Fuel injection pump for internal combustion engines

A fuel injection pump for internal combustion engines which has a moving part supported in a housing bore and on its jacket face on one side, has an exit opening that is under high pressure, and whose bearing is improved by virtue of the fact that at least one closed annular groove is provided on the jacket face of the part or in the wall of the housing bore, axially adjacent to the exit opening. As a result, a more even pressure distribution of the pressure field prevailing in the regions of the exit opening is achieved on the circumference of the moving part and as a result, a less damage prone, improved bearing with great high pressure tightness of the moving part is provided.

BACKGROUND OF THE INVENTION 
The invention relates to a fuel injection pump for internal combustion 
engines. DE-C-24 49 332 discloses a fuel injection pump of this generic 
type, which has a pump piston that is driven to reciprocate in the housing 
bore and at the same time is also driven to rotate and with its 
distributor opening, and is also used as a distributor. In this known fuel 
injection pump, another longitudinal groove is disposed on the jacket face 
of the pump piston, possibly disposed opposite the distributor opening, 
which groove continuously communicates with the fuel that is supplied 
under high pressure to the distributor opening. With an embodiment of this 
kind, a pressure application, possibly disposed diametrically opposite the 
distributor openings, is produced between the pump piston and the housing 
bore in such a way that the pump piston is evenly loaded by the 
compression forces and the tendency for the piston to score the inside of 
the housing bore is prevented. This additional groove regularly comes into 
connection with injection lines that do not participate in the injection 
and carries out a pressure compensation between these lines with an 
injection line opened at the same time by the distributor opening in an 
intake phase of the pump piston. 
This embodiment has the disadvantage that despite the fact that a force 
compensation is carried out on the pump piston, an interruption of the 
lubricating oil film occurs by means of the large-surfaced grooves in the 
jacket face of the distributor or pump piston, which film is intended to 
carry the pump piston in its rotation in the housing bore of the fuel 
injection pump. 
OBJECT AND SUMMARY OF THE INVENTION 
The fuel injection pump according to the invention has the advantage over 
the prior art that the annular groove produces a connection between the 
region directly adjacent to the exit opening, between the jacket face of 
the moving part and the housing bore, and the part disposed diametrically 
opposite this region. In the region directly adjacent to the exit opening, 
a high fuel pressure prevails in the narrow gap between the jacket face of 
the moving part and the housing bore. The high pressure forces prevailing 
there, together with the pressure field directly in the region of the exit 
opening carry out a force application of the moving part in the direction 
of its jacket face disposed diametrically opposite this. Because of the 
influence of these forces, the remaining gap between the jacket face and 
the housing bore reduces in size, which in the borderline case also leads 
to the fact that there is no longer a sufficient supply of lubricating 
fuel between these two faces to permit a damage-free sliding of these 
faces relative to each other. Since pressurized fuel can now be 
transported from the high pressure region adjacent to the exit opening, 
from the region disposed between the jacket face and the housing bore, to 
the opposite side, a pressure and force compensation occurs and it is also 
achieved that there is enough fuel on the side of the jacket face disposed 
opposite the exit opening to constitute a lubricating wedge. At the same 
time, it is not required that the annular grooves be additionally supplied 
with pressurized fuel by other sources of pressurized fuel. In comparison 
to the costly embodiment according to the prior art, in which the angular 
position of the additional groove in the jacket face must be precisely 
taken into account together with the cross sectional area of this groove, 
here it is possible to significantly reduce the damage prone nature of the 
fuel injection pump in a very simple manner merely by the placement of 
annular grooves, which can be let into the jacket face of the moving part 
and can be equivalently let into the inner jacket face of the housing 
bore. No additional bores are required and grooves of this kind can be 
produced in a very simple manner. 
The improvement relates to an advantageous application in a distributor 
fuel injection pump with a rotating distributor as the moving part. 
With the embodiment shown, it is achieved that immediately in these regions 
of a distributor, which are subject to particular displacements from the 
geometrically provided axis of the distributor, the bearing is improved by 
means of the measures set forth. 
The attachment of the annular grooves is particularly advantageous in a 
distributor that is only driven to rotate since in this connection, the 
position of other bores that lead from the housing bore does not have to 
be defined in view of an additional stroke. In the course of the steady 
rotation of the distributor, an optimal running capability can be achieved 
here with minimal play and great high pressure tightness of the fuel 
injection pump. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
preferred embodiments taken in conjunction with the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the fuel distributor injection pump shown in the drawing, a housing bore 
2 is let into a housing 1 in the form of a blind bore or a bore that is 
closed on one end; a part that is embodied in the form of a distributor 3 
is supported so that it can move, in this case, and rotate in this bore. 
On its end protruding from the housing bore 2, the distributor 3 has a 
collar 4 in which cylinder bores 5 are disposed, the cylinder bores run 
radial to the longitudinal axis of the distributor 3 and in which pump 
pistons are guided, which in the inner part of the cylinder bores, enclose 
a common pump work chamber that serves as a high pressure source and is 
not shown in detail here. The pump pistons are driven to reciprocate in a 
sealed and sliding manner by means of intrinsically known cam means not 
shown in detail here, e.g. by means of an annular cam path on which 
rolling shoes slide that are each connected to a pump piston. The cam ring 
in this case is embodied as a fixed cam ring, while at the same time the 
distributor drive, which is not shown in detail, carries out the relative 
movement of the rolling shoes along the cam path via the rotating motion 
of the distributor and is consequently used to drive the pump piston. With 
the inward stroke of the pump piston, in the pump work chamber a fuel 
pressure is produced which is of the magnitude of the fuel injection 
pressure. The fuel is conveyed from the pump work chamber via a pressure 
line 7 in the distributor 3 to an exit opening in the form of a 
distributor opening 8 on the jacket face 9 of the distributor. In the 
region of the mouth of the distributor opening in the jacket face, 
injection lines 11 are provided in the housing 1, which lead from the 
housing bore 2 and each lead to a fuel injection valve, not shown in 
detail, in order to bring the fuel there, which has been brought to high 
pressure, to injection in the engine. Also, per association with the 
respective fuel injection line 11, the high fuel injection pressure exists 
only as long as a solenoid valve that controls injection time and 
injection quantity is closed; only the valve member 15 of this solenoid 
valve is shown here. Via this solenoid valve, a connecting line 16 is 
constituted from the distributor opening 8 to a relief chamber. 
Consequently when the valve is open, the fuel displaced by the pump piston 
6 is supplied to the relief chamber in a more or less pressure free state, 
in any case at a pressure below the fuel injection pressure. Distributor 
fuel injection pumps of this type are known for example from DE-A1-43 39 
948, U.S. patent application Ser. No. 08/454,359, filed Jun. 16, 1995. Due 
to the one-sidedness of the position of the distributor opening on the 
jacket face 9 of the distributor 3 on the one hand and an intentional, 
very precise fit between distributor diameter and diameter of the housing 
bore 2 in order to produce a great high pressure tightness, brings about 
the disadvantage that in the borderline case, the rotationally driven 
distributor is no longer sufficiently supplied and lubricated with fuel 
inside the housing bore 2. This fuel enters into the gap between jacket 
face 9 and housing bore 2 as leakage fuel. In the borderline case, when 
there are high surface pressures, a sufficient lubricant wedge cannot be 
built up between the parts that are moved in relation to each other. A 
pressure field 17 is symbolically depicted in the drawing, in the region 
of the exit of the distributor opening 8. 
To solve the above-described problem, one or more annular grooves 18 are 
now let into the jacket face of the distributor, two grooves in the 
current example. These grooves are small in depth and width and perform 
the function of conveying fuel from the pressure field 17 to the side of 
the jacket face 9 disposed diametrically opposite the distributor opening 
8 or to the side of the gap located there between the distributor jacket 
face and the housing bore. Between the pressure field 17 and a 
counterpressure field 20 being formed on the opposite side, a pressure 
compensation is achieved in such a way that the pressure is built up 
better on the most heavily loaded side of the distributor and this side is 
supplied with sufficient fuel via the annular grooves 18 to maintain the 
lubricating film there, which has the function of carrying the distributor 
3 in the housing bore 2, the distributor being influenced by lateral 
forces. With the aid of these grooves, it is always assured that an 
uninterrupted fuel film remains between the two parts 3 and 2. 
The annular grooves are disposed in regions of the distributor 3 that are 
not interrupted by any other bore. In particular, this measure which 
improves the bearing of the distributor is disposed on its end remote from 
the drive end or the collar 4, inside the housing bore. Because of the 
drive end loading and the influence of forces from the pumping drive of 
the pump piston, the distributor is subject to tilting moments which lead 
to considerable dynamic effects, particularly on its end disposed inside 
the housing bore 2. The improvement of the bearing in this region is 
particularly effective as well. 
Instead of letting the annular grooves into the jacket face of the 
distributor 3, it is naturally also possible to provide corresponding 
grooves inside the inner wall of the housing bore. 
Another effect of this improved bearing is that the distributor is better 
centered in the housing bore 2, that the bearing gap between the jacket 
face of the distributor 3 and the housing bore 2 is embodied of a uniform 
thickness over the entire circumference and that as a result, the leakage 
losses are reduced or the high pressure tightness is increased. In this 
way, the consequently improved fuel injection pump is suited for producing 
higher fuel injection pressures which in the end, results in an improved 
injection with a reduction of emission values and less of a strain on the 
environment. Also, material pairings that are prone to scoring have less 
tendency toward damage with this embodiment. 
The improved bearing of a rotating part, the distributor, is shown here in 
the example of a radial piston distributor pump. The measures provided 
here, though, can be realized in just as favorable a manner in fuel 
injection pumps that are embodied differently, such as fuel injection 
pumps with reciprocating pistons or fuel injection pumps with pistons that 
reciprocate and are driven to rotate at the same time. With moving parts 
of this kind, better bearing properties of the moving part can be 
achieved. 
The foregoing relates to preferred exemplary embodiments 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.