GB1537053A - Fuel system for an internal combustion engine - Google Patents

Abstract

1537053 Spray carburetters BRITISH LEYLAND UK Ltd 5 Feb 1976 [7 Feb 1975] 5273/75 Heading F1H An I.C. engine fuel system comprises a carburetter having a fuel metering jet 1 controlled by a needle 2 in dependence upon the position of a suction operated member 3 that also controls the flow cross-sectional area of a choke 4 in the main air passage of the carburetter to ensure a depression at the metering jet 1, the system also having a pressure control valve 10 adapted to regulate fuel pressure upstream of the metering jet. A pressure sensing means 21-25 operatively connected to the valve 10 provides a load thereon responsive to engine load, fuel and/or air intake temperature and atmospheric pressure and means 31-33 regulate the effect of atmospheric pressure variations on the valve 10 in response to changes in the flow cross-sectional area of the jet. The pressure sensing means 21-25 and the regulating means 31-33 are such that the fuel pressure upstream of the jet 1 is diminished when the fuel temperature or air temperature increases or the atmospheric pressure diminishes with the other two of these remaining constant or when the fuel temperature and the air temperature both increase while the atmospheric pressure remains constant. The pressure in chamber 7 upstream of the jet 1 depends on the opening of valve 10, which depends on the pressure in chamber 25 connected by duct 27 to region 5 of the main air passage. The pressure in chamber 25 depends on the position of needles 32 and 29. The position of the needle 32 depends on air temperature by way of bi-metallic strip 33 and the position of needle 29 depends on atmospheric pressure by way of a barometric capsule 30. This capsule may contain nitrogen so that needle 29 is also responsive to air temperature. Chamber 21 bounded by diaphragm 22 is connected to substantially atmospheric pressure via orifice 34 and to the pressure in the region 5 via an orifice 35, whose size responds to engine loading by means of a piston 37 which senses manifold pressure. Movement of the diaphragm 22 is transmitted to diaphragm 8 by a rod 23 and the diaphragm 22 is loaded via a spring 43 and stem 43A by a bi-metallic strip 43 which is responsive to engine ambient temperature and is heated during engine cranking and running by a heater 40, the loading on diaphragm 22 by the bimetallic strip 43 reducing as its temperature increases. A piston 45 responsive to manifold vacuum acts upwardly on strip 43 to weaken the air-fuel mixture once the engine has started and cause enrichment of the mixture as the throttle valve 5A is opened. A further thermally sensitive member 46 causes the throttle valve 5A to be opened during cold-start and warming up. In Fig. 1 (not shown), a valve (20) is provided between chamber 7 and a fuel pump (17) and is opened by manifold vacuum. Fuel vapour and air are returned to fuel tank (15) from a de-aerator (19) and orifice 14 of chamber 7 by a scavenge pump (16).