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).
Analysis of brake judder under various conditions and a discussion of its probable causes.
| Identifier | ExFiles\Box 84\2\ scan0308 | |
| Date | 25th February 1935 | |
| -2- HS{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}20/KW.25.2.35. (7) In all cases the judder occurs just as readily with the brakes cold as when warm, but it is more consistent when the drum is thoroughly wet. If only a small amount of water is applied, the judder occurs only at lower speeds and reliable figures of speed, etc., cannot be obtained. (8) By running the wheel on the judder rig at a constant speed and applying the brake load gradually it is possible to start and maintain an incipient judder of small amplitude. By slightly increasing the load applied the incipient judder increases until it changes suddenly into the violent judder. Paragraphs 4 and 6 above rule out the possibility of exceptionally high values of /u being the cause of the judder and some variation in /u seems to be the more probable explanation. Paragraph 7 rules out the generation of steam as a cause of the judder, because the judder occurs just as readily with the drum flooded with cold water as with the drum warm. On the servo test rig it was noticed that the static /u was of approx. the normal value but that when slipping occurred it immediately dropped to about half this amount. Owing to juddering and limited speed range it was not possible to obtain accurate /u speed curves but the general shape appeared to be as shown in fig. 2 on the attached print. The characteristic shown in fig. 2 is a complete explanation of a judder once it has been started, and, if it could be proved that, during the forward swing of the carrier plate, there was no slipping occurring between the shoes and the drum. This proof was obtained by apparatus which recorded the judder on an annular paper ring attached to the brake drum. | ||