Fuel injection pump for internal combustion engines

A fuel injection pump for internal combustion engines comprising a pump plunger displaceable in a pump cylinder for delivering fuel to a plurality of injection locations, and elements for controlling fuel injection quantity. The controlling elements include a relief channel in the pump plunger for communicating a pump working space defined by the pump plunger with a relief chamber, an outlet port on an outer surface of the pump plunger for communicating the relief channel with the relief chamber, at least two connecting cross-sections of different shape for communicating the relief chamber with the outer port, and a slide valve displaceable along the outer surface of the plunger and having a control edge for controlling flow of fuel through the connecting cross-sections during a delivery stroke of the pump plunger.

BACKGROUND OF THE INVENTION 
The invention relates to from a fuel injection pump German 
Offengungsschrift 2,522,374 discloses a fuel injection pump having 
recesses which defines connecting cross-sections in the circumferential 
surface of the pump plunger, which recesses, starting at the outlet ports 
of the relief channel, extend towards the side of the pump working 
chamber. Rectangular recesses, inter alia, have been proposed which have a 
width differing from one another in the peripheral direction of the pump 
plunger and, furthermore, also differ in their axial extension, their 
length. With such an arrangement, during the course of an opening stroke 
of the pump plunger, a bent cross-sectional profile is to be achieved in 
such a way that, after initially restricted relief via one of the 
connecting ports, the relief cross-section is enlarged by the arrival of 
the second connecting port. In the connect-control cross-sections provided 
here, the restricting action occurring at different speeds of the fuel 
injection pump is especially emphasized. These control cross-sections are 
provided in particular for adaption of the fuel injection quantity as a 
function of the speed. Here, one of the connecting cross-sections is 
regularly constructed in the manner of a restricting slot. 
In internal combustion engines working with spontaneous ignition, it is 
necessary for the low-load range, in particular the idling range, for the 
fuel to be introduced into the combustion chamber with exact timing but 
long spray duration so that so called knocking of the internal combustion 
engine, especially noticeable in this area, is prevented. The long 
duration of the injection ensures that the fuel quantity introduced during 
the ignition lag does not become too large and thus not too much fuel is 
burnt suddenly, which would lead to a steep pressure rise causing 
knocking. In order to achieve a long injection duration, many proposals 
are already known which predominantly have the feature in common that, 
during the duration of the delivery, a portion of the fuel delivered under 
high pressure is introduced into a discharge chamber which is defined by a 
movable wall. This means considerable expense, the discharge volume in 
addition having to be controlled for the various operating ranges of the 
internal combustion engine. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide, a the fuel injection pump the 
advantage in which increase in the duration of injection is achieved by a 
very simple measure. The object of the invention is achieved by forming a 
connecting cross-section which, before the actual outlet port becomes 
effective and before the end of the high-pressure delivery phase, allows 
some of the fuel delivered under high pressure to flow off during every 
pump plunger stroke. This is effective in the lower speed range and, the 
idling range up to a low-load operating range. Towards high speeds and 
towards a full-load operation, the control effectiveness of this 
connecting cross section, acting in a restricting manner, decreases so 
that a sufficiently short injection duration is available in this 
operating range. Here, the fuel injection pump requires only a slight 
change in the area of the outlet ports. 
The invention as to its construction so to its mode of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following detailed description of the preferred embodiments with 
reference to the appended drawings.

DESCRIPTION THE PREFERRED EMBODIMENTS 
In a housing 1 of a fuel injection pump, a pump plunger 4, which is set in 
a reciprocating and at the same time rotating motion against the force of 
a restoring spring (not shown) by means (not shown), is movable in a bore 
defining a pump cylinder 2 of a cylinder barrel 3 inserted into the pump 
housing. In the pump cylinder 2, the pump plunger encloses at the end 
thereof a pump working chamber 6 which, via longitudinal grooves 7, 
arranged in the circumferential surface of the pump plunger and leading at 
the end face into the pump working chamber 6, and a channel 8 running 
through the cylinder barrel 3 in the housing 1, is supplied with fuel from 
a suction chamber 9 inside the fuel injection pump as long as the pump 
plunger executes its suction stroke or assumes its bottom dead center 
position. The suction chamber 9 is supplied with fuel from a fuel supply 
tank 12 via a delivery pump 11. By a pressure control valve 13, the 
pressure in the suction chamber 9 is controlled in a known manner as a 
function of speed so that the pressure in the suction chamber increases as 
speed increases. This especially applies if, e.g., a spray adjusting 
device for controlling the start of injection is to be actuated by means 
of the speed-dependent suction chamber pressure. 
Leading off from the pump working chamber 6 in the pump plunger as relief 
channel 15 is a coaxial blind bore which, in the lower pump plunger part 
protruding out of the pump cylinder 2, leads via a transverse bore 16 into 
the pump suction chamber 9. The outlet ports 14 of the transverse bore 16 
are controlled by an annular slide valve 17 interacting with the pump 
plunger. Furthermore, branching off from the relief channel 15 in the pump 
plunger part lying in the area of the pump cylinder 2 is a radial bore 18 
which leads into a distributor port 19, designed as a longitudinal groove 
in the circumferential surface of the pump plunger. Via the relief channel 
15, the radial bore 18 and the distributor port 19, one of several 
pressure lines 20 is connected to the pump working chamber 6 in each case 
during a delivery stroke of the pump plunger after the latter, by its 
rotation, has closed the connection between channel 8 and the longitudinal 
groove 7. The pressure lines 20 each lead via a non-return valve 21 to 
individual fuel injection nozzles of the cylinders of an internal 
combustion engine (not shown) and are arranged in a distributed manner on 
the periphery of the pump cylinder 2 in accordance with the number of 
cylinders to be supplied. During the delivery stroke of the pump plunger, 
fuel is thus delivered to the injection nozzles via the relief channel 15 
as long as the outlet ports 14 of the transverse bore 16 remain closed by 
the annular slide valve 17. 
The annular slide valve 17, via a governor 23, which, with a head 24, 
engages into a recess 25 of the annular slide valve and is pivotable about 
a spindle 26, is displaced in a tightly fitting manner on the pump plunger 
as a function of load and speed by a speed governor (not shown further). 
During this procedure, a displacement of the head 24 downwards towards the 
drive side of the pump plunger causes the outlet ports 14 of the 
transverse bore 16, during the delivery stroke of the pump plunger, to be 
opened in a controlled manner at an earlier partial stroke of the pump 
plunger from the start of the delivery stroke, whereupon the pump working 
chamber 6 is relieved, and no more fuel can be delivered under high 
pressure into the presure lines 20. Accordingly, with the adjustment in 
this direction, the fuel injection quantity is reduced. In the uppermost 
position of the annular slide valve 17, the outlet ports 14 are no longer 
opened during the delivery stroke of the pump plunger, so that the entire 
fuel quantity which can be delivered by the pump plunger 4 reaches 
injection. This position can correspond to a full-load position or the 
position in which an excess fuel quantity is to be delivered for the 
starting operation of the internal combustion engine. In the 
last-mentioned case, the position, in accordance with the full-load 
quantity, is slightly lower than the full-load position. 
A projection of a pump plunger circumferential surface is shown in FIG. 2 
with the outlet ports 14 of the transverse channel 16. What is difficult 
to represent graphically in FIG. 1 is here clearly shown. One of the 
outlet ports 14 is in connection with a rectangular first connecting 
cross-section 27 which is made as a recess in the circumferential surface 
of the pump plunger. Here, the first connecting cross-section has a larger 
width A than height a. In addition, this rectangular recess 27 extends 
towards the pump working chamber 6 and has towards the pump working 
chamber a straight boundary edge 28 which extends as parallel to the 
control edge 29 of the annular slide valve 17. In the exemplary 
embodiment, this control edge is formed by the end face of the annular 
slide valve 17 and extends in a radial plane relative to the axis of the 
pump plunger. The other outlet port 14' of the transverse bore is 
connected to a second connecting cross-section 31 which likewise extends 
towards the pump working chamber 6 and has a rectangular shape. In this 
case, the width B lying in the peripheral direction, unlike the width A of 
the first connecting cross-section 27, is of very narrow configuration. 
The longitudinal extent b in the direction of the pump working chamber of 
the second connecting cross-section 31 is here larger than the 
longitudinal extent a of the first connecting cross-section 27. The recess 
forming the second connecting cross section 31 thus protrudes beyond the 
first connecting cross-section 27 and, with its dimensioning, is designed 
as a restriction. Here, the restricting effect can be achieved by the 
small width B and/or the small depth of the recess forming the second 
connecting cross-section 31. During the delivery stroke of the pump 
plunger on account of the dimensioning described, the second connecting 
cross-section 31 comes into connection with the suction chamber 9 before 
the first connecting cross-section 27, by the stroke hl, the difference 
between b and a. Via the leakage distance hl thus created, a partial 
quantity of the delivered fuel can therefore flow off before the final 
relief of the pump working chamber 6 via the first connecting 
cross-section 27, so that a fuel quantity smaller than the delivered fuel 
quantity reaches injection. Accordingly, the injection rate is low and a 
prolonged delivery duration of the pump plunger is necessary to introduce 
a certain fuel quantity. This is effected by the setting of the annular 
slide valve 10 by the governor. 
In the design shown in FIG. 3, the second connecting cross-section 31 has 
been integrated with the first connecting cross-section 27, i.e., on a 
connecting cross-section 27' of the same shape as in the exemplary 
embodiment in FIG. 2, the part of the second connecting cross-section 31 
protruding in the axial direction in FIG. 2 with the length hl, has been 
attached in such a way as to adjoin the boundary edge 28. 
In the third exemplary embodiment in FIG. 4, the pump plunger is provided 
with an annular groove 33 which is made in the circumferential surface in 
the area of the outlet port 14. A first connecting cross section 27" and a 
second connecting cross-sections 31" now branch off from this annular 
groove 33 similarly to FIG. 2. The dimensioning of these cross-sections 
corresponds to the exemplary embodiment in FIG. 2. 
Now instead of providing the connecting cross-sections on the 
circumferential surface of the pump plunger, they can also be made in the 
annular slide valve, as shown by FIG. 5. This design requires the pump 
plunger to have an annular groove 33, as already provided in FIG. 4. The 
outlet ports 14 of the transverse channel 16 lead into this annular 
groove. On the annular slide valve, a first connecting cross-section 27'" 
and a second connecting cross-section 31'" are now made in the 
circumferential surface. These connecting cross-sections are produced by 
grooves which are made, e.g. ground in, from the end face 29' of the 
annular slide valve. Thus two diametrically opposite first grooves 34 are 
provided which, e.g., can be produced in a single operation with a milling 
cutter, and, displaced by 90.degree. relative thereto, second grooves 35 
can be milled in. In this arrangement, the first grooves, similarly to 
FIG. 2, together have a width which results in the width A of the first 
connecting cross-section 27 in FIG. 2, and the second grooves 35 together 
have a width B' which corresponds to the width B of the second connecting 
cross-section 31 in FIG. 2. The depth of the grooves again differs by the 
amount hl by which the second connecting cross-section 31'" comes into 
connection with the annular groove on the pump plunger before the first 
grooves 34. The mode of operation is analagous to that described with 
reference to FIGS. 2 to 4. 
Compared with the exemplary embodiment in FIG. 2, the embodiments in FIGS. 
3, 4 and 5 have the advantage that they can also be used in fuel injection 
pumps which have only one outlet port 14 on the pump plunger. This occurs 
in particular when, such as, e.g., in German Offenlegungsschrift 
3,424,883, two relief channels are provided having only one outlet port 
each in the area of the annular slide valve on the pump plunger. In the 
embodiment in FIG. 4, it is especially advantageous that here a symmetric 
pressure distribution at the pump plunger can be produced so that, when 
high pressure is applied, the slide value can be displaced on the pump 
plunger in such a way that the forces are balanced. 
Compared with the abovementioned embodiments, the design in FIG. 5 has the 
advangtage that the connecting cross-section does not have to be eroded 
but can be produced by plunge-cut grinding. In addition, a symmetric 
distribution of forces at the pump plunger can be achieved here. 
While the invention has been illustrated and described as embodied in a 
fuel injection pump for internal combustion engine, it is not intended to 
be limited to the details shown, since various modifications and 
structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.