Fuel injection pump for internal combustion engines

The invention sets forth a fuel injection pump inserted into a housing of an internal combustion engine and comprising a single pump element that supplies a cylinder of the engine with fuel. The pump element comprises a pump body, which has a cylinder bore in which a pump piston, which defines a pump work chamber in the cylinder bore is axially guided and is moved back and forth by a cam drive counter to the force of a restoring spring. For simple manufacture of the pump body with great strength and tightness, this pump body is divided into a rotationally symmetrical cylinder liner and a rotationally symmetrical intermediate part, which are axially braced in line with a magnet valve via a resilient sleeve.

BACKGROUND OF THE INVENTION 
The invention is based on a fuel injection pump as defined hereinafter. In 
a fuel injection pump of this type, known from German Patent 37 28 961, a 
fuel injection pump, which comprises a pump element and supplies one 
cylinder of an engine with fuel, is inserted into the engine housing. The 
pump element is composed of a pump body that receives a cylinder liner and 
a pump piston guided in a cylinder bore of the cylinder liner; the pump 
piston is axially moved by a cam drive counter to the force of a restoring 
spring. With its face end remote from the cam drive, the pump piston 
defines a pump work chamber in the cylinder liner; via a fuel line in 
which a magnet-controlled reversing valve is disposed, this pump work 
chamber can be made to communicate with either a high-pressure line 
leading to a location where injection is effected into the combustion 
chamber of the engine to be supplied, or a line that discharges into a 
fuel-filled low-pressure chamber. All the connection points of the fuel 
inflow and outflow lines, the faces that effect sealing with respect to 
the magnet valve and the cylinder liner, and connecting conduits are 
disposed on the pump body; hence a great number of expensive machining 
operations, of varying precision, are needed. 
This problem is even more pronounced in compact pump bodies, which are 
intended for use when the available installation space is small and are 
made as "monobloc" elements, and which, as known from German 
Offenlegungsschrift 39 43 183, not only have to have all the connections 
but also have to perform the function of the cylinder liner. Not only must 
the sealing faces at the connecting points for the fuel lines and adjacent 
components be machined, but the high-precision cylinder bore must be 
produced as well; because of the rotationally asymmetrical contour of the 
pump body, this requires a very major engineering effort and according is 
very expensive. 
OBJECT AND SUMMARY OF THE INVENTION 
The fuel injection pump according to the invention has an advantage over 
the prior art that because the pump body is assembled from a plurality of 
individual parts, it is simpler and hence less expensive to produce, and 
because of the axial bracing of the intermediate part with the cylinder 
liner and magnet valve as a result of the resilient sleeve, a 
high-pressure unit is formed, which assures reliable sealing of the 
various components from one another even at high feed pressures. In a way 
that is simple to achieve, the face ends of the components are embodied as 
ground faces. With the fuel injection pump according to the invention, it 
is accordingly possible to attain the advantages of a compact model, with 
its attendant heavy-duty capacity, with the production advantages of 
rotationally symmetrical individual parts; in terms of its shape, fit 
location, and connections, the resilient sleeve, which is simple to make 
and serves as a housing, can be embodied flexibly to meet the most various 
installation situations for engines. 
A further advantage is attained in which a flange for securing the pump to 
the engine housing and receiving the connecting lines is embodied by the 
resilient sleeve itself, so that an additional means of fastening these 
parts becomes unnecessary. 
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 drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The fuel injection pump, of which only the part essential to the invention 
is shown in the drawing, comprises a cylinder liner 1, which has a 
cylinder bore 3 in which a pump piston 5 is guided that is moved axially, 
by a cam drive, not shown, counter to the force of a restoring spring 7. 
With its face end 9 remote from the cam drive, the pump piston 5 defines a 
pump work chamber 11 in the cylinder bore 3. The cylinder liner 1, with 
its face end remote from the cam drive and embodied as a sealing face 13, 
axially adjoins a cylindrical intermediate part 15, whose two face ends 
form an upper sealing face 17 and a lower sealing face 19; the lower 
sealing face 19, which rests on the sealing face 13 of the cylinder liner 
1, has a blind bore 21 that defines the pump work chamber 11. For fixing 
the rotational position of the intermediate part 15 with respect to the 
cylinder liner 1, a close-fit bore is made in the face ends of each of 
these parts, and a set pin 23 is inserted into each bore. 
A high-pressure conduit 29 beginning at the blind bore 21 is disposed in 
the interior of the intermediate part 15 and discharges into an injection 
line, not shown in detail but containing a pressure valve, leading into 
the injection location into the combustion chamber of the engine. 
A magnet valve 25 comes to rest on the upper sealing face 17 of the 
intermediate part 15, remote from the blind bore 21, with its lower face 
end 25, which also serves as a sealing face and is machined accordingly. 
This magnet valve 25 is controlled electrically as a function of engine 
parameters and has a reversing valve, not shown in detail, with which, 
depending on its switching position, a bypass line 31 in the intermediate 
part 15 can be made to communicate with the high-pressure conduit 29 in 
such a way that during the pumping stroke of the pump piston 5, in order 
to control the high-pressure phase, either fuel flows out of the pump work 
chamber 11 into a low-pressure fuel line, or this line 31 is closed in 
order to develop the high injection pressure in the pump work chamber 11. 
In order to deliver low-pressure fuel to the pump work chamber 11 during 
the intake stroke of the pump piston 5, the intermediate part 15 also has 
an inflow line 23; the magnet valve 25 can again cause this inflow line 33 
to communicate with the conduit 29 discharging into the pump work chamber 
11, or else the inflow line 33 may discharge directly into the conduit 29, 
if it is secured against a reverse flow of fuel by a check valve that 
opens in the direction of the conduit 29. 
On its outer circumference, the cylinder liner 1 has a shoulder 35 produced 
by a decrease in diameter in the direction of the cam drive, and by which 
it comes to rest on an annular shoulder 1 of a resilient sleeve 39 that 
encompasses the cylinder liner 1, intermediate part 15, and magnet valve 
25. On the end of the annular shoulder 37 of the resilient sleeve 39 
remote from the cylinder liner 1, one end of the restoring spring 7 is 
supported. 
The inside diameter of this resilient sleeve 39 is just large enough that 
the cylinder liner 1, with its larger diameter toward the pump work 
chamber, the intermediate part 15, and a part of the magnet valve 25 
adjoining the intermediate part, all three of which are embodied in this 
region with a circular cross section of approximately the same diameter, 
are insertable with a narrow clearance fit and axially guided one after 
the other in the resilient sleeve. In the region of the magnet valve 25, 
the inside diameter of the resilient sleeve 39 widens, and it has an 
internal thread 41, into which a tensioning nut 43 is screwed that guides 
the magnet valve 25 in an axial through bore 45 and with its screwed-in 
face end 47 acts upon an annular land 49 on the magnet valve 25 and keeps 
it pressed with the intermediate part 15 and the cylinder liner 1 against 
the annular shoulder 37 of the resilient sleeve 39 in such a way that via 
the various sealing faces at the face ends, a sealing contact is assured 
between the cylinder liner 1 and the intermediate part 15 and between the 
magnet valve 25 and the intermediate part 15. The function of the 
tensioning nut 43 may also be assumed by the magnet valve 25, if that 
valve has a thread on its outer circumference with which it can be screwed 
into the internal thread 41 of the resilient sleeve 39. 
For fastening the resilient sleeve 39, which is inserted into an engine 
housing, along with the pump part braced in it, the outer circumference of 
this sleeve has a flange 51, which also receives a fuel connection 55 of 
the inflow line 33 and a fuel connection 57 of the bypass line 37. 
However, this flange may also be formed by an additional part that is 
slipped onto the resilient sleeve 39 and fastened to it which would 
greatly simplify the manufacture of the resilient sleeve 39. 
The communication between the high-pressure conduit 29 extending in the 
intermediate part 15 and the pressure line leading to the injection 
location is made via a rotationally symmetrical mass-produced part in the 
form of a connection piece 53 that is screwed radially into the 
intermediate part 15 and protrudes through a bore in the resilient sleeve 
39. 
With the fuel injection pump according to the invention, the use of a 
compound pump body thus makes it possible, with great flexibility of 
installation, a compact structure, and simple manufacture of individual 
parts, to attain the kind of high-pressure strength that is attainable 
with a single-piece pump body. The fuel injection pump of the invention 
can be used both for injection systems that are formed of a pump, a line 
and an injection nozzle, and for unit fuel injector systems. 
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.