Patent GB-592894-A (GB)
Title: Improved carburetter
IPC: F02M1/10
Filed: 1945-01-11
Abstract: 592,894. Spray carburetters. GENERAL MOTORS CORPORATION. Jan. 11. 1945, No. 908. Convention date, Oct. 22, 1943. [Class 7 (iii)] A carburetter has a throttle 39 for controlling the mixture flow, a choke valve 16 for controlling the air flow and a fuel chamber 6 which is subject to intake vacuum as varied under the control of at least one of these valves. In the downdraft form shown the fuel chamber encloses the intake passage 12 to minimise the effect of changes in level at the fuel outlet 14 due to changes of inclination of the engine and is formed in the lower body section which terminates in a flange bolted to the engine. The choke valve has a central orifice closed by a spring-pressed valve 22 which can open outwardly to relieve any pressure in the carburetter caused by a backfire, &c. Fuel passes into the chamber 6 through an inlet 38 controlled by a valve 40 operated by a float comprising cork or metal members secured to a bar which acts on the valve through an angle piece pivoted on pin 48 and having a vertical arm 50 acting on the valve through a link. The fuel inlet 14 communicates through passage 54 with a metering orifice 58 controlled by a two-diameter plunger 62 supported by a bracket 64 which is raised or lowered to control the fuel flow. In Fig. 1 the plunger is shown in its raised position giving the minimum flow of fuel. The upper body section 4 is fitted with a detachable housing 71 lined with cork and enclosing a thermostat coil 74 connected to the spindle 76 of the choke valve. Hot air is admitted to the housing by a conduit extending to a point adjacent the exhaust manifold. Another hot air passage 84 extends from the thermostat housing to the fuel nozzle to assist in vaporising the fuel and to promote a flow of hot air through the housing. The fuel nozzle extends to the throat of a venturi 88. A U-shaped piece of wire 92 extends downwards from the nozzle outlet so that any fuel drops will fall on the lower side of the throttle valve at the point of high air velocity when the throttle opening is small. The choke valve 16 is controlled jointly by the thermostat, the engine suction, and the throttle valve. The thermostat is effective to hold the choke fully closed when the engine is cold. For the two last named controls the throttle-operating arm 34 is connected through a short link 106 to a vertical rod 110, Fig. 4. carrying a member 115 fitted with a horizontal arm 116 and angle piece 124 secured on the rod. Member 115 carries a cam roller 112 coacting with an arm 130 on the choke valve spindle 18. A pin on arm 130 coacts with member 124 to cause opening of the choke valve when the throttle is fully opened so as to supply air to vaporise surplus fuel if flooding occurs at starting. For small throttle openings, the roller 122 acts as a stop to control the opening of the choke valve, under influence of engine suction, the permitted opening being gradually increased as the throttle is opened and roller 122 is moved downwards. As the throttle is closed the roller causes progressive positive closure of the choke valve. During acceleration, the choke valve is momentarily closed to provide a strengthened mixture. For this purpose, the arm 130 is connected by a link 140 to a piston 142 slidable in a cylinder 144 which can itself move in another cylinder 146. When the throttle is opened the member 114 engages and moves downwards the cylinder 144 thus closing a ball valve 154 and causing the piston 142 to move with the cylinder 144 and so close the choke valve. The same mechanism causes delay in opening movement of the choke valve under engine suction. The opening of the throttle also effects, opening of the fuel valve. For this purpose the bracket 64 slidable on the metering plug is connected to a vertical rod 162 which is biassed upwardly by a spring. A lug 170 extends from the member 114 above the rod 162 so that as the throttle is opened the plunger 62 is moved from the maximum flow position, Fig. 1, to a position wherein the smaller portion of the plunger restricts the fuel inlet and regulates the flow. For thermostatic regulation one end of the coil 74 is connected to a spindle 76 having a valve portion 180 with a reduced end 182 fitted with a pin 186 engaging a cut-away portion of the choke spindle so as to limit opening of the choke valve by engine suction. When the engine is cold the pin prevents any opening of the choke valve but as the temperature increases the pin is moved by the thermostat to permit a progressively increasing opening of the choke valve by engine suction until full working temperature is reached when no further thermostatic control is exercised. In some cases the extent of the cutaway portion may be reduced so that the pin holds the choke valve open at normal or higher operating temperatures. While the engine temperature is below normal the closing of the choke by the thermostat gives increased suction on the fuel nozzle and thus increases fuel supply to provide a fast idling speed. The extra air for the increased fuel is supplied through passages controlled by the valve portion 180. A passage 206 from the intake pipe leads through a valve 208 which opens under high engine suction to a vertical passage 200 communicating with a chamber 214 connected to passages, Fig. 12, which when the temperature is low register with passages in the part 180 communicating with the intake at one point 230 behind the choke valve at another point 234 between the choke and throttle valves. Thus at low temperatures the high vacuum created under idling conditions unseats valve 208 and causes a flow of air through passages 230, 234 to the intake 206. At moderate throttle openings the suction is not sufficient to open the valve 208. When the temperature reaches normal the valve part 180 is moved by the thermostat to a closed position to render the fast idling system inoperative. In order to maintain a partial vacuum above the fuel in the float chamber a passage 250, Fig. 1, leading to the intake pipe communicates with a passage 259 leading through a cross passage in the part 180, to a passage 270 leading to the space above the fuel in the float chamber. The float chamber vacuum so produced is modified by means of a passage 284 communicating with the float chamber and connected to the passage 200 of the fast idling system. This passage is also connected through an adjustable valve 286 with the atmosphere so as to permit variation in the amount of the fast idle system vacuum communicated to the float chamber. The vacuum control dependent on the position of the member 180 is only fully effective at low temperatures and is gradually cut out as the temperature rises. The vacuum produced by the pipe 284 is effective during normal temperature running if the throttle opening is sufficiently small for the suction to unseat the ball 208 thus tending to weaken the mixture.