GB601607A - Charge forming device for internal combustion engines - Google Patents

Abstract

601,607. Spray carburetters. BENDIX AVIATION CORPORATION. May 25, 1945, No. 13175. Convention date, April 29, 1944. [Class 7 (iii)] A charge-forming device for an internal-combustion engine has auxiliary fluid such as water metered into the air fuel mixture under prearranged conditions of engine operation the metering valve being associated with other valve means adapted to maintain a metering head of auxiliary fluid proportional to the mass flow of air and fuel to the engine. In the application to an aircraft engine 10 the air from an inlet 11 passes through a carburetter having main and boost venturies 12, 13, and throttle 14. A multi-speed supercharger 16 supplies the inlet manifolds (not shown). The controls are actuated from a unit 18 which may be as described in Specifications 572,647 and 573,691, [both in Group XXIX]. A main shaft 19 in the casing is connected by lever mechanism to the throttle 14 and also carries an arm 23 fitted with a spur wheel 24 coacting with a loose quadrant 25. Pinion 24 also coacts with a mutilated wheel 26 having a part engaging a rack 27 connected to spring-urged servo-motor pistons 28,29 operating in cylinders 30, 31. The quadrant 25 and gears 24, 26 form a planetary train whereby movement of either or both of the members 25, 26 causes opening or closing of the throttle. For this purpose a pilot's control lever 33 is connected by levers 34, 35 to the hub of quadrant 25. This quadrant also carries a cam 36 setting the manifold pressure datum, a cam 37 for the supercharger datum, and cam 38 controlling engine speed. Cam 36 is arranged through lever 39 to apply a variable load to a datum spring 41 enclosing a rod 40 connected to bellows 42 mounted in a chamber subjected to engine charging pressure by a pipe 44. Movement of rod 40 operates through lever 46 a servomotor control valve 47. The cam 37 acts through lever 57 on a sleeve 59 slidable against a spring 60 on a valve member connected to an aneroid 63 and controlling flow to a cylinder which actuates a link 80 to shift the supercharger change speed gears. Cam 38 acts through lever mechanism 83, 84 to vary the pitch of the propeller blades. Fuel is supplied by a carburetter 90 which may be of the type described in Specification 523,895. Air pressure differential chambers 91, 92 are separated by a diaphragm 95 and fuel pressure differential chambers are separated by a diaphragm 96, the diaphragms controlling a valve 98 to admit unmetered fuel to chamber 94 from which it flows to a regulator 102 which meters the fuel for passage through line 10.4 to nozzle 105. The metering jets are selected by a manual control valve which controls an automatic lean metering jet 107, automatic rich metering jet 108, power enrichment jet 109, and power "derichment" jet 110. A power enrichment valve 111 is actuated by a diaphragm whose movement is determined by the pressure differential between metered and unmetered fuel. Air scoop pressure is communicated to chamber 91 by flow past a valve 117 controlled by a density-responsive unit 120, and through passage 118. The differential pressure between the venturi throat 13 and the air inlet gives a resultant force on diaphragm 95 tending to open valve 98 allowing flow to chamber 94 and thence to the regulator section giving a metered flow to nozzle 105. The difference between metered and unmetered fuel pressure acting on diaphragm 96 tends to close the fuel valve and opposes the air differential pressure, the equilibrium position of the valve giving constant fuel-air proportion. The unit 120 modifies the action of a calibrated bleed 119 between chambers 91 and 92 by progressively restricting passage 118 thus increasing the effect of the bleed in reducing pressure in chamber 91 and maintain constant fuel-air proportion in spite of variations in air density at different altitudes. A water or other auxiliary supply tank 130 supplies an electrically-driven pump 132 which delivers to a metering unit 134 having an intake chamber 135 connected through valve 139 with a chamber 135<1> whence flow may pass through a regulating valve 141 to chamber 136. The valve 141 is controlled by a diaphragm 148 subjected to unmetered fuel pressure by line 151 and a diaphragm 147 subjected to water pressure in chamber 136. Water pressure in chamber 136 also acts on a diaphragm 152 controlling a metering valve 154 to permit flow through a metering jet 156 to pass into chamber 138 and thence through line 160 to the carburetter nozzle 105. The valve 154 is closed by a spring 154<1> which permits the valve to open at a pressure approximating the pressure differential in chambers 91, 92. During periods of water injection the mixture is deriched by a valve 161 connected to a diaphragm 162 connected to the water inlet chamber 135. When water pressure builds up in the chamber 163 the valve is closed against the pressure of a spring 166. In operation, when emergency power is required the pilot moves lever 33 to make contacts 181, 182 and start the water pump. This starts water flow to chamber 135<1>. Pressure in chamber 136 is at this time less than that in conduit 100 and valve 141 is open and flow continues to chambers 136 and 143<1> until pressures are equalized. Thus water pressure in chamber 136 is maintained at unmetered fuel pressure. When this pressure corresponds to the desired point on the power curve the valve 154 is opened by diaphragm 153. The first metering is effected by valve 154 but as the power control lever is moved further the flow attains the capacity of orifice 156 which then meters the water flow. The pressure differential of chambers 135, 135<1> determines the opening of valve 170 which admits water pressure to chamber 163 and closes the derichment valve 161 to reduce the mixture strength when the water flow exceeds a predetermined minimum. If the water supply fails the derichment valve opens to strengthen the mixture and the manifold pressure returns to that set by the datum cam. A switch 200 may replace or, as shown, be placed in series with the switch 183, this switch being operated by oil pressure in the supercharger shaft part of the system so that the electric circuit is not closed until the supercharger is moved to high speed.