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).
Secret memo discussing the cause of 'brake jaggers' (judder), raising objections to a theory, and suggesting further tests.
| Identifier | ExFiles\Box 26\4\ Scan245 | |
| Date | 30th January 1924 | |
| To Hs.{Lord Ernest Hives - Chair} from Da.{Bernard Day - Chassis Design} S E C R E T. DAL/H30.1.24. E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. BRAKE JAGGERS. X.9940 X.3409 X.9550. With reference to your Hs{Lord Ernest Hives - Chair}3/LG28.1.24., covering a suggested explanation of the cause of brake jaggers, as we think you are aware Mr. Royce proposed this explanation very early on. The following objections have been raised to the theory, but all are probably capable of another explanation:- (1) Why do not Goshawk brakes mounted in the same way also jaggers (2) Why do not the brakes of other firms jagger? (We see you are investigating this point on other cars). (3) Why does not a pothole produce the same offect? Can jaggers be obtained at all speeds of the car? One would expect that they would be worst at one particular speed. We suggest that if you greatly increase the moment of inertia of the axle it would have an effect on the jaggers because it slows down the natural period. This increase of inertia might be obtained by strapping long bar to the axle, pointing fore and aft. If you were to try Goshawk springs on the 40/50 front axle one thinks that the effect would be the opposite to the above para. namely, it would increase the speed of the vibration and thus should make some apparent difference. Do you still say that wind-off has a benefical effect even though it does not always completely cure the trouble? It is possible that considerable wind-on might have a beneficial effect. If the cause of jaggers is the difference between friction at rest and friction in motion is not this difference more marked in cast iron than in ferodo, and if you know of material in which it is very marked, would not this give a definite indication; the jaggers for instance would be much worse? On the other hand, we are under the impression that new ferodo has a very sticky co-efficient of friction when at rest, and it may be that there is a great difference between the two types of friction in the case of ferodo. Have you any data, or could you get some of what this difference is? Have you tried linings which have been baked so as to make the co-efficient of friction fairly constant? It would be of use to us to know the approximate angle through which the vibration takes place. The idea contd:- | ||