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).
Technical memo discussing the arrangement and mechanics of an improved four-wheel brake system.
| Identifier | WestWitteringFiles\K\December1923\ Scan24 | |
| Date | 1st December 1923 | |
| R.R. 2R5A(100 T)(S.H 152, 11-8-20) C. 2500 ORIGINAL TO HS.{Lord Ernest Hives - Chair} FROM R.{Sir Henry Royce} SECRET R5/117. 12. 23. c. to CJ. BJ. RG.{Mr Rowledge} DA.{Bernard Day - Chassis Design} c. to WOR.{Arthur Wormald - General Works Manager}BY. PN.{Mr Northey} E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. 11. & IMPROVED E.A.C.1. X9940 FOUR WHEEL BRAKES. The final arrangement of these has been explain- ed{J. L. Edwards} in an earlier memo. You will remember that it was intended that the whole of the foot pressure was to go to the 'servo' and the servo torque and that the single pull from the servo was to act on an equalising lever in a way shewn in the sketch which not only is a very simple and accurate compensator between the front and the back brakes, but it seems extremely convenient to suit the desired positions of the rest of the brake mechanism. The technical figures are assuming a pedal pres- sure of 150 lbs and a stroke of the foot of 5". This gives a total available energy of 750 lbs inches. To this we are endeavouring to arrange that our servo adds about twice as much, namely 1500 lbs inches, the total being 2250 lbs inches capable of being taken away from the servo. The lever on the servo shaft being 4" radius in passing through 60° of angle will give a pull on the servo connect- ing link of 550 lbs. This is divided into two pulls of about 400 lbs, the front one travelling 2" to the front brakes, and the back one travelling 3.6" to the back brakes. We should endeavour that the rod leaving the foot brake pedal should have a travel of about 3½" which would be capable of rotating the actuating lever on the servo through about 75° if this lever were 2" long. This motion will first take up the slack in the servo, pressing the plates hard on the plate clutch, then following the servo through its 60° of motion. We are anxious for the sake of the stresses to keep the forces on the servo down, otherwise we shall break the teeth on the bronze worm wheel in the gearbox. To do this we must have ample leverage through- out the system, and it would appear that counting the motion of a single shoe at the actuating end, the leverage should be approximately 25 to 1 in the front brakes, and 45 to 1 in the rear brakes. You will notice that I have said the movement of each single shoe will give this leverage when compared with the travel of the foot on the pedal. The difference be- tween this and the Hispano is that we are asking for a greater percentage of pressure direct from the foot, we are asking greater foot pressure for a given brake effect, we are asking for a greater leverage so that the brakes should skid the wheels before the servo is so heavily loaded. It will be remembered that we now have the joint- ed{J. L. Edwards} shoe as a means of safely using a long shoe on the brake drums and a means of obtaining effective braking with a given leverage. Our own particular type of arrangement (1) | ||