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).
Explanation of harmonic vibrations and their effect on a six-cylinder in-line engine crankshaft.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 45 | |
| Date | 22th April 1927 guessed | |
| contd :- -12- is considerably more severe than even the worst harmonic and gives us some idea of the difficulty we should have in providing an adequate damper to deal with it. We should not expect the life of a crankshaft to be long if running on this master vibration. The harmonic vibrations we think may be explained in the following way :- At a speed of 3300 r.p.m. the oscillation diagrams shew three cycles per rev. This would give a g frequency of 3300 X 3 = 9900 oscillations per min. Now consider the harmonics of the gas pressure torque for each cyl. taken separ- ately. Each cyl. has one firing impulse in two revs. therefore the first harmonic will have one complete swing in two revs., the second harmonic two complete swings in two revs., the third three complete swings in two revs. and so on. The firing impulses follow each other by 120º therefore the first harmonics of each cylinder - i.e. one swing in two revs. - do not act together simultaneously or reinforce each other. When however we reach the 6th. harmonic there are six swings per 2 revs. or three per rev. and those of each cyl. following each other by one-third of a revolution conincide. The harmoincs of each cyl. therefore all act together in twisting and untwisting the crankshaft. The sixth harmonic would there- fore be expected to give the most severe vibration in a six-cyl. in line engine. contd :- | ||