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, discussing damping methods, flexibility, and the effects of wet and dry conditions.
| Identifier | ExFiles\Box 84\2\ scan0311 | |
| Date | 25th February 1935 | |
| -5- Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}20/KW.25.2.35. In order to reduce the damping load required to control the incipient judder, it would be necessary to increase the torsional flexibility, and the best place to do this would be between the carrier plate and the stub axle, as suggested by E/Tsn. The damping could then be applied either between the carrier plate and the chassis, or between the carrier plate and the stub axle. The latter method would be the simpler. The flexibility added between the carrier plate and the stub axle should be at least twice as much as exists at present between the carrier plate and the anchorage. To prevent the occasional grabbing of the wrapping shoe it may be necessary to reduce the angle of embrace. The position is, therefore, that it is very unlikely that a practical arrangement of damping could be applied to the axle as it is, and that a hopeful line of attack would be to add damped flexibility between the carrier plate, brake shoes, etc., and the stub axle. The suggested explanation for the shape of the Brake Torque/speed curves in fig. 1 is that while there is slipping between the shoe and the drum a water film is formed, and so the /u is low. As the relative speed falls the film begins to break down and /u rises till at zero speed the /u is of the normal amount. Juddering, due to the alternate building up and breaking down of a liquid film, is a common phenomenon, and can easily be demonstrated by rubbing one's finger on a wet polished surface. The judder so obtained has all the characteristics of a wet brake judder. It is possible that high speed dry judders are due to the formation of an air film at high rubbing speeds. It would be interesting to obtain brake torque/speed curves at high speeds under dry conditions to see whether the torque falls as the speed increases. It would be necessary to do this on a system which could be made to judder. Up to now no success has been achieved in trying to make the rig do so under dry conditions. The Hancock shoe on the main wrapping shoe is an ideal shape for a "Mitchell Thrust Pad" and may encourage the formation of an air film. Hs{Lord Ernest Hives - Chair}/F.J.Hardy. | ||