Fuel injection pump for a compression-ignition engine

In a fuel injection pump for a compression-ignition engine which includes a fuel injection cylinder having an internal cylindrical bore, at least one control port communicating with said bore to supply fuel thereto or remove fuel therefrom, and a piston which is mounted so as to be axially reciprocated within said bore, as well as rotated therewithin, said piston including an upper control edge which determines initiation of fuel injection and a lower control edge which determines termination of fuel injection as the upper and lower control edges move past said control port, and with rotation of said piston determining the relative timing of movement of the control edges past said control port, the improvement wherein the upper and the lower control edges of said piston, when viewed in a vertical cross-section, extend with respect to an imaginary plane at the upper end of the piston perpendicular to the axis of said bore and in a direction between the respective axial points along said control edges which lie in the zone between the axial line along the piston which corresponds to a zone of the partial load area of the piston near the full load area thereof and the axial line which corresponds to the full load area, the partial load area being that portion of the piston which cooperates with the respective control bore during the partial load operation of the compression-ignition engine, as follows:

• the upper control edge curving upwardly towards said imaginary plane and the lower control edge curving downwardly and including a portion nearest the full load area which curves at a lower angle of inclination than the corresponding curved portion of said upper control edge.