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).
Comparing the horsepower absorbed by the 40/50 rear wheel foot brake shoes with the servo.
| Identifier | WestWitteringFiles\L\2Jan1924-March1924\ Scan13 | |
| Date | 12th July 1923 | |
| R.R. 493A (40 H) (SL 42 12-7-23). J.H., D.{John DeLooze - Company Secretary} EXPERIMENTAL REPORT. Expl. No. X9910394 REF: Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/LG22.1.24. TO COMPARE THE H.P. ABSORBED BY THE 40/50 REAR WHEEL FOOT BRAKE SHOES PER SQ.IN. OF LINING WITH THE H.P. ABSORBED BY THE SERVO PER SQ.IN. OF LINING SURFACE. Following conditions assumed :- Load on rear axle - 26 cwts. Coeff: of Frn. of road - .6 REAR BRAKES. Torque taken through one rear wheel brake when the wheels are about to lock = 1160 lbs.ft. Angular velocity of wheel at 20 m.p.h. = 200 radians/sec. H.P. absorbed by one brake = (1160 X 400) / 33,000 = 44 H.P. (approx.) Area of Ferodo on one pair of foot brake shoes = 72 sq.ins. H.P. absorbed per sq.in. of Ferodo = 44 / 72 = .61. SERVO. To produce a torque of 2320 lbs. ft.in. the rear brakes require a total torque input on 158 lbs.ft. at the Camshafts (from tests on our brake rig). Tangential pull on the servo drum to produce this torque with standard EAC. leverages from servo = 388 lbs. at 2 1/4" - (or 89 lbs.ft.) Additional 6 lbs.ft. required for pull off springs. . . . Total torque from servo = 95 lbs.ft. . . . Angular velocity = 2 X 745 rad: (low geared axle) . . . H.P. absorbed by servo = (2 X 745 X 95) / 33,000 = 13.5 H.P. (approx.) Area of Ferodo on servo = 21 sq. in. h.p. absorbed per sq.in. of Ferodo = 13.5 / 21 = .65. Pedal pressure required to produce this torque from the servo = 166 lbs. (Modified leverages and distributor efficiency 70% assumed). contd:- | ||