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).
Forced vibration, crankshaft deflection, and the performance of different engine vibration dampers.
| Identifier | ExFiles\Box 174\2\ img250 | |
| Date | 20th May 1938 | |
| -2- W. A.{Mr Adams} Robotham 5.20-38 between the forced vibration caused by inertia torque and the vibration due to the torsional period of the crankshaft is shown by comparisons between torsion records taken with the engine operating at full throttle and with the engine being motored. The inertia torque gives approximately the same deflection in both cases, whereas the deflections due to the natural period of the crankshaft usually are negligible when the engine is driven by the dynamometer. In the event that you may not have encountered this particular condition, I am sending a couple of photographs which illustrate the point, even though the magnitude of the deflection is much less than was obtained with some of our earlier engines. You will note that in the photograph numbered 7314, where the engine was operating at full throttle, there is a distinct 6-sided figure at 2600 r.p.m. which indicates that the fundamental period would occur at 5200 r.p.m. At 3500 r.p.m. can be seen a 9-sided figure which results from nine oscillations of the crankshaft in two revolutions. If any figure occurred at 4,000 r.p.m. as a result of a natural period of vibration, it would be a 3-sided figure. However, you can see rather clear evidence of a 3-sided figure at this speed. In the photograph numbered 7315 the figures which previously appeared at 2600 and 3500 r.p.m. have disappeared while the triangular figure at 4,000 r.p.m. is unchanged. In general, we have not found that a friction type vibration damper affected the deflection due to inertia torque except as its inertia may influence it somewhat. However, we did find that the bonded rubber type of damper, known some years ago as the Amplex, often was fairly effective in reducing the magnitude of this forced vibration. Sincerely yours, P. W. Spann Research Engineer. S:Sparrow/MCA Enc. | ||