Patent GB-1223921-A (GB)
Title: Carburetters for internal combustion engines
Inventor: SWATMAN PETER PHILLIMORE
IPC: F02M17/08
Filed: 1968-01-25
Abstract: 1,223,921. Spray carburetters. BRITISH MOTOR CORP. Ltd. Jan.9, 1969 [Jan.25, 1968; May 9, 1968], No.3856/68. Heading F1B. In a carburetter having a fuel metering jet controlled by a needle in dependence on the position of a suction-operated member which controls the area of a throat in the main air passage a single main control member 10, Fig.1, regulates the choke cross-section, a fuel discharge orifice 11 is located at smallest of the throat and an inlet manifold pressure and atmospheric pressure responsive means effects movement of the main control member so as to ensure that the depression at the fuel-discharge orifice is never less than a predetermined minimum. Fuel from a float chamber (not shown) passes via a pipe 6 through a jet 8 to the fuel discharge orifice 11. The flow cross-section of jet 8 is controlled by a contoured needle 13 moved by a diaphragm 22 through a rack and pinion connection 19, 20. Needle 13 may be attached to the rack 20 through an interposed temperature responsive bi-metallic strip to vary the area of jet 8 in accordance with air temperature. The lower side 25 of diaphragm 22 is subject to ambient air pressure whilst its upper side is acted on by a spring 26 and manifold pressure which is communicated via pipe 28 and orifice 27, ambient pressure also being admitted through a bleed orifice 29. The area of orifice 27 is controlled by a needle valve 30 carried by a block 31 in flexible diaphragm 33, the block being moved by a throttle control cable through an arm 36 and on adjustable rod 34. Shutter 10, which is mounted on ball bearings (16), Fig.7 (not shown) mounts the gear wheel 19 and is moved by the diaphragm 22. When valve 30 is fully lifted full manifold pressure acts on diaphragm 22 thus causing shutter 10 to maintain the predetermined full load pressure drop across throat 2A. With partial lifting of valve 30 the diaphragm 22 moves until orifice 27 is reduced in area and a equilibrium position is established, shutter 10 moving a corresponding amount. Air is admitted to the fuel conduit 12 through a valve 15 to correct the fuel supply for variations in pressure drop at throat 2A. In a modification a contoured needle (39), Fig.5  (not shown) moved by a manifold pressure responsive capsule (40) controls the air correction supply. In a modification the area of the bleed orifice (22), Fig.6 (not shown) is varied by a pressure sensitive device (41), Fig.6 (not shown) which reduces the air bleed during over-run conditions to increase the pressure acting on diaphragm 22 thereby increasing the area of the throat 2A. In another embodiment a diaphragm 22, Fig. 7 is subjected to ambient pressure in chamber 49 via an orifice 48 and to pressure in chamber 50 admitted via orifice 54 from the manifold or via orifice 55 from atmosphere. The orifices 54, 55 are controlled by a double-tapered needle 58 attached to a throttle cable 59. A contoured needle 60 controls the effective area of orifice 48 to provide a variable degree of pneumatic damping. In a modification a reservoir 61 and diaphragm chamber are oil filled. In a further modification an over-run device similar to Fig. 6 is incorporated in this embodiment. The needle 58 and its associated orifices, which replace the normal throttle control, may be situated in a vehicle driving compartment and connected to the carburetter by a flexible tube.