Control arrangement for a fuel injection valve

A fuel injection valve for an internal combustion engine comprises a valve body structure including a nozzle part formed with a needle passage having at least one nozzle passage at one end, a primary control chamber spaced along the needle passage from the nozzle passage, and a secondary control chamber. The primary control cheer is connected in use to a duct for supplying fuel under pressure. The nozzle part of the valve body structure has a seating surface between the nozzle passage and the primary control chamber. A needle structure is fitted slidably in the needle passage with one end of the needle structure proximate the seating surface. The needle structure has a first control surface that is exposed to pressure of fluid in the primary control chamber, a second control surface at the end of the needle structure proximate the seating surface, and a third control surface exposed to pressure of fluid in the secondary control chamber. The three control surfaces are disposed so that force generated by fluid pressure acting on each of these surfaces has a component urging the needle structure away from the seating surface against the force of a needle return spring. A control valve has a first position in which it communicates pressure of fuel in fuel supply duct to the secondary control chamber and a second position in which it cuts off the pressure of fuel in the fuel supply duct from the secondary control chamber. When the control valve is in its first position, it is urged by the pressure of fuel in the fuel supply duct toward its second position against the force of a control valve return spring.

BACKGROUND OF THE INVENTION 
This invention relates to a control arrangement for a fuel injection valve 
for an internal combustion engine, especially for a large diesel engine. 
Large diesel engines refer here to such engines that may be applied, for 
example, for the main propulsion engines or the auxiliary engines for 
ships or for power plants for producing electricity and/or heat energy. By 
means of injection valves fuel is injected directly into each cylinder of 
an engine. 
The pressure at which fuel is supplied to a fuel injection valve of a large 
diesel engine varies periodically in order to control opening and closing 
of the valve by displacing a needle that is biased toward its closed 
position by a return spring. The fuel pressure required to displace the 
needle from its closed position against the force of the return spring is 
referred to as the opening pressure, and the fuel pressure at which the 
spring is able to displace the needle back to its closed position is 
referred to as the closing pressure. 
The condition under which fuel is injected, including, e.g., the timing of 
the injection, the size of the droplets, the fuel pressure, the number of 
nozzle orifices, the orientation of the nozzle orifices in the combustion 
chamber, etc., influence significantly the NOx content of the exhaust 
gases. In an attempt to decrease the creation of nitrogen oxides, 
improvements have been made in the formation of fuel droplets, both with 
respect to size and uniformity. The size of the droplets in a fuel spray 
can be decreased by increasing the pressure of the injection of fuel, 
which for its part can be achieved for example by means of the design of 
the injection nozzle and by using higher opening pressure for the nozzle. 
Increasing the pressure of injection also improves uniformity of droplet 
size. The operating conditions of the engine and the construction of the 
nozzle, however, set limits for increasing the opening pressure. 
In a conventional nozzle, the pressure of the fuel acts only on one control 
surface in order to open the valve. In such a nozzle, after the valve is 
already open, the pressure of the fuel acts not only on the control 
surface on which it acted for opening the valve but also on the needle of 
the nozzle through the area of a control surface located at the end of the 
needle. Because of this increase in area, the closing pressure of the 
nozzle is substantially smaller than the opening pressure of the nozzle. 
As a consequence, the fuel pressure must be reduced substantially in order 
to allow the spring to close the valve and an undesirable fuel injection 
under low pressure occurs at the end of the injection period, resulting in 
injection of larger droplets. 
SUMMARY OF THE INVENTION 
An aim of the invention is to provide a new improved control arrangement 
for a fuel injection valve by means of which the closing pressure of an 
injection nozzle of the injection valve and thus the injection pressure at 
the end of the injection period can with advantage be increased, whereby 
the formation of droplets in the cylinder of an engine can be improved. A 
further aim is that the arrangement does not as such require increasing of 
the opening pressure of the nozzle. 
In accordance with the invention there is provided a fuel injection valve 
for an internal combustion engine, said valve comprising a valve body 
structure including a nozzle part formed with a needle passage having at 
least one nozzle passage at one end and a primary control chamber spaced 
from said one end, the nozzle part having a seating surface between the 
nozzle passage and the primary control chamber, said primary control 
chamber being connected in use to a duct for supplying fuel under 
pressure, and the needle passage also having a secondary control chamber, 
a needle structure fitted slidably in the needle passage with one end of 
the needle structure proximate the seating surface, the needle structure 
having a first control surface that is exposed to pressure of fluid in the 
primary control chamber, a second control surface at said one end of the 
needle structure, and a third control surface exposed to pressure of fluid 
in the secondary control chamber, the first, second and third control 
surfaces being disposed so that force generated by fluid pressure acting 
on each of said surfaces has a component directed along the needle 
structure in a direction from said one end of the needle structure toward 
an opposite end of the needle structure, a first spring urging the needle 
structure toward a position in which the second control surface seats as a 
valve surface against said seating surface, a control valve having a first 
position in which it communicates pressure of fuel in said duct to the 
secondary control chamber and a second position in which it cuts off the 
pressure of fuel in said duct from the secondary control chamber, the 
control valve being urged by the pressure of fuel in said duct toward its 
second position when it is in its first position, and a second spring 
urging the control valve toward its first position. 
During an injection cycle having at least a first phase in which the fuel 
pressure increases for opening the fuel injection valve against the force 
of the first spring and a second phase in which the fuel pressure 
decreases, the control valve is in its first position during at least an 
initial part of the first phase of the injection cycle, in which the fuel 
injection valve is closed, and is displaced to its second position after 
the fuel injection valve is open. 
In accordance with the invention, before starting the injection of fuel, 
the control valve is urged by a spring in its first position, in which it 
communicates the pressure of the fuel to be injected to the third control 
surface, and after opening of the fuel injection valve the control valve 
cuts off the connection between the pressure of the fuel to be injected 
and the third control surface. By making use of the control valve so as to 
selectively apply the pressure of the fuel to be injected to the third 
control surface in the way described it is possible to advantageously 
influence the pressures needed on the one hand for the opening and on the 
other hand for the closing of the injection nozzle. 
In an advantageous embodiment of the invention, a chamber is associated 
with the control valve. This chamber can be separately connected on the 
one hand with a fuel feeding duct and on the other hand with the third 
control surface so that in the first position of the control valve, which 
precedes the injection of fuel, the fuel feeding duct is connected to the 
third control surface. 
The valve member of the control valve can with advantage be designed to 
comprise a control surface, which responds to increase in feeding pressure 
of the fuel by moving the valve member against the force of the second 
spring so that the connection between the chamber and the fuel feeding 
duct is cut off at the same time as the chamber connects the third control 
surface to a substantially unpressurized space. 
From the viewpoint of manufacturing, it is advantageous that the control 
valve and the third control surface be located in a separate part which is 
between the first control surface in the needle member and the return 
spring for the injection valve. This is advantageous also due to the fact 
that in this case the nozzle part of the valve being most susceptible to 
wear can easily be changed. In this solution the needle member of the 
injection nozzle can be in a force transmitting connection with a guiding 
stem of the injection valve by means of a separate lifting member, which 
is supported to said separate part so that it is moveable in the axial 
direction and on which the third control surface is located. 
By selecting the areas of the second and the third control surfaces, to be 
at least substantially equal, the closing pressure and the opening 
pressure of the injection nozzle are mutually equal respectively. Hereby 
the formation of droplets of the fuel is as advantageous as possible 
during the whole injection period.

DETAILED DESCRIPTION 
In the drawings, 1 indicates a body part of an injection valve and 3 an 
injection nozzle part of the valve, between which there is an intermediate 
part 2. A lifting member 5 is moveably supported to the intermediate part 
2. The lifting member 5 provides a force transmitting connection between a 
needle member 4 of the nozzle and a guiding stem 6 of the valve. The 
guiding stem 6 is pressed by a spring 7, located in an unpressurized space 
8 in the body part 1, downwards in the figures towards a closed position 
of the valve. 
A fuel injection pump (not shown) has its pressure side connected to a fuel 
feeding duct 9, which feeds fuel into a chamber 10 in the nozzle part 3. 
In the chamber 10, the pressure of the fuel acts on a control surface 11 
of the needle member 4. In the position of FIG. 1 the needle member 4 of 
the nozzle is in a closed position, whereby a valve surface 12 engaging a 
seating surface of the nozzle part 3 prevents injection of the fuel 
through nozzle passages 13. When the pressure of the fuel in the chamber 
10 is high enough that the force effect on the control surface 11 exceeds 
the spring force of the spring 7, the valve opens and the fuel passes 
through a valve passage 14 (cf. FIG. 2) between the valve surface 12 and 
its seating surface into the nozzle passages 13, whereby injection of the 
fuel takes place. Since in this case the combined area of the control 
surface 11 and the valve surface 12 serving as a control surface is of 
course substantially larger than the area of the control surface 11 alone, 
the pressure of the fuel providing closing of the valve is substantially 
lower than the pressure of the fuel needed for opening of the valve 
respectively. As a consequence an injection under low pressure occurs at 
the end of the injection period, which is undesirable. 
In order to avoid the above mentioned phenomenon in accordance with the 
invention the injection valve is provided with a control arrangement shown 
in the figures, which includes a control surface 10 on the lifting member 
5 located in the intermediate part 2 and a control valve 15 moveable 
against the force of a spring 16 located in a space 21 in the body part 1, 
in association with the control valve there being a chamber 19 which is 
connectable with a passage 17 connected to the fuel duct 9 and a passage 
18 being in connection with the control surface 20. 
FIG. 3 corresponds to a situation before opening of the injection valve. 
Fuel is fed through the duct 9 into the chamber 10, in which it acts on 
the control surface 11 as described above. At the same time fuel passes 
through the passage 17 into the chamber 19, from which it passes further 
through the passage 18 to act on the control surface 20. Thus, the force 
provided by the pressure of the fuel and lifting the needle member 4 
against the force of the spring 7 acts in this case through both of the 
control surfaces 11 and 20. When the force due to the pressure of the fuel 
acting on the control surfaces 11 and 20 exceeds the force of the spring 7 
the injection of fuel starts. In practice the pressure can then be for 
example 600 bar. 
As is more clearly apparent from FIG. 3a, the fuel pressure acts also 
through a passage 24 on a control surface 23 located on the control valve 
15 thereby tending to lift the control valve 15 upwards in the figures 
against the force of the spring 16. When the feeding pressure of the fuel 
increases for instance up to 1000 bar, the control valve 15 moves against 
the force of the spring 16 from the position shown in FIG. 3 to the 
position shown in FIGS. 2 and 4. In this position, a surface 22 in the 
control valve 15 cuts off the connection between the passages 17 and 18. 
Thus, the pressure of the fuel to be fed can no longer act on the control 
surface 20, but the control surface 20 is connected to the unpressurized 
space 8 through the passage 18, the chamber 19 and passages 26, 27 and 28. 
The control valve 15 remains in this position during the whole remaining 
time of the injection period. When the control valve 15 is in its upper 
position, the fuel pressure acts only on the control surfaces 11 and 12, 
whereby the injection period is finished when the compression force of the 
spring 7 exceeds the force due to the fuel pressure acting on the surfaces 
11 and 12. When the areas of the control surfaces 20 and 12 are selected 
to be equal, the opening pressure of the valve corresponds to the closing 
pressure of the valve. In this way it is possible by means of the 
arrangement according to the invention to avoid fuel injection with lower 
pressure at the end of the injection period. 
After closing of the valve, in practice, the control valve 15 remains 
pressed against the force of the spring 16 for a moment as is shown in 
FIG. 4, since although the pressure of the fuel has already substantially 
decreased, the fuel pressure acts through the passage 17 not only on the 
surface 23 but also on the surface 25 of the control valve 15. The control 
valve 15 moves back into the position of FIG. 3 for a new injection period 
only when the force of the spring 16 exceeds again the force due to the 
pressure of the fuel acting on the valve 15, which in practice can then be 
for instance 200 bar. 
The invention is not limited to the embodiment shown, but several 
modifications are feasible within the scope of the attached claims.