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).
Abandonment of a high-speed servo brake system and the resulting design challenges and considerations.
| Identifier | ExFiles\Box 73\2\ scan0251 | |
| Date | 14th February 1924 | |
| To HS.{Lord Ernest Hives - Chair} RG.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} DA.{Bernard Day - Chassis Design} FROM R.{Sir Henry Royce} 49940 SECRET. R4/M14.2.24. E.A.C. BRAKES. X.9940. Very many thanks to HS.{Lord Ernest Hives - Chair} for the memo. of his tests dated 7.2.24. To avoid any loss of time I am writing all I think would be useful, and might contain something we are over-looking. The scheme of high speed servo is abandoned because of the heating etc. of the servo and the reason that with it and the direct foot pressure the brakes can be put on very suddenly, but it had some advantages which we may now lose, i.e. it permitted the car to be held better backwards, and the scheme made it impossible to get excessive braking on the front wheels. HOLDING BACKWARDS. How then are we going to hold our heavy car from running backwards on a steep piece of road, however short, except by using the self servoing long backward shoe, or having to use the side lever brakes. EQUALISING BETWEEN AXLES. It will also be noted that with Hispano one could carelessly adjust the back brakes and have all the servo and foot pull on the front brakes sufficient to skid the wheels or destroy something. We are I hope definitely avoiding this by the automatically proportioning by lever type or gear type equaliser. This must be made so that ill adjustment will not get it to the end of its stroke. The lever type would appear preferable from this point, as with the gear type the lever angles may get wrong in time. HS.{Lord Ernest Hives - Chair} says we shall be extra critical about equal braking on each side of the car. Naturally this will be so because the whole braking system is more vigorous, and I feel we are going to have some unhappy experience in putting into the hands of drivers sensitive and easily applied brakes, which in an emergency will be put on enormously hard, and (like our old countershaft brake when free from oil) would smash (or partly - which is worse) something. Perhaps it will be better to make them definitely just some percentage less easy to apply than the Hispano, say ours takes 125% to 150% of theirs for the same braking. I am still reminding you that I fear the brakes are too dependent upon bedding of the shoes, and wear. I am very anxious that we test for consistency. Two ways should improve this :- (1) Shorter forward lapping shoe, leaving more room for longer backward lapping shoe. (2) Floating fulcrum which I feel is undesirable for the same reason that we abandoned it and adopted present system - i.e. clearance and stops. R.{Sir Henry Royce} | ||