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).
Brake system development, including materials for drums, liners, and cams to address issues like squeak, rust, and overheating.
| Identifier | ExFiles\Box 85\1\ scan0270 | |
| Date | 2nd December 1936 | |
| -3- and, of course, they are fitted with tipping shoes (costing about £2 a car) which may or may not be functioning as intended. With either aluminium drums or a cool running rigid solid drum a change of rubbing surface material to something which did not oxydise quite so easily might be an advantage, or, alternatively, continued use of the tipping shoe should keep us free from the first thing in the morning squeak. Cast iron is known to be bad for rusting, and steel not so bad, so we are experimenting with high brinell steels as liners for aluminium drums, and are making enquiries about cheap rust preventing alloying elements. We are also trying Brimol austenitic iron liners as these do not rust. As far as we know this type of squeak is the only one the tipping shoe cures, and we cannot help feeling that the £2 could be more usefully put into the material. This would also ease designing problems. (2) We have been experimenting with low μ linings, and these certainly seem to be an improvement. We have found one, Ferodo S.6611, which seems to be a good thing, and if we can get supplies in time we are thinking of sending it to France on the Girling brakes. μ has not a very low figure, so that design alterations are not necessary to use it, as we had originally intended to use 45° servo cams, and, if necessary, can use 35° cams. As regards future brakes, if the design department would help produce a system with a high multiplication of leverage at the shoes we could use a low μ lining. The RR cam is not suitable for high lever ratios as it then tends to judder, the Girling wedge has a low mechanical advantage, but it is mechanically efficient, and is usually allowed to float. The best system for us would seem to be the long travel wedge recently described by us in a memo to the Design Dept. Thus a high overall ratio could be used with a low stress in the linkage and low "sponge". Increasing the servo torque multiplication we do not agree with as it reduces the efficacy of the direct braking and overheats the servo, although 35° cams on Bentley when associated with splined linings especially made of VM30 or S.5584 run satisfactorily, and have completed 15,000 miles in France. (3) High temperatures can be avoided if we want. Bentley has ridiculously small drums and they run hot, aluminium drums the same size weigh less and do not get too hot. Unfortunately the extremely efficient braking obtainable with these drums means the duty they have to do is severe with such a small drum, and this is giving us a little trouble at present. Phantom III certainly has big enough drums | ||