JP2000243536A - Spark plug and ignition system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the lifetime while restricting generation of arc discharge and restricting the consumption of electrode by forming a light emitting part of a Pt contained metal as a main component, and specifying an electric resistance between a terminal metal and the center electrode arranged through a resistor. SOLUTION: As an alloy for forming a light emitting part (chip) 31 of a spark plug 100, an alloy containing Pt at 60% or more and Ir or the like at 15-30% at a center electrode 3 side is used so as to restrict the wastage of an ignition part 31 in the high-temperature condition due to the rise of melting point. For a grounding electrode 4, an alloy mainly composed of Pt and containing Ni or the like at 10-30% is used so as to relax the thermal stress due to a thermal expansion difference and so as to restrict the generation of breakdown of the chip 31. About 0.1-15% of the oxide of a 3A group rare earth group element and a metal element such as Ti, Zr, Hf of 4A group can be contained in the material for the chip 31. Electric resistance measured between a terminal fitting 13 of a resistor 15 and the center electrode 3 is adjusted to 10 KΩ or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spark plug for an internal combustion engine and an ignition system for the internal combustion engine using the spark plug.

[0002]

2. Description of the Related Art As an ignition system for an automotive internal combustion engine using a spark plug, a system using a distributor as shown in FIG. 11 has been used for a long time. In the system 249, the primary coil 252 of the ignition coil 251 that receives power from the battery 256 via the ignition switch 257 is connected to the igniter 254, while the secondary coil 253 is connected to the distributor 250. Then, when the control unit 255 issues a cutoff command signal to the igniter 254 at a predetermined ignition timing, the igniter 254 operates the non-contact switch unit to cut off the power supply to the primary coil 252. As a result, a high-voltage induced current is generated in the secondary coil 253, and is distributed by the distributor 250 to each spark plug 100 via the high tension cable C.

[0003] However, recently, the distributor system has been gradually used, and the ignition system of a full transistor type coil-on system (hereinafter referred to as an ignition system without using a distributor), in which ignition timing control is easy and contact maintenance is unnecessary. And DL
I (Distributor-LessIgnition) system) is becoming mainstream. In this system, an ignition coil is directly mounted on each spark plug, and is driven to be cut off at a predetermined timing by a control unit. In this case, since the ignition coil is directly attached to the spark plug, a high tension cable is not required.

[0004]

By the way, conventionally,
In order to improve the spark erosion resistance of a spark plug, a spark plug formed by welding a tip of a Pt (platinum) alloy to the tip of an electrode is used. However, when the melting point of platinum becomes close to 1,769 ° C., it melts and scatters, and is relatively easily consumed.

[0005] In a spark plug in which the ignition portion is constituted by such a Pt-based tip, the change in the ignition system described above may have a considerable effect on the durability of the ignition portion. That is, spark discharges of a spark plug are roughly classified into two types: glow discharge and arc discharge. Glow discharge is a form of discharge that occurs when, for example, the power supply impedance is relatively large. Since the discharge current is not so large, the temperature rise and consumption of the ignition portion are relatively difficult to progress. On the other hand, arc discharge often occurs when the power source impedance is small, and a large current flows, and the temperature of the ignition portion is easily increased, and consequently the wear is apt to proceed. Therefore, from the viewpoint of suppressing the consumption of the ignition part, it can be said that an environment mainly composed of glow discharge is desirable.

In the distributor system, the power supply impedance is large due to the contact gap and the electric resistance derived from the high tension cable, and the discharge form is likely to be mainly glow discharge. However,
In the DLI method, since there is no contact gap or resistance of the cable, the power source impedance is small, and depending on the material used for the electrode, the discharge transition ratio of glow / arc in spark discharge increases, and the electrode may be easily consumed.
According to the study by the present inventors, in the case of a Pt-based ignition portion, the conventional distributor method uses:
Although glow discharge was mainly used, it was found that in the DLI method, the power supply impedance was small, the glow / arc discharge transition rate was high, and the life was easily shortened.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spark plug which is less likely to generate an arc discharge even if the ignition portion is made of a Pt-based metal, and has a long life with reduced electrode consumption, and an internal combustion engine using the spark plug. And an ignition system.

[0008]

In order to solve the above-mentioned problems, a spark plug according to the present invention comprises a center electrode, an insulator provided outside the center electrode, and an insulator provided outside the insulator. A metal shell provided, a ground electrode disposed so as to face the center electrode, and a firing portion fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap; and A terminal fitting is fixed to one end of the through hole formed in the axial direction of the body, a center electrode is similarly fixed to the other end, and the terminal fitting and the center are fixed in the through hole. A resistor is disposed between the electrode and the electrode, and the ignition portion is mainly composed of a metal containing 60% by weight or more of Pt, and an electric resistance value between the terminal fitting and the center electrode via the resistor. Is 10kΩ
It is characterized by being secured as described above.

Further, the ignition system for an internal combustion engine of the present invention has a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a center electrode facing the center electrode. A ground electrode, and a firing portion fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap, and a through hole formed in the insulator in the axial direction, A spark plug having a terminal fitting fixed to one end thereof and a center electrode similarly fixed to the other end thereof, a casing attached to the spark plug, a spark plug housed inside the casing and Is connected to the terminal fitting of
A coil unit having an ignition coil for applying a high voltage for discharge to the spark plug, wherein the ignition portion of the spark plug is mainly composed of a metal containing 60% by weight or more of Pt; A resistance portion is provided between the central electrode and the central electrode so as to secure an electric resistance value between the two at 10 kΩ or more.

When the ignition portion is made of a Pt-based metal, the conventional distributor system uses 60% of the metal component.
If Pt is used in an amount of not less than Pt by weight, the improvement of the spark erosion resistance due to the higher melting point of the ignition portion could be expected. However, when the ignition unit is directly connected to the spark plug by the coil unit without using a high tension cable, that is, when the DLI system is used as the ignition system,
As described above, transition to a large current such as arc discharge is likely to occur, and wear due to melting and scattering of the Pt component due to temperature rise is likely to occur.

However, as a result of intensive studies by the present inventors, in a spark plug (hereinafter, also referred to as a Pt-based plug) having an ignition portion made of a Pt-based metal as described above, the distance between the ignition coil and the center electrode is reduced. It is found that by securing the electric resistance (i.e., equivalent to the power supply impedance) of 10 kΩ or more, a discharge (glow discharge or the like) having a relatively small current can be stably maintained even in the DLI method. The invention was completed. As a result, the above Pt is added to the DLI ignition system.
When a system plug is applied, the transition to high-current discharge such as arc discharge is unlikely to occur, and thus, even during high-speed or high-load operation, consumption of the ignition portion due to melting and scattering of Pt is suppressed, and the life of the spark plug is extended. Can be The electric resistance between the ignition coil and the center electrode is more desirably 15 kΩ or more. On the other hand, if the electric resistance exceeds 100 kΩ, the ignitability may be reduced, and caution is required.

In order to secure an electric resistance value of 10 kΩ or more between the ignition coil and the center electrode, a radio noise reducing resistor incorporated in the spark plug can be used. In this case, increase the electric resistance of the resistor,
The spark plug can be configured such that an electric resistance value of 10 kΩ or more (preferably 15 kΩ or more) is secured between the terminal fitting and the center electrode. On the other hand, in the case where a resistor is not incorporated, as in an inexpensive popular type spark plug, an electric resistance value in the above range may be ensured by a resistor portion such as a resistor provided on the coil unit side. Good.

In a spark plug, as the axial cross-sectional diameter of the tip of the center electrode is reduced, the volume of the tip of the center electrode is reduced, so that the flame generated by ignition is less likely to be deprived of heat and the ignitability is improved. In the spark plug or the ignition system of the present invention, when the ignition portion made of the Pt-based metal is formed at the tip of the center electrode, the tip diameter of the center electrode is adjusted within a range of 1.2 mm or less. Is good. That is, by setting the tip diameter to 1.2 mm or less, the effect of improving the ignitability by reducing the tip diameter can be remarkably enjoyed. In addition,
The tip diameter is desirably adjusted in the range of 0.4 to 0.8 mm. By making the tip diameter 0.8 mm or less,
The effect of improving the ignitability becomes more remarkable. On the other hand, when the tip diameter is less than 0.4 mm, the temperature of the ignition portion tends to rise due to the concentration of sparks, and the consumption of the ignition portion due to melting and scattering of Pt may easily occur.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 including a resistor as an example of the present invention shown in FIG. 1 has a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that a tip portion protrudes, and a tip portion protruding. Insulator 2 in state
And a ground electrode 4 and the like, one end of which is coupled to the metal core 1 and the other end of which is opposed to the tip of the center electrode 3. As shown in FIG. 2, the ground electrode 4 is provided with a firing portion 32 facing the firing portion 31 of the center electrode.
And a gap between the opposed firing portion 32 is a spark discharge gap g.

The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride. The metal shell 1 is made of low-carbon steel or the like, constitutes a housing of the spark plug 100, and has a screw portion 7 on its outer peripheral surface for attaching the plug 100 to an engine block (not shown). ing. In addition, the nominal of the screw part 7 is M14S, for example. The metal shell 1 on the side where the center electrode 3 is projected.
From the open end of the insulator 2 to the rear edge position of the insulator 2
Is, for example, 58.5 mm.

Next, the body portions 3a and 4a (FIG. 2) of the center electrode 3 and the ground electrode 4 are made of a Ni alloy (for example, Inconel (trade name)). On the other hand, the ignition portion 31 and the opposing ignition portion 32 have a metal component of Pt.
Is mainly composed of a metal containing 60% by weight or more.

As shown in FIG. 2, the main body 3 of the center electrode 3
In a, the front end side is reduced in diameter and the front end surface is flattened. A plate-like chip made of an alloy composition constituting the ignition portion 31 is superimposed on the front end, and laser welding is performed along the outer edge of the joining surface. The welding portion W is formed by electron beam welding, resistance welding, or the like, and is fixed to form the ignition portion 31. Also, the opposing firing part 32
The chip is formed by aligning the tip with the ground electrode 4 at a position corresponding to the firing portion 31, forming a welded portion W along the outer edge of the joint surface, and fixing the same.
In addition, these chips are, for example, a melting material obtained by blending and melting each alloy component so as to have the indicated composition,
Alternatively, it can be constituted by a sintered material obtained by molding and sintering an alloy powder or a metal single component powder mixed in a predetermined ratio.

As the alloy constituting the chip, for example, the following can be used. (1) Ir is 15 to 30 mainly composed of Pt on the center electrode side
An alloy containing in the range of% by weight is used. By using the alloy, consumption of the ignition portion at a high temperature due to an increase in the melting point is effectively suppressed, and a spark plug having excellent durability is realized.

On the ground electrode side, Pt is mainly used and N
An alloy containing i in the range of 10 to 30% by weight is used. By using the alloy, the thermal stress due to the difference in thermal expansion is alleviated, the breakage of the chip is suppressed, and a spark plug excellent in durability is realized. When the center electrode side has negative polarity, if the same alloy is used for both the center electrode and the ground electrode, the degree of wear of the electrodes is greater on the center electrode side, and the temperature on the center electrode side is lower. It is preferable to use chips in the above combination in consideration of wear.

(2) Ir is 10 to 30 mainly with Pt
An alloy containing 0.5% to 2% by weight of Ni and 0.5 to 2% by weight is used. By using the alloy, the thermal stress due to the difference in thermal expansion is alleviated, the breakage of the chip is suppressed, and a spark plug excellent in durability is realized. If the content of Ir in the alloy is less than 10% by weight, the melting point of the alloy decreases, and the durability of the plug decreases. On the other hand, Ir
If the content is more than 30% by weight, the amount of oxidation and volatilization of Ir increases, and the ignition portion is easily consumed, so that the durability of the plug similarly decreases.

The material constituting the chip (ignition portion) includes an oxide (composite oxide) of a metal element belonging to Group 3A (so-called rare earth element) and Group 4A (Ti, Zr, Hf) of the Periodic Table of the Elements. ) Can be contained in the range of 0.1 to 15% by weight. Thereby, I included in the chip
Consumption by oxidation and volatilization of the r component is further effectively suppressed. In this case, since the oxidation and volatilization of the Ir component can be suppressed by the compounding of the oxide, the metal part constituting the chip can be made of a Pt-Ir alloy as described in the above (1) or (2). If the content of the oxide is less than 0.1% by weight, Ir
The effect of preventing oxidation and volatilization cannot be sufficiently obtained. on the other hand,
When the content of the oxide exceeds 15% by weight, the thermal shock resistance of the chip decreases, and for example, when the chip is fixed to the electrode by welding or the like, a problem such as cracking may occur.
In addition, as the above-mentioned oxide, Y ₂ O ₃ is preferably used, but in addition, La ₂ O ₃ , ThO ₂ , ZrO _{2 and the} like can be preferably used.

Here, the firing portion 31, that is, the center electrode 3
Has a tip diameter δ of 1.2 mm or less, preferably 0.4 to 0.1 mm.
It is set to 8 mm. Note that one of the firing unit 31 and the opposing firing unit 32 may be omitted. In this case, the firing portion 31 or the facing firing portion 32
And the ground electrode 4 or the center electrode 3 forms a spark discharge gap g.

Returning to FIG. 1, in the spark plug 100, a through hole 6 is formed in the insulator 2 in the axial direction, and a terminal fitting 13 is inserted and fixed to one end of the spark plug 100, and the other end is inserted into the same. The center electrode 3 is inserted and fixed to the end side of. A resistor 15 is arranged between the terminal fitting 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are connected to the conductive glass seal layers 16 and 17.
Are electrically connected to the center electrode 3 and the terminal fittings 13 respectively.

The terminal fitting 13 is made of low carbon steel or the like, and has a Ni plating layer (layer thickness:
m) is formed. The terminal fitting 13 has a seal portion 13c (tip portion), a terminal portion 13a protruding from a rear end edge of the insulator 2, and a rod portion 13b connecting the terminal portion 13a and the seal portion 13c. The seal portion 13 c is formed in a cylindrical shape that is long in the axial direction, is arranged so as to be immersed in the conductive glass seal layer 17, and is sealed between the inner surface of the through hole 6 and the seal layer 17.

The resistor 15 is made of a glass powder, a ceramic powder, a metal powder (mainly one or more of Zn, Sb, Sn, Ag and Ni), a nonmetallic conductive material powder (for example, amorphous carbon). (Carbon black) or graphite) and an organic binder are blended in predetermined amounts and sintered by a known method such as hot pressing. The composition and dimensions are adjusted so that the electrical resistance measured between the terminal fitting 13 and the center electrode 3 is 10 kΩ or more (preferably 15 kΩ or more).

Further, the conductive glass sealing layers 16 and 17
Is made of glass mixed with a metal powder mainly composed of one or more metal components such as Cu and Fe, and has a metal content of 35 to 70% by weight. The conductive glass seal layers 16 and 17 may include Ti if necessary.
An appropriate amount of a semiconductor inorganic compound powder such as O2 can be blended.

FIG. 3 shows an example of an ignition system using the spark plug 100. The ignition system 1
In 50, a voltage is directly applied to each spark plug 100 by an individual ignition coil 51 without using a distributor. Each ignition coil 5
1, the primary coil 52 that receives power from the battery 156 via the ignition switch 157 is connected to the igniter 154.
It is connected to the. On the other hand, the secondary coils 53 are connected to the spark plugs 100, respectively. In this case, the igniter 154 has a non-contact switch unit such as a transistor corresponding to each ignition coil 51, and these non-contact switch units individually receive a shutoff command signal from a corresponding output port of the control unit 155, The cutoff drive is performed at a predetermined timing. A diode is provided between each ignition coil 51 and the spark plug 100 to prevent re-energization of the spark plug 100 when the non-contact switch section in the igniter 154 is returned from the cut-off state to the conductive state. 51a are provided.

As shown in FIG. 4, when the internal combustion engine 180 is configured as a multi-cylinder gasoline engine, a spark plug 100 for ignition is burned in each of the cylinders 181, and a spark discharge gap g is burned by the mounting screw 7. It is installed to be located indoors. The coil units 50 correspond to the spark plugs 100 one-to-one.
Are connected to the control unit 155, respectively. The coil unit 50 has a casing 60 fitted into the rear end of the spark plug 100, and houses the ignition coil 51 and the igniter 154 inside. The ignition coil 51 is electrically connected to a terminal fitting of the spark plug 100 at a unit-side terminal (not shown).

The spark plug 100 is connected to the resistor 1
5 may be omitted, and the terminal fitting 13 and the center electrode 3 may be joined by, for example, a single conductive glass seal layer. When the resistor 15 is provided, the resistor 15 and the center electrode 3
May be omitted.
In this case, for example, a resistance is set between the ignition coil 51 and the unit-side terminal so that an electric resistance value of 10 kΩ or more (preferably 15 kΩ or more) is secured between the ignition coil 51 and the center electrode 3 of the spark plug 100. It is good to arrange a vessel.

[0030]

The following experiment was conducted to confirm the effects of the spark plug 100 and the ignition system 150. First, 30 parts by weight of fine glass powder (average particle size 80 μm), 60 parts by weight of ZrO ₂ (average particle size 3 μm) as ceramic powder, and 1 part by weight of Al powder (average particle size 20 to 50 μm) as metal powder Parts, 2 to 9 parts by weight of carbon black as a nonmetallic conductive material powder, and 3 parts by weight of dextrin as an organic binder,
Water was mixed by a ball mill using water as a solvent, and then dried to prepare a preliminary material. Then, coarse glass powder (average particle size 250 μm) was added to the above
400 parts by weight were added to 00 parts by weight to obtain a raw material powder of the resistor composition. The material of the glass powder is SiO
₂ 50 parts by weight, B ₂ O ₅ 29 parts by weight, Li ₂ O 4 parts
Parts by weight and 17 parts by weight of BaO are blended and dissolved to obtain a lithium borosilicate glass.
85 ° C.

Next, by using the resistor composition powder to form the resistor 15 by hot pressing, various samples of the spark plug 100 including the resistor shown in FIG. 1 were produced. Here, the center electrode 3 is made of a Ni alloy (Inconel 600), has an axial length of 20.7 mm,
The shaft cross-sectional diameter was set to 2.6 mm. The inner diameter of the through-hole 6 of the insulator 2 (the axial cross-sectional diameter of the obtained resistor 15 is almost the same as this) is 4.0 mm, the heating temperature of the hot press treatment is 900 ° C., and the pressing force is It was set to 100 kg / cm2. In addition, as the conductive glass powder, Cu, F
e, Sn, a mixture of a conductive powder such as TiO2 and a calcium borosilicate glass powder (the content of the conductive powder is about 5%).
0% by weight). In the obtained spark plug, the length L2 of the resistor 15 is 7.0 to 15.0 mm. The electric resistance Rk between the center electrode 3 and the terminal fitting 13 is 5 to 3 depending on the length L2 of the resistor 15 and the composition adjustment.
It is adjusted to have various values of 0 kΩ.

Next, the ignition portions 31 and 32 were formed as follows. First, a predetermined amount of Pt and Ir is blended and melted to produce an alloy containing 5% by weight of Ir and serving as a balance of Pt, and is made into a circle having a diameter of 0.2 to 1.6 mm and a thickness of 0.6 mm. It was processed into a plate-like chip. Then, the spark plug 10 shown in FIGS.
0, and the opposing firing portions 32 were formed (that is, the size of the firing portion of the center electrode 3 was set to 0.2 to 1.6).
mm). Also, the spark discharge gap g
Was set to various values of 0.6 to 1.6 mm.

Then, the above various spark plugs are
Attached to a cylinder gasoline engine (displacement 1998cc), throttle fully open, engine speed 5600rpm
m for up to 250 hours (center electrode temperature about 78
0 ° C.), and the amount of expansion of the spark discharge gap g of the plug after the operation was completed was measured. The ignition system used in the test is of the type shown in FIG. 3, and has a secondary current peak value of 70 mA and a discharge energy of 65 at the polarity where the center electrode side is negative.
The ignition discharge was performed under the condition of mJ. The current and voltage waveforms during the discharge were recorded with an oscilloscope. further,
For comparison, an experiment using the distributor-type ignition system shown in FIG. 11 was performed in the same manner. However, the electric resistance between the ignition coil 251 and the end of each high tension cable C was 5 to 10 kΩ.

First, FIG. 5 shows that the size γ of the secretary spark discharge gap is 0.8 mm and the value of the electric resistance Rk is 5 kΩ.
It is the result of measuring the consumption volume of the electrode per discharge when the center electrode was endured for 250 hours by variously changing the tip diameter. This is presumably because the smaller the δ, the higher the temperature is, that is, the more easily the platinum component melts and scatters.

Next, FIG. 6 shows that the tip diameter δ of the center electrode is φ
0.6mm, φ0.8mm and φ1.0mm,
It is the result of measuring the consumption volume of the electrode per discharge when the electric resistance value Rk was 5 kΩ and the initial spark discharge gap size γ was variously changed and the electrode was durable for 250 hours. When the γ is 1.2 mm or 1.4 mm, the consumption volume is large. FIG. 7A shows γ = 1.0 mm,
FIG. 7B is a waveform of one discharge when γ = 1.2 mm. In FIG. 7A, the current value is relatively stable, and it is presumed that glow discharge is dominant.
In (b), the behavior in which the current value suddenly increases frequently occurs, and it is presumed that a large current flows particularly at the moment when the transition from the glow discharge to the arc discharge occurs. That is, in FIG. 7B, it is considered that the frequency of glow / arc discharge transition during one discharge increases, the chances of a large current flowing instantaneously increase, and the electrode wear increases.

For example, in FIG. 7A, in a region where a glow discharge is considered to be occurring, the current change width falls within a range of approximately 5 mA, and the absolute value of the current gradually decreases toward the end of discharge. Form a current. Therefore, in the present embodiment, the background current level is obtained by calculating an average value of each section by dividing one discharge period into 0.5 ms units, and a current of at least 20 mA or more flows from the background current level. The case was determined to be a glow / arc discharge transition, and the number of occurrences (frequency) during one discharge was counted to evaluate the likelihood of the transition.

FIG. 8 shows that the electric resistance value Rk is 5 kΩ and 10 kΩ.
And the transition frequency of the glow / arc when the tip diameter δ of the center electrode is 0.8 mm and the size γ of the initial spark discharge gap is various values of 0.6 to 1.6 mm. (Γ = 1.3 m)
The results when m and Rk = 5 kΩ are represented by relative values with the result being 100. The numerical values are shown in Table 1).

[0038]

[Table 1]

That is, it is understood that the number of transitions is reduced by increasing the electric resistance value Rk.

Next, FIG. 9 shows that the initial spark discharge gap size γ is 1.3 mm and the electric resistance Rk is 5 to 30 kΩ.
The DLI ignition system of FIG.
12 shows the results of the same evaluation performed on each of the distributor type ignition systems shown in FIG. 11 (numerical values are shown in Table 2).

[0041]

[Table 2]

Even when the DLI type ignition system is used, the transition frequency decreases as the electric resistance value Rk increases, and the transition frequency is the same as that of the distributor (DIS) type by setting the resistance value to 10 kΩ or more. It turns out that it is suppressed to the extent. It can also be seen that the rate of change of the transition frequency is small when the resistance value is 20 kΩ or more.

FIG. 10 shows that the tip diameter δ of the center electrode is φ0.8.
mm, and the electric resistance Rk is 5 kΩ, 10 kΩ and 15 kΩ.
kΩ, the initial spark discharge gap size γ
Is a result obtained by measuring the consumption volume of the electrode per discharge when the electrode was endured for 250 hours with various changes. Electric resistance value R
When k = 5 kΩ, the consumption volume increases at γ of 1.2 mm or 1.4 mm, but the electric resistance Rk =
If 10 kΩ, γ is 1.2 mm or 1.4 mm
The consumption volume can be reduced at the
= 15 kΩ, the consumable volume can be made substantially constant regardless of the spark discharge gap.

[Brief description of the drawings]

FIG. 1 is a vertical partial sectional view showing one embodiment of a spark plug of the present invention.

FIG. 2 is an enlarged sectional view showing the vicinity of the spark discharge gap.

FIG. 3 is a circuit diagram showing an example of an ignition system using the spark plug of FIG. 1;

FIG. 4 is a schematic front view showing an example of a mode of attaching the ignition system of FIG. 3 to an engine.

FIG. 5 is a first graph showing the results of experiments performed in Examples.

FIG. 6 is also a second graph.

FIG. 7 is also a third graph.

FIG. 8 is also a fourth graph.

FIG. 9 is also a fifth graph.

FIG. 10 is also a sixth graph.

FIG. 11 is a circuit diagram showing an example of a distributor type ignition system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 metal shell 2 insulator 3 center electrode 4 ground electrode 6 through hole 13 terminal metal 15 resistor 31 firing part (chip) 32 facing firing part (chip) 50 coil unit 51 ignition coil 60 casing 100 spark plug 150 ignition system g Spark discharge gap

Claims (7)

[Claims] 1. A rod-shaped center electrode; an insulator provided outside the center electrode; a metal shell provided outside the insulator; and a ground electrode arranged to face the center electrode. And a firing portion fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap, and a through hole formed in an axial direction of the insulator,
A terminal fitting is fixed to one end thereof, the center electrode is similarly fixed to the other end, and a resistor is disposed between the terminal fitting and the center electrode in the through hole. The ignition portion is mainly composed of a metal containing 60% by weight or more of Pt, and an electric resistance value between the terminal metal and the center electrode via the resistor is secured to 10 kΩ or more. Spark plug characterized by the following. 2. The spark plug according to claim 1, wherein an electric resistance value between the terminal fitting and the center electrode is secured to 15 kΩ or more. 3. The ignition section is formed at the tip of the center electrode, and the tip diameter of the center electrode is 1.2 mm.
The spark plug according to claim 1, wherein: 4. A tip diameter of the center electrode is 0.4 to 0.8.
The spark plug according to claim 3, which is adjusted to a range of mm. 5. A rod-shaped center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a ground electrode arranged so as to face the center electrode. And a firing portion fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap, and a through hole formed in an axial direction of the insulator,
A terminal fitting is fixed to one end of the spark plug, and the center electrode is fixed to the other end of the spark plug, a casing attached to the spark plug, and housed inside the casing. A coil unit having an ignition coil connected to the terminal fitting of the spark plug and applying a high voltage for discharge to the spark plug, wherein the ignition portion of the spark plug contains at least 60% by weight of Pt. And the electric resistance between the ignition coil and the center electrode is 10 k.
An ignition system for an internal combustion engine, wherein a resistance portion for ensuring a resistance of Ω or more is provided. 6. The ignition system for an internal combustion engine according to claim 5, wherein a resistance value between the ignition coil and the center electrode is maintained at a value of 15 kΩ or more by the resistance portion. 7. The ignition system for an internal combustion engine according to claim 5, wherein the spark plug is the spark plug according to any one of claims 1 to 4.