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).
Poor mechanical efficiency of brake systems, particularly on the Spectre model.
| Identifier | ExFiles\Box 102\3\ scan0149 | |
| Date | 21th December 1934 | |
| To E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/AFM.{Anthony F. Martindale} c. to Wor.{Arthur Wormald - General Works Manager} c. to By.{R.W. Bailey - Chief Engineer} Mechanical Efficiency of Brake System Components. The mechanical efficiency of R.R. brake systems is not high; for instance, if 100 lbs. load is applied to a Phantom brake pedal, 30 lbs. only is required to maintain the resulting deflection. This is not of great moment on existing standard cars owing to the servo, but when this is inoperative, as in maneuvering, stopping the car by foot brake alone is very difficult. The brakes on the SpectreCodename for Phantom III, however, are far from good when cold, and when the servo gets hot they become much worse. Apart from the drop in output of the servo, the lack of braking can only be due to the inefficiency of the brake mechanism. Recently it has been determined that when the front brakes of a SpectreCodename for Phantom III are applied to their fullest possible extent, the chassis will only withstand a forward force of 1,800 lbs. before the drums rotate (skidding being prevented), while a Bentley chassis' front brakes will withstand 4,000 lbs. under similar conditions. At first this was thought to be due to the very large number of pin joints used in the SpectreCodename for Phantom III brake linkage, and accordingly experiments were made to determine what loss does occur in a pin jointed lever but while no actual measurements have been made on SpectreCodename for Phantom III brake linkage levers themselves, the results that have been obtained suggest that the loss from servo to toggle shaft is about 85%, and this cannot account for the lack of braking. It is now known that most of the loss occurs in the camshaft and toggles inside the drums, although the precise cause of the loss is still unknown. It appears that high loading produces such large friction couples that the applied torque is practically balanced by them. If the lever rotating the camshaft is depressed through its maximum possible travel, no more braking is obtained than that produced by depressing it half way. | ||