Patent GB-1470051-A (GB)
Title: Air valve carburetters of the pivoted flap type
IPC: F02M17/09
Filed: 1973-03-08
Abstract: 1470051 Spray carburetters ZENITH CARBURETTER CO Ltd 8 March 1974 [8 March 1973 1470051 Spray carburetters ZENITH CARBURETTER CO Ltd 8 March 1974 [8 March 1973 7 Nov 1973] 11240/73 and 51756/73 Heading F1H A pivoted air valve flap 40, Fig. 3, or flaps 165, 166, Figs. 5 and 6, upstream of a throttle valve 38 or valves 163, 164, Fig. 7, co-operate with the wall of the induction passage 15 or a bar 152 extending across the induction passage 117 to define a variable area throat or throats. The flap or flaps are operated in response to the depression between the flaps and throttle valves to maintain the depression substantially constant. The part of the or each flap which defines the respective throat is convexly curved, e.g. approximately an involute of a circle or an arc of a circle, and the minimum cross-sectional area of the throat preferably occurs at the upstream end, in the direction of air-flow through the throat, of a fuel discharge nozzle 37 or nozzles 156, 157, 158, 159 opening to the throat. In the embodiment of Figs. 1 and 3 a needle 28 linked to the flap 40 controls a metering orifice 26 which communicates with the nozzle 37 through a passage 36. Four radial bores 32 extend to the orifice 26 from an air supply passage 34. The air-flow to the passage 34 may be restricted by a member 35 and may be unrestricted under certain operating conditions under the control of a depression responsive  valve. Air may be fed to the passage 36 through a port 85 to weaken the mixture under part load conditions. An air supply to the passage 36 may be controlled by an aneroid device to provide adjustment of fuel metering with altitude. A damper 51 connected to the flap 40 comprises a deep drawn dashpot 50, containing a piston 49, which is spring urged into engagement with the bottom of a recess 54 in the carburetter body. To provide an additional supply of mixture at overrunning a valve 67 opens a passage 66, bypassing the valves 40 and 38. Mixture for idling is provided by a passage 71 opening downstream of the valve 38 and communicating with the passage 36 and an air passage 72. The float chamber 14 contains a pair of floats (17), Fig. 4 (not shown), which operate to provide a fuel level which results in less than half the volume of the chamber being full of fuel. A vent tube 30 extends to the centre of the chamber 14 above the fuel level so that fuel does not flow into the tube whatever the carburetter orientation. A valve 75 linked to the valve 38 controls communication between a port 79 connected to the tube 30, a port 80 communicating with atmospheric pressure and a port 81. The port 81 is connected to a port 82 in the passage 15 through a restriction controlled by an evacuated atmospheric pressure responsive capsule. The valve member 76 provides communication between the ports 79 and 81 when the valve 38 is opened so that the float chamber pressure varies with changes in atmospheric pressure in a manner similar to that described in Specification 1369832. An automatic cold starting device is located on the mounting 86 and receives fuel from a port (88), (Fig. 4) communicating with the chamber 14. In the embodiment of Figs. 5, 6 and 7 a tab projecting from the pivot 168 of the flap 166 through the induction passage wall is connected to a tab 173 of a bifurcated link 174, 175 pinned to the ends of a U-shaped link 176. Needles 139, 145 extend through apertures in the link 176 and respective coil springs constitute flexible hinges between the needle stems 140, 146 and the link. The needle controlled orifices 131, 135 have radial air inlet passages 143, 148 communicating with the passage 117 directly upstream of the flap spindle 167 or 168 to be subject to a lower pressure when the flaps are open. The mixture from the orifices 131, 135 flows through passages 155A, 155B, 154A, 154B to the slot nozzles 156 to 159 in the bar 152. The nozzles diverge in the longitudinal direction of the bar from their inlets to the passages 154A, 154B to their outlets in the outer surface of the bar. Between the outlets of adjacent nozzles and between the nozzle outlets and the ends of the bar the convexly curved surfaces of the flaps have projections which engage the bar and only narrow gaps are provided between the flaps and the bar in the region of the nozzles and the opening of a signal passage (161), Fig. 10 (not shown), to the outer surface of the bar at a projection 160, Fig. 5. An air motor diaphragm 187 subject to the depression in the signal passage (161) through a pipe 190 is connected to the flap pivots 167, 168 and opposes the bias of a spring 191 after initial flap opening. The opposite ends of the flap pivots are connected to a damper 193. A passage (202), Fig. 8 (not shown), communicating with the mixture passages 155A, 155B and an air supply passage (203) and a by-pass passage (204) communicating with the passages 118, 119, upstream of the throttle valves 163, 164 are connected to the induction passage downstream of the throttle valves. A single needle may control fuel flow to all the bar nozzles. The following Applications are referred to in this Specification:- 38860/74 (Serial No. ), Specification 1470051 and Specification 38861/74.