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 spring and cam harmonic characteristics with oscillograms and computed amplitude data.
| Identifier | ExFiles\Box 56\2\ Scan088 | |
| Date | 15th January 1929 guessed | |
| ate when actuated by cams having different har-monic characteristics. The characteristics of the cams and springs used are summarized in Tables 1 and 2, respectively. Speeds mentioned in the following description are camshaft speeds. Fig. 6 shows the operation of spring No. 1 and cam No. 1 through a range of speed from 1750 to 750 r.p.m. There are many interesting resonant points on this oscillogram. The worst surge is observed at a speed of 1650 r.p.m., at which point there are 10 free waves of fundamental frequency for the spring per revolution of the camshaft. These 10 waves are maintained by the strong tenth harmonic, which had a greater amplitude on the lift curve than any harmonic of a higher order. It is interesting to note that the 10 free waves shown at this point are not pure waves, but are influenced by a twentieth harmonic, giving rise to a very slight wave between the waves of fundamental frequency. This indicates that the spring is vibrating in its fundamental, with a very feeble first overtone. A full-size section of the oscillogram for this point is shown in Fig. 8. At a speed of 1570 r.p.m., shown also in Fig. 9, another interesting resonant point can be detected. At this speed the spring vibrates freely, with 21 waves which have double the frequency of the fundamental wave-motion. The next resonant point occurs at 1500 r.p.m., where the influence of the eleventh harmonic causes the spring to have 11 fundamental waves per camshaft revolution. As in the case of the tenth harmonic, the twenty-second harmonic gives rise to a feeble overtone in the vibration at this speed. When a speed of 1375 r.p.m. is reached, the spring surges slightly under the combined influences of the twelfth and twenty-fourth harmonics. Both of these harmonics were found to be very feeble, and the resulting wave-shape seems to be a complex wave in which the first overtone has almost the same amplitude as the fundamental. It is of interest to note that surge at this point escapes visual or audible detection. This portion of the curve is shown again in Fig. 10. TABLE 1.—COMPUTED AMPLITUDES OF HARMONICS OF VALVE-LIFT CURVES Harmonics No. | Cam No 1 In. | Cam No 2 In. 25 | 0.0004 | 0.0001 24 | 0.0001 | 0.0001 23 | 0.0000 | 0.0001 22 | 0.0006 | 0.0007 21 | 0.0002 | 0.0003 20 | 0.0003 | 0.0007 19 | 0.0000 | 0.0002 18 | 0.0005 | 0.0007 17 | 0.0007 | 0.0006 16 | 0.0004 | 0.0001 15 | 0.0003 | 0.0009 14 | 0.0011 | 0.0013 13 | 0.0010 | 0.0010 12 | 0.0000 | 0.0011 11 | 0.0028 | 0.0021 10 | 0.0031 | 0.0026 9 | 0.0015 | 0.0002 8 | 0.0029 | 0.0045 FIG. 13.—OSCILLOGRAM OF SPRING No. 1 AND CAM No. 2, FROM 2150 TO 1150 R.P.M. FIG. 14.—OSCILLOGRAM OF SPRING No. 2 AND CAM No. 1, FROM 1750 TO 750 R.P.M. FIG. 15.—OSCILLOGRAM OF SPRING No. 2 AND CAM No. 2, FROM 1750 TO 750 R.P.M. FIG. 16.—OSCILLOGRAM OF SPRING No. 3 AND CAM No. 1, FROM 1750 TO 750 R.P.M. FIG. 17.—OSCILLOGRAM OF SPRING No. 3 AND CAM No. 2, FROM 1750 TO 750 R.P.M. 6 7 | ||