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, their potential causes like torsion and gas pressure, and analysis methods.
| Identifier | ExFiles\Box 137\4\ scan0206 | |
| Date | 16th August 1931 | |
| HS.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer} FROM R.{Sir Henry Royce} BY.{R.W. Bailey - Chief Engineer} DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} ) (At Le CanadelHenry Royce's French residence.) X634 RI/M16.8.31. C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} P.2. VIBRATIONS. ENGINE SOURCES & BODY RESONANCE. X.634. X.7830. We are still somewhat in doubt about the causes of some of the above. If we take all the lower speed vibrations - i.e. those below 60 MPH., and of which the torque reaction period is the worst, I am almost certain they all come from torsion al variations either due to gas pressure or piston etc inertia - i.e. take the pistons out and they should not exist. At these speeds below 2000 RPM. there should be little crankshaft and crankchamber deflections. In our analysis we ought to try and concentrate on one particular vibration, and it should be fairly easy to find if it is 1 or 3 per engine rev. Years ago someone made a speed indicator to tell the speed of turbo-electric generating sets. It consisted of a number of strips of steel of different periods very free to vibrate, the quivering one indicating the speed of the steam turbo, although the instrument only rested upon an iron pedestal on the same foundation, which was a substantial block of concrete. I suggest a similar instrument would tell the periodicity of the source - i.e. whether the vibration was 2, 3, 4½, or 6 per rev., and it also shews extremely how sensitive is any free mass of the same periodicity in contact with it unless damped. Now with a 6 cyl. engine we have several unavoid- able impulses that can set up vibrations. They are: Gas pressures - shewn by the starter motor's varying growl, then when the engine is started, worst of all when at about 800 revs. X 3 per rev. = 2400 impulses, puts the whole engine and (frame) into a state of vibration because it has reached a synchronised period of the inertia mass of engine and frame round the centre of the crankshaft. Its vigour is much influenced by compression ratios and was the original reason for lower compressions used on Silver Ghost. Many times we tried to use higher compressions but were driven down below 5. (One should get a distinct advantage in 8 cyls., and nearly perfect freedom from this trouble in 12 cyls.) Outside the compression ratio and vigour due to perfect carburettion and high volumetric efficiency (both increasing vigour) nothing I know of can be done except | ||