WO2014009303A1

WO2014009303A1 - Piezoelectric multilayer actuator and injection valve

Info

Publication number: WO2014009303A1
Application number: PCT/EP2013/064350
Authority: WO
Inventors: Michael Denzler; Thomas Richter; Marco KEMPE; Thomas STEMPLINGER; Yanfei ZHAO
Original assignee: Continental Automotive Gmbh
Priority date: 2012-07-09
Filing date: 2013-07-08
Publication date: 2014-01-16

Abstract

A piezoelectric multilayer actuator (9) is specified. The multilayer actuator (9) has a layer stack (10) which contains a plurality of piezoelectric elements (20) stacked one above the other in a longitudinal direction. It also has an end region (30) which follows the piezoelectric elements (20) in the longitudinal direction and is piezoelectrically inactive. Between the end region (30) and the layer stack (10), the multilayer actuator (9) has a decoupling layer (40), the brittleness or fluidity of which is increased with respect to the end region (30). An injection valve (1) with such a multilayer actuator (9) is also specified.

Description

description

Piezoelectric Multilayer Actuator and Injector The present disclosure relates to a piezoelectric multilayer actuator. In addition, it relates to an injection valve with a piezoelectric multilayer actuator.

Piezoelectric multilayer actuators which are suitable for injection valves are known, for example, from document EP 2082444 B1. They contain a monolithic

Layer stack with a plurality of piezoactive elements and inactive cover layers on the end faces of the layer stack. It is an object of the present disclosure to provide a piezoelectric multilayer actuator in which the risk of the formation of uncontrolled cracks in the inactive cover layers is particularly low. This task is performed by a piezoelectric

Vielschichtaktor solved with the features of claim 1. Advantageous embodiments and further developments of

Multilayer actuators are given in the dependent claims. It is another object of the present disclosure to provide an injector that is particularly reliable at high pressures. This object is achieved by an injection valve according to claim 10. A piezoelectric multilayer actuator is specified. The piezoelectric multilayer actuator has a monolithic layer stack including a plurality of piezoelectric elements stacked in a longitudinal direction. Each piezoelectric element includes a first electric ^¬ denschicht, a second electrode layer and a

piezoceramic layer between the electrode layers. The piezoceramic layer is particularly adjacent to sides to the first and second electrode layer. The layer thickness of the piezoceramic layer has, for example, a value between 40 and 200 ym, preferably it has a value between 50 and 130 ym, in particular between 60 ym and 80 ym, the limits are included.

In the present context, a "piezoceramic" layer is to be understood as meaning, in particular, a layer which contains a ceramic material which deforms under the action of an electric field, In particular, each of the piezoelectric elements is constructed in such a way that the application of an electrical voltage to the first and second electrodes In this way, the length of the layer stack increases, that is, its expansion in the longitudinal direction

Longitudinal direction, upon application of an electrical voltage to the piezoelectric elements.

Under that the layer stack a "monolithic"

Layer stack is, is in the present context in particular ^¬ special understood that the formation of the layer stack provided starting layers - in particular those for the formation of the first and second electrode layers and the

Piezoceramic layers provided output layers - stacked into a common green body and sintered together to form the layer stack. Here, zweckmäßi ^¬ gerweise a stable connection of the layers forms from each other so that the individual piezoelectric elements in particular ^¬ sondere not have to be connected together by means of adhesive layers. In particular, the layer stack is free of adhesive layers.

In addition, the piezoelectric multilayer actuator has an end portion which is the piezoelectric elements in the

Longitudinal follows. In particular, it has a further - preferably identical - end portion, which precedes the piezoelectric elements in the longitudinal direction. to For simplicity, the following description refers to only one of the end portions.

The end region is expediently piezoelectrically inactive. Preferably, it is also electrically insulating, in particular in order to electrically isolate the multilayer actuator from other components. Preferably, the end region is thus free of metallic layers. In particular, it contains no Elect ^¬ clear layer.

In one embodiment, a layer thickness of the end region has a value between 0.2 mm and 5 mm, for example, it has a value between 0.5 mm and 3 mm, in particular between 0.8 mm and 1.6 mm, the limits each are included. The layer thickness is the dimension of the end region in

Longitudinal direction.

In one embodiment, the end portion includes a ceramic material such as alumina or a piezoceramic material. The piezoceramic material is, in particular, an oxide with a perovskite structure, for example

Lead zirconate titanate.

In one embodiment, the end region is monolithically integrated in the layer stack and preferably made of the same piezoceramic material as the piezoceramic layers of the piezoelectric elements. "Monolithically integrated into the layer stack" means in particular that the output layer provided for forming the end region and the output layers provided for forming the layer stack are joined together to form a common green body and sintered together.

If the end region is made of a piezoceramic material, the piezoelectric inactivity is achieved, in particular, by the fact that the multilayer actuator is not intended to produce an electric field in the end region by means of electrode layers. In particular, the end area is free of electrode layers which are supplied during operation of the multilayer actuator with the voltage applied to the multilayer actuator electrical operating voltage. Furthermore, the multilayer actuator has a decoupling layer between the end region and the layer stack. In particular, the layer stack, the decoupling layer and the end region directly follow one another. In other words, the decoupling layer preferably adjoins the layer stack and the end region on opposite sides.

The mechanical stability of the decoupling layer is reduced relative to the end region. Preferably, it is also reduced with respect to the mechanical stability of an end portion facing edge portion of the layer stack.

Including that the decoupling layer has a lower mechanical ^¬ African stability than the end portion or as the decoupling layer facing edge portion of the layered stack is, in particular, understood in the present context that the under sufficient tension and / or under sufficient shear stress between End region and the layer stack of the end region in the region of the decoupling layer from the layer stack detaches. In particular, the breaking edge runs in the decoupling layer or at an interface of the decoupling layer.

During operation of the multilayer actuator, the piezoelectric elements expand due to the inverse piezoelectric effect

Longitudinal, this is accompanied by a taper transverse to the longitudinal direction, that is, with a reduction in the cross-section, so that in particular the volume of

piezoceramic layers remains constant or at least approximately constant. This behavior is also referred to as "transverse contraction." The piezoelectrically inactive end region is not subject to such transverse contraction due to the inverse piezoelectric effect, so it tends to maintain its cross-sectional dimensions. _n

5

In conventional piezoelectric multilayer actuators, the end region is rigidly coupled to the layer stack. For example, it adjoins directly to the layer stack, such as one

Electrode layer of one of the piezoelectric elements, and is monolithically integrated into the layer stack.

As a result of these different transverse contraction mechanical stresses can arise in conventional piezoelectric multilayer actuators. The mechanical stresses cause, in particular, a bend or at least a bending stress in the end region. The bending stress is in particular directed so that the lateral, preferably parallel to the longitudinal direction outer surfaces of the end portion in the direction of

Layer stack are attracted. The optionally caused bending thus leads, in particular, to a convex curvature of the outer surface of the end region facing away from the layer stack.

By means of the decoupling layer, such bending stresses in the end region are advantageously reduced. Thus, advantageously, the risk is reduced that in the multilayer actuator uncontrolled cracks arise, which grow from the end region in the longitudinal direction to the piezoelectric elements of the layer stack and their operability can ^{affect ¬} , for example by causing electrical flashovers and thus the failure of the multilayer actuator to lead.

In an expedient embodiment, the positive connection and / or the frictional connection between the end region and the layer stack is canceled by means of the decoupling layer.

"Lifting the positive connection" means in particular that the distance between the end region and the layer stack - or at least between overlapping in plan view of the longitudinal direction partial regions of end region and layer stack - by means of the decoupling layer is variable. "Abolition of adhesion" means in particular that the End region and the layer stack - or in plan view of the longitudinal direction overlapping partial regions of the end region and layer stack - are mutually movable transversely to the longitudinal direction. Appropriately, by means of the decoupling layer, the transmission of shear forces acting transversely to the longitudinal direction from the layer stack to the end region is reduced compared to a rigid coupling. Alternatively or additionally, the transmission of tensile forces in the longitudinal direction relative to a rigid coupling can be reduced.

In particular, the coupling of the end region is on

Reduced cross-sectional changes of the layer stack with respect to a rigid coupling, or the end region is completely decoupled from cross-sectional changes of the layer stack.

According to at least one embodiment, one or more cracks are formed in the Entkopp ^¬ lung layer, so that a locally or complete detachment of the end region from the

Layer stack is achieved. Preferably, the end region in the region of the decoupling layer is completely from the

Demolished layer stack. In the present context, a crack which is "formed in the decoupling layer" is also understood to mean a crack which extends at an interface of the decoupling layer to the end region and / or at an interface of the decoupling layer to the layer stack.

The formation of the cracks or the detachment of the end region from the layer stack take place in particular following on

Production of the piezoelectric multilayer actuator as a result of transverse contraction and longitudinal expansion of the layer stack during operation of the multilayer actuator. For example, the cracks can increase with the service life of the multilayer actuator and only gradually lead to a complete detachment.

The reduced mechanical stability of the decoupling layer compared with the end region advantageously reduces the risk of the cracks spreading into the end region or into the layer stack. Rather, the cracks or the separation takes place due to their lower mechanical stability targeted in the decoupling layer. ^

The risk of functional failures due to bending stress-induced cracks is particularly pronounced in applications with high mechanical loads. One such application is an injection valve for a diesel engine in which fuel generally has to be metered at a pressure in the range of 2000 bar. The piezoelectric multilayer actuator according to the present disclosure is therefore particularly well suited for an injection valve for a diesel engine.

In one embodiment, the decoupling layer has a higher brittleness than the end region, and preferably also a greater brittleness as a bordering on the decoupling layer to ^¬ edge portion of the layer stack, whereby the reduced mechanical stability is achieved.

For example, the decoupling layer is a porous Kera ^¬ mix layer. A "ceramic layer" is made of a ke ^¬ ramischen material. A ceramic material comprises particles and cavities. By a "porous ceramic layer" a ceramic layer is meant in the present context in which the volume percentage of the voids is greater than the volume fraction the cavities in the end region, if it contains ceramic material, or in the kera ^¬ mixing material of the piezoceramic layers, whereby in particular the reduced mechanical stability is achieved.

In another embodiment, the decoupling layer is a perforated metal layer. For example, the perforated metal layer has a plurality of metal islands and at least one cavity surrounding the metal islands. Alternatively, the perforated metal layer may also be a metal layer which is interspersed with a multiplicity of cavities, wherein the cavity or the cavities preferably completely penetrate the decoupling layer in the longitudinal direction. The metal layer or the metal islands have in a further development of silver or consist thereof. Advantageously, the bond between the end portion and a perforated metal layer is comparatively low and the metal islands or interspersed with cavities ^¬ metal layer is relatively easily deformable whereby in particular the reduced mechanical stability is achieved by ^¬ rupted metal layer. Thus, in the case of transverse contraction and longitudinal extent of the layer stack, deformation and / or at least partial detachment of the metal layer from the end region and / or from the layer stack is preferably carried out. In this way, shear and tensile forces are transmitted only in ver ^¬ comparatively small extent from the layer stack on the end region, so that the end portion is acted upon only with a comparatively low bending stress. In a further embodiment, the decoupling layer is a ceramic layer in which the particles of the ceramic material are only weakly interconnected. For example, the particles of the ceramic layer are weaker decoupling ^¬ interconnected than the particles of the end portion when this is made ^¬ ge of a ceramic material. In this case, the sintering necks between the particles of the decoupling layer in particular in the means have a smaller cross section than the sintering necks between the Par ^¬ tikeln of the end portion. The decoupling layer embodied as a ceramic layer is preferably free of metallic layers, in particular internal electrode layers.

The decoupling layer formed, for example, as a perforated metal layer or as a porous ceramic layer is monolithically integrated in the layer stack in one embodiment. In an advantageous development, in this case also the end region is produced monolithically with the layer stack and the decoupling layer. This means in particular that in the production of the multilayer actuator to the formation of the layer stack, the decoupling layer and, if necessary. of the end region provided starting layers are joined together to a common green body and sintered together. For example, in this case, the monolithic integration of the decoupling layer or the decoupling layer and the end region may - for example for manufacturing reasons - be required or desirable that the

Layer stack has a piezoelectrically inactive edge portion which is arranged between the piezoelectric elements and the decoupling layer and in particular adjacent to the decoupling layer and to one of the piezoelectric elements. The piezoelectrically inactive edge section is made, for example, from the same piezoceramic material as the piezoceramic layers of the piezoelectric elements. The piezoelectrically inactive edge section is preferably free of metallic layers, in particular internal electrode layers.

The layer stack has a piezoelectrically inactive

Edge section on, the layer thickness is expediently as small as possible. For example, it has a value of 100 microns or less, in a development of 50 ym or less, for example, of 30 ym or less. In particular, the layer thickness has a value of one micron or greater, with the limits included.

In another embodiment, the decoupling layer is formed by an adhesive layer. For example, in this embodiment, the end portion is preferably formed as a separately manufactured tail.

In one embodiment, the adhesive layer has a greater fluidity - and thus a lower mechanical stability - than the end region. The fluidity is the reciprocal of the viscosity. In this way, the adhesive layer is in particular ^¬ special designed to absorb shear and / or tensile forces, so that they are not transmitted or only in a relatively small extent from the layer stack to the end. When

Adhesive, for example, a silicone resin is suitable. Alternatively, it is also possible to use an adhesive which has a greater brittleness than the end region, such that cracks develop during longitudinal expansion and transverse contraction of the layer stack during operation of the multilayer actuator within the adhesive layer or at the interface between the adhesive layer and end region or layer stack, or over a full-area peel he follows .

In another embodiment, the end portion of the layer stack is made separately and is loose on the

Layer stack on. In particular, no additional material is introduced between the layer stack and the end region in this embodiment. Rather, the decoupling layer is formed by the opposing outer surfaces of the end region and of the layer stack. In particular, due to the relatively low binding forces acting between these interfaces, the reduced mechanical stability of the decoupling layer is achieved in this case. The end region is thus slidably mounted on the layer stack, in particular transversely to the longitudinal direction, and is in

Removable longitudinally from the layer stack. Advantageously, a particularly good decoupling of the end region from the layer stack with respect to shear and tensile forces is achieved in this way. According to a development, the end region can adjoin directly to an electrode layer of a piezoelectric element of the layer stack.

The layer stack can have a transition region which contains a plurality of the piezoelectric elements, wherein in the transition region the layer thickness increases in each case in the longitudinal direction of successive piezoelectric elements in the direction towards the end region. By way of example, the piezoelectric elements arranged in the transition region have greater layer thicknesses than piezoelectric elements which are arranged in the layer stack on the side of the transition region facing away from the end region. In the present context, the term "layer thickness" is understood to mean the respective extent in the longitudinal direction. As the layer thickness increases, the longitudinal deflection of the piezoelectric elements decreases in the longitudinal direction, which also reduces the transverse contraction of the respective piezoelectric element. In this way, with the transition region, the bending stress acting on the end region can be further reduced.

In the multilayer actuators provided with the decoupling layer according to the present disclosure, such a transition region may advantageously be dispensed with, so that the piezoelectric elements adjacent to the end region may have the same layer thicknesses as the piezoelectric elements further away from the end region. For example, the piezoelectric multilayer actuator includes a first piezoelectric element that is be ^¬ nachbart the end portion and a second piezoelectric element which has a greater distance from the end portion, wherein, the first and the second piezoelectric element same layer thicknesses. That the first piezoelectric element is be ^¬ nachbart the end region, in particular in this context means that no more piezoelectric elements of the layer stack between the first piezoelectric element and the end portion are arranged. In this way, a greater deflection in the longitudinal direction can be achieved with the same longitudinal extent of the layer stack compared to layer stacks with transition region.

figure description

Further advantages and advantageous embodiments and further developments of the piezoelectric multilayer actuator and of the injection valve will become apparent from the following exemplary embodiments illustrated in conjunction with the figures.

Show it:

1 shows a schematic cross section through a piezoelectric multilayer actuator according to a first embodiment, FIG. 2 a shows a detail of the multilayer actuator according to FIG. 1 in the de-energized state,

FIG. 2b shows the section of FIG. 2a when it is in abutment

Operating voltage,

3 shows a piezoelectric multilayer actuator according to a second embodiment, and

4 shows an injection valve with a piezoelectric

Multilayer actuator according to a third embodiment. In the figures and embodiments of same, similar or equivalent elements having the same reference numbers are provided ^¬ Be. The figures and the proportions of the elements shown in the figures are not to be considered as true to scale. For example, individual elements can be shown exaggeratedly large or thick for better representability or better understanding.

Figure 1 shows a schematic cross-sectional view of a piezoelectric multilayer actuator 9 according to a first embodiment.

The piezoelectric multilayer actuator 9 has a stack ^¬ stack 10, which contains a plurality of piezoelectric elements 20. Each piezoelectric element 20 is made up of a first electrode layer 21, a piezoceramic layer 22 and a second electrode layer 23. The piezo-ceramic layer 22 is arranged between the two electrode layers 21, 23 and adjoins them in particular. In the present case, the layer stack 10 contains a predetermined breaking layer 15 at several locations between two successive piezoelectric elements 20. In the present case, the predetermined breaking layers 15 are unsuitable for this purpose, as electrode layers to act. In particular, they have an insufficient conductivity for electrode layers transverse to the longitudinal direction 100. The predetermined breaking layers 15 may for example be arranged between piezoelectrically inactive ceramic layers of the layer stack 10.

Such predetermined breaking layers are known to those skilled in principle. For example, the predetermined breaking layers are perforated metal layers or porous ceramic layers. Such predetermined breaking layers are for example in the

WO2009 / 092584 AI, EP 2082444 Bl and DE 10 2010 006587 AI known, the disclosure of which is taken over in the present disclosure by reference with respect to the ^¬ staltung and arrangement of the predetermined breaking layers.

In another embodiment, not shown in the figures, the predetermined breaking layers 15 are each contained in one of the piezoelectric elements 20. For example, in or against the longitudinal direction 100, the first electrode layer 21, a first section of the piezoceramic layer 22, the predetermined breaking layer 15, a second section of the

piezoceramic layer 22 and the second electrode layer 23 in this order. The piezoelectric elements 20 are followed in the longitudinal direction 100 by an optional edge section 11 of the layer stack, which is formed, for example, by a piezoelectrically inactive ceramic layer. The edge portion 11 preferably has the same piezoceramic material as the

Piezoceramic layers 22. He preferably has a

Layer thickness of 100 ym or less, preferably 50 ym or less.

In the present case, the layer stack 10 is a monolithic layer stack, which means, in particular, that the ceramic layers forming the piezoelectric elements 20, the predetermined breaking layers 15 and optionally the edge section 11 and the piezoelectrically inactive ceramic layers are provided. Seen starting layers are stacked into a common green body and sintered together. In particular, the individual piezoelectric elements are not interconnected by means of adhesive layers.

The edge portion 11 abuts on its side facing away from the piezoelectric elements 20 side to a decoupling layer 40, which adjoins on its side facing away from the layer stack 10 side to an end portion 30 of the multilayer actuator.

In the present case and preferably, the piezoelectric elements 20 are also preceded by an edge section 11 of the layer stack 10 and a decoupling layer 40 and a further end section 30 of the multilayer actuator 9, so that the piezoelectric elements 20 extend longitudinally between two end sections 30 and 30 of identical construction Decoupling layers 40 are included.

The multilayer actuator also has a first connection electrode 12 and a second connection electrode 13, the main extension planes of which extend in particular parallel to the longitudinal direction and which extend to different side surfaces of the

Layer stack 10 are applied. Expediently, the first electrode layers 21 are electrically conductively connected to one another with the first connection electrode, and the second electrode layers are electrically conductively connected to the second connection electrode. In this way, the polarity of the first electrode layers is equal to each other, the polarity of the second electrode layers is equal to each other, and the polarities of the first and second electrode layers are different from each other.

When an electrical operating voltage is applied between the first and second connection electrodes 12, 13, electric fields are produced in the piezoceramic layers 22 by means of the first and second electrode layers 21, 23, which cause an expansion of the piezoceramic layers 22 and thus of the layer stack 10 in the longitudinal direction 100 , With the Expansion in the longitudinal direction is a contraction of the

Cross-sectional area of the layer stack 10 transverse to the longitudinal direction 100 ("transverse contraction"), so that the volume of the

Layer stack 10 remains at least approximately constant.

The end regions 30 are piezoelectrically inactive, in particular since they are not arranged between two electrode layers 21, 23. In addition, they are electrically insulating. In the present case, they are made from the same piezoceramic material as the piezoceramic layers 22.

If the end regions 30 were rigidly connected, in particular frictionally and positively, to the layer stack 10, due to the different transverse contraction of layer stack 10 and end regions 30, mechanical stresses would occur in the end regions, which would in particular cause a bending of the end regions 30.

The decoupling layers 40 are provided to oppose the coupling of the end regions 30 to the layer stack 10

To reduce cross-sectional changes of the layer stack 10 compared to a rigid coupling. In particular, the transfer of shear forces acting transversely to the longitudinal direction 100 from the layer stack 10 to the end regions 30 is reduced by means of the decoupling layers 40.

This is in the figures 2a and 2b, the cutouts of

Vielschichtaktors according to the figure 1 show, shown in more detail. FIG. 2a shows one of the end regions 30 and the adjacent edge section 11 of the layer stack 10 with the decoupling layer 40 arranged therebetween in the de-energized state of the multilayer actuator. FIG. 2 b shows the section of FIG. 2 a when the operating voltage is applied to the ^terminal electrodes 12, 13. The decoupling layer 40 is herein formed by a rupted by ^¬ metal layer. The perforated metal ^¬ layer is composed for example of a plurality of metal islands 41 and one or more cavities 42. For example, by means of the metallic islands 41 a laterally connected, net-shaped cavity 42 is formed. The cavity or cavities 42 preferably extend over the entire layer thickness-that is, the extension in the longitudinal direction 100-of the decoupling layer 40. Such a decoupling layer 40 with metal islands 41 is particularly advantageous between the ceramic end region 30 and the ceramic edge section 11 good to produce.

Such perforated metal layers are known for another purpose, for example from the documents WO 2009/092584 AI and EP 2 082 444 Bl. The revelation content of this

Documents with regard to construction and production of the perforated metal layers is hereby incorporated by reference into the present disclosure.

Due to the rigid coupling of the edge portion 11 of the layer stack 10 to the piezoelectric elements 20 this is contracted transversely to the longitudinal direction with applied operating voltage, indicated by the arrows 150 in Figure 2b, and deflected in the longitudinal direction 100. In this way, a me ^¬ chanic bending stress is caused.

The coupling of the metal islands 41 to the end region 30 is comparatively weak, so that the mechanical stability of the decoupling layer 40 with respect to the end region 30 and the edge section 11 is reduced. As a result, the bending stress during operation of the multilayer actuator 9 causes cracks 45 in the decoupling layer 40, whereby the force and form fit between the facing interfaces of the end portion 11 and the end portion 30 is canceled, so that the boundary surfaces 301, 111 transverse to Longitudinal direction 100 at least in places are mutually movable. In a variant of this embodiment, the Ent ^¬ coupling layer 40 is a porous ceramic layer. Such a porous ceramic layer is known for another purpose in ^¬ example from the document DE 10 2010 006 587 AI. The disclosure of this document with regard to construction and production of the porous ceramic layer is hereby incorporated by reference into the present application.

Figure 3 shows a piezoelectric multilayer actuator according to a second embodiment in a schematic cross-sectional view.

In the second exemplary embodiment, the layer stack 10 is delimited in the longitudinal direction 100 by electrode layers 21 and 23, respectively. Thus, no tension between the piezoelectric elements and piezoelectrically inactive edge portions 11 occur, which are associated with the risk of uncontrolled cracking. However, as in the case of the first exemplary embodiment, it is also possible for an edge section 11 made of a piezoceramic material to be formed in the layer stack 10 at one or both longitudinal ends which is piezoelectrically inactive.

In contrast to the multilayer actuator according to the first ^exemplary embodiment, the layer stack 10 in the present ^exemplary embodiment has transition regions R at the ends opposite in the longitudinal direction 100, which each contain a plurality of piezoelectric elements with their electrode layers 21, 23. The spacings of successive electrode layers - which correspond to the layer thicknesses of the respective piezoelectric elements 20 - increase in the direction of the transition region R respectively adjacent end region 30, in particular d _R i <d _R 2 <d _R 3. In this way, the reduces mechanical stress to the adjacent end portion 30, since with increasing distance d _R i, d _R 2 and d _R 3, the deflection of the respective piezoelectric element 20 in the longitudinal direction and the corresponding transverse contraction decrease. Such layer stacks with transition regions R are in principle known to the person skilled in the art, for example from the document US Pat. No. 7,042,143 B2, the disclosure content of which is hereby incorporated by reference into the present disclosure. Such layer stacks with transition regions R are also suitable for the multilayer actuators according to the embodiments and embodiments of the present disclosure.

Due to the decoupling layer (s) 40, however, such transition regions R are advantageously dispensable, so that the first piezoelectric element 20A of the layer stack 10 adjacent to the respective end region 30 can have the same layer thickness and in particular the same electrode spacing d as one further from the end region 30 removed second piezoelectric element 20 B (see Figure 1). In this way, a larger number of piezoelectric elements 20 in the layer stack 10 at the same longitudinal ^¬ dimension of the layer stack 10 may be arranged as compared to layer stacks 10 with transition regions R in which enlarge the electrode spacings reasonable. In this way, a particularly large out ^¬ steering in the longitudinal direction 100 per unit length of the layer ^¬ stack 10 can be achieved.

In the present second embodiment of the

Multilayer actuator 9, the end portions 30 are not monolithically integrated into the layer stack 10. Instead, these are separately produced end pieces which are adhesively bonded to the layer stack by means of one of the decoupling layers 40, which in the present case are adhesive layers. The end pieces are preferably piezoelectrically inactive and electrically insulating.

The material of the adhesive layers 40 is selected, for example, such that it has a higher fluidity than the material of the end regions 30. In this way, the decoupling layer 40 is easily deformable, at least in the lateral direction, ie transversely to the longitudinal direction 100, compared to the end region 30. In this way, the adhesive layer 10 can absorb shear forces occurring in cross-sectional changes of the layer stack 10 and it does not transfer or only to a comparatively small extent on the respective end region 30. For example, the adhesive layer may comprise or consist of a silicone resin. Alternatively, the adhesive layer may also be formed of a material that a greater brittleness has, as the material of the end portion 30 so as to form at cross section ^¬ changes of the layer stack 10 in operation of the multilayer actuator cracks 45 in the adhesive layer 40, and so the transmission of shear and tensile forces on the respective end region 30 is reduced by means of the cracks 45.

The layer stack 10 in the second embodiment consists of the piezoelectric elements 20. In other words, it is constructed as an alternating sequence of electrode layers 21 and 23 and piezoceramic layers 22. However, as in the first exemplary embodiment, it may additionally contain predetermined breaking layers 15 in order to reduce the risk of crack-related functional impairments within the layer stack 10.

Figure 4 shows an embodiment of an injection valve 1 with a piezoelectric multilayer actuator 9 according to a third embodiment in a simplified, schematic sectional view.

The injection valve 1 has a valve body 2, which encloses an interior, in which the piezoelectric

Multilayer actuator 9 is arranged. For example, the longitudinal direction 100 of the layer stack 10 of the multilayer actuator 9 is parallel to or coincides with a longitudinal axis of the injection valve 1. The piezoelectric multilayer actuator 9 is followed in the longitudinal direction 100 by a nozzle needle 3 with which a connection between the fuel inlet 4 and the nozzle hole 5 of the injection valve 1 can be established and interrupted.

The nozzle needle 3 is pressed by means of a spring 6 in (or counter) the longitudinal direction 100 against the piezoelectric multilayer actuator. In the present exemplary embodiment, the layer stack 10 has both transition regions R and predetermined breaking layers 15, as described in connection with the preceding exemplary embodiments. Such layer stacks are also suitable for the other embodiments and embodiments of the multilayer actuator 9.

The end portions 30 of the multilayer actuator 9 preceding or following the layer stack 10 in the longitudinal direction are designed as separately produced, piezoelectrically inactive and preferably electrically insulating end pieces, as in the second embodiment of the multilayer actuator 9. They contain, for example, a ceramic material such as aluminum nitride or lead zirconate titanate.

In contrast to the second embodiment of the multilayer ^¬ actuator 9, the end regions 30 directly adjacent to the layer stack 10, so that the mutually facing outer surfaces 110 and 301 contact the layer stack 10 and the respective end piece 30th

In this case, the decoupling layer 40 between the layer stack 10 and the respective end region 30 becomes the outer surface 301 of the end region 30 facing the layer stack 10, the outer surface 111 of the end region 30 facing the end region 30

Layer stack 10 and the possibly remaining between these surfaces gas or fluid molecules from the interior of the valve body 2 is formed.

In other words, in the present embodiment ^¬ example, the respective tail without attachment layer loosely on the layer stack 10, so that it is laterally movable relative to the layer stack 10. The end pieces 30 and the layer stack 10 are held together only by the spring pressure built up by the spring 6 of the valve 1 - and, depending on the orientation of the gravity - together. The bonding forces between the outer surfaces 111, 301 are comparatively weak in comparison to the bonding forces within the particular ceramic end region 310, which corresponds to a reduced mechanical stability of the decoupling layer 40. The interface 301 of the end region 30 therefore does not follow, or only to a small extent, transverse contractions of the layer stack 10 during operation of the piezoelectric multilayer actuator. The risk of uncontrolled cracks in the end regions 30 due to the transverse contraction of the layer stack 10 during operation of the multilayer actuator 9 is reduced in this way with advantage.

The invention is not limited by the description based on the embodiments of these. Rather, it includes any combination of features in the embodiments and claims. In particular, the multilayer actuators according to the first two embodiments and the further aspects of the present disclosure are also suitable for the injection valve 1.

Claims

claims

Anspruch [en] A piezoelectric multilayer actuator (9) comprising a monolithic layer stack (10) including a plurality of piezoelectric elements (20) stacked in a longitudinal direction (100) and an end portion (30) of the piezoelectric elements (20) follows in the longitudinal direction (100) and which is piezoelectrically inactive, wherein the multilayer actuator (9) has a decoupling layer (40) between the end region (30) and the layer stack (10) whose mechanical stability relative to that of the end region (30 ) is reduced.

2. Piezoelectric multilayer actuator (9) according to claim 1, wherein the end region (30) with the layer stack (10) is made monolithic and in the decoupling layer (40) one or more cracks (45) are formed so that the end region (30). locally or completely by the layer stack (10) is released from ^¬.

3. The piezoelectric multilayer actuator (9) according to one of the preceding claims, wherein the decoupling layer (40) is a perforated metal layer or a porous ceramic layer.

4. Piezoelectric multilayer actuator (9) according to one of claims 1 to 2, wherein the decoupling layer (40) is formed by an adhesive layer.

5. Piezoelectric multilayer actuator (9) according to claim 1, wherein the end region (30) is manufactured separately and loosely rests on the layer stack (10), so that facing Au ^¬ ßenflächen the end portion (301) and the layer stack (111) the decoupling layer (40) form.

6. The piezoelectric multilayer actuator (9) according to one of the preceding claims, wherein the end region (30) contains a ceramic material such as alumina or lead zirconate titanate.

7. A piezoelectric multilayer actuator according to claim 1, wherein the layer stack includes a first piezoelectric element adjacent to the end region and a second piezoelectric element a greater distance from the end region (30), wherein the first and the second piezoe ^¬ lectric element (20A, 20B) have the same layer thicknesses (d).

8. Piezoelectric multilayer actuator (9) according to one of claims 1 to 6, wherein the layer stack (10) has an over ^¬ gang region (R), which contains a plurality of piezoelectric elements (20) and a layer thickness (d _R i, d _R , d _R 3) increases in each case in the longitudinal direction (100) of successive piezoelectric elements (20) of the transition region (R) in the direction towards the end region (30).

9. Piezoelectric multilayer actuator (9) according to one of the preceding claims, wherein the layer stack (10) has predetermined breaking layers (15).

10. injection valve (1) for a diesel engine with a piezoelectric multilayer actuator (9) according to one of the preceding claims.