A standard fuel-injection pump comprises a pump cylinder, a pump plunger subdividing the cylinder into a pump working chamber or space and a relief chamber or space and formed with a first relief passage or duct opening into the working space and also opening radially at a first outlet opening into the relief space, and formations on the plunger for periodically feeding fuel to the working space and a speed-responsive cam-type drive for periodically rotating and axially reciprocating the plunger. An annular side is displaceable in the relief space on the plunger over the first outlet opening so that a speed controller and governor can axially shift the slide and thereby vary the venting of the working space via the relief duct into the relief space.
In a fuel injection pump of this type, which is known from DE-OS 32 03 582, the first outlet opening of the first relief duct is controlled by means of an internal annular groove at the internal cylinder of the annular slide, which internal annular groove serves as a control opening, wherein the internal annular groove is constantly connected with the relief space via a duct. In addition, the first outlet opening of the second relief duct is controlled by means of the grooves proceeding from the end face of the annular slide on the pump working space side, which grooves are arranged in such a way and in such quantities that one of the grooves lies in the stroke direction of the first outlet opening of the second relief duct during every second delivery stroke of the pump plunger. However, this results in a relieving of the working space via the first relief duct, the annular groove and the second relief duct only so long as a connection is made between the first and second relief ducts and the first outlet opening simultaneously opens into one of the grooves. This is the case in the known fuel injection pump in the idling position of the annular slide. If the annular slide is displaced in the direction of higher load, the second outlet opening of the second relief duct is already closed before the first outlet opening is opened. In the known fuel injection pump, a load-dependent switching off of the injection is accordingly obtained in a portion of the delivery strokes of the pump plunger. In this way, a partial stopping of the cylinders of the internal combustion engine is achieved during low-load operation and the consumption of the internal combustion engine is optimized in that the cylinders which are not switched off are operated with relatively high load and accordingly a higher efficiency.
On the other hand, a fuel injection pump with a soft-running device is known from DE-OS 32 18 275 in which only one relief line leads from the pump working space, the single outlet opening of the relief line at the pump plunger surface within the relief space being likewise controlled by means of an annular slide. The annular slide likewise comprises grooves proceeding from its end face, which grooves have a slot-shaped throttling cross section relative to the outer surface range of the internal cylinder of the annular slide. During the delivery stroke of the pump plunger and a corresponding rotational position of the annular slide, the connection between the outlet opening and the relief space is produced first via these grooves and only then via the control edge formed by the internal bore hole and end face of the annular slide. Accordingly, in the by-pass for the fuel injection quantity delivered to the injection nozzles, a partial quantity is diverted from the total feed rate of the pump plunger as a leakage quantity, which enables a soft running of the internal combustion engine by means of an injection rate which is accordingly reduced. By means of a rotating device, which works by means of a fuel injection quantity governor irrespective of the adjustment of the annular slide, the effectiveness of the throttling grooves and the soft-running device, respectively, can be switched off.
However in this known fuel injection pump problems arise with respect to the control of the fuel quantity flowing off via the throttle cross section. In particular, problems exist in continuously increasing the fuel quantity from the transition from the idling area into the partial-load area so that no load jump occurs when load is received. In addition, problems arise when an arrangement for adjusting the start of injection, which usually consists in that the first outlet opening is adjusted relative to the rotational position of the drive shaft of the fuel injection pump, is assigned to the fuel injection pump.