EP3335252A1

EP3335252A1 - Piezoelectric component

Info

Publication number: EP3335252A1
Application number: EP16729575.7A
Authority: EP
Inventors: Jerome Acker
Original assignee: Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2015-08-14
Filing date: 2016-06-16
Publication date: 2018-06-20
Also published as: CN107851711A; JP2018525829A; KR20180037018A; DE102015215529A1; WO2017028985A1

Abstract

The invention relates to a piezoelectric component (10) which is constructed as a stack (18) of piezoceramic material layers (12) and electrode layers (14), wherein the stack (18) has at least two first active regions (36) along a longitudinal axis (16), at least two piezoceramic material layers (12) each with a first layer thickness (D1) being arranged in said first active regions, and wherein the stack (18) has at least two second active regions (38), at least two piezoceramic material layers (12) each with at least one second layer thickness (D2) being arranged in said second active regions. The second layer thickness (D2) is greater than the first layer thickness (D1) along the longitudinal axis (16).

Description

description

The invention relates to a piezoelectric component which is used for example as a so-called piezoelectric actuator in injector systems for injecting fuel into a combustion chamber of an internal combustion engine. Such a piezoelectric device includes several piezoceramic layers of material in space ^¬ common. A so-called piezoceramic, with which the material layers are formed, is a material that expands due to the piezoelectric effect when applying an electrical voltage. Such piezoceramics form the basis for the abovementioned piezoactuators which, when a voltage is applied across a

Longitudinal extent realize a travel of a few micrometers. The piezoceramic has electrical dipole moments, each of which has a preferential direction within white areas which are delimited from one another. In an unpolarized ground state of the piezoelectric ceramic are the preferred directions of the different White 'see districts disordered, so that outwardly no macroscopic electric Pola ^¬ ization of the piezoelectric ceramic is present.

To make the piezoelectric effect of piezoelectric actuators available, the piezoceramic is polarized by the alignment of the electric dipole moments, after which the electrical dipole moments in all white 'do not see districts or differ only slightly from a predetermined by the polarization axis preference ^¬ direction.

The individual piezoceramic material layers described above are usually provided with metallic electrode layers on both sides. If a voltage is applied to these electrode layers, so that they actively conduct a voltage, the piezoceramic material layers react with a lattice distortion which leads to the useful one already explained above Length expansion leads. Since this length dimension is, however, very low, piezoelectric devices at ^¬ play, in the form of piezo actuators in injector systems a plurality of individual piezoelectric ceramic material layers and electrode layers, which are arranged in a stack along a longitudinal axis alternately stacked.

FIGS. 5 to 7 show such a piezoelectric component 10 known from the prior art with a plurality of piezoceramic material layers 12 and a plurality of electrode layers 14 which are alternately stacked along a longitudinal axis 16 to form a stack 18.

As can be seen in particular in FIG. 6, the electrode layers 14 following one another along the longitudinal axis 16 are always brought in alternately only up to one side surface 20 of the stack 18. Next, it is seen that a head portion 22 and a foot portion 24 of the stack 18 as compared to a ^¬ arranged between the bulk portion 26 of the stack 18 has no electrode layers fourteenth

This results in lateral edge regions 28 of the stack 18 as well as in the head portion 22 and foot portion 24 respectively so ^¬ said piezoelectrically inactive domains that, behave differently when a voltage, as shown in Figure 7 in its length extension than the piezoceramic material layers 12 in the so-called active region (shown in dashed lines in FIG. 6). Due to the different linear expansion of the active and inactive regions of the piezoelectric component, undesirable mechanical stresses occur in the piezoelectric component. Moreover, increasing demands are made on emissions and emissions

Consumption in internal combustion engines to higher requirements for the injection of fuel into the combustion chamber. For example, higher fuel pressures and multiple required splashes, which also require a higher durability of the piezoelectric device in an injector. The described mechanical stresses in the piezoelectric component can form harmful cracks within the piezoelectric component, which significantly reduces the life of the piezoelectric component.

In order to solve this problem, that is to reduce the mechanical stress as far as possible, so far two strategies are known. On the one hand, the adhesive strength of the piezoceramic material layers of the electrode layers can be set low by a suitable selection of material and entspre ^¬ sponding process parameters that the relief of mechanical stresses is carried out by defined cracks, which preferably run between the piezoceramic material layers and a directly adjacent electrode layer.

On the other hand, can be inserted at regular distance by suitable material selection and ent ^¬ speaking process parameters as well as a particular stacking sequence of the piezoceramic material layers and the electrode layers in the piezoelectric device relieving security layers.

Both known approaches pursue the goal that emerging cracks spread in a targeted and defined manner. However, it would Wanting ^¬ rule worth to reduce the formation of cracks in principle.

The object of the invention is to propose a piezoelectric device in which the propagation of cracks is significantly reduced.

This object is achieved with a piezoelectric component having the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

A piezoelectric component has a plurality of piezoceramic material layers and a plurality of active electrode layers, wherein the piezoceramic material layers and the active electrode layers for forming a stack are alternately stacked along a longitudinal axis. The stack points along the

Longitudinal axis at least two first active areas in which at least two piezoceramic material layers are arranged, each having a first layer thickness, and at least two second active areas, in which at least two

piezoceramic material layers are each arranged with at least one second layer thickness, wherein the second

Layer thickness along the longitudinal axis is greater than the first layer thickness. The first active regions and the second active regions are alternately stacked along the longitudinal axis.

Piezoceramic material layers having a greater layer thickness are therefore introduced into the piezoelectric components in the second active regions than is the case in the first active regions. With increasingly thick

piezoceramic material layers in the active regions, the electric field is less with applied electrical voltage than in piezoceramic material layers having a smaller layer thickness, as is the case in the first active region. As a result, the mechanical stresses in the thicker piezoceramic material layers are lower than in the thinner piezoceramic material layers. At lower mechanical stresses, the potentially destructive cracks in the piezoelectric device propagate significantly less. As a result, the durability of a piezoelectric component is significantly improved by the introduction of second active regions which have piezoceramic material layers with a second layer thickness that is greater than the first layer thickness. If the piezoelectric component is now used as a piezo stack in an injector arrangement, the piezo stack in the drive can be adapted to new and more demanding requirements. This adaptation can be achieved not only by a suitable material selection as before, but in particular by the introduction of relief areas in a volume section of the piezoelectric ^¬ cal device by appropriate piezoceramic material layers and electrode layers are stacked.

Preferably, only piezoceramic material layers having the first layer thickness are arranged in the first active regions. The first active regions therefore contribute essentially to the resulting linear expansion of the piezoelectric component, since more electrode layers are arranged here over a predetermined length than is the case in the second active regions. This results in the first active areas a significantly greater length than in the second active areas.

In an advantageous embodiment, the stack along the longitudinal axis of a head portion and a foot portion and arranged between the head and the foot portion volume portion, wherein the second active areas are arranged in the volume portion, and wherein the head and the foot portion in each case by a first Area are formed.

The essential function of the second active regions is the relief of mechanical stresses in order to avoid or at least greatly reduce the propagation of cracks in the piezoelectric component. Therefore, it is useful to arrange these second active regions preferably in the volume portion where the likelihood of cracking is increased.

Preferably, in the volume portion arranged first active regions at least three piezoceramic material ^¬ layers with a first layer thickness. In order to make the longitudinal extent of the piezoelectric component particularly large, it is advantageous if the first active regions are arranged not only in the top and bottom sections of the piezoelectric component, but also in the volume section. In this case, the more piezoceramic material layers are arranged directly above one another, that is, only separated from one another by an electrode layer, the greater the length extension of the piezoelectric component can be achieved. Therefore, advantageously, the first active regions are also provided in the volume section of the piezoelectric component and then in this case have at least three piezoceramic material layers. Depending on the size of the piezoelectric component, the ge ^¬ desired length dimension and the number of further first active regions, which are arranged in the piezoelectric device has a first active region in the volume portion of the stack between three and twenty

piezoceramic material layers.

In an advantageous embodiment, in at least one of the second active regions at least one piezoceramic Ma ^¬ terialschicht is arranged with a third layer thickness, wherein the third layer thickness along the longitudinal axis is greater than the second thickness. Such a piezoceramic material ^¬ layer with a third layer thickness contributes to an even greater relief of the piezoelectric device and thus a greater reduction in the risk of cracking.

Preferably, the piezoceramic material layer with the third layer thickness along the longitudinal axis through at least one piezoceramic material layer with the second

Layer thickness of the first active area arranged spaced. Therefore, there is a slow transition from thin layer thicknesses to thick layer thicknesses of the piezoceramic material layers. In this way, an abrupt transition can be avoided, which in turn carries the risk that it will could build mechanical stresses in the piezoelectric device.

Preferably, in at least one of the second active regions, at least one security layer is arranged with a safety electrode arranged centrally in the security layer along the longitudinal axis. The layer thickness of

Safety layer along the longitudinal axis is greater than the first layer thickness. Advantageously, the layer thickness of the security layer may correspond to the second layer thickness and / or the third layer thickness. However, the layer thickness of the safety ^¬ layer may also be thicker than the second layer thickness or the third layer thickness. Security electrodes are not electrode layers in the true sense, but mostly metallic layers that are constructed so that they do not allow power line. For example, these metallic layers are deliberately weakened me ^¬ chanically, so that they can tear, for example, during operation and thus can stop resulting cracks in the piezoelectric device. By such a crack through the security electrode, these are no longer electrically conductive, as is the case with the other electrode layers.

The security layer therefore contributes to a further relief of the piezoelectric component.

Preferably, the security layer is disposed within one of the second active regions spaced from the first regions.

The security layer is preferably arranged spaced along the longitudinal axis by at least one piezoceramic material layer having the second and / or third layer thickness from the first active region. A distance between the security layer and a ^¬ along the longitudinal axis of the stack above the security layer arranged in the first active region and a along the longitudinal axis of the security layer spaced first active region below the security layer is preferably symmetrical. Thus, a uniform discharge of the piezoelectric component can be achieved.

In an advantageous embodiment, the stack parallel to the longitudinal axis of a first side surface and a second Be ^¬ tenoberfläche, which lie opposite each other, wherein along the longitudinal axis successive active electrodes are alternately brought up to the first side surface and up to the second side surface. The active electrodes brought up to the first side surface are spaced from the second side surface and the active electrodes brought up to the second side surface are spaced from the first side surface. By such an arrangement, it is possible to contact each second electrode in such a way that the contacting potential is different from the directly adjacent electrode, which is acted upon by a different contacting potential. By each other under ^¬ schiedliche contacting adjacent electrode layers, the potential gradient required for the linear expansion of the piezoelectric device can be produced.

Preferably, an external contact is applied in each case to the first side surface and to the second side surface, which covers substantially the entire length of the stack along the longitudinal axis. This means that both the first active regions and the second active regions as a whole are counted to the global active region of a piezoelectric component. In addition, applied to the piezoelectric device head and foot plates, which usually have no electrode layers and only serve for the isolation of other elements of a piezoelectric actuator, form the so-called inactive areas and usually have no Au ^¬ ßenkontaktierung on. In order to provide a particularly good discharge of the piezoelectric component, the safety electrode to the first side surface and until introduced to the second Be ^¬ tenoberfläche.

Advantageous embodiments of the invention will be explained in more detail with reference to the accompanying drawings. It shows: a longitudinal sectional view through a piezoelectric element according to a first embodiment form;

2 is a longitudinal sectional view through a piezoelectric component according to a second embodiment;

Figure 3 is a longitudinal sectional view through a piezoelectric device according to a third exporting ^¬ approximate shape.

4 is a longitudinal sectional view through a piezoelectric device according to a fourth exporting ^¬ approximate shape. Fig. 5 is a longitudinal sectional view of a piezoelectric device according to the prior art;

Fig. 6 is a longitudinal sectional view of a piezoelectric device according to the prior art; and

Fig. 7 is a longitudinal sectional view of a piezoelectric device according to the prior art.

1 shows a longitudinal section through a piezoelectric component 10 according to a first embodiment. The piezoelectric component 10 has a plurality of piezoceramic material layers 12 and a plurality of electrode layers 14 which are arranged along a longitudinal axis 16 are stacked alternately, thus forming a stack 18. The stack 18 has, parallel to the longitudinal axis 16, a first side surface 30 and a second side surface 32 facing each other. Along the longitudinal axis aufei- nanderfolgende electrode layers 14 are alternately brought up to the first side surface 30 and to the second Be ^¬ tenoberfläche 32nd On the respective gegenüberlie ^¬ ing side they are spaced from the respective side surface 30, 32. On the side surfaces 30, 32, the stack 18 each have an external contact 34, via which the respective contacted electrode layers 14 can be subjected to a voltage. The external contact extends on the side surfaces 30, 32 substantially over the entire length of the piezoelectric component 10 along the longitudinal axis 16. Therefore, the stack 18 shown in FIG. 1 globally forms an active region of a piezoelectric actuator.

The stack 18 is divided along the longitudinal axis 16 in a plurality of active areas, namely into first active regions 36 and second active portions 38, which are arranged from ^¬ alternately stacked on each other along the longitudinal axis sixteenth In the first active region 36, the piezoceramic material layers 12 all have a first layer thickness D1. In the second active region 38, the piezoceramic material layers 12 each have a second layer thickness D 2, wherein the second layer thickness D 2 is greater than the first layer thickness D 1.

The stack 18 has a plurality of first active regions 36 and also a plurality of second active regions 38. The first active regions 36 on the one hand form a head section 22 and a foot section 24 of the stack 18, but are also arranged in a volume section 26 of the stack 18 arranged between the head section 22 and the foot section 24. On the other hand, the second active areas 38 are located only in the volume section 26.

Due to the larger second layer thickness D2, in the second active regions 38 in the piezoceramic material layers 12, the electric field is less there with applied electrical voltage than in the piezoceramic material layers 12 in the first active regions 36. This results in significantly lower mechanical stresses than in the first active regions 36 and potentially destructive cracks can propagate significantly less. Therefore, the second active regions 38 essentially act as relief regions for the piezoelectric component 10, while the first active regions 36 are essentially assigned the function of a good length expansion. In order to achieve a particularly good lengths ^¬ expansion of the piezoelectric component 10, 36 are arranged in the volume portion 26 of first active areas five piezoceramic material layers 12, while the second active portions 38, which are intended as decision lastungsbereiche, only two

piezoceramic material layers 12 have.

2 shows a longitudinal section through a piezoelectric component 10 according to a second embodiment. The difference from the first embodiment is that a piezoceramic material layer 12 is arranged in the second active regions 38, which has a third layer thickness D3 which is greater along the longitudinal axis 16 than the second layer thickness D2. Thereby, the relief effect in the piezoelectric device 10 is even more enhanced, since an even thicker piezoceramic material layer 12 is present in the piezoelectric device 10, and so the propagation of unwanted cracks can be even more suppressed. In order to avoid stresses due to different expansions of the piezoceramic material layers 12 with significantly different layer thickness, the

Piezoceramic material layer 12 with the third layer thickness D3 each spaced by at least one piezoceramic material layer 12 with the second layer thickness D2 of the first active region 36.

3 shows a longitudinal sectional view of a piezoelectric component 10 according to a third embodiment. Of the In contrast to the first embodiment, in addition to the piezoceramic material layers 12 with the second layer thickness D2, in each case a security layer 40, which has a security electrode 42, is arranged in the second active regions 38. The security electrode 42 thereby extends from the first side surface 30 of the stack 18 to the second side surface 32 of the stack 18. The security electrode 42 is in each case designed such that cracks form in it in the event of mechanical stress on the piezoelectric component 10, which are then stopped in the security electrode 42 and thus no longer propagate in the piezoelectric device 10.

The security electrode 42 is viewed along the longitudinal axis 16 of the stack 18 centrally ^¬ belongs to the security layer 40 and the layer thickness of the security layer 40 is greater than the first layer thickness Dl in the first active region 36. The security layer 40 thus also forms a Ent ^¬ Lasting area in which on the one hand by a thick layer thickness, the occurrence of mechanical stresses can be generally reduced and on the other hand by the presence of the security electrode 42 cracks, which still arise, can be intercepted. The security layer 40 is arranged in the second active region 38 in such a way that it is arranged at a distance from the first active region 36 which adjoins above and below, respectively, in that a respective piezoceramic energy is generated between the respective first active regions 36 and the security layer 40 Material layer 12 is arranged with the second layer thickness D2.

In addition, in the fourth embodiment of the stack 18 shown in FIG. 4, a piezoceramic material layer 12 with the third layer thickness D3 may be arranged between the security layer 40 and the first active region 36 so as to transition from the first active region 36 to the security layer 40 continuous to design. The piezoceramic material layers 12 with the second layer thickness D 2 or the third layer thickness D 3 according to FIGS. 3 and 4 are are each arranged along the longitudinal axis 16 adjacent to the security layer 40 such that the security layer 40 is symmetrically spaced from the first active region 36 above and the first active region 36 below.

FIGS. 5 to 7 show longitudinal sectional views of prior art piezoelectric devices 10 already described above. The arrangement and the number of second active regions 38 can be adapted to the piezoelectric component 10 as desired. The same applies to the arrangement of piezoceramic material layers 12 with the second layer thickness D2 and / or with the third layer thickness D3 within the second active regions 38. These can also be provided as needed or not. Also, optionally, the security layer 40 may or may not be provided within the second active regions 38, and spaced further or less far from the adjacent first active regions 36 as required.

Overall, the mechanical stresses in the piezoceramic material layers 12 decrease with the second

Layer thickness D2 and the third layer thickness D3 compared to the piezoceramic material layers 12 with the first

Layer thickness Dl, which are arranged in the first active region 36. As a result, potentially destructive cracks generally spread less in the piezoelectric device. The result is that the durability of the piezoelectric component 10 is significantly improved.

Claims

claims

1. Piezoelectric component (10), comprising a

A plurality of piezoceramic material layers (12) and a plurality of active electrode layers (14), wherein the piezoceramic material layers (12) and the active

Electrode layers (14) for forming a stack (18) along a longitudinal axis (16) alternately stacked on ^¬ ordered,

wherein the stack (18) along the longitudinal axis (16) at least two first active areas (36), in which at least two

Piezoceramic material layers (12) each having a first layer thickness (Dl) are arranged, and at least two second active regions (38), in which at least two piezoceramic material layers (12) each having at least a second layer thickness (D2) are arranged, wherein the second layer thickness (D2) along the longitudinal axis (16) is greater than the first layer thickness (Dl),

wherein said first active areas (36) and the second active areas (38) along the longitudinal axis (16) are arranged alternately ^¬ stacked.

2. Piezoelectric component (10) according to claim 1, characterized in that in the first active regions (36) exclusively piezoceramic material layers (12) are arranged with the first layer thickness (Dl).

3. Piezoelectric component (10) according to one of claims 1 or 2,

characterized in that the stack (18) along the

A longitudinal axis (16) has a head portion (22) and a foot portion (24) and a between the head (22) and the foot portion (24) arranged volume portion (26), wherein the second active areas (38) in the volume portion (26 ), and wherein the head (22) and the foot portion (24) are each formed by a first active area (36).

4. Piezoelectric component (10) according to claim 3, characterized in that in the volume portion (26) arranged first active regions (36) at least three piezoceramic material layers (12) having a first

Layer thickness (Dl) have.

5. Piezoelectric component (10) according to one of claims 1 to 4,

characterized in that in at least one of the second active regions (38) at least one piezoceramic Mate- rialschicht (12) having a third layer thickness (D3) is arranged, wherein the third layer thickness (D3) along the longitudinal axis (16) is greater than that second layer thickness (D2).

6. Piezoelectric component (10) according to claim 5, characterized in that the piezoceramic material ^¬ layer (12) with the third layer thickness (D3) along the longitudinal axis (16) by at least one piezoceramic mate ^¬ rialschicht (12) with the second layer thickness (D2) is spaced from the first active region (36).

7. Piezoelectric component (10) according to one of claims 1 to 6,

characterized in that in at least one of the second active regions (38) at least one security layer (40) with a along the longitudinal axis (16) centrally in the security layer (40) arranged security ^electrode (42) is arranged ^¬ , wherein the layer thickness of the security layer (40) along the longitudinal axis (16) is greater than the first layer thickness (Dl).

8. Piezoelectric component (10) according to claim 7, characterized in that the security layer (40) along the longitudinal axis (16) by at least one piezoceramic material layer (12) with the second (D2) and / or third layer thickness (D3) of the first active region (36) is arranged at a distance.

9. Piezoelectric component (10) according to one of claims 1 to 8,

characterized in that the stack (18) has, parallel to the longitudinal axis (16), a first side surface (30) and a second side surface (32) facing each other, wherein along the longitudinal axis (16) successive active ones

Electrode layers (14) are alternately brought up to the first side surface (30) and to the second side surface (32), wherein the up to the first side surface (30) brought up active electrode layers (14) from the second side surface (32) are spaced apart and wherein the active electrode layers (14) brought up to the second side surface (32) are spaced from the first side surface (30), preferably with one external contact on each of the first side surface (30) and the second side surface (32) (34) is applied, that relate mainly ^¬ the entire length of the stack (18) along the longitudinal axis (16) covers 10. a piezoelectric component (10) according to claim 9 and any one of claims 7 or 8,

characterized in that the security electrode (42) is brought up to the first side surface (30) and to the second side surface (32).