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).
Clutch spring modifications and performance testing with Ferodo discs.
| Identifier | ExFiles\Box 129\4\ scan0102 | |
| Date | 13th December 1937 | |
| -3- We then fitted new springs with .080 discs of Ferodo VM.20 at the pressure plate end of each, this however only formed very incomplete heat insulation, because the springs are recessed 3/4" into holes in the pressure plate, so that the heat flow to the spring in a radial direction is unaltered and this is inherent to the design of the clutch, which was never intended for use with heat conducting facings. We also drilled 8 holes in the clutch cover into which a light air blast was directed, in the hope of inducing some circulation of air round the springs. The combined effect of these modifications enabled the springs to stand up to 700 slips without serious slipping, but we had to conclude the test at 780 slips, where it was found that the springs had dropped from 150.4 lbs. to 117 lbs. at which poundage the slipping was very excessive. The actual spring thrust at the commencement of this test was 161 lbs. per spring, owing to the Ferodo pad reducing the working length of the spring. The working /u was .157 at commencement of test and .215 at conclusion. On dismantling it was found that the driven plate was only slightly dished and the reduction in thickness was negligible. Remarks & Conclusions. The Graphite Bronze facings have a slightly lower /u than R.A.D.11 and although this is not very noticeable on the road, the dynamometer tests indicate that an increase of 8 to 10% in spring poundage is necessary to produce the same rate of pick-up. Of the cars running it has not been found necessary in a single instance to increase the thrust spring poundage, nor has any softening of the springs been observed to date, we do however recommend fitting Ferodo discs under the springs in future change-overs, these will cost approx. 3d. each or 4d. per car. The /u appears to be slightly less at high rubbing velocity because it was frequently observed that a clutch which would pick-up readily at 1000-1500 r.p.m. would fail to pick-up at over 3,000 r.p.m although the torque at 3,000 is less than at 1500. This effect was less marked with Ferodo facings. | ||