CA1121237A - Electromagnetic fuel injector - Google Patents

Abstract

ABSTRACT
ELECTROMAGNETIC FUEL INJECTOR

A high flow rate electromagnetic injector valve with a rapid response time is disclosed for utilization in a single point fuel injection system. Centrally bored end caps are fixed at the front and rear ends of a tubular injector body and a coil wound on a bobbin is disposed inside the body chamber between the end caps. The front end cap receives within its bore a valve assembly including a valve housing and a needle valve with attached armature reciprocally movable against a valve seat to obturate a metering orifice in the valve housing. The valve housing contains fuel inlets for the pressurized entry of fuel into the injector and the needle valve is ported to provide fluid communication to the armature to relieve pressure build-up. The rear end cap threadedly mounts within its bore a core member acting as a stator which extends through a central bobbin bore to form a controllable air gap adjacent the armature, and further contains internally an adjustment screw and ball member.
The ball member and adjustment screw cooperate with a recessed closure spring positioned substantially within the armature to controllably bias the needle valve against the valve seat. Because of its recessed position, the force of the closure spring is applied substantially along the central axis of the injector valve and the ball member prevents tortional windup forces from being generated by the spring. O-ring seals for the bobbin bore are provided in compression between recesses in the bobbin and the slower contracting material of the front end cap and core member to produce extended cold temperature operation.

Description

3'7 The invention pertains generally to electromagnetic injector valves and is more particularly directed to a fast-acting~high-flow rate single point injector valve.
This is a division of applicant's copending Canadian Patent Application Serial Mo. 328,901 r filed June 1, 1979.
Electromagnetic fuel injection valves are gaining wide acceptance in the fuel meteri~g art for both multi-point and single point systems where an electronic control system-produces a pulse width signal representative of the quantity of fuel to be metered to an lnternal combustion engine. These injectors operate to open fuel metering orifices leading to the air ingestion paths of the engine by means of a solenoid actuated armature responding to the electronic signal. Because of recent advances, these injectors are becoming very precise in their metering qualities and very fast in their operation. With these àdvantages, the electromagnetic fuel injector valve will continue to assist the advances in electronic fuel metering which improve economy, reduce emissions, and aid drivability of the internal combustion engine. ~-The electromagnetic injector valve lS, however, relatively expensive to manufacture because of a precision metering portion which must be carefully coupled to a magnetic motor circuit and, thereafter, to an electrical control while being contained in a single injector body. A11 of these sections must cooperate properly for the valve to provide maximum performance and should be contained in the minimum ~` space. It is important in single point metering applications ~ ~
where the injec-tor is mounted above the throttle plate that the ~ -~" injector package not block air flow into the air in~estion bore.

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The injector body manufacture has l)e~n one con~
tributor to the expense oE manu~ac~llring an injector valve. Generally, the injector body is rnanufactured from a cylindrical metal blank by a plurality of automatic S machinin~ operations. The most common c4nf;yuration is a plurality o differently stepped or diametered bores which are machined to close tolerances and which form shoulders at the steps with the bores coaxial to each other. Such an -injector body is illustrated in a U.S. Patent 3,967,597 issued to Schlagmuller. The close tolerance or the depth of ~he bores in relationship-to the others are used to locate other portions of the injector, such as the valve closure portion precisely with respect to the moving section of the valve ~ich contains the armature and stator.
` Usually, all the bores are coaxial because the fluid flow path is centraily located through the valve and the :-needle valve is biased against a conical seat and should - have an equal peripheral sealing pressue around the seat.
The precision of the depth of the multiple s-tep bores, their coaxial relationship, and their number generally requires that the in]ector body has to be chucked or remounted more than once during the machi~ing operation which adds expense to the manufacturing costs. An injector that could be manufactured from parts requirillg on]y a sinyle machining operation or by eliminating alto~ether a part requiring multiple machinin~ ope~ations w~uld be desirable.
The static and dynamic fuel flow characteris~ics are important to the operation of the injector valve and are `~ controlled by a number of dif~ere~t parameters. In an electromaynetic valve, to provide a fast acting valve with a stable dyllamic fuel flow, the opening and closing times must be minimized but kept relatively certain and reprod~lcible. One factor directly influencilly tlle openin~

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and closing times oE the injector is the closure force that the valve spring applies to the needle valve. The P
amount o~ spring pressure is linearly related to the amount the spring is compressed, or F = Kx where x is the 5 compression dis~ance. The higher the closure force, the slower the opening time o~ the valve will be, and, conversely, the faster the valve will close.
Another interrelated factor is the distance through which the magnetic force acts upon the armature, and thus, lO the amount oÇ travel the needle valve takes from the valve seat, or, as it is comrnonly called, the liEt o~ the valve.
The longer the lift or the greater the ai~ gap, the slower the valve will open. ~t the other extreme, there is a minimum air gap that shoul~ be maintained to allow the v 15 collapse of the magnetic field when the in jector is deenergized. IE the minimu1n gap is not maintained during operation, the armature will tend to stck to the stator, and thus, affect the closincJ time of the valve.
In many prior art valves the lift is designed to be 20 greater than that which would restrict static fuel flow. ~;
Therefore, the size of the metering orifice is designed to be the only controlling factor of flow rate when the valve is open. This is not an optimal design because the lift is greater thàn necessaey thereby afecting the openinq~time r 25 of the valve, and a valuable control parameter for regulating the static ~low rate has not been utilized.
In the Schlagmuller reFerence, the lift of the prior art valve is controlled by a spacer collar abutting a precisely machined spacer washer of a fixed thickness and 3~ the spring p~essure force is adjusted upon assembly o~ the ~`
valve by axial movement of the core member which is then ~inned to fix the pressure. In this valve the lift is structura3ly set and subsequently the spring pressure adjusted and ixed during assembly to a set value. The 35 li~t is such that static ~uel ~lo~ is control]ed onl~ by ~ ~ .

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tlle size of the meterincJ orifice. These valves which have a static fuel flo~ out of tolerance must be disassembled and their metering orifices rebored.
I~ would be highly desirably, since the two factors 5 of lift and closure ~orce are very much related to static fuel meterincJ and the speed of valve operation, if they could be independently adjusted so as to complement each other. Further, it would be advantageous to adjust these characteristics of the electromagnetic injector valve after assembly to precisely tailor each valve characteristic.
~ nother problem that has afÇected the speed of operation and reproducible opening and closing times of the electromagnetic injector valve has been the eccentric loads from the closure spring wh2reby the needle valve has a component or plurality of force components applied to it not acting coaxially to the spray axis. This causes wear on the bearing surfaces whicil hold the needle coaxial with the spray axis and frictional spots where the valve hesitates as it moves within the valve hQusing. The long moment arm through which the closure spring acts is primarily responsible for the eccentric loads The closure force is usually applied to the armature at the point on the needle valve farthest from the valve seat which acts as a fulcrum. Any axial ofset force is magnified by the moment arm and must be absorbed ~nd - balanced by the needle valve beaeing surfaces.
~ ortional or windup pressures on the closure spring will also produce a change in the force providecl against ~i 30 the needle valve. If possible, while adiusting the sprin~
~ressure, winding the spring or providing a tortional component to the closure force should be avoided and only ~ substantially coaxial compression should be applied to the `~ closure spring.

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Another problem that has occured in single point electromagnetic injector valves with fuel inlets located substantially at the valve end is that fuel will be drawn up the guide bore of the armature and into the air gap between the core member and the armature when movement between them occurs. As the guide bore and armature form a relatively small clearance so as to maintain the needle coaxial, fuel that finds its way into the air gap will build up pressure due to the pumping action of the armature against the core. This phenomenon of increasing hydraulic pressure at the interface of the movement ;;;
will cause a slowing in the opening time of the valve. In this ~, type of single point injector it would be highly desirable to provide a means to relieve this pressure so as not to create any detrimental affects on the dynamic operation of the valve.
According to the present invention there is provided an electromagnetic fuel injector valve having a valve assembly -including a valve housing, a needle valve reciprocal in a central bore of the valve housing, a valve seat and a meterlny orifice, the needle valve obturating the metering orifice by its closure against the valve seat. An armature is attached to the needle .
valve adjacent a core member of an electrically actuatable stator means, the armature being attracted to the core member to open the valve when the stator means is actuated. A spring member is disposed between the core member and the armature in compression to apply a closure force against the needle valve to `
close the valve. The core member includes means for adjusting the compression of the spring member includiny an adjustment screw threaded into a bore coaxial with the spriny member such that turning the adjustment screw will cause axial movement -tm~

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along the bore and change the compression on the s~ring member.
The adjusting means further includes a member located between -the adjusting screw and the spring ~ember to alleviate any torsional force component from being applied to the s~ring member.
In a specific embodiment of the invention the member located between the adjustment screw and the spring member is a spherical ball member.
These and other features, advantages and aspects : of the invention will be more fully understood and better 10explained if a reading of the detailed description is under- `
taken in conjunction with the appended drawings wherein:
BRIEF DESCRIPTION OF ~E DRAWINGS
FIGURE 1 is a partially sectioned side view of a single point injection s~stem with a high flo~ rate fast-acting electromagnetic injector valve constructed in accord-ance with the invention;
FIGURE 2 is a cross-sectional side view of~the electromagnetic injector valve illustrated in Figure l;
FIGURE 3, which appears on the same sheet of drawin,gs as Figure 1, is a cross-sectional end view of the injector valve housing of the injector illus~rated in Figure 2 wllich is taken along section line 3-3 of that figure;
~` FIGURE 4 is a graphical illustration of the static ~' fuel flow of the valve illustrated in Figure 2 as a function of the lift of the valve needle; and ~ FIGURE 5 is a graphical illustration of the dynamic ; fuel flow of the valve illustrated in Figure 2 as a function of the injection signal duration.

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LETAILED DESCRIPTION OF THE PREFERR~D EMBODIMENT
With reference now to Figure 1, there is shcwn a single point injection system for metering fuel to an internal combustion engine. The system comprises an electromagnetic injector valve 10 which is electrically connected by a set of conductors 14,16, of a connector 12 to a control unit 18. A number of engine operating parameters are input to the control unit 18 including the speed or RPM at which the engine is turning, the absolute pressure of the intake manifold (M~P), the temperature of the air ingested, and the engine coolant temperature by means of conventional sensors.
The injector 10 fits within an injector fuel jacket 22 centrally located in a single air induction bore 34 of a throttle body 25 communicating with an intake manifold 42 of the internal combustion engine. For throttle bodies with multiple air induction bores, an ~` injector per bore can be utilized. Air flow for engine ingestion is regulated by a throttle plate 30 which is rotatably mounted below the injector jacket 22. Upon the sensing of the operating conditions of the engine, the control unit will provide pulse width electronic injection signals to the connector 12 representative of fuel quantity desired for injection whereby the injector 10 will open and close relative to the leading and trailing edges of the signal to meter fuel ~rQm the injector jacket 22. The fuel is metered in a wide spray angle pattern for optimum mixture with the incGming air and delivery into the intake manifold.
Euel under pressure is delivered to the injector jacket 22 ;~
by a fuel inlet 20 and is circulated through the interior of the injector jacket and thereafter to an exit passage 24 where a pressure regulator 40 m~intains the systemic pressure constant. Spent fuel i5 returned to a .

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reservoir, s~ch as a fuel tank, where it can be then pumped ~nder pressure to the jacket 22 once more. The injector is sealed in the jacket by suitable resilient means, such as an O-ring 28 at the bottom end of the 5 jacket, and an O-ring 26 resting against a shoulder at the - top end of the jacket. The injector 10 is held in position by a spring clip 36 ~ixed by a screw 38O
Such a single point fuel injection system as sho~n is particularly adaptabl~ to run a 2.2 liter engine having 10 four cylinders. By injecting twice every revolution or 180 an air/~uel charge per eacl- cylinder iring is delivered. The injection is preferably made at some set L
angle relative to an engine event, such as just prior to top dead center ITDC) of the numbe~ 1 cylinder on the 15 intake stroke, and thereafter cyclicly related to that point. The injection ti-ning of firing just before the opening of a particular intake valve allows much of the fuel and air charge to be transported to the particular - r~
cylinder injected. This reduces condensation and helps 20 eliminate cylinder-to-cylinder distribution errors.
- To inject a system as that described above, an injector with a high sin~le point fuel rate of 400-600 cm3/min. and ~Jith a dynamic characteristic linear into the one ~illisec range is needed. The invention provide.s such 25 an electromagnetic injector valve 10 with an advantageous construction.
With reference now to Fi~ures 2 and 3, the high flow injector valve 10 is shown in cross-se~tion to advantage and comprises a tubular injector body 100 ~hich may be 30 constructed from seamed or unseamed tubin~ which has been ~-cut to length. The injector body 100 is cold-formed at each end to form a shouldei lOl wittl a radially offset rim portion 102 at the ~ront end and a shouldcr 103 with another radially ofEset rim ~ortion 104 at the rear end.
35 As the tubular body 100 is pclL-t 0~ the Inagnetic circuit o~
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the injector, the matecial used i.s preferably standard low carbon steel mechanical tubing. This material provides excellent mechanical strength and exhibits high permeability. The body 100, as well as all other outside 5 surfaces of the injector valve 10, can be treated by conventional methods for corrosion resistance and environmental hazards. ..
A front end cap 106 has a centrally bored cylindrical p~
body that is flanged to abut against the shoulder 101 and - -is fixed in position by crimping or swaginy the rim lD2 against a bevel 108 machined on the flange. Similarly, a rcar end cap 110 compris;ng a centrally bored cylindrical body is flanged and abuts the shoulder 103 and is affixed -~
thereat by deforming rim 104 to mate ~ith a bevel 112 ~ p~-;
15 machined in the flange of the cap.
Within the chamber defined by the inner ~lall of the injector body 100 and the inwardly facing surfaces of the front end cap 106 and rear end cap 110~ is a generally elongated molded bobbin 1~9 ~ound with a pl~rality of 20 turns of magnet wire forming a coil 116. The coil 116 is F~
electrically connected to a set of terminal pins 120 (only ~` one shown) which rearwardly exit throu~h an oval shaped aperture 122 in the rear end cap 110 and are protected by a ~`
connector 118 integrally molded as part of the bobbin 114. ~.
2S The bobbin 114 has a centrally located longitudinal bobbin bore 12~ ~Ihich is silbstantially coaxial with a `
th~eaded rear end cap bore 126. A rod~shaped core ~nember 128 of a soft magnetic material is screwed into the threads of the end cap bore 126 and extends substantially 30 the length of the bobbin bore. The core member 128 is slotted at its tllreaded end 130 to provide for adjustment of its extension in the bobbin bore 124. The adjustment of the core me~ber determines the air g~p distance and the lift of the valve. An adjustment scre~ 132 i6 threaded - 35 into an internal bore of the core member 17~ to provide , ,~r.
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adjustment of the valve closure force by means of a pin 140 moving against a spherical ball member 136. The internal bore of the core member 128 is sealed by an O-ring 138 slipped over the pin 140 and sealing against the inner surface of the bore.
The bobbin bore 124 is hydraulically sealed at the internal face of the rear end cap 110 by an O-ring 139 and sealed at the front end cap 106 by an O-ring 141. These sealing means are under compression, at normal ambient temp-eratures~(65 F.), between two mater~als with differing thermal expansion and contraction rates. O-ring 139 is compressed in an annular space formed by the outside cylindrical surface of the core member 128 and the inside cylindrical surface of a recessed '` area 127 of the bobbin 114. O-ring 141 is compressed in a , similar annular area formed by the outside cylindrical surface of a rearward extension of the body of the front end cap 106 and the inside cylindrical surface of a recessed area 143 in the bobbin 114. The above-described sealing means is also disclosed and is claimed in applicant's copending Canadian Application Serial No. 328,901.
, The end cap 106 and core member 12~ materials are similar low carbon steels while the bobbin 114 is molded , fro~ a glass fiber reinforced nylon. The inside cylindrical surfaces of the bobbin and the outside cylindrical surfaces ~: of the end cap and core member all contract radially during a decrease in temperature. The bobbin, however, contracts ` more rapidly because of its differing material and increases the - compression at lower temperatures. The incxeasing pressure ap,lied by the more rapidly contracting bobbin will extend the cold temperature range of operation of the valve by compensating for tmt~r~ -10-~ ~ Zl;~;37 the lack of flexibility in the O-ring seals belo~7 -20F.
Located in the central bore 107 of the front end cap 106 is a single step dividing the bore into an armature guide bore 142 and a mounting bore 144. ~ valve housing ; ::

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1~6 is eeceived in the mounting bore 14~ until it abuts ` the internal shoulder 145 formed at the step between the - bores, The valve housing 146 is held in place ~y-benaing the Eront rim of the mounting bore 14~ over, a chamfer in S the valve housing 146. The valve housing 146 has a longitudinal valve housing bore 1~8 which communicates on one end with the arrnature ~uide bore 14?. and at the other end is -terminated with a conical valve seat 150 which ,~ curves into a smooth transitional area 152 to ~inally become a cylindrical metering orifice 154.
'rhe valve housing bore 148 is in fluid communication with fuel in the jackèt 22 by means of a pluralitylof fuel inlets 1~9 spaced around the valve housing 146. The inlets 149 are proximate,to the metering orifice 15q for minimum pressure drop during low pressure operation and ` are protected from contamination by the surrounding mesh ` of a molded filter element 154 slip-fitted onto the valve ,~ - housing.
~"` ' Reciprocal in the valve housing hore 148 is a valve 20 needle 156 which is press~fitted at its distal end into a generally annular-shaped armature 158. The needle valve, - as is further illustrated in cross-section in Figure 3, has a medial section which is triangular in cross-section and at each angular apex forms a curved bearing surface 25 which slides against the valve housing bore 148 to center ehe needle valve within the ~ore.
-The needle valve extends into a valve tip 160 having a sealinq surface 162 which mates with the conical Yalve : ~, seat 150 to close the valve. From the valve tip the needle 30 valve forrn.s a pintle which encls in a deflection cap 164 r'~
which shapes the fuel spray into the hollow-cone or wide angle spray pattern as described hereinabove~ ~rhe F
deflection cap is recessed in the injector housing l~fi for protection.
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The needle valve 156 is substantially ho]low ~rith an inner passage 155 drilled ~rom the valve tip to its valve a end connection at the armature 158. The valve end has a spring recess 147 supporting a closure spring 147 within 5 the centered bore in the armatu~e 15~. The passage 155 cor~nunicates with the valve housinq bore 148 by means o a port 153 cut into each face of the medial section of the valve needle. The passage 155 and centered armature bore thus prov;des pressure relief to an air gap locat~d 10 between the armature and core member to prevent hydraulic forces from increasing there and affecting the openinc~
time of the valve.
The closllre spring is compressed ~y the ball member ~;
136 against the valve needle recess 147 to produce a p 15 closure force on t~e valve needle which can be adjusted by turning adjustment screw 132. Tortional winding forces are not generated du~ing adjustment as the pin 140 will turn on the ball member 136 and cause only axial movement of member. Any tendency on the part of the closure spring 20 to ~rind up will cause slippage against the surface of the p ball member and ~issipation of the tortional force ;
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component.
The closure spring, by being contained in the armature 158 and recessed in the valve end, applies the 25 closure force forward o~ the air gap and reduces the moment arm through which eccentric Eorce components act.
Shorter and narrower bearing surfaces on the medial section of the valve needle can be used to balance the forces. The use of a shorter triangular medial sec~ion 30 with less bearing surface in combination with the hollow valve needle and armature, ~ic3nificantly reduces the mass o~ the moving part of the injector. The reduction of the ~-mass o~ the moving section anc7 the increase in force produced by the enlarc3ement o~ the coil ~ill increase the - 35 opening time oE the valve.
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In operation, when current in the form of an injection siclnal is supplied to the termin2il pins 120 from the connector l~, and thus, to coil 116, a longitudinal mac3netic ~ield is set up through the core member 12B, the rear end cap 110, the injector body lO0, and the front end cap 106 to attract the soft magnetic ~aterial of the ~emature 15B across the air gap to abut a nonmagnetic shim 135 on the face of the core memher. The shim 13S
aids the closing time of the valve by maintain$nq a lO minimum gap during energization. When the magnetic attraction overcomes the force of the closure spring, the valve ~eedle will be lifted away from the valve seat and fuel will be metered by the valve seat interface and metering orifice un~il tlle cu~ent to the terminal pins 15 120 is terminated and the closure spring force seals the -valve once more.
After assembly, the lift and air gap can be adjusted by tùrning core member 128 and the closùre orce adjusted by turning adjustment screw 132. The two 2ldjustrnents will 20 complement each other to calibrate static and dynamic fuel flow and then be set by a sealing component 121, ;~
The static fuel flow adjustment of the valve will now be more fully explained with respect to Figure 4~ The - static fuel flow Q of the injector valve lO is c3raphically 25 illustrated as a function of valve lift L. At small valve lifts in region A, the restriction produced by th~ needle ; valve and valve seat interEace dominates and the static ~u~l flow is independent of the metering orifice size. In tl~is region ~ Qj~ L is a relative constant K related tq ~;
30 the increasing opening area between the inter~ace o~ ~he i~`
needle valve and valve sea~. --In region C where the lift is increased-beyond where ;
tlle valve needle provides a restriction to fuel flow, the ;~
mctering orifice size is the determinincJ actor of the ''' .

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is substantially a Eunction of me~eriny orifice size, but is als~ relatcd to valve li~t. ~ Q/~ L in this region-is much less than K and i~ approachin~ the value of zero found in region C. The change in static fuel ~low for a '' change of lift is related to the ratio of the changing interface area with respect to the metering orifice area.
By adjusting the li~t in this region, a relatively controllable trim can be generated to calibrate the static ~el ~low of an already assembled injector to a specified value.' Generally, it has been found that this method will provide the optimal results lf the range bf trimmin~ is 5%
o~ the static fuel flow rate or ~ .001" cllange in lift.
The adjustment threads on tll~ core member 12~ are suitably '' chosen to provide controllable liEt changes in this region.
~fter the static flow calibration, a dynamic calibra-~o tion 1s undertaken 'to match the closure force to the air gap which was'varied during static calibration and to;~
calibrate the dynarnic response. With respect to Figure 5, the dynamic fuel flow rate as a function o pulse width is ~ strated. The line D, which is dotted, indicates an ideal valve which has a static flow rate (slope) of 600cm3/min.'and whose graphical representation goes through the origin.
The opening and closing times of a real valve are, however, finite and the actual dynarnic characteristic will form a parallel line to the right of the ideal, for ~xample, line E. The less ideal and slower the valve operates, the more to the right of line P the real dynamic line will be. Critical operation at higher engine speeds-requires maximum injection quantity ~hile the time ~"
available for injection is decreasing. ~ligh flow rate . :~

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' ' valves wit~l ste~p dyna,nic slopes are necessary to meet these requirements! but cause very small pulse ~idths to be used for the minimum injection quantities, The closer the valve can be calibrated to ideal with linearity. the 5 more advantageous it will be to the sysem.
~ ith the goals in mind, thc dynamic calibration is ac,complished by picking the mini~um flow rate of the valve at point G which is some safety factor below the minimum quantity injected at idle, or point F. The clos~lre force is then adjusted to minimize the offset of line E ~rom the ideal response at line D.
~ hile the preferrecl embodi~ents o~ the invention have been shown, it will be obvious to those skilled in the art that modifications and ' changes may be made to the 15 disclosed system without departing from the spirit and scope of the invention as defined by the appended claims.
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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electromagnetic fuel injector valve comprising:
a valve assembly including a valve housing, a needle valve reciprocal in a central bore of said valve housing, a valve seat and a metering orifice; said needle valve obturating said metering orifice by its closure against said valve seat;
an armature attached to said needle valve adjacent a core member of an electrically actuatable stator means, said armature being attracted to said core member to open said valve when said stator means is actuated;
a spring member disposed between said core member and said armature in compression to apply a closure force against said needle valve to close said valve;
said core member includes means for adjusting the compression on said spring member including an adjustment screw threaded into a bore coaxial with said spring member such that turning said adjustment screw will cause-axial movement along said bore and change the compression on said spring member;
and said adjusting means further including a member located between said adjustment screw and said spring member to alleviate any torsional force component from being applied to said spring member.

2. An electromagnetic fuel injector valve according to Claim 1 wherein said member located between said adjustment screw and said spring member is a spherical ball member.

3. An electromagnetic fuel injector as defined in Claim 1 wherein:
said valve assembly includes fuel inlet ports communicating fuel under pressure to said central bore of the valve housing; said inlet ports located proximately to said metering orifice; and said valve needle having at least one fuel passage communicating fuel from said central valve housing bore to said armature bore for relieving pressure build up in the space between said core member and said armature.