Patent GB-1468674-A (GB)
Title: Fuel pumping apparatus
IPC: F02M41/14
Filed: 1973-05-09
Abstract: 1468674 Fuel pumping apparatus CAV Ltd 2 April 1974 [9 May 1973 5 Sept 1973] 22053/73 and 41719/73 Heading F1B A fuel pumping apparatus of the kind comprising an injection pump driven in synchronism with the associated engine and which supplies fuel to the engine in timed relationship therewith, first fluid-pressure operable means which adjusts the timing of delivery of fuel to the engine by the injection pump, a feedpump which supplies fuel to the injection pump, second fluid-pressure operable means which determines the amount of fuel which is supplied to the engine at each delivery stroke of the injection pump, and valve means for deriving from the outlet of the feedpump, fluid at a pressure which varies in accordance with the speed at which the apparatus is driven, is characterized in that it comprises conduit means communicating the said fluid-pressure to the first fluid-pressure operable means, the conduit means including a first variable orifice through which the fluid under pressure flows to the first fluidpressure operable means, the first variable orifice having a size which varies in accordance with the speed at which the apparatus is driven, and a second variable orifice through which fluid escapes from the conduit means at a position intermediate the first variable orifice and the first fluid-pressure operable means, the size of the second variable orifice being dependent upon the amount of fuel which is being supplied to the engine. The injection pump includes an angularly movable cam 10 and a rotary distributer which registers in turn with each of a number of ports each connected to an engine cylinder injector. The amount of fuel supplied to each cylinder is determined by the stroke of a shuttle 12, the movement of which is determined by a sloping surface 13 formed on a piston 14, which assumes a position dependent on the fluid-pressure in chamber 40 and a compression spring 49. Fuel feedpump 11 supplies chamber 25 which contains a spring-loaded piston 26 in which there is an orifice 30. In conjunction with a drain port 27, the piston acts as a pressure relief valve to maintain constant pressure in chamber 25. Fuel from the chamber outlet passes through an inlet 23 to the bore of a hollow piston 16 containing a shuttle valve-member 19, having a land which controls a port 22. The piston 16 is held in equilibrium by the valve-member which moves to the right to admit fluid to the closed space between piston 16 and the closed end of the bore 17 or moves to the left to allow fluid from the closed space to exhaust to drain 24. Fluid from pump 11 passes through restrictor 30 to cylinder bore 31 which contains piston 32. Centrifugal weights 33 driven by the engine act on piston 32, the edge of which covers drain port 34. The pressure in a duct leading to a cylinder 43 therefore varies in accordance with the square of engine speed. Fluid from the pump also passes directly from chamber 25 to a port leading to a valve-member 36, having a land which is slightly narrower than an outlet port 37. Valve-member 36 is biased to move to the right by spring 38 so that fluid passes through member 36 to a drain thus reducing the pressure at port 37. Movement to the left increases the fluid-flow into port 37 and hence the pressure in chamber 40. The spring bias is variable by an operator controlled cam 39. An increase in pressure in chamber 40 moves piston 14 to the left and reduces the movement of shuttle 12 and hence the supply of fuel to the engine. A stop 41 determines the extreme rightward position of piston 14 and thus the maximum fuel supply to the engine, the position of stop 41 being set by a cam surface 43 on piston 42. The position of piston 42 is controlled by fluid-pressure from bore 31 acting against compression spring 44. Fluid escapes from above piston 42, past tapered needle 47, through groove 45, to a similar groove in piston 14 and through orifice 48, controlled by a tapered needle to a drain. The fluid-pressure in this circuit acts on the end-face of shuttle valve-member 19, through a duct 21, so that the position of piston 16 is dependent on the speed of, and the load on the engine. In a modification, the piston 32 is integral with valve-member 36 and defines therewith a groove which controls the flow of fluid across bore 31 to the chamber above piston 42.