Patent GB-765781-A (GB)
Title: Improvements in carburetters
IPC: F02M1/00
Filed: 1952-12-22
Abstract: 765,781. Carburetters. GENERAL MOTORS CORPORATION. Dec. 22, 1952 [Dec. 29, 1951], No. 32401/52. Class 7 (3). In a carburetter having a primary mixture passage and throttle valve and a secondary mixture passage and throttle valve the throttle valves are operable sequentially and so arranged that the secondary throttle can be latched in and released from its closed position by movement of the choke the primary throttle valve being operable independently of the secondary valve when so latched. As shown, the carburetter comprises four mixture passages two of which 28 and 30 are shown in Fig. 1 the other two passages being of the same construction as those shown. The carburetter is designed to be associated with the two manifold conduits each of which is adapted to receive mixture from one primary and one secondary mixture passage. The primary throttles are open about 40‹ before the opening of the secondary throttles begins but the extent of opening of the primary throttles may be either greater or less than 40‹ as desired for different installations. Fuel is introduced into each of the mixture passages through a small venturi tube 48. Fuel is conveyed to each of the small venturi tubes 48 through a passage 52. Each passage 52 is supplied with fuel from one of four main fuel supply wells which receive fuel from one or other of two constant level fuel chambers 56, 58. Air enters by orifices 122 and mixes with fuel in the tubes 114. When the engine has stopped if vapour forms in the wells it can escape through the orifices 122. Deflectors 59, Fig. 12, control distribution of the mixture. Referring particularly to Figs. 2-4 and 25, the primary throttle valves are controlled by means of an arm 36 on their shaft 32. When the secondary throttles are unlocked the primary throttles turn through 40 degrees of opening movement before the secondary throttles 20, 24 begin to open and if the latter are locked the primary throttles can go to their fully open position while the secondary throttles remain closed. To effect this there is movably mounted on the primary throttle shaft 32 at the end opposite to the arm 36 a plate 310 which operates an arm 312 on the end of the secondary throttle shaft 34 to open the secondary throttles after 40‹ of movement of the shaft 32. The plate 310 is moved through the medium of a spring 314 which has one end anchored to a pin 316 screwed into the shaft 32 and the other end of the spring engages the lower side of a cross member 320 integral with the plate 310 and a part 322. On opening movement of the primary throttles the spring 314 tends to rotate the plate 310 counterclockwise (Fig. 2) if the arm 312 is not held against movement the plate 310 will move until the right-hand end of the slot, as seen in Fig. 2, engages the pin. Continued movement of the plate 310 effects movement of the arm 312 in a clockwise direction to open the secondary throttles. When the primary throttles are fully opened the secondary throttles are fully opened. If the secondary throttles are locked in the closed position opening of the primary throttles can continue because the spring 314 yields. When the primary throttles are returned to closed position the pin 316 engages the cross member 320 to restore the plate 310 to its initial position and if the spring 336 fails to move the secondary throttles to the fully closed position a toe 344 will engage a lug 342 and positively move the arm 312 to the closed throttle position. The end of the link 328 extends through an opening 334 in the arm 312. There can be a series of these openings 334 so that the extent of opening of the primary throttles before movement of the secondary may be changed. The secondary throttles are latched closed until a predetermined temperature is reached by mechanism operated by the fast idle cam which is controlled by the choke valve 44. Thus the fast idle cam 356 has a surface 370 which at low temperatures is engaged by a lug 372 that projects from a dog 374 mounted on the flattened end 376 of the secondary throttle shaft 34. The arrangement is such that although the cam is held only by the thermostat the cam serves as a substantially positive lock at low temperatures. At a predetermined temperature (dotted position, Fig. 3) the cam releases the secondary throttles. The fast idle cam can comprise a series of stops instead of the continuous curve 358 shown. At normal temperatures the idling position is determined by engagement of a flange 364 with an adjustable stop 'screw 366. A lug 375 is adapted to engage stop surfaces 377 on a boss 359 when the secondary throttles reach full open position and which prevents further throttle movement. A lug 379 extends outwardly from the cam 356 and the surface 381 of the throttle arm 36 will engage this lug and slightly open the choke valve to effect de-choking in the case of flooding. The choke valve shaft 46 is off centre with respect to the valve 44 so that the entering air tends to open it and is also, controlled by a thermo-sensitive coil 394 and by a piston 402 subjected to the suction posterior to the throttle valve. The coil exerts no force at normal operating temperatures. Two ports 410 in the wall of the cylinder 4U4 which are blocked by the piston 402 when the choke 44 is closed are opened when the choke has opened to a certain extent. When the engine is started the piston unblocks the passages 410 so that suction is effective to draw heated air through the housing 380. Additional fuel can be supplied to the two wells 108 which supply fuel to the primary mixture passages by auxiliary passages 126 (Fig. 12) controlled by a valve 134. The valve 134 is operated by a rod 144 which is connected to a piston 146. This piston is subjected to the suction downstream of the primary throttle valves. The valve 134 is closed when the suction is high but is opened when it is low or the engine is inoperative. There is no device for supplying additional fuel to the wells 108 which supply fuel to the secondary mixture passages but similar passages can be provided and a secondary piston can be utilised for controlling these passages. There are two idling wells 160 for each primary mixture passage. In Fig. 17 the well 160 receives fuel through a slot 162 from one of the main wells. The orifice 172 opens into the secondary passage. A passage 178 leads to a vertical passage 182. There is one secondary well for each passage 30. There are two primary wells of exactly the same construction as the secondary wells. Each of these wells has associated therewith passages similar to the passage 174, 178 Fig. 17. The passage 178 leads to a passage 192 Fig. 1. The idling passages are so arranged and calibrated that they will provide a mixture of proper ratio and quantity during all the idling and part operation. The accelerator pump is operated by the throttle arm 36 through a link 210 and levers 212, 218 secured to opposite ends of a shaft 214. The piston 238 is ordinarily moved downwardly with a delayed action by compression of the spring 258. If the piston rod 222 is moved downwardly very rapidly the pin 254 can engage the lower end of the slots 256 and move the pump piston 238 positively downward. A control valve 268 is located in the pump delivery passage 262 Fig. 11. The passage 270 leads to a passage 272. A check valve 281 controls a passage 278, Fig. 26. The valve is normally in the position shown in which the passage 278 serves as a vent to prevent fuel from being drawn into the carburetter by suction in the mixture passage. There is only one pump piston 238 and cylinder 224 but the channel 270 is so formed that it conducts fuel to two passages 274 and one of which delivers fuel to one of the passages 30 while the other delivers fuel to the second passage 30. The upper part of the cylinder 224 is connected with the fuel chamber 56 by a slot 237 which permits escape of fuel vapour. An accelerator pump could be used with the secondary mixture passages but with a pump of proper capacity supplying the primary passages a pump for the secondary passages is not required. Each of the chambers 56, 58 has a vent passage (280, 284) and an auxiliary vent 287. Another additional. vent for the chamber 56 is controlled by a member 296 (Fig. 9A) and is opened when the throttle is in idling or almost closed position. The member 296 is operated by a toe 302 which projects from an offset part 304 of the lever 212 of the accelerator pump. Fuel is supplied to the chambers 56, 58 through an inlet 60 a passage not shown leading to the inlet valve of the chamber 58. Orifices 100, 102 which are positioned approximately at the normal fuel level connect the chambers 56, 58 respectively, with a balance passage 98 (Fig. 10). There are two interconnected floats in each fuel chamber. Icing at the idle ports and the edge of the throttles is avoided by supplying exhaust gases to a heating chamber 426 (Fig. 4). The heating chamber could extend around the secondary passages 28 also. Since the tubes 114 (Fig. 1) are spaced from the well and have no metallic contact with anything other than a small casting 118 which is separated from the main casting by gasket 124 except for a very small area of contact the heating of the fuel is reduced to a minimum and there is little vaporization of the fuel within the tube 114.