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).
Technical memorandum on the torsional vibrations of a flat 12-cylinder engine crankshaft.
| Identifier | ExFiles\Box 132\2\ scan0177 | |
| Date | 24th October 1940 | |
| 1176 Crankshaft genl To Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}8/JH.24.10.40. FLAT 12 CYL. ENGINE CRANKSHAFT TORSIONALS. Herewith some 12 cyl. torsional details which I am sure are not news to Rm.{William Robotham - Chief Engineer} (1) A 12 cyl. engine may be considered as two 6 cyl. engines, one operating 180° out of phase with the other. (2) The fundamental gas torque harmonic is 6/rev. for a 4 stroke engine and 12/rev. for a 2 stroke. (3) This is a horizontally opposed engine using a 6 throw crankshaft, and we know that the large 6 throw PH.II crankshaft had a natural frequency of 1200/min. (Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}1/MH.{M. Huckerby}9.2.32.) Using a crankshaft of this type, therefore, bad gas torque vibrations would be experienced at 2000 r.p.m. and 1000 r.p.m. on a 4 stroke and 2 stroke engines respectively. (4) The big 3/rev. inertia vibration which forms the master period on a 6 cyl. engine becomes zero. but the 6/rev. half period is doubled. This would occur at 2000 r.p.m. with the above crankshaft. This is much more serious on a diesel than a petrol engine because the engine components are far heavier due to high explosion pressure. Inertia loads are thus greater and this explains why Leylands were unable to run their 6 cyl. diesel through its 6/rev. half period vibration. (5) Do you require a complete investigation of the torsionals involving amplitudes? For this piston and con. rod dimensions, a drawing of the crankshaft, and, if it is a 2 stroke diesel, some idea of the indicator diagram would be required. Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} TAS{T. Allan Swinden} | ||