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).
Procedure for testing and tuning engine crankshaft balancers by analyzing torsional vibration.
| Identifier | ExFiles\Box 125\1\ scan0304 | |
| Date | 1st December 1936 guessed | |
| -2- With the engine on a dynamometer stand a set of torsional indicator cards is taken at full throttle with no balancer, covering the used speed range of the engine. If there is risk of the engine harming itself at full throttle with no balancer the throttle opening may be reduced of course while taking cards in the periods. Later as the balancer is developed the throttle opening may be increased until the balancer will correct full throttle vibration. The result of this run will probably resemble the solid line No. 1 on the enclosed chart. This is plotted in relative amplitude of torsional vibration full throttle, against crankshaft speed. Somewhere between 1500 RPM and 3000 RPM, depending upon the stiffness and inertia of your shaft, you will find a six-sided card whose amplitude is indicated by the peak "A" on the chart. Then at twice the speed will be found the three-sided figure "B" on the chart, which, theoretically should have twice the amplitude of "A". We have never run our engines fast enough to get into any higher periods. On our V-12 the six-sided card comes at 1700 RPM and the three at 3400 RPM. The first balancer is then installed, a set of cards taken, and the results plotted over the original bare shaft curve of (Number 1). Should no effect at all be observed the balancer is either far too low in tuning and much stiffer springs are needed, or the damping is far too high making it in effect a second flywheel. The probability of either of these occurring is however remote. If the sixth harmonic (six sided card) is observed at a higher speed than before, the balancer is tuned too low - springs not stiff enough. (See curve Number 2). And conversely, see curve Number 3. When the sixth is found to occur at the same speed as with the bare shaft but at reduced amplitude the tuning is correct but too much damping is present - remedy: Fewer but heavier springs. See curve Number 4. Again should two "sixths" be found, one on either side of the bare-shaft peak, too little damping is indicated and the same tuning should be retained but with a greater number of lighter springs. See curve Number 5. After thus eliminating the sixth, proceed to the third at twice the speed. If much of it remains it is simply a matter of varying the | ||