JP6619515B2 - Multilayer piezoelectric element, injection device including the same, and fuel injection system - Google Patents

Description

  The present disclosure relates to a laminated piezoelectric element used as, for example, a piezoelectric driving element (piezoelectric actuator), a pressure sensor element, a piezoelectric circuit element, and the like, an injection device including the same, and a fuel injection system.

  As a laminated piezoelectric element, a laminated body having an active portion in which piezoelectric layers and internal electrode layers are alternately laminated and an inactive portion in which piezoelectric layers are laminated, and a side surface of the laminated body are provided. What is provided with the coating layer is known.

  The covering layer is provided for the purpose of suppressing migration and discharge between the internal electrode layers, for example.

JP 2000-323762 A

The multilayer piezoelectric element of the present disclosure includes a multilayer body having an active portion in which piezoelectric layers and internal electrode layers are alternately stacked, and an inactive portion in which piezoelectric layers are stacked, and a side surface of the multilayer body. Provided with a coating layer, and the coating layer has a two-layer structure including an inner first layer and an outer second layer, and the outer surface of the first layer has a plurality of convex portions. Or it has a some recessed part, and the said some convex part or the said some recessed part is arrange | positioned at the grid | lattice form .

  Moreover, the injection device of the present disclosure includes a container having an injection hole and the multilayer piezoelectric element described above, and the injection hole is opened and closed by driving the multilayer piezoelectric element.

  The fuel injection system of the present disclosure includes a common rail that stores high-pressure fuel, the above-described injection device that injects the high-pressure fuel stored in the common rail, a pressure pump that supplies the high-pressure fuel to the common rail, and the injection An injection control unit for supplying a drive signal to the apparatus.

It is a schematic perspective view which shows an example of the laminated piezoelectric element of this embodiment. It is a partially broken schematic perspective view of the multilayer piezoelectric element shown in FIG. It is the schematic longitudinal cross-sectional view cut | disconnected by the iii-iii line | wire of the multilayer piezoelectric element shown in FIG. It is a schematic longitudinal cross-sectional view of the other example of the multilayer piezoelectric element of this embodiment. It is a schematic longitudinal cross-sectional view of the other example of the multilayer piezoelectric element of this embodiment. It is a schematic longitudinal cross-sectional view of the other example of the multilayer piezoelectric element of this embodiment. It is a schematic longitudinal cross-sectional view of the other example of the multilayer piezoelectric element of this embodiment. It is side surface perspective drawing of the other example of the laminated piezoelectric element of this embodiment. It is side surface perspective drawing of the other example of the laminated piezoelectric element of this embodiment. It is a schematic longitudinal cross-sectional view of the other example of the multilayer piezoelectric element of this embodiment. It is a schematic longitudinal cross-sectional view of the other example of the multilayer piezoelectric element of this embodiment. It is a schematic sectional drawing which shows an example of the injection device of this embodiment. It is the schematic which shows an example of the fuel-injection system of this embodiment.

  In the conventional multilayer piezoelectric element, the coating layer forming material applied when the coating layer is formed on the side surface of the multilayer body is cured from the surface. Therefore, the surface of the coating layer has a hard and dense structure. Therefore, by forming the coating layer into a multilayer structure (formed in two steps), the coating layer can have a structure having a hard and dense structure, and this configuration further prevents discharge. Seems to be able to.

  However, the laminated piezoelectric element described above is used, for example, by being fixed. A hard and dense structure region exists in the coating layer along the stacking direction of the laminate, and the softness in the stacking direction is reduced. When driven for a period of time, a stress load is applied to the interface between the coating layer and the laminate, causing cracks, and discharging through the cracks may reduce the displacement of the multilayer piezoelectric element.

  The present disclosure has been made in view of the above circumstances, and provides a multilayer piezoelectric element in which stress load on the interface between the coating layer and the multilayer body is suppressed and discharge is less likely to occur, an injection device including the multilayer piezoelectric element, and a fuel injection system The purpose is to do.

  Hereinafter, an example of the multilayer piezoelectric element of the present embodiment will be described with reference to the drawings.

  1 is a schematic perspective view showing an example of the multilayer piezoelectric element of the present embodiment, FIG. 2 is a partially broken schematic perspective view of the multilayer piezoelectric element shown in FIG. 1, and FIG. 3 is a diagram of the multilayer piezoelectric element of the present embodiment. It is a schematic longitudinal cross-sectional view of an example.

  A laminated piezoelectric element 1 shown in FIGS. 1 to 3 includes a laminated body 10 having an active portion 13 in which piezoelectric layers 11 and internal electrode layers 12 are alternately laminated and an inactive portion 14 in which piezoelectric layers 11 are laminated. And a coating layer 16 provided so as to surround the side surface of the laminate 10. The covering layer 16 has a two-layer structure including an inner first layer 161 and an outer second layer 162, and the outer surface of the first layer 161 has a plurality of recesses 163. Yes.

  The multilayer body 10 constituting the multilayer piezoelectric element 1 includes an active portion 13 in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are alternately stacked, and the multilayer body 10 so as to be positioned outside the active portion 13 in the stacking direction. And inactive portions 14 formed by laminating piezoelectric layers 11 provided at both ends in the laminating direction. Here, the active portion 13 is a portion where the piezoelectric layer 11 extends or contracts in the stacking direction during driving, and the inactive portion 14 is a portion where the piezoelectric layer 11 does not extend or contract in the stacking direction during driving. The laminated body 10 is formed in a rectangular parallelepiped shape having a length of 0.5 to 10 mm, a width of 0.5 to 10 mm, and a height of 1 to 100 mm, for example. The height of the active portion 13 is, for example, 75 to 95% of the height of the stacked body 10. The laminate 10 may have a hexagonal column shape, an octagonal column shape, or the like.

The piezoelectric layer 11 constituting the laminated body 10 is formed of ceramics having piezoelectric characteristics. As such ceramics, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), Lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. The thickness of the piezoelectric layer 11 is, for example, 3 to 250 μm.

  The internal electrode layer 12 constituting the multilayer body 10 is formed by simultaneous firing with ceramics forming the piezoelectric body layer 11, and is alternately laminated with the piezoelectric body layers 11 so as to sandwich the piezoelectric body layers 11 from above and below. By arranging the positive electrode and the negative electrode in the order of lamination, a driving voltage is applied to the piezoelectric layer 11 sandwiched between them. As this forming material, for example, a conductor mainly composed of a silver-palladium alloy or a conductor containing copper, platinum, or the like can be used. In the example shown in the figure, the positive electrode and the negative electrode (or the ground electrode) are alternately led out to a pair of opposing side surfaces of the stacked body 10 and electrically connected to the pair of external electrodes 15 provided on the side surfaces of the stacked body 10. It is connected. The internal electrode layer 12 has a thickness of 0.1 to 5 μm, for example.

  Note that the laminate 10 may include a metal layer that is a layer for relaxing stress and does not function as the internal electrode layer 12.

  External electrodes 15 are respectively provided on a pair of opposing side surfaces of the laminate 10 from which the positive electrode or negative electrode (or ground electrode) of the internal electrode layer 12 is derived, and are electrically connected to the derived internal electrode layer 12. It is connected. The external electrodes 15 are provided from the active portion 13 to the inactive portion 14 respectively. The external electrode 15 is preferably formed by baking a conductive paste containing a metal such as Ag or Cu. Here, when the external electrode 15 is viewed in a cross section perpendicular to the side surface of the multilayer body 10, the thickness of the external electrode 15 is formed to a thickness of 5 to 70 μm.

  Then, the lead member 17 is joined to the external electrode 15 and the lead member 17 is pulled out, so that electrical connection with an external circuit is made.

  Moreover, the coating layer 16 is provided so that the side surface of the laminated body 10 may be surrounded. The covering layer 16 has an effect of suppressing migration and electric discharge on the side surface of the multilayer body 10 where both ends of the positive electrode and the negative electrode of the internal electrode layer 12 reach. The covering layer 16 is provided so as to cover the end portion of the internal electrode layer 12 so as not to be exposed. In the example shown in the figure, the covering layer 16 is covered so as to surround the side surface of the laminate 10 including the external electrode 15. Yes.

  The covering layer 16 is formed by overlapping a plurality of layers, and has a two-layer structure including an inner first layer 161 and an outer second layer 162. The first layer 161 is formed of, for example, a silicone resin or an epoxy resin, and the second layer 162 is formed of, for example, a silicone resin or an epoxy resin. Since the coating layer 16 is configured by overlapping a plurality of layers, the stress applied to the interface between the coating layer 16 and the laminate 10 is dispersed and reduced in each layer constituting the coating layer 16.

  In the covering layer 16, the outer surface of the first layer 161 has a plurality of recesses 163. Thereby, even if the surface of the first layer 161 has a hard and dense structure, the hard and dense structure bends along the plurality of recesses 163, so that the coating layer 16 extends in the stacking direction of the stacked body 10. Thus, a region having a hard and dense structure is provided inside. Therefore, a stress applied to the interface between the coating layer 16 and the laminate 10 is suppressed, and a multilayer piezoelectric element that is less likely to cause discharge over a long period of time can be realized.

  The thickness of the first layer 161 in the region excluding the plurality of recesses 163 is, for example, 10 to 150 μm, and the thickness of the second layer 162 is, for example, 20 to 200 μm. The width | variety of the some recessed part 163 is 50-500 micrometers, for example, and the depth is 5-60 micrometers. In addition, the plurality of recesses 163 may extend in the circumferential direction of the first layer 161, and may be uniformly in the circumferential direction.

  When the inner first layer 161 is made of a soft material such as a silicone resin, the plurality of recesses 163 are soft inside even if the hard portion of the surface of the silicone resin constituting the first layer 161 is not significantly deformed. Since the portion is freely deformable, for example, stress can be prevented from being concentrated in the plurality of recesses 163 even when the stacked piezoelectric element 1 is expanded and contracted at high speed.

  Instead of the above-described plurality of concave portions 163, a plurality of convex portions 164 as shown in FIG.

  Here, in FIG. 3, a plurality of concave portions 163 are arranged on the side of the inactive portion 14, but as shown in FIG. 4, a plurality of concave portions 163 are arranged on the side of the active portion 13. It is good to have. According to this configuration, since there are the plurality of concave portions 163 on the side of the active portion 13 that is easily deformed during driving, the effect of suppressing the stress load on the interface between the coating layer 16 and the laminate 10 is increased. A plurality of convex portions 164 may be used instead of the plurality of concave portions 163.

  Further, as shown in FIG. 5, the plurality of recesses 163 are preferably arranged on the side of the central portion when the active portion 13 is equally divided into three in the stacking direction. The central portion when the plurality of concave portions 163 divide the active portion 13 into three equal parts in the stacking direction is the portion most easily deformed in the active portion 13. In addition, the effect of suppressing the stress load on the interface between the coating layer 16 and the laminate 10 is further increased. A plurality of convex portions 164 may be used instead of the plurality of concave portions 163.

  Further, as shown in FIG. 6, the plurality of recesses 163 may be provided uniformly over the entire interface between the first layer 161 and the second layer 162. Further, as shown in FIG. 7, the plurality of convex portions 164 may be provided uniformly over the entire interface between the first layer 161 and the second layer 162.

  Also, as shown in FIGS. 8 and 9, a plurality of recesses 163 are preferably arranged in a lattice pattern. Here, the plurality of recesses 163 are arranged in a lattice form that the plurality of recesses 163 are arranged at positions corresponding to points (lattice points) where each lattice intersects when a lattice that virtually intersects each other is drawn. It is to be done.

  According to these configurations, since the covering layer 16 is freely deformed both vertically and horizontally, the effect of suppressing the stress load on the interface between the covering layer 16 and the laminate 10 is large, and the displacement amount is longer. Stabilize.

  Further, as shown in FIG. 10, the plurality of concave portions 163 and the plurality of convex portions 164 may have a shape in which trapezoidal irregularities are continuous when viewed in a cross section perpendicular to the coating layer 16. Thereby, the some recessed part 163 and the some convex part 164 follow the expansion-contraction of the laminated body 10, and the effect which further suppresses the stress load to the interface of the coating layer 16 and the laminated body 10 increases. In addition to the trapezoidal cross section, a tapered shape such as a semicircular cross section, a semi-elliptical cross section, and a triangular cross section may be employed.

  In addition, as shown in FIG. 11, the bottoms of the plurality of concave portions 163 and the top surfaces of the plurality of convex portions 164 are preferably rounded. Thereby, it is difficult for stress to concentrate and it is possible to prevent cracks in the coating layer 16.

  Next, an example of a method for manufacturing the multilayer piezoelectric element 1 of the present embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 11 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 12 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is applied on the ceramic green sheet in the pattern of the internal electrode layer 12 using a screen printing method. Furthermore, after laminating a plurality of ceramic green sheets printed with this conductive paste and performing a binder removal treatment at a predetermined temperature, firing at a temperature of 900 to 1200 ° C., using a surface grinder or the like The active part 13 provided with the piezoelectric body layers 11 and the internal electrode layers 12 that are alternately laminated is manufactured by performing a grinding process so as to have a shape. The inactive portion 14 is produced by laminating sheets that are not coated with the conductive paste that becomes the internal electrode layer 12. The laminated body 10 is manufactured by combining the active part 13 and the inactive part 14.

  The laminate 10 is not limited to the one produced by the above manufacturing method, and any laminate 10 can be produced as long as the laminate 10 formed by laminating a plurality of piezoelectric layers 11 and internal electrode layers 12 can be produced. It may be produced by a manufacturing method.

  Next, a conductive paste containing a metal such as Ag or Cu is used for the external electrode 15, and this is a region where one end of both electrodes of the internal electrode layer 12 on the side surface of the laminate 10 is derived. To form a thickness of 5 to 70 μm. It can be formed by controlling to a predetermined thickness or width by screen printing or dispensing.

  Next, the first layer 161 constituting the coating layer 16 can be formed by using, for example, nylon or silicone resin and controlling the thickness and width to a predetermined thickness by printing or dispensing. After drying and curing, the second layer 162 can be similarly formed by controlling to a predetermined thickness or width by printing or dispensing.

  Here, a configuration in which the outer surface of the first layer 161 has a plurality of convex portions 164 or a plurality of concave portions 163 (a configuration in which the interface between the first layer 161 and the second layer 162 is uneven) is employed. Can be prepared by adjusting the coating weight with a dispenser at a location where unevenness is to be provided and controlling the coating thickness. Moreover, unevenness | corrugation can also be produced by changing the size of a mesh and recoating.

  Thereafter, a direct current electric field of 0.1 to 3 kV / mm is applied to the external electrode 15 to polarize the piezoelectric layer 11 constituting the multilayer body 10, thereby completing the multilayer piezoelectric element 1. The multilayer piezoelectric element 1 is connected to an external power source via an external electrode 15 and applies a voltage to the piezoelectric layer 11 so that each piezoelectric layer 11 can be largely displaced by the inverse piezoelectric effect. . This makes it possible to function as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  Next, an example of the injection device of the present embodiment will be described. FIG. 12 is a schematic cross-sectional view illustrating an example of the injection device of the present embodiment.

  As shown in FIG. 12, in the injection device 19 of this example, the multilayer piezoelectric element 1 of the above example is stored inside a storage container (container) 23 having an injection hole 21 at one end.

  A needle valve 25 that can open and close the injection hole 21 is provided in the storage container 23. A fluid passage 27 is disposed in the injection hole 21 so as to be able to communicate with the movement of the needle valve 25. The fluid passage 27 is connected to an external fluid supply source, and fluid is constantly supplied to the fluid passage 27 at a high pressure. Therefore, when the needle valve 25 opens the injection hole 21, the fluid supplied to the fluid passage 27 is discharged from the injection hole 21 to the outside or an adjacent container, for example, a fuel chamber (not shown) of the internal combustion engine. It is configured.

  The upper end of the needle valve 25 has a large inner diameter, and is a piston 31 that can slide with a cylinder 29 formed in the storage container 23. In the storage container 23, the multilayer piezoelectric element 1 of the above-described example is stored in contact with the piston 31.

  In such an injection device 19, the injection hole 21 is opened and closed by driving the laminated piezoelectric element 1. Specifically, when the multilayer piezoelectric element 1 is extended by applying a voltage, the piston 31 is pressed, the needle valve 25 closes the fluid passage 27 leading to the injection hole 21, and the supply of fluid is stopped. When the voltage application is stopped, the laminated piezoelectric element 1 contracts, the disc spring 33 pushes back the piston 31, the fluid passage 27 is opened, and the injection hole 21 communicates with the fluid passage 27. Fluid injection is performed.

  Note that the fluid passage 27 may be opened by applying a voltage to the multilayer piezoelectric element 1, and the fluid passage 27 may be closed by stopping the application of the voltage.

  In addition, the multilayer piezoelectric element 1 does not necessarily have to be inside the container 23, as long as the multilayer piezoelectric element 1 is configured to apply pressure for controlling the ejection of fluid to the inside of the container 23 by driving the multilayer piezoelectric element 1. Good. In the injection device 19 of the present example, the fluid includes various liquids and gases such as conductive paste in addition to fuel, ink, and the like. By using the ejection device 19 of this example, the flow rate and ejection timing of the fluid can be stably controlled over a long period of time.

  If the injection device 19 of the present example employing the multilayer piezoelectric element 1 of the above example is used for an internal combustion engine, the fuel is accurately injected into the combustion chamber of the internal combustion engine such as an engine over a longer period of time compared to the conventional injection device. Can be made.

  Next, an example of an embodiment of the fuel injection system according to the present disclosure will be described. FIG. 13 is a schematic diagram illustrating an example of the fuel injection system of the present embodiment.

  As shown in FIG. 13, the fuel injection system 35 of the present example includes a common rail 37 that stores high-pressure fuel as a high-pressure fluid, and a plurality of injection devices 19 of the above-described examples that inject the high-pressure fluid stored in the common rail 37. A pressure pump 39 for supplying a high-pressure fluid to the common rail 37 and an injection control unit 41 for supplying a drive signal to the injection device 19 are provided.

  The injection control unit 41 controls the amount and timing of high-pressure fluid injection based on external information or an external signal. For example, if the fuel injection system 35 of this example is used for engine fuel injection, the amount and timing of fuel injection can be controlled while sensing the state of the combustion chamber of the engine with a sensor or the like. The pressure pump 39 serves to supply fluid fuel from the fuel tank 43 to the common rail 37 at a high pressure. For example, in the case of an engine fuel injection system 35, fluid fuel is fed into the common rail 37 at a high pressure of 1000 to 2000 atmospheres (about 101 MPa to about 203 MPa), preferably 1500 to 1700 atmospheres (about 152 MPa to about 172 MPa). In the common rail 37, the high-pressure fuel sent from the pressure pump 39 is stored and sent to the injection device 19 as appropriate. As described above, the ejection device 19 ejects a certain fluid from the ejection holes 21 to the outside or an adjacent container. For example, when the target for injecting and supplying fuel is an engine, high-pressure fuel is injected from the injection hole 21 into the combustion chamber of the engine in the form of a mist.

  According to the fuel injection system 35 of this example, desired injection of high-pressure fuel can be stably performed over a long period of time.

  Hereinafter, examples of the present disclosure will be described.

A multilayer piezoelectric element was produced as follows. First, a ceramic slurry was prepared by mixing a calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) having an average particle size of 0.4 μm, a binder and a plasticizer. Using this ceramic slurry, a ceramic green sheet serving as a piezoelectric layer having a thickness of 50 μm was prepared by a doctor blade method.

  Next, a binder was added to the silver-palladium alloy to produce a conductive paste to be an internal electrode layer.

  Next, a conductive paste serving as an internal electrode layer was printed on one side of the ceramic green sheet by a screen printing method, and 200 ceramic green sheets printed with the conductive paste were laminated. Further, a total of 15 ceramic green sheets on which the conductive paste serving as the internal electrode layer is not printed are stacked on the top and bottom of 200 ceramic green sheets on which the conductive paste serving as the internal electrode layer is printed. . And it baked at 980-1100 degreeC, it ground to the predetermined shape using the surface grinder, and obtained the 5 mm square laminated body.

  Next, a conductive paste containing Ag was formed on the surface of the laminate by screen printing as an external electrode.

  Next, a coating layer having a two-layer structure shown in FIG. 5 was formed. Specifically, a resin made of silicone is applied to the side surface of the laminate with a dispenser so that a convex portion having a width of 100 μm and a height of 30 μm is formed on the side of the central portion of the laminate, and cured at 150 ° C. One layer was formed. Furthermore, the same resin made of silicone was similarly applied from above to form a second layer. In addition, the thickness of the area | region except the convex part in a 1st layer was 100 micrometers, and the thickness of the area | region except the recessed part corresponding to the convex part of the 1st layer in the 2nd layer was 150 micrometers.

  Then, a 3 kV / mm direct current electric field is applied to the external electrode for 15 minutes through a lead member joined to the external electrode by welding, and polarization treatment is performed to produce the stacked piezoelectric element of the example (sample 1). did.

  On the other hand, as a comparative example (sample 2), a laminated piezoelectric element provided with a coating layer having a two-layer structure without unevenness was produced.

  When a DC voltage of 160 V was applied to these stacked piezoelectric elements, a displacement of 30 μm was obtained in the stacking direction of the stacked body.

  Furthermore, an endurance test was performed in which an alternating voltage of 0 V to +160 V was applied at a frequency of 150 Hz in a humidity of 30 ° C. and 90% and continuously driven.

As a result, the laminated piezoelectric element of Sample 2 as a comparative example cracked at the interface between the coating layer and the laminated body by 1 × 10 ⁵ continuous driving, and the end of the internal electrode layer was exposed to the air. The amount of displacement decreased due to discharge.

On the other hand, the laminated piezoelectric element of Sample 1 as an example was driven without changing the displacement even after continuous driving 1 × 10 ⁷ times. In addition, when the silicone resin was melted with a silicon remover (resin solubilizer) after driving and the surface of the laminate was observed, there was no trace of discharge of the internal electrode layer and no cracks.

  From the above results, it can be seen that according to the present disclosure, a multilayer piezoelectric element having excellent long-term durability can be realized.

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 10 ... Laminated body 11 ... Piezoelectric layer 12 ... Internal electrode layer 13 ... Active part 14 ... Inactive part 15 ... External electrode 16 ... · Coating layer 161 ··· first layer 162 ··· second layer 163 ··· concave portion 164 ··· convex portion 17 ··· lead member

Claims (5)

A laminated body having an active portion in which piezoelectric layers and internal electrode layers are alternately laminated and an inactive portion in which piezoelectric layers are laminated; and a covering layer provided so as to surround a side surface of the laminated body, the coating layer has a two-layer structure consisting of an inner first layer and an outer second layer, and an outer surface of said first layer has a plurality of protrusions or a plurality of recesses A multilayer piezoelectric element in which the plurality of convex portions or the plurality of concave portions are arranged in a lattice shape .   The multilayer piezoelectric element according to claim 1, wherein the plurality of convex portions or the plurality of concave portions are arranged on a side of the active portion.   The multilayer piezoelectric element according to claim 2, wherein the plurality of convex portions or the plurality of concave portions are arranged on a side of a central portion when the active portion is divided into three equal parts in the stacking direction. An injection apparatus comprising a container having an injection hole and the multilayer piezoelectric element according to any one of claims 1 to 3 , wherein the injection hole is opened and closed by driving the multilayer piezoelectric element. 5. A common rail for storing high-pressure fuel; an injection device according to claim 4 for injecting the high-pressure fuel stored in the common rail; a pressure pump for supplying the high-pressure fuel to the common rail; and a drive signal for the injection device. A fuel injection system comprising an injection control unit.

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