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).
Investigation into low frequency noise and vibration on Bentley cars with independent front wheel suspension.
Identifier | ExFiles\Box 154a\4\ scan0102 | |
Date | 15th March 1939 | |
SUSPENSION NOISE ON BENTLEY CARS. An investigation has been carried out on the low frequency noise and vibration present when Bentley cars with independent front wheel suspension travel over uneven road surfaces. The effect is noticeable, for example, when a car hits a depressed manhole cover. There was no equipment available for accurate noise and vibration measurement on the road. It was therefore necessary to reproduce conditions artificially. An attempt was made with a car on the drums, but there was too much extraneous noise and vibration for proper measurements to be carried out. Measurements were made at Shardlow using a weight slung from the roof. This was swung as a pendulum against one of the front wheels and the vibration and sound in the car measured. A fair approximation was given to conditions occurring when the wheel hits an irregularity in the road surface, and the noise produced had the same character. METHOD OF MEASUREMENT. The effect, as observed by a passenger, is a combination of low frequency noise and vibration. Two measuring instruments therefore were used, a moving coil microphone and a piezo-electric vibration pick-up. The output from these was taken to an amplifier and cathode ray tube and the resulting waveform photographed. EXPERIMENTAL RESULTS. The vibration pick up showed a longitudinal vibration present to about the same extent all over the car. The lateral component was negligible but there was a vertical component about 1/8th of the longitudinal on the floor boards, the radiator cap and the wings. The vibration was of frequency between 15 and 30 cycles per second with frequency rising as the amplitude decayed. Traces of higher frequency vibrations were found on the frame and body panels. The waveform of the sound showed the presence of a low frequency wave of similar frequency to the body vibration and also a very much higher frequency (at least 100 cycles per second). This suggested that the car was vibrating as a whole over the suspension, and that the sound was partly due | ||