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).
Description of a crankshaft testing rig using an exciter to induce torsional vibration.
| Identifier | ExFiles\Box 132\1\ scan0150 | |
| Date | 20th September 1939 guessed | |
| -2- magnaflux inspection showed all the cracks, sometimes as many as a dozen, which had developed. The layout is shown in attached sketches. A 7½ H.P. Polyphase AC Variable speed motor drives a long quill-shaft (of low torsional frequency) through multiple Vee belts. A magneto-type speed indicator is driven by chain. A circulating oil pump (for the exciter) is driven from the mechanism somewhere. I have sketched it on the speedometer drive, but this is probably wrong. The exciter (Sk.2) is driven from the quill shaft and clamped to the front end of the crankshaft. It contains 3 pairs of unbalance weights which rotate at 35/12 times the speed of the quill shaft. They are "timed" so as to be radially in balance and torsionally unbalanced, throwing a sinusoidal wind-up torque into the crankshaft. Just back of the exciter is a concave mirror on the end of a bracket. This with a special straight filament lamp, forms an amplitude indicator. The amplitude is shown on a graduated screen about 10 feet away so that the scale is big enough to allow control of amplitude to about .05 of a degree. The normal amplitude is 2½ degrees, so that accuracy of control is about ± 2%. The crankshaft is mounted in its proper bearings in the cylinder block, and on each pin is clamped a ring representing the rotating mass on the con. rod. The device consumes about 4 to 6 kilowatts, which comes out as torque on the crankshaft. This torque is resisted by soft balance springs on a light arm bolted to the flywheel. An obvious fault of the device is that it puts torque into the system through the timing gear drive, and therefore shows a disproportionate tendency to crack out the corners of the Woodruff keyways especially at A (Sk.2). This is not of such terrible importance because results are comparative anyway, and the crankshaft is actually run pretty close to its first resonant condition with the exciter swinging in opposition to the flywheel, and the node occurring in the rearmost crank throw. The engine block is rigidly mounted on its base plate through the two cross-bearers shown. The device is run up close to resonance and then is slowed down until the amplitude settles at the required figure (2°) | ||