Electromagnetic fuel injection valve, and method for assembling nozzle assembly

An electromagnetic fuel injection valve is provided, which allows the amount of lift to be adjusted and established following the assembly of the nozzle assembly so that it is suitable for high pressure cylinder injection of fuel and which also allows the amount of lift to be established with high precision. A method for assembling the nozzle assembly is also offered. This invention comprises a thin-walled skirt portion formed in a protruding manner at the nozzle holder, a valve seat that is introduced under pressure to the skirt portion, with the valve seat and the nozzle holder welded and joined at the skirt portion, and, preferably, the application of a load from the outside of the nozzle holder following welding to bring about the irreversible deformation of the nozzle holder and establish the final amount of lift.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electromagnetic fuel injection valve 
and to a method for assembling the nozzle assembly, and more particularly 
to an electromagnetic fuel injection valve that allows the amount of lift 
in a needle valve to be established with high precision in electromagnetic 
fuel injection valves used for high pressure fuel injection such as 
cylinder injection of gasoline, as well as to a method for assembling the 
nozzle assembly. 
2. Description of the Related Art 
In the conventional establishment of the amount of lift in needle valves 
for electromagnetic fuel injection valves employed in cylinder injection 
of gasoline, electromagnetic fuel injection valves have a configuration 
that is designed to establish the amount of needle valve lift by having 
the armature come into direct contact with the lift stopper in response to 
magnetization of the electromagnetic coil. Examples include Japanese 
Patent Nos. Hei.5-504181 and Hei.5-504182. 
FIG. 5 is a vertical cross section illustrating an example of a 
conventional electromagnetic fuel injection valve 1. This electromagnetic 
fuel injection valve 1 comprises a connector 2, a valve housing 3, a 
nozzle holder 4, a fuel supply pipe 5 consisting of a magnetic substance, 
a spring seat 6, a valve seat 7, and an electromagnetic coil 8 that is 
magnetized and demagnetized by means of control signals from the connector 
2. 
An armature 9 in the form of a tube and a needle valve 10 that is 
integrally movable with this armature 9 are provided downwardly in the 
figure and are opposite the fuel supply pipe 5. 
An injection hole 12 is formed in a steel plate 11 located at the tip of 
the valve seat 7, and the needle valve 10 is always energized in the 
direction of this injection hole 12 by the valve spring 13 so as to be 
seated in the seat portion 7A of the valve seat 7. 
A lift amount adjusting shim 14 is provided on the upstream side of the 
valve seat 7, and the steel plate 11 is held between the valve seat 7 and 
a holding plate 15 on the downstream side. 
Fuel such as gasoline is fed from the upper part (in the figure) of the 
fuel supply pipe 5 to the first fuel channel 16, from the first fuel 
channel 16 through the second fuel channel 17 inside the armature 9, 
through the third fuel channel 18 between the nozzle holder 4 and the 
armature 9 or needle valve 10, through the fourth fuel channel 19 inside 
the lift amount adjusting shim 14, and to the fifth fuel channel 20 
between the valve seat 7 and the needle valve 10. 
The interval between the fuel supply pipe 5 and the armature 9 is used as 
the amount of lift L for the needle valve 10. As a result of the 
magnetization of the electromagnetic coil 8, the armature 9 and the needle 
valve 10 are integrally lifted against the urging force of the valve 
spring 13, and the fuel is sprayed from the injection hole 12 into the 
engine cylinder 21. 
With the demagnetization of the electromagnetic coil 8, the armature 9 and 
the needle valve 10 are returned to their original positions by the urging 
force of the valve spring 13, and the injection hole 12 is closed off. 
The amount of lift L for the needle valve 10 is established in the 
following manner. 
That is, the lift amount adjusting shim 14, valve seat 7, steel plate 11, 
and holding plate 15 are inserted in that order from the downstream side 
of the tubular tip 4A of the nozzle holder 4, and the leading end portion 
of the tubular tip 4A is crimped to form a crimped portion 22, thereby 
fixing these parts. 
If a thicker lift amount adjusting shim 14 is inserted, the valve seat 7 is 
located further downstream, allowing a greater amount of lift L to be 
established, whereas the insertion of a thinner lift amount adjusting shim 
14 allows a smaller amount of lift L to be established. 
The dimensions of the valve housing 3, needle valve 10, and the like are 
thus determined, a lift amount adjusting shim 14 is selected for use to 
allow the prescribed amount of lift L to be obtained, and the leading end 
portion of the tubular tip portion 4A is crimped, so that the lift amount 
adjusting shim 14, valve seat 7, steel plate 11, and holding plate 15 are 
fixed to the tubular tip portion 4A. 
The amount of lift L in such an electromagnetic fuel injection valve 1, 
however, usually requires extremely high dimensional precision of, say, 
50.+-.5 .mu.m. In the conventional electromagnetic fuel injection valve 1 
described above, a large number of parts are connected with the amount of 
lift L, and since the crimped part 22 is formed after the selection of the 
lift amount adjusting shim 14 used to determine the final amount of lift 
L, there is a possibility that the very act of crimping results in the 
deformation of the various parts in the tubular tip portion 4A, with many 
problems arising in accurately establishing the amount of lift L. 
During the manufacturing process, moreover, the problem of loose parts in 
the tubular tip portion 4A makes it difficult to avoid the problems in 
precision described above because the portion is invariably crimped 
firmly, so that the amount of lift L cannot be adjusted after the 
crimping. 
FIG. 6 is a vertical cross section illustrating an example of another 
conventional electromagnetic fuel injection valve 30. The same parts are 
indicated by the same symbols, and their description is thus omitted. Only 
the different parts are described. In this electromagnetic fuel injection 
valve 30, a ball valve 10A which allows a fuel channel to be formed, with 
the surface 5 cut flat, is attached to the tip of the needle valve 10, and 
the ball valve 10A is seated in the seat portion 7A of the valve seat 7. 
A steel plate 31 in the form of a cross-sectional arc, in which a steel 
plate 11 has been bent on the upstream side, is used, the resilience 
resulting from its tension is utilized in bringing it under pressure into 
the tubular tip portion 4A, and two prescribed locations in the peripheral 
portion adjacent to the tubular tip 4A and in the central portion adjacent 
to the valve seat 7 (peripheral weld location 32 and central weld location 
33) are fixed by electronic seal welding such as laser welding. 
The seal welding is done, however, after the steel plate 31 as been fixed 
in a location greater than the prescribed amount of lift L (for example, 
greater than 50 .mu.m). 
A probe M for measuring the amount of lift L is then attached to the 
upstream side of the armature 9, and the steel plate 31 is pushed in, with 
the probe set up in a state allowing the amount of lift L to be measured, 
as a prescribed load is applied from the downstream side to the upstream 
side. The amount of lift L is gradually reduced, and when the prescribed 
amount of lift L has been obtained, the plate is no longer pushed in, so 
as to conclude the establishment of the amount of lift L. 
That is, the load is applied on the steel plate 31 from the downstream side 
to the upstream side, and as the amount of lift L is measured, the steel 
plate 31 is reversibly deformed in establishing and adjusting the 
prescribed amount of lift L. 
In this method for assembling the nozzle assembly (ball valve 10 A, needle 
valve 10, and valve seat 7), the amount of lift L can be adjusted as it is 
directly measured, so the precision of the amount of lift L is greater 
than in the case of the electromagnetic fuel injection valve 1 shown in 
FIG. 5. 
Since, however, the steel plate 31 has a thin plate thickness of 0.2 to 
0.25 mm, it can be used for low pressure fuel injection valves with a fuel 
pressure of about 3 kg/cm.sup.2, but it cannot be used for high pressure 
cylinder injection of fuel in fuel injection valves for cylinder injection 
of gasoline, where the fuel pressure is extremely high at 40 to 100 
kg/cm.sup.2. The high fuel pressure would cause the steel plate 31 to fly 
off in the direction of the engine cylinder 21. 
When the plate thickness of the steel plate 31 is increased to make it 
resistant to such high pressure, greater welding energy is needed to join 
the parts, and the resulting heat leads to the problems of poor roundness 
in the seat portion 7A of the valve seat 7 and poor oil-tightness. 
Problems in conventional electromagnetic fuel injection valves 1 and 30 and 
the like are that they are difficult to make resistant to high pressure 
fuel injection such as in cylinder injection of gasoline and that the 
amount of lift is difficult to adjust and establish with good precision. 
SUMMARY OF THE INVENTION 
With the foregoing in view, it is an object of the present invention to 
provide an electromagnetic fuel injection valve that is suitable for high 
pressure cylinder injection of fuel and that allows the amount of lift to 
be established with high precision, as well as a method for assembling the 
nozzle assembly. 
It is another object of the present invention to provide an electromagnetic 
fuel injection valve that allows the amount of lift to be adjusted and 
established after assembly of the nozzle assembly, as well as a method for 
assembling the nozzle assembly. 
It is yet another object of the present invention to provide an 
electromagnetic fuel injection valve in which the valve seat does not fly 
off in the direction of the engine cylinder in the unlikely event of 
defective welding, as well as a method for assembling the nozzle assembly. 
That is, the present invention is the outcome of attention to the fact that 
a thin-walled skirt portion is formed at the nozzle holder, with the valve 
seat introduced therein under pressure, the fact that the skirt portion 
and valve seat are welded, and the fact that the amount of lift is 
preferably finally established following the welding by applying a load 
from the outside to the nozzle holder to irreversibly deform the nozzle 
holder or valve seat. The first invention is an electromagnetic fuel 
injection valve comprising a valve housing, an electromagnetic coil 
located in the valve housing, an armature responding to the magnetization 
of the electromagnetic coil, a valve seat in which a fuel injection hole 
for fuel has been formed, a nozzle holder for fixing the valve seat, and a 
needle valve allowing fuel to be sprayed from the injection hole when the 
valve seat is lifted from the seat portion along with the armature in 
response to the magnetization of the electromagnetic coil, wherein a 
thin-walled skirt portion is formed in a protruding manner at the nozzle 
holder, the valve seat is introduced under pressure to the skirt portion, 
and the valve seat and nozzle holder are welded and joined at the skirt 
portion. 
A protruding step portion can also be formed along the outer peripheral 
surface of the valve seat, and a stopper portion that can be engaged with 
the protruding step portion can be formed along the inner circumferential 
surface of the nozzle holder. 
The second invention is a method for assembling the nozzle assembly of an 
electromagnetic fuel injection valve having a valve housing, an 
electromagnetic coil located in the valve housing, an armature responding 
to the magnetization of the electromagnetic coil, a valve seat in which a 
fuel injection hole for fuel has been formed, and a needle valve allowing 
fuel to be sprayed from the injection hole when the valve seat is lifted 
from the seat portion along with the armature in response to the 
magnetization of the electromagnetic coil, and a nozzle holder for fixing 
the valve seat by combining the needle valve and the valve seat in the 
form of a nozzle assembly, comprising a pressurized introduction step in 
which the valve seat is introduced under pressure to the thin-walled skirt 
portion formed in a protruding manner at the nozzle holder, and a welding 
step in which the valve seat and the nozzle holder are integrated by being 
welded and joined at the skirt portion. 
A lift amount adjusting step can also be included, wherein a load is 
applied to the outer peripheral portion while the nozzle assembly is 
fixed, so as to adjust the amount of lift for the needle valve. 
In the electromagnetic fuel injection valve and the method for assembling 
the nozzle assembly in the present invention, a thin-walled skirt is 
formed at the nozzle holder, the valve seat is introduced under pressure 
to the skirt portion, and the nozzle holder and the valve seat are then 
welded at the skirt portion, so the valve seat is introduced under 
pressure by estimating the contraction of the nozzle holder and the valve 
seat caused by the welding. The amount of lift can thereby be established. 
The crimped portion formed after the amount of lift has been established 
as in the case of the conventional electromagnetic fuel injection valve 1 
(FIG. 5) is not needed thus allowing problems of deviation in the amount 
of lift from the established value to be avoided. 
The precision of the amount of lift can be enhanced when the amount of lift 
is finally established by applying a load from the outside of the nozzle 
holder to irreversibly deform the nozzle holder after the nozzle holder 
and the valve seat have been welded. 
A thin-walled skirt portion can also be formed at the tip of the nozzle 
holder, and the parts can be welded and joined at the skirt portion, so 
that, unlike the conventional electromagnetic fuel injection valve 30 
(FIG. 6), no steel plate 31 is used, allowing the device to be adapted for 
high pressure fuel injection and allowing the thermal effects on the valve 
seat to be greatly reduced. 
When a stopper portion that can be engaged with the protruding step portion 
formed along the outer peripheral surface of the valve seat is formed 
along the inner circumferential surface of the nozzle holder, the valve 
seat can be prevented from separating from the nozzle holder and flying 
off in the direction of the engine cylinder in the unlikely event of a 
defective welding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An electromagnetic fuel injection valve 40 in a preferred embodiment of the 
present invention and a method for assembling the nozzle assembly are 
described next with reference to FIGS. 1 through 3. Parts which are the 
same as those in FIGS. 5 and 6 are indicated by the same symbols, and 
their description is thus omitted. 
FIG. 1 is a vertical cross section of an electromagnetic fuel injection 
valve 40, and FIG. 2 is an enlarged vertical cross section view in 
particular of the parts of the valve seat 7 and the needle valve 10 of the 
electromagnetic fuel injection valve 40. The electromagnetic fuel 
injection valve 40 has a flat plate-shaped armature 41 corresponding to 
the armature 9 described above, and the needle valve 10 can be moved 
integrally with the armature 41. 
A communication hole 42 connecting the second fuel channel 17 and the third 
fuel channel 18 is formed in the needle valve 10. 
A method for assembling the needle valve 10 and the valve seat 7 in the 
form of a nozzle assembly 43 in the nozzle holder 4 is described below 
along with the structure. 
As shown in the enlargement in FIG. 2 in particular, a thin-walled skirt 
portion 44 is formed in a protruding manner from the valve seat 7 at the 
tip of the nozzle holder 4. 
The skirt portion 44 has sufficient axial resistance against the fuel 
pressure and the combustion pressure from the engine cylinder 21, and it 
is formed with walls thin enough to allow for electronic seal welding such 
as laser welding, while it is long enough to fix the valve seat 7. 
A welding groove 45 is formed around an outer periphery at a prescribed 
location in the skirt portion 44. 
The nozzle assembly 43 is inserted into the skirt portion 44 while the 
needle valve 10 is inserted in the valve seat 7, so as to introduce the 
valve seat 7 under pressure (pressurized introduction step). 
A protruding step portion 46 is formed along the upper outer peripheral 
surface of the valve seat 7, a stopper portion 47 that can be formed with 
the protruding step portion 46 is formed along the inner circumferential 
surface of the nozzle holder 4, and an adjusting stroke S portion of a 
prescribed length is left in the stopper portion 47 to allow an amount of 
lift L slightly greater (60 .mu., for example) than the prescribed amount 
of lift L (50 .mu.m, for example) to be maintained in the pressurized 
introduction step described above, 
In this state, laser welding is effected in the welding groove 45 to form 
laser welded parts 48, and the nozzle holder 4 and the valve seat 7 are 
integrated at the skirt portion 44 (welding step). 
Since, however, the amount of lift L shrinks because of the contraction of 
the skirt portion 44 and the valve seat 7 due to welding holes following 
heat radiation during the welding operations, an excess amount of lift L 
is set during the pressurized introduction step, as described above, by 
estimating the welding deformation. 
The welding deformation is thus estimated, and the pressurized introduction 
step and welding step are carried out, allowing the prescribed amount of 
lift L to be obtained. 
In general, however, because of the possibility of the contraction of the 
skirt portion 44 and valve seat 7 resulting in an amount of lift L that is 
shorter than prescribed (20 to 40.mu.m, for example, with respect to the 
prescribed 50 .mu.m amount of lift), the following step for adjusting the 
amount of lift based on compression operations should be carried out. 
That is, a compression load is applied to an outer peripheral compression 
portion 49 on the upstream side from the skirt portion 44 of the nozzle 
holder 4, with the aforementioned probe M attached to the top of the 
needle valve 10 to measure the amount of lift L (compression step or lift 
amount adjusting step). 
Specifically, these compression operations can be selected from operations 
in which a number of prescribed locations in the outer peripheral 
compression portion 49 are pressed, operations in which pressure is 
applied in the circumferential direction around the outer peripheral 
compression portion 49, and the like. 
Because the nozzle holder 4 can be made of SUS 304 and the valve seat 7 can 
be made of SUS 440 or the like, they can be irreversibly deformed by such 
compression operations. 
These compression operations allow the amount of lift L to be increased 
since the nozzle holder 4 is axially extended and thus irreversibly 
deformed, so that the amount of lift L can be adjusted and set to the 
prescribed value, and the final amount of lift L can be established with 
good precision after the valve seat 7 has been fixed to the nozzle holder 
4. 
A swell-absorbing outer peripheral groove 50 can be formed on the 
downstream side of the outer peripheral compression portion 49 to prevent 
swelling from being produced by the compression operations in the seal 
surface 51 of the nozzle holder 4. 
In other words, a seal ring 54 can be provided between the seal surface 53 
of the engine cylinder block 52 and the seal surface 51 of the nozzle 
holder 4 to seal off combustion gas from the engine cylinder 21. Since a 
defective seal resulting from irregularities caused by swelling on the 
seal surface 51 can be avoided, leakage of combustion gas from the engine 
cylinder 21 can be reliably prevented. 
As shown in the partial enlargement in FIG. 2, moreover, a prescribed 
number of expansion-preventing grooves 55 were formed in the plane of 
contact between the nozzle holder 4 and the valve seat 7, so that with 
these compression operations, part of the nozzle holder 4 can penetrate 
into the expansion-preventing grooves 55, and the deformation portions in 
the nozzle holder 4 from the compression operations can be absorbed with 
the outer peripheral groove 50. 
In the unlikely event that the laser welded parts 48 in the welding groove 
45 are broken, the protruding step portion 46 and the stopper portion 47 
can be engaged. Thus, even when the laser welded parts 48 are broken by 
high pressure fuel in the third fuel channel 18 through the fifth fuel 
channel 20, or for some other reason, resulting in the detachment of the 
nozzle assembly 43, the valve seat 7 is engaged and stopped by the stopper 
portion 47, and accidents in which the nozzle assembly 43 flies off into 
the engine cylinder 21 can be prevented. 
As an alternative to the compression step in which the outer peripheral 
compression member 49 is compressed in the present invention, a tensile 
external force can be allowed to act on a downstream side step portion 57 
of the swell-absorbing outer peripheral groove 50 and an upstream side 
step portion 56 of the outer peripheral compression portion 49 to pull the 
nozzle holder 4 in the axial direction as a lift amount adjusting step. 
FIG. 4 is a vertical cross section illustrating an electromagnetic fuel 
injection valve 60 as a reference example, depicting the disadvantages of 
not forming the skirt portion 44 in the present invention. In this 
electromagnetic fuel injection valve 60, no skirt portion 44 is formed as 
in the electromagnetic fuel injection valve 40 shown in FIG. 1. As a 
result, a seal weld can be done only at the outermost tip of the nozzle 
holder 4. 
That is, during seal welding, the nozzle holder 4 and the valve seat 7 must 
be brought into close contact by being introduced under pressure to the 
welding parts, but when they are introduced with the structure shown in 
FIG. 4, the valve seat 7 is inwardly deformed in the nozzle holder 4, and 
the needle valve 10 cannot slide. 
The welding must thus be done with a loose fit between the nozzle holder 4 
and the valve seat 7. As a result, welding is done only in the welding 
parts 61 of the outermost tip of the nozzle holder 4. 
The external load on the valve seat 7 is thus applied only to the welding 
parts 61, resulting in the problem of extremely weak mechanical strength. 
Pressurized introduction operations to a thin-walled portion such as the 
skirt portion 44 in the nozzle holder 4 and welding operations should be 
implemented as shown in FIGS. 1 and 2. 
As described above, the present invention involves forming a skirt portion 
on a nozzle holder and introducing the nozzle assembly under pressure for 
welding. As such, it can be adapted to fuel injection in high pressure 
cylinders, and the amount of lift can be adjusted and set with the 
prescribed precision. 
Additionally, a load can be applied to the outer peripheral portion of the 
nozzle holder by means of compression, tension, or the like to the 
external compression portion of the nozzle holder, so that the nozzle 
holder can be extended and the precision of the amount of lift can be 
further enhanced.