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).
Continued report on isolating a centre joint using rubber and felt to reduce noise and vibration.
| Identifier | ExFiles\Box 156\4\ scan0107 | |
| Date | 9th August 1939 | |
| 2. Mx.{John H Maddocks - Chief Proving Officer}1/MG.9.8.39 continued. the rubber is as soft as possible and has the minimum pre-loading. Rubber is considered to be the most reliable insulating material when used in this exposed position where felt might become charged with wet and mud and so lose its effectiveness. Having reached this stage, it was then learned that General Motors had already produced an insulated centre joint using felt as an insulating material, mainly for the purpose of reducing gear noise. Inspection of the drawings, however, showed that it was a fairly rigid mounting with only a thin layer of felt round the centre housing, and from our experience it did not appear to be very promising, so we did not pursue it any further. It is worth noting that the bottom flange of the cruciform is less sensitive than the side walls because even a solid fixing on the flange is better than the Standard arrangement. Further advantages of isolating the centre joint are:- 1. Out of balance effect of propeller shaft is not critical. 2. There is a slight reduction in noise from gearbox on indirect gears. 3. Deflection of the road springs, or variations in car load, with resultant change in angularity of the propeller shaft did not cause vibration to become apparent. 4. It is not sensitive to variations in tilt of the axle, which with normal arrangement can only be best for one condition of load or spring deflection. Att. Sketch. P.S. It is quite possible that some advantage over an all-rubber mounting could be obtained by using one layer of felt in conjunction with soft rubber, as the latter would then accommodate any settling down of the felt. | ||