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).
Secret memorandum discussing the design and comparison of different brake systems, including servo-assisted and Hispano types.
| Identifier | ExFiles\Box 22\1\ Scan154 | |
| Date | 14th March 1924 | |
| fur214 To HS.{Lord Ernest Hives - Chair} DA.{Bernard Day - Chassis Design} FROM R.{Sir Henry Royce} S E C R E T. R3/M14.3.24. c. to CJ. BJ. RG.{Mr Rowledge} E+ BY.{R.W. Bailey - Chief Engineer} PN.{Mr Northey} E.A.C. X.9940 RRM. BRAKE SYSTEM. X.4214 You will notice that I suggested the servo should do six eighths of the brake pull. RG.{Mr Rowledge} says this in Hispano is two thirds and one third direct. Aim for somewhere between these two, because we want about twice the old braking with about half the foot pressure. For the direct unassisted braking I suggest we reduce the lever ratio to back brakes to about 75% of the present, as a practical improvement i.e., of clearance, and less frequent and exact adjustment. RG{Mr Rowledge}'s memo. of 3.3.24. seems quite right but I think this modification is desirable. DA.{Bernard Day - Chassis Design} suggests our scheme slow, but we cannot have it every way. If we run the servo so slowly as Hispano and allow the servo to move 4 times the angle we shall be 4 times slower and 4 times more gentle. This would be too slow so that we must increase the servo speed to 3 times that of Hispanon but it will be under quarter the load so that the heat will be about the same. I do not think there is any perceptible difference in the scheme we are considering in the time lost, because we close our servo first (unless it were fitted with very strong opening springs). Hispano does the same. Then the fast pressure closes the back brakes while the servo only has to overcome the hold-off springs of the front brakes, so that both go on together, unless the ratchet system in Hispano jumps a tooth, which I doubt. DA{Bernard Day - Chassis Design}'s scheme I think would work, but depends on relative strength of springs, which I think we should, and can avoid. RG.{Mr Rowledge} points out that we cannot tell by foot [struck through word] the state of front brakes adjustment. I had not thought of this and it is a point, but in any case it is always desirable to test if both front brakes are free and equal. Also in Hispano case one has to make some similar or more elaborate test between axles, because the pair on one axle may be worn more than another pair, and even one single brake may be worn. I believe with the Hispano it is desirable to jack up a wheel or wheels to test, while we have only to press the levers on the front axle by hand or foot, and we can easily see the condition. With a servo working through 80° naturally the speed can be 4 times that of Hispano if equal chance of cooling exists, so that the gear ratio may be 7 to 1 or 10 to 1 contd:- | ||