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).
The scheme and operation of the automatic choke control system for the Wraith model.
| Identifier | ExFiles\Box 7\4\ X 608 Carburetter-page51 | |
| Date | 11th January 1939 | |
| 608 To By.{R.W. Bailey - Chief Engineer} c. to Hn.{F. C. Honeyman - Retail orders} c. to Du. c. to Mx.{John H Maddocks - Chief Proving Officer} c. to Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} c. to Da{Bernard Day - Chassis Design}/Mc. Rm{William Robotham - Chief Engineer}/TA.6/JH.11.1.39. WRAITH AUTOMATIC CHOKE CONTROL - Rm.{William Robotham - Chief Engineer}579. The following scheme for automatic cold starting is at present fitted to the Wraith 23.G.VI. The general principle, subject to several complications is to operate the choke butterfly proportionally to water temperature by means of a Smith's thermostat bellows situated in the cylinder block. The general layout is illustrated in the accompanying sketch. The choke butterfly spindle itself is spring loaded towards the closed position and is actuated by a pick up lever (A). The latter ensures that the butterfly does not remain rigidly closed in event of the thermostat bellows failing. The fast idle cams (c) and the Kick lever (b) are not made in one piece, but are mounted on the same spindle and held in the position shown by a light tension spring. This is to enable the throttle to remain in the fast idle position while the engine warms up and the choke commences to open. The working of the system is shown in the four diagrammatic sketches attached. (1) Cold Start. The choke butterfly is held completely closed by the torsion spring. (2) Engine fires. Immediately on firing, the depression on a small piston in the body of the carburetter trips the kick lever B, so opening the butterfly to any desired amount (not exceeding 3/32 max. clearance between butterfly and carburetter body) The exact amount of this opening is important with regard to the ability to continue running after first firing. The sudden movement of the linkage which ensues is allowed for by the slotted link F at the thermostat. Cont'd | ||