Patent GB-975894-A (GB)
Title: Charge forming apparatus
IPC: F02M17/04
Filed: 1960-11-21
Abstract: 975,894. Charge forming apparatus. TILLOTSON MANUFACTURING CO. Nov. 21, 1960 [Nov. 27, 1959], No. 39907/60. Heading F1B. Charge forming apparatus comprises a body formed with a mixing passage, a relatively shallow fuel chamber formed in the body, a throttle valve in the mixing passage, a flexible diaphragm forming a wall of the fuel chamber, orifice means opening into the mixing passage, a fuel inlet for the fuel chamber, a valve for the fuel inlet, a fuel inlet valve control lever of the second order of levers fulcrumed at one end on the body and arranged for engagement with the inlet valve, means mounted on the diaphragm arranged for engagement with the lever at a region spaced further from the lever fulcrum than is the region of the lever which is engaged by the inlet valve, spring means arranged to bias the inlet valve toward closed position and duct means in communication with the fuel chamber for conveying liquid fuel to the orifice means, the fuel chamber being unvented whereby the diaphragm is actuated to control the fuel inlet valve by aspiration set up by air flow through the mixing passage. With the charge forming apparatus shown in Figs. 3 to 6 in starting the engine the choke valve 21 is moved to near closed position and the throttle valve 30 moved to partial or full open position. When the engine is cranked, reduced pressure or aspiration is set up in the mixing passage which is transmitted to the diaphragm chamber 38, flexing the diaphragm toward the mixing passage and opening the inlet valve to admit fuel to chamber 38 and cause fuel flow from the diaphragm chamber 38 past the valve 112 through restricted passage 110 into the duct 94, the fuel being discharged into the choke band 15 of the Venturi through the main orifice or primary outlet 84. Some air is bled into the fuel in the duct 94 through the air bleed passage 130 forming an emulsion. After the engine is started, the choke valve 21 is progressively moved to open or near open position as the engine becomes heated. During operation of the engine at intermediate or high speeds, fuel is continuously delivered through the main orifice 84 into the mixing passage. Through contact of the button or head 76 of the rivet 77 with the arm 69 of lever 68, the lever is swung by upward movement of the diaphragm in a clockwise direction about its fulcrum 65 as viewed in Fig. 4, moving the angle portion 70 of the lever in a left-hand direction and permitting the valve body 58 to move in a left-hand direction admitting fuel from the supply through fitting 54, the port in valve seat 63 into the diaphragm chamber 38 for delivery into the mixing passage. The valve 112 may be adjusted by manipulation of the knurled knob 105 to meter, regulate or control the maximum fuel flow to both the primary and secondary fuel discharge system. When the engine is operating at idling speed with the throttle valve 30 in substantially closed position as shown in Fig. 3, fuel flows from the duct 94 through the duct or channel 98, bore 96, restricted passage 122 past the tapered valve 123 through the channel 126 and supplemental chamber 90 to the idling orifice 86. When the throttle 30 is moved to partial open position, fuel may be delivered from the low speed orifice 88 and the idle orifice 86. During delivery of fuel through the idle orifice, the low speed orifice 88 or both, the pressure in the Venturi 14 is high enough whereby fuel is not delivered through the main orifice 84 until the engine speed increases through further opening movement of the throttle 30 and air flow through the Venturi 14 is increased to set up a substantially reduced pressure effective on the nozzle 85 to initiate fuel delivery from the main fuel orifice 84. As the engine speed increases, delivery of fuel through the secondary orifice system, that is, through orifices 86 and 88 gradually diminishes and at high engine speeds only a small proportion of the fuel is delivered through the secondary orifice system. The needle valve 123 may be adjusted by manipulating the knob 120 to regulate or meter fuel flow to the supplemental chamber 90 of the secondary fuel discharge system, the valve member 112 however regulating the maximum amount of fuel for delivery through the main orifice as well as through the secondary orifice system. During engine operation, a subatmospheric or reduced pressure exists in the diaphragm chamber 38 by reason of the aspiration of the engine setting up air flow through the mixing passage of the carburetor. Through this action the relative position of the diaphragm 40 is influenced by the amount of reduced pressure in the chamber 38 to regulate the extent of opening of the inlet valve 60 and thereby regulate the amount of fuel entering the diaphragm chamber 38 in accordance with the requirements of the engine. The higher the air velocity through the Venturi 14, the greater will be the reduced pressure effective in the chamber 38, and a proportionately greater amount of fuel will be withdrawn from the reservoir or diaphragm chamber 38 into the mixing passage 12. A reduction in pressure in the Venturi 14 is transmitted through the bore or channel 94, passages 110 and 108 to the diaphragm chamber 38, elevating the diaphragm 40 a greater distance and hence effecting increased movement of the valve 60 toward open position, thereby increasing the flow of liquid fuel from the supply into the carburetor. Where the air passage 130 is employed, air bleeds into the fuel in the duct 94 and a fuel emulsion is delivered through the main orifice 84. When the engine idling orifice 86 is in operation, or the idling orifice and the low speed orifice 88 are in operation, an emulsion of fuel and air is delivered through the secondary orifice system as air bleeds into the duct 94 from the mixing passage through the main orifice 84 due to the fact that the pressure in the Venturi, with the throttle 30 in closed or nearly closed position is higher than the pressure at the left-hand or engine side of the throttle 30 as viewed in Fig. 3. The extent or amount of air bleeding through the main orifice 84 is greatest at low engine speeds and such air bleeding is progressively reduced as the engine speed increases and the aspiration at the Venturi 14 becomes substantial. Through this type of metering system, the secondary orifices 86 and 88 may be made appreciably larger than conventional practice where the mixture supplied thereto is air bled as herein described. This renders the idling orifice and idling mixture less sensitive and fosters better idling of the engine. Other embodiments are described. Fig. 20 shows a modified form of fuel control lever and spring. Specifications 833,036, 975,895 and 975,896 are referred to.