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).
Testing different spring and damper settings to reduce oscillation and rattle.
| Identifier | ExFiles\Box 138\1\ scan0084 | |
| Date | 13th December 1933 | |
| -2- The serious objection to the damper in this condition was that at 550 R.P.M. the spring drive had a critical period at which it oscillated violently against its stops. With the cooling fan fitted the speed at which this rattle occurred was 450 R.P.M. With the engine running light and ignition fully retarded the spring drive still oscillated against its stops but less severely. The pinion damping was increased to 3 lbs. at 17.5" but the spring drive still hit its stops at 450 R.P.M. under full load and with the ignition advanced to the normal position. With the ignition retarded or under light load the damper was satisfactory. The incipient rattle over the whole lower speed range was much more noticeable than it was with damping of ¼ lb. at 17½". In order to reduce the speed at which the critical oscillation of the damper occurred and to reduce the amount of damping necessary, weaker driving springs were tried. The present standard driving springs give a rating of 70 lbs.ins. per degree of deflection. The first set of weaker springs tried gave a rating of 17.1 lbs.ins. per degree. The springs on the driving side of the pinion had a higher rate than the springs on the over-run side. This was done to bring the mean position of the crank pinion into the centre of its available range of deflection when under load and thus to make more efficient use of the range of deflection. With these springs the critical speed was 250 R.P.M. and the oscillation could be controlled under all conditions with a pinion damping of 1 lb. at 17.5". Up to 1000 R.P.M. the gears were entirely free from rattle. Above this speed there was a slight rattle which continued all the way up the speed range and proved to be due to the pinion hitting its stops. The rating of the driving springs was increased step by step until the working deflection of the spring drive was kept within the amount allowed by the stops. | ||