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).
Analysis of engine vibration, focusing on the factors of stiffness and inertia within the crankshaft assembly.
| Identifier | ExFiles\Box 22\4\ Scan130 | |
| Date | 22th April 1927 guessed | |
| contd :- -4- If the master period of the std. engine could be avoided until this speed we should have little fear of encountering it, and the higher engine speeds would be expected to be less rough because even when approaching the master period considerable vibration is felt before the peak value is reached. Considering the factors which determine the speed of the master period we see that it is a question of the relationship of stiffness to inertia of the crankshaft assembly. assuming the inertia of the flywheel to be by far the major part of the inertia of the assembly, the single node of the lowest fundamental vibration will consequently be very [s]forward[/s] near the flywheel and it is therefore the inertia of the parts forward of this point that is of importance. The inertia is made up of the following parts :- (1) Rigid mass at front end - such as slipper and Spring drive hub and fan pulley. (2) Crankshaft. (3) Total of big ends. (4) An amount due to the pistons which can be shewn to be equivalent to one half the reciprocating mass concentrated at the big end assuming the conn. rods to be infinitely long. The first mentioned is important as it acts at the end of a greater length of shaft and inertia of a mass here approximately three times the value of the other parts. In calculating the frequency of the crankshaft system from a knowledge of the overall [s]frequencyxofxthexcrankshaft[/s] stiffness and inertia, an approx. method consists of assuming the inertia due to the crankshaft, big ends and the pistons to be uniformly distributed along the shaft - an assumption not contd :- | ||