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 memorandum detailing modifications and specifications for the vacuum servo on a Phantom III clutch.
| Identifier | ExFiles\Box 95\4\ scan0128 | |
| Date | 21th May 1936 | |
| Vacuum Servo for Phantom III Clutch. We send herewith N.Sch.4787 which shows the above. We have made this scheme to suit the new type gearbox arms. In the event of it being desired to fit the servo to a chassis with the present gearbox, alterations to some of the pieces adjacent to the gearbox arms will be necessary. The leverage between the clutch pedal and the clutch has been reduced in order to give increased pressure plate movement. A movement of the centre of the clutch pedal plate of 5.75" will give .110" instead of the present .092", (an increase of 20%.) after deducting wear allowance and travel required for valve operation. As a result of this alteration the pedal plate load when unassisted becomes 47 lbs rising to 58 lbs when fully depressed. With a vacuum of 7 1/2 lbs sq.in. the pedal plate loads required are 20 lbs and 24.5 lbs fully out. The control valve spring gives 10 lbs at the pedal plate and the pull off spring 3 lbs, so however much the vacuum may rise, as soon as the pedal plate load is diminished to 13 lbs the control valve commences to shut off the vacuum. This will occur with a vacuum exceeding 9 1/2 lbs sq.in. and as when changing gear with the car on the move, this vacuum will no doubt be exceeded, under these conditions the control of the clutch will be done on the valve. When starting the car the vacuum will almost certainly be below 9 1/2 lbs sq.in. and in this case the valve will be held fully open and the pedal will have direct control of the clutch with no back lash effect as when the clutch is controlled by the valve. | ||