JP6337529B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug provided with a noise preventing resistor.

To ignite the air-fuel mixture introduced into the combustion chamber of the internal combustion engine, a shaft-shaped center electrode, a cylindrical insulator that holds the center electrode in a through hole provided inside, and a part of the outer periphery of the insulator are covered. A cylindrical housing that holds the insulator, and a ground electrode that extends to the front end of the housing and faces the front end of the center electrode with a predetermined discharge gap between the center electrode and the ground electrode. Spark plugs that generate spark discharge when a high voltage is applied between them are widely used.
The spark plug is provided with a noise preventing resistor in the energization path to the center electrode in order to absorb electromagnetic noise.

  In Patent Document 1, as a spark plug manufacturing equipment and a spark plug manufacturing method, a terminal fitting is fixed to one end side of a through hole of an insulator, and a center electrode is provided to the other end side. In the through hole, an assembly is produced in which a conductive glass seal layer or a filling layer of raw material powder such as resistance is formed between the terminal fitting and the center electrode, and then in the axial direction of the insulator By heating the assembly so that the center electrode side is at a higher temperature than the terminal fitting side, fixing the position of the center electrode with respect to the through hole, and pressing the terminal fitting in a direction approaching the center electrode in the axial direction of the through hole A method of pressing a packed layer of raw material powder in a through hole between a center electrode and a terminal fitting is disclosed.

In a supercharged engine, the in-cylinder pressure at the time of combustion is high, the required voltage required for dielectric breakdown in the air-fuel mixture is higher than in a naturally aspirated engine, the inrush current at the start of discharge is large, In such a case, the ground electrode on the anode side may be consumed heavily.
This is considered to be due to an increase in discharge current due to capacitive discharge as the discharge voltage increases, contributing to electrode consumption on the anode side.

  In recent years, it has been desired to reduce the diameter of the spark plug in order to increase the degree of design freedom of the engine, such as improving the cooling performance of the engine or increasing the size of the intake valve to increase the intake air amount.

JP-A-11-251033

On the other hand, the electromagnetic wave noise generated by the parasitic capacitance formed on the base end side of the noise prevention resistor can be absorbed by the noise prevention resistor, but the electromagnetic wave generated by the parasitic capacitance formed in the portion accommodating the noise prevention resistor. Noise is difficult to absorb.
For this reason, by reducing the diameter of the spark plug, the thickness of the insulator in the part accommodating the noise prevention resistor is reduced, and if the capacitance of the part is large, it becomes a new noise source, There is also a risk that plug consumption will increase due to an increase in capacity discharge current.
In addition, if the noise prevention resistor is made thin with the conventional structure in order to reduce the diameter of the spark plug by the inventors' diligent test, uniform pressurization becomes difficult when forming the noise prevention resistor. It has been found that the sintered density of the noise preventing resistor is lowered, which may lead to the durability of the noise preventing resistor.

  Accordingly, in view of such circumstances, the present invention aims to reduce the electrode capacitance due to capacitive discharge by reducing the capacitance next to the noise prevention resistor, to improve the durability of the spark plug, and to provide a noise prevention resistor. The purpose of the present invention is to provide a spark plug capable of improving the durability of a noise-preventing resistor by simultaneously densifying and simultaneously reducing electromagnetic noise.

A spark plug (100) according to an aspect of the present invention is provided in an internal combustion engine, and includes at least an axial center electrode (1), a cylindrical insulator (2) that accommodates and holds the center electrode, and the insulation. A cylindrical housing (3) for holding the insulator in an airtight manner, a ground electrode discharge part (30) extending at the front end of the housing, and a noise prevention resistor (13) disposed on a part of the conduction path of the center electrode. An ignition plug provided, wherein in the insulator, an inner diameter (ID ₁ ) of a resistor accommodating portion (21) that accommodates the noise preventing resistor is disposed on a base end side thereof, and the center electrode Is smaller than the inner diameter (ID ₂ ) of the center shaft housing portion (22) for housing the center electrode middle shaft portion (16) for electrical connection with the outside, and on the center shaft (C / L) of the spark plug. With a predetermined inclination angle (θ) with the orthogonal plane as the reference plane Oblique to the and the and the resistor housing portion inside and the middle axle housing portion inner diameter equipped diameter change portion communicating the (TP), and the inner diameter ratio of the resistor housing portion inner diameter with respect to the middle axle housing portion inner diameter (R _ID = _ID 1 / _{ID 2),} characterized in der Rukoto 80% or less.
A spark plug (100) according to another aspect of the present invention is provided in an internal combustion engine, and includes at least an axial center electrode (1), a cylindrical insulator (2) that accommodates and holds the center electrode, A cylindrical housing (3) for holding the insulator hermetically, a ground electrode discharge part (30) extending at the front end of the housing, and a noise prevention resistor (13) at a part of the conduction path of the center electrode A spark plug,
In the insulator, an inner diameter (ID ₁ ) of a resistor accommodating portion (21) that accommodates the noise preventing resistor is disposed on a base end side thereof, and a center for electrical connection between the center electrode and the outside is provided. A predetermined inclination with respect to a plane that is smaller in diameter than the inner diameter (ID ₂ ) of the middle shaft housing portion (22) that houses the electrode middle shaft portion (16) and that is perpendicular to the center axis (C / L) of the spark plug. The resistor housing portion has an inner diameter varying portion (TP) that is inclined at an angle (θ) and communicates the inner diameter of the resistor housing portion and the inner diameter of the middle shaft housing portion, and the inner diameter of the resistor housing portion with respect to the inner diameter of the middle shaft housing portion The inside diameter ratio (R _ID = ID ₁ / ID ₂ ) is 87% or less, and the inclination angle is 5 ° or more and 52 ° or less.

According to the present invention, the density of the noise prevention resistor is made uniform to improve the durability, the outside diameter of the noise prevention resistor is reduced, and the thickness of the insulator beside the noise prevention resistor is increased. It is possible to reduce the capacitance of the portion and suppress the consumption of the electrode due to capacitive discharge.
It has also been found that electromagnetic noise can be reduced because the capacitance of the insulator on the base end side of the noise preventing resistor is relatively larger than the capacitance beside the noise preventing resistor.
Further, according to the present inventors' earnest test, an inner diameter ratio R _ID (= ID ₁ / ID ₂ ) (%) between the resistor accommodating portion inner diameter ID1 and the central shaft accommodating portion inner diameter ID ₂ and the resistor accommodating portion. It has been found that a more durable spark plug can be realized by setting the inclination angle θ of the diameter changing portion TP that communicates the inner diameter ID ₁ and the central shaft housing portion inner diameter ID ₂ to a predetermined range.

Half sectional view showing an outline of the spark plug of the present invention Sectional view of the main part of a conventional spark plug shown as a comparative example Sectional drawing of the principal part of the ignition plug of this invention Cross-sectional view of relevant parts for explaining the test conducted by the present inventors Characteristic diagram showing the correlation between the inner diameter ratio R _ID (%) of the resistor housing inner diameter to the inner diameter of the middle shaft section and the resistance value change rate RR (%) Characteristic diagram showing the correlation between the inclination angle between the inner diameter of the central shaft portion and the inner diameter of the resistor housing portion and the resistance value change rate RR (%) Characteristic diagram showing correlation between straight portion formed between resistance accommodating portion and diameter changing portion and resistance value change rate RR (%) Configuration diagram showing the outline of the noise measurement method The characteristic figure which shows the noise reduction effect of the spark plug of this invention with a comparative example

The outline of the spark plug 100 of the present invention will be described with reference to FIG. In this figure, the upper side of the figure is shown as the base end side connected to an external power source, and the lower side of the figure is shown as the distal end side facing the combustion chamber of the internal combustion engine.
The spark plug 100 includes a central electrode 1 that extends in an axial shape, a cylindrical insulator 2 that covers a side surface of the center electrode 1, a housing 3 that holds the insulator 2 in an airtight manner, and a distal end side of the housing 3. The ground electrode 30 is opposed to the tip of the center electrode 1 with a predetermined discharge gap GP therebetween, and a noise preventing resistor 13 is arranged in a part of the conduction path of the center electrode 1 inside the insulator 2. Has been established.
The spark plug 100 is provided in the internal combustion engine, and is a discharge provided between the center electrode discharge portion 10 provided at the tip of the center electrode 1 and the ground electrode discharge portion 30 by applying a high voltage from a high energy power supply (not shown). Spark discharge is generated in the gap GP, and the air-fuel mixture introduced into the combustion chamber of the internal combustion engine is ignited.

The spark plug 100 of the present invention includes a center electrode middle shaft portion 16 and a middle shaft embedded portion in which the inner diameter ID ₁ of the resistor housing portion 21 that houses the noise preventing resistor 13 is disposed on the base end side in the insulator 2. A diameter changing portion TP that has a diameter smaller than the inner diameter ID ₂ of the middle shaft housing portion 22 that houses 15 and communicates the resistor housing portion inner diameter ID ₁ and the middle shaft housing portion inner diameter ID ₂ with a predetermined inclination angle θ. It is characterized by.
In addition, according to the present inventor's earnest test, the inner diameter ratio R _ID (= ID ₁ / ID ₂ ) (%) between the resistor housing inner diameter ID ₁ and the middle shaft housing inner diameter ID ₂ and the resistor housing inner diameter ID. It has been found that a highly durable spark plug 100 can be realized by setting the inclination angle θ of the diameter-changing portion TP that communicates ₁ and the central shaft housing portion inner diameter ID ₂ to a predetermined range.
Note that the inclination angle θ is an angle formed by a plane perpendicular to the central axis C / L of the spark plug 100 as a reference plane and the reference plane and the diameter changing portion TP.

The center electrode 1 includes a center electrode discharge part 10, a center electrode high heat conduction part 11, a conductive adhesive layer 12, a noise prevention resistor 13, a conductive adhesive layer 14, a middle shaft embedded part 15, a center electrode middle shaft part 16, and The center electrode terminal part 17 is comprised.
The center electrode 1 is accommodated and held in a cylindrical insulator 2, and a central electrode discharge portion 10 is provided at one end of the center electrode 1 so as to be exposed from the front end side of the insulator 2 to the combustion chamber of an internal combustion engine (not shown). At the end, a central electrode terminal portion 17 is provided which is exposed from the base end side of the insulator 2 and is connected to the outside.

For the center electrode discharge part 10, a heat resistant noble metal such as iridium or platinum or a heat resistant alloy containing these may be used in order to improve durability.
The center electrode high thermal conductivity portion 11 is made of a metal having good conductivity such as iron, nickel, nickel alloy, and a core material such as copper or copper alloy is incorporated in the inside to improve conductivity and heat dissipation. Has been.

For the conductive adhesive layers 12 and 14, a mixture of glass powder and metal powder such as copper, iron, or an alloy thereof is used. After being filled and compressed at a predetermined position in the insulator 2, it is heated and melted. ing.
The conductive adhesive layer 12 seals and fixes the base end side of the center electrode high thermal conductive portion 11 and also conducts with the noise preventing resistor 13.
The conductive adhesive layer 14 provides conduction between the noise preventing resistor 13 and the central electrode middle shaft portion 16 and seals and fixes the middle shaft pressing portion 15.
The resistance value of the conductive adhesive layers 12 and 14 is about several mΩ.

  The noise prevention resistor 13 includes B2O3-SiO2, BaO-SiO2-B2O, ZnO-B2O3-SiO2, BaO-CaO-B2O3-SiO2, Na2O-SiO2-B2O3, K2O-SiO2-B2O3. Glass powder composed of at least one selected from the group consisting of Al2O3-B2O3-SiO2, BaO-B2O3, Bi2O-B2O3 and SiO2-MgO-Al2O3, conductive powder such as carbon, Al2O3 , SiO 2, SiC, Si 3 N 4, ZrO 2, an aggregate made of an insulating material containing at least one selected from, and after being filled and compressed in the resistor housing portion 21 provided in the insulator 2 It is configured to be melted by heating.

The noise prevention resistor 13 has an outer diameter that is larger than the outer diameter of the center electrode discharge portion 10 and thinner than the outer diameter of the center electrode middle shaft portion 16.
The outer diameter of the noise prevention resistor 13 is equal to the inner diameter ID ₁ of the resistor housing portion 21 provided in the insulator 2, is set in a range to be described later.
The length L of the noise preventing resistor 13 is the same as the outer diameter (that is, the inner diameter ID ₁ of the resistor housing portion 21) so that the resistance value of the noise preventing resistor 13 is in a predetermined range (for example, 5 kΩ). Determined by relationship.

The middle shaft pushing portion 15 is formed by forming the tip of the center electrode middle shaft portion 16 in a screw shape, and is pushed in with the conductive adhesive layer 14 heated and melted.
The center electrode middle shaft portion 16 is made of metal such as iron, nickel, alloys thereof, or stainless steel, and is formed in a rod shape.
A center electrode terminal portion 17 is provided at a position exposed from the insulator 2 on the proximal end side of the center electrode middle shaft portion 16 so as to make electrical connection between the center electrode 1 and an unillustrated power source provided outside.
The center electrode terminal portion 17 is made of metal such as iron, nickel, alloys thereof, or stainless steel, and may be detachably provided from the center electrode central shaft portion 16 as necessary.

The insulator 2 is made of high-purity alumina and has a cylindrical shape, and the center electrode 1 is inserted and held inside.
The insulator 2 includes an insulator discharge part 20, a resistor housing part 21, a central shaft housing part 22, an insulator diameter increasing part 23, and an insulator head 24.
The insulator discharge part 20 is exposed from the front end side of the housing 3 so as to face a combustion chamber (not shown).
The insulator discharge part 20 holds the center electrode high heat conduction part 11 inside, and the center electrode discharge part 10 is exposed from the tip.

Between the resistor housing portion 21 and the central shaft housing portion 22 which is the main part of the present invention, a diameter changing portion TP that is reduced in diameter so as to become smaller in diameter toward the distal end side is formed.
By setting the inner diameter ratio R _ID between the inner diameter ID ₁ of the resistor accommodating portion 21 and the inner diameter ID ₂ of the central shaft accommodating portion 22 to be 66.7% or more and 92.0% or less, It has been found that the resistance change rate RR (%) can be within 20% by exhibiting the effect, and more desirably, by setting the inner diameter ratio R _ID to 66.7% or more and 80.0% or less. .
The lower limit of the resistor accommodating portion inner diameter ID ₁ is set according to the relationship with the lower limit of the outer diameter of the center electrode high thermal conductivity portion 11.
As a result of the inventor's diligent test, the inclination angle θ of the diameter changing portion TP is set to 5 ° or more and 80 ° or less, thereby exerting the effect of the present invention. It was found that the resistance value change rate RR (%) after the durability test of the noise preventing resistor 13 can be within 20% by setting it to 60 ° or less.

An insulator widening portion 23 is formed on the middle outer periphery of the insulator 2 so as to project in a bowl shape toward the outer diameter direction, and is fixed by caulking with the housing 3.
An insulator head 24 is exposed from the base end side of the housing 3.
In order to prevent leakage during discharge, a part of the insulator head 24 may be formed in a corrugated shape, and the creeping distance between the center electrode terminal portion 17 and the housing 3 may be increased.

The housing 3 is formed in a cylindrical shape using a known metal material such as iron, nickel, alloys thereof, carbon steel, and stainless steel.
The housing 3 includes a ground electrode discharge part 30, a ground electrode connection part 31, a screw part 32, a side electrode part 33, an insulator housing part 34, a caulking part 35, and a hexagonal part 36.
The ground electrode discharge part 30 is disposed at a position facing the center electrode discharge part 10 with a predetermined discharge gap GP therebetween.
The ground electrode discharge part 30 may use iridium, or a known noble metal such as iridium alloy, platinum, or platinum alloy in order to improve durability.
The ground electrode connecting portion 31 is made of a metal having excellent conductivity and heat transfer, such as iron, nickel, nickel alloy, etc., and is bent in an L shape from the tip of the housing 3 to a position facing the center electrode discharge portion 10. The ground electrode discharge part 30 is arrange | positioned at the front-end | tip.
The screw portion 32 is screwed to an internal combustion engine (not shown), and grounds the ground electrode discharge portion 30 to the engine head of the internal combustion engine via the ground electrode connecting portion 31 and the side electrode portion 33.
The insulator accommodating portion 34 accommodates and holds the insulator 2 inside, and the crimp enlarged portion 23 is crimped and fixed by a crimping portion 35 via a sealing member 37 such as a known packing or powder filler.
A hexagonal portion 36 for tightening the screw portion 32 is provided on the outer periphery on the proximal end side of the housing 3.

An outline and problems of a conventional spark plug 100z shown as a comparative example will be described with reference to FIG. 2A, and features of the spark plug 100 of the present invention will be described with reference to FIG. 2B.
In addition, the same code | symbol is attached | subjected to the part which is common in the conventional spark plug 100z and the spark plug 100 of this invention, and the branch number of the alphabet is attached | subjected to the different part.
2A and 2B, the housing 3 and the like are omitted, and only the characteristic portions of the comparative example and the embodiment are shown. The left side of the drawing is the distal end side of the spark plug, and the right side is the proximal end side. It is described as follows.

As shown in FIG. 2A, in the conventional spark plug 100z, the resistor accommodating portion inner diameter ID ₁ z and the middle shaft accommodating portion inner diameter ID ₂ Z are formed to be equal.
For this reason, when forming the noise preventing resistor 13z, the glass powder that becomes the conductive adhesive layer 12 is formed from the base end side of the insulator 2 after the central electrode high thermal conductive portion 11 is accommodated in the insulator 2. Filled with a conductive powder, and further filled with a predetermined amount of a mixture of glass powder, conductive powder, and insulating aggregate serving as a noise prevention resistor 13z, and filled with conductive powder and conductive powder 13 Fill and compress in the axial direction using the central electrode middle shaft 16.

The glass component is melted by heating from the periphery of the insulator 2 to a high temperature, and further compressed by the center electrode middle shaft portion 16, so that the noise prevention resistor 13 z is densified and the center shaft pushing portion 15 of the center electrode middle shaft portion 16 is It is embedded in the conductive adhesive layer 12.
At this time, in the conventional spark plug 100z, the center portion of the noise preventing resistor 13z is strongly pressed by the tip of the central electrode middle shaft portion 16, so that the density becomes high.
However, in the portion in contact with the inner peripheral surface of the resistor accommodating portion 21z, the filling property of the powder material is reduced by the frictional force, and the conductive adhesive layer 13z is relatively opposite to the pressing direction in the central shaft embedded portion 15. As a result, the pressure applied to the vicinity of the outer periphery of the noise preventing resistor 13z also decreases.
As a result, it was found that in the noise prevention resistor 13z of the conventional spark plug 100z, the difference in density between the high-density portion near the center and the low-density portion near the outer periphery becomes large.
For this reason, since the resistance value of the noise preventing resistor 13z is lower than that when the entire device is uniformly densified, the length Lz of the noise preventing resistor 13z is set to obtain a certain resistance value. It needs to be long.
Further, it has been found that the resistance value of the noise preventing resistor 13z provided in the conventional spark plug 100z gradually changes due to the progress of densification with long-term use.

In addition, in the conventional spark plug 100z, the inner diameter ID1z of the resistor housing portion 21z and the inner diameter ID2z of the center shaft housing portion 22z are constant. The thickness T1z of the portion 21z is thinner than the thickness T2z of the middle shaft housing portion 22z.
In particular, in the conventional spark plug 100z, the base end position of the noise preventing resistor 13z is close to the position at which the insulator enlarged portion 23z of the insulator 2z is formed.

For this reason, the resistor accommodating portion parasitic capacitance Cs1z formed in the resistor accommodating portion 21z is larger than the central axis accommodating portion parasitic capacitance Cs2z formed on the proximal end side of the resistor 13z.
Since the low-pass filter is configured by the noise preventing resistor 13z and the central axis accommodating part parasitic capacitance Cs2z formed on the base end side thereof, electromagnetic wave noise generated by the central axis accommodating part parasitic capacitance Cs2z is absorbed. Electromagnetic wave noise generated by the resistor accommodating portion parasitic capacitance Cs1z on the downstream side of the preventing resistor 13z is difficult to be absorbed, and when the resistor accommodating portion parasitic capacitance Cs1z becomes large, absorption by the noise preventing resistor 13z becomes difficult. .

On the other hand, in the spark plug 100 of the present invention, when the noise preventing resistor 13 is formed, the inner diameter ID ₁ of the resistor housing portion 21 is narrower than the inner diameter ID ₂ of the middle shaft housing portion 22 and is contracted toward the tip therebetween. A diameter changing portion TP is formed.
For this reason, when the noise prevention resistor 13 is formed, when a predetermined powder is filled and compressed by the central electrode middle shaft portion 16, the noise prevention resistor 13 is uniformly pressed to a position corresponding to the outer periphery of the noise prevention resistor 13. .
In addition, since the noise preventing resistor 13 has a small diameter, the load per unit area when pressurized by the central electrode middle shaft portion 16 becomes higher than the conventional one. For this reason, the noise preventing resistor 13 is uniformly densified, and the specific resistance is increased.
As a result, it has been found that the durability of the noise preventing resistor 13 is improved.

Furthermore, the outer diameter (φID ₁ ) necessary for the noise preventing resistor 13 to have a predetermined resistance value can be narrowed, and the length L can be shortened.
In the spark plug 100, the inner diameter ID ₁ of the resistor housing portion 21 is thinner than the inner diameter ID ₂ of the center shaft housing portion 22, and the thickness T ₁ of the resistor housing portion 21 is inevitably set to the thickness T ₂ of the middle shaft housing portion 22. The resistor accommodating portion parasitic capacitance Cs1 can be made smaller than the central axis accommodating portion parasitic capacitance Cs2.
The electromagnetic wave noise generated in the central shaft accommodating portion parasitic capacitance Cs2 on the proximal side of the noise preventing resistor 13 can be absorbed by the noise preventing resistor 13, and the resistor accommodating portion difficult to absorb by the noise preventing resistor 13. Since the parasitic capacitance Cs1 is small, it has been found that the electromagnetic noise can be reduced more than before.

With reference to FIG. 3, the test that the present inventors have obtained the present invention will be described.
The inner diameter of the resistor accommodating portion 21 that accommodates the noise preventing resistor 13 is the resistor accommodating portion inner diameter ID ₁ , and the inner diameter of the middle shaft accommodating portion 22 that accommodates the middle shaft embedded portion 15 of the center electrode middle shaft portion 16 is the middle shaft accommodating portion inner diameter ID. ₂ and the inclination angle of the diameter changing portion TP when the plane perpendicular to the central axis C / L of the spark plug 100 is used as the reference plane is the inclination angle θ.
A sample was prepared in which the inner diameter ratio R _ID was changed in the range of 66.7% to 95% and the inclination angle θ was changed from 5 ° to 80 °.

Also, the noise prevention resistor 13, since the length by the amount of variation in the powder material is compressed filling the resistor housing portion 22 is changed, the resistor housing portion inner diameter ID ₁ for accommodating the noise prevention resistor 13 The influence of the straight portion length Ls when a straight portion exists between the diameter change portion TP was also investigated.
The length L of the noise preventing resistor 13 was set so that the resistance value was constant (for example, 5 kΩ) from the relationship with the cross-sectional area of the noise preventing resistor 13 in each sample.

About the obtained sample, the plug temperature is heated to 350 ° C., and a durability test for 300 hours is performed by a method in accordance with JIS B8031 7.3. The resistance value R _I of the noise preventing resistor before durability and the resistance value after durability are measured. comparing the resistance value _{R L} of the noise prevention resistor was calculated resistance value change rate _{RR (%) (RR = 100} (R L -R I) / R I). The results are shown in Table 1, FIGS. 4A, 4B, and 4C.

As shown in FIG. 4A, in the conventional spark plug 100z shown as the comparative example, the resistance value change rate RR (%) of the noise preventing resistor 13z after the endurance load test was 75%.
As shown in FIG. 4A, when the resistor housing inner diameter ID ₁ is 91% or less of the center shaft housing inner diameter ID ₂ , the resistance value change rate RR is 50% or less regardless of the inclination angle θ. It was found that it can be reduced.

Further, as shown in FIG. 4A, when the resistor accommodating portion inner diameter ID _{1 is set} to 80% or less of the central shaft accommodating portion inner diameter ID ₂ , the resistance value change rate RR is set to 20% regardless of the inclination angle θ. It was found that the following can be reduced.
As shown in FIG. 4B, it has been found that when the inclination angle θ is 67 ° or less, the resistance value change rate RR can be reduced to 50% or less regardless of the inner diameter ratio R _ID .
As shown in FIG. 4B, it was found that when the inner diameter ratio R _ID is 87% or less and the inclination angle θ is 5 ° or more and 52 ° or less, the resistance value change rate RR can be reduced to 20% or less.
As shown in FIG. 4C, between the straight portion length Ls in the resistance value change rate RR correlation is not observed, and the resistor housing portion inner diameter ID ₁ and the diameter change portion TP to accommodate the noise prevention resistor 13, Even when there is a straight portion, it has been found that there is no influence of the length Ls of the straight portion, and that the variation in the length L of the noise preventing resistor 13 can be allowed to some extent.

If the inner diameter ratio R _ID is 66.7% or more and 87% or less and the inclination angle θ is 5 ° or more and 60 ° or less, the resistance value change rate is suppressed to 20% or less, and the highly durable spark plug 100 is obtained. It turns out that it can be realized.
For example, when the inner diameter housing portion ID ₂ is set to φ3.0 mm, the resistor housing portion inner diameter ID ₁ is set to φ2.0 mm to φ2.85 mm, and the inclination angle θ of the diameter changing portion TP is set to 5 ° to 60 °. The durability of the noise preventing resistor 13 can be improved.

Inevitably, the thickness T ₁ of the resistor housing portion 21 beside the noise preventing resistor 13 is larger than the thickness T ₂ of the central shaft housing portion 22.
Therefore, the parasitic capacitance Cs2 formed on the base end side of the noise prevention resistor 13 is larger than the parasitic capacitance Cs1 formed beside the noise prevention resistor 13.
As a result, the electromagnetic wave noise generated in the central shaft accommodating portion parasitic capacitance Cs2 on the proximal side of the noise prevention resistor 13 can be absorbed by the noise prevention resistor 13, and the resistance that is difficult to absorb by the noise prevention resistor 13 is obtained. Since the body accommodating portion parasitic capacitance Cs1 is small, it has been found that electromagnetic noise can be reduced more than before.

Here, with reference to FIG. 5A and FIG. 5B, the electromagnetic wave noise reduction effect of the ignition plug 100 of this invention is demonstrated.
As shown in FIG. 5A, the spark plug 100 of the present invention or the conventional spark plug 100z as a comparative example is a pressure vessel that can be adjusted to a predetermined pressure (0.2 MPa) by simulating a combustion chamber of an internal combustion engine. The electromagnetic wave noise generated when a high voltage (discharge voltage 15 kV) was applied was measured using an EMI receiver.
As a result, in FIG. 5B, the result using the conventional spark plug 100z is shown as a dotted line as a comparative example, and the result using the spark plug 100 of the present invention is shown as a solid line as an example.

In the spark plug 100z, as shown in FIG. 2A, the resistor housing inner diameter ID1z and the middle shaft housing inner diameter ID2z are equal.
A spark plug 100 having an inner diameter ratio R _ID (resistor housing portion inner diameter / center shaft housing portion inner diameter ID ₁ / ID ₂ ) of 80% and an inclination angle θ of 20 ° was used.
As a result, it was confirmed that the noise level can be reduced by 2 to 3 dB in the spark plug 100 of the present invention compared to the conventional spark plug 100z.

DESCRIPTION OF SYMBOLS 100 Spark plug 1 Center electrode 10 Center electrode discharge part 11 Center electrode high heat conduction part 13 Noise prevention resistor 12, 14 Center electrode electroconductive adhesive layer 15 Center axis embedding part 16 Center electrode center axis part 17 Center electrode terminal part 2 Insulator 20 Insulator discharge part 21 Resistor accommodation part 22 Middle shaft accommodation part 23 Expanded part 24 Insulator head 3 Housing 30 Ground electrode discharge part 31 Ground electrode connection part 32 Screw part 33 Side electrode part 34 Insulator accommodation part 35 Clamping part 36 Hexagon part 37 Sealing member ID ₁ Resistor accommodating portion inner diameter ID ₂ Middle shaft accommodating portion inner diameter R _ID inner diameter ratio TP Diameter changing portion θ Inclination angle GP Discharge gap
RR% Resistance value change rate C / L Spark plug center axis

Claims (4)

Provided in the internal combustion engine, at least an axial center electrode (1), a cylindrical insulator (2) for accommodating and holding the center electrode, and a cylindrical housing (3) for hermetically holding the insulator And a spark plug in which a ground electrode discharge part (30) extending at the front end of the housing and a noise prevention resistor (13) are disposed in a part of the conduction path of the center electrode,
In the insulator, an inner diameter (ID ₁ ) of a resistor accommodating portion (21) that accommodates the noise preventing resistor is disposed on a base end side thereof, and a center for electrical connection between the center electrode and the outside is provided. A predetermined inclination with respect to a plane that is smaller in diameter than the inner diameter (ID ₂ ) of the middle shaft housing portion (22) that houses the electrode middle shaft portion (16) and that is perpendicular to the center axis (C / L) of the spark plug. The resistor housing portion has an inner diameter varying portion (TP) that is inclined at an angle (θ) and communicates the inner diameter of the resistor housing portion and the inner diameter of the middle shaft housing portion, and the inner diameter of the resistor housing portion with respect to the inner diameter of the middle shaft housing portion inner diameter ratio _{(R ID = ID 1 / ID} 2) is a spark plug, characterized in der Rukoto than 80% (100) Provided in the internal combustion engine, at least an axial center electrode (1), a cylindrical insulator (2) for accommodating and holding the center electrode, and a cylindrical housing (3) for hermetically holding the insulator And a spark plug in which a ground electrode discharge part (30) extending at the front end of the housing and a noise prevention resistor (13) are disposed in a part of the conduction path of the center electrode,
In the insulator, an inner diameter (ID ₁ ) of a resistor accommodating portion (21) that accommodates the noise preventing resistor is disposed on a base end side thereof, and a center for electrical connection between the center electrode and the outside is provided. A predetermined inclination with respect to a plane that is smaller in diameter than the inner diameter (ID ₂ ) of the middle shaft housing portion (22) that houses the electrode middle shaft portion (16) and that is perpendicular to the center axis (C / L) of the spark plug. angle (theta) and with a tilting, the and the and the resistor housing portion inside and the middle axle housing portion inner diameter equipped diameter change portion communicating the (TP), and the resistor housing portion against the middle axle housing portion diameter inner diameter ratio of the diameter _{(R ID = ID 1 / ID} 2) is below 8 7%, the inclination angle is 5 ° or more, spark plugs, characterized in that it is 52 ° or less (100) The spark plug according to claim 1, wherein the inner diameter ratio is 66.7% or more and 80% or less. The spark plug according to claim 1 or 3, wherein an inclination angle (θ) of the diameter changing portion (TP) is 5 ° or more and 67 ° or less.

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