KR20000016779A - Fuel injector for an internal combustion engine - Google Patents

Abstract

PURPOSE: An injector is provided to improve a reappearance of an injected fuel amount and to precisely control an injecting operation. CONSTITUTION: A fuel injector (1) for an internal combustion engine has an outer housing(4) with a mounting flange (2) at its back end and an injection nozzle (8)protruding from the housing at its front end, and a fuel passage (34) extending centrally in the injector. A spindle (26) is mounted on the outside of a fuel tube (19) and within a spindle guide (9). A closing spring (21) biases the spindle forwards in the closing direction, and the spindle guide is pressed forwards in the injector housing by a thrust bushing (10). The fuel tube is a separate unit which is in contact with the valve member positioned behind it via an annular surface (18) which is substantially perpendicular to the longitudinal axis of the injector. The front spindle section (32) has an outer diameter which is at the most 8 micrometers smaller than the inner diameter of the spindle guide bore (27), and an inner diameter which is at the most 8 micrometers larger than the outer diameter of the front section (24) of the fuel tube.

Description

Fuel Injectors for Internal Combustion Engines

Such fuel injectors are known from DK-B-155757 which discloses injectors for injecting easily ignitable pilot oil and gaseous fuels. The thrust bushing here acts as a guide for the valve slide on the outside for opening and closing the gas supply. The fuel tube extends integrally along most of the length of the injector at its rear end and serves as a valve housing for the discharge valve. The pilot oil opening spindle has a relatively large gap between the fuel tube on one side and the bore of the spindle guide on the other side to prevent spindle misalignment or uneven wear due to incorrect alignment between the bore of the spindle guide and the long fuel tube. Is designed to have.

DK-B-167502 (EP-A 0 606 371) discloses a fuel injector in which a closing spring is received in the hollow of the central part of the slide guide and the central fuel tube is formed integrally with the rear part of the slide guide. In this case, too, a relatively large clearance is required between the front of the fuel tube and the bottom of the spindle and the bore of the slide guide to compensate for the manufacturing tolerances and thus the lack of complete coaxiality between the bore of the slide guide and the fuel tube. do.

A somewhat different kind of injector is disclosed in DE-A-2030445, wherein a hollow spindle with a relatively thin wall thickness slides in an annular space between the bore of the spindle guide and the fuel tube. The rear end of the spindle has a very heavily formed front spring guide for the closing spring. The opening movement of the spindle is limited by the backside of the spring guide striking the protrusion of the injector housing at its largest diameter. This imparts a bending moment to the thin spindle wall and consequently causes the wall to bend outward. A relatively large gap is required between the spindle and the annular surfaces on both sides of the spindle to prevent the spindle from stopping. The fuel tube has two parts and a joint face located on the rear spring guide. In such fuel injector assembly, there is a risk that the contact surfaces of the fuel tubes are misplaced because there is no means for initially placing them before the two fuel tubes are pressed together. Moreover, leakage may occur at the joint surface, which causes a change in the amount of fuel to be injected. Moreover, a disadvantage of this injector is that the total stress of the compression spring is determined by how deeply the thrust component is clamped into the injector housing. As a result, the opening pressures of many of the same injectors appear differently.

Known fuel injectors of the type with a hollow spindle disposed between the bore of the spindle guide and the fuel tube in the center are considerably smaller than when the mass of the movable spindle has a rigid spindle, with a relatively small mass of the movable part of the injector. The advantage is that the valve acts quickly. However, there was a problem involving the risk of the spindle stopping when the hollow spindle slides between two annular surfaces such that the spindle wall is deformed. In order to solve this problem and correct for the lack of coaxiality, the clearance between the spindle and the adjacent annular surface is relatively wide, which means that the clearance between the spindle guide bore and the spindle and fuel tubes is more on one side of the injector's longitudinal axis. Larger on the other side involves the possibility of the spindle moving slightly in the transverse direction and eccentric. This transverse movement is very small, however, resulting in a change in the amount of fuel leaking through the gap during fuel injection. When the spindle is fully coaxially arranged, the leakage will be 50-70% smaller than when the spindle is laterally displaced, so that the same valves have the same parameters for injection as the fuel delivery pressure and volume to the injector. Other fuel injections may also cause changes in the volume of fuel actually injected. Even if the injectors are set identically and supply the same fuel, a change in the amount of fuel injected from several different injectors can occur.

The present invention relates to a fuel injector for an internal combustion engine, in particular a two-stroke crosshead engine, comprising: an outer housing having a mounting flange at the rear end and an injection nozzle protruding from the housing at the front end, and a fuel passage extending from the center of the injector; The fuel passage is terminated in the injection nozzle through at least one thrust member, the central fuel tube, the spindle and the spindle guide from the mounting flange, the spindle guide has a circular and cylindrical inner surface of the spindle guide surface A central bore is formed, wherein the fuel tube has an outer diameter smaller than the rear portion and extends more than half into the central bore of the spindle guide, and in the direction of the injection nozzle in the transition region between the front portion and the rear portion. Back springs for axially facing annular surfaces and springs closed at a predetermined stress A front spindle having a needle valve which interacts with a stationary seat surface in the bore of the spindle guide for opening and closing the injector, and a central bore in which the front portion of the fuel tube is inserted and opened rearward; A front spring guide for the portion and the closing spring, the spring guide being disposed in the rear spindle portion protruding from the bore of the spindle guide, the closing spring biasing forward in the direction of closing the spindle, the rear end of the spindle In which the annular end face is brought into contact with the annular surface of the fuel tube by an open movement to the rear of the spindle, the spindle guide extending rearward through the closing spring and contacting the annular surface facing backwards in the spindle guide. Front of the injector housing by at least one thrust bushing The thrust member is pressed forward by the mounting flange at the same time as the closing spring is compressed at the time of injector assembly.

1 is a longitudinal sectional view of a fuel injector according to the invention.

An object of the present invention is to solve the problems of the conventional injector described above, and to provide an injector capable of improving the reproducibility of the amount of fuel injected and controlling the injection operation more accurately.

The fuel injector of the present invention for achieving the above object is that the outer diameter of the rear spring guide of the fuel tube is smaller than the inner diameter of the thrust bushing, and the fuel tube is substantially perpendicular to the longitudinal axis of the injector and surrounds the central fuel passage. It is a separate part which has an annular surface and contacts only the valve member arranged at the rear of the fuel tube via a contact surface located on the rear surface of the rear spring guide, and in the front spindle portion inserted in the spindle guide bore, the spindle is a spindle guide. And an outer diameter up to 8 μm smaller than the inner diameter of the bore and up to 8 μm larger than the outer diameter of the front portion of the fuel tube.

Such a spindle is slightly larger than the fuel tube and slightly smaller than the slide valve bore, greatly limiting the lateral movement of the spindle during sequential injection operations, in particular half of the displacement that has occurred in conventional injectors of the same kind. Reduced to less than. Fuel leakage is largely prevented by fluid friction on the cylindrical surfaces, so that the leakage change can be significantly reduced even with a minimum limit on the maximum allowable gap between the surfaces. This allows more fuel to be injected evenly, thus facilitating more accurate combustion to achieve the required energy savings, reducing energy fuel consumption, and reducing emissions of environmental pollutants such as nitrogen oxides. The heat load of the cylinder members and the adhesion problem of the combustion residue can be improved. This is a particularly beneficial advantage for most two-stroke diesel engines that burn very low fuel.

Three valve members, i.e., the spindle and the fuel tube and the spindle guide bores, must be precisely aligned with each other when the injector is operated, which is a prerequisite for precise engagement between the valve members. Contrary to conventional injectors, there is a slight inaccuracy in the alignment between the three valve members or a non-uniform load on the tubular thin-walled spindle, which causes uneven wear on the spindle, eg For example, the spindle wall is bent as a result of bending. This is solved according to the invention by constructing the fuel tube separately from the valve member behind it such that the fuel tube comprises a fuel passage portion extending into the spindle from the rear spring guide of the closing spring. In assembling the injector parts of the injector housing, the spindle can be inserted into the spindle guide, the fuel tube with the closing spring can be mounted to the spindle, the thrust bushing is pushed around the rear end of the spindle guide, These injector parts and the injector housing can be aligned with the vertical center axis. Precise engagement between the spindle and the spindle guide and the fuel tubes allows the other valve members to be inserted into the housing and the mounting flanges clamped by the components being axially adjusted to each other without load in the vertical central axis direction. When mounting the other members, the valve member located behind the fuel tube is first inserted into the thrust bushing before being moved in the direction close to the fuel tube. This results in an initial guide of the member, preventing transverse displacement at the moment the member comes into contact with the fuel tube. During continuous clamping of the injector, the valve member is pressed downwards into contact with the upward annular contact surface of the fuel tube so that the placement of the fuel tube is precisely fixed coaxially with respect to the spindle guide due to the friction between the valve member and the contact surface. Insert. It is important for accurate fixation of the fuel tube that the contact surface is substantially perpendicular to the longitudinal axis of the injector so that no lateral guiding force acts on the contact surface of the valve assembly. For this reason, there must be a gap between the rear spring guide and the thrust bushing so that the spring guide does not interfere with the correct adjustment by hitting the thrust bushing.

The outer diameter of the front spindle portion is preferably 2-4 μm smaller than the inner diameter of the spindle guide bore, and the inner diameter of the front spindle portion is 2-4 μm larger than the outer diameter of the front portion of the fuel tube. With this precise coupling, variations in leakage are greatly limited, and the gaps between the movable spindle and the stationary spindle guide and the fuel tubes are sufficient for the spindle to move longitudinally without causing any problems.

In another preferred embodiment of the present invention, the outer fuel tube surface is extended from the rear end of the spindle to at least the front spring guide, more preferably to the front spring guide located at the spindle guide bore. There is a fairly large diameter difference between the inner spindle surfaces. For example, there may be a gap between the spindle and the fuel tube that is 0.1 mm wider than the gap between the two parts of the front spindle portion in the rear spindle region. This effect is such that a pressure drop is obtained through the slits as annular slits longitudinally on the outer and inner surfaces of the spindle along the front spindle portion. The result is that the spindle wall of the front spindle part does not have to withstand the pressure difference which acts easily, which makes it possible to manufacture the spindle so that the spindle has a very small wall thickness in the front spindle part.

The present invention also provides many other means for reducing the spindle mass. It is possible to form a conical front surface in the front spring guide of the spindle and to have the smallest thickness at its largest diameter. The front spindle portion may also have a smaller wall thickness than the front portion of the fuel tube. The mass of the front end of the spindle in the region around the needle valve can be reduced by the length of the inclined bores from the bottom of the central spindle bore to the chamber around the needle valve being less than 35% of the outer diameter of the front spindle portion, which is the front Indicates that the spindle end has a small wall thickness. Further weight reduction in this area can be achieved by having the needle valve having a bore in the center opening to the front side of its end face. However, the latter possibility limits the reduction of mass. Each of these various options can be used. If several options are used in combination, a spindle with extremely low weight in relation to the size of the injector can be obtained.

The reduction in the weight of the spindle allows to improve the reproducibility of precise control of the amount of fuel injected and the injection sequence. This is because smaller spindle weights allow for faster spindle movements upon opening and closing of the injector and less wear on the valve seat, and the stopping limits of impact and opening movement on the valve seat are smaller from the lighter spindle. Quick opening allows for fast fuel injection, which promotes good and strong atomization of the injected fuel volume and thus allows the fuel to ignite well and quickly. More important is the rapid closure of the injector, which provides for abrupt stop of combustion and reduces the amount of fuel injected during the closing motion under undesirable conditions such as low pressure and insufficient injection speed (g / s of fuel). This last injected fuel contributes significantly to the formation of pollutants such as nitrogen oxides, providing heavy heat loads on the cylinder elements, soot deposition and increasing fuel consumption. Lighter spindles reduce the amount of fuel injected undesirably and increase the proportion of total injected fuel injected under optimum conditions.

In a preferred embodiment, the outer diameter of the contact surface of the fuel tube to the back of the rear spring guide is smaller than the outer diameter of the front portion of the fuel tube. First, the small outer diameter contact surface has the effect of not causing leakage at the contact surface at a small angle between the fuel tube and the longitudinal axes of the valve member behind it, which means that the manufacturing roughness of the two compressed surfaces is such that the surfaces are closest to each other. This is because a small inconsistent alignment is compensated for in the form of seal contact on the opposite side in the radially opposite side. Secondly, the small outer diameter of the contact surface results in the seal surface pressure between the contact surfaces exceeding the current fuel pressure in the fuel passage. When the injector is closed, surface pressure is created between the contact surfaces by force to the rear of the fuel tube resulting from fuel pressure to the front end surface of the fuel tube and by spring spring force to the rear spring guide. When the injector is opened, the fuel pressure acts on the fuel tube with a greater rearward force, which means that the fuel pressure acts on the entire front end of the spindle and this rearward force from the spindle is in the axial direction of the fuel tube. This is because it passes through the annular surface towards the fuel tube. The inner and outer diameters of the rear contact surfaces of the fuel tube preferably have the same dimensions as the respective inner and outer diameters of the front spindle portion, which dimensions provide a complete axial flow force at the spindle wall.

In a design that is particularly simple to manufacture and assemble, such a fuel injector is for the injection of preheated fuel such as heavy oil, the valve element located behind the fuel tube is a valve housing for the fuel circulation valve, and the annular rear end of the thrust bushing is assembled with the injector When contacting the front contact surface of the rear end of the annular groove of the front end of the outer valve housing surface, whereby the length of the thrust bushing determines the total stress of the closing spring. With this design, the thrust bushing in the mounted valve is located between the two annular contact surfaces of the valve housing and the spindle guide, and precisely between the valve seat of the spindle guide and the front surface of the valve housing in contact with the contact surface of the fuel tube. And form a predetermined interval. As the valve spindle has a front spring guide and the fuel tube has a rear spring guide of the closing spring, the closing spring is obviously subjected to prestress when the injector is assembled and at the same time the spindle is located between the closed and open positions. Has a precise and preset elevation or movement height. Such total stress and spindle lift height can be precisely adjusted for injectors in specific engines, for example by varying the length of the thrust bushings, shortening the length of the thrust bushings and keeping all others equal, resulting in higher total stresses. And a lower lift height is obtained. This provides a significant simplification in injector assembly where the injector parts should be clamped together as much as possible to obtain the correct spring total stress to obtain the correct opening and closing pressure of the injector. This precludes a significant change in the spring prestress and a significant change in the opening pressure of the valves, which may occur in valves where the spring prestress is to be fixed by fastening the mounting flange somewhat to the injector housing.

Simplification of injector assembly is achieved by spindle guide, spindle, closing spring, fuel tube and thrust bushings, and the valve housing of the circulation valve is assembled into a pre-assembled unit in which the valve housing and the spindle guide are locked to each other via a thrust bushing. Can be. This makes it possible to supply a complete and pre-assembled replacement unit for the injector so that major parts can be replaced very quickly. The locking of the valve housing and the spindle guide can be done, for example, by crimping the thrust bushings on the spindle guide and the valve housing or by pressing the thrust bushings on two injector parts and then the associated bore of the thrust bushing and the transverse direction of the part. This can be done by positioning the thrust bushings with respect to each of the two other parts by means of a pin inserted in each of them.

A through hollow may be provided in the longitudinal direction of the injector between the inner side of the injector housing and the outer side of the valve housing and between the thrust bushing and the spindle guide. The hollow provides the advantage that the stationary injector parts are fixed in the injector housing between two positions, the front surface of the inner side of the mounting flange and the rear surface of the injection nozzle, which is a rotationally symmetrical load on the parts of the injector. Promote the condition. Another advantage is that it acts as a drain passage of the fuel in which the hollow part leaks out.

Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

The fuel injector, generally shown at 1, has a mounting flange 2 with an inlet 3, to which a high pressure pipe from a fuel source, not shown, to the inlet can be connected. The fuel source may be, for example, a piston fuel pump such as a Bosch type, which may be operated periodically by a cam of the camshaft or connected to the inlet 3 periodically via a control valve. Can be a reservoir. The fuel may be a liquid or gaseous phase, a solid fuel in slurry form, or an emulsion comprising at least one of them, and the valve may be used to inject the liquid or gaseous additives into the combustion section as one or a mixture.

The outer housing 4 for the injector can be clamped to the mounting flange 2 by a union nut 5, which in turn can be clamped to the engine cylinder by bolts inserted into the holes 6 of the flange. have. The fuel passage 34 extends from the inlet 7 of the inlet through the injector along the central axis to the injection nozzle 8, from the injection nozzle through the nozzle holes (not shown) into the cylinder of the internal combustion engine. It can be injected into.

The spindle guide 9 is pressed downward against the inner surface of the injection nozzle by the thrust bushing 10, and the valve housing 11 and the thrust members 12 contact the front inner surface of the mounting flange. The thrust bushing has an outer diameter substantially the same as the rear portions of the valve housing 11 and the spindle guide 9 and is inserted into the annular groove of each of these parts so as to be axially oriented in the axial direction of the thrust bushing 10. They come into contact with the spindle guide and the surfaces 13, 14 of the valve housing.

The valve body 15 is inserted into the bores of the valve housing 11 and biased to the position shown in the figure by a relatively weak compression spring 16. The forwardly protruding contact surface 17 of the front end of the valve housing correspondingly contacts the annular contact surface 18 facing the rear of the protruding portion of the rear end of the central fuel tube 19, which is substantially parallel and planar. The engagement surface between the contact surfaces is in a plane substantially perpendicular to the longitudinal axis of the injector.

The fuel tube has a protruding collar portion 20 which constitutes a rear spring guide for the closing spring 21 in the form of a conventional mechanical compression spring just below the contact surface 18. In front of the spring guide the fuel tube continues into a circular cylindrical rear portion 22, the outer diameter of which is slightly smaller than the inner diameter of the spring. The rear end ends in front of the annular surface 23 located in a plane perpendicular to the longitudinal axis of the injector. The annular surface 23 forms a transition region between the rear part and the front part 24 of the fuel tube, the front part having a diameter smaller than the rear part and rearward of the spindle 26 up to the front end of the fuel tube. It extends into the bore 25 which is open toward the side and is positioned slightly apart from the bottom of the bore 25. The spaced distance is greater than the lift height of the spindle.

The spindle guide 9 has a central bore having a cylindrical inner surface 27 constituting a guide surface for the spindle on one side thereof. On the front side of the part, the spindle guide has a pressure chamber 28 which has a conical stationary valve seat to interact with the conical actuated valve seat at the tip of the needle valve 29 at the front end of the spindle. do. The bore of the spindle guide leads to the center bore of the injection nozzle 8 at the front side of the valve seat.

The spindle 26 has a front spring guide 30 in the form of a protruding collar, the back of which is perpendicular to the longitudinal axis of the injector, and the front side 31 of which is conical. A closing spring is located in the thrust bushing 10 between the two spring guides 20, 30. In assembling the injector parts, the closing spring is compressed with full stress. The forward sealing force generated by the spring of the front spring guide 30 of the spindle should be of a very precise size, since the compression of the spring during assembly requires that the length and load of the thrust bushing 10 remain unloaded. This is because the length of the closing spring is determined.

The diameter of the inner side of the spindle is 2-4 μm larger than the outer diameter of the front portion 24 of the fuel tube, and the outer diameter of the spindle front portion 32 inserted into the spindle guide bore is 2-4 larger than the inner diameter of the bore 27. Μm smaller. The wall thickness of the spindle front is approximately 30% smaller than the wall thickness of the front 24 of the fuel tube. The lower end wall of the spindle at the bottom of the bore 25 has a relatively small wall thickness and the annular end face surrounding the needle valve 29 is substantially perpendicular to the longitudinal axis of the injector. The inclined bore 33 connecting the compression chamber 28 and the bore 25 has a length less than 35% of the outer diameter of the portion 32 because of the small wall thickness.

The central fuel passage 34 extends through the inlet 7 through the thrust member 12 to the bore 35 in the center of the valve body 15, the passage being a plurality of slanted bores 36. Branched and the bores open into the pressure chamber 38 located near the needle valve 37. In front of the stop valve seat cooperating with the needle valve 37, the fuel passage continues forward through the fuel tube 19 through the front center of the valve housing 11 and past the contact surfaces 17, 18 of the spindle. Open at the bottom of the bore 25, from which the fuel passage leads to the inclined bore 33, the pressure chamber 28 and the nozzle holes not shown in the injection nozzle 8.

The drain holes 39 are formed such that the leaked fuel is discharged from the hollow space around the closing spring 21 to the through space extending in the longitudinal direction of the injector from the inner side of the injector housing 4.

The low pressure preheated fuel is supplied between the injection cycles with the supply port 7. This fuel is introduced into the space around the compression spring 16 through the laterally leaking channel 40 at the front of the thrust member 12. The drain holes 41 of the valve housing 11 send the circulating fuel to the chamber 42, from which a return pipe, not shown, removes the fuel from the injector. The fuel circulation during the closing period of the injector is to keep the fuel system preheated to a moderately high temperature.

As soon as the fuel pressure rises at the beginning of the injection cycle, the pressure in the pressure chamber 38 rises and the valve body is influenced by a force backwards that overcomes the force of the compression spring 16, thereby moving the valve body backwards. To shut off the leak channel 40. The fuel pressure then spreads through the fuel passage into the pressure chamber 28. When the fuel pressure reaches the opening pressure of the injector, the spindle 26 is actuated by a rearward force which is greater than the force of the closing spring 21 such that the annular end face of the spindle has an annular surface ( Allow the spindle to move backward until it hits 23). The surface 23 then acts as a limiting stopper for spindle movement to determine the lift height of the spindle. Spindle movement opens the fuel inlet to the injection nozzle. When the discharge pressure of the fuel drops again at the end of the injection, the pressure in the chamber 28 is moderately lowered so that the closing spring overcomes the pressure behind the fuel relative to the spindle so that the needle valve 29 contacts the seat. It returns to a closed initial position that blocks the entrance to the spray nozzle.

In order for the spindle to be designed with a thin wall as shown, it is important that the rear end face of the spindle is an axial extension of the cylindrical spindle wall to avoid deformation of the cylindrical spindle wall, which is This is to ensure that the shock only exerts an axial force on the spindle.

If it is not necessary to circulate the preheated fuel during the closing period of the injector, the injector can be simplified by omitting the circulation valve. In this case, the thrust member 12 and the valve housing 11 have a thrust as a whole which forms part of the fuel passage 34 through which the through bore at the center connects with the supply port 7 provided with a passage at the center of the fuel tube. It can be formed as a unit of member type.

The injector of the invention can be extended to use for injecting a variety of different fluids, for example by using the injector elements described above in connection with the injector of the type disclosed in Danish patent No. 155757. Such injectors can be used, for example, for the injection of gases or auxiliary fuels, or for injecting other fluids, such as water, for reforming combustion processes such as water to reduce the formation of undesirable emissions. It may be.

According to the present invention, fuel leakage is largely prevented by fluid friction on the cylindrical surfaces, so that the leakage change can be significantly reduced even with a minimum limit on the maximum allowable gap between the surfaces. Thus, a larger amount of fuel can be injected evenly, thus facilitating more accurate combustion to achieve the required energy savings, reducing energy fuel consumption, and emitting environmental pollutants such as undesirable nitrogen oxides. Can be reduced, and the heat load of the cylinder members and the adhesion problem of the combustion residue can be improved. Furthermore, according to the invention, the fuel tube can be configured separately from the valve member thereafter such that the fuel tube includes a fuel passage portion extending into the spindle from the rear spring guide of the closing spring, thereby causing uneven wear on the spindle or The problem of stopping as a result of, for example, bending of the spindle wall is eliminated, allowing the spindle to be manufactured such that the spindle has a very small wall thickness in the front spindle portion.

Claims (12)

An outer housing 4 having a mounting flange 2 at the rear end and an injection nozzle 8 protruding from the housing at the front end, and a fuel passage 34 extending from the center of the injector; Is terminated at the injection nozzle via at least one thrust member 12, central fuel tube 19, spindle 26 and spindle guide 9 from the mounting flange, the spindle guide having circular and cylindrical inner surfaces. A central bore 27 is formed to form the guide surface for the spindle, and the fuel tube has an outer diameter smaller than the rear portion 22 and a front portion extending more than half into the central bore of the spindle guide, and the front portion and the rear portion. In the transition region between the parts there is provided an annular surface axially directed in the direction of the injection nozzle and a rear spring guide 20 for the spring 21 which is closed with a predetermined stress, the spindle being a fuel tube A front spindle portion 32 having a central bore 25 in which the front portion is inserted and opened rearward, and a needle valve 29 which interacts with the stationary seat surface in the bore of the spindle guide for opening and closing the injector; A front spring guide 30 for a closing spring, said spring guide being disposed in the rear spindle portion protruding from the bore of the spindle guide, said closing spring biasing forward in the direction of closing the spindle, At the end the annular end face is adapted to contact the annular surface 23 of the fuel tube by an open movement to the rear of the spindle, the spindle guide extending rearward through the closing spring and facing backward at the spindle guide. Is pressed forward of the injector housing by at least one thrust bushing 10 in contact with the surface 13 of the Member is in the internal combustion engine, in particular two-stroke crosshead engine, a fuel injector for being pressed forward by the compression at the same time as the mounting flange of the closing spring when the injector assembly, The outer diameter of the rear spring guide 20 of the fuel tube is smaller than the inner diameter of the thrust bushing 10, and the fuel tube 19 is a separate unit that contacts only the valve member disposed behind it via the contact surface 18. And an annular surface disposed at the rear of the rear spring guide and having an annular surface surrounding the central fuel passage 34 and substantially perpendicular to the longitudinal axis of the injector, wherein the spindle 26 is inserted into the spindle guide bore 27. A fuel injector for an internal combustion engine, characterized in that the front spindle portion (32) has an outer diameter of at most 8 micrometers less than the inner diameter of the spindle guide bore and the inner diameter is at most 8 micrometers larger than the outer diameter of the front portion (24) of the fuel tube. 2. The outer diameter of the front spindle portion is 2-4 [mu] m smaller than the inner diameter of the spindle guide bore and the inner diameter of the front spindle portion is 2-4 [mu] m larger than the outer diameter of the front portion of the fuel tube. Fuel injectors for internal combustion engines. The diameter difference between the outer fuel tube surface and the inner spindle surface according to claim 1 or 2, from the rear end of the spindle to the spring guide, preferably up to the front spindle portion located in the spindle guide bore. Fuel injector, characterized in that is significantly larger than in the front spindle portion. The fuel for an internal combustion engine according to any one of the preceding claims, characterized in that the front spindle guide (30) of the spindle has a conical front surface (31) and has the smallest thickness in the portion of the largest diameter. Injector. 5. The fuel injector of claim 1, wherein the front spindle portion (32) has a smaller wall thickness than the front portion (24) of the fuel tube. 6. 6. The length of the inclined bore 33 according to claim 1, wherein the length of the inclined bore 33 from the bottom of the spindle bore 25 at the center to the chamber around the needle valve 29 is 35 times the outer diameter of the front spindle portion. A fuel injector for an internal combustion engine, characterized by less than%. 7. The fuel injector of claim 6, wherein the needle valve has a central bore open forward at its end face. The internal combustion according to any one of the preceding claims, characterized in that the outer diameter of the contact surface 18 of the fuel tube in contact with the rear surface of the rear spring guide 20 is larger than the outer diameter of the front portion 24 of the fuel tube. Engine fuel injectors. A fuel injector according to any one of the preceding claims, characterized in that the inner and outer diameters of the rear contact surfaces (18) of the fuel tube have substantially the same dimensions as the respective outer and inner diameters of the front spindle portion (32). The fuel injector of claim 1, wherein the fuel injector is for the injection of preheated fuel, such as heavy oil, the valve element located behind the fuel tube is the valve housing 11 for the fuel circulation valve, and the annular shape of the thrust housing 10. The rear end of the thrust bushing is configured to determine the total stress of the closing spring by contacting the front contact surface 14 at the rear end of the annular groove at the front of the outer valve housing surface when the injector is assembled. Fuel injectors for internal combustion engines. 11. The fuel injector of claim 10, wherein the valve housing of the spring guide, the spindle, the closing spring, the fuel tube, the thrust bushing and the circulation valve is locked to each other through the thrust housing. Fuel injector for an internal combustion engine according to any one of the preceding claims, characterized in that a through space is provided in the longitudinal direction of the injector between the outer surfaces of the valve housing, the thrust bushing and the spindle guide and the inner surface of the injector housing (4). .