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).
Letter to K.B. Speid Esq. explaining the issues with oil pump servo mechanisms in braking systems.
| Identifier | ExFiles\Box 66\5\ scan0149 | |
| Date | 2nd November 1928 | |
| X8420 c. to PN.{Mr Northey} Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}3/LG. Expl: Dept: 2nd. Nov. 1928. K.B. Speid Esq., The Grove, Loughborough, Leicestershire. X8320 Dear Sir, With reference to your letter of the 28th.ult. We attach herewith some details of the Rolls-Royce Braking System. We regret that we are not at liberty to give you details of experimental work we have carried out on other types of Servo Mechanism. We can however say that oil pump servos are objectionable because it is practically impossible to obtain braking just proportional to the pedal pressure throughout the whole range of car speeds. This is because the back pressure exerted by oil passing through the orifice or valve increases as the square of the oil velocity. As a direct result on cars fitted with an oil servo at high speeds the lightest pressure on the brake pedal applies the brakes violently while at low speeds the servo is almost totally ineffective. Yours faithfully, | ||