Patent GB-742171-A (GB)
Title: Improvements in carburetters for internal combustion engines
IPC: F02M1/10
Filed: 1951-10-08
Abstract: 742,171. Spray carburetters. GENERAL MOTORS CORPORATION. Oct. 8, 1951 [Oct. 25, 1950], No. 23336/51. Class 7(3) A carburetter has a choke valve automatically and jointly operable by a device responsive to temperature and by a device which is responsive to. engine intake suction and so arranged that the movement thereof in response to engine intake suction progressively increases. the suction effec- - tive thereon until a predetermined degree of opening of the choke valve is effected. The choke valve operating mechanism is shown in Figs. 1 and 7. One end of a coiled bimetallic strip 234 co-operates with an arm 231 connected to the choke valve shaft at low temperatures it holds the choke valve closed. When the temperature increases the end of the strip ultimately moves away from the arm so that the strip ; does not pull the choke valve towards open position. A plate 228 is adjustable to vary the force. exerted by the strip on the choke valve. Also connected to the choke valve, shaft is. an arm 238, Fig. 7, which is; linked to a piston 242 which latter is acted on by engine suction. When the engine starts to run the piston pulls the choke valve towards openposition. Slots 250, 250a admit air to reduce the suction acting on the piston and grooves 248 are provided which also admit air and are effective when the piston has been drawn past the left-hand end of these grooves. As the choke valve opens on increase of temperature the area of the slots is reduced to increase the suction operating on the piston. In a modification the slots 250, 250a are replaced by a series of holes which are - progressively covered. The idling position of the throttle valve is controlled by the choke valve by means of a cam 264. The cam 264 is worked by an arm 270 journalled on the choke valve shaft the arm carrying a lug 272 which co-operates with a lug 274 on a member 276 secured to the choke valve shaft. The cam 264 co-operates with an adjustable screw 262 carried by an arm 166 of the throttle valve operating lever and limits the closing of the throttle valve and determines the idling position. It is stated that the cam 264 does not move until the throttle valve is slightly opened. Referring to Figs. 1 and 10 fuel from the float chamber passes to the main fuel inlet 104 through passages 22 and 95 which lead respectively to passages 94a, 94b on opposite sides of a partition 100. It is stated that blocking of passages by vapour bubbles is most unlikely. At low throttle valve openings suction which acts above a piston 78 (Fig. 10) raises this piston and a valve 72 is kept closed.' At heavy load with open throttle, 'however, the valve 72 opens and the mixture is enriched by additional fuel which is drawn past,this valve. During idling fuel together.with air drawn in through orifices 132, 134 is drawn through a passage 120 which leads to orifices located one on each side of the throttle valve. The idling passage 114 is surrounded by an annular space 116. As the throttle valve is opened the suction in the venturi. 108 becomes so great that the idling flow ceases and a reverse flow takes place through the idling passages, mixture being drawn in through these passages and passed back to the main fuel inlet. To prevent lag in the flow of fuel from the main inlet a column of fuel which has not been mixed with air is maintained in the passages 22, 94a and 94b at a point immediately adjacent the main fuel inlet. Figs. 1 and 5 show a pump 140 for supplying additional fuel during acceleration. On sudden opening of the throttle valve port 158 of an operating member 160 strikes the bottom of a slot 156 and produces rapid discharge of fuel. This is followed by a slower discharge. A coil spring 152 is located between the pump piston 142 and its flexible cup 144. Fuel passes to the pump through a filter screen not shown. A valve 204 closes a by-pass 208 during downward movement of the piston but the by-pass is otherwise open and permits passage of vapour bubbles. In addition to a vent 210 the float chamber is vented by tortuous passages (not shown) in the carburetter casting 6. The tortuous arrangement of the passages prevents suction of dust or dirt. Also when idling at high tempertaures with the choke valve open there is a flow of fuel vapour from the float chamber through the vent 210 into the induction passage. The fuel enters the float chamber by way of a.filter (not shown). The gasket 20 prevents heat transfer.