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).
Experiments conducted on a 4-litre Bentley regarding crankshaft torsional periods.
| Identifier | ExFiles\Box 179\2\ img158 | |
| Date | 12th January 1932 | |
| ORIGINAL R.{Sir Henry Royce} From He/Gry.{Shadwell Grylls} c. to. SS.{S. Smith} or. c. to. R.{Sir Henry Royce} W. c. to. Sa. He/Gry.{Shadwell Grylls}3/WA.{Mr Wallis}12. 1. 32. x634. X3805. 4 LITRE BENTLEY - CRANKSHAFT PERIODS. We have recently had an opportunity to carry out experiments on one of these cars at high engine speeds, and find that the master period is easily attainable on the roads being at 3100 r.p.m. or 83 in top and 47 in 2nd. Though very violent this period was not nearly as bad as on our cars. On the front of the Bentley crankshaft is a Lanchester multiplate metal to metal viscous damper with a low initial friction setting. The hub of this damper has considerable inertia and drives through two fabric joints the dynamo. Our first experiment was to remove the dynamo. This reduced the speed of the period to 42 m.p.h. in 2nd, and again we were able to drive through it. The nature of the dynamo therefore drive, through a flexible coupling raises the torsional period. We next removed the damper and hub. The period was then too violent to drive through beginning at 40 in 2nd and having a maximum at approx. 50 m.p.h. Finally we fitted the damper hub shaft for the friction plate and the dynamo. The period was more violent than with a damper but less violent than with no damper, and no dynamo, and had a maximum of 45 in 2nd, and a duration from 42-50 m.p.h. above which speed, the engine is smooth. Summarising we have the torsional period with :- dynamo Hub damper and/at 47 m.p.h. in 2nd. Hub and damper at 42 m.p.h. Nothing on the front of the crankshaft at 50 m.p.h Hub and dynamo at 45 m.p.h. We find therefore from the experiments that with the type of damper fitted to this car the torsional period though very unpleasant does not break the crankshaft and that the addition of a flexibly driven inertia at the front of the crankshaft raises the torsional period and lessens the roughness on either side of it. He/Gry.{Shadwell Grylls} | ||