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).
Using rubber for mountings on cars to reduce road noise and vibration.
| Identifier | ExFiles\Box 178\2\ img013 | |
| Date | 25th April 1940 | |
| Rm.{William Robotham - Chief Engineer} - 2 Serial No. 103 OY 6/D/Apr.25.40 mountings on cars for reduction of road noise, automobile engine mounts, etc. 2) I imagine that the R.R. aero engines do not absolutely require rubber mounts like the radials to prevent them shaking the plane to pieces. The mounts shown for the Merlin in the Instruction Book appear to be a concession to non-metallic contact and can have little or no dynamic effect. They appear to be, in fact, of any obsolete form, having no bonding or enclosure of the rubber and no control of the initial compression. 3) Walter Keyes is the U.S. Rubber expert on "isolation" of vibrating mechanism, and is putting in machine mounts all over the U.S. and its possessions. He is intensely practical in his outlook, does not concern himself with major and minor inertia axes, etc., and admits that he works on three rules - Frequency/minute = 188/√d (d = defl. in inches) 30 Durometer rubber works well at 30 lbs/sq.in. 40 " " " " " 40 " The arguments for using rubber rather than anything else are its internal damping, and its high energy storage per lb. It also has unique powers in reflecting high frequency sound waves. Such waves are not associated with mass movement either of the rubber, or of the metal parts in contact with it. In mounting heavy machinery, this characteristic is generally unimportant compared with the dynamic effects. In road noise insulation of trains and motorcars, it is one of the important features, and is the particular study of Dr. Merrill. To be effective, this noise insulation must be complete, just like electrical insulation. Several cases were cited in rail road work where attempted noise insulation had proved ineffective due to metallic "leakage paths" through the horn plates, etc. Such cases are ineffective in noise insulation, but are often found highly effective in the vibration insulation which goes with it, such as overcoming the fatigue breakage of equalizer bars, etc. U.S. Rubber are taking a leading position in all forms of noise and vibration suppression, as well as determination of mechanical properties of rubber, and the dynamics of tyres. They are working close to G.M. Corp. on all this development, and are, therefore, a useful contact. OY Copy to Lessells 1 extra copy Rm.{William Robotham - Chief Engineer} | ||