Fuel injection and method for adjustment thereof

A fuel injector for fuel injection systems of internal combustion engines, in particular for direct injection of fuel into the combustion chamber of an engine, including an actuator, a valve needle which is mechanically linked to the actuator and is acted upon by a restoring spring in a closing direction, for actuation of a valve closing body, which together with a valve seat face forms a sealing seat, and including a sleeve which pre-stresses the restoring spring. An adjusting body is situated adjustably in the sleeve so that a fuel amount flowing through the fuel injector per unit of time is a function of the position of the adjusting body in the sleeve.

FIELD OF THE INVENTION

The present invention is related to a fuel injector and a method of adjusting a fuel injector.

BACKGROUND INFORMATION

German Published Patent Application No. 40 23 828 discusses a fuel injector and a method of adjusting a fuel injector. To adjust the amount of fuel to be delivered during the opening and closing operation of the electromagnetically operable fuel injector, a magnetically conductive material, e.g., in the form of a powder which alters the magnetic properties of the internal pole is introduced into a blind hole, and thus the magnetic force is varied until the actual measured flow rate of the medium corresponds to the predetermined setpoint flow rate.

Similarly, German Published Patent Application No. 40 23 826 discusses the insertion of an equalizing bolt into a blind hole of an internal pole including a recess on its periphery, inserting it to the extent that the actual measured amount corresponds to the predetermined setpoint amount, and thus varying the magnetic force until this is achieved.

German Patent Published Application No. 195 16 513 also discusses a method of adjusting the dynamic flow rate of a fuel injector. In this case, an adjusting element situated close to the magnetic coil outside the flow path of the medium is adjusted. In doing so, the size of the magnetic flux in the magnetic circuit, and thus the magnetic force, changes, so it is possible to influence and adjust the flow rate. The adjustment may be performed with when the fuel injector is either wet or dry.

German Patent Published Application No. 42 11 723 discusses a fuel injector and a method of adjusting the dynamic flow rate of the medium of a fuel injector, in which an adjusting sleeve including a longitudinal slot is pressed into a longitudinal bore in a connection piece up to a predetermined depth, the dynamic actual flow rate of medium of the injector is measured and compared with a setpoint flow rate of medium, and the pressed-in adjusting sleeve which is under a tension acting radially is advanced until the actual measured flow rate of the medium matches the predetermined setpoint flow rate of the medium.

In German Published Patent Application No. 44 31 128, to adjust the dynamic flow rate of medium of a fuel injector, the valve housing undergoes deformation due to the action of a deformation tool on the outer perimeter of the valve housing. This changes the size of the residual air gap between the core and the armature, and thus the magnetic force, so that it is possible to influence and adjust the flow rate of medium.

One disadvantage of the group of methods which influence the magnetic flux in the magnetic circuit is the great expense with regard to manufacturing costs, because the required static flow tolerances must be guaranteed, although this is difficult to implement. In particular, measurements of magnetic fields are complicated to perform and usually require cost-intensive methods and a test field.

It is believed that a disadvantage of the group of mechanical adjustment methods is the high degree of inaccuracy to which these methods may be subject. Furthermore, the opening and closing times of a fuel injector may be shortened only at the expense of electric power, so that the electric load on the components is increased, and the controllers are under greater stress.

In particular, the method referred to in German Published Patent Application No. 44 31 128, where the residual air gap between the core and the armature is varied by deformation of the valve housing, permits only a very inaccurate correction of the flow rate because shear stresses in the nozzle body may have a negative effect on the direction and size of the deforming force Therefore, a high manufacturing precision is necessary for all parts.

SUMMARY OF THE INVENTION

The exemplary fuel injector according to the present invention and the exemplary method according to the present invention for adjusting a fuel injector, due to the introduction of an adjusting body into a sleeve which may be pressed into the valve body, may allow the flow rate to be monitored and adjusted in a mechanical manner.

The flow rate may be adjusted after the fuel injector has already been installed. The adjusting body may be accessible from the outside on its end facing the fuel feed and may be displaced as desired in the sleeve and pushed into the aperture plate by an adjustment bolt after measurement of the actual amount.

The configuration of the sleeve including a thread which cooperates with a thread provided on the adjusting body may allow the adjusting body to be securely set in position very well. In addition, the adjusting body may be unscrewed from the sleeve again to replace it.

The aperture plate, whose cross section may be increased or reduced by introducing the adjusting body, may also be used in mass-produced fuel injectors. The adjustment of the adjusting body in the sleeve and the manufacture of the adjusting body, the sleeve and the aperture plate may be accomplished in a simple manner in terms of the manufacturing technology.

The static and dynamic flow rates may be adjusted separately, so that the preset flow rates need not be altered by further adjustments.

Other adjustment features of the fuel injector may not be affected by the adjustment of the flow rate through the sleeve and the adjusting body.

Exemplary embodiments of the present invention are illustrated in the diagrams and are explained in greater detail in the following description.

DETAILED DESCRIPTION

Before describing three exemplary embodiments of a fuel injector according to the present invention in greater detail on the basis ofFIGS. 2 through 5, a known fuel injector of the same design as in the exemplary embodiments, except for the measures according to the present invention, will first be explained briefly with regard to its essential components on the basis ofFIG. 1.

Fuel injector1may be configured in the form of a fuel injector for fuel injection systems of internal combustion engines having spark ignition of a fuel-air mixture. Fuel injector1may be suitable for direct injection of fuel into a combustion chamber of an engine.

Fuel injector1may include a nozzle body2in which a valve needle3may be guided. Valve needle3may be mechanically linked to a valve closing body4which cooperates with a valve seat face6situated on a valve seat body5to form a sealing seat. In this exemplary embodiment, fuel injector1may be an inwardly opening fuel injector1including an injection orifice7. Nozzle body2may be sealed by a seal8with respect to stationary pole9of a magnetic coil10. Magnetic coil10may be encapsulated in a coil housing11and may be wound on a field spool12which may be in contact with an internal pole13of magnetic coil10. Internal pole13and stationary pole9may be separated by a gap26and may be supported on a connecting component29. Magnetic coil10may be energized over a line19by electric current supplied via an electric plug contact17. Plug contact17may be surrounded by a plastic sheathing18which may be integrally molded on internal pole13.

Valve needle3may be guided in a valve needle guide14which may be designed in the shape of a disk. A matching adjustment disk15may be used to adjust the lift. On the other side of adjustment disk15there may be an armature20which may be in a friction-locked connection with valve needle3via a flange21, the valve needle being joined to flange21by a weld22. A restoring spring23may be supported on flange21; in the present design of fuel injector1, the restoring spring may be pre-stressed by a sleeve24. Fuel channels30athrough30c, which carry the fuel that may be supplied through a central fuel feed16and filtered through a filter element25to injection orifice7, run in valve needle guide14, armature20and on valve seat body5. Fuel injector1may be sealed by a seal28with respect to a receiving bore (not shown), e.g., in a fuel rail.

In the resting state of fuel injector1, armature20may be acted upon by restoring spring23against its direction of lift so that valve closing, body4may be held sealingly on valve seat6. When magnetic coil10is energized, it creates a magnetic field which moves armature20in the direction of lift against the elastic force of restoring spring23, the lift being predetermined by a working gap27between internal pole12and armature20in the resting position. Armature20also entrains flange21, which may be welded to valve needle3, in the direction of lift. Valve closing body4, which may be mechanically linked to valve needle3, may be lifted up from the valve seat face, and fuel may be injected through injection orifice7.

When the coil current may be turned off, armature20drops back from internal pole13due to the pressure of restoring spring23after the magnetic field has subsided sufficiently, so that flange21, which may be mechanically linked to valve needle3, moves against the direction of lift. Valve needle3may be thus moved in the same direction, so that valve closing body4may be set down on valve seat face6, and fuel injector1may be closed.

In an excerpt of a sectional diagram,FIG. 2shows the detail of fuel injector1which is labeled as II inFIG. 1.

The first exemplary embodiment of fuel injector1according to the present invention illustrated inFIG. 2shows the inlet-side part of fuel injector1without filter element25, which is present in central fuel feed16inFIG. 1. WhereasFIG. 1shows only sleeve24, which may be needed for adjusting the dynamic fuel flow which may be influenced by the opening and closing times, the exemplary embodiment illustrated inFIG. 2also has an adjusting body40which may be inserted into sleeve24and may be used for adjusting the static fuel flow, i.e., the flow of fuel in the opened static state. Adjusting body40has a cylindrical shape in the present exemplary embodiment and may be configured with a taper in the form of a truncated cone on injection end41. On its injection end42, sleeve24may be closed by an aperture plate43. Aperture plate43and sleeve24may be designed in one piece or they may be manufactured as two different parts. In the present exemplary embodiment, sleeve24and aperture plate43form one overall part. For the sake of facilitating installation, sleeve24may include a lateral slot44which extends as far as aperture plate43.

To regulate the static fuel flow, adjusting body40may be displaced in sleeve24in the injection direction using adjustment bolt45. Then conical injection end41of adjusting body40may be pushed into aperture plate43. The fuel flow through fuel injector1decreases depending on how far injection end41of adjusting body40projects into a borehole46in aperture plate43.

The dynamic fuel flow may be determined by the position of sleeve24. The further sleeve24may be pressed into a central recess47in fuel injector1by a suitable tool, the greater is the pre-stress acting on restoring spring23and the longer it lasts until fuel injector1is opened in the opening operation or the faster fuel injector1may be closed in the closing operation. This means that the dynamic fuel flow through fuel injector1decreases with an increase in the pre-stress on restoring spring23or with an increase in the depth of installation of sleeve24.

If sleeve24is introduced into central recess47in a certain desired position, the static fuel flow through fuel injector1when the latter is open may be adjusted via adjusting body40. To determine the proper flow rate and the correct position of adjusting body40in sleeve24, first the actual flow through fuel injector1may be measured. The actual measured value may then be compared with a predetermined setpoint value of the flow rate. Then adjusting body40may be displaced in sleeve24in the direction of injection by adjustment bolt45until the actual value matches the setpoint value. Since it is no longer possible to remove adjusting body40from sleeve24, to this end fuel injector1must have a static flow rate which is greater than the setpoint value before adjusting the static flow rate.

When the setpoint value for the flow rate through fuel injector1has been reached, adjustment bolt45may be removed and instead filter element25may be inserted into central recess47of fuel injector1, as illustrated inFIG. 1.

In a detail of a sectional diagram,FIG. 3shows the detail of a second exemplary embodiment of fuel injector1which is labeled as II inFIG. 1.

The second exemplary embodiment of fuel injector1according to the present invention differs from the first exemplary embodiment illustrated inFIG. 2in the design of adjusting body40which may be screwed into sleeve24. To do so, sleeve24may be provided with an internal thread51and adjusting body40may be provided with an external thread50. Adjusting body40is thus no longer pressed into sleeve24, but instead may be screwed into it by using a suitable adjusting tool52, e.g., a screwdriver. To this end, an inlet end53of adjusting body40may include a tool groove54in which a corresponding projection55on adjusting tool52engages.

In this exemplary embodiment of fuel injector1according to the present invention, it is not necessary for the actual flow rate of fuel injector1at the beginning of the adjustment to be higher than the setpoint flow rate, because adjusting body40may be screwed into any desired position in sleeve24via external thread50and internal thread51.

FIG. 4shows a third exemplary embodiment of fuel injector1according to the present invention in the detail labeled as II inFIG. 1.

In the present exemplary embodiment, sleeve24does not include an aperture plate43, but instead may be configured as a hollow cylinder including a side slot44. Adjusting body40may be cylindrical and may include an axial groove60on its outer periphery. Groove60may have various cross sections and begins on injection end41of adjusting body40, continuing to inlet end53of adjusting body40as it becomes wider.

The flow rate through fuel injector1may be adjusted by a displacement of adjusting body40in the direction of injection. In contrast with the exemplary embodiments inFIGS. 2 and 3, where the fuel flow rate through fuel injector1decreases with an increase in the depth to which adjusting body40may be screwed or pressed into sleeve24, in the present exemplary embodiment the flow rate increases with an increase in the depth of insertion of adjusting body40.

When adjusting body40is inserted into sleeve24and has been pushed in to the extent that injection end41of adjusting body40and injection end41of sleeve24are flush with one another, there may be only minimal fuel flow through fuel injector1or none at all. The further adjusting body40may be pressed through sleeve24in the direction of injection, the greater is the wetted cross section made available for flow through groove60.

With this arrangement the flow rate need not be measured repeatedly and compared with the setpoint value, but instead adjusting body40may be pushed continuously further into sleeve24until the actual value of flow through fuel injector1matches the setpoint value.

FIGS. 5A-5Cshow cross sections through injection end41,42of adjusting body40and sleeve24along line V-V. In adjusting body40, which fills up sleeve24, groove60may be configured so that fuel flows through it in the direction of the valve seat.

Groove60may have various cross sections. In the first exemplary embodiment, which is illustrated inFIG. 5A, groove60is U-shaped, while the exemplary embodiment illustrated inFIG. 5Bincludes a C-shaped groove60.

The exemplary embodiment illustrated inFIG. 5C, which includes a flattened planar area60instead of groove60, may be simple to manufacture. Adjusting body40thus assumes the shape of a notched cylinder.

FIG. 6Ashows a fourth exemplary embodiment of fuel injector1according to the present invention. In contrast with preceding exemplary embodiments, sleeve24may include an external thread57which cooperates with an internal thread58of central recess47of fuel injector1. The position of sleeve24in central recess47of fuel injector1may thus be adjusted by turning it by using a suitable adjusting tool56. The inlet end of sleeve24may include a two-step recess59, the diameter of which tapers in two steps61and62in the direction of the fuel flow.

In the direction of injection, sleeve24may be supported on an intermediate sleeve31which may be clamped between sleeve24and restoring spring23. This results in no rotational force being applied to restoring spring23when screwing in sleeve24, thus preventing metal shavings from being removed and also preventing the resulting contamination of fuel injector1.

The dynamic fuel flow may be defined by the position of sleeve24, as already explained above. The further sleeve24may be screwed into central recess47of fuel injector1using adjusting tool56, which may be a hexagon socket wrench, for example, the greater may be the pre-stress acting upon restoring spring23, and the longer it takes for fuel injector1to be opened in the opening operation and the more rapidly fuel injector1may be closed in the closing operation. This means that the dynamic fuel flow through fuel injector1decreases with an increase in the pre-stress of restoring spring23and with an increase in the depth of installation of sleeve24. Tool56then engages in recess59in sleeve24at the first step61. The position of adjusting body40in sleeve24is not affected by screwing in sleeve24using adjusting tool52.

When sleeve24is brought into a certain desired position in central recess47, the static fuel flow which flows through fuel injector1when the latter is opened may be adjusted via adjusting body40. In the present exemplary embodiment this second adjustment step is identical to the method illustrated inFIG. 4. Only stepped recess59in sleeve24is different, because adjusting body40may be displaced by tool45, which has a smaller diameter than adjusting tool56. Adjusting tool45thus acts on second step62, without influencing the adjustment of sleeve24in recess47of fuel injector1.

Sleeve24including external thread57may be combined with any desired adjusting body40, in particular, with adjusting bodies40described in conjunction withFIGS. 2 and 3. Thus, for example, an exemplary embodiment may allow the positions of sleeve24as well as adjusting body40to be varied by turning them by using suitable adjusting tools56and52.

The present invention is not limited to the exemplary embodiments presented here and it may be suitable for any configuration of fuel injectors1, e.g., for fuel injectors1including piezoelectric or magnetostrictive actuators or outwardly opening fuel injectors1.