EP1382838B1 - Fuel injector - Google Patents

Description

State of the art

The invention relates to a fuel injection valve according to the preamble of the main claim.

For example, is from the DE 43 06 072 A1 a device for opening and closing a present in a housing passage opening known, which can also be used as a fuel injection valve. This device has a piezoelectric, magnetostrictive or electostrictive actuator and a pressure piston operatively connected to this actuator which acts on a reciprocating piston via a hydraulic fluid. The reciprocating piston actuates the valve closing body located in its extension. Due to the size ratio of the surfaces of the reciprocating piston and the pressure piston, which face a first chamber, which is filled with hydraulic fluid, a stroke ratio is given. The hydraulic fluid directly in contact with the pressure piston is sealed against the actuator by means of an O-ring seal. A defined guide gap, with which the reciprocating piston is guided in a guide, allows the exchange of hydraulic fluid between the first chamber and a lying in a second chamber by a membrane space between the ejection and Reciprocating piston is located, wherein the membrane can be acted upon by a pressure in the second chamber. An embodiment will be described in which the exchange between the first and second chamber takes place. The gap and a pressure located in the second chamber is dimensioned so that slow, due to thermal influence length changes of the actuator can be compensated by exchange of hydraulic fluid through the guide gap.

Modern internal combustion engines often require a relatively short driving time of the fuel injection valve. The consequent steep edge profiles for driving a piezoelectric actuator cause in the piezoelectric actuator, in particular at the end of the edge to the target voltage level, relatively high-frequency undesirable vibrations, which preclude a stable operation of the fuel injection valve, especially in Teilhubbetrieb.

A disadvantage of the fuel injection valve known from the above publication is in particular that special measures or components for the suppression of undesirable vibrations of parts of the fuel injection valve, which are caused in particular by the behavior of the actuator, completely missing and insufficiently suppressed by the existing components or be compensated. Thus, a stable behavior of the fuel injection valve by the use or the utilization of frictional forces between the components of the fuel injection valve and by forces of spring elements is achieved insufficiently. Since said forces are relatively constant over a wide range, this means that in a suppression of unwanted vibrations, the valve dynamics suffers to the same extent. The use of spring forces or sliding friction forces are unsuitable for the suppression of high-frequency vibrations. If, for example, the activation times or the setpoint voltage times (plateau times) are to be shortened, in order to sufficiently increase undesired vibrations dampening, the spring forces and sliding friction between the components are increased. As already mentioned, this is detrimental to the valve dynamics and requires the actuator to overcome additional increased forces. The actuator and the parts in operative connection with it are claimed thereby increased. When from the publication DE 43 06 072 A1 known invention is therefore a shortening of driving times and target voltage times possible only within narrow limits, which also still go at the expense of the life of the fuel injector or must be accompanied by costly measures.

Advantages of the invention

The fuel injection valve according to the invention with the characterizing features of the main claim has the advantage that mechanical vibrations in the fuel injector, in particular unwanted mechanical vibrations of the actuator and caused by him unwanted vibrations in moving parts of the fuel injection valve according to the invention, are effectively attenuated in a simple and cost-effective manner without significantly affecting the valve dynamics or significantly stressing components. This makes it possible, while maintaining a stable behavior, the activation times of the actuator significantly shortened and thus in particular to allow a Teilhubbetrieb the fuel injection valve. The edge times of the Aktorerregung and the plateau times can be shortened without the vibrations generated in particular by the actuator have a negative effect on the operation of the fuel injection valve or the valve dynamics is significantly adversely affected. Since the damping effect is based on hydraulic action principles, it is largely wear-free. By flow movements of a pressure medium through a throttle point, it is particularly possible to achieve a damping force which is proportional to the speed of the actuator movements, So behaves like a linear attenuator. The assembly is also simplified.

The measures listed in the dependent claims advantageous developments of the fuel injection valve specified in the main claim are possible.

Advantageously, the throttle point is formed by a gap which is formed in cooperation with a first guide body either of a thickened or tapered part of the stage of the actuator piston. This makes it possible to respond better to design and functional requirements. It is also advantageous to produce the throttle point as a bore, especially as a laser bore, as this is particularly accurate, fast and inexpensive to produce. If fuel is used as a pressure medium, then in particular constructive measures for the separation of fuel and pressure medium can be omitted. Furthermore, it is advantageous to arrange fuel channel and throttle point so that fuel is exchanged directly between them. This reduces the design effort.

To compensate for temperature-induced changes in length of the actuator, advantageously the fuel injection valve according to the invention can be configured so that by at least one of the guide gaps of actuator piston and reciprocating pressure medium to the working space zufle relatively slowly or can escape from it.

Advantageously, realized by the size ratio of the surfaces of the two pistons, which face the working space, a stroke ratio. Thereby, the normally relatively small stroke which is possible by means of piezoelectric, magnetostrictive or electrostrictive actuators can be increased without making the actuator costly long and thin. Thick, short actuators are more resilient to mechanical influences than thin, long actuators. The Realization of the Hubübersetzung by two pressure piston with different sized force-transmitting surfaces that transmit forces via a hydraulic medium, but otherwise, has the advantage over solutions in which membrane and channels are interposed, that the compressibility of the medium has less effect. In addition, the thus realized, hubübersetzende power transmission is less prone to vibrations. There is less time between actuator and valve actuation. The system behaves stiffer.

Advantageously further developed, the fuel injection valve according to the invention can also be characterized in that the force of a spring element is at least as large that actuator piston, connecting element and actuator are kept in constant contact. As a result, during operation of the fuel injection valve, the respective components are prevented from losing contact with each other and colliding with each other. It can be dispensed with costly and wear-prone joints.

drawing

Fig. 1

einen schematischen Schnitt durch ein erstes Ausführungsbeispiel eines erfindungsgemäß ausgestalteten Brennstoffeinspritzventils,

Fig. 2

einen schematischen Schnitt durch ein zweites Ausführungsbeispiel eines erfindungsgemäß ausgestalteten Brennstoffeinspritzventils und

Fig. 3

einen schematisch dargestellten Teilschnitt des in Fig. 1 dargestellten Ausführungsbeispiels im Bereich der Stufe und der Dämpfungskammer.

Embodiments of the invention are shown in simplified form in the drawing and explained in more detail in the following description. Show it:

Fig. 1

a schematic section through a first embodiment of an inventively designed fuel injector,

Fig. 2

a schematic section through a second embodiment of an inventively designed fuel injector and

Fig. 3

a schematically illustrated partial section of the in Fig. 1 illustrated embodiment in the region of the stage and the damping chamber.

Description of the embodiments

Hereinafter, embodiments of the invention will be described by way of example. Matching components are provided in all figures with matching reference numerals.

An in Fig. 1 illustrated first embodiment of a fuel injection valve 1 according to the invention is carried out in the form of a fuel injection valve 1 for fuel injection systems of mixture-compression, spark-ignition internal combustion engines. The fuel injection valve 1 is suitable in particular for the direct injection of fuel into a combustion chamber, not shown, of an internal combustion engine.

The fuel injection valve 1 has a housing cover 2 which sits hermetically sealed on the spray-off end of a valve housing 5. Via a fuel terminal 3 on the housing cover 2, a fuel channel 6 can be acted upon with fuel. The fuel channel 6 extends only within the housing cover 2 and then within the valve housing 5, wherein in the spray-off, upper part of the fuel injection valve 1, an actuator housing 7, a seal 12, a neck ring 10 of an actuator piston 9, the spray-off part of the actuator piston 9 and a first Spring element 11 in the fuel passage 6 are surrounded by fuel. The actuator housing 7 is hermetically connected to the housing cover 2 with its end remote from the sprayer.

An actuator 4 located in the actuator housing 7 is associated with its spray-off remote side of the housing cover 2 and is based on this. A connecting element 8 is associated with its plate-shaped abspritzfernen end of the discharge side of the actuator 4 and engages with its discharge side tapered diameter profile through an opening 18 of the actuator housing 7. A seal 12 which is corrugated pipe-shaped in this embodiment of the fuel injection valve 1 according to the invention, represents by their hermetic attachment of their two ends on the one hand on injection side as an attachment ring 13 formed part of the connecting element 8 and the other on the discharge end of the actuator housing 7, sure that the fuel under pressure can not penetrate into the actuator housing 7 and the connecting element The movements of the actuator 4 and the movements of the actuator piston 9 can follow unhindered.

In this embodiment, the actuator piston 9 has a step 31, which is formed by its spray-off tapered diameter profile. The thicker, spray-side profile of the actuator piston 9 is guided in a first guide body 14 with a first guide gap 28. The abspritzferne, tapered diameter profile of the actuator piston 9 forms with the first guide body 14 has a gap which forms the throttle body 30, wherein the guide body 14 follows the tapered diameter profile of the actuator piston 9 at this point, that has a reduced inner diameter. The thus formed damping chamber 27 serves to dampen unwanted vibrations of parts of the fuel injection valve, in particular for damping Aktorschwingungen in both directions of movement of the actuator 4 during operation of the fuel injection valve 1. The damping properties are in particular by the geometric dimensions of the throttle body 30 forming gap and the damping chamber 27 determined. The perpendicular in Abspritzrichtung distance between the tapered diameter profile of the actuator piston 9 and the reduced inner diameter of the guide body 14 at this point is usually greater than the corresponding distance, which is formed by the first guide gap 28.

The actuator piston 9 is formed by the first spring element 11, which is formed in this embodiment as a spiral spring and at a distance to the spray-off tapered diameter profile of the actuator piston. 9 attached first approach ring 10 engages, biased against the Abspritznahe side of the connecting element 8 and against the actuator 4, wherein the first spring element 11 abspritzseitig against the first guide body 14 is supported. A second guide body 16 is hermetically connected to the discharge side of the first guide body 14, wherein a reciprocating piston 15 is guided with a second guide gap 29 in the second guide body 16. Between the reciprocating piston 15 and the actuator piston 9 is a working space 26, which is bounded by the first guide body 14 and the second guide body 16, wherein the two guide gaps 28, 29 each open into the working space 26 with one end. The second end of the first guide gap 28 opens into the damping chamber 27, the second end of the second guide gap opens at the discharge end of the second guide body 16 in the fuel channel. 6

Due to the different sized, the working space 27 facing surfaces of actuator piston 9 and piston 15 is given a stroke ratio. The fuel channel 6 extends in the lower discharge-side part of the fuel injection valve 1 first between the housing 5 and the two guide bodies 14, 16. Then, the fuel in the fuel passage 6 passes and flows around the part of the lifting piston 15 protruding from the guide body 16, one in the course of the lifting piston 15 formed third approach ring 19, a between the third approach ring and the discharge end of the second guide body 16 bordered second spring element 17, an associated with the reciprocating piston 15 in operative connection valve needle 20 with a fourth neck ring 25, a between the fourth neck ring 25 and a shoulder 32 bordered third spring element 24. Finally, the fuel enters when the fuel injection valve 1 is open from a spray orifice 23 between a valve seat body 21 and a valve closing body 22 arranged at the discharge end of the valve needle 20. The second spring element 17 biases the reciprocating piston 15 against the discharge side associated Valve needle 20 before. The third spring element 24 is supported on the shoulder 32 and biases the valve needle 20 via the frictionally connected with her fourth approach ring 25 against the sprayer remote associated reciprocating piston 15, wherein the third spring element is supported on the shoulder 32. The force of the third spring element 24 keeps the sealing seat formed by valve closing body 22 and valve seat body 21 closed against the fuel pressure.

• Der von Ventilschließkörper 22 und Ventilsitzkörper 21 gebildete Dichtsitz ist zunächst geschlossen. Der Aktor 4 ist entladen und die Dämpfungskammer 27 hat ein kleines Volumen. Wird der Aktor 4 nun geladen, dehnt er sich relativ schnell aus und drückt über das Verbindungselement 8 den Aktorkolben 9 in Abspritzrichtung. Dabei muß zum einen die Federkraft des ersten Federelements 11 überwunden werden, zum anderen füllt sich das größer werdende Volumen der Dämpfungskammer 27 mit Brennstoff, welcher durch die Drosselstelle 30 in die Dämpfungskammer 27 strömt. Eine dabei entstehende, der Bewegung des Aktorkolbens 9 entgegengerichtete, Dämpfungskraft ist proportional der Geschwindigkeit des Aktorkolbens 9, verhält sich also wie bei einem linearen Dämpfungsglied. Durch diesen Vorgang werden unerwünschte Schwingungen bedämpft. Der Aktorkolben 9 drückt nun über den mit Brennstoff befüllten Arbeitsraum 26 den Hubkolben 15 in Abspritzrichtung. Da die dem Arbeitsraum 26 zugewandte Fläche des Hubkolbens 15 kleiner ist als die vom Aktorkolben 9 dem Arbeitsraum 26 zugewandte Fläche, erfährt der Hubkolben 15 einen im Vergleich zum Aktorkolben 9 vergrößerten Hub. Die Ventilnadel 20 wird daraufhin entgegen einer Federkraft des dritten Federelements 24 in Abspritzrichtung bewegt, der Ventilschließkörper 22 hebt vom Ventilsitzkörper 21 ab und der unter Druck stehende Brennstoff wird abgespritzt.

The operation of the fuel injection valve is as follows:

• The sealing seat formed by valve closing body 22 and valve seat body 21 is initially closed. The actuator 4 is discharged and the damping chamber 27 has a small volume. If the actuator 4 is now charged, it expands relatively quickly and presses the actuator piston 9 in the direction of discharge via the connecting element 8. In this case, on the one hand, the spring force of the first spring element 11 must be overcome, on the other hand fills the increasing volume of the damping chamber 27 with fuel, which flows through the throttle body 30 in the damping chamber 27. A resulting, the movement of the actuator piston 9 opposite, damping force is proportional to the speed of the actuator piston 9, so behaves as in a linear attenuator. This process damps unwanted vibrations. The actuator piston 9 now presses over the fuel-filled working chamber 26, the reciprocating piston 15 in Abspritzrichtung. Since the working space 26 facing surface of the reciprocating piston 15 is smaller than the actuator piston 26 from the working space 26 facing surface, the reciprocating piston 15 experiences a larger compared to the actuator piston 9 stroke. The valve needle 20 is then moved counter to a spring force of the third spring element 24 in Abspritzrichtung, the valve closing body 22 lifts from the valve seat body 21 and the pressurized fuel is hosed.

If the actuator 4 is discharged again, its length is reduced, wherein the actuator piston 9 follows the movements of the actuator 4, since it is held by the spring element 11 and the connecting element 8 in constant operative connection to the actuator 4. By this constant operative connection and the damping effect of the resistance generating processes in the damping chamber 27 and the throttle body 30 undesirable vibrations, in particular of the actuator 4, in both directions of movement, effectively damped. The standing with the actuator piston 9 via the working chamber 26 operatively connected to reciprocating piston 15 then moves against the Abspritzrichtung, whereby the valve needle 20 follows the reciprocating piston 15 and the seated at the discharge end of the valve needle 20 valve closing body 22, the ejection opening 23 by the spring force of the third spring element closes.

Slow thermal changes in length, in particular of the actuator 4, are compensated by receiving and dispensing pressure medium, which is the fuel in this embodiment of the present invention, between the working chamber 26 and the fuel channel 6 or damping chamber 27. In the short periods of actuation of the fuel injection valve 1 by opening and closing movements, only very little pressure medium can be exchanged between the working chamber 26 and the fuel channel 6 or damping chamber 27 through at least one of the guide gaps 28, 29, wherein the pressure medium exchanged during the actuation pauses is balanced again by the fuel pressure. Slowly running exchanges of pressure medium between the working chamber 27 and the fuel channel 6 or damping chamber 27 are not significantly hindered by the guide gaps 28 and / or 29, so that, for example, a thermally induced change in length of the actuator 4 can be compensated.

In this embodiment of the present invention, the gap represented by the throttle body 30 may also be used for guiding tasks.

Fig. 2 shows in much of the in Fig. 1 illustrated first embodiment similar second embodiment. In contrast to the first embodiment in the actuator piston 9 and piston 15 are guided in a multi-part guide body 14, 16, actuator piston 9 and piston 15 in the second embodiment are guided in a one-piece guide body 14. The actuator piston 9 is cup-shaped and has in its diameter profile, the step 31, whereby the diameter profile is increased counter to the direction of discharge. By the step 31 and an enlarged inside diameter of the guide body 14 lying in the region of the step 31, the damping chamber 27 is formed. The connecting element 8 extends through to the bottom of the cup-shaped actuator piston 9, wherein the actuator piston 9 and the bottom of the actuator piston 9 are biased by the spring element 11 against the connecting element 8. The spring element 11 is designed in this embodiment as a tubular spring and secured to the inner side of the housing cover 2 and the spray-away end of the cup-shaped actuator piston 9 frictionally.

Based on Fig. 3 showing a schematically illustrated partial section of the first embodiment in the region of the stage 31 and the damping chamber 27, and the following relationships and derivatives of the proportional relationship between damping force and Aktorkolbengeschwindigkeit is shown.

The annular surface A of the actuator piston 9 on the damping chamber 27 is: $$A=\frac{\pi }{4}\left(d_a^2-{\mathrm{<figure-callout\; id="2"\; label="d\; i"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d\; </figure-callout>}}_i^{}\right)$$

If the actuator piston 9 moves about the actuator piston stroke ds, the damping volume V changes by: $$\mathit{dV}=A\cdot \mathit{ds}$$

The actuator piston velocity v is calculated from: $$v=\frac{ds}{dt}$$

For an incompressible pressure medium results with (2) and (3) for the pressure medium flow rate Q via the throttle body 30: $$Q=\frac{dV}{dt}=\frac{A\cdot \mathit{ds}}{\mathit{dt}}=A\cdot v$$

In the following applies to the pressure medium flow rate Q: $$Q=C\cdot \mathrm{\Delta }p\Rightarrow \mathrm{\Delta }p=\frac{Q}{C}=\frac{A\cdot v}{C}$$

Here, C is a constant which depends on the geometric dimensions of the annular gap and Δp represents the pressure difference.

oder $$F\sim v$$

With (5) results for the damping force F by: $$F=A\cdot \mathrm{\Delta }p=\frac{A^2}{C}\cdot v$$

or $$F~v$$

The invention is not limited to the illustrated embodiments and may, for. B. also be used for inward-opening fuel injectors.

Claims (7)

1. Fuel injection valve (1), in particular for directly injecting fuel into a combustion chamber of an internal combustion engine, having
   a piezoelectric, electrostrictive or magnetostrictive actuator (4),
   an actuator piston (9) which is operatively connected to the actuator (4) and which is guided with a first guide gap (28),
   a stroke piston (15) which is operatively connected to the actuator piston (9) by means of a pressure medium and which is guided with a second guide gap (29),
   a valve needle (20) which is operatively connected to the stroke piston (15) and which, at its discharge-side end, has a valve closing body (22) which forms a sealing seat with a valve seat body (21),
   wherein the transmission of force between actuator piston (9) and stroke piston (15) is realized by means of a working chamber (26) which is filled with pressure medium and which is enclosed by actuator piston (9) and stroke piston (15),
   wherein the actuator piston (9) has at least one step (31) which adjoins a damping chamber (27), wherein the damping chamber (27) is spatially separated from the working chamber (26) and is designed and/or arranged such that pressure medium can flow in and flow out via a throttle point (30),
   characterized
   in that the throttle point (30) is formed by a gap which 'is formed by a narrowed or thickened part of the step (31) of the actuator piston (9) and by a guide body (14), and the guide body (14) follows the narrowed diameter profile of the actuator piston (9) such that a damping force F = A² /C *v directed oppositely to the movement of the actuator piston (9) is generated proportionally to the speed (v) of the actuator piston (9) in both movement directions of the actuator (4), wherein A denotes the ring-shaped surface area of the actuator piston (9) at the damping chamber (27) and C denotes a constant which is dependent on the geometric dimensions.
2. Fuel injection valve according to Claim 1,
   characterized
   in that the guide body (14) is composed of multiple parts.
3. Fuel injection valve according to Claim 1 or 2,
   characterized
   in that the throttle point (30) is formed by an opening, in particular a bore or laser-drilled bore, which has a flow-throttling action.
4. Fuel injection valve according to one of the preceding claims,
   characterized
   in that the fuel serves as pressure medium.
5. Fuel injection valve according to Claim 4,
   characterized
   in that fuel is exchanged directly with a fuel duct (6) via the throttle point (30).
6. Fuel injection valve according to one of the preceding claims,
   characterized
   in that, for the compensation of temperature-induced changes in length of the actuator (4), pressure medium flows out of the working chamber (26) or flows into the working chamber (26) through at least one of the guide gaps (28, 29).
7. Fuel injection valve according to one of the preceding claims,
   characterized
   in that a stroke transmission ratio is realized by means of the ratio of those surface areas of the actuator piston (9) and of the stroke piston (15) which face toward the working chamber (26).

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