GB653493A - Improved carburetter - Google Patents

Abstract

653,493. Spray carburetters. GENERAL MOTORS CORPORATION. Feb. 16, 1945, No. 3911. [Class 7(iii)] The invention relates to a carburetter having an automatic choke mechanism and a throttle valve. The choke valve is air flow responsive and its open position is determined by a stop mechanism posisitioned by means responsive to different engine operating conditions. The extent to which an unbalanced choke valve 10, Fig. 1, can be opened by the pressure of the incoming air is determined by a stop 90 formed by an arcuate projection on a shaft 80 which is prevented from moving longitudinally and limited in its rotation by a screw 82 engaging a slot 88 in the shaft. The suction on the engine side of the throttle valve 24 is transmitted through passages 122, 120, 118, 114 to a cylinder 100, Fig. 2, containing a piston 99 which compresses a spring 108 and moves a piston rod 96 connected to an arm 92 on the shaft 80 to rotate it against the action of a thermally sensitive coil 130, one end of which is hooked around the end 94 of the arm 92 and the other end of which is secured to a shaft 132 which can be adjusted in a housing 102 by a screw 138 engaging a slot 139. As the temperature rises the coil expands and its end moves away from the lever 92, so that the coil no longer opposes movement of the piston. The choke valve is also controlled conjointly with the throttle valve 24. As shown in Fig. 4, one end of the choke valve shaft 12 carries an arm 142 having a roller 144 which is held by a spring 171 against a cam 150, mounted on a pin 152, and connected by links 157, 160 to an arm 28 on the throttle valve 24. Closure of the throttle valve positively closes the choke valve but if the throttle valve is opened the links 157, 160 through the spring 171 pull on the arm 142 to open the choke valve against the resistance of the thermally sensitive coil 130 and a dashpot. The piston 186 of the dashpot is connected to one of three holes 191 in the arm 142 and operates in a cylinder 180 at one side of the float chamber 50. The length of the combined links 157, 160 is adjusted by a screw 167 having threads 168, 169 of different pitch engaging gears 165, 166 carried by the links 157, 160. As the throttle valve is moved to full open position a lip 212 on a plate 210 on the cam 150 engages an arm 214 to open the choke valve. The float chamber 50, Fig. 1, surrounds the carburetter body and contains a pair of floats one only being shown, connected by an arm 68 which actuates the float valve 60 and fuel is supplied through an orifice 40 controlled manually and automatically by a valve 42 and a passage 30 to a Venturi tube 14 where a rich mixture is formed with hot air admitted through a passage 46. During idling fuel is supplied through an orifice 270 to a passage 272 in which it is emulsified by air admitted through an opening 274 and the mixture is drawn through a passage 276. Fig. 4, to a passage 278 connected to the intake passage beyond the throttle valve and having an atmospheric vent 279. The fuel valve 42 comprises a thin cylindrical part 220, a tapered portion 224 and a cylindrical part 222. During idling the suction in the intake manifold transmitted through passage 248, 246, Fig. 12, raises a spring pressed piston 232 which through a lever 226 connected to the valve 42 maintains the cylindrical portion 222 in the orifice 40. The end of the lever 226 projects through a slot 252 in a bar 250 the end of which is depressed by the plate 210 on the cam 150 as the throttle is opened fully, thereby permitting gravity and the reduced suction to lower the piston 232 and bring the smallest part 220 of the fuel valve into the orifice 40. To produce fast idling at low temperatures the passages 122, 120 connect the intake passage beyond the throttle with a passage 282, Fig. 10, opening on the air inlet side of the choke valve and communicating with a passage 290 opening on the engine side of the choke valve and having a restricted opening to the atmosphere. Some rich mixture is drawn from the Venturi tube 14 through the passages 290, 282 to the engine side of the throttle. As the temperature rises this additional supply of mixture is cut off by rotation of the shaft 80 which moves a port 296 out of register with the passage 282. Orifices not shown in the top of the float chamber vent the float chamber to atmosphere Specifications 456,943 and 653,558 are referred to.