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 description of ignition advance and carburation control mechanisms.
| Identifier | ExFiles\Box 15\6\ Scan077 | |
| Date | 9th February 1929 guessed | |
| - 2 - Ignition Advance. The control of the spark advance depends on the balance of pressure on either side of a piston, two points being chosen on the "optimum" indicator diagram at which it is considered that equal pressures should exist. "Samples" of the pressure from one cylinder are taken at these two points. For convenience one point is taken as top dead center and another at some time during the firing stroke at which the pressure should be equal to that at top dead center. The device will then always tend to reproduce these conditions, and when the ignition is switched off the differential pressure will retard the spark. No centrifugal or manual advance is used. A light spring to ensure that the spark retards when switched off can be used and the timing of the second "sample" adjusted to compensate for it. (Control of supercharge on aircraft engines is arranged similarly.) During partial throttle running the ignition will be automatically adjusted to give an indicator diagram of the same form but of less height. Since pressure effects are small but cumulative there is no tendency to "hunt", and considerable force can be exerted by the device. A magneto can be controlled as easily as a battery ignition head. The mechanism, consisting of a short 5/16" pipe from a cylinder, the two small valves and the advance piston and cylinder, occupies about the same space as the ordinary centrifugal advance. Carburation Control. Pressure at top dead center plus the manifold vacuum are balanced against a spring for the carburation control. This depends on the fact (as stated by Mr. Stanton) that in any engine a factor of the manifold depression in inches of mercury plus the pressure at top dead center is a constant, at all times when the engine is operating normally at maximum economy. Thus, on the car demonstrated which was equipped with a pressure gauge from top dead center and an intake vacuum gauge, five times the manifold vacuum in inches of mercury plus the T.D.C. pressure was at all times equal to about 120 when the car was warm and running at a constant speed. -continued- | ||