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 using a 4.6 ratio on a .650 offset Bentley fully floating axle.
| Identifier | ExFiles\Box 84\4\ scan0404 | |
| Date | 4th October 1938 | |
| 202? To By; from Da{Bernard Day - Chassis Design}/HB.{C. E. Harcombe} c. to Da.{Bernard Day - Chassis Design} c. to Rm.{William Robotham - Chief Engineer} c. to Da{Bernard Day - Chassis Design}/Hdy.{William Hardy} Da{Bernard Day - Chassis Design}/HB.{C. E. Harcombe}1/N.4.10.38. 4.6 Ratio on .650 Offset Fully Floating Axle. Bentley. If it is intended to use a lower axle ratio than the present 4.3 on the existing fully floating axle, the following points should be considered: Stresses. The stress in a 10 tooth pinion (10/46; 4.6 ratio) will be 8% higher than in the standard 10/43 combination. There is no reason to suppose that this slight additional stress will cause failure. The stress may be reduced to below that in the 10/43 pinion by using 9/42 (4.66) or 8/37 (4.625) combinations. See appended table. Tooth Load/inch on Gear. Owing to the lower ratio, the tooth load per inch on the gear is about 8% higher than on the standard 10/43 ratio, and is about 38% more than Messrs.Gleason's recommended figure, which is 1600 lb/in. on direct gear. However, the standard 10/43 ratio and Ph.III. are 28% above Messrs.Gleason's recommendation. See appended table. Pinion Nose Bearing. Due to the reduction of the pinion root cone angle, it is possible that the tooth cutter may gash the nose bearing surface. This condition will be aggravated by using 8 or 9 tooth pinions as the root cone angle will be further reduced owing to the deeper teeth. It is not possible to say whether this trouble will occur unless a test can be made on a standard pinion fitted with an aluminium sleeve to obtain some idea of the cutter clearance. If found necessary the length of the nose could probably be reduced a little, or possibly Messrs.Gleason could increase the root angle to clear, as they proposed for the Phan.III. Alternatively now that the nose bearing has two rows of rollers, a smaller size may be found satisfactory. Pinion Nose Bearing Bridge. Owing to the smaller pinion the gear approaches the bridge. It would appear that there will still be sufficient clearance between the gear teeth and the bridge, but it is unlikely that ratios lower than 4.66 could be accommodated. Cont'd.... | ||