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 General Motors regarding the principles and study of a crankshaft harmonic balancer.
| Identifier | WestWitteringFiles\Q\December1926-January1927\ 97 | |
| Date | 15th December 1926 | |
| C O P Y. OAKLAND MOTOR CAR DIVISION, General Motors Corporation, Pontiac, Michigan. Dec. 15th. 1926. Commander W. Briggs, Rolls-Royce Ltd., Conduit Street. Dear Sir, I have a letter from Mr. Crane enclosing a copy of your letter to him with reference to the crankshaft device known as the Harmonic Balancer. It is gratifying to note that you have arrived at practically the same conclusions regarding the principle of its operation that we now entertain after a number of years of rather intensive analysis, experiment, and test. Before beginning actual work on an anti-vibration device we spent considerable effort in the development of instruments and making measurements to determine quantitatively the frequency, amplitude, wave character and phase relation of torsional vibration of crankshafts. A torsional vibration indicator which has been of great service to us in this study is shown and described in a paper entitled 'Measurement of Engine Vibration Phenomena' published in the S.A.E. Journal of Feb. 1925. With the help of this instrument we studied the two periods which most six cyl. engines have in the driving range. The lower of these shows nine complete oscillations per rev. of the crankshaft while the higher shows six oscillations. For example, the Buick engine as built two years ago without counterweights or harmonic balancer, showed a period of 1600 r.p.m. the torsional vibration making nine cycles for each rev. of the shaft. At 2400 r.p.m. of the same motor the vibration shows six cycles per revolution. If the motor could be operated at a speed of 4800 r.p.m. it would be found that there were three complete cycles of vibration for each rev. of the engine, this vibration being of the very great amplitude since the shaft would be swinging directly in step with the forces which were exciting it. The frequency therefore is nine times 1600 or six times 2400, or three times 4800 which is 14400 cycles per minute or 240 cycles per second. The harmonic balancer operates on the same principle of interference and is so tuned with respect to the natural frequency of the shaft assembly that when there is contd :- | ||