead at the various loads and a pattern of the tooth contact is determined for these loads. In this way it is possible to correlate very accurately the change in tooth contact pattern with the displacements which occur at the various loadings. With the indicators mounted at vital points it is also possible to determine what factors contribute to the deflection. The deflections in the bearings alone can be determined and the individual deflections occurring in the ring gear, differential bearing pedestals and in the differential case can all be measured. This is, also, true with the pinion mounting in which the deflections occurring in the pinion bearings can be separated out from the deflection occurring in the pinion shaft and in the housing. It is by this means that gear sections, pinion shaft diameter, bearing sizes, and the structural proportion of the differential case and carrier can be arrived at for the maximum deflection values into which a good design would fall. In Figure 11 is shown the relative displacement for an overhung pinion and in Figure 12 is shown the relative displacement of the gear and pinion in the plan view. Obviously, since all of these materials are elastic in character, it is impossible to make the mountings perfectly rigid. The maximum displacements which are permissible are determined or dictated largely by limitations in contacting patterns of the gear tooth. - 5 - | ||