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).
Investigations into the causes of noisy Bentley rear axles, focusing on pinion deflection.
| Identifier | ExFiles\Box 84\4\ scan0293 | |
| Date | 23th September 1937 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} c. Hs.{Lord Ernest Hives - Chair} c. Da.{Bernard Day - Chassis Design} c. Hdy.{William Hardy} BENTLEY REAR AXLE. In our investigations into the causes of noisy axles, we have been measuring the deflections of the pinion under static loads up to 1st. speed torque. We have always known that the deflection at the oil retaining thread is considerable and always in one direction. We have therefore, used the deflection at this point as a basis for comparison of various types of pinion mounting. We suspected at first that the deflection was not only due to the pinion thrust bearing, but also distortion of the case, bridge and nose bearing. We now know that every cause except the thrust bearing is insignificant. When the thrust bearing was replaced as a solid bronze bush the usual deflection of .006 had become .00025. We have therefore tried several forms of thrust bearing and also the effect of slack in the existing bearing. Deflections are recorded in the attached blue print. The figures show the immediate increase in deflections at small torques due to lack of preload, or worse still, slack. As we are not troubled with noise under maximum torque conditions and know that overrun noise which has developed is due to loss of preload, and can be cured by reinstating the preload, the essential features of the pinion mounting seems to be complete absence of deflection up to top gear torque. The combination of a roller bearing and angular contact with free outer race, although preventing large deflections at maximum torque is not so good as a double row ball bearing with a small contact angle on the journal half and sufficiently preloaded. | ||