GB563751A - Improvements in or relating to carburetters for internal combustion engines - Google Patents

Abstract

563,751. Spray carburetters. BENDIX AVIATION CORPORATION. Oct. 26, 1942, No. 15029. Convention date, June 5, 1942. [Class 7 (iii)] A carburetter for an internal-combustion engine has an accelerating pump actuated in two stages which are of predetermined length and correspond to different ranges of vacuum in the manifold passage between the throttle and the engine, the first range being a high vacuum range when the throttle is near idling position and the second a low vacuum range for enriching the mixture under heavy loads or at high speeds. The air inlet 12 is controlled by an offset choke valve 22. The main fuel system includes a jet 30 receiving fuel from a float chamber 26 and delivering to passages 32, 34, channel 36 and slot 38. Air is bled to the main system through passages 40, 42 and 44. The idling system includes a tube 48, jet 50, and passage 56 with an adjustable air bleed 60. The accelerating device includes a piston 72 working in a pump cylinder 70 and connected by a rod 76 to a vacuum piston 74 in cylinder 80 controlled via passages 82 and 84 from the manifold vacuum. A strong inner spring 96 reacts between a flanged sleeve 92 slidable on the rod 76 and the top of piston 72, while an outer weak spring 98 reacts between a fixed collar 88 and the top of piston 72. Fuel enters cylinder 70 from the chamber 26 past a check valve 116 and two fuel discharge systems from cylinder 70 are provided. One system-the acceleration discharge, operative during the first part of the downward movement of piston 72 from the Fig. 1 position-includes passages 142, check valve 150, passage 144, nozzle 146, and jet 148. The second systemthe power and economiser system-includes a valve 128 normally seated by a spring, but opened by the piston 72 at the bottom of its stroke. When the valve is closed it is byepassed via a passage 134 and a small metering jet, while when the valve is open a larger jet meters the fuel to a passage 120 leading by passages 122 and 124 to channel 36. In some cases the byepass may be omitted. In operation, during idling a vacuum of 18-19 inches of mercury maintains the piston 74 in its Fig. 1 position. As the throttle is opened the vacuum decreases and the pistons 72, 74 are moved downwards through the greater part of their stroke by the springs 96, 98 until the piston 74 engages sleeve 92. Further expansion of spring 96 is thus checked and no further movement of the pistons occurs until the vacuum falls through the range indicated by the vertical dotted line in Fig. 6, after which a slight further fall completes the piston travel thus opening the valve 128. Fig. 6 shows the action of the two-stage pump above described compared with the usual pump which gives uniform travel throughout the range of manifold vacuum. In some cases the pump travel may be made adjustable and various characteristics different from that indicated in Fig. 6 may be obtained. In a modification, Fig. 4, for an upright carburetter, the main jet (not shown) discharges in a nozzle 412. A power and accelerating jet 424 within this nozzle is supplied from a passage 426. A valve 436 has a stem closed by a metering jet 446 which meters the flow to passage 426 when valve 436 is closed. When the valve 436 is opened, either by the pressure of fuel in cylinder 440 or by the engagement of piston 442 with the valve stem fuel is metered by the larger jet orifice 470 of nozzle 424. In a further modification, a diaphragm type of accelerating mechanism may be used. Also the accelerating discharge jet may be controlled by means other than manifold vacuum, such as by the exertion of a variable manual force in accordance with throttle position.