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).
Inertia torque, crankshaft taper erosion, and torsional vibrations, identifying a critical speed of 3350 r.p.m.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan142 | |
| Date | 4th September 1926 guessed | |
| contd :- -15- At the lower speeds the inertia torque decreases considerably and its lower harmonics do not seem to be of sufficient amplitude to cause trouble. The explosion pressures however possess the same frequency - i.e. three cycles per revolution - and would be expected to be more vigorous at the low speeds and so take the place of the decreasing inertia torque and give rise to vibrations. With regard to the erosion of the crankshaft taper carrying the spring drive, it seems that this takes place during the vibration periods and is due to the inertia of the spring drive unit acting similarly to the slipper wheels giving rise to oscillatory movement on the taper. As an example of this we started with a crankshaft taper in perfect condition and after a period of ordinary running was still undamaged. After running at the critical speed a few times - probably not much more than a minute altogether - we examined the taper and found it had 'picked up' considerably. GENERAL SUMMARY. The experiments we have carried out have given us the following information :- (1) There are torsional vibrations at various speeds, the one of maximum amplitude being at 3350 r.p.m. This is the critical speed. (2) We believe the synchronisation of the inertia torque impulses with the free period of the crankshaft is responsible for the 3350 r.p.m. vibration. contd :- | ||