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).
Leaf spring design, including grooved section steel, interleaving materials, and damper technology.
| Identifier | ExFiles\Box 153\1\ scan0062 | |
| Date | 23th September 1937 | |
| -4- Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer}1/AP.23.9.37 They also have an endurance test rig for leaf springs with a stroke of 7 1/2" and Olley considered this a more reliable way of spring testing than the 3" cams on the bump rig, which he thought unnecessarily severe. Rm{William Robotham - Chief Engineer}/Les.{Ivan A. Leslie} had asked us to find out if Woodhead Toledos' were in a position to supply springs yet, and Olley says that they can supply experimental springs only. This concern will be making the grooved section steel (see Fig.5.) and by rolling their own steel they are intending to have a range of thicknesses such that the moments of inertia of the section are in geometric progression, the common ratio being 1.35. The grooved section steel has two advantages for the normal user. First, the grooving displaces the neutral axis of the section towards the tension side of the leaf so that the maximum tensile stress is 19/20 of that in a corresponding rectangular section, the maximum compressive stress being then 21/20 of that for the rectangular section. In practice, the spring is designed to have the same maximum tensile stress, the compressive stress being increased, and the result is a spring approximately 12% lighter than standard. The second advantage is in connection with interleaving; apparently a number of types have been tried in America, but have all had the same drawback, that they have worked out sideways, and it has been impossible to prevent this. They have recently been trying a bituminised and graphited paper interleaving, and with the grooved leaf a thicker paper strip can be stapled to the interleaving paper and fitting inside the groove keeps the paper in its proper place. Springs must be assembled without 'nip' or the ends of the interleaves are torn. The result is then a spring which maintains constant friction characteristics even without spring gaiters. It is also the only interleaving which gives a spring hysteresis loop without the waves representing squeaks. Woodhead Toledos' intend to make this paper interleaving. Apart from the telescopic or 'flit-gun' type, their best type of damper is one which is similar to our standard type in principle, except that it has two separate valves instead of our combined valve. They had carried out a number of tests on the effect of velocity on damping, and even with movements of only 1/8" each way and high frequency movements they had obtained the damping corresponding to the appropriate velocity. The main advantage of the 'flit-gun' damper is the increased volume of oil in use, the figure being approximately 0.65 cub.ins/in wheel movement instead of the 0.250 cub.ins/in obtained with the bellcrank and piston type generally similar to ours. As a matter of interest the corresponding figures for our Phantom III are:- front damper with original small central tube 0.55 cub.ins/in, and with large central tube 0.47 cub.ins/in, rear damper 0.38 cub.ins/in. continued... | ||