Experiments to remove judder from the rationalised braking system by fitting a star spring to the servo.
| Identifier | ExFiles\Box 121\3\ scan0145 | |
| Date | 21th July 1941 | |
| 1029 To Rm {William Robotham - Chief Engineer} /HH. from Ra/MHR. {M. H. Rigby} Copy to Rm. {William Robotham - Chief Engineer} & Ev. {Ivan Evernden - coachwork} Rm {William Robotham - Chief Engineer} /MHR. {M. H. Rigby} 12/ET.21.7.41. JUDDER ON THE RATIONALISED BRAKING SYSTEM. Numerous experiments have been made on the rationalised braking system to try and remove judder. No lining material gave any improvement, although it was found that, in general, the larger the servo mechanical advantage, the worse the judder, this coefficient being increased either by a lower cam angle or a higher frictional coefficient of the lining. After following up several theories concerning the linkages, the only useful discovery was that, if we disconnected the rod from the pedal and pulled on it by hand, the judder went, and that this condition could be imitated with the pedal connected by inserting "sponge" in this rod. We feel that a star spring on the servo itself is a more compact method of doing the same thing, and the following is an outline of how we propose to fit it. We have found by experiment that "sponge" is required to act up to 30 lbs. pedal pressure, and this is equivalent to 414 lbs. end load on the pressure plate. We have some sample springs similar to G.53180 in everything except free movement, which is 0.050". These springs are fully compressed for a load of about 80 lbs., so we require a spring 5 times as strong. We propose to give it 8 arms instead of 4 as before, and thicken it up to 18 S.W.G. instead of the previous 20 S.W.G. Free movement is still to be 0.050". The rough sketch will serve to illustrate the following description of the scheme. The single star spring is to be situated between the inner cam lever and the pressure plate. The part of the pressure plate on which the plate levers pivot is to be shortened, and a thick washer fitted at the end, the outside diameter of the washer being sufficient to support the flat portion of the star spring, clearance being allowed for free movement of the plate levers. The thrust piece GB.3501 is to have its outside diameter increased to support the ends of the star spring arms. In order to clear this, the 5/16" pin on the inner cam lever will have to be replaced by one of the type used on the servo drag links in conjunction with a locking plate and 2.BA set screw. A special jaw will be required, which should still be tapped to take the 5/16" rod to the pedal. The sleeve GB.4061 will have to be shortened to allow for the compression of the spring. Another sleeve will have to be pressed on to the inner side of the inner cam lever in the same way as GB.3545 on the other | ||
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).