WO2007116007A1

WO2007116007A1 - Piezoelectric actuator, method for manufacturing a piezoelectric actuator, and injection system having a piezoelectric actuator of this type

Info

Publication number: WO2007116007A1
Application number: PCT/EP2007/053346
Authority: WO
Inventors: Hellmut Freudenberg; Richard Pirkl; Udo REILÄNDER; Dejan Jovovic; Maximilian Kronberger; Matthias Wicke
Original assignee: Continental Automotive Gmbh
Priority date: 2006-04-11
Filing date: 2007-04-05
Publication date: 2007-10-18
Also published as: DE102006017034B4; DE102006017034A1

Abstract

According to the invention, a piezoelectric actuator (1) is proposed for injecting fuel at a predefined fuel pressure, which piezoelectric actuator (1) has the following: a nozzle needle (2) for opening and closing a nozzle (18), into which the fuel is injected, a controllable piezoelectric stack (3) which provides a stroke for actuating the nozzle needle (2) in a closing direction (R1) or in an opening direction (R2) as a function of a control signal, and a spring apparatus (6) which, as a function of the fuel pressure (8), provides a force which at least partially counteracts a closing force which acts on the nozzle needle (2) in the closing direction (R1).

Description

description

Piezo actuator, method for producing a piezo actuator and injection system with such

The invention relates to a piezoelectric actuator, a method for producing a piezoelectric actuator and an injection system with a piezoelectric actuator.

Injection systems and in particular leak-less common rail

Injection systems require a control, such as ^¬ example, a piezo actuator in the high pressure chamber. The technical field of the invention relates in particular to piezo-controlled common rail injectors or injection systems without leak oil return with a piezo actuator or a piezo actuator for opening and closing a nozzle by means of a nozzle needle in the high pressure chamber, a hydraulic longitudinal compensation device or return device and a lever translator For actuating the nozzle needle. In particular, the return device has a hole in the bottom plate of the

Piezo stack of piezoelectric actuator engaging piston, a hyd ^¬ raulisches volume, for example, a fuel volume, between the bottom plate and the piston and a Rückstellfe ^¬ to reset the piezo stack on. Such a single injection system is known, for example, 101 45 620 B4 be ^¬ from DE.

As a result of the dependence of the closing force, which acts on the nozzle ^¬ needle and acts in a closing direction for closing the nozzle, the applied fuel pressure, the energy required to open the nozzle at high Kraftstoffdrü ^¬ bridges is relatively high, resulting in a corresponding size of the piezoelectric Actors required. As the necessary actuation energy increases, so too does the power loss of the piezo actuator. Particularly in the case of multiple injection and at a high injection pressure, for example 2000 bar, a simple oncoming flow of the control device or of the piezoelectric device is sufficient. 200602289

Actors with air to cool it no longer off, which means a significant cost penalty.

Another disadvantage of conventional injection systems is that, depending on manufacturing tolerances and elastic deformations due to external and internal forces acting on the piezoelectric actuator, a widely varying idle stroke can occur. These idle stroke differences can be compensated, inter alia, by the hydraulic longitudinal compensation device described above.

However, the Applicant has found in a variety of experiments that it is necessary in the design of the hydraulic longitudinal compensation device, the end effector o- return the bottom plate of the piezo stack as quickly as possible to its original position, so from actuation to actuation no Hubunterschiede arise. In particular, this provision should take place from injection to injection. Thus, all injection events could be handled regardless of their history. However, the information provided by the hydraulic differential coupling device restoring force must the nozzle needle in any Betriebszu ^¬ stood open the piezo actuator. This results in that the hyd may generate only a small restoring force ^¬ raulische longitudinal balancing device, since otherwise at a low

Fuel pressure or rail pressure a needle opening takes place. However, a low restoring force requires disadvantageous ^¬ example, that the reset times at higher fuel pressures or Raildrücken and thus higher nozzle needle forces are too long for the dynamic requirements of the piezoelectric actuator.

Accordingly, it is an object of the present invention to minimize the power loss of the piezoelectric actuator, in particular with konstruk ^¬ tively simple and inexpensive means.

Another object of the present invention is to provide a piezoactuator in which a closing force dependent on the fuel pressure is reduced. there 200602289

in particular, the closing force should be reduced at the beginning of the opening of the nozzle.

Another task is len a piezo actuator bereitzustel- in which differences in stroke in successive Actuate the ^¬ the nozzle needle movements are minimized or avoided.

According to the invention at least one of these questions is Aufga ^¬ ben by a piezoelectric actuator having the features of patent claim 1 and / or solved by a method for manufacturing a piezoelectric actuator having the features of claim sixteenth

Accordingly, according to the invention, a piezoactuator for injecting fuel at a predetermined fuel pressure is proposed which comprises:

a nozzle needle for opening and closing a nozzle into which the fuel is injected,

- a controllable piezo stack which provides a function ei ^¬ nes control signal for actuating a stroke of the nozzle needle in a closing direction or an opening direction, and

- A spring device, which provides a force depending on the fuel ^¬ pressure, which counteracts at least partially acting on the nozzle needle and acting in the closing direction closing force.

One advantage of the piezoelectric actuator according to the invention is that the force provided by the spring device counteracts the closing force in such a way that the opening of the nozzle is assisted. The spring device thus acts as an energy store for supporting the opening of the nozzle. Overall, therefore, the piezo stack, which performs the lifting of the nozzle needle from the nozzle seat, bring less energy ^¬ . Consequently, the power loss of the piezo actuator is reduced. It is particularly advantageous that the of the

Spring device provided power is dependent on the current fuel pressure. The following clarifies this advantage according to the invention: the higher the fuel pressure, 200602289

the greater becomes the closing force dependent on the fuel pressure, but the greater is the energy stored in the spring device or the force provided by the spring device which counteracts the closing force. Thus, although the fuel pressure always affects the closing force, but it also controls the closing force ^¬ counteracting force of the spring device ^according to the invention.

Advantageous embodiments and modifications of the invention will become apparent from the dependent claims and the description with reference to the drawings.

According to a preferred embodiment of the invention the compensated provided by the spring means force ma ^¬ Siert ximal 90%, especially a maximum of 80% of the cross at the nozzle needle to ^¬ and acting in the closing direction of the closing force. Thus, it is advantageously ensured that as a result of the force provided by the spring device no undesired needle opening can take place. Thus, the tightness between the nozzle needle and valve, for example, with respect to a combustion chamber of a motor vehicle engine for each injection pressure or fuel pressure ensured.

According to a preferred embodiment of the invention, the piezoelectric actuator has a restoring device, which is adapted to reset the piezoelectric stack in a predetermined starting position, and which has at least one coupled between the piezo-stack and the nozzle needle piston device, which provided the hub transfers.

According to a further preferred embodiment, the restoring device already provides a restoring force for resetting the piezoelectric stack, which is smaller than a minimum force in all operating states of the piezoelectric actuator to the

Opening the nozzle is necessary. Thus, an undesirable nozzle needle opening is prevented. The opening of the nozzle is 200602289

namely performed by the stroke provided by the piezo stack.

According to a further preferred refinement, a lever transmission device is provided for translating the stroke transmitted by the piston device into an enlarged stroke, which has a piezo-side lever, which is coupled to the piston device, and a nozzle needle-side lever, which is coupled to the nozzle needle. The lever translation device has the particular advantage of minimizing the necessary stroke to be provided by the piezo stack and thus the necessary energy to be provided by the piezo stack. Thus, the power loss of the piezo actuator is further minimized.

According to a further preferred embodiment, the restoring device comprises at least one return spring and a spring plate, wherein the spring plate is supported on a housing of the piezo stack and / or the return spring between see a bottom plate of the piezo stack and the spring plate is arranged. Preferably, the return device further comprises the piston device, which engages in a bore of the bottom plate of the piezo stack, and a hydraulic ^¬ cal volume, in particular a fuel volume with the predetermined fuel pressure, between the bottom plate and the coupling device.

According to a further preferred embodiment, the spring device between the restoring device and the lever-translating device is arranged such that the force provided by the spring device acts exclusively counter to the closing direction of the closing force. Thus, the support of opening the nozzle by the force provided by the spring device is optimal.

According to a further preferred embodiment, the spring device is disc-shaped, wherein the return 200602289

Device and the lever translation device are connected by a hole of the disc-shaped spring device and the disc-shaped spring device is coupled at its Außenrandbe- rich with the lever translation device. By the one-sided coupling of the spring device on the lever transmission device, in particular on the piezoelectric lever, it is ensured that the force provided by the spring device can act exclusively in the closing direction and not in the opening direction. Thus, the opening of the nozzle is advantageously not hindered after the decay of the force provided by the spring device.

According to a further preferred embodiment, the spring device is designed as a biasing element, which is connected in series with the return spring and is biased by the applied fuel pressure. A particular advantage of the spring device designed as a biasing element is that the force provided by it, which counteracts the closing force, is independent of the stroke of the nozzle needle.

According to a further preferred embodiment, the biasing element is annular, wherein the annular biasing element comprises in particular the bottom plate of the piezoelectric stack.

According to a further preferred embodiment, the annular biasing member has a cross section which is characterized by a major axis and a minor axis. For example, the cross section is substantially diamond-shaped or substantially elliptical.

According to a further preferred embodiment, the annular biasing element is arranged such that the main axis or the minor axis runs parallel to the closing ^direction . This parallel arrangement results in an opti ^¬ male effect of the provided by the spring device or the biasing force against the closing force. 200602289

According to a further preferred embodiment, the annular biasing element has a cavity. Preferably, the cavity is filled with a fluid, a gas, a liquid, a free-flowing material, a polymer and / or an elastomer for adjusting the spring constants of the annular biasing element. Thus, depending on the application or the use of the piezoelectric actuator, the spring constant of the biasing element, in particular depending on the predetermined fuel pressure can be adjusted.

According to a further preferred embodiment of the invention, the piezoelectric actuator is arranged in a high pressure chamber of an injection system, which is designed in particular as a common rail injection system.

The invention is explained below with reference to the rule in the figures of the drawing indicated schemati ^¬ embodiments. Show it:

Fig. 1 is a schematic longitudinal sectional view of a first embodiment of the piezoelectric actuator according to the invention;

FIG. 2 shows a schematic longitudinal sectional view of a second exemplary embodiment of the piezoactuator according to the invention; FIG.

Fig. 3 is a cross-section of a first embodiment of the annular biasing member according to the ahead ^¬ invention;

4 shows a cross section of a second Ausführungsbei ^¬ game of the annular biasing element according to the present invention. 200602289

5 shows a cross section of a third Ausführungsbei ^¬ game of the annular biasing element according to the present invention. and

Fig. 6 is a schematic flow diagram of a preferred embodiment of the method according to the invention.

In all figures, identical or functionally identical elements and devices-unless otherwise stated-have been provided with the same reference numerals.

The exemplary embodiments of the piezoactuator 1 according to the invention for injecting fuel at a predetermined fuel pressure P have in common that they include a nozzle needle 2 for opening and closing a nozzle 18, into which the fuel is injected, a controllable piezoelectric stack 3, which in response to a control signal (not shown) provides a stroke for actuating the nozzle needle 2 in a closing direction Rl or in an opening direction R2, and a spring device 6 which, depending on the fuel pressure P provides a force which at least partially on the nozzle needle 2 angrei ^¬ fenden and acting in the closing direction Rl closing force counteracted.

Preferably, the be of the spring device 6 ^¬ riding asked force compensated maximum of 90%, in particular maximum 80% of acting on the nozzle needle 2 and acting in the closing direction Rl closing force.

The piezoelectric actuator 1 preferably has a hydraulic return ^¬ adjusting device 5, which is adapted to reset the piezoelectric stack 3 in a predetermined starting position. The hydraulic return device 5 has a coupled between the piezo-stack 3 and the nozzle needle 2 Kolbenvor ^¬ direction 4, which transmits the provided stroke. The return device 5 generates a restoring force 200602289

to reset the piezo stack 3 in its initial position, which is smaller than a minimum force in all operating states of the piezoelectric actuator 1, which is not agile ^¬ to open the nozzle 18.

Furthermore, a lever transmission device 7 is provided for translating the transmitted from the piston device 4 stroke in an enlarged stroke. The lever transmission device 7 has a piezo-side lever 8, which is coupled to the piston device 4, and a nozzle needle-side lever 9, which is coupled to the nozzle needle 2. The nozzle needle 2 is preferably integrated in a nozzle body 19. Next, the return device 5 at least one return spring 10 and a spring plate 11, wherein the spring plate 11 is supported on a housing 12 of the piezo stack 3 and / or the return spring 10 disposed between a bottom plate 13 of the piezo stack 3 and the spring plate 11 is. The return device 5 is ^{insbesonde ¬} re by the engaging in the bore of the bottom plate 13 of the piezoelectric stack 3 piston device 4, a volume of the

Fuel with the predetermined fuel pressure P between the bottom plate 13 and the piston device 4 and the return spring 10 is formed. All volumes within the piezo-actuator 1, which have fuel with the predetermined fuel pressure P are indicated by the reference P.

Referring to FIG. 1, the spring device 6 interim ^¬ rule invention the leverage apparatus 7, and see the hydraulic return device 5 is arranged. The spring device 6 generates a fuel pressure P proportional counterforce on the piezoseitigen lever 8 of the lever translation device 7, because with increasing fuel pressure P, the nozzle needle 2 shortened as a result of closing force increase and the nozzle body 19 extended. Thereby, the force initiation ^¬ is point 20 of the piezo-sided lever displaced in the direction of the spring device 6. 8 Depending on the spring constant of the spring device 6 is characterized to the fuel pressure P 200602289

10

built proportional force that counteracts the closing force ^¬ . Thus, the piezoelectric actuator 1 is supported in particular at the beginning of the nozzle opening. For clarity of illustration, reference symbol R3 shows the expansion direction of spring device 6, reference symbol R4 shows the compression direction of nozzle needle 2, and reference symbol R5 denotes the elongation direction of nozzle body 19.

Preferably, the vertical sealing gap D between the piston device 4 and the bottom plate 13 on the piston side a cylindrical or spherical surface with a very short Längenaus ^¬ expansion. Because of the alignment of the piston end face of the piston device 4 by the disk-shaped spring device 6, the piston device 4 is guided in the bore of the bottom plate 13 at a spherical sealing surface of the sealing gap D with small inclinations or a cylindrical sealing surface without jamming. The short sealing surfaces of the Kol ^¬ benvorrichtung 4 are particularly advantageous for minimizing the moving masses and in the maintenance of close Spieltole- tolerances.

2 shows a schematic longitudinal sectional view of a second exemplary embodiment of the piezoactuator 1 according to the invention. The second exemplary embodiment of the piezoactuator 1 according to the invention differs in particular from the first exemplary embodiment according to FIG. 1 in that the spring device 6 is designed as a pretensioning element which is connected in series with the return spring 10. The biasing element 6 is biased by the applied fuel pressure P. The biasing member 6 has the property ^¬ shaft, at higher fuel pressures P bias the return spring 10 more than at smaller fuel pressures P. It is thus adjusted or adjusted by the fuel pressure P and the rail pressure itself. The biasing member 6 is in particular formed as a ring, which comprises the Bodenplat ^¬ te 13 of the piezoelectric stack 3. 200602289

11

Figures 3 to 5 show various embodiments of the annular biasing member 6. The annular pre ^¬ clamping element 6 has a cross section 14, 15, which is characterized by a main axis Ll and at least one minor axis L2. Referring to FIG. 3, the annular biasing member has 6 14. The major axis and the minor axis Ll L2 define a substantially diamond-shaped cross-section while the diamond of the cross-section ^¬.

The biasing element 6 according to FIG. 4 has a cross-section which results from a series connection of two diamond-shaped cross-sections 14.

The annular biasing element 6 according to FIG. 5 has an elliptical cross-section 15. The main axis Ll and the minor axis L2 define the dimensions of the ellipse.

Preferably, the annular biasing member is arranged in such a way check that the main axis Ll or the minor axis L2 pa rallel ^¬ extending to the closing direction Rl. For example, the main axis Ll according to the embodiment of FIG. 2 is parallel to the closing direction Rl.

Preferably, the annular biasing member 6 has a cavity 16. The cavity 16 is filled in particular with a fluid, a gas, a liquid, a free-flowing material, a polymer and / or an elastomer for adjusting the spring constant of the annular biasing element 6.

Fig. 6 shows a schematic flow diagram of a Favor ^¬ th embodiment of the inventive method for manufacturing a piezoelectric actuator 1 for injecting fuel at a predetermined fuel pressure P. The method of the invention with reference to the block ^¬ diagram in Fig. 6 will be explained. The procedural invention ^¬ ren has the following steps: 200602289

12

Process step a:

There is provided a nozzle needle 2 for opening and closing a nozzle 18 into which the fuel is injected.

Process step b:

The nozzle needle 2 is coupled to a controllable piezo-stack 3, which provides a stroke for actuating the nozzle needle 2 in a closing direction Rl or in an opening direction R2 in response to a control signal.

Process step c:

The spring device 6 is arranged such that it provides a force as a function of the fuel pressure P, which at least partially counteracts a force acting on the nozzle needle 2 ^¬ and acting in the closing direction Rl closing force.

Although the present invention has been described above with reference to the preferred embodiments, it is not limited thereto, but modifiable in many ways and Wei ^¬ se. For example, it is conceivable to design the piezo actuator as an open system as described in the preceding embodiments, or as a closed system.

Claims

20060228913Patentansprüche

A piezoelectric actuator (1) for injecting fuel under a predetermined fuel pressure (P) with:

a) a nozzle needle (2) for opening and closing a nozzle (18) into which the fuel is injected;

b) a controllable piezo stack (3), which in dependence of a control signal ness a stroke for actuating the Düsenna ^¬ provides del (2) in a closing direction (Rl), or in an opening direction (R2); and

c) a spring device (6) which, depending on the fuel pressure (P), provides a force which at least partially counteracts a closing force acting on the nozzle needle (2) and acting in the closing direction (Rl).

2. Piezoelectric actuator according to claim 1, characterized in that a force provided by the spring device (6) a maximum of 90%, in particular a maximum of 80% acting on the nozzle needle (2) and acting in the closing direction (Rl) Closing force compensated.

3. Piezoelectric actuator according to claim 1 or 2, since you rchgekennzeichnet that the piezoelectric actuator (1) has a restoring device (5) which is adapted to reset the piezoelectric stack (3) in a ne predetermined starting position, and which has a between the piezo-stack (3) and the nozzle needle (2) gekop ^¬ pelte piston device (4) which transmits the bereitgestell ^¬ th stroke.

4. Piezo actuator according to one or more of the preceding claims, characterized 200602289

14

that the restoring device (5) a restoring force (3) provide for resetting of the piezo stack, which is smaller in al ^¬ len operating states of the piezoelectric actuator (1) as a minimum force is required to open the nozzle (18).

5. Piezoelectric actuator according to one or more of the preceding claims, characterized in that a lever transmission device (7) for the translation of the piston device (4) transmitted stroke is provided in an enlarged stroke, which a piezoseitigen lever (8) with the piston device (4) is coupled, and a nozzle needle-side lever (9) which is coupled to the nozzle needle (2) has.

6. Piezo actuator according to one or more of the preceding claims, characterized in that the restoring device (5) has a return spring (10) and / or a spring plate (11), wherein the spring plate (11) on a housing (12). the piezo stack (3) and / or the return spring (10) between a bottom plate (13) of the piezo stack (3) and the spring plate (11) is arranged.

7. Piezoelectric actuator according to one or more of the preceding claims, characterized in that the spring device (6) between the restoring device (5) and the lever translation device (7) is arranged such that by the spring device (6) ^{bereitge ¬} presented force exclusively counter to the closing direction (Rl) of the closing force acts.

8th . Piezo actuator according to claim 7, characterized 200602289

15

that the spring device (6) is disc-shaped, wherein the restoring device (5) and the levers translation ^¬ device (7) are connected by a hole in the disc-shaped spring means (6) and the disk-shaped spring device (6) at its outer edge region (17) is coupled to the lever translation device (7).

9. Piezo actuator according to one or more of claims 1 to 6, characterized is that the spring device (6) is out as a biasing member ^¬ which is switched on with the restoring spring (10) ge in series ^¬ and by the applied fuel pressure (P) is biased.

10. Piezoelectric actuator according to claim 9, since you rchgekennzeichnet that the biasing element (6) is annular, where ^¬ in the annular biasing element (6) in particular the bottom plate (13) of the piezo stack (3).

11. Piezoelectric actuator according to claim 10, characterized in that the annular biasing element (6) has a cross section (14, 15) which is characterized by a main axis (Ll) and a minor axis (L2).

12. Piezoelectric actuator according to claim 10 or 11, since you rchgekennzeichnet that the annular biasing element (6) has a Wesentli ^¬ chen diamond-shaped cross-section (14) or a substantially elliptical cross-section (15).

13. Piezoelectric actuator according to claim 11 or 12, since you rchgekennzeichnet that the annular biasing element (6) is arranged such that the main axis (Ll) or the minor axis (L2) paral ^¬ lel to the closing direction (Rl). 200602289

16

14. Piezoelectric actuator according to one or more of claims 10 to 13, characterized in that the annular biasing element (6) has a cavity (16).

15. Pie zo-act or according to claim 14, characterized in that the cavity (16) filled with a fluid, a gas, a liquid, a free-flowing material, a polymer and / or an elastomer for adjusting the spring constant of the annular biasing element (6) is.

16. A method for producing a piezoelectric actuator (1) for injecting fuel under a predetermined fuel pressure (P) according to one or more of the preceding claims 1 to 15, comprising the steps of:

a) providing a nozzle needle (2) for opening and closing a nozzle (18) into which the fuel is injected;

b) coupling the nozzle needle (2) with a controllable piezo stack (3), which in response to a control signal provides a stroke for actuating the nozzle needle (2) in a closing direction (Rl) or an opening direction (R2); and

c) disposing a spring means (6) such that it provides ^¬ a force as a function of the fuel pressure (P), which at least partially counteracts a force acting on the nozzle needle (2) and acting in the closing direction (Rl) closing force.

17. Injection system with a piezoelectric actuator (1) according to one or more of claims 1 to 15, wherein the piezoelectric actuator (1) in a high-pressure chamber of the injection system, which fuel 200602289

17

having the predetermined fuel pressure (P) is arranged.

18. Injection system according to claim 17, since it is possible to control the injection system as a common-rail injection system.