JP2775280B2 - Non-resonant knock sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-resonant knock sensor that is attached to an internal combustion engine and electrically detects the occurrence of knocking.

<Prior Art> In a synthetic resin case attached to an internal combustion engine, an annular piezoelectric element having electrodes on the front and back surfaces is held in a pinched state,
A non-resonant knock sensor formed by forming a cylindrical connector portion surrounding a connection terminal rod electrically connected to the front and back electrodes of the piezoelectric element in the synthetic resin case is disclosed in
Various proposals have been made, such as 153530.

This causes a piezoelectric element sandwiched in a synthetic resin case to generate a strain in a thickness direction corresponding to the knocking frequency in accordance with the occurrence of knocking, thereby generating a signal voltage between the electrodes, and connecting the signal voltage to a connector. It is designed to be taken out from the connection terminal rod of the section.

By the way, the vibration generated in the connector portion and the female coupler fitted thereto propagates through the connector portion and reaches the piezoelectric element. For this reason, as shown in FIG. 4A, there is a drawback that a noise signal n is generated due to the vibration, which causes erroneous detection.

Therefore, in order to eliminate the above-mentioned disadvantage, a non-polarized portion is formed in a portion corresponding to the connector portion of the annular piezoelectric element so that an output is not generated from the piezoelectric element due to vibration propagated from the connector portion (Japanese Patent Application (Showa 63-120062)
Was proposed.

On the other hand, if the non-polarized portion is formed only in the portion facing the connector portion of the annular piezoelectric element, if unnecessary undulations due to engine vibration occur, the non-polarized portion of the piezoelectric element and the polarized portion on the opposite side Then, displacement (stress) about the center of the piezoelectric element as a fulcrum is alternately applied, and no charge is generated from the non-polarized portion, but a charge is generated from the polarized portion, which is output in response to unnecessary undulating vibration. Was unstable, and an abnormal signal m was generated at a specific frequency as shown in FIG. In order to solve this problem, it has been found that when a non-polarized portion is formed in a portion facing the connector portion, a non-polarized portion may be formed on the opposite side.

FIG. 4 shows a structure in which a piezoelectric element having a conventional configuration without a non-polarized portion is applied, a structure in which a non-polarized portion α is applied only to a portion facing a connector portion, and a structure in which a non-polarized portion α is applied. , Α (see FIG. 2) are applied to a portion corresponding to the connector portion and a portion to which a piezoelectric element provided on the opposite side is applied,
FIG. 4 is a graph showing the results of examining the effect of vibration from the connector part. The non-polarized parts α, α provided on the part corresponding to the connector part and the part provided on the opposite side (FIG. 4C) are shown. The noise signal n is removed as compared with the case without α and α (FIG. 4A), and the abnormal signal is compared with the case where the non-polarized portion α is provided at the portion corresponding to the connector portion (FIG. 4B). It was confirmed that m was removed.

<Problems to be Solved by the Invention> As means for forming the non-polarized portion, at least one of the electrodes is partially removed to form an electrode missing portion, and a vertical voltage is applied between the electrodes to form a polarized portion. By doing so, it is possible to propose a means for making the electrode missing portion a non-polarized portion.

However, if the electrode is left as it is, since the silver electrode has a thickness, the notch becomes a depressed surface, and does not make surface contact with the clamping members located on the front and back of the piezoelectric element. When it is attached and the occurrence of knocking is sensed, the pressing force is unevenly distributed between the portion where the electrode is present and the portion where the electrode is not present, and the output varies.

In particular, when a non-polarized portion is formed not only on the portion facing the connector portion but also on the opposite side to remove the abnormal signal m, a large area electrode missing portion occurs on the surface of the piezoelectric element, and the pressing force is increased. Uneven distribution becomes remarkable, and output variation becomes a serious problem.

An object of the present invention is to eliminate the above-mentioned problems caused by removing the electrodes.

<Means for Solving the Problems> A first means of the present invention is to form a cutout in at least one of the upper and lower electrodes of the annular piezoelectric element and apply a DC voltage between the electrodes. Then, a non-polarized portion is generated due to the missing portion of the electrode, and after removing the electrode having the missing portion, the electrode is re-formed on the element surface to form a ring-shaped piezoelectric element. .

The second means is to form at least one of the upper and lower electrodes of the annular piezoelectric element by a thin film method,
An annular piezoelectric element is formed by causing a non-polarized portion to be generated by applying a DC voltage between the electrodes and then polarizing the electrode after forming a notch in the electrode.

<Operation> In the first means, the electrode in which the notch is formed is once removed and then formed again, so that no depressed surface is formed on the front and back surfaces of the piezoelectric element.

In the second invention, since the electrode on which the notch is formed is made extremely thin by a thin film method,
Even if there is an electrode missing portion, a substantially depressed surface does not occur.

<Example> An example of a non-resonant knock sensor will be described with reference to FIG.

Reference numeral 1 denotes a synthetic resin case. The present invention 2 has a cylindrical shape, and a metal sleeve 4 is mounted at the center thereof. The metal sleeve 4 has a flange portion 5 formed at a lower portion, and a screw 7 formed around an upper portion of the cylindrical portion 6.
Further, a plurality of engagement steps are formed around the upper end of the cylindrical portion 6 and the periphery of the flange portion 5 so as to improve the connection strength with the synthetic resin case 1.

Electrode plates are fitted on the cylindrical portion 6 and on the flange 5
An annular piezoelectric element 2 having electrodes formed on the front and back surfaces via 9a and 9b
0, an insulating plate 10, a weight 11, and a washer 12 are sequentially laminated on the piezoelectric element 20, and the screw 7
A nut 13 is screwed into the nut, and the above members are clamped and held between the flange 5 and the nut 13 by screwing. Then, a synthetic resin case 1 is molded around the metal sleeve 4. The synthetic resin case 1
From the peripheral surface of the main body 2, a cylindrical connector 17
Is formed, and its cylindrical wall 16 surrounds two connection terminal rods 14, 14 (one of which is hidden and invisible) protruding inside. The connection terminal rods 14, 14 are connected to the upper and lower electrode plates 9a, 9b of the piezoelectric element 20 via the built-in resistor 15 in the synthetic resin case 1, respectively. A potential difference is generated corresponding to the strain in the thickness direction.
In order to take out this potential difference as a signal voltage, a female coupler 19 is fitted to the connector portion 17 and the connection terminal rod 1
Connect with 4,14.

In the piezoelectric element 20, non-polarized portions α and α are formed in advance in a portion x facing the connector portion 17 and a portion y opposite to the connector portion 17. The piezoelectric element 20 having the non-polarized portions α, α is formed by the following means.

 FIG. 2 shows the first means.

That is, first, the silver electrodes 22a,
22b is formed by baking. Then, one electrode 22a is cut off at two symmetrical positions to form electrode cutouts 23a, 23a, and a DC voltage is applied between the electrodes 22a, 22b to polarize the electrode 22a. Non-polarized portions α, α are generated in the electrode missing portions 23a, 23a (FIG. 2A).

Thereafter, the electrodes 22a and 22b on the front and back surfaces are removed by means such as polishing and etching to form bare surfaces 24 and 24 (FIG. 2B).

In this case, the electrode 22b on the surface having the electrode cutouts 23a, 23a
You may remove only.

Thereafter, the electrodes 22 are applied to the bare surfaces 24, 24 on the front and back of the piezoelectric ceramic 21.
c and 22c are reformed (FIG. 2C). This electrode 22c may be formed by a thin film method such as silver paint or vapor deposition.

Thus, the piezoelectric element 20 formed by such means
Has no depressed surface on its front and back surfaces and is flush.

In the first means, a conductive rubber layer may be used as a polarizing electrode instead of the silver electrodes 22a and 22b. In this case, two cutouts are formed at predetermined positions in one side of the conductive rubber layer, arranged on the front and back of the piezoelectric ceramic layer, and the non-polarized portions α and α are applied by applying a DC voltage. Cause. After that, the conductive rubber layer is removed and the electrode 22c is removed.
May be formed.

 3 shows a second means of FIG. 3;

In such means, first, by a thin film method such as evaporation,
Electrodes 22d and 22e are formed on the front and back surfaces of the annular piezoelectric ceramic 21. In the electrode 22d formed by this thin film method, electrode cutouts 23b, 23b are formed at predetermined positions simultaneously with the formation. Thereafter, a DC voltage is applied between the electrodes 22d and 22e to polarize, and the non-polarized portions α and α are generated by the electrode missing portions 23b and 23b.

The means for forming the electrode notches 23b, 23b may be formed by removing a part of the electrode 22d by polishing or etching after forming the electrode 22d, or by applying the screen printing technique to the electrode notches 23b, 23b. Various forming means can be proposed, such as forming at the same time as the electrode 20d.

In the second means, since the electrode 22d is extremely thin, no depressed surface is formed in the electrode cutouts 23b, 23b.

In both of the above configurations, the piezoelectric element 20 is distorted in the thickness direction between the electrode plates 9a and 9b due to the occurrence of knocking. At this time, the piezoelectric element 20 is pressed almost uniformly over the entire front and back surfaces. Therefore, the variation width of the output signal caused by the pressurization is narrow.

The following table shows the results of applying a piezoelectric element with a notch formed and polarized to a baked electrode as it is (A), and applying a piezoelectric element with an electrode 22d that generates electrode notches 23b and 23b by a thin film method. (B) is applied to a vibrator and its output characteristics are compared.

Here, the upper part shows the excitation frequency from the exciter. Then, change the excitation frequency in the range of 2.5 to 15.0 KHZk to 100
Each sample was tested and its average and standard deviation were calculated. The standard deviation is obtained by accumulating the square of the difference with respect to the average value and dividing the difference by the number of samples. The larger the value, the larger the output variation.

As can be seen from the preceding table, the standard deviation of the configuration (B) according to the present invention is smaller at each frequency than that of the configuration (A), and the output variation of the present invention is improved. Can be confirmed.

Incidentally, the piezoelectric element formed by the first means is obtained by regenerating the electrodes on the same surface, so that it is natural that the piezoelectric element is not affected by the missing portion.

The piezoelectric element 20 thus formed is disposed in the synthetic resin case 1 with the non-polarized portions α, α positioned at the position facing the connector portion 17 and the position opposite thereto.

In the above-described configuration, the non-polarized portion α formed in the portion x of the piezoelectric element 20 facing the connector portion 17 is for preventing electric charge from being generated by vibrations propagated from the connector portion 17, and the non-polarized portion α The non-polarized portion α formed on the opposite side portion y prevents electric charge from being generated from the non-polarized portion α due to undulating vibration propagated from the engine.

In the above embodiment, the non-polarized portions α and α are connected to the connector portion 17.
, And the configuration arranged at the opposite side, but in order to form the non-polarized portion α only at the position facing the connector portion 17, in the case where the electrode missing portions 20a, 23b are formed in one place Needless to say, the present invention is applicable.

<Effect of the Invention> As described above, the present invention relates to a piezoelectric element in which a non-polarized portion α is formed at least at a position facing the connector portion 17 in a piezoelectric element 20. Due to the absence of the electrodes, no depressed surface is formed on the front and back surfaces of the piezoelectric element 20, so that the piezoelectric element 20 is flush with the front and back, a uniform pressure is applied, and the output varies. There are excellent effects such as no.

[Brief description of the drawings]

1 is a longitudinal side view, FIG. 2 is a process diagram showing a means for forming the non-polarized portion α of the first means, FIG. 3 is a perspective view of the piezoelectric element 20 formed by the second means, and FIG. Are the unpolarized parts α, α
FIG. 4B is a graph showing a knock sensor using a piezoelectric element in which a non-polarized portion α is formed only in a portion facing a connector, and FIG. FIG. 4C is the same graph of the knock sensor to which the piezoelectric element formed on the portion where the non-polarized portion α faces the connector portion and the piezoelectric element formed on the opposite portion are shown. 1 ... case made of synthetic resin 8 ... piezoelectric element, 8a, 8b ... electrode 14 ... connecting terminal rod 16 ... cylinder wall 17 ... connector section 20 ... piezoelectric element 21 ... piezoelectric ceramics 22a to 22e ... Electrodes 23a, 23b ... electrode missing part α ... non-polarized part

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01H 11/08 G01H 17/00

Claims (2)

(57) [Claims] An annular piezoelectric element having electrodes on its front and back surfaces is held in a cylindrical synthetic resin case attached to an internal combustion engine in a pressure-tight manner.
A cylindrical connector section is formed by surrounding a connection terminal rod electrically connected to the front and back electrodes of the piezoelectric element with a cylindrical wall, and the annular piezoelectric element is provided at least at a position facing the connector section. In the one in which the polarization portion is formed, the annular piezoelectric element is formed with a cutout in at least one of electrodes arranged on the front and back surfaces of the annular piezoelectric ceramic, and a DC voltage is applied between the electrodes. A non-polarized portion is generated at the position of the missing portion of the electrode, and the electrode having the missing portion is removed, and then the electrode is formed again on the element surface. Resonance knock sensor. 2. An annular piezoelectric element having electrodes on its front and back surfaces is held in a cylindrical synthetic resin case attached to an internal combustion engine in a pressure-tight manner.
A cylindrical connector section is formed by surrounding a connection terminal rod electrically connected to the front and back electrodes of the piezoelectric element with a cylindrical wall, and the annular piezoelectric element is provided at least at a position facing the connector section. In the one in which a polarization part is formed, the annular piezoelectric element is one of front and back electrodes of the annular piezoelectric element.
A non-resonant knock sensor, wherein at least one electrode is formed by a thin film method, a cutout is generated in the electrode, and a direct current voltage is applied between the electrodes to polarize the electrode.