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).
Description of the operation of an engine control mechanism, detailing the function of plungers, air-cushions, and ignition timing.
| Identifier | ExFiles\Box 41\4\ Scan020 | |
| Date | 28th January 1930 guessed | |
| - 2 - Possible errors through backlash are eliminated since the plunger is moving inward against the considerable pressure on the "advance" side of the control piston. The lower plunger is at or near the r.h. dead center during "sampling" and its circular groove is lined up with the short passage to the cylinder so that the working pressures in the cylinder are transferred almost instantly to the control piston. The lower plunger is also drawing in crankcase-air at its left-hand end. This air is subsequently compressed and is discharged at the other end of the stroke through port 1 into the pipe leading to the cylinder. Here it acts as an air-cushion to keep combustion-gases out of the mechanism. This air must not carry too much oil as otherwise it will "coke" around 2 in pipe and ultimately may shut off the device. Means of cleaning this passage occasionally seems desirable. As will be seen the whole system is self-draining from the control piston downwards, back to the engine cylinder. This is essential. The device advances a common fixed-ignition head, without centrifugal governor, by rotating the head on its mounting spigot 3 by means of lever 4. There is no other control of ignition either manual or automatic. The plungers need not be closely fitted, the only effect of excessive leakage being a slight sluggishness in control under idling conditions. All necessity for ribbing the cylinder for cooling has disappeared because of the air-cushion. The casing is designed so that by similar plungers on the r.h. side two samples may be taken from say the two middle cylinders, so giving greater accuracy of control. The setting of the spark position is controlled by the clamping device 5 which turns the eccentrics and the ignition cam on the driving spindle. It is immaterial exactly where the samples are taken during the working stroke, points have been used from 30° apart to 130° apart, and the first sample taken at T.D.C. or considerably later. A 60° crank interval is found best to give the first sample at a place on the diagram where the pressure is rising rapidly, in practice about 5° after T.D.C. and the second sample on a steep portion of the expansion curve. This makes for sensitiveness of operation. - continued - | ||