JP2012109114A - Inspection method of insulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect inspection method of an insulator which allows for easy and accurate inspection of the presence or absence of an internal defect of the insulator.SOLUTION: In the inspection method of an insulator 1 which inspects the presence or absence of an internal defect of the insulator 1 for a spark plug having a shaft hole 11 through which a center electrode is inserted, an inner electrode 2 is arranged in the shaft hole 11 of the insulator 1, and an outer electrode 3 is arranged on the outer surface 12 of the insulator 1. A partial discharge is generated at the internal defect by applying an inspection voltage, where plus and minus are inverted temporarily and alternately, between the inner electrode 2 and the outer electrode 3. The internal defect is made conspicuous by destroying the insulator 1 with the energy of partial discharge starting from the internal defect.

Description

  The present invention relates to an insulator defect inspection method for inspecting the presence or absence of an internal defect of an insulator for a spark plug having a shaft hole through which a center electrode is inserted.

The spark plug is fixed to the housing, a cylindrical insulator having a shaft hole held inside the housing, a center electrode inserted through the shaft hole of the insulator, and the housing. A ground electrode. The center electrode and the ground electrode are arranged opposite to each other in the axial direction of the spark plug to form a spark discharge gap, and when a high voltage is applied to the center electrode, a spark discharge is generated in the spark discharge gap. Occurs.
Here, if an internal defect such as a pinhole is present in the insulator, current leaks between the center electrode and the housing through the internal defect, and normal spark discharge occurs. There is a risk of being lost. For this reason, it is necessary to inspect for the presence or absence of defects in the insulator.

  As a defect detection method for an insulator, for example, a first electrode is disposed in a shaft hole through which a center electrode of the insulator is inserted, and a second electrode is disposed on the outer peripheral side of the insulator so that a DC voltage is applied to the insulator. There is a method for inspecting the presence or absence of an internal defect by the flowing current (Patent Document 1).

  Further, in recent years, since the thickness of the insulator has been reduced as the diameter of the spark plug has been reduced, there has been a concern about the deterioration of the insulation. For this reason, improvement in inspection accuracy is required in the insulation inspection of the insulator. Therefore, in the defect inspection method, it is necessary to increase the inspection voltage. However, when the inspection voltage is increased, there is a risk that even a non-defective insulator without internal defects may be destroyed. Further, due to the high inspection voltage, a flashover in which a current flows through the surface of the insulator is likely to occur.

  Here, in order to prevent the flashover, a high-pressure air is sealed in the inspection device to improve the air insulation, and a DC voltage is applied to the inside and outside of the insulator, There has been proposed a method for inspecting the presence or absence of internal defects by measuring current (Patent Document 2).

JP 2007-134132 A JP 2004-108817 A

  However, the method described in Patent Document 2 requires a supply device for supplying high-pressure air, and the inspection device becomes large and large. Further, the problem of destruction of non-defective products caused by increasing the inspection voltage cannot be solved even by the method described in Patent Document 2. Therefore, the method of increasing the inspection voltage and increasing the inspection accuracy does not lead to a fundamental solution to the above problem.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an insulator defect inspection method capable of easily and accurately inspecting the presence or absence of an internal defect of an insulator.

The present invention is an insulator defect inspection method for inspecting the presence or absence of an internal defect of an insulator for a spark plug having a shaft hole through which a center electrode is inserted,
An inner electrode is disposed in the shaft hole of the insulator, an outer electrode is disposed on the outer surface of the insulator,
By applying an inspection voltage in which plus and minus are alternately reversed in time between the inner electrode and the outer electrode, a partial discharge is generated in the internal defect, and the internal discharge is performed by the energy of the partial discharge. The present invention provides a defect inspection method for an insulator, wherein the insulator is destroyed starting from a defect to reveal the internal defect (claim 1).

  In the insulator defect inspection method according to the present invention, the inspection voltage applied between the inner electrode and the outer electrode is not a direct current, but an inspection voltage in which plus and minus are alternately reversed in time. Is applied, a partial discharge can be generated in the internal defect which is a space such as a pinhole existing in the insulator. Then, due to the energy of the partial discharge, the insulator is broken starting from the internal defect, and the insulation state between the inside and the outside of the insulator is broken (hereinafter referred to as “insulation breakdown”). Thereby, the internal defect can be made obvious. Therefore, an internal defect can be revealed by a relatively low voltage value.

  Further, the inspection voltage is a voltage in which plus and minus are alternately inverted in time, and the sum of the absolute value of the plus side voltage and the absolute value of the minus side voltage is the magnitude of the voltage fluctuation. A large partial discharge energy can be obtained at a low voltage value. Therefore, it is possible to suppress the occurrence of flashover due to the high inspection voltage value. As a result, there is no risk of increasing the size and complexity of the inspection apparatus.

  As described above, according to the present invention, it is possible to provide an insulator defect inspection method capable of easily and accurately inspecting the presence or absence of an internal defect of an insulator.

Explanatory drawing of the state which test | inspects the presence or absence of the internal defect of an insulator in Example 1. FIG. FIG. 3 is an explanatory diagram of a waveform pattern of voltage application of an inspection voltage in the first embodiment. FIG. 3 is an enlarged explanatory diagram of an insulator in a state where an inspection voltage is applied in the first embodiment. Explanatory drawing of the relationship between the dielectric breakdown voltage and the voltage change rate of a test | inspection voltage in Experimental example 1. FIG. FIG. 6 is an explanatory diagram of a waveform pattern of voltage application of an inspection voltage in Example 2. FIG. 10 is an explanatory diagram of a waveform pattern of voltage application of an inspection voltage in Example 3.

In the present invention, the breakdown of the insulator includes not only a break that can be visually discerned but also a phenomenon that the insulation resistance inside and outside is greatly reduced due to a crack that cannot be visually recognized.
The inspection voltage preferably includes a waveform having a voltage change rate of 40 kV / ms or more.
In this case, it is possible to easily generate a partial discharge in the internal defect, and a voltage required for breaking the insulator starting from the internal defect due to the energy of the partial discharge (in this specification, this Voltage can be reduced). Therefore, the occurrence of flashover due to the voltage of the inspection voltage can be suppressed, and the inspection accuracy can be improved.
Note that when the voltage change rate changes from a minus (or plus) voltage to a plus (or minus) voltage, the voltage change from the minus (plus) voltage peak to the plus (minus) voltage peak. Divided by time.

The inner electrode is preferably a center electrode of the spark plug.
In this case, in the spark plug manufacturing process, the defect inspection of the insulator can be easily performed by using the center electrode inserted through the shaft hole of the insulator. Therefore, the production efficiency of the spark plug can be improved and the manufacturing cost can be reduced.

Further, it is preferable to use an ignition coil used as voltage applying means for discharging in the spark discharge gap of the spark plug as the inspection voltage generating means.
In this case, it is possible to easily inspect the insulator for defects using the ignition coil in the spark plug manufacturing process. Therefore, the production efficiency of the spark plug can be improved and the manufacturing cost can be reduced.

  Further, by using an ignition coil as the inspection voltage application means, it is easy to apply an inspection voltage having a high voltage change rate. That is, the inspection voltage by the ignition coil forms a vibration waveform by the mutual induction action of the primary coil and the secondary coil and the self-induction action of the secondary coil, so that the voltage change rate can be easily increased. Therefore, partial discharge can be easily generated in the internal defect.

The inspection voltage generated by the ignition coil is composed of a plurality of pulse-shaped waveform groups, and in each waveform group, plus and minus are alternately inverted in time, and the adjacent waveform groups are It is preferable that the waveform pattern is such that plus and minus are reversed.
In this case, the bias of the charge amount in the internal defect is prevented, and partial discharge is generated more efficiently. Thereby, the energy of partial discharge can be increased and the detection accuracy of internal defects can be improved.

Example 1
An insulator defect inspection method according to an embodiment of the present invention will be described with reference to FIGS. The defect inspection method of the insulator 1 of this example is to inspect for the presence or absence of the internal defect 10 (see FIG. 3) of the insulator 1 for a spark plug having the shaft hole 11 through which the center electrode is inserted.
In the inspection, as shown in FIG. 1, the inner electrode 2 is disposed in the shaft hole 11 of the insulator 1, and the outer electrode 3 is disposed on the outer surface 12 of the insulator 1.
Next, a test voltage is applied between the inner electrode 2 and the outer electrode 3 as shown in FIG. As a result, a partial discharge is generated in the internal defect 10, and the insulator 1 is broken starting from the internal defect 10 by the energy of the partial discharge, thereby revealing the internal defect 10.

An insulator 1 for a spark plug according to the inspection method of this example is a cylindrical molded body made of ceramics whose main component is alumina or the like.
The outer surface 12 of the insulator 1 has a complicated shape whose thickness changes along the axis.

The spark plug is applied to an internal combustion engine such as an automobile engine.
And the insulator 1 applied to such a spark plug detects the presence or absence of the internal defect 10 by the inspection method of this example as follows.

Below, the defect inspection method of the insulator 1 of this example is demonstrated concretely.
First, as shown in FIG. 1, the inner electrode 2 is disposed in the shaft hole 11 of the insulator 1, and the outer electrode 3 is disposed on the outer surface 12 of the insulator 1.
A locking step portion 13 for locking the inner electrode 2 is formed in the shaft hole 11 of the insulator 1. Further, the inner electrode 2 has a substantially cylindrical shape so as to be inserted into the shaft hole 11 of the insulator 1 and has a diameter changing portion 23 that is locked to the locking step portion 13. Then, the inner electrode 2 is inserted from the base end side of the shaft hole 11 of the insulator 1, and is arranged in a state where the diameter changing portion 23 is locked to the locking step portion 13. Here, the base end portion of the inner electrode 2 protrudes from the base end portion of the insulator 1.
In this example, the center electrode of the spark plug is used as the inner electrode 2, but an inner electrode for defect inspection may be separately prepared.

The external electrode 3 is made of a metal material and is formed so as to sandwich the outer surface 12 of the insulator 1. In addition, the detection range of the internal defect 10 can be widened by changing the axial dimension of the external electrode 3.
The inner electrode 2 is connected to one electrode of the power source 4, and the other electrode of the power source 4 is connected to the ground 5. The outer electrode 3 is connected to the ground 5.

  Next, as shown in FIG. 2, an AC inspection voltage in which plus and minus are alternately reversed in time is applied between the inner electrode 2 and the outer electrode 3. Here, the inspection voltage is set so that the voltage change rate has a waveform of 40 kV / ms or more.

  Note that, as shown in FIG. 2, the rate of voltage change is positive (+) from the peak of the negative voltage, where t is the time to change from the negative (or positive) voltage to the positive (or negative) voltage. The voltage fluctuation (| ΔV |) up to the peak of the minus voltage is divided by the time (t) (| ΔV | / t).

As shown in FIG. 3, when an internal defect 10 having a space such as a pinhole is present in the insulator 1 to which the inspection voltage is applied, the inspection voltage is alternately positive and negative in terms of time. Due to the inversion, partial discharge is generated in the internal defect 10.
That is, for example, in a state where a voltage is applied in a state where the inside (upper side in FIG. 3) of the insulator 1 is plus (+) and the outside (lower side in FIG. 3) is minus (−), the insulator 1 In each ceramic particle 14 constituting, electrons (-) are attracted to the inside (upward), and holes (+) are attracted to the outside (downward). As a result, in the internal defect 10 as well, electrons (−) are attracted to the inside (upward) and holes (+) are attracted to the outside (downward).

Then, when the inspection voltage is reversed between plus and minus from this state, electrons (−) in the internal defect 10 are attracted to the outside (downward), and therefore discharge (arrow A shown in FIG. 3) occurs in the internal defect 10. ) Occurs. This is a partial discharge.
And the insulator 1 will be destroyed by the internal defect 10 by the energy of said partial discharge. As a result, the internal defect 10 becomes obvious, and the presence or absence of the internal defect 10 of the insulator 1 can be easily inspected.

On the other hand, when the inspection voltage is applied and the internal defect 10 which is a void portion such as a pinhole does not exist in the insulator 1, the above partial discharge cannot occur. In such a case, the insulator 1 is determined to be a non-defective product.
In addition, you may implement the defect inspection method of this example with respect to the some test | inspection insulator 1 simultaneously (illustration omitted).

Next, the function and effect of the insulator defect inspection method of this example will be described.
In this example, the test voltage applied between the inner electrode 2 and the outer electrode 3 is not a direct current, but by applying a test voltage in which plus and minus are alternately reversed in time, the insulator 1 A partial discharge can be generated in the internal defect 10 which is a space such as a pinhole existing therein. And by the energy of partial discharge, the insulator 1 is destroyed from the internal defect 10 as a starting point, and dielectric breakdown is caused. Thereby, the internal defect 10 can be made obvious. Therefore, the internal defect 10 can be revealed by a relatively low voltage value.

  Further, the inspection voltage in this example is a voltage in which plus and minus are alternately reversed in time, and the sum of the absolute value of the plus side voltage and the absolute value of the minus side voltage is the magnitude of the voltage fluctuation. Therefore, a large partial discharge energy can be obtained at a low voltage value. Therefore, it is possible to suppress the occurrence of flashover due to the high inspection voltage value. As a result, there is no risk of increasing the size and complexity of the inspection apparatus.

  The voltage change rate of the inspection voltage has a waveform of 40 kV / ms or more. Thereby, partial discharge can be easily generated in the internal defect 10, and the dielectric breakdown voltage can be reduced. Therefore, the occurrence of flashover due to the voltage of the inspection voltage can be suppressed, and the inspection accuracy can be improved.

  The inner electrode 2 is a center electrode of the spark plug. Thereby, in the manufacturing process of a spark plug, the defect inspection of the insulator 1 can be easily performed using the center electrode inserted through the shaft hole 11 of the insulator 1. Therefore, the production efficiency of the spark plug can be improved and the manufacturing cost can be reduced.

  As described above, according to this example, it is possible to provide a defect inspection method for an insulator that can easily and accurately inspect for the presence or absence of an internal defect in the insulator.

(Experimental example 1)
In this example, as shown in FIG. 4, a comparative experiment was performed on the relationship between the dielectric breakdown voltage of the insulator and the voltage change rate.
First, as shown in FIG. 1, the inner electrode 2 is disposed in the shaft hole 11 of the insulator 1, and the outer electrode 3 is disposed on the outer surface 12 of the insulator 1.

  Next, an inspection voltage was applied to the inner electrode 2 and the outer electrode 3, and the defect inspection of the insulator 1 shown in Example 1 was performed. At this time, AC voltages having different voltage change rates were used as the inspection voltages. And the dielectric breakdown voltage in each test | inspection was investigated. The result is shown in FIG. In the figure, the ratio of the breakdown voltage at each voltage change rate to the breakdown voltage when the voltage change rate is 1 kV / ms is plotted. That is, the curve B shown in FIG. 4 represents the relationship between the voltage change rate and the breakdown voltage.

As can be seen from FIG. 4, by setting the voltage change rate of the inspection voltage to 40 kV / ms or more, the breakdown voltage can be greatly reduced, and even if the voltage change rate is increased further, the breakdown voltage does not change.
Therefore, by setting the voltage change rate of the inspection voltage of this example to 40 kV / ms or more, the dielectric breakdown voltage can be sufficiently reduced. Therefore, the occurrence of flashover due to the voltage value of the inspection voltage can be suppressed, and the inspection accuracy can be improved.

(Example 2)
This example is an example in which an ignition coil used as voltage application means for discharging in the spark discharge gap of the spark plug is used as the inspection voltage generating means.
In this example, since the ignition coil is used as the inspection voltage application means, as shown in FIG.

That is, the ignition coil uses high voltage induced electromotive force generated in the secondary coil by mutual induction when the energization to the primary coil is cut off. The voltage waveform generated by the induced electromotive force repeats positive and negative voltages while the voltage peak is attenuated like a damped oscillation wave due to self-induction. Therefore, in the ignition coil, a group of damped oscillatory pulse waves (waveform group P) is generated by energizing and shutting off the primary coil, and from the first negative (or positive) voltage peak in each waveform group P, positive The voltage change rate up to the peak of (or minus) voltage is the largest. Then, a plurality of waveform groups P as shown in FIG. 5 are generated in the ignition coil by repeatedly energizing and interrupting the primary coil at regular time intervals. In addition, in FIG. 5, the waveform for 3 times electricity supply and interruption | blocking is shown.
Others are the same as in the first embodiment.

In this example, the defect inspection of the insulator 1 can be easily performed using the ignition coil in the spark plug manufacturing process. Therefore, the production efficiency of the spark plug can be improved and the manufacturing cost can be reduced.
Further, in this example, by using an ignition coil as the inspection voltage application means, it is easy to apply an inspection voltage having a high voltage change rate. That is, the inspection voltage by the ignition coil forms a vibration waveform by the mutual induction action of the primary coil and the secondary coil and the self-induction action of the secondary coil, so that the voltage change rate can be easily increased. Therefore, partial discharge can be easily generated in the internal defect 10.
In addition, the same effects as those of the first embodiment are obtained.

(Example 3)
This example is also an example in which an ignition coil used as a voltage application means for discharging in the spark discharge gap of the spark plug is used as the inspection voltage generating means.
However, in this example, as shown in FIG. 6, the inspection voltage generated by the ignition coil has a waveform pattern in which the adjacent waveform group P is inverted between plus and minus.
This is realized by alternately performing the energization direction to the primary coil described above.
Others are the same as in the second embodiment.

In this example, the bias of the charge amount in the internal defect 10 is prevented, and partial discharge is generated more efficiently. Thereby, the energy of partial discharge can be enlarged and the detection accuracy of the internal defect 10 can be improved.
In addition, the same effects as those of the second embodiment are obtained.

1 Insulator 11 Shaft Hole 12 Outer Side 2 Inner Electrode 3 Outer Electrode

Claims (5)

An insulator defect inspection method for inspecting the presence or absence of an internal defect of an insulator for a spark plug having a shaft hole through which a center electrode is inserted,
An inner electrode is disposed in the shaft hole of the insulator, an outer electrode is disposed on the outer surface of the insulator,
By applying an inspection voltage in which plus and minus are alternately reversed in time between the inner electrode and the outer electrode, a partial discharge is generated in the internal defect, and the internal discharge is performed by the energy of the partial discharge. A method for inspecting a defect of an insulator, characterized by destroying the insulator from a defect and revealing the internal defect.   2. The defect inspection method for an insulator according to claim 1, wherein the inspection voltage includes a waveform having a voltage change rate of 40 kV / ms or more.   3. The insulator defect inspection method according to claim 1, wherein the inner electrode is a center electrode of the spark plug.   The insulator according to any one of claims 1 to 3, wherein an ignition coil used as a voltage application means for discharging in the spark discharge gap of the spark plug is used as the inspection voltage generation means. Defect inspection method.   5. The inspection voltage generated by the ignition coil according to claim 4, comprising a plurality of pulse-shaped waveform groups, and in each waveform group, plus and minus are alternately inverted in time and adjacent to each other. The method for inspecting a defect of an insulator, wherein the waveform group has a waveform pattern in which plus and minus are reversed to each other.

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