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).
Design, materials, and performance of brake servos, considering temperature effects and alternative braking systems.
| Identifier | ExFiles\Box 179b\1\ img071 | |
| Date | 14th September 1932 | |
| HS.{Lord Ernest Hives - Chair} ) FROM R.{Sir Henry Royce} DA.{Bernard Day - Chassis Design} BY.{R.W. Bailey - Chief Engineer} ) C- to SC. WOR.{Arthur Wormald - General Works Manager} PN.{Mr Northey} ER. SERVOS. I pointed out to HS.{Lord Ernest Hives - Chair}, E.{Mr Elliott - Chief Engineer}, and RM.{William Robotham - Chief Engineer}, that we must not be too ambitious about getting the servo consistent and unchangeable with temperature at the expense of any reliability. This seems to have occurred somewhat with cotton duck fabric. Of the new materials suggested I am quite willing to believe that the one which is circularly woven, having a small amount of bonding material, should prove the best of those shewn. If the little extra bonding material, though a disadvantage in maintaining the co-efficient of friction with temperature, will give some added reliability, I should favour more bonding. I did suggest that these rings, for economy, might be arranged to be cut one within the other out of a larger disc, but the makers will suggest any economy that is possible in this direction. I pointed out that no matter how consistent the servo is with temperature we still have the brakes themselves lowering their co-efficient with temperature, and as the brake temperature would probably rise 3 or 4 times quicker and higher than the servo temperature, not much good is gained by attempting to get over the trouble by making the servo independent of temperature - that is to say - it would be far more effective to see if we could get the brakes themselves more consistent with temperature. We understand that this has been done in the case of the Bendix self-serving brakes. While mentioning self-serving brakes you will remember that I have always pointed out the probable trouble with these through their uneven servoing action between one brake and another. HS.{Lord Ernest Hives - Chair} says this is reported to be the case, and that the cars do not pull up straight. In other words they are liable to skid, and we as a firm consider self serving brakes unsatisfactory. It is also considered that brakes depending for servo action from the engine vacuum are also undesirable, and the best effects have been obtained by the direct acting brakes of the hydraulic type, though I dislike carrying the fluid to the moving axle by flexible pipe, and into the drums. I think it cannot be the final form of brake. It has since occurred to me that the friction surfaces of the servo should be of cast iron, as HS.{Lord Ernest Hives - Chair} reports this to be so wonderfully superior for brakes, and hence for clutches. R.{Sir Henry Royce} | ||