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).
Servo design, braking efficiency, and proposed improvements.
| Identifier | Morton\M20.1\ img023 | |
| Date | 1st May 1924 | |
| TO RH.{R. Hollingworth}S. } FROM R.{Sir Henry Royce} C.c. to OJ. WCH. BY.{R.W. Bailey - Chief Engineer} ORIGINAL SECRET re. CONFERENCE AT DERBY ON E.A.C. 2 & 3. Y9770 Y9940 Y9910 Mr. Day has told us that servo troubles might be due to the driving dogs binding. This has proved true as regards want of efficiency and the difference between increasing and decreasing foot pressure. We think Mr. Day as well for his theory of the effect of unequal braking on the straight running of the car. I had arranged for the production servo to have 3 pins at the maximum driving radius and certain clearances to enable each pin to take its share of drive without binding the central shaft. I also arranged in this design that the lever attached to the foot pedal could not be bound by the superimposed load on the bearing, as telegraphed. To ensure this the boss on the friction plate must come through the bearing, so that none of the forces going to the brakes could keep the pressure on the friction surface except that on the 3 pins themselves. This would be less than the load so that the whole would be self releasing and not dependent upon the pedal return spring. I now suggest that if the pins mentioned above give any trouble a fabric or sheet steel disc could be used to transmit the torquefrom the second plate to the main plate. Each plate would have 3 pins passing into the 6 plates on the fabric coupling. We must do our utmost to keep the oil off the servo by additional flinging rings and shields as mentioned in my last. I was pleased to hear that the flat plate servo was now in favour because this type should give more consistent and lasting effect than either the cone or brake shoe type. In addition to the importance of a self freeing brake we must not lose sight of the point that the direct braking must be effective so that we can hold the car at short distances. Observing the shunting etc of many cars upon the narrow and dangerous roads about this part of the south of France impresses one on the importance of this point. I am asking that a car shall be fitted up each way, i.e. (1) Direct foot to rear axle only - present 40/50 leverage. } This gives equal clearances. (2) Direct foot to 4 wheels - half present 40/50 leverage. } to see which scheme gives the better direct braking. I am hoping to see these temporarily fitted during the first few days in May, at WW. R.{Sir Henry Royce} | ||