Patent GB-1425875-A (GB)
Title: Fuel injection pump for an internal combustion engine
IPC: F02D1/00
Filed: 1973-12-04
Abstract: 1425875 Fuel injection pumps; starting and regulating IC engine fuel injection FORD MOTOR CO Ltd 4 Dec 1973 [26 Dec 1972] 56106/73 Headings F1A and FIB In a fuel injection pump comprising a plurality of pumping plungers 50 reciprocated by a rotatable face cam 34 in respective bores 52 each having a valve controlled spill port 58, the actuating surface of the cam 34 is contoured to provide for a rate of plunger displacement (i.e. velocity) which does not decrease as the cam surface passes through the angular position of 90 degrees before top dead centre. In a conventional pump having a flat swash-plate surface, the 90 degrees B.T.D.C. plunger position corresponds to the point in the sinusoidal rate of displacement curve at which the rate reaches a maximum and then decreases. Thus with the known pump during injection timing advance with increasing engine speed, depending on the degree of advance, the spill ports 58 are sometimes closed when the plunger velocity is increasing and sometimes when it is decreasing. This causes the plunger to deliver a different quantity, depending on the timing, for the same period that the spill ports are open. By providing the cam surface with a contour which produces a constantly increasing plunger velocity over all or almost all of the range of spill port closure the above described variation delivery is avoided. The cam surface 36 is therefore contoured to produce a rapidly increasing plunger velocity (a), Fig. 12B (not shown) from between e.g. 180 degrees and 150 degrees B.T.D.C.; a steadily increasing velocity (b) to around 40 degrees B.T.D.C.; and finally a rapidly decreasing velocity (c) up to T.D.C. The feet 53 of the plungers have cylindrical surfaces whereby they make line contact with the cam surface 36. In order to maintain the axes of the cylindrical surfaces of the feet 53 perpendicular to the axis of rotation of the cam 34, the plungers are provided with flats which slidably engage complementary flat surfaces (55') of holes (55) in a fixed plate 54 through which the plungers pass. Opening and closing of the spill ports is controlled by a control edge 72 on a valve sleeve 70 axially and angularly movable with respect to a shaft 82 keyed for drive with the cam 34. Movement of the valve sleeve 70 is in response to the action of a centrifugal governor 122, a diaphragm 136 responsive to engine manifold pressure and an auxiliary fuel control shut-off knob 141, the latter being' movable to a position in which it lowers the shaft 82 and sleeve 70 to a position in which the spill ports are uncovered at all times. At engine start-up, the accelerator pedal 128 is fully depressed whereby the pressure in the inlet manifold 133 allows the diaphragm 136 to raise, via linkage 137, 138, 96, 95, the shaft 82. This causes closure of the spill ports 58 for almost the entire rotation of the valve 70 to provide excess fuel for starting. After start-up the release of the pedal 128 to its engine idle position causes lowering of the shaft 82 and simultaneously downward movement of the valve 70 relative to the shaft 82 due to the governor weights 124 overcoming the force of a spring 97. If the pedal 128 is now depressed, the decreased vacuum raises the shaft 82 and valve 70 to increase the delivery, the effect of the governor becoming inoperative when the upper idle speed is exceeded since the valve 70 abuts a stop 99. Accordingly delivery becomes solely under the control of the pedal 128. At a predetermined speed e.g. 2,400 r.p.m. the centrifugal governor 122 overcomes the force of a spring 114 whereby a sleeve 100 keyed to the valve 70 moves downwardly and a pin 108 fixed to the shaft 82 enters an inclined slot 112 in the sleeve 100, the resulting relative rotation between the valve 70 and the shaft causing an advance in the timing of injection.