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).
Preliminary report on the investigation of rear road springs, detailing findings on plate thickness, stress points, and leaf breakage.
| Identifier | ExFiles\Box 80\2\ scan0339 | |
| Date | 30th June 1920 | |
| R.R. 235a (100 T) (S. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 643. 19-2-20) G 2618 X.4056 To R.{Sir Henry Royce} from Da.{Bernard Day - Chassis Design} Copy to Bn.{W.O. Bentley / Mr Barrington} Copy to EFC. Da{Bernard Day - Chassis Design}23/CB30.6.20. X.2628. X.4056. RE REAR ROAD SPRINGS. We have not completed our investigations of springs. Apart from the job being a lengthy one we have been somewhat delayed by the preparation of the bodywork, etc. on 6.EX. We have, however, discovered several interesting things. (1) The present springs, though so instructed, are actually not made with plates of constant thickness. They may vary in any one spring by as much as .100 and the graduation of thickness is not regular from plate to plate. Further, the thickness varies along any one plate. (2) The place where the point of maximum stress occurs may be at the point of support of any leaf by the top of the leaf above, or it may be immediately under the central clip. Where it occurs depends on the shape and length of the overhanging tip, and very especially on the thickness of the plate underneath. It depends in fact, in the ratio between the tip load on any leaf and the reactice support offered by the leaf above. (3) Generally speaking, the effect of reducing the thickness of a leaf in springs such as our present ones, is to cause excessive stresses in the leaf immediately below. This accounts for the leaves frequently going in the centre on the bumping rig. The particular leaf which breaks depends principally on the way in which the spring is built up. It appears to us that the spring maker may be blindly putting up the stress in one leaf by substituting thinner leaves in order to get the required weight. (4) The length of time taken to break a leaf depends primarily on the stress set up as above, and secondly on the Brinell hardness of the plates, which vary in the springs we have examined, over a wide range. We expect to find, when we have completed our analysis, that the length of duration varies inversely as the stress and directly on the hardness within limits. Contd. | ||