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).
Crankshaft balancing schemes, counterweights, and vibration analysis for an engine.
| Identifier | ExFiles\Box 85\5\ scan0112 | |
| Date | 20th May 1936 | |
| -2- We ought therefore to be able to obtain the conditions of 100% balance with 4 weights only as on R.M.89 of 71% of the rotating loads. R's light weight scheme assumes the crankshaft to be infinitely rigid in the pins and infinitely weak in the journals, or in other words that a counterweight affects only the journal it is next and balances only as far as half across the neighbouring crankpin. The Packard method seems from a theoretical consideration to take into account the effect of crankshaft stiffness in the way this varies in different planes. Rocking Col. We have made and run on 6-B-IV small weights balancing all the centrifugal loads and large weights balancing also half the piston as well. Both schemes provide a smoother engine than the standard arrangement, judging both from feel and optical measurement of flywheel vibration. We have set out to obtain as an ideal an engine that is smooth and free from periods when run up light as far as 4500 r.p.m. while experimenting on 6-B-IV on these lines we found as a matter of interest that removal of the flywheel and clutch effected an improvement at all speeds and that when running with a flywheel (4 1/4 litre type) but no balance weights, the engine did not have any violent periods but was just rougher at high speeds. The Packard counterweight system provides a saving in weight and thereby raises the master period. The relative weights for the Bentley are - Standard arrangement 7.51 lbs. Large Packard 7.02 lbs. Small Packard 5.03 lbs. The attached sketch showing the balance weight arrangement is what has been necessary to get these weights on an existing shaft. Will R.{Sir Henry Royce} please send us a drawing of a Bentley crankshaft suitable for a 10,000 miles test. The size and position of this scheme of counterbalance must be found empirically for every engine. We have tested the 4-bearing shaft and a SpectreCodename for Phantom III shaft and the results could not be foretold from the Bentley arrangement. P3 Plante III Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls} | ||