Reasons for adopting specific lever lengths in an agreed brake system, including calculations.
| Identifier | ExFiles\Box 73\2\ scan0303 | |
| Date | 27th March 1924 | |
| X.9940 S E C R E T. DA {Bernard Day - Chassis Design} 1/M27.3.24. To R. {Sir Henry Royce} from DA. {Bernard Day - Chassis Design} c. to CJ. RG. {Mr Rowledge} HS. {Lord Ernest Hives - Chair} BY. {R.W. Bailey - Chief Engineer} PN. {Mr Northey} E. {Mr Elliott - Chief Engineer} A. {Mr Adams} C. AGREED & REM. BRAKE SYSTEM. X.9940 Referring to your remarks re. the length of pressure screw operating levers on N.sch.1769 and on the agreed scheme which was on a car which came to Le Canadel(Henry Royce's French residence), the following were the reasons which caused us to adopt these lever lengths. (1) In your R5/M17.12.23., there are given us instructions as to the working of the slow speed servo, viz - 750 lbs.ins. of work from pedal: (for 150 lbs.foot press:) 1500 " " " " servo. ____ 2250 " " " altogether (total). Length of servo lever to be 4". Length of lever on pressure screw to be 2". Servo lever to go through 60°. Pressure screw lever through 75°. In laying out the agreed scheme we closely followed these instructions except that the servo lever was made 4.2" long to give us a little clearance we wanted, and we found it very difficult to get the pressure screw lever to go through more than 70° because we could not get more than 2.2" linear motion off the pedal lever. But we thought this 10° would be enough to close the servo, and we might still count on the servo lever going through 60. Then the following figures followed :- Pull from pedal 380 lbs. Torque on pressure screw 380 X 2 = 780 lbs.ins. Load in plane of screw 760 / .55 = 1380 lbs. Taking 55° angle of thread (perpendicular to axis) and an efficiency of 82% - End thrust = (1380 X Tan 35 X 82) / 100 = 793 lbs. Servo work = servo torque = 1500 lbs.ins. M.R. = 2.9". μ = .5 End thrust required = 1500 / (2.9 X 2 X .35) = 740 lbs. contd:- | ||
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).