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).
Test report comparing car frame deflection, damping, and engine mounting to investigate and reduce 'jellying' vibration.
| Identifier | ExFiles\Box 182\M19\ img185 | |
| Date | 29th May 1931 | |
| (2) The next test was carried out on a P.I. car with solid rear feet and sheet aluminium dashboard Fig.VI. The obvious difference is the increase of damping over P.II. in its stiffest condition which appears to account for its freedom from jellying. As there was no P.I. car with diabolo rear feet available, tests were carried out on 14-XX. (E.A.C.VII) which approximates very nearly to P.I. The results obtained (Fig.V) again shew an increase of damping over P.II. A test was carried out with the frame tie-rods disconnected on this car but no difference in torsional stiffness was registered. A further test in which the short diagonal stays to the front crossmember were taken off was done but no increase on angular twist was recorded. From the results of these test it appears that it is not the actual magnitude/range of deflection that produces jellying but the lack of damping in the frame. 14-XX. is fitted with a subframe body and does not jelly, has greater actual deflection for load than P.II. but much more damping; it does not appear justify-able to blame the subframe. On 20-XX. the maximum deflection without the body is greater than when using no rear engine feet when the body is in position, but the damping is also greater. From Fig.III it would appear that full diamond mounting and also no rear engine feet should be better than standard for jellying; this is so to the extent that jellying can be reduced to a reasonable minimum when using full diamond mounting by the use of tightly adjusted torque reaction dampers on the front of the engine. This point has also been evident on 20/25 HP. cars using diamond mounting, jellying being reduced by the use of substantial loading of torque reaction dampers. In the case of the standard front feet and no rear engine feet the point cannot of course be proved in the same manner. Hs{Lord Ernest Hives - Chair}/Lid.{A. J. Lidsey} | ||