EP1654456B1 - Fuel injection device for an internal combustion engine - Google Patents

Description

State of the art

The invention relates first of all to a fuel injection device for an internal combustion engine, having at least two valve elements which each have a closing in the direction of hydraulic control surface, which is assigned a hydraulic control chamber, with a control valve which influences the pressure in the control chamber, and with loading devices, which can act in the opening direction of the valve elements, wherein the prevailing in the control chamber hydraulic opening pressures of the valve elements are different.

The invention further relates to a method for operating such a fuel injection device.

A fuel injection device of the type mentioned is from the DE 101 22 241 A1 known. This shows an injection nozzle for internal combustion engines with two coaxially arranged valve elements. Both valve elements are stroke controlled, that is, they open when the pressure of a hydraulic fluid in a control chamber is lowered. The force acting in the opening direction of the valve elements is provided by acting on a corresponding pressure surface injection pressure. In this case, the outer valve element opens first and then the inner Valve member. If only the outer valve element to be opened, the pressure drop in the control room must be stopped in good time and the pressure to be increased again.

The reasons for implementing fuel injectors with multiple valve elements are as follows:

Particularly in the case of diesel internal combustion engines, in order to reduce emissions and to increase the efficiency, it is necessary to inject the fuel atomized as finely as possible into the corresponding combustion chambers of the internal combustion engine. This can be achieved by the injection pressure at which the fuel reaches the fuel injection device being high.

By using a plurality of valve elements, each releasing a certain number of fuel outlet openings, even if only a small amount of fuel to be injected, a sufficiently long injection duration can be achieved with good atomization quality, without simultaneously in that case in which large amount of fuel to be injected, an excessively long injection duration and / or an excessively high injection pressure to accept.

US 5,899,389 describes a fuel injection device with two valve elements, which can be opened sequentially by a change in the pressure applied to an opening face acting pressure surface.

The present invention has the object, a fuel injection device of the type mentioned so educate that they can be controlled as easily as possible and yet works reliably. At the same time a good emission and consumption behavior should be achieved when used on the corresponding internal combustion engine. Object of the present invention is also to provide a method of educate the aforementioned type so that even if only one valve element is to be actuated, this happens if necessary as quickly as possible.

The first object is achieved in a fuel injection device of the type mentioned above in that at least three different pressure levels can be adjusted by the control valve in the control chamber, wherein closed at a relatively high pressure level all valve elements, at a mean pressure level, a valve element open, and at a comparatively low pressure level all valve elements are open.

In a method of the type mentioned, the second-mentioned object is achieved in that in a fuel injection device of the above type for opening only one valve element, first the control chamber is connected to a high pressure port and then simultaneously to the high pressure port and a low pressure port.

Advantages of the invention

In the fuel injection device according to the invention, an additional average pressure level in the control chamber can be adjusted, in which the one valve element is already open, but in which the other valve element remains closed. In this way, longer Einspitzdauern can be realized with only one open valve element, which leads, especially in part-load operation to a favorable emission and consumption behavior of an internal combustion engine, in which the Kraftstoff-Einspritzvorricbtung invention is installed. simultaneously makes the device easy, since no separate controls for the valve elements with separate control spaces is required. Optionally, the fuel injection device may also include only a single control room.

The advantage of the method proposed according to the invention is that the pressure reduction is limited by the connection of the control chamber to the low-pressure connection and additionally to the high-pressure connection, namely to the level of a corresponding intermediate pressure.

Advantageous developments of the invention are specified in subclaims.

First, it is proposed that the control chamber is connected via an inlet throttle with a high pressure port, that the control valve is connected on the one hand to the control chamber and on the other hand to a low pressure port. In such a fuel injection device, the fuel injection can be completely controlled with only two pressure ports, namely a high pressure port and a low pressure port, and a simple control valve. This embodiment is therefore inexpensive and works reliably during operation.

In a further development, it is proposed that the control valve has a switching chamber with a switching element, which in a first switching position at a first valve seat leading to the low-pressure connection is present, in a second switching position abuts a leading to a bypass passage second valve seat, wherein the bypass passage is connected to the high pressure port, and in a third switching position rests neither on the first valve seat nor on the second valve seat. Such a control valve is simple and is therefore inexpensive.

Through the bypass channel, a high, a medium, or a low fluid pressure can be set in the switching chamber. Accordingly, the respective end pressures in the control room, and accordingly, the speeds at which the pressure drops in the control room arise. In addition, by connecting the switching chamber to the high-pressure port at the end of an injection, the control chamber can also be connected to the high-pressure port via the switching chamber, so that the pressure in the control chamber rises very rapidly and the valve elements close quickly. This is particularly advantageous with regard to the emission behavior.

In a further development of this, it is proposed that the control valve forms a throttle point in the third switching position towards the low-pressure connection. This allows limiting the fuel flow from the high pressure port directly to the low pressure port. As a result, less fuel must be pumped and a smaller fuel pump can be used.

It is also possible that the control chamber is connected to the high pressure port, that the control valve is connected via at least two control channels to the control chamber, and that the control valve in a first switching position separates all the control channels from a low pressure port, in a second switching position a control channel with the Low pressure port connects, and in a third switch position connects all the control channels with the low pressure port ..

Since the maximum flow of fuel from the high-pressure port into the control chamber is limited, depending on the outflow, which is set by the number of selected control channels, a higher or lower pressure level in the control room. This makes it possible to adjust any opening time of the other valve element can. In particular, at full load both valve elements can be opened directly at the start of injection. This achieves a maximum injection quantity for a given injection duration.

This fuel injection device is technically easy to implement and therefore particularly inexpensive. In principle, it is conceivable that the control channels are identical and therefore a double Abströmguerschnitt is available at a doubling the number of control channels. But you can also configure the control channels differently with each control channel assigned very specific throttle behavior. In this way, the pressure levels prevailing in the control room can be set very precisely.

Another easy way to realize different pressure levels in the control room to realize, is that the control chamber is connected to a high pressure port that the control valve connects the control chamber in a first switching position with a low pressure port and in a second switching position separates from this, and that the control valve is continuously controlled from the first switching position to the second switching position and back.

In this particularly preferred embodiment of the fuel injection device according to the invention only a simple 2/2-way valve is required for setting the different pressure levels in the control room. In the simplest case, the valve is closed again just before the second-opening valve element begins its opening movement (preferably before the first-opening valve element reaches its open end position), and it is reopened just before the first-opening valve element closes so sharply that the leaking fuel flow is throttled in an inadmissible manner. The mean pressure level is thus an average of a pulsating pressure curve, which is caused by the opening and closing of the control valve. By a rapid sequential opening and closing, for example by a pulsed or pulsed control, alternatively, a constant average pressure level can be set.

A further advantageous embodiment of the fuel injection device according to the invention provides that the valve elements are coaxial and an axial boundary surface of the control chamber has a circumferential sealing area, which in an open end position of the outer valve element the control chamber in an outer, connected to the high pressure port area, and a divided inside, connected to the control valve area. Due to the coaxial design, the fuel injector is very compact. Due to the sealing region, in the open end position of the outer valve element, the control chamber region assigned to the control surface of the inner valve element is separated from the inflow of high-pressure fuel. The pressure in this control room area is therefore very fast so that the inner valve element opens accordingly quickly. This reduces the emissions.

In all of the above fuel injectors, it is desirable that the control valve switch very quickly. This can then be realized in a simple manner if the control valve comprises a piezoelectric actuator.

In a further development, it is proposed that the control valve comprises a valve body which is hydraulically coupled to the piezoelectric actuator, wherein leakage fluid is used as the hydraulic fluid, which occurs at a guide at least one valve element. Due to the hydraulic coupling, the comparatively small stroke of the piezoactuator can be amplified in the sense of a hydraulic transmission. A corresponding valve body of the control valve can therefore release a sufficient flow cross-section when opening, without having large dimensions. By using the already existing leakage fuel for the hydraulic coupling can be dispensed with an additional fluid supply. This fuel injection device therefore still builds compact and comparatively inexpensive.

A further advantageous embodiment of the fuel injection device according to the invention is characterized in that a valve element has a driver acting in the opening direction on the other valve element. In this way, it is ensured that the later-opening valve element opens exactly when the first-opening valve element has made a certain stroke. In certain load / speed situations of the internal combustion engine, this leads to an injection course in which particularly low emissions occur. Depending on However, pressure in the control chamber can also be that the force exerted by the driver on the later opening valve element is not sufficient to open this. In this case, the driver acts as a stop that limits the stroke of the first opening valve element. This allows the injection of extremely small amounts of fuel.

In a further development, it is proposed that the driver is designed such that it only abuts the other valve element shortly before reaching the maximum stroke of the one valve element. This ensures that, on the one hand, only one valve element can be opened as long as it does not reach its maximum stroke and, on the other hand, that the second valve element opens safely by bringing the first valve element up to the maximum stroke.

Particularly preferred is that embodiment of the fuel injection device according to the invention, in which acting in the opening direction of the other valve member and the hydraulic control surface of the other valve element are tuned so that this valve element opens only when additionally from the driver of a valve element acting in an opening direction Force is exercised. Thus, the second valve element opens, therefore, not only a reduction in the pressure in the control chamber is required, but also the entrainment by the first opening valve element. This makes it possible to design the control surfaces and the loading means so that the opening pressures of the valve elements are very different, which increases the reliability in the operation of the fuel injection device.

drawing

Figur 1

eine teilweise geschnittene Darstellung von Bereichen eines ersten Ausführungsbeispiels einer Kraftstoff-Einspritzvorrichtung mit zwei koaxialen Ventilelementen;

Figur 2

eine schematische Darstellung der Kraftstoff-Einspritzvorrichtung von Figur 1 bei geschlossenen Ventilelementen;

Figur 3

eine schematische Darstellung ähnlich Figur 2 während eines Öffnungsvorgangs zum Öffnen beider Ventilelemente;

Figur 4

eine schematische Darstellung ähnlich Figur 2 mit geöffneten Ventilelementen;

Figur 5

eine schematische Darstellung ähnlich Figur 2 mit nur einem geöffneten Ventilelement;

Figur 6

ein Diagramm, in dem ein Druckverlauf in einem Steuerraum der Kraftstoff-Einspritzvorrichtung von Figur 2 während des in den Figuren 3 und 4 gezeigten Öffnungs- und Schließvorgangs aufgetragen ist;

Figur 7

ein Diagramm ähnlich Figur 6 für den in Figur 5 gezeigten Fall;

Figur 8

ein Diagramm, in dem der Verlauf der Schaltstellungen der Ventilelemente für den in Figur 6 gezeigten Druckverlauf aufgetragen ist;

Figur 9

ein Diagramm ähnlich Figur 8 für den in Figur 7 aufgetragenen Druckverlauf;

Figur 10

eine schematische Darstellung ähnlich Figur 2 eines zweiten Ausführungsbeispiels einer Kraftstoff-Einspritzvorrichtung;

Figur 11

ein Diagramm, in dem die Stellung eines Steuerventils und eines äußeren Ventilelements über der Zeit bei einer ersten Ansteuervariante aufgetragen ist;

Figur 12

ein Diagramm, in dem die Stellung eines Steuerventils und eines äußeren Ventilelements über der Zeit bei einer zweiten Ansteuervariante aufgetragen ist;

Figur 13

einen teilweise schematischen Teilschnitt durch einen Bereich eines dritten Ausführungsbeispiels einer Kraftstoff-Einspritzvorrichtung;

Figur 14

ein Teilbereich einer abgewandelten Ausführungsform der Kraftstoff-Einspritzvorrichtung von Figur 13; und

Figur 15

ein Teilbereich einer nochmals abgewandelten Ausführungsform der Kraftstoff-Einspritzvorrichtung von Figur 13.

Hereinafter, particularly preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. In the drawing show:

FIG. 1

a partial sectional view of portions of a first embodiment of a fuel injection device with two coaxial valve elements;

FIG. 2

a schematic representation of the fuel injection device of FIG. 1 with closed valve elements;

FIG. 3

a schematic representation similar FIG. 2 during an opening operation for opening both valve elements;

FIG. 4

a schematic representation similar FIG. 2 with open valve elements;

FIG. 5

a schematic representation similar FIG. 2 with only one open valve element;

FIG. 6

a diagram in which a pressure curve in a control chamber of the fuel injection device of FIG. 2 while in the Figures 3 and 4 shown opening and closing operation is applied;

FIG. 7

a diagram similar FIG. 6 for the in FIG. 5 case shown;

FIG. 8

a diagram in which the course of the switching positions of the valve elements for the in FIG. 6 shown pressure curve is plotted;

FIG. 9

a diagram similar FIG. 8 for the in FIG. 7 applied pressure curve;

FIG. 10

a schematic representation similar FIG. 2 a second embodiment of a fuel injection device;

FIG. 11

a diagram in which the position of a control valve and an outer valve element is plotted against time at a first drive variant;

FIG. 12

a diagram in which the position of a control valve and an outer valve element is plotted against time in a second drive variant;

FIG. 13

a partial schematic partial section through a portion of a third embodiment of a fuel injection device;

FIG. 14

a portion of a modified embodiment of the fuel injection device of FIG. 13 ; and

FIG. 15

a portion of a further modified embodiment of the fuel injection device of FIG. 13 ,

Description of the embodiments

In FIG. 1 a fuel injection device collectively carries the reference numeral 10. It comprises a housing 12, which in turn consists of, among other things, a nozzle body 14. In this two mutually coaxial valve elements 16 and 18 are arranged. Both valve elements 16 and 18 have at their in FIG. 1 lower end in each case a conical pressure surface 20 and 22, respectively, which bears against a corresponding housing-side sealing edge 24 or 26 when the valve element 16 or 18 is closed. From an existing between the two sealing edges 24 and 26 annulus (without reference numeral) lead more distributed over the circumference of the nozzle body 14 arranged fuel outlet channels 28 to the outside. Furthermore, lead from a present in the nozzle body 14 at its lower end blind hole (without reference numeral) also distributed over the circumference of the nozzle body 14 arranged fuel outlet channels 30 to the outside.

This in FIG. 1 The upper end of the inner valve member 16 is formed as a push rod with a circular control surface 32. When both valve elements 16 and 18 abut against the respective sealing edges 24 and 26, is located approximately at the same height as the control surface 32 of the inner valve member 16 is a corresponding annular control surface 34 of a push rod of the outer valve member 18. Part of the annular control surface 34 is conical and is bounded radially inward by a sealing region 36, whose function will be explained in more detail below. The control surfaces 32 and 34 define a common hydraulic control chamber 38, which is further enclosed by the nozzle body 14 and a counterpart 40. A valve spring 41 acts on the outer valve element 18 in the closing direction.

The fuel injection device 10 further includes an in FIG. 1 only symbolically shown high-pressure port 42, which is connected in the operation of the fuel injection device 10 usually to a fuel rail (not shown) of a common rail injection system. From the high pressure port 42 leads a total extending in the longitudinal direction of the fuel injection device 10 channel 44 to an annular pressure chamber 46 at the lower end of the fuel injection device 10, which is closed with the outer valve element 18 from the radially outwardly of the sealing edge 26 lying area of the pressure surface 22nd the outer valve element 18 is limited.

In an in FIG. 1 above the counterpart 40 arranged housing piece 48, an annular groove 50 is introduced into the counterpart 40 facing end face, which is connected via a branch channel 52 with the channel 44. In the counterpart 40, a high pressure passage 54 is formed, which connects the annular groove 50 with the control chamber 38. The high pressure passage 54 includes an inlet throttle 56.

The fuel injection device 10 further includes an in FIG. 1 also shown only schematically low pressure port 58. This is usually connected in operation of the fuel injection device 10 with a return line (not shown), which leads back to a fuel tank. At low pressure connection 58, therefore, during operation of fuel injection device 10 there is approximately ambient pressure, whereas at high pressure connection 42 a very high pressure of up to 2000 bar is present.

The low pressure port 58 leads to a switching chamber 60, which will be discussed in detail below. From the switching chamber 60 leads in the counterpart 40, a control channel 62 to the control chamber 38. In the control channel 62, a flow restrictor 64 is present. From the switching chamber 60 further leads via a throttle point 66, a bypass channel 68 to the annular groove 50, which is in communication with the high-pressure port 42. The bypass channel 68 is realized by two angularly disposed bore sections 68a and 68b.

In the switching chamber 60, a cylindrical switching element 70 of a 3/3-way valve 72 is arranged. The switching element 70 is pressed by a valve spring 74 against a first valve seat 76, which is formed in the switching chamber 60 to the low pressure port 58 out. The switching element 70 is coupled to an actuating rod 78, which can be actuated by a piezoelectric actuator 80. In this way, the switching element 70 can be pressed against the force of the valve spring 74 against a second valve seat 82 which is formed in the switching chamber 60 to the bypass channel 68 out.

• In den Figuren 1 und 2 ist ein Betriebszustand der Kraftstoff-Einspritzvorrichtung 10 dargestellt, in dem das 3/3-Schaltventil 72 sich in einer ersten Schaltstellung 84 befindet, in der das Schaltelement 70 am ersten Ventilsitz 76 anliegt und vom zweiten Ventilsitz 82 abgehoben ist. In diesem Fall wird der am Hochdruckanschluss 42 anliegende Kraftstoff-Hochdruck einerseits über den Hochdruckkanal 54 und andererseits aber auch über die Ringnut 50, den Bypasskanal 68, die Schaltkammer 60, und den Steuerkanal 62 in den Steuerraum 38 übertragen. Im Steuerraum 38 herrscht daher der auch am Hochdruckanschluss 42 anliegende hohe Kraftstoffdruck. Entsprechend wirken an den Steuerflächen 32 und 34 in Schließrichtung der Ventilelemente 16 und 18 wirkende hydraulische Kräfte. Zusätzlich wird das äußere Ventilelement 18 noch von der Ventilfeder 41 in Schließrichtung beaufschlagt. Die Steuerflächen 32 und 34 sind dabei so bemessen, dass das innere Ventilelement 16 gegen den Brennraumdruck und das äußere Ventilelement 18 gegen den Brennraumdruck und den an der Druckfläche 22 angreifenden hohen Kraftstoffdruck sicher in der geschlossenen Position gehalten wird.

The fuel injector 10 operates as follows:

• In the FIGS. 1 and 2 an operating state of the fuel injection device 10 is shown, in which the 3/3-way switching valve 72 is in a first switching position 84, in which the switching element 70 abuts the first valve seat 76 and is lifted from the second valve seat 82. In this case, the fuel high pressure applied to the high pressure port 42 on the one hand via the high pressure passage 54 and on the other hand via the annular groove 50, the bypass passage 68, the switching chamber 60, and the control channel 62nd transferred to the control room 38. In the control chamber 38, therefore, there is also the high fuel pressure applied to the high pressure port 42. Accordingly act on the control surfaces 32 and 34 in the closing direction of the valve elements 16 and 18 acting hydraulic forces. In addition, the outer valve element 18 is still acted upon by the valve spring 41 in the closing direction. The control surfaces 32 and 34 are dimensioned such that the inner valve element 16 is securely held against the combustion chamber pressure and the outer valve member 18 against the combustion chamber pressure and acting on the pressure surface 22 high fuel pressure in the closed position.

• Hierzu wird das 3/3-Schaltventil 72 in eine zweite Schaltstellung 86 gebracht, in der es am zweiten Ventilsitz 82 anliegt. Hierdurch wird die Verbindung von der Schaltkammer 60 zum Hochdruckanschluss 42 hin unterbrochen, und stattdessen werden die Schaltkammer 60 und hierdurch auch der Steuerkanal 62 mit dem Niederdruckanschluss 58 verbunden. Daher kann nun Kraftstoff aus dem Steuerraum 38 über die Abströmdrossel 64 zum Niederdruckanschluss 58 hin abströmen.

Now, the procedure will be described, with the opening of both valve elements 16 and 18 is effected (see. Figures 3 and 4 and 6 and 8):

• For this purpose, the 3/3-way switching valve 72 is brought into a second switching position 86, in which it bears against the second valve seat 82. As a result, the connection from the switching chamber 60 to the high-pressure port 42 is interrupted, and instead the switching chamber 60 and thereby also the control channel 62 are connected to the low-pressure port 58. Therefore, fuel can now flow out of the control chamber 38 via the outflow throttle 64 to the low pressure port 58.

Due to the presence of the inlet throttle 56, this results in a pressure drop in the control chamber 38. This is in FIG. 6 indicated by the reference numeral 88. As soon as the opening pressure of the outer valve element 18 is undershot, which is higher than the opening pressure of the inner valve element 16 in the present fuel injection device 10, the outer valve element 18 raises due to the pressure surface 22 engaging hydraulic force against the force of the valve spring 41 from the sealing edge 26 (reference numeral 89 in FIG FIG. 8 ), so that the fuel from the pressure chamber 46 via the fuel outlet channels 28 can escape.

When the valve element 18 comes into abutment with the sealing region 36 on the counterpart 40 (reference numeral 90 in FIG FIG. 6 ), the region of the control chamber 38 located within the sealing edge 36 is separated from the inflow of new fuel via the high-pressure passage 54, or at least this inflow is throttled. The pressure in this radially inner region of the control chamber 38, which is further connected to the low pressure port 58 via the control channel 62, therefore continues to decrease until the inner valve element 16 with its pressure surface 20 lifts away from the sealing edge 24 (reference numeral 92 in FIG FIG. 6 or 93 in FIG. 8 ). Now fuel can also escape from the fuel outlet channels 30. This is in FIG. 4 shown.

Out FIG. 6 it can be seen that the pressure in the control chamber 38 drops to a total of approximately one-third of its original value. This value is set by a corresponding dimensioning of the inlet throttle 56 and the outflow throttle 64. In this case, the outer valve element 18 remains safe in the open position, since the sealing region or the sealing edge 36 is slightly spaced from the radially inner edge of the control surface 34, so that at the radially within the sealing edge 36 lying region of the control surface 34 continues to be a very low control pressure is applied. In addition, the sealing edge 36 can be designed so that the seal between the radially outer and the radially inner region of the control chamber 38 is not absolute, so continue to fuel can flow out of the radially outer region of the control chamber 38 and there ensures a corresponding reduction in pressure.

The injection is terminated by the switching element 70 is brought back into abutment against the first valve seat 76 (switch position 84). As a result, the switching chamber 60 is disconnected from the low pressure port 58 and reconnected to the high pressure port 42 via the bypass passage 68. The control chamber 38 is again connected to the high pressure port 42 via the control channel 62 and the high pressure passage 54, resulting in a very rapid increase in pressure (reference numeral 94) in the control chamber 38. Both valve elements 16 and 18 close in sequence almost simultaneously (reference numerals 96 and 98 in FIG FIG. 8 ).

• Das 3/3-Schaltventil 72 wird in eine dritte Schaltstellung 100 gebracht, in der sich sein Schaltelement 70 in einer Zwischenposition zwischen dem ersten Ventilsitz 76 und dem zweiten Ventilsitz 82 befindet. Es liegt also an keinem der beiden Ventilsitze 76 und 82 an. In diesem Schaltzustand 100 des 3/3-Schaltventils ist die Schaltkammer 60 einerseits mit dem Niederdruckanschluss 58 und andererseits über den Bypasskanal 68 auch mit dem Hochdruckanschluss 42 verbunden. In der Schaltkammer 60 stellt sich daher ein Druck ein, der unterhalb des hohen Kraftstoffdrucks am Hochdruckanschluss 42, jedoch oberhalb jenes Druckes liegt, der bei der in den Figuren 3 und 4 gezeigten Schaltstellung des 3/3-Schaltventils 72 in der Schaltkammer 60 herrscht.

If only the outer valve element 18 is to open, the procedure is as follows ( FIG. 5 ):

• The 3/3 shift valve 72 is brought into a third shift position 100 in which its shift element 70 is in an intermediate position between the first valve seat 76 and the second valve seat 82. It is therefore not on any of the two valve seats 76 and 82 at. In this switching state 100 of the 3/3-way switching valve, the switching chamber 60 is connected on the one hand to the low-pressure connection 58 and on the other hand via the bypass channel 68 to the high-pressure connection 42. In the switching chamber 60, therefore, sets a pressure that is below the high fuel pressure at the high pressure port 42, but above that pressure at the in the Figures 3 and 4 shown switching position of the 3/3-switching valve 72 in the switching chamber 60 prevails.

By connecting the switching chamber 60 to the control chamber 38 via the control channel 62 also decreases in the control chamber 38, the pressure (reference numeral 88 in FIG. 7 ), but also not as strong as the one in the Figures 3 and 4 and 6 and 8 shown second switching position 86 of the 3/3-way valve. The corresponding area of the pressure curve bears in FIG. 7 the reference numeral 102. It can be seen that the pressure drops to about half the output pressure. However, the pressure reduction in the control chamber 38 is sufficiently strong that the outer valve element 18 lifts off from the sealing edge 26 due to the hydraulic force acting on the pressure surface 22 (reference numeral 89 in FIG FIG. 9 ), so that the fuel from the pressure chamber 46 can flow to the fuel outlet channels 28 and escape from them. Again, the valve member 18 moves so far until it comes into contact with the sealing edge 36 on the counterpart 40 (reference numeral 90 in FIG. 7 ), which causes a further pressure reduction in the control chamber 38, which, however, is not so strong that the inner valve element 16 opens.

In order to accelerate the opening of the outer valve element 18, the 3/3-way switching valve 72 may also initially be brought into the second switching position 86, in which the switching element 70 rests against the second valve seat 82. Even before the outer valve element 18 comes into abutment with the sealing region 36 on the counterpart 40, then the 3/3-way switching valve 72 is brought into the third switching position 100, which prevents the pressure in the control chamber 38 from falling too much.

It should also be noted that the adjustment of the "intermediate pressure" prevailing in the switching chamber 60 when the switching element 70 is in the intermediate position 100 between the first valve seat 76 and the second valve seat 82, also through the gap between the switching element 70 and the first Valve seat 76 is adjusted. This Gap represents a flow restrictor from the switching chamber 60 to the low pressure port 58 out.

A modified embodiment of a fuel injection device 10 is shown in FIG FIG. 10 shown. Here and in the following figures, those elements and regions which have equivalent functions to elements and regions shown in the preceding figures carry the same reference numerals. They are not explained again in detail.

In the FIG. 10 shown fuel injection device 10 differs from the fuel injection device described above only by the configuration of the switching valve 72: This is not formed as a 3/3-way valve, but as a 3/2-way switching valve. As such, in a first switching position 84, it can connect the high-pressure port 42 directly to the control chamber 38 via the annular groove 50 and the bypass channel 68 as well as the control channel 62. In this switching position prevails in the control chamber 38 so the maximum pressure corresponding to the pressure prevailing at the high pressure port 42 pressure. In contrast, in the second switching position 86, the control chamber 38 is connected to the low-pressure connection 58 via the outflow throttle 64 and the control channel 62. In this switching position, therefore, there is a comparatively low pressure in the control chamber 38, which results from the design of the outflow throttle 64 and the inflow throttle 56.

As already mentioned in connection with the FIGS. 1 to 9 shown embodiment, both valve elements 16 and 18 are closed at high pressure in the control chamber 38. At low pressure both valve elements 16 and 18 are opened. If only the outer valve element 18 is to be opened, the control chamber 38 must have a middle one Pressure level can be adjusted. At the in FIG. 10 shown fuel injection device 10, such a mean pressure level is effected by a sequential and continued opening and closing of the switching valve 72.

As well as from the FIGS. 11 and 12 shows, this means that first the switching valve 72 is brought into the open switching position 86 (curve 96 in FIG FIG. 11 ), so that the pressure in the control chamber 38 drops, which initially leads to the opening of the outer needle 18 (curve 98 in FIG FIG. 11 ). Just before or just when the outer valve member 18 reaches its open end position in which it comes into abutment on the counterpart 40 (dashed horizontal line in FIG. 11 ), the switching valve 72 is brought back into the closed switching position 84. As a result, the pressure in the control chamber 38 increases again and the outer valve element 18 begins a closing movement. However, before the outer valve element 18 is closed so far that the flow between the sealing edge 26 and the pressure surface 22 (see. FIG. 1 ) is throttled, the switching valve 72 is brought back into the open switching position 86. In this way, a mean pressure level is established in the control chamber 38, in which the outer valve element 18 is opened, but the inner valve element 16 is still closed.

In an embodiment not shown, instead of in FIG. 10 shown 3/2-switching valve 72, a 2/2-way valve used. In the corresponding fuel injection device then no bypass channel is present, so that in the closed switching position of the 2/2-switching valve, the control channel 62 is simply locked.

How out FIG. 12 It is also possible that the switching valve 72 is opened and closed at a very fast switching frequency (curve 96 in FIG FIG. 12 ), for example with a pulsed or clocked control. The flow can not follow so quickly, so that sets in the control room not a highly fluctuating control pressure, but a relatively constant average pressure. Accordingly, the outer valve element assumes a relatively constant middle position (curve 98) just before the stop (horizontal dashed line).

Another possible embodiment of a fuel injection device 10 is shown in FIG FIG. 13 shown. In this also a 3/3-way switching valve 72 is present, but is missing a bypass channel. Instead, lead from the switching chamber 60 two parallel control channels 62a and 62b to the control chamber 38. The one control channel 62a opens into the switching chamber 60 at the second valve seat 82. When the switching valve 72 is open, this control channel 62a is thus closed. The second control channel 62b opens laterally next to the switching element 70 in the switching chamber 60. Both control channels 62a and 62b include outflow throttles 64a and 64b, the throttle effect is different.

At the in FIG. 13 Furthermore, the switching element 70 is not directly coupled to the piezoactuator 80, but by means of a hydraulic translator 104. This comprises a translator chamber 106 into which a cylindrical translator element 108 protrudes on one side via the actuating rod 78 with the Switching element 70 is connected. A coupled to the piezoelectric actuator 80 transmission body 110 also protrudes into the booster chamber 106. The diameter of the Translation body 110 is larger than that of the translator element 109.

The booster chamber 106 is filled with fuel. For this purpose, the booster chamber 106 is connected to a leakage line 116 via a branch line 112, in which a check valve 114 is arranged. This leads to the low pressure port 58. A corresponding stub 118 also leads to the switching valve 72 and an annular space 120 in which the compression spring 41 is arranged, and in which, via a leakage channel 122, leakage fluid can pass, which from the control chamber 38 through the gap between the upper portions of the two valve elements 16 and 18 passes. In this way, the booster chamber 106 is fed with the effluent from the control valve 72 and the annular space 120 leakage fluid.

Due to the different diameters of the translator element 108 and the gear body 110, a change in length of the piezoelectric actuator 80 results in a stroke of the switching element 70 which is greater than the change in length of the piezoelectric actuator 80. If the switching element 70 at the first valve seat 76, the two control channels 62a and 62b separated from the low pressure port 58. In the control chamber 38, therefore, there is a high pressure, and the two valve elements 16 and 18 are closed.

If the switching valve 72 is opened so that the switching element 70 is positioned between the first valve seat 76 and the second valve seat 82, fuel can flow out of the control chamber 38 via both control channels 62a and 62b to the low pressure port 58. The pressure in the control chamber 38 therefore drops sharply, so that both valve elements 16 and 18 open.

If, however, the switching element 70 is brought into a position in which it bears against the second valve seat 82, the control channel 62a is closed. Fuel can flow out of the control chamber 38 to the low-pressure port 58 only via the control channel 62b. The outflow throttle 64b and the inflow throttle 56 are coordinated so that in this case an average pressure level in the control chamber 38 is established, in which, although the outer valve element 18 opens, the inner valve element 16 remains closed.

A further modified embodiment is in FIG. 14 shown. The differences in this case relate to the end regions of the valve elements 16 and 18. It can be seen that on the inner valve element 16, an annular collar 124 is formed, which is positioned in a recess 126 in the end region of the outer valve element 118. In the rest position, when both valve elements 16 and 18 are closed, the axial end surfaces of the recess 126 are slightly spaced from the annular collar.

In the FIG. 14 shown fuel injector works similar to those of FIG. 13 , However, if the outer valve element 18 is opened, the in FIG. 14 The lower edge surface of the recess 126 in abutment against the annular collar 124. The thereby additionally exerted by the outer valve member 18 on the inner valve member 16 and acting in the opening direction force causes now also the inner valve member 16 opens. In the FIG. 14 The lower boundary surface of the recess 126 in the outer valve element 18 therefore acts like a driver for the inner valve element 16.

The axial position of the annular collar 124 and the recess 126 are coordinated so that the lower edge the recess 126 only abuts the annular collar 124 of the inner valve element 16 shortly before reaching the maximum stroke of the outer valve element 18. Thereby, a stepped injection rate ("boot injection") can be achieved, which enables a reduction of the emissions of the internal combustion engine, in which the fuel injection device 10 is used. The control surface 32 of the inner valve element 16 is further designed so that even if both control channels 62a and 62b are "activated", ie if the minimum possible pressure prevails in the control chamber 38, the inner valve element 16 opens only when the recess 126th abuts the annular collar 124.

A further modified embodiment of a fuel injection device 10 is shown in FIG FIG. 15 In this case, the valve elements 16 and 18 are made in one piece. The control chamber 38 is not limited radially by the housing 12, but by a sleeve 128, which at its in FIG. 15 upper edge has a sealing edge (without reference numeral). This sealing edge is pressed by the compression spring 41 against the control surfaces 32 and 34 of the valve elements 16 and 18 opposite housing surface (without reference numeral).

Claims (16)

1. Fuel injection device (10) for an internal combustion engine, having at least two valve elements (16, 18) which have in each case one hydraulic control surface (32, 34) which acts in a closing direction and to which is assigned a hydraulic control chamber (38), having a control valve (72) which influences the pressure in the control chamber (38), and having load exertion devices (20, 22) which can act in an opening direction of the valve elements (16, 18), wherein the hydraulic opening pressures, which prevail in the control chamber (38), of the valve elements (16, 18) differ, characterized in that at least three different pressure levels can be set in the control chamber (38) by the control valve (72), wherein at a relatively high pressure level, all of the valve elements (16, 18) are closed, at a medium pressure level, one valve element (18) is open, and at a relatively low pressure level, all of the valve elements (16, 18) are open.
2. Fuel injection device (10) according to Claim 1, characterized in that the control chamber (38) is connected via an inlet throttle (56) to a high-pressure port (42), and in that the control valve (72) is connected at one side to the control chamber (38) and at the other side to a low-pressure port (58).
3. Fuel injection device (10) according to Claim 2, characterized in that the control valve (72) has a switching chamber (60) with a switching element (70) which, in a first switching position (84), bears against a first valve seat (76) leading to the low-pressure port (58), in a second switching position (86), bears against a second valve seat (82) leading to a bypass duct (68), wherein the bypass duct (68) is connected to the high-pressure port (42), and in a third switching position (100), bears neither against the first valve seat (76) nor against the second valve seat (82).
4. Fuel injection device (10) according to Claim 3, characterized in that the control valve (72), in the third switching position (100), forms a throttle point in the direction of the low-pressure port (42).
5. Fuel injection device (10) according to either of Claims 1 and 2, characterized in that the control chamber (38) is connected to the high-pressure port (42), in that the control valve (72) is connected via at least two control ducts (62a, 62b) to the control chamber (38), and in that the control valve (72), in a first switching position (76), separates all of the control ducts (62a, 62b) from a low-pressure port (58), in a second switching position (82), connects a control duct (62b) to the low-pressure port (58), and in a third switching position, connects all of the control ducts (62a, 62b) to the low-pressure port (58).
6. Fuel injection device (10) according to Claim 2, characterized in that the control chamber (38) is connected to a high-pressure port (42), in that the control valve (72), in a first switching position (86), connects the control chamber (38) to a low-pressure port (58) and, in a second switching position (100), separates said control chamber from said low-pressure port, and in that the control valve (72) can be moved continuously in controlled fashion from the first switching position (86) into the second switching position (100) and back.
7. Fuel injection device (10) according to Claim 6, characterized in that the control valve (72) can be actuated in such a way that, as a result of the continuous alternation, the pressure in the control chamber (38) fluctuates about a mean pressure level.
8. Fuel injection device (10) according to Claim 6, characterized in that the control valve (72) can be actuated so quickly that, as a result of the continuous alternation, a constant mean pressure level is set.
9. Fuel injection device (10) according to one of the preceding claims, characterized in that the valve elements (16, 18) are coaxial and an axial delimiting surface of the control chamber (38) has a sealing region (36) which, when the outer valve element (18) is in an open end position, divides the control chamber (38) into an outer region, which is connected to the high-pressure port (42), and an inner region, which is connected to the control valve (72).
10. Fuel injection device (10) according to one of the preceding claims, characterized in that the control valve (72) comprises a piezo actuator (80).
11. Fuel injection device according to Claim 10, characterized in that the control valve comprises a valve body (70) which is hydraulically coupled to the piezo actuator (80), wherein as hydraulic fluid, use is made of fuel arising from fuel leakage at a guide of at least one valve element (16).
12. Fuel injection device (10) according to one of the preceding claims, characterized in that one valve element (18) has a driver (126) which acts in the opening direction on the other valve element (16).
13. Fuel injection device (10) according to Claim 12, characterized in that the driver (126) is designed such that it abuts against the other valve element (16) only shortly before the former valve element (18) reaches its maximum stroke.
14. Fuel injection device (10) according to either of Claims 12 and 13, characterized in that the load exertion device (20) which acts in the opening direction of the other valve element (16) and the hydraulic control surface (32) of the other valve element (16) are coordinated such that said valve element (16) opens only when a force acting in the opening direction is additionally imparted by the driver (124) of the former valve element (18).
15. Method for operating a fuel injection device (10), characterized in that, in a fuel injection device (10) according to one of Claims 1 to 4, to open only one valve element (18), the control chamber (38) is connected firstly to a high-pressure port (58) and then simultaneously to the high-pressure port (58) and a low-pressure port (42).
16. Method for operating a fuel injection device, characterized in that, in a fuel injection device according to Claim 6, to open only one valve element (18), the switching valve (72) is placed into the second switching position shortly before the pressure in the control chamber (38) has fallen to such an extent that the inner valve element (16) opens, and is placed into the first switching position again shortly before the outer valve element (18) closes.

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