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).
Experiments to reduce crankshaft torsional vibrations in 20 HP and Phantom engines using a non-rigidly mounted flywheel.
| Identifier | ExFiles\Box 25\3\ Scan175 | |
| Date | 9th November 1926 | |
| Copy sent to R.A.E. & Major Carter Air Ministry COPY. X634 9.11.26. TORSIONAL VIBRATIONS ON 20 HP. AND PHANTOM ENGINES. Further tests have been made on the 20 HP. engine in connection with the crankshaft torsional vibrations. The object of the following experiment was to see if it would be possible to eliminate the condition of resonance from the working speed range, or reduce the vibration amplitude, by having the engine flywheel mounted non-rigidly on the crank shaft and still be coupled with sufficient friction to the crankshaft to result in a steady transmission of torque. It is known that reducing the inertia of the system results in raising the speed at which resonance occurs and that friction damping reduces the amplitude, therefore it was thought that the above arrangement, by a combination of the above effects might prove beneficial. For the purpose of the test the stud holes in the flywheel were slotted and it was mounted between the crankshaft flange and a washer. Bakelite washers were used each side the flywheel flange as friction surfaces and the friction torque could be regulated by the tightness of the securing bolts. In addition rubber buffers were inserted in the stud slots - these being found necessary to prevent 'thrashing' at low speeds due to the firing impulses. The appended sketch shews the method of mounting the flywheel. The friction torque of the flywheel resisting motion relative to the crankshaft was varied between 400 and 2000 lbs. ins. and vibration diagrams recorded between these values. Within these limits it was found that the critical speed occurred at approx. the same speed as with a rigidly connected flywheel but as the securing friction torque was reduced so was the amplitude of the vibration. A print is appended which shews a progressive reduction of amplitude as the friction torque is decreased. These curves are reduced from the polar diagrams on to a flat crankshaft displacement base, the origin being chosen arbitrarily with respect to the crankshaft position. It is probable that this is similar to the case of the slipper wheel damper which as the friction torque was increased seemed to possess two modes of vibration - one at the original critical speed and the other at a lower speed depending on the inertia of the damper wheel. It will be remembered that as the damper friction was increased, the apparent contd :- | ||