Control valve for a fuel injection valve

A control valve for an injection valve for injecting fuel into an internal combustion engine is described. The injection valve has a control chamber which is connected via an inlet throttle to a high-pressure accumulator, and which can be connected via the control valve and an outlet throttle to an unpressurized return line to a fuel tank. The pressure prevailing in the control chamber acts on a movable nozzle body which is provided with a nozzle needle which releases and seals injection holes as the nozzle body moves. The control valve is constructed adjoining the control chamber, with the result that the pressure prevailing in the control chamber at a first operating surface also acts on the valve body of the control valve. The control valve has a valve chamber which is disposed opposite the control chamber and is connected to the control chamber via the outlet throttle and has a second operating surface, which is smaller than the first operating surface.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The invention relates to a control valve for an injection valve for 
injecting fuel into internal combustion engines. Such a control valve is 
known from Published, European Patent Application EP 0 826 876. 
For the purpose of supplying fuel to internal combustion engines, 
increasing use is being made of accumulator injection systems which 
operate with very high injection pressures. Such injection systems are 
known as common rail systems (for diesel engines) and HPDI injection 
systems (for spark-ignition engines). The injection systems are 
distinguished by the fact that the fuel is conveyed by a high-pressure 
pump into a pressure accumulator that is common to all the cylinders of 
the engine and from which the injection valves at the individual cylinders 
are supplied. The opening and closing of the injection valves are 
controlled as a rule electromagnetically, possibly also with the aid of 
piezoelements. 
The purpose of the control valve is to effect hydraulic opening and closing 
of the actual fuel injection valve, that is to say, in particular, to fix 
the beginning and the end of the injection process exactly in terms of 
time. The injection valve is intended, for example, to open under control 
and to close quickly at the end of the injection process. Then, the 
injection of very small amounts of fuel is to be possible for the purpose 
of pilot injection before the actual injection with the aid of which the 
combustion process can be optimized. 
In the above-named Published, European Patent Application EP 0 826 876 and 
in Published, European Patent Application EP 0 778 411, a 2/2 directional 
valve is used as control valve for a common rail system. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide a control valve for 
a fuel injection valve which overcomes the above-mentioned disadvantages 
of the prior art device of this general type, in which the control valve 
is configured such that the control forces to be applied are small in 
conjunction with a simple configuration of the valve. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, in an injection valve having a control 
chamber to be connected via an inlet throttle to a high-pressure 
accumulator for injecting fuel into an internal combustion engine, the 
control chamber to be further connected to a fuel tank via an 
unpressurized return line, the injection valve further having a nozzle 
seat and a movable nozzle body with nozzle needles for communicating with 
injection holes formed in the injection valve, a control valve, including: 
an axially movable valve body having a first operating surface adjoining 
the control chamber, the valve body having on a side opposite the first 
operating surface a sealing surface cooperating with a valve seat of the 
injection valve; 
an outlet throttle disposed in the valve body for connecting the control 
chamber to the unpressurized return line and dimensioned in comparison 
with the inlet throttle such that a pressure drop at the inlet throttle is 
greater than a pressure drop at the outlet throttle; 
the valve body has a valve chamber formed therein disposed opposite the 
control chamber and connected to the control chamber via the outlet 
throttle and further disposed in a flow direction downstream of the outlet 
throttle and upstream of the sealing surface; and 
the valve body further having a second operating surface defined by the 
valve chamber and acting in a fashion opposed to the first operating 
surface and being smaller than the first operating surface, the sealing 
surface of the valve body to be lifted from the valve seat for connecting 
the control chamber to the unpressurized return line via the outlet 
throttle, a pressure prevailing in the control chamber acting on the 
movable nozzle body having the nozzle needle for releasing and sealing the 
injection holes as the nozzle body moves. 
The invention accordingly represents a 2/2 directional valve integrated 
into the injection valve body. The control valve according to the 
invention is of very simple construction and fully integrated into the 
injection valve body, and requires only small control forces. The 
particular configuration of the control valve according to the invention 
renders it possible to minimize the volume of the valve space. The control 
valve, throttles and injection valve body form a compact unit. There is no 
need on the control valve for any springs or similar devices for producing 
prestresses. The control valve according to the invention can be 
configured for very small stroke movements with a stroke of only 20 to 40 
.mu.m. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
control valve for a fuel injection valve, it is nevertheless not intended 
to be limited to the details shown, since various modifications and 
structural changes may be made therein without departing from the spirit 
of the invention and within the scope and range of equivalents of the 
claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In all the figures of the drawing, sub-features and integral parts that 
correspond to one another bear the same reference symbol in each case. 
Referring now to the figures of the drawings in detail and first, 
particularly, to FIG. 1 thereof, there is shown a known injection valve 
with a 2/2 directional valve as a control valve 12. 
As shown in FIG. 1, in the case of a common rail system fuel is led with 
system pressure from a high-pressure accumulator 100 to a control chamber 
4 in an injection valve body 5 via a high-pressure bore 1 and an inlet 
bore 2 with an inlet throttle 3. In the control chamber 4, the pressure 
prevailing there acts on a rear end of a movable nozzle body 6 with a 
nozzle needle 13 at a front end which, as the nozzle body 6 moves, opens 
and closes in the injection valve body 5 injection holes 7 which lead to 
the combustion chamber of the internal combustion engine. Likewise 
connected to the high-pressure accumulator via the high-pressure bore 1 is 
a nozzle chamber 8 which is constructed at the front end of the nozzle 
body 6 in the injection valve body 5. If the full system pressure is 
present both in the control chamber 4 and in the nozzle chamber 8, the 
nozzle body 6 is pressed downward because of the larger operating surface 
in the control chamber 4, and the nozzle needle 13 then bears against a 
valve seat 15 in the nozzle chamber 8 and seals the injection holes 7. 
From the control chamber 4, a bore 9 in the injection valve body 5 with an 
outlet throttle 10 leads to the control valve 12, in the form of a 2/2 
directional valve, integrated into the injection valve body 5. An 
unpressurized fuel return line 14 departs from the control valve 12 to a 
fuel tank 101. The control valve 12 is driven and operated via a plunger 
16 by an electromagnetic and/or piezoelectric actuator 18. 
The control valve 12 controls the pressure that is exerted in the control 
chamber 4 on the movable nozzle body 6. If the control valve 12 is closed, 
the full system pressure is essentially present in the control chamber 4, 
with the result that the nozzle needle 13 seals the injection holes 7, 
which lead into the combustion chamber, at the front end of the nozzle 
body 6. If the actuator 18 is electrically driven, the plunger 16 exerts a 
force on the spring-loaded control valve 12. The control valve 12 opens as 
a consequence thereof. When the control valve 12 is open, a stationary 
flow is set up between the high-pressure accumulator, control chamber 4, 
control valve 12 and return line 14. This flow leads to a defined pressure 
drop at the individual throttles, the inlet throttle 3 and the outlet 
throttle 10. The pressure drop at the inlet throttle 3 and the outlet 
throttle 10 is dimensioned in each case such that the pressure in the 
control chamber 4 is reduced. As a result, the force acting in the control 
chamber 4 on the nozzle body 6 decreases, while the pressure in the nozzle 
chamber 8 remains equal to the system pressure, with the result that the 
injection valve is opened hydraulically by the force exerted in the nozzle 
chamber 8 on the nozzle body 6. As a result, the connection between the 
nozzle chamber 8 and the injection holes 7 is established, and the fuel is 
injected into the combustion chamber. 
This configuration has the disadvantage that the pressure acting on the 
control valve 12 in the closed state is essentially equal to the system 
pressure, that is to say is very high. Since, in the known configuration, 
this pressure acts on the control valve 12 in the opening direction, the 
closing spring of the control valve 12 must be strong in order to keep the 
control valve 12 closed. This, in turn, leads to the fact that the force 
required to open the control valve, which is to be applied by the actuator 
18, is very large. 
In order to eliminate this disadvantage, it is proposed in Published, 
European Patent Application EP C 778 411 A2 to provide the control valve 
with a pressure-compensating chamber and a pressure-compensating piston. 
As before, in this case the control valve is connected to the control 
chamber via a bore in the injection valve body with an outlet throttle. In 
a development of this configuration, the outlet bore is fitted in a 
movable, spring-loaded throttle piston that is disposed between the 
control chamber and control valve. The configuration for controlling the 
nozzle body of the injection valve is therefore very complicated. 
As in the case of FIG. 1, in the injection valve according to the invention 
as shown in FIG. 2, the control chamber 4 of the injection valve is also 
connected via the high-pressure bore 1 and the inlet bore 2 with the inlet 
throttle 3 in the injection valve body 5 to the high-pressure accumulator 
100, which is at system pressure. Although no longer represented in FIG. 
2, here, as well, the high-pressure bore 1 leads further to the nozzle 
chamber 8 at the front end of the movable nozzle body 6, which projects 
with its rear end into the control chamber 4 and forms a side of the 
control chamber 4. 
In the embodiment according to the invention shown in FIG. 2, the control 
valve 12 is disposed directly adjoining the control chamber 4. Constructed 
for this purpose in the injection valve body 5 is a cutout 30 which 
extends away from the control chamber 4 in the longitudinal direction of 
the injection valve body 5 with respect to the nozzle body 6 or the bore 
intended for holding the nozzle body 6. A valve body 20 is inserted into 
the cutout 30. Like the nozzle body 6, a valve body 20 of the control 
valve 12 can also move in the longitudinal direction of the injection 
valve body 5, but it is fitted in a sealing fashion into the cutout 30. 
The cutout 30 is open toward the control chamber 4, with the result that 
the valve body 20 inserted into the cutout 30 projects into the control 
chamber 4 with a surface A.sub.1 (its base surface) and forms a side of 
the control chamber 4 with the surface A.sub.1. As a rule, this side is 
situated opposite the side of the control chamber 4 that is formed by the 
nozzle body 6. 
On the other side (the top side) of the cutout 30, which is averted from 
the control chamber 4, there is provided in the injection valve body 5 a 
bore 40 through which the plunger 16 of the electromagnetic and/or 
piezoelectric actuator 18 (not represented in FIG. 2) runs. The diameter 
of the plunger 16 is smaller than that of the bore 40, and the bore 40 
forms a part of the unpressurized return line through which the fuel flows 
back from the control chamber 4 into the fuel tank 101 when the control 
valve 12 is open. 
The bore 40, in turn, has a smaller diameter than the cutout 30. The 
transition from the bore 40 into the cutout 30 is constructed as a valve 
seat 24 for the control valve 12, at which, with the control valve 12 
closed, a sealing surface 22 of the valve body 20 comes to bear in a 
sealing manner against the top side of the cut out 30 having the valve 
seat 24, that is to say at the side of the valve body 20 averted from the 
control chamber 4. 
On its outer circumference, the valve body 20 has a radial shoulder or a 
radial constriction 25 adjoining the sealing surface 22 corresponding to 
the valve seat 24. At a spacing from the top side of the valve body 20 and 
from the sealing surface 22, the constriction 25 widens in a stepwise 
fashion to the outside diameter of the valve body 20 which corresponds to 
the inside diameter of the cutout 30. Together with a radial shoulder 32 
at the upper end of the cutout 30, the constriction 25 produces a valve 
chamber 26 at the upper end of the control valve 12. 
With reference to the pressure prevailing in the valve chamber 26, the 
constriction 25 has an annular operating surface A.sub.2 which is situated 
opposite the operating surface A.sub.1 on the underside of the valve body 
20, and which is smaller than the operating surface A.sub.1. The ratios 
are therefore similar to the case of the nozzle body 6, which moves up and 
down taking account of the different operating surfaces at its upper and 
lower ends, respectively, as a function of the pressures in the control 
chamber 4 and the nozzle chamber 8. 
An outlet bore 27 with an outlet throttle 28 is integrated into the valve 
body 20. The outlet bore 27 with the outlet throttle 28 extends from the 
control chamber 4 to the valve chamber 26, that is to say from the side of 
the valve body 20 adjoining the control chamber 4 or projecting into the 
latter to the constriction 25. 
In the initial state, with the injection valve closed, the valve body 20 of 
the control valve 12 is pressed against the valve seat 24 by the pressure 
in the control chamber 4, which corresponds virtually to the system 
pressure, with the result that there is no connection between the valve 
chamber 26 and the bore 40, which is part of the unpressurized return line 
to the fuel tank. It is true that essentially the same pressure as in the 
control chamber 4 is present in the valve chamber 26 via the outlet bore 
27 and the outlet throttle 28, but because the surface A.sub.1, via which 
the pressure acts from the side of the control chamber 4 on the valve body 
20, is larger than the surface A.sub.2, via which the pressure acts in the 
opposite direction in the valve chamber 26, the resulting force is 
directed toward the valve seat 24. 
The system pressure is also present in the control chamber 4 at the nozzle 
body 6, with the result that the nozzle needle 13 is pressed into its seat 
15 at the front end of the nozzle body 6, and the connection to the 
injection holes 7 is interrupted. Consequently, no fuel is injected into 
the combustion chamber. 
In the case when the actuator 18 is driven electrically, the plunger 16 
exerts on the control valve 12 a force that lifts the valve body 20 off 
the valve seat 24. Since a force acting in the opening direction is 
already present at the operating surface A.sub.2 of the valve chamber 26, 
the force exerted by the plunger 16 need no longer overcome the difference 
relative to the force acting on the larger operating surface A.sub.1. 
A connection is produced between the valve chamber 26 and the bore 40, 
which is part of the unpressurized return line to the fuel tank, when the 
valve body 20 lifts off the valve seat 24. Fuel thereby flows from the 
high-pressure bore 1 through the inlet throttle 3, the control chamber 4, 
the outlet throttle 28 and the valve chamber 26 into the bore 40. The 
diameter of the outlet throttle 28 is larger than the diameter of the 
inlet throttle 3 in the injection valve body 5. The flow through the inlet 
throttle 3 is therefore less than that through the outlet throttle 28, 
with the result that the pressure in the control chamber 4 decreases. The 
nozzle body 6 is thereby relieved, and the system pressure present in the 
nozzle chamber 8 (FIG. 1) lifts the nozzle needle 13 off its seat 15 and 
opens the connection to the injection holes 7. The injection process 
thereby begins. 
The stroke of the valve body 20 when lifting off the valve seat 24, and the 
stroke of the nozzle body 6, which is directed opposite to this movement, 
can be coordinated such that the underside of the valve body 20 comes to 
bear against the top side of the nozzle body 6. Since both are plane 
surfaces, the outlet bore 27 opening into the underside of the valve body 
20 is thereby sealed. As a consequence of this, essentially no more fuel 
flows off through the return line. At the same time, the pressure in the 
control chamber 4 is increased. 
This measure has the advantage that the leakage flow of the injection 
valve, and thus the fuel unnecessarily conveyed, are reduced. However, it 
need not be provided in each case. 
After termination of the driving of the actuator 18, the valve body 20 is 
pressed against the valve seat 24 by the pressure in the control chamber 
4, which is always higher than the pressure in the valve chamber 26, which 
is connected to the unpressurized return line. Consequently, the 
connection to the bore 40 and to the unpressurized return line is 
interrupted, with the result that the full pressure can build up again in 
the control chamber 4. The pressure in the control chamber 4 leads to a 
force at the nozzle body 6 acting in a direction of the seat 15 of the 
nozzle needle 13 that presses the nozzle needle 13 into its seat 15 again 
and terminates the injection process. 
The embodiment of the valve body 20 used in the case of the injection valve 
of FIG. 2 is represented in detail in FIG. 3. The outlet bore 27 with the 
outlet throttle 28 runs from the underside of the valve body 20, which 
adjoins the control chamber 4, obliquely through the valve body 20, and 
opens directly into the constriction 25 below the sealing surface 22. 
FIG. 4 shows an alternative embodiment of the valve body 20. In this 
embodiment, the outlet bore 27 with the outlet throttle 28 runs in the 
direction of the longitudinal axis of the valve body 20 from the underside 
of the valve body 20, which adjoins the control chamber 4, through the 
valve body 20, and opens into a transverse bore 29 which runs 
perpendicular to the longitudinal axis through the valve body 20, and 
which opens into the constriction 25 below the sealing surface 22.