Description of the Smith Automatic Jet Control for the S.U. Carburetter.
| Identifier | ExFiles\Box 123\1\ scan0093 | |
| Date | 27th May 1938 guessed | |
| SMITH AUTOMATIC JET CONTROL FOR S.U. CARBURETTER This device completely eliminates the normal dashboard hand control choke on the S.U. Carburetter. During the period of warming up from cold (2½ to 3 minutes) it ensures that the mixture is correct even to the extent of providing a temporary rich mixture when accelerating, or a partially rich mixture when the engine is ticking over. It is possible to drive away with perfect ease without the annoying business of operating a hand control, and with the knowledge that the mixture is not over-rich. As soon as the engine attains a temperature of 60 degrees centigrade, the Automatic Jet Control goes out of action and maintains the Jet in the weak position until the engine cools down when it gradually returns the Jet to the rich position ready for starting from cold again. The advantages of a completely automatic choke are obvious, as in addition to eliminating the human element, and therefore misuse of the choke, it also ensures that when out of action the Jet on the Carburetter is definitely in the weak position which is not always the case with a hand control due to flexibility between dashboard and carburetter or stiffness in the control mechanism. The normal Carburetter adjustment is not interfered with and there is no load on the Jet. The device comprises a Thermostat operating in conjunction with the engine vacuum - the rise and fall in vacuum being made use of when accelerating to give the necessary rich mixture. As the outer casing is in contact with the water the gradual rise in temperature causes the highly volatile liquid to expand and compress the metallic bellows which in turn operate the bell crank lever and thus moves the Jet to the weak position. A unique feature of the design is the fact that the inside of the metallic bellows is connected with the induction manifold so that it will be clear that during the period of warming up the bellows is alternatively being compressed and expanded according to the variations in the induction manifold. The principle of operation is as follows:- When the engine is cold the mixture is full rich, but immediately it is started up and ticking over the Jet moves to a partially rich position due to maximum depression in the induction manifold which exhausts the bellows and operates the bell crank lever. | ||
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).