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 analysis of engine vibration, focusing on damper energy dissipation, friction torque, and order vibrations.
| Identifier | ExFiles\Box 124\2\ scan0299 | |
| Date | 17th February 1941 | |
| Bm/TAS.{T. Allan Swinden}4/ST.17.2.41 - 4 - The two fundamental expressions are as follows. The maximum energy dissipated per cycle by a constant friction damper is 1.273 J_d ω²α² in lb/cycle. and the corresponding optimum friction torque setting is T_d = 0.45 J_d ω²α lb in. where J_d = mom. of inertia of damper inertia member in lb.in.sec² ω = natural frequency of engine system α = max. vibration amplitude at the free end of the crankshaft in radians. is obtained by equating harmonic input energy to maximum energy dissipated. Input energy = πT_eα in lb. per cycle where T_e = resultant harmonic torque for the engine in lb.inches. = T_N ΣAR Therefore πT_N ΣARα = 1.273 J_d ω²α² and the optimum friction torque setting = T_d = 0.45 J_d ω²α = (0.45 πT_N ΣAR) / 1.273 = 1.11ΣαT_N AR. C. You were, of course, quite correct in stating that there are no odd order vibrations on a 180° bank engine having two lines of reciprocating parts to each crank. Calculations for this unwholesome engine were made as an afterthought and should never really have been included. It seems that changing from 4 stroke to 2 stroke and firing two cylinders at a time proved just too much for our phase diagrams. All the other vibrations, including the 6th order which is the same as for the 4 stroke engine, remain unchanged. | ||