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).
Letter suggesting modifications to the servo cam-levers to resolve issues with the brake servo system.
| Identifier | ExFiles\Box 41\1\ Scan104 | |
| Date | 6th May 1929 | |
| OY 4 May 6th, 1929. Mr. A.{Mr Adams} F.{Mr Friese} Sidgreaves, Rolls Royce Ltd., Dondon, England. cc - Mr. Royce Mr. Hives Mr. Bailey Dear Mr. Sidgreaves: RE BRAKES (1) SERVO. We wish to suggest for the consideration of Mr. Royce and Mr. Hives, the modification to the servo cam-levers shown in A-14285 of which copies are attached. We have found in practice on both Springfield and English cars, including the 20 HP, that the servo does not operate consistently for several thousand miles, but tends to become "jerky" in its action after use of a few hundred miles, apparently by drying, rusting and sticking of the cam faces. A typical effect is shown on SK-228 attached where a smooth curve of servo multiplication becomes irregular like the pencil curve marked "182-FR". We appear to have tried almost every way of improving this without acheiving a certain improvement. For example we have used the "Star Spring" but without definite improvement. We have put a floating bronze bushing A-11594 inside the outer cam lever so that this slides outwards with the lever and avoids the tendency of the lever to lock on its shaft through tilting. Also we have ground and lapped the helical faces. Finally we have tried omitting the bushing A-11594 and the star spring entirely so that the outer lever is centralized only by its fit on the four camfaces. The only form of lever which has given consistent servo multiplication however is one with four 1/4" balls between the cam faces. This appears to work best when the centralizing bushing is omitted, and the star spring omitted so that the lever is centralized by its fit on the four balls, and held square by the outer thrust bearing -continued- | ||