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).
Analysis of inertia torque coefficients and the effect of a frictional tuned vibration absorber on 1 node vibrations.
| Identifier | ExFiles\Box 132\2\ scan0198 | |
| Date | 29th August 1940 | |
| - 2 - The inertia torque coefficients are calculated on a basis of 7.72 lbs. reciprocating parts per cylinder for a Vee Twin Unit as on p.8. of my "Summary" of 29.8.40. The table below refers to 1 node vibrations only. The amplitudes without damper are calculated by Shannon's method. The crankpin stresses assume, (incorrectly), that the crankpin is of same bore but concentric, and that it carries a torque equal to that at the node N. Concentration of stress due to oil holes is also neglected. The damper is of the frictional tuned vibration absorber type, with a flywheel 8" dia. 1.5" wide, 5" bore. Its (ideal) tuning is to a frequency of 10600 (~/min.) Its (optimum) solid friction torque is 752 lbs.inches, (equivalent to a viscous friction damping coefficient of c = 152 lbs.ins. per radian/sec.) Single Node Vibrations | Order of Vibration | Speed RPM. | Resultant exciting torque expressed at Crk.1 = Tn Σaᵣ (lbs.inches) for engine: | Amplitude at Crk.1 with no damper. (degrees) for engine: | Approx. stress in Crkpin 4 no damper (tons/sq.in) for engine: | Amplitude at Crk.1 with damper. (degrees) for engine: | Approx. stress in Crkpin 4 with damper. (tons/sq.in.) for engine. | |---|---|---|---|---|---|---| | | | α | ρ | α | ρ | α | ρ | | 4 | 2925 | 464 | 8280 | .852 | ±6.58 | .106 | ±.819 | | 5 | 2340 | 2390 | 2225 | 0 | 0 | 0 | 0 | | 6 | - | 0 | 0 | 0 | 0 | 0 | | | 7 | 1671 | 723 | 1183 | .453 | ±3.5 | .057 | ±.437 | | 8 | 1462 | 2870 | 113 | 1.1 neg-ligible | ±8.5 neg-ligible | .137 | ±1.058 | | 9 | 1300 | | 402 | neg-ligible | neg-ligible | | | | 10 | - | 0 | 0 | neg-ligible | 0 | | | | 11 | 1063 | | 312 | 0 | neg-ligible | | | | 12 | 975 | | 1078 | .413 | ±3.19 | .052 | ±.398 | It will be observed that even the comparatively small damper assumed will reduce the amplitude of torsional vibration very considerably, e.g. in case of 5th order, from .85 to .106. | ||