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 valve spring resonance, coil surging, and the properties of taper springs, including the Ricardo formula for natural frequency.
| Identifier | ExFiles\Box 56\2\ Scan069 | |
| Date | 20th February 1929 guessed | |
| (6) The impulses occur at intervals of 100 to 260, which reduced to the simplest proportion is 5 to 13. Resonance might therefore be expected with 18 vib: per rev: or multiples of 18. The question now comes, what happens when a valve spring of 12,000 periodicity is substituted for 10,000. Should we not expect coil surging at (12,000 / 16) x 2 = 1500 eng: revs: possibly of less amplitude. We have no experimental evidence confirming this, and furthermore no explanation of why No.3. single spring in the table is apparently satisfactory when No.4. is not, although of approximately the same natural frequency. --- TAPER SPRINGS. --- The formula used for calculating the natural frequency is one which was suggested by Ricardo and has been fairly generally adopted. N = 531 * sqrt(R/W) Where N = frequency in complete vibrations per minute. R = spring rating in lbs. per inch. W = weight of active material of spring in lbs. When we come to examine a taper spring we conclude that the small end wants to vibrate at a faster rate than the large end. Assuming that W remains constant the two resulting frequencies for the Silver Ghost taper spring -e.g. 9,450 and 11,750 per min: exhibit a substantial difference in proportion to sqrt((mean radius)^3) This may not be strictly true but must be we think a Close approximation of the facts. [GRAPH] Vertical axis: SURGING Horizontal axis: CAMSHAFT SPEED We conclude that the resonant period of a taper spring may be more prolonged but of far less amplitude than a parallel one, the point of maximum surging starting at one end of the spring and travelling to the other as the camshaft speed changes. | ||