GB1487327A - Fuel injection pumping apparatus - Google Patents

Abstract

1487327 Fuel injection pumps; starting fuel injection engines CAV Ltd 8 Nov 1974 [23 Nov 1973] 54412/73 Headings F1A and F1B In fuel injection apparatus wherein a feedpump 25 supplies fuel to the pumping chamber 11 of a fuel injection pump, the latter having a cam 13 angularly adjustable by a pressure responsive piston 38 to vary the timing, during starting the piston 39 is spring urged to its maximum retard position by being isolated from the pressure supply which normally effects its adjustment and simultaneously an excess of fuel is supplied to the chamber 11. A spring-loaded servovalve 38 controls the application of pressure to the piston 39, the valve being subjected to speed dependent pressure established in a passage 36 by metering valve 33 supplied by the feedpump 25. At start-up a valve 59 is closed to prevent the feedpump pressure from moving the piston 39 in the advancing direction or, alternatively, a valve 60 is closed to prevent fuel from the passage 36 operating the servovalve 38. A latch 58 is operated in conjunction with the valve 59 or 60 and this allows a piston 35 controlling the maximum excursion of a metering shuttle 19 to move to an excess fuel position in which the shuttle is able to enter a recess (not shown) in the piston instead of abutting a cam surface 34. Thus, at start-up the bore containing the shuttle 19 receives, through a passage 21 and a rotary valve 22, an excess amount of fuel which is subsequently displaced through a rotary valve 20 into the pumping chamber 11 by fuel admitted to the opposite end of the bore through a valve 23. The metering valve 33 is centrifugally controlled and throttles the fuel supply from the feedpump 25 to the passage 21. The valve 33 also co-operates with a valve 52 to establish a pressure in the passage 36 which is proportional to the square of the speed of the centrifugal weights 43. Pressure in the passage 36 moves the piston 35 whereby the maximum delivery is speed dependent. The valves 59 or 60 may be in the form of two ports (61, 62) which become interconnected by a groove (63) in the piston 35 when the latter is released by disengagement of the latch 58. In order to delay movement of the piston 35 after start-up, the pressure in the passage 36 may be prevented from acting over its complete end surface until displaced from its end position.