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).
Letter from Packard Motor Car Company discussing clutch vacuum control and crankshaft disturbances.
| Identifier | ExFiles\Box 127\1\ scan0222 | |
| Date | 21th May 1935 | |
| PACKARD MOTOR CAR COMPANY DETROIT MICHIGAN May 21 1935 Mr. W. A.{Mr Adams} Robotham, Rolls-Royce, Ltd., Derby, England. My dear Mr. Robotham: I am enclosing a blueprint showing the clutch vacuum control with automatic adjustment as used on our twelve-cylinder car. This construction, I believe, will show you all the things you need to know to see how it works or to make one for yourself. Your comments on the Packard One Twenty are not passed unnoticed. I have been wondering what principal features of this car would have the greatest appeal to the English people. Speaking of the twelve-cylinder crankshaft periods, I am wondering whether you have actually noticed the crankshaft periods or whether you have gotten into some propeller shaft disturbance which seems to be of torsional nature. If these periods are coming at approximately 55 and 70, I feel quite definite about the propeller shaft being the cause of the disturbance. Much of this can be eliminated by being very fussy about propeller shaft flange concentricity and face squareness. On our Twelve the crankshaft disturbances that I have experienced are so minor that I have even run without dampers and not had the disturbance noticeable to passengers, but by virtue of the lack of severity of the periods, it takes much more damping action and better damper construction to make a really worthwhile improvement. In this connection, the Twelve responds very differently from our eight-cylinder engines to damper settings. Another point is that our cylinder being around 70 degrees does tend to break up the major harmonics and slightly magnify the minor harmonics which are so small anyway as to be detected only by instrumentation. I don't put quite so much value, however, into this as I do in the principle of a very stiff shaft. In this connection, I found a curious anomaly in that often a decided increase in stiffness in the shaft will not produce any marked change in the critical speeds, but will effect a large and marked reduction in amplitude. I presume that this probably is related to natural damping which is difficult to measure. | ||