JPH04155792A - Gas-filled discharge tube for high voltage switch element and ignition plug using same - Google Patents

Abstract

PURPOSE:To suppress the influence of a grounding body outside a discharge tube and stabilize a discharge voltage upon aerial discharge in the case of high voltage discharge by deflecting and setting a discharge gap position to one line-electrode side. CONSTITUTION:Line-electrodes 12, 14 are soldered at both ends of a cylindrical ceramic enclosure 10, followed by charging an innert gas therein. Discharge electrodes protruding from flange parts 12a, 14a, are formed in shorter cathode 12b and a longer anode 14b respectively so that the position of a discharge gap D is set deviated to the electrode 12 side. The outer surface of the enclosure 10 is fixed to a grounding body 18 via an adhesive 16 having electrical insulating property. Consequently, the dispersed variation in the discharge voltage seldom occurs and stable discharge can be obtained, and the influence caused by the grounding body can be minimized to a low level for practically yielding no problem. And starting characteristics of any engine can be effectively improved by applying this effect to ignition plugs for the engine.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gas-filled discharge tube for a high voltage switching element and a spark plug using the same.

(Prior Art) Gas-filled discharge tubes are used in lightning arresters and the like to protect electronic equipment from surges. FIG. 3 shows a conventional example of a gas-filled discharge tube. In the figure, 2 is an envelope made of a cylindrical ceramic body, and 4 and 6 are line electrodes that are hermetically brazed to both end surfaces of the envelope 2.

4a and 6a are discharge electrodes that protrude from the flange portion of the line electrode 4.6 to face each other within the envelope.

An inert gas is sealed in the discharge tube, and the firing voltage can be changed by changing the type of gas, the pressure, and the distance between the discharge electrodes 4a and 68.

A discharge tube with a high firing voltage can be obtained by increasing the distance between the discharge electrodes or by filling the discharge tube with gas at extremely high pressure. In this way, a gas-filled discharge tube with a discharge starting voltage of 10 kV or more has been obtained.

A discharge tube that discharges at a high voltage in this manner discharges when a certain high voltage is applied, and therefore can be used as a switching element that operates at a high voltage.

(Problems to be Solved by the Invention) When using a gas-filled discharge tube that discharges at a high voltage as described above as a switching element, the problem is whether stable discharge can be performed under high voltage.

By the way, high-voltage gas-filled discharge tubes are being considered for use as spark plugs in automobile engines because of their stable discharge performance in the high-voltage range. In some cases, a metal grounding body (also called a back electrode) is placed close to the envelope of the device. As engines become more multi-valve, spark plugs are sometimes installed at the back of the engine head, and in such cases, the ground body comes close to the spark plug.

Since the ceramic body used in the envelope of the discharge tube is a dielectric material, if a grounding body is placed close to the envelope, the discharge type starting voltage may be lowered. This is because creeping discharge (creeping flashover) is more likely to occur within the envelope due to the provision of the grounding body. Since creeping discharge occurs at a lower voltage than discharge between the discharge electrodes, when creeping discharge occurs, the discharge voltage decreases, making it impossible to obtain the desired discharge voltage.

Further, even in the case of a normal discharge between discharge electrodes that is not a creeping discharge, when the above-mentioned grounding body is provided, the discharge voltage may vary and the predetermined switching performance may not be satisfied.

This is because the electric field inside the discharge tube is affected by the grounding body.

Therefore, the present invention has been made to solve the above problems, and its purpose is to effectively prevent creeping discharge even if there is a grounding body in close proximity to the envelope of the discharge tube. Another object of the present invention is to provide a gas-filled discharge tube for a high-voltage switching element that can prevent variations in discharge voltage and perform stable switching at high voltage, and a spark plug using the same.

(Means for solving problems) The present invention has the following configuration to achieve the above object.

That is, line electrodes with discharge electrodes protruding from opposite surfaces were airtightly brazed to both ends of a cylindrical envelope, gas was sealed inside, and the discharge starting voltage was set to 10 kV or higher. The gas-filled discharge tube for a high-voltage switch element is characterized in that the discharge gap position between the end faces of the discharge electrodes is set to be offset toward the line electrode side of the cathode.

Further, in a spark plug in which an insulator is fitted into a substantially cylindrical housing and a spark gap is formed between a ground electrode provided on one end face of the housing and an end face of a center electrode fitted into the insulator, a spark gap is formed in the insulator. Gas-filled discharge tube for the above high voltage switch element.

It is characterized in that it is installed in series between the center electrode and a terminal for applying a high voltage provided on the end face of the insulator.

(Function) By moving the discharge gap between the end faces of the discharge electrode closer to the cathode side, the creepage distance becomes shorter.

Prevents creeping discharge and suppresses fluctuations in discharge starting voltage. In addition, the electric field at the discharge site is more strongly affected by the potential of the flange portion, suppressing the influence of the earth body on the outside of the discharge tube, and enabling stable discharge.

In addition, by incorporating this gas-filled discharge tube into the spark plug and applying the discharge voltage of the gas-filled discharge tube to the spark gap of the plug, stable spark discharge can be generated even when the insulation resistance value of the plug is small. Start the engine reliably.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail based on the accompanying drawings.

[Gas-filled discharge tube for high-voltage switch element] First, an example of a gas-filled discharge tube for high-voltage switch element will be described.

FIG. 1 shows a cross-sectional view of an embodiment of a gas-filled discharge tube for a high-voltage switch element.

In the figure, reference numeral 10 denotes a cylindrical ceramic envelope. Line electrodes 12 and 14 are brazed to both ends of the envelope 10, and an inert gas is sealed inside. Cylindrical discharge electrodes 12b and 14b are provided to protrude from the flange portions 12a and 14a of the line electrodes 12 and 14 to face each other within the envelope 10.

In the discharge tube according to the present invention, the lengths of the discharge electrodes 12b, 14b protruding from the flange portions 12a, 14a are set to be unequal on the anode side and the cathode side.

The line electrode 12, which has a short discharge electrode protrusion length, is a cathode.

The line electrode 14 with a long protruding length is an anode.

The protruding length of the discharge electrode 12b of the line electrode 12 is shortened,
By increasing the protruding length of the discharge electrode 14b of the line electrode 14, the position of the discharge gap is shifted closer to the line electrode 12 side.

The discharging electrodes 12b and 14b have rounded end edges, and the line electrodes 12 and 14 are metallized on both end surfaces of the envelope 10, and then nickel plated and brazed to be airtight.

An adhesive 1 having electrical insulation properties is placed around the outer periphery of the envelope 10.
The grounding body 18 is fixed via 6. The grounding body 18 is a metal body formed into a cylindrical shape, and is formed to have a considerably larger diameter than the outer diameter of the envelope 10, and is placed away from the outer peripheral surface of the envelope 10 with an adhesive 16 interposed therebetween. The grounding body 18 is set to ground potential during discharge.

The discharge starting voltage of a gas-filled discharge tube can be changed by appropriately setting the discharge gap, the pressure of the filled gas, etc., but in the gas-filled discharge tube of the example, the discharge starting voltage was set to 20 kV. For this reason, the distance between the discharge electrodes 12b and 14b is 3 mm, the protrusion length of the discharge electrode 12b of the line electrode 12 is 3.5 mm, and the discharge electrode 14 of the line electrode 14 is
The protruding length of b was set to 11.5 mm. Further, krypton gas was used as an inert gas sealed in the discharge tube, and the pressure of the sealed gas was 15 kg/cm'.

When the gas-filled discharge tube of this example was repeatedly discharged and the discharge characteristics were observed, the discharge starting voltage was 20 kV.
It was confirmed that stable discharge occurred. Furthermore, since the discharge voltage did not decrease after repeated discharges many times, it was confirmed that no creeping discharge occurred. In addition, when a creeping discharge occurs, the discharge voltage is clearly lower than 20 kV, and the discharge sustaining voltage increases compared to an air discharge, so by measuring these voltages, it is possible to determine whether creeping discharge occurs It can be easily determined whether the

As mentioned above, the reason why we were able to discharge without causing creeping discharge in the gas-filled discharge tube of the example was by shortening the length of the discharge electrode on the cathode side and moving the discharge gap closer to the cathode side. This is thought to be due to the shortening of the creepage distance.

FIG. 2 shows the results of measuring how the discharge voltage changes when the protrusion length of the discharge electrode is changed. In this measurement, a gas-filled discharge tube equipped with a grounding body 18 similar to that shown in FIG. Projection length u of the discharge electrode of the line electrode on the anode side, 112
We investigated the variation in discharge voltage by changing the The following five types of lengths of Q, , and Tori were measured.

(41,,Q2) = (7,5mm -7,5mm
), (5,5+nm, 9.5mm), (4,5m
m, 10.5mm), (3,5mm, 11.5m
m), (2.5 mm, 12.5 mm) In Fig. 2, the range of vertical arrows indicates the range in which the discharge voltage varied.

As can be seen from the figure, the length of the discharge electrode is Q, u.

When the discharge voltage was equal, the discharge voltage varied considerably, but as the length of the discharge electrode on the cathode side was shortened, the discharge voltage variation became smaller.

When the length of U was 3.5 mm and 2.5 mm, there was almost no variation in the discharge voltage, and a stable discharge voltage was obtained.

This measurement result shows that by setting the lengths of the discharge electrodes to be unequal and moving the discharge part in the discharge tube from the center to the cathode side, the influence of the ground body can be reduced to a level that does not pose a problem in actual use. It shows that it is possible.

Note that by moving the discharge site toward the cathode side as described above, creeping discharge can be prevented, and at the same time, voltage fluctuations in aerial discharge can also be suppressed. This is because as the discharge region approaches the flange on the cathode side, the electric field at the discharge region is affected by the potential of the flange, which has a relatively large diameter. This is thought to be due to the fact that it is less susceptible to

c. Spark Plug Using Gas-Filled Discharge Tube for High-Voltage Switch Element] Next, an example in which the gas-filled discharge tube for high-voltage switch element is applied to a spark plug for an engine will be described.

FIG. 4 shows a cutaway view of one embodiment of the spark plug.

The spark plug of this embodiment has a cylindrical housing 20 which is a part for attachment to an engine, and an insulator 30 caulked and fixed to the inner hole of the housing 20 via an airtight packing 22 and a ring 24. The insulator 30 is enclosed in the housing 20 on the side where the engine is attached, and the other end extends outside from the end surface of the housing 20.

A mounting screw 26 is provided on the outer peripheral surface of the housing 20,
A ground electrode 28 is joined to the annular end surface of the mounting screw 26.

An inner hole is provided in the insulator 30 in the axial direction, and a center electrode 32 is inserted into the insulator 30 on the ground electrode 24 side. The tip of the center electrode 32 protrudes from the end face of the insulator 30 to form a spark gap with the ground electrode 28. The center electrode 32 has an interior made of copper and an exterior made of a nickel-chromium alloy or a nickel-chromium-iron alloy that has excellent heat resistance and corrosion resistance.

Inside the insulator 30, a center shaft 34 follows the center electrode 32.
, spring 36, gas-filled discharge tube 38, spring 3
6 are fitted in this order, and the terminal 40 is fixed to the end face. Terminal 40 is a terminal for applying high voltage. Center shaft 34
is heat-welded within the insulator 30 and integrated with the center electrode 32 using a conductive glass sealing material 42 . Both end faces of the gas-filled discharge tube 38 are pressed together by a spring 36 and assembled by a terminal 40. The gas-filled discharge tube 38 is of the same type as the gas-filled discharge tube of the embodiment described above, and the length of the discharge electrode extending from the line electrode on the terminal 40 side is set short. In this case, the grounding body 18 is not used.Next, the function of the spark plug shown in the above embodiment will be explained with reference to FIG.

The high voltage generated by the booster coil is guided to the terminal 40 and applied to the gas-filled discharge tube 38. Gas-filled discharge tube 3
When the voltage applied to the gas-filled discharge tube 38 rises above the set discharge voltage, the gas-filled discharge tube 38 discharges.

Point A in FIG. 5 is when the gas-filled discharge tube is discharging.

When the gas-filled discharge tube 38 discharges, a high voltage due to this discharge is instantaneously applied to the spark gap between the ground electrode 28 and the center electrode 32, causing a discharge in the spark gap. Point B in FIG. 5 shows the discharge in the spark gap.

When a high voltage is applied to a spark plug whose insulation resistance value has decreased due to carbon deposits, the carbon leaks out before the voltage reaches the voltage that discharges the spark gap, causing a misfire. To avoid this problem, set the discharge voltage of the gas-filled discharge tube to a higher value than the discharge voltage of the spark gap, so that the discharge voltage is instantaneously applied to the spark gap (C in Figure 5). .

Incidentally, as engines become more numerous, the installation position of the spark plug is restricted, and a grounding body may be placed close to the periphery of the spark plug.

If a grounding body is located close to the spark plug, the discharge voltage of the discharge tube will be affected and the discharge voltage will vary. If the discharge voltage varies and discharge occurs below a predetermined value, a high voltage will not be instantaneously applied to the spark gap, but will be applied slowly, and a predetermined discharge will not occur in the spark gap.

Even when the spark plug of this embodiment is mounted close to a grounding body, the discharge can be reliably caused in the spark gap by the action of the gas-filled discharge tube described above.

Table 1 shows the results of an engine starting test using the spark plug of this example, a conventional spark plug with a built-in gas-filled discharge tube as a comparative example, and a general spark plug without a built-in discharge tube. The test was conducted using a 1600 cc, 4-cycle gasoline engine at -20° C. using plugs with various insulation resistance values to which carbon was attached, and to which insulation resistance value the engine could be started.

Table 1 In the table, the ○ mark indicates the case where the engine could be started due to the insulation resistance value of the ignition plug, and the X mark indicates the case where the engine could not be started. The horizontal axis of the table shows the insulation resistance value of the spark plug.

Note that a conventional spark plug with a built-in gas-filled discharge tube is one in which a gas-filled discharge tube is installed in series with the center electrode, similar to the spark plug of this embodiment. It uses an internal discharge tube. In the case of spark plugs using this conventional gas-filled discharge tube, although it is recognized that starting performance is significantly improved compared to commonly used spark plugs, there are variations in effectiveness. On the other hand,
In the case of the spark plug of this example, the startability was further improved, and the variation was reduced, resulting in a stable improvement effect.

This means that there is less variation in the discharge voltage of gas-filled discharge tubes.
This is due to stable discharge.

The present invention has been variously explained above using preferred embodiments, but the present invention is not limited to these embodiments.
Of course, many modifications can be made without departing from the spirit of the invention.

(Effects of the Invention) As described above, the discharge tube for a high voltage switch element according to the present invention is set so that the discharge gap position is shifted toward one line electrode, so that it is discharged at a high voltage of about 10 kV to 20 kV. In this case, stable discharge can be performed by suppressing the influence of the earth body outside the discharge tube. Furthermore, by bringing the discharge gap closer to the cathode side, the discharge voltage during aerial discharge can be stabilized, and the device can be suitably used as a high voltage switching element.

In addition, by utilizing this gas-filled discharge tube as a spark plug for an engine, remarkable effects such as being able to effectively improve the startability of the engine are achieved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of a gas-filled discharge tube for a high voltage switch element according to the present invention, and FIG. 2 is a graph showing measurement results of discharge voltage fluctuation when changing the length of the discharge electrode.
Fig. 3 is a sectional view showing a conventional example of a gas-filled discharge tube used as a lightning arrester, Fig. 4 is a cutaway view showing an example of a spark plug, and Fig. 5 is a graph showing applied voltage to the spark plug. . 10... Envelope, 12.14... Line electrode,
12a, 14a...flange portion, 12b, 14b
...discharge electrode, 16...adhesive, 18...earth body, 20...housing, 28...earth electrode, 3o...insulator, 32...center electrode, 36...・Spring, 38...Gas-filled discharge tube, 40...Terminal.

Claims (1)

[Claims] 1. Line electrodes with discharge electrodes protruding from opposite surfaces are hermetically brazed to both ends of a cylindrical envelope, and a gas is sealed inside to set the discharge starting voltage. A gas-filled discharge tube for a high-voltage switch element in which the voltage is set to 10 kV or higher, characterized in that the discharge gap position between the end faces of the discharge electrodes is set to be offset toward the line electrode side of the cathode. Gas-filled discharge tube. 2. In a spark plug in which an insulator is fitted into a substantially cylindrical housing, and a spark gap is formed between a ground electrode provided on one end face of the housing and an end face of a center electrode fitted into the insulator, a spark gap is formed within the insulator. An ignition plug characterized in that the gas-filled discharge tube for a high voltage switch element according to claim 1 is installed in series between the center electrode and a terminal for applying a high voltage provided on an end face of an insulator.