JPH0748395B2 - Constant voltage discharge tube - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage discharge tube used by being connected in series with a spark plug in an ignition device for an internal combustion engine.

2. Description of the Related Art It is known that, when considering the life of an ignition device for an internal combustion engine that has been generally used conventionally, the influence of stain on the spark plug is extremely large.

Contamination of the spark plug means that carbon, water, or a conductive compound such as a lead compound adheres to the surface of the insulating ceramic body of the spark plug.
A spark current leaks through the conductive material and laterally jumps, so that the fire does not normally fly between the electrodes, and is roughly classified into smoldering stains depending on the kind of the conductive material.

On the other hand, a series spark gap discharge tube is provided between the spark plug and the ignition coil in order to eliminate the above-mentioned adverse effects due to pollution, and the voltage applied to the spark plug is rapidly raised to contaminate the energy required for ignition. Supplying the spark plug before the leakage current flows is disclosed in, for example, JP-A-47-10.
Proposed and disclosed in Japanese Patent No. 556.

The above-mentioned reference shows that in the case where a series spark interval in a closed discharge space filled with gas is connected in a high-voltage conductor, 8 kV and 3
The free ends of the series spark gaps responsive to a fixed ignition voltage value between 0 kV are separated from each other by 1 to 5 mm, more preferably 1.5 to 3 mm, and are made of a material that does not scatter at least in the range of spark flashover, 1 to The present invention proposes an ignition coil device for operating an internal combustion engine, which is surrounded by a gas that does not react with the above material at a pressure of 10 atm, more preferably 2 to 5 atm.

The gas is nitrogen having a purity of at least 98% or argon having a purity of at least 99%, and the free end, that is, the electrode is 90% by weight or more, aluminum, cerium, hafnium, lanthanum, niobium, tantalum, It is also disclosed that it is composed of a nitride of titanium, vanadium or zirconium, or a mixture of nitrides of these metals, and that it contains an oxide or an oxynitride corresponding to an oxygen content of 25 atom% or less of the compound. ing.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The above proposal having the above-mentioned configuration is such that, even if the spark plug is contaminated, the time between the voltage application and the electrodes of the spark plug is dielectrically broken down, and the time to fly is short, and the leakage due to the pollution is caused. The effect of not being greatly affected by the current can be expected.

However, in consideration of various points described below, there is still a disadvantage that the spark plug may not be able to perform an appropriate ignition operation, and improvement is desired when considering its practical application.

That is, the ignition voltage of the spark plug responds to the average voltage value of 8 to 30 kV supplied as described in the previous proposal, and the reduced voltage is more effective in generating noise or downsizing the ignition device. It is well known from the point of view, on the other hand, in recent years, it is usually set to about 10 to 25 kV in consideration of the increasing tendency of the compression ratio for the purpose of improving fuel efficiency.

By the way, in order to reliably prevent the smoldering of the internal combustion engine, even when the voltage is rapidly supplied to the spark plug through the series spark interval, the supply voltage must be set to a high value above a certain level. It has been confirmed by experiments that, for example, in a certain internal combustion engine, the steep supply voltage value to the spark plug that can reliably prevent smoldering due to pollution was 18 kV or more.

That is, when a voltage of 18 kV or less is supplied, smoldering of the internal combustion engine occurs, and the rotational speed during idling becomes extremely unstable.

Also, even if the atmosphere is mixed in the closed discharge space where the above-mentioned series sparks are provided, the ignition coil can be supplied.
In order to reliably discharge at a voltage of 25 kV or less, it is necessary to set the series spark interval length to about 12 mm or less,
This can be confirmed from the experimental result in which the discharge voltage in the atmosphere in FIG.

Now, looking at the above-mentioned proposal here, the electrode interval is 1 to 5 mm, more preferably 1.5 to 3 mm,
In such discharge length, for example, setting the above-mentioned high-voltage discharge starting voltage of 18 kV is performed under the enclosed pressure condition of 1 to 10 atm, more preferably 2 to 5 atm with nitrogen or argon as the enclosed gas disclosed in the above proposal. When used, it is extremely difficult.In other words, the above-mentioned proposed device has a short spark interval discharge length and not too high a filled gas pressure, and it is not possible to easily set the discharge start voltage to a high voltage of 18 kV or higher, resulting in contamination. Depending on the state, there is a possibility that an appropriate ignition operation cannot be performed.

It should be noted that it is possible to set the above-mentioned discharge length to 5 mm or more, but in this case, the influence of the earth body newly existing on the outer periphery of the series spark interval begins to appear. That is, the spark interval is generally provided immediately above the spark plug in order to prevent energy loss. In this case, the internal combustion engine body serves as a grounding body, and the conductance between the body and the tip of the main electrode, that is, the discharge portion. C begins to affect, and as shown in FIG. 5, the conductance C is electrically equivalent to the state where the conductance C is connected in parallel with the spark plug and the series body of the spark plugs. There is a risk that it will decrease.

Therefore, in the above-mentioned proposed device, the discharge length could not be unnecessarily increased.

In addition, the above-mentioned discharge length is limited to 5 mm or less in view of the voltage of post-discharge in the above-mentioned proposal. That is, it is preferable that the post-discharge voltage so-called discharge sustaining voltage is low so that the amount of energy on the input side can be reduced. The electrode interval is 1 to 5 mm, more preferably 1.5 to
It is set to 3mm.

However, according to the experiments of the applicant of the present application, although the long and short discharge lengths certainly contribute to the high and low discharge sustaining voltage, the type and pressure of the gas filled in the discharge space have a greater effect. It has been confirmed that they have it.

That is, in short, the discharge sustaining voltage is much lower when argon is sealed than when nitrogen is sealed.

Therefore, in the previous proposal, if only the sustaining voltage is considered, it is sufficient to use argon, but in this case, the discharge starting voltage is also lowered, and as described in that document, for example, 12 kV or less. It can only be applied in the case of the discharge start voltage, and in the proposed device as it is, for example, it is not possible to set the above-mentioned discharge start voltage of 18 kV,
There is an inconvenience that the problem caused by the stain cannot be surely prevented.

The present invention has been made in consideration of the above points, and provides a constant voltage discharge tube for an ignition device of an internal combustion engine, which has a discharge starting voltage of a high voltage of 18 kV or higher, and a discharge sustaining voltage that is extremely low. The purpose is to do.

Means for Solving the Problems A constant voltage discharge tube of the present invention is a discharge tube having a pair of main electrodes hermetically sealed at both ends of a cylindrical envelope, and a main electrode interval G is set to 5 to 12 mm. Then, a xenon gas with a purity of 99% or more is sealed in the cylindrical envelope at a gas pressure of 6.5 to 20 atm, and the main electrode interval G and the shortest distance between the discharge part of the main electrode and the inner wall surface of the cylinder envelope. The relationship with the distance D is 0.2 × G ≦ D, and the main electrode interval G is set so that the discharge start voltage is within the range of 18 to 25 kV.
And the gas pressure is set within the range of 5 to 12 mm or 6.5 to 20 atm described above.

The constant voltage discharge tube according to the present invention is an internal combustion engine which is a discharge part of the main electrode and an earth body under the condition that the distance D between the discharge part of the main electrode and the inner wall of the envelope is 0.2 times or more the main electrode gap G. The distance to the main body can be set large.

Therefore, even when the interval between the main electrodes is increased, it is possible to prevent the influence of the conductance due to the grounding body and prevent the discharge starting voltage from decreasing.

That is, the constant voltage discharge tube according to the present invention has a main electrode spacing of
The length is set as long as 5 mm or more, and the increase in discharge start voltage will be achieved as intended due to the longer length.

Further, although xenon gas having a low discharge starting voltage and a low discharge sustaining voltage is used as the filling gas, since the filling pressure is set high, the discharge starting voltage is It will be high pressure.

Embodiment FIG. 1 is a sectional view showing an embodiment of a constant current discharge tube for an internal combustion engine according to the present invention.

As is clear from the figure, in this embodiment, the first main electrode 2 connected to the ignition coil (not shown) of the ignition device at both ends of the cylindrical envelope 1 made of an insulator such as ceramic, The second main electrode 3 connected to a spark plug (not shown) is hermetically sealed by a known heat sealing operation using the adhesive member 4.

The first main electrode 2 is formed of a metal conductor cap 5 and a sintered alloy electrode 6 containing an emission agent that is welded to the cap 5, and the second main electrode 3 is formed on the metal conductor cap 7 and the cap 7. It is formed of a rod-shaped electrode 8 to be welded.

The sintered alloy electrode 6 includes, for example, a main metal made of a refractory metal such as tungsten, tantalum, molybdenum, a reducing agent made of nickel, titanium, vanadium, zirconium, etc., and an emission agent made of cesium, aluminum, barium, strontium, etc. It is composed of. On the other hand, the rod-shaped electrode 8 is made of a high melting point pure metal such as tungsten, tantalum, molybdenum, or an oxide or nitride thereof.

A closed space 9 formed by the cylindrical envelope 1 and the first main electrode 2 and the second main electrode 3 is filled with xenon gas having a purity of 99% or more at a filling pressure of, for example, 10 atmospheres based on the experimental result described later. Has been done.

The dimensions of each part in the illustrated example are as follows: the outer diameter of the cylindrical envelope 1 is 16 mm, the inner diameter is 8 mm, the tip of the sintered alloy electrode 6 is the outer diameter of 2 mm, and the rod-shaped electrode 8 is based on the experimental results described later. Outer diameter 1m
m, the distance G between both electrodes, that is, the discharge length G is set to 10 mm.

That is, it is clear that the relationship between the discharge length G and the shortest distance D between the discharge part of the electrode and the inner wall surface of the cylindrical envelope 1 satisfies the above condition of 0.2 × G ≦ D.

Further, it goes without saying that the metal conductor caps 5 and 7 and the adhesive member 4 are appropriately selected and used so that their thermal expansion coefficients are equal or substantially equal to the thermal expansion coefficient of the cylindrical envelope 1. In addition, as apparent from FIG. 1, the metal conductor caps 5 and 7 are provided with protrusions 5a, which are located on the periphery of the groove 1a provided on the end face of the cylindrical envelope 1 via the adhesive member 4. 7a, so that the working range of the adhesive member 4 between the cylindrical envelope 1 and the metal conductor caps 5, 7 is extremely wide, this embodiment being a strong metal conductor cap.
It will be possible to form 5, 7 sealing parts.

Now, in one embodiment of the constant pressure discharge tube of the present invention having the structure as described above, when the discharge starting voltage and the discharge sustaining voltage were examined, the values were 20 kV and 0.25 kV, respectively.

That is, the discharge start voltage is a value of 18 kV or more as described above, and the discharge sustaining voltage is extremely reduced to 1/80 of that value, which reliably reduces the smoldering of the meat-burning engine due to the pollution of the spark plug with a small energy amount. It can be prevented. It was confirmed that extremely favorable characteristics could be obtained.

On the other hand, it goes without saying that the discharge starting voltage and the like are affected by the dimensions of each part such as the discharge length and the enclosed gas pressure in the illustrated embodiment, and this point will be described in detail below.

First, the relationship between the discharge length G and the shortest distance D between the electrode discharge portion and the inner wall surface of the cylindrical envelope 1 will be described.

In order to confirm the above relationship, the applicant of the present application created a discharge tube in which the relationship between the discharge length G and the distance D was variously changed, and the discharge tube was discharged alone, that is, in the state where the earth body was not present, and the internal combustion engine. An experiment was conducted to examine the discharge start voltage and the ratio when the discharge was performed in the case where the discharge was performed in the vicinity of the main body, that is, in the state where the earth body was present.

Fig. 2 is a characteristic diagram showing the experimental results, and as is clear from the drawing, the relationship between the discharge length G and the distance D, that is, when D / G is 0.2 or more, the influence of the earth body on the discharge start voltage is shown. It was confirmed that there was no. The above D /
Even if G is the same, a slight variation occurs in the characteristics depending on the value of the discharge length G, but most of the variation occurs in the region where D / G is 0.2 or less. There is no particular problem.

That is, if the distance D is set so that the above-mentioned D / G is 0.2 or more even if the discharge length G is set to be long, the discharge start voltage is increased by increasing the discharge length G regardless of the presence or absence of the earth body. You can expect what you want.

Next, the relationship between the discharge starting voltage or the discharge sustaining voltage and the enclosed gas pressure and the discharge length G will be described.

In order to ensure the above relationship, the applicant of the present application has the above-described relationship D / G between the discharge length G and the distance D of 0.2 or more and various discharge lengths of 12 mm or less, and xenon gas at various pressures. Various discharge tubes having the structure shown in FIG. 1 enclosed were prepared, and an experiment was conducted to investigate the respective discharge starting voltage and discharge sustaining voltage.

3 (a) and 3 (b) are characteristic charts showing the experimental results. As is clear from FIGS. 3 (a) and 3 (b), both the discharge start voltage and the discharge sustaining voltage have a long discharge length. It was also confirmed that the higher the voltage, the higher the voltage of the filled gas. Regarding the discharge sustaining voltage, the characteristics for various input voltage values were investigated, but there was almost no difference when discharged, and the characteristics when a high voltage of 35 kV is input are shown in FIG. 3 (b).

Now, let us first look at the relationship between the discharge start voltage, the discharge length, and the enclosed gas pressure.

Regarding the discharge start voltage, as described above, in order to reliably prevent the adverse effect of stains on the spark plug, a high voltage of 18 kV or higher must be rapidly supplied to the spark plug, and usually 10 to 25 kV. It is needless to say that it is preferable to set the ignition voltage in the range of 18 to 25 kV in consideration of the ignition voltage of the ignition plug set to 1. The applicant of the present application further studied in the above range.

That is, when the relationship between the discharge length and the enclosed gas pressure within the above voltage range is examined in more detail, the enclosed gas pressure is extremely high in the region where the discharge length is short, and therefore it is difficult to manufacture the discharge tube in such region. It is possible that

In other words, in the embodiment of the constant voltage discharge tube according to the present invention shown in FIG. 1, the envelope 1 and the electrodes 2 and 3 are hermetically sealed by the heating work using the adhesive member 4, Although depending on the heating temperature, considering the thermal expansion of the enclosed gas or the mechanical strength of the sealing portion, it goes without saying that the higher the enclosed gas pressure, the more difficult the gas sealing work and the above heat sealing work are. .

Therefore, the discharge length cannot be unnecessarily set to a short value as disclosed in the proposed device described at the beginning, and according to the study by the applicant of the present application, at present, up to about 20 atm is the limit for increasing the enclosed gas pressure. From this point, it was confirmed that it is necessary to set the discharge length to 5 mm or more when setting the discharge start voltage within the above voltage range.

On the other hand, as is clear from FIG. 3 (b), the discharge sustaining voltage is 0.6% under the conditions of 12 mm or less and 20 atm or less as described above, although there are some differences depending on the discharge length and the enclosed gas pressure. It was confirmed that the discharge voltage was less than kV and that the discharge tube having the structure as shown in FIG. 1 and filled with xenon gas had extremely preferable characteristics.

In consideration of mass production of the discharge tube or miniaturization of the ignition device, it is preferable that the enclosed gas pressure is low and the input voltage value required for discharge is also low. Therefore, the discharge length is more preferably 8 to 10 mm. In addition, the discharge start voltage should be set to about 20kV ± 2kV. The reason is that if the discharge length is set to 12 mm and the discharge start voltage of 7 atm 18 kV can be obtained by considering only the decrease of the charged gas pressure, the ignition device can reduce the discharge length.
It will be larger than 12 mm or less,
From this point of view, the discharge length and the discharge start voltage range as described above become a practical range in view of mass productivity and device shape.

Effect of the Invention The constant voltage discharge tube according to the present invention has a discharge starting voltage of 18 to 25 kV.
The discharge length is set within the range of 5 to 12 mm so that the high voltage is maintained, and the pressure of the xenon gas sealed in the discharge space is set within the range of 6.5 to 20 atm. Since the shortest distance to the wall surface is 0.2 times or more of the discharge length, it can be expected that the use in series with the spark plug of the internal combustion engine can surely prevent smoldering due to stain of the spark plug.

In addition, since the xenon gas with a purity of 99% or more is used as the enclosed gas, the discharge sustaining voltage can be controlled to a low value, and when considering the application as described above, the ignition energy amount of the ignition device can be reduced. Can be expected.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a constant voltage discharge tube according to the present invention, and FIG. 2 shows the relationship between the discharge length G and the shortest distance D between the inner wall surface of the main electrode discharge part and the earth wall. FIG. 3 is a characteristic diagram showing the ratio of the discharge start voltage in the case of performing the discharge
Figures (a) and (b) are characteristic diagrams showing the relationship between the discharge start voltage and the filling pressure of xenon gas and the relationship between the discharge sustaining voltage and the filling pressure of xenon gas at various discharge lengths, respectively.
FIG. 4 is a characteristic diagram showing the relationship between the discharge start voltage and the discharge length in the atmosphere, and FIG. 5 is an equivalent circuit diagram for explaining the influence of the earth body of the internal combustion engine body. 1 ... Cylinder envelope, 2 ... First main electrode, 3 ... Second main electrode, 4 ... Adhesive member, 5,7 ... Metal conductor cap, 6 ...
… Sintered alloy electrode, 8 …… rod-shaped electrode, 9 …… closed space.

Claims (1)

[Claims] 1. A pair of main electrodes is provided at both ends of a cylindrical envelope made of an insulating material such as ceramic, and the main electrode gap G is provided.
Is set to 5 to 12 mm, xenon gas having a purity of 99% or more is sealed in the cylindrical envelope at a gas pressure of 6.5 to 20 atm, and the main electrode gap G, the discharge part of the main electrode and the cylinder are set. The relationship with the shortest distance D to the inner wall surface of the envelope is set to 0.2 × G ≦ D, and the main electrode interval G and the enclosed gas pressure are set to 5 in order to keep the discharge starting voltage within the range of 18 to 25 kV. A constant voltage discharge tube with a range of up to 12 mm or 6.5 to 20 atm.