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).
Development and modification of an automatic choke system for carburetors.
| Identifier | ExFiles\Box 123\1\ scan0038 | |
| Date | 5th March 1940 | |
| To Bv. & Jnr.{Charles L. Jenner} c. Hm{Capt. W. Hallam - Head Repairs}/TAS.{T. Allan Swinden} 1036 Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager}7/MH.{M. Huckerby}5.3.40. CARB. AUTOMATIC CHOKES. We have been trying for some time to make a reasonable automatic choke for the Duplex Stromberg carb., and for the Twin S.U. carb. system to replace the existing ones, which have not proved satisfactory. The first job tackled was the Duplex Stromberg carb., and we have succeeded by more or less modifying their own system in obtaining a satisfactory scheme for our cars. The Stromberg carb. has a kick piston and fast idle scheme incorporated in the carb. itself, and has an electrically controlled bi-metal unit fitted directly on to the choke spindle, operated by a 6 volt current running through the resistance in the unit for heating purposes. We removed the bi-metal unit from the carb. itself and fitted it directly on to the water heated hot spot on the induction pipe, and wired up through a ballast resistance a 6 volt current in the ignition circuit. We then ran a control from the bi-metal unit to the choke valve. In this manner, when the ignition is switched on, the bi-metal strip gradually heats up, and as the engine warms up it receives heat assistance from the rising temperature of the water in the hot spot, and as the bi-metal strip expands, so it opens the choke valve. The relative movements of the bi-metal unit, and the choke valve have been so arranged that the mixture is sufficiently strong to enable the car to be driven away immediately after starting up, without being over-rich and maintaining a decent mixture until the choke valve is fully open and the carb. operating normally. It has proved satisfactory on 3.B.50, 4.B.50 and 11.B.V. cars in temperatures varying from freezing point to 20 degrees of frost. We give herewith the relative movements of the bi-metal unit and the choke valve, together with the temp. of the metal on the outside of the hot spot to which the bi-metal unit is fitted. | ||