Fuel injector and method of manufacturing

A fuel injector for an internal combustion engine includes a preassembled permanently mated needle and valve body group contained in a main housing assembly. The valve body group is assembled so that the maximum allowable stroke of the needle is established by a stop abutment, which is permanently attached to the valve body. An injector assembled according to the present method does not require the use of various shims in order to set the air gap. Moreover, precision grinding is not needed to establish the needle lift.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fuel injector for an internal combustion 
engine and to a method for manufacturing such injector. 
2. Disclosure Information 
The manufacturing of fuel injection nozzles for internal combustion engines 
has historically been marked by the use of time consuming and laborious 
grinding, fitting and lapping operations. For example, the needles of fuel 
injectors are typically ground and lapped to fit into the valve bodies of 
the injectors. In some cases, the parts are ground separately and then 
fitted according to their finished sizes. In either event, it is necessary 
that the mated valve body and injector needle be handled as a unit due to 
the lack of interchangeability of parts. 
U.S. Pat. No. 3,468,008 to Barber and U.S. Pat. No. 3,791,591 to Hedges 
disclose fuel injectors having traditional designs in which the needle is 
separable from the valve body. Because both components must be handled as 
a unit, special processing procedures which add to the cost of 
manufacturing must be used. According to the present invention, a fuel 
injector valve unit is assembled by permanently mating a valve needle to a 
valve body by caging the needle to the body in the manner shown herein. 
Because the needle, once caged to the valve body, is permanently attached 
thereto, no special handling is required to assure that the parts do not 
become mismatched after the needle and valve body have been mated. 
A method according to another aspect of the present invention is intended 
to further reduce the cost of producing fuel injectors by eliminating the 
need for lift grinding during the manufacturing of such injectors. Lift 
grinding is a process by which the stroke of the injector is set. Lift 
grinding involves the use of relatively large grinding machines and 
delicate measuring equipment to measure, grind and establish a desired 
distance between a control surface on the valve body and a control surface 
on the valve's needle. Unfortunately, problems abound with this method of 
manufacturing. For example, the large size of the grinding machines 
renders fine tolerances difficult to achieve. This in turn causes 
uncertainties and variabilities in the stroke of the injectors. 
According to conventional techniques, the desired air gap setting between 
the injector's armature and corresponding magnetic pole piece is 
established by measuring the dimensions of actual injector subassemblies 
and by performing calculations using the measured values to determine the 
thickness of a stop plate which functions as a shim to space the valve 
group from either the injector's inlet tube or some other internal 
abutment structure. This stop plate is selected from a group comprising as 
many as five dozen or more different thicknesses. Unfortunately, the 
multiplication of measurement errors plus finite differences in actual and 
nominal stop plate thicknesses results in large air gap variations. Also, 
stop plates in conventional injectors may become cocked or tilted such 
that the surface of the stop plate which contacts the injector needle in 
its fully opened position is not normal to the central axis of the 
injector needle. This condition may lead to wear and inaccurate stroke 
setting of the injector because the stroke can change as the needle wears 
into the stop plate. This is caused by high unit loading of the needle 
into the cocked stop plate. 
The method and structure of the present invention solves all of the 
previously described problems with injector manufacturing. Because lift 
grinding is eliminated, the inaccuracies in stroke setting associated 
therewith are obviated. Because shims of varying thicknesses are not 
necessary with the present injector, the injector air gap may be set to 
the desired value precisely without the associated cumbersome and 
potentially inaccurate procedures associated with the selection of shims 
or spacers of different thickness. Accordingly, it is an object of the 
present invention to provide a method for manufacturing an injector which 
produces superior results in terms of reducing injector stroke and air gap 
variability, ease of manufacturing, and cost of the end item. 
Other objects, features and advantages of the present invention will become 
apparent to those reading this specification. 
SUMMARY OF THE INVENTION 
A fuel injector for an internal combustion engine according to the present 
invention includes a main housing assembly and a preassembled, permanently 
mated needle and valve body group contained within the main housing. The 
needle and valve body group preferably comprises a valve needle caged 
within a generally cylindrical hollow valve body by a stop mechanism which 
establishes the maximum allowable stroke of the needle. The stop mechanism 
may comprise a collar permanently joined to one end of the valve body and 
having a radially inwardly extending shoulder forming an abutment for 
limiting the stroke of the needle. Alternatively, a generally annular 
washer may be permanently joined to an end of the valve body such that the 
maximum allowable stroke of the needle is limited by the washer, which 
serves as a stop abutment. The washer will preferably be telescopically 
nested within the valve body. Regardless of the type of stop abutment 
employed with a valve group according to the present invention, the valve 
body will be a generally cylindrical hollow structure having an orifice 
and seat at one end which cooperates with the needle enclosed in the valve 
body to control the flow of fuel discharged from the injector. 
According to another facet of the present invention, a method for 
constructing a permanently mated needle and valve body group for a fuel 
injector of an internal combustion engine includes the steps of: placing a 
valve needle in a valve body; placing a stop abutment washer or collar 
into or over the valve body such that the washer is resting on a shoulder 
formed on the needle; positioning the needle a predetermined distance from 
its closed position in accord with the maximum stroke of the needle while 
maintaining the washer or collar in flat contact with the needle shoulder; 
and affixing the stop abutment to the valve body so as to both determine 
the maximum stroke of the needle and to prevent the needle from 
disengaging from the valve body. The stop abutment is preferably 
permanently affixed to the valve body. 
Another aspect of the present invention is concerned with a method of 
assembling an electromagnetic fuel injector for an internal combustion 
engine comprising the steps of: preassembling a valve body and injector 
needle into a valve group including a stop abutment and an armature 
attached to the needle; inserting the valve group into the main housing 
assembly of the injector and positioning the valve group such that the 
injector needle is in its maximum stroke position with the armature 
separated from a corresponding magnetic pole piece by a desired air gap 
distance; and fixing the valve body in the main housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1, a fuel injector for an internal combustion engine 
according to the present invention comprises a main housing 10 containing 
an electromagnetic coil 12 for driving the injector. Metering of the fuel 
is controlled by a valve group comprising valve needle 18 and valve body 
20. The position of needle 18 with respect to valve body 20 is controlled 
by means of spring 19 and coil 12, which act upon armature 13. Spring 19 
urges valve needle 18 into the closed position. On the other hand, coil 12 
and armature 13, which cooperate with the lower end of inlet tube 52, urge 
needle 18 into the open position when coil 12 is energized. 
Valve body 20 is contained within lower housing 54 of the injector. One 
aspect of the present invention includes a method for positioning valve 
body 20 within lower housing 54 so that the proper air gap 50 may be 
maintained between the lower end of inlet tube 52 and armature 13 when 
valve needle 18 is in the fully opened position. 
An injector according to the present invention, as shown in FIG. 1, may be 
mounted within the intake manifold of an engine 14, and sealed thereto by 
means of O-ring 16. 
FIGS. 1 and 3 illustrate one type of injector stop abutment according to 
the present invention. Another embodiment is shown in FIGS. 2 and 4. 
As noted above, FIG. 2 illustrates a first preferred embodiment of injector 
stop abutment according to the present invention. As shown in this Figure, 
valve body 20 is a generally cylindrical structure having a cylindrical 
inner surface 22 defining a void for housing valve needle 18, which is 
allowed to stroke within valve body 20 to an extent determined by the 
axial placement of annular washer 40. The annular washer is received 
telescopically within valve body 20. As can readily be determined from 
examination of FIG. 2, once annular washer 40 is welded in place within 
valve body 20, valve needle 18 will be caged permanently within valve body 
20. Those skilled in the art will appreciate in view of this disclosure 
that annular washer 40 could be permanently attached to valve body 20 by 
means of several alternative processes and techniques known to those 
skilled in the art and suggested by this disclosure. 
FIG. 2 illustrates an apparatus and method for constructing an injector 
valve group according to the present invention. Valve needle 18 contains 
thereon a needle seat 26 which cooperates with valve body seat 28 to seal 
the needle and valve body assembly against the flow of fuel at all times 
except when the valve is opened by the axial pulling of armature 13 and 
coil 12. The maximum stroke of the needle is determined by the resting 
distance between the lower face of washer 40 and the upper surface of 
shoulder 38 located upon valve needle 18. 
The apparatus shown schematically in FIG. 2 positions washer 40 with 
respect to valve body 20 to achieve the desired maximum opening distance 
for valve needle 18 in the following manner. First, needle positioning 
fixture 44 is employed for displacing valve needle 18 upwardly the desired 
maximum opening distance, which may typically be on the order of 50 
microns. Those skilled in the art will appreciate in view of this 
disclosure, of course, that valve body 20 must be held rigidly during the 
stroke setting process by a fixture (not shown). Once needle positioning 
fixture 44 has displaced valve needle 18 the desired distance 
corresponding to the maximum opening position or stroke of the needle, 
washer 40 may be welded to valve body 20 to produce weld 36, as 
illustrated in FIG. 2. Note that washer 40 is positioned during the 
welding operation by means of clamp 46 which is loaded axially downward by 
means of spring 48. It will thus be appreciated that the action of clamp 
46 and spring 48 removes all clearance between the bottom of washer 40 and 
the top of shoulder 38, while at the same time maintaining even contact 
between the washer and the shoulder. In this manner, adverse needle wear 
and stroke changes due to stop plate cocking will be eliminated. 
Once washer 40 has been welded to valve body 20, valve needle 18 will be 
permanently caged within valve body 20 and the resulting valve group 
cannot be separated thereafter. This provides an aid to the assembly of 
injectors according to the present invention because once the valve body 
and valve needle are mated, no special handling need be performed in order 
to keep the components from becoming separated. FIG. 4 is a plan view of 
annular washer 40, as well as the injector body and needle, showing with 
particularity the plurality of radially extending notches, 42, formed in 
the washer to allow fuel to flow axially past the washer and into the 
generally annular space formed by valve needle 18 and cylindrical inner 
surface 22. Those skilled in the art will appreciate in view of this 
disclosure that as an alternative to needle positioning fixture 44, which 
pushes upward on needle 18, a fixture could be employed which pulls upward 
upon the needle. 
FIG. 3 illustrates a second valve group according to the present invention. 
In this embodiment, valve needle 18 is retained within valve body 20 by 
means of stop collar 30 which comprises a unitary cylindrical cap 32 
fitted about reduced diameter section 31 of valve body 20 with the 
cylindrical cap being integral with radially extending shoulder 34. Stop 
collar 30 performs the same function with this embodiment as does washer 
40 with the previously illustrated embodiment. Moreover, stop collar 30 is 
installed in a similar fashion by maintaining the stop collar in contact 
with shoulder 38 while valve needle 18 is lifted off valve body seat 28 a 
desired distance so that when welded in place with weld 36, the maximum 
stroke of the needle will be determined and limited by contact of the top 
surface of shoulder 38 with radially extending shoulder 34. 
The embodiments illustrated in FIGS. 2 and 3 are advantageous for several 
reasons. First, as noted above, a lift grinding process is no longer 
necessary to establish the desired needle stroke. In conventional 
processing of injectors having a valve group of the illustrated type, but 
without an integral stop abutment, a grinder is used to remove material 
from the top of the valve body until a measured dimension from the top of 
the valve body to the top of annulus 38 is established. This costly 
process is not necessary with a valve group according to the present 
invention. A second advantage arising from the present invention resides 
in the fact that conventional injectors use a stop plate which is inserted 
into the housing of the injector during the final assembly of the unit. 
The stop plate is sandwiched between valve body 20 and a mating surface in 
the injector housing so that the stop plate assumes the function of stop 
collar 30 or washer 40 of the present invention. Unfortunately, as noted 
above, prior art stop plates may on occasion become cocked or twisted in 
the injector body so that the valve needle will not contact the stop plate 
about the full circumference of shoulder 38. Rather, the needle in such a 
situation will contact the stop plate only at a very small area. As a 
result, valve needle 18 may be subject to bouncing, and also the stroke of 
the valve needle will change as the needle and stop plate wear into each 
other. If this should happen, the injector will deliver too much fuel. A 
valve group according to the present invention will obviate this 
difficulty by providing a stop abutment which contacts the upper surface 
of shoulder 38 in a continuous manner without the danger of cocking or 
twisting of the stop abutment. 
The present invention yields yet another benefit during the manufacturing 
process inasmuch as the integral stop abutments illustrated in FIGS. 2 and 
3 obviate the need for a fitting process in connection with the provision 
of the previously described prior art stop plates. Because prior art stop 
plates are used not only to retain the needle but also to establish the 
air gap between armature 13 and the lowest surface of inlet tube 52, known 
processes require the provision of dozens of various thicknesses of stop 
plates from which an appropriate thickness may be selected to achieve the 
desired air gap. 
The manner in which the need for various thicknesses of stop plates is 
eliminated is illustrated in FIG. 5. According to this aspect of the 
present invention, a valve group comprising needle 18 and valve body 20 is 
secured within lower housing 54 in the following manner. First, ram 62 is 
employed for bringing armature 13 into contact with lower annular surface 
52a of inlet tube 52, which comprises the magnetic pole piece 
corresponding to the armature. Thereafter, while upward pressure is 
maintained by ram 62 on needle 18, chuck 60 moves valve body 20 and needle 
18 in a downward direction as shown in FIG. 5 to bring armature 13 the 
specified air gap distance--say 50 microns--away from the lower annular 
surface of inlet tube 52. This distance may be measured by means of probe 
64 or by other methods known to those skilled in the art and suggested by 
this disclosure. When the correct distance has been established between 
the armature and inlet tube, the valve body will be attached to lower 
housing 54 by means of weld 37. 
As an alternative to the previously described method for mounting the valve 
group within the injector housing, a clamp and spring apparatus (not 
shown) similar to clamp 46 and spring 48 may be employed to urge valve 
body 20, containing a fully closed needle 18, upwardly until armature 13 
is in contact with the lower annular surface 52a of inlet tube 52. Then, 
probe 64 will displace the entire valve group downwardly until a desired 
distance has been established between armature 13 and annular surface 52a. 
This distance will generally correspond to the sum of the desired air gap 
at the full open needle position plus the maximum needle stroke distance. 
At such time as the valve group is properly positioned, the valve body is 
welded to the injector housing. Using either of the previously described 
methods, the valve body is attached within the lower housing without the 
need for any shims of varying thicknesses or, indeed, any shims 
whatsoever. Accordingly, an injector according to the present invention is 
ideally suited for ease of manufacturing. 
Those skilled in the art will appreciate in view of this disclosure that 
various changes and modifications may be made to the fuel system 
componentry and methods described herein without departing from the scope 
of the invention a defined by the appended claims.