EP1573197B1 - Pump-nozzle unit and method for regulating the opening pressure of the same - Google Patents

Description

The invention relates to a method for adjusting the nozzle opening pressure of a pump-nozzle unit for supplying fuel into a combustion chamber of an internal combustion engine, wherein the pump-nozzle unit comprises: a fuel injection nozzle having a nozzle needle movable back and forth between a closed position and an open position comprises a spring which exerts on the nozzle needle a closing force, the amount of which depends on a force exerted on the spring biasing force, and a first pressure chamber which can be acted upon by a first pressure, wherein an opening force is exerted on the nozzle needle by the first pressure. Furthermore, the invention relates to a pump-nozzle unit for supplying fuel into a combustion chamber of an internal combustion engine, in particular a pump-nozzle unit whose nozzle orifice pressure has been adjusted by the method according to the invention, with a fuel injector, the one between a closed position and an open position and has movable nozzle needle, and with a spring through which a closing force is exerted on the nozzle needle, the height of which depends on a force exerted on the spring selected biasing force.

Such pump-nozzle units are used in particular in connection with pressure-controlled injection systems. An essential feature of a pressure-controlled injection system is that the fuel injector opens as soon as an opening force, which is influenced at least by currently prevailing pressures, is exerted on the nozzle needle. Such pressure-controlled injection systems are used for fuel metering, fuel preparation, the formation of the course of injection and a seal of the fuel supply against the combustion chamber of the internal combustion engine. With pressure-controlled injection systems can be the timing of the flow rate during the injection control in an advantageous manner. This can have a positive influence on the engine's performance, fuel consumption and pollutant emission.

In the generic pump-nozzle units, the fuel pump and the fuel injection nozzle is formed as an integrated component. For each combustion chamber of the internal combustion engine, at least one pump-nozzle unit is provided, which is usually installed in the cylinder head. The fuel pump typically comprises a fuel pump piston which can be moved back and forth in a fuel pump cylinder and which is driven either directly by a tappet or indirectly via rocker arms by a camshaft of the internal combustion engine. The usually forming a second pressure chamber portion of the fuel pump cylinder is connected via a control valve with a fuel low pressure region, wherein sucked with the control valve open fuel from the low-pressure fuel area in the second pressure chamber and pushed back at further open control valve from the second pressure chamber in the low-pressure fuel area becomes. As soon as the control valve is closed, the fuel pump piston compresses the fuel in the second pressure chamber and thus builds up the pressure. The second pressure chamber communicates with a first pressure chamber, wherein a first pressure prevailing in the first pressure chamber exerts an opening force on the nozzle needle, for example on a section of the nozzle needle having a shoulder.

The first pressure prevailing in the first pressure chamber, in which the nozzle needle opens and an injection takes place, is referred to as nozzle opening pressure. In order to meet the functional requirements of a unit injector, it is necessary to adjust the nozzle opening pressure, and the more accurate the nozzle opening pressures, the more accurate the adjustment margin are. It is known to pre-assemble at least the spring-receiving component and the spring and the fuel injector on a base disk for adjusting the nozzle opening pressure and then to measure the actual nozzle opening pressure on a pressure test stand. From the measured actual nozzle opening pressure, a predetermined target nozzle opening pressure and the spring rate of the spring, the required thickness of an insert disc can be calculated, which is inserted to bias the spring and thus to change the nozzle opening pressure in the pump-nozzle unit. To insert the insert disk, the pump-nozzle unit in the prior art must be at least partially disassembled and reassembled after inserting the dial. Subsequently, it is necessary in many cases to check the changed by the insertion of the washer nozzle opening pressure again on the pressure test. If the desired nozzle opening pressure is not yet achieved with the mounted insert disk, it is necessary to disassemble the unit injector again and to use an insert disk with a different thickness.

The method described above is due to the required disassembly and assembly steps and the time of these separate measurement of the actual nozzle opening pressure very expensive and therefore associated with high costs.

document US 4,607,421 discloses a method for adjusting the nozzle opening pressure of a unit for supplying fuel in a combustion chamber of an internal combustion engine.

The invention has the object of developing the generic method and the generic pump-nozzle units such that an accurate nozzle opening pressure is ensured in a cost effective manner.

This object is solved by the features of the independent claims.

Advantageous embodiments and modifications of the invention will become apparent from the dependent claims.

The method according to the invention builds on the state of the art in that it comprises the following concurrently executed steps: applying the first pressure space at a first pressure, and varying the biasing force applied to the spring until a selected biasing force is reached at which moves the nozzle needle at the desired level of the first pressure in the open or closed position. In this case, in addition to the biasing force exerted on the spring optionally also the first pressure can be varied, if this is advantageous. It should also be noted that the first pressure for adjusting the nozzle opening pressure is preferably not generated via the fuel pump assigned to the pump-nozzle unit, at least in the operational state, but externally. The movement of the nozzle needle in the open or closed position, for example, directly and / or over the. History of the first pressure to be detected. The method according to the invention makes it possible to set the nozzle opening pressure very accurately without (multiple) disassembly and assembly steps and results in a stable pumping function.

The method is provided so that an end portion of the spring is locked in a selected position which the end portion of the spring occupies when the selected biasing force is applied to the spring. The locking of the end portion of the spring is preferably also fully automatically, either while the selected biasing force is detected or subsequently.

The method is further provided so that the locking of the end portion of the spring in the selected position by a inserted into the pump-nozzle unit biasing element, which is the selected position of the End section of the spring forces. In order to force the selected position of the end portion of the spring, the biasing member may act on the end portion of the spring either directly or indirectly, for example, via another member.

The method may be arranged to provide the biasing member of suitable dimensions to force the selected position of the end portion of the spring. A pump-nozzle unit whose nozzle-opening pressure has been adjusted according to this embodiment may not be differentiated from a unit injector whose nozzle-opening pressure has been adjusted by the known method explained in the opening paragraph. Nevertheless, this embodiment of the method according to the invention can also be carried out much more simply than the known methods, since the suitable dimensions of the pretensioning element, in contrast to the prior art, need not be calculated by the spring rate of the spring and so on, but for example by a length measurement or a hydraulic opening pressure measurement can be determined directly, so that a multiple disassembly and assembly can be avoided in any case.

However, the method is provided so that the biasing member is locked in a selected position to force the selected position of the end portion of the spring. In this case, since the biasing member is locked in a selected position which ensures the selected biasing force, it is not necessary in this embodiment to provide biasing members of defined length classes.

In the context described above, it is particularly preferred that the biasing element by frictional and / or positive connection locked in its selected position. In this case, a frictional engagement is particularly preferred, for example, a frictional engagement with a coefficient of friction of 0.1 ö 0.2.

However, the method is provided so that the biasing element to achieve the frictional and / or positive connection is transformed. Such reshaping can be achieved, for example, by pressing the biasing element into a conical section of the spring chamber.

Furthermore, it may be advantageous that the biasing element is in the form of a sleeve or a slotted sleeve.

Additionally or alternatively, embodiments are contemplated in which it is provided that the biasing element is designed in the form of a cup, in the bottom of which a bore is provided.

In the method according to the invention, the biasing element is arranged in a conical section of the pump-nozzle unit and formed conically at least in sections.

According to a first preferred embodiment of the method according to the invention it is provided that the variation of the biasing force is effected by changing the position of the biasing element. For this purpose, the biasing member, for example, by means of a Einziehstempels be pressed gradually or continuously into the spring chamber until the desired nozzle opening pressure results. The force required for pressing in the biasing element is preferably significantly higher than the selected Biasing force. This can be ensured, for example, by providing a suitable coefficient of friction or a suitable coefficient of friction.

In an alternative embodiment of the method according to the invention it is provided that the variation of the biasing force is effected by changing the position of a mandrel. In this embodiment, for example, it may be provided that the Einrückstempel provided for pressing in the biasing member has a bore through which the mandrel extends, wherein an end portion of the mandrel may act directly or indirectly on the end portion of the spring. In this solution, it is possible to increase the biasing force to determine the selected biasing force and then reduce again. The mandrel can act, for example via a perforated disc on the end portion of the spring. The biasing member is preferably brought to its final selected position by the retraction punch only when the selected biasing force is determined.

The inventive pump-nozzle unit is based on the generic state of the art in that the height of the selected biasing force depends on a selected position of a biasing member in which the biasing member is locked in the pump-nozzle unit. The pump-nozzle units according to the invention differ from the known pump-nozzle units in that the height of the selected biasing force not via a biasing element with defined dimensions, such as an insert disc with a defined thickness, but on the position or position of the biasing member in the Pump-nozzle unit is set. Such pump-nozzle units can be produced more cost-effectively than the known pump-nozzle units, since the adjustment of the nozzle opening pressure on the position of the biasing element can be carried out inexpensively, for example by the inventive method.

In the pump-nozzle unit according to the invention is preferably further provided that the biasing element forces a selected position of an end portion of the spring.

In preferred embodiments of the inventive pump-nozzle unit is further provided that the biasing element is locked by frictional and / or positive locking in its selected position.

In this context, it can further be provided that the biasing element is converted to achieve the frictional and / or positive connection.

Similar to the method according to the invention, the pump-nozzle unit according to the invention also comprises embodiments in which it is provided that the pretensioning element is designed in the form of a sleeve or a slotted sleeve.

Alternatively it can be provided that the biasing element is in the form of a cup, in the bottom of which a bore is provided.

In the case of the pump-nozzle unit according to the invention, provision may also be made for the pretensioning element to be conical at least in sections.

Additionally or alternatively, it may be provided that the biasing element is arranged in a conical section of the pump-nozzle unit.

Essential to the invention is the recognition that the nozzle opening pressure can be set very accurately and inexpensively, when the biasing force of the spring is varied while pressure applied to the first pressure chamber until the desired injection behavior is achieved.

The invention will now be described by way of example with reference to the accompanying drawings with reference to preferred embodiments.

Figur 1

eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Pumpe-Düse-Einheit;

Figur 2

eine schematische Darstellung, die das Einstellen des Düsenöffnungsdrucks gemäß einer ersten Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 3a

einen Graph, der einen möglichen Verlauf der auf die Feder ausgeübten Vorspannkraft in Abhängigkeit von der Zeit für die erste Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 3b

einen Graph, der einen möglichen Verlauf für den Pumpendruck in Abhängigkeit von der Zeit für die erste Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 3c

einen Graph, der einen möglichen Verlauf für den ersten Druck sowie das Öffnungs- und Schließverhalten der Düsennadel in Abhängigkeit von der Zeit veranschaulicht, für den in Figur 3a dargestellten Kraftverlauf und den in Figur 3b dargestellten Druckverlauf;

Figur 3d

das Einspritzverhalten der Pumpe-Düse-Einheit in Abhängigkeit von der Zeit, für den in Figur 3a dargestellten Kraftverlauf und den in Figur 3b dargestellten Druckverlauf;

Figur 4

eine schematische Darstellung, die das Einstellen des Düsenöffnungsdrucks gemäß einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 5a

einen Graph, der einen möglichen Verlauf der auf die Feder ausgeübten Vorspannkraft in Abhängigkeit von der Zeit für die zweite Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 5b

einen Graph, der einen möglichen Verlauf für den Pumpendruck in Abhängigkeit von der Zeit für die zweite Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 5c

einen Graph, der einen möglichen Verlauf für den ersten Druck sowie das Öffnungs- und Schließverhalten der Düsennadel in Abhängigkeit von der Zeit veranschaulicht, für den in Figur 5a dargestellten Kraftverlauf und den in Figur 5b dargestellten Druckverlauf;

Figur 5d

das Einspritzverhalten der Pumpe-Düse-Einheit in Abhängigkeit von der Zeit, für den in Figur 5a dargestellten Kraftverlauf und den in Figur 5b dargestellten Druckverlauf;

Figur 6a

einen Graph, der einen möglichen Verlauf der auf die Feder ausgeübten Vorspannkraft in Abhängigkeit von der Zeit für eine dritte Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 6b

einen Graph, der einen möglichen Verlauf für den Pumpendruck in Abhängigkeit von der Zeit für die dritte Ausführungsform des erfindungsgemäßen Verfahrens veranschaulicht;

Figur 6c

einen Graph, der einen möglichen Verlauf für den ersten Druck- sowie das Öffnungs- und Schließverhalten der Düsennadel in Abhängigkeit von der Zeit veranschaulicht, für den in Figur 6a dargestellten Kraftverlauf und den in Figur 6b dargestellten Druckverlauf;

Figur 6d

das Einspritzverhalten der Pumpe-Düse-Einheit in Abhängigkeit von der Zeit, für den in Figur 6a dargestellten Kraftverlauf und den in Figur 6b dargestellten Druckverlauf;

Figur 7

eine schematische Darstellung eines Vorspannelementes in Form einer Hülse oder einer geschlitzten Hülse;

Figur 8

eine schematische Darstellung eines Vorspannelementes in Form eines tiefgezogenen oder fliessgepressten und gelochten Napfes; und

Figur 9

eine schematische Darstellung eines Vorspannelementes in Form eines konischen Stopfens.

Show it:

FIG. 1

a schematic representation of an embodiment of the pump-nozzle unit according to the invention;

FIG. 2

a schematic diagram illustrating the setting of the nozzle opening pressure according to a first embodiment of the method according to the invention;

FIG. 3a

a graph illustrating a possible course of the force exerted on the spring biasing force as a function of time for the first embodiment of the method according to the invention;

FIG. 3b

a graph illustrating a possible curve for the pump pressure as a function of time for the first embodiment of the method according to the invention;

Figure 3c

a graph illustrating a possible course for the first pressure and the opening and closing behavior of the nozzle needle as a function of time for the in FIG. 3a shown force curve and the in FIG. 3b illustrated pressure curve;

3d figure

the injection behavior of the unit injector unit as a function of time for which FIG. 3a shown force curve and the in FIG. 3b illustrated pressure curve;

FIG. 4

a schematic diagram illustrating the setting of the nozzle opening pressure according to a second embodiment of the method according to the invention;

FIG. 5a

a graph illustrating a possible course of the force exerted on the spring biasing force as a function of time for the second embodiment of the method according to the invention;

FIG. 5b

a graph illustrating a possible course for the pump pressure as a function of time for the second embodiment of the method according to the invention;

FIG. 5c

a graph illustrating a possible course for the first pressure and the opening and closing behavior of the nozzle needle as a function of time for the in FIG. 5a shown force curve and the in FIG. 5b illustrated pressure curve;

FIG. 5d

the injection behavior of the unit injector unit as a function of time for which FIG. 5a shown force curve and the in FIG. 5b illustrated pressure curve;

FIG. 6a

a graph illustrating a possible course of the force exerted on the spring biasing force as a function of time for a third embodiment of the method according to the invention;

FIG. 6b

a graph illustrating a possible course for the pump pressure as a function of time for the third embodiment of the method according to the invention;

FIG. 6c

a graph illustrating a possible course for the first pressure and the opening and closing behavior of the nozzle needle as a function of time, for the in FIG. 6a shown force curve and the in FIG. 6b illustrated pressure curve;

FIG. 6d

the injection behavior of the unit injector unit as a function of time for which FIG. 6a shown force curve and the in FIG. 6b illustrated pressure curve;

FIG. 7

a schematic representation of a biasing element in the form of a sleeve or a slotted sleeve;

FIG. 8

a schematic representation of a biasing element in the form of a deep-drawn or flow-pressed and perforated cup; and

FIG. 9

a schematic representation of a biasing element in the form of a conical plug.

FIG. 1 shows a schematically illustrated embodiment of the pump-nozzle unit according to the invention. The illustrated pump-nozzle unit 10 for supplying fuel 12 into a combustion chamber 14 of an internal combustion engine has a fuel pump 32-40. In this case, a fuel pump piston 36 in a fuel pump cylinder 34 is movable back and forth. The fuel pump piston 36 is driven directly or indirectly via a camshaft, not shown, of the internal combustion engine. The compression space of the fuel pump cylinder 34 forms a second pressure chamber 32. The second pressure chamber 32 is connected via a fuel line 38 with a piezoelectric-operated control valve 40 known per se. The control valve 40 serves to either close the fuel line 38 or to a fuel low pressure area 42 to connect, can be sucked from the fuel 12. In its open rest position is based on a FIG. 1 upward movement of the fuel pump piston 36 fuel 12 sucked from the low-pressure fuel area 42 into the second pressure chamber 32. If the control valve 40 is based on a FIG. 1 downwardly directed movement of the fuel pump piston 36 is still in its open rest position, previously sucked into the second pressure chamber 32 fuel 12 can be pressed back into the low-pressure fuel area 42. In a control of the control valve 40. This closes the fuel line 38. This is compressed in the second pressure chamber 32 sucked fuel 12 at a downwardly directed movement of the fuel pump plunger 36, whereby the second pressure p is produced in the second pressure chamber 32 _32nd The illustrated unit injector 10 further includes a fuel injector, generally designated 16, which has a nozzle needle 18 reciprocable between a closed position and an open position. The related to FIG. 1 upper end portion of the nozzle needle 18 has a disc 48 and a guide pin 56, which in the in FIG. 1 embodiment shown in a spring chamber 30 is guided. A spring 20 is disposed in the spring chamber 30 and exerts a downward closing force on the disc 48 and the guide pin 56 and thus the nozzle needle 18 from. The upper end portion 24 of the spring 20 is supported on a cup-shaped biasing member 26 which is locked in a selected position Y _S in the spring chamber 30. In the FIG. 1 related to the upper edge of the closure element 26 selected position Y _S of the shutter member 26 forces a selected position X _S of the end portion 24 of the spring 20 via the selected position Y _S is the closure element 26 and the selected position X _S of the end portion 24 of the spring 20 set a selected biasing force F _S , which is exerted on the spring 20. The height of this selected biasing force F _S affects the nozzle opening pressure, which will be explained in more detail below. A first pressure chamber 22 surrounds a portion of the nozzle needle 18 having a shoulder 46. The first pressure chamber 22 communicates via a connecting line 44 with the second pressure chamber 32. Thus, in the first pressure chamber 22 under a first pressure p ₂₂ stationary fuel exerts an opening force on the nozzle needle 18. This opening force counteracts the force exerted by the spring 20 on the disc 48 and the guide pin 56 closing force. It can be seen that the selected position Y _{S of} the biasing member 26 and the selected position X _{S of} the end portion 24 of the spring 20, the height of the required in the first pressure chamber 22 first pressure p _22S defined to open the nozzle needle 18 and thus an injection process leads. The closure element 26 is locked in the spring chamber 30 by frictional engagement, for example, a coefficient of friction of 0.1 ö 0.2 can be provided. Although this in FIG. 1 is not shown, the closure element 26 and / or the spring chamber 30 may be at least partially conical in order to facilitate the locking of the closure element 26 in the spring chamber 30. Furthermore, although this is also not shown, the spring chamber 30 and / or another portion of the pump-nozzle unit can be pressurized to affect the opening behavior of the nozzle needle 18. For example, a pressure prevailing in the spring chamber 30 would exert a further closing force on the disc 48 and the guide pin 56 in addition to the closing force generated by the spring 20. In order to determine the selected position Y _{S of} the biasing member 26 and to lock the biasing member 26 in this position, the method according to the invention can be used in an advantageous manner, as will be explained in more detail below.

FIG. 2 FIG. 12 is a diagram illustrating the setting of the nozzle opening pressure according to a first embodiment of the method of the present invention. FIG. It is in a spring chamber 30 shown only in sections a spring 20 is arranged, whose lower end portion, not shown, exerts a closing force on a nozzle needle. A biasing member 26 formed in the form of a perforated cup forces the upper end portion 24 of the spring 20 into a selected position X _S and applies a selected biasing force F _S to the spring 20. The arrangement is chosen such that the biasing member 26 can be pressed by a Einziehstempel 50 in the spring chamber 30, wherein the force required for this purpose F _{E is} significantly higher than the selected biasing force F _S. In other words, the biasing member 26 is frictionally locked in the spring chamber 30 with respect to the selected biasing force F _s , but can be pushed further into the spring chamber 30 by a significantly higher force F _E exerted on the retractable punch 50. The biasing member 26 is based on the representation of FIG. 2 pressed so far down into the spring chamber 30 or until it assumes a selected position Y _S , in which the end portion 24 of the spring 20 is fixed in a selected position X _S , in which the selected biasing force F _S exerted on the spring 20 becomes. The setting of the selected biasing force F _S will be described below with reference to FIG FIGS. 3a to 3d explained in more detail.

FIG. 3a shows a graph illustrating a possible course of the force exerted on the spring biasing force as a function of time for the first embodiment of the method according to the invention, FIG. 3b shows a graph illustrating a possible course for the pump pressure as a function of time for the first embodiment of the method according to the invention, Figure 3c shows a graph illustrating a possible course for the nozzle chamber pressure or the first pressure and the opening and closing behavior of the nozzle needle as a function of time for the in FIG. 3a shown force curve and the in FIG. 3b illustrated pressure curve, and 3d figure shows the injection behavior of the unit injector unit as a function of time for which FIG. 3a shown Force curve and the in FIG. 3b illustrated pressure curve. FIG. 3b It can be seen that the system during the adjustment process with a constant second pressure p _{32 is applied} in the illustrated case 700 bar. The second pressure p ₃₂ is not used to adjust the nozzle opening pressure by the fuel pump 32 to 42 (see FIG. 1 ) but externally. The representation of FIG. 3a It can be seen that the biasing force exerted on the spring 20 is gradually increased. Based on the illustration of Figure 2, the increase in the biasing force F by the Einziehstempel 50 is gradually moved further down, so that the spring 20 is biased gradually over the biasing member 26 further. Figure 3c illustrates the course of the first pressure p ₂₂ within the first pressure chamber 22 (see FIG. 1 ). Furthermore is Figure 3c to take the opening and closing behavior of the nozzle needle, wherein the first pressure p ₂₂ at which the nozzle needle respectively opens, also increases with an increasing biasing force, as the first pressure p ₂₂ , in which the nozzle needle closes again. The period of time between each opening and closing of the nozzle needle 18 respectively defines the duration of an injection, as this 3d figure can be seen. The biasing force F is incrementally increased until the nozzle needle 20 opens at a selected first (opening) pressure p _22S . The biasing force F exerted on the spring 20 at this time corresponds to the selected biasing force F _S. Once this selected biasing force F _{S is} reached, the Einziehstempel 50 (see FIG. 2 ) are removed, since the biasing member 26 is in its selected position Y _S , in which it locks the end portion 24 of the spring 20 in its selected position X _S. Instead of in FIG. 3a shown stepwise increase of the biasing force F is alternatively also a continuous increase of the biasing force F in question.

FIG. 4 FIG. 12 is a diagram showing the setting of the nozzle opening pressure according to a second embodiment. FIG of the inventive method illustrated. Also in this embodiment, a spring 20 is disposed in a spring chamber 30 shown only in sections, the lower end portion, not shown, a closing force on a nozzle needle 18 exerts. A perforated disc 54 is disposed between a biasing member 26 and the upper end portion 24 of the spring 20. The biasing member 26 is formed in the form of a perforated cup, wherein a mandrel 28 extends through the recess in the biasing member 26 and a biasing force F on the perforated disc 54 and thus the spring 20 can exercise. The mandrel 28 further extends through a bore 52 provided in a retractable die 50, such that the mandrel 28 can be moved up and down in a direction Z independently of the retractable die 50. As shown by FIG. 4 is the biasing member 26 already in its selected position Y _S , in which the upper end portion 24 of the spring 20 is forced over the perforated disc 54 in its selected position X _S. During the determination of the selected biasing force F _S or the selected position X _S are the biasing member 26 and the Einziehstempel 50 with respect to the illustration of FIG. 4 positioned further upwardly so that the mandrel 28 can be moved up and down independently of the retractor 50 and the biasing member 26 until the mandrel 28 is in a selected position Z _s in which the selected biasing force F _{S is} applied to the spring 20 is exercised. Once the mandrel 28 has taken its selected position Z _S , in which the end portion 24 of the spring 20 is in its selected position X _S , the Einziehstempel 50, and with it the biasing member 26, moves down by a force F _E is applied to the Einziehstempel 50, which must preferably be significantly higher than the selected biasing force F _S to move the biasing member 26. Subsequently, the mandrel 28 and the Einziehstempel 50 can be removed because the biasing member 26 is frictionally locked relative to the biasing force F _S in the spring chamber 30.

As an alternative to locking the biasing member 26 in the spring chamber 30, it is also possible to detect, for example, the distance that the mandrel 28 has been moved into the spring chamber 30 until the selected biasing force F _{S is} reached, and then insert a biasing member of a defined length which ensures the selected position X _{S of} the end portion 24 of the spring 20. The following explanation of the determination and adjustment of the selected biasing force F _S , however, refers to an embodiment of the invention, in accordance with the representation of FIG. 4 a biasing member 26 is used, which is locked in a selected position Y _S in the spring chamber 30.

FIG. 5a shows a graph illustrating a possible course of the force exerted on the spring biasing force as a function of time for the second embodiment of the method according to the invention, FIG. 5b shows a graph illustrating a possible curve for the pump pressure as a function of time for the second embodiment of the method according to the invention, FIG. 5c shows a graph illustrating a possible course for the first pressure and the opening and closing behavior of the nozzle needle as a function of time for the in FIG. 5a shown force curve and the in FIG. 5b illustrated pressure curve, and FIG. 5d shows the injection behavior of the unit injector unit as a function of time for which FIG. 5a shown force curve and the in FIG. 5b illustrated pressure curve. Also in this embodiment, the second pressure p ₃₂ in the second pressure space 32 is preferably provided by an external pressure source to determine the selected biasing force F _S or to set the nozzle opening pressure to p _22S . How to do this by comparing the FIGS. 5b and 5c can be seen, a setting run is first performed while the nozzle needle 18 repeatedly opens and closes (see FIG. 5c ). For this purpose, a second pressure p ₃₂ of 500 bar to the system created (see FIG. 5b ). At the same time, the mandrel 28 is acted upon by the spring 20 FIG. 4 a relatively low biasing force of 500 N exercised. Subsequently, both the second pressure p ₃₂ and the biasing force F is increased, wherein to increase the biasing force F of the mandrel 28 with respect to the representation of FIG. 4 continue down. At this time, the Einziehstempel 50 and the biasing member 26 of FIG. 4 even in a higher position than shown, so that the spring 20 can be more or less compressed by an up and down movement of the mandrel 28 and thus biased. After the preload force F has been increased to more than 700 N, it is gradually reduced again (see FIG. 5a ) by the mandrel 28 of FIG. 4 is moved up again. As soon as the nozzle needle 18 opens at a desired opening pressure p _22S in the first pressure chamber, the selected biasing force E _{S is} reached and the upward movement of the mandrel 28 is stopped. Subsequently, the Einziehstempel 50 and with him the biasing member 26 based on FIG. 4 moved so far down that the biasing member 26 is locked in its selected position Y _S , based on the selected biasing force F _S by frictional engagement with the spring chamber 30. After the biasing member 26 has been locked in its selected position Y _S to the end portion 24 of Forcing spring 20 into its selected position X _S , both retractable punch 50 and mandrel 28 are removed.

FIG. 6a shows a graph illustrating a possible course of the force exerted on the spring biasing force as a function of time for a third embodiment of the method according to the invention, FIG. 6b shows a graph illustrating a possible course for the pump pressure as a function of time for the third embodiment of the method according to the invention, FIG. 6c shows a graph illustrating a possible course for the first pressure and the opening and closing behavior of the nozzle needle as a function of time for the in FIG. 6a shown force curve and the in FIG. 6b illustrated pressure curve, and FIG. 6d shows the injection behavior of the unit injector unit as a function of time for which FIG. 6a shown force curve and the in FIG. 6b illustrated pressure curve. In the in the FIGS. 6a to 6d illustrated embodiment of the method according to the invention, the biasing force F corresponding to the course of FIG. 6a continuously changed, in the case shown increased. Furthermore, the pressure, which is preferably also generated externally in this case, is p ₃₂ in FIG FIG. 6b illustrated case 750 bar. For example, in these circumstances, a buzzing of the nozzle needle 18, that is, the nozzle needle 18 opens and closes at short intervals (see FIG. 6c ). This makes it possible to detect the desired opening pressure p _22s exclusively over the course of the first pressure p ₂₂ . For this purpose, the biasing force F, for example, as long as continuous (see FIG. 6a ) or in small increments until the desired opening _pressure p _22s of the illustrated case 700 bar is reached for the first time (see FIG. 6c ). If appropriate, this procedure can be carried out both with the first embodiment according to FIG FIG. 2 as well as with the second embodiment according to FIG. 4 be combined.

In all embodiments in which the biasing element 26 is locked by frictional engagement, it is preferred that for the force F _E required to move the biasing element 26, F _E ≥ 10 * F _s , where F _{s is} the selected biasing force to be adjusted.

FIG. 7 shows a schematic representation of a biasing element in the form of a sleeve or a slotted sleeve, FIG. 8 shows a schematic representation of a biasing element in the form of a deep-drawn or flow-pressed and perforated cup and FIG. 9 shows a schematic representation of a biasing element in the form of a conical plug. Although this is not necessary in every case, all illustrated embodiments of the biasing member 26 on a breakthrough. Such a breakthrough may be required, for example, when the spring chamber 30 is filled from above with pressurized fuel to exert a further closing force on the nozzle needle 18.

The features of the invention disclosed in the foregoing description, in the drawings and in the claims may be essential both individually and in any combination for the realization of the invention as defined in the appended claims.

Claims (13)

1. Method for adjusting the nozzle opening pressure in a pump-nozzle unit (10) for feeding fuel (12) into a combustion chamber (14) of an internal combustion engine, with the pump-nozzle unit (10) comprising:

   - a fuel injection nozzle (16), which comprises a nozzle needle (18) which can be moved to and fro between a closed position and an open position,

   - a spring (2), which exerts a closing force on the nozzle needle (18), the extent of which depends on a pretensioning force exerted on the spring (20), and

   - a first pressure chamber (22) which can be subjected to a first pressure (p₂₂), with a opening force being exerted on the nozzle needle (18) by means of the first pressure (p₂₂),

   with the following steps being implemented simultaneously:

   - subjecting the first pressure chamber (22) to a first pressure (p₂₂), and

   - varying the pretensioning force (F) exerted on the spring (20) until a selected pretensioning force (F _s ) is achieved, with which the nozzle needle (20) moves into the open and/or closed position when the first pressure (p₂₂) reaches the desired level, with the end section (24) of the spring (20) being stopped in the selected position (X _S ) by means of a pretensioning element (26) inserted into the pump-nozzle unit (10), said pretensioning element (26) forcing the selected position (X _S ) of the end section (24) of the spring (20), with the pretensioning element (26) being stopped in a selected position (Y _S ) in order to force the selected position (X _S ) of the end section (24) of the spring (20), with the pretensioning element (26) being stopped in its selected position (Y _S ) by friction;

   characterised in that
   the pretensioning element (26) is embodied as a conical stopper and the pretensioning element (26) is arranged in a conical section of the pump-nozzle unit (10).
2. Method according to claim 1
   characterised in that
   an end section (24) of the spring (20) is stopped in a selected position (X _S ), which the end section (24) of the spring (20) assumes when the selected pretensioning force (F _S ) is exerted on the spring (20).
3. Method according to claim 1 or 2,
   characterised in that
   the pretensioning element (26) is provided with suitable dimensions in order to force the selected position (X _S ) of the end section (24) of the spring (20).
4. Method according to claim 1,
   characterised in that
   the pretensioning element (26) is stopped in its selected position (Y _S ) by a form-fit.
5. Method according to claim 1 or 4,
   characterised in that
   the pretensioning element (26) is formed in order to achieve the friction and/or form-fit.
6. Method according to one of claims 1 to 5,
   characterised in that
   the pretensioning element (26) is embodied in the form of a sleeve or a slotted sleeve.
7. Method according to one of claims 1 to 6,
   characterised in that
   the pretensioning element (26) is embodied in the form of a cup, in the base of which a hole is drilled.
8. Method according to one of claims 1 to 7,
   characterised in that
   the pretensioning force (F) is varied by modifying the position (Y) of the pretensioning element (26).
9. Method according to one of claims 1 to 7,
   characterised in that
   the pretensioning force (F) is varied by modifying the position of a mandrel (28).
10. Pump-nozzle-unit (10) for feeding fuel (12) into a combustion chamber (14) of an internal combustion engine, the nozzle opening pressure of which was adjusted using the method according to one of the preceding claims, comprising

    - a fuel injection nozzle (16), which comprises a nozzle needle (18) which can be moved to and fro between a closed position and an open position, and

    - a spring (20), by means of which a closing force is exerted on the nozzle needle (18), the extent of which depends on a selected pretensioning force (F _S ) exerted on the spring (20),

    with the extent of the selected pretensioning force (F _S ) depending on a selected position (Y _S ) of a pretensioning element (26), in which the pretensioning element (26) is stopped in the pump-nozzle unit (10), with the pretensioning element (26) forcing a selected position (X _S ) of an end section (24) of the spring (20), with the pretensioning element (26) being stopped in its selected position (Y _S ) by friction,
    characterised in that
    the pretensioning element (26) is embodied as a conical stopper, and the pretensioning element (26) is arranged in a conical section of the pump-nozzle unit (10).
11. Pump-nozzle unit (10) according to claim 10,
    characterised in that
    the pretensioning element (26) is formed in order to achieve the friction and/or form fit.
12. Pump-nozzle unit (10) according to one of claims 10 or 11,
    characterised in that
    the pretensioning element is embodied in the form of a sleeve or a slotted sleeve.
13. Pump-nozzle unit (10) according to one of claims 10 to 12,
    characterised in that
    the pretensioning element (26) is embodied in the form of a cup, in the base of which a hole is drilled.

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