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).
Technical memorandum regarding clutch slip and testing methods.
| Identifier | ExFiles\Box 129\4\ scan0122 | |
| Date | 8th January 1938 | |
| 110 To By.{R.W. Bailey - Chief Engineer} c. to Hs.{Lord Ernest Hives - Chair} c. to Wx. c. to Sn.{Mr Sanderson} c. to Hd.{Mr Hayward/Mr Huddy} c. to Sr. E/P. c. to Br.{T. E. Bellringer - Repair Manager} E/M.{Mr Moon / Mr Moore} c. to /K.{Mr Kilner} Am/HRC.2/JW.8.1.38. re CLUTCH SLIP AND METHOD OF TESTING. We have frequently observed that a clutch which will take up its load quite quickly at full throttle at about 2,000 r.p.m. may continue to slip if engagement is attempted at about 4,000 r.p.m. more especially if there is a great difference in speed between the flywheel and the driven plate, in spite of the fact that the engine torque is actually less at 4,000 than at 2,000. This apparent falling off of the frictional grip at high speeds is observed both on the road and on the unit dynamometer beds, and applies whether bonded asbestos or metallic facings are used, and the factors most likely to encourage slip during engagement at high revs are as follows - (a) Centrifugal force acting on the clutch fingers producing friction, which prevents the full pressure of the thrust springs from acting on the pressure plate. It is interesting to note that in the case of the Borg & Beck 10" and 11" clutches, calculation shows that the fingers and eye-bolts exert a centrifugal force of about 300 lbs. each at 4,000 r.p.m. Approximately half of this radial force is taken at the ends of the eye-bolts where they spigot into pressure plate and assuming no lubrication at this point, we estimate the friction opposing movement of the pressure plate may be as much as 260 lbs. or 20% of the total thrust spring pressure. The R.R. type of clutch does not suffer to any extent from this centrifugal force friction, and in the case of the P.III clutch may be dismissed as negligible. (b) Flywheel 'flatter' at critical speeds may cause the pressure plate to chatter against the driven plate, but this effect is probably negligible except at unduly high revs. | ||