Fuel injection pump for internal combustion engines

A fuel injection pump for internal combustion engines having housing with a plurality of in-line pump elements including pump cylinders, surrounded by separate suction chambers and communicating with them by means of overflow openings, having two primary conduits disposed parallel to a camshaft for the inflow and outflow of fuel to and from the separate suction chambers and having defined connecting conduits between each separate suction chamber and each primary conduit by means of which the same quantity of fuel is metered to all the separate suction chambers under the influence of a pressure drop produced by the connecting conduits wherein an inflow connecting conduits has one fuel inflow throttle insert for the fuel inflow primary conduits the throttle insert being closed at one end and discharges with its open end into the separate suction chamber with its closed end protruding into the fuel inflow primary conduit the throttle insert having a defined throttle opening for conducting fuel from the primary conduit into the separate suction chamber.

BACKGROUND OF THE INVENTION 
The invention is based on a fuel injection pump for internal combustion 
engines. Such fuel injection pumps are embodied either as so-called 
in-line injection pumps, in which there is a separate pump element for 
each cylinder of the engine and these pump elements are disposed in a 
line, or as so-called reciprocating slide pumps, which are primarily 
intended for heavy-duty use, for instance in trucks. 
In the second type of fuel injection pumps, not only exact metering of the 
injection quantity but a very accurate setting of the instant of injection 
onset are attained by axially displacing a control slide provided on each 
pump piston, and/or by rotating the pump piston. 
In both types of injection pumps, an overflow of the highpressure fuel at 
the metering control edges causes heating of this returning fuel, which 
also heats the fresh fuel located in the suction chamber. The heating 
changes the physical properties such as density and compressibility of the 
fuel, so that the quantity of fuel metered per pump stroke and its energy 
content both vary as well. In the ensuing injection, temperature 
differences in the fuel supplied therefore leads to changes in the output 
of the engine cylinders. 
Near the entrance of the fuel inlet conduit, the fuel temperature in the 
suction chamber is still relatively low, because of the high proportion of 
fresh fuel, but with increasing distance from the entry, this temperature 
rises until it has attained a maximum in the region of the fuel outflow 
from the suction chamber. The fuel temperatures in the various pump work 
chambers of the injection pump are correspondingly variable, with the 
abovediscussed consequences. 
To avoid nonuniform cylinder outputs, such fuel injection pumps have 
separate suction chambers, from which the injection pump is supplied with 
fuel. By means of equal volumetric flows of fuel in all the separate 
suction chambers, the fuel temperature can be kept the same in all the 
separate suction chambers. 
In a known fuel injection pump of the generic type involved of a 
reciprocating slide pump (German Offenlegungsschrift 35 46 222), the 
volumetric fuel flows in the separate suction chambers are regulated by 
providing radial branch bores, acting as throttles, in the wall of a tube 
that acts as a fuel inlet conduit and tapers in steps in the direction of 
the flow; there is one bore in each step, and via an associated connecting 
conduit, it communicates with an associated separate suction chamber. The 
cross sections of these radial branch bores and their length are adapted 
to one another such that the volumetric flow through the bores is the same 
for the all the pump elements. The rotational position of the tube is 
defined by a fixation screw running in the housing; this position must 
meet very high demands for accuracy, so that particularly with 
reciprocating slide pumps, it must first be assured that the connecting 
conduit between the throttle opening in the tube and separate suction 
chamber and the throttle opening itself are precisely in alignment, 
because otherwise the volumetric flow is reduced, and second that there be 
sufficient sealing between the tube and the pump housing to prevent 
leakage, which would also affect the volumetric flow. For the same reason, 
the tube must be fitted very accurately into the pump housing. Especially 
in pumps having a high number of cylinders, this means high production 
expense and hence high production costs. 
Production expenses and costs are also increased because of the fact that 
metering tubes for in-line pumps must be embodied differently from those 
for reciprocating slide pumps, so that in mass production, two different 
metering tubes must be produced. 
Besides an accurate positioning of the tube in the pump housing and 
fastening the tube, there are other problems. Since the position of the 
tube must meet high demands for accuracy, the fastening must be 
correspondingly reliably embodied to prevent shifting and twisting. 
Because the fuel flow is deflected sharply as it enters the suction 
chamber, there is a danger of cavitation damage to the surrounding 
material. 
In known injection systems of this generic type, the connecting conduit 
between the metering tube and an electric shutoff means must be disposed 
at a particular site. This has a disadvantage of determining the 
positioning of the electric shutoff means on the pump housing, so that it 
cannot be freely selected. 
OBJECT AND SUMMARY OF THE INVENTION 
The fuel injection pump according to the invention, has an advantage over 
the prior art that the demands for accuracy in terms of shape and location 
of the supply bore, and hence the production costs, are much lower. By 
using throttle inserts, closed on one end and having a throttle bore, 
which are standardized DIN components, for metering the fuel into the 
separate suction chambers, and then introducing them into the housing 
bores provided between the primary conduit and the separate suction 
chambers, the production costs are reduced markedly, because first, these 
components can be used for both in-line and reciprocating slide pumps 
(large-scale mass production), and second, much greater dimensional 
tolerances are allowable for the primary conduit and the housing bores 
between the primary conduit and the separate suction chambers than in the 
case of fuel injection pumps using a metering tube. The condition of the 
throttle bores in terms of dimensional accuracy, manufacturing rate, and 
so forth, can also be easily checked or monitored. 
Another advantage is that the positioning of the connecting conduit between 
the electric shutoff means and the supply bore can be selected largely 
freely. 
In an advantageous feature of the invention, the throttle insert is fitted 
with its open end into a connecting conduit leading from the primary 
conduit to the separate suction chamber. In this embodiment, the throttle 
insert performs two functions, namely not only metering of the injection 
quantity but also sealing off the connecting conduit between the separate 
suction chamber and the primary conduit from leakage. 
In another advantageous feature of the invention, the throttle insert is 
manufactured oversize, that is, with a diameter that is somewhat in excess 
of the diameter of the associated connecting conduit. By forcing the 
throttle insert into the connecting conduit, the desired position is 
attained. This has an advantage that good sealing against leakage is 
obtained, no fastening elements need to be provided for the throttle 
insert. 
In still another advantageous further feature, the throttle insert is 
additionally secured against loosening by means of circular caulking. This 
has an advantage that the position of the throttle insert is permanently 
secured by simple means. 
In a further advantageous feature of the invention, the throttle insert is 
forced flush into a housing bore provided in the pump housing in order to 
produce the conduit connecting the associated primary conduit with the 
separate suction chamber. This has the advantage that the throttle insert 
simultaneously serves to seal off the primary conduit from the outside. A 
separate sealing element, such as a screw or a forced-in ball, is 
unnecessary, but may be used in addition. 
An advantageous embodiment is obtained once again by manufacturing the 
throttle insert oversize, in this region associated with this housing bore 
as well. As a result, not only is good sealing assured, but the position 
of the throttle insert is additionally secured. 
In a further advantageous feature of the invention, the throttle opening is 
punched into the throttle insert. This is a particularly simple and 
cost-effective production method, which is suitable for mass production 
given the high number of parts produced. 
In a further advantageous feature of the invention, the throttle insert has 
the shape of a cylinder. This is a particularly simple shape to 
manufacture and therefore is costeffective. 
In another advantageous feature of the invention, the throttle insert has a 
shape that tapers conically toward the open end. This embodiment has the 
advantage that the oversize throttle insert can be forced particularly 
well into the connecting conduit between the primary conduit and the 
separate suction chamber. 
In still another advantageous feature of the invention, which is favorable 
particularly with throttle inserts that are also forced into the second 
housing bore, the throttle insert comprises a cylindrical region and a 
conically tapering region. The conical region is associated with the 
conduit connecting the primary conduit and the separate suction chamber, 
and the cylindrical region is associated with the housing bore leading to 
the outside. This has the advantage that the oversize throttle insert can 
be forced in particularly well, and the diameter can at least sometimes be 
kept smaller, compared with the purely conical throttle insert. 
In yet another advantageous feature of the invention, the connecting 
conduit between the primary conduit and the separate suction chamber 
discharges into the separate suction chamber at a tangent. This has the 
advantage that fewer gas bubbles causing cavitation damage are produced at 
the fuel entry, since the fuel is not forced to make as many changes in 
direction, and the major pressure drop characteristic of a central entry 
do not occur. 
Although German Patent 861 762 does disclose reducing the danger of 
cavitation by means of a tangential entry of the fuel into the pump work 
chamber, it relates to an injection pump of a very different design. 
Furthermore, in the present invention, although the fuel does enter at a 
tangent, it is not the pump work chamber that is entered but rather the 
separate suction chamber, which is not present in the aforementioned 
patent. Additionally, the manner in which the threatening gas bubbles are 
removed is different, because in the prior patent, the tangentially 
supplied fuel is forced along a substantially circular path during the 
intake stroke; as a result, the lightweight gas bubbles collect in the 
middle, and because of their lower specific gravity rise upward through a 
bore in the pump piston to reach an overflow opening and the return 
conduit. In the present invention, the separate suction chamber 
experiences a permanent flow of fuel, and any gas bubbles that occur 
despite the tangential entry of the fuel are entrained by the fuel stream 
into the return conduit. 
In a further advantageous feature of the invention, the fuel outlet opening 
is provided centrally and is offset in height relative to the inlet 
opening. This has the advantage that any gas bubbles produced at the fuel 
entry are rapidly removed, since the tangential entry and central exit of 
the fuel creates a swirl that entrains the bubbles and carries them 
rapidly away through the central exit opening. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
a preferred embodiment taken in conjunction with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the fuel injection pump shown, six cylinder liners 2 are inserted in 
line in a housing 1; in each of them one pump piston 3 is driven, via an 
interposed roller tappet 4 and roller 5, by a camshaft 6 counter to pump 
supply pressure and counter to the force of a spring 7, to produce its 
axial motion embodying the working stroke. Corresponding recesses in the 
cylinder liners 2 and in the housing 1 form separate suction chambers 8, 
each one associated with one pump element embodied by a cylinder liner 2 
and a pump piston 3. 
The pump piston 3, cylinder liner 2 and a pressure valve 9 define a pump 
work chamber 10, from which a pressure conduit 11 leads to a pressure 
line, not shown, that ends at an injection nozzle on the engine. Each pump 
piston 3 has an oblique groove with a control edge 12, which cooperates 
with an overflow opening 13 of the cylinder liner 2 for fuel metering; the 
overflow opening 13 leads into the separate suction chamber 8 and 
simultaneously acts as an intake opening. 
The pump piston 3 has flattened portions 14 on its lower portion, which are 
engaged by a bushing 16 rotatable in a known manner by means of a governor 
rod 15, so that an axial displacement of the governor rod 15 causes a 
rotation of the pump piston 3 and hence a change in the association of the 
control edge 12 relative to the overflow opening 13. The pump piston 3 has 
a second control edge 17, which defines the onset of fuel supply by 
covering the overflow opening 13 as the piston 3 is raised. To prevent the 
diverted outflow fuel, which is at high pressure and is flowing back into 
the separate suction chamber 8, from causing any erosion on the surface of 
the cylinder liner 2 because of its kinetic energy, an impact ring 18 is 
provided. 
The fuel supply to the various separate suction chambers 8 is effected in 
common for all six separate suction chambers 8 by means of one inflow 
conduit 19. The fuel not attaining injection leaves the separate suction 
chambers 8, each via a respective connecting conduit 20, and enters a 
return conduit 21. Connecting conduits 22 are provided between each 
separate suction chamber 8 and the inflow conduit 19, and housing bores 23 
are provided, each in the axial extension of the conduits 22, between the 
inflow conduit 19 and the outside. Throttle inserts 24, which are closed 
at one end of a blind bore 29 are shown in further detail in FIG. 3. The 
throttle inserts are forced flush into each of the associated opening 
pairs, each pair comprising a connecting conduit 22 which connects with 
the suction chamber 8 and a housing bore 23; the open end of the throttle 
insert discharges into the separate suction chamber 8. The middle region 
of each of the throttle inserts 24, located in the inflow conduit 19, is 
provided with a throttle bore 25 through which fuel flows from inflow 
conduit 19 via blind bore 29 to the connecting conduit 22 of the suction 
chamber 8. 
The direction of fuel flow into the separate suction chambers 8 is 
represented in FIG. 2 by the arrow 36. 
The throttle insert 24 shown in FIG. 3 is closed at one end and has three 
different regions 26, 27 and 28. The region 26 located on the closed end 
is embodied in solid form, and serves as a seal between the inflow conduit 
19 and the exterior of the fuel injection pump. 
The middle region 27 and the region 28 located on the open end of the 
throttle insert 24 has an axial blind bore 29, which connects the throttle 
bore 25, extending radially to the outside in the middle region 27, with 
the opening 30 of the throttle insert 24. 
The region 26 toward the closed end and the region 27 in the middle are 
preferably embodied with cylindrical outer dimensions, while the region 28 
toward the open end is preferably embodied with an outer dimension that 
tapers conically toward the opening 30. 
The fuel injection pump shown in FIGS. 1 and 2 functions as follows: 
During at least a portion of the intake stroke of the pump piston 3 and in 
the vicinity of bottom dead center of its stroke, fuel flows out each of 
the respective suction chambers 8 through the overflow opening 13 into the 
pump work chamber 10. In the ensuing compression stroke of the pump piston 
3, the pressure required for the injection does not build up in the pump 
work chamber 10 until the overflow opening 13 has been completely covered 
by the pump piston 3. Until then, fuel continues to flow out of the pump 
work chamber 10 back into the separate suction chamber 8. 
After the closure of the overflow opening 13, the high pressure required 
for the injection builds up in the pump work chamber 10, and the delivery 
to the engine and injection begin via the pressure valve 9 and pressure 
conduit 11. Once the highpressure stroke of the pump piston 3 has been 
executed, the pump work chamber 10 is made to communicate with the 
separate suction chamber 8 via the overflow opening 13, so that the fuel 
that continues to be pumped is diverted at high pressure into the separate 
suction chamber 8. This effective injection stroke of the pump piston 3 is 
determined by the rotational position of the pump piston 3, which 
variously corresponds to a predetermined distance between the control edge 
12 and the radial bore 13, so that a variously long stroke of the pump 
piston 3 must be executed before the pump work chamber 10, as a result of 
this uncovering, is made to communicate via the overflow opening 13 with 
the separate suction chamber 8 to terminate the injection. 
From the inflow conduit 19, fresh fuel continuously flows through the 
throttle bore 25 and the blind bore 29 in the throttle insert 24, and via 
the connecting conduit 22, into the separate suction chambers 8. From 
there, the excess fuel flows out via the connecting conduit 20 into the 
return conduit 21, and via further connecting conduits, not shown, is 
returned to the fuel reservoir. 
The throttle bores 25 of the various throttle inserts 24 are designed such 
that for all six pump elements, the same pressure drop between the inflow 
conduit 19 and the separate suction chamber 8 exists, and fuel of the same 
volumetric flow is delivered to each of the separate suction chambers 8. 
As a result, a uniform filling of the pump work chamber with fuel for each 
separate fuel pump piston at the same temperature, is assured, even in 
extreme operating states. 
Additionally, the tangential entry of the fuel into the separate suction 
chambers 8 not only reduces the formation of gas bubbles but also, in 
combination with the central exit that is offset in height, imparts a 
swirl to the fuel that despite any gas bubbles that may be produced 
promotes their removal. 
In in-line injection pumps, to generate a constant volumetric flow of fuel 
in the separate suction chambers 8, the throttle inserts 24 may be 
introduced into the connecting conduits 20 between the separate suction 
chamber 8 and the return conduit 21 on the outflow side instead of on the 
inflow side. The design of the return conduit 21 and the dimensional 
relationships between the connecting conduits 20 and the throttle inserts 
24 should be selected in accordance with the above-discussed version. Once 
again, by being, forced into the corresponding housing bores, the throttle 
inserts 24 can simultaneously serve as a sealing means between the 
separate suction chamber 8 and the return conduit 21, or between the 
return conduit 21 and the outside. 
In FIGS. 4 and 5, the use of the throttle inserts 24 according to the 
invention in a reciprocating slide pump is shown. Unlike the in-line pump, 
in this case because of the design of reciprocating slide pumps, the 
throttle inserts 24 can be accommodated only in the connecting conduits 22 
between the primary conduit 19 and the separate suction chamber 8. By 
exchanging the connections for the inflow and outflow, however, once again 
it becomes possible to provide the throttle inserts on the outflow side. 
The mode of operation of the throttle inserts 24 having the throttle bore 
25 to generate a constant volumetric fuel flow in each of the separate 
suction chambers 8 is identical here. The mode of operation of a 
reciprocating slide pump itself is described for instance in German 
Offenlegungsschrift 35 46 222. An essential difference in the use of the 
throttle inserts 24 according to the invention in reciprocating slide 
pumps is that a tangential fuel entry is irrelevant in reciprocating slide 
pumps. 
The foregoing relates to a preferred exemplary embodiment of the invention, 
it being understood that other variants and embodiments thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.