JP4715864B2 - Inspection method and inspection apparatus for piezoelectric actuator. - Google Patents

Description

  The present invention relates to an inspection method and an inspection apparatus for a piezoelectric actuator used for driving a fuel injection device that injects high-pressure fuel into a combustion chamber of an internal combustion engine.

  In recent years, fuel injection valves using a piezoelectric actuator as a drive source have been developed for internal combustion engines such as automobile engines from the viewpoint of improving fuel efficiency and reducing harmful substances in combustion exhaust. Since such a piezoelectric actuator is incorporated in a fuel injection valve and used in a severe environment, a more compact structure and high durability are required.

  As such a piezoelectric actuator, Patent Document 1 discloses a piezoelectric actuator module that includes at least a piezoelectric element, an actuator foot, and an actuator head, and the actuator head attempts to be operated by the piezoelectric element. In the embodiment, the actuator module is surrounded by an axially extending sleeve, and a diaphragm is provided following the actuator head, and the diaphragm extends in a substantially radial direction. A piezoelectric actuator module is disclosed which is connected to the sleeve and has cross-sections with various different radii of curvature.

  However, the piezoelectric actuator as disclosed in Patent Document 1 is assembled in a state where the actuator head and the piezoelectric element are in contact with each other, and compressive stress acts on the diaphragm when the piezoelectric element expands. There is a possibility that the responsiveness of the system may be lowered.

  Therefore, in the piezoelectric actuator 2 as shown in FIG. 1, it is elastically fixed to the casing 200 via a cylindrical casing 200, a piezoelectric element 210 housed inside the cylindrical casing 200, and a diaphragm 270 made of an elastic material. The piezoelectric element 210 includes a piston 260 that operates in the axial direction, and the piezoelectric element 210 is fixed to a sealing portion 250 provided on the proximal end side of the casing 200. A gap GP is provided between the piezoelectric element 210 and the diaphragm 270 in a state before assembly so that no load is applied.

Further, when the piezoelectric actuator 2 configured as described above is assembled as a drive source of the injector I for injecting and stopping high-pressure fuel as shown in FIG. 2, the piston 260 is moved to the proximal end side by the piston receiving portion 280. The lower end surface of the protective layer 220 of the piezoelectric element 210 and the upper end surface of the piston 260 are brought into close contact with each other, and when the piezoelectric element 210 contracts, the spring load of the diaphragm 270 acts in the direction of the anti-piezoelectric element. .
It is expected that the fatigue life of the diaphragm can be improved by assembling the piezoelectric actuator 2 having a gap GP between the piezoelectric element 210 and the piston 260 in the injector I in a state where tensile stress is applied to the diaphragm. .

In the piezoelectric actuator 2, the piezoelectric element 210 is formed by forming internal electrodes 211 a and 211 b on the surface of a piezoelectric ceramic layer 210 in which a piezoelectric ceramic material such as PZT is formed in a flat plate shape, and alternately changing the polarization directions thereof. Hundreds of layers are stacked, and the internal electrode layers 211a and 211b are alternately pulled out to the left and right in the lateral direction, and the internal electrode layers 211a and 211b are connected to the side electrodes 212a and 212b formed of expandable expander metal, etc. In order to connect to an external power source, the pair of conductive wires 214a and 214b are connected, and the side electrodes 212a and 212b are covered with insulating members 213a and 213b such as epoxy resin, and the upper and lower ends are made of an insulator. A laminated piezoelectric element 210 in which the protective layers 220 and 230 are formed and formed in a substantially long axis shape is used. .
JP 2005-533968 A

  However, in the configuration of the piezoelectric actuator 2 as shown in FIG. 1, the piezoelectric element 210 is fixed to the sealing member 250 on the base end side of the housing 200. Since the piezoelectric element 210 is difficult to be processed in a completely parallel plane in the polishing process of the upper and lower end surfaces in the axial direction, there is a possibility that a slight inclination may occur between both end surfaces. Further, when assembly is performed in a state where the piston 260 is inclined with respect to the diaphragm 270, there is a possibility that a slight inclination may occur between the lower end surface of the diaphragm 260 and the upper surface of the piston 270. For this reason, the piezoelectric actuator 2 may have a relative inclination between the lower end surface of the protective layer 220 made of an insulator and the upper surface of the piston 260 from the lower end portion of the piezoelectric element 210.

  When the piezoelectric actuator 2 is assembled in the injector I in such a state, a part of the lower end portion of the piezoelectric element 210 is locally pressed by the upper end surface of the piston 260. In such an assembled state, an unbalanced load is applied to the piezoelectric element 210 during driving, and there is a risk that fatigue cracks may occur in the diaphragm 270 when used for a long time.

  In order to further improve the reliability and responsiveness of the piezoelectric actuator provided with a gap between the piezoelectric element and the mover, the piezoelectric element is in a state before the piezoelectric actuator is assembled to the injector. It is necessary to accurately measure the gap provided between the movable element and the movable element, and to surely eliminate those having an inclination exceeding the allowable range. However, since a special technique such as X-rays is required to visually recognize the inside of the housing, it is difficult to accurately grasp the state of the piezoelectric element in the housing by an inexpensive method.

  Accordingly, the present invention provides a piezoelectric actuator inspection method capable of accurately and accurately measuring a gap provided between a piezoelectric element and a mover that transmits displacement of the piezoelectric element even in a piezoelectric actuator having poor visibility. And it aims at providing an inspection device.

  According to the first aspect of the present invention, a substantially columnar piezoelectric element that expands when energized, a substantially cylindrical casing that accommodates the piezoelectric element inside and fixes the piezoelectric element at one end thereof, and the casing A piezoelectric actuator inspection method for measuring the gap of a piezoelectric actuator having a movable element provided at the other end of the piezoelectric element via an elastic member and providing a gap between the piezoelectric element and the movable element. The displacement of the movable element is measured while pressing the movable element, and the piezoelectric effect is obtained when the movable element presses the piezoelectric element by using a pair of conductive wires connected to the piezoelectric element. A generated voltage or a generated current is measured, and a contact state between the piezoelectric element and the movable element is determined by comparing the detected piezoelectric effect with a threshold value, and the piezoelectric element and the movable element are used as a first gap. Measure the shortest distance to.

When the lower end surface of the piezoelectric element and the upper end surface of the mover are not parallel and the gap between the piezoelectric element and the mover is inclined, the mover is in contact with the piezoelectric element. When pressed, the contact portion of the piezoelectric element is locally compressed by the mover, and a piezoelectric voltage is generated in the piezoelectric element due to the piezoelectric effect.
A voltage or current generated in the piezoelectric element is measured using a pair of energized wires connected to energize the piezoelectric element, and the generated voltage or generated current is compared with a predetermined threshold value to determine the above It can be determined whether or not the piezoelectric element is in contact with the mover.
Therefore, according to the first aspect of the present invention, the amount of displacement of the mover when the piezoelectric effect is equal to or greater than the threshold value is accurately set as the shortest distance between the piezoelectric element and the mover, that is, the first gap. I can know.

  According to the invention of claim 2, while measuring the displacement amount of the mover while pressing the mover, the pressing load acting on the mover is measured, and the detected pressure load is compared with a threshold value. The contact state between the piezoelectric element and the mover is determined, and the distance between the centers of the piezoelectric element and the mover is measured as the second gap.

Until the movable element comes into contact with the piezoelectric element, the pressing load acting on the movable element is only the spring load received from the elastic member, and gradually increases according to the displacement amount of the movable element. When the mover is further pressed, the mover and a part of the piezoelectric element are brought into contact with each other. When the mover is further pressed, the mover is moved with the contact point between the mover and the piezoelectric element as a fulcrum. It contacts the lower end surface of the piezoelectric element while tilting. At this time, the rate of change of the load acting on the mover relative to the amount of displacement of the mover increases, but the rate of increase is slight, so it is difficult to detect the first gap by detecting this change. It is. When the displacement of the mover reaches the distance between the lower end surface of the piezoelectric element and the upper end surface of the mover at the axial center of the piezoelectric actuator, the lower end surface of the piezoelectric element and the upper end surface of the mover are fully covered. It will be in the state which contacted across. At this time, when the movable element is pressed, the load acting on the movable element becomes a load that pushes the piezoelectric element, so that the rate of change of the load acting on the movable element with respect to the displacement amount of the movable element is abruptly increased. It rises and it can detect easily that the said piezoelectric element and the said needle | mover became the contact | adherence state.
According to the second aspect of the present invention, it can be determined that the change rate of the pressing load with respect to the displacement amount of the mover has suddenly changed that the piezoelectric element and the mover are in close contact, and the displacement amount at this time Can be accurately measured as the second gap.

In the invention of claim 3, when the first gap is A and the second gap is B, the relative inclination ΔGrad between the piezoelectric element and the mover is calculated by the following equation (1).
ΔGrad = 2 · (B−A) Equation 1

  According to the invention of claim 3, the relative inclination of the piezoelectric element with respect to the mover can be easily measured accurately.

According to a fourth aspect of the present invention, there is provided a substantially columnar piezoelectric element that expands when energized, a substantially cylindrical casing that covers the outer periphery of the piezoelectric element and is fixed at one end thereof, and the other end of the casing A piezoelectric actuator inspection apparatus for measuring a gap of a piezoelectric actuator having a gap provided between the piezoelectric element and the movable element.
Movable element pressing means for pressing the movable element to displace the movable element, displacement amount measuring means for measuring the displacement amount of the movable element displaced by the movable element pressing means, and a load acting on the movable element A load measuring means for measuring, and a piezoelectric effect detecting means for detecting a piezoelectric effect generated in the piezoelectric element ,
The contact state between the piezoelectric element and the mover is determined by comparing the detected piezoelectric effect with a threshold value, and the shortest distance between the piezoelectric element and the mover is measured as the first gap .

According to the invention of claim 4, the movable element is pressed by the pressing means, the lower end surface of the piezoelectric element is in contact with the upper end surface of the movable element, and the piezoelectric element is pressed by the movable element. The piezoelectric effect generated in the piezoelectric element is detected instantaneously by the piezoelectric effect detecting means, and it is detected that the piezoelectric element and the movable element are in contact with each other, and the displacement amount of the movable element at this time is determined as the displacement. It can be known by means of quantity measurement. Therefore, accurate measurement of the shortest distance of the gap formed between the piezoelectric element and the mover as the first gap can be realized.
Further, when the movable element is pressed by the pressing means and the piezoelectric element and the movable element are brought into close contact with each other, the load acting on the movable element is rapidly increased. It can be easily detected that the piezoelectric element and the mover are in close contact with each other, and the displacement amount of the mover at this time can be known by the displacement measuring means. Therefore, accurate measurement of the center-to-center distance of the gap formed between the piezoelectric element and the mover as the second gap can be realized.
Further, from the measurement result of the first gap and the measurement result of the second gap, accurate measurement of the relative inclination of the lower end surface of the piezoelectric actuator with respect to the upper end surface of the mover can be realized.

A method for inspecting a piezoelectric actuator according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a configuration diagram showing an outline of an inspection apparatus when the piezoelectric actuator 2 is measured by the inspection method in the present embodiment.
As shown in FIG. 3, in the present embodiment, below the piezoelectric actuator 2, as a pressing means, for example, a pressing device 70 such as a servo motor or a hydraulic press moves up and down in the axial direction, thereby moving the mover 260. Axial pressing is possible.
The pressing device 70 is provided with a displacement measuring device 71 such as a laser displacement meter, a capacitance type displacement meter, a rotary encoder, etc. as a displacement measuring means, and can measure the displacement amount of the movable element 260.
Further, the pressing device 70 is provided with a load measuring device 72 such as a load cell as a load measuring means for measuring a load when the movable element 260 is pressed.
The pair of energization lines 214a and 214b for driving the piezoelectric actuator 2 is supplied with a piezoelectric voltage V _P or a piezoelectric current I _P generated by the piezoelectric effect when the piezoelectric element 210 is pressed as a piezoelectric effect detecting means. A voltmeter 8 or an ammeter 9 to be measured is connected.

With reference to FIGS. 4, 5, and 6, in the piezoelectric actuator 2, the lower end surface of the protective layer 220 provided at the lower end of the piezoelectric element 210 and the upper end surface of the mover 260 are not parallel to each other in the present embodiment. A method for inspecting the gap GP provided in the piezoelectric actuator 2 will be described.
As shown in FIG. 4A, in the gap GP provided between the piezoelectric element 210 and the mover 260, the narrowest portion is the first gap A, and the piezoelectric element 210 on the central axis of the piezoelectric element 210. And the movable element 260 is defined as a second gap B, and the relative inclination of the piezoelectric element 210 with respect to the movable element 260 is defined as ΔGrad.

While the displacement amount of the movable element 260 is measured by the displacement meter 71, the movable element 260 is pressed in the axial direction toward the piezoelectric element 210 by the pressing device 70. At this time, the spring load of the diaphragm 270 acts on the mover 260, and the load F acting on the mover 260 gradually increases as the displacement increases. Moreover, until the upper surface of the lower end surface and the movable element 260 of the piezoelectric element 210 are in contact, the piezoelectric effect is not generated in the piezoelectric element 210, the piezoelectric voltage V _P by the voltmeter 8 is not detected.

When the mover 260 is pressed by the first gap A by the pressing device 70, it comes into contact with a part of the lower end surface of the piezoelectric element 210, and a part of the piezoelectric element 210 is pressed by the mover 260. At this time, a piezoelectric voltage _VP is generated in the piezoelectric element 210 due to the piezoelectric effect. In the present embodiment, the piezoelectric element 210 has a piezoelectric characteristic that generates a piezoelectric voltage of 5 mV by compression of 1 μm.

When the movable element 260 is pressed until it comes into contact with a part of the lower end surface of the piezoelectric element 210, the contact portion of the piezoelectric element 210 is locally compressed by the movable element 260, and the piezoelectric element 210 is subjected to a piezoelectric voltage V due to the piezoelectric effect. _P is generated.
The piezoelectric voltage V _P which is generated in the piezoelectric element 210 as measured by voltmeter 8, by comparison with the voltage with a predetermined threshold value, it is determined whether a state in which the piezoelectric element 210 and the movable element 260 is in contact Can do.
In the present embodiment, in consideration of disturbance, it is determined that the piezoelectric element 210 and the mover 260 are in contact with each other when the piezoelectric element VP is pressed at 10 mV or more, that is, when the piezoelectric element 210 is pressed by 2 μm or more. The displacement amount X at the time can be accurately known as the first gap A.

Changes over time in the piezo voltage V _P (mV) detected by the voltmeter 8, the displacement measuring device 71, and the load measuring device 72 from the start of pressing the movable element 260 by the pressing device 70 until it contacts the lower end surface of the piezoelectric element 210. FIG. 5 shows changes in the load F (N) with respect to the displacement X (μm).
As shown in FIG. 5 (a), the movable element 260 and the piezoelectric element 210 becomes contact state, when it is pressed or 2 [mu] m, 10 mV or more piezoelectric voltage _{V P} is detected, as shown in FIG. 5 (b) The displacement X at this time can be accurately detected as the first gap A.
On the other hand, the load F (N) gradually increases due to the displacement X (μm), and after the piezoelectric element 210 and the mover 260 come into contact with each other, the increase rate of the load F (N) changes. The change is slight, and it is difficult to accurately measure the first gap A by measuring only the load F (N). The piezo voltage VP generated by the piezoelectric effect can be easily detected even if very small, and the first gap A can be accurately known by simultaneously performing the measurement of the piezoelectric effect and the measurement of the displacement amount of the present invention. .

Further, when the pressing of the movable element 260 is continued by the pressing device 70, the lower end surface of the piezoelectric element 210 and the upper end surface of the movable element 260 are in contact with each other as shown in FIG. 5C. .
At this time, since the movable element 260 is inclined along the inclination of the lower end surface of the piezoelectric element 210, the actual displacement of the movable element 260 is the lower end surface of the piezoelectric element 210 on the central axis of the piezoelectric element 210 and the movable element. The distance from the upper end surface of 260, that is, the second gap B is obtained.
At this time, as shown in FIG. 7, the load F (N) acting on the mover 260 is a load that presses the piezoelectric element 210, and is much larger than the elastic load received from the diaphragm 270. Become. Therefore, it can be determined that the change rate of the pressing load F (N) with respect to the displacement amount X (μm) of the mover 260 is abruptly changed, and that the piezoelectric element 210 and the mover 260 are in close contact with each other. The quantity X (μm) can be accurately measured as the second gap B. Further, instead of detecting a change in the increase rate of the load F (N), when the load F (N) exceeds a predetermined threshold F _L (N) (for example, 200N or more), the piezoelectric element 210 and the mover 260 may be determined to be in a close contact state.

Further, the relative inclination ΔGrad of the mover 260 with respect to the piezoelectric element 210 can be calculated from the first gap A and the second gap B by the following formula 1.
ΔGrad = 2 · (B−A) Equation 1

  In summary, the piezoelectric element inspection method of the present invention can be shown as a flowchart shown in FIG. FIG. 7A is a flowchart showing an outline of the inspection method for the first gap A, FIG. 7B is a flowchart showing an outline of the inspection method for the second gap B, and FIG. 3 is a flowchart showing a method for calculating a relative inclination ΔGrad from a gap A and a second gap B.

As shown in FIG. 7 (a), the first gap A of the piezoelectric actuator 2, while pressing the armature 260, thereby measuring the displacement amount X of the movable element 260, caused by the piezoelectric effect voltage V _P or, The generated current I _P is measured, and the contact state between the piezoelectric element 210 and the mover 260 is determined by comparing the detected piezoelectric effect V _P or I _P with the threshold value V _PC or the threshold value I _PC . As the first gap A, the shortest distance between the piezoelectric element 210 and the mover 260 is measured. Piezoelectric effect _V P, _{I P} is the threshold value _{V PC,} when: _{I PC} is not in contact with the piezoelectric element 210 and the movable element 260, the piezoelectric effect VP, _{I P} is the threshold value _{V PC,} exceeds the _{I PC,} The pressing of the movable element 260 is continued until it is determined that the piezoelectric element 210 and the movable element 260 are in contact with each other.

As shown in FIG. 7B, the second gap B of the piezoelectric actuator 2 measures the displacement amount X of the mover 260 while pressing the mover 260 and presses the load F acting on the mover 210. were measured, by comparison between the detected pressing load F and the threshold value F _L, determine the contact state between the piezoelectric element 210 and the movable element 260, a second gap B, the piezoelectric element 210 and the movable element 260 Measure the distance between the centers.

  As shown in FIG. 7C, the relative inclination ΔGrad of the movable element 260 with respect to the piezoelectric element 210 can be calculated from the measurement result of the first gap A and the measurement result of the second gap B.

In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably.
For example, in the above embodiment, the piezoelectric actuator inspection apparatus 1 is configured to press the mover 260 by the pressing device 70 provided below the piezoelectric actuator 2, but only the load measuring device 72 is disposed below the piezoelectric actuator 2. It is also possible to use a pressing means that displaces the piezoelectric actuator 2 downward.
Further, the piezoelectric actuator inspection apparatus of the present invention may be incorporated into a manufacturing process of a piezoelectric actuator, and may be part of a manufacturing method of a piezoelectric actuator that is manufactured while automatically judging the quality of the piezoelectric actuator.

These are sectional drawings which show the outline | summary of the piezoelectric actuator which can apply the test | inspection method of this invention. These are the block diagrams which show the outline | summary of the injector which assembled | attached the piezoelectric actuator to which the test | inspection method of this invention is applied. These are the block diagrams which show the outline | summary of the piezoelectric actuator test | inspection apparatus in the 1st Embodiment of this invention. (A) is principal part sectional drawing which shows the test object site | part of the 1st inspection method of this invention, this figure (b) is principal part sectional drawing which shows the measurement condition of the 1st gap | interval A, this figure (c) ) Is a cross-sectional view of the main part showing the measurement status of the second gap B. These show the example of a measurement of the 1st space | gap A of the inspection method in 1st Embodiment of this invention, This figure (a) is a characteristic view which shows the change of a piezo voltage, This figure (b) is a change of a load. FIG. These are characteristic views showing a measurement example of the second gap B in the inspection method according to the first embodiment of the present invention. These show the outline | summary of the test | inspection method of this invention, this figure (a) is a flowchart which shows the measuring method of the 1st gap | interval A, this figure (b) is a flowchart which shows the measuring method of the 2nd gap | interval B, This figure (c) is a flowchart which shows the calculation method of relative inclination (DELTA) Grad.

Explanation of symbols

1 the piezoelectric actuator inspection device 2 piezoelectric actuator 210 piezoelectric element 260 the mover 70 movable element pressing means 71 displacement measuring means 72 load measuring means _{V P,} I _P piezoelectric effect (piezoelectric voltage, a piezoelectric current)
8, 9 Piezoelectric effect detection means (piezo voltmeter, piezo ammeter)
GP gap X displacement A first gap (narrowest gap)
B 2nd gap (widest gap)
ΔG _RAD relative slope

Claims (4)

A substantially columnar piezoelectric element that extends by energization, a substantially cylindrical casing that covers the outer periphery of the piezoelectric element and is fixed at one end thereof, and an elastic member at the other end of the casing A piezoelectric actuator inspection method for measuring a gap of a piezoelectric actuator having a gap between the piezoelectric element and the mover,
While pressing the mover, the displacement of the mover is measured, and a voltage generated by the piezoelectric effect when the mover presses the piezoelectric element using a pair of conductive wires connected to the piezoelectric element. Alternatively, the generated current is measured, the contact state between the piezoelectric element and the mover is determined by comparing the detected piezoelectric effect and a threshold value, and the piezoelectric element and the mover are used as the first gap. A method for inspecting a piezoelectric actuator, characterized by measuring a shortest distance.   While pressing the movable element, the displacement amount of the movable element is measured, the pressing load acting on the movable element is measured, and the piezoelectric element and the movable element are compared by comparing the detected pressing load with a threshold value. 2. The method for inspecting a piezoelectric actuator according to claim 1, wherein the contact state with the child is judged, and the distance between the centers of the piezoelectric element and the mover is measured as the second gap. 3. The piezoelectric actuator according to claim 2, wherein when the first gap is A and the second gap is B, the relative inclination ΔGrad between the piezoelectric element and the mover is calculated by the following formula 1. Inspection method.
ΔGrad = 2 · (B−A) Equation 1 A substantially columnar piezoelectric element that expands when energized, a substantially cylindrical casing that covers the outer periphery of the piezoelectric element and is fixed at one end thereof, and an elastic member at the other end of the casing A piezoelectric actuator inspection device for measuring the gap of a piezoelectric actuator having a gap between the piezoelectric element and the movable element,
Movable element pressing means for pressing the movable element to displace the movable element, displacement amount measuring means for measuring the displacement amount of the movable element displaced by the movable element pressing means, and a load acting on the movable element A load measuring means for measuring, and a piezoelectric effect detecting means for detecting a piezoelectric effect generated in the piezoelectric element ,
A piezoelectric actuator characterized in that the contact state between the piezoelectric element and the mover is determined by comparing the detected piezoelectric effect with a threshold value, and the shortest distance between the piezoelectric element and the mover is measured as the first gap. Inspection equipment.

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