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).
Continued analysis of spring friction, including formulas and comparisons of different spring types and their performance.
| Identifier | ExFiles\Box 173\2\ img031 | |
| Date | 9th February 1934 guessed | |
| -2- SPRING FRICTION - Continued μ = Coefficient of friction (apparently about .250) W = Load on spring t = Average plate thickness N = No of plates l = Active half-length of spring f = Stress at normal load S = Rate of complete spring (clamped Olsen test) The Rolls-Royce springs in question, 53" long, show a friction of about 41.5 to 44 lbs. The Series 10 and 20, 60" rear spring with 1300 lbs load should show - 26 to 29 lbs. The Series 30 and 40, 66" spring with 1500 lbs load should show 31 to 36 lbs. Since the unsprung weight is almost the same in all three cases, the Series 10 and 20 should show the greatest difficulty in keeping the axles quiet and can probably stand either more plates or two or three friction strips. Cars with 66" rear springs should show better results. We know that static friction tests give little or no indication of what the friction actually is with the car in motion, so road test or test on bump rig seems the only way to find out. Apparently there is no difference between flat springs and pivoted cantilevers in friction effects provided that the stresses are similar. But the cantilever has thicker plates; these have to be stressed lower, and the volume of active metal in the cantilever therefore is generally much greater. For example, suppose the stresses are equal, the pivoted cantilever then has twice the plate thickness and half the no of plates. | ||