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).
Technical document detailing calculations and principles of crankshaft stiffness and vibration.
Identifier | ExFiles\Box 25\3\ Scan247 | |
Date | 22th April 1927 guessed | |
contd :- -6- 1/3 [.00799 + .00583 + .016823] + .00582 = .01597 lbs.ft2 and the crankshaft itself contributes .0168/3 or 35% which indicates that the inertia of the crankshaft is to a certain extent masked by that of the other parts. The above notes illustrate the relative importance of the inertia of the different parts of the system and while it is an advantage to keep the total inertia forward of the node as low as possible it shews that it is not necessarily the part having the greatest inertia that is the chief offender in lowering the free period of the crankshaft assembly. CRANKSHAFT STIFFNESS. The free period of vibration is proportional to the square root of the stiffness of the shaft. Naturally the inertia of the shaft would be expected to increase in some ratio with increase of stiffness and the one would therefore tend to annul the other. In the case of a simple circular section shaft or rod of a given length and material the inertia would increase in the same proportion as the stiffness and if the inertia of the system consisted only of the shaft itself an increase of stiffness would not result in raising the periodicity. In this particular case raising the free period could only be obtained by shortening the shaft. In the practical case however where the inertia is made up of various units, and some of these such as the big ends and pistons which cannot be very much altered, an increase of stiffness even with an accompanying increase of inertia will be contd :- | ||