Patent GB-392183-A (GB)
Title: Improvements in and relating to carburettors
IPC: F02M5/12
Filed: 1931-10-06
Abstract: 392,183. Spray carburetters ; valves ; thermostats. TRIGGS, W. W., 57, Lincoln's Inn Fields, London.-(Wolfard, M. R. ; 29, Everett Street, Cambridge, Massachusetts, U.S.A.) Oct. 6, 1931, Nos. 27785, 27786, and 27787. [Class 7 (iii).] In a carburetter comprising a mixing passage having a restricted portion acting as an airmetering section presenting a substantially constant cross-section during idle and light load running, means for controlling the flow through said mixing passage and a fuel inlet subject to a suction head substantially proportional to that at the air-metering section, (1) means are provided to maintain continuously a low flowing head at said fuel inlet during idle and light running to supplement the suction head, (2) the fuel inlet and the passage-controlling means are so arranged as to produce uninterrupted mixture flow and (3) the ratio of fuel to air is regulated by means responsive to changes of temperature. The carburetter, Fig. 1, comprises a casing 1 having inclined inlet and outlet passages 2, 3 forming at their junction a depression 4, adjacent which the passage is restricted by a piece 6. The fuel inlet 7 is supplied from a float chamber 8, Figs. 1 and 4, having cylindrical float sections 9, 10 symmetrically arranged and interconnected by a yoke 11, 12 pivoted at 13. The float valve 30 is shouldered at its lower end to rest on a lever 15 pivoted at 17, the free end of the lever having a knife edge 16 resting on the yoke. The float valve engages a seat in a part 26 carried by a screwed member 21 which can be adjusted to vary the fuel level, and locked by a plate 33. Fuel enters at 25. A throttling valve 39, Fig. 1, attached to a shaft 40 has its lower end slightly thickened and curved so as to lie approximately parallel to the lower wall of the outlet and produce, in the idle and light running position, a small passage 44 through which mixture is delivered. In its open position, the thickened end of the throttle reduces the area of passage at 5 and increases the suction on the fuel inlet 7. This inlet is controlled by a needle valve 45 one side of which is chamfered. The upper end of this valve, which is of larger diameter, is cut away at its lower portion to form flat faces 48 with a notch 50 adapted to be engaged by a slot in the end of a bimetallic thermal strip. This strip has a horizontal portion 52, and is bent, as shown, to pass over, and be supported by, a strut 57 and terminate in a horizontal part 56 which is adjustable by a rod 59 attached to a pressure-sensitive device 60 which can be adjusted initially by a screw 61. The thermal strip, in addition to actuating the valve 45, forces its cylindrical face against the wall of inlet 7 and renders it fluidtight. The valve 45 is forced into contact with the thermal strip by a spring 65, and may be actuated manually by lever 70, 71 and rod 72. In a modification, Fig. 5 (not shown), a manually actuated butterfly valve is provided in addition to the valve 39 which is pivoted out of centre and adapted to be opened by suction, In a further modification, Fig. 6 (not shown), the fuel valve is guided in the upper end of the fuel duct, the control and discharge of fuel taking place below the guiding means. In a modified construction, Fig. 7, the casing has inlet and outlet sections 86, 87, a Venturi 89 and a throttle valve 100. The float chamber, having symmetrical floats, lever 112 and fuel valve 127 as described with reference to Fig. 4, surrounds the fuel inlet duct 92 fed through a chamfered orifice 91. The upper end of the duct has an outlet formed by a bush 94 and controlled by a chamfered needle valve 95 forced by a spring 132 against a plate 134 adapted to be adjusted by a screw 136. The fuel is discharged into a duct 103 communicating on one hand through conduit 98 with the inlet section 86 and, on the other, through conduit 101 and slot 106 with the Venturi 89. The conduit 101 also communicates with the engine side of the throttle 100 through a duct 99 and an aperture 105 in a tubular insertion 104. A shield 107 in front of the slot 106 increases the fuel flow during heavy loads. The ratio of fuel to air is regulated by varying the air admission which comprises a hot air inlet 141 and a cold air inlet 140. Valves 142, 147 respectively, in these inlets, are interconnected by linkage 143, 144, 145, the valve 142 being actuated by thermally sensitive means, and also manually by arm 149 and rod 150. The interconnection is such that initial movement of valve 142 during cold starting has little effect on valve 147, but as valve 142 moves to open position valve 147 opens rapidly. At starting, valve 142 is moved manually to choking position, after which it is released. In the modification, Fig. 10, inlet and outlet sections 152, 153 are provided as in Figs. 1, 4 the inlet being approximately rectangular in form, and the float-feed apparatus of the kind previously described. The fuel valve extends through a slightly converging aperture in the upper casing wall and is loaded by a spring 165. The valve is actuated by a thermally sensitive strip 174 through a link 176 which exerts a lateral thrust on the valve for the purpose explained above. The strip is mounted on an arm 168 supported on a shaft 169 and its free end is connected to a spindle 170 secured to an expansible bellows 171. At starting, the air inlet may be reduced in area by a choke flap 177 mounted upon a manually actuated shaft 178. The inner end of the flap in its upper position engages flanges on a wall 179, and the outer end is curved upwardly so as to engage the upper wall when the flap is in its closed position. A throttling valve 180 extends downwardly during idling and slow running to concentrate all the air into the depression 154. The valve 180 is a flat rectangular plate with bosses 181, Fig. 13, mounted on a shaft 182, the bosses bearing against the upper wall and preventing air flow. The under-faces of the bosses have extensions 184, Fig. 16, which act, when the throttling valve is open, to close the opening between the end of the flap and the bridge wall. The valve 180, Fig. 10, is connected by link 185 to a butterfly throttle 186 mounted on a shaft 187. A thickened portion 188 at the upper edge of the valve contacts with the wall during idle and light-running and prevents mixture flowing over this edge. In a further modification, Fig. 12, a single valve 189 replaces the two throttles of Fig. 10, and the upper edge of the valve is thickened at 190 to contact with the upper wall, thus concentrating all the mixture flow below the valve. The choke flap 192 contacts throughout its length with the bridge wall 193 which has a flange 194 engaged by the lower end of the throttling valve when fully open. Specification 268,905, [Class 7 (iii), Internal-combustion engines, Carburetting-apparatus &c. for], is referred to.