Injection valve

In an injection valve, a perforated disk made from a material of relatively great hardness. The perforated disk has a tensile strength of >800N/mm.sup.2. Spray holes are punched from a downstream side of the perforated disk to an upstream side. A stamping break-out, which occurs due to the greater brittleness of the material, has no negative effects since the perforated disk is installed in the injection valve such that the direction of flow of the medium is exactly opposite to the punching direction. The injection valve is particularly suitable for fuel injection systems of mixture-compressing applied ignition internal combustion engines.

BACKGROUND OF THE INVENTION 
The present invention relates to an injection valve including a perforated 
disk having a first surface, a second surface, and at least one spray 
hole, the spray hole being punched in a direction from the first surface 
to the second surface. 
German Published Patent Application No. 40 26 721 ("the '721 application") 
discusses an injection valve which has a perforated disk downstream of its 
valve seat surface. The perforated disk of the '721 application has a 
plurality of spray holes, through which a medium such as fuel can pass. 
The spray holes in the perforated disk are made by erosion. 
Using perforated disks, with spray holes made by punching, on injection 
valves is known. For example, cup-shaped perforated disks are made from a 
thin sheet and have a tensile strength of 400 to 600N/mm.sup.2, depending 
on the material. When the spray holes are punched into the perforated 
disk, a punching draw-in is formed at the edge of the spray hole in a 
first surface (i.e., the surface of the perforated disk struck by the 
punch), and a protrusion, in the form of a burr, is formed at the edge of 
the hole in a second surface (i.e., the surface of perforated disk from 
which the punch emerges). Unfortunately, if the number of punching 
operations is large, it is impossible to keep these disadvantageous burrs 
constant and, as a result, relatively large scatter may occur in the flow 
and in the spray angle. In mass production, minimizing this scatter is 
desired. To minimize this disadvantageous scatter, the punching burrs can 
be ground off. However, the grinding process increases the cost of 
manufacturing the perforated disk. Accordingly, a process for producing 
perforated disks without burred holes, which does not require a separate 
grinding step, is needed. 
SUMMARY OF THE INVENTION 
The injection valve of the present invention includes a perforated disk 
having a tensile strength greater than 800N/mm.sup.2 and which is 
installed in the injection valve such that its first surface (i.e., the 
surface struck by the punch) is downstream from its second surface (i.e., 
the surface from which the punch emerges). The perforated disks of the 
present invention are advantageously produced economically and simply and 
have punched spray holes which are free of a disadvantageous burr. 
Consequently, the scatter in the spray angle and in the flow rate is 
markedly reduced. Moreover, an involved deburring process is automatically 
eliminated. In mass production, the quality of the spray holes can be kept 
substantially constant thereby reducing the scatter in the medium flowing 
through the spray holes.

DETAILED DESCRIPTION 
FIG. 1 shows a partial view, as an exemplary embodiment, of an injection 
valve for fuel injection systems of mixture-compressing, applied-ignition, 
internal combustion engines. The injection valve has a tubular valve seat 
carrier 1 in which a longitudinal opening 3 is formed concentrically with 
respect to a valve longitudinal axis 2. A valve needle 5 is arranged in 
the longitudinal opening 3 and is, for example, tubular. The downstream 
end 6 of the valve needle 5 is connected to, for example, a spherical 
valve-closing body 7. Five flats 8, for example, are arranged on the 
circumference of the spherical valve closing body 7. 
The injection valve is actuated in a known manner, for example 
electromagnetically. An indicated electromagnetic circuit with a magnet 
coil 10, an armature 11 and a core 12 is used for axially moving the valve 
needle 5, and hence for opening, counter to the spring force of a return 
spring (not shown), and closing the injection valve. The armature 11 is 
connected to the end of the valve needle 5 remote from the valve-closing 
body 7 by a laser weld, for example, and is aligned with the core 12. 
A guide opening 15 in a valve seat body 16 is used to guide the 
valve-closing body 7 during the axial movement. The cylindrical valve seat 
body 16 is mounted leak-tightly, by welding, in the downstream end of the 
valve seat carrier 1 (i.e., the end of the valve seat carrier 1 remote 
from the core 11), in the longitudinal opening 3 extending concentrically 
with respect to the valve longitudinal axis 2. The bottom (or downstream) 
end 17 of the valve seat body 16 (i.e., the end of the valve seat body 16 
which is opposite the valve-closing body 7), is concentrically and rigidly 
connected to a bottom part 20 of a perforated disk 21 of, for example, 
cup-shaped design. Thus, the upper (or upstream) end face 44 of the bottom 
part 20 rests against the bottom (or downstream) end 17 of the valve seat 
body 16. 
The valve seat body 16 and the perforated disk 21 are connected by, for 
example, an encircling and leak-tight first weld 22 formed by means of a 
laser. This method of assembly eliminates the risk of unwanted deformation 
of the bottom part, 20 in its central area 24, which includes at least 
one, and, for example four, spray holes 25 formed by punching. 
Adjoining the bottom part 20 of the cup-shaped perforated disk 21 is an 
encircling retaining rim 26. The retaining rim 26 exerts a radial spring 
action (i.e., a friction fit) on the wall of the longitudinal opening 3. 
In this way, as the valve-seat part, consisting of the valve seat body 16 
and the perforated disk 21, is pushed into the longitudinal opening 3 in 
the valve seat carrier 1, shavings are not formed on the valve seat part 
or on the longitudinal opening 3. The retaining rim 26 of the perforated 
disk 21 is connected to the wall of the longitudinal opening 3 by, for 
example, an encircling and leak-tight second weld 30. 
The depth of insertion of the valve-seat part, including the valve seat 
body 16 and the cup-shaped perforated disk 21, into the longitudinal 
opening 3 determines the presetting of the stroke of the valve needle 5 
because one end position of the valve needle 5, when the magnet coil 10 is 
unexcited, is defined by the abutment of the valve-closing body 7 on a 
valve seat surface 29 of the valve seat body 16. The other end position of 
the valve needle 5, when the magnet coil 10 is excited, is defined by the 
abutment of the armature 11 on the core 12, for example. The distance 
between these two end positions of the valve needle 5 thus represents the 
stroke of the valve needle. 
The spherical valve-closing body 7 interacts with the valve seat surface 29 
of the valve seat body 16. The valve seat surface 19 tapers 
frustoconically in the direction of flow and is located, axially between 
the guide opening 15 and the bottom end 17 of; the valve seat body 16. 
A protective cap 40 is arranged on the circumference of the valve seat 
carrier 1 at its downstream end (i.e., the end remote from the magnet coil 
10) and is connected to the valve seat carrier 1 by means of 
snap-fastening, for example. A sealing ring 41 provides a seal between the 
circumference of the injection valve and a valve receptacle (not shown) 
in, for example, the intake line of the internal combustion engine. 
FIG. 2 shows the cup-shaped perforated disk 21 with its spray holes 25 
arranged in the central area 24. The spray holes 25, of which there are, 
for example, four, are distributed, symmetrically for example, around the 
valve longitudinal axis 2 in the form of corners of a square. Thus, the 
spray holes 25 are each equidistant from one another and from the valve 
longitudinal axis 2. The bottom part 20 of the perforated disk 21 has the 
upper (or upstream) end face 44,, which corresponds to a second flat 
surface, and an opposite, lower (or downstream) end face 19, which 
corresponds to a first flat surface. 
As illustrated in FIG. 3, in the past, the spray holes 25 of the perforated 
disk 21 were punched in the direction which would be the direction of flow 
of the medium. Thus, in the past, the punching operation in the perforated 
disks 21 was performed from the second surface 44 to the first surface 19, 
the first surface 19 lying downstream of the second surface 44 after 
installation. 
In contrast, the spray holes 25 in the injection valve according to the 
present invention are punched in the opposite direction. The punching 
direction is indicated by an arrow 45. The punches of the punching tool 
thus first strike the first surface 19 of the bottom part 20 of the 
perforated disk 21, which lies-downstream of the second surface 44 in the 
subsequent installed position of the perforated disk 21 in the injection 
valve. The punched spray holes 25 penetrate the material of the perforated 
disk 21 as far as the second surface 44, where they emerge from the 
material. The punching direction is thus opposite to the direction of flow 
of the medium (FIG. 2). 
FIG. 3 illustrates a spray hole 25 in a perforated disk 21 as formed with 
customary punching. Depending on the material, the known perforated disks 
have a tensile strength of 400 to 600N/mm.sup.2. The relatively low 
hardness of the perforated disk, evidenced by these values, is the reason 
why a punching draw-in 50 (i.e. a cross-sectional enlargement of the spray 
hole 25) occurs in the second surface 44 due to the entry of the punch, 
while a burr 51, which protrudes from the surface 19, is formed on the 
first surface 19. The punching draw-in 50 and the burr 51, which are not 
shown to scale, on the spray hole 25 cause a comparatively large scatter 
in the flow and in the spray angle. 
In comparison, FIG. 4 illustrates a spray hole 25 in the perforated disk 
21, which is manufactured from a material of greater hardness than the 
material of the perforated disk 21 illustrated in FIG. 3. The perforated 
disk 21 now has a tensile strength of &gt;800 N/mm.sup.2, which corresponds 
approximately to a Vickers hardness of &gt;300 EV1. The hardness of the 
material of the conventional perforated disks 21 can be raised by cold 
working, for example. The greater hardness of the material reduces or 
eliminates the punching draw-in or burrs such that, if any punching 
draw-in or burrs arise, they are negligibly small. Since the material has 
a greater brittleness, no burrs are formed. Instead, a punching breakout 
52 arises at the spray hole 25. More specifically, the material breaks at 
the surface where the punch emerges (i.e., at the first surface 19). This 
punching break-out 52 enlarges somewhat the cross section of the spray 
hole 25, only in the vicinity of the first surface 19. Although this means 
can reduce the scatter in the flow rates, the scatter in the spray angle 
remains because the punching break-out 52 is the first, downstream surface 
19. 
In accordance with the present invention, FIG. 5 shows a partial view of a 
perforated disk 21 with a spray hole 25 which has been punched in a 
direction opposite to the subsequent direction of flow of the medium, 
namely from the first surface 19 to the second surface 44, as indicated by 
the arrow 45 for the punching direction. The properties of the material is 
the same as in the perforated disk 21 shown in FIG. 4, the tensile 
strength of the material thus likewise being &gt;800N/mm.sup.2. In this case, 
the punching break-out 52, caused by punching, is situated at the second, 
upstream surface 44 of the perforated disk 21 which faces the 
valve-closing body 7 after installation in the injection valve. At the 
first, downstream surface 19, at which the medium, here for example fuel, 
emerges directly from the spray hole 25, there is a good-quality spray 
area which suffers virtually no negative effects from the punching. The 
transition from the spray hole 25 to the first surface 19 is thus 
relatively sharp-edged and therefore has virtually no deformations to 
cause negative effects during spraying. The scatter of the spray angle, in 
particular, remains advantageously very low due to this arrangement. The 
scatter in the: flow rate can be even further reduced by varying the punch 
diameters of the punching tool. 
The configuration according to the present invention of the perforated disk 
21 is possible with any form of perforated disk, even, for instance, with 
perforated disks which do not have a retaining rim 26 (i.e., which are not 
cup shaped).