JPH0535304Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention is a piezoelectric element used as a piezoelectric vibrator, more specifically, a piezoelectric element that supports the center part and adjusts the output voltage by selecting an electrode pattern. This relates to a voltage element that can perform

<Prior Art> A piezoelectric element used as a piezoelectric vibrator is formed by providing electrodes on both sides of a piezoelectric body made of ceramic or the like.

When such a piezoelectric element 1 is placed with one end supported as shown in Fig. 6 or both ends supported as shown in Fig. 7, and is bent by applying force F, an output voltage is generated between the two electrodes. Taking advantage of this property, it is used in, for example, knocking sensors for automobiles.

<Problems to be solved by the invention> By the way, conventional piezoelectric elements have a structure in which electrodes are provided on both sides of the piezoelectric body, so once the characteristics of the piezoelectric element are determined, if the applied force is constant, The problem is that the output voltage cannot be adjusted, and the shape of the piezoelectric element must be changed to obtain different output voltages.

This invention was made to solve the above-mentioned problems, and the purpose is to provide a piezoelectric element whose output voltage can be adjusted simply by selecting the pattern of electrodes formed on the piezoelectric body. .

<Means for solving the problems> In order to solve the above problems, this invention is a piezoelectric element in which electrodes are provided on both sides of a circular piezoelectric body, and the central part is supported, An electrode provided on a piezoelectric body is formed by omitting the central portion.

<Operation> When vibration is applied to the piezoelectric element whose central portion is supported, an output voltage is generated between the electrodes on both sides.

At this time, the force acts most strongly on the supported central part, but since the central part of the electrode is omitted, it does not affect the output voltage generation, and the output voltage is commensurate with the electrode pattern that excludes the central part. occurs.

<Example> Hereinafter, an example of this invention will be described based on FIGS. 1 to 5.

As shown in the figure, the piezoelectric element 11 is of a type in which the center is supported, and electrodes 13 are formed on both sides of a piezoelectric body 12 formed into a disk shape using ceramic or the like.
and 14 are provided, and the electrode 13 on one side is formed in an annular pattern with the center portion omitted as shown in FIG.

The output voltage of the piezoelectric element 11 is determined by the opposing areas of the electrodes 13 and 14 provided on both sides, and the pattern of one electrode 13 excluding the central part, that is, the electrode 1
The output voltage can be adjusted by selecting the amount of center section 3.

This is because the stress applied to the piezoelectric element is greatest at the center of the disk and decreases as you move away from the center, so the generated voltage is also highest at the center of the disk and decreases toward the edges. However, if the electrodes are formed on the entire surface of the disk, an averaged voltage value will occur, whereas if the electrodes 13 are formed at the edge of the disk, the high voltage values that occur in the center will be additive. This is because if the electrode area is increased, a portion with a high output voltage will be added closer to the center, and as a result, the output voltage will become higher.

FIG. 4 shows the relationship between the change in the inner diameter dimension of the electrode 13 and the output voltage when the piezoelectric element 11 is supported at the center as shown in FIG. 3 and excited at a vibration acceleration of 6 G. The diameter is 25mm.

As is clear from the figure, the output voltage decreases as the inner diameter of the electrode 13 increases, and for a given piezoelectric body 12, a piezoelectric element with the required output voltage can be obtained by simply changing the pattern of the electrode 13. become.

FIG. 5 shows a knocking sensor for an automobile engine as an example in which the piezoelectric element 11 is supported at the center. 11, fit the plastic case 17 and the metal cover 18 on the outside into the opening of the metal case 15, bend the upper end of the metal case 15 onto the metal cover 18 and fix it by spot welding, and then attach the plastic case 17 to the plastic case 17. It has a structure in which a spring 20 is compressed between the inner end of the integrally molded + side lead-out terminal 19 and the piezoelectric element 11.

In the above knocking sensor, the piezoelectric element 11
The electrode 13 with the central part omitted faces the bottom side of the metal case 15, the other full-surface electrode 14 and the + side lead-out terminal 19 are electrically connected by the spring 20, and the heat curing of the epoxy adhesive 16 is applied to the piezoelectric element. 11, spring 2
0. After assembling the plastic case 17 and metal cover 18, the final step is to install the metal case 15 to the engine by screwing in the tapered screw 21 provided on the bottom of the metal case 15 and attaching it to the engine between the bottom of the metal case 15 and the engine. It forms a gap.

When knocking occurs, the engine emits vibrations at a certain frequency, and when this vibration is transmitted to the piezoelectric element 11, an output voltage corresponding to the vibration is generated, and the knocking is detected electrically.
1, the pattern of the electrode 13 is set in advance according to the vibration frequency of the engine to which it is attached, so that a predetermined output voltage can be obtained.

<Effects> As described above, according to this invention, in a piezoelectric element that is used by supporting the central part, the central part of the electrode provided on one side of the piezoelectric body is omitted, so it is only necessary to select the pattern shape of the electrode. , the output voltage can be adjusted without changing the shape of the piezoelectric body, and a piezoelectric element with the required output voltage can be obtained with a constant piezoelectric body.

Further, by adjusting the pattern shape of the electrodes, a constant output voltage can be obtained regardless of the magnitude of vibration acceleration.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the piezoelectric element according to this invention, Figure 2 is a front view of the same as above, Figure 3 is an explanatory diagram showing a vibration acceleration test of the piezoelectric element, and Figure 4 is a graph showing the test results of the same. , Figure 5 is a partially cutaway front view of a knocking sensor using the same as above, Figures 6 and 7 are
The figure is an explanatory diagram showing a conventional piezoelectric element. 1... Piezoelectric element, 12... Piezoelectric body, 13, 14
……electrode.

Claims (1)

[Scope of utility model registration request] A piezoelectric element in which electrodes are provided on both sides of a circular piezoelectric body, and the central portion is supported and used, and the electrodes provided on the piezoelectric body are formed by omitting the central portion.