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).
Engine vibrations, including torsional harmonics and flywheel whirl, and potential solutions.
| Identifier | ExFiles\Box 137\4\ scan0208 | |
| Date | 16th August 1931 guessed | |
| (3) During the increase of speed we pass some of the harmonics of the torsional period of the crankshaft. I have not mentioned these as they are so well known and can be so easily demonstrated by removing the inertia part of the slipper wheel, and should any vibration appear at the periodicity of these harmonics it could be put down to this cause, and we should have to endeavour to make the slipper flywheel more efficient. The master period being 3 per rev. and somewhere about 3600. - i.e. 10,800 per min, would show on our indicator at this periodicity. It will be easily understood that items (1), (2), (3), (4), and (5), cannot do any good for these torsion al periods, and item (1) might do some harm, but slight improvements might be made by - (a) Lighter pistons, and (b) Longer rods. which do definitely improve over-run vibrations. Our greatest hope of improvement is (c) More effective slipper wheel. (d) More effective engine mounting. Having discussed the low speed vibrations we next come to the 3 high speed ones as follows: Firstly, the recently discovered flywheel so called whirl due to want of rigidity of the flywheel mounting or the flexibility of the crankshaft or crankchamber. Now excepting the master torsional period of the crankshaft, thought to be somewhere between 10,000 and 12,000 complete periods per min., we probably (almost certainly) have some vibration at 1 complete cycle per rev. at its maximum when the engine is running 2700 revs. This wants proving but if at 1. 2. or 4. per rev. it cannot be torsional, but must be lateral and which the diamond mounting may not greatly improve, but it ought ot be susceptible to items (1) (2) (3) (4) (5). Item (1) would naturally bring down the master period, and perhaps make the harmonics slightly more manifest, but if the two couples trying to bend the crank-chamber are the cause of this vibration or even if the end cranks are deflecting the last crank and whirling the flywheel, then balance weights opposing the couples to the extent of even 30 to 50% would be worth fitting to reduce the flywheel whirl and save the crankshaft bearings. | ||