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).
12-cylinder engine design, crankshaft types, and vehicle vibration issues.
| Identifier | ExFiles\Box 13\7\ 07-page086 | |
| Date | 10th February 1931 guessed | |
| (3) Now you will see one reason why am I so very keen for a 12 cyl. engine, because as this will always run beyond the master period of 6 per rev. it can have balance weights of any extent that the engine weight will permit, and as there are very small reasons for putting the crankshaft into a state of vibration at its master period there should be little difficulty in keeping its shaft still from torsional vibrations by the usual slipper wheel, which naturally it seems to need for car work. Regarding the difference between a 12 cyl. at 45º and 60º my impression is that I would not attempt 45º unless forced, as 60º ought to be better for so many reasons. There are some which 'ggest 90º Some time ago I pointed the great value of the zig-zag crank Lately I have suggested the interlaced one and if counter weights are impossible it would seem that there is much to be said for this in the case of a real high speed engine when the impulses are of little importance. Naturally anything we find good should be incorporated in production as soon as it is proved, and is possible to embody. I fear we shall have to improve some back numbers. My impression is that P. 2. is not worse than P. 1. or Silver Ghost. It should be better as I think - (1) the crankshaft is stiffer, (2) the crankchamber I know is much better, and (3) the flywheel etc is exactly the same. I have thought that we have run into this vibration more often by the higher engine revs. we so often reach now for reasons given elsewhere. My experience here is that we suffer from low speed torque vibration at 20/25 MPH., and strange that Bentley is the same. It would seem to be governed by weight of engine and stiffness of frame. I asked some time ago if this speed altered by more flexible mounting, but I am not sure anyone knows. One would expect that as we made the mounting more flexible it would become slower, which would be very valuable. If we had double top so easy that it would be a pleasure to change we should be much better off for both high speed and low speed vibration, could gear our cars 25% high, and get higher top speed and better acceleration, and avoid some of the vibrations, excess consumption and engine wear. R.{Sir Henry Royce} | ||