CA1119065A

CA1119065A - Electromagnetic fuel injector

Info

Publication number: CA1119065A
Application number: CA000328901A
Authority: CA
Inventors: William B. Claxton
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1978-11-01
Filing date: 1979-06-01
Publication date: 1982-03-02
Also published as: JPH0135175B2; JPS5566657A; FR2440476A1; FR2440476B1; IT1207281B; GB2034403B; DE2942853A1; GB2034403A; IT7926864A0

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

FIELD OF 'I'IIE INVENTI()N
.

The invention pertains generally to electromagnetic injector valves and is more particularly directed to a fast-acting high-flow rate single point injector valve.

S BACKGROUND OF THE INVENTION r Electromagnetic fuel injection valves are gaining wide acceptance in the fuel metering art for both multi-point and single point systems where an electronic control system produ~:~s a pulse width signal representative of the 10 quantity of fuel to be metered to an internal 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 15 injectors are becomming very precise in their metering qualities and very fast in their operation. I~ith these advantages, the electromagnetic fuel injector valve will continue to assist the advances in electronic fuel metering which improve economy, reduce emissions, and aid 20 drivability of the internal combustion engine.
The electromagnetic injector valve is, however, relatively expen~ive to manufacture because of a precision metering portion which must be carefully coupled to a magnetic motor circuit and, thereafter, to an electrical 25 control while being contained in a single injector body.
All of these sections must cooperate properly for the r valve to provide maximum performance and should be contained in the minimum space. It is important in single r point metering applications where the injector is mounted 30 above the throttle plate that the injector package not block air flow into the air ingestion bore.

~11906S

The injector body manufacture has been one con-tributor to the expense of manufacturing an injector valve. Generally, the injector body is manu~actured from a cylindrical metal blank by a plurality of automatic 5 machining opeeations. The most common configuration is a plurality of differently stepped or diametered bores which r 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 10 issued to Schlaymuller. The close tolerance or the depth o~ the 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 which contains the armature and 15 stator.
lJsually, all the bores are coaxial because the fluid flow path is centrally located through the valve and the needle valve is biased against a conical seat and should '~
have an equal peripheral sealing pressure around the seat.
20 The precision of the depth of the multiple step bores, their coaxial relationship, and their number generally requires that the injector body has to be chucked or remounted more than once during the machining operation which adds expense to the manufacturing costs. An 25 injector that could be manu~actured from parts requiring only a single machining operation or by eliminating altogether a part requiring multiple machining operations would be desirable.
The static and dynamic fuel flow characteristics are 30 important to the operation o~ the injector valve and are controlled by a number of dif~erent parameters. In an electromagnetic valve, to provide a fast acting valve with a stable dynamic fuel flow, the opening and closing times must be minimized but kept relatively certain and 35 reproducible. One factor directly influencing the opening and closing times oE the injector is the closure force that the valve spring applies to the needle valve. The amount oE spring pressure is linearly related to the amount the spring is compressed, or F = Kx where x is the compression distance. 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, 10 the amount of travel the needle valve takes from the valve seat, or, as it is commonly called, the lift of the valve.
The longer the lift or the greater the air gap, the slower the valve will open. At the other extreme, there is a minimum air gap that should be maintained to allow the 15 collapse of the magnetic field when the injector is deenergized. IE the minimum gap is not maintained during operation, the armature will tend to stick to the stator, and thus, affect the closing 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 than necessary thereby affecting the opening time r 25 of the valve, and a valuable control parameter for regulating the static flow 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 30 the spring pressure force is adjusted upon assembly of the valve by axial movement of the core member which is then pinned to fix the pressure. In this valve the lift is structurally set and subsequently the spring pressure adjusted and fixed during assembly to a set value. The 35 lift is such that static fuel flow is controlled only by F

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the size of the metering orifice. These valves which have a static fuel flow out o~ tolerance must be disassembled and their metering orifices rebored.
It would be highly desirably, since the two factors 5 of lift and closure force are very much related to static fuel metering 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 o~ the electromagnetic injector valve 10 after assembly to precisely tailor each valve characteristic.
Another problem that has afected the speed of operation and reproducible opening and closing times of the electromagnetic injector valve has been the eccent~ic ~~
15 loads from the closure spring whereby the needle valve has a component or plurality o~ force components applied to it not acting coaxially to the spray axis. This causes wear on the bearing surfaces which hold the needle coaxial with the spray axis and frictional spots where the valve 20 hesitates as it moves within the valve housing. The long c moment arm through which the çlosure spring acts is y~
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 25 which acts as a fulcrum. Any axial offset force is magnified by the moment arm and must be absorbed and balanced by the needle valve bearing surfaces.
Tortional or windup pressures on the closure spring will also produce a change in the force provided against 30 the needle valve. If possible, while adjusting the spring pressure, 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.

, . .. _ .. .. ...

1'1 19(~6~

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 1~ 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 desirably to provide a means to relieve this pressure so as not to create any detrimental affects on the dynamic operation of the valve.
As the electromagnetic fuel injector is accepted in wide-spread use, there will have to be an extension of the environmental temperature range over which it is operational. One present limitation of prior art valves has been their cold temperature operation because of the sealing properties of the O-rings contained therein.
Generally, these O-rings are elastomeric rings of rubber or like material which remain substantially flexible at normal ambient temperatures or increased temperatures.
They seal relatively well between the dissimilar materials of the injector body and the bobbin which expand and contract at different volumetric rates. However, at colder temperatures, especially in the ranges beyond -20 F, they start to become inflexible and fairly brittle. At this point the dissimilar contraction rates between the bobbin and injector body will cause a separa-tion between the O-ring and its interface and consequent leakage of pressurized fuel. It would be advantageous to provide an injector with an extended cold temperature range whereby the O-ring sealing structure could be extended in operation to approximately -40 F.

, 1119~6S

According to the present invention there is provided an electromagnetic fuel injector which has a valve assembly for receiving pressurized fuel including a valve housing and a valve memher having an armature portion, the valve member being movable in the valve housing from a closed position to an open position in order to meter fuel from the valve housing. An injector further has an injector body in fluid communication with the valve assemhly and an elec~rically energizable stator means, contained within the injector hody, for movin~ the valve memher to one of the positions by magnetically attracting the armature portion.
Means i5 provided for moving the valve member to the other of the positions when the stator means is not energiæed.
The stator means includes a coil wound on a bobbin wherein the bobbin has a different rate of thermal volume change than the injector body. Means is provided for sealing the pressurized fuel within the injector body including resilient means compressed in at least two places between a portion of the bobbin and a portion of the injector body such that the compression increases on the resilient means during temperature decreases.
According to a specific embodiment of the invention, the valve is sealed by a pair of elastomeric O-rings cGntained under compression within recesses of the bobbin and surrounding dissimilar material of the front end cap and core member. The material of the front end cap and core member contracts more slowly than does the material of the bobbin and, therefore, as the temperature s~ , 1~119~;5 decreases a tighter squeeze will be applied to the seallng rings. The tighter s~ueeze will extend the cold tem~erature range of the injector into the -~0OF. range. The increasing pressure compensates for the decreasing elastomeric response of the O-rings and their decreased sealing properties at the colder temperatures.
These and other features, advantages and aspects of the invention will be more fully understood and better explained if a reading of the detailed description is under-taken in conjunction with the appended drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS

_ FIGURE 1 is a partially sectioned side view of a single point injection system with a high flow rate fast-acting electromagnetic injector valve construc-ted in accord-ance with the invention;
FIGURE 2 is a cross-sectional side view o~ the electromagnetic injector valve illustrated in Figure l;
FIGURE 3, which appears on the same sheet of drawings as Figure 1, is a cross-sectional end view of the injector valve housing of the injector illustrated in Figure

2 which 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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t D~ S(-RrP~ rll~ ER~D F~MBoDIM~-:Nr Wi~ re~erence now t(~ ~'igure ], there is shown a !.ill Jle point injection system Eor metering ~uel to an int.lnal comhustion engine. The system comprises an ele tromagnetic injector valve ~0 which is electrically c~..n~ec~ed hy a set oE conductors 14,16, of a connecto~ 12 to l colltrol unit 18. A number of engine operating r pa!.lnleters are input to the control unit 18 including the sp - i or RP~I at which the engine is turning, the absolute 10 pr~ lr~ of the intake maniFold (I~AP), the temperat:ure of thl aiL ir~gested, and the engine coolant temperat~lre by me3ll~. ol conventional senso~
~I~h~i injector 10 ~its ~i~hin an inje-_tor fuel ja-ket -~
2!2 ~-ntL.Illy located in a single air induction bore 34 of 15 a ! hl-O~ t:Le body 25 commullicating with an intake m.lni~oll-l 42 c)f the int-rnaL combustion engine. Yor t~,ro~tl- hodies with multiple air induction bores, an ini~(tor per bore can he utilized. Air flow for engine in~Jestion is regulated by a throttle plate 30 which is ;'0 ro~a~ably mounted below the injector jacket 22. Upon the senciing of the operating conditions of the engine, the control unit will provide pulse width electLonic injection sigllals to the connector 12 representative of fuel quanlity desired for injection whereby the injector 10 25 will open and close relative to the leading and trailing ed-Jes ol the signal to meter fuel from the injector ja(~et: 22. The fuel is metered in a wide spray angle paltern for optimum mixture with the incoming air and de~ivery into the intake manifold.
FueI under pressure is delivered to the injector jacliet 2~ by a fue] inlet 20 and is circulated through the r~-interior of the injector jack-~t and thereafter to an exit passag-- 24 where a pressure regulator 40 mailltail-s the s~ emic pressure constant. .Spent fuel is returned to a ~ - . .

~1~91~6S

ceservoir, such as a Euel tank, where it can be then pumped under pressure ta 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 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 fixed by a screw 38.
Such a single point fuel injection system as shown is particularly adaptable to run a 2.2 liter engine having four cylinders. By injecting twice every revolution or 180 an air/fuel chafge per each cylinder firing is delivered. The injection is preferably made at some set angle relative to an engine event, such as just prior to top dead center (TDC3 of the number 1 cylinder on the intake stroke, and thereafter cyclicly related to that point. The injection timing 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 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 single point fuel rate of 400-600 cm3/min. and with a dynamic characteristic linear into the one millisec range is needed. The invention provides such an electromagnetic injector valve 10 with an advantageous consteuction.
With reference now to Figures 2 and 3, the high flow injector valve 10 is shown in cross-section to advantage and comprises a tubular injector body 100 which may be 30 constructed from seamed or unseamed tubing which has been ~:
cut to length. The injector body 100 is cold-formed at each end to form a shouldei 101 with a radially offset rim portion 102 at the front end and a shoulder 103 with another radially offset rim portion 104 at the rear end.
As the tubular body 100 is part of the magnetic circuit of 1~190~65 ~D

the injector, the matecial used is 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 S surfaces o~ 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 body that is flanged to abut against the shoulder 101 and is fixed in position by crimping or swaging the rim 102 against a bevel 108 machined on the flange. Similarly, a rear end cap 110 comprising a centrally bored cylindrical body is flanged and abuts the shoulder 103 and is affixed thereat by def~fming rim 104 to mate with a bevel 112 15 machined in the flange of the cap.
Within the chamber defined by the inner wall of the injector body 100 and the inwardly facing surfaces of the front end cap 106 and rear end cap lln, is a generally elongated molded bobbin 114 wound with a plurality of 20 turns of magnet wire forming a coil 116. The coil 116 is c electrically connected to a set of terminal pins 120 (only ~~
one shown) which rearwardly exit through 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. r~-The bobbin 114 has a centrally located longitudinal bobbin bore 124 which is silbstantially coaxial with a threaded rear end cap bore 126. A rod-shaped core member 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 threaded end 130 to provide for adjustment of its extension in the bobbin bore 124. The adjustment of ~p~
the core member determines the air gap distance and the lift of the valve. An adjustment screw 132 is threaded 35 into an internal bore of the core member 128 to provide 11190~

adjustment o 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 temperatures (65 F.), between two materials with differing thermal expansion and contraction rates.
O-ring 139 is compressed in an annulac space formed by the outside cylindrical surface of the core member 128 and the inside cylindrical surface of a recessed area 127 oE 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 end cap 106 and core member 128 materials are similar low carbon steels while the bobbin 114 is molded from 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 25 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 increasing pressure applied by the more rapidly contracting bobbin will extend the cold 30 temperature range of operation of the valve by r-compensating for the lack of flexibility in the O-ring seals below -20 F. ~n-Located in the central bore 107 of the front end cap 106 is a single step dividing the bore into an armature 35 guide bore 142 and a mounting bore 144. A valve housing ~L19~6S

146 is received in the mounting bore 144 until it abuts the internal shoulder 145 Eormed at the step between the bores~ The valve housing 146 is held in place by bending the front rim of the mounting bore 144 over a chamfer in the valve housing 146. The valve housing 146 has a longitudinal valve housing bore 148 which communicates on one end with the armature guide bore 142 and at the other end is terminated with a conical valve seat 150 which _~
curves into a smooth transitional area 152 to ~inally 10 become a cylindrical metering orifice 154.
The valve housing bore 148 is in fluid communication with fuel in the jackèt 22 by means of a plurality of fuel inlets 149 spaced around the valve housing 146. The inlets 149 are proximate to the metering orifice 154 for r_ 15 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. G'.
Reciprocal in the valve housing bore 148 is a valve 20 needle 156 which is press-fitted at its distal and into a generally annular-shaped armature 158. The needle valve, as is further illustrated in cross-section in Figure 3, L
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 the needle valve within the ~ore.
The needle valve extends into a valve tip 160 having a sealing surface 162 which mates with the conical valve seat 150 to close the valve. From the valve tip the needle 30 valve forms a pintle which ends in a deflection cap 164 ~r-which shapes the fuel spray into the hollow-cone or wide angle spray pattern as described hereinabove. The ~r-deflection cap is recessed in the injector housing 146 for protection.

111'9~;5 The needle valve 156 is substantially hollow with an inner passage 155 drilled Erom the valve tip to its valve end connection at the armature 158. The valve end has a spring recess 147 supporting a closure spring 147 within the centered bore in the armature 158. The passage 155 communicates with the valve housing bore 148 by means of a port 153 cut into each face of the medial section of the valve needle. The passage 155 and centered armature bore thus provides pressure relief to an air gap located between the armature and core member to prevent hydraulic forces from increasing there and affecting the opening time of the valve.
The closure spring is compressed by the ball member 136 against the valve needle recess 147 to produce a closure force on the valve needle which can be adjusted by turning adjustment screw 132. Tortional winding forces are not generated during 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 to wind up will cause slippage against the surface of the ball member and dissipation of the tortional force component.
The closure spring, by being contained in the armature 158 and recessed in the valve end, applies the closure force forward of the air gap and reduces the moment arm through which eccentric force components act.
Shorter and narrower bearing surfaces on the medial section of the valve needle can be used to balance the forces. The use o~ a shorter triangular medial section 30 with less bearing surface in combination with the hollow ~-valve needle and armature, significantly reduces the mass of the moving part of the injector. The reduction of the r-mass of the moving section and the increase in force produced by the enlargement o the coil will increase the opening time of the valve.

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In operation, when current in the form of an injection signal is supplied to the terminal pins 120 from the connector 12, and thus, to coil 116, a longitudinal magnetic field is set up through the core member 128, the S rear end cap 110, the injector body 100, and the front end cap 106 to attract the soft magnetic material of the L-'' armature 158 across the air gap to abut a nonmagnetic shim 135 on the face of the core memher. The shim 135 r aids the closing time of the valve by maintaining a 10 minimum gap during energization. When the magnetic attraction overcomes the force of the closure spring, the valve needle will be lifted away from the valve seat and L
fuel will be metered by the valve seat interface and metering orifice until the current to the terminal pins lS 120 is terminated and the closure spring force seals the valve once more.
After assembly, the lift and air gap can be adjusted by turning core member 128 and the closure force adjusted r by turning adjustment screw 132. The two adjustments 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 10 is graphically 25 illustrated as a function of valve lift L. At small valve lifts in region A, the restriction produced by the needle valve and valve seat interface dominates and the static fuel flow is independent of the metering orifice size. In this region ~ Q/~ L is a relative constant K related to 30 the increasing opening area between the interface of the needle valve and valve seat.
In region C where the lift is increased beyond where r--tlle valve needle provides a restriction to fuel flow, the metering orifice size is the determining factor of the r--.

!r ~L11913~;5 static fuel flow. ~ Q/~ L in this region, as would be expected, is zero. Between regions A and C is a smaller region ~ where the static fuel flow of the injector valve is sùbstantially a function of metering orifice size, but is also related to valve lift. ~ Q/~L in this region is much less than K and is approaching the value of zero found in reyion C. The change in static fuel flow for a change of lift is related to the ratio of the changing ~_ interface area with respect to the metering orifice area.
10By adjusting the lift in this region, a relatively controllable trim can be generated to calibrate the static fuel ~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 of trimming is 5%
of the static fuel flow rate ~or a .001" change in lift.
The adjustment threads on the core member 128 are suitably chosen to provide controllable lift changes in this region.
After the static flow calibration, a dynamic calibra-tion is undertaken to match the closure force to the air gap which was varied during static calibration and to ~r calibrate the dynamic response. With respect to Figure 5, ~;
the dynamic fuel flow rate as a function of pulse width is illustrated. The line D, which is dotted, indicates an ideal valve which has a static flow rate tslope) 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 dynamic characteristic will 30 form a parallel line to the right of the ideal, for r~
example, line E. The less ideal and slower the valve operates, the ~ore to the right of line D the real dynamic line will be. Critical operation at higher engine speeds requires maximum injection quantity while the time available for injection is decreasing. High flow rate _ V~

valves with steep dynamic slopes are necessary to meet these requirements! but cause very small pulse widths to be used for the minimum injection quantities. The closer the valve can be calibrated to ideal with linearity, the more advantageous it will be to the sysem.
With the goals in mind, the dynamic calibration is accomplished by picking the minimum flow rate of the valve at point G which is some safety factor below the minimum quantity injected at idle, or point F. The closure force is then adjusted to minimize the offset of line E from the ideal response at line D.
While the preferred embodiments of the invention have been shown, it will be obvious to those skilled in the art that modifications and changes may be made to the disclosed system without departing from the spirit and scope of the invention as defined by the appended claims.

WHAT IS CLAIMED IS:

~t -

Claims

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

1. An electromagnetic fuel injector comprising:
a valve assembly for receiving pressurized fuel including a valve housing and a valve member having an armature portion, said valve member movable in said valve housing from a closed position to an open position in order to meter fuel from said valve housing;
an injector body in fluid communication with said valve assembly;
an electrically energizable stator means, contained within said injector body, for moving said valve member to one of said positions by magnetically attracting said armature portion;
means for moving said valve member to the other of said positions when said stator means is not energized;
said stator means including a coil wound on a bobbin wherein said bobbin has a different rate of thermal volume change than said injector body; and means for sealing the pressurized fuel within the injector body including resilient means compressed in at least two places between a portion of said bobbin and a portion of said injector body such that the compression increases on said resilient means during temperature decreases.

2. An electromagnetic fuel injector as defined in Claim 1 wherein:
said bobbin is elongated and includes a central bobbin bore with a recess at each end;
said resilient sealing means comprise a ring of an elastomeric material located in each of said recesses such that an outer surface of each recess is in contact with each elastomeric ring; and said injector body portion includes an inner surface projecting into each bobbin recess such that the inner and outer surfaces coact to compress each elastomeric ring by contracting radially upon decreases in temperatures.

3. An electromagnetic fuel injector as defined in Claim 2 wherein:
said injector body comprises a tubular body having a front and rear end cap fixed at either end; and said stator means is located between said end caps in an inner chamber of the tubular body.

4. An electromagnetic fuel injector as defined in Claim 3 wherein:
one of said inner surfaces is provided as an annular projection of said front end cap.

5. An electromagnetic fuel injector as defined in Claim 4 wherein:
said other inner surface of said rear end cap is provided by a rod shaped core member inserted through a central bore in the rear end cap and which extends into said bobbin bore.

6. An electromagnetic fuel injector as defined in Claim 1 wherein said means for moving said valve member is a spring member disposed between said stator means and said armature in compression to apply a force to said valve member to move to said valve member to the other of said position.

7. An electromagnetic fuel injector as defined in claim 6 wherein said bobbin is comprised of Nylon.

8. An electromagnetic fuel injector as defined in Claim 7 wherein said injector body portion is comprised of a low carbon steel.

9. An electromagnetic fuel injector as defined in Claim 2 wherein said resilient rings are O-rings.

10. An electromagnetic fuel injector as defined in Claim 2 wherein said inner and outer surfaces are cylindrical surfaces.

11. An electromagnetic fuel injector as defined in Claim 6 wherein said armature portion has a central bore for receiving said member.