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).
Various brake servo system designs, comparing shoe types and servo layouts.
| Identifier | ExFiles\Box 73\2\ scan0332 | |
| Date | 16th April 1924 guessed | |
| -2- (4) My long rigid shoe theory, although shortening the shoes seemed to cure the trouble, it however was reported to be so because it destroyed the efficiency of the brakes. (Semi-flexible shoes, shorter shoes, and floating fulcrum should again be tested). Conclusions were that failing a torsionally rigid control of front axle which I think irrational and impractical, at least at the moment, the slow speed large angle servo was the solution. This was quite practical and very desirable for heat and life of servo. I have pointed out that I feared we were likely to wander away from this slowness for the reasons of avoiding lag which I have pointed out can only be effectively avoided by efficient direct foot pressure. I have not done any more since yesterday to the servo design. I suggested we might use double quick angle cones but cannot think they are necessary or advisable. Correctly propor-tioned the servo should easily give a torque of 1 to 2 times the operating levers. One cannot get much more than the double multipli-cation from a cone (double flats give this). In my scheme I have done away with nearly all the sources of inefficiency and risk of sticking on. It will be noticed that by using the 90º forward and 75º rearward, my scheme of lifter pin clears easily, especially if the 75º angle is kept well up, which has advantages. It might be :- FORWARD 45º REARWARD 30º The advantage of this is more than at first sight. Lifting pins do not foul the con. rods, backward braking slight-ly more feeble but quicker and sufficient. I have to repeat much of what has previously been done and said because it seems to get lost or forgotten. So I again say that the flat servo can have no more lag (Hs.{Lord Ernest Hives - Chair} report) than any other kind. It should be more practical, lasting, and consistent, and is the favourite clutch for the full engine power, and surely ought to do this small duty. It will be noticed that the reverse action and avoiding the ratchet has put us to many limitations in the design around the servo. For instance the ordinary brake shoe type of servo seems impossible. A single or double cone has serious dis-advantages in end control, pressure and life. R.{Sir Henry Royce} | ||