Fuel injection valve for preliminary and principal injection

A fuel injection valve assembly for supplying a preliminary injection of fuel of a constant amount regardless of engine speed before the main injection of fuel begins comprising a spring biased, fuel supply pressure responsive, preliminary injection piston for the preliminary injection, a fuel supply pressure responsive loading piston for controlling the main injection fuel flow and a needle valve, both of the latter being biased oppositely by a common spring. Separate supply ducts for the preliminary and main fuel injections and the arrangement of the valve surfaces on the loading piston and needle valve enable the loading piston to be held closed and the needle valve to be opened by the pressure imposed on the preliminary injection piston and remain open long enough for the preliminary injection piston to travel its full stroke before closing and before the needle valve is opened for the main injection.

BACKGROUND OF THE INVENTION 
The present invention relates to a fuel injection valve for preliminary 
fuel injection and main fuel injection, the needle valve of which is 
opened under the pressure of the fed-in fuel acting upon a surface of the 
valve as well as on piston members which are arranged to cooperate 
therewith, such opening being accomplished counter to the force of a 
closing spring which is associated with the needle valve. 
In known fuel injection valves of this type, two pressure chambers are 
provided, each of which has one surface subjected to fuel pressure acting 
in the direction of opening of the needle valve. The supply of fuel to the 
two pressure chambers is controlled by the needle valve during its 
displacements, so that, after the preliminary injection stroke, only one 
of the surfaces is effective in the direction of opening. Apart from the 
fact that such a control requires an exceedingly precise manufacture of 
the controlling elements, the temporarily inoperative pressure chamber 
closed by the needle valve should have an additional relief valve for 
proper functioning. A further disadvantage of this known fuel injection 
valve consists in the fact that such an intervention in the fluid flow 
causes turbulence and changes in the direction of flow which may lead to 
pressure pulses which can influence the manner of injection, especially so 
as to introduce a dependence on the rotational speed. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is the primary purpose of this invention to develop a fuel 
injection valve of the initially mentioned type in which no such pressure 
shocks are created in the flow of liquid and which, moreover, can be 
produced at a much smaller expense than the known fuel injection valve of 
this type. 
It is a further object of this invention to provide piston members which 
after accomplishing a preliminary injection stroke are brought to bear 
against a stop which is fixed in the housing, so that only the needle 
valve will be effective for an additional opening stroke. Thus, the flow 
of liquid which is under pressure is not influenced in its basic direction 
of flow and no control points are provided which require a corresponding 
precision for the separation of the hydraulic flow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawings, a nozzle body 1 with an injection aperture 2 
has been clamped down by means of a coupling nut 3 on a nozzle holder 4. 
Between the nozzle holder 4 and the body of the nozzle 1, at least one 
washer 5 has been disposed. In the valve body 1, a needle valve 6 has been 
mounted shiftably which is loaded by a closing spring 8 with interposition 
of a spring plate 7. The closing spring is disposed in an annular space 9 
provided in the nozzle holder 4. 
Between the nozzle body 1 and the needle valve 6, a pressure chamber 10 has 
been provided. The fuel fed in under pressure by a fuel injection pump 
(not shown) is supplied to this pressure chamber 10 via a line 11, so that 
where sufficient pressure exists, the needle valve 6 is shifted and the 
fuel is injected into the combustion chamber of the engine via the 
injection aperture 2. 
In the case of the first embodiment shown in FIG. 1, two or more pistons 
14 are disposed in the body of the nozzle 1 in parallel to the needle 
valve 6, which pistons are guided in the body of the nozzle 1 axially 
shiftably and sealingly. The lower extremity of these pistons 14 is acted 
upon by the fuel pressure in the pressure chamber 10 and their upper ends 
are arranged in contact with a head 15 which is integral with the needle 
valve 6. After accomplishing one of the preliminary injection strokes of 
the needle valve 6 as indicated at H.sub.V during which time the parallel 
pistons 14 also move upwardly, said pistons 14 abut against the surface 16 
which is provided by the disc 17. It will be noted that the head 15 is 
guided in an axial bore in disc 17. After the pistons 14 are brought to 
bear against the stop 16, only the needle valve 6 will continue to move 
upwardly in the direction of opening, so that after increase of the 
pressure of the supplied fuel the needle valve continues its opening 
stroke for the main injection. Thus, after being advanced for the main 
injection to the point indicated by H.sub.H, the head 15 of the needle 
valve 6 is brought to bear against an intermediate plate 18 by means of 
which the maximum opening stroke of the needle valve 6 is determined. The 
area into which the pistons 14 and the head 15 move during the opening 
stroke are connected with the spring chamber 9 in an unthrottled manner. 
In the case of the embodiment shown in FIG. 2, an annular sleeve 19 
encompasses the needle valve 6 in lieu of two or more pistons as depicted 
in FIG. 1, said annular sleeve being arranged to be sealed relative to the 
inner wall of the nozzle body 1 as well as the exterior wall of the needle 
valve 6 and adapted for axial movement therebetween. Said sleeve 19 
extends up to the pressure chamber 10 provided in the body 1 of the 
nozzle, and the annular groove 20 communicates with the pressure line 11 
which in turn is connected with the pressure chamber 10 via longitudinal 
grooves 21. Thus, as explained in connection with the embodiment shown in 
FIG. 1, this annular sleeve which functions as a piston, strikes against 
the surface 16 of disc 17 after completing the preliminary injection 
stroke, as a result of which it then serves no further function as a means 
acting in the opening direction and the main injection continues. 
The third embodiment of the invention according to FIG. 3 shows an 
arrangement wherein one of two or more auxiliary pistons 22, which are 
disposed in apertures in the intermediate plate 5 are arranged to act 
directly on the spring seat disc 7. The fuel pressure is transmitted from 
the pressure chamber 10 to the lower frontal side 24 of this auxiliary 
piston 22, via a pressure line 23. The bore 23 may be omitted whenever the 
front side 24 is connected by an annular groove 23a with the pressure line 
11. After the preliminary injection stroke movement depicted at H.sub.V, 
the auxiliary piston 22 is brought into contact with the lower surface of 
the nozzle holder 4 at 25. Thereafter, as explained in connection with 
FIG. 1, the needle valve 6 will continue to move upwardly for the further 
main injection stroke as shown at H.sub.H. 
In the fourth embodiment of the invention as shown in FIG. 4, the auxiliary 
piston also comprises a slidable sleeve 26 which is generally similar to 
the embodiment shown in FIG. 2. In this embodiment also, as was explained 
earlier, the intermediate disc 5 (FIG. 3) will, after completion of the 
preliminary injection stroke, function to stop upward movement of the 
sleeve 26 as indicated at 27. The undercut shoulder 28 also provided on 
disc 5 serves as a means to limit the stroke for the main injection 
movement of the sleeve 26 as indicated and against which the spring seat 
disc 7 is brought to bear after completion of the main injection stroke.