EP1693564B1 - Fuel injector with direct needle control for an internal combustion engine - Google Patents

Abstract

Fuel injector has stroke adjustable control member (40) in addition to actuator-side transmission piston (31). First control surface (47) is hydraulically coupled to actuator-side coupler area (36) and second control surface (46) is assigned to control area (37). Actuator-side transmission piston has second pressure area (48), which is assigned to control area as further control surface.

Description

State of the art

The invention relates to a fuel injector with direct needle control for an internal combustion engine according to the preamble of claim 1.

Fuel injectors with a so-called direct needle control are known. Such fuel injectors come without an intermediate control valve between an electrically actuated actuator and a nozzle needle. The power transmission between the actuator and the nozzle needle is realized by means of a hydraulic coupler or hydraulic translator. In particular, piezoelectric actuators are suitable as actuators, which, depending on the energization in the closed state, have a direct or inverse control. In a direct control of the piezoelectric actuator is energized to open the nozzle needle, so that a linear expansion of the piezoelectric actuator realized by a pressing movement opening the injectors, which is amplified by the translator. In the closed state, the piezoelectric actuator has a smaller linear expansion. In the case of inverse activation, the piezo actuator is charged in the closed state of the nozzle needle, so that the piezo actuator keeps the nozzle needle closed in the state of its longitudinal expansion. When the piezoactuator is actuated, the piezoactuator is discharged to initiate the injection process, so that a pressure relief takes place by a pulling movement of the piezoactuator in a control space of the hydraulic booster. As a result, the lifting movement of the piezo actuator is hydraulically translated to open the nozzle needle.

A fuel injector with direct needle control is already in the DE patent application 10 2004 037 125.3 proposed. The fuel injector in this case has an actuator-side booster piston and a nozzle needle-side booster piston, wherein the actuator-side booster piston is assigned to an actuator-side coupler space and the nozzle needle-side booster piston is assigned to a nozzle needle-side coupler space. Between the actuator-side coupler space and the nozzle needle-side coupler space, a hydraulic throttle device is formed, which has different flow cross-sections for the inflow or outflow of fuel into and out of the nozzle needle-side control chamber. At the actuator-side booster piston, a first slide sleeve for limiting the actuator-side coupler space and the nozzle needle-side booster piston, a further slide sleeve for limiting the nozzle needle-side coupler space is guided axially. The pusher sleeves are biased by a compression spring so that they press with one end face against a sealing surface. The use of the pusher sleeves allows axial decoupling of the actuator-side and the nozzle needle-side booster piston, whereby the booster piston can be mounted with an axial offset.

A fuel injector with direct needle control and an outwardly opening injection valve with a hydraulic coupler to compensate for the linear expansion and pressure-induced expansion of the fuel injector is out DE 101 48 594 A1 known. The hydraulic coupler, which forms a translator assembly between an actuator and a nozzle needle, includes an actuator-side booster piston and a nozzle needle-side booster piston guided in a guide sleeve. Arranged around the guide sleeve is a corrugated tube which encloses a hydraulic fluid separated from the fuel. The stroke-adjustable guide sleeve associated with the actuator-side booster piston acts on a first control surface actuator-side coupler space and with a second control surface on a further coupler space. The actuator-side booster piston has with a first pressure surface in the first coupler space and with a further pressure surface in the further coupler space.

The object of the present invention is to provide a fuel injector with two-stage transmission with different transmission ratios.

Advantages of the invention

The object of the invention is achieved with the characterizing features of claim 1. With the features of claim 1, a fuel injector with direct needle control with compact and small size can be realized, which manages with few moving components to realize the required ratios for a two-stage translation.

The two-stage gear ratio of the Aktorhubs with different ratios is realized by the control in a first opening phase of the nozzle needle by the applied pressure at its control surfaces in an initial position and at the beginning of a second opening phase of the nozzle needle due to the changing pressure conditions on the control surfaces of the Control lifts the control from the starting position, so that increases the volume in the actuator-side coupler space, whereby the translation between aktorseitigem and nozzle-side booster piston is changed. The control chamber acts as a pressure or energy storage, so that formed to initiate the second opening phase, a pressure threshold in the control room.

Advantageous developments of the invention are possible by the measures of the subclaims.

It is particularly advantageous if an axially displaceably guided control sleeve is arranged as a control element on the actuator-side booster piston whose first end face is hydraulically coupled as a first control surface to the actuator-side coupler space and whose second end face is assigned to the control chamber as a second control surface. The first end face is in relation to a first opening phase of the nozzle needle in an initial position. With regard to a second opening phase of the nozzle needle, the first end face lifts off from the starting position, so that with respect to the second opening phase of the nozzle needle an effective surface is exposed to the actuator-side coupler space, which is composed of the pressure surface of the booster piston and the first end face.

Conveniently, the actuator-side booster piston is a stepped piston, with which the first pressure surface and the second pressure surface are formed. An expedient embodiment of the fuel injector also consists in that the coupler space associated with the actuator-side pressure booster piston is connected via a hydraulic connection to a nozzle needle-side coupler space assigned to the nozzle needle-side booster piston. To form the actuator-side booster piston associated control chamber and coupler space a slide sleeve is guided on the actuator-side booster piston.

embodiment

An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description.

• Figur 1 eine Schnittdarstellung durch einen Teil eines erfindungsgemäßen Kraftstoffinjektors,
• Figur 2 einen vergrößerten Ausschnitt X gemäß Figur 1 und
• Figur 3 ein hydraulisches Ersatzschaltbild der Wirkungsweise des erfindungsgemäßen Kraftstoffinjektors.

Show it

• FIG. 1 a sectional view through a portion of a fuel injector according to the invention,
• FIG. 2 an enlarged section X according to FIG. 1 and
• FIG. 3 a hydraulic equivalent circuit diagram of the operation of the fuel injector according to the invention.

The in FIG. 1 illustrated fuel injector has an injector 10 with a nozzle body 11 which projects with its lower end into a combustion chamber of an internal combustion engine. On the nozzle body 11, a nozzle needle guide 12 is formed, in which a nozzle needle 13 is guided with a guide portion 14 axially displaceable. Between the tip of the nozzle needle 13 and the nozzle body 11, a sealing seat 15 is formed, which are arranged downstream of the injection nozzle 16 formed in the nozzle body 11 and projecting into the combustion chamber. In an upper region, the injector housing 10 has a receiving space 18 which is connected to a fuel feed, not shown, which is connected to a high-pressure system, for example to a common-rail system of a diesel injection device. Between injector housing 10 and nozzle body 11, an intermediate body 19 with an actuator-side surface 23 and a nozzle needle-side surface 24 is arranged, which is designed with connecting bores 21 and with a hydraulic connection acting as a throttle 22. The connecting bores 21 serve to forward the fuel introduced into the receiving space 18 via the fuel supply at high pressure into a high-pressure space 25 assigned to the nozzle needle 13.

In the receiving space 18, a piezoelectric actuator 20 is arranged, which acts on a hydraulic booster 30. The hydraulic booster 30 has an actuator-side booster piston 31 which is drive-coupled to the piezo-actuator 20 and which is also housed in the receiving space 18. The actuator-side booster piston 31 is designed as a stepped piston with a first piston portion 32 with a diameter d1 and with a second piston portion 33 with a diameter d2, where d2> d1. The hydraulic booster 30 further comprises a second piston portion 33 axially guided sliding sleeve 34, an axially between the sleeve 34 and the first piston portion 32 axially guided control sleeve 35, an actuator-side coupler 36 and a control chamber 37. On the first piston portion 32 of the actuator-side booster piston 31 is according to FIG. 2 a coupler-space-side pressure surface 38 is formed, which faces into the actuator-side coupler space 36. Due to the diameter ratio d1 <d2 between the first piston section 32 and the second piston section 33, there is an annular surface with a second pressure surface 48 on the second piston section 33 which points into the control chamber 37 as a further control surface.

The control sleeve 35 has the function of a control element 40 associated with FIG. 3 generally described. The control sleeve 35 has a first end face 44 and a second end face 45 and is biased by a compression spring 43 on the actuator-side booster piston 31. The compression spring 43 causes the control sleeve 35 is held until the initiation of the second opening phase of the nozzle needle 13 in an initial position. In the starting position, the control sleeve 35 is pressed with the first end face 44 against the actuator-side surface 23 of the intermediate body 19, so that the control sleeve 35 limits the actuator-side coupler space 36 in this position. The first end face 44 forms a hydraulically coupled first control surface 47 with the actuator-side coupler space 36. The second end face 45, which is formed opposite the end face 44 on the control sleeve 35, points into the control space 37 and forms a second control surface 46 with respect to the control space 37 the control sleeve 35.

The slide sleeve 34 is also biased by a further compression spring 49 on the actuator-side booster piston 31. As a result, the sliding sleeve 34 according to FIG. 2 pressed with an end face 42 against the actuator-side surface 23 of the intermediate body 19, so that a sealing surface on the surface 23 forms.

To the hydraulic translator 30 further includes a connected to the nozzle needle 13 nozzle needle-side booster piston 51 having a diameter d3, which has a nozzle needle side pressure surface 52 in a nozzle needle side coupler 53. At the nozzle needle-side booster piston 51, a further slide sleeve 54 is guided axially, which is pressed by means of a closing spring 56 against the nozzle needle-side surface 24 of the intermediate body 19 and so the nozzle needle-side coupler space 53 limited. The nozzle needle-side coupler space 53 is connected to the actuator-side coupler space 36 via the hydraulic connection 22. The hydraulic connection 22 can act as a throttle. By using slide sleeves 34 and 54 to the booster piston 31 and 51, an axial decoupling of the actuator-side booster piston 31 and the nozzle needle-side booster piston 51 is realized.

In the closed state of the injectors 16, the sealing seat 15 of the nozzle needle 13 is closed. The system pressure, which has reached the receiving space 18 and the pressure space 25 via the fuel supply, equally rests in all pressure chambers. In this case, 35 leakage gaps are present on the slide sleeves 34, 54 and the control sleeve, such that the system pressure is present in the actuator-side coupler space 36, in the control space 37 and in the nozzle needle-side coupler space 53 via the leakage gaps. In this state, the hydraulic booster 30 is pressure compensated. In addition, in this state, the piezoelectric actuator 20 is supplied with a voltage, whereby the piezoelectric actuator 20 is elongated in its loaded state in the vertical direction. The system pressure applied in the nozzle needle-side coupler chamber 53 acts in the closing direction on the nozzle needle-side booster piston 51. As a result, the sealing seat 15 of the nozzle needle 13 is closed in this state of the piezoelectric actuator 20. In addition, acts on the nozzle needle, the closing spring 56 which holds the nozzle needle 13 closed in the idle state.

If the voltage at the piezoelectric actuator 20 is reduced or the piezoelectric actuator 20 is discharged via a current, the length of the piezoelectric actuator 20 in the vertical direction is likewise reduced. The piezo actuator 20 is thus operated inversely. Due to the biased by the compression spring 49 in the direction of the piezoelectric actuator 20 actuator-side booster piston 31 this is also moved in the vertical direction due to the reduced vertical length of the piezo-actuator 20. By this outward pulling movement of the actuator-side booster piston 31 by means of the pressure surface 38 of the first piston portion 32, an increase in the volume in the actuator-side coupler 36, whereby there takes place a pressure reduction, which provides an opening pressure for a first opening phase for opening the nozzle needle 13. The opening pressure is transmitted via the hydraulic connection 22 into the nozzle needle-side coupler space 53, so that the opening pressure also bears against the nozzle needle-side pressure surface 52. Thereby, a first gear ratio for opening the nozzle needle 13 is introduced, which is effective due to the area ratios of the pressure surfaces 38 and 52, wherein the gear ratio of the first opening phase by the area ratio d1 ² / d3 ^{2 is} determined. Simultaneously with the pulling movement of the actuator-side booster piston 31, the volume in the control chamber 37 is increased by the second piston portion 33 and pointing in the control chamber 37 upward movement of the second pressure surface 48, whereby the pressure drops in the control chamber 37. The control chamber 37 acts as a pressure accumulator or energy storage in the form of a hydraulic spring. With increasing stroke of the nozzle needle 51, the pressure in the nozzle-side coupler chamber 53 rises again because of the pressure infiltration at the sealing seat 15 of the nozzle needle 13, while the pressure in the control chamber 37 continues to drop. This leads to conditions that can lift the control sleeve 35 of the actuator-side surface 23. This is due to the control sleeve 35th the first end face 44 free, which now acts as a first control surface 47 on the actuator-side coupler 36 space. The actuator-side coupler space 36 is now bounded radially by the sliding sleeve 34. The actuator-side coupler space 36 is thus exposed to an effective pressure surface, which is composed of the actuator-side pressure surface 38 of the first piston portion 32 and the first end surface 44 of the control sleeve 35. Characterized in that the inner diameter of the slide sleeve 34 is guided on the diameter d2 of the second piston portion 33 and the control sleeve 35 between the slide sleeve 34 and the first piston portion 32 is arranged, wherein the outer diameter of the control sleeve 35 is guided on the inner diameter of the slide sleeve 34, the composite effective pressure surface determined by the outer diameter of the control sleeve 35, which corresponds to the diameter d2. The composite effective pressure surface causes a translation jump, which acts as a second gear ratio on the nozzle needle side pressure surface 52 of the nozzle needle side booster piston 51. As a result, the stroke of the piezoactuator 20 is transmitted to the nozzle needle 13 with a larger ratio, which results from the area ratios of the composite effective pressure surface to the pressure surface 52, wherein the second transmission ratio is determined by the area ratios d2 ² / d3 ² . As a result, the nozzle needle 13 is moved at a greater speed and with a larger stroke.

Based on the in FIG. 3 shown hydraulic equivalent circuit diagram, the transmission ratio for the first opening phase and the second opening phase of the nozzle needle 13 is explained in more detail. If a pulling movement is exerted by the piezoelectric actuator 20 on the first piston section 32 with the surface A3 and with the second piston section 33 on the control chamber 37 as a result of the inverse activation, a pressure reduction dependent on the surface A3 initially occurs in the actuator-side coupling chamber 36, which is transmitted via the connection 22 to the nozzle needle-side coupler space 53. A pressure reduction in the coupler chamber 36 causes the first opening phase by a first lifting the nozzle needle 13 from the sealing seat 15. The control element 40 with the control surface 46 in the control chamber 37, which is shown as a piston, initially remains in one due to the pressure prevailing in the control chamber 37 starting position. The compression spring 43 acts only supportive. With increasing pulling stroke of the piezo-actuator 20, the pressure in the control chamber 37 is further reduced by means of the second piston section 33 until the pressure applied in the space 36 'is fallen below. Upon reaching this value, the control element 40 with the area A1, which corresponds to the first control surface 47, emotional. The pulling movement of the surface A1 creates an additional volume in the space 36 ', which also becomes effective via the connection 22' in the actuator-side coupler space 36. The additional volume is transmitted via the connection 22 to the nozzle needle-side coupler space 53, so that the surface A4 of the nozzle needle-side booster piston 51 now faces the sum of the areas A1 and A3 as the ratio for realizing the second opening phase. The gear ratio of the second opening phase (A1 + A3) to A4 is thus greater than the ratio of the first opening phase resulting from the ratio of A3 to A4. Due to the larger transmission ratio of the second opening phase, a larger opening speed is realized with a larger stroke when opening the nozzle needle 13.

By energizing the piezo-actuator 20, an extension of the piezo-actuator 20 is again initiated, which is transmitted from the actuator-side booster piston 31 to the control chamber 37 and the actuator-side coupler space 36. First, the control sleeve 35 is pressed by the compression spring 43, with the end face 44 against the surface 23, so that the actuator-side coupler space 36 is formed below the actuator-side pressure surface 38. At the same time, the first piston portion 32 with the pressure surface 38 increases the pressure in the actuator-side coupler space 36, which is transmitted via the hydraulic connection 22 to the nozzle needle-side coupler space 53, wherein the nozzle needle 13 on the sealing seat due to the pressure increase in the nozzle needle-side coupler space 53 by means of the nozzle needle side booster piston 51 15 is pressed and thereby the injection nozzles 16 are separated from the pressure chamber 25. At the same time, a pressure-balanced state is again formed in the pressure chambers of the hydraulic booster 30.

LIST OF REFERENCE NUMBERS

10

injector

11

nozzle body

12

Nozzle needle guide

13

nozzle needle

14

guide section

15

sealing seat

16

injectors

18

accommodation space

19

intermediate body

20

Piezo actuator

21

connecting bore

22

hydraulic connection

22 '

connection

23

Actuator-side face

24

nozzle needle-side end face

25

High-pressure chamber

30

hydraulic translator

31

Actuator-side booster piston

32

first piston section

33

second piston section

34

sliding sleeve

35

control sleeve

36

actuator-side coupler space

36 '

room

37

control room

38

Coupling chamber-side pressure surface

40

control

42

face

43

compression spring

44

first end face

45

second end face

46

second control surface

47

first control surface

48

second printing surface

49

further compression spring

51

Nozzle needle-side booster piston

52

nozzle needle side pressure surface

53

nozzle needle-side coupler space

54

nozzle needle side slide sleeve

56

closing spring

Claims (9)

1. Fuel injector for an internal combustion engine having a nozzle needle (13) which is guided in a nozzle body and which acts on a nozzle needle sealing seat (15), having an actuator (20) and having a hydraulic booster (30) with an actuator-side booster piston (31) which is connected to the actuator and with a nozzle-needle-side booster piston (51) which is connected to the nozzle needle (13), with the actuator-side booster piston (31) and the nozzle-needle-side booster piston (51) acting on at least one booster space, with an actuator-side coupler space (36) being formed as a booster space, which coupler space (36) is assigned a pressure surface (38) of the actuator-side booster piston (31), with the nozzle needle (13) being lifted up from the nozzle needle sealing seat (15) as a function of the pressure in the actuator-side coupler space (36) and with highly pressurized fuel thereby being injected, with a stroke-adjustable control element (40) being provided in addition to the actuator-side booster piston (31), which control element (40) is hydraulically coupled with a first control surface (A1, 47) to the actuator-side coupler space (36) and is assigned with a second control surface (46) to a control space (37), and with the actuator-side booster piston (31) having a second pressure surface (48) which is assigned, as a further control surface, to the control space (37), characterized in that, in a first opening phase of the nozzle needle (13), the control element (40) is in a starting position and in that, in a second opening phase of the nozzle needle (13), the control element (40) lifts up from the starting position.
2. Fuel injector according to Claim 1, characterized in that the control element (40) is guided in a stroke-adjustable fashion on the actuator-side booster piston (31).
3. Fuel injector according to Claim 1 or 2, characterized in that the control element (40) is a control sleeve (35) which is guided axially on the actuator-side booster piston (31) and whose first end surface (44) is hydraulically coupled, as a first control surface (47), to the actuator-side coupler space (36) and whose second end surface (45) is assigned, as a second control surface (46), to the control space (37).
4. Fuel injector according to Claim 3, characterized in that, with regard to a first opening phase of the nozzle needle (13), the first end surface (44) is in a starting position, and in that, with regard to a second opening phase of the nozzle needle (13), the first end surface (44) lifts up from the starting position, such that with regard to the second opening phase of the nozzle needle (13), an effective surface, which is composed of the pressure surface (38) of the booster piston (31) and the first end surface (44), is exposed to the actuator-side coupler space (36).
5. Fuel injector according to Claim 4, characterized in that a pressure spring (43) is provided which places the control sleeve (35) into a starting position before the start of the first opening phase of the nozzle needle (13) .
6. Fuel injector according to one of the preceding claims, characterized in that the actuator-side booster piston (31) is a stepped piston with a first piston section (32) and with a second piston section (33) and in that the actuator-side coupler space (36) is assigned to the first piston section (32) with the pressure surface (38) and the control space (37) is assigned to the second piston section (33) with a second pressure surface (48).
7. Fuel injector according to Claim 6, characterized in that the control sleeve (35) is guided axially on the first piston section (32).
8. Fuel injector according to Claim 6 or 7, characterized in that a sliding sleeve (34) is guided axially on the second piston section (33) and in that the control sleeve (35) is guided axially between the first piston section (32) and the sliding sleeve (34).
9. Fuel injector according to one of the preceding claims, characterized in that a nozzle-needle-side coupler space (53) is provided, to which a nozzle-needle-side pressure surface (52) of the nozzle-needle-side booster piston (51) is exposed, and in that the actuator-side coupler space (36) and the nozzle-needle-side coupler space (53) are connected by means of a hydraulic connection (22).

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